Molybdenum dioxide material, molybdenum powder and methods of making

Abstract

The disclosure provides a molybdenum dioxide material, molybdenum powder and a preparation method, and relates to the technical field of powder material preparation. The preparation method of the molybdenum dioxide material comprises the following steps: adding a dispersing agent into water and stirring to mix uniformly to obtain a first transparent solution; adding a molybdenum salt into the first transparent solution and adjusting the pH to 3-6 to obtain a second transparent solution; transferring the second transparent solution into a reaction kettle to perform a hydrothermal homogeneous phase reaction, and performing washing and drying treatment after cooling to obtain a molybdenum trioxide material; mixing the molybdenum trioxide material with silica powder to obtain a composite powder; performing hydrogen reduction treatment on the composite powder to obtain a molybdenum dioxide material containing silica; and soaking the molybdenum dioxide material containing silica in an alkaline solution to remove the silica to obtain a molybdenum dioxide material. The disclosure can improve the quality of the molybdenum dioxide and molybdenum powder.

Description

Technical Field

[0001] This disclosure relates to the field of powder material preparation technology, and more specifically, to a molybdenum dioxide material, molybdenum powder, and a preparation method thereof. Background Technology

[0002] Molybdenum (Mo), a rare metal with a high melting point (approximately 2620℃), good electrical and thermal conductivity, a low coefficient of thermal expansion, and excellent high-temperature mechanical properties, plays an indispensable role in many strategic emerging fields such as aerospace, electronics and information technology, new energy, and powder metallurgy. With the rapid development of modern industrial technology, such as the rise of industries like 5G communication, semiconductor chips, high-end display panels, and new energy batteries, more stringent requirements have been placed on the performance of molybdenum powder. High-purity, highly dispersed ultrafine nano-molybdenum powder has gradually become the focus of industry research and application.

[0003] Molybdenum dioxide (MoO2), as a core transition metal oxide intermediate in the molybdenum industry chain, combines metal-like conductivity, good chemical stability, and controllable sintering activity. It is a key precursor for the preparation of high-purity molybdenum powder, molybdenum-based alloys, electronic functional materials, and catalytic materials, and is widely used in many high-end industrial fields such as metallurgy, electronics, energy, and aerospace.

[0004] Currently, the prepared molybdenum dioxide and molybdenum powder have poor quality issues.

[0005] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0006] The purpose of this disclosure is to provide a molybdenum dioxide material, molybdenum powder, and preparation method, thereby overcoming, at least to some extent, the problem of poor quality of molybdenum dioxide and molybdenum powder.

[0007] According to a first aspect of this disclosure, a method for preparing molybdenum dioxide material is provided, comprising: adding a dispersant to water and stirring to mix evenly to obtain a first transparent solution; adding a molybdenum salt to the first transparent solution and adjusting the pH to 3-6 to obtain a second transparent solution; transferring the second transparent solution to a reaction vessel for hydrothermal homogeneous reaction, and washing and drying after cooling to obtain molybdenum trioxide material; mixing the molybdenum trioxide material with silica powder to obtain a composite powder; subjecting the composite powder to hydrogen reduction treatment to obtain molybdenum dioxide material containing silica; and immersing the molybdenum dioxide material containing silica in an alkaline solution to remove silica to obtain molybdenum dioxide material.

[0008] Optionally, the dispersant is one or a mixture of PEG, CTAB, PVP, and tartaric acid; the molybdenum salt is one or a mixture of ammonium molybdate dihydrate, ammonium molybdate tetrahydrate, and ammonium molybdate heptahydrate.

[0009] Optionally, during the hydrothermal homogeneous reaction, the hydrothermal reaction temperature is 110℃~180℃ and the reaction time is 18h~24h.

[0010] Optionally, in the process of obtaining molybdenum trioxide material, the drying method is freeze drying or vacuum filtration drying; when the drying method is freeze drying, the freeze drying cold trap temperature is below -50℃, the vacuum degree is maintained below 15MPa during the drying process, and the drying time is greater than 12h; when the drying method is vacuum filtration drying, the vacuum filtration membrane used is an aqueous filter membrane with a pore size of 0.1μm ~ 1.2μm.

[0011] Optionally, during the hydrogen reduction treatment of the composite powder, the hydrogen reduction temperature is 400℃~700℃, the heating rate is 10℃ / min, and the reaction time is 1h~2h.

[0012] Optionally, the silica powder has a particle size of 15nm to 100nm and a purity of >99.5%.

[0013] According to a second aspect of this disclosure, a molybdenum dioxide material is provided, which is prepared using any of the above-described methods for preparing molybdenum dioxide materials.

[0014] According to a third aspect of this disclosure, a method for preparing molybdenum powder is provided, comprising: subjecting a molybdenum dioxide material to hydrogen reduction treatment to obtain an intermediate powder; wherein the molybdenum dioxide material is prepared using any of the above-described methods for preparing molybdenum dioxide material. The intermediate powder is then ball-milled and dispersed to obtain molybdenum powder.

