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Materials, Volume 6, Issue 8 (August 2013) – 39 articles , Pages 3035-3675

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751 KiB  
Article
Broadband Luminescence in Rare Earth Doped Sr2SiS4: Relating Energy Levels of Ce3+ and Eu2+
by Anthony B. Parmentier, Philippe F. Smet and Dirk Poelman
Materials 2013, 6(8), 3663-3675; https://doi.org/10.3390/ma6083663 - 21 Aug 2013
Cited by 13 | Viewed by 7477
Abstract
Sr2SiS4:Ce3+ is an efficient blue-emitting (460 nm) phosphor, excitable with light of wavelengths up to 420 nm. From the excitation spectrum, we construct the energy level scheme and use it to check the predictive power of the Dorenbos model, relating the positions of [...] Read more.
Sr2SiS4:Ce3+ is an efficient blue-emitting (460 nm) phosphor, excitable with light of wavelengths up to 420 nm. From the excitation spectrum, we construct the energy level scheme and use it to check the predictive power of the Dorenbos model, relating the positions of the Ce3+ energy levels with those of Eu2+ in the same host. For strontium thiosilicate, this method gives excellent results and allows us to determine which of two available crystallographic sites is occupied by cerium. We use the Dorenbos method for extracting information on the coordination of Ce3+ from the observed crystal field splitting. Full article
(This article belongs to the Special Issue Luminescent Materials 2013)
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Figure 1
<p>The X-ray diffraction (XRD) pattern of Sr<math display="inline"> <msub> <mrow/> <mn>2</mn> </msub> </math>SiS<math display="inline"> <msub> <mrow/> <mn>4</mn> </msub> </math>:Ce<math display="inline"> <msup> <mrow/> <mrow> <mn>3</mn> <mo>+</mo> </mrow> </msup> </math> (0.5%).</p> Full article ">Figure 2
<p>An average lattice parameter (cube root of monoclinic cell volume) as a function of Eu concentration in Eu<math display="inline"> <msub> <mrow/> <mrow> <mn>2</mn> <mi>x</mi> </mrow> </msub> </math>Sr<math display="inline"> <msub> <mrow/> <mrow> <mn>2</mn> <mo>−</mo> <mn>2</mn> <mi>x</mi> </mrow> </msub> </math>SiS<math display="inline"> <msub> <mrow/> <mn>4</mn> </msub> </math>. From the refinement results, the error on the lattice parameter is estimated around 0.01 Å. The error on the Eu/Sr ratio is determined by preparation accuracy and is estimated to be on the order of 1%.</p> Full article ">Figure 3
<p>Schematic representation of the coordination environment for both Sr sites in Sr<math display="inline"> <msub> <mrow/> <mn>2</mn> </msub> </math>SiS<math display="inline"> <msub> <mrow/> <mn>4</mn> </msub> </math>.</p> Full article ">Figure 4
<p>The emission spectrum of Sr<math display="inline"> <msub> <mrow/> <mn>2</mn> </msub> </math>SiS<math display="inline"> <msub> <mrow/> <mn>4</mn> </msub> </math>:Ce<math display="inline"> <msup> <mrow/> <mrow> <mn>3</mn> <mo>+</mo> </mrow> </msup> </math> at room temperature (red dashed line) and at 10 K (black solid line), both on excitation with 3.88 eV (320 nm). The two Gaussian curves used for fitting are represented with dotted lines. The sum of these curves is the blue dashed line.</p> Full article ">Figure 5
<p>Excitation spectrum of Sr<math display="inline"> <msub> <mrow/> <mn>2</mn> </msub> </math>SiS<math display="inline"> <msub> <mrow/> <mn>4</mn> </msub> </math>:Ce<math display="inline"> <msup> <mrow/> <mrow> <mn>3</mn> <mo>+</mo> </mrow> </msup> </math> at room temperature (green dashed line) and at 10 K (black solid line), when monitoring the emission at 2.25 eV (550 nm). A fitting curve is also shown for 10 K. The individual Gaussian curves (all with equal width) for all five peaks (X1, …, X5) are shown as dotted lines.</p> Full article ">Figure 6
<p>Energy level scheme for Ce<math display="inline"> <msup> <mrow/> <mrow> <mn>3</mn> <mo>+</mo> </mrow> </msup> </math> in Sr<math display="inline"> <msub> <mrow/> <mn>2</mn> </msub> </math>SiS<math display="inline"> <msub> <mrow/> <mn>4</mn> </msub> </math>:Ce<math display="inline"> <msup> <mrow/> <mrow> <mn>3</mn> <mo>+</mo> </mrow> </msup> </math>.</p> Full article ">
872 KiB  
Review
Progress in Titanium Metal Powder Injection Molding
by Randall M. German
Materials 2013, 6(8), 3641-3662; https://doi.org/10.3390/ma6083641 - 20 Aug 2013
Cited by 157 | Viewed by 14733
Abstract
Metal powder injection molding is a shaping technology that has achieved solid scientific underpinnings. It is from this science base that recent progress has occurred in titanium powder injection molding. Much of the progress awaited development of the required particles with specific characteristics [...] Read more.
Metal powder injection molding is a shaping technology that has achieved solid scientific underpinnings. It is from this science base that recent progress has occurred in titanium powder injection molding. Much of the progress awaited development of the required particles with specific characteristics of particle size, particle shape, and purity. The production of titanium components by injection molding is stabilized by a good understanding of how each process variable impacts density and impurity level. As summarized here, recent research has isolated the four critical success factors in titanium metal powder injection molding (Ti-MIM) that must be simultaneously satisfied—density, purity, alloying, and microstructure. The critical role of density and impurities, and the inability to remove impurities with sintering, compels attention to starting Ti-MIM with high quality alloy powders. This article addresses the four critical success factors to rationalize Ti-MIM processing conditions to the requirements for demanding applications in aerospace and medical fields. Based on extensive research, a baseline process is identified and reported here with attention to linking mechanical properties to the four critical success factors. Full article
(This article belongs to the Special Issue Progress in Net-shaped PM (Powder Metallurgical) Parts)
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Figure 1
<p>A plot of the mechanical properties for sintered Ti-6Al-4V from mixed powders <span class="html-italic">versus</span> fractional density showing the sensitivity of fatigue behavior as compared to tensile and yield strength.</p> Full article ">Figure 2
<p>An example of a Ti-MIM component, in this case a tripod base.</p> Full article ">Figure 3
<p>Oxygen content <span class="html-italic">versus</span> debinding temperature for titanium powder [<a href="#B136-materials-06-03641" class="html-bibr">136</a>].</p> Full article ">Figure 4
<p>Sintered density and tensile strength for Ti-12Mo <span class="html-italic">versus</span> the sintering temperature [<a href="#B64-materials-06-03641" class="html-bibr">64</a>].</p> Full article ">Figure 5
<p>Microstructure for Ti-6Al-4V produced by Ti-MIM prior to hot isostatic pressing.</p> Full article ">Figure 6
<p>Titanium spherical powder formed using plasma atomization of a hydride-milled-dehydride (HDH) powder.</p> Full article ">Figure 7
<p>Example Ti-MIM shapes produced by Element 22 GmbH (Kiel, Germany).</p> Full article ">
1086 KiB  
Article
The Effect of a Rapid Heating Rate, Mechanical Vibration and Surfactant Chemistry on the Structure–Property Relationships of Epoxy/Clay Nanocomposites
by Betime Nuhiji, Darren Attard, Gordon Thorogood, Tracey Hanley, Kevin Magniez, Jenny Bungur and Bronwyn Fox
Materials 2013, 6(8), 3624-3640; https://doi.org/10.3390/ma6083624 - 20 Aug 2013
Cited by 14 | Viewed by 5964
Abstract
The role of processing conditions and intercalant chemistry in montmorillonite clays on the dispersion, morphology and mechanical properties of two epoxy/clay nanocomposite systems was investigated in this paper. This work highlights the importance of employing complementary techniques (X-ray diffraction, small angle X-ray scattering, [...] Read more.
The role of processing conditions and intercalant chemistry in montmorillonite clays on the dispersion, morphology and mechanical properties of two epoxy/clay nanocomposite systems was investigated in this paper. This work highlights the importance of employing complementary techniques (X-ray diffraction, small angle X-ray scattering, optical microscopy and transmission electron microscopy) to correlate nanomorphology to macroscale properties. Materials were prepared using an out of autoclave manufacturing process equipped to generate rapid heating rates and mechanical vibration. The results suggested that the quaternary ammonium surfactant on C30B clay reacted with the epoxy during cure, while the primary ammonium surfactant (I.30E) catalysed the polymerisation reaction. These effects led to important differences in nanocomposite clay morphologies. The use of mechanical vibration at 4 Hz prior to matrix gelation was found to facilitate clay dispersion and to reduce the area fraction of I.30E clay agglomerates in addition to increasing flexural strength by over 40%. Full article
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>An X-ray diffraction (XRD) diffractogram of the epoxy/clay nanocomposites (<b>A</b>) I.30E_10MV; (<b>B</b>) I.30E_10; (<b>C</b>) C30B_10MV; and (<b>D</b>) C30B_10.</p> Full article ">Figure 2
<p>Small angle X-ray scattering data of the I.30E_10MV (<b>A</b>); and the I.30E_10 (<b>B</b>) nanocomposites.</p> Full article ">Figure 3
<p>TEM photographs of epoxy/clay nanocomposites (i) I.30E_10; (ii) I.30E_10MV; (iii) C30B_10; and (iv) C30B_10MV at (1.5 × 10<sup>5</sup>)× magnification (<b>a</b>); and at (2.5 × 10<sup>5</sup>)× magnification (<b>b</b>).</p> Full article ">Figure 4
<p>Optical images taken of the following nanocomposites (<b>A</b>) I.30E_10; (<b>B</b>) I.30E_10MV; (<b>C</b>) C30B_10; and (<b>D</b>) C30B_10MV.</p> Full article ">Figure 5
<p>Rheology curves showing that the nanocomposite incorporating C30B clays have a higher viscosity during curing than those with I.30E clays.</p> Full article ">Figure 6
<p>Schematic of the chemical reaction between the hydroxyl group (OH) in the C30B clay and an epoxy end group (CH<sub>2</sub>–O–CH<sub>2</sub>). The epoxy ring opens to react the constituents in order generate polymerisation.</p> Full article ">Figure 7
<p>Results from the three point bending tests of the nanocomposites (<b>A</b>) I.30E_10; (<b>B</b>) I.30E_10MV; (<b>C</b>) C30B_10; (<b>D</b>) C30B_10MV; and (<b>E</b>) Epoxy.</p> Full article ">Figure 8
<p>T<sub>g</sub> measured from tanδ peaks for I.30E and C30B nanocomposites.</p> Full article ">
759 KiB  
Article
Fabrication of Super-Hydrophobic Microchannels via Strain-Recovery Deformations of Polystyrene and Oxygen Reactive Ion Etch
by Anirban Chakraborty, Mingming Xiang and Cheng Luo
Materials 2013, 6(8), 3610-3623; https://doi.org/10.3390/ma6083610 - 19 Aug 2013
Cited by 18 | Viewed by 6303
Abstract
In this article, we report a simple approach to generate micropillars (whose top portions are covered by sub-micron wrinkles) on the inner surfaces of polystyrene (PS) microchannels, as well as on the top surface of the PS substrate, based on strain-recovery deformations of [...] Read more.
In this article, we report a simple approach to generate micropillars (whose top portions are covered by sub-micron wrinkles) on the inner surfaces of polystyrene (PS) microchannels, as well as on the top surface of the PS substrate, based on strain-recovery deformations of the PS and oxygen reactive ion etch (ORIE). Using this approach, two types of micropillar-covered microchannels are fabricated. Their widths range from 118 ?m to 132 ?m, depths vary from 40 ?m to 44 ?m, and the inclined angles of their sidewalls are from 53° to 64°. The micropillars enable these microchannels to have super-hydrophobic properties. The contact angles observed on the channel-structured surfaces are above 162°, and the tilt angles to make water drops roll off from these channel-structured substrates can be as small as 1°. Full article
(This article belongs to the Special Issue Smart Polymers and Polymeric Structures)
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Figure 1
<p>Schematics of the four-step procedure used to fabricate super-hydrophobic microchannels. (<b>a</b>) Generate shallow, wide channels; (<b>b</b>) Create Ag microdots on the substrate; (<b>c</b>) Produce micropillars; and (<b>d</b>) Complete the fabrication through strain recovery of the PS substrate (not to scale).</p> Full article ">Figure 2
<p>Scanning electron microscopy (SEM) images of 500-µm-wide channels with 50 × 50 µm<sup>2</sup> Ag dots. (<b>a</b>,<b>b</b>) Top view of Ag dots before recovery; (<b>c</b>,<b>d</b>) Top and side view of the sample after recovery; (<b>e</b>,<b>f</b>) Close-up of the vertical sidewall with the broken Ag dots and ripples.</p> Full article ">Figure 3
<p>SEM images of 500-µm-wide channels with 50 × 50 µm<sup>2</sup> Ag dots. (<b>a</b>,<b>b</b>) Top view of Ag dots before recovery; (<b>c</b>,<b>d</b>) Top and side views of the sample after recovery; (<b>e</b>,<b>f</b>) Close-up views of the vertical sidewall with one row of polystyrene (PS) pillars.</p> Full article ">Figure 4
<p>Two arrays of generated channels. (<b>a1</b>) 3-D; (<b>a2</b>) Top; and (<b>a3</b>) Close-up views of Channels I; (<b>b1</b>) 3-D; (<b>b2</b>) Top; and (<b>b3</b>) Close-up views of Channels II; Sub-micron wrinkles generated on the tops of Pillars. (<b>c1</b>) I; and (<b>c2</b>) II. (All are SEM images).</p> Full article ">Figure 5
<p>Contact angles on as-received PS sheets. (<b>a</b>) Before; and (<b>b</b>) After recovery; as well as those on surfaces structured with Channels (<b>b1</b>) I and (<b>b2</b>) II. The scale bars represent 450 µm.</p> Full article ">Figure 6
<p>Water drops stuck to as-received PS sheets. (<b>a1</b>) Before; and (<b>a2</b>) After recovery when the sheets were tilted by 29° and 28°, respectively. The scale bars in (<b>a1</b>) and (<b>a2</b>) stand for 1 mm. A water drop rolled off from a substrate that is structured with Channels I when this substrate was tilted at an angle of 5°. (<b>b1</b>) Produce a water drop using a syringe, (<b>b2</b>) Release it to the substrate; (<b>b3</b>) The drop moves down; and (<b>b4</b>) Gets off from this substrate. The corresponding video clip for (<b>b1</b>–<b>b4</b>) is available in the Supporting Information, and the scale bars represent 4.5 mm.</p> Full article ">
393 KiB  
Article
Drift in Diffusion Gradients
by Fabio Marchesoni
Materials 2013, 6(8), 3598-3609; https://doi.org/10.3390/ma6083598 - 19 Aug 2013
Cited by 11 | Viewed by 5110
Abstract
The longstanding problem of Brownian transport in a heterogeneous quasi one-dimensional medium with space-dependent self-diffusion coefficient is addressed in the overdamped (zero mass) limit. A satisfactory mesoscopic description is obtained in the Langevin equation formalism by introducing an appropriate drift term, which depends [...] Read more.
