Method for manufacturing titanium-based metals with reduced oxygen content

Abstract

This invention provides a method for producing titanium-based metals that allows the Ca in the deoxidizing and desulfurizing agent to contribute effectively to the deoxidation reaction, thereby reducing the O content of the titanium-based metal raw material. [Solution] The present invention provides a method for producing a titanium-based metal from a titanium-based metal raw material containing oxygen, wherein the method includes an oxygen reduction step for reducing the oxygen content of the titanium-based metal raw material, the method comprising: a melting step of heating the titanium-based metal raw material together with a sulfur source containing elemental sulfur and / or titanium sulfide to obtain a melt; a deoxidation step in which the melt contains a deoxidizing and desulfurizing agent containing Ca, and in the melt, the Ca of the deoxidizing and desulfurizing agent reacts with at least a portion of the oxygen in the titanium-based metal raw material; and a desulfurization step in which, after the deoxidation step, the melt contains a deoxidizing and desulfurizing agent containing Ca, and in the melt, the Ca of the deoxidizing and desulfurizing agent reacts with at least a portion of the sulfur in the sulfur source.

Description

[Technical Field]

[0001] This invention relates to a method for producing a titanium-based metal with a low oxygen content by reducing the oxygen content from a titanium-based metal raw material that contains oxygen (O). [Background technology]

[0002] In the industrial production of titanium-based metals such as metallic titanium and titanium alloys, a method based on the Kroll process is generally used to produce metallic titanium with a low oxygen content (commonly referred to as sponge titanium) from titanium ore, and this sponge titanium is then used.

[0003] However, this method requires the chlorination of titanium ore, the purification of the resulting titanium tetrachloride, the reduction of titanium tetrachloride with metallic magnesium, and the separation and removal of the by-product magnesium chloride. Furthermore, it necessitates the crushing of sponge titanium ingots and the electrolysis of the magnesium chloride produced by reduction, resulting in numerous batch processes. Therefore, it is difficult to say that this method can efficiently and inexpensively produce titanium-based metals. Additionally, the reaction to produce titanium tetrachloride uses coke (carbon), which releases carbon dioxide, a greenhouse gas that contributes to global warming.

[0004] Under these circumstances, for example, as described in Patent Document 1, it is being considered to reduce titanium oxide with Al (aluminum) and smelt titanium ore.

[0005] More specifically, Patent Document 1 describes "a method for extracting titanium products from titanium ore, characterized by comprising the following steps: a step of mixing a chemical blend containing titanium ore and a reducing agent, wherein the ratio of the titanium ore to the reducing agent corresponds to a mass ratio of titanium oxide component in the titanium ore to the reducing metal in the reducing agent of 0.9 to 2.4; a step of heating the chemical blend to start the extraction reaction, wherein the chemical blend is heated at a rate of increase of 1°C to 50°C / min; a step of maintaining the chemical blend at a reaction temperature of 1500 to 1800°C for a time between 5 minutes and 30 minutes; a step of cooling the chemical blend to a temperature lower than 1670°C; and a step of separating the titanium products from residual slag," and states that "the titanium ore contains titanium oxide (TiO2) and the reducing agent contains aluminum (Al)."

[0006] Furthermore, Patent Document 2 discloses "a method for producing the intermetallic compound Al3Ti, characterized by comprising: a first step of uniformly mixing an oxide mixture, which is prepared by blending titanium dioxide (TiO2) and aluminum oxide (Al2O3) such that the composition of Ti and Al is equal to or greater than that of the intermetallic compound Al3Ti, and then finely pulverizing the titanium and aluminum atoms as much as possible; a second step of reducing this oxide mixture by reacting it with calcium (Ca) or calcium hydride (CaH2) at a high temperature in the temperature range of 750 to 1200°C; and a third step of dissolving and removing the by-products CaO and CaAl2 or Ca-Al alloy from the synthesized intermetallic compound Al3Ti with water or a solvent selected from an acidic aqueous solution or an ammonium chloride aqueous solution, thereby extracting only the pure intermetallic compound Al3Ti."

[0007] Furthermore, Non-Patent Document 1 discloses a technology for reducing preforms containing titanium ore and UGI (Upgraded Ilmenite) with metallic calcium vapor.

[0008] Furthermore, Patent Document 3 describes a molten salt electrolysis technique, and discloses "a method for producing metallic titanium from a titanium compound in a molten salt electrolytic bath consisting of an inorganic molten salt containing calcium chloride, characterized in that the inorganic molten salt contains at least one of calcium sulfide and calcium oxide, and the titanium compound contains titanium sulfide." [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Special Publication No. 2015-507696 [Patent Document 2] Japanese Patent Application Publication No. 4-103732 [Patent Document 3] Japanese Patent Publication No. 2017-43819 [Non-patent literature]

[0010] [Non-Patent Document 1] Haiyan Zheng et al., "Production of Titanium Powder by the Calciothermic Reduction of Titanium Concentrates or Ore Using the Preform Reduction Process", Materials Transactions, Vol. 48, No. 8 (2007) pp. 2244 to 2251 [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] Incidentally, in order to reduce the oxygen content of titanium ore, titanium-based metals, titanium-based scrap, or other raw materials containing oxygen, it is considered effective to utilize the excellent deoxidizing power of calcium (Ca) in addition to aluminum (Al), as described in Patent Document 1, etc. Furthermore, Ca is a promising deoxidizing agent because it does not readily dissolve in solid titanium and hardly remains as an impurity in the titanium-based metal obtained after deoxidation.

