JP4743375B2 - Flammable gas concentration measurement method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a flammable gas concentration measurement method. More specifically, the present invention relates to a method for measuring a combustible gas concentration in which the concentration of a target gas is measured by measuring a potential difference between electrodes formed on a solid electrolyte body exhibiting proton conductivity. Combustible gas of the present inventionConcentration measurement methodCan be used for measuring the concentration of various combustible gases, and is particularly suitable for measuring the concentration of hydrocarbon gas contained in the exhaust gas of an internal combustion engine.
[0002]
[Prior art]
In recent years, many hydrocarbon gas sensors and the like using a solid electrolyte body having oxygen ion conductivity have been developed, and the techniques disclosed in JP-A-8-510840 and JP-A-2000-146902 are known. . However, since these all use the conductivity of oxygen ions, they are inherently affected by oxygen concentration. In addition, hydrogen, carbon monoxide, nitrogen monoxide, etc., and hydrocarbon gas, etc., should be measured separately. Is difficult. For this reason, a special technique for reducing the influence of oxygen concentration and a special technique for distinguishing hydrogen, carbon monoxide, nitrogen monoxide, and the like from hydrocarbon gas and the like are required.
On the other hand, as a hydrocarbon gas sensor using a solid electrolyte body having proton conductivity and measuring the concentration of hydrocarbon gas from a potential difference generated between a pair of electrodes, JP-A-6-242060 and JP-A-9-127055 are disclosed. Etc. are disclosed.
[0003]
[Problems to be solved by the invention]
The hydrocarbon sensor disclosed in these publications (electromotive force type hydrocarbon gas sensor in Japanese Patent Laid-Open No. 9-127070) includes a pair of electrodes. One of these electrodes is capable of burning hydrocarbon gas at its “surface” at high temperatures (770 ° C. in JP-A-6-242060, 500 ° C. in JP-A-9-127055). It is an active electrode, and the other electrode is an inactive electrode that cannot burn hydrocarbon gas even at the same temperature. On the “surface” of the active electrode, water vapor is generated by the combustion of the hydrocarbon gas, and a potential difference due to the partial pressure difference of the water vapor is generated with the inactive electrode. By measuring this potential difference, the hydrocarbon gas is detected, and further its concentration is to be measured.
[0004]
However, (1) In the above, there is a problem that it is very difficult to measure the concentration of hydrocarbon gas in an atmosphere containing a lot of water vapor such as exhaust gas of an internal combustion engine. In view of (2) actual use, since it is necessary to be able to measure the concentration of hydrocarbon gas even in the order of ppm, it is desired that the potential difference obtained between the electrodes is large.
[0005]
  The present invention solves the above problems, and can measure the concentration of combustible gas even in an atmosphere with a lot of water vapor, and can accurately measure even when the concentration of combustible gas is low. It aims at providing the combustible gas concentration measuring method.
[0006]
[Means for Solving the Problems]
  The present inventionUsed forThe combustible gas sensor is a solid electrolyte that exhibits proton conductivity.BaCeO ₃ Proton conductive oxideAnd electrodes made of a pair of different materials, each formed on the same surface in contact with the measured atmosphere of the solid electrolyte body, and the temperature of the solid electrolyte body isFor the measurement of the combustible gas concentration based on at least the mixed potential generated between the electrodes under the condition that the temperature of the solid electrolyte body is 300 to 400 ° C.Used.
[0008]
  The solid electrolyte body is BaCeO.₃Proton conductive oxideIs. Furthermore, the shortest distance between the electrodes can be 1.5 mm or less. Moreover, it uses for the density | concentration measurement of combustible gas with 2 or more carbon atoms. Furthermore, when a measurement gas containing 50 ppm of propene, 21% by volume of oxygen and 2.3% by volume of water vapor, the balance of which consists of argon is supplied at 150 ml per minute, and measured at a temperature of 350 ° C. The potential difference can be 60 mV or more.
[0009]
  The combustible gas concentration measuring method of the present invention is a solid electrolyte body showing proton conductivity.BaCeO ₃ Proton conductive oxideAnd an electrode made of a pair of different materials, each formed on the same surface in contact with the measured atmosphere of the solid electrolyte body, exposing the electrode to the measured atmosphere, and the solid electrolyte body Temperature of300-400 ° COccurs between the electrodes under the conditionsAt least mixed potentialBased on potential difference2 or more carbon atomsIt is characterized by measuring the concentration of combustible gas.
