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

Lawrence M. Anovitz, Allan H. Treiman, Eric J. Essene, Bruce S. Hemingway, Edgar F. Westrum, Victor J. Wall, Ramón Burriel, Steven 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 (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 f{hook}O2 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.

Original languageEnglish
Pages (from-to)2027-2040
Number of pages14
JournalGeochimica et Cosmochimica Acta
Volume49
Issue number10
DOIs
StatePublished - Oct 1985
Externally publishedYes

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