A magnesium fluoride polycrystalline ceramic crystal, and a production method and use thereof

Abstract

The application provides a magnesium fluoride polycrystal ceramic crystal and a production method and use thereof, and the production method comprises the following steps: purifying magnesium fluoride powder by fluorine gas under the condition of 1300-1600 DEG C; and sintering to crystallize under the condition of 1200-1400 DEG C. The production method of the magnesium fluoride polycrystal ceramic crystal provided in the application can form a crystal with high density and good consistency of density, and the yield is high, and a crystal structure with a large size can be formed, and the crystal is very suitable for being used as a moderator of BSA in a BNCT device.

Description

Technical Field

[0001] This invention relates to the field of crystal preparation, and in particular to magnesium fluoride polycrystalline ceramic crystals, their production methods, and applications. Background Technology

[0002] Boron neutron capture therapy (BNCT) is one of the most advanced methods for treating cancer. During the treatment, a boron-containing drug is first injected into the patient to "mark" the cancer cells. Then, neutron irradiation is performed. After the neutrons are captured by the boron inside the cancer cells, they produce highly lethal alpha particles and lithium ions, which precisely "kill" the cancer cells.

[0003] A suitable high-quality neutron beam is crucial for boron neutron capture therapy (BNCT). However, the initial neutron source often fails to meet the requirements, necessitating a beam shaper (BSA) to shape and slow down the initial neutron beam to obtain hyperthermic neutrons (0.5 eV < E < 10 keV). Therefore, the beam shaper (BSA) is one of the key components of a BNCT device.

[0004] In existing technologies, the moderator used in beam shaping is the core component. The role of the moderator material is to allow fast neutrons to rapidly lose energy to the range of ultrathermal neutron energy, without over-moderating them or generating excessive gamma pollution during the modulation process.

[0005] Magnesium fluoride is a commonly used moderator material. Considering the neutron flux and moderation efficiency at the exit end of BCNT, how to provide high-density magnesium fluoride polycrystalline ceramic crystals with good density uniformity has been a technical problem that the field of boron neutron capture therapy has been trying to solve.

[0006] When the beam shaping device is large, a large-sized moderator is required. However, with existing magnesium fluoride polycrystalline ceramic crystal forming processes, forming large-sized crystals is extremely difficult. This is because the overall temperature gradient during the forming process of large-sized polycrystalline ceramic crystals is significant, leading to differences in melting and crystallization rates, ultimately affecting the quality of the finished product.

[0007] During the structural design of the moderator within the beam shaping body, variations in the moderator's diameter simultaneously affect four factors: superthermal neutron flux, beam forward momentum, fast neutron contamination, and gamma contamination. Through repeated verification, it was found that when the diameter of the ceramic polycrystal reaches 500 mm, the superthermal neutron flux can reach over 10⁹, with good beam forward momentum, while fast neutron contamination and gamma contamination also meet usage requirements. Furthermore, to meet the requirements for neutron moderation effects under different treatment needs, the moderator within the beam shaping body is configured as multiple replaceable moderator cores (i.e., individual magnesium fluoride polycrystalline ceramic crystals). Based on practical experience, the thickness of the moderator core is generally less than 200 mm.

[0008] Existing hot-pressed polycrystalline magnesium fluoride (BSA) ceramics are mainly prepared using high-purity MgF2 as raw material, through vacuum hot-pressing sintering at 600–700℃ and 300MPa pressure. However, with current processes, the uniformity and consistency of polycrystalline ceramics with a thickness of 200mm and a diameter of 500mm cannot meet production requirements. Individual products are prone to defects such as cracks, voids, dents, or fissures, leading to poor uniformity between different regions within the crystal. Furthermore, the density consistency within the same batch of products needs improvement. In short, the difficulty in producing large-sized BSA ceramics is a pressing technical problem that needs to be solved. Summary of the Invention

[0009] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a magnesium fluoride polycrystalline ceramic crystal, its production method and uses, to solve the problems of low density and inconsistent density uniformity of magnesium fluoride polycrystalline ceramic crystals in the prior art.

