Surface degradation behaviour of sodium borophosphate glass in aqueous media: Some studies

Abstract

The degradation behaviour of phosphate glass with nominal composition, 40Na₂O-10BaO-xB₂O₃-(50-x)P₂O₅, where 0 ≤ x ≤ 20 mol%, was studied in water, HCl and NaOH solutions at room temperature to 60°C for different periods extending up to 300 h. These glasses were synthesized by conventional melt-quench technique. Dissolution rates were found to increase with B₂O₃ content in the glass. The dissolution rates for the glass having 10 mol% B₂O₃ were found to be 0·002 g/cm² and 0·015 g/cm² in distilled water and 5% NaOH solution, respectively, at room temperature after 225 h of total immersion period, whereas it increased considerably to 0·32 g/cm² in 5% NaOH at 60°C after 225 h. However, glass samples with x = 15 and 20 mol% B₂O₃ were dissolved in 5% HCl solution after 5 h immersion. The degradation behaviour has been correlated with the structural features present in the glass. The optical microscopy of the corroded surface revealed that the corrosion mechanism were different in acid and alkali media.