High-purity platinum-molybdenum thermocouple wire, and preparation method and application thereof

Abstract

The application belongs to the technical field of metal material preparation, and particularly relates to high-purity platinum-molybdenum thermocouple wire and a preparation method and application thereof. The preparation method of the high-purity platinum-molybdenum thermocouple wire comprises the following steps: (1) rough platinum is purified step by step to obtain high-purity sponge platinum with a purity not less than 99.999%; (2) high-purity platinum powder and high-purity molybdenum powder are mixed according to a formula ratio, and an alloy ingot is prepared through cold isostatic pressing; (3) the alloy ingot is vacuum suspension smelted to remove gas and non-metallic inclusions, and a high-purity, uniform and dense platinum-molybdenum alloy cast ingot is obtained; (4) the cast ingot is subjected to cladding, hot forging and surface milling to obtain a thermocouple wire bar; and (5) the bar is subjected to cold rolling, cold drawing and argon protection annealing to prepare the high-purity platinum-molybdenum thermocouple wire. The platinum-molybdenum thermocouple wire prepared by the method has the characteristics of high purity, accurate content, stable thermoelectric potential, radiation resistance and long service life, and can meet the performance requirements of accurate temperature measurement in a nuclear radiation environment in the field of nuclear power engineering.

Description

Technical Field

[0001] This invention belongs to the field of metal material preparation technology, specifically relating to a high-purity platinum-molybdenum thermocouple wire, its preparation method, and its application. Background Technology

[0002] The effective operation of a nuclear reactor largely depends on the accuracy of temperature measurements of its various components. The presence of radioactive irradiation poses certain challenges to temperature measurement within a nuclear reactor.

[0003] In nuclear reactors, temperatures below 1000°C can generally be well measured using nickel-chromium / nickel-aluminum thermocouples. However, for high-temperature measurements above 1000°C, platinum-rhodium or tungsten-rhenium thermocouples are commonly used. This is because rhodium, tungsten, and rhenium have large thermal neutron trapping surfaces, easily trapping neutrons and converting them into other elements, thus altering the thermocouple material composition and consequently changing its thermoelectric properties. Calculations show that at a thermal neutron flux of 1 × 10⁻⁶... 14 neutrons / cm 2 Irradiation at a density of 1 second per second can convert 20% of rhodium into palladium in just 6 months; within 20 years, 27% of tungsten can be converted into 24% of osmium and 3% of rhenium; and within 10 years, 91% of rhenium can be converted into osmium.

[0004] Besides having a small thermal neutron trapping surface, platinum and molybdenum can form a solid solution, exhibiting good processability and relative stability under nuclear irradiation. Platinum-molybdenum thermocouples possess essentially linear thermoelectric properties and exhibit high thermoelectric potential and sensitivity, making them suitable for temperature measurement in nuclear irradiation environments.

[0005] Platinum-molybdenum thermocouple wires prepared by conventional methods have low purity, poor stability, and short service life. Furthermore, the molybdenum content is prone to change during processing, making it difficult to control the thermoelectric potential effectively. Therefore, high-quality platinum-molybdenum thermocouple wires for temperature measurement in nuclear irradiation environments cannot be obtained using existing technologies. Summary of the Invention

[0006] The main objective of this invention is to provide a high-purity platinum-molybdenum thermocouple wire, its preparation method, and its application. The platinum-molybdenum thermocouple wire prepared using the method of this invention has the characteristics of high purity, accurate content, stable thermoelectric potential, radiation resistance, and long lifespan, and can meet the performance requirements for accurate temperature measurement under nuclear irradiation environments in the field of nuclear power engineering.

