Preparation method of high-purity chromium powder for target material

Abstract

The application relates to a preparation method of high-purity chromium powder for a target material, comprising the following steps: (1) performing electron beam melting treatment on pretreated electrolytic chromium sheet to obtain a chromium ingot; removing both ends of the chromium ingot to obtain a high-purity chromium ingot; the electron beam melting treatment comprises gradient temperature rising treatment, refining treatment and directional solidification treatment; (2) performing ball milling treatment and screening treatment on the high-purity chromium ingot to obtain the high-purity chromium powder. Through the electron beam melting technology and a multi-section electron beam power control strategy, the application realizes accurate regulation and control of the temperature of a molten pool and refining kinetics. The preparation method can not only efficiently remove conventional metal impurities with a vapor pressure significantly higher than that of chromium, but also promote the diffusion and selective removal of trace metal impurities with a vapor pressure similar to that of chromium, so that the limit of the original purification method is broken through.

Description

Technical Field

[0001] This invention relates to the field of high-purity chromium powder preparation technology for sputtering targets, and particularly to a method for preparing high-purity chromium powder for sputtering targets. Background Technology

[0002] As the "film" of the photolithography process, the quartz substrate of the photomask directly affects chip performance and yield due to its pattern accuracy, defect density, and durability. In the photomask fabrication process, the light-shielding material is one of the core materials. Chromium (Cr), due to its high stability, excellent corrosion resistance, and outstanding ability to form fine patterns, has become the mainstream choice for hard light-shielding materials. It is deposited on the surface of the quartz substrate in the form of a chromium target using magnetron sputtering to form a uniform and dense light-shielding thin film layer, blocking light during the photolithography process and ensuring precise pattern transfer. With the continuous advancement of semiconductor process nodes, the purity requirements for chromium targets in photomasks are becoming increasingly stringent. Current mainstream specifications require a purity of 4N (99.99%) or higher, while advanced processes require no less than 5N (99.999%).

[0003] Against this backdrop, the preparation of high-purity chromium targets has become a core step in improving photomask performance, and the purity level of the high-purity chromium powder used as its raw material is a fundamental factor restricting the quality of the chromium target and the final pattern accuracy. Powder purity not only directly affects the uniformity, defect density, and light-shielding performance of the sputtered film, but also determines the pattern fidelity and process window of the photomask in advanced processes. Therefore, obtaining high-purity chromium powder is not only a prerequisite for achieving high-precision photolithography pattern transfer, but also a key element in promoting the development of semiconductor manufacturing technology towards smaller nodes. For this reason, developing an efficient and controllable chromium powder preparation process has significant practical importance and technological urgency.

[0004] Currently, electrolysis is the most effective method for preparing high-purity chromium. The purity of electrolytic chromium sheets is usually around 99.99% (4N), but there are still certain levels of metallic and non-metallic impurities, and the content of interstitial elements such as O is still relatively high. There is a need to provide a new method for preparing high-purity chromium powder, which can reduce the O content in electrolytic chromium sheets to below 50 ppm, the C and N contents to below 30 ppm, and at the same time ensure that the contents of impurity elements such as Fe, Ni, Al, and Si are all less than 10 ppm, and further crush the metallic chromium blocks into powder.

[0005] CN119491113A discloses a method for purifying high-purity chromium for target materials. This method improves chromium purity through vacuum reduction treatment. The raw electrolytic chromium sheet is placed in a vacuum reduction furnace. After evacuating to a certain vacuum level, hydrogen gas is introduced, and the material is heated to a final temperature according to a set heating program and held at that temperature. Subsequently, it is cooled to room temperature in a hydrogen atmosphere to effectively reduce the content of oxygen, nitrogen, carbon, and various metallic impurities. The chromium prepared by this method has an O content ≤60ppm, N content ≤60ppm, C content ≤50ppm, and S, Fe, Al, and Si contents all ≤40ppm, thus improving the purity of metallic chromium.

