Measuring Method of Equivalent Temperature in Gas Adsorption Instrument in Liquid Helium Temperature Range

Abstract

The present invention provides a method for measuring the equivalent temperature in a gas adsorption instrument in the liquid helium temperature range. The method comprises: using a non-porous material with a specific surface area much smaller than that of the sample to be tested to make a substitute for the sample to be tested. After ensuring that its volume is equal to the true volume of the sample to be tested, the substitute is placed in the measurement space of the gas adsorption instrument to replace the sample to be tested; controlling the temperature of the reference space, evacuating the reference space, and then filling the reference space with a certain amount of helium. After stabilization, the pressure P1 of the reference space is measured; the measurement space is cooled to the experimental temperature T2 in the liquid helium temperature range, connecting the reference space and the measurement space, and measuring the pressure P2 after stabilization; and combining the curve of the compressibility factor of helium at pressure P2 with temperature to iteratively obtain the equivalent temperature of the measurement space at pressure P2 and experimental temperature T2. The present invention solves the technical problem of determining the equivalent temperature of the temperature gradient section during the measurement of gas adsorption using the volumetric method in the liquid helium temperature range.

Description

Technical Field

[0001] The invention relates to the technical fields of gas adsorption amount measurement, porous material specific surface area analysis and volumetric gas adsorption instrument, and in particular to a method for measuring the equivalent temperature of a gas adsorption instrument in a liquid helium temperature range. Background Art

[0002] Porous materials and their adsorption properties are widely used in chemical, biological, and energy fields. Specific surface area and pore size distribution are important factors affecting their performance. Gas adsorption experiments are often used to obtain information such as the specific surface area and pore size distribution of porous materials. The volumetric gas adsorption instrument is a commonly used measuring instrument for gas adsorption experiments. Its basic principle can be referred to the national standard GB / T 19587-2017, "Determination of the Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method." The sample to be tested is placed in the sample chamber, and the difference in gas volume before and after adsorption is measured to determine the gas adsorption amount. This method requires measuring the temperature, pressure, and gas free volume within the sample chamber so that these can be substituted into the gas state equation to determine the gas volume.

[0003] During measurement, the sample chamber is at a lower experimental temperature, and the other parts of the device are at room temperature. There is a temperature gradient in the pipe connecting the sample chamber and the room temperature part, making it difficult to directly use the gas state equation to determine the amount of gas contained in this section of the pipe. The current liquid nitrogen temperature zone (77K) volumetric gas adsorption instrument often uses the equivalent temperature method to deal with the temperature gradient problem. By introducing inert gas helium into the sample chamber and assuming that the adsorption amount of helium is negligible, the amount of helium contained in the temperature gradient section can be determined. At this time, the temperature gradient section is equivalent to a gas pipeline with the same geometric dimensions at a uniform temperature, so that the amount of helium in the pipeline before and after the equivalent is equal, then the equivalent temperature of the temperature gradient section can be obtained, which is convenient for determining the amount of adsorbate gas contained in the temperature gradient section in subsequent adsorption experiments. For specific implementation methods, please refer to patent ZL 202111021523.0 "Volumetric adsorption measurement method and device".

[0004] For adsorption measurement experiments in the liquid helium temperature range (4K), since the adsorption amount of helium at low temperatures cannot be ignored, the above method of determining the equivalent temperature is no longer applicable. Therefore, a new method of determining the equivalent temperature needs to be developed to meet the adsorption measurement needs in the liquid helium temperature range. Summary of the Invention

[0005] This paper addresses the temperature gradient issue in the sample chamber during adsorption experiments in the liquid helium temperature range (4K) by proposing a method for determining the equivalent temperature by replacing the adsorbent with an equal volume. A material with a much smaller specific surface area than the adsorbent being tested is placed in the sample chamber, ensuring its volume is equal to the true volume of the sample being tested. Because its specific surface area is much smaller than the sample being tested, the amount of helium adsorbed on its surface is negligible even at 4K temperatures. This allows the helium content and equivalent temperature within the temperature gradient segment to be determined using traditional methods.

