Electrochemical deposition of Co–Sb thin films on nanostructured gold

The electrochemical behavior of the Co–Sb system on Au substrate during cyclic voltammetry and potentiostatic deposition was investigated. Electrochemical behavior of Co and Sb was studied and compared to the Co–Sb system. At a negative potential (−0.9 V vs. Ag/AgCl) the electrochemical behavior of this binary system was similar to that of individual Co and Sb combined. For more negative vertex potentials (e.g., −1.2 V vs. Ag/AgCl), results from cyclic voltammetry have shown the presence of a new compound different from Co and Sb which could only be detected at slow sweep rate. The deposition performed at constant potentials between −1.0 and −1.2 V have resulted in films that were made of CoSb₃ and Sb as indicated by XRD. Surface film studied by SEM and EDS has shown morphological and compositional non-uniformities caused by hydrogen evolution.     

Electrohydrodynamic atomization deposition of PZT sol–gel slurry and sol infiltration on the films

This paper reports the use of a deposition technique, called electrohydrodynamic atomization, for producing PZT films from a composite sol–gel slurry. PZT slurries of different powder concentrations were prepared, and then atomization deposition of them was carried out and resultant films examined. It was observed that large splats with well-mixed PZT particles in sol and fine PZT clusters with dry PZT particle agglomeration can be deposited using this technique. In particular, intermediated sol infiltration process on the EHDA deposited film under optimized atomization condition was also studied. It was found that the film with sol infiltration process become more dense and the electrical properties (P_r, ?_r) were improved compared with that without sol infiltration after EHDA deposition.     

An Electrochemical study of the formation of Benzotriazole surface films on Copper, Zinc and a Copper–Zinc alloy

The electrochemical behaviour of Cu, Cu–37Zn and Zn in benzotriazole (BTA) containing chloride solutions was studied and compared using potentiodynamic, cyclic voltammetry and electrochemical impedance spectroscopy. The presence of BTA in the chloride-containing solutions gave rise to higher breakdown potentials, significantly higher polarisation resistances and inhibited the formation of CuCl₂ and zinc-containing corrosion products. These effects were observed for pure Cu, Cu–Zn and to a somewhat lesser extent pure Zn. The electrochemical impedance data were consistent with the formation of a polymeric BTA-containing layer for all three systems.     

Electrophoretic deposition of functionally-graded NiO–YSZ composite films

Functionally-graded NiO–8 mol % YSZ composite films were prepared by a controlled voltage-decay electophoretic deposition (EPD) process. The films consisted of three layers with varying NiO concentrations and porosities. Effects of different parameters including the type of the organic media, solid concentration, NiO:YSZ ratio, and iodine on the stability of EPD suspensions and deposition kinetics were studied. A stable NiO–YSZ suspension was attained in isopropanol with NiO–YSZ ratio of 60:40 and iodine concentration of 0.5 mM. The composite film contained varying NiO concentration from 46 wt.% near the substrate to 32 wt.% close to the electrolyte with 42 wt% NiO in the intermediate region. The thickness of each layer is about 10, 44 and 68 μm, respectively. The prepared anode could be promising for solid oxide full cells as it compromises good contact to the electrode with higher corrosion resistance and active reaction zone with the electrolyte.     

Bonding and corrosion protection mechanisms of γ-APS and BTSE silane films on aluminum substrates

Films of γ-aminopropyltriethoxysilane (γ-APS), 1,2-bis[triethoxysilyl] ethane (BTSE) and their mixtures adsorbed onto pure aluminum from aqueous solutions were characterized by means of ellipsometry, infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS). It was found that after hydrolysis in water the silanes were readily adsorbed onto aluminum oxide surfaces initially forming hydrogen bonds. Upon curing, such bonds are replaced by metallosiloxane bonds, Si - O - Al. The remaining silanol groups in the film condense and form Si - O - Si bonds. As the Si - O - Al bonds are known to hydrolyze, the corrosion protection is related to the hydrophobicity of the siloxane films formed on the metal substrate. BTSE films are acidic as they contain free silanol groups, therefore these are compatible with some paints but not with others. Electrochemical impedance spectroscopy (EIS) results, salt spray test results and filiform corrosion test results showed that some silane treatments, such as two-step γ-APS/BTSE and BTSE only, provided better corrosion protection on aluminum substrates as compared with a chromate treatment. Mechanisms of adhesion and corrosion protection of these silane films on aluminum substrates are proposed.     