[0006] CN116445745A discloses a plasma purification method for metallic chromium. This method reduces the oxygen content of metallic chromium through plasma arc melting. The raw material is placed in a crucible, and the furnace cavity is alternately purged with vacuum and high-purity argon gas. Argon gas at a certain pressure is then introduced as the working atmosphere, followed by plasma arc melting. The final product is low-oxygen, high-purity chromium metal and a small amount of chromium oxide powder. This method effectively suppresses the volatilization loss of chromium by melting at a relatively high pressure close to atmospheric pressure, solving the problems of its high melting point and easy oxidation at high temperatures, and can stably produce high-purity chromium metal with low oxygen content.

[0007] During high-temperature smelting, the vapor pressures of various metallic impurities and interstitial elements are significantly higher than that of chromium, allowing for preferential volatilization and removal under high vacuum conditions. While vacuum hydrogen reduction can effectively remove interstitial impurities such as oxygen, nitrogen, and carbon through chemical reactions, its effectiveness in eliminating metallic impurities (such as Fe, Al, and Si) already dissolved in the chromium lattice is not ideal, thus facing a bottleneck in further improving purity and failing to meet the ultra-high purity requirements of 5N and above. Plasma arc melting, conducted in an argon atmosphere, can suppress chromium volatilization loss, but it also weakens the volatilization and impurity removal capabilities under high vacuum. Furthermore, the separation effect for metallic impurities with vapor pressures close to or lower than chromium remains limited. Additionally, both methods ultimately yield metallic chromium blocks, failing to further prepare them into powder form.

[0008] To address the aforementioned issues, there is an urgent need to provide a new method for preparing high-purity chromium powder for photomasks, thereby meeting the requirements for photolithography mask fabrication. Summary of the Invention

[0009] To address the aforementioned technical problems, this invention provides a method for preparing high-purity chromium powder for target materials. This invention applies electron beam (EB) melting technology to the preparation of high-purity chromium blocks, achieving chromium block purification while further removing some metallic impurities with vapor pressures close to or lower than chromium. The powder is then prepared by ball milling, enabling its application in a wider range of fields.

[0010] To achieve this objective, the present invention adopts the following technical solution:

[0011] This invention provides a method for preparing high-purity chromium powder for target materials, the method comprising:

[0012] (1) The pretreated electrolytic chromium sheet is subjected to electron beam melting to obtain a chromium ingot; the two ends of the chromium ingot are removed to obtain a high-purity chromium ingot;

[0013] The electron beam melting process includes gradient heating, refining, and directional solidification.

[0014] (2) The high-purity chromium ingot is ball-milled and sieved to obtain the high-purity chromium powder.

[0015] The preparation method of this invention uses electrolytic chromium sheets as raw materials and employs a combination of electron beam melting purification and controlled ball milling to produce high-quality chromium powder with a purity of 5N and uniform particle size distribution. Specifically, the electron beam melting technology used to purify the chromium ingots not only effectively separates metallic impurities with high vapor pressure and stably controls interstitial impurities at extremely low levels, but also further removes some metallic impurities with vapor pressures close to or lower than chromium through directional solidification. Furthermore, through ball milling and sieving, the ingots obtained from electron beam melting are processed into high-purity chromium powder, greatly expanding its application potential in cutting-edge fields such as high-end additive manufacturing and electronic sputtering targets.

[0016] The electron beam (EB) melting of this invention is carried out in an ultra-high vacuum environment. Oxygen, carbon, nitrogen, etc. in the molten pool can form gaseous products or be directly desoluble due to the extremely low environmental partial pressure and are rapidly discharged by the vacuum system. This keeps interstitial impurities stably controlled at an extremely low level. Metal impurities with higher vapor pressure preferentially volatilize and condense on the furnace wall, achieving effective separation. At the same time, EB melting is also accompanied by a significant regional purification effect: during the directional solidification of the melt, some metal impurities with vapor pressures close to or lower than chromium have low solubility in the solid phase and are continuously pushed towards the tail of the molten pool, eventually accumulating at the top of the ingot. These impurities can be removed by "cutting off the head and tail", thereby significantly improving the purity of the ingot body.

