Direct electrochemical reduction of titanium-bearing compounds to titanium-silicon alloys in molten calcium chloride

Titanium-silicon alloys have been electrochemically extracted from the multi-component titanium compounds in molten calcium chloride electrolyte. Sintered pressed pellets of titanium-bearing compounds served as the cathode, and the electrochemical experiments were systematically carried out at 900 °C, 3.1 V and 1000 °C, 3.8 V using a graphite-based anode and an improved inert-oxygen-ion-conducting membrane-based anode, respectively. The mineral composition and morphology of the products were examined. The current feature and the reaction process are discussed, and the mechanisms involved in the electrochemical reduction of titanium-bearing compounds to titanium-silicon alloys are proposed. Comparison between the graphiteand membrane-based anode systems are also carried out, and the results show that the improved membrane-based anode electrolysis system exhibits higher current efficiency and reduction rate than the graphite-based anode electrolysis system. Interestingly, the other metallic impurities such as Ca, Mg and Al contained in the starting titanium compounds have been partly even completely removed during electro-deoxidation, and the removal mechanism is discussed in the paper too. The experimental results show that titanium-silicon alloy (Ti5Si3) can be directly extracted from titanium-bearing compounds using electro-deoxidation technology in molten CaCl2. Electrolysis of ~1.5 g titanium compounds using the membrane-based anode system can be finished within 6 h, and the current efficiency reaches approximately 50%.