JP7080848B2 - Manufacturing method of contact combustion type hydrogen gas sensor and contact combustion type hydrogen gas sensor - Google Patents

Description

The present invention relates to a contact combustion type hydrogen gas sensor for detecting hydrogen gas and a method for manufacturing a contact combustion type hydrogen gas sensor.

Conventionally, as a gas sensor having a gas sensitive portion of a sintered body, a contact combustion type gas sensor, a semiconductor type gas sensor, a solid electrolyte type gas sensor and the like are known.

For example, a contact combustion type gas sensor is known to have two elements, a detection element that has a combustion reaction to a combustible gas to be detected and a compensation element that does not have a combustion reaction (for example, Patent Document 1). reference).

Next, the general principle of detecting the concentration of combustible gas by the contact combustion type gas sensor will be described. The detection element of the contact combustion type gas sensor includes a gas sensitive part (combustion catalyst part) made of a noble metal wire such as platinum and a metal oxide sintered body such as alumina carrying a noble metal catalyst such as platinum that covers the noble metal wire. Consists of. By heating this detection element to a predetermined temperature and contacting and burning the flammable gas to be detected in the gas sensitive part with the noble metal catalyst, the temperature change that occurs during combustion is regarded as the change in the resistance value of the noble metal wire. To detect. On the other hand, the compensating element does not support the noble metal catalyst like the detection element, but other configurations are the same as those of the detection element. That is, the compensating element is composed of a noble metal wire such as platinum and a metal oxide sintered body such as alumina that covers the noble metal wire and does not support the noble metal catalyst. Since the noble metal catalyst is not supported on the compensating element, combustion of the flammable gas does not occur, and the resistance value of the noble metal wire does not change. Since the combustion heat of the combustible gas is proportional to the concentration of the combustible gas and the resistance value of the noble metal wire is proportional to the combustion heat, the change value of the resistance of the noble metal wire due to the combustion of the combustible gas is measured. The concentration of gas can be measured. Therefore, a voltage difference occurs in the bridge circuit having the detection element and the compensation element on two sides. This voltage difference is detected as an output proportional to the gas concentration up to the lower explosive limit of the flammable gas.

Such a contact combustion type gas sensor is mounted on a fuel cell vehicle (hereinafter referred to as FCV) using compressed hydrogen gas as a fuel, for example, as a hydrogen gas sensor (hydrogen detector) for detecting the leakage of hydrogen gas from the fuel cell system. ing. There are several methods (sensors) for detecting hydrogen gas, but as an in-vehicle hydrogen gas sensor that is required to detect 0 to 4 vol% hydrogen gas in order to meet FCV safety standards, a contact combustion type is used. A gas sensor is suitable.

In addition, depending on the in-vehicle environment, the hydrogen gas sensor may be unintentionally exposed to a high concentration of hydrogen. When the contact combustion type hydrogen gas sensor is placed in an environment with a high hydrogen concentration, the detection element generates heat up to a high temperature of about 800 ° C. due to the heat of combustion of hydrogen. For example, as described in Patent Document 1, in the case of a contact combustion type gas sensor element having a platinum (Pt) wire as a heater coil, when the detection element is exposed to a temperature higher than expected, the grain boundaries of Pt crystal particles inside the Pt wire The stress remaining in the detection element may be relaxed and the resistance value of the detection element may decrease. Such a decrease in resistance value adversely affects the detection accuracy of hydrogen gas. Therefore, it is required to take measures in advance so that the resistance value does not change even if the detection element is exposed to a high concentration of hydrogen and is placed at a high temperature.

Japanese Patent No. 4559894

GuidetotheRealizationoftheITS-90PlatinumResistanceThermometry (https://www.bipm.org/utils/common/pdf/ITS-90/Guide-ITS-90-Platinum-Resistance-Thermometry.pdf)

Therefore, the present invention has been made in view of the above problems, and contact combustion can suppress changes in resistance value due to stress relaxation even when the detection element is exposed to high-concentration hydrogen when the sensor is used and the temperature of the detection element becomes high. It is an object of the present invention to provide a type hydrogen gas sensor.

The problem to be solved by the present invention is as described above, and next, the means for solving this problem will be described.

