Preparation method of long-strip-shaped molybdenum powder

Abstract

The invention relates to a preparation method of long-strip-shaped molybdenum powder, belongs to the technical field of rare metal powder metallurgy, and solves the problems that in the prior art, molybdenum powder is prone to sintering, agglomeration is caused, and the morphology is not easy to control. The preparation method comprises the following steps: filling acicular crystal structure peroxymolybdic acid into a material boat of a reduction furnace, and sequentially carrying out primary reduction and secondary reduction; the temperature of the primary reduction is 540-620 DEG C; the morphology of the molybdenum powder prepared by the method is easy to control.

Description

Technical Field

[0001] This invention relates to the field of rare metal powder metallurgy technology, and in particular to a method for preparing elongated molybdenum powder. Background Technology

[0002] Currently, the most common industrial method for preparing molybdenum powder is the hydrogen reduction of molybdenum trioxide or ammonium molybdate. The raw materials for this method are typically in lumps, with a Fisher particle size often concentrated between 5-20 μm. The process generally involves first calcining ammonium molybdate to decompose it into ammonia and water, producing molybdenum trioxide. The molybdenum trioxide then undergoes a two-step hydrogen reduction: the first reduction to molybdenum trioxide is followed by further reduction to molybdenum dioxide at multiple temperature zones, and the second reduction to molybdenum dioxide is followed by further reduction to molybdenum powder at multiple temperature zones. The agglomerated powder also requires sieving during this intermediate step. Several industrial methods for preparing ultrafine / nano-sized molybdenum powder also exist, primarily including the reduction of ammonium octamolybdate, ball milling and chemical pretreatment, and the hydrogen reduction method using sublimated molybdenum trioxide.

[0003] However, existing methods for preparing molybdenum powder are prone to sintering and agglomeration, have complicated reduction processes, and are difficult to control the morphology and particle size of molybdenum powder. Furthermore, the process of roasting ammonium molybdate to produce molybdenum trioxide inevitably generates ammonia nitrogen waste gas. The pungent ammonia nitrogen waste gas not only limits workers' production but also increases the additional cost of exhaust gas recovery. Summary of the Invention

[0004] In view of the above analysis, the present invention aims to provide a method for preparing elongated molybdenum powder to solve at least one of the following problems existing in the current molybdenum powder preparation method: (1) easy to sinter and cause agglomeration; (2) cumbersome reduction process; (3) difficult to control the morphology and particle size of molybdenum powder; (4) generation of ammonia nitrogen waste gas.

[0005] This invention provides a method for preparing elongated molybdenum powder, the method comprising: loading needle-shaped peroxymolybdic acid into a boat in a reduction furnace, and performing a first reduction and a second reduction sequentially;

[0006] The temperature for the first reduction is 540-620℃.

[0007] Preferably, the hydrogen flow rate for the primary reduction is 0.5-3 m³ / h. 3 / h.

[0008] Preferably, the temperature of the secondary reduction is 650-850℃.

[0009] Preferably, the hydrogen flow rate for the secondary reduction is 5-40 m³ / h. 3 / h.

[0010] Preferably, the method for preparing the needle-like crystal structure of peroxymolybdic acid includes the following steps:

[0011] (a) Molybdenum calcined sand is leached with inorganic acid to obtain a molybdenum-containing inorganic acid leachate;

[0012] (b) Molybdenum in the leachate obtained in step (a) is extracted with a cationic extractant to obtain an organic phase loaded with molybdenum acyl cations and a raffinate;

[0013] (c) Using hydrogen peroxide solution as a back-extraction agent, it is mixed with an organic phase loaded with molybdenum acyl cations to obtain a molybdenum back-extraction solution, namely a peroxymolybdic acid solution.

[0014] (d) Evaporate the peroxymolybdic acid solution to crystallize and obtain peroxymolybdic acid with a needle-like crystal structure.

[0015] Preferably, in step (a), the leaching temperature is 75-96°C.

