二氧化硅气凝胶复合隔热材料研究进展

二氧化硅气凝胶具有高孔隙率、低热导率等特点,使其成为新型超级隔热材料。然而,二氧化硅气凝胶的柔韧性、整体性差,并且常温干燥制备的气凝胶在高温时热导率迅速上升,这些都大大限制了二氧化硅气凝胶的应用。近些年,通过原位溶胶-凝胶法和模压成型法制备得到的二氧化硅气凝胶复合隔热材料,在一定程度上提高了其韧性、整体性和高温隔热性能,使得二氧化硅气凝胶作为单独块体隔热材料成为可能。本文阐述了二氧化硅气凝胶隔热材料的隔热机理,综述了近年来抗辐射型、纤维增强型和聚合物增强型二氧化硅气凝胶复合隔热材料的研究现状,最后讨论了该领域今后研究趋势。     

SiO_2气凝胶的制备,性能及在生命医学中的应用

二氧化硅气凝胶具有独特的理化性质和生物相容性,使其成为生命医学领域基础研究的重要选择之一。阐述了二氧化硅气凝胶的制备工艺、机理及影响因素,分析了二氧化硅气凝胶的微观结构对其性能的影响,综述了二氧化硅气凝胶在药物输送系统、生物催化剂和生物传感器等方面的应用及研究现状,最后展望了二氧化硅气凝胶在生命医学领域中的应用前景。     

二氧化硅气凝胶的制备工艺与应用

三维纳米孔隙结构的二氧化硅气凝胶具有孔隙率高、密度低、比表面积大等基本特征,这些优异的特性使二氧化硅气凝胶在许多领域得到广泛研究和应用。二氧化硅气凝胶一般通过溶胶-凝胶过程、老化、干燥处理得到。主要总结了二氧化硅气凝胶的制备过程及机理,介绍二氧化硅气凝胶的相关领域的应用,并对二氧化硅气凝胶材料的发展前景进行了展望。     

二氧化硅气凝胶/玻纤棉复合材料 导热性的研究

设计制备了二氧化硅气凝胶粉体材料,使用KH550将其表面改性后与粘结剂醋酸乙烯-乙烯共聚乳液搅拌为混合液,在超声波清洗器中将厚度为9mm的玻璃纤维针刺棉浸入混合液中之后,干燥制备得二氧化硅气凝胶/玻纤棉复合材料。结果表明采用KH550表面改性的二氧化硅气凝胶材料在水性粘结剂中的溶解性良好,超声波处理有助于二氧化硅气凝胶材料均匀分散于玻璃纤维棉中;含二氧化硅气凝胶材料的玻璃纤维棉导热系数明显下降,且随温度升高,其隔热性能比普通玻璃纤维棉更好。对二氧化硅气凝胶/玻纤棉复合材料的导热机理进行了研究,结果表明二氧化硅气凝胶材料的存在有效削弱了玻璃纤维棉的热桥效应及其气相导热效果。     

纤维增强型二氧化硅气凝胶复合材料常压制备及表征

采用溶胶-凝胶法分别制备了木质素纤维、聚丙烯纤维、聚酯纤维、玻璃纤维、聚丙烯腈纤维等5种纤维增强型二氧化硅气凝胶复合材料,并对其进行了表征。结果表明：聚丙烯腈纤维增强二氧化硅气凝胶复合材料的收缩率最小（仅为9%）,且比表面积最大（为583 m2/g）;玻璃纤维增强二氧化硅气凝胶复合材料的块体光滑度最好;聚丙烯纤维增强二氧化硅气凝胶复合材料的透明度最高。纤维本身材质的差别导致了其与凝胶粒子的结合程度有所差异,因而对复合材料块体的透明度、比表面积、收缩率产生影响,而5种纤维增强二氧化硅气凝胶复合材料的疏水性能均非常良好。     