[0015] Optionally, in the process of obtaining the intermediate powder, the hydrogen used is dry hydrogen, the reduction temperature is 800℃~1000℃, the heating rate is 10℃ / min, and the reaction time is 2h~4h.

[0016] Optionally, during the ball milling dispersion process, the ball-to-material ratio is 5~10:1, and the ball milling time is 1h~3h.

[0017] According to a fourth aspect of this disclosure, a molybdenum powder is provided, prepared using any of the above-described methods for preparing molybdenum powder.

[0018] In the exemplary embodiments of this disclosure, on the one hand, compared with molybdenum trioxide prepared by traditional calcination processes, this disclosure prepares molybdenum trioxide through a hydrothermal homogeneous reaction. Combined with adjustments to raw materials and process parameters, the crystal form and morphology of molybdenum trioxide can be precisely controlled. The product has a narrow particle size distribution, good dispersibility, and almost no hard agglomerates, eliminating the need for subsequent vigorous pulverization. The reaction is a homogeneous liquid-phase nucleation, without high-temperature solid-phase diffusion or dust pollution, and introduces very few impurities, laying the foundation for the subsequent preparation of highly dispersed ultrafine nano-molybdenum dioxide and molybdenum powder. On the other hand, this disclosure adds silica as a reducing heterogeneous nucleating agent for molybdenum trioxide to generate composite powder, achieving the transformation of MoO3 into Mo4O3. 11 Precise control of the entire MoO2 reduction process effectively regulates the gas-phase dissolution, migration, and deposition growth processes during the molybdenum trioxide reduction stage. Furthermore, the use of hydrogen reduction allows for effective control of molybdenum dioxide particle size and morphology, overcoming problems such as molybdenum dioxide agglomeration, poor particle size uniformity, and preferential crystal growth inherent in traditional molybdenum trioxide reduction methods. In addition, alkaline leaching of molybdenum dioxide not only removes residual silica, improving product purity, but also increases the specific surface area of ​​molybdenum dioxide, lowering the hydrogen reduction energy barrier for subsequent molybdenum preparation and reducing the reduction temperature. This enables the subsequent hydrogen deoxygenation and ball milling dispersion processes to obtain highly dispersed, uniformly sized ultrafine molybdenum nanoparticles. Moreover, the raw materials used in this disclosed embodiment are widely available, low-cost, and easy to promote.

[0019] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0021] Figure 1 A flowchart illustrating the preparation method of molybdenum dioxide material according to an embodiment of the present disclosure is shown.

[0022] Figure 2 A flowchart illustrating a method for preparing molybdenum powder according to an embodiment of the present disclosure is shown.

[0023] Figure 3 The X-ray diffraction pattern of molybdenum trioxide prepared in Example 1 of this disclosure is shown.

[0024] Figure 4 A scanning electron microscope image of molybdenum trioxide prepared in Example 1 of this disclosure is shown.

[0025] Figure 5 A scanning electron microscope image of molybdenum trioxide prepared in Example 1 of this disclosure after filtration, drying, and sheet formation is shown.

[0026] Figure 6 A scanning electron microscope image of molybdenum dioxide prepared in Example 1 of this disclosure is shown.

[0027] Figure 7 A scanning electron microscope image of the molybdenum powder prepared in Example 1 of this disclosure is shown. Detailed Implementation

[0028] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make this disclosure more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art. The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced with one or more of these specific details omitted, or other methods, processes, steps, etc., can be employed. In other instances, well-known technical solutions are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0029] Furthermore, the accompanying drawings are merely illustrative of this disclosure and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted. The flowcharts shown in the drawings are merely exemplary illustrations and do not necessarily include all steps. For example, some steps may be broken down, while others may be combined or partially combined; therefore, the actual order of execution may change depending on the actual situation. Additionally, all terms such as "first," "second," and "intermediate" below are for distinguishing purposes only and should not be construed as limiting the content of this disclosure.

[0030] Ultrafine nano-molybdenum powder possesses significant advantages such as small particle size, large specific surface area, high sintering activity, and strong reactivity. In the field of powder metallurgy, it can achieve high-density molding at relatively low sintering temperatures, effectively avoiding grain coarsening and producing molybdenum products with uniform structure and excellent mechanical properties. Currently, some methods for preparing ultrafine nano-molybdenum powder include direct hydrogen reduction, plasma reduction, molybdenum chloride vapor hydrogen reduction, electrical pulse discharge, and mechanical alloying. However, these methods all have certain limitations in practical applications. For example, the chemical vapor transport process in some hydrogen reduction processes is difficult to control, leading to localized agglomeration and abnormal growth of molybdenum powder. Plasma reduction and molybdenum chloride vapor hydrogen reduction processes are costly and have complex parameters, making industrialization difficult. Current molybdenum dioxide and molybdenum powder preparation still rely on traditional hydrogen reduction processes, which cannot simultaneously meet the requirements of high purity, high dispersibility, fine particle size, and good uniformity. Therefore, there is an urgent need in industry for a low-cost method to prepare high-quality ultrafine nano-molybdenum dioxide and molybdenum powder to solve the problem of molybdenum dioxide and molybdenum powder required for high-end electronic packaging and high-performance molybdenum products.

