Facile and Scalable Electrochemical Synthesis of Ta-Nb Alloy Powders for Capacitors

Abstract

The cost of tantalum (Ta), and thus of Ta capacitors, is undesirably high owing to the limited availability of its ores and the energy-intensive production. Reported herein is the economically viable electrochemical synthesis of Ta-Nb alloys as a potential replacement for Ta in capacitors. Ta-xNb (x = 20, 50, 80) alloys were prepared directly by electro-deoxidation of Ta2O5-Nb2O5 mixed oxide disks in CaCl2 melt at 900 °C and the results were compared with those for the pure metals. The alloys and metals thus made were in the form of powders and consisted solely of the body-centered cubic phase. The overall compositions of the alloys were close to the target values. EDX and XPS analyses revealed that the particles underwent surface oxidation during the post-electrolytic washing process, thereby forming the required dielectric coating around the metallic cores. Cyclic voltammetry in an aqueous electrolytic cell demonstrated that all powders behaved as typical capacitor materials. TG/DSC studies on Ta and Ta-50Nb in air showed that oxidation commenced at 531 °C and 363 °C, respectively, with Ta-50Nb exhibiting an inversion in the temperature coefficient of the oxidation reaction at 650 °C. In overall, the method presented here for producing commercially relevant Ta-Nb alloys is both facile and scalable.