Method for producing high-entropy alloy, method for using high-entropy alloy

Abstract

To provide a method for producing a high entropy alloy that can be produced with simple and low cost, to provide a method for using the high entropy alloy, to provide a high entropy alloy catalyst, and a novel high entropy alloy.SOLUTION: A producing method of a high entropy alloy comprises: obtaining a mixed solution of salts of metals of 5 or more kinds selected from the group consisting of transition metals of period 4 to 6, groups of 3 to 12, aluminum, silicon, and lanthanoids in the presence of a solvent; drying and heating the mixed solution to obtain an oxide precursor; and obtaining a high entropy alloy by heating and reducing the oxide precursor, at least one reducing agent selected from CaH2, Ca, MgH2, Mg and molten salt of an alkali metal salt or alkaline earth metal salt under the presence of inert gas. The high entropy alloy may be used as a catalyst for a hydrogenation reaction in a liquid phase. Moreover, a novel high-entropy alloy can be produced by the method.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a high-entropy alloy, a method for using a high-entropy alloy, a high-entropy alloy catalyst, and a novel high-entropy alloy.

Background Art

[0002] In recent years, high-entropy alloys (hereinafter referred to as HEAs) have attracted attention as new alloy materials. HEAs are multi-component alloys of five or more components, in which various elements are randomly arranged in the crystal lattice, that is, the entropy of the arrangement is high, and basically consist of a single-phase irregular solid solution. HEAs have the following characteristics: (a) stabilization of the mixed state due to the negative increase in the mixing entropy term in the Gibbs free energy formula, (b) diffusion delay due to a complex microstructure, (c) high hardening due to high lattice strain caused by the size difference of constituent atoms and a decrease in the temperature dependence of mechanical properties, and (d) improvement of corrosion resistance due to the complex influence (also called the cocktail effect) caused by the coexistence of multiple elements. And, due to the excellent corrosion and oxidation resistance and excellent friction resistance of HEAs, their applications in various fields are being studied. For example, as the main applications, as shape memory alloys, in addition to medical devices and structural materials, they are applied in various fields such as new application fields such as 3D metal printers, and as catalyst materials.

[0003] As methods for manufacturing such high-entropy alloys, there are physical methods such as mixing, melting, and pulverizing raw materials, and chemical methods using a metal melt decomponent method. As a physical method, for example, Patent Document 1 discloses manufacturing a high-entropy alloy by steps such as a raw material mixing and melting step, an atomization step, a mixed powder preparation step, a laminated shaping step, and a quasi-solid solution heat treatment step. Patent Document 2 also discloses obtaining a solid alloy by a mechanical alloying technique in which elemental powders or pre-alloyed powders are pulverized with a ball mill until a homogeneous alloy is formed.

[0004] As a chemical method using a molten metal de-component method, a precursor alloy of each element is prepared, melted by arc melting to mix the components, and a thin plate-like precursor is cut out from the solidified alloy and immersed in a metal bath made of a specific metal to obtain a porous metal (Patent Documents 3-4).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] In a physical method, in the steps of mixing and melting raw materials, it is usually necessary to melt and mix the constituent metals at a high temperature (about 2000°C), so a large-scale and large-sized high-temperature resistant device such as a high-frequency melting furnace is required. In addition, expensive pure metals are used as the metals for raw materials, and furthermore, the number of manufacturing steps is large, which causes an increase in the work load and cost, and there is also a risk of impurity mixing in each step, for example, in the grinding step. And also in a chemical method, there are problems such as using expensive pure metals as the metals for raw materials, going through a complicated process of selecting the metals used in each step considering the heat of mixing and melting point, and having a large number of manufacturing steps.

[0007] Such HEAs are expected to have expanded applications as various catalyst materials, and in the future, it is also desirable to develop new high-entropy alloys in order to explore new applications of high-entropy alloys. The present invention has been made to solve the above problems, and it is to provide a method for producing a high-entropy alloy that can produce a high-entropy alloy simply and at low cost, and a method for using the high-entropy alloy. Further, it is to provide a high-entropy alloy catalyst and a new high-entropy alloy.

Means for Solving the Problems

[0008] The inventor of the present invention found that a high-entropy alloy can be obtained in a one-step reaction by heating and reducing a metal salt or an oxide precursor of its hydrate of each metal element in a molten salt containing an alkali metal or an alkaline earth metal using a reducing agent such as calcium hydride (CaH2) or calcium (Ca), and completed the present invention. And by this method, a high-entropy alloy catalyst and a new high-entropy alloy were produced.

[0009] The present invention relates to a method for producing a high-entropy alloy described in the following (1)-(5). (1) A step of obtaining a mixed solution in the presence of a solvent by mixing salts of five or more metals selected from the group consisting of transition metals of the 4th - 6th periods, groups 3 - 12, aluminum, silicon, and lanthanoids; a step of drying and heating the mixed solution to obtain an oxide precursor; and a step of heating and reducing the oxide precursor, at least one reducing agent selected from calcium hydride, calcium, magnesium hydride, and magnesium, and a molten salt of an alkali metal salt or an alkaline earth metal salt in the presence of an inert gas to obtain a high-entropy alloy. A method for producing a high-entropy alloy comprising these steps. (2) The method for producing a high-entropy alloy according to (1) above, wherein the step of obtaining the mixed solution is a step of mixing the metal salt and a chelating reagent in the presence of a solvent to obtain a mixed solution. (3) The step of obtaining the mixed solution is a step of mixing the metal salt and the oxide of the metal (excluding the metal of the metal salt) in the presence of a solvent to obtain a mixed solution, which is the method for producing a high-entropy alloy according to (1) above. (4) The metal is selected from Ni, Fe, Cr, Co, Al, Mn, Ti, V, Zr, Ir, Pd, Pt, Rh, Ru, Au, Ag, Y, Ga, Ln, Ce, Pr, Nd, Sm, which is the method for producing a high-entropy alloy according to (1) above. (5) At least one of the selected five or more metals is a noble metal, and the step of obtaining the mixed solution is a step of further mixing a calcium salt to obtain a mixed solution, which is the method for producing a high-entropy alloy according to (2) above.

[0010] The present invention also relates to the method for using a high-entropy alloy described in (6) and (7) below, the high-entropy alloy catalyst described in (8) and (9) below, and the novel compound described in (10) below. (6) A method for using a high-entropy alloy, which comprises producing high-entropy alloy powder by the method for producing a high-entropy alloy according to (2) above, and using the high-entropy alloy as a catalyst for a hydrogenation reaction in a liquid phase. (7) The hydrogenation reaction in the liquid phase is a synthesis reaction of an amine by hydrogenation of a nitro group or an imine, which is the method for using a high-entropy alloy according to (6) above. (8) The atomic composition ratio is AlCoCrFeNiV, AlCoCrFeNi, CoFeNiTiCr, CoFeNiTiV, Al 0.2 Co 1.5 CrFeNi 1.5 Ti 0.5 , (Ti 0.5 Zr 0.5 )(Cr 0.25 Mn 0.25 Fe 0.25 Ni 0.25 )2, and is a high-entropy alloy catalyst for a liquid-phase hydrogenation reaction containing a high-entropy alloy represented by any one of the formulas. (9) The liquid-phase hydrogenation reaction is a synthesis reaction of an amine by hydrogenation of a nitro group or an imine, which is the high-entropy alloy catalyst according to (8) above. (10) The atomic composition ratio is CeMnFeCoNiZn, or (La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 Sm 0.2 )MnFeCoNiZn, or (Y 0.2 La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 )Ga2Ni3, a high-entropy alloy represented by the formula.

