Method and device for steady-state in-situ measurement of emissivity of material

Abstract

The invention provides a method and a device for steady-state in-situ measurement of emissivity of a material, and the method comprises the following steps: constructing a sample assembly integrating a heater and a thermocouple, and suspending the sample assembly in a high-vacuum constant-temperature chamber; by applying current input power, temperature change is monitored until heat balance, and input net power, sample surface temperature and environment temperature are recorded; systematically changing the power to stabilize the sample at different temperatures to obtain a series of data points; and finally, performing function fitting based on a Stefan-Boltzmann law to obtain the full-wave band emissivity of the material at a specific environment temperature. According to the method, non-radiant heat loss is physically isolated, an accurate one-dimensional axial heat flow and surface radiation energy conservation relation is established, in-situ and continuous measurement of the emissivity in a wide temperature region is realized, the defects that a temperature region and a wave band are limited and are easily influenced by a surface state and the like in a traditional method are effectively overcome, and the measurement accuracy is improved. And a data basis can be provided for accurate thermal management in the fields of thermoelectric materials, aerospace thermal control and the like.

Description

Technical Field

[0001] This invention belongs to the field of material thermophysical property testing technology, specifically relating to a method and apparatus for in-situ steady-state measurement of material emissivity across a wide temperature range. Background Technology

[0002] Emissivity (ε) is a dimensionless physical quantity used to measure the ability of an object's surface to emit energy in the form of thermal radiation. It is defined as the ratio of the radiative heat flux of an object's surface to the radiative heat flux of an ideal blackbody at the same temperature, with a value ranging from 0 to 1. In thermal equilibrium, for any given wavelength and direction, the spectral directional absorptivity of an object is equal to its spectral directional emissivity.

[0003] Emissivity exhibits wavelength dependence, orientation dependence, temperature dependence, and surface dependence. Wavelength dependence refers to the fact that emissivity typically depends on the wavelength of radiation, with spectral emissivity describing the emissivity at a specific wavelength. Orientation dependence refers to the fact that emissivity varies depending on the viewing direction. Temperature dependence refers to the fact that emissivity typically depends on the surface temperature of an object, and this dependence may vary depending on the material. Surface dependence refers to factors such as material type, roughness, and oxide layer.

[0004] Thermoelectric materials utilize the Seebeck effect (electricity generated by temperature difference) and the Peltier effect (cooling and heating by electric current) to achieve direct interconversion between thermal energy and electrical energy. Emissivity, as a key parameter of the thermal radiation characteristics of a material surface, has a significant impact on the performance of thermoelectric materials and their devices, mainly in the following aspects:

[0005] 1. Thermal Radiation Loss: Thermoelectric materials generate thermal radiation due to their surface temperature during operation (especially at the high-temperature end). The higher the emissivity (ε) of the material, the greater the thermal radiation power P ∝ ε·σ·T, according to the Stefan-Boltzmann law (thermal radiation power P ∝ ε·σ·T). 4 The greater the radiative heat loss, the lower the temperature at the hot end. This directly leads to a drop in the hot end temperature or the need for additional heat input to maintain the target temperature gradient, thus reducing the efficiency of thermoelectric power generation (Seebeck effect). For cooling / heating modes (Peltier effect), thermal radiation loss also interferes with temperature control in the target area.

[0006] 2. Interface Thermal Management and Contact Resistance Influence (Indirect): In thermoelectric devices, the interface between the thermoelectric material and the metal electrode or heat sink / heat source module is crucial. The emissivity of the interface affects radiative heat exchange at the interface. Mismatched emissivity may increase interfacial thermal resistance or introduce additional radiative heat loss / gain, affecting the efficiency of heat flow into / out of the thermoelectric material. Furthermore, the material surface state (affecting emissivity) may also be related to contact resistance, further influencing electrical performance and Joule heat distribution.

