CN118369566A

CN118369566A - System and method for performing laser induced breakdown spectroscopy measurements on a molten metal sample

Info

Publication number: CN118369566A
Application number: CN202280074191.9A
Authority: CN
Inventors: S·H·格维兹门松; K·莱昂森
Original assignee: Dte Ltd
Current assignee: Dte Ltd
Priority date: 2021-09-08
Filing date: 2022-09-07
Publication date: 2024-07-19
Also published as: WO2023037392A2; CA3230773A1; AU2022342826A1; WO2023037392A3; JP2024536735A; EP4399509A2

Abstract

A LIBS measurement system is disclosed that is configured to monitor a temperature of a molten metal sample (10) during cooling of the molten metal sample in a crucible (20) and initiate a LIBS measurement after the temperature of the molten metal sample meets a measurement temperature criterion. The system may also monitor the temperature of the empty crucible to help ensure crucible temperature: (i) Sufficiently high to ensure that a sufficiently low cooling rate of the molten metal sample occurs during LIBS measurements after the molten metal sample is delivered to the crucible and cooled to meet the measured temperature criteria; and (ii) optionally low enough to avoid unnecessarily long cooling times of the molten metal sample before the measured temperature criteria are met and LIBS measurements are initiated. The LIBS measurement system may be mobile and battery powered and may include an integrated calibration station (500).

Description

System and method for performing laser induced breakdown spectroscopy measurements on a molten metal sample

Background

The present disclosure relates to chemical analysis of liquid metals and alloys. More specifically, the present disclosure relates to the use of laser-induced breakdown spectroscopy for chemical composition analysis of liquid metals and alloys.

In metal production, monitoring the chemical composition of the metal produced is of paramount importance. For example, in the primary production of aluminium using continuous electrolysis according to the Hall-heroult process, metal samples from the individual reduction cells are collected periodically for chemical analysis. This is done to monitor the impurity level in the metal, which is also used as an indicator of the operating condition of each cell.

A typical primary aluminum smelter will contain hundreds of reduction tanks from which samples are routinely collected during normal operation (up to daily). Current standard practice involves extracting a liquid metal sample from a reduction cell and casting a solid sample using a standard sample mold (e.g., according to ASTM standard E716). The solid sample is then analyzed to determine its chemical composition.

For decades, the standard method of analysis of solid samples in the aluminum industry has been spark atomic emission spectrometry (also known as spark optical emission spectrometry or spark OES) (e.g., according to ASTM standard E1251). The sample needs to be prepared properly (e.g., by mechanical milling to a certain depth into the cast sample) before performing the spark OES analysis. All steps of sample preparation are important to ensure accurate analytical results.

Disclosure of Invention

A LIBS measurement system is disclosed that is configured for monitoring a temperature of a molten metal sample in a crucible during cooling of the molten metal sample, and for initiating a LIBS measurement after the temperature of the molten metal sample meets a measurement temperature criterion. The system may also monitor the temperature of the empty crucible to help ensure crucible temperature: (i) Sufficiently high to ensure that a sufficiently low cooling rate of the molten metal sample occurs during LIBS measurements after the molten metal sample is delivered to the crucible and cooled to meet the measured temperature criteria; and (ii) optionally low enough to avoid unnecessarily long cooling times of the molten metal sample before the measured temperature criteria are met and LIBS measurements are initiated. The LIBS measurement system may be mobile and battery powered and may include an integrated calibration station.

Accordingly, in one aspect, there is provided a method of performing Laser Induced Breakdown Spectroscopy (LIBS) on a molten sample during cooling of the molten sample, the method comprising:

Monitoring the temperature of the molten sample during cooling of the molten sample in the crucible and comparing the temperature of the molten sample to a measured temperature standard; and

Determining that the temperature of the molten sample meets the measured temperature criteria and initiating a LIBS measurement of the molten sample.

The method may further comprise, prior to introducing the molten sample:

Measuring the temperature of the crucible one or more times, the crucible being in a preheated state and no molten sample being present, and comparing the temperature of the crucible to a crucible temperature standard; and

Determining that the temperature of the crucible meets a crucible temperature criterion and providing an indication that the crucible is ready to receive a molten sample;

wherein the crucible temperature standard is configured such that the molten sample cools less than 50 ℃ during LIBS measurement.

In some example implementations of the method, the crucible temperature criterion includes a minimum crucible temperature such that the crucible temperature criterion is satisfied when the minimum crucible temperature is exceeded. The minimum crucible temperature may reside between 100 ℃ and 60% of the melting point temperature of the molten sample, which is in degrees celsius. The minimum crucible temperature may reside between 15% of the melting point temperature of the molten sample and 60% of the melting point temperature in degrees celsius.

In some example implementations of the method, the crucible temperature criteria are met when the temperature of the crucible resides within a crucible temperature range. The maximum crucible temperature of the crucible temperature range may be defined such that when the temperature of the crucible is equal to the maximum crucible temperature and the molten sample is added to the crucible, the temperature of the molten sample satisfies the measurement temperature standard within 1 minute. The maximum crucible temperature of the crucible temperature range may be defined such that when the temperature of the crucible is equal to the maximum crucible temperature and the molten sample is added to the crucible, the temperature of the molten sample satisfies the measurement temperature standard within 30 seconds. The maximum crucible temperature may reside between 50% and 90% of the melting point temperature of the molten sample, the melting point temperature being in degrees celsius.

In some example implementations of the method, the measurement temperature criteria are selected such that the LIBS measurements are performed within a preselected measurement temperature range.

In some example implementations of the method, the measured temperature criteria include a preselected measured temperature, and the LIBS measurement is initiated immediately after (i) determining that the temperature of the molten sample is equal to the preselected measured temperature and (ii) positioning the LIBS measurement head over the crucible.

In some example implementations of the method, the measured temperature criteria include a preselected measured temperature, and the LIBS measurement is performed after determining that the temperature of the molten sample is equal to the preselected measured temperature. The preselected measurement temperature may exceed the melting point temperature of the molten sample by an amount ranging from 5% to 25% of the melting point temperature, which is in degrees celsius.

In some example implementations of the method, the measurement temperature criteria include a preselected measurement temperature range, and the LIBS measurement is performed when the temperature of the molten sample resides within the preselected measurement temperature range.

In some example implementations of the method, the measurement temperature criteria are configured such that the temperature of the molten sample exceeds the temperature of the crucible during the LIBS measurement when the crucible temperature criteria are met.

In some example implementations of the method, the crucible is preheated by a previously measured molten sample, wherein the previously measured molten sample is discarded prior to measuring the temperature of the crucible.

In some example implementations of the method, the molten sample includes aluminum, and the crucible is preheated by contact with cryolite shells formed on top of the reduction tank.

In some example implementations of the method, a common temperature sensor is used to measure the temperature of the crucible and the temperature of the molten sample.

In some example implementations of the method, the temperature of the crucible and the temperature of the molten sample are measured without contact.

In some example implementations of the method, the crucible is supported by a crucible support during LIBS measurements. The LIBS measurement may be performed by a LIBS subsystem, and wherein the measurement head of the LIBS subsystem is movable from a parked position to an operative position in which the measurement head resides above the crucible support, and the heat shield is positioned for heat shielding the measurement head from heat radiated from the crucible when the measurement head resides in the parked position.

In some example implementations of the method, the crucible is a metal crucible. The crucible may be formed of structural steel.

In some example implementations of the method, the heat capacity of the crucible resides between 400J/K and 500J/K.

In some example implementations of the method, the thermal conductivity of the crucible resides between 400W/m-K and 500W/m-K.

In some example implementations of the method, the crucible is a first crucible and the molten sample is a first molten sample, the method further comprising:

Discarding the first molten sample from the first crucible;

measuring the temperature of the first crucible;

determining that the temperature of the first crucible cannot meet the crucible temperature standard due to an excessive temperature;

replacing the first crucible with a second crucible, the second crucible having a temperature of the first crucible; and

LIBS measurements were performed on the second molten sample using the second crucible while cooling the first crucible.

During the performing of the LIBS measurement on the first molten sample, the first crucible may be supported by the main crucible support; and wherein after replacing the first crucible with the second crucible, the first crucible is placed on an auxiliary crucible support for cooling.

In some example implementations, the method further includes, prior to replacing the first crucible with the second crucible:

Preheating a second crucible;

monitoring the temperature of the second crucible; and

Indicating when the second crucible meets the crucible temperature criteria.

In some example implementations, the method further includes:

Optionally performing LIBS measurements on one or more additional molten samples using a second crucible;

emptying the second crucible;

measuring the temperature of the second crucible;

determining that the temperature of the second crucible cannot meet the crucible temperature standard due to an excessive temperature; and

Replacing the second crucible with a crucible selected from the group consisting of:

A first crucible; and

A third crucible; and

LIBS measurements were performed on another additional molten sample using the selected crucible.

