Preparation method of cylindrical metal thorium target material
By combining static pressing and vacuum melting with inert gas filling, the problems of inconsistent compaction and bubble defects in the preparation of cylindrical metal thorium targets have been solved, improving preparation efficiency and quality. This method is suitable for medical isotope production and nuclear optical clock manufacturing.
Patent Information
- Application Number
- CN202511681363.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-17
- Publication Date
- 2026-03-06
AI Technical Summary
The preparation of cylindrical thorium metal targets has problems such as inconsistent compaction due to excessively high thorium powder height inside the mold, difficulty in demolding, and defects such as bubbles and pores during the melting process.
Multiple metal thorium blanks are formed by static pressing, stacked in a cylindrical crucible for vacuum melting, and inert gas is introduced during the melting process to increase the gas pressure, eliminate air bubbles, and ensure density and structural uniformity.
This improved the efficiency and quality of cylindrical thorium metal target preparation, eliminated internal defects, and enhanced density and structural uniformity, meeting the needs of medical isotope production and nuclear optical clock manufacturing.
Smart Images
Figure CN121610752A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of metal target preparation technology, specifically relating to a method for preparing a cylindrical metal thorium target. Background Technology
[0002] Thorium (Th), a naturally occurring radioactive metal, possesses a high melting point (1750°C) and excellent thermal conductivity, maintaining stable performance even in extreme environments. Thorium targets have important applications in modern science and technology, particularly in nuclear energy, particle accelerators, and medical isotope production. In nuclear energy, thorium targets can be converted into uranium-233 during nuclear reactions, serving as a potential fission fuel with lower nuclear waste production and higher safety. In particle accelerators, the high density and resistance to high-energy radiation make thorium targets effective neutron and high-intensity radiation sources. In medical isotope production, thorium targets can serve as highly efficient neutron sources when generating radioactive isotopes (such as cesium-137 and actinium-225) using particle accelerators, supporting their use in medical diagnosis and treatment.
[0003] Currently, cylindrical thorium metal targets are widely used due to their higher utilization rate and improved economic efficiency in practical applications. However, the preparation of cylindrical thorium metal targets still faces some challenges. For example, during cold pressing, the excessive height of the thorium powder in the mold leads to inconsistent compactness of the cylindrical thorium preform, and excessive friction between the thorium powder and the inner wall of the mold makes demolding difficult. During melting, excessive air bubbles and pores inside the cylindrical thorium preform result in internal structural defects and insufficient density in the finished thorium metal target. Summary of the Invention
[0004] To address the shortcomings of the prior art, this invention provides a method for preparing cylindrical thorium metal targets. Multiple thorium metal preforms are formed by hydrostatic pressing, and then stacked in a cylindrical crucible for vacuum melting. This method solves the problems of inconsistent compactness of the metal preforms and difficulty in demolding caused by excessive height of thorium powder within the mold. By introducing inert gas during the melting process to increase the internal pressure of the melting equipment, air bubbles inside the cylindrical thorium metal target can be effectively eliminated, preventing the formation of pores and improving the density and structural uniformity of the cylindrical thorium metal target.
[0005] The technical effects to be achieved by this invention are realized through the following technical aspects: This invention provides a method for preparing a cylindrical thorium metal target, comprising the following steps: S1. Take metallic thorium powder and put it into a cylindrical mold for static pressing. After demolding, a metallic thorium preform is obtained. S2. Take multiple metal thorium blanks and stack them in a cylindrical crucible. Place the cylindrical crucible in a melting equipment, evacuate to a negative pressure state, and then heat up to melt. After the metal thorium blanks are completely melted, fill the melting equipment with inert gas to a positive pressure state, stop melting, and after the melting equipment cools to room temperature, take out the cylindrical metal thorium target crude product. S3. The cylindrical metal thorium target material is machined to remove surface oxides and impurities, thus obtaining the cylindrical metal thorium target material.
[0006] As a further description of the technical solution of the present invention, the inert gas is argon or helium.
[0007] As a further description of the technical solution of the present invention, in S2, the negative pressure state is a vacuum degree of less than 0.01 Pa, and the positive pressure state is a relative atmospheric pressure of 0.1~0.3 MPa.
