Hydrogen charging method and hydrogen embrittlement property evaluation method

Abstract

To provide a hydrogen charging method which employs a simple electrochemical approach and can increase the hydrogen charge amount by heating an electrolyte to a high temperature.SOLUTION: A hydrogen charging method is provided, comprising: immersing a metal sample in an electrolyte composed of an organic solvent containing either or both of alkali metal ions and alkali earth metal ions, having a boiling point exceeding 100°C, and having a hydroxy group; and forming an electric circuit for supplying electrons to the metal sample in the electrolyte and allowing the electrons to escape from a surface of the metal sample so as to electrochemically charge the metal sample with hydrogen.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a hydrogen charging method for a metal sample to be subjected to a hydrogen embrittlement property evaluation test, and a hydrogen embrittlement property evaluation method including the hydrogen charging method. [Background technology]

[0002] In the development of metallic materials such as steel, hydrogen embrittlement, which is a deterioration in strength and toughness due to hydrogen, has become a problem. Methods have been developed to evaluate the hydrogen embrittlement properties of metallic materials, in which hydrogen is charged into a sample made of the metallic material and the hydrogen-charged sample is subjected to hydrogen embrittlement property evaluation tests using various techniques.

[0003] One method for charging a metal sample with hydrogen is to place the metal sample in a high-pressure hydrogen gas environment, thereby charging the metal sample with hydrogen in the gas phase.

[0004] There are also known electrochemical methods for charging metal samples with hydrogen. For example, as described in Patent Document 1, a metal sample serving as a working electrode and a counter electrode are immersed in an electrolyte, and a voltage more negative than the counter electrode is applied to the metal sample to electrochemically charge the metal sample with hydrogen. In this method, an aqueous solution such as a sodium chloride (NaCl) solution, a sodium hydroxide (NaOH) solution, a sulfuric acid (H2SO4) solution, or a hydrochloric acid (HCl) solution is used as the electrolyte. In this method, hydrogen ions in the electrolyte receive electrons from the metal sample and become hydrogen atoms on the surface of the metal sample. Some of the hydrogen atoms bond with each other to form hydrogen molecules, which then leave the surface of the metal sample, while the remaining hydrogen atoms are believed to penetrate into the interior of the metal sample.

[0005] However, in the method of Patent Document 1, water in the electrolyte solidifies below 0°C, making hydrogen charging impossible at temperatures as low as 0°C or below. To solve this problem, Patent Document 2 describes a method in which a metal sample serving as a working electrode and a counter electrode are immersed in an electrolyte solution consisting of an alcohol containing alkali metal ions, and a voltage more negative than that of the counter electrode is applied to the metal sample, thereby electrochemically charging the metal sample with hydrogen. This method uses an alcohol containing alkali metal ions as the electrolyte, generates hydrogen on the surface of the metal sample through a metal alkoxide reaction, and charges the metal sample with this hydrogen. By using such a nonaqueous organic solvent as the electrolyte, the electrolyte does not solidify below 0°C, making hydrogen charging possible at temperatures as low as 0°C or below. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-184293 [Patent Document 2] Japanese Patent Publication No. 2022-53488 Summary of the Invention [Problem to be solved by the invention]

[0007] Recently, in order to realize a hydrogen society, construction of facilities for transporting and storing liquid hydrogen (temperature: -253°C) is underway as a method of storing and transporting large amounts of hydrogen. Among the metallic materials used in these facilities at such low temperatures, there are some with low hydrogen diffusion coefficients, such as austenitic stainless steel, which means that hydrogen is difficult to charge. Even for such metallic materials that are difficult to charge with hydrogen, it is necessary to charge as much hydrogen as possible in order to evaluate their hydrogen embrittlement characteristics at low temperatures.

[0008] In order to charge as much hydrogen as possible into a metal sample that is difficult to charge with hydrogen, it is possible to charge the metal sample with hydrogen in a high-temperature environment. Furthermore, not only for metal samples that are difficult to charge with hydrogen, but for metal materials in general, the higher the temperature of the hydrogen charging environment, the more hydrogen can be charged.

[0009] Therefore, hydrogen charging, in which metal samples are placed in a high-pressure hydrogen gas environment, can be performed in high-temperature environments of 85°C or higher, or even around 120°C. However, this method requires large-scale high-pressure hydrogen equipment, which is costly and not simple. Furthermore, because hydrogen charging is performed in the gas phase, the hydrogen charging rate is slow, and it takes a long time, such as 300 hours, to saturate the metal sample with hydrogen. For this reason, a simple electrochemical method for high-temperature hydrogen charging is needed.

[0010] However, in the electrochemical hydrogen charging method using an aqueous electrolyte solution described in Patent Document 1, the boiling point of water is 100°C, so even if the temperature of the electrolyte solution is increased, it is only about 85°C at most.

