Electroplating direct current

Electrodialysis is a membrane-based process which can be used for separation, removal, or concentration of ionic species present in aqueous solutions. These operations are accomplished by the selective transport of ions through an ion exchange membrane under the influence of a direct current. One of the earliest applications of electrodialysis was the desalting of brackish water. However, since the 1970s, extensive studies have been performed on the application of electrodialysis for waste-water treatment, especially in the electroplating and metal-finishing industries. 

Electroplating, Etc.—The energy required for electroplating, galvanoplasty, detinning and electrolytic refining of metals varies with the metals involved and solutions used. From 1 to 100 amp. may be needed per square inch of cathode surface, at 0.1 to 4 volts per cell. Direct current is supplied from small generators at 5 or 6 volts, and a separate rheostat is required for each cell or tank. 

Electroplating is performed by using a source of direct current, (a) Why can t an alternating current be used (b) What would happen if an alternating current were used for electroplating ... 

Electroforming is a specialized form of electroplating. The latter process is carried out in an electrolyte solution with a direct current passed between an anode and the part to be plated which is made cathodic. Usually, the anode is metallic nickel or copper which dissolves under the influence of the current passing nickel or copper ions that replace those discharged in the form of metallic nickel or copper on the cathode. The principle is illustrated in Eig. 1. 

Electroplating can be defined as the application of a metal coating to a metallic or other conducting surface using an electrochemical process. The item to be plated serves as the cathode (negative electrode) and the anode is usually the metal to be plated on the item. Both components are placed in an aqueous (aq.) solution, called an electrolyte, containing dissolved metal salts and other ions to allow for a flow of electricity. A power source provides a direct current to the anode and oxidizes its metal atoms so they are able to dissolve in the solution. These dissolved metal ions are then reduced at the cathode and deposited there as a metal coating. 

Why is direct current used instead of alternating current in the electroplating of metals ... 

Electrophoretic deposition n. A direct-current process analogous to electroplating. 

It is a rather old experience in electroplating practice that periodic changes of current lead to improvement in the quality of the deposit. Such changes are of three types periodic current reversal, sinusoidal ac superimposed on direct cathodic current, and pulsating current. A detailed review of the subject is available.The effect is well demonstrated in Figure 23, showing the yield of dendrites during cathodic deposition of zinc as a function of the ratio of the superimposed ac density to the basic direct current density. ... 

An electrolytic process in which a metai ion is reduced and a solid metai is deposited on a surface is caiied electropiating. An electroplating cell contains a solution of a salt of the plating metal, an object to be plated (the cathode), and a piece of the plating metal (the anode). A silver-plating cell contains a solution of a soluble silver salt and a silver anode. The cathode is the object to be plated. The silver anode is connected to the positive electrode of a battery or to some other source of direct current. The object to be plated is connected to the negative electrode. 

Electrophoretic Deposition n A direct-current process analogous to electroplating, used to coat electrically-conductive articles with plastics, deposited from aqueous lattices or dispersions. The cathode may be a noncorrodible metal such as stainless steel, generally serving as the container in which the process is performed. The DC potential is usually under 100 V. The deposited coatings are baked to remove residual water. Among available polymer lattices suitable for the process are PVC, polyvinylidene chloride, acrylics, nylons, polyesters, polytetrafluoroethylene, and polyethylene. 

A source of direct current such as a storage battery or a dry cell, though an electroplating power unit which permits control of current and voltage should be preferred. 

Galvanic cells in which stored chemicals can be reacted on demand to produce an electric current are termed primary cells. The discharging reaction is irreversible and the contents, once exhausted, must be replaced or the cell discarded. Examples are the dry cells that activate small appliances. In some galvanic cells (called secondary cells), however, the reaction is reversible that is, application of an electrical potential across the electrodes in the opposite direction will restore the reactants to their high-enthalpy state. Examples are rechargeable batteries for household appliances, automobiles, and many industrial applications. Electrolytic cells are the reactors upon which the electrochemical process, electroplating, and electrowinning industries are based. 

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