Hydrogen detection system and hydrogen detection method

Abstract

This invention provides a hydrogen detection system and a hydrogen detection method for detecting hydrogen in metallic materials. [Solution] A film-like sensor 2 for detecting hydrogen in a metal material by being laminated on the surface of a metal material 1 in a gas or vacuum, is composed of an organic polymer whose optical properties change depending on the hydrogen concentration, and optionally contains a dye whose optical properties change depending on the hydrogen concentration. This film-like sensor can easily detect the concentration and distribution of hydrogen present in the metal material, and can also observe changes over time.

Description

Technical Field

[0001] The present invention relates to a hydrogen detection system and a hydrogen detection method for detecting hydrogen in a metal material.

Background Art

[0002] Various metal materials such as high-strength steel, Al, Ti, and Zr alloys are at risk of hydrogen intrusion and hydrogen embrittlement due to their use environments such as atmospheric corrosion, high-temperature water, sour gas, and high-pressure hydrogen gas. Particularly in steel materials, it is known that the hydrogen embrittlement susceptibility increases as the strength increases. Hydrogen that has penetrated into the material localizes at stress concentration sites and causes fracture phenomena.

[0003] Therefore, in order to elucidate the hydrogen embrittlement mechanism and prevent embrittlement, it is essential to know the concentration of hydrogen present in the material and the location of hydrogen. In addition, there are two types of hydrogen intrusion processes: intrusion from the gas phase typified by a high-pressure hydrogen gas environment and intrusion from the liquid phase associated with the hydrogen generation reaction that occurs during the atmospheric corrosion process. The intrusion rate of hydrogen from the liquid phase varies greatly depending on the atmospheric environment. Therefore, in order to suppress hydrogen-induced fracture, a hydrogen detector that can continuously measure the local accumulation of hydrogen in the material and capture it as a still image or video is required. Also, at the site where metal materials are used, there is a need for a means to easily grasp the embrittlement situation.

[0004] As a method for visualizing the location of hydrogen in a material, a silver decoration method (see, for example, Non-Patent Document 1) and a hydrogen microprint method (see, for example, Patent Document 1) are known. The silver decoration method involves immersing a material containing hydrogen in an aqueous solution of potassium silver(I) cyanide to reduce and deposit silver particles at the locations where hydrogen atoms exposed on the material surface are ionized and released. Furthermore, the hydrogen microprinting method involves applying an emulsion mainly composed of silver(I) bromide and gelatin to the surface of a hydrogen-containing material. By reducing silver ions, the adsorbed hydrogen on the material surface is ionized, and the location of the adsorbed hydrogen is visualized from the distribution of the reduced and deposited silver particles.

[0005] Furthermore, Patent Document 2 discloses a method of providing a metal oxide layer on the surface of a metal material via a hydrogen buffer film, and measuring the time-dependent changes in the concentration and location of hydrogen present in the material or hydrogen that has entered from the outside, from the visible ultraviolet reflectance spectrum of the metal oxide layer, which changes according to the hydrogen concentration of the metal material. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2006-258595 [Patent Document 2] Japanese Patent Publication No. 2018-13424 [Non-patent literature]

[0007] [Non-Patent Document 1] T. Schober and C. Dieker, “Observation of Local Hydrogen on Nickel Surfaces”, Metall. Trans. A,, 1983, 14A, p. 2440 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Both the silver decoration method described in Non-Patent Document 1 and the hydrogen microprinting method described in Patent Document 1 visualize the location of hydrogen from the distribution of deposited silver particles, and therefore cannot measure the change in hydrogen concentration over time. Furthermore, the silver decoration method also has the problem of requiring the use of dangerous cyanide.

[0009] Furthermore, the metal oxide layer described in Patent Document 2 must be formed using sputtering or vapor deposition methods that require large-scale equipment. In addition, the hydrogen buffer film also needs to be formed using sputtering or vapor deposition methods. For these reasons, the method described in Patent Document 2 was difficult to apply to metal materials already in use in the field. Moreover, in the case of sputtering, the area that can be filmed is small, making it difficult to create a film of sufficient area necessary for hydrogen detection in metal materials in the field. In view of the above circumstances, the present invention aims to provide a film-type sensor and a hydrogen detection system that can easily detect hydrogen present in a metal material. [Means for solving the problem]

[0010] To achieve the above objectives, the present invention employs the following configuration. [1] A film-type sensor for detecting hydrogen in a metal material by being laminated on the surface of the metal material in a gas or vacuum, A film-like sensor characterized by being composed of an organic polymer whose optical properties change depending on the hydrogen concentration. [2] The film-like sensor according to [1], wherein the organic polymer whose optical properties change depending on the hydrogen concentration is a conjugated polymer. [3] The film-like sensor according to [2], wherein the organic polymer whose optical properties change depending on the hydrogen concentration is an aromatic conjugated polymer. [4] The film-like sensor according to any one of [1] to [3], wherein the organic polymer whose optical properties change depending on the hydrogen concentration has at least one of an amine structure and an imine structure. [5] The film-like sensor according to any one of [1] to [4], wherein the film-like sensor contains a dye whose optical properties change depending on the hydrogen concentration. [6] A film-type sensor for detecting hydrogen in a metal material by being laminated on the surface of the metal material in a gas or vacuum, A film-like sensor characterized by being composed of organic polymers and containing a dye whose optical properties change depending on the hydrogen concentration. A hydrogen detection system comprising a film-like sensor as described in any one of items [7][1] to [6], and an optical detector for detecting the optical properties of the film-like sensor.

