Uniform ultrafine tungsten powder and method for preparing the same

Abstract

This invention belongs to the field of metal powder preparation technology, specifically relating to a uniform ultrafine tungsten powder and its preparation method. The preparation method includes the following steps: S1, obtaining an ammonium tungstate solution and a first solvent; the first solvent is obtained by mixing water and ethanol; S2, adding the ammonium tungstate solution and hydrazine hydrate solution dropwise into the first solvent to obtain a first system; the molar ratio of hydrazine hydrate to WO3 in the ammonium tungstate solution is (4-9):1; S3, continuously stirring the first system to allow it to crystallize, then filtering and drying to obtain a precursor powder; S4, heating the precursor powder under a protective gas atmosphere to cause the precursor powder to self-reduction to obtain uniform ultrafine tungsten powder. The prepared uniform ultrafine tungsten powder has a uniform particle size, with an average particle size of 100-400 nm. This invention allows for controllable dosage of the reducing agent, thorough reduction, and uniform tungsten powder particle size; it can obtain high-purity tungsten powder and avoids the introduction of impurities; it has advantages such as simple operation, high reproducibility, short process, simple equipment, easy industrialization, and cost savings.

Description

Technical Field

[0001] This invention belongs to the field of metal powder preparation technology, specifically relating to a uniform ultrafine tungsten powder and its preparation method. Background Technology

[0002] In modern industrial production systems, cemented carbide, as a crucial material, plays an irreplaceable role in numerous fields due to its superior properties such as high hardness, high strength, excellent wear resistance, and heat resistance. Tungsten powder, as the core raw material for cemented carbide preparation, is directly influenced by the development level of its preparation technology, which impacts the development direction and quality improvement of the cemented carbide industry.

[0003] In the early days, due to the relatively low requirements for material performance in industrial production, the tungsten powder produced by traditional tungsten powder preparation processes had significant limitations in terms of purity and particle size uniformity. This resulted in cemented carbides that could not meet the actual needs of complex working conditions in terms of overall performance, such as hardness and toughness. With the rapid development of the manufacturing industry towards higher precision, higher efficiency, and higher reliability, especially the rapid rise of high-end industries such as aerospace, automotive manufacturing, and electronics, even more stringent challenges have been placed on the performance of cemented carbides. For example, in the manufacturing process of high-temperature components for aero-engines, cemented carbides are required to withstand high temperatures and pressures while also possessing excellent wear resistance and fatigue resistance. In the field of electronics manufacturing, the increasing trend of product miniaturization places extremely high demands on the precision and durability of cemented carbide cutting tools. To meet these growing high-performance requirements, researchers and enterprises are actively exploring more advanced tungsten powder preparation technologies to continuously improve the quality and performance of cemented carbide products.

[0004] Traditional tungsten powder preparation methods mainly involve reducing high-purity tungsten oxides using hydrogen reduction. The tungsten oxides are primarily obtained from tungstate and ammonium paratungstate. The preparation of tungsten oxides from tungstates is generally carried out in an open calcination furnace, using air from the factory environment, which easily leads to product contamination. At the same time, the tungstate cracking process generates a large amount of ammonia, requiring additional recovery facilities. The preparation of tungsten powder from tungsten oxides involves multiple stages of hydrogen reduction. The overall process is long, the equipment is complex, and the product quality fluctuates. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for preparing uniform ultrafine tungsten powder, comprising the following steps:

[0006] S1. Obtain an ammonium tungstate solution and a first solvent; the first solvent is obtained by mixing water and ethanol, and the temperature of the first solvent is heated and maintained at a predetermined temperature.

[0007] S2. While stirring the first solvent, the ammonium tungstate solution and hydrazine hydrate solution are added dropwise to the first solvent to obtain a first system. During the dropwise addition, the temperature of the first system is maintained at the predetermined temperature. The molar ratio of hydrazine hydrate in the hydrazine hydrate solution to WO3 in the ammonium tungstate solution is (4-9):1.

[0008] S3. While maintaining the temperature of the first system at the predetermined temperature, the first system is continuously stirred to crystallize it, and then filtered and dried to obtain precursor powder.

