In-situ elemental analysis of light metals in furnaces and molten metal baths

Abstract

An apparatus and method for safe, timely and precise analytical composition measurements of a body of molten metal or alloy arranged in a metal furnace using an evacuated hollow tube to extract a sample of a melt from the body of molten metal or alloy. With the invention, the need for human intervention in sample extraction may be minimized, e.g., transportation of and preparation of a sample. The method comprises configuring a hollow tube to a metal furnace, establishing vacuum conditions within the hollow tube to extract the molten metal or alloy into the hollow tube to form a liquid metal or alloy column within said tube and carrying out elemental composition measurements on said liquid metal or alloy using known techniques such as Laser Induced Breakdown Spectroscopy (LIBS).

Description

[0001] I n-situ elemental analysis of light metals in furnaces and molten metal baths

[0002] FIELD OF INVENTION

[0003] The disclosure is within the field of chemical analysis in metallurgy, or more specifically relates to a measurement apparatus and method for elemental analysis of molten metal or alloy, that reduces the need for manual intervention in obtaining and preparing a molten metal or alloy sample.

[0004] TECHNICAL BACKGROUND

[0005] Accurate and time-efficient measurements of elemental composition of metal or alloys in metal furnaces (or other containers / places where a significant quantity of molten metal or alloy is being produced, transported or stored) is of considerable importance in metal and alloy manufacturing, as well as in the metal recycling industry. The standard approach involves manually opening the furnace (or metal bath) to extract a sample of liquid metal or alloy which is then cast into a solid sample to be measured. The solid sample then typically undergoes transportation, suitable sample preparation, and analysis, wherein the sample preparation and analysis are typically carried out in a separate laboratory or in an on-site laboratory container. This renders the overall analysis process time-consuming and inefficient. Furthermore, this practice leads to an energy loss due to opening of the furnace, as well as further temperature drop if the burners in gas-fired furnaces need to be turned off during the opening of the furnace and sampling the molten metal or alloy. More importantly, the manual extraction of a sample of molten metal or alloy from metal furnaces poses a considerable safety hazard for the operator extracting the liquid metal or alloy sample, wherein the worst accident during operation can prove fatal to the operator. It is, therefore, highly advantageous to develop a measurement apparatus for analysing liquid metal or alloy that is without the need of manual intervention with the furnace or metal bath.

[0006] Concepts involving on-line measurements of metals or alloys in furnaces have been proposed, such as stand-off measurements through a tube immersed in the metal through a furnace wall, the tube being pressurized internally typically with inert gas, wherein emission from a laser-induced plasma at the surface of the metal is detected. The drawbacks of such stand-off measurements are well known in the field, as temperature gradients may exist close to the furnace wall and incomplete mixing may cause the melt chemistry to be different from the bulk. Furthermore, the distances required to protect the equipment from the heat load from the molten metal in such stand-off measurements will result in a reduced light collection efficiency, since the emitted light intensity drops quadratically with distance from the sampling point, and thus higher uncertainty in elemental composition measurements. It is therefore of great interest to develop a stand-off measurement apparatus and / or method to provide a molten metal or alloy sample to be measured that is representative of the bulk of the molten metal or alloy arranged in the furnace, while also minimizing the distance from the sample to the measurement apparatus without compromising the integrity of the measurement apparatus.

[0007] SUMMARY

[0008] In broad terms, the invention provides both a novel measurement apparatus and a method for carrying out elemental analysis of molten metal or alloy melt that does not require opening a vessel / bath comprising molten metal or molten alloy and does not require manual intervention over the course of the measurement process such as opening a metal furnace, extracting a sample therefrom with a ladle or the like, casting the sample into a solid, transportation, manually removing the oxidized surface layer from the sample, etc. The present invention is therefore particularly useful for both safety and efficiency of process and / or quality control within the metallurgy industry such as but not limited to aluminium plants, steel plants, ferrosilicon plants, and essentially any other industry where accurate, safe, and timely quantitative analysis of liquid metal or alloy is desired in all stages of the production process.

[0009] Herein, the terms “molten metal” and “liquid metal” may be used interchangeably.

[0010] In an aspect of the invention, a measurement apparatus for measuring elemental composition of molten metal or alloy is provided, wherein said apparatus comprises: a hollow tube with an open lower end and a closed upper end, wherein the open lower end is configured to be immersed in said molten metal or alloy such that the closed upper end is positioned above the molten metal or alloy. The apparatus further comprises a pump system connected to said hollow tube, with the pump system configured to evacuate air and / or gas from said hollow tube when the open lower end is immersed in said molten metal causing said molten metal or alloy to rise up along the inside of the hollow tube from the open lower end and towards the closed upper end, forming a column of said molten metal or alloy within said hollow tube, wherein the upper end of said column becomes positioned in vicinity to the closed upper end of said hollow tube, a laser excitation system for ablating a sample of said molten metal or alloy column through at least one optical window and an emission receiving system for detecting emitted light from said ablated sample through at least one optical window (that can be the same or another optical window than that which the laser beam passes through) at, or near, the upper end of the hollow tube.

[0011] The hollow tube may be arranged in, or configured to, a vessel containing molten metal or alloy. Herein, the term “vessel” refers to any suitable means of containing liquid / molten metal or alloy such as, but not limited to, a metal furnace and a crucible. In one embodiment, the hollow tube may be arranged at the top of the vessel extending down in a vertical manner, such that the lower end of the hollow tube is immersed in molten metal or alloy inside the vessel, while the closed upper end is positioned exterior of the vessel.

[0012] A pumping system (or an evacuation system) is connected to the upper closed end, or in vicinity thereto, and used to establish vacuum conditions within the hollow tube. As the hollow tube is evacuated, molten metal or alloy in the vessel will rise up a portion of the hollow tube to a level that is primarily defined by the specific gravity of the metal or alloy, forming a metal or alloy column within the hollow tube. In the case of pure aluminium melt arranged in for example a furnace, the liquid aluminium will rise within an evacuated hollow tube to a level of 3.83 m above the level of the melt in the furnace, when high vacuum is established (slightly less for intermediate or low vacuum, such as e.g., at 0.1 atm). One advantage of the present invention over standard off-line measurement apparatuses or methods is that the method allows immersing the hollow tube in the liquid metal or alloy to a substantial depth, e.g. 30 cm, or 40 cm, or 50 cm below the molten surface, or even more (i.e., at least well below any surface anomalies, crust etc.) and extracting liquid metal into the hollow tube from centrally within the molten metal in the furnace, resulting in that the composition of the molten metal or alloy column is an accurate representation of the bulk of the liquid metal or alloy melt in the furnace. The pump system may further comprise, besides a pump, an evacuation line and a control valve on said line. The vacuum conditions additionally serve to protect the sample surface of the molten metal or alloy column from oxidation. In one embodiment, the vacuum conditions are established prior to and further maintained during the measurement phase by using the vacuum generating system to continuously evacuate the hollow tube.

[0013] The shape of the hollow tube can be generally cylindrical but is not limited thereto, the cross- sectional profile may be of any suitable shape such as, but not limited to, round, square, rectangle, D-shape, triangular, pentagonal, hexagonal, octagonal and oval. The hollow tube may be configured on a vessel such as a furnace through an opening provided on the furnace, wherein shape and size of the opening and the hollow tube are e.g., mated. In one embodiment of the present invention, the hollow tube is welded to a furnace opening where the outer surface of the hollow tube and furnace intersect. In another embodiment, a sealant component is arranged around the outer surface of the hollow tube e.g., at a point where the hollow tube and the furnace intersect such as, but not limited to, an annular seal (in the case where the hollow tube profile and the profile of the furnace opening are both round). Additional components may be included to fix the position of the hollow tube, especially when arranged in open vessels such as, but not limited to, cables connected to the outer surface of the hollow tube and attached to structural support (beam or the-like) that is arranged outside of the vessel.