The longstanding problem of Brownian transport in a heterogeneous quasi one-dimensional medium with space-dependent self-diffusion coefficient is addressed in the overdamped (zero mass) limit. A satisfactory mesoscopic description is obtained in the Langevin equation formalism by introducing an appropriate drift term, which depends on the system macroscopic observables, namely the diffuser concentration and current. The drift term is related to the microscopic properties of the medium. The paradoxical existence of a finite drift at zero current suggests the possibility of designing a Maxwell demon operating between two equilibrium reservoirs at the same temperature. Full article
(This article belongs to the Special Issue Diffusion in Micropores and Mesopores 2013)
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<p>Sketch of the graded-channel geometries discussed in <a href="#sec3-materials-06-03598" class="html-sec">Section 3</a>: (<b>a</b>) a symmetric periodic channel; (<b>b</b>) a graded compartment, length <math display="inline"> <mrow> <mi>l</mi> <mo>(</mo> <mi>x</mi> <mo>)</mo> </mrow> </math>; (<b>c</b>) a graded compartment, volume <math display="inline"> <mrow> <mo>Ω</mo> <mo>(</mo> <mi>x</mi> <mo>)</mo> </mrow> </math>; and (<b>d</b>) graded pore size.</p> Full article ">Figure 2
<p>Sketch of the drift-based transport mechanism discussed in <a href="#sec4-materials-06-03598" class="html-sec">Section 4</a>: (<b>a</b>) thin filament connecting two particle reservoirs with temperature T; and (<b>b</b>) docking (red circle) and delivery stations (blue rectangles) in a narrow channel tailored such that <math display="inline"> <mrow> <mi>v</mi> <mrow> <mo>(</mo> <mi>x</mi> <mo>)</mo> </mrow> <mo>=</mo> <msup> <mi>D</mi> <mo>′</mo> </msup> <mrow> <mo>(</mo> <mi>x</mi> <mo>)</mo> </mrow> </mrow> </math>.</p> Full article ">
1673 KiB  
Article
Hydrothermal Growth of Vertically Aligned ZnO Nanorods Using a Biocomposite Seed Layer of ZnO Nanoparticles
by Zafar Hussain Ibupoto, Kimleang Khun, Martin Eriksson, Mohammad AlSalhi, Muhammad Atif, Anees Ansari and Magnus Willander
Materials 2013, 6(8), 3584-3597; https://doi.org/10.3390/ma6083584 - 19 Aug 2013
Cited by 98 | Viewed by 10222
Abstract
Well aligned ZnO nanorods have been prepared by a low temperature aqueous chemical growth method, using a biocomposite seed layer of ZnO nanoparticles prepared in starch and cellulose bio polymers. The effect of different concentrations of biocomposite seed layer on the alignment of [...] Read more.
Well aligned ZnO nanorods have been prepared by a low temperature aqueous chemical growth method, using a biocomposite seed layer of ZnO nanoparticles prepared in starch and cellulose bio polymers. The effect of different concentrations of biocomposite seed layer on the alignment of ZnO nanorods has been investigated. ZnO nanorods grown on a gold-coated glass substrate have been characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques. These techniques have shown that the ZnO nanorods are well aligned and perpendicular to the substrate, and grown with a high density and uniformity on the substrate. Moreover, ZnO nanorods can be grown with an orientation along the c-axis of the substrate and exhibit a wurtzite crystal structure with a dominant (002) peak in an XRD spectrum and possessed a high crystal quality. A photoluminescence (PL) spectroscopy study of the ZnO nanorods has revealed a conventional near band edge ultraviolet emission, along with emission in the visible part of the electromagnetic spectrum due to defect emission. This study provides an alternative method for the fabrication of well aligned ZnO nanorods. This method can be helpful in improving the performance of devices where alignment plays a significant role. Full article
(This article belongs to the Section Biomaterials)
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Figure 1

Figure 1
<p>(<b>a</b>) The XRD pattern of ZnO nanoparticles; (<b>b</b>) The AFM image of the biocomposite seed layer of ZnO nanoparticles.</p> Full article ">Figure 2
<p>The XRD pattern of ZnO nanorods without seed solution.</p> Full article ">Figure 3
<p>The XRD pattern of ZnO nanorods growth with seed solutions containing 3.5 mg/mL of starch concentration and different concentrations of ZnO nanoparticles: (<b>a</b>) 0.5; (<b>b</b>) 1.0; (<b>c</b>) 1.5; (<b>d</b>) 2.0; and (<b>e</b>) 2.5 mg/mL.</p> Full article ">Figure 4
<p>The XRD pattern of ZnO nanorods growth with seed solutions containing 3.5 mg/mL of cellulose concentration with different concentrations of ZnO nanoparticle: (<b>a</b>) 1.0; (<b>b</b>) 3.5; and (<b>c</b>) 7.5 mg/mL.</p> Full article ">Figure 5
<p>The FESEM image of ZnO nanorods grown with only ZnO nanoparticles seed solution.</p> Full article ">Figure 6
<p>The FESEM images of ZnO nanorods with seed solutions containing 3.5 mg/mL of starch concentration and (<b>a</b>) 0; (<b>b</b>) 0.5; (<b>c</b>) 1.0; (<b>d</b>) 1.5; (<b>e</b>) 2.0; (<b>f</b>) 2.5 mg/mL of ZnO nanoparticles concentration; and (<b>g</b>) cross section image of ZnO nanorods growth with f condition.</p> Full article ">Figure 7
<p>The FESEM images of ZnO nanorods with seed solutions containing 3.5 mg/mL of cellulose concentration with difference amount: (<b>a</b>) 0; (<b>b</b>) 1.0; (<b>c</b>) 3.5; (<b>d</b>) 7.5 mg/mL of ZnO nanoparticles concentration; and (<b>e</b>) cross section image of ZnO nanorods growth with d condition.</p> Full article ">Figure 8
<p>The EDX of ZnO nanorods.</p> Full article ">Figure 9
<p>The room temperature PL spectra of ZnO nanorods grown with difference seed layer solution consisting of (<b>a</b>) 2.0 mg/mL of ZnO nanoparticles in 3.5 mg/mL of starch concentration; (<b>b</b>) 7.5 mg/mL of ZnO nanoparticles in 3.5 mg/mL of cellulose concentration.</p> Full article ">
1072 KiB  
Article
Study of Lysozyme-Loaded Poly-L-Lactide (PLLA) Porous Microparticles in a Compressed CO2 Antisolvent Process
by Yong-Qiang Kang, Chen Zhao, Ai-Zheng Chen, Shi-Bin Wang, Yuan-Gang Liu, Wen-Guo Wu and Xiao-Qian Su
Materials 2013, 6(8), 3571-3583; https://doi.org/10.3390/ma6083571 - 19 Aug 2013
Cited by 16 | Viewed by 5661
Abstract
Lysozyme (LSZ)-loaded poly-L-lactide (PLLA) porous microparticles (PMs) were successfully prepared by a compressed CO2 antisolvent process in combination with a water-in-oil emulsion process using LSZ as a drug model and ammonium bicarbonate as a porogen. The effects of different drug loads (5.0%, [...] Read more.
Lysozyme (LSZ)-loaded poly-L-lactide (PLLA) porous microparticles (PMs) were successfully prepared by a compressed CO2 antisolvent process in combination with a water-in-oil emulsion process using LSZ as a drug model and ammonium bicarbonate as a porogen. The effects of different drug loads (5.0%, 7.5% and 10.0%) on the surface morphology, particle size, porosity, tapped density and drug release profile of the harvested PMs were investigated. The results show that an increase in the amount of LSZ added led to an increase in drug load (DL) but a decrease in encapsulation efficiency. The resulting LSZ-loaded PLLA PMs (LSZ-PLLA PMs) exhibited a porous and uneven morphology, with a density less than 0.1 g·cm?3, a geometric mean diameter of 16.9–18.8 ?m, an aerodynamic diameter less than 2.8 ?m, a fine particle fraction (FPF) of 59.2%–66.8%, and a porosity of 78.2%–86.3%. According to the results of differential scanning calorimetry, the addition of LSZ improved the thermal stability of PLLA. The Fourier transform infrared spectroscopy analysis and circular dichroism spectroscopy measurement reveal that no significant changes occurred in the molecular structures of LSZ during the fabrication process, which was further confirmed by the evaluation of enzyme activity of LSZ. It is demonstrated that the emulsion-combined precipitation with compressed antisolvent (PCA) process could be a promising technology to develop biomacromolecular drug-loaded inhalable carrier for pulmonary drug delivery. Full article
(This article belongs to the Section Biomaterials)
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<p>SEM images of lysozyme (LSZ)-loaded poly-L-lactide (PLLA) porous microparticles (PMs) (LSZ-PLLA PMs): (<b>a</b>) with magnification of 2.50 k; (<b>b</b>) with magnification of 7.00 k.</p> Full article ">Figure 2
<p>SEM images of LSZ-PLLA PMs of different drug loads (DLs) and their geometric particle size distributions.</p> Full article ">Figure 3
<p>(<b>a</b>) DL and EE of LSZ-PLLA PMs; (<b>b</b>)<span class="html-italic"> in vitro</span> release curves.</p> Full article ">Figure 4
<p>Fourier transform infrared (FTIR) spectra of pure LSZ, pure PLLA, PF127 and LSZ-PLLA PMs.</p> Full article ">Figure 5
<p>Circular dichroism (CD) spectra of pure LSZ and LSZ from LSZ-PLLA PMs.</p> Full article ">Figure 6
<p>Differential scanning calorimetry (DSC) curves of blank PLLA PMs and LSZ-PLLA PMs.</p> Full article ">Figure 7
<p>Thermogravimetric analysis (TGA) curves of pure PLLA, blank PLLA PMs and LSZ-PLLA PMs.</p> Full article ">Figure 8
<p>Enzyme activity curves of (<b>a</b>) pure LSZ; (<b>b</b>) LSZ from LSZ-PLLA PMs.</p> Full article ">
593 KiB  
Article
Periodic Mesoporous Organosilica Functionalized with Sulfonic Acid Groups as Acid Catalyst for Glycerol Acetylation
by Els De Canck, Inmaculada Dosuna-Rodríguez, Eric M. Gaigneaux and Pascal Van Der Voort
Materials 2013, 6(8), 3556-3570; https://doi.org/10.3390/ma6083556 - 16 Aug 2013
Cited by 23 | Viewed by 7190
Abstract
A Periodic Mesoporous Organosilica (PMO) functionalized with sulfonic acid groups has been successfully synthesized via a sequence of post-synthetic modification steps of a trans-ethenylene bridged PMO material. The double bond is functionalized via a bromination and subsequent substitution obtaining a thiol functionality. [...] Read more.
A Periodic Mesoporous Organosilica (PMO) functionalized with sulfonic acid groups has been successfully synthesized via a sequence of post-synthetic modification steps of a trans-ethenylene bridged PMO material. The double bond is functionalized via a bromination and subsequent substitution obtaining a thiol functionality. This is followed by an oxidation towards a sulfonic acid group. After full characterization, the solid acid catalyst is used in the acetylation of glycerol. The catalytic reactivity and reusability of the sulfonic acid modified PMO material is investigated. The catalyst showed a catalytic activity and kinetics that are comparable with the commercially available resin, Amberlyst-15, and furthermore our catalyst can be recycled for several subsequent catalytic runs and retains its catalytic activity. Full article
(This article belongs to the Section Porous Materials)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Summary of the synthetic pathways followed in this study. (<b>A</b>) Preparation of <span class="html-italic">trans</span>-ethenylene bridged Periodic Mesoporous Organosilica [EP]; (<b>B</b>) Bromination of EP [BEP]; (<b>C</b>) Substitution of the bromine with Grignard reagent of 3-chloro-1-propanethiol [EP–(CH<sub>2</sub>)<sub>3</sub>–SH] and (<b>D</b>) Oxidation with sulfuric acid [EP–(CH<sub>2</sub>)<sub>3</sub>–SO<sub>3</sub>H].</p> Full article ">Figure 2
<p>The nitrogen adsorption and desorption isotherms (<b>a</b>) and pore size distributions (<b>b</b>) of (A) EP; (B) BEP; (C) EP–(CH<sub>2</sub>)<sub>3</sub>–SH and (D) EP–(CH<sub>2</sub>)<sub>3</sub>–SO<sub>3</sub>H. The isotherms of BEP, EP–(CH<sub>2</sub>)<sub>3</sub>–SH and EP–(CH<sub>2</sub>)<sub>3</sub>–SO<sub>3</sub>H are vertically offset for clarity by 350, 700 and 900 mL (STP) g<sup>−1</sup> (Standard Temperature and Pressure), respectively.</p> Full article ">Figure 3
<p>The powder X-ray diffraction patterns of (<b>A</b>) EP; (<b>B</b>) BEP; (<b>C</b>) EP–(CH<sub>2</sub>)<sub>3</sub>–SH; and (<b>D</b>) EP–(CH<sub>2</sub>)<sub>3</sub>–SO<sub>3</sub>H.</p> Full article ">Figure 4
<p>The esterification reaction: the acetylation of glycerol with the formation of glycerol monoacetate, glycerol diacetate and glycerol triacetate.</p> Full article ">Figure 5
<p>The total acetylation yield for the catalytic reaction with EP–(CH<sub>2</sub>)<sub>3</sub>–SO<sub>3</sub>H and Amberlyst-15. Also the blank reaction is represented for clarity. A catalyst loading of 0.25 g per 40 mL of glycerol was used. The lines are intended as visual aids only.</p> Full article ">Figure 6
<p>Recyclability experiments for EP–(CH<sub>2</sub>)<sub>3</sub>–SO<sub>3</sub>H with several runs during the first hour of the reaction. The lines are intended as visual aids only.</p> Full article ">Figure 7
<p>Recyclability experiment for EP–(CH<sub>2</sub>)<sub>3</sub>–SO<sub>3</sub>H: a comparison between the catalytic activity of the pristine material and the third catalytic run. The blank reaction is presented for clarity. The lines are intended as visual aids only.</p> Full article ">Figure 8
<p>The total acetylation yield for the EP–(CH<sub>2</sub>)<sub>3</sub>–SO<sub>3</sub>H, the second and third run. After 60 min (represented by the vertical line) the liquid is separated from the catalyst and the catalytic activity of the liquid phase of run 2 and 3 is further followed in function of time (open square and triangle). The blank reaction is presented for clarity. The dotted lines are intended as visual aids only.</p> Full article ">
343 KiB  
Article
Synthesis, Structural Characterization, and Antitumor Activity of a Ca(II) Coordination Polymer Based on 1,6-Naphthalenedisulfonate and 4,4?-Bipyridyl
by Xishi Tai and Wenhua Zhao
Materials 2013, 6(8), 3547-3555; https://doi.org/10.3390/ma6083547 - 16 Aug 2013
Cited by 24 | Viewed by 4845
Abstract
A novel Ca(II) coordination polymer, [CaL(4,4?-bipyridyl)(H2O)4]n (L = 1,6-naphthalenedisulfonate), was synthesized by reaction of calcium perchlorate with 1,6-naphthalenedisulfonic acid disodium salt and 4,4?-bipyridyl in CH3CH2OH/H2O. It was characterized by elemental analysis, IR, [...] Read more.
