JP2015078089A - Thermistor element and temperature sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermistor element that, even if exposed at 900°C for a long time, can suppress a change in resistance characteristics of a thermistor part to suppress a decrease in temperature detection accuracy, and to provide a temperature sensor using the thermistor element.SOLUTION: In a thermistor element 21 that is provided in a temperature sensor 1, a cover layer 26 has a composition as shown in examples 1-8, whereby the cover layer 26 is formed as dense crystallized glass even if a baking temperature is relatively low (for example, 1,100°C or lower) at the time of its production. Since the thermistor element 21 is provided with the cover layer 26 as the dense crystallized glass, composition changes in a thermistor part 22 and the cover layer 26 are hardly caused, and changes in a resistance value and resistance characteristics of the thermistor part 22 are hardly caused.

Description

  The present invention relates to a thermistor element comprising a thermistor part made of a thermistor composition and a coating layer covering the thermistor part, and a temperature sensor having such a thermistor element.

  Conventionally, a thermistor element including a thermistor portion made of a thermistor composition and a coating layer covering the thermistor portion is known. A temperature sensor having such a thermistor element is also known.

  The covering layer of the thermistor element is provided in order to suppress the resistance characteristic from being changed due to reduction of the thermistor portion. For example, there is one formed of crystallized glass (Patent Document 1, Patent Document 2). .

JP 2009-170555 A JP 2009-182250 A

  However, when the crystallinity of the crystallized glass in the coating layer is low, the resistance characteristics of the thermistor part change due to the reaction between the amorphous phase of the coating layer and the thermistor part, and the temperature detection accuracy of the thermistor element May be reduced.

  Further, when the thermistor element is continuously exposed to a high temperature region such as 900 ° C. for a long time, the crystal phase and crystallinity of the crystallized glass in the coating layer may change. In other words, the change in the crystal phase (including the case of crystallization from the amorphous phase) may be accompanied by a volume change, and the stress applied between the thermistor part and the coating layer when the crystal phase changes due to use under high temperature There is a possibility that the resistance characteristics of the thermistor part may change due to changes in the resistance and electrode peeling.

Furthermore, if the mechanical strength of the coating layer is reduced due to the occurrence of cracks due to use at a high temperature, the effect of suppressing the reduction of the thermistor portion by the coating layer may not be maintained.
For these reasons, even if crystallized glass is used for the coating layer, the resistance characteristics of the thermistor part may fluctuate and the temperature detection accuracy of the thermistor element may be reduced when used for a long time at high temperatures. .

  The present invention provides a thermistor element that can suppress fluctuations in the resistance characteristics of the thermistor portion even when exposed to a temperature of 900 ° C. for a long time, and can suppress a decrease in temperature detection accuracy, and uses such a thermistor element. An object of the present invention is to provide a temperature sensor.

The present invention is a thermistor element comprising a thermistor part made of a thermistor composition, and a coating layer covering the thermistor part, the coating layer including at least SiO ₂ , BaO, and Al ₂ O ₃ , and SiO ₂ Is 45 to 75 mol% with respect to the total number of moles of the coating layer, Al ₂ O ₃ is 2 to 10 mol% with respect to the total number of moles of the coating layer, and BaO is the total mole of the coating layer. 20 to 40 mol% relative to the _number, contained in the content of total SiO 2, BaO, and _Al 2 _{O 3} is chosen to be 90 mol% to 100 _mol%, the B 2 _{O 3} Is a thermistor element characterized in that it is 0.1 mol% or less with respect to the total number of moles of the coating layer, and the coating layer is crystallized glass having a crystallinity of 70% or more.

  By having the above composition, the coating layer is formed as a dense crystallized glass even when the baking temperature during the production of the coating layer is relatively low (for example, 1100 ° C. or lower). Thus, by providing the coating layer as a dense crystallized glass, the composition variation of the thermistor part and the coating layer hardly occurs, and the resistance value and the characteristic of the thermistor part hardly change.

By setting the content of SiO _{2 in} the coating layer to be equal to or higher than the lower limit, the softening temperature of the glass is increased and the heat resistance of the coating layer is improved. By setting the content of SiO _{2 in} the coating layer to be equal to or less than the above upper limit value, the glass is easily softened and the fluidity is improved, so that there is an advantage that the coating operation is facilitated.

By setting the content of Al ₂ O ₃ in the coating layer to be equal to or higher than the lower limit value, the glass is less likely to be devitrified and the coating layer can be easily formed. That is, when devitrification occurs, voids are generated in the coating layer and a sufficient coating layer cannot be formed. In such a case, there is a possibility that the hermeticity of the thermistor portion cannot be ensured, but the Al ₂ O ₃ in the coating layer may not be secured. By setting the content to be equal to or higher than the lower limit, it is possible to suppress the occurrence of defects due to devitrification.

By setting the content of Al ₂ O ₃ in the coating layer to be equal to or less than the above upper limit value, the coating layer and the thermistor part are difficult to react and the resistance characteristics of the thermistor part are difficult to change.
By setting the content of BaO in the coating layer to be equal to or higher than the lower limit value, the coefficient of thermal expansion does not become too small, so that the difference in the coefficient of thermal expansion from the thermistor portion hardly occurs, and the coating layer hardly cracks. Become. By setting the content of BaO in the coating layer to the upper limit value or less, the heat resistance of the coating layer becomes good.

By setting the content of B ₂ O ₃ in the coating layer to be equal to or less than the upper limit, even if the thermistor part is exposed to a high temperature for a long time, the components forming the coating layer are difficult to move to the thermistor part. For this reason, composition fluctuations in the thermistor portion are less likely to occur. For this reason, in the thermistor element of the present invention, the coating layer and the thermistor part hardly react and the resistance characteristic (electrical characteristic) of the thermistor part hardly changes.

  Since the coating layer is a crystallized glass having a crystallinity of 70% or more, the composition of the thermistor part is less likely to move to the thermistor part even when the thermistor element is exposed to a high temperature for a long time. Thus, the resistance characteristics of the thermistor part are difficult to change.

  In addition, since the coating layer is crystallized glass having a crystallinity of 70% or more, the volume change of the coating layer due to the change of the crystal phase is reduced, so that the change in stress applied between the thermistor portion and the coating layer and the electrode Is less likely to occur, and resistance characteristics of the thermistor portion are difficult to change.

Therefore, according to the thermistor element of this invention, even if it exposes to the temperature of 900 degreeC for a long time, the fluctuation | variation of the resistance characteristic of a thermistor part can be suppressed and the fall of temperature detection accuracy can be suppressed.
In the above-described thermistor element, the coating layer can be configured to contain no B ₂ O ₃ .

