Manufacturing method

Abstract

To improve the treatment speed of the separation of a guest in the production of a guest-free silicon clathrate.SOLUTION: A method for producing a guest-free silicon clathrate includes a first step of synthesizing a silicon clathrate compound by performing a heat treatment on Si as a host material and a guest, a second step of separating the guest from the silicon clathrate by heating the silicon clathrate contained in a container in a state where the inside of the container containing the silicon clathrate is evacuated, and a third step of supplying an inert gas to the inside of the container and then sucking a gas inside the container.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to manufacturing methods. [Background technology]

[0002] Patent Document 1 describes a method for producing silicon clathrate. In the method for producing silicon clathrate described in Patent Document 1, a silicon clathrate compound is synthesized by heat treating a mixture containing Si, which is a host material, and Na, which is a guest material. Furthermore, to remove the guest Na, the Na is volatilized by irradiating the container containing the silicon clathrate compound with electromagnetic waves while suctioning the gas inside the container. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-186067 Summary of the Invention [Problem to be solved by the invention]

[0004] The evaporated Na exists as a gas inside the container, but as the Na volatilization progresses, the concentration of evaporated Na inside the container increases. This causes a problem of a slowdown in the rate of Na volatilization, i.e., the rate at which Na is released. Therefore, there was a need for a technology to improve the processing speed of guest release. [Means for solving the problem]

[0005] The present disclosure can be realized in the following forms.

[0006] According to one embodiment of the present disclosure, there is provided a method for producing a guest-free silicon clathrate, which includes a first step of synthesizing a silicon clathrate compound by heat treating a host material, Si, and a guest, a second step of heating the silicon clathrate compound contained in a container while the inside of the container is evacuated to remove the guest from the silicon clathrate compound, and a third step of supplying an inert gas into the container and then aspirating the gas inside the container containing the vaporized guest. According to the above embodiment, after the second step, an inert gas is supplied into the container, and then the vaporized guest in the container is discharged from the container together with the inert gas, thereby reducing the concentration of the vaporized guest in the container. This makes it possible to avoid a decrease in the rate of guest volatilization due to a high concentration of vaporized guest in the container, and therefore makes it possible to shorten the time required for the guest to desorb compared to conventional methods.

[0007] In the manufacturing method of the above aspect, the second step and the third step may be repeatedly performed. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is an explanatory diagram showing an example of a guest-free silicon clathrate 1. [Figure 2] FIG. 1 is a partial cross-sectional view of a manufacturing apparatus for producing guest-free silicon clathrate. [Figure 3] FIG. [Figure 4] 1 is a flowchart showing a method for producing guest-free silicon. [Figure 5] FIG. 10 is a cross-sectional view of a manufacturing apparatus according to another embodiment. [Figure 6] FIG. 2 is an explanatory diagram showing the state inside the container. DETAILED DESCRIPTION OF THE INVENTION

[0009] A. Implementation: A1. Guest-free silicon clathrate FIG. 1 is an explanatory diagram showing an example of a guest-free silicon clathrate 1. In FIG. 1, voids 2 indicate sites where guests have been released. Voids 3 represent voids formed independently of the cage-like framework structure. Voids 3 can absorb volume changes in the guest-free silicon clathrate and can also suppress defects such as cracking. Details of voids 3 will be described later.

[0010] Fig. 2 is a partial cross-sectional view of a production apparatus 10 for producing guest-free silicon clathrate. Fig. 3 is a cross-sectional view of the production apparatus 10 taken along the III-III cross-sectional line in Fig. 2. The production apparatus 10 includes a container 12, at least one electromagnetic wave irradiator 14, at least one reflector 16, a rotating shaft 18, a suction tube 20, and a suction device 24. In the production apparatus 10, the silicon clathrate workpiece is subjected to a heat treatment to remove the guest.

[0011] The container 12 contains a silicon clathrate workpiece from which a guest is to be desorbed. The container 12 is formed in a cylindrical shape and has one bottom surface and an opening opposite the bottom surface. The container 12 is capable of maintaining its shape when the inside thereof is evacuated. For example, the container 12 is formed from quartz glass.

