Effect of different binders on microstructural evolution and strength of sol-gel bonded Al₂O₃-spinel castables

Al2O3-spinel castable refractories offer several benefits, including high refractoriness, strong resistance to chemical attack, and excellent mechanical strength. These properties make them a preferred choice for steel ladle lining below the slag line. In this study, the effect of different binders on Al2O3-spinel castable refractory was investigated. Three sol systems, including alumina, spinel, and silica sol, were separately employed as bonding agents in ultra-low cement castable formulations. Key properties, such as phase composition, microstructure, and mechanical performance of castable refractories, including bulk density (BD), apparent porosity (AP), and cold compressive strength (CCS), were evaluated. The properties of the castables with sol-gel bonding were compared with those with hydraulic bonding (calcium aluminate cement). It was observed that the castables containing silica sol resulted in higher cold compressive strength (2103 kg/cm2) and higher bulk density because of the absence of low melting or eutectic phases and synthesis of the mullite phase.