Powdered liquid metal and production method thereof

Abstract

To realize a powdered liquid metal with excellent liquid metal content and superior handling properties in powder form, and a method for producing the same.SOLUTION: The powdered liquid metal contains more than 50 wt.% of liquid metal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to powdered liquid metal and a method for producing the same. [Background technology]

[0002] Drywater, which consists of numerous water droplets stabilized by solid particles, has a high water content of over 90% by weight, yet behaves as a free-flowing powder, making it suitable for applications in gas storage, catalysis, sensing, cosmetics, food, fuel cells, and more.

[0003] Liquid metals are metals that are liquid at around room temperature, and there are five types: mercury, cesium, rubidium, gallium, and francium. Liquid metals have unique properties, such as high thermal and electrical conductivity, catalytic properties, and semiconductor properties, making them promising for applications in soft electronics, soft robotics, energy storage and conversion, catalyst manufacturing, and biomedicine. However, liquid metals have problems such as high surface tension, low fluidity, and high corrosiveness to other materials, making them difficult to handle and process. Overcoming these problems and obtaining powders with a high liquid metal content, like dry water, could potentially expand the applications of liquid metals by taking advantage of their properties.

[0004] As a method for producing particles containing a liquid metal, for example, the methods described in Non-Patent Documents 1 and 2 are known. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Die Wu et. al.,Small Methods,2022, 6, 2200246 [Non-patent document 2] Lei Yu et. al., ACS Appl. Mater. Interfaces, 2022, 14, 48150-48160. Summary of the Invention [Problem to be solved by the invention]

[0006] The method described in Non-Patent Document 1 involves mixing a liquid metal with aluminum oxide or the like in a mortar to obtain a powder containing the liquid metal.The method described in Non-Patent Document 2 involves adding silicon dioxide or the like to EGaIn and subjecting the mixture to centrifugation to obtain a powder containing the liquid metal.

[0007] However, the powder obtained by these methods has an excessively high content of aluminum oxide and the like compared to the liquid metal, and therefore the content of the liquid metal is insufficient. Therefore, these methods have room for improvement in terms of providing particles that can fully utilize the properties of the liquid metal.

[0008] Therefore, one aspect of the present invention aims to provide a powdered liquid metal that has an excellent liquid metal content and is in powder form and easy to handle, and a method for producing the same. [Means for solving the problem]

[0009] In order to solve the above problems, a powdered liquid metal according to one embodiment of the present invention is a powdered liquid metal having a liquid metal content of more than 50 wt %.

[0010] Furthermore, a method for producing powdered liquid metal according to one embodiment of the present invention includes step A of oxidizing the surface of the liquid metal, step B of applying shear force to the liquid metal having the oxidized surface obtained in step A, and step C of combining the sheared liquid metal obtained in step B with a stabilizer. [Effects of the Invention]

[0011] According to one aspect of the present invention, it is possible to realize a powdered liquid metal that has an excellent liquid metal content and is in powder form and therefore easy to handle, and a method for producing the same. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing the appearance of the powdered liquid metal prepared in Example 1. [Figure 2] FIG. 1 is a graph showing that the powdered liquid metal prepared in Example 1 has fluidity. [Figure 3] FIG. 2 is a diagram showing the powder liquid metal prepared in Example 1 dispersed in n-dodecane and observed with an optical microscope. [Figure 4] FIG. 1 shows that when the powdered liquid metal prepared in Example 1 was pressed between two glass slides, the liquid metal flowed out of the powdered liquid metal. [Figure 5] FIG. 1 is a diagram showing an FE-SEM image of the powder liquid metal prepared in Example 1. [Figure 6] FIG. 1 is a diagram showing an FE-SEM image of the powder liquid metal prepared in Example 1. [Figure 7] FIG. 1 is a diagram showing an FE-SEM image of the powder liquid metal prepared in Example 1. [Figure 8] FIG. 2 is a graph showing the results of measuring the particle size distribution of the powdered liquid metal prepared in Example 1. [Figure 9] FIG. 1 is a schematic diagram showing an embodiment of preparing a powdered liquid metal using a planetary centrifugal mixer. [Figure 10] To further evaluate the morphology of the powdered liquid metal prepared in Example 1, the powder was ultrasonically cleaned in ethanol for 1 minute to remove the excess layer of adsorbed SiOx nanoparticles, and then imaged using a transmission electron microscope. [Figure 11] 2001 and 2003 show the surface temperature profile and optical microscope images of EGaIn, SiOx nanoparticles, the powdered liquid metal produced in Example 1, and a powdered liquid metal prepared by the same method as in Example 1, except that the shaken EGaIn and SiOx nanoparticles were mixed so that the EGaIn content was 98.2 wt %. [Figure 12] FIG. 1 shows a photoelectric element made by combining a powdered liquid metal and a thermoelectric element. [Figure 13]FIG. 10 is a diagram showing the difference in output performance between a thermoelectric element on which powdered liquid metal is placed and a thermoelectric element on which powdered liquid metal is not placed. [Figure 14] FIG. 10 shows the output power generated by a thermoelectric device loaded with powdered liquid metal in response to repeated on / off switching of the light source. [Figure 15] FIG. 10 shows the current values ​​generated by a photoelectric element on which powdered liquid metal prepared using various stabilizers is placed. [Figure 16] FIG. 1 shows data comparing the thermal conductivity of graphite with that of powdered liquid metal using graphite as a stabilizer. [Figure 17] FIG. 10 shows the current generated by a photoelectric device loaded with powdered liquid metal prepared with various stabilizers in response to repeated on / off switching of the light source. [Figure 18] This is an SEM photograph showing the state in which, when the liquid metal is gallium, a layer of gallium oxide with a thickness of about 3 to 5 nm is formed on the surface of the gallium through oxidation. [Figure 19] FIG. 1 is a schematic diagram showing a state in which a layer of gallium oxide is formed on the surface of gallium, and a layer of monomolecular silicon dioxide bonded to the gallium oxide is formed. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, 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. In this specification, unless otherwise specified, "A to B" representing a numerical range means "greater than or equal to A and less than or equal to B."