[0011]
The potential difference can be attributed to the concentration of combustible gas having 2 or more carbon atoms.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The inventors of the present invention repeatedly studied a known proton conductive solid electrolyte body. Among them, with respect to the proton conductive solid electrolyte body, (1) a case where the front and back surfaces of the plate-shaped solid electrolyte body are sandwiched between a pair of electrodes, and the conductivity is measured between the electrodes; It has been found that there is a difference in conductivity between the case where electrodes are arranged side by side on one surface of a plate-like solid electrolyte body and the conductivity is measured between the electrodes. Further, it has been found that higher conductivity can be obtained when the electrode is disposed as in (2) than when the electrode is disposed as in (1). This is a phenomenon that has not been known so far, and is a peculiar phenomenon that has not been recognized even if the same measurement is performed on the oxygen ion conductive solid electrolyte body that has been widely used so far. there were.
[0013]
Furthermore, until now, in a sensor using a proton conductive solid electrolyte body and measuring the concentration of hydrocarbon gas or the like, the measurement temperature (temperature of the solid electrolyte body) is adjusted to a high temperature of 500 ° C. to 800 ° C. It was. 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, rather high sensitivity can be obtained compared to the conventional case when hydrocarbon gas is hardly burned on the electrode surface. 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 three phases of the combustible gas, the electrode material, and the solid electrolyte. Therefore, it is considered that this is because a potential difference (hybrid potential) different from the potential difference caused by the conventional hydrogen partial pressure is generated.
The present inventors have completed the present invention based on these two findings.
[0014]
  The above "solid electrolyte body" has proton conductivityBaCeO which is a solid electrolyte body showing ₃ It is a system proton conductive oxide. still,As a solid electrolyte body that can exhibit such proton conductivity, for example, SrCeO₃Oxide, SrZrO₃-Based oxides and CaZrO₃Examples thereof include system oxides.
  These solid electrolyte bodies have their B sites (ABO).₃At least one of Sc, Y, In, Nd, Pm, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu is dissolved in B) when expressed as a system oxide. It may be. These solid solutions can exhibit particularly high proton conductivity. For example, BaCeO₃As the system oxide, Ba (Ce, Y) O₃Oxides and Ba (Ce, Nd) O₃Oxide, SrCeO₃Sr (Ce, Yb) O as the system oxide₃Oxide, SrZrO₃Sr (Zr, Y) O as a system oxide₃Oxides and Sr (Zr, Yb) O₃Oxide, CaZrO₃Ca (Zr, In) O as a system oxide₃Examples thereof include system oxides.
[0015]
These oxides are respectively A (B1, B2) O.₃Oxide (AB1O₃The composition ratio of the total of B1 element and B2 element to O and the composition ratio of B1 element, B2 element, and O element When the ratio B1: B2: O is y1: y2: 3-δ, 0.8 ≦ y1 ≦ 0.95, 0.05 ≦ y2 ≦ 0.2, 0.025 ≦ δ ≦ 0.1. preferable.
Furthermore, Ba (Ce, Y) O₃In the system oxide, it is more preferable that 0.7 ≦ y1 ≦ 0.9 and 0.1 ≦ y2 ≦ 0.3. Sr (Ce, Yb) O₃In the system oxide, it is more preferable that 0.9 ≦ y1 ≦ 0.98 and 0.02 ≦ y2 ≦ 0.1. Sr (Zr, Y) O₃In the system oxide, it is more preferable that 0.9 ≦ y1 ≦ 0.98 and 0.02 ≦ y2 ≦ 0.1. Ca (Zr, In) O₃In the system oxide, it is more preferable that 0.85 ≦ y1 ≦ 0.95 and 0.05 ≦ y2 ≦ 0.15.
[0016]
  BaCeO listed above₃Oxide, SrCeO₃Oxide, SrZrO₃-Based oxides and CaZrO₃Among the base oxides, BaCeO has excellent conductivity and can generate a particularly large potential difference (hybridization potential) by contact with combustible gas.₃A system oxide is used.
