JP2021106178A - Temperature sensor element - Google Patents

Abstract

To provide a temperature sensor element stable in electric resistance value even when it is continuously used in a reducing atmosphere at high temperature.SOLUTION: A temperature sensor element 1 includes: an element body 2 comprising a thermo-sensitive body 11 composed of a thermistor sintered body whose electric characteristic changes as temperature changes and a pair of lead wires 15, 15 connected to the thermo-sensitive body 11 via electrodes 13, 13; and a protective layer 3 protecting the thermo-sensitive body 11. The protective layer 3 has an internal coat layer 20 coating a part of the thermo-sensitive body 11 and the lead wires 15, 15 and an external coat layer 30 coating an outside of the internal coat layer 20. The external coat layer 30 is composed of two or more laminate bodies. The external coat layer 30 is composed of glass or a mixed body of the glass and oxide powders.SELECTED DRAWING: Figure 1

Description

The present invention relates to a temperature sensor element including a thermistor sintered body as a heat sensitive body, and particularly to a temperature sensor element having a small rate of change in electrical resistance value in a reducing atmosphere at a high temperature.

Conventionally, a temperature sensor using a thermistor whose electric resistance value (hereinafter, simply resistance value) changes with temperature as a heat sensitive body has been widely used. The characteristics of the thermistor are generally indicated by the resistance value and the temperature coefficient of resistance (temperature dependence of the resistance value).
This temperature sensor includes a temperature sensor element as a minimum unit, which includes a thermistor as a heat sensitive body, an electrode formed on the surface of the thermistor, and a lead wire bonded to the electrode. Normally, this temperature sensor element is not used when the thermistor is exposed to the outside air, and is covered with some protective layer. As an example, the thermistor has been protected from the environment in which the temperature sensor is used by providing a protective layer made of glass. For example, when measuring the temperature in a reducing atmosphere, when the thermistor, which is an oxide sintered body, is reduced, the electrical characteristics of the thermistor change. Then, even if the temperature is the same, after the reduction, the measurement result of the temperature different from that before that is output.

Patent Document 1 and Patent Document 2 propose to solve the problem of the protective layer made of glass. That is, since there is a difference in the coefficient of linear expansion between the thermistor and the lead wire, the coefficient of linear expansion of the glass forming the protective layer cannot be matched with the coefficient of linear expansion of both the thermistor and the lead wire. Therefore, if there is a difference in linear expansion coefficient between the glass and the thermistor, thermal stress is generated in the thermistor, and the electrical characteristics of the thermistor element, typically the resistance value, change, making accurate temperature measurement difficult. There is a risk of becoming.

Therefore, Patent Document 1 and Patent Document 2 propose a temperature sensor having an inner protective layer and an outer protective layer that seal the thermistor together with a part of the lead wire. The inner protective layer is exemplified by a crystallized glass to which an oxide powder, preferably a thermistor powder, is added. As the outer protective layer, which crystallized glass yttrium oxide (Y 2 _{O 3)} is added is illustrated.

Japanese Patent No. 4990256 Japanese Patent No. 5049879

According to the proposals of Patent Document 1 and Patent Document 2, a temperature sensor having excellent thermal responsiveness and lead wire sealing property is provided even in a reducing atmosphere at a high temperature of, for example, 1000 ° C. or higher.

However, it is required to be able to measure the temperature with high accuracy for a long time in such a harsh environment. Therefore, an object of the present invention is to provide a temperature sensor element having a stable electric resistance value even when continuously used in a high temperature reducing atmosphere.

The temperature sensor element of the present invention includes a heat sensitive body made of a thermistor sintered body whose electrical characteristics change depending on temperature, a pair of lead wires connected to the heat sensitive body via electrodes, and a protective layer for protecting the heat sensitive body. To be equipped.
The protective layer in the present invention has an inner layer coating that covers a part of the heat sensitive body and the lead wire, and an outer layer coating that covers the outside of the inner layer coating.

Since the present invention has a feature of the outer layer coating, a stable electric resistance value can be obtained even when used in a harsh high temperature environment. That is, the outer layer coating in the present invention is composed of two or more laminated bodies.
The outer layer coating in the present invention preferably consists of glass or glass and oxide powder.
The oxide powder in the present invention is preferably _{one or more of yttrium oxide (Y 2} O ₃ ) powder, aluminum oxide (Al ₂ O ₃ ), and thermista powder having a composition equivalent to that of a heat sensitive substance.

According to the temperature sensor element of the present invention, a stable electric resistance value can be obtained even when used in a harsh high temperature environment.

