V. P. Morozova

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.

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.

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 iron-containing coatings formed by plasma-electrolytic oxidation

The magnetic properties of iron-containing coatings formed on aluminum by plasma-electrolytic oxidation were investigated. It was shown that the magnetic state of the samples studied is most likely induced by chemically inhomogeneous (multiphase) ferromagnetic particles.

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.

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.

Bifunctional Fe-containing coatings formed on aluminum by plasma-electrolytic oxidation

Oxide coatings with a thickness of about 30 μm were deposited. The coatings contain approximately 21 at % Fe and 2.3 at % Cu and exhibit, together with ferromagnetic properties, a catalytic activity in CO oxidation at temperatures higher than 260°C.

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

The effect of annealing in air at Tan 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 Tan ≤ 500°C does not seem to affect the composition and morphology of coatings. The coercive force (Hc) of specimens equals 70 Oe at room temperature and 256 Oe at 2 K. Upon annealing at 700 or 800°C, the Hc 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.

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.