[0016] Preferably, in step (a), the inorganic acid is one or more of sulfuric acid, nitric acid, and hydrochloric acid.

[0017] Preferably, in step (a), the concentration of the inorganic acid is 2-4 mol / L.

[0018] Preferably, in step (b), the cationic extractant is mixed with kerosene to form a kerosene solution and then added to the leachate, wherein the volume fraction of the cationic extractant in the kerosene solution is 10-50%.

[0019] Preferably, in step (c), the mass concentration of hydrogen peroxide is 10-20%.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] 1. In this invention, the fast gas propagation speed of needle-shaped crystal grains allows for a rapid reaction, enabling two chemical vapor phase transport processes during a single reduction phase: from MoO3 to the mesophase and then to MoO2. Furthermore, the nano-needle-shaped crystal grains provide conditions for the formation of new nano-crystals. These nano-needle-shaped crystal grains exhibit sufficient anisotropy, and the single reduction at temperatures above 500°C causes the formation of both MoO3 and Mo4O2. 11 The formation of a fusible eutectic provides conditions for the elongated growth of MoO2. Subsequent secondary reduction, maintaining a suitable temperature and hydrogen flow rate, ensures that the crystal undergoes pseudomorphic transformation to obtain elongated molybdenum powder.

[0022] 2. The raw material peroxymolybdic acid of this invention has a needle-like crystal structure. This needle-like structure provides excellent dispersibility and an extremely high specific surface area. During the reduction process, the arrangement of the needle-like crystals changes, altering the difficulty for hydrogen to reach the interior of the crystals. This, in turn, changes the mechanism of the partial reduction reaction, ultimately resulting in the preparation of elongated molybdenum powder. This invention uses needle-like peroxymolybdic acid as a raw material, which exhibits good dispersibility and is less prone to excessive agglomeration (resulting in molybdenum powder with a Fisher particle size of 0.7-1.1 μm). The morphology is easily controlled (the preferred width of the molybdenum powder is 200-900 nm, and the length is 2-4 μm).

[0023] 3. The reduction process of this invention is a single-temperature zone, and the reduction process is simple.

[0024] 4. By controlling the reduction conditions, this invention can more precisely control the morphology and grain size of the elongated molybdenum powder.

[0025] 5. The method of the present invention uses peroxymolybdic acid as raw material, and the preparation process does not generate ammonia nitrogen waste gas that affects the environment.

[0026] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0027] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0028] Figure 1 Here is a scanning electron microscope image of the elongated molybdenum powder obtained in Example 1 of this invention;

[0029] Figure 2 This is a scanning electron microscope image of peroxymolybdic acid with a needle-like crystal structure obtained in Example 1 of the present invention;

[0030] Figure 3 Scanning electron microscope image of the elongated molybdenum powder obtained in Example 11. Detailed Implementation

[0031] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0032] This invention provides a method for preparing elongated molybdenum powder, the method comprising: loading needle-shaped peroxymolybdic acid into a boat in a reduction furnace, and performing a first reduction and a second reduction sequentially;

[0033] The temperature for the first reduction is 540-620℃, for example 550℃, 560℃, 570℃, 580℃, 590℃, or 610℃. If the temperature is too low, the grains will not grow into elongated strips; if the temperature is too high, over-reduction will occur, resulting in molybdenum powder.

[0034] Compared with existing technologies, the peroxymolybdic acid used in this invention has a needle-like crystal structure. This needle-like structure provides excellent dispersibility and an extremely high specific surface area. During the reduction process, the arrangement of the needle-like crystals changes, altering the difficulty for hydrogen to reach the interior of the crystals. This, in turn, changes the mechanism of the partial reduction reaction, ultimately resulting in the preparation of elongated molybdenum powder. This invention uses peroxymolybdic acid with a needle-like crystal structure as a raw material, which exhibits good dispersibility, is not prone to agglomeration, and allows for easy morphological control.

