Optical and structural properties of BCBS glass system with and without alumina

Abstract

BaO–CaO–Al<inf>2</inf>O<inf>3</inf>–SiO<inf>2</inf> (BCAS) glass and their derivatives have gained extreme importance for their high endurance to elevated temperatures and being suitable for various electrochemical applications. Two glass systems, one being 50mol% [SiO<inf>2</inf>–B<inf>2</inf>O<inf>3</inf>]-xBaO-(45-x)CaO–5Al<inf>2</inf>O<inf>3</inf> called as BCBSA and another without Al<inf>2</inf>O<inf>3</inf> termed as BCBS were synthesized using melt quenching technique in the present work. Addition of ZnO and MgO as flux helped in melting them at 1300 °C which is much lower than the usual melting temperature of these glasses [1–4]. Density of the quenched glasses was measured by Archimedes method and structural bond vibrations were confirmed through FTIR. UV Visible spectroscopy was used to determine band gap energy and confirm the insulating nature of the synthesized glasses. The samples were isothermally heated at 700 °C, 800 °C for 50 h and at 900 °C for 50 and 100 h duration in air to allow the devitrification process to take place. The heat treated samples were analyzed by X-ray diffraction to identify the developed phases. Five Al<inf>2</inf>O<inf>3</inf> free samples synthesized at 1300 °C by regular melt quenching technique were found to be devoid of the monocelsian phase. This is a detrimental phase for high temperature sealant applications as it has a very low coefficient of thermal expansion (CTE). Al<inf>2</inf>O<inf>3</inf> free BCBS glasses, properties of which are being reported for the first time and glasses with low BaO concentrations are found to meet the requirements for high temperature applications as sealants in Solid Oxide Fuel Cell (SOFC). © 2018 Elsevier B.V.