A method for molding calcium fluoride, a calcium fluoride molded body

Abstract

The application provides a calcium fluoride forming method and a calcium fluoride forming body, and belongs to the technical field of calcium fluoride preparation, wherein the calcium fluoride forming method comprises the following steps: performing dispersion pretreatment on calcium fluoride raw powder to obtain pretreated powder; mixing the pretreated powder with hydroxypropyl methyl cellulose, a binder and water, and then performing extrusion forming to obtain a preformed body; and performing drying and calcination on the preformed body to obtain the calcium fluoride forming body. The calcium fluoride forming method provided by the application does not require high temperature and high pressure, has mild process conditions, low cost, short reaction time, low energy consumption and high production efficiency; the calcium fluoride forming body prepared by the application has a large specific surface area, provides more action sites for water absorption in HCl and HF gas, does not need to be modified, is more safe and environmentally friendly, and has high mechanical strength.

Description

Technical Field

[0001] This invention relates to the field of calcium fluoride preparation technology, specifically to a method for molding calcium fluoride and a molded calcium fluoride body. Background Technology

[0002] Hydrogen fluoride (HF) and hydrogen chloride (HCl), as core electronic-grade gases in semiconductor manufacturing and other cutting-edge technology fields, are crucial for ensuring the superior performance of downstream products due to their purity and quality. HF is mainly 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 preparation processes of both gases are severely affected by moisture impurities. Moisture impurities can induce and accelerate the corrosion of materials by HF and HCl gases, causing the release of secondary contaminants such as corrosion products and material impurities, reducing the purity of HF and HCl gases, and leading to defects in downstream products. Therefore, the development of technologies to remove moisture impurities from the gases during preparation has received widespread attention from researchers. To address this technical challenge, researchers have explored and discovered that metal fluorides have significant application potential in removing moisture impurities from HF and HCl gases. Calcium fluoride (CFF) exhibits great promise in HF and HCl gas dehydration processes due to its excellent resistance to synergistic corrosion from HF, HCl, and H₂O, as well as its unique ability to form stable bound water with high binding energy. The strong interaction between CFF and water molecules allows it to maintain long-term stability in harsh chemical environments, effectively reducing the content of free water molecules in gases. Furthermore, CFF possesses excellent optical and mechanical properties, which opens up more possibilities for its widespread application in semiconductor manufacturing equipment.

[0003] Calcium fluoride is frequently used in HF and HCl gas dehydration processes, often employing solid granular molded forms. Molding technology plays a crucial role in the production of these forms. Common molding techniques include compression molding, extrusion molding, rotational molding, pressure molding, spheroidization, and spray molding. CN118976492A provides a catalyst molded form, its preparation method, and its application. The catalyst powder and filler are mixed, and the resulting powder mixture is then mixed with a neutral silica sol solution, followed by molding and heat treatment to obtain the catalyst molded form. However, the following issues need to be addressed during the preparation of calcium fluoride molded forms: calcium fluoride powder is prone to agglomeration during mixing, resulting in poor dispersibility. This not only affects the uniformity of the mixture but may also lead to internal defects in the molded form, such as pores or cracks, thus reducing its performance. During extrusion molding, the flowability of the material significantly impacts the quality of the molded form. High-temperature treatment may cause changes in the internal structure of the molded form, making it prone to brittleness. Therefore, developing a molding method for calcium fluoride to comprehensively improve the performance of calcium fluoride molded forms is of great significance. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a method for molding calcium fluoride and a calcium fluoride molded body, aiming to solve the technical problems of easy agglomeration, poor fluidity and easy brittleness during the molding process of calcium fluoride.

[0005] In a first aspect, this application provides a method for forming calcium fluoride, comprising the following steps:

[0006] Calcium fluoride raw powder was dispersed and pretreated to obtain pretreated powder.

[0007] The pretreated powder was mixed with hydroxypropyl methylcellulose, binder and water and then extruded to obtain a preform.

[0008] The calcium fluoride molded body is obtained by drying and calcining the preform.

[0009] Preferably, the dispersion pretreatment specifically involves adding polyacrylic acid to calcium fluoride raw powder and then ball milling it.

[0010] In this invention, a PAA (polyacrylic acid) dispersant is added during the pretreatment process of calcium fluoride raw powder. Its electrostatic repulsion and steric hindrance effects improve the powder dispersibility and reduce sedimentation in subsequent preparation processes.

[0011] Preferably, the mass of polyacrylic acid is 0.1% to 1% of the mass of calcium fluoride raw powder; more preferably, the mass of polyacrylic acid is 0.2% to 0.5% of the mass of calcium fluoride raw powder.

