Method for producing boride particles

Abstract

To provide a new method for producing boride particles. [Solution] A raw material preparation step to obtain a raw material containing an alkaline earth metal element, which is an alkaline earth metal element in its elemental form or a compound of an alkaline earth metal element, boric acid, and a transition metal element-containing compound. A heating step to obtain a compound by heating the aforementioned raw materials in an inert gas atmosphere at a temperature of 600°C to 1200°C, A method for producing boride particles, comprising a washing step of washing the aforementioned product to recover the boride particles.

Description

[Technical Field]

[0001] This invention relates to a method for producing boride particles. [Background technology]

[0002] Boride particles have been conventionally used in thick-film resistance pastes and other applications, and by processing them into fine particles, they can be used as optical materials for solar radiation shielding. For this reason, methods for producing boride particles have been studied for some time.

[0003] A known method for producing boride particles involves synthesizing them by a solid-phase reaction method and then grinding them by a dry grinding method. A common method for grinding boride particles is to collide them with each other using a high-speed airflow, such as that of a jet mill. For example, lanthanum hexaboride is obtained by heating lanthanum oxide and boron oxide to a high temperature in the presence of carbon, and then grinding them using a dry grinding device. A method for finely grinding powders using a jet mill is disclosed, for example, in Patent Document 1. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2001-314776 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, conventional solid-phase reaction methods for producing boride particles require high-temperature heating, which results in larger boride particle sizes.

[0006] One aspect of the present invention is to provide a novel method for producing boride particles. [Means for solving the problem]

[0007] A method for producing boride particles according to one aspect of the present invention comprises a raw material preparation step of obtaining a raw material containing an alkaline earth metal element, which is an alkaline earth metal element in its elemental form or a compound of an alkaline earth metal element, boric acid, and a transition metal element-containing compound, A heating step in which the raw material is heated in an inert gas atmosphere at a temperature of 600°C to 1200°C to obtain the product, The process includes a washing step of washing the product to recover the boride particles. [Effects of the Invention]

[0008] According to one aspect of the present invention, a novel method for producing boride particles can be provided. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a flowchart of a method for producing boride particles according to one aspect of the present disclosure. [Figure 2] Figure 2 shows the X-ray diffraction patterns of the products after washing with water in Example 1 and Example 2. [Figure 3] Figure 3 shows the X-ray diffraction patterns of the products after hydrochloric acid washing and drying in Examples 1 and 2. [Figure 4] Figure 4 shows the X-ray diffraction pattern of the product after the heating step in Example 3. [Figure 5] Figure 5 shows the X-ray diffraction pattern of the product after hydrochloric acid washing and drying in Example 3. [Figure 6] Figure 6 shows the X-ray diffraction pattern of the product after hydrochloric acid washing and drying in Example 4. [Modes for carrying out the invention]

[0010] The embodiments for carrying out the present invention will be described below with reference to the drawings, but the present invention is not limited to the embodiments described below, and various modifications and substitutions can be made to the embodiments described below without departing from the scope of the present invention. [Method for producing boride particles] (1) Boride particles First, a configuration example of the boride particles obtained by the method for producing boride particles of the present embodiment will be described. (Composition) The boride particles can contain a boride which is a compound of boron and a transition metal element. The boride particles may be composed only of the compound of boron and the transition metal element, but this does not exclude the presence of unavoidable impurities even in such a case.

[0011] Examples of the transition metal element include elements existing between Group 3 elements and Group 12 elements in the periodic table. Examples of the transition metal element include Sc (scandium), Ti (titanium), V (vanadium), Cr (chromium), Mn (manganese), Fe (iron), Co (cobalt), Ni (nickel), Cu (copper), Zn (zinc), Y (yttrium), Zr (zirconium), Nb (niobium), Mo (molybdenum), Tc (technetium), Ru (ruthenium), Rh (rhodium), Pd (palladium), Ag (silver), Cd (cadmium), La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Pm (promethium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), Lu (lutetium), Hf (hafnium), Ta (tantalum), W (tungsten), Re (rhenium), Os (osmium), Ir (iridium), Pt (platinum), Au (gold), and Hg (mercury).

[0012] The boride may be a compound of boron and a rare earth element.

[0013] Examples of the rare earth element include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0014] The boride is, for example, represented by the general formula XB mcan be represented. X in the above general formula is a transition metal element, and B is boron. m is a number indicating the boron content in the general formula.

