A method for preparing high-tensile-strength tungsten powder

Abstract

The present application relates to a kind of preparation methods of high-pressure green strength tungsten powder, the preparation method includes the following steps: ammonium paratungstate is pre-reduced, and intermediate is obtained with ammonium tungsten bronze as main phase;The intermediate is reduced, and tungsten powder is obtained.The present application realizes the synergistic optimization of tungsten powder morphology and particle size distribution by regulating intermediate phase composition and reduction process, significantly improves green strength, so that the obtained tungsten powder is suitable for the forming needs of large tungsten products such as tungsten crucible, and the preparation method has the advantages of short process flow, high stability and low cost.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy technology and relates to a method for preparing high-pressure billet strength tungsten powder. Background Technology

[0002] Tungsten powder, with its high melting point, high hardness, high elastic modulus, and excellent wear resistance, has been widely used in key fields such as cemented carbide, electronic devices, and aerospace high-temperature components. With the rapid development of the military, nuclear energy, and aerospace industries, the market demand for large-sized tungsten products such as large-walled tubes, thin tungsten plates, and tungsten crucibles continues to grow, while also placing more stringent requirements on the quality of related products. Taking tungsten crucible preparation as an example, it has clear and high requirements for the formability of the raw tungsten powder and the strength of the high-pressure blank.

[0003] The morphology and particle size distribution of tungsten powder are key factors affecting the strength of pressed compacts. Irregular morphology and a wider particle size distribution can significantly improve the strength of tungsten powder pressed compacts. However, conventional tungsten powder, due to its regular morphology and relatively concentrated particle size distribution, generally has a pressed compact strength below 1.8 MPa, which is insufficient to meet the production requirements of large tungsten products. Currently, the industry often improves the strength of pressed compacts by adding forming agents. However, if the process control is not properly implemented during the subsequent sintering and removal of forming agents, this method can easily cause product deformation or cracking, directly affecting the quality of the finished product.

[0004] To address the aforementioned technical challenges, CN1730208A employs a one-step reduction method with ammonium paratungstate (APT) to directly prepare irregularly shaped tungsten powder. While this improves the strength of the pressed compact, the production process is subject to significant fluctuations, resulting in poor product quality stability. CN103240421A involves mixing APT with purple tungsten oxide before reduction, which can increase the pressed compact strength to 3.0 MPa~5.0 MPa. However, the addition of a purple tungsten oxide preparation and mixing step prolongs the process and increases production costs. CN110722172A utilizes a converter furnace. The method of preparing high-phase blue tungsten as a precursor can produce tungsten powder green blanks with a strength of 2.5 MPa to 3.5 MPa after reduction, which can meet the application requirements. However, the preparation process of high-phase blue tungsten is prone to problems such as powder agglomeration and rotary kiln blockage, resulting in high production costs and large fluctuations in composition. CN112846210A uses transition-state purple tungsten as raw material and reduces it under a hydrogen atmosphere to produce tungsten powder with a pressed blank strength ≥3.5 MPa and stable performance. The process is easy to control, but this method has special requirements for raw materials and the overall cost is relatively high.

[0005] In summary, existing technologies all suffer from varying degrees of problems such as insufficient process stability, high costs, or significant operational difficulties. Therefore, developing a stable and streamlined method for preparing high-strength tungsten powder from high-pressure billets is of great significance for promoting technological progress in related industries. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing high-strength tungsten powder for high-pressure compacts. The preparation method provided by the present invention achieves synergistic optimization of tungsten powder morphology and particle size distribution by controlling the intermediate phase composition and reduction process, significantly improving the compact strength and making the obtained tungsten powder suitable for the molding requirements of large tungsten products such as tungsten crucibles. The preparation method has the advantages of short process flow, high stability and low cost.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] This invention provides a method for preparing high-strength tungsten powder from high-pressure billets, the method comprising the following steps:

[0009] S1 and ammonium paratungstate were pre-reduced to obtain an intermediate with ammonium tungsten bronze as the main phase;

[0010] S2. Reduce the intermediate to obtain high-pressure billet strength tungsten powder.

[0011] This invention achieves synergistic optimization of tungsten powder morphology and particle size distribution by controlling the intermediate phase composition and reduction process, significantly improving the compact strength and making the obtained tungsten powder suitable for the molding requirements of large tungsten products such as tungsten crucibles. The preparation method has the advantages of short process flow, high stability and low cost.

[0012] The high-pressure tungsten powder mentioned in this invention refers to tungsten powder with a pressing strength greater than 2.5 MPa.

[0013] In some embodiments, the ammonium paratungstate has a Fisher's size (FSSS) of 35 μm to 50 μm.

[0014] In some embodiments, the pre-reduction method includes gradient heating hydrogen pre-reduction.

[0015] In some embodiments, the pre-reduction of hydrogen gas by gradient heating satisfies at least one of the following conditions:

[0016] (a1) The thickness of the hull is 15mm~30mm;

[0017] (a2) Hydrogen flow rate is 0.5 m³ / s. 3 / h~2m 3 / h;

[0018] (a3) The temperature of the first temperature zone is 300℃~400℃;

[0019] (a4) The temperature of the second temperature zone is 350℃~450℃;

[0020] (a5) The temperature of the third temperature zone is 380℃~490℃;

[0021] (a6) The temperature of the fourth temperature zone is 450℃~500℃;

[0022] (a7) The time for hydrogen pre-reduction by gradient heating is 2h~3h.

