Effects of additive NaI on electrodeposition of Al coatings in AlCl3-NaCl-KCl molten salts

Effects of NaI as an additive on electrodeposition of Al coatings in AlCl₃-NaCl-KCl(80-10-10 wt-%)molten salts electrolyte at 150°C were investigated by means of cyclic voltammetry,chronopotentiometry,scanning electron microscopy and X-ray diffraction(XRD).Results reveal that addition of NaI in the electrolyte intensifies cathodic polarization,inhibits growth of Al deposits and increases number density of charged particles.The electrodeposition of Al coatings in the AlCl₃-NaCl-KCl molten salts electrolyte proceeds via three-dimensional instantaneous nucleation which however exhibits irrelevance with NaI.Galvanostatic deposition results indicate that NaI could facilitate the formation of uniform Al deposits.A compact coating consisting of Al deposits with an average particle size of 3μm was obtained at a current density of 50 mA?cm^?2 in AlCl₃-NaCl-KCl molten salts electrolyte with 10 wt-%NaI.XRD analysis confirmed that NaI could contribute to the formation of Al coating with a preferred crystallographic orientation along(220)plane.     

混凝耦合多孔陶瓷膜净化河水简

Membrane filtration technology combined with coagulation is widely used to purify river water. In this study, micro filtration （MF） and ultrafiltration （UF） ceramic membranes were combined with coagulation to treat local river water located at Xinghua, Jiangsu province, China. The operation parameters, fouling mechanism and pilot-scale tests were investigated. The results show that the pore size of membrane has small effect on the pseudo-steady flux for dead-end filtration, and the increase of flux in MF process is more than that in UF process for cross-flow filtration with the same increase of cross-flow velocity. The membrane pore size has little influence on the water quality. The analysis on membrane fouling mechanism shows that the cake filtrationhas significant in fluence on the pseudo-steady flux and water quality for the membrane with pore size of 50, 200 and 500 nm. For the membrane with pore size of 200 nm and backwashing employed in our pilot study, a constant flux of 150 L-m^-2-h^-1 was reached during stable operation, with the removal efficiency of turbidity, total organic carbon （TOC） and UV254 higher than 99%, 45% and 48%, respectively. The study demonstrates that coagulation-porous ceramic membrane hybrid process is a reliable method for river water purification.     

碳酸钙在流动过冷沸腾条件下的结垢机理研究

Fouling of heat transfer surfaces during subcooled flow boiling is a frequent engineering problem in process industries. It has been generally observed that the deposits in such industrial systems consist mainly of calcium carbonate （CaCO3）, which has inverse solubility characteristics. This investigation focused on the mechanism to control deposition and the morphology of crystalline deposits. A series of experiments were carried out at different surface and bulk temperatures, fluid velocities and salt ion concentrations. It is shown that the deposition rate is controlled by different mechanism in the range of experimental parameters, depending on salt ion concentration. At higher ion concentration, the fouling rate increases linearly with surface temperature and the effect of flow velocity on deposition rate is quite strong, suggesting that mass diffusion controls the fouling process. On the contrary, at lower ion concentration, the fouling rate increases exponentially with surface temperature and is independent of the velocity, illustrating that surface reaction controls the fouling process. By analysis of the morphology of scale, two types of crystal （calcite and aragonite） are formed. The lower the temperature and ion concentration, the longer the induction period and the higher the percentage of calcite nreciDitated.     

镁合金化学镀镍层的生长过程

The initial nickel deposition for the direct electroless nickel plating on non-catalytically active magnesium alloy is critical. The surface morphology and composition of the initial nickel plating coating are obtained by means of the scanning electron microscopy (SEM) and the energy dispersive X-ray (EDS). In addition, the mass gain/loss in the initial nickel deposition process was measured by using the electrobalance. The results showed that the MgO coating was gradually corroded by the plating solution, at the same time, MgF2 produced by F , H and MgO was deposited on the substrate during the initial electroless plating process. The nickel of the initial electroless plating was mostly growing on the boundary between the MgF2 coating and the MgO coating of the activation substrate, and then came to two sides. After that, the Ni-P coating growth rate to cover with the MgF2 coating was prior to the MgO coating. The electroless plating was in company with the substrate corrosion, but the electroless plating rate catalyzed by the exchanged nickel was more than the substrate corrosion rate.     

