Preparation and morphology control method of superfine tungsten powder, molybdenum powder and tungsten-molybdenum alloy powder

Abstract

The invention relates to a preparation and morphology regulation and control method of superfine tungsten powder, molybdenum powder and tungsten-molybdenum alloy powder, belongs to the technical field of inorganic materials, and solves the problems that tungsten / molybdenum powder prepared by adopting an existing method is large in particle size, non-uniform in alloy powder mixing, high in energy consumption, high in cost and difficult in morphology regulation and control. The method comprises the following steps: preparing a mixed solution of peroxy metal acid and peroxy metal acid ammonium; carrying out evaporative crystallization on the mixed solution to obtain a wet material; performing flash evaporation drying on the wet material to obtain raw material powder; roasting the raw material powder to obtain a metal oxide; the metal oxide is subjected to hydrogen reduction, and the superfine metal powder is obtained; the metal is at least one of tungsten and molybdenum. According to the method, the raw material powder obtained after the mixed solution is subjected to evaporative crystallization and flash evaporation drying is roasted and reduced, the superfine nearly-spherical porous metal powder can be directly obtained, the process is simple and convenient, the product purity is high, and the morphology is controllable.

Description

Technical Field

[0001] This invention relates to the field of inorganic materials technology, and in particular to a method for preparing and controlling the morphology of ultrafine tungsten powder, molybdenum powder and tungsten-molybdenum alloy powder. Background Technology

[0002] Ultrafine tungsten powder is widely used in the electronics and semiconductor industries, high-temperature industrial cemented carbide and cutting tools, new energy and catalysis, 3D printing and additive manufacturing, and other fields. Ultrafine molybdenum powder is widely used in electronics and microelectronics, high-temperature and structural materials, catalysis and chemical engineering, coatings and surface engineering, lubrication and wear-resistant materials, and biomedicine. With rapid economic growth and technological progress, their importance is becoming increasingly prominent, driving more stringent and continuously improving requirements for their material properties.

[0003] Ultrafine tungsten and molybdenum powders (<10 μm) are mainly prepared using powder metallurgy. The particle size of the powder directly affects the subsequent metal preparation method and the microstructure of the metal, thus influencing its properties. Existing methods such as ball milling produce powders with relatively large particle sizes; existing methods for preparing ultrafine powders by adding pore-forming agents to molybdates can affect the purity of the ultrafine powder. Therefore, there is an urgent need to develop new methods for preparing ultrafine tungsten and molybdenum powders. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a method for preparing and controlling the morphology of ultrafine tungsten powder, molybdenum powder and tungsten-molybdenum alloy powder, in order to solve at least one of the problems of large particle size of tungsten / molybdenum powder, uneven mixing of alloy powder, high energy consumption, high cost and difficulty in controlling morphology when prepared by existing methods.

[0005] On one hand, embodiments of the present invention provide a method for preparing ultrafine metal powder, the method comprising:

[0006] (1) Prepare a mixed solution of peroxymetallic acid and ammonium peroxymetalate;

[0007] (2) The mixed solution is evaporated and crystallized to obtain a wet material;

[0008] (3) The wet material is flash-dried to obtain raw material powder;

[0009] (4) The raw material powder is calcined to obtain metal oxides;

[0010] (5) The metal oxide is reduced with hydrogen to obtain the ultrafine metal powder;

[0011] The metal is at least one of tungsten and molybdenum.

[0012] Further, in step (1), the preparation of the mixed solution specifically includes: adding hydrogen peroxide or hydrogen peroxide and ammonia to the metal raw material solution, controlling the molar number of ammonium peroxide in the mixed solution to be 0-20% of the total molar number of ammonium peroxide and ammonium peroxide, and the volume fraction of hydrogen peroxide to be 3-15%.

[0013] Furthermore, the metal raw material is at least one of tungsten-containing raw materials and molybdenum-containing raw materials.

[0014] Furthermore, the tungsten-containing raw material is at least one of pure tungsten products, ammonium tungstates, tungsten oxides, tungstic acid, and peroxytungstic acid.

[0015] Furthermore, the molybdenum-containing raw material is at least one of pure molybdenum products, ammonium molybdates, molybdenum oxides, molybdic acid, and peroxymolybdic acid.

[0016] Furthermore, in step (2), the evaporation crystallization temperature is 80-95℃ and the time is 3-8h.

[0017] Furthermore, the stirring speed during the evaporation and crystallization process is 400-1000 r / min.

[0018] Furthermore, in step (3), the temperature of the flash drying is 100-200℃.

[0019] Furthermore, the hot air velocity during the flash drying process is 0.5–5 m / s, and the feeding speed is 2–20 cm. 3 / s.

[0020] Furthermore, in step (4), the roasting temperature is 300-500℃ and the time is 1-5h.

[0021] Furthermore, in step (5), the hydrogen reduction includes primary hydrogen reduction and secondary hydrogen reduction.

[0022] Furthermore, the temperature of the first hydrogen reduction is 300-400℃, and the time is 2-5 hours.

[0023] Furthermore, the secondary hydrogen reduction is carried out at a temperature of 650-900℃ for a time of 4-8 hours.

[0024] Furthermore, the hydrogen flow rate for the first hydrogen reduction is 0.5-3 m³ / h. 3 / h; the hydrogen flow rate for the secondary hydrogen reduction is 5-40m³ / h. 3 / h.

