JP2003083929A - Combustible gas sensor and combustible-gas-concentration measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a combustible gas sensor by which a combustible gas (especially a hydrocarbon-based gas) excluding hydrogen, carbon monoxide and nitrogen monoxide can be detected with satisfactory sensitivity without depending on steam, and to provide a combustible-gas-concentration measuring method. SOLUTION: The combustible gas sensor 1 in which a platinum electrode 121 and a gold electrode 122 are formed in parallel on the same face coming into contact with an atmosphere to be measured of a solid electrolyte body 11 displaying proton conductivity is used, the temperature of the solid electrolyte body at the sensor 1 is held so as to become 250 to 450 deg.C, a potential difference generated across the platinum electrode and the gold electrode is measured, and the concentration of the combustible gas is measured on the basis of the potential difference.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a combustible gas sensor and a combustible gas concentration measuring method. More specifically, the present invention relates to a combustible gas sensor that measures the concentration of a target gas by measuring the potential difference between electrodes formed on a solid electrolyte body that exhibits proton conductivity, and a method for measuring such a combustible gas concentration. The combustible gas sensor of the present invention can be used for measuring the concentration of various combustible gases, but is particularly suitable for measuring the concentration of hydrocarbon gas contained in the exhaust gas of an internal combustion engine.

[0002]

2. Description of the Related Art In recent years, many hydrocarbon gas sensors and the like utilizing a solid electrolyte having oxygen ion conductivity have been developed, and JP-A-8-510840 and JP-A-2000-
The technique disclosed in Japanese Patent No. 146902 is known. However, since all of them use the conductivity of oxygen ions, they are naturally susceptible to the oxygen concentration. Furthermore, the concentration of hydrogen, carbon monoxide, nitric oxide, etc. should be distinguished from that of hydrocarbon gas etc. Is difficult. Therefore, a special technique for reducing the influence of oxygen concentration and a special technique for distinguishing hydrogen, carbon monoxide, nitric oxide and the like from hydrocarbon gas and the like are required. On the other hand, as a hydrocarbon gas sensor that uses a solid electrolyte having proton conductivity to measure the concentration of hydrocarbon gas from the potential difference generated between a pair of electrodes, JP-A-6-242060 and JP-A-9-1
Japanese Patent No. 27055 is disclosed.

[0003]

The hydrocarbon sensor disclosed in these publications (electromotive force type hydrocarbon gas sensor in JP-A-9-127055) has a pair of electrodes. One of these electrodes has a high temperature (770 ° C. in JP-A-6-24060,
No. 127055) is an active electrode capable of burning hydrocarbon gas at its “surface” at 500 ° C., and the other electrode is an inert electrode capable of burning hydrocarbon gas even at the same temperature. It is an electrode. On the "surface" of this active electrode, the hydrocarbon gas burns to generate water vapor, which causes a potential difference due to the partial pressure difference of the water vapor with the inactive electrode. The hydrocarbon gas is detected by measuring this potential difference, and further, its concentration is measured.

However, (1) In the above, there is a problem that it is extremely difficult to measure the concentration of hydrocarbon gas in an atmosphere containing a large amount of water vapor such as exhaust gas of an internal combustion engine. Further, in view of (2) actual use, it is necessary that the concentration of the hydrocarbon gas can be measured even in the ppm order, so that a large potential difference obtained between the electrodes is desired.

The present invention solves the above-mentioned problems. It is possible to measure the concentration of combustible gas even in an atmosphere containing a large amount of water vapor, and accurate measurement is possible even when the concentration of combustible gas is low. An object of the present invention is to provide a combustible gas sensor and a combustible gas concentration measuring method which are possible.

[0006]

The combustible gas sensor of the present invention comprises a solid electrolyte body having proton conductivity and a pair of different materials formed on the same surface of the solid electrolyte body in contact with the atmosphere to be measured. And a temperature of the solid electrolyte body is used in the range of 250 to 450 ° C.

Another combustible gas sensor of the present invention comprises a solid electrolyte body having proton conductivity, and a pair of electrodes made of different materials formed on the same surface of the solid electrolyte body in contact with the atmosphere to be measured. It is characterized in that it is used for measuring the combustible gas concentration based on at least the mixed potential generated between the electrodes.

