Chemical Deposition of Metals and Alloys from Aqueous Solutions

Chemical Deposition of Metals and Alloys from Aqueous Solutions 

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Relatively little attention has been devoted to the direct electrodeposition of transition metal-aluminum alloys in spite of the fact that isothermal electrodeposition leads to coatings with very uniform composition and structure and that the deposition current gives a direct measure of the deposition rate. Unfortunately, neither aluminum nor its alloys can be electrodeposited from aqueous solutions because hydrogen is evolved before aluminum is plated. Thus, it is necessary to employ nonaqueous solvents (both molecular and ionic) for this purpose. Among the solvents that have been used successfully to electrodeposit aluminum and its transition metal alloys are the chloroaluminate molten salts, which consist of inorganic or organic chloride salts combined with anhydrous aluminum chloride. An introduction to the chemical, electrochemical, and physical properties of the most commonly used chloroaluminate melts is given below. 

Ionic liquids are interesting media for the electrodeposition of metals, alloys, and senoiconductors, despite the fact that they are more expensive than aqueous baths. Due to their large electrochemical windows and their good thermal and chemical stability, they are used nowadays to electrodeposit metals that can also be obtained from aqueous solution, such as Cr, Ag, Ni, Cu, but also to electrodeposit metals that cannot be obtained from aqueous baths. This paper deals with the electrodeposition of Si and Ta in the ionic liquid butyl-methyl-pyrrolidinium bis(trifluoro)sulfonyl imide ([BMP][TFSI]). Compared to other deposition techniques, such as chemical vapor deposition or plasma vapor deposition, electrodeposition is a relatively simple technique and in many cases significantly cheaper. Moreover, materials of different shapes and dimensions can be obtained relatively easy by electrodeposition. Thus, for industrial applications, it would be highly interesting to obtain reactive metals and semiconductors by electrodeposition. 

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