A novel Ca(II) coordination polymer, [CaL(4,4?-bipyridyl)(H2O)4]n (L = 1,6-naphthalenedisulfonate), was synthesized by reaction of calcium perchlorate with 1,6-naphthalenedisulfonic acid disodium salt and 4,4?-bipyridyl in CH3CH2OH/H2O. It was characterized by elemental analysis, IR, molar conductivity and thermogravimetric analysis. X-ray crystallography reveals that the Ca(II) coordination polymer belongs to the orthorhombic system, with space group P212121. The geometry of the Ca(II) ion is a distorted CaNO6 pengonal bipyramid, arising from its coordination by four water molecules, one nitrogen atom of 4,4?-bipyridyl molecule, and two oxygen atoms from two L ligands. The complex molecules form a helical chain by self-assembly. The antitumor activity of 1,6-naphthalenedisulfonic acid disodium salt and the Ca(II) coordination polymer against human hepatoma smmc-7721 cell line and human lung adenocarcinoma A549 cell line reveals that the Ca(II) coordination polymer inhibits cell growth of human lung adenocarcinoma A549 cell line with IC50 value of 27 ?g/mL, and is more resistive to human lung adenocarcinoma A549 cell line as compared to 1,6-naphthalenedisulfonic acid disodium salt. Full article
(This article belongs to the Section Biomaterials)
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<p>Coordination environment around the Ca(II) center in the coordination polymer.</p> Full article ">Figure 2
<p>1D chained helical structure of the Ca(II) coordination polymer. The uncoordinated O atoms and the O atoms from coordinated water molecules were omitted for clarity.</p> Full article ">Figure 3
<p>3D network structure of the Ca(II) coordination polymer.</p> Full article ">
592 KiB  
Article
The Influence of Phase Change Materials on the Properties of Self-Compacting Concrete
by María Fenollera, José Luis Míguez, Itziar Goicoechea, Jaime Lorenzo and Miguel Ángel Álvarez
Materials 2013, 6(8), 3530-3546; https://doi.org/10.3390/ma6083530 - 15 Aug 2013
Cited by 63 | Viewed by 7931
Abstract
The aim of this paper is to research new thermally-efficient concrete walls, analyzing the mechanical behavior of a self-compacting concrete to manufacture an uncoated solid structural panel, with the incorporation of a micro-encapsulated phase change material as additive. Different dosages are tested and [...] Read more.
The aim of this paper is to research new thermally-efficient concrete walls, analyzing the mechanical behavior of a self-compacting concrete to manufacture an uncoated solid structural panel, with the incorporation of a micro-encapsulated phase change material as additive. Different dosages are tested and mechanical properties of the product obtained from the molding of concrete specimens are evaluated, testing mechanical compressive strength, slump flow, and density. The results reveal the optimum percentage of additive in the mixture that enables compliance with the technical specifications required by the product to be manufactured. A test is also performed for measuring the thermal conductivity for the optimal sample obtained and it evidences the reduction thereof. Full article
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<p>Aggregate size distribution.</p> Full article ">Figure 2
<p>Densities by percentage of added PCM.</p> Full article ">Figure 3
<p>Density ratio to percentage of PCM.</p> Full article ">Figure 4
<p>Relation between mechanical compressive strength and percentage of added PCM.</p> Full article ">Figure 5
<p>Mechanical compressive strength at 28 days.</p> Full article ">Figure 6
<p>(<b>A</b>) Specimens of mixes; (<b>B</b>) Breakage of a specimen with 20% PCM.</p> Full article ">Figure 7
<p>State of cracking of the sample with 10% of PCM during the trial.</p> Full article ">
1334 KiB  
Article
Small-Scale Morphological Features on a Solid Surface Processed by High-Pressure Abrasive Water Jet
by Can Kang and Haixia Liu
Materials 2013, 6(8), 3514-3529; https://doi.org/10.3390/ma6083514 - 14 Aug 2013
Cited by 12 | Viewed by 6264
Abstract
Being subjected to a high-pressure abrasive water jet, solid samples will experience an essential variation of both internal stress and physical characteristics, which is closely associated with the kinetic energy attached to the abrasive particles involved in the jet stream. Here, experiments were [...] Read more.
Being subjected to a high-pressure abrasive water jet, solid samples will experience an essential variation of both internal stress and physical characteristics, which is closely associated with the kinetic energy attached to the abrasive particles involved in the jet stream. Here, experiments were performed, with particular emphasis being placed on the kinetic energy attenuation and turbulent features in the jet stream. At jet pressure of 260 MPa, mean velocity and root-mean-square (RMS) velocity on two jet-stream sections were acquired by utilizing the phase Doppler anemometry (PDA) technique. A jet-cutting experiment was then carried out with Al-Mg alloy samples being cut by an abrasive water jet. Morphological features and roughness on the cut surface were quantitatively examined through scanning electron microscopy (SEM) and optical profiling techniques. The results indicate that the high-pressure water jet is characterized by remarkably high mean flow velocities and distinct velocity fluctuations. Those irregular pits and grooves on the cut surfaces indicate both the energy attenuation and the development of radial velocity components in the jet stream. When the sample is positioned with different distances from the nozzle outlet, the obtained quantitative surface roughness varies accordingly. A descriptive model highlighting the behaviors of abrasive particles in jet-cutting process is established in light of the experimental results and correlation analysis. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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<p>Schematic diagram of phase Doppler anemometry system and jet flow measurement.</p> Full article ">Figure 2
<p>Configuration of the experimental components.</p> Full article ">Figure 3
<p>Arrangement and validation of measurement volume. (<b>a</b>) Positions of measurement volumes on a studied section; (<b>b</b>) distribution of the velocities of those droplets passing through the measurement volume deployed at the center of <span class="html-italic">Z</span> = 3.0 mm section within 57 ms.</p> Full article ">Figure 4
<p>Distributions of mean velocity at (<b>a</b>) <span class="html-italic">Z</span> = 3.0 mm and (<b>b</b>) <span class="html-italic">Z</span> = 7.0 mm.</p> Full article ">Figure 5
<p>Distributions of root-mean-square velocity at (<b>a</b>) Z = 3.0 mm; and (<b>b</b>) Z = 7.0 mm.</p> Full article ">Figure 5 Cont.
<p>Distributions of root-mean-square velocity at (<b>a</b>) Z = 3.0 mm; and (<b>b</b>) Z = 7.0 mm.</p> Full article ">Figure 6
<p>Liquid-solid two-phase jet nozzle. (<b>a</b>) Schematic view; (<b>b</b>) image of the nozzle.</p> Full article ">Figure 7
<p>Surface morphological features on cut sections: (<b>a</b>) <span class="html-italic">Z</span> = 3.0 mm; (<b>b</b>) <span class="html-italic">Z</span> = 7.0 mm.</p> Full article ">Figure 8
<p>Three-dimensional surface morphological features: (<b>a</b>) <span class="html-italic">Z</span> = 3.0 mm; (<b>b</b>) <span class="html-italic">Z</span> = 7.0 mm.</p> Full article ">Figure 9
<p>Statistical relation based on the morphological data (for comparison, a base plane where the relative height is predefined to be zero is identically set for the four zones.).</p> Full article ">Figure 10
<p>Five phases in the jet-cutting process (the blue kerf is assumed to develop primarily in the longitudinal direction).</p> Full article ">
1994 KiB  
Article
Effects on the Thermo-Mechanical and Crystallinity Properties of Nylon 6,6 Electrospun Fibres Reinforced with One Dimensional (1D) and Two Dimensional (2D) Carbon
by Fabiola Navarro-Pardo, Gonzalo Martínez-Barrera, Ana Laura Martínez-Hernández, Víctor M. Castaño, José Luis Rivera-Armenta, Francisco Medellín-Rodríguez and Carlos Velasco-Santos
Materials 2013, 6(8), 3494-3513; https://doi.org/10.3390/ma6083494 - 14 Aug 2013
Cited by 149 | Viewed by 11227
Abstract
Electrospun one dimensional (1D) and two dimensional (2D) carbon based polymer nanocomposites are studied in order to determine the effect provided by the two differently structured nanofillers on crystallinity and thermo-mechanical properties of the nanofibres. The nanomaterials studied are pristine carbon nanotubes, oxidised [...] Read more.
Electrospun one dimensional (1D) and two dimensional (2D) carbon based polymer nanocomposites are studied in order to determine the effect provided by the two differently structured nanofillers on crystallinity and thermo-mechanical properties of the nanofibres. The nanomaterials studied are pristine carbon nanotubes, oxidised carbon nanotubes, reduced graphene oxide and graphene oxide. Functional groups associated with the order structure of the polymers are analysed by infrared and Raman spectroscopies; the morphology is studied by scanning electron microscopy and the crystallinity properties are investigated by differential scanning calorimetry and X-ray diffraction. Differences in crystallisation behaviour between 1D and 2D carbon based nanofibres are shown by their crystallinity degree and their crystal sizes. The nanocomposite crystal sizes perpendicular to the plane (100) decrease with nanofiller content in all cases. The crystallinity trend and crystal sizes are in accordance with storage modulus response. The results also suggest that functionalisation favours interfacial bonding and dispersion of the nanomaterials within the polymer matrix. As a consequence the number of nucleating sites increases which in turn decreases the crystal size in the nanocomposites. These features explain the improved thermo-mechanical properties in the nanocomposites. Full article
(This article belongs to the Special Issue Carbon Nanotubes)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Fourier transform infrared spectroscopy (FTIR) spectra of: (<b>a</b>) Carbon nanotubes (CNTs); (<b>b</b>) oxidised carbon nanotubes (OCNTs); (<b>c</b>) reduced graphene oxide (RGO) and (<b>d</b>) graphene oxide (GO).</p> Full article ">Figure 2
<p>Raman spectra of: (<b>a</b>) CNTs; (<b>b</b>) OCNTs; (<b>c</b>) RGO and (<b>d</b>) GO.</p> Full article ">Figure 3
<p>Transmission electron microscopy (TEM) images of: (<b>a</b>) CNTs; (<b>b</b>) OCNTs; (<b>c</b>) RGO and (<b>d</b>) GO.</p> Full article ">Figure 4
<p>FTIR spectra of (<b>A</b>) zoom-in of ~935 cm<sup>−1</sup> peak; (<b>B</b>) zoom-in of ~1200 cm<sup>−1</sup> peak and (<b>C</b>) region of 900–3500 cm<sup>−1</sup> of the samples: (<b>a</b>) pure PA66; (<b>b</b>) PA66/01CNTs; (<b>c</b>) PA66/05CNTs; (<b>d</b>) PA66/10CNTs; (<b>e</b>) PA66/01OCNTs; (<b>f</b>) PA66/05OCNTs and (<b>g</b>) PA66/10OCNTs.</p> Full article ">Figure 5
<p>FTIR spectra of (<b>A</b>) zoom-in of ~935 cm<sup>−1</sup> peak<b>;</b> (<b>B</b>) zoom-in of ~1200 cm<sup>−1</sup> peak and (<b>C</b>) region of 900–3500 cm<sup>−1</sup> of the samples: (<b>a</b>) pure PA66; (<b>b</b>) PA66/01RGO; (<b>c</b>) PA66/05RGO; (<b>d</b>) PA66/10RGO; (<b>e</b>) PA66/01GO; (<b>f</b>) PA66/05GO and (<b>g</b>) PA66/10GO.</p> Full article ">Figure 6
<p>Nanofibres intramolecular bonding in the (<b>a</b>,<b>c</b>) PA66/OCNTs and the (<b>b</b>,<b>d</b>) PA66/GO nanocomposites.</p> Full article ">Figure 7
<p>Raman spectra of the (<b>A</b>) 800–2000 cm<sup>−1</sup> region and (<b>B</b>) zoom-out of the 2800–3350 cm<sup>−1</sup> region of the samples: (<b>a</b>) pure PA66; (<b>b</b>) PA66/01CNTs; (<b>c</b>) PA66/05CNTs; (<b>d</b>) PA66/10CNTs; (<b>e</b>) PA66/01OCNTs; (<b>f</b>) PA66/05OCNTs and (<b>g</b>) PA66/10OCNTs.</p> Full article ">Figure 8
<p>Raman spectra of the (<b>A</b>) 800–2000 cm<sup>−1</sup> region and (<b>B</b>) zoom-out of the 2800–3350 cm<sup>−1</sup> region of the samples: (<b>a</b>) pure PA66; (<b>b</b>) PA66/01RGO; (<b>c</b>) PA66/05RGO; (<b>d</b>) PA66/10RGO; (<b>e</b>) PA66/01GO; (<b>f</b>) PA66/05GO and (<b>g</b>) PA66/10GO.</p> Full article ">Figure 9
<p>Scanning electron microscopy (SEM) and TEM images of: (<b>a</b>,<b>f</b>) pure PA66; (<b>b</b>,<b>g</b>) PA66/10CNTs; (<b>c</b>,<b>h</b>) PA66/10OCNTs; (<b>d</b>,<b>i</b>) PA66/10RGO and (<b>e</b>,<b>j</b>) PA66/10GO.</p> Full article ">Figure 10
<p>Differential scanning calorimetry (DSC) (<b>A</b>) heating and (<b>B</b>) cooling thermograms of: (<b>a</b>) pure PA66; (<b>b</b>) PA66/01CNTs; (<b>c</b>) PA66/05CNTs; (<b>d</b>) PA66/10CNTs; (<b>e</b>) PA66/01OCNTs; (<b>f</b>) PA66/05OCNTs and (<b>g</b>) PA66/10OCNTs.</p> Full article ">Figure 11
<p>DSC (<b>A</b>) heating and (<b>B</b>) cooling thermograms of: (<b>a</b>) pure PA66; (<b>b</b>) PA66/01RGO; (<b>c</b>) PA66/05RGO; (<b>d</b>) PA66/10RGO; (<b>e</b>) PA66/01GO; (<b>f</b>) PA66/05GO and (<b>g</b>) PA66/10GO.</p> Full article ">Figure 12
<p>(<b>A</b>) WAXD patterns of: (<b>a</b>) pure PA66; (<b>b</b>) PA66/01CNTs; (<b>c</b>) PA66/05CNTs; (<b>d</b>) PA66/10CNTs; (<b>e</b>) PA66/01OCNTs; (<b>f</b>) PA66/05OCNTs and (<b>g</b>) PA66/10OCNTs. (<b>B</b>) WAXD patterns of: (<b>a</b>) pure PA66; (<b>b</b>) PA66/01RGO; (<b>c</b>) PA66/05RGO; (<b>d</b>) PA66/10RGO; (<b>e</b>) PA66/01GO; (<b>f</b>) PA66/05GO and (<b>g</b>) PA66/10GO.</p> Full article ">Figure 13
<p>Dynamic mechanical analyser (DMA) results; (<b>A</b>) storage modulus and (<b>B</b>) Tanδ of: (<b>a</b>) pure PA66; (<b>b</b>) PA66/01CNTs; (<b>c</b>) PA66/05CNTs; (<b>d</b>) PA66/10CNTs; (<b>e</b>) PA66/01OCNTs; (<b>f</b>) PA66/05OCNTs and (<b>g</b>) PA66/10OCNTs.</p> Full article ">Figure 14
<p>DMA results; (<b>A</b>) storage modulus and (<b>B</b>) Tanδ of: (<b>a</b>) pure PA66, (<b>b</b>) PA66/01RGO; (<b>c</b>) PA66/05RGO; (<b>d</b>) PA66/10RGO; (<b>e</b>) PA66/01GO; (<b>f</b>) PA66/05GO and (<b>g</b>) PA66/10GO.</p> Full article ">
809 KiB  
Article
Study of Radio Frequency Plasma Treatment of PVDF Film Using Ar, O2 and (Ar + O2) Gases for Improved Polypyrrole Adhesion
by Akif Kaynak, Tariq Mehmood, Xiujuan J. Dai, Kevin Magniez and Abbas Kouzani
Materials 2013, 6(8), 3482-3493; https://doi.org/10.3390/ma6083482 - 13 Aug 2013
Cited by 49 | Viewed by 8460
Abstract
Improvement of the binding of polypyrrole with PVDF (polyvinylidene fluoride) thin film using low pressure plasma was studied. The effects of various plasma gases i.e., Ar, O2 and Ar + O2 gases on surface roughness, surface chemistry and hydrophilicity [...] Read more.
