JP7106372B2 - METHOD FOR MANUFACTURING METAL REDUCTION REACTION VESSEL, METHOD FOR MANUFACTURING METAL REDUCTION REACTION VESSEL, AND TITANIUM - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a metal reduction reactor, a metal reduction reactor, and a method for manufacturing titanium.

The central portion of the sponge titanium mass produced by the so-called Kroll method, in which titanium tetrachloride is reduced with a reducing metal to produce metallic titanium, has a high degree of titanium purity, but the outer peripheral portion thereof is made of the material that constitutes the reaction vessel. It is known to diffuse under high temperature and contaminate sponge titanium, resulting in low purity. When the reaction vessel is made of stainless steel, iron, nickel and chromium are contaminants derived from the reaction vessel and contaminate the produced titanium sponge.

In recent years, a reaction vessel has been developed that can effectively suppress contamination of a high melting point metal by impurity metals from a reaction vessel for producing a high melting point metal such as titanium. In particular, the high-melting-point metal mass initially produced in the newly produced reaction vessel tends to have a high content level of the metal components Fe, Ni, and Cr contained in the reaction vessel. There is a need for a reaction vessel or a method for producing high-melting-point metals that suppresses the

For example, in Patent Document 1, by raising the temperature of a reaction vessel to 800° C. or higher while high-melting-point metal particles are in contact with the inner surface of a manufactured unused reaction vessel, the high-melting-point metal is solidified on the inner surface of the reaction vessel. A method for producing a high-melting-point metal has been proposed in which the reaction vessel after the phase diffusion treatment is used as the initial reduction reaction vessel. Further, in Patent Document 2, in a reaction vessel for producing a high melting point metal by reducing a chloride of a high melting point metal, the same metal as the high melting point metal to be produced and the reaction vessel are added to the inner wall surface of the reaction vessel. A reaction vessel for producing a high-melting-point metal in which an alloy layer with a constituent metal is formed has been proposed.

JP 2014-214356 A JP 2009-127107 A

Patent Document 1 describes that the inner surface of the reaction vessel is lined with iron to produce the first batch of titanium sponge, but does not pay attention to impurities Ni and Cr other than Fe. In addition, since the Ni and Cr concentrations of titanium sponge produced using a stainless steel reaction vessel have not been evaluated, it is unclear whether the concentrations of Ni and Cr in titanium sponge can actually be reduced.

Further, in Patent Document 2, an alloy layer containing the same metal as the high-melting-point metal to be produced is formed on the inner wall surface of the reaction vessel for the first batch. It is considered that there is still room for improvement in order to stably produce high-quality sponge titanium.

Accordingly, an object of the present invention is to solve such problems, and in one embodiment, manufacture of a metal reduction reaction vessel capable of reducing the impurity concentration of titanium in the titanium production process. The purpose is to provide a method. Another object of the present invention, in another embodiment, is to provide a metallic reduction reaction vessel manufactured in such a manner. Another object of the present invention, in another embodiment, is to provide a method for producing titanium using the metallic reduction reaction vessel thus produced.

That is, in one aspect of the present invention, a rust layer forming step of heating a metal reduction reaction vessel to form a rust layer containing oxides of elements derived from the vessel on the inner surface; A diffusion barrier layer-forming raw material containing titanium chloride and magnesium is charged and then heated under reduced pressure to vaporize the raw material to form a Ti-containing diffusion barrier layer on the inner surface of the metal reduction reactor. and a step of forming a diffusion barrier layer.

In one embodiment of the method for manufacturing a metal reduction reactor according to the present invention, the heating temperature in the rust layer forming step is 900°C to 1200°C.

In one embodiment of the method for manufacturing a metal reduction reactor according to the present invention, the rust layer has an average thickness of 1 to 40 μm.

In one embodiment of the method for manufacturing a metal reduction reaction vessel according to the present invention, in the rust layer forming step, air is supplied into the metal reduction reaction vessel while heating the metal reduction reaction vessel. to form the rust layer on the inner surface of the metal reduction reactor.

