Electrodeposition of zinc-manganese alloy coatings from ionic liquid electrolytes

Electrodeposited zinc-manganese alloys have been found to have potentially attractive corrosion resisting characteristics for ferrous substrates. However, researchers have found their formation problematic from aqueous electrolytes, due particularly to the reactive nature of manganese and its low reduction potentials. The present investigations examine the possibility of electrodepositing this alloy utilising an ionic liquid electrolyte. In this manner electrolytes based upon manganese and zinc chlorides and boric acid were made by dissolution in a 2:1 molar ratio urea: choline chloride solvent. Physical measurements of electrolyte characteristics as well as pertinent electrochemical information on alloy electrodeposition were obtained to examine the efficacy of this metal/electrolyte combination

The electrodeposition of zinc alloys from ionic liquid electrolytes

Electrodeposited zinc alloys have long been recognised as effective barrier and sacrificial coatings for ferrous substrates. The effect of alloying zinc with, in the main, more noble metals, has produced finishes of higher corrosion resistance than simply electrodeposited zinc. In this manner zinc alloys such as zinc-nickel, zinc-cobalt and zinc-iron are routinely electrodeposited on an industrial scale. A further zinc alloy, zinc-manganese, has shown a high level of promise in terms of corrosion resistance but is difficult to electrodeposit from conventional aqueous solutions. The present investigations are centred around examining the formation of zinc alloys, by electrodeposition, from non-aqueous ionic liquids. These electrolytes are essentially molten salts which maintain their liquid state at, or near, to room temperature. Being non-aqueous they are unlikely to promote significant hydrogen evolution from active metal surfaces - a severe problem for the electrodeposition of zinc-manganese alloys from aqueous electrolytes. Electrodeposition conditions for the latter will be discussed in terms of electrolyte types, current density and solution characteristics such as agitation type and temperature. Zinc-manganese alloy electrodeposits will be characterised in terms of their composition and morphology. Finally corrosion resistance data will be presented and this will be compared with other more conventionally deposited zinc alloys