Titanium-based electrolytic material, and method for producing metallic titanium or titanium aluminum alloy

Abstract

To provide a method that enables production of a high-purity titanium-based electrolytic material usable in molten salt electrolysis for production of metallic titanium or a titanium aluminum alloy.SOLUTION: A method for producing a titanium-based electrolytic material includes producing a titanium secondary alloy by subjecting a titanium primary alloy containing aluminum in an amount of 2 mass% or more and 8 mass% or less and oxygen in an amount of 10 mass% or more and 15 mass% or less to deoxidation treatment using a calcium-based deoxidizing agent. The deoxidation treatment can be carried out by treating a molten metal of the titanium primary alloy with the calcium-based deoxidizing agent in a heat-resistant container.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] One embodiment of the present invention relates to a method for producing a titanium-based electrolytic material, and a method for producing metallic titanium or a titanium-aluminum alloy using the titanium-based electrolytic material. [Background technology]

[0002] In recent years, a new method has been developed to replace the Kroll process and produce titanium metal and titanium-aluminum alloys, which emit less carbon directly from the manufacturing process. In this method, titanium ore is reduced with aluminum metal or an alloy primarily composed of aluminum to produce a titanium-aluminum alloy (see Patent Document 1). This titanium-aluminum alloy is used as an electrolytic material and subjected to repeated molten salt electrolysis, resulting in the production of high-purity titanium metal and titanium-aluminum alloys as electrodeposits on the cathode.

[0003] Titanium-aluminum alloys can also be produced by mixing and melting metallic titanium and metallic aluminum that have been produced separately. For example, in the method described in Patent Document 2, metallic titanium and metallic aluminum whose oxygen contents have been significantly reduced in advance (for example, metallic titanium and metallic aluminum having oxygen contents of 850 ppm by mass and 190 ppm by mass, respectively) are mixed and melted to form a titanium-aluminum alloy, which is then subjected to a deoxidation treatment using a calcium source to obtain a titanium-aluminum alloy with a low oxygen content (for example, 200 ppm by mass or less). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2015-507696 [Patent Document 2] Japanese Patent Application Publication No. 5-140669 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of one embodiment of the present invention is to provide a new method for producing high-purity metallic titanium or titanium-aluminum alloys. Alternatively, an object of one embodiment of the present invention is to provide a method for producing a titanium-based electrolytic material with high titanium purity that can be used in molten salt electrolysis to produce metallic titanium or titanium-aluminum alloys. [Means for solving the problem]

[0006] One embodiment of the present invention is a method for producing a titanium-based electrolytic material, which includes deoxidizing a titanium primary alloy containing 2% by mass or more and 8% by mass or less of aluminum and 10% by mass or more and 15% by mass or less of oxygen using a calcium-based deoxidizer to produce a titanium secondary alloy.

[0007] One embodiment of the present invention is a method for producing metallic titanium or a titanium-aluminum alloy, which comprises performing molten salt electrolysis using the titanium-based electrolytic material produced according to the above-described method as an anode. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a flow chart illustrating a method for producing titanium metal or a titanium aluminum alloy according to one embodiment of the present invention. [Figure 2] FIG. 1 is a schematic end view of an electrolytic cell used in a method for producing titanium metal or a titanium aluminum alloy according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, various embodiments of the present invention will be described with reference to the drawings, etc. However, the present invention can be embodied in various forms without departing from the spirit of the present invention, and should not be construed as being limited to the description of the embodiments exemplified below.

[0010] In order to clarify the description, the drawings may show the width, thickness, shape, arrangement, etc. of each part schematically compared to the actual embodiment, but these are merely examples and do not limit the interpretation of the present invention. In this specification and each drawing, elements having the same functions as those explained in the previous drawings may be assigned the same reference numerals, and duplicate explanations may be omitted.

[0011] Dissolution is a phenomenon in which a gas, liquid, or solid mixes with a liquid to form a uniform liquid phase, but in the following description, the term is used to encompass melting, which is a phenomenon in which a solid changes into a liquid.

