The Parabolic and Logarithmic Oxidation of Copper

A study of the growth of oxide films on abraded copper surfaces, made from measurements obtained by the electrolytic reduction method, shows that copper may oxidize parabolically over a limited thickness range and then change to a logarithmic growth rate. The parabolic growth is expressed by the equation y 2 = K t + A , where y is film thickness, t is time, and K and A are constants. After the rate of growth becomes logarithmic, it is expressed by y = k log a t + t ′ + 1 where y is film thickness, t is time, and k , a and t ′ are constants. Thus it appears that copper, which has been quoted often as a metal that is typical of parabolic oxidation, may also oxidize logarithmically. The results are discussed in the light of an electrical theory which provides conditions that may permit a parabolic oxidation rate for ordinary thickness ranges and require a logarithmic rate for the more advanced ranges.