JP6494023B2 - Gas sensor and gas sensor manufacturing method - Google Patents

Description

  The present invention relates to a gas sensor that measures a hydrogen partial pressure in a gas phase using a solid electrolyte in order to detect the concentration of a gas containing hydrogen atoms, and a method for manufacturing the gas sensor.

  As a gas sensor for measuring a hydrogen partial pressure in a gas phase under a high temperature environment, a solid electrolyte sensor using a ceramic having proton conductivity as a solid electrolyte is generally used. In recent years, the development of new technologies that use hydrogen as energy, such as fuel cells and hydrogen engines, has been progressing, and the concentration of hydrogen in the gas phase has increased with the increasing use of hydrogen that requires handling, such as the possibility of explosion. It is expected that the importance of the gas sensor for detecting this will increase in the future.

  In addition, it is necessary to detect the hydrocarbon concentration and water vapor concentration in the exhaust gas for feedback control of combustion in the combustion furnace and internal combustion engine, and the concentration of hydrogen and ammonia in the exhaust gas for efficient reduction treatment of NOx. There are many situations where it is necessary to know the concentration of a gas containing hydrogen atoms, such as the need to know, the need to grasp the decomposition of ammonia gas in the nitriding treatment to harden the surface of a metal material. If the hydrogen partial pressure in the gas phase is known, it is possible to detect the concentration of a gas containing hydrogen atoms such as hydrogen, ammonia, hydrocarbons, and water vapor from the temperature and the equilibrium constant.

ここで、Ｅは起電力（Ｖ）、Ｒは気体定数（８．３１Ｊ／ｍｏｌ・Ｋ）、Ｔは温度（Ｋ）、Ｆはファラデー定数（９６４８５Ｃ／ｍｏｌ）、ｔ_Ｈは固体電解質のプロトンの輸率である。従って、第一ガス及び第二ガスのうち一方の水素分圧が既知であれば、起電力Ｅと測定環境の温度Ｔを測定することにより、他方のガスの水素分圧を算出することができる。 A sensor that measures a hydrogen partial pressure in a gas phase using a solid electrolyte uses the principle of a concentration cell in which a potential difference is caused by a difference in concentration of the same ions. In this type of sensor, as shown in FIG. 1A, two types of gases having different hydrogen partial pressures (hydrogen concentrations) are separated from each other by proton-conducting solid electrolyte 100, and are respectively provided at both ends of solid electrolyte 100. Electrodes 103 and 104 are provided. When the two kinds of gases are the first gas and the second gas, and the hydrogen partial pressures are P ₁ and P ₂ , the electromotive force E (potential difference) between the two electrodes 103 and 104 is expressed by the following Nernst equation (formula (1)).

Here, E is an electromotive force (V), R is a gas constant (8.31 J / mol · K), T is a temperature (K), F is a Faraday constant (96485 C / mol), and t _H is a proton of a solid electrolyte. It is a transportation number. Therefore, if the hydrogen partial pressure of one of the first gas and the second gas is known, the hydrogen partial pressure of the other gas can be calculated by measuring the electromotive force E and the temperature T of the measurement environment. .

  In general, a mixed gas of argon and hydrogen is used as a reference gas whose hydrogen partial pressure is known. However, since hydrogen is expensive, the operation cost of measurement using a sensor increases. In addition, since the reference gas is usually supplied from a gas cylinder, the entire sensor device becomes large, inconvenient to carry, and requires a large space for storage. Furthermore, there are countries where it is difficult to obtain cylinders containing hydrogen gas overseas, and since transportation by aircraft is restricted, it is difficult to use sensors that measure hydrogen partial pressure overseas. In addition, since hydrogen burns and explodes in the presence of oxygen, there is also a problem that sufficient care is required for handling.

  On the other hand, the present applicant has proposed a gas sensor that generates a reference gas from a measurement gas and measures a hydrogen partial pressure (see Patent Document 1). The gas sensor includes a hydrogen pump that transports hydrogen from one of the two gas chambers separated by the solid electrolyte to the other when a voltage is applied thereto, and a hydrogen concentration cell that has two gas chambers. The gas chambers are connected so as to share one gas chamber. Then, the hydrogen partial pressure of the shared gas chamber is controlled by the voltage value for driving the hydrogen pump, and the hydrogen partial pressure of the measurement gas is measured using this as a reference gas.

  However, the gas sensor described above requires a power source for driving the hydrogen pump in addition to equipment for measuring a potential difference corresponding to the hydrogen partial pressure of the reference gas and the measurement gas. For high-precision measurement, it is desirable that there is some difference between the hydrogen partial pressure of the reference gas and the hydrogen partial pressure of the measurement gas. However, since the reference gas is generated from the measurement gas, It is difficult to adjust the voltage value to obtain a sufficient hydrogen partial pressure. Therefore, there has been a demand for a gas sensor having a simpler configuration that can measure the hydrogen partial pressure in the gas phase without requiring a reference gas with a known hydrogen partial pressure.

Japanese Patent No. 4111514

  Therefore, in view of the above circumstances, the present invention is a gas sensor for measuring the hydrogen partial pressure in the gas phase, and does not require a reference gas whose hydrogen partial pressure is known, and has a simpler configuration, An object of the present invention is to provide a method for manufacturing the gas sensor.

