JP2868913B2 - Solid electrolyte gas sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sensor using a permselective membrane made of a solid electrolyte. In particular, when the detection gas is electrolyzed at a speed greater than the supply speed of the detection gas supplied to the detection unit of the sensor and the voltage suddenly rises due to the discharge of the detection gas or when the supply speed of the detection gas is limited. The present invention relates to a gas sensor of a type in which the concentration of a detected gas is determined by measuring the current, that is, the limiting current, that is, the limiting current gas sensor. More specifically, the present invention relates to a solid electrolyte gas sensor having a feature in a mechanism for supplying a detection gas to a detection unit in a limiting current gas sensor.

[0002]

2. Description of the Related Art A limiting current type solid electrolyte gas sensor has been known in the art, and its advantages are that it can measure over a wide concentration range as compared with a concentration cell type oxygen sensor, can be miniaturized, and does not require a reference gas. Is known. The basic structure of the limiting current type solid electrolyte gas sensor is that the electrode to be measured is supplied to one electrode (electrode for ionizing the detected gas) of the detection part of the sensor with electrodes disposed on both sides of the ion conductive solid electrolyte. In order to control the supply amount of the mixed gas, the electrode is covered with a cap having a capillary, or the electrode is covered with a porous ceramic. In these structures, the gas mixture to be measured is supplied to the electrode through a capillary or a pore of a porous ceramic. Therefore, the detected gas in the measured gas mixture is
The electrode reaction ionizes itself or becomes another ion generated by the electrode reaction (collectively, ions generated by the electrode reaction), and reaches the opposite electrode through the solid electrolyte. Then, it is gasified and released by a reaction reverse to the ionization reaction. Here, the limiting current is generated by increasing the discharge speed of the gas at the detection portion of the sensor than the supply speed of the detection gas supplied by gas diffusion from the pores of the capillary or the porous ceramics. Since the supply to the sensor detection unit is governed by the speed at which the detection gas diffuses in the cap through the capillary or in the pores of the porous ceramic, a subtle change in the diffusion resistance in the pores, for example, the mixed gas to be measured The threshold current value fluctuates easily due to the influence of the adhesion of the solid suspended matter present therein, and the measured value of the detection gas fluctuates. In particular, in order to clearly generate the limit current value, it is necessary to increase the diffusion resistance of the detection gas. For this reason, it is necessary to lengthen the path of the pore portion. However, the gas mixture to be measured often contains suspended solids and mist, and the disadvantage that measurement values are likely to be out of order due to the adhesion of the gas to the pores is unavoidable.

[0003]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for measuring the concentration of a detection gas over a long period of time even when a solid or viscous suspended matter is present in the gas mixture to be measured. Or partial pressure) can be accurately measured.

Another object of the present invention is to provide a solid electrolyte membrane which can selectively transmit ions generated by an electrode reaction of a detection gas contained in a mixed gas to be measured, and porous conductors are present on both surfaces of the solid electrolyte membrane. Through a detection gas control screen consisting of a structure electrically connected to form an oxidation or reduction potential of the detection gas or a potential difference between the conductors, or higher,
The detection gas is supplied to a detection portion of the sensor, and the limit current value is measured by a solid electrolyte gas sensor configured to discharge the detection gas at a pumping speed higher than a speed at which the detection gas is supplied at the detection portion. To provide a method for measuring the gas concentration.

[0005]

That is, according to the present invention,
Porous conductors are present on both surfaces of the solid electrolyte membrane that can selectively transmit ions of the detection gas contained in the mixed gas to be measured or ions generated by an electrode reaction of the detection gas, and both conductors are formed of the detection gas. A detection gas control screen having a structure electrically connected to form a potential required for oxidation and reduction; and a detection unit of a solid electrolyte gas sensor, wherein the detection gas control screen covers an ionization electrode of the detection unit. And the amount of ion permeation per unit time of the solid electrolyte membrane of the detection gas control screen is set to be smaller than the amount of ion permeation of the detector under the operating conditions. A featured solid electrolyte gas sensor is provided.

Further, according to the present invention, porous conductors are present on both surfaces of a solid electrolyte membrane capable of selectively transmitting ions generated by an electrode reaction of a detection gas contained in a mixed gas to be measured, and Both conductors supply the detection gas to the detection unit of the sensor through a detection gas control screen having a structure electrically connected to form a potential required for oxidation and reduction of the detection gas, and the supplied detection A method for measuring the concentration of a detected gas in a mixed gas to be measured, characterized by measuring a limit current value by a solid electrolyte gas sensor having a detecting portion having a pumping speed higher than a gas supply speed.

As shown in FIGS. 3 and 4, a conventional limiting current type solid electrolyte gas sensor has a cap having a capillary a on one electrode of a detection portion of a sensor in which electrodes 3 and 4 are present on both surfaces of a solid electrolyte 1, respectively. 2 (in the case of FIG. 4) or the porous ceramics 20 (in the case of FIG. 3) are provided to limit the amount of gas reacting on the electrode.

