JP6504829B2 - thermocouple - Google Patents

Description

  The present invention relates to a thermocouple, and more particularly to a thermocouple in which a conductive ceramic is used as a material constituting a temperature measurement contact of the thermocouple.

  For example, there are direct temperature measurement and indirect temperature measurement as temperature measurement methods for high-temperature molten metals exceeding 1500 ° C., such as steel refining. Generally as a direct temperature measurement, the method of loading a thermocouple in a heat resistant protective tube, and immersing in a molten metal with a heat resistant protective tube is taken. This is because it is difficult to measure the molten metal using an indirect thermometer such as a radiation thermometer because the surface of the molten metal is thickly covered with an oxide called slag at the time of metal refining .

In the case of direct temperature measurement, a refractory is generally used as the heat-resistant protective tube. For example, alumina (Al ₂ O ₃ ), quartz or the like is used as the refractory.

  JP 2001-153730 A describes a protective tube for covering a thermocouple, and a ceramic protective tube made of alumina.

JP 2001-153730 A

  However, when the temperature of the high-temperature molten metal is continuously measured for a long time, the thickness of the heat-resistant protective tube needs to be as thick as several cm in order to obtain sufficient durability. In this case, the temperature measured by the thermocouple loaded in the heat resistant protective tube is the temperature at the temperature measuring junction after heat transfer from the molten metal to the temperature measuring portion (temperature measuring junction) of the thermocouple via the refractory. Therefore, even if a material having a relatively high thermal conductivity, such as alumina graphite, is used as the refractory, there is a problem that it becomes lower than the actual temperature of the molten metal. Further, in this case, since a time delay is caused by heat transfer, it is not possible to quickly follow the time-dependent change of the temperature of the molten metal, and it is difficult to perform real-time temperature measurement accurately.

  Further, in the case of direct temperature measurement of high-temperature molten metal with high accuracy, for example, a method of using a thin quartz tube having a thickness of several mm as a heat-resistant protective tube is adopted. In this case, although the temperature can be measured with high accuracy, the useful life of the heat-resistant protective tube is as short as several seconds, which is what is called spot temperature measurement. Therefore, in order to observe the time-dependent change of molten metal, it is necessary to measure repeatedly. Moreover, although a thermocouple of platinum (Pt) -platinum rhodium (PtRh), which is generally R-typed according to JIS standards, is used for these temperature measurement, such a thermocouple is expensive and the temperature measurement cost is high. .

  The present invention has been made to solve the problems as described above. The main object of the present invention is to provide a thermocouple capable of performing temperature measurement of a material in a high temperature range of 1500 ° C. or higher with high accuracy and at low cost.

  A thermocouple according to the present invention includes a first conductive member and a second conductive member. The first conductive member and the second conductive member are connected to form a temperature measurement contact, and the first conductive member is at least one of zirconium diboride and titanium diboride And a first conductive ceramic composed of silicon carbide, a sintering aid, and an unavoidable impurity. In the first conductive ceramic, the content of the silicon carbide is 5% by mass to 40% by mass. The second conductive member includes a second conductive ceramic whose main constituent material is boron carbide.

  In the second conductive ceramic, the content of the boron carbide is preferably 50% by mass or more.

  In the second conductive ceramic, the content of boron carbide is preferably 70% by mass or more.

  The second conductive ceramic preferably comprises the boron carbide and an unavoidable impurity.

  The insulating member further insulating the first conductive member and the second conductive member in a region other than the temperature measurement contact, and a material constituting the insulating member is at least one of zirconium oxide and zircon. May be included.

  According to the present invention, it is possible to provide a thermocouple capable of performing temperature measurement of a material in a high temperature range with high accuracy and at low cost.

FIG. 2 is a cross-sectional view for explaining a thermocouple according to Embodiment 1; It is sectional drawing seen from line segment II-II of FIG. FIG. 7 is a cross-sectional view for explaining a thermocouple according to a second embodiment. FIG. 5 is a diagram for describing a configuration example of a thermocouple according to the first embodiment. FIG. 5 is a diagram for describing a configuration example of a thermocouple according to the first embodiment. FIG. 5 is a diagram for describing a configuration example of a thermocouple according to the first embodiment. It is a graph which shows the thermoelectromotive force of the sample 1, the sample 2, and the sample 3 of Example 1. FIG. 5 is a graph showing the thermoelectromotive force of the sample 5 of Example 1. 5 is a graph showing the thermoelectromotive force of Sample 4 of Example 1. 15 is a graph showing the thermoelectromotive force of Sample 19 and Sample 20 of Example 3. FIG. 16 is a graph showing the thermoelectromotive forces of Sample 19, Sample 21 and Sample 22 of Example 3. FIG. It is the elements on larger scale of the graph shown in FIG.

  Hereinafter, embodiments of the present invention will be described based on the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated.

Embodiment 1
The thermocouple 10 according to the first embodiment will be described with reference to FIG. The thermocouple 10 is configured such that the first conductive member 1 and the second conductive member 2 form a temperature measurement contact portion.

  The first conductive member 1 is a member that is directly or indirectly exposed to a temperature measurement target of the thermocouple 10, such as a molten metal, and includes a first conductive ceramic formed as an end-closed tube. . Here, direct exposure to a temperature measurement target means the state in which the first conductive member 1 forms the outermost surface of the thermocouple 10, and indirect exposure refers to the first conductive It means that the member 1 is exposed to a temperature measuring object via a protective film (see Embodiment 2).

  The second conductive member 2 is a member disposed inside the first conductive member 1 formed as a one-end closed tube, and is formed of a material different from the first conductive ceramic. For example, those having a shape of linear ceramics.

The first conductive ceramic comprises zirconium diboride (ZrB ₂ ), silicon carbide (SiC), a sintering aid, and unavoidable impurities. The content of silicon carbide (SiC) in the first conductive ceramic is 5% by mass or more and 40% by mass or less, and particularly preferably 5% by mass or more and 30% by mass or less when used for members directly in contact with molten steel. More preferably, they are 5 mass% or more and 20 mass% or less. The first conductive ceramic contains, for example, boron carbide (B ₄ C) as a sintering aid. The content of boron carbide (B ₄ C) in the first conductive ceramic is, for example, 1% by mass.

The first conductive ceramic contains ZrB ₂ as the main component. In the first conductive ceramic, ZrB ₂ constitutes other than SiC and B ₄ C, and the content of ZrB ₂ is about 59% by mass to 94% by mass.

The theoretical density ratio of the first conductive ceramic is 90% or more, preferably 94% or more. Here, the theoretical density ratio is a value obtained by dividing the bulk specific gravity of the first conductive ceramic by the true specific gravity. Bulk specific gravity (bulk density) refers to the dry mass W ₁ (g) of a ceramic sample from the saturation mass W ₃ (g) of the sample to the mass W ₂ (g) in water of the sample from the definition according to JIS R 1600 the value _W 1 _/ divided by a value which subtracted _(W 3 -W _2), a medium liquid of density [rho ₁ value multiplied by the _{ρ 1 · W 1 / (W} 3 -W 2). The true specific gravity (true density) is a volume occupied by the ceramic material itself excluding the volume of a closed void in the ceramic sample, and is a theoretical value calculated by a method in accordance with JIS R 2205. That is, the volume of the pores is small inside the first conductive ceramic.

ZrB ₂ has a melting point of 3246 ° C. This is higher than the temperature of a common molten metal. The thermal conductivity of ZrB ₂ is about 100 W / (m · K). Moreover, the electrical conductivity of ZrB ₂ is 10 ⁷ S / m or more, which is equivalent to that of carbon steel. SiC has a melting point of 2730 ° C. The thermal conductivity of SiC is about 70 W / (m · K). On the other hand, SiC has high electrical resistance and exhibits semi-insulation. Inevitable impurities are, for example, hydrogen (H), nitrogen (N), oxygen (O), boron (B) and the like.

The second conductive ceramic is mainly composed of boron carbide (B ₄ C). The content of B ₄ C in the second conductive ceramic is 50% by mass or more, and may be 70% by mass or more. At this time, the second conductive ceramic may further include, in addition to B ₄ C, at least one of ZrB ₂ , SiC, and zirconium carbide (ZrC), for example. The second conductive ceramic may be composed of B ₄ C and unavoidable impurities.

