Agitator, molten salt electrolysis device, and method for manufacturing metal foil

Abstract

To provide an agitator, a molten salt electrolysis device, and a method for producing a metal foil, which can deposit a metal well on electrodes immersed in a molten salt bath.SOLUTION: An agitator 1 of the present invention is used for agitating a molten salt bath Bm in which electrodes 54 are immersed in an electrolytic cell 52, and comprises an impeller 2 having multiple blade parts 2a spaced in a rotational direction and immersed in the molten salt bath Bm, a rotary shaft part 3 for transmitting a rotational driving force from an external driving source of the molten salt bath Bm to the impeller 2, a shaft sleeve 4 surrounding the rotary shaft part 3, an impeller case 5 housing the impeller 2 inside, a suction cylinder part 6 connected to the impeller case 5 from the outside in the axial direction of the rotary shaft part 3 and guiding a molten salt of the molten salt bath Bm into the impeller case 5, and a discharge tube part 7 connected to the impeller case 5 on the outer peripheral side of the impeller 2 and discharging the molten salt from the inside of the impeller case 5. The suction cylinder part 6 has a suction opening part 6a that opens toward a space 54c between the electrodes 54 in the electrolytic cell 52.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a stirrer used for stirring a molten salt bath in which electrodes are immersed in an electrolytic cell, a molten salt electrolysis apparatus, and a method for manufacturing metal foil. [Background technology]

[0002] Metals belonging to Group 4 of the periodic table include titanium, zirconium, hafnium, etc. Among them, titanium is used in products in various fields due to its excellent properties such as high strength and corrosion resistance.

[0003] To produce such metals, molten salt electrolysis is sometimes used because it can produce foils at a relatively low cost. In molten salt electrolysis, a voltage is applied to electrodes immersed in a molten salt bath in an electrolytic cell, and metal ions in the molten salt bath are precipitated in a foil shape on the electrodes. The metal can be produced in foil form by peeling it off from the electrodes.

[0004] In relation to molten salt electrolysis, Patent Document 1 proposes "an electrolytic cell in which a low-temperature section and a high-temperature section are provided, and the electrolytic bath forms a closed loop in each of the above sections to generate a reflux, and the electrolytic bath is further circulated between the low-temperature section and the high-temperature section, so that electrolysis can be continued continuously." Patent Document 1 states that "the stirring means is a rotating blade mechanism having two or more blades, such as a propeller screw or a helical screw." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 51-38242 Summary of the Invention [Problem to be solved by the invention]

[0006] However, it has been newly discovered that the metal ion concentration may be non-uniform in the molten salt bath in the electrolytic cell. If molten salt electrolysis is performed in a state where the metal ion concentration in the molten salt bath is non-uniform, there is a concern that the smoothness of the metal deposited on the surface of the electrode in the molten salt bath may be impaired, or that it may become difficult to peel off the metal electrodeposited on the electrode from the electrode. Patent Document 1 appears to be intended to stir the entire molten salt bath, and does not pay any attention to the problem of the deposition form of the metal on the electrode as described above.

[0007] An object of the present invention is to provide a stirrer, a molten salt electrolysis apparatus, and a method for producing a metal foil, which are capable of satisfactorily depositing a metal on an electrode immersed in a molten salt bath. [Means for solving the problem]

[0008] As a result of intensive research, the inventor came up with the idea that making the metal ion concentration in the interelectrode space of electrodes immersed in a molten salt bath uniform is effective for good deposition of metal on the electrodes. Based on this idea, the inventor came up with the idea of ​​providing a suction opening that opens into the interelectrode space on the suction tube part of the agitator used to stir the molten salt bath, which guides the molten salt into the impeller case. This is thought to create an appropriate bath flow when the molten salt in the interelectrode space is sucked in, which makes the metal ion concentration in the interelectrode space uniform, allowing good deposition of metal on the electrodes.

[0009] The agitator of this invention is used for stirring a molten salt bath in which electrodes are immersed in an electrolytic cell, and comprises an impeller having a plurality of blades spaced apart in the rotational direction and immersed in the molten salt bath, a rotating shaft portion that transmits a rotational driving force from a driving source external to the molten salt bath to the impeller, a shaft sleeve that surrounds the rotating shaft portion, an impeller case in which the impeller is housed, a suction tube portion that is connected to the impeller case from the outside in the axial direction of the rotating shaft portion and guides the molten salt of the molten salt bath into the impeller case, and a discharge tube portion that is connected to the impeller case on the outer periphery of the impeller and discharges the molten salt from within the impeller case, and the suction tube portion has a suction opening that opens toward the inter-electrode space of the electrodes in the electrolytic cell.

[0010] In the above-mentioned agitator, it is preferable that the discharge tube portion has a discharge opening, the suction opening is located on one end side of the electrode, and the discharge opening is located on the other end side opposite the one end of the electrode across the inter-electrode space.

