WO1996017230A1 - Thermo-couple thermometer and method of manufacturing sintered body for the thermometer - Google Patents

Abstract

Structures of a thermometer comprising an integral unit of a thermo-couple and a protective pipe, a thermometer capable of simultaneously measuring the temperatures of multiple points, and a thermometer device comprising a combination of various external protective pipes and the thermometers described above for measuring the temperature of a molten steel or glass. An alumina sintered body comprising at least 99.5 wt.% of aluminum oxide and a composite plastic body of coarse crystal grains having a size of at least 5 νm and fine crystal grains having a size of not greater than 3 νm, and used as a material of an insulating ceramic protective pipe of the thermometer device described above. A mixture is prepared by adding 2 to 20 wt.% of a coarse alumina raw material and a crystallization assistant to a fine alumina material, formed and then sintered at a low temperature of less than 1,500 °C, preferably below 1,400 °C. Because deterioration of thermocouple wires is less, the durability is high, the handling is easy and the response is high. The device is particularly effective for measuring high temperatures in a contaminated environment, and exhibits remarkable measurement performance and economical efficiency when used in a diffusion furnace for semiconductor manufacture where multi-point measurement is necessary.

Description

 Title of the Invention Thermocouple Thermometer and Method for Manufacturing Sintered Body for the Thermometer

 The present invention relates to a thermocouple temperature measuring element in which a thermocouple and an insulative ceramic protection tube are integrated, a sintered body for the insulating ceramic protection tube, and a method for manufacturing the same. One or more thermocouples with one or more thermocouple elements integrated into a protective tube that has two or more holes and also functions as an insulating tube The structure of the thermocouple element, the structure of the thermocouple element incorporating this element in the external protective tube, and the high temperature creep resistance in the operating temperature range of 160 ° C or lower. The present invention relates to an excellent sintered ceramic protective tube and a method for producing the same. Background art

In general, thermocouples of thermocouple thermometers are thermocouples that detect temperature by the difference of thermoelectromotive force and insulators that electrically insulate the wires of the thermocouple. It consists of a protective tube. Thermocouples include insulated thermocouples that have been previously insulated with a teflon-based glass braid, etc., but this is generally limited to measuring temperatures in the low-temperature range of 500 ° C or lower, and measuring in the high-temperature range. Generally, the temperature is controlled by passing a bare thermocouple through a two-hole magnetic insulating tube and inserting the same into the above-mentioned protective tube. In addition, thermocouple materials are classified into precious metal materials using platinum rhodium and base metal materials using other metals or alloys.The base metal materials are inferior in heat resistance. Precious metal thermocouples are mainly used for high temperature measurement. When this noble metal thermocouple is exposed to the environment of reducing gas, metallic gas and impurities, the thermoelectromotive force decreases and the temperature error increases. For example, when a platinum wire is in contact with a refractory containing Si force at a high temperature, if C 0 gas is present, the Si force will be reduced and silicon will be absorbed by the platinum, resulting in a very brittle alloy and breaking. is there. In addition, most metals, such as copper, iron, lead, zinc, cadmium, aluminum, and tin, are made of low melting point alloys or compounds. The temperature cannot be measured due to deterioration or melting due to melting point drop or brittle crack. A protection tube is used to protect the thermocouple and prevent deterioration due to the adhesion of impurities and exposure to contaminant gases.However, when measuring temperature, especially high temperature measurement is performed in a severely polluted environment. Often, contaminants also enter the small gap between the protective tube and the isolation tube, affecting the heat-sensitive part of the thermocouple and the joint of the insulating tube.

 Next, during handling, contamination inside the thermocouple, storage tube and protective tube during storage or assembly also causes deterioration of the thermocouple at high temperatures. For this reason, thermocouples are inserted into insulating tubes in a clean room with gloves so that they cannot be touched with hands. In addition, this insertion work does not require much work if the strand is unused, but once used, it often causes deformation distortion and surface roughness, and this is inserted into a long hole in the insulating tube. It is an extremely difficult and tedious task to go through.

 From the viewpoint of the performance as a thermometer, it is important to have excellent temperature responsiveness in addition to temperature accuracy. There is a protective tube, a gap, and an insulation tube between the temperature measurement target and the thermosensitive part of the thermocouple, through which heat is transferred. The response speed is faster for the platform. However, conventional thermometers have not been made very thin. The outer diameter of the thinnest tube is two holes with a diameter of about 3 mm.Even if the wall thickness of the protective tube is 1 mm and the air gap is 0.5 mm, the outer diameter of the protective tube (S Is 0.6 mm. One hole has an outer diameter of up to about ø1 mm.If one thermocouple wire is inserted into this hole and the other is not inserted, a thermometer with an outer diameter of ø3 mm can be made. The strength is weak, and the long-term measurement at high temperature makes the degradation of the thermocouple wire much faster than that with two wires, and the long one is difficult to manufacture and the manufacturing cost is high.

There is a sheath thermocouple in which a thermocouple, an insulator, and a protective tube have an integral structure. In this method, magnesium oxide powder is mainly used for the insulator, and a heat-resistant metal such as stainless steel or Inconel is used for the sheath corresponding to the protective tube, and can be bent and stretched. Therefore, the risk of breakage is small and the airtightness is good, so there is no contamination from outside and the handling is simple. Very small size and very long size can be obtained, and the price is low. However, the operating temperature is up to about 100,000 During the measurement, the thermocouple may be contaminated by the outer metal.

 If the temperature is to be measured in a gas, such as in a kiln or atmosphere furnace, the temperature can be measured simply by using an oxide protective tube.In the case of measuring the temperature of molten metal or glass, however, the protective tube has corrosion resistance and heat resistance. Materials with excellent properties such as impact resistance and leak resistance are required. That is, they are often made of high corrosion resistant non-oxide ceramics such as boron nitride and aluminum nitride, and carbon-containing refractories such as molybdenum and zirconium cermets and alumina graphite. Generates reducing gas, metal vapor, glass, etc. at high temperatures and contaminates and degrades thermocouples. Therefore, in order to protect the thermocouple from contaminants generated from such a protective tube, the oxide protective tube (mainly aluminum ceramix) is protected with a thermocouple and an insulating tube and a material excellent in the above characteristics. Must be used as an internal protective tube between the tube. Therefore, two or more protective tube sections and an air layer between them exist between the thermocouple junction and the object to be measured, and steep response cannot be obtained. In addition, the size increase due to the multi-layer structure and breakage of the protection tube due to the difference in thermal expansion between the protection tubes are likely to occur.

 Among the needs for temperature measurement in the high temperature range, there are cases where it is necessary to measure the temperature at multiple points in the furnace at the same time, for example, in a diffusion furnace in a semiconductor manufacturing line. However, the conventional temperature measurement method generally involves inserting a thermocouple through a two-hole insulating tube into a large-diameter size protective tube and inserting it into each of the measuring points, or by using only the number of measuring points individually. This is performed using a thermometer. In the case of the former, there are many problems in terms of both temperature accuracy and responsiveness due to the influence of the heat flow in the air layer inside the large-diameter size protection tube. That is, when the temperature outside the protection tube changes, it takes a considerable time for the low heat conduction air layer inside the protection tube to reach a new steady state of heat flow by heat transfer. In the latter case, the overall size increases.