That is, the contact combustion type hydrogen gas sensor of the present invention is a contact combustion type hydrogen gas sensor that detects hydrogen gas, and includes a detection element having a coiled Pt wire and a carrier portion covering the Pt wire, and the Pt wire. The crystal grain orientation dispersion (GOS: Grain Origination Spread), which is an index representing the crystal orientation difference of Pt, is 1.0 to 2.0.

Further, in the contact combustion type hydrogen gas sensor of the present invention, the Pt wire is an index indicating the plastic strain of Pt, the defect near the crystal grain boundary, and the non-uniform distribution state at each grain boundary, KAM (Kernel Avenue Missionation). Is 0.6 to 0.9.

Further, in the contact combustion type hydrogen gas sensor of the present invention, the ratio of the particle size to the particle size distribution of the Pt crystal grains when observing the Pt line cross section is 0.5 to 5 μm or more, which is 70% or more of the whole. be.

Further, in the contact combustion type hydrogen gas sensor of the present invention, the detection element is heated by passing an electric current through the Pt wire, and the Pt wire is annealed by controlling the heating temperature and the heating time. be.

Further, the contact combustion type hydrogen gas sensor of the present invention is for in-vehicle use.

Further, the method for manufacturing a contact combustion type hydrogen gas sensor of the present invention is a method for manufacturing a contact combustion type hydrogen gas sensor including a detection element having a coiled Pt wire and a carrier portion covering the Pt wire. The Pt wire is annealed by heating by passing an electric current through the Pt wire, and the Pt wire after the annealing treatment has a crystal grain orientation dispersion (GOS) of 1 which is an index indicating the crystal orientation difference of Pt. It is 0.0 to 2.0.

Further, in the method for manufacturing a contact combustion hydrogen gas sensor of the present invention, the Pt wire after the annealing treatment is an index showing the plastic strain of Pt, defects near the grain boundaries, and a non-uniform distribution state at each grain boundary. A certain KAM (Kernel Averaged Distribution) is 0.6 to 0.9.

According to the present invention, it is possible to suppress a change in resistance value due to stress relaxation even when the sensor is exposed to high-concentration hydrogen and becomes hot when used. This makes it possible to realize a contact combustion type hydrogen gas sensor with improved hydrogen gas detection accuracy.

The schematic diagram which shows the contact combustion type hydrogen gas sensor which has the bridge circuit which concerns on one Embodiment of this invention. The schematic diagram which shows the structure of the detection element. The schematic diagram which shows the structure of a compensating element. The graph which shows the relationship between the annealing processing temperature / time and the resistance value change of a detection element. A graph in which the time axis of the graph shown in FIG. 4 is enlarged. The graph which shows the relationship between the annealing treatment temperature and the resistance value change of a detection element after exposure to high-concentration hydrogen. The figure which shows the result (KAM, GOS) which analyzed the Pt line part in the cross section of a detection element by the EBSD method. The graph which shows the relationship between the annealing treatment temperature and KAM. The graph which shows the relationship between the annealing processing temperature and GOS. The figure which shows the result (particle size distribution) which analyzed the Pt line part in the cross section of a detection element by the EBSD method.

Next, the contact combustion type hydrogen gas sensor 100, which is an embodiment of the present invention, will be described with reference to the drawings.

As shown in FIG. 1, the contact combustion type hydrogen gas sensor 100 has a detection element 1 that burns and detects hydrogen gas as a detected gas, and detection based on temperature changes other than hydrogen gas combustion such as changes in the environment. It has a compensating element 2 that corrects a change in the resistance value of the element 1 and fixed resistances R1 and R2, and constitutes a bridge circuit by these. The resistance value of the detection element 1 changes according to the heat of combustion of hydrogen gas. The detection element 1 and the compensation element 2 are connected in parallel to the power supply E via fixed resistances R1 and R2, which are two resistors. The bridge circuit constantly supplies a current of about 90 to 120 mA by the power source E, and holds the detection element 1 at a predetermined temperature at which hydrogen gas is likely to be contact-combusted.

The detection element 1 and the compensation element 2 are set so that the resistance values are equal to each other. Therefore, in the absence of hydrogen gas, the bridge circuit is in an equilibrium state and the sensor output V does not occur. On the other hand, when hydrogen gas is present, the temperature of the detection element 1 rises due to its combustion and the resistance value increases, so that the balance of the bridge circuit is lost and the sensor output V is generated. Since the sensor output V is proportional to the concentration of hydrogen gas, the concentration of hydrogen gas in the air can be measured by the contact combustion type hydrogen gas sensor 100.

