Tantalum oxide effect on the surface structure and morphology of the IrO<Subscript>2</Subscript> and IrO<Subscript>2</Subscript> + RuO<Subscript>2</Subscript> + TiO<Subscript>2</Subscript> coatings and on the corrosion and electrochemical properties of anodes prepared from these

Alterations in the phase composition, porosity, and surface morphology of coatings are examined following the insertion of a quantity of Ta₂O₅ into active coatings prepared from IrO₂ or IrO₂ + RuO₂ + TiO₂ (OIRTA). It is shown that even an insignificant concentration of Ta₂O₅ in a coating renders it substantially amorphous and leads to the appearance of a large number of wide protracted cracks in the coating. The latter extends the surface of anodes and boosts their apparent catalytic activity in the chlorine evolution reaction. In addition, this accelerates the diffusion of chloride ions toward the front surface of anodes, which noticeably reduces the overvoltage of the chlorine evolution reaction when manufacturing sodium chlorate. The coatings’ amorphization and the development of their surface substantially reduce the corrosion resistance of these anodes as compared with OIRTA.     

Structure of Ir and Ir-Al<Subscript>2</Subscript>o<Subscript>3</Subscript> coatings obtained by chemical vapor deposition in the presence of oxygen

By chemical vapor deposition Ir and Ir-Al₂O₃ coatings are obtained with a thickness of up to 40 fum on steel substrates precoated with a layer of Al₂O₃. Tris-acetylacetonates of iridium(III) and aluminium(III) are used as precursors. The deposition processes are carried out at atmospheric pressure in the presence of oxygen. The obtained coatings are studied by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The dependences of coating structures and compositions on the preparation conditions are found. An increase in the deposition temperature results in the formation of Ir coatings with loose discontinuous structure, an increase in the size of metal crystallites, and the growth of the oxygen concentration in their composition. An increase in the concentration of precursor vapors in the deposition zone at a constant deposition temperature results in the formation of Ir coatings that consist of differently structured layers (compact, columnar, and granular). Mixed Ir-Al₂O₃ coatings which composed of metal Ir and amorphous Al₂O₃ crystallites, which exhibit a pronounced iridium texture in the [111] direction, have the most perfect compact structure. The introduction of the oxide phase in the coating composition halves the Ir crystallite size.     

Structure of Ir-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> coatings obtained by chemical vapor deposition in the hydrogen atmosphere

Chemical vapor deposition is used to obtain Ir and Ir-Al₂O₃ coatings with a thickness of up to 5 μm and growth rate of 2.5 μm/h on steel substrates previously covered with an alumina layer. Tris-acetylacetonates of Ir(III) and Al(III) are used as precursors. The deposition process is carried out at the atmospheric pressure in the presence of hydrogen. The coatings obtained are studied by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. A dependence of the structure and composition of coatings on their preparation conditions is found.     

High temperature Ho<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript> insulation coatings on AgMg sheathed Bi-2212 superconducting tapes by sol–gel technique for magnet technology

High temperature 0, 5, 8 and 12 mol % Ho₂O₃–ZrO₂ insulation coatings were successfully deposited on Ag and AgMg/Bi-2212 superconducting tapes using sol–gel technique for magnet technologies. With this purpose, transparent solutions were prepared from Ho and Zr-based precursor materials and then Ho₂O₃ effect on thermal, structural and microstructural properties were observed and discussed in the present study. It was found that Ho₂O₃ additive has a propensity to generate tetragonal ZrO₂ and help to stabilize it. It was observed that insulation coatings with a mosaic structure having cracks were fully compatible with Ag/AgMg sheathed Bi-2212 tape substrates because of oxygen permeability, high and low actual temperatures and W&R process in comparison with the conventional insulation process. In addition, surface roughness decreased with increasing Ho₂O₃ content, thereby decreasing the grain size. Although porosity values vary considerably from one porosity mesurement expression to another, porosities of the insulation coatings can be estimated to be in the range of 3 and 30 vol %.     

