JPH06325907A - Ceramic composition for thermistor - Google Patents

Abstract

PURPOSE:To obtain a thermistor element, which is stable to the partial pressure of oxygen and is good in the stability of a resistance value at a high temperature, by a method wherein a P-type semiconductor and an N-type semiconductor, whose dependences on the partial pressure of oxygen are opposite to each other, are mixed with each other. CONSTITUTION:M' shows one or two or more of elements selected from among elements belonging to group IIIa excepting La, and P<2> shows one or two or more of elements selected from among elements belonging to groups IVa, Va, VIa, VIIa and VIII, whose oxides show P-type characteristics. N<2> shows one or two or more of elements selected from among elements belonging to groups IVa, Va, VIa, VIIa and VIII, whose oxides show N-type characterstitics. A composition which is shown as M' (P<2>1-x.N<2>x)03, (x) is 0.1<=x<=0.9 is a ceramic composition for a thermistor. Thereby, it is possible to use the composition in a wide high temperature range, and a thermistor element which has a stable resistance value in either of an oxidizing atmosphere and a reducing atmosphere can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material for a thermistor having a negative temperature coefficient which is highly stable at high temperatures.

[0002]

_2. Description of the Related Art As a material for a thermistor that can be used at high temperature, (a) a material mainly composed of a corundum type crystal structure containing Al ₂ O ₃ and Cr ₂ O ₃ as a main component (for example, Japanese Patent Laid-Open No. 50-118)
No. 294, "Fine Ceramic Handbook", Kenya Hamano, Asakura Shoten, 1984), (b) MgAl ₂ O ₄ , MgCr ₂ O
₄ , a material mainly composed of a spinel type crystal structure compound such as MgFe ₂ O ₄ (for example, JP-A-49-63995), (c) Y ₂
Materials mainly composed of ZrO ₂ stabilized with O ₃ etc. (for example, “Internal Combustion Engine” Vol. 30, No. 8, page 98), (d) Mainly composed of perovskite type crystal structure compound having high melting point and conductivity Materials having a composition of La (Al _1-X Cr _X ) O ₃ system (for example, Japanese Patent Laid-Open No. 51-108298), materials used by laminating LaCrO ₃ on an insulating substrate (for example, Japanese Laid-Open Patent Publication No. 61-161701), materials in which LaCrO ₃ and MgAl ₂ O ₄ are mixed (for example, JP-A-51-95297 and JP-A-51-23691) and the like have been used.

[0003]

However, (a) a high temperature of 1650 ° C. or higher is required for sintering a material mainly composed of a corundum type crystal structure, and resistance is increased by adding another element. Although the temperature characteristics can be slightly varied, the resistance-temperature characteristics cannot be adjusted significantly. For example, when a large amount of additive is added, the stable corundum structure is lost, and there is a problem that the thermal stability deteriorates. (b) The material mainly composed of spinel type crystal structure compound is 1600
Since it is necessary to sinter at a temperature of ℃ or more, there is a problem of deterioration of the lead wire, and there is a problem that it cannot be used in a wide temperature range due to a large temperature gradient constant β. Also,
There are materials mainly composed of NiAl ₂ O ₄ (JP-A-49-29493, etc.) and materials mainly composed of CoAl ₂ O ₄ (JP-A-48-705, etc.), both of which have heat resistance. There was a problem that it was too low to be used at high temperature.

(C) Since the material mainly composed of zirconia is oxygen ion conductive, the resistance value is unstable in the atmosphere, especially in a reducing atmosphere, or the resistance value becomes large in a low temperature range, which is practically used. There was a problem that it could not be used. (d) The material mainly composed of perovskite type crystal structure compound needs to be sintered at a temperature of 1600 ° C. or higher, so that there is a problem of deterioration of the lead wire, or even a small amount of La oxide remains unreacted. In such a case, the unreacted material reacts with moisture in the atmosphere to become unstable La (OH) ₃ , which causes problems such as element collapse and unstable resistance.

The object of the present invention is to solve these problems,
By adjusting the composition of the material, a wide range of resistance values can be obtained, and by being able to sinter at a temperature of 1600 ° C or less, deterioration of the lead wire is prevented, no hygroscopic substance is contained, and the atmosphere It is an object of the present invention to provide a porcelain composition for a thermistor which has little deterioration in characteristics due to humidity or heat history and can be used in a wide temperature range from room temperature to 1100 ° C.

