Microwave synthesis and properties of NaPO₃–SnO–Nb₂O₅ glasses

Abstract

Tin niobiophosphate glasses were produced using a domestic microwave oven under a nitrogen flow. The fast microwave melting method and the protective atmosphere prevent the oxidation of SnO. After 10 min of heating, the NaPO₃, SnO, and Nb₂O₅ mixtures are homogeneous and permit to obtain transparent glasses. Three series of glasses with different Sn/Nb ratio were studied to determine the influence of each oxide. The glass transition temperature increases linearly with the amount of Nb₂O₅ and SnO. These variations are more important for compositions with high metallic cation proportions and with a low Sn/Nb ratio. The same evolutions were observed for the density, Vickers hardness, and elastic modulus while the thermal expansion coefficient decreases monotonously. The simultaneous insertion of SnO and Nb₂O₅ in phosphate glass matrix leads to a progressive strengthening of the glass network. The chemical durability of the glasses also increases as a function of the amount of metal oxides. We prepared a bulk glass sample with a dissolution rate of about 3.3 × 10⁻⁸ g cm⁻² min⁻¹ in renewed water conditions at 95 °C. This durability is equivalent to those of the window glass whereas the glass transition temperature remains lower than 485 °C.