Emission stand for optical emission spectrometry with improved dust removal

Abstract

An emission stand (201) for an optical emission spectrometer, comprising a discharge box (210) and at least one auxiliary gas conduit (209a, 209b) for supplying an auxiliary gas flow into the discharge box (210), the at least one auxiliary gas conduit (209a, 209b) being configured to supply an auxiliary gas flow (214) into the discharge box (210) for a period of time after a spark action, but not during a spark action during which an analysis of a sample is performed. The auxiliary gas flow (214) into the discharge box (210) improves dust flushing from the discharge box (210) after the spark action.

Description

[Technical field]

[0001] The present disclosure relates to the field of spark optical emission spectroscopy. In particular, the present disclosure relates to an improved optical emission stand for an optical emission spectrometer, an optical emission spectrometer comprising the same, and a method of optical emission spectroscopy. [Background technology]

[0002] Arc / spark optical emission spectroscopy is a well-known technique used for the analysis of solid samples, typically metal samples. Optical emission spectroscopy can be performed using either a spark or an arc light source, or both. For convenience, as used herein, the term spark optical emission spectroscopy refers to any optical emission spectroscopy that uses an electrical discharge, e.g., a spark or arc discharge, to excite the sample, and the term discharge box refers to the space or volume for such a discharge, where light is emitted and measured.

[0003] In use, a conductive (typically metallic) solid sample is mounted on an emission stand above the opening leading to the discharge box, which is usually flat and thus forms an airtight seal with the stand. Within the discharge box is located an electrode, which usually functions as an anode, oriented so that it points its tapered end towards the sample. The electrode is surrounded by an electrical insulator, except for its tapered end. A series of discharges are initiated between the electrode and the sample, which acts as the cathode. The insulator ensures that the discharge is directed towards the sample and not towards the walls of the box. The sample material where the discharge is directed is ablated / vaporized, and some of the ablated / vaporized material is in an excited state. Upon relaxation, the ablated, excited material emits photons whose energy (wavelength) is characteristic of a given state transition of the elements in the material. By spectroscopic analysis of the emitted photons, the composition of the sample material can be deduced. A portion of the light emission caused by this discharge is then sent from the discharge box to an analyzer for spectroscopic analysis. Spectroscopic analysis is performed using an optical analyzer, typically using a dispersing means such as a diffraction grating to spatially disperse the light according to its wavelength. The analyzer includes a photodetector, for example an array detector, to measure the amount of light as a function of wavelength to obtain an emission spectrum.

[0004] To obtain information about the various elements in the sample, the instrument must be capable of transmitting photons below 200 nm from the discharge chamber to the detector, since some elements emit photons in the vacuum ultraviolet (VUV) wavelength range when they relax to lower energy states. To avoid the absorption of these VUV photons by air and the wavelength shift associated with changes in the refractive index of the gas (which varies with gas pressure and gas composition), the sample material is excited in the presence of a substantially UV-transparent inert gas, typically argon gas, which is fed into the discharge chamber at least while a series of spark discharges are initiated. If the gas composition is kept constant in the spectrometer, the problem of refractive index shifts is eliminated and steady-state light detection can be performed.

[0005] The problem is that atoms, agglomerates or particles of material detached from the sample surface (herein referred to as debris or dust) may remain in the discharge box and / or re-precipitate, affecting subsequent measurements. To prevent cross-contamination, the so-called memory effect, preferably all material detached from one analyzed sample should be removed from the discharge box before analyzing the next sample, so that no material from the previous sample is redeposited on the next sample and no such material is present in the discharge path. Gas flowing through the discharge box is used to sweep the detached material, such as metal dust and debris, out of the discharge box in a continuous or semi-continuous process. In this way, much of the detached material is carried away in the gas flow from the discharge box to a downstream filter.

[0006] One particular design of a discharge box using gas flow is disclosed in WO 2012 / 028484 A1 (Thermo Fisher Scientific). However, dust is not completely removed and over time, flaked sample material may still deposit and build up on the insulators and other surfaces and along the gas conduits within the discharge box. This reduces the analytical performance of the spectrometer and, when this occurs, the spectrometer cannot be used while the discharge box is being cleaned or some components are being replaced, increasing maintenance costs and downtime of the instrument. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2012 / 028484 [Patent Document 2] International Publication No. 2020 / 200757 Summary of the Invention [Problem to be solved by the invention]

[0008] One way to address the prevention of dust accumulation over multiple analysis cycles is to use a strong gas flush sequence through the discharge chamber, which occurs at the end of each spark analysis sequence. However, the direction of the strong gas flush is the same as the flush used during spark analysis, and in some discharge chamber designs, such as the design disclosed in WO 2012 / 028484 A1, the flow remains largely laminar. This is not very efficient for dust removal from the discharge chamber.