Advantages of the Invention

[0011] According to the present invention, a method for manufacturing a high-entropy alloy and a method for using the high-entropy alloy, which can manufacture a high-entropy alloy simply and at low cost, can be provided. In addition, a high-entropy alloy catalyst and a novel high-entropy alloy can be provided.

Brief Description of the Drawings

[0012]

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Mode for Carrying Out the Invention

[0013] The method for producing a high-entropy alloy according to an embodiment of the present invention is a method of reducing oxide precursors of salts and hydrates of respective metal elements serving as raw materials in a molten salt containing an alkali metal or an alkaline earth metal using a reducing agent such as calcium hydride (CaH2) or calcium, and the high-entropy alloy is obtained by a one-step reaction. And, by this method, a novel high-entropy alloy can be produced. In the present specification, when indicating a numerical range, it includes the upper limit and the lower limit.

[0014] A high-entropy alloy is a multi-component alloy of five or more components, and is basically a single-phase random solid solution alloy, and is an alloy in which the mixing state is stabilized due to a negative increase in the mixing entropy term in the Gibbs free energy formula. The stable phase formed in the equilibrium state is given when the Gibbs free energy (ΔG) is minimized. Thermodynamically, ΔG is given by ΔG = ΔH - TΔS, and as the entropy (ΔS) increases, ΔG decreases. The mixing entropy term of a random ideal solution is given by the following formula.

Number

[0015] And, the method for producing a high-entropy alloy of this embodiment includes a step of obtaining a mixed solution by mixing salts of five or more metals as raw materials in the presence of a solvent, a step of drying and heating the mixed solution to obtain an oxide precursor, and heating and reducing the oxide precursor, at least one reducing agent selected from CaH2, Ca, MgH2, and Mg, and a molten salt of an alkali metal salt or an alkaline earth metal salt in the presence of an inert gas to obtain a high-entropy alloy. As constituent elements of the high-entropy alloy, metals are selected from the group consisting of transition metals in the 4th to 6th periods and 3rd to 12th groups of the periodic table, aluminum, silicon, and lanthanoids. Although aluminum and silicon are not transition metals, they are common with the above transition metals in that they can be constituent elements forming a high-entropy alloy (solid solution or intermetallic compound). Also, strictly speaking, silicon is a non-metal, but since it has the common property of forming an alloy (solid solution or intermetallic compound) with the above transition metals and aluminum, it is included as a metal in this specification. For example, nickel (Ni), iron (Fe), chromium (Cr), cobalt (Co), aluminum (Al), manganese (Mn), titanium (Ti), vanadium (V), zirconium (Zr), platinum (Pt), ruthenium (Ru), rhodium (Rh), gold (Au), iridium (Ir), Y (yttrium), gallium (Ga), lanthanum (Ln), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), etc. are selected. Note that as the number selected, if it is 5 or more, there is no upper limit, but if the number increases, it becomes difficult to dissolve in the process of obtaining the mixed solution, so about 5 to 10 types are preferable. Also, each constituent element may be at most 35 atomic percent (mol %).

[0016] And according to this embodiment, it is characterized by using the salts of the above metals and their hydrates as raw materials. In the production of conventional high-entropy alloys, expensive pure metals were used as the raw material metals, but since the salts of the raw material metals and their hydrates are easily available and inexpensive, cost reduction can be achieved.

[0017] As salts of metals, in addition to inorganic salts such as nitrates, sulfates, carbonates, phosphates, and chlorides of these metals, there are organic salts such as alkoxides, acetates, and oxalates. In the case of inorganic salts, many nitrates or chlorides are soluble and available at low cost, which is preferable. For example, when the raw material metal is aluminum, Al(NO3)3·9 H 2O For cobalt, there are hydrated nitrates such as Co(NO3)3·6H2O; for chromium, Cr(NO3)3·9H2O; for iron, Fe(NO3)3·9H2O; and for nickel, Ni(NO3)2·6H2O. Also, for vanadium and rhodium, chlorides such as VCl3 and RhCl3, which are available at low cost, are preferred. Further, since Ti and Si are available as soluble compounds, metal alkoxides may be used. Metal alkoxides are salts commonly used in the sol-gel method. Note that Al may also use metal alkoxides. The above salts may be hydrates. Any salt may be used as long as it is an available soluble compound.

[0018] Then, a metal salt or its hydrate and a chelating reagent are mixed in the presence of a solvent to obtain a mixed solution. Examples of the solvent include ion-exchanged water, distilled water, glycerin, alcohol (especially ethanol), glycol (especially ethylene glycol and propylene glycol), and standard organic solvents (THF, acetone, toluene). Among these, distilled water and ethanol are desirable because they are easy to handle and available at low cost. Also, a chelating reagent is an organic compound that forms a chelate complex with metal ions in a solution. As standard highly safe ones, there are ethylenediaminetetraacetic acid, citric acid, phytic acid, gluconic acid, etc. By using a chelating reagent, uniform composite metal oxide powders can be obtained using the complex polymerization method of the sol-gel method. The chelating reagent may be in a molar amount of 1 to 1.5 times the total molar amount of the plurality of metals.

[0019] On the one hand, when the number of constituent elements of the alloy increases (for example, 6, 7 or more types), depending on the raw materials, it may be difficult to obtain a uniform solution in which all metals are dissolved, such as being insoluble in solvents such as water or alcohol. In that case, for some metals (one type is desirable), it is advisable to prepare a suspension in which fine oxide powders are suspended instead of salts (impregnation method). In this case, a chelating reagent is not required, but for example, when the amount of oxide is small and it is difficult to prepare a uniform suspension, a chelating reagent may be used. Using a chelating reagent has the effect of obtaining a precursor in which the metals are uniformly dispersed. Also, for oxide powders, it is advisable to use SiO2, TiO2, CeO2, etc. because the target elements have limited available soluble compounds.

[0020] Then, by drying and heating the mixed solution, an oxide precursor can be obtained. The heating can be carried out in one step or through multiple steps. For example, after calcining at a low temperature, the calcined sample is uniformly pulverized and mixed using a pestle, etc. in a mortar, etc., and then, by firing at a high temperature, an oxide precursor in which the elements are uniformly dispersed can be obtained, which is preferable. The heating temperature is generally preferably about 300 - 800 °C, but 400 - 600 °C is preferable because impurities other than metal elements (such as chelating reagents) are removed by combustion or an oxide precursor in which the metal elements are uniformly dispersed can be obtained. Also, the heating time depends on the heating temperature, but it is preferably about 0.5 - 10 hours, preferably about 3 - 6 hours.

