Phase Formation and Solid State Structure on Calcination of a Nickel Ferrite Acetate Precursor

Abstract

The thermal decomposition of a freeze dried Ni-Fe-μ-oxo-acetate results in the formation of an amorphous nickel ferrite. Crystallization of the spinel NiFe2O4 takes place between 300 and 500°C. High disperse amorphous (or less crystalline) products with specific surfaces up to 500 m2/g can be obtained by carful decomposition between 260 and 300°C. Raising the calcination temperature and calcination time effects a decrease of porosity and of the specific surface. The primary nanocrystalline spinel powder is strongly agglomerated. During an annealing process between 300 and 500°C the crystallite size is increased but the mean diameter of agglomerates of about 15 μm does not change. A combination of milling and ultrasonic dispersion allows the adjustment of grain sizes < 1 μm with a narrow grain size distribution.