Some Preparative Methods and Physical Characteristics of Uranium Dioxide Powders.

Abstract

Previous results on the dependence of UO/sub 2/ properties upon their mode of preparation are confirmed and their conclusions extended to U0/sub 2/ powders made by a large variety of oxidation and reduction methods. Low temperature preparations (350 deg C) prcduced the smallest crystallite sizes (200 A); the crystallite size of UO/sub 2/ made at 800 deg C was considerably larger (1000 A). The real density of U0/sub 2/ preparation depends upon its 0 to U ratio ard on the density of its parent higher oxide. The density was not dependent on reduction temperature up to 1200 deg C. However, heating low density U0/sub 2/ above its temperature of preparation causes an increase in density. In many cases the liquid displacement densities were considerably below the helium displacement values, indicating measurable amounts of open porosity. No correlation was found between density and total BET surface area. There also appears to be no relationship between the density and total surface area of the parent ammonium diuranate precipitates and the derivative U0/sub 2/ powders. The particle size distribution and total BET surface area of a U0/sub 2/ preparation depend upon the particle size distribution and surface area of the higher oxide frommore » which it was prepared by reduction and on the reduction temperature itself. In the reduction of UO/sub 3/, the uranium dioxide reduction product was most similar in surface area and particle size distribution to the parent oxide at low temperatures (480 deg C). Particle growth occurred at higher temperatures. No change in particle size distribution, but an increase in surface area was observed on low temperature reduction (500 deg C) of U/sub 3/O/sub 8/ to U0/sub 2/ . There was less particle breakdown at higher reduction temperatures. This suggests that frac turing occurs in the U/sub 3/O/sub 8/ particles on reduction to U0/sub 2/ at the lower temperature; at higher temperatures, the strains are annealed out. (P.C.H.)« less