Method for producing metal boride

Abstract

This method for producing a metal boride comprises preparing: a first unheated raw material containing a metal source that is a metal, a metal oxide, a metal-containing carbonate or a metal-containing hydroxide, boron oxide or boric acid, silicon dioxide, and metallic sodium; or a second unheated raw material containing the metal source, boron oxide or boric acid, and silicon dioxide. Further, this method for producing a metal boride further comprises: heating the first unheated raw material if the first unheated raw material has been prepared; and heating the second unheated raw material in Na vapor if the second unheated raw material has been prepared.

Description

Method for producing metal borides

[0001] The present disclosure relates to methods for producing metal borides.

[0002] Metal borides have high hardness, high melting points, and excellent electrical conductivity, and are used as various functional materials. For example, TiB ２ is used as an ultra-hard material (e.g. for polishing and grinding), corrosion-resistant material, evaporation boat, etc., and ZrB ２ is used as heat-resistant ceramics, fire-resistant materials, and super-hard materials, and WB ２ is used for wear resistance and corrosion resistance, and LaB ６ are used as cathode materials, heat shielding materials, etc. There are also various other engineering ceramics.

[0003] Patent Document 1 discloses a method for producing lanthanum boride. ２ O ３ ), boron oxide (B ２ 0 ３ ) powder with calcium hydride (CaH ２ ) was added and heated to 600°C or higher in a hydrogen atmosphere to reduce lanthanum oxide and boron oxide and simultaneously react to form LaB ６ It is disclosed to produce

[0004] Patent Document 2 discloses a method for growing lanthanum hexaboride single crystals by a floating zone method, in which a melting zone composition B / La (atomic ratio) is set to 6 to 60 and a growth rate is set to 1 to 10 cm / hr, thereby growing large, high-quality lanthanum hexaboride single crystals.

[0005] Japanese Patent Application Publication No. 01-320216 Publication No. 08-143395

[0006] In the method of Patent Document 1, the reactant contains CaO and unreacted CaH ２ The reaction mixture was left in humid air for about 3 days to remove CaO and CaH ２ The calcium content is dissolved in a dilute acetic acid solution, and the residue is treated with LaB ６This is then separated using filter paper. Therefore, it takes time and effort to obtain the target substance, metal boride. The method of Patent Document 2 requires heating at approximately 1800°C, and the floating zone method requires a relatively complicated device to grow a single crystal, which results in high costs. There has been a demand for an easy and inexpensive method for producing metal borides.

[0007] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a method for producing a metal boride easily and inexpensively.

[0008] The method for producing a metal boride according to the present disclosure includes preparing a pre-heating raw material containing a metal source, which is a metal, a metal oxide, a carbonate containing a metal, or a hydroxide containing a metal, boron oxide or boric acid, silicon dioxide, and metallic sodium, and heating the pre-heating raw material. This method enables production of metal borides at temperatures significantly lower than 1800°C and allows the use of inexpensive materials such as silicon dioxide. In another aspect, the method for producing a metal boride according to the present disclosure includes preparing a pre-heating raw material containing a metal source, which is a metal, a metal oxide, a carbonate containing a metal, or a hydroxide containing a metal, boron oxide or boric acid, and silicon dioxide, and heating the pre-heating raw material in sodium vapor. This method allows for immediate water washing after heating, eliminating the need to remove excess sodium. Furthermore, for example, the crucible can be reused.

[0009] Other features of the present disclosure will become apparent below.

[0010] Metal borides can be produced in an easy and inexpensive manner.

[0011] 1 is an example of a flowchart of a method for producing a metal boride; 2 is a result of X-ray diffraction of powders obtained at different heating temperatures; 3 is a result of X-ray diffraction of a sample before and after water washing after removing Na; ２ 1 shows SEM photographs of the powder obtained above and the results of composition analysis by EDX. 2 shows the results of X-ray diffraction of powders obtained after different heating times. ２ O ３1 shows the results of X-ray diffraction of powders obtained from raw materials with different composition ratios of Ta and Na. ２ O ５ 1 shows the results of X-ray diffraction of a material obtained using TiB. 2 shows the results of X-ray diffraction of a material obtained using TiB as the raw material before heating. ２ 1 shows an SEM photograph of the above and the results of composition analysis by EDX. 2 shows the results of X-ray diffraction of a material obtained by using Nb as the raw material before heating. 3 shows the results of X-ray diffraction of a material obtained by using Zr as the raw material before heating. ２ Before heating, the raw material was ZrO ２ 1 shows the results of X-ray diffraction of a material obtained using WO as the raw material before heating. ３ This is the result of X-ray diffraction of the material obtained using La. ２ O ３ 1 is a result of X-ray diffraction of a material obtained using the method of the present invention. 2 is a flowchart showing a method for manufacturing a metal boride according to a second embodiment. 3 is a result of X-ray diffraction measurement of Example A. 4 is a result of X-ray diffraction measurement of Example B. 5 is a result of X-ray diffraction measurement of Example C-1. 6 is a result of X-ray diffraction measurement of Example C-2. 7 is a result of X-ray diffraction measurement of Example C-3. 8 is a result of X-ray diffraction measurement of Example C-3'. 9 is a result of X-ray diffraction measurement of Example D-1. 10 is a result of X-ray diffraction measurement of Example D-2. 11 is a flow chart showing a method for manufacturing a metal boride according to a second embodiment. 12 is a flow chart showing a method for manufacturing a metal boride according to a second embodiment. 13 is a flow chart showing a method for manufacturing a metal boride according to a second embodiment. 14 is a flow chart showing a method for manufacturing a metal boride according to a second embodiment. 15 is a flow chart showing a method for manufacturing a metal boride according to a second embodiment. 16 is a flow chart showing a method for manufacturing a metal boride according to a second embodiment. 17 is a flow chart showing a method for manufacturing a metal boride according to a second embodiment. 18 is a flow chart showing a method for manufacturing a metal boride according to a second embodiment. 19 is a flow chart showing a method for manufacturing a metal boride according to a third embodiment. 20 is a flow chart showing a method for manufacturing a metal boride according to a third embodiment. 21 is a flow chart showing a method for manufacturing a metal boride according to a third embodiment. 22 is a flow chart showing a method for manufacturing a metal boride according to a third embodiment. 23 is a flow chart showing a method for manufacturing a metal boride according to a third embodiment. 24 is a flow chart showing a method for manufacturing a metal boride according to a third embodiment. 25 is a flow chart showing a method for manufacturing a metal boride according to a third embodiment. 26 is a ２ 1 is a SEM photograph of the X-ray diffraction measurement result of Example E-1. 2 is a result of X-ray diffraction measurement of Example E-2. 3 is a result of X-ray diffraction measurement of Example E-3. 4 is a result of X-ray diffraction measurement of Example F. 5 is a result of X-ray diffraction measurement of Example G. 6 is a result of X-ray diffraction measurement of Example H. ６ 1 shows an SEM photograph of the X-ray diffraction measurement result of Example I-1. 2 shows an X-ray diffraction measurement result of Example I-2. 3 shows an X-ray diffraction measurement result of Example I-3. CeB ６1-3 shows an SEM photograph of the metal boride obtained. 1-4 shows the results of X-ray diffraction measurement in Example I-4. 1-5 shows an SEM photograph of the metal boride obtained. 1-6 shows an SEM photograph of the metal boride obtained. 1-7 shows the results of X-ray diffraction measurement in Example I-7. ６ 1 is a SEM photograph of the result of X-ray diffraction measurement of Example I-8. 2 is a flowchart showing a method for producing a metal boride according to the third embodiment. 3 is a flowchart showing a result of X-ray diffraction measurement of Example J-0. ６ 1 shows an SEM photograph of the LaB. 2 shows the results of X-ray diffraction measurement of Example J-0'. 3 shows the results of X-ray diffraction measurement of Example J-1. ６ 1 is a SEM photograph of Example J-1; 2 is a result of X-ray diffraction measurement of Example J-2; 3 is a result of X-ray diffraction measurement of Example J-3; 4 is a result of X-ray diffraction measurement of Example J-3′.

[0012] Embodiment 1. FIG. 1 is a flowchart showing a method for producing a metal boride according to an embodiment. In step S10, a pre-heating raw material containing a metal or metal oxide, boron oxide, silicon dioxide, and metallic sodium is prepared as raw materials for producing a metal boride. According to one example, the metal contained in the metal or metal oxide is a transition metal of Groups 3 to 6 of the periodic table. In this case, the metal or metal oxide is a transition metal of Groups 3 to 6 or an oxide of any of these. According to another example, the metal contained in the metal or metal oxide is a rare earth element. In this case, the metal or metal oxide is a rare earth element or an oxide of any of these. According to another example, the metal contained in the metal or metal oxide is a transition element of Groups 4 to 6 of Periods 4, 5, or 6 of the periodic table. In this case, the metal or metal oxide is Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, or an oxide of any of these. According to another example, the metal or metal oxide may be Ta, Ti, Zr, Nb, W, La or an oxide of any of these.

