Relative Acidities of Glasses Containing Al2O3 and TiO2 as Determined by the Oxygen Electrode

Abstract

The oxygen electrode has been utilized to determine the relative acidities of sodium and potassium silicate glasses containing alumina and titania in the temperature range 300° to 500° C. The acidity of a potassium or sodium silicate glass is increased by substituting alumina or titania for the soda or potassia. The first additions of alumina tend to increase the acidity of both glasses by forming A1O4 tetrahedra which utilize a portion of the nonbridging oxygen ions to fulfill the coordination requirements. The results indicate further that the Ti4+ ion is in both fourfold and sixfold coordination in the sodium and potassium glasses. Titania increases the acidity when it is in sixfold coordination but tends to decrease it when in fourfold coordination. Both titania and alumina increase the acidity of the potassium glasses more than that of the sodium glasses. This is interpreted on the basis that the oxygen network of the potassium glass, being initially the looser, is tightened more than that of the sodium glass. However, the polymerization of the A1O4 tetrahedra at the higher alumina concentrations causes a loosening of the oxygen network. Previous assumptions that the oxygen electrode reaction is independent of the metal used for the electrodes have been verified by reproducing the data using platinum foil as the electrode material in place of silver foil.