WO2022181646A1

WO2022181646A1 - Production method for titanium foil

Info

Publication number: WO2022181646A1
Application number: PCT/JP2022/007403
Authority: WO
Inventors: 拓実金子; 雄太中條; 大輔鈴木; 松秀堀川; 秀樹藤井
Original assignee: 東邦チタニウム株式会社
Priority date: 2021-02-25
Filing date: 2022-02-22
Publication date: 2022-09-01

Abstract

This production method for titanium foil includes an electrodeposition step in which a molten salt bath that includes titanium ions and a molten chloride is used to perform electrolysis at an electrode that includes an anode and a cathode, and titanium metal is deposited at an electrolysis surface of the cathode. During the electrodeposition step, the ratio of the molar concentration of titanium ions to the total molar concentration of metal ions in the molten salt bath is kept at or above 7%, the temperature of the molten salt bath is kept at or below 510°C, and, when the electrode is energized, the energization has a continuous stop time of less than 1.0 seconds, the current density is at least 0.10 A/cm2 but no more than 1.0 A/cm2, and the electrodeposition time of the titanium metal onto the electrolysis surface of the cathode is no more than 120 minutes.

Description

Method for manufacturing titanium foil

This invention relates to a method for producing a titanium foil by electrolyzing electrodes including an anode and a cathode using a molten salt bath and depositing metallic titanium on the cathode.

Metal titanium is generally manufactured by the Kroll method, which is suitable for mass production. In the production of metallic titanium, titanium oxide contained in titanium ore is reacted with chlorine in the presence of a carbon source such as coke to produce titanium tetrachloride. Thereafter, titanium tetrachloride is reduced with metallic magnesium to obtain sponge-like metallic titanium, so-called sponge titanium.

Here, in order to manufacture a relatively thin foil-shaped titanium metal using the sponge titanium as a main raw material, the sponge titanium is melted and cast into a titanium ingot or titanium slab, and then forged, rolled, or otherwise processed. It is common to apply the required processing of It is difficult to say that it is possible to efficiently produce titanium metal in a predetermined shape such as a foil shape at a low cost by such a process that requires melting and processing.

Under these circumstances, the adoption of molten salt electrolysis, which deposits metallic titanium using a molten salt bath, instead of the melting and processing described above, is being considered from the perspective of reducing energy consumption and cost in the manufacturing process. It is

Technologies related to molten salt electrolysis include those described in Patent Documents 1 to 3, for example.

Patent Document 1 describes "a method for producing high-purity titanium by a molten salt electrolysis method, wherein electrolysis is performed in a chloride bath having a sodium ion content of 10 wt% or less as a bath composition. , ``When performing electrolysis using an electrolytic bath having a low melting point of 400° C. or lower, the electrolysis temperature should be in the range of 550 to 900° C.''.
In this patent document 1, "When using a bath with a low melting point (400° C. or lower) such as LiCl—KCl, electrolysis is usually performed at 400 to 500° C. However, the shape of the deposited Ti at this temperature is that of a sponge. In this state, the amount of oxygen is large and the loss is also large, resulting in a poor yield." By setting the temperature to 750° C., the shape of the deposited Ti is changed to coarse crystals, specifically, hexagonal plates or dendrites, thereby reducing oxygen and improving the yield.” there is

In Patent Document 2, "Titanium characterized by applying a voltage between a container filled with raw material titanium as an anode and an electrolysis container as a cathode when electrolytically refining raw material titanium by molten salt electrolysis. A manufacturing method of "is disclosed. Specifically, "as the molten salt electrolysis step, first, from a state where the raw material titanium T and the titanium rod 3 are not charged into the container body 1a, NaCl-KCl mixed in advance at a molar ratio of 1:1 The mixed chloride of is put into the container body 1a.Then, after heating to 650° C. under reduced pressure to dehydrate the mixed chloride well, the atmosphere in the furnace is replaced with an argon atmosphere, and the temperature is raised to 740° C. and maintained. to melt the mixed chloride to form an electrolytic bath 4. Next, the raw material titanium T and the titanium rod 3 are immersed in the electrolytic bath 4, and the lid 1b is closed. After an appropriate flow rate of liquid TiCl ₄ was blown into the bottom of the raw material titanium T to generate titanium ions in the electrolytic bath, voltage was applied to both the electrolysis circuit 11 and the impurity elution prevention circuit 21 by direct current. The voltage of the electrolysis circuit 11 is 100 to 1000 mV, and the voltage of the impurity elution prevention circuit 21 is 500 mV or less, preferably 10 to 150 mV, more preferably 30 to 100 mV.” .

In Patent Document 3, "A method for producing metallic titanium by performing electrolysis using an anode and a cathode in a molten salt bath, wherein an anode containing metallic titanium is used as the anode, and metallic titanium is used as a cathode. In the titanium precipitation step, the temperature of the molten salt bath is set to 250° C. or higher and 600° C. or lower, and the titanium precipitation step is started and 30 minutes have elapsed from the start of the titanium precipitation step. A method for producing titanium metal, which maintains the average current density of the cathode within the range of 0.01 A/cm ² to 0.09 A/cm ² , has been proposed. In the example section of Patent Document 3, it is stated that "a pulse current is applied to the anode and the cathode by repeating energization and stoppage at predetermined intervals, thereby performing electrolysis to dissolve the anode and form a metal titanium foil on the cathode. It was deposited in a shape.” (See Table 1).