[0021] Thereafter, by mixing the oxide precursor, a reducing agent, and a molten salt source and heating and reducing in the presence of an inert gas (nitrogen, argon, helium, etc.), HEA powder can be obtained. Note that impurities (such as LiCl, CaCl2, CaH2, CaO, etc.) can be removed by washing the product after reduction. The heating temperature during reduction varies depending on the type of molten salt, but it needs to be at a temperature above the melting temperature, generally about 300 - 1000 °C, preferably 550 - 800 °C. Alternatively, the molten salt source may be heated first, and the oxide precursor and the reducing agent may be added in a molten state. Or a method may be adopted in which the molten salt source is mixed with the oxide precursor or the reducing agent, heated, and then the remaining reducing agent or oxide precursor is added. In the case of a mixed molten salt, the melting point of the molten salt is lower than that of a single molten salt, so it melts even at a temperature of less than 600 °C, for example. The molten salt acts as a solvent, and in the molten salt, the oxide precursor is reduced by the reducing agent. By this molten salt reduction method, HEA powder can be obtained under mild conditions at a low temperature as compared with the above-described physical method (about 2000 °C). The oxide precursor is alloyed immediately after reduction by the molten salt reduction method, and via the metallic state, it becomes an alloy powder of fine particles having a large specific surface area. The heating time depends on the heating temperature, but it is preferably about 0.5 to 10 hours, more preferably about 3 to 6 hours. When the heating temperature is low (for example, about 550 °C), it is necessary to increase the heating time (for example, about 10 hours), but when the heating temperature is high (for example, about 700 - 800 °C), the heating time can be reduced (for example, about 2 hours).

[0022] Then, as the reducing agent, calcium hydride, metallic calcium, magnesium hydride, metallic magnesium, etc. may be used. These reducing agents exhibit a strong reducing action in the molten salt. The reducing agent may be used alone or in combination. When used in combination, they may be mixed in advance or added separately at the time of mixing the oxide precursor and the molten salt. In particular, CaH2 is a stable powder at room temperature in the atmosphere and can be handled relatively safely, so it is preferable. When CaH2 is used as the reducing agent, CaH2 is used in an equimolar amount or more of the number of moles of oxygen contained in the oxide precursor, taking advantage of the fact that CaH2 reacts with the oxygen contained in the oxide precursor to become CaO. Preferably, the reducing agent is used in a weight ratio of 0.1 to 4 times, more preferably about 1 to 2 times, relative to the oxide precursor.

[0023] As the molten salt, alkali metal halides, alkaline earth metal halides, or mixtures thereof are used. As the alkali metal halides, compounds such as LiF, NaF, KF, RbF, CsF, LiCl, NaCl, KCl, RbCl, CsCl, LiBr, NaBr, KBr, RbBr, CsBr, LiI, NaI, KI, RbI, CsI can be used. And as the alkaline earth metal halides, compounds such as MgF2, CaF2, SrF2, BaF2, MgCl2, CaCl2, SrCl2, BaCl2, MgBr2, CaBr2, SrBr2, BaBr2, MgI2, CaI2, SrI2, BaI2 can be used.

[0024] The above compounds can be used alone or in combination of two or more. Also, the combinations of these compounds, the number of compounds to be combined, the mixing ratio, etc. are not limited, and can be appropriately selected according to being stable and easy to handle in the atmosphere, or being available at low cost. In addition, halides of relatively base metals such as AlCl3 and ZnCl2 can also be used.

[0025] In particular, as the molten salt used in this embodiment, it is preferable to use a single molten salt such as LiCl and CaCl2, or a mixed molten salt of LiCl and KCl, or a mixed molten salt of LiCl and CaCl2. Also, compared with a single molten salt, the mixed molten salt has a lower melting point, so the reaction can occur at a lower temperature. Therefore, when the temperature at which the alloy is formed is low (for example, those containing an easily reducible oxide such as a transition metal oxide as a raw material), it is preferable to use a mixed molten salt. For example, since the melting point of the mixed molten salt of LiCl and CaCl2 is 470 °C, the reaction can be carried out even at a low temperature of about 550 °C.

[0026] The HEA produced by the above method is an alloy powder of fine particles with a large specific surface area. Such alloy powders are expected to have various uses as shape memory alloys, such as in medical instruments and structural materials, as well as materials for 3D metal printers and catalyst materials. For example, when used in shape memory alloys or 3D metal printers, taking advantage of the feature of being very small fine particles, it becomes possible to manufacture materials and molds with complex shapes. And since this HEA has a large specific surface area, in particular, as a catalyst material, it can be used as the catalyst itself or as a carrier. For example, AlCoCrFeNiV, CrMnFeCoNi, AlCoCrFeNi, CoFeNiTiCr, CoFeNiTiV, Al 0.2 Co 1.5 CrFeNi 1.5 Ti 0.5 etc. HEA powders are mainly used as structural materials that require high strength, corrosion resistance, heat resistance, etc., but CrMnFeCoNi is also used as a catalyst in the reaction of the following (C), and these HEA powders can be used as catalysts for hydrogenation reactions in the liquid phase. Also, these HEA powders function as catalysts themselves, but they may also be used as catalyst carriers.

[0027] For example, examples of hydrogenation reactions in the liquid phase are shown below. (A) Conversion of alkenes (double bonds) and alkynes (triple bonds) to alkanes (B) Deprotection of benzyl groups (A compound of alcohol and a benzyl group as a protecting group is hydrogenated to remove the benzyl group to obtain alcohol.) (C) Hydrogenating nitro groups and imines to obtain amines. (D) Dehalogenation reaction by hydrogenation of aromatic halogens (E) Synthesis of alcohol or methylene by hydrogenation of aldehydes and ketones Also, (Ti 0.5 Zr 0.5 )(Cr 0.25 Mn 0.25 Fe 0.25 Ni 0.25)2 can be used as a catalyst for hydrogenation reactions in the liquid phase by supporting metal catalysts for hydrogenation such as Ni, Pd, and Pt on the carrier of the catalyst. The reason why this alloy itself does not act as a catalyst can be considered as follows. This alloy contains Ti and Zr, but these elements are located on the left side of the periodic table, have a strong interaction with oxygen, and are prone to forming oxide films. From this, it can be said that the active transition metals of the constituent elements Cr, Mn, Fe, and Ni are difficult to be exposed on the surface. And, in particular, in organic synthesis, the hydrogenation of the nitro group of (C) is a common reaction and has a highly versatile application. For example, there is a hydrogenation reaction from p-nitrophenol to p-aminophenol, and as reducing agents, NaBH4, hydrogen gas, LiAlH4, etc. are used.

