Sintering of UN as a function of temperature and N2 pressure

The sintering of uranium mononitride (UN) depends on temperature and the N 2 pressure maintained over the nitride during heat treatment. At a given temperature, an N 2 pressure that maintained the UN in the single‐phase region slightly above the phase boundary where the reaction UN→U+½N 2 (g) occurred was most effective in accelerating the sintering of single‐phase UN. For example, specimens sintered at 1600°C under N 2 pressures of either 1140 or 1.7XlO −4 torr had essentially identical compositions, but the density of the former was 10.78 g/cm 3 (75% of theoretical), whereas that of the latter was 12.20 g/cm 3 (85% of theoretical). Results were similar at temperatures up to 2100°C. The X‐ray lattice constant of UN sintered at reduced N 2 pressures was slightly larger than that of UN sintered in 1140 torr of N 2 . The observed constants ranged from 4.88904 to 4.88991 Å; the combined O+C content varied from 400 to 900 ppm.