Method of producing max phase compound

Abstract

To provide a method of producing a MAX phase compound at a low cost, in a short time and at a high yield.SOLUTION: The method of producing the MAX phase compound has: a pressurizing step of pressurizing a mixture containing a raw material substance to obtain a solid matter; a heating step of induction-heating the solid matter to generate a self-propagating high-temperature synthesis reaction (SHS reaction) to obtain the MAX phase compound; and a processing step of forming at least one starting point of the SHS reaction in the solid matter subsequent to or concurrent with the pressurizing step.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for producing a MAX phase compound. [Background technology]

[0002] In recent years, development of a new material called MXene has been progressing. MXene is a layered transition metal carbide (or nitride or carbonitride) generally represented by the composition formula M n+1 X n T X In the composition formula, M is a transition metal (V, Ti, Mo, Ta, etc.), X is carbon or nitrogen, and T X is a surface functional group (O, OH, F, Cl, etc.), and n = 1 to 3. MXene is expected to be used in a variety of applications, including energy storage materials, electrode materials, electromagnetic wave shielding materials, and sensor materials, due to its properties such as a large specific surface area, high conductivity, and hydrophilic functional groups. For example, by using MXene as an electrode material, it becomes possible to incorporate a large number of lithium ions between layers, making it possible to produce large-capacity all-solid-state batteries.

[0003] The MXene is produced by removing an element represented by A from a MAX phase compound. The MAX phase compound has the general formula M n+1 AX n In the general formula, A is a Group 13 or 14 element such as aluminum or silicon, and M, X, and n are the same as M, X, and n in the composition formula.

[0004] Here, as a method for producing the MAX phase compound, a production method using firing in a firing furnace and sintering by Spark Plasma Sintering (SPS) has been developed. For example, Patent Document 1 discloses a method using the SPS method, which includes at least the following steps (a) to (d): (a) mixing raw material powders; (b) placing the powder mixed in the previous step into a closed container made of insulating ceramic material housed in the hollow chamber; (c) performing a spark plasma sintering operation; (d) Obtaining pellets of the MAX phase compound.

[0005] However, firing in a firing furnace involves indirect heating, which has the problem of taking a long time for firing. The method described in Patent Document 1 allows firing in a shorter time than firing in a firing furnace, but requires a large-scale device. Furthermore, even though this method is said to be short, it requires a firing time of several tens of minutes.

[0006] On the other hand, as a method with a short firing time, for example, Patent Document 2 describes a method for producing a MAX phase compound by placing a precursor material (raw material) of the MAX phase compound in a pulsed high-temperature physical field and rapidly heating and firing it. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2023-54753 [Patent Document 2] China Patent Publication No. 116495735 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the method described in Patent Document 2 does not always provide a high yield of MAX phase compounds, and there is room for improvement in yield.

[0009] Therefore, an object of one aspect of the present invention is to produce a MAX phase compound inexpensively, in a short time, and with a high yield. [Means for solving the problem]

[0010] To solve the above problems, the present inventors discovered that MAX phase compounds can be produced inexpensively, quickly, and with a high yield by utilizing induction heating and a self-propagating high-temperature thermal synthesis reaction (hereinafter also referred to as "SHS reaction"). The present inventors also discovered that the SHS reaction can be efficiently induced by induction heating a solid object that has been treated to form a site that will serve as the starting point for the SHS reaction, and arrived at the present invention.

[0011] That is, one aspect of the present invention is a compound represented by the general formula M n+1 AX n wherein M is an early transition metal, A is selected from the group consisting of Al, Si, P, S, Ga, Ge, As, Cd, In, Sn, Tl, and Pb, X is C or N, and n is 1, 2, or 3; a pressurizing step of pressurizing a mixture containing the raw material of the MAX phase compound to obtain a solid; and a heating step of inductively heating the solid material to cause a self-propagating high-temperature synthesis reaction (SHS reaction) to obtain a MAX phase compound. The method for producing a MAX phase compound includes a treatment step of forming at least one starting point for an SHS reaction in the solid material after the pressurizing step or simultaneously with the pressurizing step. [Effects of the Invention]

[0012] According to one aspect of the present invention, a MAX phase compound can be produced inexpensively, in a short time, and with a high yield. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 2 is a schematic diagram illustrating an example of the shape of a solid material that has not been subjected to a treatment process in one embodiment of the present invention. [Figure 2] 1 is a schematic diagram showing an example of the shape of a solid material that has been subjected to a treatment process in one embodiment of the present invention. [Figure 3] FIG. 2 is a schematic diagram showing the structure of a heating device used in the examples of the present invention. [Figure 4] FIG. 1 is a diagram illustrating the state of a self-propagating high-temperature thermal synthesis reaction (SHS reaction) in Example 1. [Figure 5] FIG. 1 shows electron microscope photographs of the compounds obtained in (a) Example 1 (calcination time: 1 minute) and (b) Example 5 (calcination time: 60 minutes). [Figure 6] FIG. 1 is a diagram showing X-ray diffraction spectra of the compounds obtained in Examples 1 to 5. [Figure 7] FIG. 1 is an electron microscope photograph of the compound obtained in Example 7. [Figure 8] FIG. 1 is a diagram showing X-ray diffraction spectra of the compounds obtained in Examples 6 to 8. DETAILED DESCRIPTION OF THE INVENTION

[0014] An embodiment of the present invention will be described in detail below. However, the present invention is not limited to this, and various modifications are possible within the scope of the description. For example, embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. Unless otherwise specified in this specification, "A to B" representing a numerical range means "greater than or equal to A and less than or equal to B."

[0015] 1. Method for producing MAX phase compounds The method for producing a MAX phase compound according to one embodiment of the present invention (hereinafter also referred to as "the present production method") comprises the steps of: n+1 AX n (wherein M is an early transition metal, A is selected from the group consisting of Al, Si, P, S, Ga, Ge, As, Cd, In, Sn, Tl, and Pb, X is C or N, and n is 1, 2, or 3), the method for producing a MAX phase compound having the formula (wherein M is an early transition metal, A is selected from the group consisting of Al, Si, P, S, Ga, Ge, As, Cd, In, Sn, Tl, and Pb, X is C or N, and n is 1, 2, or 3), comprises a pressurizing step of pressurizing a mixture containing raw materials for the MAX phase compound to obtain a solid, and a heating step of inductively heating the solid to cause a self-propagating high-temperature synthesis reaction (SHS reaction) to obtain the MAX phase compound, and further comprises a treatment step of forming at least one initiation site for the SHS reaction in the solid after the pressurizing step or simultaneously with the pressurizing step.