In one embodiment of the method for manufacturing a metal reduction reaction vessel according to the present invention, the raw material for forming the diffusion barrier layer is low-grade titanium sponge containing titanium chloride and magnesium.

In one embodiment of the method for manufacturing a metal reduction reaction vessel according to the present invention, the metal reduction reaction vessel is made of stainless steel.

In one embodiment of the method for manufacturing a metal reduction reactor according to the present invention, the rust layer contains chromium oxide.

In one embodiment of the method for manufacturing a metal reduction reaction vessel according to the present invention, the metal reduction reaction vessel is unused.

In one embodiment of the method for manufacturing a metal reduction reaction vessel according to the present invention, the heating temperature in the diffusion prevention layer forming step is 650 to 1200°C.

In one embodiment of the method for manufacturing a metal reduction reaction vessel according to the present invention, the average thickness of the diffusion prevention layer exceeds 5 μm.

In another aspect of the present invention, there is provided a metal reduction reactor provided with a Ti-containing diffusion prevention layer on the inner surface, wherein the diffusion prevention layer has an average thickness of more than 5 μm. is.

In another aspect of the present invention, there are provided a step of obtaining a metal reduction reaction vessel provided with a diffusion prevention layer by the method for manufacturing a metal reduction reaction vessel described above, and a metal reduction reaction vessel provided with the diffusion prevention layer. and reducing titanium tetrachloride within.

According to one embodiment of the present invention, there is provided a method for manufacturing a metal reduction reactor capable of stably reducing the impurity metal concentration of titanium in the titanium manufacturing process.

FIG. 2 is a flow diagram illustrating an example of a method for manufacturing a metal reduction reaction vessel according to the present invention; FIG. 2 is a schematic cross-sectional view schematically showing a metal reduction reaction vessel to be provided for a diffusion prevention layer forming step in the method for manufacturing a metal reduction reaction vessel according to the present invention; (A) is an enlarged cross-sectional view schematically explaining the inner surface structure of a metal reduction reaction vessel after performing a rust layer forming step in the method for manufacturing a metal reduction reaction vessel according to the present invention; FIG. 4 is an enlarged cross-sectional view schematically explaining the inner surface structure of the metal reduction reaction vessel during the diffusion prevention layer forming step in the method for manufacturing the metal reduction reaction vessel according to the present invention, and (C) is the metal reduction reaction vessel according to the present invention. FIG. 3 is an enlarged cross-sectional view schematically illustrating the inner surface structure of the metal reduction reaction vessel after performing the diffusion prevention layer forming step in the reduction reaction vessel manufacturing method. 4 is a histogram showing Fe concentration distributions in titanium sponges obtained in Examples and Comparative Examples. 4 is a histogram showing the distribution of Ni concentration in titanium sponges obtained in Examples and Comparative Examples. 4 is a histogram showing distribution of Cr concentration in titanium sponges obtained in Examples and Comparative Examples.

Specific embodiments of the present invention will be described in detail below. In addition, the present invention is not limited to the following embodiments, and various modifications are possible without changing the gist of the present invention.

[1. Overview]
The method for producing sponge titanium by the Kroll method is as follows: After making a metal reduction reaction vessel an inert atmosphere, metallic magnesium in a molten state is charged from a metallic vessel for transporting magnesium using a metallic pipe, Titanium tetrachloride is added dropwise to the charged molten magnesium to produce sponge titanium and magnesium chloride (hereinafter referred to as the "reduction step"), and then the chloride remaining in the metal reduction reactor is removed. A liquid-phase extraction operation is performed in which magnesium and unreacted magnesium are extracted from the reaction vessel through a metal pipe in a liquid phase state. Then, magnesium chloride and unreacted magnesium that remain after the liquid phase extraction operation are carried out are vacuum-separated to obtain titanium sponge (hereinafter referred to as "vacuum separation step").

