Quantitative detection method for hydrogen distribution on metal surface based on interactive use of SKPFM and TDS

Abstract

The present invention relates to the field of hydrogen energy utilization, and aims to provide a method for quantitatively detecting hydrogen distribution on the surface of metal materials based on the interactive use of SKPFM and TDS. The present invention utilizes the SKPFM and TDS methods, and first measures the change value of the surface contact potential difference caused by hydrogen dissolution, and the overall average hydrogen concentration corresponding to the change value, for hydrogen-charged metal materials with the same chemical composition and heat treatment state as the metal material to be tested, and sets different hydrogen charging conditions to obtain a corresponding relationship curve between the two. Subsequently, by scanning the change value of the surface contact potential difference caused by hydrogen dissolution on the surface of the metal to be tested by SKPFM, the hydrogen distribution in the material can be directly quantitatively obtained. The present invention simultaneously possesses the advantages of SKPFM such as non-destructive testing, time resolution, a wide range of applicable materials, high width resolution, and low testing cost, as well as the quantitative testing capability of TDS; it can effectively eliminate the influence of factors such as high temperature and high pressure during the hydrogen charging process on the surface properties of the material, and improve the accuracy of the measurement of the potential difference change value.

Description

Technical Field

[0001] The present invention belongs to the field of hydrogen energy utilization, and in particular relates to a method for quantitatively detecting hydrogen distribution on the surface of a metal material based on the interactive use of SKPFM and TDS. Background Art

[0002] Hydrogen energy high-pressure storage and transportation equipment, operating in high-pressure, high-purity hydrogen environments for extended periods, often faces challenges such as accelerated crack propagation and reduced fracture toughness caused by high-pressure hydrogen embrittlement. While numerous theories of hydrogen embrittlement exist, a unified understanding of the mechanism of action of high-pressure hydrogen remains elusive. It is generally accepted that when the hydrogen concentration near the crack tip reaches a critical value, crack propagation is accelerated, and higher hydrogen concentrations increase the severity of hydrogen embrittlement. Therefore, quantitatively measuring hydrogen distribution on the material surface is beneficial for a deeper understanding of the nature of high-pressure hydrogen embrittlement and can also provide technical support for the development of performance prediction methods for hydrogen energy storage and transportation equipment.

[0003] Currently, common hydrogen distribution detection methods include three-dimensional atom probe (APT), hydrogen micro-printing technology (HMT), scanning Kelvin probe force microscopy (SKPFM), thermal desorption mass spectrometry (TDS), and secondary ion mass spectrometry (SIMS). APT uses needle-shaped samples with a diameter of nanometers, which is difficult to prepare and hydrogen easily escapes from the sample. HMT can only qualitatively provide hydrogen distribution information at a specific moment and cannot show the evolution of hydrogen concentration over time. SKPFM can qualitatively analyze hydrogen distribution and its evolution, but due to the lack of hydrogen concentration corresponding to the potential difference, it cannot quantitatively detect hydrogen distribution data. TDS has low spatial resolution and can only obtain the average hydrogen content of the entire sample. SIMS, like APT and TDS, requires vacuum operation, which is time-consuming and complex, and the equipment is expensive. In addition, all of the above methods, except SKPFM, require hydrogen to be separated from the material, and the detection process lacks time resolution and non-destructive characteristics.

[0004] In summary, existing methods have certain limitations in measuring hydrogen distribution on the surface of metal materials. Therefore, it is necessary to propose a method that can directly, quantitatively and flexibly detect hydrogen distribution on the surface of metal materials. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a method for quantitatively detecting hydrogen distribution on the surface of a metal material based on the interactive use of SKPFM and TDS.