JP-A-3-291391 JP-A-2000-87280 WO2020/044841

In the method described in Patent Document 3, a thin layer of metallic titanium is electrodeposited on the cathode, and the metallic titanium can be separated from the cathode relatively easily. Therefore, it is considered that a thin titanium foil can be obtained by this method.

However, in the method described in Patent Document 3, an intermittent current, such as a pulse current, may flow when energizing the electrodes. In this case, it takes a certain amount of time to electrodeposit titanium metal on the cathode due to the stop time of energization in the pulse current, so there is room for improvement in the efficiency of the production of titanium foil.

An object of the present invention is to manufacture a titanium foil capable of increasing the amount of titanium metal electrodeposited per unit time without significantly reducing the ease of stripping the metal titanium deposited on the cathode from the cathode. It is to provide a method.

Electrodeposition of metallic titanium on the cathode is thought to be promoted by increasing the concentration of titanium ions in the molten salt bath, increasing the temperature of the molten salt bath, and increasing the current density when the electrode is energized. On the other hand, there is a concern that these factors may reduce the ease of peeling metal titanium from the cathode.
As a result of intensive studies, the inventors have newly found a suitable combination of the above conditions. As a result, it is possible to suppress deterioration in the ease of peeling of metallic titanium even when the time for which the energization of the electrode is stopped is sufficiently shortened or when the energization is not stopped. Further, in this case, since the energization of the electrodes is stopped only for a short period of time or is not stopped, the amount of titanium metal deposited per unit time can be increased.

In the method for producing a titanium foil of the present invention, a molten salt bath containing titanium ions and chlorides is used to perform electrolysis with electrodes including an anode and a cathode to deposit metallic titanium on the electrolytic surface of the cathode. Including an electrodeposition step, in the electrodeposition step, the ratio of the molar concentration of titanium ions to the total molar concentration of metal ions in the molten salt bath is maintained at 7% or more, and the temperature of the molten salt bath is maintained at 510 ° C. or less. When energizing the electrode, the continuous stop time of energization is less than 1.0 second, the current density is 0.10 A/cm ² or more and 1.0 A/cm ² or less, and metal titanium is applied to the electrolytic surface of the cathode. The electrodeposition time is set to 120 minutes or less.

In the method for producing a titanium foil described above, it is preferable that the anode contains Ti and that the anode is consumed during the electrodeposition process.

In addition, in the method for manufacturing a titanium foil described above, the chloride preferably contains titanium dichloride and/or titanium trichloride.

In the electrodeposition step, it is preferable to maintain the ratio of the molar concentration of titanium ions to the total molar concentration of metal ions in the molten salt bath at 10% or more.

Also, in the electrodeposition step, it is preferable to maintain the temperature of the molten salt bath at 500°C or lower.

Further, in the electrodeposition step, the current density is preferably 0.20 A/cm ² or more and 0.50 A/cm ² or less.

According to the method for producing a titanium foil of the present invention, it is possible to increase the amount of titanium metal electrodeposited per unit time without reducing the ease of separating the metal titanium deposited on the cathode from the cathode. can.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows typically the electrolysis apparatus which can be used for the manufacturing method of the titanium foil which concerns on one Embodiment of this invention. It is a fragmentary cross-sectional perspective view which shows typically parts other than an electrode as sectional drawing about another electrolysis apparatus. It is a sectional view showing other electrolysis equipment typically. It is a sectional view showing other electrolysis equipment typically. 1 is a photograph of metallic titanium electrodeposited on the cathode of Example 1. FIG. 4 is a photograph of metallic titanium electrodeposited on the cathode of Comparative Example 2. FIG. It is a cross-sectional view showing a peel strength test.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below. 1 to 4 and 7 for explaining each embodiment are schematic diagrams showing the configuration thereof. Therefore, the arrangement, size, etc. of each component shown in FIGS. 1 to 4 and 7 may not be accurate.
A method for producing a titanium foil according to one embodiment of the present invention uses a molten salt bath in which a chloride containing titanium ions is melted, is electrolyzed with electrodes including an anode and a cathode, and electrolyzes the electrolytic surface of the cathode. including an electrodeposition step of depositing metallic titanium on the In the electrodeposition step, the ratio of the molar concentration of titanium ions to the total molar concentration of metal ions in the molten salt bath is maintained at 7% or more, and the temperature of the molten salt bath is maintained at 510° C. or lower. In the electrodeposition step, when electrifying the electrode, the continuous stop time of electrification is set to less than 1.0 second, and the current density is set to 0.10 A/cm ² or more and 1.0 A/cm ² or less. The time for electrodeposition of metallic titanium onto the electrolytic surface of the cathode in the electrodeposition step is 120 minutes or less. In the description of each embodiment, the ratio of the molar concentration of titanium ions to the total molar concentration of metal ions in the molten salt bath is also simply referred to as the "ratio of titanium ions."

In this type of molten salt electrolysis, the concentration of titanium ions in the molten salt bath is increased, the temperature of the molten salt bath is increased, and the current density is increased when the electrode is energized. deposition is accelerated, and the amount of titanium metal deposited per unit time tends to increase. However, if all of them are carried out, it becomes difficult to separate the metallic titanium electrodeposited on the cathode from the cathode. In particular, it becomes difficult to physically peel off the electrodeposited metal titanium from the electrode.

