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

Method for producing iota alumina and iota alumina

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

[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 an oxygen-containing gas needs to be introduced into the melt during heating, a reaction device that allows gas exchange during heating is required.

[0003] Japanese Patent Application Publication No. 05-201723

[0004] Mullite-type Na0.67Al6O9.33 and a discussion of iota-alumina, Journal of the European Ceramic Society 40 (2020) 4276-4280.

[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.

[0006] The method for producing iota alumina according to the first aspect is characterized by comprising 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, followed by heat treatment, and a washing step of introducing the product produced in the reaction step into a polar solvent.

[0007] In a first embodiment, the alkali metal compound is sodium aluminum dioxide (NaAlO ２ ), sodium borates, sodium hydride (NaH), sodium borohydride (NaBH ４ ) and sodium oxide (Na ２O) and potassium aluminum dioxide (KAIO ２ ), potassium borates, potassium hydride (KH), potassium borohydride (KBH ４ ) and potassium oxide (K ２ O) may be at least one selected from the group consisting of:

[0008] In the first aspect, 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 ) may be at least one selected from the above.

[0009] In the first aspect, 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 ) may be at least one selected from the above.

[0010] In the first aspect, the fluoride is 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 ) and lithium fluoride (LiF).

[0011] In a first embodiment, the aluminum compound is sodium aluminum dioxide (NaAlO ２ ), potassium aluminum dioxide (KAIO ２ ), alumina (Al ２ O ３) and aluminum fluoride.

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

[0013] In a first aspect, 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 aspect, the average aspect ratio of the iota alumina crystals may be 3 or more and 30 or less.

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

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

[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.

[0019] FIG. 1A is a scanning electron microscope (SEM) backscattered electron image of a cross section of a massive reaction product that was washed by stirring with water at 80°C or higher and 100°C or lower for 1 hour. FIG. 1B is an enlarged SEM backscattered electron image of the region IB shown in FIG. 1A. 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 from that shown in FIG. 1C. FIG. 1E is an enlarged SEM backscattered electron image of iota alumina crystals for which the aspect ratio was measured for the region IE shown in FIG. 1C. FIG. 1F is an enlarged SEM backscattered electron image of iota alumina crystals for which the aspect ratio was measured for the region IF shown in FIG. 1D. FIG. 1G is an enlarged SEM backscattered electron image of potassium metaborate (KBO). ２1H is an enlarged SEM backscattered electron image of iota-alumina crystals produced using potassium metaborate (KBO) as the alkali metal compound. ２FIG. 2 is an enlarged SEM backscattered electron image of iota alumina crystals relating to a product using iota alumina ion exchange resin (Iota alumina ion exchange resin) as the alkali metal compound. FIG. 2 is an SEM backscattered electron image of powdered iota alumina crystals obtained by high-temperature washing of the reaction product with boiling water. FIG. 3 is a process diagram showing a first method for producing iota alumina. FIG. 4 is a process diagram showing a second method for producing iota alumina. FIG. 5 is a process diagram showing a third method for producing iota alumina. FIG. 6 is a process diagram showing a fourth method for producing iota alumina. FIG. 7 is a partial cross-sectional view showing an example of a sealed container used in the first to fourth production methods. FIG. 8 is a partial cross-sectional view showing another example of a sealed container used in the first to fourth production methods. FIG. 9 is a partial cross-sectional view showing another example of a sealed container used in the first to fourth production methods. FIG. 10 is a partial cross-sectional view showing another example of a sealed container used in the first to fourth production methods. FIG. 11A is a front view of the appearance of a stirrer equipped with a plate-shaped (blade) stirrer using the sealed container 10B shown in FIG. 8. FIG. 11B is a photograph of the exterior side 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, obtained by removing the reaction product from the sealed container shown in FIG. 8 after stirring for a predetermined period of time. FIG. 12B is a photograph of the reaction product, obtained by removing the reaction product from the sealed container shown in FIG. 8 after stirring for a predetermined period of time. FIG. 13A is a photograph of the sealed container shown in FIG. 10 before rotating the horizontal wide paddle (WP) stirrer to produce iota alumina. FIG. 13B is a photograph of the sealed container shown in FIG. 10 after rotating the horizontal wide paddle (WP) stirrer to produce iota alumina. FIG. 14A is a reaction schematic diagram showing the iota alumina production reaction. FIG. 14B is a reaction schematic diagram showing the iota alumina production reaction. FIG. 14C is a reaction schematic diagram showing the iota alumina production reaction. Fig. 14D is a reaction schematic diagram showing an iota-alumina production reaction. Fig. 14E is a reaction schematic diagram showing an iota-alumina production reaction. Fig. 14F is a reaction schematic diagram showing an iota-alumina production reaction. Fig. 15 is a diagram showing an X-ray diffraction pattern of the product according to Test Example 1. Fig. 16 is a diagram showing an X-ray diffraction pattern of the product according to Test Example 3.Fig. 17 is a diagram showing an X-ray diffraction pattern of a product according to Test Example 4. Fig. 18 is a diagram showing an X-ray diffraction pattern of a product according to Test Example 6. Fig. 19 is a diagram showing an X-ray diffraction pattern of a product according to Test Example 7. Fig. 20 is a diagram showing an X-ray diffraction pattern of a product according to Test Example 8. Fig. 21 is a diagram showing an X-ray diffraction pattern of a product according to Test Example 18. Fig. 22 is a diagram showing an X-ray diffraction pattern of a product according to Test Example 24.

[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 (Iota-alumina: Na ０．６７ Al ６ O ９．３３ or K ０．６７ Al ６ O ９．３３ The production method of (I) comprises 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] The alkali metal compound used as the raw material is sodium aluminum dioxide (NaAlO ２ ), sodium borates, sodium hydride (NaH), sodium borohydride (NaBH ４ ) and sodium oxide (Na ２ O), potassium aluminum dioxide (KAIO ２ ), potassium borates, potassium hydride (KH), potassium borohydride (KBH ４ ) and potassium oxide (K ２At least one selected from the group consisting of hydroxybenzoates, ...

[0025] The sodium borates used as raw materials include borax (sodium tetraborate: Na ２ B ４ O ７ ), sodium metaborate (NaBO ２ (=Na ２ B ２ O ４ )), sodium diborate (Na ４ B ２ O ５ ), potassium metaborate (KBO ２ (=K ３ (B ３ O ６ ))), potassium tetraborate (K ２ B ４ O ７ ) and sodium diborate (K ４ B ２ O ５ ) or a combination of at least two or more thereof can be exemplified, 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. That is, 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] The potassium borates used as raw materials include potassium metaborate (KBO ２ ), potassium tetraborate (K ２ B ４ O ７ ) and potassium diborate (K ４ B ２ O ５ ) or a combination of at least two or more thereof can be exemplified, but are not limited to 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 synthesizing sodium borohydride. Although a portion 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 as a 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 step.

[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, the powder is prone to dust explosions, making it 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 be significantly reduced. 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] The raw material aluminum compound is sodium aluminum dioxide (NaAlO ２ ), potassium aluminum dioxide (KAIO２ ), alumina (Al ２ O ３ ) and aluminum fluoride (AlF ３ At least one selected from the following can be used.

[0033] The raw fluorides include 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 Among these, sodium fluoride, which is an alkali metal fluoride, is particularly preferred.

[0034] The addition of fluoride promotes the crystallization of iota-alumina. Specifically, fluoride is added to the intermediate product sodium aluminum dioxide (NaAlO ２ By promoting the decomposition reaction of iota-alumina, the yield of iota-alumina, which is the product of the decomposition reaction, is improved, and the crystallization of iota-alumina proceeds satisfactorily.

[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 step is higher than 450°C. If the heating temperature is 450°C or lower, the crystallization of iota alumina does not proceed sufficiently. In addition, the heating temperature in the reaction step is lower than 710°C. If the heating temperature is 710°C or higher, the impurity sodium aluminum dioxide (NaAlO２ ) occurs, resulting in a decrease in yield. Furthermore, when the heating temperature is 710°C or higher, sodium borohydride (NaBH ４ ) decomposes, the amount of molten sodium borohydride decreases, and the reaction volume decreases.

[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 can be obtained, and the efficiency of producing iota alumina is excellent. 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 (NaBH ４ ) can be brought into a molten state to promote the reaction.

