Chemical Reactions of Ultraphosphate Glasses with Water at Various Temperatures

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Abstract
The chemical reactions between P2O5‐ZnO‐H2O ultraphosphate glasses and water were characterized between room temperature and 500°C, using thermogravimetry, differential scanning calorimetry, X‐ray diffraction, and 31P nuclear magnetic resonance. Water adsorption and hydrolysis reactions of the glass leads to the formation of H3PO4 and crystalline ZnH2P2O7 below 200°C. The rate of water adsorption increases, owing to the hygroscopicity of the hydrolysis products of the glass. Devitrification occurs at 250°C via surface reactions. The microstructure of the devitrified glass consists of crystalline Zn2P4O12 and a liquid phase containing hydrolysis products of P2O5 like metaphosphoric acid (HPO3)n. Devitrification is finally followed by water desorption at higher temperatures.