V. S. Rudnev

Anodic spark deposition of P, Me(II) or Me(III) containing coatings on aluminium and titanium alloys in electrolytes with polyphosphate complexes

The aim of this study was to characterise the correlation between the molar ratio n=[polyphosphate]/[metal cation] in aqueous electrolyte and the growth parameters, composition and surface distribution of elements of anodic coatings on aluminium and titanium alloys. Coatings were formed in electrochemical cell using the anodic spark deposition method. The two-component electrolytes contained sodium hexametaphosphate (Na6P6O18) or sodium tripolyphosphate (Na5P3O10) and acetates of Mg(II), Zn(II), Ba(II), Mn(II), Ni(II), Pb(II), Y(III), Eu(III) were used. Coatings were characterised by electron probe microanalysis, laser mass spectrometry and X-ray diffraction. It was shown that the n value essentially affects the composition and thickness of coatings when lower than a certain value n0, which lies in the range from 2.5 to 10 depending on the metal cation in the electrolyte. Coatings formed in electrolytes of n<1 consist mostly of electrolyte species. The influence of n on composition and parameters of the coatings is explained in terms of deposition and thermolysis of polyphosphate complexes on the anode surface owing to electric breakdown.

Surface morphology, composition and thermal behavior of tungsten-containing anodic spark coatings on aluminium alloy

Abstract Anodic spark coatings on aluminium alloy were prepared in aqueous electrolytes with sodium tungstate. The influence of boric acid addition in the electrolyte on the surface morphology, elemental and phase composition of the coatings was investigated. In both cases the coatings contained O, Al and W. The coatings obtained in electrolyte with boric acid and sodium tungstate contain also B at approximately 1 at.%. Scanning electron microscopy indicated that the coatings had three layers: the grey underlayer of anodic alumina, the second black layer of crystalline or amorphous aluminium tungstate agglomerated into fibers and the outer green layer of WO3. It was proposed that isopoly- and heteropolyanions in the electrolyte used take part in the coating growth.

Multiphase anodic layers and prospects of their application

Information on preparing multiphase layers on valve metals by the plasma-electrochemical oxidation and deposition from aqueous electrolytes containing polyphosphate and fluoride metal complexes, iso-and heteropolyoxoanions, as well as electrolytes evolving solid precipitates, is summarized. Possible application fields of the metal/multiphase PEOD surface structure compositions are considered.

The effect of the conditions of formation on ferromagnetic properties of iron-containing oxide coatings on titanium

Oxide coatings formed on titanium by plasma-electrolytic oxidation in a Na3PO4 + Na2B4O7 + Na2WO4 + Fe2(C2O4)3 electrolyte-suspension at different current densities and different durations of treatment are shown to have ferromagnetic properties. The coercive force of the specimens reaches maximum values of 124 and 380 Oe at 300 and 10 K, respectively, when the thickness of coatings is about 3–5 mm. Crystallites with a mean size of ∼50 nm are found to be present in pores of the coatings. Based on the experimental data, combined with the results of theoretical modeling carried out previously, crystallites are concluded to be iron particles surrounded with a shell composed of oxides and/or hydroxides. The existence of crystallites and their spatial sizes determine the ferromagnetic properties of the coatings.

Magnetoactive oxide layers formed on titanium by plasma-electrolytic technique

Two kinds of iron-containing coatings, specifically those obtained from electrolytes containing polyphosphate iron complexes (no. 1) and from electrolyte suspensions (no. 2), are formed and studied. According to the microprobe analysis, the iron content in the coatings is 6–7 at %. Coatings of type 1 are paramagnetic, while coatings of type 2 are ferromagnetic. The distribution of elements over the depth of coatings is heterogeneous and the typical components of the surfaces have different compositions. Iron and titanium are concentrated at the bottom and walls of pores. Upon annealing in air, iron and titanium phosphates crystallize in coatings no. 1, while maghemite is formed in coatings no. 2. Based on the results obtained, the supposition is made that the ferromagnetic properties of type 2 coatings are determined by the presence of fine-dispersed magnetite and/or maghemite particles in them, as well as titanium-magnetite and/or titanium-maghemite grains.

Highly efficient nanoarchitectured Ni5TiO7 catalyst for biomass gasification.

We report the synthesis of needle-shaped nanocrystals of Ni(5)TiO(7) utilizing a solid-phase reaction of NiO with a porous and rough TiO(2) surface produced by plasma electrolytic oxidation. The single crystalline orthorhombic nanocrystals are grown along the [010] axis, featuring a length of ∼10 μm and diameters varying from several tens of nanometers up to 200 nm. The resulted novel Ni(5)TiO(7)/TiO(2)/Ti nanoarchitectured compound composite has been proven outstandingly active as a catalyst and appears most suitable for high-temperature operation in biomass gasification. The findings may pave the way to an improved and environmentally friendly technology of energy generation.

Titanium-supported nickel-copper oxide catalysts for oxidation of carbon(II) oxide

Nickel-copper compositions for catalytic oxidation of carbon(II) oxide to carbon(IV) oxide were prepared by impregnation of oxide films on titanium surface, obtained by plasma electrolytic oxidation followed by annealing. Plasma electrolysis oxide coatings with a layer thickness of 5 to 50 μm were generated using different electrolytes. The compositions were studied by X-ray powder diffraction, X-ray spectral analysis, and electron microscopy, and moisture absorption of the initial plasma electrolytic structures was estimated. A linear correlation was found between the overall concentration of nickel and copper (4 to 25 mol %) in the surface layer of ∼2–5-μm compositions and their catalytic activity. The overall concentration of nickel and copper was found to increase in parallel with the moisture absorption of plasma electrolytic oxidation coatings. Nickel-copper compositions based on plasma electrolytic oxidation coatings generated in a silicate electrolyte displayed the best catalytic, mechanical, and adhesion properties.

Comparative analysis of the composition, structure, and catalytic activity of the NiO-CuO-TiO2 on Titanium and NiO-CuO-Al2O3 on aluminum composites

The catalytically active oxide structures based on Al and Ti prepared by plasma-electrolytic oxidation (PEO) and additionally modified by impregnation with an aqueous solution of nickel and copper nitrates followed by annealing were studied. The oxide film-metal composites were studied using X-ray diffraction and X-ray spectroscopic analysis, X-ray electron spectroscopy, and electron microscopy. The catalytic activity of the composites in the reaction of CO oxidation was studied. In spite of differences in the elemental composition and morphology, the initial oxide layers on Al and Ti were comparable in terms of activity. Microgranules of size ∼ 1 µm and formations from tens to hundreds of nanometers in size were detected on the surface of PEO layers. The modified layers contained crystalline CuO, NiO, and Al2O3 or TiO2 phases. The surface layers of the modified structures about 3 nm in thickness on AMg5 aluminum alloy and VT1-0 titanium had the same elemental composition but exhibited different activity in the reaction of CO oxidation to CO2.

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.

Calcium-containing biocompatible oxide-phosphate coatings on titanium

Formation of biocompatible coatings containing TiO2 along with various calcium phosphates, including hydroxyapatite, on a titanium surface was studied by plasma electrolytic oxidation.