In some example implementations of the method, the LIBS measurements are performed by a LIBS system residing on the portable support structure, and the LIBS system is battery powered.

In another aspect, a method of performing Laser Induced Breakdown Spectroscopy (LIBS) on a molten sample during cooling of the molten sample is provided, the method comprising:

preheating a crucible;

Introducing a molten sample into a crucible;

In some example implementations, the method further includes, after preheating the crucible and before introducing the molten sample into the crucible:

Measuring the temperature of the crucible one or more times and comparing the temperature of the crucible with a crucible temperature standard; and

Determining that the temperature of the crucible meets a crucible temperature criterion and providing a molten sample to the crucible;

In another aspect, a system for performing Laser Induced Breakdown Spectroscopy (LIBS) is provided, the system comprising:

A temperature sensor; and

A Laser Induced Breakdown Spectroscopy (LIBS) subsystem; and

Processing circuitry operably coupled to the temperature sensor and the LIBS subsystem, the processing circuitry comprising at least one processor and associated memory including instructions executable by the processor for performing operations comprising:

monitoring the temperature of the molten sample in the crucible during cooling of the molten sample using a temperature sensor; and

Determining that the temperature of the molten sample meets the measured temperature criteria and controlling the LIBS subsystem to initiate a LIBS measurement of the molten sample.

The processing circuitry may be further configured to, prior to introducing the molten sample into the crucible, perform the following:

measuring the temperature of the crucible by a temperature sensor, wherein the crucible is preheated; and

Providing an indication that the crucible is ready to receive a molten sample after determining that the temperature of the crucible meets the crucible temperature criteria;

In another aspect, there is provided a portable system for performing Laser Induced Breakdown Spectroscopy (LIBS), the portable system comprising:

a Laser Induced Breakdown Spectroscopy (LIBS) subsystem comprising a measurement head, the LIBS subsystem being connectable to a battery;

a main crucible support, wherein the measurement head of the LIBS subsystem is movable from a parked position to an operative position in which the measurement head resides above the main crucible support for performing LIBS measurements on a molten sample residing in a crucible supported by the main crucible support;

An auxiliary crucible support capable of supporting and cooling an additional crucible; and

A mobile support structure configured to support the LIBS subsystem, the primary crucible support, and the auxiliary crucible support.

In some example implementations, the system further includes:

A temperature sensor configured to monitor a temperature of a crucible residing in the main crucible support when the measurement head is in the parked position; and

Processing circuitry operably coupled to the temperature sensor, the processing circuitry comprising at least one processor and associated memory including instructions executable by the processor for performing operations comprising:

a temperature sensor is adopted to measure the temperature of the crucible, and the crucible is supported by a main crucible support; and

After determining that the temperature of the crucible fails to meet the crucible temperature criteria due to an excessive temperature, an indication is provided that the crucible should be cooled in the auxiliary crucible support prior to use.

In some example implementations, the system further includes a crucible and an additional crucible, wherein the crucible and the additional crucible are metallic. The crucible and the additional crucible may be formed of structural steel.

In some example implementations, the system further includes a crucible and an additional crucible, wherein a heat capacity of the crucible and the additional crucible resides between 400J/K and 500J/K.

In some example implementations, the system further includes a crucible and an additional crucible, wherein the thermal conductivity of the crucible and the additional crucible resides between 400W/m-K and 500W/m-K.

integrating a calibration device; and

A mobile support structure configured to support the LIBS subsystem and the integrated calibration device;

The measuring head of the LIBS subsystem is movable from an operative position in which the measuring head resides above the crucible for performing LIBS measurements on a molten sample residing in the crucible to a calibration position suitable for performing calibration measurements, the calibration position being suitable for calibrating at least one parameter of the LIBS subsystem.

In some example implementations of the system, the integrated calibration device includes LIBS calibration reference material adapted to calibrate signals of the LIBS subsystem when the measurement head resides in the calibration position. The integrated calibration device may include a support frame, and wherein the LIBS calibration reference material is movable relative to the support frame such that different regions of the LIBS calibration reference material may be optically interrogated by the measurement head when the measurement head is repositioned in the calibration position to perform subsequent calibration measurements, thereby facilitating reuse of the LIBS calibration reference material during multiple calibration measurements.

In some example implementations of the system, the measurement head includes a distance sensor, and wherein the integrated calibration device is an integrated distance sensor calibration device that includes a contact location and a target location, the contact location being located on the integrated calibration device such that when the measurement head resides at the calibration location and contacts the contact location after lowering the measurement head in a direction parallel to an optical axis of the measurement head, a known spatial offset resides between the distance sensor and the target location, thereby facilitating calibration of the distance sensor. The integrated distance sensor calibration device may be resiliently biased such that a known spatial offset is maintained when the measurement head is moved in a direction after having been brought into contact with the contact location.

In some example implementations, the system further includes:

A main crucible support for supporting the crucible when performing LIBS measurements; and

An auxiliary crucible support capable of supporting and cooling an additional crucible.

A further understanding of the functioning and advantageous aspects of the present disclosure may be realized by reference to the following detailed description and drawings.

Drawings

Embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 illustrates an example system for performing LIBS measurements on a molten metal sample.

Fig. 2A-2C illustrate monitoring of the temperature of a molten metal sample prior to initiating a LIBS measurement (fig. 2A), initiating a LIBS measurement after determining that the temperature of the molten metal sample meets a measured temperature criterion (fig. 2B), and measuring an empty crucible prior to introducing the molten metal sample.

FIG. 3 is a flow chart illustrating an example method for performing LIBS measurements on a molten metal sample using passive cooling and temperature monitoring of the molten metal sample prior to initiating the LIBS measurements.

Fig. 5A and 5B schematically illustrate the swapping of crucibles when the temperature of a given crucible is considered too high for further measurement.

Fig. 6 illustrates an example embodiment in which a thermal shield is used to protect the LIBS measurement head when it is parked laterally to the crucible support.

Fig. 7A-7C illustrate an example calibration subsystem for performing a calibration operation on a LIBS measurement head between measurements.

Fig. 8 illustrates an example mobile LIBS measurement system including a battery power source.

Fig. 9 illustrates an example mobile LIBS measurement system including a calibration station.

Fig. 10 shows the correspondence between (i) elemental impurity analysis performed on a liquid aluminum sample using a portable LIBS system and (ii) elemental impurity analysis performed on a solid aluminum sample using a laboratory-based spark OES system.

Detailed description of the preferred embodiments

Various embodiments and aspects of the disclosure will be described with reference to details discussed below. The following description and drawings are illustrative of the disclosure and are not to be construed as limiting the disclosure. Numerous specific details are described to provide a thorough understanding of embodiments of the present disclosure. However, in certain instances, well-known or conventional details are not described in order to provide a concise discussion of embodiments of the present disclosure.

As used herein, the terms "comprising" and "including" are to be construed as inclusive and open-ended, rather than exclusive. In particular, the terms "comprises" and "comprising," and variations thereof, when used in the specification and claims, are intended to include the specified features, steps or components. These terms should not be interpreted to exclude the presence of other features, steps or components.

As used herein, the term "exemplary" means "serving as an example, instance, or illustration," and should not be limited to being preferred or advantageous over other configurations disclosed herein.

As used herein, the terms "about" and "approximately" are intended to encompass variations that may exist in the upper and lower limits of a range of values, such as variations in properties, parameters, and dimensions. The terms "about" and "approximately" mean plus or minus 25% or less, unless otherwise indicated.

As used herein, a percentage value associated with a temperature is intended to refer to a temperature in degrees celsius.

It should be understood that any given range or group is intended to refer to each member of the range or group individually, as well as to each possible sub-range or sub-group encompassed therein, and to any sub-range or sub-group thereof by way of similar shorthand unless otherwise indicated herein. Unless otherwise indicated, this disclosure relates to and expressly encompasses each specific member as well as a combination of subranges or subgroups.

As described above, conventional methods of chemical analysis in the aluminum industry employ the use of spark OES on solid samples. Unfortunately, this conventional approach involves a number of technical problems that may hamper the ability to achieve accurate chemical analysis.

In particular, the sample preparation process may lead to errors being introduced. For example, errors may be introduced during the sample preparation process for a number of potential reasons, including but not limited to: (i) a temperature change of the melt or mold when sampling is performed; (ii) unevenly pouring into a sample mold; (iii) segregation associated with the cooling rate of the metal; (iv) voids, cracks or gaps in the sample; (v) excessive surface roughness or smoothness after grinding; and (vi) analyzing the surface contaminants prior to analysis.

