Method for producing titanium metal or titanium aluminum alloy

Abstract

To provide a method for producing a high purity titanium-based electrolytic material capable of using in molten salt electrolysis for producing titanium metal or titanium aluminum alloy.SOLUTION: This manufacturing method involves heating a primary alloy containing titanium, aluminum, and oxygen, which is generated by treating titanium oxide with metallic aluminum, at a temperature of 1500°C to 1800°C. The oxygen content in the primary alloy is 0.5 mass% or more. The aluminum content in the primary alloy may be 3 mass% or more and 35 mass% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] One embodiment of the present invention relates to a method for producing titanium metal or a titanium aluminum alloy. [Background technology]

[0002] One known method for producing titanium metal is a method based on the Kroll process. In this method, titanium tetrachloride is produced using titanium ore containing titanium oxide, coke, and chlorine, which is then reduced with metallic magnesium and crushed to produce sponge titanium. This sponge titanium is then melted and cast to produce titanium metal or a titanium-aluminum alloy. It is also known that the oxygen content can be reduced by heating and melting a titanium-aluminum alloy with a high aluminum content (see Patent Documents 1 and 2).

[0003] In recent years, a manufacturing method that can reduce carbon dioxide emissions has been developed as an alternative to the Kroll process. In this method, a raw material such as titanium ore is first melted in the presence of a viscosity agent, and then reduced with metallic aluminum to produce a titanium-aluminum alloy for molten salt electrolysis (see Patent Document 3). By using this alloy as an anode and repeating molten salt electrolysis, metallic titanium or a titanium-aluminum alloy can be obtained as a deposit on the cathode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-135907 [Patent Document 2] Japanese Patent Application Publication No. 5-59466 [Patent Document 3] Special Publication No. 2015-507696 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 high-purity titanium-based electrolytic materials 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 metallic titanium or a titanium-aluminum alloy. The method includes heating a primary alloy containing titanium, aluminum, and oxygen produced by treating titanium oxide with aluminum at a temperature of 1500°C to 1800°C. The oxygen content in the primary alloy is 0.5% by mass or more. [Brief explanation of the drawings]

[0007] [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

[0008] 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.

[0009] 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.

[0010] 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.

[0011] 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 primary alloy containing titanium, aluminum, and a certain amount of oxygen is first produced by reducing a raw material, such as titanium ore containing titanium oxide, with zero-valent metallic aluminum or an aluminum alloy. This primary alloy is then used as an anode in molten salt electrolysis, and hereinafter, this primary alloy containing titanium, aluminum, and oxygen will also be referred to as a titanium-based electrolytic material. The titanium-based electrolytic material is then subjected to a process (dealuminization) to reduce the aluminum content. The dealumination process reduces the aluminum content in the titanium-based electrolytic material, thereby relatively increasing the titanium content (purity). After dealumination, the titanium-based electrolytic material is refined by molten salt electrolysis using the material as the anode, yielding metallic titanium or a titanium-aluminum alloy. These steps are described below.

[0012] In this specification, metallic titanium may refer to commercially pure titanium. The titanium content of the total metal elements in metallic titanium is preferably 99% by mass or more and 100% by mass or less. When metallic titanium contains aluminum or oxygen, the aluminum content of metallic titanium is 0.1% by mass or less or 0.01% by mass or less. The oxygen content of metallic titanium is 0.2% by mass or less, 0.10% by mass or less, or 0.05% by mass or less. On the other hand, titanium-aluminum alloys contain, in addition to titanium, aluminum in an amount greater than 0.1% by mass. The aluminum content in titanium-aluminum alloys may be, for example, 6% by mass or less, 3% by mass or less, or 2% by mass or less. The oxygen content in titanium-aluminum alloys may be, for example, 0.3% by mass or less, or 0.15% by mass or less. Metallic titanium and titanium-aluminum alloys may contain trace amounts of other components in addition to oxygen, such as non-metallic elements such as carbon and nitrogen, or metallic elements such as iron. These elements are inevitably mixed in during the manufacturing process of titanium metal and titanium aluminum alloys.

