JPH0469746B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Fields The present invention is useful for detecting gas and kerosene stoves, boilers, automobile engines, and other combustion equipment such as gas and kerosene stoves, boilers, automobile engines, and other combustion appliances to detect oxygen depletion and air/fuel ratio (A/F), as well as for various temperature detections such as fire alarms. This invention relates to a multi-functional sensor that can perform the following functions with a single sensor. Conventional Structure and Problems 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. In addition, even if the same operation is performed, such as detecting such a state and closing the gas valve, the output form from the sensor is different, so it is necessary to provide an individual electric 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 solid electrolyte, and one electrode is connected to a device with a constant oxygen partial pressure like air. ( _Po2 =0,
21 atm) and the other 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 . A sensor is used that utilizes the fact that the electrical resistance of MgCo ₂ O ₄ changes greatly depending on the combustion equivalent composition. However, these systems cannot, of course, detect turning off or overheating at the same time, and detection of A/Fs that cause sudden changes in electromotive force or resistance has been limited to equivalent compositions. 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 consisting of Sr _1+x/2 La _1-x/2 Co _1-x Fe _x O _3- is used for detection,
Since this material itself has a catalytic effect, there is no need to add a noble metal catalyst, and it has a low resistance of 10 ^-4 S/cm ² in an oxygen-excess state, but the resistance increases in an excess of reducing gas (SnO ₂ and TiO ₂ sensors), it has become clear that it is possible to provide a sensor that is fail-safe against wire breakage and has the advantage of allowing current to flow through the sensor itself and control it directly without a circuit (Japanese Patent Application Laid-Open No. 57−103041
Publication No.). In addition, by adding SrTiO ₃ to the sensor base material _, it is possible to match the thermal expansion with the electrode metal material and thin film substrate material, achieving a _{long life. /2} Co _1-x Fe _x
By forming grain boundaries of O _3- 〓 and increasing its O ^2- ion conductivity, we can increase the sensitivity and responsiveness of the sensor, and eliminate the high temperature dependence of semiconductors around room temperature and the temperature dependence of metals around 1000℃. We have successfully developed a sensor that has both power-off detection and overheat detection. However, the sensor substrate material Sr _1+x/2
When the grain boundary forming substance mixed in La _1-x/2 Co _1-x Fe _x O _3- 〓 is SrTiO ₃ , the electrical resistance of the sensor substrate increases in response to changes in the oxygen concentration in the atmosphere. This was only shown at temperatures above 400℃. OBJECTS OF THE INVENTION It is an object of the present invention to provide a sensor that has a long life, has high sensor sensitivity and responsiveness even in a low temperature range, and can detect turning off and overheating. Structure of the Invention The present invention uses SrMeO ₃ (Me=Zr,
By adding Hf), it is possible to match the thermal expansion with _the electrode metal material and thin film substrate material, achieving a long life _.
By forming grain boundaries of Co _1-x Fe _x O _3- 〓 and increasing its O ^2- ion conductivity, the sensitivity and responsiveness of the sensor can be increased, resulting in high semiconductor-like temperature dependence near room temperature and 1000
The sensor exhibits a metallic temperature dependence around 0.degree. C., thereby providing a sensor capable of detecting both extinguishing and overheating. DESCRIPTION OF THE EMBODIMENTS FIG. 1 is a diagram showing the basic configuration of a sensor according to an embodiment of the present invention. In the figure, 1 is a sensor base made of a plate-shaped ceramic sintered body, 2 is an electrode lead wire, and 3 is a sensor holder made of an alumina ceramic material. 4 is a solenoid for attracting and keeping the gas safety valve open; 5 is a power source for supplying current to the sensor base 1 and the solenoid 4, which may be direct current or alternating current. These are circuit elements when the sensor base 1 is used in a gas safety valve. FIG. 2 shows a sensor according to a different embodiment of the present invention, and is a diagram showing the basic configuration of a thick film type sensor. In the figure, 11 is a base made of alumina ceramic, 12 is an Ag-Pd alloy lead, and 13 is a sensor base thick film made of a thick film printed and sintered thereon. The typical aspects of the sensor of the present invention have been described above, and next, more specific examples based on these aspects will be described. Example 1 Sr _0.65 La _0.35 Co _0.7 Fe _0.3 O _3- and SrZrO ₃ were blended in the proportions shown in Table 1, methylcellulose was added at a weight ratio of 20%, and the mixture was pulverized in a ball mill. The mixed mixture was molded into a plate shape and baked in air at 1350°C for 2 hours. After pulverizing this, it was pressed together with an Ag-Pd alloy (weight ratio 4:1) lead having a thickness of 0.3 mm, and it was sintered again at 1350° C. for 2 hours to produce a sensor element. This was constructed as shown in FIG. Figure 3 shows the change in electrical resistance of this sensor with respect to CO gas. The electrical resistance was measured by connecting a resistance measuring device between the pair of lead wires 2 and 2 shown in FIG.
In FIG. 3, solid lines a-1, b-1, and c-1 indicate sensor substrate materials a and a having the compositions shown in Table 1, respectively.
It shows the resistance at each temperature in the air of b and c. Solid lines a-2, b-2, c-2 are
The resistance of each of the above sensors a, b, and c is shown 30 seconds after starting to flow 10 ppm CO gas (remaining N ₂ ), solid lines a-3, b-3, and c-3 are 1 minute after starting to flow the above gas. The resistance of each of the above-mentioned sensors a, b, and c is shown.

