Method for producing iota alumina and iota alumina

Abstract

Iota-alumina is produced by a simple and low-temperature process. This method for producing iota-alumina has: a reaction step for mixing a solid starting material comprising an alkali metal compound, a fluoride, and at least one material selected from aluminum compounds and aluminum, and carrying out a heat treatment; and a washing step for introducing the product produced in the reaction step into a polar solvent.

Description

[Technical Field]

[0001] The present invention relates to a method for producing iota alumina and iota alumina. [Background technology]

[0002] Conventional methods for producing iota-alumina have required, for example, a step of mixing aluminum nitric oxide and carboxymethyl cellulose and heating the mixture to 1000°C or higher by a sol-gel method, which requires equipment that can withstand high temperatures (Non-Patent Document 1). Patent Document 1 also discloses a method for producing plate-shaped iota-alumina by oxidizing a melt of an alkali metal haloaluminate with oxygen gas or an oxygen-containing gas at a temperature of 400°C to 800°C (Patent Document 1). However, because it is necessary to introduce an oxygen-containing gas into the melt during heating, a reaction device that allows gas exchange during heating is required. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 05-201723 [Non-patent literature]

[0004] [Non-Patent Document 1] Mullite-type Na0.67Al6O9.33 and a discussion of iota-alumina, Journal of the European Ceramic Society 40 (2020) 4276-4280. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides a method for producing iota alumina at low temperature and through simple steps, and iota alumina obtained by the method, in which the crystals have a rod-like or needle-like crystal habit. [Means for solving the problem]

[0006] The method for producing iota alumina according to the first aspect is characterized by comprising a reaction step in which solid raw materials containing an alkali metal compound, a fluoride, and at least one material selected from an aluminum compound and aluminum are mixed and heated, and a washing step in which the product produced in the reaction step is introduced into a polar solvent.

[0007] In the first aspect, the alkali metal compound may be at least one selected from sodium aluminum dioxide (NaAlO), sodium borates, sodium hydride (NaH), sodium borohydride (NaBH), sodium oxide (NaO), potassium aluminum dioxide (KAlO), potassium borates, potassium hydride (KH), potassium borohydride (KBH), and potassium oxide (KO).

[0008] In the first embodiment, the sodium borates may be at least one selected from sodium metaborate (NaBO2), sodium tetraborate (Na2B4O7), and sodium diborate (Na4B2O5).

[0009] In the first embodiment, the potassium borates may be at least one selected from potassium metaborate (KBO2), potassium tetraborate (K2B4O7), and potassium diborate (K4B2O5).

[0010] In the first aspect, the fluoride may be at least one selected from sodium fluoride (NaF), sodium hexafluoroaluminate (NaAlF), potassium fluoride (KF), potassium aluminum fluoride (KAlF), potassium hexafluoroaluminate (KAlF), aluminum fluoride (AlF), and lithium fluoride (LiF).

[0011] In the first embodiment, the aluminum compound may be at least one selected from sodium aluminum dioxide (NaAlO2), potassium aluminum dioxide (KAlO2), alumina (Al2O3), and aluminum fluoride.

[0012] In a first embodiment, the polar solvent may be water.

[0013] In the first embodiment, the polar solvent may be water, and the product and the water may be stirred at a temperature of 80°C or higher and 100°C or lower in the washing step.

[0014] The iota alumina of the first embodiment has a crystal habit of rod-like, needle-like or tabular.

[0015] In the first embodiment, the average aspect ratio of the iota alumina crystals may be 3 or more and 30 or less.

[0016] In the first embodiment, the iota alumina may have a rod-like or needle-like crystal habit and may contain sodium.

[0017] In the first embodiment, the iota alumina may have a rod-like or tabular crystal habit and may contain potassium. [Effects of the Invention]

[0018] According to the first aspect, it is possible to provide a method for producing iota alumina at a low temperature and through simple steps. [Brief explanation of the drawings]

[0019] [Figure 1A] FIG. 1A is a backscattered electron image taken by a scanning electron microscope (SEM) of a cross section of the lumpy reaction product that had been washed by stirring with water at 80° C. to 100° C. for 1 hour. [Figure 1B] FIG. 1B is an enlarged SEM backscattered electron image of the area IB shown in FIG. 1A. [Figure 1C] FIG. 1C is an enlarged SEM backscattered electron image of iota alumina crystals obtained by observing the surface of the product shown in FIG. 1A. [Figure 1D] FIG. 1D is an enlarged SEM backscattered electron image of iota alumina crystals obtained by observing the surface of the product shown in FIG. 1A at a different location from that shown in FIG. 1C. [Figure 1E] FIG. 1E is an enlarged SEM backscattered electron image showing iota alumina crystals for which aspect ratios were measured in the range IE shown in FIG. 1C. [Figure 1F] FIG. 1F is an enlarged SEM backscattered electron image showing iota alumina crystals for which aspect ratios were measured in the range IF shown in FIG. 1D. [Figure 1G] FIG. 1G is an enlarged SEM backscattered electron image of iota-alumina crystals produced using potassium metaborate (KBO2) as the alkali metal compound. [Figure 1H] FIG. 1H is an enlarged SEM backscattered electron image of iota-alumina crystals from a product using potassium metaborate (KBO2) as the alkali metal compound. [Figure 2] Figure 2 is an SEM backscattered electron image of the powdered iota-alumina crystals obtained by high-temperature washing of the reaction product with boiling water. [Figure 3] FIG. 3 is a flow chart showing a first method for producing iota alumina. [Figure 4] FIG. 4 is a flow chart showing a second method for producing iota alumina. [Figure 5] FIG. 5 is a flow chart showing a third method for producing iota alumina. [Figure 6] FIG. 6 is a flow chart showing a fourth method for producing iota alumina. [Figure 7] FIG. 7 is a partial cross-sectional view showing an example of a sealed container used in the first to fourth manufacturing methods. [Figure 8] FIG. 8 is a partial cross-sectional view showing another example of a sealed container used in the first to fourth manufacturing methods. [Figure 9]FIG. 9 is a partial cross-sectional view showing another example of a sealed container used in the first to fourth manufacturing methods. [Figure 10] FIG. 10 is a partial cross-sectional view showing another example of a sealed container used in the first to fourth manufacturing methods. [Figure 11A] FIG. 11A is a front view of the exterior of a plate-shaped (blade) stirrer, using the sealed container 10B shown in FIG. [Figure 11B] FIG. 11B is a photograph of the exterior side of a plate-shaped (blade) stirrer, using the sealed container 10B shown in FIG. [Figure 12A] FIG. 12A is a photograph of a plate-shaped (blade) stirring bar in which the reaction product was removed from the sealed container shown in FIG. 8 after stirring for a predetermined period of time. [Figure 12B] FIG. 12B is a photograph of the reaction product taken out of the sealed container shown in FIG. 8 after stirring for a predetermined period of time. [Figure 13A] FIG. 13A is a photograph of the sealed vessel shown in FIG. 10 before the horizontal wide paddle (WP) stirrer was rotated to produce iota alumina. [Figure 13B] FIG. 13B is a photograph of the closed vessel shown in FIG. 10 after iota alumina was produced by rotating the horizontal wide paddle (WP) stirrer. [Figure 14A] FIG. 14A is a reaction schematic diagram illustrating the iota alumina production reaction. [Figure 14B] FIG. 14B is a reaction schematic diagram illustrating the iota alumina production reaction. [Figure 14C] FIG. 14C is a reaction schematic diagram illustrating the iota alumina production reaction. [Figure 14D] FIG. 14D is a reaction schematic diagram illustrating the iota alumina production reaction. [Figure 14E] FIG. 14E is a reaction schematic diagram illustrating the iota alumina production reaction. [Figure 14F] FIG. 14F is a reaction schematic diagram illustrating the iota alumina production reaction. [Figure 15]FIG. 15 is a diagram showing the X-ray diffraction pattern of the product according to Test Example 1. [Figure 16] FIG. 16 is a diagram showing the X-ray diffraction pattern of the product according to Test Example 3. [Figure 17] FIG. 17 is a diagram showing the X-ray diffraction pattern of the product according to Test Example 4. [Figure 18] FIG. 18 is a diagram showing the X-ray diffraction pattern of the product of Test Example 6. [Figure 19] FIG. 19 is a diagram showing the X-ray diffraction pattern of the product of Test Example 7. [Figure 20] FIG. 20 is a diagram showing the X-ray diffraction pattern of the product of Test Example 8. [Figure 21] FIG. 21 is a diagram showing the X-ray diffraction pattern of the product of Test Example 18. [Figure 22] FIG. 22 is a diagram showing the X-ray diffraction pattern of the product of Test Example 24. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings, but the present disclosure is not limited thereto. The components of the embodiments described below can be combined as appropriate. In addition, some components may not be used. Furthermore, the components in the embodiments described below include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range.

[0021] Iota-alumina (Na 0.67 AlO 9.33 or K 0.67 AlO 9.33 The production method of ) has a reaction step and an extraction step.

[0022] The reaction step is a step in which solid raw materials are mixed and heated.

[0023] The solid raw material contains at least one material selected from an alkali metal compound, a fluoride, an aluminum compound, and aluminum.

[0024] As the alkali metal compound raw material, at least one selected from sodium aluminum dioxide (NaAlO), sodium borates, sodium hydride (NaH), sodium borohydride (NaBH), sodium oxide (NaO), potassium aluminum dioxide (KAlO), potassium borates, potassium hydride (KH), potassium borohydride (KBH), and potassium oxide (KO) can be used.

[0025] Specific examples of sodium borates used as raw materials include borax (sodium tetraborate: Na2B4O7), sodium metaborate (NaBO2(=Na2B2O4)), sodium diborate (Na4B2O5), potassium metaborate (KBO2(=K3(B3O6))), potassium tetraborate (K2B4O7), and sodium diborate (K4B2O5), or a combination of at least two or more of them, but are not limited to these.

[0026] When sodium metaborate is used as the sodium borate, powdered sodium metaborate powder (sodium metaborate powder) is used. The particle size of the sodium metaborate powder is preferably 100 μm or less. The sodium metaborate powder is obtained by grinding the sodium metaborate powder to a certain degree and then passing it through a sieve with a mesh size of 100 μm. If the particle size of the sodium metaborate powder exceeds 100 μm, the production efficiency of sodium borohydride may decrease. The particle size of the sodium metaborate powder is more preferably less than 100 μm. In other words, the sodium metaborate powder is preferably obtained by passing it through a sieve with a mesh size of less than 100 μm (for example, a sieve with a mesh size of 50 μm or less). In this case, the production efficiency of iota alumina can be further improved.

[0027] Since sodium metaborate powder contains moisture, the amount of sodium metaborate powder is preferably increased by the mass of moisture relative to the amount required for synthesizing sodium borohydride.

[0028] Examples of potassium borates that can be used as raw materials include, but are not limited to, potassium metaborate (KBO), potassium tetraborate (KBO), and potassium diborate (KBO), or a combination of at least two or more of these.

[0029] The raw aluminum material may be fragments such as powder material or scrap material. The aluminum fragments may be, for example, cutting chips, waste material, or other scrap material. It is preferable that the aluminum fragments contain as little noble metals as possible, which are impurities.

[0030] The amount of aluminum is preferably 110% or more in molar ratio relative to the amount required for the synthesis of sodium borohydride. Although some of the excess aluminum is consumed by reaction with water, this also contributes to increasing the opportunity for contact with sodium metaborate when the amount of aluminum used as raw material decreases as the reaction progresses, thereby improving the yield. The excess aluminum can be recovered and reused as aluminum metal in the sodium borohydride washing process.

[0031] The average particle size of the aluminum powder is, for example, 1 μm or more, and the maximum particle size is preferably 10 mm or less. If the average particle size of the aluminum powder is less than 1 μm, it is prone to dust explosions and is difficult to handle, and the particles may easily adhere to each other and clump together. If the average particle size is greater than 10 mm, the specific surface area per mass becomes small, the reaction area decreases, and the initial reaction rate may drop significantly. The average particle size of the aluminum powder is more preferably 5 μm or more and 5 mm or less. The average particle size is obtained as the particle size of the spherical equivalent diameter using a laser diffraction particle size distribution analyzer.

[0032] As the aluminum compound as a raw material, at least one selected from sodium aluminum dioxide (NaAlO2), potassium aluminum dioxide (KAlO2), alumina (Al2O3) and aluminum fluoride (AlF3) can be used.

[0033] The fluoride raw material is at least one selected from sodium fluoride (NaF), sodium hexafluoroaluminate (NaAlF), potassium fluoride (KF), potassium aluminum fluoride (KAlF), potassium hexafluoroaluminate (KAlF), aluminum fluoride (AlF), and lithium fluoride (LiF). Among these, sodium fluoride, an alkali metal fluoride, is particularly preferred.

[0034] The addition of fluoride promotes the crystallization of iota-alumina. Specifically, fluoride promotes the decomposition reaction of the intermediate product, sodium aluminum dioxide (NaAlO), thereby improving the yield of iota-alumina, which is the product of the decomposition reaction, and promoting the crystallization of iota-alumina.

