A device and method for in-situ measurement of thermal conductivity at high temperature and high pressure

Abstract

The application relates to a device and a method for in-situ measurement of thermal conductivity under high temperature and high pressure, which comprises a pyrophyllite pressure transmission medium block and a sample body, the internal space of a boron nitride tube is a sample cavity, the sample body is arranged in the sample cavity, the upper and lower ends of the sample body are respectively provided with boron nitride sheets, and the upper and lower ends of a graphite tube are respectively provided with graphite sheets. The application combines one-dimensional hot-wire method with the large-cavity high-pressure environment of a cubic press, adopts the structure design that an electric heating wire and a K-type thermocouple vertically cross and penetrate the center of the sample body, simplifies the mode that a top hammer directly serves as an outgoing electrode, adopts a double heat preservation structure and a double insulation structure, solves the problems of short circuit, electric leakage and electrical interference of the heating circuit of the electric heating wire and the signal acquisition circuit of the K-type thermocouple under high temperature and high pressure, and directly obtains the thermal conductivity through linear fitting without complex inversion calculation, so that the test process is simplified, and the application range is significantly widened.

Description

Technical Field

[0001] This invention relates to the field of thermal conductivity measurement technology for solid materials under high temperature and high pressure, specifically to a device and method for in-situ measurement of thermal conductivity under high temperature and high pressure. It is based on the one-dimensional hot wire method and performs in-situ, real-time, and accurate measurement of the thermal conductivity of solid materials under the extreme environment of high temperature and high pressure of a six-sided press. Background Technology

[0002] Thermal conductivity of materials under high temperature and high pressure environments is a core fundamental parameter in geophysics, materials science, superhard material synthesis, and deep geological simulation. In geophysical research, the thermal conductivity of key minerals in the lower mantle directly determines the Earth's thermal evolution history, mantle convection rate, and geothermal gradient projection. In the field of superhard material synthesis, the growth temperature field distribution, defect control, and synthesis process optimization of materials such as diamond, cubic boron nitride, and polycrystalline diamond composite sheets are highly dependent on the accurate input of the thermal conductivity of the material inside the cavity. In the development of novel functional materials, thermal conduction behavior under extreme high temperature and high pressure conditions is a key indicator for evaluating material stability, service performance, and application scenarios.

[0003] Current conventional methods for measuring thermal conductivity are mainly divided into two categories: steady-state methods and transient methods. Steady-state methods, represented by the protective hot plate method and the radial heat flow method, are intuitive in principle and offer high measurement accuracy. However, they suffer from drawbacks such as long testing cycles, stringent requirements on sample size and contact conditions, and difficulty in constructing a stable and uniform heat flow field within the limited space of a high-pressure chamber, making them unsuitable for in-situ measurements under high temperature and high pressure. Transient methods, typically represented by the hot-wire method and the laser flash method, are less suitable for atmospheric or low-pressure environments and difficult to integrate into high-pressure chambers. The one-dimensional hot-wire method, based on the theory of unsteady-state heat conduction, calculates thermal conductivity by combining the temperature rise response generated by a linear heat source heating the medium with the linear relationship between temperature rise and the logarithm of time. It offers advantages such as fast measurement speed, small sample size, wide applicability, and ease of miniaturization and integration, making it the optimal technical approach for in-situ measurement of thermal conductivity under high temperature and high pressure.

[0004] In-situ thermal conductivity measurement under high temperature and pressure has long been a technical bottleneck in the field of high-pressure physics and thermophysical property testing. Existing technologies, such as Chinese patent CN111157571A, disclose a method for measuring the thermal conductivity of high-temperature and high-pressure samples based on a diamond-impregnated hammer. This method calibrates the sample's thermal conductivity through finite element simulation combined with multi-point temperature measurement. It relies on complex multi-point thermocouple arrangements and finite element simulation inversion calculations, resulting in cumbersome operation, complex data processing, extremely small sample chamber size, and extremely high requirements for sample preparation and assembly accuracy, making it difficult to promote widespread application. Another patent, CN206114568U, discloses a rock thermophysical property parameter testing system under high temperature and pressure, which uses an MTS true triaxial testing cylinder combined with a steady-state plate method for measurement. This system is bulky, has long heating and pressure holding times, and poor temperature field uniformity, making rapid in-situ measurement impossible.

[0005] The six-sided top press, a commonly used large-cavity high-pressure device in industry and scientific research, can provide extreme high-temperature and high-pressure environments up to 6 GPa and from room temperature to 1273 K, adapting to millimeter- to centimeter-sized block samples and possessing excellent potential for in-situ measurement. However, it is generally believed that the large cavity of the six-sided top press is only suitable for material synthesis and high-temperature and high-pressure processing, and cannot be integrated with the one-dimensional hot wire method to achieve in-situ thermal conductivity measurement. It is understood that there is currently no mature device or standardized method, either domestically or internationally, that can completely, stably, and efficiently integrate the one-dimensional hot wire method into the cavity of the six-sided top press, while simultaneously achieving high-temperature and high-pressure in-situ thermal conductivity measurement of solid materials. The aforementioned technical bias has led to the long-term limitation of high-temperature and high-pressure in-situ thermal conductivity measurement technology to small cavities, single material types, and complex inversion calculations, making it difficult to meet the engineering testing needs of fields such as deep geophysical simulation, superhard material synthesis, and high-temperature functional material research and development. Summary of the Invention

