Secondary Reduction of Refractory Metal near the Smooth Cathode during Molten Salt Electrolysis. 2. Calculations for Som
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ndary Reduction of Refractory Metal near the Smooth Cathode during Molten Salt Electrolysis. 2. Calculations for Some Hypothetical Experiments A. P. Khramova, *, A. A. Chernysheva, b, **, A. V. Isakova, and Yu. P. Zaykova, b aInstitute
of High Temperature Electrochemistry, Ural Branch, Russian Academy of Sciences, Yekaterinburg, 620137 Russia b Ural Yeltsin Federal University, Institute of Chemical Technology, Yekaterinburg, 620002 Russia *e-mail: [email protected] **e-mail: [email protected] Received July 17, 2019; revised December 13, 2019; accepted March 6, 2020
Abstract—Results of calculations for several hypothetical experiments are presented in terms of a steady-state process of secondary reduction of refractory metal ions with alkali metal formed on a smooth cathode during the molten salt electrolysis. Simplified expressions for approximate calculations of concentration profiles inside the diffusion layer are given. Keywords: model of the cathode process in alkali halide melt, model of secondary reduction at the cathode by alkali or alkaline earth metal DOI: 10.1134/S1023193520090062
INTRODUCTION In our preceding work [1] we presented a model of a near-cathode secondary reduction of refractory metal ions. In this work, we suggested a simple method for the calculations of all quantities introduced by the model. These quantities are calculated for some hypothetical cases; relevant conclusions are derived. The first thing we have to do is to note that we proceeded from the premise that the diffusion layer thickness δ changed with the change in the current density i. This statement was confirmed by our calculations for actual experiments; we shall discuss the matter at length in our future paper [2]. It suffices here to remark that the heavy refractory metal ion concentration gradient in near-cathode solution leads to the incipience of the liquid phase density gradient. This lead, in its turn, to the onset of convective agitation. In all probability, the process of secondary reduction till the formation of solid metal particles within diffusion layer intensifies the agitation because the particles further become pulverized. The intensifying of agitation leads to the decrease in δ. With the increasing of i the concentration and density gradients also increase, as well as the solid particles’ formation rate; hence, δ decreased. These changes unavoidably affect the form of steady-state polarization curves; and these curves are used in the numerical reproducing of actual experiments.
One should distinguish between the numerical hypothetic experiment and numerical reproducing of actual experiment. The point at issue is the values of three quantities: E, i, and δ, which must be selected prior to the calculating of all possible profiles with respect to the distance coordinate. Because the potential E actually imposes concentrations cBSCat, cASCat at the cathode boundary, while the bulk concentrations cA0, cB0 have been already set in, the matching of boundary condition is required for each value of E, as well as
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