Determination of the thermodynamic properties of compounds in the Ag-Au-Se and Ag-Au-Te systems by the EMF method

Abstract

The standard thermodynamic properties (Δ_f G°, S°, Δ_f H°) of the following synthetic minerals and compounds in the Ag-Au-Se and Ag-Au-Te systems were determined by the EMF method: β-Ag₂Se (low-temperature naumannite), α-Ag₂Se (high-temperature naumannite), Ag₃AuSe₂ (fischesserite), AuSe, Ag₅Te₃ (stützite), Ag₂ Te (hessite), and Ag₃AuTe₂ (petzite). All minerals and compounds were produced by solid-phase synthesis from elements or electrum of the given composition in evacuated ampoules made of quartz glass. The phases were verified by X-ray diffraction analysis, microscopically in reflected light, and with an electron microprobe. The absence of the ternary compound AgAuSe in the Ag-Au-Se system was confirmed by solid-phase annealing. On the basis of experimental data on the electromotive force E versus temperature, the equations E(T) were calculated, from which the temperature-dependent relationships of the Gibbs energy in the relevant reactions and the standard thermodynamic functions of compounds within the range 300–502 K were obtained.