Electrodeposition and characterization of nano-structured Ni-SiC composite films

Ni-SiC nano-composite coating, which simultaneously composed of both nanocrystalline consecutive Ni matrix and dispersed inert SiC nano-particles, has been fabricated by ultrasonic electroplating technique from a modified Watts bath containing SiC nano-particles. The influence of mechanical stirring and ultrasonication on the surface morphology of the nanocrystalline Ni-SiC nano-composite film has also been investigated. The surface morphology, microstructure, anti-corrosion property and electrocatalytic activity for hydrogen evolution of the obtained nanocrystalline Ni-SiC nano-composite film, are characterized using scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) system, atomic force microscopy (AFM), transmission electron microscope (TEM), X-ray diffraction (XRD) and electrochemical impedance spectroscopy (EIS) techniques. The results find that, mechanical stirring mainly prevents the sedimentation of the inert particles suspended in solutions, while ultrasonication mainly prevents the particles agglomeration. In the case of only mechanical stirring to disperse the SiC nano-particles, the composite surface is cauliflower alike. While in the case of both mechanical stirring and ultrasonication, the obtained Ni-SiC composite film is much smoother and composes of particles with the mean diameter of 42.9 nm, and SiC particles are uniformly dispersed into Ni matrix. Meanwhile, the results obtained by polarization curves and EIS methods show that, when compared with the traditional polycrystalline Ni film, the obtained Ni-SiC nano-composite film exhibits the enhanced corrosion resistance in NaCl solutions, possesses much higher electrocatalytic activity for hydrogen evolution in KOH solutions.     

纳米结构Ni-TiN复合薄膜的电沉积及腐蚀行为

采用电沉积方法在黄铜基底上制备纳米结构的Ni-TiN复合薄膜。用扫描电镜（SEM）及透射电镜（TEM）对其微观结构进行表征,利用X射线衍射（XRD）分析其平均晶粒尺寸,采用极化曲线及电化学阻抗谱（EIS）研究其腐蚀行为。结果表明,电沉积的电流密度、TiN纳米粒子的浓度、搅拌速度、溶液温度及pH值对电沉积薄膜形貌的影响较大。制备的Ni-TiNi电沉积薄膜的平均晶粒尺寸约为50nm。纳米结构的Ni-TiNi电沉积薄膜的耐腐蚀性能远优于纯Ni沉积薄膜的。     

Synthesis of polypyrrole–Nafion composite films by gas phase electroformation

Nafion was introduced into polypyrrole (PPy) matrix by gas phase electrochemical polymerisation. This produced a uniform, homogeneous and conductive thin film of composite polymer. The films (PPy/Nafion) also show surface features of highly ordered structural regularity. The composites obtained were characterised by cyclic voltammetry (CV) and redox performance were investigated. The relationship of the anodic current of the composite with the various experimental parameters such as concentration of Nafion, current density, polymerisation time and temperature were investigated. Anodic current increases with the Nafion concentration, polymerising time, temperature and current density.     

Preparation of mesoporous silica thin films on polystyrene substrate by electrochemically induced sol-gel technique

The mesoporous silica thin films with an oriented hexagonal mesostructure were prepared on polystyrene (PS) substrate by electrochemically induced sol-gel technique using tetraethoxyorthosilicate (TEOS) as silica source and cetyltrimethyl-ammonium bromide (CTAB) as structure-directing agent. Prior to coating deposition, the PS substrate was made hydrophilic by sulfonation with concentrated sulfuric acid for 72 h to provide better adhesion of silica films to the substrate. The effects of synthesis parameters required to obtain well-ordered crack-free layers, such as deposition voltage and deposition time, were evaluated in detail. The samples were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared-Attenuated total reflectance (FT-IR-ATR), small-angle X-ray diffraction (SAXRD) and transmission electron microscopy (TEM). According to the experimental results, the deposition voltage of 3.6 V and the deposition time of 10 s were determined as the optimum conditions. The silica films with the thickness of ca. 1.5 μm obtained under this condition was crack-free smooth and had a hexagonally ordered pore array pattern nanostructure. The pore diameter was about 3 nm and the distance between the neighboring pore centers was ca. 4.6 nm.     

