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Plasma Sci. Technol.  
  Plasma Sci. Technol.--2015, 17 (11)   Published: 20 October 2015
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Development of a Laboratory Cement Quality Analysis Apparatus Based on Laser-Induced Breakdown Spectroscopy

FAN Juanjuan (樊娟娟)1, ZHANG Lei (张雷)1, WANG Xin (王鑫)1,et al.
Plasma Sci. Technol. 2015, 17 (11): 897-903 ;  doi: 10.1088/1009-0630/17/11/01
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Determination of the chemical composition of cement and ratio values of clinker plays an important role in cement plants as part of the optimal process control and product quality evaluation. In the present paper, a laboratory laser-induced breakdown spectroscopy (LIBS) apparatus mainly comprising a sealed optical module and an analysis chamber has been designed for possible application in cement plants for on-site quality analysis of cement. Emphasis is placed on the structure and operation of the LIBS apparatus, the sealed optical path, the temperature controlled spectrometer, the sample holder, the proper calibration model established for minimizing the matrix effects, and a correction method proposed for overcoming the ‘drift’ obstacle. Good agreement has been found between the laboratory measurement results from the LIBS method and those from the traditional method. The absolute measurement errors presented here for oxides analysis are within 0.5%, while those of ratio values are in the range of 0.02 to 0.05. According to the obtained results, this laboratory LIBS apparatus is capable of performing reliable and accurate, composition and proximate analysis of cement and is suitable for application in cement plants.

Microanalysis of Multi-Element in Juncus effusus L. by LIBS Technique

LIU Xiaona (刘晓娜)1, HUANG Jianmei (黄建梅)1, WU Zhisheng (吴志生)1,et al.
Plasma Sci. Technol. 2015, 17 (11): 904-908 ;  doi: 10.1088/1009-0630/17/11/02
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Laser-induced breakdown spectroscopy (LIBS) was used to decipher the unique multi-elemental characteristics of Juncus e?usus L. The spectral fingerprints of Juncus e?usus L. were established based on elemental microanalysis via LIBS. Microanalysis and multimode sam?pling methodologies were designed in this study. The relative standard deviation (RSD) approach was performed to optimize the multi-shot measurements. Taking advantage of the capability with no or minimal sample pre-treatment of LIBS, a thermodynamic chart of four elements (Mg, Ca, Ba, and Na) was created from twelve collection regions. The diagram of elemental distribution on a micro-scale was generated to explore the nature of Juncus e?usus L. by LIBS. The results demon?strated that LIBS is a promising technique for rapid elemental microanalysis of heterogeneous samples.

Quantitative Analysis of Composition Change in AZ31 Magnesium Alloy Using CF-LIBS After Laser Material Processing

ZHU Dehua (朱德华)1, CAO Yu (曹宇)1, ZHONG Rong (钟蓉)1,et al.
Plasma Sci. Technol. 2015, 17 (11): 909-913 ;  doi: 10.1088/1009-0630/17/11/03
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The concentration of elements in molten metal of AZ31 magnesium alloy after long pulsed Nd:YAG laser processing was quantitatively analyzed by using calibration-free laser-induced breakdown spectroscopy (CF-LIBS). The composition change in AZ31 magnesium alloy under different laser pulse width was also investigated. The experimental results showed that CF-LIBS can obtain satisfactory quantitative or semi-quantitative results for matrix or major elements, while only qualitative analysis was possible for minor or trace elements. Moreover, it is found that the chemical composition of molten metal will change after laser processing. The concentration of magnesium in molten metal is lower than that present in the base metal. The Mg loss increases with an increase of pulse width in the laser processing. This result shows that the selective vaporization of di?erent elements is a?ected by the pulse width during laser processing.

