Phase stability of uranium monocarbide under laser irradiation in argon and methane environments

Abstract

Laser irradiation is becoming a technique of choice to study materials behavior under extreme conditions due to its ability of achieving very high temperatures within minute times. Recent studies have indicated that laser irradiation can be used to synthesize inorganic compounds from various organic compounds that usually decompose or oxidize if conventional heat treatment techniques are used. It was also shown that metallic uranium can be synthesized if uranium mononitride is laser irradiated under inert environments. This current study focused on the high temperature (in the order of 2500 K) behavior of laser-irradiated uranium monocarbide (UC) using a 1070 nm laser with a nominal spot size of 37 µm and 50–250 W power and density of 139 – 694 Wcm−2 under argon (Ar(g)) and methane (CH4(g)) environments. Laser irradiation of UC at 50 W did not show significant UC decomposition under Ar(g) where no change in the concentration of UO2 or formation of oxygen-dissolved carbide phases were observed. However, the presence of secondary oxygen-dissolved phases such as UC1-xOx, assuming stoichiometric compositions, and UC2-yOy in UC samples laser irradiated under a similar environment at 50–250 W suggested a slight evolution of carbon from UC in the presence of impurity oxygen. Up to 70 wt.% dicarbide (α-UC2) phase formed when UC was laser irradiated up to 50 W under CH4(g). These observations suggest high thermal stability of UC at macroscale under inert atmosphere in the absence of oxygen impurities and a high reactivity of UC with carbon-rich environment up to 50 W laser irradiation. Crystallographic properties such as lattice strain and crystallite sizes of these different phases showed complicated variation without significant correlation to the laser irradiation conditions, and these observations are also discussed here.