[0011] The present invention has the following aspects. [1] A film-type sensor for detecting hydrogen in a metal material by being laminated on the surface of the metal material in a gas or vacuum, It is composed of organic polymers whose optical properties change depending on the hydrogen concentration. The film-like sensor having a film thickness of 0.1 μm or more, preferably 0.5 μm or more. [2] The film-like sensor according to [1], wherein the film thickness of the film-like sensor is 1 mm or less, preferably 500 μm or less, more preferably 100 μm or less, even more preferably 5 μm or less, and particularly preferably 1 μm or less. [3] The film-like sensor according to [1] or [2], wherein the organic polymer whose optical properties change depending on the hydrogen concentration is a conjugated polymer, preferably an aromatic conjugated polymer. [4] The film-like sensor according to any one of [1] to [3], wherein the organic polymer whose optical properties change depending on the hydrogen concentration is a compound having at least one of an amine structure and an imine structure, preferably one or more selected from the group consisting of aromatic conjugated polymers such as polyaniline, poly(σ-methoxyaniline), poly(σ-5-toxyaniline), polypyrrole, poly(ether tert-amine), poly(N-isopropylacrylamide-co-acrylic acid), and poly(amine-ether). [5] The film-like sensor according to any one of [1] to [4], wherein the film-like sensor contains a dye whose optical properties change depending on the hydrogen concentration. [6] The film-like sensor according to [6], wherein the dye whose optical properties change depending on the hydrogen concentration is one or more selected from the group consisting of methyl red, phenolphthalein, p-nitrophenylhydrazone, alizarin yellow, and sodium fluorocein. [7] The film sensor according to [5] or [6], which contains 0.01 to 5 g, preferably 0.01 to 0.05 g, of a dye whose optical properties change depending on the hydrogen concentration, with respect to 50 g of an organic polymer whose optical properties change depending on the hydrogen concentration. [8] A film sensor for detecting hydrogen in a metal material by laminating it on the surface of the metal material in gas or in vacuum, characterized in that it is composed of an organic polymer and contains a dye whose optical properties change depending on the hydrogen concentration. [9] The film sensor according to [8], wherein the dye whose optical properties change depending on the hydrogen concentration is one or more selected from the group consisting of methyl red, phenolphthalein, p-nitrophenylhydrazone, alizarin yellow, and sodium fluorescein.

[10] The film sensor according to [8] or [9], which contains 0.01 to 5 g, preferably 0.01 to 0.05 g, of a dye whose optical properties change depending on the hydrogen concentration, with respect to 50 g of an organic polymer whose optical properties change depending on the hydrogen concentration.

[11] The film sensor according to any one of [1] to

[10] , which is laminated on the surface of the metal material in gas or in vacuum.

[12] The film sensor according to

[11] , which is laminated so as to be in direct contact with the surface of the metal material.

[13] A hydrogen detection system comprising the film sensor according to any one of [1] to

[10] and an optical detector for detecting the optical properties of the film sensor.

[14] The hydrogen detection system according to

[13] , wherein the film sensor is laminated on the surface of the metal material in gas or in vacuum.

[15] The hydrogen detection system according to

[14] , wherein the film sensor is laminated so as to be in direct contact with the surface of the metal material.

[16] A method for detecting hydrogen in the metal material by visually observing the film sensor according to

[11] or

[12] .

[17] A method for detecting hydrogen in the metal material by observing the film sensor in the hydrogen detection system according to

[14] or

[15] with an optical detector.

Advantages of the Invention

[0012] According to the film sensor and the hydrogen detection system of the present invention, hydrogen present in a metal material can be easily detected.

Brief Description of the Drawings

[0013] [Figure 1] It is a schematic diagram for explaining a method of forming a film sensor on a pipe. [Figure 2] (a) Schematic front view of the hydrogen detection system used in Experimental Example 1 etc. of the present invention, (b) Schematic diagram of the cell opening side of the acrylic cell as viewed from inside the acrylic cell 10. [Figure 3] It is an image taken by a camera after a predetermined time has elapsed after starting constant current polarization with the apparatus of FIG. 2. [Figure 4] It is a graph showing the amount of change in RGBY values after starting constant current polarization with the apparatus of FIG. 2. [Figure 5] It is a graph showing the change in R value after ending constant current polarization with the apparatus of FIG. 2. [Figure 6] It is a graph for confirming the stability of the film sensor 2 in the atmosphere. [Figure 7] (a) Schematic front view of the hydrogen detection system used in Experimental Example 5 of the present invention, (b) Schematic diagram of the cell opening side of the acrylic cell as viewed from inside the acrylic cell 10. [Figure 8] It is an image taken by a camera after a predetermined time has elapsed after starting constant current polarization with the apparatus of FIG. 7.

Embodiments for Carrying Out the Invention

[0014] In this specification and the claims, when a film sensor "is laminated on the surface of a metal material in gas or in vacuum", it means that the interface between the metal material and the film sensor, or the interface between the film sensor and a layer that may exist between the metal material and the film sensor is in gas or in vacuum and does not exist in liquid or in solid. In this specification and in the claims, "change in optical properties" includes changes such as discoloration, color development, and decolorization, as well as the occurrence of emission or absorption, such as fluorescence emission. Furthermore, it is not limited to changes in the visible region, but may include, for example, emission or absorption in the near-infrared region. In this specification and in the claims, the "~" indicating a numerical range means that the numbers before and after it are included as the lower and upper limits, respectively.

[0015] <First Embodiment> The film-like sensor of the first embodiment is composed of an organic polymer whose optical properties change depending on the hydrogen concentration (hereinafter sometimes referred to as "hydrogen-functional polymer"). The film-like sensor of the first embodiment may also contain a dye whose optical properties change depending on the hydrogen concentration (hereinafter sometimes referred to as "hydrogen-functional dye"). The film-like sensor of the first embodiment can detect hydrogen in a metal material by being laminated on the surface of the metal material in a gas or vacuum.

[0016] [Hydrogen-functionalized polymers] The hydrogen-functional polymer used in the film-type sensor can be any organic polymer whose optical properties change depending on the hydrogen concentration. As hydrogen-functionalized polymers, conjugated polymers are preferred because they readily exhibit changes in optical properties depending on the hydrogen concentration, and aromatic conjugated polymers are even more preferred.

[0017] Furthermore, having at least one of an amine structure and an imine structure is preferable because it allows for relatively large changes in optical properties depending on the hydrogen concentration. Examples of compounds having at least one of an amine structure and an imine structure include aromatic conjugated polymers such as polyaniline, poly(σ-methoxyaniline), poly(σ-5-toxyaniline), and polypyrrole, as well as poly(ether tert-amine), poly(N-isopropylacrylamide-co-acrylic acid), and poly(amine-ether).

[0018] Examples of hydrogen-functional polymers that do not have amine or imine structures include poly(methylacrylic acid), 11-methacrylamidoundecanoic acid, 2-acrylamido-2-methylpropanesulfonic acid, and polythiophene.

[0019] Hydrogen-functionalized polymers are preferably capable of forming films on their own. This allows for the construction of film-like sensors without the use of other polymers. Furthermore, hydrogen-functional polymers with film-forming properties are not limited to those that form a film upon polymerization; they may also be in powder form. Powdered polymers can be formed into films by filtration or drying.

