JP2004053507A - Concentration-cell-type hydrogen sensor for hydrocarbonaceous cracked gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a concentration-cell-type hydrogen sensor for a hydrocarbonaceous cracked gas for improving accuracy in the measurement of gaseous hydrogen when measuring hydrogen in a cracked gas forming by cracking a hydrocarbonaceous gas. <P>SOLUTION: The concentration-cell-type hydrogen sensor for the hydrocarbonaceous cracked gas is a concentration-cell-type hydrogen sensor 1 used for measuring the concentration of gaseous hydrogen in the cracked gas of a hydrocarbonaceous gas. The concentration-cell-type hydrogen sensor 1 comprises a solid electrolyte 11 having proton conductivity; a first electrode 12 to be in contact with a reference substance arranged on the side of one surface of the solid electrolyte 11; and a second electrode 13 arranged on the side of the other surface of the solid electrolyte 11 and having carbon, as a base material, to be in contact with the cracked gas of a hydrocarbonaceous gas. For the solid electrolyte 11, it is preferable to use α alumina, as a base material, in which an oxide of an alkali earth material is doped. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a concentration cell type hydrogen sensor for hydrocarbon-based decomposition gas used for measuring hydrogen in a decomposition gas of a hydrocarbon-based gas such as methane gas, and can be used for a concentration-type hydrogen sensor used for carburizing, for example. .
[0002]
[Prior art]
A description will be given of a carburizing process as an example. As a carburizing treatment, a technique using a decomposed gas obtained by decomposing a hydrocarbon-based gas as a carburizing gas is known. According to this, a hydrocarbon-based gas is decomposed to generate a decomposed gas. This cracked gas contains carbon and hydrogen as main components. Then, the carbon contained in the decomposed gas, which is the carburizing gas, is adsorbed on the surface layer of the iron-based treatment material heated to a high temperature and penetrated into the inside of the surface layer to perform carburizing treatment. In the carburizing treatment, there is a vacuum carburizing treatment in which a decomposition gas and a treatment material are brought into contact in a furnace at a pressure lower than the atmospheric pressure.
[0003]
In the above-mentioned carburizing treatment, in recent years, the hydrogen partial pressure (hydrogen concentration) of hydrogen gas in the hydrocarbon-based gas decomposition gas is measured by a concentration cell type hydrogen sensor, and based on the hydrogen partial pressure (hydrogen concentration), Attempts have been made to find potential. The above-described hydrogen sensor is composed of a solid electrolyte having proton conductivity, a first electrode contacted with a reference substance disposed on one side of the solid electrolyte, and a hydrocarbon-based gas disposed on the other side of the solid electrolyte. A second electrode with which the gas contacts. The first electrode and the second electrode are both formed of platinum.
[0004]
[Problems to be solved by the invention]
However, according to the hydrogen sensor described above, there is a limit in improving the measurement accuracy in measuring the hydrogen partial pressure (hydrogen concentration) in a cracked gas formed by cracking a hydrocarbon-based gas. Therefore, there is a limit in grasping the carbon potential of the carburizing gas, and there is a limit in controlling the carbon potential of the carburizing process.
[0005]
The present invention has been made in view of the above circumstances, and in measuring hydrogen in a cracked gas formed by decomposing a hydrocarbon-based gas, a hydrocarbon-based cracked gas capable of improving the measurement accuracy of the hydrogen gas. It is an object of the present invention to provide a concentration cell type hydrogen sensor.
[0006]
[Means for Solving the Problems]
The present inventor has been diligently developing a concentration cell type hydrogen sensor for hydrocarbon-based cracked gas based on the above-mentioned problems. Then, the solid electrolyte having proton conductivity, the first electrode contacted with the reference substance disposed on one side of the solid electrolyte, and the decomposition gas of the hydrocarbon-based gas disposed on the other side of the solid electrolyte come in contact with the first electrode. It has been found that a hydrogen gas sensor having a second electrode made of carbon as a base material can improve the measurement accuracy of hydrogen gas. The reason is presumed as follows. That is, in the above-described hydrogen sensor, there is a limit to the improvement of the measurement accuracy of the hydrogen concentration in the cracked gas formed by decomposing the hydrocarbon-based gas because of the material of the second electrode disposed on the cracked gas side. Is platinum-based, the decomposition gas of the hydrocarbon-based gas is excessively decomposed more than the equilibrium state, and it is presumed that there is a limit to the improvement of the measurement accuracy of the hydrogen gas in the decomposition gas. Therefore, if the base material of the second electrode disposed on the decomposition gas side of the hydrocarbon-based gas is carbon-based, it is possible to prevent the decomposition gas of the hydrocarbon-based gas from excessively decomposing beyond the equilibrium state as described above. The inventors have found that the concentration can be suppressed and the measurement accuracy of hydrogen gas in the cracked gas can be improved, and the concentration cell type hydrogen sensor for hydrocarbon-based cracked gas according to the present invention has been developed.