[0013] 2. Preparation of primary alloy containing titanium, aluminum, and oxygen In this process, titanium oxide is used as a raw material and reduced using metallic aluminum or an aluminum alloy, i.e., aluminum. The titanium oxide is not particularly limited, and a wide variety of titanium and oxygen-containing compounds, including titanium ore, can be used. For example, waste materials with a high titanium oxide content can also be used as titanium oxide. There are no restrictions on the titanium oxide content of the titanium ore; for example, titanium ore containing 35% to 99% by mass of titanium oxide (TiO2) can be used. There are also no restrictions 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, titanium ore may contain metal elements other than titanium, such as calcium, magnesium, manganese, iron, vanadium, aluminum, and zirconium.

[0014] The reduction is carried out by heating a mixture containing titanium oxide and aluminum. Specifically, for example, the mixture may be placed in a container made of tungsten, molybdenum, tantalum, or the like and heated using a resistance heating method in which electricity is passed through the container. Alternatively, the mixture may be placed in a crucible made of graphite, boron nitride, or other ceramic material and heated using an induction heating method. Alternatively, heating may be carried out using an 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 aluminum evaporation and achieve efficient reduction, the heating temperature can be set to, for example, 2500°C or less or 2000°C or less. The mixture ratio of titanium oxide to aluminum used in the reduction can also be appropriately determined, taking into account the titanium oxide composition, for example, so that the mass ratio of titanium oxide to aluminum is between 0.9 and 2.4. Preferably, a melting promoter is added to the mixture. The melting promoter facilitates the melting of the raw materials upon heating. Examples of the melting accelerator include halides of alkali metals or alkaline earth metals, and more specifically, calcium fluoride.

[0015] Heating the mixture causes a reduction reaction, producing a primary alloy containing titanium, aluminum, and oxygen. When the temperature of the melt drops below the melting point of the primary alloy, the primary alloy solidifies and separates from the molten slag due to the difference in specific gravity. Therefore, by cooling the mixture after reduction, solidified slag adheres to the top of the solidified primary alloy. By removing this slag, the primary alloy can be obtained as a titanium-based electrolytic material. The primary alloy can also be separated from the slag by pouring the slag away from the molten slag. While there are no restrictions on the aluminum content of the primary alloy obtained by heating the raw material mixture, the reduction conditions (e.g., the mixing ratio of titanium ore and aluminum) are preferably adjusted so that the aluminum content is 3% by mass or more and 35% by mass or less. The upper limit of the aluminum content of the primary alloy may be 30% by mass or less, or even 20% by mass or less. Furthermore, because some of the oxygen contained in the raw material titanium oxide remains in the primary alloy, a certain amount of oxygen, specifically 0.5 mass% or more, is contained in the primary alloy. The oxygen content of the primary alloy is often, for example, 15 mass% or less. In one embodiment of the present invention, the aluminum content in the obtained primary alloy is further reduced to obtain a titanium-based electrolytic material for use in molten salt electrolysis.

[0016] 3. Dealuminization and deoxidation of primary alloys containing titanium, aluminum, and oxygen As mentioned above, the primary alloy contains aluminum. Therefore, when producing metallic titanium or titanium-aluminum alloys with a relatively low aluminum content, dealumination is performed to reduce the aluminum content in the primary alloy. As described below, this production method can reduce the aluminum content of the primary alloy.

