A temperature measuring material and method based on a phase change process

Abstract

The application discloses a temperature measuring material and method based on a phase change process and belongs to the technical field of temperature measurement. The preparation method of the temperature measuring material is as follows: (1) weighing raw materials, ball milling, drying and pre-sintering; (2) rolling into a cylinder after being tamped in sections, pressing and sintering; and (3) preparing a target crystal by adopting an optical floating zone method. The temperature measuring method is as follows: (1) processing and installation; (2) emitting an ultrasonic pulse signal; (3) establishing a sound velocity-temperature calibration relationship; and (4) obtaining real-time temperature values of a high-temperature environment and recording dynamic changes of the temperature with time in real time. The detection element is preferably a high-melting-point oxide material, has excellent oxidation resistance and heat shock resistance, has a simple and reliable structure, can replace traditional noble metal thermocouples, effectively reduces application cost, can be stably used in a high-temperature, high-oxidation and high-pressure harsh environment for a long time, is suitable for extreme working conditions such as an aero-engine and a rocket propulsion system and has a good engineering application prospect.

Description

Technical Field

[0001] This invention relates to the field of temperature measurement technology, and more specifically to a temperature measuring material and method based on a phase change process. Background Technology

[0002] With the rapid development of science and technology, the application demands in the aerospace field are constantly upgrading, and the need for temperature monitoring in ultra-high temperature environments (temperatures reaching 2000℃ and above), such as those for aero engines, combustion chambers, and rocket launch devices, is becoming increasingly prominent. The complex and harsh conditions coupled with high temperature, high oxidation, and high flow velocity pose even more stringent challenges to existing temperature testing technologies. Ultrasonic sensing technology, a non-destructive testing technology that relies on ultrasonic waves for detection, has already achieved mature applications in many fields such as medical diagnostics, civil engineering, and industrial manufacturing. Leveraging the high speed of sound of ultrasound (approximately 1000 m / s), ultrasonic temperature measurement can achieve rapid signal response at the microsecond to millisecond level, effectively meeting the application requirements for real-time temperature monitoring in various high-temperature scenarios.

[0003] High-sensitivity ultrasonic temperature measurement has always been a research hotspot and a core challenge in this field. The key to its practical application lies in the material selection and structural optimization design of the sensing unit, requiring a balance between high stability and high sensitivity. However, high stability and high sensitivity are often difficult to achieve simultaneously, and suitable sensing material systems and device designs remain the core bottleneck restricting the further development of this technology. According to solid-state physics theory, the basic principle of ultrasonic temperature measurement is that the intrinsic physical properties of high-temperature detection materials change with temperature, and this change further alters the propagation speed of ultrasonic waves. Based on this, a quantitative correlation between changes in sound speed and temperature can be established. Therefore, to develop ultrasonic temperature measurement technology that combines high stability and high sensitivity, the physical properties of the functional materials must be highly sensitive to temperature changes, while maintaining stable performance across the entire temperature measurement range to meet the adaptation requirements of complex high-temperature environments.

[0004] According to solid-state physics theory, the macroscopic physical properties of materials are closely related to their intrinsic crystal structure. When a crystal undergoes a structural phase transition, it triggers a dramatic change in physical parameters, significantly altering the propagation speed of ultrasound waves and effectively improving the sensitivity of ultrasonic temperature measurement. Therefore, addressing the urgent needs in the current field of ultrasonic temperature measurement, materials exhibiting structural phase transitions within the target temperature range are selected as sensing elements. This allows for precise control of reversible phase transitions between different crystal phases. This approach not only enables high-sensitivity ultrasonic detection through structural phase transitions but also maintains the structural integrity of the sensing element throughout the entire detection process through controllable and reversible phase transitions, preventing cracking or breakage of the device. Ultimately, this achieves both high sensitivity and high stability in high-temperature ultrasonic temperature measurement, overcoming the core bottleneck restricting the development of traditional ultrasonic temperature measurement technology.

