Element for measuring oxygen content of molten metal

Abstract

To provide an oxygen detection element for measuring oxygen content of a molten metal, which offers fast response and high coating stability, and to provide an immersion sensor.SOLUTION: An oxygen detection element 4 is provided, comprising a coated pin 1 having an electrically conductive core eccentrically arranged in a coating. The coating comprises at least a two-layered coating section with an inner coating layer comprising a reference material coating 6 and an outer coating layer comprising an electrolyte material coating 7. Furthermore, an immersion sensor may be formed, consisting of the oxygen detection element and components such as a counter electrode and temperature measurement means.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an oxygen sensing element comprising a coated pin, the coated pin comprising a conductive core arranged eccentrically in the coating. The present invention further relates to an immersion sensor comprising the oxygen sensing element, and a method for measuring the oxygen content of a metal melt using such an oxygen sensing element.

[0002] During metallurgical processing, the oxygen activity of a metal melt is one of the parameters that needs to be monitored. Determining oxygen activity typically involves using an electrochemical sensor that includes a solid electrolyte material, a reference material, and an electrode. The electromotive force (EMF) generated by the difference between a constant oxygen partial pressure provided by the reference material and the oxygen partial pressure in the molten metal is then monitored and related to the oxygen activity or concentration in the liquid metal. Many electrochemical sensors for testing such melts have drawbacks, such as slow response time, high failure rate, poor reproducibility, and low sensitivity.

[0003] One type of oxygen sensor is a needle sensor, which includes a conductive wire that serves as an electrode with at least a solid electrolyte coating and a reference material coating. These sensors suffer from slow response times or poor stability for application in the harsh environment of molten metal. Electrochemical equilibrium between the molten metal and the oxygen sensor is necessary for accurate measurement of EMF values. However, electrochemical equilibrium can only occur if thermal equilibrium exists between the immersion probe and its surroundings.

[0004] To obtain highly accurate measurements, the temperature of the metal bath needs to be determined in parallel with the oxygen activity. The response time of the oxygen sensing device should ideally be faster than that of the temperature sensor. Thermocouples with response times of 3 to 6 seconds are often used for this purpose.

[0005] In commonly used needle cells, a conductive wire is concentrically surrounded by a functional coating layer, as disclosed, for example, in DE 2757985 A1. While reducing the coating thickness results in faster response times, it can also compromise the stability of the coating.

[0006] Japanese Patent Application Laid-Open No. 61-79156 (A) discloses a needle-type oxygen concentration sensing element having a metal wire, the element being provided with a conical coating to shorten the response time of the device. U.S. Patent No. 5,332,449 (A) also discloses a needle sensor. The sensing device includes a conductive wire having a uniform thickness, and the wire is coated with an electrolyte material, a reference material, and a refractory material. To improve the thermal response of the device, it is proposed to reduce the diameter of the conductive pin in areas without the functional coating. This configuration was found to reduce the mechanical stability of the device.

[0007] The present invention overcomes at least some of the problems identified in the prior art. In particular, it was an object of the present invention to provide an oxygen sensing element having a fast response time and high coating stability. A further aspect was to provide an oxygen sensing element that can be produced reliably, quickly, and efficiently. An additional object was to provide an oxygen sensing element of low-cost design that can be efficiently manufactured.

[0008] In a different aspect, it was an object to provide an immersion sensor having an oxygen sensing element of the present invention.

[0009] In a further aspect, it was an object to provide a method for measuring the oxygen content of a metal melt using the oxygen sensing element of the present invention.

[0010] The present invention provides an oxygen sensing element including a coated pin. The coated pin includes a conductive core and a coating, the coating including at least two coated sections. The two coated sections include: (i) an inner coating layer covering and in direct contact with at least a portion of the conductive core, the inner coating layer comprising a reference material; (ii) an outer coating layer covering and in direct contact with at least a portion of the inner coating, the outer coating layer comprising an electrolyte material; Includes.

[0011] A conductive core is eccentrically disposed in the sheath.

[0012] The eccentric placement of the conductive core in the coating leads to variations in the thickness of the coating around the core. While the minimum thickness appears to determine the response time of the oxygen sensing element, the maximum thickness may contribute to the stability of the coating. Thus, variations in coating thickness result in oxygen sensing elements with reduced response times that still provide the mechanical strength required for the intended application. Furthermore, these sensor elements can be manufactured in a more time- and cost-efficient manner, providing additional design advantages.

