Effects of firing temperature and Al additive on the microstructures and properties of SiC-CA6 composite refractories

Abstract

SiC-CA6 composite refractories were successfully prepared by using SiC aggregates, sintered CA6 powders, Al powders and calcined α-Al2O3 as the raw materials. The effects of the firing temperature and Al additive on the physical and mechanical properties, phase evolution and microstructures were studied. The Al additive can significantly affect the properties of the SiC-CA6 composite refractories. With the addition of metallic Al, whiskers with interlocking structures could form in the SiC-CA6 composite refractories during the firing process, which improved the properties of the materials. The SiC-CA6 composites fired at 1450 °C with Al additive had good comprehensive properties with low porosity (14.7%), high strength (15.78 MPa for CMOR and 13.98 MPa for HMOR) and high elastic modulus (54.21 GPa). Compared with the samples without the Al additive, the samples with the Al additive had a lower porosity, and higher density and strength at all firing temperatures. For the samples without Al addition, the decomposition of the phenolic resin could form residual carbon remaining in the samples, which could decrease the oxidation of the SiC in the materials and inhibit the sintering of the samples. With increasing firing temperature, the residual carbon decreased and gradually transformed from a flaky morphology to an amorphous morphology.