高分子表面活性剂对氧化物陶瓷超微颗粒的分散作用

本文针对用湿化学法制备氧化物陶瓷超细微粉过程中和其悬浮液的颗粒团聚问题,评述了表面活性剂对颗粒团聚状态的控制作用,在氧化物陶瓷微粉悬浮液中通过调节ＰＨ 值,使颗粒间具有较高静电效应的基础上加入高分子表面活性剂,使颗粒间又具有空间位阻效应,防止了颗粒间的团聚,可得到高度分散而无团聚的粉末和悬浮液     

影响纳米羟基磷灰石溶胶在水介质中分散性能的因素

目的：探讨影响纳米羟基磷灰石溶胶分散性能的因素。方法：以水分散体系下,采用化学共沉淀法制备的纳米HAP,研究了反应介质pH值、稳定剂或表面改性剂等因素对纳米粒子粒径及分散稳定性的影响。结果：调节介质的pH值,使颗粒间处于较高的静电效应,在此条件下加入表面活性剂,使颗粒间又具有空间位阻稳定效应,空间位阻稳定效应可阻止颗粒间的团聚。结论：通过优化实验条件可制得高度均匀分数状态纳米羟基磷灰石溶胶。     

氧化铝粉末胶体悬浮液的电动性能的研究

利用BDL -B型表面电位仪测试了在不同条件下氧化铝粉末的电动性能。着重研究了不同结构的阴离子聚合物分散剂对悬浮液中颗粒间的静电斥力和空间斥力的影响。研究结果表明 ,添加 1.2 5wt%的亲水比m∶n=30∶70的甲基聚丙烯酰铵 ,且将α -Al2 O3悬浮液的pH值控制在 4 .5左右或 9.0左右时均能使颗粒间具有较大的静电斥力和最大的空间斥力 ,从而使悬浮液处于稳定的分散状态     

腐植酸对固-液悬浮液稳定性影响的理论阐述

按照影响悬浮液稳定性的四种不同理论解释了腐植酸对固体颗粒的电动电位的影响、腐植酸对水的表面活性作用、吸附于颗粒表面腐植酸的空间位阻作用、溶解于水中的腐植酸高分子的排空作用,对国内外腐植酸对固-液悬浮液稳定性影响的研究进行了述评。     

水介质中高浓度电解质离子对纳米氧化锆悬浮稳定性的影响

研究了高浓度电解质离子对纳米ZrO2悬浮液稳定性的影响.对悬浮液及清液进行Zeta电位和吸光度测定,通过TEM分析,结果表明:加入大量的电解质后,纳米ZrO2的表面双电层受到压缩,ζ-电位几乎为零,只调pH值不能使纳米ZrO2悬浮起来;组成简单、分子量小的分散剂受电解质离子的影响,容易从颗粒表面脱落下来,起不到空间位阻的作用;结构复杂、分子量大的分散剂在高浓度的电解质溶液中起到很好的空间位阻作用.     

不同分散条件下重质碳酸钙的分散机制

采用zeta电位仪、p H计等分析了不同p H值条件下重质碳酸钙在纯水介质、六偏磷酸钠溶液、聚丙烯酸钠溶液中的颗粒表面zeta电位变化。结果表明:重质碳酸钙-纯水悬浮液等电点的p H值约为8.7;六偏磷酸钠对重质碳酸钙悬浮液分散的作用机制主要为离子稳定机制,而聚丙烯酸钠对重质碳酸钙悬浮液分散的作用机制主要为空间位阻机制。     

不同粒度特征的SiO_2微粉浆体流变性能研究

采用流变学的方法研究了固相体积分数为35%的4类Si O2微粉悬浮液的流变性能,从粒度特征的角度,探讨了在不添加减水剂、添加六偏磷酸钠、三聚磷酸钠及高效减水剂FS20的条件下,悬浮液表现出不同的流变行为机制。结果表明:在不添加减水剂时,粉体中含有中位径小的细颗粒比例越高,悬浮液黏度越大,而含有较多粗颗粒的Si O2微粉悬浮液出现了剪切稠化行为;添加减水剂后,悬浮液流变行为与Si O2微粉的比表面积大小及粒度分布密切相关,均表现为假塑性流体特征。FS20对Si O2微粉的分散效果明显优于六偏磷酸钠和三聚磷酸钠的,这主要是由于后者的分散机制为静电排斥作用,而FS20除了上述分散稳定机制外,还可产生很强的空间位阻效应。     

提高陶瓷墨水稳定性的途径

本文介绍了陶瓷用墨水（简称陶瓷墨水）的制备现状,通过分析双电层效应、空间位阻效应、静电位阻效应等稳定机制,提出可通过降低色料颗粒的Stocks沉降速率、选择合适的色料、对色料颗粒进行表面改性、选择合适的分散剂、对色料颗粒进行聚合物微胶囊包裹等途径提高陶瓷墨水的稳定性。     