On the other hand, ceramic materials are often used as materials for protective tubes for high-temperature measurement because they require high heat resistance and high corrosion resistance. Typical materials include oxide ceramics such as alumina, zirconia and mullite, and non-oxide ceramics such as silicon nitride and silicon carbide. Among these ceramic materials, oxide ceramics has the advantage that manufacturing costs are lower than non-oxide ceramics because sintering can be performed in the atmosphere with relatively low raw material costs. There is. Alumina ceramics in particular have excellent chemical stability and a high melting point of 250. Is an important material in the field where is required. However, alumina ceramics, which is superior in heat resistance and corrosion resistance, has defects inferior in high-temperature creep resistance because it is an oxide ceramic. Creep is a phenomenon in which when a material is exposed to a high temperature, the material is plastically deformed by an external force at a temperature lower than the melting point of the material. When polycrystalline alumina ceramics is exposed to a high temperature of 1200 or more, grain boundary sliding tends to occur between alumina crystal grains. When this phenomenon occurs, deformation of the product, cracking and the resulting decrease in material strength and airtightness occur, making it difficult to use as a high-temperature member. In particular, high temperature creep resistance at the operating temperature is required for components of high temperature measuring elements.

 In general, each atom constituting oxide ceramics such as alumina has a mixture of ion coupling and covalent bonds, and non-oxide ceramics such as silicon carbide consist of covalent bonds. In this mode of chemical bonding, covalent bonds have a stronger bond strength than ionic bonds. Therefore, at a high temperature of 1200 ° C. or higher, oxide ceramics having ionic bonds have a reduced bond strength between atoms and are liable to undergo plastic deformation. On the other hand, non-oxide ceramics have a property that plastic deformation is unlikely to occur even at a high temperature of 1200 C or higher due to covalent bonds. However, non-oxide ceramics require oxidation at a high temperature of more than 1300 ° C, high raw material costs, and a special firing furnace in a non-oxidizing atmosphere during the sintering process. In addition, there are many problems such as poor workability of the sintered body, and as a result, the product cost is high.

In order to solve this problem, it is conceivable to use oxide ceramics that are inexpensive in product cost. Aluminum oxide ceramics, which have abundant raw materials among oxide ceramics and have excellent chemical stability, have low cost and high temperature characteristics if improved high temperature creep resistance is improved. Excellent material. As an example of improving the high temperature creep resistance of this alumina ceramic, Japanese Patent Application Laid-Open No. 5-14813 discloses that the average crystal grain size of a sintered body is 99.8% by weight of alumina. A description is given of an alumina ceramic and a method for producing the same, in which the sintering temperature is set to 2 or more and the sintering temperature is set to 1500 ° C. or more. In this example, the grain boundary slip of the alumina crystal particles is prevented by setting the crystal grain size of the alumina sintered body to 2 m or more. In other words, the sintering is performed at a high temperature of 150 ° C. or higher to increase the size of the alumina crystal grains. In this example, the sintering temperature is set to a high temperature range from 150 to 170 to increase the size of the alumina ceramic crystal particles within a range where the mechanical strength does not decrease. . Sintering step _c generally Serra mix to produce crystal particles of naturally alumina The higher sintering temperatures the grain growth, sintering costs, the higher the sintering temperature is high. That is, an increase in the sintering temperature leads to wear of the furnace members, use of a high refractory material, and an increase in sintering energy, and as a result, the product cost increases. The high cost of products is one factor that hinders the development of material applications. In addition, as the sintering temperature rises, the dimensional accuracy tends to decrease due to deformation of the product. Although it depends on the operating conditions of the sintering furnace, it is generally desirable that the operating temperature of the furnace taking the production cost into account is less than 1500 ° C, preferably less than 140 ° C. In particular, for thermocouple type thermometer protection tubes, which are a type of thermometer used at high temperatures, it is extremely important to reduce the cost, so that low temperature firing is possible as much as possible and the sintering temperature is higher. Thus, an alumina sintered body having excellent high-temperature creep resistance at high temperatures, practically up to 160 ° C., is required. However, alumina ceramics that can be sintered at low temperatures, are inexpensive to manufacture, and have excellent high-temperature creep resistance at temperatures higher than the sintering temperature have not yet been developed.

 As described above, the conventional temperature measuring element has no problem in the low-temperature range, but in the high-temperature range above 100 ° C, the thermocouple deteriorates mainly due to pollutants, and handling is troublesome. The cause is easy to occur. In terms of performance and size, thinner and longer ones are required. These are only possible when the thermocouple, insulator and protective tube are integrated like a sheath thermocouple, and there is a need for a high-temperature integrated temperature measuring element at a working temperature of 100 ° C or more. . In other words, there is a demand for a sheath-ripened electric body with a ceramic sheath. Further, there is a need for a puncture element having a structure that can minimize the number of layers. In addition, there is a need for a compact, multi-point temperature measuring element with excellent temperature accuracy and responsiveness. Disclosure of the invention

The present invention has been made in view of such circumstances, and its object is to simplify handling, to have excellent temperature responsiveness, to improve the durability of a thermocouple, and to improve molten metal. We do not provide thermocouples with wide versatility such as temperature measurement and simultaneous measurement of other points It is assumed that.

 The inventor has found that the above problem can be solved by the following means. That is,

 1. An insulating ceramic protective tube with two holes, and two dissimilar metal wires that extend through each of the two holes and are joined at the tip to form one temperature measuring contact And a thermocouple stab element, wherein the thermocouple and the protection tube are integrated with each other, wherein the thermocouple comprises a thermocouple comprising: it can.

 2. The thermocouple can be solved by the thermocouple temperature measuring element as described in 1 above, wherein a gap is provided between the thermocouple and the insulating ceramic protective tube at the temperature measuring contact section. .

 3. A thermocouple measurement characterized by having a multipoint temperature measurement structure in which two or more thermocouple temperature measurement elements according to 1 or 2 above are sintered and integrated at different positions of the respective stab contacts. This can be solved by a heating element.

 4. An insulating ceramic protective tube having four or more even-numbered holes, and two different types of two different types of thermoelectric junctions that extend through each of the holes and are joined at the ends of the wires. Multi-point measurement consisting of two or more thermocouples made of metal wires, and having a structure in which the high-temperature contact side of the insulating ceramic protection tube is closed, and where the positions of the temperature measurement contacts of each thermocouple are different. The problem can be solved by a thermocouple temperature measuring element characterized by having a temperature structure.

 5. An insulative ceramic protection tube having three or more holes, and two or more different types of metal wires are placed in different positions on one metal wire while extending through each of the holes. A multi-point thermocouple branch thermocouple that forms two or more temperature measuring junctions, and that the temperature measuring contact side of the insulating ceramic protective tube is closed. The problem can be solved by the characteristic thermocouple temperature measuring element.

