Method for preparing granularity-controllable molybdenum powder based on molybdenum nitride decomposition and molybdenum powder

Abstract

The invention discloses a preparation method for preparing granularity-controllable molybdenum powder based on molybdenum nitride decomposition and molybdenum powder.The preparation method comprises the following steps that firstly, molybdenum trioxide powder serves as a raw material, heat treatment is conducted on the molybdenum trioxide powder under the condition that mixed atmosphere is introduced, low-temperature reduction and nitridation are conducted on the molybdenum trioxide, and molybdenum nitride precursor powder is obtained; and 2, the molybdenum nitride precursor powder obtained in the step 1 is subjected to thermal decomposition treatment under different temperatures and different atmosphere conditions, and the molybdenum powder with the controllable particle size, the purity larger than 99.9% and uniform distribution is obtained. According to the method, hydrogen does not need to be adopted, a series of problems caused by hydrogen intervention are successfully avoided, meanwhile, the molybdenum powder is prepared based on molybdenum nitride decomposition, the molybdenum powder with different particle size specifications can be conveniently prepared by accurately regulating and controlling different decomposition temperatures by means of the characteristic that molybdenum nitride is poor in high-temperature stability, and the method is suitable for industrial production. Accurate controllability of the granularity of the molybdenum powder is achieved.

Description

Technical Field

[0001] This invention belongs to the field of molybdenum powder preparation technology, specifically relating to a method for preparing molybdenum powder with controllable particle size based on the decomposition of molybdenum nitride and the molybdenum powder itself. Background Technology

[0002] Currently, the main industrial method for preparing molybdenum powder is a two-step hydrogen reduction of molybdenum trioxide. This method first reduces molybdenum trioxide to molybdenum dioxide with hydrogen, and then further reduces the molybdenum dioxide to molybdenum powder. However, this method suffers from problems such as low hydrogen reduction efficiency, high cost, and large particle size of the produced molybdenum powder.

[0003] Molybdenum powder, as a raw material for preparing molybdenum and molybdenum alloys, has a crucial impact on the quality of various molybdenum products due to its performance indicators. Different application fields have different requirements for its particle size. Nano-molybdenum powder has very high sintering activity, which can significantly reduce sintering temperature and shorten sintering time, thereby avoiding grain coarsening and significantly improving the mechanical properties of molybdenum and molybdenum alloys. Meanwhile, 3D printing, thermal spraying, and other fields have a greater demand for large-particle molybdenum powder. To prepare molybdenum powder with different particle sizes, many researchers have made numerous improvements to the two-step hydrogen reduction process, such as adjusting the reaction temperature, hydrogen dew point, and material layer thickness, but the results have been less than ideal and mass production has been difficult.

[0004] In addition, some researchers have proposed using carbon instead of hydrogen as a reducing agent to prepare molybdenum powder. However, the amount of carbon added is difficult to control precisely; insufficient carbon will result in incomplete reduction, while excessive carbon will easily form molybdenum carbide, severely affecting the purity of the molybdenum powder. Using active metals such as zinc and magnesium as reducing agents to reduce molybdenum trioxide can also prepare nano-molybdenum powder, but problems such as low product purity, high production costs, and complex operations make it difficult to use for industrial production. Summary of the Invention

[0005] In view of the above-mentioned shortcomings and defects of the prior art, the purpose of this invention is to provide a method for preparing molybdenum powder with controllable particle size based on the decomposition of molybdenum nitride, thereby solving the problems of large particle size and high production cost of molybdenum powder prepared by the prior art.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for preparing molybdenum powder with controllable particle size based on molybdenum nitride decomposition, comprising the following steps: Step 1: Using molybdenum trioxide powder as raw material, heat treatment is carried out under mixed atmosphere conditions to reduce and nitride molybdenum trioxide at low temperature, thereby obtaining molybdenum nitride precursor powder.

[0007] Step 2: The molybdenum nitride precursor powder obtained in Step 1 is subjected to thermal decomposition treatment under different temperatures and atmospheres to obtain molybdenum powder with controllable particle size, purity greater than 99.9%, and uniform distribution.

