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Materials, Volume 6, Issue 9 (September 2013) – 33 articles , Pages 3676-4283

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1301 KiB  
Article
Influence of Material Microstructures in Micromilling of Ti6Al4V Alloy
by Aldo Attanasio, Marcello Gelfi, Annalisa Pola, Elisabetta Ceretti and Claudio Giardini
Materials 2013, 6(9), 4268-4283; https://doi.org/10.3390/ma6094268 - 24 Sep 2013
Cited by 71 | Viewed by 7966
Abstract
In the most recent decades the introduction of unconventional machining processes allowed the development of micromachining techniques. In this work, the influence of material microstructures on the micromilling process was investigated. Ti6Al4V alloy was selected as workpiece material since it is a very [...] Read more.
In the most recent decades the introduction of unconventional machining processes allowed the development of micromachining techniques. In this work, the influence of material microstructures on the micromilling process was investigated. Ti6Al4V alloy was selected as workpiece material since it is a very common material for micro applications and because its duplex microstructure can be easily changed by proper thermal treatments. Four different microstructures (namely bimodal, fully equiaxed, fully lamellar and mill annealed) were obtained through recrystallization annealing treatments carried out at different times and temperatures. The mechanical properties of the samples were assessed by microhardness measurements. Nano-indentations were also performed on single grains to understand how the different hardness of phases and structures present in the Ti6Al4V alloy can affect the micromilling process. Microchannels using two flute flat end mills with a diameter equal to 200 µm were realized on the treated samples. Two different feed-per-tooth values were used during the tests. Cutting force, channel shape and burr dimension were investigated. Morphological and energy dispersive spectroscopy (EDS) analyses were performed on tools by means of a scanning electron microscope (SEM): in this way the phenomena mainly influencing the tool status were also identified. Lower cutting forces and reduced tool wear were observed when working fully lamellar microstructures compared to the other ones. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Figure 1

Figure 1
<p>Optical microscope images of Ti6Al4V microstructures: (<b>a</b>) mill annealed; (<b>b</b>) bimodal; (<b>c</b>) fully equiaxed and (<b>d</b>) fully lamellar.</p> Full article ">Figure 2
<p>Example of nano-indentations performed with a load of 20 mN on a bimodal etched sample.</p> Full article ">Figure 3
<p>Mitsubishi MS2SSD0020 mill.</p> Full article ">Figure 4
<p>Sample and micro channel geometry.</p> Full article ">Figure 5
<p>(<b>a</b>) Cutting force signal from Nationa Instrument LabVIEW based data acquisition system (DAQ) (bimodal microstructure and feed-per-tooth equal to 0.5 μm/tooth) and (<b>b</b>) process forces schematization.</p> Full article ">Figure 6
<p>(<b>a</b>) Mean value and standard deviation of cutting forces measured for each cutting condition and (<b>b</b>) main effects and interaction plots for the cutting forces.</p> Full article ">Figure 7
<p>Scanning electron microscope (SEM) images of (<b>a</b>) coating delamination (fully equiaxed microstructure) with corresponding energy dispersive spectroscopy (EDS) analysis results; (<b>b</b>) built up edge (mill annealed microstructure); (<b>c</b>) tool condition after machining fully lamellar microstructure and (<b>d</b>) tool condition after machining bimodal microstructure.</p> Full article ">Figure 8
<p>Main effect plot for the tool built up edge index based on SEM images. 1 = poor; 5 = good.</p> Full article ">Figure 9
<p>Optical microscope images of micro channel sections (feed-per-tooth 1.5 μm/tooth). (<b>a</b>) bimodal; (<b>b</b>) fully equiaxed; (<b>c</b>) fully lamellar and (<b>d</b>) mill annealed. The arrows show the feed and the rotation directions of the mill.</p> Full article ">Figure 10
<p>(<b>a</b>) Image from vision measuring machine (fully lamellar microstructure, 1.5 μm/tooth); (<b>b</b>) Optical microscope image of typical micro channel geometry and SEM image of burr observed from the top. In these pictures the definitions of burr’s width (<span class="html-italic">w</span>), height (<span class="html-italic">h</span>) and angle (α) are reported. The arrows show the feed and the rotation directions of the mill.</p> Full article ">Figure 11
<p>Main effect plots for burr width, height and angle.</p> Full article ">Figure 11 Cont.
<p>Main effect plots for burr width, height and angle.</p> Full article ">
496 KiB  
Article
Dislocation Energetics and Pop-Ins in AlN Thin Films by Berkovich Nanoindentation
by Sheng-Rui Jian, Yu-Chin Tseng, I-Ju Teng and Jenh-Yih Juang
Materials 2013, 6(9), 4259-4267; https://doi.org/10.3390/ma6094259 - 23 Sep 2013
Cited by 26 | Viewed by 5926
Abstract
Nanoindentation-induced multiple pop-ins were observed in the load-displacement curves when the mechanical responses of AlN films grown on c-plane sapphire substrates were investigated by using Berkovich indenters. No evidence of phase transformation is revealed by cross-sectional transmission electron microscopy (XTEM) and selected [...] Read more.
Nanoindentation-induced multiple pop-ins were observed in the load-displacement curves when the mechanical responses of AlN films grown on c-plane sapphire substrates were investigated by using Berkovich indenters. No evidence of phase transformation is revealed by cross-sectional transmission electron microscopy (XTEM) and selected area diffraction (SAD) analyses. Instead XTEM observations suggest that these “instabilities” resulted from the sudden nucleation of dislocations propagating along the slip systems lying on the {0001} basal planes and the pyramidal planes commonly observed in hexagonal compound semiconductors. Based on this scenario, an energetic estimation of dislocation nucleation is made. Full article
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Figure 1
<p>(<b>a</b>) Load-displacement curve measured by Berkovich indenter on AlN thin films at the indentation load of 100 mN and (<b>b</b>) the corresponding first pop-in event (see the arrow) from an expanded region of (<b>a</b>), where the plastic strain work is denoted as, <span class="html-italic">W<sub>p</sub></span> (critical loading times the sudden incremental displacement at constant load).</p> Full article ">Figure 2
<p>A bright-field XTEM image in the vicinity under the Berkovich indent applied on the AlN thin film with an indentation load of 100 mN. In addition, the selected area diffraction (SAD) pattern results of indented AlN thin film underneath the Berkovich nanoindentation.</p> Full article ">
957 KiB  
Communication
Co-Dispersion Behavior of ZrB2–SiC–B4C–C Powders with Polyethyleneimine
by Jie Yin, Jian Chen, Xuejian Liu, Hui Zhang, Yongjie Yan, Zhengren Huang and Dongliang Jiang
Materials 2013, 6(9), 4249-4258; https://doi.org/10.3390/ma6094249 - 23 Sep 2013
Cited by 9 | Viewed by 6196
Abstract
The aqueous dispersion behavior of ZrB2, SiC powders with B4C and C as sintering aids was investigated. Well co-dispersed suspension can be obtained in acidic solutions in presence of polyethyleneimine (PEI). The adsorption of PEI on the powder surface [...] Read more.
The aqueous dispersion behavior of ZrB2, SiC powders with B4C and C as sintering aids was investigated. Well co-dispersed suspension can be obtained in acidic solutions in presence of polyethyleneimine (PEI). The adsorption of PEI on the powder surface was measured by thermal gravimetric (TG) analysis. Rheological measurements displayed the effect of dispersant on the flow behavior of as-prepared slurries. An optimum condition was obtained with 1 wt % PEI. The viscosity of 40 vol % ZrB2–SiC–B4C–C (ZSBC) suspension at 100 s−1 was as low as 0.74 Pa·s, which was suitable for aqueous processing. Full article
(This article belongs to the Special Issue Ultra-high Temperature Ceramics)
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Figure 1
<p>Zeta potential of ZrB<sub>2</sub> suspensions with and without presence of polyethyleneimine (PEI).</p> Full article ">Figure 2
<p>Zeta potential of ZrB<sub>2</sub>, SiC, B<sub>4</sub>C, and C suspensions in the presence of PEI.</p> Full article ">Figure 3
<p>Thermal behavior of (<b>a</b>) PEI and (<b>b–d</b>) ZSBC-PEI at different pH values: (<b>b</b>) pH 3.2; (<b>c</b>) pH 6.6; (<b>d</b>) pH 10.6.</p> Full article ">Figure 4
<p>Adsorption and desorption mechanism of PEI on the powder surface.</p> Full article ">Figure 5
<p>Effect of dispersant content on: (<b>a</b>) the viscosity at 100 s<sup>−1</sup> and (<b>b</b>) rheological behavior of 30 vol % ZSB suspensions (pH 3).</p> Full article ">Figure 6
<p>Rheological properties of 40 vol % ZSB and ZrB<sub>2</sub>–SiC–B<sub>4</sub>C–C (ZSBC) suspensions (pH 3).</p> Full article ">
1869 KiB  
Article
Unified Formulation for a Triaxial Elastoplastic Constitutive Law for Concrete
by Rabah Hammoud, Rachid Boukhili and Ammar Yahia
Materials 2013, 6(9), 4226-4248; https://doi.org/10.3390/ma6094226 - 23 Sep 2013
Cited by 5 | Viewed by 6213
Abstract
A constitutive model to describe the triaxial load-response spectrum of plain concrete in both tension and shear was developed. The inelastic phenomena are described using the plastic flow with direction determined by the gradient of the plastic potential. A new plastic potential is [...] Read more.
A constitutive model to describe the triaxial load-response spectrum of plain concrete in both tension and shear was developed. The inelastic phenomena are described using the plastic flow with direction determined by the gradient of the plastic potential. A new plastic potential is introduced and experimentally fitted to ensure better estimate of the load direction. This approach allows to control the inelastic dilatancy in terms of the inelastic deformation of the material. By overlaying the plastic potential on modified Etse and Willam’s yield surface (both defined on the Haigh–Westergaard coordinates), the results showed that the two curves do not undergo similar stress states for a given strength level. It is, therefore, necessary that each surface goes through the current stress state to ensure adequate evaluation of normal vectors. A closed-form solution to accurately predict the triaxial stress state in concrete has been proposed. The predictive capabilities of the proposed model are evaluated by comparing predicted and measured stresses. The proposed model is shown to be accurate in predicting stress state of concrete. Full article
(This article belongs to the Special Issue Constitutive Behavior of Composite Materials)
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Figure 1
<p>Experimental data on Haigh–Westergaard coordinates.</p> Full article ">Figure 2
<p>Meridional sections of triaxial failure.</p> Full article ">Figure 3
<p>Deviatoric sections of triaxial failure.</p> Full article ">Figure 4
<p>Triaxial failure envelope in hardening mode.</p> Full article ">Figure 5
<p>Triaxial failure envelope in softening mode.</p> Full article ">Figure 6
<p>Ductility curve <span class="html-italic">versus</span> mean pressure.</p> Full article ">Figure 7
<p>Predictor Elastic test point.</p> Full article ">Figure 8
<p>Volumetric and deviatoric plastic components correlations for data obtained by simulation and experiment. (<b>a</b>) Volumetric; (<b>b</b>) Deviatoric.</p> Full article ">Figure 9
<p>Numerical and experimental stress-strain curve in axial compression.</p> Full article ">Figure 10
<p>Hardening and softening stages in uniaxial compression test. (<b>a</b>) Hardening; (<b>b</b>) Softening.</p> Full article ">Figure 10 Cont.
<p>Hardening and softening stages in uniaxial compression test. (<b>a</b>) Hardening; (<b>b</b>) Softening.</p> Full article ">Figure 11
<p>Hardening and softening stages in numerical triaxial compression test. (<b>a</b>) Hardening; (<b>b</b>) Softening.</p> Full article ">Figure 11 Cont.
<p>Hardening and softening stages in numerical triaxial compression test. (<b>a</b>) Hardening; (<b>b</b>) Softening.</p> Full article ">Figure 12
<p>Comparison between numerical and experimental results for concrete under triaxial compression at different confinement pressures.</p> Full article ">Figure 13
<p>Hardening and softening stages in numerical pure shear test. (<b>a</b>) Hardening; (<b>b</b>) Softening.</p> Full article ">Figure 14
<p>Stress-strains curves in numerical pure shear test.</p> Full article ">Figure 15
<p>Stress-strain curve from numerical triaxial tension test.</p> Full article ">Figure 16
<p>Softening stage in numerical triaxial tension test.</p> Full article ">
858 KiB  
Article
Healing of Fatigue Crack by High-Density Electropulsing in Austenitic Stainless Steel Treated with the Surface-Activated Pre-Coating
by Atsushi Hosoi, Tomoya Kishi and Yang Ju
Materials 2013, 6(9), 4213-4225; https://doi.org/10.3390/ma6094213 - 23 Sep 2013
Cited by 43 | Viewed by 8969
Abstract
A technique to heal a fatigue crack in austenitic stainless steel SUS316 by applying a controlled, high-density pulsed current was developed. A surface-activated pre-coating (SAPC), which eliminates the oxide layer and coats a Ni film on the crack surface, was used to improve [...] Read more.
A technique to heal a fatigue crack in austenitic stainless steel SUS316 by applying a controlled, high-density pulsed current was developed. A surface-activated pre-coating (SAPC), which eliminates the oxide layer and coats a Ni film on the crack surface, was used to improve the adhesion between crack surfaces. Cracks were observed by scanning electron microscopy before and after the application of high-density electropulsing. To evaluate the healing effect of the SAPC during crack propagation, fatigue tests were conducted under a constant stress intensity factor. The fatigue crack treated with the SAPC was found to be effectively healed as a result of electropulsing, and also showed a slower rate of crack propagation. Full article
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<p>Schematic representation of the steel samples.</p> Full article ">Figure 2
<p>Schematic diagram of the three stages involved in the surface-activated pre-coating (SAPC): (<b>a</b>) electrolytic cleaning; (<b>b</b>) HCl activation; and (<b>c</b>) Ni striking.</p> Full article ">Figure 3
<p>Photograph of the electropulsing set-up.</p> Full article ">Figure 4
<p>Relationship between the atomic concentrations of O, Cr, Fe and Ni and the depth from the sample surface after Ni striking.</p> Full article ">Figure 5
<p>Fatigue crack closure in Sample A induced by high-density electropulsing: (<b>a</b>) before; (<b>b</b>) after 8; (<b>c</b>) after 25; and (<b>d</b>) after 35 applications of electropulsing.</p> Full article ">Figure 5 Cont.
