CRYSTALLOGRAPHIC STUDY OF COBALT TREATMENT ON GAMMA-FE2O3

Chemical analysis and x-ray diffraction measurements of samples during the reaction of cobalt treatment were carried out to study the mechanism of reaction. X-ray diffraction, TEM observation, and magnetic measurements of core gamma-Fe2O3 and the modified particles were performed to investigate the crystal growth of cobalt ferrite on core gamma-Fe2O3 particles. From chemical analysis of Fe2+ and total-iron ions in the reacting suspension and x-ray diffraction measurements of samples during the reaction, it is clear that the lattice constant becomes larger due to the formation of cobalt ferrite on core gamma-Fe2O3 without decrement of Fe2+/total-iron ratio. So, cobalt ferrite on core gamma-Fe2O3 particles is formed not by the oxidation of added Fe2+ ions, but by the electron transfer from Fe(OH)2 to core material. From x-ray diffraction measurements, I400/I311, I220/I311, and I111/I311 were calculated. While I400/I311 and I220/I311 are almost constant, only I111/I311 increases with increasing the amount of cobalt and ferrous ions added. These results show that cobalt ferrite is preferentially grown on (111) plane which is the close-packed plane of spinel lattice.