Preparation method of polyhedral molybdenum powder

Abstract

The invention relates to a preparation method of polyhedral molybdenum powder, belongs to the technical field of rare metal powder metallurgy, and solves the problems that in the prior art, molybdenum powder is easy to sinter to cause agglomeration and the morphology is not easy to control. Comprising the following steps: (1) mixing a peroxymolybdic acid solution with metal cations, and performing evaporative crystallization to obtain metal cation-doped peroxymolybdic acid powder with a needle-like crystal structure; in the mixture of the peroxymolybdic acid solution and the metal cations, the mass concentration of the metal cations is 0.05-0.1%; and (2) the acicular crystal structure peroxymolybdic acid powder doped with the metal cations is put into a material boat of a reduction furnace, primary reduction and secondary reduction are sequentially carried out, and the polyhedral molybdenum powder is obtained. 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 polyhedral 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 polyhedral 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 polyhedral molybdenum powder, the method comprising:

[0006] (1) A peroxymolybdic acid solution was mixed with a metal cation and evaporated to crystallize, resulting in a peroxymolybdic acid powder with a needle-like crystal structure doped with metal cations; the mass concentration of the metal cations in the mixture of peroxymolybdic acid solution and metal cations was 0.05-0.1%.

[0007] (2) The needle-shaped peroxymolybdic acid powder doped with metal cations is loaded into the material boat of the reduction furnace and subjected to a first reduction and a second reduction in sequence to obtain polyhedral molybdenum powder.

[0008] Preferably, the concentration of molybdenum ions in the peroxymolybdic acid solution is 150-200 g / L.

[0009] Preferably, the temperature of the secondary reduction is 800-900℃.

[0010] Preferably, the hydrogen flow rate for the secondary reduction is 12-20 m³ / h. 3 / h.

[0011] Preferably, the pushing speed of the secondary reduction is 30-60 min / pass.

[0012] Preferably, the secondary reduction time is 8-15 hours.

[0013] Preferably, the metal cation is K. + .

[0014] Preferably, the evaporation and crystallization temperature is 70-95°C.

[0015] Preferably, the evaporation crystallization includes: rotating and stirring a mixture of peroxymolybdic acid solution and metal cations at an evaporation crystallization temperature; after evaporation until a large number of solid particles are suspended in the solution, performing solid-liquid separation; drying the separated solids to obtain peroxymolybdic acid powder with a needle-like crystal structure doped with metal cations.

[0016] Preferably, the rotational speed of the rotary stirrer is 200-600 r / min.

[0017] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0018] 1. In this invention, the needle-like crystal structure of peroxymolybdic acid doped with metal cations gradually grows larger and agglomerates during the first reduction, providing conditions for the new crystals to grow larger during the second reduction; during the second reduction, molten metal cation-containing crystals (e.g., KOH crystals) are formed, providing nucleation sites for molybdenum powder and helping to grow into multifaceted crystals.

[0019] 2. The raw material peroxymolybdic acid of this invention has a needle-like crystal structure. After adding cations, it forms a needle-like crystal structure peroxymolybdic acid doped with metal cations. This needle-like crystal structure of peroxymolybdic acid exhibits good dispersibility and extremely high specific surface area. By introducing metal cations, the arrangement of the needle-like crystals of peroxymolybdic acid is altered, changing the difficulty of hydrogen reaching the interior of the crystals. This changes the mechanism of the partial reduction reaction, ultimately producing a polyhedral molybdenum powder. This invention uses needle-like crystal structure peroxymolybdic acid as a raw material, which has good dispersibility, is not prone to excessive agglomeration, and its morphology is easily controlled (the Fisher particle size of the polyhedral nano-molybdenum powder is 1.7-2.3 μm).

[0020] 3. The reduction process of this invention is a single-temperature zone, and the reduction process is simple.

[0021] 4. This invention can obtain polyhedral molybdenum powder by controlling the amount of metal cations added. By further coordinating the reduction conditions, the morphology and grain size of the polyhedral molybdenum powder can be controlled more precisely.

[0022] 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.

[0023] 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

[0024] 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.

[0025] Figure 1 A scanning electron microscope image of peroxymolybdic acid with a needle-like crystal structure doped with metal cations obtained in Example 1;

[0026] Figure 2 This is a scanning electron microscope image of the polyhedral molybdenum nanoparticles obtained in Example 1. Detailed Implementation

[0027] 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.

