Method for preparing ultra-coarse tungsten powder from ammonium tungstate solution

Abstract

This invention discloses a method for preparing ultra-coarse tungsten powder from ammonium tungstate solution. Using ammonium tungstate solution as raw material, ammonium paratungstate powder with a Fisher particle size of approximately 30-40 μm is first prepared by evaporation crystallization. Then, the ammonium paratungstate powder is added to an ammonium tungstate solution with a WO3 concentration of 110-120 g / L for 2-4 cycles of crystallization to prepare coarse-grained ammonium paratungstate with a Fisher particle size greater than 50 μm. Next, using the coarse-grained ammonium paratungstate as raw material, based on the phase transition characteristic of amorphous ammonium tungsten bronze to crystalline tungsten trioxide during the calcination of ammonium paratungstate, the temperature is maintained in the range of 400-430℃ to promote the growth of amorphous ammonium tungsten bronze grains. Then, the temperature is raised to 900℃ for calcination to obtain coarse-grained tungsten trioxide powder. The coarse-grained tungsten trioxide powder is then reduced with wet hydrogen at high temperature to enhance the reduction and deposition of volatile WO2(OH)2, promoting tungsten powder growth and obtaining ultra-coarse tungsten powder.

Description

Technical Field

[0001] This invention relates to the fields of tungsten smelting and tungsten powder metallurgy, specifically a method for preparing coarse-particle tungsten powder using ammonium tungstate solution as a raw material. Background Technology

[0002] Ultra-coarse tungsten carbide cemented carbide possesses excellent toughness, wear resistance, high-temperature hardness, high thermal conductivity, low creep deformation, and superior impact resistance, making it widely used in industrial fields such as mining drill bits, oil drilling tools, tunnel boring machine cutters, and stamping dies. Due to the significant heritable relationship between the particle sizes of tungsten powder and tungsten carbide powder, coarse-grained tungsten powder is a crucial raw material and key component in the preparation of ultra-coarse tungsten carbide cemented carbide.

[0003] In the tungsten smelting process, the preparation of tungsten powder from ammonium tungstate solution generally includes the following steps: (1) evaporation and crystallization of ammonium tungstate solution to prepare ammonium paratungstate powder; (2) calcination of ammonium paratungstate to prepare tungsten trioxide; (3) reduction of tungsten trioxide with hydrogen to prepare tungsten powder. Among these, the particle size of ammonium paratungstate powder, tungsten trioxide powder, and tungsten powder also have obvious genetic characteristics. Therefore, the preparation of coarse-grained ammonium paratungstate by crystallization of ammonium tungstate solution and the preparation of coarse-grained tungsten trioxide powder by calcination of ammonium paratungstate are key to the preparation of ultra-coarse tungsten powder. In the process of preparing ammonium paratungstate by conventional evaporation and crystallization of ammonium tungstate solution, due to the gradual decrease in tungsten concentration in the solution, it is difficult to maintain the supersaturation required for the growth of ammonium paratungstate crystals, resulting in the prepared ammonium paratungstate particles not being coarse enough, approximately 30-40 μm. In the process of preparing tungsten trioxide by heating and calcining ammonium paratungstate, the rapid heating rate is not conducive to crystal growth. Furthermore, the rapid heating rate leads to the rapid decomposition of ammonia, which easily causes the tungsten trioxide particles to break, resulting in tungsten trioxide powder with a particle size of approximately 15 μm. The tungsten powder prepared by hydrogen reduction from this powder also has a insufficiently large particle size, making it difficult to prepare ultra-coarse tungsten powder with a Fisher particle size greater than 30 μm. Summary of the Invention

[0004] In order to overcome the shortcomings of the existing technology, the present invention provides a method for preparing ultra-coarse tungsten powder from ammonium tungstate solution.

[0005] The process flow for preparing coarse tungsten powder using ammonium tungstate solution as raw material proposed in this invention is as follows: Figure 1 As shown, it mainly includes the following steps:

[0006] (1) A certain concentration of ammonium tungstate solution is added to an evaporator crystallizer, stirred and heated to a certain temperature, and then evaporated at a constant temperature for a certain time. Ammonium paratungstate crystals gradually crystallize out of the solution. After filtration, ammonium paratungstate powder is obtained.

[0007] (2) An ammonium tungstate solution with a WO3 concentration of 110-120 g / L was added to an evaporator crystallizer, stirred and heated to a certain temperature, and then the ammonium paratungstate powder obtained from the first crystallization was added. The mixture was evaporated and crystallized at a constant temperature for a certain time, and then filtered to obtain secondary crystallized ammonium paratungstate powder. This process was repeated under these conditions, and after multiple cycles of crystallization, coarse-particle ammonium paratungstate with a Fisher particle size greater than 50 μm was prepared.