In order to solve the above problems, a gas sensor according to the present invention is a sensor for measuring a hydrogen partial pressure in a gas phase,
“A sensor element formed of proton conductive ceramics, a reference electrode provided at one end of the sensor element, a measurement electrode provided at the other end of the sensor element, and a gap between the reference electrode and the measurement electrode A gas sensor having an electrometer for measuring a potential difference and measuring a hydrogen partial pressure in a gas phase,
The proton conductive ceramic is
A transition represented by the chemical formula AB _1-b B ′ _b O _3-α , where A is an alkaline earth metal, B is a metal having a valence of +4, and B ′ can have both a valence of +3 and +4. A metal oxide having a perovskite crystal structure, which is a metal,
At the end on the measurement electrode side, a valence of B ′ is biased to +3 valence, a proton conduction layer having a proton transport number of 1, and
At the end on the reference electrode side, the valence of B ′ is biased to +4 valence, and the proton transport number is substantially zero under the hydrogen partial pressure in the atmosphere,
The reference electrode is divided into a space in contact with the measurement electrode and is disposed in a space in contact with the atmosphere.

The “proton conductive ceramic” is a metal oxide having a perovskite type crystal structure represented by the chemical formula A _a B _1-b B ′ _b O _3-α . Here, A is an alkaline earth metal, and strontium (Sr), magnesium (Mg), calcium (Ca), and barium (Ba) can be exemplified. B is a + 4-valent metal, and examples thereof include zirconium (Zr) and cerium (Ce). B ′ is a transition metal that can take both +3 and +4 valences, and is manganese (Mn), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), cobalt (Co), nickel ( Ni) and copper (Cu) can be exemplified. Any of A, B and B ′ may be composed of a single element or a plurality of elements.

  "Transport number" is defined as the ratio of the amount of electricity carried by the ion of interest among the total amount of electricity carried by all ions including cations and anions in the ionic conductor, and is a value between 0 and 1. I take the. Unlike a liquid electrolyte in which both cations and anions move in the electrolyte, the ion transport number of the ion-conductive ceramics in which only specific ions are conducted can be 1.

  As the “reference electrode” and the “measurement electrode”, metals such as platinum (Pt), nickel (Ni), gold (Au), palladium (Pd) can be used.

In the perovskite type metal oxide represented by the chemical formula ABO ₃ , oxygen ion vacancies are formed by substituting a part of the metal atom represented by B with an atom having a lower valence, thereby proton conductivity. Is known to express. For a sensor that measures the hydrogen partial pressure using such a general proton-conducting ceramic, the hydrogen content when the first gas is the measurement gas and the second gas is the reference gas in the description of Equation (1) above. The relationship between the pressure and the potential difference between the reference electrode and the measurement electrode will be described with reference to FIG. FIG. 1B shows the relationship between the transport number of proton-conducting ceramics and the hydrogen partial pressure. The measured electromotive force E is a characteristic line of the transport number t _H and the hydrogen content of the reference gas. This corresponds to the area of the shaded area surrounded by the pressure P ₂ and the hydrogen partial pressure P ₁ of the measurement gas. Note that the reference gas with a known hydrogen concentration is a high concentration that is not affected by fluctuations in the hydrogen partial pressure due to gas leaks, etc., and has a hydrogen concentration lower than the lower limit of the concentration that may cause an explosion. A low 1% hydrogen-99% argon gas mixture is commonly used.

  Here, if the atmosphere can be used as the reference gas of the sensor for measuring the hydrogen partial pressure, it is possible to conceive that the apparatus has a simple configuration without requiring a hydrogen gas cylinder. However, the hydrogen partial pressure in the atmosphere is very low, and the value fluctuates as shown in the figure under the influence of the water vapor partial pressure, so the measured electromotive force also fluctuates, resulting in a considerable error in the measured value. Will be included. Therefore, conventionally, the atmosphere cannot be used as the reference gas.

On the other hand, as shown in FIG. 2A, the proton conductive ceramic 10 of the present invention has a proton conductive layer 11 having a proton transport number t _H of 1 at the end on the measurement electrode 41 side, At the end on the reference electrode 31 side, the non-proton conductive layer 12 having a proton transport number t _H of substantially zero under a hydrogen partial pressure in the atmosphere is provided. Forming such proton conductive layer 11 and non-proton conductive layer 12 in one proton conductive ceramic means that both +4 and +3 valences are used as atoms represented by B ′ of the proton conductive ceramic. This is made possible by using a transition metal that can be taken, and the end of the proton conducting layer 11 after producing a ceramic in which the atoms represented by B ′ are +4 valent (the whole is a non-proton conducting layer 12). It can be formed by reducing only the part to make B ′ +3.

As described above, the proton conductive ceramic of the present invention having a bias in the proton transport number t _H by controlling the valence distribution of B ′ has a hydrogen partial pressure in the atmosphere as shown by a solid line in FIG. At higher hydrogen partial pressure (about 10 ⁻³ Pa), proton transport number t _{H is} almost zero. Therefore, when the atmosphere having a lower hydrogen partial pressure is used as the reference gas, the measured electromotive force E corresponds to the area of the hatched portion in FIG. That is, even if the hydrogen partial pressure in the atmosphere varies, the measured electromotive force E does not depend on the hydrogen partial pressure of the reference gas.