[0023] In some embodiments, the intermediate has a Fisher particle size of 8 μm to 13 μm.

[0024] In some embodiments, the intermediate contains 97 wt% or more and 3 wt% or less WO3. 2.9 .

[0025] In some embodiments, the reduction method includes gradient heating hydrogen reduction.

[0026] In some embodiments, the gradient temperature reduction of hydrogen satisfies at least one of the following conditions:

[0027] (b1) The thickness of the loading material on the upper boat is 10mm~13mm, and the thickness of the loading material on the lower boat is 10mm~20mm;

[0028] (b2) Hydrogen flow rate is 20m³. 3 / h~50m 3 / h;

[0029] (b3) The temperature of the first temperature zone is 700℃~760℃;

[0030] (b4) The temperature of the second temperature zone is 820℃~860℃;

[0031] (b5) The temperature of the third temperature zone is 900℃~930℃;

[0032] (b6) The temperature in the fourth temperature zone is 930℃~950℃;

[0033] (b7) The temperature of the fifth temperature zone is 950℃~970℃;

[0034] (b8) The time for hydrogen reduction by gradient heating is 2.5h~4.5h.

[0035] In some embodiments, the high-pressure tungsten powder has a Fisher particle size of 1.6 μm to 4.5 μm, a median particle size D50 of 2.5 μm to 6.5 μm, a particle size distribution span greater than 1.8, and a compact strength greater than 2.5 MPa.

[0036] In some embodiments, the preparation method includes the following steps:

[0037] S1. Ammonium paratungstate with a Fisher particle size of 35μm~50μm was pre-reduced to obtain an intermediate with ammonium tungsten bronze as the main phase.

[0038] The intermediate contains ammonium tungsten bronze with a mass percentage of over 97 wt% and a Fisher particle size of 8 μm to 13 μm.

[0039] The pre-reduction conditions are: boat thickness of 15mm~30mm, hydrogen flow rate of 0.5m³ / h. 3 / h~2m 3 / h; The temperature of the first temperature zone is 300℃~400℃, the temperature of the second temperature zone is 350℃~450℃, the temperature of the third temperature zone is 380℃~490℃, the temperature of the fourth temperature zone is 450℃~500℃, and the total time is 2h~3h.

[0040] S2. Reduce the intermediate and sieve to obtain high-pressure tungsten powder;

[0041] The reduction conditions are: the thickness of the upper boat loading material is 10mm~13mm, the thickness of the lower boat loading material is 10mm~20mm, and the hydrogen flow rate is 20m³ / h. 3 / h~50m 3 / h; The temperature of the first temperature zone is 700℃~760℃, the temperature of the second temperature zone is 820℃~860℃, the temperature of the third temperature zone is 900℃~930℃, the temperature of the fourth temperature zone is 930℃~950℃, the temperature of the fifth temperature zone is 950℃~970℃, and the total time is 2.5h~4.5h.

[0042] The high-pressure tungsten powder has a Fisher particle size of 1.6μm~4.5μm, a median particle size D50 of 2.5μm~6.5μm, a particle size distribution diameter greater than 1.8, and a pressing strength greater than 2.5MPa.

[0043] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] This invention achieves synergistic optimization of tungsten powder morphology and particle size distribution by controlling the intermediate phase composition and reduction process, significantly improving the compact strength and making the obtained tungsten powder suitable for the molding requirements of large tungsten products such as tungsten crucibles. The preparation method has the advantages of short process flow, high stability and low cost. Attached Figure Description

[0046] Figure 1 SEM image of the intermediate obtained in Example 1;

[0047] Figure 2 The image shows the XRD pattern of the intermediate obtained in Example 1.

[0048] Figure 3 This is a particle size distribution diagram of the tungsten powder used to increase the strength of the high-pressure billet obtained in Example 1;

[0049] Figure 4 SEM image of the tungsten powder with high-pressure billet strength obtained in Example 1;

[0050] Figure 5 The graph shows the compact strength test curve of the tungsten powder obtained in Example 1. Detailed Implementation

[0051] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0052] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0053] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0054] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0055] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0056] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0057] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0058] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0059] An embodiment of the present invention provides a method for preparing high-pressure billet strength tungsten powder, the preparation method comprising the following steps:

[0060] S1 and ammonium paratungstate were pre-reduced to obtain an intermediate with ammonium tungsten bronze as the main phase;

[0061] S2. Reduce the intermediate to obtain high-pressure billet strength tungsten powder.

[0062] This invention achieves synergistic optimization of tungsten powder morphology and particle size distribution by controlling the intermediate phase composition and reduction process, significantly improving the compact strength and making the obtained tungsten powder suitable for the molding requirements of large tungsten products such as tungsten crucibles. The preparation method has the advantages of short process flow, high stability and low cost.

