JP2000088790A - Oxygen and carbon monoxide composite sensor - Google Patents

Abstract

(57) [Problem] The present invention relates to a carbon monoxide composite sensor used for various combustion devices using gas or petroleum as a fuel, and an object thereof is to realize stable performance and life thereof. SOLUTION: By using a configuration in which a gas selective permeable body 2 made of ceramic provided with a heating means and an electrode part of a sensor related to intake of a detection gas are arranged in contact with each other, a common heat source for driving a solid electrolyte is used. The configuration is designed to prevent electrode poisoning and deterioration related to sensor and sensor durability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen / carbon monoxide composite sensor for use in various types of combustion equipment using gas or petroleum as a fuel, and more particularly to an oxygen sensor having excellent sensor operation stability and durability in a severe use environment. , A carbon monoxide composite sensor.

[0002]

2. Description of the Related Art Carbon monoxide is a colorless, tasteless and odorless gas which is slightly lighter than air but highly toxic and causes headaches when breathing for a few hours at a low concentration of about 200 PPM.
At a concentration of 00 PPM or more, it dies in about 10 minutes, and at a concentration of 6000 PPM or more, it dies by breathing for several minutes.

[0003] Even in ordinary households, carbon monoxide is generated from instantaneous water heaters, bath kettles, oil heating appliances, gas heating appliances, and the like, and is inexpensive, small, and highly reliable, which can be built into these appliances. There is a strong demand for a carbon oxide gas detection sensor.

As a conventionally proposed gas sensor, particularly a carbon monoxide detection sensor, an electrode for absorbing and oxidizing carbon monoxide (CO) in an electrolytic solution is provided, and the CO concentration is calculated from a current value proportional to the CO concentration. These semiconductors are combined with a flammable gas by using a sintered body type n-type semiconductor oxide such as tin oxide (SnO2) sensitized with a small amount of an additional element such as a noble metal. A method of detecting gas by using the property that the electric conductivity changes when contacted (semiconductor type gas sensor), a pair of comparative elements in which alumina is attached to a thin platinum wire of about 20 μm and noble metal is supported There is known a method (contact combustion type gas sensor) for detecting the difference in heat generated when a combustible gas comes into contact with this element to perform a catalytic oxidation reaction by using the element by heating it to a certain temperature using a gas. You.

[0005] As another gas sensor used by forming an electrochemical cell, there is an oxygen sensor using stabilized zirconia as an electrolyte, which is practically used for controlling exhaust gas purification of automobiles and is well known. In this system, this is a system utilizing the electromotive force of an oxygen concentration cell. Gas sensors for measuring carbon monoxide and carbon dioxide simultaneously with oxygen are disclosed in JP-A-4-320955 and JP-A-4-32095.
No. 320956.

In this method, however, it is necessary to introduce a sample gas of a known concentration into one of the electrodes in order to form a concentration cell. Can not be introduced and is not suitable for home appliances. However, this method can correct electrode deterioration and the like each time.

[0007] Of these sensors, the carbon monoxide sensor which is currently considered to be the most reliable is a catalytic combustion sensor.

On the other hand, as the oxygen sensor, an electrochemical type such as a galvanic cell type, a zirconia type of a concentration cell type, and a solid electrolyte type of a limiting current type have been proposed. The concentration cell type was put to practical use for the purpose of controlling the air-fuel ratio of a three-way catalyst of a car, but it is good for use under conditions where the oxygen concentration is close to zero, as in the case of automobile exhaust, since the sensor output for the oxygen concentration is logarithmic. However, it is not suitable for use in a consumer appliance such as a combustion appliance in which the oxygen concentration is in the range of several percent or more to slightly more than 20% of the general atmosphere. In this respect, the limiting current type is expected to provide a sensor output that is linear with respect to the oxygen concentration, and is suitable for this purpose.

The oxygen sensor is intended to be used for the purpose of air-fuel ratio control for controlling the oxygen concentration in the combustion exhaust gas to a constant value, and the oxygen sensor that can be used for this purpose is as described above. The limiting current formula using a solid electrolyte becomes the most prominent.

[0010]

Although these oxygen sensors and carbon monoxide sensors fall into the category of chemical sensors in the classification of sensors, both chemical sensors have the following disadvantages.

Basically, when a catalyst or a chemical adsorption phenomenon is applied to the operation principle of a chemical sensor as a sensor, there is generally a conflict between durability and sensitivity of the catalyst. In other words, if the operation of the chemical sensor is used on the side that controls the activation of the catalytic reaction (low temperature side) in order to increase sensitivity, adsorption of various poisonous gases on the catalyst surface is likely to occur, and the deterioration of the catalyst proceeds quickly and the durability increases. do not have. Conversely, if the operation is used on the diffusion dominant side (high temperature side), the sensitivity may deteriorate.

For example, in the case of a gas sensor utilizing a resistance change of a metal oxide semiconductor, it is generally put into practical use as a gas leak alarm, but its durability is usually about three years.

This is due to deterioration of the semiconductor oxide due to the poisoning gas. When a chemical sensor is built into a combustion device,
The durability of the gas sensor is required to be about 10 years, and it is required to greatly improve the durability compared with the conventional technology.

[0014] In describing the carbon monoxide sensor, when the carbon monoxide sensor is mounted on a combustion device and used for the purpose of detecting incomplete combustion, the risk of incomplete combustion increases because the combustion device is considerably used. However, there is a risk that the carbon monoxide sensor is deteriorating, and if the output signal decreases due to the deterioration of the carbon monoxide sensor, incomplete combustion cannot be detected. There was a point.