[0009] With the above in mind, the present disclosure is presented. [Means for solving the problem]

[0010] According to one aspect of the disclosure, an emission stand for an optical emission spectrometer is provided, the emission stand comprising: a discharge box; and at least one auxiliary gas conduit for supplying an auxiliary gas flow into the discharge box, the at least one auxiliary gas conduit being configured to supply an auxiliary gas flow into the discharge box not during spark operation but for a period of time after spark operation.

[0011] The analysis of the sample is performed during the spark action. The auxiliary gas flow into the discharge box improves the flushing of dust from the discharge box after the spark action. In this way, dust is removed from the discharge box after the sample analysis and before the next analysis is performed. The term dust in this specification refers to any material resulting from the detachment of material by the spark action, for example from the solid surface of the sample. The period during which at least one auxiliary gas conduit supplies an auxiliary gas flow into the discharge box is sufficient to allow the removal of at least a part, preferably a majority, of the dust generated by the spark action. The period of flushing dust from the discharge box by the auxiliary gas flow can be performed after each spark action and / or after multiple spark actions, for example periodically and / or after a set number of spark actions. The period of flushing dust from the discharge box by the auxiliary gas flow can be performed after each spark action and before each spark action. Thus, in such an embodiment, there can be two flush periods between each spark action (analysis period). The period of time during which the auxiliary gas flow flushes the dust from the discharge box may be, for example, 1 to 5 seconds, such as about 2 seconds, or 3 seconds, or 4 seconds. The auxiliary gas flow may be a continuous flow during that period, or preferably may include a series of short gas bursts or pulses, which may further improve dust removal. For example, each short gas burst or pulse may be less than 1 second (e.g., 0.1 to 0.9 seconds, or 0.1 to 0.5 seconds, or shorter, e.g., milliseconds or tens of milliseconds), for example, a few tenths of a second (e.g., 2 / 10 seconds, 3 / 10 seconds, 4 / 10 seconds, 5 / 10 seconds, 6 / 10 seconds, 7 / 10 seconds, or 8 / 10 seconds). This flash period is typically comprised of two or three stages of 4-8 second sparks (so that the total spark period is, e.g., 10-25 seconds), in contrast to the duration of a typical spark operation or analysis stage, which may last, e.g., 5-50 seconds, or 10-25 seconds.

[0012] In some embodiments, the at least one auxiliary gas conduit is a single auxiliary gas conduit. In some embodiments, the at least one auxiliary gas conduit is two or more auxiliary gas conduits, for example, three or four or more auxiliary gas conduits.

[0013] In some embodiments, the at least one auxiliary gas conduit is switchable between an open position and a closed position, i.e., between an open position that allows gas flow into the discharge box and a closed position that prevents gas flow into the discharge box. Thus, the at least one auxiliary gas conduit is configured to be in a closed position during sparking operation and in an open position when flushing debris from the discharge box (after sparking operation). Normally, the at least one auxiliary gas conduit may be configured to be in a closed position, e.g., when not flushing the discharge box.

[0014] In some embodiments, the at least one auxiliary gas conduit comprises at least one valve for opening and closing the at least one auxiliary gas conduit, thereby allowing or preventing auxiliary gas flow into the discharge box. For example, the valve may be closed during sparking operation to prevent auxiliary gas flow into the discharge box. The valve may be opened after sparking operation to allow auxiliary gas flow into the discharge box. A controller may be provided and configured to control the gas flow as described in this disclosure. The at least one valve may be controlled by a controller, which also preferably controls the sparking operation. The controller may comprise control logic, such as a processor or state machine, and associated control electronics for controlling the valves and / or the sparking operation (e.g., voltage source, spark frequency, total sparking time, etc.).

[0015] In some embodiments, the luminescence stand further comprises a first gas conduit for supplying the first gas flow into the discharge box at least during the spark operation. The luminescence stand may further comprise a second gas conduit for conveying the gas from the discharge box. The first gas conduit and the second gas conduit may be located diametrically opposite each other on both sides of the discharge box. The second gas conduit may be connected to an exhaust line or waste line, optionally including a debris and dust filter, or to a gas recirculation line, which may filter the gas to remove debris and dust before returning it to the first gas conduit and / or the auxiliary gas conduit. In some embodiments, the first gas conduit is for supplying the first gas flow into the discharge box during and after the spark operation, such that the auxiliary gas flow merges with the first gas flow after the spark operation. It is beneficial to continue supplying the first gas flow from the first gas conduit into the discharge box while the auxiliary gas flow is being supplied into the discharge box. This is because it is possible to prevent dust from flowing back through the first gas conduit and reaching the optical system (spectroscope).

