Preparation method of small-particle-size high-apparent-density molybdenum powder based on low-potassium ammonium molybdate

Abstract

The invention discloses a preparation method of small-particle-size high-apparent-density molybdenum powder based on low-potassium ammonium molybdate, which comprises the following steps: taking ammonium molybdate with the potassium content of less than or equal to 0.005% as a raw material, and roasting to obtain molybdenum trioxide; the molybdenum trioxide is subjected to first-stage reduction in a hydrogen atmosphere with the dew point larger than or equal to 10 DEG C, and flaky caked molybdenum dioxide is obtained; and after the flaky caked molybdenum dioxide is ground and crushed, second-stage reduction is conducted in the hydrogen atmosphere with the dew point smaller than or equal to-40 DEG C, and the molybdenum powder is obtained. The technology is stable, the yield is high, and the obtained molybdenum powder has the small Fisher particle size and the large apparent density at the same time and is excellent in pressing performance and sintering performance.

Description

Technical Field

[0001] This invention relates to the field of metal powder metallurgy technology, and in particular to a method for preparing small-particle-size, high-bulk-density molybdenum powder based on low-potassium ammonium molybdate. Background Technology

[0002] Molybdenum powder is the direct raw material for preparing various metallic molybdenum products. The particle size and loose packing density of molybdenum powder largely determine its comprehensive performance and subsequent applications. In the process of producing molybdenum powder by the two-stage hydrogen reduction method, the main factors affecting particle size are: characteristics of raw material ammonium molybdate, hydrogen dew point, hydrogen flow rate, boat loading, reduction time, and reduction temperature; the main factors affecting loose packing density include: molybdenum powder particle shape, particle size distribution, surface condition, and process conditions. The literature "Regression Equation for Quality Control of Molybdenum Powder" (China Molybdenum Industry 1993, 47(4)) reveals that under similar production processes, the particle size and loose packing density of molybdenum powder are positively correlated, and summarizes the regression equation "loose packing density = 0.404 + 0.215 × particle size".

[0003] Low-potassium ammonium molybdate (K≤0.005%) is a common raw material in the industrial production of molybdenum powder. The literature "Study on the Influence of K Content in MoO3 on the Reduction of Molybdenum Powder" (Vol. 36, No. 4, Nonferrous Metallurgical Design and Research) reveals that the particle size and yield (160-mesh sieve pass rate) of molybdenum powder generally decrease with decreasing potassium content in molybdenum trioxide (obtained from ammonium molybdate through roasting). However, there is no regular correlation between the bulk density and the potassium content in molybdenum trioxide. When the potassium content of molybdenum trioxide is below 0.008% (equivalent to 0.007% potassium content in ammonium molybdate), the particle size of molybdenum powder can be reduced to below 2.80 μm, and the yield can be reduced to as low as approximately 20%. Production practice shows that when the potassium ammonium molybdate content is ≤0.005%, using the conventional "calcination + dry hydrogen two-stage reduction" process, the molybdenum dioxide produced by the first-stage reduction has a low bulk density, which easily leads to overfilling or inability to fill the boat with the normal amount. The molybdenum powder produced by the second-stage reduction often has small Fisher particle size (≤2.80μm) and low bulk density (≤0.95 g / cm³). 3 Problems include severe agglomeration, "lightweight" material that is difficult to sieve, low yield (the sieve failure rate can be as low as 50% or less in the 200-mesh sieve), overfilling or inability to fill the mold during the pressing process, and poor hot working performance of the sintered molybdenum metal.

[0004] The literature "Research on Cost Reduction and Efficiency Improvement Process of Low-Potassium Large-Particle Molybdenum Powder" (China Molybdenum Industry 2014, 38(3)) addresses the problems of high reduction temperature leading to severe agglomeration, low yield, and high cost in the production of low-potassium molybdenum powder using low-potassium molybdenum trioxide. The first-stage reduction uses dry hydrogen at a low temperature of 390–510℃ and a dew point of -40℃, while the second-stage reduction uses wet hydrogen at a high temperature of 930–980℃ and a dew point of +130℃, resulting in a particle size of 6.0 μm and a loose packing density of 1.7 g / cm³. 3 The yield of molybdenum powder (the percentage passing through a 250-mesh sieve) reached 75%, leading to the conclusion that "using low-potassium, large-particle molybdenum trioxide is a shortcut to preparing low-potassium, large-particle molybdenum powder." However, this method still suffers from severe molybdenum powder agglomeration, requiring air jet milling, and the yield did not reach an ideal level.

