JP5403825B2 - Method for storing high-purity sponge titanium particles and method for producing high-purity titanium ingot using the same - Google Patents

Description

  The present invention relates to a method for storing high-purity sponge titanium particles that is effective for producing a high-purity titanium ingot, and a method for producing a high-purity titanium ingot using the same.

  In the field of semiconductor manufacturing, the progress of high integration is remarkable, and a device called a VLSI requires processing a fine pattern of 1 μm or less. Electrode materials used in such VLSI manufacturing processes are shifting to higher purity and strength, such as molybdenum (Mo), tungsten (W), titanium (Ti), or their silicides (silicides). High-purity refractory metal materials such as Among these, titanium is particularly promising because it exhibits excellent specific strength, workability, and corrosion resistance.

At present, all of the industrially used methods for producing titanium materials are reduction methods using titanium tetrachloride (TiCl ₄ ) obtained by chlorinating rutile (TiO ₂ ) or synthetic rutile as an intermediate raw material. They are a crawl method using magnesium (Mg) as a reducing agent, a hunter method using sodium (Na) as a reducing agent, and an electrolytic method using molten salt electrolysis. Among these, the crawl method is frequently used from the viewpoint of productivity and energy saving. FIG. 1 shows the steps from the production of a titanium material produced by the crawl method to the production of a high purity titanium ingot.

In the production of a titanium material by the crawl method, first, Mg is charged into a sealed steel reaction vessel, the inside of the vessel is replaced with an inert argon gas, and then heated to melt Mg. When TiCl ₄ is supplied from a nozzle provided in the upper part of the reaction vessel, TiCl ₄ is reduced with Mg to generate Ti, and settles in the melt (molten Mg and molten MgCl ₂ as a by-product), Deposit to form a porous sponge titanium mass.

When the reduction reaction is completed, the melt (molten MgCl ₂ ) is extracted from the bottom of the reaction vessel, but a large amount of melt remains in the sponge titanium cake. In order to remove this residual melt, the melt is evaporated and removed in a vacuum separation step. Specifically, after the reaction vessel is housed in a vacuum separation furnace, the inside of the reaction vessel is brought into a vacuum state and heated from the outside of the reaction vessel, so that unreacted Mg contained in the sponge titanium cake in the reaction vessel And residual MgCl ₂ is evaporated and separated. Sponge titanium from which unreacted Mg and residual MgCl ₂ are separated is extruded as a substantially cylindrical lump from the reaction vessel for each batch.

  The manufactured sponge titanium block is cut and pulverized, and the powder is pressed and hardened to be processed into a compact or a compact called a briquette. The produced compression-molded body is connected in a rod shape by welding to be a melting raw material. And this rod-shaped melt | dissolution raw material is melt | dissolved and it is set as a metal titanium ingot. Examples of the melting method include consumable electrode type vacuum arc melting (VAR) and electron beam melting (EB melting). Currently, the former consumable electrode type vacuum arc melting method is frequently used from the viewpoint of efficiency and the like.

  When manufacturing a high-purity titanium ingot for semiconductor wiring materials by such a method, it is necessary to devise a technique for reducing the metal impurity concentration such as Fe, Cr, Ni and the oxygen concentration, and a metal such as Cr, Ni, Fe, etc. Concerning impurities, the proportion of contamination from the reaction vessel is large, and from this point of view, the inner surface of the vessel is made of Fe, and the concentration of the impurities is reduced by so-called centering, etc., by removing the vicinity of the outer surface of the sponge titanium block contacting the inner surface It is illustrated. On the other hand, with respect to oxygen, it is said that the influence of moisture adsorbed from the atmosphere in the pulverization process of cutting and pulverizing the sponge titanium lump is great. This is because, in this crushing process, the work is performed in a normal open-type factory, and the sponge titanium is finely crushed and its surface area increases drastically.

In view of the present situation, the process of crushing sponge titanium lump and the compression molding / welding process of processing the titanium sponge particles obtained in this process into a melting raw material are described as “absolute humidity is 10 g-H ₂ O / m ³ or less. ”, Preferably“ 7 g-H ₂ O / m ³ or less ”, more preferably“ 5 g-H ₂ O / m ³ or less ”in a low-humidity atmosphere to suppress moisture absorption from the atmosphere and oxygen A method for producing a low-oxygen titanium material for reducing the concentration is proposed in Patent Document 1.

