JPH06283310A - Temperature sensor - Google Patents

Abstract

PURPOSE:To suppress change with time of resistance value of a temperature sensor to a low level even when its thermistor element loses its oxygen at a high temperature by forming the element by using the solid solution of Cr2O3 having a P-type conductivity and Fe2O3 having an N-type conductivity with a high-resistance Al2O3 having a corundum structure so that the P- and N-type conductivities can coexist in the same crystal in a mixed state. CONSTITUTION:This sensor is provided with a metallic heat resisting cap 4, thermistor element 1 provided in the cap 4, and lead wires electrically connected to the element 1 and led out from the cap 4. The element 1 is formed by using a material expressed by (Al1-x-yCrxFey)2O3, 0.05<=x+y<=0.95, and 0.05<=y/(x+y)<=0.6. Therefore, change with time of resistance value of this temperature sensor can be suppressed to a low level.

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 a catalyst for exhaust gas countermeasures for automobiles.

[0002]

2. Description of the Related Art In recent years, catalysts for exhaust gas countermeasures have been used in response to environmental problems and demands for improvement of fuel consumption. However, it is necessary to accurately measure the catalyst temperature in order to improve the catalyst performance. Therefore, 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,
As a material for the thermistor element used for a temperature sensor having a heat resistance of 1000 ° C., Mg (Al, Cr) ₂ O ₄ system has been used.

FIG. 2 is a perspective view of the thermistor element. After inserting the platinum pipes 2a and 2b into the thermistor element 1, it is fired to obtain a thermistor. The thermistor element 1 is sealed in a heat resistant cap 4 of the catalyst temperature detecting sensor shown in FIG. At this time, the platinum pipes 2a, 2b are connected to the two-core pipe 3a,
3b was welded, the lead wire was passed through, and it was drawn out of the heat resistant cap 4.

[0005]

SUMMARY OF THE INVENTION In the above conventional configuration,
When the temperature rises, the metal atoms forming the heat resistant cap 4 combine with oxygen in the heat resistant cap 4 to lower the oxygen partial pressure in the heat resistant cap 4. Therefore, oxygen was released from the thermistor element 1 in order to maintain equilibrium. Further, a reducing gas such as hydrogen or carbon monoxide was generated from the heat resistant cap 4, adsorbed to the thermistor element 1, deprived of oxygen and diffused in the element 1. As described above, the structure of the thermistor element 1 is changed due to the loss of oxygen, and as a result, the rate of change in resistance with time cannot be suppressed to within ± 20%.

The present invention solves the above-mentioned conventional problems, and an object thereof is to reduce the rate of change in resistance with time.

[0007]

In order to achieve this object, the temperature sensor of the present invention is one in which a thermistor element is formed by using an oxide having a composition represented by Chemical formula 1.

[0008]

According to the above-mentioned structure, P-type conduction Cr ₂ O ₃ and N-type conduction Fe ₂ O ₃ are added to high resistance Al ₂ O ₃ having a corundum structure.
Is a solid solution. At this time, the resistance value of the P-type increases when oxygen is lost, and the resistance value of the N-type decreases, and the presence of the P-type and the N-type in the same crystal makes it possible to suppress the change in resistance value with time.

[0009]

(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 catalyst temperature. Except for the constituent material of the thermistor element 1, it has the same structure as the conventional one, so the same reference numerals are given.

FIG. 2 is a perspective view of the thermistor element 1.
Al ₂ O ₃ , Cr ₂ O ₃ , and Fe ₂ O ₃ in (Chemical formula 1) were weighed in predetermined amounts so that x and y had the compositions shown in Table 1, and sample No.
1-27 were created. First, sample No. 1 with a ball mill
Mix for 6 hours, calcine at 1200 ° C, and then use ball mill again 1
Crushed for 8 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 thermistor element 1 was obtained by molding into the shape shown in FIG. 2, inserting the platinum pipes 2a and 2b, and firing at 1600 ° C. The same operation was performed on Sample Nos. 2 to 27.

[0011]

[Table 1]

The thermistor element 1 thus obtained
In the same manner as in the conventional case, the temperature sensor for detecting the catalyst temperature shown in FIG.
The resistance values at 0 ° C and 850 ° C were measured and are shown in Table 1 as R
It is shown as 300, R600 and R850. Again 900
After conducting a sealed endurance test at 1000C for 1000 hours, then 300 ℃
The resistance value was measured and the rate of change was calculated.
It is shown as 00.

The rate of change in resistance value was calculated by using (resistance value after sealed durability test-initial resistance value) / initial resistance value x 100 (%).

When the Fe component increases and the value of y / (x + y) exceeds 0.6 as in sample No. 20 in Table 1, the resistance change rate is as large as -30%. The reason is that Fe is inferior in durability at a high temperature and exists as Fe ₃ O ₄ which is easily deprived of oxygen in a reducing atmosphere, so that the P type and the N type cannot be balanced. Moreover, when the Fe component is increased, cracks may occur.