[0017] It should be noted that the sieving process of the present invention adopts a multi-stage vibrating sieving system, which can separate powders of different particle sizes according to different particle size ranges, and finally obtain high-purity chromium powder with uniform particle size distribution that meets the needs of different applications.

[0018] As a preferred technical solution of the present invention, the pretreatment in step (1) includes ultrasonic cleaning and vacuum drying of the electrolytic chromium sheet.

[0019] This invention, through pretreatment, can thoroughly remove surface contaminants, ensure complete drying, and prevent any impact on the vacuum level of EB melting; at the same time, it can remove surface contaminants from electrolytic chromium sheets, avoiding the introduction of secondary impurities.

[0020] It should be noted that the ultrasonic cleaning process of the present invention is carried out in an ultrasonic cleaning device, and the vacuum drying process is carried out in a vacuum drying oven.

[0021] Preferably, the ultrasonic cleaning process specifically involves cleaning the electrolytic chromium sheet alternately with deionized water and organic solvent.

[0022] Preferably, the organic solvent includes any one or a combination of at least two of anhydrous ethanol, acetone, and isopropanol, and typical but non-limiting examples of such combinations include: anhydrous ethanol and acetone, anhydrous ethanol and isopropanol, and acetone and isopropanol.

[0023] Preferably, the temperature of the vacuum drying process is 60-80℃, such as 60℃, 65℃, 70℃, 75℃, 80℃, etc., but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0024] Preferably, the vacuum drying time is 2-4 hours, such as 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, etc., but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0025] As a preferred embodiment of the present invention, the chromium content in the electrolytic chromium sheet is ≥99.995%.

[0026] The electrolytic chromium sheet used in this invention has a purity of 99.995% and is free of pores, inclusions, and surface oxide layers. By using high-purity electrolytic chromium sheet as raw material, the initial purity of the raw material can be ensured, laying the foundation for subsequent purification.

[0027] As a preferred embodiment of the present invention, the electron beam melting process in step (1) is performed in a vacuum environment; the vacuum degree of the electron beam melting process is 10. -3 -10 -4 Pa, for example, 10 -3 Pa, 2×10 -3 Pa, 4×10 -3 Pa, 6×10 -3 Pa, 8×10 -3 Pa, 10 -4 Pa, etc., but not limited to the listed values; other unlisted values ​​within the above range also apply.

[0028] It should be noted that the electron beam melting process of the present invention is carried out in an electron beam melting furnace, using a water-cooled crucible, while maintaining a clean environment to avoid contamination, thereby establishing a pure thermodynamic environment and optimizing electron beam transmission.

[0029] As a preferred technical solution of the present invention, the gradient heating process in step (1) includes a first heating process and a second heating process.

[0030] The electron beam melting process of the present invention adopts a stepped heating strategy, namely, preheating first and then full melting; the first heating process slowly heats the material to the required temperature to avoid splashing; the second heating process completely melts the chromium material to form a stable molten pool.

[0031] This invention employs a gradient heating process to ensure a smooth transition of chromium raw materials to the molten state, preventing material splashing due to thermal stress and guaranteeing subsequent refining effects.

