JP7755484B2 - Method for storing titanium sponge lumps and method for manufacturing titanium sponge - Google Patents

Description

The present invention relates to a method for storing titanium sponge blocks and a method for producing titanium sponge.

Titanium sponge can be produced by the so-called Kroll process. In the Kroll process, titanium tetrachloride is dropped into molten magnesium metal in a metal reduction reaction vessel, causing a reduction reaction to occur, resulting in a titanium sponge mass (hereinafter, this process of producing the titanium sponge mass may be referred to as the "reduction process"). This titanium sponge mass is then crushed using a crushing shear or the like to obtain the titanium sponge (hereinafter, this process of crushing the titanium sponge mass into titanium sponge mass may be referred to as the "crushing process"). The titanium sponge obtained by crushing the titanium sponge mass can be used as a melting raw material; for example, it can be melted using the electron beam melting (EB) method or vacuum arc remelting (VAR) method to produce titanium ingots.

Currently, there is a demand for extremely high-grade, high-purity titanium in technical fields such as aircraft and electronic components. Titanium sponge, obtained by crushing titanium sponge blocks, comes into contact with the atmosphere before being used to manufacture titanium ingots, increasing its oxygen content. Techniques for reducing the oxygen content in titanium sponge include those described in Patent Documents 1 to 3, for example.

Patent Document 1 proposes a method for storing high-purity titanium sponge granules, in which the center of a titanium sponge block produced by the Kroll process is removed and crushed to obtain titanium sponge granules, which are then sealed in a storage container, after which the pressure inside the storage container filled with the titanium sponge granules is reduced to 40 Pa or less and a low-humidity gas is injected into the storage container.

Patent Document 2 describes a "storage hopper used in the compounding process in which crushed and sized titanium sponge is mixed to ensure uniform quality, the hopper being characterized by having an openable lid at the top inlet that suppresses the upward flow that occurs within the hopper when the crushed and sized titanium sponge is added," and describes how "with the lid in place, dry air, nitrogen, argon, or the like is introduced into the hopper to replace the normal atmosphere."

Patent Document 3 proposes a method for producing a titanium material with low oxygen content, which comprises cutting and selecting a sponge titanium cake produced by the Kroll process and pulverizing the selected sponge titanium using a tool, the method being characterized in that the pulverization is carried out in an atmosphere with an absolute humidity of 10 g-H ₂ O/m ³ or less.

JP 2012-87373 A Japanese Patent Application Laid-Open No. 2006-291306 Japanese Patent Application Publication No. 10-259432

The titanium sponge blocks obtained in the reduction process can sometimes weigh more than 7 tons per batch. Due to the nature of the manufacturing equipment, the titanium sponge blocks may need to be temporarily stored between the time they are removed from the metal reduction reaction vessel and the time they are crushed. During this storage, the titanium sponge blocks can become discolored, for example, yellow. In this case, even if the discolored titanium sponge blocks are crushed in the subsequent crushing process, the discoloration cannot be physically removed, and the crushed titanium sponge also remains discolored. Depending on the application, such as for high-purity titanium, discolored titanium sponge may not be usable as a raw material for melting titanium ingots, which inevitably reduces the yield in titanium sponge production.

Note that Patent Documents 1 to 3 focus on suppressing the increase in oxygen content in the titanium sponge during or after crushing, and do not consider discoloration that may occur during storage of the titanium sponge mass before crushing. Therefore, the technologies in Patent Documents 1 to 3 still have room for improvement in order to resolve the decline in yield in titanium sponge production.

The present invention therefore aims to provide a method for storing titanium sponge blocks that can prevent discoloration of the titanium sponge blocks during storage.

That is, in one aspect, the present invention is a method for storing titanium sponge lumps, which comprises placing the titanium sponge lumps inside a casing, supplying dry air having an absolute humidity of 3.5 g _H2O / ^m3 or less into the inside of the casing, and discharging the gas inside the casing to the outside from the lower side of the casing so that the inside of the casing is maintained at a positive pressure relative to the outside.

