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

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.