[0013] According to one example, the boron oxide contained in the raw material before heating is B ２ O ３The above metals or metal oxides, boron oxide, and silicon dioxide (SiO ２ ) and metallic sodium (Na). The pre-heating raw material can be provided in various ways. According to one example, the pre-heating raw material is prepared by first placing a metal or metal oxide, boron oxide, and silicon dioxide in a crucible, and then placing a block of metallic sodium in the crucible. According to another example, the pre-heating raw material is prepared by first placing a powder compact (pellet) containing boron oxide and silicon dioxide and a metal or metal oxide in a crucible, and then placing metallic sodium in the crucible. According to another example, the pre-heating raw material is prepared by mixing raw material powder containing a metal or metal oxide, boron oxide, silicon dioxide, and metallic sodium in a mortar or the like. In any example, the raw materials may be mixed at any stage of preparation of the pre-heating raw material, or mixing of the raw materials may be omitted. Even if the raw materials are not mixed, a certain degree of reaction can be achieved by heating because the melting point of Na is low, about 100°C. Note that the manner of providing the pre-heating raw material is not limited to these, and any method can be adopted.

[0014] Next, the process proceeds to step S12. In step S12, the raw material prepared in step S10 is heated to, for example, 800°C or higher. In another example, the raw material is heated to, for example, 1100°C or higher. The heating time is, for example, 2 hours or more. In one example, the raw material placed in a crucible is heated by a known heating method. The crucible is made of, for example, BN, but other materials may also be used.

[0015] This heat treatment removes Na ２ SiO ３ and metal borides are produced. ２ SiO ３ Since B is a stable compound that is easy to synthesize, it is thought that as sodium silicate is produced, boron oxide is reduced to produce a product in which boron is the main component. The reaction mechanism is summarized as follows: ２ O ３ +3SiO ２ +6Na → 3Na ２ SiO ３+2B ... (Equation 1) In this embodiment, a metal or metal oxide is added to the left side of chemical reaction equation 1, so that B on the right side of equation 1 reacts with the metal or metal oxide to produce a metal boride. Note that when a metal oxide is used as a raw material, the oxygen in the metal oxide can be used as a raw material for sodium silicate.

[0016] According to one example, when Ta is used as the metal or metal oxide, the expected reaction formula is as follows: Ta + B ２ O ３ +3SiO ２ +6Na → TaB ２ +3Na ２ SiO ３ ... (Equation 2) For this reaction formula, the free energy change ΔG at 1027° C. was a large negative value of −581 kJ / mol.

[0017] According to another example, Ta as a metal or metal oxide ２ O ５ The expected reaction formula when Ta is used is as follows: ２ O ５ +2B ２ O ３ +11SiO ２ +22Na → 2TaB ２ +11Na ２ SiO ３　・・・ (Equation 3) For this reaction formula, the free energy change ΔG at 1027° C. was a large negative value of −1912 kJ / mol.

[0018] The reason why the free energy change in the reaction equations of Equation 2 and Equation 3 is a large negative value is because sodium silicate (Na ２ SiO ３ This is because borides are very stable and have a large negative energy of formation. Metal borides can also be synthesized using the above-mentioned metals or metal oxides as raw materials.

[0019] Next, the process proceeds to step S14. Step S14 is a step for removing residual Na. In step S14, for example, heating under reduced pressure or injecting ethanol is performed. When the material in the crucible is heated under reduced pressure, Na evaporates or sublimes outside the crucible. When ethanol is injected into the crucible, Na becomes sodium alkoxide, which can be removed by rinsing with water. Note that the water rinsing process washes away Na and simultaneously washes away sodium silicate. Therefore, if ethanol is injected and water rinsing is performed, the water rinsing process in step S16 can be omitted. Since step S14 is a step for removing Na, it can be omitted if there is no residual Na or if the amount of residual Na is negligible.

[0020] Next, the process proceeds to step S16. In step S16, a water washing process is carried out. ２ SiO ３ ) is water-soluble, so when the sodium silicate and metal boride synthesized in step S12 are treated with water, sodium silicate (Na ２ SiO ３ ) can be washed away with water to extract the metal boride. Therefore, the theoretical yield of metal boride is 100%. Furthermore, aqueous solutions of sodium silicate have high viscosity and can be used as water glass. Water glass is the sodium salt of metasilicic acid. For example, water glass can be reacted with a material that reacts with water glass to produce a strong solidified product, which can be used for civil engineering purposes.

[0021] According to the above-described embodiment, metal borides can be produced at a relatively low temperature of 800°C or higher. This eliminates the need for expensive production equipment that can withstand high-temperature treatment, and also reduces energy consumption. In addition, the reaction uses inexpensive materials such as boron oxide and SiO ２ Furthermore, as mentioned above, boron oxide, metal or metal oxide, SiO ２ A metal boride can be easily obtained by simply preparing a raw material containing Na and Na before heating and heating it.

[0022] Example 1B ２ O ３ , SiO ２, Na, Ta as raw materials ２ The molar ratio of the raw materials before heating was B ２ O ３ : SiO ２ :Na:Ta=1:3:10:0.25. ２ O ３ and SiO ２ Ta powder was added to the mixed powder compact, and a block of Na was added to prepare a raw material before heating. Four BN crucibles containing this raw material before heating were prepared, and each was heated from room temperature to 800°C, 900°C, 1000°C, and 1100°C over a period of 4 hours, and heated at these temperatures for 10 hours. Figure 2 shows the results of X-ray diffraction measurement of the powder obtained after heating, removing Na, and washing with water. TaB was extracted from the powder heated at 800°C for 10 hours. ２ A diffraction peak corresponding to that of TaB was observed. ２ was synthesized in the main phase, and BN was produced as a by-product.

[0023] FIG. 3 shows the results of X-ray diffraction measurements of powder before and after water washing when heated at 1100°C for 10 hours. The upper part of FIG. 3 shows the results of X-ray diffraction measurements of the material from which Na was removed after heating, and the lower part shows the results of X-ray diffraction measurements of the material after water washing. From the waveform in the upper part of FIG. 3, it can be seen that sodium silicate (Na ２ SiO ３ ) was generated. The waveform in the lower part of Figure 3 shows that sodium silicate was washed away by the water washing treatment, and TaB ２ It was found that it was possible to extract

[0024] FIG. 4A shows the TaB obtained by heating the above-mentioned raw material before heating at 1100° C. for 10 hours, removing Na, and then washing it with water. ２ This is an SEM photograph of TaB ２ It was found that TaB has a small grain size of 1 μm or less. ２ The average particle size of the primary particles of TaB in FIG. ２1 is a diagram showing the results of a composition analysis by energy dispersive X-ray spectroscopy (EDX) of 1. It was confirmed that the Ta to B ratio was approximately 1:2, which indicates that the composition was nearly stoichiometric.

[0025] Example 2B ２ O ３ , SiO ２ , Na, Ta as raw materials ２ The molar ratio of the raw materials before heating was B ２ O ３ : SiO ２ :Na:Ta=1:3:10:0.25. ２ O ３ and SiO ２ Ta powder was added to the mixed powder compact, and a block of Na was added to prepare a raw material before heating. Four BN crucibles containing this raw material before heating were prepared, and the temperature was raised from room temperature to 1100°C over 4 hours, and the materials were heated at this temperature for 1 hour, 2 hours, 4 hours, and 10 hours, respectively. Figure 5 shows the results of X-ray diffraction measurement of the powder obtained after heating, removing Na, and washing with water. TaB was extracted from the powder heated at 1100°C for 2 hours. ２ A peak corresponding to the diffraction peak of TaB was observed, and even with such a heating time of 2 hours, ２ It was found that it can be synthesized as the main phase.

[0026] Example 3B ２ O ３ , SiO ２ , Na, Ta as raw materials ２ The molar ratio of the raw materials before heating was B ２ O ３ : SiO ２ : Na:Ta = x: 3: 10: 0.25. ２ O ３ and SiO ２Ta powder was added to the mixed powder compact, and a block of Na was added to prepare a pre-heating raw material. Four pre-heating raw materials were prepared, with the respective x values ​​being x = 0.25, x = 0.5, x = 1, and x = 2. These four types of pre-heating raw materials were each placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 6 shows the results of X-ray diffraction measurement of the powder obtained after heating, removing Na, and washing with water. B ２ O ３ By setting the composition ratio x to 0.25, a small amount of B ２ O ３ When the raw material before heating having the above structure is heated, TaB ２ A peak was observed that coincided with the diffraction peak of ２ O ３ But TaB ２ It was found that it is possible to synthesize B ２ O ３ When the raw material before heating is heated with the composition ratio x increased to 0.5, 1, and 2, TaB ２ A large diffraction peak of B was observed. ２ O ３ When the raw material before heating with a composition ratio x of 1 is heated, TaB ２ was synthesized as the main phase, and BN was found to be a by-product.