  As a result, even if the thermistor part is exposed to a high temperature for a long time, the components forming the coating layer are less likely to move to the thermistor part, so that composition fluctuations in the thermistor part are less likely to occur. For this reason, in the thermistor element of the present invention, the coating layer and the thermistor part are more difficult to react, and the resistance characteristic (electrical characteristic) of the thermistor part is less likely to change.

“Non-containing” means that B ₂ O ₃ cannot be detected or identified even by ICP (Inductively Coupled Plasma) emission analysis.
In the above thermistor element, the coating layer contains a ZrO _2, 10 mol% or less greater than 0 mol% relative to the total number of moles of the coating layer for ZrO _2, to adopt a configuration that it can.

Coating layer, by containing a zirconia (ZrO _2), the crystalline phase is likely to precipitate.
Moreover, since it will become easy to produce devitrification when content of zirconia becomes excess, devitrification can be suppressed by determining the upper limit of zirconia.

  Therefore, according to the thermistor element of the present invention, it is possible to increase the crystallinity of the coating layer and to suppress defects caused by devitrification. A decrease in detection accuracy can be suppressed.

ZrO ₂ is preferably 0.1 mol% or more with respect to the total number of moles of the coating layer, since the crystal phase is likely to precipitate sufficiently.
In the thermistor element described above, the coating layer has at least one crystal phase selected from BaSi ₂ O ₅ (orthorhombic), Ba ₂ Si ₄ O ₁₀ (monoclinic), and BaAl ₂ Si ₂ O _8. The structure of containing the above crystal phase can be taken.

The coating layer having such a structure is a crystal phase in which the crystal phase hardly changes even when exposed to 900 ° C. for a long time.
That is, since the volume change of the coating layer due to the change of the crystal phase is reduced, the stress applied between the thermistor portion and the coating layer is less likely to be peeled off and the electrode is not peeled off, and the resistance characteristics of the thermistor portion are difficult to change. .

In the thermistor element described above, the coating layer may further include a Ba ₅ Si ₈ O ₂₁ crystal phase.
The crystal phase of Ba ₅ Si ₈ O ₂₁ may cause a volume change of the coating layer accompanying a change in the crystal phase when exposed to 900 ° C. for a long time. preferable.

Therefore, according to the thermistor element of this invention, even if it exposes to the temperature of 900 degreeC for a long time, the fluctuation | variation of the resistance characteristic of a thermistor part can be suppressed and the fall of temperature detection accuracy can be suppressed.
In the above-described thermistor element, the thermistor portion can be configured to include a perovskite phase represented by ABO ₃ (where A includes Sr and / or Y, and B includes Al).

The thermistor element provided with such a thermistor part can detect a temperature in a wide temperature range from a low temperature region to a high temperature region exceeding 600 ° C.
In the above thermistor element, the thermistor portion can take a configuration in which B in the ABO ₃ further contains at least one of Cr, Mn, and Fe.

  The thermistor element provided with such a thermistor part can detect temperature in a wide temperature range from a low temperature region to a high temperature region exceeding 600 ° C. more preferably and stably for a long period of time.

  In the thermistor element described above, the thermistor portion has a lower conductivity than the perovskite phase contained in the thermistor portion, and when at least one metal element selected from the metal elements forming the perovskite phase is Me. The metal oxide phase containing at least one kind of metal oxide represented by the composition formula MeOx can be employed.

  That is, the thermistor part provided in this thermistor element has a metal oxide phase containing a metal oxide (MeOx) having a lower conductivity than the conductive perovskite phase contained in the thermistor element. By adjusting the content of the metal oxide, the resistance value of the thermistor element can be shifted to a desired value while maintaining the temperature gradient coefficient (B constant) in the temperature range to be detected.

In the above-described thermistor element, a configuration in which the metal oxide contained in the metal oxide phase is SrAl ₂ O ₄ can be employed.
When the metal oxide contained in the metal oxide phase is SrAl ₂ O ₄ , when this thermistor element is used at a high temperature, the reaction between the metal oxide phase and the perovskite phase in the thermistor portion becomes difficult.

As a result, the resistance characteristics of the thermistor part are unlikely to fluctuate, and a decrease in temperature detection accuracy as a thermistor element can be suppressed.
In order to achieve the above object, a temperature sensor of the present invention has any one of the thermistor elements described above.

  Since this temperature sensor has a thermistor element that has an excellent effect as described above, even if it is exposed to a temperature of 900 ° C. for a long time, it can suppress fluctuations in the resistance characteristics of the thermistor part, and the temperature detection accuracy can be reduced. Can be suppressed.

  According to the thermistor element and temperature sensor of this invention, even if it exposes to the temperature of 900 degreeC for a long time, the fluctuation | variation of the resistance characteristic of a thermistor part can be suppressed, and the fall of temperature detection accuracy can be suppressed.

It is a fragmentary sectional view showing the internal structure of a temperature sensor. It is sectional drawing showing the internal structure of a thermistor element. It is sectional drawing in the AA cross section in the thermistor element of FIG. 3 is an X-ray diffraction pattern of a coating layer before endurance (initial stage) in Example 1. FIG. 6 is an X-ray diffraction pattern of a coating layer before endurance (initial stage) in Example 2. FIG. 6 is an X-ray diffraction pattern of a coating layer before endurance (initial) in Example 3. FIG. 2 is an X-ray diffraction pattern of a coating layer before the endurance (initial stage) of Comparative Example 1. FIG. 2 is an X-ray diffraction pattern of a coating layer after endurance in Example 1. FIG. 3 is an X-ray diffraction pattern of a coating layer after endurance in Example 2. FIG. 6 is an X-ray diffraction pattern of a coating layer after endurance in Example 3. FIG. 2 is an X-ray diffraction diagram of a coating layer after endurance of Comparative Example 1. FIG.

Embodiments to which the present invention is applied will be described below with reference to the drawings.
In addition, this invention is not limited to the following embodiment (Example) at all, and it cannot be overemphasized that various forms can be taken as long as it belongs to the technical scope of this invention.

[1. First Embodiment]
[1-1. overall structure]
The whole structure of the temperature sensor 1 provided with the thermistor element 21 of this embodiment is demonstrated based on FIG. FIG. 1 is a partially broken cross-sectional view showing the internal configuration of the temperature sensor.

  The temperature sensor 1 includes a thermistor element 21 as a temperature sensitive element. The temperature sensor 1 is attached to a mounting portion of an automobile exhaust pipe and detects the temperature of the exhaust gas by disposing the thermistor element 21 in the exhaust pipe through which the exhaust gas flows.

  The temperature sensor 1 includes a sheath member 7 in which a pair of metal sheath core wires 3 (electrode wires 3) are insulated and held inside the cylindrical member 5, and a cylindrical metal tube 9 (in the axial direction with the distal end closed) ( A housing 9), a mounting member 11 that supports the metal tube 9, a nut member 17 having a hexagonal nut portion 13 and a screw portion 15, and an outer cylinder 19 that fits inside the rear end side of the mounting member 11. Yes.