[0008] By setting different decomposition temperatures, atmosphere types, and holding times, the decomposition and reduction of molybdenum nitride to metallic molybdenum can be controlled. During this process, nitrogen is gradually released and migrates, molybdenum atoms are redeposited and grow, ultimately yielding molybdenum powder with controllable particle size, purity greater than 99.9%, and uniform distribution.

[0009] The present invention also has the following technical features: The mixed atmosphere in step one consists of ammonia and an inert gas.

[0010] The inert gas includes nitrogen or argon, and the volume fraction of ammonia in the mixed gas is 70-90%. The total flow rate of the mixed gas is controlled at 50-500 mL / min, and the linear velocity of the gas in the reaction zone is maintained in the range of 0.1-1.5 cm / s.

[0011] In step one, heat treatment is carried out in a high-temperature furnace. The low-temperature reduction and nitriding conditions are: heat treatment is carried out in the temperature range of 500℃ to 800℃ for 2 to 6 hours.

[0012] In step two, the decomposition atmosphere during the thermal decomposition of the molybdenum nitride precursor powder is nitrogen, argon, hydrogen, or a vacuum environment. The total flow rate of the decomposition atmosphere is controlled at 50-800 mL / min, and the linear velocity of the gas in the reaction zone is maintained at 0.1-2.0 cm / s.

[0013] In step two, the decomposition temperature of the molybdenum nitride precursor powder during thermal decomposition is 800℃ to 1100℃, and the holding time is 2 to 6 hours.

[0014] The present invention also provides a molybdenum powder prepared by the above method.

[0015] Compared with the prior art, the beneficial technical effects of this invention are: (I) The method of this invention eliminates the need for hydrogen as a reducing atmosphere. Traditional molybdenum powder preparation processes often rely on high-temperature hydrogen reduction. However, hydrogen is not only expensive but also poses extremely high safety risks (flammable and explosive) during storage, transportation, and use. Furthermore, it requires stringent standards for gas purity and pipeline sealing, significantly increasing equipment costs and operational risks. In addition, the hydrogen reduction process is often accompanied by a significant grain coarsening effect (affected by the CVT mechanism), leading to an increased particle size distribution in the resulting molybdenum powder that deviates from the controllable range. This invention completely avoids these problems by using ammonia instead of hydrogen as a reducing agent, reducing production costs and improving process safety.

[0016] (II) The method of this invention achieves morphological inheritance, avoiding abnormal particle growth. This invention first utilizes ammonia to perform low-temperature reduction and nitridation of molybdenum trioxide. The resulting molybdenum nitride precursor can well inherit the morphological characteristics of the original molybdenum oxide (such as spherical, flake-like, or fibrous), maintaining a stable particle size distribution. During subsequent decomposition, this morphological inheritance is continued, effectively avoiding abnormal particle growth or agglomeration, resulting in a more uniform and controllable particle size for the final molybdenum powder.

[0017] (III) The ammonia gas in the method of this invention can be recycled, further reducing production costs. In this invention, the ammonia gas used in the first step can be directly recycled from the ammonia gas produced by the decomposition of ammonium molybdate. This in-situ atmosphere supply method reduces the demand for purchased gases, lowers process costs, and has the advantages of being green, environmentally friendly, and sustainable.

[0018] (IV) The method of this invention is based on the decomposition of molybdenum nitride to prepare molybdenum powder with adjustable particle size. Molybdenum nitride has poor high-temperature stability and is easily decomposed into molybdenum powder under different atmospheres and temperatures. This invention, by controlling the decomposition atmosphere (nitrogen, argon, or vacuum) and decomposition temperature (800-1100℃), can precisely control the nitrogen release rate and the molybdenum atom deposition process, thereby obtaining molybdenum powder with a particle size range covering nanometers to micrometers, uniform distribution, and a purity greater than 99.9%. Compared with traditional processes, this invention can simultaneously achieve high purity and controllable particle size, meeting different application requirements.

