Grigorova D.Paunova R.2024-07-162024-07-162024-07-162024-07-162017-01-011314-79781314-7471SCOPUS_ID:85014100826https://rlib.uctm.edu/handle/123456789/1167The activity of FeO, SiO2, and V2O5 in V2O5 - FeO - SiO2 ternary systems has been investigated. Pure oxides were used as reference mixtures, included in the system in ratios, analogous to those of mixtures, containing waste vanadium catalyst. Two mixtures were prepared: 1st mixture - V2O5 - FeO - SiO2 (pure oxides), 2nd mixture - waste vanadium catalyst - FeO - SiO2. The oxygen potential in the systems was determined by the EMF method. The solid electrolyte was ZrO2 (Y2O3), and the reference electrode - a mixture Mo/MoO2 in 1: 1 ratio, was used as a galvanic cell. The investigations were carried out in an isothermal and a non-isothermal condition. The Gibbs free energy and the activity coefficient were calculated from the experimentally obtained oxygen potential. Equations for ΔGT = f (T) were derived for different temperature ranges. New phases were observed in the mixture containing vanadium catalyst.enArticle