<p>Fatigue crack closure in Sample A induced by high-density electropulsing: (<b>a</b>) before; (<b>b</b>) after 8; (<b>c</b>) after 25; and (<b>d</b>) after 35 applications of electropulsing.</p> Full article ">Figure 6
<p>Magnified images of fatigue cracks in <a href="#materials-06-04213-f005" class="html-fig">Figure 5</a>: (<b>a</b>) before and (<b>b</b>) after 35 applications of electropulsing.</p> Full article ">Figure 7
<p>Crack width at the measuring point in <a href="#materials-06-04213-f005" class="html-fig">Figure 5</a> as a function of the number of applications of electropulsing in Sample A.</p> Full article ">Figure 8
<p>Fatigue crack growth rate as a function of stress intensity range for CT control samples without the application of electropulsing.</p> Full article ">Figure 9
<p>Fatigue crack growth rate as a function of crack length before the application and after the 25th application of electropulsing for Sample B.</p> Full article ">Figure 10
<p>Fatigue crack growth rate as a function of crack length before the application and after the 20th application of electropulsing for Sample C.</p> Full article ">Figure 11
<p>Representation of the crack closure process by the application of the electric current: (<b>a</b>) formation of a high-density electric current field at a crack tip; (<b>b</b>) local thermal expansion due to Joule heating; (<b>c</b>) crack closure resulting from thermal compressive stress; (<b>d</b>) bonding due to energization between the crack surfaces and (<b>e</b>) crack healing after the application of electropulsing.</p> Full article ">Figure 12
<p>Closure of entire fatigue crack by multiple applications of high-density electropulsing.</p> Full article ">
733 KiB  
Article
Preparation and Morphology Studies of Nano Zinc Oxide Obtained Using Native and Modified Chitosans
by Munusamy Thirumavalavan, Kai-Lin Huang and Jiunn-Fwu Lee
Materials 2013, 6(9), 4198-4212; https://doi.org/10.3390/ma6094198 - 18 Sep 2013
Cited by 88 | Viewed by 7227
Abstract
Nano zinc oxide (ZnO) with moderate surface area and high pore volume were prepared using a facile preparation method. Chitosan was utilized as both chelating and structure directing agent. The application of chitosans in this study suggested that even biowastes can be served [...] Read more.
Nano zinc oxide (ZnO) with moderate surface area and high pore volume were prepared using a facile preparation method. Chitosan was utilized as both chelating and structure directing agent. The application of chitosans in this study suggested that even biowastes can be served in a productive manner economically. The surface modification of chitosan was carried out in order to increase the interaction between chitosan and zinc ions. The effect of sodium chloroacetate and isopropyl alcohol on the surface modification process was also explored. FT-IR (Fourier transform-infrared spectrometer) and TGA (Thermogravimetric analyses) analyses revealed that modified chitosans are more stable than those of unmodified chitosan. Among surface modified chitosans, CMC1 (1.5 M sodium chloroacetate and 75% isopropyl alcohol) showed enhanced surface properties. Freundlich adsorption isotherms as preliminary studies confirmed that modified chitosan showed enhanced interaction with zinc ions. The interaction of zinc salt with chitosans produced a zinc-chitosan polymer. This finally cleaved upon calcination to produce nano ZnO. The effects of different calcination temperatures indicated that 450 °C is the optimum calcination temperature to produce the nano ZnO with favored surface area (15.45 m2/g) and pore size (221.40 nm). SEM (Scanning electron microscope) and TEM (Transmission electron microscope) of ZnO indicated that uniform particle and shape distributions were obtained at low calcination temperature (450 °C). Full article
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>FT-IR spectra of native and modified chitosans.</p> Full article ">Figure 2
<p>TGA and DTA curves for zinc-chitosans organic polymers using (<b>a</b>) CTS; (<b>b</b>) CMC1; and (<b>c</b>) CMC4.</p> Full article ">Figure 2 Cont.
<p>TGA and DTA curves for zinc-chitosans organic polymers using (<b>a</b>) CTS; (<b>b</b>) CMC1; and (<b>c</b>) CMC4.</p> Full article ">Figure 3
<p>Adsorption of Zn<sup>2+</sup> ions by native and surface modified chitosans.</p> Full article ">Figure 4
<p>XRD patterns of various ZnO samples.</p> Full article ">Figure 4 Cont.
<p>XRD patterns of various ZnO samples.</p> Full article ">Figure 5
<p>SEM of (<b>a</b>) ZnO-CTS-450; (<b>b</b>) ZnO-CTS-850; (<b>c</b>) ZnO-CMC1-450; (<b>d</b>) ZnO-CMC1-850; (<b>e</b>) ZnO-CMC4-450; and (<b>f</b>) ZnO-CMC4-850.</p> Full article ">Figure 6
<p>TEM of (<b>a</b>) ZnO-CMC1-450; (<b>b</b>) ZnO-CMC1-650; and (<b>c</b>) ZnO-CMC1-850.</p> Full article ">Figure 6 Cont.
<p>TEM of (<b>a</b>) ZnO-CMC1-450; (<b>b</b>) ZnO-CMC1-650; and (<b>c</b>) ZnO-CMC1-850.</p> Full article ">
906 KiB  
Article
Effect of Thermal Treatment on Fracture Properties and Adsorption Properties of Spruce Wood
by Koji Murata, Yasuhiro Watanabe and Takato Nakano
Materials 2013, 6(9), 4186-4197; https://doi.org/10.3390/ma6094186 - 18 Sep 2013
Cited by 38 | Viewed by 5575
Abstract
The effect of thermal treatment on spruce is examined by analyzing the fracture and hygroscopic properties. Specimens were heated at temperatures within the range 120–200 °C for 1 h. Fracture energy was measured using a single-edge notched bending test and the strain-softening index [...] Read more.
The effect of thermal treatment on spruce is examined by analyzing the fracture and hygroscopic properties. Specimens were heated at temperatures within the range 120–200 °C for 1 h. Fracture energy was measured using a single-edge notched bending test and the strain-softening index was estimated by dividing the fracture energy by the maximum load. Adsorption properties were estimated using adsorption isotherms. Fiber saturation points (FSPs) were estimated by extrapolating the moisture adsorption isotherm curve. Langmuir’s adsorption coefficient and number of adsorption sites were obtained using Langmuir’s theory and the Hailwood-Horrobin theory, respectively. The fracture energy, FSPs, and specimen weights decreased at temperatures higher than 150 °C, but the critical point for the strain-softening index and the number of adsorption sites was shown to be 180 °C. We hypothesize that the fracture energy and FSP depend on the chemical structure of the cell wall, whereas the strain-softening behavior may be influenced by the number of adsorption sites, and in turn the number of hydrogen bonds in hemicellulose. Full article
(This article belongs to the Section Biomaterials)
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<p>Specimens used in the single-edge notched bending test; (<b>a</b>) TL system (Tangential-Longitudinal); (<b>b</b>) RL system (Radial-Longitudinal).</p> Full article ">Figure 2
<p>Changes in fracture energy: (<b>a</b>) load–displacement curves in single-end notched bending test and (<b>b</b>) fracture energy dependence on heating temperature.</p> Full article ">Figure 3
<p>Effect of weight loss on fracture energy in tangentially loaded specimens; (<b>a</b>) weight loss by heat treatment and (<b>b</b>) fracture energy dependence on weight loss.</p> Full article ">Figure 4
<p>Dependence of maximum load on heating temperature.</p> Full article ">Figure 5
<p>Strain-softening index obtained by dividing the fracture energy by the maximum load.</p> Full article ">Figure 6
<p>Moisture adsorption isotherm curves of heated specimens.</p> Full article ">Figure 7
<p>Fiber saturation point values obtained using adsorption isotherm curves. Open symbols indicate the data without heat treatment.</p> Full article ">Figure 8
<p>Langmuir’s modified adsorption coefficients for heated specimens.</p> Full article ">Figure 9
<p>Number of adsorption site in heated specimens.</p> Full article ">
808 KiB  
Article
Th(IV) Adsorption onto Oxidized Multi-Walled Carbon Nanotubes in the Presence of Hydroxylated Fullerene and Carboxylated Fullerene
by Jing Wang, Peng Liu, Zhan Li, Wei Qi, Yan Lu and Wangsuo Wu
Materials 2013, 6(9), 4168-4185; https://doi.org/10.3390/ma6094168 - 17 Sep 2013
Cited by 13 | Viewed by 6606
Abstract
The adsorption of Th(IV) onto the surface of oxidized multi-walled carbon nanotubes (oMWCNTs) in the absence and presence of hydroxylated fullerene (C60(OH)n) and carboxylated fullerene (C60(C(COOH)2)n) has been investigated. C60(OH)n [...] Read more.
The adsorption of Th(IV) onto the surface of oxidized multi-walled carbon nanotubes (oMWCNTs) in the absence and presence of hydroxylated fullerene (C60(OH)n) and carboxylated fullerene (C60(C(COOH)2)n) has been investigated. C60(OH)n, C60(C(COOH)2)n and oMWCNTs have been chosen as model phases because of their representative in carbon nano-materials family. Adsorption experiments were performed by batch procedure as a function of contact time, pH, ionic strength, and temperature. The results demonstrated that the adsorption of Th(IV) was rapidly reached equilibrium and the kinetic process could be described by a pseudo-second-order rate model very well. Th(IV) adsorption on oMWCNTs was dependent on pH but independent on ionic strength. Adsorption isotherms were correlated better with the Langmuir model than with the Freundlich model. The thermodynamic parameters calculated from temperature-dependent adsorption isotherms suggested that Th(IV) adsorption on oMWCNTs was spontaneous and endothermic. Compared with the adsorption of Th(IV) on the same oMWCNTs free of C60(OH)n or C60(C(COOH)2)n, the study of a ternary system showed the inhibition effect of C60(OH)n at high concentration on the adsorption of Th(IV) in a pH range from neutral to slightly alkaline; whereas the promotion effect of C60(C(COOH)2)n, even at its low concentration, on Th(IV) adsorption was observed in acid medium. Full article
(This article belongs to the Special Issue Carbon Nanotubes)
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Figure 1
<p>Transmission electron microscope (TEM) images of (<b>a</b>) oxidized multi-walled carbon nanotubes (oMWCNTs); (<b>b</b>) C<sub>60</sub>(OH)<span class="html-italic"><sub>n</sub></span>-adsorbed oMWCNTs; <b>(c</b>) C<sub>60</sub>(C(COOH)<sub>2</sub>)<span class="html-italic"><sub>n</sub></span>-adsorbed oMWCNTs.</p> Full article ">Figure 2
<p>Fourier transform infrared (FTIR) spectra of oMWCNTs.</p> Full article ">Figure 3
<p>FTIR spectra of the samples: (<b>a</b>) raw C<sub>60</sub>; (<b>b</b>) C<sub>60</sub>(OH)<span class="html-italic"><sub>n</sub></span>; (<b>c</b>) C<sub>60</sub>(C(COOH)<sub>2</sub>)<span class="html-italic"><sub>n</sub></span>.</p> Full article ">Figure 4
<p>Effect of contact time on Th(IV) adsorption rate onto oMWCNTs and test of pseudo-second-order adsorption kinetics plot for Th(IV), <span class="html-italic">m/V</span> = 0.1 g/L, <span class="html-italic">T =</span> 25 ± 1 °C, C[Th<sup>4+</sup>] initial = 8.86 × 10<sup>−5</sup>mol/L, <span class="html-italic">I</span> = 0.01 mol/L NaNO<sub>3</sub>, pH = 3.20 ± 0.05.</p> Full article ">Figure 5
<p>Adsorption of Th(IV) on oMWCNTs as a function of pH, <span class="html-italic">m/V</span> = 0.1 g/L, <span class="html-italic">T =</span> 25 ± 1 °C, C[Th<sup>4+</sup>] initial = 8.86 × 10<sup>−5</sup> mol/L.</p> Full article ">Figure 6
<p>Effect of solid content on the adsorption of Th(IV) onto oMWCNTs, pH = 3.20 ± 0.05, <span class="html-italic">T =</span> 25 ± 1 °C, C[Th<sup>4+</sup>] initial = 8.86 × 10<sup>−5</sup> mol/L, <span class="html-italic">I</span> = 0.01 mol/L NaNO<sub>3</sub>.</p> Full article ">Figure 7
<p>Adsorption isotherms of Th(IV) on oMWCNTs at three different temperatures, <span class="html-italic">m/V</span> = 0.1 g/L, pH = 3.20 ± 0.05, <span class="html-italic">I</span> = 0.01 mol/L NaNO<sub>3</sub>, C[Th<sup>4+</sup>] initial = 8.86 × 10<sup>−5</sup> mol/L.</p> Full article ">Figure 8
<p>Langmuir model of Th(IV) adsorption onto oMWCNTs, <span class="html-italic">m/V</span> = 0.1 g/L, pH = 3.20 ± 0.05, <span class="html-italic">I</span> = 0.01 mol/L NaNO<sub>3</sub>, C[Th<sup>4+</sup>] initial = 8.86 × 10<sup>−5</sup> mol/L.</p> Full article ">Figure 9
<p>Freundlich model of Th(IV) adsorption onto oMWCNTs, <span class="html-italic">m/V</span> =0.1 g/L, pH = 3.20 ± 0.05, <span class="html-italic">I</span> = 0.01 mol/L NaNO<sub>3</sub>, C[Th<sup>4+</sup>] initial = 8.86 × 10<sup>−5</sup> mol/L.</p> Full article ">Figure 10
<p>Effect of C<sub>60</sub>(OH)<span class="html-italic"><sub>n</sub></span> on Th(IV) adsorption onto oMWCNTs as a function of pH, <span class="html-italic">m/V</span> = 0.1 g/L, <span class="html-italic">T =</span> 25 ± 1 °C, <span class="html-italic">I</span> = 0.01 mol/L NaNO<sub>3</sub>, C[Th<sup>4+</sup>] initial = 8.86 × 10<sup>−5</sup> mol/L.</p> Full article ">Figure 11
<p>Effect of Th(IV) initial concentrations on Th(IV) adsorption onto oMWCNTs as a function of C<sub>60</sub>(OH)<span class="html-italic"><sub>n</sub></span> initial concentrations, <span class="html-italic">m/V</span> = 0.1 g/L, pH = 3.20 ± 0.05, <span class="html-italic">I</span> = 0.01 mol/L NaNO<sub>3</sub>, <span class="html-italic">T =</span> 25 ± 1 °C.</p> Full article ">Figure 12
<p>Effect of oMWCNT dosage on Th(IV) adsorption on oMWCNTs as a function of C<sub>60</sub>(OH)<span class="html-italic"><sub>n</sub></span> initial concentrations, pH = 3.20 ± 0.05, <span class="html-italic">I</span> = 0.01 mol/L NaNO<sub>3</sub>, <span class="html-italic">T =</span> 25 ± 1 °C, C[Th<sup>4+</sup>] initial = 8.86 × 10<sup>−5</sup> mg/L.</p> Full article ">Figure 13
<p>Effect of C<sub>60</sub>(C(COOH)<sub>2</sub>)<span class="html-italic"><sub>n</sub></span> on Th(IV) adsorption onto oMWCNTs as a function of pH, <span class="html-italic">m/V</span> = 0.1 g/L, <span class="html-italic">T =</span> 25 ± 1 °C, <span class="html-italic">I</span> = 0.01 mol/L NaNO<sub>3</sub>, C[Th<sup>4+</sup>] initial = 8.86 × 10<sup>−5</sup> mol/L.</p> Full article ">Figure 14
<p>Effect of C<sub>60</sub>(OH)<span class="html-italic"><sub>n</sub></span> and C<sub>60</sub>(C(COOH)<sub>2</sub>)<span class="html-italic"><sub>n</sub></span> on the zeta potential of oMWCNTs. red line represent C<sub>60</sub>(OH)<span class="html-italic"><sub>n</sub></span> effect; blue line represent C<sub>60</sub>(C(COOH)<sub>2</sub>)<span class="html-italic"><sub>n</sub></span> effect.</p> Full article ">
697 KiB  
Review
SBA-15 Mesoporous Silica as Catalytic Support for Hydrodesulfurization Catalysts—Review
by Rafael Huirache-Acuña, Rufino Nava, Carmen L. Peza-Ledesma, Javier Lara-Romero, Gabriel Alonso-Núez, Barbara Pawelec and Eric M. Rivera-Muñoz
Materials 2013, 6(9), 4139-4167; https://doi.org/10.3390/ma6094139 - 17 Sep 2013
Cited by 175 | Viewed by 18032
Abstract
SBA-15 is an interesting mesoporous silica material having highly ordered nanopores and a large surface area, which is widely employed as catalyst supports, absorbents, drug delivery materials, etc. Since it has a lack of functionality, heteroatoms and organic functional groups have been incorporated [...] Read more.