[0063] Specifically, this invention uses ammonium tungsten bronze (ATB) intermediates to optimize powder morphology and compact strength: using ATB with multi-layered or tunnel crack structures as intermediates, this multi-crack structure can significantly increase the effective reaction surface area of ​​the intermediate during the reduction process, allowing for a wider hydrogen contact range, achieving multi-point nucleation and simultaneous growth of multiple crystal nuclei, promoting rapid crystal growth along different orientations, and easily forming irregular, angular, polyhedral tungsten powder. Simultaneously, the multi-crack intermediate can significantly improve the exchange efficiency of hydrogen and water vapor during hydrogen reduction, combined with a suitable crystal growth environment during the reduction process, promoting self-growing crystals and resulting in fully developed tungsten powder particles. The loose structure of the multi-crack intermediate is retained in the final tungsten powder, ultimately forming a high-porosity, loose tungsten powder agglomerate structure. The aforementioned special morphology and agglomerate structure can effectively increase the number of contact points between tungsten powder particles, strengthening the mechanical interlocking effect between particles, thereby significantly improving the compact strength of the tungsten powder.

[0064] In some embodiments, the ammonium paratungstate has a Fisher's size (FSSS) of 35 μm to 50 μm.

[0065] This invention achieves a wide particle size distribution and high packing density of tungsten powder by controlling the composition of the pre-reduced phase and the reduction process: the transformation process of ammonium paratungstate to the intermediate involves sequentially undergoing APT, ammonium metatungstate, ammonium tungsten bronze, and WO3. x The phase transformation of ammonium tungsten bronze. Ammonium tungsten bronze is a non-stoichiometric compound, existing in both hexagonal and tetragonal crystal systems. The relative contents of amorphous, tetragonal, and hexagonal ammonium tungsten bronze dynamically change with process parameters such as reduction temperature and boat loading conditions. This invention can effectively regulate the crystal form and proportion of ammonium tungsten bronze in the intermediate by controlling the pre-reduction temperature and boat loading thickness. After reduction, the tungsten powder obtained from the intermediate mainly composed of crystalline ammonium tungsten bronze has a uniform morphology and exhibits a regular polyhedral morphology. Based on this, by further controlling process parameters such as reduction temperature, boat loading thickness, and reduction time in the reduction furnace and optimizing the reduction kinetics, tungsten powder with a wide particle size distribution (large particle size distribution diameter) can be prepared. This allows for a reasonable gradation of coarse and fine particles in the tungsten powder, with fine particles filling the gaps between coarse particles, forming a "large particle framework, small particle filling" green body structure, significantly increasing the compact density, strengthening the intermeshing and contact between particles, and thus effectively improving the compact strength of the tungsten powder.

[0066] In some embodiments, the pre-reduction method includes gradient heating hydrogen pre-reduction.

[0067] In some embodiments, the pre-reduction method includes four-zone gradient heating hydrogen pre-reduction.

[0068] In some embodiments, the pre-reduction of hydrogen gas by gradient heating satisfies at least one of the following conditions:

[0069] (a1) The thickness of the boat is 15mm~30mm, for example, it can be 15mm, 18mm, 20mm, 21mm, 24mm, 25mm, 28mm or 30mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0070] (a2) Hydrogen flow rate is 0.5 m³ / s. 3 / h~2m 3 / h, for example, could be 0.5m 3 / h, 0.6m 3 / h, 0.8m 3 / h、1m 3 / h, 1.2m 3 / h, 1.5m 3 / h, 1.6m 3 / h, 1.8m 3 / h or 2m 3 / h, but not limited to the listed values, the same applies to other unlisted values ​​within the range;

[0071] (a3) The temperature of the first temperature zone is 300℃~400℃, for example, it can be 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃ or 400℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0072] (a4) The temperature of the second temperature zone is 350℃~450℃, for example, it can be 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃ or 450℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0073] (a5) The temperature of the third temperature zone is 380℃~490℃, for example, it can be 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃ or 490℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0074] (a6) The temperature of the fourth temperature zone is 450℃~500℃, for example, it can be 450℃, 460℃, 470℃, 480℃, 490℃ or 500℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0075] (a7) The time for gradient heating hydrogen pre-reduction is 2h~3h, for example, it can be 2h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0076] In the pre-reduction process of this invention, the residence time in each temperature zone is the same.

[0077] In some embodiments, the Fisher particle size of the intermediate is 8μm to 13μm, for example, it can be 8μm, 9μm, 10μm, 11μm, 12μm or 13μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0078] In some embodiments, the intermediate contains ammonium tungsten bronze at a mass percentage of 97 wt% (e.g., 97 wt%, 98 wt%, 99 wt%, or 100 wt% etc.) and less than 3 wt% WO. 2.9 .

[0079] In some embodiments, the reduction method includes gradient heating hydrogen reduction.

[0080] In some embodiments, the reduction method includes hydrogen reduction via a five-zone dual-boat gradient heating system.