[0006] In order to solve the technical problem, the technical solution adopted by the present invention is:

[0007] A method for quantitatively detecting hydrogen distribution on the surface of a metal material based on the interactive use of SKPFM and TDS is provided, comprising the following steps:

[0008] (1) Prepare a test metal material from the same production batch as the metal material to be tested. The chemical composition and heat treatment state of the two are the same, but the latter does not contain hydrogen; process the test metal material into thin sheets and divide them into equal size specifications to obtain batch samples for testing;

[0009] (2) Randomly select three samples from the batch of samples and number them as samples 1#, 2#, and 3# respectively; place samples 1# and 2# in a gas-phase hot hydrogen charging reactor at the same time, introduce high-temperature and high-pressure hydrogen according to the preset test conditions and maintain for a certain time to obtain hydrogen-charged samples with the same hydrogen concentration; place sample 3# in an argon environment and treat it at the same temperature, pressure, and holding time;

[0010] (3) The contact potential difference distribution of the surfaces of samples 1# and 3# was measured using the SKPFM method. A contact potential difference distribution diagram was drawn based on the measurement results. Several points were randomly selected on the diagram and the average value was recorded as ΔV. CPD1 and V CPD3 ; Calculate the change in surface contact potential difference of the sample due to hydrogen dissolution: Φ CPD =ΔV CPD1 -V CPD3 ;

[0011] (4) The overall average hydrogen concentration of sample 2# was measured by TDS method, recorded as C; the Φ under the specific hydrogen charging conditions of this group was obtained. CPD The corresponding relationship between C;

[0012] (5) Repeat steps (2) to (4) to obtain at least 5 Φ CPD The data points corresponding to C; on this basis, Φ is fitted CPD Corresponding relationship curve with C;

[0013] (6) Using the SKPFM method to measure the contact potential difference distribution of the metal surface to be measured, and after the hydrogen therein is completely escaped, measuring the contact potential difference distribution of the metal surface to be measured again;

[0014] (7) At the same position on the metal surface to be measured, subtract the contact potential difference obtained from the two measurements in step (6) to obtain the Φ of the metal surface to be measured CPD distribution; and then according to the fitting relationship curve in step (5), the quantitative data of hydrogen distribution on the surface of the metal material is obtained.

[0015] As a preferred embodiment of the present invention, in step (1), the flaky metal material is first polished with 2000-mesh silicon carbide water-resistant sandpaper until the surface is smooth, and then divided and ultrasonically washed with ethanol solution for 3 minutes, and then blown dry and stored.

[0016] As a preferred embodiment of the present invention, in step (1), the sample after processing and segmentation is a square with a side length of ≤10 mm and a thickness of ≤1 mm.

[0017] As a preferred embodiment of the present invention, in step (2), the heating temperature during gas-phase thermal hydrogen charging is ≤ 200°C.

[0018] As a preferred embodiment of the present invention, in step (2), the sample treated with hydrogen and argon is taken out and directly placed in liquid nitrogen for storage for future use.

[0019] As a preferred embodiment of the present invention, in step (3), two scans are performed when measuring the contact potential difference distribution using the SKPFM method: first, a first scan is performed to obtain the surface morphology of the sample; then, the probe is lifted by 50 nm and a second reverse scan is performed to obtain the contact potential difference distribution.

[0020] As a preferred embodiment of the present invention, in step (3), at least 10 data extraction points are randomly selected on the contact potential difference distribution diagram using a random function.

[0021] As a preferred embodiment of the present invention, in step (5), the temperature, pressure and time during the sample treatment process are adjusted according to the hydrogen concentration prediction formula in Appendix E of the standard ANSI / CSA CHMC 1-2014 "Test methods for evaluating material compatibility in compressed hydrogen applications - Metals".

[0022] As a preferred embodiment of the present invention, in step (6), it is ensured that the temperature of the metal to be measured is the same when the contact potential difference distribution of the metal surface to be measured is measured twice.

[0023] As a preferred embodiment of the present invention, in step (6), the temperature can be appropriately increased to accelerate the escape of hydrogen, but the temperature must not be higher than 200°C. Excessively high temperatures may cause changes in the original stress state, plastic deformation, dislocation, etc. of the metal surface to be measured, and may also cause carbide precipitation, thereby interfering with the measurement results.

[0024] Description of the invention principle:

[0025] The present invention utilizes the SKPFM and TDS methods. First, for a hydrogen-charged metal material with the same chemical composition and heat treatment status as the metal material being tested, the change in surface contact potential difference due to hydrogen dissolution and the corresponding overall average hydrogen concentration are measured. Different hydrogen charging conditions are then set to obtain a corresponding relationship curve between the two. Subsequently, the SKPFM scan is used to measure the change in surface contact potential difference due to hydrogen dissolution on the metal surface being tested, directly and quantitatively determining the hydrogen distribution in the material.