[0025] On the other hand, embodiments of the present invention also provide an ultrafine metal powder, wherein the ultrafine metal powder is ultrafine tungsten powder, ultrafine molybdenum powder or ultrafine tungsten-molybdenum alloy powder; the powder is nearly spherical, with a particle size of <10μm and a purity of 99.9%.

[0026] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0027] 1. In this invention, the mixed solution containing peroxymetallic acid and ammonium peroxymetalate decomposes during heating, releasing oxygen and ammonia. The released gases act as pore-forming agents during crystal formation, effectively dispersing the wet materials obtained in each heating process and refining the powder. Furthermore, compared to adding additional pore-forming agents to the reaction system, the oxygen and ammonia released during heating do not affect the purity of the final metal powder product.

[0028] The ammonium ions introduced into the mixed solution can assist the crystallization process and regulate the morphology of the resulting powder.

[0029] 2. The present invention uses flash drying to dry the wet material obtained by evaporation and crystallization, so that the crystalline solid can be better dispersed by airflow to obtain a finer and more uniform powder.

[0030] 3. This invention involves calcining the powder material obtained after flash drying to completely decompose any incompletely decomposed peroxide anions in the dried powder and convert the material into metal oxides at high temperature, thereby ensuring the effectiveness, stability, and safety of subsequent reduction. In addition, during the calcination process, the thermal decomposition of peroxide metal acid or ammonium peroxide releases oxygen and ammonia, which can further refine the powder particle size. Compared with traditional calcination, this invention uses a lower temperature for calcination, which is beneficial to maintaining the morphology of the obtained powder and avoiding the impact of high-temperature calcination on the powder morphology.

[0031] 4. The present invention uses a lower reduction temperature, which can prevent the powder morphology from being damaged during the reduction process. At the same time, the present invention adjusts the reduction over a longer period of time to ensure the reduction effect and avoid the problem of incomplete reduction caused by low temperature reduction. Therefore, the present invention can ensure the ultrafine particle size of the powder and control the powder morphology while completely converting the metal oxide into metal powder.

[0032] 5. The present invention designs a process for preparing metal powders, which obtains raw material powders by direct evaporation and crystallization of solution through calcination reduction and drying. This eliminates the need for long-term ball milling of powders in traditional methods, simplifies the process, saves costs, and also enables the control of powder morphology.

[0033] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0034] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0035] Figure 1 This is a process flow diagram for preparing ultrafine metal powder according to the present invention;

[0036] Figure 2 The images show the morphology of the ultrafine raw material powder (a) and tungsten powder (b) prepared in Example 1.

[0037] Figure 3 The images show the morphology of the ultrafine raw material powder (a) and molybdenum powder (b) prepared in Example 3.

[0038] Figure 4 The images show the morphology of the ultrafine raw material powder (a) and tungsten-molybdenum alloy powder (b) prepared in Example 5.

[0039] Figure 5 The image shows the appearance of the ultrafine tungsten powder prepared in Example 6. Detailed Implementation

[0040] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0041] The particle size of tungsten / molybdenum metal powder directly affects the subsequent metal preparation method and the metal's microstructure, thus affecting its properties. In the powder metallurgy processes currently used, methods such as ball milling produce powders with larger particle sizes, while the method of adding pore-forming agents to molybdates to prepare ultrafine powders can affect the purity of the ultrafine powders.

[0042] Therefore, this invention discloses a method for preparing ultrafine metal powder, wherein the ultrafine metal powder is ultrafine tungsten powder, ultrafine molybdenum powder, or ultrafine tungsten-molybdenum alloy powder; the process flow diagram of the preparation method is shown below. Figure 1 As shown, the specific steps include:

[0043] (1) Prepare a mixed solution of peroxymetallic acid and ammonium peroxymetalate;

[0044] (2) The mixed solution is evaporated and crystallized to obtain a wet material;

[0045] (3) The wet material is flash-dried to obtain raw material powder;

[0046] (4) The raw material powder is calcined to obtain metal oxides;

[0047] (5) The metal oxide is reduced with hydrogen to obtain the ultrafine metal powder;

[0048] The metal is at least one of tungsten and molybdenum.

[0049] It should be noted that the peroxy metal acid mentioned in this invention is at least one of peroxytungstic acid and peroxymolybdic acid; the peroxy metal ammonium mentioned in this invention is at least one of peroxytungstic ammonium and peroxymolybdate; the metal acid mentioned is at least one of tungstic acid and molybdic acid; and the metal ammonium acid mentioned is at least one of ammonium tungstate and ammonium molybdate, which will not be repeated below.

[0050] This invention uses an appropriate amount of ammonium peroxide to promote the crystallization of peroxide metal acids that are not easily crystallized in solution during the evaporation and crystallization process, thereby improving the evaporation and crystallization efficiency of the solution and reducing energy consumption. On the other hand, ammonium ions can change the microstructure of the crystallized powder during the crystallization process, transforming it from its original elongated shape to a near-spherical porous structure, thereby increasing the fluidity and specific surface area of ​​the resulting powder.

[0051] Specifically, in step (1), the number of moles of ammonium peroxymetalate in the mixed solution of the present invention accounts for 0 to 20% of the total number of moles of peroxymetalic acid and ammonium peroxymetalate.

