Magnesia sinter hydration–dehydration behavior in refractory castables

Magnesia (MgO) easily reacts with water when exposed to humidity or during the mixing of refractory castables, resulting a Mg(OH)2 coating layer on a particles’ surface. When castables dewater (above 350 °C), this coating begins to decompose, generating porosity and a highly reactive magnesia. Despite the abundant literature concerning magnesia hydration–dehydration mechanisms, few studies were related to refractories. In the present work, aqueous suspensions of thermally treated magnesia sinter were prepared and the influence of the calcination temperature on magnesia reactivity was evaluated by the apparent volumetric expansion (AVE) measurements. Based on these results, the drying behavior of magnesia sinter containing castables was related to mechanical strength and porosity measurements. The effects of re-hydration damages caused by humidity exposition after drying were also investigated.