Alloy powder

Abstract

Provided is an alloy powder substantially consisting of one or more alloys A selected from the group consisting of high entropy alloys and medium entropy alloys, wherein: the alloys A contain elemental zinc and an element A other than elemental zinc; the element A is two or more elements selected from the group consisting of transition metal elements, group 13 elements, and silicon; and the alloy powder is porous.

Description

alloy powder

[0001] The present disclosure relates to alloy powders.

[0002] In recent years, medium entropy alloys (MEAs) and high entropy alloys (HEAs) have attracted attention as new alloy materials. HEAs are multi-component alloys with five or more components, in which various elements are randomly arranged in the crystal lattice, i.e., the entropy of configuration is high. HEAs are essentially single-phase disordered solid solutions. MEAs are multi-component alloys with three or four components, in which various elements are randomly arranged in the crystal lattice, i.e., the entropy of configuration is high. MEAs are essentially single-phase disordered solid solutions. MEAs and HEAs have the following characteristics: (a) stabilization of the mixed state due to a negative increase in the entropy of mixing term in the Gibbs free energy equation; (b) diffusion retardation due to a complex microstructure; (c) high lattice distortion due to the size difference of the constituent atoms, resulting in high hardness and reduced temperature dependence of mechanical properties; and (d) improved corrosion resistance due to the combined effect of the coexistence of multiple elements (also known as the cocktail effect). Because MEAs and HEAs have excellent corrosion and oxidation resistance and excellent friction resistance, their applications in various fields are being considered. For example, their main applications include use as shape memory alloys in medical devices and structural materials, as well as in new application fields such as 3D metal printers and as catalyst materials.

[0003] Methods for producing such medium-entropy and high-entropy alloys include physical methods in which raw materials are mixed, melted, and pulverized, and chemical methods using molten metal decomposition. For example, Patent Document 1 discloses a physical method for producing high-entropy alloys through processes such as raw material mixing and melting, atomization, mixed powder preparation, additive manufacturing, and pseudo-solution heat treatment. Patent Document 2 also discloses a mechanical alloying technique for obtaining solid alloys, in which elemental powders or pre-alloyed powders are pulverized in a ball mill until a homogeneous alloy is formed.

[0004] Patent Documents 3 and 4 disclose a chemical method utilizing molten metal decomposition, in which a precursor alloy of each element is prepared, melted by arc melting to mix the components, a thin plate-shaped precursor is cut out from the solidified alloy, and the precursor is immersed in a metal bath consisting of a specific metal to obtain a porous metal.

[0005] Japanese Patent Application Publication No. 2020-114948 Japanese Patent Application Publication No. 2022-530648 Japanese Patent Application Publication No. 2020-125523 International Publication No. 2011 / 092909

[0006] On the other hand, the present inventors have discovered that the following problems occur when using the methods described in Patent Documents 1 to 4 to produce medium-entropy or high-entropy alloys containing zinc. The melting point and boiling point of zinc are 420°C and 910°C, respectively, which are extremely low compared to other metals. Conventional physical synthesis methods, in which a mixture of single-metal raw materials is melted, mixed, and alloyed at high temperatures to obtain an alloy, require high-temperature conditions of approximately 2000°C to melt the raw metals. However, this temperature is higher than the boiling point of zinc. Therefore, the evaporation of zinc makes it difficult to obtain a mixed metal solution containing zinc. Therefore, it is difficult to obtain a zinc-containing alloy using conventional physical synthesis methods.

[0007] On the other hand, mechanical alloying, a mechanical alloying technique, can produce alloy powder at room temperature. However, mechanical alloying has drawbacks, such as the possibility of some balls being mixed into the alloy as impurities, the production of amorphous alloys with low crystallinity, and long mixing times. Additionally, the inventors have discovered that the long mixing time and the application of large shear forces to the alloy powder make it difficult to obtain alloy powders with a large specific surface area, which is important for catalytic applications. Without a large specific surface area, the alloy powders used as catalysts do not achieve the expected excellent catalytic performance. Therefore, the inventors have discovered that, when aiming for catalytic applications, it is necessary to obtain alloy powders with pores.

[0008] The present disclosure solves the above-mentioned problems and provides an alloy powder that contains zinc and has excellent catalytic activity.

[0009] The present disclosure relates to an alloy powder consisting essentially of one or more alloys A selected from the group consisting of high-entropy alloys and medium-entropy alloys, wherein the alloy A contains zinc and an element A other than zinc, the element A being two or more elements selected from the group consisting of transition metal elements, Group 13 elements, and silicon, and the alloy powder is porous.

[0010] According to the present disclosure, an alloy powder containing zinc and having excellent catalytic activity is provided.

