Effects of constant magnetic field on the electrodeposition reactions and cobalt–tungsten alloy structure

The paper presents a study of the effect of constant magnetic field (CMF) on the basic processes of cobalt–tungsten alloys electrodeposition. To the authorʹs knowledge, such an investigation has been performed for the first time for cobalt–tungsten alloys. The applied research methods included scanning electron microscopy (SEM), energy dispersive X-ray (EDX) microanalysis, energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). SEM images of cobalt–tungsten alloys revealed numerous fractures on the samples surface, formed as a result of residual stress during alloy deposition without CMF. In CMF such fractures disappeared. The cobalt content increased, with a simultaneous decrease of the tungsten content, under CMF condition. The XRD study of cobalt–tungsten alloys allowed to identify phase Co3W in a hexagonal system, phase Co7W6 in a trigonal (orthorhombic) system, phase α-Co in a regular system and phase W in a regular system. Under CMF conditions some crystal planes were deflected at angles ranging from 10 to 20°. The exposure to CMF caused also an increase of the volume fraction (by about 9% by volume) of the dominant phase (Co3W and Co7W6) in the alloy. The reason for these changes was the fact that the Lorentz force, generated in CMF, caused the magnetohydrodynamic (MHD) effect. This induced movement of the electrolyte. The Nernst diffusion layer was depleted, whereas a new Navier–Stokes hydrodynamic layer appeared, which determined the velocity of electroactive molecules flow to the working electrode under CMF conditions.