Fundamental Insights into Electrodeposition of Mixed Chromium Metal-Carbide-Oxides from Trivalent Chromium – Formate Electrolytes

Ankora, M. (Speaker), Mamme, M. H. (Speaker), Koen Lammers (Contributor), Jacques Wijenberg (Contributor), Arnoud de Vooys (Contributor), Terryn, H. (Speaker), Arjan Mol (Speaker)

Activiteit: Talk or presentation at a conference

Description

Recent restrictions on industrial usage of hexavalent chromium under new REACH legislation have further
sparked the development of hexavalent chromium-free chromium plating processes. An industrially
important development in this field is Trivalent Chromium Coating Technology (TCCT®), a chromium
electroplating technology for packaging steel developed at Tata Steel. In this process, aqueous trivalent
chromium electrolytes rather than hexavalent chromium electrolytes are employed for the
electrodeposition of metallic chromium. However, to deposit metallic chromium from a trivalent chromium
electrolyte, it is necessary to incorporate a complexing agent given the kinetic inertness of aqueous
trivalent chromium complexes. Formate plays this role in the TCCT® process yielding coatings
comparable to the conventional hexavalent chromium-based process [1-4].
However, understanding the mechanism and kinetics of chromium electrodeposition from this system is
quite limited. Fundamental knowledge of the deposition process is key for industrial process optimization.
Essential to determining the reaction mechanism and kinetics is the identification of the chemical species
involved in the reaction. Using a hybrid multiscale experimental and computational approach, insights into
chromium complexation in the bulk electrolytes and how this speciation influences the composition of the
deposit have been gained.
Samples electroplated in electrolytes of varied formate concentrations were characterized using X-ray
Fluorescence (XRF) spectroscopy and X-ray Photoelectron Spectroscopy (XPS). Results from these
analyses show that metallic chromium is only deposited when the electrolyte contains formate ions. In the
absence of formate, only oxide and carbide species are deposited. The characterization results also show
a current efficiency of the TCCT process of ~ 40%. From observations from surface characterization as
well as spectroscopic analysis and density functional theory (DFT) and ab initio molecular dynamics
studies (AIMD) of the bulk electrolyte, the coordination and complexation of formate ion in the chromium
complex responsible for metallic chromium deposition have also been identified. Voltammetric studies
coupled with ex-situ XPS and scanning electron microscopy (SEM) surface characterization also lead to a
clear definition of the reaction mechanism of metallic chromium deposition that the incorporation of
formate in trivalent chromium electrolytes makes possible.

[1] M. Inman et al., ‘Green Process for Functional Trivalent Chromium Electroplating’, in 223rd ECS Meeting, 2012.

[2] J. H. O. J. Wijenberg, M. Steegh, M. P. Aarnts, K. R. Lammers, and J. M. C. Mol, ‘Electrodeposition of mixed chromium metal-carbide-oxide coatings from a trivalent chromium-formate electrolyte without a buffering agent’, Electrochimica Acta, vol. 173, pp. 819–826, Aug. 2015.

[3] J. E. Edy, H. N. McMurray, K. R. Lammers, and A. C. A. deVooys, ‘Kinetics of corrosion-driven cathodic disbondment on organic coated trivalent chromium metal-oxide-carbide coatings on steel’, Corrosion Science, vol. 157, pp. 51–61, Aug. 2019.

[4] S. Hesamedini and A. Bund, ‘Trivalent chromium conversion coatings’, J Coat Technol Res, vol. 16, no. 3, pp. 623–641, May 2019.

Periode9 okt 202213 okt 2022
EvenementstitelThe 242nd ECS Meeting
EvenementstypeConference
LocatieAtlanta, United States, Georgia
Mate van erkenningInternational