It is sectional drawing which shows the schematic structure of the temperature sensor element which concerns on this embodiment. It is a flowchart which shows the outline manufacturing process of the temperature sensor element which concerns on this embodiment. It is a figure which shows the schematic manufacturing procedure of the temperature sensor element which concerns on this embodiment. It is a figure which shows the procedure of forming the outer layer coating which concerns on this embodiment.

The temperature sensor element 1 according to the embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the temperature sensor element 1 according to the present embodiment includes an element body 2 and a coating 3 as a protective layer. The element body 2 is connected to a heat sensitive body 11 whose electrical characteristics, for example, an electric resistance value changes depending on temperature, a pair of electrodes 13 and 13 formed on opposite side surfaces of the heat sensitive body 11, and electrodes 13 and 13, respectively. A pair of lead wires 15 and 15 to be formed, and connection electrodes 17 and 17 connecting the electrodes 13 and 13 and the lead wires 15 and 15 are provided. Further, the coating 3 includes an inner layer coating 20 that covers the heat sensitive body 11 together with a part of the lead wires 15 and 15, and an outer layer coating 30 that covers the outside of the inner layer coating 20.

By providing the outer layer coating 30 with a characteristic configuration, the temperature sensor element 1 can suppress the rate of change of the electric resistance value to a small value in an atmosphere containing hydrogen.
Although specific description is omitted here, the temperature sensor element 1 is housed and used inside a metal protective tube having excellent heat resistance and oxidation resistance such as stainless steel and Ni superalloy. Sometimes.
Hereinafter, each element of the temperature sensor element 1 will be described, and then the operation and effect of the temperature sensor element 1 will be described.

[Thermal body 11]
A thermistor sintered body is used as the heat sensitive body 11. Thermistor is an abbreviation for thermally sensitive resistor, which is a metal oxide that measures temperature by utilizing the fact that the electrical resistance value changes with temperature.
Thermistors are classified into NTC (negative temperature coefficient) thermistors and PTC (positive temperature coefficient), and the present invention can use any of the thermistors.

_{An oxide sintered body having a basic composition of manganese oxide (Mn 3} O ₄ ) having a typical spinel structure as an NTC thermistor can be used for the heat sensitive body 11. Used M element to the basic composition of the oxide sintered body having a composition of _{MxMn 3-x O 4} plus (Ni, Co, Fe, Cu , 1 or more kinds of Al and Cr) in the thermosensitive element 11 be able to. Further, one or more of V, B, Ba, Bi, Ca, La, Sb, Sr, Ti and Zr can be added.
Further, a composite oxide having a perovskite structure typical of an NTC thermistor, for example, an oxide sintered body having a basic structure of _{YCrO 3 can be used for the heat sensitive body 11.} As the NTC _thermistor, Y 2 and _{O 3 phase, Y} (Cr, Mn) _{O 3} phase, and at least one among the YCrO ₃ phase and YMnO _3-phase, the sintered body is most typical be.

[Manufacturing method of thermistor sintered body]
The heat-sensitive body 11 made of a thermistor sintered body undergoes the steps of weighing the raw material powder, mixing the raw material powder, drying the raw material powder, baking, mixing / crushing after baking, drying / granulating, molding, and sintering. Manufactured by Hereinafter, each step will be described by taking as an example a thermistor sintered body having _{a Y 2} O ₃ phase and a Y (Cr _, Mn) O _{3 phase.}

[Weighing of raw material powder]
Raw material powder containing yttrium oxide (Y ₂ O ₃ ) powder, chromium oxide (Cr ₂ O ₃ ) powder, manganese oxide (Mn O _{, Mn 2 O 3} , Mn ₃ O _4, etc.) powder and calcium carbonate (CaCO _{3) powder.} , Weigh so as to have the above-mentioned chemical composition.
In this embodiment, the powder is composed of a plurality of particles.

Y ₂ O ₃ powder contributes to the formation of _{Y 2} O _{3 phase, and Y 2} O ₃ powder, Cr ₂ O ₃ powder and manganese oxide powder (Mn ₃ O ₄ powder) are of Y (Cr _, Mn) O ₃ phase. Contribute to generation. In addition to functioning as a sintering aid, the _{CaCO 3 powder becomes Ca in the Y (Cr,} Mn) O ₃ phase and dissolves solidly, contributing to lowering the B constant.
As the raw material powder, a powder having a purity of 98% or more, preferably 99% or more, more preferably 99.9% or more is used in order to obtain a thermistor sintered body having high characteristics.
The particle size of the raw material powder is not limited as long as the calcining proceeds, but the particle size (d50) can be selected in the range of 0.1 to 6.0 μm.