[0014] Collectively, the uppermost part of the liquid metal or alloy column (herein referred to as the sample surface) and the inner walls of the remaining closed upper end of the hollow tube define a substantially void evacuated space (also known as vapor space) that functionally forms as a (sealed) measurement chamber for sample confinement and more readily allowing for more controllable environmental conditions. The length of the hollow tube has to necessarily be selected such that it accommodates the column length of the metal or alloy melt (i.e. depending on the specific gravity of the molten metal or alloy) arranged in the vessel such that a suitably small, evacuated space exists between the molten metal or alloy column and the top of the closed upper end of the hollow tube.

[0015] In some embodiments, the measurement apparatus may further comprise a measurement chamber, wherein at least one optical window may be arranged on the walls of the measurement chamber. In an embodiment, wherein the vapor space of the cylindrical hollow tube is the measurement chamber, at least one optical window may be arranged on top of the closed upper end of the hollow tube for light (electromagnetic radiation) to pass through such as, pulsed laser light and / or emitted plasma radiation. Additionally, at least one optical window may be arranged on the side walls of the hollow tube at or in vicinity to the closed upper end (i.e., the upper portion of said hollow tube).

[0016] In some embodiments, the hollow tube may further comprise a measurement chamber, wherein the measurement chamber may be of different geometry than the remainder of the hollow tube, for example the apparatus can comprise a round cylindrical hollow tube comprising a rectangular shaped measurement chamber. In these embodiments, the measurement chamber further comprises at least one optical window for light to pass through, wherein the at least one optical window may be located at the top face of the measurement chamber (i.e. the top of the closed upper end of the hollow tube) and / or the side walls of the measurement chamber. A hollow tube comprising a measurement chamber of different geometry compared to the base shape of the hollow tube may be formed in an integral manner or in two or more parts that are then attached and connected, e.g., by welding or alternatively using substantially air-tight clamps.

[0017] In some embodiments, the measurement chamber will lie exterior to a vessel carrying molten metal or alloy, while other parts of the hollow tube may lie interior in such a vessel.

[0018] With a molten metal or alloy column arranged inside the hollow tube and at least partially in the measurement chamber, quantitative analytical measurements of the molten metal or alloy can be carried out, conveniently circumventing both the need to open the vessel for sample extraction and the need for sample preparation.

[0019] For the quantitative elemental analysis, spectroscopic techniques known to the person skilled in the art such as, techniques employing laser excitation optics, can be used to analyse the elemental composition of the molten metal or alloy, wherein the suitable measurement apparatus may be configured and fitted in vicinity to and exterior to the upper end of the hollow tube. A point (the sampling point) on the surface of the molten metal or alloy column may then be irradiated with pulsed and focused laser light through at least one optical window arranged on, or in vicinity to, the closed upper end of the hollow tube. With suitable pulse energy, the liquid metal or alloy at and in the immediate vicinity to the sampling point can be ablated and converted into plasma forming a plasma plume, wherein the plasma plume is confined within the sealed measurement chamber. Therefore, the laser excitation system may be arranged outside of the hollow tube at a fixed distance such as, but not limited to, about 1 meter, to protect the electronics of the laser excitation from the extreme environmental conditions (in particular, temperature).

[0020] Optical emission originating from the ablated sample passes through at least one optical window arranged on, or in vicinity to, the closed upper end of the hollow tube to suitable emission receiving optics. The emission receiving optics may comprise at least one filter and / or at least one lens and / or at least one optical mirror and / or at least one optical detector and / or at least one spectrograph. The emission-receiving system collects and transmits the emission from the plasma for analysis, correlating the spectral signal intensity to concentration of different elements in the ablated sample. By keeping the emission-receiving optics in vicinity to the closed upper end of the hollow tube and extracting molten metal or alloy into the hollow tube to confine the molten metal or alloy column, the emission receiving optics can be kept significantly closer to the sampling point than in abovementioned standoff measurements, comparatively increasing the light collection efficiency and hence reducing the uncertainty in measurements of the composition of the ablated sample. In one embodiment, the apparatus comprises a laser excitation system to emit a pulse or a series of pulses of light from a laser, through a focusing element such as at least one lens, to a target sample, such as the surface of a molten metal or alloy, wherein the target spot (sample) becomes ablated and electronically excited to form a plasma.

[0021] The apparatus comprises an emission receiving system to receive and detect emitted light from said ablated sample plasma, e.g., through an optical window arranged at the upper end of the hollow tube. The emission receiving system includes, at least, an optical element for spectrally resolving received emission and a detector connected to said optical element for recording spectral information.

[0022] In an embodiment, the emission receiving system includes a control unit to analyse recorded spectral information, wherein the analysis or portion of the analysis can be carried out in an automatic fashion.

[0023] One advantage of the present invention is that the actual distance between the sample surface and the emission and / or laser excitation optics may be maintained to a fixed or substantially fixed pre-determined value by using distance sensing and (i) introducing an automatic mechanical or electrical moving means such as, but not limited to, an actuator or a robotic assembly comprising one or more motors on the emission receiving and / or laser excitation optics units and / or (ii) controlling the residual pressure within the sealed measurement chamber to align the level of the column within the hollow tube with respect to the emission receiving and / or laser excitation optics.

[0024] In an embodiment, at least one distance sensor may be arranged at, or in vicinity to, the laser excitation optics and / or the emission receiving optics.

[0025] After the measurement, the hollow tube may be flushed with inert gas (or a mixture of inert gases) causing the molten metal or alloy to exit said hollow tube., i.e., t Accordingly, the flushing of the inert gas may serve to push the molten metal or alloy out of the hollow tube and back into the metal or alloy melt bath arranged in the vessel. In such embodiments, the hollow tube may be pressurized to values above PChamber > 1 atm by feeding inert gas into the hollow tube, wherein the inert gas is fed into the measurement chamber and then flows from the upper closed end of the hollow tube towards the open lower end of the hollow tube which is immersed in the metal or alloy melt. The gas will serve to push any remaining melt out of the hollow tube and into the vessel. The inert gas will then typically bubble out of the melt. In this manner, the hollow tube can be kept clean of liquid metal or alloy between measurements. Therefore, by flushing the hollow tube with inert gas and then re-evacuating the chamber, different melt samples from the vessel can be introduced into the hollow tube between successive sample measurements. This allows accurate average elemental composition to be established that is representative of the bulk of the melt in the vessel.

[0026] Another advantage of the present invention is that the environmental conditions within the measurement chamber are readily controllable such as the pressure within the sealed measurement chamber, wherein the pump system is used to establish vacuum conditions within the hollow tube, in particular in the measurement chamber, such that the pressure may become less than 0.1 atm.

[0027] In certain useful embodiments of the invention, the pressure of the vacuum conditions may be less than about 0.1 atm, less than about 0.09 atm, less than about 0.08 atm, less than about 0.07 atm, less than about 0.06 atm, less than about 0.05 atm, less than about 0.04 atm, less than about 0.03 atm, less than about 0.02 atm, less than about 0.01 atm, less than about 0.05 atm or less than about 0.001 atm. In some embodiments, the pressure of the vacuum conditions may be in the range of about 0.001 atm to 0.1 atm, such as in the range of 0.002 atm to 0.09 atm, such as in the range of about 0.005 atm to 0.08 atm, such as in the range of about 0.01 atm to 0.05 atm. The upper limit of the range can be about 0.1 atm, about 0.09 atm, about 0.08 atm, about 0.07 atm, about 0.06 atm, about 0.05 atm, about 0.04 atm, about 0.03 atm, about 0.02 atm, about 0.01 atm, about 0.005 atm, about 0.001 atm.