[0012] To efficiently deoxidize titanium-based metal raw materials using a deoxidizing agent containing Ca, it is conceivable to contact the titanium-based metal raw materials with the deoxidizing agent in a molten or gaseous state (Non-Patent Literature 1). However, in this case, if the titanium-based metal raw material to be deoxidized is not in a molten state, i.e., in a solid state, it is not easy to deoxidize the entire material, including the central part of each individual particle, unless it is extremely fine-grained. On the other hand, if the titanium-based metal raw material to be deoxidized is also in a molten state, the following problems arise. That is, if the Ca in the deoxidizing agent is in the gaseous state, it will be discharged to the top of the molten titanium-based metal raw material and will not be able to contact the titanium-based metal raw material. Also, if the Ca in the deoxidizing agent is in the liquid state, the titanium-based metal raw material has a relatively high melting point, while the Ca in the deoxidizing agent has a relatively low boiling point. Therefore, if the titanium-based metal raw material is heated and melted as is, the Ca in the deoxidizing agent added to it will evaporate and be discharged to the top of the liquid-phase titanium-based metal raw material, and will not contribute sufficiently to the reaction. Furthermore, the deoxidizing power of Ca tends to weaken at high temperatures (e.g., above 1600°C) where titanium-based metal raw materials melt.

[0013] In Patent Document 2 and Non-Patent Document 1, the titanium-based metal raw material to be deoxidized is in a solid phase, and no consideration has been given to suppressing the evaporation of Ca to improve reaction efficiency.

[0014] The object of this invention is to provide a method for producing titanium-based metals that can efficiently reduce the oxygen content of titanium-based metal raw materials by allowing Ca to contribute well to the deoxidation reaction. [Means for solving the problem]

[0015] As a result of intensive studies, the inventors have found that by utilizing the effect of S on lowering the melting point of the titanium-based metal raw material, it is possible to make Ca contribute well to the deoxidation reaction while suppressing the evaporation of Ca in a relatively low-temperature molten (liquid phase) state. Here, sulfur or sulfur and titanium sulfide is used as the sulfur source containing S. Sulfur is difficult to dissolve in the solid titanium-based metal, and thus contamination due to the use of the sulfur source can be suppressed.

[0016] The method for producing a titanium-based metal according to this invention is a method for producing a titanium-based metal having a lower O content than that of the titanium-based metal raw material from a titanium-based metal raw material containing O, and has an oxygen reduction step for reducing the O content of the titanium-based metal raw material. The oxygen reduction step includes a melting stage in which the titanium-based metal raw material is melted together with a sulfur source containing sulfur or sulfur and titanium sulfide by heating to obtain a melt, a deoxidation stage in which the melt contains a deoxidizing and desulfurizing agent containing Ca, and in the melt, Ca of the deoxidizing and desulfurizing agent reacts with at least a part of O of the titanium-based metal raw material, and after the deoxidation stage, the melt contains a deoxidizing and desulfurizing agent containing Ca, and in the melt, Ca of the deoxidizing and desulfurizing agent reacts with at least a part of S of the sulfur source.

[0017] In the above method for producing a titanium-based metal, it is preferable that the mass ratio of the amount of S used in the oxygen reduction step to the total of the Ti content in the melt and the amount of S used in the oxygen reduction step is within the range of 0.05 to 0.15.

[0018] In the above method for producing a titanium-based metal, it is preferable that the amount of Ca used (mass %) and the amount of S used (mass %) in the oxygen reduction step, and the O content (mass %) derived from the titanium-based metal raw material in the melt satisfy the formula: amount of Ca used ≥ O content × 2.5 + amount of S used × 0.5.

[0019] In the above method for producing a titanium-based metal, in the deoxidation stage, the melt may contain a slag former.

[0020] In the above method for producing a titanium-based metal, when the sulfur source contains titanium sulfide, the titanium sulfide is TiS x (0.5 ≦ x ≦ 3.0), which is preferable.

[0021] In the above method for producing a titanium-based metal, it is preferable to use a high-frequency induction heating furnace in the oxygen reduction step.

[0022] The above method for producing a titanium-based metal obtains a titanium-based material with a reduced O content compared to the titanium-based metal raw material in the oxygen reduction step, and then uses the titanium-based material as a crude titanium-based material for the anode. By applying a voltage between the anode and the cathode in a molten salt bath, Ti is eluted from the crude titanium-based material, and an electrolysis step of depositing a purified titanium-based material on the cathode may be included.

[0023] In this case, the electrolysis step is repeated multiple times, and in the multiple electrolysis steps, the purified titanium-based material deposited on the cathode in the previous electrolysis step can be used as the crude titanium-based material in the next electrolysis step.

Advantages of the Invention

[0024] According to the method for producing a titanium-based metal of this invention, Ca of the deoxidizing and desulfurizing agent can contribute well to the deoxidation reaction, and the O content of the titanium-based metal raw material can be efficiently reduced.

Brief Description of the Drawings

[0025] [Figure 1] It is a binary phase diagram of Ti - S shown as an example.

Embodiments for Carrying Out the Invention

[0026] Hereinafter, embodiments of this invention will be described in detail. One embodiment of this invention is a method for producing a titanium-based metal from a titanium-based metal raw material containing oxygen (O), wherein the O content of the titanium-based metal is less than that of the titanium-based metal raw material, and the method includes an oxygen reduction step to reduce the O content of the titanium-based metal raw material.