[0009] S4. Under a protective gas atmosphere, the precursor powder is heated to cause the precursor powder to self-reduction to obtain uniform ultrafine tungsten powder.

[0010] Furthermore, in step S2, the molar ratio of hydrazine hydrate in the hydrazine hydrate solution to WO3 in the ammonium tungstate solution is any one of 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or a range between both.

[0011] As a preferred embodiment of the method for preparing uniform ultrafine tungsten powder according to the present invention, in step S1, the ratio of water to ethanol in the first solvent is 1:(0.5-1.5).

[0012] In a preferred embodiment of the method for preparing uniform ultrafine tungsten powder according to the present invention, in step S2, ammonium tungstate solution and hydrazine hydrate solution are added dropwise through a dropping funnel. The rate of adding ammonium tungstate solution is 25-50 mL / min, and the rate of adding hydrazine hydrate solution is 9-20 mL / min. The sum of the volumes of ammonium tungstate solution and hydrazine hydrate solution is 10-30 times that of the first solvent.

[0013] Furthermore, the ammonium tungstate solution and the hydrazine hydrate solution are added dropwise simultaneously and are added dropwise at the same time.

[0014] As a preferred embodiment of the method for preparing uniform ultrafine tungsten powder according to the present invention, in steps S1, S2 and S3, the heating and temperature maintenance method is a water bath, and the predetermined temperature is 20-90℃.

[0015] Furthermore, the predetermined temperature is any one or a range between two of 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, and 90°C.

[0016] As a preferred embodiment of the method for preparing uniform ultrafine tungsten powder according to the present invention, in step S2, the WO3 content in the ammonium tungstate solution is 130-230 g / L, and the concentration of the hydrazine hydrate solution is 4-16 mol / L.

[0017] As a preferred embodiment of the method for preparing uniform ultrafine tungsten powder according to the present invention, in step S3, the stirring time for crystallization is 4-8 hours, the drying temperature is 70-90°C, and the drying time is 7-10 hours.

[0018] As a preferred embodiment of the method for preparing uniform ultrafine tungsten powder according to the present invention, in step S4, the protective gas includes at least one of an inert gas and hydrogen.

[0019] Furthermore, the protective gas is N2.

[0020] As a preferred embodiment of the method for preparing uniform ultrafine tungsten powder according to the present invention, in step S4, the protective gas is N2 or H2 with a flow rate of 1-3 L / min, and the precursor powder is heated in a tube furnace at a temperature of 800-1000℃ for a reduction time of 3-7 h.

[0021] To solve the above-mentioned technical problems, the present invention also proposes a uniform ultrafine tungsten powder, wherein the uniform ultrafine tungsten powder is prepared by any of the above-mentioned methods for preparing uniform ultrafine tungsten powder.

[0022] As a preferred embodiment of the uniform ultrafine tungsten powder described in this invention, the uniform ultrafine tungsten powder has a uniform particle size with an average particle size of 100-400 nm.

[0023] The beneficial effects of this invention are as follows: the amount of reducing agent can be controlled, the reduction is sufficient and thorough, and the tungsten powder has a uniform particle size; high-purity tungsten powder can be obtained, avoiding the introduction of impurities; it has the advantages of simple operation, high reproducibility, short process, simple equipment, easy industrialization, and cost saving. Attached Figure Description

[0024] 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.

[0025] Figure 1 SEM image of the uniform ultrafine tungsten powder prepared in Example 1;

[0026] Figure 2 Here is a SEM image of the tungsten powder prepared in Comparative Example 1;

[0027] Figure 3 Here is a SEM image of the tungsten powder prepared in Comparative Example 2;

[0028] Figure 4 Here is a SEM image of the tungsten powder prepared in Comparative Example 3;

[0029] Figure 5 Here is a SEM image of the tungsten powder prepared in Comparative Example 5;

[0030] Figure 6 The image shows a SEM image of the tungsten powder prepared in Comparative Example 6.

[0031] 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

[0032] 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.

[0033] This invention proposes a method for preparing uniform ultrafine tungsten powder, comprising the following steps:

[0034] S1. Obtain an ammonium tungstate solution and a first solvent; the first solvent is obtained by mixing water and ethanol, and the temperature of the first solvent is heated and maintained at a predetermined temperature.

