The possibility of depositing copper powders with different apparent density by changing the shape of reversing current wave is shown. The morphology and crystallinity of powder particles can be varied considerably by changing shape of the reversing current wave and, hence, the apparent density of powders. The relation of apparent density with particle morphology and structure was illustrated.
The one of the main contributions of Belgrade Electrochemical School to the field of metal electrodeposition is investigation of a mechanism of formation and growth of the disperse deposits. Spongy-like, cauliflower-like, needle-like, carrot-like, dendrites of various shapes, etc In these publications all aspects of morphology of electrodeposited metal are discussed, from dendritic growth initiation and dendritic growth [2,3,11] to the bright deposits formation [2,3,8] and the effect of hydrogen co-deposition on morphology of electrodeposits [3,9,14]. One of the most important conclusion derived by BES is the mechanism of disperse deposits formation, based on different behaviour of the macroelectrodes and microelectrodes under the same conditions of electrodeposition. The aim of this article is to discuss this phenomenon in the way given in [11] for the growth of dendrites.
The processes of Pb electrodeposition under diffusion control were examined by scanning electron microscopy (SEM) of the formed crystals. The orientation of grains of hexagonal shape formed in the initial stage of electrodeposition strongly affected the final morphology of the Pb crystals. The formation of Pb crystals of the different shape from the same initial shape was discussed in terms of the effect of orientation of initially formed grains on the type of diffusion control. A spherical diffusion layer was formed around the tip of the hexagonal-shaped grain oriented with its tip towards the bulk solution that led to the formation of elongated crystals in the growth process. On the other hand, a cylindrical type of diffusion was responsible for the growth of hexagonal-shaped grains oriented with the lateral side towards the bulk solution. Pb crystals with well-defined sides parallel to the surface area of the macroelectrode were formed under this type of diffusion.
The structure of the surface of copper powder particles is discussed and correlated with the lowest apparent density at which copper powder can still flow. It is shown that such structures can be easily obtained in the electrodeposition of powders in reversing current regimes.
The structures of bright zinc coatings obtained from acid sulfate solutions
in the presence of dextrin/salicyl aldehyde mixture were examined. It was
shown by the STM technique that the surfaces of bright zinc coatings are
covered by hexagonal zinc crystals, the tops of planes of which are flat and
mutually parallel and which exhibit smoothness on the atomic level. X-Ray
diffraction (XRD) analysis of the bright zinc coatings showed that the zinc
crystallites are oriented in the (110) plane only.
The possibility of utilization of the lead-air electrochemical system as a power source is shown. The system consists of a standard lead electrode and H2SO4 electrolyte, used in the lead acid battery and a gas diffusion electrode developed in the Institute of Electrochemistry and Energy Systems. Three catalysts have been checked for applicability with the new system-active carbon Norit NK, cobalt tetramethoxyphenylporphyrin and cobalt phthalocyanine. Cyclic voltammetry has been applied to all three catalysts and the results have been presented as galvanostatic charge-discharge curves. Polarization and Tafel dependences have been studied in a three-electrode cell. An original method for formation of the lead electrode has been elaborated. It has been established that the gas diffusion electrode is sufficiently stable in the sulphuric acid electrolyte. The energy values obtained at laboratory conditions provide a good perspective for a practical application of the lead-air system for energy storage and in the automobile industry.
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