[0006] To achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for measuring the equivalent temperature in a gas adsorption instrument in a liquid helium temperature range, comprising the following steps:

[0008] The adsorbent in the gas adsorption instrument is used as the sample to be tested, and a substitute equal to the true volume of the sample to be tested is selected. The substitute is a solid particle made of a non-porous material and satisfies the following conditions: (1) the specific surface area per unit volume of the substitute is much smaller than the specific surface area per unit true volume of the sample to be tested; (2) the volume of a single substitute is much smaller than the total true volume of the sample to be tested;

[0009] Obtain the volume V1 of the reference space in the gas adsorption instrument;

[0010] placing the weighed substitute in a measurement space in a gas adsorption instrument, and obtaining a volume V2 of the measurement space after the substitute is added;

[0011] controlling the temperature of the reference space to be T1, evacuating the reference space, filling the reference space with a certain amount of helium, and measuring the pressure P1 of the reference space after the pressure of the reference space stabilizes;

[0012] Cooling the measurement space to an experimental temperature T2 in the liquid helium temperature range, connecting the reference space and the measurement space, and measuring the pressure P2 of the system after the pressure of the system formed by the reference space and the measurement space stabilizes;

[0013] Combined with the curve of the compressibility factor of helium at pressure P2 varying with temperature, the equivalent temperature of the measurement space at pressure P2 and experimental temperature T2 is obtained iteratively.

[0014] In some embodiments, selecting a substitute that is equal to the true volume of the sample to be tested specifically includes:

[0015] Measuring the true density ρ1 of the sample to be tested;

[0016] Measure the density ρ2 of the chosen surrogate;

[0017] Measuring the mass m1 of the sample to be tested;

[0018] Weigh the surrogate with mass m2, which is determined by the following formula:

[0019]

[0020] In some embodiments, the non-porous material includes a metal and a salt compound.

[0021] In some embodiments, the metal is an alloy composed of any one or more of chromium, nickel, aluminum and tin.

[0022] In some embodiments, the salt compound is potassium nitrate or potassium chloride.

[0023] In some embodiments, the substitute satisfies the following conditions simultaneously: (1) the specific surface area per unit volume of the substitute is no more than 10% of the specific surface area per unit true volume of the sample to be tested; -4 ; (2) The volume of a single substitute does not exceed 5‰ of the total true volume of the sample to be tested.

[0024] In some embodiments, the adsorbent is activated carbon, and the substitute is tin balls, with a diameter of a single tin ball being 0.2 mm to 0.76 mm.

[0025] In some embodiments, the step of obtaining the volume V1 of the reference space in the gas adsorption instrument comprises:

[0026] evacuating the reference space in the gas adsorption instrument;

[0027] Filling the reference space with a certain amount of helium, and measuring the pressure P3 and temperature T3 of the reference space after the pressure of the reference space stabilizes;

[0028] An object with a known volume V0 is placed in the reference space, and after the pressure of the reference space stabilizes, the pressure P4 of the reference space is measured, while the temperature of the reference space remains unchanged at T3;

[0029] The volume V1 of the reference space is calculated by the following formula:

[0030]

[0031] Wherein, Z3 is the compressibility factor of helium at temperature T3 and pressure P3, and Z4 is the compressibility factor of helium at temperature T3 and pressure P4.

[0032] In some embodiments, the step of obtaining the volume V2 of the measurement space after adding the substitute comprises:

[0033] evacuating the reference space and the measurement space;

[0034] Filling the reference space with a certain amount of helium, and measuring the pressure P5 and temperature T4 of the reference space after the pressure of the reference space stabilizes;

[0035] Connecting the reference space and the measurement space, and measuring the pressure P6 of the system after the pressure of the system stabilizes, wherein the temperatures of the reference space and the measurement space are both consistent with the temperature T4;

[0036] The volume V2 of the measurement space after adding the substitute is calculated according to the following formula:

[0037]

[0038] Wherein, Z5 is the compressibility factor of helium at temperature T4 and pressure P5, and Z6 is the compressibility factor of helium at temperature T4 and pressure P6.

