The Role of Granulometry and Additives in Optimising the Alumina Matrix in Low Cement Castables
To optimise the particle packing of the castable, different kinds of fine aluminas can be used to form the matrix: calcined, semi-reactive, monomodal reactive or multimodal reactive aluminas. A systematic approach has been conducted to investigate different ways to optimise particle size packing in low cement castable formulations thanks to the use of different kinds of aluminas. Typical average particle size for these aluminas ranges from 0,3 μm to 6 μm. The potential of a new alumina product has been explored as a competitive alternative to reactive alumina. It has a median particle diameter (d50) around 3 μm and has a monomodal granulometry with some fines particles around 0,5 μm coming from its specific milling technology. Dinger and Funk’s packing model has been used to optimise packing design of the castable with this alumina. In many cases the sole use of this alumina in the formulation can be fully satisfying for the application. In other cases, the combination with a reactive alumina (d50 = 0,5 μm) is useful to further improve rheological properties. Bimodal aluminas are usually found to be very efficient to achieve good rheological properties and high levels in applicative refractory tests. The effects of the particle size curve have been investigated to understand the impact on castable properties. Flowability behaviour and torque evolution during mixing have been followed to characterize rheology. It will be shown that differences between various aluminas can be compensated by usage of specific additives.