[0011] Furthermore, the electrochemical hydrogen charging method using an electrolyte solution made of a non-aqueous organic solvent described in Patent Document 2 is a technology aimed at hydrogen charging at low temperatures below 0°C, and does not at all consider the problem of increasing the amount of hydrogen charged by raising the temperature of the electrolyte solution. In fact, the alcohol used in Patent Document 2 has a melting point below 0°C (i.e., it does not solidify at 0°C) and a boiling point below 100°C, so there are even more restrictions on raising the temperature of the electrolyte solution than with the aqueous solution system of Patent Document 1.

[0012] In view of the above problems, the present invention aims to provide a hydrogen charging method using a simple electrochemical technique that can increase the amount of hydrogen charged by raising the electrolyte temperature, and a method for evaluating hydrogen embrittlement characteristics using this hydrogen charging method. [Means for solving the problem]

[0013] To solve the above problems, the present inventors have investigated a simple electrochemical hydrogen charging method using an organic solvent that does not boil even at high temperatures as the electrolyte. First, to generate hydrogen through a metal alkoxide reaction on the surface of a metal sample, it is necessary to use an organic solvent containing either or both alkali metal ions and alkaline earth metal ions and having a hydroxyl group as the electrolyte. Furthermore, by using an organic solvent with a boiling point above 100°C, the electrolyte temperature can be raised higher than conventional methods, thereby enabling a larger amount of hydrogen to be charged.

[0014] The present invention, which was completed based on the above findings, has the following gist and configuration. [1] A step of immersing a metal sample in an electrolytic solution containing one or both of alkali metal ions and alkaline earth metal ions, having a boiling point above 100°C, and comprising an organic solvent having a hydroxyl group; a step of electrochemically charging the metal sample with hydrogen by forming an electric circuit in which electrons are supplied to the metal sample in the electrolytic solution and the electrons are released from the surface of the metal sample; A hydrogen charging method comprising the steps of:

[0015] [2] Immersing a counter electrode in the electrolyte; Connecting the metal sample and the counter electrode to an external power source, A voltage more negative than the counter electrode is applied to the metal sample as a working electrode by the external power source. The hydrogen charging method described in [1] above, wherein the electric circuit is formed by:

[0016] [3] The hydrogen charging method described in [1] or [2] above, wherein the temperature of the electrolyte is above 0°C.

[0017] [4] A hydrogen charging method according to claim [1] or [2], wherein the temperature of the electrolyte is 85°C or higher and lower than the boiling point of the organic solvent.

[0018] [5] A hydrogen charging method according to claim [1] or [2], wherein the temperature of the electrolyte is 100°C or higher and lower than the boiling point of the organic solvent.

[0019] [6] The hydrogen charging method according to any one of the above [1] to [5], wherein the organic solvent is an alcohol.

[0020] [7] The alcohol has a viscosity of 3.2 × 10 at 25 °C. 3 The hydrogen charging method according to [6] above, wherein the hydrogen has a vapor pressure of 0.1 Pa or less.

[0021] [8] A hydrogen charging method described in [6] above, wherein the alcohol is one or more selected from the group consisting of ethylene glycol, propylene glycol, and glycerin.

[0022] [9] The metal sample has a viscosity of 1.0 × 10 at 25 °C. -15 m 2 The hydrogen charging method according to any one of the above [1] to [8], wherein the hydrogen diffusion coefficient is not more than 1 / s.

[0023]

[10] A hydrogen charging method according to [9] above, wherein the metal sample is an austenitic stainless steel.

[0024]

[11] The hydrogen charging method according to any one of the above [1] to

[10] , wherein the electrolytic solution further contains a cyanide compound.

[0025]

[12] A hydrogen embrittlement property evaluation method, comprising: performing a hydrogen embrittlement property evaluation test on the metal sample charged with hydrogen by the hydrogen charging method according to any one of [1] to

[11] above.

[0026]

[13] The hydrogen embrittlement property evaluation method according to

[12] above, wherein the hydrogen embrittlement property evaluation test is a test using tracer hydrogen analysis.

[0027]

[14] The hydrogen embrittlement property evaluation method according to

[12] above, wherein the hydrogen embrittlement property evaluation test is a physical property test performed by applying one or more stresses of tension, compression, bending, shear, and torsion to the metal sample.

