Method for producing titanium-based electrolytic raw material and method for producing metallic titanium or titanium alloy

Abstract

This method for producing a titanium-based electrolytic raw material produces a titanium-based electrolytic raw material used in molten salt electrolytic refining for obtaining metallic titanium or a titanium alloy. The method includes a reaction step for reacting a titanium oxide, elemental aluminum and / or alloy, and a calcium halide in a melt at a temperature of 1870°C or higher, and obtaining a titanium alloy product including Al and O generated by a reaction including deoxidation of a portion of O in the titanium oxide in a molten state.

Description

Method for producing titanium-based electrolytic raw materials and method for producing titanium metal or titanium alloy

[0001] The present invention relates to a method for producing a titanium-based electrolytic raw material used in molten salt electrolytic refining to obtain titanium or a titanium alloy, and a method for producing titanium or a titanium alloy.

[0002] Titanium metal (pure titanium) and titanium alloys are generally produced from titanium metal sponge, an intermediate product obtained from titanium ore by a method based on the Kroll process suitable for mass production.

[0003] However, this method requires the production of titanium tetrachloride by chlorinating titanium ore, followed by the purification of the titanium tetrachloride and its reduction with metallic magnesium, as well as the crushing of titanium sponge lumps and the electrolysis of the magnesium chloride produced by the reduction, and therefore involves a number of batch processes, making it difficult to say that metallic titanium can be produced efficiently and at low cost. Furthermore, the reaction to produce titanium tetrachloride uses coke (carbon), which emits carbon dioxide, a greenhouse gas that contributes to global warming.

[0004] In contrast, electrolytic refining using a molten salt bath (also called "molten salt electrorefining") may potentially make it possible to produce metallic titanium and titanium alloys with fewer impurities more easily than methods based on the Kroll process. Examples of this type of technology include those described in Patent Documents 1 and 2.

[0005] Patent Document 1 describes a method for extracting a titanium product from titanium ore, comprising the steps of: mixing a chemical blend containing titanium ore and a reducing agent, the ratio of the titanium ore to the reducing agent being 0.9 to 2.4, the mass ratio of the titanium oxide component in the titanium ore to the reducing metal in the reducing agent being equivalent to; heating the chemical blend to initiate an extraction reaction, the chemical blend being heated at a rate of increase of 1°C to 50°C / min; maintaining the chemical blend at a reaction temperature of 1500 to 1800°C for a time period between 5 and 30 minutes; cooling the chemical blend to a temperature below 1670°C; and separating the titanium product from the residual slag, in which "the titanium ore contains titanium oxide (TiO2) and the reducing agent contains aluminum (Al)." Patent Document 2 also describes a similar method.

[0006] Regarding the above-mentioned "chemical blend," Patent Document 1 states, "The chemical blend includes one or more viscosity agents to achieve a desired slag viscosity. ... A viscosity agent is selected that only affects the viscosity of the chemical blend and the resulting slag and only to a limited extent when the chemical blend is heated. Calcium fluoride (CaF2) is an example of such a viscosity agent. CaF2 does not participate in the chemical reaction between the titanite and the reducing agent, but only assists in adjusting the viscosity of the melt. ... In general, components that do not participate in the reaction but assist in adjusting the viscosity of the slag are good candidates. In some embodiments, various alkali halides, alkaline earth halides, and certain oxides may be used as viscosity agents" (paragraph 0042). Furthermore, Patent Document 1 states that "the final temperature is between 1500°C and 1800°C... If the final temperature is higher than 1800°C..., the extraction reaction will produce a titanium product containing a higher amount of contaminants because the molten titanium product reacts with the reaction vessel and slag" (paragraph 0052). Patent Document 2 also contains a similar statement (see paragraphs 0031 and 0033).

[0007] Although Patent Document 3 does not relate to molten salt electrolytic refining, it discloses a "method for producing a high-quality, i.e., low-oxygen Ti-Al alloy by deoxidizing a low-grade titanium raw material containing a large amount of titanium oxide (TiO2), such as low-grade sponge titanium, scrap titanium, or rutile ore, to which an aluminum raw material has been added, and dissolving the resulting mixture." More specifically, the method describes a Ti-Al alloy production method, which comprises: "adding a flux containing 35% by weight or more of calcium fluoride in calcium oxide to a molten material made of titanium and aluminum, the molten material containing 50% or more by weight of aluminum; placing the molten material to which the flux has been added into a water-cooled copper crucible having a tap hole formed at the bottom; inducing melting by creating an atmosphere of 1.33 Pa or more inside the water-cooled copper crucible; pouring the molten material induction-melted in the water-cooled copper crucible downward from the tap hole to separate the oxygen-containing flux liberated from the molten material by the induction melting; and casting the molten material from which the flux has been separated to obtain a Ti-Al alloy; and reducing the output of the induction melting to 90% or less of that used during melting prior to the casting; and pouring the molten material from the water-cooled copper crucible in the reduced output state." Patent Document 3 also states that "The content of CaF2 in the flux α is set to 35 mass% or more so that the melting point of the flux α is 1800K or less. Also, the content of CaF2 in the flux α is set to less than 95 mass% so that the Ti-Al alloy Z obtained as a product is not contaminated with fluorine in the CaF2."

[0008] JP 2015-507696 A JP 2019-533081 A JP 2021-122830 A

[0009] In electrolytic refining using a molten salt bath, a crude titanium-based material containing Ti, Al, and O and having electrical conductivity is used as an anode in a molten salt bath in an electrolytic cell, and a voltage is applied between the anode and cathode. As a result, mainly Ti is eluted from the crude titanium-based material at the anode, and a refined titanium-based material having a higher purity than the crude titanium-based material is deposited on the cathode, thereby producing a titanium-based electrodeposit.

