Thermodynamic Examination of Selected Phases in the Ag–Co–Sn–S System at T < 600 K by the Solid-State EMF Method

Abstract

Phase equilibria in the part SnS–SnS2–CoS2–CoS–Ag2CoS2–SnS of the Ag–Co–Sn–S system at T < 600 K were investigated by the modified solid-state electromotive force (EMF) method. The position of established phase regions vs point of Ag was used to express the overall potential-forming reactions. The reactions were performed in the positive electrodes of the electrochemical cells (ECCs). The positive electrodes of ECCs were prepared from carefully mixed non-equilibrium powder mixtures of Ag, Ag2S, CoS2, Co3S4, Co9S8, SnS2, Sn2S3, and SnS. Synthesis of the equilibrium set of phases in the positive electrodes of the ECCs was facilitated by Ag+ ions that shifted from the left electrode and acted as the small nucleation centers of formation of the compounds. Linear dependences of the EMF of the ECCs on temperature were used for calculating standard Gibbs energies, enthalpies, and entropies of formations of the compounds CoS, AgCoS2, Ag2CoS2, Ag2CoSnS4, and Ag2CoSn3S8. The thermodynamic data obtained in the present study were compared and analyzed in detail.KeywordsAg-based compoundsPhase equilibriaThermodynamic propertiesEMF methodGibbs energy