Patent Application
20240084469
The present invention relates to a method for producing a titanium foil by performing electrolysis with an electrode including an anode and a cathode using a molten salt bath to deposit metal titanium.
Metal titanium is generally produced by a Kroll process suitable for mass production. In the production of metal titanium, titanium oxide contained in titanium ores is firstly allowed to react with chlorine in the presence of carbon sources such as cokes to produce titanium tetrachloride. The titanium tetrachloride is then reduced with metal magnesium to obtain sponge-shaped metal titanium, so-called sponge titanium.
Here, in order to produce metal titanium in the form of a foil having a relatively lower thickness using the above sponge titanium as a main raw material, the sponge titanium is generally molten and cast into a titanium ingot or titanium slab, and then subjected to forging, rolling or other processing. With such a process requiring melting and processing, it cannot be said that metal titanium having a foil shape can be produced efficiently and at low cost.
Under such circumstances, the use of molten salt electrolysis for depositing metal titanium with a molten salt bath in place of the above melting and processing is being studied in terms of reducing energy consumption and cost in the producing process.
Techniques relating to molten salt electrolysis are described in Patent Literatures 1 to 3, for example.
Patent Literature 1 describes “a method for producing high-purity titanium by a molten salt electrolysis method, wherein the electrolysis is performed in a chloride bath having a sodium ion content of 10 wt % or less as a bath composition”, and it also discloses that “when performing the electrolysis using an electrolytic bath having a low melting point of 400° C. or less, the electrolysis temperature should be in the range of 550 to 900° C.”.
The Patent Literature 1 teaches that:
Patent Literature 2 discloses “a method for producing titanium characterized by applying a voltage between a container filled with raw material titanium as an anode and an electrolytic container as a cathode when electrolytically refining the raw material titanium by molten salt electrolysis”. More particularly, it discloses:
Patent Literature 3 proposes:
In the method described in Patent Literature 3, the metal titanium is thinly electrodeposited onto the cathode, and the metal titanium can be relatively easily peeled off from the cathode. It is, therefore, considered that a thin titanium foil can be obtained by this method.
However, in the method described in Patent Literature 3, an intermittent current such as a pulse current may be applied when conducting the current to the electrodes. In this case, it takes a certain period of time to electrodeposit the metal titanium onto the cathode due to the stop time of the current conduction by the pulse current. Therefore, there is still room for improving an efficiency of the production of the titanium foil.
An object of the present invention is to provide a method for producing a titanium foil, which can increase an amount of metal titanium electrodeposited per unit time without significantly reducing an easy peelability of the metal titanium electrodeposited onto a cathode from the cathode.
It is considered that the electrodeposition of metal titanium onto the cathode is 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 current is conducted to the electrodes. On the other hand, there is a concern that these factors may reduce the easy peelability of the metal titanium from the cathode.
As a result of intensive studies, the present inventors have newly found that an appropriate combination of the above conditions. This can reduce deterioration of the easy peelability of the metal titanium even if the stop time of the current conduction to the electrodes is sufficiently shortened or even if the current conduction is not stopped. Further, in this case, the stop time of the current conduction to the electrodes is shorter or the current conduction is not stopped, an increased amount of titanium metal deposited per unit time can be achieved.
A method for producing a titanium foil according to the present invention comprises an electrodeposition step of performing electrolysis with electrodes including an anode and a cathode using a molten salt bath comprising titanium ions and having at least one molten chloride to deposit metal titanium onto an electrolytic surface of the cathode, wherein the electrodeposition step comprises maintaining a ratio of a molar concentration of titanium ions to the total molar concentration of metal ions in the molten salt bath at 7% or more, and maintaining a temperature of the molten salt bath at 510° C. or less, and conducing a current to the electrodes under conditions where a continuous stop time of current conduction is less than 1.0 second, a current density is 0.10 A/cm2 or more and 1.0 A/cm2 or less, and a time for electrodepositing the metal titanium onto the electrolytic surface of the cathode is 120 minutes or less.
In the method for producing the titanium foil described above, it is preferable that the anode comprises Ti and the anode is consumed in the electrodeposition step.
Also, in the method for producing the titanium foil described above, it is preferable that the chloride comprises titanium dichloride and/or titanium trichloride.