[0013] For certain applications, oxygen sensing elements are mounted on an immersion apparatus so that they contact the molten metal, typically comprising at least a carrier tube. These carrier tubes must withstand the immersion conditions before disintegrating, at least long enough for measurements to be performed, which is often achieved by providing a certain amount of material. A faster response time of the oxygen sensing element can reduce material usage, resulting in a reduction in the cost of the immersion apparatus. For example, every 1 second reduction in response time can reduce the thickness of a cardboard carrier tube by approximately 1 mm in diameter.

[0014] The object of the present invention is an oxygen sensing element comprising a coated pin having a conductive core.

[0015] Examples of suitable materials for the conductive core are molybdenum (Mo) and tungsten (W), especially due to their thermal properties. Preferably, the material of the conductive core comprises Mo, and even more preferably, the conductive core consists of Mo except for unavoidable impurities. The cross-sectional area of ​​the conductive core may have any shape, preferably circular, oval, or elliptical. For short response times, the maximum cross-sectional area of ​​the conductive core is less than 0.1 mm 2 ~3mm 2 , especially, 0.3 mm 2 ~1.5mm 2 Advantageously, the range is

[0016] The conductive core extends longitudinally from the tip to the attachment end. The axis extending from the tip to the attachment end is referred to throughout this application as the longitudinal axis of the conductive core and / or the coated pin. The length of the conductive core is preferably in the range of 40 mm to 100 mm. The length of the conductive core should be understood as the length from the tip to the attachment end. The shape of the conductive core is not further limited and may be, for example, wire- or needle-shaped.

[0017] The tip may have different shapes, for example it may be dome-shaped or flat.

[0018] In a preferred embodiment, the conductive core includes a tapered section, which is a section including a cross section that tapers longitudinally toward the tip. In other words, the conductive core may include a tip and an attachment end that are tapered ends, and the cross-sectional area of ​​the conductive core is smaller at the tapered end. Unless otherwise defined, the cross section or cross-sectional area is a cross section or cross-sectional area perpendicular to the longitudinal axis along the length of the conductive core.

[0019] The tapered section can extend the entire length of the conductive core, or it can extend only a portion of its length, in which case the conductive core includes at least two sections: a tapered section and a section having a constant diameter and cross-sectional area.

[0020] The tapered section has a length L TS Preferably, the tapered section extends over at least 10% of the length of the conductive core, more preferably at least 20%, and even more preferably at least 30%. The length of the tapered section is typically in the range of 4 mm to 30 mm, preferably in the range of 8 mm to 20 mm.

[0021] The tapered section can have the same or different cross-sectional shape as any additional sections present; for example, the tapered section can have a rectangular cross-section, while the other sections can have a circular, oval, or elliptical shape. The shape of the tapered section can vary, particularly depending on the method of production of the conductive core. The tapered section can have a radially symmetrical profile relative to the central longitudinal axis of the conductive core, and in such cases, can have, for example, a conical or frustoconical shape. The tapered section can also have a profile that is not radially symmetrical relative to the central longitudinal axis, and in such cases, can have, for example, a conical, frustoconical, prismatic, or pyramidal shape.

[0022] Preferably, the tapered section has a conical shape, in other words has a circular or oval cross section and terminates in a tapered end that is circular or oval in shape.

[0023] The angle of tapering of a tapered section can be described by a taper angle, which should be understood as the angle between two tangent lines adjacent to the surface of the tapered section in the plane of the largest cross-sectional area of ​​the tapered section along the longitudinal axis. It has been shown to be advantageous if the taper angle is less than 40°, even more preferably less than 30°, and most preferably less than 20°. The taper angle may be in the range of 1° to 40°, preferably in the range of 3° to 30°, and even more preferably in the range of 5° to 20°.

[0024] In a preferred embodiment, the conductive core is needle-shaped, that is to say, it includes a region of circular cross section along its entire length, a tapered section having a conical shape, and a tapered end portion having a circular cross section.

[0025] Preferably, the cross-sectional area of ​​the tip is less than 40%, more preferably less than 30%, and even more preferably less than 20% of the maximum cross-sectional area of ​​the conductive core. For example, the cross-sectional area of ​​the pin end may be in the range of 0.5% to 40%, more preferably in the range of 2% to 30%, and most preferably in the range of 5% to 20% of the maximum cross-sectional area. For short response times, the cross-sectional area of ​​the pin end may be less than 0.01 mm 2 ~1mm 2 , preferably 0.02 mm 2 ~0.5mm 2 , more preferably 0.05 mm 2 ~0.2mm 2 It has been found to be advantageous that

[0026] A coated pin includes a coating, which should be understood as any layer of material that covers a conductive core.

