EXPERIMENTAL STUDY OF THE THERMODYNAMICS OF SOLID-STATE REACTIONS

Voronin M.V., Osadchii E.G., Brichkina E.A.

Institute of Experimental Mineralogy RAS

142432, Chernogolovka, Academica Osypyana st., 4

This report presents the most significant results obtained at the Laboratory of Electrochemistry, Thermodynamics, and Mineral Physics at the IEM RAS, using the high-temperature galvanic cell (EMF-method) and a vacuum-block calorimeter. The EMF-method can be illustrated by the example of studies of silver selenide [1]. The reaction of naumannite formation from the elements is realized in an electrochemical cell: (–)Pt | Ag | SE or LE | Ag₂Se, Se | Pt(+), in a wide temperature range determined by the solid (SE – AgI, RbAg₄I₅, AgCl) or liquid electrolyte (LE – molten salts or glycerol solution) used. Thermodynamic properties of phases and phase relations in binary and ternary silver-containing systems have been determined over a wide range of temperatures and atmospheric pressure [2-5]. Experiments at hydrostatic argon pressure up to 0.7 GPa were carried out in high-pressure gas vessels developed by the IEM RAS [6, 7]. Another important variation of the EMF-method is the use of oxygen-conducting solid electrolytes [8], which is widely used to study the thermodynamic properties of oxide systems. At the Laboratory, this method has been applied to the study of natural objects: oxygen fugacity above the bulk sample was determined for some chondrites [9], and the pO₂(T) dependence was obtained in high-temperature fumaroles on Kudryavy Volcano (Iturup Island, Kuril Islands) [10]. Standard enthalpies of formation of Sb₂Se₃ and other chalcogenides, pnictides and intermetallics were determined on a unique vacuum-block calorimeter of our own design [11].

1. Voronin M.V., Osadchii E.G. // Russ. J. Electrochem., 2011, V. 47, No. 4, P. 420-426.

2. Osadchii E.G., Chareev D.A. // Geochim. Cosmochim. Acta, 2006, V. 70, No. 22, P. 5617-5633.

3. Echmaeva E.A., Osadchii E.G. // Geol. Ore Depos., 2009, V. 51. No. 3, P. 247-258.

4. Osadchii E.G., Rappo O.A. // Am. Mineral., 2004, V. 89, No. 10, P. 1405-1410.

5. Voronin M.V. et al. // Phys. Chem. Miner., 2017, V. 44, P. 639-653.

6. Chareev D.A. et al. // Dokl. Earth Sci., 2006, V. 411, No. 1, P. 1233-1236.

7. Osadchii E.G. et al. // J. Alloys Compd., 2021, V. 855, 157407.

8. Osadchii V.O. et al. // J. Alloys Compd., 2015, V. 636, P. 368-374.

9. Osadchii V.O. et al. // Meteorit. Planet. Sci., 2017, V. 52, No. 10. P. 2275-2283.

10. Rosen et al. // Chem. Erde, 1993, V. 53, No. 3, P. 219-226.

11. Osadchii Е.G. et al. // Thermochim. Acta, 2020, V. 691, 178706.

The work was carried out within the state assignment of the IEM RAS # FMUF-2022-0002.