Improvement of the binding of polypyrrole with PVDF (polyvinylidene fluoride) thin film using low pressure plasma was studied. The effects of various plasma gases i.e., Ar, O2 and Ar + O2 gases on surface roughness, surface chemistry and hydrophilicity were noted. The topographical change of the PVDF film was observed by means of scanning electron microscopy and chemical changes by X-ray photoelectron spectroscopy, with adhesion of polypyrrole (PPy) by abrasion tests and sheet resistance measurements. Results showed that the increase in roughness and surface functionalization by oxygen functional groups contributed to improved adhesion and Ar + O2 plasma gave better adhesion. Full article
(This article belongs to the Special Issue Advances in Surface Coatings)
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<p>Water contact angle (WCA) of polyvinylidene fluoride (PVDF) thin film before and after Ar, O<sub>2</sub> and (Ar + O<sub>2</sub>) plasma treatment.</p> Full article ">Figure 2
<p>Scanning electron microscope (SEM) micrograph of polyvinylidene fluoride (PVDF): (<b>a</b>) control; (<b>b</b>) Ar plasma; (<b>c</b>) O<sub>2</sub> plasma and (<b>d</b>,<b>e</b>) (Ar + O<sub>2</sub>) plasma.</p> Full article ">Figure 3
<p>X-ray photoelectron spectroscopy (XPS) survey scan of polyvinylidene fluoride (PVDF) film before and after Ar, O<sub>2</sub> and Ar + O<sub>2</sub> plasma treatment.</p> Full article ">Figure 4
<p>C1s scan spectra of polyvinylidene fluoride (PVDF). (<b>a</b>) Control; (<b>b</b>) Ar plasma; (<b>c</b>) O<sub>2</sub> plasma and (<b>d</b>) (Ar + O<sub>2</sub>) plasma.</p> Full article ">Figure 5
<p>Polypyrrole (PPy) coated polyvinylidene fluoride (PVDF) film sample after 0, 200 and 2000 abrasion cycles in a Martindale abrasion tester for control, Ar, O<sub>2</sub> and (Ar + O<sub>2</sub>) samples; magnification 10×.</p> Full article ">Figure 6
<p>Sheet resistance of polypyrrole (PPy) coated polyvinylidene fluoride (PVDF) samples; control, Ar, O<sub>2</sub> and (Ar + O<sub>2</sub>).</p> Full article ">
3177 KiB  
Article
Cyclic Deformation of Ultra-Fine Grained Commercial Purity Aluminum Processed by Accumulative Roll-Bonding
by Charles C.F. Kwan and Zhirui Wang
Materials 2013, 6(8), 3469-3481; https://doi.org/10.3390/ma6083469 - 13 Aug 2013
Cited by 4 | Viewed by 5633
Abstract
Accumulative Roll-Bonding (ARB) is one of the more recently developed techniques capable of producing bulk ultra-fine grained (ufg) metals. There are still many aspects of the behavior of ufg metals that lacks an in-depth understanding, such as a generalized view of the factors [...] Read more.
Accumulative Roll-Bonding (ARB) is one of the more recently developed techniques capable of producing bulk ultra-fine grained (ufg) metals. There are still many aspects of the behavior of ufg metals that lacks an in-depth understanding, such as a generalized view of the factors that govern the cyclic deformation mechanism(s). This study aims to advance the understanding of the cyclic deformation behavior of ufg metals through the systematic investigation of ARB processed aluminum upon cyclic loading. It was found that the cyclic softening response often reported for ufg metals is largely influenced by the microstructure stability as the cyclic softening response is facilitated by grain coarsening which becomes inhibited with highly stable microstructure. On one hand, shear bands resembling braids of dislocations trespassing multiple grains have been observed to operate for the accommodation of the imposed cyclic strain in cases where grain coarsening is largely restricted. On the other hand, it was found that the microstructure stability can be overcome at higher applied cyclic plastic strain levels, leading to grain coarsening and thus a cyclic softening response. The findings in this study have further confirmed that the cyclic softening behavior found in many ufg metals, which may be detrimental in practical applications, can be inhibited by improvements in the microstructure stability. Full article
(This article belongs to the Section Advanced Materials Characterization)
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<p>Microstructure of the (<b>a</b>) 4p; (<b>b</b>) 6p; and (<b>c</b>) 8p Accumulative Roll Bonding (ARB) CP aluminum samples as viewed under bright field transmission electron microscope (TEM) imaging; (<b>d</b>) an Electron Channeling Contrast Imaging (ECCI) micrograph of an 8p samples showing the composite nature of the present microstructure.</p> Full article ">Figure 2
<p>Plot of the mean strain of each cycle demonstrating the cyclic creep behavior of 4p, 6p, and 8p ARBed CP aluminum samples under load controlled testing with σ<sub>peak</sub> = 100% of the respective yield strength. The curve for conventional aluminum is also shown for comparison purposes.</p> Full article ">Figure 3
<p>Plots of the trend of hysteresis loop width representing the cyclic hardening/softening behavior of ARBed CP aluminum of (<b>a</b>) an 8p sample upon cyclic deformation with different parameters; and (<b>b</b>) of 4p, 6p, and 8p samples upon cyclic loaded under total strain controlled with an amplitude of Δε<sub>total</sub>/2 = 3.2 × 10<sup>−3</sup>.</p> Full article ">Figure 4
<p>ECCI micrograph showing an 8p ARBed CP aluminum sample upon cyclic loaded under total strain controlled with an amplitude of Δε<sub>total</sub>/2 = 3.7 × 10<sup>−3</sup>, (<b>a</b>) prior to any cyclic loading; and (<b>b</b>) after cyclic fracture at 1333 cycles at the same location as (<b>a</b>). (<b>c</b>,<b>d</b>) is a similar set at higher magnification showing the minor coarsening observed (arrowed in (<b>d</b>)).</p> Full article ">Figure 5
<p>Bright field TEM micrographs of 8p ARBed CP aluminum samples (<b>a</b>) in the as-ARBed form; and (<b>b</b>) after cyclic loading under load controlled with peak stress σ<sub>peak</sub> = 90% σ<sub>y</sub> and R = 0.05 after cyclic fracture at 44404 cycles. The observed shear bands in the form of braids of dislocations are arrowed in (<b>b</b>).</p> Full article ">
1504 KiB  
Article
Manufacturing and Characterization of 18Ni Marage 300 Lattice Components by Selective Laser Melting
by Nicola Contuzzi, Sabina L. Campanelli, Caterina Casavola and Luciano Lamberti
Materials 2013, 6(8), 3451-3468; https://doi.org/10.3390/ma6083451 - 13 Aug 2013
Cited by 44 | Viewed by 8774
Abstract
The spreading use of cellular structures brings the need to speed up manufacturing processes without deteriorating mechanical properties. By using Selective Laser Melting (SLM) to produce cellular structures, the designer has total freedom in defining part geometry and manufacturing is simplified. The paper [...] Read more.
The spreading use of cellular structures brings the need to speed up manufacturing processes without deteriorating mechanical properties. By using Selective Laser Melting (SLM) to produce cellular structures, the designer has total freedom in defining part geometry and manufacturing is simplified. The paper investigates the suitability of Selective Laser Melting for manufacturing steel cellular lattice structures with characteristic dimensions in the micrometer range. Alternative lattice topologies including reinforcing bars in the vertical direction also are considered. The selected lattice structure topology is shown to be superior over other lattice structure designs considered in literature. Compression tests are carried out in order to evaluate mechanical strength of lattice strut specimens made via SLM. Compressive behavior of samples also is simulated by finite element analysis and numerical results are compared with experimental data in order to assess the constitutive behavior of the lattice structure designs considered in this study. Experimental data show that it is possible to build samples of relative density in the 0.2456–0.4367 range. Compressive strength changes almost linearly with respect to relative density, which in turns depends linearly on the number of vertical reinforces. Specific strength increases with cell and strut edge size. Numerical simulations confirm the plastic nature of the instability phenomena that leads the cellular structures to collapse under compression loading. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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<p>Comparison of performance of the most common cell topologies.</p> Full article ">Figure 2
<p>Schematic illustration of the pillar texile unit cell and main geometric dimensions.</p> Full article ">Figure 3
<p>Schematic of the Selective Laser Melting equipment.</p> Full article ">Figure 4
<p>Micrographs of part cross-sectional area recorded at 100× magnification.</p> Full article ">Figure 5
<p>(<b>a</b>) SEM image of the CL50WC powder (1000× magnification); (<b>b</b>) Chemical composition of the powder.</p> Full article ">Figure 6
<p>Schematic of optimized and alternative cell topologies including vertical reinforcements.</p> Full article ">Figure 7
<p>Samples 1, 2 and 3 built by SLM (Design A specimens): (<b>a</b>) Base structure; (<b>b</b>) Structure with 4 reinforcement columns; (<b>c</b>) Structure with 8 reinforcement columns; (<b>d</b>) Deformed base structure; (<b>e</b>) Deformed 4-column reinforced structure; (<b>f</b>) Deformed 8-column reinforced structure; (<b>g</b>) Typical collapse mode of struts observed in the experiments.</p> Full article ">Figure 8
<p>Load-displacement curves for design A type samples (<b>a</b>) and design B type samples (<b>b</b>).</p> Full article ">Figure 9
<p>Stress-strain curves corresponding to MELAS and MISO options utilized in the finite element simulations to model the nonlinear constitutive behavior of 18Ni Marage 300.</p> Full article ">Figure 10
<p>(<b>a</b>) 3D model of the pillar texile micro-cellular structure defined in ANSYS; (<b>b</b>) Finite element mesh of the 3D model.</p> Full article ">Figure 11
<p>Deformed shapes computed by ANSYS: (<b>a</b>) Specimen 1; (<b>b</b>) Specimen 2; (<b>c</b>) Specimen 3.</p> Full article ">Figure 12
<p>Comparison of the load-displacement and stress-strain curves recorded experimentally and simulated numerically: (<b>a</b>) Sample 1; (<b>b</b>) Sample 4; (<b>c</b>) Sample 2; (<b>d</b>) Sample 5; (<b>e</b>) Sample 3; (<b>f</b>) Sample 6.</p> Full article ">Figure 12 Cont.
<p>Comparison of the load-displacement and stress-strain curves recorded experimentally and simulated numerically: (<b>a</b>) Sample 1; (<b>b</b>) Sample 4; (<b>c</b>) Sample 2; (<b>d</b>) Sample 5; (<b>e</b>) Sample 3; (<b>f</b>) Sample 6.</p> Full article ">
575 KiB  
Article
Self-Healing Characteristics of Damaged Rock Salt under Different Healing Conditions
by Jie Chen, Song Ren, Chunhe Yang, Deyi Jiang and Lin Li
Materials 2013, 6(8), 3438-3450; https://doi.org/10.3390/ma6083438 - 12 Aug 2013
Cited by 87 | Viewed by 7277
Abstract
Salt deposits are commonly regarded as ideal hosts for geologic energy reservoirs. Underground cavern construction-induced damage in salt is reduced by self-healing. Thus, studying the influencing factors on such healing processes is important. This research uses ultrasonic technology to monitor the longitudinal wave [...] Read more.
