Surface Films Produced by Cathodic Polarization of Aluminum

Abstract

Cathodic polarization of aluminum in acid solution produces a surface film which was studied using infrared reflectance spectroscopy (IRS), and quartz crystal microbalance (QCM), and capacitance measurements. According to the QCM results, deposition of the film began after passage of 7.2 mC/cm2 of cathodic charge at a potential of −2.0 V. This charge was consistent with IRS and capacitance measurements. The film grew at an approximately constant rate with time, indicating that its ionic conduction resistance is small. Also, the linear increase of the reciprocal capacitance as a function of film mass is consistent with film growth occurring uniformly across the electrode surface. IRS showed that the cathodic film is an amorphous aluminum hydroxide or oxyhydroxide which contains absorbed water; QCM stripping measurements found that there was at least one water molecule per aluminum ion. This extensive hydration is perhaps related to the relatively low ion transport resistance. Mass transport calculations indicated that the film was formed by direct electrochemical growth and not by precipitation.

Structural and Electrochemical Properties of Al-Added Molybdate Conversion Coatings on Zinc

“…This band is obviously related to the Al species, most likely associated with an Al-OH vibration. 16) Also the bands at 965 cm −1 and 1010 cm −1 together with 828 cm −1 indicate that the Al hydroxide species is nordstrandite, 17,18) although the relative intensities of these bands are changed due to an amorphous nature of the conversion coatings ascertained by HR-TEM image. The relative intensity of these bands increases with the Al content in the conversion coating.…”

Effect of cathodic charging on Al-32Si-2Cu alloy in acidic solution

“…An anodic current density value which surprisingly first increases and then decreases in 3.0 M HCl indicates that the initiation of pit growth rate is considerably lower. The increased pitting susceptibility in acidic chloride solution may be due to the decreased resistance of the surface film by incorporation of H + ion into the film 61,62 which creates a way to incorporation of Clions to initiate pit into the film. A number of fluctuations seen in OCP may be attributed to the pitting activity of chloride ions [63][64][65] .…”

Formation of the Layered Etch Films on AA1050 Aluminum Plates Etched in Nitric Acid Using Alternating Currents

“…[1][2][3]16,17 However, cathodic polarization might enhance the population density of the pits formed during subsequent anodic polarization above the pitting potential. 18 This enhancement is attributed to the formation of aluminum hydroxide or oxyhydroxide, which has lower electric resistance for ionic conduction than the aluminum oxide. 19 Moreover, hydrogen formed at the oxide-metal interface generally causes the formation and subsequent rupture of blisters in the protective film.…”