JP2020132916A - Metal reduction reactor, method for producing metal reduction reactor, and method for producing sponge titanium - Google Patents

Abstract

To provide a metal reduction reactor that can inhibit elution of Fe, which is an impurity metal, in the production process of a sponge titanium lump.SOLUTION: A metal reduction reactor has an inner wall surface layer 11 containing Ti and barrier metal M, positioned inside a surface 10a of an inner wall 10.SELECTED DRAWING: Figure 1

Description

The present invention relates to a metal reduction reaction vessel, a method for producing a metal reduction reaction vessel, and a method for producing titanium sponge.

A method for producing sponge titanium, which is metallic titanium, is known by reducing titanium tetrachloride with a reducing metal. One of them is that the central part of the titanium sponge mass produced by the so-called Kroll process has high titanium purity, but the outer periphery of the titanium sponge mass has low titanium purity because the material constituting the reaction vessel diffuses at high temperature. It has been known. Since the reaction vessel is made of clad steel or stainless steel, nickel and chromium are further diffused from iron and stainless steel to contaminate titanium sponge.

In recent years, in the production of refractory metal such as titanium sponge, a reaction vessel capable of effectively suppressing impurity metal contamination from the reaction vessel has been developed. In particular, the large mass of refractory metal first 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, and thus the amount of these impurity metals. There is a demand for a reaction vessel or a method for producing a refractory metal.

For example, in Patent Document 1, by raising the temperature of the reaction vessel to 800 ° C. or higher in a state where the refractory metal particles are in contact with the inner surface of the manufactured unused reaction vessel, the refractory metal solidifies on the inner surface of the reaction vessel. A method for producing a refractory metal has been proposed in which the reaction vessel is used as the first reduction reaction vessel after being subjected to the phase diffusion treatment.

Further, in Patent Document 2, a titanium powder paste composed of polyvinyl alcohol, water and titanium powder is applied so as to have a titanium film on at least a part of the inner wall of the metal container to form a film, and then demediation or heat treatment is performed. A metal container having a titanium film on at least a part of the inner wall has been proposed.

Japanese Unexamined Patent Publication No. 2014-214356 International Publication No. 2017/146109

When the metal reduction reaction vessel is made of stainless steel, clad steel, etc., it is ideal that there is almost no contamination by Fe contained in the metal reduction reaction vessel during the production of the titanium sponge ingot. .. It is considered that there is still room for improvement in the metal container, which is a known technique disclosed in Patent Documents 1 and 2.

Therefore, an object of the present invention is to provide, in one embodiment, a metal reduction reaction vessel capable of suppressing the elution of Fe, which is an impurity metal, in the process of producing a titanium sponge mass. Another object of the present invention is to provide, in another embodiment, a method for producing a metal reduction reaction vessel capable of producing such a metal reduction reaction vessel. Another object of the present invention is to provide a method for producing titanium sponge using such a metal reduction reaction vessel in another embodiment.

That is, the present invention is a metal reduction reaction vessel having an inner wall surface layer containing Ti and a barrier metal M located inside from the surface of the inner wall on one side.

In one embodiment of the metal reduction reaction vessel according to the present invention, the total concentration of Ti and the barrier metal M in the composition on the surface of the inner wall is 3% by mass or more, and the thickness of the inner wall surface layer is 40 μm or more.

In one embodiment of the metal reduction reaction vessel according to the present invention, the concentration of the barrier metal M in the composition on the surface of the inner wall is 1% by mass or more.

In one embodiment of the metal reduction reaction vessel according to the present invention, the barrier metal M is one or more selected from the group consisting of Mo, Nb, and W.

Further, in another aspect, the present invention is a method for producing any of the above metal reduction reaction vessels, wherein a raw material powder layer containing a Ti-M-based mother alloy powder on the surface of the inner wall of the metal reduction reaction vessel. By heat-treating the raw material powder layer to form a raw material powder layer, a coating layer containing Ti and M located outside the surface of the inner wall and located inside from the surface of the inner wall. This is a method for producing a metal reduction reaction vessel, which comprises a layer forming step of forming an inner wall surface layer containing Ti and M, respectively.
(However, M indicates a barrier metal.)

In one embodiment of the method for producing a metal reduction reaction vessel according to the present invention, in the raw material powder layer forming step, the Ti—M-based mother alloy powder and an aqueous solution containing an alcohol having 1 to 4 carbon atoms are used. This includes attaching the contained suspension to the surface of the inner wall.

In one embodiment of the method for producing a metal reduction reaction vessel according to the present invention, the Ti—M-based mother alloy powder contains 30 to 70% by mass of Ti and 30 to 70% by mass of M.

In one embodiment of the method for producing a metal reduction reaction vessel according to the present invention, the raw material powder layer contains 0.05 of the Ti-M-based mother alloy powder per 1 cm ² of the inner wall surface of the metal reduction reaction vessel. Contains ~ 1.0g.

In one embodiment of the method for producing a metal reduction reaction vessel according to the present invention, the raw material powder layer further contains Ti powder, the average particle size of the Ti powder is 45 μm or less, and the Ti-M system is used. The average particle size of the mother alloy powder is 45 μm or less.

In one embodiment of the method for producing a metal reduction reaction vessel according to the present invention, the raw material powder layer has a Ti powder content of 5 to 70% by mass and contains the Ti—M-based mother alloy powder. The amount is 30 to 95% by mass.