[0017] Dealuminization is performed by heating a primary alloy, which is produced by melting and solidifying a mixture containing titanium oxide and aluminum, to a temperature between 1500°C and 1800°C. This heating melts the primary alloy, evaporating the aluminum-containing components and reducing the aluminum content. If slag is removed by pouring or other methods during the production of the primary alloy, dealumination can be performed while maintaining the molten state of the primary alloy (i.e., without solidifying it). The heating temperature for dealumination can be determined appropriately depending on the purpose. For example, if a further reduction in aluminum content is desired, high-temperature treatment is effective, so heating at a temperature between 1680°C and 1800°C is acceptable. While high-temperature heating facilitates the removal of aluminum, it also facilitates the evaporation of titanium. Therefore, from the perspective of improving titanium yield, heating at a relatively low temperature, for example, between 1500°C and 1680°C, is preferable.

[0018] The atmosphere during heating preferably does not contain oxidizing gases such as oxygen. Therefore, heating is carried out in an inert gas atmosphere such as nitrogen, helium, or argon. To suppress the formation of titanium nitride, helium or argon is preferably used. The pressure of the inert gas atmosphere may be atmospheric pressure, or a pressure lower or higher than atmospheric pressure. For example, heating may be carried out in an inert gas atmosphere with a pressure of 0.001 Pa or more and 1 Pa or less. The heating time depends on the mass of the titanium-based electrolytic material, but may be appropriately selected, for example, from a range of 3 minutes to 2 hours.

[0019] The heating method can also be selected appropriately. For example, the primary alloy can be placed in a crucible or hearth containing a metal such as copper and capable of being cooled by water or other methods, and then heated. The heat source used in this process can be an electron beam, an arc, a plasma arc, or a magnetic field generated by an induction coil. Titanium oxide has low electrical conductivity, but a primary alloy with reduced oxygen content can be electrically heated, so so-called induction heating can be used. By heating under the above conditions, the primary alloy exists as a molten metal in the crucible or hearth, and aluminum, which has a higher vapor pressure than titanium, volatilizes preferentially. As a result, the aluminum content decreases.

[0020] Alternatively, dealumination may be performed by drip melt. In this method, the molten primary alloy is poured or dripped, during which time aluminum and other components are evaporated and removed. For example, a feeder for supplying the primary alloy is installed above the crucible or mold, the primary alloy supplied from the feeder is heated and melted, and the resulting molten metal is dripped into the crucible or mold. An electron beam, arc, plasma arc, or other suitable heating source is used, with an electron beam being preferred because the heating energy and heating position can be easily adjusted. Since aluminum volatilizes during dripping, the molten metal with a reduced aluminum content can be poured into the crucible or mold.

[0021] Under these conditions, titanium is less volatile than aluminum. This allows for the production of a titanium-based electrolytic material with a significantly reduced aluminum content, while minimizing the decrease in titanium recovery. That is, the aluminum content of the titanium-based electrolytic material can be lower than that of the primary alloy before dealumination. Depending on the dealumination conditions, it is possible to obtain a titanium-based electrolytic material with an aluminum content of 1% by mass or more, reduced to 12% by mass or less, 8% by mass or less, 5% by mass or less, or 2% by mass or less. Meanwhile, the oxygen content may not change significantly. Therefore, dealumination may selectively remove aluminum. The removal of aluminum in one embodiment of the present invention is believed to be due to the presence of a certain amount of oxygen in the primary alloy before dealumination and a low aluminum content (e.g., 35% by mass or less). Conversely, if a certain amount of oxygen is not present in the primary alloy, it is believed that little aluminum will be removed. As will be described later, this feature also contributes to reducing the load on the subsequent refining process using molten salt electrolysis.

[0022] As an optional step, a deoxidation treatment may be performed to further reduce the oxygen concentration of the dealuminated titanium-based electrolytic material. Specifically, the titanium-based electrolytic material may be reheated and melted in the presence of a flux, preferably calcium fluoride or calcium oxide, with the addition of a reducing agent, such as calcium, magnesium, yttrium, cesium, or a mixture of multiple rare earth elements (misch metal). The reducing agent reacts with oxygen to form slag, which separates together with the flux into the upper layer of the molten titanium-based electrolytic material. By separating the slag and flux, it is possible to obtain a titanium-based electrolytic material having an oxygen content of, for example, 0.05% by mass or more, 0.1% by mass or more, or 0.5% by mass or more, but not more than 2.0% by mass.