[0035] In the following description, the molar ratio of the total of all alkali metals and alkaline earth metals in the raw materials to boron (B) in the sodium borates may be referred to as A / B (molar ratio). In this embodiment, the A / B (molar ratio) of the raw materials is preferably less than 2.65. If A / B is 2.65 or more, the amount of sodium ions in the reaction system becomes excessive, resulting in a reduced yield.

[0036] In the reaction step, a product containing iota alumina is obtained by heat treatment of solid raw materials.

[0037] The heating temperature in the reaction process is higher than 450°C. If the heating temperature is lower than 450°C, the crystallization of iota alumina does not proceed sufficiently. Furthermore, the heating temperature in the reaction process is lower than 710°C. If the heating temperature is higher than 710°C, sodium aluminum dioxide (NaAlO2) is generated as an impurity, resulting in a decrease in yield. Furthermore, if the heating temperature is higher than 710°C, sodium borohydride (NaBH4) decomposes, reducing the amount of molten sodium borohydride and decreasing the reaction volume.

[0038] The heating temperature in the reaction step is preferably 490°C or higher and 610°C or lower. By setting the heating temperature to 490°C or higher and 610°C or lower, a sufficient reaction rate is obtained, resulting in excellent iota-alumina production efficiency. More specifically, by setting the heating temperature to 490°C or higher, so-called needle-like iota-alumina, which has a thin and long crystal habit, is formed, and the product, sodium borohydride (NaBH4), is brought into a molten state, thereby accelerating the reaction.

[0039] Even when the heating temperature is lower than 490°C, the oxide film of aluminum (Al) turns into iota-alumina. However, the amount of molten sodium borohydride is significantly reduced, and the rate of iota-alumina formation becomes extremely slow, resulting in the formation of so-called rod-like iota-alumina with thick and short crystal habits.

[0040] The reaction step is carried out in a hydrogen-containing gas atmosphere. When a hydrogen atmosphere is used, the hydrogen gas pressure is preferably in the range of 0.5 MPa to 10 MPa, and more preferably in the range of 0.6 MPa to 1 MPa. By setting the hydrogen gas pressure to 0.6 MPa to 1 MPa, the production efficiency of sodium borohydride is excellent, and there is no need for a reaction vessel or equipment with excellent pressure resistance, which makes it possible to suppress an increase in equipment costs.

[0041] In the reaction step, a reaction occurs by heating the solid raw material, and iota-alumina is produced. The reaction for producing iota-alumina will be described in detail below.

[0042] In the early stages of the reaction, sodium metaborate (NaBO2) comes into contact with aluminum (Al) particles through stirring, and sodium metaborate adheres to the aluminum (Al) particles. As a result of this adhesion, the aluminum oxide film on the aluminum (Al) surface absorbs sodium oxide (Na2O), becoming sodium aluminum dioxide (NaAlO2). The sodium aluminum dioxide (NaAlO2) produced here is converted into iota-aluminum by the catalytic action of fluoride ions. In this way, at the initial stage of the reaction, an iota-aluminum oxide film layer with a thickness of about 100-2000 nm is formed on the surface of the aluminum particles. This allows sodium ions to easily pass through the oxide film on the aluminum (Al) surface.

[0043] At the same time as sodium aluminum dioxide (NaAlO2) is converted into iota-alumina, sodium oxide (Na2O) is produced. As a result, aluminum (Al) is oxidized by sodium oxide (Na2O) inside the oxide film layer to become aluminum oxide (Al2O3).

[0044] Aluminum oxide (Al2O3) formed on the aluminum surface is fine and highly active, functioning as a Lewis acid, while the surrounding sodium oxide (Na2O) acts as a Lewis base, neutralizing the aluminum oxide (Al2O3) to form sodium aluminum dioxide (NaAlO2). In the presence of fluoride ions, sodium aluminum dioxide (NaAlO2) is catalytically converted into iota alumina (Na 0.67 AlO 9.33 ), and expels sodium oxide (Na2O). This produces iota-alumina inside the initial aluminum oxide coating, which grows into an iota-alumina layer containing sodium oxide (Na2O).

[0045] Iota-alumina is produced in the presence of four types of ions dissolved in sodium borohydride: aluminum ions, oxygen ions, sodium ions, and fluoride ions. When sodium borohydride is in a liquid state, the diffusion of the four types of ions is promoted, accelerating the growth of iota-alumina, and making it easier to produce iota-alumina with a large aspect ratio.

[0046] The crystal habit of iota alumina crystals is often needle-like or rod-like. It is speculated that the needle-like crystal habit of iota alumina is due to a reaction in which iota alumina grows while releasing sodium oxide (Na2O) during the crystallization process. In other words, the direction in which the crystals grow is preferentially in the direction of low sodium oxide (Na2O) concentration, so iota alumina grows in one direction, and the crystal habit of iota alumina crystals is speculated to be needle-like or rod-like.

[0047] Here, in the reaction for producing iota alumina, if the heating temperature in the reaction step is set to 490° C. or higher, a particle diffusion reaction occurs. The particle diffusion reaction will be described below.

[0048] In the oxidation reaction of aluminum inside the oxide layer mentioned above, sodium oxide (Na2O) is reduced to sodium (Na). Sodium (Na) reduces hydrogen (H2) to form sodium hydride (NaH). Sodium hydride (NaH) reacts with sodium metaborate (NaBO2) to produce sodium borohydride (NaBH4) and sodium oxide (Na2O).

[0049] In addition, on the surface of aluminum particles, fluoride ions react with aluminum to form a NaAlF layer containing sodium (Na), aluminum (Al), and fluorine (F) as constituent elements. The NaAlF layer is mainly composed of sodium hexafluoroaluminate (Na3AlF6), and at the interface with the aluminum, lower aluminum fluorides (AlF 1.5 It produces low grade aluminum fluoride (AlF 1.5) has a very strong reducing property and reduces sodium oxide (Na2O), and in a hydrogen atmosphere produces sodium hydride (NaH), aluminum oxide (Al2O3), and sodium fluoride (NaF). It also produces low-grade aluminum fluoride (AlF 1.5 ) moves into the system as a gas under pressure, and together with the sodium hydride, which has also become gaseous, promotes the reduction reaction to sodium borohydride (NaBH4) within the sodium metaborate (NaBO2) particles. As a result, fluoride also contributes to the movement of aluminum within the system.

[0050] Sodium borohydride (NaBH4) becomes molten when it reaches 490°C or higher. The molten sodium borohydride (NaBH4) fills the iota-alumina layer and dissolves sodium hydride, sodium oxide, sodium ions, aluminum ions, fluorine ions, oxygen ions, and metaborate ions (BO 2- ) is dissolved. This allows the sodium borohydride (NaBH4) in the melt to act as a mass transfer medium and reaction site, allowing ions to move in and out of the oxide layer on the outer surface of the aluminum particles, creating conditions for reactions inside and outside the iota-alumina layer of aluminum (Al) particles, or on the surface of sodium metaborate (NaBO2) particles.

[0051] During this process, aluminum (Al) particles and sodium metaborate (NaBO2) particles come into contact with each other due to the stirring, and materials including raw materials, intermediate products, and products repeatedly adhere and disperse on the particle surfaces. As a result, the particles of sodium borohydride (NaBH4), sodium hydride (NaH), sodium oxide (Na2O), sodium metaborate (NaBO2), and aluminum ions move at high speeds that would not be possible through simple diffusion, accelerating the reaction that produces sodium borohydride (NaBH4).

[0052] As explained above, in the iota-alumina synthesis reaction, the raw material sodium metaborate (NaBO2) and intermediate products (NaH, Na2O, AlF2) are reacted not only inside the aluminum (Al) particles but also with each other through contact between the particles. 1.5 ) and sodium borohydride (NaBH4) as a solvent undergo mass transfer, and some intermediate products (NaH, AlF 1.5 ) moves as a gas, and a high-speed reaction occurs on the surface of each particle and inside the particle. In this embodiment, this reaction is called a "particle agitation reaction."

[0053] If the heating temperature in the reaction process is less than 490°C, sodium borohydride (NaBH4) cannot become molten, so its passage through the iota-alumina layer slows down, and the amount of sodium hydride (NaH) that seeps out of the aluminum (Al) particles is significantly reduced. Therefore, in this case, boron ions that have passed through the iota-alumina layer react with sodium hydride (NaH) inside the oxide layer of the aluminum (Al) particles, and some of the gaseous sodium hydride (NaH) reacts with sodium metaborate (NaBO2) particles.

[0054] The washing step involves pouring the mixture of solid raw materials into a polar solvent. This step removes iota alumina (Na 0.67 AlO 9.33 This allows for the production of iota alumina with fewer impurities.

[0055] In the washing step, the mixture of solid raw materials is stirred with a polar solvent. 0.67 AlO 9.33 ) can improve the dissolution rate of substances other than the above.

[0056] The polar solvent is, for example, water, and preferably pure water such as ion-exchanged water. This allows for the effective removal of sodium borohydride (NaBH4), a water-soluble impurity, from the reaction product. Furthermore, if the polar solvent is water, it is possible to remove substances that are soluble in water, such as sodium borohydride (NaBH4), sodium hydride (NaH), sodium fluoride (NaF), and lower aluminum fluorides (AlF 1.5 ), sodium borates and sodium aluminum dioxide (NaAlO2) can be removed from the reaction product.

[0057] Here, the water used as the polar solvent is not limited to pure water, but may be an acidic or alkaline aqueous solution. In this case, the water used as the polar solvent preferably has a pH of 2 or more and 11 or less. It is more preferable that the pH of the water used as the polar solvent is 9 or more. This allows impurities that are insoluble in neutral water, such as cryolite (Na3AlF6) and aluminum, to be further eluted and removed from the reaction product.

[0058] When the polar solvent is water, the washing step is preferably carried out at a temperature of 80°C or higher and 100°C or lower. In this case, the rate at which impurities are dissolved can be improved. Alternatively, the washing step may be carried out at room temperature. In this case, a block of iota alumina containing a majority of needle- or rod-shaped iota alumina crystals is obtained. In the following description of the washing step, unless otherwise specified, high temperature refers to a temperature of 80°C or higher and 100°C or lower, and room temperature refers to a temperature of 5°C or higher and 35°C or lower.

[0059] FIG. 1A is a scanning electron microscope (SEM) backscattered electron image of a cross section of an aggregated reaction product that was stirred with water at 80°C to 100°C for 1 hour and then washed. FIG. 1B is an enlarged SEM backscattered electron image of the area IB shown in FIG. 1A. The reaction product shown in FIG. 1A corresponds to the product of Test Example 7, which will be described later. The aggregated product is formed when the produced sodium borohydride (NaBH4) melts, causing what were originally aluminum particles to adhere to each other. As shown in FIG. 1B, the particles have a dense oxide layer on the surface, and the internal oxide is iota alumina, which is needle-like (whisker-like). The spaces between the iota alumina layers are the result of sodium borohydride eluting during washing. Unreacted aluminum remains in the center.

[0060] FIG. 1C is an enlarged SEM backscattered electron image of iota alumina crystals obtained by observing the surface of the product shown in FIG. 1A. FIG. 1D is an enlarged SEM backscattered electron image of iota alumina crystals obtained by observing the surface of the product shown in FIG. 1A at a different location than that shown in FIG. 1C. When the growth rate of iota alumina is high, it becomes thin and long as shown in FIG. 1C, and when the growth rate is low, it becomes wide as shown in FIG. 1D. The needle-like iota alumina crystals obtained in this manner had a width of 0.05 μm to 0.5 μm, a length of 0.5 μm to 4 μm, and an aspect ratio of 3.4 to 24.5.

[0061] Here, the aspect ratio refers to the ratio of length W to width H, i.e., the value obtained by dividing length W by width H. FIG. 1E is an enlarged SEM backscattered electron image showing iota alumina crystals within the range IE shown in FIG. 1C. As shown in FIG. 1E, in the SEM backscattered electron image, the dimension W of the iota alumina crystal C in the elongated direction is measured as the length, and the dimension H in the direction perpendicular to the electron image is measured as the width. This allows the aspect ratio of one iota alumina crystal C to be calculated.

[0062] The average aspect ratio of the iota alumina crystals is 3 to 30. The average aspect ratio of iota alumina crystals refers to the arithmetic average of the aspect ratios of multiple iota alumina crystals. Figure 1F is an enlarged SEM backscattered electron image of iota alumina crystals for which the aspect ratios corresponding to the range IF shown in Figure 1D were measured. As shown in Figure 1F, in calculating the average aspect ratio, among the crystal habits appearing in the SEM backscattered electron image within a predetermined range, multiple linear structures that clearly appear are extracted as iota alumina crystals C. In other words, among the crystal habits appearing in the SEM backscattered electron image within a predetermined range, those that do not clearly appear as linear structures are not extracted as iota alumina crystals C. Here, as shown in Figure 1F, the imaging range of the SEM backscattered electron image used to calculate the average aspect ratio is a range in which at least 10 iota alumina crystals C are extracted. When calculating the average aspect ratio for multiple imaging ranges, if the average aspect ratio calculated for at least one imaging range is 3 or more and 30 or less, it can be said that the average aspect ratio of the iota alumina crystal is 3 or more and 30 or less.