In the electrodeposition step, it is preferable that 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.
Also, in the electrodeposition step, it is preferable that the temperature of the molten salt bath is maintained at 500° C. or less.
Also, in the electrodeposition step, it is preferable that the current density is 0.20 A/cm2 or more and 0.50 A/cm2 or less.
According to the method for producing the titanium foil of the present invention, it is possible to increase an amount of metal titanium electrodeposited per unit time without significantly reducing an easy peelability of the metal titanium electrodeposited onto a cathode from the cathode.
Embodiments of the present invention will be described below in detail.
A method for producing a titanium foil according to an embodiment of the present invention includes an electrodeposition step of performing electrolysis with electrodes including an anode and a cathode using a molten salt bath containing titanium ions and having at least one molten chloride to deposit metal titanium onto an electrolytic surface of the cathode. The electrodeposition step includes maintaining a ratio of a molar concentration of titanium ions to the total molar concentration of metal ions in the molten salt bath at 7% or more, and maintaining a temperature of the molten salt bath at 510° C. or less. The electrodeposition step also includes conducing a current to the electrodes under conditions where a continuous stop time of current conduction is less than 1.0 second, a current density is 0.10 A/cm2 or more and 1.0 A/cm2 or less. A time for electrodepositing the metal titanium onto the electrolytic surface of the cathode is 120 minutes or less. In the descriptions 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 a “ratio of titanium ions”.
In such a type of molten salt electrolysis, an increase in the concentration of titanium ions in the molten salt bath, an increase in the temperature of the molten salt bath, and an increase in the current density during current conduction to the electrodes, tend to accelerate the electrodeposition and increase an amount of metal titanium deposited per unit time. However, if all of them are carried out, it will be difficult to peel off the metal titanium electrodeposited onto the cathode from the cathode. In particular, it will be difficult to physically peel off the electrodeposited metal titanium from the electrode.
In contrast, according to this embodiment, the concentration of titanium ions in the molten salt bath is increased to 7% or more, and the current density is 0.10 A/cm2 or more and 1.0 A/cm2 or less, which is higher to some extent, in the electrodeposition step. On the other hand, the temperature of the molten salt bath is a relatively low temperature of 510° C. or less. According to these conditions, it is possible to easily peel off the metal titanium from the cathode while increasing the amount of the metal titanium electrodeposited per unit time. Especially, physical releasing such as peeling of the electrodeposited metal titanium from the electrode can be easily carried out.
Although the reason is not clear, it can be presumed as follows. By increasing the ratio of titanium ions in the molten salt bath as described above, the titanium ions will be difficult to be depleted in the vicinity of the cathode, even if the titanium ions are deposited as metal titanium onto the cathode by current conduction to the electrodes. It is believed that this suppresses a current bias in the vicinity of the cathode, suppresses the deposition of dendrite-like metal titanium due to the current bias, and deposits the metal titanium in the form of a foil onto the cathode. In addition, the electric power is not concentrated due to the formation of dendrites, so that an increase in the temperature on the cathode surface can be suppressed. Furthermore, since the temperature of the molten salt bath is maintained at the appropriately low level, the increase in the temperature on the cathode surface is appropriately suppressed. As a result, interdiffusion of the metal between the cathode and metal titanium deposited thereon is suppressed. Therefore, it is believed that even if the stop time of the current conduction to the electrodes is sufficiently short, such as the continuous stop time of current conduction of less than 1.0 second, or even if the current is constant without stopping the current conduction, the electrodeposited metal titanium will be able to be easily peeled off from the cathode. However, the present invention is not limited to the above theory.
Also, in this embodiment, the continuous stop time of current conduction is less than 1.0 second, so that the amount of metal titanium electrodeposited per unit time can be increased, thereby improving a production efficiency of the titanium foil. In addition, the titanium foil thus produced has improved smoothness due to the suppression of dendrite formation.
Molten salts for forming the molten salt bath in the electrolytic bath are molten chlorides. Preferably, the molten salt bath is made by melting only chlorides as compounds. Specific chlorides include, for example, MgCl2, NaCl, KCl, CaCl2, LiCl, BaCl2, and CsCl.
