A single crystal optical fiber and a method of making and using the same

Abstract

The application relates to the technical field of new materials and temperature sensing, in particular to an XAlO3 (X=Gd, Tb) single crystal optical fiber and a preparation method and application thereof. The raw material rod is prepared through a component modulation process, so that the component of GdAlO3-TbAlO3 is suddenly changed in the axial direction, and the single crystal optical fiber with uniform diameter, consistent orientation and the lattice ion mutation at a specific position in the axial direction is obtained through a stable crystal growth process; the mutation of the lattice ion leads to the mutation of the crystal density and the intrinsic sound velocity, and then the acoustic impedance is mismatched at the position and the acoustic wave reflection signal is generated, so that the ultrasonic wave guide temperature measurement is realized.

Description

Technical Field

[0001] This invention relates to the fields of new materials and temperature sensing technology, specifically to an XAlO3 (X = Gd, Tb) single-crystal optical fiber and its preparation method and application. Background Technology

[0002] Single-crystal optical fiber is a novel "quasi-one-dimensional" functional crystal material that combines the advantages of traditional fiber materials and bulk crystals. It possesses excellent mechanical properties, good thermal management capabilities, and stable physical and chemical properties, making it promising for applications in high-energy lasers, radiation detection, information communication, and industrial manufacturing. In particular, high-melting-point oxide single-crystal optical fibers, represented by sapphire, spinel, and sesquioxide crystals, are potential high-temperature sensing media.

[0003] In recent years, fiber optic sensors based on silica optical fibers have been widely studied and applied in industrial production due to their compact structure and strong environmental adaptability. However, limited by their relatively low glass softening temperature (1000-1200 ℃), the temperature measurement accuracy and structural strength of silica optical fibers are severely affected at high temperatures, making it difficult for glass fiber sensors to reach a maximum operating temperature of 1000 ℃, thus restricting their sensing applications in high-temperature environments. In contrast, single-crystal optical fibers possess higher melting points, superior oxidation resistance, excellent mechanical properties, and stable physicochemical properties, making them a new research hotspot in the field of high-temperature environment sensing. Optical and acoustic temperature sensors based on single-crystal optical fibers have been initially applied to temperature monitoring in numerous application scenarios such as gas turbines and industrial production, demonstrating broad application prospects.

[0004] Compared to optical sensors, acoustic temperature sensors that use ultrasonic waveguides as the signal medium can avoid the influence of background radiation of optical signals at high temperatures, have lower losses at high temperatures, and have stronger anti-interference capabilities. Furthermore, their temperature measurement principle is based on the intrinsic properties of the material, avoiding the introduction of structures that may be affected by temperature. Therefore, the upper limit of the sensor's temperature measurement can approach the melting point of the waveguide material, and it has broad application prospects in the field of ultra-high temperature sensing.

[0005] Conventional single-crystal fiber ultrasonic temperature sensors use high-melting-point crystal fibers as probes. Grooves are created on the fiber surface through mechanical processing or chemical etching to induce acoustic impedance mismatch, generating echo signals at the groove structure and the end face of the crystal fiber. The region between the groove structure and the end face of the crystal fiber is defined as the temperature-sensitive zone. By analyzing the time delay between the echo signals from the groove and the end face in a specific environment, the average sound velocity in the temperature-sensitive zone can be obtained. The ambient temperature can then be deduced by analyzing the sound velocity-temperature relationship model of the single-crystal fiber. This technology is unaffected by background radiation and impurities, and has great potential for application in extreme high-temperature testing environments. However, manufacturing acoustic reflection structures through mechanical, chemical, or laser processing often compromises the stability of the single-crystal fiber structure, leading to stress concentration at the processing location. This makes the crystal highly susceptible to fracture at the reflection structure, severely affecting the mechanical strength of the crystal structure and limiting the application range of the device. Summary of the Invention

[0006] To overcome the above problems, this invention provides an XAlO3 (X = Gd, Tb) single-crystal optical fiber, its preparation method, and its application.

[0007] To achieve the above technical objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an XAlO3 (X = Gd, Tb) single-crystal optical fiber, which is a two-segment structure or a multi-segment structure; wherein, the two-segment structure is composed of a GdAlO3 single-crystal unit region and a TbAlO3 single-crystal unit region; and the multi-segment structure is composed of multiple sets of alternating GdAlO3 single-crystal unit regions and TbAlO3 single-crystal unit regions.

[0008] In one or more embodiments, the cross-section of the XAlO3 (X = Gd, Tb) single-crystal fiber is circular or polygonal, preferably circular.

