JP6149008B2 - Hydrogen sensor - Google Patents

Description

  The present invention relates to a hydrogen sensor that measures a hydrogen partial pressure in a molten metal using a solid electrolyte.

  As a hydrogen sensor used in a high temperature environment, a solid electrolyte hydrogen sensor using a ceramic having proton conductivity as a solid electrolyte is generally used. As an example of using the hydrogen sensor in a high temperature environment, there is a case where the partial pressure of hydrogen gas dissolved in a molten metal such as aluminum is measured.

  Metals that are in a molten state in the metal industry processing process such as steelmaking process dissolve hydrogen generated by the decomposition of water vapor and water adsorbed on the refractory in the atmosphere, and hydrogen slightly contained in the atmosphere. ing. The solubility of hydrogen increases as the temperature of the molten metal increases, but on the contrary, it is extremely small for solid metals. For this reason, when the molten metal is cooled in a state where hydrogen is dissolved, bubbles are generated in the solidified metal, which decreases the mechanical strength and damages the appearance. Therefore, degassing treatment such as blowing dry argon gas or nitrogen gas into the molten metal is performed. In order to manage the treatment appropriately, the hydrogen gas dissolved in the molten metal is removed. It is necessary to measure the partial pressure.

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を測定することで、他方のガスの水素分圧を算出することができる。 A hydrogen sensor using a solid electrolyte is a sensor that measures a hydrogen partial pressure using the principle of a concentration cell. A concentration cell is a cell in which a potential difference is caused by a concentration difference of the same ions. In this type of hydrogen sensor, as shown in FIG. 1 (a), two types of gases having different hydrogen partial pressures (hydrogen concentrations) are separated by a proton-conducting solid electrolyte 8, and each gas of the solid electrolyte 8 is separated. The electrodes 3 and 4 are provided at the end portion in contact with the electrode. When the two types of gases are the first gas and the second gas, and the respective hydrogen partial pressures are P ₁ and P ₂ , the electromotive force E (potential difference) between the two electrodes 3 and 4 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 cost for using a hydrogen sensor increases. In addition, since the reference gas is usually supplied from a gas cylinder, the entire hydrogen sensor device becomes large and inconvenient to carry and requires a large space for storage. Furthermore, in some countries, it is difficult to obtain cylinders containing hydrogen gas, and since transportation by aircraft is restricted, it is difficult to use hydrogen sensors 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 hydrogen sensor that generates a reference gas from a measurement gas (see Patent Document 1). This hydrogen sensor includes a hydrogen pump that transports hydrogen from one of two gas chambers separated by a solid electrolyte to the other when a voltage is applied thereto, and a hydrogen concentration cell that has two gas chambers. Are connected to each other 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 hydrogen 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, a hydrogen sensor that does not require a reference gas with a known hydrogen partial pressure and that is easier to measure with a simpler configuration has been desired.

Japanese Patent No. 4111514

  Therefore, in view of the above circumstances, the present invention is a hydrogen sensor for measuring the hydrogen partial pressure in a molten metal, and does not require a reference gas whose hydrogen partial pressure is known, and is measured with a simpler configuration. It is an object of the present invention to provide an easier hydrogen sensor.

In order to solve the above problems, a hydrogen gas sensor according to the present invention is a hydrogen sensor for measuring a partial pressure of hydrogen in a molten metal, and “a sensor element formed of proton conductive ceramics, one end of the sensor element” A hydrogen sensor comprising a reference electrode provided in the reference electrode, an electrometer connected to the reference electrode, and a measurement electrode connected to the electrometer and immersed in molten metal, wherein the proton conductive ceramics are: Perovskite represented by the chemical formula AB1-bB′bO3-α, wherein A is an alkaline earth metal, B is a metal having a valence of +4, and B ′ is a transition metal capable of taking both +3 and +4 valences The transition metal B ′ has a valence of +4 at the end on the reference electrode side of the single proton conductive ceramic represented by the chemical formula. Yo Transport number of protons in the hydrogen partial pressure in the atmosphere converting mechanism has a non-proton-conductive layer is substantially zero, the other end of a single of said proton-conductive ceramic represented by Formula, valence + Introduction of air into which the proton conduction layer having a proton transport number of 1 due to the presence of the trivalent transition metal B ′ is partitioned from the space in contact with the proton conduction layer and the atmosphere is introduced It is “placed in space”.

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), Cr (chromium), 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.

  For the “reference electrode” and the “measurement electrode”, metals such as platinum (Pt), nickel (Ni), gold (Au), palladium (Pd) can be used. The shape of the “measurement electrode” is not particularly limited, but a long bar shape is preferable because it can be easily immersed in a molten metal and can be easily handled.

