White fused alumina 325 mesh improve the quality of alumina-based castables
Generally speaking, white tabular alumina is a refractory material superior to white fused alumina. However, in some specific applications, adding White fused alumina 325 mesh can increase the quality of refractory castables.
It gets better performance in the following aspects:
Higher bulk density
Cold Bending strength
Cold compressive strength
Better thermal shock resistance.
Lower apparent porosity
Lower thermal expansion coefficient
The inner layer of RH vacuum furnace dip tube lining is generally made of refractory bricks, the middle is a metal shell, and the outer layer is made of refractory castables. The molten slag and molten steel always shock and pound on the castales. And intermittent thermal shock damage due to rapid cold and rapid heat. As a result, the castables will get spall off from the kiln. Thus, the quality of refractory castable has a direct impact on the service life of the dip tube. Most castables in the market are alumina-based castables. It is a mixture of most part sintered tabular alumina with fused alumina powder and calcium aluminate cement.
In practical applications, technicians found that adding a certain amount of white fused alumina powder to the castable can improve its performance. In the mixing process, tabular alumina reacts with calcium aluminate cement and produces calcium hexaluminate(CA6). The calcium hexaluminate gets a large volume expansion. That results in a decrease in the volume density of the castable. After adding white fused powder 325mesh, the reaction between white fused alumina and calcium aluminate cement is relatively insufficient. At the same time, there will be less calcium hexaluminate. And many tiny pores are formed inside the matrix. So it can improve the thermal shock resistance of the castable.
It will get the best performance by adding 20% white fused alumina powder 325 mesh. The volume density and thermal shock resistance of corundum castables increase significantly, and the apparent porosity and thermal expansion coefficient decrease.
