Method for manufacturing titanium electrodeposits

Abstract

To provide a method for producing electrodeposited titanium capable of producing a high purity metal titanium having very small aluminum content.SOLUTION: A method for producing electrodeposited titanium by electrolytic refining using a molten salt bath from raw materials containing titanium, aluminum, and oxygen is provided, the method comprising: an electrodeposition step for performing electrolytic refining 3 times or more such that a predetermined condition is satisfied by using an anode containing a crude titanium-based material having conductivity and a cathode where a purified titanium-based material with higher purity than the crude titanium-based material is deposited, and in the first electrolytic refining, the raw material is used as the crude titanium-based material, in the second and subsequent electrolytic refining, the purified titanium-based material deposited on the cathode in the previous electrolytic refining is used as a crude titanium-based material.SELECTED DRAWING: None

Description

[Technical Field] 【0001】 This invention relates to a method for producing titanium electrodeposits. [Background technology] 【0002】 Generally, metallic titanium is produced using the Kroll process, which involves reacting titanium ore with carbon and chlorine gas to produce titanium tetrachloride, and then reducing this titanium tetrachloride with metallic magnesium to obtain a sponge titanium ingot. However, this method requires numerous steps, including the use of titanium ore as a starting material, the chlorination and reduction processes, as well as the crushing of the sponge titanium ingot and the electrolysis of magnesium chloride produced as a by-product during reduction. 【0003】 In recent years, a smelting method other than the Kroll process has been known, which involves producing titanium alloys by electrolytic refining using a molten salt bath. For example, Patent Document 1 discloses a method of obtaining a conductive crude titanium-based material containing titanium, aluminum, and oxygen by heat-treating titanium ore containing titanium oxide, aluminum, and a separating agent such as calcium fluoride, and then electrolytically refining this crude titanium-based material to deposit a titanium-aluminum matrix alloy on the cathode. [Prior art documents] [Patent Documents] 【0004】 [Patent Document 1] Special Publication No. 2015-507696 [Overview of the Initiative] [Problems that the invention aims to solve] 【0005】 Incidentally, there is a demand for producing metallic titanium by electrolytic refining using a molten salt bath. While the above-mentioned Kroll process can produce high-purity metallic titanium, electrolytic refining using a molten salt bath, as described in Patent Document 1, has not succeeded in depositing extremely high-purity metallic titanium on the cathode. In fact, Patent Document 1 only describes depositing a titanium-aluminum matrix alloy on the cathode using a crude titanium-based material containing aluminum (see paragraph 0093). Therefore, if it were possible to obtain metallic titanium with a sufficiently low aluminum content, such as 1.0 ppm by mass or less, from a crude titanium-based material that inevitably contains aluminum, through electrolytic refining, it would be of great industrial significance. 【0006】 Therefore, in one embodiment of the present invention, the objective is to provide a method for producing titanium electrodeposition that can manufacture high-purity metallic titanium with an extremely low aluminum content. [Means for solving the problem] 【0007】 The present inventors conducted diligent studies to solve the above problems and discovered that, in a method for producing titanium electrodeposits from raw materials containing titanium, aluminum, and oxygen by electrolytic refining using a molten salt bath, by performing an electrodeposition step in which electrolytic refining is carried out three or more times in which the bath composition, current density, and bath temperature satisfy predetermined conditions, it is possible to produce high-purity metallic titanium with an extremely low aluminum content. Based on this, the inventors created the invention exemplified below. 【0008】 [1] A method for producing titanium electrodeposits from raw materials containing titanium, aluminum, and oxygen by electrolytic refining using a molten salt bath, The electrodeposition step includes performing electrolytic refining three or more times using an anode containing a conductive crude titanium-based material and a cathode on which a refined titanium-based material with a higher purity than the crude titanium-based material is deposited, such that the following (1) to (3) are satisfied. A method for producing titanium electrodeposits, comprising using the raw material as the crude titanium-based material in the first electrolytic refining, and using the refined titanium-based material deposited on the cathode in the previous electrolytic refining as the crude titanium-based material in subsequent electrolytic refining. (1) The molten salt bath is a chloride bath, and the chloride bath contains 80 mol% or more of magnesium chloride and 1 mol% or more of lower titanium chloride. (2) The average current density of the cathode is 0.6 A / cm² 2 That's all. (3) The temperature of the chloride bath is 700°C or higher. [2] A method for producing the titanium electrodeposit according to [1], wherein the aluminum content of the crude titanium-based material in the first electrolytic refining is 5% by mass or more. [3] A method for producing a titanium electrodeposit according to [1] or [2], wherein the aluminum content of the titanium electrodeposit produced is 1.0 ppm by mass or less. [Effects of the Invention] 【0009】 According to one embodiment of the present invention, it is possible to manufacture high-purity metallic titanium with an extremely low aluminum content. [Brief explanation of the drawing] 【0010】 [Figure 1A] This is a schematic diagram illustrating an example of the electrodeposition step in the method for producing titanium electrodeposits according to the present invention. [Figure 1B] This is a schematic diagram illustrating an example of the electrodeposition step in the method for producing titanium electrodeposits according to the present invention. [Figure 1C] This is a schematic diagram illustrating an example of the electrodeposition step in the method for producing titanium electrodeposits according to the present invention. [Figure 1D] This is a schematic diagram illustrating an example of the electrodeposition step in the method for producing titanium electrodeposits according to the present invention. [Figure 1E] This is a schematic diagram illustrating an example of the electrodeposition step in the method for producing titanium electrodeposits according to the present invention. [Figure 1F]It is a schematic diagram for explaining an example of an electroplating step in a method for manufacturing a titanium electroplated product according to the present invention. [Figure 2] It is a cross-sectional view taken along the line X-X of FIG. 1A. 