Metal reduction reaction vessel and titanium sponge manufacturing method

Abstract

The present invention provides a metal reduction reaction vessel that suppresses clogging of the molten material discharge pipe by metallic titanium and allows the molten material contained in the molten salt bath to be smoothly discharged from the molten material discharge port, and a method for producing sponge titanium using the same. [Solution] The metal reduction reaction vessel 1 of this invention is used for producing a sponge titanium mass TS based on the reduction reaction of titanium tetrachloride, and comprises a cylindrical body portion 2, a support base 7 provided on one axial end of the body portion 2 to support the sponge titanium mass TS, and a bottom portion 3 having a molten discharge port 3a formed on the inner surface of the vessel, spaced radially outward from the support surface 7a of the support base 7, and a shielding projection 8 is provided that covers at least the other axial end around the molten discharge port 3a and protrudes radially inward from the inner surface of the vessel.

Description

[Technical Field]

[0001] This invention relates to a metal reduction reaction vessel used to produce a sponge titanium mass by the reduction reaction of titanium tetrachloride, and to a method for producing sponge titanium. [Background technology]

[0002] The Kroll process is widely used industrially as a method for producing sponge titanium. In the Kroll process, for example, molten metallic magnesium is pre-stored in a metal reduction reaction vessel to create a molten bath, and titanium tetrachloride is supplied by dropping it onto the surface of the bath in a reduction step. During the reduction step, metallic magnesium acts as a reducing agent, reducing titanium tetrachloride to metallic titanium, and this metallic titanium grows as a sponge titanium mass within the metal reduction reaction vessel. At this time, magnesium chloride is produced in the molten bath as a byproduct. Since magnesium chloride has a higher specific gravity than metallic magnesium, it settles at the bottom of the bath below the surface.

[0003] During the reduction process, the molten by-products such as magnesium chloride contained in the molten bath within the metal reduction reaction vessel may be discharged to the outside through a molten outlet formed at the bottom of the metal reduction reaction vessel and connected to a molten outlet pipe. After the reduction process is completed, a bath discharge process may be carried out, in which the molten material containing metallic magnesium and by-products such as magnesium chloride that were not used in the reduction reaction may be discharged from the reduction vessel while maintaining its molten state.

[0004] Following the bath discharge process, a vacuum separation process is performed in which the metal reduction reaction vessel is heated to a high temperature while the pressure inside the metal reduction reaction vessel is reduced. This separates residual materials such as metallic magnesium from the sponge titanium mass inside the metal reduction reaction vessel. After the vacuum separation process is completed, the sponge titanium mass is removed from the metal reduction reaction vessel and crushed to obtain granular sponge titanium.

[0005] Patent Document 1 describes a technique for producing titanium sponge blocks by reducing titanium tetrachloride in this way, describing a "method for producing titanium sponge by adding TiCl4 dropwise to molten Mg contained in a reaction vessel, wherein a tapping operation is performed intermittently to remove the by-product MgCl2 from the vessel, and the amount of MgCl2 tapped in the latter half of the reaction is made less than in the first half of the reaction."

[0006] Furthermore, Patent Document 2 describes "a method for producing titanium sponge by reducing titanium tetrachloride with magnesium, which comprises filling a reaction vessel with molten magnesium, maintaining the average temperature of the wall surface of the reaction vessel in contact with the vicinity of the reaction surface of the molten magnesium bath in which the reduction reaction proceeds at or below the melting point of magnesium chloride, and supplying the titanium tetrachloride to the vicinity of the reaction surface of the molten magnesium bath." [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-43872 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-190024 Summary of the Invention [Problem to be solved by the invention]

[0008] A support stand may be placed at the bottom of the metallic reduction reaction vessel. The support stand supports a titanium sponge mass formed by the settling of metallic titanium particles, which are produced by contact between titanium tetrachloride and metallic magnesium on the surface of the molten bath during the reduction step. A melt discharge port, to which a melt discharge pipe is connected, may be provided on the inner surface of the vessel radially outward from the support surface of the support stand.

[0009] When the reduction process is carried out using such a metal reduction reaction vessel, some of the titanium metal generated on the surface of the molten bath may settle in a position radially outward from the support base and accumulate near the molten discharge port. In this case, when the molten material is discharged from the molten discharge port, the accumulated titanium metal can obstruct the discharge of the molten material and, in severe cases, cause blockage of the molten discharge pipe.

