Electrodeposition of Alloys from Aqueous Solutions

Magnesium. As it is well-known, electrodeposition of magnesium from aqueous solution is difficult due to its reactivity with water. In this sense, Bakkar and Neu-bert have investigated the electrodeposition of Zn onto several Mg alloys in different euteetie mixtures (ChCl/EG, ChCl/Urea, ChCl/MAc and ChCl/Gly)." After eomparing the efficiency of these DESs, ChCl/Urea was found to be the most suitable medium for the electrodeposition of Zn on Mg." ... 

Electrodeposition of antimony sesquitelluride, Sb2Tc3, or of (Bii xSbx)2Te3 alloys from aqueous solutions is challenging because it is difficult to achieve a sufficiently high concentration of antimony. Complexing agents such as tartaric acid, citric acid, or FUTA have been used to solubilize Sb in water. 

Electrodeposition of conducting polymers on copper has been investigated by several groups, and various salts have been tested to achieve the electrochemical polymerization of pyrrole from aqueous solutions in a one-step process. No serious difficulty was found, and electrolytes used previously on iron, such as oxalic acid [115,116], salicylates [117,118], and tartrate [119] were found suitable for PPy electrodeposition on copper and its alloys aqueous phosphate solutions were also found to provide highly adherent and homogenous films [120]. In all cases, PPy electrodeposition occurred after the preliminary passivation of copper through a mixed copper salt, copper oxide, or copper hydroxide layer. A two-step process, where an oxalate-doped PPy underlayer (PPy-Oxalate) is first deposited, followed by a dodecylbenzenesulfonate-doped PPy layer... 

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... 

So far little work has been performed on the UPD of pnictides N, P, As, Sb. It would appear that UPD of N, or even electrodeposition of N from an aqueous solution, is not a likely event. P has been known to deposit with ferrous metals, such as Ni, to form NiP alloys [257-261], This induced co-deposition of P with Ni suggests that it can be electrodeposited, although it does not appear that bulk P would be stable in an aqueous solution. It may be that P can be induced to form an atomic layer on the right metal, possibly Ga or In. 

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. 

Electrodeposition of alloys Electrolysis has also been used in order to obtain several metal compounds and alloys via the simultaneous co-deposition, from aqueous solutions or fused salts of the metal components. 

The preceding chapters have shown that the majority of metals can now be electrodeposited from ambient-temperature ionic liquids. However, this does not necessarily mean that the liquid with the widest potential window will negate the use of all other ionic liquids. Rather, it is most likely that ionic liquids will be task-specific with discrete anions being used for metals that cannot be electrodeposited from aqueous solutions such as Al, Li, Ti, V and W. Type I eutectics will probably be the most suitable for Al, Ga and Ge. Type II eutectics are most suitable for Cr and Type III are most suited to Zn, Cu, Ag and associated alloys. Type III will also find application in metal winning, oxide recycling and electropolishing. To date most practically important metals have been electrodeposited from ionic liquids and a comprehensive review is given in articles by Abbott [99] and Endres [100-102],... 

According to the definition of Brenner [43], it has become common to classify electrolytic metal deposition from nonaqueous electrolytes according to two groups, i. e., aqueous and nonaqueous . The aqueous group comprises all electrolyte systems from which metals or metallic alloys are deposited that can also be deposited from aqueous solutions. The nonaqueous group includes systems from which metals or metal alloys can be electrodeposited that cannot be plated from aqueous electrolytes. 

It is to be noted that almost all the metals and/or alloys that can be electrodeposited from aqueous solutions can also be electro-lessly deposited under proper conditions. Due to simplicity, excellent throwing power, uniform deposits, and ability to coat various complex shapes, electroless deposition was intensively investigated for many industrial applications. In this section, recent developments in the field of electroless deposition are discussed. Considering very different applications of electroless deposition, the discussion is presented as follows ... 

Almost all metals and/or alloys that can be electrodeposited from aqueous solutions can also be produced via electroless deposition, if proper reducing agents and conditions are applied. The advantage of electroless deposition is that an external current is not required. Furthermore, films of metals, alloys, and compounds such as ceramics or polymers are very attractive for the field of nanotechnology. It is important to note that the deposits (coatings or particulates) produced by electroless deposition are predominantly nano -crystalline. 

A phenomenon of induced codeposition, similar to that discussed above for W, is observed when Mo is codeposited with iron-group metals. Similarly to tungsten, molybdenum cannot be deposited alone from aqueous solutions. Electrodeposition of Mo alloys exhibits similar dependencies on experimental variables as that of W. It should be noted that, although the two systems are very similar, some differences are found in the literature, as described bellow. 

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