[0012] A flange 12a is provided at the opening of the container 12. The flange 12a is connected to a rotating shaft 18, which will be described later. The container 12 is rotated around the X-axis in conjunction with the rotation of the rotating shaft 18. This causes the silicon clathrate workpiece inside the container 12 to be stirred. As shown in FIG. 3, the container 12 is equipped with a stirring plate 12b. The stirring plate 12b is composed of a plate-shaped member extending axially from the inner side surface of the container 12. When the container 12 is rotated, the stirring plate 12b efficiently stirs the silicon clathrate compound. By heating the silicon clathrate compound while stirring it, the silicon clathrate workpiece can be heated evenly. This reduces uneven heating.

[0013] As shown in Fig. 2, the electromagnetic wave irradiator 14 irradiates the inside of the container 12 with electromagnetic waves. The electromagnetic wave irradiator 14 is, for example, a halogen lamp heater. The silicon clathrate compound stored inside the container 12 is heated by the irradiation of the electromagnetic waves. For example, near-infrared rays, which are electromagnetic waves with a wavelength of about 0.7 µm to 2.5 µm, are used to heat the silicon clathrate compound. As shown in Fig. 3, in this embodiment, multiple electromagnetic wave irradiators 14 are arranged along the outer periphery of the container 12 so as to cover half of the lower side (-Z side) of the container 12.

[0014] The reflector 16 reflects the electromagnetic waves emitted from the electromagnetic wave irradiator 14 that have passed through the container 12. For example, a mirror or a metal plate with a mirror finish can be used as the reflector 16. In the example shown, a plurality of reflectors 16 are arranged along the outer periphery of the container 12 so as to cover half of the upper side (+Z side) of the container 12. In this way, the electromagnetic wave irradiators 14 and reflectors 16 are arranged around the entire outer periphery of the side surface of the container 12.

[0015] As shown in FIG. 2, the rotating shaft 18 is connected to the container 12. The container 12 is rotated by the rotation of the rotating shaft 18 about the axis AL. The rotating shaft 18 is formed in a cylindrical shape. A flange 18a is provided at the end of the rotating shaft 18 on the +X side. The flange 18a is connected to a flange 12a of the container 12. The rotating shaft 18 and the container 12 are connected so as to maintain the airtightness of the container 12. For example, the flange 12a and the flange 18a are connected via a sealing member.

[0016] The suction tube 20 is a tube that passes gas from the container 12 to the aspirator 24 (described later) when the aspirator 24 aspirates the gas inside the container 12. The suction tube 20 is disposed inside the rotating shaft 18. One end of the suction tube 20 is closed by a bottom 20a. In the illustrated example, the bottom 20a is formed to have a shape that substantially matches the opening of the +X side of the rotating shaft 18. A hole 20b is formed in the bottom 20a. The hole 20b can be closed by a valve 19. An opening / closing rod (not shown) for opening and closing the valve 19 is connected to the valve 19. The opening / closing rod is disposed inside the suction tube 20 along the axis AL. A seal member is disposed in an appropriate position on the valve 19, which maintains airtightness to prevent gas from leaking from the container 12 when the valve 19 is closed. When the valve 19 is open, the gas inside the container 12 is introduced into the suction tube 20 through the hole 20b. Suction tube 20 is arranged so as not to rotate in conjunction with the rotation of rotating shaft 18. Furthermore, at the connection between container 12 and suction tube 20, airtightness is maintained by, for example, a sealing member arranged at an appropriate position on container 12 or suction tube 20 to prevent gas from leaking from the gap between the opening on the +X side of rotating shaft 18 and bottom 20a of suction tube 20.

[0017] A cooling member 21 is disposed inside the suction pipe 20. The cooling member 21 has a cylindrical shape. The cooling member 21 is disposed along the inner circumference of the suction pipe 20. A spiral flow path 21a is formed in the cooling member 21. Cooling water sent from a cooling water pump (not shown) flows through the flow path 21a.

[0018] The aspirator 24 aspirates gas from inside the container 12 through the suction tube 20. The aspirator 24 is connected to the −X side end of the suction tube 20. The aspirator 24 is, for example, a vacuum pump.

[0019] FIG. 4 is a flowchart showing a method for producing a guest-free silicon clathrate. In step S10, a silicon clathrate compound is synthesized. Step S10 is also referred to as the "first step." Here, a silicon clathrate compound is produced using Si as the host material and Na as the guest material. In this embodiment, porous Si is used as the host.