[0007]
That is, the concentration-cell-type hydrogen sensor for a hydrocarbon-based decomposition gas according to the present invention is a concentration-cell-type hydrogen sensor used for measuring the concentration of hydrogen gas in a decomposition gas of a hydrocarbon-based gas, and includes a proton-conductive hydrogen sensor. A solid electrolyte having a first electrode contacted with a reference substance disposed on one side of the solid electrolyte, and a base material composed of carbon contacted with a decomposition gas of a hydrocarbon-based gas disposed on the other side of the solid electrolyte. And a second electrode to be used.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
SrCeO conventionally used in hydrogen sensors as a solid electrolyte constituting a hydrogen sensor₃Or CaZrO₃A perovskite-type proton-conductive solid electrolyte whose base material is, can be used. In addition, as the solid electrolyte constituting the hydrogen sensor, a form using α-alumina doped with an alkaline earth metal oxide as a base material can be adopted. In such a solid electrolyte based on α-alumina, in a high temperature region, hydrogen forms a weak O—H bond and dissolves in α-alumina, thereby exhibiting proton conductivity. Due to this proton conductivity, a hydrogen sensor having a solid electrolyte based on α-alumina can operate in a high temperature region. Therefore, based on the electromotive force generated in a high temperature region (generally 700 to 1200 ° C.), it is possible to measure the hydrogen partial pressure (hydrogen concentration) of the decomposition gas of the hydrocarbon-based gas that is the measurement target. Therefore, when the solid electrolyte constituting the hydrogen sensor is based on α-alumina doped with an alkaline earth metal oxide, the SrCeO 2 conventionally used in the hydrogen sensor is used.₃Or CaZrO₃It is more suitable for the measurement of the hydrogen concentration in a strong reducing atmosphere than when a perovskite-type proton-conductive solid electrolyte whose base material is is used as a base material.
[0009]
The preferred embodiment will be described. The proton conductive solid electrolyte can be based on alpha alumina doped with alkaline earth metal oxide. That is, the solid electrolyte can include α-alumina and an oxide of an alkaline earth metal (at least one of Be, Mg, Ca, Sr, Ba, and Ra). The content of the alkaline earth metal oxide can be generally from 0.01 to 2.0 mol%, from 0.01 to 1.0 mol%, particularly from 0.02 to 0.9 mol%, It can be 0.03 to 0.8 mol% and 0.03 to 0.6 mol%, but is not limited thereto. Accordingly, the upper limit of the content of the oxide of the alkaline earth metal can be exemplified by 2.0 mol%, 1.5 mol%, 1.0 mol%, 0.5 mol%, etc., and the lower limit corresponding to the upper limit is Examples thereof include 0.02 mol%, 0.03 mol%, 0.04 mol%, and 0.05 mol%. In addition, the dope can adopt a well-known dope form, and can also include natural doping.
[0010]
As an example of a method for producing a solid electrolyte, a solid electrolyte having proton conductivity contains a predetermined amount (generally 0.01 to 2.0 mol%, or 0.01 to 1.0 mol) of an oxide of an alkaline earth metal. %) And press-molding the contained α-alumina to form a green compact, and thereafter sintering the green compact, and thereafter, in a high-temperature region (generally 700 to 1300 ° C, particularly 1200 to 1300 ° C). , Can be formed by heating and heat-treating the α-alumina in a hydrogen atmosphere or a steam atmosphere. It is presumed that the amount of the alkaline earth metal or its oxide dissolved in α-alumina is further stabilized.