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

[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, 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] At the beginning of the reaction, sodium metaborate (NaBO) was stirred. ２ ) comes into contact with the aluminum (Al) particles, and sodium metaborate adheres to the aluminum (Al) particles. This adhesion causes the aluminum oxide film on the aluminum (Al) surface to turn into sodium oxide (Na ２O) and sodium aluminum dioxide (NaAlO ２ ) is produced. ２ ) is converted to iota-alumina by the catalytic action of fluoride ions. Thus, in the early stage of the reaction, an iota-alumina oxide film layer with a thickness of about 100 nm to 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] Sodium aluminum dioxide (NaAlO ２ ) into iota alumina, and at the same time, sodium oxide (Na ２ O) is generated. As a result, aluminum (Al) is converted into sodium oxide (Na ２ O) and aluminum oxide (Al ２ O ３ )

[0044] Aluminum oxide (Al) formed on the aluminum surface ２ O ３ ) is a very fine and highly active substance that acts as a Lewis acid and dissolves the sodium oxide (Na ２ O) acts as a Lewis base and aluminum oxide (Al ２ O ３ ) is neutralized to form sodium aluminum dioxide (NaAlO ２ ) Sodium aluminum dioxide (NaAlO ２ ) is catalytically converted into iota alumina (Na ０．６７ Al ６ O ９．３３ ) and crystallized into sodium oxide (Na ２ O) is discharged. This generates iota alumina inside the initial aluminum oxide film, and sodium oxide (Na ２ O) containing iota-alumina layer.

[0045] Iota alumina is produced in the presence of four types of ions, namely, aluminum ions, oxygen ions, sodium ions, and fluoride ions, dissolved in sodium borohydride. 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 iota alumina with a large aspect ratio is likely to be produced.

[0046] The crystal habit of iota alumina crystals is often needle-like or rod-like. Iota alumina becomes needle-like crystals during the crystallization process due to the presence of sodium oxide (Na ２ It is speculated that this is due to a reaction in which the crystals grow while emitting sodium oxide (Na ２ It is presumed that the direction of low O concentration is prioritized, so that iota-alumina takes on a shape that extends in one direction, and the crystal habit of the iota-alumina crystal becomes 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 film layer mentioned above, sodium oxide (Na ２ O) is reduced to sodium (Na). Sodium (Na) is converted to hydrogen (H ２ ) is reduced to sodium hydride (NaH). Sodium hydride (NaH) is a compound that is ２ ) to produce sodium borohydride (NaBH ４ ) and sodium oxide (Na ２ O).

[0049] Furthermore, on the surface of the 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 (Na ３ AlF ６ ) and at the interface with aluminum, low-grade aluminum fluoride (AlF １．５It is assumed that lower aluminum fluoride (AlF １．５ ) has a very strong reducing effect, and sodium oxide (Na ２ O) and sodium hydride (NaH) and aluminum oxide (Al) in a hydrogen atmosphere. ２ O ３ ) and sodium fluoride (NaF). Also, lower aluminum fluoride (AlF １．５ ), part of which is under pressure as a gas, moves into the system and, together with the sodium hydride which has also become gas, forms sodium metaborate (NaBO ２ ) particles containing sodium borohydride (NaBH ４ As a result, fluoride also contributes to the transport of aluminum within the system.

[0050] Sodium borohydride (NaBH ４ ) becomes a melt at temperatures above 490°C. Molten sodium borohydride (NaBH ４ ) 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 results in molten sodium borohydride (NaBH ４ ) acts as a medium for mass transfer and a reaction field, allowing ions to move inside and outside the oxide layer on the outside of the aluminum particle. This allows ions to move inside and outside the iota-alumina layer of the aluminum (Al) particle, or sodium metaborate (NaBO ２ ) conditions that allow reaction on the particle surface.

[0051] At this time, aluminum (Al) particles and sodium metaborate (NaBO ２ The particles come into contact with each other through stirring, and materials including raw materials, intermediate products, and products are repeatedly attached and dispersed on the particle surfaces. As a result, sodium borohydride (NaBH ４ ), sodium hydride (NaH), sodium oxide (Na ２ O), sodium metaborate (NaBO ２), the aluminum ion particles move at a high speed that cannot be achieved by simple diffusion, and sodium borohydride (NaBH ４ ) The formation reaction is promoted.

[0052] As explained above, in the iota-alumina production reaction, the raw material sodium metaborate (NaBO) is dissolved not only inside the aluminum (Al) particles but also by contact between the particles. ２ ) and intermediate products (NaH, Na ２ O, AlF １．５ ) and sodium borohydride (NaBH ) as a solvent. ４ ) 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] When the heating temperature in the reaction step is less than 490° C., sodium borohydride (NaBH ４ Since boron ions cannot melt, their passage through the iota-alumina layer is slowed down, and the amount of sodium hydride (NaH) that seeps out of the aluminum (Al) particles is significantly reduced. Therefore, in this case, mainly, 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 gasified sodium hydride (NaH) is converted into sodium metaborate (NaBO ２ ) reacts with 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 Al ６ O 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 Al ６ O 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 the removal of water-soluble impurities, such as sodium borohydride (NaBH ４ If the polar solvent is water, sodium borohydride (NaBH ), which is a substance soluble in water, can be suitably removed. ４ ), sodium hydride (NaH), sodium fluoride (NaF), lower aluminum fluoride (AlF １．５ ), sodium borates and sodium aluminum dioxide (NaAlO ２ ) 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 the cryolite (Na ３ AlF ６ Impurities that are insoluble in neutral water, such as aluminum, can 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 eluted 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-like or rod-like 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 a lump reaction product that was washed by stirring with water at 80° C. or higher and 100° C. or lower for 1 hour. FIG. 1B is an enlarged SEM backscattered electron image of the area IB shown in FIG. 1A. The reaction product shown in FIG. 1A is the product of Test Example 7, which will be described later. The lump product is formed by mixing sodium borohydride (NaBH ４ ) melts, causing what were originally aluminum particles to adhere to each other. As shown in Figure 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 appear as a result of the sodium borohydride eluting during washing. Unreacted aluminum remains in the center.

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

[0061] Here, the aspect ratio refers to the ratio of the length W to the width H, i.e., the value obtained by dividing the length W by the width H. FIG. 1E is an enlarged SEM backscattered electron image showing iota alumina crystals relating to 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 extension 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 or more and 30 or less. The average aspect ratio of the iota alumina crystals refers to the arithmetic average of the aspect ratios of multiple iota alumina crystals. FIG. 1F is an enlarged SEM backscattered electron image showing iota alumina crystals for which the aspect ratios corresponding to the range IF shown in FIG. 1D were measured. As shown in FIG. 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 appear clearly 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 appear clearly as linear structures are not extracted as iota alumina crystals C. Here, as shown in FIG. 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. In addition, 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 show potassium metaborate (KBO ２1G and 1H are enlarged SEM backscattered electron images of iota alumina crystals relating to a product produced using potassium borates as a raw material alkali metal compound. The reaction products shown in FIGS. 1G and 1H are products according to Test Example 25, which will be described later. FIG. 1H is an enlarged SEM backscattered electron image obtained by observation in a different region from that shown in FIG. 1G . When potassium borates were used as raw materials, the plate-like iota alumina shown in FIG. 1G and the rod-like iota alumina shown in FIG. 1H were 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. Here, the width of the plate-like iota alumina refers to the thickness of the iota alumina crystal, and the width of the plate-like iota alumina refers to the length perpendicular to the thickness. The average aspect ratio in the imaged 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 imaged 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 with 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. Even in this case, sodium borohydride (NaBH ４ ) can be preferably removed.

[0066] Hereinafter, first to fourth manufacturing methods, which are specific examples of the manufacturing method of iota alumina according to the present embodiment, will be described in detail. In the following steps, unless otherwise specified, sodium fluoride is used as the fluoride, and sodium metaborate (NaBO) separated as crystals is used as the sodium borate. ２ The first to fourth manufacturing methods described below are merely examples, and the present invention is not limited to these.

[0067] [First Manufacturing Method] Figure 3 is a process diagram showing the 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, and then mixed with sodium borate and charged into a sealed container. The mixture is then reacted at 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 Figure 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 examples of the "reaction step," and step 4 (S-14) is an example of the "washing step."

