Molybdenum powder purification method using vacuum distillation and hydrogen reduction
By combining vacuum distillation and hydrogen reduction, the simultaneous removal of highly volatile impurities and rare earth elements from molybdenum powder is achieved. This solves the problem of the difficulty in removing highly volatile impurities and rare earth elements from molybdenum powder at the same time in existing technologies, improves the purity of molybdenum powder, and meets the requirements of high-end applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-31
- Publication Date
- 2026-04-03
AI Technical Summary
Existing technologies struggle to simultaneously and efficiently remove highly volatile impurities and rare earth elements, especially La, from molybdenum powder, limiting its application in high-end fields.
By employing the synergistic effect of vacuum distillation and hydrogen reduction, and through a two-stage migration mechanism driven by vapor pressure and induced by hydrogenation phase change, the simultaneous removal of highly volatile impurities and rare earth elements is achieved.
The purity of molybdenum powder was increased from 99.478% to 99.80%, and the total amount of impurities was significantly reduced, meeting the requirements of aerospace, vacuum electronic devices and high-performance molybdenum components. The process is environmentally friendly with no waste liquid discharge.
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Figure CN121780903A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of refractory metal powder purification and high-purity metal preparation technology, specifically to a method for purifying molybdenum powder using vacuum distillation and hydrogen reduction. Background Technology
[0002] Molybdenum powder is an important strategic material. Its high melting point, excellent thermal stability, and good electrical conductivity make it a crucial component in high-temperature structural parts, heating elements, getter materials, electronic packaging materials, and refractory metal alloys. Although industrial-grade molybdenum powder is typically obtained by hydrogen reduction of molybdenum oxide, factors such as raw materials, equipment, and the reduction process result in the presence of highly volatile metallic impurities such as K, Zn, and Cd, as well as the rare earth element La, which is tightly bound to the crystal lattice and has an extremely low vapor pressure. The presence of La can cause lattice distortion, reduce the plasticity of molybdenum powder, and lead to grain boundary enrichment during subsequent high-temperature processing, thus limiting its application in high-end fields.
[0003] Common methods for removing impurities include acid leaching, electrolytic refining, and vacuum distillation. While acid leaching can reduce metallic impurities, it generates a large amount of waste liquid containing rare earth metal ions, leading to environmental pollution and high treatment costs. Electrolytic refining equipment is complex, consumes a lot of electricity, and is not suitable for powder systems. Vacuum distillation can only remove highly volatile elements such as K, Zn, and Cd by relying on vapor pressure difference, but it cannot overcome the physical bottleneck of La's extremely low vapor pressure and inability to migrate.
[0004] Therefore, establishing a new mechanism that eliminates the need for wet extraction and liquid waste discharge, while simultaneously enabling the graded removal of highly volatile impurities and rare earth elements, is an urgent technological requirement for the large-scale, high-purity preparation of high-end molybdenum powder. Summary of the Invention
[0005] To address the aforementioned problems, the present invention aims to provide a method for purifying molybdenum powder by simultaneously removing highly volatile impurities and low-volatile rare earth elements from the powder through the synergistic effect of vacuum distillation and hydrogen reduction. By constructing a two-stage migration mechanism of "vapor pressure driven + hydrogenation phase change induced", different types of impurities are desorbed sequentially within a single system, thereby increasing the purity of molybdenum powder from 99.478% to over 99.80%, meeting the requirements of aerospace, vacuum electronic devices, and high-performance molybdenum components.
[0006] This invention discloses a method for purifying molybdenum powder using vacuum distillation and hydrogen reduction, comprising the following:
[0007] In the first stage, the raw molybdenum powder undergoes a vacuum distillation process to remove highly volatile impurities from the powder under the action of vapor pressure difference. Then, in the second stage, the non-volatile rare earth elements undergo a hydrogenation reaction under a hydrogen atmosphere to generate metal hydrides. Through hydrogenation-induced phase transformation, the non-volatile rare earth elements that were originally unable to be desorbed in the gas phase are transformed from a metallic state to a hydrogenated state, thereby significantly increasing their vapor pressure and enabling them to migrate. This allows the non-volatile rare earth elements to detach from the molybdenum lattice and migrate to the condensation zone for deposition based on the vapor pressure difference and the driving force of vapor pressure. This allows for desorption under the action of vapor pressure difference, thus achieving the purification of molybdenum powder.