In contrast, in this embodiment, in the electrodeposition step, the proportion of titanium ions in the molten salt bath is increased to 7% or more, and the current density is 0.10 A/cm ² or more and 1.0 A/cm ² . Increase to some extent below. On the other hand, the temperature of the molten salt bath is set to a relatively low temperature of 510° C. or less. According to this, it is possible to easily separate the titanium metal from the cathode while increasing the amount of the titanium metal electrodeposited per unit time. In particular, physical peeling such as peeling off the electrodeposited metal titanium from the electrode can be easily carried out.

The reason is not clear, but it can be speculated as follows. By increasing the ratio of titanium ions in the molten salt bath as described above, even if the titanium ions are deposited as metallic titanium on the cathode by energizing the electrode, the titanium ions in the vicinity of the cathode are less likely to be depleted. . It is believed that this suppresses the current bias in the vicinity of the cathode, suppresses the deposition of dendrite-like metallic titanium due to the current bias, and deposits the metallic titanium in the form of a foil on the cathode. In addition, since electric power is not concentrated due to the formation of dendrites, the temperature rise of the cathode surface can be suppressed. Furthermore, since the temperature of the molten salt bath is kept appropriately low, the temperature rise of the cathode surface is appropriately suppressed. As a result, interdiffusion of metal between the cathode and metallic titanium deposited thereon is suppressed. Therefore, even if the energization stop time to the electrode is sufficiently short, such as a continuous stop time of energization of less than 1.0 second, or even if the current is constant without stopping the energization, electrodeposition from the cathode will occur. It is presumed that it becomes possible to easily peel off the metal titanium. However, the present invention is not limited to the above theory.

In addition, in this embodiment, since the continuous stop time of energization is set to less than 1.0 second, the amount of metallic titanium deposited per unit time increases, thereby improving the production efficiency of the titanium foil. can. In addition, the titanium foil produced in this way has excellent smoothness due to the suppression of dendrite formation.

(Molten salt bath)
The molten salt forming the molten salt bath in the electrolytic cell is obtained by melting chloride. Preferably, the molten salt bath is made up of only molten chlorides as compounds. Examples of specific chlorides include MgCl ₂ , NaCl, KCl, CaCl ₂ , LiCl, BaCl ₂ and CsCl.

The molten salt bath preferably contains one or more chlorides, more preferably _two or _more chlorides selected from the group consisting of MgCl2, NaCl, KCl, CaCl2, LiCl, _BaCl2 and CsCl. The molten salt bath preferably contains one or more, two or more, or three or more chlorides selected from the group consisting of MgCl ₂ , NaCl, KCl, CaCl ₂ and LiCl. Moreover, the molten salt bath preferably contains one or more, two or more, or three or more chlorides selected from the group consisting of MgCl ₂ , NaCl, KCl and CaCl ₂ . Specific examples of such preferred chlorides include NaCl-KCl-MgCl ₂ , LiCl-KCl-MgCl ₂ , NaCl-KCl-CaCl ₂ , LiCl-KCl-CaCl ₂ , NaCl-LiCl-KCl-MgCl ₂ , NaCl- KCl--LiCl--CaCl ₂ and the like are exemplified. By containing the above-described chlorides, the molten salt bath can be kept in a good molten state even at a relatively low temperature, so that the aforementioned low temperature range of the molten salt bath in the electrodeposition process can be easily achieved.

Magnesium ion molarity, sodium ion molarity, potassium ion molarity, calcium ion molarity, lithium ion molarity, barium ion molarity and The proportion of the total molar concentration of cesium ions is preferably 80% or more, more preferably 90% or more. However, considering the operating temperature and the like, the specific type and content of the chloride can be appropriately determined. The molar concentration of each metal ion is calculated by ICP emission spectrometry and atomic absorption spectrometry.

It is desirable that the molten salt bath does not contain fluoride ions. Components of the molten salt bath often remain on the surface of the titanium foil obtained by peeling off the metallic titanium deposited on the cathode in the electrodeposition process. Cleaning such as water washing may be performed. At this time, if fluoride is contained in the components of the molten salt bath remaining on the surface of the titanium foil, harmful hydrogen fluoride or hydrofluoric acid is generated upon contact with water. Further, when the molten salt bath is formed by dissolving lithium fluoride, since lithium fluoride exhibits poor solubility in water, a large amount of water is required to remove it from the titanium foil by washing with water. . In order to reduce the burden on workers and the environment, it is preferable to use a molten salt bath that does not contain fluoride ions.

In addition, the molten salt bath contains titanium ions. In order to include titanium ions in the molten salt bath, the titanium raw material must be dissolved in advance in the molten salt bath before the electrodeposition step, and/or, as described later, before the electrodeposition step or in the electrodeposition step. During the time it is possible to dissolve the Ti-containing anode.

When the titanium raw material is preliminarily dissolved in the molten salt bath, more specifically, the titanium raw material includes titanium chloride and/or low-purity titanium containing impurities such as titanium scrap and titanium sponge. Among these, low-purity titanium containing impurities may contain relatively large amounts of Fe and O as impurities, for example. When titanium scrap or titanium sponge is used as a raw material for titanium, they are brought into contact with TiCl ₄ to produce low-grade titanium chloride such as titanium dichloride (TiCl ₂ ) and/or titanium trichloride (TiCl ₃ ). can be dissolved to form a molten salt bath containing titanium ions. Here, since the titanium raw material is dissolved in the molten salt bath and then metallic titanium is deposited on the cathode, even if the titanium raw material contains a relatively large amount of impurities, contamination of the metallic titanium can be suppressed.

