二氧化硅气凝胶制备条件的选择

二氧化硅气凝胶是典型的纳米多孔轻质材料,由于具有独特的性能并在许多领域存在潜在的应用价值而受到广泛关注。本文从气凝胶制备过程中的硅源的选择、溶剂的选择、制备工艺的选择、催化剂等方面进行了研究,有利于确定常压干燥制备二氧化硅气凝胶的生产条件。     

柔韧性二氧化硅气凝胶的研究进展

本文综述了柔韧性二氧化硅气凝胶制备的最新研究进展,介绍了最常用的制备方法和干燥工艺,并对所制得样品的结构与性能的关系进行了阐述.目前,柔韧性二氧化硅气凝胶的制备方法主要有两种:一种是采用衍生法,用来制备纯的气凝胶;另一种是交联法,可以制备聚合物交联的气凝胶.超临界流体干燥是目前最常用的干燥工艺.     

常压制备疏水型二氧化硅气凝胶及透光率分析

采用溶胶-凝胶法,通过常压干燥制备了疏水型二氧化硅气凝胶。研究了pH、水解时间等因素对二氧化硅气凝胶透光率的影响。以正硅酸乙酯为原料,通过酸（草酸）-碱（氨水）两步催化,采用溶胶-凝胶法常压干燥制备了疏水型介孔二氧化硅气凝胶。正硅酸四乙酯、乙醇、草酸、氨水物质的量比为1∶4∶5∶0.2,草酸和氨水的浓度分别为0.008、0.05 mol/L时,采用二甲基二氯硅烷为改性剂常压制备了二氧化硅气凝胶。透射电镜、扫描电镜测试表明：二氧化硅气凝胶具有纳米介孔结构。接触角测定表明：二氧化硅气凝胶与水的接触角为148°,表现出疏水性。     

二氧化硅气凝胶的扩孔研究

本文主要以正硅酸四乙酯(TEOS)、乙醇(ETOH)、去离子水为原料,稀盐酸、稀氨水为催化剂,采用溶胶-凝胶法制备二氧化硅醇凝胶,分别用两种干燥方法(常压干燥、超临界干燥)干燥制备二氧化硅气凝胶,并进一步研究了三种不同的扩孔剂(尿素、乌洛托品、聚乙二醇)对二氧化硅气凝胶孔道的影响。使用SEM、红外吸收光谱、BET吸附仪对常压干燥、超临界干燥及扩孔前后的二氧化硅气凝胶进行表征。实验表明:添加一定量的扩孔剂可以增大载体的孔容和比表面积,其中乌洛托品作为扩孔剂时的扩孔效果更好。     

纳米级增强体复合硅气凝胶的研究进展

二氧化硅气凝胶的脆性大、力学强度过低,严重限制了其应用领域。常规微米级或大于微米尺寸的增强体复合硅气凝胶可以提升硅气凝胶性能,但难以在纳米尺寸范围内对凝胶孔隙增强。目前,可以采用合成聚合物纳米纤维、纤维素纳米纤维、纳米管、无机纳米纤维、石墨烯及氧化石墨烯等增强硅气凝胶,纳米级增强材料能够均匀分散在硅气凝胶纳米孔隙中,干燥收缩小、孔比表面积大、可有效提升硅气凝胶抗压强度、改进韧性。     

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。     

干燥方法对硅气凝胶性能的影响

以正硅酸乙酯为原料,先采用溶胶-凝胶法制备湿凝胶,进行表面改性以及溶剂置换,然后分别采用常压干燥、超临界干燥方法进行制备,最终都获得轻质多孔二氧化硅气凝胶。利用红外光谱仪、扫描电镜和BET吸附仪对两种不同干燥方法制备的二氧化硅气凝胶进行表征。结果表明,由红外光谱图知两种凝胶表面结构基本相同、超临界干燥样品扫描电镜说明颗粒均匀、BET吸附仪知比表面积大。     

石棉绒增强SiO2气凝胶隔热材料常压工艺研究

气凝胶是一种优质隔热材料.本文以石棉绒纤维作为气凝胶的增强材料,以水玻璃为硅源,通过常压干燥工艺进行SiO2气凝胶块体保温隔热材料的制备.研究了湿凝胶制备工艺流程及洗涤工艺对气凝胶材料结构及性能的影响.研究发现,以石棉绒为增强材料常压制备SiO2湿凝胶的最佳制备工艺为:在水、纤维和分散剂配制的纤维分散悬浮液中首先加入乙醇搅拌均匀,然后与水玻璃和氟硅酸钠配制的水玻璃凝胶液搅拌混合,再注模固化;在固化湿凝胶的洗涤和溶剂置换工艺中,以水为洗涤溶剂效果好,产品性能高.以石棉绒为增强材料,采用常压干燥工艺制备的SiO2气凝胶隔热材料具有收缩率小,产品规整,密度小,孔隙率高,及较好的强度和隔热性能.     

