Method for preparing high-purity ultrafine tungsten powder by series impurity removal and microwave calcination

Abstract

The application discloses a method for preparing high-purity superfine tungsten powder by series impurity removal and microwave calcination, and relates to the technical field of refractory metal powder metallurgy. The method uses 99% and below industrial-grade ammonium paratungstate as raw material, and sequentially performs pyrolysis, two-stage physical purification, ultrasonic synergic acidolysis deep purification, microwave uniform calcination and sectional reduction. Firstly, the ammonia solution-evaporation crystallization method and the chemical precipitation method are connected in series to realize deep impurity removal, and the chemical precipitation method is used to directly obtain a nano tungsten oxide precursor, so that the morphology of the tungsten powder is guaranteed for subsequent reduction; secondly, the microwave calcination process is introduced to realize fast and green and environment-friendly uniform heating, and the hard agglomeration of the precursor is significantly reduced; finally, the sectional reduction method is adopted to effectively block the CVT effect in the reduction process, and abnormal grain growth is avoided. The method solves the problems of incomplete purification, sintering agglomeration of the precursor during reduction and out-of-control reduction particle size in the prior art, and the prepared tungsten powder has high purity and small average particle size.

Description

Technical Field

[0001] This invention relates to the field of refractory metal powder metallurgy technology, specifically to a method for preparing high-purity ultrafine tungsten powder by a series of impurity removal and microwave calcination. Background Technology

[0002] Tungsten, hailed as the "teeth of industry," plays an irreplaceable role in high-end fields such as high-performance cemented carbide, semiconductor sputtering targets, and microelectronics. These cutting-edge fields place extremely high demands on the raw materials for high-end tungsten products, often requiring a purity of over 99.95% and particle sizes down to the ultrafine or even nanoscale. However, existing technologies for preparing high-purity ultrafine tungsten powder from ordinary industrial-grade ammonium paratungstate (APT) generally face the following three major technical bottlenecks: Firstly, in terms of tungstate purification and impurity removal processes, existing technologies struggle to simultaneously achieve deep purification and fine-grained precursor morphology control. Industrially, thermal dissociation-ammonia dissolution, ion exchange, or solvent extraction are commonly used to purify ammonium tungstate solutions. However, thermal dissociation-ammonia dissolution relies solely on crystallization for impurity removal, resulting in low efficiency per cycle, requiring multiple cycles, high energy consumption, and producing large precursor particles. Ion exchange methods easily trap impurities such as sodium in the resin pores, hindering cleaning and generating large wastewater discharges. Solvent extraction produces ammonia nitrogen wastewater and is ineffective at removing impurities such as phosphorus, arsenic, silicon, and molybdenum. For ordinary industrial-grade ammonium paratungstate, both single evaporation crystallization and neutralization precipitation methods have limitations, failing to simultaneously achieve deep removal of key impurities such as K, Na, Fe, and Mo while effectively controlling precursor morphology.

[0003] Secondly, traditional precursor calcination processes easily damage the morphology, leading to severe agglomeration. Traditional processes often employ heat conduction heating (such as in a muffle furnace) to calcine ammonium paratungstate to prepare tungsten oxide. This process involves heat transfer from the surface inwards, which is not only energy-intensive and time-consuming, but also prone to surface sintering and hard agglomeration that is difficult to pulverize due to uneven heating of the powder. This morphological damage makes the subsequent preparation of highly dispersed ultrafine powders extremely difficult.

[0004] Finally, precursor agglomeration triggers abnormal grain growth during the reduction process, making it difficult to achieve both high purity and ultrafine particle size. During the precursor liquid-phase precipitation stage, nanoparticles are highly susceptible to soft agglomeration. In the subsequent hydrogen reduction stage, a significant chemical vapor migration (CVT) effect occurs, which easily leads to abnormal tungsten powder grain growth. To refine the grains, some existing technologies attempt to use physical methods such as high-energy ball milling, but this inevitably introduces foreign impurities such as grinding media, severely reducing the purity of the powder.

