Manufacturing process of nanoscale zirconium powder for electric vacuum

Abstract

The invention relates to the technical field of metal superfine powder preparation, in particular to a manufacturing process of nanoscale zirconium powder for electric vacuum, high-purity sponge zirconium is used as a raw material, and after being crushed by zirconium oxide equipment, the high-purity sponge zirconium is subjected to wet ball milling, freeze drying, low-temperature vacuum deoxidation and two-step passivation in an inert atmosphere. During wet ball milling, a potassium iodate-polyvinylpyrrolidone coating aid is added, so that iodate radicals are slowly released and generate a compact zirconium dioxide passivation film with zirconium powder, iodide ions are adsorbed, oxidation and agglomeration are inhibited, and steric hindrance of polyvinylpyrrolidone further stabilizes the particle size; the iodine element is sublimated and removed through low-temperature vacuum deoxidation treatment, polyvinylpyrrolidone is completely decomposed, the oxygen content of the zirconium powder is controlled to be 0.10-0.15 wt%, the particle size of a final product is 30-40 nm, the span is smaller than or equal to 2.0, and the oxygen content is smaller than or equal to 0.15%, and the zirconium powder manufactured through the method is narrow in particle size distribution, low in key impurity content and high in purity and is suitable for electric vacuum devices.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation process of nanometer zirconium powder for electric vacuum. BACKGROUND

[0002] As a core component in the fields of microwave communication, radar and medical imaging, the performance of an electric vacuum device depends on the maintenance of an internal ultra-high vacuum environment, and a zirconium-based getter is a key material for realizing the vacuum environment.

[0003] In a preparation process of the nanometer zirconium powder for electric vacuum, a traditional wet ball milling uses water or an organic solvent as a grinding medium, and can inhibit oxidation and the introduction of metal impurities, but zirconium particles are prone to agglomeration due to a cold welding effect in the ball milling process, leading to out-of-control particle size, and solvent residues will cause an increase in impurities of the zirconium powder, and the purity of the zirconium powder is insufficient. SUMMARY

[0004] The application aims to provide a preparation process of nanometer zirconium powder for electric vacuum, and the zirconium powder prepared by the application has narrow particle size distribution and low key impurities, and is suitable for electric vacuum devices.

[0005] To achieve the above-mentioned purpose, the application provides the following technical scheme. A preparation process of nanometer zirconium powder for electric vacuum comprises the following steps. S1: raw material preparation: selecting electric vacuum grade sponge zirconium with a total content of zirconium and hafnium being greater than or equal to 99.8%, iron being less than 50 mg / kg, oxygen being less than 300 mg / kg, and carbon being less than 30 mg / kg, crushing and sieving the particles to obtain particles with a particle size of less than or equal to 5 mm; S2: preparation of coating aid: dissolving potassium iodate in deionized water, adding polyvinylpyrrolidone to form a mixed solution, and ultrasonically treating the mixed solution to obtain a potassium iodate-polyvinylpyrrolidone coating aid, the mass ratio of polyvinylpyrrolidone to potassium iodate being 1:5-1:10; S3: wet high-energy ball milling: filling the tank with the sponge zirconium, zirconium oxide grinding balls and grinding agent at a mass ratio of 1:10:3, ball milling at 450-550 rpm under an argon gas overpressure of 0.05-0.10 MPa for 4-10 h; the grinding agent is mixed by water and ethanol at a mass ratio of 1.4:1, and the coating aid is added to make the final concentration of potassium iodate 0.2-1.0 mmol / L; S4: solid-liquid separation and washing: centrifugal separation under argon protection, and water-ethanol alternating washing for 3 times; S5: freeze-drying: drying at-50--45 DEG C and 10-15 Pa for 12-15 h; S6: low-temperature vacuum deoxidization: heat preservation at 380-420 DEG C and less than or equal to 0.001 Pa for 1-3 h, and synchronous removal of residual iodine and polyvinylpyrrolidone; S7: Inert atmosphere passivation: 24-30h in inert atmosphere, get nano zirconium powder.

