Breakdown Of Anodic Oxide Films Research Articles

低濃度ＫＯＨ溶液中におけるアルミニウムアノード酸化皮膜の生成挙動

Aluminum was anodized in diluted KOH solutions galvanostatically to examine the effect of KOH-concentration on the growth and breakdown of anodic oxide films. Time-variations in the anode potential, Ea, the amount of dissolved Al3+ ions, and electroluminescence intensity were measured during anodizing, and the film structure was observed by transmission electron microscopy and scanning electron microscopy.At 5×10-5 and 5×10-4M, Ea increased with time linearly at the initial stage, and the rate of increase in Ea decreased at 400V. The slow increase in Ea stopped at about 600V, and beyond the potential Ea increased at a high rate until the film breakdown started at 1600V and 1100V in 5×10-5 and 5×10-4 M solution, respectively. In both solutions, the growth of the oxide film was accompanied by the formation and growth of relatively large voids between 400V and 600V, and beyond 600V small numerous voids developed on the entire surface. The film growth can be explained by the local oxide dissolution and precipitation of hydroxide.At 5×10-3 M, Ea remained zero for the initial 1500s of anodizing, and then increased linearly with time before film breakdown started at 600V. The anodic oxide films consisted of two layers: an outer porous layer and an inner dense layer.

ChemInform Abstract: Formation and Breakdown of Anodic Oxide Films on Aluminum in Boric Acid/Borate Solutions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Formation and Breakdown of Anodic Oxide Films on Aluminum in Boric Acid/Borate Solutions

Highly pure aluminum was anodized at a constant current density of at 293 Kin 0.5 M boric acid/0, 0.005, or 0.05 M sodium tetraborate solutions, to examine the effect of sodium tetraborate concentration on the formation and breakdown characteristics of barrier oxide films by using inductively coupled plasma atomic emission spectrometry, electroluminescence/photoluminescence measurements, scanning electron microscopy, transmission electron microscopy, and electrochemical impedance spectroscopy. In boric acid/borate solutions, a crystalline alumina formed locally in the middle of the amorphous oxide film. Above the crystalline alumina, a void is formed and may lead to a breakdown of the oxide film at 420 to 540 V. In boric acid solution, an amorphous oxide film grew until 1180 V with the formation and development of imperfections and with enhancement of electroluminescence and gas evolution. At imperfections, the oxide/solution interface was convex and the oxide/metal interface curved in the opposite direction. This deformation is attributed to high‐pressure evolved in the pores of imperfections and to the local formation and dissolution of oxide. The breakdown of the oxide film started when the evolution and oxide dissolution at imperfections become predominant. The mechanism of formation and breakdown of the anodic film in the boric acid/borate solutions is discussed in terms of pH buffering of the anodizing solution, and the electronic structure of anodic oxide films is correlated with electroluminescence and photoluminescence spectrum results.

A phenomenological approach to the mechanical breakdown of anodic oxide films on zirconium

A phenomenological theory of the mechanical breakdown of films growing on valve metals during galvanostatic oxidation is presented and discussed in detail for ZrO 2 anodic films. It is shown that the mechanical breakdown voltage, V mb, can be linearly related to the logarithm of the anodizing current density both in the case of constant and variable critical thickness, L c, at which the breakdown occurs. It is also shown that the A mb and B mb parameters of the relationship: V mb = A mb + B mb log i are strictly related to the kinetic parameters of growth of the films in the different solutions. The expressions of A mb and B mb parameters are derived for films grown in the presence as well as in the absence of space-charge effects. A quantitative check of the equations obtained is presented for different ZrO 2/electrolyte systems.

Tensiostatic studies on formation and breakdown of anodic oxide films on tungsten in acidic chloride solutions

The anodic behaviour of tungsten in HCl and HCl + KCl solutions has been extensively studied. For each solution, the applied voltage was increased from 1 V up to the breakdown voltage. Values of the current and open circuit voltage decays were recorded. The HCl concentration was varied from 0.05 M to 12 M while appropriate addition to KCl was made to reach assigned molarities of the Cl − ion. The results are discussed and qualitatively interpreted in terms of the different influence of the H + and Cl − ions.

A theory for breakdown of anodic oxide films on metals

The breakdown of anodic oxide films that results in pitting and transpassive dissolution is described thermodynamically as a mechanical deformation or crack formation. The electrostriction pressure due to a high electric field of the order of 10 6 V/cm produces a compressive stress which could exceed the breakdown stress of oxide films. The surface tension stabilizes anodic oxide films, but this surface effect decreases with increasing film thickness. Thus, there is a critical thickness above which mechanical deformation or breakdown of the oxide film could occur. Anion adsorption lowers the surface tension and hence decreases the critical thickness for breakdown. The net stress in anodic oxide films produced by electrostriction and surface tension effects is derived as a function of electric field, dielectric constant, surface tension and film thickness, and the breakdown potential at which the film thickness is critical is shown to depend on the anion concentration in solution. The theory is compared with experiments on the effect of halogen ion concentration on the breakdown potential and the effect of inhibitive anions on film breakdown for aluminum and stainless steel. Pore formation and transpassive dissolution of anodic oxide films are also discussed.

Dielectric breakdown of anodic oxide films on valve metals

INTRODUCTION ALTHOUGH the various types of breakdown of anodic oxide films on metals have been recognized and partially explained for many years, few systematic studies have been conducted. The present communication reports the nature of film (particularly dielectric breakdown) on zirconium, hafnium, aluminium, tantalum, niobium, tungsten, titanium, vanadium and molybdenum, and of certain niobium-base alloys, mainly in a single electrolyte.