A method for preparing magnesium powder

Abstract

The present invention belongs to the field of metal powder manufacturing, and provides a method for preparing ultrafine magnesium powder, which is prepared by using a Venturi tube; a gas-liquid mixture enters the Venturi tube at a first speed, and magnesium liquid enters the Venturi tube at a second speed. The gas-liquid mixture and the magnesium liquid are mixed at the throat of the Venturi tube to form magnesium powder; the gas-liquid mixture does not chemically react with magnesium; the first speed is at least 5 m / s. Since the Venturi tube is used to prepare magnesium powder, magnesium powder with controllable particle size, a small particle size distribution range and high roundness can be obtained; by replacing oxygen in the preparation system with rare gas and controlling the environmental humidity, the activity of the magnesium powder is guaranteed; the preparation equipment has a simple structure, no moving parts, and the equipment investment is greatly reduced.

Description

Technical Field

[0001] The present invention relates to energetic materials, belonging to the field of metal powder manufacturing, and specifically relates to a method for preparing ultrafine magnesium powder. Background Art

[0002] Ultrafine magnesium powder with a particle size below 400 mesh (38 μm) has a large specific surface area and strong surface activity. It is an important energetic material and can be used to manufacture chemical products, explosives, fireworks, etc. It can also be used as a reducing agent, desulfurizing agent, and 3D printing raw material, and is widely used in the military industry, aerospace industry, steelmaking industry, and non-ferrous metal casting, etc. In view of the process requirements, it is necessary to prepare ultrafine magnesium powder with a smaller particle size, a smaller particle size distribution range, higher roundness, and higher activity.

[0003] However, ultrafine magnesium powder has high activity and can react with water or oxygen at room temperature, releasing heat, which may lead to combustion and explosion. Therefore, the manufacturing process of magnesium powder is relatively complex.

[0004] Existing methods for preparing magnesium powder include grinding and milling (crushing) methods, emulsification methods, vortex crushing methods, atomization methods, and air flow crushing methods.

[0005] Patents CN202011059832.2 and CN201510018764.8 adopt grinding and milling (crushing) methods, which are mechanical crushing methods. Most of the produced powders are rhombic or other irregular shapes, and the particle size is only 20 - 150 mesh, with relatively low activity and loose bulk density.

[0006] Patent No. CN101758224A provides a method for preparing nanometer magnesium powder by high-frequency cutting at low temperature. However, this method requires cutting at an ultra-high speed (5500 - 6000 revolutions per minute), consuming a large amount of energy and having low production efficiency.

[0007] Patent 201310082862.9 proposes a pneumatic atomization production method for high-purity fine spherical metallic magnesium powder, and prepares spherical magnesium powder by argon atomization and nitrogen cooling. This method requires the use of nitrogen, argon, and their cooling and separation devices, with expensive equipment and complex processes.

[0008] Patents WO2024040946A1, 201710726429.2, CN102615289A, CN103862060A, CN102615289A, and 202111623596.7 use heating magnesium raw materials to obtain magnesium vapor and then condense to obtain magnesium powder. The equipment is complex and expensive, the particle size distribution range is large, the energy consumption is high, and the large-scale applicability is poor.

[0009] Therefore, there is an urgent need for a simple and efficient method to solve the problems existing in the preparation process of ultrafine magnesium powder, including too large particle size, large particle size distribution range, insufficient roundness, low activity, expensive equipment, complex process, etc. Summary of the Invention

[0010] In order to solve the problems of large particle size, large particle size distribution range, low roundness and activity of magnesium powder, expensive equipment and complex process, the present invention provides a method for preparing ultrafine magnesium powder.

[0011] To achieve the above object, the technical means adopted by the present invention are as follows:

[0012] On the one hand, a method for preparing ultrafine magnesium powder is provided, which is prepared by a Venturi tube; the gas-liquid mixture enters the Venturi tube at a first speed, and the magnesium liquid enters the Venturi tube at a second speed. The gas-liquid mixture and the magnesium liquid are mixed at the throat of the Venturi tube to form magnesium powder; the gas-liquid mixture is composed of rare gas, and the gas-liquid mixture does not chemically react with magnesium; the first speed is at least 5 m / s.

[0013] Further, the mass ratio of the gas-liquid mixture is 1:10 - 1:30.

[0014] Further, it also includes a melting furnace, a collecting tower and pipelines. The Venturi tube, the collecting tower and the pipelines form a preparation system. The magnesium powder is collected by the preparation system. The steps are as follows:

[0015] 1) After the absolute pressure of the preparation system drops below 100 Pa, the entire preparation system is filled with rare gas;

[0016] 2) The melting furnace is heated to above 651 °C and kept at a constant temperature;

[0017] 3) Gradually increase the flow rate of the gas-liquid mixture at the throat to the first speed, and the magnesium liquid enters the Venturi tube at the second speed. The gas-liquid mixture and the magnesium liquid are mixed at the throat of the Venturi tube to form magnesium liquid droplets with uniform particle size and a first gas. The magnesium liquid droplets solidify into magnesium powder in the Venturi tube;

[0018] 4) Screen the magnesium powder to obtain ultrafine magnesium powder.

[0019] Further, the screening of the magnesium powder is carried out by a multi-stage vibrating screen. The multi-stage vibrating screen includes a primary vibrating screen and a secondary vibrating screen. The screen aperture of the primary vibrating screen is larger than that of the secondary vibrating screen.

[0020] Further, it also includes magnesium powder passivation.

[0021] Further, the passivation method is: mix rare gas and oxygen to obtain a mixed gas, slowly introduce the mixed gas into the collecting tower, vibrate or stir the magnesium powder to form a dense magnesium oxide film on the surface of the magnesium powder.

[0022] Further, the relative humidity of the gas in the preparation system does not exceed 2%.

[0023] Further, it also includes that the first gas is formed into a liquid after dust removal, pressurization and cooling, and is recycled.