 6. It is awaited that the thermocouple temperature measuring element described in 1 or 2 or 3 or 4 or 5 above has a structure including the thermocouple temperature measuring element inside and an external protective tube that cuts off from the outside by incorporating the thermocouple temperature measuring element inside. Can be solved by a thermocouple temperature measuring element.

7. The thermocouple thermometer according to the item 6, wherein the material of the outer protective tube is a non-oxide ceramic, a carbon-containing refractory, a cermet, and a metal. Can be solved.

 8. The above-mentioned insulating ceramic protection tube is made of an alumina sintered body containing aluminum oxide of 99.5% or more and a sintering aid as essential components, and the crystal structure of the sintered body is (1), (2), (3), (4), (5), (6) and (7), characterized by being an alumina sintered body mainly composed of a mixed structure of coarse grains having a crystal grain size of 5 m or more and fine grains of 3 m or less. The problem can be solved by the thermocouple temperature element described in (1).

9. As a starting material of the alumina component of the alumina sintered body composed of a substantial alumina component and a sintering aid, a fine aluminum oxide powder having an average particle size of 1 m or less and a coarse aluminum oxide powder having an average particle size of 3 m or more are used. Using a mixture of 0.5 to 20% by weight of aluminum oxide powder and adding a sintering aid, the raw material is molded, and the crystal grain size is 5 m mainly based on the crystal structure after firing. brief description of the _c drawings that can be solved by a sintered body manufacturing method of the thermoelectric material temperature measuring device according to the 8, characterized in that in the above coarse grains and 3 m below the mixed structure of fine grains

 Figure 1 is a structural diagram of a temperature measuring element with a thermocouple and a protection tube integrated with a structure in which a temperature measuring contact is embedded in a ceramic matrix.

 Fig. 2 is a structural diagram of a temperature measuring element in which a thermocouple and a protective tube are integrated with a structure in which a gap is provided between the temperature measuring contact and the substrate by a partition lid.

 Figure 3 shows that he loses heat. ! FIG. 4 is a structural diagram of a temperature measuring element in which a thermocouple and a protective tube are integrated with a structure in which a gap is provided by using a thermocouple.

 Fig. 4 shows the structure of a thermometer with a thermocouple and a protection tube integrated with a structure in which a gap is provided by hollowing one end of a green body of a two-hole pipe and sealing it by pressing from the outside. FIG.

 FIG. 5 is a structural diagram of a multi-point temperature measuring element in which two or more one-point temperature measuring elements are sintered and integrated at different positions of respective temperature measuring contacts.

 Fig. 6 shows a multipoint thermometer in which two or more thermocouples are installed in different positions of each thermocouple in an insulative ceramic protective tube with four or more even holes. FIG.

Figure 7 shows the location of the temperature measuring junction in an insulated ceramic protection tube with three or more holes. FIG. 3 is a structural view of a multipoint temperature measuring element incorporating a branch thermocouple connected in a different manner.

 FIG. 8 is a structural diagram of a conventional multipoint temperature measuring method in which a plurality of thermocouples passed through an insulating tube are inserted into a protective tube.

 FIG. 9 is a structural diagram of a temperature measuring element in which a thermocouple and a protection tube for immersing a molten metal are combined with a thermocouple and a protection tube as one body. BEST MODE FOR CARRYING OUT THE INVENTION

Figure 1 shows the structure of a temperature measuring element in which a thermocouple and a protection tube are integrated with a structure in which a temperature measuring contact is embedded in a ceramic matrix. The two wires of the thermocouple 4 extend through the two holes, and the thermocouple junction 6 of the thermocouple is in the substrate on which one end of the two-hole insulating ceramic protective tube 1 is sealed. And is protected from external contaminants and reducing atmospheres. There are many ways to incorporate a thermocouple into a ceramic body, but any method that provides sufficient airtightness is acceptable. According to this method, the thermocouple junction part of the thermocouple is embedded in the substrate, and there are some forces <with and without a gap between the thermocouple and the substrate. In other words, when there is no air gap, it is generally easy to manufacture, and a very responsive material can be obtained by direct heat transfer between the substrate and the piercing junction. Vulnerable to differential expansion. On the other hand, those with voids do not cause damage because the thermocouple can be freely expanded and contracted with the substrate, and are suitable for repeated use at high temperatures many times. FIG. 2, FIG. 3 and FIG. 4 illustrate this, and various shapes can be taken by means for forming a gap. That is, FIG. 2 is a structural diagram of a temperature measuring element in which a thermocouple and a protection tube are integrated with a structure in which a gap is provided between a temperature measuring contact and a substrate by a partition lid. This is because the thermocouple and bare body are separated by a partition lid (flat lid) 12 before the thermocouple contact of the bare thermocouple wire is embedded in the green body. It is formed. The portion surrounded by the dotted line in Fig. 2 is the flat lid 12, which is made of a material having the same composition as the ceramic base, and after firing, it is integrated with the ceramic base. ing. FIG. 3 is a structural diagram of a temperature measuring element in which a thermocouple and a protection tube are integrated with a structure in which a gap is provided by using an aging and disappearing coating. This is done by previously applying a heat-dissipating material S to the temperature measuring junction of the thermocouple wire and burying it in the ceramic substrate. After the embedding, the coated portion disappeared during firing, forming voids 9. Providing an air gap means that two holes are connected by an air gap, and the thermocouple wire passes through the connection hole without being fixed to the ceramic body. Since the position of the temperature measuring contact is shifted from the position of the distal end of the protective tube and a temperature measuring error is easily caused, it is preferable to make the temperature measuring contact as small as possible. In the case of Fig. 3, there is no worry about the displacement of the measuring junction because the measuring junction is almost immovable due to the formation of a thin L and a gap along the shape of the measuring junction. The position of the temperature measuring junction must be near the tip of the protection tube from the viewpoint of temperature measurement accuracy as described above, but from the viewpoint of responsiveness, the thickness between the temperature measurement contact and the tip of the protection tube should be as thin as possible. Good to control. This is preferably about 1 to 4 mm depending on the material of the cellar and the purpose of use, and more than this is not preferable from the viewpoint of thermal shock resistance. Figure 4 shows the structure of a thermometer with a thermocouple and a protective tube integrated with a structure in which a gap is provided by boring one end of a green body of a two-hole pipe and sealing it by pressing from the outside. FIG. This is excellent in responsiveness because it is relatively easy to manufacture and the thickness of the tip can be reduced. FIG. 5 is a structural diagram of a multi-point temperature measuring element in which two or more single-point temperature measuring elements 13 are sintered and integrated at different positions of the respective temperature measuring contacts (6, 7, 8). Fig. 6 shows two or more thermocouples 4 in an insulative ceramic protective tube 2 with four or more even holes, with the position of each temperature measuring junction (6.7.8) being changed. FIG. 2 is a structural diagram of a multipoint temperature measuring element built therein. Fig. 7 shows a multi-unit thermocouple with built-in branch thermocouples 5 that are connected at different positions of the temperature measuring contacts (6.7, 8) in an insulative ceramic protection tube 3 having three or more holes. FIG. 3 is a structural diagram of a dot piercing element. FIG. 8 is a structural diagram of a conventional multipoint temperature measuring method in which a plurality of thermocouples 4 passed through an insulation tube 14 are inserted into a protection tube 15. In the case of multipoint temperature measurement using the conventional method shown in Fig. 8, the heat transfer from the external atmosphere 19 of the protection tube to be measured to the temperature measuring junction (6, 7.8), which is the heat-sensitive part, depends on the external atmosphere. Heat transfer between 19 and the outer surface of the protection tube 16, heat conduction at the pipe wall 18 of the protection tube 15, inner surface 17 of the protection tube and the air layer 10, and the air layer 10 The heat transfer between the insulation tube 14 and the heat conduction inside the insulation tube, that is, the complicated path of the so-called multi-layered tube heat transfer. Therefore, the response is poor and the accuracy of temperature measurement is also poor. That is, in FIG. 8, since the temperature measuring contacts 7 and 8 are affected by the air convection generated in the gap 10, the steady state of the heat flow is reached after the temperature of the puncture target (external atmosphere) changes. Before you do Takes time. On the other hand, the heat transfer of the multipoint temperature measuring element of the present invention shown in FIGS. 5, 6, and 7 is based on the heat transfer between the external atmosphere and the outer peripheral surface of the protection tube and the pipe wall portion of the protection tube. This is a single-layer tube heat transfer that is directly transmitted to the temperature measuring junction by heat conduction at the point. Therefore, the responsiveness is good, and there is no air convection portion which occurs in the above-mentioned gap portion 10, so that the accuracy is good. In addition, the responsiveness is further improved because the size can be reduced compared to the conventional method. In addition, it is easy to handle because of its integral structure.