[0007] To achieve the above technical objectives, the technical solution adopted in the embodiments of the present invention is as follows: In a first aspect, embodiments of the present invention provide a method for preparing high-purity platinum-molybdenum thermocouple wire, comprising the following steps: Step S1, Mixing and Pressing: High-purity sponge platinum and high-purity molybdenum powder are thoroughly mixed evenly in a three-dimensional mixing machine according to the formula ratio for ≥40 min, and then cold isostatically pressed at 100-200 MPa to obtain alloy ingots; Step S2, Vacuum Suspension Melting: The alloy ingot formed in step S1 is placed into a cold crucible, vacuumed and filled with argon gas for protection, and the melting power is increased to the maximum. The alloy is completely melted and suspended under the action of electromagnetic force, and the surface tends to be spherical. At this time, the melting temperature is 1780-2000℃. After holding at this temperature for 2-5 minutes, it is cast into an ingot. The mold is a water-cooled copper mold. Step S3, Encasing: A box similar in shape to the ingot but slightly larger in size is made from Pt sheet. The ingot is placed inside the box and sealed by welding. A gas pipe is led out from one side along the length and connected to a vacuum unit. A vacuum is evacuated to a vacuum level of 1×10⁻⁶. -2 -1×10 -3 Pa, weld the root of the trachea together, and then cut off the trachea to complete the sheath, the thickness of the sheath being 1-3mm; Step S4, hot forging and milling: The ingot obtained in step S3 is annealed in a furnace at 1350℃±50℃, hot forging is performed using a pneumatic hammer, and the final forging temperature is 1000℃±50℃. Finally, a milling machine is used to mill off 1-2mm of thickness around the bar stock. Step S5, cold rolling: The cold rolling pass processing rate is controlled at 5%-10%, and the total processing rate between the two annealings does not exceed 60%. The intermediate annealing temperature is 1200℃±50℃, and the time is 20-30min. Argon gas is used for protection during the annealing process. The cold-rolled bar is subjected to alkali boiling and acid boiling treatment. Step S6, Cold Drawing: The cold drawing rate of the rolled bar is controlled at 10%-20%, and the total processing rate between the two annealing processes does not exceed 80%. The intermediate annealing temperature is 1200℃±50℃, and the time is 10-20min. Argon gas is used for protection during the annealing process. The finished wire is subjected to alkali boiling and acid boiling treatment to obtain high-purity platinum-molybdenum thermocouple wire with a purity >99.98%.

[0008] Furthermore, the purity of the high-purity sponge platinum in step (2) is not less than 99.999%; the purity of the high-purity molybdenum powder is not less than 99.999%.

[0009] Furthermore, the method for preparing the high-purity sponge platinum includes the following steps: (1) Crude platinum is dissolved in aqua regia, nitrate is removed and sodium salt is converted to obtain sodium chloroplatinate solution; (2) The trace impurity elements, including Pd, Rh, Ir, Au, Ag, Ni and Al, in the sodium chloroplatinate solution are removed by the oxidative carrier hydrolysis method; (3) Adjust the pH of the solution to 2-5 and perform cation exchange to further remove base metal impurities, including Cu, Mg and Fe, from the sodium chloroplatinate solution. (4) Platinum in the sodium chloroplatinate solution is precipitated as (NH4)2PtCl6 by NH4Cl precipitation method. After filtration and washing with 0.5%-5% ammonium chloride solution, high-purity sponge platinum is obtained by drying, calcining and washing with water to remove sodium.

[0010] Further, the oxidative carrier hydrolysis method described in step (2) includes the following steps: using one or more combinations of sodium bromate, chlorine and oxygen as oxidant, adding FeCl3 solution to sodium chloroplatinate solution as carrier, heating to 50-80℃ for 10-30 min, then heating to above 90℃, adjusting the pH of the solution to 7-10, maintaining for 1-5 min after hydrolysis, rapidly cooling and filtering to obtain a pure platinum solution.

[0011] Furthermore, the NH4Cl platinum precipitation method described in step (4) adopts one of the following methods: a. Directly add high-purity NH4Cl, with a purity > 99.8%; b. Acidify the solution to pH < 2 and then introduce ammonia gas.