[0005] However, although there has been considerable research and practical application in the field of high-temperature ultrasonic temperature measurement, the detection elements used in existing schemes are mostly non-phase change materials such as alumina, which generally suffer from low detection sensitivity.

[0006] Therefore, there is an urgent need to develop suitable phase change materials and device solutions based on the design concept of structural phase change, so as to promote the development of ultrasonic temperature measurement materials and technologies with both high sensitivity and high stability in high-temperature environments. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a temperature measuring material and a temperature measuring method based on a phase change process, which addresses the application requirements of high-sensitivity temperature detection in different temperature ranges by designing a detection element around the phase change material.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for preparing a thermometric material based on a phase transition process specifically includes the following steps: (1) Weigh the nanoscale raw materials according to the chemical composition of the thermometric material, then add a dispersant and ball mill, dry, and pre-calcine to obtain polycrystalline material; (2) According to the phase distribution of the thermometric material, the polycrystalline material is segmented, compacted, rolled into a cylinder, pressed, and sintered (if it is sintered directly to the corresponding temperature, a ceramic-based thermometric material can be obtained) to obtain a polycrystalline rod; (3) In a closed quartz tube with continuous oxygen supply, the polycrystalline rod and the seed crystal are fixed at the upper and lower ends of the equipment respectively. The melting zone is maintained by bidirectional rotation. After the polycrystalline rod and the seed crystal are melted by the xenon lamp heating, the docking is completed. After docking, the seed crystal and the polycrystalline rod are moved downwards simultaneously to start the crystal growth process. By adjusting the xenon lamp heating power and the downward movement rate of the polycrystalline rod, the complete growth process of necking → shouldering → equal diameter → tailing is completed in sequence, and the target crystal is finally obtained, which is the temperature measuring material based on the phase change process.

[0010] Furthermore, in step (1) above, the temperature measuring material undergoes a structural phase change within the measured temperature range, achieving precise locking of different crystal phases of the phase change material. Preferably, it is an oxide material (ceramic or crystalline), more preferably an oxide phase change material with a phase change temperature higher than 1000℃. Within the target detection temperature range of 1000-1500℃, the preferred oxide material is a phase change material such as lithium niobate, barium titanate, or strontium zirconate. Within the target detection temperature range higher than 1500℃, the preferred oxide material is a phase change material such as strontium hafnium oxide, rare earth-doped zirconium oxide, lanthanum oxide, or rare earth-doped hafnium oxide. The dispersant is anhydrous ethanol. The ball milling time is 5-12 hours. The pre-calcination temperature is 1000-1100℃, and the time is 5 hours.

[0011] Furthermore, in step (2) above, the pressing method is isostatic water pressure, the pressure is 50-80MPa, and the time is 15min; the sintering temperature is 1400-1600℃, and the time is 5h; the length of the polycrystalline rod is 40-100mm, and the diameter is 2-5mm.

[0012] Furthermore, in step (3) above, the oxygen flow rate is 100-200 mL / min, preferably 100-150 mL / min; during crystal growth, the rotation speeds of the upper and lower rotating rods are 5-15 r / min, and the rotation directions are opposite; the crystal growth rate is 5-80 mm / h; the diameter of the crystal in the constant diameter section is 1-4 mm, preferably 2-3 mm; the crystal growth length is 50-190 mm, preferably 80-150 mm; and it also includes: after the crystal growth is completed, the heating power is gradually reduced to 0 within 5 h, and after continuing to blow air to cool for 0.5 h, the entire crystal growth preparation process is completed.

[0013] The present invention also claims protection for a temperature measuring material prepared by the above-described preparation method.

[0014] The present invention also claims protection for the application of a temperature measuring material prepared by the above preparation method in temperature measurement.

