Thermodynamic Activities of Components in Homogeneous Ni–Fe–S Mattes at 1473–1673 K

Abstract

Two techniques were used to measure sulfur partial pressures at Fe/Ni ratios of 0.25, 1 and 4 at 1473, 1573 and 1673 K. Gas mixtures of H₂ and H₂S were equilibrated with liquid mattes and then analysed with a calibrated optical interferometer. In the other technique, sulfur pressures were determined along the liquidus using a dual-cell Knudsen effusion-mass spectrometer, calibrated against the sulfur pressures of the univariant Cu(1)–Cu₂S(1) system. Where measurements overlapped, the two techniques gave results in excellent agreement with each other.

The p _S2 data, together with existing information, were used in a graphical Gibbs-Duhem integration to obtairt iron and nickel activities, relative to solid elemental standard states, spanning the complete composition range of the Fe-Ni-S system up to X _s = 0.5 between 1473 to 1673 K.