Laser Induced Breakdown Spectroscopy Probe Research Articles

Mechanical stirring: Novel engineering approach for in situ spectroscopic analysis of melt at high temperature

This paper proposes a novel engineering approach to control molten metals at high temperatures considering the industrial environment of such materials. To reduce analysis time and cost, in-line analysis techniques are more advantageous as they provide real-time information about melt composition. For this reason, recent research works focus on the development of new devices based on LIBS (Laser Induced Breakdown Spectroscopy). These devices allowed for analyzing impurities inside molten metals with great performance. However, improvements related to the immersion probe conception are still required. Indeed, the previous design used bubbling inside the melt, leading to spatial instabilities of the surface analyzed by LIBS. The solution presented here is mechanical stirring by innovative rotary blades which will be a part of an immersion LIBS probe. Their rotation will generate a representative, renewed, and stable surface that will be targeted by spectroscopic techniques in general and particularly by LIBS laser for molten metal monitoring at high temperatures. This solution was validated using experimental tests based on particle imaging velocimetry (PIV) in water at room temperature and then applied to silicon melt at high temperatures. To do so, it was necessary to design a system that allows the introduction of the blade in the melt and controls its rotation.

In situ elemental analysis and failures detection during additive manufacturing process utilizing laser induced breakdown spectroscopy.

The feasibility of in situ quantitative multielemental analysis and production failures detection by laser induced breakdown spectroscopy (LIBS) has been demonstrated during direct energy deposition process in additive manufacturing. Compact LIBS probe was developed and equipped with the laser cladding head installed at industrial robot for real-time chemical quantitative analysis of key components (Ni, W) during the synthesis of high wear resistant coatings of nickel alloy reinforced with tungsten carbide particles. Owing to non-uniform distribution of tungsten carbide grains in the upper surface layer the only acceptable choice for LIBS sampling was made to the melt pool at growing clad. Laser ablation at powder particles above melt pool was insignificant for LIBS plasma properties due to low intensity and low probability of plasma breakdown at powder particles. No impact of LIBS sampling on cladding process and clad properties was observed according to optical and scanning electron microscopies. The feasibility of in situ LIBS quantitative elemental analysis of key components (tungsten and nickel) has been demonstrated during the cladding process. LIBS analysis results were in good agreement with offline measurements by electron energy dispersive X-ray spectroscopy and X-ray fluorescence spectroscopy. Finally, LIBS technique was demonstrated to be a good tool for real-time detection of cladding process failures (poor laser beam quality, undesirable variation of components concentrations).

Laser induced breakdown spectroscopy for in-situ multielemental analysis during additive manufacturing process

A feasibility of real-time quantitative multielemental analysis during parts growth by additive manufacturing technology has been demonstrating for the first time using laser induced breakdown spectroscopy (LIBS). A low weight and compact LIBS probe was developed to equip the laser cladding head installed at six axis industrial robot. LIBS quantitative analysis of key components (carbon and tungsten) has been demonstrated in real-time conditions during synthesis of high wear resistant coatings of nickel alloy reinforced with tungsten carbide particles. Hot solidified clad as well as a melt pool surface was sampled by LIBS probe but better analytical results were achieved for the latter case due to low partial sinking of heavy tungsten carbide particles in nickel matrix. LIBS system was calibrated for quantitative measurements by offline analysis with energy dispersive X-ray spectrometry (EDX). We didn’t observe any impact of laser ablation (LIBS sampling) on clad dimensions even when LIBS probe ablated melt pool. LIBS system was capable to quantify concentrations for both light (carbon, silicon) and heavy (nickel, tungsten, chromium, etc.) elements at frequency of 10 Hz. A good correspondence was achieved between online LIBS measurements and offline analysis opens wide perspectives for LIBS technique as a powerful tool for controlling process of parts growth by additive manufacturing

In situ multi-elemental analysis by laser induced breakdown spectroscopy in additive manufacturing

The feasibility of in situ quantitative multi-elemental analysis during the additive manufacturing process has been demonstrated for the first time using laser induced breakdown spectroscopy (LIBS). The coaxial laser cladding technique was utilized for the production of highly wear-resistant coatings (nickel alloy reinforced with tungsten carbide grains). High-quality production as well as gradient composition coating synthesis required an online technique for quantitative elemental analysis. A low-weight, compact LIBS probe was designed to equip the laser cladding head installed at an industrial robot. Hot solidified clad as well as a melt pool surface was sampled by the LIBS probe but meaningful analytical results were achieved only for the latter case due to non-uniform distribution of tungsten carbide grains in the upper surface layer. LIBS sampling inside the melt pool did not affect the clad properties according to optical microscopy and scanning electron microscopy measurements. On-line LIBS quantitative analysis of key components (carbon and tungsten) was demonstrated during the synthesis of highly wear-resistant coatings and obtained results were in good agreement with offline analysis performed by electron energy dispersive X-ray spectroscopy, X-ray fluorescence spectroscopy, and the combustion infrared absorption method. In situ quantitative multielemental analysis by LIBS is a perspective control or/and feedback tool to improve quality of compositionally graded materials in additive manufacturing.

