A method for preparing ultra-pure vanadium metal by zone melting

Abstract

This invention discloses a method for preparing ultrapure metallic vanadium by zone melting, belonging to the field of ultrapure metal preparation technology. The method includes: raw material pretreatment, where 99.9% pure metallic vanadium rods are polished, cleaned, dehydrated, dried, and then vacuum-sealed; and apparatus debugging and atmosphere control, where a vacuum of 3 × 10⁻⁶ is applied. ‑4 -5×10 ‑4 The process involves introducing 99.9999% high-purity argon gas and heating to 1920-1930℃, followed by holding at that temperature. Zone melting is then performed at a speed of 0.8-1 mm / h, with 8-15 alternating forward and reverse melting cycles and a temperature control accuracy of ±2℃. After cooling, the impurity zones at both ends are cut to remove impurities, yielding ultra-pure vanadium with a purity ≥99.999%. This invention, through precise control of the melting zone temperature, moving speed, melting cycles, and atmosphere, increases the purity of metallic vanadium from 99.9% to 99.999%-99.9996%, significantly reducing impurity content. The removal rate of major impurities exceeds 95%, meeting the stringent requirements for high-purity vanadium in the nuclear industry, semiconductors, and other fields.

Description

Technical Field

[0001] This invention relates to the field of ultrapure metal preparation technology, and more particularly to a method for preparing ultrapure metallic vanadium by zone melting. Background Technology

[0002] Vanadium, as an important strategic metal, is widely used in aerospace, nuclear industry, and high-end electronic devices. With the upgrading of downstream industries, the purity requirements for vanadium are becoming increasingly stringent. For example, vanadium alloys used in nuclear reactors require a vanadium purity of ≥99.995% (4.5N grade), while vanadium sputtering targets for semiconductors require a purity of ≥99.999% (5N grade).

[0003] Regarding the preparation technology of high-purity metallic vanadium, US Patent 3425826A discloses a vanadium metal purification method, which uses the aluminothermic method to reduce vanadium pentoxide, followed by treatment under high-temperature vacuum conditions, and finally electron beam melting to obtain vanadium metal with a purity exceeding 99.9%. However, the purity level of this method still cannot meet the current high-end application requirements. In recent years, zone melting technology has received widespread attention in the field of high-purity metal preparation. Chinese Patent CN105331833A discloses a purification device and method for high-purity rare earth metals, integrating electron beam melting, zone melting, and electromigration for purification. Japanese Patent JPH0717971B2 describes a method for purifying cadmium and tellurium using zone melting technology.

[0004] Despite some progress in the preparation of high-purity metals, the following technical challenges remain in the ultrapure preparation of vanadium: First, insufficient temperature control precision. Vanadium has a melting point as high as 1890℃, and existing processes struggle to precisely control the temperature gradient in the melting zone (requiring ±5℃ / cm), leading to instability and low impurity separation efficiency. Second, limited atmosphere protection. Vanadium readily reacts with oxygen and nitrogen at high temperatures, making it difficult to maintain a stable inert atmosphere in the vacuum environment of existing processes. Third, insufficient transmission stability. The melting zone movement speed needs to be controlled within a low range of 0.5-2 mm / h, and existing mechanical transmissions are prone to vibration, causing melting zone displacement. Finally, poor coordination of process parameters. Existing methods do not clearly define the correlation between melting zone temperature, movement speed, number of melting cycles, and impurity removal rate, making it difficult to stably mass-produce 5N-grade ultrapure vanadium. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for preparing ultrapure metallic vanadium through zone melting.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing ultrapure metallic vanadium by zone melting is designed, and the specific steps are as follows: Step S1, raw material pretreatment: Select vanadium metal rods with a purity of 99.9%, and after mechanical polishing, chemical cleaning, dehydration, and drying, vacuum seal them in a quartz tube; Step S2, Device Debugging and Atmosphere Control: Fix the quartz tube containing the vanadium metal rod onto the sample clamping mechanism of the zone melting equipment, and evacuate the melting chamber to 3×10⁻⁶. -4 -5×10 -4 Pa, then high-purity argon gas is introduced into the cavity, while the melting area is heated to 1920-1930℃ and kept at that temperature; Step S3, Zone Melting: Set the melting zone moving speed to 0.8-1 mm / h, and perform 8-15 melting cycles. During the melting process, move the melting zone in alternating forward and reverse directions to maintain the melting zone temperature at 1920-1930℃, with a temperature control accuracy of ±2℃. Step S4, Cooling and Post-processing: After smelting, the furnace is cooled to room temperature, and the impurity enrichment areas at both ends are cut off to obtain ultrapure metallic vanadium with a purity ≥ 99.999%.