In the case where the second conductive ceramic contains ZrB ₂ having electrical characteristics (such as electrical resistance and thermoelectromotive force) different from B ₄ C, for example, the content of ZrB ₂ makes it possible to use the second conductive ceramic. The electrical characteristics can be adjusted.

When the second conductive ceramic contains various carbides not containing boron, such as SiC and ZrC, for example, the boron (B) concentration between the second conductive ceramic and the first conductive ceramic Differences can be reduced. Specifically, in the ZrB ₂ which is the main constituent material of the first conductive ceramic and B ₄ C which is the main constituent material of the second conductive ceramic, the B concentration is approximately 19 mass% and 78 respectively. It differs greatly from mass%. In this case, if the thermocouple 10 including the first conductive ceramic and the second conductive ceramic is placed at a high temperature of, for example, about 1600 ° C. for a long time of several tens hours or more, the second conductivity having a high B concentration Boron (B) atoms may diffuse from the ceramic to the first conductive ceramic having a low B concentration, and as a result, the electrical characteristics of the thermocouple 10 may change. The diffusion rate at this time is proportional to the B concentration difference according to Fick's law. Therefore, when the second conductive ceramic contains a carbide not containing boron such as SiC or ZrC, the B concentration in the second conductive ceramic is higher than, for example, the second conductive ceramic containing ZrB ₂ or the like. And the diffusion rate can be reduced. When the second conductive ceramic contains SiC, ZrC or the like, the thermoelectromotive force is higher than when the second conductive ceramic contains ZrB ₂ or when it is composed of B ₄ C and an unavoidable impurity. Since it is thought that it will fall, it is necessary to decide addition amount in consideration of both a life and thermoelectromotive force. Here, the term "lifetime" refers to the time until temperature measurement accuracy becomes lower than the required value due to the reduction of the thermoelectromotive force due to the diffusion of B atoms, and the lifetime of the thermocouple 10 is continuous for an object It has to be at least the time required to measure the temperature (e.g. furnace life). That is, it is necessary for the thermocouple 10 to suppress the temperature measurement error when the required time has elapsed to less than or equal to the maximum allowable temperature measurement error. Since the temperature measurement accuracy required value of the thermocouple 10 and the time required for continuous temperature measurement are different depending on the use mode of the thermocouple 10, the B concentration in the second conductive ceramic according to the use mode of the thermocouple 10 The preferred range is different.

The second conductive ceramic preferably contains no oxide from the viewpoint of suppressing the oxidation of boron contained in the second conductive ceramic. For example, when the second conductive ceramic contains an oxide such as alumina (Al ₂ O ₃ ) and magnesia (MgO), boron contained in the second conductive ceramic is oxidized. At this time, if the content of the oxide in the second conductive ceramic is small, the thermoelectromotive force of the thermocouple 10 will be greatly reduced as the oxidation progresses. In addition, when the content of the oxide increases, a low melting point oxide such as B ₂ O ₃ is generated and CO gas is generated, and the second conductive ceramic is broken.

  The first conductive member 1 is configured by connecting a main body portion 1A, a plurality of extension portions 1B, and a connection portion 1C that connects the main body portion 1A and the extension portion 1B.

  The main body portion 1A is made of a first conductive ceramic, and one end thereof is configured as a closed end 1a and the other end as an open end 1b. In the inside of the closed end portion 1a, a groove 3 in which the end portion 2a of the second conductive member 2 is fixably provided is formed. For example, the groove 3 may be a female screw hole, and the end 2a of the second conductive member 2 may be a male screw, and the groove 3 and the end 2a may be screwable. By fixing the end 2a of the second conductive member 2 in the groove 3 of the closed end 1a, a temperature measurement contact of the thermocouple 10 is formed at the closed end 1a. The open end 1 b is configured as a male screw. The axial length of the main body 1A can be, for example, about 100 mm or more and 150 mm or less. The outer diameter of the main body 1A is, for example, 10 mm or more and 20 mm or less. The inner diameter of the main body portion 1A is larger than the hole diameter of the groove 3 and is, for example, 6 mm or more and 15 mm or less. The thickness of the wall surface of the main body portion 1A configured as a one-end closed tube is, for example, 1 mm or more and 5 mm or less.

  The extension portion 1B is made of the first conductive ceramic, and both ends thereof are configured as the open end portion 1b. The open end 1b of the extension 1B is configured as a male screw in the same manner as the open end 1b of the main body 1A. The axial length of the extension 1B, the thickness in the direction perpendicular to the axial direction, the outer diameter, and the inner diameter are provided in the same manner as the main body 1A.

  The connection portion 1C is formed as a female screw that can be screwed with the open end portion 1b of the main body portion 1A configured as a male screw and the open end portion 1b of the extension portion 1B. It is preferable that the material which comprises the extension part 1B and 1 C of connection parts is comprised by the same 1st electroconductive ceramics as the main-body part 1A in all.

  As described above, the first conductive member 1 assembled by screwing the main body portion 1A, the extension portion 1B and the connection portion 1C forms an end closed tube as a whole. In the first conductive member 1, an open end (one end of the extension 1 B) opposite to the closed end 1 a is sealed by a plug 9. The plug 9 is made of an electrically insulating material. Preferably, plug 9 is made of a material with high thermal conductivity, and the material constituting plug 9 is, for example, aluminum nitride (AlN). Since the first conductive member 1 is located outside the second conductive member 2 and thus has a higher temperature than the second conductive member 2, the first plug 9 is made of a material having a high thermal conductivity. The temperature difference between the electrode pad 5 electrically and thermally connected to the conductive member 1 of the second embodiment and the electrode pad 6 electrically and thermally connected to the second conductive member 2 is sufficiently small. can do. As a result, the measurement error of the thermocouple 10 can be sufficiently reduced.

  The plug 9 is formed with a through hole for introducing the second conductive member 2 from the outside to the inside of the first conductive member 1. The second conductive member 2 is configured to extend from the through hole of the plug 9 through the space formed inside the first conductive member 1 to the groove 3 of the closed end 1 a . As described above, the end 2a of the second conductive member 2 is configured as, for example, a male screw.

  In the thermocouple 10, the first conductive member 1 made of the first conductive ceramic is configured as one conductor forming the temperature measurement contact, and at the same time, the second conductive member 2 which is the other conductor. It is also configured as a heat resistant protective tube.

Referring to FIG. 2, the inside of the first conductive member 1 is filled with an insulating member 4 so as to surround the periphery of the second conductive member 2. The insulating member 4 may be made of any material which has insulating properties, has a high melting point, and does not react with the first conductive member 1 and the second conductive member 2 in the operating temperature range of the thermocouple 10. The material constituting the insulating member 4 is, for example, at least one of zirconium oxide (ZrO ₂ ) and zircon (ZrSiO ₄ ). Further, the insulating member 4 may be configured by being filled with powdery ZrO ₂ or the like, but may be filled with cylindrically shaped ZrO ₂ or the like in advance. Thereby, in the inside of the first conductive member 1, the first conductive member 1 and the second conductive member 2 are insulated by ZrO _{2 in} the region other than the temperature measurement contact (closed end portion 1 a).

  Electrode pads 5 and 6 are connected to the first conductive member 1 and the second conductive member 2, respectively. The electrode pads 5 and 6 are connected to the first conductive member 1 and the second conductive member 2 at positions having a predetermined temperature difference with respect to the temperature measurement contact. The electrode pads 5 and 6 are connected to a measurement circuit (voltmeter) 7 that measures the potential difference between the first conductive member 1 and the second conductive member 2. That is, a closed circuit is formed by the first conductive member 1, the second conductive member 2, and the measurement circuit 7. Thereby, the temperature at the temperature measurement junction of the thermocouple 10 can be measured as the thermoelectromotive force.

  The first conductive member 1 may include a plurality of extension portions 1B and connection portions 1C. The thermocouple 10 is attached, for example, to penetrate the ladle wall in the steel making process, and at this time, the configuration of the first conductive member 1 is made according to the distance from the ladle wall to the temperature measuring contact of the thermocouple 10 Any choice can be made.

