Effect of molybdenum addition on the thermal properties of silicate-phosphate glasses

Aim of the study was analysis of two groups of glasses: silicate-phosphate (41 mol.% SiO2-6 mol.% P2O5) and with inverse phosphate-silicate matrix (41 mol.% P2O5-6 mol.% SiO2) modified by the addition of molybdenum ions. Their effect on glass forming ability, glass transition effect, crystallization process, and kind of crystallizing phases was examined using such methods as DSC, XRD, and SEM. It was found that the solubility limit of MoO3 in silicate-phosphate glasses is 4.4 < [MoO3] < 5.7 mol.%, whereas in phosphate-silicate glasses MoO3 is fully dissolved. It was found that in the case of both matrixes addition of molybdenum ions decreases the glass transition temperature (T (g)), as well as the value of specific heat change (a dagger c (p) ) accompanying the glass transformation. The presence of molybdenum caused reduced the thermal stability of the studied glasses and a multi-step crystallization of silicate-phosphate glasses. It was found that the crystallizing phases were silicates and phosphates in both groups of glasses. Only in the case of silicate-phosphate glasses containing MoO3 in an amount a parts per thousand yen3.3 mol.% one of the crystallization product was powellite (CaMoO4). The nature of transitions taking place during heating of the analyzed glasses was in accordance with crystallochemical factors (strengths of bonds) and chemical affinity of the glass components (a dagger G formation).