Molybdenum dioxide powder and its preparation method

Abstract

This disclosure provides a molybdenum dioxide powder and its preparation method, relating to the field of powder material preparation technology. The method for preparing the molybdenum dioxide powder includes: adding molybdenum salt and potassium salt to water and mixing them evenly to obtain a mixed solution; drying the mixed solution to obtain a mixed powder; calcining the mixed powder in an oxygen-containing atmosphere to obtain potassium-rich molybdenum trioxide powder; uniformly mixing the potassium-rich molybdenum trioxide powder with molybdenum powder to obtain a composite powder; adding water to the composite powder using an atomization method to obtain a water-containing composite powder; and subjecting the water-containing composite powder to an atmosphere reduction treatment to obtain molybdenum dioxide powder. This disclosure can improve the quality of medium-sized molybdenum dioxide powder.

Description

Technical Field

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

[0002] 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.

[0003] As industrial technology upgrades towards refinement and customization, different application scenarios have placed varying demands on the particle size of molybdenum dioxide powder. Among these, medium-sized molybdenum dioxide powder (D50 of 15μm~25μm, preferably 20±3μm) has become a key specification bridging fine (1μm~10μm) and ultra-coarse (≥45μm) molybdenum dioxide particles. This is because it combines the sintering activity of fine particles with the good flowability and low specific surface area of ​​coarse particles. In the preparation of medium-sized molybdenum products (such as small and medium-sized molybdenum crucibles and molybdenum electrodes), this particle size can balance sintering density and molding flowability, avoiding cracking caused by excessively rapid sintering of fine particles, while reducing internal defects caused by ultra-coarse particles. In the field of medium-temperature electronic pastes, this particle size can optimize the printability and sintering stability of the paste, adapting to the fabrication needs of thick-film circuits and medium-temperature sensors.

[0004] Currently, the prepared molybdenum dioxide powder has the problem of poor quality.

[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 powder and a method for preparing the same, thereby overcoming, at least to some extent, the problem of poor quality of molybdenum dioxide powder.

[0007] According to a first aspect of this disclosure, a method for preparing molybdenum dioxide powder is provided, comprising: adding molybdenum salt and potassium salt to water and mixing them evenly to obtain a mixed solution; drying the mixed solution to obtain a mixed powder; calcining the mixed powder in an oxygen-containing atmosphere to obtain potassium-rich molybdenum trioxide powder; uniformly mixing the potassium-rich molybdenum trioxide powder with molybdenum powder to obtain a composite powder; adding water to the composite powder using an atomization method to obtain a water-containing composite powder; and subjecting the water-containing composite powder to an atmosphere reduction treatment to obtain molybdenum dioxide powder.

[0008] Optionally, the molybdenum salt is one or a mixture of ammonium molybdate dihydrate, ammonium molybdate tetrahydrate, and ammonium molybdate heptahydrate; the potassium salt is one or a mixture of potassium carbonate and potassium nitrate.

[0009] Optionally, the drying method for drying the mixed solution is one or a combination of spray drying, rotary evaporation, and stirring drying; when the drying method includes spray drying, the inlet air temperature of the spray dryer is 150℃~250℃ and the outlet air temperature is 90℃~120℃; when the drying method includes rotary evaporation, the temperature of the rotary evaporator is set to 60℃~75℃.

[0010] Optionally, the calcination process of the mixed powder in an oxygen-containing atmosphere includes a first calcination process and a second calcination process; in the first calcination process, the calcination temperature is 300℃~350℃ and the calcination time is 1h~2h; in the second calcination process, the calcination temperature is 500℃~600℃ and the calcination time is 2h~4h; wherein, in both the first and second calcination processes, the heating rate is less than 10℃ / min.

[0011] Optionally, the mass ratio of molybdenum powder to potassium-rich molybdenum trioxide powder is 5% to 15%.

[0012] Optionally, potassium-rich molybdenum trioxide powder and molybdenum powder are uniformly mixed by mechanical high-speed stirring; wherein the stirring speed is greater than 10,000 r / min and the stirring time is 20 min to 40 min.

[0013] Optionally, the water added to the composite powder by atomization is in a mass ratio of 1% to 5% of the composite powder.

[0014] Optionally, the reducing atmosphere used for atmospheric reduction treatment of the water-containing composite powder is at least one of hydrogen or a hydrogen-argon mixture; wherein the atmosphere dew point is +10℃ to +30℃ and the gas flow rate is less than 1L / min·kg.