The solid electrolyte body may be a BaCeO ₃ type proton conductive oxide. Furthermore, the shortest distance between the electrodes can be 1.5 mm or less. Further, it can be used for measuring the concentration of a combustible gas having 2 or more carbon atoms. Furthermore, 50 ppm of propene and 21
A measured gas containing volume% oxygen and 2.3 volume% steam with the balance being argon was supplied at 150 ml / min, and the potential difference when measured at a temperature of 350 ° C. was 60 m.
It can be V or higher.

The flammable gas concentration measuring method of the present invention comprises a solid electrolyte body having proton conductivity, and a pair of electrodes made of different materials formed on the same surface of the solid electrolyte body in contact with the atmosphere to be measured. The flammable gas sensor is used to measure the concentration of the flammable gas based on the potential difference generated between the electrodes under the condition that the temperature of the solid electrolyte body is 250 to 450 ° C. by exposing the electrode to the atmosphere to be measured. It is characterized by

Another combustible gas concentration measuring method of the present invention is
A combustible gas sensor comprising a solid electrolyte body having proton conductivity and a pair of electrodes made of different materials formed on the same surface of the solid electrolyte body in contact with the atmosphere to be measured is used. It is characterized by exposing to an atmosphere and measuring the concentration of the combustible gas based on a potential difference including at least a mixed potential generated between the electrodes.

The potential difference may be caused by the concentration of combustible gas having 2 or more carbon atoms.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have made extensive studies on a known proton conductive solid electrolyte body. inside that,
Regarding the proton conductive solid electrolyte body, (1) the plate-shaped solid electrolyte body is arranged such that the front and back surfaces are sandwiched by a pair of electrodes,
There is a difference in conductivity between the case where the conductivity is measured between the electrodes and the case where (2) the electrodes are arranged side by side on one surface of the plate-shaped solid electrolyte body and the conductivity is measured between the electrodes. I found that. It was also found that higher conductivity can be obtained when the electrodes are arranged as in (2) than when the electrodes are arranged as in (1). This is something that was not known so far, and for the oxygen ion conductive solid electrolyte body that has been used many times until now, even if the same measurement is performed, the difference is not a unique phenomenon. there were.

Further, a sensor for measuring the concentration of hydrocarbon gas or the like using a proton-conductive solid electrolyte has hitherto been measured at a temperature (temperature of the solid electrolyte) of 500.degree.
The temperature was adjusted to a high temperature of 800 ° C. This is because the hydrocarbon gas is burned on the electrode surface as described above.
However, the present inventors have found that at a low temperature of 450 ° C. or lower, when the hydrocarbon gas is set to a condition that it is difficult to burn on the electrode surface, the sensitivity is remarkably higher than that of the conventional one. This means that when the combustible gas reaches the interface between the electrode and the solid electrolyte body without burning on the surface of the electrode, some reaction occurs between the combustible gas, the electrode material and the three phases of the solid electrolyte. It is considered that this is because a potential difference (mixed potential) different from the potential difference due to the conventional hydrogen partial pressure is generated. The present inventors have completed the present invention based on these two findings.

The above "solid electrolyte body" is a proton conductive material.
The composition and the like are not particularly limited.
Absent. Solid electrolysis capable of exhibiting such proton conductivity
As the body, for example, BaCeO_ThreeOxides, SrC
eO_Three-Based oxide, SrZrO _Three-Based oxides and CaZ
rO_ThreeExamples thereof include system oxides. These solids
Electrolytes are used at each B site (ABO_ThreeAs a system oxide
Sc, Y, In, Nd, and P at the position of B when expressed)
m, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb
And at least one of Lu may be solid-dissolved
Yes. Particularly high proton conductivity due to their solid solution
it can. For example, BaCeO _ThreeBa as the oxide
(Ce, Y) O_Three-Based oxides and Ba (Ce, Nd) O_Three
-Based oxide, SrCeO_ThreeAs the system oxide, Sr (Ce,
Yb) O_Three-Based oxide, SrZrO_ThreeS as a system oxide
r (Zr, Y) O_Three-Based oxides and Sr (Zr, Yb) O
_ThreeOxides, CaZrO_ThreeCa (Z
r, In) O_ThreeExamples thereof include system oxides.