[0011] FIG. 1 is an explanatory diagram showing an X-ray diffraction pattern of alloy powder 1. FIG. 2 is an explanatory diagram showing the results of a nitrogen adsorption experiment on alloy powder 1. FIG. 3 is an explanatory diagram showing the pore size distribution of alloy powder 1. FIG. 4 is an explanatory diagram showing the results of an SEM measurement of alloy powder 1 (photograph substitute for drawing). FIG. 5 is an explanatory diagram showing the results of an evaluation of the catalytic activity of alloy powder 1. FIG. 6 is an explanatory diagram showing the results of an evaluation of the catalytic activity of alloy powder 1. FIG. 7 is an explanatory diagram showing an X-ray diffraction pattern of alloy powder 2. FIG. 8 is an explanatory diagram showing the results of a nitrogen adsorption experiment on alloy powder 2. FIG. 9 is an explanatory diagram showing the pore size distribution of alloy powder 2. FIG. 10 is an explanatory diagram showing the results of an SEM measurement of alloy powder 2 (photograph substitute for drawing). FIG. 11 is an explanatory diagram showing the results of an evaluation of the catalytic activity of alloy powder 2. FIG. 12 is an explanatory diagram showing the results of an evaluation of the catalytic activity of alloy powder 2. FIG. 13 is an explanatory diagram showing an X-ray diffraction pattern of alloy powder 3. FIG. 14 is an explanatory diagram showing the results of a nitrogen adsorption experiment on alloy powder 3. FIG. 15 is an explanatory diagram showing the pore size distribution of alloy powder 3. FIG. 16 is an explanatory diagram showing the results of an SEM measurement of alloy powder 3 (photograph substitute for drawing). FIG. 17 is an explanatory diagram showing the results of an evaluation of the catalytic activity of alloy powder 3. FIG. 1 is an explanatory diagram showing the evaluation results of catalytic activity of alloy powder 3. FIG. 2 is an explanatory diagram showing the X-ray diffraction pattern of alloy powder 4. FIG. 3 is an explanatory diagram showing the results of a nitrogen adsorption experiment on alloy powder 4. FIG. 4 is an explanatory diagram showing the pore size distribution of alloy powder 4. FIG. 5 is an explanatory diagram showing the results of SEM measurement of alloy powder 4 (photograph used as a substitute for a drawing). FIG. 6 is an explanatory diagram showing the results of evaluation of catalytic activity of alloy powder 4. FIG. 7 is an explanatory diagram showing the results of evaluation of catalytic activity of alloy powder 4. FIG. 8 is an explanatory diagram showing the X-ray diffraction pattern of alloy powder 5. FIG. 9 is an explanatory diagram showing the results of a nitrogen adsorption experiment on alloy powder 5. FIG. 10 is an explanatory diagram showing the pore size distribution of alloy powder 5. FIG. 11 is an explanatory diagram showing the results of SEM measurement of alloy powder 5 (photograph used as a substitute for a drawing). FIG. 12 is an explanatory diagram showing the results of evaluation of catalytic activity of alloy powder 5.

[0012] The present disclosure will be described in detail below, but is not limited to the following description. The expressions "XX or more and YY or less" and "XX to YY" that represent a numerical range mean a numerical range including the lower and upper limits, which are the endpoints, unless otherwise specified. When a numerical range is described in stages, the upper and lower limits of each numerical range can be combined in any way.

[0013] In the present disclosure, a high-entropy alloy is a multi-component alloy, for example, a five-component or higher alloy, which is essentially a single-phase disordered solid solution alloy, and whose mixed state is stabilized due to a negative increase in the entropy of mixing term in the Gibbs free energy equation. 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 entropy (ΔS) increases, ΔG decreases. The entropy of mixing term of a random ideal solution is given by the following equation: Here, R is the gas constant, N is the number of components, and ci is the fraction of component i. As is clear from this formula, the entropy is highest in alloys with equiatomic compositions, and the entropy increases as the number of components increases. Therefore, an alloy obtained when the mixed state is stabilized due to a negative increase in the entropy of mixing term is called a high-entropy alloy. Furthermore, even in intermetallic compound alloys with a regular crystal structure, alloys in which certain lattice sites are occupied by multicomponent metal elements and the mixed state is stabilized by the contribution of the entropy of mixing term also qualify as high-entropy alloys. For example, a high-entropy alloy is a solid solution alloy with a single structure in which each element is randomly mixed, stabilized by the contribution of the entropy of mixing term, even if each element has a different crystal structure on its own. Typical crystal structures include a simple body-centered cubic lattice structure (BCC) and a face-centered cubic lattice structure (FCC). Furthermore, high-entropy alloys have a structure in which many components are densely packed, compared to ordinary alloys, and have high strength and unique physical and chemical properties that are excellent.

[0014] On the other hand, while high-entropy alloys are multi-component alloys with five or more components, medium-entropy alloys are multi-component alloys with three or four components. They are similar to high-entropy alloys except that they are multi-component alloys with three or four components. That is, they are essentially single-phase disordered solid solution alloys, and the mixed state is stabilized due to the negative increase in the entropy of mixing term in the Gibbs free energy equation. Specifically, they are similar to the high-entropy alloys described above.

[0015] That is, the high-entropy alloys of the present disclosure are composed of a minimum of five elements, and the medium-entropy alloys are composed of three or four elements. High-entropy alloys and medium-entropy alloys are alloys in which the mixed state is stabilized due to a negative increase in the entropy of mixing term in the Gibbs free energy equation. Furthermore, they do not necessarily include alloys that form single-phase solid solutions, but also include single-phase intermetallic compounds stabilized by the contribution of the entropy of mixing term.

[0016] The alloy powder of the present disclosure is an alloy powder consisting essentially of one or more alloys A selected from the group consisting of high-entropy alloys and medium-entropy alloys. That is, alloy A is one or more alloys selected from the group consisting of high-entropy alloys and medium-entropy alloys. Furthermore, alloy A contains zinc and an element A other than zinc. Furthermore, element A is two or more elements selected from the group consisting of transition metal elements, Group 13 elements, and silicon. Additionally, the alloy powder is porous. This configuration results in an alloy powder with excellent catalytic activity. Each component will be described in detail below.