In the case of the limiting current method using a zirconia solid electrolyte, the oxygen sensor also adsorbs the poisonous gas to the electrode that plays a central role in the oxygen reduction function, and the deterioration proceeds with time. The biggest challenge in practical use is how to ensure durability.

The reason why the output of the chemical sensor is reduced, that is, the deterioration is due to the deterioration of the electrode or catalyst which plays a central function of the chemical sensor with time as the reaction proceeds, This deterioration is caused by reduction of the catalyst activity by reducing the catalyst with reducing gas such as hydrogen and hydrocarbons present in the exhaust gas of combustion, and strong adsorption of sulfur-based compounds on the electrode surface. Then, the adsorption reaction which is the basis of the detection of carbon monoxide and oxygen is inhibited.

In these chemical sensors, noble metals are often used for electrodes, catalysts, etc., which play a central role in the sensor function. However, these noble metals are weak to sulfur compounds and silicone compounds and are liable to be deteriorated. There was a problem that securing was very difficult.

Since hydrocarbons coexisting in the exhaust gas of combustion equipment have a large molecular weight and a large molecular size, if they are adsorbed on the surface of a noble metal such as platinum, the adsorption of carbon monoxide and oxygen is hindered and the interference gas There was also a problem that it had an adverse effect.

Furthermore, since the sensor system is not essentially fail-safe, a highly reliable sensor with extremely high durability is required in order to be able to put it to practical use with high reliability. Even at the level, there was a problem that a sensor system that could properly establish durability was not realized.

[0020]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention solves the individual problems of the oxygen sensor and the carbon monoxide sensor, and integrates the oxygen sensor and the carbon monoxide sensor to form an oxygen sensor. By using a carbon monoxide composite sensor, the sensor has excellent durability that can be widely applied to combustion equipment.

The details will be described below. The oxygen / carbon monoxide composite sensor of the present invention is used for detecting gas and the respective gases of the solid electrolyte type oxygen sensor element and the solid electrolyte type carbon monoxide sensor element via the ceramic gas selective permeable body provided with the heating means. The related electrode portions are configured to be in contact with each other. That is, high durability is ensured by a configuration in which unnecessary gases other than oxygen and carbon monoxide necessary for operation as a sensor are prevented from flowing into a sensor function portion such as an electrode as much as possible by a ceramic gas selective permeable body.

The basic idea of the present invention is that most of the deterioration of the sensor is caused by the coexisting gas, so that the coexisting gas other than the gas necessary for detecting oxygen and carbon monoxide should not touch the gas detecting element. In this case, the idea is that if permanent durability can be achieved, and if permanent durability can be achieved, fail-out will not be a problem in practice.

That is, through the gas selective permeable body,
The configuration in which the gas containing the gas to be detected comes into contact with the gas detection element restricts the arrival of the coexisting gas which adversely affects the sensor life to the gas detection element.

The gas selective permeable body uses a porous body whose pores are controlled, and utilizes the difference in the gas permeation rate in the porous body to separate a gas to be detected from a coexisting gas unnecessary for detection. Do.

Generally, the permeation mechanism of gas molecules in the pores of a porous body changes as follows. In the gas phase flow, the pore size decreases from the viscous flow region where the collision between molecules is dominant, and the Knudse where the collision between the molecule and the pore wall dominates.
Move to the n (Knussen) diffusion region. At this time, the individual properties of the molecules appear, and the ratio of the permeation rates is theoretically given by the square root of the ratio of the molecular weights. Furthermore, as the pores become smaller and the size of the molecules becomes smaller, the gas molecules lose their freedom of movement in the direction perpendicular to the flow and cannot exist as a gas. This state is called a molecular sieve. In addition, surface diffusion in which molecules are transported while being adsorbed on the pore wall surface coexists with the gas phase flow. In particular, when the pressure exceeds the capillary condensation pressure, the surface diffusion shifts to the capillary condensation flow because the adsorbent layer covers all pores.

In the case of oxygen and carbon monoxide, coexisting gases such as hydrocarbon gas such as sulfurous acid gas and kerosene vapor which have a bad influence on carbon monoxide and oxygen necessary for the operation of the gas detection element are as follows: Since the molecular weights are different, the flow into the gas detection element can be regulated by the pore size of the Knudsen diffusion region. In addition, surface diffusion, capillary condensation flow,
By using the molecular sieve, the separation ability can be improved. In the present invention, in particular, by controlling the pore diameter on the order of angstrom and forming a film in the pores for the purpose of chemically modifying the surface of the pores, an effective gas selective permeability can be obtained in the porous body. Used by giving.

In particular, the gas is brought into contact with the gas detecting element through a gas selective permeable body whose pore diameter is controlled by a film containing at least one of silica and zirconia. 1 pore size
In the case of a size of 0 ° or less, the gas molecules exhibit molecular sieve type or surface diffusion type permeability, and the inflow is regulated by the size of the gas molecules, or the affinity between the gas molecules and the inner wall of the pores causes the inside of the porous body to be in a state. It has properties that determine its diffusivity.

Since kerosene vapor and silicone compounds have a large molecular size, the inflow can be effectively controlled, and the inflow of sulfur dioxide can be largely controlled, but the water vapor has the same level as carbon monoxide molecules. In general, it is not possible to control the inflow, and depending on the conditions, there is a concern that capillary condensation occurs in the pores of the porous body and the pores are blocked. In this regard, by coating the surface of the gas selective permeable material with a film containing at least one of silica and zirconia, strong hydrophobicity can be imparted, and the surface diffusivity of water vapor can be inhibited to prevent condensation of water vapor. Similarly, it also inhibits hydrophilic surface diffusion of sulfur dioxide and can block the inflow of sulfur dioxide.