In addition, conventional methods of casting samples and performing subsequent analyses may be subject to errors due to confusion between individual samples. Another problem associated with conventional chemical analysis workflows is the potential safety hazard caused by traffic within the smelter due to transporting the cast sample to the laboratory. Considering the steps of collecting liquid metal, casting solid samples, transporting the samples to a central analysis facility, performing mechanical preparation and chemical analysis, several hours may elapse from the time the metal is sampled until the analysis results are available to plant operators to make processing decisions.

The present inventors have identified and carefully considered the above-described technical and workflow challenges, and have set out to develop a new chemical analysis method that would overcome the problems associated with conventional methods of chemical analysis. In particular, the inventors have recognized that in order to overcome these technical problems, a new chemical analysis modality would be needed that facilitates robust, rapid, and accurate chemical testing in real-time and in-situ.

Various attempts have been made to monitor the state of the reduction tank in the primary aluminium smelter in real time using different detection modalities. Some of these methods include analysis of cell temperature and bath chemistry, analysis of individual anode current signals, analysis of cell voltage noise, and optionally, analysis of a number of additional parameters affecting cell current efficiency, energy consumption, and operating life. Differential thermal analysis has been successfully applied to determine bath chemistry (i.e., bath ratio and alumina (Al ₂O₃) content) within minutes, replacing alternative time-consuming sample preparation and X-ray analysis in the central laboratory using commercially available STARprobe ^TM (x.wang: "Alcoa STARprobe ^TM -update for further development of measured cryolite properties (Update in further development for measuring cryolite properties)", TMS light metal 2016, pages 397-402).

However, real-time and in situ measurement of chemical impurities in produced metals presents unique challenges that cannot be resolved by the above-described real-time monitoring methods. Laser Induced Breakdown Spectroscopy (LIBS), an atomic emission spectroscopy technique suitable for liquid and solid measurements, has become a promising technique for liquid metal chemistry analysis. Specifically, LIBS has been previously used to measure the impurity content of liquid aluminum (A.K. Rai, F. -Y.Yueh, J.P.Singh: "Laser-induced breakdown Spectroscopy (Laser-induced breakdown spectroscopy of molten aluminum alloy) of molten aluminum alloys", optical applications, 42 (2003), pages 2078-2084; J.Herbert et al: "Industrial applications for analysis of molten metals (The Industrial Application of Molten METAL ANALYSIS)", TMS light metals 2019, pages 945-952; S.Gudmundsson et al: "Accurate Real-time elemental analysis of molten aluminum and aluminum alloys (Acurate Real-TIME ELEMENTAL (LIBS) Analysis of Molten Aluminum and Aluminum Alloys)", TMS light metals 2020, pages 860-864).

Attempts to adapt LIBS to real-time and in-situ testing in an industrial environment have been fraught with difficulties. For example, the complex and hazardous environment inside the primary aluminum smelter presents a number of technical challenges for the use of LIBS systems, as high temperatures, dust and fumes can be emitted from the tank when the LIBS system is turned on. Furthermore, the high magnetic fields present near the reduction cell present challenges to operating the measurement equipment (see, e.g., sun et al, spectroscopy report B section 142 (2018) 29-36). While compact hand-held LIBS analyzers are available from several suppliers, they are not suitable for analyzing liquid metal and do not provide the detection limits or accuracy required to monitor aluminum from a reduction cell.

Thus, while LIBS is promising for improved chemical composition analysis, there remains a need to address the pending technical challenges in order to facilitate the adaptation of LIBS to real-time and in-situ implementations that are robust enough to provide rapid and accurate chemical analysis of molten metal.

One problem encountered by the present inventors when attempting to adapt a LIBS measurement system to a portable configuration is the need to ensure a consistent measurement temperature of the molten metal sample during LIBS measurement. In particular, the relative intensity of the LIBS emission lines may depend on the sample temperature, with the result that variations in sample temperature between successive LIBS measurements may lead to significant errors in the reported impurity concentrations.

While such problems can potentially be addressed by actively controlling the temperature of the molten metal sample prior to or during LIBS measurement, such methods can be problematic for portable implementations due to the high power consumption of the active heat source, which can hamper the ability to power the portable system using the battery.

The present inventors have attempted to overcome these technical problems by developing a LIBS system employing passive cooling of a molten metal sample, thereby avoiding the need for active heating prior to or during LIBS measurement. Furthermore, it has been determined that by monitoring the temperature of a molten metal sample during cooling of the molten metal sample and initiating a LIBS measurement when or after the monitored temperature meets a preselected measurement temperature criterion, such an implementation may be adapted to facilitate accurate and repeatable LIBS measurements of subsequently measured samples without introducing significant measurement errors due to changes in the sample temperature. Such an implementation is particularly beneficial in mobile configurations, which can greatly simplify system design and facilitate battery powered configurations, since there is no need for active heating of the molten metal sample prior to and during the LIBS measurement process. Furthermore, this implementation avoids introducing additional complexity into the spectroscopic analysis to detect and correct for the effects of temperature variations of the melt.

Monitoring the temperature of the molten metal samples and initiating the LIBS measurements only when the measured temperature criteria are met ensures that LIBS measurements made on different molten metal samples (e.g., different samples from a common tank or different samples from different tanks) are performed at or near a common temperature during the LIBS measurements, although these molten metal samples may have different initial temperatures or different cooling rates due to different temperatures of the measuring crucible. Such example implementations thereby avoid, prevent, or reduce measurement errors due to changes in sample temperature.

As will be described below, the present example embodiment may be beneficial in reducing sources of error in the analysis by analyzing the metal in a liquid state and by facilitating immediate, direct, and explicit correlation of chemical analysis results to the corresponding reduction tanks. The present example systems and methods further facilitate consistent and rapid workflow when sequentially measuring samples from multiple tanks. Similarly, the present example systems and methods may be used to facilitate rapid measurements of a series of samples extracted from a single reduction cell, or any similar manner that requires analysis of multiple samples of liquid metal from a single source or multiple sources in a rapid and accurate manner.

Thus, in some example implementations, a portable chemical analysis system includes a LIBS measurement subsystem and a temperature sensor configured to monitor a temperature of a molten metal sample during passive cooling of the molten metal sample. The portable measurement system compares the measured temperatures of the molten metal samples and controls the LIBS measurement subsystem to initiate LIBS measurements after a preselected measured temperature criterion is met.

An example embodiment of such a portable LIBS system is shown in fig. 1. An example system includes a LIBS subsystem that includes a LIBS measurement head 200. The LIBS subsystem is operatively connected or connectable to the control and processing circuitry shown at 100, as described in further detail below. The LIBS measurement head 200 includes a beam delivery subsystem for delivering LIBS laser pulses onto the surface of the molten metal sample 10 and collecting optical emissions of plasma plumes generated in response to the laser pulses interacting with the target material. The LIBS measurement head 200 may include all the subassemblies of the LIBS system (including the LIBS laser source and detector). Alternatively, some of the components of the LIBS system (e.g., the LIBS laser source and/or detector) may be disposed in a housing in optical and/or electrical communication with the LIBS measurement head 200.

Prior to performing the LIBS measurement, the molten metal sample 10 is passively cooled within the crucible 20 (e.g., ladle) while monitoring the temperature of the metal molten sample 10, for example, as illustrated in fig. 2A. As shown in fig. 1, the crucible may be supported by a crucible support 30. LIBS measurements are initiated when (or after) the temperature of the molten metal sample meets a preselected measurement temperature criteria, as shown in fig. 2B.

Referring again to fig. 1, the example system includes a temperature sensor 210, which temperature sensor 210 may be positioned to permit interrogation of the surface of the molten metal sample 10. In some example implementations, the temperature sensor may be a non-contact temperature sensor, such as, but not limited to, an infrared pyrometer or a thermal camera. Such sensor responses may be corrected for the emissivity of the respective material being measured. Alternatively, the temperature sensor may be a contact-based temperature sensor, such as, but not limited to, a thermocouple or a resistance thermometer.

The measurement temperature criteria ensure that LIBS measurements are performed on different molten metal samples (e.g., different samples from a common trough or different samples from different troughs) at or near the same temperature, thereby avoiding, preventing, or reducing measurement errors due to changes in sample temperature, as discussed above. For example, the LIBS measurement head 200 may be controlled such that (i) LIBS measurements are initiated immediately after the measured temperature criteria are met; (ii) Initiating a LIBS measurement after a fixed delay after the measured temperature criterion is met; or (iii) initiate the LIBS measurement within a specified time interval after the measured temperature criteria are met, wherein the time interval may be calculated based on the observed cooling rate.