In one embodiment of the titanium sponge mass storage method according to the present invention, the casing has multiple dry air inlets, and the inlets are located at least on the top side and the bottom side of the titanium sponge mass.

In one embodiment of the titanium sponge mass storage method according to the present invention, the amount of dry air supplied to the interior of the casing is 500 L/min or more and 750 L/min or less.

In one embodiment of the method for storing titanium sponge chunks according to the present invention, the internal volume of the casing is 3 m ³ or more and 20 m ³ or less.

In one embodiment of the method for storing titanium sponge chunks according to the present invention, the absolute humidity outside the casing is 15.0 gH ₂ O/m ³ or more.

In another aspect, the present invention provides a method for producing titanium sponge, comprising: a storage step of storing titanium sponge lumps using any of the above-mentioned titanium sponge lumps storage methods; and a crushing step of crushing the titanium sponge lumps to obtain titanium sponge after the storage step.

According to one embodiment of the present invention, discoloration of titanium sponge mass can be suppressed during storage.

1 is an example of a casing used in one embodiment of a titanium sponge lump storage method according to the present invention.

The present invention is not limited to the embodiments described below, and the components can be modified and embodied without departing from the spirit of the invention. Furthermore, various inventions can be created by appropriately combining the multiple components disclosed in each embodiment. For example, an invention may be created by deleting some of the components shown in the embodiments.

[1. Storage method for titanium sponge blocks]
In one embodiment of the method for storing titanium sponge lumps according to the present invention, the titanium sponge lumps are stored in a casing. More specifically, the titanium sponge lumps are placed inside the casing, dry air having an absolute humidity below a predetermined level is supplied to the inside of the casing, and the gas inside the casing is discharged to the outside from the lower side of the casing so that the inside of the casing is maintained at a positive pressure relative to the outside.
In one embodiment, the dry air can be atmospheric air with moisture removed, and therefore contains oxygen and nitrogen. Typically, dry air is not composed of 100% nitrogen or 100% argon. Moisture removal from the atmosphere can be achieved appropriately by utilizing factory exhaust heat, etc. Furthermore, because the dry air contains an appropriate amount of oxygen, workers can pass through the vicinity of the casing located indoors in the factory. Furthermore, the storage method of one embodiment is effective in suppressing discoloration of the titanium sponge mass when the absolute humidity outside the casing is higher than the absolute humidity of the dry air. For example, when the absolute humidity outside the casing is 15.0 _gH2O / ^m3 or higher, the storage method of this embodiment is more effective in suppressing discoloration of the titanium sponge mass.

The titanium sponge mass obtained in the reduction process often has magnesium chloride adhering to it. The reason for this is that the titanium sponge mass is porous, and magnesium chloride remains in the pores. After the reduction process, the titanium sponge mass is immersed in a molten bath containing molten magnesium chloride and molten metallic magnesium, and even if these are removed by draining or vacuum separation, it is difficult to completely remove the molten magnesium chloride from within the pores of the titanium sponge mass.

And because magnesium chloride is deliquescent, it absorbs moisture from the air when it comes into contact with it. The inventors believe that this is why titanium sponge blocks in contact with magnesium chloride become discolored over time.

For example, if the technology in Patent Document 1 were to be adapted to maintain low humidity by reducing the pressure in the atmosphere surrounding the titanium sponge mass, this would require large, sealed facilities, etc., which is not realistic in terms of cost and operational load.

Therefore, the inventors conducted extensive research and came up with the idea of placing a titanium sponge mass inside a casing of relatively simple structure, and in order to suppress discoloration, supplying dry air of a predetermined absolute humidity into the inside of the casing, thereby maintaining a pressurized state between the inside of the casing and the outside.
Preferred embodiments will be described below with reference to the drawings.