[0005] In summary, current technologies lack a comprehensive, coordinated control method for the entire process. The industry urgently needs to develop a method that starts with ordinary industrial-grade ammonium paratungstate, achieves deep purification through a series of impurity removal processes while simultaneously obtaining nano-scale tungsten acid precursors, and then combines this with environmentally friendly principles such as microwave uniform heating to prevent agglomeration, thereby producing nano-tungsten oxide. This would lay a solid precursor foundation for the subsequent controlled reduction of high-purity ultrafine tungsten powder. Summary of the Invention

[0006] The purpose of this invention is to at least solve one of the technical problems existing in the prior art, and to provide a method for preparing high-purity ultrafine tungsten powder by series impurity removal and microwave calcination.

[0007] The technical solution of the present invention is as follows: A method for preparing high-purity ultrafine tungsten powder by a series of impurity removal and microwave calcination includes the following steps: S1: Thermally dissociate ammonium paratungstate raw material to obtain thermal dissociation products; S2: Dissolve the thermal dissociation product in an ammonia solution. When the solution is clear or the insoluble matter is ≤1wt%, immediately filter out the insoluble impurities. The filtered ammonium tungstate solution is kept at 80-100℃ for evaporation and crystallization. When the solution evaporates to 60%-80%, immediately filter, wash with deionized water and anhydrous ethanol, and dry to obtain the first purified product. The first purified product is thermally dissociated a second time and dissolved in ammonia to obtain a purified ammonium tungstate solution. S3: Under the synergistic effect of ultrasound, hydrochloric acid is added dropwise to the purified ammonium tungstate solution at a flow rate of 1-20 ml / min, maintaining the pH value of the system ≤2. After the reaction is complete, the solid and liquid are separated and dried to obtain nano-tungstate. S4: Place nano-tungstic acid in a microwave field and calcine it at 400-800℃ for 0.5-2 hours to obtain low-agglomeration nano-tungsten oxide; S5: Low-agglomeration nano-tungsten oxide is placed in a hydrogen atmosphere and first pre-reduced at a low temperature of 500-700℃, and then finally reduced at a high temperature of 700-900℃ to obtain high-purity ultrafine tungsten powder.

[0008] Preferably, in step S1, the thermal dissociation temperature is 300-350℃, and the thermal dissociation time is 1-3h; The ammonium paratungstate raw material is industrial-grade ammonium paratungstate with a purity of 99% or lower.

[0009] Preferably, in step S2, the concentration of the ammonia solution is 50-200 g / L; the solid-liquid ratio of the thermal dissociation product to the ammonia solution is 1:4-1:8. The thermally dissociated products were dissolved in an ammonia solution and stirred at a speed of 200-400 r / min; after filtration, they were washed alternately with deionized water and anhydrous ethanol.

[0010] Preferably, in step S3, the molar concentration of the hydrochloric acid is 6-12 mol / L, and the reaction temperature under the synergistic effect of ultrasound is 60-90℃.

[0011] Preferably, in step S5, the hydrogen flow rate in the low-temperature pre-reduction stage is 100-500 ml / min, and the holding time is 60-120 min; the hydrogen flow rate in the high-temperature final reduction stage is 100-500 ml / min, and the holding time is 120-180 min.

[0012] Preferably, in step S4, the heating rate in the microwave field is 10-30℃ / min, and the microwave power is 800-2000W.

[0013] The present invention also discloses a high-purity ultrafine tungsten powder, which is prepared by the method described in any of the preceding methods.

[0014] Preferably, the tungsten powder has a purity of ≥99.95%, a body-centered cubic crystal structure, and an average particle size of ≤1μm.

[0015] The beneficial effects of this invention are: (1) The purity meets the standard and the impurity removal effect is significant: the physical purification of "ammonia dissolution-evaporation crystallization" and the chemical deep impurity removal of "ultrasonic acid hydrolysis" are carried out in series. Starting from ordinary industrial grade ammonium paratungstate with a purity of 99.0%, the final purity of tungsten powder can be stably increased to more than 99.95%. It has a good removal effect on key impurities such as Na, Fe, Cu, and Mo, and efficiently solves the core problem of deep impurity removal of industrial grade raw materials to 99.95%.