When the above-mentioned limiting current type solid electrolyte gas sensor is used as an oxygen sensor, the electrode 3 on the side provided with the cap or the porous ceramic is a cathode, and the electrode 4 on the opposite side is an anode, so that the electrode 3 is between the two electrodes. A voltage higher than the voltage required for oxygen reduction is applied by the power supply 5. On the cathode, oxygen is reduced to oxygen and ions (O ²⁻ ), and oxygen ions move to the anode side through the ion permeable layer 1 made of a solid electrolyte, and are oxidized on the anode to be released as oxygen gas. You. A current flows due to the movement of the oxygen ions.
This current can be measured by a lead wire 15 and by an ammeter 6 connected in series with the power supply 5.

[0009] Oxygen is supplied to the negative electrode side, will be pumped to the anode side becomes oxygen ions. Therefore, oxygen supplied to the cathode side is limited by the diffusion resistance of the capillaries a of the cap or the pores of the porous ceramics 20, and a limiting current having a certain relationship with the oxygen concentration in the mixed gas to be measured appears. The oxygen concentration can be known by measuring the limit current value with the ammeter 6 and obtaining a calibration curve for the relationship between the oxygen concentration and the limit current value in advance. In a standardized device, it is also possible to directly display the oxygen concentration from the limit current value based on the calibration curve.

However, such a limiting current type solid electrolyte gas sensor has a mechanism for supplying oxygen (detection gas) to the cathode surface, as described above, in which the size of pores for limiting the amount of gas diffusion and the size of the porous ceramics are limited. Control of porosity and pore diameter is not easy, and there are problems such as large variations in output current among sensor products, and fluctuations in measured values due to clogging during long-term use.

The present invention solves the above-mentioned drawbacks by using a detection gas control screen, which will be described in detail later, in place of a method of controlling the diffusion rate or amount of a detection gas by a cap with a capillary or a porous ceramic. The method uses a method in which the detection gas in the mixed gas to be measured is restricted by moving it through a solid electrolyte as ions generated by an electrode reaction. In this way, the detection gas in the gas to be measured does not move inside the pores by diffusion at all, and it is possible to supply the detection gas to the detection portion of the sensor. Thus, a sensor having few inconveniences such as a fluctuation of the measured value due to the use of the sensor can be obtained.

A gas sensor according to the present invention will be described with reference to FIGS. As can be seen from these examples, the present invention provides a solid-state device between the detecting portion of the sensor having the ion permeable layer 9 made of a solid electrolyte interposed between the electrodes 10 and 11, and the two porous conductors 12 and 18. The detection gas control screen is constituted by interposing an ion permeable layer 8 made of an electrolyte and electrically connecting both conductors 12 and 18. Then, between the two porous conductors constituting the detection gas control screen, a potential difference or ionization of the detection gas in the mixed gas to be measured or an electric potential difference to generate an ionic substance by an electrode reaction of the detection gas. A larger potential difference is formed. Such a potential difference generally occurs when the detection gas is oxygen or the like.
Are formed by the electromotive force of the concentration cell formed by the difference between the concentrations of the detection gases in contact with each other. However, depending on the type of the detection gas, the oxidation or reduction potential for ion generation may be large, and when the overvoltage between the detection gas and the porous conductor 12 is large, FIG.
The voltage should be appropriately applied from the external power supply 22 as illustrated in FIG. The mechanism of the detection unit of the sensor is the same as that of a conventionally known limiting current type solid electrolyte gas sensor. That is, the ion permeable layer 9 made of a solid electrolyte is interposed between the electrodes 10 and 11, and the power source 5 and the ammeter 6 are connected in series between the electrodes 10 and 11 by the lead wire 15 to form a circuit. I have. The periphery of the detection gas control screen and the detection portion of the sensor are hermetically sealed by a sealing material 7. The material of the sealing material 7 is not particularly limited as long as it is impermeable to a detection gas, for example, an oxygen gas. Examples of suitable materials include glass, inorganic cement, low melting point ceramics, and the like. Among these materials, those having a thermal expansion coefficient equal to or slightly smaller than that of the ion-permeable layer are preferably used. Also, from the viewpoint of bonding properties, it is more preferable to use as a fine powder having a particle size of 10 μm or less, preferably 5 μm or less. It is also industrially meaningful to coat the side surfaces of the detection gas control screen and the detection portion of the sensor with a sealing material and form the casing 14 as necessary to increase airtightness and protect the outside.

The present invention is characterized in that an ion-permeable layer composed of two solid electrolytes is used, and these ion-permeable layers may be any solid electrolyte that transmits desired ions. Can be used. For example, when the detection gas is oxygen, generally, CeO ₂ , ZrO
_At least one kind of oxide such as H ₂ , HfO ₂ , ThO ₂ , Bi ₂ O ₃ includes CaO, Y ₂ O ₃ , Gd ₂ O ₃ , Sm ₂
A solid electrolyte in which at least one of O ₃ , MgO and the like is dissolved can be suitably used. Particularly, CeO ₂ system has high ionic conductivity at a low temperature, and therefore, it is expected that the oxygen sensor element can be operated at a low temperature and is optimal. The above-mentioned solid solution amount varies depending on the combination with the solid solution oxide, but in general, a range of 2 to 40% is sufficient. In the case of a combustible gas sensor, a known sensor can be used without limitation as long as it is proton-conductive. Generally, antimonic acid (Sb ₂ O ₅ .nH
₂ O), zirconium phosphate (Zr (HPO ₄ ) ₂ .H
₂ O), phosphomolybdic acid (H ₃ P Mo ₁₂ O ₄₀ .nH ₂
O), phosphotungstic acid _{(H 3 P W 12 O 40} · nH
₂ O), uranyl phosphate (HUO ₂ PO ₄ .nH)
₂ O), inorganic ion exchangers typified by H-type zeolite, polystyrene sulfonic acid, Nafion (can include organic polymeric ion exchangers typified by DuPont registered trademark). The proton conductive solid electrolytes can be used alone or in combination of two or more. In the case of a fluorine gas sensor, a known one can be used without any limitation as long as it is fluorine ion conductive. Generally, β-PbF ₂ , CaF ₂ , SrF ₂ , LaF ₂ , Ti
Sn ₂ F ₃ can be used alone or in combination of two or more. KAg ₄ for other halogen gases
_{I 5, PbCl 2, PbBr 2} , or the like can also be used.