[Mixing of raw material powder / ball mill]
_{The Y 2} O ₃ powder, Cr ₂ O ₃ powder, Mn ₃ O ₄ powder and CaCO ₃ powder weighed by a predetermined amount are mixed. Mixing can be performed by a ball mill, for example, in the form of a slurry in which water is added to the mixed powder. A mixer other than a ball mill can also be used for mixing.

[Drying raw material powder]
It is preferable that the mixed slurry is dried and granulated by a spray dryer or other equipment to obtain a mixed powder for calcining.

[Temporary baking]
The mixed powder for calcining after drying is calcined. By _calcining, Y 2 _{O 3} powder, provisionally with _Cr 2 _{O 3} powder, from _Mn 3 _{O 4} powder and CaCO _{3 powder,} Y 2 _{O 3} phase and _Y (Cr, Mn) composite structure of _{O 3} phase Obtain a sintered body.
The calcining is performed by putting the mixed powder for calcining into a crucible, for example, and holding it in the air in a temperature range of 800 to 1300 ° C. If the calcining temperature is less than 800 ° C., the formation of a composite structure is insufficient, and if it exceeds 1300 ° C., the sintering density may be lowered and the stability of the resistance value may be lowered. Therefore, the holding temperature of calcining is set in the range of 800 to 1300 ° C.
The holding time in the calcining should be appropriately set according to the holding temperature, but within the above temperature range, the purpose of the calcining can be achieved with a holding time of about 0.5 to 100 hours.

[Mixing / crushing / ball mill]
The powder after calcining is mixed and crushed. Mixing and crushing can be carried out by adding water to form a slurry and using a ball mill, as in the case of pre-baking.
[Drying / Granulation]
The powder after pulverization is preferably dried and granulated by a spray dryer or other equipment.

[Molding]
The granulated powder after calcining is formed into a predetermined shape.
For molding, in addition to press molding using a mold, a cold hydrostatic press (CIP: Cold Isostatic Press) can be used.
The higher the density of the molded product, the easier it is to obtain a sintered body with a higher density. Therefore, it is desired to increase the density of the molded product as much as possible. For that purpose, it is preferable to use CIP which can obtain a high density.

[Sintering]
Next, the obtained molded product is sintered.
Sintering is performed by holding in the air in a temperature range of 1400 to 1650 ° C. If the sintering temperature is less than 1400 ° C., the formation of a composite structure is insufficient, and if it exceeds 1650 ° C., the sintered body melts or reacts with a crucible for sintering. The holding time in sintering should be appropriately set according to the holding temperature, but within the above temperature range, a dense sintered body can be obtained with a holding time of about 0.5 to 200 hours.

The obtained thermistor sintered body is preferably annealed in order to stabilize its thermistor properties. Annealing is performed, for example, by holding at 1000 ° C. in the air.

[Electrodes 13, 13 and connection electrodes 17, 17]
As shown in FIG. 1, the electrodes 13 and 13 are formed in a film shape over the entire front and back surfaces of the plate-shaped heat sensitive body 11. The electrodes 13 and 13 are composed of platinum (Pt) and other precious metals.
The electrodes 13 and 13 are formed as a thick film or a thin film. The thick-film electrodes 13 and 13 are formed by applying a paste prepared by mixing an organic binder with platinum powder on both the front and back surfaces of a thermistor sintered body, drying the paste, and then sintering the paste. Further, the thin film electrode can be formed by vacuum deposition or sputtering.
The heat sensitive body 11 on which the electrodes 13 and 13 are formed is processed to a predetermined size.
The connection electrodes 17 and 17 are composed of a metal film formed on the surfaces of the electrodes 13 and 13, respectively. The connection electrodes 17 and 17 are also composed of platinum (Pt) and other precious metals.

[Lead wires 15, 15]
As shown in FIG. 1, the lead wires 15 and 15 are electrically and mechanically connected to the electrodes 13 and 13 via the connection electrodes 17 and 17 on one end side. The other ends of the lead wires 15 and 15 are connected to an external detection circuit (not shown). The lead wires 15 and 15 are made of a wire having heat resistance, for example, platinum or an alloy of platinum and iridium (Ir).