Next, a method of manufacturing the first conductive ceramic will be described. In the first conductive ceramic, a binder is added to the mixture obtained in the step (S10) of mixing the powder of ZrB _{2 and} the powder of SiC and the sintering aid and the step of mixing (S10), and heating is performed. The step of kneading while kneading (S20), the step of molding the kneaded product obtained in the step of kneading (S20) (S30), and the step of degreasing the compact obtained in the step of molding (S30) (S40) And a step (S50) of firing the degreased body obtained in the step of degreasing (S40).

First, in step (S10), powdered ZrB ₂ and SiC are prepared. Furthermore, B ₄ C powder as a sintering aid and an organic binder as a binder are prepared. The average particle diameter of each powder of ZrB ₂ , SiC, and B ₄ C, that is, the median value (d = 50) of the particle size distribution measured by the laser diffraction scattering method may have any average particle diameter. For example, ZrB ₂ powder having an average particle diameter of 0.5 μm to 3 μm, SiC powder having an average particle diameter of 0.3 μm to 2 μm, and B ₄ C powder having an average particle diameter of 0.2 μm to 4.0 μm Will be prepared.

Next, the prepared powders of ZrB ₂ , SiC and B ₄ C are mechanically mixed to obtain a mixed powder. At this time, the mixing ratio of ZrB ₂ , SiC and B ₄ C is such that, for example, the mass ratio in the conductive ceramic is 69 mass% or more and 94 mass% or less: 5 mass% or more and 30 mass% or less: 1 mass% do it.

  Next, the obtained mixture is molded (step (S30)). Specifically, the mixture is charged into a pressure-type kneader, an organic binder is added, and the mixture is heated and pressure-kneaded to prepare a kneaded material. For example, in consideration of the flowability of the kneaded product, heating and pressure kneading are carried out for 90 minutes while rotating the pressure kneader under conditions of a heating temperature of 100 ° C. to 200 ° C. and a pressure of 0.35 MPa to 0.45 MPa. At this time, the mixing ratio of the organic binder may be, for example, 20 parts by mass with respect to the mixed powder. Next, a molded body is produced by injection molding the above-mentioned kneaded material into a desired mold. At this time, the shape of the molded body can be arbitrarily selected according to the shape of the thermocouple. Referring to FIG. 1, for example, a main body portion 1A having one end closed and an open end, an extension 1B having both ends open, a main body 1A and an extension 1B. And a connection portion 1C for connecting them.

  Next, the obtained molded body is degreased (step (S40)). Specifically, the molded body is put into an air degreasing furnace, and the temperature is gradually raised from normal temperature to about 400 ° C. at a heating rate of 20 ° C./hour or less, and heat treatment is performed to produce a degreased body. At this time, most of the organic binder is oxidatively decomposed.

  Next, the degreased body is put into a graphite furnace and fired (step (S50)). For example, sintering is performed under heating conditions of 2000 ° C. or more and 2300 ° C. or less in an Ar atmosphere. Thereby, it is possible to obtain the first conductive ceramic formed as the main body portion 1A, the extension portion 1B, and the connection portion 1C.

Next, a method of manufacturing the second conductive ceramic will be described. The second conductive ceramic includes a step (S11) of preparing a powder of B ₄ C and a binder, a step of adding a binder to the powder of B ₄ C, and kneading while heating (S21), and a step of kneading ( A step (S31) of forming the kneaded product obtained in S21), a step (S41) of degreasing the formed body obtained in the step of forming (S31), and a degreased body obtained in the step of degreasing (S41) And a step of firing (S51).

First, powdered B ₄ C and an organic binder as a binder are prepared (step (S11)). The average particle diameter of the powder of B ₄ C, that is, the median value (d = 50) of the particle size distribution measured by the laser diffraction scattering method may be any arbitrary particle diameter, but for example, the average particle diameter is B ₄ C powder of 0.2 μm or more and 4.0 μm or less is prepared. The organic binder is mainly composed of thermoplastics.

Next, the prepared B ₄ C powder is charged into a pressure kneader, and an organic binder is further added thereto, followed by heating and pressure kneading to prepare a kneaded product (a molding compound excellent in uniform dispersibility) ( Step (S21)). For example, in consideration of the flowability of the kneaded product, heating and pressure kneading are carried out for 90 minutes while rotating the pressure kneader under conditions of a heating temperature of 100 ° C. to 200 ° C. and a pressure of 0.35 MPa to 0.45 MPa. At this time, the volume ratio of the B ₄ C powder to the organic binder may be, for example, 1: 1.

  After the above-mentioned kneaded material is naturally cooled at room temperature, it is put into a pulverizer and pulverized into small pieces as a molding material. The size of the small piece is, for example, 4 mm or more and 8 mm or less.

  Next, a molded body is produced by extruding the above-mentioned molding material (step (S31)). Specifically, small pieces obtained by pulverizing the kneaded material are put into the hopper of an extruder and extruded at a cylinder temperature of 140 ° C. or more and 180 ° C. or less. At this time, a metal long plate (receiving plate) having a V-shaped groove is prepared so that the molded body extruded from the die of the extrusion molding machine is not deformed, and the die of the extrusion molding machine It is preferable to arrange in series with the groove on the receiving plate. Thus, the molding extruded from the extrusion molding machine can be received by the groove, and molding can be performed while moving the receiving plate in accordance with the discharge speed and discharge direction of the molding, whereby a linear without bending. Can be obtained. Next, the obtained molded body is cut into a predetermined length as the second conductive member 2.

  Next, the obtained molded body is degreased (step (S41)). Specifically, the molded body is charged into an air degreasing furnace, and the temperature is gradually raised from normal temperature to about 400 ° C. at a heating rate of 20 ° C./hour or less, and then heat treated for 5 days to produce a degreased body. Do. In the degreased body, the organic binder contained in the molded body is oxidatively decomposed to be completely removed.

  Next, the degreased body is put into a graphite furnace and fired (step (S51)). For example, sintering is performed under heating conditions of 2000 ° C. or more and 2300 ° C. or less in an Ar atmosphere. Thereby, the second conductive ceramic formed as a linear body can be obtained. Note that one end of the linear body is processed as a male screw, and is formed into the second conductive member 2.

  Next, a method of manufacturing the thermocouple 10 will be described. First, the first conductive member 1 is formed by assembling the main body portion 1A, the extension portion 1B, and the connection portion 1C obtained in the above-described first method for producing a conductive ceramic.

  Next, the end portion 2a is screwed into the groove 3 of the closed end portion 1a through the second conductive member 2 obtained in the above-described second conductive ceramic manufacturing method inside the first conductive member 1 Then, the first conductive member 1 and the second conductive member 2 are fixed and a temperature measurement contact is formed. Thereafter, the interior of the first conductive member 1 is filled with the insulating member 4. Finally, the plug 9 is attached on the open end side of the first conductive member 1 to fix the first conductive member 1, the second conductive member 2 and the insulating member 4 to form the thermocouple 10 Ru.

Next, the operation and effect of the thermocouple 10 according to the present embodiment will be described. As a result of examining various conductive ceramics as the first conductive ceramic contained in the first conductive member 1 of the thermocouple 10, the present inventors found that ZrB ₂ and TiB ₂ are the main components of the first conductive member 1 Found to be suitable as a component material.

A material having a high melting point and a high electric conductivity is suitable for the material for the thermocouple. It is known that ZrB ₂ and TiB ₂ are materials that are inexpensive and have high melting points of 1500 ° C. or higher, and are good conductors of electricity. The melting points of ZrB ₂ and TiB ₂ are 3246 ° C. and 2900 ° C., respectively, which are higher than the temperatures of common molten metals. Furthermore, the electrical conductivity of ZrB ₂ and TiB ₂ is 10 ⁷ S / m or more, which is equivalent to that of carbon steel.