[0017] The alloy powder of the present disclosure consists essentially of one or more alloys A selected from the group consisting of high-entropy alloys and medium-entropy alloys. In the present disclosure, "consisting essentially of" means that trace amounts of other impurities are permitted. That is, an alloy powder consisting essentially of one or more alloys A selected from the group consisting of high-entropy alloys and medium-entropy alloys means that trace amounts of impurities other than alloy A (e.g., 2.5 mol% or less of alloy A) are permitted in the alloy powder. When the alloy powder contains impurities other than alloy A, the content of the impurities in the alloy powder is preferably 2.5 mol% or less, more preferably 1.5 mol% or less, even more preferably 10 mol% or less, and particularly preferably 0.7 mol% or less. However, the alloy powder of the present disclosure can also be used in combination with other powders.

[0018] Alloy A contains zinc element. By including zinc element, improved catalytic performance is likely to be achieved. In particular, an improvement in the selectivity for obtaining the target product in a selective hydrogenation reaction can be expected. The zinc element content in Alloy A is not particularly limited, but may be 5.0 to 50.0 mol%, preferably 9.0 to 18.0 mol%, and more preferably 10.7 to 16.9 mol%. The zinc element content in Alloy A and its content can be measured by elemental analysis using an X-ray fluorescence analyzer described below.

[0019] Alloy A contains an element A other than zinc, where element A is two or more elements selected from the group consisting of transition metal elements, Group 13 elements, and silicon. By including two or more elements as element A and zinc, the alloy contains three or more elements. This allows alloy A to be a medium-entropy alloy or a high-entropy alloy. The number of selected elements is not particularly limited as long as it is two or more, but is preferably three or more, and more preferably four or more. When the number of selected elements is four or more, alloy A can be a high-entropy alloy. Alloy A is preferably a high-entropy alloy. The upper limit of the number of selected elements is not particularly limited, but may be, for example, 2 to 10, 3 to 10, or 4 to 10.

[0020] The transition metal element is not particularly limited, but examples thereof include elements in periods 4 to 6 and groups 3 to 12 of the periodic table. Specific examples include one or more elements selected from the group consisting of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, lanthanides, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, and mercury. Among these, one or more elements selected from the group consisting of titanium, chromium, manganese, iron, cobalt, nickel, and copper are preferred. The lanthanoid is not particularly limited, but may be one or more elements selected from the group consisting of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Of these, one or more elements selected from the group consisting of lanthanum, cerium, praseodymium, neodymium, and samarium are preferred.

[0021] The Group 13 element is not particularly limited, but may be one or more elements selected from the group consisting of boron, aluminum, gallium, indium, and thallium. Of these, one or more elements selected from the group consisting of aluminum and gallium are preferred.

[0022] As described above, element A is two or more elements selected from the group consisting of transition metal elements, Group 13 elements, and silicon. The combination is not particularly limited, and for example, element A may be two or more elements selected from the group consisting of transition metal elements, two or more elements selected from the group consisting of Group 13 elements, or one or more elements selected from the group consisting of transition metal elements and one or more elements selected from the group consisting of Group 13 elements.

[0023] More specifically, element A is preferably two or more elements selected from the group consisting of titanium, chromium, manganese, iron, cobalt, nickel, copper, aluminum, and gallium, and more preferably four or more elements selected from the group consisting of titanium, chromium, manganese, iron, cobalt, nickel, copper, aluminum, and gallium. Element A is iron, cobalt, nickel, and gallium, aluminum, cobalt, iron, and nickel, cobalt, iron, manganese, and nickel, copper, nickel, cobalt, aluminum, and titanium, aluminum, cobalt, chromium, copper, and iron, chromium, manganese, iron, and nickel, chromium, manganese, iron, and cobalt, copper, nickel, and cobalt, copper, nickel, cobalt, and aluminum, aluminum, iron, titanium, and chromium, aluminum, Chromium, copper, iron, and titanium; cobalt, copper, iron, and nickel; cobalt, chromium, nickel, and copper; iron, cobalt, nickel, and manganese; and aluminum, cobalt, copper, and nickel are particularly preferred, and iron, cobalt, nickel, and gallium; aluminum, cobalt, iron, and nickel; cobalt, iron, manganese, and nickel; copper, nickel, cobalt, aluminum, and titanium; and aluminum, cobalt, chromium, copper, and iron are particularly preferred.

[0024] The content of each element A in alloy A is not particularly limited, but may be 5.0 to 50.0 mol%, preferably 7.1 to 23.8 mol%, and more preferably 10.0 to 22.0 mol%. The presence and content of element A in alloy A can be determined by element analysis using an X-ray fluorescence analyzer described below.

[0025] The alloy powder is porous. In the present disclosure, "porous" means that the alloy powder has one or more pores selected from the group consisting of macropores with a pore diameter of 50 nm or more, mesopores with a pore diameter of 2 nm or more but less than 50 nm, and micropores with a pore diameter of less than 2 nm. The presence of these pores in the alloy powder can be confirmed by measuring the alloy powder with nitrogen adsorption / desorption. Specific measurement methods will be described later. Porous alloy powders tend to have a larger surface area, which in turn facilitates the demonstration of high catalytic performance in catalytic reactions using alloy catalysts. It is particularly preferred that the alloy powder have one or more pores selected from the group consisting of the macropores, mesopores, and micropores, and it is more preferred that the alloy powder have one or more pores selected from the group consisting of the mesopores and micropores. It is particularly preferred that the alloy powder have pores with a pore diameter of 10 nm or less. While the lower limit of the pore diameter is not particularly limited, examples include pores with a diameter of 0.1 to 10 nm and 1 to 10 nm. Within the above range, the surface area of ​​the alloy powder tends to be larger, which in turn facilitates the demonstration of higher catalytic performance in catalytic reactions using alloy catalysts.