[0020] For a polymer to have film-forming properties, it must have a weight-average molecular weight of at least 4000. Furthermore, its number-average molecular weight must exceed the critical molecular weight. The critical molecular weight varies depending on the type of polymer. Two or more hydrogen-functionalized polymers may be used in combination. Furthermore, non-hydrogen-functionalized organic polymers may be used in combination, as long as they do not impair the effects of the present invention.

[0021] [Hydrogen-functionalized dyes] By incorporating a hydrogen-functional dye into a film composed of hydrogen-functional polymers, it is possible to significantly alter the optical properties and improve sensitivity. Dyes commonly used as pH indicators can be used as hydrogen-functionalized dyes. Examples of pH indicators include single-color indicators that change color depending on the hydrogen ion concentration, two-color indicators that change color depending on the hydrogen ion concentration, and luminescent indicators that emit light depending on the hydrogen ion concentration.

[0022] Examples of monochromatic indicators include phenolphthalein, picric acid, 2,6-dinitrophenol, para-nitrophenol, timolphthalein, 2,4,6-trinitrotoluene, 1,3,5-trinitrobenzene, 2,4-dinitrophenol, 2,5-dinitrophenol, and o-nitrophenol.

[0023] Two-color indicators include methyl violet, crystal violet, ethyl violet, methyl green, cresol red, methyl red, paramethyl red, thymol blue, metacresol purple, methyl yellow, bromophenol blue, Congo red, methyl orange, ethyl orange, bromocresol green, bromocresol blue, litmus (azolithomin), propyl red, methyl purple, chlorophenol red, bromocresol purple, alizarin, bromothymol blue, brilliant yellow, neutral red, phenol red, para-α-naphthalein, and metacresol purple. Examples include Alizarin Yellow R, Alizarin Yellow G, Alizarin Red, notricarbocyanine dyes, methanyl yellow, 4-phenylazodiphenylamine, naphthyl red hydrochloride, lacmoid, rosolic acid, α-naphtholphthalein, p-xylenol blue, o-cresolphthalein, o-cresol red, p-naphtholbenzei, tetril, tropeoline, indigo carmine, malachite green, dimethyl yellow, γ-dinitrophenol, Nile blue, nitrothymol yellow, tetrabromophenol blue, p-nitrophenylhydrazone, N,-N-dimethylaniline, and anthocyanins.

[0024] Examples of luminescent indicators include fluorocein sodium, 6-carbosylfluorescein, 2',7'-bis(2-carbosylethyl)-5-(and-6)-carboxyfluorescein, 8-hydroxypyrene-1,3,6-trisulfonic acid, seminaphtholfodafluor / seminaphtholfluorescein, and borondipyrometen.

[0025] Hydrogen-functional dyes may be used in combination of two or more types. When a film-type sensor contains a hydrogen-functional dye, the amount of hydrogen-functional dye contained in the film-type sensor is preferably 0.01 to 5 g, and more preferably 0.01 to 0.05 g, per 50 g of hydrogen-sensitive polymer.

[0026] [film thickness] For film-type sensors, a film can be formed without practical problems as long as the film thickness is 1 mm or less. The film thickness of the film-type sensor is preferably 500 μm or less, more preferably 100 μm or less, even more preferably 5 μm or less, and particularly preferably 1 μm or less. If the film thickness of the film-type sensor is below a preferred upper limit, manufacturing becomes easier and more cost-effective. Furthermore, since hydrogen movement in the film thickness direction is restricted, sensitivity tends to be better.

[0027] Furthermore, the film-type sensor can be made light-transmitting by setting the film thickness to 5 μm or less, preferably 1 μm or less. If the film-type sensor is light-transmitting, the surface state of the metal material can be observed through the film-type sensor. Therefore, it is easier to understand the correspondence between changes in the optical properties of the film-type sensor and changes in the state of the metal material.

[0028] The film thickness of the film-like sensor is preferably 0.1 μm or more, and more preferably 0.5 μm or more. If the film thickness of the film-like sensor is above the preferred lower limit, a sufficient change in optical properties due to hydrogen can be obtained.

[0029] When light transmittance is not considered, the film thickness of the film-like sensor is preferably 0.1 μm to 1 mm, more preferably 0.1 μm to 500 μm, even more preferably 0.5 μm to 500 μm, and particularly preferably 0.5 μm to 100 μm. When considering light transmittance, the film thickness of the film-like sensor is preferably 0.1 μm to 5 μm, more preferably 0.1 μm to 1 μm or 0.5 μm to 5 μm, and particularly preferably 0.5 μm to 1 μm.

[0030] [Applications of film-type sensors] Examples of metallic materials that can be used to detect hydrogen using a film-type sensor include pure iron, stainless steel, carbon steel, aluminum alloys, and magnesium alloys. Examples of applications for metal materials include piping for liquids or gases, containers such as high-pressure hydrogen gas and natural gas cylinders, and transportation equipment such as automobiles.

[0031] The film-type sensor can be used as a sensor to detect hydrogen in a metal material by being layered on the surface of the metal material in a gas or vacuum. The film-like sensor of the present invention can be laminated so as to be in direct contact with one surface of a metal material. In this case, the interface between the metal material and the film-like sensor is in a gas or vacuum and is not in a liquid or solid. The other surface of the metal material on which the film-like sensor is not laminated (for example, the inner surface of a pipe) may be in contact with a liquid or the like.

[0032] The film-like sensor of the present invention may be laminated on one side of a metal material via a buffer layer. Examples of buffer layers include nickel plating, palladium plating, copper plating, and zinc plating. When a buffer layer is present, the end face of the buffer layer is in a gas or vacuum and is not in a liquid or solid.

[0033] The inclusion of a buffer layer tends to increase the change in optical properties in response to hydrogen concentration, i.e., the sensitivity tends to increase. This is thought to be because, during the formation of the film-like sensor, the reaction solution used to form the film-like sensor does not directly come into contact with the metal material, thus preventing roughening of the metal material surface.

[0034] The thickness of the buffer layer is preferably 0.001 to 1 μm, and more preferably 0.001 to 0.05 μm. A buffer layer thickness above the lower limit of the preferred range makes it easier to achieve improved sensitivity. A buffer layer thickness below the upper limit of the preferred range makes it less likely to hinder the movement of hydrogen from the metal material to the film-like sensor.

[0035] Since the optical properties of a film-type sensor change due to hydrogen migrated from the metal material to the film-type sensor, it is possible to detect the hydrogen migrated to the film-type sensor, and consequently, the hydrogen in the metal material, by observing it from the side opposite to the side laminated on the metal material.

