JP2009182250A - Thermistor element, and temperature sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermistor element which is capable of accurately measuring a temperature in a high temperature region over 600°C under a reducing atmosphere and for which characteristic variation is suppressed, and to provide a temperature sensor using the thermistor element. <P>SOLUTION: The thermistor element has a thermistor part constituted of a thermistor composition and a cover layer for covering the thermistor part. The thermistor part includes an electrically conductive perovskite phase having a perovskite type crystal structure. The cover layer is crystallized glass containing SiO<SB>2</SB>, CaO and MgO with a containing ratio selected from the range of 40-65 mass% to the total mass of the cover layer for SiO<SB>2</SB>, 15-40 mass% to the total mass of the cover layer for CaO, and 5-30 mass% to the total mass of the cover layer for MgO so that the total of SiO<SB>2</SB>, CaO and MgO becomes 90-100 mass%, and practically not containing B<SB>2</SB>O<SB>3</SB>. The temperature sensor having the thermistor element is provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a thermistor element and a temperature sensor. More specifically, the resistance value changes according to temperature, and in particular, temperature measurement can be suitably performed even in a high temperature range exceeding 600 ° C. in a reducing atmosphere. The present invention relates to a possible thermistor element and a temperature sensor using such a thermistor element.

  2. Description of the Related Art Conventionally, a thermistor element that measures temperature using a thermistor portion made of a conductive oxide whose specific resistance value changes according to temperature, and a temperature sensor using this thermistor element are known.

  The temperature of exhaust gas discharged from an internal combustion engine such as an automobile engine can be measured using a thermistor element or a temperature sensor. In order to protect a DPF (Diesel Particulate Filter) and a NOx reduction catalyst, temperature detection in a high temperature range, for example, near 900 ° C. is required for the thermistor element. Furthermore, in order to cope with OBD (On Board Diagnosis), that is, an in-vehicle type failure diagnosis system, temperature detection at a low temperature is required for the thermistor element. For example, it may be desired to detect temperature in a wide temperature range from a low temperature range to a high temperature range such as 900 ° C. with a single thermistor element. In this technical field including the present invention, “low temperature region” or “low temperature region” means the temperature of the weather in the polar region or the northern region on the earth.

  In addition, in a temperature sensor used in an automobile or the like, in order to prevent soot that is present in the exhaust gas from accumulating on the thermistor element and to prevent water droplets from adhering to the temperature sensor, A structure in which the thermistor element to be disposed is covered with a metal tube made of a stainless alloy or the like may be employed.

  However, when the metal tube exceeds 600 ° C., it tends to be thermally oxidized. For example, at a high temperature of about 900 ° C., the inner surface of the metal tube is oxidized, and the inside of the metal tube becomes a reducing atmosphere. If it does so, the oxide which forms the thermistor element inserted and arrange | positioned in a metal tube will be reduce | restored, As a result, the resistance characteristic in a thermistor element will change.

  In order to solve such problems, the metal tube is pre-heated and a coating made of a metal oxide is formed on the inner surface thereof, thereby suppressing thermal oxidation at high temperature and reducing the thermistor element. This prevents a change in resistance characteristics due to the occurrence of this.

  In addition to temperature, if a temperature sensor is installed, for example, in an automobile, the metal oxide film is broken by vibration, or if the film originally has a defect, The metal tube is thermally oxidized at the defective portion, and as a result, the thermistor element is reduced and its resistance characteristic changes.

  An invention for solving such a problem is proposed in Patent Document 1.

  The invention described in Patent Document 1 has “a thermistor portion (13) made of a thermistor material and a reduction resistant coating (14) made of a reduction resistant composition formed on the surface of the thermistor portion (13). A thermistor element ”(refer to claim 1 of Patent Document 1).

Patent Document 1 includes a thermistor portion having a perovskite phase and a metal oxide phase, such as Y (Cr, Mn) O ₃ .Y ₂ O ₃ , Y (Cr, Mn) O ₃ .Al ₂ O ₃ , A thermistor element having a reduction-resistant film whose surface is coated with a reduction-resistant composition such as Y ₂ O ₃ , Al ₂ O ₃ , SiO ₂ , Y ₃ Al ₅ O ₁₂ , 3Al ₂ O ₃ .2SiO _2. Is disclosed (see paragraph numbers 0021 and 0022 of Patent Document 1).
However, in order to form the reduction-resistant film, for example, firing at a high temperature of 1100 to 1300 ° C. (see paragraph number 0044 of Patent Document 1) and 1200 ° C. or more (see paragraph numbers 0049 and 0068 of Patent Document 1). is required. When the firing temperature is the high temperature, the thermistor portion and the coating layer covering the same react with each other, and the characteristics such as the resistance value of the thermistor element vary. As a result, temperature measurement is performed with a temperature sensor having a thermistor portion that does not have a resistance characteristic as designed, and the reliability of the temperature sensor is lost.

JP 11-251109 A

  The thermistor element described in Patent Document 1 is a thermistor element in which a coating layer of a ceramic film is formed. Apart from such a thermistor element, there is a glass-sealed thermistor element.

