Fluorinated rare earth particles as well as preparation method and application thereof

Abstract

The invention discloses rare earth fluoride particles as well as a preparation method and application thereof. The preparation method of the rare earth fluoride particles comprises the following steps that rare earth fluoride powder is sequentially subjected to granulation, heat treatment and screening, and the rare earth fluoride particles can be obtained; wherein the initial vacuum degree of heat treatment ranges from-0.2 MPa to-1.0 MPa; the heat treatment sequentially comprises first-stage heat treatment, second-stage heat treatment and third-stage heat treatment; the temperature of the first-stage heat treatment is 200-1100 DEG C, the temperature of the second-stage heat treatment is 1000-1500 DEG C, and the temperature of the third-stage heat treatment is 400-1100 DEG C. The average particle diameter of the prepared rare earth fluoride particles can reach 1-10 mm, the situation that the rare earth fluoride particles are pumped away in the film evaporation process is avoided, and the yield of the prepared rare earth fluoride particles is high.

Description

Technical Field

[0001] The invention relates to rare earth fluoride particles and a preparation method and application thereof. Background Art

[0002] Rare earth fluoride films have a lower refractive index, a wider transmission band, and higher hardness compared to other fluorides (barium fluoride, calcium fluoride, etc.). The above advantages make rare earth fluoride films widely used in the design of anti-reflection films on various substrates.

[0003] Both rare earth fluoride powder and rare earth fluoride particles can be used to prepare rare earth fluoride films. The particle size of rare earth fluoride powder is relatively small, generally in the micron level, and it is very easy to be sucked away in the evaporation chamber during the evaporation film forming process, resulting in a low utilization rate of rare earth fluoride powder. At present, most of the rare earth fluoride particles produced in the industry are produced by melting rare earth fluoride powder into large blocks and then crushing them. On the one hand, this method will produce micropowder attached to the surface or gaps of the rare earth fluoride particles during the crushing process, causing the rare earth fluoride particles to contaminate the plated parts and the coating furnace chamber when the vacuum is drawn during the evaporation process to form a thin film; on the other hand, this method will obtain a large number of unqualified rare earth fluoride particles that do not meet the particle size requirements during the crushing process, resulting in a low yield of rare earth fluoride particles. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the defects in the prior art that the rare earth fluoride powder has a small particle size, which makes it very easy to be drawn away in the evaporation chamber during the process of evaporation to form a thin film, resulting in low utilization rate, the rare earth fluoride powder is amorphous, resulting in film defects and poor consistency of the thin film formed by evaporation, and the low yield rate of the rare earth fluoride particles obtained by the existing granulation technology, and provide a rare earth fluoride particle and its preparation method and application. The rare earth fluoride particles prepared by the present invention not only have an average particle diameter of 1-10mm, and will not be drawn away during the evaporation of the thin film, but also the prepared rare earth fluoride particles are polycrystalline and have a high yield rate.

[0005] The present invention solves the above technical problems through the following technical solutions.

[0006] The present invention provides a method for preparing rare earth fluoride particles, which comprises the following steps: granulating, heat treating and sieving rare earth fluoride powder in sequence to obtain the rare earth fluoride particles;

[0007] Wherein, the initial vacuum degree of the heat treatment is -0.2 to -1.0MPa; the heat treatment includes one stage heat treatment, two stage heat treatment and three stage heat treatment in sequence; the temperature of the one stage heat treatment is 200-1100°C, the temperature of the two stage heat treatment is 1000-1500°C, and the temperature of the three stage heat treatment is 400-1100°C.

[0008] In the present invention, the type of the rare earth fluoride powder can be conventional in the art, such as samarium fluoride or yttrium fluoride.

[0009] In the present invention, the average particle diameter of the rare earth fluoride powder may be 1-100 μm, for example, 5 μm. The rare earth fluoride powder presents an amorphous morphology. The amorphous state means that the arrangement of atoms in three-dimensional space is disordered.

[0010] In the present invention, the granulation method can be conventional in the art, for example, carried out in a double-roll extrusion granulator.

[0011] In the present invention, the pressure during granulation may be 20-50 MPa, preferably 20-40 MPa, such as 25, 30 or 35 MPa.

[0012] In the present invention, the average particle diameter of the granulated rare earth fluoride powder may be 1-10 mm, preferably 4-8 mm, such as 5 or 6 mm.