[0035] In this invention, the preparation method of the needle-like crystal structure peroxymolybdic acid includes the following steps:

[0036] (a) Molybdenum calcined sand is leached with inorganic acid to obtain a molybdenum-containing inorganic acid leachate;

[0037] (b) Molybdenum in the leachate obtained in step (a) is extracted with a cationic extractant to obtain an organic phase loaded with molybdenum acyl cations and a raffinate;

[0038] (c) Using hydrogen peroxide solution as a back-extraction agent, it is mixed with an organic phase loaded with molybdenum acyl cations to obtain a molybdenum back-extraction solution, namely a peroxymolybdic acid solution.

[0039] (d) Evaporate the peroxymolybdic acid solution to crystallize and obtain peroxymolybdic acid with a needle-like crystal structure.

[0040] For example, in step (a), the leaching temperature is 75-96°C.

[0041] For example, in step (a), the leaching pressure is atmospheric pressure.

[0042] For example, in step (a), the leaching time is 2-6 hours.

[0043] For example, in step (a), the inorganic acid is one or more of sulfuric acid, nitric acid, and hydrochloric acid.

[0044] For example, in step (a), the concentration of the inorganic acid is 2-4 mol / L, and the leaching liquid-to-solid ratio (L / Kg) is 3:1-10:1.

[0045] For example, in step (b), the cationic extractant is one or more of P507, P204 or Cyanex272.

[0046] For example, in step (b), the cationic extractant is mixed with kerosene to form a kerosene solution and then added to the leachate, wherein the volume fraction of the cationic extractant in the kerosene solution is 10-50%.

[0047] For example, in step (b), the extraction ratio O / A = 2:1-1:3; multi-stage countercurrent extraction is used, with 3-5 extraction stages.

[0048] For example, in step (c), the mass concentration of hydrogen peroxide is 10-20%.

[0049] For example, in step (c), the back-extraction ratio O / A = 3:1-5:1, and multi-stage countercurrent back-extraction is used, with 2-5 back-extraction stages. By adjusting the back-extraction ratio, peroxymolybdic acid solutions with different molybdenum ion concentrations can be obtained.

[0050] For example, the concentration of molybdenum ions in the peroxymolybdic acid solution is 90-200 g / L. Examples include 100 g / L, 110 g / L, 130 g / L, 150 g / L, 170 g / L, and 190 g / L. Too low a concentration of molybdenum ions will result in low crystallization rate and smaller, more dispersed needle-like crystals, affecting subsequent particle size distribution; too high a concentration of molybdenum ions will result in excessively large needle-like crystals.

[0051] For example, in step (d), the evaporation crystallization temperature is 70-95°C, more preferably 80-95°C. Examples include 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, and 94°C. Too low an evaporation crystallization temperature will result in excessively dispersed and fine crystal grains, while too high a temperature will cause the reaction to be too vigorous.

[0052] Specifically, the evaporation crystallization includes: rotating and stirring the peroxymolybdic acid solution at the evaporation crystallization temperature, evaporating until a large number of solid particles are suspended in the solution, performing solid-liquid separation, drying the separated solid, and obtaining peroxymolybdic acid with a needle-like crystal structure.

[0053] For example, the rotational speed of the stirring is 200-600 r / min, more preferably 200-350 r / min. Examples include 220 r / min, 240 r / min, 260 r / min, 280 r / min, 300 r / min, 320 r / min, and 340 r / min. Too low a speed will result in a large amount of solid adhering to the outer wall, while too high a speed may cause uneven grain development.

[0054] For example, a filter press is used for solid-liquid separation, and the separated wet filter cake is dried using a microwave dryer to obtain peroxymolybdic acid with a needle-like crystal structure.

[0055] The evaporation and crystallization process of this invention is simple and easy to control, resulting in needle-like crystal structures of peroxymolybdic acid with a width of 30-100 nm and a length of over 5 μm. It exhibits excellent dispersibility, with a width of less than 100 nanometers, significantly increasing its specific surface area. Simultaneously, the dispersed and interwoven arrangement of the crystal grains creates a porous structure, allowing hydrogen gas to rapidly penetrate the interior of the crystals, thereby accelerating the reduction reaction and reducing the reduction time.

