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 mechanical strength, and to provide an immersion sensor.SOLUTION: An oxygen detection element is provided, comprising a coated pin 1 having an electrically conductive core with a tapered section 3 towards one end. The coating comprises a two-layered coating structure on a tip portion and a three-layered coating structure on a main portion of the electrically conductive core, where the tapered section has the same length or is longer than the tip portion. 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 2

Description

[Technical Field]

[0001] The present invention relates to an oxygen sensing element comprising a coated pin. The coated pin includes a conductive core having a tapered section toward one end. The coating comprises a two-layer coating structure on a tip portion and a three-layer coating structure on a main portion of the conductive core, the tapered section having the same length as or longer than the tip portion. The present invention also 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] 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.

[0006] U.S. Patent No. 5,332,449(A) also discloses a needle sensor. The sensing device includes a conductive wire having a uniform thickness, which 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 mechanical strength. 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.

[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 comprising a coated pin including a conductive core extending longitudinally from a main portion to a tip portion, the tip portion terminating in a tip.

[0011] The tip part is (i) an inner coating covering and in direct contact with at least a portion of the tip portion, 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; The tip is covered by a tip coating structure (CS-T) including:

[0012] The main part is covered by the main coating structure (CS-M), (i) an inner coating covering and in direct contact with at least a portion of the main portion, the inner coating comprising a reference material; (ii) an intermediate coating covering and in direct contact with the inner coating, the intermediate coating comprising a refractory material; (iii) an outer coating covering and in direct contact with at least a portion of the intermediate coating, the outer coating comprising an electrolyte material; Includes.

[0013] The conductive core includes a tapered section, which is a section including a cross section that tapers longitudinally toward the tip. The tapered section has a length L TS The tip portion has a length L TP The oxygen sensing element has a tapered section that is the same length as or longer than the tip portion (L TS ≧L TP It is characterized in that

[0014] The tapered tip portion bearing the coating of reference material and electrolyte material functions as a measurement zone in this configuration. Surprisingly, it has been found that a measurement zone with a minimized diameter, i.e., a measurement zone with a tapered cross-sectional profile, results in an oxygen sensing element with a reduced response time while still providing the mechanical strength required for the intended application. While typical response times for such sensors are in the range of 6 to 10 seconds, oxygen sensing elements according to the present invention exhibit significantly shorter response times, in the range of 1 to 4 seconds.

[0015] 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.

[0016] The object of the present invention is an oxygen sensing element comprising a coated pin, which comprises a conductive core and a plurality of coating layers of at least two coating structures superimposed on the surface of the conductive core, the different coating structures together forming the coating of the coated pin.

[0017] 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

[0018] The conductive core extends longitudinally from a main portion to a tip portion, which terminates at a tip. The axis extending from the main portion to the tip portion is referred to throughout this application as the longitudinal axis of the conductive core and / or the coated pin. The conductive core may include further portions. 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 portion to the other end.

[0019] 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 includes a tip and another end that is a tapered end, 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.

[0020] It should be understood that the tip portion and the tapered section at least partially overlap, in other words, the tapered section includes the tip portion.

[0021] 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.

[0022] 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.

[0023] The tapered section may have the same or different cross-sectional shape as any additional sections present, for example, the tapered section may have a rectangular cross-section and the other sections may have a circular, oval or elliptical shape.

[0024] The shape of the tapered section may vary, particularly depending on the method of production of the conductive core. The tapered section may have a radially symmetrical profile relative to the central longitudinal axis of the conductive core, in which case it may be, for example, conical or frustoconical. The tapered section may also have a profile that is not radially symmetrical relative to the central longitudinal axis, in which case it may be, for example, conical, frustoconical, prismatic, or pyramidal.

[0025] 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.

[0026] 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°.

[0027] 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.

[0028] The tip may have different shapes, for example it may be dome-shaped or flat.

[0029] 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 ~1mm2 , 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

[0030] The coated pin includes a coating that includes at least a tip coating structure and a main coating structure.

[0031] The coating 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 coating may have a constant thickness perpendicular to the longitudinal axis of the conductive core, or the thickness may vary.

[0032] 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.