[0016] In this manufacturing method, since the treatment step is included, a solid substance having at least one starting point of the SHS reaction is subjected to the heating step. And in the heating step, the solid substance is induction-heated, whereby the SHS reaction is induced at a very high rate, and the MAX phase compound is fired by the SHS reaction. Hereinafter, the reaction in which the MAX phase compound is fired is referred to as the "firing reaction".

[0017] Here, it is known that the firing reaction includes an exothermic reaction. Therefore, by the SHS reaction, the firing reaction occurs at the starting point of the solid substance, and the reaction heat generated by the firing reaction propagates self-similarly as a combustion wave to the entire solid substance and is used for the firing reaction at other locations of the solid substance. Thereby, this manufacturing method can complete the firing reaction of the entire solid substance in a short time as compared with the case where the SHS reaction does not occur. Therefore, the MAX phase compound can be produced with good yield in a short time.

[0018] Also, this manufacturing method heats the solid substance by induction heating. Here, the induction heating is a method of generating heat in the object to be heated by using electromagnetic induction. The induction heating does not require a large-scale device as compared with the SPS method or the like, and can heat the solid substance at a low cost. Furthermore, by performing the induction heating, the solid substance can be rapidly heated, so that the SHS reaction from the starting point can be efficiently induced.

[0019] From the above, by this manufacturing method, the MAX phase compound can be produced at a low cost, in a short time, and with good yield.

[0020] Hereinafter, the steps of this manufacturing method will be described in detail.

[0021] <MAX phase compound> The MAX phase compound produced by this manufacturing method has the general formula M n+1 AX n(wherein M is an early transition metal, A is selected from the group consisting of Al, Si, P, S, Ga, Ge, As, Cd, In, Sn, Tl, and Pb, X is C or N, and n is 1, 2, or 3). The MAX phase compound is not particularly limited as long as it has the general formula. According to this production method, any MAX phase compound can be produced. For example, the desired MAX phase compound can be produced by controlling the type and ratio (molar ratio) of raw materials used according to the desired MAX phase compound.

[0022] Specific examples of the MAX phase compounds include V2AlC, Ti3AlC2, and Nb4AlC3.

[0023] The MAX phase compound is M n+1 X n (wherein n is 1, 2 or 3) and a layer of A are alternately stacked. n+1 X n The bond between M and X in M is a covalent bond. n+1 X n Between the layer consisting of M and the layer consisting of A, there is a metallic bond between M and A. Since the covalent bond is stronger than the metallic bond, the intermediate layer consisting of A can be selectively etched by treating the MAX phase compound with a fluoride-containing etching solution or the like. As a result, the element represented by A can be removed from the MAX phase compound, and MXene can be produced.

[0024] <Pressure process> The present production method includes a pressurizing step of pressurizing a mixture containing the raw materials of the MAX phase compound to obtain a solid. The pressurizing step allows the production of a solid containing the raw materials.

[0025] The mixture to be subjected to the pressurization step is not particularly limited as long as it contains the raw materials. The mixture may be a mixture prepared by the mixing step described below, a mixture prepared in advance and stored, or a mixture obtained separately.

[0026] The raw material may be any known material for the MAX phase compound, and is not particularly limited. Examples of the raw material include the simple substances M, A, and X, as well as compounds of M and X, compounds of A and X, and compounds of M and A. The mixture is preferably a mixture containing simple substances M, A, and X.

[0027] Furthermore, the MAX phase compound can be efficiently produced by adjusting the molar ratio of M, A, and X in the mixture to be approximately the same as the molar ratio of M, A, and X in the MAX phase compound. Therefore, the molar ratio is preferably M:A:X=n+1:1:n (where n is the same as n in the MAX phase compound).

[0028] Furthermore, n+1, 1, and n in the mixture may each independently vary by about 0.2.

[0029] For example, consider a case where the MAX phase compound is VAlC. In this case, the mixture can contain one or more raw materials selected from the group consisting of V, Al, and C, as well as vanadium carbide and aluminum carbide, such that the molar ratio of V:Al:C is 2±x:1±y:1±z. Note that x, y, and z are each independently a value between 0 and 0.2.

[0030] The shape of the raw material is not particularly limited, but is preferably powder. Specifically, the raw material is more preferably powdered, obtained by pulverizing using, for example, a ball mill. When pulverizing the raw material, each raw material may be pulverized separately and then mixed, or all raw materials may be pulverized together as a mixture containing the raw materials.

[0031] The mixture may contain additives in addition to the raw materials. The additives are not particularly limited, and examples thereof include catalysts that promote the calcination reaction and functional materials that impart various functions to the MAX phase compound. The content of the additives is not particularly limited as long as it does not impair the effects of the present invention. The shape of the additives is not particularly limited, and it is preferably powdery, similar to the raw materials. Furthermore, when pulverizing the additives, the additives may be pulverized alone, or a mixture containing the raw materials and the additives may be pulverized together, with all the raw materials and additives being pulverized.

[0032] The method of applying pressure in the pressurizing step is not particularly limited as long as the mixture can be pressurized to obtain the solid material. Examples of the pressurizing method include a method in which the mixture is placed in a mold and the mixture in the mold is pressed using a press.

[0033] The conditions for the pressurization, for example, the pressure and time applied during pressurization, are not particularly limited. The pressure applied during pressurization is, for example, 1 MPa or more and 1000 MPa or less, preferably 10 MPa or more and 100 MPa or less, and more preferably 30 MPa or more and 70 MPa or less. The pressurization time can be, for example, 1 second or more and 1000 seconds or less, preferably 3 seconds or more and 100 seconds or less, and more preferably 5 seconds or more and 60 seconds or less.

[0034] <Mixing process> The present production method may include a mixing step of mixing the raw materials and, optionally, the additives to prepare the mixture. The mixing method in the mixing step is not particularly limited. The shapes of the raw materials and the additives to be subjected to the mixing step are not particularly limited, and are preferably, for example, in powder form.