[0006] Further, the process for making a nano-scale zirconium powder for electric vacuum, in step S1, the jaw crusher of zirconium oxide jaw plate is used for crushing, the crushing gap is 3-5mm, and the inert atmosphere screening device of 10 mesh is used for screening.

[0007] Further, the process for making a nano-scale zirconium powder for electric vacuum, in step S2, the concentration of potassium iodate in coating aid is 5-10mmol / L, the resistivity of deionized water is ≥18.2MΩ·cm, the molecular weight of polyvinylpyrrolidone is 10kDa, the ultrasonic parameters are 300-400W, 30-40℃, 20-30min, and the magnetic stirring of 200-300rpm is used for auxiliary dispersion during ultrasonic.

[0008] Further, the process for making a nano-scale zirconium powder for electric vacuum, in step S3, the particle size of zirconium oxide grinding ball is 5mm, the purity is ≥99.9%, the inner wall of the ball mill tank is lined with zirconium oxide coating, and the argon overpressure is maintained at 0.05-0.10MPa every 2h.

[0009] Further, the process for making a nano-scale zirconium powder for electric vacuum, in step S4, the centrifugal speed is 8000-10000rpm, the time is 10-15min, the volume of the solvent is 5-8 times of the volume of the solid particles during washing, and the stirring time is 3-5min before centrifugal separation.

[0010] Further, the process for making a nano-scale zirconium powder for electric vacuum, in step S5, the solid particles are laid flat with a thickness of 5-10mm.

[0011] Further, the process for making a nano-scale zirconium powder for electric vacuum, in step S6, the heating element of the vacuum furnace is molybdenum wire with a purity of ≥99.95%, the heating rate is 5-10℃ / min, and the vacuum degree in the furnace is maintained at ≤0.001Pa during the holding process.

[0012] Further, the process for making a nano-scale zirconium powder for electric vacuum, in step S7, the inert atmosphere passivation adopts a two-step procedure: first, replace 30min in 99.999% argon at a flow rate of 5L / min; second, reduce the flow rate to 0.5L / min, and increase the temperature from room temperature to 60℃ at a rate of 10℃ / h, maintain the constant temperature for 24h, and then naturally cool to room temperature, get nano zirconium powder with surface oxide film thickness ≤2nm.

[0013] Further, the nano-zirconium powder prepared by the process has a particle size distribution satisfying a median particle size of 30-40 nm, a particle size distribution span of ≤2.0, an oxygen content of 0.10-0.15%, and impurity contents satisfying iron <40 mg / kg, carbon <30 mg / kg, and iodine <1 mg / kg, and the fluctuation range of the above performance indexes of three continuous batches of products is <5%.

[0014] Compared with the prior art, the application has the following beneficial effects: 1. In the process for preparing the nano-zirconium powder for electric vacuum, the potassium iodate is modified by coating, so that the polyvinylpyrrolidone molecular chain is combined with the potassium iodate through hydrogen bonds, the iodate ions are slowly dissolved in the water-ethanol grinding agent to achieve slow release, and the iodate ions are oxidized and reduced with the new zirconium surface generated by the ball milling to form a dense zirconium dioxide passivation film and adsorbed iodine ions. The generation of the zirconium dioxide passivation film can isolate water and oxygen, thereby avoiding excessive oxidation. Meanwhile, the iodine ions weaken the particle agglomeration force through charge repulsion. The synergistic effect of the zirconium dioxide passivation film and the iodine ions can further reduce the introduction of oxidized impurities. The slow release of the iodate ions avoids the excessive potassium iodate in the initial stage and prevents the cold welding agglomeration caused by the insufficient potassium iodate in the later stage. Meanwhile, the polyvinylpyrrolidone molecular chain is adsorbed on the surface of the zirconium particles to assist in inhibiting agglomeration through the steric hindrance effect, and the passivation effect of the iodate ions forms a synergistic dispersion effect, so that the median particle size of the final product is stabilized at 30-40 nm, the distribution span is ≤2.0, the uniformity of the powder is improved, and the stability of the nano-zirconium powder for electric vacuum is enhanced.