Each of these oxides is A (B1, B2) O ₃
When expressed as a system oxide (representing that B2 is a solid solution at the B1 site of the AB1O ₃ system oxide), the composition ratio of the total of B1 element and B2 element to O is B1 element, B
Composition ratio B1: B2: O of 2 elements and O elements is changed to y1: y2:
If 3-δ, 0.8 ≦ y1 ≦ 0.95, 0.05 ≦
It is preferable that y2 ≦ 0.2 and 0.025 ≦ δ ≦ 0.1. Further, in the Ba (Ce, Y) O ₃ based oxide, it is more preferable that 0.7 ≦ y1 ≦ 0.9 and 0.1 ≦ y2 ≦ 0.3. In Sr (Ce, Yb) O ₃ -based oxide, 0.9 ≦ y1 ≦ 0.98, 0.02 ≦ y2 ≦
It is more preferably 0.1. Sr (Zr, Y) O
_{For 3} type oxides, 0.9 ≦ y1 ≦ 0.98, 0.0
It is more preferable that 2 ≦ y2 ≦ 0.1. Ca (Z
In the case of r, In) O ₃ -based oxide, 0.85 ≦ y1 ≦
It is more preferable that 0.95 and 0.05 ≦ y2 ≦ 0.15.

The above-mentioned BaCeO ₃ -based oxides, Sr
CeO ₃ -based oxide, SrZrO ₃ -based oxide, and Ca
Among ZrO ₃ -based oxides and the like, BaCeO ₃ -based oxide and SrC have excellent conductivity and can generate a particularly large potential difference (mixed potential) by contact with a combustible gas.
It is preferable to use any of the eO ₃ based oxide and SrZrO ₃ based oxide, further, it is more preferable to use a BaCeO ₃ based oxide.

The shape and size of the solid electrolyte body are not particularly limited. As the shape of the solid electrolyte body, for example,
Bottomed cylinder type, plate type (rectangular type, disc type, etc., thickness 10 μm
Above), thin film type (rectangular type, disc type, etc., thickness less than 10 μm) can be appropriately selected and used. Moreover, the size of the solid electrolyte body is, for example, in the plate type, the surface area of one surface provided with the electrode is 0.09 cm ² or more (usually,
0.5 cm ² or less) is preferable.

The "electrode" comprises at least one pair. Other electrodes may or may not be provided. This electrode creates a potential difference between the two electrodes due to the flammable gas. This electrode is formed on the surface of the solid electrolyte body. Also, of both electrodes, some or all of them are arranged so as to be in direct or indirect contact with the atmosphere to be measured (when a porous protective layer that protects the detection electrode from poisonous substances, etc. is interposed). Has been done.

Further, each electrode needs to be formed on the same surface of the solid electrolyte body. The "same plane" means (1) two electrodes are formed on one plane of the solid electrolyte body, and (2) two electrodes are formed on the curved surface of the solid electrolyte body. To do. Further, in (1) and (2), when the surface of a flat surface or a curved surface has or is formed with fine irregularities, even when electrodes are formed according to the fine irregularities, these electrodes are formed on the same surface. Are formed. Among (1) and (2), it is more preferable that two electrodes are formed as in (1). By arranging the electrodes on the same surface as described above, it is possible to effectively utilize the characteristic that the electric conductivity near the surface of the solid electrolyte body is high.

The material constituting the electrodes is 250 to 450 ° C.
It suffices that it has sufficient conductivity in, and is not particularly limited.
However, the electrical resistivity at room temperature is 10^FourΩ · cm or less
(Usually 1.5^-6Ω · cm or more, Ω · cm is the sample
1 x 1 x 1 cm in size ^ThreeShows the resistance value per hit
Is preferred. Also, for example,
When used to measure the concentration of combustible gas in exhaust gas, etc.
Is exposed to high temperatures, this electrode is kept at 1000 ° C.
However, it is preferable that the
Exhaust gas immediately after operation is likely to contain flammable gas
In addition, the temperature of the exhaust gas at this initial stage is not so high.
Yes. Therefore, the effective use of the combustible gas sensor of the present invention
Can be used. However, after warming up the internal combustion engine, 1000
High temperature exhaust gas up to about ℃ will be exhausted,
Exposed to high temperatures). Furthermore, it has excellent corrosion resistance and solid-state
When a film is formed on the demolition material, it may have excellent adhesion.
preferable.