[0012] 1. Overview of the manufacturing method for titanium metal or titanium aluminum alloy FIG. 1 shows a flowchart illustrating a method for producing metallic titanium or a titanium-aluminum alloy according to one embodiment of the present invention. In this production method, a titanium-aluminum alloy (titanium primary alloy) having a relatively high oxygen content is first produced (smelting) by reducing titanium ore or other raw material containing titanium oxide with zero-valent metallic aluminum or an aluminum alloy. The titanium primary alloy is then deoxidized to produce a titanium-aluminum alloy (titanium secondary alloy) with a reduced oxygen content and a relatively increased titanium purity (refining). Molten salt electrolysis is performed using the titanium secondary alloy as a titanium-based electrolytic material, yielding high-purity metallic titanium or a titanium-aluminum alloy as an electrodeposit on the cathode. These steps are described below.

[0013] In this specification, metallic titanium refers to titanium of a grade known as commercially pure titanium. Specifically, the titanium content of the metallic titanium finally obtained by molten salt electrolysis is 99% by mass or more and 100% by mass or less. The aluminum and oxygen contents of the metallic titanium are extremely low. For example, the aluminum content is 0.1% by mass or less or 0.01% by mass or less, and the oxygen content is 0.2% by mass or less, 0.10% by mass or less, or 0.05% by mass or less.

[0014] On the other hand, titanium aluminum alloy refers to an alloy containing titanium as the main component and containing more than 0.1 mass % aluminum.

[0015] Specifically, the aluminum content of the titanium primary alloy (including the titanium primary alloy after dealumination, which will be described later; the same applies hereinafter) is 2% by mass or more and 8% by mass or 2% by mass or more and 6% by mass or less. The oxygen content of the titanium primary alloy is relatively high, 10% by mass or more and 15% by mass or less. The titanium primary alloy may contain metal elements other than titanium and aluminum. For example, the titanium primary alloy may contain 2% by mass or more and 10% by mass or less of iron or 2% by mass or more and 10% by mass or less of chromium. The sum of the iron and chromium contents is preferably 10% by mass or less.

[0016] In contrast, the aluminum content of the secondary titanium alloy obtained by refining is preferably equal to or less than that of the primary titanium alloy, for example, 2% by mass to 8% by mass, or 2% by mass to 6% by mass. The oxygen content of the secondary titanium alloy is significantly reduced compared to that of the primary titanium alloy, for example, 0.5% by mass to 6% by mass, or 0.5% by mass to 4% by mass.

[0017] The aluminum content and oxygen content of the titanium aluminum alloy obtained by molten salt electrolysis using a secondary titanium alloy as a titanium-based electrolytic material are lower than those of the secondary titanium alloy, for example, the aluminum content is 3% by mass or less or 2% by mass or less, and the oxygen content is 0.3% by mass or less or 0.15% by mass or less.

[0018] The content of aluminum and other metals in titanium metal and titanium-aluminum alloys can be measured by inductively coupled plasma (ICP) atomic emission spectroscopy. The oxygen content in titanium metal and titanium-aluminum alloys can be measured by inert gas fusion-infrared absorption spectroscopy. In addition to oxygen, titanium metal and titanium-aluminum alloys may also contain trace amounts of other components that are unavoidably mixed in, such as non-metallic elements such as carbon and nitrogen, or metallic elements such as iron. Therefore, the titanium content in titanium metal and titanium-aluminum alloys is determined by subtracting the total amount of metallic and non-metallic components other than titanium.

[0019] 2. Titanium primary alloy manufacturing (smelting) In this process, a raw material containing at least titanium oxide is used, and the titanium oxide is reduced using an aluminum-based reducing agent. Examples of aluminum-based reducing agents include metallic aluminum and aluminum alloys. Aluminum alloys are preferably alloys containing aluminum and a metal that is not easily dissolved in titanium, such as an aluminum-calcium alloy or an aluminum-magnesium alloy. The raw material containing titanium oxide is not particularly limited, and various compounds containing titanium and oxygen, including titanium ore and titanates, can be used. For example, titanium oxide or compositions with a high titanium oxide content can also be used as the raw material. There is no restriction on the titanium oxide content of the titanium ore. For example, titanium ore containing 50% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more of titanium oxide (TiO2) can be used. Since a higher titanium oxide content in titanium ore is preferable, the upper limit is not particularly limited, and can be, for example, 100% by mass or less or 99% by mass or less. There is also no restriction on the particle size of the titanium ore. For example, titanium ore with an average particle size of 100 μm to 1 mm can be used. Furthermore, the titanium ore may contain metal elements other than titanium, such as calcium, magnesium, manganese, iron, vanadium, aluminum, zirconium, chromium, etc. Furthermore, in addition to the above-mentioned raw materials, scrap of metallic titanium or scrap of titanium-aluminum alloys containing a relatively high content of oxygen may also be used.

