Effect of SiO₂ Micropowder on Properties of Calcium Hexaluminate Castables for Coal Catalytic Gasifiers

Furnace lining materials for coal catalytic gasifiers should have good high-temperature strength and alkali slag corrosion resistance. Calcium hexaluminate castable is a promising application direction. In this paper, the effect of the addition of SiO₂ micropowder on the performance of a calcium hexaluminate castable was evaluated through sintered properties, high-temperature strength, anti-alkali slag performance, and microstructural analysis. The results show a significant increase of grain and matrix bonding strength and a decrease of porosity with SiO₂ micropowder addition. The castables with 3 mass-% SiO₂ micropowder possessed 14.3 MPa CMOR (Cold Modulus of Rupture) and 107.6 MPa CCS (Cold Crush Strength) after heat treatment at 800 °C for 3 h. The hot flexural strength is 11.8 MPa and the retained residual flexural strength of the castables reached 37.13 % after five thermal shock cycles (water cooling) at 1100 °C. The potassium element in the slag has a very small amount of penetration and aggregation at the interface between the sample and the slag.