Microstructures and Properties of Carbon Refractories for Blast Furnaces with SiO₂ and Al Additions

Microstructures and properties of carbon refractories specimens for blast furnaces with SiO₂ and Al additions were investigated after coking for 3 hours at 1400 °C with the aid of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray, mercury porosimetry, and a thermal properties analyzer. Additives can influence the matrix structures and improve the properties of specimens. SiO₂ additions decreased the mean pore diameter and tremendously increased <1-μm pore volume by filling in the pores and matrix, resulting in an increased particle packing density. Addition of Al improved the thermal conductivity by the in-situ formation of well-developed Al₄C₃, AlN, and SiC whiskers. With double addition of SiO₂ + Al, not only the mean pore diameter decreased but also the thermal conductivity; <1-μm pore volume and cold crushing strength increased by combining the above mentioned superiority of single additive; and more SiC formed, providing greater assistance to improve such material properties.