[0027] The covering may have any cross-sectional shape perpendicular to the longitudinal axis of the conductive core, preferably the cross-section has a circular, oval or elliptical shape, and even more preferably the cross-section has an elliptical shape.

[0028] The cross-sectional area of ​​the cladding may be defined by two intersecting axes that meet at an intersection point (IP), with the major axis coinciding with the maximum diameter of the cross-sectional area and a length D corresponding to the maximum diameter of the cross-sectional area. MJ The minor axis is perpendicular to the major axis and has a length D MI The minor axis is located along the largest diameter perpendicular to the major axis. In the case of a circular cross-sectional area, the major and minor axes are of equal length. The intersection point IP can be considered the center of the cross-sectional area.

[0029] The conductive core is eccentrically disposed in the sheath, i.e., the center of the conductive core does not coincide with the intersection point IP of the cross-sectional area of ​​the sheath. Surprisingly, it has been found that the eccentric placement of the center of the conductive core in the sheath has a positive effect on the response time of the oxygen sensing element and the stability of the sheath.

[0030] In the eccentric configuration, the center of the conductive core is offset relative to the intersection point IP along the major axis of the cross section of the sheath, so that the sheath has two thicknesses along the major axis: a smaller thickness T S and a larger thickness T, which corresponds to the maximum thickness of the coating structure in the cross-sectional area. MAX It should be understood that the thickness of the coating and the maximum thickness of the coating may vary along the length of the coated pin.

[0031] In a preferred embodiment, the maximum thickness T MAX is the small thickness T S is at least 5% greater than the maximum thickness T MAX is the small thickness T S It is 5% to 20% larger, and more preferably 8% to 15% larger.

[0032] The maximum cross-sectional area of ​​the coated pin is 0.5 mm 2 ~7mm 2 , especially, 1.0 mm 2 ~6mm 2 The cross-sectional area of ​​the coated pin should be understood as the total cross-sectional area of ​​the conductive core and the surrounding coating layer.

[0033] The sheathing of the sheathing pin comprises at least two sheathing sections, where a section of sheathing is to be understood as a sheathing part comprising the same layer.

[0034] The inner coating layer covers and is in direct contact with at least a portion of the conductive core, and the outer coating layer covers and is in direct contact with at least a portion of the inner coating. In other words, no coating layer is disposed between the inner coating layer and the outer coating layer. An additional coating layer may be present on the outer coating.

[0035] The inner coating layer comprises a reference material. Preferably, the reference material comprises a metal-metal oxide mixture, such as a mixture of chromium and chromium dioxide (Cr-Cr2O3) or molybdenum and molybdenum oxide (Mo-MoO2). The inner coating layer preferably has a thickness of at least 0.01 mm, more preferably at least 0.03 mm, and even more preferably at least 0.05 mm. In this context, the term "thickness" or "coating thickness" refers to the minimum thickness of the coating layer perpendicular to the longitudinal axis of the conductive core. For example, the inner coating layer may have a thickness of 0.01 mm to 0.3 mm, more preferably 0.03 mm to 0.2 mm. The thickness of the reference material coating layer may be uniform along the length of the coated pin, or the thickness may vary.

[0036] The outer coating layer includes an electrolyte material. The electrolyte material is preferably a solid material having oxygen ion conducting activity. Preferably, the electrolyte material includes zirconium oxide (zirconia, ZrO2) or stabilized zirconium oxide (stabilized zirconia). As known to those skilled in the art, stabilized zirconium oxide includes at least one oxide, such as magnesia (MgO), calcium oxide (CaO), yttria (YO3), ceria (CeO2), or scandia (Sc2O3), dissolved in zirconia as a stabilizer. The outer coating layer preferably has a thickness of at least 0.05 mm, more preferably at least 0.1 mm, and even more preferably at least 0.15 mm. For example, the outer coating layer may have a thickness of 0.05 mm to 0.5 mm, more preferably 0.1 mm to 0.4 mm. The thickness of the electrolyte material coating layer may be uniform along the length of the coated pin, or the thickness may vary.