[0007] Preferably, in step S1, the mechanical polishing is performed until the surface roughness Ra ≤ 0.8 μm; the chemical cleaning is performed by ultrasonic cleaning with 5% dilute hydrochloric acid solution for 30-45 min, followed by rinsing with deionized water until pH=7; the dehydration is performed by treatment with 99.9% anhydrous ethanol; and the drying conditions are 80-100℃ and a vacuum degree of 1×10⁻⁶. -2 Pa, dry for 2 hours.

[0008] Preferably, in step S2, the purity of the high-purity argon gas is 99.9999%, the flow rate is controlled at 30-50 sccm, and the heat preservation time is controlled at 30 min.

[0009] Preferably, in step S3, the number of smelting times is 8-10 when preparing ultrapure vanadium with a purity of 99.999%, and the number of smelting times is 12-15 when preparing ultrapure vanadium with a purity of 99.9996%.

[0010] Preferably, in step S3, the length of the melting zone is controlled to be 1.5 times the diameter of the vanadium metal rod, and the temperature gradient deviation is controlled within ±5℃ / cm.

[0011] Preferably, in step S4, the cooling rate is ≤5℃ / min.

[0012] Preferably, in step S4, the ultrapure metallic vanadium contains oxygen ≤5ppm, nitrogen ≤3ppm, carbon ≤2ppm, iron ≤1ppm, and silicon ≤1ppm.

[0013] Preferably, in step S1, the mechanical polishing uses 1000-mesh silicon carbide sandpaper; and the temperature of the chemical cleaning is 50°C.

[0014] The present invention proposes a method for preparing ultrapure metallic vanadium by zone melting, which has the following advantages: (1) Significantly improved purity: Through 10-15 zone meltings and precise temperature control, the purity of metallic vanadium can be improved from 3N grade (99.9%) to 5N-5.5N grade (99.999%-99.9996%), with oxygen content ≤5ppm, nitrogen content ≤3ppm, carbon content ≤2ppm, iron content ≤1ppm, and silicon content ≤1ppm, meeting the needs of high-end applications such as nuclear industry (≥4.5N grade) and semiconductor (≥5N grade).

[0015] (2) High process stability: The temperature control accuracy of the device reaches ±2℃, the transmission accuracy is ≤0.01mm, and the atmosphere control accuracy is ±0.5%FS, ensuring the stability of the melting zone. The purity deviation of the products prepared multiple times is ≤0.0002%, which has good reproducibility.

[0016] (3) Significantly reduced energy consumption and cost: Compared with electron beam melting, the energy consumption of the present invention is reduced by 40% (unit energy consumption ≤ 500kWh / t), and the equipment maintenance cost is reduced by 30%, making it suitable for industrial mass production.

[0017] (4) High versatility: The device can be adapted to vanadium rods with a diameter of 10-30mm by adjusting the heating power, melting zone moving speed and sample clamps. It can also be extended to the ultrapure preparation of other high melting point metals such as titanium and zirconium.

[0018] (5) Strong precision control capability: The two-stage vacuum system can stably maintain 5×10 -5 The ultra-high vacuum of Pa, the 6N-level argon protection system to ensure the purity of the atmosphere, and the tungsten-rhenium thermocouple to achieve a temperature measurement accuracy of ±1℃ provide technical support for stable preparation. Attached Figure Description

[0019] Figure 1 This is a flowchart of a method for preparing ultrapure metallic vanadium by zone melting proposed in this invention. Detailed Implementation

[0020] 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.

[0021] Example 1: Preparation of 5N grade ultrapure metallic vanadium The objective of this embodiment is to prepare ultrapure metallic vanadium with a purity of 5N level (≥99.999%). The specific steps are as follows: (1) Raw material pretreatment: Select vanadium metal rods with a purity of 99.9%, with a diameter of 15 mm and a length of 600 mm. Mechanically polish them using 1000-mesh silicon carbide sandpaper until the surface roughness Ra ≤ 0.8 μm. Place the polished vanadium rods in a 5% dilute hydrochloric acid solution and ultrasonically clean them at 50℃ for 30 min. Then rinse them repeatedly with deionized water until the pH of the rinsing solution is 7. After removal, dehydrate them with 99.9% anhydrous ethanol and then place them in a vacuum drying oven at 80℃ and a vacuum degree of 1×10 -2 The vanadium rod was dried at Pa for 2 hours. The dried vanadium rod was then immediately vacuum-sealed in a quartz tube.

