间苯二酚—甲醛有机气凝胶的结构控制研究

以间苯二酚－甲醛为原料，用溶胶－凝胶法和超临界干燥工艺制备了纳米多孔ＲＦ有机气凝胶，系统研究了原料配比，催经剂的使用，反应温度及溶剂用量等因素对ＲＦ气胶胶凝结时间和结构的影响，可以实现对该材料的结构进行纳米尺寸上的控制，从而为该材料的应用开发遵定了基础。     

CRF气凝胶的结构特性研究

间苯二酚－甲醛气凝胶（ＲＦ气凝胶）是一种无序、多孔的纳米非晶固态材料，其碳化产物碳化气凝胶（ＣＲＦ气凝胶）具有大的比表面积，好的导电性和电化学稳定性。成为制备超级电化学双层电容器的理想电极材料。本文研究了ＣＲＦ的网络结构、成份组成、孔径分布及电导率等特性，为ＣＲＦ的实际应用奠定了基础。     

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。     

丙酮为溶剂制备SiO_2气凝胶

本文介绍了以ＴＥＯＳ为原料，使用丙酮为溶剂制备新型纳米多孔材料ＳｉＯ_２气凝胶的方法．并用ＢＥＴ、ＴＥＭ和ＦＴＩＲ方法研究了该材料的基本结构，与使用酒精溶剂制备的气凝胶进行了比较．并讨论Ｆ￣－对水解缩聚反应的影响．     

HF催化快速制备SiO2气凝胶

ＳｉＯ２气凝胶晃一种新型轻质纳米多孔泡沫材料,本文以正硅酸乙酯（ＴＥＯＳ）为原料,以乙醇为溶剂,以ＨＦ为催化溶胶－凝胶法快速制备出了ＳｉＯ２气凝胶。ＨＦ的加入大大加速了溶胶－凝胶反应速度,使凝胶时间减少至几分钟甚至更短;同时使凝胶温度降低至室温。ＢＥＴ及ＴＥＭ测试结果表明所制备的ＳｉＯ２气凝胶具有大比表面积（６７３．８ｍ＾２ｇ＾－１）、纳米多孔结构（骨架颗粒为几纳米,孔洞尺寸为５～３０ｎｍ）。     

溶胶—凝胶法制备SiO2气凝胶及其特性研究

本文以ＴＥＯＳ为原料，采用溶胶－凝胶法和超临界干燥工艺制备了轻质纳米多孔材料ＳｉＯ２气凝胶。研究了溶剂用量ｐＨ值对溶胶的凝胶化过程和最后制成的气凝胶的特性的影响。并用ＢＥＴ、ＸＲＤ、ＳＥＭ等实验手段研究了这些气凝胶的结构和一些基本物理现象。     

溶胶－凝胶法制备SiO_2气凝胶及其特性研究

本文以ＴＥＯＳ为原料，采用溶胶－凝胶法和超临界干燥工艺制备了轻质纳米多孔材料ＳｉＯ２气凝胶．研究了溶剂用量及ｐＨ值对溶胶的凝胶化过程和最后制成的气凝胶的特性的影响．并用ＢＥＴ、ＸＲＤ、ＳＥＭ等实验手段研究了这些气凝胶的结构和一些基本物理现象．     

丙酮为溶剂制备了SiO2气凝胶

本文介绍了以ＴＥＯＳ原料，使用丙酮为溶轩新型纳米多孔材料ｉＯ２气凝胶的方法，并用ＢＥＴ。ＴＥＭ和ＦＩＨ方法研究了该材料的基本结构，与使用酒精溶剂制备的气凝胶进行了比较，并讨论了对水解缩聚反应的影响。     

RF有机气凝胶的合成

有机气凝胶是一种８０年代末问世的新型纳米材料。本研究以间苯二酚和甲醛为原料,在碳酸钠催化作用下,经水相溶胶－凝胶聚合、溶剂转换和超临界二氧化碳干燥合成了透明、暗红色、无裂纹的块状ＲＦ有机气凝胶,所得气凝胶密度可低至０．０３２ｇ．ｃｍ＾－３。考察了溶胶－凝胶过程中的催化剂浓度、反应物总浓度及酸交联对气凝胶特性的影响。ＴＥＭ表征表明,所得气凝胶具有典型的纳米网络结构,固体相由直径约１０ｎｍ的粒子组成,孔直径小于１００ｎｍ。     

二氧化硅气凝胶合成新工艺

以Ｅ－４０（多聚硅氧烷）为硅源,以ＨＦ为催化剂,用溶胶－凝胶法制备出了ＳｉＯ２气凝胶法时研究了催化剂、溶剂、水等制备因素对其溶胶－凝胶过程的影响,用孔径分布测定仪、透射电镜（ＴＥＭ）、比表面测试（ＢＥＴ）等方法对其微结构进行了研究。研究结果表明,ＨＦ的加入大大加束字溶胶－凝胶反应速度;ＢＥＴ以及ＴＥＭ测试结果表明所制备的ＳｉＯ２气凝胶具有大的比表面积和纳米多孔结构（骨架颗粒约为１０纳米,孔洞尺政变     

