High temperature behavior of Si 3N 4-bonded SiC bricks in blast furnace environment

An extensive experimental study has been carried out to better understand the high temperature properties and behaviours, such as oxidation, alkali-erosion and thermal shock resistance of the Si N -bonded SiC refractory. The mechanism of erosion damage of the Si N -bonded SiC brick lining in the blast furnace environment was investigated by means of scanning electron microscope (SEM), electron probe micro-analysis (EPMA) and X-ray diffraction (XRD) techniques. The results show that the alkali erosion is mainly caused by potassium penetration into the brick lining. The alkali reactions with the oxidation product SiO result in the formations of low melting point potassium silicates, such as K O·SiO and K O·2SiO . These silicates are then peeled off, from time to time, leading to continuous consumption of the SiO layer formed by the oxidation of SiC. Abnormal temperature variations in the furnace wall due to blowing-on or unstable operation will create thermal shock damage to the brick lining and speed up the oxidation and alkali erosion process. As a result of the combined effect of the oxidation, alkali erosion and thermal shock, caves and cracks are generated at the working surface of the SiC brick lining. It is believed that these are the major factors that deteriorate the integrity and stability of the working surface of the SiC brick lining. Based on the current work, an erosion mechanism, namely, oxidation→alkali erosion→melting or peeling-off of silicates→new oxidation and so on, was proposed for the Si N -bonded SiC brick lining used in the blast furnace.