The glass-sealed thermistor element described in Patent Document 2 is formed by “forming electrodes on the upper and lower surfaces of a flat metal oxide sintered body composed of Y, Cr, Mn, and Ca, and providing leads on both electrodes. For the thermistor element formed by connecting wires, the thermistor element and the thermistor element connecting end side portion of the lead wire are composed of SiO ₂ , CaO, SrO, BaO, Al ₂ O ₃ and SnO _2. A wide range type thermistor having a linear expansion coefficient that is melt-sealed with a sealing glass that is equal to or smaller than the linear expansion coefficient of the metal oxide sintered body. The wide range type thermistor described in Patent Document 2 is described as follows: “An electrode is formed on both upper and lower surfaces of a flat metal oxide sintered body composed of Y, Cr, Mn, and Ca, and a lead wire is formed on each of the electrodes. A thermistor element formed by connecting the thermistor element and the thermistor element connecting end side portion of the lead wire has a composition made of SiO ₂ , CaO, SrO, BaO, Al ₂ O ₃ and SnO _2. It is characterized by being melt-sealed with a sealing glass whose linear expansion coefficient is equal to or smaller than the linear expansion coefficient of the metal oxide sintered body ”(refer to claim 1 of Patent Document 2).

  In the wide range type thermistor described in Patent Document 2, the maximum usable temperature is 700 ° C. when annealing is not performed (see Paragraph No. 0026 of Patent Document 2). In order to obtain a wide-range thermistor that can withstand a use temperature of 700 ° C. or higher, for example, “annealing by holding at 840 ° C. for 10 hours and then cooling to 700 ° C. over 100 hours” (see paragraph No. 0026 of Patent Document 2) Is required.

JP 2005-294653 A

  The problem to be solved by the present invention is to provide a thermistor element in which temperature measurement can be accurately performed even in a high temperature region exceeding 600 ° C. in a reducing atmosphere, and the characteristic variation is suppressed as much as possible. An object of the present invention is to provide a temperature sensor using such a thermistor element.

As means for solving the problems,
The means according to claim 1 is:
A thermistor element comprising a thermistor part made of a thermistor composition and a coating layer covering the thermistor part,
The thermistor portion is conductive and includes a perovskite phase having a perovskite crystal structure,
The coating layer is composed of SiO ₂ , CaO, and MgO, 40 to 65% by mass with respect to the total mass of the coating layer for SiO ₂ , and 15 to 40% by mass with respect to the total mass of the coating layer for CaO. , MgO is selected from the range of 5 to 30% by mass with respect to the total mass of the coating layer, so that the total of SiO ₂ , CaO, and MgO is 90% to 100% by mass. A thermistor element characterized by being a crystallized glass that is contained in a proportion and is substantially free of B ₂ O ₃ ,
The means according to claim 2 comprises:
The thermistor element according to claim 1, wherein the coating layer has a deposited crystal of diopside which is an electrical insulator.
The means according to claim 3 is:
The thermistor part is the thermistor element according to claim 1 or 2, comprising a perovskite phase represented by ABO ₃ (where A includes Sr and / or Y, and B includes Al).
The means according to claim 4 is:
4. The thermistor element according to claim 3, wherein B in the ABO ₃ further includes at least one metal selected from Cr, Mn, and Fe.
The means of claim 5 comprises:
The thermistor portion has a lower 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 MeOx The thermistor element according to claim 3 or 4, comprising a metal oxide phase containing at least one metal oxide represented by:
The means according to claim 6 is:
The thermistor element according to claim 5, wherein the metal oxide contained in the metal oxide phase is SrAl ₂ O ₄ .
The means according to claim 7 is:
A temperature sensor having the thermistor element according to any one of claims 1 to 5,
The means according to claim 8 comprises:
8. A thermistor element according to claim 7, wherein the thermistor element is housed inside the metal tube in a state in which the covering layer in the thermistor element according to claim 7 is not in contact with the inner peripheral surface of the metal tube. It is a temperature sensor of the said Claim 7 formed.

  The thermistor element according to the present invention includes a coating layer that covers the thermistor portion made of the thermistor composition. Therefore, when this thermistor element is used as a temperature sensor, even if the atmosphere of the thermistor element becomes a reducing atmosphere because, for example, a metal member that accommodates the thermistor element, such as a metal tube, is oxidized by high heat or the like, Since the coating layer in the present invention exists and protects the thermistor part, the thermistor part is not easily altered. Therefore, in the thermistor element according to the present invention, the thermistor portion covered with the coating layer is hardly affected by the reducing atmosphere.

  More specifically, the thermistor element according to the present invention is a crystallized glass whose coating layer has a specific composition. Therefore, when manufacturing the thermistor element, a dense crystallized glass can be formed even at a relatively low temperature. For example, since a dense coating layer made of crystallized glass can be formed even at a low baking temperature of 1000 ° C. or lower, composition variations of the thermistor portion and the coating layer are unlikely to occur when the coating layer is formed. The resistance value of the thermistor part and its characteristics are less likely to vary.

