The paper considers approaches that can lead to the growth of micro-and nanocrystals on the surface of coatings formed on valve metals by plasma electrolytic oxidation (PEO). Among these approaches, there are the use of electrolytes-suspensions, the addition of organic compounds to the electrolytes, the thermal annealing of ‘PEO layer/metal’ composites, including impregnated ones.

A multilayer material has been obtained on the basis of a prepreg modified by an aluminum layer, which is a precursor for fiberglass composite formation. An aluminum layer was preliminarily deposited on the prepreg by plasma spraying. Thereafter, a fiberglass composite with aluminum layers on the outer sides was formed using a modified prepreg and an oxide coating was fabricated on the aluminum surface by the method of plasma electrolytic oxidation. The proposed strategy can form the basis of a technology for the preparation of composites with an electrically conductive metal layer and increased fire resistance. The work presents data on the fabricated material’s structure and an evaluation of its fire resistance.

The influence of the nature of valve metals on the ferromagnetic characteristics of oxide coatings formed by plasma electrolytic oxidation (PEO) was studied for the first time. The coatings were obtained under the same current and time conditions in an alkaline electrolyte with colloidal particles of Fe(III) and Co(II) hydroxides. The magnetization dependences of the samples on the external magnetic field strength at room temperature were studied, data on the phase and elemental compositions of the coatings and the morphology of their surfaces were obtained, and the compositions of pores and crystallites in pores were studied. It is shown that the behavior of the magnetization curves for Al-samples differs noticeable from that of the Ti-, Zr-, and Nb-samples. The value of the coercive force decreases in the series Zr > Nb > Ti > Al, and the value of the saturation magnetization of the ferromagnetic component decreases in the series Al > Zr > Nb > Ti. Differences in the ferromagnetic properties of Al-samples and Ti-, Zr- and Nb-samples correlate with differences in the elemental composition of the pores of the coatings.

Electrodes of the composition Ti/TiO2,SbOx were obtained by single-stage plasma electrolytic oxidation in aqueous electrolytes with antimony hydroxocomplexes. The surface morphology and composition of TiO2,SbOx layers deposited on titanium were studied by scanning electron microscopy, X-ray diffraction analysis, and X-ray photoelectron spectroscopy. The obtained layers contain anatase TiO2 and up to 1 at % of antimony as Sb2O3 and Sb2O5. The resulting Ti/TiO2,SbOx electrodes were tested as pH sensors. They have close to Nernst electrode function in the pH range from 2 to 10 (53 ± 1 mV/pH). In the acid–base titration of strong (HCl) and weak (CH3COOH) acids with Ti/TiO2,SbOx electrodes, potential jumps are obtained that are not inferior in magnitude to the potential jump for a glass electrode. A possibility of using Ti/TiO2,SbOx electrodes to determine the alkalinity of technogenic waters is shown.

Информация об анодировании спеченных порошков (CП) ниобия ограничена изучением роста барьерных пленок. Формирование наноструктурированной анодной оксидной пленки (АОП) на поверхности частиц порошка должно привести к заметному увеличению удельной поверхности образца и росту химической активности материала. В соответствии с вышесказанным, исследование анодного наноструктурирования спеченных порошков ниобия является актуальной задачей, открывая перспективы создания новых функциональных наноматериалов. Цель статьи – изучение процесса анодирования спеченных порошков Nb во фторсодержащем водном электролите 1 М Н2SO4+1% HF.Объектами исследования являлись образцы из спеченного порошка Nb с удельной поверхностью Sуд = 800 см2/г. Анодирование проводилось в электролите 1 М Н2SO4 + 1% HF при различных значениях плотности тока ja. Морфология поверхности до и после анодирования изучалась методами сканирующей электронной микроскопии (СЭМ) и атомной силовой микроскопии (АСМ). Для исследования фазового состава применялся метод дифракции рентгеновских лучей. Выполнено изучение кинетики роста анодных оксидных пленок (АОП) на поверхности спеченных порошков СП Nb в гальваностатическом режиме. Определены оптимальные условия анодирования для получения кривых зависимости напряжения от времени Ua(t), характерных для образования самоорганизованных пористых анодных оксидных пленок АОП. Установлено, что анодирование при значениях плотности тока ja = 0.10–0.20 мA/cм2 вызывает формирование на поверхности частиц спеченных порошков СП оксидной пленки Nb2O5 с регулярно-пористым слоем, прилежащим к металлу, поверх которого располагается кристаллический микроконусный слой. Микроконусы (высота до 0.6 мкм, эффективный диаметр основания до 2 мкм) состоят из разветвленных волокон диаметром ~18–30 нм, смыкающихся на вершине. 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The regularities of the effect of the duration of coatings' galvanostatic formation in Zr(SO 4 ) 2 electrolyte on their composition, structure, surface contact angle with water, and the time of emergence of electrostimulated pitting when samples are in contact with an aqueous NaCl solution have been studied. It has been shown that coatings formed on titanium in the range of transition from the sparkling stage to that of more powerful microarc electric discharges are relevant for anticorrosive properties. The interrelation between the anticorrosive properties of PEO coatings and the stages of their growth may be of general character in PEO treatment of valve metals and alloys of different nature in electrolytes with varying compositions.