[0015] A temperature measurement method specifically includes the following steps: (1) First, process the temperature measuring material prepared by the above preparation method, and then install it inside or at the boundary of the high temperature area to be measured as a detection element; (2) The ultrasonic excitation and receiving unit transmits ultrasonic pulse signals to the detection element; (3) The ultrasonic excitation and receiving unit receives the ultrasonic echo signal after it has been propagated or reflected by the detection element, and obtains the ultrasonic signal at the temperature measurement length of the detection element. L Propagation time within t Based on the variation of propagation time with temperature, a sound speed-temperature calibration relationship is established in advance, i.e. v ( T ) = L / t ( T ); (4) The real-time measured ultrasonic data is output to the data acquisition and processing system through the signal transmission module, based on the measured propagation time. t The corresponding sound velocity is calculated, and then combined with the pre-established sound velocity-temperature calibration relationship, the real-time temperature value of the high-temperature environment is obtained; finally, the temperature data is displayed in real time on the temperature display unit, and the dynamic changes of temperature over time are recorded in real time.

[0016] Furthermore, in step (1) above, the temperature measuring material is processed into a rod-shaped structure with a diameter of 0.1-10 mm and a length greater than its diameter; the temperature measuring length of the temperature measuring material in the high-temperature region to be measured... L The transmitted and reflected ultrasonic waves must be distinguishable, preferably 1~70 mm, more preferably 5~40 mm; the temperature measuring length of the temperature measuring material in the high-temperature region to be measured. L It contains multiple detection zones suitable for different temperature ranges, supporting ultrasonic temperature detection over a wider temperature range.

[0017] Furthermore, in step (2) above, the ultrasonic excitation and receiving unit adopts an ultrasonic probe that integrates ultrasonic excitation and reception (the probe aperture size is as close as possible to the diameter of the detection element), and the excitation voltage is 100-600V; the transmission mode of the ultrasonic probe includes transverse wave mode and longitudinal wave mode, preferably transverse wave transmission mode; air isolation treatment is required between the ultrasonic probe and the detection element, preferably using high-temperature ultrasonic coupling agent to achieve air isolation coupling; the transmission frequency of the ultrasonic pulse signal is 0.5-10 MHz, preferably 1-5 MHz.

[0018] Furthermore, in step (3) above, the curve fitting of the sound speed-temperature calibration relationship adopts a polynomial fitting method, and the fitting order is not less than the second order.

[0019] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention uses phase change materials as detection elements, which can not only achieve high-sensitivity ultrasonic detection by means of structural phase change, but also maintain the structural integrity of the detection element throughout the detection process through controllable and reversible phase change, thus achieving both high sensitivity and high stability, and promoting the development of high-performance ultrasonic temperature measurement technology for extreme temperature measurement.

[0020] 2. The temperature measurement method of the present invention has a simple overall structure and high reliability. It can select high-temperature oxide phase change materials according to the detection temperature range, and can work stably in a high-temperature oxidation environment for a long time. It can solve the problem of real-time temperature monitoring in harsh environments with high temperature and high oxidation, and is suitable for the application needs of extreme working conditions such as aero-engines and rocket propulsion systems. 3. In terms of commercial applications, this invention uses an ultrasonic detection element based on material phase change to replace the traditional high-cost precious metal thermocouple, which can effectively reduce application costs. Moreover, the detection element can be modularly replaced, resulting in low maintenance costs and good engineering application prospects.

