Synthesis mechanism of AlN-SiC solid solution reinforced Al2O3 composite by two-step nitriding of Al-Si3N4-Al2O3 compact at 1500 °C

The in-situ controllable synthesis of AlN-SiC solid solution reinforcement in large-sized Al-Si3N4-Al2O3 composite refractory by two-steps nitriding sintering was examined. In the first step, a dynamic Al@AlN structure was constructed in the composite by pre-nitriding at 580 degrees C. During the subsequent sintering process, it cracked above similar to 900 degrees C, and micronized Al cluster (mixture of droplets and vapor) was extracted out gradually. As a result, multiple AlN mesophases were formed through different reaction paths, including i) initial AlN shell formed by solid Al with N-2, ii) reaction of Al cluster with N-2, and iii) reaction of Al cluster with Si3N4 from 900 degrees C to 1500 degrees C. The Si3N4 precursor serves as both a solid nitrogen source and an active Si source, and the controllable reaction between Al and Si3N4 leading to uniformly distributed AlN and Si mesophases. AlN-SiC solid solution is significantly formed when liquid Si appears. The shell, granule and whisker SiC-AlN solid solution were observed mainly depending on the dynamic AlN mesophase. The SiC-AlN solid solution reinforced Al2O3 materials is a novel promising refractory for large-scale blast furnace lining.