Polycrystalline fluoride coated particles and preparation process and device thereof

Abstract

The invention discloses polycrystalline fluoride coated particles and a preparation process and device thereof. The polycrystalline fluoride coated particles are regular cylindrical particles, the diameter is 5-20 mm, the apparent density is 99.8% of the theoretical density, and the purity is 99.995 wt.% or above. The preparation device is a vertical furnace with vacuum and inert atmosphere protection capabilities at the same time, and sequentially comprises a smelting cavity, a crystallization cavity and a discharging transition bin from top to bottom; and after the fluoride powder is completely melted, the melt enters a crystallization cavity to form a cylindrical polycrystalline rod, and then the cylindrical polycrystalline rod is cut off to a fixed length to form particles. Polycrystalline fluoride coating particles are produced through efficient continuous casting, the automation level is improved, raw materials are continuously supplemented, and continuous production can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of ceramics, and in particular relates to a polycrystalline fluoride coating particle and a preparation process and device thereof. Background Art

[0002] Polycrystalline particles of lithium fluoride are used as coating materials in the preparation of OLED display panels as a functional film layer to improve brightness. At present, the production method of lithium fluoride polycrystalline coated particles is to melt lithium fluoride powder in a graphite crucible and statically grow it into a polycrystalline block, and then crush and screen it into particles to obtain the product. This product has an irregular shape and is easy to absorb moisture. Excessive water content will cause the crystal surface to be rough, and the transparency and transmittance will also be significantly deteriorated, which will affect the product performance when used. In addition, it will also be exposed to moisture in the air during the production process. After the lithium fluoride particles after deliquescence are placed in the coating machine, they will release water vapor and poison the luminescent layer.

[0003] On the other hand, the physical properties of lithium fluoride crystals, such as low hardness, easy dissociation, easy deliquesce, and high linear thermal expansion coefficient, make them difficult to process. Summary of the invention

[0004] The object of the present invention is to provide a polycrystalline fluoride coated particle, more specifically a cylindrical polycrystalline lithium fluoride particle with a diameter of 5-20 mm, an apparent density of more than 99.8% of the theoretical density, a regular and dense surface, not easy to absorb moisture, and a moisture content not exceeding 10 ppm.

[0005] Another object of the present invention is to provide a device and process for preparing cylindrical fluoride coated particles, so as to solve the problems of irregular shape and easy moisture absorption of existing products, improve product performance, and improve product production efficiency. The object of the present invention can be achieved through the following technical approaches.

[0006] A manufacturing device for polycrystalline fluoride coated particles is a vertical furnace with both vacuum and inert atmosphere protection capabilities, which includes a smelting chamber, a crystallization chamber, and a discharge transition chamber from top to bottom; the smelting chamber is a closed chamber, and the chamber wall is provided with a vacuum system connection port; the chamber includes a smelting crucible and a heating device; the bottom of the smelting crucible is provided with an opening connected to the casting crucible in the crystallization chamber, and the opening is closed and connected with a flow control stopper rod, and the opening and closing degree of the bottom of the smelting crucible is controlled by moving the flow control stopper rod, so as to adjust the outflow speed of the molten metal in the smelting crucible; The lower end of the casting crucible in the crystal cavity is connected to the crystallizer, and a traction mechanism is provided under the crystallizer. The traction mechanism includes a traction plate and a plurality of traction rods on the traction plate, which are used to guide the polycrystalline fluoride crystal rods prepared in multiple stations down to the cutting mechanism for cutting; the crystallization cavity is a closed cavity, which is connected to the water cooling circulation system, and a vacuum system connection port is provided on the side wall. The lower end is connected to the discharge transition bin, and a first baffle valve is provided at the connection; the discharge transition bin is a closed cavity, and a vacuum system connection port is provided on the side wall. The lower end is a material discharge port, and a baffle valve is provided at the bottom to control the opening and closing of the discharge port.

