Diffusivity of point defects in the passive film on Fe

Abstract

This chapter presents a study to determine the diffusivity of point defects (Do)in the passive film on Fe based on the combination of the Point Defect Model (PDM), and the surface charge approach. The PDM provides an analytical description of the growth and breakdown of passive films on reactive metal surface. The quantitative analysis of the PDM on the concentration and the transport properties of point defects enable one to estimate the diffusivity of point defects (Do) in the passive film, which appears in the Nemst-Planck equation. The potentiostatic polarization tests revealed that the steady state current density through the passive film formed on Fe for 24 h was independent of film formation potential. The steady state thickness of passive film on Fe varied linearly with film formation potential and the donor density determined from the Mott-Schottky plots for the passive film on Fe was found to decrease exponentially with increasing film formation potential. The diffusivity of point defects in the passive film on Fe was calculated to be 1.69x10-20 cm2s-1.