[0031] To address the aforementioned problems, this disclosure provides a method for preparing ultrafine nano-molybdenum dioxide and molybdenum powder. This method involves converting molybdenum salt into ribbon-like high-purity molybdenum trioxide via a hydrothermal homogeneous reaction, and subsequently adding nano-silica to provide more heterogeneous nucleation sites for molybdenum trioxide reduction. This not only lowers the reaction barrier but also effectively regulates the chemical vapor transport process, accelerating the molybdenum atom transport efficiency during molybdenum oxide reduction. Alkali leaching further enhances sample purity and increases the surface activity of molybdenum dioxide, effectively controlling the nucleation and growth processes during the reduction of molybdenum dioxide and molybdenum powder, inhibiting powder agglomeration and abnormal growth, and obtaining ultrafine nano-molybdenum dioxide and molybdenum powder. This solves the key technical problems of large particle size, wide particle size distribution, and poor dispersibility in nano-molybdenum dioxide and molybdenum powder prepared by other techniques.

[0032] Figure 1 A flowchart illustrating a method for preparing a molybdenum dioxide material according to an embodiment of this disclosure is shown schematically. (Reference) Figure 1 The method for preparing the molybdenum dioxide material according to the present disclosure may include the following steps: S102. Add the dispersant to water and stir to mix evenly to obtain a first transparent solution.

[0033] In exemplary embodiments of this disclosure, the dispersant may be one or a mixture of PEG (Polyethylene Glycol), CTAB (Cetyltrimethylammonium Bromide), PVP (Polyvinylpyrrolidone), and tartaric acid. Additionally, the water used may be deionized water or ultrapure water.

[0034] S104. Add molybdenum salt to the first transparent solution and adjust the pH to 3-6 to obtain the second transparent solution.

[0035] In an exemplary embodiment of this disclosure, the molybdenum salt may be one or a mixture of ammonium molybdate dihydrate, ammonium molybdate tetrahydrate, and ammonium molybdate heptahydrate.

[0036] According to some embodiments of this disclosure, the pH of the solution can be adjusted to 3-6 using, for example, hydrochloric acid.

[0037] The concentration of the second transparent solution mentioned in this disclosure is 0.01 mol / L to 0.2 mol / L.

[0038] S106. The second transparent solution is transferred to a reaction vessel for hydrothermal homogeneous reaction. After cooling, it is washed and dried to obtain molybdenum trioxide material.

[0039] The reactor used in this embodiment is, for example, a polytetrafluoroethylene reactor. During the hydrothermal homogeneous reaction, the hydrothermal reaction temperature is 110°C to 180°C, and the reaction time is 18h to 24h.

[0040] After cooling to room temperature, the material is washed and dried. The drying method is either freeze-drying or vacuum filtration drying. Specifically, when freeze-drying is used, the freeze-drying cold trap temperature is below -50°C, the vacuum degree is maintained below 15 MPa during the drying process, and the drying time is greater than 12 hours. When vacuum filtration drying is used, an aqueous filter membrane with a pore size of 0.1 μm to 1.2 μm is used.

[0041] The molybdenum trioxide material obtained in this embodiment is high-purity ribbon-shaped molybdenum trioxide.

[0042] S108. Molybdenum trioxide material is mixed with silicon dioxide powder to obtain composite powder.

[0043] The nucleating agent used in this disclosure is silica powder, specifically, the silica powder has a particle size of 15nm to 100nm and a purity >99.5%. In addition, the mass of the silica powder is 0.5% to 5% of the mass of the molybdenum trioxide material.

[0044] According to some embodiments of this disclosure, the molybdenum trioxide material obtained in step S106 can be uniformly mixed with silicon dioxide powder by ultra-high-speed mechanical mixing or ball milling to obtain composite powder.

[0045] S110. The composite powder is subjected to hydrogen reduction treatment to obtain a molybdenum dioxide material containing silicon dioxide.

[0046] According to some embodiments of this disclosure, during the hydrogen reduction treatment of the composite powder, the hydrogen reduction temperature is 400℃~700℃, the heating rate is 10℃ / min, and the reaction time is 1h~2h. Furthermore, the hydrogen used in this step is either dry hydrogen or wet hydrogen.

[0047] By controlling the temperature field and gas flow field of hydrogen reduction, the Mo4O content during hydrogen reduction can be guaranteed. 11 Furthermore, the nucleation and growth process of MoO2 is controllable, effectively avoiding abnormal grain growth caused by directional deposition during the chemical vapor transport process of MoO2(OH)2. This facilitates the subsequent acquisition of ultrafine nano-molybdenum dioxide materials with regular morphology and uniform size.

[0048] S112. Molybdenum dioxide material containing silica is immersed in an alkaline solution to remove silica, thereby obtaining molybdenum dioxide material.

[0049] In an exemplary embodiment of this disclosure, the alkaline solution mentioned herein is, for example, at least one of sodium hydroxide solution and potassium hydroxide solution, and the soaking time is greater than 30 minutes.