In one embodiment of the method for producing a metal reduction reaction vessel according to the present invention, the heat treatment is performed at a heating temperature of 100 ° C. or higher and lower than 1080 ° C.

In another aspect, the present invention is a method for producing titanium sponge, which comprises a step of reducing titanium tetrachloride in any of the above metal reduction reaction vessels.

By using the metal reduction reaction vessel according to the embodiment of the present invention, it is possible to suppress the elution of Fe, which is an impurity metal, in the process of producing the titanium sponge mass.

It is an enlarged sectional view schematically showing an inner wall and a coating layer provided in the metal reduction reaction vessel which concerns on this invention. It is a flow chart which shows an example of the manufacturing method of the metal reduction reaction vessel which concerns on this invention.

Hereinafter, specific embodiments of the present invention will be described in detail. The present invention is not limited to the following embodiments, and various modifications can be made without changing the gist of the present invention.

[1. Overview]
The method for producing titanium sponge in the Kroll process is a reduction step of dropping titanium tetrachloride onto molten magnesium charged under inert conditions in a metal reduction reaction vessel to form titanium sponge lumps, and metal reduction. A vacuum separation step of extracting molten magnesium chloride, which is a by-product, and molten magnesium if it remains from the reaction vessel via a metal pipe, and then vacuum-separating the titanium sponge mass, and the titanium sponge mass. Includes a crushing step of crushing to obtain titanium sponge.

In order to reduce Fe contamination derived from the metal reduction reaction vessel when producing the titanium sponge lump, in the present embodiment, the surface layer of the inner wall including the surface of the inner wall of the metal reduction reaction vessel is modified. According to the knowledge of the present inventor, the Fe contamination can be reduced by transferring Ti to the inner wall of the metal reduction reaction vessel.
First, the present inventor repeated various studies on the assumption that contamination by impurity metals from the metal reduction reaction vessel could be further reduced by thickening the inner wall surface layer containing Ti, but only Ti was used in the metal reduction reaction vessel. It was found that the reduction of contamination by impurity metals, especially Fe, does not improve beyond a certain level even when diffused.
Therefore, the present inventor repeated diligent studies and examined the presence of metal elements other than Ti together with Ti on the inner wall of the metal reduction reaction vessel. As a result, the metal such as Mo is contained in the inner wall of the metal reduction reaction vessel. It was found that it has a barrier effect to reduce the elution of Fe into molten magnesium. As a result, the present inventor forms an inner wall surface layer containing a metal such as Ti and Mo from the surface of the inner wall to the inside, thereby producing a sponge titanium ingot with reduced Fe contamination in the manufacturing process of the sponge titanium ingot. I found that it can be manufactured. The present inventor has further studied and completed the invention including the embodiments described below.
Hereinafter, each embodiment will be described.

[2. Metal reduction reaction vessel]
FIG. 1 is an enlarged cross-sectional view schematically showing an inner wall and a coating layer of a metal reduction reaction vessel according to the present invention. Hereinafter, the metal reduction reaction vessel according to the present invention will be described with reference to the drawings.

In one embodiment, the metal reduction reaction vessel according to the present invention includes an inner wall 10 and a coating layer 20 as shown in FIG. 1, and the inner wall 10 has an inner wall surface layer 11. In the present invention, the metal reduction reaction vessel has an effect of reducing Fe contamination even if the coating layer 20 is not provided. The metal reduction reaction vessel may be a used one having a history of producing a titanium sponge ingot, or an unused one. Hereinafter, preferred embodiments of each configuration will be described.

The inner wall 10 has an inner wall surface layer 11 containing Ti and a barrier metal M inside from the surface 10a. It is considered that the inner wall surface layer 11 has a function of reducing the elution rate of Fe by using the barrier metal M together with Ti. Although Ti alone can be expected to reduce the elution rate of the impurity metal, in the present embodiment, a further synergistic effect can be expected by using the barrier metal M together with Ti.
The mechanism for reducing the elution rate of Fe from the metal reduction reaction vessel is not always clear, but the activity of Fe in the inner wall surface layer is activated by including not only Ti but also the barrier metal M in the inner wall surface layer of the metal reduction reaction vessel. We speculate that the amount will decrease efficiently. Therefore, in the present invention, even if the inner wall surface layer 11 containing Ti and the barrier metal M is thinner than the inner wall surface layer in which only Ti is diffused, the effect of reducing Fe contamination of the titanium sponge mass can be satisfactorily exhibited. In the present specification, the inner wall surface layer 11 includes the surface 10a of the inner wall 10.

The barrier metal M can be used without particular limitation as long as the elution rate of Fe is reduced and the barrier metal M is difficult to elute into Mg. The barrier metal M is preferably one or more metals selected from the group consisting of Mo, Nb, and W from the viewpoint of more effectively reducing the elution rate of Fe, and Mo is among them. More preferred.

