Comparative study on the chemical stability of Fe_3O_4 and NiFe_2O_4 in molten salts

摘要

Tests on Ni_xFe_(3-x)O_4 spinels, considered as promising materials in the aluminium production, were performed on Fe_3O_4 and NiFe_2O_4. First, FeAl_2O_4 aluminate was spontaneously formed by Fe_3O_4 immersion at 960 ℃, due to Fe~(3+)/Al~(3+) substitution into the spinel structure. Then, stability of aluminate compound was investigated into cryolite melt and results showed a rapid dissolution when the aluminate composition tends to FeAl_2O_4. Kinetic studies demonstrated that the spinel dissolution was around twentyfold higher than aluminate formation, confirming the micrographic observation. To prevent it, nickel was added in the spinel structure up to NiFe_2O_4 and no dissolution was observed.