[0026] When hydrogen atoms dissolve into metal materials, they weaken the cohesive forces between the metal atoms, reducing the energy required for electrons to escape from the atoms. Consequently, the work function of the metal surface decreases after hydrogenation. Furthermore, hydrogen dissolution causes the metal lattice to expand, and the resulting mechanical stress also reduces the work function. The relationship between contact potential difference and work function is as follows:

[0027]

[0028] In the formula and are the work functions of the probe tip and the sample surface, respectively, and e is the electron charge.

[0029] Therefore, when the hydrogen concentration in the metal material increases, the contact potential difference on the surface of the material will also increase.

[0030] Based on the above principle, the present invention makes batch samples of test metal materials with the same chemical composition and heat treatment state as the metal material to be tested. Three samples are randomly selected from the batch samples and grouped into a group. First, two samples in the same group are subjected to high-temperature and high-pressure hydrogen charging treatment, and the third sample is placed in an argon environment with the same temperature and pressure for the same time. Then, the TDS method is used to measure the overall average hydrogen concentration in the sample, and the SKPFM method is used to measure the change in the surface contact potential difference of the sample due to hydrogen dissolution (the samples after hydrogen and argon atmosphere treatment are scanned separately, and the difference between the two test results is used as the surface contact potential difference change value. In fact, it is only the change in surface work function caused by hydrogen dissolution, which can exclude the influence of factors such as high temperature and high pressure during hydrogen charging on the surface properties of the material). In this way, the corresponding relationship between the change in surface contact potential difference caused by hydrogen dissolution and the overall average hydrogen concentration of the same group of samples after hydrogen charging can be established. Finally, by changing the hydrogen charging conditions, a curve of the relationship between the change in surface contact potential difference and hydrogen concentration of the test metal material can be fitted. Since the metal material used in the test is the same as the metal material to be tested, the subsequent analysis only requires scanning the change in surface contact potential difference caused by hydrogen dissolution of the metal to be tested through SKPFM, and consulting the fitting relationship curve to directly and quantitatively obtain the hydrogen distribution in the material.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The combination of SKPFM and TDS enables quantitative measurement of hydrogen distribution on the material surface and allows observation of the evolution of hydrogen distribution over time. This method combines the advantages of SKPFM, including non-destructive testing, temporal resolution, a wide range of applicable materials, high spectral resolution, and low testing costs, with the quantitative testing capabilities of TDS.

[0033] 2. Comparative testing of samples treated with high-temperature, high-pressure argon atmosphere can effectively eliminate the influence of high temperature, high pressure and other factors during the hydrogen charging process on the surface properties of the material, further improving the accuracy of the measurement of the potential difference change value.

[0034] 3. The sample size is reasonably designed and the processing is simple, which avoids the problem of large-scale hydrogen escape during the sample processing and the significant destruction of the initial morphology of the metal to be tested. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Flow chart of the detection method of the present invention. DETAILED DESCRIPTION

[0036] The specific embodiments of the present invention will be described below with reference to the accompanying drawings.

[0037] like Figure 1 As shown, the quantitative detection method for hydrogen distribution on the surface of a metal material based on the interactive use of SKPFM and TDS of the present invention specifically includes the following four steps.

[0038] 1. Sample preparation

[0039] In order to quantitatively detect the hydrogen distribution on the surface of metal materials, it is necessary to prepare test metal materials from the same production batch as the metal material to be tested. The chemical composition and heat treatment status of the two are consistent, but the latter does not contain hydrogen.

[0040] First, the metal material to be tested was processed into thin sheets and polished to a smooth surface using 2000-grit silicon carbide water-resistant sandpaper. After being cut into equal sizes, the polished specimens were ultrasonically cleaned for 3 minutes using an ethanol solution. The specimens were then air-dried and stored, resulting in the batch of specimens used for testing.