[0007] 3. Accuracy of Intrinsic Property Characterization: When measuring the intrinsic property parameters (such as Seebeck coefficient, electrical conductivity, and thermal conductivity) of thermoelectric materials in the laboratory, accurately knowing the emissivity of the material at the test temperature and wavelength is crucial for accurately measuring its thermal conductivity (usually using methods such as laser scintillation that require thermal diffusivity data, which often needs to be corrected for radiation loss). Inaccurate emissivity data will directly lead to errors in thermal conductivity measurement, thus affecting the accurate evaluation of the material's zT value (thermoelectric figure of merit).

[0008] However, current methods for emissivity measurement, especially spectroscopic methods, have many limitations, mainly in the following aspects:

[0009] (1) Insufficient temperature range and band coverage: Traditional emissivity measurement equipment can usually only be used at discrete temperature points, making it difficult to achieve continuous characterization over a wide temperature range; at the same time, its spectral coverage is mainly limited to the visible-near infrared band, lacking key data in the mid-far infrared band, which leads to errors in thermal radiation calculation.

[0010] (2) Errors caused by cross-sample data reuse: Changes in the surface condition of the material (such as oxidation degree and roughness) can significantly affect emissivity. However, existing technologies usually adopt a measurement-then-apply approach, which fails to establish a correlation between emissivity and the actual surface condition, resulting in systematic deviations in thermal conductivity correction results.

[0011] (3) Lack of in-situ monitoring: Traditional methods can no longer measure emissivity while associating it with the sample surface state, resulting in a disconnect between data and physical state, which in turn affects the accuracy of thermophysical property analysis. Summary of the Invention

[0012] The purpose of this invention is to overcome the limitations of traditional methods and provide a method and system for steady-state in-situ measurement of emissivity. This method enables in-situ measurement of emissivity across the entire wavelength range at continuous temperatures over a wide temperature range (such as room temperature and low temperature). Furthermore, through adaptive calibration based on surface condition, it eliminates errors in cross-sample data application and provides accurate characterization data for thermal measurements such as thermal conductivity.

[0013] This invention achieves physical isolation of non-target heat loss paths through experimental design, thereby establishing an energy conservation relationship between one-dimensional axial heat conduction and surface thermal radiation under steady-state conditions, and directly and accurately calculating the full-wavelength emissivity of the material. Its basic technical concept includes: eliminating convective and conductive heat losses through a suspended structure and a high-vacuum environment; ensuring one-dimensional heat flow conduction through directional heat flow design and dual temperature measurement point monitoring; and equating net heating power to radiative heat dissipation power through precise measurement of input power and heat loss, and then applying the Stefan-Boltzmann law to solve for the emissivity.

[0014] In a first aspect, the present invention provides a method for steady-state in-situ measurement of material emissivity, comprising the following steps:

[0015] (1) Construction of sample assembly: Provide a sample of the material to be tested, attach a heater to one end face of the sample to establish a thermally conductive connection to form an axial heat conduction path; set at least two temperature measuring points along the heat conduction path on the surface of the sample, and install thermocouples for temperature monitoring, thereby constructing the sample assembly to be tested;

[0016] (2) Establishment of thermal equilibrium: The sample assembly to be tested is suspended in a vacuum chamber with constant temperature. Current is applied to the heater to input power to the sample. The temperature change of the at least two temperature measuring points is monitored in real time. When the sample reaches thermal equilibrium, the net input power, the temperature of the two temperature measuring points and the ambient temperature in the vacuum chamber are recorded.

[0017] (3) Obtaining the continuous function: By systematically changing the input power of the heater, the sample is stabilized at different surface temperatures, and a series of data corresponding to the net input power and surface temperature are recorded;

[0018] (4) Relationship fitting: According to the Stefan-Boltzmann law, the series of data obtained in step (3) are fitted with a function relationship to obtain the emissivity of the material under test at the ambient temperature.

