Temperature sensor element and temperature sensor

Abstract

A temperature sensor element is provided that can suppress the reduction reaction of a heat-sensitive body even when used in a strong reducing atmosphere for a long period of time. The temperature sensor element (1) of the present invention comprises: a heat-sensitive body (11) whose resistance changes with temperature; a first coating layer (20) that covers the periphery of the heat-sensitive body (11); a pair of lead wires (15, 15) that are connected to the heat-sensitive body (11), pass through the first coating layer (20) and are led out toward the rear end side; a second coating layer (25, 27) that covers the periphery of the pair of lead wires (15, 15) that pass through the first coating layer (20) and are led out; and a third coating layer (30) that covers the periphery of the first coating layer (20) and the second coating layer (25, 27). When the linear expansion coefficients of the lead wire (15), the second coating layer (25, 27) and the third coating layer (30) are set to α15, α25 and α30, respectively, the relationship α15<α30<α25 holds.

Description

Technical Field

[0001] The present invention relates to a temperature sensor element including a heat-sensitive body such as a thermistor whose electrical characteristics change in response to temperature changes. Background Art

[0002] The temperature sensor element includes, for example, a thermistor formed of a conductive oxide sintered body, a coating layer covering the periphery of the thermistor, and a pair of lead wires connected to the thermistor and extending through the coating layer.

[0003] The coating layer is used to improve the mechanical and thermal durability of the thermistor and to prevent foreign matter from entering the thermistor from the outside, which could potentially degrade the performance of the temperature sensor element.

[0004] Temperature sensor elements are more susceptible to ambient temperature at high temperatures than at low temperatures, so the coating layer must also be made of a material that is stable at high temperatures. Glass can be used as a high-temperature coating material for temperatures up to 800°C, but cannot be used at temperatures above 800°C, such as 900°C or higher.

[0005] To address the above challenges, Patent Document 1 proposes a thermistor element formed by bonding wires to the upper and lower surfaces of a planar sintered body comprising a combination of multiple metal oxides and a sintering-accelerating material that enhances conductivity. The proposal explains that by coating a portion of the thermistor chip with a coating material comprising a combination of the multiple metal oxides described above in a material ratio substantially equal to that of the aforementioned combination and a sintering-accelerating material that does not enhance conductivity, and then sintering the resulting thermistor, a thermistor capable of withstanding high temperatures can be provided.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2006-54258 Summary of the Invention

[0009] Problems to be solved by the invention

[0010] However, it has been discovered that if the thermistor element disclosed in Patent Document 1 is used continuously for a long time in a high-temperature atmosphere, such as above 900°C, its resistance value will change and it will not be able to maintain the desired performance. In the thermistor element disclosed in Patent Document 1, the thermistor chip, coating, and wire are made of different materials, and therefore have different linear expansion coefficients. According to the inventors, due to the different linear expansion coefficients, there is a risk of gaps forming between the wires and the protective layer if exposed to a high-temperature atmosphere for a long time. In addition, in a high-temperature atmosphere, moisture and other substances present in the gas evaporate, generating reducing gases. This reducing gas penetrates the thermistor chip through the interface between the coating and the lead wires. It is speculated that since the thermistor is an oxide, it is reduced by the invading reducing gas, which reduces the temperature detection accuracy of the temperature sensor element.

[0011] Therefore, an object of the present invention is to provide a temperature sensor element capable of suppressing a reduction reaction of a heat-sensitive body even when used in a strong reducing atmosphere for a long period of time by reducing the gap at the interface between the lead wire and the coating layer surrounding the lead wire.

[0012] Means for solving problems

[0013] The present invention comprises: a heat-sensitive body whose resistance changes with temperature; a first covering layer that covers the periphery of the heat-sensitive body; a pair of lead wires that are connected to the heat-sensitive body, pass through the first covering layer, and are led out toward the rear end side; a second covering layer that covers the periphery of the pair of lead wires that pass through the first covering layer and are led out; and a third covering layer that covers the periphery of the first covering layer and the second covering layer.

[0014] In the present invention, when the linear expansion coefficients of the lead wire, the second coating layer, and the third coating layer are α15, α25, and α30, respectively, the relationship of α15<α30<α25 holds.

[0015] Furthermore, in the present invention, it is preferred that the first coating layer is composed of a first oxide powder or a mixture of the first oxide powder and glass, the second coating layer is composed of a mixture of the second oxide powder and glass, and the third coating layer is composed of a mixture of the third oxide powder and glass.

[0016] Furthermore, when the linear expansion coefficients of the first oxide powder, the second oxide powder, and the third oxide powder are β20, β25, and β30, respectively, the relationship of β20<β30<β25 holds.

[0017] Furthermore, in the present invention, it is preferred that the first oxide powder includes powder of a thermistor constituting a heat-sensitive element, and the second oxide powder includes powder of one or more of ZrO 2 , CaO, and MgO.

[0018] Furthermore, in the present invention, it is preferred that the second covering layer covers the periphery of the pair of lead wires that penetrate the first covering layer and are led out, and covers the first covering layer between the first covering layer and the third covering layer.