Electrochemical Characterisations of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–13%TiO<Subscript>2</Subscript> Coated by Atmospheric Plasma Spray

Atmospheric plasma sprayed alumina–titania (Al₂O₃–13%TiO₂), coated on stainless steel (XC18), were characterized. The coating structure and morphology were studied by scanning electron microscopy. Their presented micro cracks, laminar splats. The coatings were studied by X-ray diffraction. The main phase transformation is that of α-Al₂O₃ into metastable γ-Al₂O₃. The α-Al₂O₃ phase is due to the occurrence of partially melted particles Electrochemical behaviours of coatings were mainly investigated by potentiodynamic polarization and electrochemical impedance spectroscopy in 0.01 M [K₃Fe(CN)₆/K₄Fe(CN)₆] as a function of process parameters. Also, schematic equivalent circuit was proposed. The results were expected to facilitate the understanding and improvement of the coating behaviours.     

Quantum-chemical analysis and experimental synthesis of titanium-vanadium-containing coatings on the silica surface from a mixture of TiCl<Subscript>4</Subscript> and VOCl<Subscript>3</Subscript> vapors

A process for the synthesis of a two-component vanadium-titanium-containing monolayer coating on the silica surface by treating the latter with a mixture of TiCl₄ and VOCl₃ vapors was considered. Quantum-chemical simulations showed that the synthesis temperature and concentrations of the reactants in the gas phase have a decisive influence on the composition and structure of the resulting coating. Based on the model predictions, two-component coatings with 0.2–0.9 ratios of the molar concentration of vanadium to that of titanium in the solid phase were synthesized. The ratio of the content of the solid-phase vanadium to titanium was shown to linearly vary with the VOCl₃ to TiCl₄ concentration ratio in the vapor mixture over wide temperature and concentration ranges, which allows controlling the composition of the two-component coatings being formed.     

Wettability characterization of transparent MgF<Subscript>2</Subscript> nanoparticle coatings with SiO<Subscript>2</Subscript> binder covered with fluoroalkylsilane self-assembled monolayers

SiO₂-added MgF₂ nanoparticle coatings with various surface roughness properties were formed on silica-glass substrates from autoclaved sols prepared at 100–180 °C. The samples were exposed to fluoro-alkyl silane (FAS) vapor to give hydrophobicity. All nanoparticle samples before FAS treatment had transmittances higher than 93% and such values were preserved even after FAS treatment. We examined root mean square roughnesses of the nanoparticle coatings with a Scanning Probe Microscope. We also examined their static and dynamic wettabilities with a contact angle meter and calculated their adhesive energies and surface free energies (SFEs). The surface roughness of the nanoparticle coating increased with the increase of the autoclave temperature. In addition, higher autoclave temperature caused increases in the sliding angle and decreases in the SFE. Interestingly, the higher the contact angle was, the larger the sliding angle was, although smaller sliding angle was expected with a larger contact angle.     

Preparation and characterization of polyurethane based self-cleaning and antibacterial coating containing silver ion exchanged montmorillonite/TiO<Subscript>2</Subscript> nanocomposite

In order to reach an antibacterial, photocatalytic, and hydrophilic coating, commercial grade polyurethane (CPU) resin was modified with silver ion exchanged montmorillonite/TiO₂ nanocomposite in various montmorillonite to TiO₂ nanoparticle ratios. To characterize the prepared nanocomposites and coatings, X-ray diffraction patterns, FTIR and UV–Vis spectroscopy and SEM images were used. The modified commercial grade polyurethane coatings containing nanocomposites show better properties, including hydrophilicity, degradation of organic pollutants, antibacterial activity and water resistivity, compared to unmodified commercial grade polyurethane coatings. The water droplet contact angle of unmodified CPU coating was 70°, however it decreased to lower than 10° in modified CPU coatings after 24 h LED lamp irradiation. Decolorization efficiency of malachite green dye solution by the use of modified CPU coatings achieved up to 70% after 5 h LED lamp illumination, compared to less than 5% for unmodified CPU coatings. Modified CPU coatings also showed significant water resistivity and antibacterial properties.     