[0019] The principle of the measurement method provided by this invention is explained as follows:

[0020] Under the experimental conditions designed in this invention, by effectively isolating non-radiative heat loss paths, when the system reaches thermal equilibrium, according to the law of conservation of energy, the net thermal power input to the sample by the heater is equal to the power lost from the sample surface to the environment through thermal radiation. Its energy balance equation can be expressed as:

[0021]

[0022] Among them, Q input = Q heat - Q loss (Q) loss (for thermocouple parasitic heat loss), Q rad Let be the radial radiative heat flux from the sample surface. According to the Stefan-Boltzmann law, its radiative power is:

[0023]

[0024] Where ε is the emissivity of the sample to be solved, σ is the Stefan-Boltzmann constant, A is the effective radiative area of ​​the sample, and T s Let T0 be the sample surface temperature and T0 be the ambient temperature. Solving the above equations simultaneously, the formula for calculating emissivity can be derived:

[0025]

[0026] In actual measurements, the above heat flow parameters are all determined through corresponding electrical power parameters: the input heat flow Q of the heater. heat The electrical power P consumed by it heat =I 2 R is determined (where I is the heater current, R is the heater resistance); parasitic heat loss flow rate Q loss The corresponding heat loss power is obtained through calibration or calculation. ε can be directly calculated by measuring or controlling all parameters in the formula.

[0027] By systematically changing the input electrical power P of the heater heat This allows the samples to be stabilized at different equilibrium temperatures T. s By repeating the above measurement and calculation process, the emissivity ε as a function of temperature T can be obtained. s The complete functional relationship of change ε(T) s ).

[0028] In some specific embodiments of the present invention, a cryostat (e.g., a liquid helium-free closed-loop cryogenic system) can be used to provide a wide range of highly stable ambient temperatures from liquid helium temperature (about 4 K) to above room temperature (e.g., 320 K), thereby enabling accurate steady-state measurements throughout the entire temperature range.

[0029] In some embodiments of the method of the present invention, the method may further include: (5) changing the ambient temperature in the vacuum chamber described in step (2), repeating steps (2)-(4), and obtaining the emissivity of the material to be tested at different ambient temperatures.

[0030] In many high-tech application scenarios, the ambient temperature of the material is subject to drastic changes. Step (5) enables the measurement capability of the method of the present invention to cover extreme and changing real environments. The obtained data can be directly used for the design and calculation of any actual working temperature, realizing the significance of "in-situ" measurement: obtaining material properties under simulated real environmental conditions.

[0031] According to a preferred embodiment of the present invention:

[0032] The heater mentioned in step (1) is preferably a fixed-value resistance heater to ensure the accuracy of power calculation. Preferably, the thermally conductive connection is achieved by coating with a high thermal conductivity insulating adhesive with a thickness of less than 50 μm. The high thermal conductivity insulating adhesive is preferably an alumina-filled epoxy resin adhesive.

[0033] Preferably, the thermocouple in step (1) can also be fixed to the temperature measuring point by coating it with a conductive adhesive with a thickness of less than 50 μm. The conductive adhesive is preferably conductive silver paste.

[0034] Preferably, the criterion for determining the thermal equilibrium state in step (2) can be: the temperature fluctuation of the at least two temperature measuring points within 3-5 minutes is less than ±0.2 K, and the absolute value of the temperature difference between the two points is less than 1.0 K, preferably less than 0.7 K.

[0035] Preferably, the vacuum degree of the vacuum chamber in step (2) is not less than 10. -2 Pa, preferably not less than 10 -3 Pa. In the method of the present invention, a high vacuum environment is used to eliminate convection and achieve controllability of the heat loss path.

[0036] To improve the measurement accuracy of the method of the present invention, the net input power in step (2) is the total input power of the heater minus the parasitic heat loss caused by the thermocouple leads.

[0037] Preferably, the sample of the material to be tested in step (1) has a regular geometric shape, particularly a long strip-shaped regular geometric shape. Preferably, the end face of the long strip-shaped regular geometric shape is circular, elliptical, rectangular, square, regular polygonal, or a closed shape composed of smooth arcs. The long strip-shaped regular geometric shape described in this invention refers to a cross-section with a constant length. Preferably, the long strip-shaped geometric shape has a regular and symmetrical cross-sectional shape to ensure that heat flow forms an approximately one-dimensional axial conduction within the sample.