[0011]
As another example of the method for producing a solid electrolyte, a powder of at least one element selected from the group consisting of alkaline earth metals (Be, Mg, Ca, Sr, Ba, Ra) is doped, It may be sintered in an oxidizing atmosphere. This is because the alkaline earth metal is oxidized in an oxidizing atmosphere, which is substantially equivalent to the case where the oxide of the alkaline earth metal is doped into α-alumina.
[0012]
The time of the above heat treatment generally depends on the purity of α-alumina. According to experiments by the present inventors, when the purity of α-alumina is 99.6% in molar ratio, the heat treatment time can be 10 to 40 hr, particularly 20 to 35 hr, and particularly 21 hr. When the purity of α-alumina is 99% or less, the heat treatment time can be 100 hours or more. A long heat treatment time is disadvantageous in terms of production cost. The heat treatment described above is effective for improving the accuracy of the hydrogen sensor. However, when high accuracy of the hydrogen sensor is not required much, the above-described heat treatment can be eliminated or shortened. Therefore, the time of the above-mentioned heat treatment can be generally less than 5 hr and less than 1 hr, but is not limited thereto. The experiments by the present inventors have also revealed that the sensitivity as a hydrogen sensor is particularly high when the alkaline earth metal oxide to be doped is magnesium oxide.
[0013]
The first electrode has conductivity and is generally formed of a metal. The first electrode can include at least one of Ni, Pt, Au, Pd, and the like as a main component. The first electrode is preferably porous so as to have gas permeability. In a preferred hydrogen sensor, a film containing at least one of Ni, Pt, Au, Pd and the like as a main component is formed on the surface of the solid electrolyte exhibiting proton conductivity, and this film can be used as the first electrode. The first electrode can also be formed by a usual coating method, PVD method, or CVD method. The first electrode is formed by applying a paste containing at least one of Ni, Pt, Au, and Pd as a main component to the surface of the solid electrolyte and baking the electrode at a high temperature (for example, 800 ° C. or higher) in a reducing atmosphere. It can also be formed by a method of providing (paste coating method). In this case, it is desirable because the electrode becomes a porous film and hydrogen can easily enter the first electrode. In the case of a metal that is hardly oxidized such as Pt or Au, the metal may be baked in the air. In some cases, the first electrode may be carbon-based.
[0014]
The second electrode is a counter electrode of the first electrode, is disposed on the other side of the solid electrolyte, and is made of carbon as a base material with which a decomposition gas of a hydrocarbon-based gas comes into contact, and has conductivity. are doing. The second electrode is preferably porous so as to have gas permeability. The second electrode can be formed using carbon powder or carbon fiber as a base material. Specifically, it may be formed by rubbing a carbon-based lump, or by applying a mixed material containing both or one of a carbon powder and a carbon fiber and an organic or inorganic binder. It may be formed, or may be formed by attaching a sheet made of carbon fiber as a base material. Another substance other than carbon may be blended with the carbon material forming the second electrode. Carbon includes graphite and activated carbon.
[0015]
When measuring the hydrogen concentration of a hydrogen-containing gas with a hydrogen sensor provided with a first electrode and a second electrode of a solid electrolyte, a high-temperature (for example, 700 ° C. or higher) hydrogen-containing gas (hydrocarbon-based gas) is applied to the second electrode. When the gas comes into contact, hydrogen becomes a proton and generates an electron. For this reason, the protons can move through the solid electrolyte and reach the first electrode facing the second electrode. On the other hand, the electrons pass through a lead connecting the first electrode and the second electrode, and reach the first electrode. The protons and electrons that reach the first electrode combine to generate hydrogen. In this series of reactions, electrons move from the second electrode side to the first electrode side, and the energy required for the movement is basically proportional to the hydrogen gas partial pressure. ) To measure the electromotive force, it is possible to detect the hydrogen gas partial pressure in the decomposition gas (hydrogen-containing gas) of the hydrocarbon-based gas to be measured, that is, the hydrogen concentration. Therefore, the hydrogen sensor according to the present invention is preferably provided with an electromotive force measuring means for measuring an electromotive force generated between the first electrode and the second electrode.