[0028] This invention provides a method for preparing polyhedral molybdenum powder, characterized in that the preparation method includes:

[0029] (1) A peroxymolybdic acid solution is mixed with metal cations and evaporated to crystallize, thereby obtaining peroxymolybdic acid powder with a needle-like crystal structure doped with metal cations; the mass concentration of metal cations in the mixture of peroxymolybdic acid solution and metal cations is 0.05-0.1%, for example, 0.06%, 0.07%, 0.08%, 0.09%; as the content of metal cations increases, the particle size of polyhedral grains can be effectively increased, but if the concentration of metal cations is too high, the width of the needle-like crystals will increase and agglomerate;

[0030] (2) The needle-shaped peroxymolybdic acid powder doped with metal cations is loaded into the material boat of the reduction furnace and subjected to a first reduction and a second reduction in sequence to obtain polyhedral molybdenum powder.

[0031] Compared with existing technologies, the peroxymolybdic acid used in this invention has a needle-like crystal structure. After adding cations, it forms a needle-like crystal structure of peroxymolybdic acid doped with metal cations. This needle-like crystal structure of peroxymolybdic acid exhibits excellent dispersibility and extremely high specific surface area. By introducing metal cations, the arrangement of the needle-like crystals of peroxymolybdic acid is altered, changing the difficulty of hydrogen reaching the interior of the crystals. This changes the mechanism of the partial reduction reaction, ultimately producing a molybdenum powder with a polyhedral morphology. This invention uses needle-like crystal structure peroxymolybdic acid as a raw material, which has good dispersibility, is not prone to agglomeration, and its morphology is easily controlled.

[0032] In this invention, the preparation method of the peroxymolybdic acid solution includes the following steps:

[0033] (a) Molybdenum calcined sand is leached with inorganic acid to obtain a molybdenum-containing inorganic acid leachate;

[0034] (b) Molybdenum was extracted from the leachate obtained in step (a) using a cationic extractant to obtain a molybdenum acyl cation loaded with molybdenum cations (MoO2). 2+ The organic phase and raffinate;

[0035] (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 peroxymolybdic acid solution.

[0036] For example, in step (a), the leaching temperature is 75-96°C, more preferably 85-95°C.

[0037] For example, in step (a), the leaching pressure is atmospheric pressure.

[0038] For example, in step (a), the leaching time is 2-6 hours.

[0039] For example, in step (a), the inorganic acid is one or more of sulfuric acid, nitric acid, and hydrochloric acid.

[0040] 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.

[0041] For example, in step (b), the cationic extractant is one or more of P507, P204 or Cyanex272.

[0042] 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%.

[0043] 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.

[0044] For example, in step (c), the mass concentration of hydrogen peroxide is 10-20%.

[0045] 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.

[0046] For example, the molybdenum calcined sand can be commercially available.

[0047] For example, the concentration of molybdenum ions in the peroxymolybdic acid solution is 100-200 g / L. Examples include 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.

[0048] For example, the metal cation is K. + Na + Ca 2+ and Mg 2+ At least one of the following. Because the national standards require low content of elements such as Ca and Mg, the preferred metal cation is K. + and / or Na + K is further preferred. + .

[0049] For example, the metal cation is added in the form of an alkali.

[0050] For example, in step (1), the evaporation crystallization temperature is 70-95°C, more preferably 80-95°C. For example, 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, and 94°C. If the evaporation crystallization temperature is too low, the crystal grains will be too dispersed and fine, and if the temperature is too high, the reaction will be too violent.

[0051] Specifically, the evaporation crystallization includes: rotating and stirring a mixture of peroxymolybdic acid solution and metal cations at an evaporation crystallization temperature; after evaporation until a large number of solid particles are suspended in the solution, performing solid-liquid separation; drying the separated solids to obtain peroxymolybdic acid with a needle-like crystal structure doped with metal cations.

[0052] 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.

[0053] For example, a pressure filter 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 doped with metal cations.

[0054] The evaporation and crystallization process of this invention is simple and easy to control, resulting in needle-like peroxymolybdic acid doped with metal cations with a width of 30-140 nm and a length of over 5 μm. It exhibits excellent dispersibility, with a width of only about 100 nanometers, significantly increasing its specific surface area. Simultaneously, the dispersed and cross-arranged 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.

