Growth behavior of anodic oxide formed by aluminum anodizing in glutaric and its derivative acid electrolytes

Abstract

The growth behavior of anodic oxide films formed via anodizing in glutaric and its derivative acid solutions was investigated based on the acid dissociation constants of electrolytes. High-purity aluminum foils were anodized in glutaric, ketoglutaric, and acetonedicarboxylic acid solutions under various electrochemical conditions. A thin barrier anodic oxide film grew uniformly on the aluminum substrate by glutaric acid anodizing, and further anodizing caused the film to breakdown due to a high electric field. In contrast, an anodic porous alumina film with a submicrometer-scale cell diameter was successfully formed by ketoglutaric acid anodizing at 293 K. However, the increase and decrease in the temperature of the ketoglutaric acid resulted in non-uniform oxide growth and localized pitting corrosion of the aluminum substrate. An anodic porous alumina film could also be fabricated by acetonedicarboxylic acid anodizing due to the relatively low dissociation constants associated with the acid. Acid dissociation constants are an important factor for the fabrication of anodic porous alumina films.Keywords: Aluminum; Anodizing; Glutaric Acid; Ketoglutaric Acid; Acetonedicarboxylic Acid IntroductionAnodic porous alumina with numerous vertical, nano-scale pores can easily be fabricated via aluminum anodizing in several types of acidic aqueous solutions and has been widely applied in the fields of corrosion protection and electronic applications [1][2][3][4][5][6]. In particular, the development of highly ordered anodic porous alumina, which is fabricated via self-ordering and two-step anodizing under appropriate electrochemical conditions, has expanded the applicability of porous alumina [7]. Accordingly, plasmonic devices [8], antireflection polymer structures[9], optical devices [10], and high-density recording media [11] have been successfully fabricated through the combination of methods for developing highly ordered anodic porous alumina and other nanostructure fabrication techniques.The electrolyte species used for anodic porous alumina fabrication can be specifically classified into the following three groups: inorganic, organic cyclic oxocarbonic, and organic carboxylic acids. It is a well-known experimental fact that anodic porous alumina can be formed by anodizing in these acidic electrolytes, which provide low acid dissociation constants. To date, sulfuric [12][13][14][15][16], selenic [17,18], phosphoric [19,20], and chromic[21] acids have been reported as useful inorganic electrolytes for fabricating anodic porous alumina. The ideal cell arrangement of porous alumina can be achieved via sulfuric, selenic, and phosphoric acid anodizing, whereas poorly ordered porous alumina is fabricated via chromic acid anodizing [22,23]. Cyclic oxocarbonic acids such as squaric [24], croconic, and rhodizonic[25] acid were very recently determined to be suitable organic electrolytes for fabricating porous alumina, although the details of the growth behavior are still unknown. Carboxylic acids can also be employed ...

Porous Aluminum Oxide Formed by Anodizing in Various Electrolyte Species

“…Citric acid (HOOC-CH 2 -C(OH)(COOH)-CH 2 -COOH) is very useful for fabrication of porous oxide films with large cell diameters [75][76][77][78] [86], and acetonedicarboxylic acid (HOOC-CH 2 -CO-CH 2 -COOH) at 150 V [86]. Because the formation of porous oxide films on aluminum is strongly affected by the acid dissociation constants of the electrolyte used, additional carboxylic electrolytes for porous oxide formation may be still found by examining dissociation constants in further research work [86].…”

“…Because the formation of porous oxide films on aluminum is strongly affected by the acid dissociation constants of the electrolyte used, additional carboxylic electrolytes for porous oxide formation may be still found by examining dissociation constants in further research work [86].…”

Self-ordered Porous Alumina Fabricated via Phosphonic Acid Anodizing

“…Phosphonic acid is one of the oxoacids of phosphorus, a diacid that features two acidic hydroxyl groups with the following acid dissociation constants, pKa [41] 3 = 11.46), it is defined as a relatively stronger acid. Empirically, the cell size of the self-ordered porous alumina showed a tendency to decrease with the lowering of the pKa value (i.e., acid strength) [42]. Therefore, phosphonic acid anodizing may exhibit an undiscovered self-ordering voltage and corresponding cell size.…”

Self-Ordered Aluminum Anodizing in Phosphonoacetic Acid and Its Structural Coloration

“…Additional dicarboxylic acids with a large molecular structure, malonic and tartaric acids, for the fabrication of anodic porous alumina were reported by Ono et al, and self-ordering was achieved by anodizing with these acids for 300 and 500 nm intervals, respectively. 22 Recently, we reported several novel electrolytes for the formation of anodic porous alumina: selenic, 23,24 acetylenedicarboxylic, 25 squaric, 26 croconic, 27 rhodizonic, 27 ketoglutaric, 28 acetonedicarboxylic, 28 and etidronic acids. 29,30 Particularly, etidronic acid anodizing exhibited large-scale self-ordering behavior measuring 530-670 nm in cell diameter.…”