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. With respect to a hydrogen sensor using such a general proton conductive ceramic, the hydrogen partial pressure when the first gas described using Equation (1) is the measurement gas and the second gas is the reference gas, and the reference electrode The relationship between the potential difference between the 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 the characteristic line of the transport number t _H and the hydrogen partial pressure of the reference gas. This corresponds to the area of the hatched portion surrounded by 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 hydrogen sensor, it can be conceived that a hydrogen gas cylinder need not be provided and the apparatus has a simple configuration. 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. For this reason, conventionally, the atmosphere could not be used as a reference gas.

On the other hand, as shown in FIG. 2A, the proton conductive ceramic 8 ′ of the present invention has a proton conductive layer 8a having a proton transport number t _H of 1 at the end on the measurement electrode 3 side. , the end portion of the reference electrode 4 side, transport number t _H proton in the hydrogen partial pressure in the atmosphere has a non-proton-conductive layer 8b which is substantially zero. Forming such a proton conductive layer 8a and a non-proton conductive layer 8b 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 after forming a ceramic in which the atoms represented by B 'are +4 valent (the whole is a non-proton conductive layer 8b), the end to be the proton conductive layer 8a It can be formed by reducing only the part to make B ′ +3.

Thus, the proton conducting ceramics of the present invention having a bias in the transport number t _H protons, as shown by the solid line in FIG. 2 (b), high hydrogen partial pressure than the hydrogen partial pressure in the atmosphere (about 10 ^{- 3} Pa), the 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, according to the hydrogen sensor of the present invention, the atmosphere can be used as a reference gas, and unlike the conventional case, hydrogen having a known concentration supplied from a cylinder is not required, so 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 hydrogen sensor according to the present invention includes, in addition to the above configuration, “a cylindrical holder that supports the sensor element, wherein the sensor element has the reference electrode positioned inside the holder, and the proton conductive layer One end of the holder is closed so as to be located outside the holder, and the internal space of the holder is the atmosphere introduction space.

  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.

  According to the hydrogen sensor of this configuration, one end of the holder is closed by the sensor element, and the reference electrode is positioned inside the holder, so that the space in which the proton conductive layer is in contact with the inside of the cylindrical holder is partitioned. Is formed. This space is an air introduction space into which air can be introduced from the other end of the holder that is an open end. On the other hand, the end of the sensor element on the proton conductive layer side is immersed in the molten metal, and the potential difference between the proton conductive layer and the reference electrode is measured via the molten metal and the measurement electrode immersed in the molten metal. Is done. Therefore, according to the present configuration, the atmosphere introduction space and the proton conductive layer side immersed in the molten metal can be easily partitioned by the configuration supporting the sensor element.

  As described above, as an effect of the present invention, a hydrogen sensor for measuring the hydrogen partial pressure in a molten metal, which does not require a reference gas with a known hydrogen partial pressure, can be measured with a simpler configuration. An easier hydrogen sensor can be provided.

(A) The figure explaining the hydrogen sensor using the conventional proton-conductive ceramics, (b) The figure explaining the electromotive force measured by the conventional hydrogen sensor. (A) The figure explaining the hydrogen sensor using the proton conductive ceramic of this invention, (b) The figure explaining the electromotive force measured with the hydrogen sensor of this invention. It is a schematic block diagram of the hydrogen sensor which is one Embodiment of this invention. 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. It is a schematic block diagram of the hydrogen sensor of other embodiment from which the shape of a sensor element differs. It is a schematic block diagram of the hydrogen sensor of other embodiment provided with a heater. It is a schematic block diagram of the hydrogen sensor of other embodiment provided with a sleeve.

  Hereinafter, a hydrogen sensor 1a according to an embodiment of the present invention will be described with reference to FIGS.

The hydrogen sensor 1a of this embodiment includes a sensor element 2 formed of proton conductive ceramics 8 ', a reference electrode 4 provided at one end of the sensor element 2, an electrometer 20 connected to the reference electrode 4, and a potential. A hydrogen sensor including a measurement electrode 3 immersed in a molten metal connected to a total 20, wherein the proton conductive ceramic 8 ′ is represented by the chemical formula AB _1-b B ′ _b O _3−α , and A is 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 a valence of +3 and +4, and a reference electrode Proton conduction layer having non-proton conduction layer 8b having a proton transport number of substantially zero under hydrogen partial pressure in the atmosphere at the end portion on the 4 side and having a proton transport number of 1 at the other end portion 8a, reference electrode Are those which are disposed to the air introducing space 30 which atmosphere is introduced with is partitioned between space proton conductive layer 8a is in contact.