  Further, since diopside crystals are precipitated in the coating layer of the thermistor element according to the present invention, the components of the coating layer are not affected even when the thermistor element according to the present invention is exposed to a high temperature of 600 ° C. or more for a long time. It is difficult to move to the thermistor portion, and therefore there is little composition variation. Therefore, the thermistor element according to the present invention has stable characteristics even in a high temperature region.

In the thermistor element according to the present invention, the coating layer substantially does not contain B ₂ O ₃ , so that the component that forms the coating layer is the thermistor part even when the thermistor part is exposed to a high temperature for a long time. Therefore, the composition variation in the thermistor portion hardly occurs. Then, the thermistor element according to the present invention has stable resistance characteristics.

In the thermistor element according to the present invention, the perovskite phase contained in the thermistor portion can be represented by the general formula ABO ₃ . When the perovskite phase is represented by the general formula ABO ₃ , a thermistor element including a thermistor portion having a perovskite phase containing Sr and / or Y at the A site in the crystal lattice and Al at the B site is more preferable. Furthermore, temperature detection in a wide temperature range from a low temperature region to a high temperature region exceeding 600 ° C. can be performed.

Furthermore, the thermistor element according to the present invention includes Sr and / or Y at the A site in the crystal lattice when the perovskite phase contained in the thermistor portion is represented by the general formula ABO ₃ , and Al and Cr at the B site, By having a thermistor portion containing at least one of Mn and Fe, it is possible to 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. it can.

  When the thermistor element according to this invention has a metal oxide phase containing a metal oxide (MeOx) having a lower conductivity than the conductive perovskite phase contained in the thermistor part, the content of the metal oxide is reduced. By adjusting, 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.

When the thermistor element is used at a high temperature when the metal oxide contained in the metal oxide phase is SrAl ₂ O _4, it is difficult to react with the perovskite phase in the thermistor portion, so that the resistance characteristics Is a thermistor element that is difficult to fluctuate.

  A temperature sensor having a thermistor element having an excellent action as described above is accurate because the characteristic fluctuation is suppressed even when exposed to a high temperature region exceeding 600 ° C. for a long time in a reducing atmosphere. Temperature can be measured.

  Therefore, according to the present invention, it is possible to provide a thermistor element in which temperature measurement can be accurately performed even in a high temperature region exceeding 600 ° C. in a reducing atmosphere, and the characteristic variation is suppressed as much as possible. A temperature sensor using a simple thermistor element can be provided.

  The temperature sensor according to the present invention accommodates the thermistor element in the metal tube so that the coating layer of the thermistor element is not in contact with the inner peripheral surface of the metal tube. When the temperature sensor is vibrated in contact with the surface, it is possible to reliably prevent breakage such as cracks in the coating layer and to maintain the effect of the coating layer over a long period of time. It can be.

  As shown in FIGS. 1 and 2, the thermistor element 2 as an example according to the present invention has electrode wires 2a and 2b, and the electrode wires 2a and 2b have one end thereof embedded in the thermistor portion 1a. The surface of the thermistor portion 1a is covered with a coating layer 1b.

The thermistor portion 2 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. Then, 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. Thereafter, 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 ABO ₃ . 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. And at least one metal oxide phase having a crystal structure represented by the composition formula MeO _x, where Me is at least one metal element selected from the metal elements constituting the perovskite phase. It is a conductive oxide sintered body.

This metal oxide phase contains an oxide (composition formula MeO _x ) 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 in this invention 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 to prepare a calcined powder having an average particle size 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.

Also, if included metal oxide phase (MeO _X) is as a raw material in the preparation of calcined powder containing a metal oxide phase, carbonates or oxides of Me may be mentioned as preferred examples. 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 to prepare a calcined powder having an average particle size 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.

  The calcined powder is wet mixed and pulverized in a dispersion medium such as water, methanol, ethanol or the like to prepare a slurry. As a container used for wet mixing and pulverization, a resin container can be usually used, and cobblestone, for example, high-purity alumina cobblestone can be used for mixing.

  The above-mentioned slurry is dried to obtain the thermistor powder. The thermistor powder and the binder are mixed, then dried and classified to obtain a granulated powder having a predetermined particle size. Examples of the binder include polymers such as polyvinyl butyral, polyvinyl alcohol, and acrylic binders. In addition to such polymers, known binders used in this technical field can be used.

  The thermistor part powder obtained as described above is loaded into a predetermined mold and press-molded to form a pair of electrode wires made of a Pt—Rh alloy, for example, as shown in FIGS. An unfired thermistor part molded body having a predetermined shape, for example, a hexagonal plate shape, having the electrode wires 2a and 2b so that one end side of 2a and 2b is embedded and the other end side protrudes in parallel is manufactured.

  Then, the thermistor part 1a can be manufactured by baking this unfired thermistor part molded body at, for example, 1400 to 1600 ° C. in an air atmosphere. The shape of the thermistor portion shown in FIG. 1 shows an example of the shape of the thermistor portion in the thermistor element according to the present invention, and the shape of the thermistor portion in the thermistor element according to the present invention varies depending on the application and the like. The shape is adopted.

  The thermistor element according to the present invention is formed by coating the surface of the thermistor portion with a coating layer described below.

