JPH0737704A - Temperature sensor - Google Patents

Abstract

PURPOSE:To make small a rate of change with time of a resistance value by forming a thermistor element with an oxide of a particular spinel type structure. CONSTITUTION:A temperature sensor comprises a metallic heat resistant cap, thermistor element housed in this heat resistant cap and a lead wire which is electrically connected to the thermistor element and is also extended to the outside of the heat resistant cap. This thermistor element uses an oxide of the spinnel type structure expressed by Mgx (Al1-y-zCryMnz)2O4'0.95<=x <=1.05, 0.1<=y<=0.9, 0.1<= z<=0.9 (where, y+z<=1.0) or Mgx (Al1-y zCryMnz)2O4+a atomic CaO+b atomic rare earth metal oxide, 0.95<=x<=1.05, 0.1<=y<=0.9, 0.1<=z<=0.9, 0.1<=a<=5, 0.1<=b<=10 [ where y+z<=1.0, a and b are given the values when Mgx (Al 1-y-zCryMnz)2 is set to 100 atomic % ]. Thereby, the rate of change with time of a resistance value can be made small and heat resistant characteristics can also be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature sensor used for detecting the temperature of an exhaust gas countermeasure catalyst for an automobile, for example.

[0002]

2. Description of the Related Art In recent years, exhaust gas countermeasure catalysts have been used due to environmental problems and demands for improvement of fuel consumption. To improve the catalyst performance, it is necessary to measure the temperature of the catalyst accurately. For that purpose, the rate of change of the resistance value of the temperature sensor with time must be small, and specifically, must be suppressed within ± 20%.

Conventionally, a temperature of 300 to 700 ° C. is detected,
The thermistor element used for the temperature sensor having a heat resistance of 1000 ° C. is formed by using an Mg (Al, Cr) ₂ O ₄ based oxide.

FIG. 2 is a perspective view of the thermistor element. That is, this is the thermistor element 1 with platinum pipes 2a, 2b.
After being inserted, it is baked. This thermistor element 1
As shown in FIG. 1, the heat-resistant cap 4 was sealed to form a temperature sensor for detecting the catalyst temperature. The platinum pipes 2a and 2b were welded to the two-core tubes 3a and 3b, and the lead wires were passed through the two pipes, so that the lead wires were drawn out of the heat resistant cap 4 from the thermistor element 1.

[0005]

When the temperature is increased in the above conventional structure, the metal atoms forming the heat resistant cap 4 are bonded with oxygen in the heat resistant cap 4, and as a result, the oxygen partial pressure in the heat resistant cap 4 is reduced. Go down. Then the thermistor element 1
Oxygen is released from the cells, which acts to maintain equilibrium. Further, when a reducing gas such as hydrogen or carbon monoxide is generated from the heat resistant cap 4, it is adsorbed by the thermistor element 1, deprives oxygen and diffuses therein. As described above, when oxygen of the thermistor element 1 is lost, the structure changes, and there is a problem that the rate of change in resistance with time cannot be suppressed within ± 20%.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a temperature sensor capable of reducing the rate of change in resistance with time.

[0007]

In order to achieve this object, the temperature sensor of the present invention comprises a thermistor element formed by using an oxide having a spinel structure represented by the chemical formula (5).

[0008]

[Chemical 5]

[0009]

According to this structure, a part of (Al, Cr) of the Mg (Al, Cr) ₂ O ₄ spinel type solid solution is replaced by Mn, and as a result, electric conduction by Mn is introduced and the change in resistance value is suppressed. It seems that you can do it.

Further, by substituting a part of (Al, Cr) for Mn, the thermistor element becomes dense and it is possible to make it difficult for the reducing adsorbed gas to take away internal oxygen.

As a result of these, it becomes possible to provide a temperature sensor having a small rate of change in resistance with time.

[0012]

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings and tables. FIG. 1 is a sectional view of a temperature sensor for detecting a catalyst temperature. Since it is the same as the conventional one, the same number is attached.

FIG. 2 is a perspective view of the thermistor element 1.
The first embodiment of the present invention will be described below.

MgO, Al ₂ O ₃ and Cr in the chemical formula 5
Predetermined amounts of ₂ O ₃ and Mn ₃ O ₄ were weighed so that x, y, and z had the composition shown in (Table 1), and samples 1 to 14 were prepared.