[0013] In the present invention, although the average particle diameter of the fluoride rare earth powder after granulation can reach the millimeter level, it still shows an amorphous morphology.

[0014] In the present invention, the initial vacuum degree of the heat treatment is preferably -0.3 to -0.8 MPa, such as -0.6 MPa or -0.7 MPa.

[0015] In the present invention, the heat treatment is preferably carried out in a vacuum muffle furnace. The heat treatment is preferably carried out by spreading the rare earth fluoride powder on a graphite plate and placing it in a vacuum muffle furnace.

[0016] In the present invention, the initial vacuum degree of the heat treatment is preferably obtained by first evacuating the vacuum muffle furnace to a vacuum degree of 1-5Pa, and then filling argon gas until the vacuum degree in the system is (-0.2) to (-1.0) MPa. Preferably, the initial vacuum degree of the heat treatment is preferably obtained by first evacuating the vacuum muffle furnace to a vacuum degree of 2Pa, and then filling argon gas until the vacuum degree in the system is -0.6MPa.

[0017] In the present invention, the temperature of the first stage heat treatment is preferably 450-1080°C, for example 490, 550, 680, 760, 870, 950 or 1075°C.

[0018] In the present invention, the heat treatment period may be 60-100 min, preferably 70-90 min, for example 80 min.

[0019] In the present invention, the rate of heating from room temperature to the temperature of the first stage heat treatment may be 0.1-1.8°C / min, preferably 0.2-1.6°C / min, for example 0.28, 0.77, 0.87, 1.2 or 1.5°C / min.

[0020] In the present invention, the temperature of the second stage heat treatment is preferably 1100-1350°C, for example, 1120, 1180, 1210, 1250, 1300 or 1330°C.

[0021] In the present invention, the time of the second stage heat treatment may be 720-1440 min, preferably 750-900 min, for example 800 min.

[0022] In the present invention, the rate of heating from the temperature of the first stage heat treatment to the temperature of the second stage heat treatment may be 0.4-12°C / min, preferably 0.42-9°C / min, for example 0.45, 0.84, 1.5, 1.17, 5 or 8°C / min.

[0023] In the present invention, the temperature of the three-stage heat treatment is preferably 450-1080°C, for example, 490, 550, 680, 760, 800, 950 or 1075°C.

[0024] In the present invention, the time of the three-stage heat treatment may be 360-720 min, preferably 360-600 min, for example 360 ​​min.

[0025] In the present invention, the rate of heating from the temperature of the second stage heat treatment to the temperature of the third stage heat treatment may be 0.4-12°C / min, preferably 0.42-9°C / min, for example 0.45, 0.84, 1.5, 4.5, 5, 7.6 or 8°C / min.

[0026] In the present invention, the heat treatment preferably also includes four-stage heat treatment, and the four-stage heat treatment is arranged after the three-stage heat treatment. The temperature of the four-stage heat treatment may be 400-1100°C, preferably 450-1080°C, such as 490, 550, 680, 760, 800, 950 or 1075°C. The time of the four-stage heat treatment may be 360-720min, preferably 360-600min, such as 360min. The rate of heating from the temperature of the three-stage heat treatment to the temperature of the four-stage heat treatment may be 0.4-12°C / min, preferably 0.42-9°C / min, such as 0.45, 0.84, 1.5, 3.1, 4.5, 5, 7.6 or 8°C / min.

[0027] In a preferred embodiment, the heat treatment includes one stage heat treatment, two stage heat treatment and three stage heat treatment in sequence, the temperature of the one stage heat treatment is 490°C, the temperature of the two stage heat treatment is 1250°C, and the temperature of the three stage heat treatment is 490°C.

[0028] In a more preferred embodiment, the heat treatment includes one stage heat treatment, two stage heat treatment and three stage heat treatment in sequence, the temperature of the one stage heat treatment is 490°C, the time of the one stage heat treatment is 80 min, and the rate of heating from room temperature to the temperature of the one stage heat treatment can be 0.77°C / min; the temperature of the two stage heat treatment is 1250°C, the time of the two stage heat treatment is 800 min, and the rate of heating from the temperature of the one stage heat treatment to the temperature of the two stage heat treatment can be 0.84°C / min; the temperature of the three stage heat treatment is 490°C, the time of the three stage heat treatment is 360 min, and the rate of heating from the temperature of the two stage heat treatment to the temperature of the three stage heat treatment can be 7.6°C / min.