[0009] In one or more embodiments, the axial crystallization direction of XAlO3 (X = Gd, Tb) single crystal fiber includes

[100] ,

[010] ,

[001] ,

[110] ,

[011] ,

[101] and

[111] .

[0010] In one or more embodiments, the diameter of the XAlO3 (X = Gd, Tb) single-crystal fiber is 10~1000 μm.

[0011] In one or more embodiments, the total length of the XAlO3 (X = Gd, Tb) single-crystal fiber is ≥10 cm.

[0012] In one or more embodiments, in the two-segment structure, the length of the GdAlO3 single crystal unit region or the TbAlO3 single crystal unit region is 1~20 cm.

[0013] In one or more embodiments, in the multi-segment structure, the length of the single crystal unit region at the end or tail and the multiple segments of single crystal unit regions connected thereto are both 1 to 20 cm.

[0014] A second aspect of the present invention provides a method for preparing the XAlO3 (X = Gd, Tb) single-crystal optical fiber described in the first aspect, comprising the following steps: (1) Gd2O3 and Tb2O3 powders were respectively mixed with Al2O3 powder according to the chemical formulas GdAlO3 and TbAlO3; after uniform mixing, GdAlO3 single crystal unit material and TbAlO3 single crystal unit material were obtained respectively. (2) The GdAlO3 single crystal unit material and the TbAlO3 single crystal unit material are filled into the cylindrical rubber mold according to the set length ratio, and then the raw material rod is obtained by vacuuming, isostatic pressing, solid-state sintering and rounding. (3) The raw material rod is subjected to laser heating base (LHPG) and annealing treatment in sequence to obtain XAlO3 (X = Gd, Tb) single crystal fiber.

[0015] In one or more embodiments, in step (1), Gd2O3 powder and Al2O3 powder are mixed according to the chemical formula GdAlO3; after uniform mixing, GdAlO3 single crystal unit is obtained. Tb2O3 powder and Al2O3 powder were mixed according to the chemical formula TbAlO3; after uniform mixing, TbAlO3 single crystal unit was obtained.

[0016] In one or more embodiments, in step (1), the method for uniform mixing is wet ball milling, which includes: mixing the prepared raw materials with anhydrous ethanol into a slurry and adding it to a ball milling jar for ball milling.

[0017] Preferably, the ball milling speed is 3~10 r / s and the ball milling time is 24~48 h.

[0018] Preferably, after ball milling, the milling jar and slurry are placed in a drying oven to dry.

[0019] More preferably, the drying temperature is 80~100 ℃ and the drying time is 10~24 h.

[0020] In one or more embodiments, in step (2), the inner diameter of the cylindrical rubber mold is 2~4 mm.

[0021] In one or more embodiments, in step (2), the isostatic pressing is carried out using an isostatic press with a pressure of 150~200 MPa and a holding time of 60~120 s.

[0022] In one or more embodiments, in step (2), the heating rate during solid-state sintering is 5~10 ℃ / min, the sintering temperature is 1500~1600 ℃, the holding time is 24~48 h, and the cooling rate is 2~5 ℃ / min.

[0023] In one or more embodiments, in step (2), the sintering crucible material used in the solid-state sintering process is Al2O3, ZrO2 or MgO ceramic.

[0024] In one or more embodiments, in step (2), the solid-state sintering process requires laying a medium material at the bottom of the crucible to prevent the raw material rod from contacting the inner wall of the crucible and introducing impurities.

[0025] Preferably, the dielectric material used is a platinum or iridium metal sheet.

[0026] In one or more embodiments, in step (2), the diameter of the raw material rod is 1~3 mm.

[0027] In one or more embodiments, in step (3), the power of the CO2 laser in the laser heating base (LHPG) method is 5~50 W.

[0028] In one or more embodiments, in step (3), the seed crystal and the raw material rod move upward at different speeds. The diameter of the grown crystal can be controlled by controlling the ratio of the seed crystal pulling speed to the raw material rod feeding speed (hereinafter referred to as "pulling-feed ratio"). Preferably, the pulling-feed ratio is less than 25:1. More preferably, the pulling-feed ratio is fixed at 3:1, 4:1, 5:1 or 6:1.

[0029] In one or more embodiments, during step (3), the furnace cavity can be filled with different types of protective atmospheres to keep it sealed throughout the growth process; preferably, the protective atmosphere is high-purity argon or nitrogen.

[0030] In one or more embodiments, in step (3), in order to further eliminate the air bubbles inside the raw material bar, the gas inside the furnace cavity is kept under negative pressure during the growth process.

[0031] Preferably, the internal air pressure is 0.5-0.8 bar.