(Electrolyzer)
Various electrolytic devices can be used in the present invention. As an example, the electrolytic device 1 shown in FIG. and a power source 4 connected to the anode 3a and the cathode 3b to energize the anode 3a and the cathode 3b. Although illustration is omitted, the electrolytic cell 2 is normally partially openable, and the electrode 3 can be arranged in the electrolytic cell 2 using the opening. On the other hand, it is also possible to seal the opening, so that it is possible to prevent air from entering the electrolytic cell 2 from the external environment while the electrode 3 is being energized. In the anodic dissolution process and/or the electrodeposition process, the inside of the electrolytic cell 2 may be maintained in a reduced pressure atmosphere or an inert gas atmosphere such as argon gas.

Here, of the anode 3a and the cathode 3b to be immersed in the molten salt bath Bf in the electrolytic bath 2, the anode 3a preferably contains Ti. The shape of the anode 3a can be various shapes such as sheet-like, cylindrical, columnar, plate-like, massive, powdery, granular, fibrous, or briquette-like. Specifically, sponge titanium, titanium scrap, titanium rod material and/or titanium plate material can be used as the anode 3a. Further, as the anode 3a, concretely sponge titanium and/or titanium scrap can be used. When titanium sponge is used as the anode 3a, a block of titanium sponge is placed in a cage made of Ni or the like, and the cage is energized. Since Ni has a lower ionization tendency than Ti, only titanium sponge can be eluted as the anode 3a without eluting Ni. In this case, the above cage is also included as part of the anode 3a, and the anode 3a contains Ti and Ni. In the anode 3a including the cage and its contents (sponge titanium, etc.), only the contents containing Ti are consumed during the anode dissolution process and the electrodeposition process, and the cage is not consumed in many cases. Further, as described above, a briquette-like material can be used as the anode 3a. When the briquette is used, the anode can be constructed without using the basket made of Ni or the like.

Also, here, the material of the cathode 3b is not particularly limited as long as Ti is electrodeposited. In some cases, the cathode 3b contains Mo, W, Ta, Nb, or any one of their alloys on the electrolytic surface on which metallic titanium is to be electrodeposited. Among them, as the cathode 3b, at least the electrolytic surface preferably contains 90% by mass or more, more preferably 99.9% by mass or more of Mo. Since Mo is less likely to dissolve into Ti at 600° C. or less, the electrolytic surface of the cathode 3b containing 90% by mass or more of Mo does not adhere to the metallic titanium deposited thereon, and the metallic titanium can be easily peeled off. , contamination of impurities such as Mo into metallic titanium is suppressed.

When the cathode 3b has a plurality of layers made of different materials, it is possible to form an electrolytic surface containing 90% by mass or more of Mo on at least the surface layer of the layers by coating the surface of the cathode. At least the electrolytic surface of the cathode 3b may contain less than 10% by mass of impurities other than Mo, such as Ti. When the cathode 3b is used repeatedly, the cathode 3b may contain Ti to some extent. In addition, not only the electrolytic surface of the cathode 3b but also the entire surface may be composed of Mo of 90% by mass or more.

The anode (the content of the cage, if it contains the cage described above) and the cathode can each be, for example, substantially rod-shaped, band-shaped, plate-shaped, cylindrical or other column-shaped, or block-shaped. In particular, as illustrated in FIG. 2, it is preferable that at least a part of the electrolytic surface on which metallic titanium is electrodeposited on the cathode 33b has a curved surface shape. However, the anode and cathode may each be plate-shaped. As for the cathode, a plate-like one can be preferably used in some cases. The electrolytic device 31 shown in FIG. 2 has substantially the same configuration as the electrolytic device 1 shown in FIG. and a cylindrical anode 33a surrounding the cathode 33b. When both the surface of the anode 33a and the surface of the cathode 33b are curved in this way, it is easy to keep the distance between the electrodes constant even if the cathode 33b is configured to be movable. Metal titanium can be deposited more uniformly. From this point of view, the surface of the anode 33a and the opposing surface of the cathode 33b preferably have similar shapes.

Another electrolytic device 11 is shown in FIG. The electrolytic apparatus 11 of FIG. 3 has a cylindrical or columnar cathode 13b as a so-called cathode drum placed in a closed electrolytic bath 12 so that a part of the cylindrical surface is immersed in a molten salt bath Bf. It is arranged. Further, in the electrolysis apparatus 11, a plate-like anode 13a curving along the surface of a cylindrical cathode 13b is arranged in the molten salt bath Bf so as to face the surface of the cathode 13b.

In the electrolysis apparatus 11 of FIG. 3, while rotating the cylindrical or columnar cathode 13b around the central axis, a power source (not shown) energizes the electrodes 13, causing the circumference of the surface of the cathode 13b immersed in the molten salt bath Bf to rise. A part of the direction mainly facing the anode 13a becomes an electrolytic surface for depositing metallic titanium, and a foil-shaped metallic titanium Ts is deposited on the electrolytic surface. The portion of the surface of the cathode 13b that is immersed in the molten salt bath Bf changes as the cathode 13b rotates, and the electrolytic surface moves along the circumferential direction of the cathode 13b accordingly. Here, by winding up the metallic titanium Ts with a winding roll 15 further provided in the electrolytic device 11, a titanium foil as the long metallic titanium Ts is continuously produced while being peeled off from the surface of the cathode 13b. can be done.