In the metal reduction reaction vessel according to the present invention, from the viewpoint of reducing the elution rate at which Fe contained in the inner wall 10 is transferred to molten magnesium, Ti and the barrier metal M on the surface 10a of the inner wall 10 are subjected to EPMA analysis described later. The total concentration is preferably 3% by mass or more. Further, the thickness of the inner wall surface layer 11 is preferably 40 μm or more. The thickness of the inner wall surface layer 11 is defined as the distance in the thickness direction from the surface 10a of the inner wall of the metal reduction reaction vessel to the thickness direction of the inner wall until the concentration of the barrier metal M becomes 0 (zero) in the EPMA analysis. Shown. Here, "0 (zero)" means that the peak height has dropped to the background height.
Here, the thickness of the inner wall surface layer 11 is preferably 80 μm or more, more preferably 100 μm or more, from the viewpoint of further reducing Fe contamination eluted from the inner wall 10 of the metal reduction reaction vessel. It is more preferably 120 μm or more. Since it is considered that the thicker the inner wall surface layer 11, the more the elution of the impurity metal can be suppressed, the upper limit side of the thickness is not particularly limited. To give an example, it may be 300 μm or less from the viewpoint of industrial manufacturing efficiency.
In the composition of the surface 10a of the inner wall 10, the total concentration of Ti and the barrier metal M is preferably 3% by mass or more, preferably 4% by mass or more, and preferably 6% by mass or more. On the other hand, the upper limit of the total concentration of Ti and the barrier metal M can be appropriately set in consideration of the operation plan of the metal reduction reaction vessel and the like. To give an example, it may be 10% by mass or less.
In the present embodiment, the concentration of the barrier metal M in the composition of the inner wall 10 on the surface 10a is preferably 1% by mass or more, from the viewpoint of ensuring a better synergistic effect with Ti in the composition of the inner wall 10 on the surface 10a. 2, 2% by mass or more is preferable. On the other hand, in the composition of the surface 10a of the inner wall 10, the upper limit of the concentration of the barrier metal M can be appropriately set in view of the operation plan of the metal reduction reaction vessel and the like. To give an example, it may be 5% by mass or less.
It is expected that the larger the amount of Ti and the barrier metal M in the inner wall 10, the higher the effect of reducing the elution of Fe into molten magnesium. Therefore, the amounts of Ti and the barrier metal M may be maximized in the composition of the inner wall 10 on the surface 10a.
When the inner wall surface layer containing Ti and the barrier metal M is formed by the method for producing a metal reduction reaction vessel described later, the amounts of Ti and the barrier metal M tend to gradually decrease from the inner wall surface along the thickness direction. On the other hand, if the metal reduction reaction vessel is repeatedly used, the inner wall will be scraped. Therefore, the thickness of the inner wall surface layer 11 is useful as an index for reasonably estimating the sustainability of the effect of reducing Fe contamination in the production of titanium sponge lumps. As the index, the total concentration of Ti and the barrier metal M described above and the concentration of the barrier metal M can be used.

The thickness of the inner wall surface layer 11 is measured by the following method. The inner wall 10 of the metal reduction reaction vessel is cut out so as to include the inner wall surface layer 11 while including the coating layer 20 if present, and then used as a test piece. Next, the coating layer 20 is removed with a chipping hammer until the surface 10a of the inner wall 10 of the metal reduction reaction vessel before treatment can be visually recognized for the test piece. A test piece from which the coating layer 20 has been removed is cut into a square of about 1 cm × 1 cm × 1 cm by a slicing machine and used as a measurement sample using an electron probe microanalyzer (example: SUPERPROBE JXA-8100, manufactured by JEOL Ltd.). , The cut surface is measured in the thickness direction of the inner wall 10 by EPMA analysis. The thickness of the inner wall surface layer 11 in the measurement sample is measured at five points based on the concentration of Ti and the concentration of the barrier metal M. Then, the minimum value among the five points is taken as the thickness of each layer. Here, the thickness direction means the normal direction of the surface 10a of the inner wall 10. From the above, the concentrations of Ti and the barrier metal M on the surface 10a of the inner wall 10 can be determined. The thickness of the inner wall surface layer 11 is the thickness of the barrier metal M layer.
As the measurement conditions, an accelerating voltage of 15 kV and an irradiation current of 5 × 10 ^-8 to 1 × 10 ^-7 A are adopted.
The Ti concentration and the M concentration referred to here are calculated by the following formulas (1) and (2) from the measurement results of each metal measured by using the electron probe microanalyzer.
(Concentration of Ti) (mass%) = {(mass% of Ti) / {(mass% of Ti) + (mass% of M) + (mass% of Ni) + (mass% of Fe) + (Cr Mass%)}} × 100 ... Equation (1)
(Concentration of M) (mass%) = {(mass% of M) / {(mass% of Ti) + (mass% of M) + (mass% of Ni) + (mass% of Fe) + (Cr Mass%)}} × 100 ... Equation (2)
If there is an element that is not contained in the formulas for determining the Ti concentration and the M concentration, the value is set to 0.
The thickness of the inner wall surface layer 11 is calculated by the EPMA analysis (5-point measurement) described above.

In one embodiment, the metal reduction reaction vessel according to the present invention may further include a coating layer 20. The coating layer 20 has a function of more efficiently reducing the elution rate of Fe. The coating layer 20 is located outside the surface 10a of the inner wall 10 of the metal reduction reaction vessel, has a layer formed of Ti, barrier metals M and Fe on the surface 10a of the inner wall 10, and Ti on the layer. And a layer formed of the barrier metal M. Usually, the concentrations of Ti and the barrier metal M in the coating layer are higher than the concentrations of Ti and the barrier metal M in the inner wall surface layer.