Asymmetric ceramic membranes from Langmuir–Blodgett deposition precursors: deposition of fatty acid salts on porous ceramic substrates

Nanoporous 7930 Vycor silica tubes and mesoporous and macroporous Anopore anodic alumina discs are examined as substrates for the multilayer Langmuir–Blodgett (LB) deposition of Cd, Mg, Zn and Ca salts of the arachidic and stearic fatty acids. Conditions for successful deposition are reported. Under appropriate conditions both mesoporous and macroporous Anopore aluminas allow for a full substrate coverage (maximum degree of deposition, D_d,max→1), while a Vycor substrate imposes a D_d,max⩽0.7 and a mechanism explaining the observed D_d,max values is presented. The produced ceramic oxide–LB film composites are prototype precursors for gas-separating all-ceramic asymmetric membranes, following the application of an oxidative plasma treatment.     

Crystallization characteristics of Li2O–Nb2O5 compound films on sapphire substrates and formation of crack-free and thick LiNbO3 epitaxial films

The formation of crystal phases in Li₂O–Nb₂O₅ compound films deposited on sapphire C-plane and A-plane substrates was studied by X-ray diffraction. Sufficiently oxidized samples with Li-deficient or stoichiometric compositions were prepared by co-sputtering from LiNbO₃ (LN) and Li₂O targets. Crystallization during deposition at elevated temperatures and solid-phase crystallization (SPC) of deposited amorphous films were investigated. For films on sapphire C-planes, nucleation into Li₃NbO₄(222) domains occurred at the onset temperature of crystallization. In the case of stoichiometric films, the LN(006) signal indicating epitaxial growth was the primary one for crystallization during deposition above 460 °C and SPC above 750 °C. Misoriented LN(104) domains tended to coexist with LN(006) domains. In the case of Li-deficient films, LiNb₃O₈(_602) domains coexisted with LN(006) at temperatures above 750 °C as a result of Li₂O loss. For films on sapphire A-planes, epitaxial LN(110) domains were predominant. Li₃NbO₄(222) domains were totally absent and the signal intensity of LiNb₃O₈(212) was less than 10% of that of LN(110) even for the Li-deficient films, which reflected fast crystallization of LN(110) domains. The SPC rate of stoichiometric film was considerably lower than that of Li-deficient film. As-crystallized LN film on the sapphire C-plane was strained with a narrow domain width. Thick film cracked as a result of stress caused by lattice mismatch with the substrate. In contrast, LN film processed by SPC was not strained and had large domains with flat film surface. Based on these results, crack-free 1-μm-thick LN epitaxial films on a sapphire C-plane were achieved. First, an amorphous LN buffer was subject to SPC to obtain a relaxed buffer layer. Subsequently, a stress-free thick LN overlayer was grown by co-sputtering from Li₂O and LN targets at 530 °C. The relaxed buffer layer effectively mitigated the strain caused by the lattice mismatch with the substrate.     

Electrochemical synthesis and surface characterization of hexagonal Cu–ZnO nano-funnel tube films

An electrochemical deposition technique was used to synthesis hexagonal nano-funnel tube films on zinc foil, utilizing an electrolyte of ZnCl₂+H₂O₂ under ambient conditions. The structures, morphologies, chemical compositions, and optical properties of the synthesized films were characterized using X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–visible diffuse reflectance spectrometry (UV-vis-DRS), photoluminescence (PL) spectrometry, and energy-dispersive X-ray spectrometry (EDS) techniques. The XRD pattern showed a set of diffraction peaks that were indexed to the ZnO, Zn(OH)₂, and Cu phases. The SEM observations revealed a cauliflower-like morphology consisting of branches in the form of nano-funnel tubes. The TEM results demonstrated that the synthesized film was comprised of several branches. The EDS studies confirmed the presence of only Cu, Zn, and O atoms. The UV-vis-DRS spectrum showed the onset of the band gap absorption peak at ～375 nm. The PL studies evaluated various emission bands that originated from different defect mechanisms. In addition, the hexagonal nano-funnel tube film showed a good superhydrophobicity, with a water contact angle of ～153°.     

Processing–structure–adhesion relationship in CVD diamond films on titanium substrates

The hardness and adhesion properties of diamond films deposited on pure Ti and Ti–6Al–4V alloy are related to the structural characteristics of the films and of the intermediate layers formed at the film/substrate interface. Deposition experiments were performed by hot-filament CVD systematically varying the deposition temperature (650–850 °C) and time (60–360 min). The morphology and structure of the coatings and interfaces were investigated by optical and electron microscopy (SEM) and by the combined use of reflection diffraction (RHEED) and X-ray powder diffraction (XRPD), used also in the GID (Grazing Incidence Diffraction) mode. Hardness measurements (HV) of the deposits were made at a constant loading of 25 g on specifically prepared transversal sections of the specimen. Only small differences concerning the mechanical properties have been found for films grown on pure Ti and Ti–6Al–4V substrates. Adhesion of diamond on the substrate has been determined by the scratch test. The analysis of the micrographs of the indenter scratches and of the fracture-correlated acoustic emissions clearly indicates the occurrence of a multi-step detachment process, leading progressively to effective delamination of the diamond coatings.     