[0035] <Processing process> The present production method includes a treatment step of forming at least one starting point for the SHS reaction in the solid material after the pressurizing step or simultaneously with the pressurizing step.

[0036] "Forming at least one starting point for the SHS reaction in the solid material after the pressurizing step" means performing a process to form at least one starting point for the SHS reaction in the solid material obtained by the pressurizing step. Hereinafter, the process to form at least one starting point for the SHS reaction in the solid material obtained by the pressurizing step will be referred to as "treatment after the pressurizing step." Note that examples of the treatment after the pressurizing step include deforming the shape of the solid material by the method described in (A) or (B) below. (A) cutting out a portion of the solid body; (B) further partially compressing the solid material.

[0037] Furthermore, "forming at least one starting point for the SHS reaction in the solid material simultaneously with the pressurizing step" means performing a process of adjusting the conditions for the pressurizing step so that a solid material having at least one starting point for the SHS reaction is obtained by the pressurizing step. Hereinafter, this process will be referred to as "treatment during the pressurizing step."

[0038] Specific examples of treatment during the pressurization step include adjusting the state of the mixture to be pressurized so that it is non-uniform, and / or adjusting the pressurization conditions so that they are non-uniform.

[0039] An example of a method for adjusting the state of the mixture to be pressurized to be non-uniform is a method in which the mixture is placed in a mold and pressurized, and the mixture is unevenly distributed on the bottom surface of the mold, for example, by disposing a larger amount of the mixture in one part of the bottom surface and a smaller amount in another part.

[0040] In particular, when the shape of the object to be pressurized has sharp points and / or locally high density points, these points are more likely to be heated from the surroundings and the electromagnetic waves generated by electromagnetic induction are more likely to be concentrated at these points, making the SHS reaction more likely to occur in the solid material.

[0041] Another method for adjusting the state of the mixture to be pressurized to be non-uniform is, for example, a method in which the mixture is placed in a mold and pressurized, and the mold is provided with irregularities to make the arrangement of the mixture in the mold non-uniform.

[0042] As a specific method for adjusting the pressure conditions to be non-uniform, for example, the following method can be mentioned. A method of applying pressure to the mixture unevenly so as to form areas where the pressure is locally high; A method in which the shape of the pressing part of a press that comes into contact with the mixture is made uneven, the mixture is pressed by the pressing part, and the shape of the resulting solid product corresponds to the shape of the pressing part.

[0043] The starting point of the SHS reaction refers to a location that is likely to become locally hot during the heating step described below. During the heating step, the starting point of the SHS reaction becomes hotter earlier than other locations in the solid material, causing the firing reaction, including an exothermic reaction, to occur at the starting point. Immediately thereafter, the reaction heat generated by the firing reaction self-propagates throughout the solid material as a combustion wave, causing firing reactions to occur at other locations in the solid material as well. In other words, by inducing the SHS reaction during the heating step, the firing reaction occurs and completes early throughout the solid material.

[0044] Furthermore, if a solid is heated evenly, the constituent materials of the solid may melt and then move to a stable state, preventing the SHS reaction from occurring. However, by locally initiating a self-propagating reaction (SHS reaction) from the starting point of the SHS reaction, the materials that are more likely to propagate melt first as the reaction propagates, and these materials come into contact with each other, forming layers as the reaction progresses, which is thought to enable the formation of a MAX layer in a short period of time.

[0045] Specific embodiments of the starting points of the SHS reaction and the treatment process for forming the starting points will be described below with reference to Figures 1 and 2. Figure 1 is a schematic diagram showing an example of the shape of a solid material that has not been subjected to a treatment process according to one embodiment of the present invention. Figure 2 is a schematic diagram (side view and top view) showing an example of the shape of a solid material that has been subjected to a treatment process according to one embodiment of the present invention. Here, the shape of a solid material that has not been subjected to the treatment process is usually a uniform shape as shown in Figure 1. In this specification, "uniform shape" refers to a shape in which none of the surfaces of the solid material have through-holes, and the two-dimensional shapes of all of the surfaces are vertically symmetrical and horizontally symmetrical.

[0046] On the other hand, the shape of a solid material that has been treated to form at least one starting point for the SHS reaction is usually an uneven shape as shown in FIG. 2, except for solid materials obtained by the process of forming locally high-density areas described below. In this specification, the term "uneven shape" refers to a shape that does not fall under the category of the uniform shape described above. "Uneven shapes" also include shapes with sharp points, such as the shapes shown in b), g), and j) to m) of FIG. 2. For example, the shapes shown in g) to i) of FIG. 2 are completely different in shape from the top to the bottom. The shapes shown in j) to m) of FIG. 2 are completely different in shape from the front to the back.

[0047] The treatment step may be a step of forming protrusions and / or recesses on at least one surface of the solid material. In this case, the shape of the solid material subjected to the heating step will be a shape having protrusions and / or recesses. Examples of solid materials having recesses include the solid materials shown in d) and e) of Figure 2. Examples of solid materials having protrusions include the solid materials shown in g), h), and i) of Figure 2.

[0048] As shown in FIGS. 1 and 2, the recesses are areas where the thickness is locally reduced compared to the solid shown in FIG. 1 that has not been subjected to the treatment process. In this specification, "thickness" refers to the distance between one surface, for example, the surface where the recesses are present, and the surface opposite the surface. The locally reduced thickness areas are more susceptible to heating and therefore more likely to reach higher temperatures during induction heating than other areas. The protrusions are smaller in volume than the solid shown in FIG. 1 that has not been subjected to the treatment process. These areas are not only more susceptible to heating, but also more likely to reach higher temperatures during induction heating than other areas because electromagnetic waves tend to concentrate at the tips, making them more susceptible to self-heating due to electromagnetic induction. From the above, the protrusions and / or recesses can serve as starting points for the SHS reaction.

[0049] The method for forming the convex portions and / or concave portions may be, for example, a method for adjusting the shape of a part of the solid material obtained in the pressurizing step to have convex portions and / or concave portions by, for example, the method (A) or (B) as a treatment after the pressurizing step. Another method for forming the convex portions and / or concave portions may be, for example, the method shown in (A1) and / or (B1) below as a treatment during the pressurizing step. (A1) A method in which, when the mixture is placed in a mold and pressed, the mixture is unevenly distributed on the bottom surface of the mold so that the protrusions and / or recesses are formed after pressing. For example, the mixture is distributed so as to form localized areas on the bottom surface of the mold where the amount of the mixture is high and where the amount of the mixture is low. (B1) A method in which, when the mixture is placed in a mold and pressed, the mold is provided with irregularities, and convex and / or concave portions are formed on at least one surface of the solid material obtained after pressing.

