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Through comprehensive density functional calculations, we predict the stability of a rheniumbased ferrite, ReFe2O4, in a distorted spinel-based structure. In ReFe2O4, all Re and half of the Fe ions occupy the octahedral sites while the... more
Through comprehensive density functional calculations, we predict the stability of a rheniumbased ferrite, ReFe2O4, in a distorted spinel-based structure. In ReFe2O4, all Re and half of the Fe ions occupy the octahedral sites while the remaining Fe ions occupy the tetrahedral sites. All Re ions are predicted to be at a +4 oxidation state with a low spin configuration (S = 3/2), while all Fe ions are predicted to be at a +2 oxidation state with a high spin state configuration (S = 2). Magnetically, ReFe2O4 adopts an unconventional ferrimagnetic state in which the magnetic moment of Re opposes the magnetic moments of both tetrahedral and octahedral Fe ions. The spin-orbit coupling is found to cause a slight spin canting of ∼ 1.5◦. The predicted magnetic ground state is unlike the magnetic alignment usually observed in ferrites, where the tetrahedral cations oppose the spin of the octahedral cations. Given that the density of states analysis predicts a half-metallic character driven by...
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This study aims to shed light on processing pathways towards functional silicate ceramics, which show some promise in various emerging applications, including dielectrics and bioactive implant materials. Polycrystalline silicate ceramics... more
This study aims to shed light on processing pathways towards functional silicate ceramics, which show some promise in various emerging applications, including dielectrics and bioactive implant materials. Polycrystalline silicate ceramics of Neso-, Soro-and Inosilicate families were synthesised by three different techniques: (i) a coprecipitation method, (ii) a modified sol-gel method and (iii) standard solid-state reactions. Co-precipitated samples show increased sintering and densification behaviour compared to sol-gel and solid-state methods, with diametral shrinkage values during sintering of 28.8%, 13.3% and 25.0%, respectively. Well-controlled phase formation in these ceramics was most readily achieved through the steric entrapment of cations and shorter diffusion pathways afforded by the modified Pechini-type sol-gel method. Substituting Zn 2+ for Mg 2+ in enstatite samples was found to enhance the formation of orthoenstatite during cooling, which is otherwise very slow. We present guidelines for the design of synthesis methods that consider the requirements for different functional silicate ceramics in terms of phase formation and microstructure.
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The inclusion of small amounts of copper is often reported to enhance the mechanical and biointegrative performance of bioceramics towards tissue engineering applications. In this work, 3D scaffolds were additively manufactured by... more
The inclusion of small amounts of copper is often reported to enhance the mechanical and biointegrative performance of bioceramics towards tissue engineering applications. In this work, 3D scaffolds were additively manufactured by robocasting of precipitation derived copper doped diopside. Compositions were chosen in which magnesium sites in diopside were substituted by copper up to 3 at.%. Microstructure, mechanical performance, bioactivity, biodegradability, drug release, biocompatibility, in vitro angiogenesis and antibacterial activity were studied. Results indicate that copper is incorporated in the diopside structure and improves materials’ fracture toughness. Scaffolds with > 80% porosity exhibited compressive strengths exceeding that of cancellous bone. All compositions showed bioactivity and drug release functionalities. However, only samples with 0–1 at.% copper substitution showed favorable proliferation of osteogenic sarcoma cells, human umbilical vein endothelial cells and fibroblasts, while larger amounts of copper had cytotoxic behavior. In vitro angiogenesis was significantly enhanced by low levels of copper. Copper-containing materials showed anti-Escherichia coli activity, increasing with copper content. We show that across multiple indicators, copper substituted diopside of the composition CaMg0.99Cu0.01Si2O6, exhibits high performance as a synthetic bone substitute, comparing favorably with known bioceramics. These findings present a pathway for the enhancement of bioactivity and mechanical performance in printable bioceramics.
