Differential thermal analysis of glass mixtures containing SiO2, GeO2, B2O3, and P2O5

The glassy phases of SiO2, GeO2, B2O3, and P2O5 as well as selected pseudo- binary, pseudo-ternary, and pseudo-quaternary compositions of these compoun ds have been examined for glass transitions by differential thermal analysi s (DTA) in the context of reflow of doped germanosilicate glasses. SiO2 doe s not exhibit a glass transition to temperatures above 1135 degrees C. GeO2 appears to exhibit a glass transition around 578 degrees C, while B2O3 app ears to exhibit a glass transition in the range of 257-268 degrees C. Altho ugh the glass transition temperature of P2O5 could not be determined, the t ransition and melting behavior of the H, O, and O' phases have been reevalu ated. Moreover, a new mechanism for conversion from H phase to O phase is p resented. Namely, the melting of H phase followed by the spontaneous recrys tallization of the resulting liquid to form the O phase was observed by DTA . Germanosilicate mixtures exhibited no glass transition, but the germanobo rates' glass transition temperatures increased linearly with increasing GeO 2 content. Examination of germanoborosilicates indicated that the addition of any germanosilicate composition to B2O3 causes a linear increase in glas s transition temperature with total germanosilicate mole fraction, independ ent of the GeO2/SiO2 mole ratio. Pseudo-binary combinations of P2O5-B2O3 sh owed no thermal anomalies on heating or cooling cycles following an initial thermal cycle. However, pseudo-binary combinations of P2O5-GeO2 exhibited exotherms on cooling following initial heating cycles, which may indicate t he occurrence of crystallizations that might interfere with reflow phenomen a. Pseudo-quaternary combinations exhibited no thermal anomalies on heating or cooling. (C) 1999 The Electrochemical Society. S0013-4651(99)05-111-3. All rights reserved.