[0016]
【Example】
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. This embodiment is a case where the present invention is applied to vacuum carburizing. FIG. 1 shows the overall configuration of a vacuum carburizing system. In FIG. 1, reference numeral 100 denotes a heat treatment furnace for vacuum carburization having a furnace chamber 101; 110, a vacuum pump for sucking the furnace chamber 101 to maintain the degree of vacuum in the furnace chamber 101; 120, a raw material gas as a hydrocarbon-based gas Is introduced into the furnace chamber 101, 130 is a pressure gauge for measuring the pressure in the furnace chamber 10, 140 is a heater for heating the heat treatment furnace 100, 1 is a hydrogen sensor for measuring the hydrogen gas concentration in the furnace chamber 10. . The furnace chamber 101 accommodates a carbon steel-based processing material 150 that can be carburized and quenched.
[0017]
The hydrogen sensor 1 according to the present embodiment is shown in FIG. As shown in FIG. 2, the hydrogen sensor 1 divides a protective tube-shaped proton-conductive solid electrolyte 11 having a closed-end cylindrical cavity 11 x with one end closed, and a cavity 11 x of the solid electrolyte 11. A first electrode 12 formed on the inner surface of the solid electrolyte 11, a second electrode 13 formed on the outer surface of the solid electrolyte 11 so as to face the first electrode 12, and one end connected to the first electrode 12 by the lead wire 15. Is an electromotive force measuring means 16 connected to the second electrode 13 by a lead wire 14, a lid member 19 for stabilizing the hydrogen partial pressure on the first electrode 12 side, and an intake air fixed to the lid member 19. It comprises a pipe 17 and an exhaust pipe 18. The intake pipe 17 and the exhaust pipe 18 are provided in the hydrogen sensor, and can function as a supply unit that supplies a reference substance to the first electrode 12 side of the solid electrolyte 11.
[0018]
The solid electrolyte 11 includes a step of sintering α-alumina (about 0.15 mol% MgO) containing an oxide of an alkaline earth metal to obtain a sintered body, and a step of sintering the sintered body with hydrogen or steam. In the presence (2% H by volume)₂O + 1% H₂(Air atmosphere) at 700 to 1300 ° C. for 0.05 to 5 hours. In some cases, depending on the type of the hydrogen sensor, the heat treatment can be eliminated in consideration of the manufacturing cost. The thickness of the solid electrolyte 11 can be, for example, 0.3 mm to 3 mm, particularly 0.5 mm to 2 mm, but is not limited thereto.
[0019]
The first electrode 12 is formed of platinum in the form of a porous film, has a thickness of about 0.1 to 20 micrometers, and has conductivity and gas permeability. In order to make the first electrode 12 a porous electrode, the first electrode 12 is formed by applying a Pt paste to the inner surface of the solid electrolyte 11 and baking it in an oxidizing atmosphere at 1300 ° C. The second electrode 13, which is a counter electrode, is formed by rubbing a carbon-based plate with a carbon-based lump on the outer surface of the solid electrolyte 11, and has a thickness of about 0.1 to 20 micrometers. And has conductivity and gas permeability. The lead wires 14 and 15 that can function as conductive paths are both Pt wires (platinum). One end 14a of the lead wire 14 is connected to the second electrode 13 with a solder paste. One end 15 a of the lead wire 15 is connected to the first electrode 12. The other ends 14 c and 15 c of the lead wires 14 and 15 are connected to a voltmeter as the electromotive force measuring means 16. The voltmeter measures the electromotive force between the first electrode 12 and the second electrode 13. The intake pipe 17, the exhaust pipe 18, and the lid member 19 are formed of a ceramic material.
[0020]
As shown in FIG. 2, the tip of the solid electrolyte 11 constituting the hydrogen sensor 1 is inserted into a furnace chamber 101 of a heat treatment furnace 100 in which a decomposition gas of a hydrocarbon-based gas as a measurement gas flows. The hydrogen sensor 1 is fixed to the heat treatment furnace 100 by a fixture (not shown). A fixed amount of a reference gas 17a controlled by a mass flow controller (not shown) and a water vapor saturator is supplied into the cavity 11x from the upper end of the intake pipe 17, and is exhausted from the exhaust pipe 18 as exhaust gas 18a. The reference gas 17a can function as a reference material of the concentration cell, and has a constant hydrogen partial pressure.₂And steam (H₂O).