[0014] [1. Powdered liquid metal] The powdered liquid metal according to one embodiment of the present invention (hereinafter also referred to as "powdered liquid metal of the present invention") has a liquid metal content of more than 50 wt %. The powdered liquid metal of the present invention has a liquid metal content that is significantly higher than that of conventional techniques, and is in powder form.

[0015] (1-1) Technical Concept of the Present Invention For example, the particles obtained by the methods described in Non-Patent Documents 1 and 2 contain stabilizers such as aluminum oxide and silicon dioxide in an amount excessively greater than the liquid metal content, making it impossible to fully utilize the properties of the liquid metal. On the other hand, the powdered liquid metal of the present invention has a much higher liquid metal content than the particles obtained by these methods, making it possible to fully utilize the properties of the liquid metal. Moreover, since the powdered liquid metal of the present invention is in powder form, it has improved handleability compared to liquid metal. Therefore, according to the above configuration, it is possible to expand the applications of liquid metal while utilizing its properties.

[0016] Since no liquid metal with a liquid metal content of more than 50% by weight and in powder form has existed until now, in this specification, such liquid metal in powder form will be referred to as "powdered liquid metal."

[0017] (1-2)Liquid metal A liquid metal is a metal with a melting point close to room temperature. The liquid metal contained in the powdered liquid metal of the present invention can be one or more liquid metals selected from the group consisting of gallium, mercury, cesium, rubidium, and francium. The liquid metal may form a eutectic with another metal. Examples of the eutectic include a eutectic alloy of gallium and indium (EGaIn); a eutectic alloy of gallium, indium, and tin (Galinstan); a eutectic alloy of gallium, indium, and bismuth; and a eutectic alloy of gallium and tin.

[0018] Gallium is particularly preferred as the liquid metal because it has low vapor pressure and toxicity and is suitable for practical use.

[0019] The liquid metal preferably has an oxidized surface. The liquid metal surface refers to the interface between the liquid metal and air. The liquid metal surface can be easily oxidized by contact with air. The oxidized liquid metal surface can be obtained, for example, by leaving the liquid metal in air. From the viewpoint of sufficient oxidation, it is preferable to obtain the surface by appropriately shaking the liquid metal in air using a shaker, as shown in the examples described later. Figure 18 is an SEM photograph showing the state in which a gallium oxide layer with a thickness of approximately 3 to 5 nm is formed on the surface of gallium by the oxidation when the liquid metal is gallium. The gallium oxide can be one or more selected from the group consisting of GaO(OH), Ga2O3, and Ga2OH.

[0020] The liquid metal having an oxidized surface can promote bonding between the stabilizer and the surface, making it easier to obtain particles that have a high liquid metal content and are in powder form.

[0021] (1-3) Stabilizer The powdered liquid metal of the present invention preferably contains a stabilizer. In this specification, a stabilizer refers to a material that can bond with the oxidized surface of the liquid metal and contribute to maintaining the powder form stably. The stabilizer may act on the liquid metal as individual particles or as agglomerated particles. The stabilizer is preferably one or more substances selected from the group consisting of silicon oxide, titanium oxide, graphite, molybdenum sulfide, and carboxylic acids that are solid at room temperature.

[0022] Examples of silicon oxides include silicon dioxide. Examples of titanium oxides include titanium(II) oxide, titanium(III) oxide, titanium(IV) oxide, and titanic acid. Examples of carboxylic acids that are solid at room temperature include saturated fatty acids with 11 or more carbon atoms (lauric acid, myristic acid, palmitic acid, stearic acid, etc.), citric acid, oxalic acid, malonic acid, succinic acid, and glutaric acid. The "room temperature" mentioned above refers to 15 to 30°C.

[0023] It is preferable that a portion of the stabilizer is bonded to the oxidized surface of the liquid metal. "A portion of the stabilizer" refers to a portion of the total amount of stabilizer used to form the powdered liquid metal. For example, if the liquid metal is gallium and the stabilizer is silicon dioxide, the surface of the gallium is oxidized to form gallium oxide, and hydrogen bonds are formed between the gallium oxide and silanol groups derived from the silicon dioxide. At this time, silicon dioxide bonds to the gallium oxide on the surface to form a monomolecular silicon dioxide layer, and other silicon dioxide molecules can be adsorbed to the surface of this layer by intermolecular forces, etc. The other silicon dioxide may or may not be present, but is preferably present from the perspective of further stabilizing gallium and making it easier to obtain the powdered liquid metal. The other silicon dioxide is a stabilizer that does not bond to the oxidized surface of the liquid metal among the stabilizers used to form the powdered liquid metal. The absence of the other silicon dioxide refers to the case where all of the stabilizer is bonded to the oxidized surface of the liquid metal.

[0024] As a result, the gallium is stabilized by the silicon dioxide and can be kept in a stable powder form, making it easier to obtain the powdered liquid metal. Although the above has been described as using gallium as the liquid metal, even when other liquid metals and other stabilizers are used, the powdered liquid metal can be easily obtained due to bonding (e.g., hydrogen bonding) between the surface of the oxidized liquid metal and the stabilizer.