WC@TiO2核壳结构纳米复合材料制备与电催特征

Monotungsten carbide and titania nanocomposite with core-shell(WC@TiO2)structure was prepared by a new approach of spray drying and reduction-carbonization reaction,with titania nanopowder and ammonium metatungstate as precursors,methane as carbon source,and hydrogen as reduction gas.The sample was characterized by X-ray diffraction,scanning electron microscope,high resolution transmission electron microscope and X-ray energy dispersion spectroscopy.The results show that its crystal phase is composed of brookite,tungsten and monotungsten carbide.The morphology of the sample particle is irregular sphere-like,with a diameter smaller than 100 nm.Its chemical components are titanium,tungsten,carbon and oxygen.Monotungsten carbide nanoparticles lie on the surface of titania core and form an incomplete shell around titania core in the nanocomposite.The measurement with a microelectrode system of three electrodes shows that the sample is electrocatalytic active to nitrophenol in basic solution at room temperature.Its peak potential is at0.988 V(vs saturated calomel electrode (SCE)),which is more negative than the peak potential,0.817 V(vs SCE),of mesoporous monotungsten carbide, and its peak current is 8.809μA,which is higher than the peak current,4.058μA,of mesoporous monotungsten carbide.The hydrogen generation potential of the sample is at1.199 V(vs SCE),which is more negative than that of pure nanosized monotungsten carbide at1.100 V(vs SCE).These results show that the presence of titania in the sample can lower the peak potential of nitrophenol electrocatalysis and its hydrogen generation potential,and increase its peak current of nitrophenol electrocatalysis in basic solution at room temperature.This indicates a synergistic effect of titania and monotungsten carbide in electrocatalysis.     

机械法合成BN纳米管

Boron nitride nanotubes （BN-NTs） with pure hexagonal BN phase have been synthesized by heating ball-milled boron powders in flowing ammonia gas at a temperature of 1200℃. The as-synthesized products were characterized by X-ray powder diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, and electron energy loss spectroscopy （EELS）. The diameters of nanotubes are in the rage of 40-120nm and the lengths are more than 10μm. EELS result identifies that the ratio of boron and nitrogen is almost 1：1 The growth temperature is a crucial growth parameter in controlling the structure and crystalline of BN-NTs. The nanotubes grown at 1100℃ possesses of a bamboo-like structure, while as the temperature increased to 1200℃, most of the nanotubes exhibited a cylindrical structure. In addition, changing the heating time can control the size of the nanotubes. The gas atmosphere has influence on the yield of BN-NTs during heating process. When heating atmosphere was replaced by nitrogen, the yield of nanotubes was remarkably decreased.     

铝在路易斯酸性1-烯丙基-3甲基米唑氯铝酸离子液体中的低温电沉积(英文)

Lewis acidic 1-allyl-3-methylimidazolium chloroaluminate ionic liquids were used as promising elec-trolytes in the low-temperature electrodeposition of aluminium.Systematic studies on deposition process have been performed by cyclic voltammetry and chronoamperometry.The surface morphology and X-ray diffraction(XRD) patterns of deposits prepared at different experimental conditions were also investigated.It was shown that the nu-cleation density and growth rate of crystallites had a great effect on the structure of aluminium deposited.The crys-tallographic orientation of deposits was mainly influenced by temperature and current density.Smooth,dense and well adherent aluminium coatings were obtained on copper substrates at 10-25 mA?cm?2 and 313.2-353.2 K.More-over,the current efficiency of deposition and purity of aluminium have been significantly improved,demonstrating that the ionic liquids tested have a prospectful potential in electroplating and electrorefining of aluminium.     

