Phase separation and crystallization of glasses in the system R2O-B2O3-SiO2 with R = Li, K, Na - Influence on thermal properties

Abstract

The dilatometric properties (α, ϑ, Tg) and viscosity of glasses within the systems Li2O-K2O-B2O3-SiO2 and Na2O-B2O3-SiO2 with constant ratios B2O3/R2O =1.5 and 1 (in mol%) were characterized. These compositions have suitable thermal properties to be used as sealants for molten carbonate fuel cells (MCFC). The changes in dilatometric properties and viscosity due to phase separation and crystallization processes were measured along the different stages of a thermal treatment simulating the startup and working conditions of the MCFC. Thus, the thermal and mechanical behaviour of the studied glasses can be evaluated for the whole thermal cycle of the cell. Transmission electron microscopy (TEM) was used to analyse the development of microstructure during the thermal treatment and X-ray diffraction (XRD) to determine the appearing crystalline phases.