[0052] According to some preferred embodiments of the present invention, the percentage of ammonium peroxide in the mixed solution of the present invention relative to the total moles of ammonium peroxide and ammonium peroxide can be any value in the range of 0% to 20%, such as 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, and 20%.

[0053] It should be noted that the presence of ammonium peroxide metal oxide in the mixed solution can adjust the morphology of the subsequently obtained powder, thereby controlling the final metal powder product to have a near-spherical porous structure. Figure 2 As shown; however, the content of ammonium peroxide cannot be too high, otherwise, during the evaporation and crystallization of the mixed solution, two crystalline solids with different structures are easily generated. One is a long strip-shaped crystal structure derived from the peroxide, and the other is a polyhedral or columnar crystal structure derived from the ammonium peroxide. Thus, the purpose of controlling the crystalline powder to present a near-spherical porous structure cannot be achieved.

[0054] It should be noted that, in the case of a mixed solution without ammonium peroxide, the final powder obtained through subsequent heating is elongated. In the subsequent evaporation, crystallization, and calcination processes, the peroxide and / or hydrogen peroxide decompose upon heating, releasing oxygen that acts as a pore-forming agent, promoting powder diffusion. Combined with flash drying, this allows for better dispersion of the solid obtained from evaporation and crystallization through airflow, resulting in a finer and more uniform powder. When ammonium peroxide is absent from the mixed solution, the metal powder obtained using the technical solution of this invention is elongated, with a diameter less than 200 nm.

[0055] It should be noted that there can be various raw materials and methods for preparing a mixed solution containing peroxymetallic acid and ammonium peroxymetalate, and the present invention does not limit the preparation of the mixed solution. Depending on the materials selected, the method for preparing the mixed solution containing peroxymetallic acid and ammonium peroxymetalate of the present invention will also differ.

[0056] Specifically, in step (1), the preparation of the mixed solution includes adding hydrogen peroxide or hydrogen peroxide and ammonia to the metal raw material solution. The metal raw material is at least one of tungsten-containing raw material and molybdenum-containing raw material.

[0057] More specifically, the tungsten-containing raw material is at least one of pure tungsten products, ammonium tungstates, tungsten oxides, and tungstic acid.

[0058] According to some preferred embodiments of the present invention, the tungsten-containing raw material is one or more of metallic tungsten, tungsten trioxide, tungstic acid, ammonium metatungstate, and ammonium tungstate.

[0059] More specifically, the molybdenum-containing raw material is at least one of pure molybdenum products, ammonium molybdates, molybdenum oxides, and molybdic acid.

[0060] According to some preferred embodiments of the present invention, the molybdenum-containing raw material is one or more of metallic molybdenum, molybdenum trioxide, molybdic acid, ammonium metamolybdate, and ammonium molybdate.

[0061] According to some preferred embodiments of the present invention, when ammonium tungstates (such as ammonium metatungstate) and tungstic acid are used as raw materials, they are dissolved in water and then hydrogen peroxide is added directly; when tungsten oxides (such as tungsten trioxide) and tungstic acid are used as raw materials, the tungsten oxides can be dissolved in ammonia water first, and then tungstic acid and hydrogen peroxide can be added; or the oxides can be dissolved in hydrogen peroxide, and then ammonium tungstates or ammonia water can be added; pure metal raw materials are dissolved in hydrogen peroxide, and then ammonium tungstates or ammonia water can be added.

[0062] It should be noted that, in order to ensure that the peroxide metal acid and ammonium peroxide obtained after the reaction of the raw materials can be completely dissolved in the solution and will not precipitate after the reaction, the present invention controls the content of hydrogen peroxide in the mixed solution after the reaction.

[0063] Specifically, in step (1), the volume fraction of hydrogen peroxide in the mixed solution obtained after the reaction is 3-15%. If the content is too low, it will cause the precipitation of peroxymetallic acid and ammonium peroxymetalate obtained from the reaction, which will affect the uniformity of mixing during the subsequent evaporation and crystallization process, thereby affecting the control effect of ammonium ions on the morphology of the powder after crystallization; however, the content of hydrogen peroxide should not be too high, so as to avoid waste of reagents and increased energy consumption.

[0064] According to some preferred embodiments of the present invention, the volume fraction of hydrogen peroxide in the mixed solution obtained after the reaction can be any value in the range of 3-15%, such as 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, and 15%.

[0065] It should be noted that all the chemicals used in this invention were obtained commercially and were of analytical purity.

[0066] It should be noted that, in order to obtain near-spherical powder raw materials, the present invention requires control of the temperature and time for evaporation and crystallization of the mixed solution.

[0067] Specifically, in step (2), the evaporation and crystallization temperature is 80-95℃. If the temperature is too high, it will affect the morphology of the obtained solid; if the temperature is too low, it will result in a lower crystallization rate.

[0068] According to some preferred embodiments of the present invention, the evaporation and crystallization temperature can be 80°C, 82°C, 85°C, 87°C, 90°C, 93°C, or 95°C.

[0069] Specifically, in step (2), the evaporation and crystallization time is 3-8 hours. If the time is too long, the morphology of the solid obtained from crystallization will change; if the temperature is too short, the crystallization rate will be low.

[0070] According to some preferred embodiments of the present invention, the evaporation and crystallization time can be 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, or 8h.