[0015]

[Table 1]

First, Sample 1 was mixed in a ball mill for 16 hours, calcined at 1200 ° C., and then ground again in a ball mill for 18 hours. Then, after drying, 8% by weight of the whole polyvinyl alcohol aqueous solution having a concentration of 10% by weight was added for granulation. Finally, the platinum pipes 2a and 2b are formed into the shape shown in FIG.
After inserting, it was baked at 1600 ° C. Sample No. Similar manufacturing was performed for 2 to 14.

The thermistor element 1 thus obtained
Was incorporated into the temperature sensor for detecting catalyst temperature shown in FIG. The heat-resistant cap 4 and the two-core tubes 3a, 3
b is formed of SUS310S which is a heat resistant material.
Then, the resistance values at 300 ° C, 600 ° C, and 900 ° C were measured, and in Table 1, R300, R600, and R90 were measured.
It is indicated by 0. Further, after conducting a sealed durability test at 900 ° C. for 1000 hours, the resistance value at 300 ° C. was measured, and the rate of change thereof was calculated and shown as ΔR300 in (Table 1).

The rate of change in resistance was calculated using (Equation 1).

[0019]

[Equation 1]

Sample No. 1 in Table 1 Nos. 11 to 14, which are outside the scope of the claims of the present invention, the resistance value change rate is 78 to 22.
It becomes 3%, which greatly exceeds the standard ± 20%.
In addition, sample No. As in Nos. 10 and 14, the thermistor element 1 not substituted with Mn becomes porous, and the reducing adsorbed gas easily enters the grain boundaries, and the rate of change in resistance value exceeds ± 20%, which is a standard.

(Second Embodiment) A second embodiment of the present invention will be described below.

MgO, Al in the chemical formula 6₂O₃, Cr
₂O₃, Mn₃O_FourAnd CaCO₃, Rare earth oxides (Y₂O₃，
La₂O₃, CeO₂, Pr₆O₁₁, Nd₂O₃, Sm₂O₃，
Eu ₂O₃, Gd₂O₃, Tb_FourO₇, Dy₂O₃, Ho₂O₃，
Er₂O₃, Tm₂O₃, Yb₂O₃, Lu₂O₃) Is x, y,
z, a, and b should have the compositions shown in (Table 2) and (Table 3).
To the sample No. Make 15-54
I made it.

[0023]

[Chemical 6]

[0024]

[Table 2]

[0025]

[Table 3]

Then, the thermistor element 1 was obtained in the same manner as in (Example 1). It is sealed in a heat-resistant cap 4 of a temperature sensor for detecting the catalyst temperature shown in FIG.
The resistance values at 00 ° C. and 900 ° C. were measured and shown in (Table 2) and (Table 3) as R300, R600, and R900. Next, after carrying out a sealed endurance test at 1000 ° C. for 500 hours, the resistance value at 300 ° C. was measured, and the rate of change was determined by (Equation 1) (Table 2) and shown in Table 3 as ΔR300.

In this embodiment, rare earth oxide and Ca are used.
O is added to achieve densification and prevent the reducing adsorption gas from depriving the thermistor element 1 of oxygen and diffusing into it. In addition, heat resistance is also improved. Note that CaO does not form a solid solution with the main component (Chemical Formula 5) and precipitates alone at the grain boundaries. Further, the rare earth oxide is precipitated at the grain boundary as (RE) CrO ₃ having a perovskite structure. RE represents a rare earth element.

Looking at (Table 2) and (Table 3), the sample No. 1
When the added amount of CaO exceeds 5 atomic% like 7, 32 and 52, CaO scatters during firing and the high temperature thermistor element 1 becomes porous. Therefore, oxygen is easily deprived, and the rate of change in resistance with time exceeds ± 20%. In addition, sample No. 25, the addition amount of rare earth oxide is 10
When it exceeds atomic%, the amount of segregation of (RE) CrO ₃ increases. Therefore, a large amount of Cr is lost from the main component (Chemical formula 5),
The semiconductor characteristics are out of balance and the rate of change in resistance over time is ± 2.
It exceeds 0%. Sample No. If the addition amount is less than 0.1 atom% like 36, densification cannot be achieved.
The same applies to the case of CaO. As a result, the rate of change in resistance over time cannot be suppressed to within ± 20%.

(Embodiment 3) A third embodiment of the present invention will be described below.

MgO, Al ₂ O ₃ and Cr in the chemical formula 7
₂ O ₃ , Mn ₃ O ₄ , CaCO ₃ , and ThO ₂ are added to x, y, z,
A predetermined amount was weighed so that each of a and b had the composition shown in (Table 4). 55-64 were created.

