CN104215654B - A kind of method for measuring thermal conductivity factor of the little power sample under different temperatures, pressure conditions under vacuum conditions - Google Patents

Abstract

The invention belongs to the field of mineral rock materials, in particular to a new method for measuring the thermal conductivity of trace (gram-level) mineral rock powder samples in a vacuum environment under variable temperature and pressure conditions. For the micro powder sample, the volume required for testing is in the range of 1.0 cm ³ to 20.0 cm ³ . The method is carried out under vacuum conditions, and the testing steps are: (1) Sample pretreatment. According to your own needs, prepare the sample into a powder sample with a particle size not greater than 1mm to ensure that the sample is mixed evenly, and dry the sample before measurement. (2) Sample installation. Select sample pools of different sizes and volumes according to the amount of samples, put the pretreated samples and test probes into the sample pool and fix them, and finally put the sample pool into the vacuum chamber of the freeze dryer. (3) Sample test. Vacuumize the vacuum chamber of the freeze dryer, the pressure can be adjusted in the range of 1Pa~1.013×10 ⁵ Pa, and the temperature in the chamber can be adjusted at the same time, the temperature can be adjusted in the range of -190℃~200℃. After the pressure and temperature reach the specified values, the thermal conductivity value of the sample under the specified test conditions is obtained by operating the relevant software of the thermal conductivity meter.

Description

A method for measuring micro-powder samples under different temperature and pressure conditions in a vacuum environment The method of thermal conductivity under

technical field

The invention belongs to the field of mineral and rock materials, in particular to a method for measuring the thermal conductivity of trace powder samples under different temperature and pressure conditions in a vacuum environment.

Background technique

In recent decades, with the continuous expansion of the application range of various materials in heat-related fields, thermal conductivity (or thermal conductivity) is often used to measure the thermal conductivity and thermal insulation properties of materials, and is an important parameter of materials. Understanding the thermal conductivity of a material is key to measuring its thermophysical properties. The lower the thermal conductivity value, the better the thermal insulation properties of the material. Since the thermal conductivity depends on many factors such as the structural composition of the measured object, average temperature, moisture content, heat transfer time, and temperature difference on both sides, it is generally determined through experiments. A variety of methods have been developed for the determination of thermal conductivity of materials. They have different application fields, measurement ranges, precision, accuracy, and sample size requirements. Different methods may have large differences in the measurement results of the same sample. Therefore, choosing the appropriate test method is the most important.

There are mainly two methods for measuring thermal conductivity: steady state and dynamic. The principle of the steady-state method is simple and clear, and the accuracy is high, but the measurement time is long and the environmental conditions are high. Among them, the heat flow meter method is a comparative method, which uses a calibrated heat flow sensor to measure the heat flow through the sample, and obtains the absolute value of the thermal conductivity. But its disadvantage is that the range of thermal conductivity of the measured material is relatively narrow, and the temperature range is limited, so it can only measure materials with low thermal conductivity and thermal insulation materials. The working principle of the guarded hot plate method is similar to that of the heat flow method. It is currently recognized as the most accurate method and can be used for the calibration of reference samples and the calibration of other instruments. But its disadvantages are that the measurement time is long, the instrument is expensive, and the thermal conductivity of wet materials cannot be studied, and it cannot be used for thin films, coatings and other samples with small thickness. The dynamic method is a new method developed in the last few decades to study materials with high thermal conductivity, or to perform measurements under high temperature conditions. Among them, the hot wire method is the most widely used method, which has the advantages of low product price, fast measurement speed, and less strict requirements on sample size. The disadvantage is that the analysis error is relatively large, generally 5% to 10%. The measurement range of the laser flash method is very wide, but what is measured is the thermal diffusivity of the material, and the specific heat and density of the sample need to be known in order to obtain the thermal conductivity through calculation, and the thermal conductivity in the hot state also needs the expansion coefficient The value of is only applicable to isotropic, homogeneous, opaque materials. The transient plane heat source method is to stick a probe on the test piece, and then calculate the thermal conductivity of the material after fitting the response of the sample surface temperature through a multivariate function. It is widely applicable and fast, but the accuracy is not necessarily high.