Analysis of electrochemical impedance of polypyrrole|sulfate and polypyrrole|perchlorate films

PPy|SO₄ and PPy|ClO₄ films have been synthesized and investigated in K₂SO₄, ZnSO₄ and NaClO₄ aqueous solutions by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and electron probe microanalysis (EPMA) methods. On the basis of obtained data and calculated impedance parameters as the potential functions, the role of different processes (diffusion of ions, double-layer charging, adsorption and charge transfer) in oxidized, partially reduced and reduced PPy films is estimated. The lowest pseudocapacitance values (from n × 10⁻⁶ to n × 10⁻⁴ μF cm⁻² for 1 μm film), independent of solution concentration, were established for PPy|SO₄ in ZnSO₄. This phenomenon is related with strongly aggravated film reduction process in the solution of double-charged cations. In the case of PPy|ClO₄ in NaClO₄ and PPy|SO₄ in K₂SO₄,where the mono-charged cations participate in redox process, the capacitance values are in the range from: n × 10⁻³ to n × 10⁻² μF cm⁻² and even somewhat higher for PPy|ClO₄ system at oxidized state. The calculated effective diffusion coefficients of ions D remain inside the range from n × 10⁻¹² to n × 10⁻¹⁴ cm² s⁻¹ for PPy|SO₄ in 0.1 M K₂SO₄ and PPy|ClO₄ in 0.1 M NaClO₄ aqueous solution. In the case of PPy|SO₄ film in ZnSO₄ solution the D values are essentially lower.     

Electrodeposition of cerium oxide films and composites

Nanostructured CeO₂ films were prepared by cathodic electrolytic deposition (ELD) and electrophoretic deposition (EPD). Benzoic acid has been utilized for the dispersion and charging of CeO₂ nanoparticles for EPD. The kinetics of ELD and EPD was investigated. Electrodeposition method has been developed for the deposition of poly(2-vinylpyridine) (PVP) films. The thickness of the films was varied in the range of 0.1-3 μm. The deposition mechanism was based on the pH increase in the cathodic reactions, electrophoresis of the protonated PVP macromolecules, neutralization of their charge and film formation at the cathode surface. The deposition yield was studied by the quartz crystal microbalance method. Two electrochemical strategies were developed for the fabrication of composite PVP-CeO₂ films, which were based on the electrodeposition of PVP and ELD or EPD of CeO₂. The composite films were studied by electron microscopy, X-ray diffraction, thermogravimetric and differential thermal analysis. The CeO₂ content in the composite films was varied by the variation of bath composition. The deposition methods allowed the fabrication of crack-free PVP-CeO₂ films, which provided corrosion protection of stainless steel substrates in aqueous NaCl solutions.     

Conductivity of silver exposed polypyrrole films

Electrochemically prepared conducting polypyrrole tosylate films were exposed to silver in a wide range of concentrations. Four-probe measurements of the dc conductivity of these films as well as two-probe ac conductivity measurements were performed. Small silver exposures lead to a dramatic change in the surface potentials and electronic structure, whereas the ac- and dc-conductivities appear not to be influenced. In the range of high silver exposures metallic conductivities due to the formation of a massive silver overlayer on top of the polypyrrole films are observed.     

Electrodeposition and characterization of Cu-Nb composite coatings

Copper coatings containing well-distributed Nb particles were obtained by co-electrodeposition in an acidic sulfate bath. Nb particle concentration in the bath was the most significant factor for the incorporation of Nb particles in copper, followed by stirring rate, whereas current density presented low significance. High Nb particle concentration and low stirring rate led to a higher incorporated Nb particle content. The microhardness of the composite layers was higher than that of pure copper deposits obtained under the same conditions due to copper matrix grain refinement and increased with the increase of both current density and incorporated Nb particle volume fraction. The corrosion resistance of Cu-Nb composites in 0.5 wt.% H₂SO₄ solution at room temperature was higher than that of pure copper and increased with the increase of the Nb content.     

On the porosity of polypyrrole films

Polypyrrole (PPy) films doped with anions of various size, charge and chemical nature (inorganic, surfactant, with aromatic ring) were electrochemically synthesized and investigated by low-temperature N₂ sorption experiments at −196 °C. The specific surface area, total pore volume, average pore radius, pore size distribution and other parameters for oxidized PPy films using dodecylsulfate, 2-naphthalene sulfonate, 1,5-naphthalene disulfonate, poly(4-styrenesulfonate), tosylate, perchlorate, nitrate and chloride as dopant ions, were calculated. The obtained data show that although the average pore radius of investigated mesoporous PPy films (17–19 Å) is practically independent of the dopant anion used, however the latter determines the total pore volume and specific surface area values in different PPy materials investigated. As the total pore volumes for PPy films doped with large amphiphilic anions show the smallest values, the corresponding values for PPy/small inorganic anions, are up to 2 times higher.     