[0012] Furthermore, in step S2, the vacuum is evacuated to a vacuum level of 1×10⁻⁶. -2 -1×10 -3 The pressure of the argon gas is 0.02-0.08 MPa, the melting power is 80-120 KW, and the water-cooled copper mold is a segmented cylindrical mold.

[0013] Furthermore, in step S4, the hot forging annealing time is 10-30 min, the pass processing rate is controlled at 10-20%, and the final forging size is 14 mm × 14 mm - 16 mm × 16 mm.

[0014] Further, the argon-protected annealing method described in steps S5 and S6 is as follows: a box is made of pure Pt sheet, with an inlet pipe and an exhaust pipe leading out from each side. The inlet pipe is connected to an argon cylinder, and the exhaust pipe is connected to a vacuum unit. A corundum vessel is placed inside the box, and the annealing material is placed inside before the box is sealed by welding. A vacuum is then drawn to 1×10⁻⁶. -2 -1×10 -3 After Pa, the vacuum is turned off and argon gas is introduced to a positive pressure of 0.02-0.04 MPa. Then the entire box is put into the furnace for annealing, and the material is cold-in and cold-out, with argon gas protection throughout the process.

[0015] Secondly, embodiments of the present invention provide a high-purity platinum-molybdenum thermocouple wire, which is prepared using the preparation method described in the first aspect.

[0016] Thirdly, embodiments of the present invention provide the application of the high-purity platinum-molybdenum thermocouple wire described in the second aspect, wherein the high-purity platinum-molybdenum thermocouple wire is used for temperature measurement in nuclear irradiation environments.

[0017] The beneficial effects of the technical solution provided by the embodiments of the present invention are as follows: (1) In the preparation of high-purity platinum sponge, the present invention adopts a distribution purification method, which first effectively removes impurity elements such as Pd, Rh, Ir, Au, Ag, Ni, and Al, and then further removes the remaining base metal impurities such as Cu, Mg, and Fe, ensuring that the platinum purity in the obtained platinum sponge is ≥99.999%, which can meet the performance requirements for accurate temperature measurement under nuclear irradiation environment in the field of nuclear power engineering.

[0018] (2) This invention employs a vacuum suspension melting process, which effectively removes gases and non-metallic inclusions. Simultaneously, because the melt is suspended under electromagnetic force during the melting process and does not contact the crucible, it avoids crucible material entering the melt at high temperatures. This differs from conventional melting processes where electromagnetic stirring of the melt scours the crucible, introducing refractory material inclusions. This method completely eliminates the introduction of crucible material inclusions. Furthermore, even if there are very small amounts of refractory material in the raw materials, they cannot be suspended in the electromagnetic field due to the inability to generate induced current, and instead accumulate at the bottom of the melt, floating at the ingot riser during casting, making them easy to remove. This method greatly avoids the introduction of foreign impurities, achieving refining and purification. In addition, the melting vacuum degree is 1×10⁻⁶. -2 -1×10 -3 Pa can not only remove the adsorbed gas in the powder, but also prevent the molybdenum from being oxidized during the smelting process; the argon gas is introduced during the smelting process to prevent splashing, reduce vacuum volatilization of the melt, and reduce smelting losses.

[0019] (3) The present invention adopts a cladding hot forging method, which can not only solve the problem of brittle cracking caused by molybdenum oxidation at the grain boundary during annealing, but also effectively solve the problem of molybdenum oxidation and volatilization during hot forging. After hot forging, the surface cladding is removed by milling to obtain a bar with molybdenum content consistent with the feed formula, thereby achieving precise control of molybdenum content during hot working and ensuring the accuracy of thermoelectric potential.

[0020] (4) The argon-protected annealing device and annealing method designed in this invention are connected to a vacuum unit via a vacuum pipe, and the vacuum is evacuated to 1×10⁻⁶. -2 -1×10 -3 The pressure of Pa effectively prevents the oxidation and volatilization of molybdenum in the thermocouple wire during annealing. Argon purging to positive pressure solves the problem of molybdenum volatilization during vacuum heating and also prevents external air from entering the apparatus and causing molybdenum oxidation in case of leaks. This differs from conventional atmosphere-protected annealing furnaces, which, due to the inability to achieve complete sealing, consume large amounts of gas and cannot completely isolate oxygen, resulting in poor performance.

