Boro/carbothermal reduction synthesis of uranium tetraboride and its oxidation behavior in dry air

Uranium tetraboride (UB 4 ) was successfully synthesized by boro/carbothermal reduction of UO 2 with B 4 C and carbon as combined reduction agents under flowing argon. The effects of processing temperature and mole ratios of starting materials on phase evolution were studied. XRD results demonstrated that UB 4 was obtained with 3.75 mol% B 4 C in excess based on the UO 2 /B 4 C/C molar ratios of 1:1:1 at 1500°C. SEM observation revealed that submicrometer-sized quasi-spherical UB 4 particles cemented together to be an aggregate. The laser particle size analysis showed that the particle size was in the range of 1-10 μm. The oxidation behavior of UB 4 was also investigated by TG and XRD. The oxidation of UB 4 started at about 500°C and it showed better oxidation resistance than other basic uranium nuclear fuels (UO 2 , UC, UN and U 3 Si 2 ). The oxidation chemical process of UB 4 was presented as a three-step process: (a) the formation of U 3 O 8 and B 2 O 3 oxidation products; (b) the formation of UB 2 O 6 intermediate product by the interaction of U 3 O 8 and B 2 O 3 ; (c) the decomposition of UB 2 O 6 to get U 3 O 8 .