Three variants of Polycrystalline Diamond (PCD) cutters were manufactured by High Pressure and High Temperature (HPHT) with varying diamond grain sizes ranging from 4 to 25 mu m with a Tungsten Carbide (WC-Co) substrate base. The structure and magnetic profiles of the PCD tables were analysed using KOERZIMAT 1.097 MS, Scanning Electron Microscopy (SEM), Image Analysis (IA), and Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). The study revealed that the size of the PCD table specimen does not impact the magnetic saturation. A relationship was observed between the amount of metal phase and the magnetic saturation level and the cobalt mean-free path and coercivity were found to be correlated. The PCD layers separated from the substrates revealed that larger diamond compact grain sizes decrease metallic cobalt phase magnetic domains. However, this also leads to a decrease in coercivity due to a decrease in cobalt content. In addition, it is worth noting that the dissolved tungsten (W) remained constant in all three variants. This indicates that the diamond grain size and the presence of the cobalt phase did not impact the amount of dissolved W during the synthesis process. The starting fine grain size (average of 4 mu m) led to a magnetic saturation value of 15.56 % after sintering, medium grain size (average of 13 mu m) with a saturation value of 13.88 %) while the coarse grain size (average of 25 mu m) resulted in a magnetic saturation value of 11.86 %. The observed phenomena can be explained by the increased size of the diamond grains, which leads to a decrease in the cobalt concentration.

This research investigates the fabrication of porous mullite filter material from reaction sintered mullite grains for high-temperature applications. Current filter types are not suitable for application in high-temperature and corrosive environments despite their high porosity. Acicular Mullite Ceramics are known for their highly porous microstructures with excellent mechanical integrity. Fabrication of a rod-like porous mullite filter from mullite grains produced from pyrophyllite clay and Al2O3 via reaction sintering was investigated. Pure mullite phase was produced at 1600 °C, and the use of a binder and foaming agent helped to obtain a porous structure. Above 1700 °C, acicular mullite grain growth via two-dimensional heterogeneous nucleation was promoted. A friable and structurally poor material was produced at temperatures just below 1800 °C. Above 1800 °C, the structural integrity of the ceramic material was improved. The measured total porosity and average pore diameter at 1800 °C were 36.20

Robocasting is an additive manufacturing (3D Printing) technique which allows the layer-wise manufacturing of complex structures through means of a CNC-controlled extrusion device depositing slurries/pastes with a high volume % solids loading onto a build plate. The aim of the study was to determine whether pyrophyllite parts could be produced using robocasting technology with a relatively simple and inexpensive paste system with inexpensive preparation and printing apparatus. Various shaped objects were produced and has shown some promising results. The use of polyethyl-glycol as an organic binder, coupled with water as the dispersant allowed for the reliable printing of complex shapes provided that adequate drying was effected and the optimised printing parameters were used. Successful drying of the printed green bodies was performed and no cracking was observed. Debindering and sintering yielded predictable anisotropic shrinkage which could be accounted for during part design and printing using scaling factors. The average relative density of sintered parts was found to be around 95% which was deemed less than ideal but various strategies could still be employed in future to improve the sintered density. The presence of bubbles/air gaps, likely introduced during mixing/printing was found to be the limiting factor in the average flexural strength of the printed products. Nevertheless, a reasonably high Weibull modulus coupled with a respectable average flexural strength of 142 MPa was measured. The measured Vickers hardness was comparable to that obtained through conventional manufacturing techniques and the fracture toughness was similar to that reported by previous studies done on robocast ceramics.

The effects of the addition of tetragonal 3mol% Y2O3 – ZrO2 into a MgAl2O4 spinel matrix were investigated. MgAl2O4 spinel's lacking mechanical properties prevent further utilization in many structural and refractory applications even though it has excellent chemical and thermal stability. The addition of tetragonal-ZrO2 was observed to improve the hardness, fracture toughness and biaxial flexural strength of MgAl2O4 materials. Moreover, the additions of 3mol% Y2O3 – ZrO2 resulted in a reduction of the mean grain size.

A boron nitride (BN) coating, prepared by the nitridation of carbon fibers dip-coated in an ethanoic boric acid and urea precursor, presented decorations of nanosphere colonies on the carbon fiber surface and nanodiscs overlying the nanospheres in the microfurrows of fibers. The presence of residual boron impurity points to the formation of the nanostructures. Oxidation and ablation resistance studies of up to about 2500°C showed that the subsequently prepared Cf/BN/C composite's ablation rate and shrinkage was three times better than that for the Cf/C composite (without BN fiber coating). The interaction of the B2O3 with the pores that formed on the fiber surface revealed the stages of protection from partial sealing to complete denudation of the B2O3 phase. The overall protection of the BN and/or B2O3 coating on the carbon fibers is dependent on the integrity of the carbon matrix.

