添加剂对气凝胶孔径分布的影响

以稻壳灰为硅源,在适宜的凝胶形成条件下,加入不同添加剂(羟基类和酰胺类有机物),通过溶胶-凝胶、溶剂置换过程及超临界二氧化碳干燥工艺制备了硅气凝胶. 结果表明,丙三醇、乙二醇添加量为15%~20%时调控作用显著,凝胶孔洞变小且分布更均匀,比表面积增大、平均孔径减小;聚乙二醇使凝胶化时间缩短,孔径分布较均匀;二甲基甲酰胺、甲酰胺调控效果最显著,所得样品孔径集中分布于20~40 nm,比表面积均在750 m2/g以上. 聚乙烯吡咯烷酮可加快缩聚速率,使小孔比例大幅增加,网络结构致密.

Influence of Additives on Pore Size Distributions of Silica Aergels

Silica aerogel is prepared using rice husk ash as silicon source. Several additives are added into the sol under suitable conditions, through the steps of sol-gel, solvent exchange and supercritical carbon dioxide drying. The added amount 15%~20% of glycerol and ethylene glycol have strongly influence on the pore size distributions (PSD). During this process, silica aerogel with smaller pores, more uniform, higher specific surface area and smaller average pore size is produced. High molecular weight polyethylene glycols can shorten the gelation time and the PSD is relatively uniform. Formamide and dimethylformamide have the most significant effect on the samples with 20~40 nm PSD and high specific surface area above 750 m2/g. Polyvinylpyrrolidone can accelerate polymerization rate and the aerogel has more small pores and dense network structure.