[0022] (2) Equipment debugging and atmosphere control: Fix the quartz tube containing the vanadium rod onto the sample clamping mechanism of the zone melting equipment. Start the vacuum system to evacuate the melting chamber to a vacuum level of 5 × 10⁻⁶. -4 After Pa, high-purity argon gas (99.9999%) is introduced into the cavity at a flow rate of 50 sccm. The heating system is then activated to heat the melting area to 1920℃ and held for 30 minutes to stabilize the temperature field.

[0023] (3) Zone melting: The melting zone moving speed is set to 1 mm / h, and the melting zone length is controlled to 22.5 mm (i.e., 1.5 times the diameter of the raw material). Ten melting cycles are performed, using an alternating forward and reverse direction (5 forward cycles, 5 reverse cycles). After each melting cycle, the temperature gradient is calibrated to ensure that the deviation is ≤5℃ / cm. Throughout the melting process, the melting zone temperature is maintained at 1920℃±2℃.

[0024] (4) Cooling and post-processing: After smelting, the vanadium rod is naturally cooled to room temperature with the furnace, and the cooling rate is controlled to be ≤5℃ / min. The cooled vanadium rod is taken out and the impurity enrichment areas of 5cm at both ends are cut off to obtain the final product.

[0025] Technical Results: Detection by inductively coupled plasma mass spectrometry (ICP-MS) and inert gas melting infrared absorption spectrometry showed that the ultrapure vanadium prepared in this embodiment achieved a purity of 99.9992%, with impurity contents of O: 4.8 ppm, N: 2.5 ppm, C: 1.8 ppm, Fe: 0.9 ppm, and Si: 0.7 ppm. Compared to the 3N-grade vanadium raw material, the removal rate of all major impurities exceeded 95%, meeting the 5N-grade standard.

[0026] Example 2: Preparation of 5.5N grade ultra-high purity metallic vanadium The objective of this embodiment is to prepare ultra-high purity metallic vanadium with a purity of 5.5N (≥99.9995%), and to optimize the process parameters based on Example 1.

[0027] (1) Raw material pretreatment: It is basically the same as in Example 1, except that the chemical cleaning time is extended to 45 min and the vacuum drying temperature is increased to 100℃.

[0028] (2) Equipment commissioning and atmosphere control: Evacuate to 3×10 -4 Pa, argon flow rate reduced to 30 sccm, heating temperature increased to 1930℃ and held for 30 min.

[0029] (3) Zone melting: The melting zone moving speed is reduced to 0.8 mm / h, the number of melting times is increased to 15 times (8 times forward and 7 times reverse), the melting zone temperature is maintained at 1930℃±2℃, and other parameters are the same as in Example 1.

[0030] (4) Cooling and post-processing: Same as in Example 1, except that 8cm is cut off at both ends.

[0031] Technical results: The test results show that the ultrapure vanadium prepared in this embodiment has a purity of 99.9996%, and the impurity content is reduced to O: 2.3ppm, N: 1.1ppm, C: 0.9ppm, Fe: 0.5ppm, and Si: 0.4ppm, reaching the 5.5N grade standard. Compared with Example 1, the impurity content is further reduced by more than 50%.

[0032] Example 3: Preparation of 5N-grade ultrapure vanadium for industrial production This embodiment optimizes process efficiency while ensuring 5N-level purity, targeting the needs of industrial production.

[0033] (1) Raw material pretreatment: Larger raw materials are used, with a diameter of 20 mm and a length of 800 mm. Other aspects are the same as in Example 1.

[0034] (2) Equipment commissioning and atmosphere control: Evacuate to 4×10 -4 Pa, argon flow rate 40 sccm, heating temperature 1925℃, hold for 30 min.

[0035] (3) Zone melting: The melting zone moving speed is increased to 1.2 mm / h, the number of melting times is controlled at 8 times (4 times forward and 4 times reverse), and the melting zone temperature is maintained at 1925℃±2℃.

[0036] (4) Cooling and post-treatment: Same as in Example 1.

