The Electrodeposition of the Less-Common Metals

Summary

The electrodeposition of metals is reviewed with reference to the position of the various metals in the periodic system and in the electrochemical series. The importance of hydrogen overpotential is then discussed and it is seen that this makes possible the deposition of a number of metals such as zinc and manganese which arc relatively active and which might be expected to displace hydrogen from aqueous electrolytes. The metallic elements are then classified into four main groups; first, those which deposit with low overpotential from aqueous solutions, such as zinc, cadmium, lead, silver, tin; secondly, those which deposit with high overpotential, such as iron, cobalt, nickel, chromium, manganese; thirdly, the “reluctant” metals which may, on thermodynamic considerations, be capable of deposition from aqueous solutions, but which are deposited only from non-aqueous solutions, such as germanium, or as alloys, such as molybdenum, tungsten; fourthly, active metals which can only be deposited from non-aqueous solutions, such as alkali metals, aluminium, beryllium. A number of the less-common metals have not been deposited in the pure state from aqueous solutions or from organic electrolyte solutions. Recent work suggests that new types of solute and solvent will be required before deposition of these metals will be successful. The alternative possibilities of deposition from liquid ammonia solutions and molten salt systems are then considered. It is concluded that deposition from organic electrolyte solutions may be a more attractive proposition. Finally, the possible applications or fields in which deposition of metals from the non-aqueous solutions might be of interest are reviewed.