硅气凝胶纳米材料的力学性与增韧

本文综述了低温超临界干燥制备的块状硅气凝胶纳米材料的力学性能特征，论核实 了材料密度与硅气凝胶的力学性能的关系。     

莫来石纤维增强SiO2气凝胶复合材料的制备及性能研究

以正硅酸乙酯为硅源,采用溶胶-凝胶及超临界干燥技术制备了掺杂莫来石纤维的SiO2气凝胶复合材料,并对材料的热学性能和力学性能进行了测试,结果表明:SiO2气凝胶复合材料的热导率与其密度、温度和纤维添加量有关;添加莫来石纤维可以明显提高SiO2气凝胶的弹性模量和机械强度,改善材料的力学性能;莫来石纤维添加量控制在3%左右可以使SiO2气凝胶材料保持较低的热导率和较高的机械强度.     

SiO2气凝胶增强增韧方法研究进展

SiO2气凝胶的轻质纳米多孔网络结构使其在热学、声学、光学及电学等领域具有广阔的应用前景,但强度低和韧性差的缺点很大程度上限制了其应用发展.分析了SiO2气凝胶的主要力学性能指标和提高其强度的两种途径(控制制备工艺参数与材料复合法),讨论了这两种增强途径的最新研究进展.通过控制制备工艺参数获得结构均匀的SiO2气凝胶,并采用材料复合技术进一步提高SiO2气凝胶的强韧性能,可望获得结构稳定并具有良好强韧性的SiO2气凝胶材料.     

硅气凝胶材料的研究进展

硅气凝胶是一种具有许多奇异性质和广泛应用前景的轻质纳米多孔性材料，近年来受到物理学家，化学家和材料学家们的重视，本文系统归纳了近年来有关硅气凝胶的研究成果，对硅气凝胶的制备原理，结构与性能以及应用开发等研究的进展作了简要的论述。     

SiO_2气凝胶力学性能的影响因素及改善方法

SiO2气凝胶的纳米多孔网络结构使其在热学、声学、光学、电学等领域具有广阔的应用前景,但其强度低和韧性差限制了发展和应用。对SiO2气凝胶力学性能的表征方法进行了概述,综述了制备工艺参数(如溶液酸碱度、组分配比、反应温度及时间、后处理工艺、干燥工艺等)对SiO2气凝胶网络结构及力学性能影响的研究进展,并介绍了材料复合法用于改善SiO2气凝胶力学性能的研究进展。     

聚合物气凝胶研究进展

气凝胶是经溶胶-凝胶过程结合一定的干燥方法制备得到的多孔纳米材料。聚合物气凝胶不仅具有聚合物材料的低介电常数、良好力学性能和灵活的分子设计性等特性,同时还具有无机气凝胶材料低密度、高孔隙率和低热导率等特点,被广泛应用于隔热、吸附和储能等领域。从合成、结构、性能和应用等方面介绍了聚氨酯(PU)、聚脲(PUA)、聚酰亚胺(PI)、聚苯并噁嗪(PBZ)和间规聚苯乙烯(sPS)类等常见聚合物气凝胶的研究进展,并对其未来的发展方向做出了展望。     

纳米多孔SiO2气凝胶的常压制备及应用

采用多聚硅(E-40)为前驱体摸索了用溶胶-凝胶方法制备SiO2气凝胶的不同反应条件,探索和采用了常压干燥技术.在免除了昂贵繁琐的超临界干燥过程之后,气凝胶的制备成本下降,生产效率提高,并能成规模批量生产多种规格的SiO2气凝胶.采用适当的方法将SiO2气凝胶与聚酰亚氨和无纺布等材料进行复合,制成能耐高温的柔性隔热保温薄膜和高效吸附材料.     

