Kinetics of high temperature oxidation and chromia volatilization for a binary Ni-Cr alloy

The volatilization of the external chromia layer formed by oxidation of a Ni-30Cr alloy was studied at 1000, 1100, 1200 and 1300 degrees C. This was done by analyzing the mass gain curves obtained by thermogravimetry on the basis of the differential equation that describes the oxidation kinetic, taking into account at each step the loss of Cr2O3 oxidized again into gaseous CrO3. The quantification of the parabolic constant and the volatilization constant was done by drawing m.dm/dt = K-p-K-v.m. This led to the values of both K-p and K-upsilon for the four tested temperatures. These were compared to chromium balance sheets obtained by measuring the thicknesses of the chromia layer and chromium depletion in the alloy. A good agreement was found between the two methods. They both follow an Arrhenius law and precise values of the two constants are provided.