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Accurate Real-Time Elemental (LIBS) Analysis of Molten Aluminum and Aluminum Alloys

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... Historically, phase diagrams have mainly been experimentally validated in the liquid phase using thermal analysis methods [9]. Recently, Gudmundsson et al. [10][11][12] showed that laser-induced breakdown spectroscopy (LIBS) can provide accurate real-time information about aluminum melt chemistry. Hudson et al. have previously used statistical LIBS analysis for detecting inclusions that can be chemically differentiated from the melt, including Al 2 O 3 [13] and TiB 2 [14]. ...
Article
We report Ti concentration measurements in dilute Al-Ti alloys, acquired from direct analysis of the molten metal by laser-induced breakdown spectroscopy (LIBS). The LIBS analysis showed approximately constant Ti concentrations at melt temperatures above the liquidus, while at lower temperatures the measured concentration followed the L/(L + Al3Ti) liquidus of the phase diagram, confirming that the LIBS measurement accurately detects the dissolved Ti concentration in the melt. The LIBS measurements furthermore demonstrated that the Al3Ti phase forms or dissolves within minutes when the melt temperature is decreased or increased, respectively. For the first time, the liquidus line at low Ti concentrations in the Al-Ti phase diagram has thus been mapped using LIBS analysis instead of the more conventional but time-consuming thermal analysis methods. We conclude that LIBS analysis of molten metal offers a unique opportunity to monitor accurately the chemical composition of the liquid phase and reveal the formation of solid precipitates in real time.
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Analyzing, and adjusting the chemical composition correctly and avoiding contamination during metal production, alloying, casting and recycling processes is critical issue for engineering applications. In metallurgical industry, required adjustments are provided by periodic elemental analyzes to ensure the correct chemical composition. The use of spark discharge-optical emission spectroscopy (spark OES) has become widespread mostly for this purpose. However, in order to take measurements with spark OES, it is necessary to take samples from molten metal and send them to analysis. Adjusting chemical composition according to the analysis result which needs a waiting time ocurring high temperature melting processes causes extra time and energy consumption. In this regard, the traditional methods, spark OES, XRF, ICP, can not meet the demand for in situ analysis and need long analysis time. Laser-induced breakdown spectroscopy (LIBS) enables big advantage of providing fast and online solutions in this field. LIBS is an atomic emission spectroscopy technique based on the generation of plasma at high temperatures by a high intensity pulsed laser source focused on the sample surface to be analyzed. Elements and their concentration are characteristically expressed by collecting the beam emitted by the microscopic plasma created on the hot metal surface. This method has been demonstrated to be a quick and reliable analysis technique for the molten metal in a production line in situ and/or in near real time. Over the past few decades, extensive researches presented on LIBS show that can be used to produce trouble-free metals and alloys for engineering applications. The method has become a significant technology for Industry 4.0 scenarios, as it provides at-line monitoring. This article reveals a short summary of literature and the need in Turkey in this field and sheds light on future studies. Turkey has a high undisputed alloy production potential and a high casting industry with low automation. The sector is growing towards to create products with high added value, especially for the automotive and defense industries. It is an important issue to provide technological developments and automation on alloy production in order to provide this added value. Entegrate LIBS technology to this sector, which has a large volume and potential, is significant for manufacturing potential. LIBS application on the production of steel alloys has been intensively studied in recent years, especially in China. The studies focus on the measurement difficulties caused by (1) spectral interference due to the emission lines of iron, (2) the separation of content of iron from iron oxide, (3) the difference in the spectral intensities of the lowtemperature-high-temperature measurements, and (4) calibration methods. Different research groups in China, the USA, UK and Iceland investigate LIBS analysis applications on the production line of aluminum alloys Two different types of probes, immersed or nonimmersed, were developed. Analysis of non-volatile trace elements at ppm levels has been confirmed with non-immersed type probes. Segregations occured while aluminum alloys solidification, induce to the measurement uncertainty in spark-OES analysis. LIBS provides more accurate analysis in this regard. LIBS system design and calibration studies need to be developed in accordance with the changing analysis conditions in the Metallurgical industry. Focusing on the studies for quantitative elemental analysis atline would provide the enhancement the quality concomitantly with energy, material and time savings.
Chapter
We report on automated analysis of the trace element content of liquid metal, implemented in a casthouse of a primary aluminumAluminum smelter. The automated analysis involves robotic sampling from transport crucibles followed by direct measurement of the chemical content of the liquid metal using laser-induced breakdown spectroscopy (LIBS)Laser-Induced Breakdown Spectroscopy (LIBS). Experiments were carried out on-site over a period of several months, sampling over 200 crucibles and comparing the LIBSLaser-Induced Breakdown Spectroscopy (LIBS) analysis with conventional laboratory spark-OES analysis of solid samples collected from the same crucibles. We discuss the predictive power of LIBSLaser-Induced Breakdown Spectroscopy (LIBS) analysis for different elements, confirming that automated analysis of the molten metal can replace manual laboratory analysis for process control for many common trace elements.
