A method for preparing ultra-high purity vanadium single crystal by cold crucible pulling method

Abstract

This invention discloses a method for preparing ultra-high purity vanadium single crystals using the cold crucible pulling method, comprising: raw material pretreatment, acid washing with a mixed acid solution of HNO3:HF:H2O=(2-4):(0.5-1.5):(8-12), and then... ‑5 Degassing at 800-900℃ under vacuum; smelting and refining: the raw material is placed in a water-cooled copper crucible with a 50-200μm thick yttrium-stabilized zirconium oxide or hafnium oxide coating, and smelted at ≤5×10⁻⁶ ℃. ‑5 Under vacuum and ≥6N ultra-high purity argon gas protection, melting is achieved through 15-25kHz radio frequency induction heating, followed by electron beam or laser scanning refining for 3-8 minutes; crystal lead-in and necking growth are then performed using… <100> or <110> Crystal orientation seed crystal, necking diameter 3-5mm, length ≥20mm; shoulder formation and constant diameter growth, pulling speed 2-10mm / h, rotation speed 5-15rpm, closed-loop diameter control, axial temperature gradient 10-30℃ / cm; tailing and cooling, programmed cooling at ≥50℃ / h. The vanadium single crystal prepared by this invention has a purity ≥99.9995%, total interstitial atoms ≤10wppm, and dislocation density ≤10 3 cm ‑2 With a diameter of 20-80mm and a length of 100-200mm, it can be applied to the fields of semiconductor devices, superconducting devices, or quantum computing devices.

Description

Technical Field

[0001] This invention relates to the fields of high-purity metal material preparation technology and single crystal growth technology, and particularly to a method for preparing ultra-high-purity vanadium single crystals using the cold crucible pulling method. Background Technology

[0002] Vanadium metal possesses excellent corrosion resistance, high-temperature strength, and unique nuclear physics properties, making it an important strategic metallic material. Ultra-high purity vanadium (purity ≥5N5, i.e., 99.9995%) single crystals have enormous application potential in fundamental physics research, superconducting devices, quantum computing, and the cutting-edge semiconductor industry.

[0003] Currently, the main methods for preparing metallic vanadium include calcothermal reduction and hydrogenation dehydrogenation. However, these methods mostly yield polycrystalline powders or ingots with low purity (usually below 3N) and contain a large number of interstitial atoms (such as oxygen, carbon, and nitrogen) and substitutional atoms (such as iron, chromium, and nickel) as impurities. These impurities severely disrupt the crystal lattice integrity of vanadium, significantly deteriorating its electrical, magnetic, and superconducting properties.

[0004] To obtain high-purity vanadium single crystals, existing technologies have attempted electron beam levitation zone melting (FZ). Although this method avoids crucible contamination, it suffers from problems such as small crystal size (typically less than 10 mm in diameter), unstable growth process, low yield, complex equipment, and high cost, making it difficult to achieve large-scale preparation of large-size, high-quality single crystals.

[0005] In the field of single crystal growth technology, US Patent 4565598 discloses a method and apparatus for controlling the diameter of a Czochralski crystal during growth by measuring the crystal weight and the crystal-melt interface temperature. European Patent EP0855455B1 describes a crucible for growing single crystals from melt in a substantially inert atmosphere, the crucible being composed of sintered rhenium. Regarding the preparation of refractory metal single crystals, the paper "Cold metal crucible system for synthesis, zone refining, and Czochralski crystal growth of refractory metals and semiconductors" published in ScienceDirect proposes a cold metal crucible apparatus combined with induction heating for the synthesis, purification, and single crystal growth of refractory semiconductors and metals. US Patent 9090989B2 and Chinese Patent CN104364428A disclose vanadium-compensated silicon carbide single crystals and their crystal growth process.

[0006] However, existing technologies still have significant shortcomings in the preparation of vanadium single crystals: First, traditional methods cannot effectively remove special impurities in vanadium materials, especially the content of interstitial atoms, which is difficult to control at ultra-low levels; second, although cold crucible technology can avoid contamination, it lacks specific process optimization for the characteristics of vanadium materials; third, existing diameter control technologies are mostly general solutions and have not been optimized in combination with the special melting and crystallization behavior of vanadium materials; fourth, there is a lack of systematic integration of multiple purification methods, making it difficult to achieve the comprehensive technical indicators of ultra-high purity (≥5N5) and ultra-low impurity content (interstitial atoms <10wppm).

