JP2000338081A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a gas sensor capable of detecting an accurate concentration of a carbon monoxide even when a zero point correction is not executed for a measured potential difference. SOLUTION: The gas sensor comprises an insulator 4, a metal film 1, an insulating film 8, a solid electrolyte film 1, a heater film 5, a pair of electrode films 2a, 2b, and a catalyst 3 in such a manner that a sheet-like metal film 1 having good thermal conductivity is provided under the film 1. Thus, a heat can be uniformly transferred, and even when a zero point correction is not executed for the measured potential difference, a concentration of a carbon monoxide can be accurately obtained from the difference between the films 2a ad 2b.

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 combustible gas, particularly carbon monoxide, contained in exhaust gas discharged from combustion equipment or an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, this kind of gas sensor is disclosed in
Those described in JP-A-31003 are generally used.

As shown in FIG. 10, the gas sensor has electrode films 2a and 2b having the same area formed on one surface of a solid electrolyte 1 having oxygen ion conductivity, a catalyst 3 formed on the surface of the electrode film 2a, On the other surface of the solid electrolyte 1,
A heater 6 having a heater film 5 formed on the surface of a substrate 4 made of an insulator was provided.

The gas sensor having the above-described structure is arranged in an atmosphere containing no flammable gas such as carbon monoxide, and the solid electrolyte 1
Is heated to a predetermined operating temperature by the heater 6, since the areas of the electrode films 2a and 2b are equal, the amount of oxygen reaching each is equal, and no potential difference occurs between the electrode films 2a and 2b. If the areas of the electrode films 2a and 2b are not equal, it is sufficient to multiply the attained oxygen amount of one of the electrode films by a coefficient and correct it so that the numerical values of the attained oxygen amount become equal. At this time, the electrode films 2a and 2
On b, the electrode reaction shown by the equation (1) occurs, and the equilibrium is maintained.

Shows the ← → O ^2- ··· (1) where the oxygen atom O _ad is adsorbed on the surface of the electrode film 2a or 2b ^- [0005] O _ad + 2e.

Next, when this gas sensor is placed in an atmosphere containing flammable gas, carbon monoxide, on the electrode film 2b where the catalyst 3 is not formed, in addition to the electrode reaction shown in the equation (1), The electrode reaction shown in (2) occurs.

CO + O _ad → CO ₂ (2) On the other hand, on the electrode film 2 a on which the catalyst 3 is formed, carbon monoxide is oxidized to carbon dioxide on the surface of the catalyst 3, and the electrode film 2 a
Can not reach the surface of. Therefore, only the electrode reaction represented by the equation (1) occurs, and a difference occurs in the concentration of the adsorbed oxygen between the electrode films 2a and 2b. At this time, oxygen ions conduct in the solid electrolyte 1 from the electrode films 2a to 2b,
A potential difference occurs between a and 2b.

The relationship between this potential difference and the concentration of carbon monoxide is N
The concentration of carbon monoxide in the gas to be detected was determined by measuring the potential difference between the electrode films 2a and 2b according to the Ernst equation.

[0009]

The gas sensor of this type has the electrode films 2a and 2b when carbon monoxide is present.
The potential difference (zero point) in the absence of carbon monoxide is subtracted from the potential difference between them, that is, the zero point is corrected to obtain the concentration of carbon monoxide. However, if the potential difference in the absence of carbon monoxide is negligibly smaller than the potential difference in the presence of carbon monoxide, that is, if the potential difference is close to zero, the electrode film 2 can be removed without performing zero point correction.
The concentration of carbon monoxide can be calculated from the potential difference between a and 2b.

Therefore, in order to equalize the amount of electrode reaction occurring on electrode films 2a and 2b when carbon monoxide does not exist, and to reduce the potential difference between electrode films 2a and 2b to zero, electrode films 2a and 2b Had the same area.

However, the displacement of the heater 6 and
If distribution occurs in the heating due to variations in the thickness or pattern width of the heater film 5, the electrode films 2a and 2
A temperature difference occurs between the electrodes b, and the balance of the electrode reactions occurring on the electrode films 2a and 2b is lost. When carbon monoxide does not exist, a large potential difference occurs between the electrode films 2a and 2b even if the areas of the electrode films 2a and 2b are equal, so that the zero point correction must be performed on the measured potential difference. There were challenges.

