Aqueous solution electroplating

Aqueous solution electroplating provides decorative and protective finishes for use at ambient temperatures and in a variety of environments. 

Characteristic Copper Electroplated nickel Electroless nickel Chromium EkclreNss nickel + chremiMB Etedreplaled kkd chromiua rir—mt 

Maximum working temperature, °C 50 650 550 650 550 650 Short dmes at temp atuies possible 

Nontoxicity Excellent Very good Very good Very good Very good Very good  

Covering complex shapes Medium Medium Excellent Very poor Very good Me um  

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Sonoelectrochemistry has been employed in a number of fields such as in electroplating for the achievement of deposits and films of higher density and superior quality, in the deposition of conducting polymers, in the generation of highly active metal particles and in electroanalysis. Furtlienuore, the sonolysis of water to produce hydroxyl radicals can be exploited to initiate radical reactions in aqueous solutions coupled to electrode reactions. 

Mercury layers plated onto the surface of analytical electrodes serve as Hquid metal coatings. These function as analytical sensors (qv) because sodium and other metals can be electroplated into the amalgam, then deplated and measured (see Electro analytical techniques). This is one of the few ways that sodium, potassium, calcium, and other active metals can be electroplated from aqueous solution. In one modification of this technique, a Hquid sample can be purified of trace metals by extended electrolysis in the presence of a mercury coating (35). 

Electroplated Metals and Alloys. The metals electroplated on a commercial scale from specially formulated aqueous solutions iaclude cadmium, chromium, cobalt, copper, gold, iadium, iron, lead, nickel, platinum-group metals, silver, tin, and ziac. Although it is possible to electroplate some metals, such as aluminum, from nonaqueous solutions as well as some from molten salt baths, these processes appear to have achieved Httie commercial significance. 

Concentrated, aqueous solutions of ZnCla dissolve starch, cellulose (and therefore cannot be filtered through paper ), and silk. Commercially ZnCla is one of the important compounds of zinc. It has applications in textile processing and, because when fused it readily dissolves other oxides, it is used in a number of metallurgical fluxes as well as in the manufacture of magnesia cements in dental fillings. Cadmium halides are used in the preparation of electroplating baths and in the production of pigments. 

Electroplating aluminium and its alloys requires a similar technique. In aqueous solutions it is impossible to lower the potential sufficiently to reduce an alumina film, so the substrate is immersed in a strongly alkaline solution capable of dissolving it ... 

Chromium metal can be electroplated from an aqueous solution of potassium dichromate. The reduction half-reaction is... 

Electroplating is the electrolytic deposition of a thin film of metal on an object. The object to be electroplated (either metal or graphite-coated plastic) constitutes the cathode, and the electrolyte is an aqueous solution of a salt of the plating metal. Metal is deposited on the cathode by reduction of ions in the electrolyte solution. These cations are supplied either by the added salt or from oxidation of the anode, which is made of the plating metal (Fig. 12.16). 

What current is required to electroplate 6.66 p,g of gold in 30.0 min from a gold(III) chloride aqueous solution ... 

A current of 15.0 A electroplated 50.0 g of hafnium metal from an aqueous solution in 2.00 h. What is the oxidation number of hafnium in the solution ... 

Another example of where ultrasound influences the discharge rate of chromium is in the chromium electroplating of steel plates. When cold-rolled steel plate is elecUo-lytically chromated from a silent aqueous solution containing chromates and dichromates, a chrome coating of 13 mg m is obtained after 1 s, whilst in the presence of ultrasound a coating of 45 mg m is obtained [25] in the same time. The product is also accompanied with an increase in the brightness of the metal. Similar results have been found by other workers [26]. 

Smooth platinum, lead dioxide and graphite are anode materials commonly used in electrooxidation processes. All show large overpotentials for oxygen evolution in aqueous solution. Platinum coated titanium is available as an alternative to sheet platinum metal. Stable surfaces of lead dioxide are prepared by electrolytic oxidation of sheet lead in dilute sulphuric acid and can be used in the presence of sulphuric acid as electrolyte. Lead dioxide may also be electroplated onto titanium anodes from lead(Il) nitrate solution to form a non-porous layer which can then be used in other electrolyte solutions [21],... 

Fine nickel powder reacts with sulfamic acid in hot aqueous solution under controlled conditions, forming nickel sulfamate tetrahydrate, Ni(S03NH2)2 4H20, used in electroplating baths. 

Waszczuk etal. [173] have performed radiometric and voltammetric studies of benzoic acid adsorption on a pc-Ag electrode in contact with 0.1 M HCIO4 solution. The electrodes were obtained by electroplating Ag black onto a vacuum-deposited silver substrate. Benzoic acid appeared to be surface active in the entire range of potentials available at Ag in aqueous solutions. Adsorption of benzoic acid increased as the potential became more positive and this surface process was... 

Electroplating from non-aqueous solutions is useful when the surface of a substrate, which easily reacts with water, should be protected with a thin metal film. For instance, a superconductor, Ba2YCu307, has a strong oxidizing ability and its surface easily reacts with air. In order to protect the surface of the Ba2YCu307 with a metal film, a method to electroplate such metals as Ag, Cu, Pb and Sn from acetonitrile has been studied [20]. In aqueous solutions, the reduction of Cu3+ in Ba2YCu307 narrows the applicable potential range and only Ag can be deposited. 

Although the entire discussion of electrochemistry thus far has been in terms of aqueous solutions, the same principles apply equaly well to nonaqueous solvents. As a result of differences in solvation energies, electrode potentials may vary considerably from those found in aqueous solution. In addition the oxidation and reduction potentials characteristic of the solvent vary with the chemical behavior of the solvent. as a result of these two effects, it is often possible to carry out reactions in a nonaqueous solvent that would be impossible in water. For example, both sodium and beryllium are too reactive to be electroplated from aqueous solution, but beryllium can be electroplated from liquid ammonia and sodium from solutions in pyridine. 0 Unfortunately, the thermodynamic data necessary to construct complete tables of standard potential values are lacking for most solvents other than water. Jolly 1 has compiled such a table for liquid ammonia. The hydrogen electrode is used as the reference point to establish the scale as in water ... 

What current is required to electroplate 6.66 xg of gold in 30.0 min from a gold(III) chloride aqueous solution (b) How much time is required to electroplate 6.66 jig of chromium from a potassium dichromate solution, using a current of 100 mA ... 

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