[3. Manufacturing method of metal reduction reaction vessel]
FIG. 2 is a flow chart showing an example of a method for manufacturing a metal reduction reaction vessel according to the present invention. Hereinafter, a method for producing a metal reduction reaction vessel according to the present invention will be described with reference to the drawings. The description that overlaps with the above-mentioned metal reduction reaction vessel will be omitted.

In one embodiment, the method for producing a metal reduction reaction vessel according to the present invention includes a raw material powder layer forming step S11 and a layer forming step S21, as shown in FIG. Hereinafter, preferred embodiments of each step will be described.

(Raw material powder layer forming step S11)
In the raw material powder layer forming step S11, a raw material powder layer containing a Ti—M-based mother alloy powder is formed on the surface 10a of the inner wall 10 of the metal reduction reaction vessel. The raw material powder layer may be further contained with Ti powder. More specifically, the raw material powder layer forming step S11 is a step of adhering a suspension containing a Ti—M-based mother alloy powder and an aqueous solution containing an alcohol having 1 to 4 carbon atoms to the surface 10a of the inner wall 10. including. The suspension may further contain Ti powder. If the Ti—M-based mother alloy powder does not have the desired particle size, the particle size can be adjusted in advance using a ball mill or the like. Further, it may include a demineralization treatment in which the suspension is attached to the surface of a metal reduction reaction vessel and then demineralized. The suspension can be attached to the surface of a metal reduction reaction vessel by, for example, spraying.
From the above, a raw material powder layer containing Ti powder or Ti-M-based mother alloy powder is formed on the surface 10a of the inner wall 10 of the metal reduction reaction vessel. Here, M represents the above-mentioned barrier metal M, and the barrier metal M is preferably at least one selected from the group consisting of Mo, Nb, and W. Examples of the Ti-M-based mother alloy powder include TiMo mother alloy powder, TiNb mother alloy powder, TiW mother alloy powder and the like. In this embodiment, the Ti—M-based mother alloy powder is used instead of giving priority to the combined use of the Ti powder and the alloy element powder of the barrier metal M. For example, when the barrier metal M is Mo, the Timo alloy has a lower melting point than Mo alone. In such a case, if only the alloy element powder of the barrier metal M alone is used, the melting point is high, so that the amount of the barrier metal M transferred to the inner wall 10 of the metal reduction reaction vessel is small, but it is larger than that of the barrier metal M. By using the Ti—M-based mother alloy powder having a low melting point, the transfer of Ti and the barrier metal M from the raw material powder layer to the inner wall 10 of the metal reduction reaction vessel can be promoted. In the present embodiment, Ti powder and Ti—M-based mother alloy powder may be used in order to promote the transfer of Ti and the barrier metal M. However, on the premise that the desired effect of the present invention is ensured, not only Ti powder and Ti-M-based mother alloy powder but also alloy element powder may be used.

In one embodiment, the average particle size of the Ti powder may be 45 μm or less, and the average particle size of the Ti—M-based mother alloy powder may be 45 μm or less. By reducing the average particle size of the Ti powder and the Ti-M alloy powder and using the alcohol having 1 to 4 carbon atoms, it is possible to efficiently secure many contact points with the inner wall 10 of the reduction reaction vessel, and further. It is considered that the total of the intermolecular force, electrostatic force, and liquid cross-linking force acting between the particles of Ti and the Ti-M alloy powder is superior to the gravity acting on the Ti particles or the particles of the Ti-M alloy powder. Increases adhesion. Then, by forming the inner wall surface layer 11 and the coating layer 20 in the layer forming step S21 which is the next step, the elution of the impurity metal derived from the metal reduction reaction vessel in the reduction step can be reduced.
The average particle size of the Ti powder may be 45 μm or less, 40 μm or less, or 35 μm or less on the upper limit side. Although the lower limit side is not particularly set for the average particle size, it is typically 10 μm or more, and may be 20 μm or more. Further, when Ti powder is used, a known one can be used. For example, Ti powder produced by the HDH method (hydrogenation dehydrogenation), Ti powder produced by the atomizing method, and Ti powder produced by the PREP method (plasma rotating electrode method) can be used.
The average particle size of the Ti-M-based mother alloy powder may be 45 μm or less, 30 μm or less, or 15 μm or less on the upper limit side. The lower limit side is not particularly set for the average particle size, but it may be typically 5 μm or more. Further, when Ti-M-based mother alloy powder is used, known ones can be used.
The average particle size of Ti powder can be measured by a laser diffraction / scattering type particle size distribution measuring device. Specifically, the average particle size of the Ti powder is determined by ultrasonically dispersing the Ti powder at an output of 30 W for 4 minutes, and then using pure water as a dispersion medium and sodium hexametaphosphate as a dispersant. It is a volume-based D50 measured by a laser diffraction / scattering type particle size distribution measuring device (example: LA-920, manufactured by HORIBA, Ltd.). The measurement is based on JIS Z 8825: 2013. Further, the measurement of the average particle size of the Ti-M-based mother alloy powder is the same as the above-described method for measuring the Ti powder.

The alcohol having 1 to 4 carbon atoms is not particularly limited, but is preferably at least one selected from the group consisting of monohydric alcohols, dihydric alcohols, trihydric alcohols, and tetravalent alcohols.