[0010] When the above electrolytic refining is continued, as Ti is eluted from the crude titanium-based material at the anode, the aluminum content and oxygen content of the crude titanium-based material increase relatively, causing a gradual increase in electrical resistance, and eventually, almost no current flows and almost no Ti is eluted from the crude titanium-based material. In particular, when a titanium-based electrolytic raw material with a high aluminum content and oxygen content is used as the crude titanium-based material, a large amount of electric power is required from the beginning of the electrolytic refining, and Ti is not sufficiently eluted from the crude titanium-based material during the electrolytic refining, making it impossible to increase the production yield.

[0011] To obtain a titanium-based electrolytic raw material for use in electrorefining, titanium oxide contained in titanium ore can be reduced by reacting Al as a reducing agent with the titanium oxide contained in the titanium ore at high temperatures in a melt, as described in Patent Documents 1 and 2. However, the methods described in Patent Documents 1 and 2 were unable to sufficiently reduce the aluminum content and oxygen content of the titanium-based electrolytic raw material.

[0012] An object of the present invention is to provide a method for producing a titanium-based electrolytic raw material that can produce a titanium-based electrolytic raw material with a relatively low aluminum content and oxygen content, and a method for producing metallic titanium or a titanium alloy.

[0013] As a result of extensive research, the inventors have discovered a new finding that when a titanium oxide reaction occurs in a melt, the aluminum content and oxygen content of a titanium alloy product (titanium-based electrolytic raw material) containing Al and O can be reduced by increasing the temperature to involve calcium halide in the reaction and facilitating evaporation of the resulting aluminum halide.

[0014] The method for producing a titanium-based electrolytic raw material of the present invention is a method for producing a titanium-based electrolytic raw material to be used in molten salt electrorefining to obtain metallic titanium or a titanium alloy, and includes a reaction step in which titanium oxide, aluminum elemental substance and / or alloy, and calcium halide are reacted in a melt at a temperature of 1870°C or higher to obtain a titanium alloy product containing Al and O produced by a reaction in a molten state, which reaction includes deoxidation of a portion of the O in the titanium oxide.

[0015] After the reaction step, it is preferable to include a separation step of lowering the temperature of the melt to 1800°C or less and separating the solid titanium alloy product from the liquid slag.

[0016] In the reaction step, it is preferable that the titanium oxide and the calcium halide are melted, and then the aluminum elemental substance and / or alloy is added to form the melt.

[0017] The calcium halide may be at least one selected from the group consisting of calcium fluoride, calcium chloride, calcium bromide, and calcium iodide.

[0018] After the separation step, it is preferable to include a remelting step in which the solid titanium alloy product obtained in the separation step is remelted under a reduced pressure atmosphere.

[0019] In the remelting step, it is preferable to remove a portion of the aluminum and oxygen in the titanium alloy product by evaporation.

[0020] The method for producing a titanium-based electrolytic raw material of the present invention preferably includes, after the remelting step, a casting step of pouring the molten titanium alloy product into a mold and casting it.

[0021] The method for producing a titanium-based electrolytic raw material of the present invention can produce a titanium-based electrolytic raw material having an aluminum content of 8 mass% or less and an oxygen content of 8 mass% or less. The titanium-based electrolytic raw material preferably has an aluminum content of 5 mass% or less and / or an oxygen content of 5 mass% or less. Furthermore, the method for producing a titanium-based electrolytic raw material of the present invention can produce a titanium-based electrolytic raw material having a resistivity of 10 μΩ·m to 150 μΩ·m. The melt preferably contains Al in a mass ratio of 0.2 to 1.0 and calcium halide in a mass ratio of 0.1 to 0.8 relative to the titanium oxide content. The reaction temperature in the reaction step is preferably 1900°C or higher and 3000°C or lower.

[0022] The method for producing metallic titanium or a titanium alloy of the present invention includes electrolytic refining in which a crude titanium-based material in an anode is dissolved in a molten salt bath and a refined titanium-based material is deposited on a cathode, and the titanium-based electrolytic raw material produced by any of the above-mentioned methods for producing a titanium-based electrolytic raw material is used as the crude titanium-based material in the anode.

[0023] The molten salt bath is preferably a chloride bath.

[0024] The chloride bath preferably contains magnesium chloride and titanium dichloride.

[0025] According to the method for producing a titanium-based electrolytic raw material of the present invention, a titanium-based electrolytic raw material having a relatively low aluminum content and oxygen content can be produced.

[0026] DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the accompanying drawings. A method for producing a titanium-based electrolytic raw material according to one embodiment of the present invention is a method for producing a titanium-based electrolytic raw material used in molten salt electrorefining to obtain metallic titanium or a titanium alloy. This method for producing a titanium-based electrolytic raw material includes a reaction step.

[0027] In the reaction step, titanium oxide, aluminum elemental element and / or alloy, and calcium halide are reacted in a melt at a temperature of 1870°C or higher. As a result, some of the O (oxygen) in the titanium oxide is deoxidized to produce various reaction products, and the reaction products obtained in the melt are a titanium alloy product containing Al and O (also simply referred to as a "titanium alloy product") and slag as a residue or residue thereof in a molten state. Note that the reaction step may be followed by a separation step, in which the temperature of the melt is lowered to 1800°C or lower to separate the solid titanium alloy product from the liquid slag.