In the electrode, materials capable of exhibiting such characteristics are noble metals (Ru, Rh, P) other than Os.
d, Ag, Ir, Pt, Au), Fe, Ni, Cr,
Examples include metals, alloys and metal oxides containing one or more metals such as Co and Cu. Among them, Pt, Au, Pd, Rh, and the like are the main components (containing 80% by mass or more, and further 90% by mass or more of one electrode as a whole) because of their excellent high-temperature durability and corrosion resistance against an oxidizing atmosphere and a reducing atmosphere. It is preferable to use a material that Also,
Since each of the pair of electrodes must be made of a different material (because the same material does not cause a potential difference),
It is necessary to use each electrode with different compositions.
The term “different materials” may mean that the contained metals themselves are different, but the contained metals are the same, and the compositions of the materials may be different due to the different contents (usually , The content of the specific metal needs to be different by 10 mass% or more with respect to the entire one electrode).

The shape, size and thickness of the electrode are not particularly limited, but the thickness is 2 μm or more (further, 2
.About.15 .mu.m, especially 5 to 12 .mu.m). If it is less than 2 μm, it may be difficult to achieve sufficient conduction. Further, the thickness of one of the electrodes is preferably 50 μm or less. When the thickness is more than 50 μm, the gas to be measured (the gas to be measured contained in the atmosphere to be measured) has a three-phase interface (the gas to be measured, the detection electrode, and the solid electrolyte body) in contact with this electrode and the solid electrolyte body.
Phase), which may lead to a decrease in sensitivity.

The shortest distance between the pair of electrodes is 1.5 mm or less (more preferably 1.0 mm or less, still more preferably 0.75 mm or less, usually 0.5 mm).
Or more) is preferable. If the shortest distance between the electrodes exceeds 2 mm, the distance that protons move within the solid electrolyte body becomes long, and it becomes difficult to obtain the effect of forming both electrodes on the surface of the solid electrolyte body, which is not preferable.

In the combustible gas sensor of the present invention, the temperature of the solid electrolyte body is 250 to 450 ° C. (more preferably 2 ° C.).
70 to 430 ° C., more preferably 300 to 400 ° C., and particularly preferably 320 to 380 ° C.), the largest potential difference can be obtained between both electrodes. This potential difference includes at least a mixed potential. When the flammable gas sensor of the present invention is used at a temperature higher than 450 ° C., in an electrode that is active against the flammable gas, the flammable gas burns on the surface of the electrode to generate water vapor, and the potential difference caused by the water vapor pressure is generated. In some cases, the measurement sensitivity may be extremely reduced because only the measurement can be performed. On the other hand, if used at less than 250 ° C., sufficient conductivity may not be obtained, reaction of the gas to be measured may not easily occur at the three-phase interface, and sensitivity may decrease (potential difference decreases).

The method of raising the temperature of the solid electrolyte body to 250 to 450 ° C. is not particularly limited. For example, since the gas to be measured itself is 250 to 450 ° C., the temperature of the solid electrolyte body may be within the above temperature range at the time of measuring the combustible gas concentration without using a separate heating means. The solid electrolyte body may be forced to 250 to 450 ° C. by using a heating device such as a heater. Further, since the resistance value of the solid electrolyte body depends on the temperature of the solid electrolyte body itself, it is possible to provide a heating device control means for measuring the resistance and feeding back the result to control the movement / stop of the heating device. . With these, more accurate concentration measurement can be performed.

The above "mixed potential" means the temperature of the solid electrolyte body.
It is an electromotive force that is not proportional to the degree (see FIG. 5). That is, like
For example, the electromotive force E due to the light and shade of water vapor_H2OThe Nerns
Formula E_H2O= (RT / 2F) ln {PH_TwoO (2)
/ PH_TwoIt is approximately calculated from O (1)}. Also acid
Electromotive force E due to light and shade_O2Is the Nernst formula E
_O2= (RT / 4F) ln {PO_Two(2) / PO
_Two(1)} is approximately calculated. Either of these
As can be seen from the above formula, the electric power also depends on the temperature T of the solid electrolyte body.
Although the values are proportional, the mixed potentials are different. Also,
This mixed potential is such that the temperature of the solid electrolyte body is 250 to 450 ° C.
It is possible to measure with high sensitivity in the range of
In order to prevent the combustible gas from burning on the electrode surface,
Electromotive force that can be measured to reach the surface).

