On the Rates of Nitrogen Absorption and Desorption in Liquid Iron

Abstract

The rates of nitrogen absorption and desorption of levitated iron droplets have been measured. This study made it clear that the rate of reaction of gas with liquid iron is determined by the mass transfers between two phases. The following equation was obtained in accordance with the two film theory.
-n_N=k_m (n_N-√ αn_N+ (α/2) ²+ (n^e_N) ²+ α/2)
where α= k_mRTK²_N/ 2k_gf′²
Applying this equation to various experimental conditions, the following became clear. The reaction is first-order when there exists no gas boundary layer, for example, the nitrogen absorption from pure nitrogen gas injection. The reaction is between first- and second-order when there are two boundary layers, for example, the nitrogen desorption into pure argon gas. Oxygen which is a surface active element, retards the reaction rate because it decreases the effective surface area. This influence disappeared at about 2 100°C. Other alloying elements change the value of a affecting the activity of nitrogen in liquid iron.