CN-122003593-A - Improved method for realizing accurate measurement of high vapor pressure elements in molten metal by using laser-induced breakdown spectroscopy

CN122003593ACN 122003593 ACN122003593 ACN 122003593ACN-122003593-A

Abstract

A method that allows reproducible, accurate and substantially temperature independent quantitative measurements of one or more high vapor pressure elements in a liquid metal or alloy sample using Laser Induced Breakdown Spectroscopy (LIBS) or other similar methods. The method introduces one or more selectively reactive species and a substantially inert carrier gas to alter the local environment at and around the sampling point of the liquid metal or alloy. This results in a significant and rapid reduction in the vapor effect of the LIBS signal to the high vapor pressure species in the metal or alloy melt, partially eliminating the temperature dependence of the high vapor pressure element and its dependence on spurious environmental factors, thereby reducing the associated uncertainty in the LIBS measurement.

Inventors

K. Leoson
K. A. Toralins Dotil

Assignees

DTE有限公司

Dates

Publication Date: 20260508
Application Date: 20241002
Priority Date: 20231002

Claims (16)

1. A method of quantitatively analyzing one or more elements in a molten metal or alloy by LIBS, wherein the negative effects of the gas of volatile trace elements or alloying elements in the molten metal or alloy on the analysis of the volatile elements are reduced or substantially eliminated, the method comprising: a. Disposing a measurement chamber facing a surface of the molten metal or alloy, wherein the measurement chamber comprises one or more openings or one or more windows to provide a path for a focused laser beam from a LIBS excitation laser to enter the chamber and reach a sampling point on the surface, and to provide a path for emitted light from the generated plasma to leave the chamber and be collected and transmitted to a detector; b. Delivering a continuous flow of a selectively reactive gas mixture to the sampling point within the measurement chamber, wherein the selectively reactive gas mixture comprises one or more substantially inert carrier gas components and one or more selectively reactive gas components, and wherein the one or more selectively reactive gas components of the selectively reactive gas mixture have the property of preferentially reacting with one or more volatile elements present in the molten metal or alloy; c. Ablating a portion of the sample by emitting one or more laser pulses at the sampling point with sufficient light energy and generating a plasma above the sampling point to perform LIBS measurements on the surface of the molten metal or alloy; d. Receiving emitted light from the generated plasma and transmitting the emitted light to a detector for recording spectral data of the detected light, and E. analyzing the spectral data to obtain a quantitative determination of the one or more elements in the molten metal or alloy.
2. The method of claim 1, wherein the selectively reactive gas mixture is mixed before being transferred into the measurement chamber and transferred to the measurement chamber through one or more gas channels and/or through a laser excitation channel and/or through a transmit receive channel.
3. The method of claim 1, wherein the selectively reactive gas mixture is mixed within the measurement chamber, wherein the one or more selectively reactive gas components are transported to the measurement chamber through one or more first gas channels, and the one or more carrier gas components are transported to the measurement chamber through one or more second gas channels.
4. A method as set forth in claim 2 or 3 wherein the method further comprises the step of controlling the flow of the one or more carrier gas components and the one or more selectively reactive gas components to provide a suitable ratio of the components prior to mixing the selectively reactive gas mixture.
5. The method of claim 1, wherein the total flow of the selectively reactive gas mixture is in the range of 1-5L/min.
6. The method of any one of the preceding claims, wherein the one or more carrier gas components are selected from the group of noble gases.
7. The method of any of the preceding claims, wherein the one or more carrier gas components comprise argon.
8. The method of any one of the preceding claims, wherein the one or more selectively reactive gas components is carbon dioxide (CO 2 ) or sulfur hexafluoride (SF 6 ).
9. The method of any one of the preceding claims, wherein the ratio of the one or more selectively reactive gas components in the selectively reactive gas mixture is in the range of 1% to 20%, preferably in the range of 2% to 10%, more preferably in the range of 4% to 8% relative to the total volume of the selectively reactive gas mixture.
10. The method of any of the preceding claims, wherein the measurement chamber allows a continuous flow of the selectively reactive gas mixture at and in close proximity to the sampling point and the generated plasma.
11. The method of claim 10, wherein the measurement chamber is formed by disposing a non-immersion LIBS instrument head above the surface of the molten metal or alloy.
12. The method of claim 10, wherein the measurement chamber is formed by immersing a LIBS tool head or a portion of a LIBS tool head in the molten metal or alloy, wherein the measurement chamber comprises one or more openings such that the openings are positioned above the surface of the molten metal or alloy to allow a continuous flow of the selectively reactive gas mixture at and in close proximity to the sampling point and the generated plasma.
13. The method of the preceding claim, wherein the one or more openings for allowing the flow of the selectively reactive gas mixture are located less than 10 millimeters above the surface of the molten metal or alloy.
14. The method of any one of the preceding claims, wherein the step of arranging the measurement chamber is performed automatically.
15. A method as claimed in any one of the preceding claims, wherein the method is used to measure the concentration of one or more major components of a molten metal or alloy and/or also to measure the concentration of one or more trace elements in the molten metal or alloy.
16. The method of the preceding claim, wherein the method is used to measure the concentration of magnesium in the molten metal or alloy.