  Therefore, the gas sensor of the present invention can use the atmosphere as a reference gas, and unlike the conventional one, does not require hydrogen having a known concentration supplied in a cylinder, so that the configuration of the apparatus is extremely simple. In addition, unlike the prior art in which the reference gas is generated from the measurement gas, it is not necessary to adjust any value during measurement, and therefore measurement is easy.

  The gas sensor according to the present invention further includes “a cylindrical holder for supporting the sensor element, wherein one of the reference electrode and the measurement electrode is located inside the holder, and The one end of the holder is closed so that is located outside the holder. "

  The material of the “cylindrical holder” is not particularly limited. For example, a dense sintered body of ceramics having high heat resistance such as alumina or mullite can be used. In addition, a holder formed in a cylindrical shape with the same proton conductive ceramic as the sensor element may be integrated with the sensor element. Here, the “tubular shape” may be a cylindrical shape, an elliptical cylindrical shape, or a rectangular cylindrical shape.

  According to the gas sensor of the present configuration, two partitioned spaces are formed inside and outside the cylindrical holder by closing one end of the holder with the sensor element. As a result, when the reference electrode is positioned inside the holder, the measurement electrode located outside the holder is brought into contact with the measurement gas, and the atmosphere is introduced from the other end of the holder which is the open end, thereby measuring gas. The hydrogen partial pressure of can be measured. On the other hand, when the measurement electrode is positioned inside the holder, the measurement gas is introduced by opening the reference electrode located outside the holder to the atmosphere as the reference gas and introducing the measurement gas into the holder. The hydrogen partial pressure of can be measured. Therefore, according to this configuration, the space for the atmosphere and the space for the measurement gas can be easily partitioned by the configuration for supporting the sensor element.

  In addition to the above configuration, the gas sensor according to the present invention further comprises “a cylindrical protective sleeve in which the holder is inserted, and the protective sleeve is external to the male screw portion formed on the outer peripheral surface and the outer peripheral surface. And at least one of a flange portion extending in the direction and a tapered portion in which the thickness of the cylindrical wall continuously decreases toward the inside.

  With such a configuration, the gas sensor can be easily and stably attached to the piping through which the gas to be measured flows and the inner peripheral wall and the bottom wall of the furnace in which the internal gas is the gas to be measured. Of the male screw part, flange part, and taper part, when at least the male screw part is adopted, the “tubular shape” becomes a cylindrical shape. In other cases, the “cylindrical shape” means a cylindrical shape or an elliptical cylinder. Shape and square tube shape.

  The gas sensor according to the present invention may be configured so that “the sensor element is a thin film having a thickness of 1 μm to 100 μm” in the above configuration.

  By setting it as such a structure, a gas sensor can be reduced in size. In addition, since the volume of the sensor element is small, the gas sensor is extremely responsive to temperature changes in the measurement environment.

Next, the manufacturing method of the gas sensor according to the present invention includes:
“A sensor element formed of proton conductive ceramics, a reference electrode provided at one end of the sensor element, a measurement electrode provided at the other end of the sensor element, and a gap between the reference electrode and the measurement electrode A method for producing a gas sensor comprising an electrometer for measuring a potential difference and measuring a hydrogen partial pressure in a gas phase,
The proton conductive ceramics,
A transition represented by the chemical formula AB _1-b B ′ _b O _3-α , where A is an alkaline earth metal, B is a metal having a valence of +4, and B ′ can have both a valence of +3 and +4. By controlling the valence distribution of B ′ in the metal oxide having a perovskite crystal structure, which is a metal, by reduction treatment,
At the end on the measurement electrode side, the valence of B ′ is biased to +3, and a proton conduction layer having a proton transport number of 1 is formed,
At the end on the side of the reference electrode, the valence of B ′ is biased to +4, and an aprotic conduction layer having a proton transport number of substantially zero under a partial pressure of hydrogen in the atmosphere is formed,
The reference electrode is arranged in a space that is partitioned from the space in contact with the measurement electrode and in contact with the atmosphere.

  This is a method of manufacturing the gas sensor having the above-described configuration. By an original method in which a transition metal B ′ capable of taking both valences of +3 and +4 is contained in a metal oxide, and the valence distribution of the transition metal B ′ is controlled by reduction treatment, It is possible to provide a novel and highly practical gas sensor that does not require a reference gas with a known pressure and can use the atmosphere as a reference gas.

  As described above, as an effect of the present invention, a gas sensor for measuring a hydrogen partial pressure in a gas phase, which does not require a reference gas having a known hydrogen partial pressure, and a gas sensor having a simpler configuration, and A method for manufacturing the gas sensor can be provided.