[0028] In some embodiments, the vacuum conditions may be maintained by continuously evacuating the hollow tube to remove the evaporated material from the hollow tube. In another embodiments, the vacuum conditions may be maintained by continually (i.e. in a sequence of steps) evacuating the hollow tube. Evacuation during the measurement may serve to partially alleviate difficulties that arise because of volatile elements that may be present in the vapor phase above the melt surface and are prone to self-absorption such as, but not necessarily limited to, Mg, Na, Li, Ca and Sr. Continuous evacuation may also facilitate the measurement of dissolved hydrogen in the melt, which is typically difficult to detect in plasma emission at ambient pressure conditions due to strong line broadening. With suitable optical windows and detection schemes, the method and apparatus can be used to detect elements emitting even in the deep ultraviolet range (e.g., A < 200 nm), where atmospheric absorption is a significant limitation. Moreover, the established vacuum conditions within the measurement chamber can prevent oxidation of the sample surface and hence improve analysis results and hence avoid the typical (manual) step of introducing a mechanical means for removing surface oxide (crust) from the sample surface. Furthermore, by preventing oxidation, a more accurate estimate of the melt temperature (using optical pyrometric detection) can be obtained. Additionally, the hollow tube may be evacuated prior to measurement and elemental analysis, such that the molten metal or alloy arranged in the vessel is rises up along the inside of the hollow tube. Therefore, the length of the hollow tube can accommodate the length the climbing column of molten metal or alloy. In one embodiment, the hollow tube has to have a total length of at least about 4 m to accommodate a column height of molten aluminium or aluminium alloy according to its specific gravity and with vacuum conditions established in the closed upper end of said hollow tube.

[0029] In one embodiment of the present invention, the inner diameter of the hollow tube may lie in the range from 5 to 30 cm, or in the range from about 5 to about 20 cm or in the range of about 5-10 cm.

[0030] In some embodiments, the measurement apparatus may further comprise at least one gas feed line connected to said hollow tube, e.g., in vicinity to said closed upper end. The one gas feed line further comprises a gas source to allow gas or gas mixture to flow from and through the at least one gas feed line and into the hollow tube, e.g., in vicinity to the closed upper end of the hollow tube. In some embodiments, the at least one gas feed line further comprises a means of flow control for regulating flow of gas or gas mixture through said at least one gas feed line.

[0031] The gas or gas mixture may be selected in such a manner that the gas or gas mixture comprises certain physical and chemical characteristics of interest. As discussed above, the gas or gas mixture may be directed from a gas-source through at least one gas line and into the measurement chamber. By feeding the gas or gas mixture into an evacuated (sealed) measurement chamber, well-defined environmental chemical conditions around the sampling point can be established, wherein quantitative elemental measurements can then be carried out under for example constant, non-reactive, environmental conditions.

[0032] In some embodiments, at least one gas feed line may be configured to allow flushing of the hollow tube with inert gas. The flushing of the hollow tube with inert gas may serve to push the molten metal or alloy column out of the hollow tube and back into the vessel comprising molten metal or alloy. Furthermore, bubbling out inert gas may serve as additional means of stirring molten metal or alloy arranged in the vessel, which may improve sampling during successive measurements. In an embodiment, at least one gas feed line may be configured to allow bleeding of gas or gas mixture into said hollow tube. Accordingly, by bleeding gas or gas through the at least one gas feed line may be used to regulate pressure inside the measurement chamber and slightly push the molten metal or alloy column slightly down to adjust the relative height of the molten metal or alloy column or the distance of the molten metal or alloy surface to a reference point on the emission receiving and / or laser excitation systems.

[0033] In some embodiments, at least one gas feed line may be configured to allow bleeding of gas or gas mixture into said hollow tube to be able to provide consistent and environmental and residual vacuum background. This may serve to for example inhibit or enable certain chemical vapor phase reactions and eliminate temperature dependency of certain chemical signals such as that of highly volatile species. Additionally, a gas or gas mixture can be allowed to bleed continuously into the chamber during measurements to provide a residual background vacuum pressure to protect the optical windows arranged on the walls and / or top face of the measurement chamber from laser-induced deposition of the sample material. The optimal background vacuum pressure may, therefore, be selected to be high enough to limit the mean free path of ablated material to far below the dimensions of the sealed measurement chamber.

[0034] In some embodiments evacuation of the hollow tube may be turned off (e.g. by closing off the line leading to the vacuum pump) prior to feeding / bleeding gas into the hollow tube. In such embodiments, the amount of gas fed may becarefully controlled to achieve the desired pressure above the column. In another embodiment the evacuation pumping may be maintained, controlling the gas flow through the gas feed line and also the pumping capacity (e.g. by a control valve on the suctioning line) to achieve a desired vacuum condition above the molten metal or alloy column.

[0035] In some embodiments, the apparatus may comprise a control unit and connection means (wired or wireless) to and from the control unit to one or more different components of the apparatus. Accordingly, in some embodiments, all or some steps of the measurement process and variations thereof may be carried out in an automated and controlled manner using a control unit such as, but not limited to, at least one computer comprising at least one processor.

[0036] The aforementioned automation is applicable both to a single quantitative elemental measurement as well as for repeated measurements as discussed above. In some embodiments, at least one step of the following is controllable through a control unit, (i) establishing vacuum, (ii) extracting molten metal or alloy into the hollow tube, (iii) aligning the distance between the laser excitation optics and / or the emission receiving unit to the surface sample, (iv) setting the desired environmental conditions (i.e. continuous or continual evacuation, introduction of a background gas pressure / bleeding a background gas) for measurements, (v) pulsing at least one laser light on a point on the liquid metal or alloy column surface ablating a sample and (vi) detecting and / or resolving and / or analysing the emitted light from ablated sample, as well as (vii) cleaning the liquid metal or alloy from the hollow tube by flushing the tube with gas. The control of at least one step may be carried out remotely through a connection means (either wired or wireless), wherein connection means is provided between the control unit and the one or more different components of the measurement apparatus.

[0037] In some embodiments, the hollow tube may comprise refractory material capable of withstanding thermal shock from immersing in and being filled with molten metal or alloy, wherein the refractory materials may be selected from for example a range of ceramic materials such as a material referred to as SiAION. The refractory material is may also be non-reactive to the metal or alloy melt inside the vessel.

[0038] In some embodiments, the hollow tube may comprise a structural outer sheath to support the structural integrity of the apparatus. The structural outer sheath may be arranged at least in an upper portion of the hollow tube. The structural outer sheath may at least partially enclose an inner layer of said refractory material. In some embodiments, the hollow tube may comprise at least in part an integral layered structure with least two layers, wherein an inner layer comprises a heat-resistant and non-reactive material such as ceramics, while an outer layer comprises a material that provides further mechanical strength to the hollow tube such as, but not limited to, high-grade steel.

[0039] The hollow tube may further comprise an annular seal around the bottom portion of the hollow tube to seal the structural layer of the hollow tube from the melt arranged in the furnace, i.e., to avoid contact between the two.

[0040] In one embodiment, the measurement apparatus may comprise a heating element to prevent solidification of molten metal or alloy inside said hollow tube. The heating element may be used to heat up and / or maintain the liquid metal or alloy column at a desired temperature to prevent solidification of the liquid metal or alloy column.. The heating of the liquid metal or alloy may be realised through induction heating, such that heat is transmitted inductively to the sample but not to the container itself except as transmitted from the sample, or by other conventional heating techniques known in the art such as by resistive or gas heating. The hollow tube may be pre-heated to a desired temperature prior to the extraction of molten metal or alloy from the vessel. In some embodiments, the hollow tube may be heated prior to and / or during the elemental composition analysis, i.e. , when spectral emission from the sample plasma is being detected / recorded. The heating means may be arranged on the hollow tube for the full length of the hollow tube or only a portion thereof, such as on the portion which is positioned above the molten surface within the vessel, or part thereof, or only on the portion of the tube being positioned outside the furnace or part thereof. This prevents the molten metal or alloy column from solidifying inside the hollow tube.