[0081] In some embodiments, the gradient temperature reduction of hydrogen satisfies at least one of the following conditions:

[0082] (b1) The thickness of the upper boat loading is 10mm~13mm (e.g., it can be 10mm, 11mm, 12mm or 13mm, etc.), and the thickness of the lower boat loading is 10mm~20mm (e.g., it can be 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm or 20mm, etc.);

[0083] (b2) Hydrogen flow rate is 20m³. 3 / h~50m 3 / h, for example, could be 20 m 3 / h、25 m 3 / h、30 m 3 / h, 35 m 3 / h, 40 m 3 / h, 45 m 3 / h or 50 m 3 / h, but not limited to the listed values, the same applies to other unlisted values ​​within the range;

[0084] (b3) The temperature of the first temperature zone is 700℃~760℃, for example, it can be 700℃, 710℃, 720℃, 730℃, 740℃, 750℃ or 760℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0085] (b4) The temperature of the second temperature zone is 820℃~860℃, for example, it can be 820℃, 830℃, 840℃, 850℃ or 860℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0086] (b5) The temperature of the third temperature zone is 900℃~930℃, for example, it can be 900℃, 905℃, 910℃, 915℃, 920℃, 925℃ or 930℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0087] (b6) The temperature of the fourth temperature zone is 930°C to 950°C, for example, it can be 930°C, 935°C, 940°C, 945°C or 950°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0088] (b7) The temperature of the fifth temperature zone is 950°C to 970°C, for example, it can be 950°C, 955°C, 960°C, 965°C or 970°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0089] (b8) The time for gradient heating hydrogen pre-reduction is 2.5h to 4.5h, for example, it can be 2.5h, 3h, 3.5h, 4h or 4.5h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0090] In the reduction process of this invention, the residence time in each temperature zone is the same.

[0091] In some embodiments, the high-pressure tungsten powder has a Fisher particle size of 1.6 μm to 4.5 μm, a median particle size D50 of 2.5 μm to 6.5 μm, a particle size distribution span greater than 1.8, and a compact strength greater than 2.5 MPa.

[0092] The median particle size D50 was determined using a laser particle size analyzer.

[0093] In some embodiments, the preparation method includes the following steps:

[0094] S1. Ammonium paratungstate with a Fisher particle size of 35μm~50μm was pre-reduced to obtain an intermediate with ammonium tungsten bronze as the main phase.

[0095] The intermediate contains ammonium tungsten bronze with a mass percentage of over 97 wt% and a Fisher particle size of 8 μm to 13 μm.

[0096] The pre-reduction conditions are: boat thickness of 15mm~30mm, hydrogen flow rate of 0.5m³ / h. 3 / h~2m 3 / h; The temperature of the first temperature zone is 300℃~400℃, the temperature of the second temperature zone is 350℃~450℃, the temperature of the third temperature zone is 380℃~490℃, the temperature of the fourth temperature zone is 450℃~500℃, and the total time is 2h~3h.

[0097] S2. Reduce the intermediate and sieve to obtain high-pressure tungsten powder;

[0098] The reduction conditions are: the thickness of the upper boat loading material is 10mm~13mm, the thickness of the lower boat loading material is 10mm~20mm, and the hydrogen flow rate is 20m³ / h. 3 / h~50m 3 / h; The temperature of the first temperature zone is 700℃~760℃, the temperature of the second temperature zone is 820℃~860℃, the temperature of the third temperature zone is 900℃~930℃, the temperature of the fourth temperature zone is 930℃~950℃, the temperature of the fifth temperature zone is 950℃~970℃, and the total time is 2.5h~4.5h.

[0099] The high-pressure tungsten powder has a Fisher particle size of 1.6μm~4.5μm, a median particle size D50 of 2.5μm~6.5μm, a particle size distribution diameter greater than 1.8, and a pressing strength greater than 2.5MPa.

[0100] In this invention, the Fisher particle size was determined using a WLP-216 average particle size analyzer according to (GB / T3249-2022) "Method for determination of Fisher particle size of metals and their compounds".

[0101] The median particle size D 50 Laser particle size analysis was performed using an MS2000+2000MV laser particle size analyzer, in accordance with (GB / T 19077-2024) "Laser diffraction method for particle size distribution".

[0102] The particle size distribution span is first determined according to the median particle size D mentioned above. 50 The particle size was determined using the specified method, and then calculated, where Span = (D 90 -D 10 ) / D 50 , where D 10 D represents the particle size corresponding to a cumulative volume distribution of 10%. 50 D represents the particle size corresponding to a cumulative volume distribution of 50%. 90 The particle size corresponding to a cumulative volume distribution of 90% is given. The above characteristic particle size is taken from the cumulative volume distribution curve of the same laser particle size test. The test was performed in parallel for 3 times, and the arithmetic mean was taken as the final result.

[0103] The strength of the pressed blank was determined according to GB / T 5160-2002 "Determination of Strength of Green Blanks of Metal Powder - Transverse Fracture Method of Rectangular Pressed Blanks" using a universal testing machine. A specified mass of tungsten powder was accurately weighed and placed into a cemented carbide mold with a cavity size of 30mm × 12mm. The mold was pressed at 200MPa for 30s, and then demolded to obtain a standard rectangular pressed blank specimen with dimensions of 30mm × 12mm × 6mm. The specimen was placed on a three-point bending fixture with a span of 25mm. The fillet radius of both the indenter and the support roller was 2.0mm. A loading rate of 0.5mm / min was applied, and the maximum load at the point of fracture was recorded. The transverse fracture strength of the pressed blank was calculated using the formula and used as the characterization value of the pressed blank strength. Three specimens were measured in parallel. When the relative deviation of the measurement results was no greater than 5%, the arithmetic mean was taken as the final result.