[0056] For example, the molybdenum calcined sand can be commercially available.

[0057] In this invention, elongated grains are formed in a single reduction process. The length and width of the elongated grains can be controlled by adjusting the temperature, hydrogen flow rate, and time of the single reduction.

[0058] Specifically, when the primary reduction temperature is 540-560℃, the higher the temperature, the longer the grains; when the primary reduction temperature is greater than 560℃ and less than or equal to 620℃, the higher the temperature, the wider the grains.

[0059] For example, the hydrogen flow rate for the first reduction is 0.5-3 m³ / h. 3 / h, further preferably 0.5-1.8m 3 / h, for example 0.7m 3 / h, 0.9m 3 / h, 1.1m 3 / h, 1.3m 3 / h, 1.5m 3 / h etc. If the hydrogen flow rate is too low during the primary reduction, the reduction will be insufficient; if it is too high, the particle size will be uneven, and the width of the long strips of molybdenum powder will be increased, causing the grains to tend to be plate-like.

[0060] For example, the pushing speed of the boat in one restoration is 15-30 min / pass.

[0061] For example, the reduction time for one cycle is 240-420 min. Examples include 260 min, 300 min, 320 min, 350 min, 380 min, and 400 min. A reduction time that is too short will result in insufficient reduction and growth, while a time that is too long may cause the grains to become larger and wider, or even lead to over-reduction.

[0062] In this invention, after the long strip of molybdenum dioxide obtained from the first reduction is cooled to room temperature, it is fed back into the material boat of the reduction furnace for a second reduction. The purpose of the second reduction is to reduce the long strip of molybdenum dioxide to long strip of molybdenum.

[0063] The present invention can control the width of elongated grains by controlling the secondary reduction temperature. For example, increasing the secondary reduction temperature can effectively increase the width of elongated grains, but it cannot be increased indefinitely, as excessively high temperatures will cause changes in morphology.

[0064] For example, the secondary reduction temperature is 650-850℃. Examples include 660℃, 670℃, 680℃, 690℃, 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃, and 840℃. If the secondary reduction temperature is too low, complete reduction is difficult, and the oxygen content is too high, making cracks more likely. If the secondary reduction temperature is too high, the elongated morphology will disappear.

[0065] For example, the hydrogen flow rate for the secondary reduction is 5-40 m³ / h. 3 / h.

[0066] For example, the pushing speed of the secondary restoration is 30-60 min / pass.

[0067] For example, the secondary reduction time is 5-15 hours, such as 7 hours, 9 hours, 11 hours, or 13 hours. Too short a secondary reduction time will result in high oxygen content, while too long a time can easily cause grain growth and affect the morphology.

[0068] The elongated molybdenum powder prepared by this invention can be used to prepare alloys that are immiscible in pairs, and the interlaced elongated molybdenum powder provides conditions for the addition of other molten metals.

[0069] The preparation method of the elongated molybdenum powder of the present invention will be further illustrated below through specific embodiments.

[0070] Example 1

[0071] This embodiment provides a method for preparing elongated molybdenum powder, including:

[0072] (1) Preparation of peroxymolybdic acid solution

[0073] (a) Molybdenum calcined sand was leached with sulfuric acid with a concentration of 3 mol / L, the liquid-to-solid ratio (L / Kg) was 5:1, the temperature was 90℃, the pressure was normal, and the time was 4h to obtain an inorganic acid leaching solution containing molybdenum.

