Aluminum Anodization in a Basic Ambient Temperature Molten Salt

Abstract

Aluminum anodization has been studied in the basic A1C13:1-methyl-3-ethylimidazolium chloride (ImC1) ambient temperature molten salt (A1C13:ImC1 molar ratio <1.0). The anodization process was studied as a function of chloride anion concentration. Two different anodization processes are observed with onset potentials of approximately -1.1 and 0 V. The more cathodic anodization involves formation of the tetrachloroaluminate anion and exhibits a limiting current controlled by diffusion of chloride to the electrode surface. The number of chlorides required for each A1 anodized was determined to be 4.6 _+ 0.4. The more anodic anodization shows no diffusion control. A value for the diffusion coefficient of chloride was obtained which is lower than previously reported; the difference involves using an n value of 1, rather than 2/3. No reduction of the tetrachloroaluminate anion was observed even at elevated temperatures.Numerous studies have been carried out on the redox chemistry of aluminum in A1C13:MC1 molten salts, where MC1 is an alkali metal chloride (1-6) or M + is an organic cation, e.g., N-butylpyridinium chloride (BuPyC1) or 1-methyl-3-ethylimidazolium chloride (ImC1) (7,8). In these chloroalumlnate melts the major equilibrium determining the anion species is 2AIC14 ~ A12C1c + C1[1]for which the equilibrium constant is 1.06 x 10 -7 for A1C13:NaC1 at 175~ (9) and 8 • 10 -'s for A1C13:ImC1 at 40~ (10). In melts with an A1C13:MC1 ratio >1.0, an acidic melt, the dominant anion species are tetrachloroaluminate and heptachlorodialuminate ions. In melts with an A1C13:MC1 ratio <1.0, a basic melt, the anion species present are tetrachloroaluminate and chloride. The electrochemistry of an aluminum electrode in these chloroaluminate melts is strongly dependent upon the melt composition.In the high temperature A1C13:alkali metal chloride melts, most studies have been performed in the acidic composition region. Aluminum deposition in acidic melts involves a nucleation process and exhibits a limiting current controlled by diffusion of the heptachlorodialuminate anion to the electrode surface (1). A number of interesting features of A1 anodization in these acidic alkali metal melts have been observed. During anodization of an A1 wire into acidic A1C13-KC1-NaC1 melts at 105~176 a passivation of the A1 anode was observed with a resultant sudden decrease in the anodic current which then achieves a steadystate value (2). This passivation was attributed to the formation of an insoluble, poorly conducting layer of A1C13 on the electrode surface. The quantity of anodic current passed before passivation occurred could be increased by cathodic prepolarization which created a diffusion layer close to the electrode depleted in A1C13, thus allowing more A1 to be anodized into the melt before formation of this passive layer of A1C13. As expected, passivation due to salt precipitation also occurred during A1 deposition. However, a decrease in the cathodic current was followed by a rapid increase in the current due to dendrite formation (...

Electrodeposition of Nano‐ and Microcrystalline Aluminium in Three Different Air and Water Stable Ionic Liquids

“…The electrodeposit is analysed as Al with some oxygen, due to the exposure to air, as revealed from the accompanied energy dispersive X-ray (EDX) profile (Figure 9 b). The cyclic voltammograms of the ionic liquid P 14,6,6,6 Tf 2 N containing 4 mol L À1 AlCl 3 on gold substrates at different temperatures, that is, 50, 75, and 100 8C, are shown in Figure 8 b. All cyclic voltammograms are similar to that recorded at 25 8C.…”

“…The above-mentioned ionic liquids ([EMIm]Tf 2 N, [BMP]Tf 2 N, and P 14,6,6,6 Tf 2 N) were purchased in the highest available (ultrapure) quality. They were dried under vacuum for 12 h at a temperature of 100 8C to water contents below 3 ppm (by Karl-Fischer titration) and stored in an argon filled glove box with water and oxygen below 1 ppm (OMNI-LAB from Vacuum-Atmospheres).…”

“…The present work shows, for the first time, a comparative experimental study on the electrodeposition of aluminium in three different water and air stable ionic liquids, namely 1-butyl-1-methylpyrrolidinium-bis(trifluoromethylsulfonyl)imide ([BMP]Tf 2 N), 1-ethyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide ([EMIm] Tf 2 N), and trihexyl-tetradecyl-phosphoniumbis(trifluoromethylsulfonyl)-imide (P 14,6,6,6 , then only one solid phase is formed. The biphasic mixture of AlCl 3 /A C H T U N G T R E N N U N G [BMP]Tf 2 N becomes monophasic by heating up to a temperature higher than 80 8C.…”

Heat-treatment induced material property variations of Al-coated Mg alloy prepared in aluminum chloride/1-ethyl-3-methylimidazolium chloride ionic liquid

“…However, if a larger Mg substrate is used, the edge effects cannot be ignored. The electrodeposition mechanism of Al in this IL has been described as follows [17,18]:…”

Anodic Dissolution of Aluminum in the Aluminum Chloride-1-Ethyl-3-methylimidazolium Chloride Ionic Liquid

“…2,[8][9][10][11][12] But only few such investigations have been undertaken in the related room-temperature ionic liquids, e.g., AlCl 3 -EtMeImCl 13 and AlCl 3 -BuMeImCl, 7 with the former study conducted in the basic (Cl − -rich) ionic liquid. However, the kinetics and mechanistic aspects of the anodization reaction remain unclear.…”