[0029] In a preferred embodiment, the heat treatment includes one stage heat treatment, two stage heat treatment and three stage heat treatment in sequence, the temperature of the one stage heat treatment is 1075°C, the temperature of the two stage heat treatment is 1120°C, and the temperature of the three stage heat treatment is 1075°C.

[0030] In a more preferred embodiment, the heat treatment includes one stage heat treatment, two stage heat treatment and three stage heat treatment in sequence, the temperature of the one stage heat treatment is 1075°C, the time of the one stage heat treatment is 60min, and the rate of heating from room temperature to the temperature of the one stage heat treatment can be 0.87°C / min; the temperature of the two stage heat treatment is 1120°C, the time of the two stage heat treatment is 800min, and the rate of heating from the temperature of the one stage heat treatment to the temperature of the two stage heat treatment can be 0.45°C / min; the temperature of the three stage heat treatment is 1075°C, the time of the three stage heat treatment is 360min, and the rate of heating from the temperature of the two stage heat treatment to the temperature of the three stage heat treatment can be 0.45°C / min.

[0031] In a preferred embodiment, the heat treatment includes one stage heat treatment, two stage heat treatment and three stage heat treatment in sequence, the temperature of the one stage heat treatment is 200°C, the temperature of the two stage heat treatment is 1250°C, and the temperature of the three stage heat treatment is 490°C.

[0032] In a more preferred embodiment, the heat treatment includes one stage heat treatment, two stage heat treatment and three stage heat treatment in sequence, the temperature of the one stage heat treatment is 200°C, the time of the one stage heat treatment is 80 min, and the rate of heating from room temperature to the temperature of the one stage heat treatment can be 0.28°C / min; the temperature of the two stage heat treatment is 1250°C, the time of the two stage heat treatment is 800 min, and the rate of heating from the temperature of the one stage heat treatment to the temperature of the two stage heat treatment can be 1.17°C / min; the temperature of the three stage heat treatment is 490°C, the time of the three stage heat treatment is 360 min, and the rate of heating from the temperature of the two stage heat treatment to the temperature of the three stage heat treatment can be 7.6°C / min.

[0033] In a preferred embodiment, the heat treatment includes one stage heat treatment, two stage heat treatment, three stage heat treatment and four stage heat treatment in sequence, the temperature of the one stage heat treatment is 490°C, the temperature of the two stage heat treatment is 1250°C, the temperature of the three stage heat treatment is 800°C, and the temperature of the four stage heat treatment is 490°C.

[0034] In a more preferred embodiment, the heat treatment includes one stage heat treatment, two stage heat treatment, three stage heat treatment and four stage heat treatment in sequence, the temperature of the one stage heat treatment is 490°C, the time of the one stage heat treatment is 80min, and the rate of heating from room temperature to the temperature of the one stage heat treatment can be 0.77°C / min; the temperature of the two stage heat treatment is 1250°C, the time of the two stage heat treatment is 800min, and the rate of heating from the temperature of the one stage heat treatment to the temperature of the two stage heat treatment can be 0.84°C / min; the temperature of the three stage heat treatment is 800°C, the time of the three stage heat treatment is 360min, and the rate of heating from the temperature of the two stage heat treatment to the temperature of the three stage heat treatment can be 4.5°C / min; the temperature of the four stage heat treatment is 490°C, the time of the four stage heat treatment is 360min, and the rate of heating from the temperature of the three stage heat treatment to the temperature of the four stage heat treatment can be 3.1°C / min.

[0035] In the present invention, a cooling step is preferably performed after the heat treatment. The end point of the cooling may be room temperature, generally 20-30°C.

[0036] In the present invention, the diameter of the mesh of the sieve used for the screening may be 1-10 mm, preferably 2-8 mm, such as 4-6 or 5-7 mm.

[0037] The present invention provides a rare earth fluoride particle, which is prepared by the above-mentioned preparation method.

[0038] In the present invention, the average particle diameter of the rare earth fluoride particles may be 1-10 mm, preferably 2-8 mm, such as 4-6 or 5-7 mm.

[0039] In the present invention, the purity of the rare earth fluoride particles may be ≥99.9%, for example, 99.99%.

[0040] In the present invention, the yield of the rare earth fluoride particles can be greater than 90%, preferably greater than 92%, for example, 95%, 98% or 98.5%.