【Embodiments for Carrying Out the Invention】 【0011】 The present invention is not limited to the embodiments described below, and components can be modified and embodied without departing from the gist thereof. Also, various inventions can be formed by appropriately combining a plurality of components disclosed in each embodiment. For example, an invention may be formed by deleting some components from all the components shown in the embodiment. Note that in the drawings, there are also members shown schematically to assist in understanding the embodiments and the like included in the invention, and the illustrated sizes, positional relationships, etc. may not always be accurate. 【0012】 [Method for Manufacturing Titanium Electroplated Product] One embodiment of the method for manufacturing a titanium electroplated product according to the present invention is by electrolytic refining using a molten salt bath from a raw material containing titanium, aluminum, and oxygen, and includes an electroplating step of performing electrolytic refining three or more times so as to satisfy the following (1) to (3) using an anode including a conductive crude titanium-based material and a cathode on which a refined titanium-based material having a higher purity than the crude titanium-based material is deposited. In the first electrolytic refining, the above raw material is used as the crude titanium-based material, and in the second and subsequent electrolytic refinings, the refined titanium-based material deposited on the cathode in the previous electrolytic refining is used as the crude titanium-based material. Thereby, high-purity metallic titanium having an aluminum content of 1.0 mass ppm or less can be manufactured. (1) The molten salt bath is a chloride bath, and the chloride bath contains 80 mol% or more of magnesium chloride and 1 mol% or more of lower titanium chloride. (2) The average current density of the cathode is 0.6 A / cm 2 or more. (3) The bath temperature of the chloride bath is 700 °C or higher. 【0013】 As mentioned above, the manufacturing method described in Patent Document 1 involves extraction by a carbon-free reaction, and the crude titanium-based material used as a raw material in electrolytic refining inevitably contains aluminum. Therefore, in order to produce titanium electrodeposits made of metallic titanium, it is important to perform electrolytic refining under conditions that can reduce the aluminum content from the above-mentioned crude titanium-based material. 【0014】 Therefore, the inventors conducted diligent research and obtained the following findings (i) to (iv), and succeeded in producing high-purity titanium electrodeposits with an aluminum content of 1.0 ppm by mass or less. (i) The molten salt bath used in electrolytic refining is a chloride bath and is advantageous in that it contains a predetermined amount of magnesium chloride. When the magnesium chloride content of the chloride bath is above a predetermined amount, the aluminum content of the refined titanium material obtained by electrolytic refining of the crude titanium material tends to decrease. (ii) The chloride bath described above is advantageous in that it contains a predetermined amount of lower titanium chloride in addition to magnesium chloride. The lower titanium chloride content of the chloride bath affects the aluminum content of the refined titanium-based material. (iii) In electrolytic refining, it is advantageous to control the cathode current density to a predetermined value or higher. This tends to reduce the aluminum content of the refined titanium-based material. In addition, in electrolytic refining, it is advantageous to keep the chloride bath temperature within a predetermined range. This also tends to reduce the aluminum content of the refined titanium-based material. (iv) Perform electrolytic purification that satisfies conditions (i) to (iii) at least three times. 【0015】 An extraction step may be performed before the electrodeposition step. Such an extraction step is described, for example, in Patent Document 1. The crude titanium-based material used in the electrodeposition step can be manufactured by such known methods, or it may be obtained and used as appropriate. The details of the extraction step and the electrodeposition step will be described below, but are not limited to these. Note that the extraction step does not contain carbon as a reaction raw material. That is, a carbon raw material is not used for the deoxidation of titanium oxide. 【0016】 <Extraction Step> The extraction step is performed to produce an extract. This extract can be used as a raw material in the electrodeposition step described later. The extraction step involves heating a chemical blend containing titanium ore with titanium oxide and aluminum, for example, in a heating device, to obtain an extract. The reaction at this time is complex, but generally, it is thought that a reaction such as 3TiO2 + 4Al → 3Ti + 2Al2O3 occurs. Here, Ti corresponds to the extract, and although it contains Al and O, it is electrically conductive. Aluminum may be contained in the anodic residue obtained in the electrodeposition step described later, and this can also be used in the extraction step, but usually, separately prepared aluminum is mixed into the chemical blend. The chemical blend may also contain a separating agent. The extract obtained in the extraction step has relatively high conductivity and can be used in the electrodeposition step described later. After the above heat treatment, from the viewpoint of removing impurities, it is preferable to remove slag etc. adhering to the surface of the extract by post-treatment (for example, blasting). The titanium oxide content in the titanium ore is not limited, but is, for example, 50% by mass or more, for example, 80% by mass or more, or for example, 90% by mass or more. Upgraded titanium ore may also be used. 【0017】 (Separating agent) A separating agent is included in the chemical blend for the purpose of separating the extract from the by-product, the slag, during the extraction step. Therefore, any substance that can separate the extract from the slag during the extraction step is considered a separating agent. For example, the separating agent preferably contains one or more selected from calcium fluoride, aluminum fluoride, potassium fluoride, magnesium fluoride, calcium oxide, calcium chloride, and sodium fluoride, and more preferably contains calcium fluoride. The separating agent may also be calcium fluoride alone. 【0018】 (Chemical blend) To prepare the above chemical blend, the molar ratio of titanium, aluminum, and separating agent is adjusted such that, for example, when titanium is set to 1, aluminum is 0.67 or more and 1.3 or less, and the separating agent is 2.0 or more and 2.3 or less. 