[0063] 1G and 1H are enlarged SEM backscattered electron images of iota-alumina crystals produced using potassium metaborate (KBO) as the starting alkali metal compound. The reaction product shown in FIGS. 1G and 1H is the product of Test Example 25, which will be described later. FIG. 1H is an enlarged SEM backscattered electron image obtained by observing a different region from that shown in FIG. 1G. When potassium borates are used as starting materials, the plate-like iota-alumina shown in FIG. 1G and the rod-like iota-alumina shown in FIG. 1H are obtained. The plate-like iota alumina crystals thus obtained had a thickness of 0.018 μm or more and 0.047 μm or less, a width of 0.499 μm or more and 1.111 μm or less, and an aspect ratio of 12.8 or more and 60.5 or less. Thickness The aspect ratio (A) of the iota-alumina crystal is the thickness of the iota-alumina crystal, and the width of the iota-alumina plate is the length perpendicular to the thickness. The average aspect ratio in the image area of ​​Figure 1G was calculated to be 25.4. The rod-shaped iota-alumina crystals thus obtained had widths of 0.298 μm to 0.400 μm, lengths of 0.879 μm to 1.444 μm, and aspect ratios of 2.4 to 4.0. The average aspect ratio in the image area of ​​Figure 1F was calculated to be 3.34.

[0064] Figure 2 is an SEM backscattered electron image of powdered iota alumina crystals obtained by washing the reaction product with boiling water. In the washing step, the water as a polar solvent may be boiled. That is, the reaction product may be washed by boiling it in water. In this case, as shown in Figure 2, powdered iota alumina with a particle size of about 1 μm to 100 μm and needle-like or rod-like iota alumina crystals on the surface is obtained.

[0065] The polar solvent is not limited to water, and diglyme (diethylene glycol dimethyl ether) may also be used. In this case, sodium borohydride (NaBH4), an impurity, can be suitably removed from the reaction product.

[0066] Hereinafter, first to fourth manufacturing methods, which are specific examples of the method for manufacturing iota alumina according to this embodiment, will be described in detail. In the following steps, unless otherwise specified, the steps will be described in the case where sodium fluoride is used as the fluoride and sodium metaborate (NaBO2) separated as crystals is used as the sodium borate. Note that the first to fourth manufacturing methods described below are merely examples and are not limited to these.

[0067] [First manufacturing method] FIG. 3 is a process diagram showing a first manufacturing method of iota alumina. In the first manufacturing method of sodium borohydride, aluminum powder and fluoride powder are mixed and preheated at a temperature of 100°C to 330°C. The mixture is then mixed with sodium borate and charged into a sealed container. The mixture is then reacted at a temperature of 490°C to 610°C in the sealed container filled with hydrogen gas, and the reaction product is washed. Here, the sodium borates and aluminum powder react in their solid phases. As shown in FIG. 3, the first manufacturing method of sodium borohydride includes steps from a first step (S-11) to a fourth step (S-14). Here, steps 1 (S-11) to 3 (S-13) are an example of a "reaction step," and step 4 (S-14) is an example of a "washing step."

[0068] (a) First step In the pretreatment process, aluminum powder and sodium fluoride are mixed and rubbed together. After the treatment, the mixture is placed in a container, covered, and kept in an atmosphere with a humidity of 10% or less. Then, the mixture is placed in a furnace and heated in an atmosphere of 100°C to 330°C for 30 minutes or more, causing the aluminum (Al) and sodium fluoride (NaF) to release moisture and forming an aluminum oxide film on the surface of the aluminum (Al) powder 52 particles. The heat-treated powder is cooled and then mixed with sodium borate powder. After or before the mixed powder is charged into a sealed container, a non-oxidizing gas is introduced into the sealed container to fill the inside with a non-oxidizing gas atmosphere. These steps constitute the first step (S-11). That is, in the first step, aluminum and sodium fluoride are premixed and heat-treated, and then all the raw materials are mixed and charged into a sealed container. In this first step, by treating in an atmosphere with a humidity of 10% or less, it is possible to prevent moisture from the air from adhering to the aluminum and fluoride and to prevent oxidation of the aluminum. After the treated powder and sodium borate powder are mixed and charged into a sealed container, the inside of the sealed container can be filled with a non-oxidizing gas atmosphere either before or after the raw materials are charged into the sealed container.

[0069] In the first step, there is no particular limitation on the temperature inside the sealed container when the raw materials are introduced, and as long as it is below 100°C, workability is good.

[0070] The sealed container used in the first step is a container that has heat resistance and pressure resistance that can withstand high temperatures (e.g., 610°C) and high pressures (e.g., 10 MPa) and can ensure a sealed space for filling with gas. The sealed container is equipped with a stirring means. Details of the sealed container will be described later.

[0071] (b) Second step In the second step (S-12) shown in Figure 3, all raw materials are mixed and placed in a sealed container. The container is then heated to 400°C to 610°C to remove residual moisture from the sodium borate and aluminum powder. The remaining moisture is then reacted with the aluminum to convert it into hydrogen gas and an aluminum oxide film, thereby removing the moisture. The aluminum fluoride (AlF) produced in the first step is converted to cryolite (NaAlF) by high-temperature heating, forming an NaAlF layer. The second step involves reacting the evaporated moisture (i.e., the residual moisture contained in the raw materials in the sealed container) with aluminum, or degassing the system with a vacuum pump to remove moisture from the reaction system, and converting the aluminum fluoride produced on the aluminum surface into cryolite.

[0072] In the second step, when the heating temperature is 530°C, the production of cryolite (NaAlF) from aluminum fluoride (AlF) takes approximately 30 minutes or more. When dry sodium metaborate with a moisture content of 0% to 3% is used as the raw material, the dehydration reaction is completed in approximately 0.5 to 1 hour.

[0073] (c) Third step The third step (S-13) shown in Figure 3 involves heating the sealed container to between 490°C and 610°C and introducing hydrogen gas. The heating process transforms the oxide film on the aluminum surface and sodium aluminum dioxide (NaAlO2) into needle-shaped iota-alumina due to the diffusion of sodium oxide and the crystallization of aluminum oxide by fluoride. When the sodium oxide reaches the aluminum (Al) surface, it is reduced by the aluminum and begins to generate sodium hydride (NaH). When sodium hydride (NaH) diffuses through the iota-alumina and comes into contact with sodium borate, the sodium borohydride reaction begins. Once sodium borohydride fills the iota-alumina layer, sodium hydride (NaH), sodium oxide (Na2O), aluminum ions, borate ions, etc. can move using sodium borohydride as a solvent, initiating the "particle agitation reaction." Since particle agitation reactions involve mass transfer through particle contact alone, weak agitation is sufficient. Agitation was performed by rotating the agitator inside the sealed container. In this way, the reaction product was obtained.

[0074] In the third step, the particle stirring reaction involves bringing the powders into contact with each other while still in a solid state and causing them to react on the surface of the aluminum, after which the product and raw materials are transported by diffusion, allowing the reaction to continue and synthesize the materials.In order to further assist this material transport, kinetic energy can also be added by stirring.

[0075] In the third step, as the reaction progresses, the amount of hydrogen in the reaction vessel decreases, but the reaction rate increases by increasing the hydrogen gas pressure. The reaction here is shown in the following reaction formula (2). 4Al+6H2+3NaBO2→3NaBH4+2Al2O3...(2)

[0076] In the third step, the sealed container used in the first and second steps may be used as is, or a different sealed container may be used. That is, the first to third steps may be carried out as steps in a single sealed container, or may be steps in different sealed containers.

[0077] (d) 4th step The fourth step (S-14) shown in FIG. 3 is a step of washing the reaction product with a polar solvent. Here, the polar solvent is water. In the fourth step, the reaction product is stirred with water at 50°C or higher and 100°C or lower for 30 minutes or longer. This allows sodium borohydride (NaBH), sodium hydride (NaH), sodium fluoride (NaF), and lower aluminum fluoride (AlF) to be released from the reaction product into the polar solvent. 1.5 ), sodium borates, and sodium aluminum dioxide (NaAlO2) are dissolved. The reaction product is then removed from the solvent and dried under reduced pressure. If an alkaline aqueous solution is used as the polar solvent in the fourth step, cryolite (Na3AlF6) and aluminum can be dissolved in addition to the above substances. In this case, iota alumina and aluminum hydroxide remain as solids, making it easier to extract the iota alumina.

[0078] Iota alumina can be produced by the above first to fourth steps.

[0079] The other manufacturing method will be described below, and the explanation of the same points as in the first manufacturing method will be omitted.

[0080] [Second manufacturing method] FIG. 4 is a process diagram showing a second method for producing iota alumina. In the second method for producing sodium borohydride, aluminum powder 52, sodium hydroxide powder 55, and fluoride powder 54 are mixed and preheated at a temperature of 100°C to 330°C. The mixture is then mixed with sodium borate powder 51 and placed in a sealed container. The mixture is then heated at a temperature of 400°C to 610°C and the moisture is removed using a vacuum pump. Hydrogen gas is then introduced into the sealed container, where the mixture is reacted at a temperature of 490°C to 610°C. The sodium borate powder 51 and aluminum powder 52 react in their solid phases. As shown in FIG. 4, the second method for producing sodium borohydride includes steps S-1 (S-21) to S-4 (S-24). The first step S-21 to the third step S-23 are examples of the "reaction step," and the fourth step S-24 is an example of the "cleaning step."

[0081] (a) First step In the pretreatment process, aluminum powder 52, fluoride powder 54, and sodium hydroxide powder 55 are mixed and rubbed together. After the treatment, the mixture is placed in a container, covered, and placed in an atmosphere with a humidity of 10% or less. It is then placed in a furnace and heated in an atmosphere of 100°C to 330°C for 30 minutes or more, causing the aluminum (Al) and sodium fluoride (NaF) to release some of the moisture contained in the sodium hydroxide, forming an aluminum oxide film and sodium oxide (NaO) on the surface of the aluminum (Al) powder 52 particles. In this case, since there is a lot of moisture from the sodium hydroxide and sodium oxide on the aluminum surface, the oxidation of the aluminum takes precedence. Therefore, the reaction that produces aluminum fluoride from hydrogen fluoride only occurs slightly. The heat-treated powder is cooled and then mixed with sodium borate powder. After or before the mixed powder is charged into a sealed container, a non-oxidizing gas is introduced into the sealed container to fill the inside with a non-oxidizing gas atmosphere. These steps constitute the first step (S-21). That is, in the first step, aluminum and sodium hydroxide are premixed and heat-treated, and then all raw materials are mixed and charged into a sealed container. In this first step, by treating in an atmosphere with a humidity of 10% or less, it is possible to prevent moisture from the air from adhering to the aluminum, sodium hydroxide, and fluoride, and to prevent oxidation of the aluminum. After mixing the treated powder with sodium borate powder, the sealed container can be filled with a non-oxidizing gas atmosphere either before or after the raw materials are charged into the sealed container.

[0082] (b) Second step The second step (S-22) shown in Figure 4 involves placing all of the mixed raw materials into a sealed container and heating it to between 400°C and 610°C to remove any residual moisture contained in the sodium hydroxide, sodium borate, aluminum powder, and fluoride powder. The remaining moisture is then reacted with the aluminum to convert it into hydrogen gas and an aluminum oxide film, thereby removing the moisture. During this process, the sodium hydroxide adhering to the aluminum surface becomes sodium oxide. Some of the sodium oxide also reacts with the oxide film on the aluminum surface to become sodium aluminum dioxide (NaAlO). The second step involves either reacting the residual moisture contained in the raw materials with the aluminum, or degassing the system using a vacuum pump to remove moisture from the reaction system.

[0083] (c) Third step The third step (S-23) shown in Figure 4 involves heating the sealed vessel to between 490°C and 610°C and introducing hydrogen gas. The heating process transforms the oxide film on the aluminum surface and sodium aluminum dioxide (NaAlO2) into needle-shaped iota-alumina due to the diffusion of sodium oxide and the crystallization of aluminum oxide by fluoride. When the sodium oxide reaches the aluminum (Al) surface, it is reduced by the aluminum and begins to produce sodium hydride (NaH). When sodium hydride (NaH) diffuses through the iota-alumina and comes into contact with sodium borate, the sodium borohydride reaction begins. Once sodium borohydride fills the iota-alumina layer, sodium hydride (NaH), sodium oxide (Na2O), aluminum ions, borate ions, etc. can migrate using sodium borohydride as a solvent, initiating the "particle agitation reaction." Since mass transfer occurs through particle contact alone, weak agitation is sufficient for particle agitation reactions. The mixture was stirred by rotating the agitator inside the sealed vessel. In this way, the reaction product was obtained.