When producing the sponge titanium, the inner surface of the metal reduction reaction vessel may be modified in order to suppress metal contamination originating from the metal reduction reaction vessel. For example, a method of coating the inner surface with a titanium film is conceivable. However, since the inner surface of an unused metal reduction reaction vessel has particularly high smoothness, it is not possible to form a diffusion barrier layer such as a titanium film on the inner surface of an untreated metal reduction reaction vessel without surface treatment. Even if the anti-diffusion layer can be formed, there is a problem that the thickness is thinner than the predetermined thickness. Therefore, the inventors of the present invention formed a rust layer on the inner surface of the metal reduction reaction vessel, and then vaporized the raw material for forming the diffusion prevention layer in order to form a good diffusion prevention layer for reducing the impurity concentration of titanium. It has been found that a Ti-containing diffusion barrier layer is formed on the inner surface of a metallic reduction reaction vessel. The present inventors have further studied and completed the invention including the embodiments described below.
Each embodiment will be described below.

[2. Method for manufacturing metal reduction reaction vessel]
FIG. 1 is a flow diagram illustrating an example of a method for manufacturing a metal reduction reactor according to the present invention. Further, FIG. 2 is a schematic cross-sectional view showing an example of a metal reduction reactor used for the diffusion prevention layer forming step in the method for manufacturing a metal reduction reactor according to the present invention. FIG. 3A is an enlarged cross-sectional view schematically illustrating the inner surface structure of the metal reduction reactor after the rust layer forming step in the method for manufacturing the metal reduction reactor according to the present invention. FIG. 3(B) is an enlarged cross-sectional view schematically explaining the inner surface structure of the metal reduction reaction vessel during the step of forming the diffusion barrier layer in the method for manufacturing the metal reduction reaction vessel according to the present invention, and FIG. ) is an enlarged cross-sectional view schematically explaining the inner surface structure of the metal reduction reaction vessel after performing the diffusion prevention layer forming step in the method for manufacturing the metal reduction reaction vessel according to the present invention.
Hereinafter, a method for manufacturing a metal reduction reactor according to the present invention will be illustrated with reference to the drawings.

In one embodiment, the method for manufacturing a metal reduction reactor according to the present invention includes a rust layer forming step S11 and a diffusion prevention layer forming step S21, as shown in FIG.

<Rust layer forming process>
In the rust layer forming step S11, the metallic reduction reaction vessel is heated to form a rust layer containing oxides of elements derived from the vessel on the inner surface of the metallic reduction reaction vessel. The material of the metal reduction reaction vessel is not particularly limited, but examples thereof include stainless steel (eg SUS316) and clad steel (eg SS400 and stainless steel). When the metal reduction reaction vessel is stainless steel, Cr contained in the stainless steel is oxidized to form a chromium oxide layer containing chromium oxide on the inner surface of the metal reduction reaction vessel as a rust layer. Further, when the metal reduction reaction vessel is clad steel, the inner surface of the metal reduction reaction vessel is carbon steel. form an iron oxide layer on the inner surface of

(Heating temperature)
The heating temperature is preferably 900 to 1200° C., and the metallic reduction reactor is preferably heated. The heating temperature is preferably 900° C. or higher, more preferably 950° C. or higher, and more preferably 980° C. from the viewpoint of oxidizing the inner surface of the metal reduction reactor by heating to grow a rust layer. ° C. or more is more preferable. From the viewpoint of production efficiency, the heating temperature is preferably 1200° C. or lower, more preferably 1150° C. or lower, and even more preferably 1050° C. or lower.

(heating time)
The heating time is preferably 5 hours or more, more preferably 7 hours or more, more preferably 9 hours, from the viewpoint of oxidizing the inner surface of the metal reduction reactor by heating to grow a rust layer. It is more preferable that it is above. The heating time is preferably 30 hours or less, more preferably 20 hours or less, from the viewpoint of production efficiency.

(Air supply)
From the viewpoint of efficiently forming a rust layer on the inner surface of the metal reduction reaction vessel, it is preferable to supply air into the metal reduction reaction vessel while heating the metal reduction reaction vessel. When the metallic reduction reaction vessel is provided with an Mg pipe for extracting and/or supplying magnesium and magnesium chloride, air may be supplied into the metallic reduction reaction vessel via the Mg pipe. Further, even after the heating and holding of the metal reduction reaction vessel is finished, air may be supplied into the metal reduction reaction vessel through the Mg pipe. As the air, dry air containing oxygen may be used.