[0011] In this case, it is preferable that the discharge opening opens toward the inter-electrode space on the other end side of the electrode.

[0012] In addition, when the electrode includes a basket-shaped container, it is preferable that the discharge opening opens toward a side wall of the basket-shaped container on the other end side of the electrode.

[0013] In the above-mentioned agitator, it is preferable that the suction tube portion has a suction main body portion connecting the suction opening and the impeller case, and at least a portion of the suction opening has an inner diameter larger than the inner diameter of the suction main body portion.

[0014] It is also preferable that at least a portion of the suction opening has an inner diameter that gradually increases toward the opening end face on the inter-electrode space side.

[0015] The above-mentioned agitator may be configured such that a bearing portion for rotatably holding the rotating shaft portion is provided at the sleeve end of the shaft sleeve that is connected to the impeller case, and at least one through hole is formed around the bearing portion, extending axially inward from the bearing portion.

[0016] The molten salt electrolysis apparatus of the present invention comprises an electrolytic cell in which molten salt is stored to form a molten salt bath, electrodes arranged in the electrolytic cell so as to be immersed in the molten salt bath, and any one of the stirrers described above.

[0017] In the above-mentioned molten salt electrolysis apparatus, the electrodes may include an anode and a drum-shaped cathode that is positioned opposite the anode and is rotatable about a rotation axis.

[0018] The method for producing a metal foil of the present invention comprises depositing a metal on an electrode using any one of the above-mentioned molten salt electrolysis apparatuses. Effect of the Invention

[0019] According to the stirrer, molten salt electrolysis apparatus, and method for producing metal foil of the present invention, metal can be satisfactorily deposited on an electrode immersed in a molten salt bath. [Brief description of the drawings]

[0020] [Figure 1] 1 is a cross-sectional view showing a stirrer according to an embodiment of the present invention together with a molten salt electrolysis apparatus. [Diagram 2] 2 is a cross-sectional view showing the agitator of FIG. 1 along the axial direction of a rotating shaft part. [Diagram 3] FIG. 11 is a cross-sectional view showing a stirrer according to another embodiment together with an electrode. [Figure 4] FIG. 11 is a cross-sectional view showing a stirrer according to still another embodiment together with another example of the electrode. [Diagram 5] FIG. 11 is a perspective view showing a schematic diagram of still another example of an electrode. [Figure 6]6(a) is a bottom view showing an impeller provided in the mixer of FIG. 1, and FIG. 6(b) is a cross-sectional view taken along line VI-VI in the bottom view (FIG. 6(a)). [Figure 7] 7(a) is a cross-sectional view along the axial direction showing the sleeve end of the shaft sleeve provided in the agitator of FIG. 1, and FIG. 7(b) is a cross-sectional view along line VII-VII in the cross-sectional view (FIG. 7(a)). [Figure 8] 8(a) is a cross-sectional view along the axial direction showing an impeller case provided in the mixer of FIG. 1, and FIG. 8(b) is a cross-sectional view along line VIII-VIII in the cross-sectional view (FIG. 8(a)). [Figure 9] FIG. 1 is a cross-sectional view showing a peel test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, some parts are shown in outline form to facilitate understanding of the embodiments included in the present invention, and the sizes of the illustrated members and their relative positions may not be accurate.

[0022] The stirrer 1 shown as an example in Fig. 1 is used for stirring a molten salt bath Bm in a molten salt electrolysis apparatus 51 as shown in the figure. An electrode 54 including an anode 54a and a cathode 54b connected to a power source is arranged so as to be immersed in the molten salt bath Bm. The electrode 54 may be partially immersed. In other words, the electrode 54 may be arranged so as to allow metal deposition.

[0023] More specifically, the molten salt electrolysis apparatus 51 includes a container-shaped electrolytic cell 52 for storing a molten salt bath Bm, a heater 53 arranged around the electrolytic cell 52, and electrodes 54 including an anode 54a and a cathode 54b that are immersed in the molten salt bath Bm in the electrolytic cell 52. Although not shown, the molten salt electrolysis apparatus 51 may further include a lid that can be arranged to cover an upper opening of the electrolytic cell 52. In addition, an inlet and an exhaust port for an inert gas such as argon gas may be provided above the bath surface of the molten salt bath Bm.

[0024] In the molten salt electrolysis using the molten salt electrolysis device 51, the electrolysis conditions are appropriately controlled to electrolytically deposit at least one metal selected from Group IV elements (titanium, zirconium, hafnium) in the form of foil on the cathode 54b. Specifically, the temperature of the molten salt bath Bm is maintained at, for example, 450° C. or higher, and a voltage is applied between the electrodes 54 immersed in the molten salt bath Bm to perform electrolysis. As a result, a metal containing at least one selected from Group IV elements is deposited on the cathode 54b. In the molten salt bath Bm containing titanium ions, a metal containing titanium, such as titanium or a titanium alloy, is deposited on the surface of the cathode 54b. As a result, a metal foil containing at least one selected from Group IV elements can be produced by electrolysis using the electrodes 54 in the molten salt bath Bm. The temperature of the molten salt bath Bm may be appropriately set with reference to the melting points and eutectic points of the components contained in the molten salt bath.