[0028]

[15] The hydrogen embrittlement property evaluation method according to

[12] above, wherein the hydrogen embrittlement property evaluation test is a hydrogen permeation test. [Effects of the Invention]

[0029] The hydrogen charging method of the present invention and the hydrogen embrittlement property evaluation method using the hydrogen charging method include hydrogen charging using a simple electrochemical technique, and the amount of hydrogen charged can be increased by raising the electrolyte temperature. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a schematic diagram of an electrochemical cell capable of carrying out a hydrogen charging method according to one embodiment of the present invention. [Figure 2] 1 is a graph showing the results of thermal desorption analysis in Examples 1 to 3 of the present invention. [Figure 3] 1 is a graph showing the amount of hydrogen versus t / L2 (t: charge time, L: sample thickness) in Example 3, Comparative Example 1, and Comparative Example 2. [Figure 4] 1 is a graph showing the results of thermal desorption analysis in Example 4 of the invention and Comparative Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0031] (Hydrogen charging method) A hydrogen charging method according to one embodiment of the present invention comprises the steps of immersing a metal sample in an electrolyte solution consisting of an organic solvent containing one or both of alkali metal ions and alkaline earth metal ions, having a boiling point above 100°C, and having a hydroxyl group, and electrochemically charging (penetrating) hydrogen into the metal sample by supplying electrons to the metal sample in the electrolyte solution and forming an electrical circuit in which the electrons escape from the surface of the metal sample.

[0032] A typical method for forming the electric circuit includes immersing a counter electrode in the electrolyte, connecting the metal sample and the counter electrode to an external power supply, and applying a voltage that is more negative than the counter electrode to the metal sample as a working electrode from the external power supply.

[0033] [Metal sample] The material constituting the metal sample used in the hydrogen charging method of this embodiment is not particularly limited, and can be any metal material, such as various steels, magnesium, or magnesium alloys. However, when using a metal sample into which hydrogen is difficult to penetrate, the effect of the present invention of increasing the amount of hydrogen charged can be significantly achieved by increasing the electrolyte temperature. For this reason, the metal sample should be made of a material into which hydrogen is difficult to penetrate, specifically, a material with a hydrogen permeability of 1.0 × 10 at 25°C. -15 m 2 It is preferable that the metal sample be made of a material having a hydrogen diffusion coefficient of 1 / s or less. Examples of such metal materials include austenitic stainless steel, nickel, and zinc. Therefore, it is preferable that the metal sample be made of these materials. The hydrogen diffusion coefficient can be determined by an electrochemical hydrogen permeation test or by a method of directly analyzing hydrogen that has permeated the metal material as a gas.

[0034] The shape and size of the metal sample are not particularly limited. The shape of the metal sample may be, for example, a plate or a cylinder. From the viewpoint of efficient hydrogen charging, it is preferable to clean the surface of the metal sample and remove dirt, oxide films, etc.

[0035] [Counter electrode and reference electrode] The material of the counter electrode is not particularly limited, and for example, a platinum or carbon electrode can be used as the counter electrode. However, if the electrolyte contains chloride ions, corrosion of the counter electrode in the high-temperature electrolyte is a concern. In such cases, a carbon electrode is preferably used as the counter electrode to suppress corrosion of the counter electrode and achieve stable hydrogen charging. The shape of the counter electrode is also not particularly limited, and it can be, for example, wire-shaped, rod-shaped, or plate-shaped. If necessary, a reference electrode may be immersed in the electrolyte. When the electrolyte contains chloride ions, a nonaqueous reference electrode, such as a silver-silver chloride electrode (without an encapsulating liquid), can be used as the reference electrode. When the electrolyte does not contain chloride ions, a silver-silver chloride electrode with ethanol containing lithium chloride as an encapsulating liquid can be used (for low-temperature testing). The use of a reference electrode enables hydrogen charging even with potential control. When hydrogen charging is performed with potential control, a potentiostat can be used as the external power source. On the other hand, when hydrogen charging is performed with current control, a galvanostat can be used as the external power source, and the reference electrode can be omitted.

[0036] [Electrolyte] In this embodiment, it is essential that the electrolyte solution contains one or both of alkali metal ions and alkaline earth metal ions, has a boiling point above 100°C, and is composed of an organic solvent having a hydroxyl group. Such an electrolyte solution can be obtained by dissolving one or both of an electrolyte containing alkali metal ions and an electrolyte containing alkaline earth metal ions in an organic solvent having a boiling point above 100°C and a hydroxyl group. Using such an electrolyte solution, hydrogen can be generated on the surface of the metal sample by a metal alkoxide reaction by applying a voltage to the metal sample that is more negative than the counter electrode, thereby charging the metal sample with hydrogen.

