Heterogeneous exchange of precipitates

Summary The heterogeneous exchange of ferric ion between a labelled aqueous ferric chloride solution and some differently prepared ferric (hydr)oxides [(1) a freshly formed “amorphous” ferric (hydr)oxide, (2) ferric oxide obtained by drying the freshly formed precipitate in the air at 165 °C for 4.5 hours, (3) ferric oxide obtained by boiling the freshly formed precipitate in water at 100 °C for 4.5 hours] was investigated at room temperature. The exchange rate decreased in the sequence: (1), (2), (3), that sequence being attributed to the recrystallization of the solid phase in the sense of lattice ordering and particle growth, related to the treatment of freshly formed precipitate before the solid was put in contact with the ferric chloride and labelled. System (1) corresponded to a positively charged precipitate near the equivalency of the system FeCl₃ + NaOH, and the exchange was governed by a rapid recrystallization (particle growth), initiated by labelling⁵⁹FeCl₃ solution in an acid (HCl) medium. In the system (2) selfdiffusion is indicated as the exchange governing process. The radionuclide⁵⁴Mn, being present without isotopic carrier in labelling⁵⁹FeCl³ solution and introduced into the liquid phase, remained in the liquid phase of systems (2) and (3). Contribution number 112 from the Department of Physical Chemistry, Faculty of Sciences, University of Zagreb.     

羧甲基淀粉与烷基二甲基苄基氯化铵的相互作用研究

通过电导法、荧光法、粒度法等方法研究了羧甲基淀粉与3种不同碳数烷基二甲基苄基氯化铵之间的相互作用。结果表明,羧甲基淀粉与长链烷基二甲基苄基氯化铵在小于单纯表面活性剂临界胶束浓度（cmc）1～2个数量级的浓度下发生复合,并产生沉淀。当表面活性剂烷基链增加且浓度增大时,表面活性剂长碳链间的疏水作用及与羧甲基淀粉间的疏水作用...     

Effect of water on foaming properties of diglycerol fatty acid ester-oil systems

We have studied the effect of added water on the nonaqueous foaming properties of diglycerol fatty acid ester nonionic surfactant systems. Diglycerol monomyristate (designated as DGM) could not foam in nonpolar oils squalane and hexadecane at normal room temperature. Nevertheless, addition of a small amount of water induces a dramatic change in foaming properties. Both the foamability and foam stability increases with the amount of added water within the studied concentration range. Phase behavior study showed that in the dilute regions there is dispersion of solid surfactant in the aforementioned oils in the DGM systems. The particle size of the dispersed solid phase was found to be several tens of microns in the water free system, and hence it tends to coagulate and precipitate. In the case of shorter alkyl chain length, diglycerol monolaurate (DGL) surfactant-oil systems, dispersion of lamellar liquid crystal (Lalpha) is observed at room temperature, and the poor foaming properties were attributed to the large particle size of the liquid crystal. In both the DGL and DGM-oil systems, we observed a tendency of the particle size to decrease with the increasing concentration of added water. At higher temperature, the solid surfactant transforms to lamellar liquid crystal phase, and foaming is improved in the DGM/squalane system. Foams are stable for several minutes. Judging from the foaming test and particle size distribution data it can be concluded that the poor foaming in the diglycerol fatty acid esters-oil systems may possibly be due to bigger particle size, which causes precipitation. Addition of water results in the dispersion of smaller particles and improves the foaming behavior.     

多孔硅上银纳米粒薄膜的制备及其表面增强红外光谱

通过简便的化学沉积法在多孔硅上制备银纳米粒薄膜用于表面增强红外光谱检测。通过Ag⁺与多孔硅表面的SiHx发生氧化还原反应将银纳米粒子沉积在多孔硅表面。红外探针分子溶解于无水乙醇中进而被均匀分散在多孔硅表面,实验结果显示：对氨基苯硫酚、对氨基苯甲酸和对氟苯硫酚3个探针分子的红外峰分别最大增强了10、85和21倍。银纳米粒的大小和形状等物理特性、探针分子是否有与银表面进行强结合的基团和芳烃结构、以及表面选律等因素影响表面增强红外的吸收效应。     