[0033] The center of the conductive core may be located at the center of the sheath, in other words, the center of the conductive core and the intersection point IP of the cross-sectional area of ​​the sheath may coincide. The center of the conductive core may also be located eccentrically in the sheath, in which case the center of the conductive core and the intersection point IP of the cross-sectional area of ​​the sheath do not coincide. Surprisingly, it has been found that the eccentric location 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.

[0034] In an eccentric configuration, the center of the conductive core is typically offset relative to the intersection point IP along the major axis of the cross section of the covering, so that the covering has two thicknesses along the major axis: a minor thickness T Sand 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.

[0035] 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.

[0036] The distal portion of the conductive core is covered by a tip covering structure (CS-T). It should be understood that the distal portion of the conductive core is characterized as being covered by a tip covering structure. The tip covering structure also covers the tip, or in other words, the tip covering structure surrounds the tip.

[0037] The tip portion and tip coating structure constitute the measurement section of the coated pin. The measurement section of the coated pin should be understood to have a tapered cross section towards the tip. In other words, not only the conductive core has a tapered end, but this tapering also exists for the entire coated pin.

[0038] 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.

[0039] In the oxygen detection element of the present invention, the length of the tapered section of the conductive core is equal to or longer than the length of the tip portion of the conductive core (L TS ≧L TPSince the measurement zone is found in the tapered section of the coated pin, such a configuration allows the measurement zone to heat up quickly, resulting in a short response time of the oxygen sensing element.

[0040] 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%.

[0041] The tip covering 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 tip covering structure may have a constant thickness perpendicular to the longitudinal axis of the conductive core, or the thickness may vary.

[0042] The cross-sectional area of ​​the tip coating structure 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 -T. The minor axis is perpendicular to the major axis and has a length D MI -T. The minor axis is aligned along the largest diameter perpendicular to the major axis.

[0043] The center of the conductive core may be located at the center of the tip covering structure, in other words, the center of the conductive core and the intersection point IP of the cross-sectional area of ​​the tip covering structure may coincide. The center of the conductive core may also be located eccentrically in the tip covering structure, in which case the center of the conductive core and the intersection point IP of the cross-sectional area of ​​the tip covering structure do not coincide. Surprisingly, it has been found that eccentric placement of the center of the conductive core in the tip covering structure shortens the response time of the oxygen sensing element.

[0044] In an eccentric configuration, the center of the conductive core is typically offset relative to the intersection point IP along the longitudinal axis of the tip coating structure, so that the tip coating structure has two thicknesses along the longitudinal axis: a smaller thickness T S-T and a larger thickness T, which corresponds to the maximum thickness of the coating structure in the cross-sectional area MAX -Includes T.

[0045] In a preferred embodiment, the maximum thickness T MAX -T is the small thickness T S -T is at least 5% greater than T, and more preferably 8% greater than T. For example, MAX -T is the small thickness T S -5% to 20% larger than T, more preferably 8% to 15% larger.

[0046] In preferred embodiments, the tip coating structure has a minimum thickness of at least 0.06 mm, more preferably at least 0.1 mm. The minimum thickness of either the coating structure or coating layer should be understood as the smallest thickness of the respective structure or layer perpendicular to the longitudinal axis of the conductive core. For example, the tip coating structure may have a thickness of 0.06 mm to 0.5 mm, more preferably 0.1 mm to 0.4 mm. The thickness of the tip coating structure may be uniform along the length of the coated pin, or the thickness may vary.

[0047] The tip coating structure (CS-T) includes an inner coating and an outer coating. The inner coating covers and is in direct contact with at least a portion of the tip section, and the outer coating 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 and the outer coating. An additional coating layer may be present on the outer coating.

[0048] The inner coating of the tip coating structure includes a reference material. Preferably, the reference material includes 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 of the tip 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. 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 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 may be uniform along the length of the coated pin, or the thickness may vary.

[0049] The outer coating of the tip coating structure 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 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. The thickness of the electrolyte material coating may be uniform along the length of the coated pin, or the thickness may vary.

[0050] The main portion of the conductive core is covered by a main covering structure (CS-M), which should be understood as being characterized by the main portion of the conductive core being covered by a main covering structure.