[0010] To achieve the above and other related objectives, the present invention is implemented by including the following technical solutions.

[0011] The first aspect of this invention provides a method for producing magnesium fluoride polycrystalline ceramic crystals, comprising:

[0012] Magnesium fluoride powder was purified using fluorine gas at 1300–1600℃.

[0013] Sintering is carried out at 1200–1400℃ to crystallize.

[0014] Preferably, the purity of the magnesium fluoride powder is at least 99.95%. More preferably, the purity of the magnesium fluoride powder is 99.99% or higher.

[0015] Preferably, the average particle size of the magnesium fluoride powder is 10–25 nm. For example, it can be 10–20 nm, specifically 10–12 nm, 12–14 nm, 14–16 nm, 16–18 nm, or 18–20 nm.

[0016] Preferably, the production method is carried out in a crystal sintering furnace.

[0017] More preferably, the crystal sintering furnace includes a cylindrical grinding mold with a height of at least 280 mm, preferably 295–305 mm. Since a surface heterogeneous layer will form on top of the crystal, a certain height is reserved in the grinding mold to ensure the final dimensions meet the thickness requirements of the final magnesium fluoride polycrystalline ceramic crystal. The surface heterogeneous layer can be removed specifically by cutting and grinding.

[0018] More preferably, the material of the contact part between the crystal sintering furnace mold and the crystal is graphite. More preferably, the heating method of the crystal sintering furnace is circumferential heating, such as the uniformly distributed heating wires on the circumference of the mold, and the heating is performed by the heating wires.

[0019] Preferably, the purification environment is treated under vacuum conditions before purification. A vacuum environment is used to avoid chemical or physical reactions between various gases in the air and the raw material powder or crystals (such as intergranular O2 contamination, cavities, etc.) in the specific steps of the production method described in this application, thereby better ensuring the sintering quality of the crystals.

[0020] Preferably, sintering is performed at 1260–1300°C to crystallize. More preferably, sintering is performed at 1265–1300°C to crystallize. For example, the sintering temperatures may be 1265°C, 1270°C, 1275°C, 1280°C, 1285°C, 1290°C, 1295°C, or 1300°C.

[0021] In this application, preferably, the vacuum has a pressure less than 1 Torr. More preferably, the pure vacuum has a pressure less than 0.1 Torr. More preferably, the vacuum has a pressure less than 0.01 Torr. More preferably, the vacuum has a pressure less than 0.001 Torr. More preferably, the vacuum has a pressure less than 0.0001 Torr. Most preferably, the vacuum has a pressure less than or equal to 10 Torr. -5 Torr.

[0022] Purification temperatures that are too high will cause the sample to melt prematurely, while temperatures that are too low (e.g., below 1000℃) will result in incomplete purification and the presence of impurities such as magnesium oxide. Preferably, the purification temperature is 1300–1500℃. More preferably, the purification temperature is 1350–1450℃, such as 1350℃, 1360℃, 1370℃, 1380℃, 1400℃, or 1450℃.

[0023] Preferably, before purification, the process further includes a step of drying the magnesium fluoride powder. Drying removes moisture from the magnesium fluoride in its powdered state, preventing water from interfering with the sintering process and affecting the quality of the finished ceramic product.

[0024] More preferably, the drying is heat drying. More preferably, the drying temperature is 400-800℃, such as 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃ or 800℃.

[0025] Preferably, the heating and drying time is at least 30 minutes, such as 40 minutes, 60 minutes, 120 minutes, 200 minutes, 360 minutes, etc. More preferably, the heating and drying time is 60 to 150 minutes, such as 60 minutes, 70 minutes, 80 minutes, 90 minutes, 100 minutes, 110 minutes, 120 minutes, 130 minutes, 140 minutes, 150 minutes.

[0026] Preferably, the drying is carried out under vacuum conditions. More preferably, the pressure during drying is less than 1 Torr. More preferably, the pressure during drying is less than 0.1 Torr. More preferably, the pressure during drying is less than 0.01 Torr. More preferably, the pressure during drying is less than 0.001 Torr. More preferably, the pressure during drying is less than 0.0001 Torr. Most preferably, the pressure during drying is less than or equal to 10. -5 Torr.