Development of a laser-induced plasma probe to measure gas phase plasma signals at high pressures and temperatures

The ability of laser induced breakdown spectroscopy (LIBS) technique for on line simultaneous measurement of elemental concentrations has led to its application in a wide number of processes. The simplicity of the technique allows its application to harsh environments such as present in boilers, furnaces and gasifiers. This paper presents the design of a probe using a custom optic which transforms a round beam into a ring (Donut) beam, which is used for forming a plasma in an atmosphere of nitrogen at high pressure (20bar) and temperature (200°C). The LIBS experiments were performed using a high pressure cell to characterize and test the effectiveness of the donut beam transmitted through the LIBS probe and collect plasma signal in back scatter mode. The first tests used the second harmonic of a Nd:YAG laser, pulse width 7ns, to form a plasma in nitrogen gas at five different pressures (1, 5, 10, 15 and 20bar) and three different gas temperatures (25, 100 and 200°C). The uniqueness of this probe is the custom made optic used for reshaping the round laser beam into a ring (Donut) shaped laser beam, which is fed into the probe and focused to form a plasma at the measurement point. The plasma signal is collected and collimated using the laser focusing lens and is reflected from the laser beam axis onto an achromatic lens by a high reflection mirror mounted in the center section of the donut laser beam. The effect of gas pressure and temperature on N(I) lines in the high pressure cell experiment shows that the line intensity decreases with pressure and increases with temperature. Mean plasma temperature was calculated using the ratios of N(I) line intensities ranging from 7400K to 8900K at 1bar and 2400K to 3200K at 20bar for the three different gas temperatures. The results show that as a proof of principle the donut beam optics in combination with the LIBS probe can be used for performing extensive LIBS measurements in well controlled laboratory environment as well as harsh and demanding environments of practical devices at both high pressures and temperatures.

Monitoring Uranium, Hydrogen, and Lithium and Their Isotopes Using a Compact Laser-Induced Breakdown Spectroscopy (LIBS) Probe and High-Resolution Spectrometer

The development of field-deployable instruments to monitor radiological, nuclear, and explosive (RNE) threats is of current interest for a number of assessment needs such as the on-site screening of suspect facilities and nuclear forensics. The presence of uranium and plutonium and radiological materials can be determined through monitoring the elemental emission spectrum using relatively low-resolution spectrometers. In addition, uranium compounds, explosives, and chemicals used in nuclear fuel processing (e.g., tributyl-phosphate) can be identified by applying chemometric analysis to the laser-induced breakdown (LIBS) spectrum recorded by these spectrometers. For nuclear forensic applications, however, isotopes of U and Pu and other elements (e.g., H and Li) must also be determined, requiring higher resolution spectrometers given the small magnitude of the isotope shifts for some of these elements (e.g., 25 pm for U and 13 pm for Pu). High-resolution spectrometers will be preferred for several reasons but these must fit into realistic field-based analysis scenarios. To address the need for field instrumentation, we evaluated a previously developed field-deployable hand-held LIBS interrogation probe combined with two relatively new high-resolution spectrometers (λ/Δλ ~75,000 and ~44,000) that have the potential to meet field-based analysis needs. These spectrometers are significantly smaller and lighter in weight than those previously used for isotopic analysis and one unit can provide simultaneous wide spectral coverage and high resolution in a relatively small package. The LIBS interrogation probe was developed initially for use with low resolution compact spectrometers in a person-portable backpack LIBS instrument. Here we present the results of an evaluation of the LIBS probe combined with a high-resolution spectrometer and demonstrate rapid detection of isotopes of uranium and hydrogen and highly enriched samples of (6)Li and (7)Li.

Comparisons between LIBS and ICP/OES

In the framework of the development of new techniques, the ability of laser-induced breakdown spectroscopy (LIBS) to analyse remotely complex aqueous solutions was investigated. The jet configuration with a collimated gas stream was chosen because it appeared to be the most promising method for the LIBS probe, particularly in terms of sensitivity and repeatability. For emission collection, the echelle spectrometer offers a simultaneously recorded wavelength range from the UV to the near IR and is interesting for multielemental analysis for LIBS and also for inductively coupled plasma (ICP) optical emission spectroscopy (OES). The importance of parameters influencing the quantitative results of LIBS such as multispecies analysis, sheath gas, use of an internal standard and temporal parameters for analysis is described. LIBS quantitative data have been directly compared with results from the more standard ICP/OES technique.

Test results from sugar cane bagasse and high fiber cane co-fired with fossil fuels

Cofiring tests were conducted in a boiler at the Hawaiian Commercial & Sugar factory at Puunene, Hawaii. Three tests were conducted; a baseline test firing coal and fuel oil (Test 1) and two cofiring tests utilizing coal, fuel oil, and biomass. In the latter two tests, bagasse (Test 2) and a blend of bagasse and fiber cane (Test 3) were used as the biomass fuel. Biomass accounted for 62% and 50% of the total energy inputs for Tests 2 and 3, respectively. All three tests were conducted in a spreader stoker-type boiler operating at a steam flow rate of 46.5 tonne h−1 at 63.2 bar and 400 °C. Fuel properties, boiler efficiency, solids removed in the pollution control devices, and stack emissions of criteria pollutants were monitored during the test campaign and results are reported herein. In addition, a laser induced breakdown spectroscopy probe and a deposition probe were installed near the superheaters to characterize fire-side ash behavior under each of the test conditions.