Moreover, when the present inventors evaluated the thermal shock resistance of the sintered compact which consists of ZrB ₂ or TiB _2, it confirmed that spalling of a crack, peeling, etc. arises by a thermal shock. Specifically, when the conductive ceramic consisting of ZrB ₂ except for the sintering aid and the inevitable impurities was immersed in molten iron at 1600 ° C. from room temperature without preheating, spalling occurred due to thermal shock. The same applies to conductive ceramics composed of TiB ₂ except for sintering aids and unavoidable impurities.

On the other hand, the inventors of the present invention conducted intensive studies and found that the conductive ceramics (having the first conductive property) contain ZrB ₂ or TiB ₂ as the main component and the content of SiC is 5% by mass or more and 30% by mass or less Ceramics) has been found to dramatically improve the thermal shock resistance. In fact, as a result of conducting the above-mentioned thermal shock test on the first conductive ceramic, no spalling occurred. On the other hand, as a result of conducting the said molten steel immersion test with respect to electroconductive ceramics whose content rate of SiC is out of the said range, it was confirmed that a spalling and a melting loss arise.

Furthermore, the inventors of the present invention have found that the electrical conductivity of the first conductive ceramic containing ZrB ₂ or TiB ₂ as the main component and having a content of SiC of 5% by mass to 40% by mass is 10 ⁶ S / It confirmed that it was m or more and had high electric conductivity sufficiently as a material of a thermocouple.

Thus, the first conductive ceramic has a high melting point and a high electrical conductivity by containing any one of ZrB ₂ and TiB ₂ as a main component. In addition, the first conductive ceramic can be manufactured at low cost as compared with conventional materials for thermocouples. Furthermore, the first conductive ceramic contains 5% by mass or more and 30% by mass or less of SiC so that the corrosion resistance and the thermal shock resistance sufficient for the temperature range of the molten metal as the first conductive member 1 in the thermocouple 10 You can have

Furthermore, the theoretical density ratio of the first conductive ceramic is 90% or more, and the inside of the first conductive ceramic is densified. In this case, the carrier density of the first conductive ceramic uniquely depends on the component composition ratio (the blending ratio of ZrB ₂ / SiC), and the measurement accuracy of the thermoelectromotive force can be kept high. Therefore, the first conductive ceramic can stably have a predetermined thermoelectromotive force at a predetermined temperature by selecting the component composition ratio appropriately. As a result, the thermocouple 10 according to the present embodiment including the first conductive ceramic can maintain high measurement accuracy. On the other hand, when the theoretical density ratio of the conductive ceramic is low, the internal resistance increases (the carrier density decreases) and the thermoelectromotive force becomes unstable. As a result, the thermoelectromotive force measurement error increases. Therefore, it is difficult to obtain a conductive ceramic having a predetermined thermoelectromotive force, and a thermocouple provided with the conductive ceramic can not maintain high measurement accuracy.

Furthermore, as a result of examining the various conductive ceramics as the second conductive ceramics included in the second conductive member 2 of the thermocouple 10, the present inventors found that B ₄ C is suitable as the second conductive ceramics. I found that. In other words, as a result of earnest research, the present inventors have studied the first conductive member 1 made of the above-described first conductive ceramic and the conductive ceramic (the second conductive ceramic) containing B ₄ C as a main component. It has been found that the thermocouple 10 including the second conductive member 2 produces extremely high thermoelectromotive force even in a high temperature environment as compared with a conventional general industrial thermocouple.

  Actually, the temperature measurement contact point of the thermocouple 10 according to the first embodiment is arranged with a B-type thermocouple as a standard thermocouple in a verification furnace heated to a temperature of 1600 ° C. While the thermoelectromotive force of the thermocouple was 20 mV or less, the thermoelectromotive force of the thermocouple 10 was 380 mV (see FIG. 10, details will be described later). That is, it was confirmed that the thermocouple 10 can generate a thermoelectromotive force about 20 times higher than that of a conventional general industrial thermocouple. It should be noted that the thermocouple 10 may be compared with a thermocouple composed of the first conductive member made of the first conductive ceramic and the second conductive member made of molybdenum (Mo) instead of the second ceramic. The present inventors have found that a higher thermoelectromotive force is generated.

  In addition, in a general sheathed thermocouple, there is a problem that the temperature measurement value becomes lower than the actual temperature of the molten metal because it is necessary to protect the surrounding with a thick refractory, and the fluctuation of the temperature measurement value concerned. There is a problem that the temperature change can not be sufficiently followed and the control of the temperature change by software must be performed.

On the other hand, the first conductive member 1 made of the first conductive ceramic has durability against molten metal and a high temperature reducing atmosphere (for example, carbon monoxide gas) as compared with the metal sheath of the conventional sheath type thermocouple. High resistance to the atmosphere). Furthermore, B ₄ C constituting the second conductive ceramic has a melting point of 2450 ° C. and is as high as ZrB ₂ or TiB ₂ . Therefore, the thermocouple 10 does not have to be protected by a thick refractory around the same as a sheathed thermocouple. As a result, the temperature measurement junction of the thermocouple 10 can be disposed closer to the molten metal to be measured than the temperature measurement junction of the sheath thermocouple, and the thermocouple 10 has higher accuracy than the sheath type thermocouple The temperature can be measured.

  Further, since the thermocouple 10 is mainly composed of the first conductive ceramic and the second conductive ceramic, the thermocouple 10 can be manufactured at low cost. Furthermore, since the thermocouple 10 can significantly extend the service life as compared to the conventional thermocouple, the measurement cost can be reduced by using the thermocouple 10.

The content of B ₄ C in the second conductive ceramic is 50% by mass or more, and may be 70% by mass or more. The second conductive ceramic may be composed of B ₄ C and unavoidable impurities. The higher the content of B ₄ C in the second conductive ceramic, the higher the thermoelectromotive force of the thermocouple 10 including the second conductive member 2 including the second conductive ceramic.

  On the other hand, the thermoelectromotive force of the thermocouple 10 is lowered by the progress of the diffusion of B atoms between the first conductive ceramic and the second conductive ceramic as described above. Therefore, in order to simultaneously satisfy two of the time required to continuously measure the temperature of a certain object (for example, the furnace life) and the maximum temperature measurement error that is allowed in that case, The B concentration in the conductive ceramic may be appropriately selected according to the use mode of the thermocouple 10.

  Also, as described above, there is no need to protect the surroundings of the thermocouple 10 with a refractory, and the temperature measuring junction of the thermocouple 10 is closer to the molten metal to be measured than the temperature measuring junction of the sheath thermocouple. Because of the arrangement, the thermocouple 10 has a faster response to temperature changes of the molten metal than the sheathed thermocouple (the temperature measurement value can quickly follow). Therefore, it is possible to eliminate the need for predictive control of software for covering the response delay that has been performed by the sheathed thermocouple. Thereby, by using the thermocouple 10, more precise temperature control can be performed on the molten metal.

Second Embodiment
Next, the conductive ceramic for thermocouples and the thermocouple 20 according to the second embodiment will be described. Referring to FIG. 3, the conductive ceramic for thermocouple and the thermocouple 20 according to the second embodiment basically have the same configuration as the conductive ceramic for thermocouple and the thermocouple 10 according to the first embodiment. Although it is provided, it differs in that a protective film 8 is formed on the surface of the first conductive member 1.

The protective film 8 is made of any material as long as the thermocouple 20 does not react with the material to be measured (for example, molten metal) and is not worn away, but is made of, for example, zircon (ZrSiO ₄ ). The film thickness of the protective film 8 is, for example, 10 μm or more and 250 μm or less, preferably 50 μm or more and 150 μm or less.

The method of manufacturing the conductive ceramic for a thermocouple further includes the step of forming the protective film 8 on the outer peripheral surface of the first conductive member 1 after the step (S50) of firing. In the step of forming the protective film 8, any method can be adopted. For example, the first conductive member 1 made of a conductive ceramic for a thermocouple containing ZrB ₂ is heated to 1450.degree. C. or more and 1600.degree. It may be heated. Thus, the protective film 8 made of ZrSiO ₄ is formed on the surface of the first conductive member 1. The film thickness of the protective film 8 formed by such a method is, for example, 10 μm or more and 80 μm or less.

  The protective film 8 may be formed on at least the outer peripheral surface of the first conductive member 1 (the surface in contact with the material to be measured).

