Kinetics of Nitrogen Transfer through an Iron Surface

Abstract

A study has been made of the kinetics of nitrogenization and denitro-genization of v- iron at 1000 ~ in the presence of nitrogen, water vapor, and hydrogen in the gas phase. For a given ratio, PHJPH.)o, the rate is shown to be directly proportional to the square root of the nitrogen partial pressure. It is shown that under these conditions nitrogen transfer is dominantly controlled by the surface reaction rather than by diffusion. A rate equation is derived for the condition of almost complete coverage of surface sites by adsorbed oxygen atoms. The rate equation derived for this l imiting case states that the rate of nitrogen reaction on the surface of iron, for a given nitrogen activity, is inversely proportional to the activity of oxygen in the system. This is in agreement with the experimental observations. In previous work by the authors (1, 2) on kinetics of solution of nitrogen in purified iron (in =, v, or b state), the reaction rate was found to be controlled