A device for measuring the 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 detection element provided with a coated pin. The coated pin includes a conductive core having a tapered section towards one end. The coating includes a two-layer coating structure on the tip portion and a three-layer coating structure on the main portion of the conductive core, and the tapered section has the same length as or longer than the tip portion. The present invention further relates to an immersion sensor provided with the oxygen detection element, and a method for measuring the oxygen content of a molten metal using such an oxygen detection element.

[0002] During metallurgical processing, the oxygen activity of a molten metal is one of the parameters that need to be monitored. To determine the oxygen activity, typically an electrochemical sensor including a solid electrolyte material, a reference material, and an electrode is used. Then, the electromotive force (EMF) generated by the difference between the constant oxygen partial pressure provided by the reference material and the oxygen partial pressure in the molten metal is monitored and associated with the activity or concentration of oxygen in the liquid metal. Many electrochemical sensors for testing such melts have weaknesses such as slow response speed, high failure rate, poor reproducibility, and low sensitivity.

[0003] One type of oxygen sensor is a needle sensor, which includes a conductive wire that functions as an electrode having at least a solid electrolyte coating and a reference material coating. These sensors have difficulties in terms of slow response time or insufficient stability for applications in the harsh environment of molten metal. An accurate measurement of the EMF value is required for the electrochemical equilibrium between the molten metal and the oxygen sensor. However, the electrochemical equilibrium occurs only when there is a thermal equilibrium between the immersion probe and its surroundings.

[0004] To obtain high-precision measurement values, 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. In many cases, a thermocouple having a response time of 3 to 6 seconds is used for this purpose.

[0005] Japanese Patent Application Laid-Open No. 61-79156(A) discloses a needle-type oxygen concentration detection element having a metal wire, and the element includes a coating having a conical shape to reduce the response time of the device.

[0006] U.S. Patent No. 5332449(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 responsiveness of the device, a reduction in the diameter of the conductive pin in the region without the functional coating has been proposed. It has been found that this configuration reduces the mechanical stability of the device.

[0007] The present invention overcomes at least some of the problems identified in the prior art. In particular, an object of the present invention was to provide an oxygen detection element having a rapid response time and high mechanical strength. A further aspect was to provide an oxygen detection element that could be produced reliably, rapidly, and efficiently. An additional object was to provide an oxygen detection element with a low-cost design.

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

[0010] The present invention provides an oxygen detection element comprising a coated pin. The coated pin includes a conductive core extending longitudinally from a main portion to a tip portion, and the tip portion ends at a tip end.

[0011] The tip portion is (i) an inner coating that covers at least a portion of the tip portion and is in direct contact with it, the inner coating containing a reference material, and (ii) an outer coating that covers at least a portion of the inner coating and is in direct contact with it, the outer coating containing an electrolyte material, and It is covered by a tip coating structure (CS-T) that includes [a specific component].

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

[0013] The conductive core includes a tapered section, which is a section containing a cross-section that is tapered towards the tip in the longitudinal direction. The tapered section has a length L TS It has a tip portion of length L TP The oxygen detection element has a tapered section that is the same length as or longer than the tip portion (L TS ≥L TP It is characterized by being.

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

[0015] For certain applications, the oxygen detection element is mounted on an immersion apparatus in contact with the molten metal and typically includes at least a carrier tube. These carrier tubes must withstand the immersion conditions for at least a sufficient time for the measurement to be performed before they disintegrate, which is often achieved by providing a certain amount of material. A faster response time for the oxygen detection element can reduce the use of material, leading to a reduction in the cost of the immersion apparatus. For example, for every 1 second reduction in response time, the thickness of the cardboard carrier tube can be reduced by approximately 1 mm in diameter.

[0016] The object of the present invention is an oxygen detection element comprising a coated pin. The coated pin includes a conductive core and a plurality of coating layers of at least two coating structures superimposed on the surface of the conductive core. Different coating structures together form the coating of the coated pin.

[0017] Examples of suitable materials for conductive cores are molybdenum (Mo) and tungsten (W), particularly due to their thermal properties. Preferably, the conductive core material contains Mo, and 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 a short response time, the maximum cross-sectional area of ​​the conductive core should be 0.1 mm. 2 ~3mm 2 , especially 0.3mm 2 ~1.5mm 2 Being within that range is advantageous.