Growth of 3C–SiC films on Si substrates by vapor–liquid–solid tri-phase epitaxy

Cubic SiC films (3C–SiC) were deposited on (111) Si substrates by a vapor–liquid–solid tri-phase growth method. In such a process a thin copper layer, which was evaporated on the Si substrate prior to the growth, was melted at high temperature as the flux and then methane (carbon source) was diffused into the liquid layer to react with Si, leading to the growth of SiC on the substrate. Copper showed some good properties as the flux, including high silicon and carbon solubility, low growth temperature and low volatility. Suitable growth parameters to go with the copper flux were identified, under which (111) textured 3C–SiC films were grown. Small numbers of (220) grains were observed to embed in the (111) films, which were difficult to avoid completely. Etching pits of the Cu melt on the substrate surface may act as the preferred sites for the growth of (220) grains.     

Influence of transition metal doping on the structural,optical, and magnetic properties of TiO2 films deposited on Si substrates by a sol–gel process

Transition metal (TM)-doped TiO₂ films (TM = Co, Ni, and Fe) were deposited on Si(100) substrates by a sol–gel method. With the same dopant content, Co dopants catalyze the anatase-to-rutile transformation (ART) more obviously than Ni and Fe doping. This is attributed to the different strain energy induced by the different dopants. The optical properties of TM-doped TiO₂ films were studied with spectroscopic ellipsometry data. With increasing dopant content, the optical band gap (E_OBG) shifts to lower energy. With the same dopant content, the E_OBG of Co-doped TiO₂ film is the smallest and that of Fe-doped TiO₂ film is the largest. The results are related to electric disorder due to the ART. Ferromagnetic behaviors were clearly observed for TM-doped TiO₂ films except the undoped TiO₂ film which is weakly magnetic. Additionally, it is found that the magnetizations of the TM-doped TiO₂ films decrease with increasing dopant content.     

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.     

Study of CrNx and NbC interlayers for HFCVD diamond deposition onto WC–Co substrates

Chromium nitride (CrN_x) and niobium carbide (NbC) films were deposited by magnetron sputtering on Co-cemented tungsten carbide (WC–Co) substrates and diamond deposition was performed by using hot-filament chemical vapor deposition (HFCVD) technique. The CrN_x and NbC interlayers have been deposited at different substrate temperatures (T_S = 400, 550 and 700 °C). The stability of these interlayers for diamond deposition has been studied by a heat treatment in H₂ atmosphere for 60 h at a temperature of 765 °C in the HFCVD reactor. X-ray diffraction (XRD), scanning electron microscopy (SEM) and glow discharge optical emission spectroscopy (GDOES) confirmed that due to this heat treatment the CrN_x films transformed into porous films composed of CrN_x, Cr₃C₂, Cr₇C₃ and Co phases, accompanied by a dramatic loss of nitrogen which is replaced by carbon. It was observed that higher nitrogen contents in the CrN_x films reduce the Co diffusion through the CrN_x layer. For NbC films, deposited by non-reactive magnetron sputtering from an NbC compound target, the heat treatment in the HFCVD reactor revealed that the films are absolutely stable during the heat treatment with some relaxation of residual stresses up to a factor of about 3. Furthermore it was found that Co diffuses through the NbC films with a T_S-dependant accumulation on the NbC film surface. By HFCVD it was possible to deposit adherent diamond coatings on the CrN_x and NbC interlayers. However, a reasonable adhesion of diamond on NbC was only obtained after different pre-treatments of the WC–Co substrates. The adhesion seems to be mainly governed by the topography of the WC–Co substrates.     

Physico-chemical and catalytic properties of Mg–Al hydrotalcite and Mg–Al mixed oxide supported copper catalysts

The Mg–Al hydrotalcite (HT) and Mg–Al mixed oxide supported copper catalysts containing 3–3.5 wt.% copper in finely dispersed form were synthesized and characterized. The effect of support nature on physico-chemical and catalytic properties of supported copper species were studied. The loading of copper on the supports was observed to be influencing the surface acidic, basic and reducibility properties, and catalytic behavior in dehydrogenation of benzyl alcohol. The high basicity and intercalated copper ions in Mg–Al hydrotalcite supported copper sample showed multifunctional activity in catalytic transformations of alcohols (primary, secondary and aromatic alcohols).     

