Research On Laser-Induced Breakdown Spectral Characteristic Of Alloy By Passively Q-switched Laser Excitation Under Vacuum And Buffer Gas

At present,in the production process of roll and other castings,the on-line analysis of multi-elements content is needed to improve the manufacturing process and guarantee the quality of the products.The elements to be detected include non-metallic components such as C,S and other metal elements.The methods currently used mainly include spark photoelectron spectroscopy,x-ray fluorescence spectroscopy and chemical analysis.Spark photoelectron spectroscopy needs at least 2 to 5 minutes to sampling and pretreatment of sample;X-ray fluorescence spectroscopy has difficulty to analyze the non-metal elements such as C,S;Chemical analysis requires several couples of minutes to finish.Laser induced breakdown spectroscopy(LIBS)is a new fast on-line detection technology which can potentially realize the rapid on-line detection of multi-elements of the casting.However,the LIBS signal of C,S is relatively small which make the analysis of these elements difficult.How to enhance its signal becomes an important problem,which is dealt with in this paper as follows.Firstly,the influence of experimental factors such as buffer gas and pressure to LIBS signal is analyzed.Secondly,the laser energy of the passively modulated Q pulse laser in LIBS system was determined.Thirdly,vacuum system with the low vacuum and argon factors is designed.Fourthly,the process of the whole LIBS experiment is worked out with the vacuum system.Finally,the LIBS experiment is carried out under the dynamic argon atmosphere and the low vacuum static argon atmosphere.The results show that the spectral intensity of the carbon 406.97nm spectra can be enhanced by about 100%when the argon flow rate is 6L/min,but the SNR of the spectral intensity is decreased;And,the spectral intensity of the carbon element of 432.5nm spectra under the-0.095MPa low vacuum atmosphere and-0.02MPa low vacuum combined with argon atmosphere is enhanced by about 120%and 15%when compared with the latm air atmosphere.And the signal noise ratio(SNR)is increased by 83%and 11%correspondingly.It means that the low vacuum atmosphere or low vacuum combined with argon atmosphere can effectively enhance the spectral signal and improve SNR.