疏水SiO2气凝胶的制备及表征

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.     

厘米级SiO2气凝胶球体的制备及表征

以正硅酸乙酯(TEOS)为硅源,采用酸碱两步催化溶胶-凝胶法和CO2超临界干燥技术成功制备出完整的厘米级SiO2气凝胶球体.当配比条件为TEOS∶ EtOH∶ H2O=1∶10∶4时制备的SiO2气凝胶球体具有典型的纳米多孔网络结构.采用扫描电镜(SEM)、透射电镜(TEM)、傅里叶变换红外光谱仪(FT-IR)、孔径分布及比表面积测试仪(BET)、纳压痕技术对SiO2气凝胶球体的表面形貌、内部结构、化学成分、比表面积、孔径分布及力学性能进行研究分析.研究表明:低温有利于制备出完整的厘米级SiO2气凝胶球体.随着凝胶温度的增加,SiO2气凝胶球体样品的收缩率逐渐增加,而孔隙率和比表面积逐渐减小.当凝胶温度为-5℃时,厘米级SiO2气凝胶球体样品的平均孔径为24.8 nm,孔体积为4.9 m3/g,比表面积高达1004.38 m2/g,密度为0.104g/cm3,收缩率约为16.2％,孔隙率约为95.3％,弹性模量和硬度最大分别为8.79 MPa与5.24 MPa.     

常压干燥溶胶-凝胶法制备的TiO_2气凝胶织构和结构研究

以廉价的四氯化钛为前驱体,环氧丙烷为促凝剂,甲酰胺为干燥控制化学添加剂,有机配体丙酸为水解降速剂,采用正交实验设计以常压干燥-溶胶-凝胶法制备TiO2气凝胶,并用BET和XRD对样品的织构和结构进行表征。结果表明,以n(四氯化钛)∶n(去离子水)∶n(甲酰胺)∶n(丙酸)∶n(环氧丙烷)=1∶14∶2∶0.5∶10制备的TiO2气凝胶,比表面积为632.87 m2·g-1,平均孔径7.87 nm,孔容1.24 cm3·g-1;当平均孔径小、孔容大时比表面积较高,反之,比表面积很低;随着焙烧温度升高,晶化度增强,但仍未出现金红石相衍射峰,表明具有较好的热稳定性。TiO2气凝胶孔容较大时,锐钛矿相结晶度差,反之,结晶度好;孔容居中的TiO2气凝胶出现游离的无定型SiO2,而较低的丙酸含量有利于提高焙烧后样品的晶化度。     

添加剂对气凝胶孔径分布的影响

以稻壳灰为硅源,在适宜的凝胶形成条件下,加入不同添加剂(羟基类和酰胺类有机物),通过溶胶-凝胶、溶剂置换过程及超临界二氧化碳干燥工艺制备了硅气凝胶. 结果表明,丙三醇、乙二醇添加量为15%~20%时调控作用显著,凝胶孔洞变小且分布更均匀,比表面积增大、平均孔径减小;聚乙二醇使凝胶化时间缩短,孔径分布较均匀;二甲基甲酰胺、甲酰胺调控效果最显著,所得样品孔径集中分布于20~40 nm,比表面积均在750 m2/g以上. 聚乙烯吡咯烷酮可加快缩聚速率,使小孔比例大幅增加,网络结构致密.     

SiO2气凝胶的非超临界干燥法制备与表征

以聚二甲基硅烷为原料,采用聚合物超临界法制备了SiO2气凝胶.聚合物超临界法制备的SiO2气凝胶除碳前为疏水性气凝胶,比表面积为27.68 m2/g,孔体积为0.103 7 cm3/g,平均孔径约为15 nm;除碳后为亲水性气凝胶,比表面积为500.6 m2/g,孔体积为0.404 3 cm3/g,平均孔径为3.23 nm.对聚合物超临界法制备SiO2气凝胶的反应机理进行了初步探讨.     