[0032] In one or more embodiments, in step (3), the annealing temperature is 1400-1600 ℃, preferably 1500 ℃; the atmosphere during annealing is nitrogen or argon.

[0033] A third aspect of the present invention provides the application of the XAlO3 (X = Gd, Tb) single-crystal optical fiber described in the first aspect or the XAlO3 (X = Gd, Tb) single-crystal optical fiber prepared by the preparation method described in the second aspect as an ultra-high temperature thermometry material.

[0034] A fourth aspect of the present invention provides an ultrasonic temperature measurement method, comprising the following steps: When the XAlO3 (X = Gd, Tb) single crystal fiber has a two-segment structure, along the direction of ultrasonic wave propagation, the single crystal unit region at the end of the XAlO3 (X = Gd, Tb) single crystal fiber constitutes the temperature-sensitive region, and the interface of the single crystal unit region is the acoustic reflection surface. When the XAlO3 (X = Gd, Tb) single crystal fiber has a multi-segment structure, along the direction of ultrasonic wave propagation, the single crystal unit region at the end of the XAlO3 (X = Gd, Tb) single crystal fiber and the multiple segments of single crystal unit regions connected to it constitute the temperature-sensitive region; the interface between adjacent temperature-sensitive regions is the acoustic reflection surface. The temperature-sensitive area is placed in the area to be measured. One end of the XAlO3 (X = Gd, Tb) single-crystal fiber is coupled to an ultrasonic probe that generates longitudinal or transverse waves. The ultrasonic waves excited by the ultrasonic probe propagate in the XAlO3 (X = Gd, Tb) single-crystal fiber. The ultrasonic echo signals from the end face and acoustic reflection surface of the XAlO3 (X = Gd, Tb) single-crystal fiber are collected. The time difference between the ultrasonic echo signals generated by the end face and different acoustic reflection surfaces of the XAlO3 (X = Gd, Tb) single-crystal fiber is obtained. Based on the length of the corresponding temperature-sensitive area, the ultrasonic velocity in the temperature-sensitive area is obtained. The temperature of the region to be measured is obtained based on the relationship model between ultrasonic velocity and temperature in single-crystal optical fiber material.

[0035] In one or more embodiments, the relationship between ultrasonic speed and temperature is modeled as a standard curve of ultrasonic speed versus temperature.

[0036] The beneficial effects of this invention are as follows: (1) This invention relates to the fields of new materials and sensing technology, specifically to an XAlO3 (X = Gd, Tb) single-crystal optical fiber and its preparation method and application. This invention prepares a raw material rod through a component modulation process, which forms a component mutation of GdAlO3-TbAlO3 in the axial direction, and obtains a single-crystal optical fiber with uniform diameter, consistent orientation, and lattice ion mutation at a specific position in the axial direction through a stable crystal growth process; the mutation of lattice ions leads to a mutation of crystal density and intrinsic sound velocity, which in turn leads to acoustic impedance mismatch at that position and generates sound wave reflection signal, thereby realizing temperature measurement.

[0037] (2) This invention uses a single-crystal optical fiber material with a mutated composition as the ultrasonic conductive medium, which avoids the structural damage and stress concentration problems caused by conventional mechanical processing or chemical corrosion to prepare the acoustic reflection structure. It has high mechanical strength, which is beneficial to improve the overall mechanical performance of the sensor and broaden its application range.

[0038] (3) By adjusting the number of abrupt change regions and the position of abrupt change interfaces in single-crystal optical fiber, this invention can achieve high spatial resolution and distributed ultrasonic temperature sensing, which can meet the application requirements of complex environments.

[0039] (4) This invention provides a high-temperature oxide single-crystal optical fiber XAlO3 (X = Gd, Tb), which has both a high melting point (~2000 ℃) and a high density (~7.3 g / cm³). 3 With advantages such as oxidation resistance and low intrinsic sound velocity (<3500 m / s), it is the preferred waveguide material for ultrasonic temperature measurement; it can increase the sensor operating temperature to above 1800 ℃ and has excellent temperature measurement sensitivity, which can further broaden the application scenarios of the sensor and realize high-performance temperature detection in ultra-high temperature environments. Attached Figure Description