[0068] (a) First Step: In the pretreatment step, aluminum powder and sodium fluoride are mixed and rubbed together. After the treatment, the mixture is placed in a container, the lid is closed, and the atmosphere is kept at a humidity of 10% or less. The mixture is then placed in a furnace and heated at a temperature of 100°C to 330°C for 30 minutes or more, causing the aluminum (Al) and sodium fluoride (NaF) to release moisture and form an aluminum oxide coating on the particle surfaces of the aluminum (Al) powder 52. The heat-treated powder is then cooled and mixed with sodium borate powder. After or before the mixed powder is placed in a sealed container, a non-oxidizing gas is introduced into the sealed container to fill the interior 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 placed in a sealed container. In this first step, treatment in an atmosphere of 10% or less humidity prevents moisture from adhering to the aluminum and fluoride in the air and oxidation of the aluminum. After the treated powder and sodium borate powder are mixed and charged into a sealed container, the sealed container may 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, the temperature inside the sealed container when the raw materials are introduced is not particularly limited, and a temperature below 100°C provides good workability.

[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 The second step (S-12) shown in FIG. 3 is a step in which all raw materials are mixed and charged into a sealed container, and the inside of the sealed container is heated to 400°C or higher and 610°C or lower to remove residual moisture contained in the sodium borate and aluminum powder, and the moisture that could not be removed is reacted with aluminum to convert it into hydrogen gas and an aluminum oxide film, thereby removing the moisture. ３) is heated at high temperatures to produce cryolite (Na ３ AlF ６ The second step is a step of reacting the evaporated water (i.e., residual water contained in the raw materials in the sealed container) with aluminum, or a step of removing water from the reaction system by degassing with a vacuum pump, and converting the aluminum fluoride formed on the surface of the aluminum into cryolite.

[0072] In the second step, when the heating temperature was set to 530°C, aluminum fluoride (AlF ３ ) to cryolite (Na ３ AlF ６ The production of sodium metaborate takes about 30 minutes or more. When dry sodium metaborate with a moisture content of about 0% to 3% is used as the raw material, the dehydration reaction is completed in about 0.5 to 1 hour.

[0073] (c) Third Step The third step (S-13) shown in FIG. 3 is a step of heating the inside of the sealed container to 490°C or higher and 610°C or lower, and introducing hydrogen gas. The heating causes the oxide film on the surface of the aluminum to be converted into sodium aluminum dioxide (NaAlO ２ ) is transformed into needle-shaped iota-alumina by the diffusion of sodium oxide and the crystallization of aluminum oxide by fluoride, and 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. When sodium borohydride fills the iota-alumina layer, sodium hydride (NaH) and sodium oxide (Na ２ O), aluminum ions, borate ions, etc. become able to move using sodium borohydride as a solvent, and the "particle agitation reaction" begins. In the particle agitation reaction, mass transfer occurs simply through particle contact, so weak agitation is sufficient. The mixture was stirred by rotating the agitation means 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, causing them to react on the surface of the aluminum, and then allowing the product and raw materials to move by diffusion, continuing the reaction and synthesizing the materials.In order to further assist this material transfer, kinetic energy can also be applied 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 + 6H ２ +3NaBO ２ → 3NaBH ４ +2Al ２ O ３ ...(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) Fourth 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 ４ ), sodium hydride (NaH), sodium fluoride (NaF), lower aluminum fluoride (AlF １．５ ), sodium borates and sodium aluminum dioxide (NaAlO ２ ) is eluted. Then, the reaction product is removed from the solvent and dried under reduced pressure. In the fourth step, when an alkaline aqueous solution is used as the polar solvent, cryolite (Na ３ AlF ６ ) and aluminum can be further dissolved, in which case the iota-alumina and aluminum hydroxide remain as solids, making it easier to remove the iota-alumina.

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

[0079] Another manufacturing method will be described below, and a description of the same points as in the first manufacturing method will be omitted.

[0080] [Second Manufacturing Method] Figure 4 is a process diagram showing a second manufacturing method of iota alumina. In the second manufacturing method of 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, and then mixed with sodium borate powder 51 and charged into a sealed container. The mixture is then heated at a temperature of 400°C to 610°C and moisture is removed using a vacuum pump. Hydrogen gas is then introduced and reacted in the sealed container 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 Figure 4, the second manufacturing method of sodium borohydride includes steps S-21 to S-24. Here, the first step (S-21) to the third step (S-23) are an example of a "reaction step", and the fourth step (S-24) is an example of a "washing step".

[0081] (a) First Step: In a pretreatment step, 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 of 10% or less humidity, and then placed in a furnace and heated at 100°C to 330°C for 30 minutes or more, causing aluminum (Al) and sodium fluoride (NaF) to release part of the moisture contained in the sodium hydroxide, and forming an aluminum oxide coating and sodium oxide (Na ２O) is produced. In this case, since there is a lot of moisture from the sodium hydroxide and sodium oxide on the surface of the aluminum, oxidation of the aluminum takes precedence. Therefore, the reaction of producing aluminum fluoride from hydrogen fluoride occurs only 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 interior 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, treatment is performed in an atmosphere with a humidity of 10% or less, which prevents moisture from the air from adhering to the aluminum, sodium hydroxide, and fluoride, and prevents oxidation of the aluminum. After mixing the treated powder with the sodium borate powder, the timing for filling the sealed container with a non-oxidizing gas atmosphere may be either after or before the raw materials are charged into the sealed container.

[0082] (b) Second Step The second step (S-22) shown in FIG. 4 is a step in which all the mixed raw materials are charged into a sealed container, and the inside of the sealed container is heated to 400°C or higher and 610°C or lower to degas the residual moisture contained in the sodium hydroxide, sodium borate, aluminum powder, and fluoride powder, and the moisture that could not be degassed is reacted with aluminum to convert it into hydrogen gas and an aluminum oxide film, thereby removing the moisture. At this time, the sodium hydroxide adhering to the surface of the aluminum becomes sodium oxide. Furthermore, some of the sodium oxide reacts with the oxide film on the surface of the aluminum to form sodium aluminum dioxide (NaAlO ２ The second step is a step of reacting the aluminum with the residual moisture contained in the raw materials in the sealed container, or a step of removing moisture from the reaction system by degassing with a vacuum pump.

[0083] (c) Third Step The third step (S-23) shown in FIG. 4 is a step of heating the inside of the sealed container to 490°C or higher and 610°C or lower, and introducing hydrogen gas. The heating causes the oxide film on the surface of the aluminum to be converted into sodium aluminum dioxide (NaAlO２ ) is transformed into needle-shaped iota alumina by the diffusion of sodium oxide and the crystallization of aluminum oxide by fluoride, and 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. When sodium borohydride fills the iota alumina layer, sodium hydride (NaH) and sodium oxide (Na ２ O), aluminum ions, borate ions, etc. become able to move using sodium borohydride as a solvent, and the "particle agitation reaction" begins. In the particle agitation reaction, mass transfer occurs simply through particle contact, so weak agitation is sufficient. The mixture was stirred by rotating the agitation means inside the sealed container. In this way, the reaction product was obtained.

[0084] (d) Fourth 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 longer. This allows sodium borohydride (NaBH ４ ), sodium hydride (NaH), sodium fluoride (NaF), lower aluminum fluoride (AlF １．５ ), sodium borates and sodium aluminum dioxide (NaAlO ２ The reaction product is then removed from the solvent and dried under reduced pressure.

[0085] [Third Manufacturing Method] Figure 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, and then mixed with fluoride powder 54 and sodium borate powder 51. The mixture is charged into a sealed container, heated at 400°C to 610°C, and moisture is removed using a vacuum pump. Hydrogen gas is then introduced and reacted at 490°C to 610°C in the sealed container filled with hydrogen gas. The sodium borate powder 51 and aluminum powder 52 react while remaining in a solid phase. As shown in Figure 5, the third manufacturing method of sodium borohydride includes steps from a first step (S-31) to a fourth step (S-34). Here, the first step (S-31) to the third step (S-33) are an example of a "reaction step", and the fourth step (S-34) is an example of a "washing step".

[0086] (a) First Step: In a pretreatment step, 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 placed in an atmosphere of 10% or less humidity, and then placed in a furnace and heated at 100°C to 330°C for 30 minutes or more to release a part of the moisture contained in the sodium hydroxide into the aluminum (Al), and an aluminum oxide film and sodium oxide (Na) are formed on the particle surfaces of the aluminum (Al) powder 52. ２O). 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 interior 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 in the air from adhering to the aluminum, sodium hydroxide, and fluoride, and to prevent oxidation of the aluminum. After mixing the treated powder and sodium borate powder, the sealed container can be filled with a non-oxidizing gas atmosphere either after or before the raw materials are charged into the sealed container.

