THE ROLE OF MAGNESIA IN STRENGTH DEVELOPMENT OF SPINEL BONDED BASIC CASTABLES

摘要

1. The compositions of hydrotalcite hydrates formedthrough the hydration-reaction of hydratable aluminaand various forms of magnesia vary with theMg(OH)_2:Al_2O_3 ratio in the hydrated mixtures, ratherthan the MgO:Al_2O_3 ratio in the starting mixtures. 2. The presence of magnesia, either as aggregate or component of the binding system in hydratable alumina-bonded castables, improves the strength after drying at 110℃, due to development of hydrogen bonding between hydrotalcite and Mg(OH)_2 on the surface of magnesite particles. 3. The polycondensation accompanying dehydroxylation of hydrotalcite and Mg(OH)_2 at 816℃ contributes tothe strength of hydratable alumina-bonded castables containing magnesia. 4. The morphological features of hydrotalcite facilitated the co-polycondensation with Mg(OH)_2 on the surfaces of magnesia grains and as a result, higher strength of the magnesia-containing castables after drying and firing at 1500℉. 5. The first stage of hydrotalcite decomposition (interlayer water at 150-220℃) provides escape channels for the vapor released in the second stage (300-400℃), lowering the risk of explosion cracking during curing and firing of hydratable alumina bonded castables.