The impact of pre-formed and in situ spinel formation on the physical properties of cement-bonded high alumina refractory castables

Alumina–magnesia and alumina–spinel castables present some unique characteristics. Whereas the in situ spinel (MgAl2O4) formation provides an enhanced corrosion and thermal-shock resistance to the castable, the composition with pre-formed grains shows higher volumetric stability and do not have the inherent MgO hydration problems. As these distinct ways of spinel incorporation result in particular properties to the refractory material, a castable containing both in situ and pre-formed spinel might present balanced properties and a suitable performance in steel ladle applications. Considering these aspects, cement-bonded high alumina castables containing both pre-formed and in situ spinel were developed and evaluated by means of assisted sintering tests, microstructural analyses, thermodynamics simulation and mechanical and thermal-mechanical properties evaluation. The CA6 formation presented different features according to the content of in situ spinel generation in the matrix, which affected the castable properties. Additionally, compositions containing both in situ and pre-formed spinel seemed to be a feasible way of attaining a designed linear dimensional change without affecting the spinel and CA6 contents.