[0007] Therefore, developing a method to effectively overcome crucible contamination and stably grow large-size, ultra-high-purity vanadium single crystals has become a pressing technical challenge in this field. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies, such as low purity of vanadium products, the presence of a large number of interstitial and substitutional atom impurities, small crystal size, complex and costly equipment, and difficulty in large-scale preparation of large-size, high-quality vanadium single crystals. Therefore, this invention proposes a method for preparing ultra-high purity vanadium single crystals using the cold crucible pulling method.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing ultra-high purity vanadium single crystals using the cold crucible pulling method is designed, including the following steps: a) The raw vanadium is pretreated by acid washing. The acid washing uses a mixed solution of ultrapure nitric acid, hydrofluoric acid, and water in a volume ratio of HNO3:HF:H2O = (2-4):(0.5-1.5):(8-12). Then, ultrasonic cleaning is performed under a vacuum degree ≤1×10⁻⁶. - 5 High-temperature degassing treatment was carried out under Pa conditions; b) Place the pretreated raw material in a water-cooled copper crucible with an inner wall coated with a yttrium-stabilized zirconium oxide or hafnium oxide refractory coating, the thickness of which is 50-200 micrometers, under a vacuum degree ≤5×10⁻⁶. -5 The chamber of Pa is filled with ultra-high purity argon gas with a purity ≥6N. The raw materials are melted to form a molten pool by radio frequency induction heating, and the surface of the melt is scanned and refined by electron beam or laser. c) Using ultra-high purity vanadium single crystal seed crystals for crystal introduction, and necking growth is carried out by controlling radio frequency power and pulling speed. The necking section has a diameter of 3-5 mm and a length of ≥20 mm. d) Perform shoulder formation and constant diameter growth. During the constant diameter growth stage, the pulling speed is 2-10 mm / h and the crystal rotation speed is 5-15 rpm. The crystal diameter is stabilized by the closed-loop linkage of the real-time weighing system and the control system, and the axial temperature gradient is maintained at 10-30℃ / cm. e) After the growth is completed, the temperature is reduced to below 200℃ at a rate of ≥50℃ / h.

[0010] Preferably, the high-temperature degassing treatment in step a) is characterized by a temperature of 800-900°C and a holding time of 1-3 hours.

[0011] Preferably, the frequency of the radio frequency induction heating in step b) is 15-25 kHz.

[0012] Preferably, the scanning and refining time in step b) is 3-8 minutes.

[0013] Preferably, the crystal orientation of the seed crystal in step c) is <100> or <110> .

[0014] Preferably, in step d), the diameter of the crystal grown in the medium diameter stage is 20-80 mm.

[0015] This invention also provides an ultra-high purity vanadium single crystal prepared by the above method, with a purity ≥99.9995%, a total content of interstitial oxygen, carbon, and nitrogen ≤10 wppm, and a dislocation density ≤10 3 cm -2 .

[0016] Preferably, its diameter is 20-80mm and its length is 100-200mm.

[0017] Preferably, the total content of metallic impurities is ≤5wppm.

[0018] This invention also relates to the application of the ultra-high purity vanadium single crystal in the fabrication of semiconductor devices, superconducting devices, or quantum computing devices.

[0019] The present invention proposes a method for preparing ultra-high purity vanadium single crystals using the cold crucible pulling method, which has the following advantages: 1. Ultra-high purity: Through multiple purification methods such as raw material pretreatment, cold crucible, dynamic high vacuum / protective atmosphere, and surface refining, interstitial atoms and metal impurities in vanadium raw materials are effectively removed. The purity of the vanadium single crystal obtained can reach 5N5 (99.9995%) or higher, the total number of interstitial atoms (O+C+N) can be controlled below 10wppm, and the total content of metal impurities is ≤5wppm.

[0020] 2. High crystal quality: The rigorous necking process effectively eliminates dislocations. Combined with precise control of the temperature field and growth rate, the grown single crystal has a low dislocation density (≤10). 3 cm -2 ), with good lattice integrity.

[0021] 3. Large size and low cost: Compared with electron beam zone melting, this invention can stably grow large single crystals with diameters of 20mm to 80mm and lengths of 100-200mm, which improves material utilization, reduces unit cost, and is more suitable for industrial applications.

[0022] 4. Stable and controllable process: The weighing method and computer closed-loop control are adopted to realize the automation and high repeatability of constant diameter growth. Through the closed-loop linkage between the real-time weighing system and the control system, the heating power and lifting speed are dynamically adjusted, which greatly improves the yield.

[0023] 5. Significant effects of multiple purification processes: The combination of technologies such as mixed acid pretreatment, YSZ or hafnium oxide refractory coating, and electron beam or laser surface scanning refining enables full purification control from raw materials to products, effectively solving the problems of crucible contamination and impurity introduction. Attached Figure Description

[0024] Figure 1 This is a flowchart of a method for preparing ultra-high purity vanadium single crystals using the cold crucible pulling method proposed in this invention. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0026] Example 1: Preparation of ultra-high purity 5N7 vanadium single crystals (standard process conditions) (1) Raw material pretreatment: Vanadium rods refined by the iodination method with a purity of 4N5 (99.995%) were selected as raw materials. The surface oxide layer was removed by mechanical grinding, and the rods were placed in a mixed acid solution with a volume ratio of HNO3:HF:H2O=3:1:10 for 2 minutes for corrosion. The rods were then rinsed with 18.2 MΩ·cm ultrapure water and ultrasonically cleaned for 15 minutes. Finally, the rods were subjected to a 1×10⁻⁶ molten metal bath. -5 Degas under vacuum at 850℃ for 2 hours.