[0032] Preferably, the electron beam power of the first heating process is 40-60kW, such as 40kW, 45kW, 50kW, 55kW, 60kW, etc., but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0033] Preferably, the temperature of the first heating process is 800-1000℃, such as 800℃, 850℃, 900℃, 950℃, 1000℃, etc., but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0034] Preferably, the electron beam power of the second heating process is 150-200kW, such as 150kW, 160kW, 170kW, 180kW, 190kW, 200kW, etc., but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0035] Preferably, the temperature of the second heating process is 1850-1860℃, such as 1850℃, 1852℃, 1854℃, 1856℃, 1858℃, 1860℃, etc., but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0036] As a preferred technical solution of the present invention, the refining temperature in step (1) is 2350-2360℃, such as 2350℃, 2352℃, 2354℃, 2356℃, 2358℃, etc., but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0037] The present invention performs refining treatment while maintaining the molten pool temperature at approximately 500°C above the melting point of chromium. At this temperature and high vacuum, it can promote the volatilization and discharge of high vapor pressure impurities, remove low boiling point, high vapor pressure metal and gaseous impurities, and achieve deep purification.

[0038] Preferably, the holding time for the refining process is 30-60 minutes, such as 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes, etc., but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0039] As a preferred technical solution of the present invention, the directional solidification process in step (1) adopts a low-speed ring and bottom focusing mode; the electron beam scanning frequency of the directional solidification process is 0.5-2Hz, such as 0.5Hz, 0.8Hz, 1Hz, 1.3Hz, 1.5Hz, 1.8Hz, 2Hz, etc., but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0040] The directional solidification process of this invention adopts a bottom-up directional solidification method to finally obtain a chromium ingot with a dense columnar crystal structure; the directional solidification process drives residual impurities to the top of the chromium ingot, and further purifies it to obtain a high-purity, dense chromium ingot.

[0041] Preferably, the cooling water flow rate for the directional solidification treatment is 15-30 L / min, such as 15 L / min, 18 L / min, 20 L / min, 22 L / min, 25 L / min, 27 L / min, 30 L / min, etc., but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0042] Preferably, the directional solidification treatment employs a bottom-up solidification method.

[0043] As a preferred technical solution of the present invention, the ball milling media used in step (2) includes high-purity zirconium oxide.

[0044] This invention uses a zirconia grinding jar and grinding balls to crush and ball mill under a protective atmosphere, and then classifies the particles through a multi-stage vibrating sieve system to obtain high-purity Cr powder with uniform particle size distribution that meets the needs of different applications.

[0045] Preferably, the ball-to-material ratio in the ball milling process is 3:1 to 6:1, such as 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, etc., but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0046] Preferably, the ball milling speed is 60-100 r / min, such as 60 r / min, 70 r / min, 80 r / min, 90 r / min, 100 r / min, etc., but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0047] As a preferred technical solution of the present invention, the ball milling process in step (2) includes primary crushing and fine grinding performed sequentially.

[0048] This invention uses ball milling to crush high-purity chromium ingots into target powder, and strictly controls the oxygen content and impurity introduction during the process by using inert gas protection and high-purity zirconium oxide grinding jars and grinding balls.

[0049] Preferably, the ball milling time for primary crushing is 8-16 hours, such as 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, etc., but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0050] Preferably, the ball milling time for fine grinding is 20-40 hours, such as 20 hours, 25 hours, 30 hours, 35 hours, 40 hours, etc., but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0051] As a preferred technical solution of the present invention, the ball milling process in step (2) is carried out under an inert atmosphere.

[0052] Preferably, the inert atmosphere comprises high-purity argon.

[0053] Preferably, the ball milling temperature is <60°C, such as 55°C, 50°C, 45°C, 40°C, 35°C, 30°C, 25°C, etc., but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0054] Preferably, the purity of the high-purity chromium powder in step (2) is ≥5N; the mass content of impurities in the high-purity chromium powder is: O≤50ppm, C≤30ppm, N≤30ppm, Fe≤10ppm, Ni≤10ppm, Al≤10ppm, Si≤10ppm.

[0055] Compared with the prior art, the present invention has at least the following beneficial effects:

[0056] (1) This invention applies electron beam melting technology to the purification of high-purity chromium blocks, which not only effectively separates metal impurities with high vapor pressure and stabilizes interstitial impurities at an extremely low level, but also further removes some metal impurities in metallic chromium with vapor pressure close to or lower than that of chromium through directional solidification.