[0035] The addition of ethanol helps to regulate the crystallization behavior and morphology of the precursor. As a dispersion medium, it can effectively prevent the agglomeration of precursor particles, thus laying the foundation for obtaining uniform ultrafine tungsten powder in the future.

[0036] S2. While stirring the first solvent, the ammonium tungstate solution and hydrazine hydrate solution are added dropwise to the first solvent to obtain a first system. During the dropwise addition, the temperature of the first system is maintained at the predetermined temperature. The molar ratio of hydrazine hydrate in the hydrazine hydrate solution to WO3 in the ammonium tungstate solution is (4-9):1.

[0037] Through extensive experimentation, this invention has determined that the molar ratio of hydrazine hydrate to WO3 should be controlled between 4:1 and 9:1. A molar ratio that is too low will result in insufficient reduction of the precursor during the subsequent heating and self-reduction step, leading to the presence of unreduced oxides in the product. A molar ratio that is too high, while achieving complete reduction, is less economical and causes waste liquid disposal problems due to excessive hydrazine hydrate. The optimal ratio of this invention ensures a thorough and complete reduction reaction, and yields high-purity, uniform, ultrafine tungsten powder with uniform particle size.

[0038] The ammonium tungstate solution and hydrazine hydrate solution are mixed by dropwise addition in order to precisely control the addition rate of the reactants, thereby controlling the temperature of the reaction system and the nucleation and growth process of the precursors. If the addition is replaced by rapid or one-time addition, the precursors will nucleate too quickly and grow unevenly, ultimately resulting in a wider particle size distribution and irregular morphology of the precursors and the final tungsten powder. Therefore, this operation should not be replaced by other mixing methods.

[0039] S3. While maintaining the temperature of the first system at the predetermined temperature, the first system is continuously stirred to crystallize it, and then filtered and dried to obtain precursor powder.

[0040] The reaction between ammonium tungstate and hydrazine hydrate is a complexation reaction, and the crystallized product is a hydrated amine tungstate, in which hydrazine hydrate is uniformly distributed.

[0041] In S1, S2 and S3 above, the heating and temperature maintenance method can be a water bath; water bath heating is used to provide a mild, uniform and controllable heating environment, avoiding local overheating and temperature runaway that may be caused by heating methods such as open flame or electric heating mantle, which is crucial for obtaining precursors with good reproducibility.

[0042] S4. Under a protective gas atmosphere, the precursor powder is heated to cause the precursor powder to self-reduction to obtain uniform ultrafine tungsten powder.

[0043] The reducing agent for obtaining uniform ultrafine tungsten powder by heating and reducing the precursor comes from hydrogen gas obtained by the decomposition of hydrazine hydrate (N2H4·H2O), eliminating the need for external hydrogen gas to participate in the reduction process. Furthermore, during precursor preparation, hydrazine hydrate enters the precursor grain boundaries. During reduction, the decomposition of hydrazine hydrate causes volume expansion, leading to grain cracking in the precursor, while simultaneously being reduced. Therefore, the reduction process of this invention can be carried out in an H2 atmosphere or other inert gases. This invention uses hydrazine hydrate as the reducing agent and performs reduction in a protective gas atmosphere. The source of the reducing agent is clear, the dosage is controllable, and the reduction process is thorough and complete, effectively avoiding the introduction of external impurities and ensuring the high purity and uniformity of the final uniform ultrafine tungsten powder.

[0044] The temperature of heating reduction also affects the uniformity of tungsten powder particle size. At lower temperatures (600-800℃), the tungsten powder grains do not grow completely, resulting in poor particle size uniformity. Increasing the temperature can improve particle size uniformity. At temperatures of 800-1000℃, the grains have grown, and the overall uniformity is good.