【0019】 (heating device) The heating device is a device for producing extracts by heat treatment. Examples of heating devices include high-frequency induction heating devices. Such a high-frequency induction heating device may include, for example, a carbon crucible, a solenoid-shaped induction heating coil on the outer wall of the crucible, and a high-frequency power supply connected to the induction heating coil. Since the chemical blend in the crucible contains conductive metals, it is considered that high-speed heating is possible. 【0020】 (Heat treatment conditions) Regarding the heat treatment conditions, for example, the temperature inside the container is set to, for example, 1500°C or higher and 1800°C or lower under an inert gas (e.g., Ar gas) atmosphere. Furthermore, the material of the inner wall of the container can be, from the viewpoint of heat resistance, carbon or ceramics, for example. 【0021】 (Composition of the extract obtained in the extraction step) The extract obtained in the extraction step has, for example, a titanium content of 60% by mass or more and 95% by mass or less, an aluminum content of 1% by mass or more and 20% by mass or less, and an oxygen content of 1% by mass or more and 20% by mass or less. Although the extract obtained in this extraction step has high aluminum and oxygen content, it is well purified in the electrodeposition step described later, reducing the aluminum and oxygen content and becoming a purified titanium-based material. The titanium content mentioned above has a lower limit, for example, of 70% by mass or more. Furthermore, the aluminum content is set at a lower limit of, for example, 5% by mass or more. On the other hand, the aluminum content is set at an upper limit of, for example, 15% by mass or less. Furthermore, the oxygen content mentioned above has an upper limit, for example, 15% by mass or less. In this invention, even with extracts that have high aluminum and oxygen content, it is possible to obtain metallic titanium with low levels of such impurities and high purity. The method for measuring the impurity content of each component in the extract is as follows: First, a sample is taken from the extract to prepare a sample for measurement. The impurity content of each component in this sample can then be measured using ICP emission spectrometry (e.g., PS3520UVDDII, manufactured by Hitachi) for metal components and inert gas fusion-infrared absorption spectroscopy (e.g., TC-436AR, manufactured by LECO) for oxygen. 【0022】 (specific resistance) The resistivity of the extract produced in the extraction step at room temperature should be set to an upper limit of, for example, 1 × 10⁻⁶, from the viewpoint of properly carrying out electrolytic purification. -4 The resistivity may be Ω·m or less. Furthermore, the extract only needs to be conductive and capable of conducting electricity to a moderate degree; therefore, the lower limit of the resistivity is not particularly limited, but if we were to give an example, it would be 1 × 10⁻⁶. -8 The resistivity may be greater than or equal to Ω·m. As an example of the measurement method, the sample taken from the extract is cut into 10 mm square blocks, and the resistivity of the cut sample is measured at room temperature using a two-terminal measurement method (for example, using a low-resistivity meter 3566-RY (manufactured by Tsuruga Electric Co., Ltd.)). 【0023】 <Electrodeposition Step> The electrodeposition step involves performing electrolytic purification three or more times under conditions that satisfy (1) to (3) above, using an anode containing a conductive crude titanium-based material and a cathode on which a purified titanium-based material of higher purity than the crude titanium-based material is deposited. In the first electrolytic purification, for example, the raw material such as the extract obtained in the extraction step is used as the crude titanium-based material, and in the second and subsequent electrolytic purifications, the purified titanium-based material deposited on the cathode in the previous electrolytic purification is used as the crude titanium-based material. As a result, the crude titanium-based material is refined, reducing the content of impurities other than titanium (aluminum and oxygen), and a refined titanium-based material with a higher titanium content than the crude titanium-based material is obtained. In this electrodeposition step, if an anode containing a crude titanium-based material containing, for example, 1% by mass or more and 20% by mass or less of aluminum is used, it is difficult to obtain a refined titanium-based material with an aluminum content of 1.0 ppm by mass or less even after performing electrolytic refining once or twice. In one embodiment, as the number of electrolytic refining steps increases, the titanium content of the refined titanium-based material increases, and the aluminum content is reduced more reliably. This results in a highly pure metallic titanium electrodeposited material. However, from the viewpoint of manufacturing costs, the number of electrolytic refining steps can be appropriately selected, but five steps or less is preferred, and four steps or less is more preferred. In the electrodeposition step, if the number of electrolytic refining steps satisfying (1) to (3) above is three or more, further electrolytic refining steps that do not satisfy at least one of (1) to (3) above may be performed. Furthermore, there is no particular limitation on the timing of performing electrolytic refining steps that do not satisfy at least one of (1) to (3) above. 【0024】 In one embodiment, by performing electrolytic refining satisfying conditions (1) to (3) above three or more times, a refined titanium-based material with a reduced aluminum content compared to the crude titanium-based material can be obtained on the cathode surface in each electrolytic refining step. Furthermore, a refined titanium-based material with a well reduced oxygen content can also be obtained. 【0025】 (electrolyzer) In one embodiment, various electrolytic devices can be used. An example of an electrolytic device 100 shown in Figure 1A is a batch type, comprising a sealed container-shaped electrolytic cell 110 for storing the chloride bath Bf, electrodes including an anode 120 and a cathode 130 immersed in the chloride bath Bf, and a power supply (not shown) connected to the anode 120 and cathode 130 via conductive wires to supply current to the anode 120 and cathode 130. Although not shown, the electrolytic device 100 is normally openable for installing or removing the anode and cathode. Also, although not shown, the electrolytic device 100 is equipped with openings for supplying and exhausting gas to create an inert gas atmosphere in the space above the chloride bath Bf. Also, although not shown, the electrolytic device 100 is equipped with heaters at appropriate locations to maintain the molten state of the chloride bath Bf by heating. The material of the electrolytic cell 110 is not particularly limited as long as it has heat resistance and corrosion resistance. Furthermore, electrodes may also contain bipolar elements. 