Further, the exhaust gas contains a trace amount of impurities, depending on the place of production of natural gas. For example, the exhaust gas of gas combustion equipment contains 2 ppm or less of sulfur dioxide.

However, when the gas to be detected contains a pollutant such as sulfur dioxide in the structure of the conventional gas sensor, the sulfur dioxide is contained in the electrode films 2a and 2b more than carbon monoxide and oxygen required for detection. Since it strongly adsorbs to noble metals such as platinum and causes poisoning and deterioration, it becomes difficult for carbon monoxide and oxygen necessary for detection to adsorb to the electrode films 2a and 2b, and there is a problem that an accurate concentration of carbon monoxide cannot be detected. Was.

[0014]

In order to solve the above problems, the present invention comprises a substrate, a metal film, an insulating film, a heater film, a solid electrolyte film, a pair of electrode films, and a catalyst. .

According to the above invention, since the sheet-like metal film having good heat conductivity is provided under the solid electrolyte film, the heat is uniformly applied to the solid electrolyte film and the pair of electrode films by the metal film heated by the heater. , And no distribution occurs in the heating, and no temperature difference occurs between the electrode films. Therefore, when no carbon monoxide is present in the gas to be detected, the amount of electrode reaction occurring on the electrode film becomes equal, the potential difference between the electrode films becomes almost zero, and the zero point correction is not required for the measured potential difference. The concentration of carbon monoxide can be accurately obtained from the potential difference between the electrode films.

Further, since the heater film and the pair of electrode films are arranged on the same plane and can be formed simultaneously, the manufacturing process is simplified, and a low-cost gas sensor can be obtained.

[0017]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a substrate, a sheet-like metal film formed on the surface of the substrate, an insulating film having electrical insulation formed on the surface of the metal film, Any of the heater film formed on the surface, the solid electrolyte film having oxygen ion conductivity formed on the surface of the metal film, the pair of electrode films formed on the surface of the solid electrolyte film, and the pair of electrode films It consists of a catalyst formed on the surface of one of the electrode films.

A sheet-like metal film having good heat conductivity is provided below the solid electrolyte film, and the metal film heated by the heater uniformly transfers heat to the solid electrolyte film and the pair of electrode films.
Since there is no distribution in the heating and no temperature difference between the electrode films, the amount of electrode reaction occurring on the electrode film when carbon monoxide is not present in the gas to be detected becomes equal, and the potential difference between the electrode films becomes almost equal. It becomes zero, and the concentration of carbon monoxide can be accurately obtained from the potential difference between the electrode films without performing zero point correction on the measured potential difference.

Since the heater film and the pair of electrode films are arranged on the same plane and can be formed simultaneously, the manufacturing process is simplified, and a low-cost gas sensor can be obtained.

The metal film contains at least one of iron, iridium, molybdenum, nickel, palladium, platinum, rhodium, tantalum and tungsten.

The thermal conductivity of the metal film is 0.5 (W /
(Cm · K)) or more, and is superior in thermal conductivity to those of insulating films and solid electrolyte films, and has a linear thermal expansion coefficient of (4-1).
3) Since it is about 10 ^-6 (deg ^-1 ), which is about the same as that of an insulator or a solid electrolyte membrane, the solid electrolyte membrane or the electrode membrane is efficiently and uniformly heated without causing peeling or cracking. be able to.

Further, an insulating film is formed between the metal film and the solid electrolyte film.

Since the insulating film reliably insulates the metal film and the solid electrolyte film and prevents the generation of a leak ion current, the concentration of carbon monoxide can be accurately detected.

[0024] Further, it is provided with a heater film and a gas selective permeable member having a pore diameter of 20 to 500 ° formed so as to cover the pair of electrode films.

The gas to be detected passes through the gas selective permeable body by Knudsen diffusion, and carbon monoxide and oxygen necessary for detection can reach the electrode membrane through the gas selective permeable body. Pollutants such as sulfur dioxide, which has a larger molecular size than oxygen and oxygen and has adsorptivity, cannot pass through the gas selective permeable body, making it difficult for the electrode membrane to be poisoned and obtaining a gas sensor with high durability against pollutants. Can be.