AbstractThe formation reaction mechanism of Ti2AlC cubic boron nitride (cBN) composite materials was investigated using different particle sizes at different volume percentages of cBN (20 and 40 vol%), at a constant moderate pressure while varying time and temperature. The results show that, under the investigated conditions, Ti2AlC decomposed at 1300°C with a simultaneous hexagonalization of the cBN, resulting in the creation of secondary phases including TiB2, TiC, TiN and AlN. It was observed that the optimum time and temperature for fabricating Ti2AlC‐cBN composites, where both phases were abundantly present, was 1250°C for 5 minutes for all composites. Under these conditions, there was no hBN in the resulting composites. Increasing the average particle size of cBN powder enhanced the stability of the Ti2AlC and cBN in the samples. Also, the increase in volume fraction of cBN was observed to further promote the stability of Ti2AlC and cBN in the samples. This was due to the decrease in surface area of cBN, which hampered hexagonalization of cBN. Whatever excess hBN present reacted completely with the MAX phase in the final composites. The secondary phases formed in the samples were TiAl2, Ti3Al, TiCb, TiB2, TiCxNy (in samples containing 100 µm cBN) and TiN (in samples containing 20 vol.% cBN). The reaction area between Ti2AlC and cBN was strongly bonded to the cBN and Ti2AlC phases. A controlled method of simultaneous hexagonalization of cBN and reaction of the resultant hBN with Ti2AlC has proved superior in forming composites of Ti2AlC with cBN.

Alumina ceramic components were produced using gelcasting and 3D printing techniques to generate the end product. The 3D printed mould made from (acrylonitrile butadiene styrene) ABS filament provides a convenient demoulding method by dissolution of the mould using acetone as a solvent. This process enables low cost production of complex shaped ceramic components. The effect of the suspension solid loading on the properties and microstructure of complex shaped alumina parts was investigated. The produced ceramic components had densities up to 99.0%, hardness of 18 GPa, flexural strength of 374 MPa and a fracture toughness of 3.8 MPa root m after sintering in air for 3h, in good agreement with published values.

A hybrid carbide ultra-high temperature ceramics matrix [(Hf,Ti)C-SiC] reinforced with BN-coated carbon fibres was fabricated and tested for surface oxidation resistance. The UHTC composite showed an average mass ablation rate of 0.0014 g/s after exposure to a high heat flux (similar to 17 MW/em(2)) oxyacetylene flame test for 30 s above 2500 degrees C. The cross-sectional profile of the oxides scale formed was characterised and analysed. The scale was multicomponent; consisting of oxides of Hf, Ti and Si, as well as HfTiO4 and HfSiO4, which underwent phase separation and immiscibility. Multiple glassy bubbles formed on the scale surface due to the impediment of escaping gases by the glassy layer on the outer scale. The largest pores in the scale and surface bubbles that resisted rupture were the dominant features of the outermost phase-separated layer. Phase separation in the scale top layer improves the resistance to scale rupture.

This paper contributes to the body of knowledge on the efforts to develop nanodielectrics as the next generation of insulation material. The time-to-failure under electrical tree-induced degradation of 1.09-1.35 vol.% hexagonal BN/Epoxy was found to be 3 times longer than in clean epoxy. For 0.31-0.33 vol.% CNS/Epoxy the time-to-failure was 24 times longer than the clean epoxy. The electrical treeing partial discharge behaviour in the BN/Epoxy and CNS/Epoxy showed distinct time-evolution characteristics different from those in the clean epoxy. The improved electrical tree endurance in BN/Epoxy relative to the clean epoxy can be attributed to increased mechanical stiffness. The superiority of the CNS/Epoxy as a nanodielectric is notable. The effect is suggested to be due to the electron affinity properties of the carbon nanospheres at appropriate dispersion levels.

AbstractThe influence of excess Al2O3 on 3:2 mullite produced from α-Al2O3 and pyrophyllite powder was examined. A mixture consisting of 28 wt.% dehydroxylated pyrophyllite and 72 wt.% α-Al2O3 was milled in an attrition mill. The milled powders were sintered by spark plasma sintering (SPS) at 1600°C for 10, 20 and 30 min. Subsequently, the samples were heated at 1350°C for 2 h to determine the influence of the excess Al2O3 on the microstructure. No glassy phase was detected in the sample containing 72 wt.% Al2O3 and sintered at 1600°C for 20 min. The sample with 72 wt.% Al2O3 had greater hardness and fracture toughness compared to 3:2 mullite. The greatest hardness and fracture toughness of 12.43 GPa and 2.71 MPa m–0.5, respectively, were obtained in the sample containing 72 wt.% Al2O3 sintered at 1600°C for 20 min.