[0021]
During the carburizing process, the vacuum degree (10 to 5000 Pa) of the furnace chamber 101 is maintained high by the vacuum pump 110 of the heat treatment furnace 100, and the temperature of the furnace chamber 101 is set to a high temperature region equal to or higher than the A1 transformation point (for example, about 900). １０００1000 ° C.). A source gas formed of a hydrocarbon-based gas is introduced into the furnace chamber 101 from a gas introduction passage 120. The hydrocarbon-based gas contains methane, propane, butane, and the like in addition to methane as a main component (80% or more by volume ratio). The hydrocarbon-based gas is quickly decomposed in the furnace chamber 101 to become a decomposed gas. The decomposition of methane is shown by the following equation. CH₄→ [C] + 2H₂
Thus, the cracked gas contains carbon and hydrogen as main components. Then, carbon contained in the decomposition gas, which is a carburizing gas, is adsorbed on the surface layer of the processing material 150 (low-carbon steel, 900 to 1000 ° C.) heated to a high temperature and penetrates into the surface layer, thereby Carburizing is performed. The treated material 150 that has been carburized is brought into contact with a quenching medium (generally oil or water, and in some cases, a quenching gas) at a temperature equal to or higher than the A1 transformation point to perform quenching.
[0022]
FIG. 3 shows typical conditions of the vacuum carburizing process. In FIG. 3, a characteristic line A10 indicates the furnace temperature of the furnace chamber 101. A characteristic line A20 indicates the furnace pressure in the furnace chamber 101. As shown by a characteristic line A10, a temperature raising step, a carburizing step, a diffusion step, and a quenching step are sequentially performed. In the temperature raising step, the temperature in the furnace is raised from room temperature to about 930 ° C. As a result, the temperature of the processing material 150 similarly rises. In the carburizing step, carbon contained in the decomposition gas is permeated into the surface layer of the processing material 150 while maintaining the furnace temperature at the carburizing temperature (A1 transformation point or higher, about 930 ° C.). In the diffusion step, the infiltrated carbon is further diffused into the processing material 150 by maintaining the furnace temperature at about 930 ° C. In the quenching step, the carburized treatment material 150 is quenched to 80 ° C. (below the A1 transformation point) by contact with a quenching medium. As shown by the characteristic line A20 in FIG. 3, the degree of vacuum in the furnace chamber 101 is increased (about 10 Pa) with the execution of the temperature raising step. In the carburizing step, introduction of a hydrocarbon-based source gas and evacuation are alternately repeated. When a hydrocarbon-based gas is introduced into the furnace chamber 101, the furnace pressure becomes about 3000 Pa. When the evacuation is performed, the pressure in the furnace becomes about 10 Pa. In the diffusion step, the furnace pressure is gradually increased to about 13 kPa. The temperature raising step, the carburizing step, and the diffusion step are each performed for one hour, but the required time in each step is changed according to the material and size of the processing material 150, and is not limited to the above value. Absent. FIG. 4 shows the hydrogen partial pressure in the furnace chamber 101 of the heat treatment furnace 100 in the carburizing step. M1 indicates the introduction of the source gas. As shown in FIG. 4, the hydrocarbon-based source gas is intermittently introduced into the furnace chamber 101. When the source gas is introduced, hydrogen gas is generated by decomposition as indicated by M2, and the partial pressure of the hydrogen gas increases.
[0023]
As described above, according to this embodiment, the hydrogen sensor 1 can accurately measure the hydrogen partial pressure (hydrogen concentration) in the cracked gas obtained by decomposing the hydrocarbon-based source gas supplied into the furnace chamber 101. it can. The reason is that the second electrode 13 that comes into contact with the decomposed gas obtained by decomposing the hydrocarbon-based source gas is not formed of platinum having a high catalytic activity but is formed of a carbon-based material. This is presumed to be because the activity was not excessive, and the hydrocarbon gas on the second electrode 13 side was not easily decomposed excessively beyond the equilibrium. In particular, according to the present embodiment, since the solid electrolyte 11 of the hydrogen sensor 1 is made of α-alumina doped with an alkaline earth metal oxide, the SrCeO 2 conventionally used in the hydrogen sensor is used.₃Or CaZrO₃It is more suitable for use in the carburizing temperature range (generally 750 to 1100 ° C., especially 850 to 1000 ° C.), as compared with the case where a perovskite-type proton conductive solid electrolyte whose main component is is used.