[0037] The two-layer covering structure preferably covers the tip portion of the conductive core, including the tip. In other words, the two-layer covering structure covers at least the tip portion of the conductive core. Therefore, the two-layer covering structure is also called a tip covering structure. The tip portion of the conductive core is characterized by being covered by the tip covering structure. The tip portion of the conductive core and the two-layer covering constitute the measurement section of the covered pin.

[0038] Preferably, the cross-sectional area of ​​the coated pin end of the conductive core is less than 40%, more preferably less than 30%, and even more preferably less than 20% of the maximum cross-sectional area of ​​the coated pin. The coated pin end should be understood as the coated end and tip coating structure. A cross-sectional percentage in this range results in a coated pin with sufficient stability and at the same time a fast response time. For example, the cross-sectional area of ​​the coated pin end may be in the range of 0.5% to 40%, more preferably in the range of 2% to 30%, and most preferably in the range of 5% to 20% of the maximum cross-sectional area of ​​the coated pin. For a short response time, a cross-sectional area of ​​the coated pin end of 0.1 mm 2 ~2.5mm 2 , especially, 0.5 mm 2 ~1.5mm 2 It has been found to be advantageous that

[0039] The tip part is length L TP Preferably, the tip portion extends over no more than 10% of the length of the conductive core, more preferably no more than 5%, and even more preferably no more than 1%. The length of the tip portion may be in the range of 0.1 mm to 10 mm, more preferably in the range of 1 mm to 8 mm.

[0040] In the case of a conductive core having a tapered section, the length of the tapered section of the conductive core is the same as or longer than the tip portion of the conductive core (L TS ≧L TP Since the measurement zone is found in the tapered section of the coated pin, this configuration in such a case allows the measurement zone to be heated quickly, resulting in a particularly short response time of the oxygen sensing element.

[0041] Length of tip L TP is preferably the length L of the tapered section of the conductive core TS of the total mass of the cellulose acetate solution, is at least 20%, more preferably at least 30%, and even more preferably at least 50%.

[0042] The sheathing of the sheathed pin may include additional sheathed sections, in other words, the conductive core may include one or more portions that are covered with additional sheath structures and / or uncovered portions.

[0043] For example, the coating may include a three-layer main coating structure (CS-M) that covers the main portion of the conductive core. Such a main portion of the conductive core should be understood to be characterized as being covered by the main coating structure. In such a case, the main portion is preferably located behind the tip portion in the direction from the tip end of the conductive core toward the attachment end.

[0044] The main part is of length L MP Preferably, the main portion extends over more than 30%, more preferably over 40%, and even more preferably over 50% of the length of the conductive core. The length of the main portion is typically in the range of 5 mm to 50 mm, preferably in the range of 10 mm to 40 mm.

[0045] The primary coating structure may have any cross-sectional shape perpendicular to the longitudinal axis of the conductive core, preferably the cross-section has a circular, oval or elliptical shape, and even more preferably the cross-section has an elliptical shape. In other words, the primary coating structure may have a constant thickness perpendicular to the longitudinal axis of the coated pin, or the thickness may vary.

[0046] In preferred embodiments, the primary coating structure has a minimum thickness of at least 0.07 mm, more preferably at least 0.12 mm. For example, the primary coating structure may have a thickness of 0.07 mm to 0.8 mm, more preferably 0.12 mm to 0.6 mm. The thickness of the primary coating structure may be uniform along the length of the coated pin, or the thickness may vary.

[0047] In a preferred embodiment, the primary coating structure has a greater minimum thickness than the tip coating structure. Preferably, the primary coating structure has a greater minimum diameter than the tip coating structure.

[0048] The primary coating structure (CS-M) preferably includes an inner coating layer, an intermediate coating layer, and an outer coating layer. The inner coating layer covers and is in direct contact with at least a portion of the main portion of the conductive core, the intermediate coating layer covers and is in direct contact with the inner coating layer, and the outer coating layer covers and is in direct contact with at least a portion of the intermediate coating layer. Additional coating layers may be present on the outer coating layer.

[0049] The inner coating layer of the primary coating structure preferably comprises a reference material, which may be the same as the reference material of the tip coating structure.

[0050] The inner coating layer of the primary coating structure preferably has a thickness of at least 0.01 mm, more preferably at least 0.03 mm, and even more preferably at least 0.05 mm. For example, the inner coating may have a thickness of 0.01 mm to 0.3 mm, more preferably 0.03 mm to 0.2 mm.

[0051] Preferably, the inner coating layer of the main coating structure and the inner coating layer of the tip coating structure are sections of the inner coating layer, in other words, they constitute a single coating layer over at least the main and tip portions of the conductive core. The thickness of the inner coating layer may be uniform along the length of the coated pin, or may vary in thickness.