 FIG. 9 is a structural diagram of a temperature measuring element in which a thermometer and a protection tube integrated with a thermocouple and a protection tube for immersion of molten gold are combined. The two strands of thermocouple 4 extend through the two holes of the two-hole insulating ceramic protection tube 1, and the thermocouple junction 6 of the thermocouple has the two-hole insulating ceramic. It is completely enclosed inside protection tube 1 and is protected from external contaminants and reducing atmospheres. A protective tube 20 for immersion of molten metal having erosion resistance and thermal shock resistance to molten steel is provided on the outside thereof. The terminal box 21 is connected to this to form a temperature measuring element.

When the above temperature measuring element is immersed in molten steel, heat transfer between the molten steel and the surface of the molten metal immersion protection tube 20, the molten metal immersion protection tube 20 and the gap 11, and a two-hole insulating ceramic Due to the heat conduction between the mix protective tubes 1, heat is transferred from the molten steel to be measured to the temperature measuring junction 6 of the thermocouple. At that time, reducing gas, glass, metal vapor, etc., which contaminate and degrade the thermocouple, are generated from the molten metal immersion protection tube. This is because, as a protective tube for immersion in molten gold, material characteristics that are excellent in erosion resistance and heat resistance to bite are first required, so non-oxidizing materials such as boron nitride, aluminum nitride and zirconium boride are generally used. This is because materials such as carbon-containing refractories such as ceramics, aluminum graphite, and zirconium graphite, molybdenum-based, and zirconium-based cermets are used. For this reason, in the conventional method, an oxide ceramic protective tube made of alumina or the like is used inside the molten metal immersion protective tube to shield the thermocouple wires exposed from the insulating tube from the above-mentioned contaminants. However, in the temperature measuring element of the present invention, the thermocouple is completely sealed in the insulative ceramic protection tube, so the protection for molten metal immersion does not require an oxide ceramic protection tube. The temperature measuring elements of the means 1 to 5 can be directly inserted into the inside of the tube 20 for use. Therefore, a sharp response can be obtained as compared with the conventional multilayer structure piercing method. Next, the action of the material of the insulating ceramic protective tube of the temperature measuring element of the present invention will be described in detail.

 As the material of the above-mentioned insulating ceramic protection tube, basically any ceramic can be used as long as it does not deteriorate the thermocouple and has excellent insulation at high temperatures. For example, in the case of a platinum-based R thermocouple that is weak in a reducing atmosphere, an oxide such as alumina or magnesium is suitable, and can be appropriately changed according to the purpose of use. However, for high temperature use, the creep characteristics of the sintered body of the insulating ceramic protection tube are very important. The alumina sintered body most suitable as the material of the insulating ceramic protection tube particularly provided in the present invention is much superior in the high-temperature cleaving property to the conventional alumina sintered body.

The higher the purity of the alumina sintered body of the present invention, the higher the heat resistance and corrosion resistance. The purity of the alumina sintered body having the heat resistance, corrosion resistance, and electrical insulation required for a thermocouple protection tube at an operating temperature of up to 160 ° C is required to be 99.5% or more. Further, the alumina sintered body of the present invention requires a sintering aid. A typical example of the sintering aid is an alkaline earth metal oxide. Magnesium oxide, calcium oxide, barium oxide, and strontium oxide are used alone or in combination of two or more types of alumina sintered bodies. It is added so as to contain 0.5% by weight or less. When a sintering aid such as an alkaline earth metal oxide is not added, crystal growth does not proceed very much at a protection tube operating temperature of about 140 ° C or lower, but the operating temperature is 1450 ° C. From around C, the grain growth proceeds and the material strength decreases. In a composition without the addition of a sintering aid, when the operating temperature is higher than the sintering temperature, for example, when the sintering temperature is 140 ° C and the operating temperature is 160 ° C, The growth proceeds rapidly, and the value of the flexural strength after sintering of 300 MPa or more decreases to 200 MPa or less. Therefore, the addition of sintering aids such as alkaline earth metal oxides is indispensable. According to the present invention, an auxiliary agent such as an alkaline earth metal oxide is added externally to alumina so as to be 0.5% by weight or less in terms of oxide relative to the alumina raw material. Addition of a sintering additive exceeding the above range is not preferable because the heat resistance and corrosion resistance are reduced because the purity of alumina itself is reduced. These sintering aids can be used as long as they do not adversely affect the characteristics of the alumina sintered body. Among them, magnesium oxide, calcium oxide, and sulfur oxide Alkaline earth metal oxides such as trontium and barium oxide are preferred.

 In the alumina sintered body of the present invention, the grain size of alumina constituting the alumina sintered body is important. The sintered body mainly consists of coarse crystal grains of 5 m or more and fine crystal grains of 3 m or less. An object of the present invention is to lower the production cost by lowering the sintering temperature and obtain an alumina sintered body having excellent heat resistance, corrosion resistance, and high-temperature creep resistance. In general, a low-temperature sinterable alumina sintered body is formed by molding a fine raw material powder having an average particle diameter of 1 m or less, especially 0. Sinter below ° C. Such a low-temperature sinterable alumina sintered body is characterized by an extremely small alumina crystal particle diameter of 3 or less. When only heat resistance and corrosion resistance are considered, there is no problem because the purity of the fine raw material powder itself is 99.5% or more. For thermocouple protection tubes that require high-temperature cleaving resistance, plastic deformation at high temperatures is a fatal problem. In other words, if the crystal grain size in the alumina sintered body is too small, plastic deformation due to grain boundary sliding of alumina occurs at a high temperature in a low temperature range of about 1400. For example, after adding a few hundred ppm of sintering aid, for example, magnesium oxide to fine alumina raw material, and forming it, and sintering it at 140 ° C or less, the alumina sintered body can be heated to 140 ° C or more. It is not suitable for thermocouple protection tube because it causes remarkable plastic deformation at the operating temperature and lowers the strength.