The lead wires 15 and 15 are connected to the electrodes 13 and 13 as follows.
A paste containing platinum powder forming the connection electrodes 17 and 17 is previously applied to one end side of each of the lead wires 15 and 15. The platinum paste is dried while the sides of the lead wires 15 and 15 coated with the platinum paste are in contact with the electrodes 13 and 13, and then the platinum powder is sintered.

[Inner layer coating 20]
Next, the inner layer coating 20 will be described.
The main function of the inner layer coating 20 is to serve as a cushioning material that alleviates the stress generated by the thermal expansion of the outer layer coating 30 from being directly applied to the heat sensitive body 11. In other words, the inner layer coating 20 receives the thermal stress due to the outer layer coating 30.
Further, the inner layer coating 20 realizes a stable electrical and mechanical connection by fixing the connection portion between the heat sensitive body 11 and the lead wires 15 and 15.

The inner layer coating 20 according to the present embodiment is made of a mixture of glass and oxide powder.
In the inner layer coating 20, the glass functions as a binder that binds oxide powders and metal powders to each other to maintain the shape of the inner layer coating 20.
The ratio of glass to oxide powder is not limited as long as the desired coefficient of linear expansion is obtained and it functions as a binder.
As the glass constituting the inner layer coating 20, one or both of crystalline glass and amorphous glass can be used, but it is preferable to use crystallized glass which is stable at high temperature. The crystallized glass, for _example, SiO 2: 30 to 60 wt%, CaO: 10 to 30 wt%, MgO: 5 to 25 _{wt%, Al} 2 O 3: applicable composition comprising a 0-15 wt%.

Examples of the oxide powder constituting the inner layer coating 20 include aluminum oxide (Al ₂ O ₃ ), magnesium oxide (MgO), calcium oxide (CaO), yttrium oxide (Y ₂ O ₃ ), and zirconium oxide (ZrO ₂ ). Can be mentioned.

As the thermistor powder, a powder having the same composition as the thermistor sintered body constituting the heat sensitive body 11 can be used. The equivalent composition means that both the thermosensitive body 11 and the thermista powder contained in the first inner layer form have, for example, the chemical composition of Cr, Mn, Ca and Y excluding oxygen described above, Cr: 3 to 15 mol%, Mn. : 5 to 15 mol%, Ca: 0.5 to 8 mol%. This includes the case where the thermistor powder and the thermistor sintered body constituting the heat sensitive body 11 have the same composition.

[Outer layer coating 30]
Next, the outer layer coating 30 will be described.
The main function of the outer layer coating 30 is to provide airtightness that airtightly seals the heat sensitive body 11 from the surrounding atmosphere. Further, the outer layer coating 30 imparts mechanical strength to protect the heat sensitive body 11 from an external force.
The outer layer coating 30 can be made of the same glass as the inner layer coating 20. Further, the outer layer coating 30 can also be composed of a mixture of glass and oxide powder similar to the inner layer coating 20. Oxide powders include aluminum oxide (Al ₂ O ₃ ), magnesium oxide (MgO), yttrium oxide (Y ₂ O ₃ ), calcium oxide (CaO), zirconium oxide (ZrO ₂ ), strontium oxide (SrO), and oxidation. One or more of titanium (TIO) and lanthanum oxide (La ₂ O ₃ ) can be used.

The outer layer coating 30 according to the present embodiment is made of a mixture of glass and oxide powder similar to the inner layer coating 20. However, the outer layer coating 30 contains more glass than the inner layer coating 20. This is to satisfy the relationship of the linear expansion rate described later.

The outer layer coating 30 is obtained by forming at least two outer layer coating layers. The required thickness and state can be obtained by the one-layer outer layer coating 30 by one formation, but a healthier outer layer coating 30 can be obtained by forming the outer layer coating 30 into a plurality of layers. When the outer layer coating 30 is formed into a plurality of layers, the thickness of each layer may be uniform or uneven.

Eliminating defects in the outer layer coating 30 formed by only one layer is not easy on an industrial production scale. As this defect, for example, a crack penetrating the front and back surfaces of the outer layer coating 30 in the thickness direction can be mentioned. This crack impairs the airtightness of the temperature sensor element 1 during use. Even if there are cracks in each of the multiple layers, the probability that the cracks in each layer will exist at the same position is equal to zero. Therefore, even if cracks are present in each layer, it can be considered that there are no cracks penetrating the front and back when viewed as a plurality of layers as a whole, that is, as a laminated body.
In the present embodiment, the number of layers of the outer layer coating 30 is arbitrary, but as shown in Examples described later, the rate of change of the resistance value can be suppressed to a small value as the number of layers increases, so that the rate of change of the resistance value can be reduced. From the viewpoint, it is preferable to increase the number of layers. On the other hand, as the number of layers increases, the number of man-hours for forming the outer layer coating 30 increases, which increases the cost. Therefore, when it is important to reduce the rate of change of the resistance value, the number of layers of the outer layer coating 30 may be increased to, for example, 10 layers, and when the cost is emphasized, it may be 7 layers or less and 5 layers or less.