[0006] The purpose of this invention is to overcome the aforementioned defects and technical biases in the prior art, and to solve the technical problem of in-situ measurement of thermal conductivity of solid materials under high temperature and high pressure. This invention organically couples the one-dimensional hot wire method with the high-pressure environment of a large cavity of a six-sided top press, providing a device and method for in-situ measurement of thermal conductivity under high temperature and high pressure that is simple in structure, accurate in measurement, widely applicable, and has good repeatability. It can realize in-situ measurement of solid materials over a wide temperature and pressure range, as detailed below.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a device for in-situ measurement of thermal conductivity under high temperature and high pressure, comprising a pyrophyllite pressure-transmitting medium block and a sample body. The pyrophyllite pressure-transmitting medium block is in the shape of a square tube. A graphite tube is coaxially sleeved inside the internal cavity of the pyrophyllite pressure-transmitting medium block, and a boron nitride tube is sleeved inside the graphite tube. The internal space of the boron nitride tube is a sample cavity, and the sample body is loaded inside the sample cavity. Boron nitride sheets are respectively provided at the upper and lower ends of the sample body, and the boron nitride sheets respectively block the upper and lower ends of the boron nitride tube. Graphite sheets are respectively provided at the upper and lower ends of the graphite tube, and the graphite sheets respectively block the upper and lower ends of the graphite tube. Molybdenum sheets are attached to the upper and lower ends of the graphite sheet, and inverted steel caps are pressed onto the outer surface of the molybdenum sheets. Meanwhile, the interior of the steel caps is filled with thermal insulation filler. A heating wire is horizontally inserted radially through the center of the sample body, and a K-type thermocouple is also horizontally inserted radially through the center of the sample body.

[0008] Preferably, an insulation tube is embedded and fixed between the inner wall of the cavity of the pyrophyllite pressure transmission medium block and the outside of the graphite tube, and both the insulation tube and the insulation filler are made of dolomite.

[0009] Preferably, the heating wire is in direct contact with two opposite unheated hammers of the six-sided press, and the K-type thermocouple is in direct contact with the other two opposite unheated hammers of the six-sided press.

[0010] Preferably, the heating wire is made of nickel-chromium alloy and has a diameter of 0.2 mm; the K-type thermocouple has a diameter of 0.2 mm; both the heating wire and the K-type thermocouple are covered with an insulating tube, and both the heating wire and the K-type thermocouple pass radially through the center of the sample body via the insulating tube.

[0011] Preferably, the insulating tube is an alumina insulating tube with an inner diameter of 0.21 mm and an outer diameter of 1.0 mm. The heating wire and the K-type thermocouple are arranged perpendicularly to each other and are in close contact under the protection of the insulating tube.

[0012] Preferably, the outer end face of the boron nitride sheet is flush with the outer end faces of the graphite tube and the boron nitride tube, and the inner end face of the graphite sheet is flush with and in close contact with the outer end faces of the graphite tube, the boron nitride tube and the boron nitride sheet.

[0013] Preferably, the sample cavity is a hollow cylinder with an outer diameter of 12 mm, an inner diameter of 10.1 mm, and a height of 8 mm; the sample body is a cylinder with a diameter of 10 mm and a height of 8 mm; and the pyrophyllite pressure-transmitting medium block is a cube with a side length of 40 mm.

[0014] A method for in-situ measurement of thermal conductivity under high temperature and high pressure includes the following steps: 1) Sample Assembly: The sample body is inserted into the sample cavity. The heating wire and the K-type thermocouple are embedded in the sample body, with their ends leading out from both sides. The assembled block is placed between the top hammers of the six-sided press. The heating wire contacts two opposite unheated hammers, and the K-type thermocouple contacts the other two opposite unheated hammers. The cylindrical sample body is inserted into the sample cavity. The heating wire and the K-type thermocouple, which are fitted with the insulating tube, are inserted radially through the center of the sample body and led out horizontally from both sides of the assembled block. The assembled block is placed between the six top hammers of the six-sided press. The two ends of the heating wire are in direct contact with two opposite unheated hammers, and the two ends of the K-type thermocouple are in direct contact with the other two opposite unheated hammers. Utilizing the conductivity of the tungsten carbide top hammers, a constant current source and a digital multimeter are connected to the corresponding top hammers to complete the construction of the power supply and temperature measurement circuit. 2) Pressurization and heating: Start the six-sided pressurizer to pressurize to the target pressure, heat to the target temperature and stabilize; start the six-sided pressurizer to pressurize to the target pressure (maximum 6GPa); use the graphite heating element composed of the graphite tube and the graphite sheet to perform step heating of the sample body, and hold it at the target temperature for more than 5 minutes after reaching the target temperature to ensure that the internal temperature field of the sample body is uniform and stable. 3) Heating and temperature acquisition of the heating wire: After the temperature of the sample body stabilizes, the constant current source is started to apply a constant current I to the heating wire, and the voltage U across the heating wire is recorded in real time using a digital multimeter to calculate the average heating power; at the same time, the temperature response T(t) of the K-type thermocouple is recorded in real time with time t using the temperature reading function of the digital multimeter. 4) Thermal conductivity calculation: Based on the principle of one-dimensional hot wire method, the time interval [t1, t2] is selected. Within this interval, the temperature response T(t) is linearly related to the logarithm of time ln(t). The time t is converted to the natural logarithm ln(t), and the T(t) – ln(t) relationship curve is plotted. The slope k is obtained through linear fitting. The thermal conductivity λ of the sample body under this temperature and pressure is calculated according to the formula.

[0015] Preferably, the average heating power is calculated using the formula P=I× Calculate, where I is a constant current, The average voltage across the heating wire is λ; thermal conductivity is calculated using the formula λ=P / (4πL)×1 / k, where P is the average heating power, L is the effective heating length of the heating wire (i.e., the diameter of the sample), and k is the linear fitting slope; data acquisition begins after the temperature stabilizes, with a total acquisition time of 60s; the linear interval is determined based on T(t). Selection of linear distribution characteristics of ln(t) curve.

[0016] Preferably, the test also includes temperature and pressure variation testing: that is, changing the pressure and heating power, repeating steps 2-4, to obtain the variation law of thermal conductivity with temperature and pressure; the measurement pressure range is ≤6GPa, and the temperature range is room temperature to 1273K; the deviation of repeated measurements of the same sample at the same temperature and pressure for 5 times is ≤1.0%; the sample body is a solid material.

