Giredmet, Moscow, Russia:

А. А. Gasanov, Head of the Department of Highly Purified Material, Rare and Rare Earth Metals, e-mail: aagasanov@giredmet.ru
Yu. B. Patrikeev, Head of the Laboratory for the Technology of Rare Earth Metals, Powders and Alloys, e-mail: ybpatrikeev@giredmet.ru
S. A. Repin, Research Fellow at the Laboratory for the Technology of Rare Earth Metals, Powders and Alloys, e-mail: sa.repin@mail.ru
Yu. M. Filyand, Senior Researcher at the Laboratory for the Technology of Rare Earth Metals, Powders and Alloys1, e-mail: jmfilyand@yandex.ru

The authors of this paper developed and implemented a process for the production of tantalum powders by closed-loop hydrogen dispersion. Production of powders by hydrogenation encompasses hydrogen saturation of compact metal, milling of the resultant hydride, screening and dehydrogenation of powder. The hydrogen generated as a result of hydride dissociation can be removed with the help of vacuum pumps or reversible sorbents. The latter stand for metals that can form hydrides or intermetallic compounds. The absorbed hydrogen can be reused in the dispersion process for the following batches of metal, which makes it a closed-loop HDH process. Two processes have been proposed. The first option is based on the use of titanium sponge as the primary sorbent. In order to save time required to heat up the titanium sponge hydride to the dissociation temperature, an additional source of hydrogen — i.e. hydrogen saturated alloy La_{1 – y}R_yNi₄Co (R — rare earth metal and/or misch metal, 0 < y ≤ 1) – is used for the activation of compact tantalum and at the early stage of its hydrogenation. This combination technique helped shorten the hydrogenation time and the overall powder production time, as well as reduce the hydrogen loss. Moreover, it prevented dangerous hydrogen pressure spikes. The second option is based on the use of the intermetallic compound LaNi₄Co, which serves not only as an additional sorbent but also as a primary one. For more efficient removal of hydrogen from the final product, the dehydrogenation process is effected in stages. At the first stage most of the generated gas is absorbed by the unsaturated hydride LaNi₄Co at ambient temperature, and during the second stage the rest of the hydrogen is absorbed by a pre-activated alloy of the same composition that was degasified when heated to 80–100 ^oC. This technique helps achieve a significant cut in the electric power consumed by the HDH process, as well as a significant cut in the equipment cost. Besides, saturation and degassing of LaNi₄Co at lower temperatures prevent the risk of emergencies related to vessel cracking.

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