[0045] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0046] Example 1

[0047] A method for preparing uniform ultrafine tungsten powder includes the following steps:

[0048] S1. Obtain an ammonium tungstate solution and a first solvent; the first solvent is obtained by mixing water and ethanol, and the temperature of the first solvent is heated and maintained at a predetermined temperature; wherein, the ammonium tungstate solution contains 150 g / L of WO3, has a volume of 1000 mL, and the number of moles of WO3 is 0.647 mol; 50 mL each of water and ethanol (volume ratio 1:1) are placed in a beaker and mixed evenly by stirring to obtain the first solvent, and the first solvent is heated in a water bath and maintained at a predetermined temperature of 50°C;

[0049] S2. Under the condition of stirring the first solvent, the ammonium tungstate solution and hydrazine hydrate solution are added dropwise to the first solvent to obtain a first system. During the dropwise addition, the temperature of the first system is maintained at the predetermined temperature. The concentration of the hydrazine hydrate solution is 12 mol / L, the volume is 350 mL, the molar number of hydrazine hydrate is 4.2 mol, and the molar ratio of hydrazine hydrate to WO3 is 6.5:1. The dropwise addition is performed using a dropping funnel, with the ammonium tungstate solution added at a rate of 40 mL / min and the hydrazine hydrate solution added at a rate of 14 mL / min. The sum of the volumes of the ammonium tungstate solution and the hydrazine hydrate solution is 13.5 times the volume of the first solvent. During the dropwise addition, the system is heated in a water bath and the predetermined temperature of the first system is maintained at 50°C.

[0050] S3. While maintaining the temperature of the first system at the predetermined temperature, the first system is continuously stirred to crystallize, then filtered and dried to obtain precursor powder; wherein, the predetermined temperature of the first system is maintained at 50°C by heating in a water bath; the crystallization time is 8 hours, the drying temperature is 80°C, and the drying time is 10 hours.

[0051] S4. Under a protective gas atmosphere, the precursor powder is heated to cause the precursor powder to self-reduction to obtain uniform ultrafine tungsten powder; wherein the protective gas is H2, the H2 flow rate is 1.5L / min, the precursor powder is heated in a tube furnace at a temperature of 850℃, and the reduction time is 5h.

[0052] Please see Figure 1 , Figure 1 The image shows a SEM image of the uniform ultrafine tungsten powder prepared in Example 1. Figure 1 It can be seen that the grains have distinct edges and corners, with virtually no flocculent crystals, and the overall grain uniformity is good, with an average grain size of about 200 nm.

[0053] Example 2

[0054] The difference from Example 1 is as follows: In S1, the ammonium tungstate solution contains 200 g / L of WO3, has a volume of 1000 mL, and contains 0.863 mol of WO3; in S2, the hydrazine hydrate solution has a concentration of 12 mol / L, a volume of 500 mL, contains 6 mol of hydrazine hydrate, has a molar ratio of hydrazine hydrate to WO3 of 7:1, the ammonium tungstate solution is added at a rate of 40 mL / min, the hydrazine hydrate solution is added at a rate of 20 mL / min, and the combined volume of the ammonium tungstate solution and the hydrazine hydrate solution is 15 times that of the first solvent. Otherwise, everything else is the same as in Example 1.

[0055] Experimental results: The obtained tungsten powder has uniform grain size, with a slightly larger particle size and an overall average particle size of about 250 nm.

[0056] Example 3

[0057] The differences from Example 1 are as follows: In S1, the ammonium tungstate solution contains 200 g / L of WO3, has a volume of 1000 mL, and contains 0.863 mol of WO3; in S2, the hydrazine hydrate solution has a concentration of 12 mol / L, a volume of 500 mL, contains 6 mol of hydrazine hydrate, has a molar ratio of hydrazine hydrate to WO3 of 7:1, the ammonium tungstate solution is added at a rate of 40 mL / min, the hydrazine hydrate solution is added at a rate of 20 mL / min, and the combined volume of the ammonium tungstate solution and the hydrazine hydrate solution is 15 times that of the first solvent; the predetermined temperature in S1, S2, and S3 is 60°C; and the crystallization time in S3 is 6 hours with continuous stirring. Otherwise, everything else is the same as in Example 1.

[0058] Experimental results: The obtained tungsten powder has uniform overall grain size and the overall morphology of the tungsten powder is similar to that of Example 2. The overall average particle size is about 250 nm, but the precursor particle size is more uniform.