[0051] The main portion and the tapered section may overlap at least partially or completely. In other words, the tapered section may include at least a portion of the main portion. The main portion may not overlap the tapered section.

[0052] 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.

[0053] The primary covering structure may have any cross-sectional shape perpendicular to the longitudinal axis of the conductive core, preferably having a circular, oval or elliptical cross-section, and even more preferably having an elliptical cross-section. In other words, the primary covering structure may have a constant thickness perpendicular to the longitudinal axis of the conductive core, or the thickness may vary.

[0054] The cross-sectional area of ​​the primary coating structure is the analogous parameter of the cross-sectional area of ​​the tip coating structure, i.e., the length D corresponding to the maximum diameter of the cross-sectional area. MJ -M has a major axis and a length D MI -M and a minor axis perpendicular to the major axis.

[0055] The center of the conductive core may be located at the center of the primary covering structure, i.e., the center of the conductive core and the intersection point IP of the cross-sectional area of ​​the primary covering structure may coincide. The center of the conductive core may also be eccentrically located in the primary covering structure, in which case the center of the conductive core and the intersection point IP of the cross-sectional area of ​​the primary covering do not coincide. In an eccentric configuration, the center of the conductive core is typically offset relative to the intersection point IP along the major axis of the primary covering structure, such that the primary covering structure has two thicknesses along the major axis: a minor thickness T S -M and a larger thickness T corresponding to the maximum thickness of the main covering structure in the cross-sectional area MAX -M and included.

[0056] In a preferred embodiment, the maximum thickness T MAX -M is the smaller thickness T S -M is at least 5% larger, more preferably at least 8% larger than the maximum thickness T MAX -M is the smaller thickness T S -5% to 20% larger than M, more preferably 8% to 15% larger.

[0057] 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.

[0058] 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.

[0059] The primary coating structure (CS-M) includes an inner coating, an intermediate coating, and an outer coating. The inner coating covers and is in direct contact with at least a portion of the main portion of the conductive core, the intermediate coating covers and is in direct contact with the inner coating, and the outer coating covers and is in direct contact with at least a portion of the intermediate coating. Additional coating layers may be present on the outer coating.

[0060] The inner coating of the primary coating structure includes a reference material, which may be the same as the reference material of the tip coating structure.

[0061] The inner coating 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.

[0062] Preferably, the inner coating of the main coating structure and the inner coating of the tip coating structure are sections of an 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.

[0063] The intermediate coating of the primary coating structure comprises a refractory material. Preferably, the refractory material comprises an oxide material, e.g., aluminum oxide such as Al2O3, magnesium oxide, titanium oxide, or mixtures thereof. Preferably, the refractory material comprises aluminum oxide. The intermediate coating 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.

[0064] The outer coating of the primary coating structure includes an electrolyte material, which may be the same as the electrolyte material of the tip coating structure.

[0065] The outer coating 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.

[0066] Preferably, the outer coating 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 main and tip portions 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.

[0067] The maximum cross-sectional area of ​​the coated pin is typically located within the main portion. 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. The maximum cross-sectional area of ​​the coated pin is 0.5 mm 2~7mm 2 , especially, 1.0 mm 2 ~6mm 2 may be in the range of

[0068] 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

[0069] The conductive core may include one or more portions that are covered with a further covering structure and / or portions that are uncovered.

[0070] In a preferred embodiment, the conductive core includes a third portion. In such a case, the conductive core extends longitudinally from the third portion toward the main portion to the tip portion. The third portion is covered with a third coating structure (CS-3), which may include an intermediate coating and an outer coating. The intermediate coating covers and is in direct contact with at least a portion of the third portion of the conductive core, and the outer coating covers and is in direct contact with at least a portion of the intermediate coating. 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.

[0071] The third portion of the conductive core and the tapered section may at least partially or completely overlap. In other words, the tapered section may include at least a portion of the third portion. The third portion may not overlap the tapered section.