[0007] Preferably, the crystallizer is a parallel multi-porous structure, and multiple crystal rods are drawn down side by side.

[0008] The present invention also provides a method for preparing polycrystalline fluoride coated particles using the above device, comprising the following steps:

[0009] (1) The flow control stopper rod at the bottom of the smelting chamber is in a closed state, the fluoride raw material is loaded, vacuum is drawn, and the heating system is turned on for preheating;

[0010] (2) Inert atmosphere gas is filled to make the pressure of the melting chamber reach 0.04MPa~0.08MPa; the temperature is continued to be raised to melt the fluoride powder in the melting crucible to obtain a melt; reducing the amount of gas filled and maintaining a high vacuum degree is conducive to reducing the gas impurity content in the melt.

[0011] (3) Open the cooling system of the crystallizer, adjust the pressure of the crystallization cavity, open the flow control stopper rod, and inject the melt into the casting crucible; when the liquid level in the casting crucible reaches three quarters, start the traction mechanism, and the traction rod introduces the melt into the crystallizer at a speed of 5 to 15 mm / min; adjust the flow control stopper rod and adjust the outflow speed of the melt in the smelting crucible to keep the liquid level in the casting crucible constant; the melt crystallizes and solidifies into a crystal rod at the outlet of the crystallizer; the speed of the traction rod is consistent with the crystallization speed of lithium fluoride.

[0012] (4) pulling the crystal rod from step (3) down into a cutting mechanism to cut the crystal rod into particles;

[0013] (5) Open the baffle valve at the bottom of the crystallization chamber, and the particles fall into the discharge transition bin. Close the baffle valve at the bottom of the crystallization chamber, open the discharge port of the discharge transition bin, and the particles fall into the vacuum packaging system for packaging.

[0014] Preferably, in step (2), the upper temperature of the crystallizer is 840°C, the middle temperature is 760±20°C, the outlet temperature is 600±50°C, and the temperature is controlled by the introduction rate of cooling water into the crystallizer.

[0015] Preferably, the preheating temperature in step (1) is 300° C. to 500° C.; the vacuum pressure in the smelting chamber does not exceed 0.01 Pa, and the temperature is kept constant for 2 to 8 hours.

[0016] Preferably, the melting temperature in step (2) is 880-900°C. After complete melting, the pressure of the melting chamber is adjusted to 0.04-0.02MPa for heat preservation. The melting point of lithium fluoride is 845°C, and the melting temperature can be 20-100°C higher than the melting point.

[0017] Preferably, the pressure of the crystallization cavity in step (3) is 0.02 MPa to 0.04 MPa.

[0018] Preferably, the method for transferring particles in step (5) is as follows: opening the baffle valve at the bottom of the crystallization cavity in sequence, allowing the particles to fall into the discharge transition bin, then closing the baffle valve at the bottom of the crystallization cavity, opening the baffle valve at the bottom of the discharge transition bin, allowing the particles to fall into the discharge port, then closing the baffle valve at the bottom of the discharge transition bin, opening the vacuum system, evacuating to a pressure better than 5 Pa, and filling with inert atmosphere gas to 1 atmosphere to complete a discharge cycle.

[0019] Beneficial effects: The present invention adopts a continuous casting dynamic crystallization method to prepare polycrystalline lithium fluoride, and can obtain regular cylindrical crystal rods of any length or specific length, with a regular and dense surface that is not easy to absorb moisture.

[0020] Continuous casting process is common in the preparation of metal materials, and there has been no report on the preparation of inorganic non-metallic materials such as fluoride crystals by continuous casting. Because the material properties of metals and inorganic non-metals are very different, the preparation of fluoride crystals depends more on specific molding methods and technologies. The preparation process requires precise control and specific technical means to ensure the quality and performance of the crystals. It can be divided into gas phase method, solution method, melt method, epitaxial method, etc. The most widely used and mature one is the melt growth method. Typical melt growth techniques mainly include Czochralski method, crucible descent method, directional solidification method, zone melting method, etc. The common feature of these crystal growth methods is slow speed.