[0016] (2) Precise morphology control and no obvious agglomeration: The ultrasonic cavitation effect inhibits the soft agglomeration of tungstic acid precursor, and the microwave homogenization calcination adopts internal heating to avoid the formation of hard agglomerates, thus controlling the agglomeration problem of precursor from the source and laying the foundation for the preparation of ultrafine tungsten powder.

[0017] (3) Narrow particle size distribution and stable ultrafine effect: The segmented airflow controlled reduction effectively blocks the chemical vapor migration (CVT) effect in the reduction process by using a large flow of hydrogen in the low-temperature pre-reduction stage, avoiding abnormal grain growth, and finally obtaining ultrafine tungsten powder with an average particle size ≤1μm and a narrow particle size distribution.

[0018] (4) Simple process and strong industrial applicability: This invention uses ordinary industrial grade ammonium paratungstate as raw material, without the need for complex anion exchange and other processes, with low reagent consumption, easy control of process parameters for microwave calcination and segmented reduction, and the equipment for each step is all conventional industrial equipment, making it easy to achieve industrial scale-up.

[0019] (5) Excellent product performance to meet high-end needs: The prepared high-purity ultrafine tungsten powder has the characteristics of high purity of over 99.95%, ultrafine particle size and good dispersibility, which can meet the application requirements of high-performance cemented carbide, semiconductor target material, high-end electronic material and other fields. Attached Figure Description

[0020] Figure 1 For process flow diagram; Figure 2 X-ray diffraction pattern of ammonium paratungstate raw material powder used in the invention; Figure 3 The X-ray diffraction pattern of tungsten oxide powder obtained by microwave calcination in Example 1 is shown below. Figure 4 The X-ray diffraction pattern of the tungsten powder prepared in Example 1; Figure 5 SEM image of the ammonium paratungstate raw material used in the invention at 120x magnification; Figure 6 SEM image of the 3000x magnification of tungstate precursor prepared in Example 1; Figure 7 The image shows the 8000x SEM image of the microstructure of tungsten oxide prepared by microwave calcination in Example 1. Figure 8 This is a 1500x SEM image of the tungsten powder prepared in Example 1. Figure 9 The image shows the 1500x SEM image of the tungsten powder prepared in Comparative Example 1. Figure 10 The image shows the microstructure of the tungsten powder prepared in Comparative Example 2 at 1500x magnification using SEM. Figure 11 The image shows the microstructure of the tungsten powder prepared in Comparative Example 3 at 1500x magnification using SEM. Figure 12 The tungsten powder particle size distribution statistical diagram prepared in Example 1 is shown below. Figure 13 The particle size distribution of tungsten powder prepared in Comparative Example 1 is shown in the figure. Figure 14 The particle size distribution of tungsten powder prepared in Comparative Example 2 is shown in the figure. Figure 15 The tungsten powder particle size distribution is shown in the statistical diagram for Comparative Example 3. Detailed Implementation

[0021] A method for preparing high-purity ultrafine tungsten powder by series impurity removal and microwave calcination, referenced Figure 1 This includes the following steps: 1. Raw material preheating treatment The ammonium paratungstate raw material is thermally decomposed at 300-350℃ for 1-3 hours to relax the ammonium paratungstate lattice and transform it into a thermally decomposed product of a mixed phase of ammonium metatungstate and tungsten oxide, laying the foundation for subsequent rapid ammonia dissolution to remove impurities. The ammonium paratungstate raw material is industrial-grade ammonium paratungstate with a purity of 99.0% or lower.

[0022] 2. Two-step impurity removal and morphology control using a combination of tandem evaporation crystallization and chemical precipitation. The thermal dissociation product was dissolved in an ammonia solution prepared with ultrapure water, with a solid-liquid ratio of 1:4-1:8. The solution was kept at 80-100℃ until the ammonium tungstate solution was clear or contained a small amount of insoluble matter (≤1wt%). The stirring speed was 200-500 r / min. If insoluble matter was present, it should be filtered immediately. Then, an evaporation crystallization process was used. When the solution was evaporated to 60%-80%, it was filtered immediately to remove alkali metal impurities by recrystallization. After filtration, the solution was washed with a mixture of deionized water and anhydrous ethanol to obtain the first purified product. The first purified product was then dissolved in ammonia for a second time to obtain the purified ammonium tungstate solution.

