Synthesis and characterization of reaction-bonded calcium alumino-titanate-bauxite-SiC composite refractories in a reducing atmosphere

To take full advantage of the excellent properties of CA6 present in calcium alumino-titanate (CAT) and reduce the formation of the low melting point phase (anorthite), CAT-bauxite-SiC composite refractories were fabricated under buried sintering in order to achieve low thermal expansion, superior high-temperature performance, and increased alkali resistance. Furthermore, the corrosion mechanism of K vapor was investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results show that CA6 present in CAT can be partially retained and the hot strength of CAT-bauxite-SiC composites slowly decreases when the amount of CAT added is less than 21.6 wt%. The cold strength and bulk density decrease with the CAT content, and the residual ratio of MOR firstly decreases and subsequently increases with the CAT content. For the specimens with CAT additions, 43.2 wt% CAT results in the highest volume expansion at high temperatures. It is proposed that the corrosion mechanism of CAT aggregates under buried sintering is as follows: 1) K vapors penetrate into the CAT with high CA6 content through the lamellar CA6 gap and deposit on the inner regions of CAT; and 2) K vapors react with corundum and anorthite present in CAT and cause the microstructural destruction of CAT due to a decrease in the amount of the Al2O3-CaO-SiO2 liquid phase in the CAT. The alkali resistance of the CAT-bauxite-SiC composites decreases as the CAT content increases, which is attributed to poor sintering densification and high apparent porosity.