[0005] The literature "Application of Low-Potassium Ammonium Tetramolybdate in Molybdenum Bar Production" (China Molybdenum Industry, 2002, 26(6)) studied the effect of potassium content in ammonium tetramolybdate on the properties of molybdenum powder and molybdenum bars. The results showed that low-potassium ammonium tetramolybdate was more easily reduced than high-potassium ammonium tetramolybdate. Under suitable process conditions, the manufacture of molybdenum bars for wire drawing using low-potassium ammonium tetramolybdate has the advantages of good product quality and low production cost. However, this study did not provide specific methods and process parameters.

[0006] The invention patent "A Method for Manufacturing Low-Potassium Large-Particle-Size Molybdenum Powder" (Application Publication No. CN 114833349 A) ​​discloses a method for manufacturing low-potassium large-particle-size molybdenum powder using low-potassium molybdenum trioxide. This method uses low-potassium molybdenum trioxide (K≤30ppm) as raw material, employs a first-stage reduction temperature of 400–700℃ and a second-stage reduction temperature of 850–1000℃, and adds a volatile substance to the molybdenum dioxide to achieve a final K content of less than 10ppm in the molybdenum powder. The particle size of the molybdenum powder can be controlled between 2.0 and 7.0 μm, resulting in uniform dispersion of the molybdenum powder particles, a sieve pass rate of over 90%, and a high yield. This method adds two steps to the conventional two-stage reduction process: "adding a volatile substance to molybdenum dioxide" and "drying the material after adding the substance." This method may be suitable for producing low-potassium molybdenum powder for applications such as target materials.

[0007] In the two-stage hydrogen reduction process for producing molybdenum powder, process parameters such as hydrogen flow rate, boat loading amount, boat pushing speed, and temperature in each temperature zone have a wide adjustable range. Different combinations of process parameters can produce molybdenum powder for different applications. However, these parameters are interrelated and mutually restrictive. Rationally formulating the process parameters for the first and second stages of reduction to ensure that the produced molybdenum powder for different applications simultaneously possesses high yield and high quality has always been a focus of scientific and technological workers in the molybdenum industry. Regarding low-potassium ammonium molybdate (low-potassium molybdenum trioxide), how to overcome the bottlenecks of severe molybdenum powder agglomeration, low yield, and high cost in producing molybdenum powder using it as a raw material, and how to make the produced molybdenum powder meet the requirements of more application fields, should become a research direction for the industry. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing small-particle-size, high-bulk-density molybdenum powder based on low-potassium ammonium molybdate. The process of this invention is stable, yields a high product rate, and produces molybdenum powder with both small Fisher particle size and high bulk density, exhibiting excellent pressing and sintering properties.

[0009] The technical solution of this invention: A method for preparing small-particle-size, high-bulk-density molybdenum powder based on low-potassium ammonium molybdate, comprising the following steps:

[0010] Molybdenum trioxide was prepared by roasting ammonium molybdate with a potassium content ≤0.005% as raw material.

[0011] The molybdenum trioxide was reduced in a hydrogen atmosphere with a dew point ≥10°C to obtain flaky agglomerated molybdenum dioxide.

[0012] After crushing the flaky agglomerated molybdenum dioxide, it was subjected to a two-stage reduction under a hydrogen atmosphere with a dew point ≤ -40℃ to obtain molybdenum powder.

[0013] The molybdenum powder prepared by the above method has a Fisher particle size of 2.72–2.85 μm and a bulk density of 1.27–1.34 g / cm³. 3 .

[0014] In the aforementioned preparation method, the hydrogen flow rate in both the first-stage and second-stage reduction is set according to the dimensions of the corresponding reduction furnace tube; specifically, for a furnace tube with an inner diameter of 6.8 cm, the hydrogen flow rate is 0.36–0.47 m³ / h. 3 For a furnace tube with an inner diameter of 8.9 cm, the hydrogen flow rate is 0.62–0.81 m³ / h. 3 For a flat rectangular furnace tube with an internal width of 30 cm and a height of 7 cm, the hydrogen flow rate is 2.10–2.73 m³ / h. 3 / h.

