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Mesoscopic density fluctuations in liquid phase sintered silicon carbide have been investigated using small angle neutron scattering (SANS). The increase in the additives results in the modification in the pore size distribution and to some extent the total porosity. SANS revealed a mass fractal nature of the agglomerated matrix microstructure. The fractal dimension of the matrix does not change appreciably with the additives although the upper cut-off value of the fractal decreases significantly with the increase in the additives. The liquid phase sintering due to the presence of additives helps to achieve higher level of densification. However, the agglomeration hinders achievement of the fully dense pellets. [ABSTRACT FROM AUTHOR]

Effects of sintering on pore morphology and dielectric response have been investigated. Pore structure has been probed by small angle neutron scattering (SANS). It has been observed that the size distribution becomes less polydisperse with a slight modification in the distribution as sintering temperature is increased. Dielectric response in the frequency range 0.02-1000 kHz is significantly altered by modification of pore structure because of sintering. A transition from non-Debye type to near-Debye type response has been observed as the sintering temperature is increased. [ABSTRACT FROM AUTHOR]

Small-angle neutron scattering technique has been employed to investigate the evolution of pore morphology during the initial and the intermediate stages of sintering in ZrO2–3 mol% Y2O3. These results show that although there is a reduction in the porosity due to the elimination of the pores, the average growth in the pore size takes place during the sintering. This trend in pore growth corroborates the results of computer simulation based on the Potts model. The SANS data has been analyzed in the light of the polydisperse spherical pore model. [Copyright &y& Elsevier]

Pore morphology and pore size distribution in yttria-stabilized zirconia (ZrO2–8 mol% Y2O3) have been investigated, for two sintering temperatures, namely 1200 and 1270 °C, using small-angle neutron scattering. The results show that the reduction in the porosity, at 1270 °C compared to that at 1200 °C, occurs by the elimination of the pores at the lower end of the pore size distribution. In addition, the polydispersity is also lower at 1270 °C and the nature of the distribution is altered significantly near the smaller radius range. The average pore size shifts towards the higher radius range. The specific surface area of the pores is also diminished at 1270 °C because of the elimination of the finer pores. [Copyright &y& Elsevier]

Lithium titanate ( Li 2 TiO 3 ) was synthesized; without and with excess lithium (Li) in quantity of its stoichiometric requirement, with 5, 10, 15 and 20% excess and pebbles were fabricated by Solid State Reaction Process (SSRP). The green pebbles were sintered at 900 °C for 6 h . XRD analysis of the synthesized powders, confirmed the formation of single phase Li 2 TiO 3 , when 0–10% excess of lithium; compared to the stoichiometric requirement; were used and the presence of multiple phases when more than 10% excess lithium were used. Morphological modifications of mesoscopic structure in Li 2 TiO 3 pebbles with different quantities of excess lithium were investigated using Ultra-Small Angle Neutron Scattering (USANS) and Scanning Electron Microscopy (SEM). USANS measurements reveal the presence of sub-micrometric pores of size about 750 nm. From the experiments it was observed that addition of 10% of excess Li in Li 2 TiO 3 is the optimum for the Li 2 TiO 3 pebbles, in which all the desired properties remain within desired limit, without any compromise of properties of Li 2 TiO 3 pebbles. [ABSTRACT FROM AUTHOR]

The isolated pores in a silica ceramic sintered at 1073 K and 1273 K have been studied by small angle neutron scattering using the technique of scattering contrast factor variation. A mixture of H 2 O and D 2 O which matched the scattering length density of the ceramic matrix was introduced into the pores of the sample. The connected pores were thus contrast matched and hence the measured intensity was solely due to the presence of the isolated pores having no contrast matched liquid inside. Analysis of the data yielded a widely separated bi-modal distribution (with modes at ∼170 nm and 35 nm) of nanopores in the compacts. A qualitative model for the sintering in this ceramic is proposed where densification of the matrix occurs by annihilation of smaller pores. However, this is associated with enhancement in the number of larger pores through pore coalescence. In this description the connected pores both – macro and nano – increase in number – simultaneous with a decrease in numbers of isolated pores. [ABSTRACT FROM AUTHOR]