【0026】 (Molten salt bath) A chloride bath containing a predetermined amount of magnesium chloride is effective in reducing the aluminum and oxygen content in the titanium electrodeposit. The magnesium chloride content is 80 mol% or more, for example, 85 mol% or more, or for example, 88 mol% or more. The above chloride bath may also contain one or more metal chlorides selected from lithium chloride, sodium chloride, potassium chloride, rubidium chloride, cesium chloride, beryllium chloride, calcium chloride, strontium chloride, and barium chloride, and the amount of such metal chloride may be, for example, 19 mol% or less, for example, 9 mol% or less, or for example, 5 mol% or less. Furthermore, from the viewpoint of reducing the aluminum content in the titanium electrodeposit, the content of lower titanium chloride in the chloride bath is 1 mol% or more, for example, 2 mol% or more, or for example, 3 mol% or more. The upper limit of the lower titanium chloride content may be, for example, 20 mol% or less. Alternatively, the upper limit of the lower titanium chloride content may be 15 mol% or less, 12 mol% or less, 8 mol% or less, or 5 mol% or less. This lower titanium chloride refers to titanium chloride of a lower grade than titanium tetrachloride, such as titanium dichloride (TiCl2) and titanium trichloride (TiCl3). To ensure the chloride bath contains lower titanium chloride, separately obtained titanium chloride may be added to the chloride bath. Alternatively, lower titanium chloride may be generated in the chloride bath by introducing metallic titanium such as sponge titanium into the chloride bath and bringing it into contact with titanium tetrachloride. Furthermore, the chloride bath may consist of magnesium chloride and lower titanium chloride, and may not contain any other metal chlorides. In this case, the aluminum content in the refined titanium-based material can be further reduced. The specific type and content of the metal chlorides described above can be appropriately determined by considering the composition of the titanium electrodeposit, the operating temperature, and other factors. Here, the molar content is calculated as follows: After solidifying a sample of molten salt taken from the chloride bath, the molar content of each metal ion in the chloride bath Bf is calculated by analyzing the components of the sample using ICP emission spectrometry and atomic absorption spectrometry. If the chloride bath contains MgCl2, NaCl, KCl, CaCl2, LiCl, TiCl2, and TiCl3, Na and K can be quantified by atomic absorption spectrometry, and the others by ICP emission spectrometry. The total content of metal ions (Mm) is obtained by adding up the content of magnesium ions, sodium ions, potassium ions, calcium ions, lithium ions, and titanium ions. The molar content of each component contained in the chloride bath can be calculated by dividing the content of the metal ion of each component by the total content of the metal ions (Mm) and expressing it as a percentage. In this way, the chloride content is determined based on the content of metal ions contained in the chloride bath. 【0027】 The temperature of the chloride bath should be 700°C or higher, preferably 700°C or higher and 900°C or lower. Within this temperature range, lower titanium chloride can be effectively incorporated into the chloride bath. Furthermore, by maintaining a certain temperature, the aluminum content of the titanium electrodeposited material can be effectively reduced. Moreover, electrolytic refining can be performed without requiring excessive heating. The lower limit of the chloride bath temperature is, for example, 730°C or higher, and also, for example, 750°C or higher. The upper limit of the chloride bath temperature is, for example, 850°C or lower. 【0028】 (anode) The shape of the anode 120 is not particularly limited, but examples include a rod shape, a long strip shape used while moving, a plate shape or cylindrical shape, a cylinder or other columnar shape, or a lump shape. The shape of the crude titanium-based material 121 is also not particularly limited, but examples include the shapes of the anodes described above, or granular shape. The number of anodes 120 can be one or more, depending on the number of cathodes 130. For example, in the case of granular crude titanium-based material 121, the crude titanium-based material may be contained in a conductive container 122 to constitute the anode 120. If the anode 120 includes the container 122, the external shape of the container 122 may be the shape of the anode 120. 【0029】 For example, the container 122 that may be included in the anode 120 may be suspended from above in the chloride bath Bf, or, although not shown in the drawings, it may be supported from below by a base (not shown) placed on the bottom surface of the electrolytic cell 110 without being suspended from above. The shape of the base can be appropriately determined in consideration of the shape of the container 122. If the bottom wall of the container 122 is annular, the base may be cylindrical to match the shape of the container 122, or it may be a series of columnar bases arranged at equal intervals. Furthermore, the base only needs to be insulating so as not to conduct electricity with the container 122 during electrolytic refining, so ceramics are preferable, and among them, refractory bricks are more preferable from the viewpoint of insolubility in the chloride bath. 【0030】 (container) Container 122 is used to store crude titanium-based material 121 and anode residues 124, 127, and 129 after electrodeposition, and is electrically conductive. The shape of container 122 is not particularly limited, and its external shape may be, for example, the shape of each of the anodes. Since container 122 stores crude titanium-based material 121 and electrolytic refining is performed in that state, it is usually provided with a number of through holes. For example, a basket-type container 122 with through holes can be used. As an example, container 122 has the external shape of a bottomed cylinder and comprises an annular bottom wall 122a, an inner wall 122b extending upward from the bottom wall 122a, and an outer wall 122c extending upward from the bottom wall 122a, with an opening formed at the top. The container 122 only needs to have through holes 122d in at least the inner wall 122b facing the cathode 130, and may further have through holes 122d in the outer wall 122c. The inner wall 122b and the outer wall 122c may more preferably have a plurality of through holes 122d. The arrangement of the plurality of through holes 122d is not particularly limited and may be in a grid pattern or a staggered pattern. Furthermore, assuming that the crude titanium-based material 121 can be held inside the container 122, the bottom wall 122a may also have through holes 122d. 