[0008] As a further description of the technical solution of the present invention, the cylindrical crucible material is one of boron nitride, silicon carbide or thorium oxide.
[0009] As a further description of the technical solution of the present invention, in step S2, the melting temperature is 1600~1800℃.
[0010] As a further description of the technical solution of the present invention, the diameter of the cylindrical mold is smaller than the diameter of the cylindrical crucible.
[0011] As a further description of the technical solution of the present invention, the purity of the metal thorium powder is 99.8%.
[0012] As a further description of the technical solution of the present invention, in S1, during static pressing, the pressing surface pressure of the metal thorium powder is 200~300MPa, and the holding time is 5~10min.
[0013] As a further description of the technical solution of the present invention, the metal thorium powder is first placed in a vacuum drying oven for drying treatment before being placed into the cylindrical mold.
[0014] As a further description of the technical solution of the present invention, the machining method includes one or more of grinding, magnetic polishing, abrasive vibration polishing, and centrifugal polishing.
[0015] In summary, the present invention has at least the following advantages: The method for preparing cylindrical thorium metal targets provided by this invention involves statically pressing thorium powder into thorium blanks, then stacking multiple thorium blanks in a cylindrical crucible for vacuum melting. This method solves the problems of inconsistent compactness of the thorium blanks and difficulty in demolding caused by excessive height of the thorium powder in the mold, thus improving the preparation efficiency and quality of cylindrical thorium metal targets. By introducing inert gas after the thorium blanks are completely melted to increase the internal pressure of the melting equipment, air bubbles inside the molten thorium are effectively eliminated, preventing the formation of pores and thus eliminating internal structural defects in the cylindrical thorium metal targets, improving their density and structural uniformity. The cylindrical thorium metal targets prepared by the method of this invention are applicable to fields such as medical isotope production and nuclear optical clock manufacturing. Attached Figure Description
[0016] Figure 1 This is a schematic diagram of the structure of the cylindrical metal thorium target crude material in Embodiment 4 of the present invention; Figure 2 This is a schematic diagram of the cylindrical metal thorium target material according to Embodiment 4 of the present invention; Figure 3 This is a SEM microstructure image of the cylindrical metal thorium target material of Embodiment 4 of the present invention; Figure 4 This is a schematic diagram of the structure of the cylindrical metal thorium target crude material of Comparative Example 1 of the present invention. Detailed Implementation
[0017] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments and accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.
[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
[0019] This invention provides a method for preparing a cylindrical thorium metal target, comprising the following steps: S1. Take metal thorium powder and put it into a vacuum drying oven for drying. After obtaining dry metal thorium powder, put it into a cylindrical mold for static pressing and molding. After demolding, metal thorium preform is obtained. S2. Take multiple metal thorium blanks and stack them in a cylindrical crucible. Place the cylindrical crucible in a melting equipment, evacuate to a negative pressure state, and then heat up to melt. After the metal thorium blanks are completely melted, fill the melting equipment with inert gas to a positive pressure state, stop melting, and after the melting equipment cools to room temperature, take out the cylindrical metal thorium target crude product. S3. The cylindrical metal thorium target material is machined to remove surface oxides and impurities, thus obtaining the cylindrical metal thorium target material.
[0020] By pressing metallic thorium powder in stages to obtain multiple metallic thorium preforms, and then stacking these preforms in a cylindrical crucible for vacuum melting, the problems of inconsistent compactness and difficulty in demolding caused by excessive height of metallic thorium powder in the mold can be solved. Simultaneously, vacuum melting effectively avoids the oxidation of metallic thorium, thereby improving the purity of the cylindrical metallic thorium target. This improves the preparation efficiency and quality of the cylindrical metallic thorium target. After the metallic thorium preforms are completely melted, inert gas is introduced to increase the internal pressure of the melting equipment, effectively eliminating air bubbles within the molten metallic thorium and preventing the formation of pores. This eliminates internal structural defects in the cylindrical metallic thorium target, improving its density and structural uniformity, which is beneficial for enhancing the strength and quality of the cylindrical metallic thorium target.
[0021] In some embodiments, the thorium powder can be ground or sieved before drying to remove large-sized thorium powder particles, thereby improving the fineness and uniformity of the thorium powder, which in turn helps to improve the density and structural uniformity of the cylindrical thorium target.
