D. Sen

Pore morphology in sintered ZrO2–8 mol% Y2O3 ceramic: a small-angle neutron scattering investigation

Abstract Pore morphology and pore size distribution in yttria-stabilized zirconia (ZrO 2 –8 mol% Y 2 O 3 ) have been investigated, for two sintering temperatures, namely 1200 and 1270xa0°C, using small-angle neutron scattering. The results show that the reduction in the porosity, at 1270xa0°C compared to that at 1200xa0°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 1270xa0°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 1270xa0°C because of the elimination of the finer pores.

Pore growth during initial and intermediate stages of sintering in ZrO2–3 mol% Y2O3 compact: a small-angle neutron scattering investigation

Abstract 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 ZrO 2 –3 mol% Y 2 O 3 . 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.

Small angle neutron scattering investigation and the low frequency dielectric response of sintered ZrO2-8 mol% Y2O3ceramic compacts: the effect of pore characteristics

The effect of the pore structure on the low frequency (0.01?100?kHz) dielectric response of sintered ZrO2?8?mol%?Y2O3 ceramic compacts has been investigated. Pore characteristics such as the pore size distribution, specific surface area and pore morphology have been estimated by means of small angle neutron scattering (SANS). It has been observed that both the real and the imaginary parts of the complex dielectric permittivity for the specimens depend not only on the porosity but also on the pore characteristics, significantly. Unlike in the normal Debye relaxation process, the imaginary part of the dielectric constant increases in the lower frequency region. The variation in the dielectric response is explained by a pore structure dependent interfacial polarization, ion hopping and conduction.

Effect of sintering temperature on pore growth in ZrO2–8 mol% Y2O3 ceramic compact prepared by citric acid gel route: a small-angle neutron scattering investigation

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.

Non-Debye to Debye transition of ac dielectric response in YCrO3 nanoceramic under sintering: effect of pore structure

Dielectric response of the porous YCrO3 nanoceramic has been investigated as a function of sintering temperature. Pore structure at different sintering temperatures has been studied by small-angle neutron scattering (SANS). It has been observed that overall polydispersity of pore-size distribution decreases and loss peak of the ac dielectric response gets pronounced with a slight peak shift towards higher frequency with increasing sintering temperature. A non-Debye to Debye type transition of the dielectric response is observed beyond a sintering temperature of 1400 °C. Dielectric results were explained on the basis of pore morphology, pore-size distribution and connectivity between the pores.

Temperature Mediated Morphological Transition during Drying of Spray Colloidal Droplets

Understanding how a tiny dilute evaporative colloidal spray droplet gets transformed into a microgranule with a characteristic morphology is crucial from scientific as well as technological points of view. In the present work, it is demonstrated that the morphology and the size distribution of the microcapsules can be tuned simply by adjusting the drying temperature. Shape and size of the capsules are quantified at four different drying temperatures. It is shown that the morphology transits gradually from sphere to toroid with increasing temperature keeping the average volume-fraction of the correlated nanoparticles nearly unaffected for the synthesized granules. A plausible mechanism for the chronological pathway of such morphological transformation is illustrated. Computer simulation corroborates the experimentally observed morphological transition. The variation in hollowness and buckling tendency of the capsules are elucidated by scattering and imaging techniques.

Formation of nano-structured core–shell micro-granules by evaporation induced assembly

Nano-structured spherical micro-granules of core–shell morphology have been realized by utilizing the contrasting interfacial interaction of two different types of nano-particles with liquid solvent. By enforcing evaporation induced assembly, a hydrophobic core has been wrapped inside a hydrophilic envelope consisting of correlated nano-particles. This is realized by a one step, fast and facile technique of spray-drying. The evaporation of water in a radially outward direction from mixed-suspension droplets enforces the hydrophobic component to travel towards the core and the hydrophilic component to reside at the surface forming a shell. Mapping the coherent neutron and X-ray scattering length density into reciprocal space, the structure as well as inter-particle correlation in such micro-granules has been characterized over a wide range of wave-vector transfers. Scattering results have been complemented with electron microscopy. Significant enhancement in specific surface-area due to core–shell morphology has been observed by gas adsorption technique. Treating the granules with hydrofluoric acid, the silica shell has been etched to unwrap the meso-porous carbon core. This demonstrates that the hydrophobic component indeed forms the nano-structured core inside the hydrophilic nano-structured shell. In view of the unique characteristics of these synthesized core–shell nano-structured micro-granules, a potential application of such granules has also been discussed.

Evolution of a fractal system with conserved order parameter under thermal annealing.

Mesoscopic structural evolution under thermal annealing of yttrium aluminium garnet fractal aggregates has been investigated by small-angle neutron scattering. Fractal dimension remains invariant with sintering temperature but the extent of the fractal realm is narrowed down significantly. A Monte Carlo simulation, based on Ostwald-ripening type of relaxation of fractal aggregates for a mass conserved system, has been attempted in order to understand the aforementioned novel observation. A local group merge sintering model was adopted for the relaxation of the fractal aggregates. Diffusion driven mass transport over local branches of fractal clusters causes smoothening of branches but keeps the overall shape unaltered at lower resolution. Predictions of the model were found to be consistent, in terms of microstructural evolution, with experimental data. The present simulation was also successful in explaining the evolution of the particle size distribution of the aggregate. To the best of our knowledge this is the first reported experimental and theoretical investigation on the effect of annealing temperature on nano-ceramic fractal aggregates.

Structural characterization of manganese‐substituted nanocrystalline zinc oxide using small‐angle neutron scattering and high‐resolution transmission electron microscopy

A series of zinc oxide (ZnO) nanoparticles, substituted with manganese di-oxide, have been synthesized through a modified ceramic route using urea as a fuel. X-ray diffraction and high-resolution transmission electron microscopy studies indicate that the sizes of the ZnO particles are of nanometer dimension. Particles remain as single phase when the doping concentration is below 15u2005mol%. Small-angle neutron scattering indicates fractal-like agglomerates of these nanoparticles in powder form. The size distributions of the particles have been estimated from scattering experiments as well as microscopy studies. The average particle size estimated from small-angle scattering experiments was found to be somewhat more than that obtained from X-ray diffraction or electron microscopy measurement.

Smoothening of the non-Euclidean surface of Nd2O3 doped CeO2 nanoceramic grains under sintering: an ultra-small angle x-ray scattering investigation and a computer simulation study

Smoothing of the fractal rough surface of Nd2O3 doped CeO2 ceramic under sintering has been observed in an ultra-small angle x-ray scattering investigation. The surface fractal dimension of 2.6 for the non-sintered specimen reduces with sintering temperature and gradually attains a value of 2.0, which corresponds to a smooth surface, at a high enough sintering temperature. A Monte Carlo based computer simulation has been attempted to explain the smoothing of such a fractally rough surface due to the diffusion based surface transport of the materials from a region of positive curvature to one of negative curvature. The variation of the interface width and the evolution of the fractal dimension with sintering have been estimated from this model simulation.