Electrocatalytic activity and anodic stability of electrodeposited ruthenium-rhodium coatings on titanium

The stabilizing effect of rhodium addition to ruthenium coatings on titanium under anodic polarization in acidic solutions is described. The addition of rhodium to the coating leads to both an overall improved stability of the electrode, and an increase of the electrochemically active surface area. The service-life of a Rh-Ru coating polarized at 0.12 A cm–2 in 0.5 mol dm–3 sulphuric acid is improved by at least two orders of magnitude, while deterioration of the electroactive surface area never exceeds 30%. The rotating ring-disc electrode measurements show the dissolution of the coating at potentials above the onset of the oxygen evolution reaction at 1.1 V versus SCE.     

Formation of zinc phosphate coatings on AA6061 aluminum alloy

Conditions for forming zinc phosphate conversion coatings on AA6061 aluminum alloy have been investigated by characterizing coatings formed for different parameters of the coating bath. Morphological and compositional information on the coatings was assessed by SEM, EDX and XPS, and simple adhesion tests were undertaken to indicate the strengths of coating attachment. The emphasis was to identify conditions that give high coverage, uniform coatings of small, strongly adhered, zinc phosphate crystals. The use of low-zinc solutions (e.g. an atomic Zn/P ratio of 0.07) and normal-zinc solutions (Zn/P ratio 0.25) were compared; coatings formed by the two solution types appear comparable at pH 2, although at pH 4 the low-zinc solution is more effective. Fluoride in the concentration range 200–400 ppm is indicated to be a useful additive for the normal-zinc coating bath and in the 600–1000 ppm range for the low-zinc process. The use of acid etching in the pre-treatment appears to yield better coatings than when mechanical polishing alone is used.     

The effect of the viscosity in the precursor solution on the structure of sol-gel derived silica films containing cobalt

Silica coatings containing cobalt have been prepared from sol-gel precursor solutions having a viscosity in the range of 3 to 40 cP. The different values of viscosity were achieved by aging the solutions with various amount of solvent (ethanol). The structure of these samples was analyzed using x-ray diffraction, Raman scattering, infrared absorption and Auger depth profiles. These measurements show that, upon heat treatments in air at 500°C, the cobalt oxidizes to form small oxide particles. However, when the coatings are prepared from precursor solutions with viscosity lower than about 9 cP, the cobalt migrates to the outer surface of the coating were it is oxidized to form the particles. On the other hand, if the coatings are prepared from solutions with a higher viscosity, the oxide particles are formed in the bulk of the coating. The infrared and Raman spectra indicate that the structure of this later set samples is more ordered with fewer amount of voids.     

Special features of the variation of properties of heatshielding coatings based on zirconia in relation to loading conditions

Investigations were carried out into the effect of the conditions of thermal and force loading on the comparative characteristics of different variants of heat-shielding coatings. The results are presented on tests of thermal fatigue and thermocyclic creep of ÉI868 nickel alloy with hot-gas sprayed coatings, whose ceramic layer of ZrO₂ contained different stabilizing additions: 6.2% Y₂O₃, 8% Y₂O₃, 20% MgO, 30% CeO₂. The results show that, depending on the loading conditions, the coatings can be distributed in a sequence depending on the improvement of the properties. The highest mechanical characteristics are obtained for coatings with a ZrO₂-20% MgO ceramic layer.Translated from Problemy Prochnosti, No. 5, pp. 13–17, May, 1992.     

Electrochemical and Corrosion Behavior of Titanium with Molybdenum-Carbide Coatings in Solutions of Sulfuric Acid

It is shown that the corrosion resistance of titanium increases as a result of deposition of molybdenum-carbide coatings from melts. The cathode passivating titanium with molybdenum-carbide coatings is much more active than the cathode made of molybdenum carbide. In solutions of sulfuric acid (9.5 mol. parts) at 70–80°C, the molybdenum-carbide coatings passivate titanium and, as a result, its corrosion resistance becomes 2000–4000 times higher.     

