The Effect of Composition of Water–Ethanol Solutions on the Kinetics of Coagulation of Fused Quartz Suspensions

The effect of composition of water–ethanol solutions containing 0–96 vol % alcohol on the coagulation kinetics of dilute fused quartz suspensions is studied using flow ultramicroscopy technique. It is established that, in both water and ethanol containing 4 vol % water, freshly prepared quartz suspensions are stable with respect to aggregation; at ethanol concentrations from 10 to 90 vol %, an ultrafast coagulation takes place, with characteristic time (coagulation period) being essentially smaller compared to a value corresponding to the Smoluchowski theory of fast coagulation kinetics. It was shown that the aging of the aforementioned suspensions for more than 24 h results in slow coagulation at high and low alcohol content, but its ultrafast character is retained in the ethanol concentrations range of 40–48 vol %. The probable reasons for the ultrafast coagulation in the disperse systems specified are discussed.     

Dispersion of Silica Fines in Water-Ethanol Suspensions

The dispersion of silica fines in water-ethanol suspensions has been studied through the measurement of settling efficiency, wetting rate, zeta potential, and viscosity. The measurements were performed on two silica samples with mean volumetric diameters of 5.02 and 0.272 &mgr;m at different fractions of ethanol in water-ethanol suspensions. The results have demonstrated that the dispersion stability of the silica suspensions increased as the fraction of ethanol increased and reached to maximum at the fraction of 50%, followed by a decline. The stability was stronger in a pure ethanol suspension than in a pure water suspension. It was observed that the stability closely correlated with the lyophilicity of the particles, but was not predominated by the surface charge of the particles as predicted by the DLVO theory. Viscosity measurements have been used to estimate the solvation film thickness on silica particles immersed in water-ethanol suspensions, on the basis of Einstein's theory of the viscosity of dispersions. It was found that the solvation film thickness on silica fines in a water-ethanol (1 : 1) suspension is about double that in a pure water suspension and about 1.4-fold that in a pure ethanol suspension, respectively, which well explains the dispersion behaviors of the silica fines in the water-ethanol suspensions because a thicker solvation film will cause a stronger disjoining pressure to prevent the proximity of the particles. Copyright 2001 Academic Press.     

二氧化硅悬浮体的絮凝

微细颗粒的胶体二氧化硅广泛应用于橡胶工业、日用化学工业、无机材料工业等众多部门,它的专门用途不下千余种[1]．二氧化硅微细悬浮体是一种典型胶体分散体系,在其中加入大分子显的有机或无机絮凝剂,研究其絮凝规律,不但对研究絮凝现象的理论和实践有意义,而且有助于认识二氧化硅颗粒的表面性质和该分散体系的稳定性．1实验1·1材料和试剂二氧化硅（上海电化厂）：以燃烧法制得的）“品（白炭黑）,D＊T法测其比表面为7（）11。’·g‘．聚丙烯酸胺（＊＊M．广州南中塑料厂）：白色粉末状,用乙醇从水溶液中沉淀、提纯,粘度法测其…     

Kinetics of the Growth of Supramolecular Crystals in a Suspension of Monodisperse Spherical Silica Particles

Kinetics of the supramolecular crystallization of monodisperse spherical silica particles (MSSP) suspended in diethyl ether with a concentration of structural units close to the phase transition point has been studied for the first time. It was found that the linear crystal growth rate depends on temperature and the process activation energy is 25 kcal/mol. The linear law of crystal growth is associated with diffusion of the structural units on the interface.     

单分散SiO2体系制备中TEOS水解动力学研究

采用一种与他人不同的萃取－冷冻分离－气相色谱法，跟踪形成单分散二氧化硅体系条件下正硅酯乙酯（TEOS）的水解过程，考察了温度（25～45℃）、氨浓度（0．5～0．2mol•L－1）、水浓度（6．0～15．0mol•L－1）等实验条件范围内，以上实验参数对TEOS水解速度的影响；并回归得到目前适用于在乙醇介质中氨催化下，形成单分散二氧化硅微粒常用实验条件范围内，唯一的较完整的水解动力学方程式．     

Er对Al-Ni-Er-Zr非晶合金动力学特性的影响

采用单辊旋淬法首次制备了Al85Ni10ErxZr5-x(x=3,4,5)非晶合金,利用X射线衍射(XRD)证明Al85Ni10ErxZr5-x(x=4,5)结构为完全非晶态,Al85Ni10Er3Zr2合金为部分非晶。应用差示热分析法(DTA)测定该合金的热学参量,分析了其晶化过程。利用Kissinger法计算了非晶合金的晶化激活能。研究了Er的增加对于Al-Ni-Er-Zr系合金非晶形成能力和热稳定性的影响。结果表明:Er的增加提高了该合金体系非晶形成能力和热稳定性。     