[0036] Furthermore, depending on the sensitivity of the film-type sensor, it is possible to evaluate the level of hydrogen concentration in the metal material and the change in concentration over time. Furthermore, by observing the differences in changes in optical properties within the plane of the film-like sensor, it is possible to evaluate the hydrogen distribution (higher or lower hydrogen concentration depending on location within the plane) within the plane of the metal material on which the film-like sensor is stacked.

[0037] Changes in the optical properties of a film-type sensor can be confirmed by visual observation if they occur in the visible spectrum. It is also preferable to combine the film-type sensor with an optical detector such as a camera to create a hydrogen detection system. By combining it with an optical detector, it becomes easier to objectively detect changes in optical properties and to record them.

[0038] If the change in the optical properties of a film-type sensor is not a change in the visible region, an optical detector is essential. For example, if near-infrared emission is used, an optical detector sensitive to the near-infrared region is required. By combining this with an analysis tool that analyzes the captured images, it becomes possible to more objectively understand changes in optical properties.

[0039] Changes in the optical properties of film-type sensors can usually be observed under general light sources such as sunlight or indoor fluorescent lights, except in cases where excitation light is required, such as in fluorescence emission. In addition to film sensors and optical detectors, a hydrogen detection system may also be constructed by adding a specific light source. Using a specific light source makes it easier to detect changes in optical properties with good reproducibility. Halogen lamps, xenon lamps, LED lights, etc., can be used as light sources. The wavelength of excitation light required to obtain fluorescence varies depending on the type of pH-functionalized dye; sometimes an ultraviolet light source is necessary, while other times general light is sufficient.

[0040] [Manufacturing method for membrane-type sensors] Film-type sensors can be obtained by electrolytic polymerization or chemical polymerization. Electrolytic polymerization is suitable for stably forming film-type sensors over a large area. Chemical polymerization allows for the formation of thin films, which suppresses hydrogen migration in the thickness direction and makes it easier to obtain high resolution. Therefore, it is suitable for highly sensitive evaluation of small areas.

[0041] To form a film-like sensor by electrolytic polymerization, a reaction solution containing monomers for obtaining a hydrogen-functional polymer, or a reaction solution containing these monomers plus a hydrogen-functional dye, should be brought into contact with one side of a metal material, and a voltage should be applied. For example, when forming a film-like sensor on the surface of a pipe, as shown in Figure 1, the opening surface of the acrylic cell 31 is pressed against the pipe 30 in a liquid-tight manner, and the acrylic cell 31 is filled with reaction liquid 32. Then, a voltage is applied from a power supply 34 between the pipe 30 and the counter electrode 33 inserted into the acrylic cell 31, causing the monomer in the reaction liquid 32 to undergo electrolytic polymerization.

[0042] To form a film-like sensor by chemical polymerization, an oxidizing agent can be added to a solution containing monomers for obtaining a hydrogen-functional polymer, or a solution containing hydrogen-functional dyes in addition to these monomers, and oxidative polymerization can be carried out to form a film using a dispersion containing hydrogen-functional polymers, or a dispersion containing hydrogen-functional dyes in addition to hydrogen-functional polymers. To promote polymerization, the reaction solution may be stirred after adding the oxidizing agent. Methods for forming a film on one surface of a metal material using a dispersion include filtering the dispersion and drying it on the metal material, or spraying the dispersion onto one surface of the metal material and drying it on the metal material.

[0043] Polymerization reactions are classified into homogeneous and heterogeneous reactions, and various reagents are selected depending on the purpose. According to chemical polymerization methods using highly oxidizing agents, hydrogen-functional polymers can be obtained through a homogeneous reaction. In this case, the hydrogen-functional polymer is formed in the form of fine particles in an aqueous solution, and the reaction proceeds relatively quickly. Examples of highly oxidizing agents include potassium dichromate, potassium iodate, iron(III) chloride, and potassium permanganate.

[0044] On the other hand, chemical polymerization methods using oxidizing agents with weak oxidizing power yield hydrogen-functional polymers through heterogeneous reactions. In this case, polymerization proceeds relatively slowly, making it easier to create homogeneous films with high mechanical strength on the surface of metal materials. Examples of oxidizing agents with weak oxidizing power include ammonium salts such as ammonium peroxodisulfate and ammonium metavanadate, and potassium peroxodisulfate. In particular, using ammonium salts as oxidizing agents makes it easier to obtain highly accurate, homogeneous, and high-strength film-like sensors.

[0045] If the dispersion contains an acidic solvent, it is preferable to replace all or part of the solvent with an organic solvent or a neutral aqueous solution. This prevents the metal material from corroding due to the acid. Furthermore, since the metal surface is not roughened by the effects of the acid, it is easier to improve the sensitivity of the film-type sensor.

[0046] <Second Embodiment> The film-like sensor of the second embodiment is composed of an organic polymer and contains a dye (hydrogen-functional dye) whose optical properties change depending on the hydrogen concentration. The film-like sensor of the second embodiment can detect hydrogen in a metal material by being laminated on the surface of the metal material in a gas or vacuum, similar to the film-like sensor of the first embodiment.

[0047] The organic polymer in this embodiment may be a hydrogen-functional polymer or not. This embodiment also includes embodiments in which a hydrogen-functional polymer and a non-hydrogen-functional organic polymer are used in combination. In this embodiment, the configuration in which all or part of the organic polymer is a hydrogen-functional polymer is the same as the configuration containing a hydrogen-functional dye in the first embodiment. Therefore, the case in which the organic polymer is not a hydrogen-functional polymer will be described below.

[0048] Examples of organic polymers that are not hydrogen-functionalized polymers include agar, polystyrene, polyvinyl chloride, butyl rubber, chlorosulfonated polyethylene, nylon, and chloroprene rubber. Organic polymers that are not hydrogen-functionalized polymers must have a weight-average molecular weight of at least 4000 and a number-average molecular weight exceeding the critical molecular weight in order to form films. For example, the critical molecular weight of polyethylene oxide is 3200.

[0049] Two or more organic polymers that are not hydrogen-functionalized polymers may be used in combination. As the hydrogen-functional dye, the same one shown in the first embodiment can be used. The amount of hydrogen-functional dye contained in the film-like sensor is preferably 0.01 to 5 g, and more preferably 0.01 to 0.05 g, per 50 g of organic polymer that is not a hydrogen-sensitive polymer.

