【作者】 李威；

【导师】 叶卫平；

【作者基本信息】 武汉理工大学 ， 材料科学与工程， 2016， 硕士

【摘要】 SiO₂气凝胶是一种具有三维孔洞骨架结构的非金属固体材料,主要通过溶胶-凝胶法和常压干燥技术制备而成。因其孔隙率和比表面积较大,这种气凝胶是目前世界上公认的密度最低,隔热效果最好的一种环境友好型固体保温材料。因其优异的隔热性能和简单的生产工艺,SiO₂气凝胶在管道保温,航天航空以及化工冶金等领域得到了广泛的应用。采用正硅酸乙酯（TEOS）为原料,酸碱两步法进行催化,通过添加莫来石纤维以提高强度,并配合涤纶有机纤维来增强气凝胶的柔韧性,其中经过了两级老化、溶剂置换、表面疏水改性,表面清洗等辅助工艺过程制备出了纤维增强疏水SiO₂气凝胶复合材料。然后采用SEM、BET、FT-IR、万能实验机和导热系数仪等测试分析手段,对莫来石-涤纶纤维增强SiO₂气凝胶隔热材料的物相、微观形貌、组织结构、孔结构、力学性能以及热传导等方面进行了测试与分析。本实验主要研究去离子水、无水乙醇、酸碱催化剂、表面改性剂以及凝胶温度等对气凝胶的凝胶时间、气凝胶的密度、体积收缩率、比表面积、孔隙率和力学性能等性能的影响,确定制备SiO₂气凝胶复合材料最佳工艺:最佳原料配比TEOS:EtOH:H₂O=1:4:3,酸催化调节pH在3-4之间,水解温度在60℃左右,碱催化调节pH在8-9之间,在凝胶温度为30℃下老化24h,溶剂置换过程先采用无水乙醇置换24h,再采用正己烷进行24h的置换,表面改性剂TMCS/正己烷（体积比）浓度为9%,改性时间为24h。经过常压干燥制备的莫来石-涤纶纤维增强SiO₂气凝胶表面平整无裂纹,颜色偏白的轻质纳米多孔块状材料,具有良好的三维空间纳米结构。通过相关测试得到SiO₂气凝胶典型样品的各项参数为:密度为0.225g/cm³,体积收缩率为3.36%,比表面积为898.55m²/g,孔隙率为82.88%,SiO₂气凝胶骨架之间的孔洞比较均匀,孔径大小集中分布在10nm以下,气凝胶骨架粒径主要分布10-100nm范围内。SiO₂气凝胶与复合纤维毡结合后,SiO₂气凝胶填充了复合纤维之间绝大多数的微米级孔洞,分布效果比较均匀,纤维和气凝胶形成比较致密的结构,使得SiO₂气凝胶复合材料的力学性能大幅提高,抗压强度2.25MPa,抗折强度1.95MPa,气凝胶的常温有效导热系数在0.025-0.050W/（m·K）之间。确定了纤维毡添加的工艺参数和常压干燥制备的工艺参数:莫来石纤维毡为增强相,涤纶纤维毡为增韧相,纤维毡体积与溶胶体积比值为0.9最佳,涤纶纤维毡和莫来石纤维毡的体积比0.8。常压干燥分三个阶段,60℃下干燥12h,90℃下干燥12h,120℃下干燥12h,最后180℃下6h低温热处理。更多还原

【Abstract】 Aerogel is a kind of porous amorphous solid material prepared by sol-gel method,keep nano gel network in three-dimension,and replace the liquid in the network structure by gas.With low density and high porosity,the nanoporous structure can effectively inhibit the gaseous heat convection,and widely used in the field of aerospace,metallurgy,chemical,electrochemical and so on.In this paper,with mullite fiber to improve strength and the organic polyester fiber to enhance the flexibility of the aerogel,the fiber-reinforced hydrophobic silica aerogels composites are made by tetraethyloxysilane（TEOS）and acid-base two step method were prepared via aging,surface hydrophobic modification and ambient pressure drying.The phases,micro morphology,organization structure and pore structure of silica aerogels material were analyzed by the methods of SEM,FT-IR,BET.The mechanical properties and heat conduction of mullite-dacron fiber reinforced heat insulating silica aerogels material were tested by the methods of universal testing machine and thermal conductivity instrument.This thesis mainly study the effect the different factors such as deionized water,ethanol,acid catalyst,surface modifier and gel temperature on the aerogel’s gelling time,density,porosity,volume shrinkage,strength.The best parameters process of SiO₂ aerogel composites:the best ratio is TEOS/EtOH/H₂O up to 1/4/3,the acid catalysis regulation of pH between 3-4,the hydrolysis temperature is 60℃,the alkali catalytic regulation of pH between 8-9,then aging 24h under the gel temperature of30℃,solvent replacement process using ethanol to replace 24h,then the replacement of n-hexane 24h,finally surface modified 24h under the condition of TMCS/n-hexane concentration was 9%（volume ratio）.With good three-dimensional nano structure,the mullite-dacron fiber-reinforced hydrophobic aerogels made by ambient pressure drying process is smooth and free crack.Through the relevant tests,the physical performance of the typical sample of SiO₂ were that:the density was 0.225g/cm³,volume shrinkage rate was 3.36%,the porosity was 82.88%,specific surface area was 898.55m²/g,the particle size is between 20nm and 100nm,with uniform pores,and most of the holes below 10nm.with the fiber dispersing in the aerogels,sol uniform dispersion between the fibers,and most of micron pores in the fiber matrices are eliminated substantially by the closely packed aerogels,and formed a relatively dense structure with the fiber,greatly improved the mechanical properties of SiO₂ aerogels,the flexural strength is 2.2 MPa,compressive strength is 1.95 MPa,the effective thermal conductivity between the0.025-0.050W/（M·K）.The process parameters of adding fiber and the ambient pressure drying were determined:the mullite fiber mat as reinforcement,the polyester fiber felt as toughening phase,the best volume ratio of fiber and sol was 0.9,and the volume ratio of polyester fiber and mullite fiber was0.8.The atmospheric pressure drying is divided into three stages,first at 60℃for 12h,then at 90℃for 12h,then at 120℃for 12h,6 hours of heat treatment at 180℃.更多还原