[0006]

[Means for Solving the Problems] As a result of earnest research by the present inventors, M ¹ is selected from elements belonging to the 3a group excluding La 1
Indicates species or two or more elements, P ² is 4a, 5a, 6a
, Oxides of elements belonging to groups 7a and 8 are one or more elements selected from elements exhibiting P-type characteristics,
N ² is one or two selected from the group of oxides of elements belonging to the 4a, 5a, 6a, 7a and 8 groups, which show N type characteristics.
In the composition represented by M ¹ (P ² _1-X · N ² _X ) O ₃ when the number of elements is ¹ or more, a porcelain composition in which X is 0.1 ≦ X ≦ 0.9 is a porcelain composition for a thermistor. It turned out to be suitable.

Particularly preferably, M ¹ is more preferably Y, Sm, Pr or N.
d, Dy, Ho, Er, Gd and Yb are one or more elements selected from Pb, and P ² is one or more elements selected from Cr, Mn, Co and Ni. As an element, N ² is Ti, V, Fe
And one or more elements selected from the group consisting of Al and Al, in the composition represented by M ¹ (P ² _1−X · N ² _X ) O ₃ , X is 0.1 ≦ X ≦ 0.9 A porcelain composition for a thermistor, which is characterized in that it is preferable. The thermistor element comprising the porcelain composition for thermistor according to the present invention has good stability of resistance value at high temperature, is less affected by the oxygen partial pressure of the atmosphere, and is used for automobiles by incorporating the thermistor element in a metal tube. It can be widely used as a sensor without special heat treatment of a metal tube.

Further, by mixing a sintering aid with the porcelain composition for a thermistor to improve the sinterability, the composition can be fired at a low temperature, and it has high strength and excellent heat resistance. Here, the sintering aid refers to a material such as silica or mullite that forms a liquid phase at grain boundaries and forms a matrix to enhance the sinterability of porcelain. Furthermore, X is 0.15 or more and 0.5
The thermistor element composed of the following porcelain composition for thermistor does not absorb moisture, has little change due to a durability test, has excellent heat resistance, and is useful because it can be easily adjusted to an optimum resistance value for practical use. .

[0009]

The material according to the present invention has a perovskite structure and can be easily replaced with each other by atoms having close ionic radii. Therefore, the replaced composition is stable and the composition can be arbitrarily adjusted within a wide range. Is something that can be done. In addition, since it does not contain La, it is not affected by the humidity of the atmosphere, etc., and has excellent stability at high temperatures. The reason is considered that the compound of the present invention is stable even at high temperature, for example, the melting point of YCrO ₃ is extremely high at about 2300 ° C.

The dependence of the p-type semiconductor and the n-type semiconductor on the oxygen partial pressure is opposite, and by mixing these two,
The characteristics are canceled by each other and stable characteristics are obtained against the oxygen partial pressure. Further, the number of lattice defects of oxygen ions or metal ions unstable to heat is reduced, and the stability of the resistance value is maintained even if a thermal history is received.

Further, the material according to the present invention can change the resistance value in a wide range by continuously adjusting the composition in a wide range, so that the resistance value and the temperature gradient constant (hereinafter referred to as β) can be freely set. There is also an advantage that you can choose.
The material according to the present invention can be sintered at a temperature of 1600 ° C or lower to prevent deterioration of the lead wire, and the sintered thermistor element can be used in a wide temperature range of 300 ° C to 1100 ° C or higher. Is something that can be done.

[0011]

[Embodiment 1] A first embodiment of the present invention will be described. First,
Y ₂ O ₃ with a purity of 99.9% or more and an average particle size of 1 μm
Cr ₂ O ₃ with an average particle size of 1 μm and a purity of 98.5% or more
%, Fe ₂ O ₃ having an average particle size of 1 μm or more is weighed so as to have the composition shown in Table 1, mixed by a wet method, dried, and then calcined by holding at 1400 ° C. for 2 hours. 1% by weight of SiO ₂ powder having an average particle size of 0.6 μm is added to the calcined powder and mixed by a wet method. Pass the mixed slurry through a 200 mesh screen and dry. After drying, PVB is 15% by weight, DBP is 10% by weight, MEK is 50% by weight and toluene is 25% by weight.
A binder consisting of wt% is added to granulate the powder for press molding.

[Table 1]

[0012] This powder was filled with a platinum wire having a diameter of 0.4 mm as a lead wire, which was placed in parallel with a 1.2 mm gap, and was pressed at a pressure of 1000 kg / cm ² . Molded into the shape shown in FIG. 1 having a diameter of 3 mm and a thickness of 2 mm and two lead wires. A thermistor element is obtained by firing the molded product in the air at 1550 ° C. About the thermistor element obtained in this way, 300 ℃, 600 ℃
And the resistance value in the atmosphere at 900 ° C was measured. next,
As a durability test, each sample was held in the atmosphere of 1000 ° C. for 300 hours, and the durability performance was examined by measuring the resistance values at 300 ° C., 600 ° C. and 900 ° C. before and after the holding. The results are shown in Table 1. As an environmental test, each sample is
The stability of the atmosphere with respect to the oxygen partial pressure was evaluated by keeping the oxygen partial pressure at 10 ° C in a test chamber at 10 ^-7 atm and measuring the resistance value at that time. The results are also shown in Table 1.