[0071] It should be noted that, in order to make the mixed solution more uniformly mixed during the crystallization process, and to make the decomposition of peroxytungsten / molybdate and peroxytungsten / ammonium molybdate in the mixed solution more consistent, and to avoid the presence of two distinct solids in the crystalline solid, the present invention requires stirring of the mixed solution undergoing evaporation and crystallization.

[0072] Specifically, in step (2), the mixed solution in the evaporation crystallization is stirred at a speed of 400-1000 r / min. If the speed is too low, it will cause clumping during the crystallization process; if the speed is too high, it will affect the crystal growth.

[0073] According to some preferred embodiments of the present invention, the stirring speed of the mixed solution in the evaporation crystallization can be 400 r / min, 450 r / min, 500 r / min, 550 r / min, 600 r / min, 650 r / min, 700 r / min, 750 r / min, 800 r / min, 850 r / min, 900 r / min, 950 r / min, or 1000 r / min.

[0074] It should be noted that during the heating, evaporation, and crystallization process of the mixed solution containing peroxymetallic acid and ammonium peroxymetalate, ammonium ions alter the microstructure of the crystallized peroxymetallic acid powder, gradually transforming it from an elongated shape into a near-spherical porous structure, thus increasing the flowability of the resulting powder. Simultaneously, ammonium ions can assist in crystallization, addressing the issue of peroxytungstic acid's difficulty in crystallizing and precipitating in solution.

[0075] It should be noted that during the heating, evaporation, and crystallization process of the mixed solution, some of the peroxy metal acid and some of the peroxy metal ammonium decompose into metal acid (such as molybdic acid) and metal ammonium (such as ammonium molybdate) respectively due to temperature influence. The decomposition of peroxide ions during crystallization, as well as the release of oxygen and ammonia gas from the excess unreacted hydrogen peroxide and ammonia water in the solution during heating, can act as pore-forming agents during crystal formation, providing excellent dispersion for the wet materials obtained after evaporation and crystallization. Furthermore, compared to adding additional pore-forming agents to the reaction system, the oxygen and ammonia gas released during heating do not affect the purity of the final metal powder product.

[0076] It should be noted that, in order to further refine the wet material obtained after evaporation and crystallization during the drying process, the present invention uses flash drying to dry the wet material.

[0077] Specifically, in step (3), the present invention flash-dries the wet material obtained in step (2) at a temperature of 100-200℃. If the temperature is too low, the drying efficiency will be reduced, and the moisture in the wet material cannot be effectively removed, which will lead to powder agglomeration and clumping during the subsequent sintering process of the raw material powder. Increasing the temperature can accelerate the heat transfer rate and improve the drying efficiency, but excessively high temperatures will cause the material to agglomerate and clump.

[0078] According to some preferred embodiments of the present invention, in step (3), the temperature at which the wet material is flash-dried can be any value in the range of 100-200℃, such as 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, or 200℃.

[0079] Specifically, in step (3), the hot air velocity during the flash drying process is 0.5–5 m / s. If the hot air velocity is too low, the heat carried by the hot air will be insufficient, resulting in a slow drying process. This is also not conducive to the dispersion and breakage of particles, causing the material particles to accumulate and agglomerate, which can easily increase the particle size of the powder. On the other hand, if the hot air velocity is too high, the residence time of the material particles in the drying chamber will be too short, which can easily lead to insufficient drying of the product and affect the drying effect.

[0080] According to some preferred embodiments of the present invention, in step (3), the hot air velocity for flash drying of the wet material can be any value in the range of 0.5 to 5 m / s, such as 0.5 m / s, 1.0 m / s, 1.5 m / s, 2.0 m / s, 2.5 m / s, 3.0 m / s, 3.5 m / s, 4.0 m / s, 4.5 m / s, and 5 m / s.

[0081] Specifically, in step (3), the feeding rate during the flash drying process is 2-20 cm. 3 / s. If the feeding speed is too fast, it is easy to cause the material to agglomerate or clump together, resulting in insufficient drying and reducing the drying rate; while reducing the feeding speed can improve the drying effect, too low a speed will result in insufficient material in the drying chamber, affecting the overall drying rate.

[0082] According to some preferred embodiments of the present invention, in step (3), the feeding speed for flash drying of the wet material can be 2-20 cm. 3 Any value within the range of / s, such as 2cm 3 / s、4cm 3 / s、6cm 3 / s、8cm 3 / s, 10cm 3 / s、12cm 3 / s、14cm 3 / s、16cm 3 / s、18cm 3 / s、20cm 3 / s.

[0083] It should be noted that although the above-mentioned evaporation and crystallization causes some of the peroxy metal acids and ammonium peroxy metal ions in the peroxy system to decompose, most of the peroxy metal acids and ammonium peroxy metal ions do not decompose. The undecomposed peroxide ions will affect the effect of subsequent hydrogen reduction in the preparation of metal powder. The oxygen produced after the thermal decomposition of peroxide ions can easily cause instability in the hydrogen reduction process. Therefore, this invention requires calcining the dried raw material powder to completely convert it into oxides, so as to ensure the effect, stability and safety of subsequent hydrogen reduction.

[0084] Specifically, in step (4), the raw material powder obtained in step (3) is roasted to obtain metal oxide; the roasting atmosphere is oxygen or air.