Further, SO ₂ , SO ₃ , CO, CO ₂ , NO
₂ etc. are respectively K ₂ SO ₄ , K ₂ CO ₃ , Ba (N
O ₃ ) _{2 and the} like can be used. The ion permeable layer used in the detection gas control screen basically needs to be configured to supply a detection gas that is less than the discharge speed of the detection gas pumped in the sensor detection unit. For this reason, as the solid electrolyte of the screen layer, a substance having a lower transport number than that of the solid electrolyte of the detection unit is used, or in the case of the same type of solid electrolyte, the effective area is reduced (for example, 10 to 90%).
%) Or increasing the thickness of the layer. To reduce the transport number, it is possible to reduce the ion exchange capacity of the solid electrolyte or to mix a highly conductive metal powder. However, the ion permeable layer
From the practical significance of being an ambassador barrier to gas passage and enduring industrial use, 0.1-5000 μm
m, especially 0.5 to 1 when the ion permeable layer is made of an inorganic material.
In the case of an organic material, the range is preferably 1 to 2000 μm.

The method for producing the ion-permeable layer is not particularly limited. In general, a method of molding the fine powder of the solid electrolyte, a method of molding and sintering, a method of sputtering, an ion plating method, a vapor deposition method and the like are suitably adopted. Of course, commercially available materials such as Nafiore can also be used as they are.

The conductors 12 and 18 and the electrodes 10 and 11 which are present on both sides of the ion permeable layer made of a solid electrolyte are made of the same or different conductors. Examples of preferable materials include noble metals such as platinum palladium, rhodium, and silver and oxides thereof, and a general formula La _1-X Sr _X BO ₃
(Where B represents an element such as Co, Cu, Fe, Ni, etc., and x
Is a number of 0.01 to 0.5), which is a perovskite-type oxide, and a composite composition obtained by mixing the above-mentioned noble metal and metal oxide.

The thickness of the porous conductor of the detection gas control screen and the thickness of the electrode layer of the detection section are generally 0.1 μm or more.
A range of 50 μm, preferably 0.2 μm to 30 μm, is suitable. Further, in order to efficiently diffuse gas molecules or generated ions into the ion-permeable layer, it is desirable to use a porous body also for the electrode layer. The conductor 12
And 18 and the method of forming the electrodes 10 and 11 are not particularly limited, and a known method is adopted without limitation. Typical examples include a method of performing screen printing, vacuum deposition, chemical plating, ion plating, and sputtering on both surfaces of the solid electrolyte membrane.

When the operating temperature of the gas sensor is high, the gas sensor may be heated if necessary.
Such heating of the gas sensor may be performed by heat radiation from a heat source outside the gas sensor, or a heater may be mounted on the gas sensor in advance, and heat conduction or heat radiation from the heater may be used. The mounting position of the heater on the gas sensor is not particularly limited as long as the position does not hinder the operation of the gas sensor.

FIG. 5 shows a specific embodiment of the present invention.
The conductors 12 and 18 of the detection gas control screen are connected at one end, and the electromotive force of the screen portion is caused by the difference between the concentration of the detection gas in contact with the conductor 12 and the concentration of the detection gas in contact with the same 18. It is. A gap b whose periphery is sealed by the sealing material 7 is formed between the screen and the detection unit of the sensor. Further, the lower part of the detection portion of the sensor is provided with a porous body 17 having an insulating property, a heater 13 and a power supply 13 for the heater, with a reduction c.
Even in the example of FIG. 5, the amount of gas supplied to the gap b through the solid electrolyte membrane 8 is configured to be smaller than the amount pumped into the gap c. The holes of the insulating porous body 17 have a diameter and the number of holes so that the gas pumped into the gap c can be discharged to the outside without any resistance.

FIG. 6 shows another embodiment of the present invention, in which an external power supply 2 is connected between the conductors 12 and 18 of the detection gas control screen.
2 is a method of applying a voltage equal to or higher than a potential difference required to cause an electrode reaction based on a detection gas in a mixed gas to be measured on the surface of the conductor 12. In addition, the porous body 17 and the electrode 11 are in close contact with each other for heating efficiency.

FIG. 7 shows another embodiment of the present invention, in which a porous spacer 19 is interposed in a gap b existing between the detection gas control screen and the detection section of the sensor. As the spacer 19, one that maintains a gap and does not restrict the permeation of the detection gas is used without any particular limitation. Generally, SiO ₂ .MgO, SiO ₂ .Al ₂ O
₃ , porous ceramics such as zeolite and SiO ₂ are preferably used. The porous ceramics can be arbitrarily selected within a range that does not hinder the permeation of the detection gas.

