Effects of Operating Conditions

Alteration of operating conditions can affect process variables such as current efficiency and the formation and size of particles.

Current Density. High current density favors the formation of powder, but has only a minor effect on current efficiency. A marked decrease in particle size occurs with rising current density. For example, in an electrolyte containing 25 g/L (3.3 oz/gal) copper and 120 g/L (16 oz/gal) free sulfuric acid, increasing the current density from 600 to 1000 A/m2 (55 to 90 A/ft2) raised the quantity of powder passing through a 300 mesh sieve from 20 to 96%.

Temperature. Raising the operating temperature of the cell increases the current efficiency and reduces the cell voltage. However, cell operation is difficult at temperatures higher than 60 °C (140 °F), and powders obtained at high temperatures are coarser than those produced at lower temperatures. Generally, electrolytic cells are operated at temperatures between 25 and 60 °C (77 and 140 °F).

Powder Removal. The method used to remove the powder from the cathode has a significant effect on powder characteristics. Usually the powder is removed mechanically by brushing. The brush-down interval aids in control of the particle size of the deposit and, as shown in Fig. 9, the powder becomes coarser as the interval is increased from 15 to 60 min. Figure 10 indicates that the apparent density increases as the brush-down interval is extended. Frequent brush-down also limits variations in cathode current density. In another approach to powder removal, an organic extract is used in combination with sodium lauryl sulfate to discharge the powder automatically from the cathode without brush-down (Ref 6).

Fig. 9 Effect of brush-down interval on particle size. Source Ref 1 and 14
Fig. 10 Effect of brush-down interval on apparent density. Source: Ref 1 and 14
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