Transformation of induction heating deposited monetite coating to hydroxyapatite coating on HT-C/C composites by hydrothermal treatment in two types of solution

Monetite coatings on H₂O₂-treated carbon/carbon composites were prepared by induction heating deposition method and then converted to HA coatings by hydrothermal treatment in an autoclave with two different types of solutions, respectively NaOH aqueous solution and ammonia solution. The structure, morphology and chemical composition of the as-achieved HA coatings were characterized by XRD, FTIR SEM and EDS. The adhesion of HA coatings to the HT-C/C substrates was evaluated by a scratch test. The results showed that there are no obvious changes in the structure and morphology for the as-achieved HA coatings except to their compositions. The average critical load of the ammonia hydrothermally treated HA coatings is 10.9 N, while the NaOH hydrothermally treated HA coatings show the average one of 51 N, and the reason for it was suggested.     

Fabrication of Superhydrophobic Zinc Stearate Hierarchical Surfaces from Different Precursors

The fabrication of zinc stearate superhydrophobic hierarchical surfaces from two precursors by a simple wet chemical route and its wettability is reported. The zinc stearate coatings were prepared from a single pot using ethanolic solutions of zinc acetate/zinc nitrate and stearic acid. The coatings were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, field emission scanning electron microscopy, water contact angle, and sliding angle measurements. The coatings obtained from zinc acetate precursor showed superhydrophobicity (WCA >150°) even at lower precursor concentrations. The morphology of the coatings varied with the nature as well as the concentration of the precursors.     

电解液对微弧氧化陶瓷膜结构与耐蚀性的影响

在3种不同的电解液体系中,利用微弧氧化技术在AZ91D镁合金表面原位生长了陶瓷膜．通过扫描电镜、X射线衍射、电化学分析等方法研究了陶瓷膜的形貌特征、相结构及耐府蚀性能．研究表明,在相同反应条件下,不同电解液体系中生成的陶瓷膜结构和性能不同,硅酸钠体系中生成的陶瓷膜厚度大、偏铝酸钠体系中生成的陶瓷膜较薄,偏铝酸钠与硅酸钠的混合体系中生成的陶瓷膜致密、耐腐蚀性能较好．三体系中生成的陶瓷膜中都含有MgO,偏铝酸钠体系陶瓷膜中含有MgAl2O4、硅酸钠体系中含有Mg2SiO4,混合体系中则这两种物质都存在．     

Some comparative properties of Laves- and carbide-strengthened coatings deposited by plasma or detonation gun

The microstructures and mechanical properties of a series of plasma and detonation coatings of cobalt and nickel alloys with molybdenum, chromium and silicon were characterized. Two of the coatings were strengthened almost entirely by Laves' phase precipitation while the other two were strengthened by a combination of carbide and Laves' phases. Limited heat treatment studies indicated that the asdeposited structures are supersaturated solutions and further precipitation, particularly of Laves' phases, occurs at elevated temperatures. The elastic moduli and moduli of rupture of the coatings were determined using a ring compression technique. These data were compared with the strain-to-failure data obtained in an expanding ring test. One of the detonation gun coatings with a combination of Laves and carbide strengthening was found to have an unusually high modulus of rupture and strain-to-fracture. The corrosion resistance of the materials in room temperature and boiling solutions of hydrochloric acid, sodium hydroxide, nitric acid and sulphuric acid was also determined.     

Studies on broad spectrum corrosion resistant oxide coatings

The corrosion resistant oxide coatings, developed and applied by the conventional vitreous enamelling techniques, showed superior resistance to a range of mineral acids at various strengths and temperatures, alkaline solutions, boiling water and chrome plating solutions. These coatings possess considerable abrasion and impact resistance as well as high thermal shock resistance. The properties of the coating system have been studied in detail and found to be strongly dependent on composition and processing parameters. These coatings have been characterized by X-ray diffraction analysis and SEM studies. Some of the coating materials have been found to be biocompatible.     

Thermal decoloration kinetics of spirooxazines in Ormocer coatings prepared via sol-gel processing

Two free and one silylated (silane-substituted) photochromic spirooxazines are doped into organically modified ceramics (Ormocer) coatings by sol-gel processing and the thermal decoloration kinetics of these coatings are investigated and compared with the corresponding ethanol solutions and PMMA coatings. The decoloration behaviour of the two free dyes (SO-1 and SO-2) in the Ormocer coatings is similar to that in ethanol solutions, obeying a first-order mechanism and possessing almost the same decoloration rates as in ethanol. This suggests that the dye molecules encapsulated within the pores of the solid matrix are as free as those in ethanol solutions. The silylated dye (SO-3) in the Ormocer coatings, however, exhibits a considerably lower decoloration rate than the corresponding free dye (SO-1) and evident deviation from the first-order mechanism. This indicates apparently that the degree of freedom of the dye molecules is reduced by the silylation. These results are discussed on the basis of solvent polarity, porous structure of the Ormocer coating, and the dye-to-matrix connectivity.     

