A method for preparing nano tungsten powder by hydrogen reduction of PEG-coated tungstic acid precursor

Abstract

The application discloses a method for preparing nano tungsten powder by hydrogen reduction of PEG-coated tungstic acid precursor, and belongs to the technical field of nano-powder material preparation. The method comprises the following steps: adding polyethylene glycol into an ammonium tungstate solution and stirring until the polyethylene glycol is completely dissolved to obtain a uniformly dispersed solution; under the condition of continuous ultrasonic, adding dilute hydrochloric acid drop by drop until no tungstic acid precipitate is generated, realizing the synchronization and cooperation of acid precipitation and ultrasonic, and obtaining a tungstic acid-polyethylene glycol composite suspension; filtering, washing, drying and sieving the tungstic acid-polyethylene glycol composite suspension to obtain a tungstic acid-polyethylene glycol composite precursor; and finally, performing three-step gradient reduction under a hydrogen atmosphere to obtain nano tungsten powder. The method adopts the synchronization and cooperation process of acid precipitation and ultrasonic, and obtains a precursor with uniform particle size; the three-step gradient reduction is matched with the thermal decomposition characteristics of polyethylene glycol in the precursor, and effectively inhibits the particle growth and agglomeration in the reduction process. The method can stably prepare high-dispersion and narrow-distribution nano tungsten powder, and has the advantages of simple process, low cost and easy industrial production.

Description

Technical Field

[0001] This invention relates to the field of nanopowder material preparation technology, and in particular to a method for preparing nano-tungsten powder by hydrogen reduction of PEG-coated tungstic acid precursor. Background Technology

[0002] As a core raw material for preparing high-performance novel tungsten materials, nano-tungsten powder's particle size distribution, purity, and microstructure directly determine the quality and performance of key products such as tungsten-based composites, cemented carbides, and ultrafine-grained tungsten products. Currently, the mainstream industrial method for preparing nano-tungsten powder is the hydrogen reduction method of tungsten oxide. However, this method has significant drawbacks: during the high-temperature reduction process, tungsten oxide easily volatilizes and deposits to form coarse particles, and the water vapor generated by the reaction accelerates particle agglomeration, making it difficult to stably produce high-quality nano-tungsten powder. While chemical precipitation methods assisted by dispersants, such as those using polyethylene glycol (PEG) or sodium dodecyl sulfate (SDS), can improve agglomeration to some extent, their conventional processes often involve first completing the acid precipitation reaction and then ultrasonically dispersing the formed precipitate. This step-by-step operation cannot intervene in the rapid nucleation and aggregation during the acid precipitation process, resulting in the initial formation of hard, difficult-to-disperse agglomerate cores, limiting the effectiveness of subsequent ultrasonic treatment. More importantly, these methods typically only focus on the preparation of the precursor, without fully considering the compatibility between the precursor characteristics and the subsequent high-temperature reduction process. Dispersants such as SDS may exhibit unstable dispersion performance in strongly acidic precipitation environments. Even with well-dispersed precursors, improper subsequent reduction processes can lead to the loss of structural advantages due to water vapor escape and particle sintering at high temperatures, ultimately making it difficult to obtain highly dispersed, narrowly distributed nano-tungsten powder. Therefore, existing technologies have failed to systematically solve the end-to-end agglomeration control challenge, from initial nucleation control to final product structure inheritance.

[0003] Other physical or chemical methods face problems such as impurity introduction, high energy consumption, long reaction cycles, and high raw material costs, making it difficult to balance performance and industrialization requirements. Therefore, developing a simple, impurity-free, low-cost method that can suppress the agglomeration of tungstic acid precursors at the source and prepare highly dispersed, narrowly distributed nano-tungsten powder is of great significance for promoting the development of high-end tungsten-based materials. Summary of the Invention

[0004] This invention aims to solve the problem that in the existing technology of preparing nano-tungsten powder by chemical precipitation with dispersant assistance, the step-by-step process of acid precipitation followed by ultrasonication is prone to the rapid precipitation of local tungstic acid during the acid precipitation stage, forming coarse particles and hard agglomerates, which are difficult to effectively disperse in subsequent ultrasonication, resulting in a wide particle size distribution and poor dispersibility of the final tungsten powder. At the same time, some improved solutions have drawbacks such as complex processes, introduction of impurities, and increased production costs.