[0020] Furthermore, raw materials containing iron and / or chromium may be used so that the titanium primary alloy contains iron and / or chromium in the above-mentioned amounts. Examples of raw materials containing iron and / or chromium include metals, alloys, and intermetallic compounds of these metals. For example, raw materials containing iron and chromium include metallic iron (such as electrolytic iron), chromium, steel, and TiFe alloys.

[0021] The reduction is carried out by heating a mixture containing titanium oxide and an aluminum-based reducing agent. Specifically, for example, the mixture may be placed in a container made of tungsten, molybdenum, tantalum, or the like and heated by resistance heating, which involves passing electricity through the container. Alternatively, the mixture may be placed in a crucible made of graphite, boron nitride, or other ceramic material, or a water-cooled copper or copper alloy crucible, and heated by induction heating (a susceptor may be used if the crucible is not induction-heatable). Alternatively, heating may be carried out by electron beam, arc, plasma arc, or the like. The heating temperature is not particularly limited as long as it can melt the raw materials, and is appropriately selected from temperatures between 1500°C and 3000°C. To suppress evaporation of aluminum and titanium and achieve efficient reduction, the heating temperature may be set to, for example, 2500°C or less, or 2000°C or less.

[0022] The mixing ratio of titanium oxide to aluminum-based reducing agent used in the reduction can be determined as appropriate. However, from the perspective of reducing the aluminum content in the titanium secondary alloy, the mixing ratio of titanium oxide to aluminum-based reducing agent is preferably selected so that the resulting titanium primary alloy has a relatively high oxygen content and a low aluminum content. Specifically, the ratio is determined in consideration of the titanium oxide composition so that the mass ratio of titanium oxide to aluminum in the aluminum-based reducing agent is 2.2 to 2.7. This allows for the production of a titanium primary alloy with aluminum and oxygen contents within the aforementioned ranges. More preferably, a melting promoter is added to this mixture. The melting promoter promotes the dissolution of the raw materials and the formation of slag. Examples of melting promoters include alkali metal or alkaline earth metal halides, such as calcium fluoride, calcium chloride, and calcium oxide.

[0023] Heating the mixture causes a reduction reaction, producing titanium, aluminum, a titanium primary alloy containing a relatively high content of oxygen, and slag. When the raw materials are molten, the slag has a lower specific gravity than the titanium primary alloy, so a layer of slag separates on top of the titanium primary alloy. As a result, solidified slag adheres to the top of the titanium primary alloy. By removing this slag, the titanium primary alloy can be obtained. The slag can also be separated from the titanium primary alloy by tilting the container or skimming.

[0024] 3. Dealuminization treatment As an optional step, the titanium primary alloy may be subjected to dealumination to further reduce the aluminum content. For example, this dealumination may be performed when the aluminum content of the titanium primary alloy exceeds 8% by mass. Note that, from the perspective of reducing the number of times the molten salt electrolysis described below is performed, dealumination may be performed even when the aluminum content of the titanium primary alloy is 2% by mass or more and 8% by mass or less. The dealumination is performed by heating the titanium primary alloy to a temperature of 1680°C or more and 1900°C or less to form a molten alloy and maintaining the molten alloy at this temperature for a certain period of time. The heating method can also be appropriately selected; the titanium primary alloy may be placed in a water-cooled copper crucible or hearth and heated and melted. Examples of heat sources that can be used include an electron beam, an arc, a plasma arc, and a magnetic field generated by an induction coil.

[0025] In dealumination, the solidified titanium primary alloy may be remelted by heating it to a temperature selected from the above-mentioned temperature range. Alternatively, in the production of the titanium primary alloy described above, the titanium primary alloy from which the slag has been separated may be heated within the above-mentioned temperature range while maintaining the molten state. In dealumination, components containing mainly aluminum evaporate from the titanium primary alloy, resulting in a reduction in the aluminum content. Therefore, to more significantly reduce the aluminum content, heating may be performed at a relatively high temperature (e.g., 1700°C to 1900°C, or 1750°C to 1900°C).

