JPH06251906A - Composition for thermistor - Google Patents

Abstract

PURPOSE:To increase the B constant by a method wherein the component ratio of Mn, Co, Zn of the title composition for thermistor comprising respective oxides of Mn, Co, Zn may be contained within a specific range. CONSTITUTION:Within the composition for thermistor comprising respective oxides of Mn, Co, Zn having the composition of Mn+Co+Zn=100%, the component ratio is contained within a specific range of Mn 20-60mol.%, Co 13.3-66.7mol.% and Zn 3.3-50mol.%. Through these specifications, the requirements for the specific resistance and the B constant of the thermistor can be met thereby enabling the title composition for thermistor having the least temporal change in the resistance value of heat resistance test and excellent reliability upon high temperature to be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermistor composition, and more particularly to a thermistor composition used for a temperature measuring thermistor, a temperature compensating thermistor, a rush current preventing thermistor and the like.

[0002]

2. Description of the Related Art Conventionally, as the thermistor composition of this type, two or more kinds of transition metal oxides such as manganese, cobalt and nickel are selected and mixed at a predetermined compounding ratio to produce a raw material of 900- A composite oxide ceramic obtained by firing at 1400 ° C. is known.

Further, in this type of thermistor composition, there is a demand for a thermistor composition having a wide range of specific resistance. In response to this request, iron, aluminum, titanium and magnesium are added to increase the resistance. Alternatively, the resistance of the thermistor was adjusted by adding copper to reduce the resistance.

Since the thermistor is a resistor sensitive to temperature, it is characterized by a large change in resistance value with respect to temperature. That is, the higher the temperature coefficient (B constant), the better the performance as a thermistor.

[0005]

A composition for a thermistor obtained by selecting two or more kinds of transition metal oxides such as manganese, cobalt and nickel has a specific resistance (ρ ₂₅ Ω.
cm) and B constant (K) have a certain relationship, and Mn-Co
Taking the case of the Ni-based composition as an example, the B constant obtained as shown by the white circle in FIG. 2 is in a state that it is roughly determined by the specific resistance, and the composition for thermistor in which the B constant is further improved. As shown in FIG. 2, there is a problem in that it is difficult to obtain a composition for a thermistor that falls into the right side region from the right side dotted line, that is, the region having a high B constant.

The present invention solves the above problems, and provides a thermistor composition having a specific resistance value satisfying the value of a thermistor and further improving the temperature characteristics as compared with the B constant of the conventional composition. With the goal.

[0007]

DISCLOSURE OF THE INVENTION As a result of intensive studies to achieve the above object, the present inventors have found that cobalt (C) in (Mn.Co) ₃ O ₄ which is a typical conventional thermistor composition.
o) is iron (Fe), magnesium (Mg), titanium (T
i), aluminum (Al), or zinc (Zn) is substituted with any metal element to prepare compositions having different composition ratios (molar ratios of metal elements), and the specific resistance value is measured.
The constants were also measured, the respective relationships were investigated, and the results are shown as a characteristic diagram in FIG. As a result of the investigation, it was found that when the cobalt in the conventional composition (Mn.Co) ₃ O ₄ was replaced with zinc, a high specific resistance value was obtained and the B constant was also improved.

The present invention has been made on the basis of such findings, and the thermistor composition is composed of oxides of manganese, cobalt and zinc, and manganese + cobalt + zinc = 1.
A composition having a composition of 00 mol%, the composition ratio of which is 20 to 60 mol% of manganese and 13.3 to cobalt.
It is characterized in that it is in the range of 66.7 mol% and zinc 3.3 to 50 mol%.

What is known so far is the mechanism of obtaining a high specific resistance value and improving the B constant when zinc is substituted for cobalt in the conventional composition (Mn.Co) ₃ O ₄ . Nickel (Ni), Iron (F
e), magnesium (Mg), titanium (Ti), and aluminum (Al) occupy the B site of the manganese-cobalt oxide spinel (a part of the Mg occupies the A site),
Since zinc (Zn) is filled with 10 3d electrons,
It is considered that this is because it is said that all of them enter the A site SP ³ instead of entering the B site d ² SP ³ . However, further research is needed to clarify the exact mechanism.

[0010]

[Function] The reason why the composition ratio of manganese, cobalt, and zinc of the thermistor composition composed of oxides of manganese, cobalt, and zinc is selected within the above range is that the thermistor composition is configured within the above range. This is because the material can satisfy both the specific resistance value and the B constant in any of them. In other words, if the composition ratio of manganese, cobalt, and zinc of the composition is out of the range of the present invention, these target values cannot be achieved.

[0011]

EXAMPLES Specific examples of the thermistor composition of the present invention will be described below together with comparative examples.

Experimental Example First, manganese oxide (Mn ₃ O ₄ ), cobalt oxide (Co ₃ O ₄ ), and zinc oxide (ZnO) each having a purity of 99.9% or more were prepared as raw materials. Next, each raw material was weighed so as to have the amounts shown in Table 1 (the composition ratio was the molar ratio of metal elements in the oxide).

Then, each raw material blended as shown in Table 1 was prepared by a ball mill using urethane balls as cobblestones.
Wet mixed for 5 hours. The mixture was calcined in a porcelain crucible in air at a temperature of 1000 ° C. for 2 hours, and then wet-milled again by the ball mill to obtain a powder mixture. Polyvinyl alcohol was added as an organic binder to this powder mixture, and the mixture was granulated and press-molded with a dry molding press at a pressure of 5 t / cm ^{2 to} obtain a diameter of 6 mm and a thickness of 1 m.
A disk-shaped molded product of m was prepared.