[0025] The top diagram in Figure 19 is a schematic diagram showing the formation of a gallium oxide layer (shown as Ga2O3 in the figure) on the surface of liquid metal gallium (shown as LM in the figure), and the formation of a monomolecular silicon dioxide layer (shown as SiO2 in the figure) bonded to the gallium oxide. Although not shown, other silicon dioxide not bonded to the gallium oxide may be adsorbed on the surface of the silicon dioxide layer. The bottom diagram in Figure 19 shows the formation of hydrogen bonds between gallium oxide and silanol groups derived from silicon dioxide.

[0026] The primary particle diameter of the stabilizer is preferably less than 1 μm, more preferably 500 nm or less, even more preferably 100 nm or less, and particularly preferably 50 nm or less. Even when a stabilizer with a primary particle diameter of 1 μm or more is used, the stabilizer can encapsulate the liquid metal, as shown in Example 1 described below. However, in this case, the amount (weight) of stabilizer required to cause the liquid metal to transition from a fluid liquid to a solid powder tends to be greater than when a stabilizer with a primary particle diameter of less than 1 μm is used. In order to utilize the properties of the liquid metal, it is preferable that the stabilizer content in the powder liquid metal of the present invention is low. Therefore, the primary particle diameter of the stabilizer is preferably less than 1 μm.

[0027] The primary particle size and secondary particle size of the stabilizer can be measured by observation with a transmission electron microscope, the BET method, or the like.

[0028] (1-4) Contact angle The contact angle of the stabilizer on the oxidized surface of the liquid metal is preferably greater than 90°. The contact angle is measured through the liquid phase. When particles with a contact angle greater than 90° come into contact with the liquid metal, they tend to separate from the liquid until they reach the liquid-air interface, which is an energetically favorable position, and then position themselves at the interface. At this time, the particles positioned at the interface have suitable wettability with the liquid metal, so they can adsorb to the interface between the liquid metal and air and efficiently encapsulate the liquid metal. Therefore, the contact angle greater than 90° is preferred.

[0029] From this viewpoint, the contact angle is preferably 95° or more, and more preferably 110° or more. The contact angle is not particularly limited, but may be 170° or less, or 150° or less. The contact angle can be measured by a colloidoscope AFM method, a penetration velocity method, FE-SEM, or the like.

[0030] The stabilizer may adhere to the periphery of the liquid metal as a single particle, or may adhere to the periphery of the liquid metal as agglomerated particles. In either case, when the shape of the stabilizer in the adhered state is considered to be a sphere, it is desirable that the contact angle is as described above.

[0031] (1-5) Liquid metal content in powder liquid metal The powdered liquid metal of the present invention has a content of liquid metal having an oxidized surface of more than 50 wt %. With this configuration, the powdered liquid metal contains more liquid metal than other materials, so the properties of the liquid metal can be fully utilized and the handling can be made easier.

[0032] From the viewpoint of more fully utilizing the properties of the liquid metal, the content of the liquid metal in the powdered liquid metal is preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more.

[0033] Furthermore, if powdered liquid metal can be obtained with a small amount of stabilizer, the properties of the liquid metal can be more easily utilized, and therefore, the greater the weight of the liquid metal having an oxidized surface relative to the weight of the stabilizer, the more preferable. From this viewpoint, the ratio of the weight of the liquid metal to the weight of the stabilizer, when the total weight of the liquid metal and the stabilizer is taken as 100% by weight, is preferably such that the weight of the liquid metal is more than 50% by weight, more preferably 70% by weight or more, even more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more.

[0034] In addition to the liquid metal and the stabilizer, other materials that can be contained in the powdered liquid metal include, for example, battery materials such as magnesium and lithium, catalytic materials such as palladium, platinum, rhodium, ruthenium, and cobalt, and low-melting-point metals such as tin and bismuth. The proportion of these materials in the powdered liquid metal is preferably 0.1% by weight or more and 10% by weight or less, from the viewpoint of fully utilizing the properties of the powdered liquid metal and maintaining its powder form.

[0035] 2. Method for producing powdered liquid metal of the present invention A method for producing powdered liquid metal according to one embodiment of the present invention (hereinafter also referred to as the "production method of the present invention") is a method comprising step A of oxidizing the surface of the liquid metal, step B of applying shear force to the liquid metal having the oxidized surface obtained in step A, and step C of combining the sheared liquid metal obtained in step B with a stabilizer.

[0036] The powdered liquid metal of the present invention described in [1.] above cannot be obtained by the methods described in Non-Patent Documents 1 and 2. In view of the fact that the powders obtained by the methods described in Non-Patent Documents 1 and 2 have a high content of aluminum oxide and the like and a low content of liquid metal, the present inventors investigated methods not described in Non-Patent Documents 1 and 2.

[0037] As a result, the present inventors noticed that neither the method of grinding materials using a mortar, as in the method described in Non-Patent Document 1, nor the method of using centrifugal separation, as in the method described in Non-Patent Document 2, applies shear stress to the liquid metal. They then discovered that the method comprising the steps A to C has a liquid metal content that is significantly higher than that of the methods described in Non-Patent Documents 1 and 2, and that the powdered liquid metal of the present invention is in powder form.

[0038] The method for step A is not particularly limited as long as it is a step that can oxidize the surface of the liquid metal. Examples of such a method include leaving the liquid metal in air, or appropriately shaking the liquid metal in air using a shaker, as described in [1.] above. From the viewpoint of sufficient oxidation, step A is preferably a step of appropriately shaking the liquid metal in air using a shaker.

