Electrochemical measurement method and apparatus for hydrogen penetration into non-ferrous metal materials

Abstract

To provide a measurement method of an amount of hydrogen intruded into metal using a test solution optimal for a Mg alloy, which can suppress reduction in residual current on a hydrogen detection side and thickness reduction due to corrosion on a hydrogen introduction side.SOLUTION: When one surface of an analyte 2 composed of a Mg-based metallic material is determined as a surface where hydrogen controlled to a potential or current to cause electrolysis of water is intruded, and the other surface is determined as a hydrogen detection surface controlled to a potential in which a hydrogen atom is oxidized to a hydrogen ion, on the hydrogen intrusion surface side, a first electrochemical cell 1a is provided; the inside of the first electrochemical cell 1a is filled with a saturated Mg (OG)2 aqueous solution; a first reference electrode 3a and a first counter electrode 4a are installed; on the hydrogen detection surface side, a second electrochemical cell 1b is provided; the inside of the second electrochemical cell 1b is filled with an organic solvent which dissolves in water and 0.01% or more and 50% or less of a solution obtained by dissolving an aqueous solution in the organic solvent; a second reference electrode 3b and a second counter electrode 4b are installed; and a first power source 6a and a second power source 6b are provided.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to an electrochemical measurement method and apparatus for measuring hydrogen penetration into a non-ferrous metal material, which can calculate the diffusion coefficient of hydrogen in the non-ferrous metal material at room temperature. [Background technology]

[0002] In recent years, with the increasing strength of metallic materials, the risk of "hydrogen embrittlement," in which hydrogen penetrates metallic materials and causes them to become brittle, is on the rise. To elucidate the mechanism of hydrogen embrittlement and develop new materials with improved resistance to hydrogen embrittlement, a method for determining the diffusion rate of hydrogen within metallic materials is necessary. Conventionally, electrochemical hydrogen permeation tests have been used as a method for determining the diffusion rate of hydrogen within steel materials (Patent Documents 1 and 2, Non-Patent Documents 1 and 2, etc.).

[0003] Thus, the electrochemical hydrogen permeation method is a technique that detects hydrogen diffused in a sample by measuring the increase or decrease in electric current. Detailed descriptions of determining the hydrogen diffusion rate in steel materials using the electrochemical hydrogen permeation method can be found, for example, in Non-Patent Documents 1 and 2. Because the current caused by hydrogen obtained on the hydrogen detection side is very small (generally around 10 μA / cm²), the current is very small. 2 (See below) It is necessary to minimize the residual current on the detection side (the dissolution current of iron that flows when immersed in an aqueous solution) as much as possible (generally 0.1 μA / cm²). 2 (See below) Up until now, in steel materials, measures have been taken such as plating the detection surface with Pd or Ni, or passivating the surface by using NaOH in an aqueous solution.

[0004] In recent years, the use of non-ferrous light metal materials such as Al alloys and Mg alloys, which have superior specific strength and are lighter than steel, has been increasing as a structural material to replace steel. Until now, the problem of hydrogen embrittlement of metallic materials has been reported mainly only for high-strength steel, and most hydrogen embrittlement research has targeted steel materials. However, with the recent expansion of the use of non-ferrous materials, research on hydrogen embrittlement of these materials is accelerating. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent No. 6172097 [Patent Document 2] Japanese Patent No. 5777098 [Non-Patent Literature]

[0006] [Non-Patent Literature 1] Toru Mizukaze, Zairyo to Kankyo (Materials and Environment), Vol. 63, pp. 3-9 (2014) [Non-Patent Literature 2] Masatoshi Sakairi, Zairyo to Kankyo (Materials and Environment), Vol. 67, pp. 191-196 (2018) [Non-Patent Literature 3] M. A. V. Devanathan, Z. Stachurski; Proc. Roy. Soc. London, Ser. A, 270, 90 (1962) [Summary of the Invention] [Problems to be Solved by the Invention]

[0007] Therefore, when applying hydrogen embrittlement research to non-ferrous metal materials represented by Al alloys and Mg alloys, the implementation of electrochemical hydrogen permeation tests that can conveniently determine the hydrogen diffusion rate in non-ferrous metal materials is expected to increase in the future. However, unlike steel materials, hydrogen permeation testing of non-ferrous metal materials is extremely difficult. The reason for this is that Al alloys and Mg alloys, which are typical examples of non-ferrous metal materials, are easily corroded. As mentioned above, the residual current of the sample on the hydrogen detection side is required to be 0.1 μA / cm 2 or less. However, the residual current of Al alloys and Mg alloys in aqueous solutions is 0.1 μA / cm 2 it is difficult to reduce the residual current to the aforementioned value or less, and no method for uniformly and conveniently applying Pd plating or Ni plating, as used for steel materials, has been established. Furthermore, regarding the hydrogen introduction side, even though a reducing environment is created by applying a cathode current or cathode potential, Al alloys and Mg alloys corrode, causing the sample to gradually thin, making it impossible to determine the accurate hydrogen diffusion rate.

[0008] In other words, the specific challenge is to simultaneously solve the following two problems necessary for conducting electrochemical hydrogen permeation tests on non-ferrous metal materials. (1) Residual current on the hydrogen detection side: 0.1 μA / cm 2 below, (2) Suppression of corrosion thinning and corrosion product formation on the hydrogen introduction side. This invention aims to solve these problems by proposing a novel electrochemical hydrogen permeation method and apparatus for measuring hydrogen penetration into non-ferrous metal materials, using a test solution optimized for non-ferrous metal materials that can suppress the decrease in residual current on the hydrogen detection side and the thinning of the material due to corrosion on the hydrogen introduction side. [Means for solving the problem]

