Hydration of hydratable alumina in the presence of various forms of MgO

This work investigates hydration behavior of hydratable alumina in the presence of several forms of magnesia used for production of refractory castables. The mixtures of hydratable alumina with reactive magnesia, fused magnesite and deadburnt magnesite were hydrated at 20 °C and 110 °C. The hydration products were determined with X-ray diffractometer and the hydration extent was calculated from thermogravimetric analysis. The results revealed significant difference in the hydration products between the hydratable alumina-reactive magnesia mixture and the hydratable alumina-fused magnesite or deadburnt magnesite mixtures under the hydration conditions. The relationships of the compositions of hydrotalcite-like hydrates with different types of magnesias are elucidated. The bonding formed between hydratable alumina and magnesite aggregate in castables and its effect on the strength of the castables dried at 110 °C and fired at 816 °C was discussed.