[0085] More specifically, in order to convert the peroxy metal acid, peroxy metal ammonium, and the metal acid and metal ammonium obtained by heating in the raw material powder into metal oxides, and to maintain the morphology of the raw material powder and avoid the morphology of the powder being affected by excessively high calcination temperature, the present invention adjusts the calcination temperature to 300-500℃.

[0086] According to some preferred embodiments of the present invention, in step (4), the temperature for calcining the raw material powder can be any value in the range of 300-500℃, such as 300℃, 320℃, 350℃, 380℃, 400℃, 430℃, 450℃, 470℃, or 500℃.

[0087] More specifically, the calcination time is 1-5 hours. If the calcination time of the raw material powder is too short, the metal acid or ammonium metal oxide will not be completely converted into oxides; if the calcination time is too long, the powder will sinter and agglomerate.

[0088] According to some preferred embodiments of the present invention, in step (4), the roasting time of the raw material powder can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, or 5h.

[0089] It should be noted that, compared with traditional calcination (500-700℃), the present invention uses a lower temperature to calcine the raw material powder, which is beneficial to maintaining the morphology of the obtained powder and can avoid the influence of high temperature calcination on the powder morphology.

[0090] It should be noted that during the roasting process, the peroxymetallic acid and ammonium peroxymetalate in the raw material powder decompose upon heating, generating metal oxides and releasing oxygen and ammonia gases, which can further refine the particle size of the roasted powder.

[0091] It should be noted that, in order to control the particle size of the powder and maintain the original morphology of the powder while ensuring that the metal oxide is completely reduced, this invention adopts a two-stage reduction process and reasonably controls the reduction process conditions of each stage.

[0092] Specifically, in step (5), the present invention performs hydrogen reduction on the metal oxide to obtain the ultrafine metal powder. The specific steps include: first, the calcined metal oxide is subjected to a first stage of hydrogen reduction at a temperature of 300-400℃, and then a second stage of hydrogen reduction is performed at a temperature of 650-900℃.

[0093] It should be noted that, in order to maintain the morphology of the powder during the reduction process, the present invention adjusts the temperature of the first stage of reduction to 300-400℃. If the temperature is too high, the morphology will be damaged during the first stage of reduction; if the temperature is too low, the first stage of reduction will not be able to proceed effectively.

[0094] According to some preferred embodiments of the present invention, the temperature of the hydrogen reduction stage can be any value in the range of 300-400℃, such as 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃, and 400℃.

[0095] More specifically, the hydrogen flow rate for the hydrogen reduction stage is 0.5-3 m³ / h. 3 If the hydrogen flow rate is too high (e.g., / h), it may result in low hydrogen utilization and safety hazards; if the flow rate is too low, it may prevent the first stage of reduction from proceeding effectively, thus affecting the reduction efficiency.

[0096] According to some preferred embodiments of the present invention, the hydrogen flow rate during the hydrogen reduction stage can be 0.5-3 m³ / h. 3 Any value within the range of / h, such as 0.5m 3 / h, 1.0m 3 / h, 1.5m 3 / h, 2.0m 3 / h, 2.5m 3 / h, 3.0m 3 / h.

[0097] More specifically, the hydrogen reduction time is 2-5 hours. If the time is too long, it will lead to changes in the morphology of the powder and waste of hydrogen; if the time is too short, the powder will not be effectively reduced.

[0098] According to some preferred embodiments of the present invention, the hydrogen reduction time can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, or 5h.

[0099] It should be noted that, in order to further maintain the morphology of the powder during the reduction process, the temperature of the two-stage hydrogen reduction is adjusted to 650-900℃. If the temperature is too high, the powder morphology cannot be maintained; if the temperature is too low, the reduction efficiency will be low and the reduction effect will be incomplete.

[0100] According to some preferred embodiments of the present invention, the temperature of the two-stage hydrogen reduction can be any value in the range of 650-900℃, such as 650℃, 700℃, 750℃, 800℃, 850℃, or 900℃.

[0101] More specifically, the hydrogen flow rate for the two-stage hydrogen reduction is 5-40 m³ / h. 3 If the hydrogen flow rate is too high ( / h), it may lead to low hydrogen utilization and safety hazards; if the flow rate is too low, a stage of reduction may not be able to proceed effectively, affecting the reduction efficiency.

[0102] According to some preferred embodiments of the present invention, the hydrogen flow rate during the hydrogen reduction stage can be 5-40 m³ / h. 3 Any value within the range of / h, such as 5m 3 / h、8m 3 / h, 10m 3 / h、12m 3 / h, 15m 3 / h、17m 3 / h, 20m 3 / h、22m 3 / h, 25m 3 / h、28m 3 / h, 30m 3 / h、32m 3 / h, 35m 3 / h, 38m 3 / h, 40m 3 / h.

[0103] More specifically, the time for the two-stage hydrogen reduction is 4-8 hours. If the time is too long, it will lead to changes in the morphology of the powder and waste of hydrogen; if the time is too short, the powder will not be effectively reduced.

[0104] According to some preferred embodiments of the present invention, the time for the two-stage hydrogen reduction can be 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, or 8h.

[0105] It should be noted that, compared with existing technologies, this invention employs a lower reduction temperature and a longer reduction time during the reduction process. Performing one or two reductions at a lower temperature can preserve the morphology of the powder during reduction; however, low-temperature reduction can lead to incomplete reduction, thus requiring a longer reduction time to ensure the desired reduction effect. This approach ensures both the ultrafine particle size of the powder and allows for control over its morphology.