[0005] To achieve the above objectives, this invention proposes a technical approach that combines precursor structure regulation with a matching reduction process, providing a method for preparing nano-tungsten powder by hydrogen reduction of a PEG-coated tungstenic acid precursor. In the precursor preparation stage, through the simultaneous synergy of acid precipitation and ultrasound, tungstenic acid particles are uniformly coated with polyethylene glycol of a specific molecular weight during the initial nucleation stage, resulting in a tungstenic acid-polyethylene glycol composite precursor with uniform particle size and good dispersibility. In the reduction stage, a three-step gradient reduction process is designed to match the thermal decomposition characteristics of the polyethylene glycol-coated precursor, allowing the decomposition process of polyethylene glycol and the reduction process of tungstenic acid to synergistically inhibit particle growth and agglomeration throughout the reduction process. By combining precursor structure regulation with a three-step gradient reduction process tailored to its characteristics, the stable preparation of highly dispersed, narrowly distributed nano-tungsten powder is achieved.

[0006] The technical solution of the present invention is as follows: This invention provides a method for preparing nano-tungsten powder by hydrogen reduction of a PEG-coated tungstate precursor, comprising the following steps: Step 1: Add polyethylene glycol to ammonium tungstate solution and stir until completely dissolved to obtain a homogeneous dispersion; Step 2: Under continuous ultrasonic conditions, dilute hydrochloric acid is added dropwise to the homogeneous dispersion until no more tungstic acid precipitate is formed, so as to achieve the synchronous synergy of acid precipitation and ultrasonication, and obtain tungstic acid-polyethylene glycol composite suspension. Step 3: Filter, wash until neutral, dry, grind and sieve the tungstate-polyethylene glycol composite suspension to obtain the tungstate-polyethylene glycol composite precursor; Step 4: The tungstate-polyethylene glycol composite precursor is subjected to a three-step gradient reduction under a hydrogen atmosphere to obtain nano-tungsten powder.

[0007] Preferably, in step 1, the concentration of the ammonium tungstate solution, calculated as WO3, is 200-300 g / L.

[0008] Preferably, in step 1, the molecular weight of the polyethylene glycol is 2000-6000, and the amount of polyethylene glycol added is 5-15% of the mass of ammonium tungstate.

[0009] Preferably, in step 1, the mixing speed is 300-500 r / min and the mixing time is 30-60 min.

[0010] Preferably, in step 2, the power of the ultrasound is 200-300W.

[0011] Preferably, in step 2, the concentration of the dilute hydrochloric acid is 10-20 wt%, and the dropping rate of the dilute hydrochloric acid is 1-2 mL / min.

[0012] Preferably, in step 2, after the dilute hydrochloric acid is added dropwise, the ultrasonication and stirring are continued for 5-10 minutes.

[0013] Further explanation of the present invention: In the precursor preparation stage, the present invention employs a simultaneous and synergistic approach of acid precipitation and ultrasound, while selecting polyethylene glycol (PEG) as a dispersant. This allows the coating effect of PEG and the cavitation effect of ultrasound to act simultaneously on the nucleation and growth process of tungstate particles. Specifically, when dilute hydrochloric acid is slowly dripped into an ammonium tungstate solution containing PEG, PEG molecules are rapidly adsorbed on the surface of the newly formed tungstate particles, forming a steric hindrance layer, thereby inhibiting direct contact and agglomeration between particles. Simultaneously, the continuously applied ultrasonic cavitation effect breaks down the local supersaturated concentration difference near the acid dripping point, preventing the rapid nucleation of tungstate into coarse particles, and promotes the uniform adsorption of PEG molecules on the surface of the tungstate particles. This synergistic effect of coating and dispersion ensures that the tungstate-PEG composite precursor possesses uniform particle size and good dispersibility from the outset, laying a solid foundation for the subsequent reduction process.

[0014] Preferably, in step 3, the filtration is performed using a Buchner funnel, the washing to neutrality is performed by repeatedly washing with water until the filtrate is neutral, and the grinding and sieving is performed through a 180-240 mesh sieve.

[0015] Preferably, in step 4, the three-step gradient reduction includes: the first step reduction temperature is 300-350℃, and the reduction time is 0.5-1h; the second step reduction temperature is 500-550℃, and the reduction time is 1-3h; the third step reduction temperature is 700-900℃, and the reduction time is 1-3h.

[0016] Preferably, in step 4, the hydrogen flow rate is 3-5 L / min and the heating rate is 8-12 °C / min.