Further, it has been found that there is significant water absorption not only in the pulverizing step of cutting and pulverizing the titanium sponge lump, but also in the step of manufacturing the compression molded body, and the countermeasure is proposed in Patent Document 2. That is, moisture in the atmosphere is taken into the compression molded body due to shrinkage accompanying the dissipation of processing heat when processing the titanium sponge particles obtained by cutting and pulverizing the sponge titanium lump into the compression molded body. It was found that there was an event that the oxygen concentration of the compression molded body was increased by being absorbed by the remaining MgCl ₂ , and in order to prevent this, the compression molded body whose temperature was increased by compression processing was subjected to pressure reduction treatment in a vacuum container. It is a measure proposed in Patent Document 2 to cool the substrate in a low humidity atmosphere later.

  In the former measure, in which the titanium sponge lump crushing process and the sponge titanium particle compression molding / welding process are performed in a low humidity atmosphere, it is necessary to maintain the entire factory in a low humidity atmosphere. . It has been found that the effect of the latter measure, in which the compression-molded body is cooled in a low-humidity atmosphere after being decompressed in a decompression vessel, varies in effectiveness. The reason for this will be described in detail later, but it has been clarified that the storage period of the sponge titanium particles obtained by cutting and pulverizing the sponge titanium lump is involved.

JP 10-259432 A JP 2008-95168 A

  An object of the present invention is to provide a high-purity sponge capable of economically producing a high-purity titanium ingot with few impurities, which can stably solve the problem of moisture absorption to the sponge titanium particles and the resulting increase in oxygen concentration of the titanium ingot with a simple operation. It is in providing the storage method of a titanium grain, and the high purity titanium ingot manufacturing method using the same.

Incidentally, it is also described in Patent Document 2 that one of the major causes of moisture absorption in the sponge titanium particles is the residual MgCl ₂ . The details are as follows.

As described above, the titanium sponge mass produced by the crawl method contains MgCl ₂ . The sponge titanium lump is cut and crushed after centering to form high-purity sponge titanium particles, and the surface area increases drastically. In order to prevent moisture absorption due to an increase in surface area, the titanium sponge particles are immediately enclosed in a storage container. Specifically, as shown in FIG. 1, after the sponge titanium particles are filled into the storage container, the container opening is sealed with a lid. Subsequently, the container is evacuated and low humidity gas is injected. That is, the space in the storage container is replaced with a low-humidity inert gas. In this state, sponge titanium is stored and transported.

Each of the high-purity sponge titanium particles filled in the storage container contains MgCl _2, and it is inevitable that only the particle surface touches the atmosphere at the moment when it is crushed into particles. The existing MgCl ₂ absorbs moisture in the atmosphere in a short time, and from anhydrous MgCl ₂ , a hydrate containing crystal water [MgCl ₂ · nH ₂ O (n: any of 6, ₄ and ₂ in terms of the number of crystal water) In general, since the grain surface comes into contact with a sufficient amount of moisture present in the atmosphere, the number of crystal water becomes the largest hexahydrate (MgCl ₂ .6H ₂ O).

However, the MgCl ₂ hydrate on the grain surface is initially present on the grain surface in a limited manner. Since the inside of the grain has a porous structure, it is difficult for the crystal water in MgCl ₂ hydrate existing on the grain surface to diffuse into the inside of the grain. Of course, the storage container is highly airtight and does not enter the atmosphere during storage. Sponge titanium particles that have come into contact with the atmosphere are subjected not only to the decompression process when replacing with low-humidity gas in the storage container, but also to the production of the rod-shaped molten raw material by welding from the compression molded body after storage, Furthermore, it also undergoes a reduced pressure treatment during the dissolution process.

For these reasons, the MgCl ₂ hydrate on the grain surface is from hexahydrate (MgCl ₂ · 6H ₂ O) to tetrahydrate (MgCl ₂ · 4H ₂ O) and tetrahydrate (MgCl ₂ · 4H ₂ O). Until now, it is thought that even if the water of crystallization decreases stepwise like dihydrate (MgCl ₂ · 2H ₂ O), it does not have a decisive influence on the oxygen concentration of the titanium ingot. It was. In the countermeasure described in Patent Document 2, the phenomenon that moisture in the atmosphere is taken into the compression molded body due to the shrinkage accompanying the dissipation of the processing heat when the titanium sponge particles are processed into the compression molded body is combined with MgCl ₂ hydrate. Such a background exists to attract attention.