[0106] The present invention also provides an ultrafine metal powder, which is prepared by the method described above. The ultrafine metal powder is ultrafine tungsten powder, ultrafine molybdenum powder, or ultrafine tungsten-molybdenum alloy powder. The metal powder is nearly spherical or elongated. The particle size of the nearly spherical metal powder is <10 μm and the purity is >99.9%. The diameter of the elongated metal powder is <200 nm.

[0107] In this invention, a mixed solution containing peroxymetallic acid and ammonium peroxymetalate decomposes during heating, releasing oxygen and ammonia. The released gases act as pore-forming agents during crystal formation, effectively dispersing the wet materials obtained in each heating process. Furthermore, compared to adding additional pore-forming agents to the reaction system, the released oxygen and ammonia do not affect the purity of the final metal powder product.

[0108] The ammonium ions introduced into the mixed solution can assist the crystallization process and regulate the morphology of the resulting powder.

[0109] This invention uses flash drying to dry the wet material obtained from evaporation and crystallization, so that the resulting crystalline solid can be better dispersed by airflow to obtain a finer and more uniform powder.

[0110] This invention involves calcining the powder material obtained after flash drying to completely decompose any incompletely decomposed peroxide anions in the dried powder. The material is then converted into metal oxides at high temperature to ensure the effectiveness, stability, and safety of subsequent reduction. In addition, during the calcination process, the thermal decomposition of peroxide metal acids or ammonium peroxide metals releases oxygen and ammonia, which can further refine the powder particle size. Compared with traditional calcination, this invention uses a lower temperature for calcination, which helps maintain the morphology of the obtained powder and avoids the impact of high-temperature calcination on the powder morphology.

[0111] This invention employs a lower reduction temperature, which prevents damage to the powder morphology during the reduction process. At the same time, this invention adjusts the reduction process over a longer period of time to ensure the reduction effect and avoid the problem of incomplete reduction caused by low-temperature reduction. Therefore, this invention ensures both the ultrafine particle size of the powder and the control of the powder morphology while completely converting the metal oxide into metal powder.

[0112] This invention designs a process for preparing metal powders. The raw material powder is obtained by calcination reduction, direct evaporation and crystallization of solution, and drying. This eliminates the need for long-term ball milling of powders in traditional methods, simplifies the process, saves costs, and also allows for control of powder morphology.

[0113] The technical solution of the present invention will be further explained and illustrated below with specific embodiments and comparative examples.

[0114] Example 1

[0115] This embodiment uses tungsten trioxide and tungstic acid as raw materials to prepare ultrafine tungsten powder, including the following steps:

[0116] (1) Dissolve tungsten trioxide in ammonia water to form ammonium tungstate solution; then add tungstic acid and hydrogen peroxide. In the resulting mixed solution, the number of moles of ammonium peroxytungstate accounts for 5% of the total number of moles of tungstic acid and ammonium peroxytungstate, and the volume fraction of hydrogen peroxide is 3%.

[0117] (2) The mixed solution obtained in step (1) is evaporated and crystallized at a temperature of 90℃ and a rotation speed of 500r / min for 3h to obtain a solution containing crystalline wet material;

[0118] (3) The crystallized solution is subjected to solid-liquid separation to obtain the crystallized wet material. The wet material is then flash-dried at a temperature of 150℃, a hot air velocity of 1.5m / s, and a feeding rate of 5cm. 3 / s, to obtain ultrafine raw material powder containing peroxytungstic acid and ammonium peroxytungstate;

[0119] (4) The ultrafine raw material powder obtained in step (4) is calcined at 300°C for 2 hours to obtain tungsten trioxide powder;

[0120] (5) The tungsten trioxide powder is subjected to a hydrogen reduction process, with specific conditions including a hydrogen flow rate of 1 m³ / h. 3 / h, temperature 300℃, time 3h;

[0121] The powder after one stage of reduction is then subjected to a two-stage hydrogen reduction, with specific conditions including a hydrogen flow rate of 10 m³ / h. 3 At a temperature of 750℃ and a time of 8 hours, ultrafine tungsten powder 1 was obtained.

[0122] The ultrafine raw material powder obtained by flash drying in step (3) and the ultrafine tungsten powder 1 obtained by flash drying in step (5) of Example 1 were examined using scanning electron microscopy. The morphology images obtained are shown below. Figure 2 As shown in (a) and 2(b). From Figure 2It can be seen that the raw material powder obtained after flash evaporation has a near-spherical structure; after subsequent calcination and staged reduction, the morphology of the powder remains basically unchanged. Testing showed that the average particle size of ultrafine powder 1 is <10μm, and its purity is 99.95%.

[0123] Example 2

[0124] This embodiment uses ammonium metatungstate and tungstic acid as raw materials to prepare ultrafine tungsten powder, including the following steps:

[0125] (1) Dissolve tungstic acid in water and hydrogen peroxide to form ammonium peroxytungstate solution; then add ammonium metatungstate solution. In the resulting mixed solution, the molar number of ammonium peroxytungstate accounts for 10% of the total molar number of tungstic acid and ammonium peroxytungstate, and the volume fraction of hydrogen peroxide is 5%.

