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The initial stages of cobalt-molybdenum electrodeposition on a vitreous carbon electrode were studied to obtain information about the mechanism of cobalt-molybdenum induced codeposition. Solutions containing cobalt sulphate, sodium molybdate and sodium citrate at pH 6.6 were used. A first step in the mechanism of alloy deposition is proposed. This step takes into account the formation of molybdenum(iv) oxides over which Co-Mo alloy may be only deposited if sufficient potential is applied. Co-Mo electrodeposition occurs through an early stage involving low reduction current, related to the formation of molybdenum oxides, followed by a later stage in which the reduction current suddenly increases, corresponding to alloy codeposition. When a low potential is applied, a continuous coloured molybdenum oxide film is formed on the electrode and Co-Mo is not deposited. To induce the alloy deposition on the `oxide film' it is necessary to apply more negative potentials than a threshold value, which depends on the composition of the electrolytic bath. By increasing molybdate concentration in solution, the `threshold potential' shifts to more negative values. intermediate molybdenum oxides were characterized using scanning electron microscopy (SEM), compositional analysis, Raman measurements and Auger and X-ray photoelectron spectroscopies. The initial stages of cobalt-molybdenum electrodeposition on a vitreous carbon electrode were studied to obtain information about the mechanism of cobalt-molybdenum induced codeposition. Solutions containing cobalt sulphate, sodium molybdate and sodium citrate at pH 6.6 were used. A first step in the mechanism of alloy deposition is proposed. This step takes into account the formation of molybdenum(iv) oxides over which Co-Mo alloy may be only deposited if sufficient potential is applied. Co-Mo electrodeposition occurs through an early stage involving low reduction current, related to the formation of molybdenum oxides, followed by a later stage in which the reduction current suddenly increases, corresponding to alloy codeposition. When a low potential is applied, a continuous coloured molybdenum oxide film is formed on the electrode and Co-Mo is not deposited. To induce the alloy deposition on the `oxide film' it is necessary to apply more negative potentials than a threshold value, which depends on the composition of the electrolytic bath. By increasing molybdate concentration in solution, the `threshold potential' shifts to more negative values. intermediate molybdenum oxides were characterized using scanning electron microscopy (SEM), compositional analysis, Raman measurements and Auger and X-ray photoelectron spectroscopies. [ABSTRACT FROM AUTHOR]

Among W alloys, Fe-W has seen much attention recently, due to the need of moving toward the design of environmentally friendly materials. Coatings with 4, 16 and 24 at.% of W were electrodeposited from an environmental friendly Fe(III)-based glycolate-citrate bath. The samples were annealed in vacuum at different temperatures up to 800 °C. Different crystalline phases are formed upon annealing: α-Fe, Fe 2 W, Fe 3 W 3 C, Fe 6 W 6 C, and FeWO 4 . Their grain size and distribution within the coating was studied by means of Electron Backscattered Diffraction (EBSD) technique. The effect of annealing on the mechanical properties of the coatings was analyzed performing nanoindentation measurements. The results show a considerable increase of the hardness followed by a rapid decrease at higher temperatures. The highest hardness value, i.e. 16.5 GPa, is measured for the sample with 24 at.% of W after annealing at 600 °C owing to the precipitation of α-Fe crystallites. This study indicates the possibility to substantially increase the hardness of electrodeposited Fe-W coatings by optimization of the annealing treatment. In addition, the critical influence of the carbide and oxide phases on the mechanical properties of alloys is discussed. Hence, Fe-W coatings rich in W can be applied as a possible candidate for protective coating applications at elevated temperatures. [ABSTRACT FROM AUTHOR]

