JPH0437940B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Fields The present invention is applicable to combustion equipment such as gas and kerosene stoves, boilers, and automobile engines, which can be used to burn out and overheat, as well as to treat oxygen deficiency conditions and air/fuel ratios (A/F) (including areas other than equivalent composition). The present invention relates to a multifunctional sensor that can detect the following with a single sensor. Conventional Technology Conventionally, in order to detect a power out or overheating, a thermistor was provided for each object to be detected, and the state was detected from the change in resistance of the thermistor. The need to provide individual sensors was due to the lack of a stable material that could measure with high sensitivity over a wide temperature range, from detecting a state near room temperature, such as turning off, to around 1,000 degrees Celsius, indicating overheating. Furthermore, even if the sensor performs the same action of detecting such a state and closing the gas valve, the output format from the sensor is different, so it is necessary to provide an individual electrical circuit for each sensor. It was hot. To detect A/F, which corresponds to an oxygen-deficient state or the equivalent composition of combustion, Pt is attached as an electrode on both sides of a stabilized or partially stabilized zirconia fixed electrolyte, and one electrode is connected to a device with a constant oxygen partial pressure like air. (P _p2 =
0.21 atm) and the other side to exhaust gas to form an oxygen concentration cell, and utilize the fact that the generated electromotive force changes greatly depending on the equivalent composition of _{combustion . , MgCo2O4}
Sensors are used that take advantage of the fact that the electrical resistance of the fuel changes greatly depending on the combustion equivalent composition. Problems to be Solved by the Invention With the conventional devices described above, it is not possible to detect turning off or overheating at the same time, and detection of A/F that causes sudden changes in electromotive force or resistance is limited to equivalent composition. . In order to sharpen the degree of change in the equivalent composition of these sensors, the catalytic action of noble metals such as Pd and Pt is required, and for this reason, sensors that utilize the resistance change of oxides contain these noble metals in the sensor substrate. was added as a catalyst. Therefore, it had the disadvantage of being expensive. The inventors first investigated the oxygen deficiency state and equivalent composition of A/F.
When an electron-oxygen ion mixed conductor made of Sr1+x/2La1-x/2Co1 _-x Fe _x O ₃ is used to detect In a state of excess oxygen
It has a low resistance of 10 ^-4 S/cm ² , and the resistance increases when there is an excess of reducing gas (opposite to the behavior of SnO ₂ and TiO ₂ sensors), so it is fail-safe against disconnection, and the sensor itself It has been revealed that a sensor can be provided which has the advantage of allowing direct control without a circuit by passing a current through the sensor (Japanese Patent Application Laid-open No. 103041/1983). Also, by hybridizing this sensor with an oxygen pump, it is possible to move the output of only the A/F with equivalent composition, where the output suddenly changes, to any A/F by changing the current flowing through the pump. I found out. Also, the sensor base material
It was revealed that when SrMeO ₃ (Me=Zr, Hf) is mixed and sintered in an appropriate ratio, it becomes possible to detect oxygen deficiency conditions at temperatures above 300°C. However, in the above sensor, the amount of change in resistance indicating an oxygen deficiency state is at most twice as large, and the sensitivity as a sensor (S = R/Ro, Ro = resistance at oxygen partial pressure of 0.21 atm, R = resistance at that time) resistance) was not large. The present invention has been made in view of this point, and an object of the present invention is to provide a sensor that has high sensitivity even in a low temperature range. Means for Solving the Problems In order to solve the above problems, the present invention aims to solve the above problems by
Sensor sensitivity is increased by replacing a portion of Me in SrMeO ₃ (Me=Zr, Hf) with A. Function The principle of increasing sensor sensitivity by replacing part of Me in the base material SrMeO ₃ (Me=Zr, Hf) with A is as follows. In other words, as the oxygen partial pressure decreases, the
O between Me-O-Me is released outside the crystal as a defect, and the resistance increases in proportion to the amount of release.
It is easier for O to break this bond, and therefore the oxygen vacancy becomes larger even at the same oxygen partial pressure. Example <Example 1> Sr _0.65 La _0.35 Co _0.7 Fe _0.3 O ₃ and SrZr _1-x A _x O ₃ were mixed at a molar ratio of 0.55:0.45 with the value of X shown in Table 1, and then methyl cellulose was added to this mixture. in weight ratio
After adding at a ratio of 20% and pulverizing and mixing in a ball mill, it was press-molded at 1 ton/cm ² and heated to 1350℃ in air.
It was baked for 2 hours. After finely pulverizing this, 0.3mm
The sensor substrate shown in FIG. 3 was obtained by pressing together with an Ag-Pd alloy (weight ratio 4:1) lead of φ and sintering it again at 1350° C. for 2 hours. This is the third
It was configured as shown in the figure. FIG. 1 shows the change in electrical resistance of this sensor with respect to oxygen partial pressure. The electrical resistance was measured by connecting a resistance measuring device between the leads shown in FIG.