[0104] In the following specific embodiments, the ammonium paratungstate used is ammonium paratungstate of grade APT-0 conforming to GB / T 10116-2007, with a Fisher particle size of 35μm~50μm.

[0105] Example 1

[0106] This embodiment provides a method for preparing high-strength tungsten powder for high-pressure billets, including the following steps:

[0107] S1. Ammonium paratungstate with a Fisher particle size of 35μm~50μm was pre-reduced to obtain an intermediate with ammonium tungsten bronze as the main phase.

[0108] The intermediate contains 100 wt% ammonium tungsten bronze and has a Fisher particle size of 8 μm.

[0109] The pre-reduction conditions are: boat thickness of 15 mm and hydrogen flow rate of 0.5 m³ / s. 3 / h; The temperature of the first temperature zone is 300℃, the temperature of the second temperature zone is 350℃, the temperature of the third temperature zone is 380℃, the temperature of the fourth temperature zone is 450℃, and the total time is 2h.

[0110] S2. Reduce the intermediate and pass it through a 200-mesh sieve to obtain high-pressure billet strength tungsten powder;

[0111] The reduction conditions are: the thickness of the upper boat loading is 10 mm, the thickness of the lower boat loading is 10 mm, and the hydrogen flow rate (dew point < -60℃) is 50 m³ / h. 3 / h; The temperature of the first temperature zone is 700℃, the temperature of the second temperature zone is 820℃, the temperature of the third temperature zone is 900℃, the temperature of the fourth temperature zone is 930℃, the temperature of the fifth temperature zone is 950℃, and the total time is 2.5h.

[0112] The morphology of the high-pressure billet strength tungsten powder is an irregular polyhedron with a Fisher particle size of 1.6 μm, a median particle size D50 of 2.5 μm, a particle size distribution diameter of 1.88, and a billet strength of 3.2 MPa.

[0113] The SEM image (magnified 2000 times) of the intermediate obtained in this embodiment is as follows: Figure 1 As shown, the XRD pattern of the intermediate is as follows: Figure 2 As shown; the particle size distribution diagram of the high-pressure billet strength tungsten powder obtained in this embodiment is as follows. Figure 3 As shown, the SEM image (magnified 10000 times) of the obtained high-pressure billet strength tungsten powder is as follows. Figure 4 As shown; the compact strength test curve of the tungsten powder obtained in this embodiment is as follows. Figure 5 As shown.

[0114] Example 2

[0115] This embodiment provides a method for preparing high-strength tungsten powder for high-pressure billets, including the following steps:

[0116] S1. Ammonium paratungstate with a Fisher particle size of 35μm~50μm was pre-reduced to obtain an intermediate with ammonium tungsten bronze as the main phase.

[0117] The intermediate contains 100 wt% ammonium tungsten bronze and has a Fisher particle size of 11 μm.

[0118] The pre-reduction conditions are: boat thickness is 30 mm, and hydrogen flow rate is 2 m³ / s. 3 / h; The temperature of the first temperature zone is 370℃, the temperature of the second temperature zone is 420℃, the temperature of the third temperature zone is 460℃, the temperature of the fourth temperature zone is 480℃, and the total time is 3h.

[0119] S2. Reduce the intermediate and pass it through a 200-mesh sieve to obtain high-pressure billet strength tungsten powder;

[0120] The reduction conditions are: the thickness of the upper boat loading is 10 mm, the thickness of the lower boat loading is 15 mm, and the hydrogen flow rate (dew point < -60℃) is 35 m³ / h. 3 / h; The temperature of the first temperature zone is 720℃, the temperature of the second temperature zone is 820℃, the temperature of the third temperature zone is 920℃, the temperature of the fourth temperature zone is 940℃, the temperature of the fifth temperature zone is 960℃, and the total time is 3h.

[0121] The morphology of the high-pressure tungsten powder is an irregular polyhedron with a Fisher particle size of 3.0 μm, a median particle size D50 of 4.7 μm, a particle size distribution spacing of 1.86, and a pressing strength of 2.9 MPa.

[0122] Example 3

[0123] This embodiment provides a method for preparing high-strength tungsten powder for high-pressure billets, including the following steps:

[0124] S1. Ammonium paratungstate with a Fisher particle size of 35μm~50μm was pre-reduced to obtain an intermediate with ammonium tungsten bronze as the main phase.

[0125] The intermediate contains 97 wt% ammonium tungsten bronze and has a Fisher particle size of 13 μm.

[0126] The pre-reduction conditions are: boat thickness is 30 mm, and hydrogen flow rate is 2 m³ / s. 3 / h; The temperature of the first temperature zone is 400℃, the temperature of the second temperature zone is 450℃, the temperature of the third temperature zone is 490℃, the temperature of the fourth temperature zone is 500℃, and the total time is 3h.