[0012] Preferably, the ball milling time is 1 to 2 hours.

[0013] Preferably, the mass of hydroxypropyl methylcellulose is 2% to 4% of the mass of calcium fluoride raw powder; more preferably, the mass of hydroxypropyl methylcellulose is 2.5% to 3% of the mass of calcium fluoride raw powder.

[0014] Adding hydroxypropyl methylcellulose during the calcium fluoride molding process can effectively increase the water absorption rate of the calcium fluoride molded body. This is attributed to the fact that the hydrophilic hydroxyl groups slightly increase the porosity of the preform, leading to an increase in water absorption.

[0015] Preferably, the binder includes at least two of boehmite, silica sol, polyethylene glycol, and polyvinyl alcohol.

[0016] Preferably, the binder is a mixture of silica sol and polyethylene glycol.

[0017] Preferably, the mass ratio of silica sol to polyethylene glycol is 1 to 3:1.

[0018] More preferably, the mass ratio of silica sol to polyethylene glycol is 2:1.

[0019] In the calcium fluoride molding process, adding binders can improve green strength, powder flowability and formability, and reduce defect generation. Compared with single binders, composite binders exhibit significant advantages through the synergistic effect of multiple components. Polyethylene glycol enhances lubricity, balancing molding efficiency and green body integrity; silica sol provides strong adhesion at room temperature and is completely converted into SiO2 after sintering, forming open pores in calcium fluoride and increasing water absorption, making it particularly suitable for the preparation of optical-grade CaF2. Furthermore, by rationally proportioning different functional binders, not only can sintering residue and cost be reduced, but environmental friendliness and performance can also be balanced.

[0020] Preferably, the mass of the binder is 5% to 20% of the mass of the calcium fluoride raw powder; more preferably, the mass of the binder is 10% to 15% of the mass of the calcium fluoride raw powder.

[0021] Preferably, the mass of water is 30% to 50% of the mass of calcium fluoride raw powder; more preferably, the mass of water is 35% to 40% of the mass of calcium fluoride raw powder.

[0022] Preferably, the preform is a spherical particle with a particle size of 3~7mm.

[0023] Preferably, the drying temperature is room temperature and the drying time is 24~48 hours.

[0024] Preferably, the roasting conditions are: roasting at 300~450℃ for 2~3 hours in an air atmosphere using a staged heating method.

[0025] Preferably, the roasting conditions are as follows: roasting at 300°C for 30 minutes in an air atmosphere, then roasting at 400°C for 30 minutes, and then roasting at 450°C for 60 minutes; the heating rate is 3~5°C / min.

[0026] In the molding process of calcium fluoride, the calcination temperature and heating rate have a significant impact on the specific surface area and properties of calcium fluoride. If the calcination temperature is too low, the binder and organic matter will not sinter sufficiently and will be prone to brittleness; 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 heating rate is too fast (>5℃ / min), cracks will easily form, and brittleness will lead to a decrease in strength; if the heating rate is too slow, unnecessary energy loss will occur.

[0027] In a second aspect, the present invention provides a calcium fluoride molded article, which is prepared by the calcium fluoride molding method described in the first aspect.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] The calcium fluoride molded body prepared by this invention has a large specific surface area, reaching 50 m². 2 The calcium fluoride, with a concentration of over / g, provides numerous absorption sites for moisture in HCl and HF gases, requiring no modification and thus being safer and more environmentally friendly. Furthermore, the calcium fluoride molded body prepared by this invention exhibits strong mechanical properties, reaching a strength of 100 N / mm and a pore volume of 0.4 cm³. 3 / g. The calcium fluoride molding method provided by this 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. Attached Figure Description

[0030] Figure 1 This is a SEM image of the calcium fluoride molded body obtained in Example 1 of the present invention;

[0031] Figure 2 This is a SEM image of the calcium fluoride molded body obtained in Example 2 of the present invention;

[0032] Figure 3 This is a SEM image of the calcium fluoride molded body obtained in Example 3 of the present invention;

[0033] Figure 4 This is a SEM image of the calcium fluoride molded body obtained in Example 4 of the present invention. Detailed Implementation

[0034] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0035] Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products or commonly used in this field.

