JP2002350392A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a gas sensor with little variation of output, which can be used stably for a long time and reduces the electric power consumption. SOLUTION: A pair of detecting electrodes 14a, 14b are formed on one surface of a porous plate 13 so as to be bonded thereto, and a solid electrolyte film 15 is formed so as to cover them, and an insulating substrate 11 forming a heater 12 on the back face is laminated. Catalyst 16 formed at the position on the other surface of the porous plate 13 opposite to the detecting electrodes 14a. The space between the porous plate 13 and the detecting electrode 14 disappears, and the variation of CO output is thus reduced. The insulating substrate 11 and the solid electrolyte are bonded to the porous plate 13 using flat surfaces, and cracking in the porous plate is prevented, and the output being stable for a long time is obtained. The solid electrtolyte film 15 and an insulating film 20 are made up of thin films, and the electric power consumption thus be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sensor for detecting gas leakage from gas combustion equipment, carbon monoxide generated by incomplete combustion of indoor combustion equipment, various toxic gases and odors.

[0002]

2. Description of the Related Art There are various types and shapes of conventional gas sensors. As an example, a gas sensor using a solid electrolyte as shown in FIG. 3 has been disclosed (JP-A-11-30).
No. 4747). In FIG. 3, reference numeral 1 denotes an insulator made of a ceramic plate such as alumina, and a heater 2 is set on the back surface. Reference numeral 3 denotes a solid electrolyte provided on the insulating plate 1, and a pair of electrodes 4 is formed on the upper surface. 5 is 1 inside
It is a porous body having a large number of minute air holes of about 0 ° to 100 °. An oxidation catalyst 6 is provided on the porous body 5 at a position corresponding to one electrode 4 ′. Reference numeral 7 denotes an adhesive that integrally fixes the insulating plate 1, the solid electrolyte 3, and the porous body 5, and seals a gap between the solid electrolyte 3 and the porous body 5, and fixes the three members on the outer periphery thereof. Reference numeral 8 denotes a partition wall on the porous body 5 for separating the electrodes 4 and 4 '.

[0003]

Generally, gas sensors are sensitive to carbon monoxide, methane, propane, hydrogen, odor and the like, and are used for applications such as gas leak alarms, CO alarms, and odor sensors. The solid electrolyte type sensor shown in FIG. 3 detects gas based on the following principle. In the following description, the case where the detection gas is carbon monoxide (hereinafter referred to as CO) will be described. Power supply (not shown) in FIG.
When power is supplied to the heater 2 to heat the solid electrolyte 3 to a predetermined temperature (400 ° C. to 500 ° C.), electrons are transferred at the interface between the electrode 4 and the solid electrolyte 2 and air, and oxygen ions are generated. Here, if CO is present, CO is oxidized by the catalyst 6 at the electrode 4 'on which the catalyst 6 is mounted, and does not reach the electrode 4'. In the other electrode 4, CO
Is oxidized to CO2 on the surface of the electrode 4. As a result, a difference occurs in the electrode reactions between the two electrodes, the equilibrium of oxygen ions is disrupted, and a potential difference occurs between the two electrodes. By detecting this potential difference, the CO concentration can be detected. Here, the porous body removes a poisonous gas such as a gas having a large molecular diameter or SO2, and selectively detects and detects CO. Since the partition walls are on the porous body 5 and isolate the electrodes 4 and 4 ′, the gas flow reaching the electrode 4 ′ on which the catalyst 6 is mounted is separated from the flow reaching the other electrode 4. Is considered. In the configuration of FIG. 3, the adhesive 7 is used to seal the gap between the solid electrolyte 3 and the porous body 5, and the insulator 1, the solid electrolyte 3, and the porous body 5 are sealed and fixed around the entire circumference. Due to the internal stress caused by the repetition of turning on and off of the heater 2 due to the difference between the two, minute cracks occur in the porous body 5 having particularly low strength, the amount of gas passing through the porous body 5 changes, and the output value of CO decreases. There were times when it fluctuated. Also, in the case of fixing at the outer periphery, it is difficult to completely adhere the porous body 5 to the electrode 4,
If an unbalance occurs in the gap between the two electrodes, the CO-free air flowing from the porous body 5 through the catalyst 6 and the air flowing from the porous body 5 without passing through the catalyst flow in the gap in a complicated manner. In some cases, it fluctuated.