二氧化硅气凝胶及其在保温隔热领域应用进展

二氧化硅气凝胶是目前已知最轻的固体材料，具有热导率低、孔隙率高和比表面积大等优点，被誉为新型超级保温隔热材料。然而，二氧化硅气凝胶自身存在力学性能差和制备成本高的问题，大大限制了其在保温隔热领域大规模推广应用。本文简述了二氧化硅气凝胶合成技术和力学性能增强方法，从制备过程控制、老化条件优化、热处理、纤维复合和高分子聚合物复合等方面分析了其对气凝胶性能和工艺的影响，重点介绍了近年来二氧化硅气凝胶保温隔热材料应用在航空航天、军工领域、工业管道、建筑保温以及新能源汽车等领域的研究进展，总结了其在各领域应用的技术挑战。指出未来需进一步拓展二氧化硅气凝胶的使用温区，利用共前体和化学交联等方法增强高温下的隔热性能，同时解决气凝胶纤维复材“掉粉”和微米级粉体分散不均匀等难题，尤其是新能源汽车等新兴应用领域发展迅猛，未来仍需针对新的应用需求对其合成技术进行设计和优化。     

Al_2O_3-SiO_2复合气凝胶制备工艺研究进展

根据Al_2O_3-SiO_2复合气凝胶制备工艺的先后顺序,分别综述了Al_2O_3-SiO_2复合醇凝胶制备过程中所涉及的金属醇盐法和金属无机盐法,以及复合醇凝胶干燥过程中所使用的超临界干燥工艺和常压干燥工艺的研究现状,并重点对比了各方法或工艺的优缺点,提出了以金属无机盐法并结合常压干燥工艺来制备Al_2O_3-SiO_2复合气凝胶的新思路。     

Synthesis and characterization of a xonotlite fibers–silica aerogel composite by ambient pressure drying

Xonotlite fibers (XFs) reinforced silica aerogel composites were prepared by a sol–gel method under ambient pressure drying. XFs were synthesized through a dynamic hydrothermal route and had a noodle-like structure with length of 5–10 μm and average diameter of 150–200 nm. The microstructure analysis showed that XFs were inlaid in silica aerogel matrix by physical combination which contributed to restrict the volume shrinkage of alcogels and maintain the integrality aerogels during drying process. The physical, naonporous and thermal properties of the as prepared aerogel composites were investigated and discussed in detail. The new aerogel composites possessed porous nanostructure, which exhibited typical properties of 0.126 g/cm³ density, 4.132 cm³/g pore volume, and thermal conductivity of 0.0285 W/(m K). The results indicated that the introduced XFs didn’t significantly alter the porosity, hydrophobicity or thermal conductivity of aerogel matrix. It was also found that the aerogel composites had much more outstanding porosity than that of pure aerogel upon calcinations at 800 °C. This study fabricated XFs–silica aerogel composites and explored a new way for silica aerogels to endure and remain monolithic under ambient pressure drying.     

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。     

Subcritical drying of silica gels

Silica aerogel is a sol-gel prepared material characterized by high porosity and large inner surface area. Aerogels can be prepared with a high transparency and low thermal conductivity, giving a material excellent for application as transparent thermal insulator. The traditional route to prepare silica aerogels is by formation of an alcogel by hydrolysis and condensation of silicon alkoxides followed by supercritical drying in an autoclave at high pressure (–100 atm). Unfortunately, this process is expensive and might be dangerous, so drying methods have been developed that operate under ambient conditions. In previous work, we have shown that gels can be strengthened and stiffened by providing new monomers to the alcogel giving xerogels with similar properties as aerogels by drying at ambient pressure (porosity up to 90%). This method of obtaining ambient pressure dried aerogels will be described and special emphasis will be given on the effect of the initial gel structure on the preparation of the xerogels.     

Surface Modification of Silica Aerogels Dried with 2-Methyl-1-Propanol in the Sub-Critical Pressure

Silica aerogels were made by sol-gel techniques using industrial silicon derivatives (polyethoxydisiloxanes, E-40), followed by drying under sub-critical pressure with iso-butanol. The shrinkage (linear), specific surface area, S_BET, SEM, TEM and the pore size distribution of the silica aerogels were investigated. The results show that the shrinkage (linear) is below 5%, diameter of the silica particles is about 6 nm and the pore size of the silica aerogels is 10 nm. The specific surface area of the silica aerogel is 559.2 m²/g. IR and NMR techniques were used to determine the organic groups on the silica matrix, GC/MS was also introduced to analyse the composition of the recycled iso-butanol. The surface modification and the reactions of iso-butanol to the silica aerogel are also discussed.     