[0039] In some embodiments, the equivalent temperature of the measurement space is T2 under the pressure P2 and the experimental temperature T2. eff , which satisfies the following formula:

[0040]

[0041] Where Z1 is the compressibility factor of helium at temperature T1 and pressure P1, Z2 is the compressibility factor of helium at temperature T1 and pressure P2, and Z eff is the equivalent temperature of helium at T eff , compression factor under pressure P2.

[0042] Features and beneficial effects of the present invention

[0043] This method utilizes a material with a smaller specific surface area as an adsorbent substitute, extending the traditional method for determining the equivalent temperature of a temperature gradient segment to the liquid helium temperature range, thereby meeting the requirements for adsorption measurements in this region. Using the common solder ball material as an example, the feasibility of using it as an alternative material is analyzed. Due to its low cost, easy availability, and flexible size selection, the present invention offers strong operability and high measurement accuracy.

[0044] The purpose of this method is to determine the equivalent temperature in the liquid helium temperature zone volumetric gas adsorption instrument, but it can also be used to measure the helium adsorption amount by volumetric method at any temperature.

[0045] Applicable occasions of the present invention

[0046] The invention is applicable to the occasion of measuring the gas adsorption amount by liquid helium temperature zone volumetric method, and determines the equivalent temperature of the temperature gradient section at a low temperature of 4K. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is an overall flow chart of a method for measuring equivalent temperature in a gas adsorption instrument in the liquid helium temperature range provided by an embodiment of the present invention.

[0048] Figure 2 The present invention is a schematic structural diagram of a volumetric adsorption measurement system to which the measurement method provided by the present invention can be applied. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solutions and advantages of this application more clearly understood, this application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0050] On the contrary, this application covers any alternatives, modifications, equivalents, and solutions made within the spirit and scope of this application as defined by the claims. Furthermore, to facilitate a better understanding of this application, certain specific details are described in detail below in the detailed description of this application. Those skilled in the art will be able to fully understand this application without these details.

[0051] See also Figure 1 The embodiment of the present invention provides a method for measuring the equivalent temperature in a gas adsorption instrument in a liquid helium temperature range, comprising the following steps:

[0052] Step (1) using the adsorbent in the gas adsorption instrument as the sample to be tested, and measuring the true density ρ1 of the sample to be tested using a true density meter;

[0053] Step (2) uses a densitometer to measure the density ρ2 of the substitute, which is a solid particle made of a non-porous material and meets the following conditions: the specific surface area per unit volume of the substitute does not exceed 10% of the specific surface area per unit true volume of the sample to be tested. 4 ; The volume of a single surrogate shall not exceed 5‰ of the total true volume of the sample to be tested.

[0054] Step (3) measuring the mass m1 of the sample to be tested;

[0055] Step (4) Weigh the substitute with a mass of m2, where m2 is determined according to the following formula:

[0056]

[0057] Step (5) obtaining the volume V1 of the reference space in the gas adsorption instrument;

[0058] Step (6) placing the weighed substitute in the measurement space of the gas adsorption instrument, and obtaining the volume V2 of the measurement space after adding the substitute;

[0059] Step (7) controlling the temperature of the reference space to T1, evacuating the reference space, filling the reference space with a certain amount of helium, and measuring the pressure P1 of the reference space after the pressure of the reference space stabilizes;

[0060] Step (8) cooling the measurement space to an experimental temperature T2 in the liquid helium temperature range, connecting the reference space and the measurement space, and measuring the pressure P2 of the system after the pressure of the system composed of the reference space and the measurement space stabilizes;

[0061] Step (9) combines the curve of the compressibility factor of helium at pressure P2 with temperature, and iteratively obtains the equivalent temperature of the measurement space under the pressure P2 and experimental temperature T2.