[0059] Example 4

[0060] The differences from Example 1 are as follows: In S1, the ammonium tungstate solution contains 210 g / L of WO3, has a volume of 1000 mL, and contains 0.906 mol of WO3; in S2, the hydrazine hydrate solution has a concentration of 12 mol / L, a volume of 500 mL, contains 6 mol of hydrazine hydrate, and has a molar ratio of hydrazine hydrate to WO3 of 6.6:1; the rate of addition of the ammonium tungstate solution is 40 mL / min, the rate of addition of the hydrazine hydrate solution is 20 mL / min, and the sum of the volumes of the ammonium tungstate solution and the hydrazine hydrate solution is 15 times that of the first solvent; the predetermined temperature in S1, S2, and S3 is 80°C; and the time for continuous stirring to allow crystallization in S3 is 4 hours. Otherwise, everything else is the same as in Example 1.

[0061] Experimental results: The obtained tungsten powder has uniform overall grain size, with an overall average particle size of about 280 nm.

[0062] Example 5

[0063] The difference from Example 1 is that the protective gas in S4 is N2. Otherwise, it is the same as Example 1.

[0064] Experimental results: The morphology of the tungsten powder obtained is similar to that of Example 1, with an overall average particle size of about 200 nm, but the edges of the tungsten powder grains are more rounded.

[0065] Example 6

[0066] The difference from Example 1 is as follows: In S1, the ammonium tungstate solution contained 130 g / L of WO3, with a volume of 1500 mL and a molar content of 0.842 mol of WO3. Water and ethanol were added in a volume ratio of 1:0.5 (50 mL and 25 mL respectively). In S2, the hydrazine hydrate solution had a concentration of 4.5 mol / L, a volume of 750 mL, a molar content of 3.38 mol of hydrazine hydrate, and a molar ratio of hydrazine hydrate to WO3 of 4:1. The ammonium tungstate solution was added dropwise... The rate of addition was 50 mL / min, the rate of addition of hydrazine hydrate solution was 9.3 mL / min, and the sum of the volumes of ammonium tungstate solution and hydrazine hydrate solution was 30 times that of the first solvent; the predetermined temperature in S1, S2 and S3 was 90°C; in S3, the crystallization time was 4 h with continuous stirring, the drying temperature was 70°C and the drying time was 10 h; in S4, the protective gas was N2 with a flow rate of 1 L / min, the reduction temperature was 800°C and the reduction time was 7 h. Otherwise, everything else was the same as in Example 1.

[0067] Experimental results: The obtained tungsten powder has uniform grain size, with an overall average particle size of about 100 nm.

[0068] Example 7

[0069] The difference from Example 1 is as follows: In S1, the ammonium tungstate solution contains 230 g / L of WO3, has a volume of 800 mL, and contains 0.794 mol of WO3. Water and ethanol are added in a volume ratio of 1:1.5 (50 mL and 75 mL respectively). In S2, the hydrazine hydrate solution has a concentration of 16 mol / L, a volume of 450 mL, contains 7.2 mol of hydrazine hydrate, and has a molar ratio of hydrazine hydrate to WO3 of 9:1. The ammonium tungstate solution is added at a rate of 25 mL / min, and the hydrazine hydrate solution is added at a rate of 18.5 mL / min. The combined volume of the ammonium tungstate solution and the hydrazine hydrate solution is 10 times that of the first solvent. The predetermined temperature in S1, S2, and S3 is 20°C. In S3, the crystallization time is 8 h with continuous stirring, the drying temperature is 90°C, and the drying time is 7 h. In S4, the protective gas is N2 with a flow rate of 3 L / min, the reduction temperature is 1000°C, and the reduction time is 3 h. Apart from the above, everything else is the same as in Example 1.

[0070] Experimental results: The obtained tungsten powder has uniform grain size, with an overall average particle size of about 400 nm.

[0071] Comparative Example 1

[0072] The difference from Example 1 is that the first solvent in S1 contains only water, and 50 mL of water is used as the first solvent. Otherwise, it is the same as Example 1.

[0073] Experimental results: Severe aggregation occurred during the crystallization process of the obtained precursor. Please refer to [link / reference needed]. Figure 2 , Figure 2 The image shows the SEM image of the tungsten powder prepared in Comparative Example 1. The tungsten powder has a wide particle size distribution and contains a large number of micron-sized agglomerates, making it impossible to obtain uniform ultrafine tungsten powder.

