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 mechan ism of reaction. X-ray diffraction, TEM observation, and magnetic meas urements of core gamma-Fe2O3 and the modified particles were performed to investigate the crystal growth of cobalt ferrite on core gamma-Fe2 O3 particles. From chemical analysis of Fe2+ and total-iron ions in th e reacting suspension and x-ray diffraction measurements of samples du ring the reaction, it is clear that the lattice constant becomes large r due to the formation of cobalt ferrite on core gamma-Fe2O3 without d ecrement of Fe2+/total-iron ratio. So, cobalt ferrite on core gamma-Fe 2O3 particles is formed not by the oxidation of added Fe2+ ions, but b y the electron transfer from Fe(OH)2 to core material. From x-ray diff raction measurements, I400/I311, I220/I311, and I111/I311 were calcula ted. 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 (1 11) plane which is the close-packed plane of spinel lattice.