Electrochemical deposition of zinc–polystyrene composites in the presence of surfactants

The electrochemical codeposition of polystyrene particles and zinc on a rotating cylinder electrode was investigated. Rheological measurements indicate strong aggregation of the PS particles in the zinc deposition electrolyte. Addition of cetylpyridinium chloride, a cationic surfactant, prevents aggregation and enhances polystyrene codeposition. Other surfactants also increase suspension stability, but diminish polystyrene codeposition, irrespective of their charge. Hence, the surfactant charge does not affect polystyrene codeposition. The variation of polystyrene incorporation with the amount of suspended polystyrene, current density and electrode rotation speed signifies that polystyrene codeposition with zinc is determined by the competition between particle removal forces and particle adhesion forces at the cathode surface. The effect of the surfactants can be related to changes in surface roughness of zinc due to surfactant adsorbed on the electrode. Cetylpyridinium chloride behaves differently from the other surfactants, because it is reduced at the cathode.     

Zn-Ni合金共沉积影响机理的拉曼光谱研究

首次利用现场表面增强拉曼光谱研究了Zn-Ni合金共沉积的机理。通过研究Ni电极在NiCl2溶液与纯水中的拉曼光谱、Ni电极与Au电极在KCl溶液中的拉曼光谱以及这2种电极在NiCl2溶液中现场电沉积的拉曼光谱,并根据前人提出的理论,得出如下结论:Zn-Ni合金共沉积中存在着较易在电极表面放电的NiClad,使Ni沉积的过电位降低,促进了Ni的沉积,导致Zn的异常共沉积。     

Electrochemical investigation of the codeposition of SiC and SiO2 particles with nickel

The use of electrochemical impedance spectroscopy (EIS) for the in situ control of the electrolytic codeposition of Ni/SiO₂ and Ni/SiC was investigated. An attempt was made to clarify why silica particles hardly codeposit in comparison to silicon carbide particles. It was found that the presence of SiO₂ and SiC particles influences the metal deposition process in different ways. SiC particles that are being embedded in the growing metal layer cause an apparent decrease in the electrode surface area, probably due to blocking off a part of the surface by partly engulfed particles. In the case of SiO₂ particles, which embed in the metal matrix to a very limited extent, no blocking was observed. It was found that the presence of particles in the solution causes an apparent increase in the electrode surface area, probably due to increased surface roughness.     

Co-electrodeposition of inorganic fullerene (IF-WS2) nano-particles with cobalt from a gluconate bath with anionic and cationic surfactants

The codeposition of IF-WS₂ particles (130 nm diameter) in a cobalt matrix has been investigated. The influence of cobalt content and anionic and cationic surfactants on composite coatings produced using direct current (DC) and pulse reverse plating (PRP) are described. The coatings were assessed by XRD, SEM and EDX. The cationic surfactant promoted particle encapsulation and high oxygen content in DC coatings, whilst anionic surfactants do not offer controlled particle codeposition. Improved particle content and distributions were obtained by PRP, on the high cobalt bath containing anionic surfactant. The particle content was optimised by fixing the anodic cycle time t_a, and varying the cathodic cycle time, t_c. Sound coatings with a high percentage (11 vol.%) of particles were produced at t_c of 60 s. This was encouraged by electrophoretic attraction of particles in the anodic phase and then encapsulation during the cathodic phase of the cycle.     

Classification of submicron Ni particles by heterocoagulation

In this work, the size classification of a mixture of submicron and micron size Ni particles dispersed in aqueous solution was investigated. The suspension of Ni particles was allowed to flow, under laminar condition, through a burette filled with an adhesion medium (i.e. substrate). The difference between zeta potentials of larger particles and adhesion medium created a base for the heterocoagulation. Thus, the larger particles move towards the medium assisted by the Saffman lift force and are attracted to its surface. The finer particles, on the other hand, flow off the burette and were collected as a separate fraction. This phenomenon was then explained by numerical simulating the particle's motion and showing that a stronger Saffman lift force will act in the direction of the substrate only for large particles, leaving the smaller ones unaffected as they sediment out.     

Deposition of magnetite particles from flowing suspensions under flow‐boiling and single‐phase forced‐convective heat transfer

The deposition rate of colloidal magnetite particles was measured under both single‐phase forced‐convective and flow‐boiling conditions. All measurements were made at alkaline pH where both the heat transfer surface and the surface of the magnetite particles appear to be negatively charged. For single‐phase forced convection, the deposition rate constant is lower than the mass transfer coefficient for colloidal particles, and the difference is attributed to the force of repulsion between the negatively charged surfaces of the particle and substrate. The deposition rate measured under flow‐boiling conditions is lower than that reported for the deposition of colloidal particles at neutral pH. The difference is, again, attributed to the force of repulsion between the particle and substrate. Particle removal rates were significantly lower than deposition rates; analysis using the theory of turbulent bursts suggests a removal efficiency of only 10^?9% for each turbulent burst. The low removal efficiency is consistent with the particle diameter being significantly smaller than the thickness of the laminar sublayer in these tests.     