[0017]
The shape, size, etc. of the solid electrolyte body are not particularly limited. As the shape of the solid electrolyte body, for example, a bottomed cylindrical type, a plate type (rectangular type, disc type, etc., thickness 10 μm or more), a thin film type (rectangular type, disc type, etc., thickness less than 10 μm), etc. are appropriately selected. Can be used. In addition, the size of the solid electrolyte body is, for example, in the plate type, the surface area of one surface including the electrode is 0.09 cm²Above (normally 0.5cm²Or less).
[0018]
The “electrode” includes at least a pair. In addition, an electrode may or may not be provided. This electrode produces a potential difference due to the flammable gas between the two electrodes. This electrode is formed on the surface of the solid electrolyte body. In addition, of both electrodes, some or all of them are placed in contact with the measurement atmosphere directly or indirectly (through a porous protective layer that protects the detection electrode from poisonous substances, etc.). Has been.
[0019]
Moreover, each electrode needs to be formed on the same surface of the solid electrolyte body. The above "same surface" means (1) when two electrodes are formed on one plane of the solid electrolyte body, and (2) when two electrodes are formed on the curved surface of the solid electrolyte body. To do. Further, in (1) and (2), when a flat or curved surface has or is formed with fine irregularities, these electrodes are formed on the same surface even when the electrodes are formed according to the fine irregularities. Is assumed to be formed. Among (1) and (2), it is more preferable that two electrodes are formed as in (1).
Thus, by arranging the electrodes on the same surface, the property that the conductivity near the surface of the solid electrolyte body is high can be effectively used.
[0020]
The material constituting the electrode is not particularly limited as long as it has sufficient conductivity at 250 to 450 ° C., but the electrical resistivity at room temperature is 10⁴Ω · cm or less (normally 1.5^-6Ω · cm or more, Ω · cm is 1 × 1 × 1 cm in the sample size³The resistance value per unit is preferable. For example, when used for measuring the concentration of combustible gas in the exhaust gas of an internal combustion engine, the electrode is preferably not melted even at 1000 ° C. because it is exposed to a high temperature (for example, immediately after starting the internal combustion engine). The exhaust gas of the present invention is likely to contain a combustible gas, and the temperature of the initial exhaust gas is not so high, so that the combustible gas sensor of the present invention can be effectively used. After the internal combustion engine is warmed up, high-temperature exhaust gas up to about 1000 ° C. is exhausted and exposed to high temperature). Furthermore, it is preferable that it is excellent in corrosion resistance, and it is excellent in adhesiveness when a film is formed on a solid electrolyte body.
[0021]
In the electrode, materials capable of exhibiting such characteristics include noble metals other than Os (Ru, Rh, Pd, Ag, Ir, Pt, Au), and one kind of metal such as Fe, Ni, Cr, Co, and Cu. Or the metal, alloy, metal oxide, etc. containing 2 or more types are mentioned. Among them, since it is excellent in high temperature durability and corrosion resistance in an oxidizing atmosphere and a reducing atmosphere, Pt, Au, Pd, Rh, etc. are contained as a main component (containing 80% by mass or more, and further 90% by mass or more of one whole electrode). It is preferable to use a material to be used. In addition, each of the pair of electrodes needs to be made of a different material (if the same material is used, a potential difference does not occur), and thus it is necessary to use the electrodes so that the compositions of the electrodes are different. In addition, although the metal itself contained may differ from the material being different, the metal contained is the same, and since the content is different, the composition of the material may be different (usually The specific metal content needs to be different by 10 mass% or more with respect to the entire one electrode).
[0022]
The shape, size and thickness of the electrode are not particularly limited, but the thickness is preferably 2 μm or more (more preferably 2 to 15 μm, particularly 5 to 12 μm). If it is less than 2 μm, it may be difficult to achieve sufficient conduction. Further, the thickness of one electrode is preferably 50 μm or less. If it is thicker than 50 μm, the gas to be measured (the gas to be measured contained in the atmosphere to be measured) is a three-phase interface where the electrode and the solid electrolyte body are in contact (the three phases of the gas to be measured, the detection electrode and the solid electrolyte body). ) May be difficult to achieve, leading to a decrease in sensitivity.