[0009] [1] The present invention provides a method for measuring the amount of hydrogen that penetrates into a non-ferrous metal material, as shown in Figure 1, for example, by measuring the amount of hydrogen that is generated as a result of corrosion of a subject 2 made of a non-ferrous metal material and penetrates into the metal, using an electrochemical hydrogen permeation method, wherein one surface of the subject 2 is a hydrogen penetration surface controlled to a potential or current at which hydrogen generation by electrolysis of water occurs, and the other surface is a hydrogen detection surface controlled to a potential at which hydrogen atoms are oxidized to hydrogen ions, A first electrochemical cell 1a is provided on the hydrogen intrusion side, and a hydrogen content of 1 μS / cm or more is present inside the first electrochemical cell 1a at 25°C, resulting in a hydrogen content of 2 × 10⁻¹⁶. 5 The device is filled with an aqueous solution having an electrical conductivity of μS / cm or less, and a first reference electrode 3a and a first counter electrode 4a are installed. A second electrochemical cell 1b is provided on the hydrogen detection surface side, and the inside of the second electrochemical cell 1b is filled with a water-soluble organic solvent and an aqueous solution of the organic solvent containing 0.01% to 50%, and a second reference electrode 3b and a second counter electrode 4b are installed. In the first electrochemical cell 1a, the first power source 6a is connected to the first reference electrode 3a and the first counter electrode 4a. When the first power source 6a performs potential control, it applies a potential higher than -10V and lower than the immersion potential of the analyte 2; when the first power source 6a performs current control, it applies a constant current of -0.01mA / cm 2 2 or more and -100mA / cm 2 2 or less, in the second electrochemical cell 1b, the second power source 6b is connected to the second reference electrode 3b and the second counter electrode 4b, and the second power source 6b applies a potential of 0V or more and 1V or less relative to a standard hydrogen electrode, wherein the residual current 24 hours after immersion of the analyte 2 is -0.1μA / cm 2 2 or more and 0.1μA / cm 2 2 or less.

[0010] [2] In the method [1] for measuring the amount of hydrogen penetrating into a non-ferrous metal material according to the present invention, preferably, the non-ferrous metal material is beryllium (Be), magnesium (Mg), aluminum (Al), calcium (Ca), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), zinc (Zn), yttrium (Y), zirconium (Zr), or an alloy containing 50 atomic% or more of any of these non-ferrous metal elements, and is preferably a non-ferrous metal element or alloy having a lower standard electrode potential than iron (Fe). [3] In the method [1] or [2] for measuring the amount of hydrogen penetrating into a non-ferrous metal material according to the present invention, preferably, the non-ferrous metal material is an Al-based metal material, and the aqueous solution filled in the first electrochemical cell 1a is preferably a citrate buffer solution (pH 5-9) or a borate buffer solution (pH 5-9). [4] In the method [1] or [2] for measuring the amount of hydrogen penetrating into a non-ferrous metal material according to the present invention, preferably, the non-ferrous metal material is an Mg-based metal material, and the aqueous solution filled in the first electrochemical cell 1a is preferably 0.001M to saturated NaOH aqueous solution, 0.001M to saturated MgSO4 aqueous solution, or 0.001M to saturated Mg(OH)2 aqueous solution. [5] In the method for measuring the amount of hydrogen that penetrates into a non-ferrous metal material of the present invention [1] to [4], preferably, the water-soluble organic solvent is at least one of ethanol, methanol, 2-propanol, and ethylene glycol, and the amount of the aqueous solution is 0.01% or more and 50% or less.

[0011] [6] The present invention provides a device for measuring the amount of hydrogen penetrating into a non-ferrous metal material, as shown in Figure 1, for example, and is a device for measuring the amount of hydrogen generated as a subject 2 made of a non-ferrous metal material corrodes and penetrates into the metal using an electrochemical hydrogen permeation method, wherein one side of the subject 2 is set to a potential at which electrolysis of water occurs and hydrogen penetrates, and the other side is set to a hydrogen detection surface controlled to a potential or current at which hydrogen atoms are oxidized to hydrogen ions, The system comprises a first electrochemical cell 1a provided on the hydrogen intrusion side, with a first reference electrode 3a and a first counter electrode 4a immersed in a first electrolyte 7a, and a second electrochemical cell 1b provided on the hydrogen detection side, with a second reference electrode 3b and a second counter electrode 4b immersed in a second electrolyte 7b, The first electrolyte 7a has a viscosity of 1 μS / cm or more at 25°C, and is 2 × 10⁻⁶. 5 It is an aqueous solution having an electrical conductivity of μS / cm or less, and which is filled inside the first electrochemical cell 1a. The second electrolyte 7b is prepared by dissolving water in a soluble organic solvent and an aqueous solution of the above organic solvent containing 0.01% to 50%, and is filled inside the second electrochemical cell 1b. In the first electrochemical cell 1a, the first power supply 6a is connected to the first reference electrode 3a and the first counter electrode 4a. When the first power supply is potential-controlled, a potential higher than -10V and lower than the immersion potential of the subject 2 is applied. When the first power supply is current-controlled, -0.01mA / cm² is applied. 2 More than -100mA / cm 2 Apply the following constant current, In the second electrochemical cell 1b, the second power supply 6b is connected to the second reference electrode 3b and the second counter electrode 4b, and the second power supply provides a potential of 0V to 1V relative to the standard hydrogen electrode. The residual current of subject 2 after 24 hours of immersion was -0.1 μA / cm². 2 More than 0.1μA / cm 2 The following are the items.

[0012] [7] The present invention provides a method for measuring the amount of hydrogen that penetrates into a non-ferrous metal material, as shown in Figure 11, for example, and is a method for measuring the amount of hydrogen that is generated as a result of corrosion of a non-ferrous metal material and penetrates into the metal, using an electrochemical hydrogen permeation method, wherein one side of the material is the corrosion surface and the other side is the hydrogen detection surface controlled to a potential at which hydrogen atoms are oxidized to hydrogen ions, The aforementioned corrosive surface is one of the following: a surface exposed to the atmosphere and subjected to atmospheric corrosion, a surface in contact with water vapor and subjected to water vapor corrosion, or a surface subjected to aqueous solution corrosion. An electrochemical cell 1c is provided on the hydrogen detection surface side, and the inside of the electrochemical cell 1c is filled with an organic solvent in which water is soluble and an aqueous solution of the above organic solvent in a concentration of 0.01% to 50%, and a reference electrode 3c and a counter electrode 4c are installed. In electrochemical cell 1c, power supply 6c is connected to the reference electrode 3c and the counter electrode 4c, and power supply 6c provides a potential between 0V and 1V relative to the standard hydrogen electrode. The residual current of subject 2 after 24 hours of immersion was -0.1 μA / cm². 2 More than 0.1μA / cm 2 The following are the items.