[0023] In this step, the ammonia dissolution process is combined with immediate filtration, which mainly utilizes the difference in solubility of impurities to effectively retain and remove insoluble impurities such as iron, calcium, and magnesium. The subsequent evaporation and crystallization process utilizes the difference in solubility between ammonium paratungstate and alkali metal salts to preferentially crystallize out the target product, while alkali metal impurities such as potassium and sodium are enriched and retained in the mother liquor. Finally, alternating washing with pure water and anhydrous ethanol removes the mother liquor adsorbed on the crystal surface, effectively avoiding the co-precipitation and encapsulation of impurities from the source, and significantly reducing the impurity load for subsequent acid hydrolysis and deep purification.

[0024] 3. Deep purification through chemical precipitation Under the action of ultrasonic cavitation at 15-40 kHz, the reaction temperature is controlled at 60-90℃, and 6-12 mol / L hydrochloric acid is added dropwise to the purified ammonium tungstate solution at a flow rate of 1-20 ml / min to maintain the pH value of the system ≤2. After the reaction, the solid and liquid are separated and dried to obtain nano-tungstate.

[0025] This step is crucial. By strictly controlling the slow dripping rate of hydrochloric acid, the low supersaturation of the reaction system is effectively maintained, thereby inhibiting the explosive nucleation of crystal nuclei and preventing impurity ions from being physically encapsulated by the rapidly growing precipitate. At the same time, the cavitation effect of ultrasound is introduced to provide strong microscopic shear force at the moment of tungstic acid crystal nucleus formation, which promptly disperses the soft agglomerates between crystal grains. This not only ensures that internal impurities can be fully released into the liquid phase and removed with the filtrate, but also ensures that the final obtained nano-tungstic acid precursor has excellent dispersibility and uniform morphology.

[0026] 4. Microwave homogenization calcination Nano-tungstic acid was placed in a microwave field with a microwave power of 800-2000W and heated to 400-800℃ at a heating rate of 10-20℃ / min. The mixture was then internally calcined for 0.5-2 hours to obtain low-agglomeration nano-tungsten oxide.

[0027] Microwave calcination uses internal heating, which ensures uniform heating of nano-tungstic acid particles, avoids the surface sintering problem caused by traditional heat conduction heating, effectively prevents hard agglomeration of tungstic acid particles, and significantly increases the specific surface area of ​​nano-tungsten oxide obtained after calcination.

[0028] 5. Segmented airflow reduction Low-agglomeration nano-tungsten oxide is placed in a hydrogen atmosphere and first pre-reduced at a low temperature of 500-700℃ with a hydrogen flow rate of 100-500 ml / min and a holding time of 60-120 min. The high-flow-rate hydrogen sweeping gas suppresses the CVT effect caused by water vapor partial pressure and simultaneously removes the generated water. Then, the temperature is raised to 700-900℃ for high-temperature final reduction with a hydrogen flow rate of 100-500 ml / min and a holding time of 120-180 min to complete the metallization of tungsten oxide and obtain high-purity ultrafine tungsten powder.

[0029] The embodiments of the present invention are described in detail below. These embodiments are exemplary and are only used to explain the present invention, and should not be construed as limiting the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0030] Example 1 1. Raw material preheating treatment: Industrial grade ammonium paratungstate with a purity of 99.0% was selected as raw material, placed in a muffle furnace, and thermally decomposed at 320℃ for 2 hours to obtain thermally decomposed products.

[0031] 2. Two-stage purification and physical retention: The thermal dissociation product was dissolved in a 5.1 wt% dilute ammonia solution prepared with ultrapure water, with a solid-liquid ratio of 1:6. The solution was kept at 90°C until clear, with a stirring speed of 300 r / min. An evaporation crystallization process was used at 90°C. When the solution was evaporated to 70%, it was immediately filtered. The filter cake was washed with deionized water and anhydrous ethanol, respectively, to obtain the first-stage purified product. The first-stage purified product was then subjected to a second ammonia dissolution according to the aforementioned ammonia dissolution step to obtain a purified ammonium tungstate solution.

