工业水玻璃制备疏水性SiO2气凝胶

以工业水玻璃为硅源,稀H2SO4为催化剂,三甲基氯硅烷(TMCS)为表面改性剂,无水乙醇和正己烷为溶剂,在常温常压下通过"两步法"成功地制备出轻质疏水性SiO2气凝胶。通过BET、FTIR、接触角测试以及SEM、EDS和TG等手段证实,所得SiO2气凝胶的比表面积为512.44~737.19m2/g,平均孔径为15.19~19.09nm,且凝胶表面-OH基团已被-OSiCH3取代,接触角高达137°,呈现出明显的疏水性和良好的热稳定性。     

常压干燥制备疏水SiO2气凝胶的影响因素分析

常压干燥制备SiO2气凝胶是近年来该领域的研究重点,工艺条件的优化是提高气凝胶性能的关键。以正硅酸乙酯为硅源,甲基三乙氧基硅烷为共前驱体,采用溶胶-凝胶法,结合老化和三甲基氯硅烷-正己烷-无水乙醇混合溶液的二次表面改性,通过常压干燥工艺制备疏水SiO2气凝胶。利用BET,FT-IR,SEM,TEM和接触角测试等手段对气凝胶进行表征,系统研究水解时间、老化时间、老化温度和改性剂用量对气凝胶性质的影响。结果表明:水解16h,凝胶于55℃下老化48h后,在三甲基氯硅烷与正硅酸乙酯的摩尔比为1.56的混合液下改性48h制备的SiO2气凝胶的性能最好,其孔隙率92%,比表面积969m2/g,接触角达157°。     

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。     

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.     

常压干燥制备SiO2气凝胶复合材料研究进展

SiO_2气凝胶复合材料具有低密度、低热导、高强度等优异性能,已在航空航天、石油化工、建筑保温等领域获得较好应用。然而现有成熟的超临界干燥制备SiO_2气凝胶复合材料工艺需要维持高温、高压条件,能耗高、危险性大且设备复杂,常压干燥制备工艺由于所需条件温和、设备简单,有望实现连续性规模化生产。本文结合国内外关于常压干燥制备SiO_2气凝胶复合材料的研究进展,按照颗粒、纤维等增强相的不同,对常压干燥制备SiO_2气凝胶复合材料进行综述并对其未来发展方向进行了展望。     

SiO2气凝胶对复合隔热涂料性能的影响

以SiO2气凝胶为功能填料,丙烯酸树脂为成膜剂,制备透明隔热涂料。将其涂覆于5mm厚的普通玻璃上制成涂层,并对涂层进行一系列性能测试,包括接触角、红外光谱、光学性能及隔热效果等。结合实验数据分析纳米SiO2含量对复合涂料性能的影响,得出最佳的涂料配方。结果表明,该透明隔热涂料具有良好的化学稳定性和隔热性能,在500W红外灯照射10min时,样品与空白玻璃温差为11℃。     

TMCS/HMDSO混合改性剂对常压制备SiO2气凝胶的影响

以TEOS为硅源,TMCS/HMDSO为混合表面改性剂,采用酸碱两步催化溶胶-凝胶法和常压干燥法制备疏水性SiO2气凝胶,并借助BET、SEM、FT-IR等测试手段对样品进行表征。结果表明:TMCS/HMDSO混合改性剂的改性效果优于单一改性剂,当TMCS体积分数为混合表面改性剂的60%,改性温度为60℃时,制备的SiO2气凝胶具有较佳的综合性能,密度为0.1213g·cm-3,比表面积高达899.8m2·g-1,孔容为2.856cm3·g-1。     

SiO2气凝胶微球的雾化制备及表征

研究硅溶胶的雾化方法和形成油包水的乳化体系,在乳化体系中加入凝胶剂制备SiO2湿凝胶微球。制得的湿凝胶微球在常温常压下老化3d后用过滤的方法分离湿凝胶微球和油相;用正己烷清洗微球表面的油和杂质,用乙醇除去湿凝胶微球内部的水;最后,用超临界CO2的方法干燥湿凝胶微球得到SiO2气凝胶微球。研究结果表明,该方法最大的优点是可以大规模化制备气凝胶微球,制得的气凝胶微球直径<50μm,大部分集中在15～35μm之间。SiO2气凝胶微球具有明显的介孔材料特征,孔径为10nm左右,比表面积高达846.14m2/g,堆积密度约为221kg/m3。     

SiO2/TiO2复合气凝胶的孔道结构研究

为了在常压干燥下制备高比表面积且具有多级孔道结构的SiO2/TiO2复合气凝胶,以正硅酸乙酯、钛酸丁酯为原料,利用低聚体聚合将分相平行引入到溶胶凝胶过程中,获得SiO2/TiO2醇凝胶,并通过溶剂替换技术实现气凝胶的常压干燥制备.不同硅钛比气凝胶的内部结构研究表明:合成的气凝胶是由纳米SiO2和TiO2颗粒分散复合而成的介孔块体,其中Ti—O—Ti、Si—O—Si和Ti—O—Si键相互交织.气凝胶的结构变化是分相与溶胶凝胶过程相互竞争的结果.Si含量能显著改善气凝胶的结构,当n(Ti)∶n(Si)为3∶1时,比表面积高达712.2 m2/g,平均孔径为3.36 nm;当n(Ti)∶n(Si)为1.5∶1时,复合气凝胶具有明显双连续孔道,比表面积高,同时孔状结构清晰.     