[0062] The measurement method proposed in an embodiment of the present invention is a method for measuring equivalent temperature by replacing an adsorbent with an equal volume. Specifically, a substitute for the sample to be tested is made of a non-porous material with a specific surface area much smaller than that of the sample to be tested (such as the adsorbent). After ensuring that its volume is equal to the true volume of the sample to be tested, it is placed in the measurement space to replace the sample to be tested. Since the specific surface area of ​​the substitute is much smaller than that of the sample to be tested, the amount of helium adsorbed on its surface can be ignored even in a low-temperature environment of 4K. Therefore, the amount of helium contained in the temperature gradient segment and the equivalent temperature can be determined according to traditional methods, thereby meeting the adsorption measurement requirements in the liquid helium temperature range.

[0063] In some embodiments, steps (1) and (2) can be completed using commercially available instruments.

[0064] Furthermore, in step (2), the material used to make the substitute can be a material that does not have a porous structure, such as a metal or salt compound, i.e., a non-porous material, and should meet the following conditions: (1) the specific surface area per unit volume of the substitute does not exceed 10% of the specific surface area per unit true volume of the sample to be tested; -4 (2) Ensure that the volume of a single substitute does not exceed 5‰ of the total true volume of the sample to be tested, so that the combination can achieve a volume equal to the total true volume of the sample to be tested.

[0065] Preferably, the metal used to make the substitute can be an alloy composed of any one or more of chromium, nickel, aluminum and tin, and the salt compound can be potassium nitrate, potassium chloride and the like.

[0066] In a specific embodiment of the present disclosure, metal tin is selected to prepare tin balls as a substitute. The diameter of a single tin ball is 0.5 mm, and its specific surface area per unit volume is about 1.2*10 -2 m 2 / cm 3 , while the commonly used adsorbent activated carbon has a specific surface area per unit true volume of more than 10 3 m 2 / cm 3The specific surface area of ​​the tin ball is much smaller than that of the activated carbon. Therefore, under the same volume conditions, the amount of helium adsorbed on the surface of the tin ball can be ignored. For a tin ball with a diameter of 0.5 mm, the volume of a single ball is about 6.5*10 -5 cm 3 The true volume of 0.1g activated carbon sample required for one adsorption measurement is about 5*10 -2 cm 3 Therefore, within an error range of less than 2‰, a volume equal to the true volume of the sample to be measured can be formed using solder balls with a diameter of 0.5mm. Furthermore, solder balls are available in a variety of diameters (0.2mm-0.76mm), making it more flexible to combine solder balls into a set volume.

[0067] In some embodiments, the specific steps of obtaining the volume V1 of the reference space in step (5) include:

[0068] Evacuate the reference space in the gas adsorption instrument;

[0069] Fill the reference space with a certain amount of helium, and after the pressure of the reference space stabilizes, measure the pressure P3 and temperature T3 of the reference space;

[0070] An object of known volume V0 (no special requirements for other properties of the object) is placed in the reference space. After the pressure of the reference space stabilizes, the pressure P4 of the reference space is measured, and the temperature of the reference space remains unchanged at T3.

[0071] The volume V1 of the reference space is calculated by the following formula:

[0072]

[0073] Wherein, Z3 is the compressibility factor of helium at temperature T3 and pressure P3, and Z4 is the compressibility factor of helium at temperature T3 and pressure P4.

[0074] In some embodiments, the specific steps of obtaining the volume V2 of the measurement space after adding the substitute in step (6) include:

[0075] Evacuate the reference space and the measurement space;

[0076] Fill the reference space with a certain amount of helium, and after the pressure of the reference space stabilizes, measure the pressure P5 and temperature T4 of the reference space;

[0077] Connect the reference space and the measurement space. After the system pressure stabilizes, measure the system pressure P6. The temperatures of the reference space and the measurement space are kept consistent with the temperature T4.