[0041] In the present invention, the rare earth fluoride particles present a polycrystalline morphology. The polycrystalline morphology is preferably as follows Figure 3 The polycrystalline state refers to a collection of many fine grains, which are in an aggregated state separated from each other by interfaces.

[0042] The present invention also provides a use of the above-mentioned rare earth fluoride particles in an anti-reflection film.

[0043] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0044] The reagents and raw materials used in the present invention are commercially available.

[0045] The positive and progressive effects of the present invention are:

[0046] The present invention conducts multi-stage heat treatment on rare earth fluoride powder in a system with a specific initial vacuum degree and at a specific temperature, thereby not only obtaining rare earth fluoride particles with an average particle diameter of the millimeter level, but also the obtained rare earth fluoride particles present a polycrystalline morphology, and the obtained rare earth fluoride particles have a high yield rate.

[0047] Preferably, the fluorinated rare earth particles obtained by the method for preparing rare earth particles of the present invention have a higher purity. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is the morphology of yttrium fluoride powder.

[0049] Figure 2 This is the morphology of yttrium fluoride powder after granulation and before heat treatment.

[0050] Figure 3 This is a morphology picture of the prepared yttrium fluoride particles. DETAILED DESCRIPTION

[0051] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0052] Example 1

[0053] Step 1: Add 500 g of samarium fluoride powder (average particle diameter of 5 μm) into a double-roll extrusion granulator, and extrude it into particles with an average particle diameter of 5 mm at a pressure of 20 MPa;

[0054] Step 2, (1) Place the particles obtained in step 1 flat on a graphite plate, and then place it in a vacuum muffle furnace, evacuate the vacuum muffle furnace to a vacuum degree of 2Pa, and then fill it with argon until the vacuum degree in the vacuum muffle furnace is -0.7MPa; (2) Turn on the vacuum muffle furnace for heating, and the first stage of heat treatment is: set the temperature rising program to rise from room temperature (30°C) to 490°C within 600min (the heating rate is 0.77°C / min), and then keep the temperature constant for 80min; the second stage of heat treatment is: rise from 490°C to 1250°C within 900min (the heating rate is 0.84°C / min), and then keep the temperature constant for 800min; start cooling for the third stage of heat treatment, and reduce the temperature from 1250°C to 490°C in 100min (the cooling rate is 7.6°C / min), keep the temperature for 360min, and then cool to room temperature with the furnace and take out;

[0055] Step 3: Screen the above materials using a sieve with a standard mesh size of 4 mm and 6 mm to obtain granular materials with an average particle diameter of 4 mm-6 mm (yield rate 98%) for packaging.

[0056] Example 2

[0057] Step 1: Add 500 g of samarium fluoride powder (average particle diameter of 5 μm) into a double-roll extrusion granulator, and extrude it into particles with an average particle diameter of 6 mm at a pressure of 20 MPa;

[0058] Step 2, (1) Place the particles obtained in step 1 flat on a graphite plate, and then place it in a vacuum muffle furnace, evacuate the vacuum muffle furnace to a vacuum degree of 5 Pa, and then fill it with argon until the vacuum degree in the vacuum muffle furnace is -0.6 MPa; (2) Turn on the vacuum muffle furnace for heating, and the first stage of heat treatment is: set the temperature rising program to rise from room temperature (30°C) to 1075°C within 1200 minutes (the heating rate is 0.87°C / min), and then keep the temperature constant for 60 minutes; the second stage of heat treatment is: rise from 1075°C to 1120°C within 100 minutes (the heating rate is 0.45°C / min), and then keep the temperature constant for 800 minutes; turn on the cooling to perform the third stage of heat treatment, and reduce the temperature from 1120°C to 1075°C within 100 minutes (the cooling rate is 0.45°C / min), keep the temperature for 360 minutes, and then cool to room temperature with the furnace and take out;

[0059] Step 3: The above materials are sieved using a sieve with a standard mesh size of 5 mm and 7 mm to obtain granular materials with an average particle diameter of 5 mm-7 mm for packaging; the finished product rate is 98.5%.