[0021] The present invention innovatively applies the continuous casting process to the growth of lithium fluoride crystals, continuously replenishes raw materials, and can also achieve continuous production. The production efficiency is higher than that of a static polycrystalline furnace, which is conducive to large-scale production and continuous production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the device of the present invention;

[0023] Figure 2 It is a schematic diagram of the process flow of the present invention;

[0024] Figure 3 The polycrystalline lithium fluoride particles prepared in the embodiment of the present invention are regular cylindrical;

[0025] Figure 4 Polycrystalline lithium fluoride made by traditional process, irregular shape.

[0026] Explanation of reference numerals: 1. Melting chamber; 2. Crystallization chamber; 3. Discharging transition chamber; 11. Melting crucible; 12. Flow control stopper rod; 21. Casting crucible; 22. Crystallizer; 23. Traction mechanism; 24. Cutting mechanism; 31. First baffle valve; 32. Second baffle valve; 33. Discharging port; 231. Traction plate; 221. Water cooling circulation system; 4. Vacuum system connection port DETAILED DESCRIPTION

[0027] In order to better understand the technical solution of the present invention, the embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. It should be clear that the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] The "first\second" mentioned in the embodiments is only to distinguish similar objects, and does not represent a specific order for the objects. It is understandable that the "first\second" can be interchanged with a specific order or sequence where permitted. It should be understood that the objects distinguished by "first\second" can be interchanged where appropriate, so that the embodiments described herein can be implemented in an order other than those illustrated or described herein. The test materials used in the present invention are common commercial products, all of which can be purchased on the market.

[0029] A manufacturing device for polycrystalline fluoride coated particles is a vertical furnace with both vacuum and argon protection capabilities, which includes, from top to bottom, a smelting chamber 1, a crystallization chamber 2, and a discharge transition chamber 3; the smelting chamber 1 is a closed chamber, and the chamber wall is provided with a vacuum system connection port 4; the chamber includes a smelting crucible 11 and a heating device; an opening is provided at the bottom of the smelting crucible 11 to communicate with a casting crucible 21 in the crystallization chamber 2, and the opening is closed and connected to a flow control stopper rod 12, and the opening and closing degree of the bottom of the smelting crucible 11 is controlled by moving the flow control stopper rod 12 to adjust the outflow speed of the molten metal in the smelting crucible; the casting crucible in the crystallization chamber 2 The lower end of 21 is connected to the crystallizer 22, and a traction mechanism 23 is provided below the crystallizer 22. The traction mechanism 23 includes a traction plate 231 and a plurality of traction rods on the traction plate 231, which are used to guide the polycrystalline fluoride crystal rods prepared in multiple stations to the cutting mechanism 24 for cutting; the crystallization cavity 2 is a closed cavity, which is connected to the water cooling circulation system 221, and a vacuum system connection port 4 is provided on the side wall, and the lower end is connected to the discharge transition bin 3, and a first baffle valve 31 is provided at the connection; the discharge transition bin 3 is a closed cavity, and a vacuum system connection port 4 is provided on the side wall, and the lower end is a material discharge port 33, and a baffle valve is provided at the bottom to control the opening and closing of the discharge port 33.

[0030] In one preferred embodiment, the crystallizer 22 is a parallel multi-hole structure, and multiple crystal rods are drawn down side by side.

[0031] The specific process steps are: 1) melting lithium fluoride powder in a melting crucible 11, 2) degassing and purification, 3) starting the continuous casting traction plate 231 below the crystallizer 22 to continuously cast multiple lithium fluoride crystal rods from the crystallizer 22, and 4) after the pulled crystal rods reach a predetermined length, a cutting device is provided below the continuous casting mechanism to cut the crystal rods into particles. This process continuously replenishes raw materials and can achieve continuous production. See the process flow Figure 2 .

