Thermodynamic activity of oxides of vanadium in sodium borovanadate glasses

Abstract

Thermodynamic activity of the oxides of vanadium was studied in sodium borovanadate glasses equilibrated with V4+-V5+ redox system at 1000° and 1400°C in air. The ratio of logarithm of activity coefficient, log[γV]1/2/[γVO] was constant over a limited range of 2.5–7.5 mol% concentration of V2O5 at 1000°C and 2.5–10.0 mol% at 1400°C. It was found to deviate from Henry’s law beyond 7.5 mol% V2O5 at 1000°C in air. The value of log[γV]1/2 [γVO] in sodium borovanadate glass equilibrated at 1000°C was found to be greater than that of 1400°C. This indicated that the V4+-V5+ system shifted more towards the reduced state with increasing temperature. Further, it was observed that the curve deviated from the Henry’s line with increasing mol% of V2O5 or decreasing mol% of Na2O at 1000°C. © 2000 Taylor and Francis Group, LLC.