[0060] Example 3

[0061] Step 1: Add 500 g of samarium fluoride powder (average particle diameter of 5 μm) into a double-roll extrusion granulator, and extrude it into particles with an average particle diameter of 5 mm at a pressure of 20 MPa;

[0062] Step 2: (1) Place the particles obtained in step 1 flat on a graphite plate, and then place it in a vacuum muffle furnace. Pump the vacuum muffle furnace to a vacuum degree of 2 Pa, and then fill it with argon until the vacuum degree in the vacuum muffle furnace is -0.7 MPa; (2) Turn on the vacuum muffle furnace for heating. The first stage of heat treatment is: set the temperature rise program to rise from room temperature (30°C) to 490°C within 600 minutes (the heating rate is 0.77°C / min), and then keep the temperature constant for 80 minutes; the second stage of heat treatment is: set the temperature rise program to rise from room temperature (30°C) to 490°C within 900 minutes (the heating rate is 0.77°C / min), and then keep the temperature constant for 80 minutes; the second stage of heat treatment is: set the temperature rise program to rise from room temperature (30°C) to 490°C within 600 minutes (the heating rate is 0.77°C / min), and then keep the temperature constant for 80 minutes. Heat from 490℃ to 1250℃ (heating rate is 0.84℃ / min), then keep constant temperature for 800min; start cooling for three-stage heat treatment, from 1250℃ to 800℃ within 100min (cooling rate is 4.5℃ / min), keep warm for 360min; step 5, continue cooling for four-stage heat treatment, from 800℃ to 490℃ within 100min (cooling rate is 3.1℃ / min), keep warm for 360min, then cool to room temperature with the furnace and take out;

[0063] Step 3: Screen the above materials using a sieve with a standard mesh size of 4 mm and 6 mm to obtain granular materials with an average particle diameter of 4 mm-6 mm (yield rate 98%) for packaging.

[0064] Example 4

[0065] Step 1: Add 500 g of samarium fluoride powder (average particle diameter of 5 μm) into a double-roll extrusion granulator, and extrude it into particles with a D50 of 5 mm at a pressure of 20 MPa;

[0066] Step 2, (1) the particles obtained in step 1 are laid flat on a graphite plate, and then placed in a vacuum muffle furnace, the vacuum muffle furnace is evacuated to a vacuum degree of 2Pa, and then argon is filled until the vacuum degree in the vacuum muffle furnace is -0.7Mpa; the vacuum muffle furnace is turned on for heating, and the first stage of heat treatment is: the temperature rise program is set to rise from room temperature (30°C) to 200°C within 600min (the heating rate is 0.28°C / min), and then the temperature is kept constant for 80min; the second stage of heat treatment is: from 200°C to 1250°C within 900min (the heating rate is 1.17°C / min), and then the temperature is kept constant for 800min; the temperature is turned on for cooling and the third stage of heat treatment is performed, from 1250°C to 490°C within 100min (the cooling rate is 7.6°C / min), the temperature is kept for 360min, and then the product is taken out after cooling to room temperature with the furnace;

[0067] Step 3: Screen the above materials using a sieve with a standard mesh size of 4 mm and 6 mm to obtain granular materials with an average particle diameter of 4 mm-6 mm (yield rate 95%) for packaging.

[0068] Example 5

[0069] Step 1: Add 500 g of samarium fluoride powder (average particle diameter of 5 μm) into a double-roll extrusion granulator, and extrude it into particles with an average particle diameter of 5 mm at a pressure of 20 MPa;

[0070] Step 2, (1) Place the particles obtained in step 1 flat on a graphite plate, and then place it in a vacuum muffle furnace, evacuate the vacuum muffle furnace to a vacuum degree of 2Pa, and then fill it with argon until the vacuum degree in the vacuum muffle furnace is -1.0MPa; (2) Turn on the vacuum muffle furnace for heating, and the first stage of heat treatment is: set the temperature rising program to rise from room temperature (30°C) to 490°C within 600 minutes (the heating rate is 0.77°C / min), and then keep the temperature constant for 80 minutes; the second stage of heat treatment is: rise from 490°C to 1250°C within 900 minutes (the heating rate is 0.84°C / min), and then keep the temperature constant for 800 minutes; start cooling for the third stage of heat treatment, and reduce the temperature from 1250°C to 490°C in 100 minutes (the cooling rate is 7.6°C / min), keep the temperature for 360 minutes, and then cool to room temperature with the furnace and take out;

[0071] Step 3: Screen the above materials using a sieve with a standard mesh size of 4 mm and 6 mm to obtain granular materials with an average particle diameter of 4 mm-6 mm (yield rate 98%) for packaging.