Still another electrolytic device 21 shown in FIG. 4 has a strip-shaped cathode 23b as a cathode strip which is annularly wound between a pair of

rotating rolls

26a and 26b. Further, here, a plate-like anode 23a such as a flat plate is arranged in the molten salt bath Bf so as to face a portion of the cathode 23b in the molten salt bath Bf. Cathode 23b is positioned within closed electrolytic cell 22 such that a portion of its annularly wound, outwardly facing surface is immersed in molten salt bath Bf. In this electrolyzer 21, of the surface of the cathode 23b immersed in the molten salt bath Bf, the portion mainly facing the anode 23a serves as the electrolysis surface.

According to the electrolysis apparatus 21 of FIG. 4, for example, by rotating the rotating roll 26a on the drive side, the strip-shaped cathode 23b and its electrolytic surface move around the rotating

rolls

26a and 26b as shown by the arrows in FIG. At the same time, the rotating roll 26b on the driven side follows it and rotates. At this time, by energizing the electrode 23 from a power source (not shown), a foil-like metal titanium Ts is deposited on the electrolytic surface outside the cathode 23b. The metallic titanium Ts is peeled off from the surface of the cathode 23b and wound up by the winding roll 25, whereby a long titanium foil of the metallic titanium Ts can be continuously produced.

The distance between the electrodes between the anode and the cathode is not particularly limited, but it is preferably 0.5 cm or more and 10.0 cm or less on any of their facing surfaces. The inter-electrode distance between the anode and the cathode is preferably 1.0 cm or more and 8.0 cm or less, and more preferably 1.0 cm or more and 5.0 cm or less. By setting the distance between the electrodes to 0.5 cm or more, it is possible to suppress the occurrence of a short circuit between the electrodes. Further, by setting the inter-electrode distance to 10.0 cm or less, an unintended increase in voltage can be suppressed, and power consumption can be saved. This inter-electrode distance means the shortest distance between the surface of the anode and the surface of the cathode. When the anode has a cage made of Ni or the like as described above and sponge titanium or the like disposed therein, the distance between the electrodes is the shortest distance from the end of the cage to the surface of the cathode. .

In the following description, the electrolytic device 1 shown in FIG. 1 will be described as an example, but the

electrolytic devices

11, 21, and 31 shown in FIGS. 2 to 4 can be used in substantially the same manner.

(anodic dissolution process)
If necessary, before the electrodeposition step, an anodic dissolution step of consuming the Ti-containing anode 3a and supplying titanium ions to the molten salt bath Bf can be performed. However, the anodic dissolution step may be omitted.

In the anodic dissolution step, in substantially the same manner as in general molten salt electrolysis, while maintaining the molten salt bath Bf at a predetermined temperature, an appropriate current of a large magnitude.
As a result, the Ti-containing anode 3a dissolves into the molten salt bath Bf, and titanium ions are present in the molten salt bath Bf. That is, here, the anode 3a functions like a so-called consumable electrode to supply titanium ions to the molten salt bath Bf.

The temperature of the molten salt bath Bf in the anode dissolution step can be 250° C. to 800° C. on the premise that it is in a molten state, and the current density of the cathode 3b is 0.01 A/cm ² to 2.00 A. / cm ² . Thereby, the melting of the anode 3a is carried out satisfactorily.
Here, the current density of the cathode 3b can be calculated by the formula: current density (A/cm ² )=current value (A)÷electrolysis area (cm ² ). Here, regarding the electrolytic area, for example, in the case of the cathode 3b having a cylindrical surface, based on the formula: electrolytic area (cm ² )=cathode immersion surface area=cathode diameter (cm)×π×cathode height (cm) calculate. Also, the current value is the average value of the current flowed during a predetermined period of time for obtaining the current density. For example, if a constant current is applied, the value of that current will be the current value. If the value of the current changes with the passage of time, for example, obtain the measured values of the current at equal time intervals during the energization, and obtain the above current value by "total measured values of the current ÷ the number of measurements". can be done. The current density of the cathode 3b can be calculated in the same manner in the electrodeposition step, which will be described later.

In addition, in the anodic dissolution process, after the supply of titanium ions to the molten salt bath Bf is completed, the cathode 3b can be replaced prior to the electrodeposition process. In the anodic dissolution step, a metal other than Ti may be deposited on the cathode 3b. Therefore, if the electrodeposition step is performed using the cathode 3b in this state, the purity of the metallic titanium obtained in the electrodeposition step may decrease. Concerned. In addition, there is a possibility that the metal titanium electrodeposited on the cathode 3b in the electrodeposition process may be alloyed, resulting in a decrease in peelability. Therefore, it is preferable to replace the cathode 3b after supplying titanium ions to the molten salt bath Bf in the anodic dissolution step.

(Electrodeposition process)
In the electrodeposition step, electricity is applied from the power supply 4 to the electrodes 3 including the anode 3a and the cathode 3b, whereby electrolysis is performed at the electrodes 3, and titanium ions in the molten salt bath Bf are deposited as metallic titanium on the cathode 3b. .

