Papers by Author: Fei He

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Authors: Fei He, Xiao Dong He, Yao Li
Abstract: Low-density xSiO2-(1-x)Al2O3 xerogels with x=0.9, 0.8, 0.7, 0.6 (mole fractions) were prepared by sol-gel and non-supercritical drying. Silica alkogels, which were the framework of binary composite materials, formed from tetraethyl orthosilicate (TEOS) by hydrolytic condensation with a molar ratio of TEOS: H2O: alcohol: hydrochloric acid: ammonia =1: 4: 10: 7.5×10-4: 0.0375. Aluminum hydroxide derived from Al(NO3)3·9H2O and NH4OH acting in the alcohol solution under the condition of catalyst. After filtrating and washing, the precipitation was mixed into silica sols to form SiO2-Al2O3 mixed oxide gels with different silicon and aluminum molar ratio. The structural change and crystallization of the binary xerogels were investigated after heat treatment at 600  for 2 h by the means of X-ray diffraction. Nitrogen adsorption experiment was performed to estimate specific surface area, porous volume and pore size distribution. The structural change of xerogels was observed by FT-IR spectroscopy. The resulting mixed xerogels possess of mesoporous structure which is characteristic of cylindrical pores, high specific surface area of 596-863 m2/g and a relatively narrow pore distribution of 2.8-30 nm. Al2O3 is introduced into the SiO2 phase and some of Al-O-Si bonds form.
Authors: Fei He, Xiao Dong He, J.F. Li, Ming Wei Li, S.M. Zhang
Abstract: The unitary thermal insulation fiber materials can not satisfy rigorous high temperature environment usually. New inorganic coatings were prepared by adding SiO2 aerogels super-insulation powder into high temperature adhesive. Aerogels are high dispersive solid materials which consist of colloid particles or high polymer molecule and have continuous random network structure filling with gaseous dispersive medium. The coatings with super insulation function were made by means of adding thermal-proof materials to the coatings. The microstructure of light porous power and the states of coatings on the surface of fiber paper under different state were observed by scanning electron microscope (SEM). The insulated effect of the composite materials was tested by considering thermal conductivity. On the basis of this, the coatings on the surface of fiber paper were optimized according to the material thermal-insulation performance and the materials that could be satisfactory to the service conditions were made in the end. The results show that silica aerogels powder is dispersed equably in high temperature adhesive. The new inorganic coatings possess themselves of good thermal-insulation effect and can be used as insulated space-layers. The insulation ability of fiber paper is improved obviously.
Authors: Xiao Dong He, Fei He, Yao Li
Abstract: Two-step acid-base catalyzed silica xerogels were prepared through sol-gel and ambient pressure drying. Various additive components were main fators which influenced the porosity of silica xerogles. An orthogonal array (OA) design OA9(34) was applied to select the optimum conditions of additives. The effects of the molar ratio of H2O, alcohol, HCl, and ammonia were evaluated on the basis of the other same process parameters. Every experiment was conducted several times under different process conditions which included reactive temperature, the acid catalyzed time, aging, exchanging solvent and drying for assuring gels formed. The porosity was an index which was used to appraise the characteristic of silica xerogels. Two kinds of silica xerogels, prepared by the most optimal molar ratio (OMR) and the best OA experiment respectively, were compared by means of SEM. The results showed that the most OMR of TEOS, H2O, alcohol, HCl and ammonia was 1:4:10:7.5× 10-4:0.0375.
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