[0050] The treatment step may be a step of rendering at least one of the two-dimensional shapes of the solid object's surfaces asymmetrical in the vertical direction and / or asymmetrical in the horizontal direction. In this case, the shape of the solid object subjected to the heating step may be, for example, a shape in which there are localized areas of reduced thickness, for example, at the edges, as shown in Figure 2(a), (b), and (c). As described above, the locally reduced thickness areas are easily heated and tend to attract electromagnetic waves, and therefore are likely to reach high temperatures during induction heating. Therefore, the locally reduced thickness areas of the solid object may be the starting points for the SHS reaction.

[0051] The method for making at least one of the two-dimensional shapes of the faces of the solid object asymmetrical in the vertical direction and / or asymmetrical in the horizontal direction may be, for example, the following method. a method for adjusting the two-dimensional shape of the surface of the solid obtained in the pressurizing step to a shape that is not vertically symmetrical and / or left-right symmetrical, for example, by the method (A) or (B) described above, as a treatment after the pressurizing step; For example, the steps shown in (A2) and / or (B2) below as treatment during the pressurizing step. (A2) When the mixture is placed in a mold and pressed, the mixture is unevenly distributed on the bottom surface of the mold so that the two-dimensional shape of the surface of the solid body after pressing is asymmetrical in the vertical direction and / or the horizontal direction. For example, the mixture is distributed so as to form localized areas on the bottom surface of the mold where the amount of the mixture is high and where the amount of the mixture is low. (B2) A method of placing the mixture in a mold and pressing it, and adjusting the shape of the mold so that the two-dimensional shape of the surface of the solid object after pressing is not vertically symmetrical and / or not horizontally symmetrical.

[0052] The treatment step may be a step of forming through-holes between at least one surface of the solid and another surface. In this case, the shape of the solid subjected to the heating step is a shape having the through-holes. Specific examples of the shape of the solid include the shape shown in FIG. 2 f). Here, the through-holes are holes that penetrate between one surface and another surface of the solid. The locations of the through-holes in the solid are small holes relative to the outer periphery, and the edges of these locations are easily affected by an external magnetic field and are easily heated, making them prone to high temperatures. Therefore, the locations of the through-holes in the solid can be the starting points of the SHS reaction.

[0053] The method for forming the through holes is not particularly limited as long as the through holes can be formed, and may be, for example, a method of forming through holes between at least one surface and another surface of the solid material obtained in the pressurizing step as a treatment after the pressurizing step. Another method for forming the through holes may be, for example, a method of adjusting the shape of a mold when the mixture is placed in a mold and pressed into the mold as a treatment after the pressurizing step so that through holes can be formed between at least one surface and another surface of the obtained solid material.

[0054] The treatment step may be a step of forming a sharp portion on the solid material. In this case, the shape of the solid material subjected to the heating step may be, for example, a shape with a sharp portion, as shown in b), g), and j) to m) of FIG. 2. The sharp portion may be, for example, a portion where the thickness is reduced at the end, as shown in b), or a portion with a small volume protruding from the surface, as shown in g). The sharp portion may also be, for example, each vertex, as shown in j) to m) of FIG. 2. These portions are also susceptible to heating and, because electromagnetic waves tend to concentrate at the tip, are susceptible to self-heating due to electromagnetic induction, and are prone to high temperatures during induction heating. Therefore, these portions may serve as starting points for the SHS reaction. The shape with a sharp portion may be a shape with a convex portion and / or a shape in which at least one of the two-dimensional shapes is asymmetrical in the vertical direction and / or the horizontal direction.

[0055] The method for forming the sharp portions may be, for example, a method for adjusting the shape of the solid obtained in the pressurizing step to have the sharp portions, for example, by the method (A) or (B) as a treatment after the pressurizing step. Another method for forming the sharp portions may include, for example, the following steps (A3) and / or (B3) as a treatment during the pressurizing step. (A3) A method in which, when the mixture is placed in a mold and pressed, the mixture is unevenly distributed on the bottom surface of the mold so that the solid has a shape with sharp points after pressing. For example, the mixture is distributed so as to form localized areas on the bottom surface of the mold where the amount of the mixture is high and low. (B3) A method in which, when the mixture is placed in a mold and pressed, the shape of the mold is adjusted so that the solid has a shape with a sharp point after pressing, for example, a mold having a pointed portion is used.

[0056] The treating step may be a step of forming locally high density areas in the solid material. In this case, the solid material subjected to the heating step has locally high density areas. The density is the mass of the mixture per unit volume of the solid material.

[0057] Here, it is considered that high-density areas are likely to be the starting points of the SHS reaction because the distance between adjacent atoms is small. Note that the shape of the solid having such areas may be the same as the shape of a solid that has not been subjected to a treatment step to form at least one starting point of the SHS reaction (e.g., FIG. 1).

[0058] The treatment for forming the locally high density portions is not particularly limited, and may be, for example, the following method (A4) and / or (B4) as a treatment after the pressurizing step. (A4) A method in which, when the mixture is placed in a mold and pressed, the mixture is arranged so that there are areas on the bottom surface of the mold where the amount of the mixture is locally high. In this case, the areas where the amount of the mixture is high are pressed, increasing the density of the areas formed, and the locally high-density areas are formed. (B4) A method of pressing the mixture into a mold by applying non-uniform pressure to the mixture so that locally high pressure is applied, in which the density of the area where the locally high pressure is applied increases, forming the locally high-density area.

[0059] In the treatment step, one or more of the methods for forming the starting points of the SHS reaction may be used. That is, it is sufficient that the solid material has at least one type of starting point of the SHS reaction. In other words, the solid material subjected to the heating step has one type of starting point of the SHS reaction or has two or more types of starting points of the SHS reaction.