[0028] Furthermore, by the above method, new HEAs such as CeMnFeCoNiZn, (La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 Sm 0.2 )MnFeCoNiZn, (Y 0.2 La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 )Ga2Ni3 can also be fabricated. These HEAs contain rare earth elements (Ce, Ln, Pr, Nd, Sm, Y) and have more basic metal properties than the above-mentioned (Ti 0.5 Zr 0.5 )(Cr 0.25 Mn 0.25 Fe 0.25 Ni 0.25 )2. They also have a large specific surface area. Therefore, they can be used as catalysts or basic carriers. That is, similar to (Ti 0.5 Zr 0.5 )(Cr 0.25 Mn 0.25 Fe 0.25 Ni 0.25 )2, CeMnFeCoNiZn, (La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 Sm 0.2)MnFeCoNiZn, (Y 0.2 La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 )Novel HEAs such as Ga2Ni3 can be used as catalyst supports. Also, in that case, since the properties of the basic metal are strong, application as a support containing a basic metal is suitable. For example, by supporting a metal catalyst for hydrogenation such as Ni, in addition to the above hydrogenation reaction in the liquid phase, it can be said that it can be applied to the synthesis of hydrocarbons or oxygen-containing hydrocarbons by the hydrogenation of carbon monoxide or carbon dioxide. For example, it can be applied to methane synthesis by the hydrogenation of carbon monoxide.

[0029] Furthermore, by the above method, HEAs containing noble metals such as IrPdPtRhRu, IrRhRuCoNi, AuPdPtRhRu, IrNiPtRhCo, RuRhPdAgIrPtAu can also be produced. These HEA powders are used as electrode catalysts and can be used, for example, as catalysts for the electrolysis of ammonia. Also, these HEA powders function as catalysts themselves. Note that since noble metals (such as Ir, Pd, Pt, Rh, Ru, Au) are stable, they may not easily become oxides even when calcined at about 500 °C in the molten salt reduction method. Therefore, for the production of HEAs containing noble metals, it is preferable to add an appropriate amount (for example, Ca = 30 mol%) of calcium salts such as Ca(NO3)2, CaCl2, (CH3COO)2Ca to the raw materials and then calcine them. In this way, a composite oxide of CaO and noble metal (or a compound in which the noble metal is dispersed in CaO) can be obtained, and it becomes easier to obtain a powder of the oxide precursor. Note that the added Ca can be removed by washing with a cleaning solution such as an NH4Cl aqueous solution in the final step and thus does not remain in the alloy.

[0030] Hereinafter, the present invention will be described more specifically by examples, but the present invention is not limited to the following examples.

Examples

[0031] (Example 1) Al(NO3)3·9 in distilled water H 2O (manufactured by Wako Pure Chemical Industries, Ltd., purity 99%), Co(NO3)3·6H2O (manufactured by Wako Pure Chemical Industries, Ltd., purity 98%), Cr(NO3)3·9H2O (manufactured by Nacalai Tesque, Inc., purity 98%), Fe(NO3)3·9H2O (manufactured by Wako Pure Chemical Industries, Ltd., purity 99%), Ni(NO3)2·6H2O (manufactured by Wako Pure Chemical Industries, Ltd., purity 99.9%), VCl3 (manufactured by Merck, purity 97%), and citric acid (manufactured by Wako Pure Chemical Industries, Ltd.) were dissolved in a molar ratio of Al / Co / Cr / Fe / Ni / V / citric acid = 1 / 1 / 1 / 1 / 1 / 1 / 7.2 and evaporated to dryness on a hot plate. Then, it was calcined at 250 °C for 2 hours. The calcined sample was crushed and mixed in a mortar using a pestle, and the particle size was made approximately uniform in powder form, and then calcined again at 500 °C for 2 hours to obtain an oxide precursor (AlCoCrFeNiV(Pre)). The obtained oxide precursor, CaH2 (manufactured by Nacalai Tesque, Inc.), and LiCl-CaCl2 (manufactured by Wako Pure Chemical Industries, Ltd., molar ratio 1:1) were mixed at a weight ratio of 2 / 6 / 3, and in a SUS tubular furnace (similarly in other examples), under an argon atmosphere, it was heated at 550 °C (reduction temperature) for 10 hours for molten salt reduction. The mixed molten salt source of LiCl and CaCl2 was prepared by mixing in a mortar using a pestle. And finally, the product was washed with 0.1 M NH4Cl aqueous solution and distilled water to remove impurities (LiCl, CaCl2, CaH2, CaO, etc.), and HEA powder AlCoCrFeNiV was obtained. In the following examples, unless otherwise specified, HEA powder was prepared in the same manner and conditions as in Example 1. Also, the same reagents were used for the common compounds.

[0032] Figure 1 shows the X-ray diffraction pattern and SEM image of the HEA powder. The X-ray diffraction pattern was measured using an X-ray diffractometer (manufactured by Rigaku Corporation, Mini Flex 600) under the following conditions. Conditions: X-ray source CuKα, output 40KV, 15mA The SEM image was measured using a scanning electron microscope (manufactured by JEOL Ltd., JSM-7800F). As can be seen from Fig. 1, a single BCC structure was confirmed, indicating that it is a single-phase solid solution alloy. Also, from the SEM image, a fine structure composed of fine particles of 1 - 10 μm or less was confirmed. And when the BET specific surface area was determined by the nitrogen adsorption experiment, the specific surface area was 33.4 m 2 / g. From these results, it can be said that the obtained HEA powder has a fine structure. Note that in the nitrogen adsorption experiment, after drying the sample at 200 °C for 30 minutes under an inert gas flow, the nitrogen adsorption amount was measured at liquid nitrogen temperature.

[0033] (Example 2) Cr(NO3)3·9H2O, Mn(NO3)2·6H2O (manufactured by Fuji Wako Pure Chemical Industries, Ltd.), Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, and citric acid were dissolved in distilled water so that the molar ratio was Cr / Mn / Fe / Co / Ni / citric acid = 1 / 1 / 1 / 1 / 1 / 7.2, and then evaporated to dryness on a hot plate. Thereafter, it was calcined at 250 °C for 2 hours. The calcined sample was crushed to make the particle size approximately uniform, and then calcined again at 500 °C for 2 hours to obtain an oxide precursor (CrMnFeCoNi(Pre)). The obtained oxide precursor, CaH2, and LiCl were mixed at a molar ratio of 2 / 6 / 3, and molten salt reduction was carried out by heating at 700 °C for 2 hours in a nitrogen atmosphere. Finally, impurities were removed by washing the product with 0.1 M NH4Cl aqueous solution and distilled water to obtain HEA powder CrMnFeCoNi. Fig. 2 shows the X-ray diffraction pattern and SEM image of the HEA powder. From Fig. 2, a single FCC structure was confirmed, indicating that it is a single-phase solid solution alloy. Also, from the SEM image, a fine structure composed of fine particles of 1 - 10 μm or less was confirmed. And the specific surface area was 12.1 m 2 / g. From these results, it can be said that the obtained HEA powder has a fine structure. Note that the above X-ray diffraction pattern, SEM image, specific surface area, etc. were measured by the same method and conditions as in Example 1. This also applies to the following examples.

