Characterization of laser-induced plasma in a vacuum using laser ablation mass spectrometry and laser-induced breakdown spectrometry

An analytical system for simultaneously monitoring laser-ablation mass spectra and laser-induced breakdown spectra for solid sample has been developed. The performance of the developed system is evaluated by measuring characteristics of laser-induced plasma such as lifetime of ions inside the plasma and laser power dependence of mass resolution for solid samples. Adopted samples are gadolinium plate, gadolinium coated on stainless steel plate, and one of the NIST standard samples, C-1248 (Ni–Cu alloy). The threshold laser energy in obtaining mass spectrum was dependent on the type of sample characteristics in the order of a few MW/cm², while a few hundred MW/cm² was necessary in order to observe emission signal. When laser energy was increased enough to produce emission signal, mass resolution of the time-of-flight mass spectrum was severely deteriorated. The lifetime of the continuum ion signal was estimated 200 and 250 ns for Gd plate and C-1248, respectively, by monitoring emission signals, while the lifetime of ions near sample surface was estimated as 400 ns and 430 ns for Gd plate and C-1248, respectively. The deterioration of mass resolution can be understood as originating from the space charge effect in high plasma density in a given space and different velocity distribution of ions inside the plasma, while longer lifetime of ions near sample surface can be understood as originating from speed of ion ejection near the sample surface. The details of the characteristics of laser-induced plasma are discussed and optimum experimental conditions for simultaneous monitoring are suggested.     

Applications of laser-induced breakdown spectrometry (LIBS) in surface analysis

The applicability of laser-induced breakdown spectrometry (LIBS) for surface analysis is presented in terms of its lateral and depth resolution. A pulsed N₂ laser at 337.1 nm (3.65 J/cm²) was used to irradiate solar cells employed for photovoltaic energy production. Laser produced plasmas were collected and detected using a charge-coupled device. An experimental device developed in the laboratory permits an exact synchronization of sample positioning using an XY motorized system with laser pulses. Multielement analysis with lateral resolution of up to 30 m is feasible with the present system. Three-dimensional capabilities of the system are used for studies on the distribution of carbon impurities at the surface of the solar cells.     

Applications of laser-induced breakdown spectrometry (LIBS) in surface analysis

The applicability of laser-induced breakdown spectrometry (LIBS) for surface analysis is presented in terms of its lateral and depth resolution. A pulsed N(2) laser at 337.1 nm (3.65 J/cm(2)) was used to irradiate solar cells employed for photovoltaic energy production. Laser produced plasmas were collected and detected using a charge-coupled device. An experimental device developed in the laboratory permits an exact synchronization of sample positioning using an XY motorized system with laser pulses. Multielement analysis with lateral resolution of up to 30 microm is feasible with the present system. Three-dimensional capabilities of the system are used for studies on the distribution of carbon impurities at the surface of the solar cells.     

Analysis of heavy metals in soils using laser-induced breakdown spectrometry combined with laser-induced fluorescence

The investigation of a hyphenated technique combining laser-induced breakdown spectrometry (LIBS) with laser-induced fluorescence (LIF) for the analysis of heavy metals in soils is described. In order to evaluate the applicability of the technique for fast in-situ analytical purposes, measurements were performed at atmospheric pressure. The plasma radiation was detected using a Paschen–Runge spectrometer equipped with photomultipliers for the simultaneous analysis of 22 different elements. The photomultiplier signals were processed by a fast gateable multichannel integrator. Calibration curves were recorded using a set of spiked soil samples. Limits of detection were derived from these curves for As (3.3 μg/g), Cd (6 μg/g), Cr (2.5 μg/g), Cu (3.3 μg/g), Hg (84 μg/g), Ni (6.8 μg/g), Pb (17 μg/g), Tl (48 μg/g) and Zn (98 μg/g) using the LIBS signals. LIBS-LIF measurements were performed for Cd and Tl. The excitation wavelength as well as the detected fluorescence wavelength for Cd was 228.8 nm. Alternatively, Tl was excited at 276.8 nm, where the observed fluorescence wavelength was 351.9 nm. The calibration curves based on the LIF signals showed significantly improved limits of detection of 0.3 and 0.5 μg/g for Cd and Tl, respectively.     

Application of laser-induced breakdown spectrometry in urban health

The use of laser-induced breakdown spectrometry (LIBS) for elemental determination and detection in urban health is reviewed. It highlights the unique use of LIBS in fiber-based optics, in process control, and for field instrumentation. Selected applications confirm that LIBS could be the technique of choice for many applications in urban health.     

