Haring-Blum cell

Fig. 12.11 (a) Haring-Blum cell for throwing index measurement, in elevation and (b) Hull cell... 

On this scale, zero represents the case when M = P, and electrolyte resistance is the main factor. Throwing power can be worse, down to a limit T = - 100% when A/ = oo, i.e. no deposit at all on the far cathode. Conversely, when M < P, T is positive. Were M to reach 1-0 despite the difference in position, 7" = -F 100%. At one time +100% was regarded as an unrealisable limit, but conditions have been found for which T = -f150% in a Haring-Blum cell. 

Throwing indices measured in a Hull cell differ from those in a Haring-Blum cell because of the differences in geometry. In a Hull cell several pairs of points can be found which have the same primary current ratio, but for which M and hence T are found to vary because of polarisation changes. 

Haring-Blum cell — A rectangular cell with two cathodes at the small ends with an anode placed between them (see Fig. 1). The two cathodes are connected electrically. Usually the ratio, L, of the two anode-cathode distances is five. Thus a high current density (hcd) and a low current density (led) edge results. The Haring-Blum cell is used to determine the macro - throwing power, TP, of an electrolyte, according to the relation TP = (L - M) / (L + M - 2) where M is the ratio of the deposited masses. 

Haring-Blum cell — Figure. Schematic representation of the Haring-... 

In practice, a general impression of the throwing power of an electrolyte can be obtained by observing deposition in a Hull [144], a Haring-Blum [75], or another suitable cell. To compare the throwing power of different organoaluminum electrolyte systems, a modified Haring-Blum cell was developed to allow work under inert atmosphere [130]. 

Figure 7.1 The Haring-Blum cell for the determination of the throwing power of a plating bath.

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