[0055] In this invention, the purpose of the first reduction is to reduce peroxymolybdic acid to molybdenum dioxide.

[0056] For example, the temperature of the first reduction is 540-580℃, such as 550℃, 560℃, or 570℃. If the first reduction temperature is too low, the reduction time will be too long; if the first reduction temperature is too high, the salt may melt, resulting in coarse grains. Furthermore, since the first reduction is an exothermic reaction, if the temperature is too high, the local temperature will exceed the reduction temperature.

[0057] For example, the hydrogen flow rate for the first reduction is 2-4 m³ / h. 3 / h. If the hydrogen flow rate is too low for a single reduction, the reduction time will increase; if the hydrogen flow rate is too high for a single reduction, it may cause uneven grain size.

[0058] For example, the pushing speed of the boat in one restoration is 30-60 min / pass.

[0059] 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 grain enlargement or even over-reduction.

[0060] In this invention, the molybdenum dioxide obtained from the first reduction is cooled to room temperature and then fed back into the material boat of the reduction furnace for a second reduction. The purpose of the second reduction is to reduce molybdenum dioxide to molybdenum and form polyhedral molybdenum powder.

[0061] For example, the secondary reduction temperature is 800-900℃, such as 820℃, 840℃, 860℃, or 880℃. Temperatures that are too high or too low during the secondary reduction will affect the formation of the polyhedral morphology.

[0062] For example, the hydrogen flow rate for the secondary reduction is 12-20 m³ / h. 3 / h. If the hydrogen flow rate is too low during the secondary reduction, the reduction time will increase; if the hydrogen flow rate is too high, the growth will be too fast, affecting the morphology.

[0063] For example, the pushing speed of the secondary restoration is 30-60 min / pass.

[0064] For example, the secondary reduction time is 8-15 hours, such as 10 hours, 12 hours, or 14 hours. If the time is too short, the reduction will be insufficient; if the time is too long, the crystal will grow too large.

[0065] In this invention, the grain size of polyhedrons can be effectively increased by raising the secondary reduction temperature, but it cannot be increased indefinitely, as excessively high temperatures will cause changes in morphology.

[0066] The polyhedral molybdenum powder prepared by this invention can be used in powder metallurgy, molybdenum sputtering targets and other fields.

[0067] The preparation method of the polyhedral molybdenum powder of the present invention will be further illustrated below through specific embodiments.

[0068] Example 1

[0069] This embodiment provides a method for preparing polyhedral molybdenum powder, including:

[0070] (1) Preparation of peroxymolybdic acid solution

[0071] (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.

[0072] (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;

[0073] (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 = 3:1 and the number of back-extraction stages is 3, to obtain a molybdenum back-extraction solution, i.e., a peroxymolybdic acid solution, with a molybdenum ion concentration of 100 g / L.

[0074] (2) Preparation of needle-like crystal structure peroxymolybdic acid doped with metal cations: Potassium hydroxide was added to a peroxymolybdic acid solution, and the mass concentration of potassium ions in the mixture was 0.06%. After complete dissolution, the mixture was placed in a crystallization vessel and evaporated at 85°C with a 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 doped with metal cations with a width of 70-130 nm and a length of 5-10 μm. Figure 1 As shown.

[0075] (3) Primary reduction: Peroxymolybdic acid powder with a needle-like crystal structure doped with metal cations is loaded into the boat of the reduction furnace for primary reduction at a temperature of 560℃ and a hydrogen flow rate of 3m³ / h. 3 The boat pushing speed is 40 min / pass, and the time is 360 min. After one reduction cycle, the molybdenum dioxide obtained from the reduction is cooled to room temperature in the cooling zone.

[0076] (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 850℃ and a hydrogen flow rate of 18m³ / h. 3 The boat pushing speed was 40 min / pass, and the time was 10 h. After the second reduction, the reduced molybdenum powder was cooled to room temperature in the cooling zone. The extracted molybdenum powder was then passed through a 200-mesh sieve to obtain polyhedral nano-molybdenum powder with a Fisher particle size of 1.8 μm. Figure 2 As shown.

[0077] Example 2

[0078] This embodiment provides a method for preparing polyhedral molybdenum powder similar to that of Example 1, except that the mass concentration of potassium ions is 0.07%. The resulting needle-like crystal structure of peroxymolybdic acid doped with metal cations has a width of 70-130 nm and a length of 5-10 μm. The resulting polyhedral nano-molybdenum powder has a Fisher particle size of 1.86 μm.