[0015] Optionally, the process of reducing the aqueous composite powder in an atmosphere includes a first atmosphere reduction process and a second atmosphere process; in the first atmosphere reduction process, the reduction temperature is 600℃~750℃ and the holding time is 1h~2h; in the second atmosphere process, the atmosphere used is argon, the treatment temperature is 850℃~1050℃, and the holding time is 1h~2h.

[0016] According to a second aspect of this disclosure, a molybdenum dioxide powder is provided, prepared using any of the above-described methods for preparing molybdenum dioxide powder.

[0017] In the exemplary embodiments of this disclosure, molybdenum powder is added to potassium-rich molybdenum trioxide powder as a crystal nucleus. On one hand, the molybdenum nucleus acts as a reducing agent, reacting with molybdenum trioxide to generate molybdenum dioxide. On the other hand, the molybdenum nucleus acts as a heterogeneous nucleation site to assist in the nucleation and growth of molybdenum dioxide. The addition of potassium reduces grain boundary energy, and further processes such as atomization with water addition and atmosphere reduction control the molybdenum dioxide nucleation and grain growth processes, resulting in medium-sized molybdenum dioxide powder with uniform size and good dispersibility, thus improving the quality of the molybdenum dioxide powder. Furthermore, the raw materials used in this disclosure are widely available, low in cost, and easy to promote.

[0018] 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

[0019] 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.

[0020] Figure 1 A flowchart illustrating a method for preparing molybdenum dioxide powder according to an embodiment of the present disclosure is shown.

[0021] Figure 2 A scanning electron microscope image of the molybdenum trioxide powder prepared in Example 1 of this disclosure is shown.

[0022] Figure 3 The X-ray diffraction pattern of the molybdenum dioxide powder prepared in Example 1 of this disclosure is shown.

[0023] Figure 4 A scanning electron microscope image of the molybdenum dioxide powder prepared in Example 1 of this disclosure is shown.

[0024] Figure 5 A scanning electron microscope image of molybdenum dioxide prepared in the comparative example of this disclosure is shown. Detailed Implementation

[0025] 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.

[0026] 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," etc., used below are for distinction purposes only and should not be construed as limiting the content of this disclosure.

[0027] In some technologies, the preparation method of molybdenum dioxide powder includes the hydrogen reduction of molybdenum trioxide method. This method uses molybdenum trioxide obtained by calcining ammonium molybdate as raw material, and hydrogen as a reducing atmosphere to carry out the reduction reaction at 450℃~680℃. The reaction equation is: MoO3+H3→MoO2+H2O. The reduction product is cooled, crushed and sieved to obtain conventional molybdenum dioxide powder.

[0028] In these methods, the obtained molybdenum dioxide suffers from overgrowth or agglomeration due to limitations in temperature and airflow fields, resulting in poor particle size uniformity and dispersibility. Furthermore, the chemical vapor transport process in these processes is difficult to control, leading to anisotropic deposition of gaseous MoO2(OH)2 on the nucleated MoO2 edge surface, ultimately resulting in large, irregular, sheet-like structures. This fails to meet the core requirements of medium-sized molybdenum products and precision electronic pastes for powder density and flowability.

[0029] To obtain molybdenum dioxide powder of a specific particle size, mechanical crushing (crushing ultracoarse particles to the target particle size) or chemical vapor deposition (CVD) and sol-gel methods can be used. However, mechanical crushing easily introduces impurities such as Fe and Ni, leading to a decrease in powder purity. Furthermore, the crushed particles have irregular morphologies and sharp edges, affecting subsequent processing performance. CVD and sol-gel methods are mainly used for preparing nano / submicron-sized powders, making it difficult to achieve controllable preparation of medium-sized molybdenum dioxide. Moreover, the processes are complex, require significant equipment investment, and are difficult to scale up for mass production. Therefore, there is an urgent need in industry for a low-cost method to prepare high-quality medium-sized molybdenum dioxide powder.

