JP7611090B2 - Agitator, molten salt electrolysis device, and method for manufacturing metal foil - Google Patents

Description

This invention relates to a stirrer used to stir a molten salt bath in which electrodes are immersed in an electrolytic cell, a molten salt electrolysis device, and a method for manufacturing metal foil.

Metals belonging to Group 4 of the periodic table include titanium, zirconium, and hafnium. Titanium in particular is used in products in a wide variety of fields due to its excellent properties, such as high strength and corrosion resistance.

To produce such metals, molten salt electrolysis is sometimes used, as it is possible to obtain foil-like products 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, causing metal ions in the molten salt bath to precipitate in the form of a foil on the electrodes. This can be peeled off from the electrodes to produce the metal in foil form.

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 within the cell, and the electrolytic bath forms a closed loop in each of the above sections to generate a reflux, and the electrolytic bath is further arranged to circulate between the low-temperature section and the high-temperature section, so that electrolysis can be continued continuously." Patent Document 1 also proposes that "the stirring means should be a rotating blade mechanism with two or more blades, such as a propeller screw or a helical screw."

Japanese Patent Application Laid-Open No. 51-38242

However, it has recently been discovered that the metal ion concentration in the molten salt bath in the electrolytic cell can be non-uniform. 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 electrode surface in the molten salt bath may be impaired, or that it may become difficult to peel the metal electrodeposited on the electrode from the electrode. Patent Document 1 appears to be attempting 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.

The object of this invention is to provide a stirrer, a molten salt electrolysis device, and a method for manufacturing metal foil that can effectively deposit metal on an electrode immersed in a molten salt bath.

After extensive research, the inventors 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, the inventors came up with the idea of providing a suction opening that opens into the interelectrode space in the suction tube section of the agitator used to stir the molten salt bath, which directs the molten salt into the impeller case. In this way, when the molten salt in the interelectrode space is sucked in, an appropriate bath flow is created, which is believed to make the metal ion concentration in the interelectrode space uniform, allowing for good deposition of metal on the electrodes.

The agitator of this invention is used for stirring a molten salt bath in which electrodes are immersed in an electrolytic cell, and is equipped with an impeller having multiple blades spaced apart in the direction of rotation and immersed in the molten salt bath, a rotating shaft that transmits a rotational driving force from a driving source outside the molten salt bath to the impeller, a shaft sleeve that surrounds the periphery of the rotating shaft, an impeller case in which the impeller is housed, a suction tube that is connected to the impeller case from the outside in the axial direction of the rotating shaft and directs the molten salt of the molten salt bath into the impeller case, and a discharge tube that is connected to the impeller case on the outer periphery side of the impeller and discharges the molten salt from inside the impeller case, and the suction tube has a suction opening that opens toward the interelectrode space of the electrodes in the electrolytic cell.

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 of the electrode, which is opposite the one end of the electrode across the interelectrode space.

In this case, it is preferable that the discharge opening opens toward the interelectrode space on the other end side of the electrode.

In addition, when the electrode includes a cage-shaped container, it is preferable that the discharge opening opens toward the side wall of the cage-shaped container at the other end side of the electrode.

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

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 interelectrode space side.

The above-mentioned agitator may be configured such that a bearing portion that rotatably holds 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 extends axially inward from the bearing portion.

The molten salt electrolysis device of the present invention comprises an electrolytic cell in which molten salt is stored to form a molten salt bath, electrodes immersed in the molten salt bath within the electrolytic cell, and any one of the above-mentioned stirrers.

In the above-mentioned molten salt electrolysis device, the electrodes may have an anode and a drum-shaped cathode that is positioned opposite the anode and can rotate around a rotation axis.

The method for producing metal foil of the present invention involves depositing metal on an electrode using any of the above-mentioned molten salt electrolysis devices.

The agitator, molten salt electrolysis device, and metal foil manufacturing method of this invention allow metal to be effectively deposited on an electrode immersed in a molten salt bath.

