Effect of MgO micropowder on sintering properties and microstructures of microporous corundum aggregates

Microporous corundum aggregates were fabricated based on superplasticity, with α-Al2O3 micropowder as the main raw material, by adding nano-sized alumina sol and MgO micropowder. The relationship between the superplasticity and the in-situ stress during sintering, the corresponding sintering properties, and the microstructures of the fabricated microporous corundum aggregates were investigated by means of X-ray diffraction (XRD), mercury porosimetry, and scanning electron microscopy (SEM). The experimental results show that the relationship between the superplasticity and the in-situ stress is the main factor that influences the sintering behavior of the microporous corundum aggregates. Various amounts of MgO micropowder were added to the α-Al2O3 micropowder for a fixed content of nano-sized alumina sol. With increasing MgO micropowder, which results in a greater in-situ stress, the total and closed porosity increased initially and decreased afterwards whereas the apparent porosity and bulk density decreased first and then increased. Microporous corundum aggregates with high closed porosity, low apparent porosity and small pore size were obtained with the addition of 1 wt% MgO micropowder. Therefore, the relationship between the superplasticity and the in-situ stress should be controlled in order to fabricate microporous refractory aggregates which have high closed porosity and small pore size.