[0016] In some embodiments, the at least one auxiliary gas conduit is configured to supply an auxiliary gas flow in a cross-flow configuration with the first gas flow. The cross-flow configuration may allow for the generation of gas turbulence in the discharge box, preferably in the vicinity where the spark is generated. When the first gas flow is configured as an axial flow through the discharge box along an axis from the first (inlet) conduit to the diametrically positioned second (outlet) conduit, the at least one auxiliary gas conduit is configured to supply the auxiliary gas flow in a cross-axial direction, i.e. at a non-zero angle with respect to the axis of the first gas flow.

[0017] In some embodiments, the first gas flow is laminar. In some embodiments, the first gas flow is preferably laminar during sparking, and the laminar flow is broken by the auxiliary gas flow after sparking. In general, it is beneficial for the auxiliary gas flow to provide a turbulent gas flow in the discharge chamber after sparking.

[0018] In some embodiments, the flow rate of the auxiliary gas flow is greater than the flow rate of the first gas flow (at least greater than the first gas flow during spark operation). For example, the flow rate of the auxiliary gas flow can be at least 2 or at least 3 times greater than the flow rate of the first gas flow used during spark operation, such as 3 to 10 or 3 to 5 times greater. In one embodiment, the auxiliary gas flow is about 15 L / min, while the first gas flow during analysis is in the range of only 2 or 3 L / min to 5 L / min. The auxiliary gas flow can include a series of gas bursts or pulses.

[0019] In some embodiments, the at least one auxiliary gas conduit is two auxiliary gas conduits, where the two auxiliary gas conduits are symmetrically positioned (laterally) on either side of the first gas conduit. In some embodiments, where the at least one auxiliary gas conduit is a single auxiliary gas conduit, the auxiliary gas conduit is positioned (laterally) on one side of the first gas conduit.

[0020] Advantageously, the auxiliary gas flow allows the laminar flow to be interrupted, especially in the region surrounding the electrode and in the insulator surrounding the electrode, especially in the embodiment where the auxiliary gas flow crosses the first gas flow. The interruption of the first gas flow by the auxiliary gas flow, especially the auxiliary gas flow, can generate gas turbulence and / or unstable vortex flows, which can interact with each other and create friction and pressure fluctuation effects. This can lift the accumulated debris and dust, resulting in improved dust removal and reduced dust accumulation. In turn, this means less instrument maintenance is required. In some embodiments, the auxiliary gas flow lifts the dust, while the first gas flow can act to push the dust down from the second gas conduit (gas outlet) to the exhaust. In one embodiment, a short delay time can be introduced between the operation of the auxiliary gas flow lifting the accumulated dust and the operation of the first gas flow pushing the dust to the outlet of the discharge box.

[0021] The discharge box, or either the auxiliary conduit, the first conduit, or the second conduit, may be provided with an anti-adhesive material on their surface to further reduce the accumulation of debris or dust. The anti-adhesive material is generally a non-metallic material. The anti-adhesive material is typically a material with a low coefficient of friction, for example, a static coefficient of friction and a dynamic coefficient of friction of 0.5 or less, 0.4 or less, or 0.3 or less. Such materials are described in WO 2020 / 200757(A1) (Thermo Fisher Scientific).

[0022] An elongated electrode having an electrode axis generally along the direction of elongation is located in the discharge box. In use, generally, there is a gas flow, in particular a laminar flow, through the discharge box, for example between the first (inlet) and second (outlet) gas conduits. Preferably, the walls of the discharge box, i.e. the radial walls (those radially facing the electrodes), are curved, thereby defining an internal volume of the discharge box having a curved outer shape, preferably a cylindrical shape, i.e. the walls of the discharge box define a cylindrical shape. Such wall surfaces may comprise an anti-adhesive material, as described above. Preferably, the discharge box is substantially cylindrical, and the electrodes are arranged approximately on the axis of the cylinder. Preferably, the first and second gas conduits are located on the curved inner wall of the cylinder, on opposite sides of the cylinder, more preferably on substantially diametrically opposed sides. Preferably, the first and second gas conduits are diametrically opposed to each other on the walls of the discharge box.

[0023] The elongated electrode may be of any cross-sectional shape (i.e., cross-section across the electrode axis), but is preferably cylindrical with a tapered conical end that extends within the discharge box towards the sample location. Preferably, the elongated electrode has a conical tip. The elongated electrode has an axis, referred to herein as the electrode axis, which generally extends along the direction of elongation, and the electrode is oriented within the discharge box such that the axis points towards the sample location. The electrode axis is preferably located substantially in the radial centre of the discharge box. In a preferred embodiment, the electrode axis also defines the axial direction of the discharge box, and gas flows generally radially from a first (inlet) gas conduit on a first side of the discharge box to a second (outlet) gas conduit on a second side of the discharge box (opposite the first side). The internal shape and components of the discharge box may be such that turbulence in the gas flow during spark operation is substantially eliminated, however, following spark operation, an auxiliary gas flow supplied in accordance with the present disclosure may create turbulence that ultimately results in better removal of detached dust and debris from the discharge box, as described, for example, in WO 2012 / 028484, which is preferred for analytical performance.

