Self-Organization Process of Secondary Crystal Nodules from Individual Nuclei in Electrodeposition

Abstract

Using nonequilibrium fluctuations in electrodeposition, the self-organization process of secondary crystal nodules from individual nuclei was examined. As a result, it was concluded that electrodeposition can be described by two types of fluctuation, i.e., symmetrical and asymmetrical fluctuations; the former yields three-dimensional (3D) nuclei, whereas the latter yields two-dimensional (2D) nuclei that determine the spatial distribution of the 3D nuclei. The complex self-organization of these two types of nuclei leads to the aggregation of each 3D nucleus. In the present paper, first, the instability of these fluctuations was discussed. Then, it was shown that asymmetrical fluctuations control the total reaction rate, and lead to nucleation currents in silver nucleation. Finally, the crystal morphology yielded by the symmetrical and asymmetrical fluctuations was visualized by computer calculation, and the aggregation process of 3D nuclei to secondary nodules was examined.

Patterning metallic electrodeposits with magnet arrays

“…Such effects have been quite extensively documented in the literature, mainly for copper, 8,17,44 and it has been suggested that they are somehow associated with convection generated by the Lorentz force. 45, 46 Aogaki 47 has proposed that the field effect on two-dimensional nucleation is related to spontaneous concentration fluctuations in the double layer, and the effect on three-dimensional nucleation depends on fluctuations in the diffusion layer.…”

“…The MHD effect, and its analog on a small length scale, the micro-MHD effect 17 are responsible for many of the influences that a magnetic field can have in electrochemistry, including the rate of electrodeposition of metals, 3,5,7 deposit morphology, 8 hydrogen production, 10,11 corrosion, [12][13][14][15][16] and rest potential. 18 The hydrodynamic conditions in any experiment are characterized by a set of dimensionless numbers whose significance in a laboratory electrochemical cell is summarized in Table I.…”

Self-organization of Copper Secondary Nodules by the Second Micro-MHD Effect

“…These two types of nucleation come from different nonequilibrium fluctuations. (10,17); one is asymmetrical fluctuation, which arises from an electrochemical reaction in an electrical double layer. As shown in this figure, this fluctuation one-sidedly changes from an electrostatic-equilibrium state toward a cathodic reaction side, controlling 2D-nucleation.…”

“…Figure 3 shows the schematic diagram of an electrical potential distribution in the double layer for the electrodeposition without any specific adsorption, where the overpotentials of the double layer are negative. As shown in this figure, let's assume that a minute 2D nucleus is accidentally formed in the diffuse layer of the double layer (10,17). Since the potential gradient in the diffuse layer is positive, at the top of the nucleus, the double-layer overpotential decreases.…”

“…As the reaction proceeds, outside the double layer, a diffusion layer is yielded. Here, it is supposed that a minute 3D nucleus is accidentally formed in the diffusion layer (10,17). In electrodeposition, since the concentration gradient is positive, the top of the projection contacts with higher concentration than other parts.…”