[0024] Further, it also includes a furnace for melting magnesium blocks. An inclined partition is fixed on the inner wall of the furnace cavity of the furnace, dividing the furnace cavity of the furnace 3 into an upper cavity and a lower cavity. The partition has a through hole. A floating ball is arranged in the lower cavity, and the diameter of the floating ball is larger than the diameter of the through hole. The cooperation between the floating ball and the through hole keeps the liquid level height of the molten magnesium within a preset range.

[0025] On the other hand, a kind of magnesium powder is also provided, which is prepared by the above-mentioned magnesium powder preparation method.

[0026] On the other hand, an ammunition is also provided, which is made of the above-mentioned magnesium powder.

[0027] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0028] 1) The turbulent flow formed by the high-speed flowing gas-liquid mixture in the venturi tube is used to simultaneously mix, crush and cool the molten magnesium. By controlling the injection speed of the gas-liquid mixture, magnesium powder with controllable particle size and a small particle size distribution range is obtained; by rapidly cooling the crushed molten magnesium, magnesium powder with high roundness is obtained.

[0029] 2) The gas-liquid mixture uses a noble gas that does not react with magnesium, and at the same time strictly controls the environmental humidity in the magnesium powder preparation system, ensuring the activity of the magnesium powder.

[0030] 3) The core component of the magnesium powder preparation system is a spray tube with a venturi effect, which has a simple structure, no moving parts, and greatly reduces the equipment investment. Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the description of the embodiments of the present invention. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0032] Figure 1 It is the flow chart of the preparation of ultrafine magnesium powder of the present invention;

[0033] Figure 2 It is the front view of the ultrafine magnesium powder preparation device of the present invention;

[0034] Figure 3 It is the right view of the ultrafine magnesium powder preparation device of the present invention;

[0035] Figure 4 Top view of the ultra-fine magnesium powder preparation device of the present invention;

[0036] Figure 5 Schematic diagram of the ultra-fine magnesium powder preparation device of the present invention

[0037] Figure 6 Cross-sectional view of the ultra-fine magnesium powder preparation device of the present invention;

[0038] Figure 7 Cross-sectional view of the ultra-fine magnesium powder preparation device of the present invention;

[0039] Figure 8 Cross-sectional view of the ultra-fine magnesium powder preparation device of the present invention;

[0040] Figure 9 Front view of the furnace of the ultra-fine magnesium powder preparation device of the present invention;

[0041] Figure 10 Top view of the furnace of the ultra-fine magnesium powder preparation device of the present invention;

[0042] Figure 11 Cross-sectional view of the furnace of the ultra-fine magnesium powder preparation device of the present invention;

[0043] Figure 12 Structural diagram of the spraying device of the ultra-fine magnesium powder preparation device of the present invention;

[0044] Figure 13 Top view of the spraying device of the ultra-fine magnesium powder preparation device of the present invention;

[0045] Figure 14 Cross-sectional view of the spraying device of the ultra-fine magnesium powder preparation device of the present invention.

[0046] Wherein:

[0047] 1. Liquid rare gas; 2. First pressure pump; 3. Furnace; 4. Molten magnesium liquid; 5. Residue; 6. Floating ball; 7. Spraying device; 8. Partition board; 9. Atomized and nucleated magnesium powder; 10. Multi-stage vibrating sieve; 11. Sieve mesh; 12. Ultra-fine magnesium powder; 13. Dust removal filter; 14. Cooler; 15. Liquid storage tank; 16. Throat tube; 17. Magnesium liquid delivery pipe; 18. Through hole; 19. Collection tower; 20. Vacuum pump; 21. Venturi tube; 22. Second pressure pump; 23. Third pressure pump; 24. First pipeline; 25. Second pipeline. Specific embodiments

[0048] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0049] In a first aspect, referring to Figure 1 and Figures 12 - 14 , this embodiment provides a method for preparing magnesium powder, which is prepared by using a Venturi tube 21; a gas-liquid mixture enters the Venturi tube 21 at a first speed, and molten magnesium enters the Venturi tube 21 at a second speed. The gas-liquid mixture and the molten magnesium are mixed at the throat 16 of the Venturi tube 21 to form magnesium powder; the gas-liquid mixture does not chemically react with magnesium; the first speed is at least 5 m / s.

[0050] Specifically, the gas-liquid mixture enters the Venturi tube 21 at a first speed, and the molten magnesium enters the Venturi tube 21 at a second speed. The gas-liquid mixture and the molten magnesium are mixed at the throat 16 of the Venturi tube 21 to form magnesium droplets with uniform particle size, and the magnesium droplets solidify into magnesium powder at the end of the Venturi tube 21.

[0051] Generally, the preparation of magnesium powder uses an inert gas to atomize molten magnesium, and then the atomized molten magnesium is cooled by a cooling system to form magnesium powder. The equipment is relatively complex, and it is difficult to control the particle size of magnesium powder by simply atomizing it with gas, and magnesium powder with a wide particle size range is often formed.

[0052] This embodiment uses a Venturi tube 21 device to prepare magnesium powder. Specifically, the gas-liquid mixture enters the Venturi tube 21 at a high speed, and a turbulent flow is formed at the throat 16. The turbulent flow has the characteristics of disorder and diffusivity, and can quickly shear and mix the substances entering the turbulent flow. The molten magnesium delivery pipe 17 is arranged at the throat 16. After the molten magnesium enters the throat 16 of the Venturi tube 21, the molten magnesium quickly enters the center of the turbulent flow of the high-speed flowing gas-liquid mixture and is crushed by the turbulent flow of the gas-liquid mixture to form magnesium droplets with uniform particle size.

[0053] This embodiment uses the gas-liquid mixture to atomize the molten magnesium. Specifically, the gas-liquid mixture enters the Venturi tube 21 at a first speed, and the molten magnesium enters the Venturi tube 21 at a second speed. The gas-liquid mixture and the molten magnesium are mixed at the throat 16 of the Venturi tube 21.

[0054] It can be understood that the greater the flow rate of the gas-liquid mixture, the better the crushing effect of the formed turbulent flow on the molten magnesium, and the smaller the particle size of the formed magnesium powder. That is to say, by controlling the injection speed of the gas-liquid mixture, magnesium powder with controllable particle size and a small particle size distribution range can be obtained. The gas-liquid mixture in this embodiment enters the Venturi tube 21 at a speed not less than 3 m / s.