(A) The figure explaining the gas sensor using the conventional proton conductive ceramics, (b) The figure explaining the electromotive force measured by the conventional gas sensor. (A) The figure explaining the gas sensor using the proton conductive ceramic of this invention, (b) The figure explaining the electromotive force measured by the gas sensor of this invention. It is the modification which changed the position of (a) schematic block diagram of the gas sensor which is one Embodiment of this invention, and (b)-(d) the measurement electrode and the reference electrode. It is a figure which shows the change of the electromotive force at the time of changing the hydrogen concentration of measurement gas. It is the figure which contrasted the measured electromotive force with a theoretical curve. (A)-(d) It is a schematic block diagram of the gas sensor of other embodiment from which the relationship between a sensor element shape and a holder differs. (A), (b) It is a schematic block diagram of the gas sensor of embodiment provided with a heater. (A), (b) It is a schematic block diagram of the gas sensor of embodiment provided with a protection sleeve. (A)-(d) It is a schematic block diagram of the gas sensor of embodiment provided with a fixing | fixed part. (A)-(d) It is a schematic block diagram of the gas sensor of embodiment provided with a filter material. It is a side view of the filter material with which the gas sensor of Drawing 9 (c) and (d) is provided in common. It is a schematic block diagram of the gas sensor of embodiment provided with a thin film sensor element.

Hereinafter, a hydrogen sensor 1a according to an embodiment of the present invention will be described with reference to FIGS. The gas sensor 1a of the present embodiment includes a sensor element 20 formed of proton conductive ceramic 10, a reference electrode 31 provided at one end of the sensor element 20, a measurement electrode 41 provided at the other end of the sensor element 20, and A hydrogen sensor including an electrometer 90 that measures a potential difference between a reference electrode 31 and a measurement electrode 41, wherein the proton conductive ceramic 10 is represented by a chemical formula AB _1-b B ′ _b O _{3 -α} , and A Is an alkaline earth metal, B is a metal having a valence of +4, B ′ is a metal oxide having a perovskite-type crystal structure, which is a transition metal capable of taking both +3 and +4 valences. The valence of B ′ is biased to +3 valence at the end on the electrode 41 side and the proton conduction layer 11 has a proton transport number of 1, and the valence of B ′ is on the end on the reference electrode 31 side. +4 values biased to the atmosphere The proton transport number is substantially zero under the partial pressure of hydrogen, and the reference electrode 31 is partitioned from the space in contact with the measurement electrode 41 and is in contact with the atmosphere (hereinafter referred to as the atmosphere). , Referred to as “atmosphere space 30”).

  The gas sensor 1 a further includes a cylindrical holder 50 that supports the sensor element 20. The sensor element 20 has a reference electrode 31 located inside the holder 50 and a measurement electrode 41 located outside the holder 50. One end of the holder 50 is closed. That is, in the gas sensor 1a, the internal space of the holder 50 is the atmospheric space 30.

More particularly, the sensor element 20 of this embodiment is formed of a sintered body of ceramics of formula _{SrZr 0.9 Mn 0.1 O 3-α} . This sintered body was produced by the following procedure. First, strontium carbonate (SrCO ₃ ), zirconium dioxide (ZrO ₂ ), and manganese dioxide (MnO ₂ ), which are raw material powders, were mixed so as to achieve a target molar ratio. Next, the mixed powder was calcined, and the calcined powder was pulverized and then formed into a bottomed cylindrical shape. This molded body was fired in an oxidizing atmosphere at a temperature of 1500 ° C. to 1600 ° C. When the X-ray diffraction pattern of the sintered body was measured, it was a single phase with a perovskite structure. Further, the relative density of the sintered body was 93% when fired at 1500 ° C. and 98% when fired at 1600 ° C., and was dense.

In the present embodiment, A is Sr, B is Zr, and B ′ is Mn in the chemical formula A _a B _1-b B ′ _b O _3-α . Here, in this embodiment, a is 1 and b is 0.1, but a can be 0.8 or more and 1.2 or less, and b is 0.01 or more and 0.3 or less. can do. Note that α is an oxygen defect, and is a value that varies depending on the atomic species of A, B, and B ′, the values of a and b, the environmental temperature, the oxygen partial pressure, and the like.

  In the sintered body obtained by the above manufacturing method, since the valence of Mn is +4, the whole is in the state of a non-proton conductive layer and does not have proton conductivity. A proton conductive layer having a proton transport number of 1 was formed by the following procedure. First, Pt porous electrodes were formed on the inner surface of the bottom of the bottomed cylindrical sintered body and the outer surface of the bottom. In this embodiment, the electrode on the inner surface at the bottom of the sintered body is used as the reference electrode 31, and the electrode on the outer surface at the bottom is used as the measurement electrode 41. As shown in FIG. 3A, the upper end side of the sintered body and the reference electrode 31 are located inside the holder 50 from one end of a ceramic cylindrical holder 50 which is an electrical insulator, The sintered body was inserted so that the bottom side of the bonded body and the measurement electrode 41 were exposed to the outside from the end of the holder 50, and the gap with the end of the holder 50 was sealed with a heat resistant sealing material 59. In this state, heat treatment was performed at a temperature of 400 ° C. to 800 ° C. with the inside of the holder 50 being an oxidizing atmosphere and the outside of the holder 50 being a reducing atmosphere containing hydrogen gas. Thereby, in the vicinity of the outer surface of the bottom of the sintered body exposed to the reducing atmosphere, the valence of Mn is changed from +4 to +3, and the proton transport number is 1 on the measurement electrode 41 side. At the same time, the sensor element 20 having the non-proton conductive layer in which the proton transport number is substantially zero under the hydrogen partial pressure in the atmosphere on the reference electrode 31 side is obtained.

