Structure and dissolution behavior of MgO-P₂O₅-TiO₂/Nb₂O₅ (Mg/P > 1) invert glasses

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, MgOP₂O₅TiO₂/ Nb2O5 glasses with Mg/P ratio between 1.00 and 1.36 were successfully prepared by a meltquenching method. Magnesium in the glasses worked as a network former to form POMg 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 POTi/ 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.