[0050] The film-like sensor of this embodiment is also preferably light-transmitting. The preferred film thickness of the film-like sensor of this embodiment is the same as that of the first embodiment. Furthermore, similar to the first embodiment, it can be used as a sensor for detecting hydrogen in a metal material by being laminated on the surface of the metal material in a gas or vacuum, and a buffer layer may be provided if necessary. The film-type sensor of this embodiment can also be combined with an optical detector and a light source to form a hydrogen detection system. The film-like sensor of this embodiment can also be obtained by electrolytic polymerization or chemical polymerization. Electrolytic polymerization uses a reaction solution containing monomers for obtaining an organic polymer and a hydrogen-functional dye. Chemical polymerization involves adding an oxidizing agent to a solution containing monomers for obtaining a hydrogen-functional polymer and a hydrogen-functional dye, carrying out oxidative polymerization, and then forming a film using filtration or spraying. [Examples]

[0051] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the descriptions in these examples.

[0052] <Experimental Example 1> We confirmed that the hydrogen intrusion status of a metal material when exposed to an electrolyte under applied voltage can be observed using the hydrogen detection system shown in Figure 2. The hydrogen detection system shown in Figure 2 comprises a film-like sensor 2 laminated on one side of a metal material 1, a camera 4 that photographs the film-like sensor 2 from the opposite side (front side) of the metal material 1, and a ring light 5 attached to the camera 4. The entire system is placed in a darkroom under atmospheric conditions.

[0053] To expose the metal material 1 to an electrolyte while applying voltage, an acrylic cell 10 having a cell opening 11 on its side, a potentiostat 16, and a counter electrode 15 connected to the potentiostat 16 were prepared. The metal material 1 was connected to the working electrode side of the potentiostat 16. Then, the side (back side) of the metal material 1 opposite to the side on which the film-like sensor 2 is laminated was pressed against the position that closes the cell opening 11.

[0054] As shown in Figure 2(b), half of the portion of the metal material 1 facing the cell opening 11 is designated as the masking portion 12, and the remaining half is designated as the exposed portion 13. The area of ​​the exposed portion 13 is 1 cm². 2 The back surface of the metal material 1 and the acrylic cell 10 are kept liquid-tight by a sealing member (not shown) surrounding the cell opening 11.

[0055] In this state, as shown in Figure 2(a), the acrylic cell 10 was filled with electrolyte 14, and the color tone of the film-like sensor 2 when constant current polarization was performed by the potentiostat 16 was photographed in a dark room with the ring light 5 turned on and the image taken with the camera 4. A single-lens reflex camera was used as the camera 4. A halogen lamp was used as the light source for the ring light 5.

[0056] For metal material 1, a piece of pure iron with a purity of 99.5% by mass, measuring 30 mm in width, 30 mm in length, and 2 mm in thickness, was pre-heat-treated at 900°C and polished to a mirror finish on both the front and back surfaces (it is believed to contain almost no hydrogen). On the back surface of the metal material 1, a film-like sensor 2 is formed in the portion that will become the masking portion 12, and then a resin (Huntsman Japan Co., Ltd.) is applied. Made, A masking treatment was performed by coating with Araldite to avoid contact with the electrolyte 14.

[0057] The film-like sensor 2 was formed on the metal material 1 as follows. Specifically, 26.75 mL of sulfuric acid (Fujifilm Wako Pure Chemical Industries, reagent grade) and 44.6 mL of aniline (Fujifilm Wako Pure Chemical Industries, reagent grade) were mixed in 800 mL of distilled water, stirred until completely dissolved, and then distilled water was added to make a total volume of 1 L to prepare the mixed solution. Here, M represents the molar concentration (mol / L). The metal material 1, with its back surface covered with acid-resistant tape (3M Japan, plating masking tape 470) and its entire surface exposed, was immersed in a mixed solution. A platinum wire was used as the counter electrode, and a voltage of 1V was applied and held for 200 seconds. The solid polyaniline layer, approximately 5μm thick, formed on the surface of the metal material 1 was thoroughly washed with high-purity water and air-dried at room temperature for 1 hour to form a film-like sensor 2.

[0058] The diameter of the cell opening 11 of the acrylic cell 10 was set to 16 mm, and a 3% by mass NaCl aqueous solution was used as the electrolyte 14. For the potentiostat 16, we used a VERTEX 100mA manufactured by Ivium Technologies. A platinum wire was used as the counter electrode, and constant current polarization at -1mA was performed.

[0059] Figure 3 shows images taken by camera 4 at the start of constant current polarization (0 minutes), and at 10 minutes, 30 minutes, 60 minutes, 120 minutes, 180 minutes, 240 minutes, and 300 minutes after the start. In each photograph in Figure 3, the left side is the exposed area 13 and the right side is the masked area 12.

[0060] As shown in Figure 3, the color tone of the exposed area 13 was initially the same as that of the masked area 12, but over time it changed to a different color tone from that of the masked area 12. When constant current polarization is performed, hydrogen is generated in the exposed portion 13 in contact with the electrolyte 14, and this hydrogen penetrates into the metal material 1. The results in Figure 3 indicate that the penetration of hydrogen into the metal material 1 was detected as a change in the color tone of the film-like sensor 2.

[0061] Furthermore, after 120 minutes, the color tone of the exposed area 13 did not change much, while the area where the color tone had changed spread beyond the exposed area 13 to the masked area 12. This means that, over time, it was possible to record how hydrogen that entered the metal material 1 from near the boundary between the exposed portion 13 and the masked portion 12 diffused in the planar direction of the metal material 1 and spread to the masked portion 12, which was not in contact with the electrolyte 14.

[0062] Figure 4 shows the results of recording the color tone change in the exposed area 13 from 0 minutes to 300 minutes later as the amount of change in RGBY values. The RGBY values ​​were the average values ​​of the RGBY values ​​of the film-like sensor 2 at the color tone measurement points 17 shown in Figure 2(b). As shown in Figure 4, the color change continued until around 100 minutes, after which the color change became smaller. This indicates that the amount of hydrogen at measurement point 17 reached the limit of the amount of hydrogen that the film-type sensor 2 could detect with high accuracy around 100 minutes from the start of measurement.