  The axial direction is the longitudinal direction of the temperature sensor 1 and corresponds to the vertical direction in the figure in FIG. Moreover, the front end side in the temperature sensor 1 is a lower side in the figure, and the rear end side in the temperature sensor 1 is an upper side in the figure.

  The temperature sensor 1 includes a thermistor element 21 as a temperature-sensitive element whose electrical characteristics change according to the temperature inside the distal end side of the metal tube 9. The details of the thermistor element 21 will be described later.

  The sheath core wire 3 has a front end portion connected to the lead portion 25 of the thermistor element 21 by, for example, laser welding, and a rear end portion connected to the crimping terminal 27, for example, by resistance welding. Thus, the sheath core wire 3 is connected at its rear end side to an external lead wire 29 for connecting an external circuit (for example, an electronic control unit (ECU) of a vehicle) via the crimping terminal 27.

  The pair of sheath core wires 3 and the pair of crimping terminals 27 are insulated from each other by an insulating tube 31, and the external lead wire 29 covers the inside of a grommet 33 made of heat-resistant rubber with a conductive wire covered with an insulating covering material. Arranged in a penetrating state.

  The sheath member 7 includes a metal cylindrical member 5 and a pair of sheath core wires 3 made of a conductive metal. The sheath member 7 includes an insulating powder (not shown) such as silica filled between the tubular member 5 and the two sheath core wires 3. This insulating powder is provided to electrically insulate between the tubular member 5 and the two sheath core wires 3 and to hold the sheath core wires 3.

  The attachment member 11 includes a protruding portion 35 that protrudes radially outward, and a rear end-side sheath portion 37 that is positioned on the rear end side of the protruding portion 35 and extends in the axial direction. The attachment member 11 surrounds the outer peripheral surface on the rear end side of the metal tube 9 and supports the metal tube 9.

  The metal tube 9 is made of a corrosion-resistant metal (for example, a stainless alloy such as SUS310S which is also a heat-resistant metal), and has a cylindrical shape extending in the axial direction in which the tube tip side is closed by deep drawing of the steel plate. The rear end side is open.

  The metal tube 9 includes a small-diameter portion 41 on the distal end side whose diameter is set small, a large-diameter portion 43 on the rear-end side whose diameter is set larger than the small-diameter portion 41, a small-diameter portion 41, and a large-diameter portion 43. And a step portion 45 between them.

  Further, the thermistor element 21 and the cement 39 are filled in the metal tube 9. The cement 39 is filled around the thermistor element 21 to prevent the thermistor element 21 from swinging. The cement 39 is formed of an insulating material containing amorphous silica and amorphous aggregate.

Further, the rear end side of the lead portion 25 of the thermistor element 21 and the front end side of the sheath core wire 3 are integrally joined by laser welding.
And the temperature sensor 1 of such a structure is measured, for example, by screwing and fixing the screw portion 15 to a sensor mounting portion provided in the exhaust pipe and arranging its tip inside the exhaust pipe. Detect the temperature of the target gas.

[1-2. Thermistor element]
Next, the thermistor element 21 will be described.
2 is a cross-sectional view showing the internal structure of the thermistor element 21, and FIG. 3 is a cross-sectional view taken along the line AA of the thermistor element 21 in FIG.

As shown in FIGS. 2 and 3, the thermistor element 21 includes a thermistor portion 22, a pair of electrode portions 24, a pair of lead portions 25, and a coating layer 26.
The thermistor portion 22 is formed mainly of a conductive oxide sintered body whose electrical characteristics (electrical resistance value) vary with temperature. The thermistor portion 22 is formed in a quadrangular prism shape.

The pair of electrode portions 24 are formed on the upper surface and the lower surface of the thermistor portion 22.
The pair of lead portions 25 are electrically connected to the thermistor portion 22 by connecting one end of each of the lead portions 25 to the electrode portion 24.

The covering layer 26 is formed so as to cover the entirety of the thermistor portion 22 and part of the lead portion 25, and has an outer appearance that is cylindrical.
[1-3. Thermistor section]
The thermistor portion 22 is conductive and contains a perovskite phase having a perovskite crystal structure. Examples of suitable perovskite phases include conductive perovskite phases in which the values a, b, c, d, and e of the composition formula (M1 _a M2 _b ) (M3 _c M4 _d ) O _e satisfy the following conditional expressions: Can do.

0 ≦ a ≦ 0.400
0.600 ≦ b ≦ 1.000
0.200 ≦ c ≦ 0.600
0.400 ≦ d ≦ 0.800
2.80 ≦ e ≦ 3.30
In the composition formula, M1 represents at least one element of the Group 2 element located at the A site of the perovskite phase, and M2 represents at least one of the Group 3 elements other than La located at the A site of the perovskite phase. M3 represents at least one element selected from Group 4, Group 5, Group 6, Group 7, Group 8, Group 8, Group 10, Group 11, and Group 12 elements. M4 represents at least one element of the Group 13 elements. In the present invention, the “periodic table” conforms to the periodic table described in “Inorganic chemical nomenclature—IUPAC 1990 recommendation—edited by GJ LEIGH, translated by Kazuo Yamazaki”. In addition, about the value e, confirm whether it exists in the range of e = 2.80-3.30 from the composition ratio of each element of M1, M2, M3, and M4 using the fluorescent X ray analysis. Can do.

A more suitable perovskite phase contained in the thermistor part in the present invention can be represented by a composition formula Sr _a Y _b Fe _c1 Mn _c2 Cr _c3 Al _d O _e . Values a, b, c1, c2, c3, d, and e in this composition formula satisfy the following conditional expressions. In addition, about Fe, Mn, and Cr, what is necessary is just to contain at least 1 type of those, and not all elements are essential. Further, a more preferred thermistor portion in the present invention is composed of a conductive perovskite phase represented by the above composition formula and a metal oxide phase having a lower conductivity than the perovskite phase, for example, SrAl ₂ O ₄ .

0 ≦ a ≦ 0.400
0.600 ≦ b ≦ 1
0.200 ≦ (c1 + c2 + c3) ≦ 0.600
0 ≦ c3 / (c1 + c2 + c3) ≦ 0.18
0.400 ≦ d ≦ 0.800
2.80 ≦ e ≦ 3.30
In addition, about the value e, the composition ratio of each element of Y, Sr, Fe, Mn, Al, Cr, O using the fluorescent X-ray analysis, the area fraction calculated by the method mentioned later, or powder X-ray From the presence / absence of the crystal phase identified by diffraction analysis and the abundance ratio, it can be confirmed whether or not e = 2.80-3.30. Specifically, in the present invention, the perovskite phase and the metal oxide phase, for example, the abundance ratio of SrAl ₂ O ₄ are specified, and the amount of each metal element is divided into the perovskite phase and the metal oxide phase. Next, after determining that the number of O contained in the metal oxide phase (SrAl ₂ O ₄ ) is 4, that is, SrAl ₂ O ₄ is used for the metal oxide phase on the assumption that there is no oxygen deficiency. By calculating the amount of O, the number of O in the perovskite phase can be calculated.