FIG. 8 shows the conductor 1 in contact with the mixed gas to be measured.
In this embodiment, a cover 23 made of a metal mesh, ceramics having a high porosity, or other porous material is provided for the purpose of protecting the cover 2.

FIG. 9 is an example of another embodiment in which the detection gas control screen covers the detection section of the sensor. The solid electrolyte membrane 8 of the detection gas control screen and the solid electrolyte membrane 9 of the detection section are integrally formed. In this mode, the gas supplied through the screen is temporarily held in the gap b formed by the cover 21 and supplied to the detection unit. That is, in this example, ions formed by the electrode reaction of the conductor 12 of the detection gas control screen are turned into gas by the conductor 18 and supplied to the gap b. The gas in the gap b is pumped out by the detection unit and discharged from the electrode 11. The feature of this example is that the detection gas control screen and the detection section of the sensor can be uniformly heated by the heater 13 on the lower surface.

FIG. 10 shows a modification of the embodiment shown in FIG. 9, in which the solid electrolyte membrane 8 and the solid electrolyte membrane 9 are separated by an insulating sealing material 7. Further, the conductor 10 of the detection gas control screen and the electrode 10 of the detection section are integrally formed. In this case, the conductor 18 and the electrode 10 have the same potential, but by keeping each potential difference between the conductors 12 and 18 and between the electrodes 10 and 11 within a range necessary for the electrode reaction based on the detection gas. Measurement can be performed without hindrance.

FIG. 11 basically shows the embodiment shown in FIG. 1, but illustrates that the structure of the sensor of the present invention is not limited to a plate.

The present invention is, of course, not limited to the illustrated embodiment, but is a limiting current type solid electrolyte gas sensor in which gas supplied to a detection portion of the sensor is permeated as ions by an ion permeable layer formed of a solid electrolyte membrane. After that, all modes characterized by using a method of supplying again as a gas are included.

The limiting current type solid electrolyte gas sensor according to the present invention comprises oxygen gas, carbon dioxide gas, various halogen gases, SO ₂ ,
The present invention can be applied to measurement of the concentration of various gases such as SO ₃ , CO, NO, NO ₂ , NH ₃ , and H ₂ S.

[0028]

As can be understood from the above description, the limiting current type solid electrolyte gas sensor of the present invention moves the detection gas in the mixed gas to be measured through the solid electrolyte as ions generated by the electrode reaction by the detection gas control screen. By limiting the movement of the detection gas to the sensor detection unit, the variation in characteristics due to manufacturing conditions is smaller than that of a conventional limiting current type solid electrolyte gas sensor of the type that limits the amount of diffusion of the detection gas, Deterioration of characteristics due to clogging of small holes is not observed, and a wide range of oxygen concentration can be accurately measured over a long period of time.

[0029]

EXAMPLES The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to these examples.

The method for measuring the limiting current characteristic of the gas sensor will be described below. Limit current characteristic measurement: Put the gas sensor in the gas to be measured having different concentrations of the detection gas, and apply a DC voltage to the electrodes of the sensor unit. The applied voltage is 0V to 0.0
The current was continuously changed at a speed of 4 V / min, and the current flowing at that time was measured by an ammeter and recorded on a recorder. Based on the results, the voltage at which the limit current was obtained in common at each test gas concentration was determined as the optimum applied voltage of the element.

Embodiment 1 As shown in FIG. 5, electrodes 10 and 1 are provided on both surfaces of an ion-permeable layer 9.
1 is formed by an oxygen detector, an oxygen control screen electrically connecting a part of the conductive layers 12 and 18 formed on both surfaces of the ion permeable layer 8 and a heater formed by forming a heater on the porous ceramics. The sensor was configured. The oxygen detector, the oxygen control screen, and the heater were joined with glass 7 and the side was sealed with glass 14. DC voltage 16 is applied to the heater 13 of the heater section,
The sensor element was heated at the same time. A DC voltage 5 was applied using the electrode 10 on the oxygen control screen side of the oxygen detection unit as a cathode and the electrode 11 on the heater unit side as an anode, and an ammeter 6 was connected in series with a power supply to measure the value of the current flowing at that time. .

In the above, the ion permeable layers 8 and 9 have
30 mol% of calcium oxide was dissolved in ceric oxide (oxygen ion conductor) (CeO ₂ ) _0.7 (Ca
O) Molded and sintered _0.3 powder, diameter 4mm, thickness about 0.3
A dense disc-shaped solid electrolyte sintered body of mm was used.

Platinum paste was screen-printed and baked at 800 ° C. as the positive and negative electrodes 10 and 11, and a platinum wire was used as the lead wire 15. Further, the conductor layers 12 and 18 of the oxygen control screen are screen-printed with platinum paste on both sides of the ion permeable layer 8 and a part thereof is connected with the platinum paste via the side surface of the ion permeable layer 8.
What was baked at 0 ° C was used.

Porous ceramics 1 used for heater part
7 has a diameter of 4 mm obtained by molding and sintering MgO.SiO ₂ powder as a heat-resistant inorganic substance having sufficient pores so that diffusion of oxygen does not become rate-determining and having a thermal expansion coefficient close to that of the ion-permeable layer. A disc-shaped sintered body having a thickness of about 0.6 mm was used.