[0026] The atmosphere during heating preferably does not contain gases such as oxygen or nitrogen to suppress the formation of titanium nitrides or titanium oxides. Therefore, it is preferable to perform heating in an inert gas atmosphere such as helium or argon. The pressure of the inert gas atmosphere is preferably lower than atmospheric pressure. For example, heating may be performed in an inert gas atmosphere with a pressure of 0.0001 Pa or more and 0.1 Pa or less. The heating time (i.e., the time for which the titanium primary alloy is maintained as a molten metal) may be appropriately selected, for example, from a range of 3 minutes to 2 hours, depending on the mass of the titanium primary alloy.

[0027] Alternatively, dealumination may be performed using the drip-melt method. In this method, a molten titanium primary alloy is poured or dripped, during which aluminum and other substances are evaporated and removed. For example, the titanium primary alloy is placed on a hearth, crucible, or mold, heated and melted, and the resulting molten alloy is dripped into the crucible or mold. When a hearth is used, the molten alloy may be dripped from the hearth into the crucible or mold. Electron beams, arcs, plasma arcs, and other heating sources are used, with electron beams being preferred because of their easy adjustment of heating energy and heating position. When an electron beam is used, the titanium primary alloy can be placed directly above the crucible or mold and heated and melted, allowing drip-melt without the use of a hearth. Because aluminum volatilizes during dripping, the molten alloy with a reduced aluminum content can be poured into the crucible or mold.

[0028] 4. Manufacturing of secondary titanium alloys (refining) As mentioned above, although the aluminum content of titanium primary alloys is relatively low, they also contain a relatively high oxygen content. When a titanium primary alloy with a high oxygen content is used as an anode in molten salt electrolysis, the high oxygen content increases the anode resistance, which increases the voltage in molten salt electrolysis and, as a result, power consumption. Furthermore, using a titanium-based electrolytic material with a high oxygen content tends to result in a large amount of anode residue after molten salt electrolysis, reducing the amount of metallic titanium or titanium-aluminum alloy obtained per unit weight from the titanium-based electrolytic material. For this reason, in an embodiment of the present invention, the titanium primary alloy is subjected to a deoxidation treatment (refining) primarily for the purpose of reducing the oxygen content. This treatment can also reduce the aluminum content.

[0029] Deoxidation is performed by treating the titanium primary alloy with a calcium-based deoxidizer. For example, the titanium primary alloy and calcium-based deoxidizer are heated in a heat-resistant container at a temperature of 1680°C to 1850°C. The heating time may be appropriately selected from a range of, for example, 3 minutes to 2 hours, or 15 minutes to 2 hours, depending on the mass of the titanium primary alloy. Examples of heat-resistant containers include graphite, ceramic, and copper crucibles, and a water-cooled copper crucible may also be used. The heating method is not limited, and may include induction heating or heating using a heat source such as an electron beam, arc, or plasma arc. Heating is performed to melt the titanium primary alloy. Therefore, the solid titanium primary alloy obtained by smelting may be remelted and the calcium-based deoxidizer may be added to the resulting molten metal. Alternatively, the solid titanium primary alloy obtained by smelting may be mixed with the calcium-based deoxidizer and then heated within the above temperature range to form the molten titanium primary alloy. Alternatively, after separating the slag in the production of the titanium primary alloy, the calcium-based deoxidizer may be added while the titanium primary alloy is still in a molten state.

[0030] Examples of calcium-based deoxidizers include calcium compounds, zero-valent metallic calcium, and calcium alloys. Examples of calcium compounds include calcium halides such as calcium fluoride and calcium chloride. The calcium-based deoxidizer may contain calcium oxide as the calcium compound. Because calcium compounds have a higher boiling point than titanium and aluminum, they prevent the calcium-based deoxidizer from volatilizing and disappearing during deoxidation. Examples of calcium alloys include calcium-aluminum alloys, calcium-magnesium alloys, and calcium-silicon alloys. Among these, calcium-magnesium alloys are preferred because they are less likely to remain in metallic titanium or titanium-aluminum alloys. Among these calcium-based deoxidizers, metallic calcium or its alloys are particularly preferred because of their high deoxidation ability due to their reducing power. The amount of calcium-based deoxidizer relative to the titanium primary alloy can be adjusted appropriately depending on the oxygen content of the titanium primary alloy. For example, the calcium content may be selected from a range of 25 g to 80 g per 100 g of titanium primary alloy.