[0022] In some embodiments, the inert gas is argon or helium, preferably argon, as its lower cost reduces preparation costs and improves the production efficiency of cylindrical thorium metal targets. By introducing argon during the vacuum melting process, oxygen and nitrogen in the air can be isolated, reducing oxidation and nitriding reactions of the thorium metal and decreasing the generation of gases and impurities, thereby improving the purity of the cylindrical thorium metal target. Simultaneously, argon can carry gases and inclusions from the molten thorium metal to the outside, eliminating internal porosity and improving the density and structural uniformity of the cylindrical thorium metal target.
[0023] In S2, the negative pressure state is a vacuum degree of less than 0.01 Pa, the positive pressure state is a relative atmospheric pressure of 0.1~0.3 MPa, and the vacuum melting temperature is 1600~1800℃, preferably 1700℃.
[0024] In some embodiments, the cylindrical crucible material is one of boron nitride, silicon carbide, or thorium oxide, preferably boron nitride. Boron nitride is relatively inexpensive, and using a boron nitride cylindrical crucible can reduce preparation costs and improve production efficiency. Boron nitride has good chemical and high-temperature stability, and it is not prone to reacting with metallic thorium during high-temperature melting, which is beneficial to improving the purity of the metallic thorium target. Simultaneously, the boron nitride cylindrical crucible possesses high mechanical strength and hardness, and will not deform under high-temperature melting conditions, ensuring the stability and consistency of the cylindrical metallic thorium target's shape and improving the preparation quality of the cylindrical metallic thorium target.
[0025] As a further optimization, the diameter of the cylindrical mold is smaller than the diameter of the cylindrical crucible. Specifically, the diameter of the cylindrical mold can be 1-3 mm smaller than the diameter of the cylindrical crucible. This ensures that the thorium metal preform can be smoothly placed into the cylindrical crucible, thereby improving the preparation efficiency. At the same time, it also reduces the contact and friction between the thorium metal preform and the inner wall of the cylindrical crucible, avoiding porosity defects in the final cylindrical thorium metal target due to a large amount of molten thorium adhering to the inner wall of the cylindrical crucible during the subsequent vacuum melting process. This is beneficial to improving the preparation quality of the cylindrical thorium metal target.
[0026] It should be noted that in S1, the purity of the metallic thorium powder is 99.8%. By using high-purity metallic thorium powder as raw material, and combining it with the protection of an inert material crucible and inert gas during the vacuum melting process, it can be ensured that the prepared cylindrical metallic thorium target material reaches the high purity standard to meet the purity requirements in subsequent applications.
[0027] In S1, during static pressing, the pressing surface pressure of the thorium metal powder is 200~300MPa, and the holding time is 5~10min.
[0028] In some embodiments, the machining methods include one or more of grinding, magnetic polishing, abrasive vibratory polishing, and centrifugal polishing, with grinding being preferred. Grinding offers high machining accuracy and can efficiently remove the oxide layer and crucible contact layer from the surface of the rough cylindrical thorium target, effectively improving the flatness and smoothness of the cylindrical thorium target surface, thereby improving the quality and performance of the cylindrical thorium target. In addition, the processing equipment used for grinding is low-cost, which can reduce manufacturing costs and improve production efficiency.
[0029] Example 1 This embodiment provides a cylindrical metal thorium target, which is prepared by the following method: S1. Weigh 20g of metallic thorium powder (purity 99.8%) and put it into a vacuum drying oven for drying to obtain dry metallic thorium powder. Then divide the dry metallic thorium powder into 6 portions, each 3g, and put them into a cylindrical mold with a diameter of 10mm for static pressing. During static pressing, the surface pressure of the metallic thorium powder is 200MPa, and the pressure is held for 5min. After demolding, 6 metallic thorium preforms are obtained. S2. Stack six metal thorium blanks in a boron nitride cylindrical crucible with a diameter of 11 mm. Place the boron nitride cylindrical crucible in a melting furnace, evacuate to below 0.01 Pa, and heat to 1700 °C for melting. After the metal thorium blanks are completely melted, close the main valve of the melting furnace, fill with high-purity argon gas to a relative atmospheric pressure of 0.2 MPa, close the melting furnace and stop melting. After the melting furnace cools to room temperature, take out the cylindrical metal thorium target crude product. S3. Grind the crude cylindrical metal thorium target material to remove surface oxides and impurities, and obtain the cylindrical metal thorium target material.
