Research On Non-metallic Element Detection Using Laser-induced Breakdown Spectroscopy Based On Molecular Spectra

As an important component of material,non-metallic elements have a vital impact on the properties of material.Therefore,the rapid and sensitive detection of non-metallic elements in materials has become an inevitable requirement in the industrial field.However,the traditional methods for sample detection have many problems,such as complex sample pretreatment process,tedious operation,poor timeliness,secondary pollution and so on.As a new detection technology,Laser-induced Breakdown Spectroscopy（LIBS）has become a potential analysis tool in the field of non-metallic elements detection because of its simple sample pretreatment,fast detection speed and convenient operation.But it is difficult to detect non-metallic elements in the atmosphere because of the high excited energy level of atoms and the few spectral lines available for analysis.Based on this,the LIBS detection method of non-metallic elements is studied from the angles of enhanced molecular spectrum.The specific research contents and results are as follows:By detecting the emission spectrum of CaCl molecule formed by the combination of chlorine element and Ca element,the highly sensitive detection of chlorine element was realized in air.Taking the detection of chlorine in cement as an example,the formation mechanism and experimental process of CaCl molecular spectra were expounded,and the experimental conditions affecting CaCl molecular spectra were studied.At the same time,in order to improve the spectral interference caused by Ca O molecular band,multiple regression algorithm was used.The linearity of analysis model was increased from 0.9344to 0.9968,and the root-mean-square error was improved from 0.4233 wt.%to 0.2537 wt.%.In order to promote the formation of Sr F molecule in plasma,the aerosol containing Sr after ultrasonic atomization was sprayed onto the surface of the sample by ultrasonic atomization assisted laser probe.Sr F molecule spectra were measured to avoid the problems of difficult excitation and spectral line interference of fluorine atom spectra.Taking the determination of fluorine in rock as an example,the optimal experimental procedure and conditions for the construction of Sr F molecules by ultrasonic atomization assisted laser probe are explored.Compared with conventional fluorine emission spectrometry,the fitting correlation coefficient based on Sr F molecular spectroscopy is 0.975,and the detection limit is 0.0014 wt.%.In order to detect silicon in iron and steel,the laser induced molecular fluorescence technique was used to enhance the emission signal intensity of SiO molecule in plasma.Two fluorescence excitation modes of SiO molecule were studied.The results show that the laser induced fluorescence assisted laser probe based on SiO molecular spectra can improve the accuracy and sensitivity of the quantitative results of silicon in iron and steel.The fitting coefficient,cross-validation root-mean-square error and detection limit were 0.988,0.046wt.%and 0.0187 wt.%,respectively.Resonance Raman effect was used to enhance and detect the Raman scattering signal of S₂ molecule in plasma,which is difficult to detect the emission spectra of sulfur elements and related molecules in laser probe.The resonance Raman scattering spectra of S₂molecules in plasma were taken as an example to explain the mechanism of resonance Raman spectra and to study the resonance Raman spectra.Based on S₂ 710 cm^-1 and S₂ 1420cm^-1 resonance Raman spectra,the fitting coefficient and detection limit were 0.976,0.1358wt.%and 0.966,0.1179 wt.%,respectively.The results are better than those of LIBS under the same experimental conditions.The preliminary detection of sulfur in air environment was achieved.To sum up,the laser probe detection methods based on molecular spectroscopy for nonmetallic elements are studied in this paper.Monopulse laser probe,ultrasonic atomization assistant laser probe,laser induced molecular fluorescence assistant laser probe and resonance Raman spectroscopy assistant laser probe are used to detect nonmetallic elements in the air,which solve the problems of nonmetallic elements,such as difficult excitation,self-absorption effect and spectral interference.