[0087] (b) Second Step The second step (S-32) shown in FIG. 5 is a step in which all the mixed raw materials are charged into a sealed container, and the inside of the sealed container is heated to 400°C or higher and 610°C or lower to degas the remaining moisture contained in the sodium hydroxide, sodium borate, aluminum powder, and fluoride powder, and the moisture that could not be degassed is reacted with aluminum to convert it into hydrogen gas and an aluminum oxide film, thereby removing the moisture. Sodium hydroxide adhering to the surface of the aluminum becomes sodium oxide. Some of the sodium oxide reacts with the oxide film on the surface of the aluminum to form sodium aluminum dioxide (NaAlO ２ The second step is a step of reacting the aluminum with the residual moisture contained in the raw materials in the sealed container, or a step of removing moisture from the reaction system by degassing with a vacuum pump.

[0088] (c) Third Step In the third step (S-33) shown in FIG. 5, the temperature inside the sealed container was heated to 490°C or higher and 610°C or lower, and hydrogen gas was introduced. The heating resulted in the oxide film on the surface of the aluminum and sodium aluminum dioxide (NaAlO ２) is transformed into needle-shaped iota-alumina by the diffusion of sodium oxide and the crystallization of aluminum oxide by fluoride, and 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. When sodium borohydride fills the iota-alumina layer, sodium hydride (NaH) and sodium oxide (Na ２ O), aluminum ions, borate ions, etc. become able to move using sodium borohydride as a solvent, and the "particle agitation reaction" begins. In the particle agitation reaction, mass transfer occurs simply through particle contact, so weak agitation is sufficient. The mixture was stirred by rotating the agitation means inside the sealed container. In this way, the reaction product was obtained.

[0089] (d) Fourth 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 longer. This allows sodium borohydride (NaBH ４ ), sodium hydride (NaH), sodium fluoride (NaF), lower aluminum fluoride (AlF １．５ ), sodium borates and sodium aluminum dioxide (NaAlO ２ The reaction product is then removed from the solvent and dried under reduced pressure.

[0090] [Fourth Manufacturing Method] Figure 6 is a process diagram showing a fourth manufacturing method of iota alumina. In the fourth manufacturing method of sodium borohydride, in a 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, which is then filled with a non-oxidizing gas and sealed. In a second step, the sealed container is heated to 400°C or higher and 610°C or lower while still sealed, causing moisture generated from the raw materials to react with the fluoride, generating gaseous hydrogen fluoride, which reacts with aluminum to form aluminum fluoride on the aluminum surface. In a third step, the mixture is reacted at a temperature of 490°C or higher and 610°C or lower in a sealed container filled with hydrogen gas. The sodium borates and aluminum powder react in their respective solid phases. As shown in Figure 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 As a 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 mixed in, and these are charged into a sealed container. After charging them into the sealed container, or before charging them, a non-oxidizing gas is introduced into the sealed container to fill the interior with a non-oxidizing gas atmosphere. The above steps constitute the first step (S-41). The timing for introducing the non-oxidizing gas may be after or before charging the raw materials into the sealed container. Note that the method for mixing the raw materials is not limited to this, and 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 FIG. 6 is a step of sealing the sealed container, and then heating the inside of the sealed container to 400°C or higher and 610°C or lower, and 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 of using the high-temperature moisture to react with fluoride, generating hydrogen fluoride (HF) vapor, and producing aluminum fluoride on the aluminum surface. At this time, the sodium hydroxide becomes sodium oxide. Furthermore, some of the sodium oxide reacts with the oxide film on the aluminum surface to form sodium aluminum dioxide (NaAlO ２ The second step is to remove the residual moisture contained in the raw materials in the sealed container to produce aluminum fluoride.

[0093] (c) Third Step The third step (S-43) shown in FIG. 6 is a step of heating the inside of the sealed container to 490°C or higher and 610°C or lower, and introducing hydrogen gas. By heating, the oxide film on the surface of the aluminum and sodium aluminum dioxide (NaAlO ２ ) is transformed into needle-shaped iota-alumina by the diffusion of sodium oxide and the crystallization of aluminum oxide by fluoride, and 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 reaction to produce sodium borohydride begins. When sodium borohydride fills the iota-alumina layer, sodium hydride (NaH) and sodium oxide (Na ２ O), aluminum ions, borate ions, etc. can move using sodium borohydride as a solvent, and the "particle stirring reaction" begins. In the second step, aluminum fluoride formed on the surface of the aluminum absorbs the diffused sodium ions and forms cryolite (Na ３ AlF ６ ) and forms a NaAlF layer on the aluminum surface. The NaAlF layer is formed by dissolving lower aluminum fluorides (AlF １．５), which travels through the system as a strong reducing agent and as a vapor-mobile substance, and sodium oxide (Na ２ O) to produce sodium hydride (NaH) and alumina, which aids in the production of sodium borohydride. Since particle-agitation reactions involve mass transfer through particle contact alone, weak agitation is sufficient. The mixture was stirred by rotating the agitation means inside the sealed vessel. In this way, the reaction product was obtained.

[0094] (d) Fourth 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 longer. This allows sodium borohydride (NaBH ４ ), sodium hydride (NaH), sodium fluoride (NaF), lower aluminum fluoride (AlF １．５ ), sodium borates and sodium aluminum dioxide (NaAlO ２ 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 described.

[0096] 7 is a partial cross-sectional view showing an example of a sealed container used in the first to fourth manufacturing methods. As shown in FIG. 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. In addition, an O-ring 18 is disposed on the upper end surface of the container body 12, which is in close contact with the lid 14 to ensure airtightness of the interior. When the lid 14 is closed, the lid 14 is in close contact with the O-ring 18 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. 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 supplied into the container body 12, and when the exhaust valve 28 is opened, the inside of the container body 12 is degassed. The second pipe 30 is also connected to a pressure gauge 32, which allows the pressure inside the container body 12 to be measured.

[0099] FIG. 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 FIG. 7 is that the sealed container 10B has a plurality of 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 a plate-shaped (blade) stirrer, obtained by removing the reaction product from the sealed container shown in FIG. 8 after stirring for a predetermined period of time. FIG. 12B is a photograph of the reaction product, obtained by removing the reaction product from 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 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 rotating inside the container body 12b is provided with a wide paddle stirrer 37 via a support. When the wide paddle stirrer 37 as 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] (Function of Fluoride) Hereinafter, the function of fluoride in the first to fourth production 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. This can suppress the dissolution of aluminum ions from alumina. Furthermore, since 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, and the production of sodium hydride (NaH) can be increased. The second effect is to form an NaAlF layer on the surface of the aluminum particles, which then dissolves lower aluminum fluoride (AlF), which has a strong reducing power. １．５ The lower aluminum fluoride migrates outward from the aluminum surface and forms sodium oxide (Na ２ O), which increases the amount of sodium hydride (NaH) produced. １．５ ) has a gaseous pressure at the reaction temperature for producing iota-alumina and can move as a gas. Sodium hydride (NaH) also has a gaseous pressure, and lower aluminum fluorides (AlF １．５ ) and migrates to the sodium borate particles to produce sodium borohydride.

[0107] 14A to 14F are reaction schematic 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 schematic diagrams (FIGS. 14A to 14F) using the first to fourth production methods using sodium fluoride (NaF) as examples. 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 moisture is reacted with fluoride to generate hydrogen fluoride, which is then reacted with aluminum to form cryolite (Na ３ AlF ６ 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, sodium oxide is generated from the sodium hydroxide, and the sodium oxide is reacted with aluminum to form sodium aluminum dioxide (NaAlO ２ )

[0109] 2) Initial stage of reaction-1 (third step) As shown in FIG. 14B, sodium aluminum dioxide (NaAlO ２ ) 106 is formed into needle-shaped iota alumina (Na) by the crystallization promoting action of sodium fluoride (NaF) 103. ０．６７ Al ６ O ９．３３ ) 101c layer and sodium oxide (Na ２ O).

[0110] 3) Initial stage of reaction-2 (third step) As shown in FIG. 14C, needle-shaped iota alumina (Na ０．６７ Al ６ O ９．３３ In the layer 101c, the hydrogen gas (H ２ ) and sodium ions (O ２－ ) moves, but other ions also move between the needle-like crystals of iota-alumina and reach the inside of the iota-alumina layer. ２ O) and the presence of hydrogen gas, sodium ions, borate ions, oxygen ions, and fluoride ions that have migrated through the iota-alumina layer, resulting in the formation of needle-shaped iota-alumina (Na ０．６７ Al ６ O ９．３３ ) 101c continuously inside the layer of sodium oxide (Na ２This reaction reduces sodium hydride (NaH) 112 and aluminum oxide (Al ２ O ３ ) is formed, and aluminum oxide immediately turns into sodium aluminum dioxide (NaAlO ２ ) is formed by the catalytic action of fluoride ions. ２ ) is iota alumina (Na ０．６７ Al ６ O ９．３３ ) 101c and sodium oxide (Na ２ Sodium hydride (NaH) decomposes into boric acid (B ２ O ３ ) to form sodium borohydride (NaBH ４ ) 111 and sodium oxide (Na ２ O) is produced. ４ ) is formed by the synthesis of acicular iota alumina (Na) with sodium hydride (NaH) 112. ０．６７ Al ６ O ９．３３ ) 101c layer. ０．６７ Al ６ O ９．３３ ) 101c layer, containing mainly sodium borohydride (NaBH ４ ) will move to the outside.