[0084] (d) 4th step The fourth step (S-24) shown in FIG. 4 is a step of washing the reaction product with a polar solvent. Here, the polar solvent is water. In the fourth step, the reaction product is stirred with water at 80°C or higher and 100°C or lower for 30 minutes or more. This allows sodium borohydride (NaBH), sodium hydride (NaH), sodium fluoride (NaF), and lower aluminum fluoride (AlF) to be released from the reaction product into the polar solvent. 1.5 ), sodium borates, and sodium aluminum dioxide (NaAlO2) are dissolved. The reaction product is then removed from the solvent and dried under reduced pressure.

[0085] [Third manufacturing method] FIG. 5 is a process diagram showing a third manufacturing method of iota alumina. In the third manufacturing method of sodium borohydride, aluminum powder 52 and sodium hydroxide powder 55 are mixed and preheated at a temperature of 100°C to 330°C. Then, the mixture is mixed with fluoride powder 54 and sodium borate powder 51 and placed in a sealed container. The mixture is then heated at a temperature of 400°C to 610°C and the moisture is removed using a vacuum pump. Hydrogen gas is then introduced into the sealed container, where the mixture is reacted at a temperature of 490°C to 610°C. The sodium borate powder 51 and aluminum powder 52 react in their solid phases. As shown in FIG. 5, the third manufacturing method of sodium borohydride includes steps S-31 to S-34. The first step S-31 to S-33 are examples of the "reaction step," and the fourth step S-34 is an example of the "cleaning step."

[0086] (a) First step In the pretreatment process, aluminum powder 52 and sodium hydroxide powder 55 are mixed and rubbed together. After the treatment, the mixture is placed in a container, covered, and kept in an atmosphere with a humidity of 10% or less, and then placed in a furnace and heated in an atmosphere of 100°C to 330°C for 30 minutes or more, causing some of the moisture contained in the sodium hydroxide to be released into the aluminum (Al), and forming an aluminum oxide film and sodium oxide (NaO) on the surface of the aluminum (Al) powder 52 particles. After cooling the heat-treated powder, it is mixed with a sodium borate powder and a fluoride powder. After or before the mixed powder is charged into a sealed container, a non-oxidizing gas is introduced into the sealed container to fill the inside with a non-oxidizing gas atmosphere. The above steps constitute the first step (S-31). That is, in the first step, aluminum and sodium hydroxide are premixed and heat-treated, and then all raw materials are mixed and charged into a sealed container. In this first step, by treating in an atmosphere with a humidity of 10% or less, it is possible to prevent moisture from the air from adhering to the aluminum, sodium hydroxide, and fluoride, and to prevent oxidation of the aluminum. After mixing the treated powder with sodium borate powder, the sealed container can be filled with a non-oxidizing gas atmosphere either before or after the raw materials are charged into the sealed container.

[0087] (b) Second step The second step (S-32) shown in Figure 5 involves placing all of the mixed raw materials into a sealed container and heating it to between 400°C and 610°C to remove any residual moisture contained in the sodium hydroxide, sodium borate, aluminum powder, and fluoride powder. The remaining moisture is then reacted with the aluminum to convert it into hydrogen gas and an aluminum oxide film, thereby removing the moisture. The sodium hydroxide adhering to the aluminum surface becomes sodium oxide. Some of the sodium oxide reacts with the oxide film on the aluminum surface to become sodium aluminum dioxide (NaAlO2). The second step involves either reacting the residual moisture contained in the raw materials with the aluminum, or degassing the container using a vacuum pump to remove moisture from the reaction system.

[0088] (c) Third step In the third step (S-33) shown in Figure 5, the sealed vessel was heated to between 490°C and 610°C, and hydrogen gas was introduced. The heating process transformed the oxide film on the aluminum surface and sodium aluminum dioxide (NaAlO2) into needle-shaped iota-alumina due to the diffusion of sodium oxide and the crystallization of aluminum oxide by fluoride. When the sodium oxide reached the aluminum (Al) surface, it was reduced by the aluminum and began to generate sodium hydride (NaH). The sodium hydride (NaH) diffused through the iota-alumina and came into contact with sodium borate, initiating the sodium borohydride reaction. Once the sodium borohydride filled the iota-alumina layer, sodium hydride (NaH), sodium oxide (Na2O), aluminum ions, borate ions, etc., became mobile using sodium borohydride as a solvent, initiating the "particle agitation reaction." Since mass transfer occurs solely through particle contact, weak agitation is sufficient for particle agitation reactions. The mixture was stirred by rotating the agitator in the sealed vessel. In this way, the reaction product was obtained.

[0089] (d) 4th step The fourth step (S-34) shown in FIG. 5 is a step of washing the reaction product with a polar solvent. Here, the polar solvent is water. In the fourth step, the reaction product is stirred with water at 80°C or higher and 100°C or lower for 30 minutes or more. This allows sodium borohydride (NaBH), sodium hydride (NaH), sodium fluoride (NaF), and lower aluminum fluoride (AlF) to be released from the reaction product into the polar solvent. 1.5 ), sodium borates, and sodium aluminum dioxide (NaAlO2) are dissolved. The reaction product is then removed from the solvent and dried under reduced pressure.

[0090] [Fourth manufacturing method] FIG. 6 is a process diagram showing a fourth manufacturing method of iota alumina. In the fourth manufacturing method of sodium borohydride, in the first step, aluminum powder 52, sodium hydroxide powder 55, fluoride powder 54, and sodium borate powder 51 are mixed and placed in a sealed container. The container is then filled with a non-oxidizing gas and sealed. In the second step, the sealed container is heated to 400°C to 610°C to react moisture generated from the raw materials with the fluoride, generating gaseous hydrogen fluoride, which reacts with the aluminum to form aluminum fluoride on the aluminum surface. In the third step, the mixture is reacted at a temperature of 490°C to 610°C in a sealed container filled with hydrogen gas. The sodium borates and aluminum powder react in their solid phases. As shown in FIG. 6, the fourth manufacturing method of sodium borohydride includes steps S-41 to S-44. Here, the first step (S-41) to the third step (S-43) are an example of a "reaction step", and the fourth step (S-44) is an example of a "washing step".

[0091] (a) First step In the pretreatment step, aluminum powder 52, sodium hydroxide powder 55, and fluoride powder 54 are mixed and rubbed together in an atmosphere with a humidity of 10% or less, and then sodium borate powder 51 is added. The mixture is then charged into a sealed container. After or before charging, a non-oxidizing gas is introduced into the sealed container to fill the interior with a non-oxidizing gas atmosphere. This is the first step (S-41). The non-oxidizing gas may be introduced either after or before the raw materials are charged into the sealed container. However, the method of mixing the raw materials is not limited to this; all of the raw materials, i.e., aluminum powder 52, sodium hydroxide powder 55, fluoride powder 54, and sodium borate powder 51, may be mixed and rubbed together at the same time.

[0092] (b) Second step The second step (S-42) shown in Figure 6 involves heating the sealed container to between 400°C and 610°C after sealing it, and then removing the residual moisture contained in the sodium hydroxide, sodium borate, aluminum powder, and fluoride powder by reacting them with aluminum (Al). This is also a step in which the high-temperature moisture reacts with the fluoride to generate hydrogen fluoride (HF) vapor, producing aluminum fluoride on the aluminum surface. During this process, the sodium hydroxide becomes sodium oxide. In addition, some of the sodium oxide reacts with the oxide film on the aluminum surface to form sodium aluminum dioxide (NaAlO2). The second step is a step in which the residual moisture contained in the raw materials in the sealed container is removed and aluminum fluoride is produced.

[0093] (c) Third step The third step (S-43) shown in Figure 6 involves heating the inside of the sealed container to between 490°C and 610°C and introducing hydrogen gas. The heating process transforms the oxide film on the aluminum surface and sodium aluminum dioxide (NaAlO2) into needle-shaped iota-alumina due to the diffusion of sodium oxide and the crystallization of aluminum oxide by fluoride. When the sodium oxide reaches the aluminum (Al) surface, it is reduced by the aluminum and begins to produce sodium hydride (NaH). When sodium hydride (NaH) diffuses through the iota-alumina and comes into contact with sodium borate, the sodium borohydride production reaction begins. Once sodium borohydride fills the iota-alumina layer, sodium hydride (NaH), sodium oxide (Na2O), aluminum ions, borate ions, etc. can move using sodium borohydride as a solvent, initiating the "particle stirring reaction." In the second step, the aluminum fluoride formed on the surface of the aluminum absorbs the diffused sodium ions and turns into cryolite (Na3AlF6), forming an NaAlF layer on the aluminum surface. The NaAlF layer is formed at the interface with the aluminum by the formation of low-grade aluminum fluoride (AlF 1.5), which travels through the system as a strong reducing agent and as a substance that can move as a vapor, reacting with sodium oxide (Na2O) to produce sodium hydride (NaH) and alumina, which assists in the production of sodium borohydride. In particle-agitation reactions, mass transfer occurs solely through particle contact, so weak agitation is sufficient. The mixture was stirred by rotating the agitator in the sealed vessel. In this way, the reaction product was obtained.

[0094] (d) 4th step The fourth step (S-44) shown in FIG. 6 is a step of washing the reaction product with a polar solvent. Here, the polar solvent is water. In the fourth step, the reaction product is stirred with water at 80°C or higher and 100°C or lower for 30 minutes or more. As a result, sodium borohydride (NaBH), sodium hydride (NaH), sodium fluoride (NaF), and lower aluminum fluoride (AlF) are released from the reaction product into the polar solvent. 1.5 ), sodium borates, and sodium aluminum dioxide (NaAlO2) are dissolved. The reaction product is then removed from the solvent and dried under reduced pressure.

[0095] (sealed container) Here, an example of a sealed container that can be used in the first to fourth manufacturing methods will be shown.

[0096] FIG. 7 is a partial cross-sectional view showing an example of a sealed container used in the first to fourth manufacturing methods. 7, the sealed container 10A has a cylindrical container body 12 with a round bottom and a removable disk-shaped lid 14 that seals the container body 12. A temperature-adjustable heater 16 is disposed on the outside of the lower part of the container body 12, and the contents of the container body 12 are heated by the heater 16. An O-ring 18 is disposed on the upper end surface of the container body 12 and fits tightly against the lid 14 to ensure airtightness inside, and when the lid 14 is closed, the lid 14 and the O-ring 18 fit tightly against the container body 12.

[0097] The lid 14 has an opening in its center, a cylindrical portion erected near the opening, and a motor 20 disposed above the cylindrical portion. The stirring device includes the motor 20, a stirring rod 22 connected to the rotation shaft of the motor 20, and a plurality of pin-shaped stirring bars 22A arranged in a direction perpendicular to the axis of the stirring rod 22. When the lid 14 is attached to the container body 12, the tip of the stirring rod 22 reaches a lower region inside the container body 12. In other words, when the motor 20 is driven, the pin-shaped stirring bars 22A rotate together with the stirring rod 22, stirring the contents of the container body 12.

[0098] The lid 14 is further provided with a first pipe 24 and a second pipe 30 that communicate with the inside of the container body 12, and the first pipe 24 is connected to a hydrogen gas supply source (not shown) via a hydrogen gas supply valve 26 and to a vacuum pump (not shown) via an exhaust valve 28. That is, when the hydrogen gas supply valve 26 is opened, hydrogen gas is Container body When the exhaust valve 28 is opened, the inside of the container body 12 is evacuated. The second pipe 30 is connected to a pressure gauge 32, which allows the pressure inside the container body 12 to be measured.

[0099] Figure 8 is a partial cross-sectional view showing another example of a sealed container used in the first to fourth manufacturing methods. The difference from the sealed container 10A in Figure 7 is that the sealed container 10B has multiple plate-shaped scrapers 35 at the lower end of the stirring rod 22 that rotates inside the container body 12, making it a multi-blade scraper (MB).

[0100] FIG. 11A is a front view of a stirrer equipped with a plate-shaped (blade) stirrer, using the sealed container 10B shown in FIG. 8. FIG. 11B is a side view of a stirrer equipped with a plate-shaped (blade) stirrer, using the sealed container 10B shown in FIG. 8. FIG. 12A is a photograph of the plate-shaped (blade) stirrer, taken out of the sealed container shown in FIG. 8 after stirring for a predetermined period of time. FIG. 12B is a photograph of the reaction product, taken out of the sealed container shown in FIG. 8 after stirring for a predetermined period of time. As shown in FIG. 12A, the reaction product in the form of balls resting on the blade and an adhesion layer adhering to the container wall can be seen.

[0101] FIG. 9 is a partial cross-sectional view showing another example of a sealed container used in the first to fourth manufacturing methods. The difference from the sealed container 10A in FIG. 7 is that the sealed container 10C has a ribbon-shaped scraper 36 at the lower end of the stirring rod 22 that rotates inside the container body 12.

[0102] Fig. 10 is a partial cross-sectional view showing another example of a sealed container used in the first to fourth manufacturing methods. The sealed container 10D shown in Fig. 10 differs from the sealed container 10A shown in Fig. 7 in that the container body 12 is horizontally placed and the stirring rod 22 that rotates inside the container body 12b is provided with a wide paddle stirrer 37 via a support. When a wide paddle stirrer 37 like that used in the sealed container 10D is used for stirring, the raw material is scooped up by the paddle surface as the wide paddle stirrer 37 rotates. While the raw material is being scooped up by this paddle surface or while the scooped raw material falls, raw material particles collide with each other, resulting in a good particle stirring reaction.