As shown in FIG. 2, the detection element 1 is a substantially spherical gas-sensitive portion that covers a coiled noble metal wire Pt (platinum) wire 11 and the Pt wire 11 and burns in contact with hydrogen gas. It has a carrier portion 12. Further, the Pt wire 11 serves as a heating means for heating the carrier portion 12.
The carrier unit 12 is configured by supporting a noble metal catalyst on a catalyst carrier. The noble metal catalyst may be any noble metal having catalytic activity for hydrogen gas, and for example, platinum (Pt), palladium (Pd), platinum and palladium and the like can be used, and the noble metal catalyst is not particularly limited. The catalyst carrier is not particularly limited as long as it supports a noble metal catalyst, and for example, a sintered body of a metal oxide such as alumina or silica alumina can be applied.
The Pt wire in the present embodiment may be a metal material consisting only of Pt (platinum) or a metal material containing Pt (platinum) as a main component, and the metal material containing platinum as a main component is platinum. And other metal material components may form an alloy, or may be crystals that exist independently of each other without forming an alloy.

In such a detection element 1, for example, a metal oxide such as alumina constituting a catalyst carrier, a noble metal catalyst such as platinum, and an organic solvent (binder) such as ethylene glycol are mixed to form a paste. The paste-like material is attached to the coil portion 11a, which is the coil-shaped portion of the Pt wire 11, so as to have a predetermined spherical diameter, and then fired by self-heating of the Pt wire 11 to sinter the carrier portion 12. It can be produced by forming it as a body.

Further, after the carrier portion 12 is formed as a sintered body, the detection element 1 is heated by passing a predetermined current through the Pt wire 11, and the Pt wire 11 is annealed by controlling the heating temperature and the heating time thereof. It is processed. The preferred annealing conditions for the Pt wire 11 and the preferred crystalline state of the Pt wire 11 cross section will be described later. In this way, the detection element 1 of the contact combustion type hydrogen gas sensor 100 is manufactured.

When the detection element 1 is placed in hydrogen gas, it generates heat by energization, so that its own noble metal catalyst is heated and reacts with hydrogen gas, and according to the reaction heat (depending on the concentration of hydrogen gas). The output value changes.

As shown in FIG. 3, the compensating element 2 has the same basic configuration as the detection element 1 shown in FIG. 2, and the different configuration does not include the precious metal catalyst. Specifically, the compensating element 2 is substantially composed of the same coiled Pt wire 11 as the detection element 1 and the same catalyst carrier as the detection element 1 that covers the Pt wire 11 and does not contain a precious metal catalyst. It has a spherical carrier portion 13. Further, the Pt wire 11 serves as a heating means for heating the carrier portion 13.
As the catalyst carrier, for example, a sintered body of a metal oxide such as alumina or silica alumina can be applied.

Similar to the detection element 1, the compensation element 2 is an element for performing temperature compensation of the detection element 1 by being placed in the air where hydrogen gas is present and energized, and is based on the precious metal catalyst of the detection element 1. It is used to extract only the change in output value according to the heat of combustion. The noble metal catalyst is not supported in the carrier portion 13 of the compensating element 2, and unlike the detection element 1, hydrogen gas is not burned by the catalytic reaction of the noble metal catalyst. The compensating element 2 generates heat when energized and heats the carrier portion 13 that covers the periphery thereof, and its resistance value changes due to the heat.

In such a compensating element 2, for example, a metal oxide such as alumina constituting a catalyst carrier and an organic solvent (binder) such as ethylene glycol are mixed to form a paste, and the paste is formed into Pt. Manufactured by attaching to the coil portion 11a, which is a coil-shaped portion of the wire 11, so as to have a predetermined spherical diameter, and then firing by self-heating of the Pt wire 11 to form the carrier portion 13 as a sintered body. can do.
As described above, the contact combustion type hydrogen gas sensor 100 is manufactured.

The other configurations and functions of the contact combustion type hydrogen gas sensor 100 provided with the detection element 1 and the compensation element 2 are the same as those of the conventionally known contact combustion type hydrogen gas sensor.