  However, although the measures described in Patent Document 2 are effective in reducing the oxygen concentration of the manufactured high-purity titanium ingot, there are variations in the effect in the process of many experiments. Surprisingly, as a result of repeated experiments to investigate the cause, the storage period when sponge titanium particles were filled in a storage container and stored unexpectedly affected the oxygen concentration of high-purity titanium ingots. In addition, the present inventor found out that the degree of influence is not related to the presence or absence of measures described in Patent Document 2.

That is, the high-purity sponge titanium lump taken at the center is cut and crushed and immediately enclosed in a storage container, and the inside of the container is replaced with low-humidity gas. The storage container is highly airtight and does not enter the atmosphere during storage. At the moment when the titanium sponge lump is crushed into grains, only the grain surface is exposed to the atmosphere, so the MgCl _{2 on} the grain surface may become MgCl ₂ .6H ₂ O due to moisture absorption. However, with regard to the crystal water, as described above, there is a possibility that the crystal water may be reduced by the vacuum exhaust operation immediately after the sealing and further by the two vacuum exhaust operations until the subsequent dissolution. Nevertheless, the oxygen concentration of the high-purity titanium ingot tends to increase as the storage period of the storage container becomes longer.

As a result of further investigation and consideration about the cause, the present inventor has come to know the following new facts. The MgCl ₂ (MgCl ₂ .6H ₂ O), which once became a hydrate on the surface of the titanium sponge particles, had an incomplete reduction in the number of hydration even by a vacuum evacuation operation immediately after. As a result, the crystal water possessed by the MgCl ₂ hydrate on the grain surface slowly diffuses inside the grain over the storage period, and eventually the MgCl ₂ inside the grain also becomes a hydrate. At the same time, the hydration number is increased, and the anhydrous MgCl ₂ inside the grains is changed to MgCl ₂ hydrate having a hydration number of 2, 4 or 6.

Once MgCl ₂ inside the grains that have become hydrates does not return to the original anhydrous MgCl ₂ by the vacuum exhaust operation, the rod-shaped melting raw material is prepared in addition to the vacuum exhaust operation at the time of sealing to the storage container. Even after the vacuum evacuation operation and the vacuum evacuation operation in the subsequent melting step, MgCl ₂ hydrate remains as it is on the sponge titanium grain surface and inside the grain, and the crystal water has an oxygen concentration of the high purity titanium ingot. Cause the rise. For this reason, in order to reduce the oxygen concentration of the high purity titanium ingot, the hydration number of MgCl ₂ that has become a hydrate on the surface of the sponge titanium particles is lowered as early as possible, that is, in the MgCl ₂ hydrate. It is effective to reduce the amount of crystallization water as early as possible, thereby suppressing the diffusion of crystallization water into the inside of the grain, and as a result, leaving as much anhydrous MgCl ₂ as possible inside the grain.

The high purity sponge titanium particles storage method of the present invention has been completed based on such knowledge, and the sponge titanium particles obtained by crushing and crushing the central portion of the sponge titanium mass produced by the crawl method are obtained. When sealed in a storage container, the inside of the storage container filled with sponge titanium particles is depressurized to 40 Pa or less, and then low humidity gas is injected into the storage container. Here, the time required from the start of crushing the sponge titanium lump to the start of decompression in the storage container is suppressed to 24 hours or less, preferably 7 hours or less, and more preferably 5 hours or less. The technical meaning will be described in detail later.

  The high purity titanium ingot production method of the present invention is a method for producing a high purity titanium ingot using this high purity sponge titanium particle storage method, and stores the high purity sponge titanium particles stored by the storage method. When taking out from a container and processing it into a compression molded body and combining the compression molded body into a melted raw material, the time required from the start of crushing of the sponge titanium mass to the start of decompression in the storage container in the storage method is 24 hours or less And the exposure time of the sponge titanium particles to the atmosphere when the sponge titanium particles are taken out from the storage container and processed into a compression molded body is suppressed to 48 hours or less.