Here, the hydrogen partial pressure in the atmosphere can be calculated from the equilibrium constant of the equilibrium reaction between water, hydrogen and oxygen. The equilibrium constant shows temperature dependence, and the higher the equilibrium is, the more the hydrogen and oxygen are generated from water. Assuming that the atmosphere saturated with water vapor at room temperature is heated up to 400 ° C. to 800 ° C., which is the usable temperature range (details will be described later) of the gas sensor of this embodiment, the hydrogen partial pressure is 1 × 10 ^−18. atm to 5 × 10 ⁻¹¹ atm (1 × 10 ⁻¹³ Pa to 5 × 10 ⁻⁶ Pa). Note that the water vapor partial pressure is a fluctuating value, and FIG. 2 shows a numerical range when the temperature is 800 ° C. as the hydrogen partial pressure in the atmosphere.

  As shown in FIG. 3A, the gas sensor 1 a including the sensor element 20 and the holder 50 includes a gas introduction pipe 35 that introduces the atmosphere, which is a reference gas, to the atmospheric space 30. The gas introduction pipe 35 also serves to protect a thermocouple (not shown), and the thermocouple is inserted into the gas introduction pipe 35. The measurement electrode 41 and the reference electrode 31 are connected to the electrometer 90 by lead wires 91, respectively.

  In the above description, the measurement electrode 41 is formed on the outer surface of the bottom of the bottomed cylindrical sensor element, and the reference electrode 31 is formed on the inner surface of the bottom. However, as another aspect, An embodiment in which the measurement electrode 41 is formed on the outer peripheral surface and the reference electrode 31 is formed on the inner peripheral surface in the vicinity of the bottom (see FIG. 3B), almost the outer surface of the sensor element 20 exposed to the outside from the holder 50 An embodiment in which the measurement electrode 41 is formed on the entire surface and the reference electrode 31 is formed on almost the entire inner surface (see FIG. 3C), the measurement electrode 41 is formed on the outer surface of the bottom, and the reference electrode 31 is formed on the upper end surface. The formed aspect (refer FIG.3 (d)) can be illustrated. Although depending on the size of the sensor element 20, in consideration of the internal resistance between the measurement electrode 41 and the reference electrode 31, the positions of both electrodes are set so that the distance between the measurement electrode 41 and the reference electrode 31 is small. It is desirable.

Next, with respect to the gas sensor 1a of the present embodiment, the result of measuring the electromotive force by changing the hydrogen concentration (hydrogen partial pressure) of the measurement gas using the reference gas as the atmosphere is shown. Hydrogen concentration, by changing the mixing ratio of hydrogen and argon _was controlled in the range of _{0.1vol% H 2 ~98vol% H 2} . Then, the electromotive force of the gas sensor 1a was measured with the electrometer 90 while changing the hydrogen partial pressure at regular intervals. The measurement temperature was 400 ° C to 800 ° C. FIG. 4 illustrates the measurement results when the measurement temperature is 750 ° C. As is clear from the figure, it was confirmed that the electromotive force is zero when the hydrogen concentration is zero (argon 100%), and the electromotive force increases as the hydrogen concentration increases. In addition, the electromotive force response when the hydrogen concentration was changed was very rapid.

  FIG. 5 shows the relationship between the electromotive force measured at the measurement temperatures of 400 ° C., 600 ° C., and 800 ° C. and the hydrogen partial pressure. A one-dot chain line in the figure is a theoretical curve of electromotive force obtained from Equation (1) at each temperature. As is apparent from the figure, the measured electromotive force value is in good agreement with the theoretical value at any measured temperature. From this, it was confirmed that the hydrogen partial pressure in the gas phase can be accurately measured in the temperature range of at least 400 ° C. to 800 ° C. by the gas sensor 1a of the present embodiment.

  The specific forms of the gas sensor, such as the shape of the sensor element and the relationship between the sensor element and the holder, are not limited to those described above, but various forms of gas sensors 1b to 1i as illustrated in FIGS. It can be. 6 to 8, illustration of the reference electrode, the measurement electrode, the gas introduction tube, the electrometer, and the lead wire is omitted.

  In the gas sensor 1b shown in FIG. 6A, the sensor element 20 has a bottomed cylindrical shape as described above, but the bottom side is located inside the holder 50 and the open end side is exposed to the outside from one end of the holder 50. This is an example. With such a configuration, the internal space of the sensor element 20 exposed from the holder 50 functions as a simple measurement gas introduction space 40 into which the measurement gas is introduced. Since the gas in the measurement gas introduction space 40 is replaced by diffusion, there is an advantage that stable measurement is possible even when the gas flow is fast in the measurement environment.

  A gas sensor 1 c shown in FIG. 6B is an example in which the sensor element 20 has a flat plate shape having a size equal to or smaller than the outer diameter of the holder 50 and is fixed to one end of the holder 50 by a sealing material 59. In this case, since the sensor element 20 is small, the responsiveness to a temperature change is high. In addition, the amount of proton conductive ceramic used to form the sensor element 20 can be reduced, and the gas sensor can be reduced in size.

