JPH08167501A - Positive thermistor and its manufacture - Google Patents

Abstract

PURPOSE: To provide a positive thermistor with little degradation of its characteristics and yet high reliability even it is used in a reducing atmosphere. CONSTITUTION: An electrode is formed after a positive thermistor is formed of material comprising a main component of barium titanate or its solid solution, a composition of an element to form a semiconductor and each oxide of Mn, Al, and Si to which 0.05 to 0.025mol of CaZrO3 , has been added.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive temperature coefficient thermistor in which a resistance value rapidly increases at a specific temperature, and in particular, a highly reliable positive temperature coefficient characteristic with less characteristic deterioration when used in a reducing atmosphere. The present invention relates to a thermistor and a manufacturing method thereof.

[0002]

2. Description of the Related Art Barium titanate is converted into a semiconductor by adding a trace amount of a rare earth element such as Y, La or Ce or a metal oxide such as Nb or Ta, and its resistance value rapidly increases at a temperature near its Curie point. Resistance temperature characteristics (Positive
Temperature Coefficient:
It has been widely known that it exhibits PTC characteristics.
Utilizing the PTC characteristics, it has been applied to various applications such as an overcurrent protection element, a temperature control element, a motor starting element, and a heater. On the other hand, as a method of manufacturing such a PTC thermistor, the following method is generally used. First, ceramic raw materials that have been compounded to have a predetermined composition are mixed using a wet ball mill, a disper mill or the like, dehydrated and dried with a filter press, a drum dryer or the like, and then these mixed powders are calcined. Next, this calcined powder is pulverized by a wet ball mill, a sand mill, or the like, and a binder is added to form a slurry, which is then granulated by a spray dryer or the like into a desired shape, followed by main calcination, and the obtained calcination The final product is formed by forming electrodes on the united body. Generally, the main calcination is performed in the air, but some elements that are required to have a low resistance may be subjected to a heat treatment in a reducing atmosphere and then a reoxidation treatment. Further, recently, environmental conditions in which such elements are used are severe, and there are various applications in which reduction resistance is particularly required, and studies on composition and process have been actively conducted.

[0003]

It has long been pointed out that the characteristics of such a positive temperature coefficient thermistor depend on the grain boundaries, but when used in a reducing atmosphere or a neutral atmosphere, the resistance The value deteriorates significantly, and the temperature coefficient of resistance is significantly reduced, resulting in deterioration of characteristics. Above all, especially under the use condition of the device using the heater element,
It consists of chemicals, fabric softening agents, organic components such as gasoline and machine oils, edible oils, and seasonings, and adheres to the element.When the element heats up, it causes a reducing action due to the combustion of these organic components, resulting in various characteristics. May deteriorate, and therefore, it is necessary to prevent contact or adhesion with such organic components, and its use is limited.

The mechanism of PTC characteristic deterioration in a reducing atmosphere is generally considered to be that electrons generated by the generation of oxygen defects contribute to conductivity.

Therefore, in order to improve the reduction resistance performance, (1) a crystal structure in which oxygen defects are not generated (oxygen is hardly released) (2) a reducing substance or the like enters the inside of the element It is considered to be difficult to make a dense and fine structure. (3) It is possible to introduce an element that acts as an acceptor that traps generated electrons.

In view of the above, the present invention has an object to provide a positive temperature coefficient thermistor which is suitable for the above-mentioned applications and has excellent reduction resistance.

[0007]

To achieve this object, the present invention provides a rare earth element or a metal oxide of Nb, Sb or Bi as a sub-component for 1 mol of the main component consisting of barium titanate or a solid solution thereof. And at least one oxide of Si, Mn, and Al are added for calcination, and CaZrO ₃ is added to the calcination powder in an amount of 0.05 to 0.05%.
0.25 mol is added and mixed, and after molding, firing is performed to form an electrode.

[0008]

The deterioration of the PTC characteristic can be considered as a decrease in the potential energy of the grain boundary where the PTC characteristic is generated.
That is, it is considered that the reducing substance comes into contact with the surface of the device, diffuses in the vicinity of the grain boundary, releases adsorbed oxygen that contributes to the formation of the potential barrier, and increases conduction electrons, which deteriorates the characteristics. It is considered that when the state is further reduced, even oxygen on the lattice is dissociated, the electron concentration is further increased, and the characteristics are deteriorated.

Therefore, according to the present invention, by adding CaZrO ₃ to the thermistor element, the sintered body itself is densified, the degree of contact with a reducing substance is reduced, and the packing property of the unit cell itself is improved. Therefore, the adsorbed oxygen and the oxygen at the lattice position are less likely to be released, and the reduction resistance performance is improved.