According to the combustible gas sensor and the method for measuring the combustible gas concentration of the present invention, the sensitivity to hydrogen, carbon monoxide, nitric oxide, etc. is very small (electromotive force when each component gas is not contained and 50 ppm is contained). The potential difference from the electromotive force at the time of the discharge is less than 10 mV. On the other hand, hydrocarbons having 2 or more carbon atoms (usually 15 or less carbon atoms, particularly 3 to 10 carbon atoms, especially 4 to 10 carbon atoms) (aliphatic hydrocarbons, cyclic hydrocarbons and aromatic hydrocarbons (these are Hydrocarbons of saturated, unsaturated, straight-chain, branched, etc.) and CH ₂ ═CHX, C
_{H 2 = CHCH 2 X, C} 3 H 7 X , and _CH 3 -CHX-
Halogenated hydrocarbons such as CH ₃ (where X is a halogen atom), alcohols such as C ₂ H ₅ OH, nitro compounds such as CH ₃ NO ₂ , amine compounds such as CH ₃ NH ₂ ,
Carboxylic acid compounds such as CH ₃ COOH, CH ₃ CHO
Since it has a measurable potential difference with respect to aldehyde compounds such as, ketone compounds such as acetone, and ether compounds such as CH ₃ OCH ₃ , it is suitable for detection and concentration measurement of these flammable gases. .

The combustible gas sensor and the method for measuring the concentration of the combustible gas according to the present invention have two carbon atoms among these combustible gases.
It has excellent sensitivity to the above hydrocarbon gases (usually having 15 or less carbon atoms, particularly 3 to 10 carbon atoms, and particularly 4 to 10 carbon atoms). Further, a hydrocarbon gas having a double bond and having a carbon number of 2 or more (usually having a carbon number of 15 or less, particularly 3 to
It is particularly excellent in sensitivity to 10, especially to 4 to 10 carbon atoms. According to the combustible gas sensor and the combustible gas concentration measuring method of the present invention, a measured gas containing 50 ppm of propene, 21% by volume of oxygen, and 2.3% by volume of water vapor, the balance being argon, The potential difference is 60 mV when supplied at 150 ml / min and measured at a temperature of 350 ° C.
Or more (further, 70 mV or more, particularly 75 mV or more, particularly 80 mV or more).

[0029]

EXAMPLES The present invention will be specifically described below with reference to examples. [1] Investigation of correlation between conductivity and solid electrolyte body temperature between an element using a proton conductive solid electrolyte body and an element using an oxygen ion conductive solid electrolyte body (1) Production of the present invention Proton conductivity Of a device 1 (combustible gas sensor 1) having a pair of electrodes formed on one surface side by using a porous solid electrolyte body (see FIG. 1): 10 mm in width, 10 mm in length, 0.75 mm in thickness, composition formula BaCe _{0 .75} Y _0.25 O _3−δ having a proton conductive solid electrolyte body 11 {hereinafter, simply referred to as “[BCY]”}, Pt powder 71 to 71
A platinum paste containing 76 mass% is applied in a predetermined shape and heated at 900 ° C. for 1 hour to obtain a width of 10 mm and a length of 1.0.
A platinum electrode 121 having a thickness of 5 mm and a thickness of 5 to 30 μm was formed.
Then, a gold paste containing 71 to 76% by mass of Au powder was applied in a predetermined shape on the same surface of the [BCY] 11 on which the platinum electrode 121 was formed, and heated at 900 ° C. for 1 hour to obtain a width of 10 mm. A gold electrode 122 having a length of 1.0 mm and a thickness of 5 to 30 μm was formed. The two electrodes are arranged side by side with a width of 1.0 mm. Then, platinum electrode 1
A platinum wire 131, which is a lead wire for extracting electromotive force to the outside, is connected to 21, and a gold wire 132, which is a lead wire, is connected to the gold electrode 122, and the element 1 (flammable gas sensor 1) is connected.
Got

