六方BN微颗粒表面化学镀镍的动力学

研究了平均粒径为104 mm的BN颗粒表面以肼为还原剂的微镀镍过程中镍沉积量随时间的变化规律；分析了温度、添加剂等对沉积镍动力学规律的影响；不同沉积时刻取样观测表面沉积金属镍颗粒的SEM形貌，并进一步分析验证了动力学规律.     

Preparation of nickel coating on ZTA particles by electroless plating

With the aim to effectively improve the interface between ZrO₂ toughened Al₂O₃ (ZTA) particles and metal matrix, nickel was deposited on the surface of ZTA particles by electroless plating method. Formation mechanism of nickel coating and effects of the solution pH, loading capacity of ZTA particles and temperature on the nickel deposition were investigated. Microstructures, thickness and element distributions of nickel coating were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results showed that the nickel was successfully deposited on the surface of ZTA particles by electroless plating without noticeable defects. The process of electroless nickel plating could be explained by combination of atomic hydrogen and electrochemistry theories. The interfacial nucleation of nickel is easier to form than spontaneous nucleation in the solution. Deposited Nickel has priority on the surface of ZTA particles comparing to that in solution. The optimal conditions to coat nickel on the surface of ZTA particles are: solution pH 4.7–4.8, loading capacity 15–20?g/L, and electroless plating temperature 85?°C. The ZTA particle reinforced iron matrix composites prepared by powder metallurgy could have better interfacial bonding between ZTA particle and iron matrix because of the nickel coating on the surface of ZTA particle. Nickel diffuses into the iron matrix during the sintering preparation of composite materials. The interface between ZTA particle and iron matrix presents the evidence of non-chemical bonding.     

氢氧化镍粉末的化学镀Co-Zn合金表面改性研究

采用化学沉积技术对由水溶液络合沉淀法合成的氢氧化镍粉末进行了表面包覆Co—Zn改性处理,利用扫描电子显微镜分析、比表面积测量、X一射线光电子能谱及原子吸收光谱等对处理前后氢氧化镍粉末的表面形貌、微晶结构、比表面积、元素化学态及镀层组成等进行了表征和研究。结果表明,Co—Zn合金镀层可以均匀包覆在氢氧化镍颗粒表面,氢氧化镍经化学镀处理后其表面微观组织形貌发生了明显变化。化学镀表面改性使氢氧化镍粉末的比表面积有所降低,镀层中的Co、Zn元素均以氧化态形式存在。     

Hybrid nickel oxide-carbon fiber composites obtained in the presence of surfactants

The composite material nickel hydroxide (oxide)/carbon fiber has been obtained by hydroxide deposition on the surface of the activated carbon fiber (ACF) via urea hydrolysis in the presence of a surfactant. The organomineral composite NiO/CHIT/carbon fiber has been obtained by electrochemical deposition of nickel hydroxide on the ACF surface in combination with chitosan as well as by cathode deposition on a carbon fiber electrode preliminarily modified by chitosan. The surface of the obtained hybrid materials has been investigated by means of the methods of X-ray photoelectron spectroscopy (XPS), atomic force and scanning electron spectroscopy (AFM and SEM), and cyclic voltamperometry. The composition and properties of the obtained composites have been discussed.     

Thin fluoropolymer films and nanoparticle coatings from the rapid expansion of supercritical carbon dioxide solutions with electrostatic collection

Application of nanometer thick fluoropolymer films onto metal and semiconducting substrates is described. In the first step, nanometer-sized polymer particles are generated by a process of homogeneous nucleation during the rapid expansion of supercritical fluid solutions. These gas-phase particles are then charged as they are being formed by application of a high voltage to the expansion nozzle. In this way the charged nanoparticles can be collected on a solid surface forming uniform coatings with thicknesses from tens of nanometers to several micrometers thick. Supercritical carbon dioxide solutions of three different fluoropolymers were used to generate different types of coatings. This represents a ‘green’ process for film deposition. A further unique aspect of this process is that the small charged nanoparticles can be deposited to electrically conducting microscopic regions with a spatial resolution better than 50 nm.     

