Method for synthesizing fluoride by solid-state reaction

Abstract

To provide a method for synthesizing fluoride by using a low-energy and low-toxicity raw material.SOLUTION: In a method for synthesizing fluoride, raw material powder of an alkali metal compound and / or an alkaline earth metal compound is prepared, and a fluoride agent selected from at least one of ammonium fluoride, sodium fluoride, and potassium fluoride is prepared. Further, the fluoride agent is brought into contact with the raw material powder, and the raw material powder is subjected to solid-state reaction to obtain fluoride. A small amount of water is added before or after the contacting step, and the raw material powder and the water are allowed to coexist. In the water-coexisting step, the weight of the water to be added is set to 0.001 or more and 1.0 or less when the total weight of the raw material powder and the fluoride agent is 1.0.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for synthesizing fluorides, and more particularly to a method for synthesizing fluorides by a solid-phase reaction under a room temperature atmosphere. [Background technology]

[0002] CaF2, a typical fluoride, exists naturally as fluorite, but because fluorite is a natural product, it contains impurities. Therefore, attempts have been made to synthesize artificial CaF2 with high purity and stable quality. To date, methods that have been proposed include reacting calcium carbonate with hydrofluoric acid (see Patent Document 1) and reacting a mixture of calcium carbonate and calcium hydroxide with gases such as hydrogen fluoride gas and fluorine gas (see Patent Document 2).

[0003] However, although the CaF2 synthesized as described above is highly pure and is an ideal material for optical applications such as optical lenses, fluorite lenses, and optical materials for window panels, it has the disadvantage that it is difficult to manufacture and dispose of because it uses highly toxic hydrofluoric acid and hydrogen fluoride gas.

[0004] Also, a method has been proposed in which polytetrafluoroethylene (PTFE) or other fluororesins are heated to 500°C together with sodium hydroxide to synthesize sodium fluoride, and this substance is then replaced with calcium fluoride (see Non-Patent Document 1). This prior art is safer because it does not use highly toxic hydrofluoric acid or hydrogen fluoride gas, but it requires heating at high temperatures, consumes a lot of energy, and there are concerns about carbon dioxide emissions.

[0005] In addition, Non-Patent Document 2 describes the synthesis of alkaline earth metal fluorides by the reaction of alkaline earth metal hydroxides with ammonium fluoride. However, this prior art only involves mixing solid raw materials together (solid-phase reaction), and there are concerns that the reaction rate is slow, the reaction varies, and it is not possible to stably produce fluorides.

[0006] As a low-temperature synthesis method for ceramics, a method in which an appropriate amount of moisture is added and synthesis is performed at room temperature or under low-temperature heating is known (Patent Document 3). However, the synthesis of fluorides has not been reported.

[0007] As described above, conventional methods for synthesizing fluorides generally use highly toxic hydrofluoric acid or hydrogen fluoride gas, while conventional manufacturing methods that do not use hydrofluoric acid or hydrogen fluoride gas require high-temperature heating. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2004-123417 A [Patent Document 2] Patent No. 6407604 [Patent Document 3] Patent No. 6382030 [Non-patent literature]

[0009] [Non-Patent Document 1] Naohisa Yanagihara, Takahiro Katoh, “Mineralization of polytetrafluoroethylene and other fluoropolymers by molten sodium hydroxide”, Green Chemistry, (2022) [Non-Patent Document 2] Gudrun Scholz, Klas Meyer, Andre Duvel , Paul Heitjans, and Erhard Kemnitz, “Fast Ion Conducting Nanocrystalline Alkaline Earth Fluorides Simply Prepared by Mixing or Manual Shaking”, Z. Anorg. Allg. Chem. (2013) Summary of the Invention [Problem to be solved by the invention]

[0010] In view of the above circumstances, an object of the present invention is to provide a method for synthesizing fluoride, which can synthesize fluoride using low-energy and low-toxicity raw materials (for example, ammonium fluoride or sodium fluoride).

[0011] The inventors had previously discovered that crystalline ceramics could be obtained by contacting at least two or more types of raw material powders in a gas at room temperature and causing a solid-state reaction; however, they had not been able to demonstrate the synthesis of fluorides.