[0050] Based on the above scheme, the crystal form, purity, morphology, particle size, and dispersibility of molybdenum trioxide (MoTrioxide) can be precisely controlled through a hydrothermal homogeneous reaction. The prepared one-dimensional ribbon-like MoTrioxide has a large specific surface area and uniform phase. Combined with nano-silica to prepare nanoscale composite powder, it can provide more heterogeneous nucleation active sites, significantly reduce the subsequent reduction temperature, and cause abnormal growth of heterogeneous MoTrioxide grains. Therefore, by controlling the hydrothermal homogeneous reaction conditions, the nucleation and growth process of MoTrioxide can be effectively controlled. By controlling the particle size of nano-silica and its ratio with MoTrioxide, the subsequent reduction preparation process of MoTrioxide can be effectively controlled, thereby controlling the morphology, particle size, and dispersibility of MoTrioxide. Subsequent alkaline leaching treatment can remove residual silica, improve product purity, increase the specific surface area of ​​MoTrioxide, and create favorable reaction conditions for the subsequent hydrogen reduction preparation of MoTrioxide powder.

[0051] Furthermore, this disclosure also provides a molybdenum dioxide material, prepared using the molybdenum dioxide material preparation method described in steps S102 to S112 above.

[0052] Figure 2A flowchart illustrating a method for preparing molybdenum powder according to an embodiment of this disclosure is shown schematically. (Reference) Figure 2 The method for preparing molybdenum powder according to the present disclosure may include the following steps: S202. Molybdenum dioxide material is subjected to hydrogen reduction treatment to obtain intermediate powder.

[0053] According to some embodiments of this disclosure, the molybdenum dioxide material can be prepared using the molybdenum dioxide material preparation method described in steps S102 to S112 above.

[0054] In this step of hydrogen reduction treatment, the hydrogen used is dry hydrogen, the reduction temperature is 800℃~1000℃, the heating rate is 10℃ / min, and the reaction time is 2h~4h.

[0055] By regulating the hydrogen gas flow field and temperature field to perform deep reduction and deoxygenation of molybdenum dioxide, and precisely controlling the water vapor partial pressure during the reaction process, the gas phase dissolution and abnormal coarsening behavior of molybdenum powder nucleation and growth stages can be effectively suppressed. This enables controllable regulation of the particle size, morphology and dispersibility of molybdenum powder, which is helpful for the subsequent preparation of highly dispersed ultrafine nano molybdenum powder.

[0056] S204. The intermediate powder is ball-milled and dispersed to obtain molybdenum powder.

[0057] According to some embodiments of this disclosure, wet milling can be used as the ball milling method, with alcohol or deionized water as the dispersion medium, a ball-to-material ratio of 5-10:1, and a milling time of 1-3 hours. By reasonably controlling the ball milling process according to this disclosure, the dispersibility of molybdenum powder can be improved.

[0058] Furthermore, this disclosure also provides a molybdenum powder prepared using the molybdenum powder preparation method described in steps S202 and S204 above.

[0059] The molybdenum powder prepared by the above-described preparation method can be applied in fields such as steel, metallurgy, machinery, chemical industry, atomic energy, electronics and aerospace, as well as in fields requiring molybdenum processed products.

[0060] In some technologies, the process of preparing molybdenum trioxide by calcining ammonium molybdate and then preparing molybdenum dioxide and molybdenum powder by hydrogen reduction is simple, but according to the chemical method of calcining ammonium molybdate 3(NH4)2O 7MoO3 The process 4H₂O→7MoO₃+6NH₃↑+7H₂O↑ shows that the entire process generates a large amount of ammonia, resulting in high environmental and safety costs. Furthermore, traditional furnaces often exhibit uneven heating, leading to localized over-burning and under-burning. The prepared molybdenum trioxide has a single crystal form, with large fluctuations in particle size and bulk density, and is prone to agglomeration, severely affecting the subsequent preparation of molybdenum dioxide and molybdenum powder. However, the hydrothermal homogeneous reaction method disclosed in this paper prepares molybdenum trioxide by hydrolyzing and protonating ammonium molybdate (APM) under acidic conditions: (NH₄)₆Mo₇O₃. 24 4H2O+6H + →7H2MoO4+6NH4 + Subsequently, molybdic acid undergoes dehydration condensation under hydrothermal conditions to produce molybdenum trioxide: H₂MoO₄ → MoO₃ + H₂O. The entire process is a homogeneous liquid phase with no solid suspension, and the product morphology is highly controllable. According to the chemical reaction equation, 1 mol of ammonium molybdate can produce 7 mol of molybdenum trioxide, indicating a theoretical yield of [missing information]. The molybdenum conversion rate is 100%, indicating that the reaction process of molybdenum trioxide can be precisely controlled through hydrothermal homogeneous reaction, including its crystal form, particle size, morphology and dispersibility. In addition, the raw material conversion rate is high, the product purity is extremely high, the pollution is low and the energy consumption is low, which lays the foundation for the subsequent reduction preparation of molybdenum dioxide and molybdenum powder.