The coating layer is composed of SiO ₂ , CaO, and MgO, 40 to 65% by mass with respect to the total mass of the coating layer for SiO ₂ , and 15 to 40% by mass with respect to the total mass of the coating layer for CaO. , MgO is selected from the range of 5 to 30% by mass with respect to the total mass of the coating layer, so that the total of SiO ₂ , CaO, and MgO is 90% to 100% by mass. It is a crystallized glass that is contained in a proportion and is substantially free of B ₂ O ₃ .

In addition, if this coating layer has a total of 90% by mass or more of SiO ₂ , CaO, and MgO, the effect of suppressing the characteristic variation of the thermistor portion can be achieved. When the total of SiO ₂ , CaO, and MgO in the coating layer is 90% by mass or more and less than 100% by mass, the remaining components in the coating layer are other than B ₂ O ₃ unless the object of the present invention is impaired. Components such as Al ₂ O ₃ may be contained.

If the content of SiO _{2 in} the coating layer is below the lower limit, the glass softening point is lowered and heat resistance is lowered, and if the upper limit is exceeded, the glass is difficult to soften and the fluidity is deteriorated. In other words, the object of the present invention cannot be achieved due to the disadvantage that the coating becomes difficult. If the content of CaO in the coating layer is below the lower limit value, the coefficient of thermal expansion becomes too small, and a mismatch with the thermistor part tends to occur, causing a problem such as cracking in the coating layer, and the upper limit value. Exceeding this causes a disadvantage that the heat resistance is lowered, and the object of the present invention cannot be achieved. If the content of MgO in the coating layer is below the lower limit, it is difficult to precipitate the desired crystals, and if it exceeds the upper limit, the fluidity of the glass is deteriorated and molding becomes difficult. The object of the present invention cannot be achieved.

Further, the coating layer does not contain a substantially B ₂ O _3. “Substantially free” means that B ₂ O ₃ cannot be detected or identified by ICP (Inductively Coupled Plasma) emission analysis. When the the coating layer is B ₂ O ₃ is B ₂ O ₃ to the extent is detected is contained in the coating layer, components of the coating layer and the thermistor element is exposed to a high temperature, where B ₂ O ₃ is a thermistor Then, the characteristics of the thermistor part fluctuate and the object of the present invention cannot be achieved.

  This covering layer is preferably a crystallized glass of an electrical insulator containing diopside. When the coating layer is formed of crystallized glass containing diopside that is an electrical insulator, the components in the coating layer may move to the thermistor portion even when the thermistor element according to the present invention is exposed to high temperature. As a result, the characteristic variation of the thermistor portion becomes extremely small.

  The coating layer can be formed on the surface of the thermistor portion as follows.

First, a slurry for a coating layer is prepared by kneading raw material powder for forming a coating layer, that is, SiO ₂ , CaO, and MgO, a binder, and a dispersion medium. In this preparation, examples of the binder include ethyl cellulose, methyl cellulose, carboxymethyl cellulose, and the like, or compositions containing these as a main component. Examples of the dispersion medium include water, methyl alcohol, ethyl alcohol, terpineol, acetone, ketone, and methyl ethyl ketone. The amounts of the binder and the dispersion medium can be determined as appropriate. The blending amount of the binder is usually 5 to 20 parts by weight, preferably 10 to 20 parts by weight with respect to the total amount of the raw material powder.

  So-called dip coating is performed by immersing the thermistor part in the obtained slurry for coating layer. When the coating layer slurry adhering to the surface of the thermistor portion is dried and baked at a predetermined temperature, the thermistor element according to the present invention can be obtained.

  In the normal case, the thickness of the coating layer is preferably 0.5 to 500 μm.

  Thus, as shown in FIG. 2, the thermistor element in which the surface of the thermistor portion 1a, which is a conductive oxide sintered body, is covered with the coating layer 1b, and one end of the electrodes 2a and 2b is embedded in the thermistor portion 1a. Is formed.

  The shape of the thermistor portion 1a shown in FIGS. 1 and 2 is expressed as a hexagonal plate, but the shape of the thermistor portion 1a is designed in accordance with the shape and structure of the temperature sensor.

  The temperature sensor according to the present invention includes the thermistor element according to the present invention. FIG. 3 shows an example of a temperature sensor according to the present invention. The temperature sensor 100 shown in FIG. 3 uses the thermistor element 2 as a temperature sensitive element. The temperature sensor 100 is attached to a mounting portion of an exhaust pipe of an automobile, and the temperature of the exhaust gas can be detected by positioning the thermistor element 2 in the exhaust pipe through which the exhaust gas flows.

