Electrodeposition of Aluminum

In many ways, chloroaluminate molten salts are ideal solvents for the electrodeposition of transition metal-aluminum alloys because they constitute a reservoir of reducible aluminum-containing species, they are excellent solvents for many transition metal ions, and they exhibit good intrinsic ionic conductivity. In fact, the first organic salt-based chloroaluminate melt, a mixture of aluminum chloride and 1-ethylpyridinium bromide (EtPyBr), was formulated as a solvent for electroplating aluminum [55, 56] and subsequently used as a bath to electroform aluminum waveguides [57], Since these early articles, numerous reports have been published that describe the electrodeposition of aluminum from this and related chloroaluminate systems for examples, see Liao et al. [58] and articles cited therein. 

Cr-Al, Mn-Al, and Ti-Al alloys can be obtained from acidic melt solutions containing Cr(II), Mn(II), or Ti(II), respectively, only if the deposition potential is held very close to or slightly negative of the thermodynamic potential for the electrodeposition of aluminum, i.e., 0 V. From these observations it can be concluded that the formal potentials of the Cr(II)/Cr, Mn(II)/Mn, and Ti(II)/Ti couples may be equal to or less than E0 for the A1(III)/A1 couple. Unlike the Ag-Al, Co-Al, Cu-Al, Fe-Al, and Ni-Al alloys discussed above, bulk electrodeposits of Cr-Al, Mn-Al, and Ti-Al that contain substantial amounts of A1 can often be prepared because problems associated with the thermodynamic instability of these alloys in the plating solution are absent. The details of each of the alloy systems are discussed below. 

A major breakthrough was achieved in 1951 with the report of Hurley and Wier. They noticed that a mixture of N-ethylpyridinium bromide (EtPyBr) and AICI3 with a eutectic composition of 1 2 X(AlCh) = 0.66 h of EtPyBr to AICI3 became liquid at unusually low temperatures [2], They investigated these melts with regard to their potential use in the electrodeposition of aluminum at ambient temperature [3]. Several studies were carried out on this system, however, its use was very limited since it is only liquid at a mole fraction of X(A1C13) = 0.66 and the ease of oxidation of the bromide ion limits the electrochemical stability. In the following years the main interest in ionic liquids was focused on electrochemical applications [4—6]. 

The electrodeposition of aluminum has enormous potential in industrial applications. The main reason for this is that aluminum reacts with oxygen to form dense layers of aluminum oxides, protecting metals from corrosion. By far most of the publications concerning the electrodeposition of metals from tetrachloroaluminate-based ionic liquids focus on aluminum. 

In this context, Osteryoung and Robinson were the first, in 1980, when they described the electrodeposition of aluminum on platinum and glassy carbon from... 

Because of its high reactivity (—1.67 V vs. NHE), the electrodeposition of aluminum from aqueous solutions is not possible. Therefore, electrolytes for A1 deposition must be aprotic, such as ionic liquids or organic solvents. The electrodeposition of aluminum in organic solutions is commercially available (SIGAL-process [56, 57]) but due to volatility and flammability there are some safety issues. Therefore, the development of room-temperature ionic liquids in recent years has resulted in another potential approach for aluminum electrodeposition. Many papers have been published on the electrodeposition of aluminum from chloroaluminate (first... 

The Lewis acidic chloroaluminate ILs are suitable for the electrodeposition of aluminum-containing alloys. Many examples have been published but those that have been reviewed in detail by Stafford and Hussey [1] will not be included in this section. 

Every single regeneration problem has to be analysed individually, however, the following case study demonstrates how a selection of separation techniques, extraction and phase separation, can successfully be applied to regenerate a spent ionic liquid based electrolyte satisfactorily. As a case study the electrolyte 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide ([BMP]Tf2N) was chosen, which is used for electrodeposition of aluminum as described in the literature [137, 138],... 

In this chapter we would like to present some plating protocols for the electrodeposition of aluminum, lithium, tantalum and zinc from different ionic liquids. These recipes have been elaborated in our laboratories and should allow the beginner to perform his first electrodeposition experiments. For aluminum we give four different recipes in order to show that the ionic liquid itself can strongly influence the deposition of metals. In the case of tantalum the deposition of the metallic phase is not straightforward as, in unstirred solutions, the more nonstoichiometric tantalum halides form the higher the current density for electrodeposition. Apart from the zinc deposition all experiments should be performed at least under dry air. 