SBA-15 is an interesting mesoporous silica material having highly ordered nanopores and a large surface area, which is widely employed as catalyst supports, absorbents, drug delivery materials, etc. Since it has a lack of functionality, heteroatoms and organic functional groups have been incorporated by direct or post-synthesis methods in order to modify their functionality. The aim of this article is to review the state-of-the-art related to the use of SBA-15-based mesoporous systems as supports for hydrodesulfurization (HDS) catalysts. Full article
(This article belongs to the Special Issue Advances in Mesoporous Materials)
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<p>High resolution transmission electron microscopy (HRTEM) micrographs of SBA-15 mesoporous silica. The size and morphology of the highly ordered hexagonal pores in a 2D array (<b>a</b>) with long 1D channels (<b>b</b>) (<span class="html-italic">p6mm</span> plane group) can be observed.</p> Full article ">
1069 KiB  
Article
High Density Polyethylene Composites Reinforced with Hybrid Inorganic Fillers: Morphology, Mechanical and Thermal Expansion Performance
by Runzhou Huang, Xinwu Xu, Sunyoung Lee, Yang Zhang, Birm-June Kim and Qinglin Wu
Materials 2013, 6(9), 4122-4138; https://doi.org/10.3390/ma6094122 - 17 Sep 2013
Cited by 87 | Viewed by 12247
Abstract
The effect of individual and combined talc and glass fibers (GFs) on mechanical and thermal expansion performance of the filled high density polyethylene (HDPE) composites was studied. Several published models were adapted to fit the measured tensile modulus and strength of various composite [...] Read more.
The effect of individual and combined talc and glass fibers (GFs) on mechanical and thermal expansion performance of the filled high density polyethylene (HDPE) composites was studied. Several published models were adapted to fit the measured tensile modulus and strength of various composite systems. It was shown that the use of silane-modified GFs had a much larger effect in improving mechanical properties and in reducing linear coefficient of thermal expansion (LCTE) values of filled composites, compared with the use of un-modified talc particles due to enhanced bonding to the matrix, larger aspect ratio, and fiber alignment for GFs. Mechanical properties and LCTE values of composites with combined talc and GF fillers varied with talc and GF ratio at a given total filler loading level. The use of a larger portion of GFs in the mix can lead to better composite performance, while the use of talc can help lower the composite costs and increase its recyclability. The use of 30 wt % combined filler seems necessary to control LCTE values of filled HDPE in the data value range generally reported for commercial wood plastic composites. Tensile modulus for talc-filled composite can be predicted with rule of mixture, while a PPA-based model can be used to predict the modulus and strength of GF-filled composites. Full article
(This article belongs to the Special Issue Constitutive Behavior of Composite Materials)
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<p>Scanning electron microscopy (SEM) micrographs of fractured surfaces of glass fiber (GF) filled high density polyethylene (HDPE) AD60 composites. (<b>a</b>) 10 wt % GF; (<b>b</b>) 30 wt % GF.</p> Full article ">Figure 2
<p>Tensile properties of GF-filled HDPE AD60 composites. Line showing predicted (PR) values with various models.</p> Full article ">Figure 3
<p>Effects of temperature level on storage modulus and loss modulus (<b>a</b>) and damping factor (<b>b</b>) of glass fiber-filled HDPE AD60 composites.</p> Full article ">Figure 4
<p>Typical dimension change-temperature history for glass fiber filled HDPE AD60 composite systems.</p> Full article ">Figure 5
<p>SEM micrograph of fractured surfaces of composites with combined fillers. Upper two charts (<b>a</b>,<b>b</b>) 10 wt % filer(talc/glass fiber = 1:2); and Lower two charts (<b>c</b>,<b>d</b>) 30 wt % filler (talc/glass fiber = 1:2).</p> Full article ">Figure 6
<p>Tensile modulus of composites filled with combined glass fiber and talc fillers. Lines in the upper chart showing predicted values.</p> Full article ">Figure 7
<p>Effects of temperature level on storage modulus and loss modulus (<b>a</b>) and damping factor; (<b>b</b>) of HDPE AD60 composites filled with combined GF and talc fillers at the 30 wt %.</p> Full article ">Figure 8
<p>Typical dimension change-temperature history for HDPE AD60 composite filled with combined glassfiber and talc fillers at the 30 wt % loading level.</p> Full article ">
2214 KiB  
Article
The Tension and Puncture Properties of HDPE Geomembrane under the Corrosion of Leachate
by Qiang Xue, Qian Zhang, Zhen-Ze Li and Kai Xiao
Materials 2013, 6(9), 4109-4121; https://doi.org/10.3390/ma6094109 - 17 Sep 2013
Cited by 8 | Viewed by 7290
Abstract
To investigate the gradual failure of high-density polyethylene (HDPE) geomembrane as a result of long-term corrosion, four dynamic corrosion tests were conducted at different temperatures and durations. By combining tension and puncture tests, we systematically studied the variation law of tension and puncture [...] Read more.
To investigate the gradual failure of high-density polyethylene (HDPE) geomembrane as a result of long-term corrosion, four dynamic corrosion tests were conducted at different temperatures and durations. By combining tension and puncture tests, we systematically studied the variation law of tension and puncture properties of the HDPE geomembrane under different corrosion conditions. Results showed that tension and puncture failure of the HDPE geomembrane was progressive, and tensile strength in the longitudinal grain direction was evidently better than that in the transverse direction. Punctures appeared shortly after puncture force reached the puncture strength. The tensile strength of geomembrane was in inversely proportional to the corrosion time, and the impact of corrosion was more obvious in the longitudinal direction than transverse direction. As corrosion time increased, puncture strength decreased and corresponding deformation increased. As with corrosion time, the increase of corrosion temperature induced the decrease of geomembrane tensile strength. Tensile and puncture strength were extremely sensitive to temperature. Overall, residual strength had a negative correlation with corrosion time or temperature. Elongation variation increased initially and then decreased with the increase in temperature. However, it did not show significant law with corrosion time. The reduction in puncture strength and the increase in puncture deformation had positive correlations with corrosion time or temperature. The geomembrane softened under corrosion condition. The conclusion may be applicable to the proper designing of the HDPE geomembrane in landfill barrier system. Full article
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>The tension and puncture properties of uncorroded geomembrane specimens.</p> Full article ">Figure 2
<p>The tension force-deformation curves of geomembrane specimens in the longitudinal grain direction. (<b>a</b>) 20 °C; (<b>b</b>) 50 °C and (<b>c</b>) 80 °C.</p> Full article ">Figure 3
<p>The tension force-deformation curves of geomembrane specimens in the cross grain direction. (<b>a</b>) 20 °C; (<b>b</b>) 50 °C and (<b>c</b>) 80 °C.</p> Full article ">Figure 4
<p>The tensile strength-temperature curves of geomembrane specimens. (<b>a</b>) 5 days; (<b>b</b>) 10 days; and (<b>c</b>) 20 days.</p> Full article ">Figure 5
<p>The puncture force-deformation curves of geomembrane specimens corroded with landfill leachate. (<b>a</b>) 20 °C; (<b>b</b>) 50 °C and (<b>c</b>) 80 °C.</p> Full article ">
415 KiB  
Article
Complete Permittivity Tensor in Sputtered CuFe2O4 Thin Films at Photon Energies between 2 and 5 eV
by Martin Veis, Roman Antos, Stefan Visnovsky, Prasanna D. Kulkarni, Narayanan Venkataramani, Shiva Prasad, Jan Mistrik and Ramanathan Krishnan
Materials 2013, 6(9), 4096-4108; https://doi.org/10.3390/ma6094096 - 16 Sep 2013
Cited by 9 | Viewed by 5217
Abstract
This work is devoted to the systematic study of the optical and magneto-optical properties of sputter deposited CuFe2O4 thin films in the photon energy region between 2 and 5 eV using spectroscopic ellipsometry and magneto-optical Kerr spectroscopy. The spectral dependence [...] Read more.
This work is devoted to the systematic study of the optical and magneto-optical properties of sputter deposited CuFe2O4 thin films in the photon energy region between 2 and 5 eV using spectroscopic ellipsometry and magneto-optical Kerr spectroscopy. The spectral dependence of both the diagonal and off-diagonal elements of the permittivity tensor is determined. A complete picture about the electron transitions in CuFe2O4 is suggested in the frame of intervalence charge transfer and intersublattice charge transfer transitions. The effect of deposition conditions and post-deposition treatment in CuFe2O4 films upon the optical and magneto-optical properties is discussed. Full article
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<p>The diagonal element, <math display="inline"> <msub> <mi>ε</mi> <mn>1</mn> </msub> </math>, of the permittivity tensor of quenched CuFe<math display="inline"> <msub> <mrow/> <mn>2</mn> </msub> </math>O<math display="inline"> <msub> <mrow/> <mn>4</mn> </msub> </math> thin film (Sample 1).</p> Full article ">Figure 2
<p>Polar Kerr rotation spectra of CuFe<math display="inline"> <msub> <mrow/> <mn>2</mn> </msub> </math>O<math display="inline"> <msub> <mrow/> <mn>4</mn> </msub> </math> thin films measured at nearly normal incidence.</p> Full article ">Figure 3
<p>Polar Kerr ellipticity spectra of CuFe<math display="inline"> <msub> <mrow/> <mn>2</mn> </msub> </math>O<math display="inline"> <msub> <mrow/> <mn>4</mn> </msub> </math> thin films measured at nearly normal incidence.</p> Full article ">Figure 4
<p>The off-diagonal elements, <math display="inline"> <msub> <mi>ε</mi> <mn>2</mn> </msub> </math>, of CuFe<math display="inline"> <msub> <mrow/> <mn>2</mn> </msub> </math>O<math display="inline"> <msub> <mrow/> <mn>4</mn> </msub> </math> thin films deduced from the polar Kerr measurements along with the fitted theoretical dependence.</p> Full article ">Figure 5
<p>Experimental and theoretical longitudinal Kerr rotation of quenched CuFe<math display="inline"> <msub> <mrow/> <mn>2</mn> </msub> </math>O<math display="inline"> <msub> <mrow/> <mn>4</mn> </msub> </math> thin film.</p> Full article ">
697 KiB  
Article
Aqueous ZrO2 and YSZ Colloidal Systems through Microwave Assisted Hydrothermal Synthesis
by Kenny Vernieuwe, Petra Lommens, José C. Martins, Freya Van Den Broeck, Isabel Van Driessche and Klaartje De Buysser
Materials 2013, 6(9), 4082-4095; https://doi.org/10.3390/ma6094082 - 16 Sep 2013
Cited by 10 | Viewed by 6205
Abstract
In this paper, the formation of ZrO2 and yttria-stabilised-zirconia (YSZ) aqueous colloidal systems via microwave assisted hydrothermal synthesis is studied. Microwave synthesis allows a fast screening of the influence of different parameters such as time and temperature. The temperature varied from 140 [...] Read more.
In this paper, the formation of ZrO2 and yttria-stabilised-zirconia (YSZ) aqueous colloidal systems via microwave assisted hydrothermal synthesis is studied. Microwave synthesis allows a fast screening of the influence of different parameters such as time and temperature. The temperature varied from 140 °C up to 180 °C and the used reaction time varied from 5 min up to 1 h. The synthesised zirconia nanoparticles have a particle size of 50 nm confirmed by TEM. A 1H NMR (nuclear magnetic resonance) study helped to understand the stabilization mechanism of the synthesised particles. By the addition of ytrrium ions into the zirconia colloidal solution, YSZ could be formed via an additional thermal treatment. Hereby, the samples are heated up to 400 °C for 1 h. YSZ colloidal solutions are synthesised by making use of complexing agents such as nitrilotriacetic acid, ethylenediaminetetraacetic acid and citric acid to control the hydrolysis and condensation of both ions to avoid non-stoichiometric phases. The ratio of Zr/Y in the particles is quantified by XRF. The amorphous structure of those particles necessitates an additional thermal treatment up to 600 °C during 1 h in order to obtain crystalline YSZ. Full article
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>(<b>a</b>) The particle size of ZrO<sub>2</sub> particles synthesized by microwave treatment of solution A at 150 °C for 30 min measured by DLS; and (<b>b</b>) TEM micrograph of the solution A treated for 30 min at 150 °C.</p> Full article ">Figure 2
<p>XRD patterns of precipitated particles derived from microwave treated solution A at (<b>a</b>) 160 °C for 5 min; (<b>b</b>) 150 °C for 30 min; (<b>c</b>) 150° C for 5 min; (<b>d</b>) 140 °C for 60 min; and (<b>e</b>) 140 °C for 5 min.</p> Full article ">Figure 3
<p>1D proton NMR spectrum of solution A after microwave treatment, purification and the addition of CA and EA.</p> Full article ">Figure 4
<p>2D NOESY spectrum of solution A microwave treated at 150 °C during 30 min after purification and the addition of CA and EA. Positive and negative NOE cross-peaks appear in red and blue and are attributed to their respective species.</p> Full article ">Figure 5
<p>The influence of the temperature on the diffusion of Y into ZrO<sub>2</sub> nanoparticles shown by XRD measurements (<b>a</b>) treated at 400 °C for 1 h; (<b>b</b>) treated at 300 °C for 1 h; and (<b>c</b>) as-synthesised, M marks the diffraction peaks of monoclinic ZrO<sub>2</sub>; and C the diffraction peaks of YSZ.</p> Full article ">Figure 6
<p>Rietveld refinement of the sample treated at 400 °C for 1 h with (<b>a</b>) the experimental data, sample inclusive internal standard; and (<b>b</b>) the calculated diffractogram.</p> Full article ">Figure 7
<p>Hydrodynamic radius of solution B microwave treated at 180 °C for 10 min determined by DLS measurements.</p> Full article ">Figure 8
<p>Hydrodynamic radius of solution B microwave treated at 180 °C for 10 min determined by DLS measurement<b>s </b>represented as a function of volume distribution.</p> Full article ">Figure 9
<p>The influence of thermal processing on the crystallinity of the YSZ nanoparticles shown by XRD measurements (<b>a</b>) treated at 600 °C for 1 h; (<b>b</b>) treated at 400 °C for 1 h; and (<b>c</b>) as-synthesised.</p> Full article ">Figure 10
<p>Rietveld refinement of the sample treated at 600 °C with (<b>a</b>) the experimental data, sample inclusive internal standard; and (<b>b</b>) the calculated diffractogram.</p> Full article ">
971 KiB  
Article
Experimental Study on Cementitious Composites Embedded with Organic Microcapsules
by Xianfeng Wang, Feng Xing, Ming Zhang, Ningxu Han and Zhiwei Qian
Materials 2013, 6(9), 4064-4081; https://doi.org/10.3390/ma6094064 - 16 Sep 2013
Cited by 124 | Viewed by 7504
Abstract
The recovery behavior for strength and impermeability of cementitious composites embedded with organic microcapsules was investigated in this study. Mortar specimens were formed by mixing the organic microcapsules and a catalyst with cement and sand. The mechanical behaviors of flexural and compression strength [...] Read more.