Next, the mechanism by which stress is generated inside the Pt wire will be described.
Residual stress inside the Pt wire is generated during the manufacturing stage of the Pt wire. When the Pt wire is thinned by the stretching process, the crystals inside the Pt wire are stretched. The crystal orientation of Pt that has undergone this processing step is random, and there are innumerable point defects at the grain boundaries of the crystal. Furthermore, when the Pt wire is processed into a coil shape in order to form the coil portion of the detection element, a dislocation defect is introduced in the Pt wire due to plastic strain inside the Pt wire, and a local change in crystal orientation occurs. Occurs.

These point defects and composition strains at the Pt crystal grain boundaries become factors that hinder electron conduction, and a portion having a locally high resistance value is left. Therefore, the detection element is manufactured with these resistance components generated in each process of manufacturing the sensor remaining. When a sensor with a detection element in such a state is used, when the detection element is exposed to high temperature due to exposure to high concentration hydrogen etc., the crystal grain boundaries are rearranged and the residual stress during processing is relaxed. And the resistance value drops. The decrease in the resistance value of the Pt wire (coil) of the detection element appears as a change in the deviation voltage of the bridge, which affects the gas detection accuracy.

The mechanism by which the resistance value of the Pt wire (coil) of the detection element is lowered is clear. For example, if the detection element is annealed to experience high temperature at the manufacturing stage, point defects and residual stress are alleviated. After that, the resistance value does not decrease and stabilizes.
However, there is a limit to the temperature that can be experienced, and excessive annealing treatment promotes the growth of Pt particles. As the grain growth of Pt particles progresses, a boundary is formed at the grain boundary, which becomes a barrier that hinders electron conduction, and thus the resistance value becomes high, which is not preferable. Further, since the Pt wire in which the grain growth has progressed, the crystal grain boundary becomes a slip surface and is easily deformed, so that the risk of disconnection due to stress such as vibration or impact increases. That is, the conditions for annealing the Pt wire for the purpose of stabilizing the hydrogen gas sensor include an appropriate heating temperature and heating time in order to keep the Pt particles in an appropriate crystalline state in which the residual stress is relaxed.

Therefore, the present invention has been made in consideration of the above mechanism, and by eliminating point defects and composition strains at the Pt crystal grain boundaries without giving excessive stress to the Pt wire coil, the invention is high in the stage of use. It realizes a highly durable contact combustion type hydrogen gas sensor whose resistance value does not change even when the detection element experiences a high temperature when exposed to a concentration of hydrogen.

Generally, when metal is processed (plastic deformation), various lattice defects are accumulated and alleviated by annealing. In the annealing process, the structure of the metal material changes depending on the treatment temperature, and the process can be classified into recovery, recrystallization, and grain growth, and the state of the crystal structure is different at each stage.

[Changes in operating resistance value difference with respect to annealing treatment time and annealing treatment temperature of detection element]
4 and 5 are the results of evaluating the change in the operating resistance value before and after the annealing treatment by changing the annealing treatment time and the annealing treatment temperature for the detection element. In the graphs of FIGS. 4 and 5, the vertical axis represents the operating resistance value (Ω) before and after the annealing treatment in the detection element, and the horizontal axis represents the annealing treatment time (sec.). Further, the graph of FIG. 5 is a change in the initial stage of the annealing process, and is shown by enlarging the graph of FIG.

When an electric current is passed through the Pt wire of the detection element to perform annealing treatment by self-heating (Joule heat), the operating resistance value of the detection element is once lowered as compared with that before the treatment, and then the resistance is increased. The Pt wire before the annealing treatment has a high resistance value due to the point defects and plastic strains existing at the grain boundaries of the Pt crystal grains hindering electron conduction, and the resistance value is eliminated by the annealing treatment. Decreases. This process corresponds to recovery and recrystallization. The annealing treatment time at which the operating resistance value is minimized depends on the annealing treatment temperature. The operating resistance value depends on the annealing treatment temperature, and the annealing time is 3 sec. At 1000 ° C. or 1050 ° C. The operating resistance value becomes the minimum value under the condition of. From the results shown in FIG. 5, it is not sufficient to increase the annealing treatment time at 700 ° C. to alleviate the point defects and strain remaining inside the Pt wire, and at 1000 ° C., 3 sec. It is shown that these are resolved by the degree.

