KR102341461B1 - Method of evaluating hydrogen permeation properties - Google Patents

Abstract

The present invention comprises the following steps of: placing a specimen to charge hydrogen in a chamber in which hydrogen is filled above atmospheric pressure; exposing the specimen and measuring residual hydrogen amount of the specimen over time; and calculating a charging amount of hydrogen for the specimen by using the measured residual hydrogen amount and a law of diffusion. The evaluation method calculates the charging amount of hydrogen for the specimen and hydrogen diffusivity by using a simple and cheap device.

Description

Method of evaluating hydrogen permeation properties

The present technology relates to a method for evaluating the permeation characteristics of hydrogen.

In order to prevent environmental degradation due to global warming, it is essential to reduce carbon dioxide emissions, and the depletion of fossil fuels is expected in the near future. .

In response to these requests, hydrogen as an energy source is receiving great attention. Hydrogen can be obtained from fossil fuels, industrial process by-products, biomass, etc., but ultimately it can be obtained through water electrolysis using renewable energy, and it is an ideal that does not emit carbon dioxide when it reacts with oxygen to generate electricity. It is a clean energy source.

Hydrogen gas has a very small molecular size and is light, so it can easily penetrate into a material, and the permeated hydrogen causes material withdrawal and fracture, and can cause enormous damage. In organic materials such as plastics and rubbers, hydrogen can easily penetrate into the material and cause deterioration of physical properties.

In the case of a hydrogen electric vehicle that uses hydrogen gas as fuel, it is necessary to eliminate the risk of explosion and gas leakage because it uses high-pressure hydrogen at 700 bar. O-ring sealing (O-ring) using rubber materials such as NBR (nitrile butadiene rubber), FKM (fluoroelastomer), EPDM (ethylene propylene diene monomer), etc. for connection with the valve system that can control the emission of hydrogen gas from the gas storage tank sealing) is used. Since these rubber materials play a very important role for safety in the movement path of hydrogen gas, it is necessary to develop a technology to evaluate the hydrogen diffusion and permeation properties and hydrogen embrittlement properties of these materials.

The present technology is to solve the above request, and to calculate the amount of hydrogen charged to the material. Another aspect of the present technology is to calculate the hydrogen charged in the material and the hydrogen diffusivity in the material.

The present technology comprises the steps of disposing a sample so that hydrogen is charged in a chamber filled with hydrogen above atmospheric pressure, exposing the sample and measuring the amount of residual hydrogen in the sample over time, and the measured residual hydrogen amount and and calculating the amount of hydrogen charged to the sample by using the diffusion law.

According to this embodiment, there is an advantage that the apparatus for evaluating the amount of hydrogen charged is simple and inexpensive.

1 is a flowchart schematically illustrating each step of the method for evaluating the amount of hydrogen charged according to the present embodiment.
2(a) to 2(e) are diagrams schematically illustrating each step of the hydrogen loading amount evaluation method according to the present embodiment.
Figure 3 (a) is a schematic diagram plotting the amount of residual hydrogen obtained in Equation (2), Figure 3 (b) is an enlarged view of the portion shown by the broken line in Figure 3 (a).
4 is an example of a device 500 such as a PC in which hydrogen loading amount calculation software is performed.
5 is a diagram illustrating an experimental result calculated by computer software according to the present embodiment.
6 is a view of measuring the change in mass of a rubber sample before and after heat treatment at 70° C. for 48 hours.
7 is a view showing the content of gas emitted after heat treatment.
8(a) and 8(b) are diagrams showing analysis results for NBR rubber at a pressure of 40 MPa.
FIG. 9(a) is a diagram illustrating the amount of hydrogen gas charged according to pressure in NBR rubber, and FIG. 9(b) is a diagram illustrating the diffusivity of the same sample.
FIG. 10(a) is a diagram illustrating the amount of hydrogen gas charged according to pressure in the EPDM rubber, and FIG. 10(b) is a diagram illustrating the diffusivity of the same sample.
11 (a) is a diagram showing the amount of hydrogen gas charged according to pressure in the FKM rubber, and FIG. 11 (b) is a diagram showing the diffusivity of the same sample.
12 is a comparative view of the results of measuring the transmittance of rubber obtained from the same sample.

