EFFECT OF ELECTROCHEMICAL SYNTHESIS CONDITIONS ON THE COMPOSITION, STRUCTURE, AND MORPHOLOGY OF TUNGSTEN CARBIDE POWDERS

I.A. Novoselova 1*,
 
S.V. Kuleshov 1,
 
A.O. Omel`chuk 1,
 
V.N. Bykov 2,
 
O.M. Fesenko 2
 

1 Vernadsky Institute of General and Inorganic Chemistry of NAS of Ukraine, Kiyv
2 Institute of Physics NAS of Ukraine, Nauky Ave., 46, Kyiv, 03028, Ukraine
inessa_nov@ukr.net

Powder Metallurgy - Kiev: Frantsevich Institute for Problems of Materials Science NASU, 2023, #03/04
http://www.materials.kiev.ua/article/3572

Abstract

High-temperature electrochemical synthesis (HTES) in molten salts is highly promising among the up-to-date methods for the production of carbide powders. Ultrafine composite powders based on tungsten carbides (WC|C, WC|C|Pt, W2C|WC, and W2C|W) were synthesized using the HTES method in electrolytic baths of different chemical composition under various synthesis conditions (cathode current density, CO2 pressure in the electrolyzer, temperature, cathode material). Composite powders WC|C (up to 3 wt.% free carbon) with a WC particle size of 20-30 nm were produced from electrolytic baths of the following compositions: Na, K|Cl (1 : 1)-Na2W2O7 (6.4 wt.%)-CO2 (1.25 MPa) and Na, K|Cl (1 : 1)-Na2WO4 (12.0 wt.%)-NaPO3 (0.7 wt. %)-CO2 (1.25 MPa) at a temperature of 750 °С. When the CO2 pressure is reduced to 0.75 MPa, composite powders of W2C|WC tungsten carbides are produced at the cathode. The ratio of carbide phases in the composite depends on the initial concentration of tungsten salt in the electrolyte and the CO2 gas pressure in the electrolyzer. The addition of Li2CO3 (4.5 wt.%) to the electrolytic salt mixture decreases the size of tungsten carbide particles to 10 nm, changes their morphology, and increases the free carbon content in the composite up to 5 wt.%. The specific surface area of the powder increases by 4-7 times (from 20-35 to 140 m2/g). The use of platinum cathodes makes it possible to modify the composition of the resulting product with fine platinum particles. The HTES method is shown to be a promising one for producing tungsten carbide powders with the properties that allow them to be used as electrocatalysts in the hydrogen evolution reaction. For the WCl|C composite powders produced from the Na, K|Cl-Na2W2O7-Li2CO3-CO2 system, the potential of hydrogen evolution was -0.02 V relative to the normal hydrogen electrode, the overpotential η at a current density of 10 mA/cm2 is -110 mV, the exchange current is 7.0• 104 A/cm2, and the Tafel slope is -85 mV/dec.


ELECTROCHEMICAL SYNTHESIS, MOLTEN SALTS, MORPHOLOGY OF COATING, NANOSIZED POWDERS, TUNGSTEN CARBIDES