[0037] The metal alkoxide reaction is typically the following reaction: M + R-OH → R-OM + 1 / 2H2 M = alkali metal, R = hydrocarbon group M' + 2(R-OH) → M'(RO)2 + H2 M' = alkaline earth metal, R = hydrocarbon group

[0038] The estimated mechanism of hydrogen charging is explained below using an example in which ethylene glycol (HO-C2H4-OH) dissolved in sodium chloride (NaCl) is used as the electrolyte. First, sodium chloride is ionized in the electrolyte as follows: NaCl → Na + + Cl - Then, electrons that escape from the surface of the metal sample are supplied to the electrolyte, causing the following reaction on the surface of the metal sample: HOC2H4OH + e - → HOC2H4O - + 1 / 2H2 (hydrogen generation) Na + + HOC2H4O - → HOC2H4ONa (alkoxide formation) That is, Na + + HOC2H4OH + e - →HOC2H4ONa + 1 / 2H2 The metal alkoxide reaction generates hydrogen on the surface of the metal sample. At the counter electrode, electrons are extracted from chloride ions in the electrolyte, causing the following reaction: 2Cl - - 2e - → Cl2 It is thought that some of the hydrogen (H2) generated in this way dissociates and penetrates into the metal sample as hydrogen atoms.

[0039] According to this embodiment, by using an organic solvent with a boiling point above 100°C as the electrolyte, the electrolyte temperature can be raised higher than conventional methods, and as a result, the amount of hydrogen charged can be increased. Because this embodiment is an electrochemical hydrogen charging method, it is lower cost and simpler than hydrogen charging methods in which a metal sample is placed in a high-pressure hydrogen gas environment.

[0040] Furthermore, it was found that when hydrogen charging is performed at a high electrolyte temperature according to this embodiment, the hydrogen charging rate can be increased and a large amount of hydrogen can be charged in a short period of time compared to when a hydrogen charging method is performed in which the metal sample is placed in a high-pressure hydrogen gas environment at the same high temperature.

[0041] The electrolyte containing alkali metal ions is not particularly limited as long as it dissolves in the organic solvent used in this embodiment to generate alkali metal ions. Examples of the electrolyte include sodium chloride (NaCl), potassium chloride (KCl), lithium chloride (LiCl), potassium acetate (CHCOOK), lithium acetate (CHCOOLi), and rubidium acetate (CHCOORb), and one or more of these can be used.

[0042] The alkaline earth metal ion-containing electrolyte is not particularly limited as long as it dissolves in the organic solvent used in this embodiment to generate alkaline earth metal ions. Examples of the electrolyte include magnesium acetate (Mg(CHCOO)), magnesium chloride (MgCl), etc., and one or more of these can be used.

[0043] The electrolytic solution used in this embodiment may contain trivalent metal ions in addition to or in place of either or both of the alkali metal ions and alkaline earth metal ions, as long as hydrogen can be generated on the surface of a metal sample by a metal alkoxide reaction. Such an electrolytic solution can be obtained by dissolving an electrolyte containing trivalent metal ions in a predetermined organic solvent. The electrolyte containing trivalent metal ions is not particularly limited as long as it dissolves in the organic solvent used in this embodiment and generates trivalent metal ions. Examples of the electrolyte include aluminum acetate (Al(CH3COO)3) and aluminum chloride (AlCl3), and one or more of these can be used.

[0044] The organic solvent used in this embodiment is not particularly limited as long as it has a boiling point above 100°C and a hydroxy group, but is preferably an alcohol from the viewpoint of favorably inducing the metal alkoxide reaction.

[0045] It is essential that the boiling point of the organic solvent, preferably alcohol, used in this embodiment is above 100°C, preferably 120°C or higher, and more preferably 150°C or higher. There is no particular upper limit to the boiling point, but from the viewpoint of preventing structural changes in the metal sample, it is preferably 200°C or lower. In this specification, the "boiling point" means the boiling point at 1 atmosphere.

[0046] The alcohol used in this embodiment is one that is not easily volatile, specifically, 3.2 × 10 3 It is preferable that the hydrogen charging liquid has a vapor pressure of 10 Pa or less. Although the hydrogen charging rate is higher than that of hydrogen charging using high-pressure hydrogen gas, even in this embodiment, it takes a certain amount of time, especially when hydrogen charging a metal sample into which hydrogen is difficult to absorb. In this case, if alcohol, which does not volatilize easily, is used, hydrogen charging can be performed efficiently without replenishing the electrolyte.

[0047] As the alcohol having the above boiling point and vapor pressure, the alcohol used in this embodiment can be a linear or branched, dihydric or trihydric lower alcohol having 10 or less carbon atoms, more preferably 6 or less carbon atoms. More specifically, it is preferable to use one or more alcohols selected from the group consisting of ethylene glycol (boiling point: 197°C, vapor pressure: 7 Pa (20°C)), propylene glycol (boiling point: 188°C, vapor pressure: 10.7 Pa (20°C)), and glycerin (boiling point: 290°C, vapor pressure: 0.01 Pa (25°C)).