SiO2气凝胶的制备及其在污水处理方面的研究进展

SiO₂气凝胶微观结构中存在不同形状、大小和排列方式的孔隙,这些孔隙可以形成细小的通道、突起、凹陷等复杂形态,具有比表面积大、孔隙率高的特点。SiO₂气凝胶被广泛应用于众多领域。因其低密度和高孔隙率性质被应用于吸声材料,低导热系数被广泛应用于保温材料,并且凭借其多孔性、高比表面积等结构特点,能够高效地吸附和去除污水中的有污染物,在污水处理方面也展现出良好的应用前景。本文综述了制备SiO₂气凝胶四个阶段的研究进展,包括溶胶-凝胶法制备SiO₂湿凝胶、SiO₂凝胶的老化、表面改性SiO₂气凝胶以及SiO₂气凝胶的干燥,归纳了每个阶段的特点,重点介绍了SiO₂气凝胶在含有机染料污水、含油污水和含重金属离子污水方面的吸附应用,并对其未来发展趋势进行了展望。     

热负载条件对SiO2气凝胶组成及微观结构的影响

通过阶梯升温并结合傅里叶变换红外光谱(FT-IR)、X射线光电子能谱(XPS)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等表征手段,研究了不同温度所得SiO₂气凝胶的组成和微观结构,在程序升温条件下通过TG-DTG曲线和无模式函数法研究了SiO₂气凝胶热重行为的变化.结果表明：SiO₂气凝胶主要由7~9 nm球状颗粒构成类线形团簇,进而以团簇为骨架构成三维网络多孔结构;阶梯升温下,随着热处理温度的升高,气凝胶中Si—O—Si基团的摩尔分数逐渐增加,Si—OH和Si—OC₂H₅的摩尔分数逐渐降低,1 073 K时Si—OH基本消失,但存在6.59%的Si—OC₂H₅基团;气凝胶颗粒逐渐长大,部分骨架坍塌,温度达到1 273 K时,颗粒长大至约50 nm,团簇彻底消失,材料发生明显烧结.程序升温下,升温速率越高,气凝胶的热稳定性越好;材料的失重过程分为3个阶段：当反应转化率α < 30%时,主要发生硅羟基(Si—OH)间的缩合;当30% < α < 70%时,主要是硅羟基(Si—OH)与/或硅乙氧基(Si—OC₂H₅)之间的缩合;当α>70%时,主要是硅乙氧基(Si—OC₂H₅)之间的缩合.     

Synthesis and optical properties of luminescent core-shell structured silicate and phosphate nanoparticles

Monodisperse, luminescent core-shell structured inorganic nanoparticles were synthesized by sol-gel technology. They exhibit an amorphous SiO₂ core and a crystalline luminescent shell. Zn₂SiO₄:Mn²⁺ and Ca₁₀(PO₄)₆OH:Eu³⁺ shell materials are investigated. The influence of the doping concentration on optical and structural properties was studied. The resulting nanoparticles were characterized by X-ray diffraction analysis, transmission electron microscopy, inductively coupled plasma optical emission spectrometry, and photoluminescence spectroscopy.     

Engineered silica nanoparticles as additives in lubricant oils

Silica nanoparticles (SiO₂ NPs) synthesized by the sol–gel approach were engineered for size and surface properties by grafting hydrophobic chains to prevent their aggregation and facilitate their contact with the phase boundary, thus improving their dispersibility in lubricant base oils. The surface modification was performed by covalent binding of long chain alkyl functionalities using lauric acid and decanoyl chloride to the SiO₂ NP surface. The hybrid SiO₂ NPs were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, simultaneous differential thermal analysis, nuclear magnetic resonance and dynamic light scattering, while their dispersion in two base oils was studied by static multiple light scattering at low (0.01% w/v) and high (0.50%w/v) concentrations. The nature of the functional layer and the functionalization degree seemed to be directly involved in the stability of the suspensions. The potential use of the functional SiO₂ NPs as lubricant additives in base oils, specially designed for being used in hydraulic circuits, has been outlined by analyzing the tribological properties of the dispersions. The dendritic structure of the external layer played a key role in the tribological characteristics of the material by reducing the friction coefficient and wear. These nanoparticles reduce drastically the waste of energy in friction processes and are more environmentally friendly than other additives.     