Studies on poly(vinyl chloride). III. The role of the precipitated polymer in the kinetics of polymerization of vinyl chloride

In polymerization of vinyl chloride monomer, free radicals precipitate on or within aggregates of partially swollen dead polymer. Polymerization on the solid polymer is characterized by autoaccelerating rates due to a progressive reduction in termination rate. This reduction in termination rate is due to the fact that as the reaction progresses and more polymer accumulates there is a decrease in probability that chain transfer of polymer radicals to monomer will generate a mobile radical, which can readily terminate an occluded or stuck free radical. From the appearance of the particles of solid polymer in the system, it has been concluded that free radicals precipitate both on polymer particle surface and inside the open structure of polymer particles.     

Determination of cadmium and zinc in fertilizer samples by FAAS after solid-phase extraction with freshly precipitated manganese-diethyldithiocarbamate.

Using freshly precipitated manganese-diethyldithiocarbamate (Mn(DDTC)(2)) as a new reagent, a solid phase extraction method (SPE) has been developed for the extraction of Cd(II) and Zn(II) in aqueous fertilizer samples. A sample solution of 300 mL was taken and 0.10 g of freshly precipitated Mn(DDTC)(2) was added. After adding a phosphate buffer solution, the mixture was stirred at 10 min, filtered with a glass filter and washed with deionized water. The solid product containing Mn(DDTC)(2)-Cd(DDTC)(2)-Zn(DDTC)(2) complexes was dissolved in concentrated nitric acid and its volume was made complete up to 10 mL with deionized water. The metal contents of the solution were measured by an atomic-absorption spectrometer.     

Separation of carrier-free 48Sc tracer and its determination by isotopic dilution

An easy method for speedy and quantitative separation of carrier-free scandium tracer formed by the (48)Ti(22)(n,p)(48)Sc(21) nuclear reaction has been developed. Separation of (48)Sc (1.83 days) from the target titanium metal was carried out by co-precipitating the tracer with calcium fluoride precipitated at pH approximately 4 from the solution of irradiated titanium in hydrofluoric acid. The freshly formed fluoride precipitate was dissolved in conc. hydrochloric acid, and the tracer extracted with tributyl phosphate and then stripped into aqueous medium. The carrier-free tracer was estimated by isotopic dilution. with calcium fluoride as non-isotopic diluent.     

Colloidal complexes from poly(vinyl amine) and carboxymethyl cellulose mixtures

The phase behaviors of polyelectrolyte complexes formed from dilute solutions of poly(vinyl amine) (PVAm) and carboxymethyl cellulose (CMC) were determined as a function of overall composition and pH. The phase diagram included regions with soluble complexes, colloidal complexes, and macroscopic precipitates. Colloidal complexes were stable when either polymer was in sufficient excess to give electrosteric stabilization. The polymer mixing ratios giving complexes with an isoelectric point of 7 could be predicted from a simple model using the degree of ionization vs pH data for PVAm and CMC. The model failed at extreme pH values because not all added polymer was incorporated into the complexes. At pH 7, essentially all the added polymer was incorporated into the colloidal complex or precipitate, as long as the mixing ratio was within +/-10% of charge stoichiometry. The interaction of PVAm and CMC at pH 7 was endothermic, supporting the generally accepted viewpoint that the interaction of oppositely charged polyelectrolytes is entropy-driven. Although the colloidal complexes had a broad particle size distribution, the average particle size was rather insensitive to mixing ratio. By contrast, complex size was sensitive to electrolyte concentration with no complex formation when the NaCl concentration was > or =2 M.     

