The metallurgical industries are very important for social development. In order to improve the metallurgical techniques and quality of products, the real-time analysis and monitoring of iron and steel manufacturing processes are very significant. Laser-induced breakdown spectroscopy (LIBS) has been studied and applied for the contents measurement of iron and steel. In this paper, the remote open-path LIBS measurement was studied under different sample temperature, lens to target distance (LTD), sample angle conditions to clarify its online measurement features. The 3D profile measurement system of parallel laser beam fringes projection was also developed to measure the sample profile at different sample temperature. The measurement results demonstrated the robustness of remote open-path LIBS system and 3D profile measurement system. However, the correction is necessary to enhance the detection ability of LIBS online measurement. In order to improve the precision and accuracy of real-time elemental measurement, an innovative co-axial laser beam measurement system combining LIBS and 3D profile techniques is proposed to automatically adjust the focus unit and measure the sample components. The further study of this promising method will be developed for online application of iron and steel manufacturing processes. KEY WORDS: laser-induced breakdown spectroscopy; 3D profile; remote measurement; iron and steel manufacturing processes.
The long–short double-pulse laser-induced breakdown spectroscopy (LS-DP-LIBS) method was applied to qualitative and quantitative analyses of underwater steel samples to improve the detection ability of underwater measurement. The stable plasma intensity and discrete emission lines were detected using LS-DP-LIBS when comparing the measured results of single-pulse LIBS (SP-LIBS) and LS-DP-LIBS. The long pulse produces a cavitation bubble without plasma, and the short pulse induces the plasma of steel samples within the bubble. The detection features of LS-DP-LIBS for underwater steel samples were discussed in different intra-pulse delay time, long-pulse width, and delay time conditions when analyzing the measured spectra, the signal intensity of Fe(I) at 400.524 nm and 402.187 nm, Mn(I) at 404.136 nm, and intensity ratio of Mn(I) 404.136 nm/Fe(I) 402.187 nm. The results indicated that the plasma stability and spectral signal intensity were improved significantly with a long-pulse width of 80 µs in the intra-pulse delay time of 70 µs, which were appropriate for bubble formation and plasma generation. According to the discussion of the delay time effect, the state of generated plasma was almost stable from 650 ns to 850 ns. Manganese (Mn) contents in steel samples were analyzed quantitatively when measuring five steel samples with different Mn contents using LS-DP-LIBS in optimal experimental conditions. A strong linear dependence was observed with R2=0.9842, which demonstrated the feasibility and appropriateness of quantitative analysis for underwater measurement using LS-DP-LIBS.
Accurate measurement of trace heavy metal mercury (Hg) in flue gas of coal-fired units is great significance for ecological and environmental protection. Mixed gas was used to simulate the actual flue gas of a power plant in this study. A laser-induced breakdown spectroscopy (LIBS) system for Hg measurement in mixed gas was built to study the effect of mixed gas pressure, Hg concentration in mixed gas and delay time on Hg measurement. The experimental results show that the appropriate low mixed gas pressure can obtain high Hg signal intensity and signal to noise ratio. The Hg signal intensity and signal to noise ratio increased with the increase of Hg concentration in mixed gas. The Hg signal intensity and signal to noise ratio decreased with the increase in delay time. According to the above results, the optimized measurement conditions can be determined. Different Hg concentrations in mixed gas were quantitatively analyzed by the internal standard method and traditional calibration method respectively. The relative error of prediction of the test sample obtained by the internal standard method was within 11.11%. The relative error of prediction of the traditional calibration method was less than 14.54%. This proved that the internal standard method can improve the accuracy of quantitative analysis of Hg concentration in flue gas using LIBS.
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