[0010] An object of the present invention is to provide a metallic reduction reaction vessel that can suppress clogging of the melt discharge pipe with metallic titanium and enable the melt contained in a molten salt bath to be smoothly discharged from the melt discharge port, and a method for producing titanium sponge using the same. [Means for solving the problem]

[0011] The metal reduction reaction vessel of this invention is used for producing a sponge titanium mass based on the reduction reaction of titanium tetrachloride, and comprises a cylindrical body, a support base provided on one axial end of the body to support the sponge titanium mass, and a bottom portion with a molten discharge port formed on the inner surface of the vessel, spaced radially outward from the support surface of the support base, and a shielding projection that extends radially inward from the inner surface of the vessel, covering at least the other axial end around the molten discharge port.

[0012] In the above-mentioned metallic reduction reaction vessel, it is preferable that the shielding protrusion is formed from one side around the melt discharge port, through the other axial end side, and up to the other side.

[0013] In the metallic reduction reaction vessel, it is preferable that the shielding protrusion is a separate member from the melt discharge pipe connected to the melt discharge port. In this case, it is preferable that the shielding protrusion is formed of a shielding protrusion member welded to the inner surface of the vessel.

[0014] In the above-described metal reduction reaction vessel, the inner surface of the bottom of the vessel has a shape that narrows radially inward toward one axial end, and when the axial end of the melt outlet is located radially inward from the other axial end of the melt outlet, it is preferable that the shielding projection protrudes radially to the same position as the axial end, or to a position radially inward from the axial end.

[0015] The above-described metal reduction reaction vessel may be made of clad steel, in which at least the body portion of the body portion and the bottom portion has an outer layer formed by stainless steel.

[0016] The method for producing sponge titanium according to this invention includes a reduction step in which a sponge titanium mass is produced using one of the above-mentioned metal reduction reaction vessels. [Effects of the Invention]

[0017] According to the metal reduction reaction vessel of this invention, clogging of the molten material discharge pipe by titanium metal is suppressed, and the molten material contained in the molten salt bath can be smoothly discharged from the molten material discharge port. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view taken along the depth direction of a metal reduction reaction vessel according to an embodiment of the present invention. FIG. [Figure 2] 2 is an enlarged cross-sectional view taken along the depth direction of the metal reduction reaction vessel of FIG. 1, showing a main part of the vessel. FIG. [Figure 3] This is a cross-sectional view along line III-III in Figure 2. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an embodiment of the present invention will be described in detail. The metal reduction reaction vessel 1 illustrated in Figure 1 is used to produce a sponge titanium mass TS based on the reduction reaction of titanium tetrachloride. This metal reduction reaction vessel 1 comprises a cylindrical body 2 and a bottom 3 provided at one end of the body 2 in the axial direction (up and down in Figure 1) (the lower side in Figure 1).

[0020] A support stand 7 is disposed on the bottom 3. The support stand 7 supports from below a titanium sponge mass TS that grows on the support surface 7a, which is flat or other flat on its upper side, as titanium metal in the form of granules produced near the bath surface Sb by the reduction reaction that settles and accumulates. The support stand 7 is also provided with a melt discharge port 3a in the bottom 3 for discharging the melt that constitutes the molten bath Bm. The melt discharge port 3a is formed on the inner surface of the vessel, spaced radially outward from the support surface 7a of the support stand 7 (left-right direction in FIG. 1 ).

[0021] 1 and 2, in this embodiment, a shielding protrusion 8 is provided on the inner surface of the vessel around the melt discharge outlet 3a, covering at least the other axial end side of the periphery and protruding radially inward from the inner surface of the vessel. With this, even if metallic titanium produced at the bath surface Sb of the molten bath Bm during the reduction reaction settles to a position near the melt discharge outlet 3a radially outward from the support base 7, the metallic titanium is prevented from reaching the melt discharge outlet 3a by the shielding protrusion 8, which covers at least the other axial end side of the periphery of the melt discharge outlet 3a. As a result, clogging of the melt discharge pipe 5 with metallic titanium is suppressed, and the melt can be smoothly discharged from the melt discharge outlet 3a.