[0072] Comparative Example 1

[0073] Step 1: Add 500 g of samarium fluoride powder (average particle diameter of 5 μm) into a double-roll extrusion granulator, and extrude it into particles with an average particle diameter of 5 mm at a pressure of 20 MPa;

[0074] Step 2: Place the particles obtained in step 1 flat on a graphite plate, and then place it in a vacuum muffle furnace. Pump the vacuum muffle furnace to a vacuum degree of 2 Pa, and then fill it with argon gas until the vacuum degree in the vacuum muffle furnace is -0.7 MPa;

[0075] Step 3: Start the vacuum muffle furnace for heating. The first stage of heat treatment is: set the temperature program to rise from room temperature (30°C) to 490°C within 600 minutes (the heating rate is 0.77°C / min), and then keep the temperature constant for 80 minutes; the second stage of heat treatment is: rise from 490°C to 1250°C within 900 minutes (the heating rate is 0.84°C / min), and then keep the temperature constant for 800 minutes, and then start cooling and cool to room temperature with the furnace before taking out;

[0076] Step 4: Screen the above materials using a sieve with a standard mesh size of 4 mm and 6 mm to obtain granular materials with an average particle diameter of 4 mm-6 mm (yield rate 80%) for packaging.

[0077] Comparative Example 2

[0078] Step 1: Add 500 g of samarium fluoride powder (average particle diameter of 5 μm) into a double-roll extrusion granulator, and extrude it into particles with a D50 of 5 mm at a pressure of 20 MPa;

[0079] Step 2, (1) Place the particles obtained in step 1 flat on a graphite plate, and then place it in a vacuum muffle furnace, evacuate the vacuum muffle furnace to a vacuum degree of 2Pa, and then fill it with argon until the vacuum degree in the vacuum muffle furnace is -0.7Mpa; (2) Turn on the vacuum muffle furnace for heating, and the first stage of heat treatment is: set the temperature rising program to rise from room temperature (30°C) to 490°C within 600min (the heating rate is 0.77°C / min), and then keep the temperature constant for 80min; the second stage of heat treatment is: rise from 490°C to 1600°C within 900min (the heating rate is 1.23°C / min), and then keep the temperature constant for 800min; turn on the cooling to perform the third stage of heat treatment, and reduce the temperature from 1600°C to 490°C in 100min (the cooling rate is 11.1°C / min), keep the temperature for 360min, and then cool to room temperature with the furnace and take out;

[0080] Step 3: Screen the above materials using a sieve with a standard mesh size of 4 mm and 6 mm to obtain granular materials with an average particle diameter of 4 mm-6 mm (yield rate 50%) for packaging.

[0081] Comparative Example 3

[0082] Step 1: Add 500 g of samarium fluoride powder (average particle diameter of 5 μm) into a double-roll extrusion granulator, and extrude it into particles with a D50 of 5 mm at a pressure of 20 MPa;

[0083] Step 2, (1) Place the particles obtained in step 1 flat on a graphite plate, and then place it in a vacuum muffle furnace, evacuate the vacuum muffle furnace to a vacuum degree of 2Pa, and then fill it with argon until the vacuum degree in the vacuum muffle furnace is -0.7Mpa; (2) Turn on the vacuum muffle furnace for heating, and the first stage of heat treatment is: set the temperature rising program to rise from room temperature (30°C) to 490°C within 600 minutes (the heating rate is 0.77°C / min), and then keep the temperature constant for 80 minutes; the second stage of heat treatment is: rise from 490°C to 1250°C within 900 minutes (the heating rate is 0.84°C / min), and then keep the temperature constant for 800 minutes; start cooling for the third stage of heat treatment, and reduce the temperature from 1250°C to 390°C in 100 minutes (the cooling rate is 8.6°C / min), keep the temperature for 360 minutes, and then cool to room temperature with the furnace and take out;

[0084] Step 3: Screen the above materials using a sieve with a standard mesh size of 4 mm and 6 mm to obtain granular materials with an average particle diameter of 4 mm-6 mm (yield rate 75%) for packaging.