Parameters Optimization of Laser-Induced Breakdown Spectroscopy Experimental Setup for the Case with Beam Expander

WANG Xin (王鑫), ZHANG Lei (张雷), FAN Juanjuan (樊娟娟),et al.
Plasma Sci. Technol. 2015, 17 (11): 914-918 ;  doi: 10.1088/1009-0630/17/11/04
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Improvement of measurement precision and repeatability is one of the issues cur?rently faced by the laser-induced breakdown spectroscopy (LIBS) technique, which is expected to be capable of precise and accurate quantitative analysis. It was found that there was great poten?tial to improve the signal quality and repeatability by reducing the laser beam divergence angle using a suitable beam expander (BE). In the present work, the influences of several experimental parameters for the case with BE are studied in order to optimize the analytical performances: the signal to noise ratio (SNR) and the relative standard deviation (RSD). We demonstrate that by selecting the optimal experimental parameters, the BE-included LIBS setup can give higher SNR and lower RSD values of the line intensity normalized by the whole spectrum area. For validation purposes, support vector machine (SVM) regression combined with principal component analysis (PCA) was used to establish a calibration model to realize the quantitative analysis of the ash content. Good agreement has been found between the laboratory measurement results from the LIBS method and those from the traditional method. The measurement accuracy presented here for ash content analysis is estimated to be 0.31%, while the average relative error is 2.36%.

Spectral Enhancement of Laser-Induced Breakdown Spectroscopy in External Magnetic Field

LI Cheng (李丞)1, GAO Xun (高勋)1, LI Qi (李奇)1, SONG Chao (宋超)2,et al.
Plasma Sci. Technol. 2015, 17 (11): 919-922 ;  doi: 10.1088/1009-0630/17/11/05
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In this paper the spectral enhancement of laser-induced breakdown spectroscopy (LIBS) for copper plasma in the presence of a magnetic field is investigated and the temporal-and spatial-resolved plasma emission spectra are analyzed. Experimental results show that the copper plasma atomic and ion spectra have been enhanced in the presence of the external magnetic field. In addition, the Cu I 521.82 nm spectral intensity evolution with delay time appears to have a double peak around the delay time of 2 μs, but that of Cu II 507.57 nm has a sharp decrease because of the electron-atom three body recombination process. The plasma temperature with magnetic confinement is lower than that of the case in the absence of magnetic fields. Finally, the spectral enhancement mechanisms of laser induced breakdown spectroscopy with magnetic confinement are analyzed.

Classification and Discrimination of Minerals Using Laser Induced Breakdown Spectroscopy and Raman Spectroscopy

BI Yunfeng (毕云峰)1, ZHANG Ying (张莹)2, YAN Jingwen (闫静文)2,et al.
Plasma Sci. Technol. 2015, 17 (11): 923-927 ;  doi: 10.1088/1009-0630/17/11/06
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he classification and discrimination of minerals are important in geological re?search. The distribution of rocks and minerals may be inferred based on their identi?cation, which is helpful for the investigation of some geological and environmental evolution problems, either on the earth or on other planets. LIBS and Raman spectra techniques have shown great advantages in simultaneous multi-component, in-situ, and non-destructive detection and they play an important role in rock composition analysis. In this presentation, six kinds of minerals (Gyp?sum, Spodumene, Barite, Haematite, Moonstone, and Labradorite) were detected by first using LIBS and Raman systems, and then several other methods (PCA, PLS-DA, ANN, and SVM) were used to evaluate the LIBS, Raman, and the fused LIBS/Raman data, respectively. The results indicate the superiority of the fused LIBS/Raman data in mineral classi?cation, which stems from their complementary analysis abilities when studying element composition and structural features.

Quantitative Analysis of Carbon Content in Bituminous Coal by Laser-Induced Breakdown Spectroscopy Using UV Laser Radiation

LI Xiongwei (李雄威)1,3, MAO Xianglei (毛向雷)2, WANG Zhe (王哲)1,et al.
Plasma Sci. Technol. 2015, 17 (11): 928-932 ;  doi: 10.1088/1009-0630/17/11/07
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The carbon content of bituminous coal samples was analyzed by laser-induced break?down spectroscopy. The 266 nm laser radiation was utilized for laser ablation and plasma gener?ation in air. The partial least square method and the dominant factor based PLS method were used to improve the measurement accuracy of the carbon content of coal. The results showed that the PLS model could achieve good measurement accuracy, and the dominant factor based PLS model could further improve the measurement accuracy. The coefficient of determination and the root-mean-square error of prediction of the PLS model were 0.97 and 2.19%, respectively; and those values for the dominant factor based PLS model were 0.99 and 1.51%, respectively. The results demonstrated that the 266 nm wavelength could accurately measure the carbon content of bituminous coal.