The performance of MXenes (Ti2CTx) combined with electrolytic manganese dioxide (EMD) in three different weight ratios (i.e. MXene: EMD = 20:80; 50:50; 80:20) were examined as anode material for Lithium-ion batteries (LIBs). A study of the structure, composition and morphology of the synthesized materials was conducted. The materials were further investigated for their electrochemical properties in a half-cell configuration using impedance spectroscopy measurements, cyclic voltammetry and galvanostatic charge-discharge cycling. Results showed that the combined MXene/EMD material has a greater cycling stability, capacity and rate capability as compared to the EMD. The best ratio was found to be MXene: EMD = 80:20. The capacity obtained for this material after 200 cycles is 460 mA h g(-1) at a current density of 100 mA g(-1). The Li-ion accessibility improved with cycling. This study provides a first insight into the viability of using one of the lightest known MXenes and EMD composite for improved LIB anodes. As EMD is a low cost and abundant material, it provides great opportunities for improved capabilities for lightweight applications at an affordable cost. (C) 2018 Elsevier Ltd. All rights reserved.

Modelling and simulation have greatly assisted in the provision of expressions and guidelines to find the practical thickness of electrodes, optimum charging current and materials utilization in cells of specific practical conductivity of electrodes and electrolyte for new-generation electrochemical capacitors (ECs) or ultracapacitors. Improved performance of ultracapacitors is attainable due to guidelines obtained via modelling, because this will eliminate materials (electrodes) underutilization, increased inefficiencies and potential drops. Optimizing electrodes and electrolyte morphology experimentally is mainly through trial and error method, which is very strenuous due to numerous parameters and contesting processes required, thus modelling and simulation are inevitable. The dependence of ECs performance on electrode and electrolyte fabricating conditions, such as mass ratio of electrode, electrode type, materials reaction, potential window of electrolyte and capacitance, has been presented from modelling and simulation. This gives absolute comprehension of the effects of various operating conditions, constructional design parameters and self-discharge on device performance, which guides in obtaining optimal design and fabrication of new-generation ultracapacitors. Perfecting the knowledge of the effects of the electrodes and separator's structural parameters, electrolyte effective conductivities and the operation conditions is inevitable in design and fabrication of new-generation ultracapacitors. Modelling provides an overall framework which permits the different factors that affect the ultracapacitors performance and implementation of the EDL differential capacitance while considering capacitance that is dependent on either potential or concentration. MD simulation results have the capacity to give the blueprints for optimizing energy density within carbon-based electrodes at microscopic level through concurrent optimization of EDL capacitance and quantum capacitance. Determination of minimum impurity or redox species concentration and the optimum total thickness of separator and anode are achievable through modelling and simulation. A theoretical guideline using optimum electrodes and potential window ratios for design and fabrication of symmetric electric double layer capacitors (EDLCs) that operate as asymmetric capacitors has been acquired through modelling. Also, useful guidelines and requirements to determine the optimum electrodes and potential window ratios, proper organic electrolyte for optimal performance, and entire design and fabrication of electrochemical energy storage devices with enhanced energy and power with a reduction in device mass and volume via modelling were presented. These guidelines and requirements aid in production of asymmetric ultracapacitors with the optimum battery-type mass ratio, potential range ratio, maximum potential range ratio and ratio of capacitance of capacitor type. Density functional theory (DFT) calculations and other types of modelling play a vital role in the discovery, synthesis, optimization and fabrication of numerous new electrode and electrolyte materials, which can help in the new-generation electrochemical capacitors with improved performance. Modelling and simulation are therefore very crucial in making great progress in area of electrodes material synthesis, optimization and fabrication, electrolytes synthesis and optimizations, separators synthesis and fabrications. Subsequently, an optimized design of the new-generation ultracapacitors with enhanced performance will be achievable by employing the electrochemical capacitors’ blueprint obtained from improved electrodes, electrolytes and separators acquired via modelling and simulation.

The properties of commercial pure titanium (CP-Ti) grade 4 produced by spark plasma sintering (SPS), cold isostatic press (CIP) and sinter and casting were compared. Pre-compacted bodies were isothermally held for 10 minutes at 1250°C under a minimum compaction pressure of 10 MPa for the SPS method, while the CIP and sinter method involved isothermal holding of pre-compacted bodies for 1 hour at 1350°C in the tube furnace under argon gas atmosphere. The casting of green bodies was performed under vacuum of 1x10-3 mbar using a ZrO2 melting crucible and a copper mold. The SPS and casting methods resulted in highly dense materials. The microstructural features were homogeneous and mainly consisted of plate-like α-Ti phase for all three technologies.

