SIGAL process

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... 

Of all aluminum electrolyte systems, to our knowledge type 3 is today the technically most accepted. This type of electrolyte was discovered and intensely studied by Ziegler and Lehmkuhl [118, 217, 218, 221]. The companies Siemens AG, HGA, MBB, SEDEC, Interatom, and ALU 2000 have developed the industrial scale process (Sigal Process = Siemens galvanoaluminum). The used electrolytes consist of aluminumalkyls as well as alkali metal halides or quaternary onium salts, which are dissolved in aromatics (i.e., toluene). Electrolysis is carried out at temperatures around 90-100°C. Electrolytes of this kind have demonstrated their high produc-... 

Several technical processes were developed to deposit aluminum from an organic electrolyte. One example is the Sigal process using alkaline haUde-alkyl complexes of aluminum... 

In the following, the Sigal process will be described in more detail. The typical complex in this process is shown in Figure l. 9 The deposition of aluminum from these complexes is a rather slow process. A mechanism was discussed by Kautek and Birkle. Typical process parameters are 5-30 V, 0.2-2 A dm" DC, and 90 °C. 

Commercial aluminium plating processes, based on aluminium triethyl at 80-100° C are currently in operation on a production scale (up to 2200 dm electrolyte volume), e.g. the Sigal process (Hegin Galvano-Aluminium bv). 

Historically, ionic liquids initial advances in electrochemistry were encouraged by difficulties and safety issues in the aluminum deposition process known as SIGAL (Siemens Galvano-Aluminium). Major concerns were related with the flammability of the aluminum precursors and of the volatile organic solvents used. In the search for low melting, nonvolatile, and nonaqueous electrolytes, pyridinium [25] and imidazolium chloroaluminates (III) were investigated [26]. These ionic liquids are able to dissolve various metal salts. Their biocompatibility is questionable due to their potential toxicity and because they are also corrosive and unstable in air and/or... 

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