Further, a catalyst is formed on the surface of the gas selective permeable body.

Further, since the gas selective permeable body and the electrode membrane are in close contact with each other and there is no gap between the gas selective permeable body and the electrode membrane, contaminants entering from the gap can be reliably shut off. On the other hand, a highly durable gas sensor can be obtained.

By forming a catalyst on the surface of the gas selective permeable member, the amount of the catalyst can be increased, the potential difference between the electrode films increases, and the catalyst activity is maintained for a long period of time. A gas sensor having a long lifetime can be obtained.

Further, a potential difference detecting means for detecting a potential difference between the pair of electrode films, a resistance detecting means for measuring a resistance of the metal film, a temperature of the solid electrolyte membrane is calculated from the resistance, and the temperature is calculated from the potential difference and the temperature. It is provided with arithmetic means for calculating the concentration of the gas to be detected.

Then, the temperature of the solid electrolyte membrane is calculated from the temperature characteristics of the resistance of the metal film, and the concentration of carbon monoxide is calculated from the potential difference between the electrode films at that temperature. Carbon monoxide concentration can be determined.

Further, there is provided control means for controlling the electric power supplied to the heater film so as to keep the resistance of the metal film constant.

Since the temperature of the solid electrolyte membrane and the temperature of the electrode membrane can be kept constant by the control means, a stable potential difference can be obtained irrespective of the surrounding temperature, and a highly reliable gas sensor can be obtained.

Further, the substrate is made of an insulator, and a pair of electrode films, a metal film and a lead-out portion of a heater film are formed on the same surface of the substrate.

Further, since the respective lead take-out portions are formed on the same surface of the insulator, the lead wires can be easily connected, and the working efficiency can be improved.

[0035]

Embodiments of the present invention will be described below with reference to the drawings. The components having the same reference numerals as those of the conventional example have the same structure, and a description thereof will be partially omitted.

(Embodiment 1) FIGS. 1 and 2 are a sectional view and a top view of a main part of a gas sensor according to Embodiment 1 of the present invention.

In FIGS. 1 and 2, reference numeral 4 denotes an insulator having electrical insulation as a substrate. A sheet-like metal film 7 having good heat conductivity is formed on the surface of the insulator 4, and an insulating film 8 having electrical insulation is formed on one of the surfaces of the metal film 7. Then, the heater film 5 is formed on the surface of the insulating film 8.
Are formed. The oxygen ion-conductive solid electrolyte film 1 is formed on the other portion of the surface of the same metal film 7 where the insulating film 8 is not formed. Further, electrode films 2a and 2b are formed on the surface of the solid electrolyte membrane 1, and a catalyst 3 for oxidizing carbon monoxide is laminated so as to cover the electrode film 2a.

As shown in FIG. 2, the lead extraction portions 2a 'and 2b' of the electrode films 2a and 2b, the lead extraction portions 5a and 5b of the heater film 5, and the lead extraction portions 7a and 7b of the metal film 7 are formed. It is formed on the same surface of the insulator 4.

A potential difference detecting means 9 for detecting a potential difference between the electrode films 2a and 2b between the electrode film lead taking-out sections 2a 'and 2b', and a metal film lead taking-out section 7a
And 7b, a resistance detecting means 10 for detecting the resistance of the metal film 7 is connected. Further, the temperature of the solid electrolyte membrane 1 is calculated from the resistance detected by the resistance detecting means 10, and the temperature and the potential difference detecting means 9 are calculated. Calculating means 11 for calculating the concentration of carbon monoxide in the gas to be detected from the potential difference detected by the heater film lead extraction portions 5a and 5b.
The control means 12 for controlling the voltage supplied to the heater so that the temperature of the solid electrolyte membrane 1 becomes constant from the resistance detected by the resistance detection means 10 is connected.