石墨烯/炭气凝胶的制备及其结构与性能研究

以间苯二酚(R)和甲醛(F)为炭前驱体原料, 通过溶胶-凝胶法制备石墨烯/炭气凝胶复合材料。采用XRD、Raman、SEM和N₂吸附/脱附等对样品进行结构表征。结果表明: 石墨烯为R和F的聚合提供形核场所, R和F首先在氧化石墨烯(GO)表面聚合, 随着RF含量的增加, 复合炭气凝胶(RF)结构从石墨烯薄片层为骨架的三维网络, 经RF基炭球包裹于石墨烯的网络结构, 最终转变为球形团簇交联的三维网络。石墨烯/炭气凝胶复合材料的比表面积随着RF的增加先增大后减小。当GO与RF质量比为1︰100时, GO/RF-100用作超级电容器电极材料, 在6 mol/L KOH电解液中的比电容达169 F/g, 具有较好的电容特性。     

The control of porosity at nano scale in resorcinol formaldehyde carbon aerogels

Organic aerogels were synthesized by sol–gel polymerization of resorcinol (R) with formaldehyde (F) catalyzed by sodium carbonate (C) followed by vacuum drying. The influence of the resorcinol/sodium carbonate ratio (R/C) on the porous structure of the resultant aerogels was investigated. The nitrogen adsorption–desorption measurements show that the aerogels possess a well developed porous structure and mesoporosity was found to increase with increasing the R/C ratio. Carbon aerogels were obtained by carbonization of RF aerogels. The carbonization temperature impacts the microstructure of the aerogels by pore transformations during carbonization probably due to the formation of micropores and shrinkage of the gel structure. The results showed that a temperature of 1073 K is more effective in the development of the pore structure of the gel. Activated carbon aerogels were obtained from the CO₂ activation of carbon aerogels. Activation results in an increase in the number of both micropores and mesopores, indicative of pore creation in the structure of the carbon. Activation at higher temperatures results in a higher degree of burn off and increases the pore volume and the surface area remarkably without change of the basic porous structure, pore size, and pore size distribution.     

RF气凝胶扩孔影响因素初探

实验需要的间苯二酚-甲醛(RF)气凝胶的孔径大于标准RF气凝胶所形成的孔径。利用双催化技术(即先加碱性催化剂,再加酸催化剂)进行了标准RF气凝胶扩孔实验,该技术通过改变碱、酸催化剂的浓度和碱催化剂作用时间来控制孔径,并缩短凝胶时间来改善微球的非均匀性以提高其产率达到可接受的范围。文中用氮吸附,透射电镜表征了双催化制得的RF气凝胶,并与标准RF小孔样品进行对比分析,并讨论了各种因素对孔径大小及孔径分布的影响。     

反应物结构对酚醛凝胶及其气凝胶的影响

为研究反应物酚与醛的结构对酚醛凝胶过程及其气凝胶结构的影响,采用不同的酚与醛制备出了多种气凝胶。研究了反应物结构对凝胶过程的影响,并通过扫描电镜和孔径分析仪等仪器详细研究了气凝胶的结构。结果表明,酚醛反应的凝胶时间受反应物的活性及位阻效应共同影响,反应体系选择不当可能导致无法凝胶。采用不同的酚-醛体系,所得气凝胶结构也...     

Synthesis of β-SiC nanostructures via the carbothermal reduction of resorcinol–formaldehyde/SiO2 hybrid aerogels

The novel resorcinol–formaldehyde/SiO₂ (RF/SiO₂) hybrid aerogels were chosen to synthesize the cubic silicon carbide (β-SiC) nanostructures via a carbothermal reduction route. In this process, the in situ polymerized RF/SiO₂ aerogels were used as both the silicon and carbon sources. The morphologies and structures of SiC nanostructures were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and high-resolution transmission electron microscope (HRTEM) equipped with EDS. The effects of C/Si atomic ratios in RF/SiO₂ aerogels and heat treatment temperatures on the formation of SiC nanomaterials were investigated in detail. It was shown that β-SiC nanowhiskers with diameters of 50–150 nm and high crystallinity were obtained at the temperatures from 1400 to 1500 °C. The role of the interpenetrating network of RF/SiO₂ hybrid aerogels in the carbothermal reduction was discussed and a possible mechanism was proposed.     