[0013] [8] In the method for measuring the amount of hydrogen entering into a non-ferrous metal material of the present invention [7], preferably the non-ferrous metal material is beryllium (Be), magnesium (Mg), aluminum (Al), calcium (Ca), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), zinc (Zn), yttrium (Y), zirconium (Zr), or an alloy containing 50 atomic percent or more of these non-ferrous metal elements, and is a non-ferrous metal element or alloy with a standard electrode potential lower than that of iron (Fe). [9] In the method for measuring the amount of hydrogen that penetrates into a non-ferrous metal material of the present invention [7] or [8], preferably the water-soluble organic solvent is at least one of ethanol, methanol, 2-propanol, and ethylene glycol, and the amount of the aqueous solution is 0.01% or more and 50% or less.

[0014]

[10] The present invention provides a device for measuring the amount of hydrogen penetrating into a non-ferrous metal material, as shown in Figure 11, for example, and is a device for measuring the amount of hydrogen generated as a subject made of a non-ferrous metal material corrodes and penetrates into the metal using an electrochemical hydrogen permeation method, wherein one side of the subject is the corroded surface and the other side is the hydrogen detection surface controlled to a potential at which hydrogen atoms are oxidized to hydrogen ions, An environment open to the atmosphere, a water vapor environment, or an aqueous solution corrosion environment is provided on the corrosive surface side. The system includes an electrochemical cell 1c provided on the hydrogen detection surface side, in which the reference electrode 3c and counter electrode 4c are immersed in a third electrolyte 7c, The third electrolyte 7c is prepared by dissolving water in a soluble organic solvent and an aqueous solution of 50% or less in the above organic solvent, and is filled inside the electrochemical cell 1c. In the electrochemical cell 1c, the power supply 6c is connected to the reference electrode 3c and the counter electrode 4c, and the power supply 6c provides a potential of 0V to 1V relative to the standard hydrogen electrode. The residual current of subject 2 after 24 hours of immersion was -0.1 μA / cm². 2 More than 0.1μA / cm 2 The following are the items. [Effects of the Invention]

[0015] The present invention's method for measuring the amount of hydrogen penetrating into non-ferrous metal materials allows for the measurement of the hydrogen diffusion coefficient due to hydrogen penetration in a room-temperature aqueous solution environment. Therefore, it is possible to measure the hydrogen diffusion coefficient in actual usage environments (i.e., hydrogen penetrating due to corrosion) with small error. Furthermore, since inexpensive and easy-to-handle organic solvents or aqueous solutions are used, the tests are easy to conduct and do not require the introduction of expensive equipment. According to the present invention's method for measuring the amount of hydrogen penetrating into a non-ferrous metal material, by using an organic solvent, the residual current is 0.1 μA / cm² in a short time immediately after immersion. 2 The following can be demonstrated, which means that waiting times can be significantly reduced. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic diagram of the electrochemical hydrogen permeation test apparatus (Devanathan-Stachurski cell) used in the present invention. [Figure 2] This figure shows the residual current of pure iron when polarized in each solution, illustrating one embodiment and a comparative example of the present invention. [Figure 3] This figure shows the hydrogen permeation current of pure iron, illustrating one embodiment of the present invention. [Figure 4] This figure shows the residual current of polarized pure Mg in each solution, illustrating one embodiment and a comparative example of the present invention. [Figure 5] This figure shows an embodiment of the present invention, illustrating the surface change of pure Mg on the hydrogen introduction side, where (A) is the surface of the sample when saturated Mg(OH)2 is used, (B) is the cross-sectional shape at the white dotted line in (A), and (C) is a vertically enlarged view of (B). [Figure 6] The figure shows a comparative example of the present invention, where (A) shows the surface of the subject when a 0.1 M NaOH aqueous solution is used, and (B) shows the cross-sectional shape at the white dotted line portion of (A). [Figure 7] The figure shows a comparative example of the present invention, where (A) shows the surface of the sample when a 0.1 M MgSO4 aqueous solution is used, and (B) shows the cross-sectional shape at the white dotted line in (A). [Figure 8] This figure shows the hydrogen permeation current of pure Mg and AZ31, illustrating one embodiment of the present invention, with (A) showing a linear axis and (B) showing a logarithmic axis. [Figure 9] This figure shows the long-term hydrogen permeation current of AZ31, illustrating one embodiment of the present invention, with (A) showing a linear horizontal axis and (B) showing a logarithmic horizontal axis. [Figure 10]This figure shows the hydrogen permeation current of pure Al, illustrating one embodiment of the present invention. [Figure 11] This is a schematic diagram of an electrochemical hydrogen permeation test apparatus (improved Devanathan-Stachurski cell) illustrating another embodiment of the present invention. [Modes for carrying out the invention]

[0017] Examples of the present invention are shown below. The samples used were pure Mg, AZ31 (Mg alloy), and pure Al as examples, and pure iron as a comparative example. In this specification, potential is expressed in terms of SHE, such as ○V (vs. SHE). SHE refers to the Standard Hydrogen Electrode.

[0018] The present invention provides a method for measuring the amount of hydrogen that penetrates into a metal. This method applies the principle of electrochemical hydrogen permeation to measure the amount of hydrogen that is generated and penetrates into a metal material during corrosion. By exposing the surface of the metal material specimen on the hydrogen penetration side to a corrosive environment, hydrogen generated during corrosion penetrates into the metal material specimen. The amount of hydrogen that penetrates is then measured by extracting the hydrogen from the opposite side.

