JPH08306509A - Positive temperature coefficient thermistor and its manufacturing method - Google Patents

Abstract

PURPOSE: To provide a high-reliability positive temperature coefficient thermistor usable for heating elements or switching elements the characteristics of which little deteriorates even when used in a reducing atmosphere. CONSTITUTION: To a main component composed of Ba titanate or its solid soln. a semiconductor element, oxides of Mn, Al and Si, and Ba(1+ X) TiO3 powder (X ranges between 0.05 and 0.03) 0.5-30mol% are added to form a compact and it is baked and electrodes are formed thereafter.

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 mixed to have a predetermined composition are mixed using a wet ball mill, a disper mill, etc., dehydrated and dried with a filter press, a drum dryer, etc., 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 softeners, organic components such as gasoline, machine oil, edible oil, seasonings, etc., and adheres to the element. There is a risk of connection. Also from the viewpoint of product assurance, it is necessary to prevent contact or adhesion with such organic components, and their intended use was limited. Therefore, the present invention can be applied to the above-mentioned applications,
It is an object of the present invention to provide a method for manufacturing a positive temperature coefficient thermistor having excellent reduction resistance.

[0004]

[Means for Solving the Problems] PT in a reducing atmosphere
The mechanism of C characteristic deterioration 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.

The present invention is the result of intensive studies on the composition and manufacturing method based on such material design.

In order to achieve the above object, the positive temperature coefficient thermistor of the present invention comprises an element and an electrode provided on the surface of the element, the element being composed of barium titanate or a solid solution thereof as a main component and a semiconducting element. As Y, La, S
At least one kind of oxide of rare earth element such as m or metal oxide such as Nb, Sb, Bi, and Si, M
n and Al oxides, and B for 1 mol of the main component
a _{(1 + X)} TiO ₃ powder (however, 0.005 ≦ X ≦ 0.0
3) is contained in an amount of 0.005 to 0.30 mol.

[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, the reason why the reduction resistance performance is improved by adopting the constitution of the present invention is that Ba _{(1 + X)} TiO ₃ (however,
0.005 ≤ X ≤ 0.03) promotes the densification of the sintered body itself, which reduces the degree of contact with the reducing substance and improves the packing property of the unit cell itself. It is thought that this is because oxygen at the lattice position is less likely to be released. 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 remarkable decrease in temperature coefficient of resistance. It is expected that the range of applications will be expanded without limiting the range of use.

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 them, the structural design becomes unnecessary, so that the man-hours can be reduced and the cost can be reduced, and the industrial utility value thereof is great. Further, in terms of safety, the element of the present invention has no deterioration of characteristics, so that it does not run away due to thermal runaway and the element is not destroyed, and is highly reliable.

[0011]

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

Example 1 The final composition is (Ba _0.8 P)
b _0.2 ) TiO ₃ + 0.002Y ₂ O ₃ + 0.02SiO ₂
Each raw material is weighed so as to be +0.0008 MnO ₂ +0.005 Al ₂ O ₃ (unit is mol). At the same time Ba
_{(1 + X)} TiO ₃ powder is weighed with the composition shown in Sample Nos. 1 to 16 of (Table 1), and all the raw materials are simultaneously wet mixed in a ball mill.

[0013]

[Table 1]

Next, after drying this mixture, 1050 ° C.
Calcination for 2 hours. Then, the calcined powder is wet-milled with a ball mill. After drying this pulverized product, 5 wt% of polyvinyl alcohol was added as a binder and granulated to obtain 800
Press molding was performed at a pressure of kg / cm ² . This molded product was fired in air at about 1300 ° C. for 1 hour to give a diameter of 20 mm,
A disk-shaped positive temperature coefficient thermistor element having a thickness of 2.0 mm was obtained. Further, these sintered bodies were plated with Ni, coated with a silver paste, and then baked to form electrodes.

This electrode is made of an ohmic metal such as N.
Any material such as i, Al, Zn, Cu may be used.

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 ), the resistance temperature coefficient (α), and the resistance change width (Ψ), as a reduction resistance evaluation, a voltage of 100 V was applied for 100 hours in nitrogen gas, and the R
₂₅ , α and Ψ were measured.

Further, the porosity was measured as an evaluation of the compactness of the sintered body. The results are shown in (Table 2).

[0018]

[Table 2]

Here, the resistance change width is a common logarithm of a numerical value obtained by dividing the maximum resistance value by the minimum resistance value, and is represented by the following formula.