[0024] The illumination stand may be configured to mount a solid (conductive) sample, typically a metal sample, for analysis, typically with the sample facing the end of the electrode in the discharge box and / or typically with the sample positioned above an opening in the discharge box wall facing the end of the electrode, usually with an airtight seal. The illumination stand generally comprises a table covering the discharge box, the table having an opening positioned above the discharge box. The table may receive the sample such that the sample faces the electrode by covering the opening, so that the surface can be analyzed. A controller may be provided to control the high voltage source to cause one or more, typically a series of discharges, between the electrode and the sample during sparking, with the electrode acting as the anode and the sample acting as the cathode. A gas, preferably an inert gas, e.g. argon, is supplied into the discharge box via a first gas conduit during sparking and analysis.

[0025] According to another aspect of the present disclosure, an optical emission spectrometer (OES) is provided that includes an optical emission stand. The optical emission spectrometer may further include an optical analyzer for analyzing and detecting the light from the discharge box according to its wavelength. For example, the optical emission spectrometer may include a spectrometer for separating the light according to its wavelength and detecting the separated light. The light is emitted by the excited sample material in the discharge box that is evaporated and excited by the spark action. In this way, a spectrum of the emitted light, i.e., a series of emission lines, can be obtained, from which the composition of the sample material can be deduced. The optical emission stand and the optical emission spectrometer can be used to perform optical emission spectroscopy.

[0026] According to a further aspect of the present disclosure, there is provided a method of optical emission spectroscopy, the method comprising supplying an auxiliary gas flow into the discharge box via at least one auxiliary gas conduit configured to supply an auxiliary gas flow into the discharge box after sparking but not during sparking. The method may be performed using an optical emission stand or an optical emission spectrometer of the present disclosure. The method of the present disclosure embodies the functionality of the optical emission stand and its components. The features of the optical emission stand and the optical emission spectrometer apply mutatis mutandis to the method.

[0027] In some embodiments, the method includes supplying a first gas flow into the discharge box during spark operation, for example, through a first gas conduit separate from the auxiliary gas conduit. Thus, the first gas flow can flow through the discharge box during spark operation, i.e., over a series of sparks applied to the sample in the discharge box during analysis of the light emission from the discharge box. The first gas flow can be a laminar gas flow. In some embodiments, the method includes conveying gas from the discharge box during and after spark operation through a second gas conduit, for example, to an exhaust line or a recirculation line.

[0028] In some embodiments, the first gas flow into the discharge box is provided during and after the spark operation, such that the auxiliary gas flow merges with the first gas flow after the spark operation. The first gas flow rate may also be increased for dust removal after the spark operation. The auxiliary gas flow may be provided in a cross-flow configuration with the first gas flow. In some embodiments, the first gas flow is laminar. In some embodiments, the first gas flow is laminar during the spark operation, and this laminar flow is interrupted by the auxiliary gas flow after the spark operation. This cross-flow may create turbulence and vortexes, which in turn lift up the accumulated dust, resulting in better dust removal and reduced dust buildup.

[0029] The disclosed method may include any of the other well-known steps of optical emission spectroscopy, such as providing a solid (typically metallic) sample for analysis, typically with the sample facing the end of an electrode in the discharge box and / or typically mounted so that the sample is positioned above an opening in the discharge box wall facing the end of the electrode, usually with an airtight seal; inducing one or more, typically a series of discharges between the electrode and the sample during a sparking action, the sample acting as a cathode; detaching and atomizing material from the sample and exciting at least a portion of the vaporized material, whereby the excited material emits photons, the energy of the photons being characteristic of the elements in the material; and performing a spectroscopic analysis of the emitted photons, thereby enabling the composition of the sample material to be deduced, wherein a gas, preferably an inert gas, such as argon, is fed into the discharge box via a gas inlet during the analysis.

[0030] The present disclosure may allow for better removal of debris and dust from the discharge box, reduced deposition of flaking material, such as metal dust, on surfaces within the emission stand. The present disclosure further allows for reduced metal dust buildup, more stable analytical performance of the spectrometer over extended periods of operation, and reduced costs associated with preventative maintenance, such as cleaning or part replacement of the emission stand.

