Hydrogen sensor

Abstract

To realize a hydrogen sensor that can measure the hydrogen concentration of melts such as copper on an industrial scale.SOLUTION: A hydrogen sensor comprises: a solid electrolyte sensor sleeve in the form of a bottomed tube having a platinum reference electrode on an inner bottom surface; a protective sleeve that is a hollow member made of a heat-resistant alloy, the protective sleeve comprising a first part into which the sensor sleeve is screwed, and a second part connected to the first part, the second part being smaller in diameter and longer than the first part and forming an internal space continuous with the sensor sleeve; an R thermocouple that is inserted into the internal space while being covered by a protective tube, wherein the Pt-Rh alloy wire and the Pt wire are connected to the reference electrode by contact between the reference electrode and welded portions at one end of the Pt-Rh alloy wire and the Pt wire; and a protective cap made of a co-material of a melt such as copper, which is attached to the outer periphery of the first part, has a conical tip, and covers an end of the sensor sleeve. Alumina powder, glass powder, and an inorganic adhesive are filled between a taper portion provided inside the first part and the sensor sleeve.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a hydrogen sensor for measuring the hydrogen concentration in molten copper or a copper alloy. [Background technology]

[0002] In the copper (Cu) material industry, it is important to measure and control the hydrogen concentration in molten copper. It is known that hydrogen dissolved from the atmosphere is released during solidification, resulting in the formation of solidification defects.

[0003] As a means for measuring the hydrogen concentration in molten copper or copper alloy, a concentration cell type hydrogen sensor using alumina as a solid electrolyte has been reported (see, for example, Non-Patent Documents 1 and 2).

[0004] Non-Patent Document 1 mentions that a hydrogen sensor with a simple structure can be constructed because oxygen ions are almost unable to move in alumina-based proton (hydrogen ion) conductors, and goes on to say that a direct immersion type battery-type hydrogen sensor can be constructed by placing a platinum electrode inside an alumina tube with one end sealed, pumping air into it, and bringing the outside into direct contact with the molten material to serve as a measuring electrode and measuring the electromotive force.

[0005] Also known in this type of hydrogen sensor is a configuration in which a protective tube containing a lead wire is inserted into a cylindrical sensor sleeve made of α-alumina from the open end of the sensor sleeve, and the tip of the lead wire protruding from the protective tube is elastically brought into contact with the inner circumferential surface of the closed end of the sensor sleeve, and a configuration in which a protective cap made of the same material (specifically, copper) is attached to the outside of the closed end of the sensor sleeve for the purposes of mitigating thermal shock when the sensor sleeve is immersed in molten copper and preventing contamination due to adhesion of molten copper slag (see, for example, Patent Documents 1 and 2). Note that this protective cap itself dissolves and disappears in the molten copper after immersion, so does not impair the sensor function.

[0006] Patent Document 1 also discloses an embodiment in which the outer periphery of the sensor sleeve, excluding the tip, is surrounded by an outer protective sleeve made of metal (for example, heat-resistant stainless steel) to prevent damage to a long sensor sleeve during handling, and an embodiment in which a layer filled with ceramic rope, inorganic adhesive, and glass powder is formed in the gap between the sensor sleeve and the outer protective sleeve to seal the intrusion of molten copper. The glass powder softens when the sensor sleeve and the outer protective sleeve are immersed in molten copper, forming a glass layer that seals the intrusion of molten copper through the gap.

[0007] Patent Document 1 further illustrates an embodiment in which a porous platinum electrode is formed by sintering a platinum paste or the like onto the inner surface of a sensor sleeve into which air is fed as a reference gas, and this is used as the reference electrode; an R thermocouple (platinum-rhodium (Pt-Rh): + side - platinum (Pt): - side) is inserted into the sensor sleeve, and the platinum wire of the R thermocouple is connected to the reference electrode as a reference electrode lead wire, while an outer protective sleeve made of conductive heat-resistant stainless steel functions as a measurement electrode.

[0008] In addition, in a hydrogen sensor having the above-mentioned configuration, an embodiment in which a mixed oxide powder is used as the standard electrode active material instead of air is already known (for example, see Non-Patent Document 3).

[0009] In addition, although the objects of measurement in Non-Patent Documents 1 and 2 are Cu and Cu-Ni alloys, attempts have also been made to measure Cu-Fe, Cu-Si, Cu-Zr, and Cu-Ti alloys, as well as Cu-Zn and Cu-Mg alloys (see, for example, Non-Patent Documents 4 and 5). [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2014-160006 A [Patent Document 2] JP 2014-160005 A [Non-patent literature]

[0011] [Non-Patent Document 1] Noriaki Kurita, Yuji Okuyama, Takayuki Sobue, Tomoko Oshima, Koji Kimata, Hiroki Teranishi, Norihiko Taketsu,"Practical application of electromotive force type hydrogen sensor for molten copper", Copper and Copper Alloys, Vol. 53 (2014), p. 171-176 [Non-Patent Document 2] Yuji Okuyama, Noriaki Kurita, Norihiko Taketsu,"Measurement of hydrogen concentration in molten Cu-Ni alloy using battery-type sensor using α-alumina", Copper and Copper Alloys, Vol. 49 (2010), p. 292-296 [Non-Patent Document 3] Noriaki Kurita, Taisuke Ueda, Osamu Kaneko, Masahiro Kamiya, Yuji Okuyama, Norihiko Taketsu, "Search for standard active materials for hydrogen sensors for molten copper using alumina as electrolyte", Proceedings of the Japan Copper Society Annual Conference (2015), p.105-106 [Non-Patent Document 4] Noriaki Kurita, Kazuma Mori, "Evaluation of hydrogen sensors for molten metals in copper alloys", Proceedings of the Japan Copper Society Conference (2019), p.119-120 [Non-Patent Document 5] Noriaki Kurita, Hiroki Sawada, "Evaluation of hydrogen sensors for molten metals in copper alloys (Part 2)", Proceedings of the Japan Copper Society Annual Conference (2022), p.115-116 Summary of the Invention [Problem to be solved by the invention]

[0012] The measurement target with the hydrogen sensor in Non-Patent Documents 4 and 5 is only about 500 g to 700 g of copper alloy melted in an alumina crucible. However, in order to expand the application of measurements with such hydrogen sensors to industrial-scale copper and copper alloys, for example, tens of kg to several tons, the following problems must be solved.

[0013] First, there are challenges associated with making the sensor sleeve long enough to accommodate the size of the industrial melting furnaces in which copper or copper alloys are melted.