[0041] In some embodiments the liquid metal or alloy column may be heated or maintained at a temperature above at least 400°C, such as above at least 600°C, such as above at least 700°C, or such as above at least 800°C. The temperature may depend on in particular, the specific type of metal or alloy being analysed, and the melting point of that metal or alloy. Accordingly, in some embodiments the sample may be heated to or maintained at a temperature of at least 400°C or at least 450°C, or at least 500°C or at least 550°C or at least 600°C. For certain metals and alloys an even higher temperature may be needed to maintain a sample in molten state, and thus in some embodiments the sample may be heated to or maintained at a temperature of at least 850°C or at least 900°C or at least 1000°C, or even higher.

[0042] As a non-limiting example, for sampling and analysing aluminium a temperature of the sample may lie in the range from about 680°C to about 780°C, such as in a range from about 680°C or from about 700°C to about 780°C or to about 760°C or to about 750°C.

[0043] In one embodiment, the hollow tube may further comprise an insulation layer to maintain temperature stability within said hollow tube and prevent the molten metal or alloy being sucked up into the hollow tube from solidifying. In another embodiment, the hollow tube may comprise two or more insulation layers. The at least one insulation layer(s) may serve to lower heat conductance between layers and / or to reduce heat loss from within the hollow tube to the environment. Moreover, in some embodiments, only parts of the hollow tube may comprise an insulation layer such as the parts comprising the heating element or the parts of the hollow tube lying above the surface level of the molten metal or alloy arranged in the vessel or the parts of the hollow tube that lie exterior to the vessel or furnace.

[0044] In some embodiments, the laser excitation system comprises a laser arranged axially above the molten metal or alloy column and is configured to direct pulsed and focused light to the surface of said molten metal or alloy column through at least one optical window arranged at or in vicinity to the upper end of said hollow tube (i.e. , the top face of the cylindrical hollow tube and / or the top face of the measurement chamber) such that the angle between the surface of the molten metal or alloy and the optical axis of the laser light is about 85-95°, or about 90°.

[0045] In some embodiments, the emission receiving system is configured to gather light emitted from the ablated molten sample, through the optical window arranged on top of the closed end of the hollow tube and / or the top face of the measurement chamber. In an alternative embodiment, the emission receiving system may be arranged at an angle to the optical axis of said laser and configured to detect light from at least one optical window arranged at or in vicinity to the upper end of said hollow tube. In such an embodiment, an optical mirror may be arranged in a position above the optical window along the optical axis on top of the closed end of the hollow tube in an angled configuration to direct refracted light to the optical detector of the emission receiving system.

[0046] In some embodiments, the hollow tube may comprise a second optical window arranged on a side wall in vicinity to the upper end of the hollow tube such that it is positioned above the surface level of the liquid metal or alloy column and the emission receiving system is arranged to detect light emitted from said ablated sample through said second optical window. This can be arranged such that the second window receives emission directly from the ablated surface or plasma, or indirectly via an optical mirror inside or outside the hollow tube. In some embodiments, the emission receiving system may comprise optical cables for capturing and transferring emitted light to said optical detector. Furthermore, in some embodiments, the emission receiving system may comprise other common components of emission receiving systems, such as lenses, as would be recognized by the person skilled in the art.

[0047] In some embodiments, the measurement apparatus may comprise at least one distance sensor to measure the relative height of the surface of the molten metal or alloy column. The at least one distance sensor may be attached to, or configured on, the laser excitation system. The at least one distance sensor may be attached to, or configured, on the emission receiving system. The at least one distance sensor may be independent of the emission receiving system and / or laser excitation system. The at least one distance sensor may be used to measure the distance of a reference point located on the apparatus, e.g., a reference point on the laser excitation system and / or a reference point n the emission receiving system, from the surface of said liquid metal or alloy.

[0048] In some embodiments, the at least one gas feed line may be configured to regulate pressure above the surface of the molten metal or alloy column arranged in the hollow tube to adjust the height level of the surface of the molten metal or alloy surface according to measurements carried out by the at least one distance sensor. This may be carried out automatically, wherein a control unit may be connected to a flow control on the at least one gas feed line and used to regulate the flow of gas through the at least one gas feed line according to the relative height of the molten metal or alloy column until a pre-determined relative height is obtained.

[0049] In some embodiments, the measurement apparatus may comprise a moving means for moving the emission receiving system and / or laser excitation system to a pre-determined distance from the surface of the molten metal or alloy to obtain a pre-determined relative height of the molten metal or alloy column. In such embodiments, the at least one distance sensor and the moving means are used to align the distance of a reference point located on the apparatus (e.g., on the laser excitation system and / or on the emission receiving system) from the surface of the liquid metal or alloy column to a pre-determined distance.

[0050] In some embodiments, both the moving means and the inlet gas feed can collectively be used to automatically regulate the air pressure above the surface of the liquid metal or alloy column in the hollow tube according to the distance sensor, to obtain a pre-determined distance from said surface of the said sample within upper end of the hollow tube to the emission receiving and / or laser excitation system.

[0051] In some embodiments, the measurement apparatus may be fitted to a metal furnace carrying molten metal or alloy. The measurement apparatus may be fitted through an opening or a hatch arranged on the molten metal or alloy furnace, wherein the opening or hatch mates with said hollow tube and the upper portion of said hollow tube lies exterior to the furnace. In some embodiments, the opening or hatch may be positioned on the top of the metal furnace. In such embodiments, the hollow tube may extend in a vertical manner down from the exterior of the furnace and into the molten metal or alloy. In another embodiment, the opening or hatch may be positioned on any of the side walls, or faces, of the metal furnace. In such embodiments, the hollow tube may in part be in an (approximately) horizontal configuration and in part be in an (approximately) vertical configuration (i.e. , the hollow tube is approximately of angled L-shape), wherein the approximately horizontal configuration of the hollow tube extends into the metal furnace with the lower end immersed in the molten metal or alloy, while the approximately vertical part of the hollow tube may lie outside of (exterior) to the metal furnace along with the laser excitation system and the emission receiving system, i.e. , the quantitative elemental measurement and analysis is carried out in the approximately vertical part of the hollow tube exterior to the metal furnace.

[0052] In an aspect of the present invention, a measurement apparatus may be provided for measuring the elemental composition of molten metal or alloy melt arranged inside a metal furnace without having to open the furnace, extract and prepare a sample melt for an elemental composition analysis. The apparatus comprises a hollow tube configured on a metal furnace that comprises an open lower end and a closed upper end. The hollow tube is configured at or in vicinity to the centre on top of the furnace and extends into the furnace, wherein the open lower end is configured to be immersed in said molten metal. The upper closed end may lie on the exterior of the furnace and comprises at least one optical window for light to pass through. The measurement apparatus further comprises a pump system (i.e. an evacuation system) to evacuate said hollow tube to suck up a molten metal or alloy column from furnace into said hollow tube to a height determined by the specific gravity of the molten metal or alloy. The measurement apparatus comprises a laser excitation system and an emission receiving system, e.g., positioned outside of said hollow tube, for ablating a sample point on the surface of the molten metal or alloy column and detecting and analysing emitted plasma radiation from ablated sample point.

[0053] In an aspect of the present invention a method for measuring chemical composition of a body of molten metal or alloy is provided. The method comprising: arranging a hollow tube with an open lower end and a closed upper end to said body of molten metal or metal alloy wherein the open lower end is immersed in said body of molten metal or alloy, the closed upper end is arranged exterior to the body of molten metal or alloy, evacuating said hollow tube causing molten metal or alloy from the body of molten metal or alloy to rise (or climb) ina column inside the hollow tube, from the immersed open lower end towards the closed upper end, emitting by a laser one or more pulses of light, through at least one optical window arranged in or in vicinity to the closed upper end, to ablate the surface of the uppermost part of the liquid metal or alloy column, receiving emitted light from the ablated molten metal or alloy, through at least one optical window, using an emission receiving system, performing spectral analysis of said emission to determine chemical composition of said molten metal. Embodiments of the method of the present invention may advantageously be performed with embodiments of the measurement apparatus, or any combination thereof, as detailed above.