[0012] Therefore, the inventors conducted extensive research and discovered that the desired fluoride can be synthesized by using ammonium fluoride or sodium fluoride as a fluorine source (also called a fluorinating agent) and adding a small amount of water when mixing (solid-phase reaction) this fluorine source with powder of an alkali metal or alkaline earth metal. [Means for solving the problem]

[0013] That is, the method for synthesizing a fluoride of the present invention has at least the following characteristics and configurations.

[0014] (Aspect 1) preparing a raw powder of an alkali metal compound and / or an alkaline earth metal compound; providing a fluoriding agent selected from at least one of ammonium fluoride, sodium fluoride, and potassium fluoride; a step of contacting the raw material powder with the fluorinating agent to cause a solid-phase reaction of the raw material powder to obtain a fluoride; a step of adding a small amount of water before or after the contact step to allow the raw material powder and the water to coexist; and In the step of allowing water to coexist, the weight of the water to be added is set to 0.001 or more and 1.0 or less, assuming that the total weight of the raw material powder and the fluorination agent is 1.0. 1. A method for synthesizing fluoride, comprising the steps of: (Aspect 2) The raw material powder is a metal compound selected from at least one of lithium, sodium, calcium, and magnesium. 2. The method for synthesizing a fluoride according to claim 1, (Aspect 3) The raw material powder is a metal compound selected from at least one of a carbonate compound and a hydroxide compound. 2. The method for synthesizing a fluoride according to claim 1, (Aspect 4) The method further includes a step of storing a mixture of the raw material powder and the fluorination agent in a sealed or semi-sealed container after the step of causing the raw material powder and the water to coexist, and heating the mixture by setting the temperature inside the container to 30° C. to 250° C., 2. The method for synthesizing a fluoride according to claim 1, (Aspect 5) The method for synthesizing a fluoride is a method for obtaining a fluoride for use in any one of an optical lens, a fluorite lens, an optical material for a window plate, a ceramic filler, a plasma-resistant surface protective film, a flux, and a hydrofluoric acid raw material. 2. The method for synthesizing a fluoride according to claim 1, Effect of the Invention

[0015] According to the present invention, instead of using highly toxic fluorine compounds such as hydrofluoric acid and hydrogen fluoride gas as a fluorinating agent, ammonium fluoride, sodium fluoride, or potassium fluoride is used, which allows various fluorides to be synthesized at low cost and with simple operations. In particular, in a system using a calcium metal compound, an optical material of calcium fluoride can be obtained. [Brief description of the drawings]

[0016] [Figure 1] 1 shows the X-ray diffraction patterns of the fluoride (CaF2) synthesized in Examples 1 and 2. [Diagram 2] 1 shows the X-ray diffraction pattern of the fluoride (NaF) synthesized in Example 3. [Diagram 3] 1 shows the X-ray diffraction pattern of the fluoride (LiF) synthesized in Example 4. [Figure 4] 1 shows the X-ray diffraction pattern of the fluoride (MgF2) synthesized in Example 5. [Diagram 5] 1 shows the X-ray diffraction pattern of the fluoride (CaF2) synthesized in Example 6. [Figure 6] 1 shows the X-ray diffraction pattern of the fluoride (CaF2) synthesized in Comparative Example 1. [Figure 7] 1 shows the X-ray diffraction pattern of the fluoride (CaF2) synthesized in Comparative Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention will be described below based on the embodiments shown in the drawings, but the present invention is not limited to the specific embodiments described below.

[0018] <Alkaline metal compounds and / or alkaline earth metal compounds> Examples of the alkali metal compound and / or alkaline earth metal compound used in the present invention include the following.

[0019] Examples of the alkali metal compounds include hydroxides, carbonates, and oxides of Li, Na, K, Rb, or Cs metals, and examples of the alkaline earth metal compounds include hydroxides, carbonates, and oxides of metals such as Be, Mg, Ca, Sr, and Ba. Among these, hydroxides and carbonates are preferred, and hydroxides and carbonates of Li metal, Na metal, Mg metal, and Ca metal are more preferred. In particular, calcium compounds that can be used to obtain calcium fluoride, which can provide hydrofluoric acid of high purity, are more preferred than fluorite, which is a raw material for hydrofluoric acid.

