LIBS Analysis of Steel Samples

Goal:
Assess the ability of LIBS to detect dirt in steel samples

Method:
LIBS

Introduction:
Two steel samples were tested for the presence of magnesium (Mg), manganese (Mn), sulfur (S) and silicon (Si) to assess the ability of LIBS to detect dirt in steel. Two samples were analyzed: approximately 38 mm diameter metal cylinder (approximately 50 mm tall) and approximately 25 mm diameter metal disk (less than 12 mm tall).

Experimental Conditions:
The smaller steel sample was measured on the flat surfaces on either side of the sample. The larger sample was measured on two of the curved surfaces. Sand was observed on the outside of the larger sample. Several single shot spectra and multi-shot spectra were acquired for each of the surfaces chosen for analysis.

Hardware Used:
LIBS2000+ broadband, high-resolution spectrometer
50 mJ Nd:YAG Big Sky laser
LIBS-SC sampling chamber with a 125 mm focal length lens

Experimental Parameters:
-2 microsecond Q-switch delay setting
1 to 10 spectra averaged

Measurement Mode:
LIBS

Results:
Average spectral data for the different surfaces measured for each of the samples are shown in Figures 1 and 2. As expected for alloy samples, the spectral data are very rich in elemental emission lines.

Results for LIBS detection of the elements of interest are presented in separate tables for each sample. The number of elemental lines identified by the Elemental Identification mode of the OOILIBS software is shown in Table 1. Note that the elemental identification library contains multiple lines for each element taken from the persistent lines in the MIT wavelength tables. The values shown represent the number of lines identified out of the total number of lines contained in the elemental identification library.

Conclusions:
Based on the results shown in Table 1 for LIBS analysis carried out with a 50 mJ laser, all of the elements were detected for the smaller steel sample. Note that sulfur was only observed for the single shot spectra acquired at fresh spots on the sample. When 10 shots were averaged at the same location on the sample, sulfur was not detected. This suggests that sulfur is only found on the surface of the samples. For the larger sample, all of the elements except sulfur were detected. The use of a more powerful laser may improve detection by allowing for the detection of additional emission lines for the elements of interest.

Figure 1: Average spectral data (n=3) for larger steel piece

Figure 2: Average spectral data (n=3) for smaller steel piece


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