基于纳米材料的气凝胶制备及应用

气凝胶是一种三维多孔材料,具有孔隙率高、比表面积大、密度低等特性。以纳米材料构筑气凝胶可进一步调控孔隙结构、改善机械强度,同时还能赋予气凝胶高导电性、低热导率、高吸附性和隔音吸声等特性,在储能、保温隔热、吸附材料等领域有重要的应用。重点对近年以纳米颗粒、纳米纤维素、碳纳米纤维、碳纳米管、石墨烯等不同形态纳米材料构筑的气凝胶的制备、结构、性能和应用进行了综述,同时展望了气凝胶的发展前景与方向。     

冰模板法制备纳米纤维素气凝胶及其性能研究

近年来，由于资源、能源和环境问题的不断加剧，低碳环保材料的开发成为研究热点。纳米纤维素气凝胶不仅具有传统气凝胶的优点，还兼具了纤维素来源广、可再生、可降解、良好的生物相容性，在保温隔热领域表现出广阔的应用前景。为了提高纳米纤维素气凝胶的力学性能和保温性能，设计了一种径向具有温度梯度的模具，采用冰模板法制备了一种具有各向异性结构的纳米纤维素气凝胶，并对比分析了冷冻方法对气凝胶结构、密度、孔隙率、收缩率、保温隔热性能的影响。结果表明：采用冰模板法制备的气凝胶在结构、力学性能和保温隔热性能上，均优于冰箱冷冻法和液氮冷冻法制备的气凝胶，是一种实现气凝胶结构调控，改善气凝胶结构与性能的有效方法。     

硅气凝胶的结构控制研究

以正硅酸乙酯为原料，用溶胶－凝胶法和超临界干燥工艺制备了纳米多孔硅气凝胶，系统研究了原料和溶剂（水或酒精）的用量及催化剂的使用，老化等因素对硅气凝胶结构的影响，利用这睦因素可以实现对该材料的结构进行纳米尺度上的控制，从而为该材料的应用开发奠定基础。     

Influence of various processing parameters on water-glass-based atmospheric pressure dried aerogels for liquid marble purpose

Experimental results on the influence of various processing parameters on water-glass-based atmospheric pressure dried aerogels for liquid marble purpose are reported. Silica aerogels were prepared by varying the parameters namely washing temperature of the gels with water, washing period of the gels, protic solvents, and drying method. The physical properties of silica aerogels were studied by measuring granular bulk density, contact angle with water, thermal conductivity, and thermal stability in the furnace. The elemental analyses were carried out using Atomic Absorption Spectroscopy (AAS) and FT-Raman spectroscopy. The structural studies were carried out using Transmission Electron Microscopy (TEM). Also, the effect of humidity on the silica aerogels was studied in humidity chamber. Opaque silica aerogels with hydrophobicity (150°), low density (0.053 g/cm³), and low thermal conductivity (0.068 W/mK) have been obtained for the molar ratio of Na₂SiO₃: H₂O: citric acid: TMCS at 1:146.67:0.72:9.46. The hydrophobic powder of silica aerogels can form the liquid marbles.     

纳米SiO2气凝胶的制备及保温隔热性应用研究进展

从SiO_2气凝胶的隔热机理出发,归纳了降低其导热系数的有效途径,概述了在溶胶-凝胶过程中硅源的甄选原则及开发趋势,总结了当前常用湿凝胶干燥工艺的优缺点并提出改进方法,着重介绍了当前保温隔热领域SiO_2气凝胶复合材料的种类及应用现状,最后对SiO_2气凝胶材料的发展前景进行了展望。     

Tailoring mechanical properties of aerogels for aerospace applications

Silica aerogels are highly porous solid materials consisting of three-dimensional networks of silica particles and are typically obtained by removing the liquid in silica gels under supercritical conditions. Several unique attributes such as extremely low thermal conductivity and low density make silica aerogels excellent candidates in the quest for thermal insulation materials used in space missions. However, native silica aerogels are fragile at relatively low stresses. More durable aerogels with higher strength and stiffness are obtained by proper selection of silane precursors and by reinforcement with polymers. This paper first presents a brief review of the literature on methods of silica aerogel reinforcement and then discusses our recent activities in improving not only the strength but also the elastic response of polymer-reinforced silica aerogels. Several alkyl-linked bis-silanes were used in promoting flexibility of the silica networks in conjunction with polymer reinforcement by epoxy.     

Glasses from aerogels

Experiments carried out to obtain monolithic silica aerogels are reported. The different ways to synthesize silica aerogels from alkoxides are investigated. The manner by which the critical point of the solvent can be reached is discussed as a function of the nature of the solvent. Physical parameters such as the amount of additional solvent or pressure, play a very important role in the direction of the liquid-vapour interface displacement during the heating of the autoclave. Some experiments performed using hypercritical drying with CO₂ liquid are also mentioned.     