[0060] <Heating process> This manufacturing method includes a heating step in which the solid material is induction-heated to generate a self-propagating high-temperature synthesis reaction (SHS reaction) to obtain a MAX phase compound. In the heating step, the solid material is heated to a temperature at which the SHS reaction starts. Once the SHS reaction starts, the heat generated by the SHS reaction causes the temperature of the solid material to rise rapidly, and the SHS reaction progresses. The temperature of the solid material then drops and stabilizes, completing the SHS reaction.

[0061] The heating device for performing induction heating used in the heating method mainly includes a container made of an electrically conductive object to be heated, a solenoid coil, and a device for passing an alternating current through the solenoid coil. Specific examples of the heating device include the heating devices described in the Examples.

[0062] In the heating process, the solid material is placed in the container, the container is inserted into the sonotrode coil, and an alternating current is passed through the coil. This causes the magnetic field in the sonotrode coil to change over time, which in turn changes the magnetic field penetrating the container. As a result, electromagnetic induction occurs, generating an electromotive force inside the heated material that constitutes the container in a direction that cancels out the change in the magnetic field, and eddy currents flow inside the container. When the eddy currents flow, Joule heat is generated inside the container due to the resistance of the heated material, causing the entire container to heat up and generate radiant heat. The solid material inside the container is heated by the radiant heat.

[0063] The heated object is not particularly limited as long as it is a material that is electrically conductive and does not melt or disintegrate due to the heat generated by the SHS reaction in the heating step. Specific examples of the heated object include graphite and silicon carbide. The container is not particularly limited as long as it is a container made of the heated object, and examples include a crucible made of the heated object. Therefore, a specific example of the container is a carbon (graphite) crucible.

[0064] The ambient conditions when the container and the solid material are heated are not particularly limited, and the container and the solid material may be heated in air at normal pressure. From the viewpoint of preventing deterioration of the container and / or the solid material due to the action of oxygen in the air, it is preferable to store the container and the solid material in a chamber and reduce the pressure inside the chamber, or to replace the air inside the chamber with an inert gas. It is preferable that the chamber has a sample removal window (port). The method of reducing the pressure is not particularly limited, and may be, for example, a method of connecting a pressure reducing device such as a rotary pump to the chamber and reducing the pressure inside the chamber using the pressure reducing device.

[0065] When the pressure inside the chamber is reduced, from the above viewpoint, the pressure inside the chamber is preferably reduced to 1000 Pa or less, and more preferably to 100 Pa or less.

[0066] The inert gas is not particularly limited, and examples thereof include argon gas and nitrogen gas.

[0067] In the heating step, the solid material is heated at a temperature increase rate of preferably 10°C / sec or more, more preferably 30°C / sec or more, and even more preferably 50°C / sec or more, which allows the SHS reaction to occur efficiently and enables the production of a MAX phase compound in a short time with a high yield.

[0068] The temperature rise rate can be controlled, for example, by adjusting the magnitude of the current flowing through the solenoid coil. Specifically, the temperature rise rate can be increased by increasing the current. Note that the correlation between the magnitude of the current and the temperature rise rate varies depending on various conditions, such as the type and number of turns of the solenoid coil, the type of the heated object, and the size of the container.

[0069] The heating time in the heating step is not particularly limited as long as it is a time that allows the SHS reaction to be initiated and completed. In one embodiment of the present invention, the heating time can be shorter than the heating time used in conventional methods for producing MAX phase compounds by calcination. As a result, MAX phase compounds can be produced in a short time with a high yield.

[0070] From the viewpoint of preventing the solenoid coil from melting due to radiant heat generated during the induction heating, it is preferable to cool the solenoid coil during the induction heating. Therefore, it is preferable that the device performing the induction heating includes a cooler that cools the solenoid coil. The cooling method is not particularly limited, and may be, for example, a method in which a pipe wound around the solenoid coil is used as the cooler, and water, preferably cold water, is circulated through the pipe.

[0071] <Sizing process> The MAX phase compound obtained by the heating step is usually a solid. On the other hand, when a treatment is performed to convert the MAX phase compound to MXene, the effect of the treatment may not reach the inside of the solid, and the efficiency of the treatment may be reduced. To improve the efficiency of the treatment, the MAX phase compound to be treated is preferably in powder form. A specific example of the treatment is etching using the aforementioned fluoride-containing etching solution.

[0072] Therefore, in order to produce the powdered MAX phase compound, the present production method may include a particle size regulating step in which the MAX phase compound obtained in the heating step is pulverized and optionally classified to obtain a powdered MAX phase compound having a desired particle size.

[0073] The methods for pulverization and classification are not particularly limited. Examples of the pulverization method include a pulverization method using a mortar and pestle, and a pulverization method using a ball mill. Examples of the classification method include a classification method using a JIS standard sieve.

[0074] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0075] [2. Summary] The present invention includes the following: <1> ~ <6> The embodiments shown in the following are included. <1> General formula M n+1 AX n wherein M is an early transition metal, A is selected from the group consisting of Al, Si, P, S, Ga, Ge, As, Cd, In, Sn, Tl, and Pb, X is C or N, and n is 1, 2, or 3; a pressurizing step of pressurizing a mixture containing the raw material of the MAX phase compound to obtain a solid; and a heating step of inductively heating the solid material to cause a self-propagating high-temperature synthesis reaction (SHS reaction) to obtain a MAX phase compound. The method for producing a MAX phase compound includes a treatment step of forming at least one starting point for an SHS reaction in the solid material after the pressurizing step or simultaneously with the pressurizing step. <2> The treatment step is a step of forming a protrusion and / or a recess on at least one of the surfaces of the solid object. <1> A method for producing the MAX phase compound described in <3> The processing step is a step of making at least one of the two-dimensional shapes of the surface of the solid object as not vertically symmetrical and / or not horizontally symmetrical. <1> or <2> A method for producing the MAX phase compound described in <4> The treatment step is a step of forming through holes between at least one of the surfaces of the solid body and another surface of the solid body. <1> ~ <3> 1. A method for producing a MAX phase compound according to any one of the above. <5> The processing step is a step of forming a sharp point on the solid material. <1> ~ <4> 2. A method for producing a MAX layer compound according to any one of the above. <6> The treatment step is a step of forming a locally high density portion in the solid material. <1> ~ <5> 1. A method for producing a MAX phase compound according to any one of the above. [Example]

[0076] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0077] [Measurement and evaluation method] The MAX phase compounds produced in the examples were measured and evaluated by the methods described below.