<Casing>
The casing 1 shown in Fig. 1 has a framework structure 2 made up of multiple frame members to form a storage space for storing titanium sponge blocks 7, a resin sheet 3 covering the framework members, air intake sections 4a, 4b, and an exhaust section 5. In addition to the above, the casing 1 may also be box-shaped. The casing 1 shown in Fig. 1 is a so-called tent type, and therefore includes a framework structure and a sheet, but the casing can also be constructed as a single unit as long as the shape of the metal or other covering can be maintained.
The internal volume of the casing 1 can be determined appropriately taking into consideration the size of the titanium sponge lumps 7, but is preferably within the range of 3 ^m3 to 20 ^m3 . The size of the titanium sponge lumps 7 is expected to be within the range of 6 tons to 15 tons. The titanium sponge lumps 7 are produced in the reduction process and are not crushed. The titanium sponge lumps obtained by removing the outer periphery of the titanium sponge lumps produced in the reduction process may be stored. In this case, the means for removing the outer periphery of the titanium sponge lumps is not particularly limited. For example, a small rock drill or the like may be used to remove a predetermined depth from the outer periphery toward the center of the titanium sponge lumps, which are laid horizontally on multiple rollers.

(frame structure, resin sheet)
The material of the frame members of the frame structure 2 is not particularly limited as long as it has high strength and corrosion resistance, but is preferably made of steel. Examples of steel include stainless steel, carbon steel, and aluminum alloy.
There are no particular restrictions on the material of the resin sheet 3, and any known material may be used. The resin sheet 3 may be transparent so that it is possible to check whether the titanium sponge mass 7 has been colored during storage.

(Air supply part)
The air intake sections 4a and 4b are used to supply dry air to the inside of the casing 1. The air intake sections 4a and 4b include dry air intake ports formed by penetrating the casing 1 (more specifically, the resin sheet 3, etc.), and air intake pipes (not shown) connected to the air intake ports.
There must be at least one air intake section 4a, 4b, but multiple intake sections 4a, 4b may be provided. The titanium sponge mass 7 is placed inside the casing 1, and dry air having an absolute humidity of 3.5 _gH2O /m3 or less is supplied into the casing 1 from the air intake ports of the air intake sections 4a, ^4b to prevent discoloration. This prevents discoloration of the titanium sponge mass 7. While the titanium sponge mass 7 is stored inside the casing 1, dry air may be supplied continuously or intermittently.
Furthermore, because dry air is heavier than gas (air) with a higher humidity, the dry air moves to the lower part of the casing 1. Here, the inside of the casing 1 is maintained at a positive pressure relative to the outside, so the inflow of outside air from the exhaust section 5 located on the lower side of the casing 1 is suppressed. Furthermore, if dry air is supplied toward the upper side inside the casing 1, gases such as air that were present inside the casing 1 before the supply of dry air can be successfully discharged from the exhaust section described below. As described above, the area around the titanium sponge mass 7 placed inside the casing 1 can be filled with the dry air.
The absolute humidity can be calculated using the following equations 1 to 3.
The method for calculating absolute humidity is applicable not only to dry air in this specification, but also to the inside and outside of a casing.

Furthermore, from the viewpoint of more reliably suppressing discoloration of the titanium sponge mass 7 during storage, it is preferable that the supply rate of dry air from the air intake parts 4a, 4b (the total supply rate if there are multiple air intake parts 4a, 4b) be within the range of 500 L/min to 750 L/min. If multiple air intake parts 4a, 4b are arranged in the casing 1, approximately the same amount of dry air may be supplied from each air intake part 4a, 4b, or the supply rates of each air intake part may be different.
Furthermore, when multiple air intakes 4a, 4b are arranged in the casing 1, the air intakes 4a, 4b are preferably arranged on both sides of the titanium sponge mass 7 in the casing 1, separating them from each other. For example, they can be arranged on the outer surface of the casing 1 on the top 8 and bottom 9 sides of the titanium sponge mass 7. In this case, the titanium sponge mass 7 is preferably arranged horizontally in the casing 1. Because titanium sponge masses typically have a certain vertical length, placing them vertically poses a risk of tipping over. Therefore, horizontal placement of the titanium sponge mass 7 is preferred. A sheet, pedestal, or the like may be provided below the horizontally laid titanium sponge mass 7 to prevent contamination and ensure safe handling. While the air intakes 4a, 4b are shown in the drawing to be centrally located in the height direction of the casing 1, their placement is not particularly limited. When the air intake sections 4a, 4b are located in the center or lower part of the casing 1 in the height direction, it is preferable that the air intake ports face upward within the casing 1, and dry air is supplied, for example, toward a position higher than the titanium sponge mass 7. This allows much of the gas (air, etc.) within the casing 1 to be exhausted from the exhaust section by the supplied dry air, and the gas is easily replaced by the dry air. Even in this case, the dry air supplied to the upper side is heavier than gas (air, etc.) with a higher humidity, and therefore subsequently migrates to the lower part of the casing 1, more reliably preventing the intrusion of outside air from the exhaust section 5. As a result, it is possible to prevent the titanium sponge mass 7 from turning yellow.
It is not always necessary to adjust the temperature of the dry air. For example, the temperature of the dry air may be within ±5° C. of the air temperature outside the casing 1.