[0022] (Metal reduction reaction vessel) More specifically, the illustrated metal reduction reaction vessel 1 is configured such that one axial end side of a cylindrical body 2 is sealed with a bottom 3 having a curved surface such as a hemispherical shape. The cylindrical body 2 can have constant inner and outer diameters over the entire axial direction, but may have a tapered or stepped portion in at least a part of the axial direction to change the inner and / or outer diameters.

[0023] The other axial end of the body portion 2 (the upper side in Figure 1) is provided with an opening that connects the inside and outside of the metal reduction reaction vessel 1. In most cases, when the metal reduction reaction vessel 1 is used in the reduction process, the opening is covered by attaching a lid member 4 to it. Here, the lid member 4 is not considered an essential component of the metal reduction reaction vessel 1. A metal reduction reaction vessel 1 without a lid member 4 is also included in this invention. If necessary, an outward-facing flange portion 2a may be formed around the entire circumference of the opening to which the lid member 4 is attached.

[0024] The support base 7 provided at the bottom 3 of the metal reduction reaction vessel 1, in the illustrated example, includes a cylindrical or columnar base 7b and a disc-shaped support plate 7c, which is a separate component from the base 7b and is placed on the base 7b with a support surface 7a on the other axial end. If the base 7b and the support plate 7c are separate components, even if the sponge titanium mass TS becomes fixed to the support plate 7c, the sponge titanium mass TS and the support plate 7c can be easily separated from the base 7b. However, although not shown in the illustration, the support base may be formed by integrally forming the base and the support plate. Also, the base 7b and the support plate 7c may be of roughly the same size (for example, approximately the same diameter) in plan view. Furthermore, the support base 7 may consist only of the base 7b.

[0025] At the bottom 3, a melt outlet 3a is formed on the inner surface of the container, spaced radially outward from the support surface 7a of the support base 7. More specifically, in this example, as shown in Figure 2, there is a gap G between the radial outer edge of the support surface 7a and the axial end E1 of the melt outlet 3a, which is furthest radially outward from the support surface 7a. The radial size of the gap G may be, for example, 30 mm to 150 mm, typically around 50 mm to 100 mm. The melt outlet 3a is provided at the bottom 3 to facilitate the discharge of magnesium chloride that settles downward in the molten bath Bm, for example, in the bath discharge process described later. In the metal reduction reaction vessel 1, the portion located one end away from the support surface 7a in the axial direction may be considered as the bottom 3.

[0026] The melt outlet 3a is formed by hollowing out a portion of the wall of the bottom 3, and as shown in Figure 3, it can be a through-hole with a front view that is, for example, elliptical, oblong, circular, or other shape. This melt outlet 3a is often connected to a melt outlet pipe 5 located outside the body 2 and bottom 3, as shown in Figures 1 and 2, to guide the melt from the internal molten bath Bm to the melt outlet pipe 5. The melt outlet pipe 5 may, for example, curve from the melt outlet 3a and extend substantially parallel to the axial direction of the body 2, and be connected to a magnesium chloride storage container or magnesium chloride transfer container (not shown).

[0027] Incidentally, during the reduction process, metallic magnesium located at the surface Sb of the molten bath Bm may come into contact with titanium tetrachloride that has been dropped onto it, causing a reduction reaction. At this time, near the surface Sb, granular metallic titanium is produced by the reduction of titanium tetrachloride by metallic magnesium. The metallic titanium settles downward in the molten bath Bm, and most of it accumulates on the support surface 7a of the support base 7, forming a sponge titanium mass TS. However, some of it may settle in a position radially outward from the support base 7. The metallic titanium that accumulates on the bottom 3 in a position away from the support base 7, especially the metallic titanium that accumulates near the molten outlet 3a, may enter the molten outlet 3a and block the molten outlet 5. If the molten outlet 5 becomes blocked, it will be necessary to insert a rod or the like from the end of the molten outlet 5 opposite to the molten outlet 3a to clear the blockage. During the reduction process, this operation may require stopping the supply of titanium tetrachloride, and in some cases, even necessitating the termination of the reduction process.

[0028] To address this issue, a shielding protrusion 8 is provided on the inner surface of the vessel around the melt discharge outlet 3a in the bottom 3, covering at least the other axial end side of the inner surface and protruding radially inward from the inner surface. In this case, metallic titanium falling onto the melt discharge outlet 3a from above is mainly deposited on the shielding protrusion 8 covering the other axial end side of the melt discharge outlet 3a, making it difficult for it to reach the melt discharge outlet 3a. This prevents metallic titanium from interfering with the discharge of the melt from the melt discharge outlet 3a, ensuring smooth discharge of the melt from the melt discharge outlet 3a.