The energy storage performance of one of the lightest-known MXenes, Ti2CTx (MX) combined with carbon nanospheres (CNS) has been investigated as a symmetric electrode system in an aqueous electrolyte (1 M Li2SO4). The energy storage properties were interrogated using cyclic voltammetry (CV), galvanostatic cycling with potential limitation (GCPL), electrochemical impedance spectroscopy (EIS) and voltage-holding tests. The combined material (MX/CNS) demonstrated a higher specific capacity compared to each of the individual components. The material was fabricated with relatively high and low mass loadings, assembled into a symmetric device and performance compared. Specific capacitance, specific power and specific energy for the lower electrode mass loading of 180 F.g(-1), 37.6 kW.kg(-1) and 14.1 W.h.kg(-1) were all higher than 86 F.g(-1), 20.1 kW.kg(-1) and 6.7 W.h.kg(-1) for the higher mass loading. A wide voltage window of 1.5 V was obtained, but with limited long-term cycling behavior, suggesting the need for future improvement. Mathematical modelling and simulation of the supercapacitor showed good correlation with the experimental results, validating the model. The results reveal the potential of the Ti2CTx to be employed as a viable energy storage system for lightweight applications. (C) The Author(s) 2018. Published by ECS.

In this work, glasses within the borosilicate borophosphate and phosphate family were sintered into 3D porous scaffolds using 60 and 70 vol. % NH 4 (HCO 3 ) as a foaming agent. All scaffolds produced remained amorphous; apart from one third of the glasses which crystallized. All produced scaffolds had porosity >50% and interconnected pores in the range of 250–570 µm; as evidenced by µCT. The in-vitro dissolution of the scaffolds in SBF and changes in compression were assessed as a function of immersion time. The pH of the solution containing the borosilicate scaffolds increased due to the typical non-congruent dissolution of this glass family. Borophosphate and phosphate scaffolds induced a decrease in pH upon dissolution attributed to the congruent dissolution of those materials and the large release of phosphate within the media. As prepared, scaffolds showed compressive strength of 1.29 ± 0.21, 1.56 ± 0.63, 3.63 ± 0.69 MPa for the borosilicate, borophosphate and phosphate samples sintered with 60 vol. % NH 4 (HCO 3 ), respectively. Evidence of hydroxyapatite precipitation on the borosilicate glass scaffolds was shown by SEM/EDS, XRD and ICP-OES analysis. The borophosphate scaffolds remained stable upon dissolution. The phosphate scaffolds were fully crystallized, leading to very large release of phosphate in the media.

This paper addresses the effects of processing technique on the synthesis of mullite from pyrophyllite and alpha-alumina powder. The influence of firing temperatures were examined in order to optimize the fabrication process to achieved a suitable mechanical properties. Feedstock powders, with stoichiometric composition, were wet milled in an Attritor mill. The dried powders were consolidated using spark plasma sintering (SPS) in the temperatures range 1400 degrees C to 1700 degrees C under pressure of 50 MPa, with a heating rate of 100 degrees C/min at different holding times. Densities of 3.25 g/cm(3) and 3.17 g/cm(3) were obtained for the samples sintered at 1400 degrees C and 1600 degrees C respectively, with a 10-min holding time. The XRD and SEM/EDS were employed to characterize the firing transformation and microstructure of the samples. The SEM micrograph of samples, sintered at 1600 degrees C with 10 min holding times, revealed that the sample retained its equiaxed grain structure. The XRD results show a reduction in alpha-alumina content after the sample was fired. Hardness and fracture toughness values up to 11.73 GPa and 1.99 MPa.m(1/2) respectively were obtained.

Improvement on the densification and fracture toughness of ceramic materials based on boron suboxide (B6O) has been of great importance. The mechanical properties of B6O with and without chromium boride addition, hot pressed at a temperature range of 1850-1900 degrees C and pressures of 50-80MPa for 20 minutes, were investigated. The relative density, phase relationship, microstructures and mechanical properties of the processed ceramics were examined. More than 96% of the theoretical density was obtained for both ceramic systems. A good combination of mechanical properties was obtained with the B6O-CrB2 material (H-V=32.1GPa, K-IC=4.5MPam(0.5)) compared to the pure B6O material (H-V=30.5GPa, K-IC=brittle). The addition of 1.7wt.% CrB2 resulted in a pronounced improvement in both the hardness and fracture toughness values. Crack bridging and deflection are some of the toughening mechanisms liable for the enhanced fracture toughness of the sintered ceramic materials.