[0008] The vacuum degree of vacuum distillation is ≤20Pa, preferably ≤10Pa; the distillation temperature is 1000℃~1200℃, preferably 1200℃; this allows highly volatile impurities, including K, Zn, and Cd, to desorb and migrate to the condensation zone; the vacuum distillation time is not particularly limited, but is generally ≥2h. When the content of K, Zn, Cd, and other elements in the molybdenum powder system decreases below the detection limit of the equipment or stops decreasing, the vacuum distillation process is considered to be over.
[0009] Then, at 1000℃~1200℃, preferably 1200℃, a mixture of hydrogen and argon gas is introduced to carry out a hydrogenation reaction. The hydrogen gas fraction is 3%~10%, preferably 4%~8%, which causes the non-volatile rare earth elements, including La, to undergo a hydrogenation reaction to generate metal hydrides such as LaH2, thereby achieving desorption and migration to the condensation zone. The vacuum degree during the hydrogenation reaction is <100Pa, preferably ≤50Pa. The hydrogenation reaction time is not particularly limited, and it can generally be 3h~6h. The hydrogenation can be stopped when the La content no longer decreases.
[0010] The raw molybdenum powder used for purification in each batch is 10g to 10kg, with a particle size of 10μm to 40μm. During vacuum distillation, the heating rate is 5℃ / min to 15℃ / min. During the purification process, the temperature of the condensation zone is at least 200℃ lower than that of the heating zone. After the purification process is completed, an inert gas is introduced, and the cooling rate is about 5℃ / min to cool the powder steadily to room temperature, avoiding structural stress that could cause powder agglomeration, thus obtaining purified molybdenum powder.
[0011] The impurity elements and their contents in the raw molybdenum powder are: La 5100ppm, K 30ppm, Zn 12ppm, Cd 1.1ppm, with a total impurity content of 0.522%; the impurity elements and their contents in the finally purified molybdenum powder are: La 1300ppm~2000ppm, K<0.05ppm, Zn≤4.0ppm, Cd<0.05ppm, with a total impurity content ≤0.20%.
[0012] This invention offers the following advantages: For the first time, it constructs an impurity migration pathway based on the coupling of vapor pressure difference and hydrogenation-induced phase transition, enabling rare earth elements that were previously unable to desorb from the gas phase to transform from a metallic state to a hydrogenated state, achieving a kinetic breakthrough in the detachment of rare earth impurities from the molybdenum lattice. By optimizing temperature, vacuum level, hydrogen gas integral number, and holding time, the time and kinetic windows of distillation migration, hydrogenation reaction, and gas phase migration are kept coupled, forming a synergistic removal effect. This impurity migration behavior has not been reported in the prior art, achieving a mechanistic breakthrough from "non-evaporable impurities" to "migratable phases."
[0013] Molybdenum powder belongs to a high-purity metal system. When the purity reaches 99.4% or higher, the total amount of impurities is already at the ppm or even sub-ppm level. At this point, any improvement of even 0.1% means removing tens to hundreds of ppm of stubborn impurities, which is extremely difficult to achieve, especially for impurities like rare earth element La, which have extremely low vapor pressure and cannot be removed by traditional distillation. After purification using the method of this invention, the La content in the molybdenum powder is reduced from 5100 ppm to 1300 ppm~2000 ppn, and the highly volatile metal impurities are reduced to below the detection limit. The overall purity is increased from 99.478% to over 99.8%, an increase of at least 0.322%, corresponding to a significant removal of at least 3220 ppm of stubborn impurities (especially La). The difficulty of achieving this is far greater than that of conventional purity improvement, fully demonstrating the effectiveness of the dual-mechanism synergistic removal technology of this invention, and completely solving the pain point of existing technologies being unable to remove rare earth impurities and highly volatile impurities simultaneously.
