Untersuchungen über die verträglichkeit von uranmononitrid mit molybdän, wolfram und thoriumoxid bei hohen temperaturen

Abstract

After annealing uranium mononitride and UN-Momixtures on molybdenum supports above 2000 °C under a vacuum of 10 −2-10 −5 torr, a molybdenum content of about 0.23 wt % in UN along with an increase of the UN lattice parameter observed at room temperature was observed. Though the appearance of substoichiometric uranium mononitride seems, in principle, to be possible, the cooling rate may not be sufficient to freeze in this condition. The decomposition of UN initiated at high temperatures under vacuum results in a γ-U-Mo-phase which can be detected by metallographic and X-ray methods; by microprobe analysis about 21–22 wt % of Mo and 78 wt % of U were detected. Moreover, the microanalytical studies showed up appreciable amounts of nitrogen (about 1 wt %). On the molybdenum sheet supports, UO 2-crystals orientated in [111] direction can be detected subsequent to annealing at 2400 °C under N 2 and X-ray diffraction also revealed a UN 2−x-phase with a lattice constant a 0 = 5.344 A ̊ . The X-ray studies with annealed UN-tungsten specimens up to 2400 °C do not give indications on possible reactions or solubilities. Changes in the lattice parameters could not be observed. After annealing of UN-ThO 2-mixtures carried out on tungsten-sheet- and ThO 2 supports no remarkable change in the UN lattice parameter is detected up to 2400 °C under 500 torr of nitrogen. After annealing on molybdenum supports a slight change Δa 0 = 0.005 A ̊ is measured following annealings at 1750 °C and 2000 °C under vacuum. However, the UO 2 impurities form a solid solution together with thorium oxide, as can be observed by the variation of the lattice constants. The upper temperature limits of satisfactory compatibility strongly depend on the annealing atmosphere. In the case of UN-Mo under 10 −5 torr of N 2 it is at 1550 °C and rises to about 2300 °C under 300 torr of N 2. Slightly higher temperatures are applicable to UN-W.