Plasticizing and wettability-enhancing coatings on carbon,silicon carbide and boron fibers

This paper is concerned with two groups of coatings on high modulus and high strength fibers for reinforcing composite materials with metal and polymer matrices.The first group includes coatings for improving and stabilizing the strength of fibers through a plasticizing effect. For carbon fibers the best results were obtained by chemically applying a nickel coating 1 μm thick with subsequent annealing at 1000°C to form a solid solution of carbon in nickel. In the case of boron and silicon carbide fibers, strength stabilization is achieved by applying coatings, 0.5–2 μm thick, of aluminum and some aluminum alloys by pulling the fibers through a melt. Analysis of the physicochemical interaction of the fibers with the coatings indicates a selective dissolution of the atoms of the fiber material in the coating at stress concentrators, with the result that the stress concentrators are smoothed out. In addition, the plasticizing effect is promoted by the relaxation of stresses in the coating at the stage of microplastic strain of the fibers.The second group includes coatings that enhance the wettability of the fibers by metal melts. An essential role in the improvement of the impregmation of carbon fiber strands and fabrics is played by the highly dispersive surface structure of the coatings, which exhibit a capillary effect as the melt spreads. The best results are obtained in double-layer coatings in which the first layer, silicon carbide, is protective and the second, molybdenum, enhances wettability.     

Preparation of Al2O3 Coatings on Metallic Foils by Sedimentation and from Solutions of Metalorganic Precursors

Alumina coatings on iron–nickel foils were prepared by sedimentation of Al₂O₃ suspensions in alcohol-in-water solutions and precipitation from aluminum acetylacetonate solutions, followed by vacuum annealing via Joule heating. The coatings consisted of alumina crystallites 15 m in size, strongly adherent to the substrate surface even after repeated boiling in water. The abrasive properties of the coatings were assessed by grinding dental enamel.     

镁合金无铬化学转化膜的研究进展

综述了国内外镁合金无铬化学转化膜研究现状,通过分析不同转化液的配方、主要处理工艺及相应转化膜的组成、结构、形貌、膜层的耐蚀性能,指出现有无铬转化技术存在的不足,并展望了无铬化学转化膜的未来发展趋势.     

Microstructures and corrosion behaviors of Zr modified CrN coatings deposited by DC magnetron sputtering

Zirconium modified chromium nitride coatings with various Zr contents have been prepared by a DC reactive magnetron sputtering technique. The detailed investigations in terms of composition, phase structure, morphology and corrosion properties have been performed by GDOES, XRD, SEM and electrochemical measurements, respectively. The as-deposited coatings with Zr contents ranging from 0 to 3.2 at. % form nanocrystalline solid solutions, where Zr substitute Cr in the CrN lattice. With increasing Zr contents, the lattice parameters increase but the grain sizes show little effects. All the coatings exhibit dense compact columnar structures in SEM cross-sectional observations. Electrochemical measurements in 3.5% NaCl solutions revealed that the additions of Zr into CrN coatings improved their chemical inertness. The coated samples with much low corrosion current densities in nA/cm² range show their excellent protective characteristics to the stainless steel substrates. The corrosion mechanism, however, was due to the slight pitting corrosions, which were mainly localized in the growth defects.     

Preparation of electroplated Ni-P-ultrafine diamond, Ni-P-carbon nanotubes composite coatings and their corrosion properties

Ni-P-ultrafine diamond (UFD) and Ni-P-carbon nanotubes (CNTs) composite coatings were deposited by electroplating at 76°C. The relation between the content of the incorporation and the amount of the UFD and CNTs in the electroplating solution was investigated. The corrosion behavior of the composite coatings was evaluated by polarization curves and electrochemical impedance spectroscopy in 0.1 M NaCl and 0.5 M H₂SO₄ solutions. It was found that increasing the UFD content in the coatings displays better corrosion performance, while a contrary result for the CNTs incorporated alloys was found due to the special structural state. The results show the incorporation of UFD and CNTs in Ni-P coatings is advantageous for forming better passive films.     