[0008] (3) Add the obtained coarse ammonium paratungstate powder into a tube furnace, control a certain heating rate to raise the temperature to 400-430℃, then keep it at that temperature for a certain time, and then continue to raise the temperature to 900℃ and keep it at that temperature for a certain time to obtain coarse tungsten trioxide powder.

[0009] (4) The obtained tungsten trioxide powder is added to a tube furnace, heated to a certain temperature, and hydrogen containing a certain proportion of water vapor is introduced into the tube furnace for reduction. The reaction is then kept at a constant temperature for a certain time to prepare coarse tungsten powder.

[0010] Furthermore, in step (1), the concentration of tungsten trioxide in the ammonium tungstate solution of a certain concentration is 200-250 g / L, the temperature is 90-95℃, and the crystallization time is 2-4 hours.

[0011] Furthermore, the crystallization temperature in step (2) is 90-95℃, the crystallization time is 1-3 hours, and the number of crystallization cycles is 2-4 times.

[0012] Furthermore, the heating rate in step (3) is 1-5℃ / min, the holding time in the temperature range of 400-430℃ is 2-3 hours, and the holding time in the temperature range of 900℃ is 1 hour.

[0013] Further, the reduction temperature in step (4) is 900-1200℃, the hydrogen flow rate is 200-1000ml / min, the water vapor flow rate is 50-150ml / h, and the reaction time is 1-5 hours.

[0014] The technical concept of this invention is as follows:

[0015] This invention uses ammonium tungstate solution as raw material. First, ammonium paratungstate powder with a Fisher particle size of approximately 30-40 μm is prepared using an evaporation crystallization process. Then, this ammonium paratungstate powder is added to an ammonium tungstate solution with a constant WO3 concentration of 110-120 g / L for secondary crystallization, resulting in coarser ammonium paratungstate powder. This process is repeated three times, adding the secondary crystallized ammonium paratungstate powder to the ammonium tungstate solution with a constant WO3 concentration of 110-120 g / L for a tertiary crystallization to obtain more ammonium paratungstate powder. This cycle is repeated multiple times to prepare coarse-grained ammonium paratungstate with a Fisher particle size greater than 50 μm. In conventional evaporation crystallization processes, the ammonium tungstate solution concentration is very high in the early stages of crystallization (WO3 concentration approximately 300 g / L), leading to a large number of ammonium paratungstate crystals nucleating. However, in the middle and later stages of crystallization, the ammonium tungstate solution concentration is low (WO3 concentration below 100 g / L), which is unfavorable for the growth of ammonium paratungstate crystals, making it difficult to prepare coarse-grained ammonium paratungstate. The core technology of this method lies in controlling the concentration of ammonium tungstate solution within a stable range (WO3 concentration of 110-120 g / L) during the cyclic crystallization process. This ensures the solution is in a stable region that is unfavorable for ammonium paratungstate nucleation but favorable for crystal growth, thus inhibiting spontaneous nucleation of ammonium paratungstate crystals and promoting their growth, thereby preparing coarse-grained ammonium paratungstate. Then, using this coarse-grained ammonium paratungstate as raw material, based on the phase transition characteristic of amorphous ammonium tungsten bronze to crystalline tungsten trioxide during the calcination of ammonium paratungstate, the solution is held at a temperature of 400-430℃ for a certain period to promote the growth of amorphous ammonium tungsten bronze grains. Finally, the temperature is raised to 900℃ for high-temperature calcination to obtain coarse-grained tungsten trioxide powder. In conventional ammonium paratungstate calcination processes, the heating rate is relatively fast, and the stabilization time of amorphous ammonium tungsten bronze is very short, which is therefore unfavorable for its crystal growth. The core of this technology lies in significantly extending the stabilization time of amorphous ammonium tungsten bronze during calcination, allowing it to grow fully, and then promoting the growth of tungsten trioxide crystals under high temperature conditions to prepare coarse-grained tungsten trioxide powder. This coarse-grained tungsten trioxide powder is then reduced with wet hydrogen under high temperature conditions to enhance the reduction deposition of volatile WO2(OH)2 (as shown in formulas (1) and (3)), promoting the growth of tungsten powder, and finally preparing coarse-grained tungsten powder.

