Far From Thermodynamic Equilibrium Conditions Of Electrolysis Sediment Complex Morphological Growth Mechanism

Electrodeposition experiments were performed in thin film CuSO4 aqueous solutions with varying concentration in a radial cell. And the electrolytes were confined inside a wire-made copper ring anode. The electric fields with different distributive natures in the cell were obtained when appropriately varying the position or the geometry of wire-made copper cathodes. The microscopic morphologies of the Cu electrodeposits were examined under the atomic force microscope (AFM). The effects of an inhomogeneous electric field on ramified electrochemical growth were investigated. On this basis, the mechanisms of the screening effect, which is a prominent feature of DLA-type fractal electrodeposits, and the effects of an applied magnetic field on the growth morphology of electrodeposits were discussed theoretically.The electrochemical cell used in the present experiments was discussed using an equivalent circuit model in consideration of the fact that the currents in the electrolyte between the anode and the electrodeposits were in series with the electrodeposits branches and distributed on each branch. The results of the experiments were discussed using the equivalent circuit model and the regulations of the effects of an inhomogeneous electric field on ramified electrochemical growth were acquired: (1) In course of electrolysis, the growth velocities of the electrodeposits branches which located at the regions with strong electric fields were larger than those of the electrodeposits branches which located at the regions with weak electric fields. And an electrodeposits branch would elongated windingly towards the side where the electric field was stronger if the electric fields which were close to this branch were not equivalent at two sides. The growth velocities of the electrodeposits branches and the strength of the electric fields facilitated mutually through a positive feedback mechanism during electrodeposition. The degree of the inhomogeneity of the electric fields and the diversity of the branches' length became larger and larger in course of electrolysis through this feedback mechanism in additional of the competition of the currents in these branches. (2) Strong convectionof electrolyte was observed when both the concentration of the CuSO4 aqueous solution and the degree of the inhomogeneity of the electric fields were large. The electrodeposits drifted with the fluid flow and led to the winding of electrodeposits branches and/or the separateness of the electrodeposits from the cathode.The mechanisms of the screening effect in fractal electrodepositon was discussed on the basis of the regulations of the effects of an inhomogeneous electric field on ramified electrochemical growth in combination with the unstable theory of the non-equilibrium thermodynamics. The electrolytic system was far from equilibrium in fractal electrochemical deposition and all kinds of random factors differentiated the growth velocities of the electrodeposits branches. It was considered that the screening effect was essentially the result of the enlargement of the difference growth velocities of the electrodeposits branches that was mentioned above through the feedback mechanism of the degree of the inhomogeneity of the electric fields and the diversity of the branches' length in additional of the competition of the currents in these branches.In this article, the mechanism of the effects of an applied magnetic field on the growth morphology of electrodeposits was also discussed theoretically. It was considered that the applied magnetic field caused the electric fields that were close to electrodeposits branches were not equivalent at two sides of each branch through the Hall effect on the electrodeposits branches. It was concluded that the applied magnetic field influenced the growth morphology of electrodeposits through the Hall effect in consideration with the regulations of the effects of an inhomogeneous electric field on ramified electrochemical growth.