[0061] The process of preparing molybdenum dioxide and molybdenum powder by hydrogen reduction is MoO3→Mo4O 11 The process of transferring MoO2 to Mo via chemical vapor transport and solid-phase diffusion leads to product agglomeration and abnormal growth, making it difficult to prepare high-purity, highly dispersed nano-molybdenum powder. However, this invention utilizes a one-dimensional high-purity molybdenum trioxide matrix prepared by hydrothermal homogeneous reaction to construct a composite powder. The nano-silica surface is rich in hydroxyl groups (-OH), exhibiting high lattice compatibility with MoO3 and providing numerous heterogeneous nucleation sites, significantly increasing the nucleation rate. Furthermore, the nano-SiO2 particles act as a physical barrier, preventing MoO2 / Mo nuclei from dissolving, depositing, and agglomerating through the chemical vapor transport of MoO2(OH)2. In addition, heterogeneous nucleation significantly reduces the nucleation barrier and lowers the reduction temperature. Subsequent alkaline leaching to remove excess silica further improves product purity, increases specific surface area, and enhances the sintering activity of the molybdenum powder.

[0062] In the technical solution provided in this disclosure, molybdenum salt is selected as a precursor, and high-purity MoO3 material is prepared by hydrothermal homogeneous reaction. By selecting dispersants and surfactants, the problems of abnormal grain growth and impurity introduction in traditional calcination processes can be effectively avoided, resulting in one-dimensional ribbon-like MoO3 material with a large specific surface area. This provides conditions for subsequent preparation of ultrafine molybdenum dioxide and molybdenum through nucleation induced by nucleating agents. Then, composite powder is prepared by adding high-purity nano-silica. The addition of nucleating agents can provide more heterogeneous nucleation active sites for the reduction of molybdenum trioxide. According to the heterogeneous nucleation theory, its critical nucleation work... ,in, For homogeneous nucleation work, wetting factor , For the wetting angle. Due to the good wettability of nano-silica and molybdenum trioxide, its heterogeneous nucleation activity... The nucleation work is significantly lower than that of homogeneous nucleation. The addition of nano-silica increases the number of molybdenum dioxide nucleation sites while reducing the heterogeneous nucleation work, resulting in a substantial increase in the heterogeneous nucleation rate. Therefore, the addition of nano-silica can successfully refine the grain size of the reduced molybdenum dioxide, while avoiding the preferred orientation of grains during the nucleation process and lowering the reduction temperature. Simultaneously, during hydrogen reduction, it can suppress abnormal grain growth and agglomeration caused by localized vapor deposition of MoO2(OH)2 during the reduction of molybdenum powder. Subsequent hydrogen reduction and ball milling dispersion can yield ultrafine nano-molybdenum powder, solving some problems such as abnormal growth, agglomeration, and uneven particle size in the production and preparation of molybdenum powder.

[0063] The advantages of the solution provided in this disclosure are as follows: First, a hydrothermal homogeneous method was used to synthesize one-dimensional ribbon-like MoO3 materials with high specific surface area. By screening suitable molybdenum salts and adding dispersants, the reaction system and reaction conditions were controlled, enabling precise control of the MoO3 nucleation and growth process. Compared with the traditional air-calcined ammonium molybdate method, this method avoids the problems of molybdenum trioxide grain coarsening and hard agglomeration caused by high-temperature calcination, and features higher purity, better dispersibility, controllable particle size, and uniform size. This lays the foundation for the subsequent preparation of highly dispersed ultrafine nano-molybdenum dioxide and molybdenum powder.

[0064] Secondly, the introduction of silica as a nucleating agent can induce the directional growth of molybdenum dioxide and limit grain agglomeration and coarsening, accurately controlling the particle size of molybdenum dioxide within the range of 50nm to 200nm. The narrow particle size distribution lays a good foundation for the subsequent preparation of ultrafine molybdenum powder. Compared with traditional industrial molybdenum powder (micron-sized, irregular morphology, etc.), the specific surface area of ​​the precursor is significantly increased, and the reduction kinetic efficiency is greatly improved.

[0065] Third, the prepared nano-molybdenum dioxide is subjected to a reasonable alkaline leaching treatment, achieving the dual effects of impurity removal and activity enhancement, which is significantly superior to the traditional reduction process without activation treatment. This disclosure employs alkaline leaching to selectively dissolve excess nano-silica without damaging the molybdenum dioxide crystal structure. Simultaneously, it constructs mesoporous and defect structures on the molybdenum dioxide surface, effectively increasing reactive sites and thus lowering the subsequent hydrogen reduction temperature, ensuring a more thorough reduction reaction. Furthermore, alkaline leaching can eliminate the passivation layer on the molybdenum dioxide surface, increasing the hydrogen reduction conversion rate and solving the problems of residual intermediate products and poor reactivity in the traditional direct reduction of molybdenum dioxide.