【0031】 From the viewpoint of performing electrolytic refining while reducing power consumption, the resistivity of the container 122 is set to an upper limit of, for example, 1 × 10⁻⁶. -4 It is sufficient if the resistivity is Ω·m or less. Furthermore, the container 122 is conductive and only needs to be able to conduct electricity to a reasonable degree, so the lower limit of the resistivity is not particularly limited, but if we were to give an example, it would be 1 × 10⁻⁶ -8 A resistance of Ω·m or greater is acceptable. As an example of a measurement method, the resistivity is measured at room temperature by measuring the resistance of a sample cut to a predetermined size using a two-terminal measurement method (low resistance meter 3566-RY, manufactured by Tsuruga Electric Co., Ltd.). 【0032】 The material of the container 122 only needs to be insoluble in the chloride bath, and examples thereof include nickel, Ni-based alloys (e.g., Hastelloy), iron, and carbon. The container 122 made of these materials is hardly eluted into the chloride bath Bf during electrolytic purification, and mainly the crude titanium-based material 121 in the container 122 is eluted. Among these materials, from the viewpoint of impact resistance, nickel, Ni-based alloys (e.g., Hastelloy), and iron are preferable, and nickel is more preferable. Further, for example, when the container 122 is made of steel, nickel plating may be formed by applying a plating treatment to the surface of the steel. 【0033】 (Cathode) During electrolytic purification, from the viewpoint of favorably reducing the aluminum content of the purified titanium-based material and titanium electrodeposits, the average current density of the cathode 130 is 0.6 A / cm 2 or more, for example 0.8 A / cm 2 or more. From the viewpoint of suppressing unintended reactions such as decomposition of the components of the chloride bath, the average current density of the cathode 130 is typically 1.5 A / cm 2 or less, and more typically 1.2 A / cm 2 or less. Here, the average current density of the cathode 130 can be calculated by the following formula (I). Average current density (A / cm 2 ) = Current (A) ÷ Electrolysis area (cm 2 ) ··· (I) Here, regarding the electrolysis area, for example, when the cathode is cylindrical, it is calculated by the following formula (II). Electrolysis area (cm 2 ) = Cathode immersion surface area = Cathode diameter (cm) × π × Cathode immersion height (cm) ··· (II) In addition to continuously flowing the current applied to the electrode (also referred to as a so-called constant current), a pulse current may be used in which a current interruption period for setting the current value to zero (i.e., not energizing) is provided and the energization period and the current interruption period are alternately repeated. In this case, the above average current density is obtained by dividing the average current by the electrolysis area. Here, the average current (A) is obtained by dividing the total amount of electricity (unit: C (coulomb)) flowed for a predetermined time by the time (unit: second). 【0034】 Furthermore, the cathode 130 may be, for example, rod-shaped, and in this case, at least a portion of the surface of the cathode 130 on which the refined titanium-based material is deposited may be curved. The shape of the cathode 130 is not particularly limited, and examples include long strip-shaped, plate-shaped, cylindrical, cylindrical, or other columnar or block-shaped cathodes that are used while being moved. The number of cathodes 130 may be one or more, depending on the number of anodes 120. The material of the cathode 130 is not particularly limited. For example, the cathode 130 may contain at least 90% by mass or more of at least one material selected from the group consisting of titanium, molybdenum, glassy carbon, and tungsten in at least its surface. The surface of the cathode 130 may be made of titanium. Furthermore, the entire cathode 130 may be composed of at least one material selected from the group consisting of titanium, molybdenum, glassy carbon, and tungsten, or it may be made of titanium. 【0035】 The distance between the anode 120 and the cathode 130 is not particularly limited, but for example, it is between 20 mm and 700 mm. 【0036】 Next, an example of producing titanium electrodeposits by performing electrolytic refining three times to satisfy the above conditions (1) to (3) will be explained using Figures 1A to 1F and Figure 2, respectively. Furthermore, if electrolytic purification is performed in a manner that satisfies conditions (1) to (3) above from the first to the third time, it is not necessary for each electrolytic purification to be performed under the same conditions. Furthermore, each conductive wire shown in Figures 1A to 1F can be connected to a power supply (not shown), and the control mechanism (not shown) of the power supply can appropriately switch the conductive wires to which current is supplied according to each anode and cathode. Please note that the container shape shown in the diagram is merely an example and is not the only possible shape. 【0037】 <First electrolytic refining> In the first electrolytic purification, the raw materials such as the predetermined extracts mentioned above are used as crude titanium-based materials, and purified titanium-based materials are obtained by electrolytic purification in a chloride bath Bf using an electrode containing the crude titanium-based materials. For the crude titanium-based materials used in the first electrolytic purification, materials with an aluminum content of 1% by mass or more, or 5% by mass or more, can be used; for example, materials obtained in the extraction step mentioned above can be used. For example, in the first electrolytic refining, as shown in Figure 1A, an anode 120 containing a nickel container 122 with numerous through-holes and a crude titanium-based material 121 placed inside the container 122, and a titanium cathode 130 are placed in the chloride bath Bf, respectively. Then, a voltage is applied by a control mechanism via conductive wires EL connected to the container 122 and the cathode 130 to energize the crude titanium-based material 121 stored in the container 122 and the cathode 130, thereby performing the first electrolytic refining. In the drawing, the crude titanium-based material 121 is stored in container 122, but for example, multiple containers may be used, and the crude titanium-based material 121 of the anode 120 may be stored in each separate container. 【0038】 The atmosphere inside the electrolytic cell 110 is controlled to an inert gas atmosphere, such as argon, in order to suppress the increase in the impurity content of the titanium electrodeposit due to the incorporation of moisture from the atmosphere. 