  The hydrogen sensor 1 a further includes a cylindrical holder 5 that supports the sensor element 2. The sensor element 2 has a reference electrode 4 located inside the holder 5 and a proton conductive layer 8 a outside the holder 5. One end of the holder 5 is closed so as to be positioned, and the internal space of the holder 5 is an atmosphere introduction space 30.

More particularly, the sensor element 2 of this embodiment is formed of a sintered body of ceramics of formula _{SrZr 0.9 Mn 0.1 O 3-δ} . 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. The mixed powder was then calcined. After the calcined powder was pulverized, it was 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. Α is an oxygen defect, and is a value that changes according to the atomic types of A, B, and B ′, the values of a and b, the temperature of the environment, and the oxygen partial pressure.

  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, a Pt porous electrode was formed as the reference electrode 4 on the upper end surface of the bottomed cylindrical sintered body. Next, as shown in FIG. 3, from one end of the cylindrical holder 5 made of ceramic, the upper end side of the sintered body and the reference electrode 4 are located inside the holder 5, and the bottom side of the sintered body is The sintered body was inserted so as to be exposed to the outside from the end portion of the holder 5, and the gap with the end portion of the holder 5 was sealed with a heat resistant sealing material 45. In this state, heat treatment was performed with the inside of the holder 5 being an oxidizing atmosphere and the outside of the holder 5 being a reducing atmosphere containing hydrogen gas. As a result, in the vicinity of the outer surface of the bottom of the sintered body exposed to the reducing atmosphere, the proton conduction layer having a valence of Mn from +4 to +3 and a proton transport number of 1 on the outer surface of the bottom is formed. And a sensor element 2 having a non-proton conductive layer having a proton transport number substantially zero under the hydrogen partial pressure in the atmosphere on the reference electrode 4 side.

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 to 400 ° C. to 800 ° C., which is the usable temperature range (details will be described later) of the hydrogen 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. 3, the hydrogen sensor 1 a including the sensor element 2 and the holder 5 includes a gas introduction pipe 35 that introduces the atmosphere, which is a reference gas, to the atmosphere introduction space 30. The gas introduction pipe 35 is electrically conductive and serves also to connect the reference electrode 4 provided at the upper end portion of the sensor element 2 and the electrometer 20 via the lead wire 25. The measurement electrode 3 is a long bar that is separate from the sensor element 2 and is made of Pt. Similarly to the reference electrode 4, the measurement electrode 3 is connected to the electrometer 20 by a lead wire 25.

Next, for the hydrogen sensor 1a of the present embodiment, electromotive force measurement was performed in order to confirm the responsiveness to the hydrogen concentration (hydrogen partial pressure) to be measured. This responsiveness test was conducted in the gas phase because the hydrogen concentration was easy to control. Air as a reference gas is introduced into the air introducing space, the hydrogen concentration in the measurement gas is varied 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 hydrogen sensor was measured with the electrometer 20 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 can be accurately measured in the temperature range of at least 400 ° C. to 800 ° C. by the hydrogen sensor of this embodiment.

  The specific form of the hydrogen sensor, such as the shape of the sensor element and the relationship between the sensor element and the holder, is not limited to the above-described one, and various forms of the hydrogen sensor 1b as illustrated in FIGS. ˜1i. 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 hydrogen sensor 1b shown in FIG. 6A, the sensor element 2 has a bottomed cylindrical shape as described above, but the bottom side is located inside the holder 5, and the open end side is exposed from one end of the holder 5 to the outside. It is an exposed example. With such a configuration, when the hydrogen sensor 1b is immersed in the molten metal, the sensor element 2 exposed from the holder 5 and an internal space closed by the molten metal are formed. The hydrogen partial pressure in this internal space is in equilibrium with the hydrogen partial pressure dissolved in the molten metal. For this reason, this internal space functions as a measurement gas introduction space 40 into which a measurement gas in equilibrium with the hydrogen partial pressure dissolved in the molten metal is introduced. As a result, even when the flow of the molten metal is fast in the measurement environment, stable measurement is possible, and the area where the sensor element 2 comes into contact with the molten metal is reduced, resulting in contact with the molten metal. The sensor element 2 can be protected from damage.

  A hydrogen sensor 1 c shown in FIG. 6B is an example in which the sensor element 2 is a flat plate having a size equal to or smaller than the outer diameter of the holder 5 and is fixed to one end of the holder 5 by a sealing material 45. . In this case, since the sensor element 2 is small, the responsiveness to a temperature change is high. In addition, the amount of proton conductive ceramics used to form the sensor element 2 can be reduced, and the hydrogen sensor can be downsized.