[0027] Preferably, the heating rate to the drying temperature is no more than 20°C / min, more preferably 5 to 20°C / min. For example, it can be 5°C / min, 8°C / min, 10°C / min, 12°C / min, 15°C / min, 18°C / min, or 20°C / min.

[0028] Preferably, the heating rate to the purification temperature is no more than 20°C / min, more preferably 5–20°C / min. For example, it can be 5°C / min, 8°C / min, 10°C / min, 12°C / min, 15°C / min, 18°C / min, or 20°C / min.

[0029] Preferably, the purity of the fluorine gas is at least 99.95%. More preferably, the purity of the fluorine gas is at least 99.99%.

[0030] Preferably, the amount of fluorine gas used is at least 100 mL relative to 100 g of magnesium fluoride powder. More preferably, the amount of fluorine gas used is no more than 500 mL relative to 100 g of magnesium fluoride powder, such as 100 mL, 150 mL, 200 mL, 250 mL, 300 mL, 350 mL, 400 mL, 450 mL, or 500 mL.

[0031] Preferably, the purification time is at least 30 minutes. More preferably, the purification time is 30 minutes to 90 minutes, such as 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes, 65 minutes, 70 minutes, 75 minutes, 80 minutes, 85 minutes, or 90 minutes.

[0032] Preferably, the cooling rate to the crystallization temperature is no more than 10℃ / min, such as 9℃ / min, 8℃ / min, 7℃ / min, 6℃ / min, 5℃ / min, 4℃ / min, 3℃ / min, 2℃ / min, or 1℃ / min.

[0033] Preferably, the sintering process for crystallization has a processing time of at least 30 minutes. More preferably, the sintering process for crystallization has a processing time of 30 to 90 minutes, such as 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes, 65 minutes, 70 minutes, 75 minutes, 80 minutes, 85 minutes, or 90 minutes.

[0034] Preferably, after crystallization, the temperature is reduced to room temperature at a rate not exceeding 10℃ / min, such as 9℃ / min, 8℃ / min, 7℃ / min, 6℃ / min, 5℃ / min, 4℃ / min, 3℃ / min, 2℃ / min, or 1℃ / min.

[0035] Preferably, after cooling to room temperature and releasing the pressure, the heterogeneous layer on the surface is removed.

[0036] Preferably, the above steps can be repeated until magnesium fluoride polycrystalline crystals are obtained.

[0037] A second aspect of the present invention also discloses a magnesium fluoride polycrystalline ceramic crystal formed using the production method described above.

[0038] Preferably, the magnesium fluoride polycrystalline ceramic crystal is cylindrical with a diameter of 400–700 mm and a height of 150–500 mm. More preferably, the diameter is 400–450 mm, 450–500 mm, 500–550 mm, 550–600 mm, 600–650 mm, or 650–700 mm. Even more preferably, the height is 150–200 mm, 200–250 mm, 250–300 mm, 300–350 mm, 350–400 mm, 400–450 mm, or 450–500 mm.

[0039] Preferably, the density of the magnesium fluoride polycrystalline ceramic crystals is 2.910–2.940 g / cm³. 3 For example, 2.910 g / cm³ 3 2.915g / cm 3 2.920 g / cm 3 2.925g / cm 3 2.930 g / cm 3 2.935g / cm 32.940 g / cm 3 .

[0040] The third aspect of the present invention also discloses the use of the magnesium fluoride polycrystalline ceramic crystal as described above as a moderator of BSA in a BNCT device.

[0041] As described above, the beam-shaping ceramic material, its preparation method, and its uses of the present invention have the following beneficial effects:

[0042] In this application, a specific production process is used to bond magnesium fluoride solid particles together during production, causing grain growth, reducing voids (pores) and grain boundaries. Through the transfer of matter, the total volume shrinks, the density increases, and finally, a hard, unified microstructured polycrystalline sintered body is formed.