Application of a modified Eulerian model to study the particle deposition on a vertical surface in turbulent flow

In this study the v2-f model was used with the two-phase Eulerian approach to predict the particle deposition rate on a vertical surface in a turbulent flow. The standard Eulerian particle model was adopted from the literature and modified, considering the majority of particle transport mechanisms in the particle deposition rate. The performance of the modified model was examined by comparing the rate of particle deposition on a vertical surface with the experimental and numerical data in a turbulent channel flow available in the literature. The model took into account the effects of drag force, lift force, turbophoretic force, electrostatic force, inertia force and Brownian/turbulent diffusion on the particle deposition rate. Electrostatic forces due to mirror charging and charged particles under the influence of an electric field were considered. The predictions of the modified particle model were in good agreement with the experimental data. It was observed that when both electrostatic forces are present they are the dominant factor in the deposition rate in a wider range of particle sizes.     

Dr. Carl W. Hall,Founding Editor

Current methods in alleviating the wall deposition problem in spray drying emphasize mainly controlling the stickiness of the drying particles and less attention is placed on the properties of the dryer wall. In this experimental study, the effect of wall surface properties on the deposition mechanism has been investigated. Properties considered in classifying different wall materials were surface energy, roughness, and dielectric properties. The model solution contained sucrose, representing low-molecular-weight sugars commonly encountered in spray drying of fruit and vegetable juices. The effect of wall properties on deposition was explored at different drying rates producing particles of different surface rigidity. Larger surface roughness produced higher deposition fluxes for particles with high impact velocity and moisture. Surface energy and surface roughness were found to have no significant effect for dry rigid particles at the middle and bottom elevation of the drying chamber. However, material with lower surface energy (Teflon) exhibited less deposition for rubbery particles at such elevations. Analysis shows that dielectric wall material (Teflon) tends to enhance deposition of dry particles because of attrition at the surface. Higher wall temperature was found to produce slightly more deposition. The results of this work give a general indication of the effect of wall material on the deposition problem and provide the fundamental understanding for further studies along this line. Proper selection of dryer wall material will provide potential alternatives for reducing the deposition problem.     

Effect of Wall Surface Properties at Different Drying Kinetics on the Deposition Problem in Spray Drying

Current methods in alleviating the wall deposition problem in spray drying emphasize mainly controlling the stickiness of the drying particles and less attention is placed on the properties of the dryer wall. In this experimental study, the effect of wall surface properties on the deposition mechanism has been investigated. Properties considered in classifying different wall materials were surface energy, roughness, and dielectric properties. The model solution contained sucrose, representing low-molecular-weight sugars commonly encountered in spray drying of fruit and vegetable juices. The effect of wall properties on deposition was explored at different drying rates producing particles of different surface rigidity. Larger surface roughness produced higher deposition fluxes for particles with high impact velocity and moisture. Surface energy and surface roughness were found to have no significant effect for dry rigid particles at the middle and bottom elevation of the drying chamber. However, material with lower surface energy (Teflon) exhibited less deposition for rubbery particles at such elevations. Analysis shows that dielectric wall material (Teflon) tends to enhance deposition of dry particles because of attrition at the surface. Higher wall temperature was found to produce slightly more deposition. The results of this work give a general indication of the effect of wall material on the deposition problem and provide the fundamental understanding for further studies along this line. Proper selection of dryer wall material will provide potential alternatives for reducing the deposition problem.     