低密度SiO2气凝胶的常压制备优化及表征

对SiO2气凝胶的醇凝胶制备过程和常压干燥过程分别选用4因素3水平的L9(34)正交试验进行制备条件优化,通过扫描电子显微镜(SEM)、热质曲线(TG-DTA)、傅立叶变换红外光谱仪(FT-IR)、N2等温吸附-脱附等表征手段分析密度对SiO2气凝胶形貌和结构性质的影响。结果表明,制备低密度SiO2气凝胶的主要因素为正硅酸乙酯(TEOS)、水、乙醇(EtOH)的体积比,氨水浓度,正己烷溶剂置换时间和老化时间;优化制备条件:V(TEOS):V(H2O):V(EtOH)为1:1.5:4、盐酸浓度为1 mol/L、氨水浓度为0.5 mol/L、静置时间为24 h、老化时间为24 h、正己烷置换时间为24 h,疏水改性剂质量分数为20%、干燥温度150℃,得到的SiO2气凝胶的密度为49 kg/m3;SiO2气凝胶的密度越低,比表面积越大,最概然孔径越大,孔容越大。但密度对其疏水改性过程和颗粒大小无明显影响。     

莫来石纤维增强SiO2气凝胶隔热材料的制备

以正硅酸乙酯（TEOS）为硅源,采用溶胶-凝胶及超临界干燥技术制备了莫来石纤维增强SiO2气凝胶隔热材料,并系统地研究了HF催化剂以及溶剂等制备因素对气凝胶品质的影响。结果表明：HF催化剂、H2O、乙醇和甲酰胺用量对TEOS的水解缩聚反应有较大影响,调节其配比可以制备具有不同密度的SiO2气凝胶隔热材料;添加甲酰胺可以调节凝胶内部网络结构,防止干燥时由于应力不均而开裂或破裂。     

以乌洛托品为扩孔剂合成SiO2气凝胶的研究

以正硅酸乙酯为硅源,用溶胶—凝胶法通过常压干燥制备SiO2气凝胶,在溶胶—凝胶的过程中加入扩孔剂,着重考察以乌洛托品作为扩孔剂的用量、水解时间、水解温度、焙烧温度等因素对SiO2气凝胶孔径的影响。采用红外波谱(FTIR)表征了样品具有SiO2气凝胶的骨架结构和特定的表面基团,电镜(SEM)说明了样品有很好的分散性,热重(TG)说明经过扩孔的SiO2气凝胶依然有良好的热稳定性、BET对SiO2气凝胶表征显示了样品有较大的比表面积(400～1 200m2/g)、孔径(10～21nm)、孔容(0.5～2.5cm3/g)。     

老化介质对常压干燥制备TiO2气凝胶性能的影响

采用不同的老化介质(乙醇、异丙醇、叔丁醇),以钛酸丁酯为原料,利用溶胶-凝胶法,在常压干燥下制备出块体TiO2气凝胶.通过SEM、BET和XRD分析可知,以乙醇为老化介质制备的TiO2气凝胶具有最佳结构与性能.其制备态表观密度为0.16 g·cm-3,比表面积为554.6 m2·g-1,平均孔径为19.37 nm,孔容为0.71 cm3·g-1.经850℃处理2h后,比表面积为179.8m2 ·g-1,平均孔径为20.97 nm.该样品制备态为无定形态,经850℃处理2h后转变为锐钛矿.光催化实验表明:以乙醇为老化介质制备的TiO2气凝胶具有较好的光催化性能.     

