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疏水性二氧化硅气凝胶的常压制备与表征 总被引:1,自引:0,他引:1
采用溶胶-凝胶技术,以正硅酸乙酯为有机前驱体,三甲基氯硅烷为改性剂,在常压下干燥制备出疏水性二氧化硅(SiO2)气凝胶,同时采用密度测量、比表面积和孔径分布仪、扫描电镜、热重分析仪对SiO2气凝胶进行表征。文章重点研究反应物配比和表面修饰对SiO2气凝胶性能的影响。结果表明,采用正硅酸乙酯、水、乙醇体积配比为25︰6︰80和三甲基氯硅烷的正己烷溶液表面修饰合成的SiO2气凝胶性能质量较好。 相似文献
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疏水SiO2气凝胶的制备及表征 总被引:5,自引:2,他引:3
以正硅酸乙酯(TEOS)为硅源,三甲基氯硅烷(TMCS)为改性剂,经老化、表面疏水改性,常压干燥制备了高比表面积疏水SiO2气凝胶.用傅立叶变换红外光谱仪(FT-IR)、扫描电镜(SEM)、比表面及孔径分布仪、热重分析仪(TG-DSC)对其疏水特性及结构进行表征.结果表明:疏水SiO2气凝胶与水的接触角达145°,在空气中的热稳定温度为269 ℃;且比表面积达1035 m2/g,具有典型的气凝胶结构特征,孔径尺寸和密度分别达9.7 nm和0.129 g/cc,骨架颗粒尺寸小于30 nm. 相似文献
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以正硅酸乙酯(TEOS)为硅源,采用酸、碱两步催化的溶胶-凝胶法,通过L9(34)四因素三水平正交试验,研究了无水乙醇(ETOH)、草酸(H2C2O4)和氨水(NH3 H2O)之间的摩尔比以及酸碱间隔时间对气凝胶性能的影响,并对所得产品结构和性能进行了比表面(BET)、傅立叶转换、红外线光谱(FTIR)和扫描电镜(SEM)表征,从而首次实现了SiO2气凝胶的常温合成。实验结果表明:原料最佳摩尔比为TEOS∶ETOH∶H2C2O4∶NH3.H2O=1∶7∶3.5∶2.5,酸碱最佳间隔时间为18 h,SiO2气凝胶的平均粒径为6.58 nm,密度为100 kg/m3,孔径分布为2~30 nm,比表面达到938.17 m2/g,室温条件下合成的SiO2气凝胶,不亚于高温合成法的产品性能。 相似文献
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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. 相似文献
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SiO2气凝胶制备过程中缩裂问题的研究 总被引:1,自引:0,他引:1
基于实验,分析了SiO2气凝胶在制备过程中收缩开裂的原因,并系统研究了原料和溶剂(水和乙醇)的用量及催化剂的使用、老化等因素对SiO2气凝胶结构的影响,利用这些因素来实现对其进行微观结构控制,采用乙醇超临界干燥技术解决该材料制备过程中的缩裂问题。 相似文献
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David D. Smith Laurent Sibille Erica Ignont Raymond J. Cronise David A. Noever 《Journal of Porous Materials》2000,7(4):499-508
We have fabricated aerogels containing gold and silver nanoparticles for gas catalysis applications. The technique of immersion spectroscopy is extended to porous or heterogeneous media allowing the surface area of metal available for catalytic gas reaction to be determined. Specifically, we apply the predominant effective medium theories to the heterogeneous interlayer surrounding each particle to determine the average fractional composition of each component in this inhomogeneous layer. The technique is satisfactory for statistically random metal particle distributions but needs further modification for aggregated or surfactant modified systems. Additionally, the kinetics suggest that collective particle interactions in coagulated clusters are perturbed during silica gelation resulting in a change in the aggregate geometry. 相似文献
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采用半连续种子乳液聚合的方式,以丙烯酸丁酯、甲基丙烯酸甲酯和甲基丙烯酸六氟丁酯为原料制备了粒径分别为30nm、75nm、210nm左右的含氟丙烯酸酯共聚物乳液。通过乳胶粒核壳结构设计与大小粒径乳液机械共混改性2种方法研究了如何在较少含氟单体用量的情况下达到较好的表面疏水性能。利用X射线光电子能谱、动态光散射仪、接触角测定仪等分析手段,研究了共聚物膜的表面性能和共聚物乳液粒径的大小及分布,测试结果表明,核壳结构乳液成膜后壳层含氟量较高,膜表面接触角大于90,°疏水性能强;而大小粒径乳液共混物成膜后表面含氟量较低,却仍能得到90°以上的接触角,表明乳胶膜表面具有粗糙结构,具有一定的仿荷叶效应。 相似文献
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Thermal Insulation Characteristics of Polybenzoxazine Aerogels 总被引:1,自引:0,他引:1
Polybenzoxazine (PBO) aerogels with low densities and low thermal conductivities are prepared from Bisphenol A (BPA) benzoxazine monomers by ring‐opened polymerisation using HCl as a catalyser at 10 °C. The obtained PBO aerogels have cross‐linked and 3D network structures with the densities ranging from 0.084 to 0.526 g cm?3. The thermal conductivities under different pressures (3–105 Pa, air) and different atmospheres (N2, Ar, and CO2, 105 Pa) are investigated. The thermal conductivities are in the range of 0.0335–0.0652 W m K?1 under ambient pressure and 0.0098–0.0571 W m K?1 at 3 Pa. The thermal transfer mechanism under different gas pressures is analyzed with increasing pressure. Under different atmospheres, the thermal conductivities decrease as the molecular weight of the gas increases. Compared with the traditional organic foam insulating materials of phenolic foam, polyurethane and polystyrene, which have similar apparent densities, PBO aerogels exhibit lower thermal conductivity of 0.0335 W m K?1 than that of traditional organic foam at room temperature. 相似文献
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Shiya Qiao Hao Zhang Shuai Kang Jiayou Quan Zuming Hu Junrong Yu Yan Wang Jing Zhu 《大分子材料与工程》2020,305(8)
Polyimide (PI) aerogels have great potential as filter materials, owing to their unique porous structure and excellent thermodynamic properties. In this work, polyvinylidene fluoride (PVDF) is introduced into the 3D network structure of crosslinked PI by phase separation to prepare PI/PVDF hybrid aerogels. By adding different amounts of PVDF, effective control of the aerogel porous structure is achieved, as a result, the air permeability of the hybrid aerogel is significantly improved while still achieving a filtration efficiency of airborne particulates of more than 99.8%. PVDF is aggregated and dispersed on the surface or inside of the aerogel in the form of nanoparticles, which effectively increases the hydrophobicity of the material. The contact angle of the prepared PI hybrid aerogel is ≈150°, and the water absorption is as low as 2.2%, which enables the aerogel to maintain structural stability in humid environments. In addition, the aerogel exhibits good adsorption effects on organic solvents. 相似文献
