Investigation On The Preparation Of Core-shell Structured Cobalt Coated Tungsten Carbide Powders By Intermittent Electrodeposition

Intermittent electrodeposition is an emerging method that used in preparing metal-powder composite materials. By adding insoluble solid particles into electrolyte, the metal ions begin to electromigration to the cathode and acquire electrons on the surface of powders, which are covering on the cathode when current is switched on. And then the metal coated powders composite materials can be obtained. This paper focused on preparing the core-shell structured cobalt coated WC (WC/Co) composite powders on the niobium cathode plate by intermittent electrodeposition. Factors such as current density, surfactants and pH were discussed to ensure that the optimum process conditions were adopted to obtain the composite powders with better characteristics. Scanning electron microscopy, energy dispersive spectroscopy and X-ray diffractometer were employed to observe and analyze the surface morphologies, chemical composition and crystal structure of the composite powders. The results are as follows:(1) By the simple pretreatment of WC powders with the mixed acids, scanning electron microscopy was used to observe the surface morphlogies of WC powders before and after pretreatment, energy dispersive spectroscopy and X-ray diffractometer were utilized to characterize the WC/Co composite powders, the mixed acids was activate the WC powders by forming surface defects on its surface.(2) The optimal process conditions of electrodeposition WC/Co composite powders such as the current density, single deposition time, pH, sufficient deposition time were decided by electrodeposition efficiency, surface morphology of the composite powders, deposition rate and cobalt content. The electrodeposition procedure included several cycle processes of electrodeposition and stirring. The pH has great impact on the crystal structure of cobalt on the WC powders, the electrolyte pH was 4-5 to fabricate the uniformly dispersed composite powders with high electrodeposition rate and current efficiency.(3) The method of potentiostatic transient step was taken to study the nucleation mechanism of cobalt on WC powders at large current density, the current-time plots of chronoapmerogram were made out to reveal the three-dimensional nucleation of cobalt.(4) The appropriate amount of surfactants can effectively change the cathodic potential of cobalt and influence the surface morphologies and dispersion of the WC/Co composite powders. PEG-2000 could easily adsorbed on the WC powders according to the IR spectrum and dispersed the composite powders for its steric hindrance effect of long chain structure.