[0021] (5) The high-purity platinum-molybdenum thermocouple wire prepared by the method of the present invention has a purity ≥99.98%. The thermocouples made from this wire were used for temperature measurement in a nuclear irradiation environment. The change in Mo content before and after processing was <0.01%. The integrated flux of fast neutrons (energy >0.18 MeV) and thermal neutrons was 1.5 × 10⁻⁶. 21 neutrons / cm 2 After irradiation, the thermoelectric potential deviation from room temperature to 1500℃ is within 0.5%, which fully meets the requirements for long-term temperature measurement in nuclear reactors. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] Example 1 The preparation methods of PtMo5 thermocouple wire and PtMo0.1 thermocouple wire include the following steps: (1) Preparation of platinum powder a. Dissolve commercially available platinum with a purity of 99.95% in aqua regia, remove nitrates, and convert to sodium salt to obtain sodium chloroplatinate solution, and adjust the Pt mass concentration to 60 g / L; b. Add sodium bromate (oxidant) and 0.3% FeCl3 solution to the above sodium chloroplatinate solution, heat the solution to 60℃ and maintain oxidation for 20 min to oxidize impurity ions including Rh, Ir and Fe to higher valence states that are more easily hydrolyzed. Then boil the solution and add NaOH solution dropwise until pH=7.5, cool it rapidly to room temperature, and immediately filter out the Na2PtCl6 solution to remove impurity elements including Pd, Rh, Ir, Au, Ag, Ni and Al. c. Add hydrochloric acid dropwise to the solution until pH=2.5, and then further remove base metal impurities, including Cu, Mg and Fe, by passing the solution through a strongly acidic styrene-based cation exchange column; d. High-purity NH4Cl with a purity >99.8% was used as a precipitant to precipitate (NH4)2PtCl6. The precipitate was filtered and washed with 1% ammonium chloride solution. After drying, calcination, and water washing to remove sodium, high-purity sponge platinum with a purity of not less than 99.999% was obtained. (2) Mixing powder and pressing into ingots Sponge platinum and high-purity molybdenum powder (purity 99.999%) were mixed at molybdenum content of 5% and 0.1% by mass, respectively. The mass of PtMo5 and PtMo0.1 was controlled at 2.1 kg. The mixture was mixed for 60 min by a three-dimensional powder mixer and then poured into a cold isostatic pressing molding sleeve. Oil was used as the pressure medium and the pressure was 150 MPa to press PtMo5 and PtMo0.1 powder alloy ingots. (3) Vacuum suspension melting Two types of shaped alloy ingots, PtMo5 and PtMo0.1, were placed into a cold crucible and evacuated to a vacuum of 1×10⁻⁶. -3 After Pa, 0.08MPa argon gas is introduced, and the power is increased to 100KW to completely melt the alloy and make it tend to float in a spherical shape. The power is then reduced to 80KW, held for 3 minutes, and then increased to 100KW again to cast them into φ35mm round ingots. (4) Wrap A φ37mm×110mm box is made using a 1.0mm thick Pt sheet. The ingots are placed inside and welded shut. A φ10mm×800mm long air pipe is led out from one side along the length and connected to a vacuum unit. A vacuum of 1×10⁻⁶ is then created. -3 After Pa, the root of the trachea is welded together, and then the trachea is cut off; (5) Hot forging and milling of surfaces The ingots obtained in step (4) are annealed in the furnace at 1350℃ for 20 minutes. The final forging temperature is controlled at 1000℃. Hot forging is carried out by air hammer. The pass processing rate is controlled at 12%. The final forging size is 15mm×15mm. Finally, a milling machine is used to mill 1.5mm of thickness off each side of the bar.

