Iron Electroplating

Industrial Wastewater Treatment. Industrial wastewaters require different treatments depending on their sources. Plating waste contains toxic metals that are precipitated and insolubiHzed with lime (see Electroplating). Iron and other heavy metals are also precipitated from waste-pidde Hquor, which requires acid neutralization. Akin to pickle Hquor is the concentrated sulfuric acid waste, high in iron, that accumulates in smokeless powder ordinance and chemical plants. Lime is also useful in clarifying wastes from textile dyeworks and paper pulp mills and a wide variety of other wastes. Effluents from active and abandoned coal mines also have a high sulfuric acid and iron oxide content because of the presence of pyrite in coal. 

Several solvent uses have been proposed. Dimethyl sulfate has been used as a solvent for the study of Lewis acid—aromatic hydrocarbon complexes (148). It also is effective as an extraction solvent to separate phosphoms haUde—hydrocarbon mixtures and aromatic hydrocarbons from aUphatics, and it acts as an electrolyte in electroplating iron (149—152). The toxicity of dimethyl sulfate precludes its use as a general-purpose solvent. 

Galvanize — (1) To stimulate living cells by means of an electric current. (2) To electroplate a metal surface with a dissimilar metal in particular, to electroplate iron with zinc. In the latter case, the term is also commonly misapplied to iron that has been dip-coated with zinc. (3) Figuratively, to restore something to life from a dormant state. 

In an industrial atmosphere, the best results were obtained with electroplated iron-zinc alloy layers with more than 20% iron (Salt et al., 1965) with a corrosion resistance 30% higher than zinc. Elsewhere, zinc-iron alloy galvanized coatings were as good as coatings with an outer zinc layer. Sherardized coatings were superior to electroplated and equal to galvanized for the same thickness. However, the structure of the alloy layer affects the corrosion resistance, as does its composition. 

Electrochemistry is the study of mutual transformation of chemical and elec-frical energy. Specifically, it deals with chemical reactions driven by an electric current and with the electricity produced by chemical reactions. Examples of electrochemistry are electroplating, iron oxidation (rusting), solar-energy conversion, electrochemical conversions (fuel cells, bafferies), phofosynfhe-sis, and respiration. In this chapter, the principles of electrochemisfry are reviewed. First, let us briefly look info fhe history of electrochemisfry. 

Electroplating Iron Lead Nickel Platinum Palladium Rhodium Tin Zinc Various Noble/cathodic Noble/cathodic Noble/cathodic Noble/cathodic Noble/cathodic Noble/cathodic Anodic > 125 >3175 0.25-50 6.5-1250 0.1-2.2 2.5-55 0.1-1 2.5-25 0.1-0.2 2.5-5 0.01-0.02 0.25-0.5 0.2-2 5-50 0.1-1 2.5-25 Wire, sheet, small parts... 

Metal Treatment. After rolling, the oxide scale on sheet steel is removed by acid treatment (pickling) (see Metal surface treatments). Phosphoric acid, a good pickling agent, leaves the steel coated with a thin film of iron phosphates. This process improves mst resistance but presents a problem if the steel is to be electroplated. 

Aqueous Electrodeposition. The theory of electro deposition is well known (see Electroplating). Of the numerous metals used in electro deposition, only 10 have been reduced to large-scale commercial practice. The most commonly plated metals are chromium, nickel, copper, zinc, rhodium, silver, cadmium, tin, and gold, followed by the less frequendy plated metals iron, cesium, platinum, and palladium, and the infrequendy plated metals indium, mthenium, and rhenium. Of these, only platinum, rhodium, iddium, and rhenium are refractory. 

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). 

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. 

In addition to the metals Hsted above, many alloys ate commercially electroplated brass, bronze, many gold alloys, lead—tin, nickel—iron, nickel—cobalt, nickel—phosphoms, tin—nickel, tin—zinc, ziac-nickel, ziac-cobalt, and ziac-iron. Electroplated alloys ia lesser use iaclude lead—iadium, nickel—manganese, nickel-tuagstea, palladium alloys, silver alloys, and zinc—manganese. Whereas tertiary and many other alloys can feasibly be electroplated, these have not found commercial appHcations. 

Practices for preparation of and electroplating on Chromium (Electrodeposits) on Chromium Copper and Copper-Base Mllojs Iron Castings Eead and EeadMllojs Magnesium and Magnesium Mllojs Molybdenum and Molybdenum Mlloys MickelMlloys... 

Special containers have been developed for anesthetic ether to prevent deterioration before use. Their effectiveness as stabHizers usuaHy depends on the presence of a lower oxide of a metal having more than one oxidation state. Thus the sides and the bottoms of tin-plate containers are electroplated with copper, which contains a smaH amount of cuprous oxide. Staimous oxide is also used in the linings for tin containers. Instead of using special containers, iron wire or certain other metals and aHoys or organic compounds have been added to ether to stabHize it. 

Dull plate 120-660 0.22 Electroplated on polished iron, then ... 

Carefully polished electrolytic copper 176 0.018 Electroplated on pickled iron, not ... 

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