Polymer-assisted precipitation of ZnO nanoparticles with narrow particle size distribution

Zinc oxide nanoparticles were produced by aqueous precipitation in mild hydrothermal conditions (90 °C). Well crystallized regular roundish particles were obtained, with a very narrow size distribution. The influence of soft templates (organic species) to control size and size distribution in the final product was investigated. No effect was observed with polyvinylpyrrolidone (PVP M_w 8000 and 40,000), (d?)fructose and hydroxypropylmethylcellulose (HPMC). A significant decrease of the particle size towards 100 nm, while conserving a very narrow size distribution was observed for poly(acrylic acid) (PAA M_w 2000), Dispex A40 (commercial PAA from CIBA M_w ～10,000), and sodium dodecylsulfate (SDS). The influence of the pH was also investigated with PAA. By increasing the pH from slightly acidic to basic conditions, the morphology was spectacularly modified from roundish nanoparticles to micronic branched flower-like particles, with an elongated primary crystal morphology.     

Synthesis of silicon nanoparticles with a narrow size distribution: A theoretical study

This work presents a study of the processes involved in synthesis of narrowly distributed silicon nanoparticles from the thermal decomposition of silane. Two models are proposed, one which simultaneously solves the kinetic mechanism of Swihart & Girshick (1999, Journal of Physical Chemistry B 103, 64–76) while adjusting the sintering parameters; and another which adjusts the kinetic and surface growth mechanisms while neglecting coagulation and sintering. The models are applied to simulate the centreline of the hot-wall reactor and process conditions of Körmer et al. (2010, Journal of Aerosol Science 41, 998–1007). Both models are shown to give good agreement with experimental PSDs at a range of process conditions. However, it is reported that an unphysical sintering process is obtained when attempting to use Swihart & Girshick's kinetic mechanism, while solving for the sintering parameters. The model with adjusted gas-phase and surface growth processes gives better quantitative and qualitative agreement with experimental results. It is therefore recommended that further study into the kinetic and heterogeneous growth mechanisms be conducted in order to better understand the fundamental processes occurring in this hot-wall reactor.     

Bulk quantity and physical properties of boron nitride nanocapsules with a narrow size distribution

A new synthesis route for the formation of boron nitride (BN) nanocapsules by means of a substitution process using single wall carbon nanotubes as templates, with yields of >95% is presented. It is also shown that these BN nanocapsules can act as ideal reference samples for the determination of the relative sp² to sp³ configuration in BN species, a value that is crucial for the physical properties of these nanostructures.     

Preparation of natural microcrystalline graphite with high sphericity and narrow size distribution

Natural microcrystalline graphite with high sphericity and narrow size distribution was prepared by powder engineering methods. The shape of microcrystalline graphite (MCG) particles was modified using a wet agitating method and then the particles were separated into groups with narrow size distribution by means of gravity settling and hydrocyclone combined. Several methods such as scanning electron microscope (SEM), Raman spectroscopy and X-ray diffraction (XRD) were employed to investigate the structure of the sample. The result showed that the present method was effective in classifying the MCG particles into a narrow size range. Galvanostatic cycling was used to investigate the electrochemical performance of the as-prepared MCG as the anode material of lithium ion cells. Compared with raw MCG, the modified MCG shows a large improvement in reversible capacity, though the cycleability is slightly reduced.     

Novel flow injection synthesis of iron oxide nanoparticles with narrow size distribution

A novel synthesis method based on a flow injection technique was developed and the synthesis of magnetite nanoparticles was performed to demonstrate the concept. The technique consisted of continuous or segmented mixing of reagents under laminar flow regime in a capillary reactor. Different schemes of the flow injection synthesis were evaluated and the continuous mode was found to be more advantageous for the synthesis of the iron oxide particles. The material was characterised by X-ray diffraction, thermal analysis, electron microscopy, and magnetic susceptometry. The obtained magnetite nanoparticles had a narrow size distribution in the range 2-7 nm. The influence of chemical parameters and conditions on properties of the material was investigated.     

窄分布低分子质量端羟基聚四氢呋喃的合成与研究

以三氟化硼乙醚配合物(BF3·OEt2)为催化剂,环氧丙烷(PO)为起始剂,二氯甲烷(CH2 Cl2)作溶剂,通过四氢呋喃的阳离子开环聚合合成了窄分子质量分布(Mw/Mn＜1.3)的端羟基聚四氧呋喃(PTHF).研究了三氟化硼乙醚配合物用量、溶剂用量、起始剂用量、反应时间对PTHF分子质量(Mn)及其分布(Mw/Mn)...     