[0063] <Experimental Example 2> After conducting the experiment in Experiment Example 1, constant current polarization was continued, and when constant current polarization was terminated 600 minutes after the start of constant current polarization, the color tone change at the color tone measurement point 17 of the exposed area 13 after the termination of constant current polarization (0 hours) was recorded. The results are shown in Figure 5. As shown in Figure 4, the R value increased while constant current polarization was being continued, but as shown in Figure 5, the R value decreased after the 600 constant current polarization was completed. After the constant current polarization is completed, more hydrogen is released from metal material 1 than enters metal material 1, so the hydrogen concentration in metal material 1 decreases. The result in Figure 5 means that the decrease in hydrogen concentration in metal material 1 was also detected as a change in the color tone of the film-like sensor 2.

[0064] <Experimental Example 3> In the apparatus shown in Figure 2, the color change of the film-like sensor 2 was investigated as a reflectance spectrum when neither the electrolyte 14 nor the potentiostat 16 was in operation. The results are shown in Figure 6. As shown in Figure 6, the reflection spectrum of the film-like sensor 2 showed almost no change even after 24 hours. This confirmed that the color changes observed in Figures 3 to 5 were not due to atmospheric effects on the film-like sensor 2.

[0065] <Experimental Example 4> Using the hydrogen detection system shown in Figure 2, the light source of the ring light 5 was changed, and the film-type sensor 2 of each example shown below was used instead of the film-type sensor 2 of Experimental Example 1. Otherwise, constant current polarization was performed for 3 hours in the same manner as in Experimental Example 1, and the sensitivity of the film-type sensor of each example was evaluated.

[0066] In ring light 5, the light source used in examples 13-15 was a blue LED (emission wavelength 470nm) as the excitation light, while in other examples, a xenon lamp was used. The evaluation was based on the difference (ΔR, ΔG, ΔB) of each RGB value at color measurement point 17 before the start of constant current polarization and after 3 hours of constant current polarization, according to the following criteria. The results are shown in Table 1.

[0067] [Evaluation Criteria] 5: The maximum value of ΔR, ΔG, and ΔB is 100 or greater. 4: The maximum value of ΔR, ΔG, and ΔB is between 50 and 100. 3: The maximum value of ΔR, ΔG, and ΔB is between 10 and 50. 2: The maximum value of ΔR, ΔG, and ΔB is between 3 and 10. 1: The maximum value of ΔR, ΔG, or ΔB is less than 3, or remains unchanged.

[0068] [Example 1] A 50 mL 0.5 M sulfuric acid aqueous solution was prepared using sulfuric acid (Fujifilm Wako Pure Chemical Industries, reagent grade). 1 mL of aniline (Fujifilm Wako Pure Chemical Industries, reagent grade) and 0.05 g of methyl red (Fujifilm Wako Pure Chemical Industries, reagent grade) were mixed and stirred until completely dissolved to prepare a mixed solution. Here, M represents the molar concentration (mol / L). Metal material 1, in which all parts except the electrode surfaces (2 cm square) on the back and front surfaces were covered with acid-resistant tape (3M Japan, plating masking tape 470), was immersed in a mixed solution, and constant current anode polarization at 3 mA was performed for 3 minutes with a platinum wire as the counter electrode. A film approximately 1 μm thick formed on the electrode surface of metal material 1 was thoroughly washed with highly pure water, dried by blowing nitrogen gas, and then air-dried at room temperature for 24 hours in an atmospheric environment to obtain a film-like sensor 2 consisting of a solid polyaniline layer containing methyl red.

[0069] [Example 2] A film-like sensor 2 was prepared in the same manner as in Example 1, except that 1 mL of thiophene (Fujifilm Wako Pure Chemical Industries, Wako Special Grade) was used instead of 1 mL of aniline. The sensor consisted of a solid polythiophene layer containing methyl red.

[0070] [Example 3] A film-like sensor 2 was prepared in the same manner as in Example 1, except that 1 mL of pyrrole (Fujifilm Wako Pure Chemical Industries, Wako Special Grade) was used instead of 1 mL of aniline. The sensor consisted of a solid polypyrrole layer containing methyl red.

[0071] [Example 4] A film-like sensor 2 was prepared in the same manner as in Example 1, except that 0.05 g of phenolphthalein (Fujifilm Wako Pure Chemical Industries, reagent grade) was used instead of 0.05 g of methyl red. The film-like sensor 2 consisted of a solid polyaniline layer containing phenolphthalein.

[0072] [Example 5] A membrane sensor 2 was prepared in the same manner as in Example 1, consisting of a solid polythiophene layer containing phenolphthalein, except that 1 mL of thiophene (Fujifilm Wako Pure Chemical Industries, Wako Special Grade) was used instead of 1 mL of aniline, and 0.05 g of phenolphthalein (Fujifilm Wako Pure Chemical Industries, Reagent Grade) was used instead of 0.05 g of methyl red.

[0073] [Example 6] A film-like sensor 2 was prepared in the same manner as in Example 1, consisting of a solid polypyrrole layer containing phenolphthalein, except that 1 mL of pyrrole (Fujifilm Wako Pure Chemical Industries, Wako Special Grade) was used instead of 1 mL of aniline, and 0.05 g of phenolphthalein (Fujifilm Wako Pure Chemical Industries, Reagent Grade) was used instead of 0.05 g of methyl red.

[0074] [Example 7] A membrane sensor 2 consisting of a solid polyaniline layer containing p-nitrophenylhydrazone was prepared in the same manner as in Example 1, except that 0.05 g of p-nitrophenylhydrazone (4-nitrohenylhydrazine hydrochloride, manufactured by Fluorochem Ltd.) was used instead of 0.05 g of methyl red.

[0075] [Example 8] A membrane sensor 2 was prepared in the same manner as in Example 1, consisting of a solid polythiophene layer containing p-nitrophenylhydrazone, except that 1 mL of thiophene (Fujifilm Wako Pure Chemical Industries, Wako Special Grade) was used instead of 1 mL of aniline, and 0.05 g of p-nitrophenylhydrazone (Fluorochem Ltd, 4-nitrohenylhydrazine hydrochloride) was used instead of 0.05 g of methyl red.

[0076] [Example 9] A membrane sensor 2 was prepared in the same manner as in Example 1, consisting of a solid polypyrrole layer containing p-nitrophenylhydrazone, except that 1 mL of pyrrole (Fujifilm Wako Pure Chemical Industries, Wako Special Grade) was used instead of 1 mL of aniline, and 0.05 g of p-nitrophenylhydrazone (Fluorochem Ltd, 4-nitrohenylhydrazine hydrochloride) was used instead of 0.05 g of methyl red.