[0019] (V) The method of this invention has a simple process flow, strong controllability, and is suitable for large-scale production. This invention adopts a two-step process with clearly defined parameter ranges, a wide temperature range, flexible atmosphere control, simple operation, and low equipment requirements. This process is not only easy to implement continuous and automated control, but also has good repeatability and scalability, making it suitable for large-scale industrial application. Attached Figure Description

[0020] Figure 1 This is a scanning electron microscope image of the molybdenum powder prepared in Example 2 of the present invention.

[0021] Figure 2 This is a scanning electron microscope image of the molybdenum powder prepared in Example 3 of the present invention.

[0022] Figure 3 This is a scanning electron microscope image of the molybdenum powder prepared in Example 4 of the present invention.

[0023] Figure 4 This is a scanning electron microscope image of the molybdenum powder prepared in Example 5 of the present invention.

[0024] Figure 5 This is a scanning electron microscope image of the molybdenum powder prepared in Example 6 of the present invention.

[0025] Figure 6 This is a scanning electron microscope image of the molybdenum powder prepared in Comparative Example 1 of the present invention.

[0026] The specific content of the present invention will be further explained in detail below with reference to the embodiments. Detailed Implementation

[0027] It should be noted that, unless otherwise specified, all raw materials used in this invention are those known in the prior art.

[0028] The molybdenum trioxide used in this invention can be a commercially available product or obtained by the pyrolysis of ammonium salts; the inert gas is high-purity nitrogen or high-purity argon; the ammonia is analytical grade or higher purity (preferably ≥99.9%). The process equipment can be a quartz or high-temperature alloy tube furnace, pusher furnace, or rotary furnace, equipped with a mass flow controller.

[0029] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0030] The technical concept of this application is as follows: Using molybdenum trioxide as the starting material, the invention first performs low-temperature reduction and nitridation in an ammonia-inert gas mixed atmosphere to obtain a molybdenum nitride precursor with heritable morphology; then, under inert atmosphere / vacuum environment and other conditions, denitrification is carried out at different temperature zones to deposit high-purity molybdenum powder. Through the coordinated control of atmosphere composition, flow rate, temperature, and time, precise controllability of particle size (nanometer to micrometer) and purity (O ≤ 0.1 wt.%, N ≤ 50 ppm) is achieved.

[0031] In this application, the requirements for the molybdenum trioxide used are as follows: the morphology can be near-spherical / plate-like / fibrous / hollow structure, etc., and the particle size range covers nanometer (10-200nm), submicron (0.2-1μm) to micrometer (1-10μm). Preferably, the total amount of impurity metals is <0.1wt.%; such as ammonium salts (e.g., (NH4)6Mo7O 24 It is prepared by pyrolysis of 4H2O and needs to be pre-baked at 300-500℃ in air or inert atmosphere for 2-4 hours to stabilize batch-to-batch differences.

[0032] In this application, the gas path requirements are as follows: the volume fraction of ammonia in the mixed gas is 70-90%; the decomposition section atmosphere can be N2, Ar, or vacuum (10-10). 3 Pa). All gases are purified by removing water and oxygen, and the total flow rate and linear velocity are controlled by a mass flow controller.

[0033] The process steps and key parameter windows for the low-temperature reduction and nitriding stages in this application are as follows: Loading: Molybdenum trioxide powder is evenly spread on a high-temperature ammonia-resistant boat (alumina or boron nitride material), with a preferred layer thickness of ≤10mm; the loading amount is matched with the gas linear velocity to avoid restricted internal diffusion.

[0034] Heating and Atmosphere: In a mixture of 70-90% ammonia and an inert gas (N2 or Ar), program the temperature to 500-800℃ at a rate of 3-10℃ / min; hold at the set temperature for 2-6 hours. Total flow rate: 50-500 mL / min; linear velocity: 0.1-1.5 cm / s. Too low a linear velocity can lead to localized ammonia deficiency / byproduct accumulation, resulting in incomplete reduction; too high a linear velocity may form a "shell effect," affecting the uniformity of nitrogen diffusion.

[0035] Key Mechanism: Molybdenum trioxide undergoes reduction and nitridation with ammonia to form molybdenum nitride. The resulting molybdenum nitride precursor retains the original morphology of molybdenum trioxide well, thus effectively avoiding abnormal particle growth and agglomeration.