[0029] The above-mentioned effect can be obtained as long as the shielding protrusion 8 is provided on the inner surface of the vessel at least on the other axial end side of the melt discharge outlet 3a and covers at least the other axial end side of the melt discharge outlet 3a. However, from the viewpoint of more effectively preventing metallic titanium from reaching the melt discharge outlet 3a, it is preferable that the shielding protrusion 8 is formed from one side around the melt discharge outlet 3a, passing through the other axial end side and reaching the other side side, as shown in Fig. 3, so as to cover not only the other axial end side but also both side sides around the melt discharge outlet 3a. This prevents metallic titanium from entering the melt discharge outlet 3a from the sides around the melt discharge outlet 3a. In the illustrated example, as shown in Figure 3, the shielding protrusion 8 is configured to include an other-end portion 8a located on the other end side of the axial position (shown by a dashed line in the same figure) of the end E1 on the other axial end side of the melt discharge outlet 3a when viewed from the front of the melt discharge outlet 3a, and a lateral portion 8b continuous with the other-end portion 8a and located on one end side of the axial position of the above-mentioned end E1.

[0030] When the vessel inner surface of the bottom 3 has a shape that tapers radially inward toward one axial end, as in the illustrated embodiment, end E2 at one axial end of the melt discharge outlet 3a provided in the bottom 3 may be located radially more inward than end E1 at the other axial end of the melt discharge outlet 3a (see FIG. 2). By configuring the vessel inner surface of the bottom 3 and the melt discharge outlet 3a in this manner, the melt discharge outlet 3a can be located considerably lower on the bottom 3, allowing a larger amount of melt to be discharged from the metallic reduction reaction vessel 1 in the bath discharge step.

[0031] In this case, it is preferable that the shielding projection 8 protrudes radially to the same position as the end E2 on one axial end, or to a position radially inward from the end E2 on one axial end, as shown in Figures 1 and 2. This is to ensure that the shielding projection 8 sufficiently covers the area around the melt discharge port 3a. In this case, the length of the shielding projection 8 protruding radially inward may decrease in a manner such as a gradual reduction from the other end portion 8a to the lateral portion 8b.

[0032] The shielding projection 8 may be formed by extending the molten discharge pipe 5, which is connected to the molten discharge port 3a, from the molten discharge port 3a into the interior of the bottom 3, but it is preferable that it be a separate component from the molten discharge pipe 5. Furthermore, it is preferable that the shielding projection 8 be composed of a shielding projection member welded to the inner surface of the container. This increases the design freedom regarding the dimensions and shape of the shielding projection 8, and makes it easy to provide the desired shielding projection 8.

[0033] The support base 7 may be installed inside the metal reduction reaction vessel 1 from the outside through an opening on the other axial end of the body 2 before the start of the reduction process. Since the shielding projection 8 is provided in the gap G, it can be visually confirmed from the opening side when installing the support base 7, and this does not significantly hinder the ease of installation.

[0034] Furthermore, it is preferable that at least the body 2 of the metal reduction reaction vessel 1 be made of clad steel, where the outer layer forming the outer surface of the vessel is stainless steel. This ensures that the mechanical strength of the body 2 is maintained even in the reduction process and vacuum separation process, where the metal reduction reaction vessel 1 is exposed to high temperatures, due to its excellent heat resistance. It also suppresses contamination of the molten bath Bm with metallic magnesium impurities on the bath surface Sb side due to the vessel material. The inner layer joined to the clad steel outer layer can be made of steel such as carbon steel or low-nickel steel. Another layer may be provided further outside the clad steel outer layer. Since the bottom 3 mainly contains magnesium chloride from the molten bath Bm, contamination prevention measures are not necessarily required, but the bottom 3 may also be made of the clad steel described above.

[0035] (Reduction process) The reduction step can be carried out with the above-mentioned metallic reduction reaction vessel 1 placed in a reduction furnace (not shown).