[0020] Porous Si is porous Si with a large amount of air inside the particles. Known methods can be used to produce porous Si. For example, an alloy of Li and Si (Li-Si alloy) is first made, and then Li is removed from the Li-Si alloy. Li-Si alloys are produced using known methods. For example, Li can be removed from Li-Si alloys by reacting the Li-Si alloy with a Li extractant such as ethanol or methanol.

[0021] Silicon clathrate compounds are prepared as follows. For example, Si and Na are mixed in a 1:1 ratio and baked at a high temperature (e.g., 850°C) to obtain Na1Si1, which is then baked further at a low temperature (e.g., 450°C) to obtain Na20Si136. The synthesized silicon clathrate compound has Na located at least partially inside the cage-like framework formed by Si bonds.

[0022] In step S20, the silicon clathrate compound is heated to cause Na, which is a guest, to be separated from the silicon clathrate compound. Step S20 is also referred to as the "second step." The silicon clathrate compound produced in step S20 is contained in a container 12. As will be described in detail later, in step S20, an inert gas is filled, a vacuum is drawn, and the silicon clathrate compound is fired.

[0023] FIG. 6 is an explanatory diagram showing the state inside the container 12. First, the container 12 is filled with an inert gas. The silicon clathrate compound is preferably heated in an atmosphere with little water, oxygen, etc., which are highly reactive with Na. In this embodiment, the silicon clathrate compound is heated in an inert gas atmosphere. Filling with an inert gas is also called purging. The inert gas is, for example, Ar. State A schematically shows the state of the container 12 filled with an inert gas.

[0024] Thereafter, the aspirator 24 is operated to draw a vacuum. When the aspirator 24 is operated, the gas inside the container 12 is sucked in. As a result, the gas inside the container 12 is discharged through the aspirator pipe 20. As a result, the pressure inside the container 12 is reduced, resulting in a vacuum state (state B). A vacuum is a space filled with gas at a pressure lower than normal atmospheric pressure. When the host is Si and the guest is Na, the pressure inside the container 12 is reduced to 10 ―3 ~10 ―2 The guest Na needs to be heated to 900°C under atmospheric pressure to vaporize it. On the other hand, the guest Na only needs to be heated to 430°C or higher under vacuum to vaporize it.

[0025] Thereafter, the silicon clathrate compound is fired. Specifically, the electromagnetic wave applicator 14 arranged along the outer periphery of the container 12 is operated to irradiate electromagnetic waves onto the silicon clathrate compound contained inside the container 12. Also, the rotating shaft 18 is operated to rotate the container 12 around the axis AL.

[0026] At least a portion of the electromagnetic waves emitted by the electromagnetic wave irradiator 14 that are transmitted through the container 12 are incident on the reflector 16. The reflector 16 reflects the electromagnetic waves and returns them to the inside of the container 12, thereby irradiating the silicon clathrate compound contained therein. In this embodiment, by using the reflector 16, electromagnetic waves can be efficiently irradiated onto the silicon clathrate compound even when the inside of the container 12 is depressurized and there is little heat-conducting medium. The guest is desorbed from the heated silicon clathrate compound by the irradiation of the electromagnetic waves. The desorbed guest is released into the container 12 as a gas. Furthermore, the contents of the container 12 are stirred by rotating the container 12. As described above, the container 12 is equipped with the stirring plate 12b. By rotating the container 12, the silicon clathrate product is heated while being stirred. Since the silicon clathrate product is uniformly heated, the desorption of the guest proceeds more smoothly. As a result, the gas inside the container 12 contains a large amount of guest. State C schematically shows the state of the container 12 after the silicon clathrate compound has been released.

[0027] As shown in Fig. 4, in step S30, a process for reducing the partial pressure of the guest is performed. Here, a process for reducing the ratio of Na, which is the guest, in the gas inside the container 12 is performed. As will be described in detail later, in step S30, filling with an inert gas and evacuation are performed. Note that even while step S30 is being performed, the operation of irradiating electromagnetic waves by the electromagnetic wave irradiator 14 and the operation of rotating the rotation shaft 18 are continued. Step S30, for discharging the vaporized guest from inside the container, is also referred to as the "third step."