Further, the fact that the minimum value of the operating resistance value differs depending on the annealing treatment temperature means that the thermal energy required to eliminate this differs depending on the state of plastic strain and point defects. For example, if the defect is almost completely eliminated by the annealing treatment at 1000 ° C., it can be seen from the result of FIG. 5 that only about 50% of the whole is eliminated by the annealing treatment at 850 ° C. This is explained in Non-Patent Document 1 by using the following equation (1) regarding the relationship between the recrystallization temperature due to annealing and time.

Equation (1) indicates that when there are many defects in Pt (Ea is low) and the annealing temperature (T) is high, the time for exponentially eliminating the defects is shortened. In addition, since the defects that are eliminated with low energy disappear in a short time, it is shown that Ea increases as the annealing progresses. Therefore, in order to eliminate half of the defects, annealing at a higher temperature is required. However, on the other hand, in the annealing treatment at a higher temperature, the reaction of grain growth tends to proceed in the portion where the defect is eliminated. The change in resistance value when the annealing treatment is continued will be described below.

When the annealing treatment is continued, the resistance value increases in proportion to the annealing treatment time except for the annealing treatment temperature of 700 ° C. as shown in FIG. This corresponds to the grain growth process described in the mechanism. That is, the annealing process started and 10 sec. Up to this point, the process of recrystallization in which the resistance value is minimized by the annealing treatment is performed, and the annealing treatment time is 5 sec. Subsequent increase in resistance is considered to be a process in which grain growth progresses by shifting from the process of recrystallization to the process of grain growth.
In the present embodiment, in the annealing treatment for the Pt wire, a current is passed through the Pt wire to directly perform the annealing by self-heating, but the Pt wire is heated from the outside using an electric furnace or the like to perform the annealing treatment. May be good. When the annealing process is performed directly by self-heating by passing a current through the Pt wire as in the present embodiment, the annealing process can be easily introduced into the manufacturing process without the need for equipment such as an electric furnace.

Based on the evaluation results shown in the graphs of FIGS. 4 and 5, when manufacturing the contact combustion type hydrogen gas sensor, the annealing treatment time is 20 seconds or more in order to alleviate the stress remaining inside the Pt wire. It is preferably within the range of seconds or less, and more preferably within the range of 3 seconds or more and 10 seconds or less. This is because if the annealing treatment time is less than 1 second, recrystallization has not progressed, and if the annealing treatment time exceeds 20 seconds, the grain growth has progressed too much and the resistance is increased, and the crystal interface is displaced. This is because slippage is likely to occur and the strength of the Pt wire may decrease.
In the evaluation results shown in the graphs of FIGS. 4 and 5, when the annealing treatment temperature is in the range of 850 ° C. to 1050 ° C., the annealing treatment time of about 5 seconds is considered to be the optimum time for obtaining a preferable crystal structure. However, when considering the manufacturing margin (variation in annealing treatment, etc.), the annealing treatment time is preferably about 5 seconds or more and 10 seconds or less. The annealing treatment temperature for relaxing the stress remaining inside the Pt wire is preferably 850 ° C. or higher and 1050 ° C. or lower. When the annealing treatment temperature is 700 ° C., the energy required to proceed with recrystallization cannot be obtained, and the residual stress or the like cannot be sufficiently relieved.
Summarizing the above, as described above, the preferred annealing conditions for the Pt wire are an annealing temperature of 850 ° C to 1050 ° C, and an annealing time in the range of 1 second or more and 20 seconds or less.

[Relationship between annealing treatment time and fluctuation value of sensor output after exposure to high-concentration hydrogen]
FIG. 6 is a graph showing the relationship between the annealing treatment temperature and the operating resistance value of the detection element before and after exposure to high-concentration hydrogen. As a high-concentration hydrogen exposure condition, the operation of spraying pure hydrogen gas on the detection element for 5 seconds was repeated three times.