[0030] To address the aforementioned problems, this disclosure provides a method for preparing medium-sized molybdenum dioxide. This method involves dissolving potassium into the molybdenum trioxide lattice to accelerate grain boundary migration and atomic diffusion, thereby reducing nucleation energy. Simultaneously, a small number of molybdenum crystal seed growth strategies are employed to provide nucleation sites. Furthermore, the reduction conditions are controlled to regulate the chemical vapor migration process during reduction, preventing preferential growth and abnormal agglomeration of molybdenum dioxide, resulting in highly dispersed medium-sized molybdenum dioxide powder.

[0031] Figure 1 A flowchart illustrating a method for preparing molybdenum dioxide powder according to an embodiment of this disclosure is shown schematically. (Reference) Figure 1 The method for preparing molybdenum dioxide powder according to the present disclosure may include the following steps: S102. Add molybdenum salt and potassium salt to water and mix thoroughly to obtain a mixed solution.

[0032] In exemplary embodiments of this disclosure, the molybdenum salt is one or a mixture of ammonium molybdate dihydrate, ammonium molybdate tetrahydrate, and ammonium molybdate heptahydrate. The potassium salt is one or a mixture of potassium carbonate and potassium nitrate. Additionally, the water mentioned in the embodiments of this disclosure can be ultrapure water or deionized water.

[0033] According to some embodiments of this disclosure, the mass of the potassium salt is 0.05% to 1.0% of the mass of the molybdenum salt, wherein when the molybdenum salt and potassium salt are dissolved in water, the total mass percentage of the molybdenum salt and potassium salt in the solid-liquid mixture is 10% to 30%.

[0034] S104. The mixed solution is dried to obtain a mixed powder.

[0035] The drying method of the drying process in the embodiments of this disclosure can be one or a combination of spray drying, rotary evaporation, and stirring drying.

[0036] When the drying method includes spray drying, the inlet air temperature for spray drying is 150℃~250℃, and the outlet air temperature is 90℃~120℃.

[0037] When the drying method includes rotary evaporation, the temperature of the rotary evaporator is set to 60℃~75℃.

[0038] It is important to note that using a mixed solution of molybdenum salt and potassium salt can achieve a more uniform mixing of materials, and selecting a specific drying method can ensure that the two salts do not segregate during the drying process, maintaining a uniform mixing state, which provides a foundation for the subsequent calcination preparation of potassium-rich molybdenum trioxide.

[0039] S106. The mixed powder is calcined in an oxygen-containing atmosphere to obtain potassium-rich molybdenum trioxide powder.

[0040] According to some embodiments of this disclosure, the calcination process can be a gradient heating and holding process, specifically including a first calcination process and a second calcination process. In the first calcination process, the calcination temperature is 300℃~350℃, and the calcination time is 1h~2h; in the second calcination process, the calcination temperature is 500℃~600℃, and the calcination time is 2h~4h. In both the first and second calcination processes, the heating rate is less than 10℃ / min.

[0041] The above calcination conditions are suitable for the nucleation and growth of potassium-rich molybdenum trioxide with moderate particle size and uniform particle size distribution.

[0042] S108. Mix potassium-rich molybdenum trioxide powder and molybdenum powder evenly to obtain composite powder.

[0043] In an exemplary embodiment of this disclosure, the mass ratio of molybdenum powder to potassium-rich molybdenum trioxide powder is 5% to 15%.

[0044] According to some embodiments of this disclosure, potassium-rich molybdenum trioxide powder and molybdenum powder can be uniformly mixed by mechanical high-speed stirring; wherein the stirring speed is greater than 10000 r / min and the stirring time is 20 min to 40 min.

[0045] S110. Water is added to the composite powder using an atomization method to obtain a water-containing composite powder.

[0046] In an exemplary embodiment of this disclosure, the water added to the composite powder by atomization is in a mass ratio of 1% to 5% of the composite powder.

[0047] S112. The aqueous composite powder is subjected to atmospheric reduction treatment to obtain molybdenum dioxide powder.

[0048] According to some embodiments of this disclosure, the first-stage reducing atmosphere used in the atmosphere reduction process is at least one of hydrogen or a hydrogen-argon mixture. The atmosphere dew point is +10℃ to +30℃, and the gas flow rate is less than 1 L / min·kg. The second-stage atmosphere is an inert gas such as argon. The reduction of molybdenum trioxide to prepare molybdenum dioxide under a hydrogen-containing atmosphere is a gas-solid heterogeneous exothermic reversible reaction, with the core reaction equation being: MoO3(s) + H2(g). The reduction process of MoO2(s) + H2O(g) involves a phase transition, initially producing the mesophase Mo4O. 11 The molybdenum dioxide is then transformed into stable MoO2. The equilibrium of this reaction is mainly controlled by temperature and the H2O / H2 partial pressure ratio. Unlike the traditional dry hydrogen process, wet hydrogen can artificially increase the water vapor partial pressure of the system. By reasonably matching the H2O / H2 ratio, the forward reaction rate can be slowed down, allowing molybdenum dioxide to have enough time for nucleation and isotropic grain growth, thereby improving the particle size of molybdenum dioxide.