1 is a cross-sectional view showing a stirrer according to an embodiment of the present invention together with a molten salt electrolysis apparatus. 2 is a cross-sectional view showing the agitator of FIG. 1 along the axial direction of a rotating shaft portion. FIG. 11 is a cross-sectional view showing a stirrer according to another embodiment together with an electrode. FIG. 11 is a cross-sectional view showing a stirrer according to still another embodiment together with another example of the electrode. FIG. 11 is a perspective view showing a schematic diagram of still another example of an electrode. 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 (a). 7A 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. 7B is a cross-sectional view along line VII-VII in the cross-sectional view (FIG. 7A). 8(a) is a cross-sectional view along the axial direction showing an impeller case provided in the agitator of FIG. 1, and FIG. 8(b) is a cross-sectional view along line VIII-VIII in the cross-sectional view (FIG. 8(a)). FIG. 1 is a cross-sectional view showing a peel test.

The following describes in detail the embodiments of the present invention with reference to the drawings. Some parts of the drawings are shown only diagrammatically to facilitate understanding of the embodiments included in the invention, and the size of each illustrated component and their relative positions may not be accurate.

The agitator 1 shown as an example in FIG. 1 is used to agitate a molten salt bath Bm in a molten salt electrolysis device 51 as shown in the figure. An electrode 54 including an anode 54a and a cathode 54b connected to a power source is immersed in the molten salt bath Bm. Note that the electrode 54 may be partially immersed. In other words, the electrode 54 needs only to be positioned so that metal can be precipitated.

More specifically, the molten salt electrolysis device 51 comprises a container-shaped electrolytic cell 52 for storing the 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 device 51 may further comprise a lid that can be arranged to cover the upper opening of the electrolytic cell 52. In addition, the molten salt electrolysis device 51 may comprise an inlet and an exhaust port for an inert gas such as argon gas above the bath surface of the molten salt bath Bm.

In the molten salt electrolysis using the molten salt electrolysis device 51, the electrolysis conditions can be appropriately controlled to electrolytically deposit at least one metal selected from Group 4 elements (titanium, zirconium, hafnium) in the form of a 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 4 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 4 elements can be produced by electrolysis using the electrode 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.

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 (MgCl ₂ ), sodium chloride (NaCl), calcium chloride (CaCl ₂ ), potassium chloride (KCl), magnesium fluoride (MgF ₂ ), and calcium fluoride (CaF ₂ ).

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 reason is 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. Also, 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 and penetrates various parts of the stirrer, and when the temperature drops, it becomes solid and its volume changes.

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 blades 2a spaced apart in the direction of rotation, a rotating shaft 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 periphery of the rotating shaft 3, an impeller case 5 in which the impeller 2 is housed, a suction tube 6 that is connected to the impeller case 5 from the outside in the axial direction of the rotating shaft 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 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 axial outer side of the rotating shaft portion 3 means the side away from the axial center of the rotating shaft portion 3, and the axial inner side 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 the shaft sleeve 4).

The agitator 1 is arranged 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 also be arranged so that a portion of the shaft sleeve 4 is immersed in the molten salt bath Bm. The impeller 2 is rotated by the rotating shaft 3, which is rotated by a driving source such as a motor, inside the shaft sleeve 4, and 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 flow of molten salt into the agitator 1 and the flow of molten salt out of the agitator 1 are repeated in this manner, and the molten salt bath Bm is stirred.

Here, the metal ion concentration in the molten salt bath Bm in the electrolytic cell 52 may become non-uniform. For example, in the molten salt bath Bm containing titanium ions, it is presumed that a disproportionation reaction in which Ti ²⁺ and Ti ³⁺ are generated occurs constantly, and Ti is generated by this reaction. This Ti in the form of fine powder or the like settles due to its own weight, which may cause the titanium ion concentration in the molten salt bath Bm to become non-uniform. 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 therefore, the metal may not be deposited in a good shape on the cathode 54b.