[0111] 4) Middle stage of reaction (third step) As shown in FIG. 14D, the particle stirring reaction produces sodium borohydride (NaBH ４ ) Liquid-filled needles of iota alumina (Na ０．６７ Al ６ O ９．３３ ) 101c, and mainly sodium hydride (NaH) and aluminum ions (Al ３＋ ), sodium metaborate (NaBO ２ ) 102 from metaborate ion (BO ２－ ), oxygen ions (O ２－ ), sodium ions (O ２－) move, and needle-shaped iota alumina (Na ０．６７ Al ６ O ９．３３ The reaction begins both inside and outside the layer of sodium metaborate granules. The reaction in the sodium metaborate granules is carried out by the reaction of sodium borohydride (NaBH ４ ) is boric acid and (B ２ O ３ ) to produce sodium borohydride (NaBH ４ ) and sodium oxide (Na ２ In this reaction, sodium oxide (Na ２ O) is brought into contact with the aluminum particles again by stirring, resulting in a circulating reaction.

[0112] 5) Peak Reaction (Third Step) As shown in Fig. 14E, the particles are stirred to exchange the surface materials of the aluminum particles and the sodium metaborate particles with each other, resulting in a particle stirring reaction. As the particles repeatedly come into contact with each other, sodium metaborate (NaBO) is transferred from the sodium metaborate 102 particles to the aluminum particles 101. ２ ) 102 and the reaction product sodium oxide (Na ２ On the other hand, sodium metaborate (NaBO ２ The particles of aluminum 102 contain the reaction product (sodium borohydride (NaBH)) from the aluminum 101 particles. ４ ) 111, sodium hydride (NaH) 112) are supplied. The particle agitation causes the exchange of these substances at high speed, which promotes the particle agitation reaction, and the aluminum particles gradually incorporate fragments of sodium metaborate and grow. Meanwhile, the sodium metaborate particles also incorporate sodium hydride, forming sodium borohydride (NaBH ４ ) and sodium oxide.

[0113] 6) End of reaction (third step) As shown in FIG. 14F, in the latter half of the reaction, the raw material aluminum and sodium oxide (Na ２ O) and boric acid (B ２ O ３ ) is consumed and the particles are converted to the product sodium borohydride (NaBH ４) and iota alumina. The reaction rate decreases as the concentration decreases, as the production of sodium hydride by the reduction of sodium oxide by aluminum decreases. On the other hand, aluminum (Al) and sodium hexafluoroaluminate (Na ３ AlF ６ ) and the NaAlF layer. １．５ The formation of sodium hydride (NaH) 117 continues regardless of the sodium oxide concentration. Since lower aluminum fluorides can be moved by sublimation, they reduce sodium oxide to form sodium hydride (NaH) 112, which in the latter half of the reaction generates sodium borohydride (NaBH ４ As a result, the aluminum (Al) 101 particles and sodium metaborate particles are reacted with each other to produce sodium borohydride (NaBH ４ ) 111 and needle-shaped iota alumina (Na ０．６７ Al ６ O ９．３３ ) layer 101c.

[0114] (Test Examples) 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]

[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 at room temperature and normal pressure, i.e., at a temperature of 5°C to 35°C and 1 atm in air, unless otherwise specified. The intensity of the peaks attributable to inclusions in the diffraction pattern of the product depends on the component ratio of the inclusions in the product, and therefore appears as strong peaks, and inclusions that are clearly present were rated as "A." Inclusions that appear as smaller peaks than in inclusions rated A and are estimated to have a small content were rated as "B." Inclusions that appear as even smaller peaks than in inclusions rated B and are estimated to have a small content were rated as "C." Inclusions that appear even smaller than in inclusions rated C, appearing as recognizable peaks, and are estimated to have a trace content were rated as "D."

[0118]

[0119]

[0120] Test Example 1 Test Example 1 is a comparative example. As shown in Table 1, sodium metaborate (NaBO) was used as a raw material. ２ ) powder 6.98 g, and sodium tetraborate (Na ２ B ４ O ７ 8.01 g of sodium fluoride (NaF) 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. Here, the Na / B ratio of Test Example 1 was 0.89. In the reaction step, 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 0.6 MPa. In Test Example 1, a cleaning step was not performed. Through the above steps, a product according to Test Example 1 was obtained.

[0121] FIG. 15 is a diagram showing the X-ray diffraction pattern of the product according to Test Example 1. In Test Example 1, iota alumina (Na ０．６７ Al ６ O ９．３３ As shown in Table 2 and FIG. 15, the product according to Test Example 1 contained iota alumina (Na ０．６７ Al ６ O ９．３３ ) and sodium borohydride (NaBH ４ ) and sodium metaborate (NaBO ２ ) and aluminum (Al) were detected, and AlB ２ The ingredients of the C classification include sodium hexafluoroaluminate (Na ３ AlF ６ ) and sodium tetraborate (Na ２ B ４ O ７ ) was detected, and aluminum diboride (AlB ２ ) was detected. From the results of Test Example 1, it can be seen that iota alumina can be produced even when the Na / B ratio is 0.89. On the other hand, since Test Example 1 does not include a washing step, sodium borohydride (NaBH ４ ) is not thought to have been removed.

[0122] Test Example 2 Test Example 2 is an example. As shown in Table 1, sodium metaborate (NaBO ２ 1.95 g of potassium fluoride (KF) powder, 0.05 g of potassium fluoride (KF) powder, and 1.06 g of aluminum (Al) powder were charged into a sealed container equipped with a stirring means. Here, the Na / B ratio of Test Example 2 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, the cleaning step involved cleaning with pure water at high temperature. Through the above steps, a product according to Test Example 2 was obtained.

[0123] In Test Example 2, iota alumina (Na ０．６７Al ６ O ９．３３ As shown in Table 2, the product according to Test Example 2 contained iota alumina (Na ０．６７ Al ６ O 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, sodium metaborate (NaBO) was used as a raw material. ２ ) powder, 17.46 g, and aluminum fluoride (AlF ３ 1.44 g of Na (Na) powder and 11.45 g of aluminum (Al) powder were charged 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 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 according to Test Example 3. In Test Example 3, iota alumina (Na ０．６７ Al ６ O ９．３３ As shown in Table 2 and FIG. 16, the product according to Test Example 3 contained sodium borohydride (NaBH ) as a component rated as A. ４ ) and iota alumina (Na ０．６７ Al ６ O ９．３３ ) and aluminum (Al) were detected, and sodium metaborate (NaBO) was detected as a B-grade component. ２ ) was detected, and sodium hexafluoroaluminate (Na ３ AlF ６ From the results of Test Example 3, aluminum fluoride (AlF３ On the other hand, in Test Example 3, the washing step was not performed, and therefore, sodium borohydride (NaBH ４ ) and sodium metaborate (NaBO ２ ) is not thought to have been removed.

[0126] Test Example 4 Test Example 4 is an example. As shown in Table 1, sodium metaborate (NaBO) was used as a raw material. ２ ) powder 17.46 g and sodium hexafluoroaluminate (Na ３ AlF ６ 1.81 g of Na / B powder and 11.45 g of aluminum (Al) powder were charged into a sealed container equipped with a stirring means. Here, the Na / B ratio of Test Example 4 was 1.10. 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 0.54 MPa. In Test Example 4, cleaning with diglyme was performed as the cleaning step. Through the above steps, the product of Test Example 4 was obtained.

[0127] FIG. 17 is a diagram showing the X-ray diffraction pattern of the product according to Test Example 4. In Test Example 4, iota alumina (Na ０．６７ Al ６ O ９．３３ As shown in Table 2 and FIG. 17, the product according to Test Example 4 contained iota alumina (Na ０．６７ Al ６ O ９．３３ ) was detected, and aluminum (Al) and sodium metaborate (NaBO) were detected as B grade components. ２ ) was detected, and sodium hexafluoroaluminate (Na ３ AlF ６ ) was detected. From the results of Test Example 4, sodium hexafluoroaluminate (Na ３ AlF ６ It can be seen that iota alumina can be produced even when iota alumina is used as a raw material.