[0127] S2. Reduce the intermediate and pass it through a 200-mesh sieve to obtain high-pressure billet strength tungsten powder;

[0128] The reduction conditions are: the thickness of the upper boat loading is 13 mm, the thickness of the lower boat loading is 20 mm, and the hydrogen flow rate (dew point < -60℃) is 20 m³ / s. 3 / h; The temperature of the first temperature zone is 760℃, the temperature of the second temperature zone is 860℃, the temperature of the third temperature zone is 930℃, the temperature of the fourth temperature zone is 950℃, the temperature of the fifth temperature zone is 970℃, and the total time is 4.5h.

[0129] The morphology of the high-pressure tungsten powder is an irregular polyhedron with a Fisher particle size of 4.5 μm, a median particle size D50 of 6.5 μm, a particle size distribution diameter of 1.81, and a pressing strength of 2.5 MPa.

[0130] Example 4

[0131] This embodiment provides a method for preparing high-strength tungsten powder for high-pressure billets, including the following steps:

[0132] S1. Ammonium paratungstate with a Fisher particle size of 35μm~50μm was pre-reduced to obtain an intermediate with ammonium tungsten bronze as the main phase.

[0133] The intermediate contains 100 wt% ammonium tungsten bronze and has a Fisher particle size of 11 μm.

[0134] The pre-reduction conditions are: boat thickness is 30 mm, and hydrogen flow rate is 2 m³ / s. 3 / h; The temperature of the first temperature zone is 370℃, the temperature of the second temperature zone is 420℃, the temperature of the third temperature zone is 460℃, the temperature of the fourth temperature zone is 480℃, and the total time is 3h.

[0135] S2. Reduce the intermediate and pass it through a 200-mesh sieve to obtain high-pressure billet strength tungsten powder;

[0136] The reduction conditions are: the thickness of the upper boat loading is 12 mm, the thickness of the lower boat loading is 15 mm, and the hydrogen flow rate (dew point < -60℃) is 38 m³ / s. 3 / h; The temperature of the first temperature zone is 720℃, the temperature of the second temperature zone is 820℃, the temperature of the third temperature zone is 920℃, the temperature of the fourth temperature zone is 940℃, the temperature of the fifth temperature zone is 960℃, and the total time is 3.5h.

[0137] The morphology of the high-pressure tungsten powder is an irregular polyhedron with a Fisher particle size of 2.9 μm, a median particle size D50 of 4.3 μm, a particle size distribution diameter of 1.91, and a pressing strength of 3.5 MPa.

[0138] Example 5

[0139] This embodiment provides a method for preparing high-pressure billet strength tungsten powder. Except for the pre-reduction conditions, which are different from those in Example 1, the rest are the same as in Example 1.

[0140] In this embodiment, the pre-reduction conditions are met: the boat thickness is 15 mm, and the hydrogen flow rate is 0.5 m³ / h. 3 / h; the temperature of the first temperature zone is 300℃, the temperature of the second temperature zone is 300℃, the temperature of the third temperature zone is 380℃, the temperature of the fourth temperature zone is 450℃, and the total time is 2h.

[0141] Example 6

[0142] This embodiment provides a method for preparing high-pressure billet strength tungsten powder. Except for the pre-reduction conditions, which are different from those in Example 1, the rest are the same as in Example 1.

[0143] In this embodiment, the pre-reduction conditions are met: the boat thickness is 15 mm, and the hydrogen flow rate is 0.5 m³ / h. 3 / h; the temperature of the first temperature zone is 300℃, the temperature of the second temperature zone is 350℃, the temperature of the third temperature zone is 350℃, the temperature of the fourth temperature zone is 450℃, and the total time is 2h.

[0144] Example 7

[0145] This embodiment provides a method for preparing high-pressure billet strength tungsten powder. Except for the pre-reduction conditions, which are different from those in Example 1, the rest are the same as in Example 1.

[0146] In this embodiment, the pre-reduction conditions are met: the boat thickness is 15 mm, and the hydrogen flow rate is 0.5 m³ / h. 3 / h; the temperature of the first temperature zone is 300℃, the temperature of the second temperature zone is 350℃, the temperature of the third temperature zone is 380℃, the temperature of the fourth temperature zone is 380℃, and the total time is 2h.

[0147] Example 8

[0148] This embodiment provides a method for preparing high-pressure billet strength tungsten powder. Except for the reduction conditions, which are different from those in Example 1, the rest are the same as in Example 1.

[0149] In this embodiment, the reduction conditions are met: the thickness of the upper boat loading is 10 mm, the thickness of the lower boat loading is 10 mm, and the hydrogen flow rate (dew point < -60℃) is 50 m³ / h. 3 / h; The temperature of the first temperature zone is 700℃, the temperature of the second temperature zone is 700℃, the temperature of the third temperature zone is 900℃, the temperature of the fourth temperature zone is 930℃, the temperature of the fifth temperature zone is 950℃, and the total time is 2.5h.