According to the above configuration, since the sheet-like metal film 7 having good heat conductivity is provided under the solid electrolyte membrane 1, the solid electrolyte membrane 1 is heated by the metal film 7 heated by the heater film 5.
In addition, heat can be uniformly transmitted to the pair of electrode films 2a and 2b, and no distribution occurs in the heating.
No temperature difference occurs between b. Therefore, when carbon monoxide does not exist in the gas to be detected, the amount of electrode reaction occurring on the electrode films 2a and 2b becomes equal, and the potential difference between the electrode films 2a and 2b becomes almost zero. Even without correction, the concentration of carbon monoxide can be accurately determined from the potential difference between the electrode films 2a and 2b.

The heater film 8 and the electrode films 2a and 2a
Since b is arranged on the same plane and can be formed simultaneously, the manufacturing process is simplified, and a low-cost gas sensor can be obtained. Further, the temperature of the solid electrolyte membrane 1 is calculated from the temperature characteristics of the resistance of the metal film 7, and the concentration of carbon monoxide is calculated from the potential difference between the electrode films 2a and 2b at that temperature. Can also obtain an accurate concentration of carbon monoxide.

Further, since the temperature of the solid electrolyte membrane 1 and the electrode membranes 2a and 2b can be kept constant by the control means 12, a stable potential difference can be obtained irrespective of the surrounding temperature, and a highly reliable gas sensor can be obtained. Obtainable.

The lead extraction portions 2a 'and 2b' of the electrode films 2a and 2b, the lead extraction portions 5a and 5b of the heater film 5, and the lead extraction portions 7a and 7b of the metal film 7 are on the same surface of the insulator 4. Therefore, the lead wires can be easily connected, and the working efficiency can be improved.

Next, a method for manufacturing the gas sensor will be specifically described.

First, an alumina substrate whose surface was polished was used as an insulator 4, and after ultrasonic degreasing with an organic solvent, a sheet-like metal film 7 made of platinum was formed by sputtering. The thermal conductivity of platinum is 0.69 (W / (cm · K)), which is larger than the thermal conductivity of aluminum oxide of the insulator 4 and the insulating film 8 of 0.30 (W / (cm · K)). Excellent in heat conduction. The linear thermal expansion coefficient of platinum is 8.9 × 10
^-6 (deg ^-1 ), and the linear thermal expansion coefficients of the aluminum oxide of the insulator 4 and the insulating film 8 and the stabilized zirconia of the solid electrolyte membrane 1 (about 5 × 10 ^-6 (deg ^-1 ) and about 10
× 10 ^-6 (deg ^-1 )), so that the solid electrolyte membrane 1 and the electrode membrane 2a do not peel or crack.
And 2b can be efficiently and uniformly heated.

In addition to the platinum, the metal film 7 has a thermal conductivity of 0.5 (W / (cm · K)) or more and a linear thermal expansion coefficient of (4 to
13) Iron, iridium, molybdenum, nickel, palladium, rhodium, tantalum, which is × 10 ^-6 (deg ^-1 )
Similar effects can be obtained with tungsten or an alloy of these metals. Also, lead take-out portions 7a and 7b for measuring the resistance at both ends of the metal film 7 are provided on the insulator 4
Formed on the surface.

Next, an insulating film 8 made of aluminum oxide is formed by sputtering to electrically insulate the metal film 7 and the heater film 5 from each other so as not to cover the lead extraction portions 7a and 7b of the metal film 7. did. The insulating film 8 can be similarly formed by printing / coating, vacuum evaporation, plating, or the like in addition to sputtering.

Next, a solid electrolyte membrane 1 made of stabilized zirconia to which 8% by mole of yttria is added is formed on the surface of the same metal film 7 by sputtering, and after sputtering, sintered at a high temperature to obtain oxygen ion conductivity. The resulting solid electrolyte membrane 1 was formed.

Next, a heater film 5 and a pair of electrode films 2a and 2b having the same area were simultaneously formed on the surfaces of the insulating film 8 and the solid electrolyte film 1 using platinum by screen printing. Heater film 5 and electrode films 2a, 2b
Can be similarly formed by sputtering or vacuum deposition other than printing, and after forming the heater film 5, a fine heater pattern can be formed by using a technique such as photolithography or etching. Further, a lead extraction unit 2 for measuring a potential difference between the electrode films 2a and 2b.
a ′, 2b ′ and a lead extraction part 5 a, 5 b for supplying a voltage to the heater film 5 are replaced with a metal film 7 lead extraction part 7.
It was formed on the same surface of the insulator 4 as a and 7b.