[0085] Comparative Example 4

[0086] Step 1: Add 500 g of samarium fluoride powder (average particle diameter of 5 μm) into a double-roll extrusion granulator, and extrude it into particles with an average particle diameter of 5 mm at a pressure of 20 MPa;

[0087] Step 2, (1) Place the particles obtained in step 1 flat on a graphite plate, and then place it in a vacuum muffle furnace, evacuate the vacuum muffle furnace to a vacuum degree of 2Pa, and then fill it with argon until the vacuum degree in the vacuum muffle furnace is -0.1MPa; (2) Turn on the vacuum muffle furnace for heating, and the first stage of heat treatment is: set the temperature rising program to rise from room temperature (30°C) to 490°C within 600min (the heating rate is 0.77°C / min), and then keep the temperature constant for 80min; the second stage of heat treatment is: rise from 490°C to 1250°C within 900min (the heating rate is 0.84°C / min), and then keep the temperature constant for 800min; start cooling for the third stage of heat treatment, and reduce the temperature from 1250°C to 490°C in 100min (the cooling rate is 7.6°C / min), keep the temperature for 360min, and then cool to room temperature with the furnace and take out;

[0088] Step 3: Screen the above materials using a sieve with a standard mesh size of 4 mm and 6 mm to obtain granular materials with an average particle diameter of 4 mm-6 mm (yield rate 90%) for packaging.

[0089] Effect Example 1

[0090] Figure 1 The morphology of yttrium fluoride powder. Figure 1 It can be seen that the yttrium fluoride powder presents an amorphous morphology. Figure 2 This is the morphology of yttrium fluoride powder after granulation and before heat treatment. Figure 2 It can be seen that the yttrium fluoride powder after granulation and before heat treatment still presents an amorphous morphology. Figure 3 The morphology of the prepared yttrium fluoride particles is shown in Figure 2. Figure 3 It can be seen that the prepared yttrium fluoride particles present a polycrystalline morphology.

[0091] Effect Example 2

[0092] Purity was determined by glow discharge mass spectrometry.

[0093] The yield rate is obtained by weight measurement, and the yield rate = weight of qualified output products / weight of input raw materials × 100%. When the particle size of the obtained rare earth fluoride particles is 1-10 mm and presents a polycrystalline morphology, it is considered to be a qualified output product.

[0094] The results are shown in Table 1.

[0095] Table 1

[0096] purity Yield Example 1 99.99% 98% Example 2 99.99% 98.5% Example 3 99.99% 98% Example 4 99.99% 95% Example 5 99.9% 98% Comparative Example 1 99.99% 80% Comparative Example 2 99.99% 50% Comparative Example 3 99.99% 75% Comparative Example 4 99.99% 90%

[0097] It can be seen from Table 1 that, compared with Examples 1-5, the yield rate of the rare earth fluoride particles prepared by the preparation method of Comparative Examples 1-4 is lower.

Claims

1. A method for preparing rare earth fluoride particles, characterized in that: The method comprises the following steps: granulating, heat treating and screening the rare earth fluoride powder in sequence to obtain the rare earth fluoride particles; Wherein, the initial vacuum degree of the heat treatment is -0.2 to -1.0MPa; the heat treatment includes one stage heat treatment, two stage heat treatment and three stage heat treatment in sequence; the temperature of the one stage heat treatment is 200-1100°C, the temperature of the two stage heat treatment is 1000-1500°C, and the temperature of the three stage heat treatment is 400-1100°C.

2. The method for preparing rare earth fluoride particles according to claim 1, characterized in that: The method for preparing the rare earth fluoride particles satisfies one or more of the following conditions (1) to (10): (1) The temperature of the first stage heat treatment is 450-1080°C; (2) The heat treatment period is 60-100 minutes; (3) The rate of heating from room temperature to the temperature of the first stage of heat treatment is 0.1-1.8°C / min; (4) The temperature of the second stage heat treatment is 1100-1350°C; (5) The time of the second stage heat treatment is 720-1440 minutes; (6) The rate of increasing the temperature from the temperature of the first stage heat treatment to the temperature of the second stage heat treatment is 0.4-12°C / min; (7) The temperature of the three-stage heat treatment is 450-1080°C; (8) The time of the three-stage heat treatment is 360-720 minutes; (9) the rate of increasing the temperature from the temperature of the second stage heat treatment to the temperature of the third stage heat treatment is 0.4-12°C / min; and, (10) The heat treatment further includes a four-stage heat treatment, and the four-stage heat treatment is arranged after the three-stage heat treatment.