[0019] The electrochemical hydrogen permeation method is a technique developed in 1962 by Devanathan and Stachurski (Non-Patent Literature 3). As schematically shown in Figure 1, two electrolytic cells 1a and 1b are arranged facing each other with a single sample 2 in between. In this case, the sample surface of the left electrolytic cell 1a is cathode-polarized with a constant potential or constant current to generate and charge hydrogen, while the sample 2 in the right electrolytic cell 1b is anode-polarized with a constant potential to oxidize the hydrogen that has permeated the sample 2 into hydrogen ions, and the amount of permeated hydrogen is determined from the current value. In the figure, reference electrodes 3a and 3b are reference electrodes, and electrodes 4a and 4b are electrodes, with 4b being specifically called the counter electrode or coefficient electrode. Electrode 4a is connected to a power supply 6a, which is a potentiostat that applies a constant potential or a galvanostat that applies a constant current, while electrode 4b is connected to a power supply 6b that is a potentiostat that applies a constant potential. 5a and 5b are O-rings that ensure tight contact between the metal sample 2 and the electrolytic cells 1a and 1b to prevent leakage. The electrolytic cell 1a is filled with electrolyte 7a, which enables electrical conduction between the reference electrode 3a, the counter electrode 4a, and the specimen 2. The electrolyte 7a has a current of 1 μS / cm or more at 25°C, for example, 2 × 10⁻¹⁶. 5 An aqueous solution with an electrical conductivity of μS / cm or less is used. The range of electrical conductivity is defined as an aqueous solution considered suitable for electrolysis, with a lower limit of 1 μS / cm or higher (similar to distilled water) and an upper limit of 1 M KCl aqueous solution (1.28 × 10⁻⁶). 5 With a margin of 2 × 10 (μS / cm), 5 The limit is set at μS / cm or less. The electrolytic cell 1b is filled with electrolyte 7b, enabling electrical conduction between the reference electrode 3b, the counter electrode 4b, and the test subject 2. For the electrolyte 7b, it is preferable to fill the cell with, for example, a water-soluble organic solvent and an aqueous solution of the above organic solvent containing 0.01% to 50%. The lower limit of 0.01% for the aqueous solution dissolved in the organic solvent is matched to the highest purity commercially available organic solvent.

[0020] The electrochemical hydrogen permeation method described above is a well-known technique for measuring the hydrogen diffusion coefficient in steel materials, and it follows the following measurement procedure. Below, we will explain the electrochemical hydrogen permeation method using steel materials developed by Devanathan et al. (i) A thin sheet of steel material is designated as the subject 2 and is fixed by sandwiching it between two electrochemical cells 1a and 1b called Devanathan-Stachurski cells. At this time, one side of the subject is often plated with Pd or Ni. (ii) The Pd-plated or Ni-plated side of the sample is designated as the hydrogen detection side, and the unplated side as the hydrogen introduction side. The respective electrochemical cells 1a and 1b are filled with aqueous solutions (electrolytes 7a and 7b). At this time, an aqueous solution 7a with high electrical conductivity (e.g., 0.5M NaCl or 0.1M NaOH) is used on the hydrogen introduction side, and a solution 7b with high electrical conductivity and low corrosivity (e.g., 0.1M NaOH in the case of steel materials) is used on the hydrogen detection side.

[0021] (iii) Install reference electrodes 3a, 3b and counter electrodes 4a, 4b in each electrochemical cell 1a, 1b, and connect them to power supplies 6a, 6b (potentiostats are generally used). (iv) On the hydrogen introduction side, a cathode current or cathode potential is applied to the subject. This causes electrolysis of water on subject 2, and some of the generated hydrogen enters the subject. (v) On the hydrogen detection side, sample 2 is polarized to a potential above the hydrogen generation potential (above 0V vs. SHE, generally around 0.2V vs. SHE). As a result, the hydrogen that diffused from the hydrogen introduction side is oxidized to hydrogen ions, and the resulting electrons are detected as an electric current. The residual current of sample 2 after 24 hours of immersion can take a negative value depending on the measurement, so -0.1 μA / cm 2 More than 0.1μA / cm 2 The following applies: <Comparative Example> <Electrochemical hydrogen permeation test using pure iron>

[0022] In the comparative example, a thin sheet of pure iron was used as the sample. Both sides of this sample were wet-polished with SiC waterproof abrasive paper up to #2000 grit, and then ultrasonically cleaned in 2-propanol for 5 minutes. The thickness of the sample was measured using a micrometer immediately before the electrochemical hydrogen permeation method.

[0023] (Residual current measurement) To compare the residual current after polarization in the solutions used for detection, the Devanathan-Stachurski cell shown in Figure 1 was filled with the test solution on only one side, and the prepared pure iron thin plate (subject 2) was polarized in each solution. When fixing to the Devanathan-Stachurski cell, O-rings 5a and 5b were used to prevent leakage of the test solution between cells 1a and 1b and subject 2. The test solutions were 0.1 M NaOH (denoted as NaOH, corresponding to the conventional method), 2-propanol (purity > 99.7%) with 1% of 0.1 M NaOH added by volume (denoted as IPA + NaOH), and 2-propanol (denoted as IPA). The reaction area of ​​the subject was 2 cm². 2 The electrodes were fixed in electrochemical cells 1a and 1b, filled with the test solution, and then polarized to +200mV (vs. SHE). Ag / AgCl was used as the reference electrodes 3a and 3b, and Pt wire was used as the counter electrodes 4a and 4b. The measurement time was 24 hours.

[0024] Figure 2 shows the residual current density of pure iron 24 hours (approximately 86,400 seconds) after the start of polarization. In all test solutions, the residual current decreased over time, and after 24 hours, the residual current in all test solutions was 0.1 μA / cm². 2 The following was achieved. Furthermore, the residual current values ​​were NaOH > IPA + NaOH > IPA, indicating a tendency for the residual current to decrease as the proportion of organic solvent in the solution increased. From the above, it was revealed that residual current can be measured in organic solvents, and that the residual current can be reduced in a shorter time by using organic solvents.

[0025] (Electrochemical hydrogen permeation test) The prepared pure iron thin plate was sandwiched between Devanathan-Stachurski cells, and secured with an O-ring to prevent leakage of the test solution between the cells and the plate. The reaction area of ​​the plate was 2 cm² on both the hydrogen introduction side and the hydrogen detection side. 2Thus, 0.1 M NaOH was used as the solution on the hydrogen introduction side, and 0.1 M NaOH was used on the hydrogen detection side for comparison between 2-propanol and the conventional method. For both the hydrogen introduction side and the hydrogen detection side, Ag / AgCl was used as the reference electrode, and a Pt wire was used as the counter electrode. First, after filling the hydrogen detection side with the test solution, the test specimen was polarized at +200 mV (vs. SHE), and after 24 hours, the residual current was 0.1 μA / cm 2 After confirming that the residual current fell below the above value, the hydrogen introduction side was filled with 0.1 M NaOH. Thereafter, hydrogen was generated by applying a current of -1 mA (5 A / m 2 ) to cause hydrogen to penetrate into the test specimen. Hydrogen that diffused through the test specimen and reached the hydrogen detection side was measured as the hydrogen permeation current.