High-concentration hydrogen was exposed to each detection element annealed for 10 seconds at each annealing treatment temperature under the above conditions, and the amount of change in the sensor output (zero point) in the air before and after that was compared. 10 sec. The resistance value of the detection element decreases after exposure to high-concentration hydrogen, but if the annealing treatment temperature is 800 ° C or higher (annealing time is 10 sec.), There is almost no change even after exposure to high-concentration hydrogen (the detection element has a high temperature). It was confirmed that the resistance value of the detection element does not change even when exposed to. Therefore, if the detection element is exposed to a high temperature of 800 ° C. or higher in advance, the resistance value of the detection element does not change even when exposed to high-concentration hydrogen during use, and the hydrogen detection accuracy is not affected. I was able to confirm that.

The problem to be solved by the present invention is to prevent the element resistance value from decreasing (detection accuracy decreases) due to external environmental factors such as high-concentration hydrogen exposure while using the contact combustion type hydrogen gas sensor. The purpose is to stabilize the resistance value of the detection element (Pt wire) in advance. In order to solve this, it is sufficient to stabilize (recrystallize) the crystal state in the Pt wire, and as shown in FIG. 5, it can be seen that annealing is performed for about 4 seconds at, for example, an annealing treatment temperature of 1000 ° C. .. If the annealing treatment is performed at a high temperature for a long time, the grain growth of the Pt wire is promoted, a slip surface is generated at the crystal interface, and the risk of disconnection increases. Therefore, the treatment time and the treatment temperature are appropriately controlled. There is a need.

[Analysis of Pt line cross section by EBSD method]
FIG. 7 shows the results (KAM, GOS) of analyzing the Pt line portion of the cross section of the detection element of each annealing treatment temperature by the EBSD method.
Here, the analysis by the EBSD method is an electron backscatter diffraction method (EBSD: Electron Backscattered) using a scanning electron microscope (SEM) for analysis of the crystal orientation and crystal structure of a local region in a crystalline material such as a metal. It is performed by using the Diffraction) method. As an analysis method, a detection element that has been annealed at each annealing treatment temperature (annealing time is 10 sec.) Is manufactured by the above-mentioned manufacturing method of the detection element 1, and a coil that is a coil portion covered with a carrier portion thereof is manufactured. The portion was cut along the axial direction of the coil portion, and one of the cut surfaces was analyzed by the EBSD method. The measurement conditions were an acceleration voltage of 15 kV, a measurement interval of 1 μm, and a measurement region (Pt wire diameter): 20 μm.

Further, according to the EBSD method, each value of the local orientation difference average (KAM: Kernel Orientation Measurement) and the crystal grain orientation dispersion (GOS: Grain Orientation Spread) can be measured. KAM is an average value of the orientation difference between the pixel of interest and the adjacent pixel from the image information obtained by EBSD, and is used as an index showing the plastic strain gradient in a minute region. GOS is an index showing the crystal orientation difference, and shows the average value of the orientation difference in the entire area in the crystal particles. GOS can also be an index showing the magnitude of strain obtained by measuring the crystal orientation of the Pt line cross section using the EBSD method.

Next, the measurement results of KAM and GOS obtained by EBSD analysis will be described.

[Local orientation difference average (KAM) and grain orientation dispersion (GOS)]
FIG. 7 shows the analysis results of KAM and GOS based on the results measured based on the Pt line cross section at each annealing treatment temperature (annealing treatment time is 10 sec.). The analysis results at each annealing treatment temperature of KAM and GOS are also shown in FIG. 6, and Table 1 below summarizes the KAM and GOS numerical values in FIG.

FIG. 8 is a graph of the measurement results of KAM shown in Table 1 above. Since KAM is a numerical value of the plastic strain gradient in a minute region, it is shown that the smaller the KAM, the more the plastic strain between adjacent crystals is eliminated, and the temperature is 1100 ° C. (treatment time: 10 sec.). It can be seen that KAM is an index for determining the degree of progress of grain growth because it is extremely lowered in the annealing treatment of. Further, since there is no big difference in KAM in the annealing at 700 to 1000 ° C., it can be seen that the plastic strain in which the crystal orientation is significantly different is eliminated even in the annealing at 700 ° C. (treatment time: 10 sec.). Therefore, when KAM is used as an index for determining that there is no (eliminate) extreme plastic strain inside the Pt line, the value is preferably in the range of 0.6 to 0.9.