[0027] The oxygen reduction process includes a melting stage, a deoxidation stage, and a desulfurization stage. In the melting stage, the titanium-based metal raw material is melted by heating together with a sulfur source containing elemental sulfur and / or titanium sulfide to obtain a melt. In the deoxidation stage, the Ca in the deoxidation and desulfurization agent is reacted with at least some of the oxygen in the titanium-based metal raw material in the melt containing a Ca-containing deoxidation and desulfurization agent to reduce the oxygen content of the titanium-based metal raw material. In the subsequent desulfurization stage, the Ca in the deoxidation and desulfurization agent is reacted with at least some of the sulfur in the sulfur source in the melt containing a Ca-containing deoxidation and desulfurization agent. By using a sulfur source, the titanium-based metal raw material melts into a melt at a relatively low temperature, so the deoxidation and desulfurization stages can be carried out at a somewhat lower temperature. This allows for more efficient utilization of the strong deoxidizing power of the Ca in the deoxidation and desulfurization agent, and evaporation is suppressed, allowing the Ca to contribute well to the deoxidation reaction. It should be noted that these three stages (the melting stage, the deoxidation stage, and the desulfurization stage) do not necessarily occur independently and sequentially; some may overlap within the reactor.

[0028] The titanium-based metal raw materials used in the oxygen reduction process can be a variety of materials as long as they contain oxygen (i.e., raw materials for titanium-based metals containing oxygen, such as metallic titanium and titanium alloys). Specific examples include industrial-grade pure titanium, titanium alloys, and titanium-based scraps, but all must contain oxygen. This titanium-based scrap may be generated from the manufacturing process or after-sales of metallic titanium products or titanium alloy products. Furthermore, titanium alloy products obtained from extraction processes using aluminum (Al) or calcium (Ca) from titanium oxides may also be used as titanium-based metal raw materials in the oxygen reduction process. Additionally, an electrolytic process may be performed after the oxygen reduction process as needed. The following describes in detail, as an example, the extraction process, oxygen reduction process, and electrolytic process in this order, but are not limited to this. The number of times the oxygen reduction process and electrolytic process are performed is not particularly limited, and the oxygen reduction process and / or electrolytic process can be performed once or multiple times. For example, at least one of the oxygen reduction process or the electrolytic process may be performed multiple times to further reduce the impurity content.

[0029] (extraction process) In the extraction process, a mixture of titanium ore containing titanium oxides such as titanium dioxide (TiO2) (which may have undergone upgrade treatments such as leaching or other treatments as needed) and a reducing agent containing Al, Ca, etc., is heated to a temperature of, for example, 1400°C to 2500°C. At this time, slag-forming agents such as calcium fluoride (CaF2), calcium chloride (CaCl2), or calcium oxide (CaO) may be added to facilitate the formation of molten slag after heating. This yields a titanium alloy product containing O (and depending on the type of reducing agent, also containing the reducing agent).

[0030] When the reducing agent contains Al, the reaction that occurs in the extraction process is complex, but generally, it can be considered to be a reaction like 3TiO2 + 4Al → 3Ti + 2Al2O3. However, in this reaction equation, a certain amount of Al and O are dissolved in Ti, and this corresponds to the titanium alloy product. A reducing agent containing Ca may also be used. After the mixture becomes molten upon heating, the titanium alloy product (liquid or solid) and the molten slag separate due to the difference in specific gravity, so the titanium alloy product (Ti in the above reaction equation) can be extracted.

[0031] Titanium alloy products obtained in extraction processes using reducing agents containing Al contain Ti, Al, and O. For example, the Ti content may be 50% to 90% by mass, the Al content 1% to 30% by mass, and the O content 5% to 20% by mass. In addition, if ores with many impurities are used, Fe and Si may also be present in amounts of a few mass percent or less. Typically, the Ti content of titanium alloy products may be 60% or more by mass, the Al content 20% or less by mass, and the O content 20% or less by mass. However, in titanium alloy products, Al and O may be present in amounts lower than the above, to the extent that they can be considered unavoidable impurities. In other words, titanium alloy products may contain only trace amounts of Al and O. Titanium alloy products include Ti-Al-O solid solution alloys (alloys in which Al and O are dissolved in Ti) obtained in extraction processes using reducing agents containing Al, and Ti-O solid solution alloys (alloys in which O is dissolved in Ti) obtained in extraction processes using reducing agents containing Ca. These can be used as titanium-based metal raw materials containing O.

[0032] (Oxygen reduction process) In the oxygen reduction process, for example, titanium-based metal raw materials are heated and melted in a crucible inside a heating furnace to form a molten state, and this heating is then maintained. At this time, the titanium-based metal raw materials generally go through the melting stage, deoxidation stage, and desulfurization stage in this order. However, some of these stages may overlap. Here, a sulfur source is used to lower the melting point of the titanium-based metal raw materials and cause the reaction to occur in a low-temperature molten state. In addition, a deoxidizing and desulfurizing agent containing calcium is used to remove oxygen from the titanium-based metal raw materials.