[0024] (6) Cold rolling The bar stock was cold-rolled to 3mm×3mm with a pass-through rate controlled at 7%. The total processing rate between the two annealing cycles was 55%. The intermediate annealing temperature was 1200℃ for 20 minutes, and annealing was carried out in an argon-protected box. The vacuum was first evacuated to 1×10⁻⁶. -3 Pa, then argon gas is introduced to a positive pressure of 0.04 MPa, and the cold-rolled bar is alkali boiled for 20 minutes and acid boiled for 20 minutes; When boiling with alkali, a sodium hydroxide solution is used, and the ratio of sodium hydroxide to deionized water in the solution is 100g / 1000ml; The acid boiling process uses a hydrochloric acid solution, which is prepared by mixing 36% analytical grade hydrochloric acid and deionized water at a volume ratio of 1:1.

[0025] (7) Cold drawing The cold drawing rate of the rolled bar was controlled at 15%, and the total processing rate between the two annealings was 75%. The intermediate annealing temperature was 1200℃ and the time was 15min. Argon gas was used for protection. The annealing method was the same as step (6). The finished wire was boiled in alkali for 20min and acid for 20min, and then rinsed with deionized water to obtain PtMo5 thermocouple wire and PtMo0.1 thermocouple wire.

[0026] The argon-protected annealing method in steps (6) and (7) is as follows: A box is made of pure Pt sheet, with an inlet pipe and an exhaust pipe leading out from both sides. The inlet pipe is connected to an argon cylinder, and the exhaust pipe is connected to a vacuum unit. A corundum vessel is placed inside the box, and the annealing material is placed inside before the box is sealed by welding. The vacuum is then evacuated to 1×10⁻⁶. -3 After Pa, the vacuum was turned off and argon gas was introduced to a positive pressure of 0.04 MPa. Then the entire box was put into the furnace for annealing, and the material was cold-in and cold-out, with argon gas protection throughout the process.

[0027] Performance testing: The contents of trace impurity elements in the PtMo5 thermocouple wire, as determined by ICP analysis, are shown in Table 1.

[0028] Table 1. Content of trace impurity elements in PtMo5 thermocouple wires in Example 1 The contents of trace impurity elements in the PtMo0.1 thermocouple wire were determined by ICP analysis and are shown in Table 2.

[0029] Table 2 shows the content of trace impurity elements in the PtMo0.1 thermocouple wire in Example 1. As can be seen from Tables 1 and 2, the purity of both PtMo5 thermocouple wire and PtMo0.1 thermocouple wire is >99.98%; the measured Mo content in PtMo5 thermocouple wire is 4.996%, and the measured Mo content in PtMo0.1 thermocouple wire is 0.098%, with the change in Mo content being <0.01%.

[0030] The prepared PtMo5-PtMo0.1 thermocouple (positive electrode: PtMo5 thermocouple wire; negative electrode: PtMo0.1 thermocouple wire) achieved a fast neutron (energy > 0.18 MeLV) integrated flux and a thermal neutron integrated flux of 1.5 × 10⁻⁶. 21 neutrons / cm 2 After irradiation, the thermoelectric potential deviation from room temperature to 1500℃ is within 0.3%.

[0031] Conclusion: The above preparation method can obtain high-purity, accurate content, stable thermoelectric potential, radiation resistance, and long lifespan PtMo5 thermocouple wire and PtMo0.1 thermocouple wire, solving the problem of preparing high-purity platinum-molybdenum thermocouple wire.