[0023]
The shortest distance between the electrodes of these pair of electrodes is preferably 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). If the shortest distance between the electrodes exceeds 2 mm, the distance that protons move in the solid electrolyte body becomes long, and it is difficult to obtain the effect of forming both electrodes on the surface of the solid electrolyte body.
[0024]
  Moreover, the combustible gas sensor of this invention can obtain the largest electric potential difference between both electrodes by using the temperature of a solid electrolyte body in 300-400 degreeC, Preferably it is 320-380 degreeC. This potential difference includes at least a hybrid potential. When the combustible gas sensor of the present invention is used at a temperature exceeding 450 ° C., in the electrode active against the combustible gas, the combustible gas burns on the surface of the electrode to generate water vapor, and the potential difference caused by the water vapor pressure However, there are cases where the measurement sensitivity is extremely lowered because only the measurement can be performed. On the other hand, if it is used at less than 250 ° C., sufficient conductivity cannot be obtained, the reaction of the gas to be measured hardly occurs at the three-phase interface, and the sensitivity may be lowered (potential difference is reduced) in some cases.
[0025]
  Solid electrolyte body temperature300-400 ° CThe method of making is not particularly limited. For example, since the gas to be measured 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. Force the solid electrolyte body by using a heating device such as a heater.300-400 ° CIt may be a thing to make. Furthermore, 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 this resistance and feeding back the result to control the movement / stopping of the heating device. . By these, it is possible to perform more accurate concentration measurement.
[0026]
The “hybrid potential” is an electromotive force that is not proportional to the temperature of the solid electrolyte body (see FIG. 5). That is, for example, electromotive force E caused by water vapor concentration_H2OIs the Nernst equation E_H2O= (RT / 2F) ln {PH₂O (2) / PH₂O (1)} is approximately calculated. In addition, the electromotive force E caused by oxygen concentration_O2Is the Nernst equation E_O2= (RT / 4F) ln {PO₂(2) / PO₂(1)} is approximately calculated. As can be seen from the above formula, these electromotive forces are values proportional to the temperature T of the solid electrolyte body, but the mixed potentials are different.
This hybrid potential can be measured with high sensitivity when the temperature of the solid electrolyte body is in the range of 250 to 450 ° C. (Because the temperature is low, the combustible gas does not burn on the electrode surface and reaches the three-phase interface. Can be measured).
[0027]
  According to the combustible gas concentration measurement method of the present invention, the sensitivity to hydrogen, carbon monoxide, nitrogen monoxide, etc. is very small (the electromotive force when each component gas is not contained and the electromotive force when 50 ppm is contained). (Potential difference is less than 10 mV), hardly detected. In contrast, hydrocarbons having 2 or more carbon atoms (usually 15 or less carbon atoms, especially 3 to 10 carbon atoms, especially 4 to 10 carbon atoms) {aliphatic hydrocarbons, cyclic hydrocarbons and aromatic hydrocarbons (these Hydrocarbons of saturated, unsaturated, straight chain, and branched are also included)}, and CH₂= CHX, CH₂= CHCH₂X, C₃H₇X and CH₃-CHX-CH₃Halogenated hydrocarbons such as X (where X is a halogen atom), C₂H₅Alcohols such as OH, CH₃NO₂Nitro compounds such as CH₃NH₂Amine compounds such as CH₃Carboxylic acid compounds such as COOH, CH₃Aldehyde compounds such as CHO, ketone compounds such as acetone, and CH₃OCH₃Since the potential difference with respect to ether compounds and the like has a measurable level, it is suitable for detection and concentration measurement of these combustible gases.
[0028]
  The flammable gas concentration measurement method of the present invention is sensitive to hydrocarbon gas having 2 or more carbon atoms (usually 15 or less carbon atoms, especially 3 to 10 carbon atoms, especially 4 to 10 carbon atoms) among these flammable gases. Are better. Furthermore, it is particularly excellent in sensitivity to a hydrocarbon gas having 2 or more carbon atoms having a double bond (usually 15 or less carbon atoms, particularly 3 to 10 carbon atoms, especially 4 to 10 carbon atoms).