[0026] Fig. 3 shows the hydrogen permeation current density of pure iron when IPA and NaOH were used as the test solution on the hydrogen detection side. In both solutions, a rise in current due to hydrogen permeation was observed approximately 200 seconds after the start of the test. Thereafter, the current increased in proportion to the logarithm of time, and became steady after approximately 20,000 seconds (about 5 hours and 30 minutes). There were no differences in the current rise time, the slope of current increase, the time to reach steady state, or the steady-state value due to differences in the test solution, and it was clarified that organic solvents enable measurement of hydrogen permeation current in the same manner as the conventional method.

Examples

[0027] <Electrochemical Hydrogen Permeation Test Using Mg-Based Materials> In Example 1, thin plates of pure Mg and AZ31 alloy (Mg-3Al-1Zn) were used as the test specimen. Both surfaces of this test specimen were wet-polished to #2000 grit with SiC waterproof abrasive paper, then ultrasonically cleaned in 2-propanol for 5 minutes. Immediately before the electrochemical hydrogen permeation test, the thickness of the test specimen was measured using a micrometer.

[0028] (Residual Current Measurement) To compare the residual current after polarization in the solutions used for detection, the prepared pure Mg samples were fixed in Devanathan-Stachurski cells and polarized in each solution. The test solutions used were 0.1 M NaOH (denoted as NaOH), 2-propanol with 10% volume of 0.1 M NaOH added (denoted as IPA+NaOH(10%)), 2-propanol with 5% volume of 0.1 M NaOH added (denoted as IPA+NaOH(5%)), 2-propanol with 1% volume of 0.1 M NaOH added (denoted as IPA+NaOH(1%)), and 2-propanol (denoted as IPA). The reaction area of ​​the sample was 2 cm². 2 The sample was fixed in an electrochemical cell, filled with the test solution, and then polarized to +200mV (vs. SHE). Ag / AgCl was used as the reference electrode, and a Pt wire was used as the counter electrode. The measurement time was 24 hours.

[0029] Figure 4 shows the residual current density of pure Mg 24 hours (approximately 86,400 seconds) after the start of polarization. In pure Mg, a tendency was observed for the residual current to decrease with decreasing NaOH aqueous solution content in NaOH, IPA + NaOH (10%), and IPA + NaOH (5%) solutions, but the residual current remained at 0.1 μA / cm². 2 The following could not be achieved. Furthermore, the surface of the test subjects was severely corroded after the test, making it clear that the electrochemical hydrogen permeation test was unsuitable. On the other hand, the residual current was 0.1 μA / cm² with IPA + NaOH (1%) and IPA alone. 2 The following was achieved, and it became clear that organic solvents with a water content of 1% or less are suitable for electrochemical hydrogen permeation tests of Mg-based materials.

[0030] (Measurement of surface changes in the subject on the hydrogen introduction side) Since magnesium-based materials corrode and thin easily in aqueous solutions, it is necessary to minimize corrosion of the magnesium-based material in the hydrogen introduction solution. Using three basic solutions with good electrical conductivity that suppress magnesium corrosion, a -1mA (5A / m) method is used, similar to the electrochemical hydrogen permeation method. 2The surface changes and amount of wall thickness of the specimens were measured when a current of 0.1M NaOH (denoted as NaOH), 0.1M MgSO4 aqueous solution (denoted as MgSO4), and saturated Mg(OH)2 aqueous solution (denoted as Mg(OH)2) were used as test solutions. The surface image of the specimens and the height difference of the specimen surfaces after the test were measured using a one-shot 3D shape analyzer (VR-3000, Keyence).

[0031] Figures 5 to 7 show photographs of the polarized surface of the subject in each test solution, along with the height difference of the subject surface. Figure 5 shows the surface change of pure Mg on the hydrogen introduction side in one embodiment of the present invention, where (A) is the surface of the sample when saturated Mg(OH)2 is used, (B) is the cross-sectional shape at the white dotted line in (A), and (C) is a vertical axis enlargement view of (B). In the samples immersed in Mg(OH)2, as shown in Figures 5(A) and (B), slight discoloration was observed on the surface of the samples, but there was almost no change. Height difference measurements also showed no formation of corrosion products, thinning, or localized corrosion. Figure 5(C) shows an enlarged view of Figure 5(B). The surface irregularities of the samples were found to be approximately 5 μm at their maximum, indicating that they remained almost smooth. Therefore, saturated Mg(OH)2 aqueous solution is suitable as the aqueous solution for the hydrogen introduction side in electrochemical hydrogen permeation tests for Mg-based materials.

[0032] Figure 6 shows a comparative example of the present invention, where (A) shows the surface of the sample when a 0.1 M NaOH aqueous solution was used, and (B) shows the cross-sectional shape at the white dotted line in (A). The height difference of the sample surface was measured at the white dotted line in the photograph of the sample surface. In the sample immersed in NaOH, the surface of the pure Mg was severely corroded (Figure 6(A)), and deep localized corrosion marks were observed in places. Figure 6(B) shows an increase in the thickness of the specimen due to the formation of corrosion products on the specimen surface, a decrease in the specimen thickness due to thinning, and localized corrosion reaching a depth of approximately 100 μm to 200 μm. This indicates that it cannot be applied to electrochemical hydrogen permeation tests, which require a uniform specimen surface.

[0033] Figure 7 shows a comparative example of the present invention, where (A) shows the surface of the subject when a 0.1 M MgSO4 aqueous solution is used, and (B) shows the cross-sectional shape at the white dotted line in (A). Similarly, as shown in Figures 7(A) and (B), although local corrosion formation was suppressed in the samples immersed in MgSO4, an increase or decrease in the thickness of the samples was observed, making it clear that this method cannot be applied to electrochemical hydrogen permeation tests. Mg-based materials are said to exhibit high corrosion resistance in basic solutions, because they form a highly corrosion-resistant Mg(OH)2 film on their surface, which is a corrosion product. However, in electrochemical hydrogen permeation tests, the formation of the Mg(OH)2 film can cause changes in the thickness of the samples, and the diffusion coefficient of hydrogen permeating through the film differs from that in the base material. Therefore, it is desirable to avoid film formation as much as possible. Thus, a test solution that suppresses both corrosion and film formation is required on the hydrogen introduction side.

