Mechanism of chromium oxidation

Abstract

The oxidation of evaporated chromium films has been investigated in the temperature range 523–723 K. The kinetics of oxidation were followed using two techniques, one which measured the resistance of the oxidizing metal film, the other which monitored the growth of the oxide layer ellipsometrically. The measurements verified the existence of a transition in the oxidation rate near 623 K, the reaction obeying a logarithmic-type rate law below this temperature and a parabolic rate law above this temperature. In conjunction with the kinetics change, the oxide film annealed to give a polycrystalline product from the original disordered layer.

The results of kinetic, higher oxide and pressure dependence experiments indicate that below the transition temperature the oxidation reaction is determined by the field assisted transport of cation holes, whilst above this temperature the reaction is diffusion controlled. A mechanism is proposed which explains the observed behaviour and the kinetic transition.