Effect of ambiance on the coal characterization using laser-induced breakdown spectroscopy (LIBS)
TL;DR: In this article, the influence of surrounding gases, such as He, N2, atmospheric air, and Ar, and gas flow rate on the laser-induced breakdown spectroscopy (LIBS) characterization of coals in free space is studied.
Abstract: The influence of surrounding gases, such as He, N2, atmospheric air, and Ar, and gas flow rate on the laser-induced breakdown spectroscopy (LIBS) characterization of coals in free space is studied. The atomic and molecular carbon (C2 and CN) emission intensities are observed to be higher in Ar and N2 ambiance. Quantitative analysis of carbon and ash content in different coal samples is carried out using the carbon bound atomic and molecular emission signals and the ash forming elements (Si, Fe, Mg, Al, Ca, Na, and K) signals. The sum of the LIBS emission of the all and major ash forming elements increased linearly with an increase in the ash content. Similarly, the ratio between the carbon signals (C I, CN, and C2) and the sum of major ash forming elements (Si, Al, Fe, and Ca) also showed a linear increase with the increase in carbon content in coal samples. The linear coefficient of regression, R2, was estimated to be 0.67, 0.58, and 0.85, and the root mean square of calibration samples was estimated to be 5.71, 5.82, and 5.57 wt% using the partial least square regression (PLSR) method for air (no flow), N2, and Ar atmosphere, respectively. The precision and accuracy of the carbon measurement in coal samples by the LIBS technique using the PLSR method were higher in the presence of Ar than air or N2 atmosphere due to the plasma shielding effect.
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TL;DR: In this article, a review of laser-induced breakdown spectroscopy (LIBS) applications for coal ranks, combustion efficiency, and environmental protection is presented, together with a description of limitations and the potential developing trend for this topic.
Abstract: With massive coal consumption in the industry, the increasing requirements for improving combustion efficiency and environmental protection raise widespread interests. Laser-induced breakdown spectroscopy (LIBS) shows the merits of high-speed, minimally destructive, simple preparation, etc. Combining it with the analytical chemistry methods have become a promising way for coal analysis. In this work, LIBS instruments for collecting coal spectra, pretreatment methods for coal samples, preprocessing of coal data, and analytical chemistry methods for coal analysis were summarized. Moreover, LIBS applications, including coal ranks, combustion efficiency, and environmental protection, are provided. Finally, this review proposes a description of limitations and the potential developing trend for this topic.
47 citations
15 Sep 2021
TL;DR: In this article, a 2D correlation analysis was used for achieving a significant improvement in the signal-to-noise (S/N) ratio of laser-induced breakdown spectroscopy (LIBS) data.
Abstract: In this study, two-dimensional (2D) correlation analysis was utilized for achieving a significant improvement in the signal-to-noise (S/N) ratio of laser-induced breakdown spectroscopy (LIBS) data. Time-resolved LIBS spectra of metallic, bimetallic targets and the normal LIBS spectra of bimetallic targets with varying compositions were used for the detailed analysis. The diagonal of the matrix in the synchronous spectra was used to demonstrate the improvement in the signal-to-noise ratio (SNR). An improvement in the peak intensities by few orders of magnitude accompanied by suppression in the noise was observed. The correlations between LIBS peaks were also visualized using the 2-D plots. The correlation strengths of atomic transitions were visualized in aluminium (Al), copper (Cu), and brass whereas correlation strengths of atomic and ionic transitions were visualized in Au-Ag bimetallic targets with different compositions (Au30Ag70, Au50Ag50, Au80Ag20). The improved spectra were subsequently used in the principal component analysis for classification studies of four compositions of bimetallic targets (Au20Ag80, Au30Ag70, Au50Ag50, and Au80Ag20). The variance of the first three principal components was found to be improved from the analysis. The accumulated percentage of explained variance of ∼95 was achieved with the first three components from improved spectra whereas only ∼80 was achieved with the regular LIBS spectra from PCA studies. Furthermore, using this correlation analysis we demonstrate a significant improvement in the SNR of CN and C2 peaks in the femtosecond LIBS spectra of two polymer samples obtained from a standoff distance of 6 m, which may prove substantial for improved classifications studies.
6 citations
6 citations
TL;DR: In this paper , a calibration-free laser-induced breakdown spectroscopy (LIBS) was used to determine phosphorus (P) concentration in phosphogypsum (PG) waste samples using a 50 mJ Q-switched Nd: YAG laser.
Abstract: This work represents a novel method to determine phosphorus (P) concentration in phosphogypsum (PG) waste samples using calibration-free laser-induced breakdown spectroscopy (LIBS). A 50 mJ Q-switched Nd: YAG laser has generated the PG LIBS spectrum. Spectroscopic analysis of plasma evolution has been characterized by electron density Ne and electron temperature Te using the emission intensity and stark broadening for P I characteristic lines 213.61, 214.91, and 215.40 nm under non-purged (air) and purged (helium) conditions. It was found that both Te and Ne have significant changes linearly with P concentrations 4195, 5288, 6293, and 6905 ppm. The plasma Te and Ne values increased from about 6900 to 10,000 K and 1.1 × 1017 to 3.4 × 1017 cm−3, respectively, for the non-purged PG. On the other hand, Te and Ne ranged from 8200 to 11,000 K and 1.4 × 1017 to 3.5 × 1017 cm−3, respectively, for the PG purged with helium. It is concluded that Te and Ne values represent a fingerprint plasma characterization for a given P concentration in PG samples, which can be used to identify P concentration without a PG's complete analysis. These results demonstrate a new achievement in the field of spectrochemical analysis of environmental applications.