[0025] The molten salt bath Bm may contain an alkali metal halide and / or an alkaline earth metal halide, or an aluminum halide. In particular, the molten salt bath Bm preferably contains at least one selected from the group consisting of magnesium chloride (MgCl2), sodium chloride (NaCl), calcium chloride (CaCl2), potassium chloride (KCl), magnesium fluoride (MgF2), and calcium fluoride (CaF2).

[0026] During molten salt electrolysis, it is desirable to stir the molten salt bath Bm continuously or intermittently at any time. However, it is difficult to use a general stirrer for the molten salt bath Bm. The reasons are as follows. The molten salt bath Bm is maintained at a relatively high temperature, but the viscosity becomes high at temperatures close to the melting point or eutectic point of the molten salt. This can cause a large resistance force from the molten salt to act on the blades of the stirrer. In addition, if the molten salt bath Bm is formed using chlorides or fluorides, the molten salt can be highly corrosive. Furthermore, the molten salt in the molten salt bath Bm has high wettability at high temperatures, so the molten salt penetrates various parts of the stirrer, and when the temperature drops, it becomes solid and its volume changes.

[0027] In order to effectively stir such a molten salt bath Bm, the stirrer 1 of this embodiment, as shown in Figures 1, 2, and 6 to 8, is equipped with an impeller 2 having a plurality of blade portions 2a spaced apart in the rotational direction, a rotating shaft portion 3 that transmits a rotational driving force to the impeller 2 from a driving source (not shown) outside the molten salt bath Bm, a shaft sleeve 4 that surrounds the rotating shaft portion 3, an impeller case 5 in which the impeller 2 is housed, a suction tube portion 6 that is connected to the impeller case 5 from the axial outside of the rotating shaft portion 3 (the lower side in Figure 1) and guides the molten salt of the molten salt bath Bm into the impeller case 5, and a discharge tube portion 7 that is connected to the impeller case 5 on the outer periphery of the impeller 2 and discharges the molten salt from within the impeller case 5. Here, the outer side in the axial direction of the rotating shaft portion 3 means the side away from the axial center of the rotating shaft portion 3, and the inner side in the axial direction of the rotating shaft portion 3 means the side closer to the axial center of the rotating shaft portion 3. The suction tube portion 6 is connected to the impeller case 5 from the side away from the axial center of the rotating shaft portion 3 (the side opposite to the shaft sleeve 4) in the axial direction.

[0028] The agitator 1 is disposed so that at least the impeller 2 is immersed in the molten salt bath Bm. As shown in FIG. 1, the shaft sleeve 4 may be disposed so that a part of the shaft sleeve 4 is immersed in the molten salt bath Bm. The impeller 2 is rotated by the rotating shaft 3 rotated by a driving source such as a motor in the shaft sleeve 4, so that the molten salt in the molten salt bath Bm is sucked into the suction tube 6 and flows into the impeller case 5 connected to the suction tube 6. The molten salt that flows into the impeller case 5 passes through the discharge tube 7 connected to the impeller case 5 and is discharged from there into the molten salt bath Bm. The inflow of the molten salt into the agitator 1 and the outflow of the molten salt from the agitator 1 are repeated in this manner, and the molten salt bath Bm is stirred.

[0029] Here, the molten salt bath Bm in the electrolytic cell 52 may have a non-uniform metal ion concentration. For example, in the molten salt bath Bm containing titanium ions, Ti 2+ and Ti 3+ It is presumed that a disproportionation reaction that produces Ti is constantly occurring, and that this reaction is what produces Ti. This Ti in the form of fine powder or the like settles due to its own weight, which can lead to a non-uniform titanium ion concentration in the molten salt bath Bm. If the metal ion concentration in the molten salt bath Bm is non-uniform, in the production of metal foil by molten salt electrolysis, metal with irregularities may be deposited on the surface of the cathode 54b, or the metal deposited on the cathode 54b may be difficult to physically peel off, and this may result in the metal not being deposited in a good shape on the cathode 54b.

[0030] In response to this, the inventors have come to the discovery that the metal ion concentration in the molten salt bath Bm, particularly in the electrodes 54, more specifically in the interelectrode space 54c between the opposing anode 54a and cathode 54b, has a significant effect on the deposition of metal on the cathode 54b. Based on this discovery, the inventors considered that if the molten salt present in the interelectrode space 54c is sucked in by the stirrer 1, an appropriate bath flow will occur, the metal ion concentration there will be uniform, and the metal will be able to be favorably deposited on the cathode 54b.

