Structure and dissolution behavior of MgO–P<sub>2</sub>O<sub>5</sub>–TiO<sub>2</sub>/Nb<sub>2</sub>O<sub>5</sub> (Mg/P ≥ 1) invert glasses

Abstract

Magnesium phosphate glasses exhibit unusual properties and were classified as ‘anomalous phosphate glasses’, because magnesium is attributed to a variation of the oxygen coordination number from 6 to 4. Magnesium in phosphate glasses acts as an intermediate oxide and its role was determined, relating to the phosphate chain length. In the present work, MgO–P2O5–TiO2/Nb2O5 glasses with Mg/P ratio between 1.00 and 1.36 were successfully prepared by a melt–quenching method. Magnesium in the glasses worked as a network former to form P–O–Mg bonds, which are cross-linked short phosphate chains that improved the glass-forming ability. Intermediate oxides (i.e., TiO2 and Nb2O5) in the glasses also cross-linked short phosphate chains to form P–O–Ti/Nb bonds. The chemical durability of the glasses decreased with an increase in the Mg/P ratio, because magnesium, which entered the phosphate network, weakened the glass network to induce hydrolysis. The dissolution rate of Ti4+ and Nb5+ ions showed a decreasing tendency with an increase in the Mg/P ratio. The surfaces of the glasses were considered to be covered with gel-like oxide layers containing titanium or niobium and phosphate.