[0028] As described above, by adding calcium halide to the melt in the reaction step and causing the reaction at a relatively high temperature, it is believed that the calcium halide participates in the reaction and promotes deoxidation of titanium oxide. It is also presumed that Al in the melt also participates in the reaction, further promoting deoxidation of titanium oxide and converting the Al into aluminum halide, which is easily removed. As a result, a titanium alloy product with sufficiently reduced aluminum and oxygen contents can be obtained.

[0029] The titanium alloy product thus obtained can be used as a raw material for molten salt electrorefining, i.e., a titanium-based electrolytic raw material, and can be provided for the production of metallic titanium or titanium alloys by molten salt electrorefining. In this electrorefining, the titanium-based electrolytic raw material is used as the anode as a crude titanium-based material, which is the raw material for molten salt electrorefining, and a purified titanium-based material is deposited on the cathode by applying a voltage between the anode and cathode. In this case, the crude titanium-based material used as the titanium-based electrolytic raw material has a low aluminum and oxygen content, so that its electrical resistance is low and power consumption during electrorefining can be kept low.

[0030] Furthermore, as electrolytic refining continues, the aluminum and oxygen contents of the crude titanium-based material gradually increase as Ti dissolves, and current ceases to flow; however, because the aluminum and oxygen contents before electrolytic refining are low, the time until current ceases to flow is long. Therefore, compared with when a crude titanium-based material with a high aluminum and oxygen content is used, more Ti dissolves from the crude titanium-based material and deposits on the cathode, thereby increasing the yield. Furthermore, when electrolytic refining is performed to obtain higher-purity metallic titanium, it is possible to reduce the number of electrolytic refining cycles, which is expected to significantly reduce the amount of power consumed throughout production.

[0031] Furthermore, this method of producing metallic titanium or titanium alloys by electrolytic refining can reduce the amount of carbon used and the resulting carbon dioxide emissions compared to methods based on the Kroll process, in which titanium ore is salified, and can therefore make a significant contribution to the realization of a carbon-neutral, and ultimately a carbon-free society.

[0032] (Production of Titanium-Based Electrolytic Raw Material) In the production of titanium-based electrolytic raw material, a reaction step is carried out, followed by a separation step, a remelting step, and a casting step, if necessary.

[0033] In the reaction step, titanium oxide or a mixture containing titanium oxide is heated to form a melt from among titanium oxide, aluminum elemental and / or alloy, and calcium halide, and the remaining substances are added as necessary. In the melt, titanium oxide, aluminum elemental and / or alloy, and calcium halide are reacted at a temperature of 1870°C or higher. At the time of heating, at least one of titanium oxide, aluminum elemental and / or alloy, and calcium halide may be pre-mixed to form a mixture, or at least one of these may be added after melting. It is sufficient that titanium oxide, aluminum elemental and / or alloy, and calcium halide are present in the melt at the time of reaction.

[0034] In the reaction step, the type and properties of titanium oxide are not particularly important, but titanium ore containing titanium oxide may be used. The embodiment described herein can be applied to the smelting of titanium ore. Examples of titanium ore include natural rutile, upgraded ilmenite (UGI) or upgraded slag (UGS) that has been subjected to leaching or other upgrading processes as necessary. The TiO2 content in the titanium ore may be, for example, 50 mass% or more, typically 80 mass% or more, and particularly 90 mass% or more. In addition to or instead of such titanium ore, metallic titanium or titanium alloy scrap may be included. Titanium oxide includes TiO2, TiO, TiO 2-x (0≦x<2) is included.

[0035] The aluminum and / or alloy may be metallic aluminum or aluminum alloy scrap, etc. The calcium halide is preferably at least one selected from the group consisting of calcium fluoride, calcium chloride, calcium bromide, and calcium iodide, and preferably contains at least calcium fluoride, and more preferably is calcium fluoride alone.

[0036] The melt preferably contains Al in a mass ratio of 0.2 to 1.0 and calcium halide in a mass ratio of 0.1 to 0.8 relative to the titanium oxide content, but the composition of the melt can be appropriately determined depending on the target composition of the titanium-based electrolytic raw material, etc.

[0037] Additionally, a small amount of CaO may be added in advance as a viscosity adjuster for the melt, etc. Furthermore, the melt may further contain, as unavoidable impurities, Ca, Na, Mg, Cu, Si, Fe, etc., which originate from impurities contained in raw materials used in the reaction step, such as titanium oxide, metallic aluminum, aluminum alloy, and calcium halide.

[0038] If the melt is heated to a temperature of 1870°C or higher in the reaction process, the reactions represented by the following formulas (1) to (3) are thought to occur in the melt. The right side of formula (3) shows CaO, a typical calcium oxide. However, it is presumed that the reaction also contains compounds of complex compositions other than CaO (Ca-O-Ti-Al-halogen (wherein the halogens are F, Cl, Br, I, etc. derived from calcium halide)). Therefore, the calcium oxide on the right side of formula (3) is represented as Ca(O). Furthermore, Ti on the right side of formulas (1) and (3) contains a certain amount of Al and O, and may also contain small amounts of impurities derived from the raw materials, such as Fe, Si, V, Cr, Ni, and Mn. Summarizing formulas (1) to (3), the reaction can be expressed by formula (4). 3TiO2+4Al→3Ti+2Al2O3 (1) 2Al+CaF2→Ca+2AlF (2) Or 4Al+2CaF2→2Ca+4AlF (2') 2Ca+TiO2→2CaO+Ti (3) (1)+(2')+(3) 4TiO2+8Al+2CaF2→4Ti+2Al2O3+2CaO+4AlF (4)

