Preparation of Microporous Corundum Aggregates and their Applications in Lightweight Alumina-Magnesia Castables

Abstract

The industrialization process all over the world has brought with it problems of energy being consumed too fast and a serious energy crisis has developed. The use of heat insulation refractories is a main factor used to reduce industrial furnace energy. Heat insulation material that is nearer the work layer provides better insulation. Two areas work are discussed in this paper. Firstly, in order to prepare the kind of high-performance microporous aggregate used for the alumina-magnesia castable in ladle linings, with α-Al₂O₃ micropowder as the main raw material, a microporous corundum aggregate was prepared by the method of wet grinding. The distribution of pore size, the thermal conductivity and the microstructure of the microporous corundum aggregate were tested by means of mercury porosimetry, a laser flash thermal analyzer and scanning electron microscopy, etc. The results show that:

• There are large numbers of pores in the microporous corundum aggregate, which are uniformly distributed on the inside, the internal corundum grains grow well and there are short columnar crystals

• Compared to the ordinary tabular corundum aggregate, the closed porosity of the microporous corundum aggregate is higher, the apparent porosity and the bulk density are lower, moreover, the pores inside it are smaller

• When the thermal conductivity of the aggregates is compared, that in the microporous corundum aggregate is significantly lower than that of ordinary tabular corundum (its bulk density is 3.63 g/cm⁻³, this is 42% less).

Secondly, a lightweight alumina-magnesia castable was obtained using this microporous corundum aggregate, fused magnesia powder and corundum powder as the main raw materials. In terms of the alumina-magnesia castable, the sintering properties, the strength after baking and the heat treatment at different temperatures, the thermal conductivity coefficient and the resistance to slag were tested in the experiment. The results show that:

• Compared with the ordinary alumina magnesia castable which is made of tabular alumina, the lightweight castable has a lower linear change rate, greater apparent porosity and smaller bulk density. Its strength after baking and medium temperature heat treatment can reach the requirements of industrial production; however, the its strength improves obviously after heat treatment at 1500°C

• When the thermal conductivity of castables are compared, the thermal conductivity of two kinds of castables is basically the same at 350°C. When the test temperature rises to 600 and 800°C, the thermal conductivity of the lightweight castable made of the microporous corundum aggregate is significantly lower

• When the resistance to slag is compared, the two kinds of castables have basically the same corrosion index; the penetration index of the lightweight alumina-magnesia castable is 14.3% larger.