Thermodynamic properties of the Pt-Fe system

R. Kessel*, J. R. Beckett, E. M. Stolper

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

58 Scopus citations

Abstract

We determined activity-composition relationships for the Pt-Fe system by equilibrating Fe-oxides with Pt-Fe alloys at temperatures in the range of 1200-1400 °C and oxygen fugacities from 1.6 to 7.7 log units above the iron-wüstite (IW) buffer. The system is characterized by strong negative deviations from ideality throughout the investigated temperature range (e.g., γalloyFe<0.02 for XalloyFe <0.3). Our data are consistent with an asymmetric regular solution of the form: RT In γalloyFe = [WG1 + 2(WG2 - WG1) XalloyFe] (XalloyPt)2 where WG1 = -138.0 ± 3.3 kJ/mol and WG2 = -90.8 ± 24.0 kJ/mol (1σ). Based on experiments at 1200-1400 °C, variations in the activity coefficients at a given composition are consistent with In γalloyFe(T1) / In γalloyFe(T2) = T2 / T1. The Pt-Fe alloy composition in equilibrium with a FeO-bearing silicate liquid can be obtained from: log10f 02 = log{exp[In aliqFe2SiO4 - In aliqSiO2 - 2 1n aalloyFe - (2Gor RT)]} where τ2Gor is the standard state free energy for the reaction 2Fealloy + Ogas2 + SiOliq2 = Fe2SiOliq4. We obtained values of alloyFe from our model and used the program MELTS together with the thermodynamic properties of these elements to evaluate activities of SiO2 and Fe2SiO4 components in the liquid and τ2GOr. We provide sample calculations showing how to predict the optimum Fe concentrations for pre-saturation of Pt-bearing containers to reduce Fe loss from the charge during experiments on magmatic liquids at high temperatures and pressures from 1 atm to 40 kbar.

Original languageAmerican English
Pages (from-to)1003-1014
Number of pages12
JournalAmerican Mineralogist
Volume86
Issue number9
DOIs
StatePublished - 2001
Externally publishedYes

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