[0103] Fig. 13A is a photograph before iota alumina was produced by rotating the horizontal wide paddle (WP) stirrer of the sealed container shown in Fig. 10. Fig. 13B is a photograph after iota alumina was produced by rotating the horizontal wide paddle (WP) stirrer of the sealed container shown in Fig. 10.

[0104] Although an example of a sealed container that can be used in the first to fourth manufacturing methods has been described above, the present embodiment is not limited to the above. For example, a ball mill that can be heated and that can introduce hydrogen gas may be used as the sealed container.

[0105] (Fluoride effects) Hereinafter, the function of fluoride in the first to fourth manufacturing methods of iota alumina will be described in detail with reference to the drawings.

[0106] As mentioned above, the function of fluoride is to promote the production of sodium hydride (NaH), thereby improving the amount of iota alumina produced. Specifically, fluoride has two effects on aluminum. The first effect is to promote the crystallization of alumina, which can suppress the dissolution of aluminum ions from alumina. Furthermore, since the aluminum ions are reduced from the reaction system, the sodium ion concentration in the reaction system can be relatively increased. As a result, when the sodium ion activity increases, the reducing power of aluminum increases, which can increase the production of sodium hydride (NaH). The second action is to form a layer of NaAlF on the surface of the aluminum particles, which converts the NaAlF into low-grade aluminum fluoride (AlF), which has a strong reducing power. 1.5 The lower aluminum fluoride moves outward from the aluminum surface and reduces sodium oxide (Na2O). This increases the amount of sodium hydride (NaH) produced. Also, the lower aluminum fluoride (AlF 1.5 ) has a gaseous pressure at the reaction temperature for the production of iota-alumina and can move as a gas. Sodium hydride (NaH) also has a gaseous pressure, and lower aluminum fluorides (AlF 1.5 ) and moves to the sodium borate particles to produce sodium borohydride.

[0107] 14A to 14F are reaction diagrams illustrating the iota-alumina production reaction. The action of fluoride in each step will be described in detail below with reference to the reaction diagrams (FIGS. 14A to 14F) using the first to fourth production methods using sodium fluoride (NaF) as an example, to explain the process of producing iota-alumina. The action described below is not limited to sodium fluoride. That is, even fluorides other than sodium fluoride become fluoride ions in the reaction system, and therefore exhibit the same action as sodium fluoride.

[0108] 1) Moisture removal and aluminum surface modification (second step) As shown in FIG. 14A, in the second step, the reaction vessel is sealed and the generated water is reacted with fluoride to generate hydrogen fluoride, which is then reacted with aluminum to generate an NaAlF layer containing cryolite (NaAlF) as a main component on the surface of the aluminum. When sodium hydroxide (NaOH) is added, in the second step, moisture remaining in the added sodium hydroxide (NaOH), sodium borates, and the aluminum oxide film 101b is removed, and sodium oxide is generated from the sodium hydroxide, which is then reacted with aluminum to form sodium aluminum dioxide (NaAlO).

[0109] 2) Initial stage of reaction-1 (Step 3) As shown in FIG. 14B, the sodium aluminum dioxide (NaAlO2) 106 formed on the surface 101a of the aluminum (Al) particle is crystallized by the crystallization promoting action of sodium fluoride (NaF) 103 to form needle-like iota alumina (Na 0.67 AlO 9.33 ) 101c layer and sodium oxide (Na2O).

[0110] 3) Initial stage of reaction-2 (third step) As shown in Figure 14C, needle-shaped iota alumina (Na 0.67 AlO 9.33 )101c layer is mainly composed of atmospheric hydrogen gas (H2) and sodium ions ( Na+ ) moves, but other ions also move between the needle-like crystals of iota-alumina and reach the inside of the iota-alumina layer. Due to the presence of sodium oxide (Na2O) produced in the initial stage of reaction 1 and hydrogen gas, sodium ions, borate ions, oxygen ions, and fluoride ions that have moved through the iota-alumina layer, the needle-like iota-alumina (Na 0.67 AlO 9.33 )101c layer, sodium oxide (Na2O) is continuously added to aluminum. Therefore A reduction reaction begins. This reaction produces sodium hydride (NaH)112 and aluminum oxide (Al2O3), which immediately turns into sodium aluminum dioxide (NaAlO2). Due to the catalytic action of fluoride ions, sodium aluminum dioxide (NaAlO2) turns into iota alumina (Na 0.67 AlO 9.33 It decomposes into sodium hydroxide (Na2O) 113 and sodium nitrate (Na2O) 101c. Sodium hydride (NaH) reacts with boric acid (B2O3) to produce sodium borohydride (NaBH4)111 and sodium oxide (Na2O). The melt sodium borohydride (NaBH4) forms needle-like iota alumina (NaH)112 along with sodium hydride (NaH)112. 0.67 AlO 9.33 ) 101c layer. And iota alumina (Na 0.67 AlO 9.33 ) 101c, the sodium borohydride (NaBH4) containing mainly sodium hydride (NaH) from the layer 101c begins to migrate outward.

[0111] 4) Mid-reaction stage (third step) As shown in Figure 14D, the particle stirring reaction produced needle-shaped iota alumina (NaBH4) particles filled with product-containing sodium borohydride (NaBH4) liquid. 0.67 AlO 9.33 ) 101c layer, and mainly sodium hydride (NaH) and aluminum ions (Al 3+ ), metaborate ion (BO ) from sodium metaborate (NaBO ) 10 .2- ), oxygen ions (O 2- ), sodium ions ( Na + ) move and needle-like iota alumina (Na 0.67 AlO 9.33 The reaction begins both inside and outside the layer of 101c. The reaction in the sodium metaborate grains is that sodium borohydride (NaBH4) containing sodium hydride (NaH) reacts with boron. acid( The reaction with sodium borohydride (NaBH4) and sodium oxide (Na2O) occurs. The sodium oxide (Na2O) is then stirred again and comes into contact with the aluminum particles, resulting in a circulating reaction.

[0112] 5) Peak reaction period (Step 3) As shown in Figure 14E, agitation causes the aluminum particles and sodium metaborate particles to exchange surface materials with each other, resulting in a particle agitation reaction. Repeated contact between the particles supplies aluminum particles 101 with sodium metaborate (NaBO2) 102 and the reaction product sodium oxide (Na2O) from sodium metaborate 102 particles. Meanwhile, aluminum particles 101 supply reaction products (sodium borohydride (NaBH4) 111 and sodium hydride (NaH) 112) to sodium metaborate (NaBO2) 102 particles. Particle agitation accelerates this material exchange, promoting the particle agitation reaction. The aluminum particles gradually incorporate fragments of sodium metaborate and grow. Meanwhile, the sodium metaborate particles also incorporate sodium hydride, transforming into sodium borohydride (NaBH4) and sodium oxide.

[0113] 6) Reaction completion (Step 3) As shown in Figure 14F, in the latter half of the reaction, the raw materials aluminum, sodium oxide (Na2O), and boric acid (B2O3) are consumed, and the particles become the products sodium borohydride (NaBH4) and iota alumina. The reaction rate slows as the concentration decreases, as less sodium oxide is reduced by aluminum to form sodium hydride. On the other hand, reducing substances (low-grade aluminum fluoride = AlF) formed at the interface between aluminum (Al) and the NaAlF layer, which is mainly composed of sodium hexafluoroaluminate (Na3AlF6) 1.5 (presumably) 117 continues to be produced regardless of the sodium oxide concentration. Lower aluminum fluorides can sublimate and move, reducing sodium oxide to produce sodium hydride (NaH) 112, improving the yield of sodium borohydride (NaBH4) in the latter half of the reaction. As a result, aluminum (Al) 101 particles and sodium metaborate particles are converted into the reaction products sodium borohydride (NaBH4) 111 and acicular iota alumina (Na 0.67 AlO 9.33 )101c layer.

[0114] (Test example) Hereinafter, the present embodiment will be described in more detail with reference to test examples that illustrate the effects of the present embodiment, but the present embodiment is not limited to these.

[0115] Table 1 shows the materials and production conditions for Test Examples 1 to 25. In the tests, products according to Test Examples 1 to 25 were synthesized using the materials and production conditions shown in Table 1. In Table 1 and the following description, Na / B or Na / B ratio refers to the A / B (molar ratio) when the alkali metal and alkaline earth metal contained in the raw material is only sodium (Na), and K / B ratio refers to the A / B (molar ratio) when the alkali metal and alkaline earth metal contained in the raw material is only potassium (K). In addition, in Table 1 and the following examples, "pure water" refers to ion-exchanged water, and the pH of the ion-exchanged water is 5.5 or more and 7.5 or less.

[0116] [Table 1]

[0117] Table 2 is a list of substances detected in the products obtained by the production methods of Test Examples 1 to 23. Table 3 is a list of substances detected in the products obtained by the production methods of Test Examples 24 and 25. Powder X-ray diffraction measurements were performed on the products of Test Examples 1 to 25, and the substances shown in Table 2 or Table 3 were identified. Here, the powder X-ray diffraction measurements were performed in air at room temperature and normal pressure, i.e., at a temperature of 5°C to 35°C and 1 atm, unless otherwise specified. The intensity of the peaks resulting from inclusions in the diffraction pattern of the product depends on the component ratio of the product's inclusions, so inclusions that appear as strong peaks and are clearly present were rated as "A." Inclusions that appear as smaller peaks than inclusions rated A and are estimated to have a small content were rated as "B." Inclusions that appear as even smaller peaks than inclusions rated B and are estimated to have a small content were rated as "C." Inclusions that appear even smaller than inclusions rated C and are noticeable as peaks and are estimated to have a trace content were rated as "D."

[0118] [Table 2]

[0119] [Table 3]

[0120] [Test Example 1] Test Example 1 is a comparative example. As shown in Table 1, 6.98 g of sodium metaborate (NaBO2) powder, 8.01 g of sodium tetraborate (Na2B4O7) powder, 2.17 g of sodium fluoride (NaF) powder, and 11.45 g of aluminum (Al) powder were charged into a sealed container equipped with a stirring means as raw materials. Here, the Na / B ratio of Test Example 1 was 0.89. In the reaction process, the inside of the sealed container was heated to 510°C, and hydrogen gas was introduced and stirred by the stirring means inside the sealed container. The maximum partial pressure of hydrogen gas in the reaction process was 0.75 MPa. The minimum partial pressure of hydrogen gas in the reaction process was 0.6 MPa. In Test Example 1, a cleaning process was not performed. Through the above processes, a product according to Test Example 1 was obtained.

[0121] FIG. 15 is a diagram showing the X-ray diffraction pattern of the product of Test Example 1. In Test Example 1, iota alumina (Na 0.67 AlO 9.33 As shown in Table 2 and FIG. 15, the product according to Test Example 1 contained iota alumina (Na 0.67 AlO 9.33 ), sodium borohydride (NaBH4), sodium metaborate (NaBO2), and aluminum (Al) were detected. 、C Sodium hexafluoroaluminate (Na3AlF6) and sodium tetraborate (Na2B4O7) were detected as judged components, and aluminum diboride (AlB2) was detected as a D-grade component. The results of Test Example 1 show that iota alumina can be produced even when the Na / B ratio is 0.89. However, since Test Example 1 did not include a washing step, it is believed that sodium borohydride (NaBH4) was not removed.

[0122] [Test Example 2] Test Example 2 is an example. As shown in Table 1, 1.95 g of sodium metaborate (NaBO2) powder, 0.05 g of potassium fluoride (KF) powder, and 1.06 g of aluminum (Al) powder were charged as raw materials into a sealed container equipped with a stirring means.A The / B ratio was 1.03. In the reaction step, the inside of the sealed container was heated to 569°C, and hydrogen gas was introduced and stirred by the stirring means in the sealed container. The maximum partial pressure of hydrogen gas in the reaction step was 0.90 MPa. The minimum partial pressure of hydrogen gas in the reaction step was 0.51 MPa. In Test Example 2, in the cleaning step, cleaning with pure water was performed at a high temperature. Through the above steps, a product according to Test Example 2 was obtained.

[0123] In Test Example 2, iota alumina (Na 0.67 AlO 9.33 As shown in Table 2, the product of Test Example 2 contained iota alumina (Na 0.67 AlO 9.33 ) and aluminum (Al) were detected. The results of Test Example 2 show that iota alumina can be produced even when potassium fluoride (KF) is used as a raw material for the fluoride.

[0124] [Test Example 3] Test Example 3 is a comparative example. As shown in Table 1, 17.46 g of sodium metaborate (NaBO2) powder, 1.44 g of aluminum fluoride (AlF3) powder, and 11.45 g of aluminum (Al) powder were charged as raw materials into a sealed container equipped with a stirring means. Here, the Na / B ratio of Test Example 3 was 1.00. In the reaction step, the inside of the sealed container was heated to 510°C, and hydrogen gas was introduced and stirred by the stirring means in the sealed container. The maximum partial pressure of hydrogen gas in the reaction step was 0.75 MPa. The minimum partial pressure of hydrogen gas in the reaction step was 0.56 MPa. In Test Example 3, a cleaning step was not performed. Through the above steps, a product according to Test Example 3 was obtained.