[0023] 4. Molten salt electrolysis As described above, dealumination can produce a titanium-based electrolytic material with a high titanium content and a significantly reduced aluminum content. To further reduce the aluminum content or to produce metallic titanium, the dealuminated titanium-based electrolytic material can be used as an anode and refined by molten salt electrolysis. Molten salt electrolysis produces an electrodeposit with even lower aluminum and oxygen contents.

[0024] 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.

[0025] The electrolytic cell 100 further includes a cathode 106 and a dealuminated 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, or the titanium-based electrolytic material may be placed in a container with numerous through-holes containing a metal, such as nickel, that has a lower ionization tendency than titanium or aluminum, and the titanium-based electrolytic material may be connected to wiring 110 via the container. The cathode 106 is made of a heat-resistant, electrically 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 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 with a low ionization tendency are preferentially reduced, and zero-valent titanium is deposited on the cathode 106.

[0026] 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, temperatures lower than the melting point of titanium. Preferably, the electrolyte contains 30 mol% to 90 mol% magnesium chloride. Using an electrolyte containing magnesium chloride allows for the production of an electrodeposit with a reduced aluminum content. Furthermore, the electrolyte may contain 3 mol% to 20 mol% titanium dichloride (TiCl2) and / or titanium trichloride (TiCl3). This ensures a high amount of titanium ions in the molten salt, facilitating the formation of an electrodeposit.

[0027] By appropriately adjusting the composition of the titanium-based electrolytic material and performing molten salt electrolysis, metallic titanium can be deposited on the cathode 106. It is also possible to obtain titanium-aluminum alloys with significantly reduced aluminum content, such as titanium-aluminum alloys with an aluminum content of 3% by mass or less or 2% by mass or less. Furthermore, by performing a deoxidation treatment before molten salt electrolysis, metallic titanium or titanium-aluminum alloys with an even lower oxygen content can be obtained. For example, metallic titanium with an oxygen content of 0.2% by mass or less, 0.1% by mass or less, or titanium-aluminum alloys with an oxygen content of 0.3% by mass or less or 0.15% by mass or less can be obtained.

[0028] As shown in the examples, the titanium-based electrolytic material described above, i.e., a primary alloy obtained by reducing titanium oxide with aluminum and having a certain oxygen content, can be heat-treated to volatilize aluminum, thereby producing a titanium-based electrolytic material with a low aluminum content.

[0029] In refining by molten salt electrolysis using a primary alloy as an anode, it is difficult to significantly reduce the aluminum content in a single refining run. Therefore, when a primary alloy that has not been dealuminated is used as a titanium-based electrolytic material, multiple molten salt electrolysis runs are usually required. Molten salt electrolysis takes a relatively long time, requires a large maintenance load for the equipment, and is a process that requires a large amount of energy and high operating costs. Therefore, by using a titanium-based electrolytic material whose aluminum content has been significantly reduced by the dealumination process described above, the titanium-based electrolytic material can be efficiently refined with a small number of molten salt electrolysis runs (for example, one run). Therefore, by applying an embodiment of the present invention, high-purity metallic titanium or titanium-aluminum alloys can be produced efficiently and at low cost without requiring multiple molten salt electrolysis runs. [Example]

[0030] In this example, a material modeled on a titanium-based electrolytic material (hereinafter referred to as the model material) was used to describe the results of the dealumination treatment described above. As exemplified in Patent Document 3, the primary alloy mainly contains titanium, aluminum, and oxygen, and may also contain a certain amount of iron. This point was taken into consideration when designing the model material.