The recovery behavior for strength and impermeability of cementitious composites embedded with organic microcapsules was investigated in this study. Mortar specimens were formed by mixing the organic microcapsules and a catalyst with cement and sand. The mechanical behaviors of flexural and compression strength were tested. The results showed that strength could increase by up to nine percent with the addition of a small amount of microcapsules and then decrease with an increasing amount of microcapsules. An orthogonal test for investigating the strength recovery rate was designed and implemented for bending and compression using the factors of water/cement ratio, amount of microcapsules, and preloading rate. It is shown that the amount of microcapsules plays a key role in the strength recovery rate. Chloride ion permeability tests were also carried out to investigate the recovery rate and healing effect. The initial damage was obtained by subjecting the specimens to compression. Both the recovery rate and the healing effect were nearly proportional to the amount of microcapsules. The obtained cementitious composites can be seen as self-healing owing to their recovery behavior for both strength and permeability. Full article
(This article belongs to the Special Issue Self-healing Concrete)
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<p>Synthesis stages of organic microcapsules. (<b>a</b>) Pre-polymer prepared; (<b>b</b>) Core material dispersed into droplet; (<b>c</b>) Pre-polymer polycondensated and (<b>d</b>) Polycondensated pre-polymer deposited on core.</p> Full article ">Figure 2
<p>Organic microcapsules under a scanning electron microscope (SEM).</p> Full article ">Figure 3
<p>Diameter distribution of the organic microcapsules (in micrometers).</p> Full article ">Figure 4
<p>Shell thickness of organic microcapsules.</p> Full article ">Figure 5
<p>Variation of the flexural strength<span class="html-italic"> versus</span> the amount of organic microcapsules.</p> Full article ">Figure 6
<p>Variation of the compressive strength<span class="html-italic"> versus</span> the amount of organic microcapsules.</p> Full article ">Figure 7
<p>Relationship between the factors and strength recovery rate.</p> Full article ">Figure 8
<p>Fracture surface of the specimens. (<b>a</b>) Microcapsules combined with mortar matrix and (<b>b</b>) Microcapsule ruptured.</p> Full article ">Figure 9
<p>Setup of rapid chloride migration (RCM) test.</p> Full article ">Figure 10
<p>Specimen colored by AgNO<sub>3</sub> water solution.</p> Full article ">Figure 11
<p>Variation of chloride ion migration coefficient.</p> Full article ">Figure 12
<p>Permeability recovery rate<span class="html-italic"> versus</span> amount of microcapsules.</p> Full article ">Figure 13
<p>Permeability healing effect<span class="html-italic"> versus</span> amount of microcapsules.</p> Full article ">
1719 KiB  
Review
Consolidation of Hierarchy-Structured Nanopowder Agglomerates and Its Application to Net-Shaping Nanopowder Materials
by Jai-Sung Lee, Joon-Phil Choi and Geon-Yong Lee
Materials 2013, 6(9), 4046-4063; https://doi.org/10.3390/ma6094046 - 16 Sep 2013
Cited by 28 | Viewed by 7991
Abstract
This paper provides an overview on our recent investigations on the consolidation of hierarchy-structured nanopowder agglomerates and related applications to net-shaping nanopowder materials. Understanding the nanopowder agglomerate sintering (NAS) process is essential to processing of net-shaped nanopowder materials and components with small and [...] Read more.
This paper provides an overview on our recent investigations on the consolidation of hierarchy-structured nanopowder agglomerates and related applications to net-shaping nanopowder materials. Understanding the nanopowder agglomerate sintering (NAS) process is essential to processing of net-shaped nanopowder materials and components with small and complex shape. The key concept of the NAS process is to enhance material transport through controlling the powder interface volume of nanopowder agglomerates. Based upon this concept, we have suggested a new idea of full density processing for fabricating micro-powder injection molded part using metal nanopowder agglomerates produced by hydrogen reduction of metal oxide powders. Studies on the full density sintering of die compacted- and powder injection molded iron base nano-agglomerate powders are introduced and discussed in terms of densification process and microstructure. Full article
(This article belongs to the Special Issue Progress in Net-shaped PM (Powder Metallurgical) Parts)
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<p>Schematic illustration of pore size distribution in agglomerated nanocrystalline powder (<b>a</b>) without and (<b>b</b>) with controlling of distribution of agglomerate size [<a href="#B13-materials-06-04046" class="html-bibr">13</a>].</p> Full article ">Figure 2
<p>Experimental procedure for synthesis and net-shaping process of metal nanopowders produced by hydrogen reduction of ball-milled oxide powder [<a href="#B3-materials-06-04046" class="html-bibr">3</a>].</p> Full article ">Figure 3
<p>SEM micrographs of (<b>a</b>) as-reduced and (<b>b</b>) wet-milled Fe nanopowder [<a href="#B18-materials-06-04046" class="html-bibr">18</a>].</p> Full article ">Figure 4
<p>Microstructure of (<b>a</b>) the die-pressed compact and (<b>b</b>) the powder injection molding (PIM) brown part of Fe–40 wt % Ni nanopowder [<a href="#B19-materials-06-04046" class="html-bibr">19</a>].</p> Full article ">Figure 5
<p>Microstructure of the Fe–40 wt % Ni nanomaterial observed by optical and transmission electron microscope and a model of nanomaterials composed of hierarchical microstructure consisting of nano- and agglomerate boundaries [<a href="#B10-materials-06-04046" class="html-bibr">10</a>].</p> Full article ">Figure 6
<p>Apparent activation energy for densification process for Fe–8 wt % Ni nanopowder agglomerates during sintering at intermediate temperatures [<a href="#B24-materials-06-04046" class="html-bibr">24</a>].</p> Full article ">Figure 7
<p>Densification process for Fe–40 wt % Ni nanopowder agglomerates during sintering at intermediate temperatures [<a href="#B6-materials-06-04046" class="html-bibr">6</a>].</p> Full article ">Figure 8
<p>Microstructures of hierarchical structured Fe–40 wt % Ni nanopowder agglomerates sintered at 616 °C for 2 h: (<b>a</b>,<b>b</b>) large agglomerate powder and (<b>c</b>,<b>d</b>) small agglomerate powder.</p> Full article ">Figure 9
<p>The densification behavior of Fe nanopowders with optimal agglomerate size during heat-up with a heating rate of 10 °C/min and subsequent isothermal sintering at 700 °C in a hydrogen atmosphere [<a href="#B12-materials-06-04046" class="html-bibr">12</a>].</p> Full article ">Figure 10
<p>SEM fractographs of Fe nanopowders showing microstructural homogenization during heat-up sintering with a heating rate of 10 °C/min up to (<b>a</b>) 600 °C, (<b>b</b>) 650 °C, (<b>c</b>) 700 °C and (<b>d</b>) sintered at 700 °C for 4 h, for comparison. * White dotted circles denote agglomerates [<a href="#B12-materials-06-04046" class="html-bibr">12</a>].</p> Full article ">Figure 11
<p>SEM micrographs and EBSD (electron backscatter diffraction) images of pure Fe nanopowders sintered at 700 °C for <b>(a)</b> 0 h and <b>(b)</b> 4 h. * The arrows indicate pores mostly locating at grain boundaries and triple junctions [<a href="#B12-materials-06-04046" class="html-bibr">12</a>].</p> Full article ">Figure 12
<p>The variation of Vickers hardness (H<sub>v</sub>) of Fe nanopowder parts sintered at 700 °C as a function of d<sup>−1/2</sup> [<a href="#B12-materials-06-04046" class="html-bibr">12</a>].</p> Full article ">Figure 13
<p>Photographs of the PIM Fe–8 wt % Ni double-gear parts and their 3-dimensional images for surface roughness by AFM: (<b>a</b>) brown part and (<b>b</b>) sintered part (sintered at 1000 °C for 1 h) [<a href="#B5-materials-06-04046" class="html-bibr">5</a>].</p> Full article ">Figure 14
<p>The fracture surface morphologies of (<b>a</b>) brown and (<b>b</b>) sintered part of PIM Fe–8 wt % Ni nanopowders (A denotes agglomerate boundary) [<a href="#B5-materials-06-04046" class="html-bibr">5</a>].</p> Full article ">Figure 15
<p>Micrographs of hierarchical structured Fe–8 wt % Ni PIM part showing (<b>a</b>,<b>b</b>) agglomerate boundary and nano-grains and (<b>c</b>) γ-precipitates favorably located at agglomerate boundaries (sintered at 800 °C for 2 h) [<a href="#B5-materials-06-04046" class="html-bibr">5</a>].</p> Full article ">Figure 16
<p>SEM fractographs of the debound parts fabricated using (<b>a</b>) Fe micro-25 vol % nano powder; (<b>b</b>) Fe micro powder and (<b>c</b>) compressive fracture strength of (<b>a</b>) and (<b>b</b>) [<a href="#B30-materials-06-04046" class="html-bibr">30</a>].</p> Full article ">Figure 17
<p>(<b>a</b>) SEM micrograph of the sintered double gear fabricated using Fe micro-25 vol % nano powder feedstock and (<b>b</b>) linear shrinkage distribution in the sintered part [<a href="#B30-materials-06-04046" class="html-bibr">30</a>].</p> Full article ">Figure 18
<p>SEM micrographs of the surface of Fe-PIM part sintered at 1250 °C for 3 h, (<b>a</b>) micro-nano powder and (<b>b</b>) micro powder [<a href="#B30-materials-06-04046" class="html-bibr">30</a>].</p> Full article ">
755 KiB  
Article
Thermally Activated Composite with Two-Way and Multi-Shape Memory Effects
by Abdul Basit, Gildas L'Hostis, Marie José Pac and Bernard Durand
Materials 2013, 6(9), 4031-4045; https://doi.org/10.3390/ma6094031 - 12 Sep 2013
Cited by 18 | Viewed by 6591
Abstract
The use of shape memory polymer composites is growing rapidly in smart structure applications. In this work, an active asymmetric composite called “controlled behavior composite material (CBCM)” is used as shape memory polymer composite. The programming and the corresponding initial fixity of the [...] Read more.
The use of shape memory polymer composites is growing rapidly in smart structure applications. In this work, an active asymmetric composite called “controlled behavior composite material (CBCM)” is used as shape memory polymer composite. The programming and the corresponding initial fixity of the composite structure is obtained during a bending test, by heating CBCM above thermal glass transition temperature of the used Epoxy polymer. The shape memory properties of these composites are investigated by a bending test. Three types of recoveries are conducted, two classical recovery tests: unconstrained recovery and constrained recovery, and a new test of partial recovery under load. During recovery, high recovery displacement and force are produced that enables the composite to perform strong two-way actuations along with multi-shape memory effect. The recovery force confirms full recovery with two-way actuation even under a high load. This unique property of CBCM is characterized by the recovered mechanical work. Full article
(This article belongs to the Special Issue Smart Polymers and Polymeric Structures)
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<p>General 3D view of thermo-mechanical shape memory cycles [<a href="#B12-materials-06-04031" class="html-bibr">12</a>].</p> Full article ">Figure 2
<p>DSC analysis of Epolam 20-25, <span class="html-italic">T</span><sub>g</sub> = 124 °C.</p> Full article ">Figure 3
<p>Example of fixing or programming cycle, fixity temperature <span class="html-italic">T</span><sub>F</sub> = 150 °C.</p> Full article ">Figure 4
<p>Recovery displacements for an unconstrained multi-step recovery cycle, <math display="inline"> <semantics> <mrow> <msubsup> <mtext>d</mtext> <mi>F</mi> <mi>I</mi> </msubsup> </mrow> </semantics> </math> = 7.28 ± 0.89 mm, ( <math display="inline"> <semantics> <mrow> <msubsup> <mi>ε</mi> <mi>F</mi> <mi>I</mi> </msubsup> </mrow> </semantics> </math> = 2.43% ± 0.30%). E = fixity; EF: heating to <span class="html-italic">T</span><sub>R</sub>, FG: cooling to <span class="html-italic">T</span><sub>a</sub>. Loading equal to the preload of 0.3 N.</p> Full article ">Figure 5
<p>Definition of the geometrical parameters.</p> Full article ">Figure 6
<p>Multi-step unconstrained recovery activation ratio <span class="html-italic">r<sub>a</sub></span> and fixity ratio <span class="html-italic">r<sub>f</sub></span> calculated for each <math display="inline"> <semantics> <mrow> <msubsup> <mi>T</mi> <mtext>R</mtext> <mtext>i</mtext> </msubsup> </mrow> </semantics> </math> and linear interpolation.</p> Full article ">Figure 7
<p>Recovery displacement for an unconstrained multi-step recovery cycle with a constant recovery temperature, <span class="html-italic">T</span><sub>R</sub> = 80 °C, <math display="inline"> <semantics> <mrow> <msubsup> <mi>d</mi> <mi>F</mi> <mi>I</mi> </msubsup> </mrow> </semantics> </math> = 6.93 ± 0.93, ( <math display="inline"> <semantics> <mrow> <msubsup> <mtext>ε</mtext> <mtext>F</mtext> <mtext>I</mtext> </msubsup> </mrow> </semantics> </math> = 2.31% ± 0.31%). EF, GF: heating, FG: cooling to <span class="html-italic">T</span><sub>a</sub>. Loading equal to the preload of 0.3 N.</p> Full article ">Figure 8
<p>Recovery and residual forces for a one-step constrained recovery test at <span class="html-italic">T</span><sub>R</sub> = 150 °C carried out three time, <math display="inline"> <semantics> <mrow> <msubsup> <mi>d</mi> <mtext>F</mtext> <mtext>I</mtext> </msubsup> </mrow> </semantics> </math> = 7.56 ± 0.69, ( <math display="inline"> <semantics> <mrow> <msubsup> <mtext>ε</mtext> <mtext>F</mtext> <mtext>I</mtext> </msubsup> </mrow> </semantics> </math> = 2.52% ± 0.23%). EF, GH, IJ: heating step; FG, HI, JK: cooling to <span class="html-italic">T</span><sub>a</sub>.</p> Full article ">Figure 9
<p>Force evolutions during a constrained multi-step recovery cycle, <math display="inline"> <semantics> <mrow> <msubsup> <mi>d</mi> <mtext>F</mtext> <mtext>I</mtext> </msubsup> </mrow> </semantics> </math> = 6.36 ± 0.84, ( <math display="inline"> <semantics> <mrow> <msubsup> <mtext>ε</mtext> <mtext>F</mtext> <mtext>I</mtext> </msubsup> </mrow> </semantics> </math> = 2.12% ± 0.28%).</p> Full article ">Figure 10
<p>Recovery displacements for a recovery under load test at <span class="html-italic">T</span><sub>R</sub> = 150 °C, <span class="html-italic">F</span><sub>B</sub> = 36.5 N (EF = Heating to <span class="html-italic">T</span><sub>R</sub> and loading to <span class="html-italic">F</span><sub>B</sub>; FG, HI, JK: heating to <span class="html-italic">T</span><sub>R</sub> under <span class="html-italic">F</span><sub>B</sub>, GH, IJ, KL: cooling to <span class="html-italic">T</span><sub>a</sub> under <span class="html-italic">F</span><sub>B</sub>.</p> Full article ">
3442 KiB  
Article
Observations of Ball-Lightning-Like Plasmoids Ejected from Silicon by Localized Microwaves
by Yehuda Meir, Eli Jerby, Zahava Barkay, Dana Ashkenazi, James Brian Mitchell, Theyencheri Narayanan, Noam Eliaz, Jean-Luc LeGarrec, Michael Sztucki and Oleg Meshcheryakov
Materials 2013, 6(9), 4011-4030; https://doi.org/10.3390/ma6094011 - 11 Sep 2013
Cited by 20 | Viewed by 9778
Abstract
This paper presents experimental characterization of plasmoids (fireballs) obtained by directing localized microwave power (<1 kW at 2.45 GHz) onto a silicon-based substrate in a microwave cavity. The plasmoid emerges up from the hotspot created in the solid substrate into the air within [...] Read more.