Hereinafter, a method for evaluating the amount of hydrogen charged according to the present embodiment will be described with reference to the accompanying drawings. 1 is a flowchart schematically illustrating each step of the method for evaluating the amount of hydrogen charged according to the present embodiment. Referring to Figure 1, the hydrogen loading amount evaluation method according to the present embodiment comprises the steps of disposing a sample such that hydrogen is charged in a chamber filled with hydrogen above atmospheric pressure (S100), exposing the sample and time-dependent It includes the steps of measuring the amount of residual hydrogen in the sample (S200), and calculating the amount of hydrogen charged to the sample using the measured residual hydrogen amount and the diffusion law (S300).

2(a) to 2(e) are diagrams schematically illustrating each step of the hydrogen loading amount evaluation method according to the present embodiment. Figure 2 (a) is a view schematically showing the step of heat-treating the sample. Referring to FIG. 2A , in an embodiment, heat treatment may be performed on the sample 100 . The heat treatment may be performed in an electric furnace at room temperature or higher and at a temperature at which thermal denaturation of the sample 100 is not performed for at least 24 hours or longer. Various types of gases may be dissolved in the sample 100 , and the dissolved gas is outgassed in the heat treatment step. After filling the sample with hydrogen in subsequent steps, in order to accurately measure the hydrogen emitted from the sample, heat treatment may be performed to remove the effect of the gas dissolved in the sample.

FIG. 2B is a diagram schematically illustrating a state in which hydrogen is disposed in the first chamber C1 to be charged into the sample. Referring to FIGS. 1 and 2 ( b ), the heat-treated sample 100 is disposed such that hydrogen is charged into the first chamber C1 filled with hydrogen above atmospheric pressure ( S100 ). In an embodiment, the first chamber C1 may be maintained at a hydrogen pressure of 1 MPa to 100 MPa and a temperature of 20° C. to 50° C. The sample 100 may be located in the first chamber C1 for 1 to 100 hours. As the sample 100 is exposed to a high-pressure hydrogen atmosphere in the first chamber C1, hydrogen gas is dissolved in the sample.

The sample is exposed to the second chamber C2 at a pressure lower than that of the first chamber C1, and a change in the amount of residual hydrogen in the sample over time is measured (S200). The hydrogen-charged sample 100 is moved to and located in the second chamber C2, and the hydrogen charged in the second chamber C2 is discharged to the outside. For example, the second chamber C2 is maintained at 15° C. to 35° C., and a humidity of 20% or less.

The sample 100 is placed on the electronic scale 200 located in the second chamber C2. Since the sample 100 discharges the charged hydrogen gas to the outside in the second chamber C2, the measured value of the electronic scale 200 is measured to decrease. As shown in FIG. 2B , the electronic scale 200 and the arithmetic device 500 connected to the GPIR (General Purpose Interface Bus) measure the mass of the sample 100 at every unit time. For example, the computing device may be a computer (PC), and may receive measurement data of the sample 100 every second from the electronic scale 200 through the GPIB interface.

The calculating device 500 calculates the mass ratio of hydrogen remaining in the sample to the mass of the sample 100 by calculating Equation 1 below from the measurement data provided for each unit time.

(C(t): residual hydrogen amount, M(t): sample mass after t unit time after exposing the sample, M ₀ : sample mass before hydrogen charging)

Next, the amount of hydrogen charged into the sample is calculated using the mass change data of the amount of residual hydrogen in the sample 100 and the diffusion law. FIG. 2( c ) is a diagram schematically illustrating a step of calculating the amount of hydrogen charged to a sample. Referring to FIGS. 1 and 2 ( c ), the hydrogen loading amount of the sample is calculated from the amount of residual hydrogen in the sample 100 calculated for every unit time.

The change in the amount of residual hydrogen in the sample 100 is determined by the diffusion law expressed by Equation 2 below. C(t) in Equation 2 represents the amount of residual hydrogen in the sample 100 at time t when hydrogen is uniformly distributed in the sample and then diffuses into the vacuum. Therefore, by calculating Equation 2 from the value of the mass ratio of hydrogen remaining in the sample calculated by Equation 1, _{it is possible to obtain the initial hydrogen charging mass C H0} in the sample 100 and the hydrogen diffusivity (D, diffusivity) in the sample.