Here, the electrolysis is performed so that the ratio of the molar concentration (Mt) of titanium ions to the total molar concentration (Mm) of metal ions in the molten salt bath Bf (percentage of Mt/Mm) is maintained at 7% or more. I do. When the proportion of titanium ions in the molten salt bath Bf is less than 7%, titanium ions around the cathode 3b become deficient, resulting in a biased current distribution around the cathode 3b and dendrite formation in the metallic titanium on the cathode 3b. can be formed. The formation of dendrites itself is undesirable because it impairs the smoothness of the titanium foil obtained from the titanium metal on the cathode 3b, and also makes it difficult to remove the titanium metal from the cathode 3b. From this point of view, the proportion of titanium ions in the molten salt bath Bf is preferably maintained at 10% or more. The upper limit of the Mt/Mm percentage is not particularly limited, and the ratio of titanium ions can be changed as appropriate within a range in which the molten salt bath can be maintained.

The molar concentration of each metal ion, including titanium ions, in the molten salt bath Bf is determined by solidifying a molten salt sample taken from the molten salt bath and then analyzing the components of the sample by ICP emission spectrometry and atomic absorption spectrometry. Calculated by If the molten salt bath contained MgCl ₂ , NaCl, KCl, CaCl ₂ , LiCl, TiCl ₂ and TiCl ₃ , then the sum of the molar concentrations of metal ions (Mm) would be the molar concentration of magnesium ions, sodium ions , the molar concentration of potassium ions, the molar concentration of calcium ions, the molar concentration of lithium ions, and the molar concentration of titanium ions (Mt). The ratio of titanium ions can be calculated by dividing the molar concentration (Mt) of titanium ions by the total molar concentration (Mm) of the metal ions and expressing it as a percentage.

During the electrodeposition process, titanium ions in the molten salt bath Bf are consumed as metal titanium is electrodeposited on the cathode 3b. On the other hand, in order to maintain the high concentration of titanium ions in the molten salt bath Bf as described above, it is preferable to use the anode 3a containing Ti in the electrodeposition step. In this case, as the electrolysis progresses, the anode 3a is consumed, and the Ti contained therein becomes titanium ions and is supplied into the molten salt bath Bf. This makes it easier to maintain the titanium ions in the molten salt bath Bf at a predetermined ratio.

In addition, the temperature of the molten salt bath Bf in the electrodeposition step is maintained at 510°C or lower, preferably 500°C or lower, more preferably 480°C or lower. If the temperature of the molten salt bath Bf is too high, the crystal grains of the metallic titanium electrodeposited on the cathode 3b are likely to coarsen, and dendrite growth may proceed. If the molten salt forming the molten salt bath Bf can be maintained in a molten state and electrolysis using the molten salt bath Bf is possible, the temperature of the molten salt bath Bf can be sufficiently lowered.

Further, when the electrode 3 is energized, the current density is 0.10 A/cm ² or more and 1.0 A/cm ² or less, and further 0.10 A/cm ² or more and 0.50 A/cm ² or less. more preferably 0.20 A/cm ² or more and 0.50 A/cm ² or less. By setting the current density to such a relatively high value, metallic titanium is electrodeposited on the cathode 3b in a short period of time. Moreover, even with the high current density as described above, in this embodiment, it is possible to easily separate the metal titanium from the cathode 3b. When the current density is less than 0.10 A/cm ² , the amount of metallic titanium deposited on the cathode 3b per unit time decreases, resulting in a decrease in the efficiency of titanium foil production. If the current density is higher than 1.0 A/cm ² , there is a possibility that the metallic titanium cannot be easily peeled off from the cathode 3b. When the current changes during electrolysis in the electrodeposition step, the above current density means an average value from the start to the end of electrolysis.

In the electrodeposition step of this embodiment, the continuous stop time of energization to the electrode 3 (that is, the time during which current does not flow continuously) is set to less than 1.0 second, and the continuous stop time of energization to the electrode 3 is sufficiently long. Either shorten it or keep the current flowing without stopping the current. Depending on the embodiment, the current may continue to flow without stopping the energization of the electrode 3 . If the continuous discontinuation time of energization to the electrode 3 is set to less than 1.0 second, the amount of metallic titanium deposited on the cathode 3b per unit time can be favorably increased. Even if a continuous stop time of energization is provided, for example, the ratio of the total continuous stop time to the electrodeposition time for electrolytically depositing metallic titanium on the electrolytic surface of the cathode is 20% or less. In addition, it is preferable to make the continuous stop time extremely short with respect to the energization time. It should be noted that the discontinuation of energization as used herein means discontinuing the forward current for electrolysis for electrodepositing metallic titanium on the cathode. Therefore, even if the reverse current flows during at least a part of the energization stop time, the forward current does not flow during that time, and thus the energization is stopped.
It is particularly preferable to use a constant current that does not stop electrifying the electrode 3 and does not change the current value or current density too much. Also in this case, the current density is preferably within the range described above.

In addition to the conditions described above, the time for electrodeposition of metallic titanium on the electrolytic surface of the cathode is set to 120 minutes or less. As a result, the production efficiency of the titanium foil can be improved, and the formation of dendrites in the metal titanium on the cathode 3b can be suppressed, so that the smoothness of the titanium foil can be improved. In the electrolysis device 11 shown in FIG. 3 and the electrolysis device 21 shown in FIG. 4, the electrolytic surfaces of the

cathodes

13b and 23b move. In this case, the electrolysis time of the titanium metal at the predetermined surface position serving as the electrolytic surface of the

cathodes

13b and 23b may be 120 minutes or less. The time after deposition begins is not included in the deposition time at the given surface location. Electrodeposition time of metallic titanium onto the electrolytic surface of the cathode is preferably 80 minutes or less, more preferably 60 minutes or less.

