氯化钾溶液的激光诱导击穿光谱研究

利用脉冲Nd:YAG激光器、光谱仪I、CCD等设备设计了一套激光诱导击穿光谱测试实验装置,并采用该装置对氯化钾溶液的全谱进行了测量,得到了含量为1mg/l的镁(Mg),3mg/l的钙(Ca),20mg/l的钠(Na)的线状谱线。实验结果表明,对氯化钾溶液做定性分析时,延时是一个非常重要的参数。合理地选取延时,利用激光诱导击穿光谱方法可以快速准确地同时检测到多种微量金属元素。同时定性分析也证明了利用激光诱导击穿光谱方法探测废水中的微量有毒金属的可行性。     

基于便携式激光诱导击穿光谱技术的耐热钢老化等级评估

长期承受高温高压耐热钢的运行状态严重影响着设备系统的安全生产,传统检验手段在时间和操作上存在一定的局限性。将开发的便携式激光诱导击穿光谱(LIBS)设备应用于耐热钢失效分析,结合化学计量学方法实现T91钢老化等级的预测评估。首先对不同老化等级T91样品的光谱特性进行了分析,研究了不同表面状态样品的元素特征谱线随脉冲数变化趋势,获取各样品的典型光谱;然后采用K折叠支持向量机递归特征消除算法(K-SVM-REF)对光谱变量进行特征选择,以提高模型预测性能。结果表明基于特征选择的光谱变量较全谱变量建立的支持向量机(SVM)预测模型测试集的分类准确率从84.38%提升到90.63%。此外还研究了样品表面状态对模型性能的影响,为开发的便携式LIBS设备用于实现金属受热面失效诊断的实际测量提供了有效的依据和方法。     

基于超小微晶片激光的便携式LIBS系统的实现

文章采用高功率、小体积的微晶片激光器,设计并实现了便携式激光诱导击穿光谱（LIBS）检测系统。该系统由激光器驱动模块、微晶片激光模块、样品和光谱分析模块及显示处理模块四部分组成。文章对铁、铜以及锌铁合金进行了样品分析测试实验,实现了物质的识别。该系统在样品制备难度、元素检测能力和分析时间上都有明显的优异表现。     

A method of laser focusing control in microlaser-induced breakdown spectroscopy

This paper presents a method for the automatic adjustment of the laser defocusing amount in micro-laser-induced breakdown spectroscopy. A microscopic optical imaging system consisting of a CCD camera and a 20× objective lens was adopted to realize the method. The real-time auto-focusing of the system was achieved by detecting the effective pixels of the light spot generated by the laser pointer. The focusing accuracy of the method could achieve 3 μm. The element concentrations of Mn and Ni in low-alloy steels were analyzed at a crater diameter of about 35 μm using the presented method. After using the presented method, the determination coefficients of Mn and Ni both exceeded 0.997, with the root-mean-square errors being 0.0133 and 0.0395, respectively. Scanning analysis was performed on the inclined plane and the curved surface by means of focusing control and non-focusing control. Ten characteristic spectral lines of Fe were selected as the analysis lines. With the focusing control, the average relative standard deviations obtained on the inclined plane and curved surface were both less than 5%, and much less than the values without focusing control, 14.6% and 40.39%.     

Mechanisms and efficient elimination approaches of self-absorption in LIBS

Laser-induced breakdown spectroscopy(LIBS) is a promising analytical spectroscopy technology based on spectroscopic analysis of the radiation emitted by laser-produced plasma.However, for quantitative analysis by LIBS, the so-called self-absorption effects on the spectral lines, which affect plasma characteristics, emission line shapes, calibration curves, etc, can no longer be neglected. Hence, understanding and determining the self-absorption effects are of utmost importance to LIBS research. The purpose of this review is to provide a global overview of self-absorption in LIBS on the issues of experimental observations and adverse effects,physical mechanisms, correction or elimination approaches, and utilizations in the past century.We believe that better understanding and effective solving the self-absorption effect will further enhance the development and maturity of LIBS.     

Accuracy improvement of quantitative analysis of calorific value of coal by combining support vector machine and partial least square methods in laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy(LIBS) is a potential technology for online coal property analysis,but successful quantitative measurement of calorific value using LIBS suffers from relatively low accuracy caused by the matrix effect.To solve this problem,the support vector machine(SVM) and the partial least square(PLS) were combined to increase the measurement accuracy of calorific value in this study.The combination model utilized SVM to classify coal samples into two groups according to their volatile matter contents to reduce the matrix effect,and then applied PLS to establish calibration models for each sample group respectively.The proposed model was applied to the measurement of calorific values of 53 coal samples,showing that the proposed model could greatly increase accuracy of the measurement of calorific values.Compared with the traditional PLS method,the coefficient of determination(R2) was improved from 0.93 to 0.97,the root-mean-square error of prediction was reduced from 1.68 MJ kg~(-1) to1.08 MJ kg~(-1),and the average relative error was decreased from 6.7% to 3.93%,showing an overall improvement.     

