Current distribution throwing power

There are other cases in practical electrochemical devices in which current distribution is important. Because of the interplay of interfacial and electrolyte resistance effects (primary and secondary current distribution, respectively , the detailed calculation involve much mathematics. Electroplating deep into crevices of the object to be plated is an example of where current distribution considerations often dominate behavior. Throwing power is a term that describes the degree of penetration of the current— hence the plating—into fissures and irregularities in electrodeposition. 

Throwing Power. It has long been observed that plate thickness distribution does not always follow the primary current distribution. 

The type and nature of the current density distributions are very important when electroplating is used for uniform deposits, appropriate conditions e.g., electrolytes of high throwing power are needed. 

Fig. 8.18 Modification of extreme current densities to provide a more uniform current distribution, (i) use of a radiused corner to reduce throwing power deficiency in a recess (ii) use of a conforming anode to overcome poor throwing power in a recess (iii) use of inert shields to prevent build-up of deposits on edges and (iv) use of cathodic burners or robbers to minimize edge build-up. (After Ashby (1982) Electroplating for Engineering Technicians, National Physical Laboratory, London and Courtesy Ionic Plating Ltd.)...

The relationship between the current density at a point on a surface and its distance from the counter electrode. The greater the ratio of the surface resistivity shown by the electrode reaction to the volume resistivity of the electrolyte, the better is the throwing power of the process. (2) The ability of a plating solution to produce a uniform metal distribution on an irregularly shaped cathode. 

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