  A gas sensor 1 d shown in FIG. 6C is an example in which the sensor element 20 has a box shape opened on one side, and is fitted around one end of the holder 50 and fixed by a seal material 59. According to such a configuration, the measurement electrode 41 can be formed in a wide area on the proton conduction layer of the sensor element 20, so that there is an advantage that measurement accuracy can be improved.

  A gas sensor 1e shown in FIG. 6 (d) is an example in which a bottomed cylindrical sensor element 20 and a cylindrical holder 5 are formed of the same proton-conducting ceramics and integrated. According to such a configuration, since it is not necessary to seal between the sensor element 20 and the holder 50, there is an advantage that there is no gas leakage due to damage to the sealed portion.

  Furthermore, the gas sensor can be configured to include a heater. The gas sensor 1 f shown in FIG. 7A is an example in which the heater 55 has a long bar shape and is inserted into the bottomed cylindrical sensor element 20. Moreover, the gas sensor 1g shown in FIG. 7B is an example in which the heater 55b is cylindrical and the holder 50 is supported inside the heater 55b. Such heaters 55 and 55b may be metal electric heaters or heaters made of conductive ceramics that generate heat when energized. By providing a heater like the gas sensors 1f and 1g, it is easy to keep the temperature of the sensor element 20 constant. Therefore, there is an advantage that stable measurement is possible even if temperature distribution occurs in the measurement environment. 7B illustrates the case where the heater 55b is provided outside the sensor element 20 and the holder 50 having the shape illustrated in FIG. 3, but the outside of the holder 50 is thus illustrated. When the heater 55b is provided, the shape of the sensor element 20 and the relationship with the holder are not questioned, and any of the gas sensors 1b to 1d illustrated in FIGS. 6A to 6D includes the heater 55b. be able to.

  Further, the gas sensor can be configured to include a cylindrical protective sleeve 60 outside the holder 50. The gas sensors 1h and 1i shown in FIGS. 8A and 8B have a cylindrical protective sleeve 60 having an inner diameter larger than the outer diameter of the holder 50, the holder 50 that supports the sensor element 20, and the tip of the sensor element 20 at the tip. It is inserted so as to be located inside the sleeve. The holder 50 and the protective sleeve 60 are sealed with a sealing material 59, and the space inside and outside the holder 50 is not communicated. By providing such a protective sleeve 60, the gas sensors 1h and 1i can be easily inserted into the measurement location, and the sensor element 20 exposed from the end of the holder 50 is protected from collision with the outside. There are advantages that can be done. The protective sleeve 60 can be formed of metal or ceramic. The gas sensor 1i has a heat insulating material layer 57 disposed between the holder 50 and the protective sleeve 60 in addition to the structure of the gas sensor 1h, and suppresses fluctuations in the temperature of the gas sensor 1i during measurement. can do.

  8A and 8B exemplify the case where the internal configuration of the protective sleeve 60 is the sensor element 20 and the holder 50 having the shape shown in FIG. 3, the present invention is not limited to this. The gas sensors 1b to 1g illustrated in FIGS. 6A to 6D and FIGS. 7A and 7B may include the protective sleeve 60.

  In addition, in the gas sensor including the protective sleeve 60 as described above, the protective sleeve 60 may include a fixing portion for fixing the gas sensor to an attachment target. The fixing portion includes a male screw portion formed on the outer peripheral surface of the protective sleeve 60, a flange portion extending outward from the outer peripheral surface, and a tapered portion in which the thickness of the cylindrical wall continuously decreases inward. At least one of them. The gas sensor of such embodiment is demonstrated using FIG. Here, the reference electrode, measurement electrode, gas introduction tube, electrometer, and lead wire are not shown.

  The gas sensor 1j shown in FIG. 9A is an example in which a male screw portion 61 is formed on the outer peripheral surface of the protective sleeve 60. By setting it as such a structure, the gas sensor 1j can be stably fixed to the location which has the internal thread screwed together with the external thread of the external thread part 61. FIG. For example, by providing a female screw in a pipe through which a gas to be measured flows or a branch pipe branched from the pipe, the hydrogen partial pressure in the flowing gas can be continuously measured in a stable posture. Further, if a hole is provided in the furnace wall and a female screw is formed on the inner peripheral surface of the hole, the gas sensor 1j is provided in the hole of the furnace wall in a state where the measurement electrode 41 protrudes toward the inner space of the furnace. Can be stably supported, and the hydrogen partial pressure in the gas inside the furnace can be measured in a stable posture.

  The gas sensor 1k shown in FIG. 9B is an example in which the protective sleeve 60 includes a flange portion 62 that extends outward from the outer peripheral surface of the protective sleeve 60. By adopting such a configuration, the gas sensor 1k can be stably fixed by fastening the flange portion 62 to the flange portion of the pipe with an overlapping bolt or the like at the end of the pipe or the connection portion of the pipe. . Moreover, the gas sensor 1k can be stably supported by the hole of a furnace wall by sticking the flange part 62 on the periphery of the hole provided in the furnace wall with a pile bolt etc. FIG. Furthermore, since the flange portion 62 is provided, the gas sensor 1k can be fixed to a pipe or a hole that is larger than the outer diameter of the protective sleeve 60 but smaller than the outer diameter of the flange portion. The range of attachment object is wide.

