Studies on Zinc and Barium Ferrites

Abstract

The formation of zinc ferrite by the direct addition of zinc and ferric oxides was studied at various temperatures between 580° and 660° C. During the first two or three hours of heating, the reaction obeys Tamman's logarithmic law on reactions between solid phases. An apparent equilibrium appears afterwards. At 580° C. the reaction takes place extremely slowly. It is found by thermal analysis that there is no evidence for the formation of a compound containing more zinc oxide than ZnFe2O4, at least not below 1,070° C. The solubility of zinc ferrite in normal and two‐normal sulfuric acid is studied. A mixture of 7.5 per cent sulfur dioxide in air, passed on zinc ferrite heated at 450° C., decomposes it slowly and liberates the zinc as zinc sulfate.The formation of barium ferrite resulting from the heating of a mixture of barium carbonate and ferric oxide was studied at 720° C. It also obeys Tamman's law. The apparent equilibrium towards which the reaction tends is destroyed when the mixture is stirred and heated again at the same temperature : the reaction goes on according to Tamman's law, the velocity of reaction being, however, considerably smaller than originally. The results are discussed and explained on the basis of diffusion.