Percolation and oxygen-induced passivation mechanisms during the anodic dissolution of Cu-Ti alloys for titanium electrorefining

This study investigates the anodic dissolution kinetics and passivation mechanisms of Cu-Ti alloy anodes during molten salt electrorefining. While thermodynamic calculations theoretically guarantee the selective separation of Ti, high-efficiency refining requires precise control of the anode's microstructural evolution. The dissolution mechanism is governed by a “percolation threshold”: a minimum titanium content of 60 wt% is required to trigger the “structural breakdown” of the copper matrix, thereby enabling effective electrolyte infiltration into the anode interior. Residual oxygen in the alloy is identified as a primary factor inducing passivation. Through electrochemical impedance spectroscopy (EIS) using a dual-loop circuit model and X-ray diffraction (XRD) analysis, we elucidate a dual-blocking mechanism where oxygen promotes the formation of stable Ti 3 O and Ti 4 Cu 2 O phases. These phases chemically stabilize the lattice and physically obstruct the formation of dissolution channels. Furthermore, density functional theory (DFT) calculations confirm that this passivation is governed by a site-by-site kinetic threshold, where a single Ti-O bond increases the dissolution activation energy by an order of magnitude. By optimizing the percolation network and controlling oxygen content below 1 wt%, a high cathodic current efficiency of 65.33% was achieved, yielding high-purity metallic titanium with minimal copper contamination (< 150 ppm). These results provide fundamental metallurgical insights for designing high-performance alloy anodes for titanium production.