[0032] Example 2 The preparation methods of PtMo5 thermocouple wire and PtMo1 thermocouple wire include the following steps: (1) Preparation of platinum powder a. Dissolve commercially available 99.95% platinum in aqua regia, remove nitrates, and convert to sodium salt to obtain sodium chloroplatinate solution, and adjust the Pt mass concentration to 60 g / L; b. Add sodium bromate (oxidant) and 0.3% FeCl3 solution to the above sodium chloroplatinate solution, heat the solution to 60℃ and maintain oxidation for 20 min to oxidize impurity ions including Rh, Ir and Fe to higher valence states that are more easily hydrolyzed. Then boil the solution and add NaOH solution dropwise until pH=7.5, cool it rapidly to room temperature, and immediately filter out the Na2PtCl6 solution to remove impurity elements including Pd, Rh, Ir, Au, Ag, Ni and Al. c. Add hydrochloric acid dropwise to the above solution until pH=2.5, and then further remove base metal impurities, including Cu, Mg and Fe, by passing the solution through a strongly acidic styrene-based cation exchange column; d. High-purity NH4Cl recrystallized as a precipitant was used to precipitate (NH4)2PtCl6. The precipitate was filtered and washed with 1% ammonium chloride solution. After drying, calcination and water washing to remove sodium, high-purity sponge platinum with a purity of not less than 99.999% was obtained.

[0033] (2) Mixing powder and pressing into ingots Sponge platinum and high-purity molybdenum powder (99.999% purity) were mixed at molybdenum content of 5% and 1% by mass, respectively. The mass of PtMo5 and PtMo1 was controlled at 2.1 kg. They were mixed for 60 min using a three-dimensional powder mixer and then poured into a cold isostatic pressing sleeve. Using oil as the pressure medium, the mixture was pressed into PtMo5 and PtMo1 powder alloy ingots at a pressure of 150 MPa.

[0034] (3) Vacuum suspension melting The formed alloy ingots were placed into cold crucibles and evacuated to a vacuum of 1×10⁻⁶. -3 After Pa, 0.08 MPa argon gas is introduced, and the power is increased to 100 KW to completely melt the alloy and make it tend to float in a spherical shape. The power is then reduced to 80 KW, held for 3 minutes, and then increased to 100 KW again to cast it into a φ35mm round ingot.

[0035] (4) Wrap A φ37mm×110mm box is made using a 1.0mm thick Pt sheet. The ingots are placed inside and welded sealed. A φ10mm×800mm long air pipe is led out from one side along the length and connected to a vacuum unit. A vacuum of 1×10⁻⁶ is then created. -3After Pa, the root of the trachea is welded together, and then the trachea is cut off.

[0036] (5) Hot forging and milling of surfaces The ingots obtained in step (4) are annealed in the furnace at 1350℃ for 20 minutes. The final forging temperature is controlled at 1000℃. Hot forging is carried out by air hammer. The pass processing rate is controlled at 12%. The final forging size is 15mm×15mm. Finally, a milling machine is used to mill 1.5mm thickness off each side of the bar.

[0037] (6) Cold rolling The bar stock was cold-rolled to 3mm×3mm with a pass-through rate controlled at 7%. The total processing rate between the two annealing cycles was 55%. The intermediate annealing temperature was 1200℃ for 20 minutes, and annealing was carried out in an argon-protected box. The vacuum was first evacuated to 1×10⁻⁶. -3 Pa, then argon gas is introduced to a positive pressure of 0.04 MPa, and the cold-rolled bar is alkali boiled for 20 minutes and acid boiled for 20 minutes.

[0038] (7) Cold drawing The cold drawing rate of the rolled bar was controlled at 15%, and the total processing rate between the two annealings was 75%. The intermediate annealing temperature was 1200℃ and the time was 15min. Argon gas was used for protection. The annealing method was the same as step (6). The finished wire was boiled in alkali for 20min and acid for 20min, and then rinsed with deionized water to obtain PtMo5 thermocouple wire and PtMo1 thermocouple wire.

[0039] The argon-protected annealing method in steps (6) and (7) is as follows: A box is made of pure Pt sheet, with an inlet pipe and an exhaust pipe leading out from both sides. The inlet pipe is connected to an argon cylinder, and the exhaust pipe is connected to a vacuum unit. A corundum vessel is placed inside the box, and the annealing material is placed inside before the box is sealed by welding. The vacuum is then evacuated to 1×10⁻⁶. -3 After Pa, the vacuum was turned off and argon gas was introduced to a positive pressure of 0.04 MPa. Then the entire box was put into the furnace for annealing, and the material was cold-in and cold-out, with argon gas protection throughout the process.

