Volume 227, Issue 8

The Cu-Mo composite coatings with different Mo microparticles (3 μm; 7 μm) as dispersed phase were obtained by electro-codeposition on copper substrate. The effect of the Mo concentration added in the sulphate electrolyte (pH 1.0), free of any additives on the surfaces morphology and layers composition were investigated. Well-distributed Cu-Mo metal matrix composite coatings were obtained and dispersed phase changes the surfaces roughness. Microhardness of Cu-Mo composite coatings follows a rule of mixture based on the volume fraction of Mo embedded in the copper matrix.

The electrochemical fabrication of nanowires of the Fe-based magnetic alloys Co-Fe, Fe-Ga and Fe-Pd is reported. Co-Fe is deposited potentiostatically from a simple sulfate electrolyte. The influence of chemical composition, diameter and length of the wires on the magnetic properties of both single wires and arrays of wires embedded in the AAO matrix is discussed. The more challenging Fe-Ga and Fe-Pd alloys required the development of new electrolyte compositions. In order to obtain homogeneous nanowires with the desired composition and length alternating potential pulses were applied and the pulse potentials had to be adjusted.

Copper-silica composite coatings were prepared by electro-codeposition on stainless steel substrates. The influence of functionalization and surface charge of SiO2 particles on the electrodeposition of Cu-SiO2 nanocomposite coating was studied. SiO2-SH particles were embedded inside the metal matrix whereas particles with other surface termination did not incorporate inside the metal matrix. Moreover, cysteamine addition to the electrolyte containing bare SiO2 particles induced embedding of particles into the metal matrix. The diameter-dependence of incorporation of -SH functionalized SiO2 particles as well as the role of the density of the effective functional group (-SH) for successful incorporation into Cu have been investigated. Infrared (IR) and X-ray photoelecotron (XPS) spectroscopy were used to observe the interaction of Cu2+ ions with thiol groups, showing a Cu2+ binding. The incorporated particles were found to increase the microhardness of the coating.

To develop an aluminum-chlorine cell, an electrochemical cell consisting of an aluminum anode and a graphite cathode was developed and evaluated in EMIC-AlCl3 ionic liquid. The open circuit voltage of the aluminum-chlorine cell was about 1 . 8-1 . 9V after introduction of chlorine gas to 66 . 7mol% EMIC-AlCl3 at 303 K. The relationship between current density and cell voltage in the cell showed an almost linear relation. The major factor in the voltage drop of the output voltage was considered to be due to resistance of electrolytic melt. The output characteristics of the cell depend on the configuration of the graphite cathode, the current density with a step type cathode at 0 . 5 V was about 20% better than that of a cylindrical type graphite cathode.

Plasma surface alloying of stainless steels with nitrogen or carbon is used to increase hardness and corrosion resistance. In this work, the electrochemical behaviour of AISI 316L steel after carburising at 470°C and nitrocarburising at 415 ◦C was examined in a solution of 0 . 1M Na 2 SO 4 +0 . 4M NaCl acidified to pH 3.0. Simultaneously with voltammetric measurements, pH was recorded with an antimony microelectrode at a distance 0 . 13mm above the sample surface. The carburising and nitrocarburising treatments made the steel fully resistant to pitting corrosion, although they increased anodic currents in the active region. Reverse cathodic sweeps of voltammograms exhibited reductive peaks, which were noticeably larger for the treated steel than those for the untreated steel, indicating the formation of larger amounts of oxide products on the treated steel. The antimony microelectrode showed an increase of pH at the surface of the nitrocarburised steel in the active region. This increase is ascribed to binding of protons into NH+ 4 following the electrochemical dissolution of nitrogen from steel. Such an effect was further examined by injection of ammonia into the solution during voltammetric measurements. It is suggested that the rise in pH induces the formation of protective Cr 2 O 3 from Cr 3+ cations and the formation of magnetite Fe 3 O 4 by anodic oxidation of Fe 2+ cations. It is proposed that the high resistance to pitting corrosion of the treated steel results mainly from the formation of large amounts of protective oxides Cr 2 O 3 and Fe 3 O 4 .

