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Effect of boron doping on waterproof and dielectric properties of polyborosiloxane coating on SiO2f/SiO2 composites

Chinese Journal of Aeronautics 2019年第8期32卷 2017-2027页

作者： Long XIA Siru LU Bo ZHONG Longnan HUANG Hua YANG Tao ZHANG Haibo HAN Pan WANG Li XIONG Guangwu WEN School of Materials Science and Engineering Harbin Institute of Technology(Weihai)Weihai 264209China School of Science Lanzhou University of TechnologyLanzhou 730050China Shanghai Institute of Spacecraft Equipment Shanghai 200240China School of Materials Science and Engineering Shandong University of TechnologyZibo 255000China

A hydrophobic coating of the silica fiber reinforced silica composites(SiO2f/SiO2) was synthesized by sol-gel method using methyltriethoxy-silane(MTES) and boric acid(B(OH)3) as raw materials. The relationship among boron doping, chemical structure of precursors and durability of hydrophobic coatings was discussed. The Si-O-B and methyl groups were successfully introduced in the gel precursors according to the FT-IR and XPS results. The resins were filled in the internal and surface holes of the SiO2f/SiO2 composites partially or completely, which is beneficial to reduce the physical adsorption of the moisture. In addition, hydroxyl groups of the SiO2f/SiO2 composites reacted with the resins and hydrophobic methyl groups were introduced, leading to the reduction of the chemical adsorption of water. Also, the boron doping was beneficial to enhancing the physical cross-linking between the coating and the SiO2f/SiO2 composites, and improved the adhesion of the coating to the substrate. The results show that the optimal hydrophobic coating with contact angle 130.33°, moisture absorption 0.33% and adhesion level 1 is obtained when the molar ratio of MTES to B(OH)3 is 10:4. The real permittivity of M10B4 is constant in the range of 2.32–2.51 and the dielectric tangent loss is constant in the range of 5.5 × 10-4–8.7 × 10-3. The hydrophobic coating has excellent dielectric properties.

关键词： Adhesion Dielectric Hydrophobic polyborosiloxane SiO2f/SiO2 composites

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Preparation and Characterization of polyborosiloxanes and Their Blends with Phenolic Resin as Shapeable Ceramic Precursors

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Chinese Journal of Polymer Science 2014年第2期32卷 187-196页

作者： Hong-ying Zhao 赵京波 Hao Li Tong Zhao Key Laboratory of Carbon Fiber and Functional Polymers Ministry of Education College of Materials Science and Engineering Beijing University of Chemical Technology Laboratory of Advanced Polymer Materials Institute of Chemistry Chinese Academy Science

Two polyborosiloxanes （PBSis） with char yield up to 74.13% at 800 ℃ were synthesized by the direct polycondensation of boric acid with phenyltrimethoxysilane in diglyme. The PBSis were characterized by gel permeation chromatography, IR spectroscopy as well as ^1H-, ^29Si- and ^11B-NMR. PBSi modified phenol-formaldehyde resins （PBSi/PFs） were prepared at different PBSi/PF mass ratios and were cured at 150 ℃. The PBSi/PFs were characterized by IR spectroscopy, scanning electron microscopy, thermogravimetric analysis and tensile test. The results revealed that the cured PBSi/PFs had sea-island morphology and higher char yield than the common PF. PBSi/PF blend with PBSi/PF mass ratio of 0.4：1 had char yield up to 70.83% at 800 ℃. The PBSi/PFs had tensile strength similar to PF. The ceramization of PBSi/PFs was also studied. The silicon boron oxycarbide （SiBOC） ceramics formed were characterized by IR spectroscopy and elemental analysis. This method provided a valuable way to prepare easily shapeable polymer blends as ceramic precursors.

关键词： polyborosiloxane Phenolic resin Preparation Ceramic precursors SiBOC ceramics.

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