The heat-capacity of ilmenite and phase equilibria in the system Fe-T-O
Low temperature adiabatic calorimetry and high temperature differential scanning calorimetry have been used to measure the heat-capacity of ilmenite (FeTiO3) from 5 to 1000 K. These measurements yield S2980 = 108.9 J/(mol · K). Calculations from published experimental data on the reduction of ilmenite yield Δ2980(I1) = −1153.9 kJ/(mol · K). These new data, combined with available experimental and thermodynamic data for other phases, have been used to calculate phase equilibria in the system Fe-Ti-O. Calculations for the subsystem Ti-O show that extremely low values of ƒO2">ƒƒO2 are necessary to stabilize TiO, the mineral hongquiite reported from the Tao district in China. This mineral may not be TiO, and it should be re-examined for substitution of other elements such as N or C. Consideration of solid-solution models for phases in the system Fe-Ti-O allows derivation of a new thermometer/oxybarometer for assemblages of ferropseudobrookite-pseudobrookitess and hematite-ilmenitess. Preliminary application of this new thermometer/oxybarometer to lunar and terrestrial lavas gives reasonable estimates of oxygen fugacities, but generally yields subsolidus temperatures, suggesting re-equilibration of one or more phases during cooling.
Citation Information
Publication Year | 1985 |
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Title | The heat-capacity of ilmenite and phase equilibria in the system Fe-T-O |
DOI | 10.1016/0016-7037(85)90061-4 |
Authors | Lawrence M. Anovitz, A.H. Treiman, E.J. Essene, B. S. Hemingway, E.F. Westrum, V.J. Wall, R. Burriel, S.R. Bohlen |
Publication Type | Article |
Publication Subtype | Journal Article |
Series Title | Geochimica et Cosmochimica Acta |
Index ID | 70012727 |
Record Source | USGS Publications Warehouse |