The molded product thus prepared was adjusted to a composition of the molded product in air on an alumina setter at a temperature of 1100 ° C. to 1 ° C.
A porcelain for a thermistor was prepared by firing at 300 ° C. for 2 hours. After applying a certain area of Ag-Pd electrode paste on the front and back surfaces of the prepared thermistor porcelain, it is baked in air at a temperature of 850 ° C. to form an electrode, and a lead wire is attached on the electrode with eutectic solder. Then, various thermistor elements having different composition ratios of manganese, cobalt and zinc were prepared.

The resistance value (R ₂₅ ) at a temperature of 25 ° C. was measured for each of the thermistor elements produced by the above method by a measuring machine (current source 224 [made by Keithley Co.] and digital multimeter 195A [made by Keithley Co.]).
Then, the resistance value (R ₈₅ ) at a temperature of 85 ° C. was measured, and the specific resistance ρ ₂₅ (Ω · cm), the thermistor B constant (K), and the resistance change rate (%) were obtained from the respective measured values. The specific resistance obtained,
Table 1 shows the B constant and the rate of resistance change.

[0016]

[Table 1]

In Table 1, no mark (no * mark) is a composition within the composition range of the present invention, and a marked mark is a composition whose composition is outside the range of the present invention.

The specific resistance of the thermistor is the resistance value (R ₂₅ ) at a temperature of 25 ° C. and the shape (diameter, thickness) of the thermistor element.
Sought by.

Further, the B constant of the temperature characteristic of the thermistor was obtained from the resistance value (R ₂₅ ) at a temperature of ₂₅ ° C. and the resistance value (R ₈₅ ) at a temperature of 85 ° C. by the following equation (Equation 1).

[0020]

[Equation 1]

The rate of change in resistance (elapsed characteristic) was measured by first measuring the resistance value (R ₂₅ A) at a temperature of 25 ° C.
After being left for 1000 hours in a constant temperature bath maintained at 5 ° C., the resistance value (R ₂₅ B) of the sample was measured again at a temperature of 25 ° C., and the resistance value before and after being left was determined by the following formula (Equation 2).

[0022]

[Equation 2]

The result of the specific resistance value of sample No. 1 in Table 1 is unmeasurable because the resistance value of the sample is 20.
This is because 0 MΩ or more, and therefore, the B constant and the resistance change rate of Sample No. 1 were stopped. In addition, in the column of the resistance change rate, the change rate value not displayed (blank) is not described because the effect of improving the B constant value cannot be seen.

FIG. 1 is a ternary diagram showing the composition ratio of each composition having various compositions of manganese, cobalt and zinc. The numbers plotted in FIG. 1 are the sample numbers in Table 1, and the samples plotted on the line surrounded by the bold line in the ternary system diagram of FIG. 1 and within the composition range surrounded by the bold line are the samples of the present invention. It is a composition within the composition range. Further, the composition range of the composition ratio of manganese, cobalt, and zinc of the thermistor composition of the present invention is shown by the composition point position in the ternary system diagram (see FIG. 1) as follows.

[0025] The composition ratio is mol%.

Further, the specific resistance and B constant of each sample of the above experimental example are plotted in FIG. 2 for each sample number (black circle). In addition, the specific resistance and B constant of the conventional manganese-cobalt-nickel-based thermistor composition are plotted in FIG. 2 for reference (open circles).

As is clear from Table 1, FIG. 1 and FIG. 2, within the composition range of the present invention (Table 1 is unmarked, FIG. 1 is in bold line,
The composition for the thermistor in the region on the right side of the dotted line in FIG. 2) has a high rate of change in resistance of ± 3% even when exposed to a high temperature of 125 ° C. for a long time, and has a high reliability against the conventional temperature. Comparing the composition of manganese-cobalt-nickel oxide with the same specific resistance value, the B constant (K) value of the composition of the present invention is the B constant of the composition of conventional manganese-cobalt-nickel oxide. It can be seen that the value is improved by 500K or more than the numerical value. On the other hand, compositions having a composition ratio outside the range of the present invention, for example, Sample Nos. 3, 22 and 33 in Table 1 above, have characteristic values equivalent to those of conventional manganese-cobalt-nickel oxides. Therefore, the effect of improving the B constant value cannot be seen. Further, although the sample No. 20 has a good B constant value, it has a low specific resistance value and a large resistance change rate, and is not suitable for practical use.

[0028]

As described above, according to the present invention, the specific resistance and B constant as a thermistor can be satisfied, and the B constant is 4060K to 5050K within the specific resistance value range of 300Ω · cm to 80KΩ · cm. , Conventional manganese-
500K compared to the B constant of cobalt-nickel composition
It is possible to provide a composition for a thermistor which is improved in reliability with respect to a high temperature, that is, a change in resistance with time in a heat resistance test at 125 ° C., that is, a rate of change in resistance of ± 3% or less. is there.

[Brief description of drawings]

FIG. 1 is a ternary system diagram showing a composition range of a composition for a thermistor of the present invention,

FIG. 2 Mn—Co—Zn composition and Mn—Co
A characteristic value plot showing the relationship between the specific resistance value of the Ni-based composition and the B constant,

FIG. 3 is a characteristic diagram showing a relationship between a specific resistance value and a B constant when Co in the Mn—Co-based composition is replaced with another metal element.

Claims (1)

[Claims] 1. A composition comprising oxides of manganese, cobalt, and zinc and having a composition of manganese + cobalt + zinc = 100 mol%, the composition ratio of which is 20 to 60 mol% of manganese and 13 of cobalt. The thermistor composition is characterized by being in the range of 0.3 to 66.7 mol% and zinc in the range of 3.3 to 50 mol%.