3. The method for preparing rare earth fluoride particles according to claim 2, characterized in that: The method for preparing the rare earth fluoride particles satisfies one or more of the following conditions (1) to (12): (1) The temperature of the first stage heat treatment is 490, 550, 680, 760, 870, 950 or 1075°C; (2) The heat treatment period is 70-90 minutes; (3) The rate of heating from room temperature to the temperature of the first stage of heat treatment is 0.2-1.6°C / min; (4) The temperature of the second stage heat treatment is 1120, 1180, 1210, 1250, 1300 or 1330°C; (5) The time of the second stage heat treatment is 750-900 min; (6) the rate of increasing the temperature from the first stage heat treatment to the second stage heat treatment temperature is 0.42-9°C / min; (7) The temperatures of the three-stage heat treatment are 490, 550, 680, 760, 800, 950 or 1075°C; (8) The time of the three-stage heat treatment is 360-600 min; (9) The rate of increasing the temperature from the temperature of the second stage heat treatment to the temperature of the third stage heat treatment is 0.42-9°C / min; (10) The temperature of the four-stage heat treatment is 400-1100°C; (11) the duration of the four-stage heat treatment is 360-720 min; and, (12) The rate of increasing the temperature from the temperature of the third-stage heat treatment to the temperature of the fourth-stage heat treatment is 0.4-12°C / min.

4. The method for preparing rare earth fluoride particles according to claim 3, characterized in that: The method for preparing the rare earth fluoride particles satisfies one or more of the following conditions (1) to (9): (1) The heat treatment time is 80 minutes; (2) the rate of heating from room temperature to the temperature of the first stage of heat treatment is 0.28, 0.77, 0.87, 1.2 or 1.5°C / min; (3) The duration of the second stage heat treatment is 800 min; (4) the rate of increasing the temperature from the temperature of the first stage heat treatment to the temperature of the second stage heat treatment is 0.45, 0.84, 1.5, 1.17, 5 or 8°C / min; (5) The time of the three-stage heat treatment is 360 minutes; (6) the rate of increasing the temperature from the temperature of the second stage heat treatment to the temperature of the third stage heat treatment is 0.45, 0.84, 1.5, 4.5, 5, 7.6 or 8°C / min; (7) The temperature of the four-stage heat treatment is 450-1080°C; (8) the duration of the four-stage heat treatment is 360-600 min; and, (9) The rate of increasing the temperature from the temperature of the third-stage heat treatment to the temperature of the fourth-stage heat treatment is 0.42-9°C / min.

5. The method for preparing rare earth fluoride particles according to claim 4, characterized in that: The method for preparing the rare earth fluoride particles satisfies the following conditions (1) and / or (2): (1) The temperatures of the four-stage heat treatment are 490, 550, 680, 760, 800, 950 or 1075°C; (2) The rate of increasing the temperature from the temperature of the third-stage heat treatment to the temperature of the fourth-stage heat treatment is 0.45, 0.84, 1.5, 3.1, 4.5, 5, 7.6 or 8° C. / min.

6. The method for preparing rare earth fluoride particles according to claim 1, characterized in that: The method for preparing the rare earth fluoride particles satisfies one or more of the following conditions (1) to (6): (1) The average particle diameter of the rare earth fluoride powder is 1-100 μm; (2) The initial vacuum degree of the heat treatment is -0.3 to -0.8 MPa; (3) The type of the rare earth fluoride powder is samarium fluoride or yttrium fluoride; (4) The granulation is carried out in a double-roll extrusion granulator; (5) the pressure during granulation is 20-50 MPa; and, (6) The mesh diameter of the sieve used for the screening is 1-10 mm.

7. The method for preparing rare earth fluoride particles according to claim 6, characterized in that: The method for preparing the rare earth fluoride particles satisfies one or more of the following conditions (1) to (4): (1) The average particle diameter of the rare earth fluoride powder is 5 μm; (2) The initial vacuum degree of the heat treatment is -0.6MPa or -0.7MPa; (3) the pressure during granulation is 20-40 MPa; and, (4) The mesh diameter of the sieve used for the screening is 2-8 mm.

8. A rare earth fluoride particle, characterized in that: It is prepared by the preparation method described in any one of claims 1 to 7.

9. The rare earth fluoride particles according to claim 8, characterized in that The rare earth fluoride particles meet one or more of the following conditions (1)-(4): (1) The average particle diameter of the rare earth fluoride particles is 1-10 mm; (2) The purity of the rare earth fluoride particles is ≥ 99.9%; (3) the yield of the rare earth fluoride particles is greater than 90%; and, (4) The rare earth fluoride particles present a polycrystalline morphology.

10. Use of the rare earth fluoride particles according to claim 8 or 9 in an anti-reflection film.

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