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We present a novel approach for the evaluation of interfacial mechanics and contact area evolution between two simulated bodies exhibiting fractal surfaces. Applying spline-discretisation to define local contact normals and curvatures, we... more
We present a novel approach for the evaluation of interfacial mechanics and contact area evolution between two simulated bodies exhibiting fractal surfaces. Applying spline-discretisation to define local contact normals and curvatures, we interpret the mechanics of these surfaces by examining discrete contact points as Hertzian spheres. This facilitates computationally efficient modelling of realistic surface-profiles, considering normal and tangential interactions between asperities. This has yielded significant improvements on existing methods, which are applicable primarily for rough-flat contacts. By modelling rough to rough contact of surface profiles with fractal dimensions in the region 1-1.9. We demonstrate the significance of fractality on interfacial stiffness with surfaces of greater fractal dimension exhibiting lower normalised stiffness. The linear development of contact area with load is consistent with contemporary numerical and experimental studies. The capabilities ...
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Research Interests: Materials Engineering, Physics, Materials Science, Biomaterials, Hydroxyapatite, and 10 moreTransmission Electron Microscopy, Doping, Bone Regeneration, Strontium, High Resolution Transmission Electron Microscopy, Bioceramics, Nanostructure, Dissolution, Bioactivity, and Bioresorbable Vascular Scaffolds
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Research Interests: Materials Engineering, Mechanical Engineering, Physics, Materials Science, Biomaterials, and 12 moreHydroxyapatite, Raman Spectroscopy, Ion beam irradiation for material modification, Biomaterials and Tissue Engineering, Manufacturing Engineering, Bioceramics, Dissolution, Ion, Irradiation, Science and Technology of Heterogeneous Materials, X Ray Photoelectron Spectroscopy, and Krypton
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Research Interests: Engineering, Materials Science, Fluid flow in porous media, Evaporation, Heat and Mass Transfer, and 10 moreTransport Phenomena in Porous Media, Porosity, Mathematical Sciences, Porous Media, Physical sciences, Porous Medium, Paper Microfluidics, Microfluidic paper-based devices, Porous imbibition, and Capillary penetration
Research Interests: Materials Engineering, Mechanical Engineering, Civil Engineering, Physics, Materials Science, and 15 moreCorrosion Science, Glass, Corrosion, Ceramics, Coating, Composite Material, Ceramic, Heat shield, Oxidation, Emissivity, Mosi, Borosilicate Glass, High temperature emissivity, molybdenum disilicide, and High Emissivity Coatings
Ce/Cr codoped TiO nanoparticles were synthesized using sol-gel and Pechini methods with heat treatment at 400 °C for 4 h. A conventional sol-gel process produced well-crystallized anatase, while Pechini synthesis yielded less-ordered... more
Ce/Cr codoped TiO nanoparticles were synthesized using sol-gel and Pechini methods with heat treatment at 400 °C for 4 h. A conventional sol-gel process produced well-crystallized anatase, while Pechini synthesis yielded less-ordered mixed-phase anatase + rutile; this suggests that the latter method enhances Ce solubility and increases chemical homogeneity but destabilizes the TiO lattice. Greater structural disruption from the decomposition of the Pechini precursor formed more open agglomerated morphologies, while the lower levels of structural disruption from pyrolysis of the dried sol-gel precursor resulted in denser agglomerates of lower surface areas. Codoping and associated destabilization of the lattice reduced the binding energies in both powders. Cr formation in sol-gel powders and Cr formation in Pechini powders suggest that these valence changes derive from synergistic electron exchange from intervalence and/or multivalence charge transfer. Since Ce is too large to allow ...
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The capillary penetration of fluids in thin porous layers is of fundamental interest in nature and various industrial applications. When capillary flows occur in porous media, the extent of penetration is known to increase with the square... more
The capillary penetration of fluids in thin porous layers is of fundamental interest in nature and various industrial applications. When capillary flows occur in porous media, the extent of penetration is known to increase with the square root of time following the Lucas-Washburn law. In practice, volatile liquid evaporates at the surface of porous media, which restricts penetration to a limited region. In this work, on the basis of Darcy's law and mass conservation, a general theoretical model is developed for the evaporation-limited radial capillary penetration in porous media. The presented model predicts that evaporation decreases the rate of fluid penetration and limits it to a critical radius. Furthermore, we construct a unified phase diagram that describes the limited penetration in an annular porous medium, in which the boundaries of outward and inward liquid are predicted quantitatively. It is expected that the proposed theoretical model will advance the understanding o...