[0032] 3. Deep purification by chemical precipitation: Turn on the 25 kHz ultrasonic generator, place the purified ammonium tungstate solution in the ultrasonic field, control the reaction temperature at 60℃, add 12 mol / L hydrochloric acid dropwise at a flow rate of 3 ml / min, maintain the pH of the system at 1, filter after the reaction is complete, and vacuum dry at 80℃ for 5 h to obtain nano-tungstate.

[0033] 4. Microwave homogenization calcination: Nano-tungstic acid was placed in a microwave high-temperature experimental furnace, and the microwave power was controlled at 1000W. The temperature was increased to 600℃ at a heating rate of 15℃ / min. The internal heating calcination lasted for 1 hour, and after natural cooling, low-agglomeration nano-tungsten oxide was obtained.

[0034] 5. Segmented airflow controlled reduction: Low-agglomeration nano-tungsten oxide is placed in a reduction furnace, and hydrogen gas is introduced at a flow rate of 300 ml / min. It is first pre-reduced at a low temperature of 600℃ for 90 min, and then the temperature is raised to a high temperature of 800℃ for a final reduction of 150 min. After the reduction is completed, it is naturally cooled to room temperature in a hydrogen atmosphere to obtain high-purity ultrafine tungsten powder.

[0035] The raw material APT used in this embodiment was subjected to XRD and SEM microstructure analysis, such as... Figure 2 , Figure 5 As shown in the figure, XRD analysis reveals that the results are basically consistent with the ammonium paratungstate standard card, with no obvious impurity peaks observed.

[0036] The SEM microstructure of the tungstic acid obtained by chemical precipitation in this embodiment was analyzed as follows: Figure 6 , Figure 7 As shown, the prepared tungstate precursor is approximately spherical.

[0037] The tungsten powder prepared in this embodiment was tested and found to have a purity of 99.97% and an average particle size of 0.80 μm. SEM analysis showed that the tungsten powder had well-developed crystallites, excellent dispersibility, and no obvious agglomeration. Figure 8 , Figure 12 As shown; XRD analysis revealed that its crystal structure is body-centered cubic.

[0038] See Figure 3 and Figure 4 It can be seen that the diffraction peak positions of the tungsten oxide powder prepared by microwave calcination and the reduced tungsten powder are highly consistent with those of the standard card, and no obvious impurity peaks are observed, indicating that the obtained products are high-purity tungsten oxide and tungsten.

[0039] Example 2 1. Raw material preheating treatment: Industrial grade ammonium paratungstate with a purity of 99.0% was selected as raw material and thermally decomposed at 300℃ for 3 hours to obtain thermally decomposed products.

[0040] 2. Two-stage purification and physical retention: The thermal dissociation product was dissolved in a 5.1 wt% dilute ammonia solution prepared with ultrapure water at a solid-liquid ratio of 1:4. The solution was kept at 80°C until clear, with a stirring speed of 200 r / min. When the solution was evaporated to 60%, it was immediately filtered and washed with a mixture of deionized water and anhydrous ethanol to obtain the first purified product. The first purified product was then subjected to a second ammonia dissolution according to the aforementioned ammonia dissolution step to obtain a purified ammonium tungstate solution.

[0041] 3. Deep purification by chemical precipitation: 15 KHz ultrasonic cavitation, reaction temperature 50℃, 10 mol / L hydrochloric acid added dropwise at a flow rate of 1 ml / min, pH=2, filtration and drying to obtain nano-tungstic acid.

[0042] 4. Microwave homogenization calcination: Microwave power 800W, heating rate 10℃ / min, calcination at 400℃ for 2h to obtain low-agglomeration nano-tungsten oxide.

[0043] 5. Segmented controlled gas flow reduction: Hydrogen flow rate 100 ml / min, low-temperature pre-reduction at 500℃ for 120 min, and high-temperature final reduction at 700℃ for 180 min to obtain high-purity ultrafine tungsten powder.

[0044] Test results: The tungsten powder has a purity of 99.97%, an average particle size of 0.82μm, good dispersibility, no agglomeration, and a body-centered cubic crystal structure, meeting the requirements for 99.98% high purity.

