Sample packaging method for under-pressure heat capacity measurement

Abstract

The invention discloses a sample packaging method for under-pressure heat capacity measurement, which comprises the following steps: (1) mixing heat-conducting foam and a sample to be measured, putting the mixture into a metal crucible plate, and covering a metal crucible cover matched with the metal crucible plate to obtain a metal crucible filled with the heat-conducting foam and the sample to be measured; (2) placing the metal crucible in a glove box, and replacing atmosphere and pressure by using the glove box; (3) after the pressure is balanced, pressing and sealing the metal crucible to realize the packaging of the sample to be detected under different pressures and atmospheres; or, the storage time of the metal crucible in the glove box is adjusted, after the gas adsorption amount of the to-be-tested sample is changed, the metal crucible is pressed and sealed, and packaging of the to-be-tested sample under different adsorption amounts is achieved. The requirement for tight sealing of samples under different pressures, atmospheres and adsorption capacities can be met at the same time, and the sample packaging device has the advantages of being suitable for various solid and liquid samples, convenient in sample packaging process, excellent in heat conduction performance between the samples and the like.

Description

Technical Field

[0001] The present application relates to a sample encapsulation method for pressure - controlled heat capacity measurement, belonging to the field of metrology and testing. Background Art

[0002] Specific heat capacity, that is, the energy required for a unit mass of a substance to increase its temperature by 1 °C, is a fundamental thermodynamic parameter of the substance and a bridge for understanding the relationship between the macroscopic and microscopic properties of the substance. Accurate measurement of the specific heat capacity of a substance can provide strong guarantee for the development of new theories, new materials, new technologies, new processes, etc. Condensed matter is the current scientific frontier and hotspot, and it plays an important role in the fields of physics, chemistry, materials, and communication. Therefore, it is particularly important to accurately and rapidly measure the heat capacity of condensed matter. It should be noted that the heat capacity of a substance not only varies with temperature but also is related to pressure. Measuring the heat capacity of a substance under different pressures and establishing comprehensive thermal property parameters are of self - evident importance for material research and development. More importantly, measuring the thermodynamic behavior characteristics of a material under different adsorption amounts can provide key support for studying the adsorption interaction between the material and gas, and provide theoretical guidance for carbon capture and sequestration applications. Thus, accurate and reliable measurement of the heat capacity under different pressures or adsorption amounts highlights important scientific value and significant economic and social value.

[0003] The main methods for measuring the heat capacity of condensed matter are: adiabatic calorimetry, relaxation calorimetry, differential scanning calorimetry (DSC) and differential thermal analysis (DTA). Among them, adiabatic calorimetry is the most accurate and reliable method. It has good compatibility with test samples and is applicable to bulk solids, solid powders and liquid samples. The sample packaging of the adiabatic calorimetry method relies on the instrument's own sample pool [a calorimeter sample pool with convenient sample replacement and good sealing, CN207764147U, 2018.04.24.], and different gases at different pressures can be sealed in the sample pool according to demand to achieve pressurized heat capacity measurement. However, the use of this instrument requires professional skills, and there is no commercial instrument yet, so it has not been widely promoted. Relaxation calorimetry is a relatively accurate (±2%) commercialized measurement method (i.e. PPMS), which has the advantages of small sample volume required for testing and low measurement temperature range. At present, the main method of sample packaging for relaxation calorimetry is to mix the solid sample with copper chips and put it into a homemade copper cup, and then press the whole into a small piece with a diameter of 3 mm [Q. Shi, CLS Snow, J. Boerio-Goates, BF Woodfield, Accurate heat capacity measurements on powdered samples using a Quantum Design physical property measurement system, J. Chem. Thermodyn. 42 (9) (2010) 1107-1115; Q. Shi, J. Boerio-Goates, BF Woodfield, An improved technique for accurate heat capacity measurements on powdered samples using a commercial relaxation calorimeter, J. Chem. Thermodyn. 43 (8) (2011) 1263-1269.]. Although this method can meet the needs of heat capacity measurement of powdered samples, it is not suitable for liquid samples and the preparation process is cumbersome. More importantly, the PPMS instrument measures heat capacity in a vacuum environment. The above method cannot completely seal the sample, so it can only test the heat capacity under vacuum conditions. It cannot meet the needs of studying the changes in the heat capacity of the sample with pressure, nor can it be used to explore the heat capacity behavior of the sample after adsorbing different amounts or different gases. DSC and DTA are the most widely used commercial instruments for measuring heat capacity. Their advantages are fast and convenient measurement, small sample size, and relatively cheap instruments. At present, their sample packaging mainly relies on placing the sample in an aluminum crucible and then pressing and sealing the entire thing.This method is convenient for sample preparation and has good sample compatibility. However, the overall measurement accuracy of the instrument is not high, with a large floating range (5 - 20%). When measuring the heat capacity under pressure, generally, the crucible is punctured or an open crucible is used to hold the sample, and then the operation is completed by changing the gas pressure of the instrument. This method can meet the need for a rough determination of the heat capacity of samples under different pressures, but due to the dynamic change of the atmosphere, it cannot guarantee high-precision results, nor can it realize the measurement of the heat capacity of volatile liquid samples under pressure, let alone the measurement and research of the heat capacity under the adsorption interaction between the sample and the gas.