  Further, when the thermistor portion includes each of the perovskite phase and the metal oxide phase, the ratio (area fraction) of the total area PS of the perovskite phase to the cross-sectional area S of the thermistor portion is the resistance value of the thermistor element. From the viewpoint of adjustment, it is preferable to satisfy 0.20 ≦ SP / S ≦ 0.80. Note that the area fraction referred to here can be calculated as follows. First, a thermistor part or a sintered body having the same composition as that of the thermistor part is embedded in a resin, and a sample whose surface is polished by buffing using a 3 μm diamond paste is prepared. Then, the cross section is photographed at a magnification of 3000 times with a scanning electron microscope (trade name: JSM-6460LA manufactured by JEOL). A 40 μm × 30 μm field of view of the photographed tissue photograph is analyzed by an image analyzer, and the ratio (area fraction) SP / S of the total area SP of the perovskite phase to the field of view (cross-sectional area S) can be obtained. .

  The perovskite phase forming the thermistor part can also be represented by the general formula ABO3. When the elements occupying the A site and the B site in the perovskite phase are appropriately selected, the thermistor portion has appropriate conductivity, and has a temperature in a low temperature range, for example, a high temperature range from −40 ° C. to 600 ° C. Can be detected. In the preferred perovskite phase forming the preferred thermistor part in the present invention, the A site contains Sr and / or Y, and the B site contains Al. When the thermistor part contains a perovskite phase having such a perovskite crystal structure, the temperature can be detected in a temperature range of, for example, -40 ° C to 1000 ° C. In a more preferred perovskite phase, the A site contains Sr and / or Y, and the B site contains Al and at least one element selected from Cr, Mn and Fe. A temperature sensor having a thermistor portion containing a perovskite phase having a perovskite type crystal structure in which Al and other specific elements are present at the B site has a low temperature region, for example, −40 ° C. to a high temperature region, for example, 1000 ° C. Temperature can be detected in a wide temperature range.

  In the preferred thermistor portion in the present invention, a, b, c, d, and e in the composition formula satisfy the above-mentioned conditional formula, and a conductive perovskite phase having a perovskite-type crystal structure is more conductive than the perovskite phase. Low, a conductive material comprising at least one metal oxide phase having a crystal structure represented by a composition formula MeOx, where Me is at least one metal element selected from metal elements constituting the perovskite phase. Oxide oxide sintered body.

This metal oxide phase contains an oxide (composition formula MeOx) of at least one metal element selected from the metal elements contained in the conductive perovskite phase in the thermistor part. This metal element is the same type of metal element as the metal element contained in the perovskite phase in the thermistor part. The metal oxide that forms the metal oxide phase may be a double oxide. As the metal oxide forming the metal oxide phase, for example, when the perovskite phase is represented by (Y, Sr) (Mn, Al, Cr) O ₃ , the composition formulas SrY ₂ O ₄ , SrY ₄ O ₇ , SrAl ₂ O ₄ , YAlO ₃ , and Y ₃ Al ₅ O _12. Among these, SrAl ₂ O ₄ is suitable as a metal oxide that forms a metal oxide phase. When this metal oxide phase contains SrAl ₂ O ₄ , even if this thermistor element is exposed to a high temperature, Sr and / or Al does not migrate to the perovskite phase and react with the perovskite phase. Therefore, the characteristic change due to the temperature of the thermistor portion is suppressed.

The thermistor part 22 in this embodiment can be manufactured as follows.
First, a calcined powder containing a conductive perovskite phase is prepared. The raw material for preparing a calcined powder containing a conductive perovskite phase, a range of perovskite phase composition formula _{M1 a M2 b M3 c M4 d} O a when the _e, b, c, d, e is the As preferred, carbonates or oxides of M1, M2, M3, and M4 are preferred examples. The element M1 includes at least one element selected from Group 2 elements of the periodic table, that is, Mg, Ca, Sr, Ba, and one or more elements selected from Mg, Ca, and Sr. The element M2 is suitable, and the element M2 is at least one element selected from the group 3 elements excluding La, that is, Y, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb, Sc The above elements can be mentioned, and one or more elements selected from Y, Nd, and Yb are preferable, and the element M3 is Group 4, Group 5, Group 6, Group 7 of the Periodic Table. , Group 8, Group 9, Group 10, Group 11 and Group 12, ie Ti, Zr, Hf (Group 4), V, Nb, Ta (Group 5), Cr , Mo, W (above, Group 6), Mn (Group 7), Fe (Group 8), Co (Group 9) ), Ni (Group 10), Cu (Group 11) and at least one element selected from Zn (Group 12), and one or more elements selected from Mn, Fe and Cr Elements are preferred. The element M4 includes at least one element selected from Group 13 elements of the periodic table, that is, Al, Ga, and In, and one or more elements selected from Al and Ga are preferable. is there. More specifically, as the raw material, SrCO ₃ , Y ₂ O ₃ , Nd ₂ O ₃ , Yb ₂ O ₃ , MgO, CaCO ₃ , Cr ₂ O ₃ , MnO ₂ , Fe ₂ O ₃ , Al ₂ O ₃ , Ga ₂ O _{3 and the} like. In addition, these raw materials can use the commercial item which has a purity of 99% or more.

  These raw materials are mixed and further dried at the time of wet mixing to obtain a raw material powder mixture. This raw material powder mixture is calcined and prepared into a calcined powder (calcined powder for a conductive perovskite phase) having an average particle diameter of, for example, 1 to 2 μm. The calcining temperature at which the calcining is performed is usually 1000 to 1500 ° C., and the time for calcining at the calcining temperature is usually 1 to 10 hours.

Moreover, when a metal oxide phase (MeOx) is contained, as a raw material at the time of preparing the calcining powder containing a metal oxide phase, a carbonate or an oxide of Me is mentioned as a suitable example. The element Me is preferably one or more elements selected from Y, Sr, and Al. Specifically, examples of the raw material include Y ₂ O ₃ , SrCO ₃ , Al ₂ O _{3 and the} like. be able to.

  These raw materials are mixed and further dried at the time of wet mixing to obtain a raw material powder mixture. This raw material powder mixture is calcined and prepared into a calcined powder (calcined powder for metal oxide phase) having an average particle diameter of, for example, 1 to 2 μm. The calcining temperature at which the calcining is performed is usually 1000 to 1500 ° C., and the time for calcining at the calcining temperature is usually 1 to 10 hours.

