Calcium fluoride forming method and calcium fluoride forming body

Abstract

The invention provides a calcium fluoride forming method and a calcium fluoride forming body, and belongs to the technical field of calcium fluoride preparation.The calcium fluoride forming method comprises the following steps that calcium fluoride raw powder is subjected to dispersion pretreatment, and pretreated powder is obtained; mixing the pretreated powder with hydroxypropyl methyl cellulose, a binder and water, and performing extrusion molding to obtain a preform; and drying and roasting the preformed body to obtain the calcium fluoride formed body. The calcium fluoride forming method provided by the invention does not need high temperature and high pressure, and is mild in process condition, low in cost, short in reaction time, low in energy consumption and high in production efficiency; the calcium fluoride forming body prepared by the method has a larger specific surface area, provides more action sites for water absorption in HCl and HF gases, does not need to be modified, is safer and more environment-friendly, and has higher mechanical strength.

Description

Technical Field

[0001] The present invention relates to the technical field of calcium fluoride preparation, and in particular to a calcium fluoride molding method and a calcium fluoride molded body. Background Art

[0002] Hydrogen fluoride (HF) and hydrogen chloride (HCl), core electronic-grade gases in semiconductor manufacturing and other cutting-edge technology fields, have a purity and quality that is crucial for ensuring the superior performance of downstream products. HF is primarily used for precision etching and surface purification of silicon wafers, while HCl plays a key role in multiple semiconductor manufacturing processes, including surface cleaning, epitaxial growth aids, and substrate pretreatment. However, the production of both gases faces significant challenges due to the presence of water impurities. This is because water impurities can induce and accelerate corrosion of the materials with which HF and HCl gases come into contact, releasing secondary contaminants such as corrosion products and impurities within the materials themselves. This reduces the purity of HF and HCl gases and can lead to defects in downstream products. Therefore, the development of technologies to remove water impurities from these gases during the production process has garnered significant attention. To address this technical challenge, researchers have conducted in-depth research and discovered that metal fluorides have significant potential for removing water impurities from HF and HCl gases. Calcium fluoride (CaF) shows great promise in HF and HCl gas dehydration processes due to its outstanding resistance to synergistic corrosion from HF, HCl, and H₂O, as well as its unique ability to form stable, high-energy bound water with water molecules. The strong interaction between CaF and water molecules enables it to maintain long-term stability in harsh chemical environments, effectively reducing the content of free water molecules in the gas. Furthermore, CaF possesses excellent optical and mechanical properties, further expanding its potential for widespread application in semiconductor manufacturing equipment.

[0003] Calcium fluoride is often used in HF and HCl gas dehydration processes in the form of solid particles. Molding technology plays a key role in the production of these shaped bodies. Common molding techniques include compression molding, extrusion molding, rotational molding, pressure molding, spherical molding, and spray molding. CN118976492A provides a catalyst shaped body, its preparation method, and application. Catalyst powder and a filler are mixed, and the resulting mixed powder is mixed with a neutral silica sol solution, followed by molding and heat treatment to obtain the catalyst shaped body. The preparation of calcium fluoride shaped bodies still requires addressing the following issues: calcium fluoride powder easily agglomerates during the mixing process, resulting in poor dispersibility. This not only affects the uniformity of the mixture but can also cause defects such as pores or cracks within the shaped body, thereby reducing its performance. During the extrusion molding process, the fluidity of the material has a significant impact on the quality of the shaped body. High-temperature treatment can cause changes in the internal structure of the shaped body, making it prone to brittle cracking. Therefore, developing a calcium fluoride molding method to comprehensively improve the performance of calcium fluoride shaped bodies is of great significance. Summary of the Invention

[0004] In view of the technical problems existing in the background technology, the present application provides a calcium fluoride molding method and a calcium fluoride molded body, aiming to solve the technical problems of easy agglomeration and poor fluidity during the calcium fluoride molding process and easy brittle cracking during the roasting process.

[0005] In a first aspect, the present application provides a method for forming calcium fluoride, comprising the following steps: Performing dispersion pretreatment on the calcium fluoride raw powder to obtain pretreated powder; The pretreated powder is mixed with hydroxypropyl methylcellulose, a binder and water, and then extruded to obtain a preform; The preform is dried and calcined to obtain a calcium fluoride molded body.