The molten salt bath preferably contains one or more chlorides, or 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 MgCl2, NaCl, KCl, CaCl2 and LiCl. The molten salt bath preferably contains one or more, two or more, or three or more chlorides selected from the group consisting of MgCl2, NaCl, KCl and CaCl2. Specific examples of such preferred chlorides include NaCl—KCl—MgCl2, LiCl—KCl—MgCl2, NaCl—KCl—CaCl2), LiCl—KCl—CaCl2), NaCl—LiCl—KCl—MgCl2, NaCl—KCl—LiCl—CaCl2) and the like. The containing of the above chlorides can allow a molten state of the molten salt bath to be satisfactorily maintained even at a low temperature to some extent, so that the above-mentioned low temperature range of the molten salt bath in the electrodeposition step can be easily achieved.
A ratio of the total molar concentration of magnesium ions, sodium ions, potassium ions, calcium ions, lithium ions, barium ions, and cesium ions to the total molar concentration of metal ions in the molten salt bath is preferably 80% or more, and more preferably 90% or more. However, in view of the operating temperature and the like, the specific types and contents of the chlorides can be determined as needed. 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 metal titanium deposited on the cathode in the electrodeposition step, and washing such as water washing may be performed in order to remove those components. In this case, if fluorides are 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, the lithium fluoride exhibits poor solubility in water, so that 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.
The molten salt bath also contains titanium ions. In order to contain the titanium ions in the molten salt bath, a titanium raw material may be previously dissolved in the molten salt bath prior to the electrodeposition step, and/or, as described later, an anode containing Ti may be dissolved prior to the electrodeposition step or during the electrodeposition step.
When the titanium raw material is previously dissolved in the molten salt bath, more specific examples of the titanium raw material include titanium chloride and/or low-purity titanium containing impurities such as titanium scrap and titanium sponge. Among these, the low-purity titanium containing impurities may contain relatively large amounts of Fe and O as impurities, for example. When the titanium scrap or titanium sponge is used as the titanium raw material, they can be brought into contact with TiCl4 to generate lower titanium chloride such as titanium dichloride (TiCl2) and/or titanium trichloride (TiCl3), which is then dissolved to form the molten salt bath containing the titanium ions. Here, since the titanium raw material is dissolved in the molten salt bath and the metal titanium is then deposited onto the cathode, any contamination of impurities into the metal titanium can be suppressed, even if the titanium raw material contains relatively large amounts of impurities.
Various electrolytic devices can be used for the present invention. As an example, an electrolytic device 1 shown in
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 anode 3a can have various shapes such as a sheet shape, cylindrical shape, pillar shape, plate shape, massive shape, powdery shape, granular shape, fibrous shape, or briquette shape. 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, the sponge titanium and/or titanium scrap can be specifically used. When the sponge titanium is used as the anode 3a, massive sponge titanium may be placed in a cage made of Ni or the like, and a current may be conducted through the cage. Since Ni has a lower ionization tendency than that of Ti, only sponge titanium can be eluted as the anode 3a without eluting Ni. In this case, the above cage is also included in a 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 step or the electrodeposition step, and the cage is not consumed in many cases. Further, as described above, the briquette-shaped material can be used as the anode 3a. When the briquette shape is used, the anode can be constructed without using the basket made of Ni or the like.
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 of their alloys on the electrolytic surface on which metal titanium is to be electrodeposited. Among them, as the cathode 3b, at least the electrolytic surface preferably contains 90% by mass or more of Mo, and more preferably 99.9% by mass or more of Mo. Since Mo is difficult to be dissolved 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 metal titanium deposited thereon, so that the metal titanium can be easily peeled off, and any contamination of impurities such as Mo into metal titanium can be 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 a 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, and the impurities include Ti and the like. When the cathode 3b is repeatedly used, the cathode 3b may contain Ti to some extent. In addition, not only the electrolytic surface of the cathode 3b but also the entire of the cathode 3b may be composed of Mo of 90% by mass or more.