[0031] Specifically, in the stirrer 1 of this embodiment, the suction tube portion 6 is provided with a suction opening 6a that opens toward the interelectrode space 54c in the electrolytic cell 52. By applying a voltage between the electrodes 54, metal ions are continuously supplied from the anode 54a to the molten salt bath Bm, and the metal ions are continuously consumed and metal is continuously precipitated at the cathode 54b. Here, when the suction opening 6a is provided as described above, the molten salt present in the interelectrode space 54c is sucked into the impeller case 5 through the suction opening 6a via the suction tube portion 6, and such a flow of molten salt occurs in the molten salt bath Bm. As a result, it is believed that the metal ion concentration in the interelectrode space 54c can be maintained uniform.

[0032] Furthermore, when molten salt electrolysis is continued for a certain period of time, sludge may be generated in the molten salt bath Bm and accumulate on the bottom side of the electrolytic cell 52. In molten salt electrolysis, unlike electrolysis using an aqueous solution, it is difficult to stop electrodeposition and remove the sludge, so the amount of sludge that accumulates on the bottom side of the electrolytic cell 52 tends to increase. If such sludge gets mixed into the metal deposited on the cathode 54b, the purity of the metal to be produced by molten salt electrolysis will decrease.

[0033] On the other hand, if the suction opening 6a is provided in the suction cylinder 6 of the agitator 1 so as to open toward the interelectrode space 54c as described above, the suction opening 6a can be easily positioned not facing the bottom side of the electrolytic cell 52 or in a shallow location away from the bottom, so that the suction of sludge deposited on the bottom side is suppressed. This can increase the purity of the metal deposited on the cathode 54b. It can also suppress clogging inside the agitator 1 due to the suction of sludge.

[0034] It is preferable that the part of the agitator 1 that is immersed in the molten salt bath Bm and the electrode 54 are both located near the bath surface away from the bottom of the electrolytic cell 52. This allows the driving force to be transmitted from the driving source to the impeller 2 of the agitator 1 via the relatively short rotating shaft portion 3. It is also preferable that the conductive wire of the electrode 54 is positioned so as not to be immersed in the molten salt bath Bm as much as possible.

[0035] With regard to the orientation of the suction opening 6a, "opening toward the interelectrode space 54c" means that the suction opening 6a faces the interelectrode space 54c between the anode 54a and the cathode 54b, and that the opening end surface 6b of the suction opening 6a is inclined or perpendicular to the direction (up-down direction in FIG. 1) perpendicular to the direction in which the anode 54a and the cathode 54b face each other (left-right direction in FIG. 1) (i.e., not parallel to the direction perpendicular to the direction in which the anode 54a and the cathode 54b face each other).

[0036] In this embodiment, the suction tube portion 6 has the suction opening 6a and an suction main body portion 6c that is bent or curved at multiple points, for example, two points, from the suction opening 6a to the impeller case 5 and connects the suction opening 6a to the impeller case 5. In this case, it is preferable that at least a part of the suction opening 6a, particularly the part in the vicinity of the opening end surface 6b, has a larger inner diameter than the suction main body portion 6c. This allows most of the molten salt in the interelectrode space 54c to be sucked by the suction opening 6a, making the metal ion concentration more uniform.

[0037] In addition, it is preferable that at least a part of the suction opening 6a has an inner diameter that gradually increases toward the opening end surface 6b located on the interelectrode space 54c side, as in the illustrated embodiment. In this way, the molten salt in the interelectrode space 54c can be more easily sucked in. Accordingly, the flow rate of the molten salt discharged from the discharge tube portion 7 may increase. It is possible to arbitrarily select a manner of connection between the suction body 6c and the suction opening 6a of the suction tube 6. Examples of the manner of connection include integrally forming the members constituting the suction body 6c and the suction opening 6a, joining the members together by welding or the like, and fixing the members together by screwing or fitting.

[0038] The discharge tube 7, which discharges the molten salt sucked from the suction tube 6 after passing through the impeller case 5, has a discharge opening 7a. Here, in a direction perpendicular to the direction in which the anode 54a and the cathode 54b face each other, when the suction opening 6a of the suction tube 6 is positioned on one end side of the electrode 54 (the lower end side in FIG. 1), it is preferable to position the discharge opening 7a of the discharge tube 7 on the other end side (the upper end side in FIG. 1) that is opposite to the one end of the electrode 54 across the interelectrode space 54c. In this case, the molten salt that is sucked from the interelectrode space 54c at the one end side of the electrode 54 to the suction opening 6a and flows into the impeller case 5 is discharged from the discharge opening 7a at the other end side of the electrode 54. Then, the molten salt easily enters the interelectrode space 54c again from the other end side of the electrode 54, and can circulate through the interelectrode space 54c and the stirrer 1. As a result, the metal ion concentration in the interelectrode space 54c becomes more stable and uniform, and the morphology of the metal deposited on the cathode 54b becomes better.