Effect of Melting Iron-Based Alloy Temperature on Carbon Content Observed in Laser-Induced Breakdown Spectroscopy

LIN Xiaomei (林晓梅), CHANG Penghui (常鹏辉), CHEN Gehua (陈戈华),et al.
Plasma Sci. Technol. 2015, 17 (11): 933-937 ;  doi: 10.1088/1009-0630/17/11/08
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Our recent work has determined the carbon content in a melting ferroalloy by laser-induced breakdown spectroscopy (LIBS). The emission spectrum of carbon that we obtained in the laboratory is suitable for carbon content determination in a melting ferroalloy but we cannot get the expected results when this method is applied in industrial conditions: there is always an unacceptable error of around 4% between the actual value and the measured value. By comparing the measurement condition in the industrial condition with that in the laboratory, the results show that the temperature of the molten ferroalloy samples to be measured is constant under laboratory conditions while it decreases gradually under industrial conditions. However, temperature has a considerable impact on the measurement of carbon content, and this is the reason why there is always an error between the actual value and the measured value. In this paper we compare the errors of carbon content determination at different temperatures to find the optimum reference temperature range which can fit the requirements better in industrial conditions and, hence, make the measurement more accurate. The results of the comparative analyses show that the measured value of the carbon content in molten state (1620 K) is consistent with the nominal value of the solid standard sample (error within 0.7%). In fact, it is the most accurate measurement in the solid state. Based on this, we can effectively improve the accuracy of measurements in laboratory and can provide a reference standard of temperature for the measurement in industrial conditions.

Improved Measurement Performance of Inorganic Elements in Coal by Laser-Induced Breakdown Spectroscopy Coupled with Internal Standardization

YAO Shunchun (姚顺春)1,2, XU Jialong (徐嘉隆)1, BAI Kaijie (白凯杰)1,et al.
Plasma Sci. Technol. 2015, 17 (11): 938-943 ;  doi: 10.1088/1009-0630/17/11/09
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Laser-induced breakdown spectroscopy was employed to determine the inorganic elements in coal. To improve the measurement’s accuracy and precision, a new internal stan?dardization scheme, which we named changed internal standardization, was compared with the traditional internal standardization and no internal standardization for the analysis of inorganic el?ements. The new internal standardization scheme used the atomic line of carbon at 247.86 nm and the molecular band of CN at 388.34 nm and C2 at 516.32 nm to normalize the lines of inorganic elements that were distributed in the same spectral channel. The performance of the utilization of the new internal standardization scheme was evaluated using a set of coal samples, including twenty calibration samples and five validation samples. The results show that the coefficients of determination R2 and the slope of calibration models coupled with changed internal standard?ization are better than that of the calibration models coupled with fixed internal standardization and no internal standardization. Moreover, the measurement accuracy and reproducibility of changed internal standardization for the analysis of five validation samples also yielded further improvement. The results that we obtained suggest that changed internal standardization could compensate for the matrix effects, as well as the influence of the difference in the spectral response of the light collection system.

Methods of Data Processing for Trace Elements Analysis Using Laser Induced Breakdown Spectroscopy

WANG Rui (王锐), MA Xiaohong (马晓红), YU Qi (余琦), SONG Yang (宋阳), et al.
Plasma Sci. Technol. 2015, 17 (11): 944-947 ;  doi: 10.1088/1009-0630/17/11/10
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With the development of Laser Induced Breakdown Spectroscopy (LIBS), increasing numbers of researchers have begun to focus on problems of the application. We are not just satisfied with analyzing what kinds of elements are in the samples but are also eager to accomplish quantitative detection with LIBS. There are several means to improve the limit of detection and stability, which are important to quantitative detection, especially of trace elements, increasing the laser energy and the resolution of spectrometer, using dual pulse setup, vacuuming the ablation environment etc. All of these methods are about to update the hardware system, which is effective but expensive. So we establish the following spectrum data processing methods to improve the trace elements analysis in this paper: spectrum sifting, noise filtering, and peak fitting. There are small algorithms in these three method groups, which we will introduce in detail. Finally, we discuss how these methods affect the results of trace elements detection in an experiment to analyze the lead content in Chinese cabbage.

