Metal by electroplating

When Au or Pt are determined by RNAA, the Au and Au indicator radionuclides have to be separated, e.g., by retention as a chlorocomplex on an anion-exchange resin, by precipitation as a reduced metal, by electroplating, or by solvent extraction. For samples containing both Au and Pt, it has to be kept in mind that Au is formed from both elements (Zeisler and Greenberg 1982). 

Stripping the cathode takes place in a second plating tank.The cathodes from the first tank must be manually removed and placed into the anodic position within the stripping tank. The copper is then recovered as a metal by electroplating the copper onto either a stainless steel or a copper laminate in a copper pyrophosphate electrolyte. The reusable cathodes are then available to be repositioned back to the first cell. 

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). 

Molten tin wets and adheres readily to clean iron, steel, copper, and copper-base alloys, and the coating is bright. It provides protection against oxidation of the coated metal and aids in subsequent fabrication because it is ductile and solderable. Tin coatings can be appHed to most metals by electro deposition (see Electroplating). 

Metal Finishing and Corrosion Control. The exceptional corrosion protection provided by electroplated chromium and the protective film created by applying chromium surface conversion techniques to many active metals, has made chromium compounds valuable to the metal finishing industry. Cr(VI) compounds have dominated the formulas employed for electroplating (qv) and surface conversion, but the use of Cr(III) compounds is growing in both areas because of the health and safety problems associated with hexavalent chromium and the low toxicity of trivalent chromium (see... 

An interesting example of judicious choice of braze filler is to be found in the selection of silver alloys for the brazing of stainless steels to be subsequently used in a tap-water environment . Although the brazed joint may appear to be quite satisfactory, after a relatively short exposure period failure of the joint occurs by a mechanism which appears to be due to the break-down of the bond between the filler and the base metal. Dezincifica-tion is a prominent feature of the phenomenon and zinc-free braze alloys based on the Ag-Cu system with the addition of nickel and tin have been found to inhibit this form of attack. A similar result is obtained by electroplating 0-007 mm of nickel over the joint area prior to brazing with a more conventional Ag-Cu-Zn-Cd alloy. 

Titanium is a very difficult metal to electroplate because of the presence of an oxide film. Sophisticated pretreatments with acids to remove the oxide film are necessary to achieve good adhesion. Improvements in the level of adhesion can, however, be obtained by heat treatment of the resultant Pt/Ti composites... 

Chromium is a hard metal with excellent corrosion and oxidation resistance. Its properties are summarized in Table 6.3. Chromium coatings are usually produced by electroplating or sputtering, but CVD is being investigated for several applications. 

Surfaces of finely divided nickel also promote the formation of aniline. A practical route to tlie preparation of electrodes coaled with a finely divided metal involves electroplating nickel onto a cathode from a solution containing a suspension of finely divided Raney nickel (Ni 50% A1 50%) or Devarda copper alloy (Cu 50% A1 45% Zn 5%), Some alloy particles stick to the cathode surface which is then activated by leaching out the aluminium using hot aqueous sodium hydroxide... 

Ammonium Fluosilicate (Cryptohalite), (NH4)2SiF6 mw 178.17 wh crystn pdr sp 2.01, mp — sublimes sol in ale w. Can be prepd by interaction of Amm hydroxide with fluosilicic acid, followed by crystn. Used for glass etching, casting of light metals and electroplating... 

Jewelry is often manufactured by electroplating an expensive metal such as gold over a cheaper metal. Sketch a setup for this process. 

The single potential of arsenic in various solutions has been determined.5 The electrodes used were made in various ways, but the most reliable results were obtained with a solid stick of arsenic electrodes made by electroplating arsenic on other metals were unsatisfactory. The following combination was used—... 

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