[Relationship of line expansion rate]
The temperature sensor element 1 in this embodiment may be used, for example, in a temperature range of room temperature to 1000 ° C.
Then, in this temperature range, it is required to reduce the thermal stress generated between the heat sensitive body 11 and the inner layer coating 20 that directly covers the heat sensitive body 11. This is to suppress changes in the electrical characteristics of the heat sensitive body 11, particularly the resistance value.
Further, in this temperature range, it is required to suppress the formation of a gap between the outer layer coating 30 that covers the inner layer coating 20 and seals the lead wires 15 and 15 and the lead wires 15 and 15. This is to prevent the reducing gas from invading the heat sensitive body 11 and to prevent changes in the electrical characteristics of the heat sensitive body 11, particularly the resistance value.

In order to satisfy the above requirements, the coefficient of linear expansion of the heat sensitive body 11, the lead wires 15, 15 and the inner layer coating 20 and the outer layer coating 30, which are the elements constituting the temperature sensor element 1, is adjusted. That is, the coefficient of linear expansion (α20) of the inner layer coating 20 is brought closer to the coefficient of linear expansion (α11) of the heat sensitive body 11, and the coefficient of linear expansion (α30) of the outer layer coating 30 is brought closer to the coefficient of linear expansion (α15) of the lead wire 15. Is desired. 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 are preferably 5 × ^10-7 / K or less, more preferably 3 × 10 ^−. Keep it below ^{7 / K.}

The coefficient of linear expansion of the thermistor sintered body constituting the heat sensitive body 11, for example platinum and oxide constituting the lead wire 15 is as follows. Based on these values, it is desirable to set the ratio of the glass and the oxide powder so that the inner layer coating 20 approaches the linear expansion coefficient α11 of the heat sensitive body 11. Further, it is desired to set the ratio of the glass and the oxide powder so that the outer layer coating 30 approaches the linear expansion coefficient α15 of the lead wire 15.
Thermal body 11 (Thermistor sintered body): 8.0 × ^10-6 / K
Lead wire 15 (platinum): 8.8 x ^10-6 / K
Glass: 9.1 x ^10-6 / K
Y ₂ O ₃ , Al ₂ O ₃ : 7.2 × ^10-6 / K
La ₂ O ₃ : 8.6 × ^10-6 / K
TiO ₂ : 9.2 × ^10-6 / K
MgO, ZrO ₂ : 10.5 × ^10-6 / K
CaO: 13.6 × ^10-6 / K
SrO: 13.8 × ^10-6 / K

[Manufacturing method of temperature sensor element 1]
Next, a method of manufacturing the temperature sensor element 1 will be described.
As shown in FIGS. 2 and 3, the temperature sensor element 1 is manufactured by the step of joining the heat sensitive body 11 and the lead wires 15 and 15 to manufacture the element main body 10 (FIGS. 2S100 and 3A). A step of forming the inner layer coating 20 on the element body 10 (FIG. 2 S200, FIG. 3B) and a step of forming the outer layer coating 30 on the inner layer coating 20 (FIGS. 2S300, 3C). And, it is manufactured through.

Regarding the inner layer coating 20, for example, using the above-mentioned oxide powder and crystallized glass powder mixed with a solvent to form a paste, a predetermined amount of the inner layer coating 20 is placed on the heat sensitive body 11 to which the lead wires 15 are bonded. To form.

Further, with respect to the outer layer coating 30, a plurality of outer layer coatings are formed on the inner layer coating 20 by using the outer layer glass paste prepared by mixing the oxide powder, the glass powder and the solvent in the same manner as described above. As shown in FIGS. 4A to 4C, the outer layer coating 30 is formed from, for example, three coating layers 31, 33, 35.

The outer layer coating is composed of two or more laminated bodies. Further, in this laminated body, the boundary between the adjacent outer layer coating layers is visually visible, but the adjacent outer layer coating layers are joined with a force sufficient to ensure the function as the outer layer coating 30.