[0072] The cross-sectional area of ​​the third coating structure is an analogous parameter of the cross-sectional area of ​​the tip coating structure and the main coating structure, i.e., a length D corresponding to the maximum diameter of the cross-sectional area. MJ -3 and a major axis of length D MI -3 and a minor axis perpendicular to the major axis.

[0073] The center of the conductive core may be located at the center of the third covering structure; in other words, the center of the conductive core may be aligned with the intersection point IP of the cross-sectional area of ​​the primary covering structure. The center of the conductive core may also be eccentrically located in the third covering structure, in which case the center of the conductive core and the intersection point IP of the cross-sectional area of ​​the third covering structure do not coincide. In an eccentric configuration, the center of the conductive core is typically located offset relative to the intersection point IP along the major axis of the third covering structure, so that the third covering structure has two thicknesses along the major axis, namely, a minor thickness T S -3 and a larger thickness T corresponding to the maximum thickness of the main covering structure in the cross-sectional area MAX -3 and more.

[0074] In a preferred embodiment, the maximum thickness T MAX -3 is a small thickness T S For example, the maximum thickness T MAX -3 is a small thickness T S It is 5% to 20% larger than -3, and more preferably 8% to 15% larger.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] The intermediate coating of the third coating structure may include 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 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.

[0079] Preferably, the intermediate coating of the third coating structure and the intermediate coating 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.

[0080] The outer coating 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 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.

[0081] Preferably, the outer coating of the third coating structure, the outer coating 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.

[0082] Preferably, the conductive core includes an uncoated attachment portion. In such a case, the conductive core extends longitudinally from the attachment portion toward the main portion to the tip portion. If a third portion is present, the third portion is located between the attachment portion and the main portion.

[0083] 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. For example, the manufacture (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:

[0084] The coating of the coated 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) processes, 3D printing, or 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.

[0085] During such a thermal spray process, the object to be coated is 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 its 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, the rotational motion may be centralized with respect to the coating source, while for eccentric coatings, the rotational motion may be eccentric with respect to the source and the horizontal motion.

[0086] In a second aspect, the invention relates to an immersion sensor comprising an oxygen sensing element according to the invention.

[0087] The immersion sensor may comprise further components 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).

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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:

[0093] 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.

[0094] 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]

[0095] 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-section of an oxygen sensing element according to the invention; [Figure 4] 1 illustrates an additional embodiment of the present invention. [Figure 5] 1 shows a schematic transverse cross-sectional view of an oxygen sensing element. [Figure 6] 4 shows the response characteristics of an oxygen sensing element according to the prior art compared to the oxygen sensing element of the present invention.

[0096] Figure 1 shows cross-sections of different geometries of the tip 2 of a conductive core 1. The tip 2 in Figure 1A is needle-shaped and terminates in a sharp point. The tip 2 shown in Figure 1B has a flattened needle shape, also called a frustoconical shape. The tip 2 shown in Figure 1C includes a dome-shaped needle tip.

[0097] FIG. 2 shows a schematic longitudinal cross section of a conductive core 1 suitable for the present invention. The pin 1 has a tapered section 3, a length (L TS) and the angle of tapering at its end. The location where the angle of tapering, denoted by the taper angle α, is found is also indicated. 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 pins 1 in Figures 2A to 2C have centrosymmetrical shapes. Figure 2A shows a needle-shaped conductive core 1 with a tapered section 3 that extends only over part of the length of the pin. Figure 2B shows a similar shape, on the one hand, but with a longer tapered section 3 and a smaller taper angle α on the other hand. The tapered section 3 of the conductive core 1 shown in Figure 2C extends over the entire length of the pin 1. The conductive core 1 in Figure 2D also has a tapered section 3 over its entire length, but the shape is not centrosymmetrical.

[0098] 3 shows a schematic longitudinal cross-section of an oxygen sensing element 4 according to the present invention. A needle-shaped conductive core 1 has a first portion, length L TP a tip covering structure 5 (CS-T) covering the tip portion of the core 1 having a length L MP The tip coating structure 5 and tip 2 provide a measurement zone for the sensor element 4 during use. The tip coating structure 5 includes a two-layer structure having a reference material coating 8 and an electrolyte material coating 9. Due to the reduced volume of the measurement zone on the tapered end of the conductive core, the oxygen sensing element has a fast response time. Surprisingly, such a geometry still allows for a robust oxygen sensing element.