[0057] (2) This invention uses multi-stage electron beam power control to perform step-by-step heating and fine melting management of chromium materials, thereby improving the stability of electron beam melting and the impurity removal effect, and achieving deep purification;

[0058] (3) The present invention uses ball milling to prepare high-purity chromium powder from the ingot obtained by electron beam melting, which greatly expands its application potential in cutting-edge fields such as high-end additive manufacturing and electronic targets. Detailed Implementation

[0059] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0060] Example 1

[0061] This embodiment provides a method for preparing high-purity chromium powder for target materials, the preparation method comprising:

[0062] (1) The electrolytic chromium sheet was cleaned alternately with deionized water and anhydrous ethanol, and then ultrasonically cleaned. It was then vacuum dried at 60°C for 4 hours. The chromium content in the electrolytic chromium sheet was 99.995%.

[0063] The pretreated electrolytic chromium sheet is subjected to electron beam melting to obtain a chromium ingot; the two ends of the chromium ingot are removed to obtain a high-purity chromium ingot.

[0064] The electron beam melting process is performed in a vacuum environment; the vacuum degree of the electron beam melting process is 10. -3 Pa; The electron beam melting process includes gradient heating, refining, and directional solidification; The gradient heating process includes a first heating process and a second heating process; The electron beam power of the first heating process is 40kW and the temperature is 800℃; The electron beam power of the second heating process is 150kW and the temperature is 1860℃; The temperature of the refining process is 2360℃ and the holding time is 30min;

[0065] The directional solidification process employs a low-speed annular and bottom-focusing mode; the electron beam scanning frequency for directional solidification is 0.5 Hz; the cooling water flow rate for directional solidification is 15 L / min; and the directional solidification process uses a bottom-up solidification method.

[0066] (2) The high-purity chromium ingot is subjected to ball milling and sieving to obtain the high-purity chromium powder;

[0067] The ball milling process is carried out under a high-purity argon atmosphere; the ball milling media used in the ball milling process is high-purity zirconium oxide; the ball-to-material ratio of the ball milling process is 3:1, and the rotation speed is 60 r / min.

[0068] The ball milling process includes primary crushing and fine grinding performed sequentially; the ball milling time for primary crushing is 8 hours; the ball milling time for fine grinding is 40 hours; and the temperature of the ball milling process is 55°C.

[0069] The purity of the high-purity chromium powder is ≥5N; the mass content of impurities in the high-purity chromium powder is: O≤50ppm, C≤30ppm, N≤30ppm, Fe≤10ppm, Ni≤10ppm, Al≤10ppm, Si≤10ppm.

[0070] Example 2

[0071] This embodiment provides a method for preparing high-purity chromium powder for target materials, the preparation method comprising:

[0072] (1) The electrolytic chromium sheet was cleaned alternately with deionized water and acetone, and then ultrasonically cleaned. It was then vacuum dried at 70°C for 3 hours. The chromium content in the electrolytic chromium sheet was 99.995%.

[0073] The pretreated electrolytic chromium sheet is subjected to electron beam melting to obtain a chromium ingot; the two ends of the chromium ingot are removed to obtain a high-purity chromium ingot.

[0074] The electron beam melting process is performed in a vacuum environment; the vacuum degree of the electron beam melting process is 5 × 10⁻⁶. - 3 Pa; The electron beam melting process includes gradient heating, refining, and directional solidification; The gradient heating process includes a first heating process and a second heating process; The electron beam power of the first heating process is 50kW and the temperature is 900℃; The electron beam power of the second heating process is 180kW and the temperature is 1855℃; The temperature of the refining process is 2355℃ and the holding time is 45min;

[0075] The directional solidification process employs a low-speed annular and bottom-focusing mode; the electron beam scanning frequency of the directional solidification is 1 Hz; the cooling water flow rate of the directional solidification process is 25 L / min; and the directional solidification process adopts a bottom-up solidification method.