In response to this, the inventors came to the realization that the metal ion concentration in the molten salt bath Bm, particularly in the electrode 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 knowledge, the inventors thought that if the molten salt present in the interelectrode space 54c is sucked in by the agitator 1, an appropriate bath flow will occur, the metal ion concentration there will be uniformized, and metal will be able to be deposited satisfactorily on the cathode 54b.

Specifically, in the agitator 1 of this embodiment, the suction tube 6 is provided with a suction opening 6a that opens toward the interelectrode space 54c in the electrolytic cell 52. Application of a voltage between the electrodes 54 causes the supply of metal ions from the anode 54a to the molten salt bath Bm, as well as the consumption of metal ions and the deposition of metal 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 tube 6 from the suction opening 6a, and a flow of such 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.

In addition, when molten salt electrolysis is performed continuously 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. Unlike electrolysis using an aqueous solution, in molten salt electrolysis, it is difficult to stop the 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 in with the metal deposited on the cathode 54b, the purity of the metal to be produced by molten salt electrolysis will decrease.

In contrast, if the suction opening 6a is provided in the suction tube portion 6 of the agitator 1, which opens toward the interelectrode space 54c as described above, the suction opening 6a does not face the bottom side of the electrolytic cell 52 or is easily positioned in a shallow area away from the bottom, suppressing the suction of sludge that accumulates on the bottom side. This makes it possible to increase the purity of the metal that deposits on the cathode 54b. It also makes it possible to suppress clogging inside the agitator 1 due to the suction of sludge.

The part of the agitator 1 that is immersed in the molten salt bath Bm and the electrode 54 are preferably positioned 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 3. It is also desirable to position the conductive wire of the electrode 54 so that it is not immersed in the molten salt bath Bm as much as possible.

Regarding 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 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).

In this embodiment, the suction tube portion 6 has the above-mentioned suction opening 6a, and an suction body portion 6c that bends or curves from the suction opening 6a at multiple points, for example two points, 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 portion of the suction opening 6a, particularly the portion near the opening end surface 6b, has a larger inner diameter than the suction body portion 6c. This allows most of the molten salt in the interelectrode space 54c to be sucked in by the suction opening 6a, making the metal ion concentration even more uniform.

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.

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 the one end of the electrode 54 and the interelectrode space 54c. In this case, the molten salt that is sucked from the interelectrode space 54c at 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 agitator 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 even better.

The anode 54a may include a cage-shaped container made of nickel, nickel alloy, Hastelloy, etc., and provided with 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 raw materials made of titanium include sponge titanium, titanium scrap, titanium rod and/or titanium plate. The sponge titanium may contain 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 with a relatively high chlorine content is used, titanium foil with fewer impurities can be produced 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 briquette-shaped sponge titanium, titanium scrap, titanium rod and/or titanium plate, etc. The cathode 54b can be shaped, for example, as a plate, a cylinder, or a rod.

When the anode 54a of the electrode 54 includes a cage-shaped container with many holes, the discharge opening 7a of the discharge tube 7 is preferably arranged so as to open toward the side wall of the cage-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 cage-shaped container of the electrode 54 passes through the side wall of the cage-shaped container and reaches the interelectrode space 54c, resulting in uniform metal ion concentration in the interelectrode space 54c.

Alternatively, regardless of whether the electrode 54 includes a cage-shaped container or not, the discharge opening 7a of the discharge tube portion 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 agitator 1.

Figure 4 shows another embodiment of the agitator 1 together with the 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 to match the outer periphery 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 to the horizontal direction or vertically.

In FIG. 4, the suction tube portion 6 of the agitator 1 is connected to the impeller case 5, and includes an suction 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 body portion 6c and opens into the interelectrode space 54c at one end side of the electrode 54. In addition, in the agitator 1 illustrated in FIG. 4, the discharge tube portion 7 extends linearly and has a discharge opening portion 7a that opens into the interelectrode space 54c at the other end side of the electrode 54. In this agitator 1, the molten salt is discharged from the discharge opening portion 7a of the discharge tube portion 7 of the agitator 1, passes through the interelectrode space 54c, is sucked into the agitator 1 through the suction opening portion 6a of the suction tube portion 6, and flows, circulating through the interelectrode space 54c and the agitator 1.