(2) Preparation of comparative product (element 2) Preparation of element 2 in which electrodes were formed on the front and back surfaces using a proton conductive solid electrolyte body (see FIG. 2) 10 mm wide, 10 mm long, 0 thickness 0.75 mm [BC
Y] 21 is coated on one surface with a platinum paste containing 71 to 76 mass% of Pt powder in a predetermined shape, and the temperature is set to 900 ° C. for 1 hour.
Heated for 10 hours, width 10mm, length 1.0mm, thickness 5-3
A platinum electrode 221 of 0 μm was formed. Then, [BC
Y] 71 on the surface opposite to the surface on which the platinum electrode 221 was formed, facing the platinum electrode 221 with Au powder 71
~ 76 mass% of the gold paste is applied in a predetermined shape and heated at 900 ° C for 1 hour to obtain a width of 10 mm and a length of 1.0.
A gold electrode 222 having a thickness of 5 mm and a thickness of 5 to 30 μm was formed. Next, the platinum electrode 221 was connected to a platinum wire 231 serving as a lead wire for extracting an electromotive force to the outside, and the gold electrode was connected to a gold wire 232 serving as a lead wire to obtain the element 2.

(3) Preparation of Comparative Product (Element 3) Instead of the preparation [BCY] of Element 3 in which a pair of electrodes were formed on one surface side using an oxygen ion conductive solid electrolyte body, the composition formula Ce _{0. 8} Sm _0.2 O
Element 3 was obtained in the same manner as in (1) above, except that a solid electrolyte body having oxygen ion conductivity represented by _1.9 {hereinafter, simply referred to as "[CSO]"} was used.

(4) Preparation of comparative product (element 4) [CSO] was used instead of preparation [BCY] of element 4 in which electrodes were formed on the front and back surfaces using an oxygen ion conductive solid electrolyte body. Element 4 was obtained in the same manner as in the above (2) except for the above.

(5) Preparation of comparative product (element 5) Instead of the preparation [BCY] of element 5 having a pair of electrodes formed on one surface side using an oxygen ion conductive solid electrolyte body, composition formula Zr _{0. 92} Y _0.08 O
Element 5 was obtained in the same manner as in (1) above, except that the solid electrolyte body having oxygen ion conductivity represented by _1.96 {hereinafter, simply referred to as "[YSZ]"} was used.

(6) Preparation of comparative product (element 6) [YSZ] was used instead of preparation [BCY] of element 6 in which electrodes were formed on the front and back surfaces using an oxygen ion conductive solid electrolyte body. Element 6 was obtained in the same manner as in (2) except for the above.

(7) Preparation of measuring device [BCY], [CSO] obtained in the above (1) to (6)
Alternatively, each of the elements 1 to 6 using [YSZ] has an outer diameter of 6 m.
It was fixed in a thin tube 31 made of alumina and having an inner diameter of 4 mm and an inner diameter of 4 mm so as to have a positional relationship as shown in FIG. Next, this thin tube 31 was fixed in an outer tube 32 having an outer diameter of 13 mm and an inner diameter of 9 mm. Then, the platinum wire and the gold wire were led out to the outside of the tube, the platinum wire was connected to the positive electrode of an electrometer (Hokuto Denko KK, type “HE-104”), and the gold wire was connected to the negative electrode. A measuring device was obtained. FIG. 3 shows a measuring device (flammable gas concentration measuring device 3) obtained by using the element 1.

(8) Measurement of conductivity Each of the six types of measuring devices including the elements 1 to 6 obtained in (7) above was placed in a heating furnace capable of keeping the entire measuring device at a predetermined temperature. . Next, a reference gas adjusted so that oxygen was 21% by volume, water vapor was 2.3% by volume, and the balance was argon was flown into the capillary at a rate of 150 ml / min. Then, a constant current was passed between the platinum electrode and the gold electrode, and the potential difference obtained at this time was measured while changing the temperature in the heating furnace from 400 to 800 ° C. in steps of 50 ° C. The resistance value was calculated from the value of the flowing current and the measured potential difference, and the conductivity, which is the reciprocal of the resistance value, was calculated.
The graph shows the correlation between conductivity and temperature.

(9) Evaluation From FIG. 4, the element using the proton conductive solid electrolyte body [BCY] also shows the oxygen ion conductive [CSO] or [Y].
It can be seen that the elements 3 to 6 using SZ] also have improved conductivity as the temperature of the solid electrolyte body rises regardless of the electrode formation location. Among these, [BCY] has a particularly low temperature (600) as compared with other oxygen ion conductive solid electrolyte bodies.
It can be seen that high conductivity can be maintained even at a temperature of not higher than 0 ° C, and further not higher than 500 ° C. Further, it can be seen that only the element 1 using [BCY] and having electrodes formed only on one surface side of [BCY] has remarkably large conductivity at a low temperature of 450 ° C. or lower. That is, 450
It is understood that in order to obtain high conductivity at a low temperature of not higher than 0 ° C., it is preferable to use a proton conductive solid electrolyte body and form the electrode only on one surface side of the solid electrolyte body.