[0006] Preferably, the dispersion pretreatment is specifically: adding polyacrylic acid to the calcium fluoride raw powder and then performing ball milling.

[0007] In the present invention, PAA (polyacrylic acid) dispersant is added during the pretreatment process of the calcium fluoride raw powder. The electrostatic repulsion and steric hindrance effects of PAA dispersant improve the dispersibility of the powder and reduce sedimentation in the subsequent preparation process.

[0008] Preferably, the mass of the polyacrylic acid is 0.1% to 1% of the mass of the original calcium fluoride powder; more preferably, the mass of the polyacrylic acid is 0.2% to 0.5% of the mass of the original calcium fluoride powder.

[0009] Preferably, the ball milling time is 1 to 2 hours.

[0010] Preferably, the mass of hydroxypropyl methylcellulose is 2% to 4% of the mass of the original calcium fluoride powder; more preferably, the mass of hydroxypropyl methylcellulose is 2.5% to 3% of the mass of the original calcium fluoride powder.

[0011] The addition of hydroxypropyl methylcellulose during the calcium fluoride molding process can effectively improve the water absorption rate of the calcium fluoride molded body, which is attributed to the fact that the hydroxyl hydrophilic group slightly increases the porosity of the body, resulting in an increase in water absorption rate.

[0012] Preferably, the binder includes at least two of pseudo-boehmite, silica sol, polyethylene glycol, and polyvinyl alcohol.

[0013] Preferably, the binder is a mixture of silica sol and polyethylene glycol.

[0014] Preferably, the mass ratio of silica sol to polyethylene glycol is 1 to 3:1.

[0015] More preferably, the mass ratio of silica sol to polyethylene glycol is 2:1.

[0016] During the calcium fluoride molding process, the addition of a binder can increase the green body strength, improve the powder fluidity and moldability, and reduce the occurrence of defects. Compared with a single binder, a composite binder shows significant advantages through the synergistic effect of multiple components. Polyethylene glycol enhances lubricity and can take into account both molding efficiency and green body integrity; silica sol can provide strong bonding at room temperature and is completely converted into SiO2 after sintering, forming open pores in calcium fluoride and increasing water absorption, which is especially suitable for the preparation of optical-grade CaF2. In addition, by rationally matching different functional binders, not only can sintering residues and costs be reduced, but also environmental protection and performance can be balanced.

[0017] Preferably, the mass of the binder is 5% to 20% of the mass of the original calcium fluoride powder; more preferably, the mass of the binder is 10% to 15% of the mass of the original calcium fluoride powder.

[0018] Preferably, the mass of water is 30% to 50% of the mass of the raw calcium fluoride powder; more preferably, the mass of water is 35% to 40% of the mass of the raw calcium fluoride powder.

[0019] Preferably, the preform is a spherical particle with a particle size of 3 to 7 mm.

[0020] Preferably, the drying temperature is room temperature and the drying time is 24 to 48 hours.

[0021] Preferably, the calcination conditions are: calcination at 300-450° C. for 2-3 h in an air atmosphere using a stepwise heating method.

[0022] Preferably, the calcination conditions are as follows: in an air atmosphere, calcining at 300°C for 30 minutes, then calcining at 400°C for 30 minutes, and then calcining at 450°C for 60 minutes; the heating rate is 3-5°C / min.

[0023] During the calcium fluoride molding process, the calcination temperature and heating rate significantly influence the specific surface area and properties of calcium fluoride. If the calcination temperature is too low, the binder and organic matter will not be fully sintered, and the product will be prone to brittle cracking. If the temperature is too high, the specific surface area will decrease rapidly, reducing the water absorption porosity of the calcium fluoride molded body. If the temperature is too fast (>5°C / min), cracks will easily form, and brittle cracking will lead to a decrease in strength. If the temperature is too slow, unnecessary energy loss will occur.

[0024] In a second aspect, the present invention provides a calcium fluoride molded body, which is produced by the calcium fluoride molding method described in the first aspect.

