Direct oxygen removal technique for recycling titanium using molten MgCl2 salt

Area of Science:

• Materials Science
• Metallurgy
• Electrochemistry

Background:

• Deoxidizing titanium (Ti) using magnesium (Mg) is challenging due to high oxygen potential, limiting purity levels.
• Achieving commercial-grade pure Ti ( < 0.05 mass% O) requires reducing MgO activity below ~0.025, which is difficult with conventional Mg deoxidation.

Purpose of the Study:

• To investigate an electrochemical technique for deoxidizing titanium in molten magnesium chloride (MgCl2) salt.
• To achieve titanium with less than 0.05 mass% oxygen using an electrochemical approach.

Main Methods:

• An electrochemical cell was established using Ti samples as the cathode and graphite as the anode in molten MgCl2 at ~1173 K.
• A constant DC voltage of approximately 3.1 V was applied, increasing the Mg chemical potential at the Ti cathode surface.
• Oxygen species were removed by reacting with the carbon anode to form CO/CO2 gas.

Main Results:

• Titanium samples with initial oxygen content of 0.12 mass% were successfully deoxidized to below 0.02 mass% oxygen.
• In some instances, oxygen concentration in Ti was reduced to 0.01 mass%, surpassing the capabilities of the conventional Kroll process.
• The molten MgCl2 facilitated deoxidation by lowering the activity of the MgO reaction product.

Conclusions:

• Electrochemical deoxidation in molten MgCl2 offers a viable method for producing high-purity titanium.
• This technique overcomes the limitations of conventional Mg deoxidation, achieving significantly lower oxygen concentrations.
• The process shows potential for application in industrial titanium recycling and purification.