  The gas sensor 1m shown in FIG. 9C is an example in which the protective sleeve 60 includes both the male screw portion 61 and the flange portion 62. In such a configuration, the gas sensor 1m can be more firmly fixed to the attachment object.

  In the gas sensor 1n shown in FIG. 9D, the protective sleeve 60 is continuously provided with an invariable portion 63a having a constant cylindrical wall thickness (an outer diameter is constant) and a cylindrical wall thickness facing inward and inward. It is an example provided with the taper part 63b which decreases automatically. By setting it as such a structure, it corresponds with the diameter of piping or a hole somewhere in the taper part 63b where an outer diameter reduces gradually. For this reason, the piping and the hole to which the gas sensor 1n can be attached have a high degree of freedom in its diameter.

  In addition to the configuration illustrated by way of illustration, the protective sleeve 60 can include both the male screw portion 61 and the tapered portion 63b. In this case, a gas sensor is attached to the object having a female screw that is screwed with the male screw part 61, and a gas sensor is attached to the object that does not have such a female screw by the taper part 63b. be able to. Or both the flange part 62 and the taper part 63b can be set as the structure with which the protective sleeve 60 is provided. In this case, the gas sensor can be attached to the object having a diameter larger than the outer diameter of the invariable portion 63a by the flange portion 62, and the gas sensor can be attached to the object having a diameter smaller than the outer diameter of the invariable portion 63a by the tapered portion 63b. . Therefore, by adopting these configurations, the range to which one gas sensor is attached becomes wider.

  Moreover, it can be set as the gas sensor provided with the filter material which coat | covers the measurement electrode 41 as other embodiment of this invention. The gas sensor of such an embodiment will be described with reference to FIGS. Here, illustration of a gas introduction pipe, an electrometer, and a lead wire is omitted.

  The gas sensor 1p shown in FIG. 10A is an example in which the filter material 71 that covers the measurement electrode 41 is a porous ceramic film. Such a filter material 71 is prepared by coating the sensor element 20 from above the measurement electrode 41 with a fluid composition having a high viscosity in which ceramic powder, a silicate glass component, and a binder component are mixed. It can be formed by heat treatment at a lower temperature than the time of the reduction treatment. The composition is cured and thermally contracted by the heat treatment, and a porous ceramic film having heat resistance is formed. Although the gas to be measured passes through the porous ceramic film, the solid particles contained in the gas are difficult to pass through, so that the filter material 71 can suppress the corrosion and damage of the measurement electrode 41.

  In the gas sensor 1q shown in FIG. 10B, the internal space of the sensor element 20 is the measurement gas introduction space 40 as in the gas sensor 1b described above, and the filter that covers the measurement electrode 41 in the measurement gas introduction space 40 In this example, the material 72 is filled with a fiber material. As the fiber material, ceramic fibers having high heat resistance such as alumina fiber can be suitably used. Although the gas to be measured passes through the gap between the fiber materials, the solid particles contained in the gas are difficult to pass through, so that the filter material 72 can suppress corrosion and damage to the measurement electrode 41.

  A gas sensor 1r and a gas sensor 1s shown in FIG. 10C and FIG. 10D are examples in which the gas sensor 1p and the gas sensor 1q further include a filter material 80 that covers the measurement electrode 41, respectively. As shown in FIG. 11, the filter material 80 is a cap having a double-walled peripheral wall formed of a metal plate, and includes a small hole 81 h that penetrates the outer peripheral wall 81 and a small hole that penetrates the inner peripheral wall 82. A number 82h are provided with different positions. With such a configuration, the measurement electrode 41 is protected by the filter material 80 from relatively large particles such as dust contained in the measurement gas, and the measurement electrode 41 is protected from the fine particles by the filter material 71 or the filter material 72. Can be protected. Therefore, early clogging of the filter materials 71 and 72 can be prevented, and the measurement electrode 41 can be more reliably protected.

  The present invention has been described with reference to the preferred embodiments. However, the present invention is not limited to the above-described embodiments, and various improvements can be made without departing from the scope of the present invention as described below. And design changes are possible.

  For example, in the above-described embodiment, the case where the internal space of the holder 50 is the atmospheric space 30 for introducing the atmospheric air, which is the reference gas, is exemplified, but conversely, the space outside the holder may be the atmospheric space. it can. In this case, in the sensor element, the proton conductive layer and the measurement electrode are positioned inside the holder, and the non-proton conductive layer and the reference electrode are positioned outside the holder. That is, the process of heating the sintered body in a reducing atmosphere in order to change the atom represented by B ′ from the +4 valence to the +3 valence is performed on the portion positioned inside the holder. In the gas sensor having such a configuration, the hydrogen partial pressure of the measurement gas can be measured by opening the reference electrode exposed outside the holder to the atmosphere and introducing the measurement gas into the inner space of the holder. .

