Microwave synthesis and physical characterization of tin(II) phosphate glasses

Tin phosphate glasses in the SnO–P₂O₅ binary diagram have been prepared by using a domestic microwave-heating device. Microwaves provide an extremely facile and automatically temperature-controlled route to the synthesis of glasses due to the specific dielectric properties of each chemical composition. Typical melting time is no longer than 10 min, limiting the oxidation of Sn²⁺ and the melt can be quenched into glass. The glass transition temperature increases with the SnO content confirming the depolymerization of the vitreous network, as expected by the relative fraction of the different Q ⁿ structural units deduced from NMR experiments. Concerning the mechanical properties, the Vickers hardness and the fracture toughness decrease while the thermal expansion coefficient and the different elastic moduli remain constants. These results confirm that those characteristics are not very sensible to structural considerations. On the contrary, the chemical durability of Sn₂P₂O₇, determined from the weight loss method, is 300 times higher than that of Sn(PO₃)₂. Furthermore, Sn₂P₂O₇ is the only glass composition that exhibits a devitrification phenomenon leading to the low-temperature phase of the crystalline tin(II) pyrophosphate.