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The heat-capacity of ilmenite and phase equilibria in the system Fe-T-O

Lawrence M. Anovitz·A.H. Treiman·E.J. Essene·B. S. Hemingway·E.F. Westrum·V.J. Wall·R. Burriel·S.R. Bohlen
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Abstract

Low temperature adiabatic calorimetry and high temperature differential scanning calorimetry have been used to measure the heat-capacity of ilmenite (FeTiO 3 ) from 5 to 1000 K. These measurements yield S 298 0 = 108.9 J /( mol · K ). Calculations from published experimental data on the reduction of ilmenite yield Δ 298 0 ( I 1) = −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 ƒO 2 ">ƒ ƒO2 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-pseudobrookite ss and hematite-ilmenite ss . 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.

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Lawrence M. Anovitz, A.H. Treiman, E.J. Essene, B. S. Hemingway, E.F. Westrum, V.J. Wall, R. Burriel, S.R. Bohlen. 1985. The heat-capacity of ilmenite and phase equilibria in the system Fe-T-O. https://doi.org/10.1016/0016-7037(85)90061-4

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