(Average thickness of rust layer)
A metal reduction reaction vessel with a diffusion prevention layer, which will be described later, is used for titanium production, but the formation of a good rust layer contributes to the formation of a good diffusion prevention layer, so the rust layer must have a certain thickness or more. is preferred. The average thickness of the rust layer is preferably 1-40 μm. The average thickness of the rust layer is preferably 1 μm or more, more preferably 3 μm or more, more preferably 5 μm, from the viewpoint of efficiently forming the titanium-containing layer in the diffusion prevention layer forming step S21, which is the next step. It is more preferable that it is above. Also, the average thickness of the rust layer is preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less, from the viewpoint of production efficiency.

When measuring the thickness of the rust layer, the following method is used. A test piece to be analyzed having a rust layer was cut from the inner surface of the metal reduction reaction vessel, cut into approximately 1 cm x 1 cm x 1 cm squares with a slicing machine, and used as a measurement sample. A cut surface is measured in the thickness direction, and the thickness of the rust layer containing oxides in the measurement sample is measured at at least five points at predetermined intervals. And let the average value of the five points|pieces be the thickness of a rust layer. The measurement conditions were an EPMA acceleration voltage of 15 kV and an irradiation current of 5×10 ^-8 to 1×10 ^-7 A.

<Diffusion prevention layer forming step>
Next, in the diffusion prevention layer forming step S21, a diffusion prevention layer forming raw material containing titanium chloride and magnesium is charged into the metal reduction reaction vessel on which the rust layer is formed, and then the raw material is heated under reduced pressure to reduce the raw material. It is vaporized to form a Ti-containing diffusion prevention layer on the inner surface of the metallic reduction reactor.

First, the metallic reduction reactor provided with the rust layer described above will be illustrated using drawings. The drawings do not accurately illustrate the configuration of the metal reduction reaction vessel, but show the outline of the configuration necessary for explaining the present embodiment.
In the rust layer forming step S11 described above, a rust layer 3 is formed on the inner surface 2 of the metallic reduction reactor 1, as shown in FIG. A pedestal 4 is provided in the lower portion of the metallic reduction reaction vessel 1 , and a raw material holding vessel 5 is provided on the pedestal 4 . The raw material holding container 5 has a plurality of stages of holding portions 5a to 5e, and each holding portion holds a diffusion preventing layer forming raw material 6 such as sponge titanium. An upper lid 7 is provided on the top of the metallic reduction reaction vessel 1 . The metal reduction reaction vessel 1 is connected to a decompression device 9 via a valve 8 , and the degree of pressure reduction in the metal reduction reaction vessel 1 can be adjusted by opening and closing the valve 8 . The metal reduction reaction vessel 1 is housed in a heating furnace (not shown), and the heating furnace can raise the temperature of the metal reduction reaction vessel 1 to a desired temperature, which will be described later.

The diffusion prevention layer forming raw material 6 used for forming the diffusion prevention layer is preferably sponge titanium. It is preferable to use so-called low-grade titanium sponge containing low-grade titanium chloride and magnesium as the titanium sponge. Since sponge titanium is porous, it is easy to obtain vapor derived from the raw material.

After placing the raw material holding container 5 in which the raw material 6 for forming the diffusion barrier layer is placed on the pedestal 4, the metal reduction reaction container 1 is sealed with the upper lid 7, the valve 8 is opened, and the metal The inside of the reduction reaction vessel 1 is vacuumed and sucked. After the predetermined conditions are met, the heating furnace containing the metallic reduction reactor 1 is energized to start raising the temperature.

By decompressing the inside of the reaction vessel 1 and heating it in the heating furnace, the diffusion prevention layer forming raw material 6 is vaporized into a raw material vapor. In the context of the present invention, vaporization indicates that a liquid or solid becomes a vapor.