[0019] Furthermore, in the present invention, it is preferred that the second covering layer covers only the peripheries of the pair of lead wires that pass through the first covering layer and are led out, and the first covering layer is in direct contact with the third covering layer.

[0020] Furthermore, in the present invention, it is preferable that when the thicknesses of the second covering layer and the third covering layer are t25 and t30, respectively, t25<t30 holds.

[0021] Furthermore, according to the present invention, there is provided a temperature sensor including the temperature sensor element described above.

[0022] Effects of the Invention

[0023] In the present invention, when the linear expansion coefficients of the lead wire, the second coating layer, and the third coating layer are set to α15, α25, and α30, respectively, the relationship α15 < α30 < α25 holds. This relationship reduces the gap between the lead wire and the first coating layer surrounding it, thereby suppressing the reduction reaction of the heat-sensitive element even when used for extended periods in a strongly reducing atmosphere. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a longitudinal sectional view showing a schematic structure of the temperature sensor element according to the first embodiment.

[0025] Figure 2 In (a), Figure 1 A cross-sectional view of the lead wire 15 and its surroundings, (b) is a schematic representation of Figure 1 A diagram showing the expansion states of the lead wires, intermediate layer, and outer coating of a thermistor element.

[0026] Figure 3 This is a flowchart showing the steps of manufacturing the temperature sensor element according to the first embodiment.

[0027] Figure 4 It is a diagram showing the steps of manufacturing the temperature sensor element according to the first embodiment.

[0028] Figure 5 It is a continuation Figure 4 The following are diagrams showing steps for manufacturing the temperature sensor element according to the first embodiment.

[0029] Figure 6In the drawings, (a) is a longitudinal sectional view showing a schematic structure of a temperature sensor element according to the second embodiment, and (b) is a transverse sectional view showing the periphery of the lead wire 15 in (a).

[0030] Figure 7 It is a continuation Figure 4 The following are diagrams showing steps for manufacturing the temperature sensor element according to the second embodiment. DETAILED DESCRIPTION

[0031] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0032] A temperature sensor element 1 according to an embodiment of the present invention will be described with reference to the drawings.

[0033] like Figure 1 As shown, the temperature sensor element 1 of this embodiment includes a thermistor element 3 and a coating layer 5. The thermistor element 3 includes a heat-sensitive element 11 whose electrical characteristics, such as resistance, change with temperature; a pair of electrodes 13, 13 formed on the opposing front and back surfaces of the heat-sensitive element 11; a pair of lead wires 15, 15 connected to the electrodes 13, 13, respectively; and connecting electrodes 17, 17 electrically connecting the electrodes 13, 13 to the lead wires 15, 15. Furthermore, the coating layer 5 includes a first coating layer 20 covering the heat-sensitive element 11 and a portion of the lead wires 15, 15; a third coating layer 30 covering the outside of the first coating layer 20; and a second coating layer 25 interposed between the first coating layer 20 and the third coating layer 30.

[0034] Temperature sensor element 1 includes a second coating layer 25 between first coating layer 20 and third coating layer 30. This second coating layer 25 provides a fastening effect, which will be described in detail later. Temperature sensor element 1 can minimize the rate of change in the resistance value of heat-sensitive element 11 in a high-temperature reducing atmosphere, such as an atmosphere containing hydrogen.

[0035] Although detailed description is omitted here, the temperature sensor element 1 may be housed in a protective tube made of a metal having excellent heat resistance and oxidation resistance, such as stainless steel or Ni superalloy, to constitute a temperature sensor.

[0036] Hereinafter, after describing each element of the temperature sensor element 1 , the operation and effects of the temperature sensor element 1 will be described.

[0037] [Thermal body 11]

[0038] A thermistor sintered body is preferably used as the heat-sensitive body 11. Thermistor is an abbreviation of a thermally sensitive resistor, and is a metal oxide that measures temperature by utilizing the fact that its resistance value changes with temperature.

[0039] Thermistors are classified into NTC (negative temperature coefficient) thermistors and PTC (positive temperature coefficient) thermistors. The present invention may use either type of thermistor.

[0040] As an NTC thermistor, an oxide sintered body having a typical spinel structure of manganese oxide (Mn3O4) as a basic composition can be used as the heat-sensitive body 11. An M element (one or more of Ni, Co, Fe, Cu, Al and Cr) added to the basic composition can be used. x Mn 3-x An oxide sintered body having an O4 composition is used for the heat-sensitive body 11. Furthermore, one or two or more of V, B, Ba, Bi, Ca, La, Sb, Sr, Ti, and Zr may be added.

[0041] Furthermore, as an NTC thermistor, a sintered oxide having a typical perovskite structure, such as YCrO3, as a basic structure can be used for the heat-sensitive element 11. A typical NTC thermistor is a sintered body having a Y2O3 phase and at least one of a Y(Cr, Mn)O3 phase, a YCrO3 phase, and a YMnO3 phase.

[0042] [Method for Manufacturing thermistor sintered body]

[0043] Thermistor sintered body heat-sensitive element 11 is manufactured through the following steps: weighing raw material powders, mixing the raw material powders, drying the raw material powders, pre-calcining, mixing after pre-calcining, pulverizing, drying, granulating, molding, and sintering. The following describes each step using a thermistor sintered body containing Y2O3 and Y(Cr,Mn)O3 phases as an example.