[0027] Example 4B ２ O ３ , SiO ２ , Na, Ta as raw materials ２ The molar ratio of the raw materials before heating was B ２ O ３ : SiO ２ :Na:Ta=1:3:x:0.25. ２ O ３ and SiO ２Ta powder was added to the mixed powder compact, and a block of Na was added to prepare a pre-heating raw material. Four pre-heating raw materials were prepared, with the respective values ​​of x being x = 3, x = 6, x = 8, and x = 10. These four types of pre-heating raw materials were each placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 7 shows the results of X-ray diffraction measurement of the powder obtained after heating, removing Na, and washing with water. From the results of this X-ray diffraction measurement, it was found that by setting x = 3, when a small amount of Na is used in the pre-heating raw material, TaB ２ On the other hand, when the molar ratio of Na contained in the raw material before heating is increased by setting x = 6, x = 8, or x = 10, TaB ２ Therefore, it was found that metallic sodium can be synthesized with boron oxide (B ２ O ３ ) in the amount of 6 times or more moles of TaB ２ It was found that it can be synthesized.

[0028] Example 5B ２ O ３ , SiO ２ , Na, Ta ２ O ５ TaB ２ The molar ratio of the raw materials before heating was B ２ O ３ : SiO ２ :Na:Ta ２ O ５ = 1:3:10:0.125. ２ O ３ and SiO ２ The mixed powder compact of Ta ２ O ５ A BN crucible was used to prepare a pre-heating raw material. The pre-heating raw material was heated from room temperature to 1100°C over 4 hours, and then heated at this temperature for 10 hours. Figure 8 shows the results of X-ray diffraction analysis of the powder obtained after heating, removing Na, and washing with water. The results of this X-ray diffraction analysis indicate that the metal oxide Ta ２ O ５ By using TaB as the raw material before heating ２ It was found that it is possible to synthesize Ta２ O ５ is a cheaper material than Ta, so Ta ２ O ５ The use of TaB can reduce the manufacturing cost. ２ It was found that BN was synthesized as the main phase and BN was produced as a by-product. The small BN peak is thought to be due to the BN crucible. In other examples, the formation of BN is also thought to be due to the BN crucible.

[0029] Example 6B ２ O ３ , SiO ２ , Na, Ti as raw materials ２ The molar ratio of the raw materials before heating was B ２ O ３ : SiO ２ : Na:Ti = 1:3:10:0.25. ２ O ３ and SiO ２ To the mixed powder compact, Ti powder was added and a block of Na was added to prepare a pre-heating raw material. The pre-heating raw material stored in a BN crucible was heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 9 shows the results of X-ray diffraction measurement of the powder obtained after heating, removing Na, and washing with water. From the results of this X-ray diffraction measurement, it was found that the use of Ti in the pre-heating raw material resulted in the formation of TiB. ２ It was found that under these production conditions, TiB ２ It was found that the main phase was synthesized, and BN was produced as a by-product. The small BN peak is thought to be due to the BN crucible.

[0030] FIG. 10 shows the TiB ２ 10A shows SEM photographs and EDX results of the TiB particles of several tens of μm in size among the fine particles. ２ Single crystal grains of TiB2 with a size of about 20 to 25 μm were observed. ２ As a result of the composition analysis by EDX shown in FIG. 10B, the ratio of Ti to B was approximately 1:2, which indicated that TiB ２ It was confirmed that the single crystal grains of this alloy had an almost stoichiometric composition.

[0031] Example 7B ２ O ３ , SiO ２ , Na, Nb as raw materials ２ The molar ratio of the raw materials before heating was B ２ O ３ : SiO ２ :Na:Nb=1:3:10:0.25. ２ O ３ and SiO ２ To the mixed powder compact, Nb powder was added and a block of Na was added to prepare a raw material before heating. The raw material before heating stored in a BN crucible was heated from room temperature to 1100°C over 4 hours and heated at this temperature for 10 hours. Figure 11 shows the results of X-ray diffraction measurement of the powder obtained after heating, removing Na, and washing with water. From the results of this X-ray diffraction measurement, it was found that NbB ２ It was found that it can be synthesized as the main phase.

[0032] Example 8B ２ O ３ , SiO ２ , Na, Zr as raw materials ２ The molar ratio of the raw materials before heating was B ２ O ３ : SiO ２ :Na:Zr=1:3:10:0.25. ２ O ３ and SiO ２ Zr powder was added to the mixed powder compact, and a block of Na was added to prepare a raw material before heating. The raw material before heating stored in a BN crucible was heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 12 shows the results of X-ray diffraction measurement of the powder obtained after heating, removing Na, and washing with water. From the results of this X-ray diffraction measurement, it was found that ZrB ２ It was found that the main phase was synthesized, and BN was produced as a by-product. The small BN peak is thought to be due to the BN crucible.

[0033] Synthesized ZrB ２ When observing the SEM photograph, it is clear that ZrB particles of several tens of micrometers in size are present among the fine particles. ２ Many single crystal grains of ZrB were observed. ２This SEM photograph shows hexagonal plate-shaped ZrB ２ Single crystals of ZnO were observed.

[0034] The melting point of zirconium boride is about 3000°C, so the particles are ZrB ２ When attempting to produce a single crystal of ZrB, a heating temperature of this magnitude is required. Even when a flux is used to lower the melting point, the heating temperature can only be lowered slightly from 3000°C, and a temperature much higher than 1100°C is required. In this example, ZrB was produced at a heating temperature of 1100°C. ２ Since we were able to synthesize single crystals of this compound, processing can be done at a much lower temperature than the required temperature of around 3000°C. Other borides also have high melting points, so if you try to create single crystals from grains, you will need to process them at a correspondingly high temperature.

[0035] Example 9B ２ O ３ , SiO ２ , Na, ZrO ２ ZrB ２ The molar ratio of the raw materials before heating was B ２ O ３ : SiO ２ :Na:ZrO ２ = 1:3:10:0.25. ２ O ３ and SiO ２ The mixed powder compact of ZrO ２ A pre-heating raw material was prepared by adding powder and adding block-shaped Na. The pre-heating raw material stored in a BN crucible was heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 14 shows the results of X-ray diffraction measurement of the powder obtained after heating, removing Na, and washing with water. The results of this X-ray diffraction measurement revealed that the metal oxide ZrO ２ By using ZrB as a raw material before heating ２ It was found that ZrO ２ is a cheaper material than Zr, so ZrO ２ The use of ZrB can reduce the manufacturing cost. ２It was found that ZrN was synthesized as the main phase, and BN and ZrN were by-produced. The small BN peak is thought to be due to the BN crucible.

[0036] Example 10B ２ O ３ , SiO ２ Tungsten boride was produced using raw materials containing Na and W. The molar ratio of the raw materials before heating was B ２ O ３ : SiO ２ :Na:W=1:3:10:0.25. ２ O ３ and SiO ２ W powder was added to the mixed powder compact, and a block of Na was added to prepare a pre-heating raw material. The pre-heating raw material stored in a BN crucible was heated from room temperature to 1100°C over 4 hours and heated at this temperature for 10 hours. Figure 15 shows the results of X-ray diffraction analysis of the powder obtained after heating, removing Na, and washing with water. The results of this X-ray diffraction analysis showed that tungsten boride of various compositions could be synthesized.

[0037] Example 11B ２ O ３ , SiO ２ , Na, W.O. ３ Tungsten boride was produced using the following raw materials. The molar ratio of the raw materials before heating was B ２ O ３ : SiO ２ :Na:WO ３ = 1:3:10:0.25. ２ O ３ and SiO ２ The mixed powder compact of WO ３ A powder was added to the BN crucible, and a block of Na was added to prepare a raw material before heating. The raw material before heating stored in a BN crucible was heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 16 shows the results of X-ray diffraction measurement of the powder obtained after heating, removing Na, and washing with water. The results of this X-ray diffraction measurement showed that tungsten boride of various compositions could be synthesized. Note that the sample before washing with water contained Na. ２ SiO ３ was confirmed to be included.

[0038] Example 12B ２ O ３ , SiO ２ , Na, La ２ O ３ LaB ６ The molar ratio of the raw materials before heating was B ２ O ３ : SiO ２ :Na:La ２ O ３ = 1:3:10:0.167. ２ O ３ and SiO ２ The mixed powder compact of La ２ O ３ The raw material before heating was prepared by adding LaB powder and adding block-shaped Na. The raw material before heating stored in a BN crucible was heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 17 shows the results of X-ray diffraction measurement of the sample obtained after heating, removing Na, and washing with water. From the results of this X-ray diffraction measurement, it was found that LaB ６ was synthesized as the main phase, and BN was found to be a by-product.