When the Fe component is not contained at all like Sample No. 5, the N-type does not exist and the resistance value change rate is +37.
It becomes as large as%.

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

Al ₂ O ₃ , Cr ₂ O ₃ and F in the chemical formula ₂
A predetermined amount of e ₂ O ₃ and CaCO ₃ was weighed so that x, y, and a had the compositions shown in Table 2, and sample Nos. 28 to 39 were prepared.

[0018]

[Table 2]

A thermistor element 1 was obtained in the same manner as in (Example 1) except that the firing temperature was 1500 ° C.
Then, it is sealed in a heat-resistant cap 4 of a temperature sensor for detecting the catalyst temperature shown in FIG.
The resistance value at 0 ° C was measured, and it was recorded in Table 2 as R30.
It is shown as 0, R600, and R850. Next, after a sealed durability test at 900 ° C. for 1000 hours, the resistance value at 300 ° C. was measured, and the resistance value change rate was obtained as in (Example 1). It is shown in Table 2 as ΔR300. Note that C
aO does not form a solid solution with the main component (Chemical Formula 1) and exists alone at the grain boundaries. Like sample No. 39 in Table 2, the amount of CaO added is 5
When it exceeds atomic%, CaO scatters during firing and the thermistor element 1 becomes porous. Therefore, oxygen is easily deprived, and the rate of change in resistance with time exceeds ± 20%.
When the amount of CaO added is less than 0.1 atom% as in sample No. 38, the firing temperature is 100 than that in (Example 1).
Since the temperature is also low, densification cannot be achieved, and the rate of change in resistance with time increases. The theoretical density ratios with and without addition of CaO are shown in Table 2 as density ratio 1 and density ratio 2. Theoretical densification is (elemental density) / (theoretical density) × 100
(%) Was used for calculation. The density ratio 2 without addition is obtained by using (Example 1). As can be seen from Table 2, the dense thermistor element 1 can be obtained by adding CaO even though the firing temperature is lowered by 100 ° C.

The addition of CaO is particularly effective for those containing a large amount of Cr. (Embodiment 3) A third embodiment of the present invention will be described below.

Al in (Chemical Formula 3)₂O₃, Cr₂O₃, F
e₂O₃, CaCO₃, Rare earth oxides (Y₂O₃, La
₂O₃, CeO₂, Pr₆O₁₁, Nd₂O₃, Sm₂O₃, Eu
₂O₃, Gd₂O₃, Tb_FourO₇, Dy₂O₃, Ho₂O₃, Er
₂O₃, Tm₂O₃, Yb₂O₃, Lu ₂O₃) Is x, y, a,
Sample N was weighed so that b had the composition shown in Table 3.
o.40-77 was created.

[0022]

[Table 3]

A high temperature thermistor element 1 was obtained in the same manner as in (Example 1). Then, the catalyst temperature detecting temperature sensor shown in FIG.
The resistance values at ℃, 600 ℃ and 900 ℃ were measured, and Table 3
Are shown as R300, R600, and R900. Then 1
After conducting a sealed endurance test at 100 ° C for 1000 hours, 3
The resistance value at 00 ° C. was measured, the rate of change was calculated in the same manner as in Example 1, and shown in Table 3 as ΔR300.

In this embodiment, rare earth oxide and CaO are used.
Is added to achieve densification and prevent the adsorbed gas from depriving oxygen and diffusing. The rare earth oxide exists as (RE) CrO ₃ having a perovskite structure at the grain boundary. Here, RE represents a rare earth element. Ca
O does not form a solid solution with the main component (Chemical Formula 1) and exists alone at the grain boundary.

When the addition amount of the rare earth oxide exceeds 10 atomic% as in Sample Nos. 42, 54 and 66 of Table 3, (R
E) The segregation amount of CrO ₃ is increased, and the main component (Chemical formula 1) of Cr
Is lost in a large amount, the balance of semiconductor characteristics is lost, and the rate of change in resistance over time exceeds ± 20%. Sample No.4
When CaO is not added and the amount of the rare earth oxide added is less than 0.1 atomic% as in Nos. 7, 61 and 75, the rate of change in resistance with time greatly exceeds ± 20%.

As can be seen by comparing the sealing endurance test temperature with those of Examples 1 and 2, the addition of the rare earth oxide improves the heat resistance temperature by 200 ° C.

(Fourth Embodiment) The fourth embodiment of the present invention will be described below.

Al ₂ O ₃ , Cr ₂ O ₃ and F in the chemical formula 4
A predetermined amount of e ₂ O ₃ , CaCO ₃ , and ThO ₂ was weighed so that x, y, a, and b had the compositions shown in Table 4, and sample Nos. 78 to 8 were used.
8 was created.