In the present invention, low-temperature sintering at 150 ° C. or less, preferably 140 ° C. or less, is possible, and heat resistance, corrosion resistance, and high-temperature creep resistance at 160 ° C. or less. In order to increase the crystallinity, it is necessary to mix two types of coarse and fine crystal grains constituting the alumina sintered body. As a method for producing this sintered pair, an average particle diameter of 1 m or less, which is excellent in low-temperature sinterability, and preferably an average particle diameter of 3 m or less for a fine alumina raw material having an average particle diameter of 0.5 m or less. The raw material is added at 2 to 20% by weight of a coarse alumina raw material having a particle size of 1 μm or more and sintered at a temperature lower than 1500 ° C., preferably at a temperature lower than 140 ° C. It is desirable that the coarse particle material used has an average particle size of 3 m or more. With raw materials having an average particle size of less than this, it is difficult to grow coarse crystal particles of 5 m or more after sintering. _C Fine alumina raw materials should have as small an average particle size as possible. Raw materials capable of sintering to a water absorption of 0.1% or less at a temperature of less than 1500 ° C when sintered alone can be used as appropriate. The average particle size of this fine raw material is approximately 1 m or less, Or less than 0.5 m. The purity of both coarse and fine raw materials should be as high as 99.5% or higher, since the higher the purity, the higher the heat resistance and corrosion resistance.

 As for the mixing ratio of the coarse raw material to the fine raw material, the higher the mixing ratio of the coarse particles, the better the higher the high-temperature cleaving resistance. However, if the distribution ratio of the coarse particles is too high, sintering at less than 1500 ° C, especially at 140 ° C or less, becomes difficult, and the water absorption becomes 0.5% or less. The required airtightness cannot be maintained. The sintering temperature at which the water absorption rate can be reduced to 0.1% or less is required to be 150 ° C. or more, which significantly increases the production cost. In the present invention, since it is important to reduce the cost, the mixing ratio of the coarse alumina particles to the fine alumina particles is preferably in the range of 2 to 20% by weight in order to enable sintering at less than 150 ° C. It is. When the blending ratio of the coarse alumina raw material is less than 2% by weight, the number of coarse alumina crystal particles in the sintered aluminum sintered body is small, and the Grain boundary sliding cannot be prevented.

In order to obtain the alumina sintered body of the present invention, a predetermined coarse alumina raw material is blended with the above-mentioned fine alumina raw material, and further, for example, an alumina earth metal oxide is sintered as an alumina sintering aid. In addition to the range of 0.5% by weight or less in the body, the normal ceramic molding process, such as rubber pressing, slip casting, injection molding, extrusion method, etc. By using the molding method described above, it is formed into the desired thermocouple protection tube shape. With the slip casting method, the end face of the protective tube can be easily sealed in a plaster-shaped shape. In the extrusion molding, after the extrusion, it may be sealed with the extruded clay. Here, the sintering aid to be added to the alumina raw material only needs to be in the form of an oxide after sintering. Therefore, in the case of magnesium oxide, magnesium carbonate, magnesium hydroxide, or the like can be used as appropriate. After forming into a thermocouple protective tube shape of specified dimensions, sintering is performed through raw processing, degreasing, and degreasing as necessary. For sintering, an electric furnace or a gas furnace, which is usually used for sintering ceramics, can be used. Depending on the shape of the product, the heating rate is less than 300 hours and less than 150 hours. Preferably, it is heated up to the following sintering temperature, and kept at the same temperature for about 1 to 4 hours, and then cooled in a furnace to have excellent heat resistance, corrosion resistance, and high temperature creep resistance. An alumina sintered body for thermocouple protection tube is obtained. The heat resistance and corrosion resistance of the alumina sintered body of the present invention were evaluated by exposing a protective tube made of the alumina sintered body manufactured according to the intended application to an environment where the temperature was 140 ° C or more. This is done by checking for the occurrence of corrosion. As shown in the examples, the high-temperature creep resistance was measured when an alumina sintered body with a protective tube or a shape close to the protective tube was prepared and subjected to an exposure test at 160 ° C for 5 hours. Judgment is made from the degree of self-weight deformation of the protection tube or a shape close to the protection tube. As a judging method, insert the test resistance into the refractory, protrude at least 120 mm from the end of the refractory, install the refractory in the furnace, and raise it at a rate of 100 ° C / hour or more. Raise the temperature to 160 ° C at a heating rate, hold at the same temperature for 5 hours, and cool the furnace. C Measure the height of the specimen before and after the test to the hearth, and measure the height deformation before and after the test (mm ) Is the weight deformation. The self-weight deformation degree means that 1 5 mm or less value, if practical problem becomes _c 1 5 mm or more does not cause the plastic deformation of the product by grain boundary sliding is large, deformation of the tensile stress of the product is loaded The cracked portion, that is, the portion extended by the grain boundary sliding, causes fine cracks between the crystal grains, resulting in a decrease in the airtightness and strength of the protective tube. In addition, the problem of difficulty in pulling out the protective tube from the refractory due to deformation arises. The same result can be obtained by inserting the specimen directly into the furnace wall and projecting it into the furnace. Although the shape and method of use of the alumina sintered body differ depending on the field of use, the alumina sintered body of the present invention has heat resistance, corrosion resistance, high temperature creep resistance and low cost in a temperature range up to 160 mm. It is the most suitable sintered body for thermoelectric protection tube requiring high heat resistance.

The crystal grain size of the alumina sintered body of the present invention is an important factor that affects the high-temperature creep resistance. For the measurement of the crystal grain size, the alumina sintered body in the shape of a protective tube is cut, polished, flat-polished, polished and the surface of the sintered body is mirror-finished, and subjected to thermal corrosion at a sintering temperature or lower. When this sample was observed with an electron microscope, if the area ratio of coarse particles of 5 m or more was 20% or more and the fine particles of 3 m or less occupied 80% or less, heat resistance, corrosion resistance, It can be used as a thermocouple protection tube with excellent high-temperature resistance. The visual field of this microscopic observation should be such that at least 20 or more coarse and fine particles are present in a mixed state. The maximum diameter of each particle is defined as crystal 結晶. The area occupied by each crystal is calculated using an image analyzer or assuming a circle with the largest diameter as the diameter for each particle. The crystal grain size and the area occupied by the crystal are determined for five different visual fields and the average value is adopted. Example

 Example 1

 The temperature measuring element in which the thermocouple and the protection tube of the means 1 and 2 are integrated into a structure in which the temperature measuring contact of the thermocouple is embedded in the substrate and a structure in which a gap is provided between the two. As for, a sample in which an R type thermoelectric element having an outer diameter of 0.4 mm, a hole diameter of ø1 mm, and a protective tube length of 50 Omm was prepared. This was used for the sintering of molten steel in a steelmaking dinner dish that is currently being carried out. In other words, the integrated heating element was inserted into an external protective tube (protective tube for ALN-based molten steel) set on the side wall of the evening dish, and the temperature of the molten steel was continuously measured. The temperature measurement time was set to 8 hours in a row, and the same device was repeatedly used 10 times (80 hours).