[0128] Test Example 5 Test Example 5 is an example. As shown in Table 1, sodium tetraborate (Na ２ B ４ O ７ 1.48 g of NaF 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. Here, the Na / B ratio of Test Example 5 was 1.17. In the reaction step, the sealed container was heated to 500°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 0.86 MPa. The minimum partial pressure of hydrogen gas in the reaction step was 0.63 MPa. In Test Example 5, cleaning with diglyme was performed as the cleaning step. Through the above steps, the product of Test Example 5 was obtained.

[0129] In Test Example 5, iota alumina (Na ０．６７ Al ６ O ９．３３ As shown in Table 2, the product according to Test Example 5 contained iota alumina (Na ０．６７ Al ６ O ９．３３ ) was detected, and aluminum (Al) was detected as a component rated B. From the results of Test Example 5, sodium tetraborate (Na ２ B ４ O ７ It can be seen that iota alumina can be produced even when iota alumina is used as a raw material.

[0130] Test Example 6 Test Example 6 is a comparative example. As shown in Table 1, sodium metaborate (NaBO) was used as a raw material. ２17.46 g of NaF powder, 2.17 g of sodium fluoride (NaF), and 11.45 g of aluminum (Al) powder were charged 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 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 Al ６ O ９．３３ As shown in Table 2 and FIG. 18, the product according to Test Example 6 contained sodium borohydride (NaBH ) as a component rated as A. ４ ) and iota alumina (Na ０．６７ Al ６ O ９．３３ ) was detected, and aluminum (Al) and sodium metaborate (NaBO) were detected as components of the B grade. ２ ) was detected. Sodium hexafluoroaluminate (Na ３ AlF ６ ) was detected. From the results of Test Example 6, it can be seen that iota alumina can be produced when the heating temperature is set to 490°C. On the other hand, since Test Example 6 does not include a washing step, sodium borohydride (NaBH ４ ) and sodium metaborate (NaBO ２ ) is not thought to have been 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 as a washing step.

[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 Al ６ O ９．３３ As shown in Table 2 and FIG. 19, the product according to Test Example 7 contained iota alumina (Na ０．６７ Al ６ O ９．３３ ) was detected, and sodium hexafluoroaluminate (Na ３ AlF ６ ) was detected, and aluminum (Al) was detected as a component for D rating. The X-ray diffraction pattern for Test Example 7 showed iota alumina (Na ０．６７ Al ６ O ９．３３ The data matched the PDF (registered trademark) (Powder Diffraction File) number 01-070-7114 data of the same company, indicating the absence of crystal defects. Furthermore, semi-quantitative analysis of the X-ray diffraction chart based on the Rietveld method showed 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). Furthermore, the specific surface area of ​​the product, calculated by the BET (Brunauer-Emmett-Teller) method, was 54 m ２ g －１ From the results of Test Example 7, it was found that washing with pure water reduced the amount of sodium borohydride (NaBH ４ ) and sodium metaborate (NaBO ２ In addition, as a result of observing the product of Test Example 7 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, sodium metaborate (NaBO) was used as a raw material. ２In Test Example 8, 17.46 g of sodium hydroxide (NaOH), 0.31 g of sodium fluoride (NaF), and 11.45 g of aluminum (Al) powder were used. In Test Example 8, sodium hydroxide (NaOH) and aluminum (Al) powder were mixed by rubbing and reacted at 240°C for 1 hour, and then the resulting mixture was mixed with sodium metaborate (NaBO ２ ) powder and sodium fluoride (NaF) were charged into a sealed container equipped with a stirring means. Here, the Na / B ratio of Test Example 8 was 1.20. In the reaction step, the inside of the sealed container was heated to 530°C, and hydrogen gas was introduced and stirred with 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 0.65 MPa. In Test Example 8, a cleaning step was not performed. Through the above steps, a product according to Test Example 8 was obtained.

[0135] 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 Al ６ O ９．３３ As shown in Table 2 and FIG. 20, the product of Test Example 8 contained sodium borohydride (NaBH ) as a component rated as A. ４ ) and iota alumina (Na ０．６７ Al ６ O ９．３３ ) was detected, aluminum (Al) was detected as a component of the B grade, and sodium hexafluoroaluminate (Na ３ AlF ６ ) and sodium fluoride (NaF) were detected. The results of Test Example 8 show that iota alumina can be produced even when dehydration is performed with sodium hydroxide. On the other hand, since Test Example 8 did not undergo a washing step, sodium borohydride (NaBH ４ ) is not thought to have been 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 a washing step.

[0137] In Test Example 9, iota alumina (Na ０．６７ Al ６ O ９．３３ As shown in Table 2, the product of Test Example 9 contained iota alumina (Na ０．６７ Al ６ O ９．３３ ) and aluminum (Al) were detected, and sodium hexafluoroaluminate (Na ３ AlF ６ ) and sodium fluoride (NaF) were detected. From the results of Test Example 9, it was found that washing with diglyme could remove sodium borohydride (NaBH ４ ) can be removed.

[0138] Test Example 10 Test Example 10 is an example. As shown in Table 1, sodium metaborate (NaBO) was used as a raw material. ２ In Test Example 10, 17.46 g of sodium hydroxide (NaOH), 0.29 g of sodium fluoride (NaF), and 11.45 g of aluminum (Al) powder were used. In Test Example 10, sodium hydroxide (NaOH) and aluminum (Al) powder were mixed by rubbing and reacted at 240° C. for 1 hour. The resulting mixture was then mixed with sodium metaborate (NaBO ２ ) powder and sodium fluoride (NaF) were charged into a sealed container equipped with a stirring means. Here, the Na / B ratio of Test Example 10 was 1.19. In the reaction step, the inside of the sealed container was heated to 470°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 0.69 MPa. In Test Example 10, the cleaning step involved cleaning with pure water at high temperature. Through the above steps, the product of Test Example 10 was obtained.

[0139] In Test Example 10, iota alumina (Na ０．６７ Al ６ O ９．３３ As shown in Table 2, the product of Test Example 10 was found to contain aluminum (Al) and iota alumina (Na) as components rated as A. ０．６７ Al ６ O ９．３３ ) was detected, and sodium hexafluoroaluminate (Na ３ AlF ６ ) was detected, and aluminum hydroxide was detected as a component rated C. The results of Test Example 10 show that iota alumina can be produced when the heating temperature is set to 470°C. Here, aluminum hydroxide (Al(OH) ３ ) was detected due to sodium metaborate (NaBO) remaining in the product. ２ ) 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, sodium metaborate (NaBO) was used as a raw material. ２ In Test Example 11, 5.82 g of sodium hydroxide (NaOH), 0.10 g of sodium fluoride (NaF), and 3.82 g of aluminum (Al) powder were used. In Test Example 11, sodium hydroxide (NaOH) and aluminum (Al) powder were mixed by rubbing and reacted at 240° C. for 1 hour, and then the resulting mixture was mixed with sodium metaborate (NaBO ２) powder and sodium fluoride (NaF) were charged into a sealed container equipped with a stirring means. Here, the Na / B ratio of Test Example 11 was 1.20. In the reaction step, the inside of the sealed container was heated to 560°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 0.63 MPa. In Test Example 11, the cleaning step involved cleaning with pure water at high temperature. Through the above steps, the product of Test Example 11 was obtained.

[0141] In Test Example 11, iota alumina (Na ０．６７ Al ６ O ９．３３ As shown in Table 2, the product according to Test Example 11 was subjected to semi-quantitative analysis by the Rietveld method, and as a result, 81% by mass of iota alumina (Na ０．６７ Al ６ O ９．３３ ) was detected, and 7 mass% of aluminum (Al) and 8 mass% of aluminum hydroxide were detected as components for the B grade, and 2 mass% of sodium hexafluoroaluminate (Na ３ AlF ６ The results of Test Example 11 show that iota alumina can be produced when the heating temperature is 560°C. Here, aluminum hydroxide (Al(OH) ３ ) was detected due to sodium metaborate (NaBO) remaining in the product. ２ ) dissolved in water during the washing process. As the water became alkaline due to the high temperature of nearly 100°C, some of the unreacted aluminum dissolved in the water to form aluminum hydroxide (Al(OH) ３ ) is thought to be the reason.