[0016] WO3 + H2O = WO2(OH)2 (1)

[0017] WO3 + H2 = W +H2O (2)

[0018] WO2(OH)2 + 8H2 = W + 4H2O (3)

[0019] Compared with the prior art, the main advantages of this invention are:

[0020] This method utilizes the genetic effect between the particle sizes of ammonium paratungstate, tungsten oxide, and tungsten powder. Starting from the source, it innovatively crystallizes coarse-grained ammonium paratungstate from an ammonium tungstate solution, and then combines this with a technological innovation in the calcination of ammonium paratungstate to produce coarse-grained tungsten trioxide. Finally, it uses wet hydrogen reduction to obtain coarse-grained tungsten powder. In this process, the particle size of the coarse-grained tungsten powder can be controlled by adjusting the particle size of the coarse-grained ammonium paratungstate. For example, the coarse-grained tungsten powder obtained from coarse-grained ammonium paratungstate with a Fisher's size of approximately 50 μm is smaller than that obtained from coarse-grained ammonium paratungstate with a Fisher's size of approximately 60 μm. Furthermore, compared to existing processes for preparing coarse-grained tungsten powder by doping with alkali metals, the new process does not introduce impurities into the tungsten powder, resulting in higher product purity, more complete tungsten powder crystal structure, and easier industrialization. Attached Figure Description

[0021] Figure 1 This is a flowchart of the method for preparing ultra-coarse tungsten powder from ammonium tungstate solution proposed in this invention;

[0022] Figure 2 This is a scanning electron microscope image of ammonium paratungstate prepared in Example 1 of the present invention;

[0023] Figure 3 This is a scanning electron microscope image of the tungsten powder obtained in Example 1 of the present invention;

[0024] Figure 4 The image shows the XRD pattern of the tungsten powder obtained in Example 1 of this invention.

[0025] Figure 5 This is a scanning electron microscope image of the tungsten powder obtained in Example 2 of the present invention;

[0026] Figure 6 This is a scanning electron microscope image of the tungsten powder obtained in Example 3 of the present invention;

[0027] Figure 7 This is a scanning electron microscope image of the tungsten powder obtained in Example 5 of the present invention;

[0028] Figure 8 The image shows the XRD pattern of the tungsten powder obtained in Example 5 of this invention. Detailed Implementation

[0029] To make the content of this invention easier to understand, the technical solutions of this invention will be further described below in conjunction with specific embodiments and accompanying drawings, but this invention is not limited thereto.

[0030] Example 1

[0031] Step 1: Add 500 mL of ammonium tungstate solution with a tungsten trioxide concentration of 200 g / L to an evaporator crystallizer, heat to 90°C, stir and maintain the temperature for 2 hours to obtain ammonium paratungstate powder and crystallization mother liquor. Filter and separate.

[0032] Step 2: Add the obtained ammonium paratungstate to 500 mL of ammonium tungstate solution (tungsten trioxide concentration of 110 g / L), heat to 90 °C, stir and crystallize at this temperature for 1 hour, then filter and separate. Add the obtained ammonium paratungstate powder back to 500 mL of ammonium tungstate solution (tungsten trioxide concentration of 110 g / L), stir and crystallize at this temperature for 1 hour. Finally, ammonium paratungstate with a Fisher particle size of 52 μm is obtained, as shown in the scanning electron microscope image below. Figure 2 As shown.

[0033] Step 3: Add the ammonium paratungstate obtained in Step 2 into a tube furnace, control the heating rate to increase the temperature to 400℃ at 5℃ / min, and hold for 2 hours. Then further increase the temperature to 900℃ and hold for 1 hour to obtain tungsten trioxide with a Fisher particle size of 18μm.

[0034] Step 4: Place the tungsten trioxide obtained in Step 3 into a tube furnace, heat to 900℃, with a hydrogen flow rate of 1000 ml / min and a water vapor flow rate of 50 ml / h, and react for 1 hour. The resulting tungsten powder has a Fisher particle size of 20.3 μm. The scanning electron microscope and XRD patterns of the tungsten powder are shown below. Figure 3 and Figure 4 As shown.

[0035] Example 2

[0036] Step 1: Add 500 mL of ammonium tungstate solution with a tungsten trioxide concentration of 230 g / L to an evaporator crystallizer, heat to 95°C, stir and maintain the temperature for 3 hours to obtain ammonium paratungstate powder and crystallization mother liquor. Filter and separate.

[0037] Step 2: Add the obtained ammonium paratungstate to 500 mL of ammonium tungstate solution (tungsten trioxide concentration is 120 g / L), heat to 95 °C, stir and crystallize at a constant temperature for 2 hours, then filter and separate. Add the obtained ammonium paratungstate powder to ammonium tungstate solution of the same composition for cyclic crystallization 3 times, and finally obtain ammonium paratungstate with a Fisher particle size of 59.2 μm.