[0039] Second Embodiment. Figure 18 is a flowchart showing a method for producing a metal boride according to a second embodiment. In step S20, a pre-heating raw material is prepared as raw materials for producing a metal boride, the raw material including a metal source, which is a metal, a metal oxide, a carbonate containing a metal, or a hydroxide containing a metal, boron oxide or boric acid, silicon dioxide, and metallic sodium. According to one example, the metal source metal includes at least one of a Group 2 metal or a Group 3 to 7 transition metal. According to another example, the metal source metal includes at least one of Ca, Ti, V, Cr, Mn, Sr, Zr, Nb, Ba, Hf, Ta, W, or a Group 3 element. The metal oxide source metal may be an oxide of a metal exemplified herein. According to another example, the metal oxide may be Ta, ２ O ５ , ZrO ２ , W.O. ３ , La ２ O ３ , TiO ２ , HfO ２ , Nb ２ O ５ , Cr２ O ３ , Mn ３ O ４ , Sc ２ O ３ , Y ２ O ３ , CeO ２ , Gd ２ O ３ , Dy ２ O ３ , Er ２ O ３ , Yb ２ O ３ , Lu ２ O ３ According to another example, the metal contained in the metal or metal oxide is a rare earth element. In this case, the metal or metal oxide is provided as a rare earth element or an oxide thereof.

[0040] According to one example, the metal source "metal-containing carbonate" is CaCO ３ , SrCO ３ , BaCO ３ According to one example, the metal source "metal-containing hydroxide" is La(OH) ３ is.

[0041] According to an example, the boron oxide or boric acid contained in the raw material before heating is B ２ O ３ , B(OH) ３ As raw materials before heating, silicon dioxide (SiO ２) and metallic sodium (Na). The pre-heating raw material can be provided in various ways. According to one example, the pre-heating raw material is prepared by first placing a metal source, boron oxide or boric acid, and silicon dioxide in a crucible, and then placing a block of metallic sodium in the crucible. According to another example, the pre-heating raw material is prepared by first placing a powder compact (pellet) containing boron oxide or boric acid and silicon dioxide and the metal source in a crucible, and then placing metallic sodium in the crucible. According to another example, the pre-heating raw material is prepared by mixing raw material powder containing the metal source, boron oxide or boric acid, silicon dioxide, and metallic sodium in a mortar or the like. In any example, the raw materials may be mixed at any stage of preparation of the pre-heating raw material, or mixing of the raw materials may be omitted. Even if the raw materials are not mixed, the reaction proceeds to a certain extent uniformly by heating because the melting point of Na is low, about 98°C. The manner of providing the raw material before heating is not limited to these, and any method can be adopted.

[0042] Next, the process proceeds to step S22. In step S22, the raw material prepared in step S20 is heated to, for example, 550°C or higher. In another example, the raw material is heated to 800°C or higher. In yet another example, the raw material is heated to 1100°C or higher. In yet another example, the raw material is heated at a low heating temperature of 550°C or higher and 800°C or lower. In this case, heating equipment such as an electric furnace with a maximum temperature of 800°C or lower can be used, thereby reducing the cost of the heating equipment and, naturally, energy consumption compared to using heating equipment with a maximum temperature of 1200°C or 1000°C. The heating time is, for example, 2 hours or longer. In another example, the heating time can be 1 hour or longer. In one example, the raw material placed in a crucible is heated by a known heating method. The crucible is made of, for example, BN, but other materials may also be used.

[0043] This heat treatment removes Na ２ SiO ３ and metal borides are produced. Here, sodium silicate (Na ２ SiO ３) is a stable compound that is easily produced, so if we assume that the pre-heating raw material does not contain a metal source, it is thought that as sodium silicate is produced, boron oxide is reduced to produce a product whose main component is boron. Because the pre-heating raw material contains a metal source, in most cases metal borides are produced directly by heating the pre-heating raw material, but a reaction in which a product whose main component is boron reacts with the metal component of the metal source to produce metal borides can also occur.

[0044] Next, the process proceeds to step S24. Step S24 is a process for removing residual Na, but since it is the same as the Na removal in step S14 described in the first embodiment, a description thereof will be omitted.

[0045] Next, the process proceeds to step S26. Step S26 is a water washing process, but since it is the same as the water washing process of step S16 described in embodiment 1, its description will be omitted. Next, the process proceeds to step S28. In step S28, the sample is subjected to acid washing. If products that cannot be removed by the water washing process remain in the sample, acid washing may be performed in step S28, which may dissolve and remove them. In one example, unwanted products are dissolved and removed using a 2 mol / L hydrochloric acid aqueous solution. In another example, a solute concentration or chemical substance suitable for dissolving and removing unwanted products can be used. An example of such a chemical substance is nitric acid. Note that step S28 is omitted, for example, if there is no substance to be dissolved and removed by acid washing, or if unwanted products cannot be dissolved and removed by acid washing.

[0046] According to the above-described embodiment, metal borides can be produced at a relatively low temperature of 550°C or higher. This eliminates the need for expensive production equipment that can withstand high-temperature treatment, and also reduces energy consumption. In addition, the reaction requires inexpensive materials such as boron oxide or boric acid and SiO ２ Furthermore, as described above, a metal source, boron oxide or boric acid, SiO ２ A metal boride can be easily obtained by simply preparing a raw material containing Na and Na before heating and heating it.

[0047] Example A Ta ２ O ５When the metal source was boron oxide and when the boron source was boric acid, TaB ２ For the first sample in which the boron source was boron oxide, ２ O ３ , SiO ２ , Na, Ta ２ O ５ The raw materials were prepared before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:Ta ２ O ５ = 1:6:20:2.3. ２ O ３ and SiO ２ and Ta ２ O ５ A block of Na was added to the mixed powder compact to prepare a pre-heated raw material. The pre-heated raw material stored in a BN crucible was heated from room temperature to 1100°C over 4 hours, and then heated at this temperature for 10 hours. The top row of Figure 19 shows the results of X-ray diffraction measurement of the powder obtained after heating, removing Na, and washing with water. From the results of this X-ray diffraction measurement, it was found that TaB ２ was synthesized as the main phase, and BN was found to be a by-product. The small BN peak is thought to be due to the BN crucible. In other examples, the formation of BN is also thought to be due to the BN crucible. For the sample in which the second boron source was boric acid, B(OH) ３ , SiO ２ , Na, Ta ２ O ５ was prepared as a raw material before heating. The molar ratio was B(OH) ３ : SiO ２ :Na:Ta ２ O ５ = 2:6:20:2.3. B(OH) ３ and SiO ２ , Ta ２ O ５A block of Na was added to the mixed powder compact to prepare a pre-heated raw material. The pre-heated raw material stored in a BN crucible was heated from room temperature to 1100°C over 4 hours, and then heated at this temperature for 10 hours. The bottom part of Figure 19 shows the results of X-ray diffraction measurement of the powder obtained after heating, removing Na, and washing with water. From the results of this X-ray diffraction measurement, it was found that TaB ２ was synthesized as the main phase.

[0048] Example B Ta ２ O ５ When using Ta as the metal source and boron oxide as the boron source, TaB ２ was manufactured. ２ O ３ , SiO ２ , Na, Ta ２ O ５ The raw materials were prepared before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:Ta ２ O ５ = 1:6:20:2.3. ２ O ３ and SiO ２ and Ta ２ O ５A block of Na was added to the powder mixture compact to prepare a pre-heating raw material. Seven such pre-heating raw materials were prepared, each stored in a BN crucible, and heated under the following temperature conditions: 1. The temperature was raised from room temperature to 1100°C over 4 hours, and the material was heated at this temperature for 10 hours. 2. The temperature was raised from room temperature to 1000°C over 3 hours and 20 minutes, and the material was heated at this temperature for 10 hours. 3. The temperature was raised from room temperature to 800°C over 2 hours and 40 minutes, and the material was heated at this temperature for 10 hours. 4. The temperature was raised from room temperature to 600°C over 2 hours, and the material was heated at this temperature for 100 hours. 5. The temperature was raised from room temperature to 600°C over 2 hours, and the material was heated at this temperature for 10 hours. 6. The temperature was raised from room temperature to 550°C over 1 hour and 50 minutes, and the material was heated at this temperature for 100 hours. 7. The temperature was raised from room temperature to 500°C over 1 hour and 40 minutes, and the samples were heated at this temperature for 10 hours. Figure 20 shows the results of X-ray diffraction measurements of the powders obtained by removing Na from these seven samples and washing them with water after heating. From the results of this X-ray diffraction measurement, it was found that when the heating temperature was 1100°C, TaB ２ can be synthesized as the main phase, and when the heating temperature is 1000°C or 800°C, TaB ２ is the main phase, Ta ３ B ４ At 600°C, the crystallinity of the metal boride was low when the heating time was 10 hours, and TaB ２ , Ta ５ B ６ Even at the same temperature of 600°C, if the heating time is 100 hours, the TaB ２ is the main phase, Ta ５ B ６ Even when the heating temperature was lowered to 550°C, TaB ２ is the main phase, Ta ５ B ６ Furthermore, when the heating temperature was 500°C, no diffraction peaks of metal borides were observed.