[0015] 2. In the application, the low-temperature vacuum deoxidation treatment of the powder after the ball milling is performed in a vacuum environment of 380-420 DEG C and ≤0.001 Pa, so that the iodine element segregated at the grain boundaries is sublimated and removed, the polyvinylpyrrolidone is completely decomposed into volatile products, the oxygen content of the zirconium powder is accurately controlled at 0.10-0.15 wt%, the influence of impurity residues on the vacuum degree of the electric vacuum device is avoided, the high oxygen content is prevented from reducing the activity of the nano-zirconium powder, the nano-zirconium powder meets the electric vacuum grade purity requirement, and the application adaptability of the nano-zirconium powder in high-end electric vacuum devices is further improved. DETAILED DESCRIPTION

[0016] The technical solutions in the experiments of the application will be clearly and completely described below by combining the experiments of the application. Obviously, the described experiments are only part of the experiments of the application, rather than all the experiments of the application. Based on the experiments in the application, all other experiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0017] The embodiment provides a process for preparing a nano-zirconium powder for electric vacuum, which comprises the following steps in sequence: S1: raw material preparation: select electric vacuum grade sponge zirconium with total zirconium and hafnium content ≥ 99.8%, iron < 50 mg / kg, oxygen < 300 mg / kg, and carbon < 30 mg / kg, crush and sieve to obtain particles with a particle size ≤ 5 mm; S2: coating aid preparation: dissolve potassium iodate in deionized water, add polyvinylpyrrolidone to form a mixed solution, and ultrasonically treat to obtain a potassium iodate-polyvinylpyrrolidone coating aid, the mass ratio of polyvinylpyrrolidone to potassium iodate being 1:5-1:10; S3: wet high-energy ball milling: load the sponge zirconium, zirconia milling balls, and grinding agent into a tank at a mass ratio of 1:10:3, mill at 450-550 rpm under an argon gas overpressure of 0.05-0.10 MPa for 4-10 h; the grinding agent is a mixture of water and ethanol at a mass ratio of 1.4:1, and the coating aid is added to make the final concentration of potassium iodate 0.2-1.0 mmol / L; S4: solid-liquid separation and washing: centrifugal separation under argon protection, and alternating water-ethanol washing for 3 times; S5: freeze-drying: dry at -50~-45℃, 10-15 Pa for 12-15 h; S6: low-temperature vacuum deoxidation: heat preservation at 380-420℃, ≤0.001 Pa for 1-3 h, and synchronous removal of residual iodine and polyvinylpyrrolidone; S7: inert atmosphere passivation: stand for 24-30 h in an inert atmosphere to obtain nano zirconium powder.

[0018] In some embodiments, in step S1, a zirconia jaw crusher is used for crushing, the crushing gap is 3-5 mm, and a 10-mesh inert atmosphere screening device is used for screening.

[0019] In some embodiments, in step S2, the concentration of potassium iodate in the coating aid is 5-10 mmol / L, the deionized water has a resistivity ≥ 18.2 MΩ·cm, the molecular weight of polyvinylpyrrolidone is 10 kDa, the ultrasonic parameters are 300-400 W, 30-40℃, and 20-30 min, and magnetic stirring at 200-300 rpm is used for auxiliary dispersion during ultrasonic treatment.

[0020] In some embodiments, in step S3, the particle size of the zirconia milling balls is 5 mm, the purity is ≥ 99.9%, and the inner wall of the ball milling tank is lined with a zirconia coating, and the argon gas overpressure is maintained at 0.05-0.10 MPa every 2 h.