[0017] The beneficial effects are as follows: 1. This invention combines the one-dimensional hot wire method with the large-cavity high-pressure environment of a six-sided top press. Through the structural design of the heating wire and K-type thermocouple perpendicularly crossing through the center of the sample body, the simplified method of using the top hammer directly as the lead electrode, and the double heat preservation structure and double insulation structure, it solves the technical problem of the difficulty in quickly and accurately measuring solid materials under high temperature and high pressure. At the same time, without the need for complex inversion calculations, the thermal conductivity can be obtained directly through linear fitting. The testing process is simplified, the accuracy is improved, and the applicable range is significantly broadened. 2. By wrapping the heating wire and K-type thermocouple with an insulating tube made of alumina and vertically penetrating the center of the sample body, the heat source and the temperature measurement point can be highly coincided and the thermal response can be delayed. This ensures that the temperature acquisition is real and reliable, the temperature rise has a significant logarithmic linear relationship with time, and the thermal conductivity calculation is more accurate. 3. The sample chamber is constructed by using boron nitride tubes and boron nitride sheets, which combines high temperature resistance, high insulation and chemical stability, thus ensuring that the sample body is in a clean environment. 4. By combining the one-dimensional hot wire method with the large-cavity high-pressure environment of the six-sided top press, in-situ measurement of solid materials can be achieved within a range of maximum measurement pressure up to 6 GPa and room temperature up to 1273 K, meeting the testing needs of extreme conditions such as deep earth simulation and superhard material synthesis. 5. The conductive properties of the top hammer of the six-sided top press are used as the conductive electrodes of the heating wire and the K-type thermocouple, respectively. No additional leads or sealing structures are required, which makes the overall structure simpler, the assembly faster, the signal more stable, and the failure rate lower under high temperature and high pressure. 6. Thermal conductivity can be directly calculated by fitting the logarithmic linear relationship between temperature rise and time, without the need for complex finite element inversion. This simplifies data processing, increases testing speed, and improves repeatability. The deviation of multiple measurements of the same sample can be controlled within ≤1.0%. 7. The double-layer insulation structure, consisting of a pyrophyllite pressure transmission medium block and a dolomite insulation tube, ensures uniform temperature within the sample chamber and maintains a stable temperature field for the sample body at high temperatures. This avoids the measurement results being affected by edge heat dissipation and helps improve the reliability of high-temperature measurements. 8. The heating wire and K-type thermocouple are wrapped in an alumina insulating tube as the first layer of insulation, and the sample body is wrapped in a sample cavity formed by a boron nitride tube and boron nitride sheet as the second layer of insulation. This double insulation structure can effectively avoid problems such as short circuits, leakage and electrical interference in the heating circuit of the heating wire and the signal acquisition circuit of the K-type thermocouple under high temperature and high pressure, ensuring stable heating, smooth temperature response signal and high curve linearity throughout the test process. 9. The above-mentioned technical effects are not simply the sum of conventional components, but the result of the synergistic effect of double insulation structure, vertical cross-center temperature measurement, top hammer direct electrode connection, and double heat preservation structure: the double insulation structure completely solves the problems of short circuit, leakage and electrical interference in the heating circuit of the heating wire and the signal acquisition circuit of the K-type thermocouple under high temperature and high pressure; the vertical cross-center temperature measurement realizes the high overlap between the heat source and the temperature measurement point; the top hammer direct electrode connection simplifies the structure and improves the signal stability; and the double heat preservation structure ensures the uniformity of the temperature field, achieving a significant synergistic effect. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a front cross-sectional view of the present invention in its assembled state; Figure 2 This is a side cross-sectional view of the present invention in its assembled state; Figure 3 This is the temperature response T(t) of the K-type thermocouple in Embodiment 4 of the present invention as a function of time t; Figure 4 This is the curve showing the temperature response T(t) versus the logarithm ln(t) over time in Embodiment 4 of the present invention; Figure 5 The curves showing the thermal conductivity of hexagonal boron nitride (h-BN) ceramic as a function of temperature and pressure are shown in Embodiment 4 of the present invention.

[0020] The annotations in the attached figures are explained as follows: 1. Pyrophyllite pressure transmission medium block; 2. Steel cap; 3. Molybdenum sheet; 4. Graphite sheet; 5. Graphite tube; 6. Boron nitride sheet; 7. Boron nitride tube; 8. Sample body; 9. Type K thermocouple; 10. Heating wire; 11. Insulation tube; 12. Insulation filler; 13. Sample chamber; 14. Insulating tube. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0022] Example 1: See Figures 1-2As shown, this invention provides a device for in-situ measurement of thermal conductivity under high temperature and high pressure, comprising a pyrophyllite pressure transmitting medium block 1 and a sample body 8. The pyrophyllite pressure transmitting medium block 1 is a square tube, made entirely of high-density pyrophyllite material, and is actually machined into a cubic structure with a side length controlled to 40mm, adapting to the cavity size of a conventional commercial six-sided top press. It can stably withstand a high-pressure load of up to 6GPa, while possessing good heat insulation and electrical insulation properties, effectively reducing heat loss inside the cavity and ensuring the uniformity of pressure transmission. The pyrophyllite pressure transmitting medium block 1 has a cylindrical cavity inside, serving as the mounting carrier for various functional components. The cavity size is precisely matched with the outer diameter of the subsequent graphite tube 5 and insulation tube 11, ensuring no gaps or looseness after assembly.