[0036] The process steps and key parameter windows of the breakdown section in this application: Atmosphere selection: The decomposition atmosphere can be nitrogen, argon, or vacuum. Total flow rate: 50-800 mL / min; linear velocity: 0.1-2.0 cm / s; under vacuum conditions, the pumping speed is used as the equivalent "displacement rate" as the control variable.

[0037] Temperature-time: Increase temperature by 3-8℃ / min to 800-1100℃, and hold for 2-6 hours.

[0038] 800-900℃: Denitrification rate is relatively slow, but ultrafine nanoscale (D) particles are easily obtained. 50 Highly active molybdenum powder (80-300nm).

[0039] 900-1000℃: Particle size in the submicron range (D 50 The particle size is 0.3-0.6 μm, with a narrow particle size distribution and regular morphology.

[0040] 1000-1100℃: Promotes grain growth and defect annealing, yielding micron-sized molybdenum powder (D). 50 (with a thickness of 1-3μm), suitable for thermal spraying / additive manufacturing needs.

[0041] Cooling and Collection: After cooling to room temperature in the furnace under inert protection or vacuum conditions, remove from the furnace. If necessary, loosen with a trace amount of anhydrous ethanol by ultrasonication, and dry under low temperature and vacuum for later use.

[0042] Impurity control: O and N residues can be reduced synergistically by increasing the decomposition stage linear velocity and selecting vacuum. Product purity ≥99.9 wt.%, O ≤0.10 wt.%, N ≤50 ppm; Metallic impurities (Fe, Ni, Cu, etc.) are controlled by raw materials, equipment and gas source, and are generally ≤100 ppm (single item).

[0043] Example 1: A method for preparing molybdenum powder with controllable particle size based on molybdenum nitride decomposition includes the following steps: Step 1: Using molybdenum trioxide powder as raw material, heat treatment is carried out in a high-temperature furnace at a set temperature under a mixed atmosphere of ammonia and inert gas to perform low-temperature reduction and nitriding of molybdenum trioxide, thereby obtaining molybdenum nitride precursor powder.

[0044] Step 2: The molybdenum nitride precursor powder obtained in Step 1 is subjected to thermal decomposition treatment in a high-temperature furnace under different temperatures and atmospheres to obtain molybdenum powder with controllable particle size, purity greater than 99.9%, and uniform distribution.

[0045] By setting different decomposition temperatures, atmosphere types, and holding times, the decomposition of molybdenum nitride into molybdenum powder can be controlled. During this process, nitrogen is gradually released and migrates, molybdenum atoms are redeposited and grow, ultimately yielding molybdenum powder with controllable particle size, purity greater than 99.9%, and uniform distribution.

[0046] The morphology of the molybdenum trioxide raw material includes various forms such as (near) spherical, flake, and fibrous, with particle size ranging from micrometer to submicrometer to nanometer. Molybdenum trioxide with different morphologies and particle sizes can be selected according to different application requirements and obtained by controlling the precursor preparation process (spray drying, sol-gel, vapor deposition, etc.) to achieve precise adjustment of the final molybdenum powder morphology and particle size distribution.

[0047] The mixed atmosphere in step one consists of ammonia and an inert gas.

[0048] The inert gas includes nitrogen or argon, and the volume fraction of ammonia in the mixed gas is 70-90%.

[0049] The total flow rate of the mixed gas is controlled at 50-500 mL / min, and the linear velocity is adjusted within the range of 0.1-1.5 cm / s according to the furnace tube diameter and charge amount to ensure sufficient gas renewal rate and diffusion capacity in the reaction zone. This avoids incomplete reduction or particle agglomeration due to local ammonia deficiency or accumulation of byproducts (such as water vapor and nitrogen oxides). Excessive flow rate can cause the precursor particles to react too quickly on the surface, resulting in a shell effect, while excessively low flow rate may cause uneven nitriding or residual oxides. Therefore, optimization within the above range is necessary.

[0050] In step one, heat treatment is carried out in a high-temperature furnace.