[0031] Further details of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings in which: [Brief description of the drawings]

[0032] [Figure 1] 1 shows an embodiment of an emission stand for OES analysis with gas flow. [Diagram 2] 1 shows a cross section of an illumination stand for OES analysis according to one embodiment of the present disclosure. [Diagram 3] 4 shows the gas flow rate into the discharge chamber as a function of time for spark operation with pre-spark and post-spark flash operations. [Figure 4] 1 shows a cross section of an illumination stand for OES analysis according to a further embodiment of the present disclosure. [Diagram 5] 1 shows a cross-section of an illumination stand for OES analysis according to another embodiment of the present disclosure. [Figure 6] 1 illustrates a schematic of an OES spectrometer with an emission stand according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] FIG. 1 shows a horizontal cross-sectional view of an emission stand 101 forming part of an optical emission spectrometer. The emission stand comprises a discharge box 110 which is generally cylindrical in shape, i.e. has a cylindrical discharge box wall. The discharge box contains a cylindrical electrode 104 which is located in the centre of the discharge box and is surrounded by an insulator 103 to prevent discharge to the discharge box wall. The insulator 103 is rotationally symmetric about the electrode 104. The view of the emission stand 1 is separated from the rest of the optical emission spectrometer. For example, the optics (such as a spectrometer) which receives the emission from the discharge box are not shown.

[0034] During operation, a spark or discharge is ignited between an electrode 104 located within the discharge box and the surface of a conductive sample (not shown) that is presented to the discharge box. This sparking action generates a plasma that causes ablation, atomization, and excitation of material from the sample, followed by light emission. The light is analyzed by an optical system (not shown) and information regarding the composition of the sample is determined through qualitative and quantitative spectroscopy. Typically, the sparking action involves a timed sequence of sparks, and the light emitted as a result of each spark is analyzed.

[0035] Spark ignition is performed under an inert gas atmosphere, such as an argon (Ar) atmosphere, which is provided by a gas flow (argon) entering the discharge box 110 through a first gas conduit 102. The gas conduit 102 is provided from an upstream gas source (not shown). The gas flows in the direction indicated by the arrow 112. For example, during the analysis of a sample, argon gas of purity higher than 99.997% (such as argon 48 grade, 99.998%) can be provided through the gas conduit 102 into the discharge box at a flow rate of 5 L / min (standard liters per minute). A quantity of the stripped material is carried out of the discharge box by the gas flow through a second gas conduit 108 to an exhaust tube 105. The gas conduits 102 and 108 are on opposite sides of the discharge box 110. The gas conduits can be provided by channels formed in the luminous stand 101.

[0036] When the spark or arc sequence is terminated, a certain amount of the ablated material tends to remain in the discharge box (as metal vapor, or dust or metal deposits). It is believed that some of this material may remain as metal vapor or dust, while some of the atomized metal dust may recombine, precipitate, deposit, and / or partially metallize above the insulating region 103 surrounding the central electrode 104, and / or on the walls of the discharge box 110, and / or on the tip of the electrode. Over multiple analysis cycles, i.e., multiple sparks, such deposited ablated material on the insulator 103 and the discharge box 110 may cause performance degradation and require regular maintenance by cleaning the insulator 103, the discharge box 110, or other parts of the light stand 101.

[0037] One approach to prevent dust buildup over several analysis cycles is to use a strong gas flush sequence at the end of each spark / arc sequence and / or at the beginning of each spark / arc sequence. The direction of the gas flush is also represented by arrow 112. Typically, the flow rate during such a flash is increased many times over the flow rate during spark / arc operation. Due to the geometry of the discharge box, the gas passing through the conduit 102 and discharge box 110 remains in a substantially laminar flow. This flow (laminar) is advantageous when the spark / arc sequence is operating and performing the analysis, since it reduces plasma oscillations, but once the spark / arc sequence is finished, it is not very efficient for dust removal. The accumulation of dust deposits causes performance degradation and, in the best case, requires very time-consuming manual maintenance. In the worst case, it requires regular replacement of some spark components, increasing the maintenance costs of the instrument.

[0038] 2 shows an embodiment that improves dust removal and therefore improves maintenance and reduces the operating costs of the optical emission spectrometer. The optical emission stand 201 has many of the same components as the optical emission stand 101, including the discharge box 210, the electrodes 204, the insulators 203, the first gas conduit 202 carrying the first gas flow 212, the second gas conduit 208, and the exhaust tube 205. The optical emission stand 201 differs from the optical emission stand 101 in that it includes two additional gas flow tubes 209a, 209b that function as auxiliary gas conduits. The gas flow tubes 209a, 209b carry the same gas as the first gas conduit 202, such as argon. However, in other embodiments, the gas flow tubes 209a, 209b may carry different inert gases to flush the discharge box. Considering that the electrode 204 is oriented longitudinally (out of the page), the gas flow tubes 209a, 209b are positioned laterally on either side of and equidistant from the first gas conduit 202. Each gas flow tube 209a, 209b is connected to a valve (not shown) that allows gas flow for flushing in an open state and blocks gas flow in a closed state. In some embodiments, each tube may be connected to a respective valve or both tubes may be connected to a common valve. The valves may be solenoid valves, gate valves, needle valves, or any other suitable type of gas valve.