[0015] In the aforementioned preparation method, during the first-stage reduction, the amount of molybdenum trioxide loaded onto the boat is calculated and set based on the bottom area of ​​the boat according to a standard conversion of 2.10–2.50 g / cm².

[0016] In the aforementioned preparation method, during the first-stage reduction, the pushing speed of the molybdenum trioxide boat is set according to the total length of the temperature zone of the reduction furnace; wherein, when the total length of the temperature zone is 400cm, the pushing speed is 125-100 cm / h; when the total length of the temperature zone is 420cm, the pushing speed is 131-105 cm / h; and when the total length of the temperature zone is 500cm, the pushing speed is 156-125 cm / h.

[0017] In the aforementioned preparation method, during the first stage of reduction, the reduction temperature gradually increases along the direction of the material boat's movement, with the low-end temperature zone being 420–480°C and the high-end temperature zone being 550–580°C.

[0018] In the aforementioned preparation method, the crushing step is as follows: the flaky agglomerated molybdenum dioxide is mechanically crushed and then passed through an 80-mesh sieve, with the sieve underrun controlled between 97% and 99%.

[0019] In the aforementioned preparation method, during the two-stage reduction, the amount of molybdenum dioxide loaded onto the boat is calculated and set according to the bottom area of ​​the boat based on a standard conversion of 1.95–2.35 g / cm².

[0020] In the aforementioned preparation method, during the two-stage reduction, the pushing speed of the molybdenum dioxide boat is set according to the total length of the temperature zone of the reduction furnace; wherein, when the total length of the temperature zone is 400 cm, the pushing speed is 108-90 cm / h; and when the total length of the temperature zone is 500 cm, the pushing speed is 113-135 cm / h.

[0021] In the aforementioned preparation method, during the two-stage reduction, the reduction temperature first increases and then decreases along the direction of the material boat's movement. The temperature in the first temperature zone is 840–880°C, the temperature in the penultimate temperature zone is 930–960°C, and the temperature in the last temperature zone is 870–910°C.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The molybdenum powder produced by the method of this invention breaks the conventional view that "molybdenum powder particle size and loose density are positively correlated, with smaller particle size resulting in lower loose density," and instead exhibits small Fisher particle size (2.72–2.85 μm) and high loose density (1.27–1.34 g / cm³). 3 Its features fill a market gap.

[0024] 2. This invention addresses the problems of high reduction temperatures leading to severe molybdenum powder agglomeration, low yield, and high cost in the production of molybdenum powder using low-potassium ammonium molybdate. Focusing on the central idea of ​​"changing the morphology of small-particle molybdenum powder to improve its loose packing density," the method employs a low-flow-rate wet hydrogen primary reduction stage and a low-flow-rate dry hydrogen secondary reduction stage. Based on the specifications of the furnace tubes, the charging boat, and the total length of the temperature zones, the method optimizes parameters such as the charging amount, the pushing speed, the hydrogen flow rate, and the temperature of each temperature zone. This effectively solves the problems commonly encountered with current technology in the production of molybdenum powder using low-potassium ammonium molybdate: "the molybdenum dioxide produced in the primary reduction stage is overfilled or cannot be loaded onto the boat at all; the loose packing density of the molybdenum powder produced in the secondary reduction stage is too low (≤0.95 g / cm³)." 3 Problems include: severe agglomeration, "lightweight" material that is difficult to sieve, low yield (the sieve failure rate can be as low as 50% or less in the 200-mesh sieve), overfilling or inability to fill the mold during the pressing process, and poor hot working performance of the sintered molybdenum metal.

[0025] 3. The molybdenum powder produced by the method of the present invention has the characteristics of good pressing performance, low temperature required for pressing and sintering, and excellent hot working performance of sintered metallic molybdenum material. It is especially suitable for manufacturing fine molybdenum wires for various purposes, and is also suitable for manufacturing other molybdenum products with high requirements for hot working performance.

[0026] 4. In the two-stage reduction method for molybdenum powder production, hydrogen is the second largest cost factor after the raw material ammonium molybdate. The hydrogen flow rates for the first and second stages of reduction in this invention are designed according to the cross-sectional area of ​​the furnace tubes of different specifications, following the principle of "minimizing flow rate." This flow rate is close to the minimum value (empirical value) required for safe production, thus reducing hydrogen consumption. Furthermore, the maximum reduction temperature (930–960℃) used in this invention is relatively low compared to current technologies. In addition, the molybdenum powder produced using this method achieves a sieve pass rate of over 93% on a 200-mesh sieve, a figure that is already at a high level in the industry. Therefore, the molybdenum powder production method of this invention has the characteristics of low hydrogen consumption, low maximum reduction temperature, and high product yield, resulting in a significant cost advantage.