As a result, the positive temperature coefficient thermistor of the present invention is
Even when used in a reducing atmosphere, there is no deterioration in PTC characteristics such as a large decrease in resistance value or a significant decrease in temperature coefficient of resistance. It can be expected that the expansion will be expanded.

On the other hand, conventionally, various measures have been taken in the structural design such as providing a cover such as a protective case for protecting the element from a reducing atmosphere, or making a sealed structure. By using the thermistor, these structural designs are unnecessary, so that the number of steps can be reduced and the cost can be reduced, and its industrial utility value is great. Further, in terms of safety, the PTC thermistor of the present invention is extremely reliable because it does not cause thermal runaway and destruction of the PTC thermistor because there is no deterioration in its characteristics.

[0012]

EXAMPLES The present invention will be described below with reference to examples.

(Example 1) Each raw material is weighed so that the final composition is (Chemical formula 1).

[0014]

Embedded image

At the same time, CaZrO ₃ was weighed with the composition shown in sample Nos. 2 to 7 of (Table 1), and all the raw materials were simultaneously wet-mixed in a ball mill.

[0016]

[Table 1]

The mixture is then dried and then 1050 ° C.
Calcination for 2 hours. Then, the calcined powder is wet-milled with a ball mill. After drying this pulverized product, 5% of polyvinyl alcohol was added as a binder and granulated to give 800 kg /
Press molding was performed at a pressure of cm ² . This molded product is about 1300
1. Calcination in air at ℃ for 1 hour, diameter 20mm, thickness 2.
A 0 mm disk-shaped positive temperature coefficient thermistor element was obtained. Further, these sintered bodies were plated with Ni, coated with a silver paste, and then baked to form electrodes.

Next, various electrical characteristics of each sample thus obtained were evaluated. By its resistance temperature characteristic curve,
After evaluating the room temperature resistance value (R ₂₅ ) and the resistance change width (Ψ),
As evaluation of reduction resistance, 100 hours in nitrogen gas, 10
A voltage of 0 V was applied, and R ₂₅ and Ψ were measured again.

The results are shown in (Table 2).

[0020]

[Table 2]

Here, the resistance change width is a common logarithm of a value obtained by dividing the maximum resistance value by the minimum resistance value, and is represented by (Equation 1).

[0022]

[Equation 1]

Sample Nos. 1, 2 and 7 in Table 1 are compositions outside the scope of the present invention, and Sample Nos. 3 to 6 are compositions within the scope of the present invention.

As is clear from the comparison of the characteristic values of the sample numbers 1 to 7 in (Table 2), the sample numbers 3 to 6 whose compositions are within the range of the present invention show no deterioration in the characteristics and are resistant to deterioration. It can be seen that the reducing performance is excellent.

Example 2 Each raw material is weighed so that the final composition becomes (Chemical Formula 2).

[0026]

Embedded image

Further, CaZrO ₃ and PbSiO ₃ are weighed so as to be sample numbers 8 to 15 in (Table 1), and all raw materials are wet mixed at the same time with a ball mill. The subsequent sample preparation process and evaluation shall be performed in the same manner as in (Example 1).

The evaluation results are shown in sample numbers 8 to 1 of (Table 2).
5 shows. As is clear by comparing the characteristic values of the sample numbers 8 to 15 in (Table 2), deterioration of the characteristic was not observed for the sample numbers 10 to 13 whose compositions are within the range of the present invention.
It can be seen that the reduction resistance is excellent.

Example 3 First, each raw material is weighed so as to have the composition of (Chemical formula 3) and wet-mixed by a ball mill.

[0030]

Embedded image

The mixture is then dried and then 1050 ° C.
Calcination for 2 hours. CaZrO ₃ is weighed and added to the calcined powder so as to have the composition of sample Nos. 16 to 20 in (Table 1), and wet mixed in a ball mill. After the mixture is dried, it is granulated, shaped and fired to form an electrode in the same manner as in (Example 1) to obtain a positive temperature coefficient thermistor. The electrical characteristics and reduction resistance performance of the obtained PTC thermistor are evaluated in the same manner as in (Example 1). The evaluation results are shown in Sample Nos. 16 to 20 of (Table 2).

From these results, it was found that by adding CaZrO ₃ after calcination within the scope of the present invention, a positive temperature coefficient thermistor having further excellent reduction resistance performance can be obtained.

(Embodiment 4) Each raw material is weighed so as to have the composition of (Chemical formula 4) and wet-mixed by a ball mill.