[0038] Preferably, the two temperature measuring points mentioned in step (1) are distributed along the axial direction, and the distance between them is recommended to be no less than 1 / 5 of the length of the sample side surface, so as to effectively monitor the temperature gradient. The at least two temperature measuring points include a first temperature measuring point close to the heater and a second temperature measuring point far away from the heater, and the distance between the first temperature measuring point and the second temperature measuring point is no less than 1 / 5 of the length of the sample side surface.

[0039] Preferably, in step (3), the input power is systematically changed to stabilize the sample at a series of different surface temperatures, thereby obtaining no fewer than 5 sets of corresponding data for different net input power and surface temperature. More data points are beneficial for improving the ε(T) fitted in step (4). s The reliability of the relationship.

[0040] In a second aspect, the present invention provides a steady-state in-situ emissivity measurement device, comprising:

[0041] Vacuum chamber and its temperature control system;

[0042] A sample rod, which is disposed within the vacuum chamber, is used to fix the sample assembly;

[0043] The sample assembly to be tested, which is suspended and fixed at the end of the sample rod, includes:

[0044] The sample to be tested;

[0045] A heater, which is electrically connected to a high-precision power supply, is attached to one end face of the sample by a thermally conductive insulating adhesive to form an axial heat conduction path;

[0046] At least two pairs of thermocouples are fixed to the sample surface along the axial heat conduction path using conductive adhesive for temperature monitoring.

[0047] In a preferred embodiment of the present invention, the suspension and fixation of the sample assembly under test is achieved by connecting its thermocouple leads to the sample rod. That is, the sample assembly under test is suspended and fixed at the end of the sample rod solely through the thermocouple leads. Preferably, the minimum distance between the suspended sample assembly and the inner wall of the vacuum chamber is greater than 20 mm.

[0048] The measurement method provided by this invention includes: constructing a sample assembly integrating a heater and a thermocouple, suspending it in a high-vacuum constant-temperature chamber; applying current input power, monitoring temperature changes until thermal equilibrium is reached, and recording the net input power, sample surface temperature, and ambient temperature; systematically changing the power to stabilize the sample at different temperatures, obtaining a series of data points; and finally, performing function fitting based on the Stefan-Boltzmann law to obtain the full-band emissivity of the material at a specific ambient temperature. This invention establishes a precise one-dimensional axial heat flow and surface radiation energy conservation relationship by physically isolating non-radiative heat loss, achieving in-situ, continuous measurement of emissivity over a wide temperature range. It effectively overcomes the shortcomings of traditional methods, such as limited temperature range and wavelength, and susceptibility to surface conditions, providing a data foundation for precise thermal management in fields such as thermoelectric materials and aerospace thermal control. Specifically, the method of this invention has the following significant beneficial effects:

[0049] 1. Wide temperature range and full-band synchronous measurement: It realizes the direct measurement of the emissivity of materials across the entire band under continuously changing temperature spectrum, completely solving the problems of data fragmentation and difficulty in extrapolating to the entire band in traditional spectroscopic methods.

[0050] 2. In-situ surface condition adaptability: By performing in-situ continuous measurements on the same sample under thermal equilibrium conditions, the systematic errors introduced by the difference in surface conditions (roughness, oxide layer, etc.) when simply applying the measurement results of a single sample to similar materials are effectively avoided, and the accuracy of parameters such as thermal conductivity is significantly improved.

[0051] 3. High versatility: The method and system of this invention are not only applicable to the study of the thermal properties of basic materials, but also have great application potential in high-tech fields such as thermal management of cryogenic environments in spacecraft, thermal-electric efficiency optimization of wearable self-powered flexible devices, and Internet of Things sensor networks. They can provide key basic data for precise thermal design and thermal management under complex working conditions.

