A.K. Patra

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.

Characterization of porous materials by small-angle scattering

Characterization of porous materials by small-angle scattering has been extensively pursued for several years now as the pores are often of mesoscopic size and compatible with the length scale accessible by the technique using both neutrons and X-rays as probing radiation. With the availability of ultra small-angle scattering instruments, one can investigate porous materials in the sub-micron length scale. Because of the increased accessible length scale vis-a-vis the multiple scattering effect, conventional data analysis procedures based on single scattering approximation quite often fail. The limitation of conventional data analysis procedures is also pronounced in the case of thick samples and long wavelength of the probing radiation. Effect of multiple scattering is manifested by broadening the scattering profile. Sample thickness for some technologically important materials is often significantly high, as the experimental samples have to replicate all its essential properties in the bulk material. Larger wavelength of the probing radiation is used in some cases to access large length scale and also to minimize the effect of double Bragg reflections.

Some key issues pertaining to analysis of small-angle scattering data affected by multiple scattering

The relevance of accounting for multiple scattering effects in small-angle scattering studies has increased today as more number of high resolution small-angle scattering facilities are available to probe large inhomogeneities. The effect of multiple scattering and the data analysis procedure depends upon the degree of multiple scattering whose measure in a specimen is conveniently expressed by N (= t/L the ratio of specimen thickness t to scattering mean free path L). It also depends upon the relative magnitude of the scattering mean free path L of radiation inside the matrix vis-a-vis the linear dimension R of the inhomogeneities. For L»R, the scattering medium can be treated in a mean field way as far as the description of multiple scattering is concerned. Such a medium is termed as effective medium. But when the condition L>>R is invalidated, the statistical nature of the medium manifests. In the present paper, some key issues pertinent to analysis of small-angle scattering data affected by multiple scattering are addressed.

Two-dimensional position sensitive neutron detector

A two-dimensional position sensitive neutron detector has been developed. The detector is a3He + Kr filled multiwire proportional counter with charge division position readout and has a sensitive area of 345 mm × 345 mm, pixel size 5 mm × 5 mm, active depth 25 mm and is designed for efficiency of 70% for 4 Å neutrons. The detector is tested with 0.5 bar3He + 1.5 bar krypton gas mixture in active chamber and 2 bar4He in compensating chamber. The pulse height spectrum recorded at an anode potential of 2000 V shows energy resolution of ∼25% for the 764 keV peak. A spatial resolution of 8 mm × 6 mm is achieved. The detector is suitable for SANS studies in theQ range of 0.02-0.25 Å−1.

SANS investigation on evolution of pore morphology for varying sintering time in porous ceria

Precipitates of ceria were synthesized by homogeneous precipitation method using cerium nitrate and hexamethylenetetramine at 80°C. The precipitates were ground to fine particles of average size ∼0.7 μm. Circular disks with 10 mm diameter, 2 and 3 mm thickness were prepared from the green compacts by sintering at 1300° C for three different sintering times. Evolution of the pore structures in these specimens with sintering time was investigated by small-angle neutron scattering (SANS). The results show that the peak of the pore size distribution shifts towards the larger size with increasing sintering time although the extent of porosity decreases. This indicates that finer pores are eliminated from the system at a faster rate than the coarser ones as sintering proceeds and some of the finer pores coalesce to form bigger ones.

Effect of porosity and pore morphology on the low-frequency dielectric response in sintered ZrO2—8 mol% Y2O3 ceramic compact

Effect of porosity and pore size distribution on the low-frequency dielectric response, in the range 0.01–100 kHz, in sintered ZrO2—8 mol% Y2O3 ceramic compacts have been investigated. Small-angle neutron scattering (SANS) technique has been employed to obtain the pore characteristics like pore size distribution, specific surface area etc. It has been observed that 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 size distribution and pore morphology significantly. Unlike normal Debye relaxation process, where the loss tangent vis-à-vis the imaginary part of the dielectric constant shows a pronounced peak, in the present case the same increases at lower frequency region and an anomalous non-Debye type relaxation process manifests.

SAXS and Photoluminescence Studies on Eu+3 and Tb+3 Doped Y2O3 Nanoparticles

Eu3+ and Tb3+ doped nanocrystalline Y2O3 powders with different Eu3+/Tb3+ concentrations were synthesized by gel‐combustion process. The photoluminescence of these nano‐particles show a strong dependence on the relative concentration of the dopants and sample annealing temperature. Based on the results from SAXS, the improved luminescence for the powders annealed at higher temperature is attributed to reduced moisture affect at relatively smaller surface area of the particles.

Carbide precipitates in solution-quenched PH13-8 Mo stainless steel: A small-angle neutron scattering investigation

This paper deals with the small-angle neutron scattering (SANS) investigation on solution-quenched PH13-8 Mo stainless steel. From the nature of the variation of the functionality of the profiles for varying specimen thickness and also from the transmission electron microscopy (TEM), it has been established that the small-angle scattering signal predominantly originates from the block-like metallic carbide precipitates in the specimen. The contribution due to double Bragg reflection is not significant in the present case. The single scattering profile has been extracted from the experimental profiles corresponding to different values of specimen thickness. In order to avoid complexity and non-uniqueness of the multi-parameter minimization for randomly oriented polydisperse block-like precipitate model, the data have been analyzed assuming randomly oriented polydisperse cylindrical particle model with a locked aspect ratio.