In principle, the steady-state method is a benchmark method, initially used to test the accuracy of other methods. But in fact, there are many influencing factors that can be accurately measured by the steady-state method, such as material properties, shape, specifications, etc., and the operation is inconvenient, requiring operators to have relatively strong professional knowledge, so the study of the transient method is the focus of research in recent years. trend. However, the existing instruments based on the transient method in the domestic market also have certain problems, such as the inability to avoid the influence of atmospheric humidity on the physical properties of the sample itself, and the inability to accurately measure micro-powder samples, etc., especially for research in the field of planetary science. Taking the moon as an example, the actual environment on the lunar surface is in an ultra-high vacuum, with a large temperature difference between day and night, especially at night. However, the currently widely used thermal conductivity meters cannot simultaneously meet the test conditions of temperature and pressure control in a vacuum environment, which has caused certain obstacles to the analysis of extraterrestrial simulated samples.

Contents of the invention

The purpose of the present invention is to provide a method for measuring the thermal conductivity of micro-powder samples under different temperature and pressure conditions in a vacuum environment. The method is applicable to most materials, especially powder samples of trace (gram-level) mineral rocks; the method is not affected by the atmosphere, and is measured in a vacuum environment; and the measurement parameters such as temperature and pressure can be changed in real time, and its Good controllability and high precision. This measurement method is especially advantageous for lunar science and comparative planetary research, and can provide experimental data support for related simulated samples.

The volume of the micro powder sample provided by the present invention is in the range of 1.0 cm ³ to 20.0 cm ³ during testing.

The method for measuring the thermal conductivity of a trace powder sample under different temperature and pressure conditions in a vacuum environment according to the present invention, the measurement steps are as follows:

(1) Sample pretreatment. According to your own needs, prepare the sample into a powder sample with a particle size not greater than 1mm to ensure that the sample is mixed evenly, and dry the sample before measurement.

(2) Sample installation. Select sample pools with different volumes according to the amount of samples, put the pretreated samples and test probes into the sample pool and fix them, and finally put the sample pool into the vacuum chamber of the freeze dryer.

(3) Sample test. Vacuumize the vacuum chamber of the freeze dryer, the pressure can be adjusted in the range of 1Pa to 1.013×10 ⁵ Pa, and the temperature in the chamber can be adjusted at the same time, and the temperature can be adjusted in the range of -190°C to 200°C. After the pressure and temperature reach the specified values, the thermal conductivity value of the sample under the specified test conditions is obtained by operating the relevant software of the thermal conductivity meter.

The present invention has the following beneficial effects:

1. The measurement method provided by the present invention has relatively low requirements on the sample demand, and the sample volume range is within 1.0cm ³ to 20.0cm ³ during measurement, which greatly reduces the sample amount, and there is no need for powder samples with a particle size of less than 1mm. damage. Especially for rare extraterrestrial powder samples (such as lunar dust and lunar soil), not only the amount is small, but also can be recovered as it is after the test is completed, and the thermal conductivity of the sample can be measured more accurately.

2. The sample loading container provided by the present invention can not only select sample pools with different volume specifications according to the demand of sample volume, but also the sample pool is equipped with a special probe socket, which simplifies operation and improves efficiency.

3. The test conditions provided by the present invention can control the two parameters of temperature and pressure at the same time, which is beneficial to conduct in-depth research on the thermal conductivity of powder samples in a systematic and multi-faceted manner. In particular, by measuring the relationship curves of the thermal conductivity of lunar dust and lunar soil with temperature and pressure, the actual thermal conductivity of lunar dust and lunar soil in the space environment at different temperatures and pressures can be estimated, which is useful for lunar exploration projects, manned lunar landings, Projects such as the establishment of lunar bases have greater guiding significance.

4. The test environment provided by the present invention is all in a vacuum environment, which advantageously eliminates the adverse effects of the external environment, such as atmospheric humidity and atmospheric convection.

Description of drawings

Fig. 1 is a schematic diagram of equipment for measuring the thermal conductivity of a micro-powder sample in a vacuum environment under variable temperature and pressure conditions according to the present invention;

Fig. 2 is the design schematic diagram of sample cell;

Fig. 3 is the temperature drift chart of the probe before measuring the pyroxene sample in Example 1. The temperature rise of the measured probe will fluctuate slightly before heating. To ensure the reliability of the data it is required that the experiments be performed with the sample isothermal and without temperature drift.

Figure 4 is the analysis result of the test pyroxene sample under certain conditions. Open the calculate button in the Hot Disk software, remove some points with large errors at the beginning and the end for analysis and calculation, and obtain the thermal conductivity and thermal diffusivity of the test sample. and heat capacity etc.

Fig. 5 is the thermal conductivity figure of measuring the pyroxene powder sample at normal temperature and pressure before the test method is improved;

Fig. 6 is after the test method is improved, that is, the method of the present invention, Example 1 measures the thermal conductivity figure of the pyroxene powder sample under normal temperature and pressure in a vacuum environment;

Fig. 7 is a trend diagram of the thermal conductivity of the pyroxene powder sample in Example 1 as a function of temperature and pressure.