[0014] This invention simultaneously removes both highly volatile and low-volatile elements, overcoming the bottleneck of traditional technologies in removing La. It provides a novel kinetic mechanism framework for molybdenum powder purification technology. The prepared molybdenum powder has a complete crystal lattice structure and exhibits excellent stability during subsequent sintering and deformation processes. The entire process does not use acid washing or electrolysis, resulting in no waste liquid discharge and significant environmental friendliness. The technical path is clear and controllable, suitable for the preparation of high-strength, high-purity, and high-stability molybdenum products. It not only solves the pain points of existing technologies but also upgrades the purification technology of refractory metal powders from a single desorption mode to a composite-driven mode. The prepared molybdenum powder can meet the requirements of aerospace, nuclear energy components, vacuum devices, and semiconductor equipment. It is simple to operate, has strong equipment compatibility, and can be directly applied to existing vacuum metallurgical equipment systems. It possesses good industrial applicability and promotion potential. It has good scalability, enabling large-scale continuous operation and laying the foundation for industrialization. Therefore, this invention is not only a process flow but also an innovative reconstruction of the impurity migration mode of molybdenum powder. Attached Figure Description
[0015] Figure 1 This is a schematic diagram of the vacuum distillation apparatus used in the purification method of the present invention.
[0016] Figure 2The graph shows the relationship between the vapor pressure of different impurity elements and temperature.
[0017] Figure 3 This is a schematic diagram of the hydrogenation-induced La migration mechanism.
[0018] Figure 4 This is a graph showing the change in the impurity content of molybdenum powder with different process stages in Example 1 of the present invention.
[0019] Figure 5 The image shows the elemental scanning diagram of rare earth element enrichment in the condensation end region of Example 1; where (a) is a morphology diagram of molybdenum powder, (b) is a magnified view of a portion of (a), and (c) is a partial elemental point scan diagram of molybdenum powder in (b).
[0020] Figure 6 for Figure 5 (a) Element surface distribution diagram. Detailed Implementation
[0021] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. It should be noted that the embodiments described in this invention are only for further explanation and illustration, and not for limiting their application scope. Based on this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this invention.
[0022] The purification method of this invention includes five steps: vacuum heating, distillation to remove highly volatile impurities, hydrogenation of rare earth elements, migration and deposition of hydrogenation products, and cooling and collection of products. Each step works synergistically to achieve graded desorption and migration of different types of impurities.
[0023] First, industrial-grade molybdenum powder is placed in a crucible at the center of the heating zone to ensure uniform heating and prevent sintering or uneven distribution. The furnace chamber is then evacuated to 1-20 Pa using a vacuum system, allowing the system to transition from atmospheric pressure convective heat transfer to a free molecular flow region. This facilitates the establishment of vapor pressure migration paths, providing the driving force for subsequent distillation. The temperature is then increased to 1000-1200℃ at a rate of 10℃ / min. During this stage, no hydrogen gas is introduced, allowing highly volatile impurities such as K, Zn, and Cd to preferentially desorb and migrate to the condenser end under the influence of the vapor pressure difference.
[0024] After removing volatile impurities, the pressure in the tubular furnace is first evacuated to maintain a low level (controlling low oxygen pressure). Then, the furnace tubes are washed three times with a hydrogen / argon mixed gas, with a vacuum evacuated after each wash, before proceeding with the hydrogenation reaction. Once the temperature stabilizes, a hydrogen / argon mixed gas with a volume fraction of 3%–10% is introduced to allow La to undergo a hydrogenation reaction with hydrogen, generating LaH2 and gaining gas-phase migration capability. In each embodiment, the vacuum degree during the hydrogenation reaction does not exceed 50 Pa. The hydrogenation products are transferred to the condensation end region under the coupling effect of vapor pressure and diffusion dynamics, achieving complete removal of rare earth elements.
