Infrared microspectroscopic studies on the pitting of AA2024‐T3 induced by acetone degreasing

Clayton

et al. 2002

The objective of the research reported in this paper was to refine an existing model for chromate conversion coatings (CCC) formed on the surface of AA2024-T3, an Al-Cu aircraft alloy, by considering the composition and structure of the CCC formed on constituent intermetallic compounds (IMCs). To achieve this aim it was necessary to develop large-area samples composed of compositionally homogeneous thin films of the various IMCs found on the AA2024-T3 surface, which were galvanically attached to thin films of Al-4.2wt.%Cu (representative of the AA2024-T3 matrix). This was performed in a two-step process: disks of IMC compositions were formed by reactive arc melting (RAM), followed by femtosecond laser ablation of the RAM IMCs, resulting in the formation of homogeneous thin films. These thin films were used to analyze the formation of CCC on IMCs, the AA2024-T3 matrix analog and matrix-IMC galvanic couples. Secondary ion mass spectrometry depth profiling revealed significant variations in CCC film thickness and composition related to the underlying IMCs. The SIMS results indicated that the CCC formed on the matrix analog had the same average thickness as the average CCC formed on AA2024-T3, whereas those formed on individual q and S phases were only 9% and 12% as thick, respectively, when uncoupled to the matrix and 11% and 14% as thick when coupled to the matrix. The CCC thickness on the Al 20 Cu 2 (MnFe) 3 was found to be variable, having an islanded structure. Topographical maps indicate that the IMC/matrix boundaries are covered with CCC of a thickness approaching that of the matrix. Inhibition of CCC growth is related to the high copper content (and therefore insufficient aluminum) present in the IMCs compared to the matrix, which provides a more accurate model of CCC formation on AA2024-T3.

Section: Resultsmentioning

confidence: 99%

On the nature of the chromate conversion coating formed on intermetallic constituents of AA2024‐T3

Vasquez

Clayton

et al. 2002

“…Further information on the VUV ring can be found elsewhere. 19 The synchrotron provided a 'white' light source about 1000 times brighter than the typical FTIR source and a 1200 K thermal source (sometimes called a 'globar'). The synchrotron light pulsed at 50 MHz with pulse widths of 500 ps and was introduced into a commercial FTIR microspectrometer.…”

Section: Synchrotron Infrared Microspectroscopymentioning

confidence: 99%

Uranium association with corroding carbon steel surfaces

Eng

Francis

et al. 2003

We investigated the association of uranium with clean and corroded surfaces of 1010 carbon steel. Studying steel contaminated by uranium species will have an important effect on the development of methods used to clean radioactively contaminated metal waste. X-ray photoelectron spectroscopy, synchrotron infrared microspectroscopy and laboratory-based Fourier transform infrared analysis of steel surfaces exposed to uranyl nitrate showed the presence of crystallized hydrated uranyl oxides, uranyl hydroxides, iron oxyhydroxides and iron oxides. In general, heavily corroded areas physically shield the uranium species, which tended to associate spatially with hydroxyl groups and lepidocrocite. Lightly corroded areas contained uranium species with stronger axial U-O bonding. Infrared spectroscopy, Rutherford backscattering spectroscopy and energy-dispersive spectroscopy mapping analysis revealed that the uranium species are well distributed within the upper micron of the thick corrosion layer and associated more with areas of high hydroxide content. Parameters such as the concentration of uranyl nitrate solution used to expose the carbon steel coupons, the method of contamination (dipped or sprayed with dilute uranyl nitrate solution) and the degree of corrosion (accelerated corrosion before and/or after contamination) played significant roles in the distribution and nature of the uranyl hydroxide/iron oxyhydroxide corrosion products found on the surface of all coupons. These factors must be considered in the development and optimization of decontamination processes for metal waste.

“…All spectra were obtained in reflection mode. Further details of this system and technique have been provided elsewhere by Carr et al 21,22 X-ray absorption near-edge structure spectroscopy (XANES)…”

Section: Synchrotron Infrared Microspectroscopy (Sirms)mentioning

confidence: 99%

Spatially resolved microchemical analysis of chromate‐conversion‐coated aluminum alloy AA2024‐T3

Vasquez

Kearns

et al. 2002

The corrosion of aerospace aluminum alloys has been linked to the electrochemical behavior and chemical composition of constituent intermetallic compounds (IMCs). In this study, secondary ion mass spectrometry (SIMS), x-ray photoelectron spectroscopy (XPS), synchrotron infrared microspectrometry (SIRMS) and xray absorption near-edge structure spectroscopy (XANES) were used to characterize chromate conversion coatings (CCCs) formed on AA2024-T3 sheet and cast IMC analogs. The nascent surface film formed on IMC and matrix surfaces was characterized to reveal the influence of microstructure on CCC structure and composition. Copper-rich regions were found on the outermost CCC surface. Intermetallic compounds rich in Cu were found to be surface depleted of Cr and enriched in CN from the ferricyanide present in the CCC as an accelerator compound. By distinguishing particle morphology and chemistry, SIMS data demonstrated that heterogeneities in CCC composition were associated with IMCs.