[0074] (b) The cationic extractant P507 was mixed with kerosene to prepare a kerosene solution, which was then added to the leachate to extract molybdenum from the leachate. The extraction ratio O / A = 1:1, the extraction stage was 4 stages, and the volume fraction of the cationic extractant in the kerosene solution was 30%. This yielded a molybdenum-loaded cation (MoO2) solution. 2+ The organic phase and raffinate;

[0075] (c) Using a 15% hydrogen peroxide solution as the back-extraction agent, it is mixed with an organic phase loaded with molybdenum acyl cations. The back-extraction ratio O / A = 4:1 and the number of back-extraction stages is 3, to obtain a molybdenum back-extraction solution, namely a peroxymolybdic acid solution, with a molybdenum ion concentration of 140 g / L.

[0076] (2) Preparation of needle-like crystal structure peroxymolybdic acid: The peroxymolybdic acid solution was placed in a crystallization vessel and evaporated at 85°C with a rotating stirring speed of 300 r / min. After evaporation until a large number of solid particles were suspended in the solution, solid-liquid separation was performed using a pressure filter. The separated wet filter cake was then dried using a microwave dryer to obtain needle-like crystal structure peroxymolybdic acid with a width of 50-100 nm and a length of 5-10 μm. Figure 2 As shown.

[0077] (3) Primary reduction: Needle-shaped peroxymolybdic acid powder is loaded into the feed boat of the reduction furnace for primary reduction at a temperature of 570℃ and a hydrogen flow rate of 2m³ / h. 3 The boat pushing speed is 20 min / pass, and the time is 300 min. After one reduction cycle, the molybdenum dioxide obtained from the reduction is cooled to room temperature in the cooling zone.

[0078] (4) Secondary reduction: The cooled molybdenum dioxide is loaded into a new boat and pushed into a secondary reduction furnace for reduction at a temperature of 700℃ and a hydrogen flow rate of 20m³ / h. 3 The boat pushing speed is 40 min / pass, and the time is 10 h. After the second reduction, the reduced molybdenum powder is cooled to room temperature in the cooling zone. The extracted molybdenum powder is then passed through a 200-mesh sieve to obtain elongated nano-molybdenum powder with a Fisher particle size of 0.78 μm, a width of 240-520 nm, and a length of 2-4 μm. Figure 1 As shown.

[0079] Example 2

[0080] This embodiment provides a method for preparing elongated molybdenum powder similar to that in Example 1, except that the primary reduction temperature is 590℃. The resulting elongated nano-molybdenum powder has a Fisher particle size of 0.88 μm, a width of 350-600 nm, and a length of 2-4 μm.

[0081] Example 3

[0082] This embodiment provides a method for preparing elongated molybdenum powder similar to that in Example 1, except that the primary reduction temperature is 610℃. The resulting elongated nano-molybdenum powder has a Fisher particle size of 0.95 μm, a width of 500-900 nm, and a length of 2-4 μm.

[0083] Comparative Example 1

[0084] This comparative example provides a method for preparing elongated molybdenum powder similar to that in Example 1, except that the primary reduction temperature is 640°C. The resulting molybdenum powder has a Fisher particle size of 1.1 μm, a width of 800-1000 nm, and a length of 1-2 μm, i.e., it is not elongated molybdenum powder.

[0085] Example 4

[0086] This embodiment provides a method for preparing elongated molybdenum powder similar to that in Example 1, except that the hydrogen flow rate for the first reduction is 1 m³ / s. 3 / h. The obtained elongated molybdenum nanoparticles have a Fisher particle size of 0.76 μm, a width of 200-500 nm, and a length of 2-4 μm.

[0087] Example 5

[0088] This embodiment provides a method for preparing elongated molybdenum powder similar to that in Embodiment 1, except that the hydrogen flow rate for the first reduction is 3m³ / h. 3 / h. The obtained elongated molybdenum nanoparticles have a Fisher particle size of 0.84 μm, a width of 350-550 nm, and a length of 2-4 μm.

[0089] Example 6

[0090] This embodiment provides a method for preparing elongated molybdenum powder similar to that in Example 1, except that the secondary reduction temperature is 750℃. The resulting elongated nano-molybdenum powder has a Fisher particle size of 0.71 μm, a width of 300-550 nm, and a length of 2-4 μm.