[0054] The hollow tube is evacuated by pumping air and / or gas out of said hollow tube to establish vacuum conditions within the hollow tube and causing molten metal or alloy from the body of molten metal or alloy to be sucked into the hollow tube and rise / climb along the hollow tube from the immersed open lower end towards the upper closed end to form a liquid metal or alloy column. The column of molten metal or alloy rises (or is sucked up) towards the upper closed end of the hollow tube to a column height characteristic of the specific gravity of said molten metal or alloy arranged in the body of molten metal or alloy. The evacuated space (i.e., the vapor space) between the upper end of the hollow tube and the surface of the liquid metal or alloy column defines a (sealed) measurement chamber. Then, a laser pulse or a series of laser pulses is directed through an optical window arranged on the hollow tube to the surface of the liquid metal or alloy. This causes the point of impact of the surface of the liquid metal or alloy to become ablated and excited forming a plasma plume that is confined within the sealed measurement chamber. Light that is emitted from the ablated metal or alloy sample travels through an optical window (the same window or a different one as described above). The emitted light is then received by an emission receiving system and analysed to determine concentration of individual elements. Generally, the signal intensity for particular elements is correlated to the concentration of said elements in the ablated sample. This can be achieved by comparing one or more selected emission peaks to calibration values for elemental analysis of the sample.

[0055] In some embodiments, the step of evacuating said hollow tube brings pressure inside said hollow tube to a vacuum pressure. In one embodiment, a pressure below 0.1 atm using a pump system connected to the upper portion of the hollow tube, e.g., in vicinity to the closed upper end of the hollow tube.

[0056] In certain useful embodiments of the invention, the pressure of the vacuum conditions may be less than about 0.1 atm, less than about 0.09 atm, less than about 0.08 atm, less than about 0.07 atm, less than about 0.06 atm, less than about 0.05 atm, less than about 0.04 atm, less than about 0.03 atm, less than about 0.02 atm, less than about 0.01 atm, less than about 0.05 atm or less than about 0.001 atm. In some embodiments, the pressure of the vacuum conditions may be in the range of about 0.001 atm to 0.1 atm, such as in the range of 0.002 atm to 0.09 atm, such as in the range of about 0.005 atm to 0.08 atm, such as in the range of about 0.01 atm to 0.05 atm. The upper limit of the range can be about 0.1 atm, about 0.09 atm, about 0.08 atm, about 0.07 atm, about 0.06 atm, about 0.05 atm, about 0.04 atm, about 0.03 atm, about 0.02 atm, about 0.01 atm, about 0.005 atm, about 0.001 atm.

[0057] In some embodiments, an additional step of flushing a stream of gas or gas mixture, preferably inert gas or gas mixture, through at least one gas feed line connected to the upper portion of said hollow tube after a measurement to clean said hollow tube of molten metal or alloy by pushing said molten metal or alloy out of the hollow tube may be provided. This step may for example be carried out after a measurement or between successive measurements.

[0058] In some embodiments, an additional step of bleeding gas or gas mixture through at least one gas feed line connected to the upper portion of said hollow tube to provide a consistent residual background vacuum pressure at and in vicinity to the surface of the molten metal or alloy column may be provided. Advantageously, this will allow the operator to control at least the neighbouring environment around the sampling point on the surface of the molten metal or alloy, wherein the gas or gas mixture comprises desired chemical and / or physical properties, during the measurement, i.e., during emission of pulsed laser light and receiving emitted light.

[0059] In some embodiments, the method may further comprise a step of measuring the relative height of the molten metal or alloy is using at least one distance sensor. The at least one distance sensor may for example be used to measure the distance between the laser excitation system and / or emission receiving system and the surface level of the molten metal or alloy column. In this embodiment, the method may comprise automatically adjusting the position of the emission detecting system and / or laser excitation system to obtain a predetermined distance between a reference point on the laser excitation system and / or emission detecting system and the surface of the molten metal or alloy prior to emitting at least one laser pulse, wherein automatically adjusting the position of the emission detecting system and / or laser excitation comprises an electrically or mechanically controlled moving means such as, but not limited to, the use of actuators. Alternatively, the method may comprise a step of bleeding in gas or gas mixture to regulate pressure above the surface of the molten metal or alloy column arranged in the hollow tube to adjust the height level of the surface of the molten metal or alloy surface. In one embodiment, both the steps of automatically adjusting the position of the emission detecting system and / or laser excitation system and the step of bleeding in gas or gas mixture to regulate pressure to control the surface level of the molten metal or alloy may be provided. In one embodiment, the gas or gas mixture is bled through at least one gas feed line connected to the upper portion of said hollow tube to adjust the level height of the liquid column.

[0060] In some embodiments, the molten metal or alloy column that is extracted into the hollow tube when the pump system is used to evacuate the hollow tube, may be representative of the bulk metal liquid in terms of its chemical composition. Thus, in some embodiments the lower open end of the hollow tube may be positioned at a depth within the molten metal of at least about 20 cm, or at least 30 cm, or at least 40 cm, or at least 50 cm

[0061] In some embodiments, the step of heating the molten metal or alloy column at a temperature above at least 600°C, above 700°C, may be provided using a heating element (as described above). Furthermore, in some embodiments, the molten metal or alloy column may be heated above the given temperature and the temperature maintained, for example, prior to and during the measurement.

[0062] The measurement apparatus and method of the invention are not limited to analysis of particular elements. The measurement apparatus and method may be used to analyse both volatile and non-volatile elements. In some embodiments the method and / or apparatus is for determining in the liquid metal or alloy sample the concentration of one or more elements selected from Aluminium, Silicon, Phosphorus, Sulphur, Chloride, Calcium, Magnesium, Sodium, Titanium, Vanadium, Chromium, Manganese, Iron, Cobalt, Nickel, Copper, Zinc, Zirconium, Niobium, Molybdenum, Ruthenium, Rhodium, Palladium, Silver, Cadmium, Tin, Antimony, Wolfram, Rhenium, Iridium, Platinum, Gold, Mercury, Lead and Bismuth, Lithium, Beryllium and Boron.

[0063] BRIEF DESCRIPTION OF FIGURES

[0064] Fig. 1 illustrates schematically the rise of molten metal or alloy in a closed vessel comprising molten metal or alloy along a vertically arranged evacuated hollow tube forming a column of the molten material inside the hollow tube, and thus enabling quantitative elemental measurement of the material on the elevated surface of the column.

[0065] Fig. 2(a) illustrates an embodiment of the measurement apparatus, wherein a single optical window is arranged on the hollow tube at the upper end of the hollow tube.

[0066] Fig. 2(b) illustrates an embodiment of the measurement apparatus where two optical windows are arranged on the hollow tube in vicinity to the upper end of the hollow tube.

[0067] Fig. 3 illustrates a hollow tube being flushed with gas or gas mixture to clean the molten metal or alloy column from the hollow tube. Fig. 4 illustrates an arrangement of a heating means enclosing a portion of the outer surface of the hollow tube to heat up the molten metal or alloy column to a desired temperature and to prevent the molten material inside the hollow tube from solidifying.

[0068] Fig. 5 shows a schematic illustration for three different arrangements of the hollow tube in a vessel comprising molten metal or alloy. In Figure 5(a), the hollow tube extends into a closed vessel through an opening in the side wall. In Figure 5(b), the hollow tube extends into a vessel via a side well. In Figure 5(a) and Figure 5(b), the form of the hollow tube is an angled L-shape. In Figure 5(c), the hollow tube is strung up vertically above an open vessel.

[0069] Fig. 6 illustrates a cross-sectional view of one embodiment of a hollow tube comprising a layered structure.

