I. A. Tkachenko

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.

Magnetic properties of plasma-electrolytic iron-containing oxide coatings on aluminum alloy

Applications of the plasma-electrolytic oxidation technique for the formation of magnetically active oxide coatings on aluminum and titanium are reviewed. Specimens of aluminum-, iron-, and tungsten-containing oxide layers on aluminum substrates with ferro- and ferrimagnetic properties are experimentally produced and studied, as well as specimens that can be remagnetized at certain external magnetic field intensities and specimens the magnetization of which is opposite to the external field. The existence of nano- and microscale crystallites, in which aluminum and metals from the electrolyte are accumulated, are found in pores of the coatings. The crystallites supposedly determine the magnetic properties of the specimens. A correlation between the Fe/Σ(W, Al) atomic ratio in crystallites and the magnetic properties of the systems studied is discovered.

Magnetic properties of surface layers formed on titanium by plasma electrolytic oxidation

The magnetic properties of the coatings formed by plasma electrolytic oxidation on titanium and modified by nanoparticles of cobalt were studied. The coercitivity of the obtained magnetoactive layer were equal to 514 Oe at room temperature and to 1024 Oe at 2 K. The high coercitivity is the result of the nanosize effects of particles embedded in the coating. The structure of the nanoparticles, which consist of a Co ferromagnetic core and a CoO antiferromagnetic shell, determines the magnetic properties of the coatings on the whole.

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

Abstract(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 Hc = 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.

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.

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.

Europium oxide-based nanocomposites synthesized by extraction-pyrolytic method

Promise was shown for a method for producing complex oxide nanocomposites of europium, iron, and bismuth both as bulk powders, and as thin-film coatings on various supports by low-temperature pyrolysis of organic extracts based on extraction systems with various polyfunctional ligands. The magnetic properties of nanosized bismuth and europium ferrites of the compositions Bi0.775Eu0.225O1.5, EuFeO3, and Eu3Fe5O12 were studied. The effect of the particle size on the magnetic characteristics of multiferroic EuFeO3 was detected.

Synthesis and complex investigation of potassium ammonium hexafluorozirconates: I. Synthesis and X-ray diffraction study of K2-x(NH4)xZrF6 (0 < x < 2) crystals

The synthesis and X-ray diffraction study of compounds K2-x(NH4)xZrF6 (0 < x < 2) were carried out. In all crystals of mixed composition, potassium cations are isomorphously replaced by ammonium cations. The compounds with x < 0.5 are isostructural to K2ZrF6 and those with x > 1.5, to (NH4)2ZrF6. At 0.5 < x < 1.5, the structures are built of linear polymeric chains formed by edge-sharing Zr dodecahedra. The distribution of potassium and ammonium cations over the cationic positions was considered.

Uranium sorption on reduced porous iron oxides

The sorption properties of materials based on iron oxides and their reduced forms with respect to uranium were studied. A description was made of a method for consolidation of porous iron oxides and its effect on such characteristics as porosity, magnetism, morphology, phase composition, and sorption properties. The mechanism of uranium sorption on the obtained materials was determined. The interaction of the studied sorbents with uranium was shown to change, depending on the phase composition and the structure of the solid matrix.