[0150] Example 9

[0151] This embodiment provides a method for preparing high-pressure billet strength tungsten powder. Except for the reduction conditions, which are different from those in Example 1, the rest are the same as in Example 1.

[0152] In this embodiment, the reduction conditions are met: the thickness of the upper boat loading is 10 mm, the thickness of the lower boat loading is 10 mm, and the hydrogen flow rate (dew point < -60℃) is 50 m³ / h. 3 / h; The temperature of the first temperature zone is 700℃, the temperature of the second temperature zone is 820℃, the temperature of the third temperature zone is 820℃, the temperature of the fourth temperature zone is 930℃, the temperature of the fifth temperature zone is 950℃, and the total time is 2.5h.

[0153] Example 10

[0154] This embodiment provides a method for preparing high-pressure billet strength tungsten powder. Except for the reduction conditions, which are different from those in Example 1, the rest are the same as in Example 1.

[0155] In this embodiment, the reduction conditions are met: the thickness of the upper boat loading is 10 mm, the thickness of the lower boat loading is 10 mm, and the hydrogen flow rate (dew point < -60℃) is 50 m³ / h. 3 / h; The temperature of the first temperature zone is 700℃, the temperature of the second temperature zone is 820℃, the temperature of the third temperature zone is 900℃, the temperature of the fourth temperature zone is 900℃, the temperature of the fifth temperature zone is 950℃, and the total time is 2.5h.

[0156] Example 11

[0157] This embodiment provides a method for preparing high-pressure billet strength tungsten powder. Except for the reduction conditions, which are different from those in Example 1, the rest are the same as in Example 1.

[0158] In this embodiment, the reduction conditions are met: the thickness of the upper boat loading is 10 mm, the thickness of the lower boat loading is 10 mm, and the hydrogen flow rate (dew point < -60℃) is 50 m³ / h.3 / h; The temperature of the first temperature zone is 700℃, the temperature of the second temperature zone is 820℃, the temperature of the third temperature zone is 900℃, the temperature of the fourth temperature zone is 930℃, the temperature of the fifth temperature zone is 930℃, and the total time is 2.5h.

[0159] Performance Characterization

[0160] The particle size distribution span and compact strength of the tungsten powder obtained in the above embodiments were measured, and the results are shown in Table 1.

[0161] Table 1

[0162]

[0163] As can be seen from the comparison between Examples 5-7 and Example 1 in Table 1, the stepped temperature gradient in the pre-reduction stage affects the compact strength of the tungsten powder. When the temperature gradient between any adjacent temperature zones disappears during the pre-reduction process, the compact strength of the obtained tungsten powder decreases to varying degrees. This is because the transformation process from ammonium paratungstate to ammonium tungsten bronze intermediate involves phase transformations of APT, ammonium metatungstate, ammonium tungsten bronze, and WOx. The stepped temperature gradient can precisely control the reaction rate at each stage, ensuring that the crystal form and proportion of ammonium tungsten bronze in the intermediate reach the optimal level. When the temperature gradient disappears, the phase transformation process becomes uneven, making it impossible to form an intermediate dominated by crystalline ammonium tungsten bronze with a suitable crystal form proportion. This leads to a decrease in the uniformity of the morphology and a narrowing of the particle size distribution of the tungsten powder obtained after subsequent reduction, ultimately reducing the compact strength.

[0164] As can be seen from the comparison between Examples 8-11 and Example 1 in Table 1, the step-by-step temperature gradient in the reduction stage also affects the compact strength of the tungsten powder. When the temperature gradient between any adjacent temperature zones disappears during the reduction process, the compact strength of the resulting tungsten powder decreases. This is because the step-by-step temperature increase in the reduction stage can optimize the reduction kinetics, promote the efficient exchange of hydrogen and water vapor, provide a suitable environment for the self-growing of crystals, and facilitate the formation of tungsten powder with a wide particle size distribution. When the temperature gradient disappears, the reduction reaction rate is inconsistent, the crystal growth process is disordered, and it is impossible to form a fully developed polyhedral morphology and a reasonable particle size distribution, resulting in weakened contact and meshing between particles and a decrease in compact strength.

[0165] In summary, this invention utilizes ammonium tungsten bronze (ATB) intermediates to optimize powder morphology and compact strength. Using ATB intermediates with multi-layered or tunnel-cracked structures significantly increases the effective reaction surface area during reduction, allowing for wider hydrogen contact and enabling simultaneous multi-point nucleation and multi-nucleus growth. This promotes rapid crystal growth along different orientations, easily forming irregular, angular, polyhedral tungsten powder. Simultaneously, the multi-cracked intermediates significantly enhance hydrogen and water vapor exchange efficiency during hydrogen reduction. Combined with a suitable crystal growth environment during reduction, this promotes self-growing crystals, resulting in fully developed tungsten powder particles. The porous structure of the multi-cracked intermediates is retained in the final tungsten powder, ultimately forming a high-porosity, porous tungsten powder agglomerate structure. These unique morphologies and agglomerate structures effectively increase the number of contact points between tungsten powder particles, strengthening the mechanical interlocking effect between particles, thereby significantly improving the compact strength of the tungsten powder.