[0049] Example C Metal borides were produced using carbonates of Group 2 elements as the metal source. Example C-1 uses CaCO3, a carbonate of Group 2 element. ３More specifically, metal borides are synthesized using B ２ O ３ , SiO ２ , Na, CaCO ３ The raw materials were prepared before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:CaCO ３ = 1:4:10:0.25. ２ O ３ and SiO ２ and CaCO ３ A block of Na was added to the mixed powder compact to prepare a raw material before heating. This raw material before heating was placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 21 shows the results of X-ray diffraction measurement of the powder obtained by removing Na from the heated sample and washing it with water. From the results of this X-ray diffraction measurement, it was found that CaB ６ It was found that SrCO, a carbonate of a Group 2 element, was synthesized as the main phase. ３ More specifically, metal borides are synthesized using B ２ O ３ , SiO ２ , Na, SrCO ３ The raw materials were prepared before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:SrCO ３ = 1:4:10:0.25. ２ O ３ and SiO ２ and SrCO ３ A block of Na was added to the mixed powder compact to prepare a pre-heating raw material. This pre-heating raw material was placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 22 shows the results of X-ray diffraction measurement of the powder obtained by removing Na from the heated sample and washing it with water. From the results of this X-ray diffraction measurement, it was found that SrB ６ It was found that BaCO, a carbonate of a Group 2 element, was synthesized as the main phase. ３More specifically, metal borides are synthesized using B ２ O ３ , SiO ２ , Na, BaCO ３ The raw materials were prepared before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:BaCO ３ = 1:4:10:0.25. ２ O ３ and SiO ２ and BaCO ３ A block of Na was added to the mixed powder compact to prepare a raw material before heating. This raw material before heating was placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 23 shows the results of X-ray diffraction measurement of the powder obtained by removing Na from the heated sample and washing it with water. From the results of this X-ray diffraction measurement, it was found that BaB ６ It was found that the unidentified phase was synthesized as the main phase. In Examples C-1, C-2, and C-3, an unidentified phase was detected in the powder after water washing. It was found that the X-ray diffraction peaks of such unidentified phases disappeared by acid washing. This will be demonstrated in the next Example. In Example C-3', the powder obtained by acid washing the water-washed sample of Example C-3 was subjected to X-ray diffraction measurement, and the results are shown in Figure 24. Comparing the XRD pattern in Figure 24 with the XRD pattern in Figure 23, it was found that the crystalline phase corresponding to the unidentified phase disappeared or decomposed into an amorphous phase by acid washing.

[0050] Example D Metal borides were produced using an oxide of a Group 4 element as the metal source. Example D-1 uses TiO, an oxide of a Group 4 element. ２ More specifically, metal borides are synthesized using B ２ O ３ , SiO ２ , Na, TiO ２ The raw materials were prepared before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:TiO ２ = 1:3:10:0.25. ２ O３ and SiO ２ The mixed powder compact of TiO ２ A pre-heating raw material was prepared by adding TiB powder and adding a block of Na. This pre-heating raw material was placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 25 shows the results of X-ray diffraction measurement of the powder obtained by removing Na from the heated sample and washing it with water. From the results of this X-ray diffraction measurement, it was found that TiB ２ It was found that HfO, an oxide of a group 4 element, was synthesized as the main phase. ２ More specifically, metal borides are synthesized using B ２ O ３ , SiO ２ , Na, HfO ２ The raw materials were prepared before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:HfO ２ = 1:3:10:0.25. ２ O ３ and SiO ２ The mixed powder compact of HfO ２ A pre-heating raw material was prepared by adding HfB powder and adding block-shaped Na. This pre-heating raw material was placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 26 shows the results of X-ray diffraction measurement of the powder obtained by removing Na from the heated sample and washing it with water. From the results of this X-ray diffraction measurement, it was found that HfB ２ was synthesized as the main phase. ２ In this SEM photograph, HfB particles of several μm size are found among the fine particles. ２ Single crystal grains of HfB in the shape of square pillars with a size of about 5 to 10 μm were observed. ２ Many single crystal grains were observed.

[0051] Example E Metal borides were produced using a Group 5 element and its oxide as the metal source. In Example E-1, a metal boride was synthesized using metal V, which is a Group 5 element. More specifically, B ２ O３ , SiO ２ , Na, and V were prepared as raw materials before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:V=1:3:10:0.25. ２ O ３ and SiO ２ V powder was added to the mixed powder compact, and a block of Na was added to prepare a raw material before heating. This raw material before heating was placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 28 shows the results of X-ray diffraction measurement of the powder obtained by removing Na from the heated sample and washing it with water. From the results of this X-ray diffraction measurement, it was found that VB ２ It was found that V, an oxide of a Group 5 element, was synthesized as the main phase. ２ O ５ More specifically, metal borides are synthesized using B ２ O ３ , SiO ２ , Na, V ２ O ５ The raw materials were prepared before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:V ２ O ５ = 1:3:10:0.25. ２ O ３ and SiO ２ V ２ O ５ A pre-heating raw material was prepared by adding powder and adding block-shaped Na. This pre-heating raw material was placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 29 shows the results of X-ray diffraction measurement of the powder obtained by removing Na from the heated sample and washing it with water. From the results of this X-ray diffraction measurement, it was found that VB ２ It was found that Nb, an oxide of a Group 5 element, was synthesized as the main phase. ２ O ５ More specifically, metal borides are synthesized using B ２ O ３ , SiO２ , Na, Nb ２ O ５ The raw materials were prepared before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:Nb ２ O ５ = 1:3:10:0.125. ２ O ３ and SiO ２ The mixed powder compact of Nb ２ O ５ A pre-heating raw material was prepared by adding NbB powder and adding block-shaped Na. This pre-heating raw material was placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 30 shows the results of X-ray diffraction measurement of the powder obtained by removing Na from the heated sample and washing it with water. From the results of this X-ray diffraction measurement, it was found that NbB ２ It was found that NbB was synthesized as the main phase. ２ Not only Nb ０．７７ B ２ was also found to be synthesized.

[0052] Example F Metal borides were produced using an oxide of a Group 6 element as the metal source. Example F uses Cr, an oxide of a Group 6 element. ２ O ３ More specifically, metal borides are synthesized using B ２ O ３ , SiO ２ , Na, Cr ２ O ３ The raw materials were prepared before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:Cr ２ O ３ = 1:3:10:0.125. ２ O ３ and SiO ２ The mixed powder compact is ２ O ３A pre-heating raw material was prepared by adding a powder and adding a block of Na. This pre-heating raw material was placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 31 shows the results of X-ray diffraction measurement of the powder obtained by removing Na from the heated sample and washing it with water. From the results of this X-ray diffraction measurement, it was found that CrB ２ It was found that CrB was synthesized as the main phase. ２ It was found that not only CrB but also CrB was synthesized.

[0053] Example G Metal borides were produced using an oxide of a Group 7 element as the metal source. In Example G, Mn, an oxide of a Group 7 element, was used. ３ O ４ More specifically, metal borides are synthesized using B ２ O ３ , SiO ２ , Na, Mn ３ O ４ The raw materials were prepared before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:Mn ３ O ４ = 1:3:10:0.125. ２ O ３ and SiO ２ The mixed powder compact of Mn ３ O ４ A pre-heating raw material was prepared by adding powder and adding block-shaped Na. This pre-heating raw material was placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 32 shows the results of X-ray diffraction measurement of the powder obtained by removing Na from the heated sample and washing it with water. The results of this X-ray diffraction measurement showed that MnB was synthesized as the main phase. Furthermore, not only MnB but also MnB were synthesized as metal borides. ２ and MnB ４ was also found to be synthesized.

[0054] Example H A metal boride was produced using a simple substance of a Group 3 element as a metal source. In Example H, a metal boride was synthesized using metal La, which is a simple substance of a Group 3 element. More specifically, B ２ O ３ , SiO ２ , Na, and La were prepared as raw materials before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:La=1:3.5:10:0.333. ２ O ３ and SiO ２ La pieces were added to the mixed powder compact, and block-shaped Na was added to prepare a pre-heating raw material. This pre-heating raw material was placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 33 shows the results of X-ray diffraction measurement of the powder obtained by removing Na from the heated sample, washing with water, and acid washing. From the results of this X-ray diffraction measurement, it was found that LaB ６ It was found that LaB was synthesized as the main phase. ６ This is an SEM photograph of LaB ６ It was found that the particles had a particle size of several hundred microns.

[0055] Example I Metal borides were produced using an oxide of a Group 3 element as the metal source. Example I-1 uses Sc, an oxide of a Group 3 element. ２ O ３ More specifically, metal borides are synthesized using B ２ O ３ , SiO ２ , Na, Sc ２ O ３ The raw materials were prepared before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:Sc ２ O ３ = 1: 3.5: 10: 0.167. ２ O ３ and SiO ２ The mixed powder compact of Sc ２ O ３A pre-heating raw material was prepared by adding powder and adding block-shaped Na. This pre-heating raw material was placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 35 shows the results of X-ray diffraction measurement of the powder obtained by removing Na from the heated sample and washing it with water. From the results of this X-ray diffraction measurement, it was found that ScB ２ was synthesized as the main phase.