Rheological Properties of Silica Suspensions in Aqueous Solutions of Block Copolymers and Their Water-Soluble Components

Dynamic moduli of fumed silica suspensions in aqueous solutions of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers and PEO homopolymers were measured as a function of surface coverage. Since the block copolymers and PEO are adsorbed on the silica surface through hydrogen bonding between the ether oxygen and the silanol group on the silica surface, the interaction between the silanol groups, which is dominant for the aggregation of silica particles, should be prohibited. Dynamic moduli in the silica suspensions were strongly related to the stability of the silica suspensions and the block copolymer, and the longest PEO portion was useful for stabilizing the silica particles. However, the PEO homopolymer did not support stability of the silica particles, suggesting that chain conformation of the PEO portion in the block copolymer is different from that for the PEO homopolymer. Copyright 2001 Academic Press.     

由硅溶胶生长单分散颗粒的研究

针对现行单分散二氧化硅颗粒制备方法的粒径预见性差、步骤繁琐、收率低等问题，研究了一种用硅溶胶作为种子，在氨、水和乙醇的混合溶液中通过水解正硅酸乙酯（ＴＥＯＳ）生长出单分散颗粒的简便方法。该方法仅在初始的悬浮液中滴加ＴＥＯＳ即可使种子正常生长，无须补充氨水以修正体系浓度的变化。最终的分散相浓度可达１０％（质量分数）。可选择生长的粒径范围在１微米以内并可精确控制。所得颗粒粒径分布偏差于Ｓｔｏｂｅｒ方法     

由硅溶胶生长单分散颗粒的研究

针对现行单分散二氧化硅颗粒制备方法的粒径预见性差、步骤繁琐、收率低等问题，研究了一种用硅溶胶作为种子，在氨、水和乙醇的混合溶液中通过水解正硅酸乙酯（TEOS）生长出单分散颗粒的简便方法．该方法仅在初始的悬浮液中滴加TEOS即可使种子正常生长，无须补充氨水以修正体系浓度的变化．最终的分散相浓度可达10％（质量分数）．可选择生长的粒径范围在1微米以内并可精确控制．所得颗粒粒径分布偏差优于Stber方法．讨论了种子数密度、生长环境和TEOS滴加速度对生长最终颗粒粒径分布偏差的影响     

Characterization of the Electrical Conductivity of Concentrated Suspensions of Silica in Aqueous Solutions of Sulfuric Acid

The electrical conductivity of stable concentrated suspensions of SiO₂ in aqueous solutions of sulfuric acid was studied as influenced by the concentration and size of SiO₂ particles.     

单分散高纯硅胶色谱柱填料的制备

在氨水和氨气催化下使单晶硅粉水解, 合成了单分散、高纯的纳米二氧化硅水溶胶; 再利用聚合诱导胶体凝聚法(PICA)制备单分散脲醛二氧化硅复合微球, 经过高温煅烧后得到球形硅胶色谱柱填料. 通过电感耦合等离子-质谱(ICP-MS)、电子显微镜和BET比表面积测试等手段对球形硅胶的纯度、粒径分布及比表面积进行了表征, 并通过色谱分离对硅胶填料的性能进行了评价. 实验结果表明, 该方法合成的色谱柱填料具有纯度高、粒径分布均匀、机械强度高及分离能力强等优点.     

无定型氧化硅转变为α-方石英的振动光谱

红外和喇曼光谱是分子结构信息的重要来源,也是研究表面和催化问题的强有力手段,常用来表征活性中心及吸附物种的结构．为提高稳定性,催化剂一般都要经过焙烧处理,在焙烧过程中,载体结构可能会发生变化,有时还会形成一定的晶相．载体结构变化时,一般会伴随振动光谱的变化,因此在利用振动光谱研究催化体系时,弄清载体的振动光谱是十分必要的．二氧化硅是最常用的催化剂载体之一,但它具有比较多的结构形式,除无定型氧化硅中硅氧四面体可连接成不同的结构外,它还具有石英、鳞石英、方石英等多个晶相系列．对氧化硅的不同结构形式,…     

Kinetics of the Formation and Dissolution of Ni Precipitates in a Gibbsite/Amorphous Silica Mixture