[0018] The conductive core extends longitudinally from the main portion to the tip portion, which terminates at the 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 covering 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 is tapered in the longitudinal direction towards the tip. In other words, the conductive core includes a tip that is a tapered end and another 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 over the entire length of the conductive core. The tapered section can also extend over only a part of its length, and in such a case, the conductive core includes at least two sections, namely, 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 over at least 20%, and even more preferably over at least 30%. The length of the tapered section typically ranges from 4 mm to 30 mm, preferably from 8 mm to 20 mm.

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

[0024] The shape of the tapered section may vary, particularly depending on the method of producing the conductive core. The tapered section may have an external shape that is radially symmetric with respect to the central longitudinal axis of the conductive core, in which case it may be, for example, a conical or frustoconical shape. The tapered section may also have an external shape that is not radially symmetric with respect to the central longitudinal axis, in which case it may be, for example, a conical, frustoconical, prism-shaped, or pyramidal shape.

[0025] Preferably, the tapered section has a conical shape, in other words, a circular or oval cross-section, and ends with a tapered end of circular or oval shape.

[0026] The angle of tapering in a tapered section can be described by the taper angle, which should be understood as the angle between two adjacent tangents to the surface of the tapered section in the plane of the maximum cross-sectional area of ​​the tapered section along the longitudinal axis. It has been shown that a taper angle of less than 40°, more preferably less than 30°, and most preferably less than 20° is advantageous. The taper angle may be in the range of 1° to 40°, preferably 3° to 30°, and more preferably 5° to 20°.

[0027] In a preferred embodiment, the conductive core is needle-shaped, in other words, it includes a region with a circular cross-section along its entire length, a tapered section having a conical shape, and a tapered end having a circular cross-section.

[0028] The tip may have a different shape, for example, it may be domed or flat.

[0029] Preferably, the cross-sectional area of ​​the tip is less than 40% of the maximum cross-sectional area of ​​the conductive core, more preferably less than 30%, and even more preferably less than 20%. For example, the cross-sectional area of ​​the pin end may be in the range of 0.5% to 40% of the maximum cross-sectional area, more preferably 2% to 30%, and most preferably 5% to 20%. For a short response time, the cross-sectional area of ​​the pin end should be 0.01 mm. 2 ~1mm2 Preferably 0.02 mm 2 ~0.5mm 2 , more preferably 0.05 mm 2 ~0.2mm 2 It was found that this was advantageous.

[0030] The covered pin includes a covering, which includes at least a tip covering structure and a main covering structure.

[0031] The coating 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 more preferably having an elliptical cross-section. In other words, the coating may have a constant thickness perpendicular to the longitudinal axis of the conductive core, and its thickness may vary.

[0032] The outer shape of the cross-sectional area of ​​the covering can be defined by two intersecting axes that meet at an intersection point (IP), where the major axis coincides with the maximum diameter of the cross-sectional area, and the length D corresponds to the maximum diameter of the cross-sectional area. MJ It has a minor axis perpendicular to the major axis, and length D MI It has the following characteristics: The minor axis is aligned 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 coating; in other words, the intersection point IP between the center of the conductive core and the cross-sectional region of the coating may coincide. The center of the conductive core may also be eccentrically located in the coating, in which case it will not coincide with the intersection point IP between the center of the conductive core and the cross-sectional region of the coating. Surprisingly, it has been found that the eccentric placement of the center of the conductive core in the coating has a positive effect on the response time of the oxygen detection element and the stability of the coating.

[0034] In an eccentric configuration, the center of the conductive core is typically offset from the intersection IP along the long axis of the coating's cross-section, and therefore the coating has two thicknesses along the long axis, namely a smaller thickness T. SAnd a large thickness T corresponding to the maximum thickness of the covering structure in the cross-sectional region. MAX This includes the following. The thickness of the coating and the maximum thickness of the coating should be understood to vary along the length of the coating pin.

[0035] In a preferred embodiment, the maximum thickness T MAX is a small thickness T S It is at least 5% greater than, and more preferably at least 8% greater than, the maximum thickness T. MAX is a small thickness T S 5% to 20% larger, and more preferably 8% to 15% larger.

