Oxide layers with ferro- and ferrimagnetic characteristics formed on aluminum via plasma electrolytic oxidation

(Fe+Co)-containing oxide coatings are formed on aluminum alloy. It is established that at a temperature of ～2 K, the coatings manifest ferromagnetic properties. The coatings, formed within 5 min, are characterized by an anomalously high coercive force H _c = 1300 Oe. At room temperature (300 K), they manifest ferromagnetic properties, whereas in external fields of ～30 kOe they tend to transition into the antiferromagnetic state. It is concluded that magnetism is in this case due to the presence in the coating’s pores of crystallites ～50–100 nm in size that consist predominantly of reduced iron, cobalt, and aluminum.     

Deposition of cobalt-containing films on titanium by plasma electrolytic oxidation

The possibility of forming Co-containing coatings on titanium by plasma electrolytic oxidation and by a combination of oxidation and impregnation methods using an aqueous solution of sodium silicate as the base electrolyte was examined. Comparative analysis of the composition and structure of the systems obtained and of their activity in oxidation of CO to CO₂ was performed.     

Anodic-spark layers on aluminum and titanium alloys in electrolytes with sodium phosphotungstate

The influence exerted by the pH of an aqueous 0.0083 M solution of Na₂H[PW₁₂O₄₀] on the composition and morphology of anodic coatings galvanostatically formed on aluminum and titanium alloys at sparking and breakdown voltages was studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 9, 2004, pp. 1472–1480.Original Russian Text Copyright © 2004 by Lukiyanchuk, Rudnev, Kuryavyi, Gordienko.     

An X-ray photoelectron spectroscopy study of Ni,Cu-containing coatings formed by plasma electrolytic oxidation on aluminum and titanium

A series of Ni- and/or Cu-containing coatings formed by plasma electrolytic oxidation on aluminum and titanium are examined by X-ray photoelectron spectroscopy. Binding energies of core electrons, elemental composition, chemical state of elements, and features of the structural organization of the surface and nearsurface layers of the coatings are determined. A combination of the data collected indicates similar regularities of the composition and significant distinctions in the structure of the coatings formed. It is shown that the coatings formed on titanium are characterized by a considerably higher phosphorus concentration, and correspondingly, phosphates, unlike the coatings formed on aluminum, in which base metal and 3d element (Ni or Cu) oxides are dominant. In both cases, Cu is mainly concentrated in the surface layers of the coatings whereas Ni is mainly concentrated in the near-surface layers.     

Calcium and strontium phosphates coatings on titanium formed by the plasma electrolytic oxidation

Oxide-phosphate coatings were formed in electrolytes with Ca(II) and Sr(II) polyphosphate complexes. The data on an effect of a ratio of metal polyphosphate complexes in the electrolyte, treatment time on an elemental and phase compositions, thickness and morphology of coatings were obtained. The approach is promising for application of the coatings containing calcium phosphate with additives of phosphates of other metals to titanium implants.     

Properties of coatings formed on titanium by plasma electrolytic oxidation in a phosphate-borate electrolyte

Effect of the component concentration of an orthophosphate-tetraborate aqueous electrolyte on the thickness, composition, surface structure, and protective properties of coatings deposited from this electrolyte was studied.     

Fabrication of polytetrafluoroethylene- and graphite-containing oxide layers on aluminum and titanium and their structure

Stable aqueous electrolyte emulsions with negatively charged micelles containing dispersed particles of polytetrafluoroethylene (PTFE) or graphite are obtained using siloxane-acrylate emulsion as an emulsifier. The oxide coatings formed in such electrolytes contain carbon, polytetrafluoroethylene, or graphite. The coatings with PTFE particles are similar to monolithic polytetrafluoroethylene with respect to its hydrophobic characteristics. According to X-ray photoelectron spectroscopy data, the surface of the formed coatings predominantly contains aliphatic carbon (C-C and C-H bonds) and some fraction of oxidized (or, in the case of PTFE-containing electrolytes, fluorinated) carbon.     

Structures and magnetic properties of iron- and cobalt-containing oxide coatings on an aluminum alloy formed in electrolytes via plasma electrolytic oxidation

The effect of the nature of the supporting electrolyte in the composition of electrolytic suspensions containing dispersed particles of Fe(III) and Co(II) hydroxides, and of anodic and bipolar anodic-cathodic polarization on features of the formation, composition, and magnetic characteristics of oxide coatings is studied. In all cases, iron and cobalt are incorporated into the coatings and are concentrated predominantly in pores. The pores of the coatings include particles consisting of the reduced metals, presumably surrounded by oxide or hydroxide shells. The electrolyte composition affects the concentration and ratio of the metals in the particles. A correlation is observed between the ferro- or ferrimagnetism of the coatings and the content and ratio of cobalt and iron in the pores.     

