Sol–Gel SiO2-ZrO2 Coatings for Optical Applications

SiO₂-ZrO₂ based nanostructured multilayers films have been prepared by sol–gel processing from metallorganic precursors by low temperature inorganic polymerization reactions. Simultaneous gelation of both precursors was realized. Homogeneous and transparent films were obtained at room temperature by dip- and spin-coating on glass and silicon wafer substrates. Samples with successively deposited layers (1–3 layers) and successive thermal treatments have been also studied. Each deposited layer was thermally treated for 1 h at 300°C. The coatings were characterized by XRD, spectroellipsometry (SE), UV-VIS spectroscopy and AFM methods. The influence of substrates, number of coatings and number of thermal treatments on the optical and structural properties of the films was established. The thickness of three deposited SiO₂-ZrO₂ layers is about 496 nm on glass substrates and 413 nm on the silicon wafer substrate. The films deposited on glass are more porous than those deposited on silicon. The properties of optical waveguide prepared from SiO₂-ZrO₂ layers on silicon substrates will be discussed.     

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 rhenium coatings obtained by CVD

By chemical vapor deposition in the hydrogen atmosphere from Re₂(CO)₁₀ and Re(CO)₃(Cp) on steel and ceramic (C/SiC) substrates, rhenium coatings are obtained with an average thickness of 3–13 μm, when Re₂(CO)₁₀ is used, and of 2–8 μm when depositing from Re(CO)₃(Cp). The coatings are studied by X-ray diffraction and scanning electron microscopy. It is shown that when Re₂(CO)₁₀ is used, an increase in the deposition temperature results in the growth of textured coatings with preferred orientation of crystallites in the [0 0 2] direction. At the same time, a tendency for decreasing the size of rhenium crystallites is observed. With the change of evaporator temperature, the structure of Re coatings obtained from Re(CO)₃(Cp) on steel substrates changes considerably: from compact non-layered without the obvious growth direction (T _evaporator = 120°C) to a three-layer structure, where the initial layer has a compact structure followed by columnar and powdered layers (T _evaporator = 110°C). A fine compact coating is formed on ceramic substrates at an evaporator temperature of 110°C.     

Fabrication,morphology and mechanical properties of Al2O3–Al graded coatings on China low activation martensitic steel substrates

Al₂O₃, Al₂O₃/Al and Al₂O₃–Al graded coatings were fabricated on China low activation martensitic steel and silicon substrates by RF magnetron sputtering. The coating composition and cross‐section morphologies were investigated using X‐ray photoelectron spectroscopy, Auger electron spectroscopy and field‐emission scanning electron microscopy. The mechanical properties of the coatings were studied using nanoindentation, wafer‐curvature measurements and microscratch tests. The results show that usable Al₂O₃–Al graded coatings could be fabricated. With a more continuous compositional gradient, the interface zone was more compact. The hardness and elastic modulus of Al₂O₃–Al graded coatings were less than those of Al₂O₃ coatings, but greater than those of Al₂O₃/Al coatings. After annealing at 773 K for 3 h, the hardness of Al₂O₃–Al graded coating showed a small increase. The residual stresses in Al₂O₃–Al graded coatings declined to about 0.3 GPa, compared with the 6.6 GPa for Al₂O₃ coating. The adhesion of Al₂O₃ was improved by deposition of Al or Al compositional gradient oxide layers. Copyright © 2011 John Wiley & Sons, Ltd.     

A Microstructural Zone Model for the Morphology of Sol-Gel Coatings

The thickness and the morphology of dip-coated single sol-gel layers is easily controlled by varying the sol compositions and the deposition parameters. A thorough study of the microstructure of transparent conducting ZnO:Al coatings deposited on fused silica substrates using X-ray diffraction, X-ray reflectometry and transmission electron microscopy cross-sections as well as of In₂O₃:Sn, SnO₂:Sb, ZnO and TiO₂ coatings reported in the literature shows that three basic morphologies can be observed: granular, layered and columnar. In multilayer systems they were found to depend essentially on the single layer thickness (SLT) and on the crystallite size determined from the data of thick films, a parameter called the “intrinsic crystallite size (ICS)”. All the results so far analysed are in agreement with a 3-zone model when ICS is plotted against SLT or in a more refined version when q = ICS/SLT is plotted against the homologous temperature T _sintering/T _melting. Comparison with the Movchan-Demchishin and Polley-Carter models proposed for PVD and CVD coatings, respectively, is presented.     