[0039] During spark operation and light emission analysis, the valves are closed to prevent gas flow through gas flow conduits 209a, 209b into the discharge box. Thus, gas flow into the discharge box 210 during spark operation is provided by the first conduit 202, as indicated by arrow 212, and is preferably laminar as determined by the geometry of the discharge box 210 and the positions of the first gas conduit 202 and second gas conduit 208.

[0040] After the spark operation and analysis are completed, a flushing operation can be initiated for a period of time to remove dust from the discharge box caused by the flaking of solid objects during the spark operation. For such an operation, valves are switched open to allow gas 214 to flow through gas flow tubes 209a, 209b into the discharge box as two auxiliary argon gas flows 207a, 207b that cross and overlap with the central argon gas flow 212 through the first conduit 202. The outlets of the gas flow tubes 209a, 209b are oriented to generally direct the auxiliary gas flows 207a, 207b toward the center of the discharge box, i.e., near the spark electrode 204. Thus, the two peripheral auxiliary gas flows 207a, 207b cross or intersect with the central first gas flow 212.

[0041] The flow rate of the auxiliary argon gas streams 207a, 207b is preferably greater than the flow rate through the first gas conduit 202 during spark operation / analysis. In this embodiment, the first gas flow rate through the first gas conduit 202 during spark operation and sample analysis may range from 2-5 L / min or 3-5 L / min. For flush operation, the gas flow rate of the central gas stream through the first gas conduit 202 is increased. For example, the gas flow rate through the first gas conduit 202 is increased by 2-10 times, or 2-5 times, for example, to 15 L / min, during flush operation. However, in other embodiments, other flow rates more suitable for the particular system may be selected. At the same time, for flush operation, the valves on the auxiliary gas conduits 209a, 209b are opened to allow the auxiliary gas streams 207a, 207b to enter the discharge box, and these gas streams have a similar gas flow rate, for example 15 L / min, as the increased central gas flow rate through the first gas conduit 202. A given flow rate of the auxiliary gas stream is the sum of the flows through the two auxiliary gas conduits 209a, 209b. Thus, the flash operation involves a total flow rate through the discharge box of 30 L / min, consisting of a flow rate of 15 L / min for gas stream 212 and a total flow rate of 15 L / min for auxiliary gas stream 214. The pressure or velocity of the auxiliary gas stream 214 also depends on the diameter of the auxiliary gas conduits 209a, 209b. For the aforementioned gas flow rates, a suitable inner diameter of the auxiliary gas conduits 209a, 209b may be 0.5-5 mm, which achieves a gas pressure or velocity into the discharge box sufficient for flashing.

[0042] The high velocity cross-flow configuration of the auxiliary gas stream allows for the breakdown of laminar flow in the areas surrounding the electrode 204 and insulator 203, creating turbulence in the gas flow. It is believed that such turbulence creates unsteady eddies that interact with each other, thereby increasing frictional effects and drag due to pressure fluctuations. This has been found to result in better exhaust dust removal from the discharge box, reduced dust buildup, and improved overall maintenance conditions.

[0043] After completion of the flush, the auxiliary flow tubes 209a, 209b are closed again by closing their valves. In some embodiments, the flush operation may be performed at the end of each spark / arc sequence, while in other embodiments, the flush operation may be performed less frequently, for example, after a certain number of spark / arc sequences. A typical flush operation may last from a few tenths of a second to a few seconds. The flush period may be, for example, 1 to 5 seconds, such as about 2 or about 3 seconds. However, in some embodiments, the flush period may be shorter or longer than this range. The auxiliary gas flow, and the first gas flow, if applicable, may be continuous during the period, or more preferably, may include a series of short gas pulses to assist in dust removal. For example, each short gas burst may last less than 1 second, such as a few tenths of a second, or less than a tenth of a second. This flash period may last, for example, 10-25 seconds, in contrast to the duration of a typical spark operation or analysis phase, which typically consists of 2-3 stages, each stage including 4-8 seconds of sparking (so that the total spark operation is, for example, 10-25 seconds).