[0024]
(Test example)
The present inventors formed a platinum-based first electrode 12 and a carbon-based second electrode 13 on a solid electrolyte 11 formed of α-alumina (0.3 mol% MgO) containing magnesium oxide, A hydrogen sensor based on the first embodiment was created. Then, using this hydrogen sensor, the hydrogen partial pressure (hydrogen concentration) in the cracked gas obtained by decomposing the hydrocarbon-based raw material gas was measured. The reference gas supplied to the cavity 11x was an argon gas containing 1.02% by volume of hydrogen gas. Then, a hydrocarbon-based gas was introduced at a rate of 100 cc / min into the furnace chamber 101 (930 ° C.) maintained at about 3000 Pa. No processing material was placed in the furnace chamber 101. The test results are shown in FIG. In FIG. 5, the horizontal axis indicates time, the right vertical axis indicates hydrogen partial pressure [atm], and the left vertical axis indicates furnace pressure [Pa]. The characteristic line B1 indicates the pressure in the furnace, and the characteristic line B2 indicates the hydrogen partial pressure of the cracked gas obtained by decomposing the hydrocarbon-based raw material gas. As shown by the characteristic line B2 in FIG. 5, when nearly 1000 seconds have passed since the start of the measurement, a flat portion was developed on the characteristic line B2, and the hydrogen partial pressure (hydrogen concentration) of the decomposition gas could be measured favorably. .
[0025]
Further, the same test was performed on the hydrogen sensor according to the comparative example. The hydrogen sensor according to the comparative example is similar to the hydrogen sensor according to the above-described test example, except that both the first electrode and the second electrode are formed of platinum. The characteristic line of the hydrogen sensor according to the comparative example showed a local maximum value, which was not sufficient for measuring the hydrogen concentration.
[0026]
Further, the present inventors conducted IR analysis on α-alumina containing magnesium oxide in order to examine proton conductivity of α-alumina containing magnesium oxide. Similarly, α-alumina (0.1 mol% SrO) containing strontium oxide was formed. IR analysis was also performed on α-alumina containing strontium oxide and α-alumina not doped with magnesium oxide. FIG. 6 shows the test results. The vertical axis in FIG. 6 indicates the transmittance (transmittance (%)) of infrared rays. The horizontal axis in FIG. 6 indicates the wave number of infrared rays (Wave @ Number). In FIG. 6, a characteristic line C1 shows a test result of α-alumina not doped with magnesium oxide. A characteristic line C2 shows a test result of α-alumina (0.3 mol% MgO) doped with magnesium oxide. A characteristic line C3 shows a test result of α-alumina (0.1 mol% SrO) doped with strontium oxide. When the wave number (Wave @ Number) is around 3000, the characteristic line C2 drops significantly. This means that proton conductivity is developed. In addition, since the wave number (Wave @ Number) is around 3000 and a decrease in the characteristic line C3 is observed, it means that α-alumina (0.1 mol% SrO) doped with strontium oxide also exhibits proton conductivity. When the doping amount of magnesium oxide and the strontium oxide were changed, proton conductivity was also exhibited. In addition, the present invention is not limited to the embodiment described above and shown in the drawings. The shape of the solid electrolyte having proton conductivity is not limited to a cylindrical shape having a bottom, and may be a plate shape or the like, and may be appropriately changed and implemented without departing from the gist of the present invention. .
[0027]
(Note)
The following technical idea can be understood from the above description.
(Supplementary item 1) The heating process of increasing the furnace temperature, the introduction and evacuation of the hydrocarbon-based source gas are repeated, and the carbon contained in the cracked gas obtained by decomposing the hydrocarbon-based gas is removed from the furnace. A carburizing and quenching method in which a carburizing step of infiltrating the surface layer of the inside of the treatment material, a quenching step of rapidly cooling the carburized treatment material by contacting the treatment material with a quenching medium, and a solid electrolyte having proton conductivity, A first electrode contacted with a reference substance disposed on one side of the solid electrolyte, and a second electrode having carbon as a base material disposed on another side of the solid electrolyte and contacting with a decomposition gas of a hydrocarbon-based gas. Using a concentration cell type hydrogen sensor for hydrocarbon-based cracked gas having a hydrogen sensor and measuring the hydrogen partial pressure of the cracked gas in which the hydrocarbon-based gas in the furnace has been cracked. . In this case, when measuring the hydrogen partial pressure (hydrogen concentration) in the cracked gas formed by decomposing the hydrocarbon-based gas, the measurement accuracy of the hydrogen gas can be improved.