[0014] The longer the sensor sleeve is, the more likely it is to be subjected to thermal shock due to the temperature difference between the closed end and the open end of the sensor sleeve, and to crack.

[0015] In addition, when the sensor sleeve is made long, the protective tube (so-called protective sheath for thermocouple) containing the lead wire must also be made long. However, it is not easy to stably and reliably contact the reference electrode lead wire (thermocouple R) protruding from the tip of the long protective tube with the platinum electrode provided on the inner surface of the alumina sensor sleeve.

[0016] Secondly, there is a problem related to the intrusion of molten copper or copper alloy (hereinafter, molten copper, etc.).

[0017] Conventional hydrogen sensors employ a sealing structure in which glass powder is held in place by an inorganic adhesive in the gap between an alumina sensor sleeve and a stainless steel outer protective sleeve in order to prevent the intrusion of molten copper, etc. However, because the inorganic adhesive has a porous structure, there is a problem that when the hydrogen sensor is in use, the softened glass is absorbed into the inorganic adhesive and disappears, allowing molten copper, etc. to break through the sealing structure and infiltrate.

[0018] Once molten copper or other material penetrates into the hydrogen sensor, the sensor sleeve inside the outer protective sleeve is subjected to thermal shock, which may cause a crack. If the molten copper or other material penetrates through the crack and further penetrates into the inner surface of the sensor sleeve and reaches the platinum electrode or lead wire, an electrical short circuit occurs, and it is no longer possible to measure the electromotive force correctly.

[0019] When the tip of the sensor sleeve and the outside of the outer protective sleeve are both immersed in molten copper or the like, Cr, a component element of the stainless steel (e.g., SUS310) that constitutes the outer protective sleeve, naturally oxidizes to form a Cr2O3 protective film on the surface of the outer protective sleeve. Since this protective film plays a role in preventing a short circuit state, immersing the tip of the sensor sleeve and the outside of the outer protective sleeve together in molten copper or the like does not affect the electromotive force measurement. The same applies when a Cr2O3 protective film is provided by thermal spraying on a stainless steel outer protective sleeve.

[0020] Thirdly, there is a problem regarding contamination of the tip of the hydrogen sensor when the sensor sleeve is immersed in molten copper or the like.

[0021] As disclosed in Non-Patent Document 4, when a sensor sleeve with a protective cap made of the same material as the molten copper attached to the tip of the sensor sleeve is immersed in the molten copper, the protective cap instantly dissolves in the molten copper and disappears, mitigating the thermal shock associated with immersion. However, slag of the molten copper may instantly rise to the surface of the sensor sleeve and adhere to the tip of the sensor sleeve. If such adhesion occurs, the correct electromotive force cannot be obtained, and the hydrogen concentration cannot be measured accurately.

[0022] The present invention has been made in consideration of the above-mentioned problems, and aims to realize a hydrogen sensor that can suitably measure hydrogen concentration in copper or copper alloys in-line on an industrial scale. [Means for solving the problem]

[0023] In order to solve the above-mentioned problems, a first aspect of the present invention is a sensor for measuring a concentration of hydrogen contained in a molten material such as copper or a copper alloy in a molten state, the sensor comprising: a sensor sleeve made of a solid electrolyte, in the form of a bottomed tube with one end open, and having a reference electrode made of platinum on the inner bottom surface of the other end; a protective sleeve which is a hollow member made of a heat-resistant alloy, the protective sleeve comprising: a first portion formed by screwing the sensor sleeve inside, and a second portion connected to the first portion, having a hollow rod shape with a smaller diameter and a longer length than the first portion, and forming an inner space continuous with the inside of the sensor sleeve screwed to the first portion; and a welded portion formed by welding one end of a Pt-Rh alloy wire and a Pt wire to each other, the protective sleeve being inserted into the inner space while being covered by a protective tube with the welded portion protruding, and the welded portion comes into contact with the reference electrode, thereby forming a first connection between the Pt-Rh alloy wire and the Pt wire and the first connection between the first connection and the second connection. the sensor sleeve includes an R thermocouple electrically connected to a reference electrode, and a protective cap made of a common material for the molten copper or the like, attached to the outer periphery of the first portion of the protective sleeve, the tip side of which is conical, the tip side of which covers the vicinity of the other end of the sensor sleeve, wherein the inside of the first portion of the protective sleeve has a tapered portion whose opening diameter becomes larger toward the end opposite the second portion, and alumina powder, glass powder, and inorganic adhesive are filled between the tapered portion and the sensor sleeve in this order from the side closest to the screw-connection portion between the sensor sleeve and the protective sleeve, and the hydrogen concentration of the molten copper or the like is measured based on the electromotive force generated between the other end of the Pt wire and the protective sleeve while the reference electrode is in contact with a reference gas introduced into the internal space and at least the other end side of the sensor sleeve is immersed in the molten copper or the like.

[0024] A second aspect of the present invention is a hydrogen sensor according to the first aspect, characterized in that the welded portion of the R thermocouple is in contact with the reference electrode by pressing the protective tube towards the side where the reference electrode is provided, and when the radius of curvature of the welded portion of the R thermocouple is r and the radius of curvature of the inner bottom surface of the sensor sleeve is R, the ratio r / R is 1 / 3 to 2 / 3.

[0025] A third aspect of the present invention is a hydrogen sensor according to the second aspect, characterized in that a biasing metal fitting is fixed to the outer periphery of the protective tube, a terminal block for connecting the Pt-Rh alloy wire and the Pt wire to the outside is abutted and fixed to the opposite side of the second part of the protective sleeve from the first part, a spring is ring-mounted on the protective tube between the biasing metal fitting and the terminal block, the spring is compressed by being sandwiched between the biasing metal fitting and the terminal block, and the protective tube is pressed toward the side where the reference electrode is provided by being biased by the repulsive force of the spring against the compression.

[0026] A fourth aspect of the present invention is a hydrogen sensor according to any one of the first to third aspects, characterized in that a volume ratio of the alumina powder to the glass powder is 1:2 to 1:10.

[0027] A fifth aspect of the present invention is a hydrogen sensor according to any of the first to fourth aspects, characterized in that the protective cap is conical from its tip to a position a predetermined distance away from the area where the reference electrode is formed on the inner bottom surface of the sensor sleeve, and the inclination angle of the conical portion of the protective cap relative to the axial direction of the sensor sleeve is 30° to 45°.