[0142] Test Example 12 Test Example 12 is an example. As shown in Table 1, sodium metaborate (NaBO) was used as a raw material. ２1.94 g of NaF powder, 0.83 g of sodium fluoride (NaF), and 1.48 g of aluminum (Al) powder were charged into a sealed container equipped with a stirring means. Here, the Na / B ratio of Test Example 12 was 1.67. In the reaction step, 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 step was 0.89 MPa. The minimum partial pressure of hydrogen gas in the reaction step was 0.45 MPa. In Test Example 12, cleaning with diglyme was performed as the cleaning step. Through the above steps, the product of Test Example 12 was obtained.

[0143] In Test Example 12, iota alumina (Na ０．６７ Al ６ O ９．３３ As shown in Table 2, the product according to Test Example 12 contained iota alumina (Na ０．６７ Al ６ O ９．３３ ) and aluminum (Al) were detected, and sodium hexafluoroaluminate (Na ３ AlF ６ ) and sodium aluminate (NaAlO ２ ) was detected. 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, sodium metaborate (NaBO) was used as a raw material. ２1.94 g of NaCl powder and 1.28 g of aluminum (Al) powder were placed in a sealed container equipped with a stirring means. 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 a main component was obtained. As shown in Table 2, sodium metaborate (NaBO) was found to be a component rated A in the product of Test Example 13. ２ ) and aluminum (Al). Iota alumina (Na ０．６７ Al ６ O ９．３３ ) was not detected. In addition, when the product of Test Example 13 was subjected to high-temperature X-ray diffraction measurement at 600°C in a nitrogen atmosphere, sodium metaborate (NaBO) was found to be a component rated as A. ２ ) and aluminum (Al) were detected, and sodium aluminum borate (Na ２ Al ２ B ２ O ７ ) was detected, but even in this case, iota alumina (Na ０．６７ Al ６ O ９．３３ 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. In addition, in a high-temperature X-ray diffraction measurement of the product in a nitrogen atmosphere at 600°C, sodium aluminum borate (Na ２ Al ２ B ２ O ７) was detected because of the non-crystalline sodium aluminum borate (Na ２ Al ２ B ２ O ７ ) was crystallized by 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 mass % aqueous sodium hydroxide (NaOH) solution at 80° C. or higher and 100° C. or lower for 1 hour as a washing step.

[0147] In Test Example 14, aluminum hydroxide (Al(OH) ３ As shown in Table 2, the product of Test Example 14 was found to contain iota alumina (Na ０．６７ Al ６ O ９．３３ ) 38% by 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 cleaning step. In Test Example 14, a 2 mass % aqueous sodium hydroxide solution was used as the solvent in the cleaning step, and therefore iota alumina (Na ０．６７ Al ６ O ９．３３ The extraction residues other than aluminum hydroxide (Al(OH) ３ ) was produced under strong alkaline conditions. ０．６７ Al ６ O ９．３３ ) also partially dissolves together with aluminum (Al) to form aluminum hydroxide (Al(OH) ３ In addition, as a result of observing the product of Test Example 14 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, sodium diborate (Na ４ B ２ O ５ 2.94 g of NaF 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. Here, the Na / B ratio of Test Example 15 was 2.65. In the reaction step, 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 step was 0.86 MPa. The minimum partial pressure of hydrogen gas in the reaction step was 0.61 MPa. In Test Example 15, cleaning with diglyme was performed as the cleaning step. Through the above steps, the product of Test Example 15 was obtained.

[0149] In Test Example 15, sodium aluminum dioxide (NaAlO ２ As shown in Table 2, the product of Test Example 15 contained sodium aluminum dioxide (NaAlO ) as a component rated as A. ２ ) and sodium fluoride (NaF) were detected, and iota alumina (Na ０．６７ Al ６ O ９．３３ 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, resulting in the formation of sodium aluminate (NaAlO ２ ) is present stably, and iota alumina (Na ０．６７ Al ６ O ９．３３ ) was not sufficiently produced.

[0150] Test Example 16 Test Example 16 is a comparative example. As shown in Table 1, sodium metaborate (NaBO) was used as a raw material. ２5.85 g of Na (Na) powder and 9.54 g of aluminum (Al) powder were charged 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, 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 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, sodium aluminum dioxide (NaAlO ２ 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 (NaAlO ２ ) and iota alumina (Na ０．６７ Al ６ O ９．３３ 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, sodium metaborate (NaBO) was used as a raw material. ２ In Test Example 17, 17.46 g of sodium hydroxide (NaOH), 0.28 g of sodium fluoride (NaF), and 11.45 g of aluminum (Al) powder were used. In Test Example 17, sodium hydroxide (NaOH) and aluminum (Al) powder were mixed by rubbing and reacted at 240°C for 1 hour, and then the resulting mixture was mixed with sodium metaborate (NaBO ２) powder and sodium fluoride (NaF) were charged into a sealed container equipped with a stirring means. Here, the Na / B ratio of Test Example 17 was 1.19. In the reaction step, the sealed container was heated to 450°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 0.76 MPa. The minimum partial pressure of hydrogen gas in the reaction step was 0.69 MPa. In Test Example 17, the cleaning step involved cleaning with pure water at high temperature. Through the above steps, the product of 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, semi-quantitative analysis of the product according to Test Example 17 by the XRD Rietveld method detected 83 mass% of aluminum (Al) as a component classified as A, and 8 mass% of iota alumina (Na) as a component classified as B. ０．６７ Al ６ O ９．３３ ) and 7% by mass of sodium hexafluoroaluminate (Na ３ AlF ６ ) was detected, and 3% by mass of aluminum hydroxide (Al(OH) ３ In Test Example 17, the temperature in the reaction step was low at 450° C., so it is believed that the crystallization of iota alumina did not occur sufficiently.

[0154] Test Example 18 Test Example 18 is a comparative example. As shown in Table 1, sodium metaborate (NaBO) was used as a raw material. ２17.46 g of NaOH powder, 2.06 g of sodium hydroxide (NaOH), and 11.45 g of aluminum (Al) powder were mixed, and then pre-baked at 510°C for 5 hours under a hydrogen gas atmosphere of 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 by the stirring means in 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 (AlB) were found to be components rated A in the product according to Test Example 18. ２ ) was detected, and iota alumina (Na ０．６７ Al ６ O ９．３３ In Test Example 18, sodium aluminum dioxide (NaAlO ２ ) was produced, but it is thought that the crystallization of iota alumina did not occur sufficiently.

[0156] Test Example 19 Test Example 19 is an example. As shown in Table 1, sodium metaborate (NaBO) was used as a raw material. ２ 19.40 g of sodium fluoride (NaF) 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. The Na / B ratio of Test Example 19 was 1.19. The amount of aluminum (Al) powder was 1.19. ２) was 100% of the amount of substance. In the reaction step, the inside of the sealed container was heated to 580°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 0.81 MPa. The minimum partial pressure of hydrogen gas in the reaction step was 0.78 MPa. In Test Example 19, in the cleaning step, cleaning with pure water at high temperature for 60 minutes was performed. Through the above steps, the product of Test Example 19 was obtained.

[0157] In Test Example 19, iota alumina (Na ０．６７ Al ６ O ９．３３ As shown in Table 2, the product according to 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 Al ６ O ９．３３ ) and 64 mass% of aluminum hydroxide (Al(OH)3) were detected. From the results of Test Example 19, it can be seen that iota alumina can be produced when the heating temperature is set to 580°C. Aluminum (Al) and sodium hexafluoroaluminate (Na ３ AlF ６ The reason why sodium metaborate (NaBO) was not detected is that sodium metaborate (NaBO) remained in the product during the washing process. ２ ) dissolved in water and became alkaline, as in Test Example 14.

[0158] Test Example 20 Test Example 20 is an example. As shown in Table 1, sodium metaborate (NaBO) was used as a raw material. ２ 19.40 g of sodium fluoride (NaF) 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. The Na / B ratio of Test Example 20 was 1.19. The amount of aluminum (Al) powder was 1.19. ２) was 100% of the amount of substance. In the reaction step, the inside of the sealed container was heated to 610°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 0.81 MPa. The minimum partial pressure of hydrogen gas in the reaction step was 0.78 MPa. In Test Example 20, in the cleaning step, cleaning with pure water was performed at room temperature of 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 a main component was obtained. As shown in Table 2, the product of Test Example 20 was subjected to semi-quantitative analysis by the XRD Rietveld method, and the components rated as A were 59 mass% aluminum (Al) and 28 mass% iota alumina (Na ０．６７ Al ６ O ９．３３ ) was detected, and the component classified as B was 9% by mass of sodium hexafluoroaluminate (Na ３ AlF ６ ) was detected, and 5 mass % of aluminum diboride (AlB ２ ) was detected. From the results of Test Example 20, it can be seen that iota alumina can be produced when the heating temperature is set to 610°C. Here, unlike Test Example 19, aluminum hydroxide (Al(OH) ３ ) was not produced 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, which is presumably why the water did not become strongly alkaline during the washing process.