[0052] In summary, the steady-state in-situ emissivity measurement method provided by this invention not only fully inherits the core advantages of stable and reliable results from traditional steady-state methods, but also achieves breakthroughs in the width of the measurement temperature range, the completeness of the wavelength range, and the adaptability to the surface condition of the sample under test. It successfully combines wide-temperature range control, full-band detection, and in-situ monitoring technology to form a novel and advanced material thermal radiation characteristic characterization technique. Attached Figure Description

[0053] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0054] Figure 1 This is a schematic diagram of the sample components prepared in the embodiments of the present invention;

[0055] Figure 2 These are photographs of the sample components prepared in the embodiments of the present invention;

[0056] Figure 3 This is the temperature distribution of two pairs of thermocouples in the sample of Example 1 of the present invention at an ambient temperature of 300K and under different radiation powers;

[0057] Figure 4 In Example 1 of this invention, the radiation power of the sample at an ambient temperature of 300K is related to the fourth power of the sample temperature (T). s 4 Linear fitting relationship graph;

[0058] Figure 5 In Embodiment 2 of the present invention, the linear fitting relationship between the radiation power of the sample and the fourth power of the difference between the sample temperature and the ambient temperature is shown.

[0059] Figure 6 This is a graph showing the relationship between the emissivity of N-type and P-type bismuth telluride samples and ambient temperature in Example 3 of the present invention. Detailed Implementation

[0060] The present invention will now be described in further detail with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention. In the embodiments of the present invention, all raw materials, equipment and methods not specifically described can be obtained commercially or implemented using conventional methods in the art.

[0061] The following is a detailed description of the structure and operation of the measurement system used in the embodiments of the present invention:

[0062] 1. Overall configuration of the measurement system:

[0063] The steady-state in-situ emissivity measurement system used in this embodiment of the invention includes: an ultra-high vacuum chamber, a sample rod, a fixed resistance heater, a type E (nickel-chromium-nickel-copper) thermocouple, a high-precision DC power supply, a data acquisition unit, and a computer control system.

[0064] 2. Vacuum and Environmental Control:

[0065] The ultra-vacuum cavity is obtained and maintained at a pressure better than 10 by a molecular pump assembly. -2 A high vacuum environment on the Pa level is provided to completely eliminate heat loss caused by air convection and heat conduction by gas molecules. The cavity is connected to a liquid helium-free closed-loop cryogenic system to provide and precisely control a wide range of stable cryogenic environments from 160 K to 300 K (and can be extended to lower levels such as 4 K). The temperature of this cryogenic environment is denoted as T0 (i.e., ambient temperature or sample stage temperature).

[0066] 3. Sample component preparation and assembly:

[0067] Sample: Select the material to be tested and process it into a regular rectangular strip sample with dimensions of 10 mm × 2 mm × 1 mm.

[0068] Heater connection: Using micro-dispensing technology, a high thermal conductivity insulating adhesive (alumina-filled epoxy resin) with a thickness of about 30 μm is applied to one end face of the sample (defined as the lower end face), and a fixed resistance plate heater with a resistance of 1000 Ω is tightly attached to it to form a directional axial heat conduction path.

[0069] Thermocouple Installation: Two temperature measuring points are arranged along the axial heat flow path on the sample side surface. The first temperature measuring point (T1) is approximately 2 mm from the heater, and the second temperature measuring point (T2) is approximately 5 mm from the heater. The axial distance L between the two temperature measuring points is 3 mm (3 / 10 of the sample length). The measuring ends of the two pairs of type E thermocouples are securely fixed to these two temperature measuring points using conductive silver paste (coating thickness <30 μm). The cold junction (reference junction) leads of the thermocouples are soldered to the copper electrode on the sample rod that maintains a constant temperature T0.

[0070] Figure 1This is a schematic diagram of the prepared sample assembly, where 1 is the sample, 2 is the heater, 21 is the heater wire, 31 is the first thermocouple fixed to the first temperature measuring point, and 32 is the second thermocouple fixed to the second temperature measuring point. The arrows indicate the direction of heat flow, and the divergence curve around the sample represents heat loss. In this embodiment, the sample assembly is in a "suspended" state by fixing the other ends of the heater wire 21, the first thermocouple 31, and the second thermocouple 32 to the sample rod 4.

