R. Divakar

PVA aided microwave synthesis: A novel route for the production of nanocrystalline thoria powder

Abstract A new method is reported for the preparation of nanocrystalline thoria powder that yields pellets of high density. The powder is prepared by denitration of an aqueous solution of thorium nitrate and polyvinyl alcohol (PVA) using microwave heating. The powder was characterized for its surface area and crystallite size by both X-ray line broadening and transmission electron microscopy. The reactivity of the powder was estimated by determining the density of the compacts prepared from these powders and sintered at 1573 K in air. For the sake of comparison, powders obtained by direct denitration were also characterized as above. The X-ray crystallite size for the calcined powders obtained by both routes is found to be ∼10 nm and found to be in agreement with the crystallite size obtained by conventional transmission electron microscopy. The density of pellets prepared from the powder produced by denitration in the presence of PVA was 92–93% of the theoretical density and that obtained with direct denitrated powder was ∼85% of theoretical density.

Thermal expansion characteristics of a titanium modified austenitic stainless steel: measurement by high-temperature X-ray diffraction and modelling using Grüneisen formalism

Abstract The thermal expansion of a titanium modified, swelling resistant austenitic stainless steel designated as D9 is studied by measuring the lattice parameter as a function of temperature in the range 300–1300 K by high-temperature X-ray diffraction technique. The thermal expansion data thus obtained is in reasonable agreement with the typical thermal expansion values reported for similar nuclear grade austenitic stainless steels. However, at temperatures exceeding 900 K, the measured thermal expansivity exhibits a pronounced non-linear increase due partly to the precipitation of complex carbide and intermetallic phases. The high-temperature thermal expansion data obtained in the present study are augmented by modelling the low-temperature thermal expansion behaviour by Gruneisen formalism.

Microwave synthesis of solid solutions of urania and thoria: a comparative study

Abstract Recently a new route for the production of thoria powder that yields pellets of high density had been communicated. In continuation of this study, the method as applied to the preparation of (U, Th)O 2 powders with various compositions is reported here. The powders were characterised for crystallite size by using XRD and transmission electron microscopy and BET surface area. As observed in the case of thoria, the powders obtained in this study were found to be nanocrystalline. The sinterability of the powder was determined by measuring the density of the sintered pellets prepared from these powders. The sintering was carried out at 1573 K in argon atmosphere. The feasibility of calcining and sintering of the solid solutions by using microwave heating was also studied.

A study on the thermal expansion characteristics of Inconel-82® filler wire by high temperature X-ray diffraction

Abstract The lattice parameter ( a ) change with respect to temperature ( T ) has been measured by high temperature X-ray diffraction (HT-XRD) technique for Inconel-82® 1 filler wire used in the TIG welding of a dissimilar joint involving Inconel-600® and commercially pure iron. By taking proper precautions to minimise the temperature gradient across the sample thickness, and by suitably calibrating the shift in 2 θ produced as a result of sample buckling at high temperatures, we could obtain fairly reliable estimates of lattice parameter in the temperature range 300–1200 K. The lattice parameter and the coefficient of mean linear thermal expansion at 300 K, have been found to be 3.546(2)×10 −10 m and 11.03×10 −6 K −1 , respectively.