EFFECT OF ADDITIVES ON THE MORPHOLOGY AND MAGNETIC-PROPERTIES OF CRO2 IN THE HYDROTHERMAL DECOMPOSITION OF CRO3

A hydrothermal decomposition reaction of CrO3 in the presence of H2O and O2 Was carried out in the range of pressure between 4000 and 4300 psig to investigate the effect of various additives on the morphology and magnetic properties of prepared CrO2 powder. The addition of 5-10 wt % Sb2O3 based on CrO3 improved the morphology and magnetic properties of CrO2 for its use as a magnetic recording powder in audiotape. CrO2 crystals containing only 0.4-3 wt % Sb2O3 as an additive produced CrO2 powder which is suitable for use in audiotape and has a high value of saturation magnetization (B(s)) and remanence magnetization (B(r)). Cr2O3, a highly ferromagnetic needle shape of gamma-Fe2O3, barium ferrite, and a rutile type of TiO2 could not improve the morphology and magnetic properties of prepared CrO2. It has been proposed that Sb2O3 interacting with CrO3 on the surface of the crystal growing plane promotes the reduction of CrO3 to produce a needle type of anisotropic CrO2 particles.