[0028] A sixth aspect of the present invention is a hydrogen sensor according to any of the first to fifth aspects, characterized in that the sensor sleeve has a total length of 100 mm or less, an inner surface depth that is less than 10 times the inner diameter, and the length of the second portion of the protective sleeve is 600 mm or more. Effect of the Invention

[0029] According to the first to sixth aspects of the present invention, a hydrogen sensor is realized that can continuously determine the hydrogen concentration of molten copper or the like on an industrial scale in almost real time. In addition, when the hydrogen sensor is immersed in the molten copper or the like for measurement, slag floating on the surface of the molten copper or the like is preferably prevented from adhering to the sensor sleeve made of a solid electrolyte. Furthermore, the molten copper or the like is preferably prevented from entering the hydrogen sensor during measurement. [Brief description of the drawings]

[0030] [Figure 1] 1 is a schematic cross-sectional view showing the configuration of a hydrogen sensor 100. FIG. [Diagram 2] 1A and 1B are diagrams showing the state of a hydrogen sensor 100 equipped with a conical protective cap 6 before and after it is immersed in a molten material MC such as copper. [Diagram 3] 1 is a diagram showing a hydrogen sensor 100 equipped with a protective cap 6 having a flat tip surface 6f being immersed in a molten material MC such as copper. [Figure 4] FIG. 11 is a graph showing the change over time of electromotive force E in Example 2. [Diagram 5] 5 is a diagram in which the measured values ​​of electromotive force E by the two hydrogen sensors 100 in the six aspects of FIG. 4 are plotted against the common logarithm of the hydrogen concentration calculated based on the electromotive force E. FIG. [Figure 6] FIG. 11 is a diagram showing the change over time of the electromotive force E in Example 3, together with the change over time of the temperature of the object to be measured identified based on the electromotive force Eh. [Figure 7] 7 is a diagram in which the measured values ​​of electromotive force E by the two hydrogen sensors 100 in the five aspects of FIG. 6 are plotted against the common logarithm of the hydrogen concentration calculated based on the electromotive force E. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] <Hydrogen sensor configuration> 1 is a schematic cross-sectional view showing the configuration of a hydrogen sensor 100 according to an embodiment of the present invention. Hydrogen sensor 100 is generally a sensor for measuring the concentration of hydrogen contained in molten copper or copper alloy (hereinafter, these will be collectively referred to as molten copper, etc.).

[0032] The hydrogen sensor 100 mainly comprises a sensor sleeve 1, a protective sleeve 2, a thermocouple protection tube 3, an R thermocouple 4, a reference electrode 5, a protective cap 6, alumina powder 7, glass powder 8, an inorganic adhesive 9, and a terminal block 10.

[0033] The sensor sleeve 1 is a cylindrical member with a bottom made of α-alumina, which is a solid electrolyte. The sensor sleeve 1 extends in the axial direction, which is the direction along the central axis. The α-alumina used is of high purity and meets the JIS PT-0 standard.

[0034] In FIG. 1, the axial direction of the sensor sleeve 1 is the z-axis direction, and the upward direction as viewed in the drawing is the z-axis positive side.

[0035] The sensor sleeve 1 has a male thread portion 1a on the outer circumferential surface at one open end side (the z-axis direction positive side in FIG. 1), and is screwed into the inside of the protective sleeve 2 at the male thread portion 1a. The inner bottom surface 1b of the sensor sleeve 1 is curved (e.g., hemispherical), and a reference electrode 5 is provided on the inner bottom surface 1b in a manner described later. An R thermocouple 4 covered with a thermocouple protection tube 3 is inserted into the inside of the sensor sleeve 1.

[0036] The sensor sleeve 1 has a dimensional relationship in which the overall length is 100 mm or less, and the inner surface depth (depth from the open end to the inner bottom surface 1b on the closed end side) is shorter than 10 times the inner diameter (opening diameter). Examples of such a sensor sleeve 1 include one having an outer diameter of about 28 mm to 9 mm, an inner diameter of about 20 mm to 6 mm, a thickness of about 4 mm to 1 mm, an overall length of about 100 mm to 30 mm, an inner surface depth of about 99 mm to 26 mm, and a curvature radius R of the inner bottom surface 1b of about 10 mm to 3 mm. For example, a sensor sleeve 1 having an outer diameter / inner diameter=10 mm / 6.5 mm, a length of 40 mm, and an inner surface depth of 38 mm can be used. In such a case, the male screw portion 1a may be, for example, an M12 screw.

[0037] The protective sleeve 2 is a member that protects the sensor sleeve 1 placed inside it, and the R thermocouple 4 that is further inserted inside the sensor sleeve 1 and covered with a thermocouple protection tube 3. The protective sleeve 2 also functions as a measurement electrode in the hydrogen sensor 100. Furthermore, in the case of the hydrogen sensor 100 according to this embodiment, the protective sleeve 2 also plays a role in ensuring the length of the hydrogen sensor 100 according to the scale of the molten material, such as copper, that is the object to be measured.

[0038] The protective sleeve 2 is made of a heat-resistant alloy and has a configuration in which a hollow thick tube section 2α, into which the sensor sleeve 1 is screwed, and a hollow rod-shaped straight tube section 2β, which is smaller in diameter and longer than the thick tube section 2α, are coaxially connected by argon welding. When the sensor sleeve 1 is screwed into the protective sleeve 2, the sensor sleeve 1 and the protective sleeve 2 are coaxial. In other words, the axial direction of the sensor sleeve 1 is also the axial direction of the protective sleeve 2.

[0039] Moreover, inside the protective sleeve 2, a continuous internal space SP is formed from the inside of the sensor sleeve 1 to the inside of the straight tube portion 2β. A thermocouple protection tube 3 covering the R thermocouple 4 is inserted into the continuous internal space SP and is disposed approximately coaxially with the sensor sleeve 1 and the protective sleeve 2.

[0040] The heat-resistant alloy used for the protective sleeve 2 is preferably SUS310, but is not limited to this, and any heat-resistant alloy that forms a chromium-based protective oxide coating can be used.

[0041] When the hydrogen sensor 100 is used, the area up to the middle of the thick tube section 2α on the side where the sensor sleeve 1 is provided (for example, the area below the dotted line L in Figure 1) is immersed in a molten material such as copper.