[0015] The element ratio (molar ratio) of boron (B) to the transition metal element (X), i.e., m (B / X), is not particularly limited, and may be 3.0 or more and 20.0 or less, may be 4.0 or more and 6.2 or less, or may be 5.8 or more and 6.2 or less.

[0016] Note that when boride particles are produced, the resulting powder containing the boride particles is not composed only of boride particles with a single composition, and may be particles containing borides of a plurality of compositions. Specifically, for example, XB₄, XB₆, XB 12 and the like can be particles of a mixture of borides.

[0017] Therefore, for example, when X-ray diffraction measurement is performed on hexaboride particles, which are typical boride particles, even if the analysis by X-ray diffraction shows a single phase, it is considered that a trace amount of other phases is actually contained.

[0018] For this reason, m in the general formula XB of borides m can be, for example, the atomic ratio of boron (B) to 1 atom of element X when a powder containing boride particles is chemically analyzed by ICP emission spectrometry (inductively coupled plasma emission spectrometry) or the like. (Average Particle Diameter) The average particle diameter of the boride particles is not particularly limited, but according to the method for producing boride particles of the present embodiment, the average particle diameter can be reduced as compared with the solid-phase synthesis methods conventionally used for producing boride particles.

[0019] The average particle diameter of the boride particles of the present embodiment may be, for example, 20 μm or more and 1000 μm or less.

[0020] In this specification, average particle size refers to volume-average particle size unless otherwise specified. Volume-average particle size is the average particle size weighted by particle volume, and is obtained by dividing the sum of the products of the diameter of each individual particle multiplied by its volume in a particle aggregate by the total volume of the particles. Volume-average particle size (MV) can be calculated, for example, using the particle size distribution measured by the laser diffraction scattering method using a laser diffraction particle size analyzer. (2) Method for producing boride particles The method for producing boride particles according to this embodiment may include a raw material preparation step S1, a heating step S2, and a washing step S3, as shown in the flow chart 10 of Figure 1.

[0021] The following describes each step. (2-1) Raw material preparation process In the raw material preparation process, a raw material can be obtained that contains an alkaline earth metal element, which is either an elemental alkaline earth metal element or a compound of an alkaline earth metal element, boric acid, and a transition metal element-containing compound.

[0022] The proportions of alkaline earth metal element-containing materials, boric acid, and transition metal element-containing compounds included in the raw materials are not particularly limited and can be selected according to the desired composition of the boride particles. The raw materials may further contain silicon-containing compounds. Furthermore, the raw materials may further contain one or more selected from alkali metal element chlorides and alkaline earth metal element chlorides.

[0023] In the raw material preparation process, each component contained in the raw material may be mixed to form a raw material mixture. In this case, the raw material preparation process can also be called a mixing process. Furthermore, each component contained in the raw material may be mixed all at once or in multiple stages. When using an alkaline earth metal element as the alkaline earth metal element-containing material, and when minimizing reaction with oxygen, etc., a first mixture may be obtained by mixing with other raw materials, and then the alkaline earth metal element-containing material may be added to the first mixture to obtain the desired raw material. Also, each component in the raw material does not need to be completely and uniformly mixed; for example, some components do not need to be mixed with other components.

[0024] The raw materials obtained in the raw material preparation process can be subjected to the heating process. At this stage, the raw materials may be in powder form or molded into pellets or the like. (Contains alkaline earth metal elements) Alkaline earth metal element-containing materials are thought to function primarily as reducing agents.

[0025] Alkaline earth metal element-containing materials may be individual alkaline earth metal elements or compounds such as hydrides. Alkaline earth metal element-containing materials may contain multiple types of substances, but may contain only one type of substance, considering workability and other factors.

[0026] In this specification, alkaline earth metal elements are used in a broad sense and include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

[0027] As mentioned above, the alkaline earth metal element-containing material may be the elemental form of the alkaline earth metal element, i.e., in its metallic state. In this case, the alkaline earth metal element may be one or more selected from magnesium, calcium, strontium, and barium. (Boric acid) Boric acid serves as the boron source for the resulting boride particles. It is thought to be reduced by alkaline earth metal elements and react with transition metal elements to produce borides. Boric acid may be one or more selected from H3BO3, the oxoacid of boron, and boron oxide (B2O3), which is boric anhydride. (Compounds containing transition metal elements) Compounds containing transition metal elements serve as a source of transition metal elements for the resulting boride particles.

[0028] The transition metal element may also be a rare earth element. In other words, the transition metal element-containing compound may also be a compound of a rare earth element.