[0028] First, the container 12 is filled with an inert gas such as Ar. In this embodiment, before filling the container 12 with the inert gas, the inside of the container 12 is heated to 1000 K. ―3 ~10 ―2 The pressure inside the container 12 is set to about 100 Pa. In addition, by filling the container 12 with an inert gas, the pressure inside the container 12 is set to about the same as atmospheric pressure. State D in Figure 6 shows a schematic diagram of the container 12 filled with argon gas.

[0029] Thereafter, the aspirator 24 is operated to draw a vacuum. As a result, the gas inside the container 12 is sucked out through the suction pipe 20. By drawing a vacuum, the pressure inside the container 12 is reduced to 10 ―3 ~10 ―2 The pressure is set to about 10 Pa. State E in FIG. 6 is a schematic representation of the state of the container 12 after evacuation. As described above, the guest released from the silicon clathrate compound is vaporized, and the guest exists as a gas inside the container 12. By suctioning the gas inside the container 12, the concentration of the guest in the gas inside the container 12 can be reduced. As a result, it is possible to avoid a decrease in the rate at which the guest is released from the silicon clathrate compound. Furthermore, by discharging the vaporized guest together with the inert gas, it is possible to suppress exposure of the guest to the atmosphere. The above is a series of processes involved in the production of guest-free silicon.

[0030] As described above, in the configuration according to this embodiment, after the guest is desorbed, an inert gas is supplied into the container, and then the vaporized guest in the container is discharged from the container together with the inert gas. This makes it possible to reduce the concentration of the vaporized guest in the container. Since it is possible to avoid a decrease in the rate of guest volatilization due to a high concentration of vaporized guest in the container, it is possible to shorten the time required for guest desorption compared to conventional methods. Therefore, it is possible to increase the productivity of producing guest-free silicon clathrate.

[0031] B. Other Embodiments: (B1) In the above embodiment, the processes of steps S20 and S30 may be repeated two or more times. In this case, after step S40, it is determined whether the processes need to be repeated, and if they need to be repeated, the processes from step S20 onwards are executed again.

[0032] (B2) In the above embodiment, porous Si is used as the host when synthesizing the silicon clathrate compound in step S10. However, Si other than porous Si may be used as the host. In the embodiment, Na is used as the guest, but Mg may be used as the guest.

[0033] (B3) FIG. 5 is a partial cross-sectional view of the production apparatus 10a. The production apparatus 10a differs from the production apparatus 10 according to the above-described embodiment in that it includes a guest adsorber 22. The guest adsorber 22 further includes the guest adsorber 22. The guest adsorber 22 adsorbs at least a portion of the guest released from the silicon clathrate compound inside the vessel 12. The guest adsorber 22 is a cylindrical metal mesh case containing granular iron oxide (FeO). The guest adsorber 22 is disposed inside the vessel 12 along the axis AL. The -X side end of the guest adsorber 22 is attached to the bottom 20a of the suction pipe 20. Note that the valve 19 is not shown in FIG. 5.

[0034] Depending on the properties of the guest, the desorbed guest may not cause any malfunction of the apparatus, and in such cases, the guest adsorber 22 is not necessary.

[0035] The present disclosure is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate. [Explanation of symbols]

[0036] 1...guest-free silicon clathrate, 2, 3...void, 10...production apparatus, 12...container, 12a...flange, 12b...stirring plate, 14...electromagnetic wave irradiator, 16...reflector, 18...rotating shaft, 18a...flange, 20...suction tube, 20a...bottom, 20b...hole, 21...cooling member, 21a...flow path, 22...guest adsorber, 22a...adsorbent, 22b...receiving vessel, 24...suction device, AL...axis

Claims

1. A method for producing a guest-free silicon clathrate, comprising: a first step of synthesizing a silicon clathrate compound by heat treating Si, which is a host material, and a guest; a second step of heating the silicon clathrate compound contained in the container while the inside of the container containing the silicon clathrate compound is evacuated to a vacuum, thereby separating the guest from the silicon clathrate compound; a third step of supplying an inert gas into the container and then aspirating the gas inside the container including the vaporized guest; A manufacturing method comprising:

2. The method of claim 1, The second step and the third step are repeatedly performed. Manufacturing method.

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