[0017] The reason this invention must employ the aforementioned three-step gradient reduction process is not independent of the precursor characteristics, but rather to match the thermal decomposition characteristics of the polyethylene glycol-coated precursor. The first reduction temperature is set at 300-350℃, corresponding to the initial decomposition temperature range of polyethylene glycol. At this temperature, the polyethylene glycol molecules coating the surface of the tungstic acid particles begin to slowly decompose and be removed, avoiding the violent decomposition of the coating layer and the collapse of the precursor structure caused by a sudden increase in temperature in traditional one-step reduction. Simultaneously, the micropores left after polyethylene glycol decomposition facilitate the diffusion of hydrogen into the particle interior, making the reduction reaction more uniform. As the temperature rises to 500-550℃ in the second step, the main reduction reaction accelerates. At this point, the advantage of the uniformity of the precursor begins to emerge: because the precursor particles themselves are uniform in size and well dispersed, sintering necks are less likely to form and grow between particles during the reduction process, thus avoiding the generation of abnormally large particles; finally, in the third step of high-temperature reduction at 700-900℃, the crystal structure is perfected, but because the uniformity and dispersion of the precursor particle size have been ensured in the previous steps, the particle growth in this stage remains within a controllable range.

[0018] More importantly, this invention reveals that the synergistic effect of the aforementioned polyethylene glycol-coated precursor and the three-step gradient reduction process depends on the coordination of multiple process parameters: If the molecular weight of polyethylene glycol is too low, steric hindrance is insufficient; if it is too high, solubility decreases and decomposition behavior changes; excessive ultrasonic power may damage the polyethylene glycol coating layer, while insufficient power cannot effectively break the local concentration gradient; excessively rapid acid drop acceleration leads to local supersaturation and the formation of coarse particles, while excessively slow acceleration affects production efficiency. Therefore, the selection of process parameters such as the molecular weight of polyethylene glycol, ultrasonic power, and acid drop acceleration in this invention is not a simple conventional optimization, but rather a matter of mutual matching with the three-step gradient reduction process. When any key parameter deviates from the range defined in this invention, or when a certain synergistic link is disrupted, the final particle size and dispersibility of the tungsten powder significantly deteriorate.

[0019] Preferably, the average particle size of the nano-tungsten powder is ≤100nm, and the specific surface area (BET) is ≥19m². 2 / g.

[0020] The present invention has the following beneficial effects: 1. This invention employs a simultaneous and synergistic process of acid precipitation and ultrasound in the precursor preparation stage. Ultrasound is initiated directly from the tungstic acid nucleation and growth stage, utilizing the cavitation effect of ultrasound to break down local concentration differences and prevent rapid precipitation of tungstic acid, thus avoiding the formation of coarse particles and hard agglomerates. This achieves uniform control of precursor particle size from the source. Compared to the existing technology that performs acid precipitation followed by ultrasound treatment, the simultaneous and synergistic process of this invention effectively prevents the formation of hard agglomerates, requires no additional raw materials or equipment, and is simple and introduces no impurities.

[0021] 2. Compared with existing technologies, this invention selects polyethylene glycol (PEG) as a dispersant. By controlling the PEG molecular weight within the preferred range of 2000-6000 and the addition amount of 5-15% by mass of ammonium tungstate, PEG can fully exert its steric hindrance coating effect, synergistically with the ultrasonic cavitation effect to obtain a precursor with uniform particle size. Based on this, the three-step gradient reduction process designed in this invention is matched with the thermal decomposition characteristics of the PEG-coated precursor. The first reduction temperature corresponds to the initial decomposition temperature range of PEG, allowing for slow pyrolysis removal of PEG and avoiding bubble impact and structural collapse caused by rapid decomposition of the coating layer, thus helping to maintain the morphological integrity of the precursor. Subsequent reduction temperatures complete the reduction reaction and lattice perfection in stages, effectively suppressing particle growth and agglomeration during the reduction process. Furthermore, this invention further limits the range of parameters such as ultrasonic power and acid drop acceleration, ensuring a good match between each process step. Through the synergistic cooperation of precursor preparation and reduction process, this invention can stably prepare highly dispersed, narrowly distributed nano-tungsten powder.