[0038] Step 3: Add the ammonium paratungstate obtained in Step 2 into a tube furnace, control the heating rate to increase the temperature to 430℃ at 2℃ / min, and hold for 2 hours. Then, further increase the temperature to 900℃ and hold for 1 hour to obtain tungsten trioxide with a Fisher particle size of 22μm.

[0039] Step 4: Place the tungsten trioxide obtained in Step 3 into a tube furnace, heat to 1000℃, with a hydrogen flow rate of 500 ml / min and a water vapor flow rate of 65 ml / h, and react for 3 hours. The resulting tungsten powder has a Fisher particle size of 30.6 μm. The electron microscopy image of the tungsten powder is shown below. Figure 5 As shown.

[0040] Example 3

[0041] Step 1: Add 500 mL of ammonium tungstate solution with a tungsten trioxide concentration of 250 g / L to an evaporator crystallizer, heat to 95°C, stir and crystallize at a constant temperature for 4 hours to obtain ammonium paratungstate powder and crystallization mother liquor. Filter and separate.

[0042] Step 2: Add the obtained ammonium paratungstate to 500 mL of ammonium tungstate solution (tungsten trioxide concentration is 120 g / L), heat to 95 °C, stir and crystallize at a constant temperature for 3 hours, then filter and separate. Add the obtained ammonium paratungstate powder to ammonium tungstate solution of the same composition for cyclic crystallization 4 times, and finally obtain ammonium paratungstate with a Fisher particle size of 68.2 μm.

[0043] Step 3: Add the ammonium paratungstate obtained in Step 2 into a tube furnace, control the heating rate to increase the temperature to 430℃ at 1℃ / min, and hold for 3 hours. Then further heat to 900℃ and hold for 1 hour to obtain tungsten trioxide with a Fisher particle size of 28.3μm.

[0044] Step 4: Place the tungsten trioxide obtained in Step 3 into a tube furnace, heat to 1200℃, with a hydrogen flow rate of 600 ml / min and a water vapor flow rate of 100 ml / h, and react for 5 hours. The resulting tungsten powder has a Fisher particle size of 45.1 μm. The electron microscope image of the tungsten powder is shown below. Figure 6 As shown.

[0045] Example 4

[0046] Step 1: Add 500 mL of ammonium tungstate solution with a tungsten trioxide concentration of 250 g / L to an evaporator crystallizer, heat to 95°C, stir and maintain the temperature for 3 hours to obtain ammonium paratungstate powder and crystallization mother liquor. Filter to separate.

[0047] Step 2: Add the obtained ammonium paratungstate to 500 mL of ammonium tungstate solution (tungsten trioxide concentration is 120 g / L), heat to 95 °C, stir and crystallize at a constant temperature for 3 hours, then filter and separate. Add the obtained ammonium paratungstate powder to ammonium tungstate solution of the same composition for cyclic crystallization 3 times, and finally obtain ammonium paratungstate with a Fisher particle size of 63.5 μm.

[0048] Step 3: Add the ammonium paratungstate obtained in Step 2 into a tube furnace, control the heating rate to increase the temperature to 420℃ at 3℃ / min, and hold for 2 hours. Then further increase the temperature to 900℃ and hold for 1 hour to obtain tungsten trioxide with a Fisher particle size of 24.7um.

[0049] Step 4: Place the tungsten trioxide obtained in Step 3 into a tube furnace, heat it to 1100℃, with a hydrogen flow rate of 800 ml / min and a water vapor flow rate of 80 ml / h, and react for 4 hours. The resulting tungsten powder has a Fisher particle size of 33.4 μm.

[0050] Example 5

[0051] Step 1: Add 500 mL of ammonium paratungstate solution with a tungsten trioxide concentration of 240 g / L to an evaporator crystallizer, heat to 95°C, stir and maintain the temperature for 3 hours to obtain ammonium paratungstate powder and crystallization mother liquor. Filter and separate.

[0052] Step 2: Add the obtained ammonium paratungstate to 500 mL of ammonium tungstate solution (tungsten trioxide concentration is 120 g / L), heat to 95 °C, stir and crystallize at a constant temperature for 3 hours, then filter and separate. Add the obtained ammonium paratungstate powder to ammonium tungstate solution of the same composition for cyclic crystallization 4 times, and finally obtain ammonium paratungstate with a Fisher particle size of 65.1 μm.