[0032] Example 1 (first-class product)

[0033] 20 kg of 99.99% pure lithium fluoride powder is loaded into the melting crucible 11, filled and compacted, the flow control stopper 12 at the bottom of the melting crucible 11 is in a closed state, the cavity is evacuated to less than 0.01 Pa, the heating system is turned on, the temperature of the melting crucible 11 reaches 460°C, and the temperature is kept constant for 2 hours. According to the shape of the material, 10-20 kg of material is loaded per furnace; the shorter the constant temperature time, the more metal impurities and gas impurities such as hydrogen and oxygen in the material.

[0034] Inert gas argon is filled to make the pressure of the melting chamber 11 reach 0.04-0.08MPa; the temperature is continued to be raised to make the temperature of the melting crucible 11 reach 880-900°C. After the raw materials in the melting crucible 11 are completely melted into liquid, the temperature is kept for 1 hour and the pressure of the melting chamber 11 is adjusted to 0.02-0.04MPa.

[0035] After keeping warm for a period of time, turn on the cooling system of the crystallizer 22, the cooling water inlet temperature is 40-65°C, and turn on the temperature control system and cooling water flow control system of the crystallizer 22; adjust the pressure of the crystallization cavity 22 to 0.02-0.04MPa, open the flow control stopper rod 12, and inject the liquid lithium fluoride melt into the casting crucible 21. When the liquid level in the casting crucible 21 reaches three quarters, start the traction mechanism 23, and the traction rod introduces the molten lithium fluoride liquid into the crystallizer 22 at a speed of 10-15mm / min; adjust the flow control stopper rod 12, and adjust the outflow rate of the molten lithium fluoride from the melting crucible 11 to keep the liquid level in the casting crucible 21 constant. Preferably, the crystallizer 22 is a parallel porous structure, which can simultaneously draw down multiple lithium fluoride polycrystalline rods side by side. The upper temperature of the crystallizer is 840°C, the middle temperature is 760±20°C, and the outlet temperature is 600±50°C. The temperature is controlled by the introduction rate of cooling water into the crystallizer 22.

[0036] When the polycrystalline lithium fluoride rod is pulled down and enters the cutting mechanism 24, the cutting machine is started and the shearing frequency is adjusted to achieve the required fixed length, such as 5mm, 8mm, 10mm. After the cut lithium fluoride particles reach a certain amount in the crystallization cavity 2, the particles are transferred to the discharge port 33 through the discharge transition bin 3, fall into the vacuum packaging system, and are directly measured and packaged into products without being exposed to the atmospheric environment during the intermediate process.

[0037] More specifically, the method for transferring particles is to open the baffle valve at the bottom of the crystallization chamber 2 in sequence, and the particles fall into the discharge transition bin 3, then close the baffle valve at the bottom of the crystallization chamber 2, open the baffle valve at the bottom of the discharge transition bin 3, and the particles fall into the discharge port 33, then close the baffle valve at the bottom of the discharge transition bin 3, open the vacuum system, evacuate to better than 5Pa, fill in inert gas argon to 1 atmosphere, and complete a discharge cycle.

[0038] Preferably, clean the equipment and processing tools with alcohol and dust-free cloth before melting; check that there are no visible water droplets on the materials entering the furnace and that the mold does not feel wet when touched by hand.

[0039] The product has a diameter of 5mm-20mm and a density of >2.63g / cm 3 , the apparent density is the theoretical density (2.64g / cm 3 ) above 99.8%; purity 99.9966wt.%, moisture content 10ug / g, other impurities are detailed in Table 1. The yield rate of continuous casting is 96%, and the cost is greatly reduced. Figure 3 As shown, Example 1 produces regular cylindrical polycrystalline lithium fluoride.

[0040] Comparative Example 1, the existing technology is used to carry out the following steps:

[0041] 1) 20 kg of 99.99% pure lithium fluoride powder was placed in a circular graphite crucible with a diameter of 150 mm × h220 mm. After compaction, the crucible was placed in a vacuum melting furnace and evacuated to 1.0 × 10 -2 Pa, raise the temperature to 850℃, keep it for 5 hours, fill with argon gas to make the vacuum in the furnace 0.08MPa, keep it warm for 3 days, cool it down to room temperature and take it out of the furnace.

