The synthesis and characterization of polymer coated iron oxide microspheres

For biomedical applications drug carrying polymers are coated around magnetic iron oxide particles to form microspheres. In the present study, the iron oxide powder was ball milled. Microspheres were then synthesized by solvent evaporation, resulting in iron oxide particles encapsulated in a polymer and drug coating. Various parameters, such as the duration of milling and agitation speed as well as the polymer concentration were varied. A milling time of 72 h was found to yield a small size and narrow size distribution of particles; the average particle size was about 600 nm. Measurements of the change in grain size and the magnetic properties of the powder with milling time were performed. It was determined that the size of the microspheres was not sensitive to the initial particle size, but it could be decreased by variation of agitation speed or polymer concentration. The agitation speed and polymer concentration of 400 rpm and 0.04 g poly(l-lactic acid) in 8 g dicholoromethane, respectively, was found to yield small, spherical microspheres with a narrow size distribution. The surface morphology and magnetic properties of the microspheres was also analyzed.     

Zinc oxide: hydrothermal growth of nano- and bulk crystals and their luminescent properties

Hydrothermal growth, crystal chemistry and catodoluminescence of ZnO single crystals were studied. Zinc oxide was grown as bulk crystals so as crystalline films and powders with different form-factors (size and shape of the particles). The dependence of form-factor on the growth conditions was studied. Growth morphology and spectra of impulse cathodoluminescence (ICL) were analysed for the samples depending on growth conditions. Two emission bands were registered in ICL-spectra with band lengths ~385 and 600 nm. The shift of the band in visible part of spectrum (VIS-band) was found depending on KOH concentration in starting solutions.     

Structure,growth and morphology polyphenylene sulphide

The crystaIIinity, particle size and morphology of polyphenylene sulphide synthesized under various conditions have been investigated by X-ray diffraction and scanning electron microscopy. It was found that crystaIIinity decreased from 71 to 66% with increase of reaction time. The growth of particle size as well as total polymer mass followed a time dependence of the formX =X ₀ (1 -e ^–t ) The particle size distribution curve was noted to be sharp centring at 3 µn for short reaction time, high speed of stirring and also for low concentration of reactants. The particle morphology showed very strong dependence on various reaction parameters. Intricate sheaf-like morphology was noted for the particles at long reaction times or low stirring speeds while oblong platelet type two-dimensional morphology was noted when a low concentration of reactants was used.NCL communication No. 3674     

Physico-chemical and NMR relaxometric characterization of gadolinium hydroxide and dysprosium oxide nanoparticles

Gadolinium hydroxide and dysprosium oxide nanoparticles, which constitute a new interesting class of magnetic nanoparticles, are characterized by different methods, using x-ray diffraction, magnetometry and NMR relaxometry at multiple fields. The rod-like particles are first shown to have a simple paramagnetic behavior, like the bulk compound, without any influence of the nanometric size of the particles. Because of their paramagnetic moment, these particles considerably shorten water relaxation times, especially the transverse relaxation time at high fields. The relaxation induced by gadolinium hydroxide particles is due to a proton exchange between the particle surface and bulk water, while the transverse relaxation caused by dysprosium oxide particles is governed by the diffusion of water protons around the magnetized particles. 1/T(2) increases linearly with the magnetic field for gadolinium hydroxide particles while a quadratic increase is observed for dysprosium oxide nanoparticles. The relaxation results are compared with those from previous studies and interpreted using different theories for the relaxation induced by magnetic particles.     

镁盐及晶种对氧化镁水化合成氢氧化镁的影响

采用氧化镁水化法制备氢氧化镁,研究硫酸镁、乙酸镁、氯化镁、硝酸镁4种镁盐的添加量对氧化镁水化率的影响,以及镁盐和晶种对氢氧化镁颗粒大小和形貌的影响,利用X射线衍射和扫描电子显微镜对合成的氢氧化镁晶体特性、颗粒大小和形貌进行表征,并对上述因素的影响机理进行探讨。结果表明,随着镁离子浓度的增大,氧化镁的水化率逐渐增大,氧化镁水化率最高可达到98.68%,水化产物氢氧化镁颗粒近似于六方片状,粒径约为200⁵00 nm。     