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

[0037] The tip portion and tip covering structure constitute the measuring section of the covering pin. The measuring section of the covering pin should be understood to have a tapered cross-section toward the tip. In other words, this tapering is not only present in the conductive core but also in the entire covering pin.

[0038] The tip is length L TP It has the following characteristics. Preferably, the tip 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 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] The oxygen detection element of the present invention has a tapered section of the conductive core that is the same length as or longer than the tip portion of the conductive core (L TS ≥L TPThe measurement zone is located in the tapered section of the coated pin, so such a configuration allows the measurement zone to be heated quickly, resulting in a short response time for the oxygen detection element.

[0040] Length of the tip L TP Preferably, the length L of the tapered section of the conductive core. TS It is at least 20%, more preferably at least 30%, and even more preferably at least 50%.

[0041] The tip coating 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 more preferably having an elliptical cross-section. In other words, the tip coating structure may have a constant thickness perpendicular to the longitudinal axis of the conductive core, and this thickness may vary.

[0042] The external shape of the cross-sectional area of ​​the tip covering structure can be defined by two intersecting axes that intersect at the intersection point (IP). The major axis coincides with the maximum diameter of the cross-sectional area, and the length D corresponds to the maximum diameter of the cross-sectional area. MJ It has -T. The minor axis is perpendicular to the major axis, and the length D MI It has -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 coating structure; in other words, the intersection IP between the center of the conductive core and the cross-sectional region of the tip coating structure may coincide. The center of the conductive core may also be eccentrically located in the tip coating structure, in which case the center of the conductive core and the intersection IP between the cross-sectional region of the tip coating structure do not coincide. Surprisingly, it has been found that eccentric placement of the center of the conductive core in the tip coating structure shortens the response time of the oxygen detection element.

[0044] In an eccentric configuration, the center of the conductive core is typically offset from the intersection IP along the long axis of the tip coating structure, and therefore the tip coating structure has two thicknesses along the long axis, namely a smaller thickness T. S-T and a large thickness T corresponding to the maximum thickness of the covering structure in the cross-sectional region. MAX -Includes T

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

[0046] In a preferred embodiment, 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 the coating layer should be understood as the smallest thickness of each 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 coating pin, and 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 portion, and the outer coating covers and is in direct contact with at least a portion of the inner coating. In other words, there is no coating layer between the inner coating and the outer coating. An additional coating layer may be present on top of 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, for example, a mixture of chromium and chromium dioxide (Cr-Cr2O3) or a mixture of 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 coating pin, and 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 is known to those skilled in the art, stabilized zirconium oxide includes at least one oxide such as magnesia (MgO), calcium oxide (CaO), yttria (Y2O3), ceria (CeO2), or scandia (Sc2O3) dissolved as a stabilizer in zirconia. 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 coating pin, and the thickness may vary.

[0050] The main portion of the conductive core is covered by the main coating structure (CS-M). It should be understood that the main portion of the conductive core is characterized by being covered by the main coating structure.

[0051] The main section 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 section. The main section does not have to overlap with the tapered section.

[0052] The main part is length L MP The main portion preferably extends over more than 30% of the length of the conductive core, more preferably over 40%, and even more preferably over 50%. 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 main coating 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 more preferably having an elliptical cross-section. In other words, the main coating structure may have a constant thickness perpendicular to the longitudinal axis of the conductive core, and the thickness may vary.

[0054] The cross-sectional area of ​​the main covering structure is the analog parameter of the cross-sectional area of ​​the tip covering structure, i.e., the length D corresponding to the maximum diameter of the cross-sectional area. MJ - A major axis having M and length D MI -This can be explained by a minor axis perpendicular to the major axis having M.

[0055] The center of the conductive core may be located at the center of the main coating structure; in other words, the center of the conductive core may coincide with the intersection IP of the cross-sectional region of the main coating structure. The center of the conductive core may also be eccentrically located in the main coating structure, in which case the center of the conductive core may not coincide with the intersection IP of the cross-sectional region of the main coating. In the eccentric configuration, the center of the conductive core is typically offset from the intersection IP along the long axis of the main coating structure, so that the main coating structure has two thicknesses along the long axis, i.e., a smaller thickness T S -M and a large thickness T corresponding to the maximum thickness of the main covering structure in the cross-sectional region. MAX -Includes M

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

[0057] In a preferred embodiment, the main coating structure has a minimum thickness of at least 0.07 mm, more preferably at least 0.12 mm. For example, the main 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 main coating structure may be uniform along the length of the coating pin, and the thickness may vary.