In one example implementation, the measured temperature criteria may be met when the measured temperature of the molten metal sample 10 reaches a measured temperature (such as, for example, the measured temperature exceeding the melting point temperature of the molten sample by up to 5%, or for example, by up to 10%, or for example, by up to 15%, or for example, by up to 20%, or for example, by up to 25%). In the example case of molten aluminum, the measured temperature is selected from the range of 700 ℃ -800 ℃ (such as 750 ℃).

In the case where the LIBS measurement head 200 resides in a parked position (e.g., as shown at 201 in fig. 1) during monitoring of the temperature of the molten metal sample 10 (e.g., so as to provide sufficient line of sight for non-contact temperature sensing), initiation of the LIBS measurement may include repositioning the LIBS measurement head 200 (e.g., as shown at 230 in fig. 1) above the molten metal sample 10, optionally lowering the LIBS measurement head 200 relative to the surface of the molten metal sample 10, and subsequently delivering a LIBS laser pulse to the molten metal sample 10. Alternatively, in the case where the temperature of the molten metal surface may be measured with a LIBS measurement head residing in a measurement location above the molten metal sample 10, the LIBS measurement may be initiated after the measured temperature of the molten metal sample 10 meets a preselected measurement temperature criterion without laterally moving the LIBS measurement head 200.

The surface of the molten metal sample may be skimmed using an automated skimmer (not shown in fig. 1) or a manually operated skimmer prior to performing the LIBS analysis. This skimming step serves to remove any dross or remaining bath material from the surface of the sample to expose the liquid metal for analysis and ensure proper measurement of the temperature of the liquid metal in the case of non-contact temperature measurement, as the formation of dross will affect the emissivity of the sample surface. After performing the LIBS measurements, the LIBS measurement head 200 may be retracted (e.g., automatically) and the measurement results may be displayed and recorded (e.g., to a database). After LIBS analysis, the molten metal sample may be returned to the reduction tank, discarded elsewhere in liquid form, or allowed to solidify and subsequently discarded or stored for reference. In some example implementations, the mobile analysis system may include an integrated disposal container for discarded samples.

The inventors have found that the cooling rate of the molten metal sample 10 during LIBS measurements may affect the accuracy of the LIBS measurements. In particular, if the cooling rate is sufficiently high, temperature variations generated during the LIBS measurement step, which may involve a duration of several seconds (such as, for example, about 5 seconds), may lead to inaccuracy in the determination of the impurity concentration. Furthermore, if the timing of the LIBS measurements is not accurately controlled with respect to the determined time at which the measured temperature criteria are met, large variations in temperature during the LIBS measurement step may make the system susceptible to measurement errors. Similarly, high cooling rates may negatively impact the consistency of the measurement conditions of a series of measurements of different liquid metal samples.

This problem is exacerbated when the crucible is made of a material that can cause rapid cooling of the molten metal sample. For example, to facilitate rapid removal of a molten metal sample after LIBS measurement, it may be useful or necessary to bring the crucible into contact with an impact surface to expel solidified metal from the crucible. In such cases, it may be beneficial to use a non-ceramic crucible that is able to withstand the impact without risk of breakage. One example of a suitable crucible is a metal crucible, such as a crucible made of structural steel. Considering that such metal crucibles generally have a high heat capacity and a high thermal conductivity, the molten metal sample can be rapidly cooled in a cold metal crucible. In some example implementations, the thermal capacity of such a crucible may reside between 400J/K and 500J/K, and the thermal conductivity of the crucible material may reside between 40W/m-K and 50W/m-K.

To avoid or reduce errors caused by rapid cooling of the molten metal sample, the inventors have found that it may be beneficial to preheat the crucible 20 prior to delivering the molten metal sample 10 to the crucible 20. Such preheating may be advantageous to reduce and/or control the cooling rate of the molten metal sample 10 after it is received by the crucible 20. In addition, preheating improves the safety of the liquid metal sampling process by ensuring that the crucible is free of moisture prior to introduction of the liquid metal.

Preheating of the crucible may be performed according to various methods. In some example embodiments, preheating is performed external to the portable LIBS measurement system, such as by utilizing available heat from the reduction tank. For example, in an example implementation involving an aluminum smelter, the crucible may be preheated by contacting the crucible with cryolite shells formed in the reduction tank for a period of time sufficient to bring the crucible to a desired temperature.

After preheating the crucible, a sample of molten metal may be delivered to the crucible (e.g., a measuring spoon). For example, a sample of liquid molten metal may be extracted using methods conventionally used to sample metal from a reduction cell, such as collecting molten metal from a reduction cell using a sampling ladle. For example, a sample of molten metal may be introduced into the sample crucible manually (e.g., by way of a human operator using such a sampling ladle). Furthermore, samples may be extracted manually or automatically from other types of sources, such as mixing ovens, holding ovens, etc., wherein in some embodiments a sampling scoop may also be used as a sample crucible that holds samples during measurement.

In some example embodiments, it may be beneficial to ensure that crucible 20 has been preheated by a sufficient amount to ensure that the cooling rate will not be too fast during LIBS measurements. For example, prior to introducing the molten metal sample 10 into the crucible 20, the temperature of the crucible 20 may be measured and compared to a crucible temperature standard to assess whether the crucible 20 has been sufficiently preheated prior to receiving the molten metal sample 10. The measurement temperature criterion is configured such that the temperature of the molten sample exceeds the temperature of the crucible during the LIBS measurement when the crucible temperature criterion is met.

In some example implementations, a temperature sensor 210 for monitoring the temperature of the molten metal sample 10 may be used to measure the temperature of the empty crucible 20. Such an example implementation is illustrated in fig. 2C. Alternatively, a separate temperature sensor may be used to monitor the temperature of the molten metal sample and may be used to measure the temperature of the crucible 20 prior to delivery of the molten metal sample 10.

In some example embodiments, the crucible temperature criteria may be defined such that when the measured crucible temperature exceeds a preselected minimum temperature value, such as, for example, a minimum temperature in the range of 100 ℃ to 60% of the melting point temperature of the molten metal, or, for example, 15% -60% of the melting point temperature (e.g., 100 ℃ -400 ℃ in the case of aluminum), the crucible temperature criteria are met, thereby ensuring that the cooling rate of the molten metal sample 10 remains within certain limits after the molten metal sample 10 is delivered to the crucible 20. For example, the crucible temperature criterion may be selected such that the molten metal sample is cooled to less than 50 ℃ during LIBS measurement, or to less than 20 ℃ during LIBS measurement, or to less than 10 ℃ during LIBS measurement, or to less than 5 ℃ during LIBS measurement, for example.

In the absence of an upper limit for the permitted initial temperature of the crucible 20, in some cases, the crucible 20 may be preheated to a temperature that is very high while meeting the crucible temperature criteria such that an excessive amount of time will elapse before the molten metal sample 10 cools to a temperature that meets the measured temperature criteria. In such cases, the time required to collect and analyze subsequent samples will increase accordingly. Such a situation may be avoided by defining the crucible temperature criterion such that the crucible temperature exceeding the upper temperature value does not meet the crucible temperature criterion. For example, the crucible temperature criteria may include a maximum crucible temperature selected to be in the range of 50% -90% of the melting point temperature (e.g., between about 330 ℃ and 600 ℃ in the example case of aluminum). The maximum crucible temperature limit additionally ensures that the contamination level of the molten metal by crucible material is minimized.

For example, the crucible temperature criterion may be met when the temperature of the crucible 20 (prior to receiving the molten metal sample 10) is within a predefined temperature range, such as, for example, a range of 100 ℃ to 60% of the melting point temperature of the molten sample, or, for example, 15% -60% of the melting point temperature (100 ℃ -400 ℃ in the example case of aluminum) or 30% -75% of the melting point temperature (200 ℃ -500 ℃ in the example case of aluminum). Thus, the predefined temperature range may be characterized as a "goldiluate" range such that when the molten metal sample 10 is delivered to a crucible that meets the crucible temperature criteria, the molten metal cools at a rate slow enough to permit accurate LIBS measurements (when the temperature of the molten metal sample meets the measurement temperature criteria) and such that the molten metal sample cools to a temperature that meets the measurement temperature criteria within a sufficiently short duration. For example, the maximum temperature permitted by the crucible measurement standard may be defined such that the molten metal sample cools to a temperature that meets the measurement temperature standard within 1 minute, or within 30 seconds, or within 15 seconds after having been delivered to the crucible.

In some example implementations, an indication may be provided to an operator when the temperature of the empty crucible 20 meets crucible temperature criteria. Non-limiting examples of suitable indications include a displayed message, a symbol or color, and an audible alarm or message. The indication may be used to alert an operator that the empty crucible 20 is ready to receive a molten metal sample. In other example implementations, the temperature of the empty crucible 20 may be displayed. In such cases, an operator with knowledge of the appropriate crucible temperature criteria (e.g., minimum crucible or desired crucible temperature range) may deliver a molten metal sample to the crucible when the displayed temperature meets the known crucible temperature criteria.

