Effect of electrolysis parameters on the coating composition and properties

1 Effect of electrolysis parameters on the coating composition and properties 

Tungsten and carbon can form two carbides, namely WC and WjC. It is impossible to crystallize WC as a continuous deposit, because WC is formed at a certain excess of carbon, which is known to passivate the electrodeposition front [11, 12], Hence, the crystallization of tungsten carbide as a continuous deposit requires a finer control over the electrosynthesis process and should be carried out under conditions of W2C formation. Experiments at 1173 K showed that tungsten carbide coatings can be deposited from a melt containing 5 wt% Na2 WO4. When the Na2C03 content does not exceed 0.2 wt%, continuous deposits of W-W2C alloys (the composition of which also depends on the carbonate concenfiation) are deposited on the cathode. Continuous W2C deposits appear at a concentration of 0.2-0.5 wt%, continuous W2C-WC deposits appear at 0.5-1.0 wt% poorly adhered deposits of W2C-WC are formed at still higher concentrations. 

The current efficiency of W2C approached 40-50%, and the deposit thickness reached 50 pm. The low current efficiency of coatings is associated with growth front disturbance of the deposit as a result of its passivation by lithium oxide formed in the electrode reaction. Further deposition largely produces a carbide powder in addition to the coating, and the thickness of the latter does not exceed 50 pm. 

The cathodic to anodic pulse duration ratio was changed within 30-60, the anodic pulse time was 0.5-1.5 s at a current density of 15-50 A/dm. This allowed us to increase the carbide coating thickness to 100pm. The optimal parameters of the reversal mode were Tj.=45s, Ta=1.5s, r c = 8-10A/dm,  

In this case, the uniform phase of zirconium diboride is formed in a wide current density range. The absolute magnitude of the overall concentration of Zr(IV) and B(III) in the electrolyte (in a range of 0.6-30 wt%) has no significant effect on the product composition, as well as technological and economic parameters of the process. As shown experimentally, the temperature threshold of synthesis in the melt studied lies in the interval 923-943 K. The temperature interval 1073-1173 K is optimum at a cathodic current density of 5-20 A/dm.  

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Effect of Electrolysis Parameters on the Coating Composition and Properties during Electrodeposition of TVingsten Carbides and Zirconium Diborides... 

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