Solid-liquid phase transition of tin particles observed by UHV high resolution transmission electron microscopy: pseudo-crystalline phase

Solid-liquid transition of fine tin particles having diameter of 2–10 nm is studied in-situ by high-resolution transmission electron microscopy under a ultra-high vacuum condition. Melting temperature is confirmed to decrease with the decrease of particle diameter. The particles less than the critical size, 2r _c?5 nm, are found to have a specific phase between the solid and the liquid phase. The particle in this “pseudo-crystalline” phase contains crystalline embryos in it. Particles larger than the critical size have sharp liquid-solid transition, which completed within the time resolution of our microscope observation, 33 ms upon heating or cooling process. Large solid particles have Wulff's polyhedron, while particles around the critical diameter have rather spherical shape. Structural anomaly at the critical size occurs all over the outer most surface layer slightly below the melting temperature. Origin of the “pseudo-crystalline” phase and surface pre-melting phenomena are discussed.     

Formation and transformation of Al<Subscript>13</Subscript> from freshly formed precipitate in partially neutralized Al(III) solution

Al₁₃ is one of the novel nanospecies in partially neutralized Al(III) solution and Al-OH sol or precipitate could be generated simultaneously in the neutralization. Unfortunately, the precipitate is believed to be harmful to the formation of Al₁₃ due to the consumption of Al(OH)₄ ⁻, which was regarded as the precursor of Al₁₃. In this paper, the feasibility and potential of transformation of freshly formed Al-OH precipitate into Al₁₃ species were studied by using ferron colorimetric method and ²⁷Al NMR spectroscopy. The Al-OH precipitates were produced by two ways: injection of base solution into Al(III) solution gradually and mixing of Al(III) and base solutions instantaneously. The re-dissolving behaviors of the freshly formed precipitates were examined under different basicities (OH/Al molar ratio) and temperatures. It has been shown that Al₁₃ could be formed through the re-dissolution of intermediate Al-OH precipitate generated in partially neutralized Al(III) solution. A possible formation mechanism of Al₁₃ was suggested. Easily transformable precipitate was developed when the OH/Al molar ratio was less than 2.5. Rapid re-dissolution of freshly formed precipitate was favorable for Al₁₃ formation, which could be enhanced by heating.     

Morphology and size control of barium carbonate in ethanol–water mixed solvents

Barium carbonate (BaCO₃) particles have been obtained by the precipitation reaction of CO₂ bubbles to barium hydroxide [Ba(OH)₂] in the ethanol–water mixed solvents. Various morphologies, from rounded peanut, leaf-like, rod, and needle particles, were controlled by the precipitation step, where CO₂ gas was fed to Ba(OH)₂ in ethanol–water mixed solvent. The CO₂ gas as a carbonate source and Ba(OH)₂ slurry as a barium ion source are dissolved in the mixed solvents, within the solubility limit, to precipitate. The reactants dissolve progressively while they precipitate to BaCO₃. Ba(OH) ₂ slurry becomes translucent and opaque while the reaction proceeds. It becomes more opaque, upon which the dissolution of Ba(OH)₂ proceeds and BaCO₃ precipitates. The opaqueness of the products depends on the particle size of BaCO₃ in the product. The characteristics of BaCO₃ were confirmed by the X-ray diffraction (XRD), transmission electron microscope (TEM), and electrophoretic light scattering methods. The amount of water in the mixed solvents and of Ba(OH) ₂ in the reaction batch is related to the reaction rate in the nucleation and growing step, so that it was possible to control the shape of particles. Based on the understanding of the size and morphology of BaCO₃ in the solid/liquid–gas system, it was possible to obtain a well-dispersed average 40-nm BaCO₃ colloid.     

Reactions at the solid-liquid interface: surface-controlled dissolution of solid particles. The dissolution of potassium bicarbonate in dimethylformamide