[0058] In preferred embodiments, the main coating structure has a minimum thickness greater than that of the tip coating structure. Preferably, the main coating structure has a minimum diameter greater than that of the tip coating structure.

[0059] The main 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 part 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. An additional coating layer may be present on top of the outer coating.

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

[0061] The inner coating of the main 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 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 coating pin, or it may vary in thickness.

[0063] The intermediate coating of the main coating structure includes a refractory material. Preferably, the refractory material includes an oxide material, such as aluminum oxide (e.g., Al2O3), magnesium oxide, titanium oxide, or a mixture thereof. Preferably, the refractory material includes 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 main coating structure includes an electrolyte material. The electrolyte material of the main coating structure may be the same as the electrolyte material of the tip coating structure.

[0065] The outer coating of the main 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 the 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 coating pin, or it may vary in thickness.

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

[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. This range of cross-sectional area results in a coated pin with sufficient stability and 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 2% to 30%, and most preferably 5% to 20% of the maximum cross-sectional area of ​​the coated pin. For a short response time, the cross-sectional area of ​​the coated pin end should be 0.1 mm 2 ~2.5mm 2 , especially 0.5mm 2 ~1.5mm 2 It was found to be advantageous in this regard.

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

[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 toward 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 top of the outer coating.

[0071] The third portion of the conductive core 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 third portion. The third portion does not have to overlap with the tapered section.

[0072] The cross-sectional area of ​​the third covering structure is the length D, which corresponds to the maximum diameter of the cross-sectional area, and is an analog parameter between the cross-sectional area of ​​the tip covering structure and the main covering structure. MJ The major axis has -3 and length D MI This can be explained by a minor axis perpendicular to the major axis having -3.

[0073] The center of the conductive core may be located at the center of the third coating structure; in other words, the centers of the conductive core may be aligned in a line on the intersection IP of the cross-sectional region of the main coating structure. The center of the conductive core may also be eccentrically located in the third coating structure, in which case the center of the conductive core and the intersection IP of the cross-sectional region of the third coating structure do not coincide. In the eccentric configuration, the center of the conductive core is typically offset from the intersection IP along the long axis of the third coating structure, so that the third coating structure has two thicknesses along the long axis, i.e., a smaller thickness T S -3 and a large thickness T corresponding to the maximum thickness of the main covering structure in the cross-sectional area. MAX Includes -3.

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

[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 coating pin, and may vary.

[0076] In a preferred embodiment, the third coating structure has a minimum thickness smaller than that of the main coating structure. Preferably, the third coating structure has a minimum diameter smaller than that of the main coating structure.

[0077] The third part is of length L 3P The third portion preferably 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 the intermediate coating layer, in other words, they construct a single coating layer over at least the third and main portions of the conductive core. The thickness of the intermediate coating layer may be uniform along the length of the coating pin, or it 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 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 the outer coating layer, in other words, they construct a single coating layer over at least the third, main, and tip portions of the conductive core. The thickness of the outer coating layer may be uniform along the length of the coating pin, or it may vary in thickness.

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

[0083] The manufacturing of the oxygen detection element of the present invention is typically carried out in a stepwise manner, in which different coating layers are applied sequentially. For example, the manufacturing is (i) A step of providing a conductive core, (ii) A step of covering the pin portion and main portion of the conductive core with a reference material, (iii) A step of masking the pin portion of the conductive core, (iv) A step of covering at least the main portion of the conductive core with a fire-resistant material, (v) The process of unmasking the pin portion of the conductive core. (vi) A step of covering at least the pin portion and the main portion with an electrolyte material. It may include.

[0084] The coating of the coating structure may be applied by methods known to those skilled in the art, such as chemical vapor deposition (CVD) or physical vapor deposition (PVD), additive manufacturing methods such as 3D printing, or thermal spraying such as plasma or flame spraying. Thermal spraying, in particular, produces a uniform and high-density coating. Preferred methods are disclosed, for example, in European Patent No. 0543081(A1).

