JPH1129358A - Positive characteristic thermistor material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the material large in the increase range of specific resistance on the rise of temperature by combining one or more kinds of metals selected from Bi, Pb, Zn, Al and Sn with one kind or more insulating ceramics to form a composite. SOLUTION: This thermistor material comprises a composite of the formula: xM(1-x)Cer [(x) is 0.05-0.9; M is a metal; Cer is an insulating ceramic] obtained by combining one more kinds of metals selected from Bi, Pb, Zn, Al and Sn with at least one or more kinds of insulating ceramics. This thermistor material has a small specific resistance of 10<-3> to 10<-2> in a normal state, but has a relatively wide increase width of the specific resistance on the rise of temperature. The insulating ceramic includes tantalum oxide, alumina, silica, aluminosilicates, feldspar, silica, kaolin, forsterite, a ceramic obtained adding an alkaline earth metal to steatite, and a ceramic obtained by adding clay, CaO and MgO to alumina.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel PTC thermistor (PTC thermistor) applied to a device for preventing heating of electronic and electric products and for a safety device, and relates to a device for starting a heater, a motor, etc., a degaussing circuit for a TV, and the like. It is suitable for use in a general positive characteristic thermistor such as the above.

[0002]

2. Description of the Related Art A thermistor has a temperature coefficient.
There are a negative characteristic thermistor (NTC thermistor) and a positive characteristic thermistor (PTC thermistor). A negative temperature coefficient thermistor is a material that has a negative temperature coefficient and decreases in specific resistance with increasing temperature, while a positive temperature coefficient thermistor is a material that has a positive temperature coefficient and a specific resistance increases rapidly at a specific temperature. is there.

As a typical material of the positive temperature coefficient thermistor, there is a BaTiO ₃ ceramic. This is Ba
A rare earth transition element such as yttrium or lanthanum or a pentavalent transition metal element such as niobium or tantalum is added to a non-conductive oxide such as TiO ₃ as a doping material for converting the oxide into a semiconductor, followed by firing. It was done. Also, composites of a conductive filler and a polymer are known.

Further, an oxide composed of a bismuth layered structure in which a part of Ti of the composition represented by Bi ₄ Ti ₃ O ₁₂ is substituted with Nb (Japanese Patent Laid-Open No. 6-163204);
It is known that a predetermined oxide containing bismuth oxide and titanium oxide is partially replaced with at least one of niobium oxide, tantalum oxide and antimony oxide (Japanese Patent Laid-Open No. 6-283308).

[0005]

Conventionally, various positive temperature coefficient thermistors as described above have been known. In these positive temperature coefficient thermistors, the specific resistance increases as the temperature rises. From the conductive region to the semiconductor region,
Alternatively, it can be obtained by a phase change from a semiconductor region to an insulating region.

[0006] Here, those which are in the conductive region in a normal state have a problem that the rise of the specific resistance is small. Meanwhile, those in the semiconductor region in normal state is wider rise in resistivity, a resistivity of 10 ^-1 to 10 about ² Omega · cm at normal, it is impossible to flow a large current. In this case, it is difficult to handle a large current, and there is a limit to the use of a large-capacity heater or the like.

In view of such circumstances, the present invention provides a new positive electrode having a specific resistance of 10 ⁻³ to 10 ⁻² Ω · cm in a normal state and a relatively wide range of increase in the specific resistance when the temperature rises. It is an object to provide a characteristic thermistor material.

[0008]

SUMMARY OF THE INVENTION The present invention for solving the above-mentioned problems is based on at least one kind of metal (M) selected from Bi, Pb, Zn, Al and Sn, and an insulating ceramic (Cer). A positive temperature coefficient thermistor material comprising a composite compounded with at least one of the above materials.

Here, the insulating ceramics include:
For example, tantalum oxide (Ta ₂ O ₅ ); alumina (Al ₂
O ₃ ); silica (SiO ₂ ); aluminosilicate; feldspar (K
₂ O.Al ₂ O ₃ .6H ₂ O); silica (SiO ₂ ); kaolin; steatite (talc (3MgO.4SiO ₂ .H)
Ceramics made by adding a small amount of alkaline earth metal to ₂ O); Forsterite (2MgO.SiO ₂ ); Ceramics made by mixing at least one of clay, CaO and MgO with alumina (Al ₂ O ₃ ); Ceramics added with at least one of zirconium silicate and clay; and ceramics added with Nb or the like to titania (TiO ₂ ), and at least one selected from these can be used.

Further, select Bi as the metal, was selected Ta ₂ O ₅ as a ceramic, Bi-Ta ₂ O ₅ is particularly preferred.