[0020] <Fluoride> The fluorinating agent of the present invention is not limited as long as it is a fluorine-containing compound having low toxicity, but ammonium fluoride, sodium fluoride, and potassium fluoride are particularly preferred, and ammonium fluoride is more preferred.

[0021] Ammonium fluoride, sodium fluoride, and potassium fluoride are less toxic and easier to handle than hydrofluoric acid. Ammonium fluoride is particularly preferred because it has excellent reactivity with various alkali metal compounds and / or alkaline earth metal compounds to synthesize fluorides, and the synthesized fluorides do not contain metals derived from the fluorinating agent.

[0022] The amount of the fluorinating agent added is adjusted to a stoichiometric ratio with respect to the alkali metal compound and / or alkaline earth metal compound used for the target fluoride.

[0023] <Water> The water that plays an important role in the synthesis of fluorides by the solid-phase reaction of the present invention is preferably pure water, distilled water, ion-exchanged water, etc. The nature of the water to be added may be normal water (liquid state) or steam state. The water addition step may include a method of directly adding water to the raw material powder, a method of adding water as a steam-like gas, etc., and is selected from the viewpoints of reaction rate, stable production with little variation, and excellent mass production.

[0024] The amount of water added is, when the total weight of the raw material powder (and the fluorinating agent powder) is taken as 1.0, the weight of the water to be added is 0.001 to 1.0, preferably 0.001 to 0.2, and more preferably 0.01 to 0.1.

[0025] When the amount of water added is at the lower limit of the above-mentioned preferred range (less than 0.001), a stable intermediate product is generated at the contact surface between the raw material powders, or a dense product layer is formed, as in a general solid-state reaction, slowing down the ion diffusion rate between the raw material powders and making it difficult for the reaction to proceed. On the other hand, when the amount of water exceeds the upper limit of the above-mentioned preferred range (1.0), the raw material powders float in the water and the contact area between the raw material powders decreases, making it difficult for the reaction to occur, and the effect of adding water cannot be obtained.

[0026] <Solid-state reaction of fluoride> The synthesis of a fluoride by a solid-phase reaction of the present invention is carried out as follows.

[0027] The synthesis method of the present invention, which is characterized by adding water, is shown below. After preparing a mixture by mixing the fluorinating agent, the raw material metal compound, and water in an agate mortar, ball mill, mixer, stirrer, etc. for about 0.2 minutes to 24 hours, a solid-phase reaction will proceed and a fluoride will be obtained by carrying out any of the following methods (reaction conditions (1) to (3) of the present invention below).

[0028] (1) Leave the sample in an atmosphere of 10°C to 100°C for 10 minutes or more. Since solid-phase reactions are generally affected by the absolute humidity and temperature of the standing environment, the standing time is longer in a low-temperature atmosphere with low absolute humidity. On the other hand, the standing time is shorter in a high-humidity, high-temperature atmosphere. Although it varies depending on the metal compound, for example, standing for 3 hours or more in a low-humidity atmosphere at 10°C is preferable. Also, in a high-humidity atmosphere at 60°C, the target compound is usually obtained by standing for less than 10 to 60 minutes.

[0029] (2) The contacted raw material powder is placed in a sealed or semi-sealed container and heated to a temperature of 30 to 250°C inside the container (low-temperature heating), whereby the heating time can be set to 2 to 120 minutes.

[0030] In the solid-phase reaction of the present invention, the solid-phase reaction time is shortened by storing the raw material powders in a sealed or semi-sealed container. With this method, a solid-phase reaction occurs even with a combination of raw material powders that would not normally cause a solid-phase reaction in an air atmosphere at 10° C. to 30° C., and a fluoride can be obtained.