This paper presents experimental characterization of plasmoids (fireballs) obtained by directing localized microwave power (<1 kW at 2.45 GHz) onto a silicon-based substrate in a microwave cavity. The plasmoid emerges up from the hotspot created in the solid substrate into the air within the microwave cavity. The experimental diagnostics employed for the fireball characterization in this study include measurements of microwave scattering, optical spectroscopy, small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Various characteristics of these plasmoids as dusty plasma are drawn by a theoretical analysis of the experimental observations. Aggregations of dust particles within the plasmoid are detected at nanometer and micrometer scales by both in-situ SAXS and ex-situ SEM measurements. The resemblance of these plasmoids to the natural ball-lightning (BL) phenomenon is discussed with regard to silicon nano-particle clustering and formation of slowly-oxidized silicon micro-spheres within the BL. Potential applications and practical derivatives of this study (e.g., direct conversion of solids to powders, material identification by breakdown spectroscopy (MIBS), thermite ignition, and combustion) are discussed. Full article
(This article belongs to the Special Issue Microwave Processing of Materials)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>The experimental setup: (<b>a</b>) The microwave cavity with a movable electrode directing the localized microwaves into the substrate, thus creating a hotspot from which the fireball is ejected to the air atmosphere within the cavity; and (<b>b</b>) A block diagram of the experimental instrumentation.</p> Full article ">Figure 2
<p>(<b>a</b>) A fire-column ejected from a hotspot created by localized microwaves in silicon, feeding an adjacent secondary fireball (plasmoid); and (<b>b</b>) The fireball evolved, floating in the air atmosphere within the microwave cavity [<a href="#B1-materials-06-04011" class="html-bibr">1</a>].</p> Full article ">Figure 3
<p>The microwave reflections from the cavity before and after ignition: (<b>a</b>) The autonomous reduction in the reflected power upon ignition of the fire-column, and its fluctuation in the fireball stage, being attracted by a minimal reflection level <math display="inline"> <semantics> <mrow> <mrow> <mo>〈</mo> <msup> <mrow> <mo>|</mo> <mi mathvariant="sans-serif">ρ</mi> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mo>〉</mo> <mo>~</mo> <mn>0.1</mn> </mrow> </mrow> </semantics> </math>; and (<b>b</b>) Smith-chart presentations of the cavity’s input impedance, before ignition, during the fire-column stage, and in the consequent fireball stage (the latter shows the tendency of the fireball to reach a self impedance matching).</p> Full article ">Figure 4
<p>Optical spectroscopy measurements. A typical spectrum of silicon plasmoid reveals silicon excited atoms, and hydroxyl and nitric oxide radical production.</p> Full article ">Figure 5
<p>Temperature evaluation by fitting the radicals emission, (<b>a</b>) OH<sup>–</sup>; (<b>b</b>) CN by the LifBase simulation [<a href="#B27-materials-06-04011" class="html-bibr">27</a>]; and (<b>c</b>) an accumulation of 941 fittings frames for OH<sup>–</sup> and 973 frames for CN with respect to the instantaneous effective microwave power. The mean temperature does not seem to vary significantly with power in this range.</p> Full article ">Figure 6
<p>A Boltzmann plot of the silicon lines resulting in a ~1 eV excitation temperature.</p> Full article ">Figure 7
<p>(<b>a</b>) An emission spectrum of silicon lines with chromium impurities; and (<b>b</b>) a Boltzmann-plot fit of the chromium lines resulting in ~0.3 eV excitation temperature. (Note a diode line defect at 485 nm in <a href="#materials-06-04011-f007" class="html-fig">Figure 7</a>a)</p> Full article ">Figure 8
<p>(<b>a</b>) Normalized SAXS intensity profiles from the silicon fireball ejected by a graphite electrode in dry air and in damp air with NaHCO<sub>3</sub> (Blue and Red curves, respectively), together with model fits; and (<b>b</b>) Particle size distribution derived from the best fit Monte-Carlo simulations corresponding to mean particle radii of 62.9 nm and 55.4 nm for the dry and damp conditions, respectively.</p> Full article ">Figure 9
<p>SEM observations: (<b>a</b>) aggregates of spherical particles, 0.1–0.3 μm in diameter, on the silicon emitter. The inset shows a typical sphere with a rough hairy surface that consists of smaller particles, ~10 nm in diameter. EDS analysis reveals mostly silicon and oxygen in these aggregates; (<b>b</b>) larger spheres, on the micrometer-scale in diameter, in a molten region, and voids of similar sizes; and (<b>c</b>) micro-spheres that seem to be smashed onto the copper collector plate. The inset shows a typical ~10 μm sphere of silicon that seemingly was crushed into the copper plate and has created a crater by hitting the surface.</p> Full article ">Figure 10
<p>A typical perfect sphere, 8 μm in diameter; (<b>a</b>) the SEM image; (<b>b</b>) its EDS spectrum showing mostly Si and O; and (<b>c</b>) examples of micro-particles observed by SEM on the copper collector as clusters in various stages of agglomeration.</p> Full article ">Figure 11
<p>The particles presented were created by a Si-emitter, C-electrode, and Cu-collector system, in water-vapor sprayed air atmosphere: (<b>a</b>) examples of micro-particle clusters observed by SEM on the silicon emitter; (<b>b</b>) a micro-particle cluster observed by SEM on the silicon emitter; and (<b>c</b>) around sphere obtained in the same conditions with sodium bicarbonate added to the water vapor inhalator.</p> Full article ">Figure 12
<p>Examples of hairy sea-urchin-like clusters observed by SEM on the copper collector, as (<b>a</b>) was created by a Si-emitter, C-electrode, and Cu-collector system, in water-vapor sprayed air atmosphere; and (<b>b</b>) was obtained in the same conditions with sodium bicarbonate added to the water vapor inhalator.</p> Full article ">Figure 13
<p>A parametric estimation of the dusty plasmoid properties by the microwave reflection measurements: (<b>a</b>) The plasmoid shape and position used in the numerical model presented by the amplitude profile of the displacement field for <span class="html-italic">ε<sub>r</sub></span> = 0.2 − <span class="html-italic">j</span>20; (<b>b,c</b>) The amplitude and phase, respectively, of the reflection coefficient as a function of the plasmoid position, for various values of <span class="html-italic">ε<sub>r</sub></span>; and (<b>d</b>) A Smith-chart presentation for the plasmoid’s impedance. The dashed Red circle indicates the self-impedance matching region (<math display="inline"> <semantics> <mrow> <mrow> <mo>|</mo> <mi mathvariant="normal">Γ</mi> <mo>|</mo> </mrow> <mo>≤</mo> <mn>0.33</mn> </mrow> </semantics> </math>) as observed experimentally in <a href="#materials-06-04011-f003" class="html-fig">Figure 3</a>b. The dotted Blue curve marks the 35 mm position at which a perfect match is obtained for <span class="html-italic">ε<sub>r</sub></span> = 0.2 – <span class="html-italic">j</span>10.</p> Full article ">
297 KiB  
Article
New Coating Technique of Ceramic Implants with Different Glass Solder Matrices for Improved Osseointegration-Mechanical Investigations
by Enrico Mick, Jana Markhoff, Aurica Mitrovic, Anika Jonitz and Rainer Bader
Materials 2013, 6(9), 4001-4010; https://doi.org/10.3390/ma6094001 - 11 Sep 2013
Cited by 8 | Viewed by 6388
Abstract
Ceramics are a very popular material in dental implant technology due to their tribological properties, their biocompatibility and their esthetic appearance. However, their natural surface structure lacks the ability of proper osseointegration, which constitutes a crucial process for the stability and, thus, the [...] Read more.
Ceramics are a very popular material in dental implant technology due to their tribological properties, their biocompatibility and their esthetic appearance. However, their natural surface structure lacks the ability of proper osseointegration, which constitutes a crucial process for the stability and, thus, the functionality of a bone implant. We investigated the application of a glass solder matrix in three configurations—consisting mainly of SiO2, Al2O3, K2O and Na2O to TZP-A ceramic specimens. The corresponding adhesive strength and surface roughness of the coatings on ceramic specimens have been analyzed. Thereby, high adhesive strength (70.3 ± 7.9 MPa) was found for the three different coatings. The obtained roughness (Rz) amounted to 18.24 ± 2.48 µm in average, with significant differences between the glass solder configurations. Furthermore, one configuration was also tested after additional etching which did not lead to significant increase of surface roughness (19.37 ± 1.04 µm) or adhesive strength (57.2 ± 5.8 MPa). In conclusion, coating with glass solder matrix seems to be a promising surface modification technique that may enable direct insertion of ceramic implants in dental and orthopaedic surgery. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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<p>(<b>a</b>) Setup for adhesive strength test sample prior to testing; (<b>b</b>) Sample after testing.</p> Full article ">Figure 2
<p>SEM image (magnification: 200X) of a TZP-A specimen coated with glass solder matrix HT1.</p> Full article ">Figure 3
<p>TZP-A specimens partly coated with glass solder: (<b>a</b>) HT1; (<b>b</b>) LT1; and (<b>c</b>) LT2 with each bottom half being uncoated, the right upper quarter being coated with raw glass solder and the left upper quarter being coated and sandblasted.</p> Full article ">
572 KiB  
Article
Effect of Nanopore Length on the Translocation Process of a Biopolymer: Numerical Study
by Suresh Alapati, Woo Seong Che and Yong Kweon Suh
Materials 2013, 6(9), 3989-4000; https://doi.org/10.3390/ma6093989 - 11 Sep 2013
Cited by 4 | Viewed by 5154
Abstract
In this study, we simulate the electrophoretic motion of a bio-polymer through a synthetic nanopore in the presence of an external bias voltage by considering the hydrodynamic interactions between the polymer and the fluid explicitly. The motion of the polymer is simulated by [...] Read more.
In this study, we simulate the electrophoretic motion of a bio-polymer through a synthetic nanopore in the presence of an external bias voltage by considering the hydrodynamic interactions between the polymer and the fluid explicitly. The motion of the polymer is simulated by 3D Langevin dynamics technique by modeling the polymer as a worm-like-chain, while the hydrodynamic interactions are incorporated by the lattice Boltzmann equation. We report the simulation results for three different lengths of the nanopore. The translocation time increases with the pore length even though the electrophoretic force on the polymer is the same irrespective of the pore length. This is attributed to the fact that the translocation velocity of each bead inside the nanopore decreases with the pore length due to the increased fluid resistance force caused by the increase in the straightened portion of the polymer. We confirmed this using a theoretical formula. Full article
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<p>Sectional view illustrating the simulation set-up used in the present work: (<b>a</b>) <span class="html-italic">yz</span>-plane and (<b>b</b>) <span class="html-italic">xz</span>-plane.</p> Full article ">Figure 2
<p>Polymer chain model used in this study for discretization of dsDNA molecule.</p> Full article ">Figure 3
<p>Solution of the Laplace equation for the potential around a 100 nm long nanopore: (<b>a</b>) electric potential and (<b>b</b>) electric field at the central <span class="html-italic">yz</span>-plane.</p> Full article ">Figure 4
<p>Variation of the translocation time <span class="html-italic">τ<sub>t</sub></span> with polymer length, <span class="html-italic">L<sub>c</sub></span>, for different nanopore lengths; <span class="html-italic">L<sub>p</sub></span> = 100 nm (○), <span class="html-italic">L<sub>p</sub></span> = 60 nm (□), and for <span class="html-italic">L<sub>p</sub></span> = 20 nm (∆).</p> Full article ">Figure 5
<p>An instantaneous configuration of the polymer of length <span class="html-italic">N</span> = 320 while it is translocating from the <span class="html-italic">cis</span> side to the <span class="html-italic">trans</span> side for pore lengths: (<b>a</b>) <span class="html-italic">L<sub>p</sub></span> = 20 nm and (<b>b</b>) <span class="html-italic">L<sub>p</sub></span> = 100 nm.</p> Full article ">Figure 6
<p>Variation of the translocation velocity of each bead <span class="html-italic">v<sub>t</sub></span><sub>,<span class="html-italic">i</span></sub> inside the nanopore for the cases with and without HI for the polymer length <span class="html-italic">N</span> = 320. The dotted lines represent the values <span class="html-italic">v<sub>t</sub></span><sub>,<span class="html-italic">i</span></sub> calculated from Equation (5).</p> Full article ">Figure 7
<p>Variation of the translocation velocity of each bead <span class="html-italic">v<sub>t</sub></span><sub>,<span class="html-italic">i</span></sub> inside the nanopore for pore lengths <span class="html-italic">L<sub>p</sub></span> = 20, 60, and 100 nm.</p> Full article ">
542 KiB  
Article
Constitutive Behavior and Finite Element Analysis of FRP Composite and Concrete Members
by Ki Yong Ann and Chang-Geun Cho
Materials 2013, 6(9), 3978-3988; https://doi.org/10.3390/ma6093978 - 10 Sep 2013
Cited by 7 | Viewed by 5682
Abstract
The present study concerns compressive and flexural constitutive models incorporated into an isoparametric beam finite element scheme for fiber reinforced polymer (FRP) and concrete composites, using their multi-axial constitutive behavior. The constitutive behavior of concrete was treated in triaxial stress states as an [...] Read more.