[0021] In some embodiments, in step S4, the centrifugal speed is 8000-10000 rpm and the time is 10-15 min, the volume of the solvent is 5-8 times the volume of the solid particles during washing, and the stirring time is 3-5 min before centrifugal separation.

[0022] In some embodiments, in step S5, the solid particles are laid flat with a thickness of 5-10 mm.

[0023] In some embodiments, the vacuum furnace heating element in step S6 is molybdenum wire with purity ≥ 99.95%, and the temperature rising rate is 5-10℃ / min. During the holding process, vacuum is continuously drawn to maintain the vacuum degree in the furnace ≤ 0.001 Pa.

[0024] In some embodiments, the inert atmosphere passivation in step S7 adopts a two-step procedure: first, 99.999% argon is used to replace the atmosphere at a flow rate of 5 L / min for 30 min; second, the flow rate is reduced to 0.5 L / min, and the temperature is raised from room temperature to 60℃ at a rate of 10℃ / h. After constant temperature holding for 24 h, the temperature is naturally cooled to room temperature, and the nano-zirconium powder with a surface oxide film thickness ≤ 2 nm is obtained.

[0025] In some embodiments, the nano-zirconium powder prepared by the process for preparing a nano-zirconium powder for electric vacuum has a particle size distribution satisfying a median particle size of 30-40 nm and a particle size distribution span ≤ 2.0, an oxygen content of 0.10-0.15%, and impurity contents satisfying iron < 40 mg / kg, carbon < 30 mg / kg, and iodine < 1 mg / kg. The fluctuation range of the above performance indicators of three consecutive batches of products is < 5%.

[0026] Based on the foregoing embodiments, the following groups of experiments are performed: It should be noted that the raw materials used in the following experiments are all commercially available.

[0027] Example 1

[0028] S1: Raw material preparation: 1000 g of electric vacuum grade sponge zirconium with total zirconium and hafnium content ≥ 99.8%, iron < 50 mg / kg, oxygen < 300 mg / kg, and carbon < 30 mg / kg is crushed using a zirconium oxide jaw crusher with a crushing gap of 4 mm, and is screened through a 10-mesh inert atmosphere screening device to obtain particles with a particle size ≤ 5 mm; S2: Coating aid preparation: 0.45 g of potassium iodate is dissolved in 300 mL of deionized water with a resistivity ≥ 18.2 MΩ·cm to prepare an aqueous solution with a concentration of 7 mmol / L. 0.064 g of polyvinylpyrrolidone (molecular weight 10 kDa) is added to the above solution to form a mixed solution (mass ratio of polyvinylpyrrolidone to potassium iodate 1:7). The mixed solution is placed in an ultrasonic device and ultrasonically treated at a power of 350 W and a temperature of 35℃ for 25 min. During the ultrasonic treatment, magnetic stirring is assisted for dispersion at a speed of 250 rpm to obtain a potassium iodate-polyvinylpyrrolidone coating aid. S3: Wet high-energy ball milling: 1000 g of sponge zirconium particles, 10,000 g of zirconium oxide grinding balls (particle size 5 mm, purity ≥ 99.9%), and 3,000 g of grinding agent (water 2,100 g + ethanol 900 g, mass ratio 1.4:1) were loaded into a ball mill tank with an inner wall coated with zirconium oxide. 300 mL of the above coating aid was added to the grinding agent (to make the final concentration of potassium iodate 0.6 mmol / L). After sealing the ball mill tank, argon was introduced to an overpressure of 0.08 MPa. The ball mill was operated at a speed of 450 rpm for 6 h, and the pressure was maintained at 0.075 MPa by repressurizing every 2 h. S4: Solid-liquid separation and washing: The slurry after ball milling was transferred to a centrifugal device under argon protection. Solid-liquid separation was achieved by centrifugation at a speed of 9,000 rpm for 12 min. Water-ethanol was used for alternating washing for 3 times. The volume of solvent added for each washing was 6 times the volume of solid particles (about 3,000 mL / time), and the mixture was stirred for 4 min before centrifugal separation. S5: Freeze-drying: The washed solid particles were spread on a drying plate (spreading thickness 8 mm, total mass about 980 g) and placed in a freeze-drying device. The drying was carried out at -48°C and 12 Pa for 13 h. S6: Low-temperature vacuum deoxidation: The dried powder (about 970 g) was transferred to a vacuum furnace (heating element: molybdenum wire with purity ≥ 99.95%) and heated to 400°C at a rate of 8°C / min. The vacuum degree was ≤0.001 Pa (actually controlled at 0.0008 Pa), and the vacuum was maintained at ≤0.001 Pa during the 2 h holding process. S7: Inert atmosphere passivation: Two-step procedure was used for passivation: first step, 30 min replacement in 99.999% argon at a flow rate of 5 L / min; second step, the argon flow rate was reduced to 0.5 L / min, and the temperature was increased from room temperature to 60°C at a rate of 10°C / h. After 24 h of constant temperature, the sample was naturally cooled to room temperature, and 965 g of nano-zirconium powder with a surface oxide film thickness of 1.5 nm was obtained.