乙醇胺为碱性催化剂对硅气凝胶性能的影响

以正硅酸乙酯为硅源,盐酸为酸性催化剂,乙醇胺(一乙醇胺、二乙醇胺、三乙醇胺)、氨水为碱性催化剂,采用酸碱两步催化溶胶-凝胶法制备二氧化硅湿凝胶,凝胶不经过表面改性,采用真空干燥制得二氧化硅气凝胶。通过对二氧化硅气凝胶样品进行比表面积测定和扫描电镜观察,表明添加不同的乙醇胺所得二氧化硅气凝胶的性能不同。采用乙醇胺作催化剂与氨水作比较所得二氧化硅气凝胶平均孔径较大。采用一乙醇胺作催化剂与氨水作比较,在添加量为（5.1～8.5）×10^-2  mol时,所得二氧化硅气凝胶的吸附能力提高,内表面粗糙度减小,孔隙率提高,减轻了孔壁的坍塌。采用二乙醇胺作催化剂与其他碱性催化剂作比较,随着其添加量的增加所得二氧化硅气凝胶平均孔径增加幅度较大。采用三乙醇胺作催化剂与其他碱催化剂相比,所得二氧化硅气凝胶的内部表面最粗糙。     

增强型二氧化硅气凝胶材料的研究进展

二氧化硅气凝胶是世界上最轻的固体材料之一，因其具有热导率低、比表面积大、孔隙率高等优良特性，在保温隔热领域具有极大的发展空间；然而，二氧化硅气凝胶具有强度低、不易成型等问题，限制了其在各应用领域的快速推广。本文综述了通过复合或掺杂增强二氧化硅气凝胶力学性能的方法，并对当前形势下二氧化硅气凝胶的应用前景进行了展望。     

二氧化硅气凝胶复合材料热导率优化研究进展

二氧化硅气凝胶复合材料由于具有良好的力学和隔热性能,在建筑、航空和其他工业领域展现出良好的节能应用前景。从增强材料的几何特征、含量、排列方式等方面概述了二氧化硅气凝胶复合材料热导率的规律,综述了二氧化硅气凝胶复合材料热导率的实验和理论优化研究进展,分析了现阶段实验和理论模型优化二氧化硅气凝胶复合材料热导率存在的问题,并提出了优化二氧化硅气凝胶复合材料热导率的方法,为制备高隔热性能的二氧化硅气凝胶复合材料提供理论指导。     

硅酸铝纤维和玻璃纤维复合二氧化硅气凝胶材料的制备与性能

分别以硅酸铝纤维和玻璃纤维为骨架材料,采用溶胶-凝胶、常压干燥制得纤维复合二氧化硅气凝胶材料,并对材料进行了结构和性能的测试分析。结果表明,二氧化硅气凝胶附着于纤维表面,提高了材料力学强度。硅酸铝纤维复合二氧化硅气凝胶材料的隔音性能优于玻璃纤维复合二氧化硅气凝胶材料。两种纤维复合二氧化硅气凝胶材料耐高温、燃烧性能均达到A级。硅酸铝纤维复合二氧化硅气凝胶材料和玻璃纤维复合二氧化硅气凝胶材料的产烟毒性分别为AQ₁级和AQ₂级,导热系数分别为0.034 W/（m·K）和0.033 W/（m·K）。     

改性二氧化硅气凝胶研究进展

二氧化硅气凝胶作为一种新型轻质多孔材料,在航空、建材和医疗等领域具有巨大的应用前景。综述了二氧化硅气凝胶的制备工艺发展史,介绍了二氧化硅气凝胶的光学、热学、电学、声学和催化方面的性质,详细讨论了二氧化硅气凝胶的两种改性思路:硅源改性(包含单一硅源、复合硅源和功能性硅源)和掺杂改性(包含非金属材料掺杂和金属材料掺杂),展望了二氧化硅气凝胶的发展方向。     

A facile method to fabricate monolithic alumina–silica aerogels with high surface areas and good mechanical properties

