On-Line Characterization of Morphology and Water Adsorption on Fumed Silica Nanoparticles

The first wetting layer on solid nanoparticles has direct implications on the roles these particles play in industrial processes and technological applications as well as in the atmosphere. We present a technique for online measurements of the adsorption of the first few water layers onto insoluble aerosol nanoparticles. Atomized fumed silica nanoparticles were dispersed from aqueous suspension and their hygroscopic growth factors (HGF) and number of the adsorbed water layers at subsaturated conditions were measured using a nanometer hygroscopic tandem differential mobility analyzer (HTDMA). Particle morphology was characterized by electron microscopy and particle density was determined by mobility analysis. The HGFs of the size-selected particles at mobility diameters from 10 to 50 nm at 90% relative humidity (RH) varied from 1.05 to 1.24, corresponding to 2–6 layers of adsorbed water. The morphology of the generated fumed silica nanoparticles varied from spheres at 8–10 nm to agglomerates at larger diameters with effective density from 1.7 to 0.8 g/cm³ and fractal dimension of 2.6. The smallest spheres and agglomerates had the highest HGFs. The smallest particles with diameters of 8 and 10 nm adsorbed two to three water layers in subsaturated conditions, which agreed well with the Frenkel, Halsey, and Hill (FHH) isotherm fitting. In comparison to the small spheres or large agglomerates, the compact agglomerate structure containing a few primary particles increased the number of adsorbed water layers by a factor of ～1.5. This was probably caused by the capillary effect on the small cavities between the primary particles in the agglomerate.     

气相法白炭黑生产技术的研究

本文介绍了气相法白炭黑的制备原理与生产工艺,以及在生产过程中的技术难题.     

气相法白炭黑生产技术的研究

本文介绍了气相法白炭黑的制备原理与生产工艺,以及在生产过程中的技术难题。     

气相二氧化硅的表面改性

简要介绍了气相二氧化硅的表面改性、改性原理、改性工艺、常用改性剂以及改性气相二氧化硅的应用。概述了我国气相二氧化硅工业的发展现状。     

气相法白炭黑的表面改性

综述了近年来气相法白炭黑表面改性的研究成果和工业化技术。     

气相法二氧化硅的表面改性

以气相法二氧化硅为原料,六甲基二硅氮烷为改性剂,采用干法工艺对气相法二氧化硅表面进行改性,探讨了六甲基二硅氮烷用量、反应温度、反应时间对气相法二氧化硅表面改性效果的影响。结果表明,当六甲基二硅氮烷用量为气相法二氧化硅质量的25%、反应温度为150℃、反应时间为40 min时,二氧化硅表面的硅羟基数量最少,比改性前减少97%。     

气相二氧化硅和胶体电池

通过对气相二氧化硅本身的特性和气相二氧化硅成胶性能的分析,提出优异的触变性能是气相二氧化硅用于胶体电池的关键因素,也是未来胶体发展的方向。使用优质气相二氧化硅,配合完善的电池组件设计和选择,可以保证较高的胶体电池气体再化合效率,也使得胶体电解液不易干涸,这样的胶体电池才会有着较长的循环寿命。     

Particle Sizes of Fumed Silica

Fumed silica is a synthetic amorphous silicon dioxide produced by burning silicon tetrachloride in an oxygen-hydrogen flame. Surface areas range from 50–400 m²/g. Using particle sizing techniques, fumed silica shows micron sized particles leading to surface areas markedly lower than expected. Fumed silica appears as a fluffy solid with bulk densities down to 0.03 g/cm³, being invariant over the wide range of surface areas. Attempts to relate the variation of the surface area directly to the performance of fumed silica in technical applications, such as its thickening efficiency in fluids, mainly fail and remain ambiguous.     