A rust layer formed on the inner surface of the metallic reduction reaction vessel reacts with the raw material vapor to form a diffusion prevention layer on the inner surface of the metallic reduction reaction vessel. The diffusion barrier layer may have a titanium-containing layer containing at least Ti and a magnesium-containing layer containing Mg inside thereof from the outside toward the inside. The details of the formation mechanism of the diffusion prevention layer are unknown, and although the present invention is not intended to be limited by theory, the following is conceivable.
For example, when the metal reduction reaction vessel is made of stainless steel and low-grade titanium sponge is used as the raw material 6 for forming the diffusion barrier layer, when the Ti component of the titanium sponge is vaporized, during the manufacturing process of the titanium sponge, Unremoved Mg and lower TiCl _x (x=2, 3) are also vaporized. The vaporized Mg reacts with the rust layer (chromium oxide layer, iron oxide layer in the case of clad steel) 3 formed on the inner surface 2 of the metal reduction reactor 1 shown in FIG. , a reaction as shown in the following reaction formula (1) is considered to occur. This reaction occurs because Mg has a lower standard Gibbs energy of reaction than Cr, so the oxygen in the chromium oxide is reduced to Mg. As a result, as shown in FIG. 3B, a magnesium-containing layer 11 containing Mg is formed on the inner surface 2 of the metal reduction reactor 1 .
Cr ₂ O ₃ +3Mg→3MgO+2Cr Reaction Formula (1)
Further, part or all of the produced MgO is thought to react with lower TiCl _x (x=2, 3) to cause the following reaction formula (2).
MgO+TiCl _x ⇒TiO+MgCl _x Reaction Formula (2)
Since the metallic reduction reaction vessel is heated to a high temperature by the heating furnace, the vaporized TiCl _x is diffused to the outer surface of the magnesium-containing layer 11, and as shown in FIG. It is thought that Mg is substituted with Ti from the surface toward the inside, part or all of the magnesium-containing layer 11 changes to the titanium-containing layer 12, and the titanium-containing layer 12 is formed outside the magnesium-containing layer 11. be. Note that the titanium-containing layer 12 may contain titanium in the form of metal Ti, titanium oxide, or the like. The titanium-containing layer 12 may contain titanium derived from titanium sponge. The thickness of the titanium-containing layer 12 can be adjusted by changing the heating time or the like. The diffusion prevention layer 10 formed on the inner surface 2 of the metallic reduction reaction vessel 1 can suppress contamination of impurity metals originating from the metallic reduction reaction vessel in the reduction step.

The raw material holding container 5 is preferably configured so that the diffusion prevention layer forming raw material 6 can be dispersedly arranged. It is good to keep it. An appropriate amount of the diffusion prevention layer forming raw material 6 may be placed in each of the dish-shaped containers.

Moreover, since the raw material holding container 5 is exposed to high temperatures, it is preferable to be made of stainless steel, which has excellent high-temperature strength. Specifically, it is preferably made of SUS304 or SUS316.

The diffusion prevention layer forming raw material 6 contains titanium chloride and magnesium. Examples of titanium chloride include titanium dichloride, titanium trichloride, and titanium tetrachloride. From the viewpoint of using a titanium raw material with an appropriate vaporization temperature, lower titanium chloride (TiCl _x (X=2,3)) is preferred. preferable. The diffusion barrier layer-forming raw material 6 may contain titanium tetrachloride, but titanium tetrachloride has a too low vaporization temperature compared to magnesium, so lower titanium chloride, which has a higher vaporization temperature, is preferable. Examples of magnesium include metallic magnesium and magnesium compounds (eg, magnesium chloride), and considering the estimation of the above reaction formula, at least metallic magnesium may be included. Furthermore, since the diffusion barrier layer forming raw material 6 efficiently forms the diffusion barrier layer using the above-described reactions (formulas (1) and (2) above), the diffusion barrier layer forming raw material 6 is a low-grade material containing titanium chloride and magnesium. Sponge titanium is preferred. In the case of sponge titanium, the raw material 6 for forming the diffusion prevention layer may be coarse-grained titanium sponge having a maximum length of 50 to 150 mm.