Each of the anode (the contents of the above cage if it is included) and the cathode can be, for example, generally rod shaped, strip shaped, plate shaped, or cylindrical or other pillar shaped, or massive shaped. In particular, as illustrated in
Another electrolytic device 11 is shown in
In the electrolytic device 11 of
Still another electrolytic device 21 shown in
According to the electrolytic device 21 of
Although the distance between the electrodes of 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 opposing surfaces. The distance between the electrodes of 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. The distance between the electrodes of 0.5 cm or more can lead to suppression of a short circuit generated between the electrodes. Further, the distance between the electrodes of 10.0 cm or less can lead to suppression of any unintended increase in voltage, and to saved power consumption. The distance between the electrodes means the shortest distance between the surface of the anode and the surface of the cathode. When the anode has the cage made of Ni or the like as described above and the sponge titanium or the like disposed therein, it is to understand that the distance between the electrodes is the shortest distance from the end of the cage to the surface of the cathode.
In the following descriptions, the electrolytic device 1 shown in
Prior to an electrodeposition step, an anode dissolution step can optionally be performed by consuming the Ti-containing anode 3a and feeding titanium ions to the molten salt bath Bf. However, the anode dissolution step may be omitted.
In the anode dissolution step, a current of an appropriate magnitude is allowed to flow between the anode 3a and the cathode 3b immersed in the molten salt bath Bf while maintaining the molten salt bath Bf at a predetermined temperature, in substantially the same manner as in general molten salt electrolysis.
As a result, the Ti-containing anode 3a is dissolved into the molten salt bath Bf, and titanium ions are present in the molten salt bath Bf. That is, here, the anode 3a functions to feed the titanium ions to the molten salt bath Bf, as in a so-called consumable electrode.
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/cm2 to 2.00 A/cm2. This allows the dissolution of the anode 3a to carried out satisfactorily.
Here, the current density of the cathode 3b can be calculated by the equation: current density (A/cm2)=current value (A)/electrolysis area (cm2). Here, for the cathode 3b having the cylindrical surface, for example, the electrolysis area is calculated based on the equation: electrolysis area (cm2)=cathode immersion surface area=cathode diameter (cm)×π×cathode height (cm). Also, the current value is an average value of the current allowed to flow during a predetermined period of time for obtaining the current density. For example, if a constant current is allowed to flow, the value of that current will be the above current value. If the value of the current changes over time, for example, the measured values of the current can be obtained at equal time intervals during the current conduction, and the above current value can be determined by “the total of the measured values of the current/the number of measurements”. The current density of the cathode 3b can be calculated in the same manner in the electrodeposition step, which will be described below.
In the anode dissolution step, the cathode 3b can be replaced after the feeding of titanium ions to the molten salt bath Bf is completed and prior to the electrodeposition step. In the anode dissolution step, a metal other than Ti may be deposited onto the cathode 3b. Therefore, if the electrodeposition step is performed using the cathode 3b in this state, the purity of the metal titanium obtained in the electrodeposition step may decrease. Also, there is a risk that the metal titanium electrodeposited onto the cathode 3b in the electrodeposition step may be alloyed, resulting in a decrease in peelability. Therefore, it is preferable to replace the cathode 3b after feeding the titanium ions to the molten salt bath Bf in the anode dissolution step.
In the electrodeposition step, the electrolysis is performed at the electrodes 3 by conducting the current from the power supply 4 to the electrodes 3 including the anode 3a and the cathode 3b, and the titanium ions in the molten salt bath Bf are deposited as metal titanium onto 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. If the ratio of the titanium ions in the molten salt bath Bf is less than 7%, the titanium ions around the cathode 3b become deficient, which may result in a biased current distribution around the cathode 3b and formation of dendrites in metal titanium on the cathode 3b. The formation of the dendrites themselves is undesirable because they impair the smoothness of the titanium foil obtained from the metal titanium on the cathode 3b, and also makes it difficult to peel off the metal titanium from the cathode 3b. From this point of view, the ratio of the titanium ions in the molten salt bath Bf is preferably maintained at 10% or more. The upper limit of the ratio Mt/Mm is not particularly limited, and the ratio of the titanium ions can be changed as appropriate in a range within 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 calculated by solidifying a molten salt sample taken from the molten salt bath and then analyzing components of the sample by ICP emission spectrometry and atomic absorption spectrometry. If the molten salt bath contains MgCl2, NaCl, KCl, CaCl2, LiCl, TiCl2 and TiCl3, the total of the molar concentrations of metal ions (Mm) is determined by adding the molar concentration of magnesium ions, the molar concentration of 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 the titanium ions can be calculated by dividing the molar concentration (Mt) of the titanium ions by the total molar concentration (Mm) of the metal ions and expressing it as a percentage.
