Oxidation kinetics of acicular iron particles for magnetic recording media

We investigated the kinetics of the oxidation of acicular iron particles by measuring the specific saturation magnetization loss of the samples kept at various temperatures and humidities. The analysis of the kinetics demonstrated that the oxidation is a diffusion-controlled reaction and that the activation energy of the reaction is reduced in the presence of water vapor. We could estimate the magnetization decay over many years, using the reaction rate constant obtained from this study. The lifetime of the iron particles for magnetic recording at 25°C and 10% relative humidity is a hundredfold longer than that at 60°C and 90% relative humidity.