[0070] Fig. 7 illustrates an embodiment similar to that of figure 2, wherein the hollow tube comprises a different geometry for the measurement chamber.

[0071] DETAILED DESCRIPTION

[0072] Fig. 1 shows molten metal or alloy (1) contained in a closed vessel comprising molten metal or alloy (2), wherein a hollow tube (3) has been arranged vertically through the top of the vessel (2). In some embodiments, the vessel may be of different type such as an open vessel, crucible or a trough. The hollow tube (3) comprises two ends, a closed upper end (4) comprising at least one optical window (5) for light (i.e., electromagnetic radiation) to pass through and a lower open end (6). The lower open end (6) is immersed in the molten metal or alloy (1) inside the vessel (2), e.g., at such a depth that the molten metal or alloy in contact with the mouth of the lower open end (6) of the hollow tube (3) is representative of the bulk of the molten metal or alloy (1) e.g., or 20 cm, or 30 cm, or 40 cm, or 50 cm. The hollow tube (3) extends to the exterior of the vessel (2), such that the closed upper end (4), or portion thereof, of the hollow tube may lie above the exterior of the furnace. The closed upper end (4) of the hollow tube (3) is connected to an evacuation system comprising a suitable pump (7), an evacuation line (8) and a control valve (9). The evacuation system is used to evacuate the hollow tube to establish vacuum conditions within the hollow tube, such as, but not limited to, pressure inside the hollow tube becomes approximately equal to or below 0.1 atm. It may be beneficial to keep the background vacuum pressure within the hollow tube (3) high enough to keep deposition of sample material off the optical windows (5). In some embodiments, the evacuation of the hollow tube (3) may be carried out in an automatic fashion using a control unit (not shown) connected to the pump system and the control valve (9). The vacuum conditions established within the hollow tube (3) cause the level of the molten metal or alloy (1) in the hollow tube (3) to rise up towards the closed upper end (4) of the hollow tube (3), in particular to a level (shown by a dotted line) defined primarily by the specific gravity of the molten metal or alloy (1), such that the suctioned molten metal or alloy forms a molten metal or alloy column (10) inside the hollow tube (3). The evacuated space (i.e., the vapor space) enclosed by the walls of the upper closed end

[0073] (4) and the surface of the molten metal or alloy column (10) defines a (sealed) measurement chamber (11) providing confinement and controllable environmental conditions for quantitative elemental measurements. In this embodiment, the at least one optical window

[0074] (5) is arranged on the top of the upper closed end (4), directly above the surface of the molten column (10). Alternatively, the at least one optical window may be arranged on the side walls at the upper closed end of the hollow tube (3), i.e., a portion that does not comprise the molten metal or alloy column (10). The hollow tube (3) profile may be chosen to be of any suitable shape such as, but not limited to, round, square or hexagonal. The length of the hollow tube may be determined to sufficiently long to account for (i) sufficient immersion of the lower open end (6) in the molten metal or alloy (2), (ii) the rise of the molten metal or alloy column (10) within the hollow tube (3) and (iii) allowing vapor space of sufficient length to be formed as the measurement chamber (11). In this embodiment, the upper portion of the hollow tube, the evacuation system, laser excitation system (not shown), emission receiving system (not shown) lie exterior to the closed vessel (2), which may be beneficial to protect the equipment from the extreme conditions within the closed vessel.

[0075] Fig. 2 illustrates quantitative elemental measurements being performed on a molten metal or alloy (1) contained inside a closed vessel (2). Prior to measurement, the measurement apparatus is configured on the vessel (2) such that a upper portion of the hollow tube (3) is arranged on the exterior of the vessel (2) and extends through the walls of the vessel and into the vessel (2). It may be replaceably configured or alternatively permanently fixed to the vessel. The hollow tube (3) is evacuated using an evacuation system (not shown) such that a column (10) of the molten metal or alloy (1) is sucked up into the hollow tube (3), leaving an evacuated vapor space at the top of the tube (i.e. determined by the pump system to a pre-determined level), defining a measurement chamber (11) between the surface of the column (10) (herein referred to as sample or sample surface) and the walls of the closed upper end (4) of the hollow tube (3). Laser excitation optics (13) are arranged axially above the closed upper end (4) of the hollow tube (3). The distance from the laser excitation system (13) to the closed upper end (4) may be chosen to be sufficiently large such as to protect the electronical equipment of the laser excitation system (13). Pulsed laser light (12) is directed from a laser through suitable laser excitation optical components such as a focusing element (not shown) to a sampling point (14) on the sample surface, through an optical window (5) arranged at the closed upper end (4) along the axial path of the laser light. The pulsed laser light ablates and excites the molten metal liquid or alloy sample at the sampling point (14) causing a plasma plume to form inside the measurement chamber (11). Light is emitted from the ablated sample, and travels through the optical window (5), wherein the emission (15) is then received by emission receiving optics (16). In some embodiments, the emission receiving optics may comprise at least one optical lens and at least one optical cable to focus and control said received emission (not shown). The emission receiving optics (16) may comprise at least one optical detector and at least one spectrograph. In some embodiments, the emission receiving optics may comprise at least one filter. The optical detector is connected to a spectrograph for resolving the received emission. In the embodiment shown in Fig. 2(a), a single optical window (5) is arranged on the top of the closed upper end (4), positioned in the plane parallel to the surface of the molten metal or alloy column (10). The optical window (10) is then used for both providing an optical path coaxial with the axis of the hollow tube, from the laser excitation optics (13) to the sampling point (14) and an optical path from emitted light from the sample to emission receiving optics (16). In such an embodiment, an optical mirror (17) may be arranged in an intermediate location between the laser excitation optics (13) and the optical window (5), wherein the optical mirror (17) is used to direct emitted light from the ablated sample, that passes through the optical window (5), to the emission receiving optics (16). In another embodiment, as shown in Fig. 2(b), two optical windows may be configured on the hollow tube (3), wherein the first optical window (5) is arranged on the top of the closed upper end (4) of the hollow tube (3). The first optical window (5) is then configured to provide an optical path for the pulsed laser light (11) from the laser excitation optics (13) to the sampling point (14), analogous to the embodiment of Fig. 2(a). The second optical window (18) may be configured on the side wall of the closed upper end (4), e.g., in vicinity to, but not in contact with, the sample surface, since the emitted light intensity drops quadratically with distance from the sampling point (14). In this embodiment, the alignment of the emission receiving optics (16) is adjusted accordingly to the position of the second optical window (18). The apparatus may comprise at least one distance sensor for measuring the distance between the sample surface and the laser excitation optics (13) and / or measuring the distance between the sample surface and the emission receiving optics (16), i.e. , to obtain the relative height of the molten metal or alloy column. The laser excitation system and / or emission receiving system may thus further comprise a moving means, wherein the moving means may be configured to mechanically or electrically adjust the position of either or both of these optical systems. Accordingly, the position of the laser excitation optics (13) and / or emission receiving optics (16) may be (automatically) adjusted accordingly to achieve a suitable pre- determined distance between the sample surface and the laser excitation optics (13) and / or the emission receiving optics (16).

