A possible mechanism of formation of flower-like MgO/Mg(OH)2 structures by galvanostatic molten salt electrolysis: The concept of local diffusion fields

Abstract

The processes of electrodeposition from magnesium nitrate hexahydrate melt by galvanostatic regime of electrolysis have been analyzed. The structure of the formed particles was examined by X-ray diffraction (XRD), which revealed formation of MgO/Mg(OH)2 mixture by molten salt electrolysis. Morphologies of the produced deposits were characterized by scanning electron microscopy (SEM) technique. The flower-like forms constructed from very thin needles with sharp tips were predominately formed by electrodeposition at various current densities and with various amounts of electricity. Aside from that, holes formed from detached hydrogen bubbles of various shapes and sizes, from dish-like holes to those resulting in honeycomb-like structures were also observed. Mechanism of formation of the flower-like forms has been elucidated applying the general theory of disperse deposits formation which is based on the concept of local (spherical and cylindrical) diffusion fields. It is shown that the growth of the needles occurs under the conditions of predominant spherical diffusion control, while the contribution of the cylindrical diffusion to the final shapes was negligible. Comparison with morphologies of deposits obtained by electrodepositions from aqueous magnesium salt electrolytes was also made and discussed.