We present a mathematical model for the surface-controlled dissolution of solid particles. This is applied to the dissolution of a solid having different particle size distribution functions: those of a monodispersed solid containing particles of all one size, a two-size-particle distribution, and a Gaussian distribution of the particle sizes. The dissolution of potassium bicarbonate in dimethylformamide is experimentally studied indirectly at elevated temperatures. We monitor the dissolution via the homogeneous deprotonation of 2-cyanophenol by dissolved KHCO3. The loss of 2-cyanophenol was detected electrochemically at a platinum microdisk electrode, and separately, the formation of the 2-cyanophenolate anion was monitored via UV-visible spectroscopic analysis. The results presented show that the kinetics of the loss of 2-cyanophenol behaves on one hand as a homogeneous chemical process and on the other hand as a dissolution-rate-controlled process. Initially, predissolved KHCO3 in solution deprotonates the 2-cyanophenol and homogeneous reaction dominates the observed kinetics, and at longer times, the observed kinetics is controlled by the rate of KHCO3 dissolution. Modeling of the experimental results for the surface-controlled dissolution of KHCO3 in dimethylformamide (DMF) yielded a mean value for the dissolution rate constant, k, at elevated temperatures; k was found to have a value of (1.1 +/- 0.3) x 10(-8) mol cm(-2) s(-1) at 100 degrees C, and the activation energy for the dissolution was 34.4 +/- 0.4 kJ mol(-1) over the temperature range 60-100 degrees C.     

Bioleaching of Zinc and Iron from Steel Plant Waste using <Emphasis Type="Italic">Acidithiobacillus Ferrooxidans</Emphasis>

The bacterial leaching of zinc and iron from solid wastes at the Isdemir iron and steel plant has been investigated using Acidithiobacillus ferrooxidans as the bacterial agent. The effects of a range of operational parameters, including particle size, solids concentration and pH, on the efficiency of the bioleaching process were investigated. In each test, several variables were determined to assess the efficiency of leaching, including slurry pH and redox potential, temperature, bacteria population and concentrations of zinc and iron in solution. Experimental results demonstrated that pulp solids concentration, slurry pH and solids particle size were all important parameters in the bacterial leaching process. Maximum extraction was achieved at pH values around 1.3 and a solids concentration of 1% w/v, with 35% of the Zn content and 37% of the Fe being dissolved.     

Synthesis of spherical polymer and titania photonic crystallites

The fabrication of small structured spherical particles that are essentially small photonic crystals is described. The particles are 1-50 microm in diameter and are porous with nearly close-packed monodisperse pores whose size is comparable to the wavelength of light. The solid matrix of the particles is titania, which provides a large refractive index contrast between the particle matrix and pores. The particles are made by encapsulating polymer colloidal particles in emulsion droplets of hexanes in which a titanium alkoxide precursor is dissolved. Subsequent osmotic removal of the hexanes from the droplets and condensation of the alkoxide precursor leads to spherical aggregates of polymer spheres with titania filling the spaces between the polymer spheres. The polymer particles are then burned out leaving behind the desired porous titania particles. The size and structure of the pores and high refractive index of the titania matrix are expected to produce particles that are very efficient scatterers of light, making them useful as pigments.     

Supersaturation Control Growth of Nanoparticle ZnO and Size Distribution Control

"Nanoparticle ZnO was synthesized in non-aqueous medium. UV adsorption spectra were measured and effective mass model was used to calculate particle size in situ. A technique method named as supersaturation control growth was developed, which dealt with addition of nanoparticle suspension with small size to another suspension with big size. As a result, those small particles completely dissolved and those big ones totally grew because of dissolution degree difference between small particles and the big ones. The particle number of big particle suspension kept being a constant and the growth rate was much higher than Ostwald ripening. Main characteristic of this technique is that size distribution of nanoparticles can be narrowed provided original size difference of two suspension is big enough and original size distribution is not too broad."     

Fabrication of Micron Level Particles of Amoxicillin by Rapid Expansion of Supercritical Solution

In this study, the rapid expansion of supercritical solution (RESS) process was used to precipitate fine solid particles of amoxiccilin where supercritical carbon dioxide was used as a solvent. The process has been done by changing the RESS parameters, including extraction pressure (150–210 bar), extraction temperature (313–333 K), nozzle length (2–15 mm), effective nozzle diameter (450–1700 µm), and spraying distance (1–10 cm), to investigate the effect of these parameters on the size and morphology of the precipitated amoxicillin particles. The characterization (size and morphology) of the particles was examined using scanning electron microscopy (SEM). Based on the different experimental conditions, the mean particle size of the fabricated particles were between 1.08 and 5.72 µm, while the intact particles of amoxicillin were about 41.46 µm. Also, no regular changes in the morphology of the processed particles were observed.     