[0031] The gas contained in the sealed container is not particularly limited as long as it is a heatable medium selected from air, water vapor, and inert gases such as nitrogen and argon, but air is preferred from the viewpoint of manufacturing costs.

[0032] On the other hand, for combinations of raw materials that undergo solid-state reactions in a room temperature environment of 10°C to 30°C, setting the low-temperature heating temperature significantly accelerates the solid-state reaction, making it possible to significantly shorten the mixing (stirring) time of the raw materials in an atmosphere of 10°C to 30°C.

[0033] Here, a sealed container is one that blocks the flow of air between the outside air and the gas partitioned within the container, allows the humidity and temperature conditions of the gas within the container to be adjusted and maintained as desired, and is not corroded by fluorinating agents. Examples include vials and hydrothermal reaction containers made of stainless steel or steel, which have better heat resistance than vials.

[0034] In addition to the above-mentioned sealed containers, containers that can be used in the present invention may be semi-sealed containers in which outside air flows into the container at an extremely slow inflow rate and gas in the container leaks out at an extremely slow outflow rate. Other examples of semi-sealed containers include containers with a flow path (container shape suitable for mass production in a factory) in which gas (e.g., air) heated to the above-mentioned desired temperature can always flow in and out of the container.

[0035] (3) A fluidized bed solid-state reactor enables continuous reactions. It is also possible to obtain fluorides by contacting the above-mentioned raw material powder and fluorinating agent with water in advance and reacting them in a fluidized bed. It is also possible to obtain fluorides by contacting a mixture of the raw material powder and fluoride with a water-containing gas in a fluidized bed and reacting them.

[0036] (4) Even in a system in which water is not added, the reaction proceeds slowly in a high-temperature and high-humidity environment to obtain a fluoride, but the standing time required for the reaction is extremely long, making it difficult to obtain a fluoride with uniform quality. Therefore, in terms of uniform quality, stable production, and mass productivity, the above methods of adding water (1) to (3) are preferable to the method (4).

[0037] Thus, according to the present invention, unlike conventional synthesis methods, fluorides can be easily synthesized without the need for calcination. The present invention is expected to be applied to various material fields such as optical lenses, fluorite lenses, optical materials for window panes, ceramic fillers, plasma-resistant surface protection films, and fluxes.

[0038] Generally, high-temperature heat treatment is required to synthesize fluorides. For example, in Non-Patent Document 1, PTFE is heated to 500°C to synthesize sodium fluoride or calcium fluoride, but a high-temperature atmosphere is required, and there are no known examples of crystallizing crystalline fluoride materials at room temperature or in a low-temperature range without a special process. The present inventors have found that by using the synthesis method and synthesis conditions of the present invention, a wide variety of fluoride materials can be produced easily and with low energy.

[0039] In addition, in the case of a form in which the above-mentioned storage step in a sealed or semi-sealed container and the low-temperature heating step are not performed, depending on the combination of raw material powders having a low solid-phase reaction rate, it is preferable to set the mixing time (raw material stirring time) in the mixing step to a relatively long time of 1 hour or more.

[0040] In contrast, in the embodiment in which the above-mentioned storing step and the above-mentioned heating step are introduced, the reaction rate in the mixture stored in the sealed space during the heating step is dramatically increased, so that a solid-phase reaction can occur throughout the mixture in an extremely short time. Therefore, the raw material stirring time in the mixing step in a gas at 10°C to 30°C before the heating step can also be significantly shortened, and the raw material stirring time is less than 60 minutes, preferably 0.2 to 40 minutes, and more preferably 0.5 to 20 minutes. Even when a combination of raw materials is used in which a solid-phase reaction hardly occurs (or does not occur easily) in a gas environment at room temperature even when water is added, the introduction of this step (storage and low-temperature heating) allows a solid-phase reaction to occur.