[2] Investigation of correlation between measured temperature and electromotive force (1) Measurement of change in electromotive force A combustible gas concentration measuring device 3 equipped with [BCY] obtained in (7) of [1] above was used. It was placed in a heating furnace kept at a predetermined temperature. The heating furnace has a temperature of 200 to 500 ° C.
It was used while maintaining each temperature up to 50 ° C.
Then, a measured gas adjusted so that propene was 50 ppm, oxygen was 21% by volume, water vapor was 2.3% by volume, and the balance was argon was flown into the capillary at a rate of 150 ml / min. At this time, the potential difference generated between the platinum electrode and the gold electrode was measured and shown in the graph of FIG.

(2) Evaluation From FIG. 5, the maximum electromotive force obtained is at temperature 300.
It can be seen that it exists in the range of 400 ° C. Further, it can be seen that the electromotive force is particularly large at 350 ° C.

[3] Examination of correlation between concentration of various gases and electromotive force (1) Measurement of concentration of various gases Combustible gas concentration measuring device 3 equipped with [BCY] obtained in (7) of [1] above The temperature inside the heating furnace to 3
It was kept warm at 50 ° C. Then methane, ethane, ethene,
Each of the measurement target gases of ethyne, propane, propene, butene, 1-butene, hydrogen and carbon monoxide was adjusted to a predetermined amount, oxygen was 21% by volume, water vapor was 2.3% by volume, and the balance was argon. 150 to be measured gas into the thin tube per minute
Flowed at a rate of ml. In addition, the above-mentioned predetermined amount of each gas to be measured is each concentration in 5 ppm increments from 5 to 50 ppm (see FIGS. 6 and 7). The potential difference generated between the platinum electrode and the gold electrode during the flow of these various gases to be measured was measured and shown as a graph in FIGS. 6 and 7.

(3) Evaluation From FIG. 6, the combustible gas sensor of the present invention is a combustible gas in the presence of a hydrocarbon-based compound such as propene, but is relatively insensitive to hydrogen and carbon monoxide. It can be seen that it has almost no sensitivity to. This is very useful when the combustible gas sensor of the present invention is used to selectively measure only the concentration of hydrocarbon compounds in the exhaust gas of an internal combustion engine. That is, it is usually possible to measure the concentration of only pure hydrocarbon compounds excluding hydrogen and carbon monoxide contained in the exhaust gas of an internal combustion engine.

From FIG. 7, it is possible to measure the concentration of a hydrocarbon compound having no unsaturated bond such as ethane, propane and butane at a high concentration (about 50 ppm or more). It can be seen that the sensitivity to ethene, propene, n-butene, 1-butene and the like having a heavy unsaturated bond is excellent. In addition, the sensitivity is higher for those having 3 carbon atoms than for those having 2 carbon atoms,
Furthermore, it can be seen that the number of carbon atoms is higher than that of three carbon atoms.

Therefore, from the above [1] to [3], as the combustible gas sensor, the solid electrolyte body having proton conductivity is used as the solid electrolyte body, and the electrode is formed only on one surface side of the solid electrolyte body. Furthermore, it can be seen that extremely excellent performance can be exhibited by maintaining the temperature of the solid electrolyte body at 250 to 450 ° C.

[0044]

According to the combustible gas sensor of the present invention and the other combustible gas sensor of the present invention, it is possible to measure the concentrations of various combustible gases except hydrogen, carbon monoxide and nitric oxide. Moreover, when the solid electrolyte body is a BaCeO ₃ -based proton conductive oxide, excellent sensitivity can be exhibited. Furthermore, when the shortest distance between the electrodes is equal to or less than a predetermined value, excellent sensitivity can be exhibited. Further, it can be preferably used particularly for measuring the concentration of a combustible gas having 2 or more carbon atoms. Furthermore, 50ppm
Of propene, 21% by volume of oxygen and 2.3% by volume of water vapor, with the balance being argon, the gas to be measured was supplied at 150 ml / min and the potential difference when measured at a temperature of 350 ° C. It can be 60 mV or more. According to the combustible gas concentration measuring method of the present invention and the other combustible gas concentration measuring method of the present invention, various combustible gases other than hydrogen, carbon monoxide and nitric oxide can be measured.
Further, it is possible to accurately and accurately measure the concentration of a combustible gas having 2 or more carbon atoms.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of an example of a gas sensor of the present invention.