  According to the method for measuring the concentration of combustible gas according to the present invention, a measured gas containing 50 ppm of propene, 21% by volume of oxygen and 2.3% by volume of water vapor, with the balance being argon, is 150 ml per minute. When supplied and measured at a temperature of 350 ° C., the potential difference can be 60 mV or more (further 70 mV or more, particularly 75 mV or more, particularly 80 mV or more).
[0029]
【Example】
  Hereinafter, the present invention will be described specifically by way of examples.
[1] Examination of correlation between conductivity and solid electrolyte body temperature of element using proton conductive solid electrolyte body and element using oxygen ion conductive solid electrolyte body
(1) The present inventionElement 1 used forMaking
  Production of element 1 (flammable gas sensor 1) having a pair of electrodes formed on one surface using a proton conductive solid electrolyte body (see FIG. 1)
  The width is 10 mm, the length is 10 mm, the thickness is 0.75 mm, and the composition formula is BaCe._0.75Y_0.25O_3-δA platinum paste containing 71 to 76% by mass of Pt powder in a predetermined shape is applied on one surface of a solid electrolyte body 11 having proton conductivity represented by the following {hereinafter referred to simply as “[BCY]”}: 900 The platinum electrode 121 having a width of 10 mm, a length of 1.0 mm, and a thickness of 5 to 30 μm was formed by heating at 0 ° C. for 1 hour. Next, on the same surface on which the platinum electrode 121 on [BCY] 11 is formed, a gold paste containing 71 to 76 mass% of Au powder is applied in a predetermined shape, heated at 900 ° C. for 1 hour, and 10 mm wide. A gold electrode 122 having a length of 1.0 mm and a thickness of 5 to 30 μm was formed. These two electrodes are arranged side by side with a width of 1.0 mm. Next, a platinum wire 131 serving as a lead wire for extracting an electromotive force to the outside is connected to the platinum electrode 121, and a gold wire 132 serving as a lead wire is connected to the gold electrode 122, and the element 1 (flammable gas sensor 1). Got.
[0030]
(2) Production of comparative product (element 2)
Fabrication of element 2 in which electrodes are formed on the front and back surfaces using a proton conductive solid electrolyte body (see FIG. 2)
On one side of [BCY] 21 having a width of 10 mm, a length of 10 mm, and a thickness of 0.75 mm, a platinum paste containing 71 to 76% by mass of Pt powder is applied in a predetermined shape and heated at 900 ° C. for 1 hour. A platinum electrode 221 having a width of 10 mm, a length of 1.0 mm, and a thickness of 5 to 30 μm was formed. Next, a gold paste containing 71 to 76% by mass of Au powder is applied in a predetermined shape at a position facing the platinum electrode 221 on the surface opposite to the surface on which the platinum electrode 221 on the [BCY] 21 is formed. And heated at 900 ° C. for 1 hour to form a gold electrode 222 having a width of 10 mm, a length of 1.0 mm, and a thickness of 5 to 30 μm. Subsequently, the platinum electrode 221 was connected with a platinum wire 231 serving as a lead wire for extracting an electromotive force to the outside, and the gold wire 232 serving as a lead wire was connected to the gold electrode, whereby the element 2 was obtained.
[0031]
(3) Production of comparative product (element 3)
Fabrication of element 3 in which a pair of electrodes are formed on one side using an oxygen ion conductive solid electrolyte body
Instead of [BCY], the composition formula Ce_0.8Sm_0.2O_1.9An element 3 was obtained in the same manner as in the above (1) except that a solid electrolyte body having oxygen ion conductivity represented by the following formula {hereinafter simply referred to as “[CSO]”} was used.
[0032]
(4) Production of comparative product (element 4)
Fabrication of element 4 in which electrodes are formed on the front and back surfaces using an oxygen ion conductive solid electrolyte body
An element 4 was obtained in the same manner as in the above (2) except that [CSO] was used instead of [BCY].
[0033]
(5) Production of comparative product (element 5)
Fabrication of element 5 in which a pair of electrodes are formed on one side using an oxygen ion conductive solid electrolyte body
Instead of [BCY], the composition formula Zr_0.92Y_0.08O_1.96An element 5 was obtained in the same manner as in the above (1) except that a solid electrolyte body having oxygen ion conductivity represented by {{hereinafter simply referred to as “[YSZ]"}} was used.