[0078] The volume V2 of the measurement space after adding the substitute is calculated according to the following formula:

[0079]

[0080] Wherein, Z5 is the compressibility factor of helium at temperature T4 and pressure P5, and Z6 is the compressibility factor of helium at temperature T4 and pressure P6.

[0081] In some embodiments, in step (9), the equivalent temperature of the measurement space under the pressure P2 and the experimental temperature T2 is set to T eff , which satisfies the following formula:

[0082]

[0083] Where Z1 is the compressibility factor of helium at temperature T1 and pressure P1, Z2 is the compressibility factor of helium at temperature T1 and pressure P2, and Z eff is the equivalent temperature of helium at T eff , the compression factor under pressure P2. The above formula is combined with the curve of the compression factor of helium under pressure P2 and temperature, and the equivalent temperature T of the measurement space under the measurement state of pressure P1 and temperature T1 can be obtained by iteration. eff Therefore, by changing the pressure P1 and changing the pressure P2, the equivalent temperature T of the measurement space can be obtained. eff The curve of the change with the measured pressure P2 under the experimental temperature T2. If only a single measurement is performed, the temperature T2 of the measurement space and the equivalent temperature T corresponding to the measured pressure P2 are obtained. eff If repeated measurements are performed, the equivalent temperature T is obtained by fitting under the condition of measurement space temperature T2. eff The curve that varies with the measured pressure P2 is better.

[0084] See also Figure 2 , is a schematic structural diagram of a volumetric adsorption measurement system constructed to implement the above-mentioned measurement method. The measurement system includes a refrigerator 1, a vacuum cover 2, a radiation cover 3, a sample chamber 6, a reference chamber 25, a helium cylinder 28, a vacuum pump 30, temperature sensors 7 and 26, a pressure sensor 15, and several gas pipelines and valves. Unit A shown in the dotted box contains the refrigerator 1, the vacuum cover 2, the radiation cover 3, the sample chamber 6, the temperature sensor 7, and a low-temperature vacuum device, which can keep the sample chamber 6 at a lower experimental temperature T2 under vacuum, and the experimental temperature T2 is in the liquid helium temperature range; the unit B shown in the dotted box contains the reference chamber 25, the temperature sensor 26, the pressure sensor 15, and gas pipelines and valves, which are in a constant room temperature environment, that is, the temperature T1 is at room temperature. Unit A and unit B are connected by a gas pipeline 16, and there is a temperature gradient in the gas pipeline 16. Wherein:

[0085] The refrigerator 1 is a GM refrigerator with two cold heads: a primary cold head 4 and a secondary cold head 5. A sample chamber 6 is connected to the secondary cold head 5 and can be cooled to 4K. A solder ball 8, serving as a substitute for the sample to be measured, is placed in the sample chamber 6. A temperature sensor 7 measures the temperature of the sample chamber 6. A vacuum hood 2 is connected to the primary cold head 4, providing a vacuum environment for the primary and secondary cold heads 4, 5, and sample chamber 6, while isolating them from the external atmosphere. A radiation hood 3 is connected to the secondary cold head 5 and positioned between the vacuum hood 2, the secondary cold head 5, and the sample chamber 6 to reduce radiation heat leakage from the low-temperature portion of the measurement system.

[0086] The gas pipeline in unit B consists of a main line 9 and several branch lines connected to it. Main line 9 is connected to branch lines 10-14. Branch line 10 is connected to sample chamber 6 via shutoff valve 20 and gas line 16. Branch line 11 is connected to reference chamber 25 via shutoff valve 21 and branch line 17. Branch line 12 is connected to helium cylinder 28 via shutoff valve 22 and branch line 18. Branch line 13 is connected to safety valve 23 to prevent excessive pressure in the measurement system. Branch line 14 is connected to vacuum pump 30 via shutoff valve 24 and branch line 19. Vacuum pump 30 is also connected to vacuum enclosure 2 via shutoff valve 29 and branch line 27 to evacuate the interior of vacuum enclosure 2. Temperature sensor 26 measures the temperature of the experimental apparatus in unit B, which is maintained at a constant room temperature. Pressure sensor 15 is located on main line 9 to measure the pressure in the gas pipeline.