[0043] The present invention provides a method for producing magnesium fluoride polycrystalline ceramic crystals, which produces crystals with high density, good density consistency, and high yield. It can also form crystal structures with large size, making it very suitable as a moderator for BSA in BNCT devices. Detailed Implementation

[0044] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0045] It should be noted that the process equipment or apparatus not specifically mentioned in the following embodiments are all conventional equipment or apparatus in the art.

[0046] Furthermore, it should be understood that the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, does not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combined connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combined devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0047] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention; in the specification and claims of the present invention, unless otherwise expressly stated in the text, the singular forms "a", "an" and "this" include the plural forms.

[0048] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or equivalent to those described, apparatus, and materials in the embodiments of this invention may be used to implement the present invention.

[0049] In the specific embodiments described below in this application, considering the purity, cost, and batch-to-batch consistency of magnesium fluoride powder, magnesium fluoride powder with an average particle size of 14-16 nm was selected as the raw material.

[0050] The following examples and comparative examples all use the same crystal sintering furnace to prepare cylindrical magnesium fluoride polycrystalline ceramic crystals with a final product size of 500 mm in diameter and 200 mm in thickness.

[0051] Ten batches were prepared for both the examples and the comparative examples, and:

[0052] 1) Visually inspect the final product for any cracks or breaks that can be observed after removing the non-dense heterogeneous crystalline layer on the surface.

[0053] 2) Test the overall density values ​​of the ten batches in each example to see if the density fluctuation of the ten consecutive batches does not exceed ±1%.

[0054] 3) Cut each of the ten products in each example and observe whether the fragments or pieces formed after cutting can have visible cavities with depressions or pits. Test the difference between the density of each fragment or piece and the overall density and take the average value (with ±2% fluctuation as the indicator of whether it is qualified).

[0055] The cutting operation steps are designed as follows: For cylindrical products, divide them into 20 equal parts along the thickness direction to form a 10mm thick cutting sheet. Then, divide the circular surface of the cutting sheet of this thickness into 8 equal parts along the diameter to form a fan-shaped cutting block with a theoretical value of (π / 4) rad.

[0056] In this application, overall density fluctuation and average density difference are used as indicators to measure the density consistency of the same batch.

[0057] In the following specific embodiments, the mold of the crystal sintering furnace is cylindrical and has a height of 300mm. The material in the mold that contacts the crystal is graphite. The mold is provided with evenly distributed heating wires around its circumference for circumferential heating.

[0058] Example 1

[0059] This embodiment provides a method for producing magnesium fluoride polycrystalline ceramic crystals, including the following steps:

[0060] 1) [Raw material feeding into the furnace] Pour a certain amount of magnesium fluoride (MgF2) powder with a purity of 99.99% or higher into the crystal sintering furnace;

[0061] 2) [Furnace Vacuuming] Shut down the crystal sintering furnace and evacuate the furnace to a vacuum level of 10. -5 Torr level;

[0062] 3) [Preparation and Drying Stage] Control the furnace temperature to rise uniformly to 600.00℃ and hold for 90 minutes to dry the powder in the furnace; the heating rate is 10℃ / min.

[0063] 4) [Fluorination Purification Stage] Fluorine gas (F2) with a purity of 99.99% is introduced into the furnace, and the temperature is raised to 1400.00℃ at a uniform rate of 13.93℃ / min, and held at this temperature for 45 minutes. The amount of fluorine gas used is 100mL for every 100g of magnesium fluoride powder. This step fluorinates the magnesium oxide impurities in the magnesium fluoride crystals, further increasing the magnesium fluoride content and purity of the powder.

[0064] 5) [Sintering and crystal growth stage] Cool down to 1265℃ at a rate of [2.09℃ / min] and hold for 45 minutes. The temperature fluctuation during holding should not exceed ±2.00℃.

[0065] 6) [Cooling-down phase] After the insulation is completed, cool down at a rate of [4.18℃ / min] until the temperature drops to room temperature.

[0066] 7) [Pressure Boosting Stage] After all the gas inside the furnace is extracted, air is introduced until the gas pressure inside and outside the furnace is balanced.