Electrochemical properties of Pb–Sb, Pb–Ca–Sn and Pb–Co3O4 anodes in copper electrowinning

Three types of anode, Pb–Sb, Pb–Ca–Sn and Pb–Co₃O₄, for copper electrowinning were investigated. The corrosion resistance, as evaluated by cyclic voltammetric (CV) measurements was higher for Pb–Co₃O₄ than for Pb–Sb and Pb–Ca–Sn. During prolonged electrowinning under galvanostatic conditions, the anodic reaction on the Pb–Co₃O₄ anode was depolarized by 0.053 V as compared to Pb–Sb, and by 0.106 V with respect to Pb–Ca–Sn. The composition and structure of the anodic layer were determined by XPS, X-ray and SEM analyses. The surface layer on the three anodes examined was composed mainly of PbSO₄, -PbO₂ and -PbO₂. Different structure of the surface layer was observed: loose and highly spread coral-like structure in the case of Pb–Sb; fibrous structure in the case of Pb–Ca–Sn and dense, fine-grained structure in the case of Pb–Co₃O₄.     

Laser approaches for deposition of carbon nitride films — chemical vapour deposition and ablation

The deposition of carbon nitride films by laser-induced chemical vapour deposition (LCVD) from the system NH₃/CCl₄ and by laser ablation of a graphite target in nitrogen atmosphere has been studied. Two types of lasers were used: a copper bromide vapour laser for LCVD and an eximer KrF laser for the ablation process. The first laser source has a set of parameters (wavelengths, repetition rate, pulse duration) which makes it unique in material processing. During the ablation deposition an additional DC discharge (ignited by each shot) or RF discharge (permanent) was utilised to increase the reactivity of the nitrogen.The deposition rate for LCVD is almost one order of magnitude higher than for the laser ablation (0.050–0.350 and 0.025–0.040 nm/pulse, respectively) due to the direct laser impact on the substrate surface.The composition of the layers was studied by Auger electron spectroscopy (AES) and wavelength dispersive X-ray analysis (WDX). For the laser ablation the N/C ratio increases when an additional DC or RF discharge was used compared to the non-assisted process. Maximum values are reached at nitrogen pressures twice lower for RF discharge than for DC discharge assisted deposition. In the case of LCVD the composition depends mainly on the laser power.Chemical bonding was investigated by Fourier transform infrared (FTIR) spectroscopy. The FTIR spectra of the films deposited by LCVD show well defined bands which are superimposed to a broad peak for samples prepared by laser ablation. At higher RF plasma power a weak band around 2200 cm⁻¹ appears in the spectra which can be attributed to the stretching mode of triple bonded C–N. Such a peak is not observed in cases of DC discharge and LCVD.     

Influence of deposition conditions on the protective behavior of tetraethyl orthosilicate sol–gel films on AA5754 aluminum alloy

The aim of this work is to compare the effect of two deposition methods, dip-coating and electrophoretic deposition, on the characteristics of tetraethyl orthosilicate (TEOS) sol–gel films on AA5754 aluminum alloy, especially in what concerns to their resistance against corrosion. The influence of pH bath on the hydrolysis of the system was analyzed. Moreover, the effect of some experimental parameters, such as deposition time and deposition voltage, was also evaluated. The results showed that pre-hydrolysis rate of the orthosilicate bath depends on the solution pH, and that at pH 2 complete hydrolysis of the solution was obtained after only 20 min. Moreover, it was observed that electrodeposited TEOS films provided better corrosion resistance than films obtained by dip-coating. The improved corrosion resistance was ascribed to a higher uniformity and density of the polysiloxane films and to an in situ modification of the aluminum–polysiloxane interface by the cathodic voltage.     

Electrochemical investigation of chromium nanocarbide coated Ti–6Al–4V and Co–Cr–Mo alloy substrates

