Electrochemical studies of Ir coating deposition from NaCl-KCl-CsCl molten salts

In this paper, the electrochemical behavior of Ir3+ ions in melting NaCl-KCl-CsCl-IrCl3 and the major kinetic parameters were investigated by transient and steady electrochemical techniques from 823 K to 913 K. Effects of the electrochemistry of Ir3+ ions on the microstructure of Ir coatings were also discussed. The electrochemical reduction of Ir3+ ions from the melts was the diffusion-controlled and irreversible reaction with exchange of three electrons at 823-883 K and converted to be a quasi-reversible one with the temperature increasing to 913 K. The major kinetic parameters of Ir3+/Ir couples, the diffusion coefficient Do and exchange current density j(0), respectively increased from 2.4 x 10(-6) cm(2)/s to 9.2 x 10(-6) cm(2)/s and from 5 mA/cm(2) to 16 mA/cm(2) with the temperature. With the temperature and applied cathodic potential decreasing, the microstructure of Ir coatings converted from the coarse and preferential oriented columnar grain structure to the fine and unoriented dispersive grain structure. (C) 2017 Elsevier B.V. All rights reserved.