Preparation of CdS coatings on the inner surface of silica aerogels by single-source metal-organic chemical vapor deposition at atmospheric pressure

CdS coatings are deposited on the external and inner surfaces of silica aerogels with a single-source metal-organic chemical vapor deposition method at atmospheric pressure. Thermogravimetry analysis and differential scanning calorimetry experiments are used to investigate the thermal behavior of silica aerogels, and the sample treated at 500 °C for 120 min has been found to possess the lowest density. The densities and morphologies of the silica aerogels under the different treatment temperatures are also studied. The CdS coatings are deposited on the inner surface of the silica aerogels with a 4 l/min flow of Ar gas. The procedure for the preparation of the CdS coatings on the inner surface is reported in details. The surface morphologies of the CdS-coated silica aerogels are analyzed by scanning electron microscopy. The results of the energy dispersive X-ray spectroscopy and X-ray diffraction analysis demonstrate that the CdS coatings are composed of cadmium and sulphur with an approximately atomic ratio of 1:1, and they are hexagonal structures.     

螺旋形碳纳米管的制备表征及其生长机理的探讨

采用气凝胶与干凝胶两种催化剂载体通过化学气相淀积方法制备出螺旋状的碳纳米管.研究结果表明:气凝胶催化剂载体所制备出的螺旋碳纳米管和干凝胶载体所制备出的螺旋碳管相比较具有以下几个特点:(1)较好的石墨化程度,(2)较小的直径,(3)较好的螺旋形态,即较好的螺距一致性.分析结果认为气凝胶独特的介孔性质是导致气凝胶样品所制备的碳管具有以上特点的根本原因.另外,还提出催化剂颗粒周边上催化活性的各向异性将导致螺旋碳管的生长.     

SiO2气凝胶的研究现状与应用

综述了SiO2气凝胶的原料、凝胶工艺、干燥工艺、性能与应用的基本规律和最新进展,展望了SiO2气凝胶未来的研究方向。在SiO2气凝胶优异性能被广泛认同的前提下,工艺研究的重心集中在克服低成本化和强度、吸湿性等,应用研究主要集中在热学、吸附与催化等领域。     

Synthesis of sustainable silica xerogels/aerogels using inexpensive steel slag and bean pod ash: A comparison study

Low cost silica xerogels/aerogels were synthesized from steel slag and bean pod ash by sol–gel method. Comparison study showed differences between structural, morphological, textural, thermal and physical properties of the silica xerogels and aerogels. Formation of amorphous structure and silica network was confirmed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy analyses, respectively. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analyses revealed that silica xerogels had smaller interlinked network in contrast to silica aerogels. Typical type IV isotherm was observed for all samples in N₂ adsorption-desorption isotherms. The highest surface area was determined as 371 m² g⁻¹ for silica aerogel synthesized from steel slag. Particle size of silica aerogels was lower than that of the silica xerogels. The more porous structure made silica aerogels desirable materials with lower bulk density and thermal conductivity when compared to silica xerogels. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) exhibited high thermal stability of the silica xerogels/aerogels. Although silica xerogels had highly hydrophilic structure, contact angle of silica aerogels synthesized from steel slag and bean pod ash was 60° and 74°, respectively. The comparison study will give a new point of view about differences between silica xerogels and aerogels synthesized from by-products or inorganic/organic waste instead of silicon alkoxides.     

超低密度SiO2气凝胶快速制备的新方法

以正硅酸乙酯(TEOS)为硅源,采用酸碱二步催化溶胶-凝胶法,结合超临界干燥技术制备了超低密度SiO2气凝胶.通过采用CH3CN为稀释剂,有效地降低了胶凝温度(室温),缩短了胶凝时间,从而达到了快速制备SiO2气凝胶的目的.利用SEM、BET等方法对干燥不同程度的低密度SiO2气凝胶微结构进行了研究.     

聚合物改性SiO2气凝胶的研究进展

采用聚合物对SiO2气凝胶进行改性,是改善其质脆易碎性的一种行之有效的方法,开创了一种对气凝胶改性的崭新思想。总结了聚合物改性SiO2气凝胶的原理、方法、进展及其性能。SiO2气凝胶经聚合物改性后,强度通常可提高2个数量级,柔韧性可调,而本身的体积密度仅增加几倍,其原有的纳米孔隙结构及其优良性能得以保留。但是,这种改性气凝胶还有诸多有待改进的地方,如常压干燥技术的研究、体积密度和热导率的降低、制备过程的简化以及耐高温性能的改善等。