[0085] During such a thermal spraying process, the object to be coated is moved horizontally through a spray cone containing the coating material, provided, for example, using a thermal spray gun, by a suitable source such as a plasma or flame source. In this case, the object is a conductive core. While passing through the spray cone, the object is typically rotated to obtain a uniform periphery coating. To obtain a coating with a centrally located conductive core, this rotational motion may be centralized with respect to the coating source, whereas, in the case of eccentric coatings, this rotational motion may be eccentric with respect to the source and the horizontal motion.

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

[0087] The immersion sensor may comprise further components such as a counter electrode, additional measuring means such as means for measuring temperature, means for mounting an oxygen sensing element, means for signal transmission, means for protecting the oxygen sensing element, and / or means for immersion. Further components of the immersion sensor are known to those skilled in the art and are disclosed, for example, in U.S. Patent Publication No. 4964736(A).

[0088] The means for measuring temperature may be, for example, a thermocouple as known to those skilled in the art. The means for measuring temperature is not essential for functional immersion sensors, and if temperature is required, it can be derived, for example, by external means.

[0089] The means for mounting the oxygen detection element may be, for example, a fire-resistant mounting material in which the oxygen detection element can be partially embedded, preferably only the uncovered mounting portion of the conductive core is embedded in such fire-resistant material.

[0090] The means for immersing the immersion sensor may be, for example, a carrier tube, preferably made of cardboard. The means for immersion is not essential for functional immersion sensors, for example, when 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 European Patent Application Publication No. 0997716(A1).

[0091] In a third aspect, the present invention relates to a method for measuring the oxygen content of a molten metal using an oxygen detection element according to the present invention. As is known to those skilled in the art, the method includes immersing the oxygen detection element in each molten metal.

[0092] For example, this method, (i) A step of providing an oxygen detection element, (ii) A step of immersing an oxygen detection element in a molten metal, (iii) Steps for measuring the oxygen content in the molten metal It may include.

[0093] The process of measuring the oxygen content in a molten metal may include measuring the oxygen activity of the molten metal and relating this measurement to the oxygen content.

[0094] In practice, a molten metal is brought into contact with an oxygen detection element according to the present invention, and the electrochemical potential of the element is preferably measured over time. The electrochemical activity is determined by the potential expressed in the analysis unit via lead means for drawing lead wires from the cell. By relating the electrochemical potential thus determined to the resulting electrochemical potential against a set of criteria, the oxygen content in the molten metal can be determined. [Brief explanation of the drawing]

[0095] The following schematic diagrams illustrate aspects of the invention to further the understanding of the invention with respect to several illustrative illustrations. However, it should be understood that the invention is not limited to the exact arrangements and means shown. The elements of the drawings are not necessarily to scale with respect to one another. Similar reference numbers refer to corresponding similar parts, as follows: [Figure 1] This shows the different external shapes of the tip of the conductive core. [Figure 2] A schematic cross-section of a conductive core suitable for the present invention is shown. [Figure 3] A schematic longitudinal cross-sectional view of the oxygen detection element according to the present invention is shown. [Figure 4] Additional embodiments of the present invention are shown. [Figure 5] A schematic lateral cross-sectional view of the oxygen detection element is shown. [Figure 6] The response characteristics of a conventional oxygen detection element compared to the oxygen detection element of the present invention are shown.

[0096] Figure 1 shows cross-sections of different external shapes of the tip portion 2 of the conductive core 1. The tip portion 2 in Figure 1A is needle-shaped and ends with a sharp tip. The tip portion 2 shown in Figure 1B has a flat needle shape, also called a frustoconical shape. The tip portion 2 shown in Figure 1C includes a domed needle tip.

[0097] Figure 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, and its length (L TS) have different external shapes with respect to the angle of tapering at its ends. The location where the angle of tapering, represented by the taper angle α, is found is also shown. The taper angle is determined by the angle between two adjacent tangents to the surface of the taper section in the plane of the maximum cross-section of the taper section along the longitudinal axis of the pin. These tangents are shown by dashed lines. The pins 1 in Figures 2A to 2C have a centrally symmetric external shape. Figure 2A shows a needle-shaped conductive core 1 with a taper section 3 that extends only over part of the length of the pin. Figure 2B shows a similar external shape on the one hand, but on the other hand, the taper section 3 is longer and the taper angle α is smaller. The taper 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 taper section 3 over its entire length, but its external shape is not centrally symmetric.

