PECULIARITIES OF COBALT CONTAINING OXIDE COATINGS FORMATION ON SILUMIN
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Keywords

plasma-electrolytic oxidation, alumina matrix, cobalt oxides, catalytic activity, intra-cylinder catalysis.

How to Cite

Sakhnenko, N., Ved’, M., & Karakurkchi, A. (2020). PECULIARITIES OF COBALT CONTAINING OXIDE COATINGS FORMATION ON SILUMIN. Ukrainian Chemistry Journal, 86(1), 12-21. https://doi.org/10.33609/0041-6045.86.1.2020.12-21

Abstract

The process of mixed oxide coatings formation on a high-silicon aluminum alloy in a cobalt-containing pyrophosphate electrolyte by the plasma-electrolytic oxidation (PEO) method is studied. It was shown that AL25 chemical composition heterogeneity causes the consumption of a part of the anode current to homogenize the treated surface, which is reflected in minimizing the content of doping components at the initial processing stage. It was established that the growth of mixed oxides Al2O3·CoxOy relative mass is a function of time with a maximum at 55 minutes. The chemical, phase composition and surface morphology of the formed oxide layer depend on the oxidation time. The catalytic component content in the surface oxides varies from 0.2 to 23.3 at.% with an increase in processing time of 10 to 60 minutes. Maximum cobalt incorporation into the oxide layer occurs at PEO of 35–50 minutes, while the silicon content in the surface layers does not exceed 2 at.%, which is favorable for the catalytic properties. The cobalt oxide, preferably Co3O4, incorporation in the alumina α-Al2O3 matrix is visualized by the blue-violet color steroidal surface structures in the sites of micro-arc discharges. The alumina cobalt oxide mixture layers are characterized by a developed micro-globular surface which consists of spheroid conglomerate with an average size of 1–2 microns. There are some amorphous phases in the structure of mixed oxides due to non-equilibrium PEO conditions. The set of detected factors is a prerequisite for the high catalytic properties of oxide coatings. A promising field of Al2O3·CoxOy systems application is intra-cylinder catalysis in internal combustion engines.

https://doi.org/10.33609/0041-6045.86.1.2020.12-21
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