Method for measuring equivalent temperature in gas adsorption instrument in liquid helium temperature region

Abstract

According to the method for measuring the equivalent temperature in the gas adsorption instrument under the liquid helium temperature zone, a non-porous material with the specific surface area far smaller than that of a to-be-measured sample is used for preparing a substitute of the to-be-measured sample, and after it is guaranteed that the volume of the substitute is equal to the true volume of the to-be-measured sample, the substitute is placed in a measuring space of the gas adsorption instrument to replace the to-be-measured sample; controlling the temperature of the reference space, vacuumizing the reference space, filling a certain amount of helium into the reference space, and measuring the pressure P1 of the reference space after the helium is stabilized; cooling the measurement space to an experimental temperature T2 of a liquid helium temperature region, communicating the reference space with the measurement space, and measuring a stabilized pressure P2; and iteratively obtaining the equivalent temperature of the measurement space under the pressure P2 and the experimental temperature T2 by combining a curve that the compression factor of the helium changes along with the temperature under the pressure P2. The invention solves the technical problem of determining the equivalent temperature of the temperature gradient section in the process of measuring the gas adsorption quantity by using the volumetric method in the liquid helium temperature region.

Description

Technical Field

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

[0002] Porous materials and their adsorption effects are widely used in the fields of chemical industry, biology, energy, etc. Specific surface area and pore size distribution are important factors affecting their performance. Gas adsorption experiments are usually used to obtain information such as 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 refer to the national standard GB / T 19587-2017 "Gas Adsorption BET Method for Determination of Specific Surface Area of ​​Solid Substances". The sample to be tested is placed in the sample chamber, and the difference in the amount of gas before and after adsorption is measured to obtain the amount of gas adsorption. This method requires measuring the temperature, pressure and free volume of the gas in the sample chamber in order to substitute them into the gas state equation to calculate the amount of gas.

[0003] During measurement, the sample chamber is at a lower experimental temperature, and the rest of the device is at room temperature. There is a temperature gradient in the pipeline 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 pipeline. 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 amount of helium adsorbed at low temperatures cannot be ignored, the above method for determining the equivalent temperature is no longer applicable. Therefore, it is necessary to develop a new method for determining the equivalent temperature to meet the adsorption measurement needs in the liquid helium temperature range. Summary of the invention

[0005] The present invention aims at the temperature gradient problem of the sample chamber in the adsorption experiment in the liquid helium temperature zone (4K), and proposes a method for determining the equivalent temperature by replacing the adsorbent with equal volume. A material with a specific surface area much smaller than the adsorbent to be tested is used, and after ensuring that its volume is equal to the true volume of the sample to be tested, it is placed in the sample chamber to replace the sample to be tested. Since its specific surface area is much smaller than the sample to be tested, the amount of helium adsorbed on its surface can be ignored even in a 4K low temperature environment, so that the amount of helium contained in the temperature gradient section and the equivalent temperature can be determined according to the traditional method.

[0006] In order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme:

[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 with the same true volume as the sample to be tested is selected, wherein the substitute is a solid particle made of a non-porous material and satisfies the following conditions at the same time: (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] The weighed substitute is placed in the measuring space of the gas adsorption instrument, and the volume V2 of the measuring space after the substitute is added is obtained;

[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 is stabilized;

[0012] The measurement space is cooled to an experimental temperature T2 in a liquid helium temperature range, the reference space and the measurement space are connected, and after the pressure of the system formed by the reference space and the measurement space is stabilized, the pressure P2 of the system is measured;

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

[0014] In some embodiments, the step of 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 selected surrogate;

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

[0018] Weigh the substitute with mass m2, which is determined according to 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 consisting 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, and the diameter of a single tin ball is 0.2 mm-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 a certain amount of helium into the reference space, and measuring the pressure P3 and temperature T3 of the reference space after the pressure of the reference space is stabilized;

