Erosion of Sintered Si3N4-Al2O3 and Si3N4-MgAl2O4 by Molten Blast Furnace Slag

Erosion of sintered Si3N4-Al2O3 and Si3N4-MgAl2O4 by molten blast furnace slag at 1500°C was studied by rotating cylinder method. Six kind of materials were prepared. They were sintered Si3N4-Al2O3 which contains 20, 40 or 60eq% Al2O3, and sintered Si3N4-MgAl2O4 which contains 10, 20 or 40mol% MgAl2O4. The material containing 60eq% Al2O3 showed poor erosion resistance, but the other five materials showed superior erosion resistance to that of sintered alumina. After the erosion test, the blast furnace slag adhered on the surface of the materials, and the slag permeated into pores in the material. At the slag-material interface, some solid particles which are considered to be β-Si3N4 or β′-sialon particles dispersed into the slag. It can be considered that the erosion mechanism of the sintered Si3N4-Al2O3 and Si3N4-MgAl2O4 by molten blast furnace slag is dissolution of some components of the material and dispersion of undissolved particles in the material into the slag. When the material contacts with the molten blast furnace slag, the slag permeates into the material through pores, and dissolves some components of the material. By the reaction, the quantity of liquid phase in the material increases. It is considered that the dissolution rate of β-Si3N4 and β′-sialon particles are lower than that of X phase sialon, Al2O3 and MgAl2O4 particles. Therefore, β-Si3N4 and β′-sialon particles scarcely dissolve into the molten slag. But because the quantity of liquid phase in the material increases, they disperse into the slag remaining the form of solid phase.