Article
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Measuring distances in the range between a few centimetres and a few metres are of special interest for automated industrial LIBS applications. They allow for a reliable optical access to measuring objects in a process line under harsh industrial environments. In that range a compromise can be found between the conflicting requirements with respect to the protection of the optics facing the measuring object on one side, and sufficiently high laser irradiance and high receiving solid angle of the measuring radiation on the other side. A concise overview about LIBS studies published in the last four years focusing on industrial applications or perspectives therefore is given. Recent R&D activities in the field of automated LIBS for industrial applications are presented focusing on the following application cases: (a) combined use of inline measured 3D geometry information and LIBS analyses for high-speed sorting tasks of piece goods; (b) sorting of refractories; (c) identification of steel blooms in a rolling mill; (d) inverse production scenario for the recovery of valuable materials from end-of-life electronic equipment. For measuring distances of only a few centimetres the size of a LIBS instrument can be downscaled significantly allowing to set up handheld LIBS analysers. Whereas the precursors of such concepts were studied already more than fifteen years ago, quite recently a competitive market arose where various models of handheld LIBS systems are offered. Industrial application fields are mainly positive material identification of metals and sorting of light metal scraps for recycling purposes. A comparative synopsis of features of these LIBS systems will be presented and arising research themes in this context are outlined.
Patent
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A measuring device is provided for measurement of parameters, in particular for measuring the temperature, in molten masses, in particular in molten metal or molten cryolite masses having a melting point above 500° C. The measuring device has an optical fiber for receiving radiation from the molten mass and a cable reel having an external circumference for winding up the optical fiber and an internal space surrounded by the external circumference. A distributor and a mode filter for the optical fiber are arranged in the internal space.
Article
We report the application of laser-induced breakdown spectroscopy (LIBS) for on-line chemical analysis in a primary aluminum smelter. Measurements were performed for fourteen trace elements (Fe,Si,Cu,Ni,Ti,Cr,Mn,Sn,V,Ga,Zn,Sb,Mg,Na) and correlated with laboratory measurements on corresponding solid samples. Real-time quantification of trace elements down to ppm levels directly in the molten aluminum has been demonstrated for a number of elements (Cu,Cr,Mn,Sn). For elements Fe and Si, typically present in elevated concentrations in primary aluminum (approximately 1000 ppm and 300 ppm, respectively, in the present work) the average difference between concentration measurement carried out on the melt and laboratory results was found to be within 2.5% and 5% of the measured concentration, respectively. The observed differences can be partly related to uncertainties in the reference laboratory measurements, originating from the process of casting of solid samples from the melt. For elements with the highest vapor pressure, comparison with laboratory results on manually collected samples is shown to be less adequate. Nevertheless, we show that LIBS can provide reliable real-time measurements of the relative concentration of volatile elements, e.g., down to ppm levels in the case of Na. We conclude that for many technically important trace elements in primary aluminum, automated LIBS analysis on the molten metal is fully competitive with off-line laboratory analysis of solid process samples in terms of accuracy and precision, in addition to improving worker safety and providing significantly faster measurement results.
Article
In order for metals to meet the demand for critical applications in the automotive, aerospace, and defense industries, tight control over the composition and cleanliness of the metal must be achieved. The use of laser-induced breakdown spectroscopy (LIBS) for applications in metal processing has generated significant interest for its ability to perform quick analyses in situ. The fundamentals of LIBS, current techniques for deployment on molten metal, demonstrated capabilities, and possible avenues for development are reviewed and discussed.
Chapter
Every pound of aluminum or aluminum alloys cast and sold is certified to meet The Aluminum Association Inc. registered limits or other specified composition limits. Certification of aluminum and aluminum alloys to specified composition limits is typically done using Spark-Atomic Emission Spectrometry (Spark-AES) following the procedures in ASTM International (ASTM) E716 Standard Practices for Sampling and Sample Preparation of Aluminum and Aluminum Alloys for Determination of Chemical Composition by Spectrochemical Analysis and ASTM E1251 Standard Test Method for Analysis of Aluminum and Aluminum Alloys by Spark–AES. Spark-AES laboratories at major aluminum production facilities normally have excellent analytical practices and follow strict quality control protocols to provide the best results possible. However, every measurement has an associated uncertainty and the measurement of composition using Spark-AES is no exception to the rule. This paper provides a brief discussion of:1. The uncertainty inherent in the elemental analysis of aluminum and aluminum alloys by Spark-AES. 2. The benefits of using guard bands to set internal operating limits, which are offset from specified composition limits. 3. A model of the risk for sale of out-of-specification product based on the analysis uncertainty relative to the specified composition limits. 4. The main sources of uncertainty of Spark-AES and their potential causes.
Chapter
Efficient aluminum smelting operation requires routine but necessary measurement and control of individual cell key parameters. Two of the critical measurement and control parameters are cell temperature and bath chemistry. Bath chemistry of interest for the cryolitic bath is cryolite molar ratio and other components such as CaF2 and Al2O3, and sometimes other additives such as LiF and MgF2. Determination of these properties requires various analytical equipment and rigorous procedures from tedious sampling to analytical preparation. STARprobe™, an Alcoa proprietary instrument specifically developed and designed for use in aluminum smelters, combines tedious time-consuming sampling procedures and all expensive analytical equipment into one simple portable instrument for potroom operators on potroom floor. Now, the STARprobe™, together with Alcoa proprietary Integrated Pot Control system, becomes an integral technology component in Alcoa smelters for an efficient operation. This paper will update our further development in more accurately measuring alumina concentration, and also addition of property measurement including %CaF2 and %LiF when needed.
Chapter
Introduction Theoretical Background Results and Discussion Summary Acknowledgment
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The construction of a sodium beta alumina probe for the determination of the sodium activity in molten aluminum alloys is described. It was found that the emf at a given sodium concentration was a strong function of the silicon content. Henry’s law was obeyed in super purity aluminum and the activity coefficient of 350 at 998 K agrees with other determinations.
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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.
Online monitoring of Hot Dip Galvanizing bath by LIBS technology
  • S Jacques-Beyssen