pH值和煅烧温度对莫来石生成的影响

以溶胶凝胶法为基础，采用正硅酸乙酯(C8H20O4Si)、硝酸铝(Al(NO3)3·9H2O)为主要原料，借助X射线衍射仪进行检测，系统研究了pH值、煅烧温度对生成3∶2型莫来石以及生成过程的影响。结果表明：莫来石凝胶介于单相凝胶和双相凝胶的混合尺度，pH值在4~10范围内均可生成莫来石，煅烧温度为1175 ℃时出现明显的莫来石化；pH=4时，不利于无定形硅的转化；在pH值为5~9范围、煅烧温度1200 ℃时完全莫来石化，且生成的莫来石结晶度总体变小，晶胞参数上下波动。莫来石的生成经历了无定形硅和铝的氧化物到铝硅尖晶石再到莫来石的过程。

Effect of precursor pH and calcination temperature on the formed of mullite

Mullite powders have been successfully prepared by a sol-gel process using tetraethyl orthosilicate(TEOS,C8H20O4Si) and aluminum nitrate(Al(NO3) 3.9H2O) as raw materials,with the pH being controlled byaddition of ammonia.The effect of varying the pH and calcination temperature on the formation of mullite was studied.It was found that mullite can be obtained when pH is in the range 4-10.When pH was in the range 5-10 and the material calcined at 1200 ℃,mullite was obtained as a pure phase,but its crystallinity was relatively lowand the cell parameters were not consistent.Formation of mullite was incomplete at pH 4.The process was shown to involve the reaction of amorphous silica and aluminum oxide to give an Al-Si spinel,which is subsequently converted to mullite.