[0027] 5. The method of the present invention effectively solves various problems that are prone to occur when producing molybdenum powder using low-potassium ammonium molybdate as raw material, and also provides the possibility for efficient and low-cost production of low-potassium molybdenum powder. Attached Figure Description

[0028] Figure 1 This is a flow chart of the molybdenum powder preparation process of the present invention;

[0029] Figure 2 This is a schematic diagram of the bypass hydrogen dew point raising device of the present invention.

[0030] The labels in the attached diagram are:

[0031] 1. Sealed water tank; 2. Water; 3. Water inlet pipe and valve; 4. Water level control device; 5. Low dew point hydrogen inlet pipe and valve; 6. Hydrogen delivery pipe and valve; 7. High dew point hydrogen outlet pipe and valve; 8. Hydrogen outlet pipe and valve for dew point detection. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.

[0033] Example 1: A method for preparing small-particle-size, high-bulk-density molybdenum powder based on low-potassium ammonium molybdate, such as... Figure 1 As shown, it includes the following steps:

[0034] Step 1. Roasting:

[0035] Industrial-grade ammonium molybdate with a potassium content of ≤0.005% was selected as raw material, and it was roasted into molybdenum trioxide according to the current conventional process and passed through a 40-mesh sieve.

[0036] Step 2. Restoring a section:

[0037] Molybdenum trioxide, which has passed through a 40-mesh sieve, is loaded into a feeding boat and subjected to wet hydrogen reduction in the reduction zone of a primary reduction furnace to produce molybdenum dioxide mixed with a large number of flaky lumps. After being mechanically crushed, the molybdenum dioxide is passed through an 80-mesh sieve (with the undersize rate controlled between 97% and 99%).

[0038] The process parameters for the first stage of reduction are set according to the specifications of the reduction furnace and the charging boat as follows:

[0039] Hydrogen dew point: ≥10℃. In actual production, dry hydrogen can be converted into wet hydrogen by passing it through a sealed water tank before being connected to the reduction furnace tube. Figure 2 ). Figure 2A schematic diagram of a bypass-type hydrogen dew point enhancement device is shown. The device operates on the principle of "bubble contact humidification," with the following process: A dry hydrogen stream is branched off from the main hydrogen supply pipeline via a hydrogen delivery pipeline (the hydrogen inlet pipe maintains a certain distance from the water surface and does not extend to the bottom of the sealed water tank). This dry hydrogen stream enters the bottom of the sealed water tank through a low-dew-point hydrogen inlet pipe. The hydrogen passes through the water layer in the form of bubbles. During the bubble rise, the hydrogen comes into full contact with the water, causing water to evaporate and enter the hydrogen, thus significantly increasing the hydrogen's humidity (i.e., raising its dew point). The humidified hydrogen (high-dew-point hydrogen) is output from the top of the water tank through a high-dew-point hydrogen outlet pipe and sent to the production equipment. Simultaneously, dew point monitoring can be performed via a hydrogen outlet pipe for dew point detection to ensure that the dew point meets the standard (≥10℃, controllable by a constant-temperature water bath device). A water level control device automatically maintains a stable water level in the tank. When the water level drops, it is replenished through the inlet pipe. This bypass hydrogen dew point raising device can conveniently and reliably humidify a portion of the main dry hydrogen to the required dew point, and then supply it independently to a first-stage reduction furnace.

[0040] Hydrogen flow rate: The hydrogen flow rate is designed based on the cross-sectional area of ​​the furnace tube, adhering to the principle of "minimizing the flow rate." For example, for a furnace tube with an inner diameter of 6.8 cm, the hydrogen flow rate is 0.36–0.47 m³ / h; for a furnace tube with an inner diameter of 8.9 cm, the hydrogen flow rate is 0.62–0.81 m³ / h. 3 / h; a flat rectangular furnace tube with an internal width of 30cm and a height of 7cm, with a hydrogen flow rate of 2.10~2.73m3 / h.

