Dissolution behavior of ZnO–P2O5 glasses in water

Bulk binary ZnO–P₂O₅ glasses with 50–70 mol% ZnO were immersed in distilled water at 30–90 °C for up to 72 h. The immersed samples were characterized by weight loss, the change in solution pH, X-ray diffraction (XRD) analysis, scanning electron microscopy and Raman spectroscopy. Weight loss decreased with ZnO concentration for all immersion temperatures. Dissolution behavior was classified into two types in terms of weight loss and macroscopic appearance. Type I was primarily recognized in 50–60 mol% ZnO glasses. In type I, the weight loss for 72 h was relatively large (>1.0 × 10^?7 kg mm^?2, >10% of initial sample weight). Raman spectra of the type I glasses indicated that the depolymerization of phosphate glass network occurred during the dissolution process. Crystalline Zn₂P₂O₇ · 3H₂O was precipitated in the water solution after immersion. Type II dissolution behavior was recognized in the 65 and 70 mol% ZnO glasses except for the 65ZnO–35P₂O₅ glass immersed at 90 °C. In the type II behavior, the weight loss for 72 h was relatively-small (<1.0 × 10^?8 kg mm^?2, <1% of initial sample weight). The microstructure of the type II glass indicated selective dissolution. The dissolution process of the type II glass is discussed.