Spatial distribution profiles of magnesium and strontium in speleothems using laser-induced breakdown spectrometry

Laser-induced breakdown spectrometry (LIBS) has been applied to spatially locate several atomic species in speleothems taken from the Nerja’s Cave (Málaga, Spain). Spatial distribution profiles of Mg at 285.21 nm and Sr at 407.77 nm were obtained while the laser was rastered through different paths along the sample. These elements were selected due to their importance as palaeoclimatic indicators. The 532 nm output of a Nd:YAG laser was used to irradiate the samples and generate the plasma that was spectrally analyzed and detected by using an intensified CCD detector. The signals were normalized to the Ca line to minimize pulse-to-pulse fluctuations in the laser source. Several studies were carried out to check for the point-to-point heterogeneity of the natural speleothem.     

Spatial distribution profiles of magnesium and strontium in speleothems using laser-induced breakdown spectrometry

Laser-induced breakdown spectrometry (LIBS) has been applied to spatially locate several atomic species in speleothems taken from the Nerja’s Cave (Málaga, Spain). Spatial distribution profiles of Mg at 285.21 nm and Sr at 407.77 nm were obtained while the laser was rastered through different paths along the sample. These elements were selected due to their importance as palaeoclimatic indicators. The 532 nm output of a Nd:YAG laser was used to irradiate the samples and generate the plasma that was spectrally analyzed and detected by using an intensified CCD detector. The signals were normalized to the Ca line to minimize pulse-to-pulse fluctuations in the laser source. Several studies were carried out to check for the point-to-point heterogeneity of the natural speleothem. Received: 1 August 1997 / Revised: 23 October 1997 / Accepted: 30 October 1997     

Multi-elemental mapping of a speleothem using laser-induced breakdown spectroscopy

Speleothems represent an important record of the paleoclimate, and more generally past environmental changes thanks to their laminar structure which is related to variations in rainfall and vegetation throughout the seasons and to their elemental as well as structural compositions which are sensitive to climatic and environmental conditions during their growth. Studies of their composition, especially those with spatial resolution, reveal rich information for paleoclimatology. In this paper, we demonstrate that laser-induced breakdown spectroscopy (LIBS) provides a suitable tool for elemental analysis and especially for 2-dimensional elemental mapping of speleothems. Main, minor, as well as trace elements can be analyzed with this technique. The temporal evolution of the induced plasma is first studied in order to determine a suitable detection window for emission spectrum recording following the impact of the laser pulse on the sample. The matrix effect is then evaluated with a scan on the sample surface by measuring the electron density and the temperature of the plasmas at different positions of the analyzed surface. Concentration mapping is performed for minor and trace elements such as Na, Mg, Al, Si, K, Fe and Sr, by measuring relative variations of line emission intensities from these elements. Finally, correlations in concentration among detected elements are determined. Groups of correlated elements can be attributed to different mineralogical phases.     

Determination of chromium in steel by atomic-absorption spectrometry with an air-acetylene flame

A new atomic-absorption procedure is described for the determination of chromium, at levels up to 1%, in steel. The method involves the use of the air-acetylene flame and incorporates 8-hydroxyquinoline as a releasing agent to suppress metallic interferences. Chemical operations have been reduced to a minimum in order to provide a simple, rapid and accurate procedure.     

Fast vacuum slag analysis in a steel works by laser-induced breakdown spectroscopy

Samples taken from the liquid slag layer in a vacuum degasser station of a steel works are analyzed after solidification by laser-induced breakdown spectroscopy (LIBS) without any further sample preparation. The mass fractions of the major components of the vacuum slags are in the range of 50–60% for CaO, 0.5–12% for SiO₂ and 20–40% for Al₂O₃. The species are distributed heterogeneously in the solid samples having diameters of 35 mm. Furthermore the color and structure of the samples is varying significantly. A fast spatial averaging of representative sample areas is realized by spatial laser beam shaping. Multivariate calibration and its validation is carried out with calibration and validation sets of production samples which are analyzed by X-ray fluorescence measurements or as borate beads for reference. The laser-induced breakdown spectroscopy instrument is installed in the steel works at a distance of about 10 m from the vacuum degasser. The laser-induced breakdown spectroscopy analysis runs automatically after the sample placement and it takes 80 s including data transfer to the host computer of the steel works. Operational tests are carried out to demonstrate the feasibility of a fast slag analysis in the harsh environment of the vacuum degasser plant.     