[0034]
(6) Preparation of comparative product (element 6)
Fabrication of element 6 in which electrodes are formed on the front and back surfaces using an oxygen ion conductive solid electrolyte body
An element 6 was obtained in the same manner as in the above (2) except that [YSZ] was used instead of [BCY].
[0035]
(7) Production of measuring device
Each of the elements 1 to 6 using [BCY], [CSO] or [YSZ] obtained in (1) to (6) above is placed in an alumina thin tube 31 having an outer diameter of 6 mm and an inner diameter of 4 mm. It was fixed so that the positional relationship shown in FIG. Next, the 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 are led out to the outside of the tube, the platinum wire is connected to the positive electrode of an electrometer (made by Hokuto Denko Co., Ltd., type “HE-104”), and the gold wire is connected to the negative electrode. A measuring device was obtained. FIG. 3 shows a measuring device (flammable gas concentration measuring device 3) obtained using the element 1.
[0036]
(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 that can keep the entire measuring device at a predetermined temperature. Next, a reference gas adjusted so that oxygen was 21 vol%, water vapor was 2.3 vol%, and the balance was argon was allowed to flow into the capillary at a rate of 150 ml per minute. 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 increments of 50 ° C. The resistance value was calculated from the current value passed and the measured potential difference, and the conductivity which was the reciprocal of this resistance value was calculated. FIG. 4 shows the correlation between the conductivity and temperature as a graph.
[0037]
(9) Evaluation
From FIG. 4, the element using the proton conductive solid electrolyte body [BCY] and the elements 3 to 6 using oxygen ion conductive [CSO] or [YSZ] are both solid electrolytes regardless of the electrode formation location. It can be seen that the conductivity improves as the body temperature increases. Among these, it can be seen that [BCY] can maintain high conductivity, especially at low temperatures (600 ° C. or less, further 500 ° C. or less), as compared with other oxygen ion conductive solid electrolytes. Furthermore, it can be seen that only the element 1 using [BCY] and having the electrode formed only on one surface side of [BCY] has a remarkably high conductivity at a low temperature of 450 ° C. or lower. That is, it can be seen that in order to obtain high conductivity at a low temperature of 450 ° C. or lower, it is preferable to use a proton conductive solid electrolyte body and have an electrode formed only on one side of the solid electrolyte body.
[0038]
[2] Examination of correlation between measured temperature and electromotive force
(1) Measurement of changes in electromotive force
The combustible gas concentration measuring device 3 provided with [BCY] obtained in (7) of the above [1] was placed in a heating furnace kept at a predetermined temperature. The heating furnace was used while maintaining the temperature from 200 to 500 ° C. in 50 ° C. increments. Next, a gas to be measured, which was adjusted so that propene was 50 ppm, oxygen was 21 vol%, water vapor was 2.3 vol%, and the balance was argon, was allowed to flow into the capillary at a rate of 150 ml per minute. The potential difference generated between the platinum electrode and the gold electrode at this time was measured and shown as a graph in FIG.
[0039]
(2) Evaluation
From FIG. 5, it can be seen that the largest electromotive force obtained exists in the temperature range of 300 to 400 ° C. Moreover, it turns out that especially the electromotive force in 350 degreeC is large.
[0040]
[3] Examination of correlation between concentration of various gases and electromotive force
(1) Measurement of various gas concentrations
Using the combustible gas concentration measuring device 3 provided with [BCY] obtained in (7) of [1] above, the temperature in the heating furnace was kept at 350 ° C. Next, methane, ethane, ethene, ethyne, propane, propene, butene, 1-butene, hydrogen, and carbon monoxide each measurement target gas is a predetermined amount, oxygen is 21 vol%, water vapor is 2.3 vol%, and the balance The gas to be measured, adjusted to be argon, was allowed to flow into the capillary at a rate of 150 ml per minute. The predetermined amounts of the various gases to be measured are concentrations of 5 ppm in increments of 5 to 50 ppm (see FIGS. 6 and 7). The potential difference generated between the platinum electrode and the gold electrode was measured while the various gases to be measured were introduced, and these are shown as graphs in FIGS.