[0052] The intermediate coating layer of the primary coating structure preferably comprises a refractory material. Preferably, the refractory material comprises an oxide material, for example, aluminum oxide such as Al2O3, magnesium oxide, titanium oxide, or a mixture thereof. Preferably, the refractory material comprises aluminum oxide. The intermediate coating layer preferably has a thickness of at least 0.01 mm, more preferably at least 0.03 mm, and even more preferably at least 0.05 mm. For example, the intermediate coating may have a thickness of 0.01 mm to 0.3 mm, more preferably 0.03 mm to 0.2 mm.

[0053] The outer coating layer of the primary coating structure preferably comprises an electrolyte material, which may be the same as the electrolyte material of the tip coating structure.

[0054] The outer coating layer of the primary coating structure preferably has a thickness of at least 0.05 mm, more preferably at least 0.1 mm, and even more preferably at least 0.15 mm. For example, the outer coating may have a thickness of 0.05 mm to 0.5 mm, more preferably 0.1 mm to 0.4 mm.

[0055] Preferably, the outer coating layer of the main coating structure and the outer coating layer of the tip coating structure are sections of an outer coating layer, in other words, they constitute a single coating layer over at least the main and tip portions of the conductive core. The thickness of the outer coating layer may be uniform along the length of the conductive pin, or may vary in thickness.

[0056] In a preferred embodiment, the coating may include a third coating structure (CS-3) covering a third portion of the conductive core. It should be understood that such a third portion of the conductive core is characterized by being covered by the third coating structure. In such a case, the third portion is preferably located behind the main portion in the direction from the tip end of the conductive core toward the attachment end.

[0057] Preferably, the third coating structure (CS-3) includes an intermediate coating layer and an outer coating layer. The intermediate coating layer covers and is in direct contact with at least a portion of the third portion of the conductive core, and the outer coating layer covers and is in direct contact with at least a portion of the intermediate coating layer. In other words, there is no coating layer between the intermediate coating and the outer coating. An additional coating layer may be present on the outer coating.

[0058] In a preferred embodiment, the third coating structure has a minimum thickness of at least 0.06 mm, more preferably at least 0.1 mm. For example, the third coating structure may have a thickness of 0.06 mm to 0.6 mm, more preferably 0.1 mm to 0.5 mm. The thickness of the third coating structure may be uniform along the length of the coated pin, or the thickness may vary.

[0059] In a preferred embodiment, the third coating structure has a smaller minimum thickness than the primary coating structure. Preferably, the third coating structure has a smaller minimum diameter than the primary coating structure.

[0060] The third part has a length L 3P Preferably, the third portion extends over 10% or less of the length of the conductive core, more preferably over 5% or less, and even more preferably over 1% or less. The length of the third portion is typically in the range of 0.1 mm to 10 mm, preferably in the range of 1 mm to 8 mm.

[0061] The intermediate coating layer of the third coating structure may comprise a fire-resistant material. The fire-resistant material of the third coating structure may be the same as the fire-resistant material of the main coating structure. The intermediate coating layer of the third coating structure preferably has a thickness of at least 0.01 mm, more preferably at least 0.03 mm, and even more preferably at least 0.05 mm. For example, the intermediate coating may have a thickness of 0.01 mm to 0.3 mm, more preferably 0.03 mm to 0.2 mm.

[0062] Preferably, the intermediate coating layer of the third coating structure and the intermediate coating layer of the main coating structure are sections of an intermediate coating layer, in other words, they constitute a single coating layer over at least the third portion and the main portion of the conductive core. The thickness of the intermediate coating layer may be uniform along the length of the coated pin, or may vary in thickness.

[0063] The outer coating layer of the third coating structure preferably includes an electrolyte material. The electrolyte material of the third coating structure may be the same as the electrolyte material of the tip coating structure and / or the main coating structure. The outer coating layer of the third coating structure preferably has a thickness of at least 0.05 mm, more preferably at least 0.1 mm, and even more preferably at least 0.15 mm. For example, the outer coating may have a thickness of 0.05 mm to 0.5 mm, more preferably 0.1 mm to 0.4 mm.

[0064] Preferably, the outer coating layer of the third coating structure, the outer coating layer of the main coating structure, and the outer coating of the tip coating structure are sections of an outer coating layer, in other words, they constitute a single coating layer over at least the third portion, the main portion, and the tip portion of the conductive core. The thickness of the outer coating layer may be uniform along the length of the coated pin, or may vary in thickness.

