Behavior of Iron Oxides in Iron-Rich Zinc Ferrites

Abstract

The changes which occur on heating Zn ferrous ferrites have been studied by means of DTA, TGA, X-ray difiractometry and chemical analysis. It is shown that the low temperature oxidation involves no phase change but that hematite precipitates at high temperatures. The increase in ferrite concentration decreases the rate of oxidation. The precipitation is characterized by an apparent incubation period and precipitation isotherms are expressed by the modified first-order equation, log(1 α) =- k (t-t₀), where α, t and k are fractional precipitation, time and proportionality constant which depends on temperature, respectively. The activation energy of this process is 30.0±0.5 kcal/mol irrespective of the ferrite compostion. Substitution of Ni for Zn decreases the rate of hematite precipitation, which has been successfully explained in terms of the cation distribution in spinel lattice.