A narrow size distribution on a high shear mixer by applying a flux number approach

High shear granulation is a common technology for particle size enlargement, but generally the product properties are badly affected by the broad size distribution generated in the process. A recently published approach by Michaels et al. [J.N. Michaels, G. Wang, L. Farber, K.P. Hapgood, J.H. Chou, S. Heidel, and G.I. Tardos, 2006, One-dimensional scale-up of high-shear granulators, Paper 243c, World Congress Particle Technology 5, Orlando (FL)] employs low binder solution spray rates and long granulation times, whilst the solids are kept in roping flow, to avoid coarse formation. The present work applies this approach to a two-component binder system with a dry powder gum and water spray as activation agent. Similarities with fluidised bed granulation and coating processes are explored. The work shows that indeed narrow size distributions of fine granules can be achieved with ease. Dimensionless numbers for spray fluxes are useful to identify operating regimes and to steer optimisation efforts. Comparison of flux numbers for different systems shows that they are not useful (yet) for detailed product and process design. Further work on material-specific quantities controlling nucleation and growth, e.g. particle wetting, is recommended.     

窄分子量分布端羟基环氧乙烷-四氢呋喃共聚醚的合成及表征

用三氟化硼乙醚络合物(BF3.OEt2)为催化剂,乙二醇(EG)为起始剂,甲苯作溶剂,通过阳离子开环聚合制备出了窄分子量分布(w/n<1.3)的端羟基环氧乙烷-四氢呋喃(TEO)共聚醚,探讨了聚合温度、时间、反应介质、加料方式、起始剂及单体配比对分子量及其分布的影响,采用凝胶渗透色谱-多角度激光散射联用仪(SEC-MALLS)对其分子量及分布进行准确的测定,并用IR和1HNMR对共聚醚结构进行了表征。研究表明:有EG存在时,采用一次加料的方式,以甲苯为溶剂,温度为0℃,单体配比为11,∶反应时间为5 h的条件下制得的共聚醚具有分子量分布较窄的特点。     

Poly(acrylonitrile) microspheres with a narrow size distribution: Synthesis by single-step swelling and properties

Poly(acrylonitrile)-poly(styrene) micrometer-sized composite particles with a narrow size distribution are prepared by single-step swelling of poly(styrene) uniform template microspheres in emulsion droplets of methylene chloride containing an acrylonitrile monomer and a benzoyl peroxide initiator. Methylene chloride is carefully evaporated with subsequent polymerization of acrylonitrile at a temperature of 70°C inside the shrunken template particles. Acrylonitrile is also polymerized at the particle surface due to the interaction of surface poly(acrylonitrile) oligoradicals with acrylonitrile dissolved in the aqueous phase. Uniform poly(acrylonitrile) particles with a larger surface area are formed by dissolving template poly(styrene) of the composite particles. The surface and bulk properties of the particles are investigated using Fourier transform IR (FTIR) spectroscopy, elemental analysis, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction, X-ray photoelectron spectroscopy (XPS), contact-angle measurements, optical microscopy, scanning electron microscopy (SEM), and cross-sectional transmission electron microscopy (TEM).Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Boguslavsky, Margel.     

A particle size distribution model for manufactured particulate solids of narrow and intermediate size ranges

Mass transport algorithms using particle size distribution equations are common where molecular mass flux across a hydrodynamic layer is present. In this paper, we suggest a unique model and prove its effectiveness in modelling particle size distributions that vary dramatically in character and propose that the model may be useful for distributions of narrow and intermediate size ranges, more specifically, for ion exchange resin and fluidised bed catalyst, both of which are manufactured particulates. The model has a single fitting parameter and can be used in the frequency form for finite-element transport phenomena calculations.     

Particle size distribution characterization from acoustic emissions

A detailed study of the acoustic signals emitted by colliding particles has led to increased precision in the determination of average particle size through an acoustic method proposed in an earlier report [1] and the derivation of methods for characterizing the shape and width of the size distributions of beds of particles. These results have been obtained by devising methods for classifying characteristics parameters of the signals into different vibration modes. The degree of precision attainable in the determination of these properties of a particle bed is directly related to the capacity of the analyzing system for distinguishing between adjacent vibrational modes.     

Preparation and characterisation of mesoporous silica–alumina and silica–titania with a narrow pore size distribution

Amorphous mesoporous materials with a different degree of order in the arrangement of pores are outlined. Particularly, the synthesis of a class of mesoporous silica–alumina (MSA) materials with narrow pore size distribution and a disordered arrangement of pores is reported and discussed. Likewise, the preparation of titanium-containing ordered mesoporous silicates (Ti-MCM-41) and disordered mesoporous silica–titania (MST) are also described in detail. The structural properties of the solids are compared by means of X-ray diffraction and UV-Vis diffuse reflectance spectroscopy. The nitrogen adsorption–desorption measurements were performed and the textural properties are evaluated by the BET, DFT, BJH and t-plot methods.

The high specific surface area and pore volume, as well as the acidity, make MSA solids interesting catalysts in several petrochemical transformations, i.e. oligomerisation, alkylation, hydroisomerisation, rearrangement reactions. Besides, thanks to the width of the mesopores of such solids, the catalytic activity of titanium-containing silicates may have a potential application in the epoxidation of bulky unsaturated fine chemical substrates.     