[0087] The volume of the measurement space includes the free volume of gas in the sample chamber 6 (the free volume of gas in the sample chamber 6 refers to the remaining volume in the sample chamber 6 after removing the space occupied by the sample) and the volume of the gas pipeline 16. The reference space volume includes the volume of the reference chamber 25, the gas pipelines 9-14 and the gas pipeline 17.

[0088] The measurement steps based on the above measurement system include:

[0089] Step (1) uses a true density meter to measure the true density ρ1 of the sample to be tested - activated carbon.

[0090] Step (2) uses a densitometer to measure the density ρ2 of the solder ball 8, and the volume of a single solder ball 8 should not exceed 0.5‰ of the true volume of the sample to be tested.

[0091] Step (3) Measure the mass m1 of the sample to be tested.

[0092] Step (4) Weigh the solder ball 8 with a mass m2, where m2 is determined according to the following formula:

[0093]

[0094] Step (5) obtains the volume V1 of the reference space. The specific steps include:

[0095] Step (5.1) Obtain any object with a known volume V0 for use. Initially, all stop valves are in the closed state, and stop valve 20 is always in the closed state;

[0096] Step (5.2) Open the stop valves 21 and 24, keep the other stop valves closed, turn on the vacuum pump 30 and evacuate the reference space to 10 -3 Below Pa;

[0097] Step (5.3): Close the stop valves 21 and 24, turn off the vacuum pump 30, open the stop valve 22, fill a certain amount of helium into the main line 9 and the branch lines 11-14, and then close the stop valve 22. Use the pressure sensor 15 to measure the pressure P7 in the pipeline, and use the temperature sensor 26 to measure the temperature T3 of the reference space;

[0098] Step (5.4): Open the stop valve 21 to connect the reference chamber 25 to the main line 9. The states of the other stop valves remain unchanged. After the pressure in the reference space stabilizes, use the pressure sensor 15 to measure the pressure P3 in the reference space.

[0099] Step (5.5) Open the stop valve 24 to exhaust, open the reference chamber 25, place the object of known volume V0 into the reference chamber 25, reinstall the reference chamber 25 and repeat step (5.2);

[0100] Step (5.6): Close the stop valves 21 and 24, turn off the vacuum pump 30, open the stop valve 22, fill a certain amount of helium into the main line 9 and the branch lines 11-14, and then close the stop valve 22 so that the pressure in the line remains unchanged at P7;

[0101] Step (5.7) Open the shut-off valve 21 to connect the reference chamber 25 to the main line 9. The states of the other shut-off valves remain unchanged. After the pressure in the reference space stabilizes, use the pressure sensor 15 to measure the pressure P4 in the reference space.

[0102] In step (5.8), the volume V1 of the reference space is calculated using the following formula:

[0103]

[0104] Where Z3 is the compressibility factor of helium at temperature T3 and pressure P3, and Z4 is the compressibility factor of helium at temperature T3 and pressure P4. During steps (5.4) to (5.7), the temperature of the reference space remains constant at T3.

[0105] Step (6) places the weighed solder ball 8 in the sample chamber 6 and evacuates the measurement space to obtain the volume V2 of the measurement space after adding the solder ball 8 with a mass of m2. The specific steps include:

[0106] Step (6.1) Place the weighed solder ball 8 in the sample chamber 6, and all stop valves are closed;

[0107] Step (6.2) Open the stop valves 20, 21, and 24, and keep the other stop valves in the same state. Turn on the vacuum pump 30 to evacuate the measurement space and the reference space to 10 -3 Below Pa;

[0108] Step (6.3): Close stop valves 20 and 24, turn off vacuum pump 30, open stop valve 22, and leave the other stop valves unchanged. A certain amount of helium is injected into the reference space, and then stop valve 22 is closed. The pressure P5 in the pipeline is measured using pressure sensor 15, and the temperature T4 of the reference space is measured using temperature sensor 26.