A novel laser-liquid-solid interaction technique for synthesis of silver, nickel and immiscible silver-nickel alloys from liquid precursors

Silver, nickel, nickel oxide and silver-nickel alloys have been produced from their inexpensive liquid precursors using CO₂ and Nd-YAG lasers. Ethylene glycol, diethylene glycol and 2-ethoxyethanol were used as reductants in the synthesis reactions. Spherical and faceted silver particles of high purity were formed by laser interaction between the precursor solution and a rotating substrate, while porous dual phase nickel and nickel oxide particles were produced when nickel nitrate was used as a precursor. The composition and morphology of the alloy particles was dependent on laser parameters and chemical composition of the precursor solution. The product composition was dependent only upon the chemistry of the precursors used. The mean particle size was dependent upon the temperature generated by irradition and the duration of exposure to the laser beam. The synthesis of nano-particles and metastable alloys is proposed to occur primarily at the laser-liquid-solid interface by a nucleation and growth mechanism.     

Synthesis and sintering of biomimetic hydroxyapatite nanoparticles for biomedical applications

Synthesis of monodisperse nanoparticles with uniform morphology and narrow size distribution as achieved by nature is a challenge to materials scientists. Mimicking the process of biomineralization has led to the development of biomolecules mediated synthesis of nanoparticles that overcomes many of the problems associated with nanoparticle synthesis. Termed as biomimetics this paradigm shift in the philosophy of synthesis of materials is very advantageous for the design-based synthesis of nanoparticles. The effect of concentration of a protein named bovine serum albumin on particle size, morphology and degree of crystallinity of biomimetically synthesized hydroxyapatite particles, has been studied. Results establish 0.5% protein as the required concentration to produce 30–40 nm sized hydroxyapatite particles with an optimum degree of crystallinity as required for biomedical applications. These particles synthesized under certain stringent conditions are found to have stoichiometric calcium:phosphorus ratio of 1.67 and exhibit restricted grain growth during sintering.     

Synthesis of ZnO nanopowder via an aqueous acetate-citrate gelation method

The synthesis of nanoparticulate ZnO via an aqueous carboxylate gelation route is presented. Starting from a solution of zinc acetate with citric acid as a complexing agent, a solid glassy gel is obtained after drying that is converted into a fine powder by calcination. It is found that a very homogeneous precursor is indispensable when preparing very fine particles with a narrow size distribution. Cryo-transmission electron microscopy (Cryo-TEM) investigation is used as a feedback tool to prevent early precipitation during gelation. Study of the thermal decomposition of the gel shows that ZnO is formed before the final decomposition step takes place. After removing the organic backbone, very small oxide particles are found. The influence of the thermal treatment parameters on the particle size is investigated and a particle growth process is found. By a proper adjustment of the final calcination temperature in dry air, the mean particle size can be controlled between ∼11 and 175 nm. It was also seen that even in inert atmosphere, ZnO is formed and that particle morphology is greatly influenced by the calcination atmosphere.     

Oxide particle size distribution function in combustion of aluminum: Quasi-steady approximation

The size distribution function for oxide particles formed in combustion of aluminum is calculated in a quasi-steady approximation. It is demonstrated that the quasi-steady approximation may be employed for aluminum particles sized 15 to 300 μm. It is observed that the conditions of combustion (temperature, pressure, oxidizer content, and size of aluminum powder particles) have a weak effect on the parameters of distribution function. The results of calculations of the parameters of oxide particles formed as a result of combustion of aluminum powder are compared with the parameters of particles formed after explosion of an explosive containing aluminum powder.     

Morphologies of coke deposited on surfaces of pure Ni and Fe-Cr-Ni-Mn alloys during pyrolysis of propane

Morphologies of coke deposited on pure Ni and Fe-Cr-Ni-Mn alloy surfaces during pyrolysis of propane at 750–1000°C have been investigated in detail. It is found that surface scales developed initially on pure Ni and Fe-Cr-Ni-Mn alloy surfaces have no catalytic effect on deposition of filamentary coke. But metal or alloy substrates under cracked scales strongly catalyze nucleation and growth of filamentary coke along the cracks. Ni is more efficient to catalyze the growth of filamentary coke than Fe-Cr-Ni-Mn alloys. The structure of oxide scales has marked influence on distribution and size of filamentary coke deposited on alloy surfaces. Coking morphology is closely dependent of coking temperature and time. Either increasing coking temperature or prolonging coking time results in coking morphology changes from filamentary to spherical. Both dissolution/precipitation mechanism and direct nucleation and growth mechanism may make a contribution to the development of graphitic film coke.     