Reduction of processing time by mechanical shaking of the ambient pressure dried TEOS based silica aerogel granules

The present paper deals with preparation of silica aerogel granules by two step acid–base sol–gel process involving ambient pressure drying of alcogels with additional use of mechanical shaker to accelerate the solvent exchange process and characterization of the yielded aerogels granules to study their physical properties. The conventional ambient pressure drying of alcogels is crucial since it needs tedious repetitive gel washing and solvent exchanges (10 times) which consumes total process time of 4 days. We have succeeded to synthesize aerogels within 2 days by making use of alcogels shaking. To get good quality aerogels in terms of low density, high optical transparency, low volume shrinkage, various base catalysts and their combinations were used. The optimal molar ratio of precursor chemicals Tetraethoxysilane (TEOS): Methanol (MeOH): Oxalic acid: NH₄OH: NH₄F: Trimethylchlorosilane (TMCS) found to be 1: 16.5: 0.49: 0.58: 0.60: 0.98, respectively. Among six catalyst studied, combination of NH₄OH and NH₄F resulted in low density and transparent aerogels. Hydrophobicity was achieved by surface silylation using TMCS silylating agent but lead to decrease in transparency due to chloride precipitation. We have improved transparency of aerogels by methanol washing of alcogels prior to silylation. The hydrophobicity has been studied by FTIR analysis and contact angle measurements. The thermal analysis indicates thermal stability of hydrophobicity up to 318 °C and the Surface morphology of aerogel has been studied by FESEM.     

氧化硅气凝胶绝热材料及其建筑减碳应用

无机氧化硅气凝胶因具有超低导热系数、A级不燃、吸湿率低、轻质等特点,在航天航空、工业及建筑领域的节能减碳方面具有广泛的应用潜力。然而氧化硅气凝胶力学性能差、制备成本高等缺点限制了其发展应用。介绍了氧化硅气凝胶绝热材料制备工艺的研究进展,对氧化硅气凝胶在建筑领域的应用形式（如超轻气凝胶泡沫混凝土、超高性能气凝胶保温隔热板、超低传热系数气凝胶节能玻璃等）进行了综述,并对氧化硅气凝胶在建筑节能领域的发展方向进行了展望。响应碳中和发展目标,随着气凝胶制备技术的发展与成本降低,氧化硅气凝胶绝热材料将在建筑墙体保温隔热方面广泛应用,同时对其性能提出了更多功能性要求,对氧化硅气凝胶材料还需开展更系统的基础研究以及工程应用技术研发,推动建筑领域的节能减碳与可持续发展。     

A novel preparation of superhydrophobic silica aerogels via the combustion drying method

Silica aerogels with prominent physical, thermal, optical, and acoustic properties are considered to be highly promising materials. However, owing to the high cost and the complex production processes associated with existing drying technologies, the application of silica aerogels is limited in many fields. In this study, a novel combustion drying method (CDM) was successfully used in the synthesis of superhydrophobic silica aerogels for the first time. It was confirmed that silica aerogel prepared by CDM has a typical aerogel structure with low density, high porosity, high specific surface area, high total pore volume, superhydrophobicity and high thermal stability. Compared with supercritical fluid drying, freeze drying and ambient pressure drying, CDM possesses significant advantages in the drying efficiency and low-cost production due to its active drying mode. Finally, the mechanism of the combustion drying method is proposed based on the combustion of organic solvents. The results will be meaningful for the design and production of aerogel materials in the future.     

Effects of silica aerogel particle sizes on the thermal–mechanical properties of silica aerogel – unsaturated polyester composites

Silica aerogels with a surface area as high as 773?m²?g^?1 and a density of 0.077?g?cm^?3 were produced from rice husk via sol–gel process and ambient pressure drying. A particulate composite material was prepared by adding silica aerogel particles of three different particle sizes (powder, granules and bead) to unsaturated polyester resin with a fixed volume fraction of 30%. Thermogravimetric and thermal conductivity studies revealed that silica aerogel composites were having higher thermal stability and thermal insulation than the neat resin. It was suggested that the preservation of aerogel pores from resin intrusion is important for better thermal properties. Larger silica aerogel particles have more porous area (unwetted region) which results in a lower degradation rate and lower thermal conductivity of the base polymer. However, the addition of silica aerogel into resin has reduced the tensile modulus of the polymer matrix where smaller particle size displayed higher toughness than those with bigger particle size.     

Preparation of Monolithic Silica Aerogel of Low Thermal Conductivity by Ambient Pressure Drying

Monolithic silica aerogels with thermal conductivity as low as 0.036 W·(m·K)⁻¹ and porosity as high as 97% were successfully prepared by ambient pressure drying through a multiple modification approach. This approach may replace the more costly and dangerous operation of supercritical drying. The tetraethoxysilane (TEOS)-derived wet gel was made hydrophobic with multiple treatments of trimethylchlorosilane and dried under ambient pressure. The multiple treatments were found to be necessary to achieve sufficient modification of the wet gel for reduction in drying-induced surface tension force to maintain product integrity and high porosity. Comparisons in nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy for surface bonding and contact angle measurement for hydrophobicity between the no, single, and multiple surface modification (MSM) samples were conducted to reveal the difference in the extent of the resulting surface modification. In conclusion, the MSM procedure reduced the volume shrinkage, increased the monolithicity and porosity, and lowered the thermal conductivity of the resulting aerogels.