[0078] <Weight> The weight of each powder used in the examples was measured using an analytical balance (Shimadzu AUW220D).

[0079] <Electron microscope image and X-ray diffraction spectrum> (Preparation of measurement samples) The solids after the SHS reaction produced in the examples were pulverized using a mortar and pestle to prepare powdered compounds. The powdered compounds were used as measurement samples. A portion of the measurement samples (powdered compounds) obtained from the solids after the SHS reaction produced in Examples 1, 5, and 7 was subjected to electron microscope image measurement, as described below, and another portion was subjected to X-ray diffraction spectrum measurement, as described below.

[0080] (Measurement of electron microscope images) Electron microscope images were taken using an electron microscope (JEOL JSM7500F) under the following conditions for each of the measurement samples obtained from compounds 1 and 5 produced in (a) Example 1 and (b) Example 5, and compound 7 produced in Example 7. The baking time for Example 1 was 1 minute, and the baking time for Example 5 was 60 minutes. The obtained electron microscope images are shown in Figures 5 and 7.

[0081] (X-ray diffraction spectrum measurement) For each of the measurement samples obtained from Compounds 1 to 8 produced in Examples 1 to 8, X-ray diffraction spectra were measured using an X-ray diffractometer (Rigaku Miniflex 600-C) under the following conditions. The resulting X-ray diffraction spectra are shown in Figures 6 and 8.

[0082] [Production Example 1: Preparation of a solid having a starting point for the SHS reaction] (Synthesis of V2AlC) Vanadium (V), aluminum (Al), and carbon (C) powders were mixed in a molar ratio of 2:1.2:0.9 to obtain 3.0 g of Mixture A. Specifically, 2.1 g of vanadium (V), 0.67 g of aluminum (Al), and 0.22 g of carbon (C) were mixed. The molar ratios were set as above to avoid a shortage of aluminum in the sintering reaction, which is the reaction that produces the MAX phase compound, due to the fact that aluminum has a lower melting point than other materials and vaporizes. In other words, to properly obtain the final MAX phase compound, the molar ratios of the raw materials were adjusted so that the molar ratio of aluminum was greater than the molar ratio of aluminum in the target compound.

[0083] 3.0 g of Mixture A was placed in a zirconia jar together with zirconia balls and milled using a ball mill (Fritsch P-7) at 500 rpm for 1.5 hours to obtain Mixture B. The weight of Mixture B was 3.0 g, unchanged from Mixture A.

[0084] (Preparation of solids) 3.0 g of Mixture B was placed in a φ15 cylindrical mold, and Mixture B was pressed at 50 MPa using a hydraulic press (Riken Kikai, product name: CDM-10M) to obtain a solid. Subsequently, a portion of the solid was notched, deforming the solid into the shape shown in Figure 2(a) (an uneven shape), thereby obtaining Solid 1. Specifically, the notching was performed by removing a portion of the uniform solid with a blade. As a result, a sharp edge was formed on Solid 1, as shown in Figure 2(a). The electric field is likely to concentrate at the sharp edge, which is thought to be the initiation point for the SHS reaction. Therefore, a site that can serve as the initiation point for the SHS reaction was formed on Solid 1.

[0085] In Production Example 1, the solid material had the shape shown in a) of Figure 2. However, in other embodiments of the present invention, the solid material may have, for example, another shape shown in Figure 2, i.e., one of the shapes shown in b) to m) of Figure 2. Even when the solid material has another shape shown in Figure 2, starting points for the SHS reaction are formed in the solid material.

[0086] [Example 1] An induction heating device 100 having the configuration shown in Figure 3 was fabricated. The induction heating device 100 is composed of an AC current regulator 10, a power source (outlet) 11, a coil 12, a cooler 13, a crucible 14, a chamber 15 equipped with a sample removal window 16, a rotary pump 17, and a flowmeter 18. The AC current regulator 10 connects the power source (outlet) 11 and the coil 12 and adjusts the voltage, current, frequency, etc. of the AC current supplied from the power source (outlet) 11 to allow a suitable AC current to flow through the coil 12. The coil 12 is a solenoid coil. The cooler 13 is a pipe wound around the coil 12. During heating, the coil 12 is cooled by circulating water within the pipe.

[0087] The crucible 14 was a carbon crucible (manufactured by Sogo Carbon Co., Ltd.), and the solid material 1 was placed therein. The crucible 14 was placed in the center of a dielectric heating device around which a coil was wound five times. A sample removal window 16 provided in the chamber 15 served as an outlet for removing the solid material after the firing reaction. A rotary pump 17 was connected to the chamber 15. The pressure inside the chamber 15 could be reduced by operating the rotary pump 17. A flow meter 18 was connected to the chamber 15. The pressure inside the chamber 15 could be measured by the flow meter 18. The temperature of the solid material 1 inside the crucible 14 was measured by a thermometer (an infrared radiation thermometer manufactured by CHINO, product name: CHINO IR-HS).

[0088] The rotary pump 17 was operated to reduce the pressure inside the chamber 15 to approximately 10 Pa. Next, an alternating current was applied to the coil 12 using the AC current regulator 10 under the conditions of a voltage of 40 to 42 V, a current of 17 A, and a frequency of 15,000 Hz. As a result, induction heating of the solid material 1 began at a temperature rise rate of 60°C / sec. Immediately after the temperature of the solid material 1 reached approximately 1100°C, the temperature of the solid material 1 rapidly rose to approximately 1700°C, and then dropped to approximately 1400°C and stabilized.

[0089] 4 is a diagram illustrating the state of the SHS reaction in Example 1 of the present application. The left, center, and right diagrams in FIG. 4 show the state of the solid material 1 before the temperature reaches about 1100°C, immediately after it reaches about 1100°C, and when it suddenly rises to about 1700°C, respectively.