6 citations
TL;DR: In this article, a benchtop laser-induced breakdown spectroscopy is demonstrated to determine the elemental carbon content present in raw coal used for combustion in power plants, and the spectral intensities of molecular CN and C2 emission are measured together with the atomic carbon (C) and other inorganic elements (Si, Fe, Mg, Al, Ca, Na, and K) in the spectrum of coal.
Abstract: A benchtop laser-induced breakdown spectroscopy is demonstrated to determine the elemental carbon content present in raw coal used for combustion in power plants. The spectral intensities of molecular CN and C2 emission are measured together with the atomic carbon (C) and other inorganic elements (Si, Fe, Mg, Al, Ca, Na, and K) in the laser-induced breakdown spectroscopy spectrum of coal. The emission persistence time of C2 molecule emission is measured from the coal plasma generated by a nanosecond laser ablation with a wavelength of 266 nm in the Ar atmosphere. The emission persistence time of molecular C2 emission along with the spectral intensities of major ash elements (Fe, Si, Al, and Ca) and carbon emissions (atomic C, molecular CN, and C2) shows a better relationship with the carbon wt% of different coal samples. The calibration model to measure elemental carbon (wt%) is developed by combining the spectral characteristics (spectral intensity) and the temporal characteristics (emission persistence time of C2 molecule emission). The temporal characteristic studies combined with the spectroscopic data in the partial least square regression model have resulted in an improvement in the root mean square error of validation, and the relative standard deviation is reduced from 10.8% to 4.1% and from 11.3% to 6.0%, respectively.
5 citations
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13 Nov 1997TL;DR: The diagnosis of plasmas using spectroscopic observations has its origins in various older disciplines, including astronomy and discharge physics as mentioned in this paper, and the need for non-interfering diagnostics arose and spectroscopy was applied to determine the physical state and chemical abundance of the studied.
Abstract: The diagnosis of plasmas using spectroscopic observations has its origins in various older disciplines, including astronomy and discharge physics. As laboratory plasma physics evolved from low-density, low-temperature discharges to higher energy density plasmas, the need for non-interfering diagnostics arose and spectroscopy was applied to determine the physical state and chemical abundance of the plasmas studied.
1,120 citations
TL;DR: In this paper, the authors reviewed the literature on laser-induced breakdown spectroscopy by dividing the literature into three categories according to target phase: solid, liquid, or gas.
Abstract: Laser-induced breakdown spectroscopy is reviewed by dividing the literature into three categories according to target phase: solid, liquid, or gas. Within each category, the literature is ...
456 citations
TL;DR: In this article, the authors used line profiles of several ionic species to infer electron temperature and density at several sections located in front of the target surface, and the validity of the assumption of local thermodynamic equilibrium was discussed in light of the results obtained.
Abstract: Plasma generated by fundamental radiation from a Nd:YAG laser focused onto a graphite target is studied spectroscopically. Measured line profiles of several ionic species were used to infer electron temperature and density at several sections located in front of the target surface. Line intensities of successive ionization states of carbon were used for electron temperature calculations. Stark broadened profiles of singly ionized species have been utilized for electron density measurements. Electron density as well as electron temperature were studied as functions of laser irradiance and time elapsed after the incidence of laser pulse. The validity of the assumption of local thermodynamic equilibrium is discussed in light of the results obtained.
323 citations
TL;DR: In this article, FactSage has been used to calculate the liquidus temperatures of coal ash samples and the proportions of the various phases present as a function of temperature, and the results show that the AFT of coal Ash samples first decrease with increasing CaO, Fe2O3, and MgO contents, then reach a minimum value, before increasing once more.
Abstract: The ash fusion temperatures (AFTs) of coal mineral matter at high temperature are important parameters for all gasifiers. Experiments have been conducted in which mixtures of selected coal ashes and SiO2, Al2O3, CaO, Fe2O3, and MgO were subjected to the standard test for ash fusibility. The computer software package FactSage has been used to calculate the liquidus temperatures of coal ash samples and the proportions of the various phases present as a function of temperature. The results show that the AFTs of coal ash samples first decrease with increasing CaO, Fe2O3, and MgO contents, then reach a minimum value, before increasing once more. However, for the effect of S/A ratio, its AFTs are always increased with increasing S/A ratios. The measured AFTs all show variations with mixture composition that correlated closely with liquidus temperatures for the appropriate pseudoternary phase diagrams. The liquidus and AFTs generally showed parallel compositional trends but are displaced from each other because ...
177 citations
TL;DR: In this paper, a container-integrated mobile femtosecond terawatt laser system with integrated detection unit (Teramobile) was used for remote laser-induced breakdown spectroscopy (R-LIBS) on copper and aluminium samples with targets located at 25 m away from the container.
Abstract: Using a container-integrated mobile femtosecond terawatt laser system with integrated detection unit (Teramobile), we have demonstrated remote laser-induced breakdown spectroscopy (R-LIBS) on copper and aluminium samples with targets located at 25 m away from the container. The ability of our laser system to generate pulses in the femtosecond, picosecond and nanosecond regimes allowed us to perform direct comparisons between these three pulse durations. The dependence of the fluorescence signal on laser pulse energy showed a nonlinear behavior with a threshold, which is consistent with the previous observations for laser ablation. Such nonlinear behavior leads to a dependence of the LIBS signal on the temporal-spectral shape of the laser pulse. We showed especially that the transform-limited pulse does not optimize the fluorescence. A properly applied chirp allows an increase of the LIBS signal. Understanding and optimization of the chirp effect would improve the detection limit of the LIBS using a femtosecond laser (Femto-LIBS) and lead to a larger detection distance. Furthermore the use of pulse shaping should enhance the detection specificity for the cases of spectral overlapping between several elements to be identified.
130 citations