2001/09/01 by Ronit Kessel, John R. Beckett, J. R. Beckett +1 · 1 citation
Engineering · #Advanced Materials Characterization Techniques #Metallurgical Processes and Thermodynamics #Microstructure and Mechanical Properties of Steels
paper · doi:10.2138/am-2001-8-907
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 \ndeviations from ideality throughout the investigated temperature range (e.g., γ^(alloy)Fe <0.02 for X^(alloy)Fe <0.3). Our data are consistent with an asymmetric regular solution of the form: \nRTln γ^(alloy)Fe = [W_(G1)+2(W_(G2)-W_(G1))X^(alloy)Fe](X^(alloy)_(Pt))2 \nwhere W_(G1) = –138.0 ± 3.3 kJ/mol and W_(G2) = –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 \nln γ^(alloy)Fe(T1)/ln γ^(alloy)Fe(T2)=T2/T1. The Pt-Fe alloy composition in equilibrium with a FeO-bearing silicate liquid can be obtained from: \nlog_(10)f_(O2) = logexp[lna^(liq)_(Fe2SiO4) - lna^(liq)Si)2 - 2 lna^(alloy)_(Fe) -(-ΔG^(0)_(r)/RT)] \nwhere ΔG^(0)_(r) is the standard state free energy for the reaction 2Fe^(alloy) + O2 + SiO^(liq)2 = Fe_(2)SiO^(liq)4. We obtained values of a^(alloy)_(Fe) from our model and used the program MELTS together with the thermodynamic properties of these elements to evaluate activities of SiO2 and Fe_(2)SiO4 components in the liquid and ΔG^(0)_(r). We provide sample calculations showing how to predict the optimum Fe concentrations \nfor 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.