Controlled current electrolytic cell

F. Zhou, G.J. Van Berkel, Characterization of an ESI ion source as a controlled-current electrolytic cell. Anal. Chem., 67 (1995) 2916. 

Van Berkel, G. J. Zhou, F. Electrospray as a controlled-current electrolytic cell electrochemical ionization of neutral analytes for detection by electrospray-mass spectrometry. Anal. Chem. 1995, 67, 3958-3964. 

Stainless steel develops a passive protective layer (<5-nm thick) of chromium oxide [1118-57-3] which must be maintained or permitted to rebuild after it is removed by product flow or cleaning. The passive layer may be removed by electric current flow across the surface as a result of dissinulat metals being in contact. The creation of an electrolytic cell with subsequent current flow and corrosion has to be avoided in constmction. Corrosion may occur in welds, between dissimilar materials, at points under stress, and in places where the passive layer is removed it may be caused by food material, residues, cleaning solutions, and bmshes on material surfaces (see CORROSION AND CORROSION CONTROL). 

Direct Current (DC). This current is transmitted for industrial uses only in exceptional situations. The most common sources of direct current are storage batteries and industrial devices called rectifiers, in which alternating current is changed (rectified) to direct current, as is used in electrolytic cells for the manufacture of chlorine gas, magnesium, aluminum, and a few other chemicals. The direct current is flowing from the source through the user application and back to the source, in one direction. The motor is primarily used for speed control of selected equipment. 

Block B shows the electrolytic copper recovery cell, which recovers metallic copper and regenerates sulfuric acid from the metal salts in the hot sulfuric acid pickle solution. It was originally felt that trace metals (zinc, tin, lead) would interfere with the recovery of pure copper. By controlling current density at 50 to 100 A/m 1 2 3, however, pure copper can be recovered while maintaining the copper concentration in the pickle bath at 15 g/L. 

The apparatus for DC polarography usually consists of three parts, i.e. the circuit to control the potential of the indicator electrode (DME), the circuit to measure the electrolytic current, and the electrolytic cell. Classically two-electrode devices as in Fig. 5.8(a) were used, but now three-electrode devices as in Fig. 5.8(b) are predominant. In the latter, the electrolytic cell is equipped with three electrodes a DME, a reference electrode and a counter electrode (Fig. 5.9). The droptime of the modem DME is controlled mechanically, and is usually between 0.1... 

Electrolytic polymerization or electrolytically initiated polymerization, or shortly electro-initiated polymerization or electropolymerization, generally means initiation by the electron transfer processes which occur at the electrodes of an electrolytic cell containing monomer and electrolyte, in that by controlling the electrolysis current it is possible to control the generation of initiating species. Under appropriate conditions it may proceed by a free radical, anionic or cationic mechanism. In addition to the electrolytic addition polymerization, production of polymers through condensation reaction by electrolytic means should also be covered. Examples of each of these propagation mechanisms have now been reported in the literature. 

This chapter has confined itself to a brief description of the common controlled potential methods which can be employed by the coordination chemist, but it is worth pointing out that far less sophisticated constant current methods, a DC supply and two electrodes in an undivided cell, have been used very successfully to electrosynthesize a wide range of coordination compounds, notably by anodic dissolution of a metal, i.e. metal ions are sprayed into an electrolyte solution containing an appropriate ligand.7 It must also be remembered that virtually all industrial-scale electrosyntheses are performed by controlling current density rather than potential.8 Nevertheless,... 

The values of plant process variables for steady-state hydrogen production rates between 75 and 100% of full power are given by the load schedule reported here. The objective in designing this schedule was to achieve near constant hot side temperatures in both the nuclear and chemical plants. Briefly, mass flow rates are maintained proportional to power throughout, inventory control is used in the PCU, and electrolytic cell area and current are maintained proportional to hydrogen production rate. 

Electroplating Objects can be electroplated with a metal such as silver in a method similar to that used to refine copper. The object to be silver plated is the cathode of an electrolytic cell that has a silver anode, as shown in Figure 21-21. At the cathode, silver ions present in the electrolyte solution are reduced to silver metal by electrons from an external power source. The silver forms a thin coating over the object being plated. The anode consists of a silver bar or sheet, which is oxidized to silver ions as electrons are removed by the power source. Current passing through the cell must be carefully controlled in order to get a smooth, even metal coating. 

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