Oxidation/Vaporization Kinetics of Cr2O3

The weight loss of Cr₂O₃ in oxidizing environments (Po₂= 1 to 10⁻³ atm) at 1200°C was measured. Both hot-pressed and sintered Cr₂O₃ pellets were investigated in O₂/Ar gas mixtures, and the dependence of the weight loss on the O₂ partial pressure, the gas flow rate, and the total pressure was determined independently. The experimentally determined O₂ partial pressure dependence (rate ∝ PO₂^3/4) corresponds to that expected for the reaction Cr₂O₃(s)+3/2O₂⇌2CrO₃(g). The flow rate and total pressure dependencies show that mass transport through a gaseous boundary layer is the rate-controlling step in the oxidation/vaporization of Cr₂O₃. Evaporation coefficients for the loss of CrO₃(g) under the experimental conditions were <0.01.