[0049] The atmosphere reduction process can employ a gradient temperature increase method, specifically including a first atmosphere reduction process and a second atmosphere treatment process. Specifically, in the first atmosphere reduction process, the reduction temperature is 600℃~750℃, and the holding time is 1h~2h. In the second atmosphere treatment process, the treatment temperature is 850℃~1050℃, and the holding time is 1h~2h.

[0050] During the implementation process, it was found that by directionally and uniformly adding potassium to molybdenum salt and then calcining it, potassium-rich molybdenum trioxide powder was obtained. The potassium doping caused lattice distortion in the molybdenum trioxide, reducing its surface energy and providing favorable conditions for grain nucleation and growth during the subsequent reduction preparation of molybdenum dioxide. Some hydrogen reduction processes for preparing molybdenum dioxide involve the process MoO3 → Mo4O. 11 →MoO2, during which the chemical vapor transport and solid-phase diffusion reactions of MoO2(OH)2 lead to product agglomeration and some abnormal growth, with obvious anisotropic grain growth characteristics, making it difficult to obtain medium-sized molybdenum dioxide with uniform particle size and good flowability. This disclosed embodiment uses potassium-rich molybdenum trioxide (which can be denoted as K-MoO3) as a precursor, adds molybdenum crystal nuclei as growth seeds, and further controls the temperature field, gas flow field, material moisture content, and reaction gas dew point. The low-temperature stage ensures the nucleation and growth of molybdenum dioxide, preventing MoO2 crystal nuclei from dissolving and depositing directionally and agglomerating through the chemical vapor migration of MoO2(OH)2. After reduction, high temperature promotes the diffusion of molybdenum dioxide atoms and grain boundary merging, completing the further growth of molybdenum dioxide grains, ultimately obtaining highly dispersed, uniformly sized medium-sized molybdenum dioxide powder.

[0051] Furthermore, this disclosure also provides a molybdenum dioxide powder that can be prepared using the preparation methods described in steps S102 to S112 above.

[0052] The molybdenum dioxide powder prepared according to the embodiments of this disclosure can be applied in fields such as steel, metallurgy, machinery, chemical industry, atomic energy, electronics and aerospace.

[0053] In the technical solution provided in this disclosure, different molybdenum and potassium salts are selected as precursors. The molybdenum and potassium salts are uniformly mixed through liquid-phase mixing supplemented by stirring and rotary evaporation or spray drying. Compared to traditional solid-solid and solid-liquid mixing methods, this approach yields a more uniform mixed powder, effectively preventing potassium segregation that could lead to potassium-rich regions during subsequent calcination, ultimately producing K₂Mo₄O. 13 Impurities and other phases can cause the material to exhibit poor uniformity in its overall properties.

[0054] By calcining a mixture of molybdenum and potassium salts in an oxygen-containing atmosphere and regulating the reaction system and conditions, precise control of the nucleation and growth process of MoO3 was achieved, resulting in potassium-rich molybdenum trioxide with controllable particle size. This lays the foundation for the subsequent preparation of medium-sized, highly dispersed molybdenum dioxide.

[0055] A small amount of molybdenum crystal nuclei were uniformly added to the prepared K-MoO3. The molybdenum crystal nuclei not only provide nucleation sites for molybdenum dioxide nucleation, but also react with MoO3 at high temperature to generate MoO2. This seed growth strategy avoids to some extent the preferential growth and agglomeration of MoO2 grains caused by the directional dissolution and deposition process during the direct hydrogen reduction of traditional MoO3.