[0031] When calcium metal or calcium alloys are used as calcium-based deoxidizers, oxygen in the titanium primary alloy is captured as metal oxides, such as calcium oxide, forming slag containing this metal oxide. Because the specific gravity of the slag is lower than that of titanium metal or titanium-aluminum alloys, the slag separates from the titanium secondary alloy as a floating layer that forms on the deoxidized titanium primary alloy (i.e., the titanium secondary alloy) in a heat-resistant container. Furthermore, because calcium metal has a lower boiling point and melting point than titanium and aluminum, it is less soluble in titanium. Therefore, excess or unreacted calcium metal can be removed by evaporation or skimming. This mechanism works to remove excess or unreacted calcium metal or calcium alloys during deoxidation, while also removing the calcium oxide resulting from oxygen capture as slag. As a result, the oxygen content of the titanium primary alloy can be reduced while suppressing calcium contamination in the titanium secondary alloy.

[0032] The same is true when calcium halides are used as calcium-based deoxidizers. The oxygen in the titanium primary alloy is captured as titanates or calcium oxide, forming slag. Titanium halides such as titanium fluoride and aluminum halides such as aluminum fluoride and aluminum chloride are also produced, which either mix with the slag or evaporate during the deoxidation process. This allows for a reduction in the aluminum content of the titanium primary alloy.

[0033] On the other hand, when calcium-based deoxidizers contain calcium oxide, the amount of slag can be increased by calcium oxide, and the aluminum and oxygen in the titanium primary alloy can be absorbed into the slag as alumina, thereby reducing the oxygen concentration in the titanium primary alloy.

[0034] The slag may be removed by tilting or skimming, or by selectively discharging the molten titanium secondary alloy from the heat-resistant container (e.g., by discharging from the bottom of the heat-resistant container). Alternatively, the titanium secondary alloy and the slag may be solidified, and then the slag separated from the titanium secondary alloy may be removed. Because oxygen can be easily separated from the titanium secondary alloy as slag, there is no need to forcibly evaporate the slag during the deoxidation treatment. Therefore, the deoxidation treatment can be carried out, for example, under atmospheric pressure or under pressure, in order to suppress the evaporation of the calcium-based deoxidizer. Similar to smelting, refining is preferably carried out in an inert gas atmosphere.

[0035] In the deoxidation treatment, iron and / or chromium may be further added to the titanium primary alloy. Adding iron and / or chromium to the titanium primary alloy is particularly preferable when the titanium primary alloy has a low iron and / or chromium content. In this case, iron and / or chromium may be added to the titanium primary alloy so that the titanium primary alloy contains 2 to 10 mass% of iron and / or chromium relative to the total amount of the titanium primary alloy. The iron and / or chromium sources may be the above-mentioned metals, alloys, intermetallic compounds, etc. containing iron and / or chromium. By including iron and / or chromium in the titanium primary alloy in the above-mentioned amounts, the oxygen content can be more effectively reduced during the deoxidation treatment. However, to prevent iron and / or chromium from being mixed into the titanium metal or titanium-aluminum alloy obtained by molten salt electrolysis, it is preferable that the total iron and chromium content of the titanium primary alloy does not exceed 10 mass%.

[0036] Refining by deoxidation treatment allows for the production of secondary titanium alloys with reduced oxygen content. Furthermore, as mentioned above, aluminum halides can also be removed, allowing for the production of secondary titanium alloys with lower aluminum contents compared to primary titanium alloys. The aluminum and oxygen contents of secondary titanium alloys are as described above. Secondary titanium alloys are used as anodes in molten salt electrolysis, as described below, and may be crushed, processed, shaped, etc., during this process. If the anode is cast by pouring molten titanium secondary alloy into a mold, the processing and shaping steps may be omitted.

[0037] 5. Molten salt electrolysis Subsequently, the titanium-based electrolytic material, which is a secondary titanium alloy that has been processed and shaped as necessary, is refined by molten salt electrolysis, which results in metallic titanium or titanium-aluminum alloy with further reduced aluminum and oxygen content as an electrodeposit.

[0038] Molten salt electrolysis is carried out, for example, in an electrolytic cell 100 shown schematically in FIG. 2. The electrolytic cell 100 shown in FIG. 2 is a heat-resistant container made of a heat-resistant material such as brick or concrete, a ceramic such as aluminum oxide or boron nitride, or a metal having a surface coated with a material such as nickel that is resistant to elution by molten salt, and is provided with a lid (not shown) as appropriate. This allows the electrolytic cell 100 to be sealed and filled with an inert gas. Molten salt 102 that functions as an electrolyte is stored in the electrolytic cell 100. Although not shown, a heater may be installed inside the electrolytic cell 100 to maintain the molten salt 102 in a molten state.