[0036] I. Preparation Method

[0037] Example 1

[0038] Mix 50g of calcium fluoride raw powder and 0.1g of PAA (polyacrylic acid) evenly and ball mill for 1 hour to obtain pretreated powder. Mix the pretreated powder with 1g of hydroxypropyl methylcellulose in a mixer and pour into a basin. Separately, mix 2.5g of silica sol, 2.5g of polyethylene glycol, and 15g of water evenly and slowly add the mixture to the basin while kneading it into blocks. Pour the block mixture into a twin-screw extruder and extrude it again until evenly mixed. Install a spherical particle mold according to a 5mm size and extrude the required preform. Dry the preform at room temperature for 24 hours and then calcine it in an air atmosphere in a muffle furnace. The calcination temperature program is as follows: calcine at 300℃ for 30 minutes, continue to calcine at 400℃ for 30 minutes, and calcine at 450℃ for 60 minutes, with a heating rate of 5℃ / min. After calcination, cool to room temperature to obtain the calcium fluoride molded body.

[0039] Example 2

[0040] Mix 50g of calcium fluoride raw powder and 0.1g of PAA evenly and ball mill for 1 hour to obtain pretreated powder. Mix the pretreated powder with 1g of hydroxypropyl methylcellulose evenly in a mixer and pour into a basin. Separately, mix 3.33g of silica sol, 1.67g of polyethylene glycol, and 15g of water evenly and slowly add the mixture to the basin while kneading it into blocks. Pour the block mixture into a twin-screw extruder and extrude it again until evenly mixed. Install a spherical particle mold according to the 5mm size and extrude the required preform. Dry the preform at room temperature for 24 hours and then calcine it in an air atmosphere in a muffle furnace. The calcination temperature program is as follows: calcine at 300℃ for 30 minutes, continue to calcine at 400℃ for 30 minutes, and calcine at 450℃ for 60 minutes, with a heating rate of 5℃ / min. After calcination, cool to room temperature to obtain the calcium fluoride molded body.

[0041] The difference between this embodiment and Embodiment 1 is that the mass ratio of silica sol to polyethylene glycol is 2:1.

[0042] Example 3

[0043] Mix 50g of calcium fluoride raw powder and 0.1g of PAA evenly and ball mill for 1 hour to obtain pretreated powder. Mix the pretreated powder with 1g of hydroxypropyl methylcellulose evenly in a mixer and pour into a basin. Separately, mix 3.75g of silica sol, 1.25g of polyethylene glycol, and 15g of water evenly and slowly add the mixture to the basin while kneading it into blocks. Pour the block mixture into a twin-screw extruder and extrude it again until evenly mixed. Install a spherical particle mold according to the 5mm size and extrude the required preform. Dry the preform at room temperature for 24 hours and then calcine it in an air atmosphere in a muffle furnace. The calcination temperature program is as follows: calcine at 300℃ for 30 minutes, continue to calcine at 400℃ for 30 minutes, and calcine at 450℃ for 60 minutes. The heating rate is 5℃ / min. After calcination, cool to room temperature to obtain the calcium fluoride molded body.

[0044] The difference between this embodiment and Embodiment 1 is that the mass ratio of silica sol to polyethylene glycol is 3:1.

[0045] Example 4

[0046] Mix 50g of calcium fluoride raw powder and 0.1g of PAA evenly and ball mill for 1 hour to obtain pretreated powder. Mix the pretreated powder with 1g of hydroxypropyl methylcellulose evenly in a mixer and pour into a basin. Separately, mix 2.5g of SB powder (pseudoboehmite), 2.5g of polyethylene glycol, and 15g of water evenly and slowly add the mixture to the basin while kneading it into blocks. Pour the block mixture into a twin-screw extruder and extrude it again until evenly mixed. Install a spherical particle mold according to the 5mm size and extrude the required preform. Dry the preform at room temperature for 24 hours and then calcine it in an air atmosphere in a muffle furnace. The calcination temperature program is as follows: calcine at 300℃ for 30 minutes, continue to calcine at 400℃ for 30 minutes, and calcine at 450℃ for 60 minutes, with a heating rate of 5℃ / min. After calcination, cool to room temperature to obtain the calcium fluoride molded body.

[0047] The difference between this embodiment and Embodiment 1 is that the adhesive is a mixture of boehmite and polyethylene glycol.

[0048] Example 5

[0049] Mix 50g of calcium fluoride raw powder and 0.1g of PAA evenly and ball mill for 1 hour to obtain pretreated powder. Mix the pretreated powder with 1.5g of hydroxypropyl methylcellulose evenly in a mixer and pour into a basin. Separately, mix 2.5g of silica sol, 2.5g of polyethylene glycol, and 15g of water evenly and slowly add the mixture to the basin while kneading it into blocks. Pour the block mixture into a twin-screw extruder and extrude it again until evenly mixed. Install a spherical particle mold according to the 5mm size and extrude the required preform. Dry the preform at room temperature for 24 hours and then calcine it in an air atmosphere in a muffle furnace. The calcination temperature program is as follows: calcine at 300℃ for 30 minutes, continue to calcine at 400℃ for 30 minutes, and calcine at 450℃ for 60 minutes. The heating rate is 5℃ / min. After calcination, cool to room temperature to obtain the calcium fluoride molded body.