[0056] Example I-2 is a Group 3 element oxide, Y ２ O ３ More specifically, metal borides are synthesized using B ２ O ３ , SiO ２ , Na, Y ２ O ３ The raw materials were prepared before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:Y ２ O ３ = 1: 3.5: 10: 0.167. ２ O ３ and SiO ２ The mixed powder compact is ２ O ３ A pre-heating raw material was prepared by adding a powder and adding a block of Na. This pre-heating raw material was placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 36 shows the results of X-ray diffraction measurement of the powder obtained by removing Na from the heated sample, washing with water, and acid washing. From the results of this X-ray diffraction measurement, it was found that YB ６ was synthesized as the main phase.

[0057] Example I-3 is an oxide of a Group 3 element, CeO ２ More specifically, metal borides are synthesized using B ２ O ３ , SiO ２ , Na, CeO ２ The raw materials were prepared before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:CeO ２= 1:3:10:0.25. ２ O ３ and SiO ２ The mixed powder compact is then coated with CeO ２ A pre-heating raw material was prepared by adding a powder and adding a block of Na. This pre-heating raw material was placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 37 shows the results of X-ray diffraction measurement of the powder obtained by removing Na from the heated sample and washing it with water. From the results of this X-ray diffraction measurement, it was found that CeB ６ It was found that the CeB ６ This is an SEM photograph of CeB ６ It was found that the particles had a particle size of about 1 μm to 10 μm.

[0058] Example I-4 is an oxide of a Group 3 element, Gd ２ O ３ More specifically, metal borides are synthesized using B ２ O ３ , SiO ２ , Na, Gd ２ O ３ The raw materials were prepared before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:Gd ２ O ３ = 1: 3.5: 10: 0.167. ２ O ３ and SiO ２ The mixed powder compact of Gd ２ O ３ A pre-heating raw material was prepared by adding a powder and adding a block of Na. This pre-heating raw material was placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 39 shows the results of X-ray diffraction measurement of the powder obtained by removing Na after heating, washing with water, and acid washing. From the results of this X-ray diffraction measurement, it was found that GdB ６ It was found that GdB was synthesized as the main phase. ６ Not only GdB ４It was found that GdB was also synthesized. Figure 40 shows an SEM photograph of the obtained metal boride. ６ is a cubic crystal, and GdB ４ Since is a tetragonal crystal system, the cubic crystal grains in the SEM photograph are the main phase GdB ６ It is thought that this is the case.

[0059] Example I-5 is an oxide of a Group 3 element, Dy ２ O ３ More specifically, metal borides are synthesized using B ２ O ３ , SiO ２ , Na, Dy ２ O ３ The raw materials were prepared before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:Dy ２ O ３ = 1: 3.5: 10: 0.167. ２ O ３ and SiO ２ The mixed powder compact is ２ O ３ A pre-heating raw material was prepared by adding DyB powder and adding block-shaped Na. This pre-heating raw material was placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 41 shows the results of X-ray diffraction measurement of the powder obtained by removing Na from the heated sample, washing with water, and acid washing. From the results of this X-ray diffraction measurement, it was found that DyB ６ It was found that DyB was synthesized as the main phase. ６ Not only DyB ４ It was found that DyB could also be synthesized. Figure 42 shows an SEM photograph of the obtained metal boride. ６ is a cubic crystal system, and DyB ４ Since is a tetragonal crystal system, the cubic crystal grains in the SEM photograph are the main phase DyB ６ and the columnar grains are DyB ４ It is thought that this is the case.

[0060] Example I-6 is an oxide of a Group 3 element, Er ２ O ３More specifically, metal borides are synthesized using B ２ O ３ , SiO ２ , Na, Er ２ O ３ The raw materials were prepared before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:Er ２ O ３ = 1: 3.5: 10: 0.167. ２ O ３ and SiO ２ The mixed powder compact of Er ２ O ３ A raw material before heating was prepared by adding ErB powder and adding a block of Na. This raw material before heating was placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 43 shows the results of X-ray diffraction measurement of the powder obtained by removing Na from the heated sample, washing with water, and acid cleaning. From the results of this X-ray diffraction measurement, it was found that ErB ６ It was found that ErB was synthesized as the main phase. ６ Not only ErB ４ It was found that ErB could also be synthesized. Figure 44 shows an SEM photograph of the obtained metal boride. ６ is a cubic crystal, and ErB ４ Since is a tetragonal crystal system, the cubic crystal grains in the SEM photograph are the main phase of ErB ６ and the columnar grains are ErB ４ It is thought that this is the case.

[0061] Example I-7 is an oxide of a Group 3 element, Yb ２ O ３ More specifically, metal borides are synthesized using B ２ O ３ , SiO ２ , Na, Yb ２ O ３ The raw materials were prepared before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:Yb ２ O ３= 1: 3.5: 10: 0.167. ２ O ３ and SiO ２ The mixed powder compact of Yb ２ O ３ A pre-heating raw material was prepared by adding a powder and adding a block of Na. This pre-heating raw material was placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 45 shows the results of X-ray diffraction measurement of the powder obtained by removing Na from the heated sample, washing with water, and acid cleaning. From the results of this X-ray diffraction measurement, it was found that YbB ６ It was found that YbB was synthesized as the main phase. ６ This is an SEM photograph of YbB ６ It was found that the particle size was about 1 μm to 20 μm.

[0062] Example I-8 is an oxide of a Group 3 element, Lu ２ O ３ More specifically, metal borides are synthesized using B ２ O ３ , SiO ２ , Na, Lu ２ O ３ The raw materials were prepared before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:Lu ２ O ３ = 1: 3.5: 10: 0.167. ２ O ３ and SiO ２ The mixed powder compact of Lu ２ O ３ A pre-heating raw material was prepared by adding a powder and adding a block of Na. This pre-heating raw material was placed in a BN crucible, heated from room temperature to 1100°C over 4 hours, and heated at this temperature for 10 hours. Figure 47 shows the results of X-ray diffraction measurement of the powder obtained by removing Na from the heated sample, washing with water, and acid washing. From the results of this X-ray diffraction measurement, it was found that LuB ６ It was found that this was synthesized as a subphase. By adjusting the synthesis conditions, it may be possible to synthesize this as the main phase.

[0063] The results of Examples H and I suggest that metal borides can be synthesized using a Group 3 element other than those listed above as a metal source, or that metal borides can be synthesized using an oxide of a Group 3 element other than those listed above as a metal source. Note that the lanthanoids, which are 15 elements with atomic numbers from 57 to 71, i.e., from lanthanum to lutetium, have similar chemical properties, and therefore it is believed that metal borides can be synthesized using a Group 3 element other than those listed above or an oxide thereof as a metal source.

[0064] Embodiment 3. Figure 48 is a flowchart showing a method for producing a metal boride according to embodiment 3. In step S30, a pre-heating raw material is prepared as raw materials for producing a metal boride, the raw material containing a metal source which is a metal, a metal oxide, a carbonate containing a metal, or a hydroxide containing a metal, boron oxide or boric acid, and silicon dioxide. The pre-heating raw material is the same as that of embodiment 2, except that it does not contain metallic sodium.

[0065] Next, the process proceeds to step S32. In step S32, the pre-heating raw material prepared in step S30 is heated to, for example, 800°C or higher. The heating time is, for example, 2 hours or more. According to another example, the heating time can be 1 hour or more. The pre-heating raw material is heated in Na vapor. According to one example, a first crucible containing the pre-heating raw material and a second crucible containing Na are stored in the same container, and the inside of the container is heated to 800°C or higher. When Na is heated to about 800°C, Na vapor of about 0.5 atmospheres (atm) can be filled inside the container. The method of supplying Na vapor is not limited to this example, and any method can be used. For example, the pre-heating raw material and Na can be heated using separate heat sources. According to yet another example, Na vapor generated outside the container can be supplied into the container. By this heating process, Na ２ SiO ３ and a metal boride are produced. The reaction mechanism is as explained in the first embodiment.

[0066] Next, the process proceeds to step S34. In step S34, after the pre-heating raw material is heated, the sample is removed from the first crucible without breaking it. For example, when synthesizing a metal boride by heating a pre-heating raw material containing metallic Na, the sample may adhere to the crucible, and therefore the crucible may need to be broken to remove the sample. In such cases, the crucible cannot be reused. On the other hand, when synthesizing a metal boride by heating a pre-heating raw material not containing metallic Na while supplying Na vapor, the sample does not adhere to the crucible, and therefore the sample can be easily removed from the crucible without breaking it. This allows the crucible to be reused and prevents the crucible material from being mixed into the sample, enabling efficient industrial production.