[0090] Before the temperature of the solid material 1 reached approximately 1100°C, as shown in the left diagram of Figure 4, no change in the state of the solid material 1 was observed, and the SHS reaction had not yet begun. Furthermore, when the temperature of the solid material 1 reached approximately 1100°C, as shown in the center diagram of Figure 4, a portion of the solid material 1 emitted light, the temperature of the luminescent area rose locally, and a calcination reaction, including an exothermic reaction, occurred, along with the generation of heat from that area. This indicated the initiation of the SHS reaction. Furthermore, when the temperature of the solid material 1 rapidly rose to approximately 1700°C, the entire solid material 1 emitted light, as shown in the right diagram of Figure 4. In other words, the heat generated by the localized calcination reaction spread throughout the solid material 1, causing a calcination reaction throughout the entire solid material 1. Therefore, it was found that a self-propagating high-temperature thermal synthesis reaction (SHS reaction) was progressing from the center diagram to the right diagram of Figure 4. Therefore, it was found that in Example 1, the SHS reaction was induced in the solid material 1, and the calcination reaction proceeded throughout the entire solid material 1.

[0091] After the temperature of solid material 1 had dropped to approximately 1400°C and remained stable for one minute, solid material 1 after the SHS reaction was obtained from crucible 14 through sample extraction window 16. This solid material 1 after the SHS reaction was designated Compound 1. As described below, Compound 1 was a MAX phase compound. Hereinafter, the time during which the temperature of the solid material rapidly rose due to the SHS reaction, then dropped and remained stable is referred to as the "firing time." For example, a firing time of one minute means that the temperature of the solid material was maintained at approximately 1400°C for one minute.

[0092] The time from when the temperature of solid material 1 began to rise rapidly immediately after reaching approximately 1100°C until the temperature dropped to approximately 1400°C and stabilized was 10 seconds. Hereinafter, the time from when the temperature of the solid material began to rise rapidly until the temperature stabilized is referred to as the "reaction time." The reaction time represents the time required for the mixture constituting the solid material to react and change into the MAX phase compound by induction heating.

[0093] [Example 2] The same procedure as in Example 1 was carried out, except that the baking time was changed to 15 minutes, to obtain solid material 2 after the SHS reaction. The solid material 2 after the SHS reaction is referred to as Compound 2. Compound 2 was also a MAX phase compound, as described below. The reaction time in Example 2 was 10 seconds.

[0094] [Example 3] The same procedure as in Example 1 was carried out, except that the baking time was changed to 30 minutes, to obtain a post-SHS reaction solid material 3. The post-SHS reaction solid material 3 is designated as Compound 3. Compound 3 was also a MAX phase compound, as described below. The reaction time in Example 3 was 10 seconds.

[0095] [Example 4] The same procedure as in Example 1 was carried out, except that the baking time was changed to 45 minutes, to obtain solid material 4 after the SHS reaction. The solid material 4 after the SHS reaction is designated as Compound 4. Compound 4 was also a MAX phase compound, as described below. The reaction time in Example 4 was 10 seconds.

[0096] [Example 5] The same procedure as in Example 1 was carried out, except that the baking time was changed to 60 minutes, to obtain solid material 5 after the SHS reaction. Solid material 5 after the SHS reaction is referred to as Compound 5. Compound 5 was also a MAX phase compound, as described below. The reaction time in Example 5 was 10 seconds.

[0097] The same procedure was carried out on each of the 14 solids 1 to obtain 14 compounds 5. As will be described later, the 14 compounds 5 were also MAX phase compounds. Furthermore, the reaction time for producing the 14 compounds 5 was also 10 seconds.

[0098] [Comparative Example 1] The same operation as in Production Example 1 was carried out, except that the notch-forming treatment was not carried out. The above-mentioned operation was repeated 24 times to obtain 24 comparative solids having the shape (uniform shape) shown in FIG. 1 . Subsequently, the same operation as in Example 5 was carried out, except that a comparative solid was used instead of Solid 1. The above-mentioned operation was carried out for each of the 24 comparative solids, to obtain 24 comparative compounds.

[0099] [Production Example 2: Preparation of a solid having a starting point for the SHS reaction] (Synthesis of Ti3AlC2) Titanium (Ti), aluminum (Al), and carbon (C) powders were mixed in a molar ratio of 3:1.1:1.9 to obtain 3.0 g of mixture C. Specifically, 4.4 g of titanium (Ti), 0.91 g of aluminum (Al), and 0.69 g of carbon (C) were mixed.

[0100] (Preparation of solids) A solid was obtained by the same method as in Production Example 1, except that Mixture C was used instead of Mixture A. Then, a portion of the solid was cut out, and the shape of the solid was deformed into the shape (uneven shape) shown in Figure 2(a), to obtain Solid 6. The cutout method was the same as in Production Example 1. As a result, a sharp edge was formed on Solid 6, as shown in Figure 2(a). It is believed that an electric field tends to concentrate on the sharp edge, and this becomes the starting point for the SHS reaction. Therefore, a point that can become the starting point for the SHS reaction was formed on Solid 6.

[0101] In Production Example 2, the solid material had the shape shown in a) of Figure 2. However, in other embodiments of the present invention, the solid material may have, for example, another shape shown in Figure 2, i.e., one of the shapes shown in b) to m) of Figure 2. Even when the solid material has another shape shown in Figure 2, starting points for the SHS reaction are formed in the solid material.

[0102] [Example 6] The same procedure as in Example 1 was carried out, except that solid 6 was used instead of solid 1, to obtain solid 6 after the SHS reaction. The obtained solid 6 after the SHS reaction is referred to as compound 6. As described below, compound 6 was a MAX phase compound. The reaction time in Example 6 was 10 seconds.

[0103] [Example 7] The same procedure as in Example 2 was carried out, except that solid 6 was used instead of solid 1, to obtain solid 7 after the SHS reaction. Solid 7 after the SHS reaction is designated as Compound 7. Compound 7 was also a MAX phase compound, as described below. The reaction time in Example 7 was 10 seconds.

[0104] [Example 8] The same procedure as in Example 4 was carried out, except that solid 6 was used instead of solid 1, to obtain solid 8 after the SHS reaction. Solid 8 after the SHS reaction is referred to as compound 8. Compound 8 was also a MAX phase compound, as described below. The reaction time in Example 8 was 10 seconds.

[0105] [result] Electron microscope images and X-ray diffraction spectra obtained for the compounds obtained in the examples are shown in FIGS.

[0106] Figure 5 shows electron microscope photographs of compounds 1 and 5 obtained in (a) Example 1 (baking time: 1 minute) and (b) Example 5 (baking time: 60 minutes). Figure 5 shows that both compounds 1 and 5 are layered compounds. From these results, compounds 2 to 4 obtained in Examples 2 to 4 are also considered to be layered compounds, like compounds 1 and 5.