[0098] Figure 3 shows a schematic longitudinal cross-sectional view of the oxygen detection element 4 according to the present invention. The needle-shaped conductive core 1 is the first part, with length L TP A tip covering structure 5 (CS-T) that covers the tip portion of the core 1 having a second part, length L MP The coating structure has two parts: a main coating structure 6 (CS-M) covering the main portion of the pin 1 having a tip coating structure 5 and a tip portion 2 that provide the measurement zone of the sensor element 4 when in use. The tip coating structure 5 includes a two-layer structure having a reference material coating 8 and an electrolyte material coating 9. Because the volume of the measurement zone on the tapered end of the conductive core is reduced, the oxygen detection element has a rapid response time. Surprisingly, such an external form still allows for a robust oxygen detection element.

[0099] The main coating structure 6 includes a three-layer structure. The tip coating structure includes two layers (8, 9) on the tip coating structure, as well as a base material layer 10 extending between the base material coating 8 and the electrolyte material coating 9.

[0100] In the embodiment described, the electrolyte material layer 9 and the reference material layer 8 extend along the entire length of the covering structure, while the fire-resistant material layer 10 has a main portion with a length L MP It exists only over a certain period.

[0101] The end 11 of the conductive core opposite the tip 2 is uncoated. Typically, this end is attached to a suitable material, for example, a fire-resistant material when the oxygen detection element is attached to a sensor assembly, and is therefore also referred to as the mounting end.

[0102] The coating layer covering the conductive core can be applied using thermal spraying, such as plasma spraying or flame spraying, thereby producing a very uniform and high-density 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 the removal of the masking, an electrolyte material such as stabilized zirconium oxide is thermal sprayed.

[0103] The thickness of the different layers may be uniform along the length of the coating pin, but they may also vary, especially when the described thermal spraying process is applied to manufacture the sensing element. These different layers may have the same thickness depending on the demand and application of the oxygen sensing element, and they may vary in shape and thickness.

[0104] Figure 4 shows an additional embodiment of the oxygen detection element 4 according to the present invention. Compared with the embodiment in Figure 3, the coating of the embodiment shown in Figure 4A has a length L 3P An additional third covering structure 7 is included on the third portion of the conductive core 1 having L 3PThis is shown in Figure 4A only 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 Figure 4B is also needle-shaped, but the tapering extends along the entire length of the pin. The coating structure includes three parts as in the embodiment of Figure 4A. The coating structure of the oxygen detection element 4 in Figure 4C is similar to the coating structure of the embodiment shown in Figure 4B. However, the shape of the outer surface of the coating differs due to the different thicknesses of the coating layers. The refractory material layer 10 in Figure 4B has essentially uniform thickness along the length of the oxygen detection element 4, while the thickness of this layer in Figure 4C includes parts with varying thicknesses. The electrolyte material layer 9 also includes parts with varying thicknesses, with a smaller diameter at the tip 2, a maximum diameter at the main part 6, and a tapered cross-sectional diameter at the third part 7, resulting in a barrel-shaped coating structure.

[0105] Figure 5 shows a schematic lateral cross-sectional view of the measurement zone of the oxygen detection element 4, i.e., a view in a plane perpendicular to the planes shown in Figures 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 that is in direct contact with the pin 1 and an electrolyte material coating 9 on top of the reference material coating 8. The coating shown in Figure 5A has a circular shape with a uniform thickness. Therefore, the length of the major axis of the cross-section D MJ -T and the length of the minor axis D MI -T is equal. Pin 1 is located at the center of the sheathing, and the center of the pin lies on the intersection IP of the two axes. The sheathing in Figure 5B has an elliptical shape, in other words, its thickness is not uniform around its perimeter. Pin 1 is located at the center of the sheathing structure. Figure 5C shows a sheathing structure with an eccentrically placed pin 1. The maximum thickness T of the sheathing 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 conventional oxygen detection element compared to the oxygen detection element (needle sensor) of the present invention. Both sensors have a Mo pin with a three-layer coating structure. The pin of the existing technology 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 had a length of 10 mm, and its uppermost 5 mm was coated with a two-layer structure including 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 which did not include the coating at the end. A 0.15 mm thick layer of Al2O3 (refractory material) was present below the zirconia layer (relative to the tip of the needle, which is above).

