1994 年 34 巻 9 号 p. 739-745
en-abstract= The phase equilibria and the activities of the constituents in FeO·Cr2O3-MgO·Cr2O3 spinel solid solution saturated with Cr2O3 have been determined at temperature ranging from 1423 to 1723 K, by the equilibrium of iron dissolved in liquid silver held in spinel crucible with CO-CO2 gas mixture, to clarify the thermodynamic properties of chromium ores in chromium ore smelting reduction process being recently developed.
The solubility of FeO·Cr2O3-MgO·Cr2O3 spinel in Cr2O3 was found to be negligible. On the other hand, very small solubility of Cr2O3 in the spinel was observed, but the nonstoichiometry of spinel solid solution was insignificant and spinel phase was reasonably approximated as stoichiometric (Fe, Mg)O·Cr2O3.
The free energy of formation of FeO·Cr2O3 was determined as
Fe (s)+1/2O2 (g)+Cr2O3 (s)=FeO·Cr2O3 (s),
ΔG°=-307600+66.82 T (1423-1723 K) (J/mol).
The activities of constituents in FeO·Cr2O3-MgO·Cr2O3 spinel solid solution coexisted with Cr2O3 showed negative deviation from ideality. It was observed that the spinel solid solution takes regular solution behavior, and α-function of FeO·Cr2O3-MgO·Cr2O3 system was determined as follows;
αFeO·Cr2O3=RT ln γFeO·Cr2O3/(1-NFeO·Cr2O3)2
=αMgO·Cr2O3=RT ln γMgO·Cr2O3/(1-NMgO·Cr2O3)2
=-12800 (J).