[0071] 4. Installation of the suspended structure: The sample assembly with heater and thermocouple is suspended on the platform at the end of the sample rod by multiple slender alloy coils (0.1 mm in diameter), so that the sample assembly is in a "suspended" state. Figure 2 This is a photograph of the sample assembly prepared in an embodiment of the present invention, where 1 is the sample and 2 is the heater. The minimum distance between the sample assembly and the inner wall of the vacuum chamber is greater than 20 mm. This design ensures that the only effective path for heat loss from the sample to the environment is radiative heat transfer (Q) between the sample surface and the low-temperature chamber wall. rad This minimizes heat loss through conduction via the solid support.

[0072] 5. Thermocouple parasitic heat loss Q loss Calculation

[0073] The heat loss at different temperatures is calculated based on the cross-sectional area, length, and thermal conductivity of the thermocouple, using the following formula:

[0074] Q loss = κ·A·L·ΔT

[0075] Where κ is the thermal conductivity of the thermocouple, L is the length of the thermocouple, A is the cross-sectional area of ​​the thermocouple, and ΔT is the sample surface temperature T. s The difference between the surface temperature and the ambient temperature T0 is taken as the average of T1 and T2 under thermal equilibrium conditions, and thus the surface temperature T. s .

[0076] Example 1

[0077] Following the configuration and operation of the measurement system described above, the N-type bismuth telluride (Bi2Te3) sample was prepared into a rectangular strip with dimensions of 10 mm × 2 mm × 1 mm. The emissivity was measured using the method of this invention within a temperature range of 160-300 K.

[0078] (1) Start the high vacuum system and maintain the cavity vacuum at 10. -3 Pa. A stable cryogenic system keeps the temperature T0 of the sample stage in the chamber stable at 300K.

[0079] (2) Apply a constant current I=1 mA to the heater through a high-precision power supply, and input power (i.e. input heat flow Q) heat ) is: P heat =Q heat =I 2 R = 1000 μW (R is the heater resistance). According to the formula Q... loss = κ·A·L·ΔT The parasitic heat loss of the thermocouple is calculated to be 47 μW. The radiant power equals the net input power, i.e.: Q rad =Q heat -Q loss =953μW, at which point the sample temperature T s =(T1+T2) / 2=299.98K.

[0080] (3) The current applied to the heater was changed sequentially to 0.9, 0.8, 0.7, 0.6, 0.5 and 0.2 mA, so that the input power was 810, 640, 490, 360, 250 and 40 μW respectively, and the radiation power was 771, 610, 467, 343, 238 and 38 μW respectively. The corresponding data of the net input power (i.e. radiation power) and the sample surface temperature were recorded, as shown in Table 1:

[0081]

[0082] Figure 3 The figure shows the temperature distribution of two thermocouple pairs when the input power is 0.04, 0.25, 0.49, and 0.81 mW (where the dashed line is T1 and the solid line is T2). As can be seen from the figure, the temperature increases with increasing power, and eventually reaches a relatively stable state as the power stabilizes.

[0083] (4) Relationship fitting: According to the Stefan-Boltzmann law, the series of data in Table 1 are fitted with a functional relationship, that is, the radiation power and the corresponding temperature are fitted to the fourth power to obtain the fitting equation for emissivity. The emissivity of N-type Bi2Te3 at an ambient temperature of 300 K is calculated based on the coefficients.

[0084] Figure 4 The table shows the relationship between radiant power and the fourth power of the corresponding sample temperature (T) at different input powers. s 4 The graph shows the linear fitting relationship between temperature and power at 300K. The emissivity of the sample at that temperature can be obtained from the slope of the fitting. The emissivity of the N-type sample at 300K is 0.65.

[0085] Example 2

[0086] Following the Bi2Te3 emissivity measurement method at an ambient temperature of 300K in Example 1, the measurement temperature range was further extended to 160-300K. Data processing parameters were adjusted for the extended temperature range, and the specific measurement results are shown in Table 2 below.