[0025] Compared with the prior art, the present invention has the following beneficial effects: The calcium fluoride molded body prepared by the present invention has a large specific surface area, which can reach 50m 2 / g or more, providing more action sites for the absorption of moisture in HCl and HF gases, without the need for modification, and being safer and more environmentally friendly. The calcium fluoride molded body prepared by the present invention has strong mechanical properties, with a strength of 100N / mm and a pore volume of 0.4cm 3 The calcium fluoride forming method provided by the present invention does not require high temperature and high pressure, has mild process conditions, low cost, short reaction time, low energy consumption and high production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is an SEM image of the calcium fluoride formed body prepared in Example 1 of the present invention; Figure 2 This is an SEM image of the calcium fluoride formed body prepared in Example 2 of the present invention; Figure 3 This is an SEM image of the calcium fluoride formed body prepared in Example 3 of the present invention; Figure 4 This is an SEM image of the calcium fluoride molded body prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0027] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0028] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. If no manufacturer is specified for the reagents or instruments used, they are all commercially available conventional products or commonly used in the field.

[0029] 1. Preparation method Example 1 50 g of calcium fluoride raw powder and 0.1 g of PAA (polyacrylic acid) were mixed evenly and ball-milled for 1 hour to obtain a pretreated powder. The pretreated powder was placed in a mixer and mixed evenly with 1 g of hydroxypropyl methylcellulose, and then poured into a basin. 2.5 g of silica sol, 2.5 g of polyethylene glycol, and 15 g of water were mixed evenly, slowly added to the basin, and kneaded into a block while adding the mixture. The block mixture was poured into a twin-screw extruder and extruded again after mixing evenly. A spherical particle mold with a size of 5 mm was installed to extrude the desired preform. The preform was dried at room temperature for 24 hours and then calcined in an air atmosphere in a muffle furnace. The calcination temperature program was as follows: calcination at 300°C for 30 minutes, further calcination at 400°C for 30 minutes, and calcination at 450°C for 60 minutes, with a heating rate of 5°C / min. After calcination, the calcium fluoride mold was cooled to room temperature to obtain the calcium fluoride molded body.

[0030] Example 2 50 g of calcium fluoride raw powder and 0.1 g of PAA were mixed uniformly and ball-milled for 1 hour to obtain a pretreated powder. The pretreated powder was then mixed uniformly with 1 g of hydroxypropyl methylcellulose in a mixer and poured into a basin. 3.33 g of silica sol, 1.67 g of polyethylene glycol, and 15 g of water were mixed uniformly, slowly added to the basin, and kneaded into a block while adding the mixture. The block mixture was poured into a twin-screw extruder and extruded again. After uniform mixing, a spherical particle mold with a size of 5 mm was installed to extrude the desired preform. The preform was dried at room temperature for 24 hours and then calcined in an air atmosphere in a muffle furnace. The calcination temperature program was as follows: calcination at 300° C. for 30 minutes, further calcination at 400° C. for 30 minutes, and calcination at 450° C. for 60 minutes, at a heating rate of 5° C. / min. After calcination, the calcium fluoride mold was cooled to room temperature to obtain a calcium fluoride molded body.

[0031] The difference between this embodiment and embodiment 1 is that the mass ratio of silica sol to polyethylene glycol is 2:1.

[0032] Example 3 50 g of calcium fluoride raw powder and 0.1 g of PAA were mixed uniformly and ball-milled for 1 hour to obtain a pretreated powder. The pretreated powder was then mixed uniformly with 1 g of hydroxypropyl methylcellulose in a mixer and poured into a basin. 3.75 g of silica sol, 1.25 g of polyethylene glycol, and 15 g of water were mixed uniformly, slowly added to the basin, and kneaded into a block while adding the mixture. The block mixture was poured into a twin-screw extruder and extruded again. After uniform mixing, a spherical particle mold with a size of 5 mm was installed to extrude the desired preform. The preform was dried at room temperature for 24 hours and then calcined in an air atmosphere in a muffle furnace. The calcination temperature program was as follows: calcination at 300° C. for 30 minutes, further calcination at 400° C. for 30 minutes, and calcination at 450° C. for 60 minutes, at a heating rate of 5° C. / min. After calcination, the preform was cooled to room temperature to obtain a calcium fluoride mold.