[0023] A heat-insulating tube 11 is embedded and fixed between the inner wall of the cavity of the pyrophyllite pressure-transmitting medium block 1 and the outer wall of the graphite tube 5. The interior of the steel cap 2 is filled with heat-insulating filler 12. Both the heat-insulating tube 11 and the heat-insulating filler 12 are made of dolomite. The heat-insulating tube 11 and the heat-insulating filler 12 constitute a double heat-insulating structure. Both are made of dolomite, which has excellent high-temperature resistance and heat insulation properties. It can maintain structural stability in a temperature range from room temperature to 1273K, effectively reducing heat exchange between the sample cavity 13 and the external environment, and ensuring a uniform and stable temperature field inside the sample body 8. The heat-insulating tube 11 is embedded and fixed between the inner wall of the cavity of the pyrophyllite pressure-transmitting medium block 1 and the outer wall of the graphite tube 5, tightly fitting the inner wall of the pyrophyllite pressure-transmitting medium block 1 and the outer wall of the graphite tube 5 without gaps or offset, thus playing a ring-shaped heat-insulating role. The heat-insulating filler 12 fills the interior of the steel cap 2, completely covering the internal space of the steel cap 2, achieving end heat insulation, preventing heat loss from the top and bottom of the device, and further improving the overall heat insulation effect.

[0024] A graphite tube 5 is coaxially fitted inside the pyrophyllite pressure transmitting medium block 1. Graphite sheets 4 are respectively provided at the upper and lower ends of the graphite tube 5, and the graphite sheets 4 respectively seal the upper and lower ends of the graphite tube 5. The graphite tube 5 and the graphite sheets 4 at the upper and lower positions constitute a graphite heating element. The core is the graphite tube 5, which is made of high-purity graphite material and has excellent conductivity, high temperature resistance and chemical stability. It can stably generate heat under high temperature and high pressure environment, realizing rapid heating and precise temperature control of the sample chamber 13. The graphite tube 5 is coaxially fitted inside the pyrophyllite pressure transmitting medium block 1 and is tightly fitted with the heat insulation tube 11. The graphite sheets 4 are made of the same high-purity graphite material as the graphite tube 5, and their size is precisely matched with the inner and outer diameters of the graphite tube 5. They respectively seal the upper and lower ends of the graphite tube 5 to form a complete heating chamber, while also playing the role of uniformly conducting heat and transmitting pressure.

[0025] A boron nitride tube 7 is fitted inside the graphite tube 5. The internal space of the boron nitride tube 7 is the sample cavity 13, and the sample body 8 is placed inside the sample cavity 13. Boron nitride sheets 6 are respectively provided at the upper and lower ends of the sample body 8, and the boron nitride sheets 6 respectively seal the upper and lower ends of the boron nitride tube 7. The boron nitride tube 7 and the boron nitride sheets 6 constitute the part used to support the sample body 8. Both are made of high-purity boron nitride material. Boron nitride has the characteristics of high temperature resistance, high insulation, and strong chemical inertness, which can effectively prevent reaction with the sample to be tested, and at the same time achieve insulation isolation between the sample body 8 and the external graphite heating element structure. The sample cavity 13 is a hollow cylinder with a strictly controlled outer diameter of 12mm. The sample body 8, with an inner diameter of 10.1 mm and a height of 8 mm, is cylindrical, with a diameter of 10 mm and a height of 8 mm. It precisely matches the dimensions of the boron nitride sample cavity 13, ensuring that the sample fits tightly against the inner wall of the boron nitride tube 7 after being loaded, without any looseness or gaps, thus ensuring uniform pressure transmission. The size of the boron nitride sheet 6 matches the inner diameter of the boron nitride tube 7 and the diameter of the sample body 8, respectively sealing the upper and lower ends of the boron nitride tube 7. The outer end face of the boron nitride sheet 6 is flush with the outer end faces of the graphite tube 5 and the boron nitride tube 7, and the outer periphery of the boron nitride sheet 6 is in contact with the inner periphery of the boron nitride tube 7, which not only fixes the sample and transmits pressure, but also further enhances the insulation effect.

[0026] The inner end face of graphite sheet 4 is flush with and in close contact with the outer end faces of graphite tube 5, boron nitride tube 7, and boron nitride sheet 6. The purpose of this arrangement is to ensure that the high pressure transmitted by the pyrophyllite pressure transmission medium block 1 is uniformly applied to the sample body 8 under test through graphite sheet 4 and boron nitride sheet 6, avoiding local pressure concentration caused by uneven end faces or gaps, thus preventing sample damage or measurement deviation. At the same time, the heat generated by the graphite heating element is efficiently and uniformly conducted to the sample cavity 13 and the sample body 8 under test through the flush and close end faces, avoiding heat loss caused by gaps, ensuring a uniform temperature field inside the sample body 8, and improving the accuracy of temperature measurement and thermal conductivity calculation. Moreover, it can maintain the coaxial alignment of graphite tube 5, boron nitride tube 7, and boron nitride sheet 6, avoiding loose assembly. In addition, in conjunction with the insulating properties of boron nitride, it further isolates the sample body 8 from the graphite heating element composed of graphite tube 5 and graphite sheet 4, preventing electrical interference.

[0027] Molybdenum sheets 3 are attached to the upper and lower ends of graphite sheet 4, and inverted steel caps 2 are pressed onto the outer surface of molybdenum sheets 3. The molybdenum sheets 3 and steel caps 2 constitute a pressure-bearing conductive structure at the end. The molybdenum sheets 3 are made of highly conductive molybdenum metal sheets, which have good conductivity and high temperature resistance, and can efficiently and stably transmit heating current. The molybdenum sheets 3 are attached to the upper and lower ends of graphite sheet 4, and are tightly fitted with graphite sheet 4 without gaps, ensuring that the current is smoothly transmitted from the steel caps 2 to the graphite heating body composed of graphite tube 5 and graphite sheet 4. The steel caps 2 are made of conductive metal material and are inverted cap-shaped structures. They are pressed onto the outer surface of the molybdenum sheets 3 at the upper and lower ends, and are tightly fitted with molybdenum sheets 3. The interior of the steel caps 2 is filled with the above-mentioned dolomite insulation filler 12. The steel caps 2 are in direct contact with the upper and lower heating hammers of the six-sided top press, which not only undertake the functions of pressure transmission and current conduction, but also achieve end insulation through the internal insulation filler 12 to prevent heat loss.

