NEGATIVE-IONS VO2-, VO3-, V2O5-, V3O8-, AND V4O10- IN THE VAPORS OF VANADIUM-OXIDES - DETERMINING ENTHALPIES OF FORMATION FROM EQUILIBRIUM-CONSTANTS

Negative ions VO—2, VO—3, V2O—5, V3O—8, and V4O—10 were found in the vapors of vanadium oxide at temperatures T = 1200 K to 1500 K. Equilibrium constants of six reactions with the participation of these ions were estimated. The reactions were chosen in such a manner that the equilibrium constants were non-correlated. Joint processing of the equilibrium constants, which may be called the mixed second- and third-law treatment, produced the enthalpies of formation of the negative ions, and molar electron affinities were determined: Em (VO2) = (223±20) kJ·mol-1, Em(V4O10) = (401±61) kJ·mol-1. The use of vanadium-containing negative ions to measure the activities of vanadium oxide and the oxygen partial pressure has been discussed. © 1993 Academic Press Ltd.