[0028] An object with a known volume V0 is placed in the reference space, and after the pressure of the reference space is stabilized, the pressure P4 of the reference space is measured, and 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] Among them, Z3 is the compression factor of helium at temperature T3 and pressure P3, and Z4 is the compression 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 a certain amount of helium into the reference space, and measuring the pressure P5 and temperature T4 of the reference space after the pressure of the reference space is stabilized;

[0035] The reference space and the measuring space are connected, and after the pressure of the system is stabilized, the pressure P6 of the system is measured, and the temperatures of the reference space and the measuring 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] Among them, Z5 is the compression factor of helium at temperature T4 and pressure P5, and Z6 is the compression factor of helium at temperature T4 and pressure P6.

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

[0040]

[0041] Where Z1 is the compression factor of helium at temperature T1 and pressure P1, Z2 is the compression 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] The present invention uses a material with a smaller specific surface area to replace the adsorbent, and can expand the traditional method of determining the equivalent temperature of the temperature gradient section to the liquid helium temperature zone to meet the adsorption measurement needs in the liquid helium temperature zone. Taking the common tin ball material as an example, the feasibility of using it as a substitute material is analyzed. Since the tin ball has the advantages of low cost, easy acquisition, and flexible ball diameter selection, the present invention has 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] Application of the present invention

[0046] The invention is suitable for 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 It is an overall flow chart of a method for measuring equivalent temperature in a gas adsorption instrument in a 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 solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0050] On the contrary, the present application covers any substitution, modification, equivalent method and scheme made on the essence and scope of the present application as defined by the claims. Further, in order to make the public have a better understanding of the present application, some specific details are described in detail in the detailed description of the present application below. Those skilled in the art can fully understand the present application without the description of these details.

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

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

[0053] Step (2) using a densitometer to measure the density ρ2 of the substitute, the substitute is a solid particle made of a non-porous material, and satisfies the following conditions at the same time: 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) weighing a 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 formed by the reference space and the measurement space after the pressure is stabilized;

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

[0062] The measurement method proposed in the embodiment of the present invention is a method for measuring equivalent temperature by replacing the adsorbent with equal volume. Specifically, a substitute for the sample to be tested is made of a non-porous material whose specific surface area is 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 the traditional method, thereby meeting the adsorption measurement requirements in the liquid helium temperature zone.

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

[0064] Furthermore, in step (2), the material used to make the substitute can be selected from materials that do not have a porous structure, such as metals and salt compounds, i.e., non-porous materials, 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, etc., and the salt compound can be potassium nitrate, potassium chloride, etc.

[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 usually has a specific surface area per unit true volume of more than 10 3 m 2 / cm 3The specific surface area of ​​the solder 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 solder ball can be ignored. For a solder 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 the error range of less than 2‰, solder balls with a ball diameter of 0.5mm can be used to combine into a volume equal to the true volume of the sample to be tested. At the same time, solder balls have a variety of ball diameter sizes (0.2mm-0.76mm) to choose from, making the operation of combining solder balls into a set volume more flexible.

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

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

[0069] Fill a certain amount of helium into the reference space, 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 are placed on other properties of the object) is placed in the reference space, and after the pressure of the reference space is stabilized, the pressure P4 of the reference space is measured, and the temperature of the reference space is kept unchanged at T3;

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

[0072]

[0073] Among them, Z3 is the compression factor of helium at temperature T3 and pressure P3, and Z4 is the compression 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 a certain amount of helium into the reference space, 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 measuring space, and after the pressure of the system is stable, measure the pressure P6 of the system, and the temperatures of the reference space and the measuring space are 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] Among them, Z5 is the compression factor of helium at temperature T4 and pressure P5, and Z6 is the compression 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 assumed to be T eff , which satisfies the following formula:

[0082]

[0083] Where Z1 is the compression factor of helium at temperature T1 and pressure P1, Z2 is the compression 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 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 that changes 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 as a function of the measured pressure P2 is better.

