Modification of the surface of nanodisperse amorphous silica prepared by fluoride technology

The physicochemical properties of amorphous silica prepared by the fluoride technology are studied; the surface of silica is modified by direct fluorination with F₂-gas or c-C4F8 radio-frequency plasma. The modification of the surface physical chemical properties after fluorination are compared with the initial silica and analyzed by X-ray photoelectron spectroscopy, IR spectroscopy, and transmission electron microscopy.     

一步固相合成Nb掺杂LiFePO4/C及其电化学性能

用廉价的三价铁离子化合物为铁源,以聚丙烯为还原剂和碳源,在一步固相法合成Nb掺杂LiFePO4的同时实现颗粒表面碳导电膜的原位包覆。结果表明:一步固相合成的Nb掺杂LiFePO4/C具有完整的橄榄石型LiFePO4晶体结构和近似球状的颗粒形貌,颗粒尺寸为100~500 nm;聚丙烯分解后在颗粒表面和颗粒之间形成连通的网络状碳膜。电化学测试结果表明,当Nb的掺入量为1.0%(摩尔分数)时具有最好的倍率放电性能和循环性能;在2C充放电时具有130 mA.h/g的放电容量,循环100次容量无衰减,在4C充放电时仍具有105 mA.h/g的放电容量。     

Formation and immobilization of silver nanoparticles onto chromia surface by novel preparation route involving polyol process

Silver nanoparticles were formed and immobilized onto the chromia surface by novel preparation route involving polyol process for the first time. (3-Mercaptopropyl) trimethoxy silane (MPTMS) was employed as a chemical protocol to make a binding between silver nanoparticle and chromia surface. UV-vis absorption spectroscopy, TEM observation and EDS analysis revealed that silver nanoparticles with a size of ∼ 50 nm in diameter were formed and immobilized onto the surface of chromia particles with an average size of 210 nm. It is thought that this novel preparation route can be extended to the preparation of various metal-inorganic heterogeneous composite particles.     

The effect of the surface chemistry of silica nanoparticles on sorption of polystyrene macromolecules

Adsorption isotherms of polystyrene from its solutions in tetrachloromethane and toluene on the hydroxylated, dehydroxylated, and silanized surfaces of nanoparticles of nonporous silica aerosil were measured. The adsorption equilibrium constants were calculated from the initial linear regions of the adsorption isotherms of polystyrene. The coefficients of distribution of polystyrene molecules between the surface and bulk phases and the changes in the free energy during the interaction between polystyrene macromolecules and hydroxylated, dehydroxylated, and silanized surfaces of aerosil nanoparticles were determined using the model of an adsorbed layer of constant thickness. The comparison of the experimental isotherms and the computed thermodynamic parameters of adsorption enabled revealing the effect of the surface state of aerosil nanoparticles and chemical nature of the solvent on the behavior of polystyrene macromolecules at the interface.     

Highly sinter-active (Mg–Cu)–Zn ferrite nanoparticles prepared by flame spray synthesis

Nanoscale ZnFe₂O₄, Mg_0.5Zn_0.5Fe₂O₄ and Mg_0.2Cu_0.2Zn_0.62Fe_1.98O_3.99 powders were prepared for the first time by flame spray synthesis (FSS). Solutions of metal β-diketonates in organic solvents were used as precursor. Crystalline particles of spinel structure with 6–13 nm primary particle size resulted from the flame process. Particle and crystallite size depended on the flow rate of the atomizing gas, the precursor and its molarity. Compacts prepared from Mg–Cu–Zn ferrite nanoparticles revealed an extremely high sinter-activity. A sintered density of 5.05 g cm⁻³ was achieved after firing for 2 h at 900 °C without any sintering additives, while a maximum density of 4.91 g cm⁻³ was obtained with particles from the conventional ceramic route. The permeability of the sintered Mg–Cu–Zn ferrite nanopowder compacts reached μ = 600 at 1 MHz and the saturation magnetisation was 80 emu g⁻¹. The outstanding sintering activity of the flame-made ferrite powders is attributed to their small primary particle size.     