[0004] Therefore, the sample encapsulation methods of current commercial heat capacity measurement instruments have their respective deficiencies and cannot meet the requirements for accurate and rapid measurement of the heat capacity of condensed matter under different pressures or adsorption amounts. In view of this situation, there is an urgent need to develop a new and general sample encapsulation method for heat capacity measurement under pressure, aiming to simultaneously meet the strict sealing of samples under different pressures, atmospheres, and adsorption amounts, laying a foundation for accurate measurement of their heat capacity; the encapsulation method is applicable to various solid and liquid samples, with convenient process operation and excellent thermal conductivity between samples, etc. Summary of the Invention

[0005] The purpose of this application is to provide a sample encapsulation method for heat capacity measurement under pressure, which simultaneously meets the requirements for strict sealing of samples under different pressures, atmospheres, and adsorption amounts, and has the advantages of being applicable to various solid and liquid samples, convenient sample encapsulation process, excellent thermal conductivity between samples, and being applicable to relaxation calorimetry, differential scanning calorimetry, and differential thermal analysis, etc., and can be used as a standard encapsulation sample method for heat capacity testing.

[0006] In one aspect of this application, a sample encapsulation method for heat capacity measurement under pressure is provided, including the following steps:

[0007] (1) Mix the thermal conductive foam with the sample to be tested, load it into a metal crucible pan, and cover it with a metal crucible lid that matches the metal crucible pan to obtain a metal crucible containing the thermal conductive foam and the sample to be tested;

[0008] (2) Place the metal crucible obtained in step (1) in a glove box and use the glove box to displace the atmosphere and pressure;

[0009] (3) After the pressure is balanced, press and seal the metal crucible to achieve the encapsulation of the sample to be tested under different pressures and atmospheres;

[0010] Or, adjust the storage time of the metal crucible in the glove box, change the amount of gas adsorbed by the sample to be tested, and then press and seal the metal crucible to achieve the encapsulation of the sample to be tested under different adsorption amounts.

[0011] Optionally, the materials of the metal crucible pan and the metal crucible lid are materials that do not react with the sample to be tested and have no catalytic effect;

[0012] The materials of the metal crucible pan and the metal crucible lid are selected from at least one of aluminum, platinum, gold, titanium, and copper.

[0013] Optionally, the heat-conducting foam is metal foam;

[0014] The material of the metal foam is a material that does not react with the sample to be measured and has no catalytic effect;

[0015] The material of the metal foam is selected from at least one of copper, nickel, aluminum, and gold.

[0016] Optionally, in step (1), before mixing the heat-conducting foam with the sample to be measured and loading them into the metal crucible pan, it further includes weighing the masses of the heat-conducting foam, the sample to be measured, the metal crucible pan, and the metal crucible lid respectively;

[0017] In step (3), after pressing and sealing, it further includes: measuring the total mass of the metal crucible after pressing and sealing;

[0018] Subtract the masses of the heat-conducting foam, the sample to be measured, the metal crucible pan, and the metal crucible lid from the total mass of the sealed metal crucible obtained, calculate the adsorption amount of the sample to be measured, or use the ideal gas state equation to calculate the internal pressure of the sealed metal crucible.

[0019] Optionally, the pressing and sealing of the metal crucible is achieved by using a supporting tablet press.

[0020] Optionally, in step (1), after mixing the heat-conducting foam with the sample to be measured and loading them into the metal crucible pan, it is compacted by a metal rod to improve the overall heat conduction performance.

[0021] Optionally, the effect of the encapsulation of the sample to be measured is inspected by the mass change of the sealed metal crucible before and after being stored in a vacuum oven or a vacuum environment.

[0022] Specifically, the existence time in this application can be 6 to 24 hours.

[0023] Optionally, the sample to be measured is a solid sample and / or a liquid sample.

[0024] As a specific implementation manner, the sample encapsulation method includes:

[0025] Mix the metal foam with the sample and load them into the metal crucible pan together. Then, place the three together with the supporting metal crucible lid in a glove box, and use the glove box to displace the atmosphere and pressure; after the pressure is balanced, use the supporting tablet press to press and seal the crucible to achieve the encapsulation of the sample under different pressures and atmospheres; or adjust the storage time of the sample in the glove box to change the amount of gas adsorbed by the sample, and then use the supporting tablet press to seal the crucible to achieve the encapsulation of the sample under different adsorption amounts.