Referring now to fig. 3, a flowchart illustrating an example method of performing LIBS analysis on a molten sample using a LIBS measurement system (such as the system illustrated in fig. 1) is provided. A preheated empty crucible (without the molten metal sample) is initially provided and its temperature is measured at step 300. At step 310, crucible temperature criteria are evaluated. If the crucible criteria are not met (as indicated at 312) because the crucible temperature is too low, the operator may heat the crucible (as indicated at 314) and the crucible temperature may be re-measured and re-evaluated at 300. If the crucible temperature is too high (as shown at 310), the crucible may be passively cooled and the crucible temperature may be re-measured and re-evaluated at 300.

If the crucible temperature criteria are met, an indication may be provided that the crucible is ready to receive a molten metal sample, as shown at 320. After the molten metal sample is received in the crucible, the temperature of the molten metal sample is monitored during cooling as indicated at 330 and the measured temperature criteria is evaluated as indicated at 340. When the measured temperature criteria are met, LIBS measurements are initiated, as shown at 350.

In the example method described above with reference to fig. 3, the empty crucible is permitted to passively cool when (in step 310) the measured temperature of the empty crucible does not meet the crucible temperature criteria. For example, when a crucible is used for multiple LIBS measurements, the crucible temperature may rise due to repeated exposure to hot molten metal samples, and after the previous molten metal sample is discarded, the crucible temperature may exceed the maximum temperature permitted by the crucible temperature standard. Unfortunately, as noted above, the step of passively cooling such overheated crucibles may introduce unnecessary delays into the measurement process, especially when it is desired to sequentially measure many samples with as low a time delay between measurements as possible.

The problems associated with the delay in passively cooling the overheated crucible can be overcome by replacing the overheated crucible with a different crucible that has been preheated to a lower temperature. This process is schematically illustrated in fig. 5A, wherein the superheating crucible 20 is replaced with a second preheating crucible 22.

Fig. 4 provides a flow chart illustrating an example method involving replacing a superheated crucible to minimize inter-measurement delays in a measurement sequence. The example flow chart begins with step 316 from the flow chart in fig. 3, corresponding to determining that an empty crucible has a temperature that is too hot to meet the crucible temperature criteria, as shown at 400. The crucible is replaced with a second preheated crucible, as shown at 410. The second crucible may have a temperature that meets the crucible temperature criteria (as illustrated in fig. 5A), or may have a temperature that exceeds the maximum allowable temperature of the crucible criteria but is less than the temperature of the first crucible, causing a shorter time delay before the second crucible will cool to a temperature that meets the crucible temperature criteria.

The first (superheated) crucible, after having been replaced by the second crucible, may be supported on a crucible holder integrated with the LIBS measurement system (e.g., integrated with a co-moving support). As illustrated in fig. 5A, the first crucible 20 may be placed onto a crucible support 32 (e.g., a spoon support stand) that has been previously used to support the second crucible. Alternatively, the first crucible 20 may be placed onto a separate crucible support. The crucible support 32 may be configured such that its effective thermal mass, heat dissipation rate, and degree of thermal contact with the installed crucible promote reasonably rapid cooling of the crucible.

As shown at step 420 in fig. 4, following steps 330-350 of fig. 3, LIBS measurements are then performed on the new molten metal sample using a second crucible. Further, as shown at step 424, the process may be repeated one or more times for different samples using the second crucible.

During use of the second crucible, the first crucible is supported by the additional crucible support 32 and passively cooled from its initial superheated state. The temperature of the first crucible may be measured intermittently in order to determine when the first crucible again meets the crucible temperature criteria, as illustrated in fig. 5A. For example, in the case where the temperature sensor 210 is fixed relative to the LIBS measurement head 200, the LIBS measurement head 200 may be translated to facilitate interrogation of the first crucible 20 residing in the crucible support 32 between LIBS measurements using the LIBS measurement head 200. In alternative example implementations, a separate temperature sensor may be provided for monitoring the temperature of the crucible residing in the additional crucible support 32. For example, a temperature sensor (e.g., such as, but not limited to, an infrared pyrometer or thermocouple sensor) may be integrated into the additional crucible support 32 for monitoring the temperature of the first crucible (e.g., as shown at 222 in fig. 1). When the first crucible again meets the crucible temperature measurement criteria, an indication may be provided to the operator. Alternatively, the temperature of the first crucible may be displayed to permit an operator to determine when the first crucible meets a predetermined crucible temperature criteria.

Referring again to fig. 4, after the second crucible is reused, the temperature of the second crucible may no longer meet the crucible measurement criteria and the second crucible may need to be cooled prior to further use. In such cases, the second crucible may be replaced with another crucible, rather than allowing the second crucible to passively cool until its temperature meets the crucible temperature criteria.

Step 450 illustrates an example scenario in which the second crucible is swapped with the preheated third crucible. Alternatively, as shown in step 460, the second crucible may be swapped with the first crucible, as the first crucible will have cooled during LIBS measurements using the second crucible. These options are schematically illustrated in fig. 5B, which shows the second crucible 22 swapped with the first crucible 20 or the third crucible 24 (residing on the third crucible support 34) in fig. 5B. The second crucible may then be passively cooled (as shown at 445) while LIBS measurements are performed on additional molten metal samples using the first crucible or the third crucible, respectively, as shown at steps 455 and 465.

While the foregoing example implementations employ one or two additional crucible supports, three or more crucible supports may be included to provide additional locations for cooling the crucible. The number of crucible supports required may depend on the analysis rate and the need to ensure continuous operation when measurements are taken from multiple sampling points.

As explained above, in some example implementations, the LIBS measurement head 200 may reside in a parked position prior to performing the LIBS analysis. For example, the LIBS measurement head may be translated (e.g., automatically translated) laterally and/or vertically to a parked position during monitoring of the molten metal sample in order to provide a sufficient line of sight for non-contact temperature sensing. The LIBS measurement head may also be translated to a park position to perform one or more calibration steps, as described in further detail below.

Fig. 6 illustrates a system state in which the LIBS measurement head 200 is parked in a lateral position to permit non-contact temperature sensing of a molten metal sample via the temperature sensor 210. The LIBS measurement head 200 includes a heat shield 220 positioned to thermally shield the LIBS measurement head 200 from heat radiated from the crucible 20. The figure illustrates a non-limiting example implementation in which the thermal shield 220 is secured to the LIBS measurement head 200 such that when the LIBS measurement head 200 resides in the parked position, the thermal shield 220 resides between the LIBS measurement head 200 and the crucible 20.

In some example embodiments, one or more calibration devices may be employed to calibrate the LIBS measurement head 200 while the LIBS measurement head 200 resides in a parked position. Fig. 1 illustrates an example implementation in which the system includes a calibration station 500 accessible by the LIBS measurement head 200 in a park position 201. As shown in fig. 1, the calibration station 500 may provide an interface to the processing and control circuitry 100 (e.g., under the control of the processing and control circuitry 100), as shown at 502. In cases where the support 50 is a mobile support and the mobile LIBS system is employed in a non-laboratory environment, an integrated calibration station may be employed to ensure accurate operation of the system even in challenging environmental conditions such as high temperature and dust.

For example, in some implementations of LIBS analysis, it may be beneficial to ensure a consistent distance between the liquid metal surface and the excitation and detection optics (e.g., the distal region of the LIBS measurement head 200). The distance may be controlled using any suitable type of distance sensor that provides feedback to the mechanical translation mechanism of the LIBS measurement head 200. However, during measurement operations, the LIBS measurement head may be subject to significant changes in ambient temperature and heat generated by heat radiation from the sample and measurement ladle, and such heat may be exacerbated in non-laboratory environments (such as in an aluminum smelter's potroom). To ensure quick and repeatable measurements, a calibration station may be incorporated into the system (e.g., supported by a moving support structure with a LIBS system) allowing the distance sensor to be calibrated prior to a given (optionally each) measurement, thereby correcting at least in part for thermal drift in the system.