Salt deposits are commonly regarded as ideal hosts for geologic energy reservoirs. Underground cavern construction-induced damage in salt is reduced by self-healing. Thus, studying the influencing factors on such healing processes is important. This research uses ultrasonic technology to monitor the longitudinal wave velocity variations of stress-damaged rock salts during self-recovery experiments under different recovery conditions. The influences of stress-induced initial damage, temperature, humidity, and oil on the self-recovery of damaged rock salts are analyzed. The wave velocity values of the damaged rock salts increase rapidly during the first 200 h of recovery, and the values gradually increase toward stabilization after 600 h. The recovery of damaged rock salts is subjected to higher initial damage stress. Water is important in damage recovery. The increase in temperature improves damage recovery when water is abundant, but hinders recovery when water evaporates. The presence of residual hydraulic oil blocks the inter-granular role of water and restrains the recovery under triaxial compression. The results indicate that rock salt damage recovery is related to the damage degree, pore pressure, temperature, humidity, and presence of oil due to the sealing integrity of the jacket material. Full article
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<p>The test device and samples: (<b>a</b>) Rock salt specimens; (<b>b</b>) UPV-1 ultrasonic detector.</p> Full article ">Figure 2
<p>Damage variation and time relation curve (<b>a</b>) The relationship between wave velocity and time curve of rock salts at room temperature, 50 °C and 70 °C, as well as constant humidity; (<b>b</b>) The relationship between wave velocity and time curve of Pakistani rock salts at 50 °C and 110 °C holding in the oven.</p> Full article ">Figure 3
<p>Value of stress-induced initial damage <span class="html-italic">vs.</span> value of damage in stable stage.</p> Full article ">Figure 4
<p>Value of stress-induced initial damage <span class="html-italic">vs.</span> total value of damage recovery.</p> Full article ">Figure 5
<p>Time of recovery <span class="html-italic">vs.</span> value of lateral damage with or without water.</p> Full article ">Figure 6
<p>The relationship curve between wave velocity in triaxial compression and recovery time.</p> Full article ">
805 KiB  
Article
Recycling of Pre-Washed Municipal Solid Waste Incinerator Fly Ash in the Manufacturing of Low Temperature Setting Geopolymer Materials
by Claudio Ferone, Francesco Colangelo, Francesco Messina, Luciano Santoro and Raffaele Cioffi
Materials 2013, 6(8), 3420-3437; https://doi.org/10.3390/ma6083420 - 12 Aug 2013
Cited by 101 | Viewed by 8504
Abstract
In this work, three samples of municipal solid waste incinerators fly ash (MSWI-FA) have been stabilized in systems containing coal fly ash to create geopolymers through a polycondensation reaction. Monolithic products have been obtained with both MSWI fly ash as received and after [...] Read more.
In this work, three samples of municipal solid waste incinerators fly ash (MSWI-FA) have been stabilized in systems containing coal fly ash to create geopolymers through a polycondensation reaction. Monolithic products have been obtained with both MSWI fly ash as received and after the partial removal of chloride and sulfate by water washing. The polycondensation products have been characterized qualitatively by means of Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy and quantitatively, through the determination of the volume of reacted water and silicate. Furthermore, the heavy metals and chloride releases together with the physico-mechanical properties have been evaluated on the hardened products. In conclusion, considering the technological and environmental performances of the obtained geopolymers, they could be suitable for many non-structural applications, such as backfilling of abandoned quarries, decorative materials or brick fireplaces, hearths, patios, etc. Full article
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<p>FT-IR characterization of system GB<sub>AR</sub> at several selected polycondensation times.</p> Full article ">Figure 2
<p>SEM Micrographs of systems (<b>a</b>) GA<sub>AR</sub> 28 days; (<b>b</b>) GB<sub>AR</sub> 28 days and (<b>c</b>) GC<sub>AR</sub> 28 days.</p> Full article ">Figure 3
<p>SEM Micrographs of system containing washed A ash, (<b>a</b>) 500× and (<b>b</b>) 5000× magnifications.</p> Full article ">Figure 4
<p>X-ray diffraction (XRD) patterns of B<sub>AR</sub>, GB<sub>AR</sub> 3 days, GB<sub>AR</sub> 14 days and GB<sub>AR</sub> 28 days samples.</p> Full article ">Figure 5
<p>Compressive strength of MSWI-FA geopolymeric cubic specimens.</p> Full article ">
393 KiB  
Case Report
Optimization of Microwave-Based Heating of Cellulosic Biomass Using Taguchi Method
by Kuo-Hsiung Tseng, Yong-Fong Shiao, Ruey-Fong Chang and Yu-Ting Yeh
Materials 2013, 6(8), 3404-3419; https://doi.org/10.3390/ma6083404 - 9 Aug 2013
Cited by 22 | Viewed by 7086
Abstract
This study discusses the application of microwave-based heating for the pretreatment of biomass material, with Pennisetum purpureum selected for pretreatment. The Taguchi method was used to plan optimization experiments for the pretreatment parameter levels, and to measure the dynamic responses. With a low [...] Read more.
This study discusses the application of microwave-based heating for the pretreatment of biomass material, with Pennisetum purpureum selected for pretreatment. The Taguchi method was used to plan optimization experiments for the pretreatment parameter levels, and to measure the dynamic responses. With a low number of experiments, this study analyzed and determined a parameter combination in which Pennisetum purpureum can be rapidly heated to 190 °C. The experimental results suggested that the optimal parameter combination is: vessel capacity of 150 mL (level 2), heating power of 0.5 kW (level 1), and mass of Pennisetum purpureum of 5 g (level 1). The mass of Pennisetum purpureum is a key factor affecting system performance. An eight-order ARX model (Auto-Regressive eXogeneous) was representative of the actual system performance, and the fit was 99.13%. The results proved that microwave-based heating, with the assistance of the Taguchi method for pretreatment of the biomass material, can reduce the parameter combination variations. Full article
(This article belongs to the Special Issue Microwave Processing of Materials)
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<p>Microwave-based heating device and measuring equipment.</p> Full article ">Figure 2
<p>Taguchi method flow.</p> Full article ">Figure 3
<p>State diagram of microwave-based heating power.</p> Full article ">Figure 4
<p>State diagram of microwave-based heating power.</p> Full article ">Figure 5
<p>System identification flow chart.</p> Full article ">Figure 6
<p>Response diagram of Taguchi experiments.</p> Full article ">Figure 7
<p>Relation between confidence intervals of predicted value and actual value.</p> Full article ">Figure 8
<p>Dynamic response of actual system input and output.</p> Full article ">Figure 9
<p>Order of optimal noise model using 4SID (SubSpace-base State Space Model Identification Method).</p> Full article ">Figure 10
<p>Simulated dynamic response of actual system and ARX881.</p> Full article ">Figure 11
<p>Relation between microwave energy transmission and system structure.</p> Full article ">Figure 12
<p>Results of residual analysis of the models.</p> Full article ">Figure 13
<p>ARX block diagram.</p> Full article ">
2049 KiB  
Article
Thermal Fatigue Behavior of Air-Plasma Sprayed Thermal Barrier Coating with Bond Coat Species in Cyclic Thermal Exposure
by Zhe Lu, Sang-Won Myoung, Yeon-Gil Jung, Govindasamy Balakrishnan, Jeongseung Lee and Ungyu Paik
Materials 2013, 6(8), 3387-3403; https://doi.org/10.3390/ma6083387 - 8 Aug 2013
Cited by 31 | Viewed by 9010
Abstract
The effects of the bond coat species on the delamination or fracture behavior in thermal barrier coatings (TBCs) was investigated using the yclic thermal fatigue and thermal-shock tests. The interface microstructures of each TBC showed a good condition without cracking or delamination after [...] Read more.
The effects of the bond coat species on the delamination or fracture behavior in thermal barrier coatings (TBCs) was investigated using the yclic thermal fatigue and thermal-shock tests. The interface microstructures of each TBC showed a good condition without cracking or delamination after flame thermal fatigue (FTF) for 1429 cycles. The TBC with the bond coat prepared by the air-plasma spray (APS) method showed a good condition at the interface between the top and bond coats after cyclic furnace thermal fatigue (CFTF) for 1429 cycles, whereas the TBCs with the bond coats prepared by the high-velocity oxygen fuel (HVOF) and low-pressure plasma spray (LPPS) methods showed a partial cracking (and/or delamination) and a delamination after 780 cycles, respectively. The TBCs with the bond coats prepared by the APS, HVOF and LPPS methods were fully delaminated (>50%) after 159, 36, and 46 cycles, respectively, during the thermal-shock tests. The TGO thickness in the TBCs was strongly dependent on the both exposure time and temperature difference tested. The hardness values were found to be increased only after the CFTF, and the TBC with the bond coat prepared by the APS showed the highest adhesive strength before and after the FTF. Full article
(This article belongs to the Special Issue Advances in Surface Coatings 2013)
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<p>Photos of each test apparatus: Cyclic furnacec thermal fatigue (CFTF), thermal shock test (TS), and flame thermal fatigue (FTF).</p> Full article ">Figure 2
<p>Cross-sectional microstructures of as-prepared thermal barrier coating (TBCs): (<b>A</b>) TBC with air-plasma spray (APS) bond coat; (<b>B</b>) Thermal barrier coating (TBC) with HVOF bond coat; and (<b>C</b>) TBC with low-pressure plasma spray (LPPS) bond coat. Each number indicates the overall and interface microstructures, respectively.</p> Full article ">Figure 3
<p>Cross-sectional microstructures of TBCs after FTF tests for 1429 cycles: (<b>A</b>) TBC with APS bond coat; (<b>B</b>) TBC with HVOF bond coat; and (<b>C</b>) TBC with LPPS bond coat. Each number indicates the overall and interface microstructures, respectively.</p> Full article ">Figure 4
<p>Cross-sectional microstructures of TBCs after CFTF tests: (<b>A</b>) TBC with APS bond coat; (<b>B</b>) TBC with HVOF bond coat; and (<b>C</b>) TBC with LPPS bond coat. Each number indicates the overall and interface microstructures, respectively.</p> Full article ">Figure 5
<p>The lifetime of TBCs with different bond coats after CFTF tests as a function of cycle number.</p> Full article ">Figure 6
<p>Surface micrographs and cross-sectional microstructures of TBCs after TS tests: (<b>A</b>) TBC with APS bond coat; (<b>B</b>) TBC with HVOF bond coat; and (<b>C</b>) TBC with LPPS bond coat. Each number indicates surface micrographs, cross-sectional interface microstructures between the top and bond coats, and high magnification interface microstructures, respectively.</p> Full article ">Figure 7
<p>Variation of delamination area with thermal fatigue cycle in thermal-shock tests. The solid curves are empirical data fits.</p> Full article ">Figure 8
<p>X-ray diffraction (XRD) pattern of TBCs of as-prepared and after cyclic thermal exposure.</p> Full article ">Figure 9
<p>Thickness of thermally grown oxide (TGO) layer with bond coat species after different thermal exposure tests. Black, gray, and white marks indicate the TGO thickness values after the CFTF, TS, and FTF tests, respectively.</p> Full article ">Figure 10
<p>Hardness values of top coats before and after cyclic thermal exposure. Indentation for hardness was conducted on the sectional plane with a load of 3 N. The nominal value of as-prepared TBC was indicated inside figure. Filled and open marks indicate the hardness values after the CFTF and ETF tests, respectively.</p> Full article ">Figure 11
<p>Hardness values of bond coats before and after cyclic thermal exposure. Indentation for hardness was conducted on the sectional plane at 3 N.</p> Full article ">Figure 12
<p>Adhesive strength values of TBCs before and after the FTF.</p> Full article ">
877 KiB  
Article
Effect of Annealing Temperature on the Water Contact Angle of PVD Hard Coatings
by Yu-Sen Yang and Ting-Pin Cho
Materials 2013, 6(8), 3373-3386; https://doi.org/10.3390/ma6083373 - 7 Aug 2013
Cited by 8 | Viewed by 8488
Abstract
Various PVD (physical vapor deposition) hard coatings including nitrides and metal-doped diamond-like carbons (Me-DLC) were applied in plastic injection and die-casting molds to improve wear resistance and reduce sticking. In this study, nitrides hcp-AlN (hexagonal close-packed AlN), Cr2N, (CrAl)2N) [...] Read more.
Various PVD (physical vapor deposition) hard coatings including nitrides and metal-doped diamond-like carbons (Me-DLC) were applied in plastic injection and die-casting molds to improve wear resistance and reduce sticking. In this study, nitrides hcp-AlN (hexagonal close-packed AlN), Cr2N, (CrAl)2N) and Me-DLC (Si-DLC and Cr-DLC) coatings were prepared using a closed field unbalanced magnetron reactive sputtering system. The coatings were annealed in air for 2 h at various temperatures, after which the anti-sticking properties were assessed using water contact angle (WCA) measurements. The as-deposited hcp-AlN, Cr2N and (CrAl)2N coatings exhibit hydrophobic behavior and exhibit respective WCAs of 119°, 106° and 101°. The as-deposited Si-DLC and Cr-DLC coatings exhibit hydrophilic behavior and exhibit respective WCAs of 74° and 88°. The annealed Cr2N and (CrAl)2N coatings exhibit hydrophobic behavior with higher WCAs, while the annealed hcp-AlN, Si-DLC and Cr-DLC coatings are hydrophilic. The increased WCA of the annealed Cr2N and (CrAl)2N coatings is related to their crystal structure and increased roughness. The decreased WCA of the annealed hcp-AlN, Si-DLC and Cr-DLC coatings is related to their crystal structures and has little correlation with roughness. Full article
(This article belongs to the Special Issue Advances in Surface Coatings 2013)
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<p>Schema of the closed field unbalanced magnetron reactive sputtering system.</p> Full article ">Figure 2
<p>Coating annealing process.</p> Full article ">Figure 3
<p>Diagrammatic sketch of water contact angle <span class="html-italic">θ</span>.</p> Full article ">Figure 4
<p>Water contact angle (WCA) of as-deposited coatings.</p> Full article ">Figure 5
<p>WCA of the AlN, Cr<sub>2</sub>N, (CrAl)<sub>2</sub>N, Si-DLC and Cr-DLC coatings annealed at various temperatures.</p> Full article ">Figure 6
<p>XRD patterns of various coatings.</p> Full article ">Figure 7
<p>Raman spectrum of Si-DLC.</p> Full article ">Figure 8
<p>XPS spectrum of (<b>a</b>) hcp-AlN annealed at 300 °C; (<b>b</b>) 600 °C annealed (CrAl)<sub>2</sub>N and (<b>c</b>) 400 °C annealed Si-DLC.</p> Full article ">Figure 9
<p>Roughness Ra of the as-deposited and annealed at various temperatures for the hcp-AlN, Cr<sub>2</sub>N, (CrAl)<sub>2</sub>N, Si-DLC and Cr-DLC coatings.</p> Full article ">Figure 10
<p>SEM images (<b>a</b>) as-deposited hcp-AlN; (<b>b</b>) 600 °C annealed hcp-AlN; (<b>c</b>) as-deposited Cr<sub>2</sub>N; (<b>d</b>) 600 °C annealed Cr<sub>2</sub>N; (<b>e</b>) as-deposited (CrAl)<sub>2</sub>N; (<b>f</b>) 700 °C annealed (CrAl)<sub>2</sub>N; (<b>g</b>) as-deposited Si-DLC; and (<b>h</b>) as-deposited Cr-DLC.</p> Full article ">
325 KiB  
Article
Microstructural Characterization of Calcite-Based Powder Materials Prepared by Planetary Ball Milling
by Wen-Tien Tsai
Materials 2013, 6(8), 3361-3372; https://doi.org/10.3390/ma6083361 - 7 Aug 2013
Cited by 27 | Viewed by 7070
Abstract
In this work, a planetary ball milling was used to modify the surface properties of calcite-based material from waste oyster shell under the rotational speed of 200–600 rpm, grinding time of 5–180 min and sample mass of 1–10 g. The milling significantly changed [...] Read more.