Engineered silica nanoparticles as additives in lubricant oils

Abstract

Silica nanoparticles (SiO₂ NPs) synthesized by the sol–gel approach were engineered for size and surface properties by grafting hydrophobic chains to prevent their aggregation and facilitate their contact with the phase boundary, thus improving their dispersibility in lubricant base oils. The surface modification was performed by covalent binding of long chain alkyl functionalities using lauric acid and decanoyl chloride to the SiO₂ NP surface. The hybrid SiO₂ NPs were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, simultaneous differential thermal analysis, nuclear magnetic resonance and dynamic light scattering, while their dispersion in two base oils was studied by static multiple light scattering at low (0.01% w/v) and high (0.50%w/v) concentrations. The nature of the functional layer and the functionalization degree seemed to be directly involved in the stability of the suspensions. The potential use of the functional SiO₂ NPs as lubricant additives in base oils, specially designed for being used in hydraulic circuits, has been outlined by analyzing the tribological properties of the dispersions. The dendritic structure of the external layer played a key role in the tribological characteristics of the material by reducing the friction coefficient and wear. These nanoparticles reduce drastically the waste of energy in friction processes and are more environmentally friendly than other additives.     

Low-temperature synthesis of Y2SiO5:Eu powders using mesoporous silica and their luminescence properties

This paper reports the synthesis of Eu³⁺ ions-doped Y₂SiO₅ (Y₂SiO₅:Eu³⁺) powders by mesoporous template route. Using mesoporous silica SBA-15 as silica source, Y₂SiO₅:Eu³⁺ powders were prepared by solid-state reaction at a calcination temperature of 1300 °C without fluxes. The prepared Y₂SiO₅:Eu³⁺ powders were characterized by X-ray diffraction, scanning electron microscope, nitrogen adsorption-desorption isotherms, and photoluminescence spectroscopy. The results show that the crystalline Y₂SiO₅:Eu³⁺ particles are dense and have a morphology similar to SBA-15. The low calcination temperature is attributed to the high reactive activity of SBA-15 with large surface area and non-crystalline structure. The Y₂SiO₅:Eu³⁺ powders prepared at a low calcination temperature show luminescence properties similar to the reported results of Eu³⁺ doped-Y₂SiO₅ samples prepared at high temperatures.     

Study of the mechanisms involved in reactive silica

The microstructure of a heterogeneous SiO₂ submitted to a depolymerisation process is studied using Transmission Electron Microscope (TEM), Environmental SEM (ESEM), and X-ray diffraction (XRD). With ESEM the formation of micro domain induced by the dissolution phenomena is shown. XRD shows the formation of a halo that is associated with the formation of amorphous phase. The parameters “position and FWHM” of the halo, enabled us to show the evolution of the disorderly phase when the reaction progresses. The hypothesis of formation of nanoparticles with different structural states was confirmed by the TEM.     

Fabrication and characterization of transparent superhydrophilic/superhydrophobic silica nanoparticulate thin films

The realization of transparent and superhydrophilic/superhydrophobic surfaces by silica nanoparticulate thin films was exploited in this work. An aqueous electrostatic layer-by-layer assembly process was utilized to fabricate nanoparticulate thin films with adhesion/body/top layer structure on glass substrates by using SiO₂ nanoparticles and polyelectrolytes. The effects of volume ratio of differently sized silica nanoparticle solutions for the body layer deposition on transmittance in visible light region and surface wettability of the nanoparticulate thin films were systematically studied. The experimental results revealed that both optical transparency and superhydrophobicity/superhydrophilicity can be achieved on the same SiO₂ nanoparticulate thin film by using appropriate volume ratios of differently sized silica nanoparticle solutions for body layer deposition, and with and without silane treatment in the fabrication process. The high contrast of wettability that can be achieved by this way suggests the possibility of the creation of superhydrophilic/superhydrophobic patterning and superhydrophilic-superhydrophobic gradient on the same surfaces.     

从稻草NaOH预处理液中制取低比表面积SiO2微球

利用化学沉淀法从稻草NaOH预处理液中制取粒径分布均匀的低比表面积SiO_2微球。制取过程包括预处理液的稀释、盐酸溶液滴定沉出SiO_2微球、SiO_2微球煅烧3个步骤。结果表明:当稀释后的预处理液pH值调为8时,预处理液、水、乙醇的体积比决定了SiO_2微球的粒径分布,盐酸溶液的滴加速率决定了SiO_2微球的粒径大小和比表面积。最优制备条件:预处理液、水、乙醇的体积比为1∶1.5∶1,盐酸溶液的滴定速率为3mL/min。在该条件下制取的SiO_2微球平均直径约为485nm,比表面积为8.23m2/g,呈现出介孔无定形结构。     

Effect of silica sol of different routes on the properties of low cement castables

Silica sols synthesized through different routes viz. inorganic, organic and ion-exchange routes, have been incorporated in the low cement alumina castable composition in various proportions and cast samples in the form of 2 inch cube briquettes were prepared. The cast briquettes after curing were subjected to heat treatment at various temperatures. The effect of different sources of such sols on the important physico-mechanical properties of the castables such as bulk density, apparent porosity, compressive strength, volume shrinkage and residual strength after spalling have been studied. Some of the selected samples were also subjected to microstructural evaluation. It is observed that silica sol synthesized through cation exchange routes has significant beneficial role on the properties of castable with 3% addition.