Ilmenite-rutile-iron and ulvospinel-ilmenite-iron equilibria and the thermochemistry of ilmenite (FeTiO₃) and ulvospinel (Fe₂TiO₄)

The ilmenite-rutile-ironequilibriaand ulvospinel-ilmenite-iron equilibria have been studied in the temperature range 990-1320 and 1050-1355 K, respectively, using an electrochemical technique. Effects on experimental results from deviations from the ideal stoichiometries FeTiO₃, TiO₂ and Fe₂TiO₄ have been modelled from available data in the literature. For ilmenite-rutile-iron (IRI), μO₂ ( ± 140) = -570745 + 97.278T + 50278T In T (800 < T < 1042) = -578438 + 139.612T (1042 < T < 1184) = -574852 + 136.606T (1184 < T < 1340) and for ulvospinel-ilmenite-iron (UII), μO₂( ± 100) = -505563 + 4.990T + 13.315T In T (900 < T < 1042) = -521274 + 112.599T (1042 < T < 1184) = -587764 + 553.582T- 54.3800T In T (1184 < T < 1500). (μO₂ = joules per mole; T = Kelvins; reference pressure = 10⁵ Pa (1 bar); quoted uncertainties are one standard deviation). Results from the IRI equilibrium are in good agreement with most of the previous phase equilibrium studies. In detail, however, there is evidence of possible error in the calorimetric data for TiO₂ or FeTiO₃, or both. For the UII equilibrium, results indicate Fe₂TiO₄ probably has the theoretically ideal zero point entropy of 2R In 2, caused by mixing of Fe²⁺ and Ti on the octahedral site of this inverse spinel.