[0026] The method for obtaining the alloy powder of the present disclosure is not particularly limited, but examples thereof include the following method. By using the following method, the obtained alloy powder is likely to be porous. The method for producing the alloy powder includes a mixing step of mixing a zinc salt and a salt of element A 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, and a step of mixing the oxide precursor with CaH ２ , Ca, MgH ２ and Mg, and a molten salt of one or more salts selected from the group consisting of alkali metal salts and alkaline earth metal salts, in the presence of an inert gas, to obtain an alloy powder.

[0027] In the mixing step, it is preferable to use a zinc salt. The zinc salt also includes a hydrate of the zinc salt. In the conventional production of medium-entropy alloys or high-entropy alloys, expensive pure metals have been used as raw material metals, but the raw material metal salts and their hydrates are easily available and inexpensive, which allows for cost reduction.

[0028] Salts of zinc and salts of element A include inorganic salts such as nitrates, sulfates, carbonates, phosphates, and chlorides, as well as organic salts such as alkoxides, acetates, and oxalates. In the case of inorganic salts, many nitrates or chlorides are suitable because they are soluble and inexpensively available. For example, when the raw material element A is aluminum, Al(NO ３ ) ３ ・9H ２ O, in the case of cobalt, Co(NO ３ ) ３ ・6H ２ O, Cr(NO ３ ) ３ ・9H ２ O, in the case of iron, Fe(NO ３ ) ３ ・9H ２ O, in the case of nickel, Ni(NO ３ ) ２ ・6H ２ In the case of vanadium and rhodium, the hydrates of nitrates such as VCl are available at low cost. ３ , RhCl ３ Chlorides such as these are preferred. Metal alkoxides are preferably used for Ti and Si because they are available soluble compounds. Metal alkoxides are salts that are often used in the sol-gel method. Metal alkoxides may also be used for Al. The above salts may be hydrates. Any salt may be used as long as it is an available soluble compound.

[0029] In the mixing step, the zinc salt and the salt of element A are mixed in the presence of a solvent to obtain a mixed solution. Examples of solvents include ion-exchanged water, distilled water, glycerin, alcohol (particularly ethanol), glycol (particularly ethylene glycol and propylene glycol), and standard organic solvents (THF, acetone, and toluene). Among these, distilled water and ethanol are preferred because they are easy to handle and inexpensive to obtain, and distilled water is more preferred. That is, the mixed solution is more preferably an aqueous solution. It is also preferable to use a chelating agent in the mixing step. For example, a chelating agent may be added when adding the zinc salt and the salt of element A to the solvent. The chelating agent is an organic compound that forms a chelate complex with metal ions in the solution. Standard, highly safe chelating agents include ethylenediaminetetraacetic acid, citric acid, phytic acid, and gluconic acid. Citric acid is particularly preferred. The use of a chelating agent facilitates the production of a uniform composite metal oxide powder using a sol-gel complex polymerization method. The amount of the chelating agent to be added is not particularly limited, but may be 1 to 1.5 times the total number of moles of zinc and element A.

[0030] On the other hand, when the number of constituent elements of an alloy is large (for example, 6 or 7 types or more), it may be difficult to obtain a uniform solution in which all metals are dissolved, as some raw materials may be insoluble in solvents such as water or alcohol. In such cases, it is advisable to use the impregnation method. That is, for some metals (preferably one type), it is advisable to prepare a suspension in which fine oxide powder is suspended instead of salt, and use the suspension. Also, when the amount of oxide is small and it is difficult to prepare a uniform suspension, it is advisable to use a chelating reagent such as the one described above. The use of a chelating reagent has the effect of obtaining a precursor in which each element is uniformly dispersed. Furthermore, oxide powder is used for elements for which available soluble compounds are limited, so SiO ２ , TiO ２ , and CeO ２ It is preferable to use one or more oxides selected from the group consisting of:

[0031] The mixed solution is then dried and heated to obtain an oxide precursor. In the process of obtaining the oxide precursor, heating may be performed in a single step or multiple steps. For example, after pre-calcination at a low temperature, the calcined sample is uniformly pulverized and mixed in a mortar or the like using a pestle, and then calcined at a high temperature to obtain an oxide precursor in which the elements are uniformly dispersed. Therefore, multiple steps are preferred. The heating temperature is preferably 200 to 800°C, and 250 to 600°C is preferred for the reasons of removing impurities (e.g., chelating agents) other than zinc and element A by combustion, and for the reasons of obtaining an oxide precursor in which the metal elements are uniformly dispersed. The heating time is preferably about 0.5 to 10 hours, and preferably about 3 to 6 hours.

[0032] Thereafter, the oxide precursor, the reducing agent, and the molten salt source are mixed, and the mixture is heated and reduced in the presence of an inert gas (nitrogen, argon, helium, etc.) to obtain an alloy powder. It is preferable to have a washing step for washing the product after reduction. By having a washing step, impurities (LiCl, CaCl ２ , CaH ２, CaO, etc.) can be removed. The heating temperature during reduction varies depending on the type of molten salt, but must be above the melting temperature, typically 300 to 1000°C, preferably 550 to 800°C. Alternatively, the molten salt source may be heated first, and the oxide precursor and reducing agent may be added to the melted molten salt source. Alternatively, the molten salt source may be mixed with the oxide precursor or reducing agent, heated, and then the remaining reducing agent or oxide precursor may be added. When the molten salt is a mixed molten salt, its melting point is lower than that of a single molten salt, and it melts even at temperatures below 600°C, for example. The molten salt acts as a solvent, and the oxide precursor is reduced by the reducing agent in the molten salt (molten salt reduction method). This molten salt reduction method allows for the production of alloy powder under milder conditions at lower temperatures than the physical method described above (approximately 2000°C). The oxide precursor is alloyed immediately after reduction by the molten salt reduction method, and becomes porous alloy powder by passing through a metallic state. The heating time depends on the heating temperature, but is preferably about 0.5 to 10 hours, and more preferably about 3 to 6 hours. When the heating temperature is low, for example, about 550°C, it is preferable to increase the heating time, for example, to about 10 hours. On the other hand, when the heating temperature is high, for example, 700 to 800°C, the heating time can be reduced to 1.5 to 3.0 hours.