[0029] The transition metal element-containing compound may be one or more selected from oxides, hydroxides, carbonates, and nitrates, and may also be one or more selected from oxides or hydroxides, depending on their availability and ease of handling. (Silicon-containing compounds) Silicon-containing compounds, after functioning as reducing agents, can form by-products with alkaline earth metal elements and other substances, creating compounds that can be removed during the washing process. Furthermore, silicon-containing compounds are thought to function as fluxes.

[0030] The silicon-containing compound may be one or more selected from silica, soda glass, borosilicate glass, and aluminosilicate glass, or one or more selected from silica and soda glass.

[0031] Since silicon-containing compounds are optional additives, they do not need to be added to the raw materials. Adding silicon-containing compounds can form by-products that can be removed in the washing process. However, since by-products produced by the reaction with silicon-containing compounds may be highly reactive with water, if by-products that can be removed in the washing process can be obtained without adding silicon-containing compounds, then it is not necessary to add them. By not adding silicon-containing compounds, the workability of the washing process can be improved. (Chlorides of alkali metal elements, chlorides of alkaline earth metal elements) The raw materials may further contain one or more chlorides selected from alkali metal elements and alkaline earth metal elements. The alkali metal elements and alkaline earth metal elements dissolve in the grain boundaries of the boride and refine the crystallite size, thus shortening the grinding time in the grinding process.

[0032] Alkali metal chlorides and alkaline earth metal chlorides are optional additives and therefore do not need to be added to the raw materials.

[0033] Alkaline earth metal element chlorides may, at least partially, function as alkaline earth metal element-containing materials. In this case, the amount added may be selected considering the proportion that functions as an alkaline earth metal element-containing material. The alkaline earth metal element-containing material may be a compound other than chloride, so as to be distinguishable from alkaline earth metal element chlorides.

[0034] In this specification, alkali metal elements include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). Alkaline earth metal elements have already been described and will therefore not be explained here. (2-2) Heating process In the heating process, the raw materials obtained in the raw material preparation process are heated at a temperature of 600°C to 1200°C under an inert gas atmosphere to obtain the product.

[0035] The raw materials obtained in the raw material preparation process can be supplied to the heating process. The raw materials may be sealed with an inert gas in a container such as a metal tube or a quartz tube before being subjected to the heating process, or they may be supplied to a heating furnace capable of atmosphere control.

[0036] Therefore, the atmosphere during the heating process may be the atmosphere inside the glove box used when sealing the raw materials in metal tubes, or it may be an atmosphere controlled by a heating furnace.

[0037] The atmosphere during the heating process may be, for example, an inert gas atmosphere.

[0038] The inert gas may be nitrogen, or it may be a noble gas such as argon or helium.

[0039] In the heating process, the temperature can be raised from room temperature to a heating temperature of 600°C to 1200°C. The heating temperature may also be between 700°C and 1100°C.

[0040] Heating to over 600°C can promote the formation of boride particles. Conversely, heating to below 1200°C can prevent the formation of unintended by-products.

[0041] The holding time at the heating temperature is not particularly limited and can be selected according to the amount of raw materials, etc., but it may be, for example, 0.5 hours or more and 12 hours or less, or 1 hour or more and 10 hours or less.

[0042] After being held at the heating temperature, it can be cooled to room temperature.

[0043] During the heating process, it is presumed that, for example, some or all of the raw materials melt, and boron, which is reduced by alkaline earth metal elements in the melt, reacts with transition metals to produce boride particles.

[0044] We will explain the reactions that are thought to proceed in the heating process, using as examples the cases where boron oxide (B2O3) is used as the raw material for boric acid, metallic calcium (Ca) for alkaline earth metal element-containing materials, and lanthanum oxide (La2O3) for transition metal element-containing compounds.

[0045] When the above raw materials are used, B2O3 melts the fastest among the raw materials when the temperature is raised, with a melting point of 450°C. During the heating process, it is thought that the reaction proceeds with the molten B2O3 permeating the solid powder La2O3 and metallic Ca until the temperature reaches 842°C, when Ca melts next.