In this work, a planetary ball milling was used to modify the surface properties of calcite-based material from waste oyster shell under the rotational speed of 200–600 rpm, grinding time of 5–180 min and sample mass of 1–10 g. The milling significantly changed the microstructural properties of the calcite-based minerals (i.e., surface area, pore volume, true density, and porosity). The surface characterization of the resulting powder should be macroporous and/or nonporous based on the nitrogen adsorption/desorption isotherms. Under the optimal conditions at the rotational speed of 400 rpm, grinding time of 30 min and sample mass of 5 g, the resulting calcite-based powder had larger specific surface area (i.e., 10.64 m2·g?1) than the starting material (i.e., 4.05 m2·g?1). This finding was also consistent with the measurement of laser-diffraction (i.e., 9.7 vs. 15.0 ?m of mean diameter). In addition, the results from the scanning electron microscope (SEM) observation indicated that surface roughness can be enhanced as particle size decreases as a result of particle-particle attrition. Thus, grinding the aquacultural bioresource by a high-energy ball milling can create the fine materials, which may be applied in the fields of inorganic minerals like aggregate and construction material. Full article
(This article belongs to the Special Issue Biointerfaces and Materials)
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<p>X-ray diffraction (XRD) diffractograms of some milling shell powders (<span class="html-italic">i.e.</span>, WOS-M3 and WOS-M4).</p> Full article ">Figure 2
<p>N<sub>2</sub> adsorption-desorption isotherms of the optimal calcite-based powder (<span class="html-italic">i.e.</span>, WOS-M3).</p> Full article ">Figure 3
<p>Pore size distribution of the optimal calcite-based powder (<span class="html-italic">i.e.</span>, WOS-M3).</p> Full article ">Figure 4
<p>Particle size distributions of the crude oyster shell powder (denoted as WOS-RW) and some calcite-based powders (<span class="html-italic">i.e.</span>, WOS-M3 and WOS-M4).</p> Full article ">Figure 5
<p>Scanning electron microscope (SEM) photograph (magnifications: 1500×) of the optimal calcite-based powder (WOS-M3).</p> Full article ">
3553 KiB  
Review
Surface Stability and Growth Kinetics of Compound Semiconductors: An Ab Initio-Based Approach
by Yoshihiro Kangawa, Toru Akiyama, Tomonori Ito, Kenji Shiraishi and Takashi Nakayama
Materials 2013, 6(8), 3309-3360; https://doi.org/10.3390/ma6083309 - 6 Aug 2013
Cited by 88 | Viewed by 9689
Abstract
We review the surface stability and growth kinetics of III-V and III-nitride semiconductors. The theoretical approach used in these studies is based on ab initio calculations and includes gas-phase free energy. With this method, we can investigate the influence of growth conditions, such [...] Read more.
We review the surface stability and growth kinetics of III-V and III-nitride semiconductors. The theoretical approach used in these studies is based on ab initio calculations and includes gas-phase free energy. With this method, we can investigate the influence of growth conditions, such as partial pressure and temperature, on the surface stability and growth kinetics. First, we examine the feasibility of this approach by comparing calculated surface phase diagrams of GaAs(001) with experimental results. In addition, the Ga diffusion length on GaAs(001) during molecular beam epitaxy is discussed. Next, this approach is systematically applied to the reconstruction, adsorption and incorporation on various nitride semiconductor surfaces. The calculated results for nitride semiconductor surface reconstructions with polar, nonpolar, and semipolar orientations suggest that adlayer reconstructions generally appear on the polar and the semipolar surfaces. However, the stable ideal surface without adsorption is found on the nonpolar surfaces because the ideal surface satisfies the electron counting rule. Finally, the stability of hydrogen and the incorporation mechanisms of Mg and C during metalorganic vapor phase epitaxy are discussed. Full article
(This article belongs to the Special Issue Compound Semiconductor Materials)
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<p>Schematic of the <span class="html-italic">ab initio</span>-based approach. By comparing the values of the chemical potential, <span class="html-italic">μ</span><sub>gas</sub>, with adsorption energy, <span class="html-italic">E</span><sub>ad</sub>, we can discuss the adsorption-desorption behavior of an adatom (a molecule).</p> Full article ">Figure 2
<p>Schematic of the GaAs(001)-(4 × 2)β2 surface. Adsorption sites are indicated by the letters A–E.</p> Full article ">Figure 3
<p>Chemical potential, <span class="html-italic">μ</span><sub>gas</sub>, as a function of temperature.</p> Full article ">Figure 4
<p>Pressure-temperature phase diagram for the GaAs(001)-(4 × 2)β2 surface.</p> Full article ">Figure 5
<p>Pressure-temperature phase diagram for the GaAs(001)-c(4 × 4).</p> Full article ">Figure 6
<p>Plane view of GaAs(001)-(2 × 4)β2. Adsorption sites for Ga are indicated by numbers. The migration barriers and desorption energies are presented in <a href="#materials-06-03309-t003" class="html-table">Table 3</a>.</p> Full article ">Figure 7
<p>(<b>a</b>) Ga surface lifetime, <span class="html-italic">τ</span>; and (<b>b</b>) diffusion coefficient, <span class="html-italic">D</span>, as a function of reciprocal temperature. Green solid and dashed lines are the calculated <span class="html-italic">τ</span> before desorption and <span class="html-italic">τ</span> before incorporation [<a href="#B66-materials-06-03309" class="html-bibr">66</a>], respectively. Brown solid lines with open and filled squares are the <math display="inline"> <semantics> <mrow> <msub> <mi>D</mi> <mrow> <mo stretchy="false">[</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>0</mn> <mo stretchy="false">]</mo> </mrow> </msub> </mrow> </semantics> </math> and <span class="html-italic">D</span><sub>[110]</sub>, respectively. The experimental results for the Ga diffusion coefficient are also presented in the diagram by orange dotted ( <span class="html-fig-inline" id="materials-06-03309-i001"> <img alt="Materials 06 03309 i001" src="/materials/materials-06-03309/article_deploy/html/images/materials-06-03309-i001.png"/></span>) [<a href="#B69-materials-06-03309" class="html-bibr">69</a>] and dashed lines ( <span class="html-fig-inline" id="materials-06-03309-i002"> <img alt="Materials 06 03309 i002" src="/materials/materials-06-03309/article_deploy/html/images/materials-06-03309-i002.png"/></span>) [<a href="#B65-materials-06-03309" class="html-bibr">65</a>].</p> Full article ">Figure 8
<p>Ga diffusion length, <span class="html-italic">L</span>, as a function of reciprocal temperature at <span class="html-italic">p</span><sub>Ga</sub> = 1.4 × 10<sup>−6</sup> Torr.</p> Full article ">Figure 9
<p>Calculated surface formation energies of polar GaN surfaces with (<b>a</b>) (0001) and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>000</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mo stretchy="false">)</mo> </mrow> </semantics> </math> orientations as a function of Ga chemical potential. Schematics of the surface structures under consideration are also presented.</p> Full article ">Figure 10
<p>Calculated phase diagrams for polar GaN surfaces with (<b>a</b>) (0001) and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>000</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mo stretchy="false">)</mo> </mrow> </semantics> </math> orientations as a function of temperature and Ga beam equivalent pressure (BEP). The stable reconstructions on these surfaces are also schematically presented. The shaded area denotes the molecular beam epitaxy (MBE) growth temperature range from Reference [<a href="#B78-materials-06-03309" class="html-bibr">78</a>].</p> Full article ">Figure 11
<p>Schematics of crystal planes with nonpolar (<b>a</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>00</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> orientations.</p> Full article ">Figure 12
<p>Calculated surface formation energies of nonpolar GaN surfaces with (<b>a</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>00</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> orientations as a function of Ga chemical potential. Schematics of the surface structures under consideration are also presented.</p> Full article ">Figure 13
<p>Calculated phase diagrams for nonpolar GaN surfaces with (<b>a</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>00</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> orientations as a function of temperature and Ga BEP. The stable reconstructions on these surfaces are also schematically presented.</p> Full article ">Figure 14
<p>Crystal plane schematics for semipolar (<b>a</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>01</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> orientations.</p> Full article ">Figure 15
<p>Calculated surface formation energies for semipolar GaN surfaces with (<b>a</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>01</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> orientations as a function of the Ga chemical potential. Schematics of the surface structures under consideration are also presented.</p> Full article ">Figure 16
<p>Calculated phase diagrams for nonpolar GaN surfaces with (<b>a</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>01</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> orientations as a function of temperature and Ga BEP. The surface stable reconstructions are also schematically presented.</p> Full article ">Figure 17
<p>Calculated surface formation energies of polar InN surfaces with (<b>a</b>) (0001) and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>000</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mo stretchy="false">)</mo> </mrow> </semantics> </math> orientations as a function of In chemical potential. Schematics of the surface structures under consideration are also presented.</p> Full article ">Figure 18
<p>Calculated phase diagrams for polar InN surfaces with (<b>a</b>) (0001) and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>000</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mo stretchy="false">)</mo> </mrow> </semantics> </math> orientations as a function of temperature and In BEP. The surface stable reconstructions are also schematically presented.</p> Full article ">Figure 19
<p>Calculated surface formation energies for nonpolar InN surfaces with (<b>a</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>00</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> orientations as a function of the In chemical potential. Schematics of the surface structures under consideration are also presented.</p> Full article ">Figure 20
<p>Calculated phase diagrams for nonpolar InN surfaces with (<b>a</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>00</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> orientations as a function of temperature and In BEP. The stable reconstructions on these surfaces are also schematically presented.</p> Full article ">Figure 21
<p>Calculated surface formation energies for semipolar InN surfaces with (<b>a</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>01</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> orientations as a function of In chemical potential. Schematics of the surface structures under consideration are also presented.</p> Full article ">Figure 22
<p>Calculated phase diagrams for nonpolar InN surfaces with (<b>a</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>01</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> orientations as a function of temperature and In BEP. The stable reconstructions on these surfaces are also schematically presented.</p> Full article ">Figure 23
<p>Calculated surface formation energies for polar AlN surfaces with (<b>a</b>) (0001) and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>000</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mo stretchy="false">)</mo> </mrow> </semantics> </math> orientations as a function of Al chemical potential. Schematics of the surface structures under consideration are also presented.</p> Full article ">Figure 24
<p>Calculated phase diagrams for polar AlN surfaces with (<b>a</b>) (0001) and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>000</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mo stretchy="false">)</mo> </mrow> </semantics> </math> orientations as a function of temperature and Al BEP. The stable reconstructions on these surfaces are also schematically presented.</p> Full article ">Figure 25
<p>Calculated surface formation energies for polar AlN surfaces with (<b>a</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>00</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> orientations as a function of Al chemical potential. Schematics of the surface structures under consideration are also presented.</p> Full article ">Figure 26
<p>Calculated phase diagrams for nonpolar AlN surfaces with (<b>a</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>00</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> orientations as a function of temperature and Al BEP. The stable reconstructions on these surfaces are also schematically presented.</p> Full article ">Figure 27
<p>Calculated H-adsorbed GaN surface phase diagrams for polar (<b>a</b>) (0001) and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>000</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mo stretchy="false">)</mo> </mrow> </semantics> </math>; nonpolar (<b>c</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>00</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> and (<b>d</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math>; and semipolar (<b>e</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>01</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> and (<b>f</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> orientations as a function of temperature and Ga BEP under high H<sub>2</sub> pressure (<span class="html-italic">p</span><sub>H2</sub> = 76 Torr) conditions. Top surface structure views are also presented. Large, small, and tiny circles represent Ga, N, and H atoms, respectively.</p> Full article ">Figure 28
<p>Calculated H-adsorbed InN surface phase diagrams for polar (<b>a</b>) (0001) and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>000</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mo stretchy="false">)</mo> </mrow> </semantics> </math>, nonpolar (<b>c</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>00</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> and (<b>d</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math>, and semipolar (<b>e</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>01</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> and (<b>f</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>22</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> orientations as a function of temperature and In BEP under high H<sub>2</sub> pressure (<span class="html-italic">p</span><sub>H2</sub> = 76 Torr) conditions. Top surface structure views are also presented. Large, small, and tiny circles represent In, N, and H atoms, respectively.</p> Full article ">Figure 29
<p>Calculated H-adsorbed AlN surface phase diagrams for polar (<b>a</b>) (0001) and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>000</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mo stretchy="false">)</mo> </mrow> </semantics> </math> and nonpolar (<b>c</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>00</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> and (<b>d</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> as a function of temperature and In BEP under high H<sub>2</sub> pressure (<span class="html-italic">p</span><sub>H2</sub> = 76 Torr) conditions. Top surface structure views are also presented. Large and small circles represent Al and N atoms, respectively. The positions of H atoms in the H-terminated surfaces are marked by crosses.</p> Full article ">Figure 30
<p>Contour potential energy surface (PES) plots for (<b>a</b>) an additional Ga atom on the GaN<math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> surface with a Ga adatom and (<b>b</b>) Ga adatom and (<b>c</b>) N adatom on a GaN<math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> surface with a Ga monolayer. Large and small circles represent Ga and N atoms, respectively. Each contour line in (<b>a</b>), (<b>b</b>), and (<b>c</b>) represents an energy step of 0.15, 0.05, and 0.15 eV, respectively. S1 represents stable adsorption sites. The dashed rectangles denote the surface unit cells.</p> Full article ">Figure 31
<p>Calculated surface phase diagrams for Ga adsorption on (<b>a</b>) a GaN<math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> surface with Ga adatom and (<b>b</b>) a GaN<math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math>surface with a Ga monolayer and (<b>c</b>) N adsorption on a GaN<math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>11</mn> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> surface with a Ga monolayer as a function of temperature and pressure. The adsorption phase boundary at the stable sites (saddle points) is represented by solid (dashed) lines. The growth temperature in Refence [<a href="#B91-materials-06-03309" class="html-bibr">91</a>] (~1000 K) is denoted by a horizontal line.</p> Full article ">Figure 32
<p>(<b>a</b>) Calculated phase diagrams for growth modes as a function of temperature a Ga BEP and (<b>b</b>) growth mode schematic representations with each corresponding to each temperature and Ga BEP region in the phase diagram.</p> Full article ">Figure 33
<p>Contour PES plots for an Al adatom on reconstructed AlN(0001) surfaces with (<b>a</b>) an N adatom and (<b>b</b>) H atoms. Large, small, and tiny circles represent Al, N, and H atoms, respectively. Each contour line in (<b>a</b>) and (<b>b</b>) represents an energy step of 0.1 and 0.2 eV, respectively. The dashed rectangles denote the surface unit cells. Arrows and crosses in the unit cell represent minima and PES saddle points, respectively.</p> Full article ">Figure 34
<p>Calculated (<b>a</b>) life time, <span class="html-italic">τ</span>, and (<b>b</b>) diffusion length, <span class="html-italic">L</span><sub>diff</sub>, of an Al adatom on a AlN(0001) surface as a function of reciprocal temperature at an Al pressure of 1 × 10<sup>−3</sup> Torr as obtained by kinetic Monte Carlo simulations.</p> Full article ">Figure 35
<p>Stable Mg-incorporated structures on (<b>a</b>) GaN(0001) and (<b>b</b>) GaN<math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>01</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> surfaces as a function of Ga chemical potential, <span class="html-italic">μ</span><sub>Ga</sub>, and Mg chemical potential, <span class="html-italic">μ</span><sub>Mg</sub>, under high H<sub>2</sub> pressure conditions (<span class="html-italic">μ</span><sub>H</sub> = (1/2)<span class="html-italic">E</span><sub>H2 </sub>− 1.05 eV, where <span class="html-italic">E</span><sub>H2</sub> is total energy of a H<sub>2</sub> molecule). The stable regions of Mg-incorporated surfaces are emphasized by the shaded areas.</p> Full article ">Figure 36
<p>Calculated temperatures for the phase transition between Mg-incorporated and Mg-free surfaces at the N-rich limit (<span class="html-italic">μ</span><sub>Ga</sub> = −1.24 eV) as a function of Mg BEP on the (<b>a</b>) GaN(0001) and (<b>b</b>) GaN<math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>01</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> surfaces. The Mg-incorporated surfaces are stabilized in the shaded regions. The GaN MOVPE growth temperature was provided by References [<a href="#B131-materials-06-03309" class="html-bibr">131</a>,<a href="#B132-materials-06-03309" class="html-bibr">132</a>] and is denoted by red lines.</p> Full article ">Figure 37
<p>Stable structures of carbon incorporated (<b>a</b>) GaN(0001) and (<b>b</b>) GaN<math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>01</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> surfaces as a function of Ga chemical potential, <span class="html-italic">μ</span><sub>Ga</sub>, and C chemical potential, <span class="html-italic">μ</span><sub>C</sub>, for high H<sub>2</sub> pressure conditions (<span class="html-italic">μ</span><sub>H</sub> = (1/2)<span class="html-italic">E</span><sub>H2</sub> − 1.05 eV, where <span class="html-italic">E</span><sub>H2</sub> is total energy of a H<sub>2</sub> molecule). The stable carbon incorporated surface regions are shaded.</p> Full article ">Figure 38
<p>Calculated surface phase diagrams for C-incorporated (<b>a</b>) GaN(0001) and (<b>b</b>) <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>01</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> GaN surfaces at the N-rich limit (<span class="html-italic">μ</span><sub>Ga</sub> = −1.24 eV) as a function of temperatures and C BEP. The carbon incorporated surfaces are stabilized in the shaded regions. Schematic views of surface structures are also presented. The growth temperature from [<a href="#B139-materials-06-03309" class="html-bibr">139</a>,<a href="#B140-materials-06-03309" class="html-bibr">140</a>] are shown by red lines. For comparison, the dashed line in (<b>b</b>) denotes the phase boundary between carbon free and incorporated surfaces on the GaN(0001) surface.</p> Full article ">
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Article
Comparison of Extruded and Sonicated Vesicles for Planar Bilayer Self-Assembly
by Nam-Joon Cho, Lisa Y. Hwang, Johan J.R. Solandt and Curtis W. Frank
Materials 2013, 6(8), 3294-3308; https://doi.org/10.3390/ma6083294 - 5 Aug 2013
Cited by 88 | Viewed by 8719
Abstract
Lipid vesicles are an important class of biomaterials that have a wide range of applications, including drug delivery, cosmetic formulations and model membrane platforms on solid supports. Depending on the application, properties of a vesicle population such as size distribution, charge and permeability [...] Read more.