[0067] 8) [Complete crystal growth] Take out the crystal and remove the heterogeneous layer on the surface to obtain BSA magnesium fluoride (MgF2) polycrystalline ceramic crystal.

[0068] The cylindrical magnesium fluoride polycrystalline ceramic crystal formed after removing the heterogeneous layer in this embodiment has a diameter of 500 mm and a thickness of 200 mm.

[0069] Ten batches of products: Upon visual inspection, no obvious cracks were observed in 8 of them, while the other 2 had minor cracks in individual areas. After cutting the 8 products for which no obvious cracks were observed, no visible cavities such as depressions or pits were observed in the resulting fragments or cut pieces.

[0070] The average overall density of the eight products tested, in which no obvious cracks were observed to the naked eye, was 2.940 g / cm³. 3 The overall density fluctuation of the eight samples did not exceed ±1%.

[0071] The test showed that after cutting 8 products with no visible cracks, the average density difference of the resulting fragments or pieces was 1.01%.

[0072] Example 2

[0073] This embodiment provides another method for producing magnesium fluoride polycrystalline ceramic crystals, including the following steps:

[0074] 1) [Raw Material Feeding into the Furnace] Pour magnesium fluoride (MgF2) powder with a purity of 99.99% or higher into the crystal sintering furnace.

[0075] 2) [Furnace Vacuuming] Shut down the crystal sintering furnace and evacuate the furnace to a vacuum level of 10. -5 Torr level.

[0076] 3) [Preparation and Drying Stage] Control the furnace temperature to rise uniformly to 600.00℃ at a heating rate of 10℃ / min and hold for 90min to dry the powder in the furnace.

[0077] 4) [Fluorination Purification Stage] Fluorine gas (F2) with a purity of 99.99% is introduced into the furnace, and the temperature is raised to 1450.00℃ at a uniform rate of 15℃ / min and held for 45 minutes; the amount of fluorine gas used is 100mL for every 100g of magnesium fluoride powder. This step fluorinates the magnesium oxide impurities in the magnesium fluoride crystals, further increasing the magnesium fluoride content in the powder and improving its purity.

[0078] 5) [Sintering and crystal growth stage] Cool down to 1300℃ at a rate of 5℃ / min and hold for 45 minutes. The temperature fluctuation during holding should not exceed ±2.00℃.

[0079] 6) [Cooling-down phase] After the insulation is completed, cool down at a rate of 5℃ / min until the temperature drops to room temperature.

[0080] 7) [Pressure Boosting Stage] After all the gas inside the furnace is extracted, air is introduced until the gas pressure inside and outside the furnace is balanced.

[0081] 8) [Complete crystal growth] Take out the crystal and remove the heterogeneous layer on the surface to obtain BSA magnesium fluoride (MgF2) polycrystalline ceramic crystal.

[0082] This embodiment produced cylindrical magnesium fluoride polycrystalline ceramic crystals. The crystals had a diameter of 500 mm and a thickness of 200 mm.

[0083] Ten batches of products: Upon visual inspection, 7 batches showed no obvious cracks, 2 batches had minor cracks in a few places, and 1 batch had minor dents in a few places. After cutting the 7 batches of products with no obvious cracks, no visible cavities, pits, or holes were observed in the resulting fragments or cut pieces.

[0084] The average overall density of the seven products tested, in which no obvious cracks were observed to the naked eye, was 2.925 g / cm³. 3 The overall density fluctuation of the seven samples did not exceed ±1%.

[0085] The test showed that after cutting seven products with no visible cracks, the average density difference between the resulting fragments or pieces was 1.515%.

[0086] Example 3

[0087] This embodiment provides a method for producing magnesium fluoride polycrystalline ceramic crystals, including the following steps:

[0088] 1) **[Raw Material Feeding into the Furnace]** Pour a certain amount of magnesium fluoride (MgF2) powder with a purity of 99.99% or higher into the crystal sintering furnace. 2) **[Furnace Vacuuming]** Close the crystal sintering furnace and evacuate the furnace to a vacuum level of 10°C. -5 Torr level.