[0046] Accordingly, when the standard free energy change ΔG of the main chemical reactions expected at 500°C in the heating step 0 is calculated, the results are as shown in (A), (B), (C), and (D) below. (A)6Ca+La2O3→2La+3CaO : ΔG 0 =-17kJ (B)3Ca+B2O3→3CaO+2B : ΔG 0 =-667kJ (C)La+6B→LaB6: ΔG 0 =-271kJ (D)La2O3+6B2O3+21Ca→2LaB6+21CaO : ΔG 0 =-4409kJ Furthermore, when the raw material contains one or more selected from chlorides of alkali metal elements and chlorides of alkaline earth metal elements, for example, containing CaCl2, the reaction (E) is also considered to proceed. (E)La2O3+6B2O3+21Ca+CaCl2→2LaB6+21CaO+CaCl2: ΔG 0 =-4409kJ

[0047] All the reactions (A), (B), (C), (D), and (E) have ΔG<0 and thus are possible in terms of equilibrium, but the reactions (A), (B), and (C), which respectively reduce the raw materials to form hexaborides, have relatively small energy changes and do not proceed very easily. In the reaction (E), calcium chloride does not contribute to the synthesis reaction of the boride, and is considered to be incorporated as it is in the grain boundaries of the boride.

[0048] Thermodynamically, since the absolute value of ΔG of the reaction (D), which directly involves the boron source and the lanthanum source raw material at the same time, 0 is overwhelmingly larger than that of the other reactions (A) to (C), it is considered that the reaction (D) proceeds to generate LaB6. Here, since the progress of the reaction is governed by the diffusion rate of the constituent elements, it is preferable to perform heating at 600°C or higher. (2-3) Washing Step In the washing step, the product obtained in the heating step can be washed to recover boride particles.

[0049] The product obtained in the heating step may also include one or more by-products selected from, for example, hydroxides of alkaline earth metal elements, oxides of alkaline earth metal elements, composite compounds of alkaline earth metal elements and silicon, chlorides of alkali metal elements, and chlorides of alkaline earth metal elements. Examples of composite compounds of alkaline earth metal elements and silicon include composite oxides of alkaline earth metal elements and silicon. Furthermore, if the raw materials do not contain silicon-containing compounds, the product does not have to contain composite compounds of alkaline earth metal elements and silicon. If the raw materials do not contain chlorides of alkali metal elements or chlorides of alkaline earth metal elements, the product does not have to contain chlorides of alkali metal elements or chlorides of alkaline earth metal elements.

[0050] Therefore, in the washing process, an inorganic acid may be used as the washing solution to wash the product and remove by-products.

[0051] As inorganic acids, hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, etc., can be used. For example, by identifying by-products contained in the product using powder X-ray diffraction, then selecting an inorganic acid according to the by-products and washing with the selected inorganic acid may be performed. Hydrochloric acid may also be used as the inorganic acid due to its availability and ease of handling.

[0052] In the cleaning process, cleaning may be performed using water or hot water as the cleaning solution, or using alcohol as the cleaning solution. Furthermore, multiple cleanings may be performed using different types of cleaning solutions.

[0053] After washing in the washing process, the recovered boride particles may be dried as needed (drying process).

[0054] Drying may be carried out by one or more methods selected from stationary drying, airflow drying, rotary kiln, roller hearth kiln, microwave heating, vacuum drying, etc. Furthermore, the recovered boride particles may be dried using multiple drying methods, such as airflow drying and stationary drying.

[0055] The atmosphere used for drying is not particularly limited and can be selected from any of the following: an air atmosphere, a vacuum atmosphere, etc.

[0056] After drying, the boride particles may exhibit aggregation or slight sintering. In such cases, they may be crushed.

[0057] Disintegration is the process of applying mechanical energy to an aggregate composed of multiple granular materials to separate the aggregated granular materials without significantly destroying the granular materials themselves, thereby loosening the aggregate.

[0058] According to the boride particle manufacturing method of this embodiment described above, boride particles can be manufactured at low temperatures of approximately 600°C to 1200°C, and boride particles with small particle sizes can also be manufactured. [Examples]

[0059] The present invention will be described more specifically below with reference to examples, but the present invention is not limited thereto. 1. Evaluation Method (1) Phase identification The X-ray diffraction patterns of the product were measured. The X-ray diffraction patterns were measured using powder X-ray diffraction (θ-2θ method) with a powder X-ray diffractometer (X'Pert-PRO / MPD, manufactured by PANalytical, Spectris Corporation). Phase identification was performed from the obtained X-ray diffraction patterns, and the components contained in the product after washing with water or hydrochloric acid were identified. 2. Regarding each example [Example 1] Lanthanum boride particles were produced according to Flow 10 shown in Figure 1. (1) Raw material preparation process 1.477 g of metallic calcium (manufactured by Mintec Japan) was weighed as an alkaline earth metal element-containing substance.

[0060] 0.976 g of silica (manufactured by Fujifilm Wako Pure Chemical Industries) was weighed out as a silicon-containing compound.