In the diffusion prevention layer forming step S21, heating is performed under reduced pressure. The degree of pressure reduction may be appropriately set from the viewpoint of obtaining raw material vapor from the raw material for forming the diffusion prevention layer. The heating in the diffusion prevention layer forming step may be heating in the presence of an inert gas such as Ar gas. In this case, after the inside of the metal reduction reaction vessel 1 is evacuated (for example, 0.01 Pa or less), an inert gas is sealed to 0.05 MPa or less, preferably 0.03 MPa or less, and then heat treatment is performed. good.

Moreover, it is preferable to heat the inside of the metal reduction reactor 1 to a high temperature range of 650 to 1200°C. The heating temperature is preferably 800° C. or higher, more preferably 900° C. or higher, and 950° C. or higher, from the viewpoint of forming a dense diffusion prevention layer on the inner surface of the metal reduction reaction vessel 1. is more preferred. From the viewpoint of safety, the temperature is preferably 1150° C. or lower, more preferably 1100° C. or lower, and even more preferably 1050° C. or lower.

For example, if the production amount of titanium is 14 tons/batch in a metallic reduction reactor, the heating time is preferably 10 to 70 hours. From the viewpoint of increasing the thickness of the diffusion prevention layer, the heating time is preferably 25 hours or longer, more preferably 35 hours or longer, and even more preferably 50 hours or longer. Further, the heating time is preferably 65 hours or less, more preferably 60 hours or less, in consideration of production efficiency.

After the diffusion prevention layer forming step S21 is finished, the substrate is usually cooled to room temperature. Although the method of cooling is not particularly limited, it may be cooled to room temperature by air cooling after removing the upper lid.

In this embodiment, the diffusion prevention layer can be formed even on unused metallic reduction reactors in which sponge titanium has not been produced.

From the viewpoint of suppressing the elution of impurity metals such as Fe, the average thickness of the diffusion prevention layer is preferably more than 5 μm, more preferably 10 μm or more, more preferably 20 μm or more, and 30 μm or more. It is even more preferable to have Moreover, the average thickness of the diffusion prevention layer is not particularly limited. If the upper limit is exemplified from the viewpoint of production efficiency, it may be 100 μm or less.
The diffusion barrier layer has at least a titanium-containing layer and may further have a magnesium-containing layer. When the diffusion prevention layer has a titanium-containing layer and a magnesium-containing layer, the titanium-containing layer is usually positioned on the outer side, and the magnesium-containing layer is positioned on the inner side (inner surface side of the metallic reduction reactor). The titanium-containing layer refers to a metal-containing layer having a Ti concentration of 50% or more among metal components based on the following measurement method. The magnesium-containing layer refers to a metal-containing layer having a Mg concentration of 35% or more among metal components based on the following measurement method. If there is a region with a Ti concentration of 50% or more and an Mg concentration of 35% or more, it is defined as a titanium-containing layer.

When measuring the thickness of the diffusion prevention layer, the following method is used. A test piece to be analyzed having a diffusion prevention layer is cut out from the inner surface of a metal reduction reaction vessel, and then cut into approximately 1 cm × 1 cm × 1 cm squares with a slicing machine. A cut surface is measured in the thickness direction of the reaction vessel, and the thickness of the titanium-containing layer and the magnesium-containing layer in the measurement sample is measured at at least five points at predetermined intervals. And let the average value of the five points|pieces be the thickness of each layer. The thickness of the diffusion barrier layer is the sum of the thickness of the titanium-containing layer and the thickness of the magnesium-containing layer.
The measurement conditions were an EPMA acceleration voltage of 15 kV and an irradiation current of 5×10 ^-8 to 1×10 ^-7 A.
The Ti concentration referred to here is calculated by the following formula (1) from the measurement results of each metal measured using the electron probe microanalyzer. Further, the Mg concentration is calculated by the following formula (2) from the measurement results of each metal measured using the electron probe microanalyzer.
(Concentration of Ti) (%) = {(mass% of Ti) / {(mass% of Ti) + (mass% of Ni) + (mass% of Fe) + (mass% of Cr) + (mass of Mg) %)}}×100 Formula (1)
(Mg concentration) (%) = {(mass% of Mg) / {(mass% of Ti) + (mass% of Ni) + (mass% of Fe) + (mass% of Cr) + (mass of Mg %)}}×100 Expression (2)