The air intake pipe is connected to a dry air supply source that supplies dry air, and may be equipped with a flow sensor that measures the flow rate of the dry air. Examples of dry air supply sources include a compressor that sends out compressed dry air, or a tank that stores dry air. From the perspective of production costs, dry air can be generated by drying the air using exhaust heat generated by other machines or equipment, but this is not limited to this method.

(Exhaust section)
The exhaust section 5 exhausts gas from the inside of the casing 1 to the outside from the lower side of the casing 1 so that the inside of the casing 1 is maintained at a positive pressure relative to the outside. The size and shape of the exhaust section 5 are not particularly limited as long as they maintain a positive pressure relative to the outside. For example, the shape of the exhaust section 5 can be appropriately determined taking into account the amount of dry air supplied to the inside of the casing 1 and the internal volume of the casing 1. The illustrated exhaust section 5 is formed between the bottom edge (e.g., skirt-shaped) of the resin sheet 3 and the bottom surface 6. If the resin sheet 3 is flexible, the pressure inside the casing 1 is made positive relative to the outside, and the resin sheet 3 flexes depending on the magnitude of the positive pressure, thereby functioning as the exhaust section 5. In another embodiment (not shown), the exhaust section may have a through-hole-shaped exhaust port formed in the casing 1 (more specifically, the resin sheet 3, etc.) and an exhaust pipe connected to the exhaust port. By disposing the exhaust section 5 on the lower side of the casing 1, the dry air remaining inside the casing 1 prevents outside air from entering through the exhaust section 5.

[2. Titanium sponge manufacturing method]
One embodiment of the titanium sponge production method according to the present invention includes a storage step in which titanium sponge lumps 7 are stored using the storage method for titanium sponge lumps 7 described above, and a crushing step in which the titanium sponge lumps 7 are removed from the inside of the casing 1 after the storage step. In the crushing step, the titanium sponge lumps 7 may be crushed by a known crushing method. In one embodiment, the method may further include a reduction step in which titanium tetrachloride is reduced with metallic magnesium in, for example, a metallic reduction reaction vessel to produce titanium sponge lumps, and a vacuum separation step in which the molten magnesium chloride and molten magnesium remaining in the metallic reduction reaction vessel are removed from the metallic reduction reaction vessel through a pipe connected to the bottom of the metallic reduction reaction vessel, and then the titanium sponge lumps are subjected to a vacuum separation treatment. The method may also include an outer periphery removal step in which the outer periphery of the titanium sponge lumps removed from the metallic reduction reaction vessel is removed after the vacuum separation step.
Note that explanations that overlap with the above-mentioned configuration will be omitted.

The titanium sponge obtained using the above manufacturing method can be melted using the VAR method, PAM method, EB method, etc. to produce titanium ingots.

The present invention will be specifically described based on examples. The following examples are merely illustrative examples for facilitating understanding of the technical content of the present invention, and the technical scope of the present invention is not limited to these examples.
In Example 1 and Comparative Examples 1 and 2, the absolute humidity of the dry air, the inside of the casing 1, and the outside of the casing 1 was calculated by the above-mentioned method using a measuring device (WATCH LOGGER data logger temperature and humidity stick USB type KT-255U, manufactured by Fujita Electric Manufacturing Co., Ltd.).