[0074] Comparative Example 2

[0075] The difference from Example 1 is that in S2, the ammonium tungstate solution and hydrazine hydrate solution are rapidly added to the first solvent in one step (not dropwise). Otherwise, it is the same as Example 1.

[0076] Experimental results: Adding ammonium tungstate solution and hydrazine hydrate solution simultaneously resulted in excessively rapid precursor nucleation and uneven crystallization. Please refer to [link / reference needed]. Figure 3 , Figure 3 The image shows the SEM image of the tungsten powder prepared in Comparative Example 2. After reduction, the tungsten powder has an irregular morphology, wide particle size distribution, and poor uniformity.

[0077] Comparative Example 3

[0078] The difference from Example 5 is that: in S2, the concentration of the hydrazine hydrate solution is 12 mol / L, the volume is 108 mL, the molar number of hydrazine hydrate is 1.3 mol, the molar ratio of hydrazine hydrate to WO3 is 2:1, the rate of adding ammonium tungstate solution is 40 mL / min, the rate of adding hydrazine hydrate solution is 4.3 mL / min, and the sum of the volumes of ammonium tungstate solution and hydrazine hydrate solution is 11 times that of the first solvent. Otherwise, it is the same as Example 5.

[0079] Experimental results: The reduced product contained a large amount of incompletely reduced oxide intermediate phases. Please refer to [link / reference needed]. Figure 4 , Figure 4 The image shows a SEM image of the tungsten powder prepared in Comparative Example 3. The grains are not obvious and the particle size uniformity is poor.

[0080] Comparative Example 4

[0081] The difference from Example 5 is that: in S2, the concentration of the hydrazine hydrate solution is 12 mol / L, the volume is 650 mL, the number of moles of hydrazine hydrate is 7.8 mol, the molar ratio of hydrazine hydrate to WO3 is 12:1, the rate of adding ammonium tungstate solution is 40 mL / min, the rate of adding hydrazine hydrate solution is 26 mL / min, and the sum of the volumes of ammonium tungstate solution and hydrazine hydrate solution is 16.5 times that of the first solvent. Otherwise, it is the same as Example 5.

[0082] Experimental results: Although the reduction was complete, it was not economical, and the excessive reducing agent led to a high ammonia content in the waste liquid, which was not beneficial to subsequent treatment.

[0083] Comparative Example 5

[0084] The difference from Example 1 is that the temperature in S4 is 650°C. Otherwise, it is the same as Example 1.

[0085] Experimental results: Please refer to Figure 5 , Figure 5 The image shows a SEM image of the tungsten powder prepared in Comparative Example 5. Figure 5 It can be seen that there are still many grains that have not grown, and they are attached to the grown grains in a flocculent structure.

[0086] Comparative Example 6

[0087] The difference from Example 1 is that the temperature in S4 is 750°C. Otherwise, it is the same as Example 1.

[0088] Experimental results: Please refer to Figure 6 , Figure 6 The image shows a SEM image of the tungsten powder prepared in Comparative Example 6. Figure 6 It can be seen that the grains have basically grown, with a grain size of about 200nm, but the overall uniformity of the grains is slightly poor.

[0089] Compared with Example 1, Comparative Example 1 illustrates the key role of adding ethanol in the solvent. The addition of ethanol helps to regulate the crystallization behavior and morphology of the precursor. As a dispersion medium, it can effectively prevent the agglomeration of precursor particles, thus laying the foundation for obtaining uniform ultrafine tungsten powder in the future.

[0090] Compared to Example 1, Comparative Example 2 illustrates the crucial role of the dropwise addition method in mixing the ammonium tungstate solution and hydrazine hydrate solution. Dropwise addition is used to precisely control the rate of reaction, thereby controlling the temperature and nucleation process of the reaction system. If the addition is replaced by rapid or one-time addition, nucleation will be too fast and uneven, ultimately resulting in a wider particle size distribution and irregular morphology of the precursor and final tungsten powder.

