Electrochemical Study on Redox Behavior of the multivalent Metal Ions in the glass Melts

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The Sn^<4+>-Sn^<2+> and Fe^<3+>-Fe^<2+> equilibrium in alkali borate and silicate melts was studied by means of differential pulse voltammetry. The half-wave potentials in Fe-containing glasses become negative with decrease of temperature and increase of alkali oxide when they exceed 20 mol%. When alkali oxide is less than about 20 mol%, the data can be fitted by two reduction peaks, i.e. the Fe^<3+>-containing complex and free Fe^<3+> to Fe^<2+>. The half-wave potentials of Sn^<4+>-Sn^<2+> equilibrium in borate melts shift to the negative with an increase in Na_2O content and a decrease in temperature. On the other hand, the half-wave potentials in the silicate melts shift to the positive with an increase in Na_2O content. There results can be interpreted in terms of complex formations of Sn^<4+> and Sn^<2+>, in which the coordination numbers of the oxide ion for both ions do not differ significantly and their equilibrium constants for complex formation depend largely on the alkali species.The ^<29>Si and ^<31>P nuclear magnetic resonance (NMR) chemical shifts and the Q_n distribution in ternary sodium phosphosilicate glasses were examined. When the P_2O_5 content increases at fixed mole fractions of SiO_2 equal to 0.1 and 0.05, the 6-coordinated silicon atoms appear. The presence of 6-coordinated silicon atoms is expected in glasses where the [P_2O_5]/[Na_2O] composition ratio is greater than unity. From the NMR spectra of 30Na_2O ・ 5SiO_2 ・ 65[(1-x)P_2O_5 ・ xB_2O_3] glasses, the distribution curves derived from the deconvolution of the spectra by component signal of each phosphate and borate species agree with those calculated using species with different [Na_2O] / [P_2O_5] ratios when P_2O_5 reacts with Na_2O and B_2O_3 preferably.