[0055] The slower the speed at which the molten magnesium enters the venturi 21, the smaller the amount of magnesium liquid entering the venturi 21, and the smaller the particle size of the magnesium powder formed. In order to obtain magnesium powder with uniform particle size, it is necessary to control the flow rate of the magnesium liquid entering the venturi 21. The magnesium liquid in this embodiment enters the venturi 21 at a speed of 10 g / s-500 g / s, preferably 200-300 g / s.

[0056] It is understandable that the flow rate of the gas-liquid mixture and the flow rate of the magnesium liquid can obtain magnesium powder of the target particle size when they are adapted. Therefore, in actual production, the flow rate of the gas-liquid mixture and the flow rate of the magnesium liquid can be adjusted accordingly.

[0057] After the magnesium liquid enters the throat 16 of the venturi 21, it meets the gas-liquid mixture and is first crushed by the turbulent flow of the gas-liquid mixture to form magnesium liquid droplets with uniform particle size. At the same time, the droplets exchange heat with the liquid rare gas and gaseous rare gas molecules, and the magnesium liquid droplets are rapidly cooled and solidified into magnesium powder at the end of the venturi 21, and then sprayed into the collection tower 19. Since the magnesium liquid is rapidly cooled and solidified after forming droplets, the roundness of the magnesium powder is better.

[0058] That is to say, in this embodiment, the mixing, crushing and cooling of the magnesium liquid can be carried out simultaneously in the venturi 21, which can ensure the formation of magnesium powder with a small particle size range and a standard roundness.

[0059] The gas-liquid mixture does not chemically react with magnesium.

[0060] It is understandable that magnesium is an active metal and is very likely to react chemically with oxygen in the air. Therefore, the preparation process of magnesium powder needs to be isolated from air. In this embodiment, a gas that does not react chemically with magnesium is used to replace the air in the magnesium powder preparation system, and the magnesium liquid is crushed with a gas-liquid mixture, which can effectively prevent the oxidation of magnesium and ensure that the activity of the magnesium powder will not be reduced.

[0061] Further, the gas-liquid mixture is composed of rare gases, including helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). It is understandable that since the outermost electrons of rare gases are fully arranged, they are generally chemically stable and not prone to chemical reactions. The air in the magnesium powder preparation system is replaced by rare gases, and under the protection of the rare gases, the magnesium powder will not be oxidized, thereby obtaining highly active magnesium powder.

[0062] The gas-liquid mixture of the rare gas enters the venturi 21 at a high speed and mixes with the magnesium liquid, absorbs heat and vaporizes, and is subsequently filtered, cooled, and pressurized for recycling.

[0063] It can be understood that the gas-liquid mixture is a combination of liquid helium and gaseous helium, or a combination of liquid helium and gaseous argon. All gas-liquid mixtures composed of rare gases belong to solid-liquid mixtures.

[0064] It is understandable that for the gas constituting the gas-liquid mixture, in addition to noble gases, chemical substances such as nitrogen that do not react with magnesium can also be used.

[0065] Furthermore, the mass ratio of the gas-liquid mixture is 1:10 - 1:30, preferably 1:15 - 1:25.

[0066] It is mainly controlled by adjusting the flow rate of liquid argon entering the venturi tube 21. The larger the flow rate of liquid argon, the smaller the mass ratio of the gas-liquid mixture formed by the vaporization of liquid argon upon encountering hot gas. The smaller the flow rate of liquid argon, the larger the mass ratio of the gas-liquid mixture formed by the vaporization of liquid argon upon encountering hot gas. And this flow rate is controlled by the first pressure pump 2 installed on the first pipeline 24.

[0067] It is understandable that the use of the gas-liquid mixture can simultaneously play the following roles:

[0068] 1. Utilize the venturi effect formed by the high-speed gas flow;

[0069] 2. Utilize the latent heat of vaporization of liquid argon to rapidly cool and solidify the pulverized magnesium droplets, forming ultrafine magnesium powder with better roundness;

[0070] 3. When the liquid argon droplets vaporize, their volume rapidly expands and further "explodes" the liquid magnesium droplets, forming ultrafine magnesium powder.

[0071] Therefore, by reasonably controlling the ratio of liquid and gaseous noble gases, magnesium powder with particle size, particle size range, and roundness meeting the actual application requirements can be obtained. Preferably, the ratio of liquid and gaseous noble gases is 1:23, and the most probable particle size of the obtained magnesium powder is 460 nm, the particle size distribution range is 350 - 510 nm, and the roundness is 0.008 μm.

[0072] Furthermore, referring to the appendix Figures 1 - 8 , it further includes a melting furnace 33, a collection tower 19, and pipelines. The venturi tube 21, the collection tower 19, and the pipelines form a preparation system. The steps for collecting magnesium powder using the preparation system are as follows:

[0073] 1). After the absolute pressure of the preparation system drops below 100 Pa, fill the entire preparation system with noble gas;

[0074] 2). Heat the melting furnace 3 to above 651 °C and maintain a constant temperature;

[0075] 3). Gradually increase the flow rate of the gas-liquid mixture at the throat 16 to the first speed, and the molten magnesium enters the venturi tube 21 at the second speed. The gas-liquid mixture and the molten magnesium are mixed at the throat 16 of the venturi tube 21 to form magnesium droplets with uniform particle size and a first gas. The magnesium droplets solidify into magnesium powder in the venturi tube 21;

[0076] 4). Screen the magnesium powder to obtain ultrafine magnesium powder.

[0077] It is understandable that magnesium is an active metal and can be oxidized by oxygen or water vapor in the air at room temperature. Therefore, during the preparation process of magnesium powder, contact with air should be avoided as much as possible. In this embodiment, rare gas is used to displace the air in the magnesium powder preparation system to avoid the oxidation reaction during the preparation of magnesium powder.

[0078] Specifically, when preparing magnesium powder, after adding magnesium metal blocks to the melting furnace 3, the magnesium powder preparation system is sealed. First, it is evacuated to make the absolute pressure of the system drop below 100 Pa, and then purged with rare gas to remove the air in the system, especially oxygen, to complete the operation of replacing air with rare gas in the system.