Fig. 8 is a trend diagram of the variation of the thermal conductivity of the simulated lunar soil samples in Example 3 with temperature under normal pressure.

detailed description

The method for measuring the thermal conductivity of micro-powder samples under different temperature and pressure conditions in a vacuum environment according to the present invention will be further described in conjunction with the examples below. The materials used in the following examples are all powders, and the particle size of the powders is not greater than 1mm; the sample cell is specially developed; the thermal conductivity meter is produced by Hot Disk Company, the model is TPS 2500S; the freeze dryer is produced by Beijing Sihuan Scientific Instrument Factory Co., Ltd., the model is LGJ-10D; the mechanical pump is produced by Shanghai Muhong Vacuum Equipment Co., Ltd., the model is DM2.

Example 1

(1) Before the test method is improved, the sample is pre-treated. Prepare the pyroxene sample into a powder sample with a particle size not greater than 1mm according to your own needs, ensure that the sample is mixed evenly, and dry the sample before measurement.

(2) Before the test method is improved, the sample is installed. Select a 13.0cm ³ sample cell, put the pretreated pyroxene powder sample and test probe into the sample cell as described in step (1), and fix the sample cell in the original sample chamber of the thermal conductivity meter.

(3) Before the test method is improved, the sample is tested. The thermal conductivity of the pyroxene powder sample was measured under normal temperature and pressure conditions, and the data analysis is shown in Figure 5. It can be seen from Figure 5 that the same sample is measured at different times, and its thermal conductivity is affected by the environment, resulting in large data fluctuations and large deviations.

(4) After the test method is improved, the sample pretreatment method is as described in step (1).

(5) After the test method is improved, the sample is installed. Select a 13.0cm sample cell, put the pretreated pyroxene powder sample and test probe into the sample cell according to step ( ⁴ ) and fix it, and finally put the sample cell into the vacuum chamber of the freeze dryer .

(6) After the test method is improved, the sample is tested. Vacuumize the vacuum chamber of the freeze dryer, the pressure can be adjusted in the range of 1Pa to 1.013×10 ⁵ Pa, and the temperature in the chamber can be adjusted at the same time, and the temperature can be adjusted in the range of -190°C to 200°C. Select a pressure and temperature for each measurement. After the pressure and temperature reach the specified values, monitor the temperature drift (see Figure 3) to ensure that the test experiment is performed when the sample is isothermal and there is no temperature drift. The thermal conductivity value of the sample under the specified test conditions is obtained by operating the relevant software of the thermal conductivity meter (see Figure 4). The thermal conductivity of the pyroxene powder sample at normal temperature and pressure was measured in a vacuum environment, and the analysis of the data results is shown in Figure 6. Compared with the data before the test method was improved, the deviation range of this group of data is smaller, and the measurement results are more stable and accurate.

(7) Repeat step (6), keep other parameters unchanged, change the temperature value, measure a set of data every half an hour, you can get the trend diagram of the thermal conductivity of the pyroxene sample as a function of temperature, see Figure 7 (vertical comparison). It can be seen from Figure 7 that the thermal conductivity of pyroxene increases with the increase of temperature.

(8) Repeat step (6) to keep other parameters unchanged, change the pressure value, and measure a set of data every half an hour to obtain a trend diagram of the thermal conductivity of pyroxene with pressure, as shown in Figure 7 ( horizontal comparison). It can be seen from Figure 7 that the thermal conductivity of pyroxene increases with the increase of pressure.

Example 2

This embodiment 2 all carries out relevant test work under the condition after test method improvement.

(1) Sample pretreatment. Prepare the olivine sample into a powder sample with a particle size not greater than 1mm according to your own needs, ensure that the sample is mixed evenly, and dry the sample before measurement.

(2) Sample installation. Select a ^4.7cm sample cell, put the pretreated olivine powder sample and test probe into the sample cell according to step (1) and fix it, and finally put the sample cell into the vacuum chamber of the freeze dryer .

(3) Sample test. Vacuumize the vacuum chamber of the freeze dryer, the pressure can be adjusted in the range of 1Pa to 1.013×10 ⁵ Pa, and the temperature in the chamber can be adjusted at the same time, and the temperature can be adjusted in the range of -190°C to 200°C. Select a pressure and temperature for each measurement. After the pressure and temperature reach the specified values, monitor the temperature drift (see Figure 3) to ensure that the test experiment is performed when the sample is isothermal and there is no temperature drift. The thermal conductivity value of the sample under the specified test conditions is obtained by operating the relevant software of the thermal conductivity meter (see Figure 4).