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Research Interests: Engineering, Fractal Geometry, Physics, Materials Science, Mechanics, and 13 moreContact Mechanics, Tribology, Surface Roughness, Hertzian contact mechanics, Stiffness, Discretization, Fractal, Contact area, Fractal Dimension, Contact Stiffness, Surface Finish, Solids and Structures, and fractal surfaces
Research Interests: Physics, Materials Science, Biotechnology, Ecology, Cell Biology, and 15 moreSpace Science, Medicine, Multidisciplinary, Adsorption, Fractal Analysis, Fractal, Electrokinetic Phenomena, Specific surface area, Ambient Temperature, Aluminum oxide, Langmuir, Parameter Optimization, Citric Acid, Aqueous Solution, and Oxalic acid
Research Interests: Materials Engineering, Chemical Engineering, Physics, Condensed Matter Physics, Materials Science, and 15 moreRaman Spectroscopy, Scanning Electron Microscopy, Thin Films, Photocatalysis, Thin Film, Titanium dioxide, Methylene Blue, Surface and Coatings Technology, Anatase, Thermal Stability, Dopant, Metal ion, TiO, Aqueous Solution, and Rutile
Research Interests: Engineering, Materials Engineering, Condensed Matter Physics, Materials Science, Magnetic Materials, and 15 moreDilute Magnetic Semiconductors, Applied Physics, Material Science, Ferromagnetics, Magnetism, Copper, DFT, Density Functional Theory, Anatase, Dopant, Ferromagnetic Materials, Ferromagnetism, Magnetic Oxides, Diluted Magnetic Semiconductors, and Dilute Magnetism
Over the past several decades, many coating techniques have been developed for titania thin and thick film fabrication. Of these, electrophoretic deposition (EPD), anodic oxidation, gel oxidation, spray pyrolysis, ultrasonic spray... more
Over the past several decades, many coating techniques have been developed for titania thin and thick film fabrication. Of these, electrophoretic deposition (EPD), anodic oxidation, gel oxidation, spray pyrolysis, ultrasonic spray pyrolysis, sol-gel spin coating, aerosol spraying, and sol-gel dipcoating have become of interest owing to the low cost of operation and the non-necessity of the use of a vacuum system. The present work briefly reviews some of the activities of the authors in the production of titania films.
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Using density functional calculations, we examine insertion/extraction of Mg ions in Mg 3 Bi 2 , an interesting Mg-ion battery anode. We found that a (110) facet is the most stable termination. Vacating a Mg 2+ ion from the octahedral... more
Using density functional calculations, we examine insertion/extraction of Mg ions in Mg 3 Bi 2 , an interesting Mg-ion battery anode. We found that a (110) facet is the most stable termination. Vacating a Mg 2+ ion from the octahedral site is more favourable for both surface and bulk regions of the material. However, the diffusion barriers among the tetrahedral sites are ~ 3 times smaller than those among octahedral sites. Consequently, during the magnesiation/demagnesiation process, Mg ions first vacate the octahedral sites and then diffuse through the tetrahedral sites. The spin-orbit interaction lowers Mg's vacancy formation energy but has a minor effect on diffusion barriers.
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The inclusion of small amounts of copper is often reported to enhance the mechanical and biointegrative performance of bioceramics towards tissue engineering applications. In this work, 3D scaffolds were additively manufactured by... more
The inclusion of small amounts of copper is often reported to enhance the mechanical and biointegrative performance of bioceramics towards tissue engineering applications. In this work, 3D scaffolds were additively manufactured by robocasting of precipitation derived copper doped diopside. Compositions were chosen in which magnesium sites in diopside were substituted by copper up to 3 at.%. Microstructure, mechanical performance, bioactivity, biodegradability, drug release, biocompatibility, in vitro angiogenesis and antibacterial activity were studied. Results indicate that copper is incorporated in the diopside structure and improves materials’ fracture toughness. Scaffolds with > 80% porosity exhibited compressive strengths exceeding that of cancellous bone. All compositions showed bioactivity and drug release functionalities. However, only samples with 0–1 at.% copper substitution showed favorable proliferation of osteogenic sarcoma cells, human umbilical vein endothelial cells and fibroblasts, while larger amounts of copper had cytotoxic behavior. In vitro angiogenesis was significantly enhanced by low levels of copper. Copper-containing materials showed anti-Escherichia coli activity, increasing with copper content. We show that across multiple indicators, copper substituted diopside of the composition CaMg0.99Cu0.01Si2O6, exhibits high performance as a synthetic bone substitute, comparing favorably with known bioceramics. These findings present a pathway for the enhancement of bioactivity and mechanical performance in printable bioceramics.