[0107] FIG. 6 shows the X-ray diffraction spectra of Compounds 1 to 5 obtained in Examples 1 to 5. In the figure, 1 minute to 60 minutes respectively represent the firing time, which corresponds to Examples 1 to 5. FIG. 6 shows that the presence of a peak due to VAlC (a peak seen at the angle of the arrow in FIG. 5) can be confirmed in the X-ray diffraction spectrum of each of Compounds 1 to 5. This is because Compounds 1 to 5, which are the layered compounds described above, have the general formula: M of the MAX phase compound described above. n+1 AX n This indicates that the compounds are compounds represented by the chemical formula V2AlC, which is within the range of 1. Therefore, compounds 1 to 5 are MAX phase compounds.

[0108] Figure 7 is an electron microscope photograph of Compound 7 obtained in Example 7. Figure 7 shows that Compound 7 is a layered compound. From this result, Compounds 6 and 8 obtained in Examples 6 and 8 are also considered to be layered compounds, like Compound 7.

[0109] FIG. 8 shows the X-ray diffraction spectra of Compounds 6 to 8 obtained in Examples 6 to 8. In the figure, 1 minute to 45 minutes represent the firing time, which corresponds to Examples 6 to 8, respectively. FIG. 8 shows that the presence of a peak due to Ti3AlC2 (a peak seen at the angle indicated by the black circle (●) in FIG. 8) can be confirmed in the X-ray diffraction spectrum of each of Compounds 6 to 8. This is because Compounds 6 to 8, which are the layered compounds described above, have the general formula: M of the MAX phase compound described above. n+1 AX n This indicates that the compounds are compounds represented by the chemical formula Ti3AlC2, which is within the range of 1. Therefore, compounds 6 to 8 are MAX phase compounds.

[0110] Furthermore, the methods for producing compounds 1 to 8 described in Examples 1 to 8 include the pressurizing step, the treatment step, and the heating step, and therefore fall under the present production method. In addition, the production methods described in Examples 1 to 8 utilize induction heating, so they can be carried out inexpensively and have been shown to be capable of producing MAX phase compounds in a short time.

[0111] (Differences due to the presence or absence of a treatment process that forms the starting point for the SHS reaction) The reaction behavior in Example 5 was observed. As a result, for each of the 15 compounds 5, a behavior specific to the SHS reaction, as shown in Figure 4, was observed during production, indicating that the SHS reaction occurred. Therefore, the SHS reaction occurrence rate in Example 5 was (15 / 15) x 100 = 100%.

[0112] In addition, electron microscope images and X-ray diffraction spectra were measured for the 15 compounds 5 obtained in Example 5. The results showed that all of the compounds 5 were layered compounds. Furthermore, peaks due to VAlC were confirmed in all of the X-ray diffraction spectra. Therefore, all of the 15 compounds 5 were shown to be MAX phase compounds.

[0113] The reaction behavior in Comparative Example 1 was observed. As a result, for the 24 comparative compounds, behavior specific to the SHS reaction, as shown in Figure 4, was observed in some cases during production, and not in others. This behavior was observed in four compounds, and not observed in 20 compounds. Therefore, the SHS reaction occurrence rate for Comparative Example 1 was (20 / 24) × 100 ≒ 16.66 % ≒ 17%.

[0114] In addition, X-ray diffraction spectra were measured for the 24 comparative compounds obtained in Comparative Example 1. As a result, among the comparative compounds, no peaks related to the MAX phase were observed in the X-ray diffraction spectra of the comparative compounds for which no behavior specific to the SHS reaction was observed during the observation. Therefore, it can be said that these comparative compounds do not fall under the category of MAX phase compounds.

[0115] As described above, Example 5 included a treatment step for forming the starting point of the SHS reaction, which enabled the SHS reaction to occur efficiently, and it was shown that the MAX phase compound could be produced with high efficiency. On the other hand, Comparative Example 1 showed that the probability of the SHS reaction occurring was low due to the shape of the solid material used, and the production efficiency of the MAX phase compound was also low.

[0116] As described above, it has been found that the present production method makes it possible to produce MAX phase compounds inexpensively, in a short time, and with a high yield. [Industrial Applicability]

[0117] A manufacturing method according to one embodiment of the present invention can be used to produce a MAX phase compound inexpensively, in a short time, and with a high yield, and to produce MXene inexpensively and in a short time using the MAX phase compound. [Explanation of symbols]

[0118] 100 Induction heating device 10 AC current regulator 11 Power supply (outlet) 12 coils 13 Cooler 14 Crucible 15 chambers 16. Sample removal window 17 Rotary Pump 18 Flow meter

Claims

1. General formula M ｎ＋１ AX ｎ wherein M is an early transition metal, A is selected from the group consisting of Al, Si, P, S, Ga, Ge, As, Cd, In, Sn, Tl, and Pb, X is C or N, and n is 1, 2, or 3, comprising: a pressurizing step of pressurizing a mixture containing the raw material of the MAX phase compound to obtain a solid; a heating step of inductively heating the solid material to cause a self-propagating high temperature synthesis reaction (SHS reaction) to obtain a MAX phase compound; A method for producing a MAX phase compound, comprising a treatment step of forming at least one starting point of an SHS reaction in the solid material after the pressurizing step or simultaneously with the pressurizing step.

2. The method for producing a MAX phase compound according to claim 1 , wherein the treatment step is a step of forming a convex portion and / or a concave portion on at least one of the surfaces of the solid body.

3. The method for producing a MAX phase compound according to claim 1, wherein the treatment step is a step of making at least one of the two-dimensional shapes of the surfaces of the solid object asymmetrical in the vertical direction and / or asymmetrical in the horizontal direction.

4. The method for producing a MAX phase compound according to claim 1 , wherein the treatment step is a step of forming through holes between at least one of the surfaces of the solid body and another surface of the solid body.

5. The method for producing a MAX phase compound according to claim 1 , wherein the treatment step is a step of forming a sharp point on the solid material.

6. The method for producing a MAX phase compound according to claim 1 , wherein the treatment step is a step of forming locally high density areas in the solid material.

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