Structure development in PP/CaSO4 composites: Part I Preparation of the filler by an in situ technique

The structure, growth and morphology of calcium sulphate prepared in situ of a polymer has been investigated using polyethylene oxide as the growth medium. The structure was predominantly the dihydrate type with monoclinic configuration for these samples as compared to the anhydrite type with orthorhombic structure obtained in commercial samples. The crystal morphology consisted of sharp needle shape, having aspect ratio of more than 10. The concentration of the polymer used had a profound effect on the crystal size and its distribution. The size distribution became narrow and the average crystal size reduced with the increase of polymer concentration. Highly oriented crystals could be obtained with application of, small shearing force on the samples. These results have been explained on the basis of polymer mediated crystallization and large interaction between the filler and the matrix. © 1998 Chapman & Hall     

活性碳纤维载银工艺及其表面银颗粒的形态特征

以自制粘胶基活性碳纤维（ＡＣＦ）为载体，通过真空浸渍和真空热分解的方法在其表面沉积银，制得了载银活性碳纤维（ＡＣＦ（Ａｇ）。研究了载银工艺参数对ＡＣＦ（Ａｇ）的银含量、表面银颗粒大小、分布及形态的影响规律，提出了银颗粒的形核与长大机制；此外，还分析了银颗粒与ＡＣＦ结合力的影响因素。     

Control of the particle size and morphology of hydrothermally synthesised lead zirconate titanate powders

The particle size and morphology of hydrothermally synthesised lead zirconate titanate (PZT) powders can be controlled by concentrations of the mineraliser such as potassium hydroxide (KOH), and the hydrothermal synthesis temperature and time, which all influence the particle nucleation and growth mechanisms. The mineraliser is crucial in facilitating both the in-situ transformation process during the nucleation stage and the nuclei-coagulation process during the subsequent growth stage. Its concentration must be high enough to ensure the formation of only pure perovskite PZT particles but low enough to prevent excessive PZT particle growth. The minimum necessary mineraliser concentration has, however, strong dependence on both the hydrothermal synthesis temperature and chemical environment in hydrothermal solution. Thus, perovskite PZT powders with ca. 200 nm particle size and narrow particle size distribution can be synthesised hydrothermally at 300°C using KOH as a mineraliser with a minimum concentration of 0.4 M.     

Liquid-Phase Preparation and Characterization of Zinc Oxide Nanoparticles

Zinc oxide (ZnO) nanoparticles have been prepared by a wet chemical method, from zinc acetate and LiOH ethanol-based solutions. The resulted nanoparticles were dispersed in a solvent. The effect of solvent (ethanol or butanol) and surfactant (polyethylene glycol-PEG 200) on the average size and size distribution of the nanoparticles was investigated by light scattering measurements. Smaller size was observed for ZnO nanoparticles dispersed in butanol and PEG 200. The statistical parameters of the Gaussian size distribution curves were calculated. ZnO nanoparticles have been prepared to be used as seeds on a substrate for the growth of ZnO nanowires. The morphology, surface roughness, crystalline structure, and orientation of the nanoparticles deposed on silicon substrate were characterized by atomic force microscopy and x-ray diffraction, respectively.     

Continuous reactor system of monosized colloidal particles

A reactor system, which continuously hydrolysed the metal alkoxide in an alcohol solution, was designed using an electromagnetic stirrer and an ageing tube. Several monosized colloidal particles were produced by this reactor system, which had high reproducibility and reliability for long-term production. The relation between powder characteristics and experimental parameters such as reagent concentration, mixing rate, ageing time, temperature, was investigated. These parameters had an effect on the particle size, size distribution, morphology and state of agglomeration. It is possible to control the particle size to between 0.1 and 1.0 μm by varying the experimental conditions. A narrower size distribution of powders was obtained by using an electromagnetic stirrer with greater flow rate. Physical and chemical properties of monosized colloidal particles obtained by this reactor were comparable to those of monosized colloidal particles obtained by the batch process.     