[0033] The reducing agent is not particularly limited, but calcium hydride (CaH ２ ), metallic calcium, magnesium hydride (MgH ２ ), and metallic magnesium. These reducing agents exhibit a strong reducing action in the molten salt. The reducing agents may be used alone or in combination. When using a plurality of reducing agents, they may be mixed in advance or may be added separately when mixing the oxide precursor and the molten salt. In particular, CaH ２ is a stable powder under room temperature and atmospheric conditions, and is therefore relatively safe to handle. ２ When used as a reducing agent, CaH ２ reacts with oxygen contained in the oxide precursor to become CaO, and CaH ２It is more preferable to use the reducing agent in an amount of 0.1 to 4 times, and preferably 1 to 2 times, the weight ratio of the reducing agent to the oxide precursor.

[0034] The molten salt is not particularly limited, but is preferably at least one selected from the group consisting of alkali metal halides and alkaline earth metal halides. Examples of alkali metal halides that can be used include compounds such as LiF, NaF, KF, RbF, CsF, LiCl, NaCl, KCl, RbCl, CsCl, LiBr, NaBr, KBr, RbBr, CsBr, LiI, NaI, KI, RbI, and CsI. Examples of alkaline earth metal halides that can be used include MgF. ２ , CaF ２ , SrF ２ , BaF ２ , MgCl ２ , CaCl ２ , SrCl ２ , BaCl ２ , MgBr ２ , CaBr ２ , SrBr ２ , BaBr ２ , MgI ２ , CaI ２ , SrI ２ , BaI ２ Compounds such as the following can be used.

[0035] The above compounds can be used alone or in combination of two or more. The combination of these compounds, the number of compounds to be combined, the mixing ratio, etc. are not limited, and can be appropriately selected depending on whether they are stable in the atmosphere, easy to handle, or inexpensively available. In addition, AlCl ３ , ZnCl ２ Even halides of relatively less noble metals such as fluorine, fluorine, thiamin ...

[0036] In particular, the molten salt used in this embodiment is LiCl, CaCl ２ A single molten salt such as LiCl and KCl, a mixed molten salt of LiCl and CaCl ２It is preferable to use a mixed molten salt of the above. In addition, the melting point of the mixed molten salt is lower than that of a single molten salt, so the reaction can occur at a low temperature. Therefore, when the temperature at which the alloy is formed is low (for example, when the raw material contains an oxide that is easily reduced, such as a transition metal oxide), it is preferable to use a mixed molten salt. For example, ２ Since the melting point of the mixed molten salt of LiCl is 470°C, the reaction can be carried out even at a low temperature of about 550°C. Furthermore, since the melting point of the mixed molten salt of LiCl and Kl is 350°C, the reaction can be carried out even at a low temperature of about 400°C.

[0037] The alloy powder preferably has a crystallite diameter of 15.0 nm or more, more preferably 30.0 nm or more, and even more preferably 60.0 nm or more. A crystallite diameter within the above range indicates that alloy A in the alloy powder is well crystallized. There is no particular upper limit to the crystallite diameter, but examples include 15.0 to 100.0 nm, 30.0 to 100.0 nm, and 60.0 to 100.0 nm. A method for measuring the crystallite diameter will be described later. By using the above-mentioned method for producing alloy powder, it is easy to adjust the crystallite diameter to within the above range. Specifically, if the heating temperature in the above-mentioned step of heating and reducing to obtain alloy powder is increased, the crystallite diameter tends to increase, while if the heating temperature is decreased, the crystallite diameter tends to decrease.

[0038] The alloy powder has a BET specific surface area of ​​5.0 m ２ / g or more, and ２ / g or more, and 10.0m ２ / g or more. When the BET specific surface area is in the above range, the catalytic activity of the alloy powder is more likely to be improved. The upper limit of the BET specific surface area is not particularly limited, but it is, for example, 5.0 to 50.0 m ２ / g, 7.0 to 50.0 m ２ / g, 10.0-50.0 m ２ / g. The method for measuring the BET specific surface area will be described later. By using the above-mentioned method for producing an alloy powder, it is easy to adjust the BET specific surface area to be within the above-mentioned range. Specifically, if the heating temperature in the step of obtaining the alloy powder by heating and reduction is lowered, the BET specific surface area tends to increase, and if the heating temperature is higher, the BET specific surface area tends to decrease.

