Sublimation Behavior of Industrial Grade Molybdenum Trioxide

Volatilization loss of molybdenum trioxide (MoO3) always takes place during the synthesis of Mo-containing alloying steel in the steelmaking process. In this work, the sublimation kinetics and mechanism of MoO3 in the range of 1273 to 1373 K were analyzed, in which the methods of model fitting, FE-SEM, EDS, and thermodynamic calculation were adopted. The results showed that sublimation of high-purity MoO3 (defined as the case III) and industrial grade MoO3 with the thickness of 3 mm (defined as the case II) were mainly controlled by the chemical reaction on the surface; increasing the thickness of industrial grade MoO3 to 7 mm (defined as the case I), the diffusion model was obeyed, instead. Activation energies of the three cases were extracted to be 127.489 (case III), 197.418 (case II), and 89.76 kJ/mol (case I), respectively. With the adoption of lever principle, the weight ratio of melting (from solid to liquid) to vaporization (from liquid to gas) during the whole volatilization process was estimated, i.e., 2.52:1 for case III, 0.84:1 for case II, and 5.89:1 for case I. The possible sublimation mechanism of industrial grade MoO3 was also proposed.