[0087]

[0088] Figure 5 The linear fit between the sample's radiant power and the fourth power of the sample temperature minus the ambient temperature is shown at ambient temperatures of 160, 220, 260, and 300 K. Figure 5 As can be seen from this, under different ambient temperatures, the radiant power is related to (T) s 4 -T0 4 The emissivity and emissivity of the samples exhibit a good linear relationship, indicating that accurate calculation of emissivity can be performed over a wide temperature range. The slope of this linear relationship is directly related to the emissivity ε of the material, demonstrating that the measurement method of this invention successfully extends single-point verification to wide-temperature characterization. By systematically changing the ambient temperature and repeating this measurement and fitting process, continuous data on the emissivity of N-type Bi₂Te₃ samples as a function of ambient temperature in the range of 160-300 K can be obtained.

[0089] In thermal analysis of devices operating over a wide temperature range (such as spacecraft and cryogenic sensors), the emissivity data measured within their actual operating temperature range using the method of this invention can be used to achieve accurate thermal prediction and control.

[0090] Example 3

[0091] Following the methods described in Examples 1 and 2, p-type bismuth telluride (Bi2Te3) was used as the test material, and the emissivity at different temperatures was measured and compared with the emissivity of n-type bismuth telluride (Bi2Te3) measured in Example 2. The results are shown in Table 3.

[0092]

[0093] Plot the emissivity of the N-type and P-type bismuth telluride samples listed in Table 3 against ambient temperature, as shown below. Figure 6 As shown. From Figure 6 As can be seen, the emissivity of the material not only varies with temperature but is also closely related to the material type (doping / composition). At 300 K, the emissivity of N-type and P-type Bi₂Te₃ is similar; however, as the temperature decreases, they show significant differences, especially the emissivity of the P-type sample, which drops sharply in the low-temperature region (<220 K). Therefore, in thermal management design, it is necessary to perform in-situ measurements within the actual operating temperature range of a specific sample to obtain reliable data.

[0094] Example 4

[0095] To verify the accuracy and reliability of the measurement method of this invention, a comparative test was conducted using the method of this invention and a standard Fourier transform infrared spectrometer (Nicolet 6700Ò). Quartz samples and p-type bismuth telluride (Bi₂Te₃) samples with different radiation characteristics were selected for the experiment. Their emissivity was measured using both methods at an ambient temperature of 300 K. The results are compared below:

[0096] For quartz samples, the emissivity measured by the method of this invention is 0.81, and the value measured by FTIR spectroscopy is 0.87;

[0097] For the p-type Bi2Te3 sample, the result obtained by the method of this invention is 0.66, and the corresponding FTIR measurement value is 0.60.

[0098] Comparative data show that the emissivity results obtained by the two methods are basically consistent in numerical value, but there are slight differences: the quartz emissivity measured by FTIR is about 7% higher than that of the method of this invention, while the FTIR value of the Bi2Te3 sample is about 9% lower.

[0099] Fourier transform infrared spectroscopy (FTIR), a classic technique in infrared spectroscopy, typically limits its measurement wavelength range to 2.5–20 μm. This range, primarily in the mid-infrared band, while sufficient for most basic infrared characterization analyses, has clear limitations in band coverage. Specifically, when the measurement scenario involves the far-infrared band beyond 20 μm, FTIR, constrained by the response range of its optical components and its adaptability to vacuum environments, cannot effectively capture the spectral signal in this band. This means that relying solely on FTIR measurements will directly miss crucial spectral information in the far-infrared band, resulting in a "band gap" in the acquired sample infrared radiation data, making it difficult to fully reflect the sample's true optical characteristics across the entire infrared spectrum.

[0100] In contrast, the method of this invention is a full-band measurement method, which not only fully covers the 2.5-20 μm mid-infrared range detectable by FTIR, but also extends the measurement range to the far-infrared band beyond 20 μm, achieving continuous spectral signal acquisition across the entire spectrum from near-infrared to far-infrared. This "gap-free" spectral data acquisition mode effectively avoids measurement errors caused by missing bands, thus providing a more complete and reliable experimental basis for subsequent data interpretation and conclusion derivation. Therefore, compared to limited-band measurement methods that rely solely on FTIR, the full-band measurement method of this invention has significant advantages in both data accuracy and analytical reliability.

