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

Abstract

The invention belongs to the technical field of metal material preparation, and particularly relates to a 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) purifying crude platinum step by step to obtain high-purity sponge platinum with the purity not lower than 99.999%; (2) mixing the high-purity platinum powder and the high-purity molybdenum powder according to a formula proportion, and performing cold isostatic pressing to obtain an alloy ingot; (3) the alloy ingot is subjected to vacuum suspension smelting, gas and non-metallic inclusions are removed, and a high-purity, uniform and compact platinum-molybdenum alloy cast ingot is obtained; (4) carrying out sheathing, hot forging and surface milling on the cast ingot to obtain a thermo wire bar; and (5) the bar is subjected to cold rolling, cold drawing and argon shield annealing, and the high-purity platinum-molybdenum thermocouple wire is prepared. The platinum-molybdenum thermocouple wire prepared by the method has the characteristics of high purity, accurate content, stable thermoelectric force, irradiation resistance, long service life and the like, and can meet the performance requirement of accurate temperature measurement in a core irradiation environment in the nuclear power engineering field.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material preparation, and specifically relates to a high-purity platinum-molybdenum thermocouple wire and a preparation method and application thereof. Background Art

[0002] The effective operation of nuclear reactors depends largely on the accuracy of temperature measurement of each component. The presence of radioactive radiation makes it difficult to measure the temperature in nuclear reactors.

[0003] In nuclear reactors, the measurement of temperature below 1000℃ is usually done well with nickel-chromium-nickel-aluminum thermocouples. However, for high temperature measurement above 1000℃, platinum-rhodium thermocouples or tungsten-rhenium thermocouples are often used. Since rhodium, tungsten and rhenium have large thermal neutron capture surfaces, they can easily capture neutrons and transform into other elements, thus changing the composition of the thermocouple material and causing changes in the thermoelectric properties. Calculations show that when the thermal neutron flux is 1×10 14 Neutrons / cm 2 · seconds, 20% of rhodium is converted into palladium in just 6 months; 27% of tungsten is converted into 24% osmium and 3% rhenium in 20 years; and 91% of rhenium is converted into osmium in 10 years.

[0004] In addition to having a small thermal neutron capture surface, platinum and molybdenum can form a solid solution, have good processing properties, and are relatively stable under nuclear irradiation. The thermoelectric characteristics of platinum-molybdenum thermocouples are basically linear, and the thermoelectric potential and sensitivity are very high, which is suitable for temperature measurement in a nuclear irradiation environment.

[0005] At present, platinum-molybdenum thermocouple wires are mainly imported and expensive, and no domestic manufacturer can produce them. The platinum-molybdenum thermocouple wires made by conventional methods have low purity, poor stability, and short service life. The molybdenum content is prone to change during processing, and the thermoelectric potential cannot be well controlled. The existing technology cannot obtain high-quality platinum-molybdenum thermocouple wires for temperature measurement in nuclear irradiation environments. Summary of the invention

[0006] The main purpose of the present invention is to provide a high-purity platinum-molybdenum thermocouple wire and its preparation method and application. The platinum-molybdenum thermocouple wire prepared by the preparation method of the present invention has the characteristics of high purity, accurate content, stable thermoelectric potential, radiation resistance, long life, etc., and can meet the performance requirements of accurate temperature measurement in the nuclear irradiation environment in the field of nuclear power engineering.

[0007] In order to achieve the above technical objectives, the technical solution adopted by the embodiment of the present invention is:

[0008] In a first aspect, an embodiment of the present invention provides a method for preparing a high-purity platinum-molybdenum thermocouple wire, comprising the following steps:

[0009] Step S1, mixing powders and pressing ingots: high-purity sponge platinum and high-purity molybdenum powder are fully mixed in accordance with the formula ratio by a three-dimensional powder mixer for ≥40 min, and then cold isostatically pressed at 100-200 MPa to obtain an alloy ingot;