[0040] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0041] Figure 1 This is a schematic diagram of a conventional single-crystal fiber ultrasonic conductor temperature sensor. Figure 2 A schematic diagram of obtaining XAlO3 (X = Gd, Tb) single-crystal fiber acoustic waveguide rods by the laser heated base (LHPG) method; Figure 3 The image shows the raw material rod and the two-segment XAlO3 (X = Gd, Tb) single crystal fiber in Example 1, with the inset showing the raw material rod. Figure 4 The XRD diffraction patterns of a two-segment XAlO3 (X = Gd, Tb) single-crystal fiber are shown, where (a) is the GdAlO3 single-crystal unit region and (b) is the TbAlO3 single-crystal unit region. Figure 5 The diagram shows a single-temperature zone ultrasonic conductive temperature measurement scheme and the acquired waveform. (a) is a schematic diagram of the single-temperature zone ultrasonic conductive temperature measurement scheme, and (b) is the acquired waveform. Figure 6The ultrasonic temperature measurement performance of a two-segment XAlO3 (X = Gd, Tb) single-crystal fiber is shown in the following figures: (a) curve of reflected wave delay time versus temperature; (b) curve of transverse wave velocity versus temperature within the temperature-sensitive region; (c) curve of transverse wave velocity within the sensitive region under room temperature and 1500 ℃ conditions during cyclic testing; and (d) curve of velocity-temperature relationship during temperature cyclic testing. Figure 7 The diagram shows a dual-temperature zone ultrasonic conductive temperature measurement scheme and the acquired waveforms; where (a) is a single-temperature zone ultrasonic conductive temperature measurement scheme and (b) is the acquired waveform. Figure 8 The diagram shows a three-temperature zone ultrasonic conductive temperature measurement scheme and the acquired waveform. (a) is a schematic diagram of a single-temperature zone ultrasonic conductive temperature measurement scheme, and (b) is the acquired waveform. Detailed Implementation

[0042] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0043] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0044] like Figure 1 As shown, conventional single-crystal fiber ultrasonic temperature sensors use high-melting-point crystal fibers as probes. Grooves are created on the fiber surface through mechanical processing or chemical etching to induce acoustic impedance mismatch, generating echo signals at the groove structure and the end face of the crystal fiber. The region between the groove structure and the end face of the crystal fiber is defined as the temperature-sensitive zone. By analyzing the time delay between the echo signals from the groove and the end face in a specific environment, the average sound velocity in the temperature-sensitive zone can be obtained. The ambient temperature can then be deduced by analyzing the sound velocity-temperature relationship model of the single-crystal fiber. This technology is unaffected by background radiation and impurities, and has great potential for application in extreme high-temperature testing environments. However, manufacturing acoustic reflection structures through mechanical, chemical, or laser processing often compromises the stability of the single-crystal fiber structure, leading to stress concentration at the processing location. The crystal is highly susceptible to fracture at the reflection structure, severely affecting the mechanical strength of the crystal structure and limiting the application range of the device.

[0045] In this invention, without changing the waveguide cross-sectional area, a raw material rod is prepared through a component modulation process to form a component mutation of GdAlO3-TbAlO3 in the axial direction. Through a stable crystal growth process, a single-crystal optical fiber with uniform diameter, consistent orientation, and component mutation at a specific position in the axial direction is obtained. The mutation of lattice ions leads to a mutation of crystal density and intrinsic sound velocity, which in turn causes acoustic impedance mismatch at that position and generates sound wave reflection signal, thereby realizing temperature measurement.

[0046] Because GdAlO3 and TbAlO3 have similar crystal structures, when the crystal growth process reaches the abrupt change point of the raw material rod, the crystal maintains its orthorhombic structure, and Gd AlO3 crystals only undergo a change at specific lattice sites. 3+ and Tb 3+ The transformation of the crystal fiber allows for abrupt changes in density and intrinsic sound velocity at specific locations while maintaining structural integrity and mechanical strength. During temperature measurement, one end of the obtained crystal fiber is placed in contact with an ultrasonic flaw detector probe, while the other end, consisting of alternating GdAlO3 and TbAlO3 single crystal units, forms a temperature-sensitive region in the field to be measured. Ultrasonic waves enter the crystal fiber, and at the location of the lattice ion abrupt change (i.e., the interface between GdAlO3 and TbAlO3 single crystal units), the abrupt change in density and intrinsic sound velocity leads to an acoustic impedance mismatch, generating a sound wave reflection peak. This signal, together with the reflection peak generated at the end face of the crystal fiber, constitutes the characteristic signal of ultrasonic temperature measurement, used to monitor the real-time sound velocity within each temperature-sensitive region inside the crystal fiber.

[0047] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0048] Example 1 Fabrication of two-segment XAlO3 (X = Gd, Tb) single-crystal optical fibers: (1) Gd2O3 powder and Al2O3 powder were prepared according to the chemical formula GdAlO3 and mixed evenly to obtain GdAlO3 single crystal unit feedstock; Tb2O3 powder and Al2O3 powder were prepared according to the chemical formula TbAlO3 and mixed evenly to obtain TbAlO3 single crystal unit feedstock. The method of even mixing was as follows: the prepared raw materials were mixed with anhydrous ethanol to form a slurry, and then added to a ball mill jar for ball milling; the ball milling speed was 6 r / s and the ball milling time was 30 h; after the ball milling was completed, the ball mill jar and the slurry were placed in a drying oven for drying at a temperature of 90 ℃ for 16 h.