[0084] See also Figure 2 , is a schematic diagram of the structure of a volumetric adsorption measurement system for realizing 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 a refrigerator 1, a vacuum cover 2, a radiation cover 3, a sample chamber 6, a temperature sensor 7, and a low-temperature vacuum device, which can make the sample chamber 6 in a vacuum at a lower experimental temperature T2, and the experimental temperature T2 is in the liquid helium temperature zone; the unit B shown in the dotted box contains a reference chamber 25, a temperature sensor 26, a pressure sensor 15, a gas pipeline and a valve, which is 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 adopts a GM refrigerator, which has two stages of cold heads, namely, a primary cold head 4 and a secondary cold head 5. The sample chamber 6 is connected to the secondary cold head 5 and can be cooled to 4K. A solder ball 8 is placed in the sample chamber 6 as a substitute for the sample to be measured. The temperature sensor 7 is used to measure the temperature of the sample chamber 6. The vacuum cover 2 is connected to the primary cold head 4 to provide a vacuum environment for the primary cold head 4, the secondary cold head 5 and the sample chamber 6 and isolate them from the external atmosphere. The radiation cover 3 is connected to the secondary cold head 5 and is arranged between the vacuum cover 2 and the secondary cold head 5 and the sample chamber 6 to reduce the radiation heat leakage of the low temperature part of the measurement system.

[0086] The gas pipeline in unit B includes a main pipeline 9 and several branch pipelines connected to the main pipeline 9. The main pipeline 9 is connected to branch pipelines 10-14 respectively. The branch pipeline 10 is connected to the sample chamber 6 through the stop valve 20 and the gas pipeline 16; the branch pipeline 11 is connected to the reference chamber 25 through the stop valve 21 and the branch pipeline 17; the branch pipeline 12 is connected to the helium gas cylinder 28 through the stop valve 22 and the branch pipeline 18; the branch pipeline 13 is connected to the safety valve 23 to prevent the pressure of the measurement system from being too high; the branch pipeline 14 is connected to the vacuum pump 30 through the stop valve 24 and the branch pipeline 19. The vacuum pump 30 is connected to the vacuum cover 2 through the stop valve 29 and the branch pipeline 27 at the same time, and is used to evacuate the vacuum cover 2. The temperature sensor 26 is used to measure the temperature of the experimental device at a constant room temperature in unit B. A pressure sensor 15 is arranged on the main pipeline 9 to measure the pressure in the gas pipeline.

[0087] The volume of the measuring 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, and the volume of the reference space 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) measures 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 of V0 for use. Initially, all stop valves are in a closed state, and stop valve 20 is always in a closed state;

[0096] Step (5.2) Open the stop valves 21 and 24, keep the other stop valves closed, and turn on the vacuum pump 30 to 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 pipeline 9 and the branch pipelines 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, connect the reference chamber 25 to the main pipeline 9, and keep the states of the other stop valves unchanged. After the pressure of the reference space is stable, use the pressure sensor 15 to measure the pressure P3 of the reference space;

[0099] Step (5.5) Open the stop valve 24 to exhaust air, open the reference chamber 25, put the object with a 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 pipeline 9 and the branch pipelines 11-14, and then close the stop valve 22 so that the pressure in the pipeline remains unchanged at P7;

[0101] Step (5.7) Open the stop valve 21, connect the reference chamber 25 to the main pipeline 9, and keep the states of the other stop valves unchanged. After the pressure of the reference space is stable, use the pressure sensor 15 to measure the pressure P4 of the reference space;

[0102] Step (5.8) calculates the volume V1 of the reference space by the following formula:

[0103]

[0104] Wherein, Z3 is the compression factor of helium at temperature T3 and pressure P3, and Z4 is the compression factor of helium at temperature T3 and pressure P4. During steps (5.4) to (5.7), the temperature of the reference space remains unchanged 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 unchanged. Turn on the vacuum pump 30 to evacuate the measurement space and the reference space to 10 -3 Below Pa;