[0039] According to the findings of the inventors, in an ideal reaction, when the melt is heated to a temperature of 1870°C or higher, not only does Al deoxidize titanium oxide as shown in formula (1) above, but also Al removes halogen from calcium halide to produce Ca as shown in formula (2) above, and this Ca also deoxidizes titanium oxide as shown in formula (3) above. In other words, the reaction between Al in aluminum elemental substance and / or alloys and calcium halide produces Ca, and Ca, which has a strong deoxidizing power, deoxidizes part of the oxygen in titanium oxide. In this way, deoxidation of titanium oxide occurs not only by Al but also by Ca, which promotes deoxidation of titanium oxide and ultimately results in a titanium-based electrolytic raw material (Ti in formulas (1), (3), and (4)) with a sufficiently low oxygen content.

[0040] The aluminum in the aluminum element and / or alloy is used to deoxidize titanium oxide as shown in the above formula (1), and also removes halogen from calcium halide to form aluminum halide as shown in the reaction shown in the above formula (2). Aluminum halide evaporates rapidly at high temperatures of 1870°C or higher and can be separated from the melt. This reduces the amount of Al in the melt, and accordingly, the amount of Al mixed into the final titanium-based electrolytic raw material (Ti in formulas (1), (3), and (4)) is also reduced. This is thought to contribute to obtaining a titanium-based electrolytic raw material with a low aluminum content.

[0041] In the reaction process, the order of melting titanium oxide, aluminum and / or alloys, and calcium halide is not particularly important. However, it is preferable to first melt titanium oxide and calcium halide and then add aluminum and / or alloys to form the melt. Alternatively, titanium oxide may be pre-melted and then aluminum and / or alloys and calcium halide may be added. Because aluminum is relatively volatile, if it is added and melted first, only the stable aluminum that does not evaporate during heating will be consumed in the reactions of the above formulas (1) and (2), resulting in insufficient reactions. On the other hand, if aluminum is added later, the reactions of the above formulas (1) and (2) occur almost instantaneously. At high temperatures above 1870°C, calcium halide is also more likely to decompose because it is higher than its melting point, which makes the reaction of the above formula (2) more likely to occur than the reaction of the above formula (1). The tendency for aluminum halide to evaporate easily is also thought to be one factor contributing to the occurrence of the reaction of the above formula (2). If titanium oxide and calcium halide are melted in advance, when elemental calcium, which is easily evaporated, is produced, the reaction of titanium oxide with the above formula (3) can occur before the elemental calcium evaporates. Generally, adding aluminum and / or an alloy later is more preferable than adding it initially, from the viewpoint of promoting deoxidation of titanium oxide through the reaction of formula (2). However, titanium oxide, aluminum and / or an alloy, and calcium halide may be mixed to form a mixture, and the mixture may be melted to form a melt. After obtaining a melt from such a mixture, additional aluminum and / or an alloy may be added later.

[0042] In order to cause the above-described reaction, the temperature during the reaction step is set to 1870° C. or higher, preferably 1900° C. or higher, more preferably 1950° C. or higher, and particularly preferably 2000° C. or higher. On the other hand, the temperature during the reaction may be set to, for example, 3000° C. or lower, typically 2500° C. or lower, but the upper limit is not particularly limited as long as the reaction step can be carried out appropriately taking into consideration the equipment and the like.

[0043] In the reaction step, a water-cooled copper crucible, a water-cooled copper alloy crucible, a calcia (CaO) crucible, or the like can be used as a container for holding the melt. Preferably, a water-cooled copper crucible or a water-cooled copper alloy crucible is used, and the reaction is carried out in a state in which a skull formed by partial solidification of the melt is present on the inner surface of the crucible. Furthermore, in order to suppress the evaporation of aluminum and calcium, it is preferable to use an inert gas atmosphere such as argon gas or helium gas rather than a vacuum atmosphere during the reaction step. More specifically, arc melting, plasma arc melting, or induction skull melting can be used under an inert gas atmosphere. Among these, plasma arc melting is particularly preferred because it is easy to maintain the high temperature range required for the reaction step. Note that the materials reacted in the reaction step may contain many substances that are non-conductive at low temperatures, such as room temperature. Therefore, when using induction skull melting, it may be advisable to heat at least aluminum and / or an alloy, and further heat a mixture containing metallic titanium or a titanium alloy, etc., in order to ensure conductivity during heating to obtain the melt.

[0044] After the reaction step is completed, a separation step can be performed to separate the titanium alloy product, which is one of the reaction products in the melt, from the slag. Here, the difference in melting points between the titanium alloy product and the slag is utilized to fully separate the titanium alloy product. Specifically, the temperature of the melt is lowered to 1800°C or below. As a result, the titanium alloy product, which mainly contains Ti, Al, and O, becomes solid, while the slag, which contains Al2O3 and Ca(O), remains liquid. The solid titanium alloy product, which has a higher specific gravity than the liquid slag, settles and accumulates at the bottom. Alternatively, if the temperature at the bottom of the vessel is low, the solid titanium alloy product will preferentially form at the bottom. The molten slag is then removed by pouring it into another vessel, or the solid titanium alloy product in the melt is removed from the slag, thereby obtaining a solid titanium alloy product from which the liquid slag has been separated. Alternatively, the titanium alloy product and slag separated in the vessel may be removed together from the vessel, and then the titanium alloy product and slag may be separated by sieving, taking advantage of the difference in specific gravity or size.