Inductively Coupled Plasma Synthesis of CeO<Subscript>2</Subscript>-based Powders from Liquid Solutions for SOFC Electrolytes

Doped cerium oxide (CeO₂) based electrolytes are attractive alternative materials to replace the existing yttria-stabilized zirconia (YSZ) used as electrolyte for SOFC (solid oxide fuel cells). Cerium oxide electrolytes offer a similar performance to YSZ electrolytes at a lower cell operating temperature (~600--800 ^°C), therefore reducing thermal stresses and solid state reactions among the cell components.Doped Ce_1-xMe_xO_2-x/2(Me = Gd, Sm or Y) fine \hbox{powders} were synthesized from nitrate salts dissolved in water using a radio frequency inductively coupled plasma reactor. It was demonstrated that the relative concentrations of Ce and dopants fed in the solutions were retained in the synthesized powders. The products were all nano-crystalline with the basic crystal structure of CeO₂ and the crystal size of the products was essentially independent of the dopant used. The particle size distributions obtained were multimodal and in most cases trimodal. The results obtained differ from a previously reported mechanism of particle synthesis from liquid precursors.     

粒径分布对水焦浆性质的影响

分析研究了不同粒径分布的石油焦成浆性及制备水焦浆的流变性和稳定性。结果表明,石油焦的成浆性较好,成浆浓度近70%,浆体的表观黏度均随浓度的增大而增大。粒径分布越宽,越有利于堆积,堆积效率越高,可制浆浓度越高,制备水焦浆的最佳药剂量越低,采用萘系分散剂制备的水焦浆呈胀塑性流型,粒径分布越宽,胀塑性越弱,利用静置观察法与Turbiscan Lab稳定性分析仪测定相结合评价水焦浆的稳定性,水焦浆的稳定性差,且粒径越大,析水率越低,沉降区的焦粉颗粒越易发生聚结,底部越易产生硬沉淀,稳定性越差。颗粒聚结是水焦浆稳定性的主要影响因素。     

磨盘碾磨聚丙烯粒度分布与接枝率的研究

用分形几何方法研究了磨盘碾磨中聚丙烯 (PP)的粉碎和固相力化学接枝 .用粒度分析仪测定经磨盘碾磨聚丙烯的粒度分布 ,用分形理论处理实验数据 .结果表明 ,PP粒度分布存在无标度区 ,具有线性分形特征 ,磨盘碾磨对PP粒子分形行为有较大影响 ,聚丙烯粒度分布的分维值随碾磨次数的增加而增大 .磨盘碾磨中聚丙烯固相力化学接枝的实验结果表明 ,N 羟甲基丙烯酰胺在聚丙烯表面上的接枝率亦随碾磨次数增加而增加 ,即与聚丙烯粒度分布的分维值相关 .因此 ,可用分数维定量描述聚丙烯粒子在磨盘碾磨中的粉碎规律 ,揭示了N 羟甲基丙烯酰胺在聚丙烯表面固相力化学接枝反应的本质 .     

Nanostructure of Solid Precipitates Obtained by Expansion of Polystyrene-block-Polybutadiene Solutions in Near Critical Propane: Block Ratio and Micellar Solution Effects

In contrast to incompressible liquid solutions, compressible near-critical solutions of block copolymers allow for controlling rapid structure transformations with pressure alone. For example, when dissolved in near-critical propane, polystyrene-block-polybutadiene can form a random molecular solution at high pressures, a micellar solution at moderate pressures, and a solvent-free precipitate at low pressures. In contrast to the unstructured virgin copolymer, such a propane-treated precipitate rapidly self assembles toward structures characteristic of equilibrated block copolymers, such as lamellae, spheres or cylinders, which depend on the block ratio rather than on the decompression rate or temperature, at least within the rate and temperature ranges investigated in this work. At lower temperatures, however, say below 40 °C, glass transition of the styrene-butadiene diblocks can inhibit independent structure formation while crystallization of their hydrogenated-butadiene analogs can preserve the micellar-solution structure.