Kinetics of N2 Desorption from the Surfaces of Iron–Nitrogen Solid Solutions

Abstract

The kinetics of nitrogen desorption from iron surfaces was studied between 400 ° and 550 °C. The nitrogen desorbed isothermally into the gas phase was made available to the surface by diffusion from within the iron at the desorption temperature. The method of rate measurement involved the collection and volumetric measurement of gas samples at low pressures from specimens only a few square centimeters in area. Specimens were prepared by nitrogenizing zone-refined iron with NH3–H2 mixtures having a range of N2 fugacity between 10 and 3000 atm. The surfaces were then cleaned by ion bombardment in a bakeable high-vacuum system.The kinetics of nitrogen desorption from iron was observed to be a surface-controlled process, which showed first-order dependence upon the nitrogen concentration in the iron when conventional ion-bombardment cleaning procedures were employed. However, it was discovered that carbon monoxide is generated in glass systems during ion bombardment and can contaminate the iron surface. When ...