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.

Studies on Preparation of Thorium-Based Intermetallics in CaCl2 Melt by Electrochemical De-Oxidation Process

“…14,15 In this high-temperature molten salt electrolysis process, also known as the direct oxide electrochemical reduction (DOER) process, the solid metal oxide cathode is directly converted to respective metal or alloys by electrons or in situ electro-generated reductant metal, e.g., Ca, Li, etc, under the application of a constant cell potential or current between the cathode and the platinum or graphite anode. [16][17][18][19][20][21][22][23][24][25] Several important metals and alloys, including actinide metals and their alloys, e.g., U, Th, U-Pu, Pu-Fe, U-Ti, U-Mo, U-Nb alloys, etc, have been prepared using this method from their respective oxides. [26][27][28][29][30][31][32][33][34][35][36][37] Fray-Farthing-Chen (FFC) Cambridge process is one such process, wherein the reduction of metal oxide cathode is effected by electrons (electro-reduction), and the process is conventionally conducted in CaCl 2 melt at 900 °C.…”

“…This argument is in line with the fact that the three-phase interline (3PI, metal|oxide|electrolyte) where the electroreduction process takes place, propagates slowly from the surface towards the bulk of the metal oxide matrix due to difficulties in mass transfer 46 and hence the completion of reduction of NiO present in bulk took longer time. The higher amount of ThO 2 in the mixed oxide pellet, which possesses high electrical resistivity and high thermodynamic stability 22 could also have contributed to the slower kinetics of bulk NiO reduction. After 2.5 h, the decrease in current was very slight.…”

Electrochemical Preparation of ZrFe2 and ZrFe1.8Ni0.2 Intermetallic Compounds by FFC Cambridge Process

“…[13][14][15][16] Recently, FFC Cambridge process has been successfully applied for the preparation of advanced materials and alloys such as Ta-Nb, Ti-Nb, Ti-5Ta-Nb, Ti-Nb-Sn, TiNbTaZr, CoCrFeNi, and various hydrogen storage alloys, such as LaNi 5 , CeCo 5 , CeNi 5 , TbNi 5 , ZrCr 2 and ZrMn 2 . 11,[17][18][19][20][21][22][23][24][25][26][27] Peng et al synthesized Zr-based AB 2 -type hydrogen storage alloys (HSAs) viz., ZrCr 2 , ZrCr 0.7 Ni 1.3 , and Zr 0.5 Ti 0.5 V 0.5 Cr 0.2 Ni 1.3 from respective mixed oxide precursors via molten salt electrolysis in CaCl 2 melt at 900 o C. 11 Electrolysis energy consumption as low as 9.59 kWh (kg-HSA) −1 and a metal recovery yield greater than 90% was reported. The reduction proceeded through CaZrO 3 , elemental Zr and Cr as reaction intermediates.…”