Cobalt oxide (Co203) is an expensive cobalt oxide with a theoretical cobalt content of 71.06%, an oxygen content of 28.94%, and a density of 6.079/cm3. It is a black amorphous powder that generates cobalt oxide (Co304) after heating. Cobalt oxide is an unstable compound and cannot be freed. The cobalt oxide commonly referred to actually still contains a certain amount of cobalt tetraoxide. Co203 is only stable in a hydrated state. This hydrate will dehydrate and transform into the intermediate oxide cobalt tetraoxide (Co304) at 265�°C. Cobalt oxide is reduced to cobalt tetraoxide (Co304) by H2 at 125�°C, reduced to CoO at 200�°C, and reduced to cobalt metal at 250�°C. Cobalt oxide is insoluble in water. After dissolving in water, it decomposes into hydrates when it encounters water. It is insoluble in water, but soluble in acid and forms corresponding salts.