[0039] Step B is a step of applying shear force to the liquid metal having an oxidized surface obtained in step A. Examples of the method of applying shear force include one or more methods selected from the group consisting of rotation-revolution mixing, mixing using an ultrasonic disperser, mixing by cyclomix, and spray mixing. Furthermore, other stirring methods may be combined with the above methods. Examples of the other stirring methods include one or more methods selected from stirring, diffusion, and convection.

[0040] Rotation-revolution mixing is a method in which a container containing materials is tilted and rotated and revolved at high speed, generating centrifugal force to cause convection in the materials and impart shear stress. Rotation-revolution mixing can be performed using a rotation-revolution mixer.

[0041] Mixing using an ultrasonic disperser is a method in which cavitation is generated in a liquid by high-frequency vibration waves emitted from an ultrasonic oscillator, and then a strong shear force is generated by collapsing the cavitation, resulting in the mixing of the sheared liquid with solid materials.

[0042] Cyclomix mixing is a method in which a liquid is subjected to powerful impact and shear forces by rotating paddles inside an inverted cone-shaped casing, resulting in the sheared liquid being mixed with solid materials.

[0043] Spray mixing is a method in which a two-fluid nozzle is used to pulverize and atomize a liquid using a high-velocity airflow such as compressed air, and the atomized liquid is then mixed with a solid material.

[0044] Step C is a step of bonding the sheared liquid metal obtained in step B with a stabilizer. In the production method of the present invention, it is preferable that step B and step C proceed simultaneously, and that the stabilizer bonds to the sheared liquid metal earlier than the liquid metals sheared in step B bond to each other.

[0045] For example, when step B is performed by rotation-revolution mixing, the liquid metal having an oxidized surface and the stabilizer are placed in the same container. Therefore, the surface of the sheared liquid metal and the stabilizer bond together simultaneously with or immediately after the liquid metal is sheared. In other words, the manufacturing method of the present invention is considered to be a technology that can be realized by covering the surface of the liquid metal with the stabilizer before the liquid metals torn by shear come into contact with each other and rebond. In this way, steps B and C can be performed by rotating and revolving the liquid metal having an oxidized surface and the stabilizer (rotation-revolution mixing).

[0046] As explained in [1.] above, the bonding is achieved by hydrogen bonding or the like between the oxidized surface of the liquid metal and the stabilizer. It is preferable that a portion of the stabilizer subjected to step C is bonded to the surface of the sheared liquid metal. The stabilizer that is not bonded to the surface of the sheared liquid metal can be adsorbed onto the surface of the stabilizer that is bonded to the surface.

[0047] When steps B and C are performed using the planetary centrifugal mixer, it is preferable to perform the steps at a speed of 1,000 to 3,000 rpm when using the planetary centrifugal mixer used in the examples described below in order to stabilize the powdered liquid metal. The effects of the stirring and shear force vary not only depending on the revolution speed and the rotation speed, but also on the amount of sample to be treated and the shape of the container. Therefore, it is preferable to change the rotation speed appropriately depending on the amount of sample to be treated, the shape of the container, etc.

[0048] When mixing using an ultrasonic disperser, mixing by a cyclomix, or spray mixing is used, it is possible to carry out the steps B and C at the same time, just as when rotation-revolution mixing is used.

[0049] In the manufacturing method of the present invention, compressive stress and tensile stress are applied to a liquid metal having an oxidized surface by these methods to shear (tear) it, and a part or all of the stabilizer is bonded to the surface of the sheared liquid metal by hydrogen bonding or the like. The size of the stabilizer is smaller than that of the liquid metal. As a result, the liquid metal is stably encapsulated by the stabilizer, and a powdered liquid metal with a liquid metal content of more than 50 wt% is obtained.

[0050] Such shearing does not occur in the methods described in Non-Patent Documents 1 and 2. In the production method of the present invention, a shearing force is applied to a liquid metal having an oxidized surface, and therefore, unlike the methods described in Non-Patent Documents 1 and 2, it is believed that a powdered liquid metal having a high liquid metal content and in powder form can be obtained.

[0051] Thus, the discovery that powdered liquid metal containing a high liquid metal content of over 50 wt. % can be obtained by applying shear force to a liquid metal and a stabilizer having an oxidized surface is a first for the present invention. The powders obtained in Non-Patent Documents 1 and 2 contain excessively high amounts of aluminum oxide and other substances compared to the liquid metal, and therefore these methods leave room for improvement in terms of utilizing the properties of liquid metal. The method of the present invention produces powdered liquid metal with an extremely low stabilizer content compared to the liquid metal content, thereby providing a material that can fully utilize the properties of liquid metal. Furthermore, the powdered liquid metal is in powder form and is easy to handle, which is advantageous for expanding the applications of liquid metal.

[0052] Details of the liquid metal having an oxidized surface and the stabilizer are as described above in [1.]. With respect to the weight ratio of the liquid metal and the stabilizer used in step C, when the total weight of these is taken as 100% by weight, the weight of the liquid metal is preferably more than 50% by weight, more preferably 70% by weight or more, still more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more.

[0053] 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.