[0027] (2) Smelting and refining: The processed raw materials are placed into a water-cooled copper crucible with a 100μm thick YSZ coating on the inner wall. A vacuum of 3×10⁻⁶ is applied. -5 After Pa, backfill with 6N high-purity argon gas to 100 Pa. Start 20kHz radio frequency induction heating to completely melt the raw material, and use an electron beam to scan the surface of the melt for 5 minutes to remove volatile impurities.

[0028] (3) Crystal introduction and necking growth: using <100> Using a 5N8 vanadium single crystal as a seed crystal, the crystal is moved down to contact the melt and then necked at a pulling speed of 15 mm / h and a rotation speed of 10 rpm to form a thin neck with a diameter of 4 mm and a length of 25 mm to eliminate dislocations.

[0029] (4) Shoulder formation and constant diameter growth: The pulling speed is reduced to 5 mm / h to form shoulders, so that the crystal diameter is uniformly enlarged to 50 mm within 40 minutes. During the constant diameter growth stage, the pulling speed is stabilized at 4 mm / h, the rotation speed is 8 rpm, the diameter is maintained at 50 mm by the automatic diameter control system, the axial temperature gradient is controlled at 20℃ / cm, and the growth length is 150 mm.

[0030] (5) Finishing and Cooling: During the finishing process, the pulling speed is rapidly increased to 20 mm / h and the power is increased so that the crystal is detached from the melt within 10 minutes. The crystal is then lifted to the upper part of the furnace and cooled to room temperature at a rate of 60℃ / h.

[0031] Technical Results: The prepared vanadium single crystals have a purity exceeding 5N7, with a total metallic impurity content of <2wppm, O, C, and N contents of <3, 2, and 1wppm respectively, a total interstitial atom content of <6wppm, and a dislocation density of approximately 5×10⁻⁶. 2 cm -2 The crystal is complete. <100> Oriented single crystal, 50mm in diameter and 150mm in length.

[0032] Example 2: Preparation of large-size 80mm vanadium single crystals (upper limit parameter conditions) (1) Raw material pretreatment: The same raw materials as in Example 1 were used, and the acid solution ratio was adjusted to HNO3:HF:H2O=4:1.5:8. The degassing temperature was increased to 900℃ and kept at that temperature for 3 hours to remove gaseous impurities more thoroughly.

[0033] (2) Melting and refining: A water-cooled copper crucible with a 200μm thick hafnium oxide coating is used to further reduce metal contamination. The radio frequency is 25kHz, and the laser scanning refining process lasts for 8 minutes.

[0034] (3) Crystal introduction and necking growth: The necking section has a diameter of 5 mm and a length of 20 mm, and the rest is the same as in Example 1.

[0035] (4) Shoulder and constant diameter growth: The target diameter for constant diameter growth is 80 mm. The lifting speed is reduced to 2 mm / h, the rotation speed is 5 rpm, and the axial temperature gradient is controlled at 30℃ / cm to maintain a stable solid-liquid interface.

[0036] (5) Finishing and cooling: The programmed cooling rate is 50℃ / h.

[0037] Technical Results: Successfully prepared large-size vanadium single crystals with a diameter of 80mm, achieving a purity of over 5N6, a total interstitial atom count of <8wppm, and a dislocation density of <8×10⁻⁶. 2 cm -2 The crystals are of good quality, with size uniformity better than ±1 mm.

[0038] Example 3: Rapid growth of medium-sized vanadium single crystals (lower limit parameter optimization) (1) Raw material pretreatment: acid solution ratio HNO3:HF:H2O=2:0.5:12, degassing temperature 800℃ and keep warm for 1 hour.

[0039] (2) Melting and refining: using a 50μm thick YSZ coating, RF frequency 15kHz, electron beam scanning for 3 minutes.

[0040] (3) Crystal introduction and necking growth: The necking section has a diameter of 3mm and a length of 20mm.

[0041] (4) Shoulder setting and equal diameter growth: The target diameter for equal diameter growth is 30mm. The lifting speed is increased to 10mm / h, the rotation speed is 15rpm, and the axial temperature gradient is controlled at 10℃ / cm.

[0042] (5) Finishing and cooling: The program cooling rate is 80℃ / h to shorten the total cycle.