[0045] The temperature of the melt to be lowered in the separation step may be equal to or higher than the temperature at which the molten state of the slag is maintained, but not higher than 1800°C. For example, the temperature after the melt is lowered may be equal to or higher than 1400°C, even 1500°C, or even 1600°C, even 1700°C. The time for holding at such a temperature may be, for example, 3 minutes or more, or even 5 minutes or more, and preferably 60 minutes or less in consideration of productivity. However, if the solid titanium alloy product separates from the liquid slag by settling, for example, by slowing the temperature drop rate, it may not be necessary to hold the temperature at a predetermined temperature higher than the temperature at which the molten state of the slag is maintained. For example, as long as the solid titanium alloy product separates from the liquid slag while the temperature is higher than the temperature at which the molten state of the slag is maintained during slow cooling, the temperature may be lowered to a lower temperature (e.g., room temperature).

[0046] In the separation step, it is preferable to use induction skull melting, which makes it easy to maintain the above temperature. In this case, when moving from the heating step to the separation step, the melting method can be changed from plasma arc melting to induction skull melting. Alternatively, if the temperature is not maintained during the separation step and the temperature is lowered at a slow rate, it may be preferable to use plasma arc melting. The separation step is also preferably performed under an inert gas atmosphere.

[0047] In addition, although the plasma arc melting method can easily perform high-temperature heating, it can be difficult to control the temperature range below 1800°C. In addition, the induction skull melting method has difficulty in heating and melting the materials to be reacted in the reaction step, but it is easy to stably control temperatures below 1800°C. From the above perspectives, it is also preferable to perform the reaction step by the plasma arc melting method and the separation step by the induction skull melting method.

[0048] The solid titanium alloy product separated from the slag in the separation step may be remelted by heating under reduced pressure in a remelting step, if necessary. The remelting step evaporates and removes a portion of the Al and O that may be contained in the titanium alloy product in the form of atomic aluminum or AlO (aluminum suboxide), thereby further reducing the aluminum and oxygen contents of the titanium-based electrolytic raw material.

[0049] In the remelting process, the degree of vacuum is set to 1×10 in order to evaporate aluminum and AlO well. -3 The pressure is preferably set to 1 Pa to 1 Pa. The temperature for the remelting step is not particularly limited as long as the titanium alloy product is melted, but may be set to 1900°C to 2500°C. The time for holding the molten metal may be, for example, 5 minutes to 1 hour. In order to effectively remove many of the above-mentioned impurities, it is preferable to use a high-vacuum electron beam melting method or an induction skull melting method for the remelting step.

[0050] If necessary, a casting process may be performed after the remelting process. In molten salt electrorefining, a large surface area of ​​the titanium-based electrolytic raw material to be dissolved is advantageous, and from this perspective, granular titanium-based electrolytic raw material may be used. On the other hand, titanium-based electrolytic raw materials with low aluminum and oxygen contents have high toughness and may be difficult to mold or pulverize for use in molten salt electrorefining. In such cases, a casting process may be performed to form the desired shape, which can then be used as an anode in molten salt electrorefining. When a casting process is performed, the titanium alloy product melted in the remelting process described above can be poured into a mold shaped like an anode by pouring or the like without cooling it, while maintaining the molten state.

[0051] The titanium-based electrolytic raw material produced as described above contains Ti, Al, O, and unavoidable impurities and is electrically conductive. The titanium-based electrolytic raw material preferably has an aluminum content of 8 mass% or less, more preferably 5 mass% or less, and even more preferably 3 mass% or less, and an oxygen content of 8 mass% or less, more preferably 5 mass% or less, and even more preferably 3 mass% or less. The aluminum content of the titanium-based electrolytic raw material may be 0.1 mass% or more, more preferably 0.3 mass% or more, and particularly 1 mass% or more, and the oxygen content may be 0.3 mass% or more, more preferably 0.5 mass% or more, and particularly 1.5 mass% or more. The resistivity of the titanium-based electrolytic raw material measured at room temperature is, for example, 10 μΩ·m to 150 μΩ·m, or, for example, 10 μΩ·m to 100 μΩ·m.

[0052] (Production of Metallic Titanium or Titanium Alloy) To produce metallic titanium or a titanium alloy, molten salt electrorefining can be performed using the titanium-based electrolytic raw material. In molten salt electrorefining, electrodes including an anode and a cathode are immersed in a molten salt bath in an electrolytic cell, and a voltage is applied between the electrodes. At this time, an anode containing the titanium-based electrolytic raw material as a crude titanium-based material is used. By applying a voltage between the electrodes, Ti is eluted from the crude titanium-based material on the anode, and is electrodeposited on the cathode to precipitate a refined titanium-based material.

[0053] The anode is not particularly limited as long as it contains the titanium-based electrolytic raw material, which is the crude titanium-based material referred to in electrorefining. For example, the titanium-based electrolytic raw material, such as a plate-shaped material obtained after the casting process described above, can be used as the anode. Alternatively, the granular or powdered titanium-based electrolytic raw material can be placed in an electrically conductive cage-shaped container with multiple through-holes and used as the anode. The cage-shaped container may have a plate-like or cylindrical outer shape and may be made of nickel, a nickel-based alloy, Hastelloy, or steel coated with nickel or a nickel-based alloy, etc., and may have multiple through-holes. The cathode can have at least its surface made of titanium, and can be, for example, a titanium plate or titanium rod made entirely of titanium. Although a bipolar electrode can be placed between the anode and the cathode, a bipolar electrode is not necessary.