[0079] The melting point of magnesium is 651 °C. Therefore, it needs to be heated to above 651 °C to melt the magnesium blocks into molten magnesium. Specifically, the heating furnace is turned on to ensure that the temperature rises above 651 °C, preferably 720 °C, and kept at a constant temperature, which can ensure that the magnesium blocks are fully melted into a liquid.

[0080] After the liquid rare gas is sent into the venturi tube 21, part of it absorbs heat and vaporizes, becoming a high-pressure and high-speed gas-liquid mixed gas flow. When the gas-liquid mixed gas flow passes through the throat 16 of the venturi tube 21 at a high speed, according to Bernoulli's equation, a negative pressure will be generated at the throat 16, sucking the molten magnesium into the throat 16 of the venturi tube 21. After the molten magnesium enters the throat 16, it is crushed and atomized by the high-speed gas flow, and at the same time, it is quickly condensed by the cold rare gas (a mixture of gaseous and liquid rare gases). The high-quality and high-speed atomization and rapid cooling ensure that the particle size and particle size distribution range of the formed ultrafine magnesium powder meet the production requirements and maintain a high roundness, and then it is collected.

[0081] That is to say, by adjusting the rotation speed and pressure of the rare gas delivery pump, the rare gas injection speed is adjusted, and then the atomization degree and cooling speed of the molten metal magnesium are adjusted to control the particle size, particle size distribution range, roundness, and production efficiency of the magnesium powder, and prepare magnesium powder with a particle size meeting the requirements. The relationship between the particle size, particle size distribution range, roundness, and the flow rate of the gas-liquid mixture and the flow rate of the molten magnesium has been described in detail above.

[0082] Further, referring to the appendix Figures 6 - 8 , the obtained magnesium powder is sieved to obtain ultrafine magnesium powder. The magnesium powder is sieved by a multi-stage vibrating sieve 10 for multi-stage sieving. The multi-stage vibrating sieve 10 includes a primary vibrating sieve and a secondary vibrating sieve, and the screen aperture of the primary vibrating sieve is larger than that of the secondary vibrating sieve.

[0083] In order to further narrow the particle size distribution range of magnesium powder, a multi-stage vibrating sieve 10 is provided in this embodiment to perform multi-stage screening on the magnesium powder. The multi-stage vibrating sieve 10 includes a primary vibrating sieve and a secondary vibrating sieve, and the screen aperture of the primary vibrating sieve is larger than that of the secondary vibrating sieve. Preferably, a 200-mesh screen is used for the primary screening, and a 400-mesh screen is used for the secondary screening.

[0084] It can be understood that by setting the multi-stage vibrating sieve 10, the magnesium powder is screened according to the particle size to obtain magnesium powder with different particle size distribution ranges. A 200-mesh screen is used for the primary screening, and magnesium powder with a particle size range of 33 - 74 μm can be obtained. A 400-mesh screen is used for the secondary screening, and magnesium powder with a particle size less than 33 μm can be obtained.

[0085] Furthermore, it also includes passivation of magnesium powder.

[0086] The passivation method is as follows: a rare gas and oxygen are mixed to obtain a mixed gas, and the mixed gas is slowly introduced into the collection tower 19, and the magnesium powder is vibrated or stirred to form a dense magnesium oxide film on the surface of the magnesium powder.

[0087] It can be understood that by slowly introducing the pre-mixed rare gas and oxygen mixed gas into the collection tower 19, under the vibration and stirring state, the surface of the magnesium powder is controllably and limitedly oxidized to form a dense magnesium oxide film to prevent further deep oxidation of the magnesium powder.

[0088] Furthermore, the relative humidity of the gas in the preparation system does not exceed 2%, and preferably, the relative humidity of the gas in the system does not exceed 0.5%.

[0089] This is to reduce the water content in the magnesium powder preparation system, prevent water from reacting with the magnesium powder, and reduce the activity of the magnesium powder. During the whole process, the dew point (humidity) of the gas in the system needs to be strictly monitored, the relative humidity is controlled not to exceed 2%, and preferably, the relative humidity of the gas in the system does not exceed 0.5%. If necessary, an inert desiccant should be added to the system.

[0090] Furthermore, referring to Attach Figure 1 、 2 、4、6, it also includes that the first gas is formed into a liquid after dust removal, pressurization, and cooling, and then recovered and recycled.

[0091] Specifically, the liquid rare gas enters the venturi tube 21 and absorbs heat to partially vaporize. After contacting the molten magnesium liquid, it further vaporizes to form the first gas. The first gas is filtered by dust removal, pressurized to about 10 MPa, sent to the cooler 14 for cooling to below -80 °C, and then sent back to the liquid storage tank 15 to realize the recovery and recycling of the rare gas.

[0092] After processing the molten magnesium, the rare gas contains ultrafine magnesium powder, which needs to be dust-removed and filtered by the dust-removing filter 13 before it can be put into use again. Therefore, ultrafine magnesium powder remains in the dust-removing filter 13, and by regularly cleaning the dust-removing filter 13, ultrafine magnesium powder can be recovered.

[0093] Furthermore, referring to the attached Figures 9 - 11 , it further includes a furnace 3 for melting magnesium blocks. An inclined partition 8 is fixed to the inner wall of the furnace cavity of the furnace 3, dividing the furnace cavity of the furnace 3 into an upper cavity and a lower cavity. The partition 8 has a through hole 18. A floating ball 6 is arranged in the lower cavity. The diameter of the floating ball 6 is larger than the diameter of the through hole 18. By the cooperation of the floating ball 6 and the through hole 18, the liquid level height of the molten magnesium is maintained within a preset range. As a possible implementation manner, the preset range can be between 1 / 10 and 1 / 2 of the furnace cavity height; the preset range can also be between 1 / 5 and 1 / 3 of the furnace cavity height, preferably 1 / 4 of the furnace cavity height.