[0039] The alloy powder has a pore volume of 0.014 cm ３ / g or more, and ３ / g or more, and more preferably 0.050 cm ３ / g or more is more preferable. When the pore volume is in the above range, the catalytic activity of the alloy powder is more likely to be improved. The upper limit of the pore volume is not particularly limited, but it is, for example, 0.014 to 0.180 cm ３ / g, 0.020-0.180 cm ３ / g, 0.050-0.180 cm ３ / g. The method for measuring the pore volume will be described later. By using the above-mentioned method for producing an alloy powder, it is easy to adjust the pore volume to the above-mentioned range. Specifically, if the heating temperature in the step of obtaining the alloy powder by heating and reduction is lowered, the pore volume tends to increase, and if the heating temperature is higher, the pore volume tends to decrease.

[0040] The alloy powder preferably has a specific surface area diameter of 15.0 nm or more, more preferably 30.0 nm or more, and even more preferably 50.0 nm or more. When the specific surface area diameter is within the above range, the catalytic activity of the alloy powder is likely to be further improved. There is no particular upper limit to the specific surface area diameter, but examples include 15.0 to 160.0 nm, 30.0 to 160.0 nm, and 50.0 to 160.0 nm. The method for measuring the specific surface area diameter will be described later. By using the above-mentioned method for producing alloy powder, it is easy to adjust the specific surface area diameter to be within the above range. Specifically, if the heating temperature in the above-mentioned step of obtaining alloy powder by heating and reduction is increased, the specific surface area diameter tends to increase, and if the heating temperature is decreased, the specific surface area diameter tends to decrease.

[0041] Although the structure of alloy A is not particularly limited, it is preferably a body-centered cubic lattice structure (BCC structure) or a face-centered cubic lattice structure (FCC structure). As described above, these structures are typical crystal structures of medium-entropy alloys and high-entropy alloys.

[0042] The methods for measuring the physical properties of the alloy powder will be described below.

[0043] <Method for measuring the crystalline structure and crystallite size of the alloy> The X-ray diffraction pattern is measured by XRD of the alloy powder using an X-ray diffractometer (SmartLab (registered trademark), manufactured by Rigaku Corporation) under the following conditions. Conditions: X-ray source: CuKα, output: 40 kV, 40 mA. The crystalline structure of the alloy is determined from the obtained X-ray diffraction pattern. The crystallite size is calculated using the Scherrer equation using the full width at half maximum of the main peak observed around 2θ = 42 to 45°.

[0044] <Method for measuring BET specific surface area, pore volume, and specific surface area diameter of alloy powder> Nitrogen adsorption experiments are carried out using a nitrogen adsorption amount measuring device (BELLSORP mini-II, manufactured by Microtrac-Bell Corporation). Alloy powder samples are dried at 150°C for 60 minutes under an inert gas flow, and then the nitrogen adsorption amount (BET specific surface area, pore volume) is measured at liquid nitrogen temperature. Pore size distribution diagrams are created using the BJH method. Furthermore, the average density of the alloy sample is calculated from the metal density listed in the database, The Materials Project, and the specific surface area diameter is calculated using the obtained average density and the BET specific surface area obtained from the nitrogen adsorption experiment, assuming that the sample powder consists of spherical particles.

[0045] <Elemental Analysis of Alloy Powder> The alloy powder was used as a sample, and the sample was set in a dedicated sample holder. Then, the alloy powder was measured under vacuum with an X-ray fluorescence analyzer (ZSX Primus II, manufactured by Rigaku Corporation) using an X-ray tube (3 kW) with a Rh target, and the proportion of each element in the alloy powder was calculated from the measurement results.

[0046] <SEM Measurement of Alloy Powder> The alloy powder is measured using a scanning electron microscope (JSM-7800F, manufactured by JEOL Ltd.).

[0047] The present invention will be explained in more detail below with reference to examples, but is not limited to these examples as long as they do not depart from the gist of the invention.

[0048] Example 1 (Synthesis of oxide precursor) Fe(NO ３ ) ３ ・9H ２ O (Fujifilm Wako Pure Chemical Industries, Ltd., purity 99%) Co(NO ３ ) ２ ・6H ２ O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 99.5%) Ni(NO ３ ) ２ ・6H ２ O (Fujifilm Wako Pure Chemical Industries, Ltd., purity 98%) Zn(NO ３ ) ２ ・6H ２ O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 99%) Ga(NO ３ ) ３ ・8H ２ O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 99.9%). The above salt was used as a salt containing the constituent metals of the alloy. The above salt and citric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 98%) were dissolved in distilled water so that the molar ratio of the raw materials was 1.0 for each metal ion and 6.0 for citric acid, to obtain an aqueous solution. The obtained aqueous solution was evaporated to dryness on a hot plate to obtain a solid. The obtained solid was then pre-fired at 250°C for 2 hours. The pre-fired sample was crushed and mixed in a mortar and pestle to form a powder with a nearly uniform particle size, and then fired again at 800°C for 2 hours to obtain an oxide precursor.

[0049] (Synthesis of Alloy Powder) LiCl (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and KCl (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed in a mortar with a pestle in a molar ratio of 60:40 to prepare a molten salt source. The obtained oxide precursor and CaH ２ (manufactured by Nacalai Tesque, Inc.) and the prepared mixed molten salt were mixed in a mass ratio of 2:6:3. The mixture was then heated at 400°C for 5 hours in an SUS cylindrical container under an argon atmosphere to reduce the molten salt. Finally, 0.1M NH４ The product was washed with a Cl aqueous solution and distilled water to remove impurities (LiCl, KCl, CaH2, CaO, etc.), yielding Alloy Powder 1. The physical properties of the resulting Alloy Powder 1 were measured using the methods described above. The results are shown in Table 1 and Figures 1 to 4. Figure 1 confirms a single BCC structure, indicating that it is a single-phase solid solution alloy. Furthermore, an SEM image confirmed a microstructure consisting of fine particles of 1 to 10 μm or smaller (Figure 4). Furthermore, elemental analysis revealed that Alloy Powder 1 contained 0.6 mol% Si and 0.1 mol% S as impurities. In Table 1, the results of XRF measurement show the molar ratio of each element in the elemental analysis of the alloy powder described above, when the total of each element described in the composition of the alloy powder is taken as 100 mol %.