羟基氧化镍的电解制备，结构表征和电化学性能研究

NiOOH was prepared by one-step electrolysis of spherical Ni（OH）2 and the effects of electrolysis parameters were examined. The highly pure NiOOH was obtained after electrolysis at a current density of 60mA.g^-1 and 30℃ with anodic potential controlled in the range of 1.73-1.85V （vs. Zn/ZnO） for 360min. The NiOOH samriles were characterized bv X-ray oowder diffraction （XRD） and scanning electron microscope （SEM） analysis.Resuits indicate that the electrolysis product is spherical NiOOH doped with graphite. Charge and discharge tests show that the prepared NiOOH offers a discharge capacity of over 270mAh·g^-1 at current density of 30mA·g^-1 and can be directly used as cathode material of alkaline Zn/NiOOH batteries. Galvanostatic charge/discharge and cyclic voltammetry （CV） tests reveal good cycling reversibility, of the NiOOH electrode.     

A simple plasma reduction for synthesis of Au and Pd nanoparticles at room temperature☆

A simple and fast plasma reduction method is developed for synthesis of Au and Pd metal nanoparticles. The scanning electron microscopy (SEM) analysis indicates a formation of aggregates of Au and Pd nanoparticles with branched structure. The transmission electron microscopy (TEM) image shows that the inclusive nanopar-ticles are al about 5 nm in size. Compared to conventional hydrogen reduction method, plasma method inhibits the agglomeration of metal particles. The room temperature operation is very helpful to limit the nanoparticle size. Most interestingly, plasma reduction produces more flattened metal particles. This plasma reduction does not require the use of any hazardous reducing chemicals, showing the great potential for the fabrication of noble metal nanoparticles.     

Preparation and water sorption properties of novel SiO2-LiBr microcapsules for water-retaining pavement

Novel SiO_2-LiBr microcapsules for water-retaining pavement were prepared and firstly characterized by scanning electron microscope(SEM), particle size analysis, and Fourier transform infrared spectroscopy(FT-IR). The water vapor sorption and desorption of the formulated microcapsules was then experimentally studied using dynamic vapor sorption(DVS), with the results fitted to three kinds of adsorption kinetics models. In addition, the specific surface area(SSA) was also calculated based on BET theory;and the thermal performance was investigated by laser flash analysis(LFA). Experimental results show a change of 103% in mass of the microcapsule sample under 90% relative humidity(RH) at 30 ℃ after water vapor sorption. The fitting of results indicates that the adsorption process is mainly governed by the intra-particle diffusion mechanism, followed by the pseudo-first-order adsorption process. In comparison with most conventional pavement materials, it is found that the SSA of the formulated microcapsules is much larger while the thermal conductivity is lower. The unique properties of the formulated SiO_2-LiBr microcapsules have significant potential to take the edge off the urban heat island effect and reduce rutting when applied to water-retaining pavement materials.     

Electrodeposition behavior of nickel in the water- and air-stable 1-ethyl-3-methylimidazolium-dicyanamide room-temperature ionic liquid

The electrodeposition behavior of nickel was investigated at glassy carbon and polycrystalline copper electrodes in the 1-ethyl-3-methylimidazolium dicyanamide (EMI-DCA) room-temperature ionic liquid. Amperometric titration experiments suggest that Ni(II) reacted with DCA⁻ anions forming [Ni(DCA)₄]²⁻ complex anion, which could be reduced to nickel metal via a single-step electron transfer process. However, the anodic dissolution of the nickel deposits was sluggish. The electrodeposition of nickel proceeds via three-dimensional progressive nucleation with diffusion-controlled growth on both glassy and copper substrates. Scanning electron microscopy images of the nickel deposits indicated that the morphology of the nickel electrodeposits is dependent on the deposition potential. Atomic force microscopy topography illustrated that the roughness of the nickel-deposited surface increased with decreasing deposition potential. The crystalline nature of the nickel deposits was revealed by powder X-ray diffraction spectroscopy results which indicated that the grains size of the nickel deposits decreased with decreasing deposition potential.     

Electrodeposition of bismuth from nitric acid electrolyte

The electrodeposition of Bi from acidic nitrate solution was examined. Bismuth deposition was determined to be quasi-reversible on Au, with a current efficiency of 100%, based on integration of deposition and stripping voltammetric waves. No interference from nitrate reduction was found on Bi and Au, whereas nitrate reduction occurred on W and Cu electrodes. Analysis of current-time transients clearly shows nucleation on Au to be instantaneous. Field emission SEM revealed nodular deposits with moderate surface roughness. Nodule size varied from 1 to 5 μm depending on deposition potential and deposit thickness. X-ray diffraction (XRD) patterns for all deposits were indexed to rhombohedral bismuth. The deposits showed fairly strong (0 1 2) crystallographic texture at high deposition overpotentials.     