[0045] Example 3 1. Raw material preheating treatment: 99% pure industrial grade ammonium paratungstate was selected as raw material and thermally dissociated at 350℃ for 1 hour to obtain thermal dissociation products.

[0046] 2. Two-stage purification and physical retention: The thermal dissociation product was dissolved in a 5.1 wt% dilute ammonia solution prepared with ultrapure water at a solid-liquid ratio of 1:8. The solution was kept at 100°C until clear, with a stirring speed of 400 r / min. When the solution was evaporated to 80%, it was immediately filtered and washed with a mixture of deionized water and anhydrous ethanol to obtain the first purified product. The first purified product was then subjected to a second ammonia dissolution according to the aforementioned ammonia dissolution step to obtain a purified ammonium tungstate solution.

[0047] 3. Deep purification by chemical precipitation: 40 KHz ultrasonic cavitation, reaction temperature 70℃, 12 mol / L hydrochloric acid added dropwise at a flow rate of 5 ml / min, pH=1.5, filtration and drying to obtain nano-tungstic acid.

[0048] 4. Microwave homogenization calcination: Microwave power 1500W, heating rate 20℃ / min, calcination at 800℃ for 0.5h to obtain low-agglomeration nano-tungsten oxide.

[0049] 5. Segmented airflow controlled reduction: hydrogen flow rate 500 ml / min, low-temperature pre-reduction at 700℃ for 60 min, and high-temperature final reduction at 900℃ for 120 min to obtain high-purity ultrafine tungsten powder.

[0050] Test results: Tungsten powder purity 99.96%, average particle size 0.78μm, excellent dispersibility, no agglomeration, body-centered cubic crystal structure.

[0051] Comparative Example 1 The difference between this comparative example and Example 1 is that step 3, the chemical precipitation method, is omitted, and the ammonium paratungstate crystallized by evaporation after ammonia dissolution is directly calcined and reduced. The remaining steps and parameters are the same as in Example 1.

[0052] Test results: The tungsten powder purity was 99.75%, failing to meet the 99.95% high purity requirement. Impurities such as Na, Fe, Cu, and Mo were present in high concentrations, and the tungsten powder precursor was not well controlled, ultimately leading to tungsten powder growth with an average particle size of 1.7 μm. Figure 9 , Figure 13 As shown.

[0053] Comparative Example 2 The difference between this comparative example and Example 1 is that the segmented gas flow controlled reduction in step 5 is replaced by direct hydrogen reduction at 800°C for 240 min with a hydrogen flow rate of 300 ml / min. All other steps and parameters are the same as in Example 1.

[0054] Test results: A significant CVT effect was observed during the reduction process, resulting in severe tungsten powder grain growth with an average particle size of 2.4 μm. Figure 10 , Figure 14 As shown, it cannot meet the requirements for ultrafine tungsten powder. Although the purity is 99.96%, the particle size index does not meet the standard.

[0055] Comparative Example 3 The difference between this comparative example and Example 1 is that the microwave calcination in step 4 is replaced by muffle furnace heating, while the remaining steps and parameters are the same as in Example 1.

[0056] Test results: A significant agglomeration effect was observed during the reduction process, with tungsten powder grains growing and exhibiting a severely broadened particle size distribution, averaging 1.5 μm. Figure 11 , Figure 15 As shown, it cannot meet the requirements for ultrafine tungsten powder. Although the purity is 99.95%, the particle size index does not meet the standard.

[0057] The contents of key impurities Na, Fe, Cu, and Mo in the tungsten powders prepared in Examples 1-3 and Comparative Examples 1-3 were tested, and the results are shown in Table 1 below. All examples met the impurity control requirements for 99.95% high-purity tungsten powder.