[0126] (2) The mixed solution obtained in step (1) is evaporated and crystallized at a temperature of 80℃ and a rotation speed of 800r / min for 5h to obtain a solution containing crystalline wet material;

[0127] (3) The crystallized solution is subjected to solid-liquid separation to obtain crystalline wet material. The wet material is then flash-dried at a temperature of 150℃, a hot air velocity of 1.5m / s, and a feeding rate of 5cm. 3 / s, to obtain ultrafine raw material powder containing peroxytungstic acid and ammonium peroxytungstate;

[0128] (4) The ultrafine raw material powder obtained in step (4) is calcined at 400℃ for 2.5h to obtain tungsten trioxide powder;

[0129] (5) The tungsten trioxide powder is reduced in one stage, under the following conditions: hydrogen flow rate of 1.5 m³ / h. 3 / h, temperature 300℃, time 3h;

[0130] The powder after the first stage of reduction is then subjected to a second stage of reduction, with specific conditions including a hydrogen flow rate of 15 m³ / h. 3 At a temperature of 800℃ and a time of 6 hours, ultrafine tungsten powder 2 was obtained.

[0131] Scanning electron microscopy (SEM) was used to examine the ultrafine raw material powder obtained after flash drying in step (3) and the ultrafine tungsten powder 2 obtained after flash drying in step (5) of Example 2. The results showed that the raw material powder obtained after flash drying had a near-spherical structure, and its morphology remained essentially unchanged after subsequent calcination and segmented reduction. The ultrafine powder 1 had an average particle size of <10 μm and a purity of 99.9%.

[0132] Example 3

[0133] This embodiment uses molybdenum trioxide and ammonium molybdate as raw materials to prepare ultrafine molybdenum powder, including the following steps:

[0134] (1) Dissolve molybdenum trioxide in hydrogen peroxide to form molybdenum peroxy acid solution; then add ammonium molybdate. In the resulting mixed solution, the number of moles of ammonium peroxytungstate accounts for 2% of the total number of moles of peroxytungstate and ammonium peroxytungstate, and the volume fraction of hydrogen peroxide is 10%.

[0135] (2) The mixed solution obtained in step (1) is evaporated and crystallized at a temperature of 95℃ and a rotation speed of 1000r / min for 3h to obtain a solution containing crystalline wet material;

[0136] (3) The crystallized solution is subjected to solid-liquid separation to obtain the crystallized wet material. The wet material is then subjected to flash drying at a temperature of 200℃, a hot air velocity of 3m / s, and a feeding rate of 4cm. 3 / s, to obtain ultrafine raw material powder containing peroxymolybdic acid and ammonium peroxymolybdate;

[0137] (4) The ultrafine raw material powder obtained in step (4) is calcined at 380°C for 1 hour to obtain molybdenum trioxide powder;

[0138] (5) The molybdenum trioxide powder was subjected to a single-stage reduction, with specific conditions including a hydrogen flow rate of 1 m³ / h. 3 / h, temperature 350℃, time 2.5h;

[0139] The powder after the first stage of reduction is then subjected to a second stage of reduction, with specific conditions including a hydrogen flow rate of 10 m³ / h. 3 At a temperature of 900℃ and a time of 7 hours, ultrafine molybdenum powder 3 was obtained.

[0140] The ultrafine raw material powder obtained after flash drying in step (3) and the ultrafine molybdenum powder 3 obtained after flash drying in step (5) of Example 3 were analyzed using scanning electron microscopy. The results are as follows: Figure 3 As shown in (a) and (b), the test results indicate that the raw material powder obtained after flash evaporation has a near-spherical structure, and its morphology remains essentially unchanged after subsequent calcination and staged reduction. The average particle size of the ultrafine molybdenum powder 3 is <10 μm, and its purity is 99.97%.

[0141] Example 4

[0142] This embodiment uses ammonium molybdate and molybdic acid as raw materials to prepare ultrafine molybdenum powder, including the following steps:

[0143] (1) Dissolve ammonium molybdate in water to form an ammonium molybdate solution; then add peroxymolybdic acid. In the resulting mixed solution, the molar number of ammonium peroxytungstate accounts for 20% of the total molar number of peroxytungstic acid and ammonium peroxytungstate, and the volume fraction of hydrogen peroxide is 12%.

[0144] (2) The mixed solution obtained in step (1) is evaporated and crystallized at a temperature of 92℃ and a rotation speed of 750r / min for 4h to obtain a solution containing crystalline wet material;

[0145] (3) The crystallized solution is subjected to solid-liquid separation to obtain the crystallized wet material. The wet material is then flash-dried at a temperature of 180℃, a hot air velocity of 3.5 m / s, and a feeding rate of 3.5 cm. 3 / s, to obtain ultrafine raw material powder containing peroxymolybdic acid and ammonium peroxymolybdate;

[0146] (4) The ultrafine raw material powder obtained in step (4) is calcined at 400℃ for 3 hours to obtain ultrafine molybdenum trioxide powder;

[0147] (5) The molybdenum trioxide powder was subjected to a single-stage reduction, with specific conditions including a hydrogen flow rate of 1.5 m³ / h. 3 / h, temperature 400℃, time 3.5h;

[0148] The powder after the first stage of reduction is then subjected to a second stage of reduction, with specific conditions including a hydrogen flow rate of 15 m³ / h. 3 At a temperature of 750℃ and a time of 7 hours, 4 ultrafine molybdenum powders were obtained.