[0042] A female thread portion 2a is provided on the inner peripheral surface of the central portion of the thick tube portion 2α, and the male thread portion 1a of the sensor sleeve 1 is screwed into the female thread portion 2a, thereby screwing the sensor sleeve 1 into the protective sleeve 2. The portion where the sensor sleeve 1 is screwed into the protective sleeve 2 by screwing the male thread portion 1a into the female thread portion 2a is also referred to as the screw region.

[0043] Additionally, on the inside of the thick tube section 2α, a truncated cone-shaped tapered section 2b is provided, the opening diameter of which increases from the screw region toward the end 2c of the protective sleeve 2 on the opposite side to the straight tube section 2β (the negative side in the z-axis direction in FIG. 1). The tapered section 2b is configured to be more spaced apart from the sensor sleeve 1 as it approaches the end 2c. The female thread section 2a and the tapered section 2b have approximately the same length in the axial direction (the z-axis direction in FIG. 1).

[0044] The region between the tapered portion 2b and the sensor sleeve 1 is filled with a sealing material to prevent the intrusion of molten copper or the like during use of the hydrogen sensor 100. This point will be described later.

[0045] On the other hand, a terminal block 10 is fixed in contact with the end 2d of the protective sleeve 2 on the straight tube section 2β side. The terminal block 10 has connection terminals 10a, 10b on one main surface, which are connected to the R thermocouple 4 and external connection wires w1, w2. The other main surface, which is the back surface of the terminal block 10 (the surface on the negative side in the z-axis direction in FIG. 1), is fixed in contact with the end 2d of the protective sleeve 2 so as to be detachable.

[0046] The straight tube section 2β is longer than the thick tube section 2α and the sensor sleeve 1, and more specifically, is provided at a length such that the terminal block 10 is sufficiently separated from the liquid surface of the molten copper or the like when the molten copper or the like to be measured is stored in a storage container. For example, when measuring a large amount of molten copper or the like on an industrial scale during a manufacturing process for copper plates or copper alloys, it is desirable to ensure a sufficient distance between the tip of the sensor sleeve 1 and the terminal block 10 in consideration of the ease of handling of the hydrogen sensor 100 and the ambient temperature, and the straight tube section 2β is provided at a length that allows such a distance to be ensured. For example, the straight tube section 2β is provided so that the length of the protective sleeve 2 is 600 mm to 1000 mm or more.

[0047] Note that, instead of providing the protective sleeve 2 with a straight tube portion 2β, the embodiment of lengthening the sensor sleeve 1 is not preferable because it is difficult to handle the sensor sleeve 1 in the first place, and the sensor sleeve 1 is prone to cracking due to thermal shock caused by the temperature difference between both ends of the sensor sleeve 1. In addition, it is not easy to form the reference electrode 5 inside the elongated sensor sleeve 1, and further, it is not easy to insert the thermocouple protective tube 3 covering the R thermocouple 4 and stably contact its tip with the reference electrode 5 in the embodiment described below.

[0048] In the hydrogen sensor 100 of this embodiment, the sensor sleeve 1 remains short enough to fit into the thick tube section 2α that is immersed in the molten copper or the like, and instead a long straight tube section 2β that is coaxial with the sensor sleeve 1 extends from the thick tube section 2α, making it possible to suitably measure large amounts of molten copper or the like on an industrial scale.

[0049] The R thermocouple 4 is configured by welding one end of each of a Pt-Rh alloy wire 4a and a Pt wire 4b. The R thermocouple 4 is generally intended to measure the temperature at the welded portion 4c based on the electromotive force (potential difference) generated between the Pt-Rh alloy wire 4a and the Pt wire 4b. However, as described later, in this embodiment, the Pt wire 4b and the welded portion 4c of the R thermocouple 4 are also used to measure the hydrogen concentration in molten copper or the like. In this case, the Pt wire 4b functions as a reference electrode lead wire. The welded portion 4c is formed into an approximately spherical shape with a curvature radius r of about 6.7 mm to 2 mm.

[0050] Most of the R thermocouple 4 is covered with a ceramic (e.g., commercially available arsinth) thermocouple protection tube 3 while maintaining insulation between the Pt-Rh alloy wire 4a and the Pt wire 4b. A commercially available thermocouple protection sheath or the like can be used for the thermocouple protection tube 3. For example, even if the thermocouple protection tube 3 has four holes, only two of the holes need to be used.

[0051] However, the vicinity of the welded portion 4c protrudes from one end 3a (the end on the negative side in the z-axis direction in Figure 1) of the thermocouple protection tube 3, and the welded portion 4c is in contact with a reference electrode 5 provided on the curved inner bottom surface 1b of the sensor sleeve 1.

[0052] The reference electrode 5 is a porous electrode made of platinum. The reference electrode 5 can be formed, for example, by applying a high-purity platinum paste having an appropriate viscosity to the curved inner bottom surface 1b with a brush, and then sintering it in an electric furnace. The high-purity platinum paste is preferably one that does not contain other metals such as lead or inorganic oxides, and the diluent (dilution solvent) for adjusting the viscosity volatilizes completely during firing. For example, platinum paste (No. 8103) manufactured by Tokuriki Honten can be suitably used. As the diluent, for example, a commercially available diluent such as a cyclohexanone solution can be used.

[0053] On the other hand, the thermocouple protection tube 3 passes through a through hole 10h provided in the terminal block 10 near the other end portion 3b (the end portion on the positive side in the z-axis direction in FIG. 1), and from the other end portion 3b, portions of the Pt-Rh alloy wire 4a and the Pt wire 4b opposite to the welded portion 4c are exposed and are connected to a connection terminal (anode terminal) 10a and a connection terminal (negative terminal) 10b provided on the terminal block 10, respectively.

[0054] Furthermore, a biasing metal fitting 11 is fixed with cement 12 to the outer periphery of the thermocouple protection tube 3 at a predetermined location inside the straight tube portion 2β. A spring 13 is ring-mounted on the outside of the thermocouple protection tube 3 extending along the z-axis direction between the biasing metal fitting 11 and the terminal block 10. The spring 13 is compressed in the z-axis direction by being sandwiched between the biasing metal fitting 11 and the terminal block 10, and a repulsive force against the compression acts via the biasing metal fitting 11, biasing the thermocouple protection tube 3 covering the R thermocouple 4 in the negative z-axis direction where the reference electrode 5 is provided. The pressure caused by the biasing force holds the thermocouple protection tube 3 in the internal space SP, and the contact (conduction) of the welded portion 4c of the R thermocouple 4 covered by the thermocouple protection tube 3 with the reference electrode 5 is suitably and reliably maintained.

