A recent study published in Sensors explores a novel way to tackle corrosion in coated aluminum surfaces. By combining in situ Raman spectroscopy with a pH-sensitive molecular sensor, researchers have developed a method for detecting corrosion earlier and with greater accuracy. This approach uses gold nanoparticles to enhance Raman signals, providing real-time insights into corrosion processes.
Study: In Situ Raman Spectroscopy for Early Corrosion Detection in Coated. Image Credit: SvedOliver/Shutterstok.com
Why Corrosion Detection Matters
Corrosion poses a significant challenge to aerospace materials, especially aluminum alloys like AA2024-T3, which are widely used in aircraft structures. This electrochemical process, often accelerated by moisture and salts, can compromise material integrity over time. Early detection is crucial to maintain safety and reduce costly repairs, yet conventional methods such as visual inspections and electrochemical techniques often identify corrosion only after substantial damage has occurred.
This study investigates SERS as a more effective alternative. The technique amplifies Raman signals, allowing the detection of subtle chemical changes that signify the early stages of corrosion. Central to the approach is a pH-sensitive molecule, which reacts to local pH changes—a key indicator of proton production during corrosion. By attaching this molecule to gold nanoparticles, the researchers enhanced the sensitivity of the Raman signal, offering a robust solution for early corrosion detection.
The Experimental Approach
To develop the sensing system, researchers synthesized gold nanoparticles and characterized their size and distribution using dynamic light scattering (DLS). The nanoparticles had an average diameter of 99.8 nm and a polydispersity index (PDI) of 0.108, reflecting their uniformity. These nanoparticles were then functionalized with the pH-sensitive molecule, creating a SERS-active sensor.
The functionalized sensors were integrated into coatings and applied to AA2024-T3 panels. These panels were subjected to accelerated corrosion tests in a 0.5 % NaCl solution to simulate harsh environmental conditions. Raman spectra were recorded at various intervals, capturing shifts in local pH that indicated corrosion activity.
To complement the Raman measurements, the study employed electrical impedance spectroscopy (EIS), which provided insights into the electrochemical properties of the coatings. Parameters like charge transfer resistance and coating capacitance were extracted using Gamry’s Echem Analyst software, offering additional data to validate the findings from Raman spectroscopy.
Results and Discussion
The results showed that the SERS-based sensors were highly effective in detecting localized pH changes tied to corrosion. For example, the Raman signal intensity dropped significantly near scribe marks on the panels, where corrosion activity was most pronounced. These changes corresponded to proton production, confirming the sensors’ ability to detect early-stage corrosion.
The study also found that these sensors could distinguish between different stages of corrosion. They picked up on subtle chemical changes long before visible damage occurred, demonstrating their potential for real-time monitoring. The strong correlation between Raman data and EIS measurements further validated the accuracy of this approach.
Another key takeaway was the importance of optimizing the gold nanoparticles. The researchers found that the size and shape of the nanoparticles played a big role in enhancing the Raman signal. By tweaking these parameters, they developed a sensor that was not only sensitive but also reliable for detecting even the smallest pH changes.
Conclusion
This research represents a major advancement in corrosion detection technologies for aerospace materials. By integrating in situ Raman spectroscopy with pH-sensitive molecular sensors and gold nanoparticles, the study provides a precise and effective tool for real-time corrosion monitoring. The ability to detect pH fluctuations at the earliest stages of corrosion offers critical insights, enabling proactive maintenance strategies that enhance the safety and longevity of aerospace structures.
The implications of this work extend beyond aerospace, presenting opportunities for broader applications in industries where material integrity is paramount. The findings reinforce the potential of SERS as a powerful method for advancing corrosion monitoring and material diagnostics.
Journal Reference
Delluva A. K., Cook R. L., et al. (2025). In Situ Raman Spectroscopy for Early Corrosion Detection in Coated AA2024-T3. Sensors, 25(1), 179. DOI: 10.3390/s25010179, https://www.mdpi.com/1424-8220/25/1/179