[Table] In Figure 1, curve A-1 is Sample A in Table 1.
Curve A-2 shows the specific resistance at P _p2 (oxygen partial pressure) = 0.21 atm of the same sample A, P _p2 = 1×10 ^-4
This shows the specific resistance in ATM. Similarly, curves B-1 and C-1 have P _p2 =0.21 atm, B-2, C-
2 shows the specific resistance of samples B and C at P _p2 =1×10 ⁻⁴ atm. As can be seen from this figure, at 400°C, the sensor sensitivity of sample A is 1.4, but the sensitivity of sample B and this sensor are 3.2 and 3.2, respectively.
4.2, indicating that the sensor sensitivity was high even at this temperature. Example 2 A sensor similar to Example 1 was manufactured using SrHf _1-x A _x O ₃ as the sensor substrate material, and its characteristics were investigated. That is, Sr _0.65 La _0.35 Co _0.7 Fe _0.3 O ₃ and SrHf _1-x A
FIG. 2 shows the electrical resistance of _x O ₃ mixed and sintered at a molar ratio of 0.65:0.35 with the value of X shown in Table 2 and used as a sensor base material.

[Table] In Figure 2, curve D-1 shows the resistivity of sample D in Table 2 at P _p2 = 0.21 atm, and curve D-2 shows the resistivity of sample D at P _p2 = 1× This shows the specific resistance at 10 ^-4 atm. Similarly, curve E-1,
F-1 is P _p2 = 0.21 atm, E-2, F-2 is P _p2 =
It shows the specific resistance of samples E and F at 1×10 ⁻⁴ atm. As you can see in this diagram, 400
The sensor sensitivity of Sample D was 1.1 at ℃, while Samples E and F had a sensor sensitivity of 2.2 and 5.8, respectively, which was high even at this temperature. Effects of the Invention As can be seen in Fig. 1, the present invention uses Sr1+x/2La1-x/2Co _1-x Fe _x O ₃ and SrMe _1-y A _y O ₃ (Me=Zr, Hf) (0 <x<0.3, 0<y
By using a mixed sintered body of 0.2), a sensor with high sensitivity is produced even in the low temperature range.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram of the electrical resistance of the sensor base material.
FIG. 2 is a characteristic diagram of electrical resistance of different sensor base materials, FIG. 3 is a top view of a gas sensor according to an embodiment of the present invention, and FIG. 4 is a sectional view thereof. 1...Alumina holding tube, 2...Sensor base.

Claims (1)

[Claims] 1. A powder of a substance represented by the chemical formula Sr1+x/2La1-x/2Co _1-x Fe _x O ₃ (0<x<0.3) and
SrMe _1-y A _y O ₃ (Me=Zr or Hf, 0<y
A sensor base is a sintered body obtained by mixing and sintering powders of substances represented by 0.2), at least two electrodes are connected to the base, and changes in electrical resistance between the electrodes are measured. gas sensor. 2. The gas sensor according to claim 1, wherein the sensor base is a sintered film. 3. The gas sensor according to claim 1, wherein the electrode is an alloy of at least two of Pt, Pd, and Ag. 4 Stabilized zirconia and a third layer on the surface of the sensor base
2. The gas sensor according to claim 1, wherein the electrodes are sequentially provided. 5 Sensor base Claims 1 to 4 characterized in that sputtered layers of Sr1+x/2La1-x/2Co _1-y Fe _y O ₃ and SrMe _1-y A _y O ₃ are laminated alternately. The gas sensor described in any of paragraphs.