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Calcium alumino-titanate (CAT) is characterized by low thermal conductivity, low thermal expansion coefficient, and high refractoriness. The phase changes and microstructural evolution of a CAT-SiC composite refractory are investigated using X-ray diffraction, scanning electron microscopy, and thermodynamic analysis. Results show that the cold crush strengths of specimens fired in an oxidizing atmosphere are higher than those of specimens fired in a reducing atmosphere. In a reducing atmosphere, composites with SiO2 addition fired at 1350 °C exhibited the highest strengths. Good bonding occurred between different local reaction zones in specimens fired in an oxidizing atmosphere compared to those fired in a reducing atmosphere. Furthermore, a coexistent state of CA6 and corundum in CAT is observed in specimens fired in a reducing atmosphere, and mullite whisker growth occurred for composites without AlF3·3H2O addition, where the TiO2 present in CAT acts as a catalyst.

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.

Calcium alumino-titanate (CAT) is a composite refractory material that exhibits a low thermal conductivity, high melting point, high refractoriness, low thermal expansion coefficient, and good thermal shock resistance. CAT-bauxite-SiC composites were prepared by using bauxite, CAT, SiC, α-Al2O3, metallic Si, and Guangxi white clay as starting materials and an Al(H2PO4)3 solution as a binder. Their densification behavior, phase changes, and microstructures were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermodynamic analysis. The results show that the bulk density initially increases and then decreases with temperature because of SiC oxidation and the formation of a liquid phase. In addition, the aggregation of corundum particles is enhanced at higher temperatures for bauxite grains, and excessively high temperatures cause abnormal growth of the corundum particles. Furthermore, the mullite whiskers present in the CAT grains begin to break through the surface of the liquid phase at firing temperatures above 1450 °C; these whiskers show perfect crystallization at 1600 °C. Finally, the quantity of Ca-rich (anorthite) regions around the SiC grains increase with temperature due to an increase in SiC oxidation and calcium ion diffusion.

Alkali resistance and thermo-mechanical properties of the transition zone of cement rotary kilns refractories are the key factors affecting their service life. Calcium alumino-titanate (CAT) containing bauxite-SiC composites were prepared using bauxite, SiC, CAT, Guang Xi white clay, α-alumina, and metallic silicon powder as starting materials and Al(H2PO4)3 as the binder. The effects of the CAT particle size on the phase composition, microstructure, thermo-mechanical properties, and alkali resistance of the CAT-containing bauxite-SiC composites during firing were investigated. The results reveal that the CAT particle size strongly affects the composites’ microstructure and sintering densification. With decreasing particle size, the particle-particle and particle-matrix interfacial bonding deteriorates gradually. When CAT particles are added, the specimens show higher strength, refractoriness under load, and residual rupture strength than the specimens with fine CAT powders. Specimens with fine CAT powders show lower coefficient of thermal expansion compared to the specimens with CAT aggregates. The alkali attack test confirms that the bauxite-SiC composite refractories with CAT aggregates show better alkali resistance than those with CAT fine powder. According to the alkali mechanism, 1) K vapors penetrate the specimen through the open and connected pores and cracks, 2) K vapors react with anorthite and corundum to form kalsilite accompanied by the formation of a liquid phase and new cracks.

Calcium alumino-titanate (CAT) is obtained by processing titanium-iron slag in an industrial process that involves melting, homogenization, de-ironing, and silicon reduction. The correlation between CAT addition and the microstructures, phase compositions, thermo-mechanical properties, and alkali resistance of bauxite-SiC refractories were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), as well as by thermodynamic analysis. The results show that CAT can react with SiO 2 to form a low-melting-point phase (anorthite), causing the CA 6 , CA 2 , and CaTiO 3 phases to disappear. In addition, the formation of the liquid phase in the Al 2 O 3 -TiO 2 -CaO-SiO 2 system at high temperatures deteriorates the properties of the composite. The strength and refractoriness under load of the composite decrease with the addition of CAT. Moreover, the thermal shock resistance of the composite first increase and then decrease with the addition of CAT. For CAT concentrations ≤10.8 wt%, the composite demonstrates good alkali resistance. The alkali resistance of the CAT-containing bauxite-SiC composite is mainly dependent on the external dense regions.