Electrochemically deposited polypyrrole films and their characterization

Ionically conductive polypyrrole films have been deposited at 295 K from anhydrous acetonitrile, acetonitrile/H₂O and NaBF₄ aqueous solutions onto platinum, mild steel and stainless steel discs, using cyclic voltammetry, potentiostatic and galvanostatic techniques. Cyclic voltammetry of the polymer films has been studied as a function of water content of the acetonitrile solvent, polypyrrole concentration and potential sweep rate. Potentiostatic growth of thicker (< 30 micron) films on stainless steel allowed free-standing polypyrrole membranes to be produced. Well adherent and conductive films were deposited at constant potential in stirred solutions from acetonitrile electrolytes containing 1% (v/v) of water. The membrane resistivity of the reduced films in 0.5 mol dm^− 3 KCl_(aq) at 295 K was ≈ 1 × 10⁶ Ω cm, while the resistivity of the oxidised membrane was 2700 Ω cm.     

Electrodeposition of polypyrrole on 316L stainless steel for corrosion prevention

The electrosynthesis of polypyrrole films onto 316L stainless steel from near neutral and alkaline solutions containing molybdate and nitrate is reported. The corrosion behavior of the coated electrodes was investigated in NaCl solutions by electrochemical techniques and scanning electron microscopy. The polymer formed potentiostatically in a solution of pH 12 is the most efficient in terms of adhesion and corrosion protection. The coating significantly reduces the pitting corrosion of the substrate. The results are interpreted in terms of the nature of dopants, the good electroactivity of the polymer formed in alkaline solution and the passivating properties of the oxide layer.     

镍-铝复合涂层的电沉积机理

在改进的Watts溶液中电沉积镍-铝复合涂层。采用Z电位分析、伏安法和电化学阻抗谱（EIS）,研究涂层的电化学行为。结果发现,铝颗粒的Z电位是-4 mV,与氧化铝的非常接近。添加导电铝颗粒到电解液中,导致极化曲线向负电位方向移动,且EIS曲线的环路尺寸增大。结果表明,镍-铝复合层的共沉积行为服从Guglielmi模型。加入的导电铝颗粒起惰性粒子的作用,证实在铝颗粒表面存在薄的氧化铝层。     

Electrodeposition of polypyrrole onto NiTi and the corrosion behaviour of the coated alloy

Polypyrrole (PPy) films were electrodeposited onto nickel--titanium alloy (NiTi) employing sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol OT or AOT) solutions. Polarizing anodically NiTi samples recovered by PPy in a monomer-free solution increases adhesion of the coating. Electrochemical techniques, scanning electron microscopy (SEM) and element analysis were used in determining the corrosion performance of the coated samples in chloride solution. The polymer improves the corrosion performance at the open circuit potential and at potentials where the bare substrate suffers pitting attack. The improvement in both, adhesion and corrosion performance, is discussed considering substrate/polymer interaction, overoxidation of PPy and the role played by AOT.     

Synthesis and characterization of cerium-modified cubic mesoporous silica

The cerium-modified cubic mobil composition of matters 48 (MCM-48) molecular sieves were synthesized using cetyltrimethylammonium bromide (CTAB) as templates at low molar ratio of surfactant to inorganic precursor. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results show that the well-ordered cubic mesostructure was obtained when the Ce/Si molar ratio is less than 0.05. With the increase of Ce/Si molar ratio, the increase of unit cell parameters and the change of Fourier transform infrared spectroscopy (FTIR) provide powerful evidences for the incorporation of cerium in the framework of mesoporous molecular sieves. Nitrogen sorption data indicate that the Brunauer-Emmett-Teller (BET) surface area and the average pore diameter of Ce(Ⅲ)-MCM-48 are 1288 m 2·g -1 and 4.2 nm, and those of Ce(Ⅳ)-MCM-48 are 1228 m 2·g -1 and 3.7 nm, respectively. Diffuse reflectance UV-visible (UV-vis) spectroscopy confirms the presence of Ce(Ⅲ) in the octahedral position and Ce(Ⅳ) in the fluorite structure. X-ray photoelectron spectroscopy (XPS) studies further reveal that Ce(Ⅲ) and Ce(Ⅳ) coexist in the framework of mesoporous molecular sieves.     