[0021] In summary, this invention addresses the shortcomings of existing high-temperature detection elements, such as insufficient melting point, poor oxidation resistance, and high cost, which make it difficult to meet the long-term temperature measurement requirements under extreme conditions. It proposes using a phase change material as a highly sensitive ultrasonic detection element. By transmitting and receiving ultrasonic echoes to obtain the signal propagation time, the real-time temperature is obtained based on a pre-calibrated sound velocity-temperature relationship. This invention clarifies the specifications and fabrication method of the detection element, the ultrasonic operating mode, and the data processing method. The detection element is preferably made of a high-melting-point oxide material, possessing excellent oxidation and thermal shock resistance. Its simple and reliable structure can replace traditional precious metal thermocouples, effectively reducing application costs. It can operate stably for extended periods in harsh environments of high temperature, high oxidation, and high pressure, making it suitable for extreme conditions such as aero-engines and rocket propulsion systems, with excellent engineering application prospects. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the temperature measuring device in Example 1; Figure 2 This is a photograph of the yttrium oxide-doped zirconium oxide (Y:ZrO2) crystal material from Example 1. Figure 3 This is a comparative example of variable-temperature ultrasonic velocity data. Figure 4 This is a graph showing the velocity data of the variable-temperature ultrasonic waves in Example 1. Figure 5 This is a graph showing room temperature ultrasound data from Example 1; Figure 6 This is a graph showing room temperature ultrasonic data from Example 2; Figure 7 This is a graph showing room temperature ultrasound data from Example 3; Figure 8 This is a graph showing room temperature ultrasound data from Example 4; Figure 9 This is a schematic diagram of the detection element in the temperature measurement method of Example 5; Figure 10 This is a schematic diagram of the detection element in the temperature measurement method of Example 6. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1 Temperature measurement method, using Figure 1 The temperature measuring device shown includes the following steps: (1) The two ends of yttrium-doped zirconium oxide (Y:ZrO2) crystal material (yttrium mass fraction of 5 wt.%) are cut and rounded and polished to obtain a detection element with a diameter of 0.7 mm and a length of 100 mm. Then, it is installed inside or at the boundary of the high-temperature region to be measured. The detection element is located at the temperature measurement length of the high-temperature region to be measured. L It is 32 mm; The preparation method of yttrium oxide-doped zirconium oxide crystal material is as follows: 1) Calculate and weigh yttrium oxide (Y2O3) and zirconium oxide (ZrO2) with a purity of 99.99% according to the above chemical molar ratio, then ball mill them for 10 h with anhydrous ethanol as a dispersant, dry them in an oven, take them out and put them in a corundum crucible for pre-calcination at 1100℃ for 5 h to obtain polycrystalline material; 2) After the polycrystalline material is loaded into a balloon and compacted in sections, it is rolled into a cylinder. After vacuuming, it is pressed under isostatic water pressure of 70MPa for 15 minutes. Then it is placed in a sintering furnace and sintered at 1450℃ for 5 hours to obtain a polycrystalline rod with a length of 80mm and a diameter of 4mm. 3) In a sealed quartz tube continuously supplied with oxygen at 150 mL / min, a seed crystal is fixed at the lower end of a growth furnace in the optical flotation zone by a rotating rod, while a polycrystalline rod is fixed at the upper end directly above it by a rotating rod. The xenon lamp is turned on, and the temperature is increased at a rate of 30% / h until the upper end of the seed crystal and the lower end of the polycrystalline rod melt. The rod is moved to bring them into contact, and the seed crystal and polycrystalline rod are moved downwards to begin crystal growth. Crystals continuously precipitate from the solid-liquid interface at the melt contact point at the upper end of the seed crystal, while the downward-moving polycrystalline rod continuously melts to replenish the raw material content in the molten zone. By adjusting the heating power of the xenon lamp and the downward movement rate of the polycrystalline rod, the complete growth process of necking, shoulder formation, equal diameter, and tailing is completed sequentially. During crystal growth, the rotation speeds of both the upper and lower rotating rods are 10 r / min, and they rotate in opposite directions. The crystal growth rate is 20 mm / h; the diameter of the equal diameter section of the crystal is 2.5 mm; and the total length of the crystal is 100 mm. mm; after the crystal growth is complete, the power is reduced to 0 within 5 hours, and after blowing air for 0.5 hours, the power is turned off to obtain yttrium oxide-doped zirconium oxide crystal material; (2) The ultrasonic excitation and receiving unit transmits ultrasonic pulse signals to the detection element; wherein, the ultrasonic excitation and receiving unit is a CTS-9006 plus ultrasonic flaw detector, which uses an ultrasonic probe with integrated ultrasonic excitation and reception in the MHz range, the transmission mode is set to transverse wave mode, the excitation voltage is 400V, and the working frequency is 2.5 MHz; the air gap between the ultrasonic probe and the detection element is eliminated, and the acoustic coupling is achieved by using an ultrasonic coupling agent; (3) A calibration test platform is built in conjunction with a temperature-changing device. The ultrasonic excitation and receiving unit receives ultrasonic echo signals propagated or reflected by the detection element at different temperatures, and the ultrasonic signal is obtained at the temperature measurement length of the detection element.L Propagation time within t Based on the variation of propagation time with temperature, a sound speed-temperature calibration relationship is established in advance, i.e. v ( T ) = L / t ( T The calibration curve was obtained by fitting a second-order polynomial. (4) Real-time feedback of the measured temperature based on the above calibration relationship: The ultrasonic data obtained in real time is output to the data acquisition and processing system through the signal transmission module, based on the measured propagation time. t The corresponding sound velocity is calculated, and then combined with the pre-established sound velocity-temperature calibration relationship, the real-time temperature value of the high-temperature environment is obtained; finally, the temperature data is displayed in real time on the temperature display unit, and the dynamic changes of temperature over time are recorded in real time.