[0044] A flush operation to remove dust from the discharge box by an auxiliary gas flow may be performed after each spark operation and before each spark operation. Thus, there may be two flush periods during each spark operation or analysis period. This sequence is shown diagrammatically in FIG. 3, which shows the gas flow rate into the discharge box as a function of time for a spark operation with a pre-spark flush operation and a post-spark flush operation. The upper trace (A) shows the gas flow rate of the first gas flow 212 over time. The first gas flow 212 flows through a first period t, which is the pre-analysis flush period. pre A steady flow (3 L / min in this embodiment) is maintained until the pre-analysis flush period t pre During the pre-analysis flush period t, the flow rate of the first gas flow 212 is increased in a series of gas bursts, or pulses (for simplicity, three bursts of 15 L / min are shown). As shown by the lower trace (B), the auxiliary gas flow is increased during the pre-analysis flush period t preThe analysis period t is then turned off until the auxiliary gas conduits are opened to release the auxiliary gas streams 207a, 207b as a series of gas bursts (in this embodiment at the same flow rate as the bursts in the primary gas stream, i.e. 15 L / min) that coincide in time with the gas bursts in the primary gas stream 212. The gas bursts may be caused by the rapid opening and closing of valves on the respective gas conduits. analysis When t reaches t, the auxiliary gas flows 207a, 207b are switched off again and the first gas flow 212 is reduced to a steady flow of 3 L / min. Under this low, steady laminar first gas flow, t analysis During this period, a spark occurs in the discharge chamber, and the light emission is analyzed. At the end of the spark, the period t post A post-analysis flush operation is performed during the post-analysis flush. Similar to the pre-analysis flush, the flow rate of the first gas stream 212 during the post-analysis flush is increased from 3 L / min to 15 L / min in a series of gas bursts, and the auxiliary gas conduit is again opened to release the auxiliary gas streams 207a, 207b as a series of 15 L / min gas bursts. During the post-analysis flush period t post Later the auxiliary gas flows 207a, 207b are switched off again and the first gas flow 212 is reduced to a steady flow of 3 L / min. This cycle is repeated for each analysis that is performed.

[0045] The disclosed embodiments can advantageously allow a controlled, e.g. laminar, gas flow through the discharge chamber during the spark / arc sequence by providing gas flow through the central gas conduit 202 while the auxiliary gas conduits 209a, 209b are valved closed. This allows the analytical conditions in the discharge chamber to be stable and optimal during the spark / arc sequence, which is paramount for reproducible and accurate analytical results. When dust flushing is required, the controlled, e.g. laminar, gas flow can be interrupted by providing auxiliary gas flow from the auxiliary gas conduits 209a, 209b by opening the valve, which results in a high velocity cross flow that creates turbulence that aids in dust removal.

[0046] A further embodiment is shown in Fig. 4. The luminescence stand 301 has many of the same components as the luminescence stand 201, including the discharge box 310, the electrode 304, the insulator 303, the first gas conduit 302 carrying the first gas flow 312, the second gas conduit 308, and the exhaust tube 305. The luminescence stand 301 is completely similar to the luminescence stand 201, but differs from the luminescence stand 201 mainly in that the stand 301 comprises a single auxiliary gas flow tube 309. The auxiliary gas flow tube 309 is positioned transversely to the side of the first gas conduit 302. A valve (not shown) is provided upstream of the gas flow tube 309 to open and close the gas flow tube to the auxiliary gas flow 314. When open, the auxiliary gas flow 307 is directed into the discharge box. The advantage of the embodiment of Fig. 4 is that it creates turbulence in both the x and y dimensions in the area surrounding the insulator 303 and the electrode 304. This allows the exhaust dust to be more efficiently lifted and removed in the gas flow, thereby improving dust removal and maintenance in general. The embodiment shown in Fig. 2, when provided with two lateral auxiliary flow tubes, produces strong turbulences, especially in the x dimension, which are almost cancelled out in the y dimension due to the geometric symmetry. Nevertheless, the advantage of the embodiment of Fig. 2 is that it provides an auxiliary flow aimed at lifting the dust and actively pushing them in the x dimension towards the outlet conduit 308 for removal, thus avoiding any recirculation in the discharge box 310 and ensuring that these dust are collected through the exhaust pipe 305.

[0047] Another embodiment is shown in FIG. 5. The luminescence stand 501 has many of the same components as the luminescence stand 201, including a first gas conduit 502 carrying a first gas flow 512 and a second gas conduit 508 for collecting and removing the gas flow. The luminescence stand 501 is similar to the luminescence stand 201, but differs from the luminescence stand 201 mainly in that the stand 501 includes four auxiliary gas flow tubes 503a, 503b, 503c, and 503d. The four auxiliary gas flow tubes are oriented in an X-configuration, i.e., a cross-configuration, to direct their auxiliary gas flows toward the center of the discharge box, i.e., near the spark electrode. Thus, the four auxiliary gas flows cross or intersect with the central first gas flow 512 in the discharge box, creating turbulence to remove dust from the discharge box.