[0108] Step (6.3) closes the stop valves 20 and 24, turns off the vacuum pump 30, opens the stop valve 22, keeps the states of the other stop valves unchanged, injects a certain amount of helium into the reference space, then closes the stop valve 22, measures the pressure P5 in the pipeline using the pressure sensor 15, and measures the temperature T4 of the reference space using the temperature sensor 26;

[0109] Step (6.4) Open the stop valve 20, and keep the other stop valves unchanged, connect the reference space and the measurement space, and use the pressure sensor 15 to measure the pressure P6 in the pipeline after stabilization. During this process, the temperature of the reference space remains unchanged at T4;

[0110] Step (6.5) calculates the volume V2 of the measurement space after adding the solder ball 8 by the following formula:

[0111]

[0112] Among them, Z5 is the compression factor of helium at temperature T4 and pressure P5, and Z6 is the compression 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 of 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] Step (7.2) closes the stop valves 20 and 24, turns off the vacuum pump 30, opens the stop valve 22, keeps the states of the other stop valves unchanged, fills a certain amount of helium into the reference space, then closes the stop valve 22, measures the pressure P1 in the pipeline using the pressure sensor 15, measures the temperature T1 of the reference space using the temperature sensor 26, and keeps the temperature of the reference space unchanged at T1.

[0116] Step (8) cools the measurement space to the 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 is stabilized. The specific steps include:

[0117] Step (8.1) Open the stop valve 29, 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 zone, 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 zone;

[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, and after the system pressure constituted by them is stabilized, the pressure P2 in the system is measured using the pressure sensor 15.

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

[0120]

[0121] Where Z1 is the compression factor of helium at temperature T1 and pressure P1, Z2 is the compression 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 the compression factor of helium 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] In the description of this specification, the description with reference to the terms "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 schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0123] Although 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 a 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 at the same time: (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; The weighed substitute is placed in the measuring space of the gas adsorption instrument, and the volume V2 of the measuring space after the substitute is added is obtained; 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 is stabilized; The measurement space is cooled to an experimental temperature T2 in a liquid helium temperature range, the reference space and the measurement space are connected, and after the pressure of the system formed by the reference space and the measurement space is stabilized, the pressure P2 of the system is measured; Combined with the curve of the compressibility factor of helium at pressure P2 varying with temperature, the equivalent temperature of the measurement space under the conditions of pressure P2 and experimental temperature T2 is obtained by iteration.

2. The measuring method according to claim 1, characterized in that: The step of selecting a substitute having a true volume equal to that 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 substitute with mass m2, which is determined according to the following formula:

3. The measuring method according to claim 1, characterized in that: 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, the substitute is tin ball, and the diameter of a single tin ball is 0.2 mm-0.76 mm.

8. The measuring 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 a certain amount of helium into the reference space, and measuring the pressure P3 and temperature T3 of the reference space after the pressure of the reference space is stabilized; An object with a known volume V0 is placed in the reference space, and after the pressure of the reference space is stabilized, the pressure P4 of the reference space is measured, and the temperature of the reference space remains unchanged at T3; The volume V1 of the reference space is calculated by the following formula: Among them, Z3 is the compression factor of helium at temperature T3 and pressure P3, and Z4 is the compression factor of helium at temperature T3 and pressure P4.

9. The measuring method according to claim 1, characterized in that: 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 a certain amount of helium into the reference space, and measuring the pressure P5 and temperature T4 of the reference space after the pressure of the reference space is stabilized; The reference space and the measuring space are connected, and after the pressure of the system is stabilized, the pressure P6 of the system is measured, and the temperatures of the reference space and the measuring 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: Among them, Z5 is the compression factor of helium at temperature T4 and pressure P5, and Z6 is the compression factor of helium at temperature T4 and pressure P6.

10. The measuring 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 compression factor of helium at temperature T1 and pressure P1, Z2 is the compression 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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