Electrodeposition and characterization of Ni-TiB2 composite coatings

Nickel-titanium diboride (Ni-TiB₂) composite coatings were successfully fabricated by pulse electrodeposition techniques from nickel sulfamate bath containing dispersed submicron TiB₂ particles. The effect of TiB₂ codeposition on the morphological, microstructural, microhardness and anti-corrosive properties of the composite coatings have been investigated by using scanning electron microscopy coupled with energy dispersive spectroscopy system, X-ray diffraction (XRD), vickers microhardness, and electrochemical impedance spectroscopy (EIS) techniques. Incorporation of TiB₂ particles into the nickel matrix has modified the regular crystal growth of nickel. The XRD patterns revealed that the preferred (100) crystallite orientation of pure nickel has been modified into mixed orientations by the enhancement of (111) and attenuation of (200) diffraction intensities by the incorporation of TiB₂ particles into the nickel matrix. Vickers microhardness of the Ni-TiB₂ composite coating is found to be increased which is nearly 3 times higher than pure nickel coating. The results obtained by polarization curves and EIS analysis in 3.5 wt% NaCl solution have shown the improved corrosion resistance properties of Ni-TiB₂ composite coating over pure nickel electrodeposit.     

Electromagnetic composite films based on polypyrrole hydro-sponge and Fe3O4 ferrofluid

The preparation of free-standing electromagnetic composite films based on conductive polypyrrole (PPy) hydro-sponge and the Fe₃O₄ ferrofluid have been successfully accomplished via self-assembly in the presence of β-cyclodextrin sulfate and under static condition. Transmission electron microscope (TEM), scanning electron microscope (SEM) and X-ray diffraction (XRD) are used to study the morphology of the PPy-Fe₃O₄ composite. Structural characterizations by Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA) have proved the interactions between Fe₃O₄ and PPy chains. As-prepared films possess high electrical conductivity, remarkable magnetic response as well as appropriate flexility. Both the conductivity and magnetization of the composite, the latter in particular, depend strongly on the Fe₃O₄ content and thus can be optimized by adjusting the relative content of Fe₃O₄ in the composite. The combination of both magnetic and conducting activities of the resulting composite makes it be a potential candidate as functional material in electromagnetic devices, such as magnetic-controlled switches.     

Electrodeposition of Pr-Fe alloy films in urea-dimethylsulfoxide

Cyclic voltammetry and chronoamperometry were used to investigate the electrochemical behavior of Pr3 ions in a system of 0.01 mol·dm-3 Pr(CH3SO3)3 0.01 mol·dm-3 FeCl2 3.0 mol·dm-3 urea     

Electroless plating of palladium and copper on polypyrrole films

A novel process for the metallization of polypyrrole (PPY) film surface through consecutive electroless plating of palladium and copper in the complete absence of the SnCl₂ sensitization step was demonstrated. X-ray photoelectron spectroscopy (XPS) technique was used to characterize the polymer surface at each stage of the metallization process. It was found that only the fully reduced PPY film could reduce palladium ions to palladium metal (Pd(0)) in substantial amounts from either the Pd(NO₃)₂ or PdCl₂ acid solution. The palladium metal was necessary for catalyzing the subsequent electroless plating of copper. The reduction of Pd(II) ions in acid solution to Pd(0) on the film surface was accompanied by a simultaneous increase in intrinsic oxidation state and doping level of the film. The copper plating process after the palladium uptake step was highly dependent on the [Pd]/[N] ratio on the film. Through XPS and Auger photoeletron spectroscopy measurements, it was postulated that during the electroless copper plating process, the Cu(II) ions were first reduced to Cu(I) on the PPY film surface before complete reduction to copper metal.     

Multi-layered type hybrid glass/polypyrrole composite

Multilayer organic xerogel—polypyrrole composites have been prepared by alternate successive treatments of a glass substrate with a siloxane functionalized pyrrole, pyrrole, oxidant, and a sol precursor of the xerogel. An increase of the conductivity is seen upon the first depositions, but increasing the deposit numbers over three fourfold layers does not lead to a further improvement of the conductivity. The loss of conductivity upon aging in air of the composites is weaker than in the case of ordinary unprotected polypyrrole.     

纳米结构黑镍薄膜的电沉积制备及其电化学行为

采用电沉积方法制备具有整体纳米结构的黑镍镀层,并通过肉眼观察结合扫描电镜、X射线衍射等测试技术研究电沉积过程中的主要参数(电解液pH、搅拌速度、制备温度及电流密度)对镀层颜色及整体微观结构的影响。进一步采用动电位极化及电化学阻抗等电化学测量技术研究黑镍镀层在中性3.5%NaCl溶液中的腐蚀行为及腐蚀机理。结果表明：黑镍镀层的颜色变化趋势决定于电沉积制备参数的选择;通过优化本工艺制备的黑镍镀层平均粒径约为50 nm。对比了近似条件下制备的光亮镍镀层,发现黑镍镀层在耐蚀性方面具有较大优势。