[0039] The anode 54a may include a cage-shaped container made of nickel, nickel alloy, Hastelloy, or the like, having a large number of holes through which the molten salt can pass, and a raw material such as titanium placed in the cage-shaped container. Examples of the raw material made of titanium include sponge titanium, titanium scrap, titanium rod and / or titanium plate. The sponge titanium may be one containing a relatively large amount of magnesium chloride. A sponge titanium or titanium scrap containing a relatively large amount of magnesium chloride is desirable from the viewpoint of effective use of materials, and may be briquetted and placed in the cage-shaped container. When using sponge titanium, even if a sponge titanium containing a relatively large amount of chlorine is used, it is possible to produce titanium foil with few impurities by molten salt electrolysis. When performing molten salt electrolysis, when electricity is applied to a cage-shaped container made of nickel, nickel has a smaller tendency to be ionized than titanium, so that the elution of nickel from the cage-shaped container is suppressed and the raw material titanium is eluted. However, the anode 54a may not include a cage-shaped container, and a conductive wire may be directly connected to a briquetted sponge titanium, titanium scrap, titanium rod and / or titanium plate. The cathode 54b may be in the shape of, for example, a plate, a cylinder, or a rod.

[0040] When the anode 54a of the electrode 54 or the like includes a basket-shaped container having a large number of holes, the discharge opening 7a of the discharge tube 7 is preferably arranged to open toward the side wall of the basket-shaped container around the other end of the electrode 54, as shown in Fig. 1. The molten salt discharged from the discharge opening 7a toward the side wall of the basket-shaped container of the electrode 54 passes through the side wall of the basket-shaped container and reaches the interelectrode space 54c, resulting in uniform metal ion concentration in the interelectrode space 54c.

[0041] Alternatively, regardless of whether the electrode 54 includes a cage-shaped container or not, the discharge opening 7a of the discharge tube part 7 may be open toward the interelectrode space 54c on the other end side of the electrode 54 as in the embodiment shown in Fig. 3. In this way, the molten salt can circulate more easily between the interelectrode space 54c and inside the stirrer 1.

[0042] FIG. 4 shows the stirrer 1 of another embodiment together with an electrode 54. The electrode 54 has a drum-shaped cathode 54b that is at least partially immersed in the molten salt bath Bm and is rotated by a rotating shaft 54d, and an anode 54a that is arranged opposite the drum-shaped cathode 54b in the molten salt bath Bm and has a plate-like or block-like shape that curves along the outer circumferential surface of the drum-shaped cathode 54b. An interelectrode space 54c is defined between the cathode 54b and the anode 54a opposite the cathode 54b in the molten salt bath Bm. In this example, the rotating shaft 54d that rotates the cathode 54b extends parallel to the horizontal direction, but the rotating shaft 54d may extend in a direction inclined relative to the horizontal direction or vertically.

[0043] In FIG. 4, the suction tube portion 6 of the stirrer 1 is connected to the impeller case 5, and includes an suction main body portion 6c that is bent at two points and extends from the other end side (left side in FIG. 4) of the electrode 54 to one end side (right side in FIG. 4) at a position deeper than the anode 54a in the molten salt bath Bm, and an suction opening portion 6a that is connected to the suction main body portion 6c and opens into the interelectrode space 54c at one end side of the electrode 54. In addition, in the stirrer 1 illustrated in FIG. 4, the discharge tube portion 7 extends linearly and is provided with a discharge opening portion 7a that opens into the interelectrode space 54c at the other end side of the electrode 54. In this stirrer 1, the molten salt is discharged from the discharge opening portion 7a of the discharge tube portion 7 of the stirrer 1, passes through the interelectrode space 54c, is sucked into the stirrer 1 through the suction opening portion 6a of the suction tube portion 6, and flows, circulating through the interelectrode space 54c and the stirrer 1.

[0044] In the stirrer 1 in Fig. 4, at least a part of the suction tube part 6 has an inner diameter larger than the inner diameter of the suction main body part 6c, and has an inner diameter that gradually increases toward the open end face on the interelectrode space 54c side. The other configurations are substantially similar to those shown in Fig. 1.

[0045] In the electrode 54 shown in FIG. 4, a voltage is applied between a drum-shaped cathode 54b and an anode 54a that are rotated by a rotating shaft 54d, and as the cathode 54b rotates, metal is deposited over the entire outer periphery of the cathode 54b. Alternatively, as shown in FIG. 5, a conductive belt 54e may be wound around the outer periphery of the drum-shaped cathode 54b. In this case, the belt 54e is transported by the rotation of the cathode 54b, and a voltage is applied between the electrodes 54 to continuously deposit metal on the belt 54e. In both of the electrodes 54 shown in FIGS. 4 and 5, the anode 54a may be one that includes the above-mentioned basket-shaped container, instead of being plate-shaped or block-shaped.

