Ellipsometry of the Growth and Dissolution of Anodic Oxide Films on Aluminum in Alkaline Solution

Abstract

Ellipsometry has been used to study the growth of anodic films on superpure aluminum in sodium hydroxide of concentration range 0.1-4M. The ellipsometer used was a self-nulling type, and all experiments were performed in situ at a constant wavelength of 632.8 nm. The results are explained by the growth and dissolution of anodic films that are duplex in nature. During the dissolution process, at certain potentials, a highly reproducible transient effect in the optical signal is seen. This effect has been related to roughening of the underlying aluminum substrate, followed by subsequent smoothing upon completion of the dissolution process. The latter is indicated by the optical signal returning close to its initial value prior to film growth. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35 Downloaded on 2015-03-13 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35 Downloaded on 2015-03-13 to IP ABSTRACTThe cyclic voltammograms in 98% H~SO4 were measured on the mesophase-pitch-based carbon fibers heat-treated at various temperatures. They showed a marked dependence on the heat-treatment temperature of the carbon fibers. The electrochemical formation of graphite-sulfuric acid intercalation compounds was confirmed by x-ray diffraction. The change of graphite layer planes in the carbon fibers due to electrolysis was examined by Raman spectra.

Participation of Aluminum Hydride in the Anodic Dissolution of Aluminum in Alkaline Solutions

“…The samples were then washed in deionized water and mounted in a glass electrochemical cell used for both alkaline treatment and voltammetry. The exposed sample area in the cell was 1.77 cm 2 . The edge of the electropol-ished area was deliberately covered because of indications that preferential dissolution had occurred in this region.…”

“…In moderately basic solutions, the rate of anodic dissolution may be controlled by the combination of electrode kinetics, mass transport, or conduction through a surface film. [2][3][4][5][6][7] The dissolution reaction mechanism in concentrated KOH solutions was investigated by Macdonald et al using electrochemical impedance spectroscopy. 8 They determined that the metal corrodes by a reaction pathway in which OH − ions are added sequentially to Al atoms, until the stable aluminate ion, Al͑OH͒ 4 − , is formed.…”

Formation of Aluminum Hydride during Alkaline Dissolution of Aluminum

“…That is, upon removal from the alkaline bath, a film of alkaline solution was present on the Al surfaces that would have contained Al͑OH͒ 4 − ions dissolved from the metal. The deionized water used to wash the samples was neutral in pH and may have precipitated these ions as Al͑OH͒ 3 . This precipitation should have been expected after all dissolution times, but in the SIMS experiments, it would not have contributed to the AlD − and OD − signals.…”

“…Investigations of pure aluminum in alkaline solutions have clarified important aspects of the electrochemical behavior. [2][3][4][5][6][7][8][9] The potential dependence of anodic dissolution was revealed by measurement of the rate of concurrent cathodic hydrogen evolution. [4][5][6][7] The formation of aluminum hydroxide or oxide corrosion product films by dissolution has been deduced from studies of anodic kinetics using rotating disk electrodes, 2,6 and from ellipsometry.…”

“…[4][5][6][7] The formation of aluminum hydroxide or oxide corrosion product films by dissolution has been deduced from studies of anodic kinetics using rotating disk electrodes, 2,6 and from ellipsometry. 3 Impedance studies have revealed complex dynamic behavior, which has been attributed to the contribution of multiple reaction steps to dissolution. 5,9 In all cases, it has been assumed that the overall anode process is simply the oxidation of aluminum metal to aluminate ions.…”