COMPOSITION AND SURFACE MORPHOLOGY OF COMPOSITE ELECTROLYTIC COATINGS CO-W-ZRO2
| Autor: | Maryna Ved, Valeria Proskurina, Tetiana Nenastina |
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| Rok vydání: | 2020 |
| Předmět: | |
| Zdroj: | Bulletin of the National Technical University "KhPI". Series: Chemistry, Chemical Technology and Ecology. :12-17 |
| ISSN: | 2708-5252 2079-0821 |
| Popis: | possibility of electrosynthesis and control of the composition and surface morphology of the composite electrolytic coatings of cobalt with refractory metals by varying the pulse current density has been proved. Composites deposited on copper substrate from biligand citrate-pyrophosphate electrolytes at 4 A/dm 2 are distinguished by a developed surface and a more uniform distribution of components on the surface, increased tungsten content, almost 5 times higher than coatings deposited at 10 A/dm 2 , and a half reduction in oxygen percentage (up to 5.5%). This is explained by the inhibition of the hydrogen gas evolution reaction and the participation of hydrogen ad-atoms in the chemical reduction of intermediate tungsten oxides to metal when polarization is interrupted. Coatings obtained using pulsed current can be considered as composites of the composition Co-W-ZrO 2 , in which the oxide phase is formed directly in the electrode process as an intermediate for the incomplete reduction of tungstates. The topography of the films is characterized by the presence of grains of elliptical and spherical shape with crystallite sizes of 80 – 180 nm. On the main surface there are protrusions (large grains) with a diameter of 1 – 3 microns. The fractal dimension of the surface is 2.77, which indicates the 3D crystal growth mechanism during coating formation. According to the surface roughness parameters Ra and Rq, coatings belong to the 9th roughness class. By phase composition, composites are predominantly amorphous materials, which include nanocrystalline cobalt and intermetallic compounds Co3W and Zr 3 Co. Due to the quantitative and phase composition, surface morphology and fractality, the microhardness and corrosion resistance of Co-W-ZrO 2 systems deposited at a current density of 4 А/dm 2 are 20% higher than the coatings obtained at 10 A/dm 2 , and 3 times higher than the corresponding characteristics of the substrate. |
| Databáze: | OpenAIRE |
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