聚乙二醇对硅灰石制多孔SiO2粉体多孔性与粒径影响的研究

以400目硅灰石粉配成质量分数为10%的悬浮液,加无机助剂和聚乙二醇作酸化处理,制得比表面积100～600m2/g、颗粒粒径6～12μm的多孔性SiO2粉体.研究表明,当其他工艺条件和添加量相同时,使用平均相对分子质量为6000的同种聚乙二醇,在100g质量分数为10%的硅灰石悬浮液中,其添加量为9.4g的样品的比表面积和粒径都最大.初步研究表明,这是由于聚乙二醇的高分子网络凝聚和空间位阻效应所致.     

炭黑表面改性对硅酸锆包裹炭黑色料的影响

本文以无水四氯化锆和正硅酸乙酯为前驱体,氟化锂为矿化剂,炭黑为着色剂,研究了炭黑的硝酸氧化改性和表面活性剂改性对炭黑悬浮液的稳定分散和硅酸锆包裹炭黑(ZrSiO4/C)色料黑度的影响.电动电位(Zeta电位)、红外(FTIR)、白度仪、扫描电镜(SEM)、紫外-可见分光光度计分析测试的结果表明:硝酸氧化改性炭黑表面含氧官能团增多,并且颗粒表面带电量发生改变,有助于炭黑的悬浮和硅酸锫对炭黑的包裹;聚乙烯醇缩丁醛(PVB)的空间位阻作用和增大体系粘度的双重效应有利于炭粉在乙醇中的稳定悬浮;聚乙烯吡咯烷酮(PVP)、十二烷基硫酸钠(SDS)和十六烷基三甲基溴化铵(CTAB)通过静电机理和空间位阻作用使炭粉在水中稳定悬浮,但考虑到对炭黑悬浮液Zeta电位的改变,PVP和SDS更有利于硅酸锆溶胶对炭黑的包裹.     

Effects of hydrophobic interaction on rheological behavior and microstructure of carboxylated core‐shell latex suspension

We have investigated the effects of hydrophobic interactions on the rheological behavior and microstructure of suspension of carboxylated core‐shell latex particles with changing hydrophobicity of shell polymer and suspending medium. The carboxylated core‐shell latex particles formed lattice‐like microstructures in aqueous suspension with dissociation of carboxyl groups. With increasing hydrophobicity of the shell polymer, the interparticle distance ξ in the microstructure decreased. However, ξ increased with increasing hydrophobicity of the suspending medium. The effect of hydrophobic interaction on ξ was explained by the steric stabilization theory for particles with grafted polymer on the surface. As the carboxylated core‐shell latex particles overlapped each other in the microstructure, an attractive force was generated between the particles in aqueous suspension. With increasing hydrophobicity of the shell, the attractive force increased, but with increasing hydrophobicity of the suspending medium, the attractive force decreased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4153–4158, 2006     

Time dependent rheology of artificial slurries

Gels, formed by suspending cellulose acetate particles of regular shape and size in a Newtonian medium, were sheared in a rotational viscometer to study their time dependent rheological behavior. Qualitative observations of the effect of the well defined particle parameters, shape surface area and concentration on the flow parameters were made. The viscosity decay behavior fitted the model previously proposed by Pinder for slurries of natural particles. By considering the effect of the weighting salt used in the suspending medium, it was found that the theory that ionic forces are active in stabilizing the thixotropic gel structure was supported.     

Chemical absorption into concentrated slurry: Absorptions of carbon dioxide and sulfur dioxide into aqueous concentrated slurries of calcium hydroxide

The absorption of sulfur dioxide and carbon dioxide into aqueous calcium hydroxide slurries were performed using a stirred tank with a plane gas-liquid interface at 308 K. The absorption rates were found to be lower than those predicted by assuming that the solid particles are uniformly suspending in the liquid-film as well as the bulk liquid phase.It might be due to the possibility that there is no particle suspending in the vicinity of the interface. The process of gas absorption with reaction in the slurry was formulated by film-theory model incorporating the presence of an inert region in which there is no particle. The observed absorption rates of sulfur dioxide and carbon dioxide were successfully predicted by the proposed model.     