By adjusting various conditions as described above, the metal titanium electrodeposited on the cathode 3b in the electrodeposition step can be easily separated from the cathode 3b. The peeling here means physically peeling off the metal titanium from the cathode 3b without using leaching or the like.

For example, even if the electrolytic surface on the surface of the cathode 3b is set to 78 cm ² or more and relatively large-sized foil-shaped titanium metal is deposited, the metal titanium can be peeled off from the surface of the cathode 3b satisfactorily. obtain. Furthermore, even if the electrolytic surface of the surface of the cathode 3b is set to 500 cm ² or more, good peelability may be ensured in some cases.

The area of the front and back surfaces of the titanium foil obtained by peeling off the cathode 3b may be 78 cm ² or more, and further 500 cm ² or more. The average thickness of the titanium foil is preferably 10 μm to 1000 μm, more preferably 50 μm to 500 μm. To calculate the average thickness of the titanium foil, observe the cross section in the thickness direction along one side of the foil with an optical microscope at a magnification of 100, obtain the thickness at 10 points, and take the average value as the average thickness of the titanium foil. . Incidentally, the titanium metal on the cathode 3b tends to become thicker as the electrodeposition time is lengthened.

Further, here, since the titanium foil is produced by depositing metallic titanium on the cathode 3b by electrolysis as described above, the contents of oxygen and iron that can be contained in this titanium foil are the same as those of the titanium of the anode 3a and the like. It can be less than what the raw material can contain. For example, in the titanium foil produced according to this embodiment, the oxygen content can be reduced to 400 mass ppm or less. The oxygen content can be measured by an inert gas fusion method.

Next, the method for producing a titanium foil of the present invention was experimentally carried out, and the effect was confirmed, which will be explained below. However, the description herein is for illustrative purposes only and is not intended to be limiting.

Using the electrolytic apparatus shown in FIG. 2, an electric current was applied to the anode and the cathode, and electrolysis was performed in a molten salt bath. The dimensions and shape of the bath portion of the electrolytic device were 500 mmΦ×800 mm depth. The molten salt bath uses lower titanium chloride (titanium dichloride and titanium trichloride) as a titanium raw material, and the ratio of the molar concentration of titanium ions to the total molar concentration of metal ions in the molten salt bath is 6 to 10%. The values shown in Table ₁ were maintained, and the balance was NaCl, KCl and MgCl2. A JIS class 2 titanium plate (thickness 6 mm) was used as the anode. The cathode had a molybdenum plate with a thickness of 0.2 mm and a cylindrical shape with an inner diameter (diameter) of 96 mm. In Example 5, the material of the outermost surface of the cathode was changed from molybdenum to tantalum. The cathode was placed inside the cylindrical anode in the electrolytic cell of the electrolyzer. Here, the height direction of the anode and the cathode was set substantially parallel to the depth direction of the molten salt bath, and the central axis of the anode and the central axis of the cathode were positioned at the same position. As a result, the inter-electrode distance was constant over the entire circumference of the anode and cathode.

The conditions were changed as shown in Table 1, and the electrodeposition process was carried out for Examples 1 to 6 and Comparative Examples 1 to 4 to deposit relatively large foil-shaped metallic titanium on the surface of the cathode. During the electrodeposition process, in Examples 1 to 6 and Comparative Examples 1, 2 and 4, a constant current was passed through the electrode without stopping the current supply. On the other hand, in Comparative Example 3, a pulse current was applied, the current density when the pulse current was ON was 0.18 A/cm ² , the ON time was 1.5 seconds, and the current density was 0 (no current flow) when the pulse current was OFF. was 1.5 seconds, and the average current density was 0.09 A/cm ² . The "electrodeposition time" in Comparative Example 3 is the total from the start to the end of the electrodeposition, so it includes the OFF time. Further, the temperature of the molten salt bath was maintained at the values shown in Table 1 during the electrodeposition process.

After the electrodeposition process, the cathode on which metallic titanium was electrodeposited was pulled up from the molten salt bath. The metallic titanium electrodeposited on the cathode had the appearance shown in FIG. 5 in Example 1 and the appearance shown in FIG. 6 in Comparative Example 2. FIG.

After that, the metal titanium on the cathode was washed with water to remove the molten salt adhering to its surface. Then, a peel strength test, which will be described later, was carried out. Table 1 shows the ease of peeling at that time.

The peelability was determined by a peel strength test to determine whether it was "○", "△" or "×". "○" means that the peel strength was 0.2 N / mm or less, "△" means that the peel strength was more than 0.2 N / mm and 1.0 N / mm or less, "× ” means that the peel strength was greater than 1.0 N/mm. The ◯ and △ evaluations are acceptable, and the ◯ evaluation means better. x evaluation is unacceptable.