[0031] 1. Preparation of Model Materials Titanium sponge granules (3625 g) passed through a 1 mm mesh, aluminum granules with an average particle size of 0.5 mm (640 g, Minalco Corporation, model number #208SP), titanium oxide (1958 g, powder, Toho Titanium Co., Ltd.), and magnetite (177 g, Kojundo Chemical Co., Ltd., model number FE019PB) were placed in a water-cooled copper crucible (approximately 3.5 L capacity). The mixture was then heated for 60 minutes using induction heating to melt the mixture. The mixture was then cooled and solidified to produce a model material (Sample 1). Note that the magnetite and titanium oxide served as oxygen sources. In addition to Sample 1, model materials with different compositions (Samples 2 and 3) were also prepared by varying the amounts of titanium sponge granules, aluminum granules, titanium oxide, and magnetite.

[0032] The results of measuring the compositions of Samples 1 to 3 are shown in Table 1. The oxygen content was measured by inert gas fusion-infrared absorption spectroscopy, and the aluminum and iron contents were measured by high-frequency inductively coupled plasma atomic emission spectroscopy. The titanium content was calculated by subtracting the amounts of aluminum, oxygen, and iron from the total amount (100%). As shown in Table 1, it was confirmed that all samples contained 1 mass% or more of oxygen.

[0033] [Table 1]

[0034] 2. Dealuminization treatment 5000 g of the model material was placed in a water-cooled copper crucible (volume approximately 3.5 L) and heated for 30 minutes using induction heating in an argon atmosphere at 0.10 Pa to 0.02 Pa. The model material was then cooled and solidified. The composition of the solidified model material was measured using inert gas fusion-infrared absorption spectroscopy and high-frequency inductively coupled plasma atomic emission spectroscopy. The heating temperature and composition measurement results are shown in Table 2.

[0035] [Table 2]

[0036] As can be seen from Table 2, we confirmed that dealumination of titanium-aluminum alloys containing a certain amount of oxygen or more significantly reduces the aluminum content. Furthermore, we found that the higher the oxygen content of the model material, the greater the reduction in aluminum content. For example, Sample 1, which had a high oxygen content (13% by mass), yielded a titanium-based electrolytic material with an aluminum content reduced to 2% by mass. This suggests that the significant reduction in aluminum content is due to the relatively low aluminum content in the sample and a certain amount of oxygen. Furthermore, the results of Sample 3 confirmed that the higher the heating temperature, the more effectively the aluminum content can be reduced. Analysis of the composition of the deposit on the upper inner wall of the crucible used for Sample 1 revealed aluminum, titanium, and iron at 86% by mass, 4% by mass, and 2% by mass, respectively. This indicates that dealumination of titanium-based electrolytic materials containing a certain amount of oxygen results in almost selective removal of aluminum, with almost no loss of titanium. Furthermore, the results of Sample 2 suggest that the dealumination also partially removes oxygen. The above results suggest that by subjecting the titanium-based electrolytic material obtained by dealumination to molten salt electrolysis, it is possible to produce not only titanium aluminum alloys but also high-purity metallic titanium while suppressing titanium loss.

[0037] 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]

[0038] 100: electrolytic cell, 102: molten salt, 104: anode, 106: cathode, 108: power supply, 110: wiring

Claims

1. The method includes preparing a titanium-based electrolytic material by treating a titanium oxide with aluminum to produce a primary alloy containing titanium, aluminum, and oxygen, and heating the primary alloy at a temperature of 1500°C or higher and 1800°C or lower; A method for producing metallic titanium or a titanium-aluminum alloy, wherein the oxygen content in the primary alloy is 0.5 mass% or more.

2. The manufacturing method according to claim 1 , wherein the aluminum content in the primary alloy is 3% by mass or more and 35% by mass or less.

3. The method of claim 1 , wherein the heating is performed by hearth melting or drip melting.

4. The method according to claim 1 , further comprising carrying out molten salt electrolysis using the titanium-based electrolytic material as an anode.

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