In recent years, the trend of power saving has become remarkable even in household appliances, and there has been a strong demand for reduction in standby power, especially for a gas sensor for incorporation in a combustion appliance, in terms of miniaturization and power saving. . In addition, the development of gas alarms and the like aimed at battery operation has been spurred by significant power savings. However, in the above conventional method, the insulator 1,
As the solid electrolyte 3 and the porous body 5, plate-like ones are used, and several watts of electric power are required to heat them to a predetermined temperature, and these requirements cannot be met.

An object of the present invention is to provide a gas sensor which solves the above-mentioned conventional problems, can be used stably for a long period of time, eliminates variations in output, and greatly reduces power consumption.

[0006]

To solve the above-mentioned conventional problems, a gas sensor according to the present invention comprises a porous plate having a large number of fine holes, and a pair of electrodes formed on one surface of the porous plate. An oxygen ion conductive solid electrolyte membrane provided so as to cover the electrode, a catalyst provided at a position opposite to one of the electrodes on the other surface of the porous plate, and a heat-resistant insulating material. A heater formed on one side of the conductive substrate,
The heat-resistant substrate comprises another surface and an adhesive for bonding the surface of the porous plate on which the solid electrolyte membrane is formed.

Thus, the porous plate and the electrode are brought into close contact with each other, and the air containing no CO passing through the catalyst and the air containing CO without passing through the catalyst are allowed to reach different electrodes, respectively. Only at this time, an oxidation reaction of CO occurs, and a stable output is obtained. In addition, since the porous plate is not fixed on the outer periphery but joined on the surface, stress is hardly applied even if the heater is turned on and off repeatedly, and the generation of minute cracks on the porous plate is suppressed, so it can be used for a long time. A stable output is obtained. Further, since the solid electrolyte membrane is formed as a thin film, the heat capacity of the sensor is reduced, so that power can be saved.

[0008]

DETAILED DESCRIPTION OF THE INVENTION According to the first aspect of the present invention, there is provided a porous plate having a large number of fine holes, a pair of electrodes closely bonded to one surface of the porous plate, and a cover for the electrodes. And a catalyst provided on the other surface of the porous plate at a position facing one of the electrodes, and one of a heat-resistant insulating substrate Having a heater formed on the surface of the insulating substrate and an adhesive for bonding the other surface of the insulating substrate to the porous plate, the porous plate and the electrode are brought into close contact with each other, and the CO that has passed through the catalyst
The air containing no CO and the air containing CO without passing through the catalyst are allowed to reach different electrodes, respectively, so that the oxidation reaction of CO occurs only at the electrode without the catalyst, and a stable output is obtained. In addition, since the porous plate is not fixed on the outer periphery but bonded on the surface, stress is less likely to be applied even if the heater is repeatedly turned on and off, and the generation of fine cracks on the porous plate is suppressed, so that it is possible to reduce A stable output is obtained. Further, since the solid electrolyte membrane is formed as a thin film, the heat capacity of the sensor is reduced, so that power can be saved.