[0022] 3. Compared with existing technologies, the method provided by this invention has a simple overall process flow, requires no special equipment such as freeze drying, has low raw material costs, and offers strong controllability of process parameters, making it easy to achieve industrial production. The nano-tungsten powder prepared using the method provided by this invention has controllable particle size, good dispersibility, high specific surface area, and high activity, enhancing its application potential in high-performance novel tungsten materials. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0024] Figure 1 This is a SEM image of the nano-tungsten powder obtained in Example 1 of the present invention; Figure 2 This is a SEM image of the nano-tungsten powder obtained in Example 2 of the present invention; Figure 3 This is a SEM image of the nano-tungsten powder obtained in Example 3 of the present invention; Figure 4 This is a SEM image of the tungsten powder obtained in Comparative Example 1 of the present invention. Figure 5 This is a SEM image of the tungsten powder obtained in Comparative Example 2 of this invention; Figure 6 This is a SEM image of the tungsten powder obtained in Comparative Example 3 of the present invention. Figure 7This is a SEM image of the tungsten powder obtained in Comparative Example 4 of this invention; Figure 8 This is a SEM image of the tungsten powder obtained in Comparative Example 5 of this invention; Figure 9 This is a SEM image of the tungsten powder obtained in Comparative Example 6 of this invention; Figure 10 This is a SEM image of the tungsten powder obtained in Comparative Example 7 of the present invention. Figure 11 This is a SEM image of the tungsten powder obtained in Comparative Example 8 of this invention; Figure 12 This is a SEM image of the tungsten powder obtained in Comparative Example 9 of this invention.

[0025] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0026] The technical solutions described below in conjunction with the embodiments will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] This invention provides a method for preparing nano-tungsten powder by hydrogen reduction of a PEG-coated tungstate precursor, comprising the following steps: Step 1: Add polyethylene glycol to ammonium tungstate solution and stir until completely dissolved to obtain a homogeneous dispersion; Step 2: Under continuous ultrasonic conditions, dilute hydrochloric acid is added dropwise to the homogeneous dispersion until no more tungstic acid precipitate is formed, so as to achieve the synchronous synergy of acid precipitation and ultrasonication, and obtain tungstic acid-polyethylene glycol composite suspension. Step 3: Filter, wash until neutral, dry, grind and sieve the tungstate-polyethylene glycol composite suspension to obtain the tungstate-polyethylene glycol composite precursor; Step 4: The tungstate-polyethylene glycol composite precursor is subjected to a three-step gradient reduction under a hydrogen atmosphere to obtain nano-tungsten powder.

[0028] Preferably, in step 1, the concentration of the ammonium tungstate solution, calculated as WO3, is 200-300 g / L.

[0029] Specifically, the concentration of the ammonium tungstate solution, calculated as WO3, can be any one of 200 g / L, 220 g / L, 240 g / L, 260 g / L, 280 g / L, 300 g / L, or a range between two of these.

[0030] Preferably, in step 1, the molecular weight of the polyethylene glycol is 2000-6000, and the amount of polyethylene glycol added is 5-15% of the mass of ammonium tungstate.

[0031] Specifically, the molecular weight of the polyethylene glycol can be any one of 2000, 3000, 4000, 5000, 6000 or a range between two; the amount of polyethylene glycol added can be any one of 5%, 7%, 9%, 10%, 12% or 15% of the mass of ammonium tungstate or a range between two.

[0032] Preferably, in step 1, the mixing speed is 300-500 r / min and the mixing time is 30-60 min.

[0033] Preferably, in step 2, the power of the ultrasound is 200-300W.

[0034] Preferably, in step 2, the concentration of the dilute hydrochloric acid is 10-20 wt%, and the dropping rate of the dilute hydrochloric acid is 1-2 mL / min.

[0035] Specifically, the concentration of the dilute hydrochloric acid can be any one of 10wt%, 12wt%, 14wt%, 15wt%, 16wt%, 18wt%, 20wt%, or a range between two of these; the dropping rate of the dilute hydrochloric acid can be any one of 1mL / min, 1.2mL / min, 1.5mL / min, 1.8mL / min, 2mL / min, or a range between two of these.

[0036] Preferably, in step 2, after the dilute hydrochloric acid is added dropwise, the ultrasonication and stirring are continued for 5-10 minutes.

[0037] Preferably, in step 3, the filtration is performed using a Buchner funnel, the washing to neutrality is performed by repeatedly washing with water until the filtrate is neutral, and the grinding and sieving is performed through a 180-240 mesh sieve.

[0038] Preferably, in step 4, the three-step gradient reduction includes: the first step reduction temperature is 300-350℃, and the reduction time is 0.5-1h; the second step reduction temperature is 500-550℃, and the reduction time is 1-3h; the third step reduction temperature is 700-900℃, and the reduction time is 1-3h.

[0039] Specifically, the reduction temperature in the first step can be any one or a range between 300℃, 310℃, 320℃, 330℃, 340℃, and 350℃, and the reduction time can be any one or a range between 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, and 1h; the reduction temperature in the second step can be any one or a range between 500℃, 510℃, 520℃, 530℃, 540℃, and 550℃, and the reduction time can be any one or a range between 1h, 1.5h, 2h, 2.5h, and 3h; the reduction temperature in the third step can be any one or a range between 700℃, 750℃, 800℃, 850℃, and 900℃, and the reduction time can be any one or a range between 1h, 1.5h, 2h, 2.5h, and 3h.