添加甲酰胺和二甲基甲酰胺对SiO2气凝胶性能的影响

以工业硅溶胶作为硅源,分别添加甲酰胺(FA)、二甲基甲酰胺(DMF)(其与SiO2的物质的量比分别为0∶1、0.1∶1、0.25∶1、0.5∶1、0.75∶1、1∶1),经溶胶-凝胶过程,结合CO2超临界干燥工艺制备了SiO2气凝胶,研究了FA、DMF对体系凝胶时间、SiO2气凝胶密度以及比表面积的影响。结果表明:FA、DMF的加入有利于体系获得完整、无开裂的气凝胶样品,且随着FA、DMF添加量的增大,由于其延缓羟基的缩聚反应以及和乙醇的亲和作用,使得体系的凝胶时间越来越长,但气凝胶密度和比表面积并无显著变化,同时FA、DMF对体系影响的差别不大。所制备的气凝胶样品具有纳米多孔结构,比表面积为220～235 m2·g-1,密度为180～198 kg·m-3。     

A Thermoporometry Study of Fumed Silica/aerogel Composites

The porous texture of fumed silica/aerogel composite materials is studied by thermoporometry. The effect of fumed silica (Aerosil) powder in aerogels, added during the sol-gel processing is investigated. The textural change due to the autoclave drying process as a function of the fumed silica/aerogel ratio of the systems is investigated. The meso- and macro porosity of the fumed silica/aerogel composites is mainly influenced by the ratio fumed silica/aerogel and only slightly by the autoclave drying process. Addition of fumed silica powder results in an increase of the mean pore radius of the system and in a decrease of the meso- and macro-pore volume. By contrast, the micro-porosity is hardly affected by the addition of the fumed silica powder; it is only influenced by the autoclave drying process.     

Synthesis of water‐glass‐based silica aerogel powder via with and without squeezing of hydrogels

The present article describes the synthesis of water‐glass‐based silica aerogel powder via coprecursor method, using with and without squeezing, in drying technique. The present research was aimed to develop a simple, cost‐effective, and rapid drying process, i.e., squeezing through sol–gel synthesis. The physical and textural properties of the aerogel powder synthesized with and without squeezing process via ambient pressure drying (APD) have been studied and compared. For characterization of aerogel powder, we employed Brunauer, Emmett, and Teller, Barrett‐Joyner‐Halenda, and field emission scanning electron microscope techniques. The experimental results showed that the properties of the aerogel powder obtained by squeezing are superior to those dried in a furnace one. The squeeze‐dried aerogel powder exhibited lower tapping density (0.126 g/cm³) than furnace dried. Furthermore, textural investigations revealed that the aerogel powder has high‐specific surface area (752.3 m²/g), high porosity, low shrinkage, and uniform pore size distribution, which is obtained by squeezing process via APD. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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.     

超临界流体干燥技术在纳米粉体制备中的应用

由于纳米粒子的表面效应，用传统的干燥方法干燥纳米粉体时极可能产生团聚结构。超临界流体干燥技术是制备具有高比表面积、孔体积、较低密度和低热导率的块状气凝胶和纳米粉体的重要途径之一。介绍了超临界流体的性质、超临界流体干燥技术的研究进展、超临界流体干燥的工艺与设备及过程的影响因素，阐述了超临界流体干燥技术在纳米材料制备中的应用，并指出了超临界流体干燥过程的控制技术及注意点，为进一步加强超临界流体干燥技术的理论研究和拓展超临界流体干燥技术的应用领域奠定了基础。     

Preparation and characterization of nitrogen-doped mesoporous titania with high specific surface area

Nitrogen-doped mesoporous titania aerogel photocatalysts were prepared by supercritical drying technique with carbon dioxide (SCCO₂) and calcination the urea impregnated TiO₂ aerogel at 773 K under NH₃ or N₂ + NH₃aq gaseous atmosphere. The pore properties were investigated from nitrogen adsorption measurement at 77 K. The prepared N-doped TiO₂ aerogel had a high specific surface area (116 m²/g), a total pore volume (0.33 cm³/g) and a sharp pore radius distribution (r_peak = 4.2 nm). The doping of the nitrogen atom into the TiO₂ lattice is expected from X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), and UV–Vis spectroscopy. Nitrogen states in the lattice and crystalline structure were measured using X-ray photoelectron spectroscopy and X-ray diffractometry. The N-doped TiO₂ aerogel absorbed well into the visible region up to 600 nm.     