Lipid vesicles are an important class of biomaterials that have a wide range of applications, including drug delivery, cosmetic formulations and model membrane platforms on solid supports. Depending on the application, properties of a vesicle population such as size distribution, charge and permeability need to be optimized. Preparation methods such as mechanical extrusion and sonication play a key role in controlling these properties, and yet the effects of vesicle preparation method on vesicular properties and integrity (e.g., shape, size, distribution and tension) remain incompletely understood. In this study, we prepared vesicles composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid by either extrusion or sonication, and investigated the effects on vesicle size distribution over time as well as the concomitant effects on the self-assembly of solid-supported planar lipid bilayers. Dynamic light scattering (DLS), quartz crystal microbalance with dissipation (QCM-D) monitoring, fluorescence recovery after photobleaching (FRAP) and atomic force microscopy (AFM) experiments were performed to characterize vesicles in solution as well as their interactions with silicon oxide substrates. Collectively, the data support that sonicated vesicles offer more robust control over the self-assembly of homogenous planar lipid bilayers, whereas extruded vesicles are vulnerable to aging and must be used soon after preparation. Full article
(This article belongs to the Special Issue Biointerfaces and Materials)
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<p>Stability of lipid vesicles produced by different processing techniques. 1-palmitoyl-2-oleoyl-<span class="html-italic">sn</span>-glycero-3-phosphocholine (POPC) lipid films dispersed in aqueous buffer and homogenous vesicle suspensions were prepared by pressure extrusion (red diamond) or sonication (blue square). Preparation-dependent effects on vesicle size were monitored by dynamic light scattering as a function of time after processing. Note that the vesicle drawings are merely illustrative and not drawn to scale.</p> Full article ">Figure 2
<p>Effects of vesicle aging on the self-assembly of planar lipid bilayers. The interactions of POPC lipid vesicles with silicon oxide substrates were followed by quartz crystal microbalance with dissipation (QCM-D) monitoring as a function of vesicle aging. Normalized changes in (<b>a</b>) resonance frequency and (<b>b</b>) energy dissipation as a function of time were recorded for lipid vesicles prepared by the extrusion method. Corresponding changes in (<b>c</b>) resonance frequency and (<b>d</b>) energy dissipation as a function of time were also recorded for lipid vesicles prepared by the sonication method.</p> Full article ">Figure 3
<p>Age-dependent mobility of planar lipid bilayers. Fluorescence recovery after photobleaching (FRAP) experiments were performed on planar lipid bilayers self-assembled from (<b>a</b>) extruded or (<b>b</b>) sonicated vesicle suspensions of varying age from 1 to 11 days. After photobleaching, fluorescence microscopy images were recorded at 1 min intervals.</p> Full article ">Figure 4
<p>Morphology of planar lipid bilayers as a function of vesicle aging. Atomic force microscopy (AFM) was employed to investigate the morphology of planar bilayers assembled on silicon oxide supports. (<b>a</b>) AFM scans presented in height mode were recorded for planar bilayers prepared from extruded lipid vesicles. The scan size is 2 µm × 2 µm; (<b>b</b>) Identical scans were also recorded for planar bilayers prepared from sonicated lipid vesicles.</p> Full article ">
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Article
In Vitro Activity of Gentamicin-Loaded Bioabsorbable Beads against Different Microorganisms
by Eric Thein, Ulrika Furustrand Tafin, Bertrand Betrisey, Andrej Trampuz and Olivier Borens
Materials 2013, 6(8), 3284-3293; https://doi.org/10.3390/ma6083284 - 5 Aug 2013
Cited by 4 | Viewed by 5686
Abstract
Osteomyelitis is responsible for high treatment costs, long hospital stays, and results in substantial morbidity. Treatment with surgical debridement and antibiotic-impregnated Polymethylmetacrylate (PMMA) beads is the standard of care, providing high local but low serum antibiotic concentrations, thereby avoiding systemic toxicity. However, for [...] Read more.
Osteomyelitis is responsible for high treatment costs, long hospital stays, and results in substantial morbidity. Treatment with surgical debridement and antibiotic-impregnated Polymethylmetacrylate (PMMA) beads is the standard of care, providing high local but low serum antibiotic concentrations, thereby avoiding systemic toxicity. However, for several reasons, the beads require surgical removal. Alternative antibiotic delivery systems should improve the treatment of bone infection, actively encourage bone healing and require no additional surgery for removal. We investigated the activity of gentamicin-loaded bioabsorbable beads against different microorganisms (Staphylococcus epidermidis, S. aureus, Escherichia coli, Enterococcus faecalis, Candida albicans) commonly causing surgical site bone infection, by microcalorimetry. Calcium sulphate beads containing gentamicin were incubated in microcalorimetry ampoules containing different concentrations of the corresponding microorganism. Growth medium with each germ and unloaded beads was used as positive control, growth medium with loaded beads alone as negative control. Bacterial growth-related heat production at 37 °C was measured for 24 h. Cultures without gentamicin-loaded beads produced heat-flow peaks corresponding to the exponential growth of the corresponding microorganisms in nutrient-rich medium. In contrast, cultures with gentamicin-loaded beads completely suppressed heat production during 24 h, demonstrating their antibiotic activity. Gentamicin-loaded beads effectively inhibited growth of susceptible microorganisms, under the described in vitro conditions. Full article
(This article belongs to the Special Issue Biointerfaces and Materials)
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<p>Thermokinetic profiles of <span class="html-italic">S. aureus</span> (<b>A</b>); <span class="html-italic">S. epidermidis</span> (<b>B</b>); <span class="html-italic">E. faecalis</span> (<b>C</b>); <span class="html-italic">E. coli</span> (<b>D</b>) and <span class="html-italic">C. albicans</span> (<b>E</b>) in the presence of calcium-sulphate beads with or without (positive control) gentamicin. Beads in growth media without microorganisms served as negative control (<b>F</b>).</p> Full article ">
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Article
Bactericidal Activity of Aqueous Acrylic Paint Dispersion for Wooden Substrates Based on TiO2 Nanoparticles Activated by Fluorescent Light
by Tommaso Zuccheri, Martino Colonna, Ilaria Stefanini, Cecilia Santini and Diana Di Gioia
Materials 2013, 6(8), 3270-3283; https://doi.org/10.3390/ma6083270 - 2 Aug 2013
Cited by 43 | Viewed by 7068
Abstract
The photocatalytic effect of TiO2 has great potential for the disinfection of surfaces. Most studies reported in the literature use UV activation of TiO2, while visible light has been used only in a few applications. In these studies, high concentrations [...] Read more.
The photocatalytic effect of TiO2 has great potential for the disinfection of surfaces. Most studies reported in the literature use UV activation of TiO2, while visible light has been used only in a few applications. In these studies, high concentrations of TiO2, which can compromise surface properties, have been used. In this work, we have developed an acrylic-water paint dispersion containing low TiO2 content (2 vol %) for the inactivation of microorganisms involved in hospital-acquired infections. The nanoparticles and the coating have been characterized using spectroscopic techniques and transmission electron microscopy, showing their homogenous dispersion in the acrylic urethane coating. A common fluorescent light source was used to activate the photocatalytic activity of TiO2. The paint dispersion showed antimicrobial activity against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. The coating containing the TiO2 nanoparticles maintained good UV stability, strong adhesion to the substrate and high hardness. Therefore, the approach used is feasible for paint formulation aimed at disinfection of healthcare surfaces. Full article
(This article belongs to the Special Issue Biointerfaces and Materials)
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<p>TEM images of TiO<sub>2</sub> Aeroxide<sup>®</sup> TiO<sub>2</sub> P25.</p> Full article ">Figure 2
<p>Aeroxide<sup>®</sup> TiO<sub>2</sub> P25 nanoparticles size distribution from TEM analysis.</p> Full article ">Figure 3
<p>The solid-state diffusion-reflectance UV-Vis spectrum of Aeroxide<sup>®</sup> TiO<sub>2</sub> P25 (in red), and the UV-Vis emission spectrum of fluorescent light at 6500 K Daylight.</p> Full article ">Figure 4
<p>SEM images of the sprayed aqueous acrylic-urethane dispersion containing TiO<sub>2</sub> nanocrystals at (<b>a</b>) 100×; and (<b>b</b>) 1000× magnification.</p> Full article ">Figure 5
<p>(<b>a</b>) SEM of aqueous TiO<sub>2</sub> acrylic dispersion and (<b>b</b>) SEM-EDS of titanium electron emission of the same area.</p> Full article ">Figure 6
<p>Percentage of surviving bacteria (<span class="html-italic">E. coli</span>, <span class="html-italic">P. aeruginosa</span> and <span class="html-italic">S. aureus</span>) on the control sample (without TiO<sub>2</sub>) and on the active sample (containing 2% w/w Aeroxide<sup>®</sup> TiO<sub>2</sub> P25) after 24 h of incubation at room temperature. The percentage of surviving bacteria was normalized to the inoculum (cells present at the beginning of the incubation). * <span class="html-italic">p</span> &lt; 0.01 between T0 and T = 24 h.</p> Full article ">
1032 KiB  
Article
Properties of Cast Films Made from Different Ratios of Whey Protein Isolate, Hydrolysed Whey Protein Isolate and Glycerol
by Markus Schmid
Materials 2013, 6(8), 3254-3269; https://doi.org/10.3390/ma6083254 - 2 Aug 2013
Cited by 59 | Viewed by 6869
Abstract
Whey protein isolate (WPI)-based cast films are very brittle, due to several chain interactions caused by a large amount of different functional groups. In order to overcome film brittleness, plasticizers, like glycerol, are commonly used. As a result of adding plasticizers, the free [...] Read more.
Whey protein isolate (WPI)-based cast films are very brittle, due to several chain interactions caused by a large amount of different functional groups. In order to overcome film brittleness, plasticizers, like glycerol, are commonly used. As a result of adding plasticizers, the free volume between the polymer chains increases, leading to higher permeability values. The objective of this study was to investigate the effect of partially substituting glycerol by hydrolysed whey protein isolate (h-WPI) in WPI-based cast films on their mechanical, optical and barrier properties. As recently published by the author, it is proven that increasing the h-WPI content in WPI-based films at constant glycerol concentrations significantly increases film flexibility, while maintaining the barrier properties. The present study considered these facts in order to increase the barrier performance, while maintaining film flexibility. Therefore glycerol was partially replaced by h-WPI in WPI-based cast films. The results clearly indicate that partially replacing glycerol by h-WPI reduces the oxygen permeability and the water vapor transmission rate, while the mechanical properties did not change significantly. Thus, film flexibility was maintained, even though the plasticizer concentration was decreased. Full article
(This article belongs to the Section Biomaterials)
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<p>Effect of increased h-WPI content (reduced protein molecular weight (M<sub>W</sub>)) and reduced glycerol contents on the equilibrium moisture content of WPI-based films at 23 °C and 50% r.h.</p> Full article ">Figure 2
<p>Effect of increased h-WPI content (reduced protein M<sub>W</sub>) and reduced glycerol content on the water vapor transmission rate of WPI-based films.</p> Full article ">Figure 3
<p>Effect of increased h-WPI content (reduced protein M<sub>W</sub>) and reduced glycerol content on the oxygen permeability of WPI-based films.</p> Full article ">Figure 4
<p>Effect of increased h-WPI content (reduced protein M<sub>W</sub>) and reduced glycerol content on the tensile strength values of WPI-based films.</p> Full article ">Figure 5
<p>Effect of increased h-WPI content (reduced protein M<sub>W</sub>) and reduced glycerol content on the Young’s Modulus values of WPI-based films.</p> Full article ">Figure 6
<p>Effect of increased h-WPI content (reduced protein M<sub>W</sub>) and reduced glycerol content on the disperse part, polar part and total surface energy of WPI-based films.</p> Full article ">Figure 7
<p>Effect of increased h-WPI content (reduced protein M<sub>W</sub>) and reduced glycerol content on yellow coloration (b-value) of WPI-based films.</p> Full article ">
461 KiB  
Article
Dynamic Initiation and Propagation of Multiple Cracks in Brittle Materials
by Jie Li, Qiaoping Huang and Xiaodan Ren
Materials 2013, 6(8), 3241-3253; https://doi.org/10.3390/ma6083241 - 31 Jul 2013
Cited by 13 | Viewed by 6487
Abstract
Brittle materials such as rock and ceramic usually exhibit apparent increases of strength and toughness when subjected to dynamic loading. The reasons for this phenomenon are not yet well understood, although a number of hypotheses have been proposed. Based on dynamic fracture mechanics, [...] Read more.