[0030] Tests showed that the cylindrical thorium metal target had a relative density of 99% and a purity of 99.95%, with a dense and defect-free microstructure.
[0031] Example 2 This embodiment provides a cylindrical metal thorium target, which is prepared by the following method: S1. Weigh 20g of metallic thorium powder (purity 99.8%) and place it in a vacuum drying oven for drying to obtain dry metallic thorium powder. Then, divide the dry metallic thorium powder into 5 portions, each 3g, and place them into cylindrical molds with a diameter of 9mm for static pressing. During static pressing, the surface pressure of the metallic thorium powder is 200MPa, and the pressure is held for 5min. After demolding, 5 metallic thorium preforms are obtained. S2. Stack five thorium metal blanks in a boron nitride cylindrical crucible with a diameter of 10 mm. Place the boron nitride cylindrical crucible in a melting furnace, evacuate to below 0.01 Pa, and heat to 1700 °C for melting. After the thorium metal blanks are completely melted, close the main valve of the melting furnace, fill with high-purity argon gas to a relative atmospheric pressure of 0.2 MPa, close the melting furnace and stop melting. After the melting furnace cools to room temperature, take out the cylindrical thorium metal target crude product. S3. Grind the crude cylindrical metal thorium target material to remove surface oxides and impurities, and obtain the cylindrical metal thorium target material.
[0032] Tests showed that the cylindrical thorium metal target had a relative density of 99% and a purity of 99.95%, with a dense and defect-free microstructure.
[0033] Example 3 This embodiment provides a cylindrical metal thorium target, which is prepared by the following method: S1. Weigh 45g of metallic thorium powder (purity 99.8%) and put it into a vacuum drying oven for drying to obtain dry metallic thorium powder. Then divide the dry metallic thorium powder into 8 portions, each 5g, and put them into a cylindrical mold with a diameter of 18mm for static pressing. During static pressing, the surface pressure of the metallic thorium powder is 300MPa, and the pressure is held for 5min. After demolding, 8 metallic thorium preforms are obtained. S2. Stack eight thorium metal blanks in a boron nitride cylindrical crucible with a diameter of 20 mm. Place the boron nitride cylindrical crucible in a melting furnace, evacuate to below 0.01 Pa, and heat to 1700 °C for melting. After the thorium metal blanks are completely melted, close the main valve of the melting furnace, fill with high-purity argon gas to a relative atmospheric pressure of 0.2 MPa, close the melting furnace and stop melting. After the melting furnace cools to room temperature, take out the cylindrical thorium metal target crude product. S3. Grind the crude cylindrical metal thorium target material to remove surface oxides and impurities, and obtain the cylindrical metal thorium target material.
[0034] Tests showed that the cylindrical thorium metal target had a relative density of 99% and a purity of 99.95%, with a dense and defect-free microstructure.
[0035] Example 4 This embodiment provides a cylindrical metal thorium target, which is prepared by the following method: S1. Weigh 55g of metallic thorium powder (purity 99.8%) and place it in a vacuum drying oven for drying to obtain dry metallic thorium powder. Then, divide the dry metallic thorium powder into 5 portions, each 10g, and place them into cylindrical molds with a diameter of 28mm for static pressing. During static pressing, the surface pressure of the metallic thorium powder is 300MPa, and the pressure is held for 5min. After demolding, 5 metallic thorium preforms are obtained. S2. Stack five thorium metal preforms in a 30mm diameter boron nitride cylindrical crucible. Place the boron nitride cylindrical crucible in a melting furnace, evacuate to below 0.01Pa, and heat to 1700℃ for melting. After the thorium metal preforms are completely melted, close the main valve of the melting furnace, introduce high-purity argon gas to a relative atmospheric pressure of 0.2MPa, and close the melting furnace to stop melting. After the melting furnace body cools to room temperature, remove the cylindrical thorium metal target rough product. The structural schematic diagram of the cylindrical thorium metal target rough product is shown below. Figure 1 As shown; S3. The rough cylindrical thorium metal target is ground to remove surface oxides and impurities, yielding the cylindrical thorium metal target. A schematic diagram of the cylindrical thorium metal target structure is shown below. Figure 2 As shown.