An example implementation of a calibration station for calibrating a distance sensor is shown in fig. 7A. The LIBS measurement head 200 includes a distance sensor 510, and the remainder of the LIBS measurement subsystem (e.g., including source and detection components) is schematically illustrated at 205. The LIBS measurement head 200 is shown in a parked position away from the crucible, with the distance sensor residing above the calibration reference surface 522 of the distance sensor calibration station 520. The calibration reference surface 522 provides a fixed reference position that may be used to calibrate the distance sensor 510. For example, the LIBS measurement head 200 may be lowered (manually or automatically) in a direction parallel to the optical axis of the LIBS measurement head 200 until the LIBS measurement head 200 contacts the contact location 526 (e.g., the contact may be detected, for example, via a contact sensor, such as a conductive or mechanical contact sensor). Contact of the distal end of the LIBS measurement head 200 (or another suitable location within the distal region of the LIBS measurement head) with the contact location 526 of the distance sensor calibration station 520 ensures that the distance sensor 510 and the reference surface 522 are separated by a known distance, thereby facilitating calibration of the distance sensor 510 via interrogation of the reference surface by the distance sensor 510.

Fig. 7B illustrates an alternative example implementation in which the distance sensor calibration station 530 is resiliently biased, such as by one or more springs 535 or other suitable resiliently deformable components, which may be used to ensure that a known spatial offset is maintained between the distance sensor 510 and the reference surface 522 when the LIBS measurement head 200 is further lowered after having been contacted with the contact surface 526 without having to rely on a separate contact sensor. The one or more springs 535 may also advantageously ensure accurate and repeatable leveling of the reference surface 522 relative to the LIBS measurement head 200 when the contact location 526 is provided as a contact surface or as a plurality of contact locations defining a contact plane.

Fig. 7C illustrates an example of a calibration station 540 for calibrating the optical response of the LIBS subsystem. The example calibration station 540 supports (e.g., via a rack) interchangeable solid state reference samples of a known chemical concentration of reference material 545 to correct for drift in the signal response of the LIBS subsystem. For example, the analysis of a solid state reference sample is compared to a previous analysis of the same reference sample, and the system is calibrated to accommodate observed concentration differences of the detected reference material. In some example implementations, the calibration station may advantageously facilitate translational and/or rotational functionality to ensure that the reference material may be measured at a new location when a subsequent drift correction measurement is performed. The rotation and/or translation function may also be used to interrogate a plurality of reference materials mounted on the calibration station. Such rotation and/or translation of the calibration reference station 540 may be autonomously controlled by the control and processing circuitry 100, for example, as shown at 502 in fig. 1. Fig. 7C illustrates an example implementation in which the motor 550 is controlled to rotate the solid state reference sample relative to the LIBS interrogation location as subsequent calibration is performed.

In some example embodiments, the calibration station may facilitate a variety of calibrations including, but not limited to, calibration of the distance sensor and calibration of the response of the LIBS measurement system using one or more reference materials. In some example implementations, one or more calibration steps may be performed autonomously when one or more conditions are met (such as, for example, after a selected number of samples have been measured, after a detected change in environmental conditions, and/or after an elapsed time).

Referring again to fig. 1, the libs subsystem is supported on a support 50. As described above, in some example implementations, the support 50 may be a mobile (portable) support. For example, the support 50 may be a manually movable cart (trolley) or a motorized vehicle (e.g., a trolley with battery-powered translation), including semi-autonomous (self-driving) vehicles. In some example embodiments, the portable LIBS system may be battery powered. As described above, the present example method involving passive cooling and temperature monitoring prior to initiating LIBS measurements is well suited for battery-powered implementations, as there is no active heating source with high power requirements.

Fig. 8 illustrates an example of a mobile LIBS measurement system comprising: a LIBS subsystem (200, 205); a main crucible support 30 for supporting the crucible in a measurement position for performing LIBS measurements; and at least one additional crucible support for supporting the additional crucible during passive cooling prior to being used for LIBS measurements (the example system includes two additional crucible supports 32 and 34); a battery source 260; the support 55 is moved. Fig. 9 illustrates that the calibration station 500 is included in a mobile configuration, wherein the calibration station 500, the LIBS subsystem, and one or more crucible supports (e.g., crucible supports 30, 32, and 34) are supported by the mobile support 55.

Although many of the present example embodiments relate to portable LIBS systems, it should be noted that in other example embodiments, the support that supports the LIBS measurement subsystem may be a fixed support. For example, any of the present example systems or methods may be applicable to non-portable configurations, such as system configurations applicable to implementation at a furnace, launder, or other stationary source of liquid metal in a plant/smelter or laboratory environment. In such environments, sampling may be advantageously automated (e.g., through the use of robotic arms).

Furthermore, while many of the foregoing example implementations employ passive cooling of the molten metal sample prior to LIBS analysis and/or passive cooling of the superheated crucible prior to further use, it will be appreciated that some implementations may employ active heating and/or active cooling. For example, in some example implementations, forced air cooling (forced air) may be employed to cool the overheated empty crucible residing on the crucible support. Feedback from a temperature sensor measuring the crucible temperature can be used to control the cooling device to bring the empty crucible to a temperature that meets the crucible temperature criteria. Active heating may also optionally be employed to preheat one or more crucibles. For example, in some example implementations, one or more crucible supports can include a heat source (e.g., an induction or resistive heater or a gas burner). Feedback from a temperature sensor measuring the crucible temperature can be used to control the heat source to bring the empty crucible to a temperature that meets the crucible temperature criteria. In some example implementations, the system may include both active heating and cooling devices to control the temperature of one or more crucibles.

In other example implementations, active heating (such as induction heating) and/or cooling (such as forced air cooling) may be employed in conjunction with the monitored temperatures of the molten metal sample and crucible to stabilize the temperature of the molten metal sample prior to or during LIBS measurements.

Embodiments of the present disclosure are applicable to a variety of metals and metal alloys, such as, but not limited to, aluminum, steel alloys, iron alloys, copper, zinc, lead, and other metals and metal alloys in their liquid state, and may be useful in the industrial environments and applications mentioned above.

It will be understood that the present disclosure is not intended to be limited to the analysis of any particular element and may be used to determine the concentration of a major or minor component in a metal or alloy sample. Thus, in some embodiments, the method and/or apparatus is used to determine the true volume concentration of one or more elements selected from the following elements in a liquid metal or alloy sample: aluminum, silicon, phosphorus, sulfur, chloride, calcium, magnesium, sodium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, strontium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, cadmium, tin, antimony, tungsten, rhenium, iridium, platinum, gold, mercury, lead, and bismuth. The method is also suitable for quantifying very light impurity elements such as hydrogen, lithium, beryllium, boron, carbon, etc., which are difficult to detect using some other analytical method. Furthermore, it will be appreciated that trace impurities may be introduced into the liquid metal from the sampling equipment (e.g., the sampling ladle and the measuring crucible) itself. The present disclosure is equally applicable to the measurement and identification of such contaminants.

Referring again to fig. 1, the libs system generally includes excitation and detection means for generating and receiving atomic emissions from the sample. This includes, but is not limited to, all variants of laser guided plasma excitation methods known in the art, including but not limited to, the use of conventional LIBS methods, LIBS with dual collinear or non-collinear pulses, combined LIBS/discharge methods, and the like.

In some example embodiments, the spectroscopic analysis is based on the LIBS method, wherein one or more laser pulses are directed to the sample surface sequentially through excitation optics, and light emitted from the sample is received through receiving optics and passed to a detector for recording spectroscopic information of the detected light. Optical detection methods and subsequent processing of the detected emissions are well known to those skilled in the art. The emission peak or peaks are then analyzed from the spectral information and typically compared to a calibration value in order to obtain a quantitative determination of the element or elements.

The excitation optics and the receiving optics of the LIBS measurement subsystem may be completely separate or partially comprise the same optical elements. In a preferred implementation, the excitation device and the receiving optics may be accurately positioned at a predetermined distance from the sample surface for each individual excitation event. During field operation, the accuracy of the positioning over time is advantageously maintained using the distance calibration function as described above.

The pulsed excitation lasers employed in the various example embodiments may generally be of the conventional type used in current LIBS configurations. According to the invention, stable excitation conditions may be provided, wherein the optical excitation is configured such that a sufficiently large and reproducible volume of the liquid metal sample is ablated during excitation, and such that the chemical composition of this ablated portion of the sample represents the composition of the whole sample.

In some embodiments, an inert gas stream (such as argon, helium, or nitrogen) is fed from a source (such as a pressurized tank mounted on the same portable support as the LIBS system) through one or more gas channels near the sampling point in order to maintain an inert atmosphere during LIBS measurements.

In some example embodiments, the receiving optics of the LIBS measurement head may include more than one lens, wherein the lenses are optionally arranged radially around the point of contact of the laser pulse with the sample surface. Light collected by one or more receiving optics 10 may be transmitted to the same spectrometer or to a different spectrometer via an optical fiber or other optical transmission device (e.g., each of the plurality of lenses may transmit light to its respective spectrometer). In some embodiments, such multiple spectrometers may be configured such that each spectrometer collects emissions over a limited range of wavelengths such that the multiple spectrometers together cover the entire desired range of wavelengths. In some embodiments, spectral detection may also include detecting the selected wavelength band using one or more suitable bandpass filters and optical sensors.