[0048] The concentration of the electrolyte in the organic solvent is preferably below the solubility of the electrolyte and within a concentration range that provides good stability of the current and voltage during hydrogen charging. For example, in the case of sodium chloride and ethylene glycol, the sodium chloride concentration is preferably 1% by mass or more and 7% by mass or less relative to the ethylene glycol. If the concentration is 7% by mass or less, there is no insoluble sodium chloride that has become insoluble in ethylene glycol, and the potential or current during hydrogen charging is reliably stable. If the concentration is 1% by mass or more, there is no increase in electrical resistance, and the current or voltage is reliably stable. Within this concentration range, if it is desired to increase the current under conditions of a constant potential, it is preferable to increase the electrolyte concentration further in order to reduce the solution resistance.

[0049] From the viewpoint of increasing the amount of hydrogen charge, the electrolyte preferably further contains a cyanide compound (a compound containing cyanide ions) as an additive. Examples of this additive include ammonium thiocyanate (NH4SCN), potassium thiocyanate (KSCN), etc., and one or more of these can be used. From the viewpoint of enhancing the hydrogen charge effect, the concentration of the additive is preferably in the range of 0 to 5 g / L.

[0050] The temperature of the electrolyte is not particularly limited, but is preferably above 0°C, more preferably above 85°C, even more preferably above 100°C, and most preferably above 120°C. In this embodiment, since a high-boiling organic solvent is used as the electrolyte, the amount of hydrogen charge can be increased by increasing the temperature of the electrolyte. On the other hand, the temperature of the electrolyte is preferably below the boiling point of the organic solvent.

[0051] [Hydrogen charging process] After assembling the electrochemical cell, the temperature of the electrolyte is raised, and after the temperature of the electrolyte reaches a predetermined temperature, the sample is placed in the electrolyte and hydrogen charging is performed. During hydrogen charging, it is preferable to ventilate the space above the cell (the space above the electrolyte) with dry nitrogen or air. If necessary, a cooling tube is installed above the cell, and the gas generated during charging is preferably vented from the outlet of the cooling tube through an absorption solution (such as a sodium hydroxide solution) to a local exhaust system.

[0052] The (ambient) temperature of the hydrogen charging environment is not particularly limited and can be room temperature. However, when the electrolyte is heated to a temperature higher than room temperature, it is preferable to heat the electrolyte with a heater rather than controlling the ambient temperature.

[0053] The hydrogen charging method may be potential control using a potentiostat or current control using a galvanostat. After hydrogen charging, the external power supply is turned off, and if necessary, the cell is brought into a local exhaust facility and the metal sample is removed from the electrolyte.

[0054] [Cleaning and storage] After hydrogen charging, it is preferable to wash the metal sample with running water and then with acetone. After washing with acetone, the metal sample is lightly wiped with a nonwoven cloth and stored in liquid nitrogen.

[0055] [Other embodiments] In addition to hydrogen charging methods that use an external power source to form an electrical circuit, a hydrogen charging method can also be performed that utilizes bimetallic corrosion between a metal sample and a more noble metal. Specifically, by contacting a metal sample with a more noble metal (a dissimilar metal) and immersing them in an electrolyte, electrons are supplied to the metal sample in the electrolyte, and electrons are removed from the surface of the metal sample, forming an electrical circuit. A "metal more noble than the metal sample" refers to a metal with a lower corrosion potential than the metal sample. Suitable dissimilar metals include, for example, Mg and Al, which increase the potential difference with the metal sample. The dissimilar metal may be, for example, plate-shaped or granular, such as a pellet. However, a pellet-like granular shape is preferred to ensure sufficient surface area. Hydrogen charging can be achieved by simply immersing a metal sample in contact with a dissimilar metal in an electrolyte. Bimetallic corrosion generates a metal alkoxide reaction on the surface of the metal sample, allowing hydrogen to be charged. In this embodiment, hydrogen charging can be achieved using a simple immersion method without using an external power source. However, it is more difficult to control the amount of hydrogen charged than when an external power source is used, and charging takes longer.

[0056] (Hydrogen embrittlement property evaluation method) A hydrogen embrittlement property evaluation method according to one embodiment of the present invention is characterized in that a hydrogen embrittlement property evaluation test is performed on a metal sample that has been charged with hydrogen by the hydrogen charging method according to the present embodiment described above. The hydrogen embrittlement property evaluation test can be performed in the atmosphere or while hydrogen charging is continued.

[0057] The (ambient) temperature when conducting the hydrogen embrittlement property evaluation test is not particularly limited. For metal samples with a small hydrogen diffusion coefficient, hydrogen is less likely to dissipate in the atmosphere even after charging, so the hydrogen embrittlement property evaluation test can be conducted in the atmosphere. Furthermore, when conducting the test while charging hydrogen, an appropriate electrolyte for charging is selected depending on the test temperature, and the hydrogen embrittlement property evaluation test is conducted.