[0036] Testing revealed that the cylindrical thorium metal target had a relative density of 99% and a purity of 99.95%. The SEM microstructure image of the cylindrical thorium metal target is shown below. Figure 3As shown, the microstructure is dense and defect-free.
[0037] Comparative Example 1 This comparative example provides a cylindrical metal thorium target, which is prepared by the following method: S1. Weigh 30g of metallic thorium powder (purity 99.8%) and put it into a vacuum drying oven for drying to obtain dry metallic thorium powder. Then divide the dry metallic thorium powder into 5 portions, each 5g, and put them into a cylindrical mold with a diameter of 18mm for static pressing. During static pressing, the surface pressure of the metallic thorium powder is 300MPa, and the pressure is held for 5min. After demolding, 5 metallic thorium preforms are obtained. S2. Stack five metal thorium blanks in a boron nitride cylindrical crucible with a diameter of 20 mm. Place the boron nitride cylindrical crucible in a melting furnace, evacuate to below 0.01 Pa, and heat to 1700℃ for melting. After the metal thorium blanks are completely melted, turn off the melting furnace to stop melting. After the melting furnace body cools to room temperature, take out the cylindrical metal thorium target rough product. S3. Grind the crude cylindrical metal thorium target material to remove surface oxides and impurities, and obtain the cylindrical metal thorium target material.
[0038] A schematic diagram of the structure of the crude cylindrical metal thorium target is shown below. Figure 4 As shown, obvious porosity defects are observed at the bottom of the crude cylindrical metal thorium target, with a relative density of 74%.
[0039] The above description is merely an example and illustration of the structure of this invention, and while the description is specific and detailed, it should not be construed as limiting the scope of this invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this invention, and these obvious substitutions all fall within the protection scope of this invention.
Claims
1. A method for producing a cylindrical metal thorium target material, characterized by, The method comprises the following steps: S1, taking metal thorium powder into a cylindrical mold for static pressure forming, and obtaining a metal thorium blank after demolding; S2, stacking a plurality of the metal thorium blanks in a cylindrical crucible, placing the cylindrical crucible in a smelting device, vacuumizing to a negative pressure state, heating for smelting, filling inert gas into the smelting device to a positive pressure state after the metal thorium blanks are completely melted, stopping smelting, taking out the cylindrical metal thorium target crude product after the smelting device is cooled to room temperature; S3, machining the cylindrical metal thorium target crude product to remove surface oxides and impurities, and obtaining a cylindrical metal thorium target.
2. The method of claim 1, wherein the cylindrical metal thorium target is prepared by the steps of: The inert gas is argon or helium. 3. The method of claim 1, wherein the cylindrical metal thorium target is prepared by the steps of: In the S2, the negative pressure state is a vacuum degree less than 0.01 Pa, and the positive pressure state is a relative atmospheric pressure of 0.1-0.3 MPa. 4. The method of claim 1, wherein the cylindrical metal thorium target is prepared by the steps of: The cylindrical crucible material is one of boron nitride, silicon carbide or thorium oxide. 5. The method of claim 1, wherein the cylindrical metal thorium target is prepared by the steps of: In the S2, the smelting temperature is 1600-1800 DEG C. 6. The method of claim 1, wherein the cylindrical metal thorium target is prepared by the steps of: The diameter of the cylindrical mold is less than the diameter of the cylindrical crucible.
7. The method of claim 1, wherein the method further comprises: The purity of the metal thorium powder is 99.8%.
8. The method of claim 1, wherein the cylindrical metal thorium target is prepared by the steps of: In the S1, the pressing surface pressure of the metal thorium powder is 200-300 MPa during static pressure forming, and the pressure maintaining time is 5-10 min. 9. The method of claim 1, wherein the cylindrical metal thorium target is prepared by the steps of: The metal thorium powder is dried in a vacuum drying box before being put into the cylindrical mold. 10. The method of claim 1, wherein the cylindrical metal thorium target is prepared by the steps of: The machining mode comprises one or more of grinding machine machining, magnetic polishing, abrasive vibration polishing and centrifugal polishing.