Among the above alcohols, examples of monohydric alcohols having 1 to 4 carbon atoms include methanol, ethanol, propanol, butanol, isopropanol, isobutanol and the like.
Examples of the dihydric alcohol having 1 to 4 carbon atoms include methanediol, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,2-pentanediol, and 1,4-pentanediol. Can be mentioned.
Further, examples of the trihydric alcohol having 1 to 4 carbon atoms include glycerin and the like.
Examples of the tetravalent alcohol having 1 to 4 carbon atoms include erythritol and the like.
The alcohol having 1 to 4 carbon atoms may be used alone or in combination of two or more. In addition, the monohydric alcohol having 1 to 4 carbon atoms may be used alone or in combination of two or more.
Among these, Ti powder and Ti-M-based mother alloy powder improve the wettability with respect to the surface 10a of the inner wall 10 of the metal reduction reaction vessel, particularly to the surface 10a of the inner wall 10 of the unused metal reduction reaction vessel. It is particularly preferable to use ethanol from the viewpoint of suppressing the residual amount of carbon in the metal reduction reaction vessel after the inner wall surface layer 11 is formed while ensuring the safety of the operator.

The content of Ti powder and Ti-M-based mother alloy powder in the suspension is not particularly limited. It can be adjusted as appropriate in consideration of the coating conditions.

The suspension contains alcohol having 1 to 4 carbon atoms and water (for example, pure water). At that time, the alcohol content having 1 to 4 carbon atoms is preferably 0.5 to 10% by volume with respect to the total amount of water and alcohol. The upper limit side of the alcohol content may be 5% by volume or less.

The raw material powder layer formed by applying the suspension preferably contains 0.05 to 1.0 g of Ti-M-based mother alloy powder per 1 cm ² of the surface of the inner wall 10 of the metal reduction reaction vessel. .. The lower limit side is 1 cm ^{2 on} the surface of the inner wall 10 of the metal reduction reaction vessel from the viewpoint of securing the necessary amount for transferring Ti and the barrier metal M from the surface 10a of the inner wall 10 to the inside in the layer forming step S21 described later. It may contain 0.05 g or more of Ti-M-based mother alloy powder. However, on the upper limit side, from the viewpoint of production efficiency, 1.0 g or less of Ti-M-based mother alloy powder may be contained per 1 cm ² of the surface of the inner wall 10 of the metal reduction reaction vessel, and 0.5 g or less may be contained. Good. The raw material powder layer may further contain Ti powder, and the amounts of Ti powder and Ti—M-based mother alloy powder contained per 1 cm ² of the surface of the inner wall 10 of the metal reduction reaction vessel are described above. The amount may be the same as that of the Ti-M-based mother alloy powder.

The raw material powder layer in the raw material powder layer forming step S11 preferably has a Ti powder content of 5 to 70% by mass and a Ti—M-based mother alloy powder content of 30 to 95% by mass. From the viewpoint of increasing the amount of the barrier metal M transferred to the inner wall, Ti powder and Ti—M-based mother alloy powder may be used in combination.
The Ti powder in the raw material powder layer is preferably 5% by mass or more, more preferably 15% by mass or more, still more preferably 30% by mass or more, still more preferably 40% by mass or more on the lower limit side. The Ti powder in the raw material powder layer is preferably 70% by mass or less, more preferably 65% by mass or less, and further preferably 60% by mass or less on the upper limit side.
The Ti—M-based mother alloy powder in the raw material powder layer is preferably 30% by mass or more, more preferably 35% by mass or more, and further preferably 40% by mass or more on the lower limit side. The Ti—M-based mother alloy powder in the raw material powder layer is preferably 95% by mass or less, more preferably 80% by mass or less, and further preferably 60% by mass or less on the upper limit side.

The Ti-M-based mother alloy powder contains 30 to 70% by mass of Ti and 30 to 70% by mass of the barrier metal M. The balance of the Ti-M-based mother alloy powder may be an unavoidable impurity. The Ti content of the Ti—M-based mother alloy powder is preferably 30% by mass or more, more preferably 35% by mass or more, and further preferably 40% by mass or more on the lower limit side. Further, the Ti content is preferably 70% by mass or less, more preferably 65% by mass or less, and further preferably 60% by mass or less on the upper limit side.
Further, the content of the barrier metal M in the Ti—M-based mother alloy powder is preferably 30% by mass or more on the lower limit side from the viewpoint of reducing the elution rate of Fe contained in the inner wall 10 during the reduction step. It is more preferably 35% by mass or more, still more preferably 40% by mass or more. Further, the M content is preferably 70% by mass or less, more preferably 65% by mass or less, and further preferably 60% by mass or less on the upper limit side. The reason for this is that if Ti has a lower melting point than M and the content of the barrier metal M is too high, the amount of the barrier metal M transferred into the inner wall in the layer forming step S21 described later is reduced, and a desired effect can be obtained. This is because it may not be obtained.

The material of the metal reduction reaction vessel is not particularly limited, and examples thereof include clad steel (bonded steel of carbon steel and stainless steel) and stainless steel whose inner wall 10 is at least. Generally, when the metal reduction reaction vessel is clad steel, Fe as an impurity metal tends to be mixed into the sponge titanium ingot via molten magnesium in the reduction step. Further, when the inner wall 10 of the metal reduction reaction vessel is made of stainless steel, Fe, Ni, and Cr as impurity metals tend to be mixed into the sponge titanium lump via molten magnesium in the reduction step. According to one embodiment of the present invention, the amount of Fe in the titanium sponge lump titanium produced by the reduction step is reduced by forming the coating layer 20 and the inner wall surface layer 11 described later in the metal reduction reaction vessel, respectively. be able to. It is also possible to form the coating layer 20 and the inner wall surface layer 11 in an unused metal reduction reaction vessel. Therefore, the suspension may be applied to an unused metal reduction reaction vessel to form a raw material powder layer containing Ti powder or Ti-M-based mother alloy powder. Further, the stainless steel in the present embodiment does not have to contain Mo, Nb or W.

