Thermodynamic stabilities of complex phases and their assemblages in Ag-Te, Ag-Bi-S and Ag-Cu-S systems

Fiseha Tesfaye

    Research output: ThesisDoctoral ThesisCollection of Articles

    Abstract

    Currently, most of the available sulphide ores are low-grades and also becoming increasingly complex. The complex groups of ores can constitute anything from trace amounts to major proportions of minerals; such as tellurides, sulphides and sulfosalts. Among these minerals, the silver-based tellurides and sulfosalts are commonly encountered in ores for the production of base and precious metals. However, unlike the binary sulphides, their thermodynamic properties are poorly known. Recently, the silver-based chalcogenides have also emerged as promising novel functional materials for many applications. Therefore, accurate thermodynamic data concerning the silver-based chalcogenides determined within this thesis have considerable fundamental and practical importance in many aspects of extractive and physical metallurgy. To acquire thermodynamic data the solid state EMF method was used. The method has been improved for more accurate thermodynamic measurements as well as to overcome experimental challenges in the presence of volatile components. State-of-the-art equipment has been utilized and a new philosophy for constructing the galvanic cell and a new experimental arrangement to control the temperature gradient over the galvanic EMF cell were employed. The thermodynamic measurements on the phases of interest were conducted below T = 700 K. Based on the experimental results, thermodynamic properties of equilibrium phase assemblages in the two-phase regions of the Ag-Te system have been explicitly determined. New experimental data were also obtained and used to determine eutectic, eutectoidic decomposition and phase transition temperatures. In the Ag-Bi-S system, thermodynamic properties of pavonite, matildite and schapbachite at bismuth- and sulphur-saturation conditions have been determined. Prior to this work, the effects of saturation of sulphur and bismuth on the thermodynamics of the ternary phases were not known distinctively. In addition, new experimental thermodynamic data of the ternary phases over wide temperature ranges were obtained. Thermodynamic properties of the other silver-based phases of interest, stromeyerite and the solid solution (Ag,Cu)2Sss, were also studied. For the first time, thermodynamic properties of the solid solution were experimentally determined. The experimental data obtained within this thesis together with the selected literature data enabled the determination of accurate thermodynamic functions for 36 selected equilibrium reactions.
    Translated title of the contributionKompleksifaasien termodynaamiset stabiilisuudet systeemeissä Ag-Te, Ag-Bi-S ja Ag-Cu-S
    Original languageEnglish
    QualificationDoctor's degree
    Awarding Institution
    • Aalto University
    Supervisors/Advisors
    • Taskinen, Pekka, Supervisor
    • Taskinen, Pekka, Advisor
    Publisher
    Print ISBNs978-952-60-5763-7
    Electronic ISBNs978-952-60-5764-4
    Publication statusPublished - 2014
    MoE publication typeG5 Doctoral dissertation (article)

    Keywords

    • silver-based phases
    • solid solubility
    • equilibrium
    • electrochemistry
    • thermodynamic and thermochemical properties

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