[0044] [Weighing of raw material powder]

[0045] Raw material powders including yttrium oxide (Y2O3) powder, chromium oxide (Cr2O3) powder, manganese oxide (MnO, Mn2O3, Mn3O4, etc.) powder and calcium carbonate (CaCO3) powder are weighed so as to obtain the above-mentioned chemical composition.

[0046] It should be noted that in this embodiment, the powder is composed of a plurality of particles.

[0047] Y2O3 powder contributes to the formation of the Y2O3 phase, while Y2O3 powder, Cr2O3 powder, and manganese oxide powder (Mn3O4 powder) contribute to the formation of the Y(Cr, Mn)O3 phase. CaCO3 powder not only functions as a sintering aid but also dissolves as Ca in the Y(Cr, Mn)O3 phase, contributing to a lowering of the B constant.

[0048] In order to obtain a high-performance thermistor sintered body, the raw material powder used has a purity of 98% or higher, preferably 99% or higher, and more preferably 99.9% or higher.

[0049] The particle size of the raw material powder is not limited as long as it can be pre-calcined, and the particle size (d50) can be selected within the range of 0.1 to 6.0 μm.

[0050] [Mixing and ball milling of raw material powders]

[0051] Y2O3 powder, Cr2O3 powder, Mn3O4 powder, and CaCO3 powder weighed in predetermined amounts are mixed. Mixing can be performed, for example, using a ball mill to form a slurry by adding water to the mixed powder. Mixing can also be performed using a mixer other than a ball mill.

[0052] [Drying of raw material powder]

[0053] The mixed slurry is preferably dried and granulated using a spray dryer or other equipment to prepare a mixed powder for pre-calcination.

[0054] [Pre-calcination]

[0055] The dried mixed powder for pre-calcination is pre-calcined to obtain a pre-sintered body having a composite structure of Y2O3 phase and Y(Cr, Mn)O3 phase from Y2O3 powder, Cr2O3 powder, Mn3O4 powder and CaCO3 powder.

[0056] Pre-calcination is performed by placing the pre-calcination mixed powder into a crucible, for example, and maintaining it in the air at a temperature range of 800-1300°C. Pre-calcination temperatures below 800°C may result in insufficient formation of a composite structure, while temperatures exceeding 1300°C may lead to a decrease in sintered density and resistance stability. Therefore, the holding temperature for pre-calcination is set within the range of 800-1300°C.

[0057] The holding time of the preliminary calcination should be appropriately set according to the holding temperature. However, as long as the temperature is within the above-mentioned temperature range, the purpose of preliminary calcination can be achieved with a holding time of about 0.5 to 100 hours.

[0058] [Mixing, crushing, ball milling]

[0059] The pre-calcined powder is mixed and pulverized. The mixing and pulverization are the same as before the pre-calcination. Water can be added to form a slurry and then the slurry can be pulverized using a ball mill.

[0060] [Drying, granulation]

[0061] The pulverized powder is preferably dried and granulated using a spray dryer or other equipment.

[0062] [forming]

[0063] The pre-calcined granulated powder is formed into a predetermined shape.

[0064] Molding can be performed by cold isostatic pressing (CIP: Cold Isostatic Press) in addition to press molding using a mold.

[0065] Since the higher the density of the molded body, the easier it is to obtain a high-density sintered body, it is desirable to increase the density of the molded body as much as possible. Therefore, it is preferable to use CIP that can achieve high density.

[0066] [sintering]

[0067] Next, the obtained compact is sintered.

[0068] Sintering is performed by maintaining the material in the air within a temperature range of 1400-1650°C. If the sintering temperature is less than 1400°C, the composite structure will not be fully formed. If the temperature exceeds 1650°C, the sintered body will melt or react with the crucible used for sintering. The holding time for sintering should be appropriately set according to the holding temperature. However, within the above temperature range, a dense sintered body can be obtained with a holding time of approximately 0.5 to 200 hours.

[0069] The obtained thermistor sintered body is preferably subjected to annealing (tempering) in order to stabilize its thermistor characteristics. Annealing is performed, for example, by maintaining it at 1000° C. in the atmosphere.

[0070] [Electrodes 13, 13 and connecting electrodes 17, 17]

[0071] like Figure 1 As shown, the electrodes 13, 13 are formed in a film-like manner over the entire area of ​​both the front and back surfaces of the plate-shaped heat-sensitive body 11. The electrodes 13, 13 are made of, for example, platinum (Pt) or other precious metals.

[0072] Electrodes 13, 13 are formed as thick or thin films. Thick film electrodes 13, 13 are formed by applying a paste made by mixing platinum powder with an organic binder to both the front and back surfaces of the thermistor sintered body, drying it, and then sintering it. Thin film electrodes can also be formed by vacuum deposition or sputtering.

[0073] The heat-sensitive body 11 on which the electrodes 13 and 13 are formed is processed into a predetermined size.

[0074] The connection electrodes 17, 17 are respectively composed of metal films formed on the surfaces of the electrodes 13, 13. The connection electrodes 17, 17 are also preferably composed of platinum (Pt) or other noble metals.