Computational investigation of the mechanisms of particle separation and “fish‐hook” phenomenon in hydrocyclones

The motion of solid particles and the “fish‐hook” phenomenon in an industrial classifying hydrocyclone of body diameter 355 mm is studied by a computational fluid dynamics model. In the model, the turbulent flow of gas and liquid is modeled using the Reynolds Stress Model, and the interface between the liquid and air core is modeled using the volume of fluid multiphase model. The outcomes are then applied in the simulation of particle flow described by the stochastic Lagrangian model. The results are analyzed in terms of velocity and force field in the cyclone. It is shown that the pressure gradient force plays an important role in particle separation, and it balances the centrifugal force on particles in the radial direction in hydrocyclones. As particle size decreases, the effect of drag force whose direction varies increases sharply. As a result, particles have an apparent fluctuating velocity. Some particles pass the locus of zero vertical velocity (LZVV) and join the upward flow and have a certain moving orbit. The moving orbit of particles in the upward flow becomes wider as their size decreases. When the size is below a critical value, the moving orbit is even beyond the LZVV. Some fine particles would recircuit between the downward and upward flows, resulting in a relatively high separation efficiency and the “fish‐hook” effect. Numerical experiments were also extended to study the effects of cyclone size and liquid viscosity. The results suggest that the mechanisms identified are valid, although they are quantitatively different. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Spherical agglomeration in a conical drum

The spherical agglomeration process is a means of size enlargement in which agitated particles, suspended in a liquid, are bonded together by a second liquid, which will wet the solid surfaces and be immiscible with the suspending medium. A process is described in which agglomeration takes place in a cone shaped vessel, rotating horizontally about its symmetric axis. The cone configuration of the agglomerator imparts a longitudinal impulse to the charge, which is most effective on the largest particles. This causes a size classification within the cone, with the largest agglomerates congregating at the base. The result is the continuous production of uniformly sized, highly spherical pellets. The factors affecting agglomerate growth and size are outlined and discussed.     

Effects of poly(vinyl acetate) suspending agents on suspension polymerisation of vinyl chloride monomer

Abstract

When partially hydrolysed poly(vinyl acetate) (PVAc) is used as a suspending agent in the suspension polymerisation of vinyl chloride monomer, it has significant effects on the morphology of the resulting poly(vinyl chloride) (PVC) particles. At the initial step of polymerisation, PVC molecules are grafted onto the molecules of the suspending agent forming a PVC–PVAc membrane. The properties of this membrane depend on the type of suspending agent, the polymerisation temperature, the mixing efficiency, and other factors. The morphology of the growing PVC particles and the properties of the PVC resin obtained depend in turn on the characteristics of the membrane. A model has been developed relating to the connection between the polymerisation conditions and the characteristics of the suspending agent on one hand, and on the PVC properties on the other hand. The model is based on an analysis of the characteristics of the PVC–PVAc membrane and their effect on PVC properties.     

The effects of non-continuum hydrodynamics on the Brownian coagulation of aerosol particles

Most theoretical predictions of the rate of Brownian-induced coagulation have considered the continuum hydrodynamic resistance of the suspending gas or liquid as well as van der Waals and/or electrostatic forces. However, the mean-free path of the gas is comparable with the length scale at which van der Waals forces become important during the collision of two Brownian aerosol particles. We predict the initial rate of coagulation in a monodisperse aerosol driven by Brownian motion in the presence of van der Waals forces and non-continuum lubrication forces when the Knudsen number (ratio of the mean-free path to the particle radius) is small but non-zero. A comparison with experiments demonstrates the accuracy of the predictions and the importance of accounting for non-continuum effects to provide quantitative predictions of coagulation rates.     

橡胶促进剂M过滤分离工艺实验研究

由于橡胶促进剂M在酸化后含有大量的水分,前期研究表明通过添加表面活性剂预处理可以有效降低固液分离后滤饼的含水量。为了研究经表面活性剂处理后悬浮液的过滤方法与效果,分别采用加压过滤、真空抽滤、离心过滤的分离方法进行了过滤分离实验,并对不同分离方法下滤饼质量进行检测。研究结果表明,采用真空抽滤方法对添加表面活性剂预处理后的橡胶促进剂M悬浮液进行过滤分离,并通过水洗滤饼,可以大幅度降低滤饼的含水量,并能满足橡胶促进剂M的质量要求。     

The use of polyelectrolyte stabilisers for suspension polymerisation: the effect of pH on particle size distribution

Ammonium polymethacrylate (APMA) and sodium polymethacrylate (PMA‐Na) were used as suspending agents for the suspension polymerisation of methyl methacrylate (MMA). The effect of pH on particle sizes and the stabilisation mechanism were examined. Increasing the pH caused a decrease in the particle sizes, and the formation of fine particles with diameters smaller than 10 µm. The amount of suspending agent required to stabilise a monomer dispersion and to prevent coalescence during suspension polymerisation decreases with increasing pH. The prevailing stabilisation mechanism that governs the dispersion stability is probably the electrosteric mechanism. Copyright © 2006 Society of Chemical Industry     

气溶胶用石墨/白碳黑超细复合粒子的制备及表征

通过对石墨/白碳黑复合粒子的制备及性能的分析测试研究,表明石墨复合粒子较纯石墨粉具有更好的分散性、更大的比表面积及孔容,更高的悬浮稳定性及红外吸收特性。