[0149] Scanning electron microscopy (SEM) was used to examine the ultrafine raw material powder obtained after flash drying in step (3) and the ultrafine molybdenum powder 4 obtained after flash drying in step (5) of Example 4. The results showed that the raw material powder obtained after flash drying had a near-spherical structure, and its morphology remained essentially unchanged after subsequent calcination and segmented reduction. The ultrafine powder 1 had an average particle size of <10 μm and a purity of 99.91%.

[0150] Example 5

[0151] Using the same method as in Example 1, except that the tungsten trioxide in the mixed solution obtained in step (1) was replaced with tungsten trioxide and molybdenum trioxide in a mass ratio of 1:1, and finally ultrafine tungsten-molybdenum alloy powder 5 was obtained.

[0152] The ultrafine raw material powder obtained after flash drying in step (3) and the ultrafine molybdenum powder obtained after flash drying in step (5) of Example 5 were analyzed using scanning electron microscopy. The results are as follows: Figure 4 As shown in (a) and (b), the test results show that the raw material powder obtained after flash evaporation has a near-spherical structure, and the morphology of the powder remains basically unchanged after subsequent calcination and segmented reduction. The test results show that the average particle size of the ultrafine powder 5 is <10μm, the purity is 99.96%, and the tungsten and molybdenum elements in the ultrafine tungsten-molybdenum alloy powder 5 are uniformly mixed.

[0153] Example 6

[0154] Using the same method as in Example 1, except that the mixed solution prepared in step (1) of Example 6 does not contain ammonium ions, and finally ultrafine tungsten powder 6 is obtained.

[0155] The ultrafine tungsten powder 6 obtained in Example 6 was analyzed using a scanning electron microscope. The results are as follows: Figure 5 As shown in the figure, the ultrafine tungsten powder 6 has a long strip structure with a diameter of <200nm.

[0156] Comparative Example 1

[0157] Using the same method as in Example 3, except that in the mixed solution prepared in step (1) of Comparative Example 1, the proportion of ammonium peroxymolybdate is 30%, and the final product is ultrafine molybdenum powder 7.

[0158] The ultrafine tungsten powder 7 obtained in Comparative Example 1 was detected by scanning electron microscopy. The detection results showed that the ultrafine tungsten powder 7 has two structures: a strip-shaped structure and a polyhedral structure.

[0159] Comparative Example 2

[0160] Using the same method as in Example 1, except that Comparative Example 2 does not include the flash drying process in step (3), the final product is ultrafine tungsten powder 8 with a size of 20 μm.

[0161] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing ultrafine metal powder, characterized in that, The preparation method includes: (1) Prepare a mixed solution of peroxymetallic acid and ammonium peroxymetalate; (2) The mixed solution is evaporated and crystallized to obtain a wet material; (3) The wet material is flash-dried to obtain raw material powder; (4) The raw material powder is calcined to obtain metal oxides; (5) The metal oxide is reduced with hydrogen to obtain the ultrafine metal powder; The metal is at least one of tungsten and molybdenum.

2. The preparation method according to claim 1, characterized in that, In step (1), the preparation of the mixed solution specifically includes: adding hydrogen peroxide or hydrogen peroxide and ammonia to the metal raw material solution, controlling the molar number of ammonium peroxide in the mixed solution to be 0-20% of the total molar number of ammonium peroxide and ammonium peroxide, and the volume fraction of hydrogen peroxide to be 3-15%.

3. The preparation method according to claim 2, characterized in that, The metal raw material is at least one of tungsten-containing raw materials and molybdenum-containing raw materials; The tungsten-containing raw material is at least one of pure tungsten products, ammonium tungstates, tungsten oxides, tungstic acid, and peroxytungstic acid. The molybdenum-containing raw material is at least one of pure molybdenum products, ammonium molybdates, molybdenum oxides, molybdic acid, and peroxymolybdic acid.

4. The preparation method according to claim 1, characterized in that, In step (2), the evaporation crystallization temperature is 80-95℃ and the time is 3-8h.

5. The preparation method according to claim 1, characterized in that, The stirring speed during the evaporation and crystallization process is 400–1000 r / min.

6. The preparation method according to claim 1, characterized in that, In step (3), the temperature of the flash drying is 100-200℃.

7. The preparation method according to claim 6, characterized in that, The hot air velocity during the flash drying process is 0.5–5 m / s; And / or, the feeding rate during the flash drying process is 2–20 cm. 3 / s.

8. The preparation method according to claim 1, characterized in that, In step (4), the roasting temperature is 300-500℃ and the time is 1-5h.

9. The preparation method according to claim 1, characterized in that, In step (5), the hydrogen reduction includes primary hydrogen reduction and secondary hydrogen reduction; The temperature of the first hydrogen reduction is 300-400℃, and the time is 2-5 hours. The secondary hydrogen reduction is carried out at a temperature of 650-900℃ for 4-8 hours.

10. The preparation method according to claim 9, characterized in that, The hydrogen flow rate for the first hydrogen reduction is 0.5-3 m³ / h. 3 / h; the hydrogen flow rate for the secondary hydrogen reduction is 5-40m³ / h. 3 / h.

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