[0042] 2) Take out the round lithium fluoride ingot from the graphite crucible and use a grinding device to remove the graphite adhering to the surface.

[0043] 3) Use a jaw crusher to crush the polished lithium fluoride ingot into particles.

[0044] 4) Use 20-mesh and 3-mesh sieves to sieve the crushed particles to remove the fine powder under the 20-mesh sieve and the coarse particles on the 3-mesh sieve.

[0045] 5) Use compressed air to blow off the screened particles and package the product.

[0046] The product prepared according to the above steps, from crystal ingot to granular finished product, has a yield rate of 65%, a purity of 99.9843%, and a moisture content of 100ug / g, which is much higher than that of Example 1. Figure 4 As shown, the polycrystalline lithium fluoride obtained by the conventional process in Comparative Example 1 is irregular in shape and easily absorbs moisture.

[0047] Table 1 Purity test results of Example 1 (first-class product) and Comparative Example 1

[0048]

[0049] Example 2 (superior product), follow the steps of Example 1,

[0050] Before melting, clean the equipment and processing tools with alcohol and dust-free cloth; check that there are no visible water drops on the materials entering the furnace and that the molds do not feel wet when touched. Load 20 kg of 99.999% pure lithium fluoride powder into the melting crucible 11, fill it up and compact it, keep the flow control stopper 12 at the bottom of the melting crucible 11 in a closed state, evacuate the cavity to less than 0.005 Pa, turn on the heating system, and make the temperature of the melting crucible 11 reach 500°C, and keep the temperature constant for 8 hours. Depending on the shape of the material, charge 10-20 kg per furnace; the shorter the constant temperature time, the more metal impurities and gas impurities such as hydrogen and oxygen in the material.

[0051] Inert gas argon is filled to make the pressure of the melting chamber 11 reach 0.04-0.08MPa; the temperature is continued to be raised to make the temperature of the melting crucible 11 reach 880-900°C. After the raw materials in the melting crucible 11 are completely melted into liquid, the temperature is kept for 2 hours and the pressure of the melting chamber 11 is adjusted to 0.02-0.04MPa.

[0052] After keeping warm for a period of time, turn on the cooling system of the crystallizer 22, the cooling water inlet temperature is 40-65°C, and the temperature control system and cooling water flow control system of the crystallizer 22 are turned on; adjust the pressure of the crystallization cavity 22 to 0.02-0.04MPa, open the flow control stopper rod 12, and inject the liquid lithium fluoride melt into the casting crucible 21. When the liquid level in the casting crucible 21 reaches three quarters, start the traction mechanism 23, and the traction rod introduces the molten lithium fluoride liquid into the crystallizer 22 at a speed of 5-10mm / min; adjust the flow control stopper rod 12, and adjust the outflow rate of the molten lithium fluoride in the melting crucible 11 to keep the liquid level in the casting crucible 21 constant. Preferably, the crystallizer 22 is a parallel porous structure, which can simultaneously draw down multiple lithium fluoride polycrystalline rods side by side. The upper temperature of the crystallizer is 840°C, the middle temperature is 760±20°C, and the outlet temperature is 600±50°C. The temperature is controlled by the introduction rate of cooling water into the crystallizer 22.

[0053] When the polycrystalline lithium fluoride rod is pulled down and enters the cutting mechanism 24, the cutting machine is started and the shearing frequency is adjusted to achieve the required fixed length, such as 5mm, 8mm, 10mm. After the cut lithium fluoride particles reach a certain amount in the crystallization cavity 2, the particles are transferred to the discharge port 33 through the discharge transition bin 3, fall into the vacuum packaging system, and are directly measured and packaged into products without being exposed to the atmospheric environment during the intermediate process.