[0034] (Example 3) Al(NO3)3·9H2O, Co(NO3)2·6H2O, Cr(NO3)3·9H2O, Fe(NO3)3·9H2O, Ni(NO3)2·6H2O, and citric acid were dissolved in distilled water at a molar ratio of Al / Co / Cr / Fe / Ni / citric acid = 1 / 1 / 1 / 1 / 1 / 7.2 and evaporated to dryness on a hot plate. Then, it was calcined at 250 °C for 2 hours. The calcined sample was crushed to make the particle size approximately uniform and then calcined again at 500 °C for 2 hours to obtain an oxide precursor (AlCoCrFeNi(Pre)). The obtained oxide precursor, CaH2, and LiCl-CaCl2 were mixed at a molar ratio of 2 / 6 / 3 and melted and reduced by heating at 550 °C for 10 hours under an argon atmosphere. Finally, the product was washed with 0.1 M NH4Cl aqueous solution and distilled water to remove impurities, and HEA powder AlCoCrFeNi was obtained. Figure 3 shows the X-ray diffraction pattern and SEM image of the HEA powder. From Figure 3, a single BCC structure was confirmed, indicating that it is a single-phase solid solution alloy. Also, from the SEM image, a fine structure composed of fine particles of 1-10 μm or less was confirmed. And the specific surface area was 67.5 m 2 / g. From these results, it can be said that the obtained HEA powder has a fine structure.

[0035] (Example 4-5) Co(NO3)2·6H2O, Fe(NO3)3·9H2O, Ni(NO3)2·6H2O, [(CH3)2CHO]4Ti (manufactured by Wako Pure Chemical Industries, Ltd.), Cr(NO3)3·9H2O, VCl3, and citric acid were dissolved on a hot plate in a molar ratio of Co / Fe / Ni / Ti / Cr or V / citric acid = 1 / 1 / 1 / 1 / 1 / 6 and evaporated to dryness in a dryer at 65 °C. Then, it was calcined at 250 °C for 2 hours. The calcined sample was crushed to make the particle size approximately uniform and then calcined again at 500 °C for 2 hours to obtain an oxide precursor (CoFeNiTiCr(Pre) or CoFeNiTiV(Pre)). The obtained oxide precursor was mixed with CaH2 and LiCl in a molar ratio of 2 / 6 / 3 and subjected to molten salt reduction by heating at 800 °C for 2 hours in a nitrogen atmosphere. Finally, the product was washed with 0.1 M NH4Cl aqueous solution and distilled water to remove impurities, and HEA powder CoFeNiTiCr (Example 4) and HEA powder CoFeNiTiV (Example 5) were obtained.

[0036] Figures 4-5 show the X-ray diffraction patterns and SEM images of the HEA powders. In Example 4, from Figure 4, a single FCC structure was confirmed, indicating that it is a single-phase solid solution alloy. Also, from the SEM image, a fine structure composed of fine particles of 1-10 μm or less was confirmed. And the specific surface area was 23.1 m 2 / g. From these results, it can be said that the obtained HEA powder has a fine structure. Furthermore, in Example 5, from Figure 5, a single FCC structure was confirmed, indicating that it is a single-phase solid solution alloy. Also, from the SEM image, a fine structure composed of fine particles of 1-10 μm or less was confirmed. And the specific surface area was 22.1 m 2 / g. From these results, it can be said that the obtained HEA powder has a fine structure.

[0037] (Example 6) Al(NO3)3·9H2O, Co(NO3)2·6H2O, Cr(NO3)3·9H2O, Fe(NO3)3·9H2O, Ni(NO3)2·6H2O, TiCl4, and citric acid were dissolved in distilled water in a molar ratio of Al / Co / Cr / Fe / Ni / Ti / citric acid = 0.2 / 1.5 / 1 / 1 / 1.5 / 0.5 / 7.2 and evaporated to dryness on a hot plate. Then, it was calcined at 250 °C for 2 hours. The calcined sample was crushed to make the particle size approximately uniform and then calcined again at 500 °C for 2 hours to obtain the oxide precursor (Al 0.2 Co 1.5 CrFeNi 1.5 Ti 0.5 (Pre)). The obtained oxide precursor, CaH2, and LiCl were mixed in a molar ratio of 2 / 6 / 3 and subjected to molten salt reduction by heating at 600 °C for 2 hours under a nitrogen atmosphere. Finally, the product was washed with 0.1 M NH4Cl aqueous solution and distilled water to remove impurities, obtaining the HEA powder Al 0.2 Co 1.5 CrFeNi 1.5 Ti 0.5 . Also, when the reduction temperature was 800 °C (heating time was 2 hours), the HEA powder Al 0.2 Co 1.5 CrFeNi 1.5 Ti 0.5 was obtained in the same manner. Figure 6 shows the X-ray diffraction patterns and SEM images of the HEA powder. From Figure 6, a single FCC structure was confirmed even when the reduction temperature was 600 °C (Figure 6(A)) and 800 °C (Figure 6(B)), indicating that it is a single-phase solid solution alloy. Also, from the SEM images, a fine structure composed of microparticles of 1 - 10 μm or less was confirmed. And the specific surface areas were 91.7 m 2 / g (600 °C) and 13.6 m 2 / g (800 °C). From these results, it can be said that the obtained HEA powder has a fine structure.

[0038] (Example 7) TiO2 (manufactured by Sakai Chemical Industry Co., Ltd.), ZrO(NO3)2·2H2O (manufactured by Fuji Wako Pure Chemical Industries, Ltd.), Cr(NO3)3·9H2O, Mn(NO3)2·6H2O, Fe(NO3)3·9H2O, Ni(NO3)2·6H2O, and citric acid were dissolved in distilled water so that the molar ratio was Ti / Zr / Cr / Mn / Fe / Ni / citric acid = 1 / 1 / 1 / 1 / 1 / 1 / 7.2, and then evaporated to dryness on a hot plate. Thereafter, it was calcined at 250 °C for 2 hours. The calcined sample was crushed to make the particle size substantially uniform, and then calcined again at 500 °C for 2 hours to obtain an oxide precursor ((Ti 0.5 Zr 0.5 )(Cr 0.25 Mn 0.25 Fe 0.25 Ni 0.25 )2(Pre)). The obtained oxide precursor, CaH2, and LiCl were mixed at a molar ratio of 2 / 6 / 3, and melt salt reduction was carried out by heating at 800 °C for 2 hours in a nitrogen atmosphere. Finally, impurities were removed by washing the product with 0.1 M NH4Cl aqueous solution and distilled water to obtain HEA powder (Ti 0.5 Zr 0.5 )(Cr 0.25 Mn 0.25 Fe 0.25 Ni 0.25 )2 (the composition is TiZrCrMnFeNi). Figure 7 shows the X-ray diffraction pattern and SEM image of the HEA powder. From Figure 7, it can be said that a hexagonal close-packed structure is confirmed and an intermetallic compound is formed. From the XRD measurement results, the prepared (Ti 0.5 Zr 0.5 )(Cr 0.25 Mn 0.25 Fe 0.25 Ni 0.25 )2 has a hexagonal crystal structure similar to TiCr2, and a single-phase intermetallic compound stabilized by the contribution of the mixing entropy term is formed. Also, from the SEM image, a fine structure composed of fine particles of 1 - 10 μm or less was confirmed. And the specific surface area was 22.5 m 2 / g. From this result, it can be said that the obtained HEA powder has a fine structure.