Referring again to fig. 1, an example implementation of control and processing circuitry 100 is shown that includes one or more processors 110 (e.g., CPU/microprocessor), a bus 105, a memory 115, the memory 115 may include Random Access Memory (RAM) and/or Read Only Memory (ROM), a data acquisition interface 120, a display 125, an external storage 130, one or more communication interfaces 135, a power supply 140, and one or more input/output devices and/or interfaces 145 (e.g., speakers, user input devices such as a series of buttons, a joystick, a keyboard, a keypad, a mouse, a position tracking stylus, a position tracking probe, a foot switch, and/or an acoustic transducer for capturing voice commands).

The previous example methods may be autonomously implemented according to the modules 155, 160 and 165 of the control and processing circuitry 100. For example, measurement of the temperature of the empty crucible, monitoring of the temperature of the molten metal sample, and evaluation of crucible temperature criteria and measured temperature criteria may be performed in accordance with executable instructions implemented by the temperature monitoring module 155. Robot control of the LIBS measurement head (and optionally one or more components of the calibration station 500) may be controlled in accordance with the robotic actuation module 160, and LIBS measurement acquisition and data processing may be performed in accordance with the LIBS measurement module 165.

It should be understood that the example system shown in FIG. 1 is illustrative of a non-limiting example embodiment and is not intended to be limited to the components shown. Further, one or more components in the control and processing circuitry 100 may be provided as external components that provide an interface to the processing device.

For example, the control and processing circuitry may include a local computing subsystem comprising a first set of components supported by the support 50, wherein the local computing subsystem may be connected to one or more external computing devices via a network. The network may include local and/or external networks, wherein one or more segments of the network may be wireless. For example, in some implementations, data obtained locally by the local computing subsystem and optionally processed may be transferred to one or more external computing devices (such as, for example, an external control system residing within or remote from the process plant, or one or more mobile computing devices such as, for example, mobile phones, laptops, and tablet computing devices). Examples of such data include raw data, analysis results, and/or equipment status (which may include, for example, environmental variables, error messages, alarms, or other measurements or indications). Communication between the local computing subsystem and one or more external computing devices may be unidirectional (e.g., for autonomous uploading of data to a remote computing device) or bidirectional. In some example implementations, the local computing subsystem may be configured to receive one or more portable computing devices in a "docked (docked)" configuration for transmitting data over a wired or wireless connection.

Although only one of each component is illustrated in fig. 1, any number of each component may be included in the control and processing circuitry 100. For example, computers typically include a variety of different data storage media. Further, while bus 105 is depicted as a single connection between all components, it should be appreciated that bus 105 may represent one or more circuits, devices, or communication channels (which may optionally include wireless communication channels) linking two or more of the components. For example, in a personal computer, bus 105 typically includes or is a motherboard. Control and processing circuitry 100 may include more or fewer components than those shown.

Control and processing circuitry 100 may be implemented as one or more physical devices coupled to processor 110 through one of a plurality of communication channels or interfaces. For example, control and processing circuitry 100 may be implemented using an Application Specific Integrated Circuit (ASIC). Alternatively, the control and processing circuitry 100 may be implemented as a combination of circuitry and software, where the software is loaded into the processor from memory or through a network connection.

Some aspects of the present disclosure may be at least partially embodied in software. That is, the techniques may be implemented in a computer system or other data processing system in response to a processor (such as a microprocessor) of the computer system or other data processing system executing sequences of instructions contained in a memory (such as ROM, volatile RAM, nonvolatile memory, cache, magnetic and optical disks, or remote storage). Further, the instructions may be downloaded into the computing device over a data network in the form of compiled and linked versions. Alternatively, the logic for performing the processes discussed above may be implemented in additional computer and/or machine-readable media, such as discrete circuitry components, e.g., large scale integrated circuits (LSIs), application Specific Integrated Circuits (ASICs), or firmware, such as electrically erasable programmable read-only memory (EEPROM) and Field Programmable Gate Arrays (FPGA).

The computer readable medium may be used to store software and data that when executed by a data processing system cause the system to perform various methods. Executable software and data may be stored in a variety of places including, for example, ROM, volatile RAM, non-volatile memory, and/or cache. Portions of the present software and/or data may be stored in any one of these storage devices. Generally, a machine-readable medium includes any mechanism that provides (i.e., stores and/or transmits) information in a form accessible by a machine (e.g., a computer, network device, personal digital assistant, manufacturing tool, any device with a set of one or more processors).

Examples of computer readable media include, but are not limited to, recordable and non-recordable type media such as volatile and non-volatile memory devices, read Only Memory (ROM), random Access Memory (RAM), flash memory devices, floppy and other removable disks, magnetic disk storage media, optical storage media (e.g., compact Disks (CDs), digital Versatile Disks (DVDs), etc.), among others. The instructions may be embodied in digital and analog communications links for electrical, optical, acoustical or other form of propagated signals (such as carrier waves, infrared signals, digital signals, etc.). As used herein, the phrases "computer readable material" and "computer readable storage medium" refer to all computer readable media except the transient propagated signal itself.

Example

The following examples are presented to enable those skilled in the art to understand and practice the embodiments of the disclosure. They should not be considered as limiting the scope of the disclosure, but merely as being illustrative and representative thereof.

Fig. 10 shows the results of analysis of liquid aluminum samples from hundreds of reduction tanks performed using passive cooling and automated initiation of LIBS measurements, in comparison with the results of laboratory spark OES analysis from conventionally prepared solid samples, in accordance with an embodiment of the present disclosure. Data from several primary aluminum smelters have been combined. Measurements were performed using a portable battery powered LIBS analyzer mounted on an electric vehicle, containing a distance calibration function as described above and three interchangeable measuring scoops.

The measuring crucible is preheated to a temperature that meets the crucible temperature criteria prior to introducing the molten aluminum sample into the measuring crucible. After a given molten aluminum sample is introduced into the measuring crucible, a non-contact thermometer is used to monitor the temperature of the molten aluminum sample while passively cooling the molten aluminum sample without performing active heating or active cooling of the crucible. LIBS measurements are made when the measured temperature criteria described above are met.

As shown in fig. 10, the agreement (one standard deviation) between the results from the portable LIBS measurement and the results from the laboratory reference measurement is better than 90ppm in the case of Fe and better than 30ppm in the case of Si, as schematically illustrated by the width of the gray line in the figure.

Measurements are typically collected sequentially from up to 50 reduction cells, with the characteristics of the present example portable LIBS system being such that the average cycle time per cell is about 90 seconds. This includes the time for sampling aluminum from the tanks, cooling the aluminum to meet measured temperature standards, making LIBS measurements, and transporting the analyzer between tanks using electric vehicles.

The specific embodiments described above have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure.

Claims

1. A method of performing Laser Induced Breakdown Spectroscopy (LIBS) on a molten sample during cooling of the molten sample, the method comprising:

Monitoring the temperature of the molten sample during cooling of the molten sample within the crucible and comparing the temperature of the molten sample to a measured temperature standard; and

2. The method of claim 1, further comprising: prior to introducing the molten sample:

Measuring the temperature of the crucible one or more times, the crucible being in a preheated state and the molten sample being absent, and comparing the temperature of the crucible to a crucible temperature standard; and

Determining that the temperature of the crucible meets the crucible temperature criteria and providing an indication that the crucible is ready to receive the molten sample;

wherein the crucible temperature standard is configured such that the molten sample cools less than 50 ℃ during the LIBS measurement.

3. The method of claim 2, wherein the crucible temperature criteria comprises a minimum crucible temperature such that when the minimum crucible temperature is exceeded, the crucible temperature criteria is satisfied.

4. A method according to claim 3, wherein the minimum crucible temperature resides between 100 ℃ and 60% of the melting point temperature of the molten sample, the melting point temperature being in degrees celsius.

5. A method according to claim 3, wherein the minimum crucible temperature resides between 15% and 60% of the melting point temperature of the molten sample, the melting point temperature being in degrees celsius.

6. The method of claim 2, wherein the crucible temperature criteria is met when the temperature of the crucible resides within a crucible temperature range.

7. The method of claim 6, wherein a maximum crucible temperature of the crucible temperature range is defined such that when the temperature of the crucible is equal to the maximum crucible temperature and the molten sample is added to the crucible, the temperature of the molten sample meets the measurement temperature criterion within 1 minute.

8. The method of claim 6, wherein a maximum crucible temperature of the crucible temperature range is defined such that when the temperature of the crucible is equal to the maximum crucible temperature and the molten sample is added to the crucible, the temperature of the molten sample meets the measurement temperature criterion within 30 seconds.