Next, the calcined powder for the conductive perovskite phase and the calcined powder for the metal oxide phase are weighed, and the calcined powder is measured using a resin pot and high-purity Al ₂ O ₃ spherulite. Then, wet mixed pulverization is performed using ethanol as a dispersion medium. Next, the obtained slurry is dried at 80 ° C. for 2 hours to obtain a thermistor synthetic powder.

  Next, 20 parts by weight of a binder mainly composed of polyvinyl butyral is added to 100 parts by weight of the thermistor synthetic powder, mixed and dried. Further, granulation is performed through a 250 μm mesh sieve to obtain a granulated powder. As the binder, in addition to polyvinyl butyral, for example, polymers such as polyvinyl alcohol and acrylic binders can be used. Besides such polymers, known binders used in this technical field can be used.

Next, the above granulated powder is molded into a disk shape by a mold molding method, and a disk-shaped green thermistor part molded body is obtained by cold isostatic pressing (press pressure: 1500 kg / cm ² ).

  Thereafter, the green thermistor part molded body is fired at 1400 to 1600 ° C. for 3 hours, for example, in an air atmosphere. A disc-shaped thermistor wafer is manufactured by grinding and polishing the upper and lower surfaces of the obtained sintered body to a thickness of 0.35 mm.

  In order to stabilize the characteristics of the thermistor wafer, annealing is performed at 900 ° C. for 50 hours. Pt paste is printed on the upper and lower surfaces of the thermistor wafer after annealing to a thickness of about 15 μm, dried, and baked at 1200 ° C. for 4 hours to form the electrode portion 24.

  Next, the thermistor wafer having the electrode portions 24 baked on both sides is cut into a 0.5 mm square by a dicing machine. A Pt paste similar to the above is applied to the pair of electrode portions 24 of the cut chip-like thermistor portion 22, and a lead portion 25 made of Pt—Rh alloy having a cross-sectional shape with a diameter of 0.3 mm is pasted, 1200 ° C. The thermistor portion 22 and the lead portion 25 are joined via the electrode portion 24 by baking for 4 hours.

Thereby, the structure (Thermistor part 22, a pair of electrode part 24, a pair of lead part 25) except the coating layer 26 among the thermistor elements 21 of the structure shown in FIG. 2 and FIG. 3 is obtained.
[1-4. Coating layer]
Next, the covering layer 26 of the thermistor element 21 will be described.

The coating layer 26 is a crystallized glass that includes at least SiO ₂ , BaO, and Al ₂ O ₃ . Of these, a 45 to 75 mol% based on the total moles of the coating layer 26 for the SiO _2, 2-10 mol% based on the total moles of the coating layer 26 for the _Al 2 _{O 3,} BaO Is about 20 to 40 mol% with respect to the total number of moles of the coating layer 26. Further, the coating layer _26, SiO 2, BaO, and a total of _Al 2 _{O 3} is is contained in the content that is selected to be 90 mol% to 100 _mol%, the coating layer for the B 2 _{O 3} It is 0.1 mol% or less with respect to the total number of moles of 26. Furthermore, the coating layer 26 is crystallized glass having a crystallinity of 70% or more.

Further, the coating layer 26 is contained ZrO _2, for ZrO ₂ is not more than 10 mol% greater than 0 mol% relative to the total number of moles of the coating layer 26.
In the present invention, the coating layer 26 is not necessarily required to contain ZrO _2, as in Example 6 described below, may comprise a coating layer containing no ZrO _2.

The coating layer 26 is formed in a form that covers the thermistor portion 22 as follows.
First, the glass powder for forming the coating layer 26 is adjusted as follows.
That is, as a raw material powder, 5 parts by weight of a binder mainly composed of poval with respect to 100 parts by weight of crystallized glass powder each containing a predetermined component (SiO ₂ , BaO, Al ₂ O ₃ , ZrO _2, etc.) Add part. These are mixed and pulverized using a resin pot and high-purity Al ₂ O ₃ spherulite and water as a dispersion medium. Next, the obtained slurry is dried and granulated by spray drying to obtain glass powder.

  Next, the above-described thermistor portion 22 and the above-described glass powder for forming the coating layer 26 are press-molded by a mold molding method, and a cylindrical unfired coating as shown in FIGS. Form a layer.

Next, the thermistor element 21 having a predetermined coating layer 26 that covers the thermistor portion 22 is obtained by baking this under predetermined conditions.
[1-5. Comparative measurement]
The comparative measurement performed in order to confirm the effect of the thermistor element of this invention is demonstrated.

  Specifically, with respect to Examples 1 to 8 which are thermistor elements 21 of the present invention and Comparative Examples 1 to 7 which are thermistor elements to be compared, before and after being held at 900 ° C. for 500 hours in the atmosphere. Later, the change in crystallinity of each crystal phase and the change in resistance value of the thermistor element were measured.

  In each of Examples 1 to 8 and Comparative Examples 1 to 7 used in this comparative measurement, the thermistor portion 22 is configured to include the conductive perovskite phase and the metal oxide phase shown in [Table 1].

For the thermistor element 21, the B constant (temperature gradient constant) was measured as follows. That is, first, the thermistor part 22 was left in an environment of absolute temperature T (100) = 373 K (= 100 ° C.), and the initial resistance value R (100) of the thermistor part 22 in that state was measured. Next, the thermistor part 22 was left in an environment of absolute temperature T (300) = 573 K (= 300 ° C.), and the initial resistance value R (300) of the thermistor part 22 in that state was measured. Similarly, R (600) and R (900) were also measured.

  And B constant: B (100-900) was computed according to [Equation 1]. The initial resistance values R (100), R (300), R (600), R (900) and the B constant: B (100-900) are shown in [Table 1].

In Examples 1 to 8 and Comparative Examples 1 to 7 of this comparative measurement, the coating layer is composed of any of the 12 types of glass compositions shown in [Table 2].

About each of Examples 1-8 of this comparative measurement and Comparative Examples 1-7, a glass composition and coating layer baking conditions are shown in [Table 3].

Here, in order to confirm the change of the crystal phase of the coating layer before and after the endurance held at 900 ° C. for 500 hours in the atmosphere, the coating layer in the thermistor element 21 in Examples 1 to 3 and Comparative Example 1 26 X-ray diffractions were performed.

4 to 7 show X-ray diffraction patterns of the coating layer before durability, and FIGS. 8 to 11 show X-ray diffraction patterns of the coating layer after durability.
4 and 8, in Example 1, it can be seen that the coating layer 26 includes BaSi ₂ O ₅ (orthorhombic crystal) as a crystal phase both before (initial) and after durability.