Next, a catalyst 3 mainly composed of platinum and palladium for oxidizing carbon monoxide was applied onto one electrode film 2a and fired. When the substrate is not an insulator and has conductivity, it is a matter of course that the lead must be washed so as not to cause a short circuit at each lead extraction portion.

To age the gas sensor produced as described above, the gas sensor was exposed to an atmosphere containing 3,000 ppm of carbon monoxide, 20% of oxygen and 20 ppm of sulfur dioxide, and the temperature of the atmosphere was maintained at 500 ° C. A current larger than the current flowing during use was passed between the heater film lead take-out portions 5a and 5b and left for about 24 hours. The concentrations of various gases are considerably harsher than those of actual combustion exhaust gas, and they are exposed to an atmosphere containing high concentrations of carbon monoxide, oxygen and sulfur dioxide in advance and heat-treated, resulting in excellent initial stability and durability. A highly sensitive gas sensor can be obtained.

At the same time, since a current larger than that at the time of use is passed through the heater film 5 for heating the solid electrolyte membrane 1 in advance and the current is applied, a gas sensor having excellent initial stability and high durability can be obtained.

In order to examine the basic characteristics of the gas sensor obtained as described above, the gas sensor is arranged in the gas to be detected, and a voltage is supplied between the heater film lead outlets 5a and 5b. And heated. This temperature is an operating temperature at which oxygen ion conductivity of the solid electrolyte membrane 1 is obtained and a temperature at which sufficient catalytic activity to oxidize carbon monoxide of the catalyst 3 is obtained. At this time, the flow rate of the detected gas was about 185 cm / min.

Then, a potential difference detecting means 9 is connected between the electrode film lead take-out portions 2a 'and 2b', and the electrode film 2a
And the potential difference generated between 2b was measured.

FIG. 3 shows a change in the potential difference generated between the electrode films 2a and 2b when the oxygen concentration is kept constant at 20% and the concentration of carbon monoxide is changed from 0 → 1,000 → 0 ppm. From FIG. 3, when the concentration of carbon monoxide was 0 ppm, the potential difference between the electrode films 2a and 2b was almost 0 mV. This is because not only the areas of the electrode films 2a and 2b are equal but also the metal films 7 heat the electrode films 2a and 2b uniformly,
This is because there is no temperature difference between the electrode films 2a and 2b, and the amount of electrode reaction occurring on each electrode film becomes equal. When the concentration of carbon monoxide was 1,000 ppm, the potential difference was about 8 mV, and the 90% response time was about 90 seconds.

FIG. 4 shows the concentration characteristics of carbon monoxide. FIG. 4 shows that the potential difference is proportional to the logarithm of the concentration of carbon monoxide, and follows the Nernst equation.

Therefore, it was found that the gas sensor according to the first embodiment can provide a highly responsive gas sensor that does not require zero point correction.

If this gas sensor is mounted on a combustion device or an internal combustion engine, and the concentration of carbon monoxide in the exhaust gas is monitored, combustion is forcibly performed when the amount of carbon monoxide exceeds an allowable value. It can be stopped or controlled to maximize the combustion efficiency within the allowable concentration range of carbon monoxide, which not only improves the safety of combustion equipment or internal combustion engines, but also saves energy. .

Next, metal film lead take-out portions 7a and 7
FIG. 5 shows the temperature characteristics of the resistance of the metal film 7 measured by the resistance detecting means 10 connected between the terminals b. By measuring the resistance of the metal film 7 from FIG. 5, the operating temperatures of the solid electrolyte membrane 1 and the electrode films 2a and 2b can be detected, and the arithmetic means 11 determines the concentration of carbon monoxide from the temperature and the potential difference at that time. Since the calculation is performed, an accurate concentration of carbon monoxide can be obtained even when the ambient temperature changes.

The control means 12 further controls the solid electrolyte membrane 1
In addition, since the voltage supplied between the heater film lead take-out portions 5a and 5b is controlled so that the temperatures of the electrode films 2a and 2b become constant, a stable potential difference is obtained irrespective of the ambient temperature and high reliability is obtained. A gas sensor can be obtained.