一步还原法制备纳米铁粉

本文采用一种新方法——一步还原法制备了纳米铁粉颗粒。过量的柠檬酸在620_oC有助于形成纯相、结晶高的α-Fe。纳米铁粉被X射线衍射(XRD)、透射电子显微镜(TEM)、振动样品磁强计(VSM)进行了表征,形貌结果表明产物形成了粒径在30nm左右的近球形的纳米颗粒。磁滞回线说明了纳米铁颗粒的饱和磁化强度为198.97 emu/g,作为磁性材料具有很好的铁磁性能。一步还原法生产颗粒粒径分布窄、可控、流程短,可用于大规模生产。     

Structure and composition heterogeneity of a FeAl alloy prepared by one-step synthesis and consolidation processing and their influence on grain size characterization

This paper aims to characterize a bulk dense FeAl (47 at.%) alloy synthesized and consolidated by one-step current-activated pressure-assisted processing of nanocrystalline elemental powders. The end-product was analyzed using a combination of scanning (SEM) and transmission electron microscopies (TEM), electron back-scattering diffraction (EBSD) as well as electron probe microanalysis (EPMA). Special attention was paid to verify the grain size (32–89 nm) previously determined by X-ray diffraction peak profile analysis. It has been found that this material displays equiaxed grains (0.8–4 μm in size) and contains limited structural defects like subgrains and dislocations. The EPMA result reveals that a variability in Al content (36–47 at.%) is present within the synthesized FeAl phase. Thus, the local variation of lattice parameters resulting from this heterogeneity accounts for the broadening of X-ray diffraction peaks instead of the common idea that the broadening is due to the small grain size. The formation mechanisms of the structure and the composition heterogeneity are also discussed and related to the combustion reaction process.     

A study on the effects of silica particle size and milling time on synthesis of silicon carbide nanoparticles by carbothermic reduction

Silicon carbide nanoparticles were produced by a carbothermic reduction of nano and micro size silica with graphite at 1450 °C for 1 h. The SiC nanoparticles were characterized by XRD, SEM and TEM. The results showed that in the case of nano silica, milling up to 20 h could develop SiC particles of 5–25 nm with some residual SiO₂ particles. By extending milling time to 40 h, more energy was provided and produced Fe contamination, which could act as catalyst and increased SiC yield as well as Fe₂Si phase formation after heat treatment. Coarser particles of micro silica caused higher Fe erosion, more SiC formation with 20–70 nm size and presence of Fe₂Si phase at shorter milling times after heat treatment. Leaching treatment could purify SiC nanoparticles. Increase of milling from 20 to 40 h changed the morphology from polygonal shape to spherical with some reduction in the particle size.     

Surface-silvered polyimide films prepared by plasma-induced grafting of viologen and electroless plating

A vinyl-containing viologen, 1,1'-bis(4-vinylbenzyl)-4,4'-bipyridinium dinitrate (VBVN), was synthesized and subsequently graft-copolymerized on argon plasma-pretreated polyimide (PI) films. Silver nanoparticles can be deposited on the surface of the PI grafted with VBVN film through photo-induced reduction of the silver ions in salt solution. The surface compositions of the modified PI films were studied by X-ray photoelectron spectroscopy (XPS). The topography of the electroless deposited PI films was characterized by SEM and AFM. The results show that the silver nanoparticles are uniformly distributed on the surface of PI films, and the size and distribution of the nanoparticles can be varied by changing the UV irradiation time.     

The one-step synthesis of dense titanium-carbide tiles

Self-propagating, high-temperature synthesis (SHS), which is an attractive process for forming alloys, cermets, ceramics, and composites, has been combined with a rapid quasi-isostatic consolidation technology called the Ceracon^TM process. This one-step synthesis and densification route has been applied to the rapid fabrication of large 15 cm × 15 cm × 2.5 cm titanium carbide tiles. A cost analysis of this process based on prototype quantities shows that the cost of the process is 30–50% of that of current manufacturing processes.     

Room temperature ferromagnetism of boron-doped ZnO nanoparticles prepared by solvothermal method

In this study, B-doped ZnO nanoparticles were synthesized by template-free solvothermal method. X-ray diffraction analysis reveals that B-doped ZnO nanoparticles have hexagonal wurtzite structure. Field emission scanning electron microscopy observations show that the nanoparticles have a diameter of 50 nm. The room temperature ferromagnetism increases monotonically with increasing B concentration to the ZnO nanoparticles and reaches the maximum value of saturation magnetization 0.0178 A·m2 ·kg-1 for 5 % B-doped ZnO nanoparticles. Moreover, photoluminescence spectra reveal that B doping causes to produce Zn vacancies (VZn ). Magnetic moment of oxygen atoms nearest to the B-VZn vacancy pairs can be considered as a source of ferromagnetism for B-doped ZnO nanoparticles.     

铝酸钠溶液中和制备纳米丝状氢氧化铝

研究铝酸钠溶液的盐酸中和过程对氢氧化铝晶体的形貌、晶型和铝酸钠溶液分解率的影响.结果表明:随着反应体系pH值的下降,氢氧化铝的形貌不断发生变化,且pH值越大,晶体越粗大;不论pH 值如何变化,氢氧化铝的晶型总是gibbsite型;铝酸钠溶液的分解率随溶液pH值降低而升高.     

