溶胶-凝胶法低温合成莫来石的研究

Synthesis of Mullite at Low Temperature via Sol-Gel Route

以去离子水和无水乙醇为分散介质,以六水合氯化铝为铝源、正硅酸乙酯为硅源,通过1,2-环氧丙烷调凝,采用溶胶-凝胶法合成了莫来石前驱体凝胶。考察了环氧丙烷用量以及水浴温度对凝胶时间及莫来石合成的影响。研究表明,水浴温度65℃、1,2-环氧丙烷与铝的摩尔比为3:1时可以较快的制备出均匀稳定的莫来石前驱体凝胶。利用TG-DTA、XRD、FT-IR对干凝胶热处理过程中的结构变化及相演变进行了分析,结果表明,前驱体凝胶为第一类莫来石凝胶,在热处理过程中没有形成γ-Al_2O_3、铝硅尖晶石等中间相,在990℃左右凝胶晶化放热直接转变成单相莫来石。干凝胶经1000℃煅烧1h后可形成莫来石,1200℃煅烧后莫来石晶相发育良好。在热处理之前凝胶中已经形成Si-O-Al结构,这是莫来石低温合成的最主要原因。

Mullite has been synthesized at low temperature via sol-gel route using aluminium chloride hexahydrate and tetraethyl orthosilicate as the precursors,deionized water and ethanol as the dispersion mediums,and propylene oxide as the gelling accelerator.The effect of the amounts used of propylene oxide and the reaction temperature on the gelation time was investigated.The effect of the reaction temperature on the mullite was also studied.The results showed that uniform and stable.mullite precursor gel could be synthesized when the reaction temperature was 65°C and the mole ratio of propylene oxide and aluminum chloride hexahydrate was 3:1.The phase transformation of mullite precursor xerogels during the thermal process and the reaction mechanism during the synthesis process of mullite via sol-gel route at low temperature were also investigated by TG-DTA,XRD and IR.The results indicated that mullite phase occurred as the sole phase when the calcination temperature increased to 1000°C,the diffraction peak of Al,Si-spinel orγ-Al2O3 was not formed at any heat treatment temperature,Si-O-Al bond formed in the precursor xerogels and the precursor xerogels transformed into mullite after being calcined at different temperatures for 1 h.