[0041] For example, in this example, the specimens are square sheets with a side length of 10 mm and a thickness of 1 mm, with a quantity of at least 30 sheets. Each group of 3 specimens is randomly divided into 10 test groups (with extra specimens reserved) and tested separately. Before each test, the three specimens in the group are numbered 1#, 2#, and 3#, respectively.

[0042] 2. Comparison of hydrogen charging

[0043] Hydrogen concentration intervals were defined between test groups, and the equilibrium hydrogen concentration values for each test group were preliminarily set. The corresponding hydrogen charging conditions (hydrogen pressure, temperature, and charging time) for different equilibrium hydrogen concentration values were predicted based on the thermodynamic relationships in Appendix E of the ANSI / CSA CHMC 1-2014 "Test Methods for Evaluating Material Compatibility in Compressed Hydrogen Applications - Metals" standard. The charging conditions for each group were set based on the calculated results. For each test group, samples 1# and 2# were placed in a high-temperature, high-pressure, vapor-phase hot hydrogen charging reactor for hydrogen charging, yielding two hydrogen-charged samples with the same hydrogen concentration within the same test group. The heating temperature during vapor-phase hot hydrogen charging was kept ≤200°C to prevent carbide precipitation within the metal due to excessive temperatures. Sample 3# was placed in an argon atmosphere with the same pressure and temperature as the hydrogen charging phase of the group and maintained at this temperature for the same period of time. Samples 1#, 2#, and 3 were then removed from the reactor and immediately stored in liquid nitrogen at -200°C for cryogenic storage.

[0044] 3. Fitting relationship curve

[0045] (1) For each test group, the SKPFM method was used to measure the sample 1# and 3# respectively, and the change in contact potential difference caused only by hydrogen dissolution was obtained, which was recorded as Φ CPD ; Each group Φ CPD The measurement process mainly includes the following 4 steps:

[0046] (a) Install the sample: Fix sample 1# to the sample holder, and attach the sample holder to the magnetic sample plate.

[0047] (b) Focusing the sample: Move the probe tip to the surface of sample 1# and adjust the optical focus until the surface of sample 1# is clearly visible;

[0048] (c) Scanning image: A two-scan method was used. The first scan obtained the surface morphology of sample 1#; then the probe was lifted 50nm and a second reverse scan was performed to obtain the contact potential difference distribution image of the surface of sample 1#.

[0049] Referring to the operation contents of steps (a) to (c), the contact potential difference distribution image of the surface of sample 3# is obtained.

[0050] (d) Calculate Φ CPD : On the contact potential difference distribution images of samples 1# and 3#, 10 points were randomly selected using the random function; the average value of the contact potential difference of the 10 points was calculated and recorded as ΔV CPD1 and ΔV CPD3; Then the change in contact potential difference caused by hydrogen dissolution of the sample is: Φ CPD =ΔV CPD1 -V CPD3 .

[0051] (2) Measure sample 2# using the TDS method to obtain the overall average hydrogen concentration, which is recorded as C.

[0052] (3) Obtain Φ for each of the 10 experimental groups CPD The corresponding relationship with C, after eliminating abnormal points, is used to fit the Φ of the metal material used in the test. CPD Corresponding relationship curve with C.

[0053] 4. Measuring hydrogen distribution

[0054] (1) Referring to the previous operation content, the contact potential difference distribution of the metal surface to be measured is measured using the SKPFM method. After the hydrogen in it is completely released, the contact potential difference distribution of the metal surface to be measured is measured again. In this process, ensure that the temperature of the metal to be measured is the same during the two measurements.

[0055] Hydrogen escape is carried out at a temperature of ≤200°C. For specific operations, please refer to the scheme recorded in the public document "Research Progress on the Application of Thermal Desorption Spectroscopy Technology in the Study of Hydrogen Traps in Hydrogen Storage Container Materials".

[0056] (2) At the same position on the metal surface to be measured, the contact potential difference obtained from the two measurements is subtracted to obtain the Φ of the metal surface to be measured. CPD distributed;

[0057] (3) According to the fitting relationship curve in step 3, the quantitative data of hydrogen distribution on the surface of the metal material is obtained.

