Tungsten oxide films on aluminum and titanium

Experimental data are presented which demonstrate that plasma electrolytic processing of aluminum and titanium in room-temperature aqueous solutions containing tungstate iso-and heteropolyoxoanions is a viable approach to producing Al/Al₂O₃/WO₃ and Ti/TiO₂/WO₃ structures. Tungsten trioxide can be obtained both in the form of a continuous layer and surface islands.     

The effect of Fe-containing colloid particles in electrolyte on the composition and magnetic characteristics of oxide layers on titanium formed using the method of plasma electrolytic oxidation

The composition, structure, and magnetic characteristics of oxide layers on titanium formed in electrolytes containing colloid particles of iron hydroxo-compounds and their filtrates have been investigated. The obtained results corroborate that formation of Fe-containing crystallites in coating pores occurs due to ingress of negatively charged particles of hydroxo-compounds of transition metals from the electrolyte into breakdown channels and their transformation in local spaces of electric breakdowns. The presence of crystallites in pores is responsible for coatings ferromagnetic properties. Fe-containing crystallites were not found in pores of coatings formed in the electrolyte after filtering of iron hydroxides and hydroxo-salts, whereas coatings contained small concentrations of iron homogeneously distributed over the surface and manifested paramagnetic properties at room temperature.     

The thermal effect on magnetic properties of iron-containing coatings formed on titanium by plasma-electrolytic oxidation

The effect of annealing in air at T _an temperature up to 800°C on the magnetic characteristics, elemental and phase composition, and surface morphology of iron-containing oxide coatings on titanium is studied. Annealing at T _an ?? 500°C does not seem to affect the composition and morphology of coatings. The coercive force (H _c ) of specimens equals 70 Oe at room temperature and 256 Oe at 2 K. Upon annealing at 700 or 800°C, the H _c value decreases to 13 Oe. The change in the magnetic characteristics correlates with the crystallization of a number of iron and titanium phosphates, the redistribution of elements in the coatings and pores, and the surface formation of microcrystals and whiskers.     

Titanium-supported Ce-, Zr-containing oxide coatings modified by platinum or nickel and copper oxides and their catalytic activity in CO oxidation

A combination of plasma electrolytic oxidation (PEO) and impregnation techniques followed by annealing in air has been used to obtain composites Pt/nZrO₂ + pTiO₂/Ti, Pt/nZrO₂ + pTiO₂ + zCeO_x/Ti, NiO + CuO/nZrO₂ + pTiO₂/Ti, NiO + CuO/nZrO₂ + pTiO₂ + zCeO_x/Ti with different zirconium and titanium contents and ZrO₂/TiO₂ phase ratio. The composites have been investigated by means of XRD, XPS and SEM/XSA methods. According to the XPS data, the platinum content on the coating surface is ~ 0.4 at.%, whereas the XSA measurements have shown that the nickel and copper contents in coatings attain 16 and 8 at.%, respectively, depending on the initial oxide coatings composition. Nickel and copper oxides form either extended islets or solid layers (“crusts”) on the coating surface. Both the composites promoted with platinum and those with the “crust” built from nickel and copper oxides are active in CO oxidation at the temperatures above 200 °C and 300 °C, respectively.     

Catalytically active composite materials with porous aluminum oxide matrix modified by γ-MnO<Subscript>2</Subscript> nanoparticles

Manganese dioxide has been deposited on the surface of an aluminum foil anodized in 3% solution of oxalic acid using the methods of thermal decomposition of manganese nitrate and potassium permanganate, as well as chemical synthesis, in the same solutions with intermediate drying and subsequent annealing. It has been demonstrated that the method of thermal decomposition of potassium permanganate is the most suitable for producing thermally stable “ultradispersed γ-MnO₂/nanostructured Al₂O₃/Al” composites. The produced composites are active in the reaction of oxidation of CO into CO₂ at temperatures above 180°C. Studies by means of the methods of scanning electron and atomic force microscopies have shown that the concentration and surface distribution of γ-MnO₂ particles depend on the morphological structure of aluminum oxide that is determined by conditions of the metal surface pretreatment and application of the pore broadening operation.     

Thermally Stimulated Evolution of the Surface of Ni- and Cu-Containing Plasma-Electrolytic Oxide Coatings on Titanium

Protection of Metals and Physical Chemistry of Surfaces - The effect of the temperature of annealing in air on the surface architecture and composition of oxide layers has been studied....     

Eu2O3/SiO2 nanocomposites obtained by extraction pyrolysis

The conditions of the formation of nanosized Eu₂O₃/SiO₂ composites were studied. Amorphous silicon dioxide was coated with europium oxide by extraction pyrolysis. The resulting samples were studied by X-ray phase analysis and atomic force microscopy. The Eu₂O₃/SiO₂ composites were tested as catalysts of CO conversion.     

Micrograins on the surface of anodic films

Data on the composition and structure of micrograins located on the surface of oxide films formed on aluminum by the plasma-electrochemical (PE) method are shown. The studied micrograins represent polyhedral tubes narrowing towards one end with the characteristic size of about 1μm. They are concentrated on the defective surface sites. Micrograins contain considerably higher amounts of carbon, nickel, copper, and other electrolyte components but lower amounts of aluminum and oxygen compared with the oxide film surface. The formation of micrograins and their deposition on the film followed by their treatment with electric discharges is, apparently, one of the mechanisms of the formation of multiphase and multicomponent anodic oxide layers by the PE method.     

Catalytically active cobalt-copper-oxide layers on aluminum and titanium

Oxide coatings modified with cobalt and copper oxides are obtained on titanium and aluminum by means of combining plasma electrolytic oxidation (PEO) in silicate and zirconate electrolytes and impregnation in nitrate solutions followed by annealing. The effect of PEO coatings that were preliminarily formed on aluminum and titanium in different electrolytes on the composition and surface morphology of cobaltcopper oxide composites and their activity with respect to CO oxidation is studied. The maximum total concentration of cobalt and copper is found to be typical of composite layers based on SiO₂ + Al₂O₃/Al, while the minimum content is observed in the case of layers based on ZrO₂ + TiO₂/Ti, the PEO bases being characterized by the highest and lowest water-absorbing capacity, respectively. The effect of PEO coatings on the catalytic activity of cobalt-copper oxide catalysts decreases in the series SiO₂ + TiO₂/Ti > SiO₂ + Al₂O₃/Al > Ce₂O₃ + ZrO₂ + TiO₂/Ti > ZrO₂ + TiO₂/Ti.