As the heater 13, a conventionally known heater can be used. However, in this embodiment, a platinum paste is screen-printed on the porous ceramic in a wave form and baked at 900 ° C. in view of stability and heat resistance. Was used.

The bonding glass 7 preferably has a coefficient of thermal expansion equal to or slightly smaller than that of the ion-permeable layer and a particle size of 10 μm or less, preferably 5 μm or less. Therefore, in this embodiment, a glass powder having an average particle diameter of 6 μm is pulverized by a ball mill for 3 hours, pasted with TVneol and ethylcellulose, and screen-printed on a portion of the ion-permeable layer 9 where the electrodes are not formed by oxygen. The detection part, the heater part, and the oxygen control screen were joined. The glass 14 for sealing was formed by applying the same glass paste as described above to the side face of the sensor element twice. By sintering at 620 ° C., these glasses 7 and 14 became dense without oxygen permeation.

FIG. 12 shows an oxygen sensor placed in gases to be measured having different oxygen concentrations, changing the voltage applied between the electrodes 10 and 11 and measuring the current value at each voltage. ), And the voltage (V) is shown on the horizontal axis. In FIG. 12, a portion showing a line substantially parallel to the horizontal axis where the current does not change even when the voltage changes is recognized, and the current value indicated by the line is the limit current value at each oxygen concentration.

Table 1 shows the relationship between the limiting current value and the oxygen concentration at a voltage of 800 mV at which a limiting current is obtained in common at each oxygen concentration from FIG. FIG.
In Table 1, the vertical axis indicates the limit current (μA), and the horizontal axis indicates the function of the oxygen concentration −ln (1−PO ₂ / P) [P is the total pressure of the gas to be measured and PO ₂ is the oxygen partial pressure. Respectively, the oxygen concentration (%) is shown on the upper line of the horizontal axis. FIG.
It is used as a calibration curve when measuring the oxygen concentration of the gas to be measured whose oxygen concentration is unknown. That is, by measuring the limiting current value of the oxygen sensor shown in FIG. 5 in the gas to be measured, the oxygen concentration of the gas to be measured whose oxygen concentration is unknown can be measured.

Further, as a measurement of the variation of the output current, the optimum applied voltage obtained by the measurement of the limiting current characteristic was applied to each of the 30 oxygen sensors, and the output current in the atmosphere was measured. Table 4 shows the maximum value, average value, and variation coefficient of the output current. From Table 4, it can be seen that the oxygen sensor of the present invention has less variation in output current among sensors than conventional oxygen sensors using small holes or porous ceramics, and can be manufactured with good reproducibility.

Further, as a measure of durability against clogging, 30 oxygen sensors were inserted into the exhaust gas of a boiler cooked with heavy oil, and the oxygen sensor was applied with the optimum applied voltage obtained by the limiting current characteristic measurement to output current. Was measured. Table 5 shows the number of oxygen sensors whose output current after 3, 5, 10, 20, and 30 days became less than half of the initial output current. From Table 5, it can be seen that the output current of the sensor of the present invention is clogged by clogging like a conventional oxygen sensor using small holes or porous ceramics even in a very dusty and soot-rich atmosphere, such as in the exhaust gas of a heavy oil boiler. , And it was found that the output was stable over a long period of time.

Example 2 An oxygen sensor element as shown in FIG. 7 was manufactured. In this sensor, the portion where the oxygen detection section and the oxygen control screen are bonded by the glass 7 in FIG. 5 is bonded with a ceramic paste, and a porous ceramic 19 is present in the space b between the oxygen detection section and the oxygen control screen. is there. Further, the heater 13 was also formed on the porous ceramics 17 formed by screen-printing a ceramic paste on the side of the oxygen detector not in contact with the oxygen control screen.
The porous ceramics 17 and 19 had sufficient pores so that the transmission of oxygen was not limited.

As in the first embodiment, a limit current having a certain relationship with the oxygen concentration of the gas to be measured was obtained in the present sensor.

Table 4 shows the results of measuring the variation in the output current of the oxygen sensor in the same manner as in Example 1. From Table 4, it can be seen that the oxygen sensor of the present invention has less variation in output current among sensors than conventional oxygen sensors using small holes or porous ceramics, and can be manufactured with good reproducibility.

Further, the results of measuring the durability against clogging in the same manner as in Example 1 are shown in Table 5. From Table 5, it can be seen that the oxygen sensor of the present invention shows almost no decrease in output current due to clogging unlike the conventional oxygen sensor using small holes or porous ceramics, and shows stable output for a long period of time. all right.

Example 3 An oxygen sensor element as shown in FIG. 8 was manufactured. This sensor is a sensor having substantially the same structure as that of FIG. 5, except that a protective cover 23 is provided to prevent dust, dust, soot and the like from being volumeized on the conductive layer 12 directly exposed to the gas to be detected. It is provided. This protective cover 23 is formed of the conductor layer 12.
Those that do not limit the permeation of oxygen supplied to the water are used without particular limitation. Generally, SiO ₂ · MgO, SiO _{2
· Al 2 O 3, SiO 2} , in which the porous ceramic such as zeolite, a metal mesh such as stainless steel, ceramics cotton such as asbestos can be suitably used.