[0041] Loading weight: Based on the bottom area of ​​the material boat, the loading weight of molybdenum trioxide is calculated according to the standard of 2.10~2.50g / cm². For example: a material boat with dimensions of 36cm×5cm×3.5cm and a wall thickness of 0.25cm has a loading weight of 335~399g; a material boat with dimensions of 40cm×5cm×3.5cm and a wall thickness of 0.25cm has a loading weight of 373~444g; a material boat with dimensions of 50cm×7cm×4cm and a wall thickness of 0.25cm has a loading weight of 676~804g; a material boat with dimensions of 32cm×28cm×4.5cm and a wall thickness of 0.4cm has a loading weight of 1782~2122g.

[0042] Pushing speed: Determined based on the total length of each temperature zone in a reduction furnace section. For example: for a reduction furnace with a total temperature zone length of 400cm, the pushing speed is 125-100cm / h; for a reduction furnace with a total temperature zone length of 500cm, the pushing speed is 156-125cm / h; for a reduction furnace with a total temperature zone length of 420cm, the pushing speed is 131-105cm / h.

[0043] Reduction temperature: Regardless of the number of temperature zones, the reduction temperature of a single reduction is set as follows: the temperature of each temperature zone increases gradually along the direction of material boat movement, with the low-end temperature zone at 420-480℃ and the high-end temperature zone at 550-580℃.

[0044] Step 3. Two-stage restoration:

[0045] Molybdenum dioxide that has passed through an 80-mesh sieve is loaded into a material boat and subjected to dry hydrogen reduction in the reduction temperature zone of a two-stage reduction furnace to produce molybdenum powder.

[0046] The process parameters for the two-stage reduction are set according to the specifications of the reduction furnace and the charging boat as follows:

[0047] Hydrogen dew point: Hydrogen dew point ≤ -40℃.

[0048] Hydrogen flow rate: The hydrogen flow rate is designed according to the principle of "minimizing the flow rate" based on the cross-sectional area of ​​the furnace tube. For example, the hydrogen flow rate for a furnace tube with an inner diameter of 6.8 cm is 1.38–1.60 m³ / h; the hydrogen flow rate for a furnace tube with an inner diameter of 8.9 cm is 2.36–2.74 m³ / h.

[0049] Loading weight: Based on the bottom area of ​​the material boat, the loading weight of molybdenum dioxide is calculated according to the standard of 1.95~2.35g / cm². For example: a material boat with dimensions of 36cm×5cm×3.5cm and a wall thickness of 0.25cm has a loading weight of 312~375g; a material boat with dimensions of 40cm×5cm×3.5cm and a wall thickness of 0.25cm has a loading weight of 347~417g; a material boat with dimensions of 50cm×7cm×4cm and a wall thickness of 0.25cm has a loading weight of 627~756g; and a material boat with dimensions of 25cm×5cm×3.5cm and a wall thickness of 0.25cm has a loading weight of 215~259g.

[0050] Pushing speed: Determined based on the total length of each temperature zone in the two-stage reduction furnace. For example, for a reduction furnace with a total temperature zone length of 400cm, the pushing speed is 108-90cm / h; for a reduction furnace with a total temperature zone length of 500cm, the pushing speed is 135-113cm / h.

[0051] Reduction temperature: Along the direction of material boat movement, the temperature of each temperature zone is set according to the principle of first increasing and then decreasing. The first temperature zone has the lowest temperature, at 840-880℃; the last temperature zone has the second lowest temperature, at 870-910℃; and the second to last temperature zone has the highest temperature, at 930-960℃.

[0052] Step 4. Screening and mixing:

[0053] After the crude molybdenum powder is produced from the furnace, it is directly passed through a 200-mesh sieve. The material passing through the sieve is mixed in a mixer according to the conventional process, and after natural cooling, the finished molybdenum powder is obtained.

[0054] Example 2: This example is based on the preparation method in Example 1, illustrating the preparation of molybdenum powder with specific process parameters:

[0055] 1. Raw materials: MSA-1 grade ammonium tetramolybdate (potassium content 0.0042%).

[0056] 2. Equipment:

[0057] Roasting equipment: rotary kiln.

[0058] A reduction device: a push-boat type 11-tube reduction furnace (furnace tube inner diameter: 6.8cm, number of temperature zones: 5, total length of temperature zones: 500cm, outer dimensions of the material boat: 40cm×5cm×3.5cm, wall thickness of the material boat: 0.25cm).