In the agitator 1 of FIG. 4, at least a portion of the suction tube portion 6 has an inner diameter larger than the inner diameter of the suction body portion 6c, and has an inner diameter that gradually increases toward the open end face on the interelectrode space 54c side. The rest of the configuration is substantially the same as that shown in FIG. 1.

In the electrode 54 shown in FIG. 4, by applying a voltage between the drum-shaped cathode 54b and the anode 54a, which are driven to rotate by the rotating shaft 54d, metal is deposited over the entire outer surface as the cathode 54b rotates. Alternatively, as shown in FIG. 5, a conductive belt 54e may be wrapped around the outer surface of the drum-shaped cathode 54b. In this case, the belt 54e is transported by the rotation of the cathode 54b, and by applying a voltage between the electrodes 54 at that time, metal can be continuously deposited on the belt 54e. In both electrodes 54 shown in FIGS. 4 and 5, the anode 54a may be a cage-shaped container as described above, rather than a plate or block shape.

As shown in FIG. 7, the agitator 1 of the embodiment has a bearing 8 that rotatably holds the rotating shaft 3 at the sleeve end 4a of the shaft sleeve 4 that is connected to the impeller case 5. With this, even if the rotating shaft 3 has a long axial length, it rotates while being held by the bearing 8 at the sleeve end 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 3 and the impeller 2 is stable, even if the axial length of the rotating shaft 3 is long, the occurrence of vibration of the agitator 1 is suppressed. Furthermore, even if a large resistance force from the molten salt acts on the rotating impeller 2, the rotating shaft 3 is held by the bearing 8, so deformation or damage of the rotating shaft 3 can be suppressed.

Specifically, the bearing portion 8 can be disposed, for example, on the 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 this 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.

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

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 components 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 preferred. Nickel and carbon steel are relatively resistant to corrosion by molten salt and are relatively inexpensive. Furthermore, nickel is preferred because it is less likely to dissolve in molten salt electrolysis (it is a more noble metal).

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 that accumulates 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 and remain there. It is not easy to completely remove such solidified molten salt, which reduces maintainability. In addition, there is a concern that 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 subsequently used, leading to damage to the agitator 1.

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 axially inward (upward in FIG. 2) around the bearing portion 8. As a result, when the agitator 1 is lifted 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, thereby suppressing the generation of the above-mentioned solidified matter near the bearing portion 8. 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.

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. There is no particular restriction on the shape of the through holes 10 as long as they extend axially inward beyond 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.

While each blade portion 2a of the impeller 2 can be shaped to extend radially in a straight line around the rotating shaft portion 3, it is preferable that it has a shape that extends in a curved radial direction, as shown in FIG. 6(a). By making each blade portion 2a curved so that at least a portion of the way it extends radially protrudes in the direction of rotation, and by rotating the impeller 2 in the protruding direction (clockwise in FIG. 6(a)), the molten salt is more easily discharged due to the action of centrifugal force.

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

As shown in FIG. 8, it is preferable that the discharge tube section 7, through which the molten salt discharged from the impeller case 5 into the molten salt bath Bm passes, is connected to the impeller case 5 in an inclined direction relative to the radial direction. In this embodiment, as can be seen from FIG. 8(b), the discharge tube section 7 is connected to the impeller case 5 in an inclined direction relative to the radial direction of the rotating shaft section 3 and the central axis of the discharge tube section 7. 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.

In the illustrated agitator 1, the inner diameter of the suction tube section 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 section 7 can also be smaller than the inner diameter of the suction tube section 6. The flow rate of the molten salt discharged from the discharge tube section 7 can be increased. This increase in flow rate can improve the stirring efficiency of the molten salt bath Bm.

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

In the illustrated example, flange-shaped disk members 4c and 5a that protrude radially outward beyond 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. When the agitator 1 is assembled, the disk members 4c and 5a are positioned overlapping each other, and the rotating shaft portion 3 is positioned passing through a through hole formed in the center of each of the disk members 4c and 5a.