[0107] To obtain the curve, 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 occurs only when thermal equilibrium exists between the sensor and its surroundings.

[0108] The data shows that the response time of the needle-shaped oxygen detection element, i.e., the time it takes to achieve a constant signal, is significantly shorter compared to existing sensors without a tapered tip. Therefore, faster measurements can be achieved. [Explanation of Symbols]

[0109] 1 Conductive core 2. Tip of the 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 coating structure (CS-3) 8. Standard material coating 9. Electrolyte material coating 10. Fire-resistant coating 11 Mounting end of the covering pin L TS Length of the tapered section L TP Length of the tip L MP Length of the main part L 3P Length of the third part D MJ -T Long axis of the tip covering structure D MI -T Short axis of tip covering structure T MAX -T Maximum thickness of the tip coating structure T S -T Small thickness of tip coating structure α Taper angle

Claims

1. An oxygen detection element equipped with a coated pin, The aforementioned covered pin includes a conductive core that extends longitudinally from the main portion to the tip portion, and the tip portion terminates at the tip. (a) The tip portion is the part covered by the tip covering structure (CS-T), The tip covering structure (CS-T) is (i) An inner covering that covers the tip portion and is in direct contact with it, comprising an inner covering including a reference material, (ii) An outer covering that covers the inner covering and is in direct contact with it, the outer covering comprising an electrolyte material, Includes, (b) The main part is the part covered by the main covering structure (CS-M), The main covering structure (CS-M) is (i) An inner covering that covers and is in direct contact with the main part, comprising an inner covering containing a reference material, (ii) An intermediate covering that covers and is in direct contact with the inner covering, and the intermediate covering includes a fire-resistant material, (iii) An outer covering that covers the intermediate covering and is in direct contact with it, the outer covering comprising an electrolyte material, Includes, The conductive core includes a tapered section, the tapered section is a section having a tapered cross-section that narrows toward the tip in the longitudinal direction, and the tapered section extends over at least 10% of the length of the conductive core. The aforementioned tapered section has a length L. TS It has a tip portion with a length L TP It has, L TS ≥ L TP An oxygen detection element characterized by the following:

2. The oxygen detection element according to claim 1, wherein the taper angle of the tapered section is less than 40°.

3. The oxygen detection element according to claim 1, wherein the cross-sectional area of ​​the tip portion is less than 40% of the maximum cross-sectional area of ​​the conductive core.

4. Length L of the aforementioned tip portion TP However, the length L of the tapered section TS The oxygen detection element according to claim 1, wherein the oxygen is at least 20% of the total oxygen.

5. The oxygen detection element according to claim 1, wherein the covering of the covering pin has an elliptical shape, and the covering includes at least the tip covering structure and the main covering structure.

6. The oxygen detection element according to claim 1, wherein the center of the conductive core is eccentrically positioned within the coating, and the coating includes at least the tip coating structure and the main coating structure.

7. The oxygen detection element according to claim 1, wherein the main portion extends over more than 30% of the length of the conductive core.

8. The oxygen detection element according to claim 1, wherein the main coating structure has a minimum thickness greater than that of the tip coating structure.

9. The oxygen detection element according to claim 1, wherein the tip covering structure has a minimum thickness of at least 0.06 mm.

10. The oxygen detection element according to claim 1, wherein the main coating structure has a minimum thickness of at least 0.07 mm.

11. The oxygen detection element according to claim 1, wherein the maximum cross-sectional area of ​​the covering pin is located within the main portion.

12. The conductive core includes a third portion, and the third portion is (i) an intermediate coating that covers the third portion of the conductive core and is in direct contact with it, the intermediate coating comprising a fire-resistant material, (ii) An outer covering that covers at least a portion of the intermediate covering and is in direct contact with it, the outer covering comprising an electrolyte material, The oxygen detection element according to claim 1, wherein the portion is covered with a third coating structure (CS-3) including the above.

13. An immersion sensor comprising the oxygen detection element described in claim 1.

14. A method for measuring the oxygen content of a molten metal using the oxygen detection element described in claim 1.

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