[0054] 〔summary〕 The present invention includes the following aspects. <1> A powdered liquid metal having a liquid metal content of more than 50% by weight. <2> The liquid metal contains a stabilizer, and the liquid metal has an oxidized surface. <1> The powdered liquid metal according to claim 1. <3> a portion of the stabilizing agent is bonded to the surface, and the contact angle of the stabilizing agent on the surface is greater than 90°; <2> The powdered liquid metal according to claim 1. <4> The liquid metal contains gallium and one or more metals selected from the group consisting of indium, bismuth, and tin. <1> The powdered liquid metal according to claim 1. <5> The stabilizer is one or more substances selected from the group consisting of silicon oxide, titanium oxide, graphite, molybdenum sulfide, and carboxylic acids that are solid at room temperature. <2> from <4> 1. The powdered liquid metal according to any one of the preceding claims. <6> A method for producing powdered liquid metal, comprising: step A of oxidizing the surface of liquid metal; step B of applying shear force to the liquid metal having the oxidized surface obtained in step A; and step C of bonding the sheared liquid metal obtained in step B with a stabilizer. <7> The step B and the step C proceed simultaneously, and the stabilizer binds to the sheared liquid metal faster than the liquid metals sheared in the step B bind to each other. <6> 10. A method for producing the powdered liquid metal according to claim 9. <8> The steps B and C are carried out by rotating and revolving the liquid metal having an oxidized surface and the stabilizer. <6> or <7> 10. A method for producing the powdered liquid metal according to claim 9. [Example]

[0055] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0056] Example 1 (Preparation of powdered liquid metal) (1) Materials used Gallium and indium (both 99.99% pure) were purchased from Kojundo Chemical Co., Ltd. Ethanol (99.5%) was purchased from Fujifilm Wako Pure Chemical Industries, Ltd., and n-dodecane (98%) was purchased from Sigma-Aldrich Japan. Ethanol and n-dodecane were used as dispersion media in the preparation of eutectic gallium-indium-based powdered liquid metal. Molybdenum sulfide nanopowder (particle diameter approximately 90 nm) was purchased from Sigma-Aldrich Japan. Anhydrous citric acid (98%) was purchased from Fujifilm Wako Pure Chemical Industries, Ltd. The particle diameter was 10-20 nm, and the BET specific surface area was 118 m. 2 Fused amorphous SiOx nanoparticles (Calplex® CS-7) with a SiOx content of 0.1g / g were kindly provided by Evonik Japan Co., Ltd. TiO2 nanoparticles (No. 718467-100G) with a primary particle diameter of 20 nm as measured by transmission electron microscopy (TEM) were obtained from Sigma-Aldrich. Graphite (product name GR-10) was obtained from Nippon Graphite Trading Co., Ltd.

[0057] (2) Production of powdered liquid metal (2-1) Production of powdered liquid metal using nano-sized stabilizers 1.54 g of gallium and 0.50 g of indium were placed in a container and heated to 180°C on a hot plate. As soon as the mixture became fluid, it was removed from the hot plate and stirred with a surface-coated microspatula to obtain a liquid metal eutectic alloy of gallium and indium (EGaIn). The above operation was carried out for approximately 10 minutes to prevent oxidation due to prolonged heating.

[0058] Next, the EGaIn was gently shaken in air at 80 rpm for 3 days using a shaker (MMS1020, EYELA, Japan), which allowed the surface of the EGaIn to oxidize.

[0059] 0.50 g of the shaken EGaIn was mixed with 0.01 g of SiOx nanoparticles (Calplex (registered trademark) CS-7) that had been crushed in a mortar. The weight ratio of EGaIn to SiOx nanoparticles was 98:2.

[0060] The resulting mixture was placed in a planetary centrifugal mixer (Nanko Rentaro (registered trademark) NRE120, manufactured by Thinky Corporation) and subjected to shear mixing to obtain a powdered liquid metal. The shear mixing conditions were rotation at 2000 rpm for 1 minute and revolution at 2200 rpm for 1 minute. Shear mixing was performed without using an organic solvent.

[0061] As a result, a black, fluid liquid metal powder containing 98% by weight of EGaIn was obtained. Figure 1 shows the appearance of the liquid metal powder, and Figure 2 shows that the liquid metal powder is in powder form and has fluidity.

[0062] (2-2) Preparation of powdered liquid metal using TiO2 nanoparticles as a stabilizer A powdered liquid metal was obtained by the same method as in (2-1) above, except that 97 wt% of EGaIn and 3 wt% of TiO nanoparticles were used. Although not shown, the powdered liquid metal was in powder form and had fluidity, similar to the powdered liquid metal obtained in (2-1) above.

[0063] (2-3) Preparation of powdered liquid metal using graphite as a stabilizer Powdered liquid metal was obtained by the same method as in (2-1) above, except that 96 wt% EGaIn and 4 wt% graphite, or 96.5 wt% EGaIn and 3.5 wt% graphite, was used. Although not shown, the powdered liquid metal was in powder form and had fluidity, similar to the powdered liquid metal obtained in (2-1) above.

[0064] (2-4) Production of powdered liquid metal using micron-sized stabilizers 0.50 g of the shaken EGaIn and 0.075 g of silica fine particle powder (manufactured by Nippon Shokubai, product name: SeaHostar (registered trademark) KE S-30) ground in a mortar were placed in the planetary centrifugal mixer. The mixture was then subjected to shear mixing at 2000 rpm for 1 minute and 2200 rpm for 1 minute. As a result, a powdered liquid metal was obtained.

[0065] Furthermore, 0.50 g of the shaken EGaIn and 0.125 g of silica fine particle powder (manufactured by Nippon Shokubai, trade name SeaHostar (registered trademark) KE S-30) ground in a mortar were placed in the planetary centrifugal mixer. Next, the mixture was subjected to shear mixing under the conditions of 2000 rpm for 1 minute of rotation and 2200 rpm for 1 minute of revolution. As a result, a powdered liquid metal was obtained. The average particle size of the SeaHostar (registered trademark) KE S-30 was 0.3 μm (catalog value).