[0039] The electrolytic cell 100 further includes a cathode 106 and a titanium-based electrolytic material as an anode 104. The anode 104 and cathode 106 are electrically connected to a power source 108. The titanium-based electrolytic material may be directly connected to wiring 110. Alternatively, for example, a titanium secondary alloy containing a metal, such as nickel, that has a lower ionization tendency than titanium or aluminum may be placed in a container with numerous through-holes as the titanium-based electrolytic material, and the titanium-based electrolytic material may be connected to wiring 110 via this container. The cathode 106 preferably has at least its surface made of a heat-resistant, conductive material such as titanium, molybdenum, carbon, or steel, such as carbon steel. There is no limit to the number of anodes 104 and cathodes 106; multiple anodes 104 and one or more cathodes 106 may be used. Although not shown, one or more bipolar electrodes may be placed between the anode 104 and the cathode 106. When a current is applied between the anode 104 and the cathode 106 using a power source 108, the titanium-based electrolytic material that constitutes the anode 104 is oxidized to generate titanium ions, which migrate to the molten salt 102. Meanwhile, on the cathode 106, titanium ions, which have a low ionization tendency, are preferentially reduced, and metallic titanium is deposited on the cathode 106.

[0040] Examples of electrolytes include chlorides of alkali metals and alkaline earth metals, such as lithium chloride, sodium chloride, potassium chloride, magnesium chloride, and calcium chloride. The use of multiple chlorides causes a freezing point depression, allowing the electrolyte to be maintained in a molten state at lower temperatures, specifically, at temperatures between 480°C and 850°C. Preferably, the electrolyte contains 30% to 90% by mass of magnesium chloride. Using an electrolyte containing magnesium chloride allows for the production of electrodeposits with a reduced aluminum content, making the addition of magnesium chloride particularly preferable when producing metallic titanium. Furthermore, the electrolyte may contain 3% to 20% by mass or 6% to 10% by mass of titanium dichloride (TiCl2). This ensures a high amount of titanium ions in the molten salt, facilitating current flow to the electrode and the formation of an electrodeposit. Note that titanium dichloride can undergo a disproportionation reaction in the molten salt bath to form titanium trichloride (trivalent) or titanium tetrachloride (tetravalent). Fluorides, bromides, or iodides of alkali metals or alkaline earth metals may be used as the electrolyte, but in consideration of operating costs and equipment life, it is preferable to set the content of these electrolytes to, for example, 5 mass % or less, or 2 mass % or less.

[0041] As shown in the examples, the above-mentioned titanium-based electrolytic material, i.e., a titanium secondary alloy produced by deoxidizing a titanium primary alloy smelted by reduction of titanium oxide using an aluminum-based reducing agent, can be used as an anode in molten salt electrolysis to produce high-purity metallic titanium or a titanium-aluminum alloy with an extremely low oxygen content. Conventionally, in refining using a smelted titanium-aluminum alloy as an anode in molten salt electrolysis, it has been difficult to significantly reduce the oxygen and aluminum content in a single refining run, and multiple molten salt electrolysis runs have typically been required. Furthermore, molten salt electrolysis is a relatively long process, requires significant equipment maintenance, and is energy-intensive, resulting in high operating costs.

[0042] In contrast, by employing the method for producing metallic titanium or a titanium-aluminum alloy according to an embodiment of the present invention, a secondary titanium alloy with low aluminum and oxygen contents can be obtained. Therefore, high-purity metallic titanium or a titanium-aluminum alloy with an extremely low oxygen content can be provided without repeating molten salt electrolysis (for example, by a single molten salt electrolysis). Furthermore, this method does not require the prior preparation of aluminum with a significantly reduced oxygen content. Therefore, high-purity metallic titanium or a titanium-aluminum alloy with an extremely low oxygen content can be produced at lower cost.

[0043] Furthermore, in the production of the above-described titanium primary alloy, coke, which is used in the Kroll process, is not used as a reducing agent, thereby reducing carbon dioxide emissions. Furthermore, by using the titanium secondary alloy obtained by deoxidation treatment as a titanium-based electrolytic material, the number of times molten salt electrolysis, which requires a lot of electricity, can be performed can be reduced. Therefore, it can be said that the production method of metallic titanium or a titanium aluminum alloy according to one embodiment of the present invention is a method that places a smaller burden on the environment than conventional methods. [Example]

[0044] Hereinafter, an example will be described in which a titanium primary alloy and a titanium secondary alloy were produced according to the above embodiment, and then metallic titanium was produced using the titanium secondary alloy as a titanium-based electrolytic material.

