National University of Science and Technology “MISIS”, Moscow, Russia:

V. N. Averkin, Engineer of a Chair of Physical Chemistry, e-mail: averkin@misis.ru
M. V. Astakhov, Head of a Chair of Physical Chemistry, e-mail: astahov@phch.misa.ac.ru
Zh. V. Eremeeva, Assistant Professor of a Chair of Powder Metallurgy and Functional Coatings, e-mail: eremeeva-shanna@yandex.ru
K. A. Semushin, Post-Graduate Student of a Chair of Physical Chemistry, e-mail: kirill143@gmail.com

We considered the technology of production of high-porous electrodes from tantalum powder for miniaturization and increasing the specific capacitance of the electronic devices components, particularly tantalum electrodes. The two types of tantalum powders obtained by two different methods were compared: one is the tantalum powder obtained by sodium thermal reduction from potassium heptafluorotantalate, FTD-35 (“Ningxia oriental tantalum industry CO”, China) and the second is the tantalum powder obtained by reduction of tantalum pentoxide, TU-1 (ТУ-1) (“Metsintez” LLC, Russia). Specific surface and porosity of the powders were determined by the method of low-temperature nitrogen adsorption (BET (БЭТ) method). In addition, the powders were investigated by means of scanning and transmission electron microscopy, and micro-X-ray spectral analysis. Granulometric analysis of tantalum powders was carried out. The powder obtained by tantalum pentacoside reduction has a higher specific surface area and porosity, which makes it more attractive for manufacturing of high-capacity tantalum electrodes. A method for increasing the ratio of available pores and for optimizing the porous structure of tantalum powder by using the NH₄Cl salt as a pore-forming salt during sintering is proposed. The use of a pore-forming salt during sintering makes it possible to increase the residual porosity of tantalum powders from 28 to 35% for TU-1 powder and from 20 to 28% for FTD-35 powder. These increases are also accompanied by corresponding decreases in the density of sintered powders. Moreover, as a result of the carried out studies, it is possible to obtain tantalum electrodes with increased porosity having a specific capacity of up to 900 μF/g due to the use of a poreforming salt during sintering of pressed tantalum powder preforms in vacuum at the temperature of 1000 ^оC.
Our work was carried out with the support of the subsidiary agreement of the Ministry of Education and Science of the Russian Federation No. 14.577.21.0123 on 20.10.2014 (unique ID of the applied research: RFMEFI57714X0123).

1. Kokatev A. N., Gilev A. A., Orlov V. N., Kryzhanov M. V. Application of AFM to research of morphology of surface of magnesium-thermal tantalum powders. Researches and developments in chemistry and technology of 45 functional materials : proceedings of International Scientific and Technical Conference. Apatity : Izdatelstvo KNTs RAN, 2015. pp. 372–375.
2. Rietveld H. M. A Profile Refinement Method for Nuclear and Magnetic Structures. Journal of Applied Crystallography. 1969.Vol. 2. pp. 65–71.
3. F. Fairbrother. The chemistry of niobium and tantalum. Moscow : Khimiya, 1972. 280 p.
4. Vamsi Krishna Balla, Subhadip Bodhak, Susmita Bose, Amit Bandyopadhyay. Porous tantalum structures for bone implants: Fabrication, mechanical and in vitro biological properties. Acta Biomaterialia. 2010. Vol. 6, No. 8. pp. 3349–3359.
5. Orlov V. M., Kryzhanov M. V., Kalinnikov V. T. Magnesium-reduced tantalum and niobium powders with great specific surface areas. Trudy Kolskogo nauchnogo tsentra RAN. 2015. Vol. 31, No. 5. pp. 182–185.
6. Goroshchenko Ya. G. The chemistry of niobium and tantalum. Kiev : Naukova dumka, 1965. 484 p.
7. Efe M., Hyun Jun Kim, Chandrasekar S., Trumble K. P. The chemical state and control of oxygen in powder metallurgy tantalum. Materials Science and Engineering: A. 2012. Vol. 544. pp. 1–9.
8. Jae Sik Yoon, Byung Il Kim. Characteristics and production of tantalum powders for solid-electrolyte capacitors. Journal of Power Sources. 2007. Vol. 164, No. 2. pp. 959–963.
9. Youngmoo Kim, Eun-Pyo Kim, Joon-Woong Noh, Sung Ho Lee. Fabrication and mechanical properties of powder metallurgy tantalum prepared by hot isostatic pressing. International Journal of Refractory Metals and Hard Materials. 2015. Vol. 48. pp. 211–216.
10. Nedal T. Nassar. Shifts and trends in the global anthropogenic stocks and flows of tantalum. Resources, Conservation and Recycling. 2017. Vol. 125. pp. 233–250.
11. Aiqin Jiang, Anto Yohannan, Neme O Nnolim, Trevor A. Tyson, Lisa Axe, Sabrina L. Lee, Paul Cote. Investigation of the structure of-tantalum. Thin Solid Films. 2003. Vol. 437, No. 1–2. pp. 116–122.
12. Dae-Hwan Kwon, Seong-Hyeon Hong, Byoung-Kee Kim. Fabrication of ultrafine TaC powders by mechano-chemical process. Materials Letters. 2004. Vol. 58, No. 30. pp. 3863–3867.
13. ISO 13320: 2009. Particle size analysis — Laser diffraction methods.
14. GOST 19440–94. Metallic powders. Determination of apparent density. Part 1. Funnel method. Part 2. Scott volumeter method. State Standard. Introduced: 1997–01–01.