5 and 9, in Example 2, it can be seen that the coating layer 26 includes Ba ₂ Si ₄ O ₁₀ (monoclinic crystal) as a crystal phase both before (initial) and after durability. Moreover, in Example 2, the coating layer 26 after durability contains BaSi ₂ O ₅ (orthorhombic crystal) as a crystal phase.

6 and 10, in Example 3, it can be seen that the coating layer 26 includes Ba ₂ Si ₄ O ₁₀ (monoclinic crystal) as a crystalline phase both before (initial) and after durability. Moreover, in Example 3, the coating layer 26 after durability contains BaSi ₂ O ₅ (orthorhombic crystal) as a crystal phase.

7 and 11, it can be seen that in Comparative Example 1, the coating layer 26 includes Ba ₂ Si ₄ O ₁₀ (monoclinic crystal) as a crystalline phase both before (initial) and after durability. In Comparative Example 1, it can be seen that there is little Ba ₂ Si ₄ O ₁₀ (monoclinic crystal) before endurance (initial), but there is much Ba ₂ Si ₄ O ₁₀ (monoclinic crystal) after endurance.

Subsequently, the resistance change of the thermistor element in Examples 1 to 8 and Comparative Examples 1 to 3 and 6 before and after durability maintained at 900 ° C. for 500 hours in the atmosphere was confirmed.
Specifically, first, before the endurance, the thermistor element 21 is arranged in an environment of absolute temperature T (100) = 373K (= 100 ° C.), and the initial resistance value Rt (100 ) Was measured. Next, the thermistor element 21 was placed in an environment of absolute temperature T (300) = 573 K (= 300 ° C.), and the initial resistance value Rt (300) of the thermistor portion 22 in that state was measured. Similarly, Rt (600) and Rt (900) were also measured.

  In addition, regarding the initial resistance value, the initial resistance value when the thermistor part 22 is measured alone is represented by R, and the initial resistance value when the thermistor part 22 is provided with the coating layer 26 (thermistor element 21) is represented by Rt. ing.

  After the endurance, the resistance values Rt ′ (100), Rt ′ (300), Rt ′ (600), and Rt ′ (900) after heat treatment are similarly measured by measuring the resistance value of the thermistor 22. Each was measured.

  Then, from the comparison between the initial resistance value Rt (100) at 100 ° C. and the post-heat treatment resistance value Rt ′ (100), the temperature change converted value CT (100) (unit: deg. C) of the resistance change due to the heat treatment is obtained. Calculated from [Equation 2].

Similarly, temperature change conversion values CT (300), CT (600), and CT (900) were calculated from [Equation 3], [Equation 4], and [Equation 5], respectively.

Each value of the calculated temperature change conversion value CT is shown in [Table 3] as “indicated temperature change after endurance”. [Table 3] also shows other measurement results (the crystallinity of the coating layer and the state of the coating layer).

  According to the measurement results shown in Table 3, in the thermistor elements of Examples 1 to 8, the temperature change converted values CT (100), CT (300), CT (600), CT (900) after heat treatment Also, the absolute value shows a small value, and specifically, it can be seen that it falls within the range of ± 3 ° C. On the other hand, in the thermistor elements of Comparative Examples 1 to 3 and 6, the temperature change converted values CT (100), CT (300), CT (600), and CT (900) after the heat treatment all have large absolute values. Specifically, it exceeds the range of ± 3 ° C.

  According to this measurement result, it can be seen that the thermistor element of the present invention can suppress fluctuations in the resistance characteristics of the thermistor portion and suppress a decrease in temperature detection accuracy even when exposed to a temperature of 900 ° C. for a long time.

In Example 1 and Example 2, regarding the crystallinity of the coating layer, the crystallinity is 95% or more before and after durability, and hardly contains an amorphous phase.
In Example 3 and Comparative Example 1, the crystallinity of the coating layer is increased after endurance compared to before endurance. This is considered that the amorphous phase in the coating layer 26 changed during the durability test.

  Regarding Examples 1 to 8, since the absolute value of the temperature change converted value CT after the durability test is 3 ° C. or less (CT ≦ ± 3 ° C.), the electrical characteristics of the thermistor portion deteriorated even by the durability test. You can see that they are not. Therefore, it was shown that the coating layer 26 of Examples 1 to 8 covered the thermistor part 22 without adversely affecting the thermistor part 22.

In particular, Example 1 has the smallest temperature change conversion value CT. It is understood that this is because both the crystallinity and the crystal phase (FIGS. 4 and 8) hardly change before and after the durability test.
In Comparative Example 1, the absolute value of the temperature change converted value CT after the durability test is larger than 3 ° C. (CT> ± 3 ° C.). This is understood because the crystallinity of the coating layer 26 before durability deviates from an appropriate range. That is, the volume change accompanying the change of the crystal phase of the coating layer 26 is large due to the heat treatment, the reaction between the coating layer 26 and the thermistor 22, or the change in stress applied between the coating layer 26 and the thermistor 22 or the electrode peeling. It can be understood that the electrical characteristics have changed.

  In Example 3, since the degree of crystallinity of the coating layer 26 before durability is 74%, which exceeds 70%, the volume change accompanying the change of the crystal phase of the coating layer 26 by heat treatment is relatively small. It can be understood that the electrical characteristics did not change as much as in Comparative Example 1.

  In Comparative Examples 2, 3, and 6, the absolute value of the temperature change converted value CT after the durability test is greater than 3 ° C. (CT> ± 3 ° C.). This is understood because the component of the crystallized glass constituting the coating layer 26 deviates from an appropriate range. That is, it can be understood that the electrical characteristics of the thermistor portion 22 are changed by the reaction between the coating layer 26 and the thermistor portion 22 due to the heat treatment.

  In Comparative Examples 4 and 5, the meltability of the glass deteriorated and a dense coating layer could not be formed. This is understood because the components of the crystallized glass constituting the coating layer 26 deviate from an appropriate range.

  In Comparative Example 7, the glass was easily devitrified, the fluidity was lowered, and the dense formation was not possible. This is because the components of the crystallized glass constituting the coating layer 26 deviate from an appropriate range.

[1-6. effect]
As described above, in the thermistor element 21 provided in the temperature sensor 1 of the present embodiment, the coating layer 26 has the above composition, so that the baking temperature at the time of manufacturing the coating layer 26 is relatively low (for example, 1100 ° C. or less), it is formed as a dense crystallized glass. Thus, by providing the coating layer 26 as a dense crystallized glass, the composition of the thermistor portion 22 and the coating layer 26 hardly changes, and the resistance value and the characteristics of the thermistor portion 22 hardly change.