[0025] Example 2 The temperature measurement method differs from that in Example 1 only in that a Y:ZrO2 crystal material with a diameter of 0.9 mm and a length of 20 cm is selected as the detection element, and the temperature measurement length... L It is 12 mm.

[0026] Example 3 The temperature measurement method differs from that in Example 1 only in that a transverse wave ultrasonic probe with a working frequency of 5 MHz is selected.

[0027] Example 4 The temperature measurement method differs from that in Example 1 only in that a Y:ZrO2 crystal material with a diameter of 2 mm is selected as the detection element, and a longitudinal wave ultrasonic probe with a working frequency of 1 MHz is selected.

[0028] Example 5 The temperature measurement method differs from that in Example 1 only in that two different Y:ZrO2 crystal materials are used as the detection elements, and the temperature measurement length... L 0、 L 1 and L 2 correspond to yttrium oxide mass fractions of 8 wt.%, 5 wt.%, and 2 wt.%, respectively, and lengths of 100 mm, 15 mm, and 15 mm, respectively, to extend the temperature range of the corresponding high-sensitivity temperature measurement interval.

[0029] Example 6 The temperature measurement method differs from that in Example 1 only in that two different Y:ZrO2 crystal materials are used as the detection elements, and the temperature measurement length... L 0、 L 1. L 2 and L3 correspond to yttrium oxide mass fractions of 8 wt.%, 5 wt.%, 2 wt.%, and 1 wt.%, respectively, with lengths of 100 mm, 15 mm, 15 mm, and 15 mm, respectively, to extend the temperature range of the corresponding high-sensitivity temperature measurement intervals.

[0030] Comparative Example 1 The temperature measurement method differs from that in Example 1 only in that an alumina crystal with a diameter of 0.7 mm and a length of 20 cm is used as the detection element.

[0031] Performance testing The following are the testing steps for variable-temperature ultrasonic velocity data: Select a suitable ultrasonic probe and detection element, complete the circuit connection with the ultrasonic flaw detector, and optimize the instrument parameters to establish an ultrasonic testing system. A sound velocity-temperature calibration test platform is built using the variable-temperature device, and calibration experiments are conducted to establish the correlation between the material's sound velocity and temperature. During the experiment, the temperature is maintained at each set point for 5 minutes until the temperature field stabilizes, after which ultrasonic signal acquisition is initiated; the ultrasonic signal is measured by obtaining the ultrasonic wave's length at the detection element. L Propagation time within t The ultrasonic velocity of the medium under different temperature conditions was calculated, and the evolution law of sound velocity with temperature was obtained.

[0032] The following are the testing steps for room temperature ultrasonic data: Select a suitable ultrasonic probe and detection element, complete the wiring connection with the ultrasonic flaw detector, and optimize the instrument parameters to establish an ultrasonic testing system. Measure the temperature length using different detection elements. L Determine the corresponding room temperature ultrasonic velocity, and use this to determine the propagation time under different conditions. t difference.