[0075] [Lead lines 15, 15]

[0076] like Figure 1 As shown, one end of lead wires 15, 15 is electrically and mechanically connected to electrodes 13, 13 via connection electrodes 17, 17. The other end of lead wires 15, 15 is connected to an external detection circuit (not shown). Lead wires 15, 15 are made of heat-resistant wire material, such as platinum or an alloy of platinum and iridium (Ir).

[0077] The lead wires 15 and 15 are connected to the electrodes 13 and 13 as follows.

[0078] A paste containing platinum powder forming connection electrodes 17 is previously applied to one end of each lead wire 15. The platinum paste is dried while the lead wires 15 are in contact with electrodes 13, 13 on their respective ends. The platinum powder is then sintered.

[0079] [First Covering Layer 20]

[0080] Next, the first covering layer 20 will be described.

[0081] The main function of the first cover layer 20 is to serve as a buffer material to alleviate the stress generated by the thermal expansion of the third cover layer 30 and directly applied to the heat-sensitive body 11. In other words, the first cover layer 20 receives the thermal stress generated by the third cover layer 30.

[0082] Furthermore, the first covering layer 20 fixes the connection portion between the heat-sensitive body 11 and the lead wires 15 , 15 , thereby achieving stable electrical and mechanical connection.

[0083] The first covering layer 20 of this embodiment includes two preferred aspects.

[0084] The first embodiment comprises a mixture of glass and oxide powder (first oxide powder), while the second embodiment comprises an aggregate of the first oxide powder. In the first and second embodiments, the terms "second oxide powder" and "third oxide powder" are used in addition to the first oxide powder. However, these terms are merely used to distinguish the first coating layer 20, the second coating layer 25, and the third coating layer 30. Therefore, for example, the same oxide powder can be used as the first and third oxide powders.

[0085] In the first covering layer 20 of the first embodiment, the glass functions as a binder that binds the oxide powders together and maintains the shape of the first covering layer 20 .

[0086] The ratio of glass to oxide powder is not limited as long as a desired linear expansion coefficient is obtained and the oxide powder functions as a binder.

[0087] The glass constituting the first coating layer 20 may be either crystalline glass or amorphous glass, but crystalline glass, which is stable at high temperatures, is preferably used. For example, the crystalline glass may contain the following composition: silicon oxide (SiO2): 30-60% by weight, calcium oxide (CaO): 10-30% by weight, magnesium oxide (MgO): 5-25% by weight, and aluminum oxide (Al2O3): 0-15% by weight, totaling 100% by weight.

[0088] Examples of the oxide powder constituting the first covering layer 20 include aluminum oxide (Al2O3), magnesium oxide (MgO), calcium oxide (CaO), yttrium oxide (Y2O3), and zirconium oxide (ZrO2). A preferred form of the oxide powder is thermistor powder.

[0089] Thermistor powder can be a powder having the same composition as the thermistor sintered body constituting the heat-sensitive element 11. The term "same composition" means that the chemical composition of Cr, Mn, Ca, and Y, excluding the aforementioned oxygen, in both the heat-sensitive element 11 and the thermistor powder contained in the first inner layer is within the range of 3-15 mol% Cr, 5-15 mol% Mn, and 0.5-8 mol% Ca. This includes the case where the thermistor powder and the thermistor sintered body constituting the heat-sensitive element 11 have the same composition.

[0090] The second form of the first coating layer 20 is composed of an aggregate of oxide powders (first oxide powders). Because this first coating layer 20 does not contain glass, its ability to withstand thermal stress is enhanced. The first coating layer 20 formed from an aggregate of oxide powders differs from that formed from glass in how it withstands thermal stress. Specifically, the first coating layer 20 in the first form containing glass withstands thermal stress by ensuring its rigidity, whereas the first coating layer 20 formed from oxide powders without glass withstands thermal stress by causing the particles constituting the oxide powders to be misaligned.

[0091] In the second embodiment, the first coating layer 20, which does not contain glass, has difficulty maintaining its shape on its own. Therefore, the third coating layer 30 is solely responsible for maintaining this shape. Specifically, the third coating layer 30 is formed around the first coating layer 20, sandwiching the second coating layer 25. Without the application of external forces, the third coating layer 30 supports the first coating layer 20, thereby maintaining its shape even without the presence of glass.

[0092] Furthermore, during the firing of the third coating layer 30, there are also portions where elements diffuse between the particles constituting the first coating layer 20 and adjacent particles, forming bonds. These bonds not only help maintain the third coating layer 30 but also the first coating layer 20. However, these adjacent particles do not necessarily need to be firmly bonded to each other. Rather, from the perspective of the stress relaxation effect of the first coating layer 20, it is preferable to make the bonds between adjacent particles weaker.

[0093] [Third Covering Layer 30]

[0094] Next, the third covering layer 30 will be described.

[0095] The third covering layer 30 has a main function of providing airtightness to hermetically seal the heat-sensitive member 11 from the surrounding atmosphere. Furthermore, the third covering layer 30 imparts mechanical strength to protect the heat-sensitive member 11 from external forces.