[0041] The following describes the present invention based on specific examples. EXAMPLES

[0042] (CaF2 synthesis method 1 (mixing (adding water) + leaving it still)) CaCO3 powder (0.29g) and NH4F powder (0.21g) were weighed out in air at room temperature to a stoichiometric ratio (CaCO3 / NH4F=1mol / 2mol), and 0.05g of pure water was added and mixed in an agate mortar for 2 minutes. This mixture was left on an alumina board for 8 days (192 hours). The total weight of the raw material powder and fluorination agent used in Example 1 was 0.5g, and the above amount of pure water added was equivalent to 0.1, which is 10wt% of the raw material powder, assuming that the total weight of the raw material powder is 1. In the examples described later, the amount of water added relative to the total weight of the raw material powder was set to the same ratio.

[0043] The X-ray diffraction pattern of the synthesized product after standing is shown in the middle of Figure 1. When comparing this X-ray diffraction pattern of Example 1 with the simulated crystal pattern of the target product (target compound) shown in the upper part of the figure, the peaks match, confirming that crystalline CaF2 was produced by the synthesis method of Example 1. EXAMPLES

[0044] (CaF2 synthesis method 2 (mixing (adding water) + container storage + low temperature heating)) The mixture prepared in the same manner as in Example 1 was placed in a sealed container (bias flask) and heated (low-temperature heating) at 220°C for 30 minutes. The X-ray diffraction pattern of this compound is shown in the lower part of Figure 1. From this result, it was confirmed that crystalline CaF2 could be produced by the synthesis method of Example 2 as in Example 1. EXAMPLES

[0045] (NaF synthesis method (mixing (adding water) + leaving it still)) In Example 3, similarly to Example 1, 0.800g (0.02mol) of NaOH powder and 0.741g (0.02mol) of NHF powder were weighed out to obtain a raw powder mixture (1.541g) with a stoichiometric ratio of NaOH / NH4F=1mol / 1mol in air at room temperature, and 0.154g of pure water (when the total weight of the raw powder and the fluorinating agent is 1, the amount of added pure water is equivalent to 0.1) was added and mixed in an agate mortar for 2 minutes. This mixture was left to stand on an alumina board for 192 hours.

[0046] The X-ray diffraction pattern of this synthesis product is shown in Figure 2. When comparing the X-ray diffraction pattern of Example 3 with the simulated crystal pattern of the target product (target compound) shown in the upper part of the figure, the respective peaks match, confirming that crystalline NaF was produced. EXAMPLES

[0047] (LiF synthesis method (mixing (adding water) + leaving it)) In Example 4, similarly to Example 1, 0.839 g (0.02 mol) of LiOH·H2O powder and 0.741 g (0.02 mol) of NHF powder were weighed out to obtain a raw material powder mixture (1.580 g) with a stoichiometric ratio of LiOH·H2O / NH4F = 1 mol / 1 mol in air at room temperature, and 0.158 g of pure water (assuming that the total weight of the raw material powder and the fluorinating agent is 1, the amount of added pure water is equivalent to 0.1) was added and mixed in an agate mortar for 2 minutes. This mixture was left to stand on an alumina board for 192 hours.

[0048] The X-ray diffraction pattern of this synthesis product is shown in Figure 3. By comparing the X-ray diffraction pattern of this Example 4 with the simulated crystal pattern of the target product (target compound) shown in the upper part of the figure, it was confirmed that crystalline LiF was produced. EXAMPLES

[0049] (MgF2 synthesis method (mixing (adding water) + container storage + low temperature heating)) In Example 5, similarly to Example 1, 0.583g (0.01mol) of Mg(OH2) powder and 0.741g (0.02mol) of NH4F powder were weighed out to obtain 1.324g of raw powder so that the stoichiometric ratio of Mg(OH2) / NH4F=1mol / 2mol was obtained at room temperature in air, and 0.132g of pure water (assuming that the total weight of the raw powder and the fluorinating agent is 1, the amount of added pure water is equivalent to 0.1) was added and mixed in an agate mortar for 2 minutes. This mixture was placed in a 25ml high-pressure reaction and decomposition vessel and heated at 220°C for 24 hours.