[0076] (2) The high-purity chromium ingot is subjected to ball milling and sieving to obtain the high-purity chromium powder;

[0077] The ball milling process is carried out under a high-purity argon atmosphere; the ball milling media used in the ball milling process is high-purity zirconium oxide; the ball-to-material ratio in the ball milling process is 4.5:1, and the rotation speed is 80 r / min;

[0078] The ball milling process includes primary crushing and fine grinding performed sequentially; the ball milling time for primary crushing is 12 hours; the ball milling time for fine grinding is 30 hours; and the temperature of the ball milling process is 50°C.

[0079] The purity of the high-purity chromium powder is ≥5N; the mass content of impurities in the high-purity chromium powder is: O≤50ppm, C≤30ppm, N≤30ppm, Fe≤10ppm, Ni≤10ppm, Al≤10ppm, Si≤10ppm.

[0080] Example 3

[0081] This embodiment provides a method for preparing high-purity chromium powder for target materials, the preparation method comprising:

[0082] (1) The electrolytic chromium sheet was cleaned alternately with deionized water and isopropanol, and then ultrasonically cleaned and vacuum dried at 80°C for 2 hours; the chromium content in the electrolytic chromium sheet was 99.995%;

[0083] The pretreated electrolytic chromium sheet is subjected to electron beam melting to obtain a chromium ingot; the two ends of the chromium ingot are removed to obtain a high-purity chromium ingot.

[0084] The electron beam melting process is performed in a vacuum environment; the vacuum degree of the electron beam melting process is 10. -4 Pa; the electron beam melting process includes gradient heating, refining, and directional solidification; the gradient heating process includes a first heating process and a second heating process; the electron beam power of the first heating process is 60kW and the temperature is 1000℃; the electron beam power of the second heating process is 200kW and the temperature is 1850℃; the temperature of the refining process is 2350℃ and the holding time is 60min;

[0085] The directional solidification process employs a low-speed annular and bottom-focusing mode; the electron beam scanning frequency of the directional solidification is 2Hz; the cooling water flow rate of the directional solidification process is 30L / min; and the directional solidification process adopts a bottom-up solidification method.

[0086] (2) The high-purity chromium ingot is subjected to ball milling and sieving to obtain the high-purity chromium powder;

[0087] The ball milling process is carried out under a high-purity argon atmosphere; the ball milling media used in the ball milling process is high-purity zirconium oxide; the ball-to-material ratio of the ball milling process is 6:1, and the rotation speed is 100 r / min.

[0088] The ball milling process includes primary crushing and fine grinding performed sequentially; the ball milling time for primary crushing is 16 hours; the ball milling time for fine grinding is 20 hours; and the temperature of the ball milling process is 50°C.

[0089] The purity of the high-purity chromium powder is ≥5N; the mass content of impurities in the high-purity chromium powder is: O≤50ppm, C≤30ppm, N≤30ppm, Fe≤10ppm, Ni≤10ppm, Al≤10ppm, Si≤10ppm.

[0090] Example 4

[0091] This embodiment provides a method for preparing high-purity chromium powder for target materials. The difference from Embodiment 1 is that the electron beam power of the second heating process in step (1) is adjusted to 140kW, while the rest is the same as in Embodiment 1.

[0092] Example 5

[0093] This embodiment provides a method for preparing high-purity chromium powder for target materials. The difference from Embodiment 1 is that the electron beam power of the second heating process in step (1) is adjusted to 210kW, while the rest is the same as in Embodiment 1.

[0094] Example 6

[0095] This embodiment provides a method for preparing high-purity chromium powder for target materials. The difference from Embodiment 1 is that the refining temperature in step (1) is adjusted to 2260°C, while the rest is the same as in Embodiment 1.