  In the temperature sensor 100, the metal tube 3 extending in the direction along the axis (hereinafter also referred to as the axial direction) is formed in a bottomed cylindrical shape in which the tip 31 side, that is, the lower side in FIG. . The thermistor element 2 which is an example of the present invention is housed in the internal space of the tip portion 31. The metal tube 3 does not need to be heat-treated in advance as in the conventional metal tube, and therefore it is not necessary to form an oxide film by oxidizing the outer surface and the inner surface. This is because the thermistor element 2 according to the present invention is unlikely to cause fluctuations in the characteristics of the thermistor portion due to the presence of the coating layer even when the atmosphere becomes a reducing atmosphere, and therefore prevents the atmosphere surrounding the thermistor element 2 from being reduced. This is because it is not necessary, and it is not necessary to make the surface of the metal tube 3 an oxide film. When the thermistor element 2 according to the present invention is inserted and disposed in the metal tube 3, the thermistor element 2 is filled with cement 10 inside the metal tube 3 to hold the thermistor element 2. Yes. The rear end 32 of the metal tube 3 is open, and the rear end 32 portion is press-fitted and inserted into the flange member 4.

  Further, in the temperature sensor according to the present invention, the covering layer 1b of the thermistor element 2 has a dimensional relationship such that the covering layer 1b of the thermistor element 2 is not in contact with the inner peripheral surface of the metal tube 3. The cement 10 is interposed between the inner peripheral surface 3 and the inner surface of the metal tube 3 so as to reliably prevent direct contact between the coating layer 1b and the inner peripheral surface of the metal tube 3 when the temperature sensor is used. .

  The flange member 4 has a cylindrical sheath portion 42 extending in the axial direction, and is positioned on the distal end side of the sheath portion 42, that is, on the lower side in FIG. 3, and has a larger outer diameter than the sheath portion 42 and radially outward. And a projecting flange portion 41. On the distal end side of the flange portion 41, there is a tapered seating surface 45 that performs sealing with the attachment portion of the exhaust pipe. Moreover, the sheath part 42 has comprised the two-stage shape which consists of the front end side sheath part 44 located in the front end side, and the rear end side sheath part 43 smaller in diameter than this.

  The metal tube 3 press-fitted into the flange member 4 is firmly fixed to the flange 4 by laser welding of the outer peripheral surface of the metal tube 3 at the site L1 over the entire circumference in the circumferential direction. Yes. Moreover, the substantially cylindrical metal cover member 6 is press-fitted into the distal end side sheath portion 44 of the flange member 4 and is laser-welded at a portion L2 over the entire circumference in the circumferential direction and joined in an airtight state.

  Further, a mounting member 5 having a hexagonal nut portion 51 and a screw portion 52 is rotatably fitted around the flange member 4 and the metal cover member 6. The temperature sensor 100 shown in FIG. 1 is configured so that a seat surface 45 of the flange portion 41 of the flange member 4 is brought into contact with a mounting portion of an exhaust pipe (not shown) and a nut 5 is screwed into the mounting portion. To fix.

  A sheath member 8 including a pair of core wires 7 is disposed inside the metal tube 3, the flange member 4, and the metal cover member 6. The sheath member 8 includes a metal outer cylinder, a pair of conductive core wires 7, and an insulating powder that fills the outer cylinder and holds the core wire 7 while insulating the outer cylinder and the core wires 7. It is configured. In the conventional temperature sensor, it is necessary to previously form an oxide film on the outer cylinder of the sheath member 8 by heat treatment. However, in the temperature sensor 100 equipped with the thermistor element 2 according to the present invention, It is not necessary to form an oxide film on the outer cylinder of the sheath member 8.

  The electrode wires 2a and 2b of the thermistor element 2 are connected by laser welding to the core wire 7 protruding from the tip of the outer cylinder of the sheath member 8 inside the metal tube 3, that is, downward in the drawing.

  On the other hand, the core wire 7 protruding to the rear end side of the sheath member 8 is connected to a pair of lead wires 12 via a crimping terminal 11. The core wires 7 and the crimping terminals 11 are insulated from each other by an insulating tube 15.

  The pair of lead wires 12 are drawn out from the inside of the metal cover member 6 to the outside through the lead wire insertion holes of the elastic seal member 13 inserted inside the rear end portion of the metal cover member 6, (It is not shown. For example, it is connected to the terminal member of the connector 21 for connecting with ECU.). As a result, the output of the thermistor element 2 is taken out from the core wire 7 of the sheath member 8 to the external circuit (not shown) via the lead wire 12 and the connector 21, and the temperature of the exhaust gas is detected. The lead wire 12 is covered with a glass braided tube 20 for protection from external forces such as stepping stones, and the glass braided tube 20 is fixed by crimping to the metal cover member 6 with its elastic end member 13 together with the elastic seal member 13. Has been.

  In the temperature sensor 100 having such a structure, the thermistor element 2 made of the above-described conductive oxide sintered body is used. Therefore, the exhaust gas temperature of the automobile engine is about 1000 from a low temperature of −40 ° C. The temperature sensor can measure the temperature appropriately over a wide range up to a high temperature of ° C.

(Examples 1 and 2 and Comparative Example 1)
Production of the thermistor elements in Examples 1 and 2 and Comparative Example 1 will be described.

Using SrCO ₃ , Y ₂ O ₃ , Cr ₂ O ₃ , MnO ₂ , Fe ₂ O ₃ , Al ₂ O ₃ , the composition formula is (M1 _a M2 _b ) (M3 _c M4 _d ) O _e Commercial products having a purity of 99% or more were weighed so that a, b, c, and d were the number of moles shown in Table 1.