[0040] Preferably, in step 4, the hydrogen flow rate is 3-5 L / min and the heating rate is 8-12 °C / min.

[0041] Specifically, the hydrogen flow rate can be any one of 3L / min, 3.5L / min, 4L / min, 4.5L / min, 5L / min or a range between two of them, and the heating rate can be any one of 8℃ / min, 9℃ / min, 10℃ / min, 11℃ / min, 12℃ / min or a range between two of them.

[0042] Preferably, the average particle size of the nano-tungsten powder is ≤100nm, and the specific surface area (BET) is ≥19m². 2 / g.

[0043] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0044] Example 1 A method for preparing nano-tungsten powder by hydrogen reduction of PEG-coated tungstate precursor includes the following steps: Step 1: Add polyethylene glycol to ammonium tungstate solution and mix and stir at 300 r / min for 30 min until polyethylene glycol is completely dissolved to obtain a homogeneous dispersion. The concentration of ammonium tungstate solution is 200 g / L (WO3), the molecular weight of polyethylene glycol is 2000, and the amount of polyethylene glycol added is 5% of the mass of ammonium tungstate. Step 2: Under continuous ultrasonic conditions, add 10wt% dilute hydrochloric acid to the homogeneous dispersion obtained in Step 1 at a dropping rate of 1mL / min until no more tungstic acid precipitate is formed, so as to achieve the synchronous synergy of acid precipitation and ultrasonication. After the addition is completed, continue to maintain ultrasonication and magnetic stirring for 5min to obtain tungstic acid-polyethylene glycol composite suspension, wherein the ultrasonic power is 200W. Step 3: Filter the tungstic acid-polyethylene glycol composite suspension obtained in Step 2 through a Buchner funnel, wash it repeatedly with water until the filtrate is neutral, dry it, grind and crush it and pass it through a 200-mesh sieve to obtain the tungstic acid-polyethylene glycol composite precursor. Step 4: Place the tungstate-polyethylene glycol composite precursor obtained in Step 3 into a tube furnace and perform a three-step gradient reduction under a hydrogen atmosphere. The first step reduction temperature is 300℃ and the reduction time is 0.5h; the second step reduction temperature is 500℃ and the reduction time is 1h; the third step reduction temperature is 700℃ and the reduction time is 1h. The hydrogen flow rate is 3L / min and the overall heating rate is 10℃ / min to obtain nano-tungsten powder.

[0045] The nano-tungsten powder prepared in this embodiment was tested and characterized. The test results showed that the average particle size of the nano-tungsten powder was 67 nm, and the BET was 22.5 nm. 2 / g; SEM image of the nano-tungsten powder is as follows Figure 1 As shown, the SEM images reveal no obvious aggregation and a uniform particle size distribution.

[0046] Example 2 A method for preparing nano-tungsten powder by hydrogen reduction of PEG-coated tungstate precursor includes the following steps: Step 1: Add polyethylene glycol to ammonium tungstate solution and mix and stir at 500 r / min for 60 min until polyethylene glycol is completely dissolved to obtain a homogeneous dispersion. The concentration of ammonium tungstate solution is 300 g / L (WO3), the molecular weight of polyethylene glycol is 6000, and the amount of polyethylene glycol added is 15% of the mass of ammonium tungstate. Step 2: Under continuous ultrasonic conditions, add 20wt% dilute hydrochloric acid to the homogeneous dispersion obtained in Step 1 at a dropping rate of 2mL / min until no more tungstic acid precipitate is formed, so as to achieve the synchronous synergy of acid precipitation and ultrasonication. After the addition is completed, continue to maintain ultrasonication and magnetic stirring for 10min to obtain tungstic acid-polyethylene glycol composite suspension, wherein the ultrasonic power is 300W. Step 3: Filter the tungstic acid-polyethylene glycol composite suspension obtained in Step 2 through a Buchner funnel, wash it repeatedly with water until the filtrate is neutral, dry it, grind and crush it and pass it through a 200-mesh sieve to obtain the tungstic acid-polyethylene glycol composite precursor. Step 4: Place the tungstate-polyethylene glycol composite precursor obtained in Step 3 into a tube furnace and perform a three-step gradient reduction under a hydrogen atmosphere. The first step reduction temperature is 350℃ and the reduction time is 1h; the second step reduction temperature is 550℃ and the reduction time is 3h; the third step reduction temperature is 900℃ and the reduction time is 3h. The hydrogen flow rate is 5L / min and the overall heating rate is 10℃ / min to obtain nano-tungsten powder.