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《分离科学与技术》2012,47(8):1149-1155
The adsorption process of Ce(IV) ions from aqueous solution by the silica aerogels was studied. The silica aerogels with hydrophobicity were prepared by the sol-gel process, supercritical drying, and heat treatment. The SEM image and nitrogen adsorption-desorption isotherm show that the heat-treated silica aerogel was a co-continuous porous structure with high BET surface area and narrow pore size distribution. The adsorption of Ce(IV) ions onto the silica aerogels was found to be fitted well by pseudo-second-order kinetics and Langmuir isotherm model. The activation energy for Ce(IV) adsorption onto silica aerogels could be calculated to be about 17.88 kJ/mol, which implied that the attractive forces of adsorption were weak electrostatic forces accompanying most ion-exchange reactions. The thermodynamic parameters showed that the adsorption process was spontaneous and endothermic. 相似文献
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Sergey A. Baskakov Yuliya V. Baskakova Svetlana S. Krasnikova Eugene N. Kabachkov Maria A. Kapustyanskaya Nadezhda N. Dremova Filipp O. Milovich Yury M. Shulga Xiaowu Wang Zhi Li 《Polymer Engineering and Science》2023,63(1):305-313
Polytetrafluoroethylene/cellulose composite aerogels containing PTFE from 0 to 40 wt.% were obtained by drying the corresponding suspension mixtures at a temperature of 50°C. Cellulose isolated from the stem of Sosnowski hogweed was used as the main component of the aerogels. In present work, the composite aerogels were heated in an inert atmosphere at a temperature of 370°C to partially hydrophobize cellulose and remove surfactants that were present in the initial PTFE suspension. It was found that at this temperature, the thermal degradation of cellulose proceeded differently in the presence and absence of PTFE. The maximum water contact angle (156°) was obtained for the sample with 10 wt.% PTFE. Hydrophobized samples of aerogels were studied with the help of infrared spectroscopy, scanning electron microscopy, and powder x-ray diffractometry and tested as sorbents for various solvents. It was found that the volume of solvent absorbed by the aerogel, in the case of a sample with a PTFE content of 40 wt.%, can even exceed the initial volume of the absorber. 相似文献
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T. G. Maci -Agull J. C. Fern ndez-Garcí a A. Torr palau A. C. Orgil s Barcel J. M. Martí n-Martí nez 《The Journal of Adhesion》1995,50(4):265-277
Two hydrophilic and two hydrophobic fumed silicas of different characteristics were added to solvent-based polyurethane adhesives (PU). IR spectroscopy, contact angle measurements and rheology (viscosity measurements, determination of viscoelastic properties) were used to monitor the variation of properties of PU adhesives produced by addition of silica. Immediate (green) adhesion was determined by T-peel testing of halogenated synthetic rubber/PU adhesive/halogenated synthetic rubber joints. Silica addition produced a noticeable increase in the PU adhesive viscosity which can be related to the variation of viscoelastic properties. Viscosity of PU adhesives containing hydrophilic silica slightly increased with time after preparation; the increase was less significant in PU adhesives with hydrophilic silica. In the rheological studies, silica imparted shear thinning and negative thixotropy to PU adhesives due to a better dispersion of the silica in the polyurethane during shearing. The addition of silica produces an increase in the storage modulus (G') of PU adhesives, the values obtained being independent of the hydrophilic or hydrophobic nature of the fumed silica. The increase of G' and the changes in tan δ of PU adhesives containing silica corresponded to an improvement in the green adhesion properties of chlorinated rubber/PU adhesive/chlorinated rubber joints. In general, in disagreement with previous results,1 the presence of silica did affect the properties of solvent-based PU adhesives, but these properties were not dependent on the type of silica (hydrophobic or hydrophilic) used in this study. 相似文献