[0091] Compared with Comparative Example 3 and Example 5, it is shown that an excessively low molar ratio of hydrazine hydrate to WO3 will lead to insufficient reduction and the presence of unreduced oxides in the product.

[0092] Compared with Comparative Example 4 and Example 5, it is shown that when the molar ratio of hydrazine hydrate to WO3 is greater than 9:1, the precursor can be completely reduced, but the economy is poor.

[0093] Compared with Comparative Examples 5 and 6, and Example 1, it is shown that at lower temperatures (600-800℃), the tungsten powder grains did not all grow, resulting in poor particle size uniformity. Increasing the temperature can improve the particle size uniformity. At a temperature of 800-1000℃, the grains have grown, and the overall uniformity is good.

[0094] This invention prepares a precursor by hydrazine hydrate complexation and then uses self-reduction technology to prepare uniform ultrafine tungsten powder, achieving the following beneficial effects: the amount of reducing agent is controllable, the reduction is sufficient and thorough, and the tungsten powder has a uniform particle size; high-purity tungsten powder can be obtained, avoiding the introduction of impurities; it has the advantages of simple operation, high reproducibility, short process, simple equipment, easy industrialization, and cost saving.

[0095] 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 producing uniform ultrafine tungsten powder, characterized by, The method comprises the following steps: S1, obtaining an ammonium tungstate solution and a first solvent; the first solvent is obtained by mixing water and ethanol, and the temperature of the first solvent is maintained at a predetermined temperature by heating; S2, under the condition of stirring the first solvent, the ammonium tungstate solution and a hydrazine hydrate solution are added dropwise into the first solvent to obtain a first system, and the temperature of the first system is maintained at the predetermined temperature during the dropwise adding process; the molar ratio of hydrazine hydrate in the hydrazine hydrate solution to WO3 in the ammonium tungstate solution is (4-9):1; S3, under the condition of maintaining the temperature of the first system at the predetermined temperature, the first system is continuously stirred to crystallize, and then is subjected to suction filtration and drying to obtain a precursor powder; S4, under the atmosphere of a protective gas, the precursor powder is heated to self-reduce the precursor powder to obtain a uniform ultrafine tungsten powder; In the step S2, the ammonium tungstate solution and the hydrazine hydrate solution are added dropwise through a dropping funnel, the rate of adding the ammonium tungstate solution is 25-50 mL / min, and the rate of adding the hydrazine hydrate solution is 9-20 mL / min; In the step S4, the protective gas is an inert gas; In the step S1, the ratio of water to ethanol in the first solvent is 1:(0.5-1.5).

2. The method of claim 1, wherein the tungsten powder has a D50 of 0.1 to 0.5 μm. In the step S2, the sum of the volumes of the ammonium tungstate solution and the hydrazine hydrate solution is 10-30 times that of the first solvent.

3. The method of claim 1, wherein the tungsten powder has a D50 of 0.1 to 0.5 μm. In the steps S1, S2 and S3, the heating and temperature maintaining mode is water bath, and the predetermined temperature is 20-90℃.

4. The method of claim 1, wherein the tungsten powder has a D50 of 0.1 to 0.5 μm. In the step S2, the content of WO3 in the ammonium tungstate solution is 130-230 g / L, and the concentration of the hydrazine hydrate solution is 4-16 mol / L.

5. The method of claim 1, wherein the tungsten powder has a D50 of 0.1 to 0.5 μm. In the step S3, the time for stirring to crystallize is 4-8 h, the drying temperature is 70-90℃, and the drying time is 7-10 h.

6. The method of claim 1, wherein the tungsten powder has a D50 of 0.2 to 0.5 μm. In the step S4, the protective gas is N2, and the flow rate is 1-3 L / min.

7. The method of claim 1, wherein the tungsten powder has a D50 of 0.2 to 0.5 μm. The uniform ultrafine tungsten powder is prepared by the method for preparing a uniform ultrafine tungsten powder according to any one of claims 1-7.

8. A uniform ultrafine tungsten powder, characterized by, The uniform ultrafine tungsten powder has uniform particle size, and the average particle size is 100-400 nm.

9. The uniform ultrafine tungsten powder of claim 8 wherein, ​

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