Investigation Of Quantitative Analysis For Alloys Using One-point Calibration Laser-induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy(LIBS)is a technology of atomic spectrometry,which has the advantages of remote,in-situ,online,no sample pretreatment and multi-element analysis.LIBS technology has shown great potential in environmental monitoring,metallurgical technology,explosives detection,biomedicine and many other fields.At present,the low accuracy of LIBS quantitative analysis is the technical bottleneck of LIBS application.In this thesis,An improving approach for the quantitative accuracy of LIBS has been investigated.In comparison of traditional calibration curve method,the calibration-free LIBS(CF-LIBS)approach is based on the measurement of line intensities and plasma parameters(plasma electron density and temperature)and on the assumption of a Boltzmann population of excited states to calculate multi-elemental concentrations,which overcomes the limitation of using standard samples and avoids the need for any comparison with calibration curves.However,the precision and accuracy of CF-LIBS results can be compromised by uncertainties associated with Einstein coefficientsA_ij and efficiency of spectral detection system F(?),inaccurate plasma temperature calculations and self-absorption of emission lines.The one-point calibration(OPC)LIBS method has been studied for improving the reliability of quantitative analysis for both major and minor elements.This method can be considered as a variation of the CF-LIBS method,which used one standard of known composition and similar matrix to synchronously correct the essential experimental and spectroscopic parameters to get a more accurate determination.Firstly,we compared the results of calculations using CF-LIBS and OPC-LIBS for major and minor constituents of seven certified Ti-6Al-4V alloys,which are the widely used titanium alloys for Additive manufacturing to date.For stable measurement,LIBS spectrum was averaged over ten laser shots.The analysis results show that the relative error of the CF-LIBS quantitative analysis of the major element titanium(85.07?91.70 at.%)in the Ti-6Al-4V alloy is about 5.42?7.14%,while the relative error of the OPC-LIBS quantitative analysis is only 0.33?1.08%;The relative error of CF-LIBS quantitative analysis of aluminum(5.66-11.48 at.%)in the Ti-6Al-4V alloy is about 36.62?59.51%,while the relative error of OPC-LIBS quantitative analysis is only 2.09?9.95%;The relative error of CF-LIBS quantitative analysis of vanadium(2.65?5.21 at.%)is about 43.40?60.51%,and the relative error of OPC-LIBS quantitative analysis is 2.83?6.89%.Secondly,a vacuum chamber was pumped down to a pressure of 3×10^-5mbar to simulate the pressure condition in the fusion vessel.A certified molybdenum-tungsten alloys were chosen as a replacement for the high Z impurities deposited on PFCs in EAST.I compared the results of calculations using CF-LIBS and OPC-LIBS for major and minor constituents.LIBS spectrum was also averaged over ten laser shots.The results show that the relative error of the CF-LIBS quantitative analysis for the major element molybdenum(81.72?88.46 at.%)in the Mo W alloy is about 3.7?3.9%,while the relative error of the OPC-LIBS quantitative analysis is only 0.7?1.87%;The relative error of CF-LIBS quantitative analysis of tungsten(11.54?18.28 at.%)is about 17.23?29.87%,and the relative error of OPC-LIBS quantitative analysis of tungsten is 1.60?9.93%.From comparison,the OPC-LIBS method leads to a more accurate determination of the alloy composition compared with the conventional CF-LIBS approach in the open air and in vacuum.The OPC-LIBS method has great potential in the real-time,online,and quantitative analysis of LIBS in the field of industrial applications.