TiC-Fe coatings prepared by flame spray synthesis process

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Preparation of novel core-shell nanoparticles by electrochemical synthesis

Nanostructural gold/polyaniline core/shell composite particles on conducting electrode ITO were successfully prepared via electrochemical polymerization of aniline based on 4-aminothiophenol （4-ATP） capped Au nanoparticles. The new approach to the fabrication included three steps： preparation of gold nanoparticles as core by pulse electrodeposition; formation of ATP monolayer on the gold particle surface, which served as a binder and an initiator; polymerization of aniline monomer initiated by ATP molecules under controlled voltage lower than the voltammetric threshold of aniline polymerization, which assured the formation of polyaniline shell film occurred on gold particles selectively Topographic images were also studied by AFM, which indicated the diameter of gold nanoparticles were around 250 run. Coulometry characterization confirmed the shell thickness of polyaniline film was about 30 nm A possible formation mechanism of the Au/polyaniline core-shell nanocomposites was also proposed. The novel as-prepared core-shell nanoparticles have potential application in constructing biosensor when bioactive enzymes are absorbed or embedded in polyaniline shell film.     

钢表面激光熔覆原位合成TiN复合涂层

选用Ti机械球磨粉末在Q235钢基体表面进行激光熔覆,并实时通入氮气,使钛与氮气发生反应原位合成TiN涂层.运用SEM,XRD,EDS和BSE分析方法对激光熔覆层的组织及成分进行分析,并对熔覆层硬度、高温稳定性及耐腐蚀性进行测试.结果表明,涂层由TiN,TiO₂和铁组成,涂层与基体形成了冶金结合,熔覆区组织成球形颗粒状,而稀释区组织多为树枝晶和针状晶,机械球磨过程可起到细化涂层晶粒作用.同时激光熔覆涂层具有较高的硬度及高温稳定性,当激光功率为1 000 W,扫描速度为600 mm/min时,TiN复合涂层最高表面显微硬度为951.5MPa,涂层耐腐蚀性不佳主要是因为涂层中孔洞及疏松等缺陷导致.     

Synthesis of Y2SiO5:Eu nanoparticles from a hydrothermally prepared silica sol

In this paper, a novel route for the synthesis of Y₂SiO₅ (YSO) nanoparticles doped with Eu³⁺ ions, based on the use of a hydrothermally prepared silica sol as a chemical precursor and nanostructuring template, is presented. X-ray powder diffraction revealed crystallization of nanoparticles in an X₁ monoclinic structural type (P2₁/c) with well pronounced diffraction peaks and without any sign of additional phases. Transmission electron microscopy showed that the particle diameter was around 40 nm and that the particles formed loose aggregates. The synthesized materials exhibited characteristic luminescence emission of the trivalent europium ion, with the strongest emission (⁵D₀ → ⁷F₂ transition) at 611.5 nm and a corresponding lifetime of 1.8 ms. Two site occupancy, as expected, were demonstrated.     

Structure and Raman scattering of Mg-doped ZnO nanoparticles prepared by sol-gel method

Mg-doped ZnO (Mg_xZn_(1-x)O, x=0-0.10)nanoparticles were prepared by sol-gel method. Structural characterization by X-ray diffraction (XRD) indicates that the lattice parameter a increases and c decreases linearly with the increase in Mg content (x) due to the substitution of Mg~(2+) for Zn~(2+) in ZnO lattice. The blueshift of Raman modes is observed, impling the increase in force constant of atom vibration in the Mg_xZn_(1-x)O (MgZnO) nanoparticles. Resonant Raman spectra show longitudinal optical phonon overtones up to fifth order, revealing that the short part of the electron-phonon interaction is enhanced and long-range part is weakened by Mg doping.     

Functionally graded NiTi strips prepared by laser surface anneal

In this study, two-dimensional functionally graded NiTi thin plates were created by laser surface scanning anneal. Owing to the natural degradation of heat penetrating into the material, a temperature gradient within the thickness was created by laser surface interaction and heat conduction. A microstructural gradient was created due to partial annealing within the temperature field. The microstructural variation through the thickness was characterized by hardness measurement and layered differential scanning calorimetry analysis. The microstructural gradient led to a unique shape memory effect, involving shape change in two opposite directions upon one heating, analogous to stingray motion. Such behaviour also experiences enlarged temperature windows for both the forward and reverse martensitic transformations, rendering high controllability of actuation.