As described above, the poisoning effect on the electrodes constituting the solid electrolyte type device can be reduced. The material of the porous base material must be made of ceramic from the viewpoint of heat resistance.

As the heating means, various means such as a heating wire and a resistance heater film can be applied. As a material used for the resistance heater film, a noble metal based material such as platinum is preferable in terms of durability. , An iron-chromium type and a nickel-chromium type can be used. The temperature control is carried out in combination with a heating means and, if necessary, with a temperature detecting means such as a thermistor or a thermocouple. Among these heating means, it is desirable to form and use a platinum resistance film on the gas selective permeable body from the viewpoint of uniform heating of the sensor. As a method for forming the platinum resistance film, any method such as a thick film printing method, a thin film method such as sputtering, and an electroless plating method may be used.

The ceramic porous substrate serving as the base of the gas selective permeable body will be described below. The ceramic porous substrate is prepared using a commercially available porous ceramic or porous glass. It is well known that porous ceramic or porous glass is used for various applications as a ceramic filter, for example, for separation of yeast from beer.
Although the pore diameter is about 0.05 μm to several μm, the gas cannot be selectively permeated as it is, so that it is necessary to fill the pores and control the pore diameter.

The method for controlling the pore diameter is to form a sol-gel film on the surface of the pores.

Alternatively, a CVD method in which a film is formed in the pores by thermal decomposition to control the pores is a promising method, but various known film formation methods can be applied.

Of these, for example, a method utilizing a metal alkoxide decomposition reaction (sol-gel method) or a CVD reaction is effective, and the pore diameter can be controlled to the diameter of the gas molecular diffusion region. According to these methods, the pore diameter can be controlled to uniform pores having an average pore diameter of 10 ° or less. The CVD method can control the pore diameter finer and more uniformly than the sol-gel method. In this case, the size of the pores must be reduced to the size of the gas molecules, and the movement of gas in the pores of the porous body is affected by the interaction between the gas and the substance on the surface of the pores. Has complex diffusion properties, but basically the gas permeation process is in the region of molecular sieve diffusion or surface diffusion, which significantly impedes the permeation of large molecules or has an affinity with the inner wall of the pore. Therefore, it is necessary to prevent molecules having a large size or molecules having low affinity with the inner wall of the pore from passing through the gas selective permeator so as to have a property such that the diffusion property is regulated by the gas.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention is directed to a method in which a detection gas is taken in through a ceramic gas selective permeable body provided with a heating means, so that each gas of a solid electrolyte type oxygen and carbon monoxide sensor is supplied. Is configured so that the electrode section involved in taking in the ceramic gas comes into contact with the ceramic gas selective permeable body.

The solid electrolyte type oxygen sensor is heated by heating means,
In addition, the carbon monoxide sensor has oxygen ion conductivity of the solid electrolyte, and the operation as a sensor under a predetermined temperature condition such as the adsorption characteristics of the electrode and the oxidation activity of the catalyst is ensured. The temperature is 400 to 50 by the heating means.
It is desirable to heat the sensor element to 0 ° C.

Although the solid electrolyte type oxygen sensor and the solid electrolyte type carbon monoxide sensor are different in the structure in detail, the operating temperature is common in relation to the driving temperature of the solid electrolyte. Operation is possible under the same temperature environment conditions with a common heat source. In addition, an electrode commonly arranged on the solid electrolyte has a function of taking in oxygen, and the function of taking in oxygen is related to the operating principle of the oxygen and carbon monoxide sensor itself, and is a source of gas detection as a sensor. By arranging the electrode which is the source in contact with the ceramic gas selective permeable body provided with the heating means, all of the gas can be taken into the oxygen and carbon monoxide sensor through the ceramic gas selective permeable body.

Therefore, the gas flowing toward the electrode is restricted by the ceramic gas selective permeable material from flowing into the electrode, such as sulfur dioxide, which adversely affects the electrode deterioration. Durability.

The solid electrolyte type carbon monoxide sensor can obtain an electromotive force output by the ratio of oxygen adsorbed on a pair of platinum electrodes in a potentiometric manner, while the oxygen sensor is a coulometric and reduction reaction in a cathode. It is necessary to apply a DC voltage from the outside for performing (ie, a reaction of reducing oxygen gas into oxygen ions) and an oxidation reaction (ie, a reaction of oxidizing oxygen ions into oxygen gas). Therefore,
It is necessary that the ceramic gas selective permeable member is arranged such that three electrodes of a pair of electrodes of a carbon monoxide sensor and an electrode (cathode) of the oxygen sensor which performs a reduction reaction are brought into contact with each other. These electrodes are generally platinum electrodes, but are not limited thereto.

One of the pair of electrodes of the carbon monoxide sensor needs to be provided with a porous carbon monoxide oxidation catalyst having the ability to oxidize carbon monoxide and the permeability to gases such as oxygen. is there. Since the porous carbon monoxide oxidation catalyst only needs to be in a flow path through which the gas to be detected can diffuse to one of the pair of electrodes, outside or inside the ceramic gas selective permeable body provided with the heating means, or It may be arranged inside the ceramic gas selective permeable body. The porous carbon monoxide oxidation catalyst may be any porous body that has the ability to oxidize carbon monoxide under the temperature conditions provided by the heating means and has the ability to diffuse oxygen gas. Transition metals such as oxides, composite oxides, and noble metals such as platinum and palladium supported on various carriers such as porous ceramics can be used. The heat-resistant metal sintered body whose surface is treated with a porous ceramic may be used as the carrier. Further, a ceramic sheet or the like manufactured by mixing ceramic fibers such as silica / alumina fibers and a powdery oxidation catalyst may be used.