[0094] It can be understood that after the magnesium blocks are completely melted, metals with higher melting points (such as iron, copper, etc.) and non-metallic residues will precipitate at the bottom of the inclined surface of the partition 8 and be collected; while the round hole of the ball valve is in the middle position, and the residues will not enter the lower part of the furnace cavity through the round hole, and thus will not enter the injection port, thereby ensuring the purity of the produced magnesium powder.

[0095] It can be understood that by the cooperation of the floating ball 6 and the through hole 18, the liquid level of the molten magnesium is maintained within a suitable height range, that is, after the magnesium blocks in the upper cavity of the furnace are melted into molten magnesium, the molten magnesium flows into the lower cavity through the through hole 18. The floating ball can float on the liquid surface of the molten magnesium. As the molten magnesium in the lower cavity increases, the liquid level of the molten magnesium rises, and the floating ball rises accordingly until the floating ball blocks the through hole, and the molten magnesium in the upper cavity cannot continue to flow into the lower cavity, and the liquid level of the molten magnesium in the lower cavity no longer rises. When the position of the partition and the through hole is fixed, a smaller-diameter floating ball requires a higher liquid level of the molten magnesium in the lower cavity to reach the position of the through hole, while a larger-diameter floating ball requires a lower liquid level of the molten magnesium in the lower cavity to reach the position of the through hole. Therefore, by selecting floating balls with different diameters, the liquid level height of the molten magnesium in the lower cavity can be made to be within the preset range.

[0096] When preparing magnesium powder, the molten magnesium in the lower cavity of the furnace flows out, the liquid level of the molten magnesium drops, the floating ball 6 drops accordingly, and the floating ball 6 separates from the contact state with the through hole 18 on the partition 8. The molten magnesium in the upper cavity flows into the lower cavity through the gap between the through hole 18 and the floating ball 6, causing the liquid level of the molten magnesium in the lower cavity to rise, and the floating ball 6 rises accordingly and contacts the through hole 18 again, thereby blocking the through hole 18 and preventing the molten magnesium in the upper cavity from flowing into the lower cavity, so as to adjust and control the liquid level height of the molten magnesium in the lower cavity to always be within the preset range.

[0097] The above preset range can ensure the flow rate of the molten magnesium flowing out of the pipeline. From Figure 1It can be seen that the first end of the molten magnesium delivery pipe 17 is arranged at the middle position of the lower cavity of the furnace chamber, and the molten magnesium enters the throat 16 of the Venturi tube 21 from the lower cavity of the furnace chamber through the molten magnesium delivery pipe 17. The flow rate of the molten magnesium is positively correlated with the pressure of the molten magnesium at the first end of the molten magnesium delivery pipe 17, and the pressure of the molten magnesium at the first end depends on the height of the molten magnesium liquid level. Therefore, in order to maintain the stability of the molten magnesium flow rate, the liquid level height of the lower-layer molten magnesium needs to be kept within a preset range all the time.

[0098] The flow rate of the molten magnesium is closely related to the particle size of the magnesium powder. Specifically, the smaller the speed of the molten magnesium entering the Venturi tube 21, relatively speaking, the less the amount of molten magnesium entering the Venturi tube 21, and the smaller the particle size of the formed magnesium powder. In order to obtain magnesium powder with uniform particle size, it is necessary to control the flow rate of the molten magnesium entering the Venturi tube 21.

[0099] In the second aspect, the present embodiment also provides a kind of magnesium powder, which is prepared by the above-mentioned preparation method of magnesium powder.

[0100] In the third aspect, the present embodiment also provides an ammunition, which is made of the above-mentioned magnesium powder.

[0101] The particle size of the magnesium powder directly affects the combustion and explosion activity of the magnesium powder and the stability of the product.

[0102] The smaller the particle size of the magnesium powder, the greater the activity. Specifically, the minimum ignition temperature, the minimum ignition energy, and the explosion lower limit concentration parameters of the magnesium powder decrease with the decrease of the particle size; the maximum explosion pressure and the maximum pressure rise rate parameters of the magnesium powder increase with the decrease of the particle size. Therefore, magnesium powder with a small particle size is required in the ammunition field.

[0103] However, the smaller the particle size of the magnesium powder, the worse the stability. Therefore, the particle size of the magnesium powder should also meet the stability requirements to ensure the safety of storage and transportation.

[0104] Therefore, there is an optimal particle size requirement for the magnesium powder used in ammunition to balance the activity (usage requirement) and stability (storage requirement).

[0105] From the perspective of use, the narrower the particle size distribution range, the better the uniformity and homogeneity of the powder, which is more conducive to the filling of ammunition and the full play of the explosion performance.

[0106] The roundness of the magnesium powder will affect the quality and usage performance of the ammunition.

[0107] The non-roundness of the powder will affect:

[0108] 1) The loose packing density and the filling density, and further affect the size of the package and the filling amount; further, it will affect the explosion speed and the uniformity of the explosion temperature;

[0109] 2) When the roundness is not enough or there are even spikes, it may lead to local hot spots and non-critical point detonation.

[0110] The ammunition manufactured by the above method uses magnesium powder with small particle size, small particle size distribution range, and good roundness, improving the safety during production, assembly, and transportation and the controllability of ammunition explosion.

[0111] Specifically, the most probable particle size of the magnesium powder in this embodiment is 480 nm, the particle size distribution range is 330 - 610 nm, and the roundness is not greater than 0.01 μm.

[0112] Fourthly, this embodiment also provides a kind of fireworks manufactured by the above magnesium powder. The fireworks include military illuminating projectiles, flash bombs, interference bombs, and civilian fireworks, etc.

[0113] Fifthly, this embodiment also provides a preparation device for ultrafine magnesium powder, which includes a melting furnace 3, a vacuum pump 20, a spraying device 7, a collection tower 19, a liquid storage tank 15, a first pressure pump 2, and a second pressure pump 22. The spraying device 7 includes a Venturi tube 21 and a molten magnesium delivery pipe 17. The Venturi tube 21 includes an inlet, a throat 16, and a spraying port;

[0114] The liquid storage tank 15 is connected to the inlet of the Venturi tube 21 through a first pipeline 24. The diameter of the first pipeline 24 is the same as the diameter of the inlet of the Venturi tube 21, and a first pressure pump 2 is arranged on the first pipeline 24;

[0115] One end of the molten magnesium delivery pipe 17 is connected to the melting furnace 3, and the other end is inserted into the throat 16;

[0116] A vacuum pump 20 is arranged on the melting furnace 3;

[0117] The melting furnace 3 is connected to the liquid storage tank 15 through a second pipeline 25, and a second pressure pump 22 is arranged on the second pipeline 25.