[0040] Performance testing: The contents of trace impurity elements in the PtMo5 thermocouple wire, as determined by ICP analysis, are shown in Table 3.

[0041] Table 3. Content of trace impurity elements in PtMo5 thermocouple wires in Example 2 The contents of trace impurity elements in the PtMo1 thermocouple wire, as determined by ICP analysis, are shown in Table 4.

[0042] Table 4. Content of trace impurity elements in PtMo1 thermocouple wires in Example 2 As can be seen from Tables 3 and 4, the purity of both PtMo5 thermocouple wire and PtMo1 thermocouple wire is >99.98%; the measured Mo content in PtMo5 thermocouple wire is 4.997%, and the measured Mo content in PtMo1 thermocouple wire is 0.998%, with the change in Mo content being <0.01%.

[0043] The prepared PtMo5-PtMo1 thermocouple (positive electrode: PtMo5 thermocouple wire; negative electrode: PtMo1 thermocouple wire) achieved a fast neutron (energy > 0.18 MeLV) integrated flux and a thermal neutron integrated flux of 1.5 × 10⁻⁶. 21 neutrons / cm 2 After irradiation, the thermoelectric potential deviation from room temperature to 1500℃ is within 0.2%.

[0044] Conclusion: This method can obtain high-purity, accurate-content, thermoelectrically stable, radiation-resistant, and long-life PtMo5 and PtMo1 thermocouple wires, solving the problem of preparing high-purity platinum-molybdenum thermocouple wires.

[0045] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing high-purity platinum-molybdenum thermocouple wire, characterized in that, Includes the following steps: Step S1, Mixing and Pressing: High-purity sponge platinum and high-purity molybdenum powder are thoroughly mixed evenly in a three-dimensional mixing machine according to the formula ratio for ≥40 min, and then cold isostatically pressed at 100-200 MPa to obtain alloy ingots; Step S2, Vacuum Suspension Melting: The alloy ingot formed in step S1 is placed into a cold crucible, vacuumed and filled with argon gas for protection, and the melting power is increased to the maximum. The alloy is completely melted and suspended under the action of electromagnetic force, and the surface tends to be spherical. At this time, the melting temperature is 1780-2000℃. After holding at this temperature for 2-5 minutes, it is cast into an ingot. The mold is a water-cooled copper mold. Step S3, Encasing: A box similar in shape to the ingot but slightly larger in size is made from Pt sheet. The ingot is placed inside the box and sealed by welding. A gas pipe is led out from one side along the length and connected to a vacuum unit. A vacuum is evacuated to a vacuum level of 1×10⁻⁶. -2 -1×10 -3 Pa, weld the root of the trachea together, and then cut off the trachea to complete the sheath, the thickness of the sheath being 1-3mm; Step S4, hot forging and milling: The ingot obtained in step S3 is annealed in a furnace at 1350℃±50℃, hot forging is performed using a pneumatic hammer, and the final forging temperature is 1000℃±50℃. Finally, a milling machine is used to mill off 1-2mm of thickness around the bar stock. Step S5, cold rolling: The cold rolling pass processing rate is controlled at 5%-10%, and the total processing rate between the two annealings does not exceed 60%. The intermediate annealing temperature is 1200℃±50℃, and the time is 20-30min. Argon gas is used for protection during the annealing process. The cold-rolled bar is subjected to alkali boiling and acid boiling treatment. Step S6, Cold Drawing: The cold drawing rate of the rolled bar is controlled at 10%-20%, and the total processing rate between the two annealing cycles does not exceed 80%. The intermediate annealing temperature is 1200℃±50℃ for 10-20 minutes, and argon gas is used for protection during the annealing process. The finished wire is subjected to alkali boiling and acid boiling treatments to obtain high-purity platinum-molybdenum thermocouple wire with a purity ≥99.98%. The thermocouples are subjected to temperature measurement in a nuclear irradiation environment. The change in Mo content before and after processing is <0.01%, and the fast neutron integral flux and thermal neutron integral flux are both 1.5×10⁻⁶. 21 neutrons / cm 2 After irradiation, the thermoelectric potential deviation from room temperature to 1500°C is within 0.5%, and the energy of the fast neutron is >0.18 MeV; The purity of the high-purity platinum sponge mentioned in step S1 is not less than 99.999%; the purity of the high-purity molybdenum powder is not less than 99.999%. In step S2, the vacuum level is evacuated to 1×10⁻⁶. -2 -1×10 -3 Pa, the pressure of the argon gas is 0.02-0.08MPa, the melting power is 80-120KW, and the water-cooled copper mold is a segmented cylindrical mold; The argon-protected annealing method described in steps S5 and S6 is as follows: A box is made of pure Pt sheet, with an inlet pipe and an exhaust pipe leading out from each side. The inlet pipe is connected to an argon cylinder, and the exhaust pipe is connected to a vacuum unit. A corundum vessel is placed inside the box, and the annealing material is placed inside before the box is sealed by welding. A vacuum of 1×10⁻⁶ is then applied. -2 -1×10 -3 After Pa, the vacuum is turned off and argon gas is introduced to a positive pressure of 0.02-0.04 MPa. Then the entire box is put into the furnace for annealing, and the material is cold-in and cold-out, with argon gas protection throughout the process.

