The V3+-V5+ Redox Equilibrium Reaction and Magnetic Properties of Vanadium Ions in Binary Alkali Silicate Glasses

Abstract

The oxidation-reduction equilibrium in binary alkali silicate glasses containing V3+, V4+ and V5+ ions was studied at 1400°C in air atmosphere. The ionic equation representing the V3+-V5+ redox equilibrium reaction was used to represent the V3+-V4+-V5+ redox reactions in glasses as V4+ ion was an intermediate species. The V3+-V5+ redox equilibrium was found to shift more towards the oxidized state with the increasing ionic radii of alkali ions or with the increasing concentration of alkali oxide in the same series of glasses. The slopes of the straight lines obtained on plotting log ([V5+]/[V3+][pO2]1/2) against mol% R2O (R+ = Li+, Na+ and K+ ions) in binary alkali silicate glasses were approximately inversely proportional to the coulombic force between the alkali ions and nonbridging oxygen ions. This indictates that the redox equilibrium shifted more towards oxidized state with increasing oxygen ion activity in the glass. The loss of vanadium from the glass melts with the duration of heat treatment was observed due to volatilization at high temperature, which did not influence the V3+-V5+ redox equilibrium. Magnetic susceptibility of the present glasses, measured at room temperature, did not show any sign of paramagnetism which might be due to the presence of smaller concentration of V3+ and V4+ ions in the glass. Further, it indicated a strong diamagnetism because of the presence of higher proportion of vanadium in pentavalent state in the glasses. However, the optical absorption spectra of a silicate glass containing ions of vanadium indicated the presence of V3+, V4+ and V5+ ions.