[0029] Example 2

[0030] S1: Raw material preparation: 800 g of electric vacuum grade sponge zirconium with total zirconium and hafnium content ≥ 99.8%, iron < 50 mg / kg, oxygen < 300 mg / kg, and carbon < 30 mg / kg was crushed using a zirconium oxide jaw crusher with a crushing gap of 3 mm. The particles with a particle size ≤ 5 mm were obtained by screening through a 10 mesh inert atmosphere screening device. S2: Coating aid preparation: 0.17 g of potassium iodate was dissolved in 158 mL of deionized water with a resistivity of ≥18.2 MΩ·cm to prepare a 5 mmol / L aqueous solution. 0.034 g of polyvinylpyrrolidone (molecular weight 10 kDa) was added to the above solution to form a mixed solution (mass ratio of polyvinylpyrrolidone to potassium iodate 1:5). The mixed solution was placed in an ultrasonic device and ultrasonically treated at 300 W power and 30°C for 20 min. Magnetic stirring was assisted for dispersion at a speed of 200 rpm during the ultrasonic treatment. Potassium iodate-polyvinylpyrrolidone coating aid was obtained. S3: Wet high-energy ball milling: 800 g of sponge zirconium particles, 8000 g of zirconium oxide grinding balls (particle size 5 mm, purity ≥99.9%), and 2400 g of grinding agent (water 1680 g + ethanol 720 g, mass ratio 1.4:1) were loaded into a ball mill tank with an inner wall coated with zirconium oxide. 158 mL of the above coating aid was added to the grinding agent (final concentration of potassium iodate 0.3 mmol / L). After sealing the ball mill tank, argon was introduced to a pressure of 0.05 MPa. The ball mill was operated at a speed of 500 rpm for 4 h, and the pressure was maintained at 0.05 MPa by repressurizing every 2 h. S4: Solid-liquid separation and washing: The slurry after ball milling was transferred to a centrifugal device under argon protection. Solid-liquid separation was achieved by centrifugation at a speed of 8000 rpm for 10 min. Water-ethanol was used for alternating washing for 3 times. The volume of solvent added was 5 times the volume of solid particles (about 2000 mL / time), and stirring was performed for 3 min before centrifugal separation. S5: Freeze-drying: The washed solid particles were spread on a drying plate (spreading thickness 5 mm, total mass about 785 g) and placed in a freeze-drying device. The drying was carried out at -50°C and 10 Pa for 12 h. S6: Low-temperature vacuum deoxidation: The dried powder (about 775 g) was transferred to a vacuum furnace (heating element: molybdenum wire with a purity of ≥99.95%). The temperature was raised to 380°C at a rate of 5°C / min. The vacuum degree was ≤0.001 Pa (actually controlled at 0.001 Pa) during the 1 h holding period. The vacuum degree was maintained at ≤0.001 Pa by continuous vacuum pumping during the holding period. S7: Inert atmosphere passivation: Two-step procedure was used for passivation: first step, 30 min replacement in 99.999% argon at a flow rate of 5 L / min; second step, the argon flow rate was reduced to 0.5 L / min, and the temperature was raised to 60°C at a rate of 10°C / h. After 24 h of constant temperature holding, the temperature was naturally cooled to room temperature. Nanometer zirconium powder with a surface oxide film thickness of 1.8 nm was obtained, with a yield of 770 g.