Two different nanoporous materials, porous copper prepared by dealloying and porous nickel prepared by electrodeposition, have been studied by means of nanoindentation experiments at different maximum applied loads. While nanoporous Cu is homogeneous along its cross-section, the electrodeposited Ni films show a graded porosity, with smaller pores and thicker pore walls close to the film’s surface. The mechanical properties of the two materials have been extracted using a methodology based on scaling laws and subsequent interpretation has been performed using finite element simulations. Two different deformation mechanisms are observed for nanoporous Cu and nanoporous Ni, respectively. Dealloyed porous copper behaves as a homogeneous material without evident effect of densification and with mechanical properties that are independent of the applied load. Given this homogeneity, it is possible to fit the entire loading - unloading curve for different maximum applied loads with a single set of mechanical properties. Conversely, electrodeposited porous nickel shows a decrease in the reduced Young’s modulus, an increase in yield stress and a constant hardness when the maximum applied load during nanoindentation is increased. While the decrease in the reduced Young’s modulus can be explained in the context of thickness inhomogeneity of the electrodeposited porous nickel (i.e., increase of porosity with depth), this cannot explain, and actually would go against, the observed increase in the yield stress, which is instead associated to the decrease in the ligament size. [ABSTRACT FROM AUTHOR]

1.5 μm-thick molybdenum oxide films have been electrodeposited potentiostatically from 0.2 M Na 2 MoO 4 electrolyte onto indium tin oxide (ITO)/glass substrates at pH = 1, 6 and 9. The influence of cetyltrimethylammonium bromide (CTAB) surfactant on films' adhesion, morphology, degree of porosity, molybdenum speciation, and crystallographic structure has been systematically investigated. The addition of CTAB (0.01 M) to the bath clearly improves film adherence to the substrate, reduces cracking, and increases crystallinity. This has an impact on the physical properties of the films. In particular, both hardness ( H ) and Young's modulus ( E ) increase, as determined from nanoindentation tests. The growth of ordered arrays of molybdenum oxide submicrometer structures, including pillars and stripes, by electrodeposition onto e-beam lithographed Au/Ti/Si substrates is also reported. [ABSTRACT FROM AUTHOR]

Abstract: The effects of ultrasound (US) agitation (at different intensities of ultrasound) on the codeposition of inorganic fullerene-like (IF) WS2 in a metallic Ni matrix are investigated. The wt.% of IF-WS2 particles in the nanocomposite coatings increases from 4.5wt.% (in films grown under mechanical stirring but without US agitation) up to about 7wt.% (in films prepared under US agitation at the optimum intensity of ultrasound). While composite coatings obtained only under mechanical stirring exhibit a rather irregular surface morphology, with pronounced 3D multinodular protrusions, a more uniform and compact coating is attained under application of US agitation. In turn, the introduction of WS2 particles significantly modifies the growth of Ni, inducing grain size refinement, increasing the stacking fault probability and causing a drastic change of crystallographic texture. These microstructural features act in a synergistic manner to simultaneously increase the hardness of the composite coatings while causing the expected decrease in the friction coefficient (due to the presence of WS2 solid lubricant particles), therefore enhancing the wear resistance, particularly when the coatings are deposited under the presence of US. [Copyright &y& Elsevier]

Abstract: The feasibility of growing nanostructured films composed of cobalt and yttrium hydroxide/oxide phases by electrodeposition is demonstrated. Particle-free aqueous solutions containing YCl3 and CoCl2 salts and glycine were used. The incorporation of yttrium compounds into the cobalt deposit was achieved using pulse deposition (t on =0.1ms, t off =0.9ms) and for cathodic pulses higher than −500mAcm−2. Deposits obtained were crack-free, typically with 1–5wt% yttrium, and exhibited morphologies markedly different from the ones shown by pure cobalt deposits. Moreover, yttrium-rich films (up to 30wt% Y) could be deposited under certain conditions, though incipient cracking developed in this case. X-ray photoelectron spectroscopy analyses revealed that Y(OH)3/Y2O3 compounds were present in the films. From the structural viewpoint, the composites exhibited a partially amorphous/nanocrystalline character, with the crystalline fractions originating from the hexagonal-close packed structure of α-Co. A refinement of the α-Co crystallite size was observed in deposits containing higher weight percentage of yttrium compounds. Nanoindentation tests revealed that hardness increased with the yttrium content. This result can be explained by taking into account both the presence of intrinsically hard oxide phases and the effects promoted by incorporation of yttrium hydroxides/oxides on the α-Co matrix (namely, grain-refining and higher concentration of stacking faults). [Copyright &y& Elsevier]