[0047] The nano-tungsten powder prepared in this embodiment was tested and characterized. The test results showed that the average particle size of the nano-tungsten powder was 84 nm, and the BET was 19.2 nm. 2 / g; SEM image of the nano-tungsten powder is as follows Figure 2 As shown, the SEM images reveal no obvious aggregation and a uniform particle size distribution.

[0048] Example 3 A method for preparing nano-tungsten powder by hydrogen reduction of PEG-coated tungstate precursor includes the following steps: Step 1: Add polyethylene glycol to ammonium tungstate solution and mix and stir at 400 r / min for 40 min until polyethylene glycol is completely dissolved to obtain a homogeneous dispersion. The concentration of ammonium tungstate solution is 250 g / L (WO3), the molecular weight of polyethylene glycol is 4000, and the amount of polyethylene glycol added is 10% of the mass of ammonium tungstate. Step 2: Under continuous ultrasonic conditions, add 15wt% dilute hydrochloric acid to the homogeneous dispersion obtained in Step 1 at a dropping rate of 1.5mL / min until no more tungstic acid precipitate is formed, so as to achieve the synchronous synergy of acid precipitation and ultrasonication. After the addition is completed, continue to maintain ultrasonication and magnetic stirring for 8min to obtain tungstic acid-polyethylene glycol composite suspension, wherein the ultrasonic power is 250W. Step 3: Filter the tungstic acid-polyethylene glycol composite suspension obtained in Step 2 through a Buchner funnel, wash it repeatedly with water until the filtrate is neutral, dry it, grind and crush it and pass it through a 200-mesh sieve to obtain the tungstic acid-polyethylene glycol composite precursor. Step 4: Place the tungstate-polyethylene glycol composite precursor obtained in Step 3 into a tube furnace and perform a three-step gradient reduction under a hydrogen atmosphere. The first step reduction temperature is 320℃ and the reduction time is 0.8h; the second step reduction temperature is 520℃ and the reduction time is 2h; the third step reduction temperature is 800℃ and the reduction time is 2h. The hydrogen flow rate is 4L / min and the overall heating rate is 10℃ / min to obtain nano-tungsten powder.

[0049] The nano-tungsten powder prepared in this embodiment was tested and characterized. The test results showed that the average particle size of the nano-tungsten powder was 71 nm, and the BET was 20.8 nm. 2 / g; SEM image of the nano-tungsten powder is as follows Figure 3 As shown, the SEM images reveal no obvious aggregation and a uniform particle size distribution.

[0050] Comparative Example 1 The only difference between this comparative example and Example 1 is step 2, which is as follows: Add 10wt% dilute hydrochloric acid to the homogeneous dispersion obtained in step 1 at a dropping rate of 1 mL / min until no more tungstic acid precipitate is formed. After the addition is completed, continue to sonicate and magnetically stir for 5 min to obtain a tungstic acid-polyethylene glycol composite suspension, wherein the ultrasonic power is 200W.

[0051] The tungsten powder prepared in this comparative example was tested and characterized. The results showed that the average particle size of the tungsten powder was 180 nm, and the BET was 11.35 nm. 2 / g; SEM image of the tungsten powder is as follows Figure 4 As shown, the SEM images reveal significant aggregation and uneven particle size distribution.

[0052] Comparative Example 2 The only difference between this comparative example and Example 1 is that the ultrasonic power in step 2 is 400W.

[0053] The tungsten powder prepared in this comparative example was tested and characterized. The results showed that the average particle size of the tungsten powder was 87 nm, and the BET was 13.72 nm. 2 / g; SEM image of the tungsten powder is as follows Figure 5 As shown, the SEM images reveal significant aggregation and uneven particle size distribution.

[0054] Comparative Example 3 The only difference between this comparative example and Example 1 is that the dilute hydrochloric acid is added at a rate of 3 mL / min in step 2.

[0055] The tungsten powder prepared in this comparative example was tested and characterized. The results showed that the average particle size of the tungsten powder was 346 nm, and the BET was 13.67 nm. 2 / g; SEM image of the tungsten powder is as follows Figure 6 As shown, the SEM images reveal significant aggregation and uneven particle size distribution.

[0056] Comparative Example 4 The only difference between this comparative example and Example 1 is that the molecular weight of the polyethylene glycol in step 1 is 1000.

[0057] The tungsten powder prepared in this comparative example was tested and characterized. The results showed that the average particle size of the tungsten powder was 183 nm, and the BET was 8.34 nm. 2 / g; SEM image of the tungsten powder is as follows Figure 7 As shown, the SEM image reveals that the grains are adhered to each other, with severe overall agglomeration and a wide particle size distribution.

