| The oxidation-reduction equilibrium in binary alkali silicate
glasses containing V3+, V4+ and V5+ ions was studied at 14oo•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+-vs+ 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+]/[V31[p02] 1r.z) against mol% R20
(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+-vs+ 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 ys+ ions. |