[0077] [Example 10] A film-like sensor 2 was prepared in the same manner as in Example 1, except that 0.05 g of alizarin yellow (Fujifilm Wako Pure Chemical Industries, Alizarin Yellow R, reagent grade) was used instead of 0.05 g of methyl red.

[0078] [Example 11] A membrane sensor 2 was prepared in the same manner as in Example 1, consisting of a solid polythiophene layer containing Alizarin Yellow, except that 1 mL of thiophene (Fujifilm Wako Pure Chemical Industries, Wako Special Grade) was used instead of 1 mL of aniline, and 0.05 g of Alizarin Yellow (Fujifilm Wako Pure Chemical Industries, Alizarin Yellow R, Reagent Grade) was used instead of 0.05 g of methyl red.

[0079] [Example 12] A membrane sensor 2 was prepared in the same manner as in Example 1, consisting of a solid polypyrrole layer containing Alizarin Yellow, except that 1 mL of pyrrole (Fujifilm Wako Pure Chemical Industries, Wako Special Grade) was used instead of 1 mL of aniline, and 0.05 g of Alizarin Yellow (Fujifilm Wako Pure Chemical Industries, Alizarin Yellow R, Reagent Grade) was used instead of 0.05 g of methyl red.

[0080] [Example 13] A film-like sensor 2 was prepared in the same manner as in Example 1, except that 0.05 g of sodium fluorocein (Fujifilm Wako Pure Chemical Industries, Uranine, Reagent Grade) was used instead of 0.05 g of methyl red. The film-like sensor 2 consisted of a solid polyaniline layer containing sodium fluorocein.

[0081] [Example 14] A membrane sensor 2 was prepared in the same manner as in Example 1, consisting of a solid polythiophene layer containing sodium fluorocein, except that 1 mL of thiophene (Fujifilm Wako Pure Chemical Industries, Wako Special Grade) was used instead of 1 mL of aniline, and 0.05 g of sodium fluorocein (Fujifilm Wako Pure Chemical Industries, Uranine, Reagent Grade) was used instead of 0.05 g of methyl red.

[0082] [Example 15] A membrane sensor 2 was prepared in the same manner as in Example 1, consisting of a solid polypyrrole layer containing sodium fluorocein, except that 1 mL of pyrrole (Fujifilm Wako Pure Chemical Industries, Wako Special Grade) was used instead of 1 mL of aniline, and 0.05 g of sodium fluorocein (Fujifilm Wako Pure Chemical Industries, Uranine, Reagent Grade) was used instead of 0.05 g of methyl red.

[0083] [Example 16] 50 mL of agar solution was prepared by dissolving 3 g of agar (Fujifilm Wako Pure Chemical Industries, reagent grade) in 50 mL of a saturated solution of KCl (Fujifilm Wako Pure Chemical Industries, reagent grade) heated to 90°C. 0.05 g of methyl red (Fujifilm Wako Pure Chemical Industries, reagent grade) was added and the mixture was stirred until completely dissolved to prepare a mixed solution. A metal material 1, with its entire back surface and the area of ​​the electrode surface (2 cm square) on the front surface covered with acid-resistant tape (3M Japan, plating masking tape 470), was dropped with a mixed solution of agar and methyl red, and dried at room temperature to form a film, thereby creating a film-like sensor 2 consisting of a solid agar layer containing methyl red.

[0084] [Example 17] A membrane sensor 2 consisting of a solid agar layer containing phenolphthalein was prepared in the same manner as in Example 16, except that 0.05 g of phenolphthalein (Fujifilm Wako Pure Chemical Industries, reagent grade) was used instead of 0.05 g of methyl red.

[0085] [Example 18] A film-like sensor 2 was prepared in the same manner as in Example 2, except that methyl red was not added, and consisted of a solid polythiophene layer that did not contain hydrogen-functional dyes.

[0086] [Example 19] A membrane sensor 2 was prepared in the same manner as in Example 3, except that methyl red was not added, and consisting of solid polypyrrole without hydrogen-functional dyes.

[0087] [Table 1]

[0088] As shown in Table 1, it was confirmed that hydrogen can be detected by using various hydrogen-functional polymers and hydrogen-functional dyes.

[0089] <Experimental Example 5> We confirmed that the corrosion of metal materials exposed to the electrolyte can be observed using the hydrogen detection system shown in Figure 7. The hydrogen detection system shown in Figure 7 comprises a film-like sensor 2 laminated on one side of a metal material 1, a camera 4 that photographs the film-like sensor 2 from the opposite side (front side) of the metal material 1, and a ring light 5 attached to the camera 4. A single-lens reflex camera was used as the camera 4. A halogen lamp was used as the light source for the ring light 5.

[0090] Then, the side (back side) of the metal material 1 opposite to the side on which the film-like sensor 2 is laminated was pressed against the position that closes the cell opening 11. Furthermore, liquid-tightness is maintained between the back surface of the metal material 1 and the acrylic cell 10 by a sealing member (not shown) surrounding the cell opening 11. The acrylic cell 10 was filled with a 3% by mass NaCl aqueous solution as the electrolyte 14.

[0091] In this experimental example, as shown in Figure 7(b), the central part of the metal material 1 facing the cell opening 11 was designated as a square exposed area 13 (width 10 mm × length 10 mm), and the area outside of it was designated as a masking area 12 (diameter 16 mm). The film-like sensor 2 was formed on the metal material 1 in the same manner as in Experimental Example 1. The same metal material 1 used in Experimental Example 1 was used for Metal Material 1, and the masking portion 12 was formed in the same manner as in Experimental Example 1.

[0092] Figure 8 shows an image taken with camera 4 24 hours after the exposed portion 13 of metal material 1 was exposed to electrolyte 14. In the photograph in Figure 8, the change in G value (ΔG) is shown in shades of black and white. As shown in Figure 8, a discolored area 20 was observed in the portion corresponding to approximately the upper half of the exposed area 13. Upon observation of the exposed area 13 on the back surface of the metal material 1, corrosion was observed in the portion corresponding to the discolored area 20. When corrosion of metal material 1 occurs at the interface with the electrolyte, hydrogen is generated. The results of this experiment indicate that the increase in hydrogen concentration due to the corrosion of metal material 1 was detected as a change in the color tone of the film-like sensor 2. [Industrial applicability]

[0093] The film-type sensor and hydrogen detection system of the present invention can be applied to the detection of hydrogen present in metal materials used in liquid or gaseous piping, containers such as high-pressure hydrogen gas and natural gas cylinders, and transport equipment such as automobiles. [Explanation of Symbols]

[0094] 1 Metal materials 2. Membrane Sensor 4 cameras 5 Ring Lights 10 Acrylic Cells 11 Cell openings 12 Masking section 13 Exposed part 14 Electrolyte 15 Opposite 16 Potentiostat 20 Discolored area

Claims

1. A film-like sensor having the function of detecting hydrogen atoms dissolved in a metal material by being layered on the surface of the metal material in a gas or vacuum, and composed of an organic polymer whose optical properties change depending on the concentration of the hydrogen atoms, with a film thickness of 0.1 μm or more and 1 mm or less, A hydrogen detection system comprising an optical detector for detecting the optical properties of the aforementioned film-like sensor.