[Example 1]
(reduction and vacuum separation)
First, titanium tetrachloride was reduced with metallic magnesium to produce a titanium sponge mass (approximate production volume: 8 tons) in a cylindrical metallic reduction reactor (clad steel with an outer wall made of stainless steel and an inner wall made of carbon steel). The remaining molten magnesium chloride and molten magnesium metal were removed from the metallic reduction reactor through a pipe connected to the bottom of the vessel, and the titanium sponge mass was then subjected to a vacuum separation process. The titanium sponge mass was then removed from the metallic reduction reactor. Next, the outer periphery of the titanium sponge mass (the portion with a high iron content) was ground to a roughly cylindrical shape (φ1.7 m × 2.0 m). Similar operations were performed to produce a total of 30 batches of titanium sponge mass, which were then ground to obtain roughly cylindrical titanium sponge masses.

(storage)
As shown in FIG. 1 , a casing 1 was assembled by forming a frame structure 2 from stainless steel frame members and covering it with a resin sheet 3. A titanium sponge block 7 was placed inside the casing 1 (volume: 12 m ³ ) lying on a stainless steel base on the floor. After placement, dry air with an absolute humidity of 3.5 g H ₂ O/m 3 or less was supplied into the casing 1 at 300 L/min (600 L/min in total) through the air inlets 4 a and 4 b provided on the top 8 and bottom ⁹ sides of the titanium sponge block, as shown in FIG. 1 . During this operation, internal gas was exhausted through the exhaust unit 5, while the interior of the casing 1 was maintained at a positive pressure relative to the outside. That is, dry air was continuously supplied into the casing 1, and air was also continuously exhausted from the exhaust unit 5, maintaining a positive pressure inside the casing 1 relative to the outside. The temperature of the dry air supplied to the inside of the casing 1 was not adjusted in any particular way, and the temperature of the dry air was within ±5°C of the air temperature outside the casing 1.
Ten hours after the start of the dry air supply, the supply of dry air was stopped, and the titanium sponge mass 7 was promptly removed from the casing 1. From the time two hours after the start of the dry air supply until the dry air supply was stopped, the absolute humidity inside the casing 1 was within the range of 7 _gH2O / ^m3 to 9 _gH2O / ^m3 . The absolute humidity outside the casing 1 (outside air) was within the range of 15 _gH2O / ^m3 to 20 _gH2O / ^m3 .
A total of 30 titanium sponge lumps were stored in separate casings using the same procedure.

<Evaluation (presence or absence of yellow coloration and amount of coloration)>
An expert visually checked whether the titanium sponge lumps 7 had turned yellow after storage. As a result, no yellow coloring was confirmed in the 30 titanium sponge lumps after storage.

(Crushing)
Thereafter, the titanium sponge mass 7 was crushed to obtain titanium sponge.

[Comparative Example 1]
In Comparative Example 1, the same operations as in Example 1 were carried out to produce a total of 14 batches of titanium sponge blocks, which were then chipped to obtain approximately cylindrical titanium sponge blocks.
Next, a total of 14 titanium sponge lumps were stored in the same manner as in Example 1, except that dry air was not used and the titanium sponge lumps were stored exposed to the outside air. The absolute humidity of the outside air at the storage location was within the range of 15 g _H2O / ^m3 to 20 g _H2O / ^m3 .
After 10 hours had passed since the storage, the titanium sponge lumps were promptly removed from the room. Then, as in Example 1, it was confirmed whether the titanium sponge lumps had turned yellow after storage. As a result, yellow coloration was confirmed in various parts of 14 of the titanium sponge lumps after storage. After crushing the titanium sponge lumps, the colored parts were collected and weighed, and the total weight of the colored parts was found to be 95 tons.