Electrodeposition behavior of nickel and nickel-zinc alloys from the zinc chloride-1-ethyl-3-methylimidazolium chloride low temperature molten salt

The electrodeposition of nickel and nickel-zinc alloys was investigated at polycrystalline tungsten electrode in the zinc chloride-1-ethyl-3-methylimidazolium chloride molten salt. Although nickel(II) chloride dissolved easily into the pure chloride-rich 1-ethyl-3-methylimidazolium chloride ionic melt, metallic nickel could not be obtained by electrochemical reduction of this solution. The addition of zinc chloride to this solution shifted the reduction of nickel(II) to more positive potential making the electrodeposition of nickel possible. The electrodeposition of nickel, however, requires an overpotential driven nucleation process. Dense and compact nickel deposits with good adherence could be prepared by controlling the deposition potential. X-ray powder diffraction measurements indicated the presence of crystalline nickel deposits. Non-anomalous electrodeposition of nickel-zinc alloys was achieved through the underpotential deposition of zinc on the deposited nickel at a potential more negative than that of the deposition of nickel. X-ray powder diffraction and energy-dispersive spectrometry measurements of the electrodeposits indicated that the composition and the phase types of the nickel-zinc alloys are dependent on the deposition potential. For the Ni-Zn alloy deposits prepared by underpotential deposition of Zn on Ni, the Zn content in the Ni-Zn was always less than 50 atom%.     

Electrochemical studies of Zn–Ni alloy coatings from acid chloride bath

The electrodeposition of Zn–Ni alloy from chloride bath was carried out in presence of condensation product (CP) formed between vanillin and hexamine. The investigation of electrodeposition and nucleation process was carried out on glassy carbon electrode using cyclic voltammetric and chronoamperometric techniques. During the anodic scan of cyclic voltammetry, three anodic peaks were observed corresponding to the dissolution of zinc and nickel from different phases of Zn–Ni alloy. The model of Scharifker and Hills was used to analyze the current transients and it revealed that Zn–Ni electrocrystallization process in the presence of CP, under the studied conditions, is governed by three-dimensional nucleation process controlled by diffusion. In presence of CP, the results indicated that nucleation process changes from progressive to instantaneous when the deposition potential becomes more negative. The phase structure and surface morphology of the deposits were characterized by means of X-ray diffraction analysis and Scanning electron microscopy, respectively.     

Electrodeposition of antimony in a water-stable 1-ethyl-3-methylimidazolium chloride tetrafluoroborate room temperature ionic liquid

The electrochemistry and electrodeposition of antimony were investigated on glassy carbon and nickel electrodes in a basic 1-ethyl-3-methylimidazolium chloride-tetrafluoroborate room temperature ionic liquid. Cyclic voltammetry results show that Sb(III) may be either oxidized to Sb(V) via a quasi-reversible charge-transfer process or reduced to Sb metal. Diffusion coefficients for both Sb(III) and Sb(V) species were calculated from rotating disc voltammetric data. Analysis of chronoamperometric current–time transients indicates that the electrodeposition of Sb on glassy carbon proceeded via progressive three-dimensional nucleation with diffusion-controlled growth of the nuclei. Raising the deposition temperature results in decreased average radius of the individual nuclei. Dense deposits can be obtained within a deposition temperature range between 30 to 120 °C. Scanning electron microscopy revealed dramatic changes in the surface morphology of antimony electrodeposits as a function of deposition temperature; deposits obtained at 30 °C had a nodular appearance whereas those obtained at 80 and 120 °C consisted of evenly distributed fine polygonal crystals.     

