激光诱导击穿光谱定量分析及应用研究

发布时间：2018-08-27 11:21

【摘要】：激光诱导击穿光谱(Laser-Induced Breakdown Spectroscopy, LIBS)作为一种原子辐射光谱技术,与传统的化学分析技术相比,具有远程、非接触、可原位、可实时、可全元素同时测量的巨大优势；与一般光谱分析技术相比,又具有快速、可便携、样品制备简单或者无需制备、适用固体液体气体的优点。这些优势和优点决定了LIBS技术在诸多领域极具应用潜力。但是,由于激光与物质相互作用的非线性过程极为复杂,这直接导致了LIBS在定量分析上遇到很大的困难,严重地限制了它的实际应用。因此,定量分析应用的研究和分析性能的改善是当前LIBS研究领域的聚焦热点。实际应用中分析物质和测量条件多样复杂,一方面不同样品产生的信号差异明显,所谓的基体效应影响了定标定量分析的精确度,另一方面激光与物质的耦合效率等因素也限制了LIBS技术的分析灵敏度。本论文针对生活环境中经常检测的分析对象包括油液、水溶液、土壤,开展了LIBS的定量分析研究,有效地提高了LIBS应用的定量分析性能,深入的研究可以促进LIBS发挥更大的应用潜力。本论文首先设计搭建了稳定的笼式结构的LIBS实验系统,实现了样品表面扫描精确控制、光谱采集和数据分析以及LIBS信号的测量优化。然后在实验系统搭建的基础上,开展了油液、水溶液和土壤的定量分析方法研究。本论文将金属表面增强的机制应用于油液的金属元素定量分析。将少量油液在金属表面形成薄膜,脉冲激光聚焦于金属表面击穿烧蚀产生高温金属等离子体,从而间接击穿了表层的薄油膜,提高了油膜的元素分析灵敏度。通过对油液中所含九种金属元素(Mg、Cu、Ag、Ti、Si、Sn、Cr、Fe、Ni)的定标曲线以及定量分析,得到金属元素分析的探测极限为亚ppm或者ppm。进一步对10种不同机油或蔬菜油的分析比较,发现不同油液的基体效应在金属表面增强方法中基本可忽略。本论文应用该方法测量了废机油中的磨损金属元素。本论文开展了水溶液的金属表面增强LIBS方法研究。将少量的含氯矿物质粉末的水溶液沉积在光滑的金属表面形成沉积薄层,同时也将粉末压片,通过对两种制样方法的LIBS分析测量比较,研究了基体效应在两种方法中表现的差异。通过对金属表面增强方法产生的等离子体演化特性诊断,表明金属表面增强LIBS方法中,其产生的等离子体特性主要取决于金属基底,因而大大减小了分析物质所带来的基体效应。本论文提出了激光预处理金属表面的方法,有效克服了水溶液在光滑基底表面扩散慢、沉积分布不均匀的问题。由于规则微结构的存在,水溶液在激光预处理的有限表面区域均匀扩散,与光滑金属表面相比,大大提高了测量的重复精度,张力的变化使得水溶液在该区域扩散十分迅速,且很好地被约束在区域内,使得水溶液多次沉积富集成为可能。最后实现了水溶液的重金属测量探测极限达到亚μg/L (Cd、Ni为例)或μg/L(以Cd为例),比常规LIBS方法提高了三个数量级,比文献报道的最优的LIBS测量方法也有约两个数量级的提高。本论文提出了溴化钾凝结压片的土壤LIBS定量分析方法。土壤是异质物质的代表,基体效应严重影响LIBS定量分析应用。本论文使用了溴化钾作为凝结物质进行土壤粉末压片,通过改变溴化钾含量以及烧蚀坑的分析,发现澳化钾的添加明显提高了土壤与激光的耦合效率,且由于高含量溴化钾的添加,基体效应明显下降,最后得到了不同类型土壤定量分析的共同定标曲线,预测误差小于20%。本论文主要创新之处：1)利用金属表面增强的LIBS液体分析方法,提高了激光与液体的耦合效率,增强了分析物质测量的灵敏度,分析发现了在混合等离子体中起决定性作用的金属基底使得分析物质带来的基体效应可以忽略。2)提出激光预处理金属表面和金属表面增强相结合的方法,使LIBS分析水溶液的灵敏度提高了2-3个数量级,明显改善了测量重复精度。3)利用溴化钾凝结土壤进行压片的LIBS定量分析方法,有效提高了激光消融土壤物质的效率,明显改善了土壤砂岩物质的基体效应。
[Abstract]:Laser-Induced Breakdown Spectroscopy (LIBS) is a kind of atomic radiation spectroscopy technology. Compared with traditional chemical analysis technology, LIBS has the advantages of remote, non-contact, in-situ, real-time and simultaneous measurement of all elements. Compared with general spectrum analysis technology, LIBS is fast, portable and sample preparation. These advantages determine that LIBS technology has great potential in many fields. However, due to the extremely complex nonlinear process of laser-matter interaction, LIBS has encountered great difficulties in quantitative analysis, which severely limits its practical application. Therefore, the application of quantitative analysis and the improvement of analytical performance are the focus of the current LIBS research field. In practical application, the analytical materials and measurement conditions are various and complex. On the one hand, the signals produced by different samples are obviously different. The so-called matrix effect affects the accuracy of the calibration and quantitative analysis, on the other hand, laser and material. The coupling efficiency and other factors restrict the sensitivity of LIBS. In this paper, the quantitative analysis of LIBS is carried out for the analysis objects in living environment, including oil, water and soil. The quantitative analysis performance of LIBS is effectively improved. The further study can promote the application potential of LIBS. Firstly, a stable cage-type LIBS experimental system is designed and constructed to realize the precise control of sample surface scanning, spectrum acquisition and data analysis, and the optimization of LIBS signal measurement. Then on the basis of the experimental system, the quantitative analysis methods of