Deposition,composition, and activity in CO oxidation of anodic layers with platinum on aluminum and titanium

Pt + TiO₂/Ti(Al) and Pt + CeO₂ + ZrO₂ + TiO₂/Ti composites were formed by plasma electrolytic oxidation and their surface composition and catalytic activity in CO oxidation to CO₂ were studied.     

Preparation,properties, and catalytic activity of platinum-modified plasma electrolytic oxide structures on aluminum

Catalytically active Pt-containing oxide composites on aluminum have been prepared by plasma electrolytic oxidation (PEO) and by additional modification of the resulting coating by impregnation with an aqueous solution of chloroplatinic acid followed by calcination. The oxide film/metal composites have been characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and electron microscopy. The modified films contain the γ-Al₂O₃ and Pt crystalline phases. Platinum in the surface and subsurface layers is in the Pt⁰ state. There are platinum-rich areas on the surface of the PEO films. A higher catalytic activity in CO oxidation into CO₂ is shown by the samples whose oxide film contains nickel and copper along with platinum.     

Iron- and nickel-containing oxide-phosphate layers on aluminum and titanium

Oxide-phosphate surface structures with thicknesses of 5 to 50 μm containing iron and nickel compounds have been synthesized by plasma electrolysis (PE) in aqueous electrolytes with polyphosphate nickel(II) and iron(III) complexes. The elemental and phase compositions have been studied as affected by polarization parameters, electrolytes, and annealing parameters. Simple and complex oxides and phosphates crystallize in layers: on aluminum, AlPO₄, NiAl₂O₄, and Fe₂O₃ crystallize; on titanium, Ni₂P₂O₇, Ni_0.5TiOPO₄, NaTi₂(PO₄)₃, M^(II)M^(III)Ti(PO₄)₃, FePO₄, and Fe₂Fe(P₂O₇)₂ crystallize.     

Tetracyanoquinodimethanide adsorbed on a silica gel modified with titanium oxide for electrocatalytic oxidation of hydrazine

The electrocatalytical oxidation of hydrazine at low potential using tetracyanoquinodimethanide adsorbed on silica modified with titanium oxide was investigated by cyclic voltammetry and amperometry. The modified electrode was prepared modifying a carbon paste electrode employing lithium tetracyanoquinodimethanide adsorbed onto silica gel modified with titanium oxide. This electrode showed an excellent catalytic activity and stability for hydrazine oxidation. With this modified electrode, the oxidation potential of hydrazine was shifted toward less positive value, presenting a peak current much higher than those observed on a bare GC electrode. The linear response range, sensitivity and detection limit were, respectively, 2 up to 100 μmol l⁻¹, 0.36 μA l μmol⁻¹, and 0.60 μmol l⁻¹. The repeatability of the modified electrode evaluated in term of relative standard deviation was 4.2% for 10 measurements of 100 μmol l⁻¹ hydrazine solution. The number of electrons involved in hydrazine oxidation (4), the heterogenous electron transfer rate constant (1.08 × 10³ mol⁻¹ l s⁻¹), and diffusion coefficient (5.9 × 10⁻⁶ cm² s⁻¹) were evaluated with a rotating disk electrode.     

GDOES,XPS, and SEM with EDS analysis of porous coatings obtained on titanium after plasma electrolytic oxidation

In the paper, the glow discharge optical emission spectroscopy, X‐ray photoelectron spectroscopy, scanning electron microscopy, and energy‐dispersive X‐ray spectroscopy results of a commercial purity titanium grade 2 after plasma electrolytic oxidation (PEO), also known as micro arc oxidation (MAO), are presented. The PEO treatment was performed in the electrolyte containing concentrated (85%) phosphoric acid with copper nitrate at the voltage of 450 ± 10 V for 1 min. For the electrolyte, copper nitrate addition from 300 to 600 g/l was used. Porous coatings of specific properties were obtained. The measurements results allow to state that the copper and nitrogen ions can be introduced into the surface layer formed on pure titanium by the plasma electrolytic oxidation. The distributions of these elements were detected to depend on the electrolyte composition, with the highest amounts revealed in the coating created in the electrolyte containing 600 g Cu(NO₃)₂ in 1 l H₃PO₄. Three sub‐layers of the coating, displayed in this work by two models, were developed in the study. The analysis performed shows that under the PEO treatment in each of the electrolytes used, the formation of coating with the top sub‐layers always enriched in copper compounds was found. Copyright © 2016 John Wiley & Sons, Ltd.     

