Preparation and blast furnace slag corrosion behavior of SiC–Sialon–ZrN free-fired refractories

Abstract Sialon–ZrN powders were synthesized from low-grade bauxite using a zirconite additive by carbothermal reduction nitridation (CRN). The as-synthesized Sialon–ZrN powders were subsequently used as SiC-based free-fired refractories. Their phase compositions and microstructures of the powders were determined using X-ray diffraction and scanning electron microscopy. The physical properties and blast furnace (BF) slag resistance of the SiC–Sialon–ZrN free-fired refractories were also studied. The results show that the low-grade bauxite and zirconite powders were transformed to β-Sialon and ZrN by the CRN process at 1600 °C. The phenolic resin provided a strongly bonded interface between the Sialon–ZrN matrix and SiC particles and thus enhanced their combined strength after drying at 150 °C. The strength increased as the temperature was elevated from 1000 °C to 1500 °C. As the ZrN content increased, the slag erosion rate of the SiC–Sialon–ZrN free-fired refractories initially decreased and then increased after being heated at 1500 °C. The presence of ZrO 2 in the slag (oxidized from ZrN) revealed that the ZrO 2 did not react with other oxides in the BF slag to form low melting point phases. This may play a crucial role in its BF slag erosion resistance. The corrosion mechanism of the BF slag towards the as-prepared SiC–Sialon–ZrN free-fired refractories was determined to be oxidation-erosion-dissolution-penetration.