(C _H0 : the amount of hydrogen charged in the sample, l: the thickness of the sample, ρ: the radius of the sample, βn: the root of the zero-order Bessel function. D: the diffusivity of hydrogen, C(t): the amount of residual hydrogen)

Figure 3 (a) is a schematic view plotting the residual hydrogen amount C (t) obtained in Equation 2, Figure 3 (b) is an enlarged view of the portion shown by the broken line in Figure 3 (a). _{Although not shown in FIG. 3A , the movement time t 0} is consumed in the process of moving the sample from the first chamber C1 (see FIG. 2 ) to the second chamber C2 (see FIG. 2 ).

In Equation 2, the derivative of the function when t=0 is -∞. This means that the rate at which hydrogen escapes in the first place is extremely high. It is understood that this occurs because of the discontinuous difference in pressure from high pressure inside the sample to vacuum outside.

Therefore, the hydrogen loading amount (CH ₀ ) in the sample must be determined in consideration of the movement time (t _{0 ). Referring to FIG. 3(b) , the hydrogen loading amount C H0} just before depressurization in the first chamber C1 may be calculated by performing extrapolation from the measurement data obtained from Equation 1 as shown by a dotted line. In addition, by calculating the data calculated from Equation 1 and C _H0 obtained by extrapolation together with Equation 2, the hydrogen diffusivity D in the sample 100 can be calculated.

1 and 2(e), by calculating Equation 3 from the hydrogen loading amount C _H0 and the hydrogen diffusivity (D) obtained in Equation 2, the permeability (P) and the solubility of hydrogen (solubility, S) can be calculated.

(D: hydrogen diffusivity, S: hydrogen loading, P: permeability, S: solubility)

4 is an example of a device 500 such as a PC in which hydrogen loading amount calculation software is performed. The hydrogen loading amount calculation software may be provided in a circuit or a chipset composed of a memory and an operation element. 4 is an example showing the configuration of the device 500 equipped with the hydrogen loading amount calculation software without limiting the physical configuration. 4 may be a configuration of a PC, a server, or a chip.

The device 500 equipped with the hydrogen loading amount calculation software includes an input device 510 , a calculation device 520 , and a storage device 530 . Furthermore, the device 500 equipped with the hydrogen loading amount calculation software may further include an output device 540 .

The input device 510 receives measurement data from the GPIB (refer to FIG. 2 ). The input device 510 may be a communication device or an interface device that receives measurement data from a network. Also, the input device 510 may be an interface device for receiving measurement data through a wired network. Meanwhile, the input device 510 may receive an external control signal. As an example, the measurement data may be input by the user through the input device 510 data read by the voltage meter and/or the current meter.

The storage device 530 may store a hydrogen loading amount calculation software model. The storage device 530 may be implemented in various media such as a semiconductor storage device and a hard disk capable of storing data. The storage device 530 may store the hydrogen loading amount calculation software, store various information and parameters used in the calculation process, and store the calculated result.

The arithmetic unit 520 operates and calculates the hydrogen loading amount calculation software using the provided measurement data. In addition, the calculator 520 calculates the mass ratio of hydrogen remaining in the sample to the mass of the sample 100, and uses the residual hydrogen mass change data and the diffusion law to calculate the amount of hydrogen charged to the sample, extrapolation, The diffusivity, permeability and solubility can be calculated. The calculation device 520 may derive a result value by inputting the provided measurement data into the hydrogen loading amount calculation software.

The arithmetic unit 520 corresponds to a device that processes data by driving a predetermined command or program. The arithmetic unit 520 may be implemented as a memory (buffer) for temporarily storing instructions or information and a processor for performing arithmetic processing. The processor may be implemented as a CPU, AP, FPGA, or the like, depending on the type of device.

The output device 540 may be a communication device that transmits necessary data to the outside. The output device 540 may transmit a result value derived by the learned hydrogen loading amount calculation software to the outside. In some cases, the output device 540 may be a device for outputting a hydrogen loading amount calculation software learning process or a result value to be derived by the learned hydrogen loading amount calculation software on a screen.

In addition, calculation of the mass ratio of hydrogen remaining in the sample to the mass of the sample 100 described above, calculation of the amount of hydrogen charged to the sample using the residual hydrogen mass change data and diffusion law, extrapolation calculation, as well as diffusivity, permeability And the solubility calculation method may be implemented as a program (or application) including an executable algorithm that can be executed in a computer. The program may be provided by being stored in a non-transitory computer readable medium.