[0056] By controlling the potassium content and distribution in molybdenum trioxide, potassium enrichment at the grain boundaries of molybdenum dioxide during subsequent reduction lowers the grain boundary energy. Based on nucleation theory, the critical nucleation work... ,in, For grain boundary energy, For the free energy difference, with the grain boundary energy The decrease in surface energy reduces the critical nucleation barrier, but during the hydrogen reduction of MoO3, potassium promotes the formation of gaseous MoO2(OH)2. According to the Kelvin equation, small crystallites have higher vapor pressures. Under potassium catalysis, small crystallites undergo Oswald ripening due to their higher vapor pressure, involving dissolution, vapor migration, and deposition of larger crystallites. This allows atoms to preferentially grow on existing nuclei, inhibiting the formation of a large number of new nuclei. This significantly enhances chemical vapor transport and Oswald ripening. By adding a small amount of molybdenum nuclei, atoms can preferentially deposit and grow on existing molybdenum nuclei and initially formed MoO2 crystallites, ultimately resulting in grain coarsening. Secondly, in the subsequent high-temperature stage, the decrease in surface energy helps accelerate grain boundary migration and grain merging between the already formed MoO2 crystallites, thereby regulating the growth process of molybdenum dioxide grains. The hydrogen reduction process of molybdenum trioxide (MoO3) is represented by the equation MoO3 + H2 → MoO2 + H2O. By controlling the moisture content in the reducing raw materials, as well as the gas flow and temperature field, the forward reaction can be slowed down, reducing the reaction rate and providing sufficient time for molybdenum dioxide nucleation and growth, which is conducive to the isotropic growth of molybdenum dioxide. A lower gas flow rate also reduces the scouring and breakage of particles by the gas flow. After the molybdenum dioxide particles are initially stabilized through reduction growth at a lower temperature field, high-temperature treatment above 850℃ further completes the diffusion of molybdenum dioxide atoms and grain boundary merging, causing smaller grains to merge and grow into larger particles, thus obtaining molybdenum dioxide powder with good uniformity and large particle size.

[0057] The advantages of the preparation method of this disclosed embodiment include: First, a pretreatment of calcination with molybdenum and potassium salts is adopted to achieve uniform solid solution of potassium in the molybdenum trioxide lattice. The potassium is uniformly distributed in the lattice without local potassium segregation. During the reduction process, it promotes grain growth and inhibits the formation of fine grains throughout the entire process. This solves the technical pain points of uneven potassium distribution and large particle size fluctuation caused by traditional exogenous potassium doping, and lays the foundation for subsequent directional grain coarsening.

[0058] Secondly, the introduction of trace molybdenum crystal nuclei to construct composite structure powder replaces the traditional spontaneous random nucleation mode, inducing grains to grow directionally along the crystal nuclei, effectively eliminating fine-grained inclusions, and significantly improving the particle size uniformity and product purity of medium-sized molybdenum dioxide. Relying on the dual effects of potassium lattice solution and crystal nucleus induction, the reduction temperature is lowered, the holding time is shortened, and hydrogen consumption and equipment heat loss are significantly reduced, resulting in lower production energy consumption.

[0059] Third, by adjusting the humidity of the composite powder, the hydrogen reduction kinetics can be optimized, the reduction reaction rate can be slowed down, the lattice phase transformation stress can be buffered, the product structural defects can be reduced, and the particle integrity and crystallinity can be improved. At the same time, problems such as grain cracking, lattice vacancies and defects caused by excessively fast reduction in traditional high temperature can be avoided.

[0060] Fourth, the process of this disclosed solution is simplified, requiring no secondary potassium replenishment or prolonged high-temperature curing. The raw materials are compatible with conventional industrial molybdenum and potassium salts, resulting in low energy consumption and preparation costs. Furthermore, the only reaction byproduct is water vapor, thus ensuring both environmental protection and safety.

[0061] Fifth, the medium-sized molybdenum dioxide prepared in this disclosure has good sphericity, excellent flowability, and strong batch stability, which can meet the material requirements of high-end powder metallurgy and molybdenum-based composite materials. It takes into account both the precision preparation in the laboratory and the applicability to industrial mass production, and effectively overcomes the technical bottlenecks of existing processes, such as difficulty in preparing medium-sized products, uneven performance, and high energy consumption.

[0062] The following describes Embodiment 1 of this disclosure.

[0063] Step 1: Place 150 mL of deionized water on a magnetic stirrer and slowly add 0.129 g of potassium nitrate and 60.409 g of ammonium molybdate tetrahydrate. Stir at 300 r / min until completely dissolved to obtain a homogeneous and transparent mixed solution.