The operation of the oxygen / carbon monoxide composite sensor will be described. In the oxygen sensor section, a DC voltage is applied to electrodes on both surfaces of the solid electrolyte. With this voltage, oxygen passes through the ceramic gas selective permeable material and reaches the cathode electrode, where it is reduced and receives a negative charge,
It becomes oxygen ions and moves in the solid electrolyte to reach the anode, where it is oxidized and receives a positive charge, and escapes to the back side as oxygen gas. During this time, the diffusion of oxygen is restricted where it passes through the ceramic gas selective permeable body,
A limiting current occurs. Since this limit current is proportional to the oxygen concentration of the environment where the sensor is placed, the oxygen concentration is detected by knowing the limit current. As for carbon monoxide, on a pair of platinum electrodes on the solid electrolyte, one electrode has no carbon monoxide because carbon monoxide is oxidized by a porous carbon monoxide oxidation catalyst on the way, A gas containing oxygen reaches the other electrode, and carbon monoxide and oxygen reach the other electrode. However, on this electrode, it is reduced by carbon monoxide and the oxygen concentration becomes low. That is, since the oxygen concentration is different between the pair of electrodes, an electromotive force output by the oxygen concentration cell is generated between the electrodes. Since this electromotive force output is related to the carbon monoxide concentration, the carbon monoxide concentration is detected. It is to be noted that a lead wire is necessary for extracting these output signals, and an amplifier, a circuit, and the like are also necessary.

According to the above-described structure, the detection gas which has an adverse effect on the electrode is a gas selective permeable member, and is regulated and reaches the electrode portion, thereby realizing an oxygen / carbon monoxide composite sensor having excellent durability.

In the second embodiment of the present invention, a pair of platinum electrodes are formed on the front and back surfaces in contact with a ceramic gas selective permeable body having a heating means on the surface and a porous catalyst in a part of the heating means. And an oxygen ion conductive solid electrolyte provided with a pair of platinum electrodes on one surface. A porous carbon monoxide oxidation catalyst required for the operation of the carbon monoxide sensor is arranged in a part of the heating means of the ceramic gas selective permeable body. The region is arranged at a position suitable for gas to flow onto one of the pair of platinum electrodes. The composite sensor is manufactured by bonding an independent oxygen and carbon monoxide solid electrolyte element to a ceramic gas selective permeable material using glass or an inorganic adhesive. As the solid electrolyte, a bulk sintered product is used.

As described above, the oxygen / carbon monoxide composite sensor having excellent durability can be obtained by the above configuration.

A third embodiment of the present invention is directed to a ceramic gas selective permeable body provided with a heater membrane, a platinum electrode layer divided into three regions on its surface, and then two platinum electrode layers and one platinum electrode layer. And a platinum electrode layer formed on the yttria-stabilized zirconia layer coated with one platinum electrode layer. A part is provided with a porous carbon monoxide oxidation catalyst.

The present sensor uses a ceramic gas selective permeable member on which a heater film has been formed in advance as a substrate, and uses a predetermined pattern, for example, a thin film method such as sputtering to form platinum, yttria-stabilized zirconia,
Furthermore, after forming a composite element by laminating with platinum to form a film, a porous carbon monoxide oxidation catalyst is bonded to a part corresponding to one side of a pair of platinum electrodes in a part of the heater film. Is done. Although there is a technical problem in forming the solid electrolyte layer as a thin film as compared with the second embodiment, the adhesion between the ceramic gas selective permeable body and the platinum electrode is improved.

The oxygen / carbon monoxide composite sensor having excellent durability can be obtained by the above-described configuration in the same manner as in the first and second embodiments.

The fourth embodiment of the present invention relates to an oxygen ion conductive solid electrolyte having a pair of platinum electrodes formed on the front and back surfaces in contact with a ceramic gas selective permeable body having heating means on the front surface. An oxygen ion conductive solid electrolyte formed by forming a pair of platinum electrodes on the front and back surfaces is provided with a ceramic gas selective permeable body provided with a porous carbon monoxide oxidation catalyst on the opposite surface. In the present embodiment, the platinum electrode of the carbon monoxide sensor with respect to the oxygen ion conductor solid electrolyte,
Since they are arranged in a facing type, two ceramic gas selective permeable members are arranged on each electrode. One is a ceramic gas selective permeable body provided with a heating means and is used in common with the electrode of the oxygen sensor, and the other is used exclusively for the carbon monoxide sensor. Since the gas flow into the electrode is all performed through the ceramic gas selective permeable body, in the case of this embodiment, oxygen having excellent durability as in the first to third embodiments, A carbon monoxide composite sensor is obtained.

In the fifth embodiment of the present invention, a ceramic gas selective permeable material whose pore size is controlled using at least one selected from the group consisting of silica and zirconia is used. When the pore diameter is controlled and, for example, pores of 10 ° or less are formed, if the pore surface is a hydrophilic material, there is a risk that water vapor will condense and block the pores. In the case of a hydrophilic material, an acid gas such as a sulfurous acid gas is also not desirable because it easily penetrates into the pores. This is the same even when the pore diameter is even larger. When the pore size is controlled using at least one selected from the group consisting of silica and zirconia, the coating has excellent acid resistance and shows stable characteristics. In the environment such as the exhaust gas of the combustion equipment, the effect of the above treatment is particularly effective.
As described above, according to the present embodiment, a composite sensor having excellent durability can be obtained.