Application of Laser Induced Breakdown Spectroscopy in Early Detection of Red Palm Weevil: (Rhynchophorus ferrugineus) Infestation in Date Palm

W. A. FAROOQ1, K. G. RASOOL2, Walid TAWFIK1,3,et al.
Plasma Sci. Technol. 2015, 17 (11): 948-952 ;  doi: 10.1088/1009-0630/17/11/11
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The Kingdom of Saudi Arabia is one of the leading date producing countries. Un?fortunately, this important fruit crop is under great threat from the red palm weevil (RPW) (Rhynchophorus ferrugineus), which is a highly invasive pest. Several techniques, including vi?sual inspection, acoustic sensors, sniffer dogs, and pheromone traps have been tried to detect the early stages of a RPW infestation; however, each method has suffered certain logistical and im-plementation issues. We have applied laser induced breakdown spectroscopy (LIBS) for the early detection of RPW infestation. Through the analysis of the observed LIBS spectra of different infested and healthy samples, we have found presence of Ca, Mg, Na, C, K elements and OH, CN molecules. The spectra also reveal that with the population growth of the pest, the intensity of Mg and Ca atomic lines in LIBS spectra increases rapidly. Similar behavior is observed in the molecular lines of LIBS spectra. The obtained results indicate that the LIBS technique can be used for the early detection of RPW infestation without damaging the date palms.

Signal Detection of Carbon in Iron-Based Alloy by Double-Pulse Laser-Induced Breakdown Spectroscopy

LIN Xiaomei (林晓梅), LI Han (李晗), YAO Qinghua (姚清华)
Plasma Sci. Technol. 2015, 17 (11): 953-957 ;  doi: 10.1088/1009-0630/17/11/12
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Although single-pulse lasers are often used in traditional laser-induced breakdown spectroscopy (LIBS) measurements, their measurement outcomes are generally undesirable be?cause of the low sensitivity of carbon in iron-based alloys. In this article, a double-pulse laser was applied to improve the signal intensity of carbon. Both the inter-pulse delay and the combina?tion of laser wavelengths in double-pulse laser-induced breakdown spectroscopy (DP-LIBS) were optimized in our experiment. At the optimized inter-pulse delay, the combination of a first laser of 532 nm and a second laser of 1,064 nm achieved the highest signal enhancement. The proper?ties of the target also played a role in determining the mass ablation enhancement in DP-LIBS con?guration.

Characterization of Carbon Plasma Evolution Using Laser Ablation TOF Mass Spectrometry

ZHANG Lei (张磊), FENG Chunlei (冯春雷), XIAO Qingmei (肖青梅), et al.
Plasma Sci. Technol. 2015, 17 (11): 958-963 ;  doi: 10.1088/1009-0630/17/11/13
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In this work, a time-of-flight (TOF) mass spectrometer has been used to investigate the distribution of intermediate species and formation process of carbon clusters. The graphite sample was ablated by Nd:YAG laser (532 nm and 1064 nm). The results indicate that the maximum size distribution shifted towards small cluster ions as the laser fluence increased, which happened because of the fragmentation of larger clusters in the hot plume. The temporal evolution of ions was measured by varying the delay time of the ion extraction pulse with respect to the laser irradiation, which was used to provide distribution information of the species in the ablated plasma plume. When the laser fluence decreased, the yield of all of the clusters obviously dropped.

Selection of Spectral Data for Classification of Steels Using Laser-Induced Breakdown Spectroscopy

KONG Haiyang (孔海洋)1,2,3, SUN Lanxiang (孙兰香)1,3, HU Jingtao (胡静涛)1,3,et al.
Plasma Sci. Technol. 2015, 17 (11): 964-970 ;  doi: 10.1088/1009-0630/17/11/14
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Principal component analysis (PCA) combined with artificial neural networks was used to classify the spectra of 27 steel samples acquired using laser-induced breakdown spec?troscopy. Three methods of spectral data selection, selecting all the peak lines of the spectra, selecting intensive spectral partitions and the whole spectra, were utilized to compare the influ?ence of different inputs of PCA on the classification of steels. Three intensive partitions were selected based on experience and prior knowledge to compare the classification, as the partitions can obtain the best results compared to all peak lines and the whole spectra. We also used two test data sets, mean spectra after being averaged and raw spectra without any pretreatment, to verify the results of the classification. The results of this comprehensive comparison show that a back propagation network trained using the principal components of appropriate, carefully se?lected spectral partitions can obtain the best results. A perfect result with 100% classification accuracy can be achieved using the intensive spectral partitions ranging of 357-367 nm.