Similar to the AlCl3/[EMIM]TFSA mixture, the mixture of AlCh/IPyip] TFSA shows biphasic behavior with increase in the concentration of AlCh up to 1.6 M. In contrast to the AlQj/tEMIMJTFSA mixture, the lower phase is colorless while the upper one is pale and more viscous. By adding more AICI3 the volume of the lower phase decreases till a concentration of 2.7 mol L-1 is reached, then only one solid phase can be formed at room temperature. The biphasic mixture of AlCb/ITyi TFS A becomes monophasic by heating to a temperature of about 80 0 C. The electrodeposition of aluminum occurs only from the upper phase at AICI3 concentrations > 1.6 mol L . 

H. Lehmkuhl, K. Mehler, and U. Landau provide a summary of the criteria and problems associated with the electrodeposition of aluminum at ambient temperature. Special emphasis is given to the organo-aluminum electrolyte developed in the laboratory of Karl Ziegler, winner of the Nobel prize in 1963. Although difficult to handle, these electrolytes offer some unique advantages for the deposition of aluminum. 

HurieyFH, Weir TP (1951) The electrodeposition of aluminum from nonaqueous solutions at room temperature. J Electrochem Soc 98 207—212... 

The first electrodeposition of aluminum from an ionic liquid was reported in 1994 by Carlin etal. [157], Two years later, Zhao et al. [158] smdied the aluminum deposition processes on tungsten electrodes in trimethylphenylanunonium chlo-ride/aluminum chloride with mole ratio 1 2. It was shown that the deposition of aluminum was instantaneous as a result of three-dimensional nucleation with hemispherical diffusion-controlled growth, underpotential deposition of aluminum, corresponding to several monolayers. Liao et al. investigated the constant current electrodeposition of bulk aluminum on copper substrates was in 1-methyl-... 

Ah MR, Nishikata A, Tsuru T (1997) Electrodeposition of aluminum-chromium alloys from AlQj-BPC melt and its corrosion and high temperatrrre oxidation behaviors. Electrochim Acta 42 2347-2351... 

Liao Q, Pitner WR (1997) Electrodeposition of aluminum from the aluminum chloride-1-methyl-3-ethyhmidazolium chloride room temperature molten salt with benzene. J Electrochem Soc 144 936-942... 

Jiang T, Chollier MJ, Brym B (2006) Electrodeposition of aluminium from ionic liquids part 11 - studies on the electrodeposition of aluminum from aluminum chloride (Ald ) trimeth-ylphenylammonium chloride (TMPAC) ionic liquids. Surf Coat Technol 201 10-18... 

Vaughan J, Dreisinger D (2008) Electrodeposition of aluminum from aluminum chloride-tiihexyl(tetradecyl) phosphonium chloride. J Electrochem Soc 155 D68-D72... 

The early history of ionic liquids research was dominated by their application as electrochemical solvents. One of the first recognized uses of ionic liquids was as a solvent system for the room-temperature electrodeposition of aluminum [1]. In addition, much of the initial development of ionic liquids was focused on their use as electrolytes for battery and capacitor applications. Until recently, electrochemical studies in the ionic liquids were primarily carried out in the haloaluminate-based systems, and this work has been extensively reviewed [2-9]. Development of non-haloaluminate ionic liquids over the past fifteen years, however, has led to an explosion of research in these systems [10,11]. Much of the initial interest in these new ionic liquids has been in areas other than electrochemistry. However, this initial slight has been largely corrected, as evidenced by the dramatic growth over the past five years in electrochemically related publications involving non-haloaluminate ionic liquids and the appearance of several good reviews on the subject [12-17]. 

Electrodeposition of aluminum is severely limited by the necessity of using molten salt baths or anhydrous organic electrolytes. 

The electrodeposition of aluminum from ionic liquids has been intensively investigated. The principal rule for ionic liquids is the special design of the anion-cation combination for the metal to be deposited, hr Figure 7.20 the usual ionic liquid for aluminum deposition is shown. 

Chloroaluminate ionic liquids have been used in the electrodeposition of aluminum and aluminum-transition metal alloys. Transition metal-aluminum alloys are valued for their corrosion resistance and magnetic properties. A convenient method for creating thin alloy films is through the electrodeposition of two or more metals. The electrodeposition of aluminum and aluminum alloys from aqueous solutions is complicated by the fact that... 

Gandhi T, Raja KS, Misra M (2008) Room temperature electrodeposition of aluminum antimonide compound semiconductor. Electrochim Acta 53(24) 7331-7337. doi 10.1016/j. 

Chang J-K, Chen S-Y, Tsai W-T, Deng M-J, Sun IW (2007) Electrodeposition of aluminum on magnesium alloy in aluminum chloride (AlC13)-l-ethyl-3-methylimidazolium chloride (EMIC) ionic liquid and its corrosion behaviw. Electrochem Commun 9(7) 1602-1606. doi 10.1016/j.elecom.2007.03.009... 

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