Initial corrosion behavior of composite coatings obtained by co-electrodeposition of zinc with nanoparticles of Ti and Ce oxides

The present work reports the results obtained for the electrodeposition of composite Zn coatings on steel by using Ti and Ce oxides nanopowders, separately or in mixture, and a TiO₂·CeO₂ binary oxide. In an attempt to correlate the effects of nanoparticles on corrosion behavior of the composite deposits, the properties of Zn–TiO₂·CeO₂ layers were compared with those referring to similar coatings prepared by using a simple mixture of the two oxides or individual oxides. Corrosion measurements were performed in 0.2 g?L^?1 Na₂SO₄ solution (pH?=?5). The results of electrochemical measurements (open circuit potential measurements, polarization curves, and electrochemical impedance spectroscopy) were corroborated with those obtained by using X-ray diffraction, atomic force microscopy, scanning electron microscopy, and salt spray tests. The results indicate that the composite Zn–(TiO₂?+?CeO₂) coatings exhibit the highest corrosion resistance from all investigated Zn coatings.     

Stabilization of TiO<Subscript>2</Subscript>–Co<Subscript>3</Subscript>O<Subscript>4</Subscript> thin films on a glass fiber material by introduction of silica into the matrix

The TiO₂–Co₃O₄–SiO₂ oxide system supported on glass fiber was synthesized and studied. The oxide layers attached to the glass fiber surface have a porous structure. Characteristics of thin-film coatings on the glass fiber substrate (oxide layer phase composition and adhesion to the glass fiber surface) depend on the silica concentration. The obtained materials are catalytically active towards the exhaustive oxidation of propane.     

Charakterisierung anodischer Deckschichten an Platin-Elektroden mittels R?ntgen-Photoelektronenspektroskopie

Zusammenfassung Eine Platinelektrode wurde bei 3 V vs. SHE in 0,5 M H₂SO₄ und bei 3 V vs. Ag/AgCl-Bezugselektrode in 1 M NaOH anodisch polarisiert und die entstandenen oxidischen Deckschichten spektroskopisch analysiert. Mittels Röntgen-Photoelektronen- und Elektronenenergieverlust-Spektroskopie konnten die Passivschichten nach Transfer der Elektrode aus der elektrochemischen Zelle in ein Ultrahochvakuumsystem als Pt(OH)₄ (saurer Elektrolyt) und PtO(OH)₂ (alkalischer Elektrolyt) charakterisiert werden. Auch bei niedrigeren Potentialen scheint in H₂SO₄ Hydroxid als Oberflächenspezies vorzuliegen. Diese Untersuchungen stehen in Einklang mit voltammetrischen In-situ-Messungen.

---

Characterization of anodic coatings on platinum electrodes by X-ray photoelectron spectroscopy

Summary A platinum electrode was anodically polarized at 3 V vs. SHE in 0.5 M H₂SO₄ and in 1 M NaOH at 3 V vs. Ag/AgCl reference electrode and the oxidic coatings formed were spectroscopically analyzed. The passive layers could be characterized by X-ray photoelectron and electron energy loss spectroscopy after transferring the electrode from the electrochemical cell into a UHV system. The coatings were found to consist of Pt(OH)₄ (acid electrolyte) and PtO(OH)₂ (alkaline electrolyte). Hydroxide seems also to be the predominant surface species at lower potentials in H₂SO₄. These investigations are in agreement with voltammetric in situ measurements.

