Eliminating carbon contamination with improved one-step electrochemical preparation of refractory high-entropy alloy TiZrHfNbTa

Abstract

Creating refractory high-entropy alloys (RHEAs) effectively without impurities is a momentous challenge. Conventional methods for the preparation of RHEAs have exacting requirements for raw material purity and energy consumption. Molten salt electrolytic oxides are applied to the preparation of HEAs by virtue of their low cost and high efficiency. However, the use of graphite anodes in electrolysis will result in the carbon contamination of the products due to the deposition of CO32− at the cathode. Increasing the reaction temperature accelerates the deoxidation of the oxide, thus reducing the amount of carbide but not eliminating it. Switching HfH2 instead of HfO2 and using Nb2O5 to shield the precursor can effectively remove carbon contamination. However, this leads to a complicated preparation process and energy waste. Herein, we use the solid oxygen ion-conducting membrane (SOM) containing graphite and Sn (named as SOM@C/Sn) anode to separate the carbon from the molten salt and prevent the circulation of CO32−. The pure single-phase TiZrHfNbTa RHEA can be produced in only one-step with the SOM@C/Sn anode, which completely solves the problem of carbon contamination in the molten salt electrolysis preparation of HEAs. This work provides a feasible solution for the preparation of novel complex alloys such as carbon-free RHEAs in a low-cost short process.