[0031] Example 3

[0032] S1: raw material preparation: select zirconium hafnium total content ≥ 99.8%, iron < 50 mg / kg, oxygen < 300 mg / kg, carbon < 30 mg / kg of electric vacuum grade sponge zirconium 1200g, broken by zirconia jaw crusher, crushing gap 5mm, screened by 10 mesh inert atmosphere screening device, get the particle size ≤5mm; S2: preparation of coating aid: weigh potassium iodate 0.95g, dissolved in 444mL deionized water with resistivity ≥18.2MΩ·cm, prepared into an aqueous solution with a concentration of 10mmol / L, weighed 0.095g polyvinylpyrrolidone (molecular weight 10kDa) into the above solution, forming a mixed solution (polyvinylpyrrolidone and potassium iodate mass ratio 1:10), the mixed solution was placed in the ultrasonic device, ultrasonic treatment for 30min under the power of 400W and the temperature of 40℃, magnetic stirring was assisted for dispersion at the speed of 300rpm during the ultrasonic process, and the potassium iodate-polyvinylpyrrolidone coating aid was obtained; S3: wet high-energy ball milling: 1200g of sponge zirconium particles, 12000g of zirconia grinding balls (particle size 5mm, purity ≥99.9%), 3600g of grinding agent (water 2520g+ethanol 1080g, mass ratio 1.4:1) were loaded into the ball mill tank with zirconia coating on the inner wall, 444mL of the above coating aid was added to the grinding agent (the final concentration of potassium iodate was 1.0mmol / L), the ball mill tank was sealed and argon was introduced to 0.10MPa overpressure, and the ball mill was carried out at a speed of 550rpm for 10h, and the pressure was maintained at 0.10MPa every 2h to maintain the stability of argon overpressure; S4: solid-liquid separation and washing: under the protection of argon, the slurry after ball milling was transferred to a centrifugal device, and the solid-liquid separation was realized by centrifugation at a speed of 10000rpm for 15min, and the water-ethanol was used for alternating washing for 3 times, and the volume of solvent was 8 times (about 4800mL / time) of the volume of solid particles for each washing, and the stirring was carried out for 5min and then the centrifugal separation was carried out; S5: freeze-drying: the washed solid particles were spread on the drying plate (spreading thickness 10mm, total mass about 1180g), and were placed in the freeze-drying equipment, and were dried at-45℃ and 15Pa for 15h; S6: low temperature vacuum deoxidation: the dried powder (about 1170g) was transferred to a vacuum furnace (heating element was molybdenum wire with purity ≥99.95%), heated to 420℃ at a heating rate of 10℃ / min, and kept at 420℃ for 3h under a vacuum degree of ≤0.001Pa (actual control was 0.0005Pa), and the vacuum degree in the furnace was maintained at ≤0.001Pa during the heat preservation process; S7: Inert atmosphere passivation: passivation was carried out by a two-step procedure: first, 99.999% argon was used to replace the atmosphere at a flow rate of 5 L / min for 30 min; second, the argon flow rate was reduced to 0.5 L / min, and the temperature was raised to 60°C at a rate of 10°C / h from room temperature, and then kept constant for 24 h before naturally cooling to room temperature, to obtain the nano-zirconium powder 1165 g with a surface oxide film thickness of 1.3 nm.