[0010] Step S2, vacuum suspension melting: the alloy ingot formed in step S1 is placed in a cold crucible, evacuated and filled with argon gas for protection, the melting power is increased to the melting power, the alloy is completely melted, and under the action of electromagnetic force, the melt is suspended and the surface tends to be spherical. At this time, the melting temperature is 1780-2000°C, and after keeping warm for 2-5 minutes, it is cast into an ingot, and the casting mold is a water-cooled copper mold;

[0011] Step S3, encapsulation: a box similar in shape to the ingot and slightly larger in size is made with a Pt sheet, the ingot is placed in the box and welded to seal, an air pipe is led out from one side in the length direction to connect to the vacuum unit, and the vacuum is evacuated to a vacuum degree of 1×10 -2 -1×10 -3 Pa, weld the root of the trachea, and then cut off the trachea to complete the sheath, the thickness of the sheath is 1-3mm;

[0012] Step S4, hot forging and surface milling: the ingot obtained in step S3 is put into a furnace for annealing at 1350°C±50°C, hot forging is performed by a pneumatic hammer, and the final forging temperature is 1000°C±50°C. Finally, a milling machine is used to mill off the jacket around the bar material to a thickness of 1-2 mm;

[0013] Step S5, cold rolling: the cold rolling pass processing rate is controlled at 5%-10%, the total processing rate between two annealings does not exceed 60%, the intermediate annealing temperature is 1200℃±50℃, the time is 20-30min, the annealing process is protected by argon, and the cold-rolled bar is subjected to alkali boiling and acid boiling treatment;

[0014] Step S6, cold drawing: the processing rate of the cold drawing pass of the rolled bar is controlled at 10%-20%, the total processing rate between the two annealings does not exceed 80%, the intermediate annealing temperature is 1200℃±50℃, the time is 10-20min, the annealing process is protected by argon, the finished wire is alkali boiled and acid boiled to obtain high-purity platinum-molybdenum thermocouple wire with a purity of >99.98%.

[0015] 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%.

[0016] Furthermore, the method for preparing high-purity sponge platinum comprises the following steps:

[0017] (1) Crude platinum is dissolved in aqua regia, nitrate is removed and converted into sodium salt to obtain sodium chloroplatinate solution;

[0018] (2) removing trace impurity elements including Pd, Rh, Ir, Au, Ag, Ni and Al from the sodium chloroplatinate solution by an oxidative carrier hydrolysis method;

[0019] (3) adjusting the pH of the solution to 2-5, and performing cationic resin exchange to further remove base metal impurities including Cu, Mg and Fe in the sodium chloroplatinate solution;

[0020] (4) using NH4Cl platinum precipitation method to precipitate the platinum in the sodium chloroplatinate solution in the form of (NH4)2PtCl6, filtering and washing with 0.5%-5% ammonium chloride solution, drying, calcining, and washing with water to remove sodium, to obtain high-purity sponge platinum.

[0021] Furthermore, the oxidation carrier hydrolysis method described in step (2) comprises the following steps: using a combination of one or more of sodium bromate, chlorine and oxygen as an oxidant, adding FeCl3 solution as a carrier to the sodium chloroplatinate solution, heating to 50-80°C for oxidation for 10-30 minutes, then heating to above 90°C, adjusting the pH of the solution to 7-10, maintaining the solution for 1-5 minutes after hydrolysis, rapidly cooling and filtering to obtain a pure platinum solution.

[0022] Furthermore, the NH4Cl platinum precipitation method in step (4) adopts one of the following methods:

[0023] a. Directly add high-purity NH4Cl, purity> 99.8%;

[0024] b. Acidify the solution to pH < 2 and then introduce ammonia gas.

[0025] Furthermore, in step S2, the vacuum is evacuated to a vacuum degree of 1×10 -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 split cylindrical mold.

[0026] 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.

[0027] Furthermore, the argon protection annealing method in steps S5 and S6 is as follows: a box is made of pure Pt sheet, an air inlet pipe and an air exhaust pipe are led out from both sides, the air inlet pipe is connected to the argon gas bottle, and the air exhaust pipe is connected to the vacuum unit; a corundum vessel is placed in the box, the annealing material is placed in it, and then the box is sealed by welding; vacuuming to 1×10 -2 -1×10 -3After reaching Pa, the vacuum is turned off and argon is filled in to a positive pressure of 0.02-0.04MPa. Then the whole box is put into the furnace for annealing, and the materials are cooled in and out cold, with argon protection throughout the whole process.

