Degradation of passivated iron particles in humid atmospheres

The interaction of water vapor with passivated iron particles used in magnetic recording was studied under different temperature and humidity conditions using a flow microcalorimetric (FMC) technique. Water uptake by passivated iron particles increased linearly with relative humidity ranging from 30% to 70% RH in the temperature range 30°C to 70°C. Mossbauer measurements showed that the ratio of core iron to oxide iron decreased during aging. Particles coated with hydrophobic WC exhibited much less water uptake than particles coated with a less hydrophobic polymer, poly(vinyl alcohol)