[0096] Example 7

[0097] This embodiment provides a method for preparing high-purity chromium powder for target materials. The difference from Embodiment 1 is that the refining temperature in step (1) is adjusted to 2460°C, while the rest is the same as in Embodiment 1.

[0098] Comparative Example 1

[0099] This comparative example provides a method for preparing high-purity chromium powder for target materials. The difference from Example 1 is that a second heating treatment is not performed, and the electrolytic chromium sheet is directly melted. All other aspects are the same as in Example 1.

[0100] Comparative Example 2

[0101] This comparative example provides a method for preparing high-purity chromium powder for target materials. The difference from Example 1 is that no refining process is performed, but all other aspects are the same as in Example 1.

[0102] Comparative Example 3

[0103] This comparative example provides a method for preparing high-purity chromium powder for target materials. The difference from Example 1 is that the two ends of the chromium ingot are not removed, and the chromium ingot is directly subjected to ball milling and sieving. All other aspects are the same as in Example 1.

[0104] Comparative Example 4

[0105] This comparative example provides a method for preparing high-purity chromium powder for target materials. The difference from Example 1 is that the electron beam melting treatment is replaced with plasma arc melting treatment, while all other aspects are the same as in Example 1.

[0106] Performance testing

[0107] The purity and impurity content of the high-purity chromium powders prepared in Examples 1-7 and Comparative Examples 1-4 were tested, and the test results are shown in Table 1.

[0108] Table 1

[0109]

[0110] The test results show that:

[0111] (1) As can be seen from Examples 1 to 3, the present invention can prepare high-purity chromium powder with a purity of 5N and low impurity content by using electron beam melting combined with ball milling process.

[0112] (2) By comparing Example 1 with Examples 4-5, it can be seen that the power of the second heating process in Example 4 is low, resulting in insufficient melting of chromium raw materials, poor fluidity of the molten pool, formation of unmelted and cold shut defects, and the inability of gas and some impurity elements to completely volatilize or settle to the bottom, so the chromium material obtained in the end cannot meet the 5N requirement; the power of the second heating process in Example 5 is high, the molten pool heats up too quickly, material splashes, and the loss of liquid chromium volatilization is aggravated, and the control of the molten pool is poor, so the impurity elements cannot be fully removed to the top of the ingot, so the chromium material obtained in the end has a large loss and cannot stably meet the 5N requirement.

[0113] (3) By comparing Example 1 with Examples 6-7, it can be seen that by maintaining the temperature of the molten pool at 500°C above the melting point of chromium during the refining process, the present invention can further promote the volatilization and discharge of high vapor pressure impurities, and ultimately improve the purity of high-purity chromium powder.

[0114] (4) By comparing Example 1 with Comparative Examples 1-4, it can be seen that in Comparative Example 1, the second heating process was not performed, and the electrolytic chromium sheet was directly melted. The resulting thermal stress caused material splashing, and the control of the molten pool was poor, making it impossible to fully remove impurity elements to the top of the ingot, thus resulting in the purity of the high-purity chromium powder not reaching 5N; in Comparative Example 2, the refining process was not performed, and the low-boiling-point, high-vapor-pressure metal and gaseous impurities could not be removed, resulting in a significant reduction in the purity of the high-purity chromium powder; in Comparative Example 3, the chromium casting was not removed. At both ends of the ingot, the chromium ingot is directly subjected to ball milling and sieving. Since electron beam melting will concentrate difficult-to-remove impurities at the top of the ingot, without removing the two ends of the chromium ingot, the purity of the final high-purity chromium powder cannot reach 5N. In Comparative Example 4, the electron beam melting is replaced with plasma arc melting. Although plasma arc melting can suppress the volatilization loss of chromium, it also weakens the volatilization and impurity removal ability under high vacuum, and cannot achieve deep purification, resulting in the purity of the final high-purity chromium powder not reaching 5N.