[0025] After the flame is extinguished, inert gas is introduced to maintain a cooling rate of approximately 5°C / min, ensuring stable cooling and preventing powder agglomeration caused by structural stress. The crucible is then removed, and the high-purity molybdenum powder product processed according to this invention is collected.
[0026] Figure 1 The structural partition layout of the distillation furnace of the present invention is shown. Figure 2 This indicates that the vapor pressure of La changes very little in the same temperature range, while the vapor pressure of K, Zn, and Cd increases significantly with increasing temperature. Therefore, hydrogenation needs to be introduced to change the migration state of La. Figure 3 The gas-phase migration pathway of La after hydrogenation to form LaH2 is shown, demonstrating the crucial role of hydrogenation in impurity separation.
[0027] In this invention, the detection limit for each element is 0.05 ppm; it cannot be detected when the concentration to be measured is <0.05 ppm. The content of each element is determined by glow discharge mass spectrometry. Specifically, the molybdenum powder sample to be tested is processed and used as the cathode target. High-purity argon gas is introduced as the discharge gas, and the sample is sputtered under glow discharge conditions. The signal is collected and calculated to obtain the content of each element.
[0028] Example 1
[0029] 100g of industrial-grade molybdenum powder with a particle size of 8μm was selected and distilled at 1200℃ for 2h under a vacuum of 5Pa. This desorbed highly volatile impurities such as K, Zn, and Cd, which migrated to the condensation zone, completing the first stage of purification. Then, a hydrogen / argon mixture with a 5% hydrogen content was introduced at the same temperature for 6h of hydrogenation. This converted non-volatile rare earth elements such as La, which were originally unable to desorb in the gas phase, into metal hydrides (LaH2), increasing the vapor pressure of La and causing it to desorb from the molybdenum lattice and migrate to the condensation zone. After deposition, the mixture was collected, completing the second stage of purification. The impurity elements and their contents in the molybdenum powder are shown in Table 1. After purification, the La content decreased from 5100ppm in the original molybdenum powder to 1300ppm, achieving a purity of 99.869%.
[0030] Table 1. Impurity elements and their contents (ppm) in molybdenum powder
[0031] As shown in Table 1, the first stage, the vacuum distillation stage, mainly aims to remove highly volatile impurity elements such as K, Zn, and Cd. These impurity elements, totaling 43.1 ppm, are present in relatively small amounts. After vacuum distillation, the content of highly volatile impurities K and Cd in the original molybdenum powder decreased to below the equipment detection limit of 0.05 ppm; the content of La decreased from 5100 ppm to 5000 ppm. The second stage, the hydrogenation reaction stage, mainly aims to remove non-volatile rare earth elements such as La. La constitutes the majority of the impurities. After being converted to LaH2 and removed through migration, the La content decreased from 0.51% to 0.13%, removing approximately 75%, and the total impurity content decreased from 0.522% to 0.131%.
[0032] Figure 4 The record shows the changes in impurity content during the impurity removal process, reflecting the differences in removal at different stages of the invention. Figure 4 Table 1, together with the table, illustrates the changing trends of the main impurity element content in the molybdenum powder at different processing stages. Highly volatile metal impurities such as K, Zn, and Cd rapidly decreased to below the detection limit during the distillation stage, while the rare earth element La, after undergoing a phase transition to form LaH2 during the hydrogenation stage, migrated to the condensation end region, reducing its content from 5100 ppm to 1300 ppm. These impurity content trajectories demonstrate that the present invention achieves a purification path where impurities with different volatility characteristics are removed sequentially according to their migration kinetics, verifying the effectiveness of the dual-mechanism synergistic removal. The morphology of the purified molybdenum powder is as follows: Figure 5 As shown in (a), Figure 5 (b) is Figure 5 (a) is a magnified view of the morphology of a part. Figure 5 (c) and Figure 6 This explains the enrichment and deposition phenomenon of La after hydrogenation migration, and verifies that the hydrogenation migration mechanism is valid.