[0058] The hydrogen embrittlement property evaluation test may be any known or arbitrary test method, and is not particularly limited, but may be one or more of (i) a test using a tracer hydrogen analysis method, (ii) a physical property test in which a metal sample is subjected to one or more stresses of tension, compression, bending, shear, and torsion, and (iii) a hydrogen permeation test.

[0059] [Tracer hydrogen analysis method] Tracer hydrogen analysis is a technique in which hydrogen is charged to lattice defects such as dislocations, vacancies, and grain boundaries in a metal sample, and the charged hydrogen is analyzed using a thermal desorption analyzer. The resulting profile is used to determine the lattice defect profile in the metal sample. Examples of thermal desorption analyzers include thermal desorption spectrometry (TDS), which uses a mass spectrometer as the detection system, and thermal desorption analysis (TDA), which uses a gas chromatograph as the detection system. The conditions for measuring the hydrogen concentration in a metal sample using TDS or TDA are not particularly limited. The amount of released hydrogen can be measured by heating the metal sample from a starting temperature of -100 to -50°C at a temperature increase rate of 50 to 100°C / h to a final temperature of 200 to 600°C.

[0060] When this embodiment is applied to tracer hydrogen analysis, the following effects can be obtained. Hydrogen can be charged at high temperatures, and the sample can be stored in liquid nitrogen in a short time after hydrogen charging, compared to hydrogen charging methods using high-pressure hydrogen gas. This prevents hydrogen from diffusing from the metal sample after hydrogen charging, making it possible to measure the hydrogen concentration with high accuracy and ultimately to evaluate hydrogen embrittlement characteristics with high precision. In particular, in tracer hydrogen analysis, it is preferable to use a thin metal sample with a thickness of 0.5 mm or less so that the peak temperature is proportional to the trap energy (i.e., so that the thermal diffusion rate is limited). However, when the metal sample is thin, hydrogen is likely to diffuse after hydrogen charging, so the effect of this embodiment in suppressing hydrogen diffusion is significant.

[0061] [Stress load physical property test] One or more stresses of tension, compression, bending, shear, and torsion are applied to the metal sample. The stress may be applied to the metal sample after hydrogen is charged to the metal sample by the above-mentioned method, or may be applied while hydrogen is being charged. The type of stress applied to the metal sample is not particularly limited, and may be any of tensile stress, compressive stress, bending stress, shear stress, and torsional stress. These stresses may further be either static stress or dynamic stress. Then, for example, by measuring the stress at which the metal sample breaks, it is possible to directly evaluate the hydrogen embrittlement properties of the metal sample.

[0062] When this embodiment is applied to stress load physical property testing, the following effects can be obtained. Hydrogen charging can be performed at high temperatures, and the sample can be stored in liquid nitrogen in a short time after hydrogen charging, compared to hydrogen charging methods using high-pressure hydrogen gas. This prevents hydrogen from diffusing from the metal sample after hydrogen charging, which results in highly accurate measurement of hydrogen concentration and ultimately enables highly accurate evaluation of hydrogen embrittlement characteristics.

[0063] [Hydrogen permeation test] A hydrogen permeation test is a technique in which hydrogen is charged onto one side of a plate-shaped metal sample, permeates through the interior of the metal sample, and the hydrogen released from the other side is detected. The hydrogen charging method of this embodiment can be applied as a method for charging hydrogen onto one side of a metal sample. On the hydrogen detection side, the permeated hydrogen may be measured electrochemically or evaluated as a gas using a gas chromatograph or the like. However, when the hydrogen charging method of this embodiment is performed at a high temperature of 85°C or higher, hydrogen is detected as a gas using a gas chromatograph or the like. The hydrogen permeation test can evaluate the penetration rate and diffusion rate of hydrogen into a metal sample.

[0064] When this embodiment is applied to a hydrogen permeation test, the following effects can be obtained: By carrying out hydrogen charging and hydrogen permeation tests at high temperatures, the hydrogen diffusion coefficient can be plotted with high accuracy. [Example]

[0065] [Experimental Example 1] (Example 1) A hydrogen charging test was conducted on a metal sample (4) using the electrochemical cell shown in Figure 1. The metal sample (4) was made of SUS316 stainless steel (austenitic stainless steel) and was a thin plate measuring 20 mm in length, 10 mm in width, and 1.86 mm in thickness. The metal sample (4) was spot-welded to a stainless steel wire (5). An electrolyte (3) was placed in a separable flask (1) placed in a room temperature (25°C) atmosphere. The electrolyte (3) was a liquid prepared by dissolving 10 g of sodium chloride in 400 mL of ethylene glycol. A mantle heater (10) was placed around the separable flask (1) to heat the electrolyte. The temperature of the electrolyte was measured with a thermocouple (8) and maintained at 100°C. A carbon electrode (7) was used as the counter electrode.