Electrodeposition of thin Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> films

The electrochemical behavior of copper(II), zinc(II), and thiosulfate (S₂O₃ ^2-) ions on the molybdenum electrode in individual 0.2 М sodium sulfate solutions (рН 6.7) and with addition of either 0.1 М tartaric acid (рН 4.6) or 0.1 М citric acid (рН 4.7) is studied. A one-step electrochemical method is developed for the deposition of thin Cu₂ZnSnS₄ films, which is carried out on the molybdenum electrode at a constant potential in sodium sulfate solutions containing tartaric acid. The effect of the concentration of electrolyte components on the chemical composition of Cu₂ZnSnS₄ films is determined. The phase composition is confirmed by the Raman spectroscopy data. The surface morphology of synthesized films is studied by means of scanning-electron and atomic-force microscopes. The photoelectrochemical characteristics of Cu₂ZnSnS₄ films are determined. Samples of these coatings on the Mo electrode are found to be highly photosensitive.     

Electrodeposition of Al-Ti alloy on mild steel from AlCl<Subscript>3</Subscript>-BMIC ionic liquid

The electrodeposition of Al-Ti alloy on a mild steel substrate is examined in a Lewis acidic 66.7–33.3 mol% AlCl₃-1-buthyl-3-methylimidazolium chloride ionic liquid containing TiCl₄. Dense and compact Al-Ti alloy coatings with Ti content ranging from 5.3 to 11.4 at.% can be obtained under optimized conditions. The applied current densities and TiCl₄ concentration are found to play central roles in controlling the alloy compositions and surface morphologies of the resultant Al-Ti alloy coatings. Ti content in Al-Ti alloys increases with initial increase in the current density and decreases when the current density is beyond 5 mA cm^?2. In addition, the enhanced corrosion resistance of the mild steel substrate by the deposited Al-Ti alloy layers is evaluated via electrochemical techniques. The Al-Ti alloy coatings show much higher corrosion resistance than single Al coating, and this performance is improved with the increase of the Ti content.     

Effect of C<Subscript>2</Subscript>H<Subscript>4</Subscript>/N<Subscript>2</Subscript> Ratio in an Atmospheric Pressure Dielectric Barrier Discharge on the Plasma Deposition of Hydrogenated Amorphous Carbon-Nitride Films (a-C:N:H)

The goal of this study was to investigate the properties and growth mechanisms of nitrogen-containing carbon-based coatings obtained with an atmospheric pressure dielectric barrier discharge in an N₂-C₂H₄ atmosphere. Radically different chemical compositions were observed depending on C₂H₄/N₂ ratio. With a low C₂H₄ concentration (<400 ppm) as a function of the residence time in the discharge, two different growth mechanisms were observed consisting of a highly nitrogenated coating (N/C > 0.8) and low hydrogen content. At the short residence time, growth was due to mobile small radicals that procured a smooth yet soluble coating, while at the longer residence time, diffusion-limited aggregation of high sticking N-containing radicals produced a cauliflower-like structure. With a high C₂H₄ concentration (≥2,000 ppm), a polymer-like coating with relatively lower nitrogen content (N/C ~ 0.2) was observed with a cauliflower morphology for the entire coating. Nanoindentation measurements revealed very different physical properties in the two types of coatings.     

Structures and antifouling properties of low surface energy non-toxic antifouling coatings modified by nano-SiO<Subscript>2</Subscript> powder

Antifouling coatings are used to improve the speed and energy efficiency of ships by preventing organisms, such as barnacles and weed, building up on the underwater hull and helping the ships movement through the water. Typically, marine coatings are tributyltin self-polishing copolymer paints containing toxic molecules called biocides. They have been the most successful in combating biofouling on ships, but their widespread use has caused severe pollution in the marine ecosystem. The low surface energy marine coating is an entirely non-toxic alternative, which reduces the adhesion strength of marine organisms, facilitating their hydrodynamic removal at high speeds. In this paper, the novel low surface energy non-toxic marine antifouling coatings were prepared with modified acrylic resin, nano-SiO₂, and other pigments. The effects of nano-SiO₂ on the surface structure and elastic modulus of coating films have been studied, and the seawater test has been carried out in the Dalian Bay. The results showed that micro-nano layered structures on the coating films and the lowest surface energy and elastic modulus could be obtained when an appropriate mass ratio of resin, nano-SiO₂, and other pigments in coatings approached. The seawater exposure test has shown that the lower the surface energy and elastic modulus of coatings are, the less the marine biofouling adheres on the coating films. Supported by High-Tech Research and Development Program of China (Grant No. 2004AA001520)     

