Mechanism of growth of the open circuit insulating Oxide films on valve metals

Abstract

The kinetics of growth of the open circuit insulating oxide films on Hf, T i . Nb, Zr and Al were studies in many salt solutions using potential and capacitance measurements. The effect of salt type and concentration, oxygen concentration, temperature and surface pretreatment on the growth kinetics were also investigated. In all cases, the potential and the reciprocal capacitance were found to increase linearly with logarithm of time. It is assumed that the oxide film grows via the solid state mechanism under the influence of highly enough electric field strength to cause the ionic migration. The field is created as a result of the adsorption of the electrolyte anions onto the metal oxide surface. The estimated field strengths (H = lo6 Vcm-I) are in favour with the proposed mechanism.The resultsshowed also that the growth rate constant is a function of the field strength.