Water adsorption and desorption kinetics on silica insulation
Water adsorption and desorption kinetics on silica insulation
复制标题
二氧化硅绝缘体上的水吸附和解吸动力学
DOI：
10.1006/jcis.1996.0300
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发表时间：
1996
期刊：
影响因子：
--
通讯作者：
D. E. Cagliostro
中科院分区：
文献类型：
--
作者：
A. Feng;B. J. McCoy;Z. Munir;D. E. Cagliostro
摘要二氧化硅是航天运输车辆隔热材料的重要组成部分。虽然二氧化硅绝缘层通常是亲水的，并且在飞行后需要再防水，但据报道，在真空中加热和冷却时，二氧化硅绝缘层会变得疏水，因此，在重返大气层后可能会疏水。为了理解和模拟这些过程，用热重法、傅立叶变换红外光谱法和x射线光电子能谱法研究了水在二氧化硅上的解吸和吸附速率。在真空条件下，在200 ~ 1000℃范围内加热具有高比表面积的二氧化硅粉末，获得不同温度下的红外吸收光谱，并用x射线光电子能谱分析表面结构。基于Langmuir速率表达式建立了吸附动力学模型。通过数值拟合实验结果，确定了吸附和解吸活化能。研究发现，经过热处理的二氧化硅在几秒钟内就会吸附水，这意味着经过热处理的二氧化硅暴露于水后，疏水性会迅速丧失。
Abstract Silica is an important component of thermal insulation used in aerospace transport vehicles. Although normally hydrophilic and requiring rewaterproofing after flight, silica insulation has been reported to become hydrophobic on heating and cooling in a vacuum and, therefore, potentially hydrophobic after reentry. To understand and model these processes, the rates of desorption and adsorption of water on silica were studied by thermogravimetry, Fourier transform infrared spectrometry, and X-ray photoelectron spectroscopy. Silica powders with a high surface area were heated in vacuo in the temperature range 200–1000°C, infrared absorbance spectra were obtained at various temperatures, and surface structure was examined by X-ray photoelectron spectroscopy. A kinetic sorption model was developed based on a Langmuir rate expression. Activation energies for adsorption and desorption were determined by fitting the experimental results numerically. The study found adsorption of water on the heat-treated silica occurs within seconds, implying hydrophobicity is lost rapidly after the heat-treated silica is exposed to water.