Electrolytic reduction of mixed (Fe, Ti) oxide using molten calcium chloride electrolyte

The production of high-purity metals or alloys using effective technologies is critical for future industrialization. With this aim in mind, a fundamental study of electrolysis in molten CaCl2 electrolytes was conducted to develop a new production process for ferrotitanium (Fe–Ti) intermetallic alloys. Mixed solid oxides of TiO2 and Fe2O3 were used in a molar ratio of 5.44:1.00. In this composition of Ti and Fe, FeTi and β-Ti containing iron can co-exist in equilibrium. A mixed solid (Fe, Ti) oxide was reduced electrochemically in a molten CaCl2 electrolyte at 950 °C. The metallic samples formed by electrolytic reduction of the mixed solid (Fe, Ti) oxide were analyzed using X-ray diffraction, scanning electron microscopy/energy-dispersive X-ray spectroscopy, electron-probe microanalysis, X-ray fluorescence spectrometry, inductively coupled plasma atomic emission spectroscopy, ion chromatography, and oxygen and carbon analyzers. The oxide pellets were successfully reduced to a highly purified dense intermetallic solid of β-Ti (FeTi4) and FeTi containing low levels of impurities, for example, less than 0.01 mass% of carbon.

► Tan et al. have electrolyzed mixtures of TiO2 and Fe2O3 to produce alloys containing Fe–Ti intermetallic phases such as FeTi and Fe2Ti using the FFC process. However, the produced alloys have a porous structure with many carbon impurities, e.g., titanium carbide (TiC). Most of the carbon contamination could be caused by the presence of carbon particles in the porous alloy structure. They did not mention any obvious ways of excluding carbon and other impurities, and only suggested that the use of mixed oxides with refined structures or using a single phase, namely ilmenite (FeO·TiO2), were methods of decreasing impurities in the formed alloys. For future industrialization, there is an urgent need for obvious ways of producing purer Fe–Ti alloys with dense structures, rather than porous structures, as these absorb carbon impurities.
► Finally, we successfully reduced to a highly purified Fe–Ti intermetallic alloy of FeTi and β-Ti (FeTi4) phases. FeTi phases of size around 5–10 μm were dispersed in a matrix of the β-Ti (FeTi4) phase. The carbon content of the electrolyzed alloy was as low as less than 0.01 mass%. It was suggested that the dense structure of the alloy of FeTi and β-Ti (FeTi4) avoided the inclusion of carbon particle impurities, unlike the porous alloy structure.