Soil deposition on shrink-resist-treated wool fabrics in the presence of anionic and non-ionic surfactants

The deposition behaviour of carbon black on shrink-resist-treated wool fabric, and on untreated wool, in the presence of different mixtures of anionic and non-ionic surfactants has been investigated. Two types of surfactant mixtures were studied; sodium dodecylbenzenesulphonate and sodium dioctylsulphosuccinate were used as anionic surfactants and Triton X-100 as a non-ionic surfactant. An electrokinetic study was also carried out, under similar conditions; the zeta potential was obtained, which was related to the amount of deposition found. From these zeta potential measurements the surface charge density was determined.     

Electrochemical aspects of the codeposition of gold and copper with inert particles

In the present paper, data on the codeposition of fine Al₂O₃ particles with copper from an acidified copper sulphate bath and on the codeposition of Au-Al₂O₃ from a gold cyanide bath are compared. Based on these results, it is shown that the mechanism of codeposition of inert particles is similar in both systems. The reduction of ions adsorbed on alumina particles is the rate-determining step. The rate of codeposition is further dependent on the mass transport to the electrode and on the applied voltage. Based on the information gained from these experiments on the electrolytic codeposition of inert particles with a metal, the electrolytic deposition process of the pure metal and the incorporation of foreign ionic species in such an electrolytic deposit are discussed.     

Axial Equilibrium Distance and Positioning of Particles in a Laminar Tube Flow

Particle transport in a laminar tube flow at low Reynolds numbers leads to accumulation of particles at specific equilibrium radii. The equilibrium radius depends on the particle size. Small particles find their equilibrium radius near the wall and large particles near the tube axis. During their radial migration to the equilibrium position, the particles move in axial direction with the flow. In an experimental setup, the axial equilibrium distance is measurement for several tube Reynolds numbers. The axial equilibrium distance is the distance a particle migrates in the flow direction, until it reaches its radial equilibrium position. The results are compared with CFD‐simulations of single particle movement in a laminar tube flow.     

温度梯度场内可吸入颗粒物运动特性及热泳沉积

对温度梯度场内垂直管中可吸入颗粒物在湍流工况下的运动特性和热泳沉积规律进行了实验研究,使用颗粒动态分析仪（PDA）在线测量了颗粒物在管道截面上的速度和浓度分布。重点研究了主流与水冷壁面的温差对粒径范围0～2.5 μm颗粒（PM2.5）的运动和沉积的影响,得到其沉积效率。结果表明,湍流扩散作用使颗粒在近壁面富集,而热泳力是PM2.5在冷壁面上发生沉积的最主要因素。得到了PM2.5热泳沉积的半经验公式,计算值与实验结果较为接近。     

Thermophoretic Deposition of Particles in Laminar and Turbulent Tube Flows

Thermophoretic deposition of aerosol particles (particle diameter ranges from 0.038 to 0.498 μm) was measured in a tube (1.18 m long, 0.43 cm inner diameter, stainless steel tube) using monodisperse NaCl test particles under laminar and turbulent flow conditions. In the previous study by Romay et al., theoretical thermophoretic deposition efficiencies in turbulent flow regime do not agree well with the experimental data. In this study, particle deposition efficiencies due to other deposition mechanisms such as electrostatic deposition for particles in Boltzmann charge equilibrium and laminar and turbulent diffusions were carefully assessed so that the deposition due to thermophoresis alone could be measured accurately. As a result, the semiempirical equation developed by Lin and Tsai in laminar flow regime and the theoretical equation of Romay et al. in turbulent flow regime are found to fit the experimental data of thermophoretic deposition efficiency very well with the differences of less than 1.0% in both flow regimes. It is also found that Talbot's formula for the thermophoretic coefficient is accurate while Waldmann's free molecular formula is only applicable when Kn is greater than about 3.0.     

Migration and Deposition of Submicron Particles in Crossflow Microfiltration

Abstract

The migration and deposition of submicron particles in laminar crossflow microfiltration is simulated by integrating the Langevin equation. The effects of operating conditions on the particle trajectories are discussed. It is found that the Brownian motion of particles plays an important role in particle migration under a smaller crossflow velocity of suspension or a smaller filtration rate. Based on the simulated trajectories of particles, the transported flux of particles arriving at the membrane surface can be estimated. The particle flux increases with an increase of filtration rate and with a decrease of particle diameter; however, the effect of crossflow velocity on the particle flux is not obvious. The forces exerted on particles are analyzed to estimate the probability of particle deposition on the membrane surface. The probability of particle deposition increases with an increase of filtration rate, with a decrease of crossflow velocity, with a decrease of particle diameter, or with an increase of zeta potential on the particle surfaces. The simulated results of packing structures of particles on the membrane surface at the initial stage of filtration show that a looser packing can be found under a larger crossflow velocity, a smaller filtration rate, or a smaller diameter of filtered particles. Crossflow micro-filtration experiments are carried out to demonstrate the reliability of the proposed theory. The deviation between the predicted and experimental data of filtration rate at the initial period of filtration is less than 10% when the Reynolds number of the suspension flow ranges from 100 to 500.     