[0066] A lid (2) was attached to a separable flask (1), and a carbon electrode (7), a glass tube (6) with a stainless steel wire (5) passing through it, a thermocouple (8), a glass tube (11), and a cooling tube (12) were fixed thereto. The metal sample (4) and the carbon electrode (7) were immersed in the electrolyte (3), and the carbon electrode (7) and the stainless steel wire (5) connected to the metal sample (4) were connected to a potentiogalvanostat (9). The potentiogalvanostat (9) applied a voltage to the metal sample (4) that was more negative than the counter carbon electrode (7) under constant current control, electrochemically charging the metal sample (4) with hydrogen. The current density was 1 mA / cm. 2 The hydrogen charging time was 6 days (144 hours). During the hydrogen charging, air was ventilated into the upper space in the cell through the glass tube (11).

[0067] After hydrogen charging, the metal sample was removed from the electrolyte, washed with running water, and then ultrasonically cleaned with acetone. The metal sample was then lightly wiped with a Kimwipe and immediately stored in liquid nitrogen. The time from removing the metal sample from the electrolyte to placing it in liquid nitrogen was approximately 3 minutes.

[0068] The metal sample was then removed from the liquid nitrogen and the hydrogen concentration in the metal sample was measured. Specifically, the frozen metal sample was placed in a TDA (JTF-20AL, manufactured by J Science Labs, Inc.) and the amount of hydrogen released was measured while the metal sample was heated from -100°C to 600°C at a heating rate of 100°C / h. The results of this hydrogen analysis are shown in Figure 2. The values ​​in the graph (unit: ppm) indicate the amount of hydrogen.

[0069] (Example 2) Hydrogen charging and hydrogen concentration measurement were performed in the same manner as in Example 1, except that the electrolyte (3) was a liquid prepared by dissolving 10 g of sodium chloride in 400 mL of ethylene glycol and further adding 2 g of ammonium thiocyanate (NH4SCN). The hydrogen analysis results are shown in Figure 2. Note that adding ammonium thiocyanate to the electrolyte generates a high concentration of hydrogen cyanide. Therefore, a 1N aqueous solution of sodium hydroxide was placed in a glass flask (14), and the gas in the cell was introduced into the aqueous solution of sodium hydroxide via a cooling tube (12) attached to the lid (2) through a Teflon® tube (13), thereby absorbing the hydrogen cyanide. The gas from which the hydrogen cyanide had been removed was discharged through a Teflon® tube (15).

[0070] (Example 3) Current density: 3A / cm 2 Except for this, hydrogen charging and measurement of hydrogen concentration were carried out in the same manner as in Invention Example 2. The results of the hydrogen analysis are shown in FIG.

[0071] (Considerations of Examples 1 to 3) As shown in Figure 2, by using ethylene glycol with sodium chloride dissolved in it as the electrolyte and heating the electrolyte to a high temperature of 100°C, it was possible to electrochemically charge 3 ppm of hydrogen in Example 1 and 30 ppm in Example 3 over a period of 6 days, even into austenitic stainless steel, which has a small hydrogen diffusion coefficient.

[0072] (Comparative Examples 1 and 2) SUS316L steel was charged with high-pressure hydrogen gas, and the results of measuring the hydrogen concentration are shown as Comparative Examples 1 and 2. Comparative Example 1 had a sample thickness of 0.25 mm, a hydrogen gas pressure of 45 MPa, a gas temperature of 85°C, and a hydrogen gas charging time of 300°C, and is based on the data shown in Fig. 2 of "Effect of Surface Hydrogen Concentration on Hydrogen Embrittlement Susceptibility of Stainless Steels," by Tomohiko Omura et al., Zairyo-to-Kankyo, 55, 537-543 (2006). Comparative Example 2 had a sample thickness of 0.33 mm, a hydrogen gas pressure of 78 MPa, a gas temperature of 110°C, and a hydrogen gas charging time of 100°C, and is based on the data shown in Fig. 9(b) of "Fatigue Crack Growth Behavior and Hydrogen Penetration Characteristics of Austenitic Stainless Steels Exposed to High-Pressure Hydrogen Gas Atmospheres," by Yoji Mine et al., Tetsu-to-Hagane, Vol. 93 (2007), No. 3, pp. 247-256.