[0054] The molten salt bath may be a chloride bath containing primarily metal chlorides, such as alkali metal chlorides and / or alkaline earth metal chlorides, at 70 mol% or more, 90 mol% or more, or even 95 mol% or more. Such chloride baths are preferred over fluoride, bromide, and iodide baths because of their low corrosiveness, low environmental impact, and low cost. In particular, when a chloride bath containing magnesium chloride (MgCl) is used, a purified titanium-based material can be obtained with a sufficiently reduced oxygen content and aluminum content. The magnesium chloride content in the chloride bath is preferably 30 mol% or more, more preferably 50 mol% or more, even more preferably 80 mol% or more, even more preferably 85 mol% or more, and particularly preferably 95 mol% or more. The chloride bath may contain one or more metal chlorides selected from lithium chloride (LiCl), sodium chloride (NaCl), potassium chloride (KCl), rubidium chloride (RbCl), cesium chloride (CsCl), beryllium chloride (BeCl), calcium chloride (CaCl), strontium chloride (SrCl), and barium chloride (BaCl), for example, in an amount of 70 mol% or less, further 50 mol% or less, further 20 mol% or less, further 10 mol% or less, or even 5 mol% or less.

[0055] Furthermore, the molten salt bath may contain, as necessary, a lower titanium chloride having a Ti valence lower than that of titanium tetrachloride, specifically titanium dichloride (TiCl2) or titanium trichloride (TiCl3), etc. The content of Ti ions in the molten salt bath is preferably 3 mol% or more, more preferably 5 mol% or more, even more preferably 6 mol% or more, or even 10 mol% or more, and is preferably 20 mol% or less.

[0056] In particular, when the molten salt bath is a chloride bath, the chloride bath preferably contains magnesium chloride and titanium dichloride. In this case, a purified titanium-based material with an even lower aluminum content can be obtained, which is suitable for producing metallic titanium. Note that in the chloride bath, some of the titanium dichloride may become titanium trichloride due to a disproportionation reaction.

[0057] The contents of metal chlorides and metal ions in the molten salt bath can be measured by ICP emission spectrometry or atomic absorption spectrometry. The content of Ti ions is calculated as a percentage of the total content of metal ions in the molten salt bath.

[0058] The conditions for electrolytic refining are, for example, a molten salt bath temperature of 450°C to 900°C, a current density at the cathode of 0.01 A / cm 2 ~3 A / cm 2 The current density can be calculated using the formula: current density (A / cm 2 ) = current (A) ÷ macroscopic electrodeposition area (cm 2 ) can be calculated. The electrodes may be supplied with a continuous current, or may be supplied with a pulsed current in which a current-on period and a current-off period are alternately repeated, with a current-off period during which the current value is set to zero. The maximum voltage between the electrodes may be, for example, 0.2 V to 3.5 V. During electrolytic refining, the interior of the electrolytic cell is preferably maintained in an inert gas atmosphere such as argon.

[0059] Electrorefining can be repeated multiple times to further refine the purified titanium-based material obtained thereby. When electrorefining is performed multiple times, in the next electrorefining, the purified titanium-based material deposited on the cathode in the previous electrorefining is used as the crude titanium-based material and is used as the anode containing the crude titanium-based material. As a result, in the next electrorefining, a purified titanium-based material from which impurities have been further removed is deposited on the cathode. By performing electrorefining multiple times, it is also possible to produce high-purity metallic titanium that is almost free of impurities.

[0060] However, from the viewpoint of suppressing increases in energy consumption and costs, it is desirable to reduce the number of electrolytic refining processes. Since the titanium-based electrolytic raw material produced by the above-mentioned method has a reduced aluminum content and oxygen content, good metallic titanium or titanium alloys can be produced even with a small number of electrolytic refining processes. It is preferable to perform electrolytic refining only once rather than twice or more times. However, even when electrolytic refining is performed twice or more, it is possible to suppress power consumption and improve yields due to the low aluminum and oxygen contents of the titanium-based electrolytic raw material.

[0061] When titanium metal is produced as described above, the aluminum content of the finally obtained titanium metal is, for example, 0.1% by mass or less, preferably 0.01% by mass or less, and the oxygen content is, for example, 0.2% by mass or less, preferably 0.10% by mass or less, and more preferably 0.05% by mass or less. Alternatively, when a titanium alloy is produced, the finally obtained titanium alloy may have an aluminum content of, for example, 3% by mass or less, preferably 2% by mass or less, and an oxygen content of 0.3% by mass or less, preferably 0.15% by mass or less.

[0062] Next, the method for producing a titanium-based electrolytic raw material and the method for producing metallic titanium or a titanium alloy of the present invention were experimentally carried out, and the effects thereof were confirmed, which will be described below. However, the description here is merely for illustrative purposes and is not intended to be limiting.

[0063] Test Example 1 The reaction step and separation step described above were carried out, and a titanium-based electrolytic raw material was obtained, which was a titanium alloy product separated from the slag in the separation step.

[0064] The reaction process used granular titanium ore (a mixture of UGS and UGI) containing at least 90% by mass of titanium oxide TiO2, the granular calcium halides (ceramic grade) shown in Table 1, and metallic aluminum shot (granules) as aluminum. The mass ratio of titanium oxide (TiO2):aluminum:calcium halide was 1:0.5:0.5. In Example 13, half of the calcium halide was CaCl2, and the other half was CaF2. In Example 14, CaO was further added in an amount equivalent to 10% of the mass of CaF2.

