Kinetic and Passivation Limitations in Titanium Reduction via Molten Oxide-Fluoride Electrolysis

Area of Science:

• Materials Science
• Electrochemistry
• Metallurgy

Background:

• Titanium and its alloys are crucial in various industries due to their unique properties.
• Molten oxide electrolysis offers a direct route for metal extraction, producing only oxygen.
• Direct electrolytic deposition of titanium from oxides remains a significant challenge.

Purpose of the Study:

• To systematically investigate the limitations of molten oxide-fluoride electrolysis for titanium deposition.
• To identify the fundamental barriers hindering efficient titanium extraction from its oxides.
• To provide strategic insights for optimizing titanium metallurgy.

Main Methods:

• Electrochemical experiments using tungsten and iron electrodes in a CaF2-CaO-TiO2 melt.
• Cyclic and square-wave voltammetry to analyze the reduction mechanism.
• Investigation of Fe2O3 deposition to understand related processes.

Main Results:

• Negligible metallic titanium deposition observed on tungsten electrodes.
• Only micrometer-thick titanium layers formed on iron electrodes or with Fe2O3.
• Identified two primary limitations: slow titanium ion reduction and cathode passivation by CaTiO3 formation.

Conclusions:

• The reduction rate of titanium ions is comparable to the dissolution rate of metallic titanium.
• Calcium titanate (CaTiO3) formation rapidly passivates the cathode, impeding continuous titanium deposition.
• Optimizing titanium metallurgy requires addressing these fundamental barriers in molten oxide-fluoride electrolysis.