[0166] Furthermore, this invention achieves a wide particle size distribution and high packing density of tungsten powder by controlling the composition of the pre-reduced phase and the reduction process: the transformation process of ammonium paratungstate to the intermediate involves APT, ammonium metatungstate, ammonium tungsten bronze, and WO3 in sequence. x The phase transformation of ammonium tungsten bronze. Ammonium tungsten bronze is a non-stoichiometric compound, existing in both hexagonal and tetragonal crystal systems. The relative contents of amorphous, tetragonal, and hexagonal ammonium tungsten bronze dynamically change with process parameters such as reduction temperature and boat loading conditions. This invention can effectively regulate the crystal form and proportion of ammonium tungsten bronze in the intermediate by controlling the pre-reduction temperature and boat loading thickness. After reduction, the tungsten powder obtained from the intermediate mainly composed of crystalline ammonium tungsten bronze has a uniform morphology and exhibits a regular polyhedral morphology. Based on this, by further controlling process parameters such as reduction temperature, boat loading thickness, and reduction time in the reduction furnace and optimizing the reduction kinetics, tungsten powder with a wide particle size distribution (large particle size distribution diameter) can be prepared. This allows for a reasonable gradation of coarse and fine particles in the tungsten powder, with fine particles filling the gaps between coarse particles, forming a "large particle framework, small particle filling" green body structure, significantly increasing the compact density, strengthening the intermeshing and contact between particles, and thus effectively improving the compact strength of the tungsten powder.

[0167] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing high-pressure billet strength tungsten powder, characterized in that, The preparation method includes the following steps: S1 and ammonium paratungstate were pre-reduced to obtain an intermediate with ammonium tungsten bronze as the main phase; The pre-reduction method is gradient heating hydrogen pre-reduction, wherein the thickness of the boat used for gradient heating hydrogen pre-reduction is 15mm~30mm, and the hydrogen flow rate is 0.5m³ / h. 3 / h~2m 3 / h, the temperature of the first temperature zone is 300℃~370℃, the temperature of the second temperature zone is 350℃~420℃, the temperature of the third temperature zone is 380℃~460℃, the temperature of the fourth temperature zone is 450℃~480℃, and the time for hydrogen pre-reduction by gradient heating is 2h~3h. The intermediate contains ammonium tungsten bronze at a mass percentage of 97 wt% or more; S2. Reduce the intermediate to obtain high-pressure billet strength tungsten powder; The reduction method is gradient heating hydrogen reduction, wherein the thickness of the upper boat loading material is 10mm~12mm, and the thickness of the lower boat loading material is 10mm~15mm; the hydrogen flow rate is 35m³ / h. 3 / h~50m 3 / h; the temperature of the first temperature zone is 700℃~720℃; the temperature of the second temperature zone is 820℃~830℃; the temperature of the third temperature zone is 900℃~920℃; the temperature of the fourth temperature zone is 930℃~940℃; the temperature of the fifth temperature zone is 950℃~960℃; the time for hydrogen reduction by gradient heating is 2.5h~3.5h; The tungsten powder has a Fisher particle size of 1.6 μm to 3 μm, a median particle size D50 of 2.5 μm to 4.7 μm, a particle size distribution diameter greater than 1.86, and a compact strength greater than 2.5 MPa.

2. The preparation method according to claim 1, characterized in that, The ammonium paratungstate has a Fisher particle size of 35 μm to 50 μm.

3. The preparation method according to claim 1, characterized in that, The intermediate has a Fisher particle size of 8 μm to 13 μm.

4. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: S1. Ammonium paratungstate with a Fisher particle size of 35μm~50μm was pre-reduced to obtain an intermediate with ammonium tungsten bronze as the main phase. The intermediate contains ammonium tungsten bronze with a mass percentage of over 97 wt% and a Fisher particle size of 8 μm to 13 μm. The pre-reduction conditions are: boat thickness of 15mm~30mm, hydrogen flow rate of 0.5m³ / h. 3 / h~2m 3 / h; The temperature of the first temperature zone is 300℃~370℃, the temperature of the second temperature zone is 350℃~420℃, the temperature of the third temperature zone is 380℃~460℃, the temperature of the fourth temperature zone is 450℃~480℃, and the total time is 2h~3h. S2. Reduce the intermediate and sieve to obtain high-pressure tungsten powder; The reduction conditions are: the thickness of the upper boat loading material is 10mm~12mm, the thickness of the lower boat loading material is 10mm~15mm, and the hydrogen flow rate is 35m³ / h. 3 / h~50m 3 / h; The temperature of the first temperature zone is 700℃~720℃, the temperature of the second temperature zone is 820℃~830℃, the temperature of the third temperature zone is 900℃~920℃, the temperature of the fourth temperature zone is 930℃~940℃, the temperature of the fifth temperature zone is 950℃~960℃, and the total time is 2.5h~3.5h. The high-pressure tungsten powder has a Fisher particle size of 1.6μm~3μm, a median particle size D50 of 2.5μm~4.7μm, a particle size distribution diameter greater than 1.86, and a pressing strength greater than 2.5MPa.

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