JPH03271153A - Composition for theremistor - Google Patents

Abstract

PURPOSE:To reduce the variation ratio of resistance of a thermistor by adding CrO and FeO to oxides of Mn, Co and Cu having specific metallic element ratios. CONSTITUTION:A mixed oxide produced by compounding MnO, CoO and CuO in such a manner as to get a mixture containing 15-70atom% of Mn, 25-80atom% of Co and <=25atom% of Cu (in terms of metallic element: the sum of the elements is 100 atom%) is added with 0.01-10wt.% each of CrO and FeO and the composition is mixed in wet state. The mixture is dehydrated, dried, crushed, calcined, pulverized, mixed with a proper amount of a binder such as PVA, kneaded, granulated and compression-molded. The molded article is heat-treated to remove the binder and subjected to main calcination in air at a prescribed temperature to obtain a composition for thermistor exhibiting small variation ratio of resistance even after the use over a long period at a high temperature, i.e., at 125 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a composition for a thermistor that has a small rate of change in resistance when used at high temperatures.

[Conventional technology]

Conventionally, manganese has been used as a thermistor composition consisting of an oxide semiconductor whose main component is manganese oxide.

A composition consisting of an oxide containing cobalt and copper is used.

[Problem to be solved by the invention]

However, in thermistor compositions made of oxides of three metal elements, manganese-cobalt-copper, there is a problem that compositions with a large mixing ratio of copper have a large rate of change in resistance when used at high temperatures.

Therefore, it is an object of the present invention to provide a thermistor composition comprising a manganese-cobalt-copper oxide having a small rate of change in resistance when used at high temperatures.

[Means to solve the problem]

In order to solve the above problems, the inventors of the present invention conducted intensive research and found that the ratio of only metal elements was 15 to 70 at% of manganese.
Cobalt: 25 to 80 atoms 2 degrees Copper: 25 atoms z or less (not including 0 atoms), making an oxide consisting of 100 atoms 2 in total.

0.01-10% by weight of chromium oxide and iron oxide each
It has been found that the purpose stated in #2 can be achieved by adding the above.

〔Example〕

The present invention will be described in detail.

Manganese oxide, cobalt oxide, steel oxide, chromium oxide, and iron oxide are weighed and blended so that the bottom of the boat after sintering has the composition ratio shown in Table 1, and mixed in a bowl at 16:00.

Afterwards, it is dehydrated and dried, and ground into powder using a mortar and pestle.

Next, put this powder in an alumina sagger and add 800 to 1000
Temporarily bake at ℃ for 2 hours.

After finely pulverizing the calcined body in a ball mill, it is dehydrated and dried.

Polyvinyl alcohol (27 people) was added as a binder, and the mixture was granulated using a mortar and pestle, and then pressure-molded into a disc shape with a diameter of 16 squares and a thickness of 2.5 cm.

Next, the binder is removed by heating at 600° C. for 2 hours in the air, and then main firing is performed in the air at a temperature of 1000 to 1400° C. for 2 hours to obtain a sample.

Screen print Ag paste on both sides of the obtained sample and bake at 800°C to form electrodes. Using the DC 4-terminal method, each completed sample has a resistance value (R25) of 25°C and a resistance value of 85°C. Measure the resistance value (R85) of
Using equation (2), the B constant (B25/85), (3
) was used to calculate the coefficient of variation (C,'V,) of the characteristic values, and the results shown in Table 1 were obtained.

Furthermore, the resistance value of each sample was measured after a high temperature storage test at 125°C for 1000 hours, and the resistance change rate (
ΔR25) was calculated, and the results shown in Table 1 were obtained.

R25 (Ω・an) = X R25・・・・・・
・・・・・・・・・(1) However, R25: Specific resistance at 25°C (Ω・aD) S: Electrode area (c!Ist: Thickness of sample (an) R25: Resistance value at 25°C (Ω) However, B25/85: B constant (K) R25:25
Resistance value at °C (Ω) R85: Resistance value at 85 °C (Ω) However, C6V, : Coefficient of variation (%) ~14°20
-23, 29, 30 (X mark) are outside the scope of the present invention.

As is clear from Table 1, the two thermistor compositions of the present invention have specific resistance and B constant.

Both coefficients of variation are practical values, and chromium oxide.

Due to the addition of iron oxide, the resistance change rate after storage at 125° C. for 1000 hours is as small as 5% or less, making it a very stable composition.

Next, the reasons for limiting the composition of the present invention will be explained.

Items with a manganese ratio of less than 15% have specific resistance.

The B constant, coefficient of variation, and rate of change in resistance after high-temperature storage are all large and impractical (see, for example, sample N12 in Table 1).

If the ratio of manganese exceeds 70%, both the specific resistance and the B constant are large and it is not practical (for example, sample N1 in Table 1).
(see 11).

Items with a cobalt ratio of less than 25% have specific resistance.

Both B constants are large, making it impractical (see, for example, sample N111 in Table 1).

Items with a cobalt ratio of over 80% have a large specific resistance, B constant, coefficient of variation, and rate of change in resistance after high-temperature storage.
It is not practical (for example, see sample N111 in Table 1).

If the proportion of steel exceeds 25%, the specific resistance is too low and the practicality is poor (see, for example, sample No. 3 in Table 1).

As mentioned above, compositions outside these ranges have significantly increased or decreased characteristic values as a thermistor and are of poor practical use.

The amount of chromium oxide and iron oxide added according to the present invention is 0.
．． 01 weight duck has a large resistance change rate of 5% or more after the high temperature storage test (for example, Table 1 samples PkL4, 5,
13, 14, 22, 23).

Furthermore, if the amount of chromium oxide or iron oxide added exceeds 10% by weight, the sinterability will be significantly reduced, and the resistance change rate under high temperature use will be less than 5%, but the coefficient of variation of the characteristic value will be 3%. Therefore, it is not practical (for example, sample NcL11 in Table 1).
, 12, 20, 21°29.30).

By the way, for example, as described in Japanese Patent Application Laid-Open No. 58-6102, Mn-Ni-Cu based thermistors have been proposed for high temperature applications, but as shown in Table 2, two of the present invention (D Mn-Co- The Cu-based Mn −Ni −
Compared to Cu-based materials, it has a low resistance in its initial electrical characteristics, so a high B constant can be obtained. Therefore, it is possible to provide a material with a high B constant and excellent reliability under high-temperature use.

A stable composition with a very small conversion rate can be obtained.

Claims (1)

[Claims] The ratio of only metal elements is 15 to 70 at% of manganese, 25 to 80 at% of cobalt, and 25 at% or less of copper (only 0
1. A composition for a thermistor, characterized in that 0.01 to 10% by weight of chromium oxide and iron oxide are added to an oxide having a total of 100 atomic% (excluding atomic%).