Thermoanalytical study and crystallization of Ba(PO3)2-WO3 glasses

Barium phosphate glasses of the composition (100 - x)Ba(PO3)(2)-xWO(3) with 0-60 mol% WO3 were prepared and studied. Thermal studies of the glasses were carried out with DTA, dilatometry and hot-stage microscopy. Glass transition temperature in this glass series increases with increasing WO3 content from 461 degrees C (x = 0) to 623 degrees C (x = 60). Most glasses containing WO3 crystallize on heating within the range of 650-750 degrees C with the exception of glasses with 20-30 mol% WO3, which are thermally stable. Very high chemical durability of these glasses with dissolution rate of 1.4 x 10(-8)-6.2 x 10(-9) g cm(-2) min(-1) was also revealed. Crystallization of glasses revealed the existence of a new compound Ba(WO2)(2)(PO4)(2) in the studied compositional series. The compound Ba(WO2)(2)(PO4)(2) possess hexagonal unit cell of dimensions a = 11.5191(1) A and c = 6.3437(1) A, and its melting point is 936 degrees C. Raman spectra of crystallized glasses confirmed the formation of crystalline compound in this glass series and revealed the presence of glass phase in some thermal-treated samples. P-31 MAS NMR showed on only one coordination of phosphorus atoms in the Ba(WO2)(2)(PO4)(2) compound.