Kinetics of the Nitrogen Desorption of Liquid Fe-Cr Alloys under Reduced Pressure

Abstract

The rates of nitrogen desorption of liquid Fe-Cr alloys up to 25% Cr were measured under the reduced pressure at 1 600°C.
The rates of nitrogen desorption of liquid Fe-Cr alloys are apparently expressed by the equation of 2nd order reaction in terms of nitrogen content in melts, as shown in the case of the nitrogen desorption of liquid iron, and the rate constant obtained decreases with increasing chromium and oxygen contents. The results are explained by the application of the mixed-control model including the resistances of the mass transfer in the liquid phase and that at the interface where the nitrogen atom transfers into the gas phase only through the effective sites determined by the adsorption equilibrium.
The contributions of the resistance of the mass transfer in the liquid phase and the interfacial resistance to the nitrogen desorption process were considered. The mass transfer in melt may play an important role on the nitrogen desorption at the lower chromium and lower oxygen levels. On the other hand, at higher chromium content, the contribution of the interfacial resistance becomes important even if the oxygen content is low, because the activity coefficient of nitrogen decreases.
The effect of the air leak in the vacuum reaction chamber on the rate of nitrogen desorption is considered by using the present experimental results. It is suggested that, at higher chromium contents, the nitrogen desorption is remarkably retarded in the presence of a small amount of air leak.