9. The method of claim 7, wherein the maximum crucible temperature resides between 50% and 90% of the melting point temperature of the molten sample, the melting point temperature being in degrees celsius.

10. The method of any of claims 1 to 9, wherein the measurement temperature criteria is selected such that the LIBS measurement is performed within a preselected measurement temperature range.

11. The method of any of claims 1-9, wherein the measurement temperature criteria comprises a preselected measurement temperature, and the LIBS measurement is initiated immediately after (i) determining that the temperature of the molten sample is equal to the preselected measurement temperature and (ii) positioning a LIBS measurement head over the crucible.

12. The method of any of claims 1 to 9, wherein the measured temperature criteria comprises a preselected measured temperature, and the LIBS measurement is performed after determining that the temperature of the molten sample is equal to the preselected measured temperature.

13. The method of claim 12, wherein the preselected measurement temperature exceeds the melting point temperature of the molten sample by an amount ranging from 5% to 25% of the melting point temperature, the melting point temperature being in degrees celsius.

14. The method of any of claims 1 to 9, wherein the measurement temperature criteria comprises a preselected measurement temperature range, and the LIBS measurement is performed while the temperature of the molten sample resides within the preselected measurement temperature range.

15. The method of any of claims 2 to 9, wherein the measured temperature criteria is configured such that the temperature of the molten sample exceeds the temperature of the crucible during the LIBS measurement when the crucible temperature criteria are met.

16. The method of any of claims 2 to 15, wherein the crucible is preheated by a previously measured molten sample, wherein the previously measured molten sample is discarded prior to measuring the temperature of the crucible.

17. The method of any one of claims 2 to 15, wherein the molten sample comprises aluminum, and wherein the crucible is preheated by contact with cryolite shells formed on top of a reduction tank.

18. The method of any of claims 2 to 17, wherein the temperature of the crucible and the temperature of the molten sample are measured using a common temperature sensor.

19. The method of any of claims 2 to 18, wherein the temperature of the crucible and the temperature of the molten sample are measured in the absence of contact.

20. The method of any of claims 2 to 19, wherein the crucible is supported by a crucible support during LIBS measurements.

21. The method of claim 20, wherein LIBS measurements are performed by a LIBS subsystem, and wherein a measurement head of the LIBS subsystem is movable from a parked position to an operative position in which the measurement head resides above the crucible support, and wherein a heat shield is positioned for shielding the measurement head from heat radiated from the crucible while the measurement head resides in the parked position.

22. The method of any one of claims 2 to 21, wherein the crucible is a metal crucible.

23. The method of claim 22, wherein the crucible is formed of structural steel.

24. The method of any one of claims 2 to 21, wherein the thermal capacity of the crucible resides between 400J/K and 500J/K.

25. The method of any one of claims 2 to 21, wherein the thermal capacity of the crucible resides between 400W/m-K and 500W/m-K.

26. The method of any of claims 6 to 8, wherein the crucible is a first crucible and the molten sample is a first molten sample, the method further comprising:

discarding the first molten sample from the first crucible;

measuring the temperature of the first crucible;

Determining that the temperature of the first crucible fails to meet the crucible temperature criterion due to an excessive temperature;

Replacing the first crucible with a second crucible, the second crucible having a temperature lower than the temperature of the first crucible; and

LIBS measurements are performed on a second molten sample using the second crucible while cooling the first crucible.

27. The method of claim 26, wherein the first crucible is supported by a main crucible support during the performing of the LIBS measurement on the first molten sample; and

Wherein after replacing the first crucible with the second crucible, the first crucible is placed on an auxiliary crucible support for cooling.

28. The method of claim 26, further comprising, prior to replacing the first crucible with the second crucible:

Preheating the second crucible;

monitoring the temperature of the second crucible; and

Indicating when the second crucible meets the crucible temperature criteria.

29. The method of any of claims 26 to 28, further comprising:

Optionally performing LIBS measurements on one or more additional molten samples using the second crucible;

Emptying the second crucible;

Measuring the temperature of the second crucible;

Determining that the temperature of the second crucible fails to meet the crucible temperature criterion due to an excessive temperature; and

the first crucible; and

A third crucible; and

30. The method of any of claims 1-29, wherein the LIBS measurements are performed by a LIBS system residing on a portable support structure, and wherein the LIBS system is battery powered.

31. A method of performing Laser Induced Breakdown Spectroscopy (LIBS) on a molten sample during cooling of the molten sample, the method comprising:

preheating a crucible;

Introducing a molten sample into the crucible;

32. The method of claim 31, further comprising, after preheating the crucible and before introducing the molten sample into the crucible:

measuring the temperature of the crucible one or more times and comparing the temperature of the crucible to a crucible temperature standard; and

Determining that the temperature of the crucible meets the crucible temperature criteria and providing the molten sample to the crucible;

33. A system for performing Laser Induced Breakdown Spectroscopy (LIBS), the system comprising:

A temperature sensor; and

A Laser Induced Breakdown Spectroscopy (LIBS) subsystem; and

monitoring the temperature of the molten sample within the crucible during cooling of the molten sample using the temperature sensor; and

Determining that the molten sample meets a measured temperature criterion and controlling the LIBS subsystem to initiate a LIBS measurement of the molten sample.

34. The system of claim 33, wherein the processing circuitry is further configured to, prior to introducing the molten sample into the crucible:

measuring the temperature of the crucible with the temperature sensor, the crucible being preheated; and

Providing an indication that the crucible is ready to receive the molten sample after determining that the temperature of the crucible meets a crucible temperature criterion;

35. A portable system for performing Laser Induced Breakdown Spectroscopy (LIBS), the portable system comprising:

a Laser Induced Breakdown Spectroscopy (LIBS) subsystem comprising a measurement head, the LIBS subsystem connectable to a battery;

36. The portable system of claim 35, further comprising:

A temperature sensor configured to monitor a temperature of the crucible residing in the main crucible support when the measurement head is in the parked position; and

Processing circuitry operably coupled to the temperature sensor, the processing circuitry comprising at least one processor and associated memory, the memory comprising instructions executable by the processor for performing operations comprising:

Measuring a temperature of the crucible with the temperature sensor, the crucible being supported by the main crucible support; and

After determining that the temperature of the crucible fails to meet crucible temperature criteria due to an excessive temperature, an indication is provided that the crucible should be cooled in the auxiliary crucible support prior to use.

37. The portable system of claim 35 or 36, further comprising the crucible and the additional crucible, wherein the crucible and the additional crucible are metallic.

38. The portable system of claim 37 wherein the crucible and the additional crucible are formed of structural steel.

39. The portable system of claim 35 or 36 further comprising the crucible and the additional crucible, wherein the heat capacity of the crucible and the additional crucible resides between 400J/K and 500J/K.

40. The portable system of claim 35 or 36 further comprising the crucible and the additional crucible, wherein the thermal conductivity of the crucible and the additional crucible resides between 40W/m-K and 50W/m-K.

41. A portable system for performing Laser Induced Breakdown Spectroscopy (LIBS), the portable system comprising:

integrating a calibration device; and

The measuring head of the LIBS subsystem is movable from an operative position in which the measuring head resides above a crucible for performing LIBS measurements on a molten sample residing in the crucible to a calibration position suitable for performing calibration measurements, the calibration position being suitable for calibrating at least one parameter of the LIBS subsystem.

42. A portable system as claimed in claim 41, wherein the integrated calibration means comprises LIBS calibration reference material adapted to calibrate signals of the LIBS subsystem when the measurement head is resident in the calibration position.

43. The portable system of claim 42 wherein the integrated calibration device comprises a support frame, and wherein the LIBS calibration reference material is movable relative to the support frame such that different regions of the LIBS calibration reference material are optically interrogated by the measurement head when the measurement head is repositioned at the calibration position to perform subsequent calibration measurements, thereby facilitating reuse of the LIBS calibration reference material during multiple calibration measurements.

44. The portable system of claim 41 wherein the measurement head comprises a distance sensor and wherein the integrated calibration device is an integrated distance sensor calibration device comprising a contact location and a target location, the contact location being located on the integrated calibration device such that a known spatial offset resides between the distance sensor and the target location when the measurement head resides at the calibration location and contacts the contact location after lowering the measurement head in a direction parallel to an optical axis of the measurement head, thereby facilitating calibration of the distance sensor.

45. The portable system of claim 44 wherein the integrated distance sensor calibration device is resiliently biased such that the known spatial offset is maintained when the measurement head moves in the direction after having contacted the contact location.

46. The portable system of any one of claims 41-45, further comprising:

a main crucible support for supporting the crucible while performing the LIBS measurement; and