【table】

[Table] Table 2 also shows the above CO at 200℃ and 800℃.
This shows the time it takes to reach 90% of the steady resistance after gas is supplied. As is clear from FIG. 3, when SrZrO ₃ is used instead of SrTiO ₃ , CO gas detection ability is obtained from about 200°C. Example 2 Instead of SrZrO ₃ in Example 1 above
Example 2 uses SrHfO ₃ . Table 3 shows the compounding ratio of sensor base materials as in the previous example, and Table 4 shows the 90% response time.
FIG. 4 is a table showing the resistance change. As is clear from Table 3 and Figure 4,
It can be seen that when SrHfO ₃ is used instead of SrTiO ₃ , CO gas detection ability is obtained from about 150°C. It can also be seen that the 90% response time at 800°C is shortened, and responsiveness can be improved. An oxygen pump made of an oxygen ion conductive solid electrolyte is hybridized to a sensor whose resistance suddenly changes only at the combustion equivalence point, and a certain current is applied to the oxygen pump to draw out oxygen, even in the lean combustion region where the oxygen concentration is high. , the resistance can change suddenly.

【table】

[Table] Effects of the invention As described above, the present invention can be used as a sensor base.

By adding SrMeO ₃ (Me = Zr, Hf) to [Formula], it becomes possible to detect CO gas at temperatures above about 200°C or about 150°C, that is, to detect the oxygen partial pressure in the atmosphere, and at temperatures above about 200°C or about 150°C. In the following temperature range, the electrical resistance of the sensor element shows temperature dependence like a semiconductor and is not affected by the oxygen partial pressure of the atmosphere, making it possible to realize a sensor element that also functions as a temperature sensor. be.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing a typical structural example of the temperature gas dual-purpose sensor of the present invention, FIG. 2 is a conceptual diagram of a different embodiment of the present invention, _{and FIG.} Figure 4 shows the effect of addition in terms of the relationship between resistance and temperature dependence of gas sensitivity.
FIG. 3 is a diagram showing the effect of adding SrHfO ₃ . 1... Sensor base, 2... Lead wire, 3... Sensor holder, 4... Solenoid, 5... Power supply, 1
1...Substrate, 12...Lead, 13...Substrate thick film.

Claims (1)

[Claims] 1. A powder of a substance represented by the chemical formula Sr _1+x/2 La _1-x/2 Co _1-x Fe _x O _3- (0≦x≦1) and
A sintered body made by mixing and sintering SrMeO ₃ (Me=Zr or Hf) powder is used as a sensor base, at least two electrodes are connected to the base, and changes in electrical resistance between the electrodes are measured. Features: Temperature gas dual-purpose sensor. 2. The temperature gas dual-use sensor according to claim 1, wherein the sensor base is a sintered film. 3. The temperature gas dual-purpose sensor according to claim 1, wherein the electrode is an alloy of at least two of Pt, Pd, and Ag.