[0026] The beneficial effects that this application can produce include:

[0027] (1) The encapsulation method of this application can simultaneously meet the requirements of tightly sealing samples under different pressures, atmospheres, and adsorption amounts, and can significantly improve the thermal conductivity between samples and between the sample and the container, laying a solid experimental foundation for accurate measurement of the heat capacity under pressure.

[0028] (2) The encapsulation method of this application is convenient to operate and has strong versatility. It is applicable to most solid and liquid samples. The sample encapsulation process is convenient, the thermal conductivity between samples is excellent, and it is applicable to heat capacity measurement methods such as relaxation calorimetry, differential scanning calorimetry, and differential thermal analysis. Description of the Drawings

[0029] Figure 1 It is the polymer heat capacity curve measured in Example 1 and Comparative Example 1.

[0030] Figure 2 It is the molecular sieve heat capacity curve measured in Example 2. Detailed Description of the Invention

[0031] The following describes this application in detail with reference to the examples, but this application is not limited to these examples.

[0032] Unless otherwise specified, the raw materials in the examples of this application are all purchased through commercial channels.

[0033] Example 1

[0034] Select a magnetic coordination polymer powder {[W(CN) 8 [(Fe II )(bib) 2 (bibH)}·2CH 3 OH as the test sample, and use PPMS (commercial relaxation calorimetry) to measure the heat capacity:

[0035] 1. Select a covered aluminum crucible and copper foam that do not react with the polymer and have no catalytic effect for sample encapsulation;

[0036] 2. Blend 12.45 mg of the polymer powder and 4.83 mg of copper foam, and then put them into an aluminum crucible pan with a mass of 23.79 mg. Then use a stainless steel metal rod to compact the polymer powder and copper foam in the aluminum crucible pan to ensure good thermal contact between the three;

[0037] 3. Transfer the aluminum crucible pan containing the polymer powder and copper foam and an aluminum crucible lid with a mass of 5.16 mg to the glove box, use the vacuum pump and high-purity nitrogen source in the glove box for three gas replacements, and raise the pressure to about 6 bar;

[0038] After 20 minutes of pressure balance, cover the aluminum crucible with an aluminum crucible lid, use the supporting press to press and seal the aluminum crucible, take out the sealed aluminum crucible, and weigh the total mass as 46.28 mg; use the ideal gas state equation (temperature 298.15 K, volume 7.5 uL, nitrogen mass 0.05 mg) to calculate that the internal pressure of the aluminum crucible is about 5.9 bar;

[0039] Place the sealed aluminum crucible in a vacuum oven, take it out after storing it under vacuum for 6 hours, and weigh it again. The mass is still 46.28 mg, proving that the aluminum crucible is tightly sealed;

[0040] Load the prepared sealed polymer sample into the sample stage of the PPMS instrument, measure the overall heat capacity, and then subtract the heat capacity contributions of the aluminum crucible and copper foam of the corresponding mass (the total heat capacity contribution of the aluminum crucible and copper foam can be obtained by measuring the heat capacity of the aluminum crucible and copper foam of the same mass as the sample during sample testing using PPMS) to obtain the heat capacity value of the polymer under 5.9 bar nitrogen (see Figure 1 the red dots in).

[0041] Comparative Example 1

[0042] Select a magnetic coordination polymer powder {[W(CN) 8 [(Fe II )(bib) 2 (bibH)}·2CH 3 OH as the sample, and according to the method described in the patent document CN202010771349.0, select the same mass of polymer powder, aluminum crucible and copper foam as in Example 1 for sample encapsulation. After sealing the sample, use PPMS (commercial relaxation calorimetry) to measure the heat capacity.

[0043] The measured heat capacity value of the polymer is shown in Figure 1 the black dots in.

[0044] As can be seen from the figure, there are obvious differences between the heat capacity curves measured by using the encapsulation method of the present application and the results obtained by using the method of Comparative Example 1 at 77 K and 250 - 300 K. Among them, the additional heat capacity peak measured at 77 K by using the method of the present application should be caused by the liquid-gas transition of nitrogen, and the heat capacity anomaly above 250 K may be caused by the heat capacity of nitrogen; thus, it can be seen that the present application has obvious beneficial effects in studying the heat capacity under pressure compared with Comparative Example 1.

