Thermal and fragility aspects of microwave synthesized glasses containing transition metal ions and heavy metal ions

A simple, clean and energy efficient microwave heating route is used to prepare glasses in the systems xMnO33(0.09PbCl(2):0.91PbO)-(67-x) NaPO3 and xPbCl(2)-33PbO-(67-x) NaPO3 where 0.1 <= x <= 4 (mol%). Thermal data extracted from differential scanning calorimetry (DSC) thermograms are used to study the composition dependence of glass transition temperature (T-g), heat capacity, thermal stability and fragility. The decrease in glass transition temperature with modifier oxide (Na2O + MnO) content can be ascribed to network degradation and the volume increasing effect caused by PbCl2. The change in heat capacity of MnPb glass being greater than that of PbNP glass, suggests that MnPb glasses are more covalent than PbNP glasses. DSC thermograms taken at different heating rates (phi) reveal the dependence of T-g on phi, and the thermal stability of the glass increases due to MnO addition. Fragility aspects have also been studied by calculating the fragility functions (Delta C-p/C-pl and |NBO|/(VmTg)-T-3). Results obtained from both the fragility functions compare well and reveal the dependence of fragility functions on modifier content and PbCl2 mol%. Further, the decrease in T-g and H-v are suggested to be due to the increase in the number of non-bridging oxygens, which results in the lowering of stiffness and rigidity of the glass network. Analysis of the infrared spectra confirms that the glassy matrix is composed of P-O-P, P-O-Pb, P=O and P-O- bonding.