[0066] Fourth, the synergistic effect of hydrogen reduction and ball milling dispersion yields highly dispersed and high-purity ultrafine molybdenum nanoparticles. This disclosure utilizes a highly active molybdenum dioxide precursor and a low-temperature hydrogen reduction process (400℃~700℃) to avoid secondary grain growth and sintering caused by traditional high-temperature (>700℃) reduction. Subsequent deep deoxidation further yields molybdenum powder with fine particle size, good sphericity, and regular morphology. Subsequent light ball milling only breaks up soft agglomerates without damaging the molybdenum powder's crystal structure, significantly improving its dispersibility and enabling stable dispersion in water / oil systems. This overcomes the shortcomings of traditional high-energy ball milling, which easily introduces impurities, causes lattice defects and oxidation, leading to a decrease in molybdenum powder purity (<99.5%). The molybdenum powder prepared by this disclosure achieves a purity of over 99.9%.

[0067] Fifth, the disclosed solution features a mild process, low cost, and ease of industrial-scale production, making it highly practical. The hydrothermal reaction temperature is controlled between 110℃ and 180℃, eliminating the need for high-temperature calcination and reducing energy consumption compared to traditional processes. The raw materials used, such as ammonium molybdate, nano-silica, sodium hydroxide, and hydrogen, are all commonly used industrial raw materials, with costs far lower than those of high-purity molybdenum chloride and carbonyl molybdenum. The entire process is concise, comprising only four core steps: hydrothermal treatment, alkali leaching, reduction, and ball milling. It eliminates the need for complex vapor deposition or high-energy ball milling equipment, resulting in low equipment investment and good batch stability. This allows for smooth scale-up from laboratory to pilot-scale and then to mass production, solving the technical challenges of expensive and difficult-to-scale equipment in vapor-phase and plasma methods, and the poor purity and unstable performance of mechanical alloying methods.

[0068] The following describes Embodiment 1 of this disclosure.

[0069] Step 1: Place 300 mL of deionized water on a magnetic stirrer and slowly add 0.025 g of PEG. Stir at 300 r / min until the dispersant is completely dissolved to obtain a homogeneous and transparent first transparent solution.

[0070] Step 2: Add 3.7g of ammonium molybdate tetrahydrate to the first transparent solution from Step 1, and stir at 300r / min until completely dissolved to obtain an intermediate transparent solution. Then, slowly add 2mol / L hydrochloric acid solution dropwise to the intermediate transparent solution to adjust the pH to 3, thus obtaining the second transparent solution.

[0071] Step 3: The second transparent solution was transferred to a polytetrafluoroethylene high-pressure reactor for hydrothermal reaction. After reacting at 120°C for 18 hours, it was slowly cooled to room temperature. After the reaction was completed, the sample was repeatedly washed with deionized water and ethanol until neutral. Then, 200 mL of deionized water was added to the sample and dispersed. The sample was then filtered and dried in a vacuum filter. After 12 hours, a grayish-white ultrafine molybdenum trioxide material was obtained. Figure 3 The X-ray diffraction pattern of molybdenum trioxide prepared in Example 1 of this disclosure is shown. Figure 4 A scanning electron microscope (SEM) image of molybdenum trioxide prepared in Example 1 of this disclosure is shown. Based on Figure 4 The ribbon-like morphology of the molybdenum trioxide material prepared in this disclosure can be seen. Figure 5 A scanning electron microscope image of molybdenum trioxide prepared in Example 1 of this disclosure after filtration, drying, and sheet formation is shown.

[0072] Step four: 0.03g of nano-silica and the molybdenum trioxide obtained in step three are poured into a ball mill jar for mechanical composite processing. The silica particle size is 15nm, the ball milling speed is 200r / min, and the ball milling time is 4h to obtain composite powder.

[0073] Step 5: The composite powder obtained in Step 4 is subjected to the first stage of hydrogen reduction treatment in a tube furnace. The reduction temperature is 700℃, the hydrogen flow rate is 0.5L / min, the heating rate is 10℃ / min, and the reaction time is 2h to obtain ultrafine nano molybdenum dioxide.

[0074] Step six: The molybdenum dioxide obtained in step five was slowly added to a 2 mol / L NaOH solution, and the alkaline leaching time was 1 hour. The sample was then ultrasonically washed with deionized water until neutral and dried to obtain high-purity ultrafine nano-molybdenum dioxide. After alkaline leaching treatment, the specific surface area of ​​the molybdenum dioxide material increased from 3.34 m² / s before treatment. 2 / g increased to 4.92m 2 / g, to enhance its reactivity. Figure 6 A scanning electron microscope image of molybdenum dioxide prepared in Example 1 of this disclosure is shown.

[0075] Step seven involves subjecting the molybdenum dioxide powder obtained in step six to a second-stage atmosphere reduction treatment at 800℃. The atmosphere used is dry hydrogen, with a hydrogen flow rate of 0.5 L / min, a heating rate of 10℃ / min, and a reaction time of 2 h, yielding ultrafine nano-molybdenum powder. To further improve the dispersibility of the molybdenum powder, the product is ball-milled at 140 r / min for 4 h and then sieved through a 200-mesh sieve to obtain highly dispersible ultrafine nano-molybdenum powder. Figure 7 A scanning electron microscope image of the molybdenum powder prepared in Example 1 of this disclosure is shown.

