The effect of Si content, firing temperature, and urea additive on the properties of nitride-bonded SiC refractories

Abstract

The microstructure/properties relationship of nitride-bonded SiC refractories has been studied in the presence of Si and urea additives. The samples were prepared by mixing, shaping, and firing at 1450 to 1600 o C in a controlled atmosphere. Physical properties were evaluated by measuring density, porosity, and cold crushing strength (CCS). XRD, SEM, and TEM were employed to study the phase and microstructural evolution. The increase of Si enhanced the bond formation, which contributed to density and strength improvement. The firing temperature had the same effect up to 1550 o C. At 1600 o C, however, the density and CCS decreased, which were attributed to nitride phase decomposition. The urea addition improved the mechanical properties and increased the depth of nitridation.