Effect of size of reinforcement on thickness of anodized coatings on SiC/Al matrix composites

The effect of size of reinforcements on morphology and thickness of anodic coatings on 3.5 μm and 10 μm SiC particles reinforced 2024Al metal matrix composites (SiC_p/Al MMCs) formed in sulfuric acid was investigated with optical microscopy and scanning electron microscopy. The thickness of anodized coating on the MMCs is strongly dependent of size of SiC particles, and it is smaller for the MMC with smaller SiC particles because growth of more pores is affected when the concentration of SiC particles is fixed. The oxide/substrate interface became locally scalloped, and the anodized coatings formed on the MMCs were non-uniform in thickness, especially for the MMC reinforced by bigger particles.     

SIMULATION OF SPRAY PYROLYSIS FOR CERAMIC POWDER PREPARATION

A mathematical model was developed for spray pyrolysis to produce hollow spherical ceramic particles. The mechanism was established based on the previous experimental results. The transfer of mass, momentum, and heat inside and around the aerosol droplets was considered simultaneously. Simulation was carried out to study the effects of operating parameters on the quality of derived particles. The simulated and experimental results were in agreement and showed that: (a) raising the pyrolysis temperature increased the size and size distribution of resultant particles, and decreased the specific surface area and the bulk density; (b) lowering the concentration of starting solution decreased the size and size distribution of resultant particles, and increased the specific surface area and bulk density.     

酒石酸对直接沉淀法制备纳米Bi_2O_3晶体结构的影响

以高氯酸铋和氢氧化钠为原料,采用一步直接沉淀法,通过添加和控制酒石酸的用量,制备出纺锤形的纳米氧化铋粒子,采用X射线衍射、扫描电镜和差热分析等手段对产品进行分析与表征,并且对反应机理进行初步分析。结果表明:当酒石酸盐的质量分数为8%左右时,合成的纳米氧化铋为纺锤形,粒子分布均匀,粒度较小,平均粒度约为90 nm。     

Synthesis and growth mechanism of ThO2–W–Mo alloy nanocomposite powder

Nanocomposite ultrafine powders of thorium oxide and tungsten molybdenum alloy were prepared by arcing between a pure molybdenum cathode and a thoriated tungsten anode under an argon–hydrogen atmosphere. The microstructure, morphology and chemical analyses of the ultrafine powders were examined by X-ray diffraction, transmission electron microscopy and associated techniques. The powders are composed of thorium oxide single-crystalline nano-grains decorated by tungsten molybdenum alloy particles which are crystallized in a metastable A15 structure. Two morphologies were observed: octahedra and needle-like particles. Every octahedral particle bigger than 15 nm had on each corner a metallic grain generally less than 8 nm in size. The needles had a length below 600 nm and their width to length ratio ranged from 1/3–1/15. They all presented on one of their ends a metallic particle which was comparable in size to the needle width. Other smaller particles (<10 nm) may be encountered along the edges. The metallic particles were found to be epitaxial on the thorium oxide grains according to the relation: (100) [011]_ThO2∥(100) [011]_A15. The extensive study of the microstructural and morphological properties of the powders leads us to suggest a growth mechanism of the nanocomposite particles. This revised version was published online in November 2006 with corrections to the Cover Date.     

Selective synthesis of metallic nickel particles with control of shape via wet chemical process

Metallic nickel particles with shapes varying from sea urchin-like to spherical have been selectively synthesized via aqueous chemical reduction. The phase structure and morphology of particles have been investigated by means of X-ray diffraction and scanning electron microscopy. It was found that sodium carbonate greatly accelerated the reduction process to form needle-like dendrites under atmospheric pressure. The probable formation mechanism of the sea urchin-like particles is also discussed. In the mild reduction process, the particle size of nickel nanospheres could be easily controlled by adjusting the experimental parameters.