[0109] In step (6.4), the stop valve 20 is opened, and the states of the other stop valves remain unchanged. The reference space and the measurement space are connected. After stabilization, the pressure P6 in the pipeline is measured using the pressure sensor 15. During this process, the temperature of the reference space remains unchanged at T4.

[0110] In step (6.5), the volume V2 of the measurement space after adding the solder ball 8 is calculated using the following formula:

[0111]

[0112] Wherein, Z5 is the compressibility factor of helium at temperature T4 and pressure P5, and Z6 is the compressibility factor of helium at temperature T4 and pressure P6.

[0113] Step (7) controls the temperature of the reference space to T1, evacuates the reference space, fills the reference space with a certain amount of helium, and measures the pressure P1 in the reference space after the pressure in the reference space stabilizes. The specific steps include:

[0114] Step (7.1) Close each stop valve, open stop valves 20, 21, 24, and turn on the vacuum pump 30 to evacuate the reference space and the measurement space to 10 -3 Below Pa;

[0115] In step (7.2), the stop valves 20 and 24 are closed, the vacuum pump 30 is turned off, the stop valve 22 is opened, and the states of the other stop valves remain unchanged. A certain amount of helium is filled into the reference space, and then the stop valve 22 is closed. The pressure P1 in the pipeline is measured using the pressure sensor 15, and the temperature T1 of the reference space is measured using the temperature sensor 26, and the temperature of the reference space is kept constant at T1.

[0116] Step (8) cools the measurement space to an experimental temperature T2 in the liquid helium temperature range, connects the reference space and the measurement space, and measures the pressure P2 in the system after the pressure of the system composed of the reference space and the measurement space stabilizes. The specific steps include:

[0117] Step (8.1) Open the stop valve 29, and keep the other stop valves in the same state. Turn on the vacuum pump 30 to evacuate the inside of the vacuum cover 2 to 10 -3 Pa, then turn off the vacuum pump 30, close the stop valve 29, turn on the refrigerator 1 to cool the measurement space to the liquid helium temperature range, and use the temperature sensor 7 to measure the temperature of the measurement space until it reaches the experimental temperature T2 in the liquid helium temperature range;

[0118] In step (8.2), the stop valve 20 is opened, and the states of the other stop valves remain unchanged, connecting the reference space and the measurement space. After the system pressure constituted by them stabilizes, the pressure P2 in the system is measured using the pressure sensor 15.

[0119] Step (9) At this time, the equivalent temperature T of the measurement space is eff Satisfy the following formula:

[0120]

[0121] Where Z1 is the compressibility factor of helium at temperature T1 and pressure P1, Z2 is the compressibility factor of helium at temperature T1 and pressure P2, and Z eff is the equivalent temperature of helium at T eff , compression factor under pressure P2. The above formula is combined with the curve of helium compression factor under pressure P2 and temperature change, and the equivalent temperature T of the measurement space under the measurement state of pressure P2 and temperature T2 can be obtained by iteration. eff .

