Electrode processes in the production of microdispersed titanium powder by volumetric electrolytic reduction of its ions with sodium dissolved in the BaCl2–CaCl2–NaCl melt in the absence of titanium halides in the initial melt

Abstract

The paper is devoted to a detailed study of cathodic processes, their influence on the anode process, and electrolysis performance. The polarization of a steel cathode in a CaCl2–BaCl2–NaCl melt at t = 610 °C was measured. The polarization curve clearly shows the potentials and current densities of the formation of a saturated sodium solution in the electrolyte (Esat = –2.97 V, ic = 0.04 A/cm2, lgic = –1,4), and the occurrence of sodium metal on the cathode (ENa = –3.22 V, iNa = 0.12 A/cm2, lgiNa = –0.92).The value of Esat was used to calculate the concentration of sodium in the electrolyte at t = 610 °С (1.3·10–4 mol. fr.). The values of Esat, ENa, and their difference (E = 0,25 В) were confirmed by long-term electrolysis. These fundamental characteristics are the basis for process control and management. During long-ter 3 regions close to rectilinear ones were revealed: the discharge of sodium ions from supersaturated solutions at E more negative than Esat (from ENa to Esat), from mixtures of supersaturated and saturated solutions (at a constant E equal to Esat), from diluted solutions (with E more positive than Esat). The activity coefficients of sodium in supersaturated solutions are close to 1, which ensures their increased reducing ability. Maximum degrees of supersaturation (>100) are created at formation and decomposition on the cathode of metallic sodium nuclei, which are sufficient to intensify and prolong electrolysis, to lower the lower temperature limit of its realization from 600 to 350 °С. The formation of metallic titanium in the near-anode layer is explained by the disproportionation of Ti2+ ions entering the near-anode electrolyte from the anode surface and from the near-cathode melt.