Yu. G. Mikhalev, N. Yu. Zharinova.
ABSTRACT
This work is a continuation of studies of nonstationary dependences (inclusion curves) during cathodic polarization of liquid electrodes made of lead, bismuth, cadmium, aluminum in chloride melts, when structures in the form of vortices – circulation cells (CC), due to the Marangoni microeffect. In this case, the time dependences of the overvoltage η and the current density i with a stepwise setting of the current under galvanostatic conditions or the potential under potentiostatic conditions (inclusion curves) have extrema of the current or overvoltage, decreasing in magnitude until a steady state is established. The values of η and i at the first extremum ηextr and iextr always have the largest amplitude. The time of τextr achievement ηextr and iextr and the values of ηextr and iextr themselves characterize the process of forming the CC. The τextr value is the most convenient for analysis, since it does not depend on the concentration of electrochemically active particles. It is assumed that the formation of circulation cells is the slower, and the value of τextr is the greater, the greater the intensity of mass transfer processes at the electrode-electrolyte interface, which is determined by the polarization conditions.
It is shown in the work that with increasing temperature τextr increases, which means that the formation of the CC proceeds more slowly. When an external magnetic field is applied, which helps to slow down mass transfer, τextr decreases and when the electrode is immersed in a quartz holder τextr also decreases. On the whole, these results indicate the correctness of the assumption about the rate of CC formation.
When the current pulses are successively applied to the already polarized electrode, the overvoltage extremum is clearly visible on the turn-on curves, the value of which decreases in the sequence of pulses. τextr values are also reduced. The existence of overvoltage extrema can be associated with energy difficulties in the integration of newly formed CC into the structure of existing ones.
KEYWORDS
molten salts, liquid metal electrodes, circulation cells, formation time of circulation cells, current density, overvoltage, turn-on curves.
DOI: 10.31857/S0235010622020049