[0096] The third coating layer 30 can be formed of a mixture of the same glass and oxide powder (third oxide powder) as the first coating layer 20. As the oxide powder, one or more of aluminum oxide (Al2O3), magnesium oxide (MgO), yttrium oxide (Y2O3), calcium oxide (CaO), zirconium oxide (ZrO2), strontium oxide (SrO), titanium oxide (TiO), and lanthanum oxide (La2O3) can be used.

[0097] The third coating layer 30 of this embodiment is composed of a mixture of glass and oxide powder, similar to the first coating layer 20. However, the third coating layer 30 contains more glass than the first coating layer 20. This is to satisfy the relationship of linear expansion coefficients described below.

[0098] The third coating layer 30 can be formed into a single layer to obtain the desired thickness and state, but it can also be formed into multiple layers. When the third coating layer 30 is formed into multiple layers, the thickness of each layer may be uniform or uneven.

[0099] [Second coating layer 25]

[0100] Next, the second covering layer 25 will be described.

[0101] like Figure 1 and Figure 2 As shown in (a), the second covering layer 25 is provided between the first covering layer 20 and the third covering layer 30. In addition to covering the first covering layer 20, it also covers the outer peripheral surface of the lead wire 15 led out from the first covering layer 20. The periphery of the second covering layer 25 covering the lead wire 15 is covered by the third covering layer 30.

[0102] The second covering layer 25 is preferably composed of a mixture of glass and oxide powder (second oxide powder) similar to the first covering layer 20 .

[0103] It is believed that when the temperature sensor element 1 is used in a high-temperature region, the compressive stress σ1 applied to the lead wire 15 causes the second coating layer 25 to come into close contact with the interface between the lead wire 15. The application of this compressive stress σ1 reduces the minute gap between the lead wire 15 and the second coating layer 25, thereby improving the reduction resistance of the temperature sensor element 1.

[0104] [Compressive Stress Generated by the Second Covering Layer 25]

[0105] The temperature sensor element 1 is sometimes used in a reducing atmosphere containing hydrogen, for example, within a temperature range of room temperature to 1050°C. The second coating layer 25 is provided to suppress the reduction reaction of the heat-sensitive body 11 of the temperature sensor element 1 in the reducing atmosphere, that is, to impart reduction resistance to the temperature sensor element 1. According to the research of the present inventors, it is speculated that the reason why the second coating layer 25 imparts reduction resistance is that when the temperature sensor element 1 is used at high temperatures, a compressive stress σ1 acts from the second coating layer 25 toward the lead wire 15. That is, it is believed that the compressive stress σ1 is generated by the relationship between the linear expansion coefficients of the lead wire 15 and the third coating layer 30 and the second coating layer 25. Below, refer to Figure 2 Provide explanation.

[0106] Regarding the structure around the second coating layer 25, Figure 2 As shown in (a), the second covering layer 25 is in contact with the outer peripheral surface of the lead wire 15 and surrounds the lead wire 15. When viewed from the lead wire 15 side, the lead wire 15, the second covering layer 25, and the third covering layer 30 are arranged in this order.

[0107] Next, the relationship between the linear expansion coefficients α15, α25, and α30 of the lead wire 15, the second coating layer 25, and the third coating layer 30 is expressed by the following formula (1). Among the three elements, the linear expansion coefficient α25 of the second coating layer 25 is the largest.

[0108] α15<α30<α25 (1)

[0109] When the temperature sensor element 1, which includes the lead wire 15, the second coating layer 25, and the third coating layer 30, is exposed to a high-temperature atmosphere, it expands in the radial direction (D). Since the lead wire 15, the second coating layer 25, and the third coating layer 30 have the relationship shown in equation (1), the second coating layer 25, which is sandwiched between the lead wire 15 and the third coating layer 30, is affected by the expansion of the lead wire 15 and the third coating layer 30. Therefore, from the perspective of the relationship between the lead wire 15 and the second coating layer 25, since the linear expansion coefficient of the second coating layer 25 is larger than that of the lead wire 15, the lead wire 15 and the second coating layer 25 are not restrained from each other and each expands EX. outward in the radial direction D. On the other hand, from the perspective of the relationship between the second coating layer 25 and the third coating layer 30, since the linear expansion coefficient of the third coating layer 30 is smaller than that of the second coating layer 25, the expansion EX. of the second coating layer 25 outward in the radial direction (D) is restrained. As a result, compressive stress σ1 is generated radially (D) inward from the second coating layer 25 toward the lead wire 15. This compressive stress σ1 prevents gaps from forming at the boundary between the lead wire 15 and the second coating layer 25, ensuring strong contact. Thus, the temperature sensor element 1 according to the first embodiment suppresses the intrusion of reducing gas containing hydrogen from the boundary between the lead wire 15 and the second coating layer 25.

[0110] The second coating layer 25, which produces the above-mentioned effects, uses oxide powder (second oxide powder) with a large linear expansion coefficient, such as one or more of ZrO2 powder, MgO powder, and CaO powder. As with the third coating layer 30, glass is used as a component other than the oxide powder.