Abstract: Sodium zirconium phosphate and calcium zirconium phosphate, two potential radioactive wasteforms, were treated with fluoride, and different methods of sintering were evaluated. Different compositions were prepared by adding calcium fluoride to sodium zirconium phosphate and sodium fluoride to calcium zirconium phosphate. These mixtures were calcined in a microwave furnace and then sintered. The increase in densification of the samples sintered in a hot isostatic press were observed to be nearly uniform, while other samples that were sintered in a microwave and in a resistance furnace were inhomogeneous. The concentration of inhomogeneities was higher in fluorinated samples prepared under closed conditions in a hot press than samples prepared under microwave conditions in air. [Copyright &y& Elsevier]

Abstract: Ceramic powder has been synthesized from rice husk as the source of silica. In order to probe the evolution of its hierarchical mesoscopic and microscopic porous structure, the ceramic powder was compacted at different pressures and was sintered at different temperatures. A glassy ceramic to crystalline transition under thermal treatment (up to 1000°C) was revealed by X-ray diffraction. Existence of pores in two widely separated length scales was indicated by small angle neutron scattering with the smaller ones having mass fractal arrangement. Although no significant change in small pore structure under thermal effect was indicated, a significant modification of the same has been revealed by small angle neutron scattering at different compaction pressures. Connectivity between the pores was ascertained from scattering experiments on the ceramic compact impregnated with heavy water. Scanning electron microscopy shows the microstructure to undergo appreciable coalescence of micrometric ceramic particles for sintering temperature and pressure changes. [Copyright &y& Elsevier]

Abstract: Nano-crystalline ceria powders have been synthesized by gel combustion process. The effect of sintering temperature on the pore morphology of the powder compacts has been investigated by small-angle neutron scattering (SANS) in the accessible scattering wave vector ‘q’ range of 0.003–0.17nm−1 of a double crystal based instrument. The scattering profiles do not follow normal ‘q −4’ power law at higher q-values. The X-ray diffraction and light scattering results indicate that the ceria nano-powders are in the form of porous agglomerates. The porosity of the sintered compacts has been attributed to inter-agglomerate, inter-aggregate and intra-aggregate pores. Scattering profiles have been modeled by using a tri-modal size distribution of pores. [Copyright &y& Elsevier]

Abstract: La1−x Ca x CrO3 (x =0.3) powder has been synthesized by gel combustion process. Fractal behavior of the agglomerates and pore morphology of the sintered compacts have been studied by small-angle neutron scattering. At low scattering vector (q) regime the ‘’ power law variation of intensity of the powder sample and the green compact indicates that the powder particles are agglomerates and are composed of fractal aggregates. The value of the mass fractal dimension D f of these aggregates was found to be ∼2.2. The Porod exponent of the scattering profiles of the sintered specimens shows deviation from its normal value of −4 to ∼−3. This has been attributed due to superposition of scattering intensities from fine intra-granular pores on the scattering intensity from inter-granular pores. Loss of fractal structure of the aggregates upon heat treatment of the compacts at higher temperature has been observed. The pore size distribution gradually shifts towards higher radius size with the increase in sintering temperature due to faster elimination of finer pores. [Copyright &y& Elsevier]

Abstract: High pure titania powder was prepared by solution based hydroxide precipitation technique using chloride precursor and ammonia as precipitating agent. Effect of sintering temperature on fractal microstructure and pore size distribution in pressed compacts of titania with graded porosity obtained by firing at various temperatures have been investigated by small-angle neutron scattering technique. The results showed that the powder granules are aggregates and composed of fine primary particles of average size 2.5nm. The granules possess a fractal structure of mass fractal dimension 2.4. With increase in sintering temperature the granules gradually lost their fractal microstructure and the intra- and inter-granular pore size distributions in the compacts shifted towards higher radius size with a decrease in porosity. A power law size distribution for the intra-granular fine pores and lognormal size distribution for the inter-granular coarse pores were used for fitting the model. [Copyright &y& Elsevier]

ZrO2–8 mol% Y2O3 powder compact prepared by citric acid gel route has been sintered at different temperatures to achieve different porosity levels. The effect of sintering temperature on the pore morphology and pore size distribution in the same has been investigated using small-angle neutron scattering (SANS). The results reveal pore size growth with increase in the sintering temperature, although a reduction in the porosity occurs because of the elimination of pores from the system. The quantitative analysis of the SANS data has been carried out in the light of the polydisperse globular pore model. The growth of the average size of the pores with sintering temperature could be fitted to an Arrhenius type growth. The necessity of considering a realistic model approximation in interpreting the data has also been dwelt upon. [Copyright &y& Elsevier]