利用激光诱导击穿光谱定性与定量分析固体中元素方法研究

发布时间：2018-03-14 08:21

本文选题：激光诱导击穿光谱　切入点：定性分析　出处：《山西大学》2013年硕士论文　论文类型：学位论文

【摘要】：激光诱导击穿光谱(Laser-Induced Breakdown Spectroscopy, LIBS)是一种新型光谱分析技术。利用激光诱导击穿光谱的方法对未知样品进行元素分析,具有可多元素同时分析,速度快,无辐射等优势,在电力、地矿、环保、冶金、考古等领域有广阔的应用前景。本文首先概述了LIBS技术的基本原理、理论以及应用现状。然后针对目前该技术进行元素分析时,定性分析需采用人工方式寻峰,再确定谱线归属；而在定量分析过程中,由于脉冲激光能量起伏会导致测量的长期稳定性差的缺点,从原理上和技术上解决了上述关键问题,开发煤质分析设备,可实现对煤样灰分、发热量等工业分析指标的测量,推动了该技术的实用化。本文主要研究内容概括如下： 1.介绍了激光诱导击穿光谱的电子密度、等离子体温度等参数的计算方法,局部热平衡态的判定。用LabVIEW编写了等离子参数计算程序,根据高斯公式的面积与峰值关系建立了谱峰半高宽的算法,基于Boltzmann-Maxwell分布和Saha-Eggert公式计算电子密度、温度。 2.利用二次微商法和阈值判定法对LIBS光谱数据进行降噪、寻峰,并通过参考NIST原子光谱数据库,确定谱线归属。基于LabVIEW编写了分析程序,确定了多种常见元素的特征波长,可以自动识别元素谱线,建立了定性分析算法。在此基础上设计了便携式元素分析设备,可通过手持式测量,实现对样品所含元素种类的定性分析,快速确定未知样品中所含元素种类。 3.建立闭环负反馈式激光能量锁定装置,通过将激光输出能量与预设值进行比较并负反馈至激光电源,利用PID控制根据能量偏差值得到相应的控制量,自动调整氙灯供电电压将脉冲激光能量锁定在预设值附近。通过优化PID参数,使激光能量起伏稳定在士3.2%以内,实现长期稳定测量,提高了LIBS技术在元素分析领域的可靠性和实用性。 4.利用二阶多元非线性回归建立了煤炭工业分析指标的定标模型,构建了新的数据分析方法,通过归一化提高谱线相对强度计算精度,由LIBS分析得到的各元素谱线的相对强度拟合得到煤样的灰分值和发热量,测量的相对误差分别为4.61%和7.32%。 5.基于上述研究,研制了适用于化验室分析的光电一体化的全自动激光煤质分析设备,可在30-60s内完成对煤样进行分析,得到其硫分、灰分、发热量。该设备操作简单,激光输出功率稳定,测量速度快,能实现长期稳定测量。
[Abstract]:Laser-Induced Breakdown Spectroscopy (Libs) is a new spectral analysis technique. The method of laser-induced breakdown spectroscopy is used to analyze the elements of unknown samples. It has the advantages of simultaneous analysis of multiple elements, high speed, no radiation and so on. Geological and mineral resources, environmental protection, metallurgy, archaeology and other fields have broad application prospects. In this paper, the basic principle, theory and application status of LIBS technology are summarized firstly. Then, in the process of element analysis, the qualitative analysis needs to find the peak manually, and then determine the spectral line attribution, and in the process of quantitative analysis, Because the fluctuation of pulsed laser energy will lead to poor long-term stability of measurement, the above key problems are solved in principle and technology. The development of coal quality analysis equipment can realize the measurement of coal sample ash, calorific value and other industrial analysis indexes. It promotes the practicality of the technology. The main contents of this paper are summarized as follows:. 1. The calculation method of electron density, plasma temperature and the determination of local thermal equilibrium state of laser induced breakdown spectrum are introduced. The calculation program of plasma parameters is compiled by LabVIEW. Based on the relationship between the area and peak value of Gao Si formula, an algorithm for calculating the half-width of spectral peak is established. The electron density and temperature are calculated based on Boltzmann-Maxwell distribution and Saha-Eggert formula. 2. The LIBS spectral data are de-noised and peak-seeking by using the quadratic microquotient method and threshold determination method, and the spectral line attribution is determined by referring to the NIST atomic spectrum database. The analysis program based on LabVIEW is compiled and the characteristic wavelengths of various common elements are determined. On the basis of this, a portable element analysis device is designed, which can be used for qualitative analysis of elements in samples by hand-held measurement. Identify elements in unknown samples quickly. 3. The closed-loop negative feedback type laser energy locking device is established. By comparing the laser output energy with the preset value and negative feedback to the laser power supply, the corresponding control quantity is obtained by using PID control according to the energy deviation value. By automatically adjusting the power supply voltage of xenon lamp, the pulse laser energy is locked near the preset value. By optimizing the PID parameters, the laser energy fluctuation is stabilized within 3.2%, and the long-term stability measurement is realized. The reliability and practicability of LIBS in element analysis are improved. 4. The calibration model of coal industry analysis index is established by using second-order multivariate nonlinear regression, and a new data analysis method is constructed. The accuracy of relative intensity calculation of spectral line is improved by normalization. By fitting the relative strength of the spectral lines of each element from LIBS analysis, the ash score and calorific value of the coal samples were obtained. The relative errors of the measurements were 4.61% and 7.32, respectively. 5. Based on the above research, a fully automatic laser coal quality analysis equipment, which is suitable for laboratory analysis, has been developed. It can be used to analyze coal samples in 30-60 seconds and obtain its sulfur, ash and calorific value. The equipment is simple to operate. The laser output power is stable, the measuring speed is fast, and the long-term stable measurement can be realized.
【学位授予单位】：山西大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：O433.4

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