秤量された前記原料粉末を湿式混合して乾燥することにより、ペロブスカイト相用の原料粉末混合物を調製した。次いで、この原料粉末混合物を大気雰囲気下で１４００℃で２時間仮焼し、平均粒径１〜２μｍのペロブスカイト相用の仮焼粉末をそれぞれ得た。

The raw material powder mixture for the perovskite phase was prepared by wet-mixing the weighed raw material powder and drying. Subsequently, this raw material powder mixture was calcined at 1400 ° C. for 2 hours in an air atmosphere to obtain a calcined powder for a perovskite phase having an average particle diameter of 1 to 2 μm.

  Next, the calcined powder corresponding to Example 1 is put into a resin pot together with ethanol as a dispersion medium, and wet mixed pulverization is performed using high-purity alumina cobblestone to form the thermistor portion in the thermistor element according to Example 1. A slurry (hereinafter sometimes referred to as a first slurry) was prepared.

On the other hand, the calcined powder for the metal oxide phase according to Example 2 and Comparative Example 1 was prepared as follows. That is, SrCO ₃ and Al ₂ O ₃ , which are commercially available products having a purity of 99% or more, were weighed, wet-mixed and dried as raw material powders so as to have the composition formula SrAl ₂ O ₄ . This prepared the raw material powder mixture for metal oxide phases. Next, this raw material powder mixture for the metal oxide phase was calcined at 1200 ° C. for 2 hours in an air atmosphere to obtain a calcined powder for the metal oxide phase having an average particle diameter of 1 to 2 μm.

Next, the calcined powder for the perovskite phase and the calcined powder for the metal oxide phase corresponding to Example 2 and Comparative Example 1 described above are weighed, and these calcined powder and dispersion medium are used. Slurry used in Example 2 and Comparative Example 1 (hereinafter sometimes referred to as a second slurry) may be obtained by adding ethanol to a resin pot and performing wet mixing and grinding using high-purity Al ₂ O ₃ cobblestone. .) Was prepared.

  Next, the first slurry was dried at 80 ° C. for 2 hours to obtain a thermistor part synthetic powder used in Example 1. Moreover, the said 2nd slurry was dried at 80 degreeC for 2 hours, and the synthetic powder for the thermistor parts used in Example 2 and Comparative Example 1 was obtained. Thereafter, 20 parts by weight of a binder mainly composed of polyvinyl butyral was added to 100 parts by weight of the synthetic powder for the thermistor, mixed and dried. Furthermore, it granulated through the sieve of a 250 micrometers mesh, and the granulated powder for the thermistor part was obtained.

Next, the granulated powder for the thermistor part is press-molded by a mold molding method (press pressure: 4500 kg / cm ² ), and as shown in FIG. 1, a pair of electrode wires made of Pt—Rh alloy A molded body for an unfired thermistor part having a hexagonal plate shape (thickness: 1.24 mm) in which one end side of 2a and 2b was embedded was obtained.

  Thereafter, the green body for the thermistor part was fired at 1450 ° C. to 1550 ° C. for 2 hours in the air. Thus, a pair of electrode wires 2a and 2b and a hexagonal plate-like thermistor portion in which one end side is embedded and the other end side protrudes in parallel were manufactured.

  The X-ray diffraction pattern of the thermistor part in Example 1 is shown in FIG. 4, and the X-ray diffraction patterns of the thermistor part in Example 2 and Comparative Example 1 are shown in FIG.

  As shown in FIG. 1, each thermistor element 2 has a hexagonal shape with a side of 1.78 mm, a thickness of 1.00 mm, a diameter φ0.3 mm of the electrode wires 2a and 2b, and an electrode center distance of 0.85 mm. (Gap 0.55 mm) and electrode insertion amount 1.36 mm.

  Next, a slurry for the coating layer was prepared as follows. That is, a commercially available crystallized glass powder having the composition shown in Table 2 as a raw material powder, a binder mainly composed of ethyl cellulose, and terpionol and acetone as dispersion media are kneaded with a mixer to prepare a slurry for a coating layer. did. In addition, the numerical value shown in Table 2 is mass%.

  Thereafter, the thermistor portions prepared for Examples 1 and 2 and Comparative Example 1 were dipped in the coating layer slurry to dip coat the thermistor portion with the coating layer slurry. Next, the thermistor element having a thermistor portion and a dense coating layer covering the thermistor portion was manufactured by baking the resultant at 1000 ° C. after drying.

  The X-ray diffraction pattern of the coating layer in the thermistor element in Example 1 and Example 2 is shown in FIG. Further, an X-ray diffraction pattern of the coating layer in the thermistor element in Comparative Example 1 is shown in FIG.

  Next, the B constant (temperature gradient constant) of the thermistor elements according to Examples 1 and 2 and Comparative Example 1 was measured as follows.