[0089] 3) [Preparation and Drying Stage] Control the furnace temperature to rise at a uniform rate to 500.00℃ and hold for 100 minutes to dry the powder inside the furnace.

[0090] 4) [Fluorination Purification Stage] Fluorine gas (F2) with a purity of 99.99% is introduced into the furnace, and the temperature is raised to 1350.00℃ at a uniform rate of 10℃ / min and held for 45 minutes; the amount of fluorine gas used is 100mL for every 100g of magnesium fluoride powder. This step fluorinates the magnesium oxide impurities in the magnesium fluoride crystals, further increasing the magnesium fluoride content in the powder and improving its purity.

[0091] 5) [Sintering and crystal growth stage] Cool down to 1270℃ at a rate of 5℃ / min and hold for 45 minutes. The temperature fluctuation during holding should not exceed ±2.00℃.

[0092] 6) [Cooling-down phase] After the insulation is completed, cool down at a rate of 5℃ / min until the temperature drops to room temperature.

[0093] 7) [Pressure Boosting Stage] After all the gas inside the furnace is extracted, air is introduced until the gas pressure inside and outside the furnace is balanced.

[0094] 8) [Complete crystal growth] Take out the crystal and remove the heterogeneous layer on the surface to obtain BSA magnesium fluoride (MgF2) polycrystalline ceramic crystal.

[0095] This embodiment produced cylindrical magnesium fluoride polycrystalline ceramic crystals. The crystals had a diameter of 500 mm and a thickness of 200 mm.

[0096] Ten batches of products: Upon visual inspection, no obvious cracks were observed in 8 of them, while the other 2 had minor cracks in individual areas. After cutting the 8 products for which no obvious cracks were observed, no visible cavities such as depressions or pits were observed in the resulting fragments or cut pieces.

[0097] The average overall density of the eight products tested, in which no obvious cracks were observed to the naked eye, was 2.931 g / cm³. 3 The overall density fluctuation of the eight samples did not exceed ±1%.

[0098] The test showed that after cutting 8 products with no visible cracks, the average density difference of the resulting fragments or pieces was 1.262%.

[0099] Example 4

[0100] This embodiment provides a method for producing magnesium fluoride polycrystalline ceramic crystals, including the following steps:

[0101] 1) **[Raw Material Feeding into the Furnace]** Pour a certain amount of magnesium fluoride (MgF2) powder with a purity of 99.99% or higher into the crystal sintering furnace. 2) **[Furnace Vacuuming]** Close the crystal sintering furnace and evacuate the furnace to a vacuum level of 10°C. -5 Torr level.

[0102] 3) [Preparation and Drying Stage] Control the furnace temperature to rise at a uniform rate to 700.00℃ and hold for 90 minutes to dry the powder inside the furnace.

[0103] 4) [Fluorination Purification Stage] Fluorine gas (F2) with a purity of 99.99% is introduced into the furnace, and the temperature is raised to 1400.00℃ at a uniform rate of 13.93℃ / min, and held for 30 minutes. The amount of fluorine gas used is 100mL for every 100g of magnesium fluoride powder. This step fluorinates the magnesium oxide impurities in the magnesium fluoride crystals, further increasing the magnesium fluoride content and purity of the powder.

[0104] 5) [Sintering and crystal growth stage] Cool down to 1290℃ at a rate of 8℃ / min and hold for 45 minutes. The temperature fluctuation during holding should not exceed ±2.00℃.

[0105] 6) [Cooling-down phase] After the insulation is completed, cool down at a rate of 8℃ / min until the temperature drops to room temperature.

[0106] 7) [Pressure Boosting Stage] After all the gas inside the furnace is extracted, air is introduced until the gas pressure inside and outside the furnace is balanced.

[0107] 8) [Complete crystal growth] Take out the crystal and remove the heterogeneous layer on the surface to obtain BSA magnesium fluoride (MgF2) polycrystalline ceramic crystal.

[0108] This embodiment produced cylindrical magnesium fluoride polycrystalline ceramic crystals. The crystals had a diameter of 500 mm and a thickness of 200 mm.

