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Microstructural development in sintered uranium dioxide pellets was studied with reference to (1) origin of the powder and (2) time, temperature and other conditions of sintering. Changes in the microstructure of the sintered pellets when reheated at temperatures below and above sintering temperature for various periods of time have also been studied. It was found that a judicious choice of the powder with desired characteristics and a judicious choice of optimum conditions for sintering of the powder have to be utilized to attain controlled microstructure. The grain size can be increased and grain development made more perfect by an appropriate thermal treatment of the sintered pellets.

It was shown earlier that uranium dioxide derived from different compounds exhibited variations in the sintering behaviour and to attain maximum densification, the sintering should be carried out within a temperature range, specific for each of the powders.In the present work, the sintering behaviour of uranium dioxide derived from ammonium diuranate prepared by different methods, was studied in an atmosphere of hydrogen. Significant differences in the sintering (densification) behaviour of the powders was noted under identical sintering (firing) treatments. The influence of variations in sintering treatment, such as rates of heating or soaking periods, on the densification of the samples of different origins was studied. It was found that the sintering behaviour depended on both the powder characteristics and the sintering treatment. Attempts were made to relate the origin and thermal history of the UO2 with its powder characteristics; and its sintering behaviour to its powder characteristics and the fir...

The influence of powder properties and sintering treatments on the development of microstructure in sintered UO2 pellets was studied. The nature and type of porosity and grain morphology are influenced by the calcination temperature and sintering treatment and these influences persist even at a high sintering temperature.

The investigation is aimed at a study of the relations between powder properties, sintering treatments and the densification and microstructure development in urania pellets. Urania powders for this study were prepared from ammonium diuranate by decomposition and reduction at various temperatures, namely, 400°, 600°, 900°, 1200° and 1500°C. Pellets prepared from these powders were sintered at temperatures in the range of 1200° to 1700°C with different soaking periods.The influence of (i) sintering temperatures, (ii) soaking periods at different temperatures, (iii) intermediate soaks at varying time periods at various temperatures, (iv) reheating of prepared sintered pellets and (v) rates of heating during sintering, on the density and microstructure development of pellets was studied in this investigation.The study revealed that urania pellets of specified density and grain development can be prepared by first attempting to achieve densification and then continuing the thermal treatments to attain the des...

As reported earlier, electrical conductivity of sintered uranium dioxide pellets depended on the calcination temperature and the sintering treatments, and could be related to the microstructure attained. The highest sintering temperature studied was 1700° C. In the present study, high density pellets prepared by sintering at 1500° C were refired at 1800°, 1900° and 2000°C. Though there were no significant changes in the densities, the electrical conductivity of the samples varied considerably showing a minima at a refiring temperature of 1900°C. Attempts were made to correlate the changes in electrical conductivity to the microstructural changes which still seem to be influenced by the thermal history of the samples.

In an earlier investigation, it was reported that the electrical conductivity of sintered compacts of urania powders depended on the calcination temperature and the sintering treatments. In the present study, the conductivity of the samples sintered at temperatures between 1100°C to 1700°C were studied. Attempts were made to correlate the changes in the conductivity with the microstructure of the samples. The details of the microstructure were studied by electron microscopy.