[0033] Example 1: A physical image of yttrium oxide-doped zirconium oxide (Y:ZrO2) crystal material is shown below. Figure 2 As shown, the crystalline material exhibits excellent crystal quality, proving its feasibility.

[0034] The variable-temperature ultrasonic velocity data measured in Comparative Example 1 and Example 1 are as follows: Figure 3 and Figure 4 As shown, the ultrasonic velocity of the alumina crystal in Comparative Example 1 exhibits a linear change overall. In contrast, the ultrasonic velocity of the Y:ZrO2 crystal material in Example 1 shows a more pronounced nonlinear change between 400-800℃ and 1300-1600℃, corresponding to monoclinic / tetragonal and tetragonal / cubic phase transitions, respectively. This result further confirms that the structural phase transition of Y:ZrO2 crystal material can effectively induce changes in ultrasonic velocity, which is beneficial for improving detection sensitivity.

[0035] The room temperature ultrasonic data measured in Example 1 are as follows: Figure 5 As shown in the image, the detection length is clearly visible. L The two corresponding ultrasonic peaks are located at ~6 μs and ~22 μs, respectively, further confirming the signal response capability of this temperature measurement method.

[0036] The room temperature ultrasonic data measured in Example 2 are as follows: Figure 6 As shown. It is clearly visible that the detection length... L The two corresponding ultrasonic peaks are located at ~5 μs and ~12.5 μs, respectively, further confirming that transverse waves can adapt to ultrasonic detection of different probe materials with different diameters and lengths.

[0037] The room temperature ultrasonic data measured in Example 3 are as follows: Figure 7 As shown in the image, the detection length is clearly visible. L The two corresponding ultrasonic peaks are located at ~4 μs and ~22 μs, respectively, further confirming that the detection element can adapt to the detection of different ultrasonic frequencies.

[0038] The room temperature ultrasonic data measured in Example 4 are as follows: Figure 8 As shown in the image, the detection length is clearly visible. L The two corresponding ultrasonic peaks are located at ~7 μs and ~20 μs, respectively, further confirming that the detection element can adapt to ultrasonic detection with different transmission modes.

[0039] A schematic diagram of the detection element in the temperature measurement method of Example 5 is shown below. Figure 9 As shown, it can be clearly seen that the temperature measurement range of the detection element can be designed using different compositions of Y:ZrO2 crystal materials. L 1 and L 2) Based on these two different monoclinic / tetragonal and tetragonal / cubic phase transitions, the application of this phase change material in ultrasonic temperature detection with high sensitivity over a wider temperature range can be expanded.

[0040] A schematic diagram of the detection element in the temperature measurement method of Example 6 is shown below. Figure 10 As shown, it can be clearly seen that the temperature measurement range of the detection element can be designed using different compositions of Y:ZrO2 crystal materials. L 1. L 2 and L 3) Based on these three different monoclinic / tetragonal and tetragonal / cubic phase transitions, the application of this phase change material in ultrasonic temperature detection with high sensitivity over a wider temperature range can be further expanded, thereby improving the wide-band temperature adaptability of the temperature detection element.

[0041] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a thermometric material based on a phase transition process, characterized in that, Specifically, the following steps are included: (1) Weigh the nanoscale raw materials according to the chemical composition of the thermometric material, then add a dispersant and ball mill, dry, and pre-calcine to obtain polycrystalline material; (2) According to the phase distribution of the thermometric material, the polycrystalline material is segmented, compacted, rolled into cylinders, pressed, and sintered to obtain polycrystalline rods; (3) In a closed quartz tube with continuous oxygen supply, the polycrystalline rod and the seed crystal are fixed at the upper and lower ends of the equipment respectively. The melting zone is maintained by bidirectional rotation. After the polycrystalline rod and the seed crystal are melted by the xenon lamp heating, the docking is completed. After docking, the seed crystal and the polycrystalline rod are moved downwards simultaneously to start the crystal growth process. By adjusting the xenon lamp heating power and the downward movement rate of the polycrystalline rod, the complete growth process of necking → shouldering → equal diameter → tailing is completed in sequence, and the target crystal is finally obtained, which is the temperature measuring material based on the phase change process.