[0033] More specifically, in the melting stage, the titanium-based metal raw material is melted by heating along with a sulfur source containing elemental sulfur and / or titanium sulfide to obtain a melt. Here, by using a sulfur source, the melting point of the titanium-based metal raw material is lowered, and the titanium-based metal raw material melts into a melt even at relatively low temperatures (e.g., around 1200°C to 1400°C). In the deoxidation stage, some of the Ca (calcium) in the deoxidizing and desulfurizing agent contained in the melt is reacted with at least some of the oxygen in the titanium-based metal raw material. This causes a deoxidation reaction in which the oxygen is removed from the titanium-based metal raw material by the Ca, mainly producing CaO. CaO has a melting point of about 2600°C and a specific gravity (approximately 3.3) that is lower than the specific gravity of Ti (approximately 4.4 to 4.6), so it floats up as a solid phase upon formation. Here, the deoxidizing power of Ca is somewhat weak at the original melting point of titanium-based metal raw materials (around 1600°C to 1800°C), but when the melting point is lowered to around 1200°C to 1400°C by S, a strong deoxidizing power is exhibited. For example, when Ti-Al-O solid solution alloys or Ti-O solid solution alloys are used as titanium-based metal raw materials, Ti-Al-S-Ca and Ti-S-Ca may be formed in the melt in response to the formation of CaO. Subsequently, in the desulfurization step, the deoxidizing and desulfurizing agent Ca is reacted with at least some of the sulfur source S in the melt. Here, S and Ca are removed from Ti-Al-S-Ca and Ti-S-Ca, and it is thought that CaS is mainly produced. CaS has a high melting point of about 2500°C and a low specific gravity of about 2.8, so it is presumed to float. At this time, due to the decrease in S, the melting point of the deoxidized metal rises, and the titanium-based material with reduced O content precipitates as a solid phase. As a result, a titanium-based material is obtained in which the O content is reduced and which contains almost no S or Ca. Titanium-based materials are βTi at relatively high temperatures, and when cooled, they often become αTi. The fact that the addition or reduction of S causes a decrease or increase in the melting point of Ti can be understood, for example, from the phase diagram in Figure 1 (Source: Joanne L. Murray, “Phase Diagrams of Binary Titanium Alloys”, ASM INTERNATIONAL, 1987, page 276, Fig. 1).The form at a given temperature changes depending on the type and amount of impurity elements, but Figure 1 shows a Ti-S binary phase diagram as an example to facilitate understanding. Even if CaO, CaS, Ca, S, etc. are incorporated into titanium-based materials in granular or small lump form and remain, they can be easily removed by heating and melting them again during ingot manufacturing, etc., as Ca and S will volatilize and CaS and CaO will float to the surface. In addition to or instead of this, CaO, CaS, Ca, S, etc. can also be separated by performing the electrolytic process described later.

[0034] Thermodynamic studies show that at room temperature, Ca bonds more strongly with oxygen than sulfur, but at high temperatures such as the melting point of typical titanium and titanium alloy raw materials (approximately 1600°C to 1800°C), the bonding between sulfur and oxygen becomes equal or even stronger. Therefore, the deoxidation efficiency decreases at such high temperatures. However, in this embodiment, the use of a sulfur source lowers the melting point of the titanium-based metal raw material, allowing the above reaction to occur at relatively low temperatures. In this case, it is thought that Ca bonds with oxygen before sulfur, similar to room temperature, and the deoxidation and desulfurization steps can proceed in this order.

[0035] The titanium-based metal raw materials used in the oxygen reduction process contain Ti and O, and are typically titanium alloy products obtained in the extraction process described above, or industrial pure titanium or titanium alloys. However, trace amounts of oxides and other compounds, such as surface oxide films, may be present.

[0036] More specifically, titanium-based metal raw materials include titanium alloy products obtained in the extraction process described above (Ti-Al-O solid solution alloys and Ti-O solid solution alloys), titanium-based scrap, and other metallic titanium raw materials and titanium alloy raw materials. Specific examples of metallic titanium raw materials and titanium alloy raw materials include sponge titanium, molten products of metallic titanium or titanium alloys, wrought materials, powders and their sintered bodies, and their scraps. The metallic titanium raw material may contain a relatively high amount of oxygen (for example, metallic titanium equivalent to JIS Grade 2 or JIS Grade 3), and then undergo an oxygen reduction process to reduce the oxygen content (for example, metallic titanium equivalent to JIS Grade 1, i.e., industrial pure titanium). The Ti content of industrial pure metallic titanium raw materials may be 98% by mass or more, and the Ti content of titanium alloy raw materials may be 50% by mass or 60% by mass or more. The above-mentioned titanium-based scrap may include cutting chips (so-called metal shavings) generated during grinding and cutting processes of various products. The term "alloy" as used here refers to a solid solution in which multiple metallic elements are mixed. This includes not only alloys in the narrow sense with an irregular lattice structure (e.g., Ti-3Al-2.5V, Ti-5Al-1Fe, Ti-6Al-4V, Ti-6Al-2Mo-4Zr-2Sn), but also ordered alloys and intermetallic compounds that form an ordered lattice structure, as well as solid solutions with a body-centered cubic structure as well as a closely packed hexagonal structure. Specific examples of intermetallic compounds include TiAl, Ti3Al, and FeTi, while specific examples of solid solutions with a body-centered cubic structure include Ti-Nb, Ti-Mo, Ti-Mo-Al, Ti-V-Cr-Al-Sn, Ti-Mo-V-Cr-Al-Sn, and Ti-Al-V-Fe.

[0037] The oxygen reduction process often corresponds to refining, which is a process that removes at least some of the impurities (in this case, oxygen) from the products of the extraction process or titanium-based metal raw materials such as titanium-based scrap. The oxygen reduction process is performed at least once and may be repeated multiple times as needed. When the oxygen reduction process is performed multiple times, the titanium-based material obtained in the previous oxygen reduction process, with reduced oxygen content, can be used as the titanium-based metal raw material in the next oxygen reduction process to further reduce the oxygen content.

[0038] Any deoxidizing and desulfurizing agent containing calcium (Ca) will suffice. Ca possesses excellent deoxidizing properties, making it effective in reducing the oxygen content of titanium-based metal raw materials. However, since Ca hardly dissolves in solid Ti, when cooled after deoxidation and desulfurization reactions, it is thought that the high-melting-point Ti solidifies first, leaving the Ca in the liquid phase. Further cooling would then result in a phase almost entirely separated from the Ti phase. Even if Ca were incorporated into the Ti phase, it is presumed that such Ca would combine with any oxygen present in the Ti phase to form CaO or CaTiO3, etc., meaning that even if it were to dissolve in Ti, the amount would be extremely small. Thus, Ca is useful as a deoxidizing and desulfurizing agent because it is unlikely to be introduced as an impurity.