[0065] Preferably, the conductive core includes an attachment portion located at the uncoated attachment end. In such a case, the conductive core extends longitudinally from the attachment portion toward the main portion to the tip portion. In such a case, the attachment portion is preferably located behind the coated portion or portions in the direction from the tip toward the attachment end of the conductive core.

[0066] The manufacture of the oxygen sensing element of the present invention is typically carried out in a stepwise manner, during which different coating layers are applied sequentially. The coating of the coating structure can be applied by techniques known to those skilled in the art, for example, by additive manufacturing methods such as chemical vapor deposition (CVD) or physical vapor deposition (PVD), 3D printing, or by thermal spraying processes such as plasma or flame spraying. Thermal spraying processes, in particular, produce uniform and dense coatings. Suitable methods are disclosed, for example, in EP 0 543 081 A1. During such a thermal spraying process, the object to be coated is typically moved horizontally through a spray cone containing the coating material provided by a suitable source, such as a plasma or flame source, for example, using a thermal spray gun. In this case, the object is a conductive core. During the passage through the spray cone, the object is typically rotated to obtain a uniform peripheral coating. To obtain a coating with a centrally located conductive core, this rotational movement can be centralized relative to the coating source. This rotational motion may be off-center relative to the source and horizontal motion to achieve off-center coating. Such an off-center configuration allows more conductive cores to be coated simultaneously, leading to a more time- and cost-efficient manufacturing process.

[0067] For example, manufacturing (i) providing a conductive core; (ii) at least partially coating the conductive core with a reference material; (iii) at least partially coating the conductive core with an electrolyte material. may include:

[0068] For embodiments in which the coating includes a tip coating section and a main coating section, for example, manufacturing may include: (i) providing a conductive core; (ii) coating the pin and main portions of the conductive core with a reference material; (iii) masking the pin portion of the conductive core; (iv) coating at least a major portion of the conductive core with a fire-resistant material; (v) unmasking the pin portion of the conductive core; (vi) coating at least the pin portion and the main portion with an electrolyte material. may include:

[0069] In a second aspect, the invention relates to an immersion sensor comprising an oxygen sensing element according to the invention.

[0070] The immersion sensor may comprise further parts such as a counter electrode, additional measuring means such as means for temperature measurement, means for mounting the oxygen sensing element, means for signal transmission, means for protecting the oxygen sensing element and / or means for immersion, etc. Further components of immersion sensors are known to those skilled in the art and are disclosed, for example, in U.S. Patent Publication No. 4,964,736(A).

[0071] The means for measuring the temperature may be, for example, a thermocouple, as known to those skilled in the art. The means for measuring the temperature is not essential for a functional immersion sensor, and if the temperature is required, the temperature can also be derived, for example, by external means.

[0072] The means for mounting the oxygen sensing element may be, for example, a fire-resistant mounting material in which the oxygen sensing element may be partially embedded, preferably with only the uncoated mounting portion of the conductive core being embedded in such a fire-resistant material.

[0073] The means for immersion of the immersion sensor may be, for example, a carrier tube, preferably made of cardboard. The means for immersion is not essential for a functional immersion sensor, for example, if the immersion sensor is a droplet sensor. Droplet sensors and their components are known to those skilled in the art and are disclosed, for example, in EP 0 997 716 A1.

[0074] In a third aspect, the present invention relates to a method for measuring the oxygen content of a metal melt using an oxygen sensing element according to the invention. As known to those skilled in the art, the method comprises immersion of the oxygen sensing element in the respective metal melt.

[0075] For example, the method comprises: (i) providing an oxygen sensing element; (ii) immersing an oxygen sensing element in the metal melt; (iii) measuring the oxygen content in the metal melt may include:

[0076] The step of measuring the oxygen content in the metal melt may include measuring the oxygen activity of the metal melt and correlating this measurement with the oxygen content.