[0041]
(3) Evaluation
  From FIG. 6, the present inventionUsed forIt can be seen that the combustible gas sensor has relatively little sensitivity to hydrogen and carbon monoxide although it is a combustible gas when a hydrocarbon-based compound such as propene coexists. This is very useful when the combustible gas sensor of the present invention is intended to selectively measure only the concentration of the hydrocarbon compound in the exhaust gas of the 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.
[0042]
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 saturated bond is excellent. Moreover, the sensitivity is higher for those having 3 carbons than those having 2 carbons, and for those having 4 carbons compared to those having 3 carbons. It can be seen that it is expensive.
[0043]
Therefore, from the above [1] to [3], as the combustible gas sensor, a solid electrolyte body having proton conductivity is used as the solid electrolyte body, and an electrode is formed only on one surface side of the solid electrolyte body. It can be seen that extremely excellent performance can be exhibited by maintaining the temperature of the electrolyte body at 250 to 450 ° C.
[0044]
【The invention's effect】
  The present inventionUsed forAccording to the combustible gas sensor, the concentration of various combustible gases excluding hydrogen, carbon monoxide and nitric oxide can be measured. Further, the solid electrolyte body is BaCeO.₃By using a system 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. In particular, it can be suitably used for measuring the concentration of combustible gas having 2 or more carbon atoms. Furthermore, when a measurement gas containing 50 ppm of propene, 21% by volume of oxygen and 2.3% by volume of water vapor, the balance of which consists of argon is supplied at 150 ml per minute, and measured at a temperature of 350 ° C. The potential difference 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 nitrogen monoxide can be measured. In particular, the concentration measurement of combustible gas having 2 or more carbon atoms can be accurately performed with high sensitivity.
[Brief description of the drawings]
FIG. 1 shows the present invention.Used forIt is a typical perspective view of an example of a gas sensor.
FIG. 2 is a schematic perspective view of an example of a comparative gas sensor.
FIG. 3 is a schematic cross-sectional view of a combustible gas concentration measuring device used in Examples.
FIG. 4 is a graph showing the correlation between the temperature of the solid electrolyte body and the electromotive force.
FIG. 5 shows the present invention.Used forIt is a correlation of the temperature of the solid electrolyte body by a combustible gas sensor, and the electromotive force obtained.
FIG. 6Used forIt is a graph which shows the correlation with the density | concentration of various gas by a combustible gas sensor, and the electromotive force obtained.
FIG. 7Used forIt is a graph which shows the correlation with the density | concentration of various gas by a combustible gas sensor, and the electromotive force obtained.
[Explanation of symbols]
  DESCRIPTION OF SYMBOLS 1; Flammable gas sensor (element 1), 11; Solid electrolyte body ([BCY]) which has proton conductivity, 121; Platinum electrode, 122; Gold electrode, 131; Platinum wire, 132; Gold wire, 2; , 21; solid electrolyte body having proton conductivity ([BCY]), 221; platinum electrode, 222; gold electrode, 231; platinum wire, 232; gold wire, 3; combustible gas concentration measuring device, 31; 32; outer tube.

Claims (4)

A flammability comprising a BaCeO ₃ -based proton conductive oxide, which is a solid electrolyte body showing proton conductivity, and electrodes made of a pair of different materials, each formed on the same surface in contact with the measured atmosphere of the solid electrolyte body Using a gas sensor, the electrode is exposed to the atmosphere to be measured, and the combustibility of 2 or more carbon atoms based on the potential difference including at least the mixed potential generated between the electrodes under the condition that the temperature of the solid electrolyte body is 300 to 400 ° C. A method for measuring the concentration of a combustible gas, comprising measuring the concentration of a gas.   The combustible gas concentration measuring method according to claim 1, wherein the shortest distance between the electrodes is 1.5 mm or less.   The method for measuring a combustible gas concentration according to claim 1 or 2, wherein the electrode has a thickness of 2 to 50 µm. When the solid electrolyte is represented by Ba (Ce _y1 Y _y2 ) O _3-δ , 0.7 ≦ y1 ≦ 0.9 , 0.1 ≦ y2 ≦ 0.3, and 0.025 ≦ δ ≦ 0. The combustible gas concentration measuring method according to claim 1 , wherein the combustible gas concentration measuring method is one.

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