Oxidation kinetic analysis of a mixed uranium dicarbide and graphite compound

The oxidation of a mixed uranium dicarbide and graphite powder has been investigated by simultaneous thermal gravimetric (TGA) and differential thermal (DTA) analyses coupled with gas phase chromatography. For isothermal oxidation conditions with temperatures below 330 °C, only the UC2 chemical phase is progressively oxidised into U3O8 oxides. Parabolic weight gain curves as a function of oxidation over time were obtained. A detailed kinetic study is proposed to establish a pseudo-steady-state during the oxidation process. Using an experimental method based on the sudden temperature increases, a single rate-limiting step has been validated and then modelled by a 3D diffusion law. An apparent activation energy calculated from the Arrhenius representation has been evaluated at −35 kJ/mol, thus describing the diffusion of oxygen through the oxide layer.

► Experimental study of uranium carbides and graphite powder oxidations. ► Single rate limiting step identification by extensive kinetic analysis. ► Pseudo-steady-state validation during chemical conversion. ► Combination of TGA, TDA, XRD and gas phase chromatography results.