Brittle materials such as rock and ceramic usually exhibit apparent increases of strength and toughness when subjected to dynamic loading. The reasons for this phenomenon are not yet well understood, although a number of hypotheses have been proposed. Based on dynamic fracture mechanics, the present work offers an alternate insight into the dynamic behaviors of brittle materials. Firstly, a single crack subjected to stress wave excitations is investigated to obtain the dynamic crack-tip stress field and the dynamic stress intensity factor. Second, based on the analysis of dynamic stress intensity factor, the fracture initiation sizes and crack size distribution under different loading rates are obtained, and the power law with the exponent of ?2/3 is derived to describe the fracture initiation size. Third, with the help of the energy balance concept, the dynamic increase of material strength is directly derived based on the proposed multiple crack evolving criterion. Finally, the model prediction is compared with the dynamic impact experiments, and the model results agree well with the experimentally measured dynamic increasing factor (DIF). Full article
(This article belongs to the Section Advanced Materials Characterization)
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<p>Crack geometry and loading.</p> Full article ">Figure 2
<p>Dynamic stress intensity factor.</p> Full article ">Figure 3
<p>Wave fronts emanating from crack tip.</p> Full article ">Figure 4
<p>Critical crack length <span class="html-italic">vs.</span> loading rates.</p> Full article ">Figure 5
<p>Fracture stress <span class="html-italic">vs.</span> crack size at constant strain-rate loading.</p> Full article ">Figure 6
<p>Logarithmic normalized specific energy dissipation with loading rates.</p> Full article ">Figure 7
<p>(<b>a</b>) Dynamic increasing factors (DIFs) under compression; and (<b>b</b>) DIFs under tension [<a href="#B39-materials-06-03241" class="html-bibr">39</a>,<a href="#B40-materials-06-03241" class="html-bibr">40</a>,<a href="#B41-materials-06-03241" class="html-bibr">41</a>,<a href="#B42-materials-06-03241" class="html-bibr">42</a>,<a href="#B43-materials-06-03241" class="html-bibr">43</a>].</p> Full article ">
1535 KiB  
Article
A New Metasurface Superstrate Structure for Antenna Performance Enhancement
by Mohammad Tariqul Islam, Mohammad Habib Ullah, Mandeep Jit Singh and Mohammad Rashed Iqbal Faruque
Materials 2013, 6(8), 3226-3240; https://doi.org/10.3390/ma6083226 - 31 Jul 2013
Cited by 49 | Viewed by 8108
Abstract
A new metasurface superstrate structure (MSS)-loaded dual band microstrip line-fed small patch antenna is presented in this paper. The proposed antenna was designed on a ceramic-filled bioplastic sandwich substrate with a high dielectric constant. The proposed 7 × 6 element, square-shaped, single-sided MSS [...] Read more.
A new metasurface superstrate structure (MSS)-loaded dual band microstrip line-fed small patch antenna is presented in this paper. The proposed antenna was designed on a ceramic-filled bioplastic sandwich substrate with a high dielectric constant. The proposed 7 × 6 element, square-shaped, single-sided MSS significantly improved the bandwidth and gain of the proposed antenna. The proposed MSS incorporated a slotted patch antenna that effectively increased the measured operating bandwidth from 13.3% to 18.8% and from 14.8% to 23.2% in the lower and upper bands, respectively. Moreover, the average gain of the proposed MSS-based antenna was enhanced from 2.12 dBi to 3.02 dBi in the lower band and from 4.10 dBi to 5.28 dBi in the upper band compared to the patch antenna alone. In addition to the bandwidth and gain improvements, more directive radiation characteristics were also observed from the MSS antenna compared to the patch itself. The effects of the MSS elements and the ground plane length on the reflection coefficient of the antenna were analyzed and optimized. The overall performance makes the proposed antenna appropriate for RFID and WLAN applications. Full article
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<p>Substrate material structure.</p> Full article ">Figure 2
<p>Schematic of the radiating patch.</p> Full article ">Figure 3
<p>Effect of ground plane length on reflection coefficient of the proposed antenna.</p> Full article ">Figure 4
<p>Schematic of the proposed 7 × 6 element metasurface.</p> Full article ">Figure 5
<p>Effective permittivity and effective permeability of the metasurface superstrate structure (MSS) loaded antenna.</p> Full article ">Figure 6
<p>Effect of metasurface element sets over the reflection coefficient of the proposed antenna.</p> Full article ">Figure 7
<p>Influence of the MSS position on the directivity (<b>a</b>); and (<b>b</b>) reflection coefficient of the proposed antenna.</p> Full article ">Figure 8
<p>Photograph of fabricated prototype of (<b>a</b>) radiating patch; (<b>b</b>) ground plane; (<b>c</b>) metasurface; and (<b>d</b>) metasurafce superstrate loaded antenna.</p> Full article ">Figure 9
<p>Simulated and measured reflection coefficient of the proposed antenna.</p> Full article ">Figure 10
<p>Gain and directivity of the proposed antenna with MSS and without MSS.</p> Full article ">Figure 11
<p>Measured radiation pattern of the antenna at both resonant frequencies with and without MSS.</p> Full article ">Figure 12
<p>Surface current distribution of the proposed antenna with and without MSS at both lower and upper resonant frequencies.</p> Full article ">Figure 13
<p>Smith chart of the proposed MSS loaded antenna.</p> Full article ">
648 KiB  
Article
Fluorescent Magnetic Bioprobes by Surface Modification of Magnetite Nanoparticles
by Paula C. Pinheiro, Ana L. Daniel-da-Silva, Daniela S. Tavares, M. Pilar Calatayud, Gerardo F. Goya and Tito Trindade
Materials 2013, 6(8), 3213-3225; https://doi.org/10.3390/ma6083213 - 31 Jul 2013
Cited by 32 | Viewed by 8589
Abstract
Bimodal nanoprobes comprising both magnetic and optical functionalities have been prepared via a sequential two-step process. Firstly, magnetite nanoparticles (MNPs) with well-defined cubic shape and an average dimension of 80 nm were produced by hydrolysis of iron sulfate and were then surface modified [...] Read more.
Bimodal nanoprobes comprising both magnetic and optical functionalities have been prepared via a sequential two-step process. Firstly, magnetite nanoparticles (MNPs) with well-defined cubic shape and an average dimension of 80 nm were produced by hydrolysis of iron sulfate and were then surface modified with silica shells by using the sol-gel method. The Fe3O4@SiO2 particles were then functionalized with the fluorophore, fluorescein isothiocyanate (FITC), mediated by assembled shells of the cationic polyelectrolyte, polyethyleneimine (PEI). The Fe3O4 functionalized particles were then preliminary evaluated as fluorescent and magnetic probes by performing studies in which neuroblast cells have been contacted with these nanomaterials. Full article
(This article belongs to the Special Issue Luminescent Materials 2013)
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<p>Scheme for the surface modification of Fe<sub>3</sub>O<sub>4</sub> nanoparticles.</p> Full article ">Figure 2
<p>XRD diffraction patterns of the magnetite powders.</p> Full article ">Figure 3
<p>TEM images for magnetite (<b>a</b>); and silica coated magnetite (<b>b</b>,<b>c</b>) particles.</p> Full article ">Figure 4
<p>ATR-FTIR spectra of magnetite nanoparticles (Fe<sub>3</sub>O<sub>4</sub>) and silica coated magnetite nanoparticles (Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>).</p> Full article ">Figure 5
<p>Magnetization of Fe<sub>3</sub>O<sub>4</sub> and Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub> as a function of the magnetic field measured at 273 K in a diamagnetic sample holder.</p> Full article ">Figure 6
<p>Scheme of a possible chemical path for the functionalization of polyethyleneimine (PEI) with the fluorophore FITC.</p> Full article ">Figure 7
<p>Normalized fluorescence spectra of FITC, PEI conjugated with FITC (PF) and functionalized Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub> with PEI-FITC (Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>-PF) (λ<sub>exc</sub> = 494 nm).</p> Full article ">Figure 8
<p>Optical microscopy images of neuroblast cells prior to interaction with ferromagnetic nanoparticles (<b>a</b>); after contact with Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub> (<b>b</b>); and after contact with Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>-PF (<b>c</b>).</p> Full article ">Figure 9
<p>Optical microscopy images of neuroblast cells incubated with Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>-PF particles: (<b>a</b>) control sample in fluorescence mode; (<b>b</b>) light transmission mode, 60×; and (<b>c</b>) fluorescence mode, 60×.</p> Full article ">Figure 10
<p>Zeta potential as a function of pH for Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub> and Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>-PF nanoparticles.</p> Full article ">
839 KiB  
Concept Paper
A Perspective on the Flame Spray Synthesis of Photocatalyst Nanoparticles
by Wey Yang Teoh
Materials 2013, 6(8), 3194-3212; https://doi.org/10.3390/ma6083194 - 31 Jul 2013
Cited by 62 | Viewed by 8492
Abstract
The synthesis of functional nanoparticles via one-step flame spray pyrolysis (FSP), especially those of catalytic nature, has attracted the interests of scientists and engineers, as well as industries. The rapid and high temperature continuous synthesis yields nanoparticles with intrinsic features of active catalysts, [...] Read more.
The synthesis of functional nanoparticles via one-step flame spray pyrolysis (FSP), especially those of catalytic nature, has attracted the interests of scientists and engineers, as well as industries. The rapid and high temperature continuous synthesis yields nanoparticles with intrinsic features of active catalysts, that is, high surface area and surface energetics. For these reasons, FSP finds applications in various thermally inducible catalytic reactions. However, the design and synthesis of photocatalysts by FSP requires a knowledge set which is different from that established for thermal catalysts. Unknown to many, this has resulted in frustrations to those entering the field unprepared, especially since FSP appears to be an elegant tool in synthesising oxide nanoparticles of any elemental construct. From simple oxide to doped-oxide, and mixed metal oxide to the in situ deposition of noble metals, this Perspective gives an overview on the development of photocatalysts made by FSP in the last decade that led to a better understanding of the design criteria. Various challenges and opportunities are also highlighted, especially those beyond simple metal oxides, which perhaps contain the greatest potential for the exploitation of photocatalysts design by FSP. Full article
(This article belongs to the Special Issue Advances in Catalytic Materials)
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<p>Transmission electron micrograph of TiO<sub>2</sub> nanoparticles prepared in an (<b>a</b>) open ambient FSP; and (<b>d</b>) quartz tube-enclosed FSP, adapted with permission from [<a href="#B45-materials-06-03194" class="html-bibr">45</a>]; Schematic illustration of (<b>b</b>) small open flame-synthesised photocatalyst with charge trapping defects; and (<b>c</b>) large enclosed flame-synthesised photocatalyst with minimum charge trapping defects; (<b>e</b>) Compared to commercial P25, as-prepared open flame FSP TiO<sub>2</sub> particles show the presence of more reductive sites,<span class="html-italic"> i.e.</span>, Ti<sup>4+</sup> + e<sup>−</sup> → Ti<sup>3+</sup>, as measured by electron paramagnetic resonance (EPR) under UV exposure at 77 K; (<b>f</b>) Schematic of the process of aerosol nanoparticles formation by the gas-to-particle route (not to scale) and a photograph of the actual aerosol flame; (<b>g</b>) Schematic diagram of the quartz-tube enclosed FSP preventing the entrainment of ambient air thereby prolonging the high temperature region in the aerosol flame, adapted with permission from [<a href="#B50-materials-06-03194" class="html-bibr">50</a>]; (<b>h</b>) Capacitance measurements of FSP TiO<sub>2</sub> synthesised in an open flame shows more charge traps (hence higher capacitance), compared to those synthesised in a quartz tube-enclosed flame, adapted with permission from [<a href="#B49-materials-06-03194" class="html-bibr">49</a>].</p> Full article ">Figure 2
<p>Half-life mineralisation rates of (<b>a</b>) oxalic acid; (<b>b</b>) sucrose and (<b>c</b>) phenol over TiO<sub>2</sub> nanoparticles of different anatase content (Rutile (mol %) = 100% minus Anatase) prepared in a quartz tube-enclosed FSP. Catalyst loadings 0.2 g/L; Initial carbon loading 2000 µg; Initial pH 3.0; Light source: 16 W Blacklight blue fluorescence. Data courtesy of Rose Amal and coworkers [<a href="#B55-materials-06-03194" class="html-bibr">55</a>].</p> Full article ">Figure 3
<p>(<b>a</b>) Normalised Kubelka-Munk absorbance of various photocatalysts prepared by FSP as measured in diffuse-reflectance mode in an integrating sphere; and (<b>b</b>) absorbance of a range of commonly employed substrates (0.1 mM) used in the assessment of photocatalysts.</p> Full article ">Figure 4
<p>Tauc plot of pristine and metal-doped TiO<sub>2</sub> at various loadings (expressed in atomic percentage with respect to Ti) prepared in a one-step FSP. The metal dopants include (<b>a</b>) Fe; (<b>b</b>) Co; (<b>c</b>) Mn and (<b>d</b>) V.</p> Full article ">Figure 5
<p>Transmission electron micrographs of FSP-made Ag/TiO<sub>2</sub> samples after UV and visible light irradiation. Under UV irradiation, Ag(I) oxide deposits are photoreduced and result in the increase in surface plasmon resonance as characteristics of metallic Ag. Irradiation by visible light resulted in the injection of excited electrons from metallic Ag to the conduction band of TiO<sub>2</sub>, and in the process oxidising it back to Ag(I) oxide. This resulted in the loss of surface plasmon resonance effects. Adapted with permission from [<a href="#B26-materials-06-03194" class="html-bibr">26</a>].</p> Full article ">
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