Imaging aerogels at the molecular level

Aerogels are a special class of open-cell foams that have an ultrafine cell/pore size (<50 nm), high surface area (400–1000 m² g^–1), and an ultrastructure composed of interconnected colloidal-like particles or polymeric chains with characteristic dimensions of 10 nm. The purpose of this paper is to directly image a series of resorcinol-formaldehyde (RF) and silica aerogels by high resolution transmission electron microscopy (HRTEM). A new vertical replication technique allows us to examine aerogels at the molecular level in situ so that differences in polymeric and colloidal aerogels can be visualized. Such information is crucial for nano-engineering the structure and properties of these novel materials.     

Carbon aerogel composites prepared by ambient drying and using oxidized polyacrylonitrile fibers as reinforcements

Carbon fiber-reinforced carbon aerogel composites (C/CAs) for thermal insulators were prepared by copyrolysis of resorcinol-formaldehyde (RF) aerogels reinforced by oxidized polyacrylonitrile (PAN) fiber felts. The RF aerogel composites were obtained by impregnating PAN fiber felts with RF sols, then aging, ethanol exchanging, and drying at ambient pressure. Upon carbonization, the PAN fibers shrink with the RF aerogels, thus reducing the difference of shrinkage rates between the fiber reinforcements and the aerogel matrices, and resulting in C/CAs without any obvious cracks. The three point bend strength of the C/CAs is 7.1 ± 1.7 MPa, and the thermal conductivity is 0.328 W m(-1) K(-1) at 300 °C in air. These composites can be used as high-temperature thermal insulators (in inert atmospheres or vacuum) or supports for phase change materials in thermal protection system.     

Carbon fiber reinforced carbon aerogel composites for thermal insulation prepared by soft reinforcement

To overcome the brittleness and the pyrolysis shrinkage of carbon aerogels, carbon fiber reinforced composites were prepared by copyrolysis of polyacrylonitrile fiber reinforced resorcinol-formaldehyde aerogel composites (PAN/RFs). The PAN/RFs were obtained by impregnating the PAN fiber felt with RF sol and then supercritical drying. Upon carbonization the PAN fiber shrinks with the RF aerogel, thus reducing the shrinkage differences between the fiber and the aerogel, and results in crack-free carbon fiber reinforced carbon aerogel composites, with a thermal conductivity of 0.073 W/m K at 25 °C in air. Our new method may greatly expand the usage of carbon aerogels in general applications.     

Study of transport properties and conduction mechanism of pure and composite resorcinol formaldehyde aerogel doped with Co-ferrite

A series of resorcinol formaldehyde aerogels (RF aerogels) composite with nanoparticles of CoFe₂O₄ have been prepared by sol–gel method. Four samples of pure RF aerogels were prepared at different concentrations of Na₂CO₃ as catalyst (0.02, 0.025, 0.03, and 0.04 wt.%) and four samples of composite RF aerogels were prepared at different concentration of doped CoFe₂O₄ (0.075, 0.1, 0.125, and 0.15 wt.%; Na₂CO₃ concentration = 0.03 wt.%). DC electrical conductivity as a function of temperature was studied in the temperature range 25 °C–200 °C for all samples. AC electrical conductivity and dielectric properties were determined using RLC Bridge in the frequency range 100 Hz–1 MHz at different temperature (25–200 °C). The pore size of the samples was determined using positron annihilation lifetime spectroscopy (PALS). RF aerogels are found to exhibit a semiconducting behavior and characterized by two transition temperatures T₁ and T₂. Also σ_DC increases with increase of Co-ferrite contents. Pure RF aerogels posses a very low dielectric constant, where the lowest value of ?′ is ∼4 times as that of air. ?′ decreases with increase of frequency, and increases with increase of temperature. Large overlapping polaron (OLP) is found to be the preferred conduction mechanism in these materials. The results of PALS show that there are two types of pore size in these samples; the first ranges from 1.9 to 2.5 nm, while the second ranges from 3.2 to 5.3 nm.     

炭气凝胶结构的形成和控制

炭气凝胶是一种新型的多孔炭材料,具有可调控的独特的孔结构和良好的导电性,可应用于超级电容器、高效吸附材料、催化剂载体等.本文研究了酚醛基炭气凝胶纳米结构的形成过程和控制方法.炭气凝胶的孔结构主要取决于其前驱体--有机气凝胶.有机气凝胶结构源于溶胶-凝胶聚合中的微相分离过程,相分离经历了从成核--生长--亚稳分解的过渡,在成核--生长区停留时间的长短决定了气凝胶的骨架结构和孔结构.微相分离过程受到酚醛团簇的化学结构和溶剂环境的影响,通过调控酚醛团簇的化学结构和溶胶-凝胶聚合的溶剂环境,可以实现有机气凝胶的纳米结构调控,结合干燥和炭化控制,可以实现炭气凝胶结构的有效调控.