(Embodiment 2) FIG. 6 is a sectional view showing a main part of a gas sensor according to Embodiment 2. FIG. 6 differs from the gas sensor of the first embodiment in that an insulating film 8 is also formed between the metal film 7 and the solid electrolyte film 1. Otherwise, components having the same reference numerals have the same configuration as in the first embodiment, and a description thereof will be omitted.

After a metal film 7 is formed on the surface of the insulator 4 in the same manner as in the first embodiment, an insulating film made of aluminum oxide is used to electrically insulate the metal film 7, the heater film 5 and the solid electrolyte film 1 from each other. 8 was formed by sputtering. Then, the solid electrolyte membrane 1 is formed on the surface of the insulating film 8, and the heater film 5 and the pair of the heater film 5 are formed on the portion of the insulating film 8 where the solid electrolyte membrane 1 is not formed and the surface of the solid electrolyte membrane 1 by screen printing. Electrode films 2a, 2
b was formed at the same time. Then, as in Example 1, the catalyst 3 was formed on the surface of the electrode film 2a.

When the metal film 7 and the solid electrolyte film 1 come into contact with each other, the metal film 7 functions as an electrode at the three-phase interface between the metal film 7 and the solid electrolyte film 1 and the gas phase, and an electrode reaction may occur on the metal film 7. There is. However, according to the gas sensor of the second embodiment, since the insulating film 8 reliably insulates the metal film 7 and the solid electrolyte film 1 and prevents the generation of a leak ion current, it is possible to accurately detect the concentration of carbon monoxide. Can be.

By forming the insulating film 8 between the metal film 7 and the solid electrolyte film 1, the potential difference between the electrode films 2a and 2b may change, or the temperature characteristic of the resistance of the metal film 7 may change. It was confirmed that an accurate concentration of carbon monoxide was detected in the same manner as in Example 1.

(Embodiment 3) FIG. 7 is a sectional view of a main part of a gas sensor according to Embodiment 3. 7 is different from the gas sensor of the second embodiment in that the pore diameter formed to cover the electrode films 2a and 2b, the catalyst 3 and the heater film 5 is 20 to 500.
The gas selective permeator 13 is provided. Otherwise, components having the same reference numerals have the same configuration as in the second embodiment, and a description thereof will be omitted.

In the same manner as in Example 2, a metal film 7, an insulating film 8, a solid electrolyte film 1, a heater film 5, electrode films 2a and 2b, and a catalyst 3 are sequentially formed on the surface of an insulator 4. The gas selective permeable member 13 was disposed so as to cover the electrode films 2 a and 2 b and the catalyst 3, and was laminated on the insulator 4 via the bonding material 14.

Next, a method of manufacturing the gas selective permeable body 13 will be specifically described.

The gas selective permeable material 14 has an average pore diameter of about 1
A porous ceramic substrate having a diameter of less than μm is used, and gas permeability cannot be obtained as it is.
A thin film was formed by a gel method, and pore control was performed. Specifically, a porous ceramic substrate is immersed in a sol coating solution,
After being pulled up at a constant speed, it was dried and fired. At this time, gelation occurs in the pores, a uniform coating is formed on the pore surface, and by adjusting the immersion time and the number of immersions,
A gas selective permeable body 13 having a pore diameter of (20 to 500) Å was obtained.

By the way, the exhaust gas contains many pollutants such as sulfur dioxide having a large molecular size. Example 3
According to the gas sensor described above, molecules having a particle size larger than 500 ° among the contaminants cannot pass through the gas selective permeable body 13. Further, in the gas selective permeator 13 having a pore diameter of (20 to 500) Å, the gas basically diffuses while adsorbing the inner surface of the pores by Knudsen diffusion. At this time, the gas permeability coefficient ratio is inversely proportional to the square root of the product of the molecular weight and the absolute temperature, so that a gas with a large molecular weight such as sulfur dioxide and an adsorbent gas permeates the pores compared to a gas such as oxygen or carbon monoxide. It becomes difficult to do. Therefore, contaminants reaching the electrode films 2a and 2b are reduced, and the electrode films 2a and 2b are reduced.
b becomes hard to poison.