[0046] In the agitator 1 of the embodiment, as shown in FIG. 7, a bearing portion 8 for rotatably holding the rotating shaft portion 3 is provided at the sleeve end portion 4a of the shaft sleeve 4 connected to the impeller case 5. With this, even if the rotating shaft portion 3 has a long axial length, it rotates while being held by the bearing portion 8 at the sleeve end portion 4a near the impeller 2, so that the impeller 2 rotates stably and the molten salt bath Bm can be stirred well. In addition, since the rotation of the rotating shaft portion 3 and the impeller 2 is stabilized, even if the axial length of the rotating shaft portion 3 is long, the occurrence of vibration of the agitator 1 is suppressed. Furthermore, even if a large resistance force acts on the rotating impeller 2 from the molten salt, the rotating shaft portion 3 is held by the bearing portion 8, so that deformation or damage of the rotating shaft portion 3 can be suppressed.

[0047] Specifically, the bearing portion 8 can be disposed, for example, on an annular bearing holder 4b disposed inside the sleeve end portion 4a. A cylindrical member 9 can be provided around the rotating shaft portion 3 inserted into the bearing portion 8, and the rotating shaft portion 3 can be disposed by contacting the cylindrical member 9 with the bearing portion 8. By supporting the rotating shaft portion 3 on the bearing portion 8 with the cylindrical member 9, the impeller 2 is disposed at an appropriate axial (height) position, and contact between the impeller 2 and the impeller case 5 is suppressed. However, the structure of the bearing portion 8 and its surroundings is not limited to that shown in the figure, as long as the bearing portion 8 can rotatably hold the rotating shaft portion 3.

[0048] Although not shown in the drawings, a bearing portion can also be provided at the end of the shaft sleeve 4 on the drive source side, opposite the sleeve end 4a. This can further stabilize the rotation of the rotating shaft portion 3 and the impeller 2.

[0049] The material of the bearing portion 8 is preferably ceramics, particularly silicon nitride or silicon carbide, because silicon nitride and silicon carbide have excellent heat resistance, corrosion resistance against molten salt, and abrasion resistance between the bearing portion 8 and other members of the agitator 1, and are also resistant to thermal shock. The materials of the other members of the stirrer 1 are preferably carbon steel or stainless steel (SUS304, SUS316, etc.), other steels, nickel, nickel-based alloys, tungsten, molybdenum, tantalum, or niobium. Nickel or carbon steel is particularly preferable. Nickel and carbon steel are relatively resistant to corrosion by molten salt and are relatively inexpensive. Furthermore, nickel is preferable because it is less likely to dissolve in molten salt electrolysis (it is a more noble metal).

[0050] When the bearing portion 8 is provided at the sleeve end 4a, the molten salt in the impeller case 5 may penetrate into the shaft sleeve 4 from between the rotating shaft portion 3 and the impeller case 5, or between the bearing portion 8 and the rotating shaft portion 3, and accumulate on the bearing portion 8. The molten salt accumulated on the bearing portion 8 may solidify when the agitator 1 is lifted from the molten salt bath Bm, and may adhere to the bearing portion 8 and remain there. It is not easy to completely remove such solidified molten salt, which reduces maintainability. In addition, the solidified molten salt near the bearing portion 8 may hinder the smooth rotation of the rotating shaft portion 3 when the agitator 1 is used thereafter, and may cause damage to the agitator 1.

[0051] In order to easily discharge the molten salt that has entered the bearing portion 8 inside the shaft sleeve 4, in the illustrated embodiment, at least one through hole 10 is provided in the sleeve end 4a, which extends around the bearing portion 8 and toward the inside in the axial direction (upward in FIG. 2) of the bearing portion 8. As a result, when the agitator 1 is pulled up from the molten salt bath Bm, the molten salt in the shaft sleeve 4 flows from the through hole 10 in the sleeve end 4a to the outside of the shaft sleeve 4 and is discharged, so that the generation of the above-mentioned solidified matter near the bearing portion 8 can be suppressed. As a result, the maintainability of the agitator 1 can be improved, and the agitator 1 can be used repeatedly for a long period of time, thereby extending the life of the agitator 1.

[0052] As shown in FIG. 7, it is preferable to form a plurality of through holes 10 at intervals in the circumferential direction of the sleeve end 4a. This is because the presence of a plurality of through holes 10 in the circumferential direction makes it easier for the molten salt near the bearing portion 8 to be discharged to the outside of the shaft sleeve 4. In this embodiment, four through holes 10 are formed at equal intervals in the circumferential direction, but the number of through holes 10 can be changed as appropriate. The shape of the through holes 10 is not particularly important as long as they extend axially inward from the bearing portion 8 and penetrate the shaft sleeve 4 in the thickness direction. In the illustrated example, each through hole 10 has a rectangular shape with the inner short side in the axial direction rounded when viewed from the front.

