Speciation, physical and electrolytic properties of eutectic mixtures based on CrCl3·6H2O and urea

• Published in: Physical chemistry chemical physics : PCCP Vol. 16; no. 19; pp. 947 - 955
• Main Authors: Abbott, Andrew P, Al-Barzinjy, Azeez A, Abbott, Paul D, Frisch, Gero, Harris, Robert C, Hartley, Jennifer, Ryder, Karl S
• Format: Journal Article
• Language: English
• Published: England 21.05.2014
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c4cp00057a

The electrodeposition of chromium is a technologically vital process, which is principally carried out using aqueous chromic acid. In the current study, it is shown that eutectic mixtures of urea and hydrated chromium( iii ) chloride provide a liquid which reduces the toxicological issues associated with the current aqueous Cr( vi ) electroplating solution. Using EXAFS, mass spectrometry and UV-Vis spectroscopy, it is shown that chromium is present predominantly as a cationic species. Conductivities are higher than for most comparable ionic liquids. It is shown that the electrodeposition of chromium is electrochemically reversible, with a current efficiency much higher than in aqueous electrolytes. Surface tension and density measurements indicate that hole theory is a valid model to describe transport properties in these liquids. Bulk Cr deposits are not macrocrystalline but they are generally crack-free. The deposits have a hardness of 600 ± 10 Vickers and, as such, are comparable to deposits from aqueous systems. The electrodeposition of hard chromium is demonstrated from a novel deep eutectic solvent with high current efficiency resulting from a cationic metallic species in the liquid.