[0037] Technical Results: Test results show that the product purity is consistently above 99.999%, with impurity contents of O: 4.5ppm, N: 2.8ppm, C: 1.9ppm, Fe: 1.0ppm, and Si: 0.8ppm, meeting the 5N grade requirements. The single-batch production cycle is 80 hours, 33% shorter than the standard process, making it suitable for industrial mass production.

[0038] Comparative Example 1: Conventional Zone Melting Process The conventional zone melting process was adopted, without a precise temperature control system (temperature control accuracy is only ±10℃), without high-purity argon protection (only ordinary argon with a purity of 99.99% was used), and other conditions were basically the same as in Example 1.

[0039] Technical results: The final product purity only reaches 99.99% (4N grade), with impurity contents of O: 15ppm, N: 12ppm, C: 8ppm, Fe: 5ppm, and Si: 4ppm, which cannot meet the 5N grade requirements.

[0040] Comparative Example 2: No alternating forward and reverse melting was used. Based on Example 1, the alternation of forward and reverse directions was eliminated, and only 10 unidirectional meltings were performed, while other conditions remained unchanged.

[0041] Technical results: The product purity reaches 99.998%, but the impurities are unevenly distributed, with a long impurity enrichment area near the tail end, resulting in a 30% reduction in the effective product length and poor batch stability.

[0042] 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 ultrapure metallic vanadium by zone melting, characterized in that, The specific steps are as follows: Step S1, raw material pretreatment: Select vanadium metal rods with a purity of 99.9%, and after mechanical polishing, chemical cleaning, dehydration, and drying, vacuum seal them in a quartz tube; Step S2, Device Debugging and Atmosphere Control: Fix the quartz tube containing the vanadium metal rod onto the sample clamping mechanism of the zone melting equipment, and evacuate the melting chamber to 3×10⁻⁶. -4 -5×10 -4 Pa, then high-purity argon gas is introduced into the cavity, while the melting area is heated to 1920-1930℃ and kept at that temperature; Step S3, Zone Melting: Set the melting zone moving speed to 0.8-1 mm / h, and perform 8-15 melting cycles. During the melting process, move the melting zone in alternating forward and reverse directions to maintain the melting zone temperature at 1920-1930℃, with a temperature control accuracy of ±2℃. Step S4, Cooling and Post-processing: After smelting, the furnace is cooled to room temperature, and the impurity enrichment areas at both ends are cut off to obtain ultrapure metallic vanadium with a purity ≥ 99.999%.

2. The method for preparing ultrapure metallic vanadium by zone melting according to claim 1, characterized in that, In step S1, the mechanical polishing is performed until the surface roughness Ra ≤ 0.8 μm; the chemical cleaning is performed by ultrasonic cleaning with 5% dilute hydrochloric acid solution for 30-45 min, followed by rinsing with deionized water until pH=7; the dehydration is performed by treatment with 99.9% anhydrous ethanol; and the drying conditions are 80-100℃ and a vacuum degree of 1×10⁻⁶. -2 Pa, dry for 2 hours.

3. The method for preparing ultrapure metallic vanadium by zone melting according to claim 1, characterized in that, In step S2, the purity of the high-purity argon gas is 99.9999%, and the flow rate is controlled at 30-50 sccm; and the heat preservation time is controlled at 30 min.

4. The method for preparing ultrapure metallic vanadium by zone melting according to claim 1, characterized in that, In step S3, the number of smelting operations is 8-10 when preparing ultrapure vanadium with a purity of 99.999%, and the number of smelting operations is 12-15 when preparing ultrapure vanadium with a purity of 99.9996%.

5. The method for preparing ultrapure metallic vanadium by zone melting according to claim 1, characterized in that, In step S3, the length of the melting zone is controlled to be 1.5 times the diameter of the vanadium metal rod, and the temperature gradient deviation is controlled within ±5℃ / cm.

6. The method for preparing ultrapure metallic vanadium by zone melting according to claim 1, characterized in that, In step S4, the cooling rate is ≤5℃ / min.

7. The method for preparing ultrapure metallic vanadium by zone melting according to claim 1, characterized in that, In step S4, the ultrapure metallic vanadium contains oxygen ≤5ppm, nitrogen ≤3ppm, carbon ≤2ppm, iron ≤1ppm, and silicon ≤1ppm.

8. The method for preparing ultrapure metallic vanadium by zone melting according to claim 1, characterized in that, In step S1, the mechanical polishing uses 1000-mesh silicon carbide sandpaper; and the temperature of the chemical cleaning is 50°C.

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