Liquidus Temperature and Electrical Conductivity of the Molten CsCl–NaCl–KCl Eutectic Containing IrCl3

The (CsCl–NaCl–KCl)eut–IrCl3 melt is promising for the production of iridium coatings and composites. The liquid temperature and the electrical conductivity are determined for several compositions of the melt by thermal analysis and impedance spectroscopy. The temperature ranges of liquidus (753–983) ± 5 K and solidus (751–755) ± 4 K are established and the corresponding parts of the phase diagram for the quasi-binary system (CsCl–NaCl–KCl)eut–(0–2.12 mol %) IrCl3 is plotted. The lowest liquidus temperature is shown to be observed for the melt containing 1.4 mol % IrCl3. The increase in the liquidus temperature in the molten mixtures with more than 1.5 mol % IrCl3 is explained by the formation of the Cs3IrCl6 compound, which was detected by XRD analysis. The electrical conductivity of the melts (in the homogeneity region) is found to linearly decrease as the temperature decreases or the IrCl3 concentration increases. The coefficients that describe the temperature dependences of the electrical conductivity of the (CsCl–NaCl–KCl)eut–(0–2.12 mol %) IrCl3 melts are determined. For all the studied iridium-containing compositions, the average temperature coefficient is (2.35 ± 0.02) × 10–3 Ω–1 cm–1 K–1. The addition of 1 mol % IrCl3 leads to a decrease in the electric conductivity by about 7%. It is found that the operating temperature can be decreased to ~800 K in the melt with iridium trichloride concentrations of 1.4–1.5 mol %; the process temperature can be varied from 850 K to 1030 K at lower and higher IrCl3 contents depending on the electrodeposition conditions.