[0028] In a second aspect, an embodiment of the present invention provides a high-purity platinum-molybdenum thermocouple wire, which is prepared by the preparation method described in the first aspect.

[0029] In a third aspect, an embodiment of the present invention provides an application of the high-purity platinum-molybdenum thermocouple wire described in the second aspect, wherein the high-purity platinum-molybdenum thermocouple wire is applied to temperature measurement in a nuclear irradiation environment.

[0030] The technical solution provided by the embodiment of the present invention has the following beneficial effects:

[0031] (1) The present invention adopts a distributed purification method when preparing high-purity sponge platinum, first effectively removing impurity elements such as Pd, Rh, Ir, Au, Ag, Ni, Al, etc., and then further removing the remaining base metal impurities such as Cu, Mg, Fe, etc., to ensure that the platinum purity in the obtained platinum sponge is ≥99.999%, which can meet the performance requirements of accurate temperature measurement in the nuclear irradiation environment in the field of nuclear power engineering.

[0032] (2) The present invention adopts a vacuum suspension smelting process, which can effectively remove gas and non-metallic inclusions. At the same time, because the melt is suspended under the action of electromagnetic force during the smelting process and does not contact the crucible, the crucible material is prevented from entering the melt at high temperature. This is different from the conventional smelting process, in which electromagnetic stirring of the melt flushes the crucible and introduces refractory inclusions. This method can completely eliminate the introduction of crucible material inclusions. In addition, even if there is a very small amount of refractory material in the raw materials, it cannot be suspended in the electromagnetic field because no induced current can be generated. It is concentrated at the bottom of the melt and floats on the ingot riser during casting, making it easy to remove. This method can avoid the introduction of foreign impurities to a great extent, thereby playing a role in refining and purification. In addition, the smelting vacuum degree is 1×10 -2 -1×10 -3 Pa can not only remove the gas adsorbed in the powder, but also prevent the oxidation of molybdenum during the smelting process; the argon gas during the smelting process can prevent splashing, reduce the vacuum volatilization of the melt, and reduce smelting losses.

[0033] (3) The present invention adopts a jacket hot forging method, which can not only solve the brittle cracking problem caused by molybdenum oxidation at the grain boundary during annealing, but also effectively solve the oxidation and volatilization of molybdenum during hot forging. After the hot forging is completed, the surface jacket is milled off to obtain a bar with a molybdenum content consistent with the feed formula, thereby achieving precise control of the molybdenum content during hot processing and ensuring the accuracy of the thermoelectric potential.

[0034] (4) The argon protection annealing device and annealing method designed by the present invention are connected to a vacuum unit through a vacuum pipe, and the vacuum is evacuated to 1×10 -2 -1×10-3 Pa can effectively prevent the thermocouple wire from oxidizing and volatilizing molybdenum during the annealing process; filling argon gas to positive pressure can solve the problem of molybdenum volatilization when heated in a vacuum, and prevent external air from entering the device when the device leaks, causing molybdenum oxidation. Different from conventional atmosphere protection annealing furnaces, because the furnace body cannot be completely sealed, not only does it consume a lot of gas, but it also cannot completely isolate oxygen, and the effect is poor.