[3. Metal Reduction Reaction Vessel]
In one embodiment, the metallic reduction reaction vessel according to the present invention is provided with a Ti-containing diffusion prevention layer on the inner surface.

As described above, from the viewpoint of suppressing the elution of impurity metals such as Fe, the average thickness of the diffusion prevention layer preferably exceeds 5 μm.

[4. Method for producing titanium]
In one embodiment of the method for producing titanium according to the present invention, a step of obtaining a metal reduction reaction vessel provided with a diffusion prevention layer by the method for producing a metal reduction reaction vessel described above; and reducing the titanium tetrachloride in the reduction reaction vessel. The method for producing titanium is suitable for producing sponge titanium. The manufacturing conditions, equipment, etc. may be appropriately selected.

[EXAMPLES] Hereafter, although an Example and a comparative example demonstrate the content of this invention still more concretely, this invention is not limited at all by these examples.

(Confirmation of rust layer formation using a test piece)
A stainless steel (SUS316) test piece was prepared to simulate an unused metal reduction reaction vessel, and after heating at 1000 ° C. for 10 hours, 15 hours, and 20 hours under the supply of dry air containing oxygen, chromium oxidation was performed. The layer thickness was confirmed by EPMA measurements.
As a result, the thickness of the chromium oxide layer was as shown in Table 1 below.

From the above, a rust layer was confirmed on the surface of the stainless steel. Also, the rust layer tended to thicken as the heating time increased.

(Confirmation of diffusion prevention layer formation using rust layer formation test piece)
The rust layer-forming test piece prepared in the above test was placed in a bottomed cylindrical stainless steel (SUS316) metal reduction reaction vessel (outer diameter: 2200 mmφ, height: 5400 mm). A raw material holding container made of stainless steel, in which dish-shaped containers were vertically dispersed in multiple layers, was arranged in the reaction container, and coarse-grained, low-grade sponge titanium containing low-grade titanium chloride and magnesium was charged. After decompression, argon gas was sealed to 0.03 MPa and heated at 1000° C. for 55 hours. After that, it was cooled by air cooling, and the test piece was collected after the cooling was completed.

The recovered test piece was subjected to EPMA measurement to measure the thickness of the anti-diffusion layer. The measurement results are shown in Table 2 below.

As described above, the diffusion prevention layer thicker than the rust layer was formed on the test piece.

<Example>
An unused, bottomed cylindrical stainless steel (SUS316) metal reduction reaction vessel (outer diameter: 2200 mmφ, inner diameter: 2100 mmφ, height: 5400 mm) was prepared. In the example, a rust layer was formed by heating at 1000° C. for 10 hours while supplying dry air containing oxygen. The thickness of the rust layer was 5 μm as measured by EPMA. On the other hand, in the comparative example, the rust layer was not formed on the metallic reduction reactor.

In the metal reduction reaction vessel of the examples and comparative examples, a stainless steel raw material holding vessel in which dish-shaped vessels are dispersed in the vertical direction and arranged in multiple layers is arranged, and coarse particles of low grade containing low grade titanium chloride and magnesium are arranged. of sponge titanium was charged. After decompression, argon gas was sealed to 0.03 MPa and heated at 1000° C. for 55 hours. In the example, the thickness of the anti-diffusion layer was 30 μm as measured by EPMA.

Next, sponge titanium was produced using the metal reduction reaction vessel, and after removing the peripheral wall iron part of the sponge titanium mass, the sponge titanium was collected. Furthermore, the following evaluations were performed on the sampled sponge titanium.