The temperature conversion values of β, resistance change rate (hereinafter referred to as ΔR rate) and ΔR rate are defined by the following equations. β = ln (R / R ₀ ) / (1 / K-1 / K ₀ ) ΔR rate = (R _t −R ₀ ) / R ₀ × 100% where ln represents the common logarithm, and R and R _0. Indicates resistance values at absolute temperatures K and K ₀ in the atmosphere. 300-650
And 650-900 are 300 ℃, 650 ℃, and 650 ℃, respectively
And β between 900 and 900 ° C are shown. Further, R _t is the absolute temperature K _t in the atmosphere after the durability test in the durability test and in the oxygen partial pressure decompression chamber in the environment test respectively (t = 300 ° C. or 900 ° C. in the durability test, t
= 900 ° C). The temperature conversion value of the ΔR rate is shown in brackets in the ΔR rate column, and is defined by the following equation. Temperature conversion value = β × K ₀ / (ln (R _t / R ₀ ) × K ₀ + β)
-K ₀

As is clear from Table 1, M ¹ (P ² _1- X.N ² _X ) O
_{In the} composition represented by ₃ and the general formula, the solid solution can be obtained by continuously changing the mixing ratio of P ² and N ² , whereby the resistance value can be easily adjusted. For example YCrO
_{This is} because by substituting the Cr site of ₃ with Fe, the resistance value and β can be increased without impairing other properties. Therefore, it is possible to easily supply a thermistor element having a resistance value or β required for practical use.

It is considered that this reaction system is a simple substitution solid solution and therefore has no by-products, and the resistance value can be easily adjusted. Further, as can be seen from the results of the durability test and the environment resistance test, it can be seen that the properties are very stable against heat history and oxygen partial pressure in the atmosphere. This is because the mixing of the p-type semiconductor material YCrO ₃ and the n-type semiconductor material Fe ₂ O ₃ reduces the amount of metal ion defects and oxygen ion defects unstable to thermal history. Conceivable. Further, since the p-type semiconductor and the n-type semiconductor show the opposite dependence on the oxygen partial pressure, it is considered that the mixing of both components cancels the oxygen partial pressure dependence.

Particularly, when X = 0.2 to 0.3, the number of lattice defects is the smallest, and as a result, the resistance change before and after the durability test is small, or the resistance change after the environmental test is small. Also, it is most suitable for use in a direction that requires high detection accuracy or in an atmosphere where the oxygen partial pressure changes.

[0017]

According to the present invention, it is possible to provide a thermistor element which can be used in a wide temperature range of 300 ° C. to 1100 ° C. and has a stable resistance value in both oxidizing and reducing atmospheres. is there. In addition, because it was possible to prevent the deterioration of the lead wire, stability at high temperature is excellent,
It can be used in a wide temperature range and has high mechanical strength.For example, an overheat detection device for an automobile exhaust gas purification catalyst, a recirculation gas temperature detection device for an exhaust gas recirculation device, or a high temperature gas temperature measurement device or vibration. It was possible to provide a porcelain composition for a thermistor which can be used as a measuring device in a severe place and as a temperature detecting device for various furnaces.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

[Explanation of symbols]

 1 Thermistor element 2 Lead wire

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiro Suematsu 14-18 Takatsuji-cho, Mizuho-ku, Nagoya, Aichi Nihon Special Ceramics Co., Ltd.

Claims (2)

[Claims] 1. M ¹ represents one or more elements selected from elements belonging to the 3a group except La, P ² represents the 4a group,
The oxides of the elements belonging to the 5a group, 6a group, 7a group, and 8 group represent one or more elements selected from the elements exhibiting p-type characteristics, and N ² represents 4a group, 5a group, and 6a. Assuming that the oxides of the elements belonging to Group 7, 7a, and 8 represent one or more elements selected from the elements exhibiting n-type characteristics, M ¹ (P ² _1-X・ N ² _In a composition represented by _X ) O ₃ , X is
A ceramic composition for a thermistor, characterized in that 0.1 ≦ X ≦ 0.9. 2. M ^{1 represents} one or more elements selected from Y, Sm, Pr, Nd, Dy, Ho, Er, Gd and Yb, and P ² represents Cr, Mn, Co. And one or more elements selected from Ni and N ² is one or more elements selected from Ti, V, Fe and Al,
In the composition represented by M ¹ (P ² _1- X.N ² _X ) O ₃ , X is
A ceramic composition for a thermistor, characterized in that 0.1 ≦ X ≦ 0.9.