[0076] The average particle size of the primary particles of the nano-molybdenum powder prepared in Example 1 was found to be 200 nm.

[0077] Embodiment 2 of this disclosure will be described below.

[0078] Step 1: Place 300 mL of deionized water on a magnetic stirrer and slowly add 0.01 g of PVP. Stir at 400 r / min until the dispersant is completely dissolved to obtain a homogeneous and transparent first transparent solution.

[0079] Step 2: Add 7.4g of ammonium molybdate dihydrate to the first transparent solution from Step 1, and stir at 400r / min until completely dissolved to obtain an intermediate transparent solution. Then, slowly add 2mol / L hydrochloric acid solution dropwise to the intermediate transparent solution to adjust the pH to 4, thus obtaining the second transparent solution.

[0080] Step 3: The second transparent solution was transferred to a polytetrafluoroethylene high-pressure reactor for hydrothermal reaction. After reacting at 150°C for 20 hours, it was slowly cooled to room temperature. After the reaction was completed, the sample was repeatedly washed with deionized water and ethanol until neutral, and then placed in a freeze dryer with a cold trap temperature of -70°C and a sample chamber vacuum of 2 Pa. After 24 hours, grayish-white ultrafine molybdenum trioxide was obtained.

[0081] Step 4: 0.1g of nano-silica and the molybdenum trioxide obtained in Step 3 are poured into a ball mill jar for mechanical composite processing. The silica particle size is 30nm, the ball milling speed is 200r / min, and the ball milling time is 4h to obtain composite powder.

[0082] Step 5: The composite powder obtained in Step 4 is subjected to the first stage of hydrogen reduction treatment in a tube furnace. The reduction temperature is 600℃, the hydrogen flow rate is 0.8L / min, the heating rate is 10℃ / min, and the reaction time is 1h to obtain ultrafine nano molybdenum dioxide.

[0083] Step six: Slowly add the molybdenum dioxide obtained in step five into a 2 mol / L KOH solution and soak it in the alkali solution for 1 hour. Then, ultrasonically clean the sample with deionized water until it is neutral and dry it to obtain high-purity ultrafine nano molybdenum dioxide.

[0084] Step seven involves subjecting the molybdenum dioxide powder obtained in step six to a second-stage atmosphere reduction treatment at 900℃. The atmosphere used is dry hydrogen, with a hydrogen flow rate of 0.8 L / min, a heating rate of 10℃ / min, and a reaction time of 3 h, yielding ultrafine nano-molybdenum powder. To further improve the dispersibility of the molybdenum powder, the product is ball-milled at 140 r / min for 4 h and then sieved through a 200-mesh sieve to obtain highly dispersible ultrafine nano-molybdenum powder.

[0085] Embodiment 3 of this disclosure will be described below.

[0086] Step 1: Place 300 mL of ultrapure water on a magnetic stirrer and slowly add 0.05 g of CTAB. Stir at 600 r / min until the dispersant is completely dissolved to obtain a homogeneous and transparent first transparent solution.

[0087] Step 2: Add 11.1g of ammonium molybdate heptahydrate to the first transparent solution from Step 1, and stir at 600r / min until completely dissolved to obtain an intermediate transparent solution. Then, slowly add 2mol / L hydrochloric acid solution dropwise to the intermediate transparent solution to adjust the pH to 6, thus obtaining the second transparent solution.

[0088] Step 3: The second transparent solution was transferred to a polytetrafluoroethylene high-pressure reactor for hydrothermal reaction. After reacting at 180°C for 24 hours, it was slowly cooled to room temperature. After the reaction was completed, the sample was repeatedly washed with deionized water and ethanol until neutral, and then placed in a freeze dryer with a cold trap temperature of -70°C and a sample chamber vacuum of 2 Pa. After 24 hours, grayish-white ultrafine molybdenum trioxide was obtained.

[0089] Step 4: 0.26g of nano-silica and the molybdenum trioxide obtained in Step 3 are poured into a ball mill jar for mechanical composite processing. The silica particle size is 15nm, the ball milling speed is 200r / min, and the ball milling time is 4h to obtain composite powder.

[0090] Step 5: The composite powder obtained in Step 4 is subjected to the first stage of hydrogen reduction treatment in a tube furnace. The reduction temperature is 650℃, the hydrogen flow rate is 0.8L / min, the heating rate is 10℃ / min, and the reaction time is 2h to obtain ultrafine nano molybdenum dioxide.

[0091] Step six: Slowly add the molybdenum dioxide obtained in step five into a 2 mol / L NaOH solution and soak it in the alkali solution for 2 hours. Then, ultrasonically clean the sample with deionized water until it is neutral and dry it to obtain high-purity ultrafine nano molybdenum dioxide.