[0035] (5) The high-purity platinum-molybdenum thermocouple wire prepared by the preparation method of the present invention has a purity of ≥99.98%. The thermocouple prepared by the method is used for temperature measurement in a nuclear irradiation environment. The change in Mo content before and after processing is less than 0.01%. The fast neutron (energy>0.18 MeV) integrated flux and thermal neutron integrated flux are both 1.5×10 21 Neutron / 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 DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] Example 1

[0038] The preparation method of PtMo5 thermocouple wire and PtMo0.1 thermocouple wire comprises the following steps:

[0039] (1) Preparation of platinum powder

[0040] a. Take commercially available platinum with a purity of 99.95% and dissolve it in aqua regia, drive out nitrate, and convert it into sodium salt to obtain sodium chloroplatinate solution, and adjust the Pt mass concentration to 60g / L;

[0041] b. Add sodium bromate (oxidant) and 0.3% FeCl3 solution by mass to the above sodium chloroplatinate solution, heat the solution to 60°C and keep oxidizing for 20 minutes to oxidize impurity ions including Rh, Ir and Fe into a high-valent state that is more easily hydrolyzed, then boil the solution and simultaneously add NaOH solution dropwise until pH = 7.5, quickly cool to room temperature, immediately filter out Na2PtCl6 solution, and remove impurity elements including Pd, Rh, Ir, Au, Ag, Ni and Al;

[0042] c. Hydrochloric acid was added dropwise to the solution until pH = 2.5, and then the base metal impurities including Cu, Mg and Fe were further removed through a strong acid styrene cationic resin exchange column;

[0043] d. Using high-purity NH4Cl with a purity of >99.8% as a precipitant to precipitate (NH4)2PtCl6, filtering and washing with a 1% ammonium chloride solution, drying, calcining, and washing with water to remove sodium, a high-purity sponge platinum with a purity of not less than 99.999% was obtained;

[0044] (2) Mixed powder tablet pressing

[0045] Sponge platinum and high-purity molybdenum powder (purity 99.999%) were respectively prepared according to the molybdenum content of 5% and 0.1% by mass fraction, and the mass of PtMo5 and PtMo0.1 were both controlled at 2.1kg. They were mixed by a three-dimensional powder mixer for 60 minutes, and then poured into a cold isostatic pressing package, and pressed into powder alloy ingots of PtMo5 and PtMo0.1 with oil as the pressure medium and a pressure of 150MPa;

[0046] (3) Vacuum suspension melting

[0047] The two alloy ingots of PtMo5 and PtMo0.1 were placed in a cold crucible and evacuated to 1×10 -3 After the temperature reaches 0.08MPa, argon gas is filled in, and the power is increased to 100KW, so that the alloy is completely melted and tends to be suspended in a spherical shape. The power is then reduced to 80KW, kept warm for 3 minutes, and then increased to 100KW, and cast into φ35mm round ingots respectively;

[0048] (4)Packaging

[0049] A φ37mm×110mm box was made with a 1.0mm thick Pt sheet. The ingots were placed in the box and sealed by welding. A φ10mm×800mm long gas pipe was led out from one side of the length direction to connect to the vacuum unit. The vacuum was evacuated to 1×10 -3 After Pa, weld the root of the trachea and then cut off the trachea;

[0050] (5) Hot forging and milling surface

[0051] The ingots obtained in step (4) were respectively put into the furnace for annealing at 1350°C for 20 min, the final forging temperature was controlled at 1000°C, and the hot forging was performed by a pneumatic hammer. The pass processing rate was controlled at 12%, and the final forging size was 15mm×15mm. Finally, a milling machine was used to mill off 1.5mm of thickness on all sides of the bar.

[0052] (6) Cold rolling

[0053] The bar was cold rolled to 3 mm × 3 mm according to the pass processing rate of 7%, and the total processing rate between the two annealings was 55%. The intermediate annealing temperature was 1200 ° C, the time was 20 min, and the annealing was carried out in an argon protection box. The vacuum was first evacuated to 1 × 10 -3Pa, then filled with argon to a positive pressure of 0.04MPa, the cold-rolled bar was boiled in alkali for 20min and in acid for 20min;

[0054] Sodium hydroxide solution is used during alkali boiling, and the ratio of sodium hydroxide to deionized water in the solution is 100g / 1000ml;

[0055] The hydrochloric acid solution used in acid boiling is prepared by mixing 36% analytical pure hydrochloric acid and deionized water in a volume ratio of 1:1.