     

Formation mechanism of HA-based coatings by micro-arc oxidation

Hydroxyapatite (HA)-based coatings were prepared by micro-arc oxidation (MAO) in an aqueous electrolyte containing calcium acetate and β-glycerophosphate disodium at high applied voltage. The structure and evolution of phase components in the coatings as a function of duration time (1–20 min) were investigated. It was observed that some granules started to appear in the electrolyte adjacent to anode after MAO duration for about 5 min and become more in amount with prolonging duration time. The obtained results show that the coatings consist of HA- and TiO₂-based two layers, in which the HA-based outerlayer contains small amounts of α-TCP (α-Ca₃(PO₄)₂) and CaCO₃ while the TiO₂-based innerlayer contains CaTiO₃. The granules are negatively charged amorphous HA, TCP and CaCO₃. It is suggested that formation of the granules in the electrolyte adjacent to anode, electro-migration of the granules onto the pre-formed TiO₂-based layer and sintering-caused phase transformation of the adhered granules are possible mechanism for HA-based layer formation.     

Ormocer (ZrO2-PMMA) Films for Stainless Steel Corrosion Protection

The chemical protection of 316 L stainless steel coated with ORMOCER coatings of polymethylmethacrylate (PMMA) and ZrO₂ has been verified. The coatings were dip-coated on the substrates from sols prepared by mixing zirconium propoxide (ZrOC₃H₇)₄, isopropanol (C₃H₇OH), glacial acetic acid (CH₃COOH), polymethylmethacrylate and water under application of ultrasounds. The films were heat treated between 40 and 300°C in air up to 20 h. Their morphology was studied by electron scanning microscopy (SEM). Their anticorrosion behavior was analysed in 0.5M-H₂SO₄ solutions through potentiodynamic polarization curves at room temperature.The influence of the sol preparation, coating composition as well as of the duration and temperature of heat treatments on the corrosion parameters is reported. The films act as geometric blocking layers against the corrosive media and increase the lifetime of the substrate up to a factor 30.     

Contribution to the analytical characterization of coatings produced by thermal spraying

This paper reports on the use of Auger electron spectroscopy (AES)/ depth profile analysis for the investigation of plasma-sprayed coatings. Prior to spraying the St 37 substrates are heated to 300 °C or 500 °C for ceramic or metallic layers, respectively. Studies of the starting materials and of the interfaces are important if the adhesion mechanism is to be understood. Therefore the initial components—the unheated and heated substrates and the powder particles NiCrAl, Al₂O₃ and ZrO₂-7.25Y₂O₃—are analyzed. Depth profiles obtained from two coatings St 37/NiCrAl and St 37/Al₂O₃ show the influence of plasmaspraying on substrate surfaces and sprayed particles. Plasma-spraying mainly causes a decrease of superficial carbon contamination for both coating layers. In the case of St 37/NiCrAl incorporation of carbon in the sprayed layer is observed. The whole layer is almost completely oxidized except for some areas where substrate and particle material are present. It is assumed that these areas are identical with so-called adherence zones.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

Impact of Al nanoparticles upon the microstructure and wear properties of Ni-Cr-Al nanocomposite coatings

Ni–7Cr and Ni–7Cr–2Al (wt.%) nanocomposite coatings were fabricated by co-electrodeposition of Ni with Cr (40 nm) or and Al (75 nm) nanoparticles from a nickel sulfate bath, their microstructure, friction and wear performance were comparably evaluated in order to elucidate the effect of Al nanoparticles on the properties of nanocomposite coatings. The results indicated that the co-deposition of minor Al nanoparticles significantly increases the microhardness and wear resistance because Al nanoparticles with surface amorphous oxides layers exert the dispersion-strengthening effect like Al₂O₃ nanoparticles.     

