Preparation and Characterization of Silica Aerogels Derived from Ambient Pressure

Silica aerogels were prepared by sol-gel technique from industrial silicon derivatives （polyethoxydisiloxanes, E40）, followed by silylation and drying under ambient pressure. The specific surface area, pore size distribution and thermal conductivity of the silica aerogels were investigated and the results showed that the diameter of the silica particles is about 6 nm and the average pore size of the silica aerogels is 14.7 nm. The specific surface area of which is about 1000 m^2.g^-1 and the thermal conductivity is about 0.014 wm^-l.K^-1 at room temperature and pressure of 1.01×10^5 Pa. The Si-CH3 groups were also detected on the internal surface of the silica aerogels, which show hydrophobic. Silica aerogels derived by this technique is low cost and have wide applications.

Preparation and Properties of PMMA Modified Silica Aerogels from Diatomite

Diatomite was used as raw material to prepare sodium silicate with a modulus of 3.1 by alkali dissolution method and the resulted sodium silicate solution was employed as a precursor. Methyl methaerylate monomers were introduced in wet gels through solution-immersion, and upon heating at 70 ℃, the mesoporous surfaces throughout the skeletal framework were coated with the polymer layer. PMMA modified silica aerogels were successfully synthesized via ambient pressure drying. The properties were investigated by FT- IR, NMR, TGA, nitrogen adsorption-desorption, FESEM and nano-indentation, etc. Results indicate that with the increasing of PMMA incorporated into silica aerogels, the bulk density and the BET surface area increase, the porosity decreases. Through the observation of FESEM, it is found that the interconnecting pores and the big pores add, the pore size distribution expands from 5-17 to 28-150 urn. By comparison, the PMMA modified silica aerogels achieve a 52-fold increase in hardness and a 10-fold increase in modulus.

Synthesis and Characterization of Multi-walled Carbon Nanotube Doped Silica Aerogels

Multi-walled carbon nanotube doped silica aerogels（MWCNT-SAs） were synthesized from a wet gel of well-dispersed MWCNT by one-step solvent exchange/surface modification and ambient pressure drying（APD）. Waterglass was employed as a precursor to prepare wet gel. The content of MWCNT varied from 0 to 15% volume by wet gel. The surface group, thermal stability and microstructure of pure silica aerogel and MWCNT-SAs were investigated by FTIR, DTA, and TEM. Experimental results show that MWCNT-SAs are hydrophobic when the temperature is below 400 ℃, MWCNT-SAs exhibit a mesoporous network structure, and they achieve the largest scale with least shrinkage and lowest density when doped with 5 vol% MWCNT.

Synthesis of monolithic carbon aerogels with high mechanical strength via ambient pressure drying without solvent exchange

A simple,fast and cost-effective method for monolithic carbon aerogels(CAs) preparation was proposed through sol-gel polycondensation of resorcinol with fo rmaldehyde in a basic aqueous solution followed by ambient pressure drying without solvent exchange,and carbonization.The microstructure and network strength of CAs were tailored by adju sting the catalyst concentration([resorcinol]/[sodium carbonate] in the range of 300-2000),water content([deionized water]/[resorcinol] equals to 17 and 24,respectively),and gelation temperature(Tgel in the range of 30-90℃).Resultantly,the CAs with a wide range of density(0.30-1.13 g/cm3),high specific surface area(465-616 m2/g),high compressive strength(6.5-147.4 MPa)and low thermal conductivity(0.065-0.120 W·m-1 K-1) were obtained in this work.Moreover,the largesized CAs(100×100×20 mm3) can also be prepared by this method since the formed robust skeleton network can resist shrinkage/collapse of pore structure and prevent cracking during drying.The improved mechanical strength and monolithic forming abilities could be mainly attributed to the uniform arrangement of carbon particles and pores,fine particle size,abundant network structure and enhanced particle neck.

Effect of sodium bicarbonate solution on methyltrimethoxysilane-derived silica aerogels dried at ambient pressure

Here we present an economical ambient pressure drying method of preparing monolithic silica aerogels from methyltrimethoxysilane precursor while using sodium bicarbonate solution as the exchanging solvent.We prepared silica aerogels with a density and a specific surface area of 0.053 g·cm^(-3) and 423 m^(2)·g^(-1) respectively.The average pore diameter of silica aerogels is 23 nm as the pore specific volume is 1.11 cm^(3)·g^(-1),Further,the contact angle between water droplet and the surface of silica aerogels in specific condition can be as high as 166°,which indicates a super-hydrophobic surface of aerogels.