[0054] The method of particle transfer is the same as that in Example 1.

[0055] The obtained regular cylindrical product has a diameter of 5mm-20mm and a density of >2.63g / cm 3 , the apparent density is the theoretical density (2.64g / cm 3 ) above 99.8%; purity 99.9992wt.%, moisture content 5ug / g, other impurity contents are detailed in Table 2. The yield rate of continuous casting is 96%, and the cost is greatly reduced.

[0056] Comparative Example 2: According to the steps of Comparative Example 1, 1) 20 kg of 99.999% pure lithium fluoride powder was placed in a circular graphite crucible with a diameter of 150 mm × h220 mm, and after compaction, the crucible was placed in a vacuum melting furnace and evacuated to 1.0 × 10 -2 Pa, raise the temperature to 850℃, keep it for 5 hours, fill with argon gas to make the vacuum in the furnace 0.08MPa, keep it warm for 3 days, cool it down to room temperature and take it out of the furnace.

[0057] 2) Take out the round lithium fluoride ingot from the graphite crucible and use a grinding device to remove the graphite adhering to the surface.

[0058] 3) Use a jaw crusher to crush the polished lithium fluoride ingot into particles.

[0059] 4) Use 20-mesh and 3-mesh sieves to sieve the crushed particles to remove the fine powder under the 20-mesh sieve and the coarse particles on the 3-mesh sieve.

[0060] 5) Use compressed air to blow off the screened particles and package the product.

[0061] According to the above steps, irregular shaped products are made, from crystal ingots to granular finished products, with a yield of 65%, a purity of 99.9944%, and a moisture content of 50ug / g, which is significantly higher than that of Example 2.

[0062] Table 2 Purity test results of Example 2 (superior product) and Comparative Example 2

[0063]

[0064] The smelting crucible and the casting crucible of the present invention remain stationary, and holes are opened at the bottom of the smelting crucible and the casting crucible, and liquid flows out of the holes and flows to the crystallizer (cooling zone). The cooled cylinder is pulled downward, becoming longer and longer little by little, and then cut to a fixed length. The present invention satisfies the integrated and automated production of cylindrical polycrystalline lithium fluoride particles, improves production efficiency while improving material performance, and solves the problem that the material is easy to absorb moisture and has poor stability during use.

[0065] The above contents are only basic descriptions of the present invention, and any equivalent changes made according to the technical solution of the present invention shall fall within the protection scope of the present invention.

Claims

1. A polycrystalline fluoride coated particle, characterized in that The polycrystalline fluoride coating particles are cylindrical particles with a diameter of 5mm-20mm, an apparent density of more than 99.8% of the theoretical density, a purity of not less than 99.995wt.%, and a moisture content of not more than 10ppm; the fluoride is selected from lithium fluoride.

2. A method for preparing polycrystalline fluoride coated particles, characterized in that: The following steps are involved: Step 1, loading the fluoride raw material into the smelting chamber (1), evacuating the chamber, and turning on the heating system for preheating; Step 2: Filling the inert atmosphere gas to make the pressure of the smelting chamber (1) reach 0.04MPa-0.08MPa; continuing to raise the temperature to 880°C-900°C to melt the fluoride raw material in the smelting crucible (11) to obtain a melt; Step 3, opening the cooling system of the crystallizer (22), adjusting the pressure of the crystallization cavity (2), opening the flow control stopper rod (12), and injecting the melt obtained in step 2 into the casting crucible (21); when the liquid level in the casting crucible (21) reaches three quarters, starting the traction mechanism (23), and the traction rod introduces the melt into the crystallizer (22), and the traction rod speed is 5 to 15 mm / min; adjusting the flow control stopper rod (12) to adjust and control the outflow speed of the melt in the smelting crucible (11), so that the liquid level in the casting crucible (21) remains constant; the melt crystallizes and solidifies into a crystal rod at the outlet of the crystallizer (22); Step 4, pulling the crystal rod obtained in step 3 down into a cutting mechanism (24), and cutting the crystal rod into particles; Step 5: open the baffle valve at the bottom of the crystallization chamber (2), and the particles fall into the discharge transition bin (3); close the baffle valve at the bottom of the crystallization chamber (2), open the discharge port (33) of the discharge transition bin (3), and the particles fall into the vacuum packaging system for packaging.