[0118] The Venturi tube 21 is connected to the upper end of the collection tower 19 through the spraying port.

[0119] Specifically, the melting furnace 3 is used to melt magnesium blocks. After adding magnesium metal blocks to the melting furnace 3, the magnesium powder preparation device is closed. First, use the vacuum pump 20 to evacuate the entire magnesium powder preparation device to make the absolute pressure of the system drop below 100 Pa, and then purge with rare gas to remove the air in the magnesium powder preparation device, especially oxygen, to complete the operation of replacing air with rare gas in the magnesium powder preparation device.

[0120] The melting point of magnesium is 651 °C. Turn on the heating furnace to ensure that the temperature rises above 651 °C, preferably 720 °C, and keep it at a constant temperature, which can ensure that the magnesium blocks are fully melted into liquid.

[0121] After the liquid rare gas is fed into the injection device 7, the endothermic part vaporizes, turning into a high-pressure and high-speed gas-liquid mixed gas flow. When the gas-liquid mixed gas flow passes through the throat 16 of the injection device 7 at high speed, according to Bernoulli's equation, a negative pressure will be generated at the throat 16, sucking the molten magnesium into the throat 16 of the Venturi tube 21. After the molten magnesium enters the throat 16, it is crushed and atomized by the high-speed gas flow and is quickly condensed by the cold rare gas (a mixture of gaseous and liquid rare gases). The high-quality and high-speed atomization and rapid cooling ensure that the formed ultrafine magnesium powder maintains a high roundness and is then sprayed into the collection tower 19 for collection.

[0122] That is to say, by adjusting the rotation speed and pressure of the rare gas delivery pump, the spraying speed of the rare gas is adjusted, and further the atomization degree and cooling speed of the molten metal magnesium are adjusted to control the particle size and distribution of the magnesium powder, as well as the production efficiency, so as to prepare magnesium powder with a particle size meeting the requirements.

[0123] Furthermore, a valve is provided on the magnesium liquid delivery pipe 17, preferably a high-temperature mechanical valve.

[0124] The particle size of the magnesium powder is related to the liquid inlet speed of the magnesium liquid. The smaller the speed of the magnesium liquid entering the Venturi tube 21, the smaller the particle size of the formed magnesium powder. By effectively and stably controlling the liquid inlet speed of the magnesium liquid, the particle size stability of the prepared magnesium powder product is ensured, and the particle size distribution range of the magnesium powder is small.

[0125] The control mode of the magnesium liquid entering the Venturi tube 21 can also adopt valve control, preferably a high-temperature mechanical valve. The high-temperature mechanical valve is arranged on the magnesium liquid delivery pipe 17 and is used to adjust the flow rate of the magnesium liquid.

[0126] As a possible implementation manner, the control mode of the magnesium liquid entering the Venturi tube 21 can adopt pressure control. Specifically, the melting furnace 3 is connected to the liquid storage tank 15 through the second pipeline 25, and a second pressure pump 22 is arranged on the second pipeline 25. The pressure of the gas entering the melting furnace 3 from the liquid storage tank 15 is adjusted by the pump so that the air pressure in the melting furnace 3 reaches the set value. At this set value, the flow rate of the magnesium liquid can meet the requirements of the particle size of the prepared magnesium powder.

[0127] As a possible implementation manner, the control mode of the magnesium liquid entering the Venturi tube 21 can also be controlled by the air flow speed according to the Venturi effect, that is, the greater the flow rate of the gas-liquid mixture, the greater the liquid inlet speed of the magnesium liquid, and the smaller the flow rate of the gas-liquid mixture, the smaller the liquid inlet speed of the magnesium liquid.

[0128] Further, referring to the appendix Figures 12 - 14 , the diameter of the inlet of the Venturi tube 21 is 30 - 100 mm, the diameter of the throat 16 is 3 - 10 mm, and the diameter of the outlet is 10 - 80 mm.

[0129] Furthermore, the inner diameter of the magnesium liquid delivery pipe 17 is 2.0 mm.

[0130] Further, a partition plate 8 is fixed to the inner wall of the furnace chamber of the melting furnace 3. The partition plate 8 divides the furnace chamber into an upper chamber and a lower chamber. The partition plate 8 has a through hole 18. A floating ball 6 is arranged in the lower chamber. The diameter of the floating ball 6 is larger than the diameter of the through hole 18. The cooperation of the floating ball 6 and the through hole 18 keeps the liquid level height of the molten magnesium within a preset range. As a possible implementation manner, the preset range may be between 1 / 10 and 1 / 2 of the furnace chamber height; the preset range may also be between 1 / 5 and 1 / 3 of the furnace chamber height, preferably 1 / 4 of the furnace chamber height.

[0131] Further, one end of the molten magnesium delivery pipe 17 is connected to the lower chamber of the melting furnace 3.

[0132] It can be understood that the cooperation of the floating ball 6 and the through hole 18 keeps the liquid level of the molten magnesium within a suitable height range, that is, after the magnesium blocks in the upper chamber of the melting furnace are melted into molten magnesium, the molten magnesium flows into the lower chamber through the through hole 18. The floating ball can float on the liquid surface of the molten magnesium. As the molten magnesium in the lower chamber increases, the liquid level of the molten magnesium rises, and the floating ball rises accordingly until the floating ball blocks the through hole, and the molten magnesium in the upper chamber cannot continue to flow into the lower chamber, and the liquid level of the molten magnesium in the lower chamber no longer rises. When the positions of the partition plate and the through hole are fixed, a floating ball with a smaller diameter requires a higher liquid level of the molten magnesium in the lower chamber to reach the position of the through hole, while a floating ball with a larger diameter requires a lower liquid level of the molten magnesium in the lower chamber to reach the position of the through hole. Therefore, by selecting floating balls with different diameters, the liquid level height of the molten magnesium in the lower chamber can be made to be within the preset range.