Quantification of sodium contaminant on steel surfaces using pulse CO2 laser-induced breakdown spectroscopy

Corrosion is one of the main reasons for in-core accidents in liquid sodium-cooled fast reactors, especially accidents due to fuel cladding pipe damage. It is urgently required to investigate what kind of compound is produced as a corrosion product after the interaction between stainless steel and sodium in fast breeder reactors (FBR). In this work, the identification and quantification of sodium contaminant on steel surfaces has been conducted using laser-induced breakdown spectroscopy utilizing the specific characteristics of a pulse transversely excited atmospheric CO₂ laser. Experimentally, a pulse TEA CO₂ laser (Shibuya, 10.64 μm, 200 ns) was directed and bombarded onto the sodium contaminant deposited on the surface of stainless steel. An excellent emission spectrum of sodium from the contaminant was obtained without any disturbance from analytical lines from the steel itself. A quantification of sodium contaminant on the steel surface has been successfully made by a linear calibration curve obtained from steel containing various concentrations of sodium. The limit of detection of sodium on the metal surface was estimated to be 0.5 mg/kg. Also, a comparative sodium analysis study was qualitatively made by using LIBS utilizing a pulse Nd:YAG laser. The results demonstrate that the present technique of TEA CO₂ LIBS is far superior to the case of Nd:YAG LIBS, as proven by an excellent emission spectrum of sodium with optimum intensity, and low noise and background emission.     

Quantitative analysis of samples at high temperature with remote laser-induced breakdown spectrometry using a room-temperature calibration plot

A method for measurement of composition in samples at high temperature using a calibration curve performed at low temperature is presented. The method uses a transfer function which avoids the need for building a calibration plot at high temperature. The method has shown suitability for high-temperature measurements up to 850 °C in steel slags exhibiting coefficients of correlation of 0.991 and 0.989 for Si / Ca and Mg / Ca ratios, respectively. The accuracy of the method has been assessed by comparing the results with remote LIBS at high temperature to those by XRF at room temperature. As an example of its versatility, the method has been applied to the determination of the basicity index of steel slags at high temperature.     

Determination of phosphorus in steel by the combined technique of laser induced breakdown spectrometry with laser induced fluorescence spectrometry

Laser induced breakdown spectrometry (LIBS) combined with laser induced fluorescence spectrometry (LIFS) has been applied for detection of trace-level phosphorus in steel. The plasma induced by irradiation of Nd:YAG laser pulse for ablation was illuminated by the 3rd harmonic of Ti:Sapphire laser tuned to one of the resonant lines for phosphorus in the wavelength region of 253–256 nm. An excitation line for phosphorus was selected to give the highest signal-to-noise ratio. Fluorescence signals, P213.62 and P214.91 nm, were observed with high selectivity at the contents as low as several tens µg g^− 1. Fluorescence intensities were in a good linear correlation with the contents. Fluorescence intensity ratio of a collisionally assisted line (213.62 nm) to a direct transition line (214.91 nm) was discussed in terms of the analytical conditions and experimental results were compared with a calculation based on rate equations. Since the fluorescence signal light in the wavelength range longer than 200 nm can be transmitted relatively easily, even through fiber optics of moderate length, LIBS/LIFS would be a versatile technique in on-site applications for the monitoring of phosphorus contents in steel.     

Determination of poisonous metals in wastewater collected from paint manufacturing plant using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) system was developed for determination of toxic metals in wastewater collected from local paint manufacturing plant. The plasma was generated by focusing a pulsed Nd:YAG laser at 1064 nm on the solid residue from wastewater collected from paint industry. The concentration of different elements of environmental significance like, lead, copper, chromium, calcium, sulphur, magnesium, zinc, titanium, strontium, nickel, silicone, iron, aluminum, barium, sodium, potassium and zirconium, in paint wastewater were 6, 3, 4, 301, 72, 200, 20, 42, 4, 1, 35, 120, 133, 119, 173, 28 and 12 mg kg⁻¹, respectively. The evaluation of potential and capabilities of LIBS as a rapid tool for paint industry effluent characterization is discussed in detail. Optimal experimental conditions were evaluated for improving the sensitivity of our LIBS system through parametric dependence study. The laser-induced breakdown spectroscopy (LIBS) results were compared with the results obtained using standard analytical technique such as inductively coupled plasma emission spectroscopy (ICP). The relative accuracy of our LIBS system for various elements as compared with ICP method is in the range of 0.03-0.6 at 2.5% error confidence. Limits of detection (LOD) of our LIBS system were also estimated for the above mentioned elements.     