Nucleation and crystal growth in gold electrodeposition from acid solution Part I: Soft gold

The initial stages of gold electrodeposition on a gold electrode were studied in a proprietary bath (Renovel N) using linear sweep voltammetry and chronoamperometry. Tafel plots with two different slopes were obtained, indicating that the mechanism for gold deposition depends on potential. An inhibition phenomenon was observed during gold electrocrystallization. Experimental current-time transients were analysed using nonlinear least-squares approximations by various models of nucleation and crystal growth. The electrodeposition mechanism changes from three-dimensional progressive at lower overpotentials to three-dimensional instantaneous at higher overpotentials. Moreover, additional two-dimensional progressive or a secondary three-dimensional progressive processes take place in certain potential ranges. It was shown that the outward growth rate of the substrate's base plane displays a linear Tafel relationship whereas the vertical growth rate of gold crystals decreases at more negative potentials due to an inhibition process.     

Electrocrystallization of Au nanoparticles on glassy carbon from HClO4 solution containing [AuCl4]

The mechanism and kinetics of electrocrystallization of Au nanoparticles on glassy carbon (GC) were investigated in the system GC/1 mM KAuCl₄ + 0.1 M HClO₄. Experimental results show that the gold electrodeposition follows the so-called Volmer-Weber growth mechanism involving formation and growth of 3D Au nanoparticles on an unmodified GC substrate. The analysis of current transients shows that at relatively positive electrode potentials (E ≥ 0.84 V) the deposition kinetics corresponds to the theoretical model for progressive nucleation and diffusion-controlled 3D growth of Au nanoparticles. The potential dependence of the nucleation rate extracted from the current transients is in agreement with the atomistic theory of nucleation. At sufficiently negative electrode potentials (E ≤ 0.64 V) the nucleation frequency becomes very high and the nucleation occurs instantaneously. Based on this behaviour is applied a potentiostatic double-pulse routine, which allows controlled electrodeposition of Au nanoparticles with a relatively narrow size distribution.     

Nucleation and crystal growth in gold electrodeposition from acid solution Part II: Hard gold

The mechanism of nucleation and crystal growth of hard gold (Au-Ni) on a gold rotating disc electrode from a proprietary bath (Renovel N) was investigated using linear sweep voltammetry and chronoamperometry. It was shown that two distinct mechanisms in two potential ranges are involved in this process. Experimental current-time transients at more positive potentials were described in terms of three-dimensional progressive nucleation and growth of right-circular cones. Time-independent inhibition of the vertical crystal growth was observed with an increase in negative potential, similar to the soft gold deposition. A modified inhibition model, in which vertical growth rate was assumed to decrease exponentially with time to a constant value, was derived to interpret experimental current-time transients recorded at more negative potentials. The chronoamperometric transients were well described by this model. Potential dependence of initial minima, maxima and final steady-state current was discussed.     

Effect of nickel impurities on zinc electrodeposition

The kinetics of nickel-zinc co-deposition and the effect of nickel on zinc morphology have been studied by means of chemical analysis, X-ray diffraction and SEM observations of cathodic deposits obtained in various experimental conditions, including acid and alkaline baths. It has been shown that nickel ions, even if present in the electrolyte at very low concentrations (1 ppm), do not deposit under mass transport controlled conditions but are dragged by zinc ions whose concentration influences the nickel current. With regard to zinc morphology, it has been observed that nickel reduces the grain size of the zinc crystals formed during the electrodeposition.     

Effect of tartaric acid in the electrodeposition of zinc

The electrodeposition of zinc from sulphate-tartrate baths on a vitreous carbon electrode has been studied. The influence of the tartrate ion on the reduction kinetics of Zn(II) metal ion, and on the mechanism of the electrodeposition process, has been investigated using potentiodynamic and potentiostatic electrochemical techniques and scanning electron microscopy. The voltammetric analysis has shown that the presence of tartrate species in the sulphate bath shifts the reduction potential of Zn(II) to more positive values. A set of equilibria have been proposed to represent the electrochemical process and the influence of pH. From the analysis of the chronoamperometric transients and the SEM images, an instantaneous nucleation with 2D growth at the initial stages has been proposed, and a nucleus density of the order of 10⁹ cm⁻² has been calculated from both techniques. In order to elucidate the correct mechanism of the electrodeposition process the results obtained from chronoamperometric transients must be corroborated by those of direct observation using microscopic techniques.