[0079] Example 3

[0080] This embodiment provides a method for preparing polyhedral molybdenum powder similar to that of Example 1, except that the mass concentration of potassium ions is 0.1%. The resulting needle-like crystal structure of peroxymolybdic acid doped with metal cations has a width of 70-140 nm and a length of 5-15 μm. The resulting polyhedral nanoparticle molybdenum powder has a Fisher particle size of 1.94 μm.

[0081] Example 4

[0082] This embodiment provides a method for preparing polyhedral molybdenum powder similar to that in Embodiment 1, except that the crystallization evaporation temperature is 70°C.

[0083] The needle-like crystal structure of peroxymolybdic acid doped with metal cations was obtained with a width of 50-90 nm and a length of 3-8 μm.

[0084] Example 5

[0085] This embodiment provides a method for preparing polyhedral molybdenum powder similar to that in Embodiment 1, except that the rotational stirring speed during crystallization and evaporation is 450 r / min.

[0086] The needle-like crystal structure of peroxymolybdic acid doped with metal cations was obtained with a width of 50-130 nm and a length of 5-10 μm. The Fisher particle size of the polyhedral molybdenum nanoparticles was 1.79 μm.

[0087] Example 6

[0088] This embodiment provides a method for preparing polyhedral molybdenum powder similar to that in Example 1, except that the reduction temperature is 520°C. The resulting polyhedral nano-molybdenum powder has a Fisher particle size of 1.95 μm.

[0089] Example 7

[0090] This embodiment provides a method for preparing polyhedral molybdenum powder similar to that in Example 1, except that the secondary reduction temperature is 780℃. The resulting powder is a mixture of non-polyhedral and polyhedral nano-molybdenum powders with a Fisher particle size of 2.23 μm.

[0091] Example 8

[0092] This embodiment provides a method for preparing polyhedral molybdenum powder similar to that in Example 1, except that the secondary reduction temperature is 880℃. The resulting polyhedral nano-molybdenum powder has a Fisher particle size of 1.82 μm.

[0093] Example 9

[0094] This embodiment provides a method for preparing polyhedral molybdenum powder similar to that in Example 1, except that the secondary reduction temperature is 910℃. The resulting molybdenum powder has a Fisher particle size of 1.73 μm. At high temperatures, some grains do not nucleate using molten salt, resulting in uneven morphology, including both polyhedral nanoparticles and non-polyhedral molybdenum powder.

[0095] 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 polyhedral molybdenum powder, characterized in that, The preparation method includes: (1) A peroxymolybdic acid solution was mixed with a metal cation and evaporated to crystallize, resulting in a needle-like crystal structure of peroxymolybdic acid doped with metal cations; the mass concentration of the metal cations in the mixture of peroxymolybdic acid solution and metal cations was 0.05-0.1%; (2) The needle-shaped peroxymolybdic acid doped with metal cations is loaded into the boat of the reduction furnace and subjected to a first reduction and a second reduction in sequence to obtain polyhedral molybdenum powder.

2. The preparation method according to claim 1, characterized in that, The concentration of molybdenum ions in the peroxymolybdic acid solution is 150-200 g / L.

3. The preparation method according to claim 1, characterized in that, The temperature for the secondary reduction is 800-900℃.

4. The preparation method according to claim 1, characterized in that, The hydrogen flow rate for the secondary reduction is 12-20 m³ / h. 3 / h.

5. The preparation method according to claim 1, characterized in that, The speed of the secondary reduction is 30-60 min / pass.

6. The preparation method according to claim 1, characterized in that, The secondary reduction takes 8-15 hours.

7. The preparation method according to claim 1, characterized in that, The metal cation is K. + Na + Ca 2+ and Mg 2+ At least one of them.

8. The preparation method according to claim 1, characterized in that, The evaporation and crystallization temperature is 70-95℃.

9. The preparation method according to claim 8, characterized in that, The evaporation crystallization process includes: rotating and stirring a mixture of peroxymolybdic acid solution and metal cations at an evaporation crystallization temperature; after evaporation until a large number of solid particles are suspended in the solution, solid-liquid separation is performed; the separated solids are dried to obtain peroxymolybdic acid with a needle-like crystal structure doped with metal cations.

10. The preparation method according to claim 9, characterized in that, The rotational speed of the stirring is 200-600 r / min.

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