Standard Formation Enthalpy of Na2O–ZnO–P2O5 Series Glasses

Abstract

(100 − x)NaPO3–xZnO (0 ≤ x ≤ 33 mol%) phosphate glasses have been prepared using the conventional melt quenching technique. Amorphous state was checked up by X-ray diffraction. Glasses have been investigated in detail by mean of differential scanning calorimetry, inductively coupled plasma. Incorporation of ZnO oxide increases the Tg value and the thermal stability of samples. For this glass series, 31P solid state magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy revealed the decrease of Q2 tetrahedral sites and the increase of phosphate dimers (Q1), when ZnO oxide is progressively introduced, suggesting the shortening of metaphosphate chains. Dissolution of glasses has been followed calorimetrically and showed a change in thermal signs resulting from the depolymerization of metaphosphate groups when ZnO oxide is added. A thermochemical cycle involving a number of dissolution and mixing processes have been carried out in order to get the standard enthalpy of formation of these glasses. Calculation of these quantities needs the standard enthalpy of formation of sodium trimetaphosphate. Formation enthalpy of glasses increases with the incorporation of ZnO oxide.