Monodisperse polymer/metal composite particles by electroless chemical deposition: Effect of surface functionality of polymer particles

Micron‐sized polymer particles were coated with layers of nickel compounds by plating electrolessly in the presence of aqueous solutions of nickel chloride, sodium hypophosphite, sodium citrate, and ammonium chloride at elevated temperature. The uniform functional polymer particle could be obtained by seeded polymerization. To investigate the effect of surface functionality on the conditions for nickel deposition, the polymer particle was functionalized with the thiol group. From morphological observation, it was found that the mode of nickel deposition was greatly dependent on the surface functionality of the polymer particle. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 420–424, 2003     

Characterization of carbons formed on nickel surfaces

Carbonaceous materials formed in small quantities (?4 mg) on nickel surfaces by pyrolysis of buta-1,3-diene and propene have been characterized by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) in conjunction with electron and X-ray diffraction techniques, laser Raman studies, density measurements, hydrogen microanalysis and plasma gasification experiments. The products identified were nickel carbide, a disordered carbon of columnar morphology, a more-ordered laminar material, filamentous carbon and a polymeric species that condensed out as droplets on the nickel foil surface during cooling. The relative amounts of these products were dependent upon the temperature of reaction as measured at the centre of the foil. The different forms of carbonaceous material could be produced simultaneously on the foil surface as a consequence of the temperature gradient along the length of the foil. The formation of carbon on thin crystalline evaporated films of nickel is also described and compared with deposition on the bulk nickel foils. Carbon growth mechanisms are discussed.     

Influence of gas velocity on the particle collection and reentrainment in an air-cleaning electrostatic precipitator

Particle deposition and reentrainment experiments were performed in a two-stage electrostatic precipitator (ESP), consisting of positive corona precharger and collecting electrode sections. Attention was focused on studying the indoor air pollution deposition and reentrainment into six size ranges from 0.3 to >10?μm. Tests were performed in an office room (200?m³) for airflow velocities from 1.4 to 8?m/s. The effect of airflow velocity on the collection efficiency of the ESP was investigated both experimentally and analytically to study reentrainment phenomena in a turbulent flow. A stationary two-dimensional analytical model was carried out by modeling the particle transport. The boundary conditions for charged particles on collecting and repelling electrodes were determined by physical considerations, including chaotic and drift motions, the reflection of charged particles from a surface, and the reentrainment of charged particles. A decrease in the experimental collection efficiency for large particle diameters (≥0.5?μm), as compared to the theoretical prediction, was interpreted as the reentrainment of particles. The size-resolved dust reentrainment fluxes from the collecting electrode were evaluated in two limiting cases, considering that either the reentrained particles are not charged or that they are charged as the particles in the deposition flux. Dimensional analysis is applied to these results, introducing the wall friction velocity as a universal parameter that determines the flow character. In general, the particles with diameters <5?μm and >5?μm exhibit different reentrainment behavior.

Copyright © 2018 American Association for Aerosol Research     

Cationic latex interaction with pulp fibers. I. Deposition of styrene-butadiene latex having quaternized amino groups

Four experimental latexes of different styrene-butadiene ratios stabilized with quaternized amino groups were employed in deposition studies on unbeaten kraft pulp fibers. The attraction between the oppositely charged latex and fibers facilitates a ready latex deposition in the pH region between the points of zero charge of the latex and of the fibers. The rate of deposition appears to be controlled by latex diffusion and convection up to the fiber surface. The distribution of latex particles deposited on the fiber surface is related to the butadiene content and the latex stability. Polystyrene latex is the most stable and covers the fibers uniformly as individual particles. With increased butadiene content, the coagulation region of the latex is more extended and the tendency to deposit as aggregates is promoted.     