The present study concerns compressive and flexural constitutive models incorporated into an isoparametric beam finite element scheme for fiber reinforced polymer (FRP) and concrete composites, using their multi-axial constitutive behavior. The constitutive behavior of concrete was treated in triaxial stress states as an orthotropic hypoelasticity-based formulation to determine the confinement effect of concrete from a three-dimensional failure surface in triaxial stress states. The constitutive behavior of the FRP composite was formulated from the two-dimensional classical lamination theory. To predict the flexural behavior of circular cross-section with FRP sheet and concrete composite, a layered discretization of cross-sections was incorporated into nonlinear isoparametric beam finite elements. The predicted constitutive behavior was validated by a comparison to available experimental results in the compressive and flexural beam loading test. Full article
(This article belongs to the Special Issue Constitutive Behavior of Composite Materials)
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<p>(<b>a</b>) fiber reinforced polymer (FRP) laminated composite; and (<b>b</b>) FRP jacketed concrete cylinder in compression.</p> Full article ">Figure 2
<p>(<b>a</b>) In-plane stresses in FRP jacket; (<b>b</b>) triaxial stresses in concrete; and (<b>c</b>) equilibrium in cross-section.</p> Full article ">Figure 3
<p>(<b>a</b>) Five-parameter failure surface of concrete; and (<b>b</b>) confined and unconfined stress-strain curve of concrete in compression.</p> Full article ">Figure 4
<p>(<b>a</b>) Layered isoparametric beam finite element; and (<b>b</b>) four-point bending test of FRP and concrete circular beam.</p> Full article ">Figure 5
<p>(<b>a</b>) Prediction of compression test for CFRP thickness of 2.29 mm; and (<b>b</b>) prediction of compression test for CFRP thickness of 4.57 mm.</p> Full article ">Figure 6
<p>(<b>a</b>) Prediction of compression test for CFRP thickness of 0.676 mm; and (<b>b</b>) prediction of compression test for CFRP thickness of 0.338 mm.</p> Full article ">Figure 7
<p>Transverse load and displacement responses of the beam.</p> Full article ">Figure 8
<p>(<b>a</b>) Axial strains and bending moment relationship at center span; and (<b>b</b>) hoop strains and bending moment relationship at center span.</p> Full article ">
683 KiB  
Article
Microstructural and Wear Behavior Characterization of Porous Layers Produced by Pulsed Laser Irradiation in Glass-Ceramics Substrates
by Daniel Sola, Ana Conde, Iñaki García, Elena Gracia-Escosa, Juan J. De Damborenea and Jose I. Peña
Materials 2013, 6(9), 3963-3977; https://doi.org/10.3390/ma6093963 - 9 Sep 2013
Cited by 12 | Viewed by 6800
Abstract
In this work, wear behavior and microstructural characterization of porous layers produced in glass-ceramic substrates by pulsed laser irradiation in the nanosecond range are studied under unidirectional sliding conditions against AISI316 and corundum counterbodies. Depending on the optical configuration of the laser beam [...] Read more.
In this work, wear behavior and microstructural characterization of porous layers produced in glass-ceramic substrates by pulsed laser irradiation in the nanosecond range are studied under unidirectional sliding conditions against AISI316 and corundum counterbodies. Depending on the optical configuration of the laser beam and on the working parameters, the local temperature and pressure applied over the interaction zone can generate a porous glass-ceramic layer. Material transference from the ball to the porous glass-ceramic layer was observed in the wear tests carried out against the AISI316 ball counterface whereas, in the case of the corundum ball, the wear volume loss was concentrated in the porous layer. Wear rate and friction coefficient presented higher values than expected for dense glass-ceramics. Full article
(This article belongs to the Special Issue Advances in Surface Coatings 2013)
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<p>Scheme of ablation process and molten layer of thickness <span class="html-italic">h<sub>l</sub></span> formed in the interaction zone at room temperature <span class="html-italic">T</span><sub>1</sub> (<b>a</b>) and at high temperature <span class="html-italic">T</span><sub>2</sub> (<b>b</b>). The thickness increases when the surface temperature of the glass-ceramic substrate is heated.</p> Full article ">Figure 2
<p>Top view (<b>a</b>) and cross-section view (<b>b</b>) of the porous layer generated at 600 °C with a laser system emitting at 1064 nm.</p> Full article ">Figure 3
<p>Top view (<b>a</b>) and cross-section micrograph (<b>b</b>) of the porous coating produced with a laser system emitting at 532 nm.</p> Full article ">Figure 4
<p>Friction coefficient, COF, recorded during the wear tests against AISI316 ball at 1 and 3 N of normal load with 200 and 500 m of sliding distance, respectively.</p> Full article ">Figure 5
<p>Appearance of the worn surface for the AISI 316 ball showing the areas in which the EDX analyses were carried out (see <a href="#materials-06-03963-t003" class="html-table">Table 3</a>).</p> Full article ">Figure 6
<p>Appearance and profile of the wear track in a glass-ceramic sample after wear test against AISI 316 ball with a normal load of 3 N and sliding distance of 500 m.</p> Full article ">Figure 7
<p>Friction coefficients, COF, for the porous layer against corundum counterbody with the sliding distance for loads of 1 N and sliding distance of 100 m (<b>a</b>) unpolished and (<b>b</b>) polished samples and for loads of 2 N and sliding distance of 50 m.</p> Full article ">Figure 8
<p>Appearance of the wear track in the unpolished glass-ceramic porous layer performed against corundum balls.</p> Full article ">Figure 9
<p>Friction coefficients, COF, for the glass-ceramic substrate against corundum counterbody with the sliding distance for loads of 1 and 2 N and sliding distance of 100 m.</p> Full article ">
989 KiB  
Article
Synthesis and Characterization of Novel Epoxy Geopolymer Hybrid Composites
by Giuseppina Roviello, Laura Ricciotti, Claudio Ferone, Francesco Colangelo, Raffaele Cioffi and Oreste Tarallo
Materials 2013, 6(9), 3943-3962; https://doi.org/10.3390/ma6093943 - 9 Sep 2013
Cited by 57 | Viewed by 7600
Abstract
The preparation and the characterization of novel geopolymer-based hybrid composites are reported. These materials have been prepared through an innovative synthetic approach, based on a co-reticulation in mild conditions of commercial epoxy based organic resins and a metakaolin-based geopolymer inorganic matrix. This synthetic [...] Read more.
The preparation and the characterization of novel geopolymer-based hybrid composites are reported. These materials have been prepared through an innovative synthetic approach, based on a co-reticulation in mild conditions of commercial epoxy based organic resins and a metakaolin-based geopolymer inorganic matrix. This synthetic strategy allows the obtainment of a homogeneous dispersion of the organic particles in the inorganic matrix, up to 25% in weight of the resin. The materials obtained present significantly enhanced compressive strengths and toughness with respect to the neat geopolymer, suggesting their wide utilization for structural applications. A preliminary characterization of the porous materials obtained by removing the organic phase from the hybrid composites by means of heat treatments is also reported. Possible applications of these materials in the field of water purification, filtration, or as lightweight insulating materials are envisaged. Full article
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<p>Thermal gravimetric analysis (TGA) (continuous line) and differential scanning calorimetry (DSC) (dashed line) curves of the neat geopolymer cured at room temperature for seven days in 99% relative humidity conditions.</p> Full article ">Figure 2
<p>TGA (continuous lines) and DSC (dashed lines) curves of Epojet<sup>®</sup> (a,c) and EpojetLV<sup>®</sup> (b,d) resins cured at room temperature for seven days in 99% relative humidity conditions.</p> Full article ">Figure 3
<p>TGA (continuous lines) and DSC (dashed lines) curves of Geo-Epojet20 (a,c) and Geo-EpojetLV20 (b,d) specimens cured at room temperature for seven days in 99% relative humidity conditions.</p> Full article ">Figure 4
<p>FT-IR spectra of (a) metakaolin; (b) geopolymer; (c) Epojet<sup>®</sup>; (d) EpojetLV<sup>®</sup>; (e) Geo-Epojet20; and (f) Geo-EpojetLV20.</p> Full article ">Figure 5
<p>X-ray powder diffraction patterns of (a) metakaolin; (b) Geopolymer; (c) GeoEpojetLV20; (d) GeoEpojet20; (e) GeoEpojet20 after 12 h at 500 °C; and (f) GeoEpojet20 after 24 h at 800 °C. * = anatase; ° = quartz.</p> Full article ">Figure 6
<p>X-ray powder diffraction patterns of (a) GeoEpojet20 sample after 24 h at 800 °C; (b) nepheline (PDF n° 04-012-4977); and (c) residual.</p> Full article ">Figure 7
<p>Scanning electron microscope (SEM) micrographs of (<b>A</b>) neat geopolymer; (<b>B</b>,<b>D</b>) GeoEpojet20; and (<b>C</b>) GeoEpojetLV20.</p> Full article ">Figure 8
<p>SEM micrographs of GeoEpojetLV20 sample kept for 24 h at 800 °C in air, at 1 × 10<sup>3</sup> (<b>A</b>) and 5 × 10<sup>3</sup> (<b>B</b>) amplifications.</p> Full article ">Figure 9
<p>Cumulative pore volume<span class="html-italic"> vs.</span> pore radius as obtained by mercury intrusion porosimetry analyses.</p> Full article ">Figure 10
<p>Compressive strength of the geopolymer, hybrid GeoEpojet and GeoEpojetLV specimens as function of resin content.</p> Full article ">Figure 11
<p>Stress-strain curves of the geopolymer, GeoEpojet20 and GeoEpojetLV20 specimens.</p> Full article ">Figure 12
<p>Schematic representation of the addition of the partly reticulated Epojet<sup>®</sup> resin to the geopolymeric aqueous mixture.</p> Full article ">
2259 KiB  
Review
Calcium Orthophosphate-Based Bioceramics
by Sergey V. Dorozhkin
Materials 2013, 6(9), 3840-3942; https://doi.org/10.3390/ma6093840 - 6 Sep 2013
Cited by 221 | Viewed by 17765
Abstract
Various types of grafts have been traditionally used to restore damaged bones. In the late 1960s, a strong interest was raised in studying ceramics as potential bone grafts due to their biomechanical properties. A bit later, such synthetic biomaterials were called bioceramics. In [...] Read more.
Various types of grafts have been traditionally used to restore damaged bones. In the late 1960s, a strong interest was raised in studying ceramics as potential bone grafts due to their biomechanical properties. A bit later, such synthetic biomaterials were called bioceramics. In principle, bioceramics can be prepared from diverse materials but this review is limited to calcium orthophosphate-based formulations only, which possess the specific advantages due to the chemical similarity to mammalian bones and teeth. During the past 40 years, there have been a number of important achievements in this field. Namely, after the initial development of bioceramics that was just tolerated in the physiological environment, an emphasis was shifted towards the formulations able to form direct chemical bonds with the adjacent bones. Afterwards, by the structural and compositional controls, it became possible to choose whether the calcium orthophosphate-based implants remain biologically stable once incorporated into the skeletal structure or whether they were resorbed over time. At the turn of the millennium, a new concept of regenerative bioceramics was developed and such formulations became an integrated part of the tissue engineering approach. Now calcium orthophosphate scaffolds are designed to induce bone formation and vascularization. These scaffolds are often porous and harbor different biomolecules and/or cells. Therefore, current biomedical applications of calcium orthophosphate bioceramics include bone augmentations, artificial bone grafts, maxillofacial reconstruction, spinal fusion, periodontal disease repairs and bone fillers after tumor surgery. Perspective future applications comprise drug delivery and tissue engineering purposes because calcium orthophosphates appear to be promising carriers of growth factors, bioactive peptides and various types of cells. Full article
(This article belongs to the Special Issue Ceramics for Healthcare 2013)
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<p>Several examples of the commercial calcium orthophosphate-based bioceramics.</p> Full article ">Figure 2
<p>Soft X-ray photographs of the operated portion of the rabbit femur. (<bold>a</bold>) Four weeks; (<bold>b</bold>) 12 weeks; (<bold>c</bold>) 24 weeks; and (<bold>d</bold>) 72 weeks after implantation of CDHA. (<bold>e</bold>) Four weeks; (<bold>f</bold>) 12 weeks; (<bold>g</bold>)24 weeks; and (<bold>h</bold>) 72 weeks after implantation of sintered HA. Reprinted from Reference [<xref ref-type="bibr" rid="B141-materials-06-03840">141</xref>] with permission.</p> Full article ">Figure 3
<p>A schematic of 3D printing and some 3D printed parts (fabricated at Washington State University) showing the versatility of 3D printing technology for ceramic scaffolds fabrication with complex architectural features. Reprinted from Reference [<xref ref-type="bibr" rid="B74-materials-06-03840">74</xref>] with permission.</p> Full article ">Figure 4
<p>A schematic diagram representing the changes occurring with particles under sintering. Shrinkage is noticeable.</p> Full article ">Figure 5
<p>Linear shrinkage of the compacted ACP powders that were converted into β-TCP, BCP (50% HA + 50% β-TCP) and HA upon heating. According to the authors: “At 1300 °C, the shrinkage reached a maximum of approximately ~25%, ~30% and ~35% for the compacted ACP powders that converted into HA, BCP 50/50 and β-TCP, respectively” [<xref ref-type="bibr" rid="B261-materials-06-03840">261</xref>]. Reprinted from Reference [<xref ref-type="bibr" rid="B261-materials-06-03840">261</xref>] with permission.</p> Full article ">Figure 6
<p>Transparent HA bioceramics prepared by spark plasma sintering at 900 °C from nano-sized HA single crystals. Reprinted from Reference [<xref ref-type="bibr" rid="B414-materials-06-03840">414</xref>] with permission.</p> Full article ">Figure 7
<p>Photographs of a commercially available porous calcium orthophosphate bioceramics with (<bold>a,b</bold>) different porosity; and (<bold>c</bold>) a method of their production. For photos, the horizontal field width is 20 mm. The picture (<bold>c</bold>) is reprinted from Reference [<xref ref-type="bibr" rid="B457-materials-06-03840">457</xref>] with permission.</p> Full article ">Figure 8