[0036] Specifically, for example, metallic magnesium (Mg) as a reducing agent is stored in a molten state in a metallic reduction reaction vessel 1, and the interior of the metallic reduction reaction vessel 1 becomes a molten bath Bm. Then, while the metallic reduction reaction vessel 1 is heated in a reduction furnace and locally cooled, titanium tetrachloride (TiCl4) as a raw material is supplied dropwise onto the bath surface Sb of the molten bath Bm from above through a supply pipe 6 attached to the lid member 4. The titanium tetrachloride thus supplied comes into contact with the metallic magnesium in the molten bath Bm and is reduced by the metallic magnesium based on the reaction: TiCl4 + 2Mg → Ti + 2MgCl2. The metallic titanium (Ti) produced by the reduction of titanium tetrachloride is deposited mainly on the support surface 7a of the support stand 7 and becomes a titanium sponge mass TS.

[0037] Magnesium chloride (MgCl2), which is produced in the molten bath Bm as a by-product of this reaction, sinks downward from the bath surface Sb due to its greater specific gravity than metallic magnesium. Meanwhile, metallic magnesium in the molten bath Bm rises toward the bath surface Sb due to its relatively small specific gravity. This difference in specific gravity between magnesium chloride and metallic magnesium causes the bath to flow, and metallic magnesium is located at the bath surface Sb. As a result, a reaction continues between metallic magnesium and the dripping titanium tetrachloride at the bath surface Sb, and titanium sponge mass TS grows primarily in the molten bath Bm.

[0038] The magnesium chloride that has settled downward in the molten bath Bm can be extracted, for example, intermittently at regular intervals, from the melt discharge outlet 3a provided in the bottom 3 through the melt discharge pipe 5 to the outside of the metallic reduction reaction vessel 1. As described above, the shielding protrusion 8 that covers at least the other axial end of the melt discharge outlet 3a prevents metallic titanium that has been produced by the reduction of titanium tetrachloride and settled radially outward from the support surface 7a from entering the melt discharge outlet 3a.

[0039] Furthermore, the titanium tetrachloride used in the reduction process can be, for example, liquid purified titanium tetrachloride obtained after purification in a rectification column. This purified titanium tetrachloride is obtained, for example, by purifying crude titanium tetrachloride, which is produced by reacting raw materials such as titanium ore with a carbon source such as coke and chlorine gas, in a rectification column. However, the titanium tetrachloride is not limited to the purified titanium tetrachloride described above, as long as it is suitable for use in the reduction process.

[0040] Furthermore, the magnesium chloride produced in the reduction step can be decomposed into metallic magnesium and chlorine gas by subjecting it to molten salt electrolysis in an electrolytic cell. The metallic magnesium thus obtained can be reused in the reduction step.

[0041] (Bath discharge process) After the reduction step is completed, a melt containing metallic magnesium that was not used in the reduction reaction in the reduction step and magnesium chloride, a by-product produced in the reduction reaction, is stored in the metallic reduction reaction vessel 1, and the titanium sponge mass TS is immersed in the melt.

[0042] In the bath discharge step, the melt is discharged from the metallic reduction reaction vessel 1 using the melt discharge pipe 5, with the titanium sponge mass TS remaining in the metallic reduction reaction vessel 1. By providing the shielding protrusion 8, clogging of the melt discharge pipe 5 with metallic titanium can be suppressed even in this case.

[0043] (Decompression separation process) In the reduced pressure separation process performed after the bath discharge process, the metallic reduction reaction vessel 1 is heated in a heating furnace (not shown) while being connected to a recovery vessel (not shown), and the inside of the metallic reduction reaction vessel 1 is made into a vacuum or reduced pressure atmosphere of 30 Pa or less.

[0044] As a result, the melt in the metallic reduction reaction vessel 1 evaporates into vapor, which separates from the titanium sponge mass TS and is sucked into the recovery vessel. At this time, the vapor is cooled in the low-temperature recovery vessel and liquefied or solidified, adhering to the inner surface, etc.

[0045] After the vacuum separation process, the sponge titanium mass TS can be removed from the metal reduction reaction vessel 1 by, for example, pushing it out from the bottom 3 side toward the opening side of the metal reduction reaction vessel 1 via the support base 7. Since the shielding projection 8 is provided in the gap G, it does not have a significant effect on the extrusion of the sponge titanium mass TS.

