Laser-induced breakdown spectroscopy (LIBS) techniques have been researched since nearly the invention of the laser itself. Only recent developments, however, have finally made LIBS a suitable measurement technique for industrial applications. Recent advances in miniaturization and industrial hardening of key system components have had a positive impact on LIBS industrial adoption.
Avantes is leading the way in the development of fibre-optic spectroscopy instrumentation. Our modular design, small footprint, and advanced engineering design have helped numerous researchers develop methods and systems that are taking LIBS out of the lab and putting it to work in countless industries.
The LIBS Challenge
Laser-induced breakdown spectroscopy has both advantages and disadvantages. LIBS offers rapid measurements of multiple atomic elements simultaneously in a single scan. It requires less sample preparation than other methods and with the use of fibre optics, can be deployed from a distance or used to sample on a very small scale. Even with its benefits, there have been obstacles to wider LIBS adoption.
First, the advantage of being able to perform measurements at a distance is especially useful for measurements in hostile environments, but those same environments offer ambient conditions that are less than ideal. Airborne particulates, condensation, and temperature fluctuations can impede a LIBS system’s ability to capture spectral data and distinguish it from background noise.
Hardening instruments to ambient conditions is crucial in LIBS measurements where, for example, low-light conditions would be adversely affected by thermal instability. Adjusting focal length, selecting ideal wavelength regions, and processing out matrix effects are variables that can drastically change measurement parameters. LIBS generally requires a robust set of matrix-matched samples to develop a calibration model which can support qualitative and quantitative measurements. These standards may or may not exist and require validation using more traditional methods of testing such as ICP MS.
In spite of these challenges, however, LIBS is beginning to make steady progress in select industries.
LIBS Industrial Success Stories
These applications are supported by a large body of research into the elemental analysis of ores and metals. Recent work from researchers at the Wuhan National Laboratory, Wuhan, China has demonstrated the suitability of fibre-optic LIBS over traditional stand-off LIBS methods for quantifying Manganese and Titanium content in Iron-Carbon alloys.
They obtained calibration curves for Mn at 0.997 and Ti at 0.998 coefficients of determination (percent accuracy) using the FO-LIBS method. Their system employed a compact Nd:YAG laser fiber coupled to deliver a plasma-inducing pulse. Resultant plasma spectra were collected with the AvaSpec-ULS2048CL-EVO spectrometer with 2400 g/mm grating, CCD detector, and resolution of about 0.08 nm. The system was synchronized with an external trigger and captured the wavelength range from 393 to 488 nm. The fibre-optic LIBS system was more compact, cost-effective and also more suitable for adverse ambient conditions.
Geochemistry & Ore/Mineral Extraction
Laser-induced breakdown spectroscopy is gaining a foothold in mining, mineral extraction, and metallurgy, with a large body of research supporting the development of reference calibration data, and in turn leading to increased adoption for industrial applications.
LIBS can be applied throughout the ore extraction and processing industries. Monitoring metallurgical processes involves the measurement of plasma created at the surface of molten metals, inline systems that monitor raw ore composition in pre-processing, and quality management testing the composition of alloys in finished ingots.
LIBS can also be deployed in energy production. Coal-fired power generation requires precisely calibrated fuel mixtures to run most efficiently. Coal is monitored for ash content and other constituents before entering the plant combustion zone. Adjusting the fuel mix helps plants prevent slagging and reduces greenhouse gas emissions.
While the phrase ‘clean coal’ might be a misnomer, controlling greenhouse gas emissions from existing coal-fired power plants is valuable to reducing the carbon impact of our existing infrastructure. Researchers at Shanxi University, Taiyuan, China, developed a system designed for inline quality analysis of pulverized coal. The plasma spectra were captured by a three-channel spectrometer system based on the AvaSpec-ULS2048CL-EVO with one 3600 g/mm grating and two 1200 g/mm gratings, and numerical apertures of 0.22. The wavelength range for the system of 227-816 nm with resolution of 0.3 nm measured C, Ca, Mg, Ti, Si, H, Al, and Fe as well as Ash, Free Carbon, and Moisture Content of samples. The elemental LIBS system passed proof of capability testing with measurement errors within 10% and was deemed capable of providing rapid, efficient inline analysis of coal quality for plant operators.
Laser-induced breakdown spectroscopy is at work in the recycling industry, too. Plastics and metals can be more easily separated using the rapid material identification capabilities of a LIBS system. In aluminium recycling, LIBS allows faster and more accurate sorting of scrap metal, because it can differentiate alloys in the same family. The recycling relies heavily on handheld LIBS instruments.
Sponsored by SHREDDERSORT, the European project to improve recycling rates of non-ferrous metal automotive waste, researchers in Italy are using artificial neural networks to process LIBS spectra of primarily aluminium alloys. Conventional sorting methodologies, such as X-ray Transmission (XRT) are not adequate for determining specific alloys. Paired with the artificial neural network was a dual-channel spectrometer system featuring AvaSpec-ULS4096CL-EVO instruments.
This system collected spectra simultaneously between 200-430 nm at 0.1 nm resolution and 415-900 nm at 0.3 nm resolution. Multiple spectra per sample were fed into the ANN; this method was shown to improve classification of the non-ferrous metallic automotive scrap to more than 75% in conditions simulating an industrial environment.
Standard LIBS Solutions
LIBS applications defy standard solutions because each application requires a unique measurement methodology. Laser-induced breakdown spectroscopy can offer robust solutions for industry, but there is no one-size-fits-all off-the-shelf solution that will work for every application. Easily customizable modular solutions can open the door to LIBS industrialization.
Identifying relevant spectral ranges and overcoming ambient conditions are the first considerations when designing a LIBS system. While multivariate elemental analysis is possible, the wavelength data may require multiple detector channels to adequately cover the ranges of absorption lines and spectral peaks in question.
Even when reference calibration curves are available, bringing an industrial-suited solution to market requires expertise and dedication to finding the right solution. Work with a partner that can help you navigate the challenges. Contact your Avantes sales engineer today.
Campanella, B., et al. ‘Classification of wrought aluminum alloys by ANN evaluation of LIBS spectra from aluminum scrap samples.’ Spectrochimica Acta Part B: Atomic Spectroscopy(2017).
Li, Jie, et al. ‘Effects of experimental parameters on elemental analysis of coal by laser-induced breakdown spectroscopy.’ Optics & Laser Technology 41.8 (2009): 907-913. https://orbi.ulg.ac.be/bitstream/2268/145058/1/Effects%20of%20experimental%20parameters%20on%20elemental%20analysis%20of%20coal%20by%20laser-induced%20breakdown%20spectroscopy.pdf
Mirzaee, Fateme Hadavand, et al. ‘Laser induced fluorescence and breakdown spectroscopy and acoustic response, to discriminate malignant and normal tissues.’ European Conference on Biomedical Optics. Optical Society of America, 2013. https://www.researchgate.net/publication/256093830_Laser_induced_fluorescence_and_breakdown_spectroscopy_and_acoustic_response_to_discriminate_malignant_and_normal_tissues
Xia, H., and M. C. M. Bakker. ‘Online sensor system based on laser-induced breakdown spectroscopy in quality inspection of demolition concrete.’ 27th International Conference on Solid Waste Technology and Management, Philadelphia, USA 11-14 March 2012. International Society for Industrial Ecology, 2012. https://repository.tudelft.nl/islandora/object/uuid:73f5290f-1563-45b3-9dd2-023cd7598947/datastream/OBJ