As can be seen from the comparison between Example 5 (the content of SiO ₂ is 50 mol%) and Comparative Example 3 (the content of SiO ₂ is 40 mol%), the content of SiO ₂ in the coating layer 26 is 45. By setting to mol% or more, the softening temperature of glass becomes high and the heat resistance of the coating layer 26 improves.

As can be seen from the comparison between Example 6 (the content of SiO ₂ is 70 mol%) and Comparative Example 4 (the content of SiO ₂ is 77 mol%), the content of SiO ₂ in the coating layer 26 is 75. By setting it to less than mol%, the glass is easily softened and the fluidity is good, so that there is an advantage that the coating operation becomes easy.

Since none of the above-described Examples 1 to 8 causes devitrification of the glass constituting the coating layer 26, the content of Al ₂ O ₃ in the coating layer 26 is set to 2 mol% or more. Is less likely to occur, and the coating layer 26 can be easily formed. That is, if devitrification occurs, voids are generated in the coating layer 26 and the sufficient coating layer 26 cannot be formed. In such a case, there is a possibility that the hermeticity of the thermistor portion 22 cannot be secured. _By setting the content of ₂ O ₃ to 2 mol% or more, it is possible to suppress the occurrence of defects due to devitrification.

As can be seen from the comparison between Example 4 (the content of Al ₂ O ₃ is 8 mol%) and Comparative Example 2 (the content of Al ₂ O ₃ is 20 mol%), Al ₂ O in the coating layer 26 is used. _By setting the content of ₃ to 10 mol% or less, the coating layer 26 and the thermistor portion 22 are less likely to react, and the resistance characteristics of the thermistor portion 22 are less likely to change.

  As can be seen from the comparison between Example 7 (BaO content is 25 mol%) and Comparative Example 5 (BaO content is 17 mol%), the BaO content in the coating layer 26 is 20 mol% or more. Since the coefficient of thermal expansion does not become too small by setting to, a difference in coefficient of thermal expansion from the thermistor portion 22 is less likely to occur, and cracks and the like are less likely to occur in the coating layer 26.

  As can be seen from the comparison between Example 8 (BaO content is 35 mol%) and Comparative Example 6 (BaO content is 45 mol%), the BaO content in the coating layer 26 is 40 mol% or less. By setting to, the heat resistance of the coating layer 26 becomes good.

By setting the content of B ₂ O ₃ in the coating layer 26 to 0.1 mol% or less, even if the thermistor portion 22 is exposed to a high temperature for a long time, the components forming the coating layer 26 are the thermistor portion. Therefore, it is difficult for the thermistor portion 22 to change in composition. For this reason, in the thermistor element 21 of the present embodiment, the coating layer 26 and the thermistor portion 22 are less likely to react, and the resistance characteristics (electrical characteristics) of the thermistor portion 22 are less likely to change.

  If the coating layer 26 is crystallized glass having a crystallinity of 70% or more, the components of the coating layer 26 hardly move to the thermistor portion 22 even when the thermistor element 21 is exposed to a high temperature for a long time. The composition variation is reduced, and the resistance characteristic of the thermistor portion 22 is difficult to change. Further, since the coating layer 26 is a crystallized glass having a crystallinity of 70% or more, the volume change of the coating layer 26 due to the change of the crystal phase is reduced, so that the stress applied between the thermistor portion 22 and the coating layer 26 is reduced. Change and electrode peeling are less likely to occur, and the resistance characteristics of the thermistor portion 22 are less likely to change.

  This is because the “indicated temperature change after endurance” of Examples 1 to 3 shown in [Table 3] is ± 3 ° C. or less, while the “indicated temperature change after endurance” of Comparative Example 1 It is clear from the fact that CT (600) and CT (900) exceed the range of ± 3 ° C. The “crystallinity (before durability)” in Examples 1 to 3 is 70% or more, whereas the “crystallinity (before durability)” in Comparative Example 1 is less than 70%. From these, it can be seen that the resistance characteristic of the thermistor portion 22 is less likely to change when the coating layer is made of crystallized glass having a crystallinity of 70% or more.

Therefore, according to the thermistor element 21 of this embodiment, even if it is exposed to a temperature of 900 ° C. for a long time, fluctuations in resistance characteristics of the thermistor portion 22 can be suppressed, and a decrease in temperature detection accuracy can be suppressed.
In the thermistor elements 21 of the present embodiment, in Examples 1 to 5, 7, and 8, the coating layer 26 contains ZrO ₂ .

Thus, in the coating layer 26 containing zirconia (ZrO ₂ ), the crystal phase is likely to precipitate, and the crystallinity can be further increased.
Further, in the thermistor element 21 of the present embodiment, ZrO ₂ contained in the coating layer 26 is 10 mol% or less with respect to the total number of moles of the coating layer 26.

  When the content of zirconia is excessive, devitrification is likely to occur. Therefore, the coating layer 26 having the upper limit value of zirconia determined in this manner can suppress devitrification, and thus the formation of the coating layer 26 is facilitated.

  Therefore, according to the thermistor element 21 of the present embodiment, the crystallinity of the coating layer 26 can be increased, and defects caused by devitrification can be suppressed, so that the resistance characteristics of the thermistor portion 22 can be further varied. It is possible to suppress the decrease in temperature detection accuracy.

Note that the content of zirconia is preferably 0.1 mol% or more with respect to the total number of moles of the coating layer 26, since the crystal phase is easily precipitated.
In the thermistor element 21 of the present embodiment, as shown in FIGS. 4 to 6 and 8 to 10, in all of Examples 1 to 3, the coating layer 26 has a crystal phase of BaSi ₂ O ₅ (orthorhombic crystal), This is a structure containing at least one crystal phase selected from Ba ₂ Si ₄ O ₁₀ (monoclinic) and BaAl ₂ Si ₂ O ₈ .

The coating layer 26 having such a configuration is a crystal phase in which the crystal phase hardly changes even when exposed to 900 ° C. for a long time.
In Examples 1 to 3, as shown in “Indicated temperature change after endurance” in [Table 3], the temperature change is ± 3 ° C. or less, and it is understood that the resistance characteristics of the thermistor portion 22 are difficult to change. .

  That is, in the thermistor elements 21 of the first to third embodiments, the volume change of the coating layer 26 due to the change of the crystal phase is reduced. The resistance characteristic of the thermistor portion 22 hardly changes.

Therefore, according to the thermistor element 21 of this embodiment, even if it is exposed to a temperature of 900 ° C. for a long time, fluctuations in resistance characteristics of the thermistor portion 22 can be suppressed, and a decrease in temperature detection accuracy can be suppressed.
The thermistor element 21 may have a configuration in which the coating layer 26 does not contain ZrO2 as in the sixth embodiment.

