Synthesis and characterisation of silica aerogel/carbon microfibers nanocomposites dried in supercritical and ambient pressure conditions

摘要

Experimental results on the physical and chemical properties of silica aerogel and its composites with carbon microfibers are reported. The aerogels and silica aerogel/carbon microfibers nanocomposites were prepared via the sol-gel process of organosilicon compound followed by successive washing and drying in different conditions. Part of nanomaterials was surface modified in TMCS-hexane mixture in 50 A degrees C and dried in ambient pressure. Simultaneously, the supercritical drying of aerogels and its nanocomposites in CO2 atmosphere was carried out. The carbon microfibers before usage in silica aerogel composites were chemically treated in nitric acid. The physical properties of silica aerogels were studied by measuring the bulk density, volume shrinkage, porosity, pore volume and thermal conductivity. In the case of pure aerogels dried via supercritical conditions, the structure presented much less contraction during drying and was more resistant to higher temperature. However, the properties of silica aerogels composites with carbon microfibers drying in ambient pressure were better than corresponding composites subjected to supercritical drying. It was shown that simultaneous oxidation of carbon fibres and chemical modification of silica aerogel in TMCS-hexane mixture contributed to the stable mesoporous structure of composite with very good physical properties, especially lower shrinkage.