This study investigated the electrochemical behavior of chromium nano-carbide cermet coating applied on Ti–6Al–4V and Co–Cr–Mo alloys for potential application as wear and corrosion resistant bearing surfaces. The cermet coating consisted of a highly heterogeneous combination of carbides embedded in a metal matrix. The main factors studied were the effect of substrate (Ti–6Al–4V vs. Co–Cr–Mo), solution conditions (physiological vs. 1 M H₂O₂ of pH 2), time of immersion (1 vs. 24 h) and post coating treatments (passivation and gamma sterilization). The coatings were produced with high velocity oxygen fuel (HVOF) thermal spray technique at atmospheric conditions to a thickness of 250 μm then ground and polished to a finished thickness of 100 μm and gamma sterilized. Native Ti–6Al–4V and Co–Cr–Mo alloys were used as controls. The corrosion behavior was evaluated using potentiodynamic polarization, mechanical abrasion and electrochemical impedance spectroscopy under physiologically representative test solution conditions (phosphate buffered saline, pH 7.4, 37 °C) as well as harsh corrosion environments (pH ～ 2, 1 M H₂O₂, T = 65 °C). Severe environmental conditions were used to assess how susceptible coatings are to conditions that derive from possible crevice-like environments, and the presence of inflammatory species like H₂O₂. SEM analysis was performed on the coating surface and cross-section. The results show that the corrosion current values of the coatings (0.4–4 μA/cm²) were in a range similar to Co–Cr–Mo alloy. The heterogeneous microstructure of the coating influenced the corrosion performance. It was observed that the coating impedances for all groups decreased significantly in aggressive environments compared with neutral and also dropped over exposure time. The low frequency impedances of coatings were lower than controls. Among the coated samples, passivated nanocarbide coating on Co–Cr–Mo alloy displayed the least corrosion resistance. However, all the coated materials demonstrated higher corrosion resistance to mechanical abrasion compared to the native alloys.     

Fretting wear and electrochemical corrosion of well-adhered CVD diamond films deposited on steel substrates with a WC–Co interlayer

Diamond films have been grown on carbon steel substrates by hot-filament chemical vapour deposition methods. A Co-containing tungsten-carbide (WC–Co) coating prepared by high velocity oxy-fuel spraying was used as an intermediate layer on the steel substrates to minimize the early formation of graphite (and thus growth of low quality diamond films) and to enhance the diamond film adhesion. The effects of the WC–Co interlayer on nucleation, quality, adhesion, tribological behaviour and electrochemical corrosion of the diamond film were investigated. The diamond films exhibit excellent adhesion under Rockwell indentation testing (1500 N load) and when subjected to high-speed, high-load, long-time reciprocating dry sliding ball-on-flat wear tests against a Si₃N₄ counterface in ambient air (500 rpm, 200 N, 300,000 cycles). A WC–Co interlayer with appropriate chemical pretreatment is shown to play an important role in improving the nucleation, quality and adhesion of the diamond film, relative to that shown by substrates without such pretreatment.     

TPR and XPS study of cobalt–copper mixed oxide catalysts: evidence of a strong Co–Cu interaction

In this work the results of a TPR and XPS investigation of Co_xO_y–CuO mixed oxides in the range of composition Co : Cu=100:0–8:92 are reported and compared. The final catalysts were obtained by thermal decomposition in air and N₂ at 723 K for 24 h of singlephase cobalt–copper hydroxycarbonates prepared by coprecipitation at constant pH. The Co : Cu=100 : 0 specimen calcined in air formed the Co²⁺[Co³]₂O₄ (Co₃O₄) spinel phase. The coppercontaining catalysts (Co : Cu=85 : 15–8 : 92) showed mainly two phases: (i) spinels, like Co²⁺[Co³⁺]₂O₄, Co _1-x ²⁺ Cu _x ²⁺ [Co³⁺]₂O₄ and (ii) pure CuO, the relative amount of each phase depending on the Co : Cu atomic ratio. The results of the XPS study are consistent with the bulk findings and revealed the presence of Co²⁺, Co³⁺ and Cu²⁺ species at the catalyst surface. Moreover, the surface quantitative analysis evidenced a cobalt enrichment, in particular for the most diluted cobalt samples. The TPR study showed that the catalyst reduction is affected by a strong mutual influence between cobalt and copper. The reducibility of the mixed oxide catalysts was always promoted with respect to that of the pure Co₃O₄ and CuO phases and the reduction of cobalt was markedly enhanced by the presence of copper. Cobalt and copper were both reduced to metals regardless of the catalyst composition. On the other hand, the Co : Cu=100 : 0 specimen calcined in N₂ formed, as expected, CoO. The initial addition of copper resulted in the formation of the Cu⁺Co³⁺O₂ compound, besides CoO, up to a Co/Cu=1 atomic ratio at which the CuCoO₂ phase was the main component. A further addition of copper led to the formation of CuCoO₂ and CuO phases. The XPS results were in good agreement with these findings and the surface quantitative analysis revealed a less enrichment of cobalt with respect to the catalysts calcined in air. The TPR analysis confirmed that the reduction of the N₂calcined catalysts was also remarkably promoted by the presence of copper. Also in this case cobalt and copper metal were the final products of reduction.