Electroplating current supply

Mardi provides the chemical agent for Crodel s electroplating process. The application equipment in this case is owned and operated by both companies (current supply, dosage for the brighteners), located at Crodel. The recycling is done by Mardi. The unit of payment is the amount of ampere-hours, which corresponds to the surface of the galvanised pieces (Fig. 8). 

In 1800. William Nicholson and Anthony Carlisle decomposed water into hydrogen and oxygen by an electric current supplied by a voltaic pile. Whereas Volta had pruduced electricity from chemical action these experimenters reversed the process and utilized electricity to produce chemical changes. In 1807. Sir Humphry Davy discovered two new elements, potassium and sodium, by the electrolysis of ihe respective solid hydroxides, utilizing a voltaic pile as the source of electric power. These electrolytic processes were the forerunners of the many industrial electrolytic processes used today to obtain aluminum, chlorine, hydrogen, or oxygen, for example, or in die electroplating of metals such as silver or chromium. 

The essential components of an electroplating process are an electrode to be plated (the cathode) a second electrode to complete the circuit (the anode) an electrolyte containing the metal ions to be deposited and a d-c power source. The electrodes are immersed in the electrolyte such that the anode is coimected to the positive leg of the power supply and the cathode to the negative. As the current is increased from 2ero, a minimum point is reached where metal plating begins to take place on the cathode. The physics of this process has been the topic of many studies, and several theories have been proposed. A discussion of these theories can be found elsewhere (19). 

Because of the excellent conducting properties of a metallic sail solution, only a low voltage is required. As this must be D.C. the process of electroplating calls lor a supply nT current from special low-voltage D.C. generators or rectifiers. The voltage will be of the order of 6 volts or less between anode and cathode. 

Copper is electroplated from a CuS04 solution. A constant current of 2.00 amps is applied by an external power supply. How long will it take to deposit 1.00 X 102 g of Cu ... 

Connect the anode and cathode of the electroplating cell to a constant current power supply. 

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. 

This raises some important possibilities, which have not escaped the attention of the electroplating community. For example, while metal deposition is conducted in fairly concentrated solutions of the metal being plated, and at current densities well below the mass-transport limit, additives acting as inhibitors for metal deposition are often introduced at concentrations that are several orders of magnitude lower, to ensure that their supply to the surface will be mass-transport limited. In this way, the tendency for increased rate of metal deposition on certain features on the surface, such as protrusions, will be moderated by the faster diffusion of the inhibitor to the very same areas. Furthermore, if deposition occurs in the region of mixed control, which is usually the case, it must be remembered that the relevant roughness factor is quite different for the charge-transfer and the mass-transport processes, and this may well be a function of current density, since the Faradaic resistance is inherently potential dependent. 

Most electroplating processes are cathodic processes in which the layers are formed by cathodic reduction. As an example let us consider the technically important process of zinc deposition. A simple zinc electroplating bath could be made up by dissolving zinc sulfate in water. The part to be coated with metallic zinc would then be coimected to the negative pole of a power supply. The positive pole could be coimected to solid zinc bar. Both electrodes would be immersed into the zinc sulfate solution and an electrical current would pass through the... 

In electrolytic plating, a substrate is immersed into an aqueous solution containing ions of the metal to be plated (M ) and an anode which is a solid form of the metal to be plated (M). In this case the substrate acts as the cathode, and when the anode and cathode are linked through an external power supply and current is apphed, electroplating occurs by virtue of the following reactions ... 

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