According to the fifth embodiment of the present invention, the voltage is continuously or periodically applied to the oxygen sensor in accordance with the operation information of the combustor in a state where the composite sensor is heated by the heating means. The combustion characteristics are evaluated and determined using the continuous or intermittent oxygen concentration signal obtained as a result thereof and the carbon monoxide concentration signal obtained as a continuous output value, and an alarm signal is output and the combustion air amount is output. Is provided. The responsiveness of the limiting current type oxygen sensor is related to the characteristics of the electrode, the voltage, and the like, but is related to the volume of the diffusion channel of the sensor. In the configuration of the present invention, the platinum electrode and the ceramic gas selective permeable body are arranged in a close contact configuration, so that
Since the volume in the pores of the ceramic gas selective permeable body is very small, high-speed response within 1 second is realized. Since the usage of the water heater and the heater is basically different in a consumer combustion machine, the required durability time is different. That is, in the case of a water heater, the time is from 3,000 hours to 5,000 hours, whereas in the case of a heater, it is 15,000 to 25.0 hours
00 hours and the heater is long. However, regarding the combustion control, the required level of responsiveness differs between the heater and the water heater. That is, in the heater, the demand for the responsiveness of the water heater is 1
While quick response at the second level is required, there is no problem even if the response is slow at the 30-second level in the heater. Possibly, assuming that the oxygen sensor had the durability to withstand 5,000 hours of electricity,
Even if it can be put to practical use with a water heater, it will not be possible with a heater. When used for heating, taking into account the demand for responsiveness, 1
If an intermittent operation that responds once every 0 seconds but responds for 1 second is carried out, 50, which is ten times 5,000 hours as it is
A durability of 000 hours will be realized. In the configuration of the present invention, the response of the oxygen sensor is as fast as 1 second or less, so that such usage is possible. However, if a slightly faster response is desired, for example, at the timing of switching the combustion amount, it is also possible to output a signal from the combustor to switch the operation timing. Further, by referring to both the signal of the carbon monoxide concentration and the signal of the oxygen concentration, it is possible to grasp information related to the combustion state more effectively than when the sensor is used alone. As described above, according to the present embodiment, a composite sensor having excellent durability can be obtained.

[0051]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A more specific embodiment of the present invention will be described below with reference to FIGS.

(Embodiment 1) FIG. 1 is a schematic sectional view of an oxygen / carbon monoxide composite sensor according to Embodiment 1 of the present invention. In FIG. 1, reference numeral 1 denotes a heating unit which is formed, for example, of a resistance film. 2 is a ceramic gas selective permeable body. The ceramic gas selective permeable body 2 is formed by using a ceramic porous base material having a pore diameter of 0.1 to 1 μm produced by a sintering method such as alumina or zirconia.
A pore control film is formed on the pore surface by a sol-gel method or a CVD method and used. The ceramic raw material powder is formed as it is or mixed with an organic substance such as a resin, molded into a predetermined shape, and then sintered at a temperature lower than the temperature for complete sintering. The average pore diameter of the porous body produced by the sintering method is limited to 0.1 μm.

Therefore, in order to use it for the purpose of the present invention, it is necessary to use a porous substrate produced by a sintering method and treat its pores with a coating film. Since the porous body produced by the sintering method is generally commercially available as a microfiltration membrane, the commercially available ceramic porous substrate can be used in the present invention.

Next, a method for controlling pores by the sol-gel method will be described below. After hydrolyzing a metal alkoxide such as zirconium isopropoxide or tetraethoxysilane, it is subjected to polycondensation under catalytic conditions such as hydrochloric acid to prepare a desired sol solution. When the porous ceramic is contacted with a porous ceramic having pores penetrating the sol solution, for example, when the porous ceramic is immersed in the sol, the sol solution is sucked by capillary force, and when the sol is dried, the sol solution is dried in the pores of the porous ceramic. Concentration of the sol and further gelation occur. Further, when heating is further advanced, sintering proceeds from gelation to form a coating film. If necessary, a method of filtering the sol solution using a porous ceramic can also be adopted. Using this method, the pore size can be controlled. By adjusting the wettability of the pore surface of the porous ceramic, the solvent of the sol, the concentration of the sol, the immersion time, the pulling speed of the ceramic, and the like, a gas selective permeable material having a relatively uniform pore diameter can be obtained.

In addition to the sol-gel method, the pores may be controlled by forming and growing an oxide film in the pores of the porous body while thermally decomposing the compound in a flow system by a CVD method. Reference numeral 3 denotes a solid electrolyte type oxygen sensor, that is, a limiting current type oxygen sensor. 4 is a solid electrolyte type carbon monoxide sensor.
Nos. 3 and 4 are arranged in such a manner that the electrode portion that comes into contact with the gas is in contact with the ceramic gas selective permeable body. In any case, the gas component which is adsorbed on the electrode and adversely affects the sensor life is obtained by the ceramic gas selective permeable body 2 having a controlled pore diameter.
Since the arrival at the electrode surface is suppressed or prevented, the life can be extended.

(Embodiment 2) FIG. 2 is a conceptual cross-sectional view of a main part of an oxygen / carbon monoxide composite sensor according to Embodiment 2 of the present invention. In FIG. 2, a pair of platinum electrodes 6 are formed on the front and back surfaces in contact with a ceramic gas selective permeable body 2 provided with a heating means 1 on a front surface and a porous carbon monoxide oxidation catalyst 5 in a partial area thereof. And an oxygen ion conductive solid electrolyte 9 having a pair of platinum electrodes 8 on one side.