[0033] The difference between this embodiment and embodiment 1 is that the mass ratio of silica sol to polyethylene glycol is 3:1.

[0034] Example 4 50 g of calcium fluoride raw powder and 0.1 g of PAA were mixed uniformly and ball-milled for 1 hour to obtain a pretreated powder. The pretreated powder was then mixed uniformly with 1 g of hydroxypropyl methylcellulose in a mixer and poured into a basin. 2.5 g of SB powder (pseudo-boehmite), 2.5 g of polyethylene glycol, and 15 g of water were mixed uniformly and slowly added to the basin, while kneading the mixture into a block. The block mixture was poured into a twin-screw extruder and extruded again. After uniform mixing, a spherical particle mold with a size of 5 mm was installed to extrude the desired preform. The preform was dried at room temperature for 24 hours and then calcined in an air atmosphere in a muffle furnace. The calcination temperature program was as follows: calcination at 300°C for 30 minutes, further calcination at 400°C for 30 minutes, and calcination at 450°C for 60 minutes, at a heating rate of 5°C / min. After calcination, the preform was cooled to room temperature to obtain a calcium fluoride mold.

[0035] The difference between this embodiment and embodiment 1 is that the binder is a mixture of pseudo-boehmite and polyethylene glycol.

[0036] Example 5 50 g of calcium fluoride raw powder and 0.1 g of PAA were mixed uniformly and ball-milled for 1 hour to obtain a pretreated powder. The pretreated powder was then mixed uniformly with 1.5 g of hydroxypropyl methylcellulose in a mixer and poured into a basin. 2.5 g of silica sol, 2.5 g of polyethylene glycol, and 15 g of water were mixed uniformly, slowly added to the basin, and kneaded into a block while adding the mixture. The block mixture was poured into a twin-screw extruder and extruded again. After uniform mixing, a spherical particle mold with a size of 5 mm was installed to extrude the desired preform. The preform was dried at room temperature for 24 hours and then calcined in an air atmosphere in a muffle furnace. The calcination temperature program was as follows: calcination at 300° C. for 30 minutes, further calcination at 400° C. for 30 minutes, and calcination at 450° C. for 60 minutes, at a heating rate of 5° C. / min. After calcination, the calcium fluoride mold was cooled to room temperature to obtain a calcium fluoride molded body.

[0037] The difference between this embodiment and embodiment 1 is that the mass of hydroxypropyl methylcellulose is 0.3% of the mass of the original calcium fluoride powder.

[0038] Comparative Example 1 The difference between this comparative example and Example 1 is that the binder is replaced by a single polyethylene glycol instead of a mixture of polyethylene glycol and silica sol.

[0039] 50 g of calcium fluoride raw powder and 0.1 g of PAA were mixed uniformly and ball-milled for 1 hour to obtain a pretreated powder. The pretreated powder was then mixed uniformly with 1 g of hydroxypropyl methylcellulose in a mixer and poured into a basin. 5 g of polyethylene glycol and 15 g of water were mixed uniformly, slowly added to the basin, and kneaded into a block while adding the mixture. The block mixture was poured into a twin-screw extruder and extruded again. After mixing uniformly, a spherical particle mold with a size of 5 mm was installed to extrude the desired preform. The preform was dried at room temperature for 24 hours and then calcined in an air atmosphere in a muffle furnace. The calcination temperature program was as follows: calcination at 300° C. for 30 minutes, further calcination at 400° C. for 30 minutes, and calcination at 450° C. for 60 minutes, at a heating rate of 5° C. / min. After calcination, the preform was cooled to room temperature to obtain a calcium fluoride mold.

[0040] Comparative Example 2 The difference between this comparative example and Example 1 is that the binder is replaced by a single SB powder (pseudo-boehmite) instead of the mixture of polyethylene glycol and silica sol.