AES investigation of thermally sprayed Al2O3 coatings on steel

Summary The investigation of plasma sprayed steel/Al₂O₃ composites by means of Auger Electron Spectroscopy (AES) combined with depth profile analysis is described. Incomplete sprayed Al₂O₃ layers permit analysis of single sprayed particles and of surrounding uncovered steel substrate regions. More complete coatings are separated from the substrates, so that contact surfaces of substrates and Al₂O₃ layers can be analyzed. In order to determine the influence of preheating the substrates on the interface widths between steel substrate and Al₂O₃ coating and therefore on the adherence mechanism, both procedures are carried out for two preheating temperatures. It is shown that preheating hardly effects the interface widths beneath single sprayed particles but it causes laterally constant widths for complete layer fragments. Additionally, a comprehensive view about oxide layer thicknesses on the steel substrates before and after plasma spraying is offered.     

Experimental and theoretical studies on the corrosion properties of some conducting polymer coatings

In this study, the effects of poly(N-ethylaniline) (PNEA) monolayer coating and PPY/PNEA and PNEA/PPY bilayer coatings, which were formed on the low carbon steel (LCS) surface by electropolymerization in 0.1 M monomer + 0.3 M oxalic acid medium, on the corrosion of the LCS in 1 M H₂SO₄ medium have been investigated. LCS electrodes, which were coated with each of these conductive polymer layers, were held in 1 M H₂SO₄ medium for various time periods, in order to obtain current potential curves, and with the help of these curves, the corrosion parameters have been determined. Experimental findings show that the LCS coated with polymer layers prevent the corrosion of bare LCS in 1 M H₂SO₄ medium and bilayer PPY/PNEA and PNEA/PPY coatings are better than monolayer PNEA coating. In order to elucidate the interaction between the coatings and the metal, theoretical calculations have been done using AM1 semiempirical method. The calculated data have been found to support experimental findings.     

Characterization of cerium-based conversion coatings for corrosion protection of AISI-1010 commercial carbon steel

The role of hydrogen peroxide in the formation of cerium conversion coatings by immersing AISI 1010 commercial carbon steel substrates into solutions containing various concentrations of CeCl₃ (0.1, 1, and 10 g L⁻¹) has been investigated as an alternative method for their protection against corrosion. The deposits prepared from the solutions with H₂O₂ consist of yellow thin and non-uniform coatings with agglomerates of small CeO₂ and Ce₂O₃ crystallites whose sizes increased over the metallic surface as the cerium concentration was increased. Cerium pre-treatments in the presence of H₂O₂ displayed layers that were rougher than those synthesized without H₂O₂. A comparison with the chromate conversion pre-treatment is also simultaneously carried out with the discussion of the possible reactions involved in the different stages of process. The coating obtained from the solution containing 0.1 g in 1,000 mL produced better corrosion resistance on the substrate than that observed for its counterparts due to the fact that the surface was more uniformly covered by the conversion coating. The addition of H₂O₂ to the cerate baths improves visible roughness, corrosion resistance of the conversion coatings and bond strength because hydrogen peroxide acts as an oxygen source during the formation of the coatings.     

Effect of Y2O3 on microstructural characteristics and wear resistance of cobalt‐based composite coatings produced on TA15 titanium alloy surface by laser cladding

The effects of Y₂O₃ on the microstructure, phase composition of the coatings, microhardness and wear resistance of cobalt‐based composite coatings prepared by laser cladding were investigated. The TA15 titanium alloy was selected as substrate which the cobalt‐based composite powder with different content of Y₂O₃ was cladded on. The microstructure of the coatings was observed by scanning electron microscope (SEM) and metallurgical microscope. The phase structure of the coatings was determined by X‐ray diffraction (XRD), and the microhardness and wear resistance of the coatings were measured by hardness tester and wear testing machine. The results show that the rare earth oxide Y₂O₃ can refine and purify the microstructure of the coatings, reduce the porosities and cracks and improve compactness of the coatings. Moreover the addition of Y₂O₃ improves the microhardness of the coatings and reduces the friction coefficient, thus improving the wear property of the coatings. And the wear resistance of the coating with Y₂O₃ has improved about 50 times; the highest value of microhardness in the coating is HV1181.1. And 0.8 wt% content of Y₂O₃ in the coating is the best choice for improving the microhardness and wear resistance of the coating. It is feasible to improve the microstructure and tribological properties of laser cladding coatings by adding of Y₂O₃. Copyright © 2014 John Wiley & Sons, Ltd.     