[0076] Fig. 3 illustrates how the hollow tube (3) may be flushed with a gas or a gas mixture using at least one gas feed line (19). Herein, the gas or gas mixture may comprise a substantially pure gas comprising only a single component or comprise a plurality of gas components forming a gas mixture. In some embodiments, the gas or gas mixture may be selected to be inert gas or a mixture of inert gases. The closed upper end (4) of the hollow tube (3) is connected to a gas feed line (19) (or in vicinity thereto) that also comprises a gas source (not shown) configured to store the gas, wherein the feed-line (19) is configured to direct a stream of gas from the gas source and into the upper portion of the hollow tube (3). The flow of gas through the gas feed line (19) is controlled by a control valve (20). In some embodiments, the control valve (20) also gives substantial control over the gas flow rate and may be connected to a control unit such as, but not limited to, a microcontroller or a computer, e.g., through a wired or wireless connection means for remote and / or automatic control of the control valve (20). The flow of gas, directed from the gas source to the upper end of the hollow tube (3) flows from the closed upper end (4) (or in vicinity thereto), through the hollow tube (3) and to the open lower end (6) and from there into the molten metal or alloy (1) to become immersed (21) and later, e.g., evaporated. If a molten metal or alloy column has been sucked into the hollow tube (3) prior to the flushing the hollow tube (3) with (inert) gas, the flow of gas will serve to exert pressure on the sample surface of the molten metal or alloy column and with sufficient pressure of flowing gas or gas mixture, the gas or gas mixture will push the molten metal or alloy column out of the hollow tube (3) through the open lower end (6), in particular through the mouth of the open lower end, and back into the molten metal or alloy (1) of the vessel (2). In other words, flushing the hollow tube (3) with gas or gas mixture will serve to clean the hollow tube (3) from molten metal or alloy. The process of flushing the hollow tube (3) with gas may be carried out in-between elemental composition measurements, e.g., for preventing introduction of unwanted material into the hollow tube (3) and to aid in stirring of the molten metal or alloy and / or to introduce fresh samples of molten metal or alloy for subsequent measurements. Additionally, or alternatively, the feeding of gas may be used to bleed gas into the hollow tube (3) to provide a residual background vacuum pressure within the hollow tube (3) e.g., during measurements and / or to configure the relative height of the molten metal or alloy column to a pre-determined value, e.g., by obtaining a pre-determined distance from a reference point (could be located on any point on the apparatus) to the molten metal or alloy column. Fig. 4 illustrates how a heating element (22) can be arranged on the hollow tube (3) to heat up and / or maintain the temperature of the liquid metal or alloy column (10) within the hollow tube (3) at or above a desired temperature, e.g., above 600°C, or above 800°C, or above 1000°C. The heating means serve to prevent the molten metal or alloy column (10) from solidifying when the molten metal or alloy (1) is extracted from the metal furnace (2) and into the hollow tube (3). This may involve, in some embodiments, that the hollow tube is actively heated, either continuously or periodically, such as during sample introduction into the hollow tube (3) and / or in the period leading up to the measurements and analysis. In some embodiments the hollow tube may be pre-heated to ensure that the sample maintains a substantially steady temperature or at least does not cool down too rapidly. In some embodiments, the liquid metal or alloy column (10) may be heated through induction heating, wherein the heat is transmitted inductively to the column but not to the hollow tube (3) itself except as transmitted from the sample column (10) to the hollow tube (3). In some embodiments, such induction heating may be turned off during the sample analysis, i.e., when spectral emission from the sample plasma is being detected / recorded. In some embodiment, the heating element may be configured to be attached to the exterior of the hollow tube (3) and may extend over the full length of the hollow tube (3), alternatively it may extend over only a portion of the length of the hollow tube (3) such as, but not limited to, the part of the hollow tube (3) that is arranged on the exterior of the vessel (2). In the embodiment, shown in Fig. 4, the heating element (22) encompasses a portion of the upper closed end region and extends vertically down into the closed vessel (2) encompassing a portion of the hollow tube (3) inside the closed vessel (2). In some embodiments, at least one temperature sensor (not shown) is provided to monitor the temperature of the hollow tube (3). In some embodiment, at least one temperature sensor (not shown) is provided to monitor the temperature inside of the hollow tube. In some embodiments, the temperature of the hollow tube (3) is monitored along the lengthwise direction of the hollow tube (3). The at least one temperature sensor may be used to aid in controlling the heating element through a connection means to e.g., a control unit configured to maintain the temperature of the hollow tube (3) and the molten metal or alloy column (10) at a predetermined temperature. In some embodiments, the hollow tube may comprise an outer thermal insulation layer or coating (not shown) to prevent heat being lost to the environment, often in embodiments or parts of the hollow tube where there is no heating element.

[0077] Fig. 5 shows a schematic drawing for three different arrangements and connections of the hollow tube to a vessel (2) comprising molten metal or alloy (1). These arrangements are not meant to be considered limiting for the present invention but rather server as illustrative examples of the present invention. The hollow tube (3) may assume any suitable shape, or profiles, to be mated with different types of molten metal or alloy vessels such as furnaces, troughs, crucibles and the like. Accordingly, the hollow tube may be formed in different shapes such as, but not limited to, linear vertical extending cylindrical or angled cylindrical L-shape. Hence, depending on the shape and application, the hollow tube may be formed integrally or in parts, wherein the different parts of the hollow tube may be connected or coupled together to form the hollow tube. As described above, the hollow tube may be equipped with systems and / or components (not shown) such as laser excitation system, emission receiving system, pump / evacuation system, gas feed line and a gas source, optical windows, heating element, at least one distance sensor, and temperature sensors and so forth.

[0078] In Fig. 5(a), the hollow tube is connected to a closed rectangular vessel (2) such as, but not limited to, a metal furnace. In this embodiment, the hollow tube (3) comprises two parts to form an angled L-shape), wherein the open lower part of the hollow tube (3b) extends into the closed vessel through an opening arranged on one of the side walls of the vessel below the surface level of the molten metal or alloy (2) arranged in the vessel (1). Alternatively, the opening may be positioned above the surface level of the molten metal or alloy (2) arranged in the vessel (2). In this embodiment, the closed upper part of the hollow tube (3a) extends vertically up from the open lower part (3b) of the hollow tube (3). For measurements, the evacuation system is used to suck up molten metal or alloy (1) from the vessel and into the hollow tube (3), wherein the molten metal or alloy will climb up along the hollow tube (3) until it reaches a height corresponding to the specific gravity of the molten metal or alloy, with the surface level of the column (10) arranged in the closed upper part of the hollow tube (3a).

[0079] In Fig. 5(b), the hollow tube is connected to a rectangular vessel (2) comprising a side well or equivalently a trough with an opening. In this embodiment, the hollow tube comprises two parts to form an angled L-shape, wherein a portion of the upper part of the hollow tube (3a) extends into the vessel trough the opening. In this embodiment, the lower part of the hollow tube (3b) is substantially submerged in the molten metal or alloy (2). In other embodiments, it may be sufficient for the lower part (3b) to only marginally extend into the vessel, for example, if a stirring mechanism is provided, as will be recognized by a person skilled in the art.

[0080] In Fig. 5(c), the hollow tube is connected (shown by a dashed line) to a support element (shown by a box) and strung up above an open vessel (2), e.g., a crucible, comprising molten metal or alloy (1). In some embodiments, the hollow tube (3) may comprise a layered structure, or portions of the hollow tube (3) may comprise a layered structure, as described above, e.g., comprising a structural outer sheath and / or an insulating layer. Fig. 6 illustrates a cross-sectional view of a layered hollow tube (3) comprising a layered structure enclosing the hollow space (23) within the hollow tube (3). The inner-most layer (24) of the hollow tube (3) may then be in direct contact with the liquid metal and or alloy arranged in a vessel comprising molten metal or alloy (2), as well as, the molten metal and or alloy column (10). Accordingly, the hollow tube (3) may comprise a heat-resistant material that is able to withstand the heat shock of being in contact with molten metal or alloy and not react with the molten metal or alloy. Accordingly, in some embodiments, the inner-most layer (24) may be formed from a heat resistant material such as, but not limited to, a heat-resistant ceramic material e.g., SiAION.

[0081] In some embodiments, the hollow tube (3) may comprise a second layer (25) for increasing the structural integrity of the hollow tube (3), wherein the structural layer may comprise materials such as, but not limited to, high grade steel, titanium, or alloys. The length of the second structural layer (25) may be selected such that the lower end of the second layer is not immersed in the molten metal or alloy (1) inside the body of molten metal or alloy (2).