According to a second aspect of the present invention, there is provided a porous plate having a large number of fine holes, a pair of electrodes closely bonded to one surface of the porous plate, and provided so as to cover the electrodes. A solid electrolyte membrane having oxygen ion conductivity, an insulating film provided to cover the solid electrolyte film, a heater provided on the insulating film, and one of the electrodes on the other surface of the porous plate. By having a catalyst provided at a position facing one of the electrodes, the porous plate and the electrode are brought into close contact with each other, so that air that does not contain CO passing through the catalyst and air that does not pass through the catalyst contain CO. Since it reaches another electrode, the oxidation reaction of CO occurs only at the electrode without the catalyst, and a stable output is obtained. In addition, since the porous plate is not fixed on the outer periphery but joined on the surface, stress is hardly applied even if the heater is turned on and off repeatedly, and the generation of minute cracks on the porous plate is suppressed, so it can be used for a long time. A stable output is obtained. In addition, since the solid electrolyte and the insulating film are formed as thin films, the heat capacity of the sensor is significantly reduced, so that power can be saved.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view of a gas sensor according to an embodiment of the present invention. In FIG. 1, reference numeral 11 denotes a heat-resistant insulating substrate on which a heater 12 is disposed on the back surface. Any material can be used for the insulating substrate 11 as long as the insulating property with the solid electrolyte plate described later can be ensured, but alumina is preferable from the viewpoint of the coefficient of thermal expansion and availability. The heater 12 is obtained by, for example, forming a platinum resistance film on the insulating substrate 11 by a screen printing method, a sputtering method, or an electron beam evaporation method and then performing a heat treatment. 13
Is applicable to any ceramic or glass flat plate having a large number of through holes from the front surface to the back surface.
Since these porous plates usually have a pore diameter of about several μm, gas selectivity cannot be obtained as it is, a sol-gel film is formed in the pores to control the pore diameter to about several to several hundred degrees. 14a and 14b are detection electrodes, and the porous plate 1
Platinum is formed on the back surface of 3 by a sputtering method, an electron beam evaporation method, or the like. Reference numeral 15 denotes a solid electrolyte membrane provided so as to cover the detection electrodes 14a and 14b, which is made of yttria-stabilized zirconia having excellent conductivity and relatively inexpensive by a sputtering method, an electron beam evaporation method, or the like.

Reference numeral 16 denotes a catalyst set on the porous plate 13, which is located immediately above one of the electrodes 14a. Catalyst 16
Any substance can be used as long as it oxidizes and decomposes the gas to be measured, but noble metals such as platinum, palladium, ruthenium, and rhodium, and metal oxides such as tin oxide and zinc oxide can be used. The catalyst 16 is formed by a screen printing method, a metal fiber,
It is formed by impregnating a ceramic fiber sheet in the form of a nitrate or the like, followed by baking, but is preferably formed by a screen printing method in order to reduce the heat capacity. 17 is electrode 1
4b is a lead electrode for joining the lead wire 18 with the lead wire 4b. 19
Is an adhesive for bonding the insulating substrate 11 and the porous plate 13, and pastes glass to form a thick film on the insulating substrate 11 by screen printing, and after bonding with the porous plate 13, baking while applying a load, Join. The adhesive 19 is used for the insulating substrate 1
1 and the porous plate 13 are bonded with a glass adhesive having a similar thermal expansion coefficient.

In the above configuration, when power is supplied from a power source (not shown) to the heater 12 to heat the solid electrolyte 13 to a predetermined temperature (400 ° C. to 500 ° C.), the electrodes 14a, 1
Electrons are exchanged at the interface between 4b, the solid electrolyte membrane 15 and the air, and oxygen ions are generated. Here, if CO is present, CO is oxidized by the catalyst 16 at the electrode 14a on which the catalyst 16 is mounted, and does not reach the electrode 14a. In the other electrode 14b, CO is CO2 on the surface of the electrode 14b.
Is oxidized to As a result, a difference occurs in the electrode reactions between the two electrodes, the equilibrium of oxygen ions is disrupted, and a potential difference occurs between the two electrodes. By detecting this potential difference, the CO concentration can be detected. Here, the porous plate 13 has a pore diameter of 1
Knud because it is controlled between 0Å and 100Å
Owing to the sen diffusion, oxygen and CO having a small molecular diameter can pass, but contaminants such as sulfur dioxide having a large molecular diameter cannot pass through the porous plate 13. Gas passing through the catalyst 16 and containing no CO and CO 2 passing through the catalyst 16
Pass through the porous plate 13 and reach the other detection electrodes 14a and 14b, respectively. Since there is no space between the porous plate 13 and the detection electrode 14 as in the conventional configuration, variations in output can be suppressed. Also, instead of fixing the insulating substrate 11 and the porous plate 13 on the outer periphery,
Since bonding is performed on the surface, stress is hardly applied even when the heater is repeatedly turned on and off, and generation of minute cracks in the porous plate 13 is suppressed, so that stable output can be obtained for a long period of time.
In addition, since the solid electrolyte is formed as a thin film, the heat capacity can be reduced in the conventional configuration compared to the conventional configuration.
Power consumption can be reduced, for example, standby power when incorporated into a combustion device can be reduced. When compared with a gas sensor having a size of 5 mm square, the conventional configuration consumes about 2 W, whereas the configuration of the first embodiment has a power consumption of about 1 W.
/ 2 or less.