On the other hand, FIG. 9 is a graph of the measurement results of GOS. Since GOS is the average value of the orientation difference in the entire area of the crystal particles, it can be said that the degree of progress of recrystallization and grain growth of the entire observed Pt line cross section is quantified. That is, it can be determined that the larger the GOS, the more recrystallization and grain growth are progressing. Considering the results shown in FIGS. 4 and 5 and Table 1, the annealing treatment temperature shown in FIG. 9 is 1100 ° C. (annealing treatment time 10 sec.), Although not disclosed in FIGS. 4 and 5. As described above, when the GOS exceeds 2, it is considered that the grain growth has progressed too much. In that case, a boundary is formed at the grain boundary to increase the resistance, and the crystal interface is liable to shift or slip. It is not preferable because the strength of the Pt wire may decrease. Further, the GOS at 1050 ° C. (annealing time 10 sec.) Disclosed in FIGS. 4 and 5 can be extrapolated from the graph shown in FIG. 9 when it is in the vicinity of 2.0. That is, the upper limit of GOS is preferably 2.0 or less, which corresponds to 1050 ° C. (annealing time 10 sec.) In which the residual stress is relaxed and becomes a crystalline state. Looking at the measured values of GOS, it is considered that there is almost no change at 700 ° C., 800 ° C., and 900 ° C., and the crystal state is the same. Further, although not disclosed in FIG. 9, when the annealing treatment temperature is 600 ° C. (annealing treatment time 10 sec.), Recrystallization and grain growth are not considered to proceed in view of the theoretically assumed active energy. , GOS is estimated to be less than 1.0. As a result, the lower limit of GOS is preferably 1.0 or more, which is a crystalline state in which the residual stress is relaxed.
Based on the above results, it is preferable that the Pt line has a grain orientation dispersion (GOS) of 1.0 to 2.0, which is an index indicating the crystal orientation difference of Pt.
In the analysis by the EBSD method, the annealing treatment time was set to 10 sec. However, since the progress of recrystallization and grain growth is related to the magnitude of the applied activation energy, the activation energy can be controlled by the height of the annealing treatment temperature and the length of the annealing treatment time. Specifically, as shown in FIG. 4, it can be said that the annealing treatment temperature contributes more to the progress of recrystallization and grain growth than the annealing treatment time. Further, although the crystal state cannot be directly expressed by the annealing temperature and the annealing time, the crystal state can be quantified by using the indexes of KAM and GOS, which is advantageous in that the crystal state can be quantitatively determined. Has an effect.

[Particle size distribution of Pt crystal grains]
FIG. 10 shows the measurement results of the particle size distribution of Pt crystal grains when observing the Pt line cross section at each annealing treatment temperature (annealing treatment time is 10 sec.) Using the EBSD method. The image column on the left side in FIG. 8 shows the particle size distribution of the Pt line cross section at each annealing treatment temperature in different colors for each crystal orientation (orientation). The bar graph on the right side corresponding to each particle size distribution shows the particle size distribution corresponding to the color coding of the particle size distribution. The vertical axis of the bar graph of the particle size distribution is the area ratio (Area Fraction) of the Pt particles in the Pt line cross-sectional area, and the horizontal axis is the particle size (Grain Size [μm]). Comparing the particle size distributions of the Pt line cross sections at each annealing treatment temperature, when the annealing treatment temperature is 700 ° C to 1000 ° C, the particle size is the sum of the particle size of 0.5 μm, which is the minimum particle size of Pt particles, and the particle size of 5.0 μm. The distribution accounts for more than 70% of the total. On the other hand, when the annealing treatment temperature is 1100 ° C., the area ratio of the particles having a particle size of 0.5 μm to 5.0 μm, which is the minimum particle size of the Pt particles, is very small, but the area ratio of the particles in the vicinity of the particle size of 18 μm is very small. Is over 80%. In this case, it is considered that the grain growth has progressed considerably. If the grain growth is advanced, a boundary is formed at the grain boundary to increase the resistance, and the crystal interface is liable to shift or slip, so that the strength of the Pt wire may decrease, which is preferable when constructing a sensor. do not have. Therefore, it is preferable that the ratio of the particle size to the particle size distribution of the Pt crystal grains when observing the Pt line cross section is 0.5 to 5 μm is 70% or more of the whole.