[0066] (3) Microscopic characterization The powdered liquid metal obtained in (2-1) above was imaged using a field emission scanning electron microscope (FE-SEM; JSM-6700, manufactured by JEOL) at an accelerating voltage of 5.0 kV. Scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDX) was performed using a scanning electron microscope JCM-6000Plus (manufactured by JEOL). Transmission electron microscopy analysis was performed using a JEM-1400Plus (manufactured by JEOL) operating at 120 kV after a sample suspension in ethanol prepared by ultrasonic treatment for 1 minute was cast onto a carbon grid and dried in air. The sample suspension was the powdered liquid metal suspension obtained in (2-1) above. The visible and near-infrared (NIR) reflectance spectra of the powdered liquid metal obtained in (2-1), EGaIn, and SiOx nanoparticles were recorded using a portable fiber optic reflectance spectrophotometer (USB 4000-Vis-NIR, Ocean Optics Inc.). The powdered liquid metal obtained in (2-1) (containing 2 wt% SiOx nanoparticles) was dispersed in n-dodecane and observed without a cover glass using an optical microscope (Motic BA200, Shimadzu Corporation).

[0067] Figure 3 shows the liquid metal powder dispersed in n-dodecane and observed under an optical microscope. As shown in Figure 3, the liquid metal powder was composed of irregularly shaped micron-sized particles. When the liquid metal powder was pressed between two glass slides, the liquid metal flowed out of the liquid metal powder. Figure 4 shows this state. This indicates that the liquid metal forms a core in the liquid metal powder.

[0068] 5 to 7 are FE-SEM images of the liquid metal powder, which confirm that the liquid metal powder is composed of liquid metal particles with a maximum diameter of approximately 10 μm coated with SiOx nanoparticles.

[0069] Fig. 8 shows the results of measuring the particle size distribution of the powdered liquid metal. The particle size distribution was measured using an SEM. The diameters of most of the powdered liquid metal were in the range of 2 to 10 µm. These results demonstrate that the powdered liquid metal is a novel dry liquid.

[0070] It was also confirmed that the powdered liquid metal produced in (2-2) and (2-3) above was encapsulated by SiOx fine particles (not shown).

[0071] In this example, powdered liquid metal was prepared using a planetary centrifugal mixer instead of grinding using an agate mortar. Fig. 9 is a schematic diagram showing an embodiment of preparing powdered liquid metal using a planetary centrifugal mixer. As shown in the center of Fig. 9, the planetary centrifugal mixer has a mechanism in which a container containing the material rotates counterclockwise while revolving clockwise, with the rotation axis tilted at 45°.

[0072] The three-dimensional shear flow caused by the tilt of the rotation axis causes a sudden change in flow velocity between the liquid surface and the wall of the container, resulting in high shear and stirring forces. This shear force causes the liquid metal (EGaIn) to first break up into large droplets, which then undergo surface oxidation instantaneously and are subsequently broken up into smaller droplets by stirring. While the liquid metal is breaking up into these small droplets, SiOx nanoparticles acting as stabilizers are adsorbed to the interface between the liquid metal and air and bond to this interface (the surface of the liquid metal). Other SiOx nanoparticles are adsorbed to the SiOx nanoparticles that have bonded to the interface. As a result, it is believed that the surface of the liquid metal is coated with SiOx nanoparticles, stabilizing it and forming a powdered liquid metal.

[0073] SEM-EDX analysis showed that the distribution of Ga and In in the liquid metal powder obtained in (2-1) was consistent with the distribution of Si in the SiOx nanoparticles, revealing that the SiOx nanoparticles encapsulate droplets of the liquid metal (not shown).

[0074] Figure 10 (1000) shows the results of imaging with a transmission electron microscope after ultrasonic cleaning in ethanol for 1 minute to remove the excess layer of adsorbed SiOx nanoparticles in order to further evaluate the morphology of the powder liquid metal obtained in (2-1) above.

[0075] From 1001 and 1002, it can be seen that EGaIn particles coated with SiOx nanoparticles (powdered liquid metal having a liquid metal with an oxidized surface and a stabilizer) exist without agglomeration.

[0076] 1003 shows the result of a magnified observation of the surface of the powder liquid metal. From 1003, it can be seen that SiOx nanoparticles are adhered to the surface of EGaIn. The surface of EGaIn is oxidized by shaking with the shaker, and Ga2O3 is generated. This Ga2O3 is bonded to the SiOx nanoparticles by hydrogen bonds. In other words, some of the SiOx nanoparticles, which act as stabilizers, are bonded to the surface of the liquid metal whose surface has been oxidized. This is confirmed by the peak at about 3500 cm in the attenuated total reflectance Fourier transform infrared spectroscopy (FT-IR-ATR) spectrum of EGaIn subjected to the shaking. -1 and 550-600cm -1 This was suggested by the fact that oxygen-related bands were observed in the SiO2 solution; oxygen was detected by EDX (not shown).

[0077] In the liquid metal powder, based on the behavior between the EGaIn droplets and the solid SiOx nanoparticles, it is believed that the filling of the SiOx nanoparticles at the interface between EGaIn and air reduces the shape relaxation of the liquid metal powder from non-spherical to spherical and maintains the non-spherical shape. 1004 is a diagram showing the liquid metal powder taking on a non-spherical shape.

[0078] The particle indicated by the arrow 1001 is an EGaIn particle with a coating of scattered SiOx nanoparticles, which is likely generated by the breakup of EGaIn droplets and / or the rupture of the SiOx nanoparticle coating during ultrasonic cleaning.

