Abstract
Novel two-layer chromium-based coatings comprised of a first layer containing chromium, oxygen and carbon (Cr-O-C) and an oxygen rich (Cr-O) topcoat were electrodeposited from trivalent chromium electrolyte. The complex structure and composition of the coatings were studied using complementary characterization techniques. The electrodeposited oxide was found to be amorphous and oxygen-deficient. In operando ambient pressure X-ray photoelectron spectroscopy when heating the sample from room temperature to 450 °C and Raman spectroscopy after the heating ascertained the metastable nature of the oxide. The cathodic delamination of a weak model polymer on these samples was studied using in situ scanning Kelvin probe.
Highlights
Chromium-based coatings are of great importance because of their ability to protect the substrate against wear and corrosion [1]
The results show that the delamination resistance of coatings with 6 nm Cr-O layer thickness is similar to that of conventional electrolytic chro mium coated steel (ECCS) (Fig. 14b)
Cr-O oxide layers of various thicknesses be tween 1.5 nm and 12 nm were electrodeposited on a metallic Cr-O-C layer of 10 nm thickness, from a trivalent chromium electrolyte
Summary
Chromium-based coatings are of great importance because of their ability to protect the substrate against wear and corrosion [1]. Electrodeposition from an electrolyte containing Cr3+ ions is more complicated than that from the Cr6+ electrolyte This is because of the tendency of Cr3+ ions to form kinetically inert hexaqua coordinated complex [Cr(H2O)6]3+ in aqueous solutions [1,10]. The rapid evolution of hydrogen results in reduced faradaic efficiency of the deposition process and leads to increased pH resulting in precipitation of hydroxides. To overcome these complications, a complexing agent is usually used to destabilize the kinetically inert hexaqua complex and a buffering agent is used to reduce the fluctuations in pH [1,10]. The complex mechanism involved in this electrodeposition process results in a complicated structure of the electrodeposit, like formation of bridged complexes [1,10]
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