[0043] Technical results: The prepared 30mm diameter vanadium single crystals have a purity ≥5N5, a total interstitial atom count <10wppm, and a dislocation density <10 3 cm -2 The total preparation cycle is shortened by 40% compared to the standard process, production efficiency is significantly improved, and product quality is stable.

[0044] Comparative Example 1: The Cold Crucible Lifting Method of the Present Invention Experimental conditions: The complete process conditions of Example 1 were adopted, including key technologies such as mixed acid pretreatment, YSZ coated water-cooled copper crucible, electron beam surface refining, and closed-loop weighing control.

[0045] Experimental results: Vanadium single crystal purity 5N7, total metallic impurities <2wppm, interstitial atoms O+C+N <6wppm, dislocation density 5×10 2 cm -2 The crystal has a diameter of 50mm and a length of 150mm, with a yield rate of >90%.

[0046] Comparative Example 2: Traditional Electron Beam Zone Melting Method Experimental conditions: Using raw materials of the same purity, electron beam levitation melting equipment, no crucible contact, argon protective atmosphere, and the same analytical detection methods.

[0047] Experimental results: Vanadium single crystal purity 5N3, total metallic impurities <10wppm, interstitial atoms O+C+N approximately 25wppm, dislocation density 2×10 3 cm -2 The crystal has a diameter of 8mm and a length of 60mm, with a yield of approximately 60%.

[0048] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing ultra-high purity vanadium single crystals using the cold crucible pulling method, characterized in that, Includes the following steps: a) The raw vanadium is pretreated by acid washing. The acid washing uses a mixed solution of ultrapure nitric acid, hydrofluoric acid, and water in a volume ratio of HNO3:HF:H2O = (2-4):(0.5-1.5):(8-12). Then, ultrasonic cleaning is performed under a vacuum degree ≤1×10⁻⁶. -5 High-temperature degassing treatment was carried out under Pa conditions; b) Place the pretreated raw material in a water-cooled copper crucible with an inner wall coated with a yttrium-stabilized zirconium oxide or hafnium oxide refractory coating, the thickness of which is 50-200 micrometers, under a vacuum degree ≤5×10⁻⁶. -5 The chamber of Pa is filled with ultra-high purity argon gas with a purity ≥6N. The raw materials are melted to form a molten pool by radio frequency induction heating, and the surface of the melt is scanned and refined by electron beam or laser. c) Using ultra-high purity vanadium single crystal seed crystals for crystal introduction, and necking growth is carried out by controlling radio frequency power and pulling speed. The necking section has a diameter of 3-5 mm and a length of ≥20 mm. d) Perform shoulder formation and constant diameter growth. During the constant diameter growth stage, the pulling speed is 2-10 mm / h and the crystal rotation speed is 5-15 rpm. The crystal diameter is stabilized by the closed-loop linkage of the real-time weighing system and the control system, and the axial temperature gradient is maintained at 10-30℃ / cm. e) After the growth is completed, the temperature is reduced to below 200℃ at a rate of ≥50℃ / h.

2. The method for preparing ultra-high purity vanadium single crystals using the cold crucible pulling method according to claim 1, characterized in that, The high-temperature degassing treatment in step a) is performed at a temperature of 800-900℃ and the holding time is 1-3 hours.

3. The method for preparing ultra-high purity vanadium single crystals using the cold crucible pulling method according to claim 1, characterized in that, The frequency of the radio frequency induction heating described in step b) is 15-25 kHz.

4. The method for preparing ultra-high purity vanadium single crystals using the cold crucible pulling method according to claim 1, characterized in that, The scanning and refining time described in step b) is 3-8 minutes.

5. The method for preparing ultra-high purity vanadium single crystals using the cold crucible pulling method according to claim 1, characterized in that, The crystal orientation of the seed crystal mentioned in step c) is <100> or <110> .

6. The method for preparing ultra-high purity vanadium single crystals using the cold crucible pulling method according to claim 1, characterized in that, In step d), the diameter of the medium-diameter grown crystal is 20-80 mm.

7. An ultra-high purity vanadium single crystal prepared by the method according to any one of claims 1-6, characterized in that, Its purity is ≥99.9995%, the total content of interstitial oxygen, carbon, and nitrogen is ≤10wppm, and the dislocation density is ≤10 3 cm -2 .

8. The ultra-high purity vanadium single crystal according to claim 7, characterized in that, Its diameter is 20-80mm and its length is 100-200mm.

9. The ultra-high purity vanadium single crystal according to claim 7, characterized in that, The total content of metallic impurities is ≤5wppm.

10. The application of the ultra-high purity vanadium single crystal according to any one of claims 7-9 in the preparation of semiconductor devices, superconducting devices or quantum computing devices.

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