2. The hydrogen detection system according to claim 1, wherein the organic polymer whose optical properties change depending on the concentration of hydrogen atoms is a conjugated polymer.

3. The hydrogen detection system according to claim 2, wherein the organic polymer whose optical properties change depending on the concentration of hydrogen atoms is an aromatic conjugated polymer.

4. The hydrogen detection system according to any one of claims 3, wherein the organic polymer whose optical properties change depending on the concentration of hydrogen atoms has at least one of an amine structure and an imine structure.

5. A film-like sensor having the function of detecting hydrogen atoms dissolved in a metal material by being layered on the surface of the metal material in a gas or vacuum, composed of an organic polymer whose optical properties change depending on the concentration of the hydrogen atoms, having a film thickness of 0.1 μm or more and 1 mm or less, and containing a dye whose optical properties change depending on the concentration of the hydrogen atoms, A hydrogen detection system comprising an optical detector for detecting the optical properties of the aforementioned film-like sensor.

6. A film-like sensor having the function of detecting hydrogen atoms dissolved in a metal material by being layered on the surface of the metal material in a gas or vacuum, containing a dye composed of an organic polymer whose optical properties change depending on the concentration of the hydrogen atoms, and having a film thickness of 0.1 μm or more and 1 mm or less, A hydrogen detection system comprising an optical detector for detecting the optical properties of the aforementioned film-like sensor.

7. The hydrogen detection system according to any one of claims 1 to 6, wherein the weight-average molecular weight of the organic polymer is 4000 or more, and the number-average molecular weight exceeds the critical molecular weight.

8. The hydrogen detection system according to claim 1, wherein the organic polymer whose optical properties change depending on the concentration of hydrogen atoms is one or more selected from the group consisting of aromatic conjugated polymers such as polyaniline, poly(σ-methoxyaniline), poly(σ-5-toxyaniline), polypyrrole, poly(ether tert-amine), poly(N-isopropylacrylamide-co-acrylic acid), and poly(amine-ether).

9. The hydrogen detection system according to any one of claims 5 or 6, wherein the dye whose optical properties change depending on the concentration of hydrogen atoms is one or more selected from the group consisting of methyl red, phenolphthalein, p-nitrophenylhydrazone, alizarin yellow, and sodium fluorocein.

10. The hydrogen detection system according to claim 5, comprising 0.01 to 5 g of a dye whose optical properties change depending on the concentration of hydrogen atoms, per 50 g of an organic polymer whose optical properties change depending on the concentration of hydrogen atoms.

11. The hydrogen detection system according to any one of claims 1 to 10, wherein the film-like sensors are laminated so as to be in direct contact with the surface of a metal material.

12. A method for detecting hydrogen in a metallic material, comprising a lamination step and a detection step, In the lamination process, a film-like sensor, composed of an organic polymer whose optical properties change depending on the concentration of hydrogen atoms and having the function of detecting hydrogen atoms dissolved in the metal material in a gas or vacuum, is laminated on the surface of the metal material to a thickness of 0.1 μm or more and 1 mm or less in a gas or vacuum. In the detection step, hydrogen in the metal material is detected by visually observing the optical properties that have changed due to hydrogen migrated from the metal material to the film-like sensor using an optical detection device from the side opposite to the side laminated on the metal material. A method for detecting hydrogen in metallic materials.

13. A method for detecting hydrogen in a metallic material, comprising a lamination step and a detection step, In the lamination process, a film-like sensor, composed of an organic polymer whose optical properties change depending on the concentration of hydrogen atoms and containing a dye whose optical properties change depending on the concentration of hydrogen atoms, and having the function of detecting hydrogen atoms solid-dissolved in the metal material in a gas or vacuum, is laminated on the surface of the metal material with a thickness of 0.1 μm or more and 1 mm or less in a gas or vacuum. In the detection step, hydrogen in the metal material is detected by visually observing the optical properties that have changed due to hydrogen migrated from the metal material to the film-like sensor using an optical detection device from the side opposite to the side laminated on the metal material. A method for detecting hydrogen in metallic materials.

14. A method for detecting hydrogen in a metallic material, comprising a lamination step and a detection step, In the lamination process, a film-like sensor, composed of an organic polymer containing a dye whose optical properties change depending on the concentration of hydrogen atoms, and having the function of detecting hydrogen atoms dissolved in the metal material in a gas or vacuum, is laminated on the surface of the metal material with a thickness of 0.1 μm to 1 mm in a gas or vacuum. In the detection step, hydrogen in the metal material is detected by visually observing the optical properties that have changed due to hydrogen migrated from the metal material to the film-like sensor using an optical detection device from the side opposite to the side laminated on the metal material. A method for detecting hydrogen in metallic materials.

15. In the detection step, the change in optical properties is observed visually. A method for detecting hydrogen in a metallic material according to any one of claims 12-14.

16. In the detection step, the change in optical properties is observed using an optical detection device. A method for detecting hydrogen in a metallic material according to any one of claims 12-14.

17. In the detection step, the change in optical characteristics occurs when the maximum value of the difference between each of the RGB values ​​(ΔR, ΔG, ΔB) is 10 or more. A method for detecting hydrogen in a metallic material according to any one of claims 12-14.

18. In the detection step, the change in optical characteristics is such that the maximum value of the difference between each of the RGB values ​​(ΔR, ΔG, ΔB) is 50 or more. The method for detecting hydrogen in the metallic material according to claim 17.

19. In the detection step, the change in optical characteristics occurs when the maximum value of the difference between each of the RGB values ​​(ΔR, ΔG, ΔB) is 100 or more. The method for detecting hydrogen in the metallic material according to claim 18.

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