[0045] 1. Titanium primary alloy manufacturing (1) Example 1 196 g of titanium oxide (titanium ore, purity 95% by mass), 79 g of metallic aluminum (manufactured by Minalco Corporation, purity 99.7% by mass), and 163 g of calcium fluoride (purity 94% by mass) were placed in a graphite heat-resistant container (volume approximately 0.4 L) and heated at approximately 1650°C for 60 minutes using a resistance heating method in an argon atmosphere at approximately atmospheric pressure. After the heat-resistant container was cooled to room temperature, the separated slag was removed, yielding 83 g of titanium primary alloy.

[0046] To determine the composition of the obtained titanium primary alloy, first, the contents of metal elements other than titanium and the oxygen content were measured by ICP atomic emission spectroscopy and inert gas fusion-infrared absorption spectroscopy, respectively. The titanium content was determined by subtracting the contents of metal elements other than titanium and the oxygen content from the total amount of the titanium primary alloy, which was set to 100 mass%. As a result, the composition of the titanium primary alloy in Example 1 was Ti-5.8Al-12.7O-2Fe (the number before the element symbol represents mass%. However, the titanium primary alloy contains unavoidable impurities other than aluminum, oxygen, and iron. The same applies below.).

[0047] (2) Example 2 2.7 kg of titanium oxide (manufactured by Toho Titanium Co., Ltd., purity 98% by mass), 1.1 kg of metallic aluminum (manufactured by Minalco Corporation, purity 99.7% by mass), and 2.2 kg of calcium fluoride (purity 94% by mass) were placed in a water-cooled copper hearth (volume approximately 10 L) and heated at approximately 2000°C for 10 minutes using a plasma arc heating method in an argon atmosphere at approximately atmospheric pressure. After the heat-resistant container was cooled to room temperature, the separated slag was removed, yielding 1.4 kg of titanium primary alloy. The composition of the titanium primary alloy of Example 2 was measured using the same method as in Example 1, and the composition was Ti-4.4Al-12.6O-0.4Fe.

[0048] (3) Example 3 1.6 kg of titanium oxide (titanium ore, purity 95% by mass), 0.6 kg of metallic aluminum (manufactured by Minalco Corporation, purity 99.7% by mass), and 1.3 kg of calcium fluoride (purity 94% by mass) were placed in a graphite heat-resistant container (volume approximately 5 L) and heated at approximately 1640°C for 60 minutes using induction heating in an argon atmosphere at atmospheric pressure. After the heat-resistant container was cooled to room temperature, the separated slag was removed, yielding 0.9 kg of titanium primary alloy. The composition of the titanium primary alloy was measured using the same method as in Example 1, and was found to be Ti-7.1Al-13.9O-2Fe.

[0049] As shown in Examples 1 to 3, it was confirmed that a titanium primary alloy with an aluminum content of 2% by mass to 8% by mass could be obtained by reducing titanium oxide with an aluminum-based reducing agent. It was also confirmed that the titanium primary alloy had a relatively high oxygen content.

[0050] 2. Dealumination Treatment (Example 4) As described above, depending on the aluminum content (for example, when the aluminum content in the titanium primary alloy exceeds 8 mass %), the titanium primary alloy can be subjected to dealumination treatment. In this Example 4, the results of dealumination of the titanium primary alloy are described.

[0051] A titanium primary alloy (composition: Ti-10Al-13O-2Fe, 5 kg) was placed in a water-cooled copper crucible and dealuminated by induction heating at 1700°C for 10 minutes under an argon atmosphere of 0.02 Pa. As a result, a titanium primary alloy having a composition of Ti-4.1Al-13.8O-1.5Fe was obtained. This result confirmed that dealumination effectively reduces the aluminum content, and that a titanium primary alloy having an aluminum content of, for example, 8% by mass or less or 6% by mass or less can be obtained.