2. The method for preparing a temperature-sensing material based on a phase transition process according to claim 1, characterized in that, In step (1), the temperature measuring material is lithium niobate, barium titanate, strontium zirconate, strontium hafnium oxide, rare earth-doped zirconium oxide, rare earth-doped lanthanum oxide, or rare earth-doped hafnium oxide; the dispersant is anhydrous ethanol; the ball milling time is 5-12 h; the pre-calcination temperature is 1000-1100℃ and the time is 5 h.

3. The method for preparing a thermometric material based on a phase transition process according to claim 1, characterized in that, In step (2), the pressing method is isostatic water pressure, the pressure is 50-80MPa, and the time is 15min; the sintering temperature is 1400-1600℃, and the time is 5h; the length of the polycrystalline rod is 40-100mm, and the diameter is 2-5mm.

4. The method for preparing a thermometric material based on a phase transition process according to claim 1, characterized in that, In step (3), the oxygen flow rate is 100-200 mL / min; during crystal growth, the rotation speeds of the upper and lower rotating rods are 5-15 r / min, and the rotation directions are opposite; the crystal growth rate is 5-80 mm / h; the diameter of the constant diameter crystal is 1-4 mm; the crystal growth length is 50-190 mm; and the process also includes: after crystal growth is completed, the heating power is gradually reduced to 0 within 5 hours, and after continuing to cool by blowing air for 0.5 hours, the entire crystal growth preparation process is completed.

5. A temperature measuring material prepared by the preparation method according to any one of claims 1-4.

6. The application of a thermometric material prepared by the preparation method according to any one of claims 1-4 in temperature measurement.

7. A temperature measurement method, characterized in that, Specifically, the following steps are included: (1) First, the temperature measuring material prepared by the preparation method described in any one of claims 1-4 is processed, and then installed inside or at the boundary of the high temperature area to be measured as a detection element; (2) The ultrasonic excitation and receiving unit transmits ultrasonic pulse signals to the detection element; (3) The ultrasonic excitation and receiving unit receives the ultrasonic echo signal after it has been propagated or reflected by the detection element, and obtains the ultrasonic signal at the temperature measurement length of the detection element. L Propagation time within t ; Based on the variation of propagation time with temperature, a sound speed-temperature calibration relationship is established in advance, i.e. v ( T ) = L / t ( T ); (4) The real-time measured ultrasonic data is output to the data acquisition and processing system through the signal transmission module, based on the measured propagation time. t The corresponding sound velocity is calculated, and then combined with the pre-established sound velocity-temperature calibration relationship, the real-time temperature value of the high-temperature environment is obtained. Finally, the temperature data is displayed in real time on the temperature display unit, and the dynamic changes of temperature over time are recorded in real time.

8. A temperature measurement method according to claim 7, characterized in that, In step (1), the temperature measuring material is processed into a rod-shaped structure with a diameter of 0.1-10 mm and a length greater than its diameter; the temperature measuring length of the temperature measuring material in the high-temperature region to be measured... L The range is 1 to 70 mm.

9. A temperature measurement method according to claim 7, characterized in that, In step (2), the ultrasonic excitation and receiving unit adopts an ultrasonic probe that integrates ultrasonic excitation and reception, and the excitation voltage is 100-600V; the transmission mode of the ultrasonic probe includes transverse wave mode and longitudinal wave mode; the ultrasonic probe and the detection element are coupled in air-free environment using a high-temperature ultrasonic coupling agent; the transmission frequency of the ultrasonic pulse signal is 0.5-10 MHz.

10. A temperature measurement method according to claim 7, characterized in that, In step (3), the curve fitting of the sound speed-temperature calibration relationship adopts a polynomial fitting method, and the fitting order is not less than the second order.

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