As described above, in the contact combustion type hydrogen gas sensor 100 of the present embodiment, the internal crystal orientation of the Pt wire 11 is determined by subjecting the detection element 1 having the Pt wire as a coil to an annealing process at the sensor manufacturing stage. Since it can be rearranged and the machining stress can be eliminated, it is possible to suppress the change in the resistance value of the detection element 1 during use (for example, at a high temperature when exposed to high-concentration hydrogen gas). Further, the Pt wire 11 thus annealed is a local azimuth difference average (KAM: Kernel) which is an index showing the magnitude of plastic strain, defects in the vicinity of crystal grain boundaries, and non-uniform distribution state at each grain boundary. The Averaged Missionation) is in the range of 0.6 to 0.9, or the grain orientation dispersion (GOS), which is an index indicating the crystal orientation difference, is in the range of 1.0 to 2.0. The inventor of the present application has found that there is. By applying an index such as KAM and GOS to the annealing process of the detection element 1 in the above-mentioned manufacturing method of the contact combustion type hydrogen gas sensor 100, it is possible to provide the contact combustion type hydrogen gas sensor 100 which exhibits the effect of the present invention. can.

As described above, according to the contact combustion type hydrogen gas sensor 100 according to the present embodiment, it is possible to suppress the change in the resistance value due to stress relaxation even when the sensor is exposed to high-concentration hydrogen and becomes high in temperature. This makes it possible to realize a contact combustion type hydrogen gas sensor 100 with improved hydrogen gas detection accuracy.

Further, the contact combustion type hydrogen gas sensor 100 according to the present embodiment can be mounted on, for example, a vehicle (passenger vehicle, truck, work vehicle, etc.) equipped with a fuel cell such as FCV, a ship, an aircraft, a train, a mobile robot, or the like. Therefore, hydrogen gas leaking from the fuel cell can be detected.

INDUSTRIAL APPLICABILITY The present invention can be used for a contact combustion type hydrogen gas sensor provided with a detection element whose resistance value changes according to the combustion heat of hydrogen gas.

1 Detection element 2 Compensation element 11 Pt wire 11a Coil part 12 Carrier part 100 Contact combustion type hydrogen gas sensor

Claims (7)

It is a contact combustion type hydrogen gas sensor that detects hydrogen gas.
A detection element having a coiled Pt wire and a carrier portion covering the Pt wire is provided.
The Pt line is a contact combustion type hydrogen gas sensor having a crystal grain orientation dispersion (GOS: Grain Orientation Spread) of 1.0 to 2.0, which is an index showing the orientation difference and the amount of deformation of the entire crystal grain of Pt. A claim that the Pt line has a KAM (Kernel Averaged Missionation) of 0.6 to 0.9, which is an index showing the plastic strain of Pt, defects near the grain boundaries, and a non-uniform distribution state at each grain boundary. The contact combustion type hydrogen gas sensor according to 1. The contact combustion hydrogen according to claim 1 or 2, wherein the ratio of the particle size of the Pt crystal grains to the particle size distribution when observing the Pt line cross section is 70% or more of the whole. Gas sensor. The contact according to any one of claims 1 to 3, wherein the detection element is heated by passing an electric current through the Pt wire, and the Pt wire is annealed by controlling the heating temperature and the heating time. Combustion type hydrogen gas sensor. The contact combustion type hydrogen gas sensor according to any one of claims 1 to 4.
The contact combustion type hydrogen gas sensor is a contact combustion type hydrogen gas sensor for vehicles. A method for manufacturing a contact combustion type hydrogen gas sensor including a detection element having a coiled Pt wire and a carrier portion covering the Pt wire.
The Pt wire is heated by passing an electric current through the Pt wire to anneal the Pt wire.
The Pt wire after the annealing treatment is a method for manufacturing a contact combustion type hydrogen gas sensor in which the grain orientation dispersion (GOS: Grain Orientation Spread), which is an index indicating the crystal orientation difference of Pt, is 1.0 to 2.0. The Pt wire after the annealing treatment has a KAM (Kernel Used Missionation) of 0.6 to 0.9, which is an index showing the plastic strain of Pt, defects near the grain boundaries, and a non-uniform distribution state at each grain boundary. The method for manufacturing a contact combustion type hydrogen gas sensor according to claim 6.

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