Abstract
The Al coatings were electrodeposited on the Cu substrate from AlCl3-EMIC ionic liquid (AlCl3:EMIC = 2:1 molar ratio) containing three cyanopyridine additives with different positions of the substituent group on the pyridine ring, which were 2-cyanopyridine, 3-cyanopyridine, and 4-cyanopyridine. The effects of cyanopyridine additives on the deposition potential, morphology, brightness, and corrosion properties of Al coatings were investigated. It was considered that the deposition potential of Al shifted to more negative overpotentials, the quality of Al coatings was promoted, and the corrosion property was improved by the cyanopyridine additives to a varying degree. Especially in the presence of 4-cyanopyridine, the flattest mirror bright Al coating was obtained, which had the smallest homogeneous nanocrystal grain size and strongest Al (200) crystallographic orientation. The average roughness Ra value was as low as 31 nm compared to that in the absence of cyanopyridine additives, which was 417 nm. Furthermore, the corrosion current density of the bright Al coating was three orders of magnitude lower than the rough Al coating, which resulted from the dense nanocrystal structure.
Highlights
Ionic liquids are a new kind of green solvent that allow the electrodeposition of Al and many other water-sensitive metals because of their outstanding properties, such as wide electrochemical potential windows, nonvolatility, and high thermal and electrochemical stability [1,2,3,4]
EMIC-AlCl liquid affected by the 3 ionic additives.responsive, It could be obviously seen the additives had a symbolized impact on the tametric suggesting thethat process of nucleation and growth affected by the ad voltametric responsive, suggesting the process of nucleation and growth affected by the ditives [17,36]
3were very consistent with the results demonstrated cyanopyridine and 4-cyanopyridine additive were 32 and 24 nm, which were very conthat cyanopyridine had an obvious on the preferred orientation ofcyanothe Al sistent with the SEMadditives micrographs in Figure results demonstrated that peaks and refining grains, and both of them led to the increasing brightness of the pyridine additives had an obvious effect on the preferred orientation of the Al (200) peaks and refining grains, and both of them led to the increasing brightness of the Al coatings
Summary
Ionic liquids are a new kind of green solvent that allow the electrodeposition of Al and many other water-sensitive metals because of their outstanding properties, such as wide electrochemical potential windows, nonvolatility, and high thermal and electrochemical stability [1,2,3,4]. Electrodeposited Al and Al alloy coatings from ionic liquids have received considerable attention because of their excellent physicochemical properties in the past decades, which had low density and good strength, and possessed outstanding corrosion resistance [5,6,7,8]. Compared to various other available coating techniques, electrodeposition is such a widely applied, low-cost, and highly developed technology that it permits the coating of complex geometries homogeneously, offers high-purity deposits (≥99.99% Al), and allows for the deposition of thick layers at room temperature [9,10,11,12]. The use of appropriate additives into the electrolyte is one of the key technologies to regulate the microstructure and enhance the quality of the Al electrodeposit [19,20]
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