Synthesis of silica aerogel thin sheets and evaluation of its thermal,electrical, and mechanical properties

Silica aerogels are excellent thermal and acoustic insulators because of interconnected open nanopores with more than 90% porosity and higher surface area. Silica aerogel is derived by sol-gel process and dried under super-critical, sub-critical or ambient pressure conditions. Thin silica aerogel sheets could be effective thermal insulators but high fragility hinders the wider applications. We have successfully developed a synthesis method for thin, flexible, and non-fragile aerogel sheets with excellent hydrophobicity, lower thermal conductivity, and non-combustible properties via ambient drying method. The silica aerogel sheets prepared compose of silica aerogel powder, fiber glass chopped strands, and solvent-based binder. Aerogel thin insulation sheets of thickness 164 μm were prepared by pressing through rollers using aerogel paste composed of aerogel powder, fiber glass strands, and binders. The thermal conductivity values obtained were between 0.02~0.63 W/mK at temperature 25~400°C, contact angle θ = 121‘_, weight loss 3.91% when heated up to 800°C in air, dielectric voltage breakdown 3.67 kV, dielectric strength 6.37 kV/mm and tensile strength of 2.65 N/mm². The overall thermal, electrical, and mechanical evaluation of aerogel thin insulation sheet showed they have higher potential to replace existing thick and bulky aerogel composites as thermal and electrical insulators in aviation, automobiles, electronics, and high power batteries.     

以煤矸石为原料制备Al2O3-SiO2气凝胶的工艺与性能

煤矸石作为固体废弃物虽然被用作发电燃料、煤矿填料与建筑材料,但其利用率仍然不高,如何提高煤矸石的高值化利用率成为了目前研究的热点。本文以山西煤矸石为原料,采用一步酸溶和溶胶-凝胶法,并经过常压干燥得到了Al₂O₃-SiO₂气凝胶粉体。在溶剂置换与改性过程中引入超声波,研究了其对气凝胶的制备与性能的影响。采用BET、XRD、SEM、FT-IR、TG-DSC及接触角测试对所得Al₂O₃-SiO₂气凝胶粉体的结构与性能进行表征。结果表明,超声波的引入加快了反应速率,缩短了气凝胶的制备周期,所制备的Al₂O₃-SiO₂气凝胶是一种具有纳米三维网络结构的介孔材料,堆积密度低至0.120 g/cm³,比表面积为635 m²/g,高温下收缩性小于传统水玻璃制备的SiO₂气凝胶,并具有较好的疏水性。     

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.     

对位芳纶气凝胶粉体的制备与性能研究

以对位芳纶纳米纤维(PANF)水凝胶为原料,将冻凝胶粉碎法与冷冻干燥法相结合,制备出PANF气凝胶粉体。系统研究了对位芳纶气凝胶粉体的微观结构及性能参数,以及制备条件对产物形貌的影响,并初步探究了其应用。结果表明,液氮冷冻制备的PANF气凝胶粉体具有多孔结构,松装密度约为17.0 kg?m^-3,孔隙率约为98.8%,BET比表面积可达126.30 m²?g^-1。PANF气凝胶粉体的耐热性优异,在氮气气氛下500℃前几乎无分解;热导率较低,约为0.03 W?m^-1·K^-1。气凝胶粉体具有吸附罗丹明B等染料的特征,同时可作为纳米填充材料增强聚氨酯乳胶膜等聚合物材料的硬度,其低热导率表明其有望应用于绝热领域。     

常压干燥合成水玻璃基SiO_2气凝胶

以水玻璃和双氧水为原料一步合成二氧化硅湿凝胶,经老化、溶剂置换及三甲基氯硅烷修饰后,并于常压干燥后获得二氧化硅气凝胶。样品经低温N_2吸附-脱附、红外光谱和扫描电镜测试表明所得二氧化硅气凝胶具有三维多孔结构,且其比表面积可达482 m~2·g~(-1)、平均孔径为24.9nm及表观密度为0.12g·cm~(-3)。