Description

Improved method for realizing accurate measurement of high vapor pressure elements in molten metal by using laser-induced breakdown spectroscopy Technical Field The present disclosure relates to the field of spectroscopy, or more particularly to Laser Induced Breakdown Spectroscopy (LIBS) methods for achieving accurate and (near) temperature independent quantitative elemental analysis of volatile elements in liquid metals and alloys. Background Laser Induced Breakdown Spectroscopy (LIBS) is a well established technique for chemical analysis of solid, liquid and gaseous samples. The method can be used for quantitative elemental analysis by suitable sample preparation and suitable plasma radiation analysis. LIBS methods have been applied to chemically analyze a variety of materials, mainly in solid form. The potential for the chemical analysis of liquid metals using laser-induced plasma was found as early as 1966 [ range, bonfiglio, bryan, spectrochimica Acta, 1678-1680 (1966) ]. With improvements in optical technology, efforts to achieve LIBS systems for analyzing molten metals (including zinc, aluminum, and steel) have increased significantly over the past 25 years due to the industrial significance of such measurements. Previously proposed LIBS systems for molten metal analysis typically involve immersion probes or non-contact measurements, where the measurement device may be located close to or remote from the surface to be analyzed. Applicant's earlier application EP4009037 discloses a non-immersion LIBS device for high precision elemental analysis of the principal non-volatile elements in liquid metals or alloys. The device comprises a measuring chamber open at the bottom through which a laminar flow of preferably inert gas is arranged. It is known in LIBS measurement to control the atmosphere in the vicinity of a measurement point. This is typically achieved by introducing an inert gas around the measurement point, most often providing an environment that ensures a strong and stable LIBS signal. Inert or substantially inert gases having different physical properties (such as atomic/molecular weight, thermal conductivity) have been used to affect plasma expansion. In addition, helium has been used to facilitate energy transfer between individual atomic species in a plasma by a collision process. In some cases, gas mixtures have been used to obtain the most suitable parameters for enhancing LIBS signals and improving accuracy. CN110132943a discloses a method using a gas mixture of Ar, ne, he as ambient gas around the measurement point, wherein the composition of the mixture is optimized to slightly improve the reproducibility of the LIBS spectrum on solid alloy samples. In the prior art, the gas flow or pressure in the LIBS measurement is also used for secondary purposes. US 6,909,505 discloses a LIBS probe in which a gas stream is used to generate bubbles inside the molten metal and laser excitation is performed on the inner surface of the bubbles. US 6,762,835 discloses a LIBS probe for liquid metal in which the flow of inert gas (nitrogen, argon, helium or mixtures of the three) and hence the gas pressure inside the probe is modulated to position the metal surface inside the probe at a specific distance from the excitation and collection optics. Thus, in the prior art describing LIBS analysis of liquid metal for quantifying trace elements present in the metal, the purpose of introducing a flow of or controlling the pressure of a gas or gas mixture around a sampling point is to achieve one or more of 1) increasing the overall signal strength, 2) increasing the reproducibility of plasma emission by using a chemically inert gas with suitable physical parameters, and 3) applying positive or negative pressure on the liquid metal surface to control the metal level or create bubbles. As non-inert gases, oxygen is known to play a role in the development of plasma emission by the so-called oxygen quenching effect (oxygen quenching effect) which shortens the lifetime of the plasma emission. For aluminum targets, the presence of oxygen in the ambient gas also causes significant molecular emissions from AlO (K.C.Hartig, B.E.Brumfield, M.C.Phillips, S.S.Harilal, part B of spectrochemistry: atomic spectroscopy (Spectrochimica Acta Part B: atomic Spectroscopy); 135, 2017, 54-62) and thus the presence of oxygen results in a reduction in the time-integrated LIBS signal and potential spectral interference from the molecular emissions, both of which are detrimental to quantitative chemical analysis. Furthermore, in the case of liquid metal analysis by LIBS, the presence of oxygen gas in the environment around the measurement point results in rapid oxidation of the ablated metal and the resulting oxides accumulate around the measurement point, further increasing the measurement instability. In LIBS analysis of liquid metals, it has been recognized that quantification of trace elements or alloying elements with high vapor