[0064] Step 2: Place the mixed solution in a spray dryer and spray dry it at 150°C to obtain the mixed powder.

[0065] Step 3: The mixed powder is calcined in air to obtain potassium-rich molybdenum trioxide. The first calcination stage is at 300℃ for 1 hour to complete dehydration and ammonia removal. The second calcination stage is at 500℃ for 4 hours. Figure 2 A scanning electron microscope image of the molybdenum trioxide powder prepared in Example 1 of this disclosure is shown.

[0066] Step 4: Place 10g of potassium-rich molybdenum trioxide and 0.5g of molybdenum powder in a high-speed mixer and mix evenly to obtain composite powder.

[0067] Step 5: Add water at a mass of 2% to the composite powder using an atomization method to obtain a water-containing composite powder.

[0068] Step Six: The aqueous composite powder is placed in a tube furnace and subjected to a gradient temperature reduction process. The first stage reduction temperature is 600℃, the holding time is 2 hours, and the reducing atmosphere is a hydrogen-argon mixture with a dew point of +20℃. The hydrogen content in the mixture is 5%, the gas flow rate is 0.5 L / min, and the heating rate is 5℃ / min. The second stage treatment temperature is 850℃, the holding time is 1 hour, and the atmosphere used is argon with a gas flow rate of 0.5 L / min and a heating rate of 5℃ / min, to obtain molybdenum dioxide powder with a medium particle size. Figure 3 The X-ray diffraction pattern of the molybdenum dioxide powder prepared in Example 1 of this disclosure is shown. Figure 4 A scanning electron microscope image of the molybdenum dioxide powder prepared in Example 1 of this disclosure is shown.

[0069] Embodiment 2 of this disclosure will be described below.

[0070] Step 1: Place 300 mL of deionized water on a magnetic stirrer and slowly add 0.18 g of potassium carbonate and 84.57 g of ammonium molybdate heptahydrate. Stir at 300 r / min until completely dissolved to obtain a homogeneous and transparent mixed solution.

[0071] Step 2: Place the mixed solution in a spray dryer and spray dry it at 150°C to obtain the mixed powder.

[0072] Step 3: The mixed powder is calcined in air to obtain potassium-rich molybdenum trioxide. The first calcination stage is at 350℃ for 2 hours to complete the dehydration and ammonia removal. The second calcination stage is at 600℃ for 2 hours.

[0073] Step 4: Mix 14g of potassium-rich molybdenum trioxide and 1g of molybdenum powder in a high-speed mixer until homogeneous to obtain composite powder.

[0074] Step 5: Add water at a mass of 3% to the composite powder using an atomization method to obtain a water-containing composite powder.

[0075] Step Six: The aqueous composite powder is placed in a tube furnace and a gradient temperature reduction process is adopted. The first stage reduction temperature is 750℃, the holding time is 1 hour, the reducing atmosphere used is hydrogen, the gas dew point is +30℃, the hydrogen content in the mixed gas is 5%, the gas flow rate is 0.5 L / min, and the heating rate is 5℃ / min. The second stage treatment temperature is 1050℃, the holding time is 2 hours, the atmosphere used is argon, the gas flow rate is 0.5 L / min, and the heating rate is 5℃ / min, to obtain molybdenum dioxide powder with medium particle size.

[0076] The following is an explanation of the proportions of this disclosure.

[0077] Step 1: Crush 60g of ammonium molybdate and sieve it through a 100-mesh sieve to obtain ammonium molybdate powder with uniform and dispersed particle size.

[0078] Step two involves calcining ammonium molybdate powder in a crucible to obtain molybdenum trioxide. The first stage of calcination is carried out at 300℃ for 1 hour to complete the dehydration and ammonia removal. The second stage of calcination is carried out at 550℃ for 2 hours.

[0079] Step 3: Place molybdenum trioxide in a tube furnace, reduce it at 600℃ for 2 hours, at a heating rate of 5℃ / min, using hydrogen as the reducing atmosphere at a flow rate of 0.5L / min. Molybdenum dioxide powder is obtained.

[0080] Figure 5A scanning electron microscope (SEM) image of molybdenum dioxide prepared in the comparative example of this disclosure is shown. (Comparison) Figure 4 and Figure 5 As can be seen, the molybdenum dioxide prepared in the comparative example exhibits plate-like growth, poor particle size uniformity, and poor dispersibility.