Particle deposition velocity onto a face-up flat surface in a laminar parallel flow considering Brownian diffusion and gravitational settling

The Gaussian Diffusion Sphere Model (GDSM) was developed and improved to reflect the effects of gravitational settling as well as Brownian diffusion of aerosol particles on deposition velocity onto a face-up flat surface in a laminar parallel flow. The model improvement also includes the applicability of the GDSM to a flat surface of any shape with finite dimensions. When deposition velocity for a face-up circular flat plate of 45 cm diameter, representing e.g. a semiconductor wafer in a laminar parallel flow, was calculated by the GDSM and compared with that by the theory of Liu and Ahn (1987). Particle deposition on semiconductor wafers. Aerosol Science and Technology, 6, 215–224, the agreement was good for the tested particle sizes ranging 0.003–1 μm and free stream velocities ranging 5–500 cm/s. Based on this result, deposition velocities onto the face-up square flat plates with different orientations in a laminar parallel flow, simulating e.g. photomasks, were predicted.     

High-Resolution Analysis of Particle Deposition and Resuspension in Turbulent Channel Flow

Particle deposition and resuspension during turbulent flow were investigated using a rectangular channel with glass side walls. Micrometer-sized alumina particles were used in the experiments. Particle behavior in the rectangular channel was observed through a high-speed microscope camera with a resolution of 0.3 μm and a speed of 87,600 fps, and particle deposition and resuspension fluxes were quantified using digital image analysis. The experimental results showed that particle resuspension was caused by the collision of airborne particles with those deposited on the surface. The resuspension flux was found to be correlated with the deposition flux. Furthermore, the average residence time between particle deposition and resuspension was several tens of milliseconds, which was very short but much longer than the contact time at the collision. Additionally, the residence time decreased as the particle diameter increased.

Copyright 2015 American Association for Aerosol Research     

氨基磺酸体系Co-Ni合金电化学共沉积行为及动力学机理

通过稳态阴极极化和电化学交流阻抗(EIS)等方法,研究了在不同钴镍金属离子比例的氨基磺酸电解液中,Co-Ni合金的电化学共沉积行为。结果表明在氨基磺酸体系中,导致Co-Ni合金异常共沉积行为的原因和在硫酸盐,或氯化物体系中的不同。不是由于Co^2 抑制了Ni的沉积,而是由于NH2SO3^-作为双齿配体形成的异核络合物在电极表面吸附,阻滞了镍离子的还原过程。并且以晶体场理论为基础解释了Co^2 和NH2SO3^-形成的高自旋络合物,比Ni^2 所形成的络合物具有较高的晶体场稳定化能(CFSE),容易分解。因此吸附在电极表面的氨基磺酸根离子对Co2^2 沉积的阻滞作用小于对Ni2^ 的。这样就导致了在氨基磺酸电解液体系中Co^2 的优先沉积。阳极线性扫描曲线表明．钴镍合金中镍含量越高,沉积层在热力学上越稳定,耐蚀性也越好。同时通过EIS的测试,利用等效电路的分析方法和交流阻抗谱解析理论,提出了氨基磺酸电解液中Co-Ni合金共沉积的动力学机理,较好地解释了实验结果。     

Reactivity and codeposition of Co3O4 powderswith nickel in a Watts bath

The effect of the physico-chemical characteristics of Co3O4 powders on their reactivity in solution and their incorporation in a nickel matrix has been investigated in a Watts nickel plating bath. The results showed that the surface area of the powder present in suspension not only catalyses the adsorption or desorption phenomena occurring at the particle/solution interface but also has a significant effect on the incorporation of the particles into the nickel matrix. It has been found that the use of Co3O4 with high specific surface area (40m2g–1) significantly limits the growth rate of the electrodeposited composite coatings. Furthermore, it has been shown that the codeposition of these more reactive particles leads to significant changes in the microstructure and texture of the nickel matrix. Finally, it has been found that, according to their specific surface areas, the amount of H+, Ni2+ and Ni[B(OH)4]+ ions adsorbed on the Co3O4 oxide surfaces and the quantities of particles codeposited can vary considerably.     