[0048] An embodiment of an OES spectrometer with an emission stand of the present disclosure is shown diagrammatically in FIG. 6. The emission stand 401 includes a discharge box 409 housing a spark electrode 422 facing a sample 420 to be analyzed. A controller 430, including a computer or other processor and associated control electronics for controlling high voltage discharge, is connected to the emission stand to initiate a high voltage spark / arc discharge between the electrode and the sample. During spark operation and analysis of the sample, light 440 emitted from the discharge box is collected and detected by an optical analyzer 420, such as a spectrometer. Detection signals from the optical analyzer 420 are sent to the controller 430 for storage and processing by a computer or other processor to generate optical emission data (e.g., spectrum or light intensity at specific wavelengths) to determine information regarding the composition of the sample. The controller 430 further controls an argon gas source 410 that supplies gas into the discharge box via a first central gas conduit 402. The gas flows through the discharge box and is carried away by a second gas conduit to an exhaust line 408. An argon flow is provided by the central gas conduit 402 through the discharge box during the spark operation. After the spark operation, the controller 430 initiates a flush operation and opens the valves 406a and 406b on the auxiliary gas lines 403a and 403b, respectively, that were previously closed during the spark operation. The auxiliary gas lines 403a and 403b provide a high velocity (preferably pulsed) cross flow of argon gas that crosses the central flow from the conduit 402 within the discharge box, lifting dust within the discharge box and assisting in its removal to the exhaust line 408. After flushing with argon from the auxiliary gas lines 403a and 403b, the controller closes the valves 406a and 406b again in preparation for the next spark operation and sample analysis. A further flush operation can be performed immediately before the next spark operation and sample analysis.

[0049] It will be appreciated that variations to the above-described embodiments of the present disclosure can be made while still falling within the scope of the present disclosure.

[0050] The use of any and all examples or exemplary language provided herein (such as "for instance," "such as," "for example," and similar language) is intended merely to better illustrate the invention and does not pose a limitation on the scope of the disclosure unless specifically claimed. No language in the specification should be construed as indicating any element not claimed as essential to the practice of the disclosure.

[0051] As used herein, including in the claims, the singular forms of the terms herein are to be construed as including the plural forms, and vice versa, unless the context indicates otherwise. For example, singular referents herein, including in the claims, such as "a" or "an" mean "one or more," unless the context indicates otherwise.

[0052] Throughout this specification and the claims, the terms "comprise," "including," "having," and "contain," as well as variations of these terms, such as "comprising," "comprises," and others, mean "including, but not limited to," and are not intended to (and therefore do not) exclude other elements.

Claims

1. An emission stand for an optical emission spectrometer, comprising: A discharge box; and at least one auxiliary gas conduit for supplying an auxiliary gas flow into the discharge box, the at least one auxiliary gas conduit being configured to supply the auxiliary gas flow into the discharge box not during spark operation but for a period of time after spark operation.

2. 3. A light stand according to claim 1 or 2, wherein said at least one auxiliary gas conduit is a single auxiliary gas conduit.

3. 3. A luminous stand according to claim 1 or 2, wherein said at least one auxiliary gas conduit is two or more auxiliary gas conduits.

4. A luminous stand according to any one of claims 1 to 3, wherein said at least one auxiliary gas conduit is switchable between an open position and a closed position.

5. 5. The luminous stand according to claim 4, wherein the at least one auxiliary gas conduit comprises at least one valve for opening and closing the at least one auxiliary gas conduit, thereby allowing or preventing the auxiliary gas flow from entering the discharge box.

6. a first gas conduit for supplying a first gas flow into the discharge chamber at least during spark operation; The luminous stand according to any one of claims 1 to 5, further comprising a second gas conduit for conveying gas from the discharge box.

7. 7. The luminous stand according to claim 6, wherein the first gas conduit is for supplying the first gas flow into the discharge box during and after sparking operation, so that the auxiliary gas flow merges with the first gas flow after sparking operation.

8. 8. The light stand of claim 7, wherein the at least one auxiliary gas conduit is configured to provide the auxiliary gas flow in a cross-flow configuration with the first gas flow.

9. The light emitting stand according to claim 8, wherein the cross-flow configuration enables the generation of turbulent gas flow within the discharge box.

10. 10. The light stand according to claim 8 or 9, wherein the first gas flow is a laminar flow during sparking action, and the laminar flow is broken by the auxiliary gas flow after sparking action.

11. A light stand according to any one of claims 6 to 10, wherein the flow rate of the auxiliary gas flow is greater than the flow rate of the first gas flow during spark operation.

12. The luminous stand according to any one of claims 6 to 11, wherein the at least one auxiliary gas conduit is two auxiliary gas conduits, the two auxiliary gas conduits being symmetrically positioned on either side of the first gas conduit.

13. A luminous stand according to any one of the preceding claims, wherein the auxiliary gas flow comprises a series of gas pulses.

14. An optical emission spectrometer comprising an optical emission stand according to any one of claims 1 to 13.

15. 1. A method of optical emission spectroscopy comprising the steps of:

11. The method of claim 10, further comprising: supplying an auxiliary gas flow into a discharge box via at least one auxiliary gas conduit configured to supply the auxiliary gas flow into the discharge box for a period of time after spark operation but not during spark operation.

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