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This study aims to shed light on processing pathways towards functional silicate ceramics, which show some promise in various emerging applications, including dielectrics and bioactive implant materials. Polycrystalline silicate ceramics... more
This study aims to shed light on processing pathways towards functional silicate ceramics, which show some promise in various emerging applications, including dielectrics and bioactive implant materials. Polycrystalline silicate ceramics of Neso-, Soro-and Inosilicate families were synthesised by three different techniques: (i) a coprecipitation method, (ii) a modified sol-gel method and (iii) standard solid-state reactions. Co-precipitated samples show increased sintering and densification behaviour compared to sol-gel and solid-state methods, with diametral shrinkage values during sintering of 28.8%, 13.3% and 25.0%, respectively. Well-controlled phase formation in these ceramics was most readily achieved through the steric entrapment of cations and shorter diffusion pathways afforded by the modified Pechini-type sol-gel method. Substituting Zn 2+ for Mg 2+ in enstatite samples was found to enhance the formation of orthoenstatite during cooling, which is otherwise very slow. We present guidelines for the design of synthesis methods that consider the requirements for different functional silicate ceramics in terms of phase formation and microstructure.
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Abnormal grain growth (AGG) was observed in rutile TiO2 formed by the thermal treatment of anatase TiO2 in the presence of zirconium silicate. This morphological behaviour was seen to occur in sintered powder compacts and thin films with... more
Abnormal grain growth (AGG) was observed in rutile TiO2 formed by the thermal treatment of anatase TiO2 in the presence of zirconium silicate. This morphological behaviour was seen to occur in sintered powder compacts and thin films with solid state zircon dopants and in TiO2 coatings on grains of zircon sand. In order to clarify the mechanism of AGG in this system, various doping methods were employed and the morphological consequences of these doping methods were investigated. It was found that doping by Zr and Si does not give rise to abnormal grain growth. The observed phenomena were discussed in terms of morphological and energetic considerations. It is likely that a distinct orientation relationship between rutile TiO2 and ZrSiO4 and possible grain boundary liquid formation play a role in giving rise to the rapid growth of faceted prismatic rutile.
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Through comprehensive density functional calculations, we predict the stability of a rheniumbased ferrite, ReFe 2 O 4 , in a distorted spinel-based structure. In ReFe 2 O 4 , all Re and half of the Fe ions occupy the octahedral sites... more
Through comprehensive density functional calculations, we predict the stability of a rheniumbased ferrite, ReFe 2 O 4 , in a distorted spinel-based structure. In ReFe 2 O 4 , all Re and half of the Fe ions occupy the octahedral sites while the remaining Fe ions occupy the tetrahedral sites. All Re ions are predicted to be at a +4 oxidation state with a low spin configuration (S = 3/2), while all Fe ions are predicted to be at a +2 oxidation state with a high spin state configuration (S = 2). Magnetically, ReFe 2 O 4 adopts an unconventional ferrimagnetic state in which the magnetic moment of Re opposes the magnetic moments of both tetrahedral and octahedral Fe ions. The spin-orbit coupling is found to cause a slight spin canting of ∼ 1.5 •. The predicted magnetic ground state is unlike the magnetic alignment usually observed in ferrites, where the tetrahedral cations oppose the spin of the octahedral cations. Given that the density of states analysis predicts a half-metallic character driven by the presence of Re t2g states at the Fermi level, this compound shows promise towards potential spintronics applications.