During the electrodeposition step, the titanium ions in the molten salt bath Bf are consumed as metal titanium is electrodeposited onto 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 is converted to the titanium ions, which are fed into the molten salt bath Bf. This makes it easier to maintain the titanium ions in the molten salt bath Bf at the predetermined ratio.
The temperature of the molten salt bath Bf in the electrodeposition step is maintained at 510° C. or less, and preferably 500° C. or less, and more preferably 480° C. or less. If the temperature of the molten salt bath Bf is too high, crystal grains of the metal titanium electrodeposited onto the cathode 3b are likely to coarsen, and dendrite growth may proceed. If the molten salts 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 conducting the current to the electrodes 3, the current density is preferably 0.10 A/cm2 or more and 1.0 A/cm2 or less, and more preferably 0.10 A/cm2 or more and 0.50 A/cm2 or less, and even more preferably 0.20 A/cm2 or more and 0.50 A/cm2 or less. By setting the current density to such a relatively high value, the metal titanium is electrodeposited onto the cathode 3b in a short period of time. Moreover, even with the high current density as described above, in this embodiment, the metal titanium can be easily peeled off from the cathode 3b. If the current density is less than 0.10 A/cm2, an amount of metal titanium electrodeposited onto the cathode 3b per unit time decreases, resulting in a decrease in an efficiency of titanium foil production. If the current density is higher than 1.0 A/cm2, there is a risk that the metal titanium cannot be easily peeled off from the cathode 3b. It should be noted that when the current varies 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 according to this embodiment, the continuous stop time of current conduction to the electrodes 3 (that is, the time during which the current does not flow continuously) is set to less than 1.0 second to provide a sufficient short continuous stop time of current conduction to the electrodes 3, or the current continuously flows without stopping the current conduction. Depending on the embodiments, the current may continue to flow without stopping the current conduction to the electrodes 3. When the continuous stop time of the current conduction to the electrodes 3 is set to less than 1.0 second, the amount of the metal titanium electrodeposited onto the cathode 3b per unit time can be satisfactorily increased. Even if the continuous stop time of the current conduction is provided, the continuous stop time of the current conduction is preferably very shorter than the current conduction time, for example, the ratio of the total continuous stop time to the electrodeposition time for electrolytically depositing the metal titanium onto the electrolytic surface of the cathode is 20% or less. In addition, it should be noted that the stop of the current conduction as used herein means that the forward current for electrolysis for electrodepositing the metal titanium onto the cathode is stopped. Therefore, even if the reverse current flows during at least a part of the stop time of the current conduction, the forward current does not flow during that time, which thus corresponds to the stop of the current conduction.
Particularly preferably, the current conduction to the electrodes 3 is not stopped, and a constant current that does not significantly change the current value or current density is used. Also in this case, the current density is preferably in the range described above.
In addition to the conditions described above, the time for electrodepositing the metal titanium onto the electrolytic surface of the cathode is 120 minutes or less. This allows the production efficiency of the titanium foil to be improved, and the formation of dendrites in the metal titanium on the cathode 3b to be suppressed, so that the smoothness of the titanium foil can be improved. In the electrolytic device 11 shown in
By adjusting the various conditions as described above, the metal titanium electrodeposited onto the cathode 3b in the electrodeposition step can be easily peeled off from the cathode 3b. The peeling as used herein means that the metal titanium is physically peeled off 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 cm2 or more and a foil-shaped titanium metal having a relatively large size is deposited, the metal titanium can be satisfactorily peeled off from the surface of the cathode 3b. Furthermore, even if the electrolytic surface on the surface of the cathode 3b is set to 500 cm2 or more, good peelability may be ensured.
Each of surface areas of the front and back surfaces of the titanium foil obtained by peeling-off from the cathode 3b may be 78 cm2 or more, and even 500 cm2 or more. The titanium foil preferably has an average thickness of 10 μm to 1000 μm, and more preferably 50 μm to 500 μm. To calculate the average thickness of the titanium foil, a cross section in the thickness direction along one side of the foil is observed with an optical microscope at magnifications of 100, the thicknesses are determined at 10 points, and an average value thereof is determined to be the average thickness of the titanium foil. It should be noted that the titanium metal on the cathode 3b tends to become thicker as the electrodeposition time is longer.