[0061] 0.308 g of boron oxide (manufactured by Shin-Nippon Denko Co., Ltd.) was weighed out as boric acid.

[0062] As a transition metal element-containing compound, 0.241 g of lanthanum oxide (manufactured by Nikki Co., Ltd.) was weighed out.

[0063] Then, the weighed alkaline earth metal element-containing material, silicon-containing compound, boric acid, and transition metal element-containing compound were placed in a mortar and ground and mixed with a pestle.

[0064] The raw materials, which are crushed and mixed into a powder, were put into a tablet mold and pressed to form a compacted powder. (2)Heating process The compressed powder raw material prepared in the raw material preparation process was placed into an iron crucible, and the crucible containing the raw material was placed in a high-frequency furnace. Furthermore, the furnace was depressurized to a vacuum, the interior was replaced with argon gas, and the temperature was raised to 1000°C under an inert gas atmosphere, and then held at 1000°C for 10 hours.

[0065] After the holding time at 1000°C was complete, the furnace temperature was cooled to room temperature and the crucible was removed. (3) Washing process The crucible was immersed in pure water, and unreacted metallic calcium was removed by oxidizing it to calcium oxide and calcium hydroxide. Furthermore, the water containing dissolved calcium hydroxide and calcium oxide was replaced, and the crucible was washed multiple times.

[0066] Figure 2 shows the X-ray diffraction pattern of the product after washing with water. As shown in Figure 2, it was confirmed that the product contains not only the target product, lanthanum hexaboride (LaB6), but also CaO, Ca(OH)2, and CaSiO3.

[0067] Subsequently, the washed product was filtered and separated, and the water-insoluble calcium metasilicate (CaSiO3) contained in the separated product was washed with an inorganic acid, hydrochloric acid.

[0068] After washing and drying, the X-ray diffraction pattern was measured. As shown in Figure 3, almost no by-product peaks were observed, confirming that high-purity lanthanum hexaboride particles were obtained. [Example 2] In the raw material preparation process, 0.976 g of soda glass was weighed and used as the silicon-containing compound instead of silica.

[0069] Except for the points mentioned above, boride particles were manufactured under the same conditions and procedures as in Example 1.

[0070] Figure 2 shows the X-ray diffraction pattern of the product after washing with water, and Figure 3 shows the X-ray diffraction pattern of the product after washing with hydrochloric acid and drying.

[0071] After washing with water and after washing with hydrochloric acid, the product was found to exhibit almost the same X-ray diffraction pattern as in Example 1. Furthermore, it was confirmed that high-purity lanthanum hexaboride particles were obtained after washing with hydrochloric acid. [Example 3] (1) Raw material preparation process In the raw material preparation process, 0.862 g of metallic calcium (manufactured by Mintec Japan) was weighed as an alkaline earth metal element-containing material.

[0072] 0.359 g of boron oxide (manufactured by Shin-Nippon Denko Co., Ltd.) was weighed out as boric acid.

[0073] As a transition metal element-containing material, 0.280 g of lanthanum oxide (manufactured by Nikki Co., Ltd.) was weighed out.

[0074] Then, the weighed alkaline earth metal element-containing material, boric acid, and transition metal element-containing compound were placed in a mortar and ground and mixed with a pestle. In this example, silicon-containing compounds were not added to the raw materials.

[0075] The raw materials, which are crushed and mixed into a powder, were put into a tablet mold and pressed to form a compacted powder. (2)Heating process The compressed powder, which was prepared in the raw material preparation process, was placed into an iron crucible, and the crucible containing the raw material was placed in a high-frequency furnace. Furthermore, the furnace was depressurized to a vacuum, the interior was replaced with argon gas, and the temperature was raised to 1000°C under an inert gas atmosphere, and then held at 1000°C for 4 hours.

[0076] After the holding time at 1000°C was complete, the furnace temperature was cooled to room temperature and the crucible was removed. Figure 4 shows the X-ray diffraction pattern of the product immediately after synthesis. As shown in Figure 4, it was confirmed that the product contains CaO in addition to the target compound, lanthanum hexaboride (LaB6). (3) Washing process The crucible was immersed in pure water, and unreacted metallic calcium was removed by oxidizing it to calcium oxide and calcium hydroxide. Furthermore, the water containing dissolved calcium hydroxide and calcium oxide was replaced, and the crucible was washed multiple times.

[0077] Subsequently, the washed product was filtered and separated, and the Ca(OH)2 contained in the separated product was washed with hydrochloric acid, an inorganic acid.