Next, functions and effects of the conductive ceramic for thermocouple and the thermocouple 20 according to the second embodiment will be described. When the thermocouple 20 is used to measure the temperature of a molten metal, the first conductive member 1 constituting the outermost surface of the thermocouple 20 is placed under a high oxygen atmosphere. Specifically, the molten metal contains oxygen, and the oxygen content generally fluctuates in a range of several ppm to several hundred ppm. Therefore, the thermocouple 20 immersed in the molten metal is placed under a high oxygen atmosphere. Further, for example, when attached to a ladle in a steelmaking process, the thermocouple 20 is placed under a high temperature atmosphere even in a state not immersed in the molten metal. The present inventors confirmed that the conductive ceramic for thermocouples placed in such an atmosphere gradually wears out due to the oxidation of ZrB ₂ and TiB ₂ .

It is known that when ZrB ₂ having a SiC content of 5% by mass is heated to a high temperature, a film of silicon oxide (SiO ₂ ) is formed on the surface, and the progress of oxidation is suppressed in the air (F. Peng et al, J. Am. Ceram. Soc, 91 [5] 1489-1494 (2008)). However, the present inventors confirmed that the SiO ₂ film, when immersed in the molten metal, combines with other oxides in the molten metal to form a low melting point oxide and easily exfoliates. did. That is, the SiO ₂ film does not function as the oxidation resistant film of the first conductive member in the molten metal thermocouple for temperature measurement.

The present inventors easily form a film (protective film 8) of ZrSiO _{4 on} the surface of the first conductive member 1 made of the first conductive ceramic so that it can be easily dissolved even if it is immersed in molten metal. It was also confirmed that wear due to oxidation of the conductive ceramics for thermocouples can be suppressed.

Further, since ZrSiO ₄ has an insulating property, it is possible to electrically insulate the first conductive member made of the thermocouple conductive ceramic from the surrounding environment (molten metal or the like). As a result, since the protective film 8 can block electrical noise from the surrounding environment, the thermocouple 20 can measure temperature with high accuracy.

The protective film 8 can be formed by thermal spraying ZrSiO ₄ on the surface of the conductive ceramic for thermocouples, in addition to the method of heating and oxidizing the conductive ceramic for thermocouples described above.

The material constituting the protective film 8 is not limited to ZrSiO _4, it may be ZrO _2. Even in this case, it is considered that the same effect as ZrSiO ₄ can be exhibited.

  Moreover, although the 1st electroconductive ceramics which concern on Embodiment 1 and Embodiment 2 are formed by the injection molding method, it is not restricted to this. Moreover, although 2nd electroconductive ceramics are formed by the extrusion molding method, it is not restricted to this. The first conductive ceramic and the second conductive ceramic may be respectively formed by any of, for example, an injection molding method, a pressure sintering (hot press) method, and an extrusion molding method.

  The thermocouples 10 and 20 according to the first embodiment and the second embodiment are suitable for the following applications, for example.

  First, since the thermocouples 10 and 20 have high durability to the molten metal, they are suitable for thermocouples capable of measuring the temperature of the molten metal continuously.

  FIG. 4 shows a thermocouple 10 embedded in the converter wall and configured as a thermocouple for continuous measurement of molten steel temperature. The converter is covered with an iron shell 103 made of steel plate and is internally lined with a refractory 102, and the inside of the converter is surrounded by the refractory 102 to form a furnace interior 101 into which molten steel is put. The thermocouple 10 is provided with a temperature measurement contact in the furnace 101 and a reference contact in the refractory 102. That is, the closed end 1 a of the first conductive member 1 of the thermocouple 10 and the end 2 a of the second conductive member 2 are both positioned in the furnace 101. In addition, an electrode pad 6 connected to the second conductive member 2 is provided so as to be located in the refractory 102. Furthermore, one end (a temperature measurement contact) is disposed in the vicinity of the electrode pad 6, and a thermocouple 11 (for example, a sheath type thermocouple) extending through the refractory 102 and the iron shell 103 to the outside of the converter. ) Is provided. The thermocouple 11 is connected to a thermometer which is provided outside the converter, and is provided so as to be able to measure the temperature in the vicinity of the electrode pad 6 (that is, the reference contact).

  Furthermore, an electrode pad 5 connected to the first conductive member 1 is provided so as to be located in the refractory 102. The electrode pad 5 and the electrode pad 6 are each connected to a voltmeter 12 (mV meter) provided outside the converter, and the voltmeter 12 can measure the thermoelectromotive force of the thermocouple 10 Provided in

  Thus, for example, when the temperature of the reference contact measured by the thermocouple 11 is 800 ° C. and the thermoelectromotive force measured by the voltmeter 12 is 220 mV, the thermoelectromotive force of the thermocouple 10 shown in FIG. The molten steel temperature can be calculated to be 1575 ° C. from the graph showing the relationship between the power and the temperature difference.

  In addition, in the converter in which the thermocouple 10 is configured as described above, it is not necessary to form a through hole for causing the thermocouple 10 to penetrate through the iron shell 103.

  FIG. 5 also shows a thermocouple 10 embedded in the converter bottom and configured as a thermocouple for continuous measurement of molten steel temperature.

  The bottom of the converter is composed of, for example, a shell 107, a permanent brick 110 lined with the shell 107, and a refractory 111 as a consumable member lined inside the permanent brick 110. The iron skin 107 is formed with a flange 108.

  The bottom blowing nozzle 104 is provided to penetrate the permanent brick 110 and the refractory 111. The bottom blowoff mouth 104 includes a tuyere brick 105 and a tuyere surrounding brick 106 that surrounds the tuyere brick 105 and is embedded in a through hole formed in the refractory 111 and the permanent brick 110. The bottom blowing nozzle 104 is held in the opening of the flange 108 formed in the iron shell 107 by a pressing lid 109 fixed to the flange 108.

  The thermocouple 10 is provided with a temperature measurement contact in the furnace 101 and a reference contact in the bottom blowoff 104 provided at the furnace bottom. A thermocouple 11 for measuring the temperatures of the electrode pads 5 and 6 and the reference contact of the thermocouple 10 is further disposed in the bottom spray nozzle 104. In the bottom spray nozzle 104, for example, a stirring gas or a refining gas flows into the furnace 101, and this mixed gas is provided to function as a cooling gas for the reference contact.

  Alternatively, the thermocouple 10 may be configured as a thermocouple embedded in the bottom of the electric furnace to continuously measure the temperature of the molten steel.

  FIG. 6 also shows a thermocouple 10 configured as a thermocouple embedded in the sidewall of an AOD (Argon Oxygen Decarburization) furnace to continuously measure the temperature of the molten steel. The thermocouple 10 has a temperature measurement contact in the furnace 101, and a reference contact in the side blow nozzle 112 provided on the side wall of the AOD furnace. A thermocouple 11 for measuring the temperatures of the electrode pads 5 and 6 and the reference contact of the thermocouple 10 is further disposed in the side blow nozzle 112. In the side blow nozzle 112, for example, an oxygen-argon mixed gas flows from the outside of the AOD furnace into the furnace 101, and this mixed gas is provided to function as a cooling gas for the reference contact.

  Furthermore, since the thermocouples 10 and 20 have high durability to a reducing atmosphere in a high temperature environment, they are also suitable as thermocouples for measuring the temperature of the reducing atmosphere.

  For example, the inside of the blast furnace is a reducing CO gas atmosphere, and the furnace wall of the blast furnace is also made of a graphite brick such as carbon brick as a refractory, so it can be said to be a reducing atmosphere. The thermocouple 10 is provided such that the temperature measurement contact point is located in the furnace and the reference contact point is located in the inside of the graphite brick, and it is suitable for a thermocouple for continuously measuring the reducing atmosphere temperature in the furnace. is there. Further, the thermocouple 10 is provided such that the temperature measurement contact point is located immediately inside the outlet of the outlet of the blast furnace, and the reference contact is located inside the graphite-based brick as a refractory surrounding the outlet, It is also suitable for a thermocouple for continuously measuring the temperature. The control of the output temperature of the blast furnace is an important factor that serves as an indicator of the reaction in the blast furnace, the control of the charge, and the air flow control. To measure this accurately, it is continuous immediately after the outlet. It is necessary to measure the temperature. However, the temperature of the hot metal drops sharply when it goes out of the furnace after pouring, and it is already considerably lower than the pouring temperature in the temperature measurement at the feeding which is generally measured, and its value is also due to disturbance factors. It is easy to vary. Therefore, in order to use the tapping temperature for feedback to the blast furnace operation, it is preferable to measure temperature continuously immediately after the tapping point. The thermocouple 10 is suitable for use as described above because it has high durability to a reducing hot metal.