Implementation of Charged Particles Deposition in Stochastic Lung Model and Calculation of Enhanced Deposition

The experimental studies using hollow lung cast of human tracheobronchial (TB) tree and in-vivo experiments have demonstrated enhanced charged deposition in the lung. The present study was carried out to implement charge particle deposition into the stochastic human lung model and to estimate enhanced deposition for various charged particles at the airway generation level. Enhanced deposition calculations of charged particles are performed by implementing two different efficiency equations derived for the TB and alveolar (Al) region. Deposition fractions of inhaled charged particles are computed by the stochastic airway generation model IDEAL (Inhalation, Deposition and Exhalation of Aerosols in the Lung) for various breathing conditions and particle sizes. Enhanced deposition of charged particles in the Al region is found to be up to five times higher than in the TB region. Enhanced deposition in the TB region is higher under sitting breathing condition than under light exercise breathing condition. The introduction of pause time, during inhalation, increases the probability of increased enhanced deposition up to a certain breath-hold time limit. The calculated enhancement factors (EF) reveals that more than two times higher deposition can be achieved in the lung by the introduction of charged particles during inhalation. By introducing the charged particles during inhalation and by optimizing the flow rate, tidal volume, and particle size, the targeted deposition in the lung is improved for the best therapeutic aerosols utilization. In addition, the unnecessarily high deposition of toxic particles in the sensitive lung regions can be avoided.

Copyright 2012 American Association for Aerosol Research     

Electrochemical preparation and characterization of Ni/SiC compositionally graded multilayered coatings

In our study, Ni/SiC functionally graded coatings have been obtained by electrochemical deposition of silicon carbide microparticles (mean diameter 2 μm) from nickel Watts baths with different concentrations of SiC particles in solution. The SiC particles were characterized by electroacustics technique in order to determine zeta potential and particle size. Moreover, the effect of the concentration of SiC particles in solution on the amount of SiC deposited in the nickel layer was investigated. Further experiments showed that the degree of particle incorporation provoked changes in the texture of the nickel matrix. The characterization of the coatings proved that the Ni/SiC graded composite coatings were bright and compact, presented good adhesion and improved the hardness and wear resistance of pure nickel electrodeposits.     

高湿黏性颗粒在聚四氟乙烯微孔膜滤料表面沉积特性的数值模拟

基于聚四氟乙烯(PTFE)微孔膜滤料扫描电镜(SEM)图像,建立PTFE微孔膜滤料微观结构模型,采用计算流体力学和离散单元法(CFD?DEM)耦合的方法对黏性颗粒在微孔膜滤料表面沉积特性进行模拟,引入液桥力模型,忽略范德华力的作用,统计计算域内颗粒的受力情况,分析了不同表面能条件下3~6 ?m粒径颗粒在微孔膜滤料表面的沉积特性,将模拟结果与黏附效率的经验公式进行对比。结果表明,黏附效率与经验值、颗粒受力与液桥力模型的相对误差均在6%以内,CFD?DEM耦合计算方法可用于模拟不同环境湿度条件下的颗粒沉积;过滤风速、粒径与黏性是影响沉积形态的重要因素,提高过滤风速及增大颗粒粒径与黏性,颗粒更易在滤料表面形成稳定的树突结构,黏附效率及含尘压降增加。环境相对湿度影响两物体间液桥体积,接触力影响颗粒沉积,当增加表面能与液桥体积时,接触力及液桥力均相应增加,根据受力平衡原理,环境相对湿度对颗粒沉积影响很大。     

Electrochemical and AFM study of nickel nucleation mechanisms on vitreous carbon from ammonium sulfate solutions

Reaction and nucleation mechanisms of nickel in ammoniacal solutions have been investigated as a function of nickel concentration, solution pH, deposition potential, temperature and conditioning potential. Electrochemical mechanisms of nickel reduction were found to be pH dependent, while their kinetics was concentration dependent. A surface film formed by anodic oxidation passivates nickel clusters preventing their further oxidation. Nickel nucleation on vitreous carbon, which proceeds according to the progressive nucleation model, shows a large degree of inhibition at both pH 6 and pH 9. Cluster sizes were larger when electrodeposition was carried out from solutions with higher nickel concentrations. The clusters were also larger at more negative deposition potentials and at higher solution pH. Cluster population density increased with the increasing solution temperature. Different activation energies for the nickel-aquo and nickel-ammino complexes calculated from Arrhenius diagram indicate that electroreduction of nickel-ammino complex is energetically more demanding. All electrochemical results were further verified by the atomic force microscopy investigations.     

