导　　师： 曾令可

学科专业： 080502

授予学位： 硕士

作　　者： ;

机构地区： 华南理工大学

摘　　要： 随着科学技术的发展和新应用领域的开发,对材料提出了更高的要求;绝热材料作为材料研究领域的一个重要方向,越来越受到人们的重视。 纳米多孔SiO/_2气凝胶隔热复合材料具有低导热系数、良好力学性能、低密度、易加工等优点,在航天飞行器热防护系统、军用热电池以及热力、化工、冶金、消防等领域都具有广阔的应用前景。迄今为止,国内外关于纳米孔超级绝热材料大多是以Si02气凝胶作为纳米孔的载体,SiO/_2气凝胶从结构上完全符合超级绝热材料的基本特征。SiO/_2气凝胶的微孔尺寸小于空气分子的平均自由程,从本质上切断了气体分子的热传导,而且微孔足够小,可有效控制气体对流传热。 气凝胶的制备方法多采用超临界干燥工艺,但超临界干燥工艺复杂、成本高,而且有一定的危险性。因此,为了实现气凝胶的大规模生产及其在诸多领域的实际应用,研究低成本常压干燥工艺制备气凝胶非常必要;纯SiO/_2气凝胶的脆性很大,力学性能差,对其力学性能的提高也是现代绝热材料研究的主要方向。 本文以正硅酸已酯/(TEOS/)为前驱体,乙醇和水为溶剂,采用HCl和NH3·H/_2O两步催化法,以莫来石纤维为增强材料,在溶胶-凝胶过程后,经过表面改性,采用常压干燥工艺、真空干燥工艺,制备了轻质纳米SiO/_2气凝胶//莫来石纤维复合材料。 在莫来石纤维含量不变的情况下,分别对水的用量、乙醇的用量、甲酰胺的用量、反应温度及pH值等各条件对凝胶时间的影响作了讨论,得出当TEOS:ETHOS:H/_2O:甲酰胺=1:4:6:0.4时,能得到较为理想的复合材料。 采用XRD、TG-DSC、IR、SEM、BET等测试方法对SiO/_2气凝胶//莫来石纤维复合材料的微观结构、形貌及化学组成进行了测试分析。结果表明所制备的样品为多孔、轻质、高比表面积的纳米复合材料。当纤维含量在0-20/%的时候,平均密度在0.188-0.292g//cm~3之间,比表面积在779.29-1046.73m~2//g之间,孔径分布在3-14nm之间。 对复合材料的热学性能进行表征,结果表明纯SiO/_2气凝胶的导热系数很低,为0.031W//mK,随着莫来石纤维的加入,当含量达到10/%以后,复合材料的导热系数迅速增大。 With the development of technology and new process, the research of thermal insulationmaterial becomes an important direction. Most of nano-pore super thermal insulation materialhas been silica aerogel as vector of nano-pore in home and abroad. Nanoporous SiO/_2 aerogel based thermal insulation composite could be widely used inthermal protection systems of space aircrafts, military thermal battery, heat energy, chemical,metallurgy and fire protection for its low thermal conductivity, high mechanical property, lowbulk density and easy-to-handle. Silica aerogels are full compliance with the basiccharacteristics of super-insulation materials on the structure. Silica aerogels can essentiallycut off the heat conduction of gas molecules because its porous size is smaller than theaverage free path of air molecules, and its enough small porous can control the convectionheat conduction of gas molecules. Traditionally, aerogels were prepared by super critical drying /(SCD/) method, which iscomplicated, costly and dangerous. It is very necessary that study a drying technique atambient pressure, and then it will permit a production in an industrial scale and application inmore fields. However, fragility restricts the application of this material, so how to improve themechanical property becomes an important direction in new material field. In this thesis, this composite material was synthesized by a two-step sol-gel. TEOS wasused as precursor, ethanol and water were used as solvent, mullite fiber was used asreinforced material. After the Sol-gel process and surface modification, atmospheric pressureand vacuum drying process were used to get this composite material. In this thesis two-step catalytic process was used, HCl and NH/_3·H/_2O were used ascatalyzes. The influences and principles of water//TEOS, ethanol//TEOS, formamide//TEOS,temperature and PH value on the gelation time were investigated and we found that when theTEOS: Ethanol: H/_2O: formamide =1:4:6:0.4, the ideal composite material can be get. By X-ray diffraction /(XRD/), scanning electron microscopy /(SEM/), specific surface areaand pore size analyzers, FTIR and some other experimental methods, the structure and otherphysical properties of these aerogels were primarily investigated. The results show thatcomposite material was coherent, non-crystalline, nano-sized porous solids. With the increaseof fiber the destiny increased. When the content of fiber was 0-20/%,the average density in fallin the rage of 0.0188-0.292g//cm~3, the BET specific surface areas measured by nitrogenadsorption were 779.29-1046.73m~2//g, the pore size distribution were 0.5-3nm. The thermal conductivity was measured by transient method. The result shows that the thermal conductivity of pure SiO/_2 aerogels was 0.031W//mK, very low, with the addition ofmullite fiber the conductivity was increase slowly, when the content reached 10/%, the thermalconductivity of the composite material increased rapidly.

关 键 词： 非超临界干燥 绝热复合材料 气凝胶 莫来石纤维

分 类 号： [TB383.1]

领　　域： [一般工业技术]