Laser-induced breakdown spectroscopy of molten aluminum alloy.

We have demonstrated that a fiber-optic laser-induced breakdown spectroscopy (LIBS) probe is suitable for measuring the concentration of minor constituents of a molten Al alloy in a laboratory furnace. For the first time to our knowledge we are able to record the LIBS spectra in several spectral regions of seven different molten Al alloy samples by inserting the LIBS probe inside the molten alloys, allowing us to obtain a ratio calibration curve for minor constituents (Cr, Mg, Zn, Cu, Si, etc.), using Fe as a reference element. A ratio calibration curve for Fe with a major element (Al) can also be obtained with which the concentration of Fe in the alloy can be determined. The effects of the surrounding atmosphere on the LIBS spectra of the molten alloy were investigated. Effects of focal length of the lens on the LIBS signals were also studied. LIBS spectra of a solid Al alloy recorded with the same LIBS probe were compared with the LIBS spectra of the molten alloy. Our results suggest that the LIBS probe is useful for monitoring the elemental composition of an Al melt in an industrial furnace at different depths and different positions inside the melt.

High temperature fiber optic laser-induced breakdown spectroscopy sensor for analysis of molten alloy constituents

A fiber optic (FO) laser-induced breakdown spectroscopy (LIBS) sensor that measures the on-line, in situ elemental composition of a molten alloy inside the melt in a furnace is described. This sensor has applications as a process monitor and control tool for glass, aluminum, and steel melters. The sensor is based on the transmission of laser energy through a multimode optical fiber. The laser radiation from the fiber is collimated and finally focused inside the aluminum melt in the furnace by a specially designed stainless steel holder that holds the collimating and focusing lens. Atomic emission from sparks from the laser plasma is collected by the same stainless steel lens holder and transmitted back through the optical fiber and finally fed into the entrance slit of the spectrograph. The present design of the stainless steel holder is useful for obtaining a collimated LIBS signal over a long distance (the distance between the focusing and collimated lenses is more than 200 cm). Parametric studies such as sample-to-lens distance and the effect of the angle of incidence of the laser beam on the sample surface were performed. Calibration curves for minor elements were obtained for solid Al alloys as well as for a molten Al alloy in the laboratory furnace by inserting the FO LIBS probe inside the molten material. The performance of the probe was also tested by inserting the stainless steel holder into the melt at a 45° angle, which is necessary for collecting LIBS data in an industrial furnace. LIBS spectra in different spectral regions were recorded in the pilot furnace during different tests where known amounts of minor elements were added to the melt. The results obtained from this sensor for different Al alloys demonstrate the usefulness of this sensor to monitor the concentration of different constituents of the molten Al alloy in an industrial furnace.

Subsurface heavy-metal detection with the use of a laser-induced breakdown spectroscopy (LIBS) penetrometer system

U.S. Army Engineer Waterways Experiment Station (WES) investigators have designed, fabricated, and demonstrated a cone penetrometer sensor for sub-surface in situ field screening based on LIBS. The LIBS probe (patent pending) presented here is one of a suite of contaminant and geophysical probes developed by the WES Site Characterization and Analysis Penetrometer System (SCAPS) program. The LIBS probe includes a laser as part of the optical LIBS sensor section for metals analysis and a cone and sleeve soil classification module at its tip. Soil classification data are acquired during the push, while LIBS data are recorded during probe retraction, after shedding a sacrificial sleeve. Optical design concerns are discussed including the recessed window geometry to avoid output window damage and associated problems. Calibration, peak identification and peak confidence software are discussed. Although producing lower signal strength, the nonimaging optical receiver utilized is based on a simple design. Its performance is less dependent on soil conditions and produces a more consistent optical signal when compared to an imaging optical receiver design. Field results from four sites are discussed. Some spectral samples from a site indicate contaminant material that is not mixed with soil, as evidenced by spectra with a total lack of characteristic iron peaks in the background. Soil grain size and soil moisture are discussed in the context of empirical calibration and their effect on LIBS measurements.

A real-time fiber-optic LIBS probe for thein situ delineation of metals in soils

Detection-limit determination and field-deployment results for the SCAPS fiber-optic laser-induced breakdown spectroscopy (LIBS) cone penetrometer probe are presented. Probe design and issues concerning sample presentation and in situ matrix effects are also addressed. It was observed that a design in which measurements are made by a scanning optical system through a sapphire window in the probe produces detection limits that are at or below the EPA's site screening levels (SSLs) for Pb, Cd, and Cr in sand. © 1998 John Wiley & Sons, Inc. Field Analyt Chem Technol 2: 117–125, 1998