[0079] As shown in Figure 10, the SiOx nanoparticles were nanostructured aggregates with a primary particle diameter of 10-20 nm, and were adsorbed onto the surface of EGaIn in the form of aggregates of 50-200 nm in size. As mentioned above, the surface of EGaIn was oxidized, and the SiOx nanoparticles were thought to be bonded to the surface by hydrogen bonding. Furthermore, the contact angle at the interface between the SiOx nanoparticles and the EGaIn, which were bonded to the oxidized surface of EGaIn, was estimated to be 117° from FE-SEM images.

[0080] Example 2 (Study on the photothermal properties of powdered liquid metal) The EGaIn and SiOx nanoparticles used in Example 1 and the powdered liquid metal produced in (2-1) of Example 1 were placed on a flat glass substrate and irradiated with laser light using a near-infrared laser pointer. This allowed us to examine the ability of the powdered liquid metal to convert energy from light to heat.

[0081] The near-infrared laser pointer was manufactured by Shanghai Dream Lasers Technology, and had a wavelength of 808±5 nm, a spot size of 1 mm × 5 mm, and an output of 500 mW. Four cycles of 7 seconds of irradiation followed by 60 seconds of no irradiation were performed. The distance between the laser pointer and the sample was fixed at 3 cm. The temperature change of the sample was monitored using an 890-2 thermography (manufactured by Test GmbH, Lenz-Kirch, Germany).

[0082] The powdered liquid metal used was the powdered liquid metal produced in (2-1) of Example 1 (referred to as powdered liquid metal 1). Also used was a powdered liquid metal (referred to as powdered liquid metal 2) prepared in the same manner as in (2-1) of Example 1, except that the shaken EGaIn and SiOx nanoparticles were mixed so that the EGaIn content was 98.2 wt %.

[0083] FIG. 11 (2000) shows the surface temperature profile (2001) and optical microscope images (2002 and 2003) of EGaIn and SiOx nanoparticles, and the powdered liquid metals 1 and 2.

[0084] As shown in 2001, after 7 seconds of near-infrared laser irradiation, the temperatures of powdered liquid metals 1 and 2 immediately increased, reaching 181.5 ± 1.0 °C for powdered liquid metal 1 and 219.5 ± 0.2 °C for powdered liquid metal 2. As shown in 2001, no significant decrease in maximum temperature was observed during the first three cycles. No temperature change was observed for EGaIn and SiOx nanoparticles. Furthermore, as shown in 2002 and 2003, optical microscopy imaging revealed that the powder morphology of the powdered liquid metals was maintained.

[0085] These results demonstrate that the powdered liquid metal has the effect of converting light irradiated with a near-infrared laser into heat. The light-to-heat energy conversion efficiency (η) of the powdered liquid metal 2 was calculated to be 69% using the following method. Thus, the powdered liquid metal can retain heat inside the liquid metal, resulting in a strong photothermal effect. <Calculation method for the efficiency of energy conversion from light to heat> The energy required to raise the temperature (E temp ) was calculated as follows: E temp =CWΔT=0.4Jg -1 K -1 x31x10 -3 g×(220-25)K=2.4J Here, C is the specific heat of EGaIn, W is the weight of the sample (powdered liquid metal with an EGaIn content of 98.2 wt%), and ΔT is the temperature change of the sample. Because it is difficult to measure the exact weight of powdered liquid metal irradiated with a near-infrared laser, the weight of the sample was assumed to be equal to the weight of pure EGaIn (1 mm × 1 mm × 5 mm, 31 mg). The penetration depth of the near-infrared light was set to 1 mm.

[0086] The efficiency of light-to-heat energy conversion (η) was calculated as follows: Note that the weight and specific heat of powdered liquid metal are not identical to those of pure EGaIn, and the penetration depth of near-infrared light is unknown, so the following values ​​are approximate. η=100%×E temp / E NIR=100%×2.4 / 3.5=69%.

[0087] Example 3 (Evaluation of photothermoelectric properties of powdered liquid metal) Figure 12 shows a photoelectric element made by combining powdered liquid metal and a thermoelectric element. In the figure, 10 is the photoelectric element, 11 is the powdered liquid metal, 12 is the thermoelectric element, 13 is the glass plate, 14 is the copper film, 15 is the aluminum for heat dissipation, 16 is the water in the water bath 20, and 17 is the electrode. 20 is the water bath, 30 is the light source, 40 is the cooling plate, 50 is the thermometer, and 60 is the digital ammeter.

[0088] The powdered liquid metal 11 was prepared by the same method as in Example 1 (2-1) and contained 2.0 wt % (0.6 g) of SiOx nanoparticles (Calplex (registered trademark) CS-7). The content of EGaIn was 98.0 wt %.

[0089] As shown in FIG. 12, powdered liquid metal 11 was poured onto the heating side of the thermoelectric element 12 (area 4 cm 2 A copper film 14 coated on the powder liquid metal 11 was placed on top of the powder liquid metal 11. A glass plate 13 was placed on top of the powder liquid metal 11. The copper film 14 was 0.05 mm thick and was used to ensure thermal contact between the powder liquid metal 11 and the thermoelectric element 12. An aluminum plate 15 for heat dissipation was placed on the cooling side of the thermoelectric element 12, and the aluminum plate 15 was immersed in water 16 in a water bath 20, as shown in Figure 12. The temperature of the water 16 was maintained at 20 ± 1.0 °C during light irradiation. A halogen lamp (250 W) emitting visible light and near-infrared light was used as the light source 30. The intensity of the light received by the powder liquid metal 11 was measured using a laser power meter (Sanwa Electric Instruments, LP1, not shown). The power output of the thermoelectric element 12 during light irradiation was measured using a digital ammeter 60 (Toho Giken, AM06). When irradiated with light, the photoelectric element 10 generates electric power due to the temperature difference between the heated powder liquid metal 11 side of the thermoelectric element 12 and the cooling portion side of the thermoelectric element 12.