[0039] (Example 8) Ce(NO3)3·6H2O (manufactured by Fujifilm Wako Pure Chemical Corporation), Mn(NO3 ) 2 ·6 H2O, Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Zn(NO3)2·6H2O (manufactured by Fujifilm Wako Pure Chemical Corporation), and citric acid were dissolved in distilled water so that the molar ratio was Ce / Mn / Fe / Co / Ni / Zn / citric acid = 1 / 1 / 1 / 1 / 1 / 1 / 7.2, and then evaporated to dryness on a hot plate. Thereafter, it was calcined at 250 °C for 2 hours. The calcined sample was crushed to make the particle size substantially uniform, and then calcined again at 500 °C for 2 hours to obtain an oxide precursor (CeMnFeCoNiZn(Pre)). The obtained oxide precursor, CaH2, and LiCl were mixed at a molar ratio of 2 / 6 / 3 and melted and reduced by heating at 800 °C for 2 hours in a nitrogen atmosphere. Finally, impurities were removed by washing the product with 0.1 M NH4Cl aqueous solution and distilled water to obtain a novel HEA powder CeMnFeCoNiZn. Figure 8 shows the X-ray diffraction pattern and SEM image of the HEA powder. From Figure 8, a single FCC structure was confirmed, indicating that it is a single-phase solid solution alloy. Also, the specific surface area was 51.2 m 2 / g. From these results, it can be said that the obtained HEA powder has a fine structure.

[0040] (Example 9) La(NO3)3·6H2O (manufactured by Fujifilm Wako Pure Chemical Corporation), Ce(NO3)3·6H2O, Pr(NO3)3·nH2O (manufactured by Fujifilm Wako Pure Chemical Corporation), Nd(NO3)3·6H2O (manufactured by Fujifilm Wako Pure Chemical Corporation), Sm(NO3)3·6H2O (manufactured by Fujifilm Wako Pure Chemical Corporation), Mn(NO3 ) 2 ·6 H2O, Fe(NO3 ) 3 ·9H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Zn(NO3)2·6H2O, and citric acid were dissolved in a molar ratio of La / Ce / Pr / Nd / Sm / Mn / Fe / Co / Ni / Zn / citric acid = 0.2 / 0.2 / 0.2 / 0.2 / 0.2 / 1 / 1 / 1 / 1 / 1 / 7.2 and evaporated to dryness on a hot plate. Then, it was calcined at 250 °C for 2 hours. The calcined sample was crushed to make the particle size approximately uniform and then calcined again at 500 °C for 2 hours to obtain an oxide precursor ((La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 Sm 0.2 )MnFeCoNiZn(Pre)). The obtained oxide precursor, CaH2, and LiCl were mixed in a molar ratio of 2 / 6 / 3 and subjected to molten salt reduction by heating at 800 °C for 2 hours in a nitrogen atmosphere. Finally, impurities were removed by washing the product with 0.1 M NH4Cl aqueous solution and distilled water to obtain a novel HEA powder (La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 Sm 0.2 )MnFeCoNiZn). Figure 9 shows the X-ray diffraction pattern and SEM image of the HEA powder. From Figure 9, a single FCC structure was confirmed, indicating that it is a single-phase solid solution alloy. Also, the specific surface area was 25.8 m 2 / g. From these results, it can be said that the obtained HEA powder has a fine structure.

[0041] (Example 10) Y(NO3)3·nH2O (manufactured by Fujifilm Wako Pure Chemical Corporation), La(NO3)3·6H2O, CeO2 (manufactured by Merck), Pr(NO3)3·nH2O (manufactured by Fujifilm Wako Pure Chemical Corporation), Nd(NO3)3·6H2O, Ga(NO3)3·nH2O (manufactured by Fujifilm Wako Pure Chemical Corporation), Ni(NO3)2·6H2O, and citric acid were dissolved in distilled water in a molar ratio of Y / La / Ce / Pr / Nd / Ga / Ni / citric acid = 0.2 / 0.2 / 0.2 / 0.2 / 0.2 / 2 / 3 / 7.2, and then evaporated to dryness on a hot plate. Subsequently, it was calcined at 250 °C for 2 hours. The calcined sample was crushed to make the particle size approximately uniform, and then calcined again at 500 °C for 2 hours to obtain an oxide precursor ((Y 0.2 La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 )Ga2Ni3(Pre)). The obtained oxide precursor, CaH2, and LiCl were mixed in a molar ratio of 2 / 6 / 3 and subjected to molten salt reduction by heating at 600 °C for 2 hours under an argon atmosphere. Finally, impurities were removed by washing the product with 0.1 M NH4Cl aqueous solution and distilled water to obtain a novel HEA powder (Y 0.2 La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 )Ga2Ni3. Figure 10 shows the X-ray diffraction pattern and SEM image of the HEA powder. From Figure 10, it can be confirmed that a hexagonal close-packed structure is present and an intermetallic compound is formed. Also, the specific surface area was 19.9 m 2 / g. From these results, it can be said that the obtained HEA powder has a fine structure. Also, the Hermann–Mauguin symbol and space group number of LnGa2Ni3 (Ln = La, Ce, Pr, Nd) are P62m and 189, respectively. From the XRD measurement results, the prepared (Y 0.2 La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 )Ga2Ni3 has a single-phase crystal structure with the same P62m and 189 as LnGa2Ni3, and a single-phase intermetallic compound stabilized by the contribution of the mixing entropy term is formed.

[0042] (Example 11) IrCl3·nH2O (manufactured by Tokyo Chemical Industry Co., Ltd.), (NH4)2PdCl4 (manufactured by Fuji Wako Pure Chemical Industries, Ltd.), H2PtCl6·6H2O (manufactured by Fuji Wako Pure Chemical Industries, Ltd.), RhCl3 (manufactured by Tanaka Precious Metals Industry Co., Ltd.), RuCl3·nH2O (manufactured by Fuji Wako Pure Chemical Industries, Ltd.), and Ca(NO3)2·4H2O (manufactured by Fuji Wako Pure Chemical Industries, Ltd., 30 mol% added) were dissolved in distilled water so that the molar ratio of Ir / Pd / Pt / Rh / Ru / citric acid was 1 / 1 / 1 / 1 / 1 / 7.2, and then evaporated to dryness on a hot plate. Thereafter, it was calcined at 250 °C for 2 hours. The calcined sample was crushed to make the particle size substantially uniform, and then calcined again at 500 °C for 2 hours to obtain an oxide precursor (IrPdPtRhRu(Pre)). The obtained oxide precursor, CaH2, and LiCl were mixed at a molar ratio of 2 / 6 / 3 and melt-reduced by heating at 600 °C for 2 hours in an argon atmosphere. Finally, impurities were removed by washing the product with 0.1 M NH4Cl aqueous solution and distilled water to obtain HEA powder IrPdPtRhRu. Fig. 11 shows the X-ray diffraction pattern and SEM image of the HEA powder. From Fig. 11, a single FCC structure was confirmed, indicating that it is a single-phase solid solution alloy. Also, the specific surface area was 32.6 m 2 / g. From these results, it can be said that the obtained HEA powder has a fine structure.