High ethoxylated alcohols with narrow distribution of homologues

Homologue distributions of alcohol ethoxylates obtained with an unconventional calcium-based catalyst and NaOH as the conventional catalyst are studied in the range of average polyaddition degree from 8 to 15. The fractional compositions of those high molecular weight derivatives of dodecanol and other technical alcohols, Lial 125 and Radianol 1724, are determined as peak area percentages from HPLC chromatograms. Some physico-chemical characteristics of the products as well as by-product contents are also presented. It is shown that the differences in fractional contents between the broad and narrow homologue distributed equivalents remain very significant in that range of higher ethoxylation grades. Consequently, the influence of homologue distributions on some properties of the products can be expected in their practical applications.     

Synthesis of narrow distribution polytetrahydrofuran

Bulk polymerizations of tetrahydrofuran (THF) have been studied kinetically at reaction temperatures in the range ?10 to +80°C using p-chlorophenyldiazonium hexafluorophosphate initiator. Initiation has been studied to enable selection of a ‘clean’ initiation condition (95°C for 4 min). Factors causing broadening of the molecular weight distribution are discussed, the main causes of such broadening being chain transfer reactions and concurrent initiation with propagation. These could be minimized by using a low reaction temperature (?10°C). Molecular weight distributions were measured by gel permeation chromatography. Propagation rate constants were determined and found to increase with increasing temperature according to an Arrhenius expression giving an activation energy of 51 kJ/mol. The method will produce monodisperse samples of THF polymer over a wide molecular weight range from 5 × 10³ to 10⁶.     

Design and fabrication of whisker hybrid ceramic membranes with narrow pore size distribution and high permeability via co-sintering process

Ceramic microfiltration membranes (MF) with narrow pore size distribution and high permeability are widely used for the preparation of ceramic ultrafiltration membranes (UF) and in wastewater treatment. In this work, a whisker hybrid ceramic membrane (WHCM) consisting of a whisker layer and an alumina layer was designed to achieve high permeability and narrow pore size distribution based on the relative resistance obtained using the Hagen-Poiseuille and Darcy equations. The whisker layer was designed to prevent the penetration of alumina particles into the support and ensure a high porosity of the membrane, while the alumina layer provided a smooth surface and narrow pore size distribution. Mass transfer resistance is critical to reduce the effect of the membrane layers. It was found that the resistance of the WHCM depended largely on the alumina layer. The effect of the support and whisker layer on the resistance of the WHCM was negligible. This was consistent with theoretical calculations. The WHCM was co-sintered at 1000?°C, which resulted in a high permeability of ~?645?L?m^?1 h^?1 ;bar^?1 and a narrow pore size distribution of ~?100?nm. Co-sintering was carried out on a macroporous ceramic support (just needed one sintering process), which greatly reduced the preparation cost and time. The WHCM (as the sub-layer) also showed a great potential to be used for the fabrication of ceramic UF membranes with high repeatability. Hence, this study provides an efficient approach for the fabrication of advanced ceramic MF membranes on macroporous supports, allowing for rapid prototyping with scale-up capability.     

Methanol synthesis over Pd/SiO2 with narrow Pd size distribution prepared by using MCM-41 as a support precursor

All silicious MCM-41 was investigated as a support or a support precursor for Pd/SiO₂ and prepared catalysts were tested for methanol synthesis from CO and H₂. The methods of Pd loading on the MCM-41 were impregnation, seed impregnation and chemical vapor deposition (CVD). For both impregnations, most Pd existed outside of the pore as large particles, and only a small part of Pd was inserted into the pore of MCM-41 retaining the initial structure. On the contrary, in the catalyst prepared by CVD method, the MCM-41 structure was completely destroyed to become amorphous SiO₂. Yet the average Pd particle size in this catalyst was smaller and its distribution was narrower than those of the catalysts prepared by impregnation methods. In the methanol synthesis from CO hydrogenation the catalyst prepared by CVD showed higher methanol selectivity than other MCM-41-derived catalysts. This result was considered to be due to the more uniform distribution of the Pd particle size.     

窄分布脂肪醇聚氧乙烯醚硫酸盐

介绍了宽、窄两种EO分布的AES的应用性能,及后者更有利于生产低二恶烷产品。通过对两种产品作EO分布测定认为,作为日化洗涤剂和化妆品的原料,以N约等于2—2．5的窄分布AES为佳。     

Preparation and characterization of protein imprinted agarose microspheres

Agarose hydrogel microspheres imprinted with bovine serum albumin (BSA) were prepared by inverse suspension gelating method. The experimental conditions related with beads’ shape and uniformity were studied, including temperature, surfactant content, and stirring speed. The size and distribution of the pores were found related with porogen and surfactant content. Rebinding properties were influenced by the diameter and porosity. The beads with the smallest diameter exhibited the greatest rebinding capacity, rebinding speed, and imprinting efficiency (IE). Smaller pores provided higher rebinding capacity and IE, but lower rebinding speed. Imprinted microspheres showed good specificity toward templating protein compared to others.