 Five

This test was conducted by examining the temperature error with respect to a standard thermocouple at 1200 ° C in an electric furnace, and was accepted if the error was within ± 3 (including the error of the electric furnace itself ± 1). did. As a result, all of the samples subjected to the above test did not cause any damage to the protection tube or breakage of the thermocouple, and the test result passed.

It should be noted that the actual situation concerning the durability of the conventional continuous temperature measurement method (assembled with thermocouples, protective tubes, and insulated tubes) actually used in the above-mentioned tundish and the test results of the above-mentioned temperature measuring elements were used. Table 1 shows examples of the comparison.

table 1

 Durable comparison example between conventional type and integrated type temperature sensor in continuous molten steel temperature measurement

 (note)

 • The number of samples is 144 conventional temperature measuring methods and 12 integrated temperature measuring elements. * 'The test stand was continued until the thermocouple was disconnected or reached 10 times (80 hours), replacing only the base where the thermowell was damaged or the damaged thermowell.

According to Table 1, in the case of the conventional temperature measurement method described above, the protection tube is easily damaged (cracked), and contaminant gas enters the protection tube, rapidly deteriorating the thermocouple and causing a disconnection. . Even if the protection tube was small (outer diameter ø6 mm, inner diameter ø4 mm), it was not improved. (Protection tube breakage time: 2.5 times on average (20 hours)). On the other hand, in the case of the integrated temperature measuring element, there is no problem under the above It was found that long-term durability was achieved many times and steepness was obtained because of its small size in terms of responsiveness.

 Example 2

As the multi-point temperature measuring elements of the means 3.4 and 5, a sample was prepared in the following manner. _CThe above three types of multi-point temperature measuring elements have different manufacturing methods. In other words, in the case of the multi-point temperature measuring element shown in Fig. 5, first, a pair of thermocouples are inserted into the two-hole pipe-shaped ceramic green body, the end faces are sealed, and the green body of the single-point temperature measuring element is formed. create. Next, the raw green bodies having different lengths are immersed in water to make the surface water-absorbing, and then the temperature measuring contact is set at a predetermined position and the whole is overlaid. Finally, it is sintered and integrated. In the case of the multi-point heating element shown in Fig. 6, two holes are formed as one set from one end face of a pipe-shaped ceramic raw element having an even number of holes of 4 or more, so that a thermocouple can be inserted. Drill the hole to the required temperature measuring contact position. There is also a method in which each thermocouple is inserted and sealed at the end face to make a bundle of multi-point temperature measuring elements, which is put into a protective tube, a slurry is poured into the gap, and sintered and integrated. It is not preferable because the size increases and the manufacturing cost increases. In the case of Fig. 7, two or more different types of metal wires are connected to one metal wire at different positions to form two or more temperature measuring junctions. Into a bundle of one-hole pipe-shaped ceramic green body cut to the required length up to the required length, apply heat-dissipative coating to the exposed portion of the thermocouple wire, put it in a protective tube, and put it in a slurry. One is poured into the gap and sintered and integrated. Although this method has the disadvantage of increasing the size, one of the two thermocouple strands is shared by one strand, so the overall length of the strand is short, and the longer the number of temperature measuring contacts, the longer the length. The smaller the length, the more advantageous in terms of cost.

The samples of the multipoint temperature measuring element shown in Figs. 5, 6, and 7 were manufactured by the above method, and the comparison with the conventional method shown in Fig. 8 was attempted. The test method is as follows: pre-heat the above sample to 100 ° C, quickly insert it into a semiconductor high-temperature diffusion furnace maintained at around 100 ° C, and change the temperature from the preheat temperature (100 ° C) to Estimate the response time (5 τ) by measuring the time elapsed until the temperature (1 1 26.4 ° C) equivalent to 62.3% of the temperature difference before and after the change, that is, the time constant (T) did. Table 2 shows the results of the comparison. Table 2 Response time ratio of various puncture elements

 f.: As shown in Fig. 5, the temperature measuring element diameter is 93 mm

 Diameter of multi-point temperature measuring element φ from Fig. 6: 5 mm

 Fig. 7 Multi-point temperature measuring element Φ 7.5 mm

 Figure 8 (conventional type): Insulated tube diameter 0 3 mm, protective tube diameter 07.5 mm According to Table 2, the multipoint temperature measuring element of the present invention (Figures 5, 6, and 7) Compared to Fig. 8), the response is faster and the difference between the temperature measuring junction 6 and the temperature measuring junctions 7, 8 is small. In particular, the case of Fig. 5 is a bundle of small-diameter one-point temperature measuring elements, and the response is extremely steep.

 Example 3

As the temperature measuring element combined with the external protective tube of the means 6 and 7, the temperature measuring element in which the thermocouple and the protective tube described in Example 1 were integrated was manufactured with an outer diameter of ø3 mm, and Was inserted into a protective tube for immersion in molten metal to obtain a sample. Pass a thermocouple through a 0.3 mm aluminum insulation tube for specific contraction, insert it into an alumina protection tube with an outer diameter of 0.6 mm and an inner diameter of 4 mm, and insert it into the same material and the same size as the above sample. The sample inserted into the protective tube for immersion in molten metal was used as a specific drawing sample. These samples were rapidly immersed in molten steel kept isothermally at 1550 ° C in a melting furnace from a constant preheating temperature of 10000 ° C. The time constant (r) was measured in the same manner as in 2, and the response time was measured. Table 1 shows the results of the comparison. The temperature corresponding to 63.2% in this case is 134.77.6 ° C. Table 3

 Table 1 Response time between the conventional method and the method of the present invention in molten steel temperature measurement (5)

According to Table 3, the response time of the temperature measuring element of the present invention is reduced to 60 to 80% of the conventional method. Furthermore, when a thin protective tube for molten metal is used, it can be reduced to about 50%.

 The sintered bodies of the temperature measuring elements of the means 8 and 9 and the method of manufacturing the same will be described in detail with reference to the following examples.

 Example 4

99.9% purity, 99.9% pure alumina powder with an average particle diameter of 0.23 / m, coarse alumina raw material with an average particle diameter of 5 / m to 0% to 30% by weight Aluminum blended Add 0 to 1% of magnesium oxide, a kind of alkaline earth metal oxide, to the raw materials, and add water and organic binders, lubricants and wetting agents. The mixture was kneaded to produce a kneaded extruded soil. This was put into the extruder. The extruder base was 3.5 mm in outer diameter, and two cores of about 0.4 mm diameter were installed in parallel so that two thermoelectric wires could pass through. The extrusion pressure was 3 O kgf per square centimeter, and the material was extruded to a total length of about 20 Omm and cut. After sealing the end face of the molded body with the same extruded consolidation soil, it is degreased for 700 hours and kept for 1 hour, and the degreased body can be put in an electric furnace and sintered in air. The sintered body was sintered at the same temperature for 2 hours ₍ no deformation or cracks were observed in the sintered body. The thermal etching treated surface of the mirror-polished surface of the obtained sintered body was observed with an electron microscope. The occupied area ratio of the crystal system and the alumina crystal grain size of 3 m or less was calculated.

