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RUDNEV, V.; LUKIYANCHUK, I.; VASILYEVA, M.; CHASOVNIKOV, I.. Sn-containing oxide coatings: formation, composition, and catalytic properties. In: Materials Science and Condensed Matter Physics. Ediția a 9-a, 25-28 septembrie 2018, Chișinău. Chișinău, Republica Moldova: Institutul de Fizică Aplicată, 2018, p. 257.
|Materials Science and Condensed Matter Physics
Ediția a 9-a, 2018
Conferința "International Conference on Materials Science and Condensed Matter Physics" |
Chișinău, Moldova, 25-28 septembrie 2018
SnO2 is a wide-gap n-type semiconductor that has practically important optical, gas sensitive, electrical, catalytic and sensory properties [1-3]. The report will present the data on the production of oxide coatings modified with SnO2 by plasma electrolytic oxidation (PEO) technique. For fabricating the PEO coatings, two aqueous electrolytes were used. The first contained SnSO4 + EDTA-Na2 (I). The formula of second electrolyte was Na2SiO3 + SnO2 + sodium oleate as surfactant (II). The composition and morphology of the coatings were investigated with help of scanning electron microscopy, energy dispersive analysis, and X-ray diffraction. In the electrolyte I, PEO coatings are formed by the island mechanism: the islets of new phase appear on the primary anodic titania film, Fig. 1. Such islets contain up to 32 at. % Sn in form of SnO2 and have a developed coral-like structure, Fig. 2. When the coatings are obtained in the anodic-cathodic mode, metallic tin Sn0 is found in their composition. In the electrolyte II, the coral-like structure are not formed on the surface of PEO coatings. The crystalline SnO2 in their composition is found only when the surfactant is present in the electrolyte formula. The content of tin in such layers does not exceed 10 at. %. Catalytic tests of the coated samples (Fig. 3) showed that the coatings I are active in the catalysis of CO oxidation into CO2 at temperatures above 350 °C (curve I), while the coatings II are not active (curve II) possibly due to the lower content of tin. For the samples with coatings I, the temperatures of 50% CO conversion are equal 433 and 405 OC in the two consecutive cycles of catalytic tests (with heating). The developed surface of the islets allows filling the PEO coatings with catalytically active substances. Impregnating the coated samples of both types with PdCl2 solution leads to a decrease in the initial temperature of CO oxidation (curves Pd-I and Pd-II in Fig. 3). In the first case, the temperature of 50% CO conversion is equal 187 OC, and in the second case, T50 decreases from 238OC in the first cycle to 206 OC in the third cycle of catalytic tests. Thus, the method of plasma electrolytic oxidation in electrolytes with complex EDTA-Sn2+ ions is substantiated for obtaining SnO2 structures on the surface of titanium. It is shown that such structures can be the basis for the preparation of carriers of catalytically active compounds and catalysts for redox reactions.