[0090] 13 is a diagram showing the difference in output performance between a thermoelectric element 12 (LM-TEG in the figure) on which powdered liquid metal 11 is placed and a thermoelectric element 12 (TEG in the figure) on which powdered liquid metal 11 is not placed. The light intensity is 34 mWcm -2 and 94mWcm -2 The steady-state output current of the LM-TEG increased with increasing light intensity compared to that observed with the TEG, indicating that higher light intensities improved the output performance.

[0091] Figure 14 shows the power output generated by the LM-TEG in response to repeated on / off switching of the light source. Figure 14 shows that the photovoltaic device 10 has good device controllability and stability. This demonstrates that the powdered liquid metal 11 can be applied to photothermal power generation.

[0092] Example 4 (Evaluation of photothermoelectric properties of powdered liquid metals using graphite as a stabilizer) Instead of the SiOx nanoparticles (Calplex® CS-7) used in Example 1 (2-1), 0.033 g, 0.036 g, or 0.055 g of graphite ground in a mortar was used. Powdered liquid metals a to c were obtained by the same method as in Example 1 (2-1), except for this. The graphite contents of powdered liquid metals a to c were 6.0 wt%, 6.5 wt%, and 10 wt%, respectively, and the EGaIn contents were 94.0 wt%, 93.5 wt%, and 90 wt%, respectively. Powdered liquid metal d, which contained 2.5 wt% SiOx nanoparticles (Calplex® CS-7) (the remainder was EGaIn), and powdered liquid metal e, which contained 20 wt% molybdenum sulfide (the remainder was EGaIn), were also prepared by the same method as in Example 1 (2-1).

[0093] Next, except for using powdered liquid metals a to e, the photothermoelectric properties of the powdered liquid metals were evaluated in the same manner as in Example 3. As a control, a thermoelectric element without powdered liquid metal placed thereon was used, as in Example 3.

[0094] Figure 15 shows the current values ​​generated by thermoelectric devices equipped with powdered liquid metal prepared using various stabilizers. The "graphite" in the figure represents the results when only graphite was used instead of powdered liquid metal. The horizontal axis of the figure represents the time of light irradiation. As shown in Figure 15, the photoelectric devices equipped with powdered liquid metals a to e have significantly higher efficiency in converting heat into current compared to the control.

[0095] FIG. 16 shows data comparing the thermal conductivity of graphite with that of powdered liquid metals (powdered liquid metals a to c) using graphite as a stabilizer, using photoelectric elements with powdered liquid metals a to c placed on them, respectively. As in Example 3, a thermoelectric element without powdered liquid metal was used as a control. The horizontal axis of the figure represents the time of light irradiation. The surface temperatures shown in FIG. 16 are those of the photoelectric elements measured by thermography (infrared camera).

[0096] 16, the photoelectric elements including powdered liquid metals a to c had better thermal conductivity than the photoelectric element including graphite alone. From this result, it is believed that the powdered liquid metal of the present invention has a higher heat dissipation effect than graphite alone, and therefore has utility as a heat dissipation material in devices such as smartphones and personal computers.

[0097] FIG. 17 shows the current generated by a photoelectric element loaded with powdered liquid metal prepared using various stabilizers, responding to repeated on / off switching of the light source. As a control, a thermoelectric element without powdered liquid metal was used, as in Example 3. The horizontal axis of the figure represents the time of light irradiation. From FIG. 17, it can be seen that the photoelectric element has good device controllability by light. [Industrial Applicability]

[0098] The liquid metal powder of the present invention has a high liquid metal content and is easy to handle in powder form, and therefore can be applied to fields that require full utilization of the properties of liquid metal, such as soft electronics, soft robotics, energy storage and conversion, catalyst production, biomedicine, and photovoltaic power generation. [Explanation of symbols]

[0099] 10 Photoelectric element 11...Powdered liquid metal 12 Thermoelectric element 13 Glass Plate 14 Copper film 15 Aluminum for heat dissipation 16 Water in the water bath 17...electrode 20 Water Bath 30...Light source 40 Cooling plate 50...Thermometer 60 ···Digital ammeter

Claims

1. A powdered liquid metal having a liquid metal content of more than 50% by weight.

2. Contains a stabilizer, The powdered liquid metal according to claim 1 , wherein the liquid metal has an oxidized surface.

3. a portion of the stabilizing agent is associated with the surface; 3. The powdered liquid metal of claim 2, wherein the contact angle of the stabilizer on the surface is greater than 90 degrees.

4. 2. The powdered liquid metal according to claim 1, wherein the liquid metal comprises gallium and one or more metals selected from the group consisting of indium, bismuth, and tin.

5. 5. The powdered liquid metal according to claim 2, wherein the stabilizer is one or more substances selected from the group consisting of oxides of silicon, oxides of titanium, graphite, molybdenum sulfide, and carboxylic acids that are solid at room temperature.

6. A step A of oxidizing the surface of the liquid metal; a step B of applying a shear force to the liquid metal having an oxidized surface obtained in the step A; and step C of combining the sheared liquid metal obtained in step B with a stabilizer.

7. 7. The method for producing powdered liquid metal according to claim 6, wherein the steps B and C proceed simultaneously, and the stabilizer bonds to the sheared liquid metal faster than the liquid metal particles sheared by the step B bond together.

8. 8. The method for producing powdered liquid metal according to claim 6 or 7, wherein steps B and C are carried out by rotating and revolving the liquid metal having an oxidized surface and the stabilizer.

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