The obtained alumina sintered body having the shape of a thermoelectric protection tube has a diameter of about 3.2 mm. A tube of about 16.5 mm in length is sealed at one end, and a hole of about 0.3 mm is formed in the cross section. Two were in parallel. Next, drill a hole of about 3.5 mm and a length of about 30 mm in a drill of 100 mm x 100 mm x 70 mm alumina K refractory. And protruded 120 mm from the end of the refractory surface. The alumina refractory in which one end of the alumina sintered body was inserted was placed in an electric furnace. The installation was made so that the protective tube was horizontal to the hearth and at least 80 mm apart from the hearth. In this state, an exposure test (creep test) was performed under the conditions of a heating rate of 200 ° C / h, a maximum temperature of 160 ° C, and a holding time of 5 h. Since the alumina test specimen protrudes 120 mm horizontally from the end of the refractory surface, it receives external stress due to its own weight. The creep characteristics were evaluated by determining the amount of change (mm) in the height h (mm) of the alumina specimen from the hearth before and after the test, and evaluating the creep characteristics by its own weight deformation. The smaller the degree of deformation, the higher the high-temperature creep resistance. As the specific drawing material, an alumina sintered body obtained by adding 0.05% by weight of magnesium oxide to 99.9% purity alumina and sintering at 180 ° C for 1 hour at a high temperature was used. . Table 4 shows the mixing ratio of the coarse raw material to the fine raw material, the magnesium oxide addition ratio, and the sintering temperature. Also Table 5, baked tracks of each composition corresponding to the numbers in Table 4, the flexural strength values before and after the test, where _c indicating the occupancy of the alumina sintered grain size constituting the sintered body after sintering The number 10 in the table is the alumina sintered body of the high-temperature sintering type used as a comparative sample. It is. The specimen consisting of fine alumina raw material alone (specimen number 1) was creep

(Bending degree test) The bending strength value after the test was remarkably reduced, and the composition (specimen No. 2) in which 0.05% by weight of magnesium oxide was externally added as a sintering aid to the fine alumina raw material had a remarkable plasticity. Deformation was shown. The creep characteristics were excellent when the fine alumina raw material was 70% by weight and the coarse alumina raw material was 30% by weight, but the sintered body could not be completely sintered at 140 ° C sintering, and water absorption of 0.5% or more remained. It is clear from Table 4 that these complete sintering requires a high temperature of more than 150 ° C. On the other hand, a composition in which a coarse alumina raw material is added to the fine alumina raw material within the range of the present invention in the range of 2 to 20% by weight, and magnesium oxide is externally added so as to be 0.5% by weight or less. The sintered body has a small degree of bending of 15 mm or less, and even after being compared with the 180 ° C high-temperature sintering type alumina sintered body (specimen number 11). It is clear that the degree of curvature is comparable. By the way, the alumina sintered body (No. 9) with a mixture of fine particles and coarse particles without adding magnesium oxide as a sintering aid was slow in maintaining the high temperature at the creep test temperature of 160. Grain growth occurred, and the bending strength after the test decreased to 200 MPa or less. Although it depends on the shape and protruding length of the protective tube, it is difficult to use a composition without adding a sintering aid because the practical protective tube requires a bending strength of about 300 MPa.

Four

Fine raw material Coarse raw material Sintering aid Sintering temperature number (% by weight) (% by weight) (% by weight) CC)

1 1 0 0 0 0 1 3 0 0

2 1 0 0 0 0. 0 5 1 3 0 0

3 9 8 2 0. 0 5 1 3 5 0

4 9 5 5 0. 0 5 1 3 5 0

5 9 0 1 0 0. 0 5 1 4 0 0

6 9 0 1 0 0 .5 1 4 0 0

7 9 0 1 0 1.0 1 0 0

8 8 0 2 0 0. 0 5 1 4 5 0

9 8 0 2 0 0 1 4 5 0

1 0 7 0 3 0 0. 0 5 1 5 0 0

1 1 1 0 0 0 0. 0 5 1 8 0 0 Four

Degree of bending Flexural strength (MPa) Area occupancy (%)

(mm) Before test After test 5 Um or more 3 u τηϊίλ

1 1 4 5 0 1 5 0 0 1 0 0

6 5 5 3 0 4 9 0 0 1 0 0

1 4 5 1 0 4 5 5 1 0 8 5

8 4 9 5 4 9 0 2 5 6 5

7 4 8 5 4 7 0 3 7 5 4

1 2 3 7 0 3 6 0 3 5 5 9

3 2 3 3 5 3 2 0 3 0 5 7

9 3 4 5 3 5 5 4 0 4 6

8 3 4 0 1 7 5 4 6 4 9 0 6 3 1 5 3 7 0 4 5 4 3 1 7 3 3 0 3 2 0 9 5 5 Example 5

 As in Example 4, each alumina sintered body is converted into a thermoelectric protection tube (diameter 5 mm × 200 L, inner diameter 0.5 mm.2 hole) for heating steel at 150 ° C. And molded under the same sintering conditions. A thermocouple protection tube made of alumina passed through a single-piece platinum wire was protruded 120 mm from the furnace wall to measure the temperature of molten steel, and the temperature was measured continuously for about 30 minutes. The thermocouple protection tube made of an alumina sintered body having a composition within the range of the present invention endured continuous temperature measurement for 30 minutes, and was good in appearance without melting or corrosion. The sintered couple containing the coarse grains of 30% by weight reacted violently with the molten steel and slag, and fell into a temperature-measurable state only three minutes after the start of the temperature measurement. This is considered to be due to incomplete sintering, which easily reacts with molten steel and slag, and because of its water absorption, corrosive gas penetrates into the protective tube, reacts with the single-port platinum wire, and melts the wire. In addition, in the composition of magnesium oxide added to the fine alumina raw material (No. 2 in Table 4), the strand broke in 18 minutes after the start of the test. The protruding part into the furnace was bent due to plastic deformation so that it was difficult to remove the specimen after the test. When the wire breaks, the plastic deformation of the test specimen is large, so a fine crack runs on the sliding part of the grain boundary of the test specimen, losing the confidentiality of the protective tube, and gas in the furnace penetrates into the protective tube. It is presumed that a chemical reaction occurred with the strand.

 It goes without saying that the present invention is not limited to only the above embodiment. For example, the R thermocouple of this example can be changed to another type of thermocouple, and the external shape of the thermometer with the thermocouple and the protection tube integrated is also made to be square or elliptical, including round. The tip of the element may be rounded or flat. Further, the multi-point heating element may have a plurality of temperature measuring contacts. The temperature measuring element combined with the external protective tube is not limited to molten steel, but may be other molten metal or molten glass.The material of the protective tube for molten metal is non-oxide, carbon-containing refractory, Any cermet or gold can be used.

