Corrosion electroplating

HOCH2C = CCH2OH. White solid, m.p. 58 C, b.p. 238- C prepared by the high pressure reaction between ethyne and methanol and also from BrMgCCMgBr and methanal. Used in electroplating (Ni), as a corrosion inhibitor, and in paint and varnish removal. 

Indium chemicals and electroplated metal deposits ate replacing mercury (qv) in the manufacture of alkaline batteries (qv). Indium, like mercury, functions to reduce outgassing within the battery and promotes the uniform corrosion of the anode and cathode while the battery is under electrical load. Indium inorganic chemicals also find use as catalysts in various chemical processes. 

Electroplating. Chromium is electroplated onto various substrates in order to realize a more decorative and corrosion- or wear-resistant surface (24—32). About 80% of the chromium employed in metal treatment is used for chromium plating over 50% is for decorative chromium plating (see Metal surface treatments). Hard chromium plating differs from decorative plating mostiy in terms of thickness. Hard chromium plate may be 10 to several 100 p.m thick, whereas the chromium layers in a decorative plate may be as thin as 0.25 p.m, which corresponds to about two grams Cr per square meter of surface. 

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... 

Electrochemical systems are found in a number of industrial processes. In addition to the subsequent discussions of electrosynthesis, electrochemical techniques are used to measure transport and kinetic properties of systems (see Electroanalyticaltechniques) to provide energy (see Batteries Euel cells) and to produce materials (see Electroplating). Electrochemistry can also play a destmctive role (see Corrosion and corrosion control). The fundamentals necessary to analyze most electrochemical systems have been presented. More details of the fundamentals of electrochemistry are contained in the general references. 

Electroplated materials are generally employed for a specific property or function. There is, of course, some ovedap for example, decorative use certainly requires some degree of corrosion resistance. The various usages and the principal plating metals employed are as hsted. There are also smaller amounts of other metals and alloys used for specific apphcations. 

Plate thickness is an important factor in electroplating, in terms of both performance and economics. Corrosion resistance, porosity, wear, appearance, and several other properties are proportional to plate thickness. Minimum plate thicknesses are, or should be, specified as should the location, or check-point, where the thickness is to be measured. In some appHcations, such as threaded fasteners, maximum thicknesses should be specified. Root diameters of finer machine threads can be adversely affected by as Htde as 10 p.m of plating. 

Poor preparation of the substrate can result in loss of adhesion, pitting, roughness, lower corrosion resistance, smears, and stains. Because electroplating takes place at the exact molecular surface of a work, it is important that the substrate surface be absolutely clean and receptive to the plating. In the effort to get the substrate into this condition, several separate steps may be required, and it is in these cleaning steps that most of the problems associated with plating arise. 

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