A new electrolytic dissolution of aluminum alloys and determination of some constituents by inductively coupled plasma optical emission spectrometry

The new electrolytic dissolution in batch of aluminum alloys samples as grains or turns and the determination of Fe, Cu, Mn, Mg, Cr, Ni, Zn, Pb and Ti by ICP OES was investigated. In on-line electrodissolution procedures described in the literature, samples were restricted to be in the form of solid blocks or plates with one polished flat face. Here, the sample was loaded in the barrel of a modified disposable syringe (the anodic semi-cell) and pressed with a modified plunger fitted with a platinum disk to establish electrical contact with the analyte. This arrangement was introduced in a beaker containing the electrolyte (1 mol L⁻¹ HNO₃) and a platinum wire as the cathode. The resulting solution from electrodissolution (0.6 A) was used for the ICP OES determinations. The influence of the aluminum concentration increase on the determination of the elements was evaluated. Electrodissolution of certified reference materials and commercial samples revealed relative errors lower than 10% for the elements Fe, Cu, Mg, Ni, Cr, Zn and Ti (when their content is above 0.1%). Higher inaccuracies (>10%) were observed for Mn and for Fe in B.C.S. 268/1 reference material certified. The proposed method presented a relative standard deviations (R.S.D.) lower or circa 10% to all of the elements (except Pb). In comparison with traditional acid dissolution, the proposed electrodissolution method is relatively fast (about 30 min), it is clean (there is no projection of solution) and simple (heating and fumes exhaust system were not necessaries).     

Effect of electrolyte components on the magnetic and magnetoresistive characteristics of Fe-containing plasma electrolytic oxide coatings on titanium

The effect replacing Na₃PO₄ with Na₂HPO₄ in aqueous phosphate–borate–tungstate electrolyte that additionally contains Fe₂(C₂O₄)₃ on the magnetic and magnetoresistive characteristics of oxide coating/ titanium composites formed by means of plasma electrolytic oxidation (PEO) is investigated. It is established that PEO coatings with ferromagnetic characteristics form on titanium in an electrolyte containing Na₃PO₄ (pH ~ 11) upon adding iron(III) oxalate, while replacing Na₃PO₄ with Na₂HPO₄ and the respective drop in the pH of the base electrolyte down to 9.8 results in the formation of coatings with different magnetic characteristics. The correlation between changes in the values of the charge carriers’ activation energy and the magnetic susceptibility is demonstrated for the latter. An increase in the electric resistance of coatings in a magnetic field is observed, and the type of the magnetic resistance temperature dependence is established.

     

Sorbent based on aluminum oxide modified with Tiron

The adsorption of Tiron (disodium 4,5-dihydroxy-m-benzenedisulfonate) on aluminum oxide surface was studied, and optimum conditions for the modification of aluminum oxide surface were determined. The sorption of copper(II) on aluminum oxide modified with Tiron was studied. It was shown that the sorption of copper occurs by the mechanism of complex formation with the modifier (Tiron). The composition of the surface complex and its stability constant were determined: Cu: Tiron = 1: 1, logβ = 14.0 ± 0.4. Original Russian Text ? T.I. Tikhomirova, S.S. Kubyshev, A.V. Ivanov, P.N. Nesterenko, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 7 pp. 1360–1364.     

Corrosion and electrochemical behavior of water glass coatings embedded with graphite/titanium oxide on 2A12 aluminum alloy

Journal of Solid State Electrochemistry - Graphite/titanium oxide composite anti-corrosion coatings with five proportions of graphite were applied on the surface of aluminum alloy. The surface...     

Magnetic characteristics of iron-modified oxide layers on titanium

Iron-modified TiO₂ coatings on titanium exhibiting ferromagnetic properties are formed by combining plasma electrolytic oxidation (PEO) and impregnation with subsequent annealing. It is found that iron is contained in the composition of dispersed particles with sizes of 1–10 μm distributed over the surface of the coatings. It is shown that the coercive force of the coating on titanium samples is 20–70 Oe. The composition, structure, and magnetic properties of the samples with coatings prepared via direct PEO and by combining PEO and impregnation are compared. It is concluded that impregnation and annealing procedures can be used to impart ferromagnetic properties to PEO coatings with different compositions, e.g., protective coatings and coatings applied in catalysis or medicine.