[0028] A heating wire 10 is horizontally and radially inserted through the center of the sample body 8. A K-type thermocouple 9 is also horizontally and radially inserted through the center of the sample body 8. The heating wire 10 is in direct contact with two opposing non-heated hammers of the six-sided press, and the K-type thermocouple 9 is in direct contact with the other two opposing non-heated hammers of the six-sided press. Specifically, the heating wire 10 and the K-type thermocouple 9 constitute the temperature measurement and heating components. Both are horizontally and radially inserted through the center of the sample body 8 to ensure that the heat source and the temperature measurement point are highly aligned, improving measurement accuracy. The heating wire 10 is made of nickel-chromium alloy with a strictly controlled diameter of 0.2 mm, possessing good conductivity, high temperature resistance, and oxidation resistance, serving as a one-dimensional linear heat source for sample heating. The K-type thermocouple 9 also has a diameter of 0.2 mm, featuring high temperature measurement accuracy, fast response speed, and high temperature resistance, used to acquire the temperature response signal during the sample heating process in real time. Both the heating wire 10 and the K-type thermocouple 9 are encased in an insulating tube 14. The heating wire 10 and the K-type thermocouple 9 pass radially through the center of the sample body 8 via the insulating tube 14. The insulating tube 14 is made of alumina material, with an inner diameter of 0.21 mm and an outer diameter of 1.0 mm. It tightly wraps the heating wire 10 and the K-type thermocouple 9 wires without loosening or gaps, ensuring reliable insulation under high temperature and high pressure conditions. This prevents chemical reactions between the heating wire 10 / thermocouple and the sample, while also reducing heat loss and ensuring a no-delay thermal response. The heating wire 10 and the K-type thermocouple 9 are arranged perpendicularly to each other and in close contact under the protection of the alumina insulating tube 14, ensuring that the heat source and the temperature measurement point are highly aligned, minimizing measurement errors and ensuring the authenticity and accuracy of temperature acquisition.

[0029] Example 2: See Figures 1-2 As shown, this invention provides a method for in-situ measurement of thermal conductivity under high temperature and high pressure, comprising the following steps: 1) Sample Assembly: Insert the sample body 8 into the sample cavity 13, embed the heating wire 10 and the K-type thermocouple 9 into the sample body 8, and extend them from both sides respectively; place the assembled block between the top hammers of the six-sided press, with the heating wire 10 in contact with two opposite unheated hammers and the K-type thermocouple 9 in contact with the other two opposite unheated hammers; insert the cylindrical sample body 8 into the sample cavity 13, and insert the heating wire 10 and the K-type thermocouple 9, which are fitted with insulating tubes 14, radially through the center of the sample body 8 and extend them horizontally from both sides of the assembled block respectively; place the assembled block between the six top hammers of the six-sided press, with the two ends of the heating wire 10 in direct contact with two opposite unheated hammers and the two ends of the K-type thermocouple 9 in direct contact with the other two opposite unheated hammers; utilize the conductivity of the tungsten carbide top hammers, connect the constant current source and the digital multimeter to the corresponding top hammers respectively to complete the construction of the power supply and temperature measurement circuit; 2) Pressurization and heating: Start the six-sided pressurizer to pressurize to the target pressure, heat to the target temperature and stabilize; start the six-sided pressurizer to pressurize to the target pressure (maximum 6GPa); use the graphite heating element composed of graphite tube 5 and graphite sheet 4 to perform step heating of the sample body 8, and hold it at the target temperature for more than 5 minutes after reaching the target temperature to ensure that the internal temperature field of the sample body 8 is uniform and stable. 3) Heating and temperature acquisition of heating wire 10: After the temperature of the sample body 8 stabilizes, the constant current source is started to apply a constant current I to the heating wire 10, and the voltage U across the heating wire 10 is recorded in real time using a digital multimeter to calculate the average heating power; at the same time, the temperature response T(t) of the K-type thermocouple 9 is recorded in real time with time t using the temperature reading function of the digital multimeter. 4) Thermal conductivity calculation: Based on the principle of one-dimensional hot wire method, the time interval [t1, t2] is selected. Within this interval, the temperature response T(t) is linearly related to the logarithm of time ln(t). The time t is converted to the natural logarithm ln(t), and the T(t)–ln(t) relationship curve is plotted. The slope k is obtained through linear fitting. The thermal conductivity λ of the sample body 8 under this temperature and pressure is calculated according to the formula.

[0030] The average heating power mentioned above is calculated using the formula P=I× Calculate, where I is a constant current, The average voltage across the heating wire 10 is given; the thermal conductivity is calculated using the formula λ=P / (4πL)×1 / k, where P is the average heating power, L is the effective heating length of the heating wire 10 (i.e., the diameter of the sample), and k is the linear fitting slope; data acquisition begins after the temperature stabilizes, with a total acquisition time of 60s; the linear interval is determined based on T(t). Selection of linear distribution characteristics of ln(t) curve.

[0031] Optional features also include variable temperature and pressure testing: that is, changing the pressure and heating power, repeating steps 2-4 to obtain the variation of thermal conductivity with temperature and pressure; the measurement pressure range is ≤6GPa, and the temperature range is room temperature to 1273K; the deviation of repeated measurements of the same sample at the same temperature and pressure is ≤1.0%; the sample body 8 is a solid material, and it is doubly insulated from the sample cavity 13 by an alumina insulating tube 14, so as to avoid problems such as short circuit, leakage and electrical interference of the heating circuit of the heating wire and the signal acquisition circuit of the K-type thermocouple under high temperature and high pressure.

[0032] Example 3: See Figures 1-2 As shown, this embodiment illustrates a standardized assembly process before testing, applicable to all solid sample testing: 1. Take a 40mm cube-shaped pyrophyllite pressure transmission medium block 1 and embed an insulation tube 11 into the inner wall of its central cavity to improve the insulation effect and temperature uniformity.

[0033] 2. Graphite tube 5 and boron nitride tube 7 are sequentially and coaxially installed in the inner cavity of pyrophyllite pressure transmission medium block 1 to ensure concentricity and form sample cavity 13 for heating and sample bearing.