A comprehensive study of the magnetic behavior, morphology, and composition of Fe-containing oxide coatings on aluminum and titanium has been carried out to investigate the origin of their ferromagnetism. The coatings have been formed by the plasma electrolytic oxidation (PEO) technique in slurry electrolytes containing colloidal particles of iron(III) hydroxides. On the surface of coatings on Al, iron is distributed unevenly concentrating in defective areas with a large number of small pores, and near large pores. On the surface of coatings on Ti, iron and titanium are distributed in antiphase in areas of comparable size. Within the pores, iron concentration appears about 5-10 times higher and oxygen concentration 3-4 times lower than their average concentration over the surface. In both cases, localization of the areas with ferromagnetic properties follows the peculiarities of iron distribution on the surface. The magnetic fraction in the coatings on aluminum appears to be represented by iron-aluminum spinel Fe3-xAlxO4 with x > 0.06, likely cation-deficient. Elemental iron and traces of iron hydroxides are also possibly present. In the coatings on titanium, titanomagnetite (Fe3-xTixO4, where x similar to 0.2-0.3) or its oxidized analogue, titanomaghemite, appear to be present, and possibly also some Fe-Ti alloy particles. (C) 2019 Elsevier B.V. All rights reserved.

Titanium-supported oxide layers of W, W + Zn and W + Mn, formed by plasma electrolytic oxidation, were established to catalyze the peroxide oxidation of thiophene. The most active compositions based on Zn-W-containing PEO layers were also tested in the oxidation of a number of organosulfur compounds and diesel fuel desulfurization. Preliminary covering the samples by zwitterionic liquid (ZIL) made it possible to achieve residual sulfur content as low as 6 ppm. The change in the morphology and composition of samples with and without ZIL was studied during catalytic tests. It was found that ZIL reduces the etching of the sample surfaces when interacting with the reaction medium.

The peroxide oxidation of thiophene, thioanisole, and dibenzothiophene in the presence of Ce, Zr, Ce + Zr, W, and W + Zn oxide layers formed by plasma electrolytic oxidation on the titanium surface was studied. The composition of the resulting composites was found to affect the activity and conversion of the organosulfur substrates. It was shown by the radical inhibition method that the composites differed in the mechanism of their catalytic action.

The oxide layers on titanium were formed by plasma electrolytic oxidation technique in acid aqueous electrolytes containing sodium tungstate and copper acetate. The coatings with WO3-CuO or WO3-CuWO4 oxide layers have been formed in the electrolytes with H2C2O4 (pH~6) or H2SO4 (pH~4) accordingly. The coatings with WO3-CuWO4 have a developed surface architecture. The surface is constructed from coral-like structures with lamellar nanocrystals containing copper tungstate and tungsten oxide. The layers of tungsten oxide nanocrystals occupy the depressions between these structures. The band gap of the mixed WO3CuWO4 oxide layers is 2.8 eV.

Sn-containing oxide coatings were prepared via plasma electrolytic oxidation (PEO) of Ti plate in the electrolytes with [SnII-EDTA]2- complex anions or SnO2 particles in the anode and anodic-cathodic modes. The coatings formed in electrolyte with SnO2 particles stabilized by SAS contain SnO2 and Sn0. In the electrolyte with [Sn-EDTA]2- complex anions, the SnO2-containing coatings were formed in the anodic mode while Sn0-containing ones were obtained in the anodic-cathodic mode. SnO2-containing structures formed in the electrolytes with [Sn-EDTA]2- anions are shown to be active in catalytic oxidation of CO into CO2 at temperatures above 350 °C. They can be the basis for the preparation of both carriers of catalytically active compounds and catalysts for redox reactions. Potentiometric tests showed that the Sn-containing PEO layers on titanium exhibit the most characteristic pH function for the metal oxide electrodes in the direct potentiometry and acid-base titration.

The effect of the temperature of annealing in air on the surface architecture and composition of oxide layers has been studied. Copper-enriched nanosized crystals of triangular shape are present on the surface at the annealing temperatures of 500–700°С. Rectangular nano- and microcrystals of a possible composition of NiWO 4 are formed on the surface after annealing at 750–850°С. Nanowhisker brushes, similar in composition to nickel titanates, cover the surface after annealing at 900–950°С. Transformation of the surface architecture and composition on the micro- and nanolevels correlates to the coatings’ activity in the catalysis of the reaction of oxidation of CO to CO 2 .

Mixed cerium-zirconum-titanum oxide layers: CeOx + TiO2, CeOx + ZrO2 + TiO2, ZrO2 + TiO2 - on titanium were formed by plasma electrolytic oxidation technique in the electrolytes with different ratio of Ce(SO4)(3): Zr (SO4)(2) and investigated by the complex of physical-chemical methods. Their activity was studied in the peroxide oxidation of sulfur compounds (thiophene, thioanizole and dibenzothiophene) and the desulfurization of diesel fuel. Element and phase composition of the PEO-coated samples affect their catalytic activity. ZrO2 + TiO2 + CeOx systems with the largest content of zirconium showed the highest catalytic activity in oil desulfurization. Their catalytic activity correlates with the presence of the double oxides ZrTiO4 and Ti2ZrO6 in the coating composition. The decrease in the activity of catalysts when they are used in consecutive cycles can be accounted for by the etching of the coatings in the area of the pores. This drawback one can overcome by the addition of an ionic liquid namely 4-(3'-ethylimidazolium)-butanesulfonate, which increases not only the activity, but also the stability of the catalysts. Under these conditions, the structure and activity of the catalyst did not change significantly over several reaction cycles. The combination of PEO treatment and deposition of the ionic liquid allowed one not only to oxidize model substrates, but also carry out the desulfurization of diesel fuel to a residual sulfur content of less than 10 ppm.