[0058] Comparative Example 5 The only difference between this comparative example and Example 1 is that the molecular weight of the polyethylene glycol in step 1 is 10,000.

[0059] The tungsten powder prepared in this comparative example was tested and characterized. The results showed that the average particle size of the tungsten powder was 342 nm, and the BET was 6.81 nm. 2 / g; SEM image of the tungsten powder is as follows Figure 8 As shown, the SEM images reveal that the particles are generally large and uneven in size.

[0060] Comparative Example 6 The only difference between this comparative example and Example 1 is that polyethylene glycol (molecular weight 2000) is replaced with sodium dodecyl sulfate.

[0061] The tungsten powder prepared in this comparative example was tested and characterized. The results showed that the average particle size of the tungsten powder was 124 nm, and the BET was 13.74 nm. 2 / g; SEM image of the tungsten powder is as follows Figure 9 As shown in the image, the SEM image reveals obvious flocculent aggregation between particles and poor dispersibility.

[0062] Comparative Example 7 A method for preparing tungsten powder by hydrogen reduction includes the following steps: Step 1: Under continuous ultrasound conditions, add 10wt% dilute hydrochloric acid to the ammonium tungstate solution at a dropping rate of 1mL / min until no more tungstate precipitate is formed, so as to achieve the synchronous synergy of acid precipitation and ultrasound. After the addition is completed, continue to maintain ultrasound and magnetic stirring for 5min to obtain a suspension. The concentration of the ammonium tungstate solution is 200g / L (WO3), and the ultrasound power is 200W. Step 2: Filter the suspension obtained in Step 1 through a Buchner funnel, wash it repeatedly with water until the filtrate is neutral, dry it, grind and crush it and pass it through a 200-mesh sieve to obtain the tungstic acid precursor. Step 3: Place the tungstate precursor obtained in Step 2 into a tube furnace and perform a three-step gradient reduction under a hydrogen atmosphere. The first step reduction temperature is 300℃ and the reduction time is 0.5h; the second step reduction temperature is 500℃ and the reduction time is 1h; the third step reduction temperature is 700℃ and the reduction time is 1h. The hydrogen flow rate is 3L / min and the overall heating rate is 10℃ / min to obtain tungsten powder.

[0063] The tungsten powder prepared in this comparative example was tested and characterized. The results showed that the average particle size of the tungsten powder was 462 nm, and the BET was 4.67 nm. 2 / g; SEM image of the tungsten powder is as follows Figure 10 As shown, the SEM images reveal that the particles are generally large, unevenly distributed in size, and exhibit agglomeration and poor dispersion.

[0064] Comparative Example 8 The only difference between this comparative example and Example 1 is step 4, which is as follows: The tungstate-polyethylene glycol composite precursor obtained in step 3 above was placed in a tube furnace and reduced in one step under a hydrogen atmosphere. The temperature was increased to 900°C at a heating rate of 10°C / min for 2.5 hours, and the hydrogen flow rate was 3L / min to obtain nano-tungsten powder.

[0065] The tungsten powder prepared in this comparative example was tested and characterized. The test results showed that the average particle size of the tungsten powder was 724 nm, and the BET was 1.97 nm. 2 / g; SEM image of the tungsten powder is as follows Figure 11 As shown, the SEM images reveal that the particles are large, irregular flakes with coarse size, severe boundary fusion, severe aggregation, and poor dispersibility.

[0066] Comparative Example 9 The only difference between this comparative example and Example 1 is that the reduction temperature in the first step of step 4 is 250°C.

[0067] The tungsten powder prepared in this comparative example was tested and characterized. The results showed that the average particle size of the tungsten powder was 175 nm, and the BET was 12.11 μm. 2 / g; SEM image of the tungsten powder is as follows Figure 12 As shown, the SEM image reveals a large number of fine flocculent aggregates, interspersed with obvious coarse particles, with uneven particle size distribution and poor overall dispersion.