[0059] Two-stage reduction equipment: a push-boat type 9-tube reduction furnace (furnace tube inner diameter: 6.8cm, number of temperature zones: 5, total length of temperature zones: 500cm, outer dimensions of the material boat: 40cm×5cm×3.5cm, wall thickness of the material boat: 0.25cm).

[0060] Screening equipment: vibrating screen.

[0061] Mixing equipment: V-type mixer.

[0062] 3. Process parameters and test results

[0063] (1) Roasting:

[0064] Roasting temperature: 540~560℃.

[0065] Molybdenum trioxide passes through a 40-mesh sieve with a 100% sieve clearance. The Fisher particle size is 5.0–5.3 μm.

[0066] (2) A section is restored:

[0067] Hydrogen flow rate: 0.38-0.42 m³ / h per tube.

[0068] Hydrogen dew point: ≥10℃ (dry hydrogen passing through a water tank).

[0069] Molybdenum trioxide boat weight: 400g.

[0070] Pushing speed: 141cm / h (one boat every 17 minutes).

[0071] Reduction temperatures: The first to fifth temperature zones are 420–460℃, 515℃, 540℃, 560℃, and 560–575℃, respectively.

[0072] After being crushed, the flake molybdenum dioxide was passed through an 80-mesh sieve, with a sieve clearance of 97.62% and a Fisher particle size of 3.8–4.3 μm.

[0073] (3) Two-stage restoration:

[0074] Hydrogen flow rate: 1.44-1.52 m³ / h per tube.

[0075] Hydrogen dew point: ≤-40℃.

[0076] Molybdenum dioxide loading: 380g.

[0077] Pushing speed: 120cm / h (one boat every 20 minutes).

[0078] Reduction temperatures: The first to fifth temperature zones are 840–870℃, 910℃, 930℃, 930–950℃, and 880–910℃, respectively.

[0079] The molybdenum powder passed through a 200-mesh sieve with a sieve clearance of 93.03% and a Fisher particle size of 2.72–2.81 μm.

[0080] (4) Mixing powder:

[0081] The mixed molybdenum powder has a Fisher particle size of 2.78 μm and a loose bulk density of 1.31 g / cm³. 3 .

[0082] (5) Performance of molybdenum powder in subsequent processing:

[0083] Pressing: The molding volume is normal, and the pressing performance is good.

[0084] Sintering: Requires a lower maximum temperature, exhibits good sintering performance, and produces a high density (9.72–9.76 g / cm³) in the sintered molybdenum rod. 3 ).

[0085] Molybdenum wire processing: In the test batch (10 molybdenum rods), no wire breaks occurred when the wires were drawn to Φ0.12mm.

[0086] Example 3: This example, based on the preparation method in Example 1, illustrates the preparation of molybdenum powder with another specific process parameter:

[0087] 1. Raw materials: MSA-1 grade ammonium tetramolybdate (potassium content 0.0028%).

[0088] 2. Equipment:

[0089] Roasting equipment: rotary kiln.

[0090] A reduction device: a pushboat-type 11-tube reduction furnace (inner diameter of furnace tubes: 6.8cm, number of temperature zones: 5, total length of temperature zones: 400cm, outer dimensions of the material boat: 36cm×5cm×3.5cm, wall thickness of the material boat: 0.25cm).

[0091] Two-stage reduction equipment: a push-boat type 9-tube reduction furnace (furnace tube inner diameter: 6.8cm, number of temperature zones: 5, total length of temperature zones: 400cm, outer dimensions of the material boat: 36cm×5cm×3.5cm, wall thickness of the material boat: 0.25cm).

[0092] Screening equipment: vibrating screen.

[0093] Mixing equipment: V-type mixer.

[0094] 3. Process parameters and test results:

[0095] (1) Roasting:

[0096] Roasting temperature: 540~560℃.

[0097] Molybdenum trioxide passes through a 40-mesh sieve with a 100% sieve clearance. The Fisher particle size is 4.8–5.2 μm.

[0098] (2) A section is restored:

[0099] Hydrogen flow rate: 0.38-0.42 m³ / h per tube.

[0100] Hydrogen dew point: ≥10℃ (dry hydrogen passing through a water tank).

[0101] Molybdenum trioxide boat weight: 360g.

[0102] Pushing speed: 108cm / h (one boat every 20 minutes).

