二氧化硅气凝胶具有极高的孔隙率和非常低的热导率,在保温隔热领域应用前景十分广阔。探究了二氧化硅气凝胶在不同温度热处理条件下热导率的变化情况,并从微观结构角度解释了其变化机理。随着热处理温度升高,气凝胶热导率先降低后升高。当热处理温度低于400 ℃时,气凝胶的热导率随热处理温度的升高而降低,这是因为较低温度的热处理去除了气凝胶内部的大部分杂质,并且使气凝胶的内部孔隙结构更加均匀;当热处理温度处于400~700 ℃时,更高温度的热处理使得气凝胶内部的孔径明显增大,气凝胶颗粒增大,使得热导率随热处理温度的升高而增加;当热处理温度高于700 ℃时,气凝胶颗粒开始烧结,骨架结构坍塌,密度显著增大,热导率也急剧上升,此时已不具备气凝胶轻质多孔的典型特征,可以认为已经失效。实验结果对亲水型气凝胶的应用给出了一定的指导:为保证气凝胶绝热能力的最优化,可以对气凝胶在400 ℃的温度下进行一段时间的保温;工作温度应在700 ℃以下,温度的升高会轻微降低气凝胶的隔热能力;气凝胶在700 ℃以上时会失去其绝热能力,因此不宜用于温度高于700 ℃的环境。

Silica aerogel has a broad application prospect in the field of thermal insulation due to its very high porosity and very low thermal conductivity.Tthe change of thermal conductivity of silica aerogel under different temperature heat treatment conditions was studied,and the related mechanism was explained on the basis of microstructure evolution.With the increase of heat treatment temperature,the thermal conductivity of aerogels first decreases and then rises.When the heat treatment temperature was lower than 400 ℃,the thermal conductivity of the aerogel decreased as the heat treatment temperature increase.This is because the lower temperature heat treatment removes most of the impurities inside the aerogel and makes the internal pore structure more uniform.When the heat treatment temperature was at 400~700 ℃,the higher temperature made the pore diameter inside increase significantly,and the aerogel particles increase,so that the thermal conductivity increased with the heat treatment temperature increase.When the heat treatment temperature was higher than 700 ℃,the aerogel particles began to sinter,the skeleton structure collapsed,the density increased remarkably,and the thermal conductivity also rised sharply.At this time,the typical characteristics of aerogel lightweight porous were not available.It is considered to have expired.Results showed that some guidance for the application of hydrophilic aerogel:the aerogel will have a best thermal insulation performance when treatment at 400 ℃ for a period of time.The aerogel′s working temperature should be below 700 ℃,and increase of temperature will slightly decrease the thermal insulation capacity of the aerogel;The aerogel will lose its thermal insulation capacity at temperatures above 700 ℃,so it should not be used at this temperature.