JPH0696905A - Material for thermister - Google Patents

Abstract

PURPOSE:To obtain a material for thermisters having an inverse spinel structure which has not been seen in the conventionally used material and is high in grain size uniformity, grain boundary uniformity after burning, electric characteristic stability, and reproducibility. CONSTITUTION:This material is prepared by using a compound which is composed of composite oxides, Co2TiO2, Ni2TiO4, and Zn2TiO4, and has an inverse spinel structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material for a thermistor, and more particularly to a material for a high temperature thermistor which works effectively at a high temperature used in an automobile temperature sensor or the like.

[0002]

2. Description of the Related Art Conventionally, a high temperature thermistor used for a temperature sensor for an automobile is a semiconductor that works stably in high temperature air of 350 [° C.] to 1000 [° C.] and has a large resistance coefficient. It is used. In addition, this semiconductor is generally
It has a resistance value of 10 [Ω] to several 10 [kΩ]. for that reason,
This high temperature thermistor is a catalyst converter for automobiles,
It is used as a temperature sensor in an exhaust gas purification system using a thermal reactor, or as a temperature sensor in a relatively high temperature part such as a combustor.

Further, the crystal structure of the conventional high temperature thermistor includes a fluorite type structure, a spinel type structure, a corundum type structure, a perovskite type structure and the like.

A high temperature thermistor having a fluorite-type crystal structure is a ZrO ₂ , CaO, Y ₂ O ₃ , MgO, Nd.
Made of materials such as ₂ O ₃ and ThO ₃ , 750 [℃]
Shows the resistance value of 0.8 to 8 [kΩ] at the temperature of B = 5000 to 1800
It has a thermistor constant of 0K.

The high temperature thermistor of spinel type structure is C
oO, MnO, NiO, Al ₂ O ₃ , Cr ₂ O ₃ , Ca
It is made of materials such as SiO ₃ , MgO, and Fe ₂ O ₃ and shows a resistance value of 10 to 10 ¹⁷ [Ω] at a temperature of 600 [° C] and a service temperature of B = 2000 to 17,000 [° K]. A thermistor having a thermistor constant and a thermistor showing a resistance value of 0.9 to 500 [kΩ] at a temperature of 700 [° C] and a thermistor constant of B = 2900 to 11000 [° K]. -And 1 to 10 ⁶ at a temperature of 1050 [℃]
There is a thermistor having a specific resistance of [Ω · cm] and a thermistor constant of B = 15000 ± 5000 [° K].

The high temperature thermistor of corundum type structure is
It is made of materials such as Al ₂ O ₃ , Fe ₂ O ₃ and MnO, has a specific resistance of 4.5 [kΩ · cm] at a temperature of 600 [℃], and has a thermistor constant of B = 11300K. Have. The high temperature thermistor having a perovskite structure shows a resistance value of 0.1 to 9.2 [kΩ] at a temperature of 500 [° C].

The high temperature thermistor as described above is used, for example, in a temperature sensor for automobiles, and the thermistor constant of this high temperature thermistor for automobiles is B = 10000 to 15
It is said to be about 000 [° K], and the temperature dependence of the resistance value is large. That is, even when the temperature is slightly changed, a clear change in the resistance value can be read.

In these thermistor materials, powder raw materials composed of oxides and carbonates are mixed in appropriate amounts, and after being mixed, the powder raw materials are dried in a drying chamber, and the powder raw materials thus dried are mixed. Is formed by being pressure-molded into a desired shape and then fired. After that, the thermistor material is subjected to a cutting process, an electrode applying process, a lead wire attaching process,
It is processed into a thermistor through a baking process. As described above, the conventional thermistor is manufactured by the dry method.

[0009]

In the conventional method for producing the material for the thermistor by the dry method, the particles of the material are not uniformly formed, and the uniformity of the grain boundary of the fired product is poor, so that electrical There was a drawback that the stability of the characteristics was poor.

Further, even if the thermistor material is repeatedly manufactured by the same material and method, the thermistor characteristics are not constant and there is a problem that reproducibility is poor.

In view of the above circumstances, the present invention is for a thermistor having high uniformity of material particles, high uniformity of grain boundaries of a fired product, good stability of electric characteristics, and high reproducibility. It is intended to provide a material and a manufacturing method thereof.

[0012]

According to the present invention, kCo ₂ TiO ₄ .mNi ₂ Ti having an inverse spinel type structure is provided.
There is provided a material for a thermistor having an O ₄ · nZn ₂ TiO ₄ compound sintered body. However, 0 <k ≦ 100 capacitance part, 0 ≦ m ≦ 50 capacitance part, 0 ≦ n ≦ 50 capacitance part, k + m
+ N = 100 parts by volume.