[0082] In some embodiments, a heat-resistant seal may be configured at and around the bottom of at least the second structural layer (25) such that the structural layer is not in direct contact with the molten metal or alloy (1) and also further protected against the heat emitted from the molten metal or alloy (1), as well as, from corrosion. In another embodiment, the length of the second structural layer may encompass parts of the hollow tube (3) that lie exterior to the vessel (2).

[0083] In some embodiments, a thermal insulation layer may be added to the interior or exterior of the second structural layer (25).

[0084] Fig. 7 shows one embodiment, wherein the upper closed end of the hollow tube (3) comprises a measurement chamber (11) comprising a different geometry than the geometry of the lower portion of the hollow tube. In this embodiment, the measurement chamber is a rectangular box, while the lower portion of the hollow tube (3) may be a cylinder with a round profile. In some embodiments, the molten metal or alloy may column be sucked up to a level equal to the interface / entrance of the measurement chamber (11). In other embodiments, the molten metal or alloy column may be sucked, at least partially, into the measurement chamber (11).

Claims

CLAIMS1. A measurement apparatus for measuring elemental composition of molten metal or alloy, said apparatus comprising; a. a hollow tube with an open lower end and a closed upper end, wherein the open lower end is configured to be immersed in said molten metal or alloy, and to have the closed upper end positioned above the molten metal or alloy; b. a pump system connected to said hollow tube and configured to evacuate air and / or gas from said hollow tube when the open lower end is immersed in said molten metal causing said molten metal or alloy to rise up along the inside of the hollow tube from the open lower end and towards the closed upper end, to form a column of said molten metal or alloy within said hollow tube, such that the upper end of said column is positioned in vicinity to the closed upper end of said hollow tube; c. a laser excitation system for ablating a sample of said molten metal or alloy column through at least one optical window; and, d. an emission receiving system for detecting emitted light from said ablated sample through at least one optical window at, or in vicinity to, the upper end of the hollow tube.

2. The measurement apparatus according to claim 1 , wherein said closed upper end of said hollow tube comprises a measurement chamber, and wherein said at least one optical window is arranged on the walls of the measurement chamber.

3. The measurement apparatus according to claims 1 or 2, wherein the pump system is configured to establish vacuum conditions within the hollow tube.

4. The measurement apparatus according to claim 3, wherein the pump system is configured to maintain the said vacuum conditions by continuously evacuating the hollow tube to remove evaporated material from the molten metal inside the hollow tube.

5. The measurement apparatus according to any of claims 1-4, wherein said hollow tube has a total length of at least about 4 m to accommodate a column height of molten aluminium or aluminium alloy according to its specific gravity when vacuum conditions are established in the closed upper end of said hollow tube.

6. The measurement apparatus according to any of claims 1-5, wherein the inner diameter of said hollow tube is in the range of 5 cm to 20 cm.

7. The measurement apparatus according to any of claims 1-6, wherein said measurement apparatus further comprises at least one gas feed line connected to said hollow tube in vicinity to said closed upper end.

8. The measurement apparatus according to any of claims 1-7, wherein said at least one gas feed line comprises a means of flow control for regulating flow of gas or gas mixture through said at least one gas feed line.

9. The measurement apparatus according to claims 7 or 8, wherein said at least one gas feed line is configured to allow flushing of the hollow tube with inert gas.

10. The measurement apparatus according to claims 7 or 8, wherein said at least one gas feed line is configured to allow bleeding of gas or gas mixture into said hollow tube.

11. The measurement apparatus according to any of claims 1-10, wherein the hollow tube comprises refractory material capable of withstanding thermal shock from immersing in and being partially filled with molten metal or alloy.

12. The measurement apparatus according to claim 11, wherein said hollow tube further comprises a structural outer sheath.

13. The measurement apparatus according to claim 12, wherein said structural outer sheath is at least arranged on an upper portion of the hollow tube.

14. The measurement apparatus according to any of claims 1-13, wherein said measurement apparatus further comprises a heating element to prevent solidification of molten metal or alloy inside said hollow tube.

15. The measurement apparatus according to any of claims 1-14, wherein said hollow tube further comprises an insulation layer.

16. The measurement apparatus according to any of claims 1-15, wherein said laser excitation system comprises a laser arranged axially above the hollow tube and configured to direct pulsed and focused light to the surface of said molten metal or alloy column inside the hollow tube through at least one optical window arranged at or in vicinity to the upper end of said hollow tube.

17. The measurement apparatus according to any of claims 1-16, wherein said emission receiving system is arranged at an angle to the optical axis of said laser and configured to detect light through at least one optical window arranged at or in vicinity to the upper end of said hollow tube.

18. The measurement apparatus according to any of claims 1-17, wherein said measurement apparatus further comprises at least one distance sensor to measure the relative height of the surface of the molten metal or alloy column.

19. The measurement apparatus according to any of claims 1-18, wherein the at least one gas feed line is configured to regulate pressure above the surface of the molten metal or alloy column arranged in the hollow tube to adjust the height level of the surface of the molten metal or alloy surface.

20. The measurement apparatus according to either claim 18 or 19, wherein the measurement apparatus further comprises a moving means for moving the emission receiving system and / or laser excitation system to a pre-determined distance from the surface of the molten metal or alloy.

21. The measurement apparatus according to any of claims 1-20, wherein the measurement apparatus is fitted to a metal furnace.

22. The measurement apparatus according to claim 21 , wherein the measurement apparatus is fitted through an opening, or a hatch arranged on the metal furnace, wherein the opening or hatch mates with said hollow tube and the upper portion of said hollow tube lies exterior to the furnace.

23. A method for measuring chemical composition of a body of molten metal or alloy, said method comprising;a. arranging a hollow tube with an open lower end and a closed upper end by said body of molten metal or metal alloy wherein i. the open lower end is immersed in said body of molten metal or alloy, and, ii. the closed upper end is arranged exterior to the body of molten metal or alloy; b. evacuating said hollow tube causing molten metal or alloy from the body of molten metal or alloy to climb in a column inside the hollow tube, from the immersed open lower end towards the closed upper end; c. emitting by a laser one or more pulses of light, through at least one optical window on the hollow tube arranged in or in vicinity to the closed upper end, to ablate the surface of the uppermost part of the liquid metal or alloy column; d. receiving emitted light from the ablated molten metal or alloy, through at least one optical window, using an emission receiving system; and, e. performing spectral analysis of said emission to determine chemical composition of said molten metal.

24. The method according to claim 23, wherein evacuating said hollow tube brings pressure inside said hollow tube to vacuum pressure.

25. The method according to claim 23, wherein the method further comprises flushing a stream of gas, which is preferably inert gas, through at least one gas feed line connected to the upper portion of said hollow tube after a measurement to clean said hollow tube of molten metal or alloy by pushing said molten metal or alloy out of the hollow tube.

26. The method according to claim 23, wherein the method further comprises bleeding gas or gas mixture through at least one gas feed line connected to the upper portion of said hollow tube to provide a consistent residual background vacuum pressure at and in vicinity to the surface of the molten metal or alloy column.

27. The method according to claim 23, wherein the method further comprising measuring the relative height of the molten metal or alloy using at least one distance sensor.

28. The method according to claim 27, wherein the method further comprises automatically adjusting the position of the emission detecting system and / or laserexcitation system to obtain a pre-determined distance between the laser excitation system and / or emission detecting system and the surface of the molten metal or alloy prior to emitting at least one laser pulse.

29. The method according to either claim 27 or claim 28, wherein the method further comprises bleeding in gas or gas mixture to regulate pressure above the surface of the molten metal or alloy column arranged in the hollow tube to adjust the height level of the surface of the molten metal or alloy surface.

30. The method according to either claim 29, wherein a gas or gas mixture is bled through at least one gas feed line connected to the upper portion of said hollow tube to adjust the level height of the liquid column.

31. The method according to any of claims 23 to 30, wherein the method further comprises heating the molten metal or alloy column to maintain a temperature above at least 600°C.

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