[0051] The low-temperature reduction and nitriding conditions are as follows: heat treatment is carried out in the temperature range of 500℃ to 800℃ for 2 to 6 hours.

[0052] In step two, the decomposition atmosphere during the thermal decomposition of the molybdenum nitride precursor powder is nitrogen, argon, or a vacuum environment.

[0053] The total flow rate of the decomposition atmosphere is controlled at 50-800 mL / min, and the linear velocity of the gas in the reaction zone is maintained at 0.1-2.0 cm / s.

[0054] The specific atmosphere can be adjusted according to the target particle size, reduction rate, and product purity requirements. In particular, a vacuum environment can significantly improve the driving force of the decomposition reaction and the denitrification efficiency.

[0055] Appropriate flow rate and velocity can effectively remove nitrogen and byproducts released during decomposition, avoiding excessively high local nitrogen partial pressure that inhibits decomposition or impurity retention that causes particle agglomeration and surface contamination. Excessive flow rate may cause powder to fly away or uneven reaction, while excessively low flow rate leads to incomplete reduction. Therefore, it is necessary to optimize and control the flow rate within the above range to achieve the goal of uniform molybdenum powder particle size distribution, stable specific surface area, and purity exceeding 99.9%.

[0056] In step two, the decomposition temperature of the molybdenum nitride precursor powder during thermal decomposition is 800℃ to 1100℃, and the holding time is 2 to 6 hours.

[0057] At lower decomposition temperatures, ultrafine nanoscale molybdenum powder (particle size less than 200 nm) can be obtained, while higher decomposition temperatures promote grain growth and increased crystallinity, resulting in micron-sized molybdenum powder with a narrower particle size distribution and regular morphology. The nitrogen released under these conditions is removed through an atmosphere or vacuum environment, and molybdenum atoms are deposited into high-purity molybdenum powder. The final product purity can reach over 99.9%, with an oxygen content of less than 0.1% and a nitrogen content of less than 50 ppm.

[0058] A molybdenum powder is prepared by the above method.

[0059] This method first utilizes ammonia gas to reduce and nitride molybdenum trioxide at low temperatures, successfully preparing molybdenum nitride. Subsequently, taking full advantage of the poor stability of molybdenum nitride at high temperatures, it is decomposed under different temperature conditions to precisely obtain molybdenum powder with effectively controllable particle size and extremely high purity.

[0060] Example 2: The raw material used in this embodiment is near-spherical molybdenum trioxide powder, whose D 50The powder is approximately 0.6 μm in size, with a total mass fraction of impurity metal elements of approximately 0.06 wt.%. This powder is uniformly spread in a calcination boat made of ammonia-resistant material and placed in a tubular high-temperature furnace. A mixed atmosphere of ammonia and argon, with a volume ratio of 80:20, is introduced. The total flow rate of the mixed gas is set to 200 mL / min using a mass flow controller, and the linear velocity of the gas in the reaction zone is maintained at 0.6 cm / s. The temperature is increased to 700 °C at a rate of 5 °C / min and held at this temperature for 4 hours to complete low-temperature reduction and nitriding. Subsequently, the decomposition stage begins. Under a vacuum degree not exceeding 100 Pa, the temperature is increased to 880 °C at a rate of 5 °C / min and held for 3 hours. After cooling to below 150 °C, samples are taken from the furnace.

[0061] X-ray diffraction analysis of the obtained powder revealed a molybdenum phase, with no nitride diffraction peaks detected. Oxygen and nitrogen analysis showed an oxygen content of 0.08 wt.% and a nitrogen content of 28 ppm. Laser particle size distribution showed D... 50 Approximately 0.12 μm, D 90 Approximately 0.28 μm. Specific surface area is 4.8 m² / g. Scanning electron microscopy (SEM) Figure 1 Observations show that the particles are evenly dispersed with slight agglomeration. The loose density is approximately 0.62 g / cm³.