[0034]

[Chemical 4]

Next, after drying this mixture, 1050 ° C.
Calcination for 2 hours. CaZrO ₃ and P were added to this calcined powder.
bSiO ₃ is weighed and added so as to have the composition of sample Nos. 21 to 28 in (Table 1), and wet mixed in a ball mill. After drying the mixture, granulation, as in (Example 1),
The PTC thermistor is obtained by forming and firing and forming electrodes. The electrical characteristics and reduction resistance performance of the obtained PTC thermistor are evaluated in the same manner as in (Example 1). The evaluation results are shown in sample numbers 21 to 28 of (Table 2).

From these results, it is understood that by adding CaZrO ₃ and PbSiO ₃ after calcination within the scope of the present invention, a positive temperature coefficient thermistor having further excellent reduction resistance can be obtained.

(Example 5) In (Example 4), the amounts of CaZrO ₃ and PbSiO ₃ added to the calcined powder and the particle size were adjusted so that the particle size ratio shown in Table 3 was obtained.
A sample is prepared in the same manner as in (Example 4).

[0038]

[Table 3]

Further, the electrical characteristics and reduction resistance performance of the obtained positive temperature coefficient thermistor are evaluated in the same manner as in (Example 1). The evaluation results are shown in (Table 4).

[0040]

[Table 4]

From these results, it is understood that by controlling the particle sizes of CaZrO ₃ and PbSiO ₃ within the scope of the present invention, a positive temperature coefficient thermistor having excellent reduction resistance can be obtained.

[0042]

As described above, the reduction resistance performance is improved by adopting the constitution of the present invention. The reason is that the addition of CaZrO ₃ promotes the densification of the sintered body itself, the degree of contact with the reducing substance is reduced, and the packing property of the unit cell itself is improved. It is thought that this is because it became difficult to release.

As a result, by using the positive temperature coefficient thermistor of the present invention, even when used in a reducing atmosphere or the like, there is no deterioration in PTC characteristics such as a large decrease in resistance value or a marked decrease in resistance temperature coefficient. Therefore, it can be expected that the range of use will be expanded without limiting the range of use as in the past.

On the other hand, conventionally, various measures have been taken in structural design such as providing a cover such as a protective case for protecting the element from a reducing atmosphere, or making a sealed structure. By using the thermistor, these structural designs are unnecessary, so that the number of steps can be reduced and the cost can be reduced, and its industrial utility value is great. Further, in terms of safety, the PTC thermistor of the present invention is extremely reliable because it does not cause thermal runaway and destruction of the PTC thermistor because there is no deterioration in its characteristics.

Claims (6)

[Claims] 1. A thermistor element and an electrode provided on the surface of the thermistor element, wherein the thermistor element comprises:
Main component 1m consisting of barium titanate or its solid solution
With respect to ol, at least one kind of oxides of rare earth elements or oxides of Nb, Sb, and Bi as auxiliary components, oxides of Si, Mn, and Al, and CaZrO ₃ of 0.05 to 0.25 mol. A positive temperature coefficient thermistor formed of the contained one. 2. A thermistor element and the thermistor element
And an electrode provided on the surface of, the thermistor element,
Main component 1m consisting of barium titanate or its solid solution
or an oxide of a rare earth element as an accessory component to ol
Is at least one of Nb, Sb, and Bi oxides
And Mn and Al oxides and CaZrO ₃To 0.05
~ 0.25 mol, PbSiO₃0.005-0.0
A positive temperature coefficient thermistor formed by containing 4 mol. 3. At least one of an oxide of a rare earth element or an oxide of Nb, Sb, Bi as a subcomponent with respect to the main component made of barium titanate or a solid solution thereof.
Calcination is performed by adding the types and oxides of Si, Mn, and Al, and then CaZrO ₃ is added to the calcined powder as the main component 1 m.
A method for producing a positive temperature coefficient thermistor, in which 0.05 to 0.25 mol is added to and mixed with ol, and the mixture is molded and fired to form an electrode. 4. The method for manufacturing a positive temperature coefficient thermistor according to claim 3, wherein CaZrO ₃ has a particle size larger than that of the calcined powder. 5. At least one of an oxide of a rare earth element or an oxide of Nb, Sb, or Bi as a subcomponent with respect to the main component made of barium titanate or a solid solution thereof.
Calcination is performed by adding the kind and each oxide of Mn and Al. Then, Ca is added to the calcined powder with respect to 1 mol of the main component.
A method for manufacturing a positive temperature coefficient thermistor, in which ZrO ₃ is added in an amount of 0.05 to 0.25 mol, PbSiO ₃ is added in an amount of 0.005 to 0.04 mol, and the mixture is molded and fired to form an electrode. 6. The method for producing a positive temperature coefficient thermistor according to claim 5, wherein CaZrO ₃ and PbSiO ₃ have a particle size larger than that of the calcined powder.