[0039] The deoxidizing and desulfurizing agent may include, for example, metallic calcium and / or calcium alloys. Examples of calcium alloys include Ca-Mg alloys, Ca-Si alloys, and Ca-Al alloys. If Mg, Si, Al, etc. from the calcium alloy are mixed as impurities into the titanium-based material obtained in the oxygen reduction process, the content of these impurities can be reduced in the electrolytic process described later. If the electrolytic process is not performed, it is preferable to select metallic calcium as the deoxidizing and desulfurizing agent.

[0040] The deoxidizing and desulfurizing agent only needs to be added by the time Ca and O react in the deoxidation stage at the latest. It can be added before heating in the oxygen reduction step, or it can be added after heating in the melting and / or deoxidation stages. In other words, it is sufficient that the melt contains a deoxidizing and desulfurizing agent containing Ca in the deoxidation stage. Preferably, from the viewpoint of suppressing evaporation, the deoxidizing and desulfurizing agent is added after the melt is obtained in the melting stage. Since the Ca contained in the deoxidizing and desulfurizing agent has the ability to remove not only O but also S, additional deoxidizing and desulfurizing agent may be added in the desulfurization stage. It is also sufficient that the melt contains a deoxidizing and desulfurizing agent containing Ca in the desulfurization stage.

[0041] The sulfur source may contain S, but it is preferably one containing elemental sulfur and / or titanium sulfide. Since elemental sulfur and titanium sulfide do not substantially contain other elements other than S and Ti, using them as a sulfur source can suppress the contamination of titanium-based metals and titanium-based materials by other elements.

[0042] Since elemental sulfur has a relatively low melting point, it may be preferable to use titanium sulfide as at least a part of the sulfur source from the viewpoint of suppressing the evaporation of the sulfur source in the melting stage. When the sulfur source contains titanium sulfide, the titanium sulfide can be TiS x (0.5 ≦ x ≦ 3.0). Specifically, the titanium sulfide may contain at least one selected from the group consisting of Ti3S, Ti2S, TiS, Ti6S9, Ti8S 10 , Ti 16 S 21 and TiS2. Among them, the titanium sulfide preferably contains at least one selected from the group consisting of Ti2S, TiS, Ti6S9, Ti8S 10 and Ti 16 S 21 and preferably contains TiS x (0.75 ≦ x ≦ 2.25). Thereby, the sulfur source is less likely to evaporate and the utilization efficiency of sulfur is increased. Titanium disulfide (TiS2) can be obtained, for example, by the elemental reaction of metallic titanium (Ti) and sulfur (S) at about 500°C. When titanium disulfide and metallic titanium are sintered in the solid phase, the titanium sulfide obtained thereby has a higher Ti ratio, a higher melting point and a higher boiling point, and is less likely to be lost by heating in the melting stage.

[0043] Regarding the amount of sulfur source added, it is preferable to add the sulfur source such that the mass ratio of the amount of sulfur used in the oxygen reduction process ((amount of sulfur used) / (Ti content + amount of sulfur used)) to the sum of the Ti content in the molten material and the amount of sulfur used in the oxygen reduction process is within the range of 0.05 to 0.15, and more specifically, within the range of 0.075 to 0.125. Here, the Ti in the molten material is at least that contained in the titanium-based metal raw material, and if the sulfur source contains titanium sulfide, it is also contained in the titanium sulfide. The sulfur originates from the sulfur source. By appropriately controlling the amount of sulfur relative to the Ti, the melting point of the titanium-based metal raw material can be lowered even more effectively. Furthermore, the amount of Ca required in the desulfurization step, and consequently the amount of Ca required in the oxygen reduction process, can be reduced, thereby suppressing cost increases.

[0044] Furthermore, the amount of Ca (mass%) and S (mass%) used in the oxygen reduction process, as well as the O content (mass%) derived from the titanium-based metal raw material in the melt, preferably satisfy the formula: Ca usage ≥ O content × 2.5 + S usage × 0.5. Since CaO has a molar ratio of Ca to O of 1:1 and a mass ratio of 40:16, it is desirable to add at least 40 / 16 times (2.5 times) the amount of O in order to remove O from the titanium-based metal raw material. Similarly, since CaS has a molar ratio of Ca to S of 1:1 and a mass ratio of 40:32, it is desirable to add at least 40 / 32 times (1.25 times) the amount of S in order to remove S from the sulfur source. However, even if not all S is removed, it is released into the liquid phase during solidification and hardly dissolves in the solid phase, so the amount of Ca consumed to remove S may be less than 1.25 times the amount of S. On the other hand, from the viewpoint of improving yield, it is preferable that the amount of Ca used, the amount of O content, and the amount of S used satisfy the following formulas: Ca used ≥ O content × 2.5 + S used × 1.0, and further, Ca used ≥ O content × 2.5 + S used × 1.2. The above amounts of Ca and S can be determined from the Ca content of the deoxidation and desulfurization agent used in the oxygen reduction process and the S content of the sulfur source, respectively. The amounts of Ca and S are calculated as the mass ratios of Ca and S to the total amount of melt (including the amount of additives if anything is added after the melt is obtained). In addition, the O content derived from titanium-based metal raw materials can be determined as the mass ratio obtained by dividing the O content contained in the titanium-based metal raw materials by the total amount of melt (including the amount of additives if anything is added after the melt is obtained).