[0053] Incidentally, each blade portion 2a of the impeller 2 can be shaped to extend linearly in the radial direction around the rotating shaft portion 3, but preferably has a shape that extends curvedly in the radial direction as shown in Fig. 6(a). By making each blade portion 2a curved so that at least a part of the way along its radial extension protrudes in the rotation direction and rotating the impeller 2 in the protruding direction (clockwise direction in Fig. 6(a)), the molten salt is more easily discharged due to the action of centrifugal force.

[0054] In this embodiment, as shown in Fig. 6(b), the height of the blades 2a (the length in the vertical direction in Fig. 6(b)) gradually decreases as it moves radially outward from the rotating shaft 3. However, the shape of the blades 2a is not limited to this and can be changed as appropriate.

[0055] The discharge tube portion 7, through which the molten salt discharged from the impeller case 5 to the molten salt bath Bm passes, is preferably connected to the impeller case 5 in an orientation inclined with respect to the radial direction, as shown in Fig. 8. In this embodiment, as can be seen from Fig. 8(b), the discharge tube portion 7 is connected to the impeller case 5 in an orientation in which the radial direction of the rotating shaft portion 3 and the central axis of the discharge tube portion 7 are inclined. This makes it easier for the molten salt to be discharged from the impeller case 5, and the stirring of the molten salt bath Bm is performed more effectively.

[0056] In the illustrated stirrer 1, the inner diameter of the suction tube portion 6 is smaller than the inner diameter of the impeller case 5. In this case, the amount of molten salt that can be sucked in can be increased. The inner diameter of the discharge tube portion 7 can be smaller than the inner diameter of the suction tube portion 6. The flow rate of the molten salt discharged from the discharge tube portion 7 can be increased. This increase in flow rate can improve the stirring efficiency of the molten salt bath Bm.

[0057] In this example, the angle between the central axis of the suction tube portion 6 and the central axis of the discharge tube portion 7 at the connection point with the impeller case 5 is approximately a right angle, but is not limited to this and may be an acute angle or an obtuse angle. In addition, multiple suction tube portions 6 and / or multiple discharge tube portions 7 may be provided.

[0058] In the illustrated example, flange-shaped disk members 4c and 5a protruding outward from the shaft sleeve 4 are provided on the end face of the sleeve end 4a and the end face of the impeller case 5 on the shaft sleeve 4 side, respectively. When the agitator 1 is assembled, the disk members 4c and 5a are positioned overlapping each other, and the rotating shaft portion 3 is disposed passing through through holes formed in the centers of the disk members 4c and 5a. EXAMPLES

[0059] Next, a prototype of the agitator of the present invention was produced and its performance was confirmed, which will be described below. However, the description here is merely for illustrative purposes and is not intended to be limiting.

[0060] In Example 1, a molten salt electrolysis apparatus as shown in FIG. 1 was used. As the anode, a titanium sponge was placed in a nickel cage-shaped container having a large number of through holes. The cage-shaped container had a cylindrical outer shape, and a cylindrical cathode was placed inside the anode. Example 2 was almost the same as Example 1, except that an electrode and agitator as shown in FIG. 4 were used. Example 3 was almost the same as Example 2, except that an electrode as shown in FIG. 5 was used. In Examples 2 and 3, a titanium cast piece was used as the anode.

[0061] Comparative Example 1 was almost the same as Example 1, except that the entire molten salt bath was stirred using stirrers with bare propellers exposed to the molten salt bath, one on the bottom side of the electrolytic cell and the other on the bath surface side.

[0062] In all of Examples 1 to 3 and Comparative Example 1, a quaternary molten salt bath of NaCl-KCl-MgCl2-TiCl2 was used as the molten salt bath, and the temperature of the molten salt bath was set to 500° C. As electrolysis conditions, the average current density was 0.1 A / cm 2 The electrodeposition time was 1.5 h. A pulse current may be used, and a reverse voltage may be applied to reverse the anode and cathode during the electrodeposition, but a constant current was applied for the electrodeposition time.

[0063] After the molten salt electrolysis was completed, the metal foil was physically peeled off from the cathode to check for wrinkles and for the presence of sludge in the metal foil. The results are also shown in Table 1.

[0064] [Table 1]

[0065] In Table 1, the occurrence of wrinkles after peeling was judged as either "good" or "good" by the peeling test. "Good" means that no wrinkles were observed visually after peeling, and "good" means that wrinkles were observed visually after peeling. A good evaluation is pass, and a good evaluation is fail.

[0066] The peel test was performed as shown in FIG. 9. First, a sample 103 of 70 mm×10 mm was cut from the cathode and the metal foil deposited on the cathode by a cutter or the like. Next, the sample 103 was placed on the stage 111 of a 90° peel tester, and 10 mm of the metal foil 101 was peeled off from the cathode 102 at one end of the sample 103, and the peeled part of the metal foil 101 was clamped by a chuck. Next, the cathode 102 at one end of the sample 103 on the stage 111 and the other end of the sample 103 located opposite to the one end were fixed by a fixing jig 112. Then, as shown by the arrow in FIG. 9, the chuck was raised vertically upward at 20 mm / sec, and the stage 111 was moved horizontally at 20 mm / sec. The angle between the direction in which the metal foil 101 was peeled off and the surface of the cathode 102 was set to 90° measured from the surface of the cathode. The peel tester used was a digital force gauge ZTS-200N manufactured by Imada Co., Ltd. and a slide table for 90-degree peel tests P90-200N.