The non-transitory readable medium refers to a medium that stores data semi-permanently, rather than a medium that stores data for a short moment, such as a register, cache, memory, and the like, and can be read by a device. Specifically, the various applications or programs described above may be provided by being stored in a non-transitory readable medium such as a CD, DVD, hard disk, Blu-ray disk, USB, memory card, ROM, and the like.

5 is a diagram illustrating an experimental result calculated by computer software according to the present embodiment. Referring to FIG. 5 , measured values are indicated by a red + mark, and a result of calculating the hydrogen loading amount obtained by performing curve fitting therefrom is indicated in dark green. Furthermore, it can be seen that diffusivity, hydrogen loading amount, and transmittance values are calculated and displayed in the lower part of FIG. 5 .

Experimental example

6 is a view of measuring the change in mass of the rubber sample 100 before and after heat treatment at 70° C. for 48 hours. The mass decreased by about 1200 ppm before and after the heat treatment. Before the heat treatment, the gas dissolved in the sample was discharged, and the mass of the rubber decreased by about 140 ppm for two days. However, after the heat treatment, the mass decreased to less than 10 ppm for two days compared to before the heat treatment. 10 ppm is identified as the effect of offset or drift of the electronic balance. After the heat treatment, it was confirmed that other gases were not released as will be described later. Accordingly, the hydrogen gas permeation characteristic of the sample 100 may be evaluated by performing heat treatment.

7 is a view showing the content of gas emitted after heat treatment. After the heat treatment, other gases were not released, hydrogen was charged for 24 hours, and the gas component released from the rubber sample after depressurization in the second chamber (C2) was measured for 24 hours using TDS-GC. As shown in Figure 7, after the heat treatment, it can be confirmed that only the peaks _{of oxygen (O 2} ) and nitrogen (N ₂ ) and hydrogen (H _{2 ) dissolved in the sample exist in the tube for moving the sample.} .

After the heat treatment, hydrogen was charged by applying a pressure of 7 MPa to 70 MPa in the first chamber with respect to the three types of rubber. Then, the change in mass after decompression was measured using an electronic balance. By substituting the residual hydrogen amount at each time into Equation 4, each parameter was optimized by the least squares method to obtain the diffusion coefficient and the hydrogen loading amount.

8(a) and 8(b) are diagrams showing analysis results for NBR rubber at a pressure of 40 MPa. FIG. 8(a) is an analysis result obtained by calculating the diffusion coefficient and the hydrogen loading amount, and FIG. 8(b) is a diagram showing the analysis result of the hydrogen residual amount in log scale in the origin program of the left analysis result.

FIG. 9(a) shows the amount of hydrogen gas charged according to pressure in the NBR rubber, and FIG. 9(b) shows the diffusivity of the same sample. The charging amount of hydrogen gas in the NBR rubber shown in FIG. 9(a) follows Henry's law, which increases in proportion to the pressure up to 40 MPa (solid blue line), and the increase rate decreases at the pressure above that.

_{The solubility (S) of hydrogen can be obtained by dividing the charge (C H0} ) by the pressure (P) by Henry's law exemplified by Equation ① of Equation 3, which is a slope shown by a straight line in Fig. 9(a). corresponds to In Fig. 9(a), solubility S = (22.45±0.49) mol/m ³ MPa. The error bar was taken from the FOM value in the analysis program.

On the other hand, since the hydrogen charge deviates from Henry's law at 40 MPa or more, it was analyzed using the Langmuir model expressed as follows, and the result is shown in Equation 5 below.

(P: pressure, a: langumir adsorption quantity, b: langumir adsorption pressure)

The analysis result using Equation 5 is shown by the black dotted line on the left side of FIG. 9(a), where a = 5442 wt ppm and b = 140 MPa.

The measurement result of the hydrogen diffusivity of the NBR rubber shown in FIG. 9(b) increases in proportion to the pressure up to 40 MPa, similar to the measurement result of the charging amount, and does not show a pressure dependence result at a pressure higher than that. Therefore, since the diffusivity does not show pressure dependence over the entire pressure range and is in the range of (0.8 ∼ 5.9) × 10 ^-10 m ² /s, the average value is taken and the average diffusivity D _ave = (2.3 ± 0.8) × 10 ^-10 m ² /s get Error bars represent the uncertainty of each measurement.