[0103] Reduction temperatures: The first to fifth temperature zones are 440–470℃, 520℃, 540℃, 560℃, and 560–580℃, respectively.

[0104] The flaky molybdenum dioxide was crushed and passed through an 80-mesh sieve, with a sieve clearance of 97.83% and a Fisher particle size of 3.7–4.2 μm.

[0105] (3) Two-stage restoration:

[0106] Hydrogen flow rate: 1.44-1.52 m³ / h per tube.

[0107] Hydrogen dew point: ≤-40℃.

[0108] Molybdenum dioxide loading: 330g.

[0109] Pushing speed: 98cm / h (one boat every 22 minutes).

[0110] Reduction temperatures: The first to fifth temperature zones are 850–880℃, 920℃, 930℃, 930–950℃, and 870–900℃, respectively.

[0111] The molybdenum powder passed through a 200-mesh sieve with a sieve clearance of 93.54% and a Fisher particle size of 2.65–2.78 μm.

[0112] (4) Mixing powder:

[0113] The mixed molybdenum powder has a Fisher particle size of 2.72 μm and a loose bulk density of 1.27 g / cm³. 3 .

[0114] (5) Performance of molybdenum powder in subsequent processing:

[0115] Pressing: The molding volume is normal, and the pressing performance is good.

[0116] Sintering: Requires a relatively low maximum temperature, exhibits good sintering performance, and produces a high density (9.73–9.79 g / cm³) in the sintered molybdenum rod. 3 ).

[0117] Molybdenum wire processing: In the test batch (10 molybdenum rods), no wire breaks occurred when the wires were drawn to Φ0.12mm.

[0118] Example 4: This example is based on the preparation method in Example 1, illustrating the preparation of molybdenum powder with the third specific process parameters:

[0119] 1. Raw materials: MSA-1 grade ammonium tetramolybdate (potassium content 0.0033%).

[0120] 2. Equipment:

[0121] Roasting equipment: rotary kiln.

[0122] A reduction device: a push-boat type 4-tube reduction furnace (furnace tube inner cavity width and height: 30cm×7cm, number of temperature zones: 3, total length of temperature zones: 420cm, outer dimensions of the material boat: 32cm×28cm×4.5cm, material boat wall thickness: 0.4cm).

[0123] Two-stage reduction equipment: 11-tube pushboat reduction furnace (inner diameter of furnace tube: 6.8cm, number of temperature zones: 5, total length of temperature zones: 500cm, outer dimensions of material boat: 25cm×5cm×3.5cm, wall thickness of material boat: 0.25cm).

[0124] Screening equipment: vibrating screen.

[0125] Mixing equipment: V-type mixer.

[0126] 3. Process parameters and test results:

[0127] (1) Roasting:

[0128] Roasting temperature: 540~560℃.

[0129] Molybdenum trioxide passes through a 40-mesh sieve with a 100% sieve clearance. The Fisher particle size is 4.6–5.0 μm.

[0130] (2) A section is restored:

[0131] Hydrogen flow rate: 2.28–2.36 m³ / h per tube.

[0132] Hydrogen dew point: ≥10℃ (dry hydrogen passing through a water tank).

[0133] Molybdenum trioxide loading: 2000g.

[0134] Pushing speed: 120cm / h (one boat every 16 minutes).

[0135] Reduction temperatures: The first to third temperature zones are 450–480℃, 530℃, and 550–565℃, respectively.

[0136] The flaky molybdenum dioxide was crushed and passed through an 80-mesh sieve, with a sieve clearance of 97.21% and a Fisher particle size of 3.9–4.4 μm.

[0137] (3) Two-stage restoration:

[0138] Hydrogen flow rate: 1.44-1.52 m³ / h per tube.

[0139] Hydrogen dew point: ≤-40℃.

[0140] Molybdenum dioxide loading: 240g.

[0141] Pushing speed: 120cm / h (two boats every 25 minutes).

[0142] Reduction temperatures: The first to fifth temperature zones are 840–870℃, 910℃, 930℃, 930–950℃, and 880–910℃, respectively.

[0143] The molybdenum powder passed through a 200-mesh sieve with a sieve clearance of 93.09% and a Fisher particle size of 2.75–2.87 μm.

[0144] (4) Mixing powder:

[0145] The mixed molybdenum powder has a Fisher particle size of 2.85 μm and a bulk density of 1.34 g / cm³. 3 .