[0034] (Electrochemical hydrogen permeation test) For the electrochemical hydrogen permeation test, a Devanathan-Stachurski cell, as shown in Figure 1, was used. Pure Mg and AZ31 were used as the test subjects. The prepared test subjects were sandwiched between Devanathan-Stachurski cells and secured with O-rings to prevent leakage of the test solution between the cells and the test subjects. The reaction area of ​​the test subjects was 2 cm² on both the hydrogen introduction side and the hydrogen detection side. 2 The following procedure was performed: a saturated Mg(OH)2 aqueous solution was used as the hydrogen introduction solution, and 2-propanol was used as the hydrogen detection solution. SSE was used as the reference electrode and Pt wire as the counter electrode on both the hydrogen introduction and detection sides. First, the hydrogen detection side was filled with IPA, then the sample was polarized at +200mV (vs. SHE), and the residual current was 0.1μA / cm². 2 After confirming the following conditions, the hydrogen introduction side was filled with a saturated Mg(OH)2 aqueous solution. Subsequently, -1mA (5A / m) was applied to the hydrogen detection side. 2 Hydrogen was generated by passing an electric current through the sample and allowed to penetrate it. The hydrogen that diffused through the sample and reached the hydrogen detection side was measured as the hydrogen permeation current.

[0035] Figure 8 shows the hydrogen permeation current densities for pure Mg and AZ31. Figure 8(A) shows the hydrogen permeation current density with the horizontal axis being linear time, and Figure 8(B) shows the hydrogen permeation current density with the horizontal axis being logarithmic time. For pure Mg, a rise in hydrogen permeation current was observed after approximately 50,000 seconds (approximately 14 hours), and for AZ31, a rise in current was observed after approximately 100,000 seconds (approximately 28 hours). In both samples, the rise in hydrogen permeation current was clearly measured by using IPA on the hydrogen detection side.

[0036] Figure 9 shows the results of continuously measuring the hydrogen permeation current over a long period (approximately 3 months) using AZ31 (Figure 9(A) shows the linear axis of time on the horizontal axis, and (B) shows the logarithmic axis of time on the horizontal axis). The hydrogen permeation current from the rise time to the steady-state value after approximately 5 million seconds (approximately 58 days) can be clearly measured. Several methods have been proposed for determining the hydrogen diffusion coefficient from the hydrogen permeation current. Here, the hydrogen diffusion coefficient in AZ31 was determined using the Half-rise time method and the Breakthrough time method (both of which are described in detail in Non-Patent Document 1).

[0037] Half-rise time method The time t at which the hydrogen permeation current becomes half of the steady-state value 1 / 2 It can be expressed by the following formula. t 1 / 2 = 0.14L 2 / D H Here, L is the thickness of the sample (m), D h The diffusion coefficient of hydrogen (m 2 / s). As shown in Figure 9(B) t 1 / D H When you calculate D H = 4.89 × 10 -15 m 2 / s was obtained.

[0038] Breakthrough time method As shown in Figure 8(B), if we let tb be the point where the tangent line of the curve drawn by the hydrogen permeation current intersects with the time axis, we obtain the following equation. tb = 0.5L 2 / π 2 D H From here D H When you calculate D H = 4.56 × 10 -15 m 2 / s was obtained. Based on the above results, it can be inferred that the hydrogen diffusion coefficient in AZ31 at room temperature is on the order of 10-15 m² / s. [Examples]

[0039] <Electrochemical hydrogen permeation test using pure aluminum> In Example 2, a thin sheet of pure Al (A1050) was used as the test subject. Both sides of the test subject were wet-polished with SiC waterproof abrasive paper up to #2000 grit, and then ultrasonically cleaned in 2-propanol for 5 minutes. The thickness of the test subject was measured using a micrometer immediately before the electrochemical hydrogen permeation method.

[0040] (Electrochemical hydrogen permeation test) For the electrochemical hydrogen permeation test, a Devanathan-Stachurski cell, as shown in Figure 1, was used. The prepared sample was sandwiched between the Devanathan-Stachurski cells and secured with an O-ring to prevent leakage of the test solution between the cell and the sample. The reaction area of ​​the sample was 2 cm² on both the hydrogen introduction side and the hydrogen detection side. 2 The following was performed: 0.1 M citrate buffer solution (pH 5.1) and 0.1 M borate buffer solution (pH 8.4) were used as the hydrogen introduction solution, and 2-propanol was used as the aqueous solution on the hydrogen detection side. Ag / AgCl was used as the reference electrode and Pt wire as the counter electrode on both the hydrogen introduction and detection sides. First, the hydrogen detection side was filled with IPA, then the sample was polarized at +200 mV (vs. SHE), and the residual current was 0.1 μA / cm². 2 After confirming the following conditions, the hydrogen introduction side was filled with citrate buffer solution or borate buffer solution. Subsequently, -1mA (5A / m) was applied to the hydrogen detection side. 2 ) or -10mA (50A / m 2Hydrogen was generated by passing an electric current through the sample and allowed to penetrate it. The hydrogen that diffused through the sample and reached the hydrogen detection side was measured as the hydrogen permeation current.

[0041] Figure 10 shows the hydrogen permeation current density of pure Al when IPA is used as the test solution on the hydrogen detection side, and citrate buffer solution and borate buffer solution are used as the test solutions on the hydrogen introduction side. When a current of -1 mA was applied, no rise in hydrogen permeation current was observed in either the citrate buffer solution or the borate buffer solution within 300,000 seconds (approximately 84 hours). On the other hand, when a current of -10 mA was applied, a rise in current was observed in the citrate buffer solution at approximately 50,000 seconds (approximately 14 hours) and in the borate buffer solution at approximately 150,000 seconds (approximately 42 hours). Generally, the current value on the input side affects the amount of hydrogen introduced and the absolute value of the hydrogen permeation current, but does not affect the rise time of the hydrogen permeation current or the general shape of the hydrogen permeation current. However, in pure Al, it is known that the oxide film formed on the surface prevents hydrogen from entering, and furthermore, the diffusion rate of hydrogen within the oxide film is also small. In the case of -1mA, the surface oxide film was not destroyed, so hydrogen could not be detected within the measurement period, while in the case of -10mA, the surface oxide film was destroyed, and it is thought that hydrogen diffused into the pure Al could be measured. The time required for oxide film breakdown differed between the citrate buffer solution and the borate buffer solution due to the difference in their pH levels. The reason the oxide film was broken when the hydrogen introduction current was high is likely due to a decrease in pH near the surface. H+ ions are generated on the Al surface on the hydrogen introduction side due to the electrolysis of water. As the current increases, more H+ ions are generated, so the pH near the sample surface decreased, leading to oxide film breakdown. This indicates that in Al-based materials, the hydrogen permeation current is affected by the surface oxide film, and the behavior of the hydrogen permeation current changes depending on the current and solution used on the hydrogen introduction side.