[0046] (Crushing process) The sponge titanium mass TS removed from the metal reduction reaction vessel 1 can be crushed, for example, in a crushing process to form sponge titanium in the form of granules of a predetermined size. The weight of the sponge titanium mass TS may be set appropriately considering the manufacturing schedule, for example, within the range of 5 tons to 15 tons.

[0047] Here, for example, the sponge titanium ingot TS is first chipped away by hand, and then a guillotine-type shear is used to remove the upper, lower, and outer parts of the sponge titanium ingot TS, which often contain many impurities. After that, the desired parts of the sponge titanium ingot TS can be crushed to a certain size. In this way, sponge titanium is manufactured. [Example]

[0048] Next, a metallic reduction reaction vessel according to the present invention was fabricated as a prototype, and its effects were confirmed. The following description will be given, however, for illustrative purposes only and is not intended to be limiting.

[0049] In the examples, the reduction process was carried out using a metal reduction reaction vessel as shown in Figures 1-3, and 22 tests were conducted to produce a sponge titanium mass (weighing approximately 13 tons). In the comparative example, the procedure was the same as in the examples, except that a metal reduction reaction vessel without shielding protrusions was used, and the number of tests was increased to 57.

[0050] As a result, the average frequency of blockage in the molten discharge pipe per test was 2.6 times in the example, compared to 5.1 times in the comparative example. It should be noted that blockage in the molten discharge pipe can occur not only due to the ingress of metallic titanium, but also due to the cooling of magnesium chloride along the way. In the example, the frequency of blockage caused by metallic titanium is considered to be sufficiently low.

[0051] In the comparative example, observation of the molten material outlet revealed that titanium powder was concentrated in the molten material outlet area of ​​the molten material outlet pipe. In this case, the blockage of titanium powder reduced the cross-sectional area of ​​the liquid-passable portion of the molten material outlet pipe. In the example, no such blockage of titanium powder was observed.

[0052] From the above, it was suggested that this invention may be able to effectively prevent clogging of the melt discharge pipe with metallic titanium. [Explanation of symbols]

[0053] 1. Metal reduction reactor 2. Torso 2a Outward flange 3 bottom 3a Melt outlet 4 Cover member 5 Melt discharge pipe 6 Supply pipe 7 Support stand 7a Support surface 7b Pedestal 7c Support plate 8 Shielding protrusion 8a: Other end portion of the shielding protrusion in the axial direction 8b Side portions of the shielding protrusion Bm molten bath E1 End of the melt outlet on the other axial end E2 End of one axial end of the melt discharge port G Gap Sb bath surface TS Titanium sponge mass

Claims

1. A metallic reduction reaction vessel used for producing titanium sponge mass based on the reduction reaction of titanium tetrachloride, a cylindrical body portion; a support stand for supporting a titanium sponge mass, the support stand being disposed at one axial end of the body portion; and a bottom portion having a melt discharge port formed on an inner surface of the vessel spaced radially outward from a support surface of the support stand, A metallic reduction reaction vessel is provided with a shielding protrusion that covers at least the other axial end side of the periphery of the melt discharge port and protrudes radially inward from the inner surface of the vessel.

2. 2. The metallic reduction reaction vessel according to claim 1, wherein the shielding protrusion is formed from one side around the periphery of the melt discharge port, through the other axial end, and to the other side.

3. 2. The metallic reduction reaction vessel according to claim 1, wherein the shielding protrusion is a separate member from a melt discharge pipe connected to the melt discharge port.

4. 4. The metallic reduction reaction vessel according to claim 3, wherein the shielding protrusion is formed of a shielding protrusion member welded to the inner surface of the vessel.

5. the inner surface of the container at the bottom has a shape that tapers radially inward toward one axial end, and an end portion of the melt discharge outlet at one axial end is located radially more inward than an end portion of the melt discharge outlet at the other axial end, 2. The metallic reduction reaction vessel according to claim 1, wherein the shielding protrusion protrudes radially to the same position as the end portion on the one axial end side or to a position radially inward of the end portion on the one axial end side.

6. 2. The metallic reduction reaction vessel according to claim 1, wherein at least the body of the body and the bottom is made of clad steel having an outer layer of stainless steel that forms the outer surface of the vessel.

7. A method for producing titanium sponge, comprising a reduction step of producing titanium sponge lumps using the metallic reduction reaction vessel according to any one of claims 1 to 6.

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