[0049] (2) Prepare a cylindrical rubber mold with a diameter of about 3 mm. Rinse it with alcohol and deionized water in turn to remove the adhering substances on its inner wall, and then place it in an oven to dry. First fill the mold with GdAlO3 single crystal unit material from the top entrance until the filling length reaches 5 cm. Then take TbAlO3 single crystal unit material and continue filling until the filling length reaches 7 cm. During the material filling process, squeeze it to make it densely filled until the outer diameter reaches 4 mm, and keep it as a cylindrical shape with a uniform diameter. The mold was then vacuumed, and cotton was stuffed into the mold opening to prevent powder from escaping. The vacuum pump was used for 10 minutes, and then the mold end was sealed by tying a knot. The mold was then placed vertically into an isostatic press, pressurized to 200 MPa and held for 90 seconds. After removal, the rubber mold was removed and the compressed dense round bar was taken out. The round bar was then sintered at high temperature in a sintering furnace at 1500 ℃ for 24 h to obtain a dense polycrystalline rod. The polycrystalline rod was then processed into a uniform raw material rod with a diameter of 2 mm using a ceramic rounding process.

[0050] (3) Figure 2 A schematic diagram of obtaining a crystal waveguide rod using the Laser Heated Mount Pedal (LHPG) method, referenced. Figure 2The raw material rod was bonded to the alumina ceramic feed rod using high-temperature ceramic adhesive and dried at 70 ℃ for 6 h to cure the ceramic adhesive. The furnace cavity and laser reflector of the laser heating base (LHPG) equipment were cleaned, and the optical path was finely adjusted to ensure uniformity. The alumina ceramic feed rod with the raw material rod bonded was securely installed on the feeding device, and the

[100] oriented YAlO3 seed crystal was fixed on the upper lifting device. Then, the feeding device was raised and the lifting device was lowered so that both were close to the laser focus. The furnace door was closed and sealed, and the vacuum pump was started to evacuate the furnace cavity until the internal pressure was less than 0.01 bar. The vacuum pump was then turned off, and the inlet valve was opened to fill the furnace cavity with protective gas until the internal pressure reached 0.8 bar. Increase the laser power to 10 W to melt the tip of the raw material rod. Adjust the horizontal position of the raw material rod so that the laser focus falls on the center of the raw material rod to achieve uniform heating. Continue to increase the power to 25 W to form a stable hemispherical molten zone and hold it at this temperature for 8 min. Adjust the position of the seed crystal to contact the molten zone and be coaxial with the raw material rod. Adjust the heating power until the interface size is stable, then start the lifting device and gradually increase the power to 45 W for necking. When the seed crystal diameter is reduced to 0.7 mm, adjust the power to 40 W to begin shoulder formation and constant diameter growth. Adjust the lifting speed to 0.6 mm / min and the feed speed to 0.15 mm / min. After the crystal grows to the required length, gradually increase the power to 43 W and stop feeding the polycrystalline raw material rod, then remove the crystal waveguide rod. Subsequently, reduce the laser power at a rate of 25 W / min until the laser is turned off, and purge with a flowing argon atmosphere for 10 minutes. After a few minutes, the furnace is opened, and the grown crystal waveguide rod, along with the seed crystal, is removed from the lifting fixture. A grinding wheel is then used to slowly cut the seed crystal and separate it from the crystal waveguide rod.

[0051] The crystal waveguide rod was placed in an annealing furnace for high-temperature atmosphere annealing to obtain a two-segment XAlO3 (X = Gd, Tb) single-crystal fiber. High-temperature atmosphere annealing can eliminate residual stress and color center defects inside the single-crystal fiber, and improve the crystal quality; the annealing temperature was 1500 ℃, the annealing time was 24 h, and the annealing atmosphere was nitrogen.

[0052] Figure 3 The images shown are of the raw material rod and the two-segment XAlO3 (X = Gd, Tb) single crystal fiber in this embodiment, with the inset showing the raw material rod.