In the high purity sponge titanium particle storage method and the high purity titanium ingot manufacturing method of the present invention, the ultimate pressure in the decompression operation when replacing the inside of the storage container filled with the sponge titanium particles with low humidity gas is 40 Pa or less. By doing so, the moisture absorbed in the MgCl ₂ on the surface of the sponge titanium particles between the start of crushing the sponge titanium lump and the start of decompression in the storage container decreases before diffusing into the inside of the particles. Specifically, MgCl ₂ hydrate on the surface of titanium sponge particles is hexahydrate (MgCl ₂ · 6H ₂ O) is tetrahydrate (MgCl ₂ · 4H ₂ O) and tetrahydrate (MgCl ₂ · 4H). ₂ O) reduces crystallization water to dihydrate (MgCl ₂ .2H ₂ O) and so on. As a result, the amount of moisture diffused from the MgCl ₂ hydrate on the grain surface to the inside of the grain during storage of the sponge titanium grain is suppressed, and anhydrous MgCl ₂ remains inside the grain even after long-term storage. Anhydrous MgCl ₂ remains in the range, and the amount of MgCl ₂ retained in the whole grains decreases, so that the oxygen concentration of the high purity titanium ingot produced from the sponge titanium grains decreases.

  The long-term storage here is specifically storage for 2 months or more, and even when storage for 4 months or more is performed, the oxygen concentration lowering effect of the high purity titanium ingot is not deteriorated.

  Incidentally, the conventional value of the ultimate pressure in the depressurization operation when replacing the inside of the storage container filled with sponge titanium particles with low-humidity gas was 100 Pa or more, usually about 500 Pa. The purpose of the decompression operation here is to remove moisture in the space in the container by replacing the air remaining in the storage container with low-humidity gas, and an ultimate pressure of about 500 Pa is sufficient to achieve the purpose. Because there was.

The vacuum reaching pressure of the storage vessel was less 40Pa, the water absorbed by the MgCl ₂ of titanium sponge particles surface until start of evacuation in the storage container from fracture initiation titanium sponge mass at 40Pa than (crystal water ) Is not effectively reduced. As for the lower limit of the pressure reduction ultimate pressure in the storage container, this pressure should be as low as possible from the viewpoint of removing crystal water, but the equipment cost increases to lower it, but the ultimate pressure holding time can be reduced even if it is not particularly low. Since the removal of water of crystallization can be promoted by increasing the length, it is not particularly specified, but it is preferably 0.1 Pa or more in terms of processing efficiency in terms of processing efficiency.

  In addition to these, in the high purity titanium ingot production method of the present invention, when storing the sponge titanium particles, the time required from the start of crushing the sponge titanium lump to the start of decompression in the storage container is suppressed to 24 hours or less, and In using the stored sponge titanium particles, the exposure time of the sponge titanium particles when the sponge titanium particles are taken out from the storage container and processed into a compression-molded body is suppressed to 48 hours or less, so that the high purity titanium ingot The oxygen concentration can be further reduced.

That is, the former required time is the atmospheric exposure time before storage of sponge titanium particles. By suppressing the exposure time to the atmosphere, moisture absorption of MgCl _{2 on} the surface of the titanium sponge particles before storage is suppressed, and an increase in the hydration number near the surface slightly deeper than the surface is suppressed. Increases the moisture removal effect of the vacuum exhaust operation. The latter air exposure time is the air exposure time before use after storage of sponge titanium particles. By suppressing the exposure time to the atmosphere, the moisture absorption of MgCl _{2 on} the grain surface before use after the sponge titanium grains are stored is suppressed. As a result of these, an increase in oxygen concentration of the high purity titanium ingot due to moisture absorption of MgCl ₂ is suppressed.

The air exposure time before storage of the former was set to 24 hours or less, but from the viewpoint of suppressing the moisture absorption of MgCl _{2 on} the surface of the sponge titanium particles and thereby suppressing the increase in the oxygen concentration of the high purity titanium ingot, the range in which work is not hindered. The shorter the better, the shorter it is, preferably 7 hours or shorter, and more preferably 5 hours or shorter. In addition, after the latter storage, the atmospheric exposure time before use is set to 48 hours or less. However, from the same viewpoint, it is better that the exposure time is shorter, preferably 14 hours or less, and more preferably 10 hours or less.