[0045] It is preferable to add the slag-forming agent before the deoxidation stage so that the molten material contains the slag-forming agent. This slag-forming agent may melt to become molten slag or partially solidify to become solid-phase slag, and it will exist floating on top, acting to absorb the CaO generated and suspended during the deoxidation stage, and the CaS generated and suspended during the subsequent desulfurization stage. Adding the slag-forming agent is thought to make it easier to suppress the residue of CaO and CaS in the manufactured titanium-based material.

[0046] The slag-forming agent preferably contains Ca, and specifically, for example, CaF2, CaCl2, CaO, MgCl2, etc. can be used. When the deoxidizing and desulfurizing agent is metallic calcium, CaF2 and CaCl2 are preferred as slag-forming agents with low melting points. The content of the slag-forming agent in the molten material when the slag-forming agent is melted is preferably 10% by mass or less. However, the use of a slag-forming agent is not always necessary.

[0047] In the oxygen reduction process described above, various types of heating furnaces can be used. Examples of such heating furnaces include high-frequency induction heating furnaces, electro-slug remelting (ESR) furnaces, electric furnaces, and gas furnaces.

[0048] Among these, the use of a high-frequency induction heating furnace is preferred. In a high-frequency induction heating furnace, induction heating using a magnetic field generated by passing an electric current through a coil can directly and / or indirectly heat titanium-based metal raw materials, deoxidizing and desulfurizing agents, sulfur sources, slag-forming agents, etc., placed inside a crucible or the like. The crucible may be made of water-cooled copper or a water-cooled copper alloy, and induction skull melting may be performed. A susceptor (magnetic field-sensitive heating element) may be used to assist in heating. Generally, melting titanium-based metals in crucibles other than water-cooled copper crucibles is considered difficult because they react with the crucible material. However, in this embodiment, the melting point of the titanium-based metal raw material is significantly lowered by the addition of sulfur, so even when using calcia-coated crucibles, graphite crucibles, or calcia crucibles, contamination of the crucible material is suppressed and the titanium-based metal raw material can be melted.

[0049] The oxygen reduction process is preferably carried out by creating an inert gas atmosphere such as argon or helium inside the heating furnace, typically by flowing the inert gas through the furnace or by replacing the inside of the furnace with an inert gas. This suppresses the incorporation of contaminating gases such as oxygen and nitrogen into the crucible, allowing for better deoxidation of titanium-based metal raw materials. Furthermore, maintaining a high-pressure state inside the heating furnace with an inert gas suppresses the evaporation of Ca and S, thereby increasing their utilization efficiency.

[0050] In the oxygen reduction process, the melting point of the titanium-based metal raw material is lowered by the use of a sulfur source inside the crucible or the like mentioned above. Therefore, a melt can be obtained by heating to, for example, 1200°C to 1400°C, and the various reactions can be carried out. Until the titanium-based metal raw material melts and sulfur is dissolved, it may be heated to a relatively high temperature, for example, 1200°C to 1750°C. However, once the titanium-based metal raw material begins to melt, the temperature can be lowered, and as mentioned above, it can be 1200°C to 1400°C, or even 1250°C to 1400°C. As the deoxidation reaction progresses, the melting point may decrease further. In contrast, the boiling point of metallic calcium, which may be contained in the deoxidation and desulfurization agent, is approximately 1484°C. This allows for the deoxidation reaction of the titanium-based metal raw material by Ca to occur while suppressing the evaporation of Ca from the deoxidation and desulfurization agent. If the heating temperature is too low, the reaction will take a long time, and if it is too high, there is a concern that the evaporation of the deoxidation and desulfurization agent and the gasification of other components and reaction products will proceed. Furthermore, there is concern that some materials may react with the crucible.

[0051] The titanium-based material obtained in the oxygen reduction process can be considered a titanium-based metal if the electrolytic process described below is not performed.

[0052] (Electrolysis process) After obtaining a titanium-based material with a lower oxygen content than the titanium-based metal raw material through the oxygen reduction process described above, an electrolytic process can be performed on the titanium-based material as an electrolytic refining step, if necessary. In the electrolytic process, it is possible to further reduce the oxygen content of the titanium-based material and reduce the content of other impurities (Al, Mg, Si, Fe, CaS, CaO, Ca, S, etc.).

[0053] In the electrolysis process, titanium-based material is used as the anode consumable raw material as crude titanium-based material. By applying a voltage between the anode, which is immersed in a molten salt bath in the electrolytic cell, and a cathode made of titanium or the like, Ti is eluted from the crude titanium-based material. The Ti eluted from the crude titanium-based material of the anode consumable raw material is electrodeposited onto the cathode to become the refined titanium-based material. The anode consumable raw material can contain the above-mentioned titanium-based material. For example, granular or powdered titanium-based material may be placed in a cage-like container made of nickel or a nickel-based alloy with numerous through-holes that allows current to pass through, and this may be used as the anode. Alternatively, a thin-walled plate-shaped casting of titanium-based material may be used directly as the anode.

[0054] The molten salt bath may be a chloride bath mainly containing metal chlorides, for example, alkali metal chlorides and / or alkaline earth metal chlorides such as magnesium chloride (MgCl2) may be contained in amounts of, for example, 70 mol% or more, more specifically 90 mol% or more, or even 95 mol% or more. When a chloride bath containing magnesium chloride (MgCl2) is used, a purified titanium-based material can be obtained in which not only the O content but also the Al content has been sufficiently reduced. The magnesium chloride content in the chloride bath is preferably 30 mol% or more, more specifically 50 mol% or more, more specifically 80 mol% or more, more specifically 85 mol% or more, and particularly 95 mol% or more.