[0053] Figure 4 The XRD diffraction pattern of the two-segment XAlO3 (X = Gd, Tb) single-crystal fiber obtained in this embodiment is shown below. Figure 4As shown, the XRD diffraction peaks of both the GdAlO3 single crystal unit region and the TbAlO3 single crystal unit region in the single crystal fiber are in good agreement with the standard cards of pure-phase GdAlO3 and pure-phase TbAlO3, indicating that the two sections of crystal fiber are pure-phase GdAlO3 and pure-phase TbAlO3 respectively, which proves that the single crystal fiber with GdAlO3-TbAlO3 component abrupt structure is obtained.

[0054] The melting point of the dual-segment XAlO3 (X = Gd, Tb) single crystal fiber is about 2000 °C, and the density is about 7.3 g / cm 3 , the intrinsic sound velocity is less than 3500 m / s, which can be used for ultrasonic waveguide temperature measurement.

[0055] Experimental Example 1 The dual-segment XAlO3 (X = Gd, Tb) single crystal fiber (total length L0) prepared in Example 1 is used for single-temperature-zone ultrasonic waveguide temperature measurement: As shown in Figure 5 (a), the shear wave mode ultrasonic transducer matched with the ultrasonic flaw detector is connected to the GdAlO3 single crystal unit region of the dual-segment XAlO3 (X = Gd, Tb) single crystal fiber, so that acoustic waves enter the dual-segment XAlO3 (X = Gd, Tb) single crystal fiber; along the propagation direction of the ultrasonic wave, the TbAlO3 single crystal unit region at the end of the XAlO3 (X = Gd, Tb) single crystal fiber forms a temperature-sensitive measurement region (length L S ), the interface between the GdAlO3 single crystal unit region and the TbAlO3 single crystal unit region is an acoustic reflection surface; and the abscissa t of the reflection signal of the component mutation interface (acoustic reflection surface) at room temperature is read on the display of the ultrasonic flaw detector P and the abscissa t of the reflection signal of the end face E , the length L of the temperature-sensitive measurement region is accurately calculated according to formula (1) S .

[0056] Formula (1).

[0057] The acoustic wave characteristic signals are identified on the ultrasonic flaw detector, and the results are as shown in Figure 5 (b), the reflection signals from the component mutation interface and the end face are clear, which can be used for ultrasonic waveguide temperature measurement.

[0058] The temperature response capability in the range of 20-1500 °C is tested, as shown in Figure 6 (a) and (b), the delay time Δt (t E -t p ) between the reflection signals of the dual-segment XAlO3 (X = Gd, Tb) single crystal fiber gradually increases as the ambient temperature increases, and the shear wave sound velocity gradually decreases as the temperature increases, and the fitting of the sound velocity and temperature curve is good, v=5.35×10 -5T 2 -0.18T+3264.12. The high-temperature stability and temperature measurement accuracy are further evaluated, as Figure 6 shown in (c) and (d) herein, three heating and cooling cycles are performed on the obtained two-segment XAlO₃ (X = Gd, Tb) single-crystal optical fiber. Both the sound velocity and the ambient temperature satisfy the polynomial fitting law, and the cycle stability is good. During the high-temperature cycle, the average transverse wave sound velocity at 1500 °C is 2872.75 m / s, the maximum error is 10.75 m / s, and the deviation is 0.37%, demonstrating good temperature measurement accuracy and environmental stability.

[0059] Example 2 Preparation of three-segment XAlO₃ (X = Gd, Tb) single-crystal optical fiber: The difference from Example 1 lies in step (2): TbAlO₃ single-crystal unit ingredients are firstly filled from the inlet at the top of the mold until the filling length reaches 5 cm, then 1 cm-length GdAlO₃ single-crystal unit ingredients and 1 cm-length TbAlO₃ single-crystal unit ingredients are sequentially filled into the rubber mold. A component distribution of TbAlO₃→GdAlO₃→TbAlO₃ is formed in the mold, with lengths of 5 cm, 1 cm and 1 cm respectively.

[0060] Other methods are the same as those in Example 1.