[0042] Figure 11 is a schematic diagram of an electrochemical hydrogen permeation test apparatus (improved Devanathan-Stachurski cell) illustrating another embodiment of the present invention. The corroded surface of specimen 2 is exposed to an atmospheric corrosion environment, a water vapor corrosion environment, or an aqueous solution corrosion environment 7d, and specimen 2 is corroded during the electrochemical permeation test. Note that the atmospheric corrosion environment, water vapor corrosion environment, or aqueous solution corrosion environment 7d may be separated from the external environment by an electrochemical cell 1d. In the case of an atmospheric corrosion environment, an electrochemical cell 1d is not required. Methods for inducing corrosion include corrosion by droplets, corrosion by immersion in a solution, corrosion by steam, and corrosion by cyclic corrosion testing (CCT). One cycle of CCT may consist of stages such as drying (50% RH, 5.75 h), wetting (98% RH, 1.75 h), and salt spray (0.5% NaCl aqueous solution, 0.5 h), but is not limited to this. The temperature should be maintained at 30°C throughout the entire CCT process. After CCT, the corroded sample 2 is subjected to an electrochemical hydrogen permeation test under temperature and humidity control. Preferably, the surface of the corroded sample is observed with a scanning electron microscope (SEM). When using a non-ferrous metal material for the subject 2, it is preferable to use a water-soluble organic solvent as the aqueous solution (electrolyte 7c) that fills the electrolytic cell 1c. As the water-soluble organic solvent, it is preferable to use at least one of ethanol, methanol, 2-propanol, and ethylene glycol, and the amount of the aqueous solution should be between 0.01% and 50%, however, the water-soluble organic solvent is not limited to these.

[0043] In the electrochemical permeability test of subject 2, one side of subject 2 is corroded and open to the atmosphere. One side of subject 2 is in contact with electrolytic cell 1c. In electrolytic cell 1c, subject 2 is anodically polarized at a constant potential, oxidizing the hydrogen that has permeated through subject 2 into hydrogen ions, and the amount of hydrogen that has permeated is determined from the current value. In the diagram, 3c is a reference electrode, and 4c is an electrode, specifically 4c is called a counter electrode or coefficient electrode. Electrode 4c is connected to a power supply 6c, which is a potentiostat that applies a constant potential. 5c is an O-ring used to ensure a tight seal between the test subject 2 and the electrolytic cell 1c, preventing leakage of the test solution.

[0044] Using the electrochemical hydrogen permeation test apparatus configured in this way, the experiment should be carried out as follows: The sample 2, which has corrosion on one side, is fixed to a modified Devanathan cell. Next, the sample surface on the hydrogen extraction side is directed towards the organic solvent in the cell (electrolytic cell) 1c, and an Ag / AgCl reference electrode and a Pt counter electrode are placed inside the electrolytic cell 1c. The electrolytic cell 1c is placed in a constant temperature and humidity chamber (not shown), and the sample 2 and each electrode 3c, 4c are connected to the corresponding terminals R, C, and W of the potentiostat 6c through the ports of the constant temperature and humidity chamber. The hydrogen extraction side is polarized at +200mV, and the hydrogen permeation current is recorded every 5 seconds using a data logger (not shown). Prior to the permeation test, the passivation holding current density, which is the background for the hydrogen permeation current, is set to 0.1 μA / cm². 2 The following is recommended: Maintain the temperature inside the constant temperature and humidity chamber at 30°C, and gradually increase the relative humidity in the order of, for example, 50, 70, 80, and 98% RH, although this is not the only option. Maintain each humidity level between 50-70% RH for approximately 2 hours. After raising the humidity to 98% RH, maintain that level for 10 hours, and then gradually decrease the relative humidity.

[0045] In the embodiment shown in Figure 11, one side of the specimen 2 is shown as the corrosion surface and is open to the atmosphere. However, the present invention is not limited to this, and one side of the specimen 2 may also be the corrosion surface and be the surface in a water vapor corrosion environment, or the surface may be the surface in an aqueous solution corrosion environment where the potential for electrolysis of water occurs. [Industrial applicability]

[0046] As detailed above, the method for measuring the amount of hydrogen penetrating into a metal according to the present invention uses a test solution optimized for non-ferrous metal materials that allows for a reduction in the residual current on the hydrogen detection side. Therefore, it is possible to measure the hydrogen diffusion coefficient in the actual usage environment (i.e., hydrogen penetrating due to corrosion) with small errors, and the practical effect is significant. [Explanation of Symbols]

[0047] 1a, 1b, 1c Electrolytic cell (electrochemical cell) 1d. Corrosive environments in the atmosphere, steam, or aqueous solutions. 2. Metal sample (subject) 3a, 3b, 3 reference electrodes 4a, 4b, 4 opposite poles 5a, 5b O-rings 6a, 6b, 6 Power supply (potentiostat) 7a, 7b, 7c Electrolyte