[0062] Example 3: The raw material used in this embodiment is flake-shaped molybdenum trioxide powder, whose D 50 The powder is approximately 1.2 μm in size, with a total mass fraction of impurity metal elements of approximately 0.04 wt.%. This powder was uniformly spread in an ammonia-resistant sintering boat and placed in a tubular high-temperature furnace. A mixed atmosphere of ammonia and argon was introduced, with a volume ratio of ammonia to argon of 70:30. The total flow rate of the mixed gas was set to 150 mL / min using a mass flow controller, and the linear velocity of the gas in the reaction zone was maintained at 0.4 cm / s. The temperature was increased to 650 °C at a rate of 5 °C / min and held at this temperature for 3 hours to complete low-temperature reduction and nitriding. Subsequently, the decomposition stage was carried out under a high-purity argon atmosphere, with a total flow rate of 300 mL / min, a linear velocity of 1.2 cm / s, and the temperature was increased to 960 °C at a rate of 5 °C / min and held for 4 hours. After cooling to below 150 °C, the powder was removed from the furnace and samples were taken.

[0063] X-ray diffraction analysis of the obtained powder showed it to be a metallic molybdenum phase, with no nitride diffraction peaks detected. Oxygen and nitrogen analysis results showed an oxygen content of 0.09 wt.% and a nitrogen content of 36 ppm. Laser particle size distribution showed D... 50 Approximately 0.45 μm, D 90 Approximately 0.92 μm. Specific surface area is 2.6 m². 2 / g, loose bulk density is 0.85g / cm³ 3( Figure 2 This powder exhibits excellent sintering properties and is suitable for high-density sintering and powder metallurgy applications.

[0064] Example 4: The raw material used in this embodiment is flake-shaped molybdenum trioxide powder, whose D 50 The powder is approximately 2.5 μm in size, with a total mass fraction of impurity metal elements of approximately 0.02 wt.%. This powder was uniformly spread in an ammonia-resistant sintering boat and placed in a tubular high-temperature furnace. A mixed atmosphere of ammonia and argon was introduced, with a volume ratio of ammonia to argon of 90:10. The total flow rate of the mixed gas was set to 300 mL / min using a mass flow controller, and the linear velocity of the gas in the reaction zone was maintained at 1.5 cm / s. The temperature was increased to 750 °C at a rate of 5 °C / min and held at this temperature for 6 h to complete low-temperature reduction and nitriding. Subsequently, the decomposition stage was carried out under a high-purity argon atmosphere, with a total flow rate of 500 mL / min, a linear velocity of 1.8 cm / s, and the temperature was increased to 1080 °C at a rate of 5 °C / min and held for 5 h. After cooling to below 150 °C, samples were taken from the furnace.

[0065] X-ray diffraction analysis of the obtained powder revealed a molybdenum phase, with no nitride diffraction peaks detected. Oxygen and nitrogen analysis showed an oxygen content of 0.07 wt.% and a nitrogen content of 42 ppm. Laser particle size distribution showed D... 50 Approximately 1.8 μm, D 90 Approximately 3.2 μm ( Figure 3 The specific surface area is 1.1 m² / g, and the bulk density is 1.12 g / cm³. This powder has good flowability and is suitable for thermal spraying and metal additive manufacturing.

[0066] Example 5: The raw material used in this embodiment is hollow molybdenum trioxide particles obtained by spray drying, whose D 50 The powder has a particle size of approximately 0.9 μm and a total mass fraction of impurity metal elements of approximately 0.01 wt.%. This powder was uniformly spread in an ammonia-resistant sintering boat and placed in a tubular high-temperature furnace. A mixed atmosphere of ammonia and argon was introduced, with a volume ratio of ammonia to argon of 80:20. The total gas flow rate was set to 200 mL / min using a mass flow controller, and the linear velocity of the gas in the reaction zone was maintained at 0.6 cm / s. The temperature was increased to 700 °C at a rate of 5 °C / min and held at this temperature for 4 h to complete low-temperature reduction and nitriding. Subsequently, the decomposition stage was carried out under a high-purity argon atmosphere with a total flow rate of 400 mL / min and a linear velocity of 1.6 cm / s. The temperature was increased to 900 °C at a rate of 5 °C / min and held for 2.5 h. During the decomposition reaction, nitrogen atoms were gradually removed, and molybdenum atoms were deposited to form molybdenum powder. The sample was removed after cooling to below 150 °C.