Also in this sensor, a limit current having a certain relation with the oxygen concentration of the gas to be measured was obtained as in the first embodiment.

Table 4 shows the results of measuring the variation in the output current of the oxygen sensor in the same manner as in Example 1. From Table 4, it can be seen that the oxygen sensor of the present invention has less variation in output current among sensors than conventional oxygen sensors using small holes or porous ceramics, and can be manufactured with good reproducibility.

Further, the results of measuring the durability against clogging in the same manner as in Example 1 are shown in Table 5. From Table 5, it can be seen that the oxygen sensor of the present invention shows almost no decrease in output current due to clogging unlike the conventional oxygen sensor using small holes or porous ceramics, and shows stable output for a long period of time. all right.

Example 4 An oxygen sensor element as shown in FIG. 9 was manufactured. In this sensor, the oxygen ion permeable layer 8 is made of the same material and the same manufacturing method as the sintered body used in Example 1, and has a shape of about 4 mm in length, about 3 mm in width,
A rectangular parallelepiped having a thickness of about 0.6 mm was used. Conductor layers 11 and 12 are formed on the interface of the oxygen ion permeable layer 8, and conductor layers 10 and 18 are formed on the other surface. Dense ceramics 21 is joined to the conductor layers 10 and 18 side, and Heater 1
3 was formed.

In the present sensor, as in the case of the first embodiment, a limit current having a fixed relationship with the oxygen concentration of the gas to be measured was obtained.

Table 4 shows the results of measuring the variation in the output current of the oxygen sensor in the same manner as in Example 1. From Table 4, it can be seen that the oxygen sensor of the present invention has less variation in output current among sensors than conventional oxygen sensors using small holes or porous ceramics, and can be manufactured with good reproducibility.

Further, the results of measuring the durability against clogging in the same manner as in Example 1 are shown in Table 5. From Table 5, it can be seen that the oxygen sensor of the present invention shows almost no decrease in output current due to clogging unlike the conventional oxygen sensor using small holes or porous ceramics, and shows stable output for a long period of time. all right.

Example 5 An oxygen sensor element as shown in FIG. 10 was manufactured. In this sensor, two layers similar to the oxygen ion permeable layer used in Example 4 were used, and conductor layers 12 and 11 were formed on one surface of the oxygen ion permeable layers 8 and 9, respectively. The oxygen ion permeable layers 8 and 9 are electrically insulated by bonding one side by glass 7 with the surfaces on which the conductor layers 11 and 12 are formed facing upward, and the conductor layers 11 and 12 are not formed. On the side, the conductor layer 1 formed as a single conductor layer in FIG.
0,18 were formed as a common conductor layer. On the side where the common conductor layers 10 and 18 were formed, dense ceramics 21 was joined, and the heater 13 was formed thereon.

In this sensor, as in the case of the first embodiment, a limit current having a fixed relationship with the oxygen concentration of the gas to be measured was obtained.

Table 4 shows the results of measuring the variation in the output current of the oxygen sensor in the same manner as in Example 1. From Table 4, it can be seen that the oxygen sensor of the present invention has less variation in output current among sensors than conventional oxygen sensors using small holes or porous ceramics, and can be manufactured with good reproducibility.

Further, the results of measuring the durability against clogging in the same manner as in Example 1 are shown in Table 5. From Table 5, it can be seen that the oxygen sensor of the present invention shows almost no decrease in output current due to clogging unlike the conventional oxygen sensor using small holes or porous ceramics, and shows stable output for a long period of time. all right.

Example 6 An oxygen sensor element as shown in FIG. 11 was manufactured. This sensor is provided on the inside of an oxygen control screen in which conductor layers 12 and 18 are formed on both sides of a cylindrically formed ion permeable layer 8, and on both sides of an ion permeable layer 9 formed in the same shape but smaller than the ion permeable layer 8. The oxygen sensor section on which the electrode 11 is formed is fitted with the glass 7. In FIG.
The oxygen control screen is outside and the oxygen sensor part is inside, but if this structure is reversed, if the electrode of the oxygen sensor part on the side in contact with the oxygen control screen is the cathode and the reverse is the anode, there is no problem. Absent.

In the present sensor, as in the case of the first embodiment, a limit current having a fixed relationship with the oxygen concentration of the gas to be measured was obtained.

Table 4 shows the results of measuring the variation in the output current of the oxygen sensor in the same manner as in Example 1. From Table 4, it can be seen that the oxygen sensor of the present invention has less variation in output current among sensors than conventional oxygen sensors using small holes or porous ceramics, and can be manufactured with good reproducibility.

Further, the results of measuring the durability against clogging in the same manner as in Example 1 are shown in Table 5. From Table 5, it can be seen that the oxygen sensor of the present invention shows almost no decrease in output current due to clogging unlike the conventional oxygen sensor using small holes or porous ceramics, and shows stable output for a long period of time. all right.

Example 7 A sintered body of (ZrO ₂ ) _0.93 (Y ₂ O ₃ ) _0.07 in which yttrium oxide was solid-dissolved in zirconium oxide as an oxygen ion conductor in a concentration of 7 mol% was used for the ion permeable layers 8 and 9. Electrode 1
5, platinum is used for the conductor layers 12 and 18, and the heater 13 and the glasses 7 and 14 are the same as in the first embodiment.
An oxygen sensor element having the structure shown in FIG.

