Effect of chemical composition on microstructural properties and sintering kinetics of (Ba,Sr)TiO3 powders

Barium strontium titanate powders with different Ba:Sr ratios were investigated to determine the influence of the initial composition of powder mixture on microstructural properties and sintering kinetics. It was determined that BaCO3 and SrCO3 react differently to mixing, resulting in Ba0.5Sr0.5CO3 in the sample with 80% Ba and different contents of Ba1- xSrxTiO3 in samples with 50% and 20% Ba. In addition, the morphology is also different, with higher Sr content leading to larger particles size and less agglomeration. The different chemical content of the initial powder mixture also has a marked impact on the sintering process: the onset of sintering shifts towards higher temperature with higher Sr content, while the average apparent activation energy of sintering is the highest for the sample with 80% Ba and the lowest for the mixture with 50% Ba. In addition, hexagonal-to-cubic phase transformation was observed in parallel with the sintering process, where the position of the phase transition shifts to lower temperatures with an increase in Sr content. This is consistent with the behavior of low-temperature phase transitions of BST. The phase transition was not observed in sintered samples, suggesting that there is a size-dependence of the phase transition temperature.

Sonochemical Synthesis of Nano-Structured Hydroxyapatite with unique morphologies and Evaluation of Sintering Kinetics

Phase pure hydroxyapatite (HAp) (Ca10(PO4)6(OH)2) ceramic powder was synthesized from the stoichiometric solution of calcium hydroxide and orthophosphoric acid employing sonochemical technique. Crystallinity of the HAp powder is found to be a strong function of amplitude of the ultrasound generator as revealed by XRD patterns and FTIR recorded on the samples prepared using varying amplitudes. Calcination of HAp powder beyond 700°C has resulted in the initiation of sintering as is evident from dilatometric studies and are complimented by the SEM micrographs. Activation energy of sintering of hydroxyapatite pellets using dilatometric sintering kinetic analysis has estimated to be 668±45kJ/mole corresponding to grain boundary diffusion as the prominent mass transport mechanism. Samples exhibited a density of 3.12g/cm3, close to theoretical density (~ 99 %) at the peak temperature of 1200°C. Studies on AC conductivity of the sintered samples exhibited relatively high room temperature conductivity of 5.07x10-8 S/m and a rising trend with temperature probably due to mobility of H+ and OH- ions. Attempts were also made to produce HAp nanorods sonochemically on the ordinary glass substrates immersed in the stoichiometric HAp precursor solution. Surface topographic images of the HAp deposited on glass substrate exhibited nanorods almost individually separated with an average diameter of 50 nm and 200 nm in length providing a process for synthesizing nano-structured HAp with simultaneous deposition exhibiting unique morphologies.

Preparation of Apatite-Wollastonite-Phlogopite glass-ceramic composites by powder sintering method

An Apatite-Wollastonite-Phlogopite glass-ceramic composite, was developed by sintering and crystallization of the powdered glass. The non-isothermal and isothermal sintering kinetics were studied for this glass-ceramic. Hot-stage microscopy (HSM) measurements demonstrated that it is possible to sinter and crystallize this glass-ceramic with 80% relative density. The activation energy of sintering was analyzed using previously reported model of sintering and it was obtained Q=193.83 KjmolK-1. Also it was shown that the microstructure of sample is a function of particle size distribution.

Investigation of sintering kinetics of ZnO by observing reduction of the specific surface area

Reduction of the specific surface area of porous ZnO during the sintering process was studied. ZnO powder was sintered at temperatures from 673 K to 1173 K. The decrease in the specific surface area was observed as a function of temperature and sintering time. Two different models were involved in order to define the appropriate parameters. The Arrhenius equation was used to give information on the activation energy of sintering. The LSE method was applied for determining optimum parameter values.

The Effect of Calcium Doping on the Surface and Catalytic Properties of Cobaltic Oxide Catalysts

The effects of calcium oxide doping (0.75, 1.5 and 3 mol% CaO) and calcination temperature (400, 500, 600 and 700°C) on different surface properties of Co3O4 were investigated. The structural properties of pure and doped oxide samples were determined by XRD methods, the textural properties were investigated via the adsorption of nitrogen at −196°C while the hydrogen peroxide decomposition activity of the investigated solids was determined by oxygen gasometric measurement of the reaction kinetics at 20–40°C. The dissolution of calcium ions in the Co3O4 lattice at temperatures in the range 400–600°C was accompanied by a marked decrease in the mean hydraulic radii (rh) and an increase in the surface area (SBET) and total pore volume (Vp) of the prepared oxide samples. In contrast, doping at 700°C brought about a decrease in the SBET and Vp values of the investigated solids. The catalytic activity for H2O2 decomposition on cobaltic oxide calcined at 400–700°C was found to decrease considerably on doping with CaO. The activation energy for sintering (ΔEs) of the pure and doped solids was determined from the variation in their SBET values as a function of the calcination temperature of these solids. Calcium oxide treatment resulted in a 50% increase in the activation energy of sintering of cobaltic oxide solid calcined at 400–600°C. This increase reflects the role of CaO doping in hindering the sintering of cobaltic oxide.

Determination of activation energy of sintering of ThO2-U3O8 pellets using the master sintering curve approach

ThO2 containing around 2 to 3 % U233O2 is considered as fuel for the forthcoming Indian Advanced Heavy Water Reactor (AHWR). High-density ThO2-UO2 pellets have been fabricated by powder metallurgy route using ThO2 and U3O8 powders as the starting materials. U3O8 decomposes to UO2 during high temperature sintering and forms a solid solution with ThO2. The densification behaviour and sintering kinetics of the above were evaluated using a high temperature dilatometer using constant heating rate experiments. To evaluate the activation energy of sintering, a master sintering curve approach has been used. The activation energy for sintering for the above composition in air was found to be 500 kJ/mol.