[0122] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0123] Although the embodiments of the present disclosure have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and alterations may be made to the embodiments without departing from the principles and spirit of the present disclosure, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for measuring the equivalent temperature of a gas adsorption instrument in the liquid helium temperature range, characterized in that: The following steps are involved: The adsorbent in the gas adsorption instrument is used as the sample to be tested, and a substitute with the same true volume as the sample to be tested is selected. The substitute is a solid particle made of a non-porous material and satisfies the following conditions: (1) the specific surface area per unit volume of the substitute is much smaller than the specific surface area per unit true volume of the sample to be tested; (2) The volume of a single surrogate is much smaller than the total true volume of the sample to be tested; Obtain the volume V1 of the reference space in the gas adsorption instrument; placing the weighed substitute in a measurement space in a gas adsorption instrument, and obtaining a volume V2 of the measurement space after the substitute is added; controlling the temperature of the reference space to be T1, evacuating the reference space, filling the reference space with a certain amount of helium, and measuring the pressure P1 of the reference space after the pressure of the reference space stabilizes; Cooling the measurement space to an experimental temperature T2 in the liquid helium temperature range, connecting the reference space and the measurement space, and measuring the pressure P2 of the system after the pressure of the system formed by the reference space and the measurement space stabilizes; Combined with the curve of the compressibility factor of helium at pressure P2 varying with temperature, the equivalent temperature of the measurement space at pressure P2 and experimental temperature T2 is obtained iteratively.

2. The measuring method according to claim 1, wherein The selection of a substitute equal to the true volume of the sample to be tested specifically includes: Measuring the true density ρ1 of the sample to be tested; Measure the density ρ2 of the chosen surrogate; Measuring the mass m1 of the sample to be tested; Weigh the surrogate with mass m2, which is determined by the following formula:

3. The measuring method according to claim 1, wherein The non-porous material includes metal and salt compounds.

4. The measuring method according to claim 3, characterized in that The metal is an alloy consisting of any one or more of chromium, nickel, aluminum and tin.

5. The measuring method according to claim 3, characterized in that The salt compound is potassium nitrate or potassium chloride.

6. The measuring method according to claim 1, characterized in that The substitute meets the following conditions at the same time: (1) the specific surface area per unit volume of the substitute does not exceed 10% of the specific surface area per unit true volume of the sample to be tested; -4 ; (2) The volume of a single substitute does not exceed 5‰ of the total true volume of the sample to be tested.

7. The measuring method according to claim 1, characterized in that The adsorbent is activated carbon, and the substitute is tin balls, with a diameter of a single tin ball ranging from 0.2 mm to 0.76 mm.

8. The measurement method according to claim 1, characterized in that The specific steps of obtaining the volume V1 of the reference space in the gas adsorption instrument include: evacuating the reference space in the gas adsorption instrument; Filling the reference space with a certain amount of helium, and measuring the pressure P3 and temperature T3 of the reference space after the pressure of the reference space stabilizes; An object with a known volume V0 is placed in the reference space, and after the pressure of the reference space stabilizes, the pressure P4 of the reference space is measured, while the temperature of the reference space remains unchanged at T3; The volume V1 of the reference space is calculated by the following formula: Wherein, Z3 is the compressibility factor of helium at temperature T3 and pressure P3, and Z4 is the compressibility factor of helium at temperature T3 and pressure P4.

9. The measuring method according to claim 1, wherein: The step of obtaining the volume V2 of the measurement space after adding the substitute comprises: evacuating the reference space and the measurement space; Filling the reference space with a certain amount of helium, and measuring the pressure P5 and temperature T4 of the reference space after the pressure of the reference space stabilizes; Connecting the reference space and the measurement space, and measuring the pressure P6 of the system after the pressure of the system stabilizes, wherein the temperatures of the reference space and the measurement space are both consistent with the temperature T4; The volume V2 of the measurement space after adding the substitute is calculated according to the following formula: Wherein, Z5 is the compressibility factor of helium at temperature T4 and pressure P5, and Z6 is the compressibility factor of helium at temperature T4 and pressure P6.

10. The measurement method according to claim 1, characterized in that Assume that the equivalent temperature of the measurement space under the pressure P2 and experimental temperature T2 is T eff , which satisfies the following formula: Where Z1 is the compressibility factor of helium at temperature T1 and pressure P1, Z2 is the compressibility factor of helium at temperature T1 and pressure P2, and Z eff is the equivalent temperature of helium at T eff , compression factor under pressure P2.

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