Influence of Ambient Gas on Laser-Induced Breakdown Spectroscopy of Uranium Metal

ZHANG Dacheng (张大成)1, MA Xinwen (马新文)1, WANG Shulong (王书龙)1,2,et al.
Plasma Sci. Technol. 2015, 17 (11): 971-974 ;  doi: 10.1088/1009-0630/17/11/15
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Laser-induced breakdown spectroscopy (LIBS) is regarded as a suitable method for the remote analysis of materials in any phase, even in an environment with high radiation levels. In the present work we used the third harmonic pulse of a Nd:YAG laser for ablation of uranium metal and measured the plasma emission with a fiber-optic spectrometer. The LIBS spectra of uranium metal and their features in different ambient gases (i.e., argon, neon, oxygen, and nitrogen) at atmospheric pressure were studied. Strong continuum spectrum and several hundreds of emission lines from UI and UII were observed. It is found that the continuum spectrum observed in uranium not only comes from bremsstrahlung emission but is also due to the complex spectrum of uranium. The influence of ambient gas and the gas flow rate for ablation of uranium metal was investigated. The experimental results indicate that the intensity of the uranium lines was enhanced in argon and nitrogen. However, the intensity of uranium lines was decreased in oxygen due to the generation of UO and other oxides. The results also showed that the highest intensity of uranium lines were obtained in argon gas with a gas flow rate above 2.5 L/min. The enhanced mechanism in ambient gas and the influence of the gas flow rate were analyzed in this work.

Determination of Iron in Water Solution by Time-Resolved Femtosecond Laser-Induced Breakdown Spectroscopy

Sergey S. GOLIK1,2, Alexey A. ILYIN1,2, Michael Yu. BABIY1,et al.
Plasma Sci. Technol. 2015, 17 (11): 975-978 ;  doi: 10.1088/1009-0630/17/11/16
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The influence of the energy of femtosecond laser pulses on the intensity of Fe I (371.99 nm) emission line and the continuous spectrum of the plasma generated on the surface of Fe3+ water solution by a Ti: sapphire laser radiation with pulse duration <45 fs and energies up to 7 mJ is determined. A calibration curve was obtained for Fe3+ concentration range from 0.5 g/L to the limit of detection in water solution, and its saturation was detected for concentrations above 0.25 g/L, which is ascribed to self-absorption. The 3σ-limit of detection obtained for Fe in water solution is 2.6 mg/L in the case of 7 mJ laser pulse energy. It is found that an increase of laser pulse energy insignificantly affects on LOD in the time-resolved LIBS and leads to a slight improvement of the limit of detection.

Ultrasonic Nebulizer Assisted LIBS: a Promising Metal Elements Detection Method for Aqueous Sample Analysis

ZHONG Shilei (钟石磊)1,2, ZHENG Ronger (郑荣儿)2, LU Yuan (卢渊)2,et al.
Plasma Sci. Technol. 2015, 17 (11): 979-984 ;  doi: 10.1088/1009-0630/17/11/17
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A newly developed approach for trace metal elements detection for aqueous samples analysis is presented in this paper. The idea of this approach is to improve ablation efficiency by transforming the liquid sample into a dense cloud of droplets using an ultrasonic nebulizer. The resulting droplets are then subjected to analysis by laser induced breakdown spectroscopy (LIBS). A purpose-built ultrasonic nebulizer assisted LIBS (UN-LIBS) system has been applied to the analysis of aqueous samples at trace levels of concentration. Experimental investigations of solution samples were carried out with various dissolved trace metal elements (Mn, Zn, Cu, Pb, Fe, Mg and Na) using this approach. The characteristics of UN-LIBS signal of the elements were investigated regarding the lifetime and S/B ratio and the calibration curves for trace metal elements analyses. The obtained LODs are comparable or much better than the LODS of the reported signal enhancement approaches when the laser pulse energy was as low as 30 mJ. The good linearity of calibration curves and the low LODs shows the potential ability of this method for metal elements analysis application. The density of the electrons was calculated by measuring the Stark width of the line of Hα. The possible mechanism of the LIBS signal enhancement of this approach was briefly discussed.
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