Synthesis Of Al₄SiC₄ From Al₂O₃, Al₂Si₂O₅(OH)₄ And C As Raw Materials

Al₄SiC₄ probably can be used as nonoxide raw material for structure ceramics and refractories with excellent properties.From the reports so far, Al₄SiC₄ was synthesized by using starting materials of metal+carbon, metal+oxide+carbon or carbides.The present research investigated factors influencing the synthesis of Al₄SiC₄ by using starting materials of Al₂O₃, Al₂Si₂O₅(OH)₄ and C.Powder mixture or compact mixture had no obvious difference on Al₄SiC₄ formation. Al₄SiC₄ was observed from 1500℃and the formation quantity was increased with raised temperature. Al₄O₄C was detected from 1550℃and was decreased after increased with raised temperature. There was not mullite phase in the samples heated at 1450℃and higher temperatures and all SiO₂ had been reducted into SiC at 1450℃. For the mixtures with C:Al₂O₃:Al₂Si₂O₅(OH)₄=24:3:1 and 16:3:1, the reactions were sufficient when heated at 1700℃for 5h and 7h. The residual SiC in the formation product was gradually decreased by reducing the ratio of Al₂Si₂O₅(OH)₄ in the mixtures. Pure Al₄SiC₄ phase was formed when heating the mixture with C:Al₂O₃:Al₂Si₂O₅(OH)₄=16:3.3:0.7. The residual Al₄C₃ was observed when further reducing the ratio of Al₂Si₂O₅(OH)₄ in the mixtures. The pure Al₄SiC₄ phase had grain sizes with about 4～7μm length, about 2～4μm width and about 1～2μm thickness. Grain sizes of Al₂O₃ or Al₂Si₂O₅(OH)₄ had remarkable influence on composition of the product. When the grain size of Al₂O₃ or Al₂Si₂O₅(OH)₄ was increased, there was residual SiC besides Al₄SiC₄ in the formation products. Graphite or carbon black as C material had no obvious influence on composition of the product. Combining the test results and thermodynamics calculations, it was known that SiC was formed firstly, Al₄O₄C secondly and Al₄SiC₄ lastly when the mixture was heated. Al(g),Al₂O(g),SiO(g) and CO(g) were primary volatility gases in the reactions.