3. The method according to claim 2, characterized in that In step 3, the upper temperature of the crystallizer (22) is 840°C, the middle temperature is 760±20°C, and the outlet temperature is 600±50°C. The temperature is controlled by the speed of cooling water introduced into the crystallizer (22), and the cooling water inlet temperature is 40-65°C.

4. The method according to claim 2, characterized in that: The preheating temperature in step 1 is 300° C. to 500° C.; the vacuum pressure of the smelting chamber (1) does not exceed 0.01 Pa, and the temperature is kept constant for 2 to 8 hours.

5. The method according to claim 2, characterized in that: After the fluoride raw material in step 2 is completely melted, the pressure of the smelting chamber (1) is adjusted to 0.02MPa-0.04MPa for heat preservation.

6. The method according to claim 2, characterized in that The pressure of the crystallization cavity (2) in step 3 is 0.02MPa-0.04MPa.

7. The method according to claim 2, characterized in that The method for transferring particles in step 5 is specifically as follows: the baffle valve at the bottom of the crystallization chamber (2) is opened in sequence, the particles fall into the discharge transition bin (3), the baffle valve at the bottom of the crystallization chamber (2) is closed, the baffle valve at the bottom of the discharge transition bin (3) is opened, the particles fall into the discharge port (33), the baffle valve at the bottom of the discharge transition bin (3) is closed, the vacuum system is opened, the vacuum is evacuated to less than 5 Pa, and an inert atmosphere gas is filled in to 1 atmosphere to complete a discharge cycle.

8. The device used in the method for preparing polycrystalline fluoride coated particles according to any one of claims 2 to 7, characterized in that: The invention comprises a vertical furnace having both vacuum and inert atmosphere protection capabilities, and comprises, from top to bottom, a smelting chamber (1), a crystallization chamber (2), and a discharge transition chamber (3); the smelting chamber (1) is a closed chamber, and a vacuum system connection port (4) is provided on its chamber wall; the smelting chamber (1) comprises a smelting crucible (11) and a heating device; an opening is provided at the bottom of the smelting crucible (11) to communicate with a casting crucible (21) in the crystallization chamber (2), and the opening is closed and connected with a flow control stopper rod (12); the opening is controlled by moving the flow control stopper rod (12) to control the opening and closing degree of the bottom of the smelting crucible (11), and the outflow speed of the melt in the smelting crucible (11) is adjusted; the casting crucible (21) in the crystallization chamber (2) is opened and closed, and the flow control stopper rod (12) is moved to control the opening and closing degree of the bottom of the smelting crucible (11), and the outflow speed of the melt in the smelting crucible (11) is adjusted; 1) The lower end is connected to the crystallizer (22), a traction mechanism (23) is provided below the crystallizer (22), the traction mechanism (23) comprises a traction plate (231) and a plurality of traction rods on the traction plate (231), and is used to guide the polycrystalline fluoride crystal rods prepared at multiple stations downward to the cutting mechanism (24) for cutting; the crystallization cavity (2) is a closed cavity, the side wall of which is provided with a vacuum system connection port (4), the lower end is connected to the discharge transition bin (3), and a baffle valve is provided at the connection point for controlling the opening and closing of the bottom of the crystallization cavity (2); the discharge transition bin (3) is a closed cavity, the side wall of which is provided with a vacuum system connection port (4), the lower end is a material discharge port (33), and the bottom of which is provided with a baffle valve for controlling the opening and closing of the discharge port (33).

9. The device according to claim 8, characterized in that: The crystallizer (22) is a parallel multi-porous structure, and multiple crystal rods are drawn downward in parallel.

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