[0061] Experimental Example 2 The three-segment XAlO₃ (X = Gd, Tb) single-crystal optical fiber (total length L₀) prepared in Example 2 is used for dual-temperature-zone ultrasonic waveguide temperature measurement: As Figure 7 shown in (a) herein, the transverse wave mode ultrasonic transducer matched with the ultrasonic flaw detector is connected to the longer TbAlO₃ single-crystal unit region of the three-segment XAlO₃ (X = Gd, Tb) single-crystal optical fiber, so that sound waves enter the three-segment XAlO₃ (X = Gd, Tb) single-crystal optical fiber. Along the propagation direction of the ultrasonic wave, the XAlO₃ (X = Gd, Tb) single-crystal optical fiber sequentially comprises a first TbAlO₃ single-crystal unit, a first GdAlO₃ single-crystal unit and a second TbAlO₃ single-crystal unit; the second TbAlO₃ single-crystal unit region at the end of the XAlO₃ (X = Gd, Tb) single-crystal optical fiber forms a first temperature measurement sensitive region (length L S1 ), and the first GdAlO₃ single-crystal unit region connected thereto forms a second temperature measurement sensitive region (length L S2 ), the interface between the second TbAlO₃ single-crystal unit region and the first GdAlO₃ single-crystal unit region is a first sound reflection surface, and the interface between the first GdAlO₃ single-crystal unit region and the first TbAlO₃ single-crystal unit region is a second sound reflection surface; and the abscissa t of the reflection signal of the first sound reflection surface at room temperature is read on the display of the ultrasonic flaw detectorP1 , the abscissa t of the reflection signal of the second reflective reflecting surface P2 and the abscissa t of the reflection signal of the end face E1 , the length L of the first temperature measurement sensitive region is accurately calculated according to formulas (2) and (3) S1 and the length L of the second temperature measurement sensitive region S2 ; The acoustic characteristic signals are identified on the ultrasonic flaw detector, and the results are shown in Figure 7 as (b), the reflection signals of the component mutation interface and the end face are clear, which can be used for ultrasonic waveguide temperature measurement.

[0062] .

[0063] Example 3 Preparation of four-segment XAlO3 (X = Gd, Tb) single crystal optical fiber: The difference from Example 1 lies in step (2): GdAlO3 single crystal unit ingredients are firstly filled from the top inlet of the mold until the filling length reaches 5 cm, then TbAlO3 single crystal unit ingredients with a length of 1 cm, GdAlO3 single crystal unit ingredients with a length of 1 cm and TbAlO3 single crystal unit ingredients with a length of 1 cm are sequentially filled into the rubber mold. A component distribution of GdAlO3→TbAlO3→GdAlO3→TbAlO3 is formed in the mold, with lengths of 5 cm, 1 cm, 1 cm, and 1 cm respectively.

[0064] Other methods are the same as those in Example 1.

[0065] Experimental Example 3 The four-segment XAlO3 (X = Gd, Tb) single crystal optical fiber (total length L0) prepared in Example 3 is used for three-temperature-zone ultrasonic waveguide temperature measurement: As shown in Figure 8 (a), the shear wave mode ultrasonic transducer matched with the ultrasonic flaw detector is connected to the longer GdAlO3 single crystal unit region of the three-segment XAlO3 (X = Gd, Tb) single crystal optical fiber, so that acoustic waves enter the three-segment XAlO3 (X = Gd, Tb) single crystal optical fiber; along the propagation direction of the ultrasonic wave, the XAlO3 (X = Gd, Tb) single crystal optical fiber sequentially comprises a first GdAlO3 single crystal unit, a first TbAlO3 single crystal unit, a second GdAlO3 single crystal unit and a second TbAlO3 single crystal unit; the second TbAlO3 single crystal unit region at the end of the XAlO3 (X = Gd, Tb) single crystal optical fiber constitutes a first temperature measurement sensitive region (length L S11 ), the sequentially connected second GdAlO3 single crystal unit region and the first TbAlO3 single crystal unit region sequentially constitute a second temperature measurement sensitive region (length L S22 ) and a third temperature measurement sensitive region (length LS33 ); The interface between the second TbAlO3 single crystal unit region and the second GdAlO3 single crystal unit region is the first acoustic reflection surface, and the interface between the second GdAlO3 single crystal unit region and the first TbAlO3 single crystal unit region is the second acoustic reflection surface. The interface between the first TbAlO3 single crystal unit region and the first GdAlO3 single crystal unit region is the third acoustic reflection surface. The abscissa t of the reflection signal of the first acoustic reflection surface at room temperature is read on the display of the ultrasonic flaw detector. P11 The horizontal coordinate t of the reflected signal from the second sound reflecting surface P22 The horizontal coordinate t of the reflected signal from the second sound reflecting surface P33 The x-coordinate t of the reflected signal from the end face E11 The length L of the first temperature-sensitive zone is accurately calculated according to formulas (4), (5) and (6). S11 The length L of the second temperature sensing zone S22 And the length L of the third temperature sensing zone S33 ; The acoustic wave characteristic signals were identified using an ultrasonic flaw detector, and the results are as follows: Figure 8 As shown in (b), the component abrupt change interface and end face reflection signal are clear and can be used for ultrasonic temperature measurement.

[0066]

[0067]

[0068] .