Determination of silicon in plant materials by laser-induced breakdown spectroscopy

In spite of the importance of Si for improving the productivity of many important crops, such as those from the Poaceae family (e.g. sugar cane, maize, wheat, rice), its quantitative determination in plants is seldom carried out and restricted to few laboratories in the world. There is a survey of methods in the literature, but most of them are either laborious or difficult to validate in view of the low availability of reference materials with a certified Si mass fraction. The aim of this study is to propose a method for the direct determination of Si in pellets of plant materials by laser-induced breakdown spectroscopy (LIBS). The experimental setup was designed by using a Q-switched Nd:YAG laser at 1064 nm (5 ns, 10 Hz) and the emission signals were collected by lenses into an optical fiber coupled to an Echelle spectrometer equipped with an intensified charge-coupled device. Experiments were carried out with leaves from 24 sugar cane varieties, with mass fractions varying from ca. 2 to 10 g kg^− 1 Si. Pellets prepared from cryogenically ground leaves were used as test samples for both method development and validation of the calibration model. Best results were obtained when the test samples were interrogated with laser fluence of 50 J cm^− 2 (750 μm spot size) and measurements carried out at Si I 212.412 nm emission line. The results obtained by LIBS were compared with those from inductively coupled plasma optical emission spectrometry after oven-induced alkaline digestion, and no significant differences were observed after applying the Student's t-test at 95% confidence level. The trueness of the proposed LIBS method was also confirmed from the analysis of CRM GBW 07603 (Bush branches and leaves).     

Three-dimensional distribution analysis of platinum,palladium and rhodium in auto catalytic converters using imaging-mode laser-induced breakdown spectrometry

Laser-induced breakdown spectrometry (LIBS) is reported here as an effective technique to describe the volume distribution of platinum, rhodium and palladium in catalytic converters installed in motor vehicles. Using the second harmonic output of a Nd:YAG laser and a CCD-based atomic emission spectrometer, LIBS is used in multielemental, imaging-mode to permit the simultaneous analysis of the several elements present in the converter, including the internal standard. The data are reported with a lateral resolution of 1.75 mm over a fresh catalytic structure which is 128 mm long. The concentrational variability of the platinum group metals (PGMs) varies in the range ∼3–23% relative standard deviation depending on the element, the substrate and the direction investigated. The causes of the dispersion observed are discussed.     

Processing of shot-to-shot raw data to improve precision in laser-induced breakdown spectrometry microprobe

In order to set up the precision limit that can be reached with laser-induced breakdown spectrometry microprobe, a steel sample was scanned by using a 6-µm diameter spot. Besides being close to the limit of the technique, such a spot diameter resulted in a small plasma size that minimized self-absorption effects. To minimize shot noise, Cr and Fe were used as test elements because of their high contents. Scan consisted of 25 successive matrices formed by 5 × 6 shots, i.e. a total of 750 shots. Results were studied as a whole, as well as between matrices and within matrices, to search for inhomogeneity, outliers and drift. Except a few outliers, the main contribution in the experimental RSD was the drift either within a matrix or between matrices. Drift attributed to laser warm up could be compensated for either by using a polynomial fitting or by using the other element. %RSD significantly below 2 were then obtained demonstrating that there is no penalty in terms of precision to perform laser microprobe using a series of single shots.     

The effect of cerium pre-treatment on the corrosion resistance of steel sheets

The steel samples have been coated with cerium layer by cathodic electrolytic deposition from the Ce(NO₃)₃·6H₂O solution in aqueous ethyleneglycol in the presence of hydrogen peroxide. The influence of the coating parameters (cathodic current density, pH, cerium concentration, hydrogen peroxide concentration, temperature, and treatment duration) on the surface properties; the optimum conditions of the formation of corrosion preventing coating have been elucidated. Hydrogen peroxide concentration and pH are the major factors influencing the deposition process. The corrosion resistance has been further enhanced after treatment with Na₃PO₄·12H₂O solution. The cerium-coated samples have been subsequently coated by cathodic electrostatic deposition from the colloidal solution of the paint. The coated materials have been subjected to mechanical testing (hardness, impact, cross cut, bending, and cupping tests), and their structure has been visualized by electron microscopy. The cerium coating has been found to improve the steel corrosion resistance by 15%.     

On chemical reactions in the laser-induced breakdown of a liquid

It is shown experimentally that a laser-induced breakdown of a liquid is accompanied by chemical reactions initiated by radicals and excited species formed in the spark. It is found that, in water, the laser-induced breakdown is accompanied by the dissociation of water and dissolved nitrogen molecules with the formation of HNO₂ and HNO₃, while, in a FeSO₄ aqueous solution, by the Fe²⁺ → Fe³⁺ oxidation reaction. It is assumed that the mechanism of the process is analogous to that of the action of ionizing radiations and the chemical action of ultrasonically induced cavitation (it is proposed that this mechanism of chemical action of a laser-induced spark proposed be termed indirect). Energy yields of these reactions are found to be of the same order of magnitude as for sonochemical redox reactions. It is shown that the laser-induced breakdown of an aqueous solution of maleic acid is accompanied by its stereoisomerization into fumaric acid, a process catalyzed by small amounts of an alkyl bromide. It is established that, for the formation of fumaric acid in a laser-induced spark, the energy yield is about five orders of magnitude higher than that typical of the above-mentioned redox reactions in the laser-induced spark.