Next, the durability of the gas sensor against sulfur dioxide was examined. FIG. 8 shows a change in potential difference between the electrode films 2a and 2b when 100 ppm of sulfur dioxide is added to a mixed gas of 1,000 ppm of carbon monoxide and air.
It was shown to. From FIG. 8, the potential difference was almost constant regardless of the presence or absence of sulfur dioxide, and no effect due to sulfur dioxide was observed. The actual concentration of sulfur dioxide contained in the exhaust gas was 2 ppm or less, and a stable potential difference was obtained in an accelerated endurance test with a sulfur dioxide concentration of about 50 times that of the sulfur dioxide. It was found that the durability against contaminants was extremely stable.

(Embodiment 4) FIG. 9 is a sectional view of a main part of a gas sensor according to Embodiment 4. FIG. 9 differs from the gas sensor of the third embodiment in that the catalyst 3 is formed on the surface of the gas selective permeable member 13. The other components having the same reference numerals have the same configurations as those of the third embodiment, and a description thereof will be omitted.

After forming a metal film 7, an insulating film 8, a solid electrolyte film 1, a heater film 5, and electrode films 2a and 2b on the surface of the insulator 4 in the same manner as in Example 3, the heater film 5 and the electrode film 2a are formed. 2b, the gas selective permeable member 13 was disposed so as to cover the electrode film 2a, and the catalyst 3 was laminated on the surface of the gas selective permeable member 13 so as to cover the electrode film 2a.

Next, a method for producing the catalyst 3 will be described.
A stainless steel fiber sheet is used as a carrier to support the catalyst.An inorganic binder such as alumina sol or colloidal silica is supported on the fiber, and then carbon monoxide consisting of a noble metal such as platinum or palladium is oxidized. The oxidized catalyst was carried and calcined.

According to the gas sensor of the fourth embodiment, the gas selective permeable member 13 and the electrode films 2a and 2b are in close contact with each other, and there is no gap between the gas selective permeable member 13 and the electrode films 2a and 2b. Therefore, a gas sensor having high durability against pollutants can be obtained.

By forming the catalyst 3 on the surface of the gas selective permeable member 13, the amount of the catalyst 3 can be increased, the potential difference between the electrode films 2a and 2b increases, and the catalyst activity is maintained for a long time. Therefore, a gas sensor having high sensitivity and a long lifetime can be obtained.

[0076]

As is clear from the above description, the gas sensor according to the present invention has the following effects.

(1) A sheet-like metal film having good heat conductivity is provided under the solid electrolyte film, and the metal film heated by the heater uniformly transmits heat to the solid electrolyte film and the pair of electrode films, and is distributed to the heating. Does not occur, and no temperature difference occurs between the electrode films, so that when carbon monoxide is not present in the gas to be detected, the amount of electrode reaction occurring on the electrode films is equal, and the potential difference between the electrode films is almost zero. The concentration of carbon monoxide can be accurately obtained from the potential difference between the electrode films without performing temperature correction on the measured potential difference.

(2) Since the heater film and the pair of electrode films are arranged on the same plane and can be formed simultaneously, the manufacturing process is simplified, and a low-cost gas sensor can be obtained.

(3) The thermal conductivity of the metal film is 0.5 (W /
(Cm · K)) or more, and is superior in thermal conductivity to those of insulating films and solid electrolyte films, and has a linear thermal expansion coefficient of (4-1).
3) Since it is about 10 ^-6 (deg ^-1 ), which is about the same as that of an insulator or a solid electrolyte membrane, the solid electrolyte membrane or the electrode membrane is efficiently and uniformly heated without causing peeling or cracking. be able to.

(4) Since the insulating film reliably insulates the metal film and the solid electrolyte film and prevents the generation of a leak ion current,
The concentration of carbon monoxide can be accurately detected.

(5) The gas to be detected passes through the gas selective permeable body by Knudsen diffusion, and carbon monoxide and oxygen necessary for detection can reach the electrode film through the gas selective permeable body. Contaminants such as sulfur dioxide, which has a larger molecular size than carbon and oxygen and has adsorptive properties, cannot pass through the gas selective permeable body, making it difficult for the electrode membrane to be poisoned.
A gas sensor having high durability against contaminants can be obtained.

