Electroplated titanium coatings

Bettley, Alison (1992). Electroplated titanium coatings. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.00010168

Abstract

Electroplated titanium coatings on substrates such as steels have many potential industrial applications. The low cost of the substrate is combined with the excellent corrosion-resistance of the coating. However, titanium cannot be electrodeposited from aqueous systems because the hydrogen evolution reaction is always preferred. Proton-free media must be used. The electrodeposition of titanium from molten chlorides is well-known: large-scale titanium electrowinning processes have been operated, to produce high quality particulate material in an energy efficient way. The production of thick compact electroplates, however, has not been demonstrated consistently. It was therefore the objective of this work to determine the principal operating parameters for a titanium electroplating process based on a molten chloride (LiCl-KCl) bath.
Studies of substrate oxide film reduction, the electro-reduction of divalent titanium, the nature of electrodeposits produced under various plating conditions, and the behaviour of the dissolving titanium anode have been undertaken.
The following have been identified as the most important factors:
(1) Substrate pre-treatment
(2) Melt composition (titanium concentration, average valency, level of oxygen contamination)
(3) Electrochemical parameters (chosen so as to combine good nucleation characteristics with avoidance of mass transport control effects)
It has been demonstrated that thick, adherent, relatively smooth, compact coatings of titanium can be produced from molten chlorides at 450°C. Pulse plating and periodic current reversal are the most promising techniques for future optimisation with the objective of developing a commercial process.

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