[0034] 3. Place the standard cylindrical sample body 8 with a diameter of 10mm and a height of 8mm into the boron nitride tube 7, and cover it with boron nitride sheets 6 on the top and bottom to ensure that the height of the sample body 8, boron nitride sheets 6, graphite tube 5, and boron nitride tube 7 are consistent to ensure uniform pressure transmission.

[0035] 4. Take a heating wire 10 with a diameter of 0.2 mm and a K-type thermocouple 9, and insert them into an insulating tube 14 with an inner diameter of 0.21 mm and an outer diameter of 1.0 mm, respectively. They should be inserted horizontally along the radial direction of the center of the sample body 8. At the same time, the heating wire 10 and the K-type thermocouple 9 should be perpendicular to each other and in close contact. They should be led out from the corresponding side of the pyrophyllite pressure transmission medium block 1 to ensure that the heat source and the temperature measuring point are located at the geometric center of the sample.

[0036] 5. Place graphite sheet 4, molybdenum sheet 3 and steel cap 2 with embedded thermal insulation filler 12 in sequence at the upper and lower ends of the sample body 8. The steel cap 2 should be set upside down to close the upper and lower ends of the pyrophyllite pressure transmission medium block 1, and complete the overall assembly to form an assembly block.

[0037] 6. Place the assembly block into the six-sided press, so that the heating wire 10 contacts two opposite unheated top hammers of the six-sided press, and the K-type thermocouple 9 contacts the other two opposite unheated top hammers of the six-sided press. Let the top hammers corresponding to the heating wire 10 and the K-type thermocouple 9 be used as conductive electrodes to connect the constant current source and the digital multimeter to complete the test preparation.

[0038] Example 4: See Figures 3-5As shown, this embodiment demonstrates a high-temperature, high-pressure in-situ thermal conductivity test on an insulator sample: 1. The insulator sample is a hexagonal boron nitride (h-BN) ceramic. The sample morphology is a dense cylinder with a diameter of 10 mm and a height of 8 mm. The sample characteristics are high insulation, high temperature resistance, strong chemical inertness, and thermal conductivity sensitive to temperature and pressure changes. It is an ideal standard insulation test sample for high temperature and high pressure environments.

[0039] 2. Detailed testing process: (1) Sample assembly: Following the device assembly process of Example 1, a channel is pre-formed in the hexagonal boron nitride (h-BN) ceramic sample to allow the heating wire 10 and the corresponding alumina insulating tube 14 of the K-type thermocouple 9 to pass through the center perpendicularly. Then, the hexagonal boron nitride (h-BN) ceramic sample is placed into the sample cavity 13 formed by the inner circumference of the boron nitride tube 7, so that the sample is in close contact with the upper and lower boron nitride sheets 6. The 0.2 mm diameter nickel-chromium alloy heating wire 10 and the K-type thermocouple 9 are respectively inserted into the alumina insulating tube 14 with an inner diameter of 0.21 mm and an outer diameter of 1.0 mm, and passed horizontally along the radial center of the sample body 8, so that the two are in a perpendicular and close contact state. They are led out from the corresponding two sides of the assembly block. The integrity of the alumina insulating tube 14 should be checked to ensure that the heating wire 10, the K-type thermocouple 9 and the hexagonal boron nitride (h-BN) ceramic sample are completely insulated and isolated to avoid short circuits or signal interference under high pressure and high temperature.

[0040] (2) High pressure loading: Place the assembly block in the center of the six top hammers of the six-sided top press to ensure that the assembly block is centered. Start the press and slowly increase the pressure at a rate of 0.5 GPa / min, and increase the pressure to the three target pressure points of 1 GPa and 3 GPa respectively, and hold the pressure until the pressure stabilizes.

[0041] (3) Heating and temperature stabilization: The sample chamber 13 is heated in a stepwise manner by a graphite heating element consisting of graphite tube 5 and graphite sheet 4, with the heating rate controlled at 20K / min. When a set temperature point is reached, the heating is stopped and held for 5min to ensure that the internal temperature field of the sample is completely uniform and without temperature gradient, so as to avoid the influence of temperature fluctuation on the thermal conductivity test results.

[0042] (4) Heating and Data Acquisition: After the temperature stabilizes, turn on the high-precision constant current source and apply a constant DC current to the heating wire 10. Use a digital multimeter to acquire the voltage signal across the heating wire 10 in real time, and simultaneously acquire the temperature response signal output by the K-type thermocouple 9. Continuously record the temperature T(t) versus time t curve over 60 seconds, as shown below. Figure 3 As shown.

[0043] (5) Data processing and thermal conductivity calculation: Convert the collected time t into the natural logarithm ln(t) and plot T(t). ln(t) relationship curve, such as Figure 4 As shown. Linear fitting was performed on the interval with the optimal curve linearity to obtain the slope k. The thermal conductivity λ of the sample under the corresponding temperature and pressure conditions was calculated using the one-dimensional hot-wire method formula. Each set of conditions was tested five times, and the average value and measurement deviation were calculated.

[0044] 3. Key Test Parameters and Results Table:

[0045] 4. Test conclusions: such as Figure 5 As shown, the thermal conductivity of hexagonal boron nitride (h-BN) ceramics decreases with increasing temperature and increases slightly with increasing pressure, which is consistent with the known thermal properties of materials (where the black data "1 atm." represents the variable-temperature thermal conductivity measured by laser scintillation at normal pressure, serving as a control group for thermal conductivity data obtained under high temperature and high pressure using the method of this device).

[0046] Regarding stability testing, all samples were repeatedly measured five times under the same temperature and pressure conditions, and the thermal conductivity deviation did not exceed 1.0%, indicating that the present invention has excellent data repeatability and measurement accuracy. In terms of structural reliability, the double insulation design formed by the alumina insulating tube 14 and the boron nitride sample chamber 13 effectively avoids problems such as short circuits, leakage, and electrical interference in the heating circuit of the heating wire and the signal acquisition circuit of the K-type thermocouple under high temperature and pressure. The entire testing process exhibits stable heating, smooth temperature response signals, and high curve linearity.