(concentration analysis)
Fe, Ni, and Cr were each analyzed by XRF analysis. The analysis results are shown in FIGS. 4-6. The concentrations were analyzed to evaluate whether or not the Fe concentration, Ni concentration, and Cr concentration exceeded the standard values (Table 3).

The number of tests for the example was 7, and the number of tests for the comparative example was 25. In both cases, an unused metal reduction reaction vessel was subjected to the above-described treatment, and the sponge titanium produced in the first time was subjected to concentration analysis. Table 4 below shows the average values of the concentrations of Fe, Ni, and Cr in Examples and Comparative Examples.

(Consideration by Example)
The measurement results of each example are classified by two digits below the decimal point, and the distributions of the concentration values of Fe, Ni, and Cr are confirmed, respectively, as shown in FIGS. 4 to 6. FIG. The metallic reduction reaction vessel in the example can be said to be useful because the concentration of impurities in sponge titanium can be stably reduced compared to the metallic reduction reaction vessel in the comparative example.

1 metal reduction reaction vessel 2 inner surface 3 rust layer (Cr ₂ O ₃ layer)
4 pedestal 5 raw material holding container 6 raw material for forming diffusion prevention layer 7 upper lid 8 valve 9 decompression device 10 diffusion prevention layer 11 magnesium -containing layer 12 titanium -containing layer S11 rust layer forming step S21 diffusion preventing layer forming step

Claims (12)

A rust layer forming step of heating a metal reduction reaction vessel to form a rust layer containing oxides of elements derived from the vessel on the inner surface;
A raw material for forming a diffusion prevention layer containing titanium chloride and magnesium is charged into the metal reduction reaction vessel with a rust layer formed thereon, and then the raw material is vaporized by heating under reduced pressure to form the metal reduction reaction vessel. a diffusion prevention layer forming step of forming a diffusion prevention layer containing Ti on the inner surface;
A method for manufacturing a metal reduction reaction vessel, comprising: 2. The method for manufacturing a metal reduction reaction vessel according to claim 1, wherein the heating temperature in said rust layer forming step is 900.degree. C. to 1200.degree. 3. The method for manufacturing a metal reduction reactor according to claim 1, wherein the rust layer has an average thickness of 1 to 40 μm. 2. In the rust layer forming step, the rust layer is formed on the inner surface of the metal reduction reaction vessel by supplying air into the metal reduction reaction vessel while heating the metal reduction reaction vessel. 4. A method for manufacturing a metal reduction reaction vessel according to any one of items 1 to 3. 5. The method for manufacturing a metal reduction reaction vessel according to claim 1, wherein said diffusion prevention layer forming raw material is low-grade titanium sponge containing titanium chloride and magnesium. The method for producing a metallic reduction reaction vessel according to any one of claims 1 to 5, wherein the metallic reduction reaction vessel is made of stainless steel. The method for manufacturing a metal reduction reactor according to any one of claims 1 to 6, wherein the rust layer contains chromium oxide. The method for producing a metal reduction reaction vessel according to any one of claims 1 to 7, wherein the metal reduction reaction vessel is unused. The method for producing a metal reduction reaction vessel according to any one of claims 1 to 8, wherein the heating temperature in the diffusion prevention layer forming step is 650 to 1200°C. 10. The method for manufacturing a metal reduction reaction vessel according to any one of claims 1 to 9, wherein the diffusion prevention layer has an average thickness exceeding 5 µm. A metal reduction reactor provided with a diffusion prevention layer containing Ti on the inner surface,
The average thickness of the diffusion prevention layer exceeds 5 μm ,
The diffusion barrier layer includes a titanium-containing layer and a magnesium-containing layer,
A metallic reduction reaction vessel, wherein the magnesium-containing layer is located inside the titanium-containing layer . A step of obtaining a metallic reduction reaction vessel provided with a diffusion prevention layer by the method for producing a metallic reduction reaction vessel according to any one of claims 1 to 10;
a step of reducing titanium tetrachloride in a metallic reduction reaction vessel provided with the diffusion barrier;
A method of manufacturing titanium comprising:

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