After applying the suspension to the surface 10a of the inner wall 10 of the metal reduction reaction vessel, for example, removing the medium while flowing dry air at 80 to 120 ° C. for 1 to 3 hours is performed by vacuum heating in the layer forming step S21 described later. It is preferable because it can prevent deterioration of the vacuum pump used at times.

(Layer forming step S21)
In the layer forming step S21, the coating layer 20 and the inner wall surface layer 11 are formed by heat-treating the raw material powder layer. The coating layer 20 is located outside the surface 10a of the inner wall 10 and contains Ti and the barrier metal M, and the surface layer 11 of the inner wall contains Ti and the barrier metal M diffused inward from the surface 10a of the inner wall 10. (See FIG. 1). For example, in the case of producing a titanium sponge mass, the bath surface fluctuates when magnesium chloride is removed (tapped) in the reduction step, and the titanium sponge mass and the coating layer 20 may come into contact with each other, and a metal caused by a temperature change. The coating layer 20 is relatively easy to peel off due to cracks generated due to deformation of the reduction reaction vessel. When the coating layer 20 is peeled off, Fe contamination derived from the metal reduction reaction vessel may occur in the generated titanium sponge mass. However, when the inner wall surface layer 11 in which Ti and the barrier metal M are diffused is formed from the surface 10a of the inner wall 10 of the metal reduction reaction vessel, the activity of Fe is active on the surface 10a side of the inner wall 10 of the metal reduction reaction vessel. Since the amount is reduced, it is considered that even if the coating layer 20 is peeled off, the contamination of Fe derived from the metal reduction reaction vessel can be suppressed. Since the inner wall surface layer 11 is formed inside from the surface 10a of the inner wall 10 of the metal reduction reaction vessel, even if the coating layer 20 is peeled off, the elution of Fe can be suppressed. Therefore, an operation is performed to form the coating layer 20 again. The problem of stopping does not occur.

For example, in the heat treatment of the raw material powder layer formed on the surface 10a of the inner wall 10 of the metal reduction reaction vessel, since titanium is contained in the raw material powder layer, a vacuum or an inert gas atmosphere (argon gas atmosphere, helium) It is preferable to carry out at 100 ° C. or higher and lower than 1080 ° C. in a gas atmosphere or the like. The reason for performing the heat treatment in this temperature range is that the eutectic melting temperature of iron and titanium is 1080 ° C., and if the heat treatment is performed at 1080 ° C. or higher, there is a risk that the inner wall of the metal reduction reaction vessel will melt.

The heating temperature of the heat treatment is preferably 100 ° C. or higher, preferably 700 ° C. or higher, from the viewpoint of satisfactorily diffusing Ti and the barrier metal M from the surface 10a of the inner wall 10 of the metal reduction reaction vessel to the inside. Is more preferable, and 850 ° C. or higher is even more preferable. However, the heating temperature is preferably less than 1080 ° C., more preferably 1050 ° C. or lower, because there is a risk that the inner wall 10 of the metal reduction reaction vessel will melt if the heat treatment is performed at 1080 ° C. or higher. ..
Further, the heat holding time of the heat treatment may be held for 1 to 24 hours after reaching the predetermined heating temperature described above, and may be further held for 2 to 12 hours. The heat treatment may be heating in the presence of an inert gas. In this case, after the inside of the metal reduction reaction vessel is evacuated (for example, 0.01 Pa or less), an inert gas is sealed so that the degree of decompression is 0.05 MPa or less, preferably 0.03 MPa or less in gauge pressure. Heat treatment may be performed.

[4. Titanium manufacturing method]
In one embodiment, the method for producing titanium according to the present invention includes a step of reducing titanium tetrachloride in a metal reduction reaction vessel provided with the above-mentioned inner wall surface layer 11. The titanium production method includes, for example, a sponge titanium production method.

Hereinafter, the content of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these examples. The manufacturing conditions are shown in Table 1. Further, the average particle size of the Ti powder and the Ti _0.5 Mo _0.5 mother alloy powder (the mother alloy powder with a mass ratio of Ti: Mo = 1: 1) is determined by the method described above by the laser diffraction / scattering type particle size distribution measuring device (LA). -920, manufactured by HORIBA, Ltd.).

(Performance evaluation of barrier metal)
First, in samples 1 to 3, SUS316 pieces were used, and a barrier metal M was sprayed on the surface of the SUS316 pieces so that the film thickness was within the range of 200 to 300 μm, and cooled and solidified to form a barrier metal layer. The area where the barrier metal layer was formed was 1 cm × 1 cm square, and the other parts of the SUS316 piece were coated with a coating material made of zirconia and magnesia. In sample1, Mo was used as the barrier metal M, in sample2, W was used as the barrier metal M, and in sample3, Nb was used as the barrier metal M.
On the other hand, in sample4, the same treatment as above was performed except that the barrier metal M was not sprayed on the surface of the SUS316 piece. Further, in sample5, Cr was sprayed on the surface of the SUS316 piece so that the film thickness was within the range of 200 to 300 μm, and the Cr layer was formed by cooling and solidifying to form a Cr layer.