Here, the tolerance of the air exposure time before use after storage of the latter is greater than the air exposure time before storage of the former. This is because moisture absorbed in the MgCl ₂ on the grain surface due to atmospheric exposure before storage diffuses into the grain during the subsequent long storage period and changes anhydrous MgCl ₂ inside the grain to MgCl ₂ hydrate. On the other hand, after the latter storage, the moisture absorbed in the MgCl ₂ on the grain surface by exposure to the atmosphere before use has a small influence on the increase in oxygen concentration of the high purity titanium ingot because the subsequent diffusion period is short. .

  After the latter storage, the atmospheric exposure period before use is basically until the sponge titanium particles are taken out from the storage container and processed into a compression molded body, and until the subsequent processing into a melted raw material. Can be excluded. This is because, in the compression molded body, the sponge titanium particles are pressed and hardened, so that the diffusion into the crystal water particles becomes slow.

  The melting raw materials are specifically consumable electrodes for consumable electrode type vacuum arc melting (VAR) and bar materials for electron beam melting (EB melting). In order to suspend the consumable electrode, strong welding is required, so that the compression degree of the compression molded body is large, and when the compression molded body is formed, the diffusion into the crystal water grains becomes extremely slow. For this reason, the atmospheric exposure period after storage in the case of consumable electrode type vacuum arc melting (VAR) is limited to the time until the sponge titanium particles are taken out from the storage container and processed into a compression molded body, The impact is particularly small.

The object of the present invention is high-purity sponge titanium particles and high-purity titanium ingots produced therefrom. The average particle size of the expanded titanium sponge particles having a required purity lower than that of the high-purity sponge titanium particles is about 1 to 8 mm at D50, but the average particle size of the high-purity sponge titanium particles is as large as 15 mm or more at D50. Since the rate of crystallization water diffusion into the grain becomes slower as the particle size becomes larger (because the particle volume becomes larger), the present invention for high purity sponge titanium particles having a larger particle size is very effective. In particular, when the average particle diameter is D50 of 25 mm or more, the anhydrous MgCl ₂ region inside the grains becomes larger and the crystallization water diffusion into the grains becomes slower, so the effectiveness of the present invention is particularly great. In addition, if the particle diameter of the high-purity sponge titanium particles is too large, it becomes difficult to form a compression-molded body or to perform sampling for analysis. Therefore, the upper limit of the average particle diameter is preferably 300 mm or less at D50.

  The melting raw material is specifically a consumable electrode for consumable electrode type vacuum arc melting (VAR) or a bar material for electron beam melting (EB melting). Consumable electrode type vacuum arc melting (VAR) requires strong welding to suspend a large consumable electrode, and therefore the compression degree of the compression molded body is large. Is extremely slow. For this reason, in the case of consumable electrode type vacuum arc melting (VAR), the atmospheric exposure period after storage is until the sponge titanium particles are taken out from the storage container and processed into a compression molded body.

The storage method of the high purity sponge titanium particles of the present invention is that the titanium sponge particles obtained by cutting and crushing after filling the center of the sponge titanium lump are filled in the storage container, and then the storage container is filled with low humidity gas. By setting the ultimate pressure in the decompression operation at the time of replacement to 40 Pa or less, the moisture absorbed in the MgCl2 on the surface of the titanium sponge grains from the start of crushing of the sponge titanium lump to the start of decompression in the storage container enters the inside of the grains. since reduced prior to diffusion, the amount of water diffusing into the grain interior from MgCl2 hydrate particle surface during storage of the titanium sponge particles is suppressed, after long-term storage in the grain interior anhydrous MgCl2 Ru residue. Moreover, by suppressing the time required from the start of crushing of the sponge titanium lump to the start of decompression in the storage container to 24 hours or less, the moisture absorption of MgCl2 on the surface of the titanium sponge particles before storage is suppressed, and from the surface Since an increase in the hydration number in the vicinity of a slightly deep surface is suppressed, the moisture removal effect by the vacuum exhaust operation before storage is enhanced. As a result of these, the oxygen concentration of the high-purity titanium ingot produced from the sponge titanium particles can be suppressed low.

High-purity titanium ingot production method of