[0067] X-ray diffraction analysis of the obtained powder showed it to be a metallic molybdenum phase, with no nitride diffraction peaks detected. Oxygen and nitrogen analysis results showed an oxygen content of 0.05 wt.% and a nitrogen content of 18 ppm. Laser particle size distribution showed D... 50 Approximately 0.22 μm, D 90 Approximately 0.40 μm. Specific surface area is 5.6 m². 2 / g, loose bulk density is 0.58g / cm³ 3 Scanning electron microscopy observation ( Figure 4 This indicates that the particles are fine and uniformly distributed, with high surface cleanliness. The powder exhibits high activity, making it suitable for achieving dense sintering at lower temperatures or for the preparation of high-performance molybdenum-based alloys.

[0068] Example 6: Ammonium heptamolybdate tetrahydrate [(NH4)6Mo7O 24 [·4H2O] was heated to 450℃ in air and held for 3 hours to pyrolyze and generate molybdenum trioxide powder. During the nitriding stage, ammonia gas generated from the pyrolysis of ammonium salts was used to form a closed-loop circulating mixture with an inert gas. The ammonia gas integral was approximately 75%, the total flow rate was 250 mL / min, and the linear velocity was 0.8 cm / s. The temperature was programmed to rise to 680℃ and held for 4 hours to obtain the molybdenum nitride precursor. In the decomposition stage, the temperature was first raised to 900℃ under a vacuum of 200 Pa and held for 2 hours to promote denitrification and the removal of volatile impurities. Then, high-purity argon gas was switched at a flow rate of 300 mL / min and held for another 1 hour to stabilize lattice defects. The sample was then cooled and taken.

[0069] The resulting molybdenum powder had an oxygen content of 0.08 wt.% and a nitrogen content of 25 ppm; D 50 Its thickness is 0.30 μm, and its specific surface area is 3.8 m². 2 / g, loose bulk density is 0.74g / cm³ 3 ( Figure 5 According to cumulative flow meter statistics, the ammonia consumption of this solution is reduced by approximately 40% compared to the conventional continuous ammonia supply method.

[0070] Comparative Example 1 (Two-step hydrogen reduction of molybdenum trioxide): Molybdenum trioxide was placed in a high-purity hydrogen atmosphere at a flow rate of 300 mL / min. In the first stage, the temperature was kept constant at 600℃ for 3 hours to reduce molybdenum trioxide to molybdenum dioxide. In the second stage, the temperature was kept constant at 1050℃ for 4 hours to reduce molybdenum dioxide to molybdenum.

[0071] Test results show that the particles grew significantly, D 50 Between 3.4 μm and 5.7 μm, with a wide particle size distribution ( Figure 6The oxygen content is 0.12-0.18 wt.%, and the nitrogen content is less than 10 ppm. The powder surface activity is low, and the sintering performance is inferior to that of Examples 1 and 2 of this invention. The amount of hydrogen used is large, and the cost and safety protection investment are significantly higher than those of this invention.

[0072] Comparative Example 2 (Carbothermic Reduction): Molybdenum trioxide and carbon black were mixed uniformly in a stoichiometric ratio and then subjected to carbothermic reduction at 1000℃ for 6 hours in a high-purity argon atmosphere. The resulting powder easily produces molybdenum carbide or residual carbon, making it difficult to achieve a product purity of 99.9 wt.%, requiring further decarburization treatment. Simultaneously, it is difficult to simultaneously achieve optimal particle size and phase purity, making process scale-up complex.

[0073] Compared with the comparative example, this invention achieves the preparation of high-purity molybdenum powder with controllable particle size through "morphologically inherited nitriding precursor → controllable decomposition and denitrification": (i) The nitriding stage is carried out in the low temperature range of 500-800℃ to avoid high temperature coarsening and retain the original morphology and particle size.

[0074] (ii) The decomposition section determines the final particle size through coordinated control of atmosphere composition, flow rate, temperature and time.

[0075] (iii) Using a closed-loop / partially recycled ammonia source (such as from ammonium salt pyrolysis) can significantly reduce operating costs.

