Development of Surface Impurity Segregation during Dissolution of Aluminum

Abstract

Caustic dissolution, when used as a pretreatment for etching of aluminum in chloride solutions, is observed to increase the rate of pit nucleation. Rutherford backscattering spectrometry (RBS) and Auger electron spectroscopy were used to measure the composition in the near-surface region of 99.98% purity aluminum after dissolution in 1 N NaOH at room temperature. During dissolution, concentrations of impurities such as Fe, Cu, and Ga were found to accumulate continuously within a layer less than about 10 nm thick adjacent to the surface, because they dissolved more slowly than did aluminum. Impurity concentrations on the order of 1 atom percent (a/o) in this layer, much higher than equilbrium values, were found after 40 min dissolution. It is argued that the large impurity concentrations are consistent with a highly defective region in the metal near the metal/oxide interface, which has been detected using positron annihilation measurements. Dissolution produced a scalloped surface topography with typically 30 nm high ridges separated by 130 nm. A simulation of RBS measurements based on scattering from spherical particles was developed to test for the possibility of preferential impurity segregation to ridges. No such segregation was detected, suggesting that this is not the reason for the strong tendency for pit nucleation to occur on ridges, as has been observed previously. 5. K. Shimizu, G. E. Thompson, G. C. Wood, and Y Xu, Thin Solid Films, 88, 255 (1982 13. P. Skeldon, K. Shimizu, G. E. Thompson, and G. C. Wood, Thin Solid Films, 123, 127 (1985).14. P. Skeldon, K. Shimizu, G. E. Thompson, and G. C. Wood, Surf. Interface Anal., 5, 247 (1983). 15. G. Amsel, C. Cherki, G. Feuillade, and J. P. Nadai, J.Phys. Chem. Solids, 30, 2117Solids, 30, (1961 16. K. Shimizu, P. Skeldon, G. E. Thompson, and G. C. Wood, Surf. Interface Anal., 4, 208 (1981 Acta, 20, 663 (1975). 42. J. J. Randall, W. J. Bernard, and R. R. Wilkinson, ibid., 10, 183 (1965). Development of Surface Impurity Segregation during Dissolution of Aluminum Xiaolin Wu and Kurt HebertDepartment of Chemical Engineering, Iowa State University, Ames, Iowa 50011, USA ABSTRACT Caustic dissolution, when used as a pretreatment for etching of aluminum in chloride solutions, is observed to increase the rate of pit nucleation. Rutherford backscattering spectrometry (EBS) and Auger electron spectroscopy were used to measure the composition in the near-surface region of 99.98% purity aluminum after dissolution in 1 N NaOH at room temperature. During dissolution, concentrations of impurities such as Fe, Cu, and Ga were found to accumulate continuously within a layer less than about 10 nm thick adjacent to the surface, because they dissolved more slowly than did aluminum. Impurity concentrations on the order of 1 atom percent (a/o) in this layer, much higher than equilbrium values, were found after 40 mm dissolution. It is argued that the large impurity concentrations are consistent with a highly defective region in the metal near the metal/oxide interface...

Positron Annihilation Spectroscopy Study of Interfacial Defects Formed by Dissolution of Aluminum in Aqueous Sodium Hydroxide

“…The resulting thickness is 9 nm for the as-received foil, and between 3 and 7 nm for the samples dissolved in NaOH. While this estimate for the as-received sample is somewhat higher than the Auger-determined thickness of 5 nm, 9 the calculated thickness is on the correct order of magnitude, and decreases as expected due to the NaOH treatment. Therefore, the calculation confirms the presence of the oxide over the defect layer, further demonstrating that the defects are located at or close to the metal-film interface.…”

“…Wu and Hebert used Rutherford backscattering spectrometry ͑RBS͒ to analyze the surface composition of foils after 1 M NaOH treatment. 9 The concentrations of iron, copper, and gallium accumulated at a constant rate during the treatment, within a layer no thicker than about 10 nm adjacent to the metal-oxide interface. Significant concentration increases were noted after 5 min dissolution.…”

Microscopic Observations of Voids in Anodic Oxide Films on Aluminum

“…16 Impurities include Cr, Cu, Fe, Ga, Mg, Si, and Zn with bulk concentrations of the order 10 wt-ppm. 17 Caustic treatment was carried out by immersion of foils in 1 N NaOH solution for different lengths of time at room temperature, after which they were washed thoroughly with deionized ͑DI͒ water. Prior to anodic oxidation, the samples were dipped in 1 N HNO 3 at ambient temperature for 1 min to avoid the erratic anodizing behavior sometimes encountered on foils anodized directly after NaOH treatment.…”

Particle Characterisation and Depletion of Li2CO3 Inhibitor in a Polyurethane Coating

“…The presence of Cu and Mn in the matrix can be explained by a small but significant solubility of Cu in Al, as well as Cu and Mn being present in a number of IM particles (hardening precipitates (Cu) and dispersoids (Al20Mn3Cu2)), which are much smaller than the resolution of the technique [68]. Elements such as Ga have been reported before when using Rutherford Backscattering spectroscopy (RBS) to examine aluminium alloys [69]. In some Al-alloys, Zn is used for precipitate hardening using the ƞ-phase (Zn2Mg) in 7xxx series alloys [70] but, again, it is not expected as an alloy addition here, even though Zn is detected in the AA2024-T3 sheet product [60].…”