Further, according to the present invention, a step of preparing an acidic solution containing Ni ions and Zn ions as necessary together with Co ions and Ti ions, a step of precipitating the metal sol with this solution and precipitating the precipitated metal There is provided a method for producing a material for a thermistor, which comprises a step of filtering and drying the sol and a step of sintering the powder obtained in this step.

In order to solve the problem, a thermistor material having the above-mentioned reverse spinel type structure and a method for manufacturing the thermistor material are provided. The structure will be described.

FIG. 1 shows a crystal model of a spinel structure, which is a form of the crystal structure found in the oxide represented by the chemical formula XY ₂ O ₄ . This crystal structure belongs to the cubic system, and as shown in FIG. 2, a unit cell 1 is formed by eight chemical units (XY ₂ O ₄ ). Figure 1
Shows two kinds of chemical units I and II which are 2/8 of the unit lattice 1, and the chemical units I and II are alternately arranged when viewed from the whole lattice.

In the figure, black spheres represent X, triangles represent Y, and white spheres represent O atoms (ions), respectively. O forms a substantially face-centered cubic lattice and has a close-packed structure. 6 O in between
A space surrounded by a regular octahedron by (3 in unit cell 1
2), and a gap surrounded by the four O's in a regular tetrahedron shape (64 in the unit cell 1) is partially occupied by X and Y.

As shown in FIG. 3, in the crystal having the reverse spinel type structure, half of Y is replaced at the X position of the above spinel type structure, and the remaining Y and X are arranged at the Y position. It has a structure. Therefore, this crystal is Y (XY) O
Can be written as ₄ .

In the compound having the reverse spinel type structure as described above, kCo ₂ TiO ₄ .mNi ₂ TiO ₄ .n
The present inventors have found that the compound represented by Zn ₂ TiO ₄ is a compound that exhibits stable thermistor characteristics particularly at high temperatures.

The resistance value of this thermistor is determined by the k, m, and n capacitance parts of the above chemical formula. When the k capacitance part is increased, the resistance value is decreased, and the m and n capacitance values are decreased. When the capacitance section is increased, the resistance value is increased. Also, if this resistance value is greatly reduced, it approaches the conductor infinitely, or
When the resistance value is greatly increased, it approaches the insulator as much as possible,
Stop working as a thermistor. Therefore, the above k,
The values of m and n are limited to 0 <k ≦ 100 capacitance part, 0 ≦ m ≦ 50 capacitance part, 0 ≦ n ≦ 50 capacitance part, and k + m + n = 100 capacitance part.

High temperature thermistor represented by the above chemical formula
Is atmospheric pressure molding of carbonate and oxide raw material powder and firing in air,
Although it can be prepared by sintering, it is preferably prepared by a coprecipitation method.

[0021]

The operation will be described based on the structure of the present invention.
KCo ₂ TiO ₄ .mNi ₂ TiO ₄ .nZn ₂ Ti having an inverse spinel type structure forming a material for a thermistor
In the O ₄ compound sintered body, complex oxide Co ₂ TiO
₄ is the center of the component. Therefore, when the complex oxide Co ₂ TiO ₄ does not exist as a constituent element of the compound, the above compound does not exhibit the property as a high temperature conductor. Therefore, when manufacturing the thermistor of the present invention, the complex oxide CoTiO ₄ must be present as a constituent element.

Further, when the above-mentioned thermistor constant B is increased, the contents of the composite oxides Ni ₂ TiO ₄ and Zn ₂ TiO ₄ which are the other constituent elements of the above-mentioned compound are also important. Therefore, the above composite oxide Co ₂ TiO
₄ , the compound oxide Ni ₂ TiO ₄ and / or the compound oxide Zn ₂ TiO ₄ is contained in a predetermined amount, and the compound sintered body is fired to obtain a thermistor. A high temperature thermistor having a large constant B can be obtained.

[0023]

EXAMPLES The method for producing the thermistor material of the present invention will be described below with reference to examples.

Example 1 Co ₂ TiO ₄ (cobalt titanate), Ni ₂ TiO ₄ (nickel titanate), Zn
_{In the} material for the thermistor of the present invention having ₂ TiO ₄ (zinc titanate) as a constituent element, Co is used as the first embodiment.
_A case of forming crystals of a material for a thermistor having an inverse spinel type structure only with ₂ TiO ₄ will be described.