[Additional Item 2] The carburizing and quenching method according to Additional Item 1, wherein the solid electrolyte of the concentration cell type hydrogen sensor is made of α-alumina doped with an alkaline earth metal oxide. Since the solid electrolyte is based on α-alumina doped with an alkaline earth metal oxide, the concentration cell type hydrogen sensor is used in a carburizing temperature range (generally 750 to 1100 ° C., particularly 850 to 1000 ° C.). It is suitable for use and can measure hydrogen partial pressure (hydrogen concentration) well in the carburizing temperature range.
[Appendix 3] A concentration cell type hydrogen sensor used for measuring hydrogen gas in a decomposition gas of a hydrocarbon-based gas used for carburizing treatment, comprising: a solid electrolyte having proton conductivity; and one side of the solid electrolyte. A first electrode contacted with a reference substance disposed on the other side, and a second electrode having carbon as a base material disposed on the other side of the solid electrolyte and contacting a decomposition gas of a hydrocarbon-based gas for carburizing treatment. Concentration cell type hydrogen sensor. Since the second electrode is carbon-based, the concentration and partial pressure of hydrogen gas in the hydrocarbon-based gas decomposition gas used for carburizing can be measured well.
[0028]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a concentration cell type hydrogen sensor capable of improving the measurement accuracy of hydrogen gas when measuring the hydrogen concentration in a decomposition gas formed by decomposing a hydrocarbon gas. Can be. Particularly in the case where the solid electrolyte is based on α-alumina doped with an alkaline earth metal oxide, use in the carburizing temperature range (generally 750 to 1100 ° C., particularly 850 to 1000 ° C.) And a concentration cell type hydrogen sensor suitable for the present invention.
[Brief description of the drawings]
FIG. 1 is a system diagram showing an entire system of a heat treatment furnace used in a vacuum carburizing process.
FIG. 2 is a sectional view schematically showing a hydrogen sensor used in vacuum carburizing.
FIG. 3 is a graph showing a process of a vacuum carburizing process.
FIG. 4 is a graph showing a relationship between a time in a vacuum carburizing process and a hydrogen partial pressure in a furnace.
FIG. 5 is a graph showing the relationship between the time measured using the hydrogen sensor according to the present embodiment and the hydrogen partial pressure.
FIG. 6 is a graph showing an IR analysis result of α-alumina containing magnesium oxide and strontium oxide, and an IR analysis result of undoped α-alumina.
[Explanation of symbols]
In the figure, 100 is a heat treatment furnace, 101 is a furnace chamber, 150 is a processing material, 1 is a hydrogen sensor, 11 is a solid electrolyte, 12 is a first electrode, 13 is a second electrode, and 16 is an electromotive force measuring means.

Claims (6)

What is claimed is: 1. A concentration cell type hydrogen sensor used for measuring hydrogen gas in a decomposition gas of a hydrocarbon-based gas, wherein a solid electrolyte having proton conductivity is brought into contact with a reference substance disposed on one side of the solid electrolyte. A concentration cell type hydrogen sensor for a hydrocarbon-based decomposed gas, comprising: an electrode; and a second electrode disposed on the other side of the solid electrolyte and having a base material of carbon in contact with the decomposed gas of the hydrocarbon-based gas. 2. The concentration cell type hydrogen sensor for hydrocarbon-based cracked gas according to claim 1, wherein the solid electrolyte is based on α-alumina doped with an oxide of an alkaline earth metal. 3. The concentration for a hydrocarbon-based cracked gas according to claim 1, wherein the solid electrolyte is based on α-alumina containing 0.01 to 2.0 mol% of an oxide of an alkaline earth metal. Battery type hydrogen sensor. The method according to any one of claims 1 to 3, wherein the solid electrolyte is a step of sintering α-alumina containing an oxide of an alkaline earth metal to obtain a sintered body; And performing a heat treatment in a temperature range of 700 to 1300 ° C. in the presence of water to form a concentration cell type hydrogen sensor for hydrocarbon-based cracked gas. The concentration cell type hydrogen sensor according to any one of claims 2 to 4, wherein the alkaline earth metal oxide is magnesium oxide. The hydrocarbon decomposition according to any one of claims 1 to 5, further comprising an electromotive force measuring means for measuring an electromotive force generated between the first electrode and the second electrode. Concentration cell type hydrogen sensor for gas.

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