[0077] In practice, the metal melt is contacted with an oxygen sensing element according to the invention and the electrochemical potential of the element is measured, preferably over time. The electrochemical activity is determined by the potential presented to an analytical unit via lead means from the cell. By relating the electrochemical potential thus determined to the electrochemical potential generated against a set of standards, the content of oxygen in the metal melt can be determined. [Brief explanation of the drawings]

[0078] The following schematic drawings illustrate aspects of the present invention with respect to several exemplary illustrations to enhance understanding of the invention. However, it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals refer to corresponding like parts. [Figure 1] 1 shows different geometries of the tip of the conductive core. [Figure 2] 1 shows a schematic cross section of a conductive core suitable for the present invention. [Figure 3] 1 shows a schematic longitudinal cross-sectional view of an oxygen sensing element according to the present invention; [Figure 4]1 shows a schematic transverse cross-sectional view of an oxygen sensing element. [Figure 5] 1 shows a schematic transverse cross section of the measurement zone of an oxygen sensing element.

[0079] FIG. 1 shows cross-sections of different geometries of the tip 2 of a conductive core 1. The tip 2 in FIGS. 1A-1C is essentially flat and dome-shaped, although to varying degrees. The tip 2 shown in FIG. 1A has sharp edges, while the edges in FIGS. 1B and 1C are rounded, resulting in a circular (i.e., dome-shaped) tip. The tip 2 in FIG. 1D is needle-shaped and terminates in a sharp point. The tip 2 shown in FIG. 1E has a flattened needle shape, also referred to as a frustoconical shape. The tip 2 shown in FIG. 1F comprises a dome-shaped, needle-like tip.

[0080] FIG. 2 shows a schematic longitudinal cross section of a conductive core 1 suitable for the present invention. The core 1 in FIG. 2A is a wire with no tapered end. The pin 1 in FIGS. 2B-2D has a tapered section 3, the length of this section (L TS ) and the angle of tapering at its ends. The location where the angle of tapering, denoted by taper angle α, is found is also shown. The taper angle is determined by the angle between two tangent lines adjacent to the surface of the tapered section in the plane of the largest cross section of the tapered section along the longitudinal axis of the pin. These tangent lines are indicated by dashed lines. The cores 1 in Figures 2B-2C have centrosymmetrical contours. Figure 2B shows a needle-shaped conductive pin 1 with a tapered section 3 that extends only part of the length of the pin. The tapered section 3 of the conductive core 1 shown in Figure 2C extends the entire length of the pin 1. The conductive core 1 in Figure 2D also has a tapered section 3 along its entire length, but the contour is not centrosymmetrical.

[0081] Figure 3 shows a schematic longitudinal cross-section of an oxygen sensing element 4 according to the present invention. The conductive wire 1 in Figure 3A has two layers of coating 5, including a reference material coating 6 and an electrolyte material coating 7. The end 9 of the conductive pin opposite the tip 2 is uncoated. Typically, this end is attached to a suitable material, for example, a refractory material when the oxygen sensing element is attached to a sensor assembly, and is therefore also referred to as the attachment end.

[0082] The coating layer over the conductive pin can be applied using a thermal spray process, such as plasma spraying or flame spraying, which produces a very uniform and dense coating. First, a base material such as chromium-chromium dioxide is applied to the conductive substrate, followed by a coating step with an electrolyte material such as stabilized zirconium oxide.

[0083] The thicknesses of the different layers can be uniform along the length of the coated pin, but they can also vary, especially when the described thermal spraying process is applied to manufacture the sensing element. These different layers can have the same thickness, or they can vary in shape and thickness depending on the needs and applications of the oxygen sensing element.

[0084] The conductive core in FIG. 3B is divided into two parts: a first part with a length L TP a tip coating structure 10 (CS-T) covering the tip portion of the pin 1 having a length L MP The tip coating structure 10 and tip portion 2 provide the measurement zone for the sensor 4 in use. The tip coating structure 10 includes a three-layer structure. In addition to the two layers (6, 7) on the tip coating structure, it includes a reference material layer 8 extending between the reference material coating 6 and the electrolyte material coating 7.

[0085] In the embodiment described, the electrolyte material layer 7 and the reference material layer 6 extend over the entire length of the covering structure, while the refractory material layer 8 has a main length L MP exists only throughout the

[0086] In the views of Figures 3A and 3B, the conductive pin is eccentrically positioned in the covering structure, whereas for clarity, the views of Figures 3C and 3D show the pin centrally positioned.

[0087] The needle-shaped conductive pin 1 also has a coating structure having two sections, namely, a tip coating structure 10 (CS-T) that covers the tip portion, and a main coating structure 11 (CS-M) that covers the main portion of the pin 1, as shown in FIG. 3C.