【0039】 During electrolytic refining, as shown in Figure 1B, crude titanium-based material 121 containing titanium, which has a higher ionization tendency than nickel, and aluminum dissolves into the chloride bath Bf, thus consuming the crude titanium-based material 121, and purified titanium-based material 123 with reduced impurity content precipitates on the surface of the cathode 130. Consequently, the crude titanium-based material 121 in the container 122 becomes anode residue 124. To terminate the electrolytic refining, the control mechanism stops the application of voltage between the anode 120 and the cathode 130. 【0040】 After the electrolytic refining is complete, the cathode 130 is removed from the electrolytic cell 110, and the refined titanium-based material 123 deposited on the surface of the cathode 130 can be recovered by peeling it off with a cutting tool or the like. In this case, the refined titanium-based material 123 may be washed and dried, or vacuum separation may be performed. This treatment can be performed on the refined titanium-based material 123 before or after peeling it off from the cathode 130. As an example, the cathode 130 is removed from the electrolytic cell 110, and the cathode 130 and the refined titanium-based material 123 are cleaned with acid and / or water to dissolve and remove any molten salt components adhering to them. Next, the refined titanium-based material 123 is peeled off the surface of the cathode 130 using a cutting tool or the like. Then, the refined titanium-based material 123 is placed in a container such as a crucible and vacuum-dried to evaporate any moisture. As an example, the cathode 130 is removed from the electrolytic cell 110 and subjected to vacuum separation treatment. In the vacuum separation treatment, the molten salt components are removed by evaporation. The refined titanium-based material 123 has reduced aluminum and oxygen content compared to the crude titanium-based material 121. 【0041】 <Second electrolytic purification> The second electrolytic refining is performed using an anode 125 containing the refined titanium-based material 123 as the crude titanium-based material after the first electrolytic refining. This further refines the refined titanium-based material 123 obtained in the first electrolytic refining, resulting in a refined titanium-based material 126 with an even lower impurity content. For example, as shown in Figure 1C, in the first electrolytic refining, the crude titanium material 123, the nickel container 122 with numerous through-holes in which the crude titanium material is placed, and the titanium cathode 130 are placed in the chloride bath Bf, respectively. Next, a voltage is applied by a control mechanism via conductive wires EL connected to the container 122 and the cathode 130 to energize the crude titanium material stored in the container 122 and the cathode 130, thereby performing the second electrolytic refining. The cathode 130 may be the same as the cathode 130 used in the first electrolytic refining, or it may be replaced with a new cathode. 【0042】 The composition of the chloride bath Bf, the temperature of the chloride bath, the current density, etc., in the second electrolytic purification are the same as in the first electrolytic purification, so the explanation will be omitted. If the composition of the chloride bath Bf after the first electrolytic purification is within the range specified in (1) above, the chloride bath Bf may be used as is for the second electrolytic purification without preparing a new one. In addition, if a relatively large amount of impurities have accumulated on the bottom wall of the electrolytic cell after the electrolytic purification is completed, these deposits may be removed before the next electrolytic purification to prevent the impurities from becoming trapped in the purified titanium-based material on the cathode. 【0043】 During electrolytic refining, as shown in Figure 1D, the refined titanium material 123 (see Figure 1C) as crude titanium material is consumed as the titanium-containing anode dissolves into the chloride bath Bf, and refined titanium material 126 with reduced impurity content is deposited on the surface of the cathode 130. Consequently, the refined titanium material 123 in the container 122 becomes anode residue 127. To terminate the electrolytic refining, the control mechanism stops the application of voltage between the anode 120 and the cathode 130. 【0044】 After the electrolytic refining is complete, the cathode 130 is removed from the electrolytic cell 110, as in the first electrolytic refining, and the refined titanium-based material 126 deposited on the surface of the cathode 130 is recovered by peeling it off with a cutting tool or the like. Alternatively, the washing and drying described above for the first electrolytic refining may be performed on the refined titanium-based material 126. Furthermore, the washing and drying of the refined titanium-based material 126 may be performed while it is electrodeposited on the cathode 130, or after it has been separated from the cathode 130. 【0045】 <Third electrolytic refining> The third electrolytic refining is performed using an anode 125 containing the refined titanium-based material 126 as the crude titanium-based material after the second electrolytic refining. As shown in Figure 1E, the third electrolytic refining is carried out in the same manner as the second electrolytic refining, except that the anode 125 contains the refined titanium-based material 126 as the crude titanium-based material and a nickel container 122 with numerous through-holes in which the refined titanium-based material is placed. As a result, as shown in Figure 1F, the crude titanium-based material is consumed as the titanium-containing anode dissolves into the chloride bath Bf, and a refined titanium-based material (titanium electrodeposited 128) with reduced impurity content is deposited on the surface of the cathode 130. Since the aluminum content of this refined titanium-based material is well reduced and its purity is high, it can be used as titanium electrodeposited 128. If further electrolytic refining is performed to reduce the impurity content, the refined titanium-based material can be used as the crude titanium-based material in the next electrolytic refining. On the other hand, after electrolytic refining, the crude titanium-based material in the container 122 becomes the anode residue 129. Then, the titanium electrodeposit 128 formed on the surface of the cathode 130 is recovered by the method described above. This yields metallic titanium with a reduced aluminum content. Since the third electrolytic purification process is the same as the second electrolytic purification process, a detailed explanation will be omitted. 