Electrodeposition of Purified Aluminum Coatings from AlCl₃-Dimethylsulfone(DMSO₂) Electrolytes with Isopropylamine Hydrochloride

Abstract

Aluminum (Al) have played an important role in the recent advance of civilization and as a basic material for industry, construction, and agriculture. Because of its glossy appearance, low weight, and good mechanical properties, Al has been widely used in the information technology and electronics industries, e.g., smart phones, notebooks, netbooks, etc. However, Al requires surface treatment to improve corrosion resistance, durability, wear resistance, abrasion resistance. Al coatings have been electrodeposited from AlCl3 - dimethylsulfone (DMSO2) electrolytes at 403K. The coatings usually contained trace amounts of sulfur (S) due to DMSO2 and chlorine (Cl) due to AlCl4 - as impurities. Since these impurities make the coatings hard and brittle, and moreover may adversely affect the corrosion- and oxidation resistances of the Al coatings, it would be desirable to decrease their contents in the Al coatings. Examination of the Al coatings electrodeposited from the electrolytes with the addition of various amounts of isopropylamine hydrochloride (IPA) revealed that the S and Cl contents of the Al coatings decreased with increasing concentration of IPA in the electrolyte. The addition of IPA also brought about changes in the surface morphology and crystal orientation of the Al coatings. Preferential adsorption of IPA on the surface of the Al deposit was inferred to be a cause of the exclusion of S and Cl from the Al coating. As a result of the decrease in S and Cl contents, the Al coatings were softened. Cyclic voltammgram shows 23 mol % AlCl3 / DMSO2 electrolytes contain from 0 to 0.4mmol IPA with respect to 10 M DMSO2. Most of the cycles of precipitation and dissolution of Al was occurs at the potential of - 0.5V. The addition of IPA, lead to decreasing of the flowing current and produce smooth stable films. The higher current density was observed at 0.1mmol IPA among using additives. On the other hand, the lower and stable cathodic current 0.2mmol produces smooth film. S and Cl contents plots the Al coatings determined by EDX against the IPA content in the electrolyte. While the Al coatings from the electrolyte without IPA contained 2.1 mass % S and 1.4 mass% Cl, both the contents decreased with increasing content of IPA in the electrolyte. The decrease leveled off when the amount of IPA was 0.2mmol, at which point the S and Cl contents were below 1 mass %. SEM images shows the surface of these samples. It can be seen that the film formed in the solution without additive is many cracks are observed. On the other hand, the film fotmed on the solution with the using 0.2mmol IPA contains no crack. Figure 1