[0076] (iv) The product purity is stable at ≥99.9 wt.%, O≤0.10 wt.%, N≤50 ppm, covering the application spectrum from nano to micro (highly active sintered powder, powder metallurgy powder, larger particle powder for spraying / additive manufacturing, etc.).

[0077] This invention discloses a novel method for synthesizing high-purity molybdenum powder with controllable particle size. Compared to other methods, it offers the following advantages: ① It eliminates the need for hydrogen, successfully avoiding a series of thorny problems caused by hydrogen's introduction. Hydrogen is expensive, extremely inconvenient to store and transport, and is flammable and explosive. Furthermore, its CVT mechanism can lead to increased molybdenum powder particle size. ② Simultaneously, this invention uses low-temperature ammonia reduction and molybdenum trioxide nitride to prepare molybdenum nitride. This process exhibits morphological inheritance, resulting in molybdenum nitride with the same morphology as molybdenum oxide, effectively preventing abnormal growth. The ammonia reducing agent can directly utilize the ammonia produced by the decomposition of ammonium molybdate, achieving recycling and significantly reducing production costs. ③ In addition, based on the decomposition of molybdenum nitride to prepare molybdenum powder, and taking advantage of the poor high-temperature stability of molybdenum nitride, different particle size specifications can be conveniently prepared by precisely controlling different decomposition temperatures, achieving precise control over the particle size of the molybdenum powder.

[0078] The entire invention process is simple and clear, the process is easy to control, and it has excellent adaptability to large-scale industrial production. It has undoubtedly opened up a new technological path with great application value and development potential for the field of molybdenum powder preparation.

[0079] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions conceived by those skilled in the art within the scope of the technology disclosed in the present invention without creative effort are covered within the scope of protection of the present invention.

Claims

1. A method for preparing molybdenum powder with controllable particle size based on the decomposition of molybdenum nitride, characterized in that, Includes the following steps: Step 1: Using molybdenum trioxide powder as raw material, heat treatment is carried out under mixed atmosphere conditions to reduce and nitrid molybdenum trioxide at low temperature, thereby obtaining molybdenum nitride precursor powder. Step 2: The molybdenum nitride precursor powder obtained in Step 1 is subjected to thermal decomposition treatment under different temperatures and atmospheres to obtain molybdenum powder with controllable particle size, purity greater than 99.9%, and uniform distribution.

2. The preparation method for preparing molybdenum powder with controllable particle size based on the decomposition of molybdenum nitride as described in claim 1, characterized in that, The mixed atmosphere in step one consists of ammonia and an inert gas; The inert gas includes nitrogen or argon, the volume fraction of ammonia in the mixed gas is 70-90%, the total flow rate of the mixed gas is controlled at 50-500 mL / min, and the linear velocity of the gas in the reaction zone is maintained in the range of 0.1-1.5 cm / s.

3. The preparation method for preparing molybdenum powder with controllable particle size based on the decomposition of molybdenum nitride as described in claim 1, characterized in that, In step one, heat treatment is carried out in a high-temperature furnace; The low-temperature reduction and nitriding conditions are as follows: heat treatment is carried out in the temperature range of 500℃ to 800℃ for 2 to 6 hours.

4. The preparation method for preparing molybdenum powder with controllable particle size based on the decomposition of molybdenum nitride as described in claim 2, characterized in that, In step two, the decomposition atmosphere during the thermal decomposition of the molybdenum nitride precursor powder is nitrogen, argon, hydrogen, or a vacuum environment. The total flow rate of the decomposition atmosphere is controlled at 50-800 mL / min, and the linear velocity of the gas in the reaction zone is maintained at 0.1-2.0 cm / s.

5. The preparation method for preparing molybdenum powder with controllable particle size based on the decomposition of molybdenum nitride as described in claim 2, characterized in that, In step two, the decomposition temperature of the molybdenum nitride precursor powder during thermal decomposition is 800℃ to 1100℃, and the holding time is 2 to 6 hours.

6. A molybdenum powder, characterized in that, It is prepared by the method of any one of claims 1-5.

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