In the refractory industry, the powder with particle size less than or equal to 5um is generally called ultra-fine powder, which has many varieties, mainly including active SiO2 powder (i.e. silica fume), &-AL2O3, white corundum powder, brown corundum powder, SiC powder, magnesium aluminum spinel powder, etc. In amorphous refractories, the particle size, shape, density, activity and specific surface area of ultra-fine powder will affect the fluidity, filling and sintering of the material. The most widely used are active SiO2 and &-AL2O3 ultrafine powders. The dosage of 5-7% is appropriate. However, the filling effect of activated SiO2 ultrafine powder is better than & - Al2O3 powder, and the dosage is also less.
In the refractory castable, the function of adding ultra-fine powder is to enhance the filling, increase the fluidity, improve the density, reduce the apparent porosity, reduce the water consumption and improve the construction performance