[Example]
Next, an example of the present invention will be described based on specific examples.
A temperature sensor element 1 including the inner layer coating 20 and the outer layer coating 30 described below was manufactured, and the rate of change of the resistance value was measured. The results are shown in Table 1.
The raw material powder having the following particle size (d50) was prepared as the mixing ratio shown below, and the heat sensitive body 11 was manufactured according to the above-mentioned steps. Pre-baking was performed under the conditions of 1300 ° C. × 24 hours, and sintering was performed under the conditions of 1500 ° C. × 24 hours, both of which were performed in the air.
Y ₂ O ₃ : 79.5 mol% Particle size: 0.1 μm
Cr ₂ O ₃ : 8.5 mol% Particle size: 2.0 μm
CaCO ₃ : 3.5 mol% Particle size: 2.0 μm
Mn ₃ O ₄ : 8.5 mol% Particle size: 5.0 μm

The electrode 13, the lead wire 15, and the connection electrode 17 are all made of platinum (Pt), and the element body 10 is manufactured by the procedure described in the embodiment.

An inner layer coating 20 and an outer layer coating 30 were formed on the above element body 10.
For the inner layer coating 20, crystalline glass and a thermistor powder having the same composition as that of the heat sensitive body 11 were used as the glass. The weight ratio of thermistor powder to crystalline glass is 80:20. In addition, an organic binder was used as the binder. The inner layer coating 20 is formed from one inner layer precursor layer.

As for the outer layer sheath 30, with Y ₂ O ₃ as an oxide powder and a crystalline glass. Weight ratio of _Y 2 _{O 3} crystalline glass and the oxide powder is 80:20.

Using the above element body 10, inner layer liquid composition and outer layer liquid composition, four types of temperature sensor elements (Sample Nos. 1 to 6) shown in Table 1 were obtained. Using the obtained temperature sensor elements (Sample Nos. 1 to 6), the rate of change of the resistance value under the following conditions was measured.
The results are shown in Table 1, and it can be seen that the outer layer coating 30 is composed of a plurality of layers of two or more layers, and the rate of change of the resistance value can be remarkably reduced as the number of coating layers increases. When the number of layers is 10 (Sample No. 6), the rate of change after 10 hours can be suppressed to 5% or less of that of 1 layer (Sample No. 1).

In Table 1, for example, sample No. 2 having 2 layers is fired after forming two precursor layers in order by dipping, and sample No. 4 having 4 layers has four precursor layers by dipping. After forming in order, it was fired. Further, the outer layer coatings 30 of Samples Nos. 1 to 6 are formed so that the overall thickness is about 80 to 1000 μm and is the same regardless of the number of dippings. Therefore, assuming that the thickness per layer in sample No. 4 is t, the thickness of the outer layer coating 30 composed of one layer in sample No. 1 is 4 × t, and the thicknesses of both outer layer coatings 30 are equal. ..

When the vertical cross section of the temperature sensor element according to Sample Nos. 2 to 6 was observed after firing, the boundary between adjacent layers could be visually confirmed.
Further, from the results shown in Table 1, the temperature sensor elements according to Sample Nos. 2 to 6 were stable even when used in a harsh high temperature environment without increasing the thickness of the outer layer coating 30 as a whole. It can be seen that the electrical resistance value can be obtained.

Holding temperature: 900 ° C
Atmosphere: Hydrogen 5 vol.% + Nitrogen 95 vol.%
Holding time: 5 hours, 10 hours Resistance value measurement: 25 ° C

Although the preferred embodiments of the present invention have been described above, the configurations listed in the above embodiments can be selected or replaced with other configurations as long as the gist of the present invention is not deviated.

1 Temperature sensor element 2 Element body 3 Coating 11 Heat sensitive body 13 Electrode 15 Lead wire 17 Connection electrode 20 Inner layer coating 30 Outer layer coating

Claims (3)

A heat-sensitive body made of a thermistor sintered body whose electrical characteristics change depending on the temperature,
A pair of lead wires connected to the thermal body via electrodes,
A protective layer that protects the heat sensitive body is provided.
The protective layer is
It has an inner layer coating that covers a part of the heat sensitive body and the lead wire, and an outer layer coating that covers the outside of the inner layer coating.
The outer layer coating is
Composed of two or more layers,
A temperature sensor element characterized by this.
The outer layer coating is
Glass or the glass and oxide powder
The temperature sensor element according to claim 1.
The oxide powder is
One or more of yttrium oxide (Y ₂ O ₃ ) powder, aluminum oxide (Al ₂ O ₃ ) and thermistor powder having the same composition as the heat sensitive substance.
The temperature sensor element according to claim 2.

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