Abstract

Mathematical study of the effects of the mass gain achieved during heating and of the mass loss by Cr2O3 volatilization on the constants characterizing the high temperature oxidation rate of chromiaforming alloys

Author(s): Patrice Berthod

After a first recently presented numerical work concerning the effect of the existence of an initial mass gain – for example achieved during the heating up to the stage temperature – on the determined values of the parabolic constant, the present study is devoted to the influence of the same initial mass gain on the couple of kinetic values describing the thickening of the chromia external scale (kp) on Cr-rich alloys aswell as the volatilization of a part of this oxide when temperature is high enough to allow having a significant chromia loss by this phenomenon (kv). For that several theoretical mass gainswere built fromvalues of kinetic constants selected in the available experimentally determined ones, for different values ofmass gain at heating chosen in a range of credible values. It appeared that an initial mass gain effectively influences the values of kp and kv determined according to the {(m/S)×d(m/S)/dt = kp – kv × m} method. The higher the initial mass gain the farer the obtained values by comparison with the injected ones. In contrast, if the initial mass gain is taken into account the exact values of the injected kp and kv are found.