Titanium sulphate solution diluted to 30% 60.10
[ml] and 99.0% concentration of cobalt chloride hexahydrate 51.2775 [g]
And prepare. Next, each of these ingredients is 100 [ml]
Put in a volumetric flask and pour the ion-exchanged water up to the marked line to stir. Next, these aqueous solutions are transferred to a 1000 [ml] beaker and mixed, and then vigorously stirred for about 1 [hr] using a stirrer. The pH of the thus mixed and stirred aqueous solution is adjusted to pH = 7.80 ± 0.03 with 6N aqueous ammonia. At this time, the metal sol obtained by coprecipitation is washed with water by decantation, then passed through an organic solvent such as toluene, and then filtered. The filtered material thus filtered is put into a dryer and dried at a temperature of about 80 [° C.] for about 20 [hr]. Next, dry and pulverize using an agate mortar, and then use an electric furnace for about 2
[hr] Baking gives powder raw material.

The powder raw material thus obtained is molded into a pellet form by applying a pressure of 277 [MPa] at room temperature. The powder raw material formed into pellets is heated in an electric furnace at about 1000 [° C] for 24 [hr] and sintered.

The electric conductivity of the thermistor material molded as described above was measured in the temperature range of about 417 [K] to 625 [K], and the measurement results shown in FIG. 4 were obtained. As an optional temperature, T = 433 [K], when choosing the T ₀ = 613 [K], each of the resistance values, R = 181820 [Ω], R 0 = 140 [Ω] , and the these service - Mist-Equation expressing temperature dependence of resistance value R = R ₀ e
Substitution into xpB (1 / T-1 / T ₀ ) resulted in a thermistor constant B of this compound being B = 10575K.

(Embodiment 2) Next, as a second embodiment,
KCo ₂ TiO ₄ · mNi ₂ having an inverse spinel structure
In the TiO ₄ .nZn ₂ TiO ₄ compound, k = 30
A method of manufacturing the material for the thermistor in the case of the capacitance part, m = 50 capacitance part, and n = 20 capacitance part will be described.

30% dilute titanium sulfate solution 60.10
[ml] and 99.0% concentration of cobalt chloride hexahydrate 51.3460
[g] and nickel chloride hexahydrate with a concentration of 98.0% 15.3842 [g]
And 92.0% concentration of zinc sulfate heptahydrate 12.0589 [g]. Each of these raw materials is put into a 100 [ml] volumetric flask, and ion-exchanged water is injected up to the marked line to dilute the mixture.
Next, these aqueous solutions are transferred to a 1000 [ml] beaker and mixed, and stirred vigorously for about 1 [hr] using a stirrer. The pH of the thus mixed and stirred aqueous solution is adjusted to pH = 7.80 ± 0.03 with 6N aqueous ammonia. At this time, the metal sol obtained by coprecipitation is washed with water by decantation, then passed through an organic solvent such as toluene, and then filtered. The filtered material thus filtered is put into a dryer and dried at a temperature of about 80 [° C.] for about 20 [hr]. Next, dry and pulverize using an agate mortar, and then bake for about 2 [hr] at a temperature of about 1000 [° C] in an electric furnace.
A powder raw material is produced.

The powder raw material thus obtained is pressed into a pellet at a pressure of 277 [MPa] at room temperature. The powder raw material formed into pellets is heated in an electric furnace at about 1000 [° C] for 24 [hr] and sintered.

The electric conductivity of the thermistor molded as described above was measured in the temperature range of about 417 [K] to 625 [K], and FIG.
The measurement results shown in are obtained. As arbitrary temperature, T = 51
When 3 [K] and T ₀ = 613 [K] are selected, the respective resistance values are R = 296190 [Ω] and R ₀ = 7190 [Ω], and these are the temperature dependence of the thermistor resistance. The expression R = R ₀ expB (1
Substituted for / T-1 / T ₀ ). As a result, the thermistor constant B of this compound was B = 11698K.

Although two examples have been described above, a thermistor material having a thermistor constant comparable to the conventional thermistor material could be obtained. Further, the material for the thermistor of the present invention is not limited to these examples, and a plurality of materials for the thermistor can be obtained by changing the mixing ratio of the constituent elements. For example, kCo ₂ TiO ₄ · mNi ₂ TiO ₄ ·
In the nZn ₂ TiO ₄ compound, when the material for the thermistor is made with a mixing ratio of k: m: n = 50 parts by volume: 50 parts by volume: 0 part by volume, the thermistor constant of B = 9474 [k]. When the material for the thermistor having a mixing ratio of k: m: n = 50 parts by volume: 0 parts by volume: 50 parts by volume is prepared, the material for the thermistor having B = 10958 [k] is obtained. A thermistor material having a thermistor constant was obtained.

