Stirring, effect electrolytic deposits

The formation of new nuclei and of a fine-crystalline deposit will also be promoted when a high concentration of the metal ions undergoing discharge is maintained in the solution layer next to the electrode. Therefore, concentration polarization will have effects opposite those of activation polarization. Rather highly concentrated electrolyte solutions, vigorous stirring, and other means are employed to reduce concentration polarization. Sometimes, special electrolysis modes are employed for the same purposes currents that are intermittent, reversed (i.e., with periodic inverted, anodic pulses), or asymmetric (an ac component superimposed on the dc). 

Stirring the solution has several beneficial effects it can improve the deposit by replenishing metal ions in the vicinity of the electrode, decrease hydrogen evolution, and increase the electrolysis rate, i.e., decrease analysis time. Temperature effects are less predictable. Temperatures in the range 60-90°C are sometimes used for increasing mass transport and decreasing electrolyte resistance, resulting in denser, more adherent deposits. 

The electrodeposition process is comparatively easy to control. Virtually any size and shape of substrate can be plated once it is conductive. This method can therefore be used to deposit semiconductors on patterned substrates. By adjusting the pH of the deposition bath, undesired effects such as sulphur precipitation can be controlled in certain electrolytes such as ones containing elements like sulphur and selenium. By simply varying the stirring rate, the... 

---