[0115] In summary, this invention provides a method for preparing high-purity chromium powder for target materials. By employing electron beam melting technology and combining it with a multi-stage electron beam power control strategy, precise control of the molten pool temperature and refining kinetics is achieved. This method not only efficiently removes conventional metallic impurities with vapor pressures significantly higher than chromium, but also promotes the diffusion and selective removal of trace metallic impurities with vapor pressures similar to chromium, thus breaking through the limitations of existing purification methods. Furthermore, by using protective atmosphere ball milling technology, the obtained high-purity chromium ingots are transformed into chromium powder with excellent performance, greatly expanding its application potential in cutting-edge fields such as high-end additive manufacturing and electronic target materials.

[0116] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing high-purity chromium powder for target materials, characterized in that, The preparation method includes: (1) The pretreated electrolytic chromium sheet is subjected to electron beam melting to obtain a chromium ingot; the two ends of the chromium ingot are removed to obtain a high-purity chromium ingot; The electron beam melting process includes gradient heating, refining, and directional solidification. (2) The high-purity chromium ingot is ball-milled and sieved to obtain the high-purity chromium powder.

2. The preparation method according to claim 1, characterized in that, The pretreatment in step (1) includes ultrasonic cleaning and vacuum drying of the electrolytic chromium sheet; Preferably, the ultrasonic cleaning process specifically involves cleaning the electrolytic chromium sheet alternately with deionized water and organic solvent; Preferably, the organic solvent includes any one or a combination of at least two of anhydrous ethanol, acetone, and isopropanol; Preferably, the temperature of the vacuum drying process is 60-80℃; and the time of the vacuum drying process is 2-4 hours.

3. The preparation method according to claim 1 or 2, characterized in that, The electrolytic chromium sheet contains ≥99.995% chromium.

4. The preparation method according to any one of claims 1-3, characterized in that, The electron beam melting process in step (1) is performed in a vacuum environment; the vacuum degree of the electron beam melting process is 10. -3 -10 -4 Pa.

5. The preparation method according to any one of claims 1-4, characterized in that, The gradient heating process in step (1) includes a first heating process and a second heating process; Preferably, the electron beam power of the first heating treatment is 40-60kW; the temperature of the first heating treatment is 800-1000℃. Preferably, the electron beam power of the second heating treatment is 150-200kW; the temperature of the second heating treatment is 1850-1860℃.

6. The preparation method according to any one of claims 1-5, characterized in that, The refining temperature in step (1) is 2350-2360℃; the holding time for the refining process is 30-60 min.

7. The preparation method according to any one of claims 1-6, characterized in that, The directional solidification process in step (1) adopts a low-speed annular and bottom-focusing mode; the electron beam scanning frequency of the directional solidification is 0.5-2Hz; Preferably, the cooling water flow rate for the directional solidification treatment is 15-30 L / min; Preferably, the directional solidification treatment employs a bottom-up solidification method.

8. The preparation method according to any one of claims 1-7, characterized in that, The ball milling media used in step (2) include high-purity zirconium oxide; Preferably, the ball-to-material ratio in the ball milling process is 3:1 to 6:1; Preferably, the ball milling rotation speed is 60-100 r / min.

9. The preparation method according to any one of claims 1-8, characterized in that, The ball milling process in step (2) includes primary crushing and fine grinding performed sequentially; Preferably, the ball milling time for the primary crushing is 8-16 hours; Preferably, the ball milling time for fine grinding is 20-40 hours.

10. The preparation method according to any one of claims 1-9, characterized in that, The ball milling process described in step (2) is carried out under an inert atmosphere; Preferably, the inert atmosphere comprises high-purity argon; Preferably, the temperature of the ball milling process is <60°C; Preferably, the purity of the high-purity chromium powder in step (2) is ≥5N; the mass content of impurities in the high-purity chromium powder is: O≤50ppm, C≤30ppm, N≤30ppm, Fe≤10ppm, Ni≤10ppm, Al≤10ppm, Si≤10ppm.

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