(4) Repeat step (3), keep other parameters unchanged, change the temperature value, measure a set of data every half hour, you can get the trend graph of the thermal conductivity of olivine with temperature, the result is similar to Figure 7.

(5) Repeat step (3), keep the other parameters unchanged, change the pressure value, measure a set of data every half hour, you can get the trend graph of the thermal conductivity of olivine with pressure, and the result is similar to Figure 7.

Example 3

This embodiment 3 all carries out relevant test work under the condition after test method improvement.

(1) Sample pretreatment. Prepare the simulated lunar soil sample into a powder sample with a particle size not greater than 1mm according to your own needs, ensure that the sample is mixed evenly, and dry the sample before measurement.

(2) Sample installation. Select a sample cell of 1.0 cm ³ , put the simulated lunar soil powder sample and test probe that have been pretreated according to step (1) into the sample cell and fix it, and finally put the sample cell into the vacuum chamber of the freeze dryer in vivo.

(3) Sample test. Vacuumize the vacuum chamber of the freeze dryer, the pressure can be adjusted in the range of 1Pa to 1.013×10 ⁵ Pa, and the temperature in the chamber can be adjusted at the same time, and the temperature can be adjusted in the range of -190°C to 200°C. Select a pressure and temperature for each measurement. After the pressure and temperature reach the specified values, monitor the temperature drift (see Figure 3) to ensure that the test experiment is performed when the sample is isothermal and there is no temperature drift. The thermal conductivity value of the sample under the specified test conditions is obtained by operating the relevant software of the thermal conductivity meter (see Figure 4).

(4) Repeat step (3), keep other parameters unchanged, change the pressure value, measure a set of data every half an hour, and you can get the trend graph of the thermal conductivity of the simulated lunar soil changing with the pressure, and the results are similar to in Figure 7.

(5) Repeat step (3), keep other parameters unchanged under normal pressure conditions, change the temperature value, and measure a set of data every half an hour to get the trend diagram of the thermal conductivity of the simulated lunar soil changing with temperature (Fig. 8).

Claims (5)

1. A method for measuring the thermal conductivity of a trace powder sample under different temperature and pressure conditions in a vacuum environment, characterized in that the measurement steps are as follows: (1) Before the measurement, the sample is prepared into a granular shape with a particle size not greater than 1mm, and it is dried; (2) After putting the powder sample and the probe into the sample cell, put the sample cell into the vacuum chamber of the freeze dryer; the sample volume is within the range of 1.0cm ³ to 20.0cm ³ ; The sample cell includes a sample cell body and an upper cover. The sample cell body is cylindrical. A stepped hole is opened in the sample cell body along the axial direction of the sample cell body. The upper transverse dimension of the stepped hole is larger than the lower transverse dimension and the upper end is open. Closed, the lower part of the stepped hole close to the closed end is the sample tank, the shape of the upper cover matches the shape of the stepped hole above the sample tank, and an open slot is opened on the sample tank body to connect the sample tank with the side of the sample tank body ;The sample cell is made of stainless steel; (3) Vacuumize the vacuum chamber of the freeze dryer, and adjust the temperature and pressure in the chamber at the same time. After the temperature reaches -190 ° C ~ 200 ° C and the pressure reaches the set value, through the operation of the relevant software of the thermal conductivity meter To obtain the thermal conductivity value of the sample under the specified test conditions. 2. the method for measuring the thermal conductivity of trace powder samples under different temperature and pressure conditions under vacuum environment according to claim 1, it is characterized in that the whole process of described measurement all carries out test work under vacuum condition. 3. the method for measuring the thermal conductivity of trace powder samples under different temperature and pressure conditions in a vacuum environment according to claim 1, it is characterized in that the method can simultaneously regulate two parameters of temperature and pressure, and the powder sample can be measured at Thermal conductivity under different temperature or different pressure conditions. 4. The method for measuring the thermal conductivity of micro-powder samples under different temperature and pressure conditions in a vacuum environment according to claim 1, characterized in that the volume specification of the sample cell is customized according to the demand, and its volume range is 1.0cm ³ ~20.0cm within ³ . 5. The method for measuring the thermal conductivity of trace powder samples under different temperature and pressure conditions in a vacuum environment according to claim 1, characterized in that the pressure range is 1 Pa to 1.013×10 ⁵ Pa.