[0056] (7) Cold drawing

[0057] The processing rate of the cold drawing pass of the rolled bar is controlled at 15%, the total processing rate between the two annealings is 75%, the intermediate annealing temperature is 1200°C, the time is 15 min, argon gas is used for protection, and the annealing method is the same as step (6). The finished wire is alkali boiled for 20 min, acid boiled for 20 min, and rinsed with deionized water to obtain PtMo5 thermocouple wire and PtMo0.1 thermocouple wire.

[0058] The argon protection annealing method in steps (6) and (7) is as follows: a box is made of pure Pt sheet, an air inlet pipe and an air exhaust pipe are led out from both sides, the air inlet pipe is connected to the argon gas bottle, and the air exhaust pipe is connected to the vacuum unit; a corundum container is placed in the box, the annealing material is placed in it, and then the box is sealed by welding; vacuum is drawn to 1×10 -3 After reaching Pa, the vacuum is turned off and argon is filled in to a positive pressure of 0.04MPa. Then the whole box is put into the furnace for annealing, and the materials are cooled in and out cold, with argon protection in the whole process.

[0059] Performance testing:

[0060] The contents of trace impurity elements in the PtMo5 thermocouple wire are shown in Table 1 after ICP testing.

[0061] Table 1 Content of trace impurity elements in PtMo5 thermocouple wire in Example 1

[0062] element content% element content% element content% Ag ＜0.0005 Cu 0.0007 Pd ＜0.0005 Al ＜0.0005 Fe 0.0008 R ＜0.0005 Au ＜0.0005 Ir ＜0.0005 Ru 0.0007 Bi ＜0.0005 Mg ＜0.0005 Si ＜0.0005 Cd ＜0.0005 Mn ＜0.0005 Sn ＜0.0005 Co ＜0.0005 Ni ＜0.0005 Ti ＜0.0005 Cr ＜0.0005 Pb ＜0.0005 Zn ＜0.0005

[0063] The contents of trace impurity elements in the PtMo0.1 thermocouple wire are shown in Table 2 after ICP testing.

[0064] Table 2 Content of trace impurity elements in PtMo0.1 thermocouple wire in Example 1

[0065] element content% element content% element content% Ag ＜0.0005 Cu 0.0007 Pd ＜0.0005 Al ＜0.0005 Fe 0.0007 R ＜0.0005 Au ＜0.0005 Ir ＜0.0005 Ru 0.0006 Bi ＜0.0005 Mg ＜0.0005 Si ＜0.0005 Cd ＜0.0005 Mn ＜0.0005 Sn ＜0.0005 Co ＜0.0005 Ni ＜0.0005 Ti ＜0.0005 Cr ＜0.0005 Pb ＜0.0005 Zn ＜0.0005

[0066] It can be seen from Table 1 and Table 2 that the purity of PtMo5 thermocouple wire and PtMo0.1 thermocouple wire is both greater than 99.98%; the Mo content in PtMo5 thermocouple wire is actually measured to be 4.996%, and the Mo content in PtMo0.1 thermocouple wire is actually measured to be 0.098%, and the change of Mo content is both less than 0.01%.

[0067] The prepared PtMo5-PtMo0.1 thermocouple (the positive electrode is the PtMo5 thermocouple wire, the negative electrode is the PtMo0.1 thermocouple wire) was subjected to fast neutron (energy> 0.18 MeV) integrated flux and thermal neutron integrated flux of 1.5×10 21 Neutron / cm 2 After irradiation, the thermoelectric potential deviation from room temperature to 1500°C is 0.3%.

[0068] Conclusion: The above preparation method can obtain PtMo5 thermocouple wire and PtMo0.1 thermocouple wire with high purity, accurate content, stable thermoelectric potential, radiation resistance and long life, which solves the preparation problem of high-purity platinum-molybdenum thermocouple wire.