The present paper deals with some preliminary experimental results regarding electrodeposition of polypyrrole films doped with phosphomolybdate anions onto Al substrates involving an initial anodizing in nitric acid electrolyte; early studies proved that this stage offers a very good adherence of the further layer on Al surfaces. The phosphomolybdate doped polypyrrole films have been formed both galvanostatically and involving cyclic voltammetry, in aqueous solutions containing phosphomolybdic acid and pyrrole. In several experiments Tiron (4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt) has been added, acting as mediator and improving the layer morphology and aspect. The films exhibited a very good adherence on the metallic substrate, with a uniform black color and showed classical cauliflower morphology, more dense and ordered in the presence of Tiron, according to SEM investigations. Raman spectroscopy and EDX analysis revealed the presence of doping anion within polypyrrole layer. Also EDX measurements suggested that the film incorporates a 1 : 9 ratio of phosphomolybdate anion to PPy units. When both Tiron and phosphomolybdate anions are present in the solution, phosphomolybdate and other related anions are preferentially incorporated within the layer. Based on the continuous immersion test in NaCl 0 . 5M solution for 240 h, the phosphomolybdate entrapping into the polymer matrix was shown to provide a better corrosion protection in chloride medium.

The electrochemical behavior of copper-aluminum-nickel alloy with different Ni content in sodium hydroxide solutions was investigated. The alloys are usually used as tubes and reservoirs in basic solutions for the production of salts from marine solutions. The role of the Ni-content on the corrosion resistance of the alloy was evaluated. Different electrochemical methods were used. The increase of the nickel content in the alloy and increased immersion time in the solution improve the alloy stability due to the formation of a stable passive film. The experimental impedance data were fitted to theoretical data. The results of these experiments are discussed in reference to potential-pH (Pourbaix) diagrams. Surface morphology and barrier film constituents were examined by SEM.

Experimental data on the transients of the electric double layer (EDL) capacitance measured after the mechanical renewal of the surface of electrodes of eutectic Sn-Pb and Ag-Bi alloys with small concentrations of second components at the interface with sodium fluoride solutions are analyzed and generalized. The observed transients are associated with the surface segregation of second components of alloys at the boundary with the solution. Phenomenological models of the electrode / solution interface which make it possible to calculate the surface coverage of the metal phase with different alloy components in different times after the renewal are proposed and substantiated. It is shown that the kinetics of surface segregation of lead and bismuth atoms at the alloy electrode interfaces with electrolyte solutions can be described in the first approximation by a model of nonsteady-state surface diffusion.

The photoluminescence (PL) properties of TOPO capped CdSe quantum dots (Q-CdSe) monolayers deposited on indium tin oxide (ITO) substrates and incorporated into an electrochemical cell have been studied. In particular, the effect of electrochemical charge injection by combining the electrochemical set-up with fluorescence spectroscopy has been investigated. It was observed that when positive potentials are applied to the film in electrolyte solution, the PL is irreversibly quenched. However, the PL quenching observed after applying negative potentials to the substrate was reversible. In addition, the changes in the PL exhibit characteristic profiles at particular applied potentials. Voltammetric measurements were performed to further understand the possible origins of the specific PL changes as a function of applied potential. The results have the prospect to prove helpful in explaining the phenomenon of PL intermittency or blinking in semiconductor quantum dots.

The stable zoles of metal nanoparticles can be electrosynthesized in a reactor consisting of sacrificial anode, rotated ring cathode and layers of immiscible aqueous and organic solvents. The technique provides an instrumental approach to multiparametric control over the rates of size determining processes such as nucleation, growth, stabilization and dispersion of metal clusters. The ability to tune the particle size by variation in the residence time τ R, during which metal cluster formed at a cathode in an aqueous electrolyte is allowed to adsorb amphiphile molecules of surfactant dissolved in an organic solvent is demonstrated.