<p>β-TCP porous ceramics with different pore sizes prepared using polymethylmethacrylate balls with diameter equal to: (<bold>a</bold>) 100–200 μm; (<bold>b</bold>) 300–400 μm; (<bold>c</bold>) 500–600 μm; and (<bold>d</bold>) 700–800 μm. Horizontal field width is 45 mm. Reprinted from Reference [<xref ref-type="bibr" rid="B92-materials-06-03840">92</xref>] with permission.</p> Full article ">Figure 9
<p>SEM pictures of HA bioceramics sintered at <bold>(A)</bold> 1050 °C; and <bold>(B)</bold> 1200 °C. Note the presence of microporosity in (<bold>A</bold>) and not in (<bold>B</bold>). Scale bar is 1 μm. Reprinted from Reference [<xref ref-type="bibr" rid="B563-materials-06-03840">563</xref>] with permission.</p> Full article ">Figure 10
<p>Different types of biomedical applications of calcium orthophosphate bioceramics. Reprinted from Reference [<xref ref-type="bibr" rid="B623-materials-06-03840">623</xref>] with permission.</p> Full article ">Figure 11
<p>A typical microstructure of calcium orthophosphate cement after hardening. The mechanical stability is provided by the physical entanglement of crystals. Reprinted from Reference [<xref ref-type="bibr" rid="B629-materials-06-03840">629</xref>] with permission.</p> Full article ">Figure 12
<p>Shows how a plasma-sprayed HA coating on a porous titanium (dark bars) dependent on the implantation time will improve the interfacial bond strength compared to uncoated porous titanium (light bars). Reprinted from Reference [<xref ref-type="bibr" rid="B66-materials-06-03840">66</xref>] with permission.</p> Full article ">Figure 13
<p>A schematic diagram showing the arrangement of the FA/β-TCP biocomposite layers. (<bold>a</bold>) A non-symmetric functionally gradient material (FGM); and (<bold>b</bold>) symmetric FGM. Reprinted from Reference [<xref ref-type="bibr" rid="B636-materials-06-03840">636</xref>] with permission.</p> Full article ">Figure 14
<p>Schematic illustrations of fabrication of pore-graded bioceramics: (<bold>a</bold>) lamination of individual tapes, manufactured by tape casting; and (<bold>b</bold>) a compression molding process. Reprinted from Reference [<xref ref-type="bibr" rid="B429-materials-06-03840">429</xref>] with permission.</p> Full article ">Figure 15
<p>Rounded β-TCP granules of 2.6–4.8 mm in size, providing no sharp edges for combination with bone cement. Reprinted from Reference [<xref ref-type="bibr" rid="B665-materials-06-03840">665</xref>] with permission.</p> Full article ">Figure 16
<p>A sequence of interfacial reactions involved in forming a bond between tissue and bioactive ceramics. Reprinted from References [<xref ref-type="bibr" rid="B66-materials-06-03840">66</xref>,<xref ref-type="bibr" rid="B67-materials-06-03840">67</xref>,<xref ref-type="bibr" rid="B68-materials-06-03840">68</xref>,<xref ref-type="bibr" rid="B69-materials-06-03840">69</xref>] with permission.</p> Full article ">Figure 17
<p>A schematic diagram representing the events, which take place at the interface between bioceramics and the surrounding biological environment: (<bold>1</bold>) dissolution of bioceramics; (<bold>2</bold>) precipitation from solution onto bioceramics; (<bold>3</bold>) ion exchange and structural rearrangement at the bioceramic/tissue interface; (<bold>4</bold>) interdiffusion from the surface boundary layer into the bioceramics; (<bold>5</bold>) solution-mediated effects on cellular activity; (<bold>6</bold>) deposition of either the mineral phase (<bold>a</bold>) or the organic phase (<bold>b</bold>) without integration into the bioceramic surface; (<bold>7</bold>) deposition with integration into the bioceramics; (<bold>8</bold>) chemotaxis to the bioceramic surface; (<bold>9</bold>) cell attachment and proliferation; (<bold>10</bold>) cell differentiation; and (<bold>11</bold>) extracellular matrix formation. All phenomena, collectively, lead to the gradual incorporation of a bioceramic implant into developing bone tissue. Reprinted from Reference [<xref ref-type="bibr" rid="B76-materials-06-03840">76</xref>] with permission.</p> Full article ">Figure 18
<p>A schematic diagram representing the phenomena that occur on HA surface after implantation: (<bold>1</bold>) beginning of the implant procedure, where a solubilization of the HA surface starts; (<bold>2</bold>) continuation of the solubilization of the HA surface; (<bold>3</bold>) the equilibrium between the physiological solutions and the modified surface of HA has been achieved (changes in the surface composition of HA does not mean that a new phase of DCPA or DCPD forms on the surface); (<bold>4</bold>) adsorption of proteins and/or other bioorganic compounds; (<bold>5</bold>) cell adhesion; (<bold>6</bold>) cell proliferation; (<bold>7</bold>) beginning of a new bone formation; and (<bold>8</bold>) new bone has been formed. Reprinted from Reference [<xref ref-type="bibr" rid="B707-materials-06-03840">707</xref>] with permission.</p> Full article ">Figure 19
<p>A schematic view of a third generation biomaterial, in which porous calcium orthophosphate bioceramics acts as a scaffold or a template for cells, growth factors, <italic>etc.</italic> Reprinted from Reference [<xref ref-type="bibr" rid="B62-materials-06-03840">62</xref>] with permission.</p> Full article ">Figure 20
<p>A schematic drawing presenting the potential usage of HA with various degrees of porosity. Reprinted from Reference [<xref ref-type="bibr" rid="B542-materials-06-03840">542</xref>] with permission.</p> Full article ">
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Article
Dopamine-Mediated Sclerotization of Regenerated Chitin in Ionic Liquid
by Dongyeop X. Oh, Sara Shin, Chanoong Lim and Dong Soo Hwang
Materials 2013, 6(9), 3826-3839; https://doi.org/10.3390/ma6093826 - 6 Sep 2013
Cited by 46 | Viewed by 7948
Abstract
Chitin is a promising structural material for biomedical applications, due to its many advantageous properties and abundance in nature. However, its usage and development in the biomedical field have been stagnant, because of chitin’s poor mechanical properties in wet conditions and the difficulties [...] Read more.
Chitin is a promising structural material for biomedical applications, due to its many advantageous properties and abundance in nature. However, its usage and development in the biomedical field have been stagnant, because of chitin’s poor mechanical properties in wet conditions and the difficulties in transforming it into an applicable form. To overcome these challenges, we created a novel biomimetic chitin composite. This regenerated chitin, prepared with ionic liquid, showed improved mechanical properties in wet conditions by mimicking insect cuticle and squid beak sclerotization, i.e., catechol-meditated cross-linking. By ionic liquid-based heat treatment, dopamine oxidation produced melanin-like compounds and dopamine-meditated cross-links without any solvent evaporation and oxidant utilization. The dopamine-meditated sclerotization increased the ultimate tensile strength (UTS) of the regenerated chitin by 2.52-fold, measured after six weeks of phosphate-buffered saline (PBS) submersion. In addition, the linear swelling ratio (LSR) of the chitin film was reduced by about 22%. This strategy raises a possibility of using regenerated chitin as an artificial hard tissue in wet conditions. Full article
(This article belongs to the Section Biomaterials)
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<p>Nitrogen 1s narrow scans in X-ray photoelectron spectroscopy (XPS) spectra of (<b>A</b>) pure chitin; (<b>B</b>) non-heat-treated 10 wt % dopamine-containing composite; and (<b>C</b>) 10 wt % dopamine-containing composite. Carbon 1s narrow scans in XPS spectra of (<b>D</b>) pure chitin; (<b>E</b>) non-heat-treated 10 wt % dopamine-containing composite; and (<b>F</b>) 10 wt % dopamine-containing composite.</p> Full article ">Figure 2
<p>(<b>A</b>) Water contact angle; (<b>B</b>) equilibrium water content (EWC); and (<b>C</b>) linear swelling ratio (LSR) values of pure regenerated chitin, 5 wt % dopamine-containing composite and 10 wt % dopamine-containing composite. Each value represents the mean of five analyses and its standard deviation.</p> Full article ">Figure 3
<p>(<b>A</b>) X-ray diffraction (XRD) spectra of native chitin (black curve), pure regenerated chitin (red curve), 10 wt % dopamine-containing composite (blue curve); scanning electron microscope (SEM) images of (<b>B</b>) pure regenerated chitin; and (<b>C</b>) 10 wt % dopamine-containing composite.</p> Full article ">Figure 4
<p>(<b>A</b>) Strain-stress curves of pure regenerated chitin (black curve), 5 wt % dopamine-containing composite (red curve) and 10 wt % dopamine-containing composite (blue curve); (<b>B</b>) Young’s modulus; and (<b>C</b>) ultimate tensile strength (UTS) values of pure regenerated chitin, 5 wt % dopamine-containing composite and 10 wt % dopamine-containing composite depending on submersion time in phosphate-buffered saline (PBS).</p> Full article ">Figure 5
<p>Comparison of MC3T3 cell proliferation on pure regenerated chitin (black); 10 wt % dopamine-containing composite (blue); and negative control (red, culture dish).</p> Full article ">Figure 6
<p>Pure regenerated chitin film (<b>A</b>) and 10 wt % dopamine-containing composite (<b>B</b>).</p> Full article ">Figure 7
<p>Carbon 1s narrow scans in XPS spectra of extracted melanin-like compound from 10 wt% dopamine containing composite (<b>A</b>) and <span class="html-italic">Sepia</span> melanin (control, <b>B</b>).</p> Full article ">
837 KiB  
Article
Microgel Modified UV-Cured Methacrylic-Silica Hybrid: Synthesis and Characterization
by Carola Esposito Corcione, Raffaella Striani and Mariaenrica Frigione
Materials 2013, 6(9), 3805-3825; https://doi.org/10.3390/ma6093805 - 6 Sep 2013
Cited by 18 | Viewed by 6941
Abstract
An innovative photopolymerizable microgel modified UV-cured acrylic-silica hybrid formulation was developed and characterized for possible use as protective coating for different substrates. A deep investigation, aiming at providing a strong scientific basis for the production of organic-inorganic (O-I) hybrids exhibiting phase co-continuity, was [...] Read more.
An innovative photopolymerizable microgel modified UV-cured acrylic-silica hybrid formulation was developed and characterized for possible use as protective coating for different substrates. A deep investigation, aiming at providing a strong scientific basis for the production of organic-inorganic (O-I) hybrids exhibiting phase co-continuity, was firstly carried out. The O-I hybrid first proposed in this study was obtained from organic precursors with a high siloxane content, which are mixed with tetraethoxysilane (TEOS) in such a way to produce co-continuous silica nanodomains dispersed within the crosslinked organic phase, as a result of the sol-gel process. The first part of the research deals with the selection and optimization of suitable systems through appropriate chemical modifications, in order to ensure that curing reactions can be carried out at room temperature and in the presence of UV radiation. Firstly, the silica domains are formed, followed by crosslinking reactions of the acrylic groups in the oligomer via a free radical polymerization. The crosslinking reaction was controlled with the use of a suitable photoinitiator. Most of the experimental work was devoted to understanding the morphology of the hybrid system, both in uncured and cured states, and to assess its final thermal and optical properties, using different experiential techniques. Full article
(This article belongs to the Special Issue Nanocomposites of Polymers and Inorganic Particles 2013)
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<p>XRD spectrogram of amorphous silica obtained after burning out uncured Hybrid<sub>85T</sub> formulation.</p> Full article ">Figure 2
<p>Particle size distribution calculated through dynamic light scattering (DLS) analysis for uncured Hybrid<sub>85T</sub> formulation (<b>a</b>) after one day and (<b>b</b>) after five months.</p> Full article ">Figure 3
<p>Rheological curves of uncured Ctrl Silane and Hybrid<sub>85T</sub> formulations.</p> Full article ">Figure 4
<p>(<b>a</b>) Fourier transform infrared (FTIR) spectra of Ctrl Silane formulation at different stages of curing. In the frame on the right, there is enlargement of the peak at 1638 cm<sup>−1</sup>; and (<b>b</b>) Raman spectra of Ctrl Silane formulation at different stages of curing. In the frame on the right, there is enlargement of the peak at 1638 cm<sup>−1</sup>.</p> Full article ">Figure 5
<p>(<b>a</b>) FTIR spectra of Hybrid<sub>85T</sub> formulation at different stages of curing. In the frame on the right, there is enlargement of the peak at 1638 cm<sup>−1</sup>; and (<b>b</b>) Raman spectra of Hybrid<sub>85T</sub> formulation at different stages of curing. In the frame on the right, there is enlargement of the peak at 1638 cm<sup>−1</sup>.</p> Full article ">Figure 5 Cont.
<p>(<b>a</b>) FTIR spectra of Hybrid<sub>85T</sub> formulation at different stages of curing. In the frame on the right, there is enlargement of the peak at 1638 cm<sup>−1</sup>; and (<b>b</b>) Raman spectra of Hybrid<sub>85T</sub> formulation at different stages of curing. In the frame on the right, there is enlargement of the peak at 1638 cm<sup>−1</sup>.</p> Full article ">Figure 6
<p>Light transmittance spectra of dual-cured Ctrl Silane and Hybrid<sub>85T</sub> systems.</p> Full article ">Figure 7
<p>(<b>a</b>) Scanning electron microscopy (SEM) image of dual-cured Hybrid<sub>85T</sub> applied on glass substrate; and (<b>b</b>) Energy-Dispersive X-ray spectroscopy (EDS) analysis of the same system.</p> Full article ">Figure 8
<p>(<b>a</b>) TGA curves of dual-cured Ctrl Silane and Hybrid<sub>85T</sub> systems; and (<b>b</b>) derivative TGA curves of dual-cured Ctrl Silane and Hybrid<sub>85T</sub> systems.</p> Full article ">Figure 9
<p>Chemical formula of each component used. TMPTMA, Trimethylolpropane trimethacrylate; MEMO; VT PDMS, vinyl terminated polydimethylsiloxane; MPTS, 3-Mercaptopropyltriethoxysilane; TEOS, tetraethoxysilane.</p> Full article ">
927 KiB  
Review
Monitoring the Cure State of Thermosetting Resins by Ultrasound
by Francesca Lionetto and Alfonso Maffezzoli
Materials 2013, 6(9), 3783-3804; https://doi.org/10.3390/ma6093783 - 5 Sep 2013
Cited by 117 | Viewed by 8479
Abstract
The propagation of low intensity ultrasound in a curing resin, acting as a high frequency oscillatory excitation, has been recently proposed as an ultrasonic dynamic mechanical analysis (UDMA) for cure monitoring. The technique measures sound velocity and attenuation, which are very sensitive to [...] Read more.