[0133] During the preparation of magnesium powder, the molten magnesium in the lower chamber of the melting furnace flows out, the liquid level of the molten magnesium drops, and the floating ball 6 drops accordingly. The floating ball 6 and the through hole 18 on the partition plate 8 are separated from the contact state. The molten magnesium in the upper chamber flows into the lower chamber through the gap between the through hole 18 and the floating ball 6, causing the liquid level of the molten magnesium in the lower chamber to rise, and the floating ball 6 rises accordingly and contacts the through hole 18 again, thereby blocking the through hole 18 and preventing the molten magnesium in the upper chamber from flowing into the lower chamber, so as to adjust and control the liquid level height of the molten magnesium in the lower chamber to always remain within the preset range.

[0134] The above preset range can ensure the outflow speed of the molten magnesium from the pipeline. From Figure 1 it can be seen that the first end of the molten magnesium delivery pipe 17 is arranged at the middle position of the lower chamber of the furnace chamber, and the molten magnesium enters the throat 16 of the Venturi tube 21 from the lower chamber of the furnace chamber through the molten magnesium delivery pipe 17. The flow rate of the molten magnesium is positively correlated with the pressure of the molten magnesium at the first end of the molten magnesium delivery pipe 17, and the pressure of the molten magnesium at the first end depends on the liquid level height of the molten magnesium. Therefore, in order to maintain the stability of the molten magnesium flow rate, the liquid level height of the lower layer of molten magnesium needs to always remain within the preset range.

[0135] The flow rate of the molten magnesium is closely related to the particle size of the magnesium powder. Specifically, the smaller the velocity of the molten magnesium entering the Venturi tube 21, relatively speaking, the less the amount of molten magnesium entering the Venturi tube 21, and the smaller the particle size of the formed magnesium powder. In order to obtain magnesium powder with a uniform particle size, it is necessary to control the flow rate of the molten magnesium entering the Venturi tube 21.

[0136] Further, referring to the appendix Figure 11 , the partition plate 8 is inclined, and the center point of the through hole 18 is higher than the center point of the partition plate 8.

[0137] It can be understood that after the magnesium block is completely melted, metals with higher melting points (such as iron, copper, etc.) and non-metallic residues will precipitate at the bottom of the inclined surface of the partition plate 8 and be collected; while the round hole of the ball valve is in the upper-middle position, and the residues will not enter the lower cavity of the furnace 3 through the round hole, and thus will not enter the injection port, thereby ensuring the purity of the produced magnesium powder.

[0138] Further, referring to the appendix Figures 6 - 8 , a multi-stage vibrating sieve 10 is provided inside the collection tower 19.

[0139] In order to further screen the magnesium powder, different mesh screens are set in this embodiment to further screen the magnesium powder with a smaller particle size range.

[0140] Further, referring to the appendix Figures 6 - 8 , the multi-stage vibrating sieve 10 includes a primary vibrating sieve and a secondary vibrating sieve, and the mesh aperture of the primary vibrating sieve is larger than that of the secondary vibrating sieve.

[0141] The mesh aperture of the primary vibrating sieve is 150 - 300 mesh, preferably 200 mesh, and the secondary vibrating sieve is equipped with a 300 - 500 mesh, preferably 400 mesh screen.

[0142] It can be understood that by setting the multi-stage vibrating sieve 10, the magnesium powder is screened according to the particle size to obtain magnesium powder with different particle size distribution ranges.

[0143] By setting the multi-stage vibrating sieve 10, the magnesium powder is screened according to the particle size to obtain magnesium powder with different particle size distribution ranges. The primary screening uses a 200-mesh screen, and the secondary screening uses a 400-mesh screen; two specifications of magnesium powder with a particle size range of 33 - 74 um and a particle size less than 33 um can be obtained.

[0144] Further, referring to the appendix Figure 1 、 2 、4、6, it further includes a gas circulation system, and the gas circulation system includes a gas recovery device, a liquid storage tank 15 and the above-mentioned first pipeline 24;

[0145] The gas recovery device includes a dust removal filter 13, a cooler 14 and a third pressure pump 23;

[0146] One end of the dust removal filter 13 is connected to the collection tower 19, and the other end is connected to the cooler 14. A third pressure pump 23 is arranged between the dust removal filter 13 and the cooler 14;

[0147] The other end of the cooler 14 is connected to the liquid storage tank 15.

[0148] Specifically, when the liquid rare gas enters the spraying device 7, it absorbs heat and partially vaporizes. After contacting the molten magnesium liquid, it further vaporizes, forming a first gas in the collection tower 19. The first gas enters the dust removal filter 13, and after dust removal and filtration, it is pressurized to about 10 MPa, sent to the cooler 14 for cooling to below -80 °C, and then sent back to the liquid storage tank 15 to realize the recovery and recycling of the rare gas.

[0149] After processing the magnesium liquid, the rare gas contains ultrafine magnesium powder and needs to be dust-removed and filtered by the dust removal filter 13 before it can be used again. Therefore, ultrafine magnesium powder remains in the dust removal filter 13. By regularly cleaning the dust removal filter 13, the collected ultrafine magnesium powder can be recovered.

[0150] Furthermore, the working process of the gas recovery device is as follows: After the gas is dust-removed and filtered by the dust removal filter 13, it is pressurized to 10 MPa by the third pressure pump 23, transported into the cooler 14 for cooling to below -80 °C, and then transported into the liquid storage tank 15 to realize the recovery and recycling of the gas.

[0151] Next, the magnesium powders obtained by different preparation methods and under different preparation conditions are compared.

