Thermodynamic Measurements on Alloys and Compounds in Ag-Au-Se and Ag-Pd systems by the Electromotive Force Method

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Volume Title
School of Chemical Technology | Doctoral thesis (article-based) | Defence date: 2014-11-28
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Author
Date
2014
Department
Materiaalitekniikan laitos
Department of Materials Science and Engineering
Major/Subject
Mcode
Degree programme
Language
en
Pages
58 + app. 50
Series
Aalto University publication series DOCTORAL DISSERTATIONS, 172/2014
Abstract
Gold and silver chalcogenides are significant minerals and major carriers of precious metals, and silver palladium alloy is one of the most important silver alloys with various industrial applications. The Ag-Au-Se ternary system and the Ag-Pd binary system have been investigated by the electromotive force (EMF) method in this study. For the Ag-Au-Se ternary system, the numerical values of the standard thermodynamic functions of the compounds Ag2Se (naumannite), AuSe, and Ag3AuSe2 (fischesserite) have been determined by the EMF method in a solid-state galvanic cell with superionic conductor RbAg4I5 and AgI as solid state electrolyte. The compounds Ag2Se, AuSe, and Ag3AuSe2 were synthesized from pure elements in evacuated quartz glass ampoules and then examined to be homogenous by Scanning Electron Microscope (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS). According to the experimental data on the EMF versus temperature, the analytical equations were obtained for the polymorphic forms of the compounds Ag2Se, AuSe, and Ag3AuSe2. The temperature-dependent relationships of the Gibbs energy of formation on the compounds Ag2Se, AuSe and Ag3AuSe2 in their polymorphic forms and the standard thermodynamic functions of the compounds within the temperature range were also obtained. For the Ag-Pd binary system, thermodynamic measurements of silver-palladium binary alloys have been performed over the temperature range 450–750 K by the EMF method with the superionic conductor AgI as the solid electrolyte. The activity and partial molar Gibbs energy of silver were obtained for Ag-Pd alloys over the whole composition range and the thermodynamic properties of palladium were calculated using the Gibbs-Duhem equation. The results show that chemical activities of silver exhibit negative deviations over most of the composition range, and the activities of palladium are characterized by both negative and positive deviations from the ideal Raoultian behavior. The results also show the minimum integral enthalpy of mixing on Ag-Pd alloys is located at 60 at.% Ag. The thermodynamic properties of the Ag-Au-Se ternary system and the Ag-Pd binary system obtained are significant for the production and recycling of precious metals. Moreover, the EMF method has been improved by advanced cell design, gas purification system, as well as temperature measurement, which can be used as an experimental tool for thermodynamic measurement for other alloys and compounds.
Description
Supervising professor
Taskinen, Pekka, Prof., Aalto University, Department of Materials Science and Engineering, Finland
Thesis advisor
Taskinen, Pekka, Prof., Aalto University, Department of Materials Science and Engineering, Finland
Keywords
electromotive force method, Gibbs energy, entropy, enthalpy
Other note
Parts
  • [Publication 1]: D. Feng, P. Taskinen, F. Tesfaye, Thermodynamic stability of Ag2Se from 350 to 500 K by a solid state galvanic cell, Solid State Ionics II. 231 (2013) 1-4.
    DOI: 10.1016/j.ssi.2012.10.013 View at publisher
  • [Publication 2]: D. Feng, P. Taskinen, Thermodynamic properties of Ag3AuSe2 from 300 to 500 K by a solid state galvanic cell, Journal of Alloy and Compounds III. 583 (2014) 176-179.
    DOI: 10.1016/j.jallcom.2013.08.170 View at publisher
  • [Publication 3]: D. Feng, P. Taskinen, Thermodynamic stability of AuSe from 400 to 700 K by a solid state galvanic cell, Journal of Chemical Thermodynamics IV. 71 (2014) 98-102.
    DOI: doi:10.1016/j.jct.2013.11.031 View at publisher
  • [Publication 4]: D. Feng, P. Taskinen, Thermodynamic properties of Ag3AuSe2, submitted to Physics and Chemistry of Minerals
  • [Publication 5]: D. Feng, P. Taskinen, Thermodynamic properties of silver-palladium alloys determined by a solid state electrochemical method, Journal of Materials Science, 49 (2014), 5790-5798.
    DOI: 10.1007/s10853-014-8310-4 View at publisher
Citation
Permanent link to this item
https://urn.fi/URN:ISBN:978-952-60-5935-8
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[diss] Kemian tekniikan korkeakoulu / CHEM