[0099] The primary coating structure 6 includes a three layer structure. The tip coating structure includes a reference material layer 10 extending between the reference material coating 8 and the electrolyte material coating 9 in addition to the two layers (8, 9) on the tip coating structure.

[0100] In the embodiment described, the electrolyte material layer 9 and the reference material layer 8 extend over the entire length of the covering structure, while the refractory material layer 10 has a main length L MP exists only throughout the

[0101] The end 11 of the conductive core opposite the tip 2 is uncoated and is typically attached to a suitable material, for example, a refractory material if the oxygen sensing element is attached to the sensor assembly, and is therefore also referred to as the attachment end.

[0102] The coating layer over the conductive core can be applied using a thermal spray process, such as plasma spraying or flame spraying, which produces a highly uniform and dense coating. First, a reference material, such as chromium-chromium dioxide, is applied to the conductive core. Subsequently, a portion of the tapered section that will become the measurement zone is masked, and a refractory material, such as aluminum oxide, is applied to the unmasked portion of the conductive core. Following removal of the masking, an electrolyte material, such as stabilized zirconium oxide, is sprayed.

[0103] 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.

[0104] Figure 4 shows a further embodiment of an oxygen sensing element 4 according to the invention. Compared to the embodiment of Figure 3, the coating of the embodiment shown in Figure 4A has a length L 3P The third coating structure 7 is included on the third portion of the conductive core 1 having the 3PThe third coating structure 7 is only shown in FIG. 4A for a better overview. The third coating structure 7 includes a two-layer structure of a refractory material layer 10 and an electrolyte material layer 9. The two layers have essentially the same thickness. The conductive core 1 in the embodiment of FIG. 4B is also needle-shaped, but tapering extends along the entire length of the pin. The coating structure includes three sections, as in the embodiment of FIG. 4A. The coating structure of the oxygen sensing element 4 in FIG. 4C is similar to that of the embodiment shown in FIG. 4B. However, the outer shape of the coating differs due to the different thicknesses of the coating layers. While the refractory material layer 10 in FIG. 4B has an essentially uniform thickness along the length of the oxygen sensing element 4, the thickness of this layer in FIG. 4C includes sections with varying thicknesses. Additionally, the electrolyte material layer 9 includes sections with varying thicknesses, resulting in a barrel-shaped coating structure with a small diameter at the tip 2, a maximum diameter at the main portion 6, and a tapered cross-sectional diameter at the third portion 7.

[0105] FIG. 5 shows a schematic transverse cross-section of the measurement zone of the oxygen sensing element 4, i.e., in a plane perpendicular to the plane shown in FIGS. 1 to 4 in the region of the tip coating structure 5. The coating has a two-layer structure consisting of a reference material coating 8 directly contacting the pin 1 and an electrolyte material coating 9 on top of the reference material coating 8. The coating shown in FIG. 5A has a circular shape with a uniform thickness. Therefore, the length D of the major axis of the cross-section is MJ -T and the length of the minor axis D MI -T is equal. Pin 1 is located at the center of the coating, and the center of the pin is located at the intersection point IP of the two axes. The coating in Figure 5B has an elliptical shape, in other words, its thickness is not uniform around the circumference. Pin 1 is located at the center of the coating structure. In Figure 5C, a coating structure with an eccentrically located pin 1 is shown. The maximum thickness T of the coating structure along the major axis MAX -T and small thickness T S -T is also displayed.

[0106] Figure 6 shows the response characteristics of a prior art oxygen sensing element compared with the oxygen sensing element (needle sensor) of the present invention. Both sensors have a Mo pin with a three-layer coating structure. The pin of the state-of-the-art sensor was a wire with a constant diameter of 1 mm. The pin of the sensor of the present invention was a Mo needle with a base diameter of 0.8 mm and a tip diameter of 0.2 mm. The tapered section was 10 mm long, and the top 5 mm of it was coated with a two-layer structure consisting of a 0.1 mm Cr / Cr2O3 mixture layer (electrolyte material) and a 0.2 mm stabilized zirconia layer (reference material). The zirconia layer extended almost the entire length of the Mo needle, except for the mounting section at the end, which did not contain a coating. A 0.15 mm thick layer of Al2O3 (refractory material) was present at the bottom (relative to the tip of the needle, which is the top) below the zirconia layer.