The propagation of low intensity ultrasound in a curing resin, acting as a high frequency oscillatory excitation, has been recently proposed as an ultrasonic dynamic mechanical analysis (UDMA) for cure monitoring. The technique measures sound velocity and attenuation, which are very sensitive to changes in the viscoelastic characteristics of the curing resin, since the velocity is related to the resin storage modulus and density, while the attenuation is related to the energy dissipation and scattering in the curing resin. The paper reviews the results obtained by the authors’ research group in the last decade by means of in-house made ultrasonic set-ups for both contact and air-coupled ultrasonic experiments. The basics of the ultrasonic wave propagation in polymers and examples of measurements of the time-evolution of ultrasonic longitudinal modulus and chemical conversion of different thermosetting resins are presented. The effect of temperature on the cure kinetics, the comparison with rheological, low frequency dynamic mechanical and calorimetric results, and the correlation between ultrasonic modulus and crosslinking density will be also discussed. The paper highlights the reliability of ultrasonic wave propagation for monitoring the physical changes taking place during curing and the potential for online monitoring during polymer and polymer matrix composite processing. Full article
(This article belongs to the Section Advanced Materials Characterization)
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<p>Schematic drawing of the ultrasonic set-up for cure monitoring (adapted from [<a href="#B18-materials-06-03783" class="html-bibr">18</a>]).</p> Full article ">Figure 2
<p><b>(a)</b> Longitudinal velocity; and <b>(b)</b> attenuation measured at 2 MHz during the isothermal cure of an unsaturated polyester resin at 30 °C.</p> Full article ">Figure 3
<p>Longitudinal modulus <span class="html-italic">L</span>′ measured at 2 MHz during the isothermal cure of unsaturated polyester resin at different cure temperatures.</p> Full article ">Figure 4
<p>Loss modulus <span class="html-italic">L</span>″ measured at 2 MHz during the isothermal cure of unsaturated polyester resin at different cure temperatures.</p> Full article ">Figure 5
<p>Arrhenius plot of the gel times calculated by different techniques <span class="html-italic">versus</span> the reciprocal of the isothermal cure temperature. Reprinted with permission from [<a href="#B45-materials-06-03783" class="html-bibr">45</a>]. Copyright 2007 WILEY-VCH Verlag GmbH &amp; Co.</p> Full article ">Figure 6
<p>Normalized degree of reaction calculated from DSC and longitudinal modulus (measured at 2 MHz) for an UPE resin during the isothermal cure at 50 °C (adapted from [<a href="#B18-materials-06-03783" class="html-bibr">18</a>]).</p> Full article ">Figure 7
<p>Scheme of the probability distribution.</p> Full article ">Figure 8
<p>Correlation between <span class="html-italic">L</span>′ and the concentration of active network chains ν after the gel point, during the cure of epoxy resin DGEBA at 85 °C with Jeffamine D230 and D400.</p> Full article ">Figure 9
<p>Frequency dependence of the relaxation peaks of unsaturated polyester networks as measured by DMA (square), DEA (circles) and UDMA (triangle). The data are fitted by the WLF equation (continuous line). Reprinted with permission from [<a href="#B8-materials-06-03783" class="html-bibr">8</a>]. Copyright 2005 Wiley Periodicals, Inc.</p> Full article ">Figure 10
<p>Experimental set-up for the generation and detection of longitudinal waves by air-coupled ultrasound in the pitch-catch mode (adapted from [<a href="#B45-materials-06-03783" class="html-bibr">45</a>,<a href="#B68-materials-06-03783" class="html-bibr">68</a>]).</p> Full article ">Figure 11
<p>Comparison of longitudinal velocity changes, obtained both by air-coupled (0.5 MHz) and contact (2 MHz) transmission mode, during the cure at room temperature of an unsaturated polyester resin (adapted from [<a href="#B68-materials-06-03783" class="html-bibr">68</a>]).</p> Full article ">
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Article
Homogenized Elastic Properties of Graphene for Small Deformations
by Eduard Marenić, Adnan Ibrahimbegovic, Jurica Sorić and Pierre-Alain Guidault
Materials 2013, 6(9), 3764-3782; https://doi.org/10.3390/ma6093764 - 3 Sep 2013
Cited by 17 | Viewed by 6035
Abstract
In this paper, we provide the quantification of the linear and non-linear elastic mechanical properties of graphene based upon the judicious combination of molecular mechanics simulation results and homogenization methods. We clarify the influence on computed results by the main model features, such [...] Read more.
In this paper, we provide the quantification of the linear and non-linear elastic mechanical properties of graphene based upon the judicious combination of molecular mechanics simulation results and homogenization methods. We clarify the influence on computed results by the main model features, such as specimen size, chirality of microstructure, the effect of chosen boundary conditions (imposed displacement versus force) and the corresponding plane stress transformation. The proposed approach is capable of explaining the scatter of the results for computed stresses, energy and stiffness and provides the bounds on graphene elastic properties, which are quite important in modeling and simulation of the virtual experiments on graphene-based devices. Full article
(This article belongs to the Special Issue Computational Modeling and Simulation in Materials Study)
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<p>Distribution of the Morse potential and equivalent harmonic potential for the pair part (<b>a</b>) and for the angular part (<b>b</b>).</p> Full article ">Figure 2
<p>Scheme of the lattice sample with the traction (Reuss) (<b>a</b>), mixed (<b>b</b>) and displacement (Voigt) boundary conditions (BC) (<b>c</b>). The envelope of the sample is composed of lines <math display="inline"> <msub> <mi>L</mi> <mn>1</mn> </msub> </math>–<math display="inline"> <msub> <mi>L</mi> <mn>4</mn> </msub> </math>, which coincides with boundary atoms.</p> Full article ">Figure 3
<p>The initial and deformed shapes (scale factor 10) of the nearly square lattice of size 5 (<math display="inline"> <mrow> <msub> <mi>L</mi> <mrow> <mn>1</mn> <mo>,</mo> <mn>2</mn> </mrow> </msub> <mo>≈</mo> <msub> <mi>L</mi> <mrow> <mn>3</mn> <mo>,</mo> <mn>4</mn> </mrow> </msub> </mrow> </math>) is shown for the three types of BC. The two chiralities armchair (left) and zigzag (right) are presented for every BC case.</p> Full article ">Figure 4
<p>The change of Young’s modulus with respect to the size of the lattice specimen based upon the harmonic potential.</p> Full article ">Figure 5
<p>Plot of factors, including the stress ratio, that scales the expression for Young’s modulus in the plane stress state, which corresponds to the “V” BC case and a sample size of eight.</p> Full article ">Figure 6
<p>Stress-strain dependence for large strain using the Morse interatomic potential for (<b>a</b>) armchair and (<b>b</b>) zigzag graphene samples of a size of eight.</p> Full article ">Figure 7
<p>Tangential modulus-strain dependence for large strain using the Morse interaction shown for: (<b>a</b>) armchair and (<b>b</b>) zigzag graphene sample of the size of eight.</p> Full article ">Figure 8
<p>The pair bond separation (left) and angular bond (right) evolution with respect to strain increase for armchair graphene.</p> Full article ">Figure 9
<p>The pair bond separation (left) and angular bond (right) evolution with respect to strain increase is presented for zigzag graphene.</p> Full article ">Figure 10
<p>The strain energy density plot shows the dependence on the chirality (armchair and zigzag) and BC types, “R”, “m” and “V”, in (<b>a</b>) and the influence of size and chirality to the strain energy density in (<b>b</b>) (for the “m” BC case and strain <math display="inline"> <mrow> <msub> <mi>ϵ</mi> <mn>22</mn> </msub> <mo>=</mo> <mn>15</mn> <mo>%</mo> </mrow> </math>).</p> Full article ">
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Article
Construction of a Novel Magnetic Targeting Anti-Tumor Drug Delivery System: Cytosine Arabinoside-Loaded Bacterial Magnetosome
by Qiongjia Deng, Yuangang Liu, Shibin Wang, Maobin Xie, Shenjian Wu, Aizheng Chen and Wenguo Wu
Materials 2013, 6(9), 3755-3763; https://doi.org/10.3390/ma6093755 - 3 Sep 2013
Cited by 23 | Viewed by 6116
Abstract
To ease the side effects triggered by cytosine arabinoside (Ara-C) for acute leukemia treatment, a novel magnetic targeting anti-tumor drug delivery system was constructed through bacterial magnetosomes (BMs) from Magnetospirillum magneticum AMB-1 combined with Ara-C by crosslinking of genipin (GP). The results showed [...] Read more.
To ease the side effects triggered by cytosine arabinoside (Ara-C) for acute leukemia treatment, a novel magnetic targeting anti-tumor drug delivery system was constructed through bacterial magnetosomes (BMs) from Magnetospirillum magneticum AMB-1 combined with Ara-C by crosslinking of genipin (GP). The results showed that Ara-C could be bonded onto the membrane surface of BMs effectively through chemical crosslinking induced by dual hand reagents GP. The average diameters of BMs and Ara-C-coupled BMs (ABMs) were 42.0 ± 8.6 and 72.7 ± 6.0 nm respectively, and the zeta potentials (−38.1 ± 9.1) revealed that these systems were stable, confirming the stability of the system. The optimal encapsulation efficiency and drug loading were 89.05% ± 2.33% and 47.05% ± 0.64% respectively when crosslinking reaction lasted for 72 h. The system also presented long-term stability and release behaviors without initial burst release (Ara-C could be released 80% within three months). Our results indicate that BMs have great potential in biomedical and clinical fields as a novel anti-tumor drug carrier. Full article
(This article belongs to the Section Biomaterials)
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<p>TEM images of bacterial magnetosomes (BMs) and Ara-C-coupled BMs (ABMs): (<b>a</b> and <b>b</b>: BMs) and (<b>c</b> and <b>d</b>: ABMs); (<b>b</b>) BMs showed the narrow size distribution and uniform lipid membrane; (<b>d</b>) Black arrow pointed to thickened and blurred materials surrounding ABMs.</p> Full article ">Figure 2
<p>The FTIR spectra of Ara-C, ABMs and BMs.</p> Full article ">Figure 3
<p>Drug loading and encapsulation efficiency of ABMs prepared with different reaction time by genipin (GP).</p> Full article ">Figure 4
<p>Cumulative release of (<b>a</b>) free Ara-C and (<b>b</b>) ABMs.</p> Full article ">
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Review
Nanoscale Design of Nano-Sized Particles in Shape-Memory Polymer Nanocomposites Driven by Electricity
by Haibao Lu, Wei Min Huang, Fei Liang and Kai Yu
Materials 2013, 6(9), 3742-3754; https://doi.org/10.3390/ma6093742 - 2 Sep 2013
Cited by 15 | Viewed by 6207
Abstract
In the last few years, we have witnessed significant progress in developing high performance shape memory polymer (SMP) nanocomposites, in particular, for shape recovery activated by indirect heating in the presence of electricity, magnetism, light, radio frequency, microwave and radiation, etc. In this [...] Read more.
In the last few years, we have witnessed significant progress in developing high performance shape memory polymer (SMP) nanocomposites, in particular, for shape recovery activated by indirect heating in the presence of electricity, magnetism, light, radio frequency, microwave and radiation, etc. In this paper, we critically review recent findings in Joule heating of SMP nanocomposites incorporated with nanosized conductive electromagnetic particles by means of nanoscale control via applying an electro- and/or magnetic field. A few different nanoscale design principles to form one-/two-/three- dimensional conductive networks are discussed. Full article
(This article belongs to the Section Advanced Composites)
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<p>An initial diagram showing the mechanism of actuation via electrically resistive Joule heating of shape-memory polymer (SMP) nanocomposite.</p> Full article ">Figure 2
<p>Typical scanning electron microscopy (SEM) images prior to (left column) and after (right column) five stretching-recovery cycles of the Ni chains in three SMP nanocomposites with a different volume fraction of Ni powder: (<b>a</b>) 5%; (<b>b</b>) 10%; (<b>c</b>) 20%. Reproduced with permission from [<a href="#B43-materials-06-03742" class="html-bibr">43</a>]. Copyright 2008 American Institute of Physics.</p> Full article ">Figure 3
<p>Snapshot of shape recovery process (and temperature distribution). Sample A: SMP/CB; Sample B: SMP/CB/CNT (random); Sample C: SMP/CB/CNT (chained). Right inset: sample dimension and experimental setup for Sample C. Reproduced with permission from [<a href="#B46-materials-06-03742" class="html-bibr">46</a>].Copyright 2011 American Institute of Physics.</p> Full article ">Figure 4
<p>Snapshot of the shape recovery process in an SMP nanocomposite integrated with 1.2 g of CNT nanopaper. Reproduced with permission from [<a href="#B49-materials-06-03742" class="html-bibr">49</a>]. Copyright 2012 Wiley-Vch Verlag Gmbh &amp; Co.</p> Full article ">Figure 5
<p>Schematic illustration of vertically aligned nickel nanostrands to help resistive heating power to transfer from the nanopaper to the underlying SMP. Reproduced with permission from [<a href="#B41-materials-06-03742" class="html-bibr">41</a>]. Copyright 2011 RSC Publishing.</p> Full article ">Figure 6
<p>SEM image of the orientation of the nickel nanostrands observed via the thickness of the SMP nanocomposite. Reproduced with permission from [<a href="#B41-materials-06-03742" class="html-bibr">41</a>]. Copyright 2011 RSC Publishing.</p> Full article ">Figure 7
<p>(<b>a</b>) Recovery profiles of the SMP composites with aligned and randomly dispersed 8 wt % of magnetic CNTs under 12 V and 36 V voltages, respectively; (<b>b</b>) induction and recovery times of the SMP composites for the two voltages studied. Reproduced with permission from [<a href="#B54-materials-06-03742" class="html-bibr">54</a>].Copyright 2011 American Institute of Physics.</p> Full article ">
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Article
Synthesis and Characterization of Encapsulated Nanosilica Particles with an Acrylic Copolymer by in Situ Emulsion Polymerization Using Thermoresponsive Nonionic Surfactant
by Mostafa Yazdimamaghani, Tannaz Pourvala, Elaheh Motamedi, Babak Fathi, Daryoosh Vashaee and Lobat Tayebi
Materials 2013, 6(9), 3727-3741; https://doi.org/10.3390/ma6093727 - 28 Aug 2013
Cited by 80 | Viewed by 13433
Abstract
Nanocomposites of encapsulated silica nanoparticles were prepared by in situ emulsion polymerization of acrylate monomers. The synthesized material showed good uniformity and dispersion of the inorganic components in the base polymer, which enhances the properties of the nanocomposite material. A nonionic surfactant with [...] Read more.
Nanocomposites of encapsulated silica nanoparticles were prepared by in situ emulsion polymerization of acrylate monomers. The synthesized material showed good uniformity and dispersion of the inorganic components in the base polymer, which enhances the properties of the nanocomposite material. A nonionic surfactant with lower critical solution temperature (LCST) was used to encapsulate the silica nanoparticles in the acrylic copolymer matrix. This in situ method combined the surface modification and the encapsulation in a single pot, which greatly simplified the process compared with other conventional methods requiring separate processing steps. The morphology of the encapsulated nanosilica particles was investigated by dynamic light scattering (DLS) and transmission electron microscopy (TEM), which confirmed the uniform distribution of the nanoparticles without any agglomerations. A neat copolymer was also prepared as a control sample. Both the neat copolymer and the prepared nanocomposite were characterized by Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analyses (TGA), dynamic mechanical thermal analysis (DMTA) and the flame resistance test. Due to the uniform dispersion of the non-agglomerated nanoparticles in the matrix of the polymer, TGA and flame resistance test results showed remarkably improved thermal stability. Furthermore, DMTA results demonstrated an enhanced storage modulus of the nanocomposite samples compared with that of the neat copolymer, indicating its superior mechanical properties. Full article
(This article belongs to the Section Advanced Composites)
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Graphical abstract
Full article ">Figure 1
<p>Schematic mechanism of the formation process of encapsulated nanosilica particles with the acrylic copolymer by <span class="html-italic">in situ</span> emulsion polymerization using thermoresponsive nonionic surfactant.</p> Full article ">Figure 2
<p>Fourier transform infrared spectroscopy (FTIR) spectra of nanosilica particles, plain copolymer and encapsulated nanosilica particles with the acrylic copolymer.</p> Full article ">Figure 3
<p>Dynamic light scattering (DLS) results obtained for (<b>a</b>) nanosilica sol; and (<b>b</b>) prepared nanocomposite.</p> Full article ">Figure 4
<p>Transmission electron microscopy (TEM) micrographs of the composite latex particles containing silica/acrylate polymer core-shell morphology.</p> Full article ">Figure 5
<p><b>(a)</b> Thermal gravimetric analyses (TGA) curves; and <b>(b)</b> DTA thermographs nanocomposite (dashed line) and plain copolymer (solid line).</p> Full article ">Figure 6
<p>Temperature dependence of storage modulus and loss tangent (tan δ) for (<b>a</b>) neat copolymer; and (<b>b</b>) synthesized nanocomposite.</p> Full article ">Figure 7
<p>Flammability test for (<b>a</b>) neat copolymer; and (<b>b</b>) synthesized nanocomposite.</p> Full article ">
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