[0055] The thermocouple protection tube 3 is inserted into the internal space SP during the assembly of the hydrogen sensor 100, but as described above, the straight tube section 2β of the protective sleeve 2 is longer than the thick tube section 2α and the sensor sleeve 1, and the thermocouple protection tube 3 is held in the internal space SP only by the force of the spring 13. Therefore, it is not easy to insert and hold the thermocouple protection tube 3 so that its extension direction completely coincides with the axial direction of the sensor sleeve 1 and the protective sleeve 2, and it may be held in a state slightly inclined with respect to the axial direction. Even in such an inclined state, from the viewpoint of ensuring stable contact between the welded portion 4c of the R thermocouple 4 and the reference electrode 5, it is preferable that the ratio r / R of the radius of curvature r of the outer surface of the welded portion 4c of the R thermocouple 4 to the radius of curvature R of the inner bottom surface 1b of the sensor sleeve 1 on which the reference electrode 5 is provided be approximately 1 / 3 to 2 / 3, and that the reference electrode 5 be provided over the entire inner bottom surface 1b so that its maximum thickness is 1 μm or less and the radius of curvature of its surface is equal to the radius of curvature R of the inner bottom surface 1b.

[0056] For example, if the ratio r / R exceeds 2 / 3, in other words, if the difference between the radius of curvature r of the outer surface of the welded portion 4c of the R thermocouple 4 and the radius of curvature R of the inner bottom surface 1b of the sensor sleeve 1 is small, depending on the degree of inclination of the thermocouple protection tube 3, the welded portion 4c of the R thermocouple 4 may not reach the inner bottom surface 1b and may not come into contact with the reference electrode 5. In addition, it is difficult to insert the thermocouple protection tube 3 in the first place, which is not preferable.

[0057] Furthermore, if the ratio r / R falls below 1 / 3 due to a small radius of curvature of the welded portion 4c, this is undesirable because it may cause disconnection of the welded portion 4c under the biasing force of the spring 13, or contact failure due to bending of the Pt-Rh alloy wire 4a or Pt wire 4b exposed near the welded portion 4c. Note that a case where the ratio r / R falls below 1 / 3 due to a large radius of curvature R of the inner bottom surface 1b corresponds to a case where the sensor sleeve 1 is excessively thick, and it is considered that there is little need to use such a sensor sleeve 1.

[0058] A protective cap 6 is attached to the outer periphery of the end 2c side of the protective sleeve 2, covering the vicinity of the tip 1c (the end on the negative side in the z-axis direction in FIG. 1) of the sensor sleeve 1. The protective cap 6 is made of the same material as the molten copper or the like that is the measurement target of the hydrogen sensor 100, and is provided for the purpose of mitigating the thermal shock that acts on the sensor sleeve 1 when the side of the hydrogen sensor 100 that has the sensor sleeve 1 is immersed in the molten copper or the like for measurement.

[0059] Roughly speaking, the moment the hydrogen sensor 100 equipped with the protective cap 6 is immersed in a molten material such as copper for measurement, the sensor sleeve 1 does not come into direct contact with the molten material such as copper; instead, the protective cap 6 provided on its outside comes into contact with the material. This reduces the thermal shock acting on the sensor sleeve 1 during immersion. Note that the protective cap 6 that comes into contact with the molten material such as copper instantly dissolves and disappears, so there is no disruption to the measurement. Note that this means that a new protective cap 6 can be attached each time a measurement is performed.

[0060] The protective cap 6 is attached, for example, by screwing a screw (not shown) provided on its inner peripheral surface into a screw (not shown) provided on the outer peripheral surface (the outer surface parallel to the z-axis direction in FIG. 1) in the vicinity of the end 2c of the protective sleeve 2. Note that the protective cap 6 may be fixed to the protective sleeve 2 by a means other than such screwing.

[0061] In the hydrogen sensor 100 according to this embodiment, the tip 6a of the protective cap 6 (the end on the z-axis direction negative side in FIG. 1) is conical. More specifically, the conical portion of the protective cap 6 is inclined at an inclination angle of 30° to 45° with respect to the axial direction. Furthermore, the conical portion extends from the tip 6a to a position (the position on the z-axis direction positive side in FIG. 1) that is separated by a predetermined distance d from the area where the reference electrode 5 is formed on the inner bottom surface 1b of the sensor sleeve 1. This is intended to prevent slag floating on the surface of the molten material such as copper from adhering to the sensor sleeve 1 (particularly in the vicinity of the reference electrode 5) during measurement. The distance d is, for example, 30 mm to 5 mm.

[0062] This is shown in schematic diagrams in Figures 2 and 3. Figure 2 shows the hydrogen sensor 100 equipped with a conical protective cap 6 according to this embodiment before and after it is immersed in a molten material MC such as copper. However, the illustration of the hydrogen sensor 100 is simplified, and only the sensor sleeve 1 and the protective cap 6 are shown.

[0063] As shown in Fig. 2(a), slag SG of impurities or the like usually floats in a film on the surface of the molten copper or the like MC. In the case of the hydrogen sensor 100 according to this embodiment, the protective cap 6 is cone-shaped, so that when the hydrogen sensor 100 is immersed, the protective cap 6 breaks through the film of slag SG while covering the sensor sleeve 1 and penetrates into the molten copper or the like MC, as shown in Fig. 2(b). Therefore, as shown in Fig. 2(c), even if the protective cap 6 melts and disappears, the slag SG floating on the surface of the molten copper or the like MC does not adhere to the tip 1c of the sensor sleeve 1 that has already penetrated into the molten copper or the like MC.

[0064] On the other hand, FIG. 3 shows a state in which a conventionally used hydrogen sensor 100 equipped with a protective cap 6 having a flat tip surface 6f is immersed in a molten material MC such as copper.

[0065] In the case of such a hydrogen sensor 100, as shown in Fig. 3(a), the protective cap 6 penetrates into the molten copper or the like MC with slag SG adhering to the tip surface 6f during immersion. Therefore, as shown in Fig. 3(b), after the protective cap 6 melts and dissipates, the slag SG that has already penetrated into the molten copper or the like MC may adhere to the tip portion 1c of the sensor sleeve 1.

[0066] Comparing FIG. 2 with FIG. 3, it can be seen that the conical protective cap 6 employed in the hydrogen sensor 100 according to the present embodiment is suitable for preventing adhesion of slag to the sensor sleeve 1.

