Anion Effects in Anodization of Aluminum

Anodization of aluminum in aqueous maleic acid at constant current densities showed that the formation of the anodic film took place competitively with the oxidation of maleic acid. In dilute electrolyte, except for the initial short period where the colorless Chin film was formed, the over-all current served to oxidize the double bond of maleic acid into glyoxal or carbon monoxide. In concentrated electrolyte, the brownish anodic film was readily formed and became black as it thickened. The colored film was shown to favor the passage of ionic current and was made up of aluminum oxide complexed with maleate. The coloration of the film was considered to be induced from carboxylate anion radicals, which were coordinated to the aluminum ion as a ligand, as in the case of oxalic acid film reported previously. ExperimentalAnodization.--Aqueous maleic acid electrolyte of 0.1-1.0 moles/liter was prepared from analytical grade reagent and distilled water. Cleaned 99.99% aluminum sheets and wires were anodized at 15~176 in vessels filled with stirred electrolytes with current supplied from a galvanostat or selenium rectifier.Measurement o~ ESR spectra.--For the anodized aluminum wire, ESR spectra were measured in air using a JEOL, JES-PE 3X instrument.Analysis of gases generated at the anode.--In order to prevent mixing of gases generated at the anode and cathode, a closed vessel with two compartments, each of which was fitted with a silicone rubber stopper, was used as the anodizing cell (4). Prior to anodization, the electrolyte was flushed with argon for several minutes. During galvanostatic anodization at 20 mA/

Section: Table ! Ionic Current Efficiency Of the Anodizationsupporting

confidence: 90%

Section: Gaseous Products At the Anode--generation Of Gasesmentioning

confidence: 99%

mentioning

confidence: 99%

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Behavior of Maleic Acid during the Anodization of Aluminum

Shimura

1978

“…Under this condition, the ionic transport number of the SrCe 0.95 Yb 0.05 O 3-␣ electrolyte will be close to unity, since the electromotive force of hydrogen concentration cells with such moist hydrogen gases obeyed the Nernst equation as reported previously. [20][21][22] The shortage of water vapor at the hydrogen-evolving electrode resulted in a decrease in the current efficiency from unity as shown in Fig. 3 and 5.…”

Section: Discussionmentioning

confidence: 95%

Electrochemical Hydrogen Pump Using SrCeO[sub 3]-Based Proton Conductor: Effect of Water Vapor at the Cathode on the Pumping Capacity

Matsumoto

Hamajima

Yajima

et al. 2001

Electrochemical pumping of hydrogen through high temperature-type proton-conducting solid electrolytes has been studied. The effect of water vapor introduced to the cathode on the hydrogen-pumping capacity of the SrCe0.95Yb0.05O3α proton conductor cell was investigated in the present study. The pumping capacity of the cell was greatly enhanced when water vapor was introduced to the cathode. The water vapor was consumed at the cathode due to the minor partial oxide ionic conduction in the electrolyte. The role of the water vapor at the cathode in the hydrogen pump is discussed. © 2001 The Electrochemical Society. All rights reserved.

“…Shimura and Tajima suggest that this is a carboxylate anion, "considered to exist as a cross-linking agent in the oxide matrix." 14 Oxide grown in a vanadate/EG electrolyte contained both vanadate and carbon species from the solvent. 7 Morlidge et al 15 found solvent species within aluminum oxide grown in a tungstate/EG electrolyte, and the species was mobile inward in the anodizing field.…”

Section: Discussionmentioning

confidence: 99%

Cellular Porous Anodic Alumina Grown in Neutral Organic Electrolyte I. Structure, Composition, and Properties of the Films

Liu¹,

Alwitt²,

Shimizu

2000

Anodic alumina films grown in aqueous electrolytes, that are not highly alkaline, have either barrier or cellular porous structures. Barrier oxide grows in near neutral electrolyte and is a layer of uniform thickness that supports a high electric field. Cellular porous oxide grows in acid solutions in which the Al cation has high solubility, and the faradaic efficiency is substantially less than 100%. The oxide consists of a close-packed array of cells, each penetrated by a central pore with a barrier oxide at the pore base. Cell density is of the order 10 10 cm Ϫ2 and pore diameter is of the order 10 nm. Porous oxide also grows in barrier film-forming electrolyte at low field (low current density) when anodizing conditions promote oxide dissolution, e.g., soluble Al-anion complexes and elevated temperature. 1-3 A more complete description of porous films is in a review by Thompson and Wood. 4 Barrier oxide films grow in nonaqueous electrolytes, too, but a variety of other structures are found that depend on the bath composition. Reports from Ue and co-workers describe films grown in electrolytes with low water content, utilizing ethylene glycol or ␥-butyrolactone as solvent, and with solutes suitable for use in electrolytic capacitors. 5-7 Films with fibrous surface texture are frequently found, as well as films with irregular porosity. A substantial amount of organic material is incorporated into these oxide coatings, particularly when grown in the lowest water content electrolytes. Investigations have been limited to films grown to no more than 100 V, and a well developed porous cellular structure is not reported.We report here on anodic alumina with ordered porous cellular structure grown in organic electrolytes with near neutral pH and low water content, and in which aluminum cations are insoluble. The particular solution compositions were formulated for use in high voltage aluminum electrolytic capacitors 8,9 as part of a program to develop capacitors for space applications. 10 In contrast to the organic grown films cited in the previous paragraph, anodic oxide can be grown to 600 V in these electrolytes, so the development of film structure over a substantial range of barrier oxide thickness is possible. The results are presented in two parts: Part I describes the cellular oxide structure, specifies the conditions under which it forms, and gives the growth kinetics, composition and properties of the films. Part II 11 gives details of the structural changes during growth as revealed by transmission electron microscopy (TEM) examination of ultrathin oxide cross sections, and using that information an explanation is presented for the structural development of these films. Considering anodization in both aqueous and organic media, essential conditions for growth of a porous cellular structure are discussed. ExperimentalFoil coupons, 1 ϫ 1 cm, were cut from 100 m thick, fully annealed 99.99% aluminum foil. The foil has high cubicity texture, so most grains have {100} orientation. The coupons were cleaned by i...