Conversion‐coating treatment applied to in situ TiB2p reinforced Al?Si‐alloy composite for corrosion protection

In this work, continuous conversion coatings on the surface of in situ TiB₂ particulate reinforced A356 composite were formed successfully by cerium surface treatment for the first time. Scanning electron microscope (SEM) analysis showed that the conversion coatings were inhomogeneous and could be divided into two types of regions, namely, fine crack region and noncrack region. Many cerium‐rich nano‐nodules were uniformly distributed in the whole coatings. Energy dispersive spectroscopy (EDS) analysis testified that the crack coatings mainly covered the interdendritic sites occupied by TiB₂ particulates and Si phases. X‐ray photoelectron spectroscopy (XPS) analysis indicated that the conversion coatings were composed of CeO₂, Ce₂O₃, Ce(OH)₄, Ce(OH)₃, and a little amount of Al₂O₃. The electrochemical polarization tests showed that the cerium‐conversion treatment markedly improved the corrosion resistance of in situ TiB_2p/A356 composite in chloride environment, and the protection degree of the coatings was superior to that of conventional chromate‐conversion coating. According to these results, the formation mechanism of cerium‐conversion coatings was discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Thin Coatings of α- and β-Bi2O3 by Ultrasonic Spray Coating of a Molecular Bismuth Oxido Cluster and their Application for Photocatalytic Water Purification Under Visible Light

Thin coatings of Bi₂O₃ were deposited on glass substrates by ultrasonic spray coating of THF solutions of the molecular precursor [Bi₃₈O₄₅(OMc)₂₄(DMSO)₉] ⋅ 2DMSO ⋅ 7H₂O (OMc=O₂CC₃H₅) followed by hydrolysis and subsequent annealing. Depending on the synthetic protocol, the bismuth oxido cluster was transformed into either α- or β-Bi₂O₃. The as-synthesized Bi₂O₃ coatings were characterized by powder X-ray diffraction (PXRD), thickness measurements, diffuse reflectance UV-Vis spectroscopy (DRS), photoluminescence (PL) spectroscopy, Raman spectroscopy and scanning electron microscopy (SEM). The thin coatings (thickness: 5–16 μm) were compared with regard to their performance in photocatalytic rhodamine B (RhB) decomposition under visible light irradiation. The β-Bi₂O₃ coatings, that showed the highest photocatalytic activity, were used for the photocatalytic decomposition of other pollutants such as triclosan and ethinyl estradiol. In addition, the interplay between the photooxidation that is induced by the excitation of the catalyst using visible light and the photosensitized decomposition pathway was studied by degradation experiments of aqueous rhodamine B solutions using β-Bi₂O₃ coatings.     

Dépôt chimique en phase vapeur à basse température de revêtements dans le système V-C-N à partir de bis(arene)vanadium

Vanadium carbide coatings V₈C₇ have been deposited on steel substrates by MOCVD using bis(arene)vanadiums as precursors at temperatures lower than 550 °C. Addition of C₆Cl₆ in the gas phase allows to reduce the carbon content of the films to 13 at. %. These metal coatings exhibit the features of a metastable carbon-rich solid solution. Carbonitride V(C,N) and nitride δ-VN layers with only 5 at. % carbon have been deposited in the presence of NH₃. These reactive gas phases allow to grow almost all the phases of the V-C-N ternary diagram.     

Micro- and Nanostructures of Fe2O3-SiO2 Sol-Gel Derived Thick Coatings

Thick Fe₂O₃−SiO₂ sol-gel coatings with 30 wt%Fe₂O₃ were prepared on glass substrates under different conditions. These were investigated by scanning electron and atomic force microscopies. The performance of the layers depended also on the way the substrate surface was pretreated. Annealed bulk gel pieces showed phases like FeCl₂×2H₂O and presumably C₉Fe₂O₉ (300°C); at higher annealing temperatures, hematite, cristobalite and magnetite could be found.