  In addition, the inside of the coke oven is filled with coke and CO gas, which is a reducing atmosphere. Thus, the thermocouple 10 is suitable for such applications for the reasons described above.

  Furthermore, since the thermocouples 10 and 20 do not have to protect the surroundings with a thick refractory like the conventional sheathed thermocouples, the temperature of the actual molten steel metal can be measured with high accuracy, and the temperature changes It has high response to Therefore, the thermocouples 10 and 20 are also suitable for measuring the temperature of a high temperature part requiring high-precision temperature control.

  For example, in order to improve the mechanical properties of the steel sheet, temperature control of the steel sheet at the time of rolling and fine heat treatment after rolling (for example, rapid heating, quenching, etc. of the steel sheet) are required. In order to realize the temperature pattern during heat treatment as designed, the temperature of the object (steel plate) is measured continuously, and based on the measurement results, cooling conditions (for example, cooling water volume) and heating conditions (for example, heating temperature by a heater) Need to control. For this reason, the thermocouples 10 and 20 having excellent response are suitable for such applications.

  Next, an example of the thermocouple according to the first embodiment will be described. In the present embodiment, the first conductive member 1 was evaluated from the viewpoint of the thermoelectromotive force of the thermocouple.

<Sample>
(Sample 1)
The first conductive member 1 was produced in accordance with the first method for producing a conductive ceramic according to the first embodiment. Specifically, first, SiC powder having an average particle diameter of 0.7 μm, ZrB ₂ powder having an average particle diameter of 2.1 μm, and B ₄ C powder as a sintering aid having an average particle diameter of 0.4 μm were prepared. The SiC powder, the ZrB ₂ powder, and the B ₄ C powder were mechanically mixed at a ratio of 5% by mass, 94% by mass, and 1% by mass, respectively. After 20 parts of an organic binder was added to the obtained mixture, the mixture was heated and pressurized with a pressure kneader to prepare a uniformly dispersed compound (kneaded product). Thereafter, the compound was pelletized into a molding material. The molding material was introduced into an injection molding machine, and the plasticized molding material was injected at a pressure of 50 to 100 MPa into a mold cavity having a length of 62 mm, a width of 19 mm and a thickness of 4.5 mm. The dimensions of the mold can be selected according to the external dimensions of the thermocouple, for example, with an assumed shrinkage of about 16% of the fired product relative to the molded product. After cooling and solidification in the mold, it was taken out to produce a molded body. The compact was put into a degreasing furnace to thermally decompose the organic binder contained in the compact. The obtained degreased body was heated and sintered in an atmosphere of Ar at 2250 ° C. in a graphite furnace to prepare a sintered body (conductive ceramic for thermocouple). Thereafter, the obtained fired product is ground using a surface grinder to form a first conductive member by processing into a desired shape.

A metal material made of Mo was prepared as the second conductive member, and the end of this was fixed to the closed end of the first conductive member. The first conductive member and the second conductive member were insulated by ZrO ₂ . Electrodes were attached to each of the first conductive member and the second conductive member to obtain a thermocouple of Sample 1.

(Sample 2)
The first conductive member is formed by setting the proportions of the SiC powder, the ZrB ₂ powder, and the B ₄ C powder in the above mixture to a proportion of 30% by mass, 69% by mass, and 1% by mass. The thermocouple of sample 2 was obtained as a configuration.

(Sample 3)
The first conductive member is formed by setting the proportions of the SiC powder, the ZrB ₂ powder, and the B ₄ C powder in the above mixture to 40% by mass, 59% by mass, and 1% by mass. The thermocouple of sample 3 was obtained as a configuration.

(Sample 4)
The ratio of the SiC powder, the ZrB ₂ powder, and the B ₄ C powder in the above mixture was 5% by mass, 94% by mass, and 1% by mass to form the first conductive member.

Furthermore, the second conductive member is formed by setting the proportions of the SiC powder, the ZrB ₂ powder, and the B ₄ C powder in the above mixture to 40% by mass, 59% by mass, and 1% by mass, It fixed to the closed end of the 1 conductive member. The first conductive member and the second conductive member were insulated by ZrO2. Electrodes were attached to each of the first conductive member and the second conductive member to obtain a thermocouple of sample 4. That is, as the second conductive member, a conductive ceramic for thermocouples having a different content of silicon carbide from that of the first conductive member was used, and the thermocouple of sample 4 was obtained as a configuration similar to that of sample 1 except the above.

(Sample 5)
A thermocouple of sample 5 was obtained as a configuration similar to sample 1 except that a metal material consisting of W was used as the second conductive member.

<Evaluation>
Thermoelectric force is produced by causing a temperature difference between the temperature measurement contact provided at one end of each thermocouple of sample 1, sample 2, sample 3, sample 4 and sample 5 and the other end Was measured. The measurement results are shown in FIG. 7, FIG. 8 and FIG. The horizontal axis of each of FIG. 7 and FIG. 8 indicates the temperature difference (unit: ° C.), and the vertical axis indicates the thermoelectromotive force (unit: mV). In FIG. 7, the result of sample 1 is shown as G1, the result of sample 2 as G2, and the result of sample 3 as G3. In FIG. 8, the result of sample 5 is shown as G5. In FIG. 9, the result of sample 4 is shown as G4.

  Referring to FIG. 7, it was confirmed that all of Sample 1, Sample 2 and Sample 3 have sufficient thermoelectromotive force as a thermocouple and can stably measure temperature even in a high temperature range. Moreover, it was confirmed that the higher the first conductive ceramic with a higher content of SiC, the higher the thermoelectromotive force when the thermocouple is configured. In particular, sample 2 and sample 3 have larger thermoelectromotive force than sample 1, and the difference between the thermoelectromotive force between sample 2 and sample 1 and the difference between the thermoelectromotive force between sample 3 and sample 1 are all 1000 ° C. or more It was particularly remarkable at high temperatures. It was confirmed that the thermocouple of sample 1 had a thermoelectromotive force almost equal to that of the S-type thermocouple in JIS standard. It was confirmed that the thermocouple of sample 2 had a thermoelectromotive force almost equal to that of the B-type thermocouple in JIS standard.

  Referring to FIG. 8, it was confirmed that sample 5 had a sufficient thermoelectromotive force as a thermocouple similar to sample 1, sample 2 and sample 3, and that it was possible to measure temperature stably even in a high temperature range . As for the thermoelectromotive force of sample 5, the first conductive member is made of the first conductive ceramic having the SiC content that is equivalent to that of the first conductive member of sample 5, and the second conductive member is made of Mo. It is larger than the thermoelectromotive force of the sample 1 which is configured. Further, in the thermoelectromotive force of sample 5, the first conductive member is formed of the first conductive ceramic having a higher SiC content than the first conductive member of sample 5, and the second conductive member is formed of Mo. A tendency smaller than that of the sample 2 configured was confirmed.

  Referring to FIG. 9, sample 4 has a sufficient thermoelectromotive force as a thermocouple similar to sample 1, sample 2, sample 3 and sample 5, and can stably measure temperature even in a high temperature range. confirmed. The thermoelectromotive force of the sample 4 is the thermoelectromotive force of the sample 1 in which the first conductive member is made of the first conductive ceramic having a SiC content of 5%, and the SiC content of the first conductive member is 40%. It was confirmed that the difference with the thermoelectromotive force of the sample 3 made of the first conductive ceramic was matched. It was confirmed that the thermocouple of sample 4 had a thermoelectromotive force almost equal to that of the R-type thermocouple in the JIS standard.