[0152] In Examples 1, 2, 3, 4, and 5, magnesium powders are prepared according to the preparation conditions in Table 1, and the specific operation steps are as follows:

[0153] 1. Cut the purchased magnesium bars or magnesium blocks into small magnesium blocks with a side length of less than 10 cm and put them into the heating furnace;

[0154] 2. Evacuate the entire system with the argon valve closed; after the absolute pressure of the system drops below 100 Pa, maintain the evacuation for more than 10 minutes, and then slowly open the argon valve to fill the entire system with argon;

[0155] 3. Turn on the heating furnace and heat it up to 720 °C at a rate of 10 °C per minute and keep it at a constant temperature for more than 30 minutes;

[0156] 4. Adjust the rotation speed of the first argon pressure pump 2 connected to the injection port, gradually increase the flow rate at the injection port to the set speed, and make the gas-liquid mixture ratio (gas: liquid) reach the set value;

[0157] 5. Open the valve of the magnesium liquid delivery pipe 17;

[0158] 6. The multi-stage vibrating sieve of the collection tower 19 screens the dropped magnesium powder.

[0159] 7. High-purity and high-roundness magnesium powder is collected at the bottom of the collection tower 19.

[0160] 8. After the argon gas is dust-removed and filtered, it is pressurized to about 10 MPa, sent to the cooler 14 for cooling down to below -80 °C, and then sent back to the liquid argon tank to achieve recovery and recycling.

[0161] 9. Close all the valves connecting the collection tower 19, and then transfer to the next post-treatment processes such as magnesium powder passivation (if necessary), collection, and encapsulation.

[0162] Comparative Examples 1 and 2 are prior arts, and magnesium powder is prepared according to conventional conditions and steps.

[0163] Table 1. Comparison of the performance parameters of magnesium powder obtained by different preparation methods and conditions

[0164]

[0165] As can be seen from Table 1, for the magnesium powder prepared by the Venturi tube in Examples 1, 2, 3, 4, and 5, various indexes such as the most probable particle size, particle size distribution range, roundness, and activity are superior to those of the magnesium powder prepared by the mechanical method and the ordinary atomization method.

[0166] As can be seen from Examples 1, 2, and 3, the greater the injection speed of the gas-liquid mixture, the smaller the particle size of the obtained magnesium powder, the narrower the particle size distribution range, and the better the roundness. By setting the injection speed of the gas-liquid mixture, magnesium powder of different specifications can be obtained.

[0167] As can be seen from Examples 1, 4, and 5, when the gas-liquid mixture ratio (gas: liquid) is 23:1, the most probable particle size of the obtained magnesium powder is the smallest, which is 460 nm, the particle size distribution range is the narrowest, which is 350 - 510 nm, and the roundness is the best, not greater than 0.008 μm. This is the optimal value of the gas-liquid mixture ratio. Under this optimal value, all parameters of the obtained magnesium powder are the best.

[0168] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0169] It is not difficult for those skilled in the art to understand that the present invention includes any combination of the invention content and the specific implementation part of the above description and each part shown in the drawings. Due to space limitations and to make the description concise, the various solutions formed by these combinations are not described one by one. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0170] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, replacements, and variations to the above embodiments within the scope of the present invention without departing from the principle and purpose of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing magnesium powder, characterized in that, Prepared by a Venturi tube; The gas-liquid mixture enters the Venturi tube at a first speed, and the molten magnesium enters the Venturi tube at a second speed. The gas-liquid mixture and the molten magnesium are mixed at the throat of the Venturi tube to form magnesium powder; The gas-liquid mixture is composed of rare gases and does not chemically react with magnesium; The first speed is at least 5 m / s; The mass ratio of the gas-liquid mixture is 1:10 - 1:30; For the gas-liquid mixture, after the liquid rare gas is fed into the Venturi tube, a part of it absorbs heat and vaporizes to become a gas-liquid mixed gas stream.

2. The method for preparing magnesium powder according to claim 1, characterized in that, It also includes a melting furnace, a collection tower and pipelines. The Venturi tube, the collection tower and the pipelines form a preparation system. The steps of collecting magnesium powder using the preparation system are as follows: 1) After the absolute pressure of the preparation system drops below 100 Pa, fill the entire preparation system with rare gases; 2) Heat the melting furnace to above 651 °C and keep it at a constant temperature; 3) Gradually increase the flow rate of the gas-liquid mixture at the throat to the first speed. The molten magnesium enters the Venturi tube at the second speed. The gas-liquid mixture and the molten magnesium are mixed at the throat of the Venturi tube to form magnesium liquid droplets with uniform particle size and a first gas. The magnesium liquid droplets solidify into magnesium powder in the Venturi tube; 4) Screen the magnesium powder to obtain magnesium powder.

3. The preparation method of magnesium powder according to claim 1, characterized in that, The screening of the magnesium powder is carried out by a multi-stage vibrating sieve. The multi-stage vibrating sieve includes a first-stage vibrating sieve and a second-stage vibrating sieve. The screen aperture of the first-stage vibrating sieve is larger than that of the second-stage vibrating sieve.

4. The preparation method of magnesium powder according to claim 2, characterized in that, It also includes passivation of magnesium powder.

5. The preparation method of magnesium powder according to claim 4, characterized in that, The passivation method is: mix rare gases and oxygen to obtain a mixed gas, slowly introduce the mixed gas into the collection tower, vibrate or stir the magnesium powder to form a dense magnesium oxide film on the surface of the magnesium powder.

6. The method for preparing magnesium powder according to claim 2, wherein The relative humidity of the gas in the preparation system does not exceed 2%.

7. The method for preparing magnesium powder according to claim 2, wherein It also includes that the first gas is formed into a liquid after dust removal, pressurization and cooling, and is recycled.

8. The method for preparing magnesium powder according to claim 1, wherein, It also includes a melting furnace for melting magnesium blocks. An inclined partition is fixed on the inner wall of the furnace cavity of the melting furnace, dividing the furnace cavity of the melting furnace into an upper cavity and a lower cavity. The partition has a through hole. A floating ball is arranged in the lower cavity. The diameter of the floating ball is larger than the diameter of the through hole. The liquid level height of the molten magnesium is maintained within a preset range through the cooperation of the floating ball and the through hole.

9. A kind of magnesium powder, characterized in that, Prepared by the method for preparing magnesium powder according to any one of claims 1 - 8.

10. A kind of ammunition, characterized in that, Manufactured from the magnesium powder according to claim 9.

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