CHEMICAL-REACTIONS OF ULTRAPHOSPHATE CLASSES WITH WATER AT VARIOUS TEMPERATURES

The chemical reactions between P2O5-ZnO-H2O ultraphosphate glasses and water were characterized between room temperature and 500 degrees C, using thermogravimetry, differential scanning calorimetry, X-ray diffr action, and P-31 nuclear magnetic resonance. Water adsorption and hydr olysis reactions of the glass leads to the formation of H3PO4 and crys talline ZnH2P2O7 below 200 degrees C, The rate of water adsorption inc reases, owing to the hygroscopicity of the hydrolysis products of the glass. Devitrification occurs at 250 degrees C via surface reactions. The microstructure of the devitrified glass consists of crystalline Zn 2P4O12 and a liquid phase containing hydrolysis products of P2O5 like metaphosphoric acid (HPO3)(n). Devitrification is finally followed by water desorption at higher temperatures.