  A hydrogen sensor 1 d shown in FIG. 6C is an example in which the sensor element 2 has a box shape opened to one side, and is externally fitted to one end of the holder 5 and fixed by a sealing material 45. According to such a configuration, since the area of the proton conductive layer in contact with the molten metal in the sensor element 2 is increased, there is an advantage that the measurement accuracy can be improved.

  A hydrogen sensor 1e shown in FIG. 6 (d) is an example in which a bottomed cylindrical sensor element 2 and a cylindrical holder 5 are formed of the same proton-conducting ceramics and integrated with each other. . According to such a configuration, since it is not necessary to seal between the sensor element 2 and the holder 5, there is an advantage that there is no gas leakage due to damage of the sealed portion and no intrusion of molten metal.

  Furthermore, the hydrogen sensor can be configured to include a heater. A hydrogen sensor 1 f shown in FIG. 7A is an example in which the heater 50 has a long bar shape and is inserted into the bottomed cylindrical sensor element 2. 7B is an example in which the heater 51 is cylindrical and the holder 5 is supported inside the heater 51. The hydrogen sensor 1g shown in FIG. Such heaters 50 and 51 may be heaters made of conductive ceramics that generate heat when energized. By providing a heater like the hydrogen sensors 1f and 1g, it is easy to keep the temperature of the sensor element 2 constant. Therefore, there is an advantage that stable measurement is possible even if temperature distribution occurs in the measurement environment.

  Further, the hydrogen sensor can be configured to include a sleeve 60 outside the holder. The hydrogen sensors 1h and 1i shown in FIGS. 8A and 8B have a cylindrical sleeve 60 whose inner diameter is larger than the outer diameter of the holder 5, the holder 5 that supports the sensor element 2, and the front end of the sensor element 2 It is inserted so as to be located inside the sleeve. The holder 5 and the sleeve 60 are sealed with a sealing material 45, and the space inside and outside the holder 5 is not communicated. By providing such a sleeve 60, in addition to easy insertion of the hydrogen sensors 1h and 1i at the measurement location, the sensor element 2 exposed from the end of the holder 5 is protected from collision with the outside. There are advantages that can be done. The sleeve 60 can be formed of, for example, a ceramic sintered body. Further, the hydrogen sensor 1h has a configuration having a heat insulating material layer 61 disposed between the holder 5 and the sleeve 60 in addition to the configuration of the hydrogen sensor 1i, and changes in temperature of the hydrogen sensor 1i during measurement. Can be suppressed.

  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, the outer surface of the sensor element on the proton conductive layer side can be coated with a metal film that can permeate hydrogen. In addition, Pt, Ni, Au, Pd etc. can be used as a metal. As a result, the sensor element can be protected from damage due to contact with the molten metal. In addition, because the wettability between the sensor element and the molten metal is improved by the metal film, when the hydrogen sensor is immersed in the molten metal, bubbles are attached to the sensor element, suppressing the measurement from being a factor that disturbs the measurement. can do.

1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1i Hydrogen sensor 2 Sensor element 3 Measuring electrode 4 Reference electrode 5 Holder 8 'Proton conducting ceramic 8a Proton conducting layer 8b Non-proton conducting layer 20 Electrometer 30 Atmosphere Introduction space

Claims (2)

Sensor element formed of proton conductive ceramics, reference electrode provided at one end of the sensor element, electrometer connected to the reference electrode, and measurement immersed in molten metal connected to the electrometer A hydrogen sensor comprising an electrode,
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,
Since the valence of the transition metal B ′ is +4 at the end of the single proton conductive ceramic represented by the chemical formula on the reference electrode side, the proton transport number is substantially reduced under the hydrogen partial pressure in the atmosphere. A non-proton conductive layer that is zero in nature , and the presence of a transition metal B ′ having a valence of +3 at the other end of the single proton-conductive ceramic represented by the chemical formula allows proton transfer. Having a proton conducting layer with a rate of 1;
Hydrogen for measuring the partial pressure of hydrogen in molten metal, characterized in that the reference electrode is separated from a space in contact with the proton conducting layer and is disposed in an air introduction space into which air is introduced. Sensor. A cylindrical holder for supporting the sensor element;
The sensor element has one end of the holder closed so that the reference electrode is located inside the holder and the proton conductive layer is located outside the holder, and the internal space of the holder is introduced into the atmosphere. The hydrogen sensor according to claim 1, wherein the hydrogen sensor is a space.

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