Unravelling the Fe Effect on the Corrosion of Chromium Coatings: Chemical Composition and Semiconducting Properties

A model trivalent chromium-based electroplating bath doped with different concentration of Fe was used to obtain the different metallic coatings. The impact of the Fe was investigated on the Cr layer and on its native passive film by a detailed characterisation using X-ray Photoelectron Spectroscopy (XPS), Angle Resolved XPS and Auger Electron Spectroscopy. Moreover, the semiconducting properties of their oxide layers were explored by Mott-Schottky and the corrosion performance by the linear polarisation resistance and kinetics of the oxide formation. Results revealed not only a homogeneous Fe distribution into the Cr layer but also the presence of an iron-chromium duplex oxide layer for concentrations ≥ 100 mg/L Fe in the bath. The Mott-Schottky analysis showed a p-n junction for such coatings due to the presence of an iron oxide layer on the top of a chromium oxide one which increases the total amount of point defects (charge carrier density) and drastically affects their corrosion resistance (the polarisation resistance decreased by one order of magnitude and their oxide layer showed slower kinetics and a higher passivation current). In contrast, coatings with a single chromium oxide layer showed a p-type semiconducting behaviour as well as the best corrosion performance.

3-Sulphinyl-5-Amino-1H-1,2,4-Triazoles as Inhibitors of Copper Corrosion

A set of electrochemical and full-scale corrosion testing methods demonstrates that 3-sulphinylalkyl-5-amino-1H-1,2,4-triazoles can be used as inhibitors of copper corrosion in neutral chloride solutions and under atmospheric corrosion. It was shown that the inhibition effect of 3-sulphinylalkyl derivatives of 5-amino-1H-1,2,4-triazole increases with the growth of the chain of the additive. By means of the impedance spectroscopy method, the authors determined that the polarisation resistance and the Warburg impedance increases whereas the double-layer capacitance decreased with the growth of the inhibitor chain and the concentration of the inhibitor. In addition, the period when the first signs of corrosion attack appear on the copper plates in the salt spray chamber increased with the growth of the inhibitor chain and its concentrations. The lowest value of this period was measured for 3-sulphinylpropyl derivatives. However, it is still 12 times higher that this value measured without any inhibitors. Full-scale testing in 1% HCl solution showed that the corrosion rate slows down by 10–20 times upon the introduction of the derivatives of 3-sulphinylbutyl and 3-sulphinylpentyl at a concentration of ≥5.00 mM. If the concentration of 3-phenethylsulphinyl is equal to or higher than 1.00 mM, then the protection level is about 85%.

Enhanced mechanical, electrical and corrosion characteristics of Al-CNTs-Nb composite processed via spark plasma sintering for conductor core

Monolithic aluminium has low density and high conductivity required in transmission conductors. However, it lacks the requisite strength necessary for long space crossing. To augment the strength, it needs to be reinforced with adequate materials. So, this work is focused on spark plasma sintering of Al-CNTs-Nb composite for power transmission conductor core. Spark plasma sintering of the samples was carried out with pre-determined optimum sintering parameters. After the sintering, the density of the sintered samples was calculated using Archimedes principle, while the micro hardness was tested with Vickers hardness tester. The polarisation test was carried out with Autolab (PGSTAT302N), while the electrical conductivity was tested with four-point probe meter. The results gave a 37% improvement in micro hardness and 30% increase in tensile strength with Al-8CNTs-1Nb. Al-1CNTs-4Nb gave the best corrosion characteristics of 51% and 57% improvements in corrosion rates and 443% and 323% improvements in polarisation resistance in NaCl and H2SO4 media, respectively. Electrical conductivity showed a little increase by 2%. In all, it is evident that this composite is a suitable material for power transmission conductor core for upgrading the power grid.