Next, in each of Examples 1 to 8 and Comparative Examples 1 to 7 of the comparative measurement, the thermistor portion 22 is configured to have the composition shown in the above [Table 1].
In the thermistor element 21 of Examples 1 to 8, the thermistor portion 22 includes a perovskite phase represented by ABO ₃ (where A includes Sr and / or Y, and B includes Al). The thermistor element 21 provided with such a thermistor section 22 can detect a temperature in a wide temperature range from a low temperature region to a high temperature region exceeding 600 ° C.

In the thermistor elements 21 of Examples 1 to 8, the thermistor portion 22 is configured such that B in the ABO ₃ further includes at least one of Cr, Mn, and Fe. The thermistor element 21 having such a thermistor portion 22 can detect temperature in a wide temperature range from a low temperature region to a high temperature region exceeding 600 ° C. more preferably and stably for a long period of time.

  In the thermistor elements 21 of Examples 1 to 8, the thermistor portion 22 is at least one metal selected from metal elements that have a lower conductivity than the perovskite phase included in the thermistor portion 22 and form the perovskite phase. When the element is Me, a metal oxide phase containing at least one metal oxide represented by the composition formula MeOx is contained.

  That is, the thermistor portion 22 included in the thermistor element 21 has a metal oxide phase containing a metal oxide (MeOx) having a lower conductivity than the conductive perovskite phase contained in the thermistor element 21. By adjusting the content of the metal oxide, the resistance value of the thermistor element 21 can be shifted to a desired value while maintaining the temperature gradient coefficient (B constant) in the temperature range to be detected. .

In the thermistor elements 21 of Examples 1 to 8, the metal oxide contained in the metal oxide phase is SrAl ₂ O ₄ .
When the thermistor element 21 is used at a high temperature when the metal oxide contained in the metal oxide phase is SrAl ₂ O ₄ , the reaction between the metal oxide phase and the perovskite phase in the thermistor portion 22 becomes difficult. Become.

Thereby, the resistance characteristic of the thermistor portion 22 is unlikely to fluctuate, and a decrease in temperature detection accuracy as the thermistor element 21 can be suppressed.
The temperature sensor 1 of the present embodiment includes any one of the thermistor elements 21 described above.

  Since the temperature sensor 1 has the thermistor element 21 having an excellent action as described above, even if the temperature sensor 1 is exposed to a temperature of 900 ° C. for a long time, it is possible to suppress fluctuations in the resistance characteristics of the thermistor portion 22 and to detect the temperature. Can be suppressed.

[1-7. Correspondence with Claims]
Here, the correspondence of the words in the claims and the present embodiment will be described.
The temperature sensor 1 corresponds to an example of a temperature sensor, the thermistor element 21 corresponds to an example of a thermistor element, the thermistor part 22 corresponds to an example of a thermistor part, and the covering layer 26 corresponds to an example of a covering layer.

[2. Other Embodiments]
As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, In the range which does not deviate from the summary of this invention, it is possible to implement in various aspects.

  For example, the thermistor element 21 of the above embodiment is configured to include the thermistor portion 22 having a metal oxide phase as shown in [Table 1] above, but the thermistor portion does not necessarily have a metal oxide phase. Not limited. Specifically, it may be a second thermistor portion having the composition shown in [Table 4].

For the second thermistor part, as with the thermistor part 22 shown in [Table 1] above, the B constant (temperature gradient constant) is measured and the initial resistance values R (100), R (300), R (600) and R (900) were also measured.

  As shown in [Table 4], the second thermistor portion has a configuration that does not have a metal oxide phase, but the B constant [B (100 to 900)] is 4554K [= B (100 to 900)]. . For this reason, the 2nd thermistor part can detect each temperature accurately.

Furthermore, in the thermistor element 21 of the present embodiment, the coating layer 26, the B ₂ O ₃ can take a structure which is free content.
Thereby, even if the thermistor part 22 is exposed to a high temperature for a long time, the components forming the coating layer 26 are less likely to move to the thermistor part 22, so that composition fluctuations in the thermistor part 22 are less likely to occur. . For this reason, in the thermistor element 21 of the present embodiment, the coating layer 26 and the thermistor portion 22 are more difficult to react, and the resistance characteristics (electrical characteristics) of the thermistor portion 22 are less likely to change.

“Non-containing” means that B ₂ O ₃ cannot be detected or identified even by ICP (Inductively Coupled Plasma) emission analysis.

  DESCRIPTION OF SYMBOLS 1 ... Temperature sensor, 3 ... Sheath core wire (electrode wire), 5 ... Cylindrical member, 7 ... Sheath member, 9 ... Housing (metal tube), 11 ... Mounting member, 17 ... Nut member, 19 ... Outer cylinder, 21 ... Thermistor element, 22: thermistor part, 24 ... electrode part, 25 ... lead part, 26 ... coating layer, 39 ... cement.

Claims (8)

A thermistor element comprising a thermistor part made of a thermistor composition, and a coating layer covering the thermistor part,
The coating layer contains at least SiO ₂ , BaO, and Al ₂ O ₃ , and the SiO ₂ content is 45 to 75 mol% with respect to the total number of moles of the coating layer, and the Al ₂ O ₃ content is the coating layer. 2 to 10 mol% based on the total molar amount, 20 to 40 mol% based on the total moles of the coating layer for _BaO, SiO 2, BaO, and a total of _Al 2 _{O 3} is 90 It is contained at a content ratio selected to be from mol% to 100 mol%, and B ₂ O ₃ is 0.1 mol% or less with respect to the total number of moles of the coating layer,
The coating layer is a crystallized glass having a crystallinity of 70% or more;
Thermistor element characterized by The coating layer contains ZrO ₂ , and ZrO ₂ is greater than 0 mol% and 10 mol% or less with respect to the total number of moles of the coating layer,
The thermistor element according to claim 1. The coating layer contains at least one crystal phase selected from BaSi ₂ O ₅ (orthorhombic), Ba ₂ Si ₄ O ₁₀ (monoclinic), and BaAl ₂ Si ₂ O _8. To do,
The thermistor element of Claim 1 or Claim 2 characterized by these. The thermistor portion includes a perovskite phase represented by ABO ₃ (where A includes Sr and / or Y, and B includes Al).
The thermistor element as described in any one of Claims 1-3 characterized by these. B in the ABO ₃ further contains at least one of Cr, Mn and Fe;
The thermistor element according to claim 4. The thermistor portion is lower in conductivity than the perovskite phase contained in the thermistor portion, and when the at least one metal element selected from the metal elements forming the perovskite phase is Me, the composition formula is MeOx. Containing a metal oxide phase containing at least one of the metal oxides represented,
The thermistor element of Claim 4 or Claim 5 characterized by these. The oxide contained in the metal oxide phase is SrAl ₂ O ₄ ;
The thermistor element according to claim 6.   The temperature sensor which has a thermistor element as described in any one of Claims 1-7.