Next, we have created a prototype of the agitator of this invention and confirmed its performance, which will be described below. However, the description here is merely for illustrative purposes and is not intended to be limiting.

In Example 1, a molten salt electrolysis apparatus as shown in Figure 1 was used. A titanium sponge was placed in a nickel cage-shaped container with many through holes as the anode. 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 Figure 4 were used. Example 3 was almost the same as Example 2, except that an electrode as shown in Figure 5 was used. In Examples 2 and 3, a titanium cast piece was used as the anode.

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

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 500°C. The electrolysis conditions were an average current density of 0.1 A/ ^cm2 and an electrodeposition time of 1.5 h. A pulse current may be used, and the current may be stopped or a reverse voltage may be applied to reverse the anode and cathode during the electrodeposition, but here a constant current was applied for the above-mentioned electrodeposition time.

After the molten salt electrolysis was completed, we checked whether wrinkles occurred after the metal foil was physically peeled off from the cathode, and whether sludge was mixed into the metal foil. The results are also shown in Table 1.

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 with the naked eye after peeling, and "Good" means that wrinkles were observed with the naked eye after peeling. A good rating is a pass, and a good rating is a fail.

The peeling test was performed as shown in FIG. 9. First, a 70 mm×10 mm sample 103 was cut from the cathode and the metal foil deposited on the cathode using a cutter or the like. Next, the sample 103 was placed on the stage 111 of the 90° peeling 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 fixture 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 P90-200N for 90-degree peel tests.

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, and dried, and Na, K, and Mg were analyzed by ICP emission spectrometry. The components of the molten salt bath were sufficiently dissolved in the liquid by the above washing, but sludge is thought to be generated when the molten salt bath reacts with traces of air and moisture, and the three components Na, K, and Mg remain without being removed by the above washing. Therefore, if 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."

As can be seen from Table 1, in Examples 1 to 3, by using a specified agitator, 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 into the metal foil. This is presumably because the molten salt was sucked into the suction tube of the agitator, resulting in an appropriate bath flow, making the metal ion concentration in the space between the electrodes uniform and suppressing 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 into the metal foil.

From the above, it has been found that this invention allows metal to be effectively deposited on an electrode immersed in a molten salt bath.

REFERENCE SIGNS LIST 1 Agitator 2 Impeller 2a Blade portion 3 Rotating shaft portion 4 Shaft sleeve 4a Sleeve end portion 4b Bearing holder portion 4c, 5a Disk member 5 Impeller case 6 Suction tube portion 6a Suction opening portion 6b Open end surface 6c Suction main body portion 7 Discharge tube portion 7a Discharge opening portion 8 Bearing portion 9 Cylindrical member 10 Through hole 51 Molten salt electrolysis device 52 Electrolytic cell 53 Heater 54 Electrode 54a Anode 54b Cathode 54c Interelectrode space 54d Rotating shaft 54e Belt Bm Molten salt bath

Claims (10)

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 circumferential side of the impeller and discharging the molten salt from inside the impeller case,
The agitator, wherein the suction tube portion has a suction opening that opens toward the interelectrode space of the electrodes in the electrolytic cell. 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. The agitator according to claim 2, wherein the discharge opening opens toward the interelectrode space at the other end of the electrode. 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. 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. The agitator according to any one of claims 1 to 5, wherein at least a portion of the suction opening has an inner diameter that gradually increases toward the opening end face on the interelectrode space side. The agitator according to any one of claims 1 to 6, in which a bearing portion that rotatably holds 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 extends axially inward from the bearing portion. A molten salt electrolysis device comprising an electrolytic cell in which molten salt is stored to form a molten salt bath, an electrode immersed in the molten salt bath and disposed in the electrolytic cell, and the agitator according to any one of claims 1 to 7. 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 can rotate around a rotation axis. A method for producing metal foil, comprising depositing a metal on an electrode using the molten salt electrolysis device according to claim 8 or 9.