Experimental thermodynamic studies are nowadays rare, but the need for thermodynamic data has increased as the metal industry has been obligated to use the low-grade ores resulting from the intensive mining and the high consumption of metals. Furthermore, thermodynamic data obtained by the EMF method has impact in materials science and, for example, concerning thermoelectric generators. In this study, an advanced EMF method has been developed and a compilation of thermodynamic data has been measured by applying improved practices and arrangements. Not only was experimental apparatus developed, but also the sample preparation method and measurement procedures were improved. During the development of the experimental arrangement, the studied chemical assemblages were selected from well-known systems in order to compare the impact of the modifications to the measured EMF with reliable reference data presented in the literature. A number of different approaches were tested and the modifications with a beneficial outcome were combined in the final experimental procedure. Different solid electrolytes were applied to measure chemical oxide systems as well as systems with silver content. Yttria stabilized zirconia was implemented as an O2- conducting electrolyte whereas AgI was used in silver systems as a Ag+ conducting solid electrolyte. The experimental temperature ranges as well as the capability to measure volatile test electrodes were improved by the use of ion exchanged B''-alumina as a solid Ag+ conducting electrolyte together with AgI. Finally, the improvements were applied to study the thermodynamic properties of a number of intermetallic compounds and oxides with little or no previously measured thermodynamic data but a notable practical importance in many areas. Particularly, the studied alloys and compounds have been selected to respond to the specific needs of the metal industry and to support the development of thermoelectric materials. All in all, the advanced EMF method has been applied to measure the thermodynamic properties of the following compounds: Ag3Sb, Ag6Sb, SbxTe1-x, AgSbTe2, AgSbS2, Ag3SbS3, Bi2O3, Sb2O3, TeO2, Ca4Fe9O17. Also, the thermodynamics of the virtual cell reactions, taking place in the experimental cells, have been experimentally measured. The determined values include Gibbs energies of reactions and formations as well as enthalpies and entropies. Third law analysis has been applied to calculate standard thermodynamic properties of the oxide compounds measured at high temperatures if the specific heat capacity as function of temperature is known.
|Translated title of the contribution
|Kehittyneellä koelaitteistolla mitattu kokoelma termodynaamisia arvoja.
|Published - 2016
|MoE publication type
|G5 Doctoral dissertation (article)
- thermodynamic properties