[0125] FIG. 16 is a diagram showing the X-ray diffraction pattern of the product of Test Example 3. In Test Example 3, iota alumina (Na 0.67 AlO 9.33As shown in Table 2 and FIG. 16, the product according to Test Example 3 contained sodium borohydride (NaBH4) and iota alumina (Na 0.67 AlO 9.33 ) and aluminum (Al) were detected, sodium metaborate (NaBO2) was detected as a component classified as B, and sodium hexafluoroaluminate (Na3AlF6) was detected as a component classified as C. The results of Test Example 3 show that iota-alumina can be produced even when aluminum fluoride (AlF) is used as a raw material for the fluoride. However, since Test Example 3 did not include a washing step, it is believed that sodium borohydride (NaBH) and sodium metaborate (NaBO) were not removed.

[0126] [Test Example 4] Test Example 4 is an example. As shown in Table 1, 17.46 g of sodium metaborate (NaBO2) powder, 1.81 g of sodium hexafluoroaluminate (Na3AlF6), and 11.45 g of aluminum (Al) powder were charged as raw materials into a sealed container equipped with a stirring means. Here, the Na / B ratio of Test Example 4 was 1.10. In the reaction process, the inside of the sealed container was heated to 510°C, and hydrogen gas was introduced and stirred by the stirring means inside the sealed container. The maximum partial pressure of hydrogen gas in the reaction process was 0.75 MPa. The minimum partial pressure of hydrogen gas in the reaction process was 0.54 MPa. In Test Example 4, washing with diglyme was performed as a washing process. Through the above processes, a product according to Test Example 4 was obtained.

[0127] FIG. 17 is a diagram showing the X-ray diffraction pattern of the product of Test Example 4. In Test Example 4, iota alumina (Na 0.67 AlO 9.33 As shown in Table 2 and FIG. 17, the product according to Test Example 4 contained iota alumina (Na 0.67 AlO 9.33) was detected, aluminum (Al) and sodium metaborate (NaBO2) were detected as components classified as B, and sodium aluminate hexafluoride (Na3AlF6) was detected as a component classified as C. The results of Test Example 4 show that iota alumina can be produced even when sodium hexafluoroaluminate (Na3AlF6) is used as a raw material fluoride.

[0128] [Test Example 5] Test Example 5 is an example. As shown in Table 1, 1.48 g of sodium tetraborate (Na2B4O7) powder, 0.83 g of sodium fluoride (NaF), and 1.27 g of aluminum (Al) powder were charged into a sealed container equipped with a stirring means as raw materials. Here, the Na / B ratio of Test Example 5 was 1.17. In the reaction process, the inside of the sealed container was heated to 500°C, and hydrogen gas was introduced and stirred by the stirring means inside the sealed container. The maximum partial pressure of hydrogen gas in the reaction process was 0.86 MPa. The minimum partial pressure of hydrogen gas in the reaction process was 0.63 MPa. In Test Example 5, cleaning with diglyme was performed as a cleaning process. Through the above processes, a product according to Test Example 5 was obtained.

[0129] In Test Example 5, iota alumina (Na 0.67 AlO 9.33 As shown in Table 2, the product of Test Example 5 contained iota alumina (Na) as a component rated as A. 0.67 AlO 9.33 ) was detected, and aluminum (Al) was detected as a component rated B. The results of Test Example 5 show that iota alumina can be produced even when sodium tetraborate (Na2B4O7) is used as a raw material for the alkali metal compound.

[0130] [Test Example 6] Test Example 6 is a comparative example. As shown in Table 1, 17.46 g of sodium metaborate (NaBO2) powder, 2.17 g of sodium fluoride (NaF), and 11.45 g of aluminum (Al) powder were charged as raw materials into a sealed container equipped with a stirring means. Here, the Na / B ratio of Test Example 6 was 1.19. In the reaction step, the inside of the sealed container was heated to 490°C, and hydrogen gas was introduced and stirred by the stirring means in the sealed container. The maximum partial pressure of hydrogen gas in the reaction step was 0.75 MPa. The minimum partial pressure of hydrogen gas in the reaction step was 0.64 MPa. In Test Example 6, a cleaning step was not performed. Through the above steps, a product according to Test Example 6 was obtained.

[0131] FIG. 18 is a diagram showing the X-ray diffraction pattern of the product of Test Example 6. In Test Example 6, iota alumina (Na 0.67 AlO 9.33 As shown in Table 2 and FIG. 18, the product according to Test Example 6 contained sodium borohydride (NaBH4) and iota alumina (Na 0.67 AlO 9.33 ) was detected, and aluminum (Al) and sodium metaborate (NaBO2) were detected as components classified as B. Sodium aluminate hexafluoride (Na3AlF6) was detected as a component classified as C. The results of Test Example 6 show that iota alumina can be produced when the heating temperature is 490° C. However, since Test Example 6 did not include a washing step, it is believed that sodium borohydride (NaBH4) and sodium metaborate (NaBO2) were not removed.

[0132] [Test Example 7] Test Example 7 is an example. As shown in Table 1, the product of Test Example 7 was obtained by washing the product of Test Example 6 with pure water at a high temperature of 80°C or higher and 100°C or lower for 1 hour.

[0133] FIG. 19 is a diagram showing the X-ray diffraction pattern of the product of Test Example 7. In Test Example 7, iota alumina (Na 0.67 AlO 9.33 As shown in Table 2 and FIG. 19, the product of Test Example 7 contained iota alumina (Na 0.67 AlO 9.33 ) was detected, sodium hexafluoroaluminate (Na3AlF6) was detected as a component classified as C, and aluminum (Al) was detected as a component classified as D. The X-ray diffraction pattern of Test Example 7 showed iota alumina (Na 0.67 AlO 9.33 ) Powder Diffraction File (PDF®) No. 01-070-7114 data, indicating the absence of crystal defects. Furthermore, semi-quantitative analysis of the X-ray diffraction chart based on the Rietveld method revealed that the product contained 95% by mass of iota alumina, 5% by mass of sodium hexafluoroaluminate, and 1% by mass or less of aluminum (Al). The specific surface area of ​​the product, calculated by the BET (Brunauer-Emmett-Teller) method, was 54 m 2 g -1 It was. The results of Test Example 7 show that sodium borohydride (NaBH4) and sodium metaborate (NaBO2) can be removed by washing with pure water. Furthermore, when the product of Test Example 7 was observed with an SEM, 80 iota-alumina crystals were extracted from the imaging range, and the average aspect ratio of the iota-alumina crystals was calculated to be 10.8.

[0134] [Test Example 8] Test Example 8 is a comparative example. As shown in Table 1, the raw materials used were 17.46 g of sodium metaborate (NaBO2) powder, 0.31 g of sodium hydroxide (NaOH), 1.86 g of sodium fluoride (NaF), and 11.45 g of aluminum (Al) powder. In Test Example 8, the sodium hydroxide (NaOH) and aluminum (Al) powder were mixed by rubbing and reacted at 240°C for 1 hour. The resulting mixture, sodium metaborate (NaBO2) powder, and sodium fluoride (NaF) were then charged into a sealed container equipped with a stirring device. The Na / B ratio in Test Example 8 was 1.20. In the reaction process, the sealed container was heated to 530°C, and hydrogen gas was introduced and stirred with the stirring device in the sealed container. The maximum partial pressure of hydrogen gas during the reaction process was 0.75 MPa. The minimum partial pressure of hydrogen gas during the reaction process was 0.65 MPa. No washing step was performed in Test Example 8. Through the above steps, a product according to Test Example 8 was obtained.

[0135] FIG. 20 is a diagram showing the X-ray diffraction pattern of the product of Test Example 8. In Test Example 8, iota alumina (Na 0.67 AlO 9.33 As shown in Table 2 and FIG. 20, the product of Test Example 8 contained sodium borohydride (NaBH4) and iota alumina (Na 0.67 AlO 9.33 ) was detected, aluminum (Al) was detected as a component rated B, and sodium aluminate hexafluorohydrate (Na3AlF6) and sodium fluoride (NaF) were detected as components rated C. The results of Test Example 8 show that iota alumina can be produced even when dehydration is performed with sodium hydroxide. However, since Test Example 8 did not include a washing step, it is believed that sodium borohydride (NaBH4) was not removed.

[0136] [Test Example 9] Test Example 9 is an example. As shown in Table 1, the product of Test Example 9 was obtained by washing the product of Test Example 8 with diglyme as the washing step.

[0137] In Test Example 9, iota alumina (Na 0.67 AlO 9.33 As shown in Table 2, the product of Test Example 9 contained iota alumina (Na 0.67 AlO 9.33 ) and aluminum (Al) were detected, and sodium hexafluoroaluminate (Na3AlF6) and sodium fluoride (NaF) were detected as components classified as C. The results of Test Example 9 show that sodium borohydride (NaBH4) can be removed by washing with diglyme.

[0138] [Test Example 10] Test Example 10 is an example. As shown in Table 1, the raw materials used were 17.46 g of sodium metaborate (NaBO2) powder, 0.29 g of sodium hydroxide (NaOH), 1.86 g of sodium fluoride (NaF), and 11.45 g of aluminum (Al) powder. In Test Example 10, the sodium hydroxide (NaOH) and aluminum (Al) powder were mixed by rubbing and reacted at 240°C for 1 hour. The resulting mixture, sodium metaborate (NaBO2) powder, and sodium fluoride (NaF) were then charged into a sealed container equipped with a stirring device. The Na / B ratio in Test Example 10 was 1.19. In the reaction process, the sealed container was heated to 470°C, and hydrogen gas was introduced and stirred using the stirring device in the sealed container. The maximum partial pressure of hydrogen gas during the reaction process was 0.75 MPa. The minimum partial pressure of hydrogen gas during the reaction process was 0.69 MPa. In Test Example 10, the washing step involved washing with pure water at a high temperature. Through the above steps, a product according to Test Example 10 was obtained.

[0139] In Test Example 10, iota alumina (Na 0.67 AlO 9.33As shown in Table 2, the product of Test Example 10 contained aluminum (Al) and iota alumina (Na) as components rated as A. 0.67 AlO 9.33 ) was detected, sodium hexafluoroaluminate (Na3AlF6) was detected as a component classified as B, and aluminum hydroxide was detected as a component classified as C. The results of Test Example 10 show that iota alumina can be produced when the heating temperature is set to 470°C. The reason aluminum hydroxide (Al(OH)3) was detected here is presumably because sodium metaborate (NaBO2) remaining in the product dissolved in water during the washing process, and the high temperature of nearly 100°C increased the basicity of the water, making it alkaline, causing some of the unreacted aluminum to dissolve in the water and become aluminum hydroxide.

[0140] [Test Example 11] Test Example 11 is an example. As shown in Table 1, the raw materials used were 5.82 g of sodium metaborate (NaBO2) powder, 0.10 g of sodium hydroxide (NaOH), 0.62 g of sodium fluoride (NaF), and 3.82 g of aluminum (Al) powder. In Test Example 11, the sodium hydroxide (NaOH) and aluminum (Al) powder were mixed by rubbing and reacted at 240°C for 1 hour. The resulting mixture, sodium metaborate (NaBO2) powder, and sodium fluoride (NaF) were then charged into a sealed container equipped with a stirring device. The Na / B ratio in Test Example 11 was 1.20. In the reaction process, the sealed container was heated to 560°C, and hydrogen gas was introduced and stirred using the stirring device in the sealed container. The maximum partial pressure of hydrogen gas during the reaction process was 0.75 MPa. The minimum partial pressure of hydrogen gas during the reaction process was 0.63 MPa. In Test Example 11, the washing step involved washing with pure water at a high temperature. Through the above steps, a product according to Test Example 11 was obtained.

[0141] In Test Example 11, iota alumina (Na 0.67 AlO 9.33As shown in Table 2, the product of Test Example 11 was subjected to semi-quantitative analysis by the Rietveld method, and as a result, 81 mass % of iota alumina (Na 0.67 AlO 9.33 ) was detected, and 7 mass% of aluminum (Al) and 8 mass% of aluminum hydroxide were detected as components rated B, and 2 mass% of sodium hexafluoroaluminate (Na3AlF6) was detected as a component rated C. The results of Test Example 11 show that when the heating temperature is set to 560°C, iota alumina can be produced. The reason aluminum hydroxide (Al(OH)3) was detected here is presumably because sodium metaborate (NaBO2) remaining in the product dissolved in water during the washing process, and the high temperature of nearly 100°C increased the basicity of the water, making it alkaline, causing some of the unreacted aluminum to dissolve in the water and become aluminum hydroxide (Al(OH)3).