[0050] (Evaluation of catalytic activity) The obtained alloy powder 1 was used in the hydrogenation reaction of p-nitrophenol to p-aminophenol to evaluate its catalytic activity. p-Nitrophenol (maximum absorption wavelength: 401 nm) is converted to p-aminophenol (maximum absorption wavelength: 303 nm) by the hydrogenation reaction. Alloy powder 1 (10 mg), 1 mL of 14 mM p-nitrophenol solution, and 0.42 M NaBH were placed in a glass tube. ４ 1 mL of the solution and 7 mL of distilled water were added and heated to initiate the hydrogenation reaction. The reaction temperature was set to 50°C. At the start of the reaction and at regular intervals thereafter, 100 μL of the test solution was taken from the glass tube, added to a 5 mL measuring flask, and diluted to volume with distilled water. The absorbance of the resulting diluted solution was then measured at 300-500 nm using a UV-Vis spectrophotometer (Shimadzu Corporation, UV-1280) to measure the changes in the concentrations of p-nitrophenol and p-aminophenol. The measurement results are shown in Figures 5 and 6. These results demonstrate that the hydrogenation reaction of p-nitrophenol proceeded using Alloy Powder 1.

[0051] Example 2 Alloy powder 2 was obtained in the same manner as in Example 1, except that the following salts were used as salts containing the constituent metals of the alloy, the temperature and time of molten salt reduction were changed to those shown in Table 1, and the molten salt source was changed to LiCl (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). Furthermore, measurements of physical properties and evaluation of catalytic activity were carried out in the same manner as in Example 1. The results of the physical property measurements are shown in Table 1 and Figures 7 to 10. As a result of elemental analysis, alloy powder 2 contained 0.6 mol% Si, 0.1 mol% Cu, 0.1 mol% S, and 0.1 mol% Cl as impurities. Al(NO ３ ) ３ ・9H ２ O (Fujifilm Wako Pure Chemical Industries, Ltd., purity 98%) Co(NO ３ ) ２ ・6H ２ O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 99.5%). Fe(NO ３ ) ３ ・9H ２ O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 99%) Ni(NO ３ ) ２ ・6H ２ O (Fujifilm Wako Pure Chemical Industries, Ltd., purity 98%) Zn(NO ３ ) ２ ・6H ２ O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 99%)

[0052] The catalytic activity evaluation results are shown in Figures 11 and 12. These results indicate that the hydrogenation reaction of p-nitrophenol proceeded using Alloy Powder 2. Figure 7 confirms a single BCC structure, indicating that it is a single-phase solid solution alloy. Furthermore, SEM images confirmed a microstructure consisting of fine particles of 1 to 10 μm or smaller (Figure 10).

[0053] Example 3 Alloy powder 3 was obtained in the same manner as in Example 2, except that the salts listed below were used as salts containing the constituent metals of the alloy, and the temperature and time of molten salt reduction were changed to those shown in Table 1. Furthermore, measurements of physical properties and evaluation of catalytic activity were carried out in the same manner as in Example 1. The results of the measurement of physical properties are shown in Table 1 and Figs. 13 to 16. The results of the evaluation of catalytic activity are shown in Figs. 17 and 18. As a result of elemental analysis, alloy powder 3 contained 0.5 mol% of Si, 0.1 mol% of Ca, and 0.1 mol% of S as impurities. Co(NO ３ ) ２ ・6H ２ O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 99.5%). Fe(NO ３ ) ３ ・9H ２ O (Fujifilm Wako Pure Chemical Industries, Ltd., purity 99%) Mn(NO ３ ) ２ ・6H ２ O (Fujifilm Wako Pure Chemical Industries, Ltd., purity 98%) Ni(NO ３ ) ２ ・6H ２ O (Fujifilm Wako Pure Chemical Industries, Ltd., purity 98%) Zn(NO ３ ) ２ ・6H ２ O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 99%)

[0054] The evaluation results of catalytic activity are shown in Figures 11 and 12. These results indicate that the hydrogenation reaction of p-nitrophenol proceeded using Alloy Powder 3. Figure 13 confirms an almost single FCC structure, which indicates that the alloy is a nearly single-phase solid solution alloy. Furthermore, SEM images confirmed a microstructure consisting of fine particles of 1 to 10 μm or less (Figure 16).

[0055] Example 4 Alloy Powder 4 was obtained in the same manner as in Example 2, except that the following salts were used as salts containing the constituent metals of the alloy, the molar ratio of the raw materials was changed to a ratio of 7.2 citric acid to 1.0 metal ion, and the temperature and time of molten salt reduction were changed to those shown in Table 1. Furthermore, physical property measurements and catalytic activity evaluation were carried out in the same manner as in Example 1. The results of the physical property measurements are shown in Table 1 and Figs. 19 to 22. The results of the catalytic activity evaluation are shown in Figs. 23 and 24. As a result of elemental analysis, Alloy Powder 4 contained 0.3 mol% Si, 0.3 mol% Ca, 0.1 mol% Mn, and 0.1 mol% Cl as impurities. Cu(NO ３ ) ２ ・3H ２ O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 99.9%) Ni(NO ３ ) ２ ・6H ２ O (Fujifilm Wako Pure Chemical Industries, Ltd., purity 98%) Co(NO ３ ) ２ ・6H ２ O (Fujifilm Wako Pure Chemical Industries, Ltd., purity 99.5%) Zn(NO ３ ) ２ ・6H ２ O (Fujifilm Wako Pure Chemical Industries, Ltd., purity 99%) Al(NO ３ ) ３ ・9H ２ O (Fujifilm Wako Pure Chemical Industries, Ltd., purity 98%) ・[(CH ３ ) ２ CHO] ４ Ti (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 95%)