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A single-crystal optical fiber, characterized in that, It has a two-segment structure or a multi-segment structure; the two-segment structure consists of a GdAlO3 single crystal unit region and a TbAlO3 single crystal unit region; the multi-segment structure consists of multiple sets of alternating GdAlO3 single crystal unit regions and TbAlO3 single crystal unit regions.

2. The single-crystal optical fiber as described in claim 1, characterized in that, Single-crystal optical fibers have a circular or polygonal cross-section; The axial crystallization directions of single-crystal optical fibers include [100], [010], [001], [110], [011], [101], and [111]. The diameter of single-crystal optical fibers ranges from 10 to 1000 μm; The total length of the single-crystal optical fiber is ≥10 cm.

3. The single-crystal optical fiber as described in claim 1, characterized in that, In the two-segment structure, the length of the GdAlO3 single crystal unit region or the TbAlO3 single crystal unit region is 1~20 cm.

4. The method for preparing a single-crystal optical fiber according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Gd2O3 and Tb2O3 powders were respectively mixed with Al2O3 powder according to the chemical formulas GdAlO3 and TbAlO3; after uniform mixing, GdAlO3 single crystal unit material and TbAlO3 single crystal unit material were obtained respectively. (2) The GdAlO3 single crystal unit material and the TbAlO3 single crystal unit material are filled into the cylindrical rubber mold according to the set length ratio, and then the raw material rod is obtained by vacuuming, isostatic pressing, solid-state sintering and rounding. (3) The raw material rod is successively subjected to laser heating base method and annealing treatment to obtain single crystal optical fiber.

5. The preparation method according to claim 4, characterized in that, In step (1), the method for uniform mixing is wet ball milling, which includes: mixing the prepared raw materials with anhydrous ethanol into a slurry, and then adding it to a ball milling jar for ball milling; The ball milling speed is 3~10 r / s, and the ball milling time is 24~48 h; After ball milling, the ball mill jar and slurry are placed in a drying oven for drying; the drying temperature is 80~100 ℃ and the drying time is 10~24 h.

6. The preparation method according to claim 4, characterized in that, In step (2), the inner diameter of the cylindrical rubber mold is 2~4mm; In step (2), the isostatic pressing is carried out using an isostatic press with a pressure of 150~200 MPa and a holding time of 60~120s. In step (2), the heating rate during solid-state sintering is 5~10 ℃ / min, the sintering temperature is 1500~1600 ℃, the holding time is 24~48 h, and the cooling rate is 2~5 ℃ / min. In step (2), the sintering crucible used in the solid-state sintering process is made of Al2O3, ZrO2 or MgO ceramic. In step (2), the diameter of the raw material rod is 1~3 mm.

7. The preparation method according to claim 4, characterized in that, In step (3), the power of the CO2 laser in the laser heating base method is 5~50 W; In step (3), during the growth of crystal optical fiber, the furnace cavity can be filled with different types of protective atmospheres to keep it sealed throughout the growth process; the protective atmosphere is high-purity argon or nitrogen. In step (3), the gas inside the furnace cavity is kept under negative pressure during the growth process; the internal gas pressure is 0.5-0.8 bar. In step (3), the annealing temperature is 1400-1600 ℃; the annealing atmosphere is nitrogen or argon.

8. The application of the single-crystal optical fiber according to any one of claims 1 to 3 or the single-crystal optical fiber prepared by the preparation method according to any one of claims 4 to 7 as an ultra-high temperature measurement material.

9. A method for ultrasonic temperature measurement using a single-crystal optical fiber prepared by any one of claims 1-3 or by any one of claims 4-7, characterized in that, Includes the following steps: When the single-crystal optical fiber has a two-segment structure, along the direction of ultrasonic wave propagation, the single-crystal unit region at the end of the single-crystal optical fiber constitutes the temperature-sensitive region, and the interface of the single-crystal unit region is the acoustic reflection surface. The temperature-sensitive area is placed in the area to be measured. One end of the single-crystal fiber is coupled to an ultrasonic probe that generates longitudinal or transverse waves. The ultrasonic waves excited by the ultrasonic probe propagate in the single-crystal fiber. The ultrasonic echo signals from the end face and acoustic reflection surface of the single-crystal fiber are collected. The time difference between the ultrasonic echo signals generated by the end face and different acoustic reflection surfaces of the single-crystal fiber is obtained. Based on the length of the corresponding temperature-sensitive area, the ultrasonic velocity in the temperature-sensitive area is obtained. The temperature of the region to be measured is obtained based on the relationship model between ultrasonic velocity and temperature in single-crystal optical fiber material.

10. The method as described in claim 9, characterized in that, The model for the relationship between ultrasonic velocity and temperature is the standard curve of ultrasonic velocity versus temperature.

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