(6) The gas selective permeable member and the electrode film are brought into close contact with each other,
Since there is no gap between the gas selective permeable body and the electrode membrane, contaminants entering through the gap can be reliably shut off,
A gas sensor having high durability against contaminants can be obtained.

(7) By forming a catalyst on the surface of the gas selective permeable member, the amount of the catalyst can be increased, the potential difference between the electrode films increases, and the catalyst activity can be maintained for a long time. Thus, a gas sensor having high sensitivity and a long lifetime can be obtained.

(8) The temperature of the solid electrolyte membrane is calculated from the temperature characteristics of the resistance of the metal film, and the concentration of carbon monoxide is calculated from the potential difference between the electrode films at that temperature. An accurate concentration of carbon monoxide can be determined.

(9) Since the temperatures of the solid electrolyte membrane and the electrode membrane can be kept constant by the control means, a stable potential difference can be obtained irrespective of the surrounding temperature, and a highly reliable gas sensor can be obtained. .

(10) When an electrical insulator is used as the substrate, each lead-out portion can be formed on the same surface of the insulator, so that lead wires can be easily connected and work efficiency can be improved. Can be.

[Brief description of the drawings]

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

FIG. 2 is a top view of the gas sensor.

FIG. 3 is a diagram showing the responsiveness of the gas sensor.

FIG. 4 is a diagram showing carbon monoxide concentration characteristics of the gas sensor.

FIG. 5 is a diagram showing temperature characteristics of resistance of a metal film of the gas sensor.

FIG. 6 is a sectional view of a main part of a gas sensor according to a second embodiment of the present invention.

FIG. 7 is a sectional view of a main part of a gas sensor according to a third embodiment of the present invention.

FIG. 8 is a view showing sulfur dioxide durability of the gas sensor.

FIG. 9 is a sectional view of a main part of a gas sensor according to a fourth embodiment of the present invention.

FIG. 10 is an assembly configuration diagram of a conventional gas sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solid electrolyte membrane 2a, 2b Electrode film 3 Catalyst 4 Insulator (substrate) 5 Heater film 7 Metal film 8 Insulating film 9 Potential difference detecting means 10 Resistance detecting means 11 Computing means 12 Control means 13 Gas selective permeable body

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Niwa 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Kunihiro Tsuruta 1006 Kadoma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial F Terms (reference) 2G004 BB04 BE03 BE11 BE22 BE30 BJ03 BL08 BM04 BM07 BM10

Claims (8)

[Claims] 1. A substrate, a sheet-like metal film formed on a surface of the substrate, an insulating film having electrical insulation formed on one of the surfaces of the metal film, and one of the surfaces of the insulating film. A solid electrolyte film having oxygen ion conductivity formed on the other of the surfaces of the metal film, a pair of electrode films formed on the surface of the solid electrolyte film, and the pair of electrode films A gas sensor comprising a catalyst formed on the surface of one of the electrode films. 2. The metal film is made of iron, iridium, molybdenum,
2. The gas sensor according to claim 1, comprising at least one of nickel, palladium, platinum, rhodium, tantalum, and tungsten. 3. The gas sensor according to claim 1, wherein an insulating film is formed between the metal film and the solid electrolyte film. 4. The gas sensor according to claim 1, further comprising a heater film and a gas selective permeable member having a pore diameter of 20 to 500 ° formed so as to cover the pair of electrode films. 5. The gas sensor according to claim 1, wherein a catalyst is formed on the surface of the gas selective permeable body. 6. A potential difference detecting means for detecting a potential difference between a pair of electrode films, a resistance detecting means for measuring a resistance of a metal film,
The gas sensor according to claim 1, further comprising a calculating unit configured to calculate a temperature of the solid electrolyte membrane from the resistance and calculate a concentration of the gas to be detected from the potential difference and the temperature. 7. The gas sensor according to claim 1, further comprising control means for controlling electric power supplied to the heater film so as to keep the resistance of the metal film constant. 8. The gas sensor according to claim 1, wherein the substrate is formed of an insulator, and a pair of electrode films, a metal film, and a lead-out portion of the heater film are formed on the same surface of the substrate.