Oxidation protection of CaO–ZrO2–C refractories by addition of SiC

The effect of SiC used as antioxidant in carbon-containing CaO–ZrO2 refractories and the behaviour of SiC in CO gas were studied. SiC was found to react initially with CO to form SiO2(s) and C(s) at ∼1200 °C, and then the formed SiO2 reacted with CaO in the refractories to form belite (2CaO·SiO2). The refractory microstructure was modified by addition of SiC. Due to the deposition of SiO2 in the large (2–10 μm) pores of the refractory through the reaction of SiO(g) with CO, the percentage of large pores decreased and a dense layer, mainly consisting of belite, was formed near the surface of the refractory after it was heated at high temperature (1500 °C). The oxidation resistance of CaO–ZrO2–C refractories was improved by reaction of SiC with CO to deposit C(s) and decrease the size of the large pores. The oxidation resistance of such refractories can be improved significantly when such a dense layer is formed near their surfaces.