[0069] Example 2

[0070] The preparation method of PtMo5 thermocouple wire and PtMo1 thermocouple wire comprises the following steps:

[0071] (1) Preparation of platinum powder

[0072] a. Take commercially available 99.95% platinum and dissolve it in aqua regia, drive out nitrate, and convert it into sodium salt to obtain sodium chloroplatinate solution, and adjust the Pt mass concentration to 60g / L;

[0073] b. Add sodium bromate (oxidant) and 0.3% FeCl3 solution by mass to the above sodium chloroplatinate solution, heat the solution to 60°C and keep oxidizing for 20 minutes to oxidize the impurity ions including Rh, Ir and Fe into a high-valent state that is more easily hydrolyzed, then boil the solution and simultaneously add NaOH solution dropwise until pH = 7.5, quickly cool to room temperature, immediately filter out Na2PtCl6 solution, and remove impurity elements including Pd, Rh, Ir, Au, Ag, Ni and Al;

[0074] c. hydrochloric acid was added dropwise to the above solution until pH = 2.5, and then the base metal impurities including Cu, Mg and Fe were further removed by a strong acid styrene cationic resin exchange column;

[0075] d. Use recrystallized high-purity NH4Cl as a precipitant to precipitate (NH4)2PtCl6, filter and wash with 1% ammonium chloride solution, and then dry, calcine, and wash with water to remove sodium to obtain a high-purity sponge platinum with a purity of not less than 99.999%.

[0076] (2) Mixed powder tablet pressing

[0077] Sponge platinum and high-purity molybdenum powder (purity 99.999%) are formulated according to the molybdenum content of 5% and 1% by mass, respectively. The masses of PtMo5 and PtMo1 are controlled at 2.1kg. They are mixed in a three-dimensional powder mixer for 60 minutes, and then poured into a cold isostatic pressing package. Oil is used as the pressure medium and the pressure is 150MPa to press them into PtMo5 and PtMo1 powder alloy ingots respectively.

[0078] (3) Vacuum suspension melting

[0079] The formed alloy ingots were placed in cold crucibles and vacuumed to 1×10 -3 After 0.08MPa argon gas is filled in, the power is increased to 100KW, so that the alloy is completely melted and tends to be suspended in a spherical shape. The power is then reduced to 80KW, kept warm for 3 minutes and then increased to 100KW to cast into a φ35mm round ingot.

[0080] (4)Packaging

[0081] A φ37mm×110mm box was made with a 1.0mm thick Pt sheet. The ingots were placed in the box and sealed by welding. A φ10mm×800mm long gas pipe was led out from one side of the length direction to connect to the vacuum unit. The vacuum was evacuated to 1×10 -3 After Pa, weld the root of the trachea and then cut off the trachea.

[0082] (5) Hot forging and milling surface

[0083] The ingots obtained in step (4) were respectively put into the furnace for annealing at 1350°C for 20 min, the final forging temperature was controlled at 1000°C, and the hot forging was performed by a pneumatic hammer. The pass processing rate was controlled at 12%, and the final forging size was 15mm×15mm. Finally, a milling machine was used to mill off 1.5mm thickness on all sides of the bar.

[0084] (6) Cold rolling

[0085] The bar was cold rolled to 3mm×3mm with the processing rate of 7% per pass. The total processing rate between the two annealings was 55%. The intermediate annealing temperature was 1200℃ for 20min. The annealing was performed in an argon protection box. The vacuum was first drawn to 1×10 -3 Pa, and then filled with argon to a positive pressure of 0.04MPa. The cold-rolled rods were alkali boiled for 20min and acid boiled for 20min.

[0086] (7) Cold drawing

[0087] The processing rate of the cold drawing pass of the rolled bar is controlled at 15%, the total processing rate between the two annealings is 75%, the intermediate annealing temperature is 1200°C, the time is 15 min, argon gas is used for protection, and the annealing method is the same as step (6). The finished wire is alkali boiled for 20 min, acid boiled for 20 min, and rinsed with deionized water to obtain PtMo5 thermocouple wire and PtMo1 thermocouple wire.

[0088] The argon protection annealing method in steps (6) and (7) is as follows: a box is made of pure Pt sheet, an air inlet pipe and an air exhaust pipe are led out from both sides, the air inlet pipe is connected to the argon gas bottle, and the air exhaust pipe is connected to the vacuum unit; a corundum container is placed in the box, the annealing material is placed in it, and then the box is sealed by welding; vacuum is drawn to 1×10 -3 After reaching Pa, the vacuum is turned off and argon is filled in to a positive pressure of 0.04MPa. Then the whole box is put into the furnace for annealing, and the materials are cooled in and out cold, with argon protection in the whole process.