Claims

1. A method for measuring the amount of hydrogen generated and penetrating into the interior of a non-ferrous metal material due to corrosion, using electrochemical hydrogen permeation. When one side of the sample is designated as the side into which hydrogen enters, with a potential at which the electrolysis of water occurs, and the other side is designated as the hydrogen detection surface, controlled by a potential or current at which hydrogen atoms are oxidized to hydrogen ions, A first electrochemical cell is provided on the side into which the hydrogen enters, and a hydrogen content of 1 μS / cm or more and 2 × 10⁻¹⁶ at 25°C is introduced into the interior of the first electrochemical cell. ５ A saturated Mg(OH)₂ aqueous solution having an electrical conductivity of μS / cm or less is filled, and a first reference electrode and a first counter electrode are installed. A second electrochemical cell is provided on the hydrogen detection surface side, and the inside of the second electrochemical cell is filled with 2-propanol, or a 0.1 M aqueous solution of 2-propanol in a volume equivalent of 0.01% to 1%, and a second reference electrode and a second counter electrode are installed. In the first electrochemical cell, the first power supply is connected to the first reference electrode and the first counter electrode. When the first power supply is potential-controlled, a potential higher than -10V and lower than the immersion potential of the sample is applied. When the first power supply is current-controlled, -0.01mA / cm² is applied. ２ -100mA / cm or more ２ Apply the following constant current, In the second electrochemical cell, the second power supply is connected to the second reference electrode and the second counter electrode, and the second power supply provides a potential of 0V to 1V relative to the standard hydrogen electrode. The residual current of the aforementioned sample after 24 hours of immersion was -0.1 μA / cm². ２ 0.1μA / cm or more ２ A method for measuring the amount of hydrogen that penetrates into a non-ferrous metal material, characterized by the following:

2. The method for measuring the amount of hydrogen penetrating into a non-ferrous metal material according to claim 1, wherein the non-ferrous metal material is beryllium (Be), magnesium (Mg), aluminum (Al), calcium (Ca), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), zinc (Zn), yttrium (Y), zirconium (Zr), or an alloy containing 50 atomic percent or more of these non-ferrous metal elements, and the non-ferrous metal element or alloy has a lower standard electrode potential than iron (Fe).

3. An apparatus for measuring the amount of hydrogen generated and penetrating into the interior of a non-ferrous metal material due to corrosion, using an electrochemical hydrogen permeation method, When one side of the sample is designated as the side into which hydrogen enters, with a potential at which the electrolysis of water occurs, and the other side is designated as the hydrogen detection surface, controlled by a potential or current at which hydrogen atoms are oxidized to hydrogen ions, A first electrochemical cell is provided on the hydrogen intrusion surface side and is installed with the first reference electrode and the first counter electrode immersed in the first electrolyte, A second electrochemical cell is provided on the hydrogen detection surface side and is installed with the second reference electrode and the second counter electrode immersed in the second electrolyte, It is equipped with, The first electrolyte has a concentration of 1 μS / cm or more and 2 × 10 at 25°C. ５ A saturated Mg(OH)₂ aqueous solution having an electrical conductivity of μS / cm or less, which is filled inside the first electrochemical cell. The second electrolyte is 2-propanol, or a 0.1 M aqueous solution of NaOH dissolved in 2-propanol in a volume-based concentration of 0.01% to 1%, and is filled inside the second electrochemical cell. In the first electrochemical cell, the first power supply is connected to the first reference electrode and the first counter electrode. When the first power supply is potential-controlled, a potential higher than -10V and lower than the immersion potential of the sample is applied. When the first power supply is current-controlled, -0.01mA / cm² is applied. ２ -100mA / cm or more ２ Apply the following constant current, In the second electrochemical cell, the second power supply is connected to the second reference electrode and the second counter electrode, and the second power supply provides a potential of 0V to 1V relative to the standard hydrogen electrode. The residual current of the subject after 24 hours of immersion is −0.1 μA / cm ２ or more and 0.1 μA / cm ２ or less, which is an apparatus for measuring the amount of hydrogen penetrating into the interior of a non-ferrous metal material.

4. A method for measuring the amount of hydrogen generated and penetrating into the interior of a non-ferrous metal material due to corrosion, using electrochemical hydrogen permeation. When one side of the sample is designated as the etching surface and the other side as the hydrogen detection surface controlled to a potential at which hydrogen atoms are oxidized to hydrogen ions, The aforementioned corroded surface is one of the following: a surface exposed to the atmosphere, a surface in a water vapor environment, or a surface in an aqueous solution corrosive environment. An electrochemical cell is provided on the hydrogen detection surface side, and the inside of the electrochemical cell is filled with 2-propanol, or a 0.1 M aqueous solution of 2-propanol containing 0.01% to 1% by volume of NaOH, and a reference electrode and a counter electrode are installed. In the electrochemical cell, the power supply is connected to the reference electrode and the counter electrode, and the power supply provides a potential of 0V to 1V relative to the standard hydrogen electrode. The residual current of the aforementioned sample after 24 hours of immersion was -0.1 μA / cm². ２ 0.1μA / cm or more ２ A method for measuring the amount of hydrogen that penetrates into a non-ferrous metal material, characterized by the following:

5. The method for measuring the amount of hydrogen penetrating into a non-ferrous metal material according to claim 4, wherein the non-ferrous metal material is beryllium (Be), magnesium (Mg), aluminum (Al), calcium (Ca), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), zinc (Zn), yttrium (Y), zirconium (Zr), or an alloy containing 50 atomic percent or more of these non-ferrous metal elements, and the non-ferrous metal element or alloy has a lower standard electrode potential than iron (Fe).

6. An apparatus for measuring the amount of hydrogen generated and penetrating into the interior of a non-ferrous metal material due to corrosion, using an electrochemical hydrogen permeation method, When one side of the sample is designated as the etching surface and the other side as the hydrogen detection surface controlled to a potential at which hydrogen atoms are oxidized to hydrogen ions, The corrosive surface side is provided with an environment open to the atmosphere, a water vapor environment, or an aqueous solution corrosive environment, An electrochemical cell is provided on the hydrogen detection surface side and is installed with the reference electrode and counter electrode immersed in a third electrolyte, It is equipped with, The third electrolyte is 2-propanol, or a 0.1 M aqueous solution of NaOH dissolved in 2-propanol in a volume-based concentration of 0.01% to 1%, and is filled inside the electrochemical cell. In the electrochemical cell, the power supply is connected to the reference electrode and the counter electrode, and the power supply provides a potential of 0V to 1V relative to the standard hydrogen electrode. The residual current of the aforementioned sample after 24 hours of immersion was -0.1 μA / cm². ２ 0.1μA / cm or more ２ A device for measuring the amount of hydrogen that penetrates into a non-ferrous metal material, characterized by the following:

Images