[0111] [Relationship between the Thickness of the Second Covering Layer 25 and the Third Covering Layer 30]

[0112] When the thickness of the second coating layer 25 is t25 and the thickness of the third coating layer 30 is t30, the relationship t25 ≤ t30 is preferred, and t25 < t30 is more preferred. Within this range, a smaller t25 is ideal to maximize the tightening effect of the second coating layer 25. Specific values ​​for t25 and t30 can be selected from the following ranges. Note that the units are in mm.

[0113] t25: 0.03~0.3, 0.05~0.2, 0.07~0.15

[0114] t30: 0.20~2.0, 0.3~1.25, 0.45~1.0

[0115] [Compressive stress σ2 on heat-sensitive body 11]

[0116] When the temperature sensor element 1 is exposed to a temperature range of, for example, room temperature to 1000° C., the compressive stress σ2 applied to the heat sensitive body 11 is preferably kept low. This is to suppress changes in the electrical characteristics of the heat sensitive body 11 , particularly the resistance value.

[0117] To meet this requirement, it is desirable to adjust the linear expansion coefficients of the heat-sensitive element 11, the lead wires 15, the first coating layer 20, and the third coating layer 30. Specifically, it is desirable to adjust the linear expansion coefficient α20 of the first coating layer 20 to be close to the linear expansion coefficient α11 of the heat-sensitive element 11, and to adjust the linear expansion coefficient α30 of the third coating layer 30 to be close to the linear expansion coefficient α15 of the lead wires 15. Specifically, the difference between the linear expansion coefficient α20 and the linear expansion coefficient α11, and the difference between the linear expansion coefficient α30 and the linear expansion coefficient α15, is preferably 5×10 -7 / K or less, more preferably 3×10 -7 / K or less.

[0118] The linear expansion coefficients of the thermistor sintered body constituting the heat-sensitive element 11 and the various oxides, such as platinum, constituting the lead wires 15, at temperatures between 25°C and 900°C are shown in Table 1 below. Based on these values, it is recommended that the ratio of glass to oxide powder be set so that the linear expansion coefficient α11 of the heat-sensitive element 11 is close to that of the first coating layer 20. Furthermore, it is recommended that the ratio of glass to oxide powder be set so that the linear expansion coefficient α15 of the third coating layer 30 is close to that of the lead wires 15.

[0119] Table 1

[0120]

[0121] [Method of Manufacturing Temperature Sensor Element 1]

[0122] Next, refer to Figure 3 、 Figure 4 and Figure 5 A method for manufacturing the temperature sensor element 1 will be described.

[0123] like Figure 3 As described above, the temperature sensor element 1 is manufactured by the following steps: a step of joining the heat-sensitive body 11 and the lead wires 15, 15 ( Figure 3 S100, Figure 4 (a)), forming a first coating layer 20 on the bonded heat-sensitive body 11 ( Figure 3 S200, Figure 4 (b)), a step of forming a second coating layer 25 around the first coating layer 20 ( Figure 3 S300, Figure 5 (a)), a step of forming a third coating layer 30 around the first coating layer 20 and the second coating layer 25 ( Figure 3 S400, Figure 5 (b)).

[0124] [Formation of the first coating layer 20 ( Figure 3 S200, Figure 4 (b))]

[0125] The first coating layer 20 is prepared by mixing the above-mentioned oxide powder, preferably thermistor powder and crystal glass powder, with a solvent to prepare a paste. This paste is applied to the surface of the heat-sensitive body 11, dried, and the glass component is fired to form the first coating layer 20.

[0126] When applying the paste to the surface of the heat-sensitive body 11 , it is appropriate to immerse the heat-sensitive body 11 in the paste from one side to a predetermined range of the lead wires 15 and then lift it out of the paste.

[0127] If the first coating layer 20 is formed of multiple layers, multiple impregnations are performed followed by drying and calcination. Furthermore, if the first coating layer 20 is formed of multiple layers, while the boundaries between adjacent coating layers can be visually confirmed, the adjacent coating layers are bonded with a force sufficient to ensure the function of the first coating layer 20. This also applies to the second coating layer 25 and the third coating layer 30.

[0128] [Formation of the Second Coating Layer ( Figure 3 S300, Figure 5 (a)]

[0129] The second coating layer 25 is prepared by mixing, for example, an oxide powder having a larger linear expansion coefficient than the oxide powder contained in the third coating layer 30, preferably a powder of one or more of ZrO2, CaO, and MgO, and a crystalline glass powder with a solvent to prepare a paste. This paste is formed on the first coating layer 20, dried, and the glass component is fired to form the second coating layer 25.

[0130] [Formation of the third coating layer ( Figure 3 S400, Figure 5 (b))]

[0131] Furthermore, the third covering layer 30 is also formed on the second covering layer 25 using the outer layer glass paste prepared by mixing oxide powder, glass powder, and solvent in the same manner as described above.

[0132] [Second embodiment]

[0133] Next, refer to Figure 6 A temperature sensor element 2 according to the second embodiment will be described.