Reference numeral 10 denotes a seal for realizing a sealed structure between the electrode and the ceramic gas selective permeable body. The seal joins both using various inorganic adhesives and glass compositions. The porous carbon monoxide oxidizing catalyst may be any one having a property of oxidizing carbon monoxide when a gas containing carbon monoxide permeates between the gas and the gas. What carried the oxidation catalyst in the porous body can be used. For example, as the porous carbon monoxide oxidation catalyst, ceramic paper obtained by mixing oxidation catalyst particles together with ceramic fibers may be used. This ceramic paper is made of iron, manganese, copper, nickel, cobalt,
A transition metal oxide catalyst powder such as chromium, or an oxidation catalyst powder supported on a porous carrier such as alumina together with a noble metal element in water together with ceramic fibers such as silica / alumina fibers and an inorganic binder such as alumina sol or colloidal silica. It is prepared by filtering, compressing and drying from the dispersed state. The porous carbon monoxide oxidation catalyst film of this example has an excellent porous property because the oxidation catalyst having a function is maintained in a state of being uniformly dispersed in the matrix and has excellent oxygen diffusibility. The catalytic carbon monoxide oxidation catalyst film can be formed.

The composite sensor of this embodiment is manufactured by bonding an independently manufactured oxygen and carbon monoxide solid electrolyte element to a ceramic gas selective permeable material using glass or an inorganic adhesive. . Using two solid electrolytes such as yttria-stabilized zirconia, one formed a pair of platinum electrodes on one surface and the other formed platinum electrodes on both surfaces, and then used a heater film or the like. A composite sensor element is formed by forming a heating means and joining with a ceramic gas selective permeable body whose pore control has already been performed with an inorganic adhesive or the like. Further, a porous carbon monoxide oxidation catalyst is formed at a position corresponding to one of the pair of platinum electrodes on the heating means to obtain a composite sensor.

Also in this embodiment, the gas component adsorbed on the electrode and adversely affecting the sensor life is prevented or prevented from reaching the electrode surface by the ceramic gas selective permeable body 2 having a controlled pore diameter. Long life can be achieved.

(Embodiment 3) FIG. 3 is a conceptual sectional view of a main part of an oxygen / carbon monoxide composite sensor according to Embodiment 3 of the present invention. The configuration is very similar to that of Embodiment 2 in FIG.
The same components as those in FIG. 2 are denoted by the same reference numerals. The difference from FIG. 2 is that the oxygen ion conductive solid electrolytes 7 and 9 are in close contact with the ceramic gas selective permeable body 2. Basically, the configuration is also different because the manufacturing method of the sensor is different. That is, in the case of the third embodiment, the present sensor uses a ceramic gas selective permeable body on which a heater film has been formed in advance as a substrate, uses a predetermined pattern, and uses, for example, a thin film method such as sputtering to form platinum, After forming a composite element by laminating yttria-stabilized zirconia and further platinum to form a composite element, a porous carbon monoxide oxidation catalyst is applied to a part of the heater film corresponding to one side of a pair of platinum electrodes. Are bonded by using an inorganic adhesive or the like. The platinum electrode is formed with a part thereof protruding from the oxygen ion conductive solid electrolyte so that a lead wire can be taken out later. Since the electrode is formed in close contact with the ceramic gas selective permeable body, it is guaranteed that the gas will reach the electrode only through the ceramic gas selective permeable body. In addition, since the diffusion volume of the oxygen sensor is only the pore volume of the ceramic gas selective permeable body, high-speed response is realized. Other basic operations are the same as those in the first and second embodiments.
Also in the present embodiment, the gas component adsorbed on the electrode and adversely affecting the sensor life is prevented or prevented from reaching the electrode surface by the ceramic gas selective permeable body 2 whose pore diameter is controlled, thereby extending the life. Can be achieved.

(Embodiment 4) FIG. 4 is a conceptual sectional view of a main part of an oxygen / carbon monoxide composite sensor according to Embodiment 4 of the present invention. In the present embodiment, since the platinum electrode 8 of the carbon monoxide sensor section is arranged to face the solid electrolyte 9, the ceramic gas selective permeable body 2 is additionally provided. is there. The first ceramic gas selective permeable member is used in contact with one surface of a platinum electrode 6 for an oxygen sensor by a ceramic gas selective permeable member 2 provided with a heating means 1, and the other ceramic gas selective permeable member is monoxide. It is used exclusively for the platinum electrode 8 on the opposite side of the carbon sensor. The oxygen / carbon monoxide composite sensor of the present embodiment is formed by separately forming individual elements and then bonding and sealing with the large size ceramic gas selective permeable body 2 using the sealing agent 11.

The method of manufacturing the composite sensor of this embodiment is similar to that of the second embodiment, except that the independently manufactured oxygen and carbon monoxide solid electrolyte elements are made of a large size using glass or an inorganic adhesive. It is manufactured by bonding with a ceramic gas selective permeable body. Using a pair of solid electrolytes such as yttria-stabilized zirconia, a pair of platinum electrodes are formed on both surfaces facing each other. One corresponding to the oxygen sensor is as it is, and the other corresponding to the carbon monoxide sensor is
A small sized ceramic gas selective permeable body is bonded on one side of the platinum electrode, and a porous carbon monoxide oxidation catalyst body 5 is formed on the surface thereof. The element in such a state is joined to a ceramic gas selective permeable body 2 provided with a heating means 1 of a large size to complete. Also in the present embodiment, the gas component adsorbed on the electrode and adversely affecting the sensor life is prevented or prevented from reaching the electrode surface by the ceramic gas selective permeable body 2 whose pore diameter is controlled, thereby extending the life. Can be achieved.

(Embodiment 5) FIG. 5 is a schematic sectional view of a pore portion of a ceramic gas selective permeable body of an oxygen / carbon monoxide composite sensor according to Embodiment 3 of the present invention. In FIG. 5, reference numeral 12 denotes a substrate of a ceramic gas selective permeable body,
Reference numeral 13 denotes a surface film, and pore control is performed by one or more films selected from the group consisting of silica and zirconia.

