Thermal transformations of iron(III)-nickel(II) mixed oxide gels

Iron-nickel mixed oxide gels have been prepared by a hydroxide co-precipitation technique and their thermal transformation has been studied by thermal analyses, X-ray diffraction and infra-red spectroscopy. Differential thermal analysis (DTA) of the hydrated ferric oxide gel indicates the presence of three exothermic peaks along with a broad endotherm. Addition of nickel oxide decreases the intensities of the exotherms and the peaks are completely absent in the samples containing more than 10 mol % of NiO. On the other hand these samples show the presence of three endothermic peaks. Thermal analysis of the sample containing 50 mol % of NiO indicates the formation of a precursor at around 185° C which changes to nickel ferrite at around 275° C. This ferrite slowly crystallizes with a broad exotherm in the range 280 to 550° C.