[0134] When comparing the temperature sensor element 2 with the temperature sensor element 1, the second coating layer 27 does not cover the first coating layer 20, but covers the periphery of the lead wires 15, 15. That is, in the temperature sensor element 2, the first coating layer 20 and the third coating layer 30 are in direct contact, and the second coating layer 27 only covers the periphery of the lead wires 15, 15. Therefore, the cross section of the portion provided with the second coating layer 27 is different from that of the first embodiment. Figure 2 Similarly to (a), the lead wire 15, the second covering layer 27, and the third covering layer 30 are arranged in this order from the inside or the center.

[0135] In the temperature sensor element 2 having the above cross-sectional structure around the lead wire 15 , similarly to the temperature sensor element 1 of the first embodiment, the second covering layer 27 applies compressive stress σ1 to the lead wire 15 , thereby improving reduction resistance.

[0136] Furthermore, the temperature sensor element 2 is not covered by the first cover layer 20. The first cover layer 20 is in direct contact with the third cover layer 30, and the periphery of the third cover layer 30 is open. Therefore, there is no member to restrict the thermal expansion of the third cover layer 30. Since the relationship between the linear expansion coefficients α20 and α30 of the first cover layer 20 and the third cover layer 30 is expressed as shown in the following equation (2), when the temperature sensor element 2 is used in a high temperature range, the first cover layer 20 and the heat-sensitive body 11 disposed within the first cover layer 20 are theoretically not subjected to the compressive stress σ2 from the third cover layer 30.

[0137] α20<α30 Formula (2)

[0138] The second covering layer 27 is difficult to form by dipping, but can be formed by applying a paste to the region using a liquid quantitative discharge device called a dispenser, and then drying and firing the paste.

[0139] [First embodiment]

[0140] Next, an example of the present invention will be described based on specific embodiments.

[0141] A temperature sensor element 1 including the first covering layer 20 , the second covering layer 25 , and the third covering layer 30 described below was manufactured, and the rate of change in resistance value was measured.

[0142] [Manufacturing of Heat Receptor 11]

[0143] Raw material powders having the following particle sizes (d50) were prepared at the following mixing ratios and the heat-sensitive body 11 was manufactured according to the above steps. The pre-calcination conditions were set at 1300°C for 24 hours and the sintering conditions were set at 1500°C for 24 hours, both performed in air.

[0144] Y2O3: 79.5 mol% Particle size: 0.1 μm

[0145] Cr2O3: 8.5mol% Particle size: 2.0μm

[0146] CaCO3: 3.5 mol% Particle size: 2.0 μm

[0147] Mn3O4: 8.5 mol% Particle size: 5.0 μm

[0148] The electrodes 13 , the lead wires 15 , and the connection electrodes 17 are all made of platinum (Pt), and the thermistor element 3 is manufactured by the steps described in the embodiment.

[0149] [Formation of coating layer]

[0150] On the above thermistor element 3 , the first covering layer 20 , the second covering layer 25 , and the third covering layer 30 are formed.

[0151] The first coating layer 20 is made of crystalline glass and thermistor powder with the same composition as the heat-sensitive element 11. The mass ratio of crystalline glass to thermistor powder is set at 20:80. A paste for the first coating layer 20 is prepared using an organic binder as a binder and impregnated to form a single precursor layer. This is then dried and heat-treated for firing to form the first coating layer 20 of this embodiment. The linear expansion coefficient of the first coating layer 20 is set to α20.

[0152] The second coating layer 25 is made of crystalline glass and oxide powders consisting of ZrO2 powder, MgO powder, and CaO powder. The mass ratio of crystalline glass to oxide powders (ZrO2 powder, MgO powder, and CaO powder) is 90:10. However, for MgO powder, a sample with a mass ratio of crystalline glass to MgO powder of 80:20 was also prepared. The linear expansion coefficient of the second coating layer 25 was set to α25.

[0153] The third coating layer 30 is made of crystalline glass and Y2O3 as oxide powder. The mass ratio of crystalline glass to Y2O3 as oxide powder is 80:20. The linear expansion coefficient of the third coating layer 30 is set to α30.

[0154] The linear expansion coefficients of the heat-sensitive body 11, lead wire 15, first coating layer 20, second coating layer 25, and third coating layer 30 described above are shown in Table 2. In Table 2, the linear expansion coefficients of the first coating layer 20, second coating layer 25, and third coating layer 30, which are mixtures of crystalline glass and oxide powder, are calculated from the mass ratio (%) of the crystalline glass to the oxide powder.

[0155] Note that the thickness t25 of the second covering layer 25 and the thickness t30 of the third covering layer 30 are as follows.

[0156] t25=0.1mm、t30=0.6mm

[0157] Table 2

[0158]

[0159] Linear expansion coefficient: 25-900℃

[0160] [First embodiment: first measurement condition]

[0161] The rate of change of the resistance value was measured under the following conditions using the four types of temperature sensor elements (samples No. 1 to 4) shown in Table 3. The measurement results are shown in Table 3.

[0162] Maintaining temperature: 900℃

[0163] Atmosphere: Hydrogen 5vol.% + Nitrogen 95vol.%

[0164] Holding time: 10 hours

[0165] Resistance measurement temperature: 25°C

[0166] Table 3

[0167]

[0168] [First embodiment: Second measurement condition]

[0169] The rate of change in resistance was measured under the same second measurement conditions as the first measurement conditions, except that the holding temperature was set at 1050°C. The measurement results are shown in Table 4. Note that a sample was also prepared in which the second coating layer 25 was omitted and the third coating layer 30 was formed directly above the first coating layer 20. This sample is shown as Sample No. 9 in Table 4, and the same applies to Sample No. 16 in Table 5.

