Institute of High Temperature Electrochemistry of Ural Branch of RAS, Ekaterinburg, Russia:

A. V. Isakov, Senior Researcher, e-mail: ihte_uran@mail.ru
A. O. Nikitina, Engineer, e-mail: info@ihte.uran.ru

¹Institute of High Temperature Electrochemistry of Ural Branch of RAS, Ekaterinburg, Russia ; ²Ural Federal University named after the first President of Russia B. N. Yeltsin, Ekaterinburg, Russia:

A. P. Apisarov, Researcher^{1, 2}, e-mail: aap@ihte.uran.ru

We investigated the electrodeposition of a multilayer material based on iridium and rhenium in the CsCl – NaCl – KCl – IrCl₃ and CsCl – Cs₂ReCl₆ melts. The thermodynamic calculations were carried out for the exchange reaction of the rhenium and iridium chloride in a CsCl – NaCl – KCl – IrCl₃ melt. The calculations of the isobaric-isothermal potential for the exchange reaction show the temperature range below 873 K for the rhenium-iridium pair, in which the reaction is unlikely; and the reverse reaction, thermodynamically probable at the temperatures below 830 K. Based on the calculations, the electrodeposition conditions were chosen and the multilayer compositions of the Ir – Re – Ir were obtained. Taking into account the exchange processes in the molten salts, it is possible to obtain the continuous coatings on substrates with a more negative conventional standard potential by electrodeposition. The Ir – Re – Ir material consisting of the homogeneous iridium and rhenium layers without the formation of diffusion layers was produced by the sequential galvanostatic electrolysis. This is confirmed by the X-ray phase analysis of the cross-section. The iridium layers were obtained in the CsCl – NaCl – KCl – IrCl₃ melt at the temperature of 853 K. The rhenium layers were obtained in the CsCl – Cs₂ReCl₆ melt at the temperature of 1073 K. The behavior of the Ir – Re – Ir composition under vacuum annealing at 2073 K was studied. The microhardness of the Ir – Re – Ir material was measured before and after annealing. The microhardness of the iridium and rhenium layers increases after annealing. The microhardness of iridium rises from 320 HV to 520 HV. In this case, the microhardness of the rhenium layer increases less significantly, from 380 to 435 HV. The formation of the diffusion layers after annealing, consisting of rhenium and iridium, was revealed by the optical and electron microscopy, coupled with micro-X-ray spectral analysis. The microhardness of the diffusion layers exceeds the parameters of the homogeneous layers of iridium and rhenium after annealing. At the same time, the microhardness of the intermediate layer in the sample is 720 HV after annealing.
This investigation was carried out with the financial support of the Federal Target Programm “Investigations and developments on the priority ways of development of scientific and technological complex of Russia for 2014–2020”. Agreement No. 14.578.21.0238.

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