The impact of additives on aqueous metal electrodeposition has fascinated the electroplating community for several decades. Additives can be classified into organic and inorganic compounds. The former are most common as they act as hydrogen permeation inhibitors, crystal growth modifiers, brighteners, levellers, wetting agents, and stress relievers. Even if added to the electrolyte in small amounts, their effect on coatings’ morphology and structure is remarkable, often without changing their chemical composition. For example, saccharine, a well-known sweetener to sprinkle onto food or added to coffee, is a typical grain-refining agent in metal electrodeposition. Saccharine is thus widely used in nickel plating as a brightener. Polyethylene glycol (PEG) is also added to nickel electrolytes to reduce surface roughness, refine grains, and promote twinning. In turn, the mechanical properties of the resulting coatings such as hardness greatly improve. Caution must be taken, though, regarding the incorporation of sulphur and carbon impurities that...
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