[0045] Example 2

[0046] Select 5A molecular sieve as the sample and use DSC to measure the heat capacity:

[0047] 1. Select a covered copper crucible and nickel foam that do not react with 5A molecular sieve and have no catalytic effect for sample encapsulation;

[0048] 2. Blend 9.74 mg of 5A molecular sieve and 5.26 mg of nickel foam by mass and put them together into a copper crucible pan weighing 27.67 mg. Then use a stainless steel metal rod to compact the 5A molecular sieve and nickel foam in the copper crucible pan to ensure good thermal contact among the three;

[0049] 3. Transfer the copper crucible pan containing 5A molecular sieve and nickel foam and a copper crucible lid weighing 6.62 mg into the glove box. Use the vacuum pump and high-purity carbon dioxide source in the glove box for three gas replacements and raise the pressure to about 1.2 bar;

[0050] 4. Let the 5A molecular sieve be stored in the glove box for 8 hours to adsorb carbon dioxide gas. Cover the copper crucible lid and use a supporting tablet press to press and seal the copper crucible. Take out the sealed copper crucible and weigh the total mass as 50.93 mg. Subtract the masses of the above four from the mass of the sealed copper crucible to get the mass of carbon dioxide gas as 1.64 mg, that is, the molecular sieve adsorption capacity is 0.168 g / g;

[0051] 5. Place the sealed copper crucible in the environment and weigh it again after 24 hours of storage. The mass is still 50.93 mg, proving that the copper crucible is tightly sealed;

[0052] 6. Load the prepared 5A molecular sieve sample into the sample stage of the DSC instrument. Repeat the measurement of the overall heat capacity three times and take the average value. Then subtract the heat capacity contributions of the corresponding mass of the copper crucible and nickel foam (the total heat capacity contributions of the copper crucible and nickel foam can be obtained by measuring the heat capacity of the copper crucible and nickel foam with the same mass as the sample three times using DSC and then taking the average value) to obtain the heat capacity value of the molecular sieve after adsorbing carbon dioxide (see Figure 2 ).

[0053] The above are only several embodiments of the present application and do not impose any form of limitation on the present application. Although the present application is disclosed above with preferred embodiments, it is not intended to limit the present application. Any person skilled in the art, without departing from the technical solution of the present application, makes some changes or modifications using the technical content disclosed above, which are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A sample encapsulation method for pressure-dependent heat capacity measurement, characterized in that, it includes the following steps: (1) Mix the thermal conductive foam with the sample to be measured, load it into a metal crucible pan, and cover it with a metal crucible lid that matches the metal crucible pan to obtain a metal crucible containing the thermal conductive foam and the sample to be measured; (2) Place the metal crucible obtained in step (1) in a glove box, and use the glove box to displace the atmosphere and pressure; (3) After the pressure is balanced, press and seal the metal crucible to achieve the encapsulation of the sample to be measured under different pressures and atmospheres; Or, adjust the storage time of the metal crucible in the glove box, change the amount of gas adsorbed by the sample to be measured, and then press and seal the metal crucible to achieve the encapsulation of the sample to be measured under different adsorption amounts.

2. The sample encapsulation method according to claim 1, characterized in that, the materials of the metal crucible pan and the metal crucible lid are materials that do not react with the sample to be measured and have no catalytic effect; the materials of the metal crucible pan and the metal crucible lid are selected from at least one of aluminum, platinum, gold, titanium, and copper.

3. The sample encapsulation method according to claim 1, characterized in that, the thermal conductive foam is a metal foam; the material of the metal foam is a material that does not react with the sample to be measured and has no catalytic effect; the material of the metal foam is selected from at least one of copper, nickel, aluminum, and gold.

4. The sample encapsulation method according to claim 1, characterized in that, in step (1), before mixing the thermal conductive foam with the sample to be measured and loading it into the metal crucible pan, it further includes weighing the masses of the thermal conductive foam, the sample to be measured, the metal crucible pan, and the metal crucible lid respectively; in step (3), after pressing and sealing, it further includes: measuring the total mass of the pressed and sealed metal crucible; Subtract the masses of the thermal conductive foam, the sample to be measured, the metal crucible pan, and the metal crucible lid from the total mass of the sealed metal crucible obtained, calculate the adsorption amount of the sample to be measured, or use the ideal gas state equation to calculate the internal pressure of the sealed metal crucible.

5. The sample encapsulation method according to claim 1, characterized in that, the pressing and sealing of the metal crucible is achieved by using a matching tablet press.

6. The sample encapsulation method according to claim 1, characterized in that, in step (1), after mixing the thermal conductive foam with the sample to be measured and loading it into the metal crucible pan, it is compacted by a metal rod.

7. The sample encapsulation method according to claim 1, characterized in that, the effect of the encapsulation of the sample to be measured is tested by the mass change of the sealed metal crucible before and after storage in a vacuum oven or a vacuum environment.

8. The sample encapsulation method according to claim 1, characterized in that, the sample to be measured is a solid sample and / or a liquid sample.

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