Ilmenite-rutile-iron and ulvospinel-ilmenite-iron equilibria and the thermochemistry of ilmenite (FeTiO 3) and ulvospinel (Fe 2TiO 4)

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 FeTiO 3, TiO 2 and Fe 2TiO 4 have been modelled from available data in the literature. For ilmenite-rutile-iron (IRI), μO 2 ( ± 140) = −570745 + 97.278 T + 50278 T In T (800 < T < 1042) = −578438 + 139.612 T (1042 < T < 1184) = −574852 + 136.606 T (1184 < T < 1340) and for ulvospinel-ilmenite-iron (UII), μO 2( ± 100) = −505563 + 4.990 T + 13.315 T In T (900 < T < 1042) = −521274 + 112.599 T (1042 < T < 1184) = −587764 + 553.582 T- 54.3800 T In T (1184 < T < 1500). ( μO 2 = joules per mole; T = Kelvins; reference pressure = 10 5 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 TiO 2 or FeTiO 3, or both. For the UII equilibrium, results indicate Fe 2TiO 4 probably has the theoretically ideal zero point entropy of 2 R In 2, caused by mixing of Fe 2+ and Ti on the octahedral site of this inverse spinel.