A direct current voltage is applied to the heater 13,
The device was heated to 500C. As in the first embodiment, the electrode 1
A direct current voltage was applied with 0 as the cathode and the electrode 11 as the anode, and the current flowing at that time was measured by the ammeter 6.

As a result, similar to the one shown in FIG.
The limiting current was obtained at each oxygen concentration.

Table 2 shows the relationship between the limiting current value and the oxygen concentration at a voltage of 1.3 V at which a limiting current is obtained in common at each oxygen concentration. FIG. 14 shows the limit current value (μA) on the ordinate and the oxygen concentration function −ln on the abscissa.
It illustrates taking (1-PO ₂ / P) and oxygen concentration (%). (ZrO ₂ ) _0.93 (Y ₂ O ₃ )
This element using _0.07 is (CeO ₂ ) _0.7 (CaO) _0.3
Although the device temperature was higher than that of the device using, a large limit current value was shown, and a calibration curve as shown in FIG. 14 was obtained.

[0065] Example 8 electrodes 10 and 11, the conductor layer 12 and 18, a La _0.6 Sr _0.4 CoO ₃ and complex composition of platinum is perovskite-type oxide, the ion permeable layer 8, 9 (CeO ₂ )
An oxygen sensor having the structure shown in FIG. 5 was manufactured by using a sintered body of _0.7 (CaO) _0.3 and using the heater 13 and the glasses 7 and 14 in the same manner as in Example 1.

The composite composition used for the electrodes 10 and 11 and the conductor layers 12 and 18 was obtained by mixing lanthanum carbonate, strontium carbonate, and cobalt acetate at a predetermined molar ratio, and firing and pulverizing the perovskite-type oxide. Product La _0.6 Sr _0.4
The powder obtained by mixing CoO ₃ powder and platinum paste at a weight ratio of 2: 8 to form a paste was formed by screen printing.

A direct current voltage was applied to the heater 13 to heat the element to 400.degree. As in Example 1, a DC voltage was applied using the electrode 10 as a cathode and the electrode 11 as an anode, and the current flowing at that time was measured with an ammeter 6.

As a result, similar to the one shown in FIG.
The limiting current was obtained at each oxygen concentration.

Table 3 shows the relationship between the limiting current value and the oxygen concentration at a voltage of 1.0 V at which a limiting current can be obtained in common at each oxygen concentration. FIG. 15 shows the data of Table 3 on the vertical axis as the limiting current value (μA) and on the horizontal axis as a function of oxygen concentration −ln.
It illustrates taking (1-PO ₂ / P) and oxygen concentration (%). This device using the composite electrode as the electrode showed a large limit current value despite the device temperature being lower than the device using the platinum electrode, and a calibration curve as shown in FIG. 15 was obtained.

Example 9 A hydrogen sensor having the structure shown in FIG. 1 was manufactured. The ionic conductors 8 and 9 include antimony (Sb ₂ ) which is a proton conductor.
It was a mixture of Teflon powder O ₅ · nH ₂ O). Platinum black was used for the positive and negative electrodes 10 and 11 and the conductor layers 12 and 18, and the proton conductor was formed at the same time as forming a disk having a diameter of 5 mm. The ion conductors 8, 9 are
The ion conductor 8 was made thicker than the ion conductor 9 in order to have a difference in the amount of ion permeated per unit time. The sensor portion and the ion permeable layer were joined by the glass 7 in the same manner as in Example 1, and the side surface was sealed by the glass 14. Glasses 7 and 14 were sintered at 250 ° C. and became dense without gas permeation.

Also in this sensor, a DC voltage 5 was applied using the electrode 10 as the anode and the electrode 11 as the cathode, and the limiting current characteristic was measured in the same manner as in Example 1. As a result, the hydrogen concentration in the gas to be measured was kept constant. A relevant limiting current is obtained. Table 6 shows the relationship between the hydrogen concentration and the limiting current value at that time.

FIG. 16 shows the limiting current (μ
A), the function of the hydrogen concentration -ln (1-PO ₂ /
P) [P is total pressure, PO ₂ represents respectively a hydrogen partial pressure in the measurement gas] illustrates taking the hydrogen concentration in the same horizontal axis upper line (%). FIG. 16 is used as a calibration curve when measuring the hydrogen concentration of the gas to be measured whose hydrogen concentration is unknown. That is, by measuring the limiting current value of the hydrogen sensor in the gas to be measured, the hydrogen concentration of the gas to be measured whose hydrogen concentration is unknown can be measured.

Further, it was found that this sensor has sensitivity not only to hydrogen but also to combustible gases such as carbon monoxide and ethanol.

Example 10 A fluorine gas sensor having a structure as shown in FIG. 6 was manufactured.
The ion conductors 8 and 9 include fluorine ion conductor Ca
Used doped with NaF to F _2, and molded into a disk having a diameter of 5 mm, a thickness of 0.4 mm, sintered at 900 ° C.. Since the ion conductor 8 needs to have a smaller ion permeation amount per unit time than the ion conductor 9, the transport number was changed by changing the doping amount of NaF. actually,
The ion conductor 8 was doped with 0.5% of NaF, and the ion conductor 9 was doped with 1% of NaF. Electrodes 10, 11, conductor layer 1
Screen printing using platinum for 2, 18 and 800 ° C
Formed by baking. The sensor section and the ion permeable layer are joined by glass 7,
4 and sintering at 620 ° C., it became dense without gas permeation.