[0031]

[Chemical 7]

[0032]

[Table 4]

Then, in the same manner as in Example 1, a thermistor element 1 was obtained, and the thermistor element 1 was incorporated into the heat resistant cap 4 of the temperature sensor for detecting the catalyst temperature shown in FIG.
The resistance values at temperatures of 600 ° C., 900 ° C., and 900 ° C. were measured and shown in Table 4 as R300, R600, and R900. Next, after conducting a sealing durability test at 1000 ° C. for 500 hours,
The resistance value at 300 ° C. was measured, and the rate of change was determined by (Equation 1), and shown in Table 4 as ΔR300.
As can be seen from Table 4, the same effect as that of the second embodiment is obtained.

Note that CaO and ThO ₂ do not form a solid solution with the main component (Chemical Formula 1), but precipitate alone at the grain boundaries. Also, since ThO ₂ is stable in a reducing atmosphere, when compared with rare earth oxides,
The same effect can be obtained with an addition amount of 1/10.

However, the sample No. ThO ₂ like 61
The effect is not observed unless the element is added at all, and the sinterability deteriorates rapidly when the content exceeds 10 atomic% as in the case of Sample 64, and the rate of change in resistance with time cannot be suppressed within ± 20%.

(Embodiment 4) A fourth embodiment of the present invention will be described below.

ZnO, MgO, Al ₂ in (Chemical Formula 8)
O ₃ , Cr ₂ O ₃ , CaCO ₃ , and ZrO ₂ are added to x, y, z,
Predetermined amounts were weighed so that a and b had the compositions shown in (Table 5), and sample No. 65-77 were created.

[0038]

[Chemical 8]

[0039]

[Table 5]

Similar to the first embodiment, the thermistor element 1
Of the temperature sensor for detecting the catalyst temperature shown in FIG.
Built in heat resistant cap 4, 300 ℃, 600 ℃, 9
The resistance value at 00 ° C was measured, and it was recorded in (Table 5) as R3.
00, R600 and R900 are shown. And 100
After carrying out a sealed durability test at 0 ° C for 500 hours, then at 300 ° C
The resistance value was measured and the rate of change is shown in (Table 5).
It was Also in this case ZrO ₂Example by adding
Like 2 and 3, the heat resistance is improved. Sample No. Like 67
To ZrO₂If the amount of addition of Al exceeds 30 atomic%, the sinterability will increase.
It deteriorates and the rate of change of resistance with time cannot be suppressed within ± 20%.
Yes. Sample No. ZrO like 71₂Addition amount of 0.1
If it is less than atomic%, no effect is seen.

If the composition of the main component (Chemical Formula 5) is constant, the resistance value can be widely controlled by adjusting the addition amount of ZrO ₂ .

As can be seen from Examples 1 to 4, the thermistor material used for the temperature sensor of the present invention is resistant to environmental changes. Therefore, even if the shape is changed, such as a disk type or glass-sealed disk type or glass-sealed, it can be sufficiently used as a temperature sensor.

[0043]

As described above, in the temperature sensor of the present invention, the thermistor element is formed by using the oxide of the spinel type structure represented by (Chemical formula 5) to achieve densification and to introduce electric conduction by Mn. is doing. As a result, the rate of change in resistance with time can be suppressed to a small level even if oxygen is lost.

Further, by adding CaO and a rare earth oxide, thorium oxide or zirconium oxide, it is possible to further densify. And the heat resistance of the thermistor element is also improved.

[Brief description of drawings]

FIG. 1 is a sectional view of a temperature sensor for detecting a catalyst temperature according to an embodiment of the present invention.

FIG. 2 is a perspective view of a thermistor element according to an embodiment of the present invention.

[Explanation of symbols]

 1 Thermistor element 2a, 2b Platinum pipe 4 Heat resistant cap

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takuko Hata 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. A thermistor element comprising: a metal heat-resistant cap; a thermistor element housed in the heat-resistant cap; and a lead wire which is electrically connected to the thermistor element and which is drawn out of the heat-resistant cap. Is a temperature sensor formed by using an oxide having a spinel structure represented by (Chemical Formula 1). [Chemical 1] 2. The temperature sensor according to claim 1, wherein the thermistor is formed by using a substance represented by (formula 2) instead of the oxide represented by (formula 1). [Chemical 2] 3. The thermistor element is formed by using a substance represented by (Chemical Formula 3) instead of the oxide of (Chemical Formula 1).
The temperature sensor described. [Chemical 3] 4. The thermistor element is formed by using a substance represented by (Chemical Formula 4) instead of the oxide of (Chemical Formula 1).
The temperature sensor described. [Chemical 4]