Goal:
Determine the sensitivity of LIBS for the detection of silicone release reagent contamination on commercial airplane couponsMethod:
LIBS

Experimental Conditions:
The coupons were sent with tape protecting the analysis surface. The tape was peeled back and 3 spectra were acquired at different locations on each sample. Additional spectra for silicone RTV were acquired to provide a reference for the silicone peaks.

Hardware Used:
LIBS2000+ broadband, high-resolution spectrometer
200 mJ Nd:YAG Big Sky laser
LIBS-SC sampling chamber with imaging module
Experimental Parameters:
Laser at full power (setting 8)
-1.5 Q-switch setting (1.5 microsecond delay between firing laser and data acquisition)
Measurement Mode:
LIBS

Results:
LIBS spectra for the coupons and silicone RTV are shown in Figure 1. In Figures 2 and 3, the regions where several silicone peaks occur are shown. The LIBS spectrum for silicone RTV is included with the coupon spectra for comparison.

All of the silicone spectral lines contained in the Element Identification software (5 lines total) were detected in samples labeled 0.2, 0.5, 1, 1.5 and 2. Four out of five spectral lines were detected in the sample labeled 0.1. For the 0 sample, 1 – 2 silicone lines were detected although they are difficult to see in the spectral data (low intensity). Note that it may be possible to obtain a standard curve for silicone by taking the ratio of each silicone peak to the carbon peak at ~247 nm. This ratio may provide a method for addressing shot-to-shot reproducibility issues.

Figure 1: LIBS spectra for coupons

Figure 2: LIBS spectra for coupons: Region where silicone is detected

Figure 3: LIBS spectra for coupons: Region where silicone is detected (cont)

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