[0170] Table 4

[0171]

[0172] [First embodiment: third measurement condition]

[0173] Next, the resistivity change rate was measured in the same manner as in the first measurement condition, except that a cycle of heating from room temperature (25°C) to 1050°C and then cooling from 1050°C to room temperature was repeated 2000 times and then the resistivity was measured. The results are shown in Table 5.

[0174] Table 5

[0175]

[0176] [Second embodiment]

[0177] Next, the second embodiment will be described. In this second embodiment, the first coating layer 20 is formed solely of thermistor powder having the same composition as the heat-sensitive element 11, without glass. This first coating layer 20 is formed by immersing the heat-sensitive element 11 in a liquid mixture of thermistor powder and an organic binder, followed by evaporation of the solvent and drying. This results in a precursor of the first coating layer 20, in which the particles constituting the first coating layer 20 are bonded together by the binder. Subsequently, the second coating layer 25 and the third coating layer 30 are sequentially formed on the first coating layer 20, following the same procedures as in the first embodiment.

[0178] The samples obtained above were used to measure the rate of change in resistivity under the first measurement condition (holding at 900°C), the second measurement condition (holding at 1050°C), and the third measurement condition (room temperature to 1050°C cycle) described in Example 1. The results for the first, second, and third measurement conditions are shown in Tables 6, 7, and 8, respectively.

[0179] Table 6

[0180]

[0181] Table 7

[0182]

[0183] Table 8

[0184]

[0185] It should be noted that, in the measured values ​​of the first and second examples, more suitable results were obtained for CaO at a holding temperature of 1050°C compared to a holding temperature of 900°C. This indicates that CaO is preferably used as the oxide powder in the second coating layer 25 when continuously used in a higher temperature atmosphere.

[0186] Preferred embodiments of the present invention have been described above. However, the configurations described in the above embodiments may be selected or replaced with other configurations without departing from the spirit of the present invention.

[0187] For example, in Figure 1 and Figure 5 In (b), the second and third covering layers 25 and 30 surround the lead wires 15 in a substantially uniform area in the direction in which the lead wires 15 extend. This is merely a preferred example. For example, the second covering layer 25 may protrude further than the third covering layer 30. Although not shown, the opposite is also possible, with the third covering layer 30 protruding further than the second covering layer 25.

[0188] Description of Reference Numerals

[0189] 1.2 Temperature sensor element

[0190] 3 Thermistor element

[0191] 5 Coating layer

[0192] 11. Heat-sensitive body

[0193] 13 electrodes

[0194] 15 lead wire

[0195] 17. Connecting Electrodes

[0196] 20 First coating layer

[0197] 25, 27 Second coating layer

[0198] 30 Third coating layer

Claims

1. A temperature sensor element, characterized in that: It has: a thermosensitive body, whose resistance changes with temperature; a first covering layer covering the periphery of the heat-sensitive body; a pair of lead wires connected to the heat-sensitive body and passing through the first coating layer to be led out; a second covering layer covering the first covering layer and the periphery of the pair of lead wires that pass through the first covering layer and are led out; and a third coating layer covering the first coating layer and the second coating layer; The second covering layer covers each lead wire at a portion where the second covering layer contacts the outer peripheral surface of the lead wire and surrounds the lead wire. In this portion, a pair of lead wires each includes a lead wire, a second covering layer surrounding the lead wire, and a third covering layer surrounding the second covering layer. When the linear expansion coefficients of the lead wire, the second coating layer, and the third coating layer are α15, α25, and α30, respectively, the relationship α15<α30<α25 holds true, and the first coating layer is composed of a first oxide powder or a mixture of the first oxide powder and glass. The second coating layer is composed of a mixture of second oxide powder and glass, The third covering layer is composed of a mixture of third oxide powder and glass.

2. The temperature sensor element according to claim 1, wherein When the linear expansion coefficients of the first oxide powder, the second oxide powder, and the third oxide powder are β20, β25, and β30, respectively, the relationship β20<β30<β25 holds.

3. The temperature sensor element according to claim 2, wherein The first oxide powder includes thermistor powder constituting the heat-sensitive body. The second oxide powder includes powder of one or more of ZrO 2 , CaO, and MgO. The temperature sensor element according to claim 1 , wherein: The second covering layer covers the periphery of the pair of lead wires that pass through the first covering layer and are led out, and covers the first covering layer between the first covering layer and the third covering layer.

5. The temperature sensor element according to claim 1, wherein The second covering layer covers the periphery of the pair of lead wires that pass through the first covering layer and are led out. The first covering layer is in direct contact with the third covering layer. The temperature sensor element according to claim 1 , wherein When the thicknesses of the second coating layer and the third coating layer are denoted as t25 and t30, respectively, t25<t30 holds true.

7. A temperature sensor, characterized in that: The temperature sensor comprises the temperature sensor element according to any one of claims 1 to 6.

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