EXPERIMENTAL AND MODEL EVALUATION OF DIFFUSION COEFFICIENTS OF BARIUM IN LIQUID GALLIUM AND LEAD

Abstract

Gallium and lead are used as liquid cathodes to produce alloys of alkaline earth metals, including barium. Data on the diffusion coefficients of barium (DBa) in liquid metals obtained by anodic chronopotentiometry are very limited. In this paper, an experimental evaluation of DBa in liquid gallium and lead was carried out by a combined method. It is based on the joint processing of the measurement data of the cathode chronopotentiometry in the coordinates E–ln√τ and the equations of the isotherms of the potentials of the alloys of the E–lnXBa obtained under the same conditions. Measurements were carried out in the melt KCl– 26 mol % BaCl2, at temperatures from 953 to 1073 K. The basis for the calculation of DBa is the Sanda equation. The features of electrode processes on liquid metal cathodes in barium-containing chloride melts are taken into account. The values of stabilized residual current densities depending on the temperature are established. It is shown that at the beginning of the process of barium separation into alloys, the effect of joint potassium deposition is manifested, especially on the lead cathode. The contribution of barium current output is proposed to be estimated by the current selectivity index, which depends on the potential of the alloy. It is shown that the joint discharge of potassium and barium into alloys leads to an overestimation of dva on gallium and lead from 5 to 12%. The activation energies of barium diffusion in gallium and lead, respectively 20.7 and 16.2 kJ/mol, were calculated on the basis of the obtained temperature dependences of DBa. Calculations show that on liquid thallium, bismuth, antimony measurement of cathode chronopotentiograms for barium is impossible, because of significant potassium co-deposition. Based on the data on the structure of dilute alloys and thermodynamic characteristics of alkaline earth metals, the method of calculation of reduced radii of microgroups-diffusers in the Stokes – Einstein equation is proposed. The DMe values calculated using the reduced radii are in satisfactory agreement with the majority of experimental data. These facts confirm the validity of the model of collective diffusion of barium and other alkaline earth metals in alloys as part of microgroups by translational mechanism.