Embodiment 2 FIG. 2 is a plan view of a main part of a gas sensor according to Embodiment 2 of the present invention. Since the basic configuration is the same as that of FIG. 1, only different points will be described.

Reference numeral 20 denotes an insulating film formed so as to cover the solid electrolyte film 15, and is formed of an insulating material such as SiO2, Al2O3, Si3N4 by a sputtering method or an electron beam evaporation method. The heater 12 is formed on the insulating film 20 so as to have a predetermined resistance value by a sputtering method, an electron beam evaporation method, or the like. The effect on the detection of CO is the same as that of the first embodiment. However, by forming the insulating film 20 with a thin film, it is possible to significantly reduce power consumption. When the operating temperature of the solid electrolyte membrane 15 is 450 ° C., only the solid electrolyte membrane 15 should be heated, but in the first embodiment, the insulating substrate 11 which does not need to be heated is also heated at the same time. It was not enough in terms of conversion. In the second embodiment, the insulating film 20 is used.
Is formed as a thin film, so that it can be almost neglected in terms of heat capacity. The catalyst 16 does not need to be heated to 450 ° C.
Since about 200 ° C. is sufficient for the oxidation of O, the solid electrolyte membrane 15 which can sufficiently cope with residual heat due to heat conduction when the solid electrolyte membrane 15 is heated is also a thin film.
The operating temperature can be raised to 450 ° C. at the msec level. Therefore, the power consumption can be significantly reduced by applying a voltage in a pulsed manner and increasing the temperature instead of energizing the heater 12 constantly, and the heater 12 can be driven by a battery power supply.

[0016]

As described above, according to the first and second aspects of the present invention, since the solid electrolyte thin film is formed in close contact with the porous plate, it does not pass through the catalyst-free air and the catalyst. In this case, air containing CO can reach different electrodes, and the oxidation reaction of CO occurs only at the electrode without a catalyst, so that a stable output can be obtained. Also, since the insulating substrate and the porous plate are not fixed at the outer periphery but are bonded at the surface, even if the heater is repeatedly turned on and off, stress is not easily applied, and the occurrence of fine cracks on the porous plate is suppressed. Therefore, a stable output can be obtained for a long time. Further, since the solid electrolyte film and the insulating film are formed as thin films, the heat capacity of the sensor can be reduced, and power can be saved.

[Brief description of the drawings]

FIG. 1 is a perspective view of a gas sensor according to a first embodiment of the present invention.

FIG. 2 is a perspective view of a gas sensor according to a second embodiment of the present invention.

FIG. 3 is a perspective view of a conventional gas sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Insulating substrate 12 Heater 13 Porous plate 14a, 14b Detection electrode 15 Solid electrolyte film 16 Catalyst 19 Adhesive 20 Insulating film

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Takashi Niwa, Inventor 1006 Kadoma, Kazuma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Kunihiro Tsuruta 1006, Kadoma, Kazuma, Kadoma City, Osaka Matsushita Electric Industrial Co. 72) Inventor Takahiro Umeda 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture F-term in Matsushita Electric Industrial Co., Ltd. (reference) 2G004 BB04 BD04 BE12 BE22 BF07 BF08 BH08 BH15 BJ03 BL08 BM04

Claims (2)

[Claims] 1. A porous plate having a large number of fine holes, and a pair of electrodes closely bonded to one surface of the porous plate,
An oxygen ion conductive solid electrolyte membrane provided so as to cover the electrode, and a catalyst provided at a position opposite to one of the electrodes on the other surface of the porous plate,
A gas sensor comprising: a heater formed on one surface of a heat-resistant insulating substrate; and an adhesive bonding the other surface of the insulating substrate to the porous plate. 2. A porous plate having a large number of fine holes, and a pair of electrodes closely bonded to one surface of the porous plate,
An oxygen ion conductive solid electrolyte film provided to cover the electrode, an insulating film provided to cover the solid electrolyte film, a heater provided to the insulating film, and the other of the porous plate A gas sensor having a catalyst provided at a position facing one of the electrodes on the surface.