[0033] Example 2
[0034] 1 kg of industrial-grade molybdenum powder with a particle size of 10 μm was weighed and distilled at 1100 °C for 2 h under a vacuum of 20 Pa. This desorbed highly volatile impurities such as K, Zn, and Cd, which migrated to the condensation zone, completing the first stage of purification. Then, a hydrogenation reaction was carried out under 3% hydrogen gas for 4 h, converting non-volatile rare earth elements such as La, which were originally unable to be desorbed in the gas phase, into metal hydrides (LaH2). This increased the vapor pressure of La, causing it to desorb from the molybdenum lattice and migrate to the condensation zone, where it was deposited and collected, completing the second stage of purification. The impurity elements and their contents in the molybdenum powder are shown in Table 2. After purification, the La content decreased from 5100 ppm in the original molybdenum powder to 2000 ppm, achieving a purity of 99.80%.
[0035] Table 2. Impurity elements and their contents (ppm) in molybdenum powder
[0036] Example 3
[0037] 500g of industrial-grade molybdenum powder with a particle size of 20μm was selected and distilled at 1200℃ for 2 hours under a vacuum of 15Pa. This desorbed highly volatile impurities such as K, Zn, and Cd, which migrated to the condensation zone, completing the first stage of purification. Then, a hydrogenation reaction was carried out under 5% hydrogen gas for 4 hours, converting non-volatile rare earth elements such as La, which were originally unable to be desorbed in the gas phase, into metal hydrides (LaH2). This increased the vapor pressure of La, causing it to desorb from the molybdenum lattice and migrate to the condensation zone, where it was deposited and collected, completing the second stage of purification. The impurity elements and their contents in the molybdenum powder are shown in Table 3. After purification, the La content decreased from 5100ppm in the original molybdenum powder to 1900ppm, achieving a purity of 99.81%.
[0038] Table 3. Impurity elements and their contents (ppm) in molybdenum powder
[0039] Example 4
[0040] 100g of industrial-grade molybdenum powder with a particle size of 30μm was selected and distilled at 1200℃ for 2 hours under a vacuum of 10Pa. This desorbed highly volatile impurities such as K, Zn, and Cd, which migrated to the condensation zone, completing the first stage of purification. Then, a hydrogenation reaction was carried out under 8% hydrogen gas for 4 hours, converting non-volatile rare earth elements such as La, which were originally unable to be desorbed in the gas phase, into metal hydrides (LaH2). This increased the vapor pressure of La, causing it to desorb from the molybdenum lattice and migrate to the condensation zone, where it was deposited and collected, completing the second stage of purification. The impurity elements and their contents in the molybdenum powder are shown in Table 4. After purification, the La content decreased from 5100ppm in the original molybdenum powder to 1300ppm, achieving a purity of 99.87%.
[0041] Table 4. Impurity elements and their contents (ppm) in molybdenum powder
[0042] As demonstrated by the above embodiments, under the aforementioned conditions, both hydrogenation and diffusion migration are successfully completed, resulting in the synergistic removal of multiple impurities from the molybdenum powder, achieving a stable purity of no less than 99.80%. Consistent purification effects were maintained even after expanding the dosage range to 1 kg, indicating the scalability potential of this invention. Experiments using raw molybdenum powder with particle sizes ranging from 10 μm to 40 μm showed consistent removal effects, proving that this invention is independent of powder particle size.
[0043] When the vacuum degree exceeds 20 Pa during vacuum distillation or 100 Pa during hydrogenation, the vapor pressure of highly volatile metallic impurities (such as K, Zn, Cd, etc.) and non-volatile rare earth impurities is significantly lower than the critical vapor pressure required for distillation, making them difficult to effectively evaporate and migrate. Actual measured impurity residues are significantly higher than expected, rendering purification essentially ineffective. When the distillation and hydrogenation temperatures are below 1000℃, the vapor pressure of volatile impurities is insufficient, the hydrogenation reaction is slow, and the minimum requirements for distillation migration cannot be met. The reaction rate of H2 with La is low, resulting in poor La removal and high impurity residues. Temperatures above 1200℃ can lead to abnormal growth of molybdenum grains. During hydrogenation, an H2 concentration of less than 3% results in incomplete reaction and insignificant La removal. A hydrogen concentration above 10% can easily induce abnormal surface reconstruction of Mo.