激光诱导击穿光谱结合间隔偏最小二乘法检测土壤中的Pb

为了提高激光诱导击穿光谱(LIBS)技术检测自然土壤中Pb的检测精度,提出采用间隔偏最小二乘法(IPLS)定量预测模型。对土壤在400~417nm波段的特征光谱进行平滑预处理后,建立偏最小二乘法(PLS)定量模型,得到训练集的相关系数为0.974 2,且斜率为0.983。建立IPLS模型时,把所选波段均分成了25个子区间,得到第八个子区间包含了Pb的特征光谱405.78nm,且交叉验证均方根误差最小,选择该区间建立模型得到训练集相关系数为0.985 3,斜率为1.121。预测集中,土壤样品Pb的真实浓度与预测浓度之间的相对误差在13%以内,平均相对误差为7.00%。研究表明IPLS法应用于LIBS定量检测土壤中的Pb是可行的,且该定量模型预测效果优于PLS法。     

Quantitative analysis of uranium in electrorecovery salt of pyroprocessing using laser-induced breakdown spectroscopy

The amounts of nuclear materials in the Li Cl-KCl salt in pyroprocessing have to be analyzed to prevent the diversion of the nuclear material. An alternative method to the chemical analysis has been pursued, and laser-induced breakdown spectroscopy(LIBS) is one candidate. In the present work, an in situ and quantitative analysis method of electro-recovery(ER) salt was proposed and demonstrated by using LIBS combined with dipstick sampling. Two types of simulated salt samples were prepared: ER salt sample and salt obtained from the dipstick sampling, and pulsed neodymium-doped yttrium aluminum garnet(Nd:YAG) laser with a wavelength of 532 nm was focused on the salt to generate plasma. The plasma emission was measured by using an Echelle spectrometer with a resolution of 0.01 nm in conjunction with an Intensified Charge-Coupled Detector camera. The U and other rare earth peaks in the spectra were identified. The best Limit of Detection and Root Mean Square Error of Calibration of U were 38 ppm and 0.0203 wt%,respectively. Our work shows that the U in the pyroprocessing ER salt can be monitored with LIBS.     

基于互信息特征筛选偏最小二乘的激光诱导击穿光谱铁矿浆定量分析

目前检测矿浆品位相对准确的方法是传统化学分析,但周期长、有滞后性,无法实现在线检测。实验利用激光诱导击穿光谱(Laser induced breakdown spectroscopy,LIBS)在线、原位、快速等优点,分析了铁矿选矿过程尾矿浆中铁元素的品位值。由于LIBS采集到的光谱数据中存在大量对成分分析无用的冗余信息,进而增加了建模复杂程度,导致建立的模型精确度不够、泛化能力不强。因此,在偏最小二乘(PLS)模型基础上,提出了基于互信息特征筛选的偏最小二乘模型。实验结果表明,与传统的PLS模型相比,基于互信息特征筛选的偏最小二乘模型在分析精度上得到了明显改善,测试样品的决定系数R²从0.52提高到0.90,测试样本的平均绝对误差(MAEP)从2.87%下降到1.38%,总样本的平均绝对误差(MAE)从1.0%下降到0.60%。     

新型便携式激光诱导击穿光谱仪器及其应用研究

针对我国成熟且商业化的便携式激光诱导击穿光谱仪器缺乏,且现有便携设备光谱稳定性和抗干扰性能差的现状,提出并成功开发了一种新型小型化、集成化的便携式激光诱导击穿光谱仪器。采用该仪器成功实现了对24种金属矿石的准确分类和微合金钢样品中Cr、Ni、Si、Cu、Ti、V元素的精准定量分析,其对24种金属矿石的平均分类准确率达到了95.83%,微合金钢中各元素定量分析模型的决定系数R²分别达到了0.993、0.984、0.996、0.990、0.980、0.999,检出限(LOD,质量分数)分别达到了0.035 5%、0.058 7%、0.077 3%、0.012 0%、0.008 5%和0.008 2%,交叉验证的平均相对误差(ARECV)分别达到了5.20%、11.30%、18.18%、9.63%、9.73%、9.17%。结果表明,所开发仪器具备良好的定性、定量分析性能,其为便携式激光诱导击穿光谱仪器的国产化提供了新的解决方案。