[0043] (Example 12) IrCl3·nH2O, RhCl3 (manufactured by Tanaka Kikinzoku Kogyo K.K.), RuCl3·nH2O (manufactured by Wako Pure Chemical Industries, Ltd.), Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Ca(NO3)2·4H2O, and citric acid were dissolved in distilled water so that the molar ratio was Ir / Rh / Ru / Co / Ni / citric acid = 1 / 1 / 1 / 1 / 1 / 7.2, and then evaporated to dryness on a hot plate. Thereafter, it was calcined at 250 °C for 2 hours. The calcined sample was crushed to make the particle size substantially uniform, and then calcined again at 500 °C for 2 hours to obtain an oxide precursor (IrRhRuCoNi(Pre)). The obtained oxide precursor, CaH2, and LiCl were mixed at a molar ratio of 2 / 6 / 3 and melted and reduced by heating at 600 °C for 2 hours in an argon atmosphere. Finally, the product was washed with 0.1 M NH4Cl aqueous solution and distilled water to remove impurities, and HEA powder IrRhRuCoNi was obtained. Figure 12 shows the X-ray diffraction pattern and SEM image of the HEA powder. From Figure 12, a single FCC structure was confirmed, indicating that it is a single-phase solid solution alloy. Also, the specific surface area was 69.9 m 2 / g. From these results, it can be said that the obtained HEA powder has a fine structure.

[0044] (Example 13) HAuCl4·4H2O (manufactured by FUJIFILM Wako Pure Chemical Corporation), (NH4)2PdCl4 (manufactured by FUJIFILM Wako Pure Chemical Corporation), H2PtCl6·6H2O (manufactured by FUJIFILM Wako Pure Chemical Corporation), RhCl3, RuCl3·nH2O, Ca(NO3)2·4H2O, and citric acid were dissolved in distilled water so that the molar ratio of Au / Pd / Pt / Rh / Ru / citric acid was 1 / 1 / 1 / 1 / 1 / 7.2, and then evaporated to dryness on a hot plate. Subsequently, it was calcined at 250 °C for 2 hours. The calcined sample was crushed to make the particle size approximately uniform, and then calcined again at 500 °C for 2 hours to obtain an oxide precursor (AuPdPtRhRu(Pre)). The obtained oxide precursor, CaH2, and LiCl were mixed at a molar ratio of 2 / 6 / 3, and melt-salt reduction was carried out by heating at 600 °C for 2 hours under an argon atmosphere. Finally, impurities were removed by washing the product with 0.1 M NH4Cl aqueous solution and distilled water to obtain HEA powder AuPdPtRhRu. Figure 13 shows the X-ray diffraction pattern and SEM image of the HEA powder. From Figure 13, a single FCC structure was confirmed, indicating that it is a single-phase solid-solution alloy. Also, the specific surface area was 50.2 m 2 / g. From these results, it can be said that the obtained HEA powder has a fine structure.

[0045] (Example 14) IrCl3·nH2O, Ni(NO3)2·6H2O, H2PtCl6·6H2O, RhCl3·3H2O, Co(NO3)2·6H2O, Ca(NO3)2·4H2O, and citric acid were dissolved in distilled water so that the molar ratio of Ir / Ni / Pt / Rh / Co was 1 / 1 / 1 / 1 / 1 / 7.2, and then evaporated to dryness on a hot plate. Subsequently, it was calcined at 250 °C for 2 hours. The calcined sample was crushed to make the particle size approximately uniform, and then calcined again at 500 °C for 2 hours to obtain an oxide precursor (IrNiPtRhCo(Pre)). The obtained oxide precursor, CaH2, and LiCl were mixed at a molar ratio of 2 / 6 / 3, and melt-salt reduction was carried out by heating at 600 °C for 2 hours under an argon atmosphere. Finally, impurities were removed by washing the product with 0.1 M NH4Cl aqueous solution and distilled water to obtain HEA powder IrNiPtRhCo. Figure 14 shows the X-ray diffraction pattern and SEM image of the HEA powder. From Figure 14, a single FCC structure was confirmed, indicating that it is a single-phase solid solution alloy. Also, the specific surface area was 25.5 m 2 / g. From these results, it can be said that the obtained HEA powder has a fine structure.

[0046] (Example 15) RuCl3-nH2O, RhCl3·3H2O, (NH4)2PdCl4, AgNO3 (manufactured by Fuji Wako Pure Chemical Industries, Ltd.), IrC l 3 ·nH 2O, H2PtCl6·6H2O, HAuCl4·4H2O, Ca(NO3)2·4H2O, and citric acid were dissolved in distilled water in a molar ratio of Ru / Rh / Pd / Ag / Ir / Pt / Au = 1 / 1 / 1 / 1 / 1 / 1 / 1 / 7.2 and evaporated to dryness on a hot plate. Then, it was calcined at 250 °C for 2 hours. The calcined sample was crushed to make the particle size approximately uniform and then calcined again at 500 °C for 2 hours to obtain an oxide precursor (RuRhPdAgIrPtAu(Pre)). The obtained oxide precursor, CaH2, and LiCl were mixed in a molar ratio of 2 / 6 / 3 and reduced by molten salt reduction by heating at 600 °C for 2 hours in an argon atmosphere. Finally, impurities were removed by washing the product with 0.1 M NH4Cl aqueous solution and distilled water to obtain HEA powder RuRhPdAgIrPtAu. Figure 15 shows the X-ray diffraction pattern and SEM image of the HEA powder. From Figure 15, a single FCC structure was confirmed, indicating that it is a single-phase solid solution alloy. Also, the specific surface area was 34.2 m 2 / g. From these results, it can be said that the obtained HEA powder has a fine structure.

[0047] Table 1 shows the summarized results for the HEA powders prepared in Examples 1-15 above.

Table 1

[0048] (Example 16) The HEA powder obtained in Examples 1 - 6 was used in the hydrogenation reaction from p - nitrophenol to p - aminophenol to evaluate the HEA catalytic activity. p - Nitrophenol (maximum absorption wavelength: 401 nm) changes to p - aminophenol (maximum absorption wavelength: 303 nm) by the hydrogenation reaction. 100 mg of HEA powder, 1 mL of a 14 mM p - nitrophenol solution, 1 mL of a 0.42 M NaBH4 solution, and 7 mL of distilled water were added to a glass tube and heated to start the hydrogenation reaction. The reaction temperature (heating temperature) was set within the range of about 20 - 60 °C according to each HEA powder. The methods and conditions of the above experiment are common to all examples, but in Examples 1 - 3, the experiment was carried out at multiple reaction temperatures, and in Examples 4 - 6, the reaction temperature was 50 °C. The HEA powder may be added to p - nitrophenol in a weight ratio of 1 - 500 times, preferably about 10 - 100 times. Starting from the start of the reaction, 100 - 500 μL of the test solution was aliquoted from the glass tube every certain time, diluted (by adding distilled water) in a 5 mL volumetric flask, and then the absorbance at 300 - 500 nm was measured using a UV-Vis spectrophotometer (UV-1280, manufactured by Shimadzu Corporation) to measure the concentration changes of p-nitrophenol and p-aminophenol. The results are shown in Figures 16 - 21. Figures 16 - 21 correspond to Examples 1 - 6 respectively.