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It is well known that crystallinity is required for photocatalytic activity in TiO2 and that the metastable anatase phase usually exhibits photocatalytic activity superior to that of the equilibrium rutile phase. This phase transformation... more
It is well known that crystallinity is required for photocatalytic activity in TiO2 and that the metastable anatase phase usually exhibits photocatalytic activity superior to that of the equilibrium rutile phase. This phase transformation temperature often is observed to occur at ∼600°C, although temperatures in the range 400°–1200°C have been observed. Therefore, retention of anatase below 400°C is considered a
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We present a newly developed approach for the calculation of interfacial stiffness and contact area evolution between two rough bodies exhibiting self-affine surface structures. Using spline assisted discretization to define localised... more
We present a newly developed approach for the calculation of interfacial stiffness and contact area evolution between two rough bodies exhibiting self-affine surface structures. Using spline assisted discretization to define localised contact normals and surface curvatures we interpret the mechanics of simulated non-adhesive elastic surface-profiles subjected to normal loading by examining discrete contact points as projected Hertzian spheres. The analysis of rough-to-rough contact mechanics for surface profiles exhibiting fractal structures, with fractal dimensions in the regime 1-2, reveals the significant effect of surface fractality on contact mechanics and compliance with surfaces having the same mean roughness but higher fractality showing lower contact stiffness in conditions of initial contact for a given load. The predicted linear development of true contact area with load was found to be consistent with diverse existing numerical and experimental studies. Results from this model demonstrate the applicability of the developed method for the meaningful contact analysis of hierarchical structures with implications for modelling tribological interactions between pairs of rough surfaces
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Microporous organosilicas assembled from polysilsesquioxane (POSS) building blocks are promising materials that are yet to be explored in-depth. Here, we investigate the processing and molecular structure of bispropylurea bridged POSS... more
Microporous organosilicas assembled from polysilsesquioxane (POSS) building blocks are promising materials that are yet to be explored in-depth. Here, we investigate the processing and molecular structure of bispropylurea bridged POSS (POSS-urea), synthesised through the acidic condensation of 1,3-bis(3-(triethoxysilyl)propyl)urea (BTPU). Experimentally, we show that POSS-urea has excellent functionality for molecular recognition toward acetonitrile with an adsorption level of 74 mmol/g, which compares favourably to MOFs and zeolites, with applications in volatile organic compounds (VOC). The acetonitrile adsorption capacity was 132-fold higher relative to adsorption capacity for toluene, which shows the pores are highly selective towards acetonitrile adsorption due to their size and arrangement. Theoretically, our tight-binding density functional and molecular dynamics calculations demonstrated that this BTPU based POSS is microporous with an irregular placement of the pores. Structural studies confirm maximal pore sizes of ∼1 nm, with POSS cages possessing an approximate edge length of ∼3.16 Å.
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Control of capillary flow through porous media has broad practical implications. However, achieving accurate and reliable control of such processes by tuning the pore size or by modification of interface wettability remains challenging.... more
Control of capillary flow through porous media has broad practical implications. However, achieving accurate and reliable control of such processes by tuning the pore size or by modification of interface wettability remains challenging. Here we propose that the liquid flow by capillary penetration can be accurately adjusted by tuning the geometry of porous media. Methodologies: On the basis of Darcy’s law, a general framework is proposed to facilitate the control of capillary flow in porous systems by tailoring the geometric shape of porous structures. A numerical simulation approach based on finite element method is also employed to validate the theoretical prediction.
Findings: A basic capillary component with a tunable velocity gradient is designed according to the proposed framework. By using the basic component, two functional capillary elements, namely, (i) flow accelerator and (ii) flow resistor, are demonstrated. Then, multi-functional fluidic devices with controllable capillary flow are realized by assembling the designed capillary elements. All the theoretical designs are validated by numerical simulations. Finally, it is shown that the proposed concept can be extended to three-dimensional design of porous media
Findings: A basic capillary component with a tunable velocity gradient is designed according to the proposed framework. By using the basic component, two functional capillary elements, namely, (i) flow accelerator and (ii) flow resistor, are demonstrated. Then, multi-functional fluidic devices with controllable capillary flow are realized by assembling the designed capillary elements. All the theoretical designs are validated by numerical simulations. Finally, it is shown that the proposed concept can be extended to three-dimensional design of porous media