Distribution of elements in the surface layer of plasma-electrolytic coatings formed on titanium in electrolytes with MnO<Subscript>2</Subscript> particles

The influence of electrolytes (aqueous solutions of H₂SO₄, Na₂SO₃, and K₂B₄O₇ (group I) and Na₂SiO₃ (group II)), as well as the effects of pores and ridges around them, on the element composition of oxide coatings was studied. The addition of MnO₂ particles to electrolytes initiated the formation of large pores. The pores had increased titanium and decreased oxygen contents. Coatings I contained, on average, up to 1 at % Mn, and coatings II had up to 8 at % Mn; in the pores of II, the Mn concentration was increased to 18 at %. The coatings contained 7–28 at % carbon, which was concentrated in pores in I and on the surface of the oxide coating in II.     

Characterization of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles synthesized by various methods

Microwave-induced combustion with glycine, CTAB-assisted hydrothermal process with NaOH and NH3, EDTA assisted-hydrothermal methods have been applied to prepare NiFe₂O₄ nanoparticles for the first time. Structural and magnetic properties of the products were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmison electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and electron spin resonance spectrometry (EPR). TEM measurements showed that morphology of the product depends on the synthesis method employed. The average cystallite size of NiFe₂O₄ nanoparticles was in the range of 14–59 nm as measured by XRD. The uncoated sample (Method A) had an EPR linewidth of 1973 Oe, the coated samples reached lower values. The magnetic dipolar interactions existing among the Ni ferrite nanoparticles are reduced by the coatings, which could cause the decrease in the linewidth of the EPR signals. Additionally, the linewidth increases with an increase in the size and the size distribution of nanoparticles.     

Surface topography control of NiS/Ni<Subscript>3</Subscript>S<Subscript>4</Subscript> nanosheets for the promotion of electrochemical performance

One of the promising candidates to replace the chromate conversion coatings for corrosion protection of aluminium alloy AA7075 are the hybrid sol–gel coatings. In the present work hybrid silica sol–gel coatings doped with cerium nitrate were prepared and characterized. Tetraethoxysilane (TEOS) and 3-glycidoxypropyl-trimethoxysilane (GPTMS) were used as precursors. Silica SiO₂ (Ludox) particles were added to achieve a barrier properties of coating, while Ce(NO₃)₃·6H₂O was added in order to obtain an active corrosion protection. Optimization of sol synthesis was based on the results of ATR-FTIR spectroscopy and UV–vis–NIR spectroscopy. Opening of epoxy rings and completion of hydrolysis and the condensation reactions during the synthesis process were confirmed. Coatings were characterized through thickness, water contact angle, roughness, adhesion, electrochemical properties (potentiodynamic and electrochemical impedance spectroscopy) and the response to prolonged immersion time in 0.1?M NaCl. The high degree of cross-linking of Si–O–Si network structure and high density was achieved during the synthesis of the sol. Moreover, the results showed that the curing process and the incorporation of cerium nitrate into the hybrid sol–gel coating affected to the corrosion properties of the coating. The observed enhancement in corrosion protection properties is attributed to the combination of the barrier properties of the silica matrix with the active protection of the cerium nitrate.

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Synthesis of nanocrystalline ZnO by the thermal decomposition of [Zn(H<Subscript>2</Subscript>O)(O<Subscript>2</Subscript>C<Subscript>5</Subscript>H<Subscript>7</Subscript>)<Subscript>2</Subscript>] in isoamyl alcohol

It was studied how the conditions of heat treatment of a [Zn(H₂O)(O₂C₅H₇)₂] solution in isoamyl alcohol at 120–140°C for 2–60 min affect the precursor decomposition mechanism and the characteristics of the obtained nanocrystalline zinc oxide. In all the cases, the product was a crystalline substance with the wurtzite structure and a size of crystallites of 14–18 nm, which was independent of the synthesis conditions. The thermal behavior and microstructure of the separated and dried nanostructured ZnO powder were investigated. It was determined how the duration and temperature of the heat treatment of the precursor solution affects the microstructure of ZnO coatings dip-coated onto glass substrates using dispersions produced at 120 and 140°C. The nanosized ZnO application procedure was shown to be promising for creating a gas-sensing layer of chemical gas sensors for detecting 1% H₂ (\(R_0 /R_{H_2 } \) was 58 ± 2 at an operating temperature of 300°C) and 4 ppm NO₂ (\(R_{NO_2 } /R_0\) were 15 ± 1 and 1.9 ± 0.1 at operating temperatures of 200 and 300°C, respectively).     