  In the above embodiment, the sensor element 20 is a block having a certain thickness (for example, 5 mm or more) such as a bottomed cylindrical shape, a flat plate shape, a box shape, etc. As illustrated in FIG. It can be set as the gas sensor 1t provided with the sensor element 20t of the thin film of thickness 1 micrometer-100 micrometers. In the same manner as described above, a metal oxide thin film that is the basis of such a sensor element 20t is prepared by preparing a sintered body of a metal oxide having a valence of B ′ of +4, and using this as a target. It can be formed by sputtering using the electrode 41 or the reference electrode 31 as a substrate. Then, after appropriate masking, the thin film sensor element 20t can be obtained by subjecting only one surface of the metal oxide thin film to a reduction treatment similar to that described above for a very short time.

  A laminated body (hereinafter referred to as “sensor laminated body”) composed of the thin film sensor element 20t, the reference electrode 31 laminated on one side thereof, and the measurement electrode 41 laminated on the other side is electrically insulating as described above. It can be supported by the cylindrical holder 50. Here, the case where the short-circuit between the reference electrode 31 and the measurement electrode 41 is prevented by covering the side peripheral surface (the peripheral surface in the stacking direction) of the sensor stacked body with the electrical insulating material 45 is illustrated. . In this embodiment, the gas sensor 1t is provided with the conductive cap 43 made of an electrically conductive material and formed in a bottomed cylindrical shape and having a through hole in the bottom. The conductive cap 43 is fitted into the sensor laminate from the outside of the electrical insulating material 45 in a state where the periphery of the through hole is in contact with the measurement electrode 41. With such a configuration, the lead wire 91 can be connected to the measurement electrode 41 via the conductive cap 43, so that the lead wire 91 connected to the measurement electrode 41 and the reference electrode 31 are connected. The lead wire 91 can be extended in the same direction. In addition, the sensor stack can be protected by the conductive cap 43.

  Here, the thicknesses of the measurement electrode 31 and the reference electrode 41 stacked on the thin-film sensor element 20t can be 10 μm to 100 μm. In FIG. 12, the thickness of the thin film sensor element 20t, the measurement electrode 31, and the reference electrode 41 are exaggerated. Instead of the electrical insulation material 45, the holder 50 also serves as the electrical insulation material 45 by covering the side circumferential surface of the sensor laminate with the inner circumferential surface of the end portion of the electrical insulation holder 50. It can also be configured.

1a to 1t Gas sensor 10 Proton conductive ceramic 11 Proton conductive layer 12 Non-proton conductive layer 20, 20t Sensor element 30 Air space (space in contact with air)
31 Reference electrode 41 Measuring electrode 50 Holder 60 Protective sleeve 61 Male thread part 62 Flange part 63 Taper part 90 Electrometer

Claims (5)

A sensor element formed of proton conductive ceramics, a reference electrode provided at one end of the sensor element, a measurement electrode provided at the other end of the sensor element, and a potential difference between the reference electrode and the measurement electrode A gas sensor for measuring a hydrogen partial pressure in a gas phase, comprising an electrometer for measuring
The proton conductive ceramic is
A transition represented by the chemical formula AB _1-b B ′ _b O _3-α , where A is an alkaline earth metal, B is a metal having a valence of +4, and B ′ can have both a valence of +3 and +4. A metal oxide having a perovskite crystal structure, which is a metal,
At the end on the measurement electrode side, a valence of B ′ is biased to +3 valence, a proton conduction layer having a proton transport number of 1, and
At the end on the reference electrode side, the valence of B ′ is biased to +4 valence, and the proton transport number is substantially zero under the hydrogen partial pressure in the atmosphere,
The gas sensor according to claim 1, wherein the reference electrode is partitioned from a space in contact with the measurement electrode and disposed in a space in contact with the atmosphere. A cylindrical holder for supporting the sensor element;
The sensor element has one end of the holder closed so that one of the reference electrode and the measurement electrode is located inside the holder and the other is located outside the holder. The gas sensor according to 1. The holder further comprises a cylindrical protective sleeve inserted therein,
The protective sleeve includes at least one of a male screw portion formed on the outer peripheral surface, a flange portion extending outward from the outer peripheral surface, and a tapered portion in which the thickness of the cylindrical wall continuously decreases inward. The gas sensor according to claim 2, further comprising: The gas sensor according to any one of claims 1 to 3, wherein the sensor element is a thin film having a thickness of 1 µm to 100 µm. A sensor element formed of proton conductive ceramics, a reference electrode provided at one end of the sensor element, a measurement electrode provided at the other end of the sensor element, and a potential difference between the reference electrode and the measurement electrode A method of manufacturing a gas sensor comprising an electrometer for measuring the hydrogen pressure in a gas phase,
The proton conductive ceramics,
A transition represented by the chemical formula AB _1-b B ′ _b O _3-α , where A is an alkaline earth metal, B is a metal having a valence of +4, and B ′ can have both a valence of +3 and +4. By controlling the valence distribution of B ′ in the metal oxide having a perovskite crystal structure, which is a metal, by reduction treatment,
At the end on the measurement electrode side, the valence of B ′ is biased to +3, and a proton conduction layer having a proton transport number of 1 is formed,
At the end on the side of the reference electrode, the valence of B ′ is biased to +4, and an aprotic conduction layer having a proton transport number of substantially zero under a partial pressure of hydrogen in the atmosphere is formed,
A method of manufacturing a gas sensor, characterized in that the reference electrode is disposed in a space that is partitioned from a space in contact with the measurement electrode and in contact with the atmosphere.

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