[0073] In Figure 3, the horizontal axis is t / L 2 1 is a graph plotting the results of Example 3, Comparative Example 1, and Comparative Example 2, with the vertical axis representing the amount of detected hydrogen (t: charging time (hr), L: sample thickness (mm)). The slope of this graph represents the hydrogen penetration rate. While the hydrogen penetration rate of Comparative Example 2, with a hydrogen gas pressure of 78 MPa, is higher than that of Comparative Example 1, with a hydrogen gas pressure of 45 MPa, the hydrogen charging method of Example 3, with a slope of approximately 90°, demonstrates an even higher hydrogen penetration rate than Comparative Example 2. In the present invention, the electrolyte can be heated to a high temperature, allowing electrochemical hydrogen charging. Furthermore, a larger amount of hydrogen was able to be dissolved in the austenitic stainless steel in a shorter time and more simply than in Comparative Examples 1 and 2, which involve hydrogen penetration in the gas phase.

[0074] [Experimental Example 2] (Example 4) Current density is 2A / cm 2 Except for changing the hydrogen charging time to 3 days (72 hours), hydrogen charging and hydrogen concentration measurement were carried out in the same manner as in Invention Example 2. The results of the hydrogen analysis are shown in FIG.

[0075] (Comparative Example 3) Except for the electrolyte being a liquid prepared by adding 3 g / L of ammonium thiocyanate (NH4SCN) to a 3 mass % aqueous sodium chloride solution and the electrolyte temperature being room temperature (25°C), hydrogen charging and measurement of hydrogen concentration were carried out in the same manner as in Invention Example 4. The results of the hydrogen analysis are shown in Figure 4.

[0076] 4, in Example 4, the peak temperature was shifted to a higher temperature by approximately 220°C compared to Comparative Example 3, and more hydrogen could be charged than in Comparative Example 3. The shift in the peak temperature to a higher temperature indicates that hydrogen penetrated deeper into the metal sample. [Industrial Applicability]

[0077] The hydrogen charging method according to the present invention can be applied to various hydrogen embrittlement property evaluation methods, such as tests using tracer hydrogen analysis, physical property tests in which metal samples are subjected to one or more stresses of bending, compression, tension, and torsion, and hydrogen permeation tests. [Explanation of symbols]

[0078] 1 separable flask 2 Lid 3 Electrolyte 4 Metal sample (working electrode) 5 Stainless steel wire 6 glass tubes 7 Carbon electrode (counter electrode) 8 Thermocouples 9 Potentiogalvanostat 10. Mantle heater 11 Glass tube 12 Cooling pipe 13 Teflon tube 14 glass flasks 15 Teflon tube

Claims

1. immersing a metal sample in an electrolytic solution comprising an organic solvent containing one or both of alkali metal ions and alkaline earth metal ions, having a boiling point above 100°C, and having a hydroxyl group; a step of electrochemically charging the metal sample with hydrogen by forming an electric circuit in which electrons are supplied to the metal sample in the electrolytic solution and the electrons are released from the surface of the metal sample; and A hydrogen charging method, wherein the temperature of the electrolyte is 85°C or higher and lower than the boiling point of the organic solvent.

2. Immersing a counter electrode in the electrolyte solution; Connecting the metal sample and the counter electrode to an external power source, A voltage more negative than the counter electrode is applied to the metal sample as a working electrode by the external power source. The hydrogen charging method according to claim 1, wherein the electric circuit is formed by:

3. 2. The hydrogen charging method according to claim 1, wherein the temperature of the electrolytic solution is 100°C or higher and lower than the boiling point of the organic solvent.

4. The hydrogen charging method according to claim 1 , wherein the organic solvent is an alcohol.

5. The alcohol has a viscosity of 3.2 x 10 at 25°C. ３ The hydrogen charging method according to claim 4, wherein the hydrogen has a vapor pressure of 100 Pa or less.

6. The hydrogen charging method according to claim 4, wherein the alcohol is one or more selected from the group consisting of ethylene glycol, propylene glycol, and glycerin.

7. The metal sample has a viscosity of 1.0 × 10 at 25 °C. －１５ m ２ 2. The hydrogen charging method according to claim 1, wherein the hydrogen diffusion coefficient is 1 / s or less.

8. The hydrogen charging method according to claim 7, wherein the metal sample is an austenitic stainless steel.

9. The hydrogen charging method according to claim 1 , wherein the electrolyte further contains a cyanide compound.

10. A hydrogen embrittlement property evaluation method, comprising: conducting a hydrogen embrittlement property evaluation test on the metal sample charged with hydrogen by the hydrogen charging method according to any one of claims 1 to 9.

11. The hydrogen embrittlement property evaluation method according to claim 10 , wherein the hydrogen embrittlement property evaluation test is a test using a tracer hydrogen analysis method.

12. 11. The hydrogen embrittlement property evaluation method according to claim 10, wherein the hydrogen embrittlement property evaluation test is a physical property test performed by applying one or more stresses of tension, compression, bending, shear, and torsion to the metal sample.

13. The hydrogen embrittlement property evaluation method according to claim 10 , wherein the hydrogen embrittlement property evaluation test is a hydrogen permeation test.

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