Glass Formation Range, Acid Resistivity, and Surface Charge Density of ZnO-B2O3-SiO2 Passivation Glass Containing Al2O3

The glass formation range in the system ZnO-B₂O₃-SiO₂ increases when 5% Al₂O₃ is added and then decreases with further Al₂O₃ additions. The acid resistivity of the glass also increases when Al₂O₃ is added. An observed increase in negative charge with Al content until the system contains equal amounts of Al and Si (in forms of mole %) is explained by the formation of AlO₄⁻ tetrahedra which substitute in the SiO₄ network. Alkaline-earth oxides cause a positive charge which compensates for the negative charge formed by Al₂O₃. Antimony oxide and lanthanum oxide result in a negative charge in the glass. The formation of a negative or positive charge in the glass is thought to reflect the acidity or basicity of the glass, respectively.