oil, water and soil are studied. The mechanism is applied to the quantitative analysis of metal elements in oil. A small amount of oil is formed on the surface of the metal, and pulsed laser is focused on the surface of the metal to break down and ablate to produce high-temperature metal plasma, which indirectly breaks through the thin oil film on the surface and improves the sensitivity of element analysis of the oil film. The calibration curves and quantitative analysis of Ti, Si, Sn, Cr, Fe, Ni show that the detection limit of metal element analysis is sub-ppm or ppm. Further analysis and comparison of 10 different oil or vegetable oil shows that the matrix effect of different oil can be neglected basically in the metal surface strengthening method. This paper uses this method to measure the abrasion in waste engine oil. Metal elements are destroyed. In this paper, the metal surface-enhanced LIBS method of aqueous solution is studied. A small amount of chlorine-containing mineral powder is deposited on the smooth metal surface to form a thin layer of deposition. At the same time, the powder is pressed into sheets. By diagnosing the plasma evolution characteristics produced by metal surface enhancement method, it is shown that the plasma characteristics produced by metal surface enhancement LIBS method mainly depend on the metal substrate, thus greatly reducing the matrix effect caused by the analytical material. It overcomes the problem of slow diffusion and uneven distribution of aqueous solution on smooth substrate surface.Due to the existence of regular microstructure,aqueous solution diffuses uniformly in the limited surface area of laser pretreatment.Compared with smooth metal surface,the repetition precision of measurement is greatly improved.The change of tension makes the diffusion of aqueous solution very fast in this area. Finally, the detection limit of heavy metals in aqueous solution reaches sub-g/L (Cd, Ni for example) or micro-g/L (Cd for example), which is three orders of magnitude higher than the conventional LIBS method and about two orders of magnitude higher than the optimal LIBS method reported in the literature. In this paper, a quantitative analysis method of soil LIBS for potassium bromide condensation tablets is proposed. Soil is the representative of heterogeneous materials, and matrix effect seriously affects the application of LIBS quantitative analysis. The coupling efficiency between soil and laser is improved obviously, and the matrix effect is decreased obviously due to the addition of high content of potassium bromide. Finally, the common calibration curve of different types of soil quantitative analysis is obtained, and the prediction error is less than 20%. The main innovations of this paper are as follows: 1) The LIBS liquid analysis method enhanced by metal surface is used to improve the laser intensity. The coupling efficiency with the liquid enhances the sensitivity of the analytical material measurement. It is found that the metal substrate plays a decisive role in the mixed plasma makes the matrix effect of the analytical material negligible. The LIBS quantitative analysis method using potassium bromide condensate soil for compaction can effectively improve the efficiency of laser ablation of soil material and improve the matrix effect of soil sandstone material.
【学位授予单位】：华东师范大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN249;O433.4

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