Transpassive and abnormal dissolution of titanium electrodes in hydrofluoric acid aqueous solution

Abstract

Introduction. One of the urgent problems of electrochemistry is the reuse of production waste of a relatively expensive metal – titanium, which is in great demand in mechanical, aircraft engineering, medicine, and nanotechnology. The purpose of this work is to study the abnormal cathodic and transpassive anodic dissolution behavior of a titanium electrode in an aqueous hydrofluoric acid solution. Methodology. The anode and cathode spaces are separated by an anion exchange membrane. As a result of the electrochemical dissolution of titanium Ti⁴⁺ ions are formed in the anode space, and Ti³⁺ ions are formed in the cathode space due to the chemical dissolution of titanium. The influence of the main electrochemical parameters on the titanium dissolution process in the anode and cathode spaces has been studied. Results and discussions. The current efficiency of titanium anodic dissolution slowly increased with increasing current density, and its maximum value (82.5%) was observed at a current density of 800 A/m². With an increase in the concentration of hydrogen fluoride, the current efficiency rapidly increased, and its maximum value at a current density of 200 A/m² was determined at a concentration of 0.6 mol/l and was equal to 78.1%. Titanium dissolves forming Ti³⁺ ions along with Ti⁴⁺ ions in the anode space with an increase in the electrolyte temperature. The current efficiency of Ti⁴⁺ ions decreases while sharply increasing for Ti³⁺ ions. Conclusion. The optimal conditions for transpassive anodic and anomalous cathodic dissolution of a titanium electrode in an aqueous solution of hydrofluoric acid and the kinetic parameters of the electrode process are determined.