Microstructure and Electrochemical Characteristics of Aluminum Anodized Film Formed in Ammonium Adipate Solution

Abstract

The morphology, chemical composition, and crystal structure of aluminum anodized films formed in 85°C aqueous ammonium adipate electrolyte at various forming voltages ͑20-200 V͒ were investigated. The relationship between the microstructure and the electrochemical behavior of the anodized oxide film was also explored. The results showed that an amorphous oxide film was formed when the forming voltage was 100 V or lower. Both the increase of film thickness per increase in voltage and the relative dielectric constant were independent of the forming voltage. When the forming voltage exceeded 100 V, crystalline ␥Ј-Al 2 O 3 was observed. The crystalline clusters first appeared at the center of the amorphous anodized oxide film and extended outward as the forming voltage increased. Two well-defined layers could be clearly recognized when the forming voltage was 200 V. The presence of crystalline ␥Ј-Al 2 O 3 was beneficial in raising the relative dielectric constant and the dielectric strength of the anodized oxide films. The relative dielectric constant ͑13.2͒ of the anodized oxide film formed at 200 V was higher than that of the film formed at a lower voltage. However, the increase of film thickness per increase in voltage was decreased. Microscopic examination revealed that crystallization induced the formation of defects which caused a decrease in the resistivity of the anodized oxide films.

Material characteristics and capacitive properties of aluminum anodic oxides formed in various electrolytes

“…It has been found that a uniform distribution of Al and O existed within the oxide formed by single-stage anodization of aluminum in ammonium adipate electrolyte. 25 Thus, the concentration gradient revealed in Fig. 4(b) seemed to result from the re-anodization stage.…”

“…The results confirmed that it was ␥Ј-Al 2 O 3 with FCC structure. 25,26,31 The results demonstrated that the heat treatment could induce amorphous-to-crystalline transformation for the aluminum anodic oxide film. Interestingly, the induced crystalline formation predominantly occurred in the outer layer of the oxide.…”

“…By comparing the anodic films formed by conditions I1-I5, it was found that the oxide film re-anodized in phosphoric acid electrolyte (condition I2) had the highest capacitance. The distinctly higher capacitance of the oxide could be contributed from its higher degree of crystallinity (consequently, the higher relative dielectric constant 23,25 ) and thinner oxide film. It was observed that, between groups II and III, the respective film capacitances of the oxides re-anodized in the same electrolyte were similar, nevertheless, they were lower than those belonging to group I.…”

“…Fundamental research on the features of the anodic barrier films formed in the bases of boric acid, [13][14][15][16][17] citric acid, 18,19 tartaric acid, 1,[20][21][22] phosphoric acid, 23,24 and ammonium adipate electrolytes, 25,26 and so forth, are comprehensive. Katoh 27 summarized the performance of the aluminum oxide films formed in various electrolytes.…”

Improving the Corrosion Behaviour of 6061 Aluminum Alloy by Controlled Anodic Formed Oxide Layer

“…Anodic films, composed, in specially, of amorphous alumina, are formed by application of an anodic potential *email: Lidia Benea@ugal.ro to aluminum sheet which is immersed in a suitable electrolytes. When are used slightly alkaline electrolytes or close to neutrality due to lowest solubility of the oxide, a compact oxides (barrier-type layer) are usually generated [12]. In contrast, when the solubility of the oxide is increased, porous oxide layers can be formed [10].…”