  Next, in Example 2, the first conductive ceramic according to Embodiment 1 was evaluated from the viewpoint of thermal shock resistance and erosion resistance. Specifically, in the present example, conductive ceramics for thermocouples having different contents of SiC were immersed in molten steel to evaluate its thermal shock resistance and erosion resistance.

<Sample>
(Samples 6 to 13)
In accordance with the first method for producing a conductive ceramic according to the first embodiment, the thermoelectric conversion of samples 6 to 13 is based on ZrB ₂ and the content of SiC is changed in the range of 0% by mass to 40% by mass. A pair of conductive ceramics was obtained. Specifically, the SiC content of each of Sample 6, Sample 7, Sample 8, Sample 9, Sample 10, Sample 11, Sample 12, and Sample 40 is 40% by mass, 30% by mass, 20% by mass, and 12% by mass , 5% by mass, 2% by mass, 1% by mass and 0% by mass. The content of B ₄ C, which is a sintering aid, is 1% by mass. That is, the content of each ZrB ₂ of sample 6, sample 7, sample 8, sample 9, sample 10, sample 11, sample 12, sample 13 is 59% by mass, 69% by mass, 79% by mass, 87% by mass, 94% by mass, 97% by mass, 98% by mass, and 99% by mass. The external dimensions of each sample were 2 mm × 2 mm × 30 mm. In addition, the detailed manufacturing method of each sample was performed similarly to the sample 1 in Example 1 mentioned above.

(Sample 14 to Sample 18)
According to the first method for producing a conductive ceramic of the first embodiment, the content of SiC is changed in the range of 0% by mass to 40% by mass based on TiB ₂ as a main component, and 1 conductive ceramic was obtained. Specifically, the SiC contents of the sample 14, the sample 15, the sample 16, the sample 17, and the sample 18 were set to 30% by mass, 20% by mass, 12% by mass, 5% by mass, and 0% by mass. The content of B ₄ C, which is a sintering aid, is 1% by mass. That is, the content rates of each TiB ₂ of sample 14, sample 15, sample 16, sample 17, and sample 18 were set to 69 mass%, 79 mass%, 87 mass%, 94 mass%, and 99 mass%. The external dimensions of each sample were 2 mm × 2 mm × 30 mm. In addition, the detailed manufacturing method of each sample was performed similarly to the sample 1 in Example 1 mentioned above.

<Evaluation>
A 1 kg resistance heating furnace was heated to 1630 ° C. to form a molten steel, and the first conductive ceramics of Samples 6 to 18 were immersed in the molten steel to evaluate the occurrence of spalling and erosion. The evaluation was performed independently in two ways: when each sample was preheated and then immersed, and when each sample was immersed without preheating. Here, “preheated and then immersed” means that a sample (about room temperature) placed at room temperature is held for about 10 seconds immediately above the molten steel and then immersed in the molten steel. In the case of immersion without preheating, a sample (about room temperature) placed at room temperature was immediately immersed in molten steel. Moreover, the said evaluation was performed by immersing about 10 mm of the longitudinal direction of a sample in molten steel, and observing the presence or absence of the spalling and melting loss of the said part. The evaluation results are shown in Table 1.

  Samples 8 and 9 did not have spalling and no dissolution was observed. When the sample 10 was immersed after being preheated, neither spalling nor dissolution was confirmed. When the sample 10 was immersed without preheating, no dissolution was confirmed, but a minute spalling was confirmed. However, the degree was not a problem even when continuously measuring temperature as a thermocouple. In addition, although a slight dissolution loss was confirmed for sample 7, for example, it was confirmed that the sample 7 is sufficiently applicable to a thermocouple for spot temperature measurement application in which the immersion time is within 10 seconds.

On the other hand, in Samples 11 to 13 having a lower SiC content than Sample 10, spalling was confirmed regardless of the presence or absence of preheating. In this regard, it is considered that ZrB _{2 in} the first conductive ceramic is oxidized and damaged by oxygen in the molten steel.

  Moreover, it was confirmed that sample 6 having a higher content of SiC than sample 7 was melted away regardless of the presence or absence of preheating. In this regard, it is considered that molten steel infiltrates into the structure of SiC in the first conductive ceramic to cause melting loss.

That is, the first conductive ceramic containing ZrB ₂ as the main component and containing 5% by mass to 30% by mass of SiC is excellent in thermal shock resistance and corrosion resistance, and, for example, temperature measurement of molten steel metal It was confirmed that it is suitable for use. Furthermore, the first conductive ceramic according to the first embodiment having ZrB ₂ as a main component and a content of SiC of 5% by mass to 20% by mass has higher corrosion resistance and thermal shock resistance. For example, it has been confirmed that it is suitable for applications in which the temperature of molten steel metal is continuously measured for a long time.

In addition, although the first conductive ceramic containing ZrB 2 as the main component and containing 40 mass% of SiC has problems in thermal shock resistance and corrosion resistance, it is shown in sample 4 of Example 1 As it has a sufficiently practical thermoelectromotive force, it has been confirmed that it functions as a first conductive member such as the sample 4 which is not in direct contact with molten steel.

  Similarly, in Samples 15 to 17, spalling did not occur when preheating was performed, and no dissolution was observed. On the other hand, when samples 15 to 17 were immersed without preheating, no dissolution was confirmed, but minute spalling was confirmed.

Further, in the sample 14 having a SiC content higher than that of the sample 15, spalling did not occur when preheating was performed, but a slight erosion was confirmed. On the other hand, when the sample 14 was immersed without preheating, slight dissolution was confirmed, and minute spalling was also confirmed. In addition, in the sample 18 having a lower SiC content than the sample 17, spalling was confirmed regardless of the presence or absence of preheating. In this regard, it is considered that TiB _{2 in} the first conductive ceramic is oxidized and damaged by oxygen in the molten steel.

That is, it was confirmed that the first conductive ceramic containing TiB ₂ as the main component also has the same tendency as the first conductive ceramic containing ZrB ₂ as the main component. Therefore, when the content of SiC exceeds 30%, it is considered that melting occurs regardless of the presence or absence of preheating, and when it is less than 5%, spalling is considered to occur regardless of the presence or absence of preheating. Furthermore, even in the case of a mixed ceramic of ZrB ₂ and TiB ₂ , it is considered that similar effects can be achieved if the SiC content is made 5% by mass or more and 30% by mass or less.

As mentioned above, the conductivity for thermocouples which consists of at least any one of ZrB ₂ and TiB ₂ , SiC, a sintering aid, and an unavoidable impurity, and whose content of SiC is 5 mass% or more and 40 mass% or less It has been confirmed that ceramics have sufficient performance as a material for high-temperature thermocouples and that the manufacturing cost is low. Furthermore, a first conductive ceramic comprising at least one of ZrB ₂ and TiB ₂ , SiC, a sintering aid, and unavoidable impurities, wherein the content of SiC is 5% by mass to 30% by mass. It was confirmed that the production cost is low, and the thermal shock resistance and the erosion resistance are excellent. Also, a first conductive ceramic comprising at least any one of ZrB ₂ and TiB ₂ , SiC, a sintering aid, and unavoidable impurities, and having a content of SiC of 5% by mass to 20% by mass. Were confirmed to have low manufacturing costs and higher thermal shock resistance and erosion resistance.

Next, in Example 3, the thermocouple 10 according to Embodiment 1 was evaluated from the viewpoint of the magnitude of the thermoelectromotive force and the heat responsiveness.
<Sample>
(Sample 19)
The thermocouple 10 was manufactured in accordance with the method of manufacturing a thermocouple according to the first embodiment. Specifically, first, SiC powder having an average particle diameter of 0.7 μm, ZrB ₂ powder having an average particle diameter of 2.1 μm, and B ₄ C powder as a sintering aid having an average particle diameter of 0.4 μm were prepared. The SiC powder, the ZrB ₂ powder, and the B ₄ C powder were mechanically mixed at a ratio of 10% by mass, 89% by mass, and 1% by mass, respectively. After 20 parts of an organic binder was added to the obtained mixture, the mixture was heated and pressurized with a pressure kneader to prepare a uniformly dispersed compound (kneaded product). Thereafter, the compound was pelletized into a molding material. This molding material is introduced into an injection molding machine, and the plasticized molding material has a cylindrical shape with an outer diameter of mm 20 mm, an inner diameter of mm 14 mm, and a length of 130 mm, and one end is closed. It injected with the following pressure. The dimensions of the mold can be selected according to the external dimensions of the thermocouple, for example, with an assumed shrinkage of about 16% of the fired product relative to the molded product. In addition, the mold is capable of forming a groove as a female screw hole inside the first conductive ceramic. After cooling and solidification in the mold, it was taken out to produce a molded body. The compact was put into a degreasing furnace to thermally decompose the organic binder contained in the compact. The obtained degreased body was heat sintered in an atmosphere of Ar at 2250 ° C. in a graphite furnace to prepare a sintered body (first conductive ceramic).