Then, SUS316 pieces of samples 1 to 5 were brought into contact with Mg at 950 ° C. for 3 hours, and the amount of Fe eluted in Mg (mass ppm) was measured by an inductively coupled plasma (ICP) emission spectrometer.

As a result, the amount of Fe eluted in samples 1 to 3 was reduced to 1/4 or less of that in sample 4. In sample4, the elution amount of Fe was 300 mass ppm. From the above, it was confirmed that Mo, Nb, and W have the effect of suppressing the elution of Fe.
In addition, the elution amount of Fe in sample5 was reduced to 1/4 or less of that in sample4. However, when the SUS316 piece after the test was confirmed, the Cr layer was thinned. Since the inventor has empirically known that Cr dissolves in Mg, when the amount of Cr in Mg was measured, 420 mass ppm of Cr was detected.
Therefore, sample 6 was produced by performing the same treatment as that of sample 5 except that the thickness of Cr was reduced to 20 μm. When the sample 6 was brought into contact with Mg at 950 ° C. for 3 hours and the amount of Fe eluted in Mg (mass ppm) was measured, 280 mass ppm of Fe was detected. From the above, it was determined that Cr has no effect of suppressing the elution of Fe.

(Surface modification of test piece)
Next, the test pieces used in Examples 1 and 2 and Comparative Examples 1 and 2 were prepared according to the conditions shown in Table 1, respectively.

First, Ti powder having an average particle size of 30 μm and Ti _0.5 Mo _0.5 mother alloy powder having an average particle size of 10 μm were prepared.

Next, 1.8 kg of Ti powder, 1.8 kg of Ti _0.5 Mo _0.5 mother alloy powder, 3 kg of water, and 60 mL (47.4 g) of ethanol were put into a container and mixed to prepare a suspension.

Next, four unused clad steel (SS400) test pieces (length 2.0 cm × width 2.0 cm × thickness 0.3 cm) were prepared. The clad steel is formed of two layers of carbon steel and stainless steel, and carbon steel is regarded as the inner wall.

Next, a foundation containing magnesia and zirconia as the main components was prepared. The test piece was embedded in the base so that only one main surface (1.0 cm × 1.0 cm square) of the test piece was exposed.

After applying the above suspension to the exposed surface of the test piece by a spray method so that Ti powder and Ti _0.5 Mo _0.5 mother alloy powder become 0.1 g / cm ² (Comparative Example 2 does not have this spray treatment). A raw material powder layer was obtained by installing in a furnace and heating at 100 ° C. for 3 hours while aerating dry air to remove the medium. Here, the coating amount was obtained by subtracting the weight of the uncoated test piece and the base from the weight of the test piece and the base, and dividing the value by the area of the main surface.

The test piece was placed in a container to create an Ar atmosphere, the heating temperature was 1050 ° C., and then the heat treatment was carried out with a heating holding time of 8 hours. After the heating was completed, it was allowed to cool in the air. As a result, a test piece having a coating layer on the surface was obtained.

The coating layer was then removed with a chipping hammer until the surface of the untreated test piece was visible. As a result, a test piece (hereinafter referred to as "test piece A") having a surface layer containing Ti and Mo diffused inward from the surface of the inner wall was obtained.

In addition, the same preparation as test piece A except that a suspension was prepared by putting 0.36 kg of Ti powder, 3.24 kg of Ti _0.5 Mo _0.5 mother alloy powder, 3 kg of water, and 60 mL of ethanol into a container and mixing them. By the method, a test piece (hereinafter, referred to as "test piece B") having a surface layer in which Ti and Mo were diffused was produced.
In addition, a surface layer in which Ti was diffused was provided by the same preparation method as that of test piece A, except that a suspension was prepared by putting 3.6 kg of Ti powder, 3 kg of water, and 60 mL of ethanol into a container and mixing them. A test piece (hereinafter referred to as "test piece C") was produced. Further, unlike the test pieces A to C, the one in which the exposed surface of the test piece was not modified was designated as the test piece D.

(Measurement of thickness, metal concentration)
The thickness of the surface layer provided on the test pieces A to C was determined by the following measuring methods.
These test pieces A to C are cut along the thickness direction and embedded in a molding mold using about 20 g of a cold-embedded resin (main component polyester resin) and about 2 g of a curing agent (methyl ethyl ketone peroxide, methyl ethyl ketone). The resin was hardened by leaving it for about a day to prepare a sample. Then, polishing was performed using water-resistant abrasive paper so that the cut surface of the sample came out of the resin layer, and the surface of the sample to be measured was platinum-coated with a vacuum vapor deposition machine. With respect to the sample obtained in this manner, the amounts of Ti and Mo were measured along the thickness direction of the test pieces A to C by EPMA analysis using an electron probe microanalyzer (SUPERPROBE JXA-8100, manufactured by JEOL Ltd.). The thickness of the surface layer was measured at 5 points, and the minimum value among them was taken as the thickness of the surface layer. Since the test piece C does not contain Mo, the thickness was determined based only on the amount of Ti. The results are shown in Table 1. Both Ti and Mo were detected up to almost the same position in the thickness direction.