[0055] Furthermore, if necessary, lower titanium chlorides with a lower Ti valence than titanium tetrachloride, specifically titanium dichloride (TiCl2) or titanium trichloride (TiCl3), may be added to the molten salt bath. The Ti ion content in the molten salt bath is preferably 3 mol% or more, more preferably 5 mol% or more, even more preferably 6 mol% or more, and may even be 10 mol% or more, but is preferably 20 mol% or less. Due to disproportionation reactions, some of the titanium dichloride may be converted into titanium trichloride or titanium tetrachloride.

[0056] The content of metal chlorides and metal ions in a molten salt bath can be measured by ICP emission spectrometry or atomic absorption spectrometry. The content of Ti ions is determined as a percentage of the total content of metal ions in the molten salt bath.

[0057] For example, the conditions for electrolytic refining include a molten salt bath temperature of 450°C to 900°C and a cathode current density of 0.01 A / cm². 2 ~3A / cm 2 This is sometimes done. Current density is given by the formula: Current density (A / cm²). 2 ) = Current (A) ÷ Macroscopic electrodeposition area (cm²) 2 It can be calculated by ( ). The maximum voltage between electrodes may be, for example, 0.2V to 3.5V. During electrolytic refining, it is preferable to maintain an inert gas atmosphere such as argon inside the electrolytic cell.

[0058] The electrolysis process can be repeated multiple times to further refine the purified titanium-based material obtained. When multiple electrolysis processes are performed, the purified titanium-based material deposited on the cathode in the previous electrolysis process is used as the crude titanium-based material in the next electrolysis process, and this crude titanium-based material is used as the anode consumable material. From the viewpoint of suppressing increased energy consumption and rising costs, it is desirable to reduce the number of electrolysis processes. Since the titanium-based material obtained in the oxygen reduction process described above has a reduced oxygen content, good titanium-based metals can be produced even with fewer electrolysis processes. However, even when electrolytic refining is performed two or more times, the reduction in electrical resistance due to the low oxygen content of the titanium-based electrolytic raw material can reduce power consumption and improve yield.

[0059] As described above, when producing metallic titanium as a titanium-based metal, the final metallic titanium obtained has an Al content of, for example, 0.1 mass% or less, preferably 0.01 mass% or less, and an O content of, for example, 0.2 mass% or less, preferably 0.10 mass% or less, and more preferably 0.05 mass% or less. Alternatively, when producing a titanium alloy containing Al as a titanium-based metal, the final titanium alloy (typically a Ti-Al alloy) may have an Al content of, for example, 3 mass% or less, preferably 2 mass% or less, and an O content of 0.3 mass% or less, preferably 0.15 mass% or less. It is also preferable that other impurities contained in metallic titanium or titanium alloys be 0.1 mass% or less and 0.05 mass% or less for each element. [Examples]

[0060] Next, the method for producing titanium-based metals according to this invention was experimentally implemented, and its effects were confirmed, which are described below. However, this description is for illustrative purposes only and is not intended to limit the invention to this method.

[0061] (Test Example 1) Tests were conducted to produce titanium-based metals by melting the titanium-based metal raw materials shown in Table 1 together with a deoxidizing and desulfurizing agent and a sulfur source to form a molten material, reacting the Ca in the deoxidizing and desulfurizing agent with the O in the titanium-based metal raw materials, and then reacting the Ca with the S in the sulfur source. In all the tests, the above tests were conducted using an induction skull melting furnace and a water-cooled copper crucible, with the furnace atmosphere replaced by Ar. The total amount of additives in the crucible was 7 kg, the titanium-based metal raw materials were in granular or chip form, the sulfur source was in granular form, and the deoxidizing and desulfurizing agent was in powder form. The slag-forming agent was in powder form. The conditions for each test are as shown in Table 1.

[0062] The Ti-O solid solution alloy in Table 1 was prepared by plasma arc melting titanium ore (UGS, TiO295%) + Ca + CaF2 + CaO at a temperature of 1500°C or higher, and had the following composition: Al: 0.05 mass%, O: 10 mass%, Fe: 1.5 mass%, Si: 0.8 mass%. The Ti-Al-O solid solution alloy in Table 1 was prepared by plasma arc melting titanium ore (UGS, TiO295 mass%) + Al + CaO at a temperature of 1900°C or higher, and had the following composition: Al: 6 mass%, O: 10 mass%, Fe: 1.2 mass%, Si: 0.5 mass%. The JIS Class 3 industrial pure titanium scrap (chips) in Table 1 had the following composition: Al: 0.05 mass%, O: 0.25 mass%, Fe: 0.2 mass%, Si: 0.02 mass%. Table 1 shows that the Ti-6Al-4V scrap (chips) had the following composition: Al: 6.5 mass%, V: 4.1 mass%, O: 0.21 mass%, Fe: 0.2 mass%, and Si: 0.03 mass%. Table 1 also shows that the Ti-15V-3Cr-3Sn-3Al β-type titanium alloy scrap (chips) had the following composition: Al: 3.3 mass%, V: 14.9 mass%, Cr: 3.1 mass%, Sn: 3.0 mass%, O: 0.20 mass%, Fe: 0.2 mass%, and Si: 0.02 mass%. The Ti-O solid solution alloy extracted from industrial waste TiO2 shown in Table 1 is a Ti-O solid solution alloy prepared by heating industrial waste high-purity titanium oxide (powder, TiO2 97% by mass) + Ca + CaCl2 in a titanium container at 1100°C. The composition was Al: 0.01% by mass, O: 2.1% by mass, Fe: 0.05% by mass, and Si: 0.01% by mass.

