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SM ISO690:2012 KUZEI, A., FILIMONOV, V., YAKUBOVSKAYA, S.. Mechanism of the (nickel – tungsten) – carbon composites electrochemical crystallization. In: Materials Science and Condensed Matter Physics, Ed. 8-th Edition, 12-16 septembrie 2016, Chişinău. Chişinău: Institutul de Fizică Aplicată, 2016, Editia 8, p. 350. ISBN 978-9975-9787-1-2. |
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Materials Science and Condensed Matter Physics Editia 8, 2016 |
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Conferința "International Conference on Materials Science and Condensed Matter Physics" 8-th Edition, Chişinău, Moldova, 12-16 septembrie 2016 | ||||||
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Pag. 350-350 | ||||||
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Using aprotic compounds such as carbamide, dimethylformamide, acetonitrile, etc., as solvents for the transition metals salts allows varying values of electrochemical reduction potentials of some metals as compared with values of the latter in water electrolyte solutions. Electrochemical coatings in the form of metallic ‘alloys’ and composites, more complex in composition and structure than those obtained from water based electrolytes containing some metal salts, can be deposited from aprotic electrolytes containing the same metal salts. The morphology of surface of the coatings deposited from the electrolyte of the system ‘carbamide – nickel chloride – sodium tungstate’ represents a set of irregularly shaped crystals (dendrites). The surface morphology and the composition of coatings are determined by the values of the electrolysis current density. Enhancing the current density from 5..10 to 15..25 mA/cm2 results in some increase of dendrites size and increased carbon and tungsten concentrations (from 0.1 to 1.2 and from 0.01 to 3.5 wt.%, correspondingly) in the coating. The carbon particles reach the size of 0.5..2.0 microns at a current density of 15..25 mA/cm2 (see fig.). The character of the coatings’ surface morphology, structure and composition changes indicates the independent nature of the nucleation and growth of crystallization centers of nickel and carbon. Nucleation and growth of carbon crystallization centers occurs on the surface of the nickel (‘solid solution’ of tungsten in nickel) crystallites. Nickel crystallization centers’ nucleation and growth occur on the surface of carbon particles in the electrolysis current density range 15..25 mA/cm2. Formation of the composite structure of the coatings such as ‘matrix (nickel – tungsten) – disperse particle (carbon)’ is caused by electrochemical reduction of carbon under the electrochemical decomposition of carbamide. Thus, the use of carbamide based aprotic electrolyte allows forming disperse reinforcing phase of a composite coating side by side with the matrix of the same. The microstructure of the composites represents a complex-doped "solid solution" of carbon and tungsten in nickel, wherein the dispersed carbon particles are located. |
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