[0067] As described above, the region between the tapered portion 2b of the thick tube portion 2α of the protective sleeve 2 and the sensor sleeve 1 is filled with a sealant. Specifically, from the side closer to the screw region, alumina powder 7, glass powder 8, and inorganic adhesive 9 are filled as sealants.

[0068] The alumina powder 7 and the glass powder 8 preferably have a particle size distribution in which D50 is 10 μm or less, more preferably have a particle size distribution in which D50 is 3 μm or less, and even more preferably have a particle size distribution in which D50 is 1 μm or less.

[0069] As the alumina powder 7, a commercially available product having a particle size of reagent grade can be used.

[0070] Also, it is preferable to use glass powder having a thermal expansion coefficient close to that of alumina and a softening point about 200° C. to 300° C. lower than the melting points of copper and copper alloys (1100° C. to 1200° C.) as the glass powder 8. An example of such glass powder is powder glass GA manufactured by Nippon Electric Glass Co., Ltd.

[0071] The alumina powder 7 and the glass powder 8 are filled at a volume ratio (bulk ratio) of 1:2 to 1:10.

[0072] On the other hand, the inorganic adhesive 9 is not particularly limited as long as it has heat resistance at the melting point of copper and copper alloys, has a thermal expansion coefficient similar to that of α-alumina, and is in a paste form (has a suitable viscosity) when filled. For example, Aron Ceramic D manufactured by Toa Gosei Co., Ltd. can be used.

[0073] The inorganic adhesive 9 is applied so as to leave no gap between the tapered portion 2b and the sensor sleeve 1 on the end 2c side of the protective sleeve 2 so that the previously filled alumina powder 7 and glass powder 8 do not fall off. In this case, the inorganic adhesive 9 may be applied so as to overflow from the end 2c of the protective sleeve 2 as shown in FIG.

[0074] When the hydrogen sensor 100 is used, the glass powder 8 softens and melts to form a glass layer. Meanwhile, the inorganic adhesive 9 becomes porous as the organic components volatilize during use. Therefore, the softened glass penetrates into the porous inorganic adhesive 9. However, in the hydrogen sensor 100 according to this embodiment, the alumina powder 7 functions as the final sealing layer, and the filling ratio of the glass powder 8 to the alumina powder 7 is set to be large enough so that the glass powder 8 is not absorbed and lost by the inorganic adhesive 9, thereby suitably suppressing the intrusion of molten copper and the like.

[0075] In addition, in order to improve the airtightness and sealing property between the sensor sleeve 1 and the protective sleeve 2, an inorganic adhesive 9b may be applied in advance to the area near the tapered portion 2b of the screwed portion between the male threaded portion 1a and the female threaded portion 2a prior to screwing.

[0076] The hydrogen sensor 100 further includes a voltage measuring device 20 and a controller 30 as components for identifying the hydrogen concentration of the molten material such as copper.

[0077] The voltage measuring device 20 is configured to be capable of continuously measuring the voltage (electromotive force) Eh generated between the anode terminal 10a of the terminal block 10 to which the Pt-Rh alloy wire 4a of the R thermocouple 4 is connected and the negative terminal 10b of the terminal block 10 to which the Pt wire 4b is connected, and the voltage (electromotive force E) generated between the protective sleeve 2 functioning as a measurement electrode and the Pt wire 4b which also functions as a reference electrode lead wire by contacting the welded portion 4c with the reference electrode 5. Connection wires w1, w2, and w3 for enabling the measurement of each electromotive force are provided between the terminals 20a, 20b, and 20c of the voltage measuring device 20 and the anode terminal 10a, the negative terminal 10b, and the protective sleeve 2, respectively. Note that the connection wire w3 is connected to a portion of the protective sleeve 2 that is not immersed in the molten material such as copper.

[0078] The respective measured values ​​are provided to the controller 30. As the voltage measuring device 20, a commercially available device can be used.

[0079] The controller 30 determines the hydrogen concentration of the molten copper or the like based on the electromotive forces Eh and E provided by the voltage measuring device 20. Various numerical data, conversion data, and the like required for such determination are stored in advance in the controller 30. The controller 30 can be realized by a computer (not shown) equipped with a CPU, ROM, RAM, and the like, and may be, for example, a commercially available personal computer. The previously stored measurement program is loaded into the CPU and executed, thereby calculating the hydrogen concentration of the molten copper or the like based on the values ​​of the electromotive forces Eh and E obtained from the voltage measuring device 20.

[0080] <Hydrogen concentration measurement> When the hydrogen sensor 100 having the above configuration is used to measure the hydrogen concentration in a molten material such as copper, a predetermined area of ​​the hydrogen sensor 100 on the side where the sensor sleeve 1 and protective cap 6 are provided (for example, the area below the dashed dotted line L in FIG. 1) is immersed in the molten material such as copper. As described above, the hydrogen sensor 100 used has a length that matches the scale of the molten material such as copper to be measured.

[0081] Meanwhile, air is introduced as a reference gas (e.g., air) G into the internal space SP through the thermocouple protection tube 3. This keeps the reference electrode 5 provided on the inner bottom surface 1b of the sensor sleeve 1 in contact with the reference gas G.

[0082] When the protective cap 6 melts and dissolves due to immersion in the molten copper or the like, and the sensor sleeve 1, which is a solid electrolyte, is in contact with the molten copper or the like, a battery (hydrogen concentration cell) having the following configuration is formed between the protective sleeve 2, which serves as a measurement electrode, and the reference electrode 5.

[0083] Protective sleeve 2 (measurement electrode)--molten copper or the like--sensor sleeve 1 (solid electrolyte)--reference electrode 5 (-welded part 4c--Pt wire 4b).

[0084] At this time, an electromotive force E is generated between the protective sleeve 2, which is the measurement electrode, and the reference electrode 5 (and further the Pt wire 4b connected via the welded part 4c). If the activity of hydrogen contained in the molten copper or the like is a, the electromotive force E can be expressed by the following relational formula.

[0085] E=-(RT / F)·ln[A / {a 1 / 2 +A}] ···(1) where R is the gas constant 8.31 J / (unit: K mol), T is the temperature of the molten material (unit: K), and F is the Faraday constant 9.65×104 (unit: C / mol).

[0086] Moreover, it has been experimentally found that the following relationship exists between A and temperature T:

[0087] lnA=-1.96×10 4 / T+10.5 ···(2) Furthermore, the activity a can be expressed as follows using the hydrogen concentration C and the existing activity coefficient γ:

[0088] a = γC (3) Therefore, by measuring the temperature of the molten copper or the like and the electromotive force between the protective sleeve 2 and the Pt wire 4b connected to the reference electrode 5, the hydrogen concentration of the molten copper or the like can be calculated based on equations (1) to (3).