2. The method for preparing high-purity platinum-molybdenum thermocouple wire according to claim 1, characterized in that, The method for preparing the high-purity sponge platinum includes the following steps: (1) Crude platinum is dissolved in aqua regia, nitrate is removed and sodium salt is converted to obtain sodium chloroplatinate solution; (2) The trace impurity elements, including Pd, Rh, Ir, Au, Ag, Ni and Al, in the sodium chloroplatinate solution are removed by the oxidative carrier hydrolysis method; (3) Adjust the pH of the solution to 2-5 and perform cation exchange to further remove base metal impurities, including Cu, Mg and Fe, from the sodium chloroplatinate solution. (4) Platinum in the sodium chloroplatinate solution is precipitated as (NH4)2PtCl6 by NH4Cl precipitation method. After filtration and washing with 0.5%-5% ammonium chloride solution, high-purity sponge platinum is obtained by drying, calcining and washing with water to remove sodium.

3. The method for preparing high-purity platinum-molybdenum thermocouple wire according to claim 2, characterized in that, The oxidative carrier hydrolysis method described in step (2) includes the following steps: using one or more combinations of sodium bromate, chlorine and oxygen as oxidants, adding FeCl3 solution to sodium chloroplatinate solution as a carrier, heating to 50-80℃ for 10-30 min, then heating to above 90℃, adjusting the pH of the solution to 7-10, maintaining for 1-5 min after hydrolysis, rapidly cooling and filtering to obtain a pure platinum solution.

4. The method for preparing high-purity platinum-molybdenum thermocouple wire according to claim 2, characterized in that, The NH4Cl platinum precipitation method described in step (4) can be performed using one of the following methods: a. Directly add high-purity NH4Cl, with a purity > 99.8%; b. Acidify the solution to pH < 2 and then introduce ammonia gas.

5. The method for preparing high-purity platinum-molybdenum thermocouple wire according to claim 1, characterized in that, In step S4, the hot forging annealing time is 10-30 min, the pass processing rate is controlled at 10-20%, and the final forging size is 14 mm × 14 mm - 16 mm × 16 mm.

6. A high-purity platinum-molybdenum thermocouple wire, characterized in that, It is prepared by the preparation method according to any one of claims 1-5.

7. The application of the high-purity platinum-molybdenum thermocouple wire according to claim 6, characterized in that, The high-purity platinum-molybdenum thermocouple wire is used for temperature measurement in nuclear irradiation environments.

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