[0058] Table 1. Detection results of key impurities in tungsten powder (ppm)

[0059] In summary, this invention first combines ammonia dissolution-evaporation crystallization with chemical precipitation to achieve deep impurity removal, and directly obtains nano-tungsten oxide precursors using chemical precipitation, providing morphological assurance for subsequent reduction of ultrafine tungsten powder. Secondly, it introduces microwave calcination to achieve rapid, environmentally friendly, and uniform heating, significantly reducing precursor agglomeration. Finally, it employs a segmented reduction method to effectively block the CVT effect during reduction, preventing abnormal grain growth. This invention solves the problems of incomplete purification, sintering and agglomeration during precursor reduction, and uncontrolled reduction particle size in existing technologies. The prepared tungsten powder has a purity ≥99.95% and an average particle size ≤1μm. The process is green, efficient, and easy to industrialize, meeting the needs of high-end fields such as high-performance cemented carbide and semiconductor sputtering targets.

[0060] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various other corresponding changes and modifications based on the technical solutions and concepts described above, and all such changes and modifications should fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing high-purity ultrafine tungsten powder by a series of impurity removal and microwave calcination, characterized in that, Includes the following steps: S1: Thermally dissociate ammonium paratungstate raw material to obtain thermal dissociation products; S2: Dissolve the thermal dissociation product in an ammonia solution. When the solution is clear or the insoluble matter is ≤1wt%, immediately filter out the insoluble impurities. The filtered ammonium tungstate solution is kept at 80-100℃ for evaporation and crystallization. When the solution evaporates to 60%-80%, immediately filter, wash with deionized water and anhydrous ethanol, and dry to obtain the first purified product. The first purified product is thermally dissociated a second time and dissolved in ammonia to obtain a purified ammonium tungstate solution. S3: Under the synergistic effect of ultrasound, hydrochloric acid is added dropwise to the purified ammonium tungstate solution at a flow rate of 1-20 ml / min, maintaining the pH value of the system ≤2. After the reaction is complete, the solid and liquid are separated and dried to obtain nano-tungstate. S4: Place nano-tungstic acid in a microwave field and calcine it at 400-800℃ for 0.5-2 hours to obtain low-agglomeration nano-tungsten oxide; S5: Low-agglomeration nano-tungsten oxide is placed in a hydrogen atmosphere and first pre-reduced at a low temperature of 500-700℃, and then finally reduced at a high temperature of 700-900℃ to obtain high-purity ultrafine tungsten powder.

2. The method for preparing high-purity ultrafine tungsten powder by series impurity removal and microwave calcination according to claim 1, characterized in that, In step S1, the thermal dissociation temperature is 300-350℃, and the thermal dissociation time is 1-3h; The ammonium paratungstate raw material is industrial-grade ammonium paratungstate with a purity of 99% or lower.

3. The method for preparing high-purity ultrafine tungsten powder by series impurity removal and microwave calcination according to claim 1, characterized in that, In step S2, the concentration of ammonia water is 50-200 g / L; the solid-liquid ratio of the thermal dissociation product to the ammonia water solution is 1:4-1:

8. When the thermal dissociation product is dissolved in an ammonia solution, it is stirred at a speed of 200-400 r / min, filtered immediately, and then washed alternately with deionized water and anhydrous ethanol.

4. The method for preparing high-purity ultrafine tungsten powder by series impurity removal and microwave calcination according to claim 1, characterized in that, In step S3, the molar concentration of the hydrochloric acid is 6-12 mol / L, and the reaction temperature under the synergistic effect of ultrasound is 60-90℃.

5. The method for preparing high-purity ultrafine tungsten powder by series impurity removal and microwave calcination according to claim 1, characterized in that, In step S5, the hydrogen flow rate during the low-temperature pre-reduction stage is 100-500 ml / min, and the holding time is 60-120 min. The hydrogen flow rate during the high-temperature final reduction stage is 100-500 ml / min, and the holding time is 120-180 min.

6. The method for preparing high-purity ultrafine tungsten powder by series impurity removal and microwave calcination according to claim 1, characterized in that, In step S4, the heating rate in the microwave field is 10-30℃ / min, and the microwave power is 800-2000W.

7. A high-purity ultrafine tungsten powder, characterized in that, It is prepared by the method described in any one of claims 1-6.

8. The high-purity ultrafine tungsten powder according to claim 1, characterized in that, The tungsten powder has a purity of ≥99.95%, a body-centered cubic crystal structure, and an average particle size of ≤1μm.

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