可吸入颗粒物在管内湍流流动时的动力学特性及热泳沉积

The kinematical characteristics and thermophoretic deposition of inhalable particles with the diameters of 0-2.5μm （hereafter referred to as PM2.5） suspended in turbulent air flow in a rectangular duct with temperature distribution were experimentally studied. Particle dynamics analyzer （PDA） was used for the on-line measurement of particle motion and particle concentration distribution in the cross-sections of the duct. The influences of the parameters such as the ratio of the bulk air temperature to the cold wall temperature and the air flow rate in the duct on the kinematical characteristics and the deposition efficiencies of PM2.5 were investigated. The experimental re- sults show that the deposition efficiencies of PM2.5 mainly depend on the temperature difference between the air and the cold wail, wffile the air flow rate and the particlecon~centration almost affect hardly tile clep0si-tion-effi ciency. The radial force thermophoresis to push PM2.5 to the cold wail is found the key factor for PM2.5 deposition.Based on the experimental results, an empirical modified Romay correlation for the calculation of thermophoretic deposition efficiency of PM2.5 is presenlext. The empirical correlation agrees reasonably well with the experimental data.     

Effect of particle size on the co-deposition of diamond with nickel in presence of a redox-active surfactant and mechanical property of the coatings

Particle reinforced Ni/diamond composite coatings containing various amount of the reinforcement (up to 57.6 vol.%) were prepared by the electroplating technique using a Watt's nickel bath in which the diamond particles were dispersed with the aid of a redox-active surfactant containing an azobenzene moiety. Five different sizes of diamond particles with the mean diameter ranging from 0.21 to 2.91 μm were used to investigate the effect of the particle size in their co-deposition with nickel under the influence of the above redox-active surfactant and the mechanical property especially the micro-hardness and the abrasion wear of the composite coatings reinforced with various amount of the diamond particles was studied. Among all, the smallest diamond particles exhibited the highest particle co-deposition of 57.6 vol.%. The micro-hardness and the wear resistance of this composite with the 57.6 vol.% diamond were about 4.5 and 14 times, respectively, than that of a nickel coating without any reinforcement.     

Effect of some operating variables on the characteristics of electrodeposited Cu?Ni alloys with and without α-Al2O3 and TiO2 inert particles

A study was carried out on the electrodeposition of Cu Ni alloys containing inert (α-Al₂O₃ and TiO₂) particles from a selected citrate bath. The cathodic polarization curves show that alloy deposition occurs at more noble potentials relative to either of the two parent metals and this indicated the formation of a solid solution. The addition of the inert particles into the selected bath led to a polarization-increasing effect and this increased with increases in the size and concentration of the particles in the bath. An explanation of the mechanism of codeposition of the inert particles with the alloy has been presented. On controlling the bath composition, Cu Ni alloys containing 11–40% of nickel could be deposited. The effect of the operating variables such as the concentration of the metal ions in the bath, pH and current density on the alloy composition indicated that the formation of the Cu Ni alloy belongs to the regular alloy deposition system. The current efficiency of the alloy deposition is relatively lower than for either of the two parent metals, from similar baths, and ranges between 76 and 84%. The microhardness of the deposited Cu Ni alloy improved from 170 to 248 kfg mm⁻² as a result of codeposition of 1–2% of the inert particles. A direct correlation between the surface morphology of the deposited Cu Ni alloy, as revealed by SEM, and its microhardness could be detected. X-ray diffraction studies confirmed the dispersion of the α-Al₂O₃ and TiO₂ phases in the Cu Ni alloy phase.     

Hardening effect induced by incorporation of SiC particles in nickel electrodeposits

Pure Ni and nickel matrix composite electrocoatings containing micron- and nano-SiC particles (1 μm and 20 nm respectively) were produced under direct and pulse current conditions from an additive-free Watts type bath. The effect of the particle size, codeposition percentage of SiC and type of imposed current on the microhardness as well as on the microstructure of the electrodeposits were investigated. Ni/SiC composite deposits prepared under either direct or pulse current conditions exhibited a considerable strengthening effect with respect to pure Ni coatings. The improved hardness of composite coatings was associated to specific structural modifications of Ni crystallites provoked by the adsorption of H⁺ on the surface of SiC particles, thus leading to a (211) texture mode of Ni crystal growth. Pulse electrodeposition significantly improved the hardness of the Ni/SiC composite coatings, especially at low duty cycles, in which grain refinement and higher SiC incorporation (vol. %) was achieved. The enhanced hardness of Ni/nano-SiC deposits, as compared to Ni/micron-SiC composites, was attributed to the increasing values of the number density of embedded SiC particles in the nickel matrix with decreasing particle size. In addition, the observed hardening effects of the SiC particles might be associated to the different embedding mechanisms of the particles, which could be characterized as inter-crystalline for micron-SiC and partially intra-crystalline for nano-SiC particles.