[0089] Performance testing:

[0090] The contents of trace impurity elements in the PtMo5 thermocouple wire are shown in Table 3 after ICP testing.

[0091] Table 3 Content of trace impurity elements in PtMo5 thermocouple wire of Example 2

[0092] element content% element content% element content% Ag ＜0.0005 Cu 0.0007 Pd ＜0.0005 Al 0.0005 Fe 0.0009 R ＜0.0005 Au ＜0.0005 Ir ＜0.0005 Ru 0.0006 Bi ＜0.0005 Mg ＜0.0005 Si ＜0.0005 Cd ＜0.0005 Mn ＜0.0005 Sn ＜0.0005 Co ＜0.0005 Ni ＜0.0005 Ti ＜0.0005 Cr ＜0.0005 Pb ＜0.0005 Zn ＜0.0005

[0093] The contents of trace impurity elements in the PtMo1 thermocouple wire are shown in Table 4 after ICP testing.

[0094] Table 4 Content of trace impurity elements in PtMo1 thermocouple wire of Example 2

[0095] element content% element content% element content% Ag ＜0.0005 Cu 0.0005 Pd ＜0.0005 Al 0.0006 Fe 0.0007 R ＜0.0005 Au ＜0.0005 Ir ＜0.0005 Ru 0.0005 Bi ＜0.0005 Mg ＜0.0005 Si ＜0.0005 Cd ＜0.0005 Mn ＜0.0005 Sn ＜0.0005 Co ＜0.0005 Ni ＜0.0005 Ti ＜0.0005 Cr ＜0.0005 Pb ＜0.0005 Zn ＜0.0005

[0096] It can be seen from Table 3 and Table 4 that the purity of PtMo5 thermocouple wire and PtMo1 thermocouple wire are both greater than 99.98%; the Mo content in PtMo5 thermocouple wire is actually measured to be 4.997%, and the Mo content in PtMo1 thermocouple wire is actually measured to be 0.998%, and the change of Mo content is less than 0.01%.

[0097] The prepared PtMo5-PtMo1 thermocouple (the positive electrode is the PtMo5 thermocouple wire, the negative electrode is the PtMo1 thermocouple wire) was subjected to fast neutron (energy> 0.18 MeV) integrated flux and thermal neutron integrated flux of 1.5×10 21 Neutron / cm 2 After irradiation, the thermoelectric potential deviation from room temperature to 1500°C is 0.2%.

[0098] Conclusion: This method can be used to obtain PtMo5 thermocouple wire and PtMo1 thermocouple wire with high purity, accurate content, stable thermoelectric potential, radiation resistance and long life, which solves the problem of preparation of high-purity platinum-molybdenum thermocouple wire.