[0089] Specifically, the controller 30 stores in advance the constant values ​​of the equations (1) to (3) and conversion data or conversion equations for converting the electromotive force Eh into temperature.

[0090] In this case, the electromotive force Eh corresponds to the electromotive force generated in the R thermocouple 4 according to the temperature of the welded portion 4c. The temperature of the welded portion 4c is determined almost in real time. The temperature converted from the electromotive force Eh can be regarded as the temperature of the molten material such as copper at the time of measurement. That is, the controller 30 determines the value of T in the formulas (1) and (2) almost in real time based on the value of the electromotive force Eh acquired from the voltage measuring device 20.

[0091] The controller 30 further determines the value of A in (2) corresponding to the value of T in almost real time by substituting the obtained value of T into the equation (2).

[0092] On the other hand, the value of electromotive force E that the controller 30 obtains from the voltage measuring device 20 is nothing but the value of the left side of equation (1). The controller 30 calculates the activity a from (1) based on the value of electromotive force E and the already specified values ​​of T and A, and further calculates the hydrogen concentration C using equation (3).

[0093] That is, in the hydrogen sensor 100 of this embodiment, the hydrogen concentration in a molten material such as copper can be determined continuously and almost in real time by acquiring the electromotive force Eh and the electromotive force E by the voltage measuring device 20 and performing calculations in the controller 30 based on these values ​​and on the equations (1) to (3).

[0094] As described above, the hydrogen sensor according to the present embodiment can continuously determine the hydrogen concentration of molten copper or the like on an industrial scale in almost real time. That is, the hydrogen concentration can be suitably measured not only in simple Cu, but also in alloys such as Cu-Fe, Cu-Si, Cu-Zr, Cu-Ti, Cu-Zn, and Cu-Mg.

[0095] In addition, when the hydrogen sensor is immersed in molten copper or the like for measurement, slag floating on the surface of the molten copper or the like is preferably prevented from adhering to the sensor sleeve of the hydrogen sensor made of a solid electrolyte. Furthermore, the intrusion of molten copper or the like into the hydrogen sensor during measurement is preferably prevented.

[0096] <Modification> In the above-described embodiment, the protective sleeve 2 is constructed by joining the thick tube section 2α and the straight tube section 2β by argon welding. However, instead of this, the protective sleeve 2 may be constructed of a straight tube over its entire length as long as it is possible to provide a tapered section 2b.

[0097] Also, instead of argon welding the thick tube portion 2α and the straight tube portion 2β, they may be connected by screws or the like made of a common material such as molten copper. In such a case, it is also possible to connect straight tube portions 2β of different lengths depending on the usage mode.

[0098] In the above embodiment, the alumina powder 7, the glass powder 8, and the inorganic adhesive 9 are filled in this order from the side closest to the screw region of the sealing region, but an inorganic adhesive may be further filled in the region closest to the sealing region. In such a case, it is possible to more reliably prevent the intrusion of molten copper or the like.

[0099] Furthermore, it is not essential to measure the temperature of the molten material such as copper using the R thermocouple, and the temperature may be measured using a separately provided temperature sensor or the like. EXAMPLES

[0100] Example 1 The hydrogen sensor 100 was used to continuously measure the electromotive force E for 5 hours for 15 kg of oxygen-free copper melted in a storage container. The sensor sleeve 1 had an outer diameter of 10 mm, an inner diameter of 6.5 mm, a length of 40 mm, an inner depth of 38 mm, and a radius of curvature R of the inner bottom surface 1b of 3 mm. The protective sleeve 2 was made of SUS310. The radius of curvature r of the welded portion 4c was 2 mm. The volume ratio of the alumina powder 7 to the glass powder 8 was 1:4. The inclination angle of the protective cap 6 was 45°.

[0101] The electromotive force could be measured continuously without any slag contamination of the tip 1c of the sensor sleeve 1. After the measurement, a portion of the hydrogen sensor 100 including the sensor sleeve 1 and the thick tube portion 2α of the protective sleeve 2 was cut and observed at a cross section passing through the axial portion. No intrusion of molten copper into the screw region was confirmed.

[0102] Comparative Example 1 A hydrogen sensor having the configuration disclosed in Patent Document 1 was fabricated, and the electromotive force E was measured continuously for 5 hours in the same manner as in Example 1.

[0103] As a result, the tip of the solid electrolyte, which corresponds to the sensor sleeve 1, became contaminated with slag, and it was not possible to continuously measure the electromotive force. After the measurement, the hydrogen sensor was cut at a cross section passing through the axis and observed. It was confirmed that molten copper had broken the sealing part and entered the inside of the sensor, causing a short circuit.

[0104] Example 2 The electromotive force E of 15 kg of Cu-2.4 wt% Fe alloy melted in a storage vessel was measured continuously for 50,000 seconds using two different hydrogen sensors 100, with the hydrogen concentration intentionally varied. The configuration of each hydrogen sensor 100 was the same as in Example 1. The temperature of the Cu-2.4 wt% Fe alloy was set to 1150°C.

[0105] Hydrogen was added to the Cu-2.4wt%Fe alloy by introducing a hydrogen-argon mixed gas into a storage vessel, contacting the molten Cu-2.4wt%Fe alloy, and diffusing hydrogen from the mixed gas. At this time, the hydrogen concentration in the Cu-2.4wt%Fe alloy was varied by changing the hydrogen concentration in the mixed gas to different known values.

[0106] Fig. 4 is a diagram showing the change over time of electromotive force E in this embodiment. Fig. 4 also shows the hydrogen concentration in a hydrogen-argon mixed gas (hereinafter, contact mixed gas) with a known hydrogen concentration that was brought into contact with a Cu-2.4 wt% Fe alloy. As can be seen from Fig. 4, there was almost no difference between the measurements of the two hydrogen sensors 100, and both changed in accordance with the change in hydrogen concentration in the contact mixed gas.

[0107] 5 is a plot of the measured values ​​of electromotive force E by two hydrogen sensors 100 at six points indicated by circles 1 to 6 in FIG. 4 where the hydrogen concentration in the contact mixed gas is different, against the common logarithm of the hydrogen concentration (p'H2 in FIG. 5) calculated based on the electromotive force E. However, since there was almost no difference between the measured values ​​of the two hydrogen sensors 100 as described above, there is almost no difference between them in the plot in FIG. 5. FIG. 5 also shows a curve showing the theoretical dependence of electromotive force E on hydrogen concentration.