In particular, the ceramic gas selective permeable material is preferably set at 10 °
In the case where the film is processed to have the following average pore diameter, the control of the pores by the film formation of the present example becomes effective. Pores of 10 ° or less show an effective molecular sieving effect that does not allow passage of high molecular weight gas in the gas flow flowing from the outside to the inside of the ceramic gas selective permeable body. In addition, the interaction with the gel film formed inside the pores, that is, the pore control treatment film, increases selectivity in gas permeability. That is, the intermolecular force between the gas molecule and the gel molecule is determined by the orientation force due to the interaction between the permanent hyperboloids, the induced force between the permanent hyperboloid and the induced hyperboloid, and the gas permeation due to the dispersion force based on the van der Waals interaction. Has a selectivity, that is, a surface diffusivity, but a hydrophobic pore control film containing one or more of silica and zirconia is a problem in applying a porous body having a pore diameter of a region of 10 ° or less. There is no problem of clogging of pores due to capillary condensation, and it is possible to completely block the entry of a gas that degrades a platinum electrode such as SO2, thereby contributing to a longer life of the electrode of the composite sensor.

(Example 6) Hereinafter, experimental results relating to the effects of the present invention will be described.

The ceramic gas selective permeable body was manufactured in the following procedure. Using a zirconia porous substrate (average pore diameter of 0.2 μm, cut into dimensions of 12 mm × 5 mm × 0.5 mm) prepared by adjusting the particle size distribution and firing temperature by the doctor blade method, zirconia isopropoxide is used. The pores were controlled by immersion treatment in an alkoxide solution containing as a main component. The fine pores were controlled by applying a 20 Wt% solution of alkoxide and applying the same again. The average pore diameter was evaluated by a mercury porosimetry using a porosimeter. The average pore size is
Since the thickness was 0.1 μm and the thickness was 0.08 μm in three coats, three coats were used as a sample. Using this ceramic gas selective permeable material as a substrate, a patterned platinum resistance film was formed by applying, drying and firing by a thick film printing method. Resistance value is about 5Ω
Met.

Next, two yttria-stabilized zirconia (YSZ) substrates manufactured by Nippon Fine Ceramics Co., Ltd., each having a size of 5 mm × 5 mm × 0.35 mm, were used. Was used to form a pair of 3 mm × 1.5 mm platinum electrodes by a sputtering method.

On the other YSZ, platinum electrodes of 3 mm × 3 mm were formed on both surfaces by the same sputtering method. In each case, a platinum lead wire having a diameter of 0.1 mm was taken out of the platinum electrode in a state where the joint was baked using a platinum paste and fixed. The above solid electrolyte element was fired using a commercially available inorganic adhesive "Sumiceram" (trade name),
It was joined with the above-mentioned ceramic gas selective permeator.

Next, a porous carbon monoxide oxidation catalyst was prepared in the following procedure. First, the catalyst has a particle size of 40 /
0.1wt% platinum and palladium supported on 60 mesh γ alumina (chloroplatinic acid, nitric acid of palladium chloride,
After adsorbing the aqueous hydrochloric acid solution, reduction with an aqueous sodium borohydride solution) an oxidation catalyst powder was produced.

The oxidation catalyst powder was mixed with silica-alumina fiber at a basis weight of 500 g / m 2 using colloidal silica as a binder to obtain a 30 cm square sheet having a thickness of 1 mm.

Next, this sheet was cut into 2.5 mm × 5 mm for use. The porous carbon monoxide oxidation catalyst was bonded from above the platinum resistance film to the position corresponding to one electrode of the carbon monoxide element of the ceramic gas selective permeable body formed with the platinum resistance film using an inorganic adhesive. .

As a comparative sensor, a 5 mm square element exactly the same as the previously manufactured solid electrolyte system was prototyped, and a porous carbon monoxide catalyst was directly bonded to one side, and a ceramic gas selective permeable body and a surface heater were provided. A solid electrolyte type carbon monoxide sensor containing no carbon monoxide was prototyped. The element of the corresponding part of the oxygen sensor is bonded to a 5 mm × 5 mm × 0.5 mm alumina substrate with a laser and a base material with a 30 μm diameter through hole, and a pinhole type limiting current type An oxygen sensor was prototyped.

The basic characteristics of each sensor were evaluated using a flow-through test apparatus. Both the oxygen sensor portion of the composite sensor and the pinhole type oxygen sensor showed limiting current characteristics with respect to oxygen concentration. At an applied voltage of 0.8 V, the composite sensor showed a limit current value of about 60 μA in contrast to about 95 μA of the pinhole type in the atmosphere in all cases. The response when the oxygen concentration was changed from 10% to the atmosphere was 13 seconds in the pinhole method, whereas the response was 0.2 seconds in the composite sensor.
Seconds and good response characteristics. In the case of a sensor that does not include a ceramic gas selective permeator, about 53 ppm for carbon monoxide,
For mV, the carbon monoxide sensor section of the present composite sensor
Although the sensitivity was reduced to about 11 mV, the responsiveness was not different between both in about 30 seconds.