[0049] From these results, it was shown that the hydrogenation reaction of p-nitrophenol proceeded with the HEA catalyst. Also, in the HEA powder obtained in Examples 1 - 3, an activity effect was observed at any temperature, and in particular, as the temperature increased, the concentration decreased significantly, and it was confirmed that the reaction rate improved. And it was found that almost all or most of p-nitrophenol was converted to p-aminophenol in a short time of about 10 - 30 minutes. And from these results, it was confirmed that the obtained HEA catalyst exhibited excellent liquid-phase hydrogenation activity. In heterogeneous catalytic reactions, the reaction proceeds on the surface of the catalyst. Therefore, it is preferable to use a catalyst with a high specific surface area. The result that the high specific surface area of the HEA catalyst obtained in this example effectively acts on the hydrogenation reaction was shown. In particular, Al 0.2 Co 1.5 CrFeNi 1.5 Ti 0.5 catalyst (Example 6) showed the fastest reaction rate (Figure 21), so it can be said that Al 0.2 Co 1.5 CrFeNi 1.5 Ti 0.5 is suitable. Also, in AlCoCrFeNi (Example 3, Figure 18), since almost the entire amount reacted within 3 minutes, it can be said to be preferable. In particular, in Example 3, even though the reaction temperature was relatively low (38 °C), good results were obtained.

[0050] Also, the HEA powder obtained in Example 7 was evaluated for HEA catalyst activity as a Ni-supported catalyst supporting 10 wt% of Ni. The Ni-supported catalyst was prepared by the following method. The HEA powder ((Ti 0.5 Zr 0.5 )(Cr 0.25 Mn 0.25 Fe 0.25 Ni 0.25 )2) obtained in Example 7 was suspended in distilled water, and then Ni(NO3)2·6H2O was dissolved so that the weight ratio of HEA / Ni was 9 / 1, and the solution was evaporated to dryness on a hot plate. Then, it was heated at 500 °C for 1 hour under an argon flow to obtain a Ni-supported catalyst supporting 10 wt% of Ni.

[0051] And for the Ni-supported catalyst (100 mg) and the HEA powder (100 mg) obtained in Example 7, the HEA catalytic activity was evaluated in the same manner and under the same conditions as the HEA powder obtained in Examples 1-6 (the reaction temperature was 50 °C). The results are shown in Figure 22. From these results, almost no catalytic activity was observed with only the HEA powder, but good catalytic activity could be confirmed with a short reaction time when using the Ni-supported catalyst.

[0052] (Example 17) Table 2 shows the results of calculating the crystallite size of the HEA powder obtained in Examples 8-15 from each XRD measurement result using the Scherrer equation.

Table 2

[0053] It can also be said from Table 2 that the HEA powder obtained in Examples 8-15 is an alloy powder of nano-sized fine particles. And the HEA powder obtained in Examples 8-10 is also suitable as a catalyst material that requires a large specific surface area and nano-sized fine particles. For the HEA powder obtained in Examples 11-15, the calculation limit is around 3-5 nm, and a quantitative crystallite size cannot be clearly shown, but since a broad peak is observed in XRD, it is clear that crystallites smaller than 5 nm are formed. And the HEA powder obtained in Examples 11-15 can be used as an electrode catalyst such as a catalyst for the electrolysis of ammonia.

Industrial Applicability

[0054] As a shape memory alloy, the present invention can be used in various fields such as medical instruments, structural materials, and new application fields such as 3D metal printers, and as a catalyst material.

Claims

1. A step of obtaining a mixed solution by mixing salts of five or more metals selected from the group consisting of transition metals of the 4th - 6th periods, groups 3 - 12, aluminum, silicon, and lanthanoids in the presence of a solvent; A step of drying and heating the mixed solution to obtain an oxide precursor; A step of heating and reducing the oxide precursor, at least one reducing agent selected from calcium hydride and magnesium hydride, and a molten salt of an alkali metal salt or an alkaline earth metal salt in the presence of an inert gas to obtain a high - entropy alloy; Comprising: A method for producing a high - entropy alloy containing fine particles of 10 μm or less.

2. The step of obtaining the mixed solution is a step of mixing the metal salt and a chelating reagent in the presence of a solvent to obtain a mixed solution, the method for producing a high - entropy alloy according to Claim 1.

3. The step of obtaining the mixed solution is a step of mixing the metal salt and an oxide of the metal (excluding the metal of the metal salt) in the presence of a solvent to obtain a mixed solution, the method for producing a high - entropy alloy according to Claim 1.

4. The metal is selected from Ni, Fe, Cr, Co, Al, Mn, Ti, V, Zr, Ir, Pd, Pt, Rh, Ru, Au, Ag, Y, Ga, Ln, Ce, Pr, Nd, Sm, the method for producing a high - entropy alloy according to Claim 1.

5. A step of obtaining a mixed solution by mixing salts of five or more metals selected from the group consisting of transition metals of the 4th - 6th periods, groups 3 - 12, aluminum, silicon, and lanthanoids in the presence of a solvent; A step of drying and heating the mixed solution to obtain an oxide precursor; A step of heating and reducing the oxide precursor, at least one reducing agent selected from calcium hydride, calcium, magnesium hydride, and magnesium, and a molten salt of an alkali metal salt or an alkaline earth metal salt in the presence of an inert gas to obtain a high - entropy alloy; comprising The step of obtaining the mixed solution is a step of mixing a salt of the metal and a chelating reagent in the presence of a solvent to obtain a mixed solution. At least one of the five or more selected metals is a noble metal, and the step of obtaining the mixed solution is further a step of mixing a calcium salt to obtain a mixed solution. A method for producing a high-entropy alloy containing fine particles of 10 μm or less.

6. A step of mixing salts of five or more metals selected from the group consisting of transition metals of the 4th - 6th periods, groups 3 - 12, aluminum, silicon, and lanthanoids in the presence of a solvent to obtain a mixed solution; A step of drying and heating the mixed solution to obtain an oxide precursor; A step of heating and reducing the oxide precursor, at least one reducing agent selected from calcium hydride, calcium, magnesium hydride, and magnesium, and a molten salt of an alkali metal salt or an alkaline earth metal salt in the presence of an inert gas to obtain a high-entropy alloy; comprising By the method for producing a high-entropy alloy, in which the step of obtaining the mixed solution is a step of mixing a salt of the metal and a chelating reagent in the presence of a solvent to obtain a mixed solution, a high-entropy alloy containing fine particles of 10 μm or less is produced, and the high-entropy alloy is used as a catalyst for a hydrogenation reaction in a liquid phase. A method of using a high-entropy alloy.

7. The method of using a high-entropy alloy according to claim 6, wherein the hydrogenation reaction in the liquid phase is a synthesis reaction of an amine by hydrogenation of a nitro group or an imine.

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