[0108] 5 shows that electromotive force E close to the theoretical value was obtained from both hydrogen sensors 100. Note that the theoretical hydrogen concentration at point 5, where the hydrogen concentration in the contact mixed gas was 10%, was 1.4 ppm, but the measured value was 1.8 ppm.

[0109] Example 3 The electromotive force E of 15 kg of Cu-1.0 wt% Si alloy melted in a storage vessel was measured continuously for 18,000 seconds using two different hydrogen sensors 100, with the hydrogen concentration intentionally varied. The configuration of each hydrogen sensor 100 was the same as in Example 1. The temperature of the Cu-1.0 wt% Si alloy was set to 1150°C.

[0110] FIG. 6 shows the time change of the electromotive force E in this embodiment together with the time change of the temperature of the Cu-1.0 wt% Si alloy, which is the measurement object identified based on the electromotive force Eh. In FIG. 6, the hydrogen concentration in the hydrogen-argon mixed gas contacted with the Cu-1.0 wt% Si alloy in the storage container is also shown, as in FIG. 4. As can be seen from FIG. 6, the temperature of the Cu-1.0 wt% Si alloy measured by the hydrogen sensor 100 was 1150° C. immediately after the start of the measurement. Moreover, the measured values ​​of the two hydrogen sensors 100 were generally similar, and both changed following the change in the hydrogen concentration in the contact mixed gas.

[0111] 7 is a diagram in which the measured values ​​of electromotive force E by two hydrogen sensors 100 at five points indicated by circles 1 to 5 in FIG. 6, where the hydrogen concentration values ​​in the contact mixed gas are different, are plotted against the common logarithm of the hydrogen concentration (p'H2 in FIG. 7) calculated based on the electromotive force E. FIG. 7 also shows a curve showing the theoretical dependence of electromotive force E on hydrogen concentration.

[0112] It can be seen from FIG. 7 that both hydrogen sensors 100 provide electromotive forces E that are roughly close to the theoretical value. [Explanation of symbols]

[0113] 1 Sensor sleeve 1a Male thread (of sensor sleeve) 1b Inner bottom surface (of sensor sleeve) 1c (Sensor sleeve) tip 2 Protective sleeve 2α (Protective sleeve) thick tube section 2β (Protective sleeve) straight tube section 2a (Protective sleeve) female thread 2b Tapered part (of protective sleeve) 3 Thermocouple protection tube 4 R thermocouple 4a (R thermocouple) Pt-Rh alloy wire 4b Pt wire (R thermocouple) 4c (R thermocouple) weld 5 Reference electrode 6 Protective cap 7. Alumina Powder 8. Glass Powder 9, 9b Inorganic adhesives 10 Terminal block 11. Biasing fitting 13. Spring 20 Voltage measuring device 100 Hydrogen Sensor MC Copper and other molten materials SG Slug SP Inner Space w1, w2, w3 connection wiring

Claims

1. A sensor for measuring the concentration of hydrogen contained in a molten material such as copper or a copper alloy in a molten state, a sensor sleeve made of a solid electrolyte, in the form of a tube with one end open and a reference electrode made of platinum on the inner bottom surface of the other end; A hollow member made of a heat-resistant alloy, a first portion having the sensor sleeve threadably engaged therewith; a second part connected to the first part, having a hollow rod shape smaller in diameter and longer than the first part, and forming an internal space continuing from the inside of the sensor sleeve screwed to the first part; A protective sleeve comprising: an R thermocouple including a welded portion formed by welding one end of a Pt-Rh alloy wire and one end of a Pt wire, the R thermocouple being inserted into the inner space while being covered with a protective tube with the welded portion projecting, and the Pt-Rh alloy wire and the Pt wire being electrically connected to the reference electrode by contacting the welded portion with the reference electrode; a protective cap made of the same material as the molten material such as copper, attached to the outer periphery of the first portion of the protective sleeve, the protective cap having a conical tip side, the protective cap covering the vicinity of the other end of the sensor sleeve; Equipped with The inside of the first portion of the protective sleeve has a tapered portion whose opening diameter becomes larger toward the end opposite the second portion, alumina powder, glass powder, and an inorganic adhesive are filled between the tapered portion and the sensor sleeve in this order from a side closer to a screw-fitting portion between the sensor sleeve and the protective sleeve, a hydrogen concentration in the molten copper or the like is measured based on an electromotive force generated between the other end of the Pt wire and the protective sleeve in a state where at least the other end side of the sensor sleeve is immersed in the molten copper or the like while the reference electrode is brought into contact with a reference gas introduced into the internal space; A hydrogen sensor comprising:

2. 2. The hydrogen sensor according to claim 1, the welded portion of the R thermocouple is in contact with the reference electrode by pressing the protective tube toward the side where the reference electrode is provided, When the radius of curvature of the welded portion of the R thermocouple is r and the radius of curvature of the inner bottom surface of the sensor sleeve is R, the ratio r / R is 1 / 3 to 2 / 3. A hydrogen sensor comprising:

3. 3. The hydrogen sensor according to claim 2, A biasing metal fitting is fixed to the outer periphery of the protective tube, A terminal block for connecting the Pt-Rh alloy wire and the Pt wire to an outside is fixed to the second portion of the protective sleeve on the opposite side to the first portion, A spring is attached to the protective tube between the biasing metal fitting and the terminal block, The spring is compressed by being sandwiched between the biasing metal fitting and the terminal block, The protective tube is pressed toward the side where the reference electrode is provided by being biased by a repulsive force of the spring against the compression. A hydrogen sensor comprising:

4. 3. The hydrogen sensor according to claim 1, The volume ratio of the alumina powder to the glass powder is 1:2 to 1:10; A hydrogen sensor comprising:

5. 3. The hydrogen sensor according to claim 1, the protective cap has a conical shape from its tip to a position spaced a predetermined distance from an area where the reference electrode is formed on the inner bottom surface of the sensor sleeve, The inclination angle of the conical portion of the protective cap with respect to the axial direction of the sensor sleeve is 30° to 45°. A hydrogen sensor comprising:

6. 3. The hydrogen sensor according to claim 1, The sensor sleeve has a total length of 100 mm or less and an inner surface depth of less than 10 times the inner diameter. The length of the second portion of the protective sleeve is 600 mm or more. A hydrogen sensor comprising:

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