  That is, first, the thermistor element was left in an environment of absolute temperature T (100) = 373 K (= 100 ° C.), and the initial resistance value R (100) of the thermistor element in that state was measured. Next, the thermistor element was left in an environment of absolute temperature T (300) = 573 K (= 300 ° C.), and the initial resistance value R (300) of the thermistor element in that state was measured. Similarly, R (600) and R (900) were also measured. And B constant: B (100-900) is computed according to the following formula | equation (1), initial resistance value R (100), R (300), R (600), R (900) and B constant: B (100-900) is shown in Table 3.

B (100−900) = ln [R (900) / R (100)] / [1 / T (900) −1 / T (100)] (1)
Next, in order to confirm the change in resistance of the thermistor element before and after forming the coating layer, the resistance value after the formation of the coating layer of the thermistor element at 100 ° C., 300 ° C., 600 ° C. and 900 ° C. in the same manner as described above. That is, the resistance values Rs (100), Rs (300), Rs (600), and Rs (900) were measured after the coating layer was formed. Then, from the comparison between the initial resistance value R (100) at 100 ° C. and the resistance value Rs (100) after coating layer formation, the temperature change converted value DT (100) (unit: deg) C) was calculated according to (2) below. Similarly, the temperature change conversion values DT (300), DT (600), and DT (900) were respectively calculated by the equations (3), (4), and (5), and are shown in Table 3.

DT (100) = [(B (100-900) * T (100)) / [ln (Rs (100) / R (100)) * T (100) + B (100-900)]]-T (100 (2)
DT (300) = [(B (100-900) * T (300)) / [ln (Rs (300) / R (300)) * T (300) + B (100-900)]]-T (300 (3)
DT (600) = [(B (100-900) * T (600)) / [ln (Rs (600) / R (600)) * T (600) + B (100-900)]]-T (600 (4)
DT (900) = [(B (100−900) × T (900)) / [ln (Rs (900) / R (900)) × T (900) + B (100−900)]] − T (900 (5)
Further, the thermistor elements prepared for Examples 1 and 2 and Comparative Example 1 are incorporated into the temperature sensor shown in FIG. 3 as described later, and the initial resistance value Rt (100 of the thermistor element in this temperature sensor state is set. ), Rt (300), Rt (600), Rt (900). Subsequently, it is kept at 900 ° C. in the atmosphere for 500 hours, and then the resistance value Rt ′ (100 after heat treatment of the thermistor element in the state of the temperature sensor at 100 ° C., 300 ° C., 600 ° C. and 900 ° C. in the same manner as described above. ), Rt ′ (300), Rt ′ (600), and Rt ′ (900) were measured. Then, from a comparison between the initial resistance value Rt (100) at 900 ° C. and the post-heat treatment resistance value Rt ′ (100), the temperature change converted value CT (100) of the resistance change due to heat treatment (unit: (unit: deg. C) was calculated by the following formula (6): Similarly, the temperature change converted values CT (300), CT (600), CT (900) were calculated by formulas (7), (8), and (9). The results are shown in Table 3.

CT (100) = [(B (100−900) × T (100)) / [ln (Rt ′ (100) / Rt (100)) × T (100) + B (100−900)]] − T ( 100) (6)
CT (300) = [(B (100−900) × T (300)) / [ln (Rt ′ (300) / Rt (300)) × T (300) + B (100−900)]] − T ( 300) (7)
CT (600) = [(B (100−900) × T (600)) / [ln (Rt ′ (600) / Rt (600)) × T (600) + B (100−900)]] − T ( 600) (8)
CT (900) = [(B (100−900) × T (900)) / [ln (Rt ′ (900) / Rt (900)) × T (900) + B (100−900)]] − T ( 900) (9)

  In addition, the temperature sensors according to Examples 1 and 2 and Comparative Example 1 shown in FIG. 3 did not previously form an oxide film on the surface of the metal tube and the metal outer cylinder constituting the sheath member. . This is because even if the temperature sensor vicinity of the temperature sensor is heated to a high temperature, the outer tube of the metal tube or the sheath member is oxidized, and the atmosphere in the metal tube becomes a reducing atmosphere, the temperature sensor according to the first and second embodiments. This is because the thermistor portion is reduced and the characteristics do not change. Therefore, in the temperature sensors according to the first and second embodiments, as described later, the resistance value is prevented from changing due to the reduction of the thermistor element.

  From the results shown in Table 3, in the thermistor elements of Examples 1 and 2, the resistance change temperature converted values DT (100), DT (300), DT (600), and DT (900) after forming the coating layer are Also, it was a low value, and specifically, it was within the range of ± 0.3 ° C. at most. That is, in the thermistor elements of Examples 1 and 2, the resistance value at each temperature is stable, and it can be seen that the amount of change in the resistance value is small even after the coating layer is formed. In such a thermistor element, the resistance value can be stably measured regardless of the thermal history, and an accurate temperature can be measured.

  On the other hand, in Comparative Example 1, the indicated temperature change after the formation of the coating layer has a larger value than the result of the example. This is understood to be because in Comparative Example 1, the coating layer has a configuration outside the range of the coating layer defined in the present invention. That is, when firing the coating layer, in Comparative Example 1, the metal elements Sr, Y, Mn, Cr, and Al located at the A site and the B site in the perovskite phase move to the coating layer or form the coating layer. It can be understood that the element moves to the thermistor part and causes the composition of the thermistor part to change, which causes the characteristics of the thermistor element to change.