Further, the composite may be, for example, xM
It is represented by (1-x) Cer, and x is preferably in the range of 0.05 to 0.9, particularly preferably in the range of 0.25 to 0.5. If it is smaller than this range, a conductive path will not be formed in the composite, while if it is larger than the range, the properties of the metal alone will be strong and the characteristics as a positive temperature coefficient thermistor will not be remarkably exhibited.

The present invention makes use of the fact that metals such as Bi, Pb, Zn, Al, and Sn have the property that the specific resistance rises sharply when heated to the melting point, and this is used as a predetermined ceramic which is an insulator. By combining these, a new PTC thermistor is obtained.

The conductivity of the composite of the present invention is established by forming a conductive path of a metal in the composite. Therefore, the specific resistance under normal conditions is 10 ^−3.
It is as small as 10 ^-2 Ω · cm.

On the other hand, when the composite of the present invention is heated to a temperature close to the melting point of the metal, the specific resistance of the conductive path sharply increases, thereby increasing the resistance of the entire composite. It begins to occur and the resistance of the composite rises further. As a result, the positive characteristic of the thermistor is exhibited, but the rise width at this time is relatively large, and preferably about 10 ⁵ to 10 ⁷ .

In the composite of the present invention, the electric resistance can be controlled by the resistance of the metal, the type of the ceramics to be mixed, and the ratio thereof, and the temperature at which the specific resistance increases can be controlled by the type of the metal used. .

The positive temperature coefficient thermistor material of the present invention comprises Bi,
A metal selected from Pb, Zn, Al, and Sn;
_{Ta 2 O 5, Al 2 O} 3, and at least one ceramic selected from SiO ₂ were mixed at a predetermined ratio,
The mixture can be manufactured by sintering and compounding. Since such a composite is more advantageous in high density, it is particularly preferable to perform sintering by spark plasma sintering (pulse current pressure sintering). Of course, the present invention is not limited to this.
It may be sintered in a normal furnace at about 0 ° C.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.

(Examples 1 to 4) xBi- (1-x) T
Production of iO ₂ Composite Bi and Ta ₂ O ₅ were mixed with each other, as shown in Table 1 below, where x was 0.
It was weighed at a molar ratio of 30, 0.20, 0.10, and 0.05, and mixed in an agate mortar for 30 minutes. Each mixture has an outer diameter of 40 mm, an inner diameter of 20 mm, and a height of 40 mm
, And pressurized at 400 kg / cm ² while holding both sides with a punch rod having an outer diameter of 20 mm. In this state, a pulse energization of ON / OFF = 12/2 is performed,
900 ° C. at 100 ° C./min under reduced pressure of 10 ⁻² Torr
To 950 ° C at a rate of 50 ° C / min.
It cooled and the composite of Examples 1-4 was manufactured.

(Examples 5 to 10) xBi- (1-x)
Production of Ta ₂ O ₅ Composite Bi and Ta ₂ O ₅ were mixed with each other, as shown in Table 1 below, in which x was 0.
20, 0.30, 0.40, 0.50, 0.70,.
Example 1 described above, except that it was weighed at a molar ratio of 80
The composites of Examples 5 to 10 were produced in the same manner as in Examples 4 to 4.

(Examples 11 to 12) xBi- (1-
x) Production of Al ₂ O ₃ Composite Bi and Al ₂ O ₃ were mixed with each other, as shown in Table 1 below, in which x was 0.
The composites of Examples 11 and 12 were manufactured in the same manner as in Examples 1 to 4 except that the molar ratios were 30 and 0.40.

(Examples 13 to 16) In addition, xM-
(1-x) Production of Cer Composite Pb, Zn, Sn and Al ₂ O ₃ were weighed at the molar ratios shown in Table 1 below, and were weighed in the same manner as in Examples 1 to 4.
Sixteen composites were produced.

(Specific Resistance Temperature Characteristic Measurement Test) Examples 1 to 1
The specific resistance / temperature characteristics of the sample composed of each composite of No. 6 were measured as follows using a direct current two-terminal method.

First, both electrodes were formed on both surfaces of each sample by gold vapor deposition, and a platinum wire was held tightly on these electrodes by an alumina plate. Thereafter, while raising and lowering the temperature in the air, an electric field of 5 mV / cm was applied, the current flowing through each sample was measured, the specific resistance ρ was obtained, and the specific resistance change width Δ was obtained. In addition, as a measuring device, a generator (Adpantest R6142) and a digital multimeter (Advantest R6452E) were used.

Here, the specific resistance ρ and the specific resistance width Δ were obtained from the following equations.