[0029]

[Table 4]

In the same manner as in (Example 1), the thermistor element 1 was obtained, and the thermistor element 1 was sealed in the heat resistant cap 4 of the catalyst temperature detecting temperature sensor shown in FIG.
The resistance values at 0 ° C. and 900 ° C. were measured and shown in Table 4 as R300, R600, and R900. And 1
After conducting a sealed endurance test at 100 ° C for 1000 hours, 3
The resistance value at 00 ° C. was measured, and the rate of change was calculated in the same manner as in (Example 1), which is shown in Table 4 as ΔR300.

ThO ₂ and CaO do not form a solid solution with the main component (Chemical Formula 1) and exist alone at grain boundaries. Since ThO ₂ is stable in a reducing atmosphere, a similar effect can be obtained even with an addition amount of 1/10 that of rare earth oxides.

However, as shown in sample No. 82 of Table 4, ThO ₂
When the amount of addition of Al exceeds 10 atomic%, the sinterability rapidly deteriorates, the generation of porous particles increases, and the rate of change in resistance with time is −.
It exceeds 20%. Also, as in sample No. 85, C
aO is not added and the amount of ThO ₂ added is 0.01 atom%.
If it is less than the lower limit, the rate of change in resistance over time exceeds -20%.

Further, ThO ₂ can also improve the heat resistance temperature by 200 ° C. like the rare earth oxide. (Fifth Embodiment) The fifth embodiment of the present invention will be described below.

Al ₂ O ₃ , Cr ₂ O ₃ and F in the chemical formula 5
A predetermined amount of e ₂ O ₃ , CaCO ₃ , and ZrO ₂ was weighed so that x, y, a, and b had the compositions shown in Table 5, and sample No.
89-101 was created.

[0035]

[Table 5]

In the same manner as in (Example 1), the thermistor element 1 was obtained and sealed in the heat-resistant cap 4 of the catalyst temperature detecting temperature sensor shown in FIG.
The resistance value at 900 ° C. was measured.
It is shown as 600 and R900. And 1 at 1100 ° C
After performing the sealed endurance test for 000 hours, the resistance value at 300 ° C. was measured, and the rate of change was calculated in the same manner as in (Example 1), and shown in Table 5 as ΔR300.

Both ZrO ₂ and CaO do not form a solid solution with the main component (Chemical Formula 1), and each exists alone at the grain boundary. Table 5 samples
Like Nos. 92 and 96, the amount of ZrO ₂ added is 30 atom%.
If it exceeds, the sinterability deteriorates and the rate of change in resistance with time is -2.
It exceeds 0%.

Like ZrO ₂ and ThO ₂ and the rare earth oxides, the heat resistance temperature is improved by 200 ° C.

Further, when the composition of the main component (Chemical Formula 1) is constant, the resistance value can be widely controlled by adjusting the addition amount of ZrO ₂ .

As can be seen from the above (Examples 1 to 5), the thermistor material used in the temperature sensor of the present invention is
Strong against environmental changes. Therefore, it can be sufficiently used as a temperature sensor even if the shape is changed, such as a disk type or glass sealed.

[0041]

As described above, the thermistor element used in the temperature sensor of the present invention has a dam structure of high resistance Al ₂ O ₃ and P
It is formed by a solid solution of Cr ₂ O ₃ of type conductivity and Fe ₂ O ₃ of N type conductivity. By mixing P type and N type in the same crystal, the thermistor element can generate oxygen at high temperature. Even if it is lost, the change in resistance with time can be suppressed to be small.

[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 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 (5)

[Claims] 1. A thermistor comprising: a metal heat-resistant cap; a thermistor element provided in the heat-resistant cap; and a lead wire that is electrically connected to the thermistor element and is drawn out of the heat-resistant cap. A temperature sensor in which an element is formed using a substance represented by (Chemical Formula 1). [Chemical 1] 2. The constituent metal atom of (Chemical formula 1) is 100 atom%.
The temperature sensor according to claim 1, wherein the thermistor element is formed by using a substance represented by (Chemical Formula 2). [Chemical 2] 3. The constituent metal atom of (Chemical formula 1) is 100 atom%.
In this case, the temperature sensor according to claim 1, wherein the thermistor element is formed by using a substance represented by (Chemical Formula 3). [Chemical 3] 4. The constituent metal atom of (Chemical formula 1) is 100 atom%.
In this case, the temperature sensor according to claim 1, wherein the thermistor element is formed by using a substance represented by (Chemical Formula 4). [Chemical 4] 5. The constituent metal atom of the chemical formula 1 is 100 atom%.
In this case, the temperature sensor according to claim 1, wherein the thermistor element is formed by using the substance represented by (Chemical Formula 5). [Chemical 5]