[Comparative Example 2]
In Comparative Example 2, the same operations as in Example 1 were carried out to produce a total of 30 batches of titanium sponge blocks, which were then subjected to a chipping process to obtain approximately cylindrical titanium sponge blocks.
Next, in Comparative Example 2, titanium sponge lumps 7 were placed lying down inside the casing 1 shown in Figure 1. After placement, dry air with an absolute humidity of 3.5 _gH2O /m3 or ^less was supplied into the casing through the air inlets of each air inlet 4a, 4b at 300 L/min (600 L/min in total), as shown in Figure 1. Once it was confirmed that the internal absolute humidity had reached 9 _gH2O / ^m3 or less from the start of supply, the supply of dry air was stopped and the casings were stored. A total of 30 titanium sponge lumps were stored in the same manner as in Example 1, except that after the supply of dry air was stopped, exhaust from the inside of the casing 1 to the outside ceased, and the pressure inside and outside the casing 1 became the same.
Eight hours had passed since the supply of dry air was stopped (a total of 10 hours including the time for supplying dry air), so the titanium sponge lumps 7 were quickly removed from the casing 1. Then, as in Example 1, it was confirmed whether the titanium sponge lumps had turned yellow after storage. As a result, yellow coloration was confirmed in various parts of the five titanium sponge lumps after storage. After crushing the titanium sponge lumps, the colored parts were collected and weighed, and the total weight of the colored parts was found to be 25 tons.

(Considerations based on examples)
In Example 1, discoloration of the titanium sponge lumps during storage was suppressed, and it was confirmed that it was useful to place the titanium sponge lumps inside a casing, supply dry air with an absolute humidity of 3.5 _gH2O /m3 or ^less into the inside of the casing, and vent the gas inside the casing from the lower side of the casing to the outside so that the inside of the casing was maintained at a positive pressure relative to the outside. The storage method in Example 1 consisted mainly of simple tasks such as constructing and removing the casing and then supplying dry air. In other words, unlike when the atmosphere around the titanium sponge lumps is reduced in pressure, the storage method of Example 1 did not require the workload of constructing an airtight warehouse or rigorously sealing the entire warehouse, and therefore required a small workload.
On the other hand, it is presumed that the titanium sponge mass in Comparative Example 1 was discolored because it was exposed to the open air for as long as 10 hours. Observation during the crushing process confirmed that the titanium sponge mass was discolored yellow not only on the surface but also inside.
Furthermore, in Comparative Example 2, unlike Example 1, the supply of dry air was stopped, and therefore the inside of the casing could not maintain a positive pressure relative to the outside. Therefore, in Comparative Example 2, it is presumed that the coloring of the titanium sponge mass during storage was caused by the stoppage of the supply of dry air.

REFERENCE SIGNS LIST 1 Casing 2 Frame structure 3 Resin sheets 4a, 4b Air intake section 5 Exhaust section 6 Bottom surface 7 Titanium sponge mass 8 Top portion 9 Bottom portion

Claims (6)

A method for storing titanium sponge mass, comprising:
A method for storing titanium sponge lumps, comprising placing the titanium sponge lumps inside a casing, supplying dry air having an absolute humidity of 3.5 g _H2O /m3 or less into the inside of the casing, and discharging the gas inside the casing from the ^lower side of the casing to the outside so that the inside of the casing is maintained at a positive pressure relative to the outside. the casing has a plurality of dry air inlets,
2. A method for storing titanium sponge lumps according to claim 1, wherein the air inlets are arranged at least on the top side and the bottom side of the titanium sponge lumps. The method for storing titanium sponge blocks according to claim 1 or 2, wherein the amount of dry air supplied to the interior of the casing is 500 L/min or more and 750 L/min or less. 4. The method for storing titanium sponge chunks according to claim 1, wherein the internal volume of the casing is 3 ^m3 or more and 20 ^m3 or less. 5. The method for storing titanium sponge chunks according to claim 1, wherein the absolute humidity outside the casing is 15.0 gH ₂ O/m ³ or more. a storage step of storing the titanium sponge lump by the method for storing the titanium sponge lump according to any one of claims 1 to 5;
a crushing step of crushing the titanium sponge mass to obtain titanium sponge after the storing step.