[0056] The catalytic activity evaluation results are shown in Figures 11 and 12. These results indicate that the hydrogenation reaction of p-nitrophenol proceeded using Alloy Powder 4. Figure 19 confirms a single BCC structure, indicating that it is a single-phase solid solution alloy. Furthermore, SEM images confirmed a microstructure consisting of fine particles of 1 to 10 μm or less (Figure 22).

[0057] Example 5 Alloy Powder 5 was obtained in the same manner as in Example 2, except that the salts listed below were used as salts containing the constituent metals of the alloy, and the temperature and time of molten salt reduction were changed to those shown in Table 1. Furthermore, measurements of physical properties and evaluation of catalytic activity were carried out in the same manner as in Example 1. The results of the measurement of physical properties are shown in Table 1 and Figs. 25 to 28. The results of the evaluation of catalytic activity are shown in Figs. 29 and 30. As a result of elemental analysis, Alloy Powder 5 contained 1.3 mol% of Mg, 0.1 mol% of Ca, and 1.0 mol% of Si as impurities. Al(NO ３ ) ３ ・9H ２ O (Fujifilm Wako Pure Chemical Industries, Ltd., purity 98%) Co(NO ３ ) ２ ・6H ２ O (Fujifilm Wako Pure Chemical Industries, Ltd., purity 99.5%) Cr(NO ３ ) ３ ・9H ２ O (manufactured by Strem Chemicals, purity 99%) ・Cu (NO ３ ) ２ ・3H ２ O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 99.9%). Fe(NO ３ ) ３ ・9H ２ O (Fujifilm Wako Pure Chemical Industries, Ltd., purity 99%) Zn(NO ３ ) ２ ・6H ２ O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 99%)

[0058] The evaluation results of catalytic activity are shown in Figures 11 and 12. These results indicate that the hydrogenation reaction of p-nitrophenol proceeded using Alloy Powder 5. Figure 25 confirms the presence of a nearly single BCC structure, indicating that the alloy is a nearly single-phase solid solution alloy. Furthermore, SEM images confirmed a microstructure consisting of fine particles of 1 to 10 μm or less (Figure 28).

[0059] Examples of the inventions grasped from the above disclosure are as follows. [1] An alloy powder consisting essentially of one or more alloys A selected from the group consisting of high-entropy alloys and medium-entropy alloys, wherein the alloy A contains zinc and an element A other than zinc, and the element A is two or more elements selected from the group consisting of transition metal elements, Group 13 elements, and silicon, and the alloy powder is porous. [2] The alloy powder according to [1], which has pores with a pore diameter of 10 nm or less. [3] The alloy powder according to [1] or [2], which has a crystallite diameter of 15 nm or more. [4] The alloy powder according to [1] or [2], which has a BET specific surface area of ​​5.0 m ２ [5] The alloy powder according to any one of [1] to [3], wherein the pore volume is 0.014 cm 3 / g or more. ３ / g or more. [6] The alloy powder according to any one of [1] to [5], wherein the specific surface area diameter is 15.0 nm or more. [7] The alloy powder according to any one of [1] to [6], wherein the element A is four or more elements selected from the group consisting of transition metal elements, Group 13 elements, and silicon. [8] The alloy powder according to [7], wherein the element A is four or more elements selected from the group consisting of titanium, chromium, manganese, iron, cobalt, nickel, copper, aluminum, and gallium. [9] The alloy powder according to any one of [1] to [8], wherein the alloy powder contains impurities other than the alloy A, and the content of the impurities in the alloy powder is 2.5 mol% or less.

Claims

1. An alloy powder consisting essentially of one or more alloys A selected from the group consisting of high-entropy alloys and medium-entropy alloys, wherein the alloy A contains zinc and an element A other than zinc, the element A being two or more elements selected from the group consisting of transition metal elements, Group 13 elements, and silicon, and the alloy powder is porous.

2. The alloy powder according to claim 1, having pores with a pore diameter of 10 nm or less.

3. The alloy powder according to claim 1 or 2, having a crystallite diameter of 15 nm or more.

4. BET specific surface area is 5.0m ２ The alloy powder according to any one of claims 1 to 3, wherein the Mo content is 1 / g or more.

5. Pore volume is 0.014 cm ３ The alloy powder according to any one of claims 1 to 4, wherein the Mo content is 1 / g or more.

6. The alloy powder according to any one of claims 1 to 5, having a specific surface area diameter of 15.0 nm or more.

7. The alloy powder according to any one of claims 1 to 6, wherein the element A is four or more elements selected from the group consisting of transition metal elements, Group 13 elements, and silicon.

8. The alloy powder according to claim 7, wherein the element A is four or more elements selected from the group consisting of titanium, chromium, manganese, iron, cobalt, nickel, copper, aluminum, and gallium.

9. The alloy powder according to any one of claims 1 to 8, wherein the alloy powder contains impurities other than alloy A, and the content of the impurities in the alloy powder is 2.5 mol % or less.

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