Resistance change width Ψ = Log ₁₀ (maximum resistance value / minimum resistance value) Sample numbers 1 to 4, 8 to 10 and 15, 16 of (Table 1) are compositions outside the scope of the present invention. Sample numbers other than are compositions within the scope of the present invention.

As is clear from comparison of the characteristic values in (Table 2), it can be seen that the samples having the composition within the range of the present invention show no deterioration in the characteristics and have excellent reduction resistance performance.

(Example 2) First, (Ba _0.8 Pb _0.2 ) T
iO ₃ + 0.002Y ₂ O ₃ + 0.02SiO ₂ +0.00
Each raw material is weighed so as to have a composition of 08MnO ₂ + 0.005Al ₂ O ₃ (the unit is mol), and wet mixed by a ball mill. The mixture is then dried and then at 1050 ° C for 2
Calcination for an hour. Ba _{(1 + X)} TiO ₃ having a particle size larger than the particle size of the calcined powder is weighed and added to the composition of sample Nos. 17 to 21 (Table 1) in a ball mill. Wet mix. After the mixture is dried (Example 1), granulation, molding and firing are performed in the same manner to form electrodes to obtain a positive temperature coefficient thermistor element. The electrical characteristics and reduction resistance performance of the obtained device are evaluated in the same manner as in (Example 1).
The evaluation results are shown in sample numbers 17 to 21 of (Table 2). From these results, within the scope of the present invention, Ba
It was found that by adding _{(1 + X)} TiO ₃ after calcination, a device having further excellent reduction resistance performance was obtained.

By adding Ba _{(1 + X)} TiO ₃ (0.005 ≦ X ≦ 0.03) having a particle size larger than that of the calcined powder, the calcined powder and Ba ₍₁₊ ) are added. _X) The reaction of TiO ₃ is promoted.

In Examples 1 and 2, the main component B
Although a portion of aTiO ₃ in which Ba is partially substituted with Pb was used, the same effect can be obtained by using a substance in which Sr and Ca are substituted in addition to Pb.

Although Y ₂ O ₃ is used as a semiconductor element, at least one or more kinds of oxides of rare earth elements such as La, Sm and Dy or oxides of Nb, Sb and Bi are also used. You can use it. The addition amount of the main component is ((Ba _0.8 Pb _0.2 ) T in this embodiment).
0.003 to 0.005 m for 1 mol of iO ₃ ].
The range of ol is preferable.

Further, Si is 0.005 to 0.05 mo.
It is preferable to add 1 and Mn in the range of 0.001 to 0.0015 mol and Al in the range of 0.0005 to 0.005 mol. Further, a trace amount of additive such as Mn is easily mixed uniformly by mixing the raw materials in the form of an aqueous solution.

The raw material is not limited to oxides, but carbonates,
Any nitrate, hydroxide or the like that becomes an oxide when fired may be used.

The shape of the element is not limited to the disk shape, and the same effect can be obtained with any shape.

[0029]

As described above, by using the present invention, it is possible to obtain a positive temperature coefficient thermistor with less characteristic deterioration even when used in a reducing atmosphere, and its industrial utility value is great.

Claims (3)

[Claims] 1. An element and an electrode provided on the surface of the element, wherein the element is an oxide of a rare earth element or Nb, Sb as a semiconducting element with respect to a main component made of barium titanate or a solid solution thereof. At least one of Bi oxides, Si, Mn, and Al oxides;
_{(1 + X)} TiO ₃ powder (however, 0.005 ≦ X ≦ 0.03)
0.005 to 0.30 m with respect to 1 mol of the main component
A positive temperature coefficient thermistor characterized by containing ol. 2. A main component consisting of barium titanate or a solid solution thereof, and at least one of oxides of rare earth elements or oxides of Nb, Sb, Bi as a semiconducting element, and Si, Mn, Al. For the calcined powder containing each oxide, Ba _{(1 + X)} TiO ₃ powder (however, 0.005
≦ X ≦ 0.03) is 0.0 with respect to 1 mol of the main component.
A method for producing a positive temperature coefficient thermistor, which comprises adding 05 to 0.30 mol, mixing, molding, firing, and then forming an electrode on this sintered body. 3. Ba having a particle size larger than that of the calcined powder.
_The method for manufacturing a positive temperature coefficient thermistor according to claim 2, wherein _{(1 + X)} TiO ₃ is used.