Synthesis of Fe–4.6 wt% B alloy via electro-deoxidation of mixed oxides

Abstract

Fe–4.6 wt% B alloy was synthesized via electro-deoxidation of the mixed oxide precursor. The oxides, Fe2O3 and B2O3, mixed in suitable proportions were sintered at 900 °C yielding pellets with a two-phase structure; Fe2O3 and Fe3BO6. The sintered pellets, connected as cathode, were then electro-deoxidized in molten CaCl2 or in CaCl2–NaCl eutectic, against a graphite anode at 3.1 V. The electrolysis at 850 °C has successfully yielded a powder mixture of Fe and Fe2B. Sequence of changes during the electrolysis was followed by interrupted experiments conducted at 850 °C. This has shown that iron is extracted quite early during the electrolysis through the depletion of oxygen from the starting oxide; Fe2O3, forming the other iron oxides in the process. Boron follows a more complicated route. Fe3BO6, the initial boron-bearing phase, was depleted in the early stages due to its reaction with molten salt. This gave rise to the formation of calcium borate. Boron was extracted from calcium borate in later stages of electrolysis, which appeared to have reacted in situ with the iron forming compound Fe2B.