[0091] Example 7

[0092] This embodiment provides a method for preparing elongated molybdenum powder similar to that in Example 1, except that the secondary reduction temperature is 800℃. The resulting elongated nano-molybdenum powder has a Fisher particle size of 0.9 μm, a width of 400-600 nm, and a length of 2.3-4 μm.

[0093] Example 8

[0094] This embodiment provides a method for preparing elongated molybdenum powder similar to that in Example 1, except that the secondary reduction temperature is 880°C. The resulting molybdenum powder is elongated and exists alongside other powder morphologies.

[0095] Example 9

[0096] This embodiment provides a method for preparing elongated molybdenum powder similar to that in Embodiment 1, except that the crystallization evaporation temperature is 70°C.

[0097] The needle-like crystal structure of peroxymolybdic acid was obtained with a width of 30-70 nm and a length of 2-7 μm.

[0098] Example 10

[0099] This embodiment provides a method for preparing elongated molybdenum powder similar to that in Embodiment 1, except that the rotation speed of the stirring during crystallization and evaporation is 450 r / min.

[0100] The needle-like crystal structure of peroxymolybdic acid was obtained with a width of 30-150 nm and a length of 2-14 μm. The elongated nanoparticles of molybdenum had a Fisher particle size of 0.77 μm.

[0101] Example 11

[0102] This embodiment provides a method for preparing elongated molybdenum powder similar to that in Example 1, except that the molybdenum ion concentration in the peroxymolybdic acid solution is 90 g / L, resulting in elongated nano-molybdenum powder as shown in Example 1. Figure 3 As shown, the Fisher particle size is 0.55 μm, the width is 20-100 nm, and the length is 0.5-2 μm.

[0103] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing elongated molybdenum powder, characterized in that, The preparation method includes: loading needle-shaped crystal structured peroxymolybdic acid into a boat in a reduction furnace, and performing a first reduction and a second reduction in sequence; The temperature for the first reduction is 540-620℃.

2. The preparation method according to claim 1, characterized in that, The hydrogen flow rate for the first reduction is 0.5-3 m³ / h. 3 / h.

3. The preparation method according to claim 1, characterized in that, The temperature for the secondary reduction is 650-850℃.

4. The preparation method according to claim 1, characterized in that, The hydrogen flow rate for the secondary reduction is 5-40 m³ / h. 3 / h.

5. The preparation method according to claim 1, characterized in that, The preparation method of the needle-like crystal structure of peroxymolybdic acid includes the following steps: (a) Molybdenum calcined sand is leached with inorganic acid to obtain a molybdenum-containing inorganic acid leachate; (b) Molybdenum in the leachate obtained in step (a) is extracted with a cationic extractant to obtain an organic phase loaded with molybdenum acyl cations and a raffinate; (c) Using hydrogen peroxide solution as a back-extraction agent, it is mixed with an organic phase loaded with molybdenum acyl cations to obtain a molybdenum back-extraction solution, namely a peroxymolybdic acid solution. (d) Evaporate the peroxymolybdic acid solution to crystallize and obtain peroxymolybdic acid with a needle-like crystal structure.

6. The preparation method according to claim 5, characterized in that, In step (a), the leaching temperature is 75-96°C.

7. The preparation method according to claim 5, characterized in that, In step (a), the inorganic acid is one or more of sulfuric acid, nitric acid, and hydrochloric acid.

8. The preparation method according to claim 5, characterized in that, In step (a), the concentration of the inorganic acid is 2-4 mol / L.

9. The preparation method according to claim 5, characterized in that, In step (b), the cationic extractant is mixed with kerosene to prepare a kerosene solution, which is then added to the leachate. The volume fraction of the cationic extractant in the kerosene solution is 10-50%.

10. The preparation method according to claim 5, characterized in that, In step (c), the mass concentration of hydrogen peroxide is 10-20%.

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