10(a) shows the amount of hydrogen gas charged according to pressure in the EPDM rubber, and FIG. 10(b) shows the diffusivity of the same sample. The charged amount of hydrogen gas in the EPDM rubber shown in FIG. 10(a) follows Henry's law, which increases in proportion to the pressure up to 50 MPa (solid blue line), similar to the previous NBR. According to Henry's law, the solubility of hydrogen corresponds to the slope of the solid line in FIG. 10(a), and the value was determined to be S = (16.13±1.11) mol/m ³ MPa. Here, the error bar takes the FOM value from the simulation in the same way as the NBR. On the other hand, above 50 MPa, the hydrogen charge deviates from Henry's law, so the analysis was performed using the Langmuir model of Equation 5 (black dotted line), and the results are a = 3200 wt ppm, b = 65 MPa.

The measurement result of the hydrogen diffusivity of the EPDM rubber shown in FIG. 10(b) increases in proportion to the pressure up to 50 MPa, similar to the measurement result of the charging amount, and does not show a pressure dependence result at a pressure higher than that. This trend is similar to the previous NBR. Therefore, since the diffusivity does not show any pressure dependence over the entire pressure range and is in the range of (0.5 ~ 6.7) × 10 ^-10 m ² /s, the average value is taken and the average diffusion D _ave = (2.9 ± 0.8) × 10 ^-10 m ^{We get 2} /s.

Fig. 11 (a) shows the amount of hydrogen gas charged according to pressure in the FKM rubber, and Fig. 11 (a) shows the diffusivity of the same sample. Similar to the results of NBR and EPDM, the charged amount of hydrogen gas in the FKM rubber shown in FIG. According to Henry's law, the solubility of hydrogen corresponds to the slope of the solid line in FIG. 11(a), and the value is S = (632±0.60) mol/m ³ MPa. Here, the error bar takes the FOM value from the simulation in the same way as before. On the other hand, since the amount of hydrogen charged above 50 MPa deviates from Henry's law, it was analyzed using the Langmuir model of Equation 5 (black dotted line), and the results are a = 832 wt ppm, b = 85 MPa.

Since the measurement result of hydrogen diffusivity of FKM rubber illustrated in FIG. 11(b) does not show a pressure dependence result and is in ^{the range of (0.7 to 4.6) × 10 -10} m ² /s, the average value is taken and the average diffusivity D _ave = (2.41 ± 0.82) × 10 ^-10 m ² /s is obtained.

12 is a comparative view of the results of measuring the transmittance of rubber obtained from the same sample. In FIG. 12, ■, ●, and ▲ are the results measured in this experiment, respectively. From the solubility and average diffusivity obtained above, the hydrogen gas permeability was obtained using the relationship of Equation ② in Equation 3, and the results for the three types of rubber are shown in FIG. 12 . In order to verify the effectiveness of the method for evaluating the permeation characteristics of hydrogen gas measured with an electronic scale, the transmittance measurement results for the same type of sample performed in the previous study were compared with each other, and the results are shown in FIG. 12 . The two measurement results agree with each other except for the case of NBR within the range of uncertainty. Even in the case of NBR, if the uncertainty of the shore 70 sample is included, the agreement can be achieved within the uncertainty range.

For three types of rubber samples, at a pressure of 40 to 50 MPa, the hydrogen loading can be explained by Henry's law proportional to the pressure, and for the full range of pressures, it can be better explained by the Langmuir model. In all three rubber samples, the diffusion of hydrogen is explained by a single hydrogen diffusion within the polymer.

The present embodiment has the advantage that the apparatus is simple and inexpensive, and can also be measured in the field.