[0033] Comparative Example 1: In S2, polyvinylpyrrolidone was omitted, and only a potassium iodate aqueous solution (concentration 7 mmol / L) was used, and the grinding agent was directly added; the remaining steps were the same as in Example 1.

[0034] Comparative Example 2: In S6, the step was omitted, and passivation was directly carried out after ball milling; the remaining steps were the same as in Example 1.

[0035] Comparative Example 3: S7: One-step passivation: 99.999% argon was used to replace the atmosphere at a flow rate of 5 L / min for 30 min, and then the sample was left to stand at room temperature for 24 h without temperature increase; the remaining steps were the same as in Example 1.

[0036] Performance test: The zirconium powders prepared in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2 and Comparative Example 3 were tested for performance, and the test data obtained are recorded in the following table:

[0037] In the performance test, the zirconium powders prepared in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2 and Comparative Example 3 were tested, the particle size was tested according to GB / T 19077-2016, the oxygen content was tested according to GB / T 14265-2017, and the impurity (iron, carbon and iodine) content was tested according to GB / T 23364.2-2009.

[0038] It can be seen that the zirconium powder prepared in Examples 1-3 has a median particle size of 30-40 nm, a distribution span of ≤2.0, an oxygen content of 0.10-0.15%, and low contents of iron, carbon and iodine impurities, and the purity of the zirconium powder is good, indicating that the potassium iodate-polyvinylpyrrolidone coating aid and low-temperature vacuum deoxidization and two-step passivation in the process of the application not only effectively inhibit oxidation and agglomeration, ensuring the stability of the powder particle size, but also can reduce the low impurity content of the zirconium powder and improve the purity of the zirconium powder.

[0039] Comparative Example 1 lacks polyvinylpyrrolidone, and the potassium iodate cannot be released slowly, resulting in excessive oxidation at the beginning and cold welding agglomeration at the end, which increases the particle size and increases the oxygen content, proving that the steric hindrance and slow-release effect of polyvinylpyrrolidone are crucial. Comparative Example 2 does not have low-temperature vacuum deoxidization, and the residual iodine and carbon are significantly over-standard, and the oxygen content is as high as 0.35%, indicating that this step is crucial for removing impurities, improving purity and accurately controlling oxygen.

[0040] The simplification of passivation of Comparative Example 3 leads to poor particle size distribution, which proves that the two-step temperature rising passivation can guarantee the stable distribution of the particle size of the powder.

[0041] By comparing and analyzing the related data in the table, it can be known that the zirconium powder prepared by the process has not only a uniform nanoscale particle size, but also a high purity, which shows that the process for preparing the nanoscale zirconium powder for electric vacuum has a broader market prospect and is more suitable for promotion.

[0042] In the description of the specification, the description referring to the terms "one experiment", "example", "specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the experiment or example are contained in at least one experiment or example of the present application. In the specification, the illustrative description of the above terms does not necessarily refer to the same experiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more experiments or examples in a suitable manner.

[0043] The above-disclosed preferred experiments of the present application are only used to help illustrate the present application. The preferred experiments do not describe all the details and limit the present application to the specific embodiments described. Obviously, according to the content of the specification, many modifications and changes can be made. The specification selects and specifically describes these experiments in order to better explain the principles and practical applications of the present application, so that those skilled in the art can well understand and utilize the present application. The present application is limited only by the claims and their full scope and equivalents.