FIG. 5 shows a SEM photograph of the powder of the thermistor material prepared by the wet method, and FIG.
Shows a SEM photograph of the powder of the thermistor material prepared by the dry method. As is clear from these photographs, the particles produced by the wet method are more uniform than those produced by the dry method, and the respective particle diameters are smaller. In addition, as shown in FIG. 7, the accumulation rate of the thermistor material powder formed by the wet method increases more rapidly than that of the thermistor material powder formed by the dry method. I understand. Thus, by preparing the material for the thermistor by the wet method, it was possible to obtain the material for the thermistor with high particle uniformity.

When the material particles have high uniformity, the uniformity of the grain boundaries of the fired product also becomes high, and a material for the thermistor having high stability of electric characteristics can be obtained.

The thermistor material prepared with a constant mixing ratio is excellent in reproducibility because a thermistor material having the same characteristics can be obtained no matter how many times it is prepared.
Since the same result was obtained even if the measurement was repeated, it was found to have excellent stability.

[0036]

As described above, according to the method for producing a thermistor material of the present invention, the uniformity of the particles of the material is high,
Provided is a material for a thermistor, which has good grain boundary uniformity of the fired product, good stability of electrical characteristics, and high reproducibility.

[Brief description of drawings]

FIG. 1 is a schematic view showing a crystal model of a material for a thermistor having an inverted spinel type structure of the present invention.

FIG. 2 is a schematic view showing a crystal model of a thermistor material having a spinel structure.

FIG. 3 is a schematic view showing a unit cell of a thermistor material having a spinel structure.

FIG. 4 is an absolute temperature T in the first and second embodiments of the thermistor material having the reverse spinel type structure of the present invention.
The graph which shows the reciprocal of and the relation of the common logarithm of electric conductivity (sigma).

FIG. 5 is an enlarged view of a surface particle structure of a thermistor material formed by a wet method.

FIG. 6 is an enlarged view of the surface particle structure of the thermistor material formed by the dry method.

FIG. 7 is a graph showing cumulative particle size distribution curves of the thermistor material formed by the wet method and the dry method in FIGS.

[Explanation of symbols]

 1 ... Unit lattice I, II ... Chemical unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuya Kawamura 1-2-25-1408 Minoki, Yokkaichi-shi, Mie (72) Inventor Atsushi Yamada 23-13-1101 Kawaramachi, Yokkaichi-shi, Mie

Claims (8)

[Claims] 1. A Co ₂ TiO ₄ having an inverse spinel structure.
A material for a thermistor having a compound sintered body. 2. kCo ₂ TiO having an inverse spinel type structure.
_A material for a thermistor having a ₄ · mNi ₂ TiO ₄ · nZn ₂ TiO ₄ compound sintered body. However, 0 <k ≦ 100
Capacitance part, 0 <m ≦ 50 capacitance part, 0 <n ≦ 50 capacitance part, k
+ M + n = 100 parts by volume. 3. A kCo ₂ TiO having an inverted spinel structure.
_A material for a thermistor having a ₄ · mNi ₂ TiO ₄ compound sintered body. However, 0 <k ≦ 100 capacity part, 0 <m ≦ 5
0 capacitance part and k + m + n = 100 capacitance part. 4. kCo ₂ TiO having an inverted spinel type structure.
_A material for a thermistor having a ₄ · nZn ₂ TiO ₄ compound sintered body. However, 0 <k ≦ 100 capacity part, 0 <n ≦ 5
0 capacitance part and k + m + n = 100 capacitance part. 5. A step of preparing an acidic solution containing Co ions and Ti ions, a step of precipitating a metal sol by using this solution as an alkaline solution, a step of filtering and drying the precipitated metal sol, and a step of obtaining in this step. And a step of sintering the powder thus obtained, a method for producing a material for a thermistor. 6. A step of preparing an acidic solution containing Co ions, Ti ions, Ni ions, and Zn ions, a step of precipitating a metal sol by using the solution as an alkaline solution, and filtering and drying the precipitated metal sol. A method for producing a material for a thermistor, comprising a step and a step of sintering the powder obtained in this step. 7. A step of preparing an acidic solution containing Co ions, Ti ions, and Ni ions, a step of precipitating a metal sol using the solution as an alkaline solution, and a step of filtering and drying the precipitated metal sol, A method of manufacturing a material for a thermistor, comprising the step of sintering the powder obtained in this step. 8. A step of preparing an acidic solution containing Co ions, Ti ions and Zn ions, a step of precipitating a metal sol by using this solution as an alkaline solution, and a step of filtering and drying the precipitated metal sol, A method of manufacturing a material for a thermistor, comprising the step of sintering the powder obtained in this step.