[0053] Step 3: Add the ammonium paratungstate obtained in Step 2 into a tube furnace, control the heating rate to increase the temperature to 430℃ at 2℃ / min, and hold for 2 hours. Then, further increase the temperature to 900℃ and hold for 1 hour to obtain tungsten trioxide with a Fisher particle size of 24.8 μm.

[0054] Example 6

[0055] Step 1: Add 500 mL of ammonium tungstate solution with a tungsten trioxide concentration of 250 g / L to an evaporator crystallizer, heat to 95°C, and stir and crystallize at a constant temperature for 3 hours. Step 4: Place the tungsten trioxide obtained in Step 3 into a tube furnace, heat to 1200°C, with a hydrogen flow rate of 400 mL / min and a water vapor flow rate of 120 mL / h, and react for 3 hours. The tungsten trioxide is not completely reduced to tungsten powder and contains some tungsten dioxide. Its Fisher particle size is 23.5 μm. Scanning electron microscopy and XRD analysis images are shown below. Figure 7 and Figure 8 As shown. From reaction equations (2) and (3), it can be seen that the higher the water content in the hydrogen gas, the more it inhibits the reaction from proceeding to the right, which is detrimental to the complete reduction of tungsten powder. Because the water vapor flow rate is relatively large in this embodiment, tungsten trioxide is not completely reduced to tungsten powder, and some tungsten dioxide remains. Ammonium paratungstate powder and crystallization mother liquor. Filtration separation.

[0056] Step 2: Add the obtained ammonium paratungstate to 500 mL of ammonium tungstate solution (tungsten trioxide concentration is 120 g / L), heat to 95 °C, stir and crystallize at a constant temperature for 2 hours, then filter and separate. Add the obtained ammonium paratungstate powder to ammonium tungstate solution of the same composition for three cycles of crystallization, and finally obtain ammonium paratungstate with a Fisher particle size of 57.6 μm.

[0057] Step 3: Add the ammonium paratungstate obtained in Step 2 into a tube furnace, control the heating rate to increase the temperature to 420℃ at 3℃ / min, and hold for 3 hours. Then further increase the temperature to 900℃ and hold for 1 hour to obtain tungsten trioxide with a Fisher particle size of 22.3 μm.

[0058] Step 4: Place the tungsten trioxide obtained in Step 3 into a tube furnace, heat it to 1100℃, with a hydrogen flow rate of 1000ml / min and a water vapor flow rate of 150ml / h, and react for 5 hours to obtain tungsten powder with a Fisher particle size of 36.6um.

Claims

1. A method for preparing ultra coarse tungsten powder from an ammonium tungstate solution, characterized in that, The method comprises the following steps: Step one, add a certain concentration of ammonium tungstate solution into an evaporative crystallizer, stir and heat to a certain temperature, then evaporate at constant temperature for a certain time, separate by filtration to obtain ammonium paratungstate powder, wherein the tungsten trioxide concentration in the certain concentration of ammonium tungstate solution is 200-250 g / L; Step two, add ammonium tungstate solution with WO3 concentration of 110-120 g / L into an evaporative crystallizer, stir and heat to a certain temperature, then add the ammonium paratungstate powder obtained in step one, evaporate and crystallize at constant temperature for a certain time, filter to obtain secondary crystallized ammonium paratungstate powder; repeat the crystallization to prepare coarse-grained ammonium paratungstate with Fisher particle size greater than 50 μm, wherein the number of times of the repeated crystallization is 2-4 times; Step three, add the obtained coarse-grained ammonium paratungstate powder into a tube furnace, control a certain heating rate to raise the temperature to 400-430 ºC, then keep the temperature for a certain time, continue to raise the temperature to 900 ºC and keep the temperature for a certain time to obtain coarse-grained tungsten trioxide powder, wherein the heating rate is 1-5 ºC / min, and the temperature interval of 400-430 ºC is kept for 2-3 hours; Step four, add the obtained tungsten trioxide powder into a tube furnace, raise the temperature to a certain temperature, introduce hydrogen containing a certain proportion of water vapor into the tube furnace for reduction, then keep the temperature for a certain time to obtain super coarse tungsten powder, wherein the water vapor flow rate is 50-150 ml / h.

2. The method of claim 1, wherein, Step one, the temperature is 90-95 ºC, and the crystallization time is 2-4 hours.

3. The method of claim 1, wherein, Step two, the crystallization temperature is 90-95 ºC, and the crystallization time is 1-3 hours.

4. The method of claim 1, wherein, Step three, the temperature interval of 900 ºC is kept for 1 hour.

5. The method of claim 1, wherein, Step four, the reduction temperature is 900-1200 ºC, the hydrogen flow rate is 200-1000 ml / min, and the reaction time is 1-5 hours.

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