[0041] 50 g of calcium fluoride raw powder and 0.1 g of PAA were mixed uniformly and ball-milled for 1 hour to obtain a pretreated powder. The pretreated powder was then mixed uniformly with 1 g of hydroxypropyl methylcellulose in a mixer and poured into a basin. 5 g of SB powder and 15 g of water were mixed uniformly, slowly added to the basin, and kneaded into a block while adding the mixture. The block mixture was poured into a twin-screw extruder and extruded again. After mixing uniformly, a spherical particle mold with a size of 5 mm was installed to extrude the desired preform. The preform was dried at room temperature for 24 hours and then calcined in an air atmosphere in a muffle furnace. The calcination temperature program was as follows: calcination at 300° C. for 30 minutes, further calcination at 400° C. for 30 minutes, and calcination at 450° C. for 60 minutes, at a heating rate of 5° C. / min. After calcination, the calcium fluoride mold was cooled to room temperature to obtain the calcium fluoride molded body.

[0042] Comparative Example 3 The difference between this comparative example and Example 1 is that the binder is replaced by a single polyvinyl alcohol instead of a mixture of polyethylene glycol and silica sol.

[0043] 50 g of calcium fluoride raw powder and 0.1 g of PAA were mixed uniformly and ball-milled for 1 hour to obtain a pretreated powder. The pretreated powder was then mixed uniformly with 1 g of hydroxypropyl methylcellulose in a mixer and poured into a basin. 5 g of polyvinyl alcohol and 15 g of water were mixed uniformly, slowly added to the basin, and kneaded into a block while adding the mixture. The block mixture was poured into a twin-screw extruder and extruded again after mixing uniformly. A spherical particle mold with a size of 5 mm was installed to extrude the desired preform. The preform was dried at room temperature for 24 hours and then calcined in an air atmosphere in a muffle furnace. The calcination temperature program was as follows: calcination at 300° C. for 30 minutes, further calcination at 400° C. for 30 minutes, and calcination at 450° C. for 60 minutes, at a heating rate of 5° C. / min. After calcination, the preform was cooled to room temperature to obtain a calcium fluoride mold.

[0044] Comparative Example 4 The difference between this comparative example and Example 1 is that the heating method during calcination is different.

[0045] 50 g of calcium fluoride raw powder and 0.1 g of PAA were mixed uniformly and ball-milled for 1 hour to obtain a pretreated powder. The pretreated powder was mixed uniformly with 1 g of hydroxypropyl methylcellulose in a mixer and poured into a basin. 2.5 g of silica sol, 2.5 g of polyethylene glycol, and 15 g of water were mixed uniformly, slowly added to the basin, and kneaded into a block while adding the mixture. The block mixture was poured into a twin-screw extruder and extruded again. After mixing uniformly, a spherical particle mold with a size of 5 mm was installed to extrude the desired preform. The preform was dried at room temperature for 24 hours and then calcined in an air atmosphere in a muffle furnace. The calcination temperature program was as follows: heating to 450° C. for 120 minutes at a heating rate of 5° C. / min. After the calcination was completed, cooling to room temperature was performed to obtain a calcium fluoride molded body.

[0046] Comparative Example 5 The difference between this comparative example and Example 1 is that the heating rates during calcination are different.

[0047] 50 g of calcium fluoride raw powder and 0.1 g of PAA were mixed uniformly and ball-milled for 1 hour to obtain a pretreated powder. The pretreated powder, 1 g of hydroxypropyl methylcellulose, was mixed uniformly in a mixer and poured into a basin. 2.5 g of silica sol, 2.5 g of polyethylene glycol, and 15 g of water were mixed uniformly, slowly added to the basin, and kneaded into a block while adding the mixture. The block mixture was poured into a twin-screw extruder and extruded again. After mixing uniformly, a spherical particle mold with a size of 5 mm was installed to extrude the desired preform. The preform was dried at room temperature for 24 hours and then calcined in an air atmosphere in a muffle furnace. The calcination temperature program was as follows: calcination at 300° C. for 30 minutes, further calcination at 400° C. for 30 minutes, and calcination at 450° C. for 60 minutes, at a heating rate of 10° C. / min. After calcination, the preform was cooled to room temperature to obtain a calcium fluoride mold.

[0048] Comparative Example 6 The difference between this comparative example and Example 1 is that hydroxypropyl methylcellulose is not added.