[0065] In the reaction step, the titanium ore, calcium halide, and aluminum shot were melted in a water-cooled copper crucible under an argon gas atmosphere by plasma arc melting, and the melt was heated to the maximum temperature shown in Table 1 to cause a reaction.

[0066] In Examples 1 to 7 and 10 to 14 and Comparative Examples 1 to 5, a mixture of titanium ore, calcium halide (except Comparative Example 5), and metallic aluminum shot was placed in a water-cooled copper crucible before melting and melted together. In Example 8, the mixture of titanium ore and calcium halide was melted first, and then the entire amount of metallic aluminum shot was added thereto. In Example 9, a mixture of titanium ore, calcium halide, and half the amount of metallic aluminum shot was melted first, and then the remaining half of the amount of metallic aluminum shot was added.

[0067] Then, except for Comparative Example 3, the melt was poured into a slit-type water-cooled copper crucible for induction skull melting, and cooled there in an argon gas atmosphere to the temperature shown in Table 1 and maintained at that temperature, or slowly cooled to room temperature at a rate of about 0.5°C / s. The slag was then poured out of the water-cooled copper crucible to separate the titanium alloy product from the slag. In Example 5, slow cooling to room temperature was performed, so the slag and titanium alloy product solidified separately in the upper and lower parts of the crucible, resulting in a lower layer of titanium alloy product. It is believed that in Example 5 as well, the titanium alloy product formed in a solid phase and settled to the bottom while the slag was in a molten state during slow cooling.

[0068] In Comparative Example 2, the temperature in the separation step was relatively high, in Comparative Example 3 the separation step was omitted, and in Comparative Example 4 the temperature was lowered to a level at which the slag solidified at a fairly rapid rate, so in all cases the separation of the slag and the titanium alloy product was insufficient and a sufficient amount of titanium-based electrolytic raw material was not obtained.In Comparative Example 5, calcium halide was not used, so the deoxidation reaction was insufficient and a sufficient amount of titanium-based electrolytic raw material was not obtained.

[0069] In Examples 1 to 14 and Comparative Example 1, a sufficient amount of titanium-based electrolytic raw material was obtained as a titanium alloy product, and the aluminum content and oxygen content thereof were measured. Here, the aluminum content was measured by ICP atomic emission spectroscopy using a PS3520UVDDII manufactured by Hitachi High-Tech Science Corporation, and the oxygen content was measured by inert gas fusion-infrared absorption spectroscopy using an ON736 manufactured by LECO Corporation. The titanium-based electrolytic raw material consisted of titanium and inevitable impurities as the remainder, other than aluminum and oxygen.

[0070] The resistivity values ​​of the titanium-based electrolytic raw materials were measured by a two-terminal measurement method using a low-resistivity meter 3566-RY manufactured by Tsuruga Electric Co., Ltd. The resistivity values ​​were measured at room temperature, and the magnitude relationship between the resistivity values ​​at high temperatures during molten salt electrolytic refining can be inferred from the magnitude relationship. The results are shown in Table 1.

[0071]

[0072] As can be seen from Table 1, the titanium-based electrolytic raw materials of Examples 1 to 14 all had low aluminum and oxygen contents and low resistivity values. In comparison, the titanium-based electrolytic raw material of Comparative Example 1 had high aluminum and oxygen contents and a high resistivity value.

[0073] (Test Example 2) In Examples 15 to 18, titanium alloy products obtained by carrying out the same reaction and separation steps as in Example 1 or 8 were subjected to a remelting step or a casting step to obtain titanium-based electrolytic raw materials. More details are as follows. The remelting step was carried out under a vacuum atmosphere (1 × 10 -3Pa or more and 5 x 10 -1 The test was carried out at a pressure of 1000 kJ / cm2 (within the range of 1000 kJ / cm2 or less).

[0074] In Example 15, the titanium alloy product obtained in the same manner as in Example 1 was remelted in a vacuum atmosphere by an electron beam using the so-called drip melt method, and the molten metal was poured into a water-cooled copper crucible to prepare a titanium-based electrolytic raw material.

[0075] In Example 16, the titanium alloy product obtained in the same manner as in Example 1 was remelted in a hearth under a vacuum atmosphere using an electron beam, and then the remelted product was poured into a mold to produce a titanium-based electrolytic raw material.

[0076] In Example 17, the titanium alloy product after removing the slag in the separation process in the same manner as in Example 1 was remelted in a vacuum atmosphere without being taken out of the water-cooled copper crucible of the induction skull melting method, and then poured into a mold to prepare a titanium-based electrolytic raw material.

[0077] In Example 18, the titanium alloy product obtained in the same manner as in Example 8 was remelted in a vacuum atmosphere by an electron beam using a drip melt method, and the molten metal was poured into a water-cooled copper crucible to prepare a titanium-based electrolytic raw material.

[0078] For each of the titanium-based electrolytic raw materials obtained in Examples 15 to 18, the aluminum content, oxygen content, and specific resistance were measured in the same manner as in Test Example 1. The results are shown in Table 2.

[0079]

[0080] From Table 2, it can be seen that the titanium-based electrolytic raw materials of Examples 15 to 18 have reduced aluminum contents and oxygen contents and smaller resistivities than the titanium-based electrolytic raw materials of Examples 1 and 8 shown in Table 1.

[0081] Test Example 3 Using each of the titanium-based electrolytic raw materials of Comparative Example 1, Example 1 or Example 8 of Test Example 1, or Example 18 of Test Example 2, molten salt electrolytic refining was carried out to produce metallic titanium or a titanium alloy.

