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In This Article

  • Summary
  • Abstract
  • Introduction
  • Protocol
  • Representative Results
  • Discussion
  • Acknowledgements
  • Materials
  • References
  • Reprints and Permissions

Summary

Time-of-flight secondary ion mass spectrometry is applied to demonstrate the chemical mapping and corrosion morphology at the metal-paint interface of an aluminum alloy after being exposed to a salt solution compared with a specimen exposed to air.

Abstract

Corrosion developed at the paint and aluminum (Al) metal-paint interface of an aluminum alloy is analyzed using time-of-flight secondary ion mass spectrometry (ToF-SIMS), illustrating that SIMS is a suitable technique to study the chemical distribution at a metal-paint interface. The painted Al alloy coupons are immersed in a salt solution or exposed to air only. SIMS provides chemical mapping and 2D molecular imaging of the interface, allowing direct visualization of the morphology of the corrosion products formed at the metal-paint interface and mapping of the chemical after corrosion occurs. The experimental procedure of this method is presented to provide technical details to facilitate similar research and highlight pitfalls that may be encountered during such experiments.

Introduction

Al alloys have wide applications in engineering structures, such as in marine technology or military automotive, attributable to their high strength-to-weight ratio, excellent formability, and resistance to corrosion. However, localized corrosion of Al alloys is still a common phenomenon which affects their long-term reliability, durability, and integrity in various environmental conditions1. Paint coating is the most common means to prevent corrosion. Illustration of the corrosion developed at the interface between metal and paint coating can provide insights in determining the appropriate remedy for corrosion prevention.

Protocol

1. Corrosion sample preparation

  1. Al sample fixation in resin, and polishing
    1. Mount two Al alloy coupons (1 cm x 1 cm) using epoxy resin in 1.25 inch metallographic sample cups and place the coupons in the fume hood overnight or till the resin is completely cured.
    2. Take out the Al resin cylinders cups from the sample cups. Polish the Al resin cylinders using 240 grit paper with water at a 300 rpm platen/150 rpm in the holder for 1 min.
    3. Polish the Al resin cylinde.......

Representative Results

Figure 3 presents the comparison of mass spectra between the metal-paint interface treated with salt solution and the interface exposed to air. The mass spectra of the two samples were acquired using a 25 kV Bi3+ ion beam scanning in 300 µm x 300 µm ROIs. The mass resolution (m/∆m) of the salt solution-treated sample was approximately 5,600 at the peak of m/z- 26. The raw data of the mass spectra were exported after binning 10 channels. A grap.......

Discussion

ToF-SIMS differentiates the ions according to their time of flight between two scintillators. The topography or sample roughness affects the flight time of the ions from different starting positions, which usually leads to a poor mass resolution with an increased width of peaks. Therefore, it is critical that the ROIs being analyzed are very flat, to ensure good signal collection8.

Another pitfall to avoid is charging. Since the Al-paint interface was fixed with the ins.......

Acknowledgements

This work was funded by the QuickStarter Program supported by Pacific Northwest National Laboratory (PNNL). PNNL is operated by Battelle for the U.S. DOE. This work was performed using the IONTOF ToF-SIMS V, located in the Biological Sciences Facility (BSF) at PNNL. JY and X-Y Yu also acknowledged the support from the Atmospheric Sciences & Global Change (ASGC) Division and Physical and Computational Sciences Directorate (PCSD) at PNNL

....

Materials

NameCompanyCatalog NumberComments
0.05 µm Colloidal Silica polishing SolutionLECO812-121-300Final polishing solution
1 µm polishing solutionPace TechnologiesPC-1001-GLBWater based polishing solution
15 µm polishing solutionPace TechnologiesPC-1015-GLBRWater based polishing solution
3 µm polishing solutionPace TechnologiesPC-1003-GLGWater based polishing solution
6 µm polishing solutionPace TechnologiesPC-1006-GLYWater based polishing solution
BalanceMettler Toledo11106015It is used for measuring the chemicals.
Epothin 2 epoxy hardenerBuehler20-3442-064Used for casting sample mounts
Epothin 2 epoxy resinBuehler20-3440-128Used for casting sample mounts
Fast protein liquid chromatography (FPLC) conductivity sensorAmersham AKTA FPLCUsed to measure the conductivity of the salt solution.
Final B padAllied90-150-235Used for 1 µm and 0.05 µm  polishing steps
KCl Sigma-AldrichP9333Used to make the salt solution.
Low speed sawBuehler Isomet11-1280-160Used to cut the Al coupons that are fixed in the epoxy resin.
MgCl2Sigma-Aldrich63042Used to make the salt solution.
MgSO4Sigma-AldrichM7506It is used to make the salt solution.
NaClSigma-AldrichS7653It is used to make the salt solution.
NaOHSigma-Aldrich306576It is used for adjusting pH of the salt solution.
PaintRust-Oleum 245217Universal General Purpose Gloss Black Hammered Spray Paint. It is used to spray on the Al coupons. 
Pan-W polishing padLECO809-505Used for 15, 6, and 3 µm polishing steps
pH meterFisher Scientific13-636-AP72It is used for measuring the pH of the salt solution.
Pipette Thermo Fisher Scientific Range: 10 to 1,000 µL
Pipette tip 1Neptune 2112.96.BS 1,000 µL
Pipette tip 2Rainin1700186520 µL
Silicon carbide paperLECO810-251-PRMGrinding paper, 240 grit
Sputter coaterCressington108 sputter coaterIt is used for coating the sample.  
Tegramin-30 Semi-automatic polisherStruers6036127Coarse/fine polishing/grinding
ToF-SIMSIONTOF GmbH, Münster, GermanyToF-SIMS V, equipped with Bi liquid metal ion gun and flood gunIt is used to acquire mass spectra and images of a specimen.
Vibromet 2 vibratory polisherBuehler67-1635-160Final polishing step

References

  1. Szklarska-Smialowska, Z. Pitting corrosion of aluminum. Corrosion Science. 41, 1743-1767 (1999).
  2. Liu, M., et al. A first quantitative XPS study of the surface films formed, by exposur....

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