Effect of different aqueous synthesis parameters on the size of CdSe nanocrystals

The variation of CdSe nanoparticle size as a function of synthesis conditions is presented. Cadmium sulphate (CdSO₄), cadmium chloride (CdCl₂) and sodium selenosulphate (Na₂SeSO₃) solutions were used as precursors. Nanoparticles were synthesized by aqueous chemical methods. The synthesis parameters studied were pH, Cd:Se ratio and the type of stabilizing agent. Three different stabilizing agents were used, thioglycolic acid, mercaptoethanol and poly(vinyl pyrrolidone). Fourier transform infrared spectroscopy results confirmed the presence of the stabilizing agent on the surface of the nanoparticles. Ultraviolet visible and X-ray powder diffraction measurements were used to estimate the trend of size variations of the particles with different synthesis parameters, which agreed fairly by both techniques and the crystal structure. Additionally, the size of the nanoparticles was obtained by transmission electron microscopy measurements. Whilst the effect of pH was different for each of the different stabilizing agents due to the different chemical groups in the thiol compounds and the size of the nanoparticles varied with the used stabilizing agents, the effect of Cd:Se ratio in the size of nanoparticles showed the same tendency for the several stabilizing agents.     

Thermal Aging of Combustion Chemical Vapor Deposited Oxide Coatings

Zirconia coatings containing yttria were deposited onto sapphire substrates using liquid fuel combustion chemical vapor deposition (CCVD^sm ) and subsequently aged in air at 1,200°C. Toluene solutions, containing 2.5 and 7.5 mole percent Y 2-ethylhexanoate (Y 2-EH) (balance Zr 2-EH( and total metal concentrations (Zr + Y) of 0.005 M and 0.02 M, were used. All coatings were polycrystalline with those produced from the higher Y 2-EH solutions displaying complex microstructures, including dendrites at the higher molarity. Gas temperatures measured with a thermocouple during deposition near the substrate surfaces were between 1,200 and 1,400°C

Thermal aging produced significant effects on the coatings' morphologies and x-ray diffraction-patterns. Diffusional processes during annealing caused particle coalescence, and smoothed and densified the coatings. The x-ray diffraction data indicate that substantial micro structural! changes occur in these coatings at 1,200° C.     

Microneedles coated with porous calcium phosphate ceramics: Effective vehicles for transdermal delivery of solid trehalose

Trehalose (-D-glucopyranosyl--D-glucopyranoside) is recognized as a promising fast-dissolving solid reservoir capable of stabilizing the native structure of proteins and suitable for loading with a wide variety of bioactive substances. Currently, there is a growing interest in developing cost-effective methods for immobilizing solid trehalose on arrays of microneedles for delivering protein-based and DNA-based vaccine to the epidermis. In the present work, micro-porous calcium phosphate coatings were used to provide a biocompatible interface with a large surface area for the effective immobilization of trehalose on microneedles. Calcium phosphate coatings with varying degrees of porosity were electrochemically synthesized on the tips of stainless steel acupuncture needles and loaded with solid trehalose. Skin experiments were designed to determine the ability of micro-porous calcium phosphate coatings to deliver solid trehalose into epidermis without breaking during insertion. The mechanical performance of the coatings was assessed by inserting the tips of the coated needles into human skin to an average depth of 100–300 m and then removing them for analysis by scanning electron microscopy. Microporous calcium phosphate coatings loaded with trehalose effectively breached the stratum corneum and allowed direct access to the epidermis without breaking and without stimulating nerves in deeper tissues.     

Effect of Growth Conditions on the Structural Properties of Calcium Phosphate Coatings Prepared in the System CaCl<Subscript>2</Subscript>-KH<Subscript>2</Subscript>PO<Subscript>4</Subscript>-KOH-HCl-H<Subscript>2</Subscript>O

The effect of growth conditions (supersaturation, relative concentrations of precursors, solution pH, and process duration) on the phase composition and structural properties of calcium phosphate coatings is studied. The results are used to determine the concentration boundary of metastable, supersaturated solutions at 37°C and a Ca/P molar ratio of 1.67 (hydroxyapatite stoichiometry). High supersaturations are shown to result in the growth of mixed-phase coatings: hydroxyapatite + octacalcium phosphate. At low supersaturations, single-phase hydroxyapatite coatings are obtained. The coatings consist of preferentially oriented nanocrystallites, independent of the growth conditions. The texture of the coatings and the size of the nanocrystallites are most sensitive to the growth duration.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 8, 2005, pp. 985–989.Original Russian Text Copyright © 2005 by Savvin, Kryzhanovskaya, Tolmachev.