[0067] Next, the process proceeds to step S36. Step S36 is a process of subjecting the sample removed from the crucible to a water washing treatment. The water washing treatment is, for example, as described in embodiment 1. According to one example, the pre-heated raw material heated in Na vapor contains almost no excess metallic Na, so the water washing treatment can be performed without heat treatment or ethanol treatment to remove excess Na. Furthermore, by performing the water washing treatment after removing the sample from the crucible, it is not necessary to expose the crucible to water, which is convenient for reusing the crucible. Steps S36 and S34 can be interchanged. That is, the sample may be subjected to a water washing treatment before being removed from the crucible.

[0068] According to the third embodiment described above, in addition to the effects described in the first and second embodiments, it is possible to omit the step of removing excess Na and to reuse the crucible.

[0069] Embodiment 4. Embodiment 4 is a method for producing a metal boride according to any one of embodiments 1 to 3, in particular, LaB ６ The metal source is, for example, La, La ２ O ３ or La(OH) ３According to one example, in the heating of the raw material before heating, the raw material before heating is heated to a temperature of 600°C or higher but lower than 1000°C to produce metal borides having a particle size of several tens to several hundreds of nanometers or less. Metal borides having a particle size of several tens to several hundreds of nanometers or less are, for example, metal borides having a particle size of less than 1 μm. According to another example, a heating temperature of 1000°C or higher produces metal borides having a particle size larger than 1 μm.

[0070] Example J-0 Example J-0 is a compound in which La was used as a metal source. ２ O ３ The metal borides were produced under various heating conditions using B. ２ O ３ , SiO ２ , Na, La ２ O ３ The raw materials were prepared before heating. The molar ratio of the raw materials was B ２ O ３ : SiO ２ :Na:La ２ O ３ = 1: 3.5: 10: 0.167. ２ O ３ and SiO ２ and La ２ O ３ A block of Na was added to the powder mixture and pressed compact to prepare a pre-heated raw material. Six of these pre-heated raw materials were prepared, each stored in a BN crucible, and heated from room temperature to 1100°C, 1000°C, 800°C, 700°C, 600°C, and 500°C over a period of 4 hours. These temperatures were maintained for 10 hours, 2 hours, 10 hours, 10 hours, 10 hours, and 10 hours, respectively. Figure 49 shows the results of X-ray diffraction measurement of the powder obtained by removing Na from the sample after heating, washing with water, and acid washing. The results of this X-ray diffraction measurement revealed that LaB ６ On the other hand, when the heating temperature was 500°C, LaB ６ Figure 50 shows the LaB ６ 50A and 50B are SEM photographs of LaB obtained at high heating temperatures of 1100°C and 1000°C. ６50C and 50D are SEM photographs of LaB obtained at low heating temperatures of 800°C and 700°C. ６ At 1000°C or higher, LaB ６ On the other hand, when the temperature is below 800°C, the grain size of LaB ６ It was found that the particle size was significantly smaller.

[0071] Example J-0' Example J-0' shows the results of investigating the influence of post-treatment after heating on the crystalline phase in the sample. In Example J-0', the same pre-heating raw material as in Example J-0 was placed in a BN crucible, and the temperature was raised from room temperature to 1000°C over 4 hours, and this temperature was maintained for 4 hours. Thereafter, X-ray diffraction measurements were carried out on the powder obtained after removing Na, the powder obtained by further washing the powder with water, and the powder obtained by further washing the Na-removed and water-washed powder with acid. Figure 51 shows the results of the X-ray diffraction measurements on these three powders. As a result, as shown in the upper part of Figure 51, the powder obtained after removing Na contained Na as the main phase. ２ SiO ３ and LaB ６ was obtained, and NaLaSiO ４ As shown in the middle of Figure 51, the powder obtained by washing with water after removing Na contained LaB as the main phase. ６ was obtained, and NaLaSiO ４ As shown in the lower part of Figure 51, the powder obtained by washing with water and then acid washing after removing Na contains LaB as the main phase. ６ Thus, it was found that impurity crystals can be removed more effectively by adding a water washing treatment than by performing only the Na removal treatment, and that impurity crystals can be removed even more effectively by further performing an acid washing treatment.

[0072] Example J-1 Example J-1 uses La as a metal source. ２ O ３ or La(OH) ３ In this example, a short heating time was used, and Na vapor was used as the Na source. More specifically, the following three examples were tested. ２ O ３ , SiO２ , Na, La ２ O ３ is used as the raw material before heating, and the molar ratio is B ２ O ３ : SiO ２ :Na:La ２ O ３ = 1: 3.5: 10: 0.167. ２ O ３ and SiO ２ and La ２ O ３ A block of Na was added to the mixed powder compact to prepare a raw material before heating. The raw material before heating was placed in a BN crucible, heated from room temperature to 1000°C over 4 hours, and heated at this temperature for 2 hours. ２ O ３ , SiO ２ , La ２ O ３ is used as the raw material before heating, and the molar ratio is B ２ O ３ : SiO ２ :La ２ O ３ = 1: 3.5: 0.167. ２ O ３ and SiO ２ and La ２ O ３ The mixed powder compact was used as the raw material before heating. The raw material before heating was placed in a BN crucible, heated from room temperature to 1000°C over 4 hours, and then heated at this temperature in Na vapor for 6 hours. ２ O ３ , SiO ２ , Na, La(OH) ３ is used as the raw material before heating, and the molar ratio is B ２ O ３ : SiO ２ :Na:La(OH) ３ = 1:3.5:10:0.29. ２ O ３ and SiO ２ and La(OH) ３A block of Na was added to the mixed powder compact to prepare a raw material before heating. The raw material before heating was placed in a BN crucible, heated from room temperature to 1000°C over 4 hours, and heated at this temperature for 1 hour. Figure 52 shows the results of X-ray diffraction measurement of the powder obtained by removing Na from the sample after heating, washing with water, and acid cleaning. The top row of Figure 52 shows the results of X-ray diffraction of the first sample. This shows that La was used as a metal source. ２ O ３ When using LaB as the main phase, the heating time is 2 hours. ６ The middle part of Figure 52 shows the results of X-ray diffraction of the second sample. From the results of this X-ray diffraction, it was found that LaB was obtained as the main phase by using Na vapor as the Na source. ６ The bottom row of Figure 52 shows the X-ray diffraction results for the third sample. From these X-ray diffraction results, it was found that La(OH) ３ When using LaB as the main phase, the heating time is 1 hour. ６ It was found that the obtained LaB ６ The first sample from Figure 53A shows LaB particles with a particle size of 1 μm or more. ６ From Figure 53B, it was found that the second sample contained LaB particles with a particle size of 1 μm or less. ６ From FIG. 53C, it was found that the third sample had LaB particles with a particle size of 1 μm or more. ６ and LaB with a particle size of 1 μm or less ６ was found to be synthesized.

[0073] Example J-2 Example J-2 is an example in which the heating time and heating temperature were changed when Na vapor was supplied as the Na source. More specifically, the following four examples were tested. The first example is B ２ O ３ , SiO ２ , La ２ O ３ is used as the raw material before heating, and the molar ratio is B ２ O ３ : SiO ２ :La ２ O ３ = 1: 3.5: 0.167. ２ O３ and SiO ２ and La ２ O ３ A mixed compact of powders was used as the pre-heating raw material. The pre-heating raw material was placed in a BN crucible, heated from room temperature to 1000°C over 4 hours, and then heated in Na vapor at this temperature for 6 hours. The second sample was essentially the same as the first sample, except that the heating temperature was 900°C. The third sample was essentially the same as the first sample, except that the heating temperature was 800°C and the heating time was 10 hours. The fourth sample was essentially the same as the first sample, except that the heating temperature was 700°C and the heating time was 10 hours. Figure 54 shows the results of X-ray diffraction measurements of the powders obtained by removing Na from each sample after heating, washing with water, and acid cleaning. Figure 54 shows the X-ray diffraction results for the first, second, third, and fourth samples from the top. These results indicate that heating in Na vapor at 700°C produces LaB. ６ It was found that it is possible to synthesize

[0074] Example J-3 Example J-3 is SiO ２ This is an example of investigating the influence of the presence or absence of B on the synthesis results. ２ O ３ , SiO ２ , Na, La ２ O ３ The molar ratio of the raw materials was 1:X:10:0.167, and a raw material before heating in which X was 3.5 and a raw material before heating in which X was 0 were prepared. ２ O ３ and SiO ２ and La ２ O ３ Block-shaped Na was added to the mixed powder compact. ２ O ３ and La ２ O ３A block of Na was added to the compacted powder. These samples were placed in BN crucibles, heated from room temperature to 800°C over 4 hours, and then heated at this temperature for 10 hours. ２ For the sample using SiO, the results of X-ray diffraction measurement of the powder obtained by removing Na after heating and washing with water and acid are shown. ２ For the sample that did not use SiO, the results of X-ray diffraction measurement of the powder obtained by removing Na after heating and washing with water are shown. ２ In the sample containing LaB, even when heated to 800°C ６ On the other hand, it was found that the raw material before heating could be synthesized with SiO ２ In the sample not containing LaB ６ could not be synthesized.