[0160] Test Example 21 Test Example 21 is an example. As shown in Table 1, sodium metaborate (NaBO) was used as a raw material. ２17.46 g of sodium fluoride (NaF) 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. The Na / B ratio of Test Example 21 was 1.22. In the reaction step, the sealed container was heated to 510°C, hydrogen gas was introduced, and the mixture was stirred by 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 21, the cleaning step involved cleaning with pure water at a high temperature of 100°C for 60 minutes. Through the above steps, a product according to Test Example 21 was obtained.

[0161] In Test Example 21, iota alumina (Na ０．６７ Al ６ O 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 Al ６ O ９．３３ ) was detected, and 20% by mass of aluminum hydroxide (Al(OH) ３ 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, water was used in the washing step to remove sodium metaborate (NaBO) remaining in the product. ２ ) makes the solution alkaline, and at a high temperature of 100°C, aluminum (Al) dissolves and aluminum hydroxide (Al(OH) ３ ) is produced, and sodium hexafluoroaluminate (Na ３ AlF ６ ) also dissolved.

[0162] Test Example 22 Test Example 22 is an example. As shown in Table 1, sodium metaborate (NaBO) was used as a raw material. ２17.46 g of sodium fluoride (NaF) 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. The Na / B ratio of Test Example 22 was 1.22. In the reaction step, the sealed container was heated to 510°C, hydrogen gas was introduced, and the mixture was stirred by 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 22, the cleaning step involved 60 minutes of cleaning with pure water at room temperature (25°C). Through the above steps, a product according to Test Example 22 was obtained.

[0163] In Test Example 22, iota alumina (Na ０．６７ Al ６ O 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% by mass of iota alumina (Na ０．６７ Al ６ O ９．３３ ) was detected, and the components classified as B were 16% by mass of aluminum (Al), 6% by mass of sodium hexafluoroaluminate (Na ３ AlF ６ From the results of Test Example 22, it was found that even if the temperature of the polar solvent used in the washing step was room temperature, iota alumina (Na ０．６７ Al ６ O ９．３３ In Test Example 22, sodium metaborate (NaBO) remaining in the product was removed during the washing process at room temperature. ２ Although the water becomes alkaline due to the dissolution of aluminum, the dissolution reaction of aluminum is mild because it is at room temperature, and aluminum hydroxide (Al(OH) ３ ) is thought to have suppressed the production of

[0164] Test Example 23 Test Example 23 is an example. As shown in Table 1, sodium metaborate (NaBO) was used as a raw material. ２17.46 g of sodium fluoride (NaF) 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. The Na / B ratio of 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 mass%) hydrochloric acid at room temperature for 60 minutes. The pH after cleaning was 6. Through the above steps, a product according to Test Example 23 was obtained.

[0165] In Test Example 23, iota alumina (Na ０．６７ Al ６ O 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% by mass of iota alumina (Na ０．６７ Al ６ O ９．３３ ) was detected, and the components classified as B were 17% by mass of aluminum (Al), 4% by mass of sodium hexafluoroaluminate (Na ３ AlF ６ ) was detected. 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, washing with 0.24 mol / L hydrochloric acid (HCl) at room temperature did not remove sodium metaborate (NaBO) remaining in the reaction product. ２ The pH was 6 due to a neutralization reaction with aluminum hydroxide (Al(OH) ３ ) is suppressed, and sodium hexafluoroaluminate (Na ３ AlF ６ ) is thought to have decreased slightly.

[0166] Test Example 24 Test Example 24 is a comparative example. As shown in Table 1, potassium metaborate (KBO) was used as a raw material. ２7.24 g of potassium fluoride (KF) 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. The K / B ratio of Test Example 24 was 1.19. The amount of aluminum (Al) powder was 1.00 g of potassium metaborate (KBO). ２ ) was 160% of the amount of substance. In the reaction step, the inside of the sealed container was heated to 522°C, hydrogen gas was introduced, and the mixture was stirred by the stirring means in the sealed container. The maximum partial pressure of hydrogen gas in the reaction step was 0.78 MPa. The minimum partial pressure of hydrogen gas in the reaction step was 0.68 MPa. In Test Example 24, a cleaning step was not performed. Through the above steps, the product of 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, potassium metaborate (KBO) was used as the main component. ２ As shown in Table 2 and FIG. 22, the product according to Test Example 24 contained potassium metaborate (KBO) as a component rated as A. ２ ) and aluminum (Al) were detected, and iota alumina (K) was detected as a component of the B grade. ０．６７ Al ６ O ９．３３ ) and potassium borohydride (KBH ４ ), potassium hexafluoroaluminate (K ３ AlF ６ From the results of Test Example 24, it can be seen that even when potassium is used instead of sodium as the alkali metal, iota alumina (K ０．６７ Al ６ O ９．３３ ) can be generated.

[0168] Test Example 25 Test Example 25 is an example. As shown in Table 1, potassium metaborate (KBO) was used as a raw material. ２ 7.24 g of potassium fluoride (KF) 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. The K / B ratio of Test Example 25 was 1.19. The amount of aluminum (Al) powder was 1.19. ２) was 160% of the amount of substance. In the reaction step, the inside of the sealed container was heated to 522°C, hydrogen gas was introduced, and the mixture was stirred by the stirring means in the sealed container. The maximum partial pressure of hydrogen gas in the reaction step was 0.78 MPa. The minimum partial pressure of hydrogen gas in the reaction step was 0.68 MPa. In Test Example 25, in the cleaning step, cleaning with pure water was performed at room temperature. Through the above steps, the product according to Test Example 25 was obtained.

[0169] In Test Example 25, iota alumina (K ０．６７ Al ６ O 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 Al ６ O ９．３３ ) was detected, and 14% by mass of potassium hexafluoroaluminate (K ３ AlF ６ ) and 15% by mass of aluminum hydroxide (Al(OH) ３ From the results of Test Example 25, even when potassium was used instead of sodium as the alkali metal, iota alumina (K ０．６７ Al ６ O ９．３３ ) can be generated.

[0170] Iota alumina (Na ０．６７ Al ６ O ９．３３ or K ０．６７ Al ６ O 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 production method. According to this method, sodium aluminum dioxide (NaAlO ２ ) is converted to iota alumina (Na ０．６７ Al ６ O ９．３３), and by heating inexpensive materials such as aluminum, sodium borates, and hydrogen gas, needle-shaped (whisker-shaped) iota alumina (Na ０．６７ Al ６ O ９．３３ ) into sodium borohydride (NaBH ４ ) can be produced together with inexpensive iota alumina (Na ０．６７ Al ６ O ９．３３ ) can be used as a raw material for producing beta alumina (β Alumina, β" Alumina). Also, iota alumina (Na ０．６７ Al ６ O ９．３３ or K ０．６７ Al ６ O ９．３３ ) can be used as a composite material to improve the strength of resins and metals.

[0171] 10A to 10D Sealed container 12, 12b Container body 14 Lid 16 Heater 18 O-ring 20 Motor 22 Stirring rod 22A Stirring bar 24 First pipe 26 Hydrogen gas supply valve 28 Exhaust valve 30 Second pipe 32 Pressure gauge 35 Scraper 36 Ribbon-shaped scraper 37 Wide paddle stirrer 51 Sodium borate powder 52 Aluminum powder 54 Fluoride powder 55 Sodium hydroxide powder 101 Aluminum particle 101a Aluminum particle surface 101b Aluminum oxide coating 101c Iota alumina (Na ０．６７ Al ６ O ９．３３ ) 102 Sodium metaborate (NaBO ２ ) 103 Sodium fluoride (NaF) 106 Sodium aluminum dioxide (NaAlO ２ ) 111 Sodium borohydride (NaBH ４ ) 112 Sodium hydride (NaH) 113 Sodium oxide (Na ２ O) 115 reactant layer (sodium borohydride (NaBH ４) 111, sodium hydride (NaH) 112) 117 Reducing substances (lower aluminum fluoride = AlF １．５ (Estimated)

Claims

1. A method for producing iota alumina, 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.

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 is 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. Iota alumina according to claim 8, characterized in that the average aspect ratio of the crystals of said iota alumina is 3 or more and 30 or less.