[0142] [Test Example 12] Test Example 12 is an example. As shown in Table 1, 1.94 g of sodium metaborate (NaBO2) powder, 0.83 g of sodium fluoride (NaF), and 1.48 g of aluminum (Al) powder were charged as raw materials into a sealed container equipped with a stirring means. Here, the Na / B ratio of Test Example 12 was 1.67. In the reaction process, the inside of the sealed container was heated to 495°C, and hydrogen gas was introduced and stirred by the stirring means in the sealed container. The maximum partial pressure of hydrogen gas in the reaction process was 0.89 MPa. The minimum partial pressure of hydrogen gas in the reaction process was 0.45 MPa. In Test Example 12, washing with diglyme was performed as the washing process. Through the above processes, the product of Test Example 12 was obtained.

[0143] In Test Example 12, iota alumina (Na 0.67 AlO 9.33 As shown in Table 2, the product of Test Example 12 contained iota alumina (Na 0.67 AlO 9.33) and aluminum (Al) were detected, and sodium aluminate hexafluoride (Na3AlF6) and sodium aluminate (NaAlO2) were detected as components classified as B. The results of Test Example 12 show that iota alumina can be produced when the heating temperature is 495°C.

[0144] [Test Example 13] Test Example 13 is a comparative example. As shown in Table 1, 1.94 g of sodium metaborate (NaBO) powder and 1.28 g of aluminum (Al) powder were charged into a sealed container equipped with a stirring means as raw materials. Alumina balls (5 mm in diameter) were placed in the sealed container as a stirring medium, and the weight ratio of the stirring medium to the raw materials was 50. The Na / B ratio in Test Example 13 was 1.00. In the reaction process, the sealed container was heated to 330°C, hydrogen gas was introduced, and the mixture was stirred while being rolled and crushed at a rotation speed of 1150 rpm using the stirring means in the sealed container. The maximum partial pressure of hydrogen gas in the reaction process was 0.78 MPa. The minimum partial pressure of hydrogen gas in the reaction process was 0.59 MPa. A cleaning process was not performed in Test Example 13. Through the above processes, a product according to Test Example 13 was obtained.

[0145] In Test Example 13, a product containing aluminum (Al) as the main component was obtained. As shown in Table 2, sodium metaborate (NaBO2) and aluminum (Al) were detected as components rated as A in the product of Test Example 13. Iota alumina (Na 0.67 AlO 9.33 ) was not detected. Furthermore, when high-temperature X-ray diffraction measurement was performed on the product of Test Example 13 at 600°C in a nitrogen atmosphere, sodium metaborate (NaBO2) and aluminum (Al) were detected as components classified as A, and sodium aluminum borate (Na2Al2B2O7) was detected as a component classified as B. However, even in this case, iota alumina (Na 0.67 AlO 9.33 ) was not detected. In Test Example 13, the temperature in the reaction step was low at 330°C, and the product was rolled and crushed, so it is believed that iota-alumina was not produced. Note that, in the high-temperature X-ray diffraction measurement of the product in Test Example 13 at 600°C in a nitrogen atmosphere, sodium aluminum borate (NaAlBO) was detected. This is believed to be because the non-crystalline sodium aluminum borate (NaAlBO) contained in the product crystallized due to heating.

[0146] [Test Example 14] Test Example 14 is an example. As shown in Table 1, the product of Test Example 14 was obtained by washing the product of Test Example 6 with a 2% by mass aqueous solution of sodium hydroxide (NaOH) at 80°C or higher and 100°C or lower for 1 hour as a washing step.

[0147] In Test Example 14, a product containing aluminum hydroxide (Al(OH)3) as the main component was obtained. As shown in Table 2, the product of Test Example 14 was subjected to semi-quantitative analysis by the Rietveld method based on the X-ray diffraction chart, and was found to contain iota alumina (Na 0.67 AlO 9.33 ) and 62 mass% aluminum hydroxide (Al(OH)3). The results of Test Example 14 show that iota alumina can be produced when a 2 mass % aqueous sodium hydroxide solution is used as the solvent in the washing step. In Test Example 14, a 2% by mass aqueous solution of sodium hydroxide was used as the solvent in the cleaning process, so that the iota alumina (Na 0.67 AlO 9.33 The extraction residues other than iota alumina (Na) were dissolved. Here, aluminum hydroxide (Al(OH)3) was produced under strongly alkaline conditions. 0.67 AlO 9.33 ) was dissolved along with aluminum (Al) and precipitated as aluminum hydroxide (Al(OH)3). Furthermore, when the product of Test Example 14 was observed with an SEM, 11 iota-alumina crystals were extracted from the imaging range, and the average aspect ratio of the iota-alumina crystals was calculated to be 8.3.

[0148] [Test Example 15] Test Example 15 is a comparative example. As shown in Table 1, 2.94 g of sodium diborate (Na4B2O5) powder, 0.83 g of sodium fluoride (NaF), and 1.28 g of aluminum (Al) powder were charged into a sealed container equipped with a stirring means as raw materials. The Na / B ratio of Test Example 15 was 2.65. In the reaction process, the sealed container was heated to 495°C, and hydrogen gas was introduced and stirred using the stirring means in the sealed container. The maximum partial pressure of hydrogen gas in the reaction process was 0.86 MPa. The minimum partial pressure of hydrogen gas in the reaction process was 0.61 MPa. In Test Example 15, cleaning with diglyme was performed as a cleaning process. Through the above processes, a product according to Test Example 15 was obtained.

[0149] In Test Example 15, a product containing sodium aluminum dioxide (NaAlO2) as the main component was obtained. As shown in Table 2, sodium aluminum dioxide (NaAlO2) and sodium fluoride (NaF) were detected as components rated A in the product of Test Example 15, and iota alumina (Na 0.67 AlO 9.33 ) and aluminum (Al) were detected. In Test Example 15, the Na / B ratio was as large as 2.65, so that sodium ions were present in excess in the reaction system, and sodium aluminate (NaAlO2) was present stably, and iota alumina (Na 0.67 AlO 9.33 ) was not generated sufficiently.

[0150] [Test Example 16] Test Example 16 is a comparative example. As shown in Table 1, 5.85 g of sodium metaborate (NaBO) powder and 9.54 g of aluminum (Al) powder were charged as raw materials into a sealed container equipped with a stirring means. Here, the Na / B ratio of Test Example 16 was 1.00. In the reaction process, the sealed container was heated to 710°C, hydrogen gas was introduced, and the mixture was stirred using the stirring means in the sealed container. The maximum partial pressure of hydrogen gas in the reaction process was 1.05 MPa. The minimum partial pressure of hydrogen gas in the reaction process was 0.89 MPa. In Test Example 16, sublimates were generated due to the high temperature in the reaction process. Therefore, the material that remained in the sealed container without sublimation was designated as the product of Test Example 16. In Test Example 16, a cleaning process was not performed. The product of Test Example 16 was obtained through the above processes.

[0151] In Test Example 16, a product containing sodium aluminum dioxide (NaAlO2) as the main component was obtained. As shown in Table 2, aluminum (Al) was detected as a component rated A in the product of Test Example 16, and sodium aluminum dioxide (NaAlO2) and iota alumina (NaAlO2) were detected as components rated B. 0.67 AlO 9.33 ) was detected. In Test Example 16, the temperature in the reaction step was as high as 710°C, which is thought to have produced a large amount of sodium aluminum dioxide as an impurity, resulting in a decrease in the yield of iota alumina.

[0152] [Test Example 17] Test Example 17 is a comparative example. As shown in Table 1, the raw materials used were 17.46 g of sodium metaborate (NaBO2) powder, 0.28 g of sodium hydroxide (NaOH), 1.86 g of sodium fluoride (NaF), and 11.45 g of aluminum (Al) powder. In Test Example 17, the sodium hydroxide (NaOH) and aluminum (Al) powder were mixed by rubbing and reacted at 240°C for 1 hour. The resulting mixture, sodium metaborate (NaBO2) powder, and sodium fluoride (NaF) were then charged into a sealed container equipped with a stirring device. The Na / B ratio in Test Example 17 was 1.19. In the reaction process, the sealed container was heated to 450°C, and hydrogen gas was introduced and stirred using the stirring device in the sealed container. The maximum partial pressure of hydrogen gas during the reaction process was 0.76 MPa. The minimum partial pressure of hydrogen gas during the reaction process was 0.69 MPa. In Test Example 17, the washing step involved washing with pure water at a high temperature. Through the above steps, a product according to Test Example 17 was obtained.

[0153] In Test Example 17, a product containing aluminum (Al) as a main component was obtained. As shown in Table 2, as a result of semi-quantitative analysis of the product according to Test Example 17 by the XRD Rietveld method, 83 mass% of aluminum (Al) was detected as a component classified as A, and 8 mass% of iota alumina (Na) was detected as a component classified as B. 0.67 AlO 9.33 ) and 7 mass% sodium aluminate hexafluoride (Na3AlF6) were detected, and 3 mass% aluminum hydroxide (Al(OH)3) was detected as a component classified as C. In Test Example 17, the temperature in the reaction step was low at 450° C., which is thought to be why crystallization of iota alumina did not occur sufficiently.

[0154] [Test Example 18] Test Example 18 is a comparative example. As shown in Table 1, 17.46 g of sodium metaborate (NaBO) powder, 2.06 g of sodium hydroxide (NaOH), and 11.45 g of aluminum (Al) powder were mixed as raw materials, and then pre-baked at 510°C for 5 hours under a hydrogen gas atmosphere at 0.35 MPa. The pre-baked mixture was placed in a sealed container equipped with a stirring means. The Na / B ratio of Test Example 18 was 1.19. In the reaction step, the sealed container was heated to 510°C, hydrogen gas was introduced, and the mixture was stirred using the stirring means inside the sealed container. The maximum partial pressure of hydrogen gas in the reaction step was 0.74 MPa. The minimum partial pressure of hydrogen gas in the reaction step was 0.69 MPa. In Test Example 18, a cleaning step was not performed. Through the above steps, a product according to Test Example 18 was obtained.

[0155] In Test Example 18, a product containing aluminum (Al) as a main component was obtained. FIG. 21 is a diagram showing the X-ray diffraction pattern of the product according to Test Example 18. As shown in Table 2 and FIG. 21, sodium fluoride (NaF) and aluminum boride (AlB2) were detected as components rated A in the product according to Test Example 18, and iota alumina (Na 0.67 AlO 9.33 ) was detected. In Test Example 18, since no fluoride was added, sodium aluminum dioxide (NaAlO2) was produced, but it is thought that crystallization of iota alumina did not occur sufficiently.

[0156] [Test Example 19] Test Example 19 is an example. As shown in Table 1, 19.40 g of sodium metaborate (NaBO2) powder, 2.41 g of sodium fluoride (NaF), and 10.60 g of aluminum (Al) powder were charged into a sealed container equipped with a stirring means as raw materials. The Na / B ratio of Test Example 19 was 1.19. The mass of the aluminum (Al) powder was 100% of the mass of sodium metaborate (NaBO2). In the reaction process, the sealed container was heated to 580°C, hydrogen gas was introduced, and the mixture was stirred using the stirring means in the sealed container. The maximum partial pressure of the hydrogen gas in the reaction process was 0.81 MPa. The minimum partial pressure of the hydrogen gas in the reaction process was 0.78 MPa. In Test Example 19, the cleaning process involved rinsing with pure water at high temperature for 60 minutes. Through the above steps, a product according to Test Example 19 was obtained.

[0157] In Test Example 19, the main component was iota alumina (Na 0.67 AlO 9.33 As shown in Table 2, the product of Test Example 19 was subjected to semi-quantitative analysis by the XRD Rietveld method, and as a result, 36 mass % of iota alumina (Na 0.67 AlO 9.33 ) and 64 mass% aluminum hydroxide (Al(OH)3) were detected. The results of Test Example 19 show that iota-alumina can be produced when the heating temperature is set to 580°C. The reason why aluminum (Al) and sodium hexafluoroaluminate (Na3AlF6) were not detected is presumably because sodium metaborate (NaBO2) remaining in the product dissolved in water during the washing process, making it alkaline, as in Test Example 14.

[0158] [Test Example 20] Test Example 20 is an example. As shown in Table 1, 19.40 g of sodium metaborate (NaBO2) powder, 2.41 g of sodium fluoride (NaF), and 10.60 g of aluminum (Al) powder were charged into a sealed container equipped with a stirring means as raw materials. The Na / B ratio of Test Example 20 was 1.19. The mass of the aluminum (Al) powder was 100% of the mass of sodium metaborate (NaBO2). In the reaction process, the sealed container was heated to 610°C, and hydrogen gas was introduced and stirred using the stirring means in the sealed container. The maximum partial pressure of the hydrogen gas in the reaction process was 0.81 MPa. The minimum partial pressure of the hydrogen gas in the reaction process was 0.78 MPa. In Test Example 20, the cleaning process involved pure water cleaning at room temperature (22°C). Through the above steps, the product of Test Example 20 was obtained.