[0047] In summary, this invention realizes integrated in-situ measurement of thermal conductivity of various types of solid materials under high temperature and high pressure environments. It has outstanding advantages such as wide applicability, wide temperature and pressure range, high measurement accuracy, good repeatability, simple structure, and convenient operation. It can meet the needs of geophysics, superhard material synthesis, high temperature structural material research and development and other fields for thermal property testing under extreme conditions, and has high scientific research value and engineering application prospects.

[0048] Meanwhile, the technical effect of this invention is not a simple superposition of conventional components, but rather a deep coupling, mutual support, and synergistic effect of four core designs: a double insulation structure, a vertical cross-center temperature measurement structure, a top hammer direct-connection electrode structure, and a double insulation structure. This forms a closed-loop measurement system of "reliable insulation—accurate temperature measurement—stable signal—uniform temperature field," and unexpected synergistic effects are produced between the various structures, as detailed below: 1. Synergy between the double insulation structure and the heating / temperature sensing components The inner alumina insulating tube 14 encloses the heating wire 10 and the K-type thermocouple 9, directly blocking direct contact between the heating / temperature measuring element and the sample. This avoids chemical reactions between the heating / temperature measuring element and the sample, and prevents short circuits and leakage at the source. The outer boron nitride tube 7 and boron nitride sheet 6 form the sample cavity 13, completely electrically isolating the sample from the graphite heating element and eliminating crosstalk of the heating current to the temperature measurement signal. The two insulating layers reinforce each other under high temperature and high pressure, with a gapless fit, ensuring stable insulation resistance without hindering heat transfer and pressure conduction. Together, they enable interference-free and short-circuit-free measurement of solid materials under 6GPa / 1273K conditions.

[0049] 2. Synergy between vertical cross-center temperature measurement and double insulation structure: The heating wire 10 and the K-type thermocouple 9 intersect perpendicularly through the geometric center of the sample body 8, ensuring complete spatial overlap between the heat source and the temperature measurement point, thus eliminating heat conduction delay and temperature measurement deviation in principle. Combined with the double insulation structure of the dolomite insulation tube 11 and insulation filler 12, heat dissipation from the edge of the sample cavity 13 is blocked, ensuring the uniformity of the internal temperature field of the sample is ≤±5K. These two elements work together to ensure a true, synchronous, and linear temperature response from heating, giving the T(t)–ln(t) curve excellent linearity, significantly improving fitting accuracy and the reliability of thermal conductivity calculation, and solving the problems of inaccurate and signal distortion in traditional high-pressure temperature measurement.

[0050] 3. Synergy between the top hammer direct-connected electrode and the insulation / temperature sensing structure: By utilizing the inherent conductivity of the six-sided top hammer as the lead electrode, the complex structures of high-voltage leads, seals, and adapters are eliminated, significantly simplifying device assembly. This structure, in conjunction with the double insulation structure, prevents short circuits between the top hammer electrode and the sample chamber 13 or the sample body 8. Furthermore, its synergy with the centrally perpendicular cross-temperature measurement minimizes the transmission path of the temperature measurement / heating signal, reduces interference, and minimizes signal noise. The coupling of these three elements achieves zero signal drift under high voltage, highly convenient assembly, and highly stable operation, solving the problems of complex structures, high failure rates, and easy signal attenuation in traditional high-voltage devices.

[0051] 4. The overall synergy between the graphite heating element (composed of graphite tube 5 + graphite sheet 4) and the insulation / heat preservation / temperature measurement structure: A uniform surface heating assembly consisting of 5 graphite tubes and 4 graphite sheets, combined with double insulation, enables rapid and uniform heating of samples. Double insulation completely decouples the heating circuit from the temperature measurement circuit, preventing heating current from interfering with temperature acquisition. Central vertical temperature measurement accurately captures the true thermal response of the sample. These four components work together to achieve simultaneous compatibility of high-temperature loading, high-pressure transfer, stable heating, and accurate temperature measurement. The one-dimensional hot wire method measurement conditions are completely reproduced in the large cavity of the six-sided top press, making this solution directly adaptable to commercial equipment and possessing engineering and promotion value.

[0052] In summary, this invention overcomes long-standing technical biases in the field and solves many long-standing technical problems through the systematic synergistic coupling of four parts, realizing in-situ, rapid, and high-precision measurement of the thermal conductivity of solid materials under high temperature and high pressure. The aforementioned synergistic gains cannot be achieved by single conventional technical means, and it has outstanding substantive features and significant progress.

[0053] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A device for in-situ measurement of thermal conductivity under high temperature and high pressure, characterized in that: The sample includes a pyrophyllite pressure-transmitting medium block (1) and a sample body (8). The pyrophyllite pressure-transmitting medium block (1) is a square tube. A graphite tube (5) is coaxially fitted inside the cavity of the pyrophyllite pressure-transmitting medium block (1). A boron nitride tube (7) is fitted inside the graphite tube (5). The internal space of the boron nitride tube (7) is a sample cavity (13). The sample body (8) is installed in the sample cavity (13). A boron nitride sheet (6) is provided at the upper and lower ends of the sample body (8). The boron nitride sheet (6) seals the upper and lower ends of the boron nitride tube (7). A graphite sheet (4) is provided at the upper and lower ends of the graphite tube (5). The graphite sheet (4) seals the upper and lower ends of the graphite tube (5). The graphite sheet (4) is attached to the upper and lower ends of a molybdenum sheet (3), and the outer surface of the molybdenum sheet (3) is pressed with an inverted steel cap (2), while the inside of the steel cap (2) is filled with thermal insulation filler (12). A heating wire (10) is horizontally inserted through the center of the sample body (8) in a radial direction, and a K-type thermocouple (9) is also horizontally inserted through the center of the sample body (8) in a radial direction.