[0078] After washing and drying, the X-ray diffraction pattern was measured. As shown in Figure 5, although a peak for LaB4 was observed as a byproduct, it was confirmed that high-purity lanthanum hexaboride particles were obtained. [Example 4] (1) Raw material preparation process In the raw material preparation process, the raw material preparation process, heating process, and washing process were carried out under the same conditions and procedures as in Example 3, except that 0.028 g of calcium chloride was added as an alkaline earth metal element chloride.

[0079] After washing and drying, the X-ray diffraction pattern was measured. As shown in Figure 6, although a peak of LaB4 was observed as a byproduct, it was confirmed that high-purity lanthanum hexaboride particles were obtained. Furthermore, the dried material disintegrated even when simply poked with a spatula, confirming that a powder that easily disintegrates, meaning that the particle size and crystallite size can be easily reduced, was obtained.

[0080] Examples of embodiments of the present disclosure are as follows:

[0081] <1> A raw material preparation step to obtain a raw material containing an alkaline earth metal element, which is either an elemental alkaline earth metal element or a compound of an alkaline earth metal element, boric acid, and a transition metal element-containing compound. A heating step in which the raw material is heated in an inert gas atmosphere at a temperature of 600°C to 1200°C to obtain the product, A method for producing boride particles, comprising a washing step of washing the aforementioned product to recover the boride particles.

[0082] <2> The aforementioned raw material includes a silicon-containing compound. <1> A method for producing boride particles as described above.

[0083] <3> The silicon-containing compound is one or more selected from silica and soda glass. <2> A method for producing boride particles as described above.

[0084] <4> The alkaline earth metal element-containing material is the alkaline earth metal element in its elemental form. The aforementioned alkaline earth metal element is one or more selected from magnesium, calcium, strontium, and barium. <1> from <3> A method for producing boride particles as described in any of the above.

[0085] <5> The transition metal element-containing compound is one or more selected from oxides, hydroxides, carbonates, and nitrates. <1> from <4> A method for producing boride particles as described in any of the above.

[0086] <6> The aforementioned transition metal element-containing compound is a rare earth element compound. <1> from <5> A method for producing boride particles as described in any of the above.

[0087] <7> The aforementioned raw material further comprises one or more selected from alkali metal element chlorides and alkaline earth metal element chlorides. <1> from <6> A method for producing boride particles as described in any one of the items.

[0088] <8> The product comprises one or more selected from the hydroxide of the alkaline earth metal element, the oxide of the alkaline earth metal element, a composite compound of the alkaline earth metal element and silicon, a chloride of the alkali metal element, and a chloride of the alkaline earth metal element. <1> from <7> A method for producing boride particles as described in any of the above. [Explanation of symbols]

[0089] 10 Flow S1 Raw material preparation process S2 heating process S3 Cleaning process

Claims

1. A raw material preparation step to obtain a raw material containing an alkaline earth metal element, which is either an elemental alkaline earth metal element or a compound of an alkaline earth metal element, boric acid, and a transition metal element-containing compound. A heating step in which the raw material is heated in an inert gas atmosphere at a temperature of 600°C to 1200°C to obtain a product, A method for producing boride particles, comprising a washing step of washing the aforementioned product to recover the boride particles.

2. The method for producing boride particles according to claim 1, wherein the raw material includes a silicon-containing compound.

3. The method for producing boride particles according to claim 2, wherein the silicon-containing compound is one or more selected from silica and soda glass.

4. The alkaline earth metal element-containing material is the alkaline earth metal element in its elemental form. A method for producing boride particles according to any one of claims 1 to 3, wherein the alkaline earth metal element is one or more selected from magnesium, calcium, strontium, and barium.

5. A method for producing boride particles according to any one of claims 1 to 3, wherein the transition metal element-containing compound is one or more selected from oxides, hydroxides, carbonates, and nitrates.

6. A method for producing boride particles according to any one of claims 1 to 3, wherein the transition metal element-containing compound is a rare earth element compound.

7. The method for producing boride particles according to any one of claims 1 to 3, wherein the raw material further comprises one or more selected from alkali metal element chlorides and alkaline earth metal element chlorides.

8. A method for producing boride particles according to any one of claims 1 to 3, wherein the product comprises one or more selected from the hydroxide of the alkaline earth metal element, the oxide of the alkaline earth metal element, a composite compound of the alkaline earth metal element and silicon, a chloride of the alkali metal element, and a chloride of the alkaline earth metal element.

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