[0058] Finally, it should be noted that the above examples are merely specific embodiments of the present invention. The present invention is not limited to the above examples and is subject to numerous variations. All variations that can be directly derived or imagined by a person skilled in the art from the disclosure of the present invention, as well as any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention, are intended to be included within the scope of protection of the present invention.

Claims

1. A quantitative detection method for hydrogen distribution on the surface of metal materials based on the interactive use of SKPFM and TDS, characterized in that: The following steps are involved: (1) Prepare a test metal material from the same production batch as the metal material to be tested. The chemical composition and heat treatment state of the two are the same, but the latter does not contain hydrogen; process the test metal material into thin sheets and divide them into equal size specifications to obtain batch samples for testing; (2) Randomly select three samples from the batch of samples and number them as samples 1#, 2#, and 3# respectively; place samples 1# and 2# in a gas-phase hot hydrogen charging reactor at the same time, introduce high-temperature and high-pressure hydrogen according to the preset test conditions and maintain for a certain time to obtain hydrogen-charged samples with the same hydrogen concentration; place sample 3# in an argon environment and treat it at the same temperature, pressure, and holding time; (3) The contact potential difference distribution of the surfaces of samples 1# and 3# was measured using the SKPFM method. A contact potential difference distribution diagram was drawn based on the measurement results. Several points were randomly selected on the diagram and the average value was recorded as ΔV. CPD1 and ΔV CPD3 ; Calculate the change in surface contact potential difference of the sample due to hydrogen dissolution: Φ CPD =ΔV CPD1 -ΔV CPD3 ; (4) The overall average hydrogen concentration of sample 2# was measured by TDS method, recorded as C; the Φ under the specific hydrogen charging conditions of this group was obtained. CPD The corresponding relationship between C; (5) Repeat steps (2) to (4) to obtain at least 5 Φ CPD The data points corresponding to C; on this basis, Φ is fitted CPD Corresponding relationship curve with C; (6) Using the SKPFM method to measure the contact potential difference distribution of the metal surface to be measured, and after the hydrogen therein is completely escaped, measuring the contact potential difference distribution of the metal surface to be measured again; (7) At the same position on the metal surface to be measured, subtract the contact potential difference obtained from the two measurements in step (6) to obtain the Φ of the metal surface to be measured CPD distribution; and then according to the fitting relationship curve in step (5), the quantitative data of hydrogen distribution on the surface of the metal material is obtained.

2. The method according to claim 1, characterized in that In the step (1), the flaky metal material is first polished with 2000-mesh silicon carbide water-resistant sandpaper until the surface is smooth, and then divided and ultrasonically cleaned with an ethanol solution for 3 minutes, and then blown dry and stored.

3. The method according to claim 1, characterized in that In the step (1), the sample after processing and segmentation is a square with a side length of ≤10 mm and a thickness of ≤1 mm.

4. The method according to claim 1, wherein In the step (2), the heating temperature during gas-phase thermal hydrogen charging is ≤ 200°C.

5. The method according to claim 1, wherein In the step (2), the sample treated with hydrogen and argon is taken out and directly placed in liquid nitrogen for storage for future use.

6. The method according to claim 1, characterized in that In the step (3), two scans are performed when measuring the contact potential difference distribution using the SKPFM method: first, a first scan is performed to obtain the surface morphology of the sample; then, the probe is lifted by 50 nm and a second reverse scan is performed to obtain the contact potential difference distribution.

7. The method according to claim 1, characterized in that In the step (3), at least 10 data extraction points are randomly selected on the contact potential difference distribution diagram using a random function.

8. The method according to claim 1, characterized in that In step (5), the temperature, pressure and time during the sample treatment process are adjusted according to the hydrogen concentration prediction formula in Appendix E of the standard ANSI / CSA CHMC1-2014 "Test methods for evaluating material compatibility in compressed hydrogen applications-Metals".

9. The method according to claim 1, characterized in that In the step (6), it is ensured that the temperature of the metal to be measured is the same when the contact potential difference distribution of the metal surface to be measured is measured twice.

10. The method according to claim 1, characterized in that In the step (6), hydrogen escape is carried out at a temperature ≤ 200°C.

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