[0044] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.
Claims
1. A method for purifying molybdenum powder using vacuum distillation and hydrogen reduction, characterized in that, Includes the following: The raw molybdenum powder is first desorbed by vacuum distillation under the action of vapor pressure difference to remove highly volatile impurities. Then, in a hydrogen atmosphere, the non-volatile rare earth elements undergo a hydrogenation reaction to generate metal hydrides. Through hydrogenation-induced phase transformation, the non-volatile rare earth elements that could not be desorbed in the gas phase are transformed from a metallic state to a hydrogenated state, which can then be desorbed under the action of vapor pressure difference, thus achieving the purification of molybdenum powder.
2. The method for purifying molybdenum powder using vacuum distillation and hydrogen reduction according to claim 1, characterized in that, The original molybdenum powder contained the following impurity elements and their contents: La 5100ppm, K 30ppm, Zn 12ppm, Cd 1.1ppm, with a total impurity content of 0.522%; the final purified molybdenum powder contained the following impurity elements and their contents: La 1300ppm~2000ppm, K<0.05ppm, Zn≤4.0ppm, Cd<0.05ppm, with a total impurity content ≤0.20%.
3. The method for purifying molybdenum powder using vacuum distillation and hydrogen reduction according to claim 1, characterized in that, The raw molybdenum powder used for purification in each batch is 10g to 10kg in weight and has a particle size of 10μm to 40μm. The heating rate during vacuum distillation is 5℃ / min to 15℃ / min.
4. The method for purifying molybdenum powder using vacuum distillation and hydrogen reduction according to claim 1, characterized in that, The highly volatile impurities include K, Zn, and Cd elements, and the non-volatile rare earth elements include La element.
5. The method for purifying molybdenum powder using vacuum distillation and hydrogen reduction according to claim 1, characterized in that, The vacuum degree of the vacuum distillation is ≤20Pa, and the temperature of the vacuum distillation is 1000℃~1200℃; the temperature of the hydrogenation reaction is 1000℃~1200℃, and the vacuum degree during the hydrogenation reaction is <100Pa.
6. The method for purifying molybdenum powder using vacuum distillation and hydrogen reduction according to claim 5, characterized in that, The vacuum degree of the vacuum distillation is ≤10Pa, and the temperature of the vacuum distillation is 1200℃; the temperature of the hydrogenation reaction is 1200℃, and the vacuum degree of the hydrogenation reaction is ≤50Pa.
7. The method for purifying molybdenum powder using vacuum distillation and hydrogen reduction according to claim 1, characterized in that, The hydrogen atmosphere is a mixture of hydrogen and argon with a hydrogen gas fraction of 3% to 10%.
8. The method for purifying molybdenum powder using vacuum distillation and hydrogen reduction according to claim 7, characterized in that, The hydrogen atmosphere is a mixture of hydrogen and argon with a hydrogen gas integral of 4% to 8%.
9. The method for purifying molybdenum powder using vacuum distillation and hydrogen reduction according to claim 1, characterized in that, The vacuum distillation time is no less than 2 hours, and the hydrogenation reaction time is 3 to 6 hours.
10. The method for purifying molybdenum powder using vacuum distillation and hydrogen reduction according to claim 1, characterized in that, During the purification process, the temperature of the condensation zone is at least 200°C lower than that of the heating zone. After the purification process is completed, an inert gas is introduced and the cooling rate is 5°C / min to allow the molybdenum powder to cool steadily to room temperature and avoid powder agglomeration caused by structural stress.