In this study, monolithic alumina–silica aerogels with high surface areas and good mechanical properties were synthesized via a facile sol–gel method without solvent exchange. Furthermore, surface areas, microstructures (up to 1300 °C), and mechanical properties of the prepared alumina–silica aerogels were investigated. The sintering and phase transformations of metastable alumina nanoparticles are suppressed owing to the uniformly distributed Si in the alumina–silica aerogels; therefore, the alumina–silica aerogels can maintain much higher specific surface areas after being calcined at 800 °C (575.5 m²/g), 1000 °C (443.2 m²/g), and 1200 °C (120.6 m²/g) compared to pristine alumina aerogels. In addition, the prepared high surface area alumina–silica aerogels show considerably higher strengths than those obtained in previous works. The compressive stress (3 % strain) and elastic modulus of the alumina–silica aerogels reached 1.78 and 65.6 MPa, respectively. The reported alumina–silica aerogels in this study can be good candidates as high-temperature thermal insulators and catalysts.     

疏水SiO2气凝胶的制备及应用研究进展

介绍了SiO2气凝胶的特性,阐述了疏水性SiO2气凝胶的制备方法,综述了气相氧化法、表面后处理法、原位法等制备疏水性SiO2气凝胶的原理和方法,简述了疏水SiO2气凝胶在热学、光学、化学(吸附和催化)及医学等领域的应用现状,最后展望了疏水性SiO2气凝胶的发展和应用前景,其在隔热、超疏水功能纺织材料上的应用也具有较好的发展前景.     

Influence of Catalyst (Citric Acid) Concentration on the Physical Properties of TEOS Silica Aerogels

In the present paper, the experimental results on the influence of catalyst (citric acid) concentration on the physical properties of TEOS silica aerogels, are reported. The aerogels have been prepared by hydrolysis and polycondensation of tetraethoxysilane (TEOS) using citric acid (CTA) as a new catalyst followed by supercritical drying in an autoclave. In order to obtain the best quality silica aerogels in terms of monolithy, high transparency, low density, large surface area and high porosity with uniform pore size distribution, the catalyst concentrations were varied from 0.0005 M to 0.1 M by keeping the molar ratio of TEOS : EtOH : H₂O constant at 1 : 5 : 7, respectively. It has been found that the lower (<0.001) CTA concentration resulted in low density, smaller surface area but opaque aerogels whereas higher (>0.005 M) CTA concentration resulted in high density, large surface area, highly transparent but cracked aerogels. On the other hand, medium (between 0.001 and 0.005 M) CTA concentration resulted in monolithic, low density, large surface area and highly transparent silica aerogels. The pore size distribution (PSD) for higher (0.1 M) and lower (0.0005) CTA concentrations shifted towards smaller and larger pore radii respectively, whereas for medium (0.001 M) CTA concentration, the PSD is narrow and uniform, which reduces the differential pressure during supercritical solvent extraction leading to monolithic silica aerogels. These results have been supported and discussed by considering the particle and pore sizes observed by Scanning Electron Microscopy (SEM). The surface area was measured by BET analysis.     

一种新型保温材料—掺杂改性SiO2气凝胶

介绍了新型掺杂杂性气凝胶的制备工艺以及其导热九与气压，温度的关系。该材料在高温下具有比普通隔热材料低得多的导热系数，因此作高效温隔热材料将颇具前景。     

通过控制醇凝胶强度常压制备低密度疏水SiO2气凝胶

常压干燥制备低密度气凝胶是促进高性能气凝胶发展应用的重要途径。以正硅酸乙酯为硅源,采用溶胶-凝胶和常压干燥工艺制备出低密度(<100 kg·m^-3)的疏水SiO₂气凝胶,通过工艺参数的控制制备出不同压缩模量的醇凝胶,探讨了反应物配比对醇凝胶压缩模量和气凝胶密度间的影响关系,获得了通过控制醇凝胶压缩模量制备低密度疏水SiO₂气凝胶的方法;发现将醇凝胶压缩模量控制在0.25~2.5 kPa范围内,可制备出密度小于100 kg·m^-3的疏水SiO₂气凝胶,该研究可以为低密度疏水SiO₂气凝胶的低成本常压制备及其控制方法提供指导。     