[0088] In comparison with the embodiment of FIG. 3C, the covering of the embodiment shown in FIG. 3D has a length L 3P The third coating structure 12 includes an additional third coating structure 12 on a third portion of the needle-shaped conductive pin 1 having a thickness of 1. The third coating structure 12 includes a two-layer structure of a refractory material layer 8 and an electrolyte material layer 7. The two layers have essentially the same thickness.

[0089] FIG. 4 shows a schematic transverse cross-section of the oxygen sensing element 4, i.e., a view in a plane perpendicular to the plane shown in FIGS. 1 to 3. The overall structure of the coating 5 is such that the coating may comprise multiple layers, although the inner layer structure is not shown. The major axis D of the cross-sectional area of ​​the coating 5 is MJ and its minor axis D MI , as well as the intersection point IP of these axes, and the maximum thickness T of the coating structure along the long axis. MAX and small thickness T S is displayed.

[0090] The coating 5 in FIG. 4A has a circular shape. Therefore, the length D of the major axis of the cross section MJ and the length of the minor axis D MI The pin 1 is eccentrically positioned in the sheath, with the center of the pin 1 offset relative to the intersection point IP. The sheath of FIG. 4B has an elliptical shape and a major axis D MJ Length and minor axis D MI The lengths are different.

[0091] Figure 5 shows a schematic transverse cross-section of the measurement zone of the oxygen sensing element in the region of the tip coating structure, with a circular coating in Figure 5A and an elliptical coating in Figure 5B. The coating has a two-layer structure, i.e., a reference material coating 6 directly on the pin 1 and an electrolyte material coating 7 on top of the reference material coating. [Explanation of symbols]

[0092] 1 conductive core 2 Tip of conductive core 3 Tapered section of conductive core 4. Oxygen detection element 5. Covering 6 Reference Material Coating 7. Electrolyte material coating 8. Fire-resistant material covering 9 Mounting end of coated pin 10 Tip coating structure (CS-T) 11 Main coating structure (CS-M) 12 Third Covering Structure (CS-3) L TS Tapered Section Length L TP Length of tip L MP Length of main part L 3P Length of the third section IP intersection L TS Tapered Section Length L TP Length of tip L MP Length of main part L 3P Length of the third section D MJ Long axis of the coating D MI Minor axis of coating T MAX Maximum coating thickness T S Small coating thickness D MJ -T Long axis of tip coating structure D MI -T Tip coated structure minor axis T MAX-T Maximum thickness of tip coating structure T S -T Small thickness of tip coating structure α Taper angle

Claims

1. An oxygen sensing element comprising a coated pin, The coated pin includes a conductive core and a coating, The coating is (i) an inner coating covering and in direct contact with at least a portion of the conductive core, the inner coating comprising a reference material; (ii) an outer coating covering and in direct contact with at least a portion of the inner coating, the outer coating comprising an electrolyte material; at least two coated sections including 10. An oxygen sensing element, wherein the conductive core is eccentrically disposed in the coating.

2. 2. The oxygen sensing element of claim 1, wherein the cross-sectional shape of the coating perpendicular to the longitudinal axis of the conductive core has a circular, oval, or elliptical shape.

3. 2. The oxygen sensing element of claim 1, wherein the coating has a minimum thickness of at least 0.06 mm.

4. The coating has two thicknesses along the major axis of the cross-sectional area of ​​the coating: a minor thickness T Ｓ and maximum thickness T ＭＡＸ Including T ＭＡＸ T Ｓ 2. The oxygen sensing element of claim 1, wherein the oxygen sensing element is at least 5% greater than

5. The maximum cross-sectional area of ​​the coated pin is 0.5 mm ２ ~7mm ２ 2. The oxygen sensing element according to claim 1, wherein the oxygen sensing element has a capacitance in the range of 1.0 to 1.5 .mu.m.

6. 2. The oxygen sensing element of claim 1, wherein the coating comprises a three-layer primary coating structure covering a major portion of the conductive core.

7. 7. The oxygen sensing element of claim 6, wherein the coating includes a third coating structure covering a third portion of the conductive core.

8. 2. The oxygen sensing element of claim 1, wherein the conductive core includes a mounting portion located at the uncoated mounting end.

9. The oxygen sensing element of claim 1 , wherein the conductive core includes a tapered section.

10. 10. The oxygen sensing element of claim 9, wherein the tapered section extends over at least 10% of the length of the conductive core.

11. An immersion sensor comprising the oxygen detection element according to claim 1.

12. 10. A method for measuring the oxygen content of a metal melt using the oxygen sensing element of claim 1.

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