Kinetics of electrodeposition of Ni–ZrO<Subscript>2</Subscript> nanocomposite coatings from methanesulfonate electrolytes

Regularities of incorporation of zirconia nanoparticles into a nickel matrix in the course of electrodeposition of Ni–ZrO₂ coatings from methanesulfonate electrolyte are established. The content of the dispersed phase in coatings grows at an increase in its concentration in electrolyte. Moreover, nanocomposites containing a greater amount of zirconia are deposited from the methanesulfonate electrolyte as compared to sulfate electrolyte. This is explained by the greater partial concentration of ZrO₂ in the solution due to enhanced aggregative stability of the dispersed phase in methanesulfonate electrolyte. The mechanism of formation of the composite coating is considered that is based on the concept of particle incorporation into the metal matrix due to the different rates of metal electrodeposition on the electrode surface free of nonmetallic particles and on the electrode surface conditionally occupied by them. A physically substantiated mathematical model is suggested that describes the kinetics of formation of the composite coating that agrees well with the experimental data.     

MgF<Subscript>2</Subscript> films prepared from solvothermally treated precursor solutions

MgF₂ coating solutions were solvothermally treated at 160?°C for different time periods, this procedure induced crystallization and particle growth. Antireflection coatings prepared on glass from these solutions were compared to films derived from untreated precursor material. Ellipsometric porosimetry (EP) was employed to characterize structural features of coatings on glass as function of annealing temperature. Based on precursor solutions that had undergone solvothermal treatment antireflective coatings with a peak transparency exceeding 99% were prepared on PMMA substrates.

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Solvothermal treatment of MgF₂ precursor solutions results in crystallization of particles that can directly be applied to PMMA substrates for λ/4 antireflective films.

     

TiO<Subscript>2</Subscript>/WO<Subscript>3</Subscript> photoanodes with enhanced photocatalytic activity for air treatment in a polymer electrolyte cell

The application of electrochemically enhanced photocatalysis in air treatment using a Nafion-based photoelectrochemical cell and TiO₂/WO₃ photoanodes for organic vapor photooxidation under both UV and visible light irradiation is briefly presented. In that direction, the obtained results regarding the preparation and characterization of the TiO₂/WO₃ photoanodes with enhanced photocatalytic activity are reviewed. Particular emphasis is given in the comparison of the photocatalytic behavior of bilayer TiO₂/WO₃ coatings, electrosynthesized on stainless steel mesh and powder C + mixed (WO₃ + TiO₂) photoanodes. The advantages of using a high surface area C + mixed (WO₃ + TiO₂) powder catalysts as photoanodes against their plain TiO₂ + C and WO₃ + C analogues are discussed.     

Ultrasound technique as a tool for high-rate incorporation of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> in NiCo layers

NiCo–Al₂O₃ composite coatings were prepared by electrodeposition in a sulfamate plating bath containing Al₂O₃ particles to be co-deposited under sonication. For reliable determination of the microstructure, detailed studies on composite cross-sections were carried out by energy-dispersive spectrometer (matrix composition, particle content) and FE-SEM/electron backscattered diffraction data (particle distribution, grain size), accompanied by XRD analyses concerning texture, lattice parameter, grain size, and residual stress. The NiCo matrix with a Co/Co + Ni ratio up to 0.4 is a face-centered cubic solid solution with <100> and <110> fiber textures. The distribution of the particles (size 250 nm) was well-dispersed and enhanced up to 15 wt.% by ultrasound application during plating. Vickers hardness increased up to 50% by dispersion hardening. First-order residual stress in the matrix increased with rising Co content, thus decreasing wear resistance and revealing the complex of composite properties with partially opposite effects.