溶胶凝胶一步溶剂交换与表面改性制备疏水硅气凝胶

以正硅酸乙酯为硅源,采用酸碱两步催化的溶胶-凝胶法,以无水乙醇/六甲基二硅氮烷/正己烷为溶剂交换与表面改性试剂,通过一步溶剂交换与表面改性和常压干燥工艺制备疏水SiO2气凝胶。用傅立叶变换红外光谱(FTIR)、X射线衍射(XRD)、热重-差示(TG-DSC)、场发射扫描电镜(F-SEM)和比表面积(BET)等检测手段对样品的结构、形貌和性能进行了表征。结果表明,将传统的溶剂交换与表面改性由多个步骤改为一步完成,使制备周期从原来的6d缩减到3d,不仅缩短了周期,而且使所得的SiO2气凝胶样品具有842.63m2/g的高比表面积、130kg/m3的低密度、15nm的超细颗粒、2～170nm的孔洞结构和良好的疏水性能。     

Thermal,mechanical, and acoustic properties of silica‐aerogel/UPVC composites

The properties of silica‐aerogel/UPVC composites have been investigated with emphasis on sound and heat insulation. UPVC is a material of construction for window profiles and drainage pipes. Hydrophobic silica aerogels were synthesized using silicate sodium as a precursor through a two‐step sol–gel process. The physical and textural properties of the synthesized silica aerogels such as density, surface area, and particle size were analyzed using SEM and BET analysis. Then, the synthesized aerogels were mixed with Unplastisized Polyvinyl Chloride (UPVC) compound at five different weight ratios in an internal mixer to find out the effects of silica aerogels on the thermal, mechanical, and acoustical characteristics. The prepared UPVC/aerogel composites were characterized for tensile properties, impact strength, hardness, Vicat softening temperature, thermal conductivity, sound absorption, and sound transmission loss. The results revealed that adding silica aerogel in to the matrix of UPVC increases its hardness and softening temperature while decreases impact strength. The thermal conductivity of UPVC was decreased by up to 50% using silica aerogel. The sound absorption property of UPVC was increased up to three times by using silica aerogels due to its high porosity. Silica aerogel increased the maximum sound transmission loss of UPVC in the low frequency range. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44685.     

Enhancing aerogel mechanical properties with incorporation of POSS

Silica aerogels consisting of nanoparticles and numerous nano-pores have many attractive attributes. However, the weak mechanical properties severely limited the practical application of the silica aerogel. In this work, a facile approach was employed to strengthen the silica aerogel while the multi-alkoxy polyhedral oligomeric silsesquioxane (POSS) joined with methyltriethoxysilane (MTES) as the co-precursor. Three kinds of stiff core POSS with different amount of alkoxy groups were chosen to prepare aerogels. The result attributes showed all aerogels owned mesoporous structure (10–20 nm), high specific surface area (760–877 m² g⁻¹) and good thermal stability. Moreover, with the introduction of POSS, the mechanical properties had been apparently enhanced. The suitable addition of functional groups and the adjustment of cross-linking density made the aerogel own more room to deform and the skeleton still strong enough to endure large deformation. In addition, new peaks appeared in the XRD patterns at the same time. The preparation strategy of composite aerogels may guide a facile way to regulate the aerogel attributes. Furthermore, the aerogel potential application in oil-water separation has also been investigated.     

Photoluminescence and FTIR studies of pure and rare earth doped silica xerogels and aerogels

The luminescence properties of silica xerogels and aerogels have been studied using PL spectroscopy. Both silica xerogels and aerogels exhibit photoluminescence in the visible region when excited with UV radiation. The luminescence observed in xerogels and aerogels is attributed due to defect centers. Silica aerogels exhibit better photoluminescence than xerogels due to the increase in defect sites. The incorporation of rare earth ions (La³⁺, Nd³⁺and Sm³⁺) enhanced the luminescence of both silica xerogels and aerogels. La³⁺ shows least and Nd³⁺ shows maximum enhancement. Increase in the concentration of Nd³⁺ resulted in an increase in the luminescence intensity. The change in the environment of the defect centers due to the incorporation of rare earth ions and the superposition of 4f-f transitions of rare earths are considered as the reasons for the luminescence enhancement.