Fig 3 - uploaded by Timur A. Labutin
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Boltzmann plots obtained at 2 μs (a) and 5 μs (b) for three group of lines: Fe I (black squares), Mn I (red circles) and Cr I (green triangles).
Source publication
Strong effect of steel hardness on the parameters of laser-induced plasma (e.g., temperature) and on the calibration curves for manganese and chromium in steels has been demonstrated. The presence of the inverse correlation between the steel hardness and the excitation temperature determined by Mn I lines was explained by the confinement of laser p...
Contexts in source publication
Context 1
... function is plotted with the use of available emission lines, which were not self-absorbed. The examples of this approach are shown in Fig.3, where Boltzmann plots obtained for Fe, Mg and Cr lines are compared for two delays. ...
Context 2
... lines with high upper level energy were chosen to avoid a mistake that could be appeared from invalid value of the slope. As plasma is decayed, its temperature is decreased too as can be seen from Fig.3. Actually, LTE seems to be not realized at the first moments of plasma life (before 2 μs) because straight lines were unparallel and temperatures were sufficiently differed for each element. ...
Context 3
... function is plotted with the use of available emission lines, which were not self-absorbed. The examples of this approach are shown in Fig.3, where Boltzmann plots obtained for Fe, Mg and Cr lines are compared for two delays. ...
Context 4
... lines with high upper level energy were chosen to avoid a mistake that could be appeared from invalid value of the slope. As plasma is decayed, its temperature is decreased too as can be seen from Fig.3. Actually, LTE seems to be not realized at the first moments of plasma life (before 2 μs) because straight lines were unparallel and temperatures were sufficiently differed for each element. ...
Citations
... However, LIBS technology is also impacted by physical and chemical matrix effects that affect the measurement accuracy and precision of the quantitative analysis. These impacts and affects have been investigated by many researchers [11][12][13][14][15][16][17] the quantitative analysis [18,19]. Actually, the physical and chemical properties of the sample are the main reasons for the matrix effect [12,20]. ...
... In order to solve the problems of the matrix-matched standards, Labutin and his co-workers committed to analyze the correlation between the properties of analyzed samples and the laser induced plasma parameters [42][43][44]. Recently, a correction procedure with the sum of analytical lines was proposed and proved by the determination of chromium and manganese in steels [45]. ...
Laser induced breakdown spectroscopy (LIBS) which is used traditionally as a spectrochemical analytical technique was employed to analyze the grade of pearlite spheroidization. Three 12Cr1MoV steel specimens with different grades of pearlite spheroidization were ablated to produce plasma by pulse laser at 266 nm. In order to determine the optimal temporal condition and plasma parameters for correlating the grade of pearlite spheroidization and laser induced spectra, a set of spectra at different delays were analyzed by the principal component analysis method. Then, the relationship between plasma temperature, intensity ratios of ionic to atomic lines and grade of pearlite spheroidization was studied. The analysis results show that the laser induced spectra of different grades of pearlite spheroidization can be readily identifiable by principal component analysis in the range of 271.941–289.672 nm with 1000 ns delay time. It is also found that a good agreement exists between the Fe ionic to atomic line ratios and the tensile strength, whereas there is no obvious difference in the plasma temperature. Therefore, LIBS may be applied not only as a spectrochemical analytical technique but also as a new way to estimate the grade of pearlite spheroidization.
A steel wire rod is one of the cast steel products used for springs to absorb repeated shocks, particularly in harsh conditions. Quality assessment of steel wire rods is critically important to prevent unwanted breakage during their lifetime. However, centerline segregation is the most common cause of weakened steel wire rods. Currently, centerline segregation is monitored using an optical microscope and an electron probe microanalyzer (EPMA). Herein, we demonstrate quantitative concentration mapping of Mn and Cr, the representative alloying elements, in steel wire rods using laser-induced breakdown spectroscopy (LIBS) as an alternative centerline segregation monitoring methodology. Sensitivity, detection limit, precision, and spatial resolution were found to be enough to observe centerline segregation. Concentration maps obtained by LIBS were very similar to those from EPMA. Microscopic matrix changes due to segregation were also identified. The resulting decrease in plasma temperatures was rationalized by formation of metal carbides that hardened local segregated areas. Considering the rapid multi-elemental mapping capability of LIBS in open air, LIBS is suggested as a practical alternative to optical microscope limited to carbon mapping and EPMA that needs high-vacuum equipment for screening faulty steel wire rod products.
Remote and on-line measurement of chromium on structural steel surface in nuclear power plants is critical for protection against fluid accelerated corrosion. To improve the insufficient sensitivity of fiber-optic laser-induced breakdown spectroscopy toward trace element detection, a dual-pulse spectral enhancement system is set up. In an iron matrix, for the purpose of improving sensitivity of trace chromium analysis and reducing the self-absorption of iron, the effects of key parameters are investigated. The optimal values of the parameters are found to be: 450 ns inter-pulse delay, 700 ns gate delay, 30 mJ/6 mJ pulse energy ratio, and 19.8 mm lens-to-sample distance (corresponding to a 799 μm laser focused spot size). Compared to the single-pulse system, the shot number of dual-pulse ablation is limited for reducing surface damage. After the optimization of the dual-pulse system, the signal-to-noise ratio of the trace chromium emission line has been improved by 3.5 times in comparison with the single-pulse system, and the self-absorption coefficient of matrix iron has been significantly reduced with self-reversal eliminated. The number of detectable lines for trace elements has more than doubled thus increasing the input for spectral calibration without significantly increasing the ablation mass. Three calibration methods including internal standardization, partial least squares regression and random forest regression are employed to determine the chromium and manganese concentrations in standard samples of low alloy steel, and the limit of detection is respectively calculated as 36 and 515 ppm. The leave-one-out cross validation method is utilized to evaluate the accuracy of chromium quantification, and the concentration mapping of chromium is performed on the surface of a steel sample (16MND5) with a relative error of 0.02 wt.%.