The peel strength test was performed as shown in Fig. 7. First, a sample 103 of 70 mm×10 mm is cut from the cathode and metallic titanium electrodeposited on the cathode with a cutter or the like. Next, the sample 103 is placed on the stage 111 of a 90° peeling tester, 10 mm of the titanium metal 101 is peeled off from the cathode 102 at one end of the sample 103, and the peeled portion of the titanium metal 101 is clamped with 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 on the side opposite to the one end are fixed with a fixing jig 112 . Then, as indicated by the arrow in FIG. 7, the chuck is lifted vertically upward at 20 mm/sec, and the stage 111 is moved horizontally at 20 mm/sec. From the load measured at this time, the peel strength is determined using the formula: peel strength=average load (N)/width of metal titanium foil (mm). Here, the average load means the average value of the load acting on the chuck in the vertical direction while the stage 111 is horizontally displaced by 20 mm from 5 mm to 25 mm. The width of the titanium metal means the width of the titanium metal 101 on the stage 111 along the direction perpendicular to the moving direction of the stage 111 (the depth direction of the paper surface of FIG. 7). The angle formed by the direction in which the metal titanium 101 was peeled off and the surface of the cathode 102 was 90° measured from the surface of the cathode. As the peel tester, a digital force gauge ZTS-200N (measurable load: 200 N) manufactured by Imada Co., Ltd. and a slide table P90-200N for 90 degree peel test were used.

Moreover, in Table 1, the dendrite number density is obtained by measuring the number of dendrites per unit area. Specifically, using a scanning electron microscope (SEM), the number of dendrites present on the surface of the titanium metal on the cathode was measured for each of five fields of view with a magnification of 50 times, and the number of dendrites in each of these five fields of view. was converted into the number per 1 cm ² (rounded off to the first decimal place). “◯” indicates a dendrite number density of less than 1/cm ² , “Δ” indicates a dendrite number density of 1/cm ² or more and less than 2/cm ² , and “×” indicates a dendrite number density. is 2 pieces/cm ² or more. The ◯ and △ evaluations are acceptable, and the ◯ evaluation means better. x evaluation is unacceptable.

Also, in Table 1, the amount of metallic titanium deposited was evaluated from the result of converting the thickness of the metallic titanium electrodeposited on the cathode per 60 minutes of the electrodeposition time. “◯” means that the thickness of the metallic titanium per 60 minutes of electrodeposition time was 80 μm or more, and “Δ” means that the thickness of the metallic titanium per 60 minutes of electrodeposition time was 60 μm or more and less than 80 μm. "x" means that the thickness of metallic titanium per 60 minutes of electrodeposition time was less than 60 µm. The ◯ and △ evaluations are acceptable, and the ◯ evaluation means better. x evaluation is unacceptable.

From Table 1, it can be seen that in Examples 1 to 6, the metallic titanium was easily separated from the cathode, and the metallic titanium was deposited sufficiently thickly per unit of electrodeposition time. On the other hand, in Comparative Examples 1 to 4, there were cases in which the separation of the metallic titanium from the cathode was not easy, and cases in which the thickness of the metallic titanium deposited per unit electrodeposition time was thin. In addition, it can be said that Examples 1 to 6 generally suppressed the formation of dendrites on the cathode.

Therefore, according to the present invention, it was found that the amount of titanium metal electrodeposited per unit time can be increased without greatly reducing the ease of stripping of the titanium metal electrodeposited on the cathode.

1, 11, 21, 31

electrolyzer

2, 12, 22, 32

electrolytic cell

3, 13, 23, 33

electrode

3a, 13a, 23a,

33a anode

3b, 13b, 23b,

33b cathode

4, 34

power source

15, 25 winding Take-up

rolls

26a, 26b Rotation roll 101 Metal titanium 102 Cathode 103 Sample 111 Stage 112 Fixing jig Bf Molten salt bath Ts Metal titanium

Claims

A method of manufacturing a titanium foil, comprising:
Electrolysis is performed with electrodes including an anode and a cathode using a molten salt bath in which chloride containing titanium ions is melted, and an electrodeposition step of depositing metallic titanium on the electrolytic surface of the cathode,
In the electrodeposition step, the ratio of the molar concentration of titanium ions to the total molar concentration of metal ions in the molten salt bath is maintained at 7% or more, the temperature of the molten salt bath is maintained at 510° C. or less, and the electrodes are energized. In this case, the continuous stop time of energization is set to less than 1.0 second, the current density is set to 0.10 A/cm 2 or more and 1.0 A/cm 2 or less, and the time to deposit metallic titanium on the electrolytic surface of the cathode is 120 minutes. A method for manufacturing a titanium foil as follows.
the anode contains Ti,
2. The method for producing a titanium foil according to claim 1, wherein said anode is consumed in the electrodeposition step.
The method for producing a titanium foil according to claim 1 or 2, wherein the chloride contains titanium dichloride and/or titanium trichloride.
The titanium foil according to any one of claims 1 to 3, wherein in the electrodeposition step, the ratio of the molar concentration of titanium ions to the total molar concentration of metal ions in the molten salt bath is maintained at 10% or more. Production method.
The method for producing a titanium foil according to any one of claims 1 to 4, wherein the temperature of the molten salt bath is maintained at 500°C or less in the electrodeposition step.
The method for producing a titanium foil according to any one of claims 1 to 5, wherein in the electrodeposition step, the current density is 0.20 A/cm 2 or more and 0.50 A/cm 2 or less.
The method for producing a titanium foil according to any one of claims 1 to 6, wherein the molten salt bath does not contain fluoride ions.
The method for producing a titanium foil according to any one of claims 1 to 7, wherein the surface of the anode and the facing surface of the cathode have shapes similar to each other.
The method for producing a titanium foil according to any one of claims 1 to 8, wherein the inter-electrode distance between the anode and the cathode is 0.5 cm or more and 10.0 cm or less.