 The temperature measuring element in which the thermocouple and the protective tube of the means 1 and 2 are integrated is narrowed down to the conventional thermocouple, the insulated tube and the protective tube assembled temperature measuring element, and the following points are excellent. ing.

 a. Both protective tube and protective tube can be used.

 b. Outer diameter can be reduced without the need for a protection tube, so it has excellent temperature response.

c As it is an integral structure like a sheath thermocouple, there is a danger of thermocouple contamination during assembly. There is no.

d. Since there is no exposed part of the thermocouple wire like a sheath thermocouple, the thermocouple degradation is small and the life is extended by measuring the temperature in a polluted environment.

e. It is easy to handle because it has an integral structure like a sheath thermocouple.

f. Because thin objects can be obtained, high temperature measurement can be performed in places where measurement is difficult.

 In a specific row, the difference is large especially in a contaminated environment such as molten steel temperature measurement, and the deterioration and consumption of precious metal thermocouples, which are effective with conventional assembled temperature measuring elements, are severe, and the running cost and cost are high. Although there is a problem on both sides of the temperature accuracy, the temperature measuring element of the present invention can measure the temperature with high accuracy for a long time, so that its practical and economical effects are extremely large. Also, when measuring the temperature of dangerous places such as the pot bottom and the furnace bottom, which were difficult in the past, the temperature measurement holes can be kept to a minimum, so that the method can be used safely. In other words, it can be said to be a sheath thermocouple for high temperature.

 The multi-point temperature measuring element of the means 3.4, 5 does not require a large-diameter size protective tube unlike the conventional multi-point temperature measuring method in which a plurality of thermocouples passed through an insulating tube are inserted into the protective tube. Since there is no influence of the air layer and air convection with low thermal conductivity, it is excellent in temperature responsiveness and temperature measurement accuracy, and it is compact and easy to handle. It is most suitable for measuring the temperature distribution of diffusion furnaces for semiconductor manufacturing and for measuring the temperature distribution of melting furnaces, pots, tandems, etc. for steel, ferrous and non-ferrous metals. However, if it is used as a temperature measuring element of an automatic control system for these high-temperature holding devices, its practical and economical effects are extremely large. The temperature measuring element in which an external protective tube such as the protective tube for molten steel of the means 6.7 described above is combined with the above-mentioned temperature measuring element is a conventional temperature measuring element comprising an external protective tube, an internal protective tube, an insulating tube and a thermocouple. Since it is not a multi-layer structure like the temperature measurement method, it has excellent temperature responsiveness and can prevent breakage due to the difference in thermal expansion between protective tubes and thermocouple deterioration due to breakage. That is, the durability of the temperature measuring device can be improved.

The sintered body of the temperature measuring element of the means 8 has excellent high-temperature creep characteristics. That is, the sintered body is composed of 99.5% or more of alumina ceramics and 0.5% by weight or less of an alkaline earth metal oxide as a sintering aid. An alumina sintered body composed of a composite structure of coarse crystal grains having a crystal grain size of mainly 5 m or more and fine crystal grains of 3 am or less has excellent creep characteristics up to 160 ° C. The means 9 Depending on the production method, this alumina sintered body is obtained by adding 2 to 20% by weight of a coarse alumina raw material having an average particle size of 3 m or more to a fine alumina raw material having an average particle size of 1 m or less, and adding a sintering aid. For example, after the mixed raw material to which the alkaline earth metal oxide is added is formed into a predetermined shape by extrusion molding or the like, the sintering temperature is lower than 150 ° C., preferably lower than 140 ° C. The sintered body is densified, and the sintered body is obtained by sintering such that the alumina crystal grain diameter is mainly composed of coarse particles of 5 or more and fine particles of 3 μm or less. The alumina sintered body obtained by the present invention is excellent not only in heat resistance and corrosion resistance but also in high-temperature creep resistance, and has a low sintering temperature, so that the production cost is low and the field of application is greatly expanded. Thus, it can be applied to high temperature members such as thermocouple protection tubes. Industrial applicability

 INDUSTRIAL APPLICABILITY The thermocouple temperature measuring element according to the present invention can be used for temperature measurement, temperature distribution measurement, and the like in a diffusion furnace for semiconductor production, steel, iron, non-ferrous metal melting pots, pots, tundishes, and the like.

 Further, the sintered body and the method of manufacturing the same according to the present invention can be used for manufacturing the above-described thermocouple temperature measuring element.

Claims

The scope of the claims  1. An insulative ceramic protection tube having two holes, and two two tubes that extend through each of the two holes and are joined at the tip to form one temperature measuring contact A thermocouple comprising a thermocouple made of a different kind of metal wire and having a structure in which the temperature measuring contact side of the insulative ceramic protective tube is bound to the thermocouple; Temperature measuring element.  2. The thermocouple element according to the item 1, wherein a gap is provided between the thermocouple and the insulating ceramic protection tube in the temperature measuring contact section.  3. It has a multipoint temperature measurement structure in which two or more thermocouple temperature measurement elements described in the above item 1 or 2 are sintered and integrated at different positions of the respective heating contacts. Thermocouple element.  4. An insulative ceramic protective tube with four or more even holes, and two different types of two different types that extend through each of the holes and are joined at the ends of the wires to form a temperature measuring contact. Multi-point measurement consisting of two or more pairs of thermocouples made of metal wires, with a structure in which the heating contact side of the insulating ceramic protection tube is closed, and where the positions of the temperature measuring contacts of each thermocouple are different A thermocouple temperature measuring element having a temperature structure.  5. An insulative ceramic protection tube with three or more holes, and two or more different types of metal wires connected to one metal wire at different positions while extending through each of the holes. It consists of a multipoint thermocouple branch thermocouple that forms two or more stab junctions, and has a structure in which the insulating contact is closed on the insulating ceramic protective tube. Thermocouple temperature sensor.  6. A structure comprising the thermocouple temperature measuring element described in any of the above items 1 to 5 and an external protection tube that incorporates the thermocouple temperature measuring element inside and shuts off from the outside world. Characteristic thermocouple temperature measuring element.  7. The thermocouple temperature measuring element as described in the above item 6, wherein the material of the outer protective tube is a non-oxide ceramic, a carbon-containing refractory, a cermet, and a metal. 8. The insulative ceramic protective tube is made of an alumina sintered body containing aluminum oxide of 99.5% or more and a sintering aid as essential components, and the crystal structure of the sintered body is Mainly crystal grains ii Consisting of a mixed structure of coarse grains of 5 m or more and fine grains of 3 m or less 8. The thermocouple temperature measuring element according to any one of the above items 1 to 7, which is an alumina sintered body.  9. As a starting material for the alumina component of the alumina sintered body composed of a substantial alumina component and a sintering aid, fine aluminum oxide powder having an average particle size of 1 m or less and coarse aluminum oxide powder having an average particle size of 3 m or more are used. After the raw material is molded, the powder is mixed with 0.5 to 20% by weight and a sintering aid is added. 9. The method for producing a sintered body for a thermoelectric temperature measuring element according to the above item 8, wherein the sintered body has a mixed structure of grains and fine grains of 3 m or less.