[0159] In Test Example 20, a product containing aluminum (Al) as the main component was obtained. As shown in Table 2, the product of Test Example 20 was subjected to semi-quantitative analysis using the XRD Rietveld method, and the components classified as A were 59 mass% aluminum (Al) and 28 mass% iota alumina (Na 0.67 AlO 9.33 ) was detected, 9 mass% of sodium hexafluoroaluminate (Na3AlF6) was detected as a component rated B, and 5 mass% of aluminum diboride (AlB2) was detected as a component rated C. The results of Test Example 20 show that when the heating temperature is set to 610°C, iota alumina can be produced. Unlike Test Example 19, aluminum hydroxide (Al(OH)3) was not produced. This is presumably because the reaction temperature was as high as 610°C, and the raw material sodium metaborate was converted into a neutral oxide containing aluminum during the reaction, preventing the water from becoming strongly alkaline during the washing process.

[0160] [Test Example 21] Test Example 21 is an example. As shown in Table 1, 17.46 g of sodium metaborate (NaBO2) powder, 2.42 g of sodium fluoride (NaF), and 11.45 g of aluminum (Al) powder were charged into a sealed container equipped with a stirring means as raw materials. The Na / B ratio of Test Example 21 was 1.22. In the reaction process, the sealed container was heated to 510°C, hydrogen gas was introduced, and the mixture was stirred using the stirring means inside the sealed container. The maximum partial pressure of hydrogen gas in the reaction process was 0.84 MPa. The minimum partial pressure of hydrogen gas in the reaction process was 0.78 MPa. In Test Example 21, the cleaning process involved 60 minutes of cleaning with pure water at a high temperature of 100°C. Through the above steps, the product of Test Example 21 was obtained.

[0161] In Test Example 21, iota alumina (Na 0.67 AlO 9.33 As shown in Table 2, the product according to Test Example 21 was subjected to semi-quantitative analysis using the XRD Rietveld method, and as a result, 80 mass % of iota alumina (Na 0.67 AlO 9.33 ) was detected, and 20% by mass of aluminum hydroxide (Al(OH)3) was detected as a component rated B. The results of Test Example 21 show that iota alumina can be produced even when the heating temperature is set to 510°C. In Test Example 21, during the washing process, the water became alkaline due to the sodium metaborate (NaBO) remaining in the product, and aluminum (Al) dissolved at a high temperature of 100°C, producing aluminum hydroxide (Al(OH)), and sodium hexafluoroaluminate (NaAlF) also dissolved.

[0162] [Test Example 22] Test Example 22 is an example. As shown in Table 1, 17.46 g of sodium metaborate (NaBO2) powder, 2.42 g of sodium fluoride (NaF), and 11.45 g of aluminum (Al) powder were charged into a sealed container equipped with a stirring means as raw materials. The Na / B ratio of Test Example 22 was 1.22. In the reaction process, the sealed container was heated to 510°C, hydrogen gas was introduced, and the mixture was stirred using the stirring means inside the sealed container. The maximum partial pressure of hydrogen gas in the reaction process was 0.84 MPa. The minimum partial pressure of hydrogen gas in the reaction process was 0.78 MPa. In Test Example 22, the cleaning process involved 60 minutes of cleaning with pure water at room temperature (25°C). Through the above steps, the product of Test Example 22 was obtained.

[0163] In Test Example 22, iota alumina (Na 0.67 AlO 9.33 As shown in Table 2, the product according to Test Example 22 was subjected to semi-quantitative analysis using the XRD Rietveld method, and as a result, 79 mass % of iota alumina (Na 0.67 AlO 9.33 ) was detected, and 16 mass% of aluminum (Al) and 6 mass% of sodium hexafluoroaluminate (Na3AlF6) were detected as components rated B. From the results of Test Example 22, even if the temperature of the polar solvent used in the washing step is room temperature, the iota alumina (Na 0.67 AlO 9.33 ) can be extracted. 。 In Test Example 22, although the water was alkalized by dissolving sodium metaborate (NaBO2) remaining in the product during the washing process at room temperature, the aluminum dissolution reaction was mild because it was at room temperature, and aluminum hydroxide (Al(OH)3 )of It is believed that the production was suppressed.

[0164] [Test Example 23] Test Example 23 is an example. As shown in Table 1, 17.46 g of sodium metaborate (NaBO) powder, 2.42 g of sodium fluoride (NaF), and 11.45 g of aluminum (Al) powder were charged into a sealed container equipped with a stirring means as raw materials. The Na / B ratio in Test Example 23 was 1.22. In the reaction step, the sealed container was heated to 510°C, hydrogen gas was introduced, and the mixture was stirred using the stirring means in the sealed container. The maximum partial pressure of hydrogen gas in the reaction step was 0.84 MPa. The minimum partial pressure of hydrogen gas in the reaction step was 0.78 MPa. In Test Example 23, the cleaning step involved cleaning with 50 ml of 0.24 mol / L (0.875% by mass) hydrochloric acid at room temperature for 60 minutes. The pH after cleaning was 6. Through the above steps, the product of Test Example 23 was obtained.

[0165] In Test Example 23, iota alumina (Na 0.67 AlO 9.33 As shown in Table 2, the product according to Test Example 23 was subjected to semi-quantitative analysis using the XRD Rietveld method, and as a result, 78 mass % of iota alumina (Na 0.67 AlO 9.33 ) was detected, and 17% by mass of aluminum (Al) and 4% by mass of sodium hexafluoroaluminate (Na3AlF6) were detected as components rated B. The results of Test Example 23 show that iota alumina can be extracted even if the water in the washing step is acidic. In Test Example 23, when washing with 0.24 mol / L hydrochloric acid (HCl) at room temperature, the pH became 6 due to a neutralization reaction with sodium metaborate (NaBO2) remaining in the reaction product. As a result, aluminum did not dissolve in the washing process, which is thought to have suppressed the generation of aluminum hydroxide (Al(OH)3) and slightly reduced sodium hexafluoroaluminate (Na3AlF6).

[0166] [Test Example 24] Test Example 24 is a comparative example. As shown in Table 1, 7.24 g of potassium metaborate (KBO2) powder, 1.00 g of potassium fluoride (KF), and 3.82 g of aluminum (Al) powder were charged into a sealed container equipped with a stirring means as raw materials. The K / B ratio of Test Example 24 was 1.19. The mass of the aluminum (Al) powder was 160% of the mass of potassium metaborate (KBO2). In the reaction step, the sealed container was heated to 522°C, and hydrogen gas was introduced and stirred using the stirring means in the sealed container. The maximum partial pressure of the hydrogen gas in the reaction step was 0.78 MPa. The minimum partial pressure of the hydrogen gas in the reaction step was 0.68 MPa. A cleaning step was not performed in Test Example 24. Through the above steps, a product according to Test Example 24 was obtained.

[0167] FIG. 22 is a diagram showing the X-ray diffraction pattern of the product of Test Example 24. In Test Example 24, a product containing potassium metaborate (KBO2) as the main component was obtained. As shown in Table 2 and FIG. 22, potassium metaborate (KBO2) and aluminum (Al) were detected from the product of Test Example 24 as components rated A, and iota alumina (KBO2) was detected as a component rated B. 0.67 AlO 9.33 ), potassium borohydride (KBH4), and potassium hexafluoroaluminate (K3AlF6) were detected. From the results of Test Example 24, even when potassium was used instead of sodium as the alkali metal, the iota alumina (K 0.67 AlO 9.33 ) can be generated.

[0168] [Test Example 25] Test Example 25 is an example. As shown in Table 1, 7.24 g of potassium metaborate (KBO2) powder, 1.00 g of potassium fluoride (KF), and 3.82 g of aluminum (Al) powder were charged into a sealed container equipped with a stirring means as raw materials. The K / B ratio of Test Example 25 was 1.19. The mass of the aluminum (Al) powder was 160% of the mass of potassium metaborate (KBO2). In the reaction step, the sealed container was heated to 522°C, hydrogen gas was introduced, and the mixture was stirred using the stirring means in the sealed container. The maximum partial pressure of the hydrogen gas in the reaction step was 0.78 MPa. The minimum partial pressure of the hydrogen gas in the reaction step was 0.68 MPa. In Test Example 25, the cleaning step involved cleaning with pure water at room temperature. Through the above steps, a product according to Test Example 25 was obtained.

[0169] In Test Example 25, iota alumina (K 0.67 AlO 9.33 As shown in Table 2, the product according to Test Example 25 contained 35 mass % aluminum (Al) and 36 mass % iota alumina (K) as components rated as A. 0.67 AlO 9.33 ) was detected, and 14 mass% of potassium hexafluoroaluminate (K3AlF6) and 15 mass% of aluminum hydroxide (Al(OH)3) were detected as components rated B. From the results of Test Example 25, even when potassium was used instead of sodium as the alkali metal, the iota alumina (K 0.67 AlO 9.33 ) can be generated. [Industrial Applicability]

[0170] Iota alumina (Na 0.67 AlO 9.33 or K 0.67 AlO 9.33) has never been mass-produced, and as of July 2022, it is not even sold as a reagent. This is because there has been no cheap and highly pure method for producing it. According to this method, sodium aluminum dioxide (NaAlO2) is converted into iota alumina (Na 0.67 AlO 9.33 ), and by heating inexpensive materials such as aluminum, sodium borates, and hydrogen gas, needle-shaped (whisker-shaped) iota alumina (Na 0.67 AlO 9.33 ) can be produced along with the valuable product sodium borohydride (NaBH4). 0.67 AlO 9.33 ) can be used as a raw material for producing beta alumina (β Alumina, β" Alumina). Also, iota alumina (Na 0.67 AlO 9.33 or K 0.67 AlO 9.33 ) can be used as a composite material to improve the strength of resins and metals. [Explanation of symbols]

[0171] 10A~10D Airtight container 12, 12b Container body 14 Lid 16 Heater 18 O-rings 20 motors 22 Stirring rod 22A Stirring bar 24 No. 1 Pipe 26 Hydrogen gas supply valve 28 Exhaust valve 30 Second Pipe 32 Pressure gauge 35 Scraper 36 Ribbon scraper 37 Wide paddle stirrer 51 Sodium borate powder 52 Aluminum powder 54 Fluoride Powder 55 Sodium hydroxide powder 101 Aluminum particles 101a Aluminum particle surface 101b Aluminum oxide coating 101c Iota Alumina (Na 0.67 AlO 9.33 ) 102 Sodium metaborate (NaBO2) 103 Sodium Fluoride (NaF) 106 Sodium aluminum dioxide (NaAlO2) 111 Sodium borohydride (NaBH4) 112 Sodium hydride (NaH) 113 Sodium oxide (Na2O) 115 Reactant layer (sodium borohydride (NaBH4) 111, sodium hydride (NaH) 112) 117 Reducing substances (lower aluminum fluoride = AlF 1.5 (Estimated)

Claims

1. a reaction step of mixing solid raw materials containing an alkali metal compound, a fluoride, and at least one material selected from an aluminum compound and aluminum, and performing a heat treatment on the mixture at a temperature of 450°C or higher and lower than 710°C in a hydrogen-containing gas atmosphere; A method for producing iota alumina, comprising: a washing step of introducing the product produced in the reaction step into a polar solvent.

2. The alkali metal compound is sodium aluminum dioxide (NaAlO ２ ), sodium borates, sodium hydride (NaH), sodium borohydride (NaBH ４ ), sodium oxide (Na ２ O), potassium aluminum dioxide (KAIO ２ ), potassium borates, potassium hydride (KH), potassium borohydride (KBH ４ ) and potassium oxide (K ２ 2. The method for producing iota alumina according to claim 1, wherein the iota alumina is at least one selected from the group consisting of iota alumina, ...

3. The sodium borates are sodium metaborate (NaBO ２ ), sodium tetraborate (Na ２ B ４ O ７ ) and sodium diborate (Na ４ B ２ O ５ 3. The method for producing iota alumina according to claim 2, wherein the iota alumina is at least one selected from the group consisting of iota alumina, ...

4. The potassium borates are potassium metaborate (KBO ２ ), potassium tetraborate (K ２ B ４ O ７ ) and potassium diborate (K ４ B ２ O ５ 3. The method for producing iota alumina according to claim 2, wherein the iota alumina is at least one selected from the group consisting of iota alumina, ...

5. The fluoride may be sodium fluoride (NaF), sodium hexafluoroaluminate (Na ３ AlF ６ ), potassium fluoride (KF), potassium aluminum fluoride (KAIF ４ ), potassium hexafluoroaluminate (K ３ AlF ６ ), aluminum fluoride (AlF ３ 2. The method for producing iota alumina according to claim 1, wherein the iota alumina is at least one selected from the group consisting of iota alumina (IOTA), ... and lithium fluoride (LiF).

6. The aluminum compound is sodium aluminum dioxide (NaAlO ２ ), potassium aluminum dioxide (KAIO ２ ), alumina (Al ２ O ３ ) and aluminum fluoride (AlF ３ 2. The method for producing iota alumina according to claim 1, wherein the iota alumina is at least one selected from the group consisting of iota alumina, ...

7. The method for producing iota alumina according to claim 1 , wherein the polar solvent is water.

8. Iota alumina, whose crystals have a rod-like or needle-like habit.

9. 9. The iota alumina according to claim 8, wherein the average aspect ratio of the iota alumina crystals is 3 or more and 30 or less.

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