[0081] In the embodiments disclosed herein, molybdenum salt is used as a raw material, and potassium salt is added to synthesize potassium-rich molybdenum trioxide powder with moderate and uniform particle size through a calcination process. This provides a foundation for obtaining molybdenum dioxide with medium particle size and good dispersibility. Then, potassium-rich molybdenum trioxide is combined with a small amount of molybdenum crystal nuclei to provide heterogeneous nucleation sites for the nucleation and growth of molybdenum dioxide. In addition, multiple coupled controls of the moisture content of the reaction raw materials, the dew point of the reducing gas, the reaction temperature field, and the gas flow field are used to effectively control the nucleation and growth process of molybdenum dioxide. This eliminates the anisotropic growth process of molybdenum dioxide products caused by the directional dissolution and deposition of molybdenum trioxide due to traditional hydrogen reduction. Through the control of multi-stage reducing atmosphere and temperature, molybdenum dioxide powder with medium particle size and good dispersibility is obtained, solving the problems of abnormal growth, flaky growth, uneven particle size, and poor dispersibility of molybdenum dioxide powder obtained by traditional preparation processes.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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 molybdenum dioxide powder, characterized in that, include: The molybdenum salt and potassium salt are added to water and mixed thoroughly to obtain a mixed solution; The mixed solution is dried to obtain a mixed powder; The mixed powder was calcined in an oxygen-containing atmosphere to obtain potassium-rich molybdenum trioxide powder. The potassium-rich molybdenum trioxide powder is uniformly mixed with molybdenum powder to obtain a composite powder; Water is added to the composite powder using an atomization method to obtain a water-containing composite powder; The aqueous composite powder was subjected to atmospheric reduction treatment to obtain molybdenum dioxide powder.

2. The preparation method according to claim 1, characterized in that, The molybdenum salt is one or a mixture of ammonium molybdate dihydrate, ammonium molybdate tetrahydrate, and ammonium molybdate heptahydrate; The potassium salt is one or a mixture of two of potassium carbonate and potassium nitrate.

3. The preparation method according to claim 1, characterized in that, The drying method for drying the mixed solution is one or a combination of spray drying, rotary evaporation, and stirring drying. When the drying method includes spray drying, the inlet air temperature for spray drying is 150℃~250℃, and the outlet air temperature is 90℃~120℃. When the drying method includes rotary evaporation, the temperature of the rotary evaporator is set to 60℃~75℃.

4. The preparation method according to claim 1, characterized in that, The process of calcining the mixed powder in an oxygen-containing atmosphere includes a first calcination process and a second calcination process. In the first roasting process, the roasting temperature is 300℃~350℃ and the roasting time is 1h~2h; In the second roasting process, the roasting temperature is 500℃~600℃ and the roasting time is 2h~4h; In both the first and second roasting processes, the heating rate is less than 10℃ / min.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the molybdenum powder to the potassium-rich molybdenum trioxide powder is 5% to 15%.

6. The preparation method according to claim 1 or 5, characterized in that, The potassium-rich molybdenum trioxide powder and the molybdenum powder were uniformly mixed by high-speed mechanical stirring. The stirring speed is greater than 10,000 r / min, and the stirring time is 20 min to 40 min.

7. The preparation method according to claim 1, characterized in that, The water added to the composite powder using an atomization method has a mass ratio of 1% to 5% of the composite powder.

8. The preparation method according to claim 1, characterized in that, The reducing atmosphere used for the atmospheric reduction treatment of the water-containing composite powder is at least one of hydrogen and a hydrogen-argon mixture; The atmosphere dew point is +10℃ to +30℃, and the gas flow rate is less than 1L / min·kg.

9. The preparation method according to claim 1 or 8, characterized in that, The process of reducing the aqueous composite powder under atmosphere includes a first atmosphere reduction process and a second atmosphere process. During the first atmosphere reduction process, the reduction temperature is 600℃~750℃, and the holding time is 1h~2h; In the second atmosphere treatment process, the atmosphere used is argon, the treatment temperature is 850℃~1050℃, and the holding time is 1h~2h.

10. A molybdenum dioxide powder, characterized in that, The molybdenum dioxide powder was prepared using the method described in any one of claims 1 to 9.

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