Claims

1. A method for steady-state in-situ measurement of material emissivity, characterized in that, Includes the following steps: (1) Sample assembly construction: Provide a sample of the material to be tested, and attach the heater to one end face of the sample to establish a thermally conductive connection to form an axial heat conduction path; At least two temperature measurement points are set on the surface of the sample along the heat conduction path, and thermocouples are installed for temperature monitoring, thereby constructing the sample assembly to be tested; (2) Establishment of thermal equilibrium: The sample assembly to be tested is suspended in a vacuum chamber with constant temperature. Current is applied to the heater to input power to the sample. The temperature change of the at least two temperature measuring points is monitored in real time. When the sample reaches thermal equilibrium, the net input power, the temperature of the two temperature measuring points and the ambient temperature in the vacuum chamber are recorded. (3) Obtaining the continuous function: By systematically changing the input power of the heater, the sample is stabilized at different surface temperatures, and a series of data corresponding to the net input power and surface temperature are recorded; (4) Relationship fitting: According to the Stefan-Boltzmann law, the series of data obtained in step (3) are fitted with a function relationship to obtain the emissivity of the material under test at the ambient temperature.

2. The method according to claim 1, wherein, The method further includes: (5) changing the ambient temperature in the vacuum chamber described in step (2), and repeating steps (2)-(4) to obtain the emissivity of the material under test at different ambient temperatures.

3. The method according to claim 1, wherein, The heater mentioned in step (1) is a fixed-value resistance heater, and the thermally conductive connection is achieved by coating with a high thermal conductivity insulating adhesive with a thickness of less than 50 μm. Preferably, the high thermal conductivity insulating adhesive is an epoxy resin adhesive filled with alumina. Preferably, in step (1), the thermocouple is fixed to the temperature measuring point by coating a conductive adhesive with a thickness of less than 50 μm, wherein the conductive adhesive is preferably conductive silver paste.

4. The method according to claim 1, wherein, The criteria for determining the thermal equilibrium state in step (2) are: the temperature fluctuation of the at least two temperature measuring points is less than ±0.2 K within 3 to 5 minutes, and the absolute value of the temperature difference between the two points is less than 1.0 K, preferably less than 0.7 K.

5. The method according to claim 1, wherein, The vacuum level of the vacuum chamber in step (2) shall not be less than 10. -2 Pa, preferably not less than 10 -3 Pa.

6. The method according to claim 1, wherein, The net input power mentioned in step (2) is the power after deducting the parasitic heat loss of the thermocouple from the input power of the heater.

7. The method according to any one of claims 1 to 6, wherein, The sample of the material to be tested in step (1) has a regular geometric shape; preferably, it is a long strip regular geometric shape; preferably, the end face of the long strip regular geometric shape is a circle, ellipse, rectangle, square, regular polygon or a closed shape composed of smooth arcs.

8. The method according to any one of claims 1 to 6, wherein, The at least two temperature measuring points mentioned in step (1) include a first temperature measuring point close to the heater and a second temperature measuring point far away from the heater, wherein the axial distance between the first temperature measuring point and the second temperature measuring point is not less than 1 / 5 of the sample surface length.

9. The method according to any one of claims 1 to 6, wherein, In step (3), the input power is systematically changed to stabilize the sample at a series of different surface temperatures, thereby obtaining no less than 5 sets of corresponding data of different net input power and surface temperature.

10. A steady-state in-situ emissivity measurement device, characterized in that, include: Vacuum chamber and its temperature control system; A sample rod, which is disposed within the vacuum chamber, is used to fix the sample assembly; and The sample assembly to be tested, which is suspended and fixed at the end of the sample rod, includes: The sample to be tested; A heater, which is electrically connected to a high-precision power supply, is attached to one end face of the sample by a thermally conductive insulating adhesive to form an axial heat conduction path; At least two pairs of thermocouples are fixed to at least two temperature measuring points on the sample surface via conductive adhesive along the axial heat conduction path for temperature monitoring.

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