The in-situ formation of Mg-Al hydrotalcite and its effect on the properties of MgO-bonded alumina castables

Abstract

MgO-bonded castables are one of the promising non-cement bonded refractories used for ladle lining. To make crack-free MgO bonded castables, the formation of layered double hydroxides (Mg-Al hydrotalcite) is proposed. In the present work, the influences of Al(OH)3 and hydratable alumina (ρ-Al2O3) and different curing temperatures (40 °C, 60 °C, 80 °C) on the formation of hydrotalcite are investigated. The hydration behavior and corresponding hydrates are examined using electrical conductivity, XRD, SEM, FTIR, and TG-DSC analyses. The results show that the increase in curing temperature is more conducive to the formation of hydrotalcite, where ρ-Al2O3 significantly promotes the formation due to the enhanced reactions between intermediates of Mg(OH)2 and Al(OH)3. After high-temperature treatment, the decomposition of a larger amount of hydrotalcite and Al(OH)3 and thereafter growth of microcrystalline spinel contribute to refined pore size distribution. Consequently, a higher hydration degree of ρ-Al2O3 and the formation of more hydrotalcite provide a higher bonding strength at room temperature, and the optimized microstructure enhances high-temperature strengths.