Furthermore, B ₄ C powder having an average particle diameter of 2.5 μm is prepared, 20 parts by mass of an organic binder is added thereto, and the mixture is heated and pressurized with a pressure kneader to form a uniformly dispersed compound (kneaded material) Made. Small pieces obtained by pulverizing the kneaded material were charged into the hopper of an extruder and extruded at a cylinder temperature of 140 ° C. or more and 160 ° C. or less. At this time, the die of the extruder had a bore diameter of 5 mm, and was formed by continuous extrusion. In addition, a metal long plate (receiving plate) in which a V-shaped groove is formed is prepared so that the molded product extruded from the die of the extrusion molding machine is not deformed, and the die and reception of the extrusion molding machine The grooves on the plate were arranged in series. Thus, a linear molded product without bending was obtained. The obtained molded product was cut into a predetermined length as a second conductive member 2. The compact was put into a degreasing furnace to thermally decompose the organic binder contained in the compact. The obtained degreased body was heated and sintered in an atmosphere of Ar at 2250 ° C. in a graphite furnace to prepare a sintered body (second conductive ceramic). Thereafter, the sintered body was divided into a predetermined length, and the end portion was subjected to thread cutting to form a second conductive member whose end portion is a male screw.

The groove of the first conductive member and the end of the second conductive member were screwed and fixed. The first conductive member and the second conductive member were insulated by ZrO ₂ . Electrodes were attached to each of the first conductive member and the second conductive member to obtain a thermocouple of sample 19.

(Sample 20)
As a second conductive member, a metal material made of Mo was prepared, and a thermocouple of sample 20 was obtained as the same configuration as sample 1 except for the above.
<Evaluation 1>
The thermoelectromotive force was measured by causing a temperature difference between the temperature measurement contact provided at one end of each of the thermocouples of sample 19 and sample 20 and the other end. The measurement results are shown in FIG. The horizontal axis of FIG. 10 shows a temperature difference (unit: ° C.), and each vertical axis shows a thermoelectromotive force (unit: mV).
In addition, about the sample 19, after performing the 1st measurement to the temperature difference 700 degreeC, the 2nd measurement to the temperature difference 1600 degreeC was performed again. In FIG. 10, the first measurement result of the sample 19 is G19-1 (plot of ● in the figure), the second measurement result of the sample 19 is G19-2 (plot of ▲ in the figure), and the result of the sample 20 is G20. As shown.

  Referring to FIG. 10, it was confirmed that the sample 19 has a sufficient thermoelectromotive force as a thermocouple and can stably measure temperature even in a high temperature range. Specifically, for example, the sample 19 has an extremely large value of 95 mV at a temperature difference of 500 ° C., 141 mV at a temperature difference of 700 ° C., 234.5 mV at a temperature difference of 1050 ° C., and 380 mV at a temperature difference of 1600 ° C. The thermoelectromotive force was generated.

  On the other hand, sample 20 is 31 mV at a temperature difference of 1600 ° C., for example, and is higher than a conventional industrial thermocouple (such as a B-type thermocouple) having a thermal electromotive force of about 20 mV at a temperature difference of 1600 ° C. It had a thermoelectromotive force. However, it was confirmed that the sample 19 can generate a thermoelectromotive force higher than the sample 20, and can generate a thermoelectromotive power of about 20 times as compared with the conventional industrial thermocouple. That the thermoelectromotive force of the sample 19 is about 20 times larger than that of the conventional industrial thermocouple, that is, the resolution when converting the thermoelectromotive force to the temperature of the temperature measurement object is large. That is, the thermocouple of the sample 19 can measure temperature with a high accuracy of about 20 times that of the conventional thermocouple.

(Sample 21, sample 22)
A commercially available type B thermocouple was prepared as sample 21, and a commercially available type K thermocouple was prepared as sample 22.
<Evaluation 2>
The thermal response (response) of each of the thermocouples of the sample 19 and the samples 21 and 22 was evaluated. Specifically, the thermocouples of Sample 19, Sample 21 and Sample 22 were simultaneously immersed in hot water at a liquid temperature of 50 ° C., and changes in the thermoelectromotive force under the same conditions were measured. The measurement results are shown in FIG. 11 and FIG. FIG. 12 is a partial enlarged view of FIG. The horizontal axis of FIG. 11 and FIG. 12 shows the elapsed time (unit: second) on the assumption that the moment of immersion is 0 seconds, and the vertical axis shows the thermoelectromotive force (unit: mV). In FIG. 11 and FIG. 12, the result of sample 19 is shown as G19, the result of sample 21 as G21, and the result of sample 22 as G22. FIG. 12 shows the scale of the vertical axis (thermoelectromotive force) of G19 as S1, the scale of the vertical axis (thermoelectromotive force) of G20 as S2, and the scale of the vertical axis (thermoelectromotive power) of G21 as S3. It is a thing.

  As shown in FIG. 11, it was confirmed that the thermocouple of sample 19 can generate extremely large thermoelectromotive force in a short time as compared with the thermocouples of sample 21 and sample 22. Furthermore, as shown in FIG. 12, it was confirmed that the thermocouple of sample 19 has a shorter elapsed time from immersion to measurement of the thermoelectromotive force than the thermocouples of sample 21 and sample 22. . In the B-type thermocouple of sample 21, generation of the thermoelectromotive force was not confirmed. Generation of a thermoelectromotive force was confirmed within 0.5 seconds after immersing the K-type thermocouple of the sample 22. However, the thermocouple of sample 19 was confirmed to generate a thermoelectromotive force within about 0.2 seconds after immersion, and was found to exhibit a thermal response superior to that of the K-type thermocouple of sample 22. The

  It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is indicated not by the above description but by the claims, and is intended to include all the modifications within the meaning and scope equivalent to the claims.

  DESCRIPTION OF SYMBOLS 1 1st electrically-conductive member, 1A main-body part, 1B extension part, 1C connection part, 1a closed end, 1b open end, 2 2nd conductive member, 2a end, 3 groove, 4 insulating member, 5, 6 Electrode pad, 8 protective films, 10 thermocouples.

Claims (6)

A first conductive member and a second conductive member,
The first conductive member forms a one-end closed tube,
The second conductive member is disposed inside the first conductive member,
The first conductive member and the second conductive member are connected to form a temperature measurement contact,
The first conductive member includes a first conductive ceramic composed of at least one of zirconium diboride and titanium diboride, silicon carbide, a sintering aid, and unavoidable impurities.
In the first conductive ceramic, the content of the silicon carbide is 5% by mass or more and 20 % by mass or less,
The thermocouple according to claim 1, wherein the second conductive member includes a second conductive ceramic whose main constituent material is boron carbide.   The thermocouple according to claim 1, wherein in the second conductive ceramic, the content of the boron carbide is 50% by mass or more.   The thermocouple according to claim 1, wherein in the second conductive ceramic, the content of the boron carbide is 70% by mass or more.   The thermocouple according to claim 1, wherein the second conductive ceramic comprises the boron carbide and an unavoidable impurity. The semiconductor device further includes an insulating member that insulates the first conductive member and the second conductive member in a region other than the temperature measurement contact.
The thermocouple according to any one of claims 1 to 4, wherein the material forming the insulating member contains at least one of zirconium oxide and zircon. The thermocouple according to any one of claims 1 to 5, wherein the second conductive ceramic does not contain an oxide .

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