[0063] [Table 1]

[0064] In tests 12, 13, and 15, as explained in Test Example 3 below, subsequent dissolution and casting of the product resulted in nearly zero mass percent of Ca and S, yielding titanium-based metals usable as industrial products. A similar trend is expected for test number 14. In the tests with other test numbers, some other impurities were present, but by performing electrolytic refining as described in Test Example 4 below, titanium-based metals usable as industrial products were obtained.

[0065] In test number 3, the amount of sulfur used was small, which meant that a higher temperature was required to maintain the titanium-based molten material. This reduced the deoxidizing effect of calcium, resulting in a relatively high oxygen content. Furthermore, in test number 5, the opposite of test number 3 occurred; a larger amount of sulfur was used, which is thought to have resulted in a higher sulfur content in the resulting product. Furthermore, in test number 6, the amount of Ca used was insufficient, resulting in inadequate deoxidation or desulfurization. This is thought to have led to higher levels of oxygen and sulfur in the resulting product. Furthermore, in test number 11, the high proportion of sulfur in the sulfur source caused it to evaporate easily during heating. This prevented a sufficient decrease in the melting point of the Ti-Al-O solid solution alloy, resulting in insufficient deoxidation ability of Ca and consequently a relatively high oxygen content. However, while the melting point of the Ti-Al-O solid solution alloy is approximately 1800°C, industrial-grade pure titanium has a lower melting point (approximately 1680°C), resulting in good deoxidation in test number 12.

[0066] (Test Example 2) As shown in Table 2, a test to produce titanium-based metals was conducted in almost the same manner as in Test Example 1, except that a different dissolution method was used and the conditions were changed (Test No. 20).

[0067] [Table 2]

[0068] Table 2 shows that good titanium-based metals can be obtained using other dissolution methods as well.

[0069] (Test Example 3) The products obtained in tests 12, 13, and 15 of Test Example 1 were melted with an electron beam and then cast to obtain 5 kg ingots. The composition of each ingot is shown in Table 3.

[0070] [Table 3]

[0071] As shown in Table 3, none of the ingots contained nearly any Ca or S.

[0072] (Test example 4) The product obtained in Test No. 1 of Test Example 1 was used as the crude titanium-based material for the anode. Electrolytic refining (molten salt electrolysis process) was performed by applying a voltage between the anode and cathode in a molten salt bath to elute Ti from the crude titanium-based material and deposit the refined titanium-based material on the cathode. The conditions for electrolytic refining and the composition of the refined titanium-based material are shown in Table 4.

[0073] [Table 4]

[0074] As shown in Table 4, all of the refined titanium-based materials were of a quality suitable for use as industrial-grade pure titanium.

[0075] (Test Example 5) The product obtained in Test No. 10 of Test Example 1 was subjected to electrolytic purification in almost the same manner as in Test Example 4, except that the conditions were changed as shown in Table 5. The composition of the purified titanium-based material obtained is also shown in Table 5.

[0076] [Table 5]

[0077] As shown in Table 5, in test number 47, further purity was achieved by repeating the electrolytic purification process twice, and Al was sufficiently removed.

[0078] From the above, it has been found that the method for producing titanium-based metals according to this invention can reduce the oxygen content of the titanium-based metal raw material.

Claims

1. A method for producing a titanium-based metal with a lower O content than the titanium-based metal raw material, from a titanium-based metal raw material containing O, The titanium-based metal raw material has an oxygen reduction step that reduces the O content, and the oxygen reduction step is A melting step in which the titanium-based metal raw material is melted together with a sulfur source containing elemental sulfur and / or titanium sulfide by heating to obtain a molten material, The melt contains a deoxidizing and desulfurizing agent containing Ca, and the melt includes a deoxidizing step in which the Ca of the deoxidizing and desulfurizing agent reacts with at least a portion of the O of the titanium-based metal raw material. After the deoxidation step, the melt contains a deoxidizing and desulfurizing agent containing Ca, and a desulfurization step is performed in which the Ca of the deoxidizing and desulfurizing agent reacts with at least a portion of the S of the sulfur source in the melt. A method for manufacturing titanium-based metals, including [the specified element].

2. The method for producing a titanium-based metal according to claim 1, wherein the mass ratio of the amount of S used in the oxygen reduction step to the sum of the Ti content in the melt and the amount of S used in the oxygen reduction step is within the range of 0.05 to 0.

15.

3. The method for producing a titanium-based metal according to claim 1, wherein the amount of Ca used (mass%) and the amount of S used (mass%) in the oxygen reduction step, and the O content (mass%) derived from the titanium-based metal raw material in the melt satisfy the formula: amount of Ca used ≥ O content × 2.5 + amount of S used × 0.

5.

4. The method for producing a titanium-based metal according to claim 1, wherein the melt contains a slag-forming agent in the deoxidation step.

5. The sulfur source contains titanium sulfide, and the titanium sulfide is TiS x A method for producing a titanium-based metal according to claim 1, wherein (0.5 ≤ x ≤ 3.0).

6. A method for producing a titanium-based metal according to claim 1, wherein a high-frequency induction heating furnace is used in the oxygen reduction step.

7. After obtaining a titanium-based material with a lower oxygen content than the titanium-based metal raw material in the oxygen reduction step, A method for producing a titanium-based metal according to any one of claims 1 to 6, comprising an electrolysis step of using the aforementioned titanium-based material as the crude titanium-based material for the anode, and applying a voltage between the anode and the cathode in a molten salt bath to dissolve Ti from the crude titanium-based material and deposit a refined titanium-based material on the cathode.

8. A method for producing a titanium-based metal according to claim 7, wherein the electrolysis step is repeated multiple times, and in each of the multiple electrolysis steps, the refined titanium-based material deposited on the cathode in the previous electrolysis step is used as the crude titanium-based material in the next electrolysis step.

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