[0050] The difference between this embodiment and Embodiment 1 is that the mass of hydroxypropyl methylcellulose is 0.3% of the mass of calcium fluoride raw powder.

[0051] Comparative Example 1

[0052] The difference between this comparative example and Example 1 is that the binder is replaced by a mixture of polyethylene glycol and silica sol with a single polyethylene glycol.

[0053] Mix 50g of calcium fluoride raw powder and 0.1g of PAA evenly and ball mill for 1 hour to obtain pretreated powder. Mix the pretreated powder with 1g of hydroxypropyl methylcellulose evenly in a mixer and pour into a basin. Separately, mix 5g of polyethylene glycol and 15g of water evenly and slowly add the mixture to the basin while kneading it into blocks. Pour the block mixture into a twin-screw extruder and extrude it again until evenly mixed. Install a spherical particle mold according to the 5mm size and extrude the required preform. Dry the preform at room temperature for 24 hours and then calcine it in an air atmosphere in a muffle furnace. The calcination temperature program is as follows: calcine at 300℃ for 30 minutes, continue to calcine at 400℃ for 30 minutes, and calcine at 450℃ for 60 minutes. The heating rate is 5℃ / min. After calcination, cool to room temperature to obtain the calcium fluoride molded body.

[0054] Comparative Example 2

[0055] The difference between this comparative example and Example 1 is that the binder was replaced by a mixture of polyethylene glycol and silica sol with a single SB powder (pseudoboehmite).

[0056] Mix 50g of calcium fluoride raw powder and 0.1g of PAA evenly, and ball mill for 1 hour to obtain pretreated powder. Mix the pretreated powder with 1g of hydroxypropyl methylcellulose evenly in a mixer and pour into a basin. Take 5g of SB powder and 15g of water evenly, and slowly add it to the basin while kneading the mixture into blocks. Pour the block mixture into a twin-screw extruder and extrude it again until evenly mixed. Install a spherical particle mold according to the 5mm size and extrude the required preform. Dry the preform at room temperature for 24 hours and then calcine it in an air atmosphere in a muffle furnace. The calcination temperature program is as follows: calcine at 300℃ for 30 minutes, continue to calcine at 400℃ for 30 minutes, and calcine at 450℃ for 60 minutes. The heating rate is 5℃ / min. After calcination, cool to room temperature to obtain calcium fluoride molded body.

[0057] Comparative Example 3

[0058] The difference between this comparative example and Example 1 is that the binder is replaced by a mixture of polyethylene glycol and silica sol with a single polyvinyl alcohol.

[0059] Mix 50g of calcium fluoride raw powder and 0.1g of PAA evenly and ball mill for 1 hour to obtain pretreated powder. Mix the pretreated powder with 1g of hydroxypropyl methylcellulose evenly in a mixer and pour into a basin. Separately, mix 5g of polyvinyl alcohol and 15g of water evenly and slowly add the mixture to the basin while kneading it into blocks. Pour the block mixture into a twin-screw extruder and extrude it again until evenly mixed. Install a spherical particle mold according to the 5mm size and extrude the required preform. Dry the preform at room temperature for 24 hours and then calcine it in an air atmosphere in a muffle furnace. The calcination temperature program is as follows: calcine at 300℃ for 30 minutes, continue to calcine at 400℃ for 30 minutes, and calcine at 450℃ for 60 minutes. The heating rate is 5℃ / min. After calcination, cool to room temperature to obtain calcium fluoride molded body.

[0060] Comparative Example 4

[0061] The difference between this comparative example and Example 1 is that the heating method during roasting is different.

[0062] Mix 50g of calcium fluoride raw powder and 0.1g of PAA evenly and ball mill for 1 hour to obtain pretreated powder. Mix the pretreated powder with 1g of hydroxypropyl methylcellulose evenly in a mixer and pour into a basin. Separately, mix 2.5g of silica sol, 2.5g of polyethylene glycol, and 15g of water evenly and slowly add the mixture to the basin while kneading it into blocks. Pour the block mixture into a twin-screw extruder and extrude it again until evenly mixed. Install a spherical particle mold according to the 5mm size and extrude the required preform. Dry the preform at room temperature for 24 hours and then calcine it in an air atmosphere in a muffle furnace. The calcination temperature program is: calcine at 450℃ for 120 minutes at a heating rate of 5℃ / min. After calcination, cool to room temperature to obtain the calcium fluoride molded body.

