The Optimisation of Magnesia Containing Castables Containing Calcium Magnesium Aluminate Cement

摘要

Calcium magnesium aluminate (CMA) is a novel binder for steel ladle castables. It was reported previously that CMA has hydraulic properties and is beneficial in the matrix of castables to prevent ladle slag penetration and corrosion [1, 2]. The CMA grain contains microcrystalline magnesium aluminate spinel which is homogeneously distributed between hydraulic calcium aluminate phases. Applied in castables it develops an unique microspinel matrix. This study presents further application studies of magnesia containing castables based upon CMA. Both pre-formed magnesium aluminate spinel and magnesia are combined in different model systems. The matrix spinel contained within the model castables is derived from fused spinel, sintered spinel and combined with different quantities of spinel from CMA. At equal CaO contents CMA develops the same strength after drying but higher strength after firing is found than with a reference system of calcium aluminate cement (CAC) + spinel. This is assumed to be the effect of a higher sintering reactivity of the microspinel in CMA. Model alumina magnesia castables can be formulated around the addition of magnesia and CMA inside the castable matrix. The magnesia addition in CMA enables a reduction of free magnesia leading to an improvement of rheological properties and reduction of cracking risk associated with brucite formation during drying. This will still deliver improved corrosion resistance relative to reference alumina magnesia castable systems. Furthermore with a reduced magnesia content a lower permanent expansion due to less in situ spinel formation had been observed [2]. The present study shows that this enables a reduction of silica and improves the thermomechanical properties. However, it was found that with CMA the quantity of silica can be reduced, but nonetheless a small silica addition is recommended inside the castable matrix as it minimises the magnesia hydration and crack formation during castable drying.