Oxidation/Vaporization Kinetics of Cr 2 O 3

The weight loss of Cr 2 O 3 in oxidizing environments (Po 2 = 1 to 10 −3 atm) at 1200°C was measured. Both hot‐pressed and sintered Cr 2 O 3 pellets were investigated in O 2 /Ar gas mixtures, and the dependence of the weight loss on the O 2 partial pressure, the gas flow rate, and the total pressure was determined independently. The experimentally determined O 2 partial pressure dependence (rate ∝ PO 2 3/4 ) corresponds to that expected for the reaction Cr 2 O 3 (s)+3/2O 2 ⇌2CrO 3 (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 Cr 2 O 3 . Evaporation coefficients for the loss of CrO 3 (g) under the experimental conditions were <0.01.