2. The device for in-situ measurement of thermal conductivity under high temperature and high pressure according to claim 1, characterized in that: A heat-insulating pipe (11) is embedded and fixed between the inner wall of the cavity of the pyrophyllite pressure transmission medium block (1) and the outside of the graphite tube (5), and both the heat-insulating pipe (11) and the heat-insulating filler (12) are made of dolomite.

3. The device for in-situ measurement of thermal conductivity under high temperature and high pressure according to claim 1, characterized in that: The heating wire (10) is in direct contact with two opposite unheated hammers of the six-sided press, and the K-type thermocouple (9) is in direct contact with the other two opposite unheated hammers of the six-sided press.

4. The device for in-situ measurement of thermal conductivity under high temperature and high pressure according to claim 1, characterized in that: The heating wire (10) is made of nickel-chromium alloy and has a diameter of 0.2 mm; the K-type thermocouple (9) has a diameter of 0.2 mm. Both the heating wire (10) and the K-type thermocouple (9) are covered with an insulating tube (14), and both the heating wire (10) and the K-type thermocouple (9) pass radially through the center of the sample body (8) through the insulating tube (14).

5. The device for in-situ measurement of thermal conductivity under high temperature and high pressure according to claim 4, characterized in that: The insulating tube (14) is an alumina insulating tube (14) with an inner diameter of 0.21 mm and an outer diameter of 1.0 mm. The heating wire (10) and the K-type thermocouple (9) are arranged perpendicular to each other and are in close contact under the protection of the insulating tube (14).

6. The device for in-situ measurement of thermal conductivity under high temperature and high pressure according to claim 1, characterized in that: The outer end face of the boron nitride sheet (6) is flush with the outer end faces of the graphite tube (5) and the boron nitride tube (7), and the inner end face of the graphite sheet (4) is flush with and in contact with the outer end faces of the graphite tube (5), the boron nitride tube (7) and the boron nitride sheet (6).

7. The device for in-situ measurement of thermal conductivity under high temperature and high pressure according to claim 1, characterized in that: The sample cavity (13) is a hollow cylinder with an outer diameter of 12 mm, an inner diameter of 10.1 mm, and a height of 8 mm; the sample body (8) is a cylinder with a diameter of 10 mm and a height of 8 mm; and the pyrophyllite pressure transmission medium block (1) is a cube with a side length of 40 mm.

8. The method for in-situ measurement of thermal conductivity under high temperature and high pressure according to any one of claims 1-7, characterized in that: Includes the following steps: 1) Sample assembly: The sample body (8) is inserted into the sample cavity (13), the heating wire (10) and the K-type thermocouple (9) are embedded in the sample body (8) and the two ends are led out from the two sides respectively; the assembled block is placed between the top hammers of the six-sided top press, the heating wire (10) is in contact with two opposite non-heated hammers, and the K-type thermocouple (9) is in contact with the other two opposite non-heated hammers; the cylindrical sample body (8) is inserted into the sample cavity (13), and the insulating tube ( The heating wire (10) and the K-type thermocouple (9) of 14) penetrate radially along the center of the sample body (8) and are horizontally led out from both sides of the assembly block respectively; the assembly block is placed between the six top hammers of the six-sided top press, the two ends of the heating wire (10) are in direct contact with two opposite unheated top hammers, and the two ends of the K-type thermocouple (9) are in direct contact with the other two opposite unheated top hammers; using the conductivity of the tungsten carbide top hammers, the constant current source and the digital multimeter are respectively connected to the corresponding top hammers to complete the construction of the power supply and temperature measurement circuit; 2) Pressurization and heating: Start the six-sided pressurizer to pressurize to the target pressure, heat to the target temperature and stabilize; start the six-sided pressurizer to pressurize to the target pressure (maximum 6GPa); use the graphite heating element composed of the graphite tube (5) and the graphite sheet (4) to perform step heating on the sample body (8), and hold it at the target temperature for more than 5 minutes after reaching the target temperature to ensure that the internal temperature field of the sample body (8) is uniform and stable; 3) Heating and temperature acquisition of heating wire (10): After the temperature of the sample body (8) stabilizes, the constant current source is started to apply a constant current I to the heating wire (10), and the voltage U across the heating wire (10) is recorded in real time using a digital multimeter to calculate the average heating power; at the same time, the temperature response T(t) of the K-type thermocouple (9) is recorded in real time with time t using the temperature reading function of the digital multimeter. 4) Thermal conductivity calculation: Based on the principle of one-dimensional hot wire method, select the time interval [t1, t2]. In this interval, the temperature response T(t) is linearly related to the logarithm of time ln(t). Convert time t to the natural logarithm ln(t), plot the T(t)–ln(t) relationship curve, obtain the slope k through linear fitting, and calculate the thermal conductivity λ of the sample body (8) at this temperature and pressure according to the formula.

9. The method for in-situ measurement of thermal conductivity under high temperature and high pressure according to claim 8, characterized in that: Average heating power is calculated using the formula P = I × Calculate, where I is a constant current, The average voltage across the heating wire (10) is given; the thermal conductivity is calculated using the formula λ=P / (4πL)×1 / k, where P is the average heating power, L is the effective heating length of the heating wire (10), i.e., the diameter of the sample to be tested, and k is the slope of the linear fitting; data acquisition begins after the temperature stabilizes, with a total acquisition time of 60s; the linear interval is determined based on T(t). Selection of linear distribution characteristics of ln(t) curve.

10. The method for in-situ measurement of thermal conductivity under high temperature and high pressure according to claim 8, characterized in that: It also includes temperature and pressure variation testing: that is, changing the pressure and heating power, repeating steps 2-4, to obtain the change law of thermal conductivity with temperature and pressure; the measurement pressure range is ≤6GPa, and the temperature range is room temperature to 1273K; the deviation of repeated measurements of the same sample at the same temperature and pressure is ≤1.0%; the sample body (8) is a solid material.

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