【0046】 (Composition of titanium electrodeposits, etc.) Titanium electrodeposits are produced by carrying out the above-described method for producing titanium electrodeposits. The metallic purity of the titanium electrodeposit is 99.999% by mass or higher. This metallic purity is the purity excluding gaseous components (O, N, H, Cl, F). Furthermore, in the titanium electrodeposit produced by the said titanium electrodeposit manufacturing method, it is preferable that the aluminum content is 1.0 ppm by mass or less. The titanium electrodeposit consists, for example, of an aluminum content of 1.0 ppm by mass or less, an oxygen content of 90 ppm by mass or less, and the remainder being titanium and unavoidable impurities. These unavoidable impurities are often impurities derived from ore or components derived from the chloride bath. The titanium electrodeposit referred to here has a composition that allows it to be handled as metallic titanium. Therefore, the titanium electrodeposit is a metallic titanium electrodeposit. The aluminum content mentioned above has an upper limit, for example, 0.8 ppm by mass or less, and also a lower limit, for example, 0.6 ppm by mass or less. On the other hand, the lower limit of the aluminum content is not particularly limited, but to give an example, it is 0.1 ppm by mass or more. The oxygen content mentioned above has an upper limit of, for example, 80 ppm by mass or less. On the other hand, the oxygen content has a lower limit of, for example, 30 ppm by mass or more, or for example, 40 ppm by mass or more, or for example, 45 ppm by mass or more. The method for measuring the impurity content of each component in the titanium electrodeposit is as follows: First, a sample is taken from the titanium electrodeposit to prepare a sample for measurement. The impurity content of each component in this sample can then be measured: for metal components, glow discharge mass spectrometry (e.g., using Astrum, manufactured by Nu Instruments); and for oxygen, inert gas fusion-infrared absorption spectrometry (e.g., using TC-436AR, manufactured by LECO). [Examples] 【0047】 The present invention will be specifically described based on examples and comparative examples. The following descriptions of examples and comparative examples are merely experimental examples intended to facilitate understanding of the technical content of the present invention, and the technical scope of the present invention is not limited by these examples. 【0048】 [Preparation of crude titanium-based material (extraction step)] A chemical blend containing titanium ore with titanium dioxide, aluminum, and calcium fluoride as a separating agent was heat-treated under the conditions described below, and then post-treated according to known methods to prepare an extract. <Manufacturing conditions for extracts> Titanium ore: Titanium oxide content 95% by mass The molar ratio of the chemical blend was adjusted so that, with titanium set at 1, aluminum was between 0.67 and 1.3, and the separating agent was between 2.0 and 2.3. Inert gas: Argon gas Heating temperature: 1500°C or higher and 1800°C or lower 【0049】 The composition of the sample taken from the above extract was measured using the method described above. As a result, the titanium content of the extract was 70% by mass, the aluminum content was 9% by mass, and the oxygen content was 13% by mass. Furthermore, the resistivity of the sample taken from the extract was measured using the method described above. As a result, the resistivity of the extract was 5 × 10⁻⁶. -5 It was less than Ω·m. 【0050】 [Manufacturing of titanium electrodeposits] <Example 1> (First electrolytic purification) Next, an electrolytic apparatus 100 having the configuration shown in Figures 1A to 1B and Figure 2 was prepared. The electrolytic apparatus 100 included a sealed container-shaped electrolytic cell 110 for storing a chloride bath Bf, an anode 120 immersed in the chloride bath Bf and containing a crude titanium-based material 121 made from the extract and a nickel cage-shaped container 122 on which the crude titanium-based material 121 was placed, a titanium cathode 130, and a power supply (not shown) connected to the anode 120 and the titanium cathode 130 via a conductive wire EL to supply current to the anode 120 and the cathode 130. The container 122 has a bottomed cylindrical shape and comprises an annular bottom wall 122a, an inner wall 122b extending upward from the bottom wall 122a, and an outer wall 122c extending upward from the bottom wall 122a. An opening is formed at the top, and multiple through holes 122d are formed in the inner wall 122b and the outer wall 122c of the container 122. The power supply was connected to a control mechanism (not shown). Although not illustrated, the electrolytic cell 110 was designed to be openable and closable at the top. Therefore, the ingress of outside air can be suppressed during the electrodeposition step. The dimensions and shape of the bath portion of the electrolytic cell 110 of the electrolytic device 100 were set to 300 mmΦ × 570 mm depth. Next, magnesium chloride was added to the electrolytic cell 110 of the electrolytic device 100 and dissolved while controlling the bath temperature as shown in Table 1 to obtain chloride bath Bf. Subsequently, titanium tetrachloride was brought into contact with sponge titanium obtained by the Chlor method to supply lower titanium chloride to chloride bath Bf and prepare the bath composition shown in Table 1. In Table 1, "TiCl2" refers to lower titanium chloride. 【0051】 Next, crude titanium-based material 121 is placed in container 122 as the anode raw material (resistivity: 7 × 10 -8 It was placed within a Ω·m or less. A titanium cylinder measuring 50 mm in diameter and 300 mm in length was prepared as the cathode 130. The container 122 on the anode 120 side and the cathode 130 were positioned so that their height directions were approximately parallel to the depth direction of the chloride bath Bf. 【0052】 Electrolytic refining was performed in a chloride bath Bf by applying a voltage to the crude titanium-based material 121 of the anode 120 and the cathode 130 via a conductive wire EL connected to the container 122 on the anode 120 side and the cathode 130 using a control mechanism. After 1 hour from the start of voltage application, the voltage application was stopped by the control mechanism. As shown in Figure 1B, purified titanium-based material 123 was obtained deposited over the entire surface of the cathode 130. The conditions for electrolytic refining are shown below. <Conditions for electrolytic refining> Inside the electrolytic cell: Ar gas atmosphere Chloride bath temperature: 850℃ Current density: 0.6A / cm 2 Interelectrode distance: 50mm Voltage: 1.0V or higher and 2.5V or lower 【0053】 After the voltage application was stopped, the container 122 and cathode 130 were removed from the electrolytic cell 110, and the container 122, the anode residue 124 inside the container 122, the cathode 130, and the refined titanium-based material 123 were washed with water to remove any adhering molten salt components. The anode residue 124 was recovered from the container 122. The refined titanium-based material 123 was peeled off and recovered from the cathode 130 using a cutting tool. After recovery, the refined titanium-based material 123 and the anode residue 124 were dried separately by vacuum drying to remove moisture. 