There have been a number of studies that have examined metal precipitation reactions on an array of natural soil materials. While many of these investigations have focused on model single-component systems, recent research has appeared on metal precipitation on soils and clay fractions of soils. However, few studies have explored mixed model component systems, which may lead to a better understanding of metal reactions on soils and clay fractions. Furthermore, only a few studies have appeared on the stability of the metal surface precipitates. In light of this, we investigated Ni sorption and dissolution kinetics and mechanisms on a mixture of gibbsite and amorphous silica by combining macroscopic studies with X-ray absorption fine structure (XAFS) and diffuse reflectance spectroscopies (DRS), and high-resolution thermogravimetric analysis (HRTGA). Batch sorption experiments were conducted at pH 7.5 and at different reaction times to elucidate the sorption process and to study the role of residence time on metal precipitate stability. Spectroscopic and HRTGA investigations revealed alpha-Ni(OH)(2) precipitates formed on the gibbsite/silica mixture initially and over time evolved to a Ni phyllosilicate. The available Si source was derived from partial dissolution of the sorbent during Ni sorption. With increasing residence time, the precipitate phases drastically increased in stability, as shown by decreasing amounts of Ni release as effected by nitric acid (HNO(3)) and ethylenediaminetetraacetic acid (EDTA) treatments. This aging effect may be explained by the silicate-for-nitrate exchange during the first days of reaction and subsequently by silicate polymerization and partial grafting onto the hydroxide layers to form a phyllosilicate precursor phase (R. G. Ford, A. C. Scheinost, K. G. Scheckel, and D. L. Sparks, Environ. Sci. Technol. 33(18), 3140-3144, 1999). Copyright 2000 Academic Press.     

Mechanism of Reversible Thixotropic Transformation in Concentrated Suspensions of Monodisperse Spherical Silica Particles: Analysis in Terms of Colloidal Crystal Formation and Growth

The mechanism of thixotropic transformation of concentrated suspension of monodisperse spherical silica particles into gel made of blocks with regular structure was considered in terms of colloidal crystal formation and the Alder–Hoover model of phase transition. The kinetics of linear growth of colloidal crystals as structural blocks was experimentally studied. This process was shown to have the activation nature determined by the diffusion of structural units at the interface and can be described in terms of Frenkel's kinetic theory of liquids.     

无孔单分散离子交换硅胶键合相用于蛋白质的高效液相色谱分离

将新合成的无孔硅胶二乙基氨基新型离子交换填料 (NPS-DEA)用于蛋白质的液相色谱分离。考察了流动相的pH值、盐浓度、流速及梯度程序对蛋白质分离的影响 ,并考察了蛋白质的质量回收率。实验结果表明 ,所得阴离子交换固定相的色谱性能良好。在梯度淋洗条件下 ,卵清蛋白、牛血清蛋白、胰岛素、γ-球蛋白、核糖核酸酶、溶菌酶获得了较好的分离。蛋白质的保留符合一般的保留值规律。柱填充床稳定 ,而柱负载较小 ,可用于高纯度的微量制备。     

The Effect of Supporting Electrolyte Concentration on Zinc Electrodeposition Kinetics from Methimazole Solutions

The kinetic parameters of Zn²⁺ ion electroreduction in sodium perchlorate used as the supporting electrolyte on the mercury electrode in the presence of methimazole were determined using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and DC polarography. The two‐stage nature of this process was demonstrated. Both steps are catalysed by a methimazole. The size of the acceleration effect depends on the concentrations of methimazole and the supporting electrolyte. The acceleration of the electrode process involves the formation of active complexes between the depolarizer ions and methimazole on the electrode surface. These complexes facilitate the exchange of charge between the electrode and zinc ions during electroreduction process. The change of the hydrating sphere of the zinc ion is also important here. This in turn depends on its oxidation state and the concentration of the supporting electrolyte.     

Role of Electrostatic Repulsion on the Viscosity of Bidisperse Silica Suspensions

The flow behavior of bidisperse aqueous silica suspensions has been studied at different electrolyte concentrations as a function of shear rate, total volume fraction of the particles, and volume ratio of small to large particles. It is shown that the range of the electrostatic repulsion plays an important role in determining the viscosity of the suspension. Binary mixtures of particles of longer range repulsive forces showed higher viscosities than the suspensions of shorter range electrostatic interactions. Bimodal suspensions of long-range interactions showed non-Newtonian behavior over wider ranges of shear due to the deformation of the ionic cloud around the particles, which is larger in these systems. The viscosity of bimodal suspensions used in this study was scaled with respect to the viscosity of the related monosized systems and the viscosity of one bimodal suspension at a fixed total volume fraction of the particles, employing our earlier scaling method. The model normalizes the effect of colloidal forces by introducing a scaling factor that collapses the data into a single curve for bimodal suspensions of a particular size ratio, and it is shown that the model is valid for systems with both short-range and long-range repulsive forces. Copyright 1999 Academic Press.