莫来石纤维增强SiO_2气凝胶隔热材料的制备工艺研究

以正硅酸乙酯(TEOS)为硅源,氢氟酸(HF)为催化剂,采用溶胶-凝胶法及超临界干燥技术制备了莫来石纤维增强S iO2气凝胶隔热材料,研究了HF催化剂、溶剂等制备因素对溶胶-凝胶过程的影响。结果表明,加入HF可以大大加快凝胶化过程,使凝胶时间从几小时缩短至几分钟;溶剂EtOH对凝胶化过程有明显的抑制作用,凝胶时间随其用量的增加而增加;H2O对凝胶化过程的影响比较复杂,凝胶时间随其用量的增加先减后增,转折点处水硅摩尔比为5∶1;气凝胶制备过程中加入甲酰胺可以调节凝胶内部网络结构,防止干燥时由于应力不均而开裂或破裂;适宜的原料配比(摩尔比)为:TEOS∶H2O∶HF∶EtOH∶甲酰胺=1∶(4~6)∶(0.05~0.1)∶(3~6)∶(0.3~0.5)。

Study on the preparation technique of SiO2 aerogels heat insulation composites reinforced by mullite fiber

SiO_2 aerogels heat insulation composites were prepared via sol-gel process and super drying technique using tetraethoxysilane(TEOS)and hydrofluoric as precursor and catalyst,respectively,and studied the effects of many factors on sol-gel process,such as the hydrofluoric acid catalyst,solvent and so on.The results showed that adding hydrofluoric can quicken the process of gelation,and as a result the gelation time was shortened from several hours to several minutes;the solvent ethanol have restraint on the process of gelation evidently,and the gelation time increases with the increase of the ethanol dosage;the effect of water on the process of gelation was complex,and the gelation time decreases first and then increases with the increase of the water dosage,the ratio of water to tetraethoxysilane is 5∶1 at the turning point.Adding formamide can adjust the network fabric within the gel,and prevent the gel from crazing or breaking in the process of drying because of the uneven stress.The suitable mole ratio of the tetraethoxysilane,water,hydrofluoric,ethanol and formamide is 1∶(4~6)∶(0.05~0.1)∶(3~6)∶(0.3~0.5).