FIG. 2 is a schematic perspective view of an example of a gas sensor of a comparative product.

FIG. 3 is a schematic cross-sectional view of a combustible gas concentration measuring device used in an example.

FIG. 4 is a graph showing a correlation between a temperature of a solid electrolyte body and an electromotive force.

FIG. 5 is a correlation between the temperature of the solid electrolyte body and the electromotive force obtained by the combustible gas sensor of the present invention.

FIG. 6 is a graph showing the correlation between the concentrations of various gases and the electromotive force obtained by the combustible gas sensor of the present invention.

FIG. 7 is a graph showing the correlation between the concentrations of various gases and the electromotive force obtained by the combustible gas sensor of the present invention.

[Explanation of symbols]

1; flammable gas sensor (element 1), 11; solid electrolyte body ([BCY]) having proton conductivity, 121; platinum electrode, 122; gold electrode, 131; platinum wire, 132; gold wire, 2; element 2 , 21; solid electrolyte body ([BCY]) having proton conductivity, 221; platinum electrode, 222; gold electrode, 231; platinum wire, 232; gold wire, 3; combustible gas concentration measuring device, 31; capillary tube, 32; outer tube.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shiro Kakimoto             14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi Japan special             Within Toyo Co., Ltd. (72) Inventor Ryuji Inoue             14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi Japan special             Within Toyo Co., Ltd. (72) Inventor Noboru Ishida             14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi Japan special             Within Toyo Co., Ltd. F term (reference) 2G004 ZA05                 2G060 AA02 AA03 AA04 AD01 AE40                       AF09 AG10 AG11 HB06 KA01

Claims (9)

[Claims] 1. A solid electrolyte body having proton conductivity,
The solid electrolyte body is provided with a pair of electrodes made of different materials formed on the same surface in contact with the atmosphere to be measured, and the solid electrolyte body is used at a temperature of 250 to 450 ° C. Combustible gas sensor. 2. A solid electrolyte body having proton conductivity,
It is provided with a pair of electrodes made of different materials formed on the same surface in contact with the atmosphere to be measured of the solid electrolyte body, and is used for measuring the concentration of flammable gas based on a potential difference including at least a hybrid potential generated between the electrodes. A combustible gas sensor characterized in that 3. The flammable gas sensor according to claim 1, wherein the solid electrolyte body is a BaCeO ₃ -based proton conductive oxide. 4. The flammable gas sensor according to claim 1, wherein the shortest distance between the electrodes is 1.5 mm or less. 5. The combustible gas sensor according to claim 1, which is used for measuring the concentration of a combustible gas having 2 or more carbon atoms. 6. A measured gas containing 50 ppm of propene, 21% by volume of oxygen and 2.3% by volume of water vapor, the balance being argon, is supplied at 150 ml / min,
The combustible gas sensor according to any one of claims 1 to 5, wherein the potential difference when measured at a temperature of 350 ° C is 60 mV or more. 7. A solid electrolyte body having proton conductivity,
Using a flammable gas sensor having a pair of electrodes made of different materials formed on the same surface in contact with the atmosphere to be measured of the solid electrolyte body, exposing the electrodes to the atmosphere to be measured, the temperature of the solid electrolyte body Is 250 to 450 ° C., the combustible gas concentration is measured based on the potential difference generated between the electrodes. 8. A solid electrolyte body having proton conductivity,
A flammable gas sensor comprising a pair of electrodes made of different materials formed on the same surface in contact with the atmosphere to be measured of the solid electrolyte body is used, and the electrodes are exposed to the atmosphere to be measured to generate at least between the electrodes. A combustible gas concentration measuring method comprising measuring the concentration of a combustible gas based on a potential difference including a mixed potential. 9. The combustible gas concentration measuring method according to claim 7, wherein the potential difference is caused by the concentration of the combustible gas having 2 or more carbon atoms.