[0067] The presence or absence of sludge in the metal foil was confirmed as follows. The metal foils obtained in Examples 1 to 3 and Comparative Example 1 were washed with 0.05M HCl aqueous solution and water in that order, dried, and analyzed for Na, K, and Mg by ICP emission spectrometry. The components of the molten salt bath were sufficiently dissolved in the liquid by the above washing, but the sludge is thought to be generated when the molten salt bath reacts with a small amount of air or moisture, and the three components Na, K, and Mg remain without being removed by the above washing. Therefore, when the total content of these three elements was more than 0.06 mass%, it was considered that sludge was involved, and it was judged that "sludge was present."

[0068] From Table 1, in Examples 1 to 3, by using a specified stirrer, the metal foil could be physically peeled off from the cathode, no wrinkles were found on the surface after peeling, and no sludge was mixed in the metal foil. This is presumably because the molten salt was sucked in by the suction tube of the stirrer, which caused an appropriate bath flow, made the metal ion concentration in the space between the electrodes uniform, and suppressed the suction of sludge on the bottom side. On the other hand, in Comparative Example 1, wrinkles were found after the metal foil was peeled off from the cathode, and sludge was mixed in the metal foil.

[0069] From the above, it has been found that according to the present invention, metal can be satisfactorily deposited on an electrode immersed in a molten salt bath. [Explanation of symbols]

[0070] 1 Mixer 2 Impeller 2a Wing 3 Rotating shaft 4-axis sleeve 4a Sleeve end 4b Bearing holding part 4c, 5a Disc member 5 Impeller case 6 Suction cylinder part 6a Suction opening 6b Opening end surface 6c Suction main body 7 Discharge cylinder part 7a Discharge opening 8 Bearing section 9 Cylindrical member 10 Through hole 51 Molten salt electrolysis equipment 52 Electrolytic cell 53 Heater 54 electrode 54a anode 54b Cathode 54c Interelectrode space 54d Rotation axis 54e Belt Bm molten salt bath

Claims

1. A stirrer used for stirring a molten salt bath in which electrodes are immersed in an electrolytic cell, comprising: an impeller having a plurality of blades spaced apart in a rotational direction and immersed in a molten salt bath; a rotating shaft portion that transmits a rotational driving force from a driving source outside the molten salt bath to the impeller; a shaft sleeve surrounding the rotating shaft portion; an impeller case containing an impeller therein; a suction tube portion connected to the impeller case from the outside in the axial direction of the rotating shaft portion and configured to guide the molten salt of the molten salt bath into the impeller case; a discharge tube portion connected to the impeller case on the outer periphery side of the impeller and discharging the molten salt from inside the impeller case; Equipped with The agitator, wherein the suction tube portion has a suction opening that opens toward the interelectrode space of the electrodes in the electrolytic cell.

2. The exhaust tube portion has an exhaust opening, 2. The mixer according to claim 1, wherein the suction opening is located on one end side of the electrode, and the discharge opening is located on the other end side opposite the one end of the electrode across the interelectrode space.

3. 3. The agitator according to claim 2, wherein the discharge opening is open toward the interelectrode space at the other end of the electrode.

4. The electrode includes a cage; 3. The mixer according to claim 2, wherein the discharge opening is open toward a side wall of the basket-shaped container at the other end of the electrode.

5. The suction tube portion has a suction main body portion that connects the suction opening portion and the impeller case, The agitator according to any one of claims 1 to 4, wherein at least a portion of the suction opening has an inner diameter larger than an inner diameter of the suction main body.

6. 6. The stirrer according to claim 1, wherein at least a portion of the suction opening has an inner diameter that gradually increases toward an open end face on the interelectrode space side.

7. The agitator according to any one of claims 1 to 6, wherein a bearing portion for rotatably holding the rotating shaft portion is provided at the sleeve end of the shaft sleeve that is connected to the impeller case, and at least one through hole is formed around the bearing portion and extending axially inward from the bearing portion.

8. A molten salt electrolysis apparatus comprising: an electrolytic cell in which a molten salt is stored to form a molten salt bath; electrodes arranged in the electrolytic cell so as to be immersed in the molten salt bath; and the stirrer according to any one of claims 1 to 7.

9. 9. The molten salt electrolysis apparatus according to claim 8, wherein the electrodes include an anode and a drum-shaped cathode that is positioned opposite the anode and is rotatable about a rotation axis.

10. A method for producing a metal foil, comprising depositing a metal on an electrode by using the molten salt electrolysis apparatus according to claim 8 or 9.

Images