[0082] In the molten salt electrorefining, a voltage was applied between the anode and cathode in a molten salt bath having the composition shown in Table 3, dissolving the crude titanium-based material from the anode and depositing a refined titanium-based material on the cathode. The molten salt bath contained 4% to 6% by mass of TiCl2. In examples containing multiple bath components other than TiCl2, the other bath components were contained in equal mass proportions. The titanium-based electrolytic raw materials of Comparative Example 1, Example 1, and Example 8 were crushed to produce crude titanium-based materials, which were then housed in a nickel cage-like container with numerous through-holes. The titanium-based electrolytic raw material of Example 18 was poured into a plate-shaped crucible to produce a plate-shaped crude titanium-based material, which was then used as the anode. A titanium plate was used as the cathode.

[0083] Electrolytic refining was carried out by applying a constant voltage, and when the current value suddenly decreased, it was determined that no further electrolysis was occurring and the process was terminated. The weight of the remaining crude titanium-based material in the anode cage was measured, and the yield was calculated using the following formula. The results are shown in Table 3. Yield (%) = 100 x (weight of crude titanium-based material before electrolytic refining - weight of remaining portion after termination) / weight of crude titanium-based material before electrolytic refining

[0084] After electrolytic refining was completed, the cathode was removed, and the metallic titanium or titanium alloy deposited on the cathode was collected and washed with dilute hydrochloric acid, then washed with water, and then air-dried at a temperature of about 50° C. to 60° C. The aluminum content, oxygen content, and resistivity of the metallic titanium or titanium alloy were measured in the same manner as for the titanium-based electrolytic raw material in Test Example 1. The results are also shown in Table 3.

[0085]

[0086] In Comparative Examples 6 to 8, the yield was low because the titanium-based electrolytic raw material obtained in Comparative Example 1 was used. On the other hand, in Examples 19 to 27, the yield was high.

[0087] Furthermore, in Examples 22 and 25, titanium alloys with the desired aluminum and oxygen contents were obtained in a single electrolytic refining step, eliminating the need for multiple electrolytic refining steps. Furthermore, the titanium metals of Examples 26 and 27 had sufficiently low aluminum and oxygen contents even after a single electrolytic refining step, making further electrolytic refining unnecessary. It is believed that the other examples also yield high-quality titanium metals or titanium alloys by performing two electrolytic refining steps.

Claims

1. A method for producing a titanium-based electrolytic raw material used in molten salt electrolytic refining to obtain metallic titanium or a titanium alloy, comprising a reaction step of reacting titanium oxide, aluminum elemental substance and / or alloy, and calcium halide in a melt at a temperature of 1870°C or higher, and obtaining a titanium alloy product containing Al and O produced by a reaction that includes deoxidation of a portion of the O in the titanium oxide in a molten state.

2. A method for producing a titanium-based electrolytic raw material as described in claim 1, which includes a separation step of lowering the temperature of the melt to 1800°C or less after the reaction step, and separating the solidified titanium alloy product from the liquid slag.

3. A method for producing a titanium-based electrolytic raw material as described in claim 1 or 2, wherein in the reaction process, after the titanium oxide and the calcium halide are melted, the aluminum element and / or alloy are added to obtain the melt.

4. A method for producing a titanium-based electrolytic raw material according to any one of claims 1 to 3, wherein the calcium halide is at least one selected from the group consisting of calcium fluoride, calcium chloride, calcium bromide and calcium iodide.

5. A method for producing a titanium-based electrolytic raw material according to claim 2, further comprising a remelting step of remelting the solid titanium alloy product obtained in the separation step under a reduced pressure atmosphere after the separation step.

6. The method for producing a titanium-based electrolytic raw material according to claim 5, wherein in the remelting step, a portion of the aluminum and oxygen in the titanium alloy product is removed by evaporation.

7. A method for producing a titanium-based electrolytic raw material according to claim 5 or 6, further comprising a casting step of pouring the molten titanium alloy product into a mold and casting it after the remelting step.

8. A method for producing a titanium-based electrolytic raw material according to any one of claims 1 to 7, which produces a titanium-based electrolytic raw material having an aluminum content of 8 mass% or less and an oxygen content of 8 mass% or less.

9. A method for producing a titanium-based electrolytic raw material according to claim 8, wherein the titanium-based electrolytic raw material has an aluminum content of 5 mass% or less and / or an oxygen content of 5 mass% or less.

10. A method for producing a titanium-based electrolytic raw material according to any one of claims 1 to 9, which produces a titanium-based electrolytic raw material having a resistivity of 10 μΩ·m to 150 μΩ·m.

11. A method for producing a titanium-based electrolytic raw material according to any one of claims 1 to 10, wherein the melt contains, in mass ratios relative to the titanium oxide content, 0.2 to 1.0% Al and 0.1 to 0.8% calcium halide.

12. A method for producing a titanium-based electrolytic raw material according to any one of claims 1 to 11, wherein the reaction temperature in the reaction step is 1900°C or higher and 3000°C or lower.

13. A method for producing metallic titanium or a titanium alloy, comprising electrolytic refining in which a crude titanium-based material of an anode is dissolved in a molten salt bath and a refined titanium-based material is deposited on a cathode, and a titanium-based electrolytic raw material produced by the method for producing a titanium-based electrolytic raw material according to any one of claims 1 to 12 is used as the crude titanium-based material for the anode.

14. The method for producing metallic titanium or a titanium alloy according to claim 13, wherein the molten salt bath is a chloride bath.

15. The method of producing titanium metal or titanium alloy as set forth in claim 14, wherein the chloride bath comprises magnesium chloride and titanium dichloride.

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