This sensor heated the sensor element to 450 ° C. by applying a DC voltage 16 to the heater 13.
Further, in order to promote ionization in the conductor layer 12, the conductor layers 1 formed on both sides of the detection gas control screen are provided.
1V was applied between DC and DC voltage 22 between 2 and 18.

In this sensor, the limiting current characteristic was measured in the same manner as in Example 1 by applying a DC voltage 5 with the electrode 10 serving as a cathode and the electrode 11 serving as an anode. As a result, a limiting current depending on the fluorine concentration in the gas to be measured was obtained. Table 7 shows the relationship between the fluorine gas concentration and the limiting current value at that time.

FIG. 17 shows the limit current (μ
A), a function of fluorine concentration on the horizontal axis underlined -ln (1-PO ₂ /
P) [P is total pressure, PO ₂ represents respectively fluorine partial pressure in the measurement gas] illustrates taking the fluorine concentration in the same horizontal axis upper line (%). FIG. 17 is used as a calibration curve when measuring the fluorine concentration of the gas to be measured whose fluorine concentration is unknown. That is, by measuring the limit current value of the fluorine sensor in the gas to be measured, the fluorine concentration of the gas to be measured whose fluorine concentration is unknown can be measured.

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[Table 5]

[Table 6]

[Table 7]

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a basic configuration of a limiting current type solid electrolyte gas sensor of the present invention.

FIG. 2 is a conceptual diagram showing a basic configuration of a gas sensor of the present invention.

FIG. 3 is a conceptual diagram of a conventional limiting current type solid electrolyte gas sensor.

FIG. 4 is a conceptual diagram of a conventional limiting current type solid electrolyte gas sensor.

FIG. 5 is a diagram showing another embodiment of the limiting current type solid electrolyte gas sensor of the present invention.

FIG. 6 is a diagram showing another embodiment of the limiting current type solid electrolyte gas sensor of the present invention.

FIG. 7 is a diagram showing another embodiment of the limiting current type solid electrolyte gas sensor of the present invention.

FIG. 8 is a diagram showing another embodiment of the limiting current type solid electrolyte gas sensor of the present invention.

FIG. 9 is a diagram showing another embodiment of the limiting current type solid electrolyte gas sensor of the present invention.

FIG. 10 is a diagram showing another embodiment of the limiting current type solid electrolyte gas sensor of the present invention.

FIG. 11 is a diagram showing another embodiment of the limiting current type solid electrolyte gas sensor of the present invention.

FIG. 12 is a diagram illustrating a relationship between a voltage and a current for an example in which the oxygen concentration in the sample mixed gas is different in the oxygen sensor according to the first embodiment.

FIG. 13 is a diagram illustrating a relationship between a limiting current density and an oxygen concentration in the first embodiment.

FIG. 14 is a diagram showing a relationship between a limit current density and an oxygen concentration in Example 7.

FIG. 15 is a diagram showing a relationship between a limit current density and an oxygen concentration in Example 8.

FIG. 16 is a diagram showing a relationship between a limit current density and an oxygen concentration in Example 9.

FIG. 17 is a diagram showing a relationship between a limit current density and an oxygen concentration in Example 10.

[Explanation of symbols]

 Reference Signs List 1 ion permeable layer (solid electrolyte membrane) 2 electrode 3 electrode 4 cap 5 power supply 6 ammeter 7 sealing material 8 ion permeable layer (solid electrolyte membrane) 9 ion permeable layer (solid electrolyte membrane) 10 electrode 11 electrode 12 porous conductive Body 13 Heater 14 Casing 15 Lead wire 16 Power supply 17 Insulating porous body 18 Porous conductor 19 Spacer 20 Porous ceramic a Capillary b Gap c Gap

Claims (2)

(57) [Claims] 1. A porous conductor is present on both surfaces of a solid electrolyte membrane capable of selectively transmitting ions of a detection gas contained in a gas mixture to be measured or ions generated by an electrode reaction of the detection gas, and both porous conductors are provided. The conductor has a detection gas control screen having a structure electrically connected so as to form a potential required for oxidation and reduction of the detection gas, and a detection unit of the solid electrolyte gas sensor, and is supplied to the ionization electrode of the detection unit.
The entire amount of the detected gas is detected by the detection gas control screen.
The detection gas control screen is configured so as to be composed of gas permeated as ions, and the ion permeation amount per unit time of the solid electrolyte membrane of the detection gas control screen is smaller than the ion permeation amount of the detection unit under the operating condition. A solid electrolyte gas sensor characterized in that: 2. A porous electrolyte is present on both sides of a solid electrolyte membrane capable of selectively transmitting ions generated by an electrode reaction of a detection gas contained in a mixed gas to be measured, and both conductors are detection gases. Of the detection unit of the solid electrolyte gas sensor through a detection gas control screen having a structure electrically connected to form a potential required for oxidation and reduction of the gas.
Supply the entire amount of the detection gas to the ON electrode, and
Pump at a speed higher than the supply speed of the supplied detection gas.
A method for measuring a concentration of a detected gas in a mixed gas to be measured, wherein a limit current value generated by the detection is measured.