[0109] Ten batches of products: Upon visual inspection, 7 of them showed no obvious cracks, 1 had a slight dent in one place, and 2 had slight cracks in another place; after cutting the 7 products that showed no obvious cracks, no visible cavities such as dents or pits were observed in the resulting fragments or cut pieces.

[0110] The average overall density of the seven products tested, in which no obvious cracks were observed to the naked eye, was 2.919 g / cm³. 3 The overall density fluctuation of the seven samples did not exceed ±1%.

[0111] The test showed that after cutting seven products with no visible cracks, the average density difference of the resulting fragments or pieces was 1.713%.

[0112] Example 5

[0113] The only difference between Example 5 and Example 1 is that the sintering temperature is 1400°C for crystallization.

[0114] Ten batches of products: Upon visual inspection, no obvious cracks were observed in 6 of them, while the other 4 had minor cracks, pits, or holes in individual areas. After cutting the 6 products for which no obvious cracks were observed, no visible cavities such as depressions or pits were observed in the resulting fragments or cut pieces.

[0115] The average overall density of the six products tested, in which no obvious cracks were observed to the naked eye, was 2.915 g / cm³. 3 The overall density fluctuation of the six samples did not exceed ±1%.

[0116] The test showed that after cutting six products with no visible cracks, the average density difference of the resulting fragments or pieces was 2.098%.

[0117] Comparative Example 1

[0118] The only difference between Comparative Example 1 and Example 1 is that the purification process was carried out at a temperature of 1200°C.

[0119] Of the ten batches of products, only three showed no obvious cracks upon visual inspection, but some cracks or small pits were present. The remaining seven batches had numerous obvious cracks or significant dents.

[0120] It is evident that excessively low purification temperatures, such as 1200℃ in this comparative example, result in a low pass rate for the final ten batches of products, which is due to incomplete fluorination.

[0121] Comparative Example 2

[0122] The only difference between Comparative Example 2 and Example 1 is that the cooling rate to the crystallization temperature is 12°C / min.

[0123] Of the ten batches of products, only two showed no obvious cracks upon visual inspection, but some cracks or small pits were present. The remaining eight batches exhibited cracking, numerous obvious cracks, a large number of voids, or significant dents.

[0124] It is evident that excessively rapid cooling rates and large radial temperature gradients can lead to uneven crystallization and anomalies such as cracks.

[0125] Comparative Example 3

[0126] The only difference between Comparative Example 3 and Example 1 is that fluorine gas is not used.

[0127] Of the ten batches of products, only four showed no obvious cracks upon visual inspection, but some cracks or small pits were present. The remaining six batches showed obvious cracks, some voids, or numerous dents.

[0128] The average overall density of the four products for which no obvious cracks were observed with the naked eye was 2.895 g / cm³. 3 The overall density fluctuation of the four exceeded ±1%.

[0129] It is evident that, without the use of fluorine gas, residual impurities such as magnesium oxide can affect the crystallization quality, thereby impacting the quality of the final product.

[0130] Comparative Example 4

[0131] The only difference between Comparative Example 4 and Example 1 is that the sintering temperature is 1100°C for crystallization.

[0132] Of the ten batches of products, only one batch showed no obvious cracks upon visual inspection, but some cracks or numerous small pits were present. The remaining nine batches exhibited obvious cracks, numerous obvious cracks, large cavities, or numerous obvious dents.

[0133] It is evident that when the crystallization temperature is too low, the crystallization effect deteriorates, and all ten batches of products are prone to significant defects.

[0134] Comparative Example 5

[0135] The only difference between Comparative Example 5 and Example 1 is that the amount of fluorine gas used is 10 mL relative to 100 g of magnesium fluoride powder.

[0136] Of the ten batches of products, only four showed no obvious cracks upon visual inspection, but some had minor cracks or small pits. The remaining six had more obvious cracks, larger cavities, or more noticeable dents.

[0137] The average overall density of the four products for which no obvious cracks were observed with the naked eye was 2.901 g / cm³. 3 The overall density fluctuation of the four exceeded ±1%.