Claims

1. A process for manufacturing nano-sized zirconium powder for electrovacuum applications, characterized in that, Includes the following steps: S1: Raw material preparation: Select vacuum-grade sponge zirconium with a total zirconium and hafnium content ≥99.8%, iron <50mg / kg, oxygen <300mg / kg, and carbon <30mg / kg, crush and screen to obtain particles with a particle size ≤5mm; S2: Preparation of coating agent: Dissolve potassium iodate in deionized water, add polyvinylpyrrolidone to form a mixture, and sonicate to obtain potassium iodate-polyvinylpyrrolidone coating agent. The mass ratio of polyvinylpyrrolidone to potassium iodate is 1:5-1:

10. S3: Wet high-energy ball milling: Sponge zirconium, zirconium oxide grinding balls, and abrasive are loaded into a container at a mass ratio of 1:10:3, and ball milled at 450-550 rpm under an argon pressure of 0.05-0.10 MPa for 4-10 hours; the abrasive is a mixture of water and ethanol at a mass ratio of 1.4:1, and a coating agent is added to make the final concentration of potassium iodate 0.2-1.0 mmol / L; S4: Solid-liquid separation and washing: Centrifugation under argon protection, followed by three alternating washes with water and ethanol. S5: Freeze-drying: Dry at -50~-45℃ and 10-15Pa for 12-15 hours; S6: Low-temperature vacuum deoxidation: Hold at 380-420℃ and ≤0.001Pa for 1-3 hours to simultaneously remove residual iodine and polyvinylpyrrolidone; S7: Inert atmosphere passivation: Let stand in an inert atmosphere for 24-30 hours to obtain nano-zirconium powder.

2. The fabrication process of nano-sized zirconium powder for electrovacuum applications according to claim 1, characterized in that, In step S1, a jaw crusher with zirconia jaw plates is used for crushing, with a crushing gap of 3-5mm, and the material is screened by a 10-mesh inert atmosphere screening device.

3. The manufacturing process of nano-sized zirconium powder for electrovacuum applications according to claim 1, characterized in that, In step S2, the concentration of potassium iodate in the coating agent is 5-10 mmol / L, the resistivity of deionized water is ≥18.2 MΩ·cm, the molecular weight of polyvinylpyrrolidone is 10 kDa, and the ultrasonic parameters are 300-400 W, 30-40 ℃, 20-30 min, with magnetic stirring at 200-300 rpm to assist dispersion during ultrasonication.

4. The manufacturing process of nano-sized zirconium powder for electrovacuum applications according to claim 1, characterized in that, In step S3, the zirconia grinding balls have a particle size of 5 mm and a purity of ≥99.9%. The inner wall of the grinding jar is lined with a zirconia coating, and the argon overpressure is maintained at 0.05-0.10 MPa every 2 hours.

5. The fabrication process of nano-sized zirconium powder for electrovacuum applications according to claim 1, characterized in that, In step S4, the centrifugation speed is 8000-10000 rpm and the time is 10-15 min. During washing, the solvent volume is 5-8 times the volume of the solid particles. After stirring for 3-5 min, centrifuge to separate the particles.

6. The fabrication process of nano-sized zirconium powder for electrovacuum applications according to claim 1, characterized in that, In step S5, the solid particles are laid out to a thickness of 5-10 mm.

7. The manufacturing process of nano-sized zirconium powder for electrovacuum applications according to claim 1, characterized in that, In step S6, the heating element of the vacuum furnace is a molybdenum wire with a purity of ≥99.95%, a heating rate of 5-10℃ / min, and continuous vacuuming during the heat preservation process to maintain the vacuum degree inside the furnace ≤0.001Pa.

8. The manufacturing process of nano-sized zirconium powder for electrovacuum applications according to claim 1, characterized in that, Step S7, inert atmosphere passivation, employs a two-step procedure: First, purging is performed in 99.999% argon gas at a flow rate of 5 L / min for 30 min; second, the flow rate is reduced to 0.5 L / min, and the temperature is increased from room temperature to 60℃ at a rate of 10℃ / h, held at a constant temperature for 24 h, and then naturally cooled to room temperature to obtain nano-zirconium powder with a surface oxide film thickness ≤2 nm.

9. A nano-sized zirconium powder for electrovacuum applications, characterized in that, It is manufactured using the process described in any one of claims 1-8 for producing nano-sized zirconium powder for electrovacuum applications.

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