[0052] 3. Deoxidation treatment This example describes the results of deoxidizing a titanium primary alloy by treating it with a calcium-based deoxidizer. Specifically, a mixture containing a titanium primary alloy and a calcium-based deoxidizer with the composition shown in Table 1 was placed in a water-cooled copper crucible and heated by induction heating under a reduced pressure (45 kPa) argon atmosphere to melt the mixture. The heating conditions were as shown in Table 1. After the water-cooled copper crucible was cooled to room temperature, the layered slag was separated to obtain a titanium secondary alloy. The composition of the resulting titanium secondary alloy is also shown in Table 1.

[0053] [Table 1]

[0054] As shown in Table 1, deoxidation treatment reduces the oxygen content. It is particularly noteworthy that the oxygen content is significantly reduced in the case of titanium primary alloys with a high iron content (Example 7). Furthermore, while the aluminum content increases in Example 8 due to deoxidation treatment, it was confirmed that the aluminum content also decreases in the other examples. While the primary titanium alloy of Example 8 had a large discrepancy between the aluminum content and the oxygen content, the oxygen content of the secondary titanium alloy was reduced, and the increase in aluminum content was within an acceptable range, improving the compositional balance. These results indicate that deoxidation treatment can produce secondary titanium alloys with an aluminum content reduced to a level of 2% by mass or more and 8% by mass or less, or 2% by mass or more and 6% by mass or less.

[0055] 4. Production of titanium metal by molten salt electrolysis The titanium secondary alloy obtained in Example 7 was processed into a size of 1 cm x 1 cm x 1 cm, filled into a nickel container with multiple through-holes, and used as an anode. A titanium cathode was used. These anode and cathode were placed in an electrolytic cell, and magnesium chloride, sodium chloride, potassium chloride, and titanium dichloride were further added to the electrolytic cell as an electrolyte. The electrolyte had a composition ratio of magnesium chloride, sodium chloride, and potassium chloride of 50 mass%, 25 mass%, and 25 mass%, respectively, and was prepared by using 7 mass% titanium dichloride for a total of 93 mass% of magnesium chloride, sodium chloride, and potassium chloride. The electrolyte was heated to 600°C to form a molten salt, and a current of 0.4 A / cm was applied between the cathode and anode. 2 After the current was passed through the cathode, metallic titanium was obtained as an electrodeposit on the cathode.

[0056] Measurement of the aluminum and oxygen contents in the obtained titanium metal revealed that they were 0.01% by mass and 0.04% by mass, respectively, demonstrating that titanium metal with an extremely low oxygen concentration could be obtained by a single molten salt electrolysis without the need for repeated molten salt electrolysis.

[0057] The above results indicate that metallic titanium and titanium-aluminum alloys with significantly reduced oxygen content can be produced at low cost by subjecting primary titanium alloys with a relatively high oxygen content to deoxidation treatment to produce secondary titanium alloys, and then using these as titanium-based electrolytic materials in molten salt electrolysis.

[0058] Based on the above-described embodiments of the present invention, those skilled in the art may add, delete, or modify components, or add, omit, or modify processes as appropriate, as long as they comply with the spirit of the present invention. Even if there are other effects and advantages different from those achieved by the aspects of the above-described embodiments, those that are clear from the description in this specification or that can be easily predicted by those skilled in the art are naturally considered to be achieved by the present invention. [Explanation of symbols]

[0059] 100: electrolytic cell, 102: molten salt, 104: anode, 106: cathode, 108: power supply, 110: wiring

Claims

1. A method for producing a titanium-based electrolytic material includes producing a titanium secondary alloy by deoxidizing a titanium primary alloy containing 2% by mass or more and 8% by mass or less of aluminum and 10% by mass or more and 15% by mass or less of oxygen using a calcium-based deoxidizer.

2. The manufacturing method according to claim 1 , wherein the deoxidation treatment is performed by treating the molten titanium primary alloy with the calcium-based deoxidizer in a heat-resistant container.

3. The method of claim 1 further comprising preparing the titanium primary alloy by treating titanium oxide with an aluminum-based reducing agent.

4. The method according to claim 1 , wherein the calcium-based oxygen absorber is one or more selected from the group consisting of metallic calcium, calcium alloys, calcium fluoride, calcium chloride, and calcium oxide.

5. The manufacturing method according to claim 1 , wherein the deoxidation treatment is carried out so that the oxygen content of the titanium secondary alloy is 6 mass % or less.

6. A method for producing metallic titanium or a titanium-aluminum alloy, comprising carrying out molten salt electrolysis using the titanium-based electrolytic material produced by the method according to any one of claims 1 to 5 as an anode.

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