[0138] It is evident that insufficient fluorine gas usage can lead to residual impurities such as magnesium oxide, which can affect crystallization quality and thus the quality of the final product.

[0139] Comparative Example 6

[0140] The only difference between Comparative Example 6 and Example 3 is that the vacuum level is 10. -2 Torr.

[0141] Of the ten batches of products, only 5 showed no obvious cracks upon visual inspection, but some had minor cracks or small pits. The remaining 5 had more obvious cracks, larger cavities, or more noticeable dents.

[0142] The average overall density of the five products tested, in which no obvious cracks were observed to the naked eye, was 2.887 g / cm³. 3 The overall density fluctuation of the five exceeded ±1%.

[0143] The test showed that after cutting five products with no visible cracks, the average density difference of the resulting fragments or pieces was 2.865%.

[0144] It is evident that insufficient vacuum will result in residual gas, which can easily lead to problems such as cracks and cavities during the crystallization process, ultimately affecting product quality.

[0145] The above embodiments are for illustrating the implementation schemes disclosed in this invention and should not be construed as limiting the invention. Furthermore, various modifications listed herein, as well as variations in the methods and compositions of the invention, will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been specifically described in conjunction with various specific preferred embodiments, it should be understood that the invention should not be limited to these specific embodiments. In fact, various modifications as described above that are obvious to those skilled in the art to obtain the invention should be included within the scope of this invention.

Claims

1. A method for producing magnesium fluoride polycrystalline ceramic crystals for use as beam shapers and moderators, wherein the magnesium fluoride polycrystalline ceramic crystals are cylindrical with a diameter of 400–700 mm and a height of 150–250 mm; and the density of the magnesium fluoride polycrystalline ceramic crystals is 2.910–2.940 g / cm³. 3 Its characteristics are, The production method is carried out in a crystal sintering furnace. The mold of the crystal sintering furnace is cylindrical with a height of 300 mm. The material of the part of the mold that contacts the crystal is graphite. The mold is equipped with evenly distributed heating wires around its circumference for circumferential heating. The production method includes: Magnesium fluoride powder with a purity of at least 99.95% is added to the crystal sintering furnace, and the average particle size of the magnesium fluoride powder is 14-16 nm. Shut down the crystal sintering furnace and evacuate the furnace. The magnesium fluoride powder is dried by heating to 400~800℃; Magnesium fluoride powder is purified by fluorine gas at a rate not exceeding 20℃ / min to 1350~1500℃, the purity of the fluorine gas is at least 99.95%, the purification environment is under vacuum conditions, the purification time is at least 30min, and the amount of fluorine gas used is 100mL~500mL relative to 100g of magnesium fluoride powder. The temperature is lowered to 1265~1300℃ at a cooling rate not exceeding 10℃ / min, and sintered to crystallize; the sintering is carried out in a vacuum environment, and the processing time for crystallization is at least 30min. After crystallization, cool to room temperature at a rate not exceeding 10℃ / min; The vacuum refers to a pressure of less than 0.001 Torr.

2. The production method according to claim 1, characterized in that, The purity of the magnesium fluoride powder is above 99.99%; and / or, after cooling to room temperature, the pressure is released and the isomeric layer on the surface is removed.

3. The production method according to claim 2, characterized in that, The heating rate to the drying temperature shall not exceed 20℃ / min.

4. The production method according to claim 1, characterized in that, The vacuum refers to a pressure of less than 0.0001 Torr.

5. The production method according to claim 1, characterized in that, The vacuum refers to a pressure less than or equal to 10. -5 Torr.

6. The production method according to claim 1, characterized in that, The purification temperature is 1350~1450℃.

7. A magnesium fluoride polycrystalline ceramic crystal formed by the production method according to any one of claims 1 to 6; wherein the magnesium fluoride polycrystalline ceramic crystal is cylindrical with a diameter of 400–700 mm and a height of 150–250 mm; and the density of the magnesium fluoride polycrystalline ceramic crystal is 2.910–2.940 g / cm³. 3 .

8. The use of the magnesium fluoride polycrystalline ceramic crystal as described in claim 7 as a beam shaper / moderator.