The durability of the prototype composite sensor was evaluated by an acceleration test using a flow-type test device through 100 ppm of sulfur dioxide gas. The test was conducted by continuously ventilating air containing sulfur dioxide at a concentration of 100 ppm into the general atmosphere and stopping intermittently with the sulfur dioxide gas. The sensor output when air containing 1000 ppm of carbon monoxide was supplied was confirmed. However, for the oxygen sensor, 0.8
V voltage is continuously applied. In the case of a carbon monoxide sensor that does not include a ceramic gas selective permeator produced at the same time as a comparative sample, the zero point is 150 mV in about 13 hours.
While the output was lost and the output was lost, in the case of the composite prototype sensor, the sensor output was maintained at a stable output of about 10 mV even after about 650 hours had elapsed. Also,
In the case of the pinhole type oxygen sensor, the output decreased when the limit current value was about 35 hours, whereas in the case of the composite sensor, the current value decreased to 52 μA, which was slightly less than 20% after about 650 hours. However, stable characteristics were maintained. In particular,
As the usage of the oxygen sensor, the amount of gas flowing into the electrode is
Since the flow of the poisoning gas into the electrode is suppressed by controlling the total amount of the current, the voltage applied to the oxygen sensor is intermittently increased by, for example, 3
It is possible to extend the life by turning on and off such as 2 seconds at 0 seconds and using the battery while holding the limit current value during that time. In particular, in the case of a heater for a consumer appliance that requires a long life, the above-described operation can be performed because high-speed response is not required. This usage is due to the rapid response of the oxygen sensor due to the pore characteristics of the present composite sensor. Further, when a transient change is expected for the oxygen sensor according to the operation information provided by the combustor, fine operations such as changing the voltage from periodic to continuous can be performed. In addition, since the oxygen sensor and the carbon monoxide sensor are integrated, it is possible to grasp an accurate combustion state such as abnormal combustion by combining both signal information.

[0075]

The oxygen / carbon monoxide composite sensor of the present invention is implemented in the form described above, and the following effects can be obtained.

(1) Regarding the detection of oxygen and carbon monoxide, the effect of protecting the electrode of the ceramic gas selective permeator is
The extremely long service life can cover the weak points of fail-out, and practical fail-safe can be expected. Therefore, an oxygen / carbon monoxide composite sensor integrating these sensor functions has high reliability and is suitable for installation in a combustion device or the like.

(2) By combining the sensors, it is possible to share the ceramic gas selective permeable body for controlling the inflow of the poisoning gas reaching the electrodes and the heating means for operating the solid electrolyte type sensor. it can.

(3) A compact sensor system can be configured as a whole, can be easily installed in the exhaust gas flow path of the combustion equipment, and the operation mode can be used continuously or intermittently. Widely applicable to combustion equipment.

(4) By integrating the respective sensor information of the composite sensor, it is possible to accurately grasp the combustion state over a long period of time.

[Brief description of the drawings]

FIG. 1 is a conceptual sectional view showing a composite sensor of oxygen and carbon monoxide according to a first embodiment of the present invention.

FIG. 2 is a conceptual sectional view showing a composite sensor of oxygen and carbon monoxide according to a second embodiment of the present invention.

FIG. 3 is a conceptual sectional view showing a composite sensor of oxygen and carbon monoxide according to a third embodiment of the present invention.

FIG. 4 is a conceptual sectional view showing a composite sensor of oxygen and carbon monoxide according to a fourth embodiment of the present invention.

FIG. 5 is a sectional view of a main part of a ceramic gas selective permeable body according to a fifth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating means 2 Ceramic gas selective permeable body 3 Solid electrolyte type oxygen sensor 4 Solid electrolyte type carbon monoxide sensor 5 Porous carbon monoxide oxidation catalyst 6, 8 Platinum electrode (electrode) 7, 9 Oxygen ion conductive solid electrolyte

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Takahiro Umeda 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Kunihiro Tsuruta 1006 Odaka Kadoma Kadoma City Osaka Pref.

Claims (6)

[Claims] 1. A solid electrolyte type oxygen / carbon monoxide composite sensor having a configuration in which a detection gas and an electrode portion for taking in gas of each element come into contact with each other via a ceramic gas selective permeable body provided with a heating means. 2. An oxygen ion conductive material comprising a pair of electrodes formed on the front and back surfaces in contact with a ceramic gas selective permeable member having a heating means on its surface and a porous carbon monoxide oxidation catalyst in a part of the heating means. An oxygen / carbon monoxide composite sensor comprising a conductive solid electrolyte and an oxygen ion conductive solid electrolyte having a pair of electrodes on one surface. 3. A ceramic gas selective permeable body provided with a heater membrane, an electrode layer separated into three regions on the surface thereof, and then two electrode layers and one electrode layer, respectively, and are separated into two regions. Yttria stabilized zirconia layer,
An oxygen / carbon monoxide composite sensor comprising an electrode layer formed on a yttria-stabilized zirconia layer coated with one electrode layer, and a porous carbon monoxide oxidation catalyst disposed on a part of the heater film. 4. An oxygen ion conductive solid electrolyte comprising a pair of electrodes formed on the front and back surfaces in contact with a ceramic gas selective permeable body provided with a heating means on the front surface, and a pair of electrodes formed on the front and back surfaces. An oxygen / carbon monoxide composite sensor comprising a ceramic gas selective permeable body provided with a porous carbon monoxide oxidation catalyst on the opposing surface using an oxygen ion conductive solid electrolyte. 5. The oxygen gas according to claim 1, wherein a ceramic gas selective permeator whose pore diameter is controlled using at least one selected from the group consisting of silica and zirconia is used.
Carbon monoxide composite sensor. 6. In a state where the composite sensor is heated by the heating means, the voltage is continuously or periodically applied to the oxygen sensor in accordance with the operation information of the combustor, and the continuous sensor is obtained. Or means for evaluating and determining combustion characteristics using an intermittent oxygen concentration signal and a carbon monoxide concentration signal obtained as a continuous output value, outputting a warning signal and controlling the amount of combustion air. 1
An oxygen-carbon monoxide composite sensor according to claim 1.