(Evaluation of Fe concentration)
Four bottomed cylindrical MgO crucibles (φ47 mm (outer diameter) x φ39 mm (inner diameter) x 160 mm (height)) were prepared. On the bottom of each crucible, test pieces A to C were placed so that the surface provided with the surface layer was facing upward, and test pieces D were placed so that one exposed surface was facing upward. Next, 200 g of solid Mg was put into each of the four crucibles. At that time, solid Mg was placed on each of the test pieces A to D. The set temperature was set to 995 ° C., and the outer peripheral surface of the crucible was heated to raise the temperature inside the crucible. Stirring was started when the temperature inside the crucible reached 720 ° C. to melt the solid Mg. Then, after the inside of the crucible reached 800 ° C., it reached 950 ° C. over 1.5 hours and then kept at 950 ° C. for another 1.5 hours. After that, heating was stopped and the crucible was pulled up.
Then, the molten magnesium was sampled, and the amount of Fe eluted in the molten magnesium was measured by an inductively coupled plasma (ICP) emission spectrometer. The results are shown in Table 2 of Examples 1 and 2 and Comparative Examples 1 and 2, respectively. The test piece A is Example 1, the test piece B is Example 2, the test piece C is Comparative Example 1, and the test piece D is Comparative Example 2.

(Discussion by Example)
It was confirmed that Examples 1 and 2 were able to reduce the amount of eluted Fe as compared with Comparative Example 1. Further, although the thickness of the surface layer of Example 1 was thinner than the thickness of the surface layer of Example 2, it was confirmed that the amount of Fe could be reduced as compared with Example 2.
In particular, in Example 1, the amount of Fe eluted in molten magnesium can be reduced to 1/15 as compared with Comparative Example 1, and the amount of Fe eluted in molten magnesium is 1/15 as compared with Comparative Example 2. It was confirmed that it could be reduced to 50.
In Examples 1 and 2, the thicknesses of Ti and Mo present on the inner wall surface layer were almost the same.

In Example 2, the Fe concentration of molten magnesium was slightly higher than that in Example 1. In Example 2, since the amount of Mo was smaller than that in Example 1, it is estimated that the amount of Mo transferred from the surface of the inner wall toward the inside was small.

From the above, it can be said that a metal reduction reaction vessel provided with a surface layer containing Ti and Mo diffused inward from the surface of the inner wall is useful.

10 Inner wall 10a Inner wall surface 11 Inner wall surface layer 20 Coating layer S11 Raw material powder layer forming step S21 Layer forming step

Claims (12)

A metal reduction reaction vessel having an inner wall surface layer located inside from the surface of the inner wall and containing Ti and a barrier metal M. The metal reduction reaction vessel according to claim 1, wherein the total concentration of Ti and the barrier metal M in the composition on the surface of the inner wall is 3% by mass or more, and the thickness of the surface layer of the inner wall is 40 μm or more. The metal reduction reaction vessel according to claim 1 or 2, wherein the concentration of the barrier metal M in the composition on the surface of the inner wall is 1% by mass or more. The metal reduction reaction vessel according to any one of claims 1 to 3, wherein the barrier metal M is one or more selected from the group consisting of Mo, Nb, and W. The method for producing a metal reduction reaction vessel according to any one of claims 1 to 4.
A raw material powder layer forming step of forming a raw material powder layer containing Ti-M-based mother alloy powder on the surface of the inner wall of the metal reduction reaction vessel, and
By heat-treating the raw material powder layer, a coating layer containing Ti and M located outside the surface of the inner wall and an inner wall surface layer containing Ti and M located inside the surface of the inner wall. A method for producing a metal reduction reaction vessel, which comprises a layer forming step for forming each of the above.
(However, M indicates a barrier metal.) The claim includes that the raw material powder layer forming step includes attaching a suspension containing the Ti-M-based mother alloy powder and an aqueous solution containing an alcohol having 1 to 4 carbon atoms to the surface of the inner wall. 5. The method for producing a metal reduction reaction vessel according to 5. The method for producing a metal reduction reaction vessel according to claim 5 or 6, wherein the Ti-M-based mother alloy powder contains 30 to 70% by mass of Ti and 30 to 70% by mass of M. Any one of claims 5 to 7, wherein the raw material powder layer contains 0.05 to 1.0 g of the Ti-M-based mother alloy powder per 1 cm ² of the surface of the inner wall of the metal reduction reaction vessel. The method for producing a metal reduction reaction vessel according to. The raw material powder layer further contains Ti powder and contains
The average particle size of the Ti powder is 45 μm or less.
The method for producing a metal reduction reaction vessel according to any one of claims 5 to 8, wherein the average particle size of the Ti-M-based mother alloy powder is 45 μm or less. The metal reduction according to claim 9, wherein the raw material powder layer has a content of the Ti powder of 5 to 70% by mass and a content of the Ti-M-based mother alloy powder of 30 to 95% by mass. Method for manufacturing a reaction vessel. The method for producing a metal reduction reaction vessel according to any one of claims 5 to 10, wherein the heat treatment is performed at a heating temperature of 100 ° C. or higher and lower than 1080 ° C. A method for producing titanium sponge, which comprises a step of reducing titanium tetrachloride in the metal reduction reaction vessel according to any one of claims 1 to 4.