Epoxy primer thickness on aluminum measured with the handheld Agilent 4100 ExoScan FTIR

Importance of the Topic

Accurate determination of primer thickness on aluminum surfaces is essential for quality control in industries such as aerospace, where uniform coating ensures corrosion protection and paint adhesion. Conventional probes often lack the sensitivity needed for very thin layers. Handheld FTIR spectroscopy offers a non-destructive, rapid solution for both chemical identification and thickness measurement of organic coatings.

Objectives and Study Overview

This application note demonstrates the use of the Agilent 4100 ExoScan handheld FTIR to quantify the thickness of epoxy primers on aluminum panels. A series of calibration samples with known primer thicknesses was analyzed to establish a correlation between infrared absorbance and coating thickness. A set of unknown samples was then tested to validate the prediction accuracy.

Methodology and Instrumentation

The study employed the Agilent 4100 ExoScan FTIR with an external reflectance interface. Key parameters included 32 co-added scans at 8 cm-1 resolution, resulting in an 8-second measurement time per sample. Background spectra were collected from a bare aluminum reference after each sample measurement. Infrared absorbance at 1610 cm-1, corresponding to an epoxy functional band, was integrated to derive a calibration curve.

Results and Discussion

Calibration standards with primer thicknesses of 1.5, 2.3, 4.3, 7.6 and 9.9 μm produced a linear response in the 1610 cm-1 band, with absorbance values between 0.07 and 0.7. The excellent linear fit enabled accurate thickness predictions for unknown samples, demonstrating sensitivity to small variations in coating thickness typical of aircraft primers.

Benefits and Practical Applications

• Non-destructive, in situ thickness measurement on large or complex parts
• Chemical specificity to epoxy resin, minimizing interference from additives
• Rapid analysis suitable for field and production environments
• Improved quality assurance for aerospace and industrial coatings

Future Trends and Opportunities

Development of even more compact handheld FTIR devices and wireless data transfer will enhance field deployment. Expanded calibration libraries and machine-learning algorithms could allow multi-layer coating analysis and automated quality feedback. Integration with other handheld analytic tools may lead to comprehensive on-site surface characterization.

Conclusion

The Agilent 4100 ExoScan FTIR provides a reliable and sensitive method for measuring thin epoxy primer coatings on aluminum. Its linear calibration, rapid analysis time, and non-destructive nature make it well suited for aerospace quality control and other industrial applications.

Reference

Seelenbinder J. Epoxy primer thickness on aluminum measured with the handheld Agilent 4100 ExoScan FTIR. Agilent Technologies Application Note 5990-7795EN, 2015.