[0068] In summary, this invention provides a method for preparing nano-tungsten powder by hydrogen reduction of a PEG-coated tungstate precursor. The method first involves mixing polyethylene glycol (PEG) with an ammonium tungstate solution to obtain a homogeneous dispersion. Then, dilute hydrochloric acid is added dropwise under continuous ultrasonication to achieve simultaneous acid precipitation and ultrasonication, resulting in a tungstate-PEG composite suspension. After solid-liquid separation, washing, drying, and sieving, the tungstate-PEG composite precursor is obtained. Finally, a three-step gradient reduction is performed under a hydrogen atmosphere to obtain nano-tungsten powder. This invention employs a simultaneous acid precipitation and ultrasonication process to directly inhibit agglomeration at the tungstate nucleation stage. By selecting PEG as the dispersant and selecting a preferred range of PEG molecular weight (2000-6000) and addition amount (5-15%), the PEG fully utilizes its steric hindrance coating effect, which synergizes with the ultrasonic cavitation effect, resulting in a precursor with uniform particle size. Based on this, the three-step gradient reduction process is matched with the thermal decomposition characteristics of the polyethylene glycol-coated precursor. The first reduction temperature corresponds to the initial decomposition temperature range of polyethylene glycol, allowing for slow pyrolysis removal of polyethylene glycol and avoiding bubble impact and structural collapse caused by rapid decomposition of the coating layer. This helps maintain the morphological integrity of the precursor. Subsequent reduction processes complete the reduction reaction and lattice perfection in stages, effectively suppressing particle growth and agglomeration during the reduction process. Through the synergistic combination of precursor preparation and reduction process, this invention can stably prepare highly dispersed, narrowly distributed nano-tungsten powder. The process is simple, requires no special equipment, has low raw material costs, strong parameter controllability, and is easy to implement for industrial production.

[0069] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for preparing nano-tungsten powder by hydrogen reduction of PEG-coated tungstate precursor, characterized in that, Includes the following steps: Step 1: Add polyethylene glycol to ammonium tungstate solution and stir until completely dissolved to obtain a homogeneous dispersion; Step 2: Under continuous ultrasonic conditions, dilute hydrochloric acid is added dropwise to the homogeneous dispersion until no more tungstic acid precipitate is formed, so as to achieve the synchronous synergy of acid precipitation and ultrasonication, and obtain tungstic acid-polyethylene glycol composite suspension. Step 3: Filter, wash until neutral, dry, grind and sieve the tungstate-polyethylene glycol composite suspension to obtain the tungstate-polyethylene glycol composite precursor; Step 4: The tungstate-polyethylene glycol composite precursor is subjected to a three-step gradient reduction under a hydrogen atmosphere to obtain nano-tungsten powder.

2. The method for preparing nano-tungsten powder by hydrogen reduction of PEG-coated tungstate precursor according to claim 1, characterized in that, In step 1, the concentration of the ammonium tungstate solution, expressed as WO3, is 200-300 g / L.

3. The method for preparing nano-tungsten powder by hydrogen reduction of PEG-coated tungstate precursor according to claim 1, characterized in that, In step 1, the molecular weight of the polyethylene glycol is 2000-6000, and the amount of polyethylene glycol added is 5-15% of the mass of ammonium tungstate.

4. The method for preparing nano-tungsten powder by hydrogen reduction of PEG-coated tungstate precursor according to claim 1, characterized in that, In step 1, the mixing speed is 300-500 r / min and the mixing time is 30-60 min.

5. The method for preparing nano-tungsten powder by hydrogen reduction of PEG-coated tungstate precursor according to claim 1, characterized in that, In step 2, the power of the ultrasound is 200-300W.

6. The method for preparing nano-tungsten powder by hydrogen reduction of PEG-coated tungstate precursor according to claim 1, characterized in that, In step 2, the concentration of the dilute hydrochloric acid is 10-20 wt%, and the dropping rate of the dilute hydrochloric acid is 1-2 mL / min.

7. The method for preparing nano-tungsten powder by hydrogen reduction of PEG-coated tungstate precursor according to claim 1, characterized in that, In step 2, after the dilute hydrochloric acid is added dropwise, continue to sonicate and stir for 5-10 minutes.

8. The method for preparing nano-tungsten powder by hydrogen reduction of PEG-coated tungstate precursor according to claim 1, characterized in that, In step 4, the three-step gradient reduction includes: the first step reduction temperature is 300-350℃, and the reduction time is 0.5-1h; the second step reduction temperature is 500-550℃, and the reduction time is 1-3h; the third step reduction temperature is 700-900℃, and the reduction time is 1-3h.

9. The method for preparing nano-tungsten powder by hydrogen reduction of PEG-coated tungstate precursor according to claim 1, characterized in that, In step 4, the hydrogen flow rate is 3-5 L / min, and the heating rate is 8-12 °C / min.

10. The method for preparing nano-tungsten powder by hydrogen reduction of PEG-coated tungstate precursor according to claim 1, characterized in that, The average particle size of the nano-tungsten powder is ≤100nm, and the specific surface area BET is ≥19m². 2 / g.

Images