Potential Application of Silica Aerogel Granules for Cleanup of Accidental Spillage of Various Organic Liquids

The experimental work has been carried out to study the absorption-desorption properties of the silica aerogels, for their use in oil spill cleanup application. For these studies, silica aerogel granules were prepared by two step acid– base catalyzed sol–gel process, involving ambient pressure drying of alcogels, were made use for absorption & desorption studies of different organic liquids. The optimal molar ratio of precursors tetraethoxysilane (TEOS):Methanol (MeOH):Oxalic acid:NH4OH:NH4F:trimethylchlorosilane (TMCS) was kept constant at 1:16.5:0.71:0.58:0.60:0.98, respectively. In all, four alkanes, four aromatic compounds, four alcohols and three oils were used for absorption and desorption studies of organic liquids. The absorption capacity of aerogel sample was quantified by measuring the mass of the organic liquid absorbed by unit mass of the aerogel sample. The hydrophobic aerogel granules showed a very high uptake capacity and high rate of uptake. The desorption of solvents and oils was studied by keeping the liquid absorbed aerogel granules at various temperatures and weighing them at regular time intervals until all the absorbed liquid got totally desorbed. The Fourier transform infrared spectroscopy analysis showed that the aerogel structure was not much affected by the solvent absorption, while the oil absorption led to the shrinkage, resulting in a dense structure after desorption.

SiO2气凝胶常压干燥工艺与隔热应用进展

综述了SiO2气凝胶常压制备技术及其复合隔热材料的最新研究进展。着重介绍了提高凝胶网络基架强度、添加干燥控制化学添加剂、表面改性、降低毛细管力等几种SiO2气凝胶常压干燥工艺,并回顾了几种SiO2气凝胶复合隔热材料的应用现状。

气凝胶低成本制备及其在建筑保温领域中的应用

气凝胶是一种新型的纳米多孔材料,以其孔隙率高、密度低、比表面积大等独特的性能受到人们广泛的关注。这些优异的性能使得气凝胶在声阻抗耦合、高效保温隔热、催化剂及其载体航空航天等方面拥有非常广泛的应用前景。阐述了气凝胶的低成本制备及常压干燥技术,介绍了气凝胶在建筑保温隔热领域的应用现状和发展前景,并且分析了其与主流建筑保温隔热材料的优劣。

疏水SiO_2气凝胶的常压制备及在建筑隔热涂料中的应用

以廉价的工业级正硅酸乙酯为原料,经过酸碱两步催化制备二氧化硅凝胶,分别以三甲基氯硅烷(TMCS)/六甲基二硅氧烷(HMDSO)溶液和TMCS/n-C6H14溶液对凝胶进行改性,常压干燥下制得产品。用FT-IR、TEM、XRD等手段对样品进行表征,并考察了产品的疏水性能和在外墙涂料中的隔热性能。在相同的条件下,前者可以使凝胶溶剂交换和表面改性同时完成,而后者则不能。以TMCS/HMDSO改性所得产品为无定型非晶态结构,具有5～10 nm孔径。改性后的SiO2气凝胶具有较强的疏水性,在外墙建筑涂料中具有优良的隔热性能。

疏水性木粉-SiO2气凝胶复合材料的制备及其性能研究

以正硅酸乙酯(TEOS)和甲基三甲氧基硅烷(MTMS)为共前驱体,利用溶胶-凝胶法和常压干燥工艺制备疏水性木粉-SiO2气凝胶复合材料。探讨了不同粒径(0.42~0.84 mm、0.25~0.42 mm、0.18~0.25 mm)巴尔杉木木粉对木粉-SiO2气凝胶复合材料性能的影响,结果表明:木粉-SiO2气凝胶复合材料的密度、导热系数、抗压强度、接触角均随木粉粒径尺寸的减小而增大。木粉粒径为0.25~0.42 mm可获得性能较好的材料,复合材料密度为0.168 g/cm3,导热系数为0.0337 W/(m·K),抗压强度为0.15 MPa,接触角为155.72°。制备的木粉-SiO2气凝胶复合材料具有保温性能优异、轻质高疏水的特性。

基于水性气相二氧化硅浆料制备柔性二氧化硅气凝胶复合毡

二氧化硅气凝胶由于其低导热率在隔热应用方面具有巨大的潜力.然而,它们通常具有较差的机械性能,需要在保持低热导率的同时增强机械性能.本研究以商业化气相二氧化硅和甲基三甲氧基硅烷为硅源,并以水和乙醇为溶剂形成浆料.基于此,二氧化硅气凝胶块体(SAMs)可通过常压干燥进行制备,且无需额外的表面改性或溶剂置换.制备的SAMs保持了典型的纳米孔结构,具有低密度(0.24 g cm^(-3))、收缩率(4%)和热导率(0.046 W m^(-1)K^(-1)).通过辊压将浆料浸渍到纤维毡中,并通过浆料热固化和常压干燥制备出二氧化硅气凝胶毡(SABs).制备的SABs具有良好的柔韧性和机械性能,便于安装和隔热应用,并显著减少了生产周期和成本.此外,基于SAMs的纳米孔结构和低收缩率,通过调控遮光剂的粒径和质量分数进一步降低了SABs的高温热导率,优化后的SABs在800℃的热导率低至0.054 W m^(-1)K^(-1).