Further, here, since the titanium foil is produced by depositing the metal titanium onto the cathode 3b by electrolysis as described above, the contents of oxygen and iron that can be contained in the titanium foil can be lower than those contained in the titanium raw material such as the anode 3a. For example, in the titanium foil produced according to this embodiment, the oxygen content can be reduced to 400 ppm by mass or less. The oxygen content can be measured by an inert gas fusion method.
Next, the method for producing the titanium foil according to the present invention was experimentally carried out, and effects thereof were confirmed as described below. However, descriptions herein are merely for illustration, and are not intended to be limited thereto.
Using the electrolytic device shown in
The conditions were changed as shown in Table 1, and the electrodeposition step was carried out for Examples 1 to 6 and Comparative Examples 1 to 4 to deposit relatively large foil-shaped metal titanium onto the surface of the cathode. During the electrodeposition step, a constant current was passed through the electrode without stopping the current conduction for Examples 1 to 6 and Comparative Examples 1, 2 and 4. On the other hand, for Comparative Example 3, a pulse current was applied, the current density when the pulse current was ON was 0.18 A/cm2, the ON time was 1.5 seconds, and the current density was zero when the current was OFF (no current flowed), the OFF time was 1.5 seconds, and the average current density was 0.09 A/cm2. 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 each value shown in Table 1 during the electrodeposition step.
After the electrodeposition step, the cathode on which metal titanium was electrodeposited was pulled up from the molten salt bath. The metal titanium electrodeposited onto the cathode had the appearance shown in
Subsequently, 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 conducted. Table 1 shows the easy peelability at that time.
The easy peelability was determined by the peel strength test to determine whether it was “circle”, “triangle” or “X”. The “circle” means that the peel strength was 0.2 N/mm or less, the “triangle” means that the peel strength was more than 0.2 N/mm and 1.0 N/mm or less, the “X” means that the peel strength was more than 1.0 N/mm. The evaluations as “circle” and “triangle” are acceptable, and the evaluation as “circle” means that the evaluation is better. The evaluation as “X” is unacceptable.
The peel strength test was conducted as shown in
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 at magnifications of 50, and an average value of the numbers of dendrites in these five fields of view was converted to the number per 1 cm2 (rounded off to the first decimal place). The “circle” means that the dendrite number density was less than 1/cm2, the “triangle” means that the dendrite number density was 1/cm2 or more and less than 2/cm2, and the “X” means that the dendrite number density was 2/cm2 or more. The evaluation as the “circle” and “triangle” are acceptable, and the evaluation as “circle” means that the evaluation is better, and the evaluation as “X” is unacceptable.
In Table 1, the amount of metal titanium electrodeposited was evaluated from the results obtained by converting the thickness of the metal titanium electrodeposited onto the cathode per 60 minutes of electrodeposition time. The “circle” means that the thickness of the metal titanium per 60 minutes of electrodeposition time was 80 μm or more, and the “triangle” means that the thickness of the metal titanium per 60 minutes of electrodeposition time was 60 μm or more and less than 80 μm, and the “X” means that the thickness of metal titanium per 60 minutes of electrodeposition time was less than 60 μm. The evaluation as the “circle” and “triangle” are acceptable, and the evaluation as “circle” means that the evaluation is better. The evaluation as “X” is unacceptable.
It is found from Table 1 that in Examples 1 to 6, the metal titanium was easily peeled off from the cathode, and the metal titanium was electrodeposited in a sufficiently high thickness per unit time of electrodeposition. On the other hand, in Comparative Examples 1 to 4, there were cases where the peeling of the metal titanium from the cathode was not easy, and cases where the thickness of the metal titanium electrodeposited per unit time of electrodeposition was thinner. Also, 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 metal titanium electrodeposited per unit time can be increased without greatly deteriorating the easy peelability of the metal titanium electrodeposited on the cathode.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-029246 | Feb 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/007403 | 2/22/2022 | WO |
