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The yttrium-segregation-dependent phase partitioning and residual stress development that influence both the aging and the fracture behaviour in 3Y-TZP bioceramics were studied by sintering alumina-free 3Y-TZP, varying the sintering temperature and the time, to yield ceramics with identical grain size distributions, but with different phase compositions. The structure and stability of the resulting tetragonal phases, in the form of transformable, yttria-lean t -ZrO 2 (YLZ) and non-transformable, yttria-rich t ″-ZrO 2 and/or t ′-ZrO 2 (YRZ), were studied by X-ray diffraction (XRD) and focused ion beam scanning electron microscopy (FIB-SEM). The accelerated aging kinetics was fitted to the Mehl-Avrami-Johnson equation. The specimen sintered at the lowest sintering temperature but with the longest dwell time contained the smallest and the largest concentrations of yttria in the YLZ and YRZ phases, respectively, as well as the largest amount of YRZ. As a consequence, it exhibited the fastest linear aging kinetics accompanied by more extensive micro-cracking of the transformed layer, as well as largest amount of intergranular fracture and the greatest resistance to fracture. These properties were ascribed to the increased transformability of the YLZ phase and the greatest propensity of the YRZ phase to relax the accumulated residual stresses during transformation (tetragonal to monoclinic, t – m ) manifested as a ∼2.4% unit-cell volume increase. The observed relaxation provides additional understanding of the t – m transformation mechanism, which governs both the aging and fracture behaviour of 3Y-TZP. Statement of Significance A novel approach to understanding the effect of yttrium segregation on t–m transformation of 3Y-TZP zirconia bioceramics is presented. Carefully designed sintering strategy facilitated fabrication of ceramics with identical grain size distributions but with different yttrium concentrations. The influence of phase partitioning on stability and structure of transformable yttria-lean tetragonal phase (YLZ) and non-transformable yttria-rich phases (YRZ; t ″ – and t ′ – prime) and on the formation of residual stresses in YRZ were investigated. It is shown that YRZ phases are under compressive stresses in YLZ matrix, since a systematic relaxation after ageing was observed and explained for the first time. It puts additional perspective on the understanding of the t–m transformation mechanism ultimately governing both the ageing and fracture behaviour of 3Y-TZP. [ABSTRACT FROM AUTHOR]

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Fine tungsten carbide (WC) powder was prepared by solid state reaction between tungsten powder (W) and activated carbon cloth as a new carbon (C) source. The effect of temperature and time of heat treatment as well as the effect of C/W ratio on WC phase formation was studied. The results obtained by X-ray powder diffraction (XRPD) show that obtained powder is single WC. Microstructure and morphology was determinate by means of scanning electron microscopy (SEM). Brunauer–Emmett–Teller (BET) method was used for examining specific surface area and texture of obtained powders. It was found that WC powder was successfully synthesized in excess carbon after eight-hour heat treatment at relatively low temperature (1000 °C). [ABSTRACT FROM AUTHOR]

Abstract: Hafnium carbide powder was synthesized by sol–gel polycondensation of hafnium chloride with citric acid. The starting materials were dissolved in water and mixed homogeneously on a hot plate until precursor gel was formed. Pyrolysis of this gel resulted in monoclinic hafnia which after subsequent heat treatment transformed into hafnium carbide. The obtained materials were analyzed by means of X-ray diffraction and scanning electron microscopy. The results showed that the obtained carbide powders were composed of nearly equiaxed particles with narrow size distribution. Characterization by nitrogen adsorption showed that the obtained powders were micro- and mesoporous materials with high specific surface area. [Copyright &y& Elsevier]

Abstract: Nanometric ceria powders with fluorite-type structure were obtained by applying self-propagating room temperature method. The obtained powders were subsequently thermally treated (calcined) at different temperatures for different times. Powder properties such as specific surface area, crystallite size, particle size and lattice parameter have been studied. Roentgen diffraction analysis (XRD), BET and Raman scattering measurements were used to characterize the as-obtained (uncalcined) powder as well as powders calcined at different temperatures. It was found that the average diameter of the as-obtained crystallites is in the range of 3–5nm whereas the specific surface area is about 70m2/g. The subsequent, 15min long, calcination of as-obtained powder at different temperatures gradually increased crystallite size up to ∼60nm and reduced specific surface down to 6m2/g. Raman spectra of synthesized CeO2−y depicts a strong red shift of active triply degenerate F2g mode as well as additional peak at 600cm−1. The frequency of F2g mode increased while its line width decreased with an increase in calcination temperature. Such a behavior is considered to be the result of particle size increase and agglomeration during the calcination. After the heat treatment at 800°C crystallite size reached value larger than 50nm. Second order Raman mode, which originates from intrinsic oxygen vacancies, disappeared after calcination. [Copyright &y& Elsevier]

Abstract: Amorphous Pr6O11 powder was obtained by applying self-propagating room temperature method (SPRT). After calcination, the amorphous powder converted to nanometric Pr6O11 powder with cubic fluorite-type structure. Powder properties such as crystallite size, lattice strain and lattice parameter were studied by X-ray diffraction (XRD) at room temperature. The crystallite size was estimated by means of the full width at half maxima (FWHM) of XRD peaks. Williamson–Hall plots were used to determine the lattice strain whereas the Ritveld analysis was employed for crystal structure refinement. It was found that the powder properties are affected by both calcination temperature and duration of thermal treatment. The crystallite size varied from 5 to ∼250nm, whereas the lattice parameter varied from 5.461 to 5.494Å. The powder obtained after four-hour long calcination was almost free of internal strain. [Copyright &y& Elsevier]

Abstract: The ordered mesoporous silica SBA-15 materials were synthesized using Pluronic P123 (non-ionic triblock copolymer, EO20PO70O20), under acidic conditions. SBA-15/carbon cryogel composites were obtained by sol–gel polycondensation of resorcinol and formaldehyde followed by freeze drying, and subsequent pyrolysis, in the presence of different amounts of SBA-15. For comparison purpose, SBA-15/carbon composite was also prepared using sucrose as carbon source. These materials were characterized by room temperature nitrogen adsorption–desorption measurement, X-ray diffraction, scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. It was revealed that the samples have amorphous structure, high specific surface area (350–520m2 g−1) and developed meso- as well as microporosity. The porosity of structure depends on the carbon source and Si/C ratio which can be easily controlled by varying concentration of starting solution. [Copyright &y& Elsevier]