【0054】 (Second electrolytic purification) Next, the electrolytic apparatus 100 used in the first electrolytic purification was cleaned and dried, and then prepared again. Next, a chloride bath Bf was prepared in the electrolytic cell 110 of the electrolytic apparatus 100 under the same conditions as in the first electrolytic purification. 【0055】 Next, as shown in Figures 1C to 1D, the entire amount of the purified titanium-based material obtained in the first electrolytic refining was prepared, and the anode 125 containing the purified titanium-based material 123 as crude titanium-based material and a container 122 on which the purified titanium-based material 123 was placed was arranged, and the second electrolytic refining was carried out in the same manner as the first electrolytic refining, thereby obtaining the purified titanium-based material 126 from which the water had been evaporated. 【0056】 (Third electrolytic purification) Next, the electrolytic apparatus 100 used in the second electrolytic purification was cleaned and dried, and then prepared again. Next, a chloride bath Bf was prepared in the electrolytic cell 110 of the electrolytic apparatus 100 to be the same as the conditions for the second electrolytic purification. 【0057】 Next, as shown in Figures 1E to 1F, the entire amount of the purified titanium-based material obtained in the second electrolytic refining was prepared, and the anode 125 containing the purified titanium-based material 126 as the crude titanium-based material and the container 122 on which the purified titanium-based material 126 was placed was arranged, and the third electrolytic refining was carried out in the same manner as the first electrolytic refining, thereby obtaining titanium electrodeposit 128, which is a purified titanium-based material from which the water has been evaporated. 【0058】 [evaluation] The aluminum and oxygen content of the sample taken from the titanium electrodeposit 128 obtained in Example 1 was measured using the method described above. The results are shown in Table 2. Furthermore, the metallic purity of titanium electrodeposit 128 in Example 1 was 99.999% by mass or higher. This metallic purity was determined after removing gaseous components (O, N, H, Cl, F). 【0059】 <Examples 2-7, Comparative Examples 1-6> In Examples 2-7 and Comparative Examples 1-6, electrolytic purification was performed three times in the same manner as in Example 1, except that the composition of the chloride bath, the average cathode current density, and the bath temperature were changed as shown in Table 1. This yielded titanium electrodeposits. In addition, the aluminum and oxygen content of the titanium electrodeposits were measured, as in Example 1. The results are shown in Table 2. Furthermore, the metallic purity of the titanium electrodeposits 128 in Examples 2 to 7 was 99.999% by mass or higher for titanium. 【0060】 [Table 1] 【0061】 [Table 2] 【0062】 [Discussion based on examples] The titanium electrodeposits obtained in Examples 1 to 7 had an aluminum content of 1.0 ppm by mass or less. Furthermore, the metal purity was such that the titanium content was 99.999% by mass or higher. Therefore, in Examples 1 to 7, it was possible to produce high-purity metallic titanium with an extremely low aluminum content. Thus, in the method for producing titanium electrodeposits by electrolytic refining using a molten salt bath from raw materials containing titanium, aluminum, and oxygen, it was useful to perform the electrodeposition step in which electrolytic refining was carried out three or more times, satisfying predetermined conditions for bath composition, current density, and bath temperature. 【0063】 On the other hand, in Comparative Examples 1 to 3, unlike Examples 1 to 7, electrolytic refining was performed three times in which the bath composition, current density, and bath temperature did not satisfy the predetermined conditions. As a result, the aluminum content of the obtained titanium electrodeposit was 10 ppm by mass or more. In other words, Comparative Examples 1 to 3 were unable to produce high-purity metallic titanium with an extremely low aluminum content. Furthermore, in Comparative Examples 4 to 6, electrolytic refining was performed twice under predetermined conditions for bath composition, current density, and bath temperature, and once under conditions where any of the composition, current density, or bath temperature did not meet the predetermined conditions. As a result, the aluminum content of the obtained titanium electrodeposit was 3 ppm by mass or more. In other words, it was not possible to produce high-purity metallic titanium with an extremely low aluminum content in Comparative Examples 4 to 6. [Explanation of symbols] 【0064】 100 Electrolyzer 110 Electrolytic cell 120, 125 anode 121 Crude titanium-based materials 122 Container 122a Bottom wall 122b Inside wall 122c outer wall 122d through hole 123, 126 Refined Titanium-Based Materials 124, 127, 129 Anode residue 128 Titanium Electrodeposition 130 Cathode Bf Chloride Bath EL conductive wire

Claims

[Claim 1] A method for producing titanium electrodeposits from raw materials containing titanium, aluminum, and oxygen by electrolytic refining using a molten salt bath, The electrodeposition step includes performing electrolytic refining three or more times using an anode containing a conductive crude titanium-based material and a cathode on which a refined titanium-based material with a higher purity than the crude titanium-based material is deposited, such that the following (1) to (3) are satisfied. A method for producing titanium electrodeposits, comprising using the raw material as the crude titanium-based material in the first electrolytic refining, and using the refined titanium-based material deposited on the cathode in the previous electrolytic refining as the crude titanium-based material in subsequent electrolytic refining. (1) The molten salt bath is a chloride bath, and the chloride bath contains 80 mol% or more of magnesium chloride and 1 mol% or more of lower titanium chloride. (2) The average current density of the cathode is 0.6 A / cm². 2 That's all. (3) The bath temperature of the chloride bath is 700°C or higher. [Claim 2] A method for producing a titanium electrodeposit according to claim 1, wherein the aluminum content of the crude titanium-based material in the first electrolytic refining is 5% by mass or more. [Claim 3] A method for producing a titanium electrodeposit according to claim 1 or 2, wherein the aluminum content of the titanium electrodeposit produced is 1.0 ppm by mass or less.

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