S100, S200, S300: Each step of the method of calculating the hydrogen loading according to this embodiment
100: sample 200: electronic balance
500: Device equipped with hydrogen loading amount calculation software
510: input device 520: arithmetic device
530: storage device 540: output device

Claims (17)

Placing the sample in a chamber filled with hydrogen above atmospheric pressure so that hydrogen is charged;
Depressurizing the sample and calculating the amount of residual hydrogen in the sample over time;
Comprising the step of obtaining the amount of hydrogen charged to the sample by using the residual hydrogen amount and diffusion law,
prior to the step of placing the sample
A method for evaluating the amount of hydrogen charged by performing the step of heat-treating the sample. delete According to claim 1,
The heat treatment is
A method for evaluating the amount of hydrogen charged at room temperature or higher, at a temperature at which thermal denaturation of the sample is not performed for at least 24 hours. According to claim 1,
Placing the sample comprises:
A method of evaluating a hydrogen loading amount performed for 1 hour to 100 hours in a chamber maintained at any one of a pressure of 1 MPa to 100 MPa and any one of a temperature of 20° C. to 50° C. According to claim 1,
Measuring the amount of residual hydrogen comprises:
Place the sample in a chamber of 15 ℃ to 35 ℃, humidity of 20% or less,
A method for evaluating the amount of hydrogen charged by measuring the mass of the sample with an electronic balance. According to claim 1,
Measuring the amount of residual hydrogen comprises:
calculating a mass ratio of hydrogen remaining in the sample to the mass of the sample per unit time;
A method for evaluating a hydrogen loading amount, comprising calculating a hydrogen diffusivity in the sample and a hydrogen loading amount of the sample using a diffusion law from a calculation result. 7. The method of claim 6,
Calculating the mass ratio of hydrogen remaining in the sample to the mass of the sample for each unit time comprises:
formula

(C(t): residual hydrogen amount, M(t): the mass of the sample after t time after exposing the sample, M ₀ : the sample mass before hydrogen charging) 7. The method of claim 6,
The hydrogen diffusivity and the hydrogen loading amount of the sample are
formula

(CH ₀ : hydrogen loading of the sample, l: thickness of sample, ρ: radius of sample, βn: root of zero-order Bessel function. D: diffusivity of hydrogen, C(t) ): Residual hydrogen amount) 9. The method of claim 8,
The step of calculating the hydrogen loading amount,
exposing the sample;
A method for evaluating the amount of hydrogen charged by extrapolating from the equation to compensate for the time between the steps of measuring the amount of residual hydrogen in the sample. According to claim 1,
The hydrogen loading amount evaluation method,
formula

calculating permeability by calculating
formula

A method for evaluating the loading amount of hydrogen further comprising at least one or more of the steps of calculating solubility by calculating . (P: penetration, S: solubility, CH ₀ : hydrogen loading of the sample, D: diffusivity) According to claim 1,
The hydrogen loading amount evaluation method,
A method for evaluating a hydrogen loading amount by calculating the hydrogen loading amount using a Langumir model. A method for calculating the amount of residual hydrogen in a sample loaded with hydrogen is a recording medium in which computer software that is read by a machine and can be executed by the machine is recorded, the method comprising:
calculating a mass ratio of hydrogen remaining in the sample to the mass of the sample per unit time;
Comprising the step of calculating the hydrogen diffusivity in the sample and the hydrogen loading amount of the sample by using the diffusion law from the calculation result,
The hydrogen diffusivity and the hydrogen loading amount of the sample are
formula

is performed by calculating
Measuring the hydrogen loading is,
A recording medium performed by extrapolating from the above equation to compensate for the time between the steps of measuring the amount of residual _{hydrogen in the sample after depressurizing the sample in the chamber. (CH 0} : hydrogen loading amount of the sample, l: thickness of sample, ρ: radius of sample, βn: root of zero-order Bessel function, D: diffusivity of hydrogen, C(t): amount of residual hydrogen) 13. The method of claim 12,
Calculating the mass ratio of hydrogen remaining in the sample to the mass of the sample for each unit time comprises:
formula

(C(t): residual hydrogen amount, M(t): sample mass after t time after exposing the sample, M ₀ : sample mass before hydrogen charging) delete delete 13. The method of claim 12,
The hydrogen loading amount evaluation method,
formula

calculating permeability by calculating
formula

The operation to a recording medium further includes at least any one or more of the step of computing the solubility (solubility). (P: penetration, S: solubility, CH _0: the sample jangipryang hydrogen, D: Wild) 13. The method of claim 12,
The hydrogen loading amount evaluation method,
A recording medium for calculating the hydrogen loading amount using a langumir model.

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