  Such an understanding is that when the thermistor element after coating layer formation according to Comparative Example 1 is polished and the cut surface is observed with an electron micrograph, a reaction layer is observed near the interface between the thermistor portion and the coating layer. It was confirmed that the components in the thermistor part and the coating layer diffused to each other.

On the other hand, in the thermistor element according to Example 1, the coating layer has a composition of SiO ₂ 40 to 65% by mass, CaO 15 to 40% by mass, and MgO 5 to 30% by mass, and substantially contains B ₂ O ₃ . When the coating layer is formed, the metal element located at the A site or B site in the perovskite phase moves to the coating layer, or the element that forms the coating layer is formed. It becomes difficult to move to the perovskite phase. Further, when this thermistor element is exposed to a high temperature for a long time, even if Y, Sr, Mn, Fe, Al located at the A site or B site in the perovskite phase try to move to the coating layer, Since it is crystallized glass, these metal elements are suppressed from moving into the coating layer. The same applies to Example 2.

  Furthermore, the temperature change conversion values CT (100), CT (300), CT (600), and CT (900) in Example 1 and Example 2 are all low values, specifically, a range of ± 3 ° C. at most. It became the value of. That is, the thermistor elements according to Example 1 and Example 2 have a stable resistance value at each temperature, and even when the thermistor element is exposed to a high temperature for a long time, the amount of change in the resistance value is small. Such a thermistor element can accurately perform stable resistance measurement regardless of the thermal history.

  According to Table 3, the thermistor element according to Example 1 has a B constant [B (100 to 900)] of 4500 K [= B (100 to 900)], and can detect each temperature with high accuracy. Further, the thermistor element according to the second embodiment is a thermistor element having a relatively low value of 2400K [= B (100 to 900)] as compared with the conventional one.

FIG. 1 is a perspective view showing a thermistor element according to an embodiment of the present invention. FIG. 2 is a partially cutaway sectional view showing a thermistor element according to an embodiment of the present invention. FIG. 3 is a partially cutaway cross-sectional view showing a temperature sensor according to an embodiment of the present invention. FIG. 4 is an X-ray diffraction diagram of the thermistor portion in the thermistor element according to Embodiment 1 of the present invention. FIG. 5 is an X-ray diffraction diagram of the thermistor portion in the thermistor element according to Example 2 and Comparative Example 1 of the present invention. FIG. 6 is an X-ray diffraction pattern of the coating layer in the thermistor element according to Example 1 and Example 2 of the present invention. FIG. 7 is an X-ray diffraction pattern of the coating layer in the thermistor element according to Comparative Example 1 which is outside the scope of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a Thermistor part 1b Coating layer 2 Thermistor element 2a, 2b Electrode wire 3 Metal tube 4 Flange member 5 Mounting member (nut)
6 Metal cover member 7 Core wire 8 Sheath member 10 Cement 11 Clamping terminal 12 Lead wire 13 Elastic seal member 15 Insulating tube 21 Connector 20 Glass braided tube 31 Front end portion 32 Rear end 41 Flange portion 42 Sheath portion 43 Rear end side sheath portion 44 Tip side sheath portion 45 Seat surface 51 Hexagon nut portion 52 Screw portion 100 Temperature sensor

Claims (8)

A thermistor element comprising a thermistor part made of a thermistor composition and a coating layer covering the thermistor part,
The thermistor portion is conductive and includes a perovskite phase having a perovskite crystal structure,
The coating layer is composed of SiO ₂ , CaO, and MgO, 40 to 65% by mass with respect to the total mass of the coating layer for SiO ₂ , and 15 to 40% by mass with respect to the total mass of the coating layer for CaO. , MgO is selected from the range of 5 to 30% by mass with respect to the total mass of the coating layer, so that the total of SiO ₂ , CaO, and MgO is 90% to 100% by mass. A thermistor element characterized by being a crystallized glass which is contained in a proportion and is substantially free of B ₂ O ₃ .   2. The thermistor element according to claim 1, wherein the covering layer has a deposited crystal of diopside which is an electrical insulator. _3. The thermistor element according to claim 1, wherein the thermistor portion includes a perovskite phase represented by ABO ₃ (where A includes Sr and / or Y, and B includes Al). 4. The thermistor element according to claim 3, wherein B in the ABO ₃ further contains at least one metal selected from Cr, Mn, and Fe.   The thermistor portion has a lower 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 MeOx The thermistor element of Claim 3 or 4 containing the metal oxide phase containing at least 1 type of the metal oxide represented by these. The thermistor element according to claim 5, wherein the metal oxide contained in the metal oxide phase is SrAl ₂ O ₄ .   The temperature sensor which has the thermistor element as described in any one of the said Claims 1-6.   8. A thermistor element according to claim 7, wherein the thermistor element is housed inside the metal tube in a state in which the covering layer in the thermistor element according to claim 7 is not in contact with the inner peripheral surface of the metal tube. The temperature sensor according to claim 7, wherein the temperature sensor is formed.

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