[0075] Example J-3' Example J-3' was basically the same as Example J-3, but differed from Example J-3 in that the heating temperature was 1100°C. Figure 56 shows the results of X-ray diffraction measurement. Even when the heating temperature was 1100°C, as in Example J-3 where the heating temperature was 800°C, the raw material before heating contained SiO ２ In the sample containing LaB ６ can be synthesized as the main phase, and the raw material before heating is SiO ２ In the sample not containing LaB ６ In addition, considering the example of Example B in which metal borides were synthesized by heating at 550°C, it is considered that La ２ O ３ Even when using LaB, the heating temperature is as low as 550°C. ６ It is possible to combine the following. All of the examples described so far are not dependent on a specific embodiment. That is, the examples are not limited to being examples of one embodiment, but are examples of multiple embodiments.

[0076] The metal boride manufacturing methods according to Embodiments 1-4 can synthesize metal borides by heating raw materials at low heating temperatures, such as 550°C to 600°C or 550°C to 800°C. This is because the free energy change ΔG in the synthesis reaction of various metal borides predicted in this synthesis method is a large negative value even at low heating temperatures (e.g., 527°C). Furthermore, according to research by the inventors, the value of ΔG at low heating temperatures is a larger negative value than the value of ΔG at high heating temperatures. In fact, ΔG was calculated from the predicted reaction formula for several examples of the synthesis of metal borides for which thermodynamic parameters have been reported, and these are shown below as examples.

[0077] TiO ２ +5SiO ２ +B ２ O ３ +10Na → TiB ２ +5Na ２ SiO ３　 (Equation 4) In this reaction formula, the free energy changes ΔG at 1027° C. and 527° C. were large negative values ​​of −870 kJ / mol and −1141 kJ / mol, respectively.

[0078] HfO ２ +5SiO ２ +B ２ O ３ +10Na → HfB ２ +5Na ２ SiO ３　 (Equation 5) In this reaction formula, the free energy changes ΔG at 1027° C. and 527° C. were large negative values ​​of −689 kJ / mol and −906 kJ / mol, respectively.

[0079] ZrO ２ +5SiO ２ +B ２ O ３ +10Na → ZrB ２ +5Na ２ SiO ３　 (Equation 6) In this reaction formula, the free energy changes ΔG at 1027° C. and 527° C. were large negative values ​​of −725 kJ / mol and −993 kJ / mol, respectively.

[0080] V ２ O ５ +11SiO ２ +2B ２ O ３ +22Na → 2VB ２ +11Na ２ SiO ３ ... (Equation 7) For this reaction formula, the free energy change ΔG at 1027°C and 527°C was -2352 kJ / mol and -2977 kJ / mol, respectively, which were large negative values. The ΔG for the reaction producing 1 mol of metal boride was -1176 kJ / mol and -1489 kJ / mol at 1027°C and 527°C, respectively.

[0081] Nb ２ O ５ +11SiO ２ +2B ２ O ３ +22Na → 2NbB ２ +11Na ２ SiO ３ ... (Equation 8) For this reaction formula, the free energy change ΔG at 1027°C and 527°C was -2139 kJ / mol and -2731 kJ / mol, respectively, which were large negative values. The ΔG for the reaction producing 1 mol of metal boride was -1070 kJ / mol and -1366 kJ / mol at 1027°C and 527°C, respectively.

[0082] Ta ２ O ５ +11SiO ２ +2B ２ O ３ +22Na → 2TaB ２ +11Na ２ SiO ３ ... (Equation 9) For this reaction formula, the free energy change ΔG at 1027°C and 527°C was a large negative value of -1912 kJ / mol and -2506 kJ / mol, respectively. The ΔG for the reaction producing 1 mol of metal boride was -956 kJ / mol and -1253 kJ / mol at 1027°C and 527°C, respectively.

[0083] Cr ２ O ３ +9SiO ２ +2B２ O ３ +18Na → 2CrB ２ +9Na ２ SiO ３　 ... (Equation 10) For this reaction formula, the free energy change ΔG at 927°C and 527°C was a large negative value of -1734 kJ / mol and -1984 kJ / mol, respectively. The ΔG for the reaction producing 1 mol of metal boride was -867 kJ / mol and -992 kJ / mol at 1027°C and 527°C, respectively.

[0084] Mn ３ O ４ +13SiO ２ +3B ２ O ３ +26Na → 3MnB ２ +13Na ２ SiO ３ ... (Equation 11) For this reaction formula, the free energy change ΔG at 927°C and 527°C was -2536 kJ / mol and -2954 kJ / mol, respectively, which were large negative values. The ΔG for the reaction producing 1 mol of metal boride was -845 kJ / mol and -985 kJ / mol at 1027°C and 527°C, respectively.

[0085] 2Mn ３ O ４ +17SiO ２ +3B ２ O ３ +34Na→6MnB+17Na ２ SiO ３ ... (Equation 12) For this reaction formula, the free energy change ΔG at 927°C and 527°C was -3625 kJ / mol and -4160 kJ / mol, respectively, which were large negative values. The ΔG for the reaction producing 1 mol of metal boride was -604 kJ / mol and -693 kJ / mol at 1027°C and 527°C, respectively.

[0086] La ２ O ３ +21SiO ２ +6B ２ O ３ +42Na → 2LaB ６ +21Na ２ SiO ３... (Equation 13) In this reaction formula, the free energy change ΔG at 1027°C and 527°C was -3033 kJ / mol and -4146 kJ / mol, respectively, which were large negative values. The ΔG for the reaction producing 1 mol of metal boride was -1517 kJ / mol and -2073 kJ / mol at 1027°C and 527°C, respectively. Note that this reaction formula is a hypothetical reaction formula that significantly simplifies the reaction of this synthesis method. In reality, LaB ６ Na is used for the production of ２ SiO ３ Besides NaLaSiO ４ is also produced as a by-product. ６ When ΔG was calculated for the synthesis of the same compound using a similar simplified reaction formula, large negative values ​​were obtained at both temperatures.

[0087] When a metal oxide is used as the metal source, ΔG has a larger negative value than when an elemental metal is used. Therefore, although low-temperature synthesis is possible using either metal source, in one example, the heating temperature for synthesizing a metal boride can be reduced by using a metal oxide as the metal source rather than using an elemental metal.

Claims

1. A method for producing a metal boride, comprising: preparing a pre-heating raw material having a metal source which is a metal, a metal oxide, a carbonate containing a metal, or a hydroxide containing a metal, boron oxide or boric acid, silicon dioxide, and metallic sodium; and heating the pre-heating raw material.

2. By the heating, metal borides and Na ２ SiO ３ The method for producing a metal boride according to claim 1, wherein 3. The above Na ２ SiO ３ 3. The method for producing a metal boride according to claim 2, further comprising: washing the metal boride with water to remove the metal boride.

4. The method for producing a metal boride according to claim 1, characterized in that the heating is performed at 550°C or higher.

5. The method for producing a metal boride according to claim 1, wherein the heating is carried out for 2 hours or more.

6. The method for producing a metal boride according to claim 1, wherein the metallic sodium is present in an amount six times or more by mole relative to the boron oxide.

7. The method for producing a metal boride according to any one of claims 1 to 6, wherein the metal source contains a Group 2 metal or a Group 3 to 7 transition metal.

8. The method for producing a metal boride according to any one of claims 1 to 6, wherein the metal source contains Ca, Ti, V, Cr, Mn, Sr, Zr, Nb, Ba, Hf, Ta, W or a Group 3 element.

9. The metal boride is LaB ６ The method for producing a metal boride according to claim 1, wherein 10. The metal source is La, La ２ O ３ or La(OH) ３ 2. The method for producing a metal boride according to claim 1, wherein the heating of the pre-heating raw material is performed by heating the pre-heating raw material to a temperature of 600°C or higher but lower than 1000°C to produce a metal boride having a particle size of several hundred nanometers or less.

11. A method for producing a metal boride, comprising: preparing a pre-heating raw material containing a metal source which is a metal, a metal oxide, a carbonate containing a metal, or a hydroxide containing a metal; boron oxide or boric acid; and silicon dioxide; and heating the pre-heating raw material in sodium vapor.

12. A method for producing a metal boride as described in claim 11, wherein the heating of the raw materials before heating comprises storing a first crucible containing the raw materials before heating and a second crucible containing Na in a container, and heating the inside of the container to 700°C or higher.

13. The method for producing a metal boride according to claim 12, further comprising removing the sample from the first crucible without breaking the first crucible after heating the unheated raw material.

14. The method for producing a metal boride according to claim 11, further comprising washing the unheated raw material after heating with water without performing any heat treatment or ethanol treatment.

15. The metal source is La, La ２ O ３ or La(OH) ３ and heating the pre-heating raw material to a temperature of 600° C. or higher and lower than 1000° C. to produce metal borides having particle sizes of less than 1 μm.

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