[0025]

Ρ = (E / I) × (S / h) E: applied charge I: current flowing through the sample S: cross-sectional area of the sample h: thickness of the sample

[0026]

## EQU2 ## Δ = log (ρ _MAX / ρ _MIN ) ρ _MAX : maximum specific resistance in the heating process ρ _MIN : minimum specific resistance in the heating process

[0027]

[Table 1]

(Test Results) Example 1 of Bi and TiO ₂
1 to 4, as shown in Table 1 and FIG. 1, the specific resistance in a normal state is as small as 10 ⁻¹ to 10 ⁻³ Ω · cm, and the specific resistance change width is not so large. The characteristics were shown. In Example 4, where x was 0.05, the properties were almost similar to those of titanium oxide, and no remarkable properties were observed.

In Examples 5 to 10 of Bi and Ta ₂ O ₅ ,
As shown in Table 1 and FIGS. 2 and 3, the specific resistance in the normal state is 1
⁰ 0 ~10 ^-4 Ω · cm and less, also, the resistivity variation was also large as 4-6. In particular, Examples 6 to 8 where x is 0.3 to 0.5 exhibited ideal characteristics of the positive temperature coefficient thermistor.

Examples 11 and 12 of Bi and Al ₂ O ₃
Is, as shown in Table 1 and FIG.
^The resistivity was as small as about ^-2 Ω · cm, and the specific resistance change width was as large as about 5, showing characteristics as a positive temperature coefficient thermistor.

Examples 13 and 14 of Pb and Al ₂ O ₃
As shown in Table 1 and FIG.
^It is as small as ^-2 Ωcm, and the specific resistance change width is 3-4.
It was relatively large and showed characteristics as a positive temperature coefficient thermistor.

In Example 15 of Zn and Al ₂ O ₃ , as shown in Table 1 and FIG. 6, the specific resistance in the normal state was 10 ⁻³ Ω · cm.
Although the specific resistance change width was as small as about 1 and not as large as about 1, it exhibited characteristics as a positive temperature coefficient thermistor.

In Example 16 of Sn and Al ₂ O ₃ , as shown in Table 1 and FIG. 7, the specific resistance in a normal state was 10 ^-1 to 10 ^-3.
Although it was as small as about Ω · cm, and the specific resistance change width was not so large, it exhibited characteristics as a positive temperature coefficient thermistor.

[0034]

As described above, the positive temperature coefficient thermistor material of the present invention has a specific resistance in a normal state of 10 ⁻³ to 10 ⁻² Ω ·.
cm and a relatively wide range of increase in specific resistance when the temperature rises, and it is an excellent material that can be used for large current applications.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between temperature and specific resistance in composites of Examples 1 to 4.

FIG. 2 is a diagram showing a relationship between temperature and specific resistance in composites of Examples 5 to 8.

FIG. 3 is a diagram showing the relationship between temperature and specific resistance in composites of Examples 9 and 10.

FIG. 4 is a diagram showing a relationship between temperature and specific resistance in composites of Examples 11 and 12.

FIG. 5 is a diagram showing the relationship between temperature and specific resistance in composites of Examples 13 and 14.

FIG. 6 is a diagram illustrating a relationship between temperature and specific resistance in a composite of Example 15.

FIG. 7 is a diagram showing a relationship between temperature and specific resistance in a composite of Example 16.

Claims (5)

[Claims] 1. A composite made of a composite of at least one metal (M) selected from Bi, Pb, Zn, Al, and Sn and at least one metal selected from insulating ceramics (Cer). A positive temperature coefficient thermistor material. 2. The method according to claim 1, wherein the ceramic is tantalum oxide (Ta ₂ O ₅ );
₂ O ₃ ); silica (SiO ₂ ); aluminosilicate; feldspar;
Silica; Kaolin; Ceramics made by adding alkaline earth metal to steatite; Forsterite; Ceramics made by mixing at least one of clay, CaO and MgO with alumina; Zircon added with at least one of zirconium silicate and clay A positive temperature coefficient thermistor material, wherein the positive temperature coefficient thermistor material is at least one selected from the group consisting of ceramics obtained by adding Nb to titania. 3. The method according to claim 1, wherein the metal is Bi,
The positive temperature coefficient thermistor material, wherein the ceramic is Ta ₂ O ₅ . 4. The positive temperature coefficient thermistor material according to claim 1, wherein said composite is represented by xM (1-x) Cer, and said x is 0.05 to 0.9. . 5. The method according to claim 4, wherein x is 0.25.
A positive temperature coefficient thermistor material characterized by being 0.5 to 0.5.