[0099] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a high-purity platinum-molybdenum thermocouple wire, characterized in that: The following steps are involved: Step S1, mixing powders and pressing ingots: high-purity sponge platinum and high-purity molybdenum powder are fully mixed in accordance with the formula ratio by a three-dimensional powder mixer for ≥40 min, and then cold isostatically pressed at 100-200 MPa to obtain an alloy ingot; Step S2, vacuum suspension melting: the alloy ingot formed in step S1 is placed in a cold crucible, evacuated and filled with argon gas for protection, the melting power is increased to the melting power, the alloy is completely melted, and under the action of electromagnetic force, the melt is suspended and the surface tends to be spherical. At this time, the melting temperature is 1780-2000°C, and after keeping warm for 2-5 minutes, it is cast into an ingot, and the casting mold is a water-cooled copper mold; Step S3, encapsulation: a box similar in shape to the ingot and slightly larger in size is made with a Pt sheet, the ingot is placed in the box and welded to seal, an air pipe is led out from one side in the length direction to connect to the vacuum unit, and the vacuum is evacuated to a vacuum degree of 1×10 -2 -1×10 -3 Pa, weld the root of the trachea, and then cut off the trachea to complete the sheath, the thickness of the sheath is 1-3mm; Step S4, hot forging and surface milling: the ingot obtained in step S3 is put into a furnace for annealing at 1350°C±50°C, hot forging is performed by a pneumatic hammer, and the final forging temperature is 1000°C±50°C. Finally, a milling machine is used to mill off the jacket around the bar material to a thickness of 1-2 mm; Step S5, cold rolling: the cold rolling pass processing rate is controlled at 5%-10%, the total processing rate between two annealings does not exceed 60%, the intermediate annealing temperature is 1200℃±50℃, the time is 20-30min, the annealing process is protected by argon gas, and the cold-rolled bar is subjected to alkali boiling and acid boiling treatment; Step S6, cold drawing: the processing rate of the cold drawing pass of the rolled bar is controlled at 10%-20%, the total processing rate between the two annealings does not exceed 80%, the intermediate annealing temperature is 1200℃±50℃, the time is 10-20min, the annealing process is protected by argon, the finished wire is alkali boiled and acid boiled to obtain high-purity platinum-molybdenum thermocouple wire with a purity of >99.98%.

2. The method for preparing the high-purity platinum-molybdenum thermocouple wire according to claim 1, characterized in that: 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%.

3. The method for preparing the high-purity platinum-molybdenum thermocouple wire according to claim 1, characterized in that: The preparation method of the high-purity sponge platinum comprises the following steps: (1) Crude platinum is dissolved in aqua regia, nitrate is removed and converted into sodium salt to obtain sodium chloroplatinate solution; (2) removing trace impurity elements including Pd, Rh, Ir, Au, Ag, Ni and Al from the sodium chloroplatinate solution by an oxidative carrier hydrolysis method; (3) Adjusting the pH of the solution to 2-5, performing cationic resin exchange to further remove base metal impurities including Cu, Mg and Fe in the sodium chloroplatinate solution; (4) The platinum in the sodium chloroplatinate solution is precipitated in the form of (NH4)2PtCl6 by the NH4Cl platinum precipitation method, filtered and washed with 0.5%-5% ammonium chloride solution, and then dried, calcined, and washed with water to remove sodium to obtain high-purity sponge platinum.

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

5. The method for preparing high-purity platinum-molybdenum thermocouple wire according to claim 3, characterized in that: The NH4Cl platinum precipitation method in step (4) adopts one of the following methods: a. Directly add high-purity NH4Cl, purity> 99.8%; b. Acidify the solution to pH < 2 and then introduce ammonia gas.

6. The method for preparing high-purity platinum-molybdenum thermocouple wire according to claim 1, characterized in that: In step S2, the vacuum is evacuated to a vacuum degree of 1×10 -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 split cylindrical mold.

7. The method for preparing high-purity platinum-molybdenum thermocouple wire according to claim 1, characterized in that: The hot forging annealing time in step S4 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.

8. The method for preparing high-purity platinum-molybdenum thermocouple wire according to claim 1, characterized in that: The argon protection annealing method in steps S5 and S6 is as follows: a box is made of pure Pt sheet, an air inlet pipe and an air exhaust pipe are led out from both sides, the air inlet pipe is connected to the argon gas bottle, and the air exhaust pipe is connected to the vacuum unit; a corundum container is placed in the box, the annealing material is placed in it, and then the box is sealed by welding; vacuum is drawn to 1×10 -2 -1×10 -3 After reaching Pa, the vacuum is turned off and argon is filled in to a positive pressure of 0.02-0.04MPa. Then the whole box is put into the furnace for annealing, and the materials are cooled in and out cold, with argon protection throughout the whole process.

9. A high purity platinum-molybdenum thermocouple wire, characterized in that: The method is prepared by the method according to any one of claims 1 to 8.

10. The use of the high-purity platinum-molybdenum thermocouple wire according to claim 9, characterized in that: The high-purity platinum-molybdenum thermocouple wire is used for temperature measurement in nuclear irradiation environment.