[0092] Step seven involves subjecting the molybdenum dioxide powder obtained in step six to a second-stage atmosphere reduction treatment at 850℃. The atmosphere used is dry hydrogen, with a hydrogen flow rate of 0.8 L / min, a heating rate of 10℃ / min, and a reaction time of 4 h, yielding ultrafine nano-molybdenum powder. To further improve the dispersibility of the molybdenum powder, the product is ball-milled at 160 r / min for 4 h using low energy, and then sieved through a 200-mesh sieve to obtain highly dispersible ultrafine nano-molybdenum powder.

[0093] In the exemplary scheme of this disclosure, molybdenum salt is used as a raw material, and the nucleation and growth process of molybdenum trioxide is precisely controlled through a hydrothermal homogeneous reaction to synthesize one-dimensional ribbon-like molybdenum trioxide powder with a large specific surface area and uniform phase. Based on the prepared molybdenum trioxide, composite powder is prepared by combining it with nano-silica. Silica is used as a heterogeneous nucleating agent to effectively control the MoO3→Mo4O transition during hydrogen reduction. 11 →The reaction process of MoO2 enhances reactivity, reduces the Gibbs free energy required for reduction, and effectively controls the chemical vapor transport process of MoO2(OH)2. Excess silica in the product is then removed by alkaline leaching, yielding high-purity, fine-sized, and uniform molybdenum dioxide powder, providing a foundation for the subsequent preparation of nano-molybdenum powder. Further hydrogen deoxygenation and ball milling dispersion treatments yield highly dispersed, uniformly sized ultrafine nano-molybdenum powder. This process solves the problems of abnormal growth, uneven particle size, and poor dispersibility of molybdenum dioxide and molybdenum powder obtained by traditional molybdenum powder preparation processes.

[0094] It should be noted that although the steps of the method in this disclosure are described in a specific order in the accompanying drawings, this does not require or imply that the steps must be performed in that specific order, or that all the steps shown must be performed to achieve the desired result. Additional or alternative steps may be omitted, multiple steps may be combined into one step, and / or a step may be broken down into multiple steps.

[0095] Furthermore, the above figures are merely illustrative of the processes included in the method according to exemplary embodiments of this disclosure and are not intended to be limiting. It is readily understood that the processes shown in the above figures do not indicate or limit the temporal order of these processes. Additionally, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0096] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the claims.

[0097] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. A method for preparing a molybdenum dioxide material, characterized in that, include: Add the dispersant to water and stir until homogeneous to obtain a first transparent solution; Molybdenum salt was added to the first transparent solution, and the pH was adjusted to 3-6 to obtain the second transparent solution; The second transparent solution was transferred to a reaction vessel for hydrothermal homogeneous reaction. After cooling, it was washed and dried to obtain molybdenum trioxide material. The molybdenum trioxide material is mixed with silicon dioxide powder to obtain a composite powder; The composite powder is subjected to hydrogen reduction treatment to obtain a molybdenum dioxide material containing silicon dioxide; The molybdenum dioxide material containing silica is immersed in an alkaline solution to remove the silica, thereby obtaining the molybdenum dioxide material.

2. The preparation method according to claim 1, characterized in that, The dispersant is one or a mixture of PEG, CTAB, PVP, and tartaric acid. The molybdenum salt is one or a mixture of ammonium molybdate dihydrate, ammonium molybdate tetrahydrate, and ammonium molybdate heptahydrate.

3. The preparation method according to claim 1, characterized in that, During the hydrothermal homogeneous reaction, the hydrothermal reaction temperature is 110℃~180℃ and the reaction time is 18h~24h.

4. The preparation method according to claim 1, characterized in that, In the process of obtaining the molybdenum trioxide material, the drying method is freeze drying or vacuum filtration drying; When the drying method is freeze drying, the freeze drying cold trap temperature is below -50℃, the vacuum degree is maintained below 15MPa during the drying process, and the drying time is greater than 12h. When the drying method is vacuum filtration, the vacuum filtration membrane used is an aqueous filter membrane with a pore size of 0.1 μm to 1.2 μm.

5. The preparation method according to claim 1, characterized in that, During the hydrogen reduction treatment of the composite powder, the hydrogen reduction temperature is 400℃~700℃, the heating rate is 10℃ / min, and the reaction time is 1h~2h.

6. A molybdenum dioxide material, characterized in that, The molybdenum dioxide material was prepared using the preparation method described in any one of claims 1 to 5.

7. A method for preparing molybdenum powder, characterized in that, include: Molybdenum dioxide material is subjected to hydrogen reduction treatment to obtain intermediate powder; wherein the molybdenum dioxide material is prepared by the preparation method of molybdenum dioxide material according to any one of claims 1 to 5; The intermediate powder was ball-milled and dispersed to obtain molybdenum powder.

8. The preparation method according to claim 7, characterized in that, In the process of obtaining the intermediate powder, the hydrogen used is dry hydrogen, the reduction temperature is 800℃~1000℃, the heating rate is 10℃ / min, and the reaction time is 2h~4h.

9. The preparation method according to claim 7, characterized in that, During the ball milling dispersion process, the ball-to-material ratio is 5~10:1, and the ball milling time is 1h~3h.

10. A molybdenum powder, characterized in that, The molybdenum powder was prepared using the method described in any one of claims 7 to 9.

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