[0049] 2. Test Method The performance of the calcium fluoride molded bodies prepared in the examples and comparative examples was evaluated and compared in terms of their compressive strength, water absorption, specific surface area, and pore volume parameters.

[0050] Compressive strength test: The calcium fluoride molded body particles were tested using a KQ-2 particle strength tester.

[0051] Water absorption test: Using the normal pressure test method, dry the sample at 110°C to constant weight (m1); immerse it in deionized water at room temperature and pressure for 24 hours; after taking it out, gently wipe the surface moisture with wet gauze and weigh it immediately (m2); water absorption = [(m2-m1) / m1]×100%.

[0052] 3. Analysis of test results of various embodiments and comparative examples The performance evaluation results of the calcium fluoride molded bodies prepared in the examples and comparative examples are shown in Table 1.

[0053] Table 1 Comparison of performance parameters of calcium fluoride prepared by different methods

[0054] The data in Table 1 show that the specific surface area of ​​the calcium fluoride particles prepared by the calcium fluoride forming method provided by the present invention can reach 50m 2 / g or more, with a moderate pore size, good stability and water absorption. The data of Comparative Examples 1 to 3 and Examples 1 to 3 show that compared with a single binder, the composite binder with a reasonable ratio shows significant advantages through the synergistic effect of multiple components. Comparative Examples 4 to 5 show that in the calcium fluoride molding process, the calcination temperature and heating rate have a great influence on the specific surface area and performance of calcium fluoride. If the calcination temperature is too low, the binder and organic matter are not fully sintered and are prone to brittle cracking; if the temperature is too high, the specific surface area decreases rapidly, reducing the water absorption porosity of the molded calcium fluoride. Heating too quickly (>5℃ / min) is prone to cracking, which is prone to brittle cracking and leads to a decrease in strength, while heating too slowly causes unnecessary energy loss. Comparative Example 6 does not add hydroxypropyl methylcellulose, and the water absorption rate is reduced. This is because the hydroxyl hydrophilic group slightly increases the porosity of the green body, further improving the water absorption rate.

[0055] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for forming calcium fluoride, characterized in that: The following steps are involved: Performing dispersion pretreatment on the calcium fluoride raw powder to obtain pretreated powder; The pretreated powder is mixed with hydroxypropyl methylcellulose, a binder and water, and then extruded to obtain a preform; The preform is dried and calcined to obtain a calcium fluoride formed body.

2. The calcium fluoride forming method according to claim 1, characterized in that: The dispersion pretreatment specifically includes: adding polyacrylic acid to the calcium fluoride raw powder and then ball milling.

3. The calcium fluoride forming method according to claim 2, characterized in that: The mass of the polyacrylic acid is 0.1% to 1% of the mass of the original calcium fluoride powder.

4. The method for forming calcium fluoride according to claim 1, wherein: The binder includes at least two of pseudo-boehmite, silica sol, polyethylene glycol, and polyvinyl alcohol.

5. The calcium fluoride forming method according to claim 4, characterized in that: The binder is a mixture of silica sol and polyethylene glycol; the mass ratio of the silica sol to the polyethylene glycol is 1-3:

1.

6. The calcium fluoride forming method according to claim 1, characterized in that: The mass of the hydroxypropyl methylcellulose is 2% to 4% of the mass of the original calcium fluoride powder; the mass of the binder is 5% to 20% of the mass of the original calcium fluoride powder; and the mass of the water is 30% to 50% of the mass of the original calcium fluoride powder.

7. The calcium fluoride forming method according to claim 1, characterized in that: The preformed body is a spherical particle with a particle size of 3 to 7 mm.

8. The calcium fluoride forming method according to claim 1, characterized in that: The calcination conditions are: calcining at 300-450° C. for 2-3 hours in an air atmosphere using a staged heating method.

9. The calcium fluoride forming method according to claim 8, characterized in that: The specific calcination conditions are: in an air atmosphere, heating to 300° C. and calcining for 30 minutes, then heating to 400° C. and calcining for 30 minutes, and then heating to 450° C. and calcining for 60 minutes; the heating rate is 3-5° C. / min.

10. A calcium fluoride formed body obtained by the calcium fluoride forming method according to any one of claims 1 to 9.

Images