An Electrochemical Quartz Crystal Microbalance Study on Electrodeposition of Aluminum and Aluminum-Manganese Alloys

Abstract

The electrodeposition process of aluminum and aluminum-manganese alloys was studied in situ, by using an electrochemical quartz crystal microbalance, EQCM, with damping monitoring, in AlCl 3 based ionic liquids. Cyclic voltammetry, potentiostatic and galvanostatic deposition were performed at different temperatures, from 25 • C up to 100 • C. The morphology of the deposits was investigated by SEM and AFM, and their composition by EDX. The stoichiometry of the alloys was calculated from the EQCM data, based on Sauerbrey's equation. We could show that for thin films electrodeposited on gold electrodes, one can tune their morphology, and in the case of the alloys, also their composition, by modifying the deposition current or potential, as well as by modifying the temperature of the electrolyte. The morphology of the deposits changed gradually with increasing the amount of Mn in the electrolyte from a polyhedral like structure for Al films to round granules for the AlMn alloys. The mechanism for electrodeposition and dissolution of Al and AlMn alloys were analyzed and discussed based on the EQCM data. Some of the chemicals used nowadays in industrial applications are toxic and/or environmentally benign. Alternatives are searched for those chemicals both by industry, as well as in academia. One of the metals of concern is Cd. Its corrosion and wear behavior are excellent. However, it is one of the metals of high concern for our health. According to some recent reports published by the Rowan Technology Group, 1 one promising alternative to replace Cd layers which could offer similar properties to these coatings are Al and Al alloys, in particular Al-Mn.2 It was previously shown that alloying of Al with Mn produces layers that have better corrosion resistance 3,4 and improved mechanical properties 5 compared to pure Al films. This was the reason for choosing in this paper Al and AlMn alloys for a detailed study. The aim was to understand better the effect of the deposition parameters on the properties of the deposited films.Electrodeposition of aluminum and its alloys has been intensively studied both in molten salts, 4,6 as well as in ionic liquid 7-12 electrolytes. Electroless deposition of Al films in room temperature ionic liquids has also been recently reported. 13 The reason for the interest in obtaining dense and uniform aluminum films is due to the special properties of this metal and its alloys, such as good corrosion resistance and wear resistance, light weight, and other more.14 Thus, Al is well known to self-passivate in air, which means it forms an oxide layer that protects it from further corrosion. Aluminum and its alloys can be used in both decorative and functional coatings.Different types of electrolytes were used for electrodeposition of Al and its alloys, such as organic electrolytes (toluene in the SIGAL process), 14 molten salts (such as Li + /K + /AlCl 3 eutectic system) 14 and ionic liquids (with ammonium, pyrrolidinium and imidazolium based cations).14 The source for deposition of aluminum is...

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Electrochemical Studies of Green Corrosion Inhibitors

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