[0146] (5) Performance of molybdenum powder in subsequent processing:

[0147] Pressing: The molding volume is normal, and the pressing performance is good.

[0148] Sintering: Requires a relatively low maximum temperature, exhibits good sintering performance, and produces high-density molybdenum rods after sintering (10.01–10.02 g / cm³). 3 ).

[0149] Molybdenum wire processing: In the test batch (10 molybdenum rods), no wire breaks occurred when the wires were drawn to Φ0.12mm.

[0150] The above embodiments are only used to illustrate the method of the present invention and are not intended to limit the process or parameter range involved in the method. Any other modifications or equivalent substitutions made by those skilled in the art to the present invention, as long as they do not depart from the spirit and scope of the present invention, should be covered within the scope of the claims of the patent of the present invention.

Claims

1. A method for preparing small-particle-size, high-bulk-density molybdenum powder based on low-potassium ammonium molybdate, characterized in that, Includes the following steps: Molybdenum trioxide was prepared by roasting ammonium molybdate with a potassium content ≤0.005% as raw material. The molybdenum trioxide was reduced in a hydrogen atmosphere with a dew point ≥10°C to obtain flaky agglomerated molybdenum dioxide. After crushing the flaky agglomerated molybdenum dioxide, it was subjected to a two-stage reduction under a hydrogen atmosphere with a dew point ≤ -40℃ to obtain molybdenum powder.

2. The preparation method according to claim 1, characterized in that, The molybdenum powder prepared by the method has a Fisher particle size of 2.72–2.85 μm and a loose packing density of 1.27–1.34 g / cm³. 3 .

3. The preparation method according to claim 1, characterized in that, In both the first-stage and second-stage reduction processes, the hydrogen flow rate is set according to the dimensions of the corresponding reduction furnace tubes; specifically, for a furnace tube with an inner diameter of 6.8 cm, the hydrogen flow rate is 0.36–0.47 m³ / h. 3 For a furnace tube with an inner diameter of 8.9 cm, the hydrogen flow rate is 0.62–0.81 m³ / h. 3 For a flat rectangular furnace tube with an internal width of 30 cm and a height of 7 cm, the hydrogen flow rate is 2.10–2.73 m³ / h. 3 / h.

4. The preparation method according to claim 1, characterized in that, In the aforementioned reduction process, the amount of molybdenum trioxide loaded onto the boat is calculated and set based on the bottom area of ​​the boat according to a standard conversion of 2.10–2.50 g / cm².

5. The preparation method according to claim 1, characterized in that, In the aforementioned reduction process, the pushing speed of the molybdenum trioxide boat is set according to the total length of the reduction furnace temperature zone; specifically, when the total temperature zone length is 400cm, the pushing speed is 125-100cm / h; when the total temperature zone length is 420cm, the pushing speed is 131-105cm / h; and when the total temperature zone length is 500cm, the pushing speed is 156-125cm / h.

6. The preparation method according to claim 1, characterized in that, During the reduction process, the reduction temperature gradually increases along the direction of the material boat's movement, with the low-end temperature zone being 420–480℃ and the high-end temperature zone being 550–580℃.

7. The preparation method according to claim 1, characterized in that, The crushing and grinding step is as follows: after mechanically crushing the flaky agglomerated molybdenum dioxide, it is passed through an 80-mesh sieve, and the undersize rate is controlled between 97% and 99%.

8. The preparation method according to claim 1, characterized in that, In the two-stage reduction process, the amount of molybdenum dioxide loaded onto the boat is calculated and set according to the bottom area of ​​the boat, based on a standard conversion of 1.95 to 2.35 g / cm².

9. The preparation method according to claim 1, characterized in that, In the two-stage reduction process, the pushing speed of the molybdenum dioxide boat is set according to the total length of the temperature zone of the reduction furnace; when the total length of the temperature zone is 400 cm, the pushing speed is 108-90 cm / h; when the total length of the temperature zone is 500 cm, the pushing speed is 113-135 cm / h.

10. The preparation method according to claim 1, characterized in that, In the two-stage reduction process, the reduction temperature first increases and then decreases along the direction of material boat movement. The temperature in the first temperature zone is 840–880℃, the temperature in the penultimate temperature zone is 930–960℃, and the temperature in the last temperature zone is 870–910℃.

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