Growth of nitrogenated fullerene-like carbon on Ni islands by ion beam sputtering

The synthesis and properties of fullerene-like carbon materials containing nitrogen deposited by ion beam sputtering in a high-vacuum chamber are reported. The samples are grown on Si substrate by sequentially depositing a titanium nitride thin film, nanometric nickel particles, and carbon. The carbon nanostructured samples were prepared by sputtering a carbon target in nitrogen and helium-nitrogen atmospheres. The effect of the noble gas on the nanostructure formation is reported. X-ray photoelectron spectroscopy performed in an ultra high-vacuum chamber, attached to the deposition system, reveals the incorporation of nitrogen in the carbon layer coating the nickel particles. Atomic force microscopy shows dome-like shaped structures. Raman spectroscopy and high-resolution transmission electron microscopy show multi-wall graphenes covering the nickel particles. The field emission properties of the structures are reported.     

Electrodeposition of nickel oxide nanoparticles on glassy carbon surfaces: application to the direct electron transfer of tyrosinase

This work describes the performance of a tyrosinase/nickel oxide nanoparticles/glassy carbon (Tyr/NiO NPs/GC) electrode. This electrode was prepared by first applying a NiO NPs electrochemical deposition onto the GC electrode surface and then tyrosinase immobilization was applied to the surface of electrodeposited NiO NPs. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) procedures demonstrated the existence of different NiO NP geometrical structures. These geometrical structures could lead to better immobilization of proteins on their surfaces. The copper containing enzyme tyrosinase successfully achieved electrical contact with the electrode because of the unique structural alignment of tyrosinase enzyme on the nanometer-scale nickel oxide surfaces. This method could be suitable for application to nanofabricated devices facilitating better performance. It was concluded that tyrosinase can be effectively applied to nanometer-scale nickel oxide surfaces.     

Ni—LDPE复合材料的研究

报道了Ni-LDPE复合材料中镍粉含量对材料的导电性及力学性能影响的研究结果。实验表明,在低密度聚乙烯中加入片状镍粉以后,随着镍粉含量的增加,导电性上升,但力学强度先上升后下降。在镍粉体积分数为8％～15％时,电阻率急剧下降,然而力学强度仍然上升,直至达最大值后才急剧下降。这说明,在此期间镍粒子之间巳能充分接近、接触,形成导电通路;但是,如果聚乙烯份量太少,镍粒子被润湿、粘结不充分时,力学强度就会恶化。总之,复合材料的结构对其导电性及力学强度同时产生强烈的影响。     

Electrophoretic deposition of titania nanostructured coatings with different porous patterns

Titania nanostructured coatings with different porous patterns were fabricated by electrophoretic deposition (EPD) in isopropanolic suspension including different concentrations of carbon active (CA) or carbon black (CB) particles as the porogen additives. Finer and negatively charged CA particles were electrostatically adsorbed on the coarser and positively charged titania particles and formed CA-titania particles. While, finer and positively charged titania particles were electrostatically adsorbed on the coarser and negatively charged CB particles to form titania-CB particles. Both CA-titania and titania-CB particles had the net positive surface charge and so cathodic EPD was applicable. EPD was carried out at optimized conditions of 60?V and 10?s. Thermogravimetry (TG) analysis showed that CA and CB burn out between 450?°C and 600?°C. The higher the carbon content in the suspension the higher was their content in the coating. The coatings were characterized by SEM, AFM, adhesion strength and bioactivity tests. Even coatings with interconnected fine pores and low roughnesses were obtained after the heat treatment of CA-titania coatings. While, rough coatings with coarse and isolated pores were obtained after the heat treatment of titania-CB coatings. The porosity of coating increased as the carbon content increased in the suspension. The hydroxyapatite layer grew on the coatings after their soaking in simulated body fluid for 1week at 37.5?±?1.5?°C.