[0050] The X-ray diffraction pattern of this synthesis product is shown in Figure 4. When comparing the X-ray diffraction pattern of Example 5 with the simulated crystal pattern of the target product (target compound) shown in the upper part of the figure, the peaks match, confirming that crystalline MgF2 was produced. EXAMPLES

[0051] (CaF2 synthesis method 3 (mixing (steam addition) + standing)) 20.0 g of CaCO3 powder and 14.8 g of NH4F powder were weighed out into a 10 L flask so that the stoichiometric ratio of CaCO3 / NH4F was 1 mol / 2 mol. The mixture was stirred and mixed for 5 minutes, and then steam was added at 100°C (594.51 g / m2 in terms of water). 3 (For 10 L, 5.95 g (if the total weight of the raw material powder and fluorinating agent (34.8 g) is taken as 1, the amount of steam added is equivalent to 0.171)) was introduced into a 10 L flask, the environment inside the flask was replaced with steam, and the flask was left to stand for 1 hour.

[0052] The X-ray diffraction pattern of the synthesized product after standing is shown in Figure 5. When comparing the X-ray diffraction pattern of this Example 6 (lower part in the figure) with the simulated crystal pattern of the target product (target compound) (upper part in the figure), the peaks match, confirming that crystalline CaF2 was produced.

[0053] [Comparative Example 1] (CaF2 synthesis method 4 (mixing (no water added) + standing)) A solid-phase reaction was carried out under the same synthesis conditions as in Example 1, except that 0.05 g of pure water was not added. The X-ray diffraction pattern of the synthetic product produced in this Comparative Example 1 is shown in the lower part of Figure 6. When the results of this Comparative Example 1 are compared with the simulated crystal pattern of the target product (target compound) (upper part in the figure), there are some matching peaks, but the peak intensity is low, and it is estimated that the synthesis ratio of CaF2 is low.

[0054] [Comparative Example 2] (CaF2 synthesis method 5 (mixing (adding excess water) + leaving it still)) The synthesis of CaF2 was attempted under the same conditions as in Example 1, except that the amount of pure water added was changed from 0.05 g to 1.0 g (if the total weight of the raw material powder and the fluorinating agent is 1, the amount of pure water added is equivalent to 2). The X-ray diffraction pattern of this mixture is shown in the lower part of Figure 7. When the X-ray diffraction pattern of the synthetic product of Comparative Example 2 was compared with the crystal pattern of the simulated target product (target compound), the respective peaks did not match, and it was estimated that CaF2 was not produced. [Industrial Applicability]

[0055] As described above, the method of the present invention makes it possible to synthesize fluoride using a low-energy and low-toxicity fluorine source without using any special equipment, and therefore has extremely high industrial value and applicability.

Claims

1. preparing a raw powder of an alkali metal compound and / or an alkaline earth metal compound; providing a fluoriding agent selected from at least one of ammonium fluoride, sodium fluoride, and potassium fluoride; a step of contacting the raw material powder with the fluorinating agent to cause a solid-phase reaction of the raw material powder to obtain a fluoride; a step of adding a small amount of water before or after the contact step to make the raw material powder and the water coexist; and In the step of allowing water to coexist, the weight of the water to be added is set to 0.001 or more and 1.0 or less, assuming that the total weight of the raw material powder and the fluorinating agent is 1.

0.

1. A method for synthesizing fluoride, comprising the steps of:

2. The raw material powder is a metal compound selected from at least one of lithium, sodium, calcium, and magnesium.

2. The method for synthesizing fluoride according to claim 1 .

3. The raw material powder is a metal compound selected from at least one of a carbonate compound and a hydroxide compound.

2. The method for synthesizing fluoride according to claim 1 .

4. The method further includes a step of storing the mixture of the raw material powder and the fluorination agent in a sealed or semi-sealed container after the step of causing the raw material powder and the water to coexist, and heating the mixture by setting the temperature inside the container to 30° C. to 250° C., 2. The method for synthesizing fluoride according to claim 1 .

5. The method for synthesizing a fluoride is a method for obtaining a fluoride for use in any one of an optical lens, a fluorite lens, an optical material for a window plate, a ceramic filler, a plasma-resistant surface protective film, a flux, and a hydrofluoric acid raw material.

2. The method for synthesizing fluoride according to claim 1 .

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