Corrosion of high alumina castables by CaO-Al2O3-(SiO2-MgO) system slag

The results of the static crucible tests of refractory alumina concretes with high content of fused corundum and MA–spinel are presented in the work. Two types of refractory materials: A–standard low cement castable (LCC) and B–ultra-low cement castable (ULCC) were tested. The corrosion tests were conducted with the real calcium-alumina slag, which is created in steel production. The refractory materials were annealed in the electric resistance furnace at the temperature of 1 450 °C for 5 hours in a static air atmosphere. The corrosion of materials was evaluated comparing the results of the chemical analyses of slag before and after corrosion tests, followed by the macroscopic and microscopic observations of the vertical cuts along the line at the refractory-slag boundary and X-ray phase analyses. Based on the results of chemical analyses it is evident that the progress of wear is in both tested concretes (high-alumina LCC and ULCC) similar. The corundum and corundum-spinel grains of matrix are dissolving in slag-melt. However, certain differences in the corrosion mechanism were found. Despite the minimal changes in the chemical composition of the aggressive slags, an intensive flow of slags at the surface and sub-surface occurs. In case of A sample, the corundum-spinel matrix is attacked predominantly and it creates a rough surface at the crucible wall. Therefore the larger grains (corundum and spinel) are released from matrix. In case of B sample, the corrosion process is steady and the interface is smooth.