[0063] Comparative Example 5

[0064] The difference between this comparative example and Example 1 is that the heating rate during calcination is different.

[0065] Mix 50g of calcium fluoride raw powder and 0.1g of PAA evenly and ball mill for 1 hour to obtain pretreated powder. Mix 1g of hydroxypropyl methylcellulose in a mixer evenly and pour into a basin. Separately, mix 2.5g of silica sol, 2.5g of polyethylene glycol, and 15g of water evenly and slowly add the mixture to the basin while kneading it into blocks. Pour the block mixture into a twin-screw extruder and extrude it again until evenly mixed. Install a spherical particle mold according to the 5mm size and extrude the required preform. Dry the preform at room temperature for 24 hours and then calcine it in an air atmosphere in a muffle furnace. The calcination temperature program is as follows: calcine at 300℃ for 30 minutes, continue to calcine at 400℃ for 30 minutes, and calcine at 450℃ for 60 minutes. The heating rate is 10℃ / min. After calcination, cool to room temperature to obtain the calcium fluoride molded body.

[0066] Comparative Example 6

[0067] The difference between this comparative example and Example 1 is that hydroxypropyl methylcellulose was not added.

[0068] II. Testing Methods

[0069] The performance of the calcium fluoride molded bodies prepared in the examples and comparative examples was evaluated, and their compressive strength, water absorption, specific surface area, and pore volume parameters were compared.

[0070] Compressive strength test: The calcium fluoride shaped particles were tested using a KQ-2 particle strength tester.

[0071] Water absorption rate test: The sample was dried at 110℃ to constant weight (m1) using the atmospheric pressure test method; it was then immersed in deionized water and soaked at room temperature and pressure for 24 hours; after removal, the surface moisture was gently wiped with a damp gauze and weighed immediately (m2); water absorption rate = [(m2-m1) / m1]×100%.

[0072] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0073] The performance evaluation results of the calcium fluoride molded articles prepared in the examples and comparative examples are shown in Table 1.

[0074] Table 1 Comparison of various performance parameters of calcium fluoride under different preparation methods

[0075]

[0076] Table 1 shows that the calcium fluoride particles prepared using the calcium fluoride molding method provided in this invention have a specific surface area of ​​up to 50 m². 2 The pore size is above / g, and it exhibits good stability and water absorption. Data from Comparative Examples 1-3 and Examples 1-3 show that, compared to a single binder, a rationally proportioned composite binder demonstrates significant advantages through the synergistic effect of multiple components. Comparative Examples 4-5 indicate that during the calcium fluoride molding process, the calcination temperature and heating rate have a significant impact on the specific surface area and properties of calcium fluoride. Too low a calcination temperature results in insufficient sintering of the binder and organic matter, and makes it prone to brittleness; too high a temperature leads to a rapid decrease in specific surface area, reducing the water absorption porosity of the molded calcium fluoride. Excessive heating (>5℃ / min) easily causes cracks, leading to brittleness and decreased strength; excessively slow heating results in unnecessary energy loss. Comparative Example 6, without the addition of hydroxypropyl methylcellulose, shows a lower water absorption rate because the hydroxyl hydrophilic groups slightly increase the porosity of the green body, further enhancing the water absorption rate.

[0077] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for molding calcium fluoride, characterized in that, Includes the following steps: Calcium fluoride raw powder is subjected to dispersion pretreatment to obtain pretreated powder; the dispersion pretreatment specifically involves adding polyacrylic acid to the calcium fluoride raw powder and then ball milling; the mass of the polyacrylic acid is 0.1%~1% of the mass of the calcium fluoride raw powder; The pretreated powder is mixed with hydroxypropyl methylcellulose, a binder, and water, and then extruded to obtain a preform. The binder includes at least two of boehmite, silica sol, polyethylene glycol, and polyvinyl alcohol. The mass of the hydroxypropyl methylcellulose is 2% to 4% of the mass of the calcium fluoride powder. The mass of the binder is 5% to 20% of the mass of the calcium fluoride powder. The mass of the water is 30% to 50% of the mass of the calcium fluoride powder. The calcium fluoride molded body is obtained by drying and calcining the preform; the calcination conditions are as follows: calcining at 300°C for 30 min in air atmosphere, then calcining at 400°C for 30 min, and then calcining at 450°C for 60 min; the heating rate is 3~5°C / min.

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

1.

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

4. A calcium fluoride molded body obtained by the molding method of calcium fluoride as described in any one of claims 1 to 3.

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