Abstract: The silica aerogels are super thermal insulating materials due to their extremely low thermal conductivities.The gaseous thermal conductivity in aerogels is much smaller than that of the gas in free space since the motions of gas molecules are greatly restricted by the fine solid matrix and extremely fine pore sizes in aerogels.This study presented several models to relate the pore sizes and the nanoscale solid skeleton with the gaseous thermal conductivity.The results show that the gaseous thermal conductivity in the silica aerogels decreases dramatically with reducing the pressure and pore sizes and with increasing the density.Thus，the gaseous thermal conductivity in aerogels at very low pressures is far smaller than that of the free gas at the ambient pressure.The nanoscale solid structure of the silica aerogels has a significant effect on the gaseous thermal conductivity，especially for pressures between 0.01×10⁵ Pa and 100×10⁵Pa.

Key words: silica aerogel, gaseous thermal conductivity, pore size, nanopore

摘要： 气凝胶是一种超级隔热材料，具有极低的整体热导率。气凝胶的纳米多孔网络结构极大限制了气体分子热运动，使得气凝胶中的气相热导率低于自由气体的气相热导率。本文介绍并讨论了气凝胶气相热导率的基本理论和模型，考察了孔径尺度和气凝胶固相骨架对气相热导率的影响。结果表明，气凝胶气相热导率随气压和孔径的减小而迅速降低，随气凝胶密度的增大而降低。当压力极低时，气凝胶的气相热导率远低于常压下大空间的静止空气。气凝胶纳米固体网格对气相热导率存在重要影响，在(0.01～100)×10⁵ Pa的压力范围内影响尤其显著。

关键词: 气凝胶, 气相热导率, 孔径, 纳米孔