Yu. G. Mikhalev, N. Yu. Zharinova.
ABSTRACT
During polarization of liquid metal electrodes in diluted melts, dissipative structures arise due to natural and interphase (Marangoni-effect) convections. The type of structures determines the shape of the polarization dependence.
In the case of cathodic polarization of liquid electrodes made of lead, bismuth, cadmium, aluminum in chloride melts in the range from the potential without current to the zero charge potential at the interface, structures in the form of vortices – circulation cells, due to the Marangoni microeffect – dominate. In this case, the stationary polarization dependences obtained under potentiostatic conditions have a characteristic maximum of current density, and the dependences of the overvoltage η and current density i on time with stepwise setting of the current under galvanostatic conditions or potential under potentiostatic conditions (non-stationary curves) have characteristic current or overvoltage extrema that decrease in magnitude up to the establishment of a stationary state, i.e. the system from the moment of closing of the circuit evolves according to the law of damped oscillations, with a period that depends on time. The values of η and i in the first extremum always have the largest amplitude. At the time textr of reaching the first extremum of the current density iextr or overvoltage hextr at the interphase boundary, circulation cells become visible. Until textr no movements are visually observed at the interface.
The time interval from the moment of circuit closing to textr (0.1–1 s) is a transition period during the formation of circulation cells, during which two conditions must be fulfilled simultaneously:
- a) the diffusion front would move a sufficient distance from the electrode and a diffusion layer would form with a concentration gradient normal to the interface;
- b) the difference between the concentrations at the electrode surface and in the electrolyte volume would reach a certain critical value.
In the work in the form of a criterion equation, the dependence is obtained between textr, the properties of systems and the geometric dimensions of the electrodes. textr calculated by the equation satisfactorily coincide with the experimental values.
It is shown that the work of the formation of circulation cells is determined by the properties of the salt and metal phases, depends on the current density or potential and varies over a wide range (0.3 – 68 J / m2).
KEY WORDS:
molten salts, liquid metal electrodes, dissipative structures, circulation cells, laminar electrolyte layer, polarization dependences, current density, overvoltage, non-stationary curves, interfacial tension.
DOI: 10.31857/S0235010621040058