Influence of (CoO, CaO, B2O3) additives on thermal and dielectric properties of BaO-Al2O3-SiO2 glass-ceramic sealant for OTM applications

The efficiency of glass ceramic sealants plays a crucial role in high temperature applications' performance and durability, such as oxygen separation from air. In order to develop suitable sealants, operating at about 950 degrees C, several glass ceramics with different compositional additives and ratios in BaO-Al2O3-SiO2 system have been prepared and investigated. The effect of additive oxides (CaO, CoO, B2O3) as network modifiers on the thermal and dielectric properties of BaO-Al2O3-SiO2 glass ceramic for further oxygen transport membrane (OTM) applications was evaluated and discussed. The introduction of additives has evident effects on the main crystalline phases and physical properties of the glass ceramics. Among these systems, B2O3-rich BAS system (BABS) can be densified at the sintering temperature below 700 degrees C through viscous sintering. Also, BABS shows the lowest dilatometric softening temperature at 675 degrees C, which can be explained by a fast densification associated with shrinkage of 25%. After devitrification for 200 h at 950 degrees C, BABS exhibits excellent thermal stability, suffering a weight loss of maximum 0.04%. It has the highest conductivity and resistivity, a high dielectric constant of 67.8 and a loss of 0.029 at 10 MHz, which provide an attractive insulating feature for many technological applications. However, considering all other properties investigated besides the electric ones, only B2O3-rich BAS meets the requirements for use as a sealant for BSCF membrane. Low softening temperature of BABS opens more ways for adding additives to tailor its functional properties, which enables it to being used as sealant material for OTM applications. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.