[0107] To obtain the curves, each sensing element was immersed in a molten steel bath and the detected electromotive force (EMF) was recorded over time. Electrochemical equilibrium between the molten metal and the immersed sensor is necessary for accurate measurement of the EMF value. Such electrochemical equilibrium can only occur if thermal equilibrium exists between the sensor and its surroundings.

[0108] The data presented shows that the response time of the needle-shaped oxygen sensing element, i.e., the time until a constant signal can be achieved, is significantly reduced compared to state-of-the-art sensors without tapered tips, so that faster measurements can be achieved. [Explanation of symbols]

[0109] 1 conductive core 2 Tip of conductive core 3 Tapered section of conductive core 4. Oxygen detection element 5 Tip coating structure (CS-T) 6 Main coating structure (CS-M) 7. Third Covering Structure (CS-3) 8 Reference Material Coating 9 Electrolyte material coating 10 Fire-resistant material covering 11 Mounting end of coated pin 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 -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 extending longitudinally from a main portion to a tip portion, the tip portion terminating in a tip; (a) the tip portion is covered with a tip covering structure (CS-T); The tip covering structure (CS-T) is (i) an inner coating covering and in direct contact with at least a portion of the tip portion, 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; Including, (b) the main portion is covered by a main covering structure (CS-M); The main covering structure (CS-M) is (i) an inner coating covering and in direct contact with at least a portion of the main portion, the inner coating comprising a reference material; (ii) an intermediate coating covering and in direct contact with the inner coating, the intermediate coating comprising a refractory material; (iii) an outer coating covering and in direct contact with at least a portion of the intermediate coating, the outer coating comprising an electrolyte material; Including, the conductive core includes a tapered section, the tapered section including a cross section that tapers longitudinally toward the tip; The tapered section has a length L ＴＳ and the tip portion has a length L ＴＰ and L ＴＳ ≧L ＴＰ An oxygen detection element characterized by:

2. 2. The oxygen sensing element of claim 1, wherein the tapered section extends over at least 10% of the length of the conductive core.

3. 2. The oxygen sensing element of claim 1, wherein the taper angle of the tapered section is less than 40 degrees.

4. 2. The oxygen sensing element of claim 1, wherein the cross-sectional area of ​​the tip is less than 40% of the maximum cross-sectional area of ​​the conductive core.

5. The length L of the tip portion ＴＰ The length L of the tapered section ＴＳ 2. The oxygen sensing element of claim 1, wherein the oxygen sensing element has a specific surface area of ​​at least 20% of the surface area of ​​the oxygen sensing element.

6. 2. The oxygen sensing element of claim 1, wherein the coating of the coated pin has an oval shape, the coating including at least the tip coating structure and the main coating structure.

7. 2. The oxygen sensing element of claim 1, wherein the center of said conductive core is eccentrically disposed within said coating, said coating including at least said tip coating structure and said main coating structure.

8. 2. The oxygen sensing element of claim 1, wherein the main portion extends over more than 30% of the length of the conductive core.

9. 2. The oxygen sensing element of claim 1, wherein the primary coating structure has a greater minimum thickness than the tip coating structure.

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

11. 2. The oxygen sensing element of claim 1, wherein the primary coating structure has a minimum thickness of at least 0.07 mm.

12. 2. The oxygen sensing element of claim 1, wherein the largest cross-sectional area of ​​said coated pin is located within said main portion.

13. the conductive core includes a third portion, the third portion comprising: (i) an intermediate coating covering and in direct contact with at least a portion of the third portion of the conductive core, the intermediate coating comprising a refractory material; (ii) an outer coating covering and in direct contact with at least a portion of the intermediate coating, the outer coating comprising an electrolyte material; 2. The oxygen detection element according to claim 1, which is covered with a third covering structure (CS-3) comprising:

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

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

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