Effect of Fumed Silica Nanoparticles on the Gas Permeation Properties of Substituted Polyacetylene Membranes

Summary The gas permeability of three substituted polyacetylenes, poly(1-chloro-2-phenylacetylene) (PClPA), poly[1-phenyl-2-(4-trimethylsilyl)phenylacetylene] (PTMSDPA), and poly[1-(trimethylsilyl)-1-propyne] (PTMSP), increased systematically with increasing content of nonporous fumed silica (FS) nanoparticles. For instance, the oxygen permeability coefficient (PO₂) of PClPA containing 30 wt % FS was 86 barrers, which was 10 times higher than that of the unfilled polymer (PO₂=8.6 barrers). The extent of permeability increase with the addition of FS was smaller when the permeability of the original polymer was higher. The order of the permeability increase in FS-filled polymers was as follows: PClPA > PTMSDPA > PTMSP. The addition of FS resulted in the decrease of O₂/N₂ permselectivity of these polymers. The H₂/CH₄ permselectivity largely decreased with increasing FS content in PClPA, while it hardly changed with FS loading in PTMSP. The gas solubility of PClPA was practically independent of FS content, and the increase in gas permeability in filled PClPA resulted from an increase in diffusivity with the addition of FS.     

气相法白炭黑在涂料中的应用

综述了气相法白炭黑的特性及其在涂料中应用的关键技术，并提出了发展建议。     

气相法白炭黑的市场分析

简述了世界气相法白炭黑生产厂的生产能力、国内外差距和国内需求预测。     

Reaction of Ammonia with Fumed Silica

The reaction between fumed silica and ammonia has been studied between 600° and 1200°C. Up to 24 wt% nitrogen can be introduced into vitreous silica by adjusting the partial pressure of ammonia, temperature, and reaction time. The experiments show that the amount of nitrogen incorporated into silica has a linear dependence on the partial pressure of ammonia and a square root dependence on the reaction time. The activation energy for the reaction was found to be 76.0 kJ/mol. The nitrided powders as well as several hotpressed samples were crystallized at 1550° to 1650°C. Silica glasses containing 0 to 1 wt% nitrogen crystallize to cristobalite. Glasses containing 2 to 10 wt% nitrogen are stable against devitrification in nitrogen, even at 1650°C. Glasses with 12 to 28 wt% nitrogen crystallize to fine-grained Si₂N₂O with residual glass.     

气相法二氧化硅在硅橡胶中的应用

介绍了气相法二氧化硅在硅橡胶中的用量对其拉伸强度、伸长率及硬度的影响。此外,分析了硫化后产生气泡的各种原因。     

Effect of Nano‐Aluminum and Fumed Silica Particles on Deflagration and Detonation of Nitromethane

The heterogeneous interaction between nitromethane (NM), particles of nanoscale aluminum (38 and 80 nm diameter), and fumed silica is examined in terms of the deflagration and detonation characteristics. Burning rates are quantified as functions of pressure using an optical pressure vessel up to 14.2 MPa, while detonation structure is characterized in terms of failure diameter. Nitromethane is gelled using fumed silica (CAB‐O‐SIL^®), as well as by the nanoaluminum particles themselves. Use of nanoaluminum particles with fumed silica slightly increases burning rates compared to the use of larger diameter Al particles; however distinct increases in burning rates are found when CAB‐O‐SIL is removed and replaced with more energetic aluminum nanoparticles, whose high surface area allows them to also act as the gellant. Mixtures including fumed silica yield a reduced burning rate pressure exponent compared to neat NM, while mixtures of aluminum particles alone show a significant increase. Failure diameters of mixture detonations are found to vary significantly as a function of 38 nm aluminum particle loading, reducing more than 50% from that of neat nitromethane with 12.5% (by mass) aluminum loading. Failure diameter results indicate a relative minimum with respect to particle separation (% loading) which is not observed in other heterogeneous mixtures.     

气相法白炭黑在消泡剂中的应用

论述了气相法白炭黑的结构特点及在消泡剂中的作用,表明比表面积为200～380m2/g的气相法白炭黑具有最佳应用效果。接着,讲述了它的应用特点、配比和应用体系。     

合成条件对气相法白炭黑性能的影响

以甲基三氯硅烷、氢气、空气为原料,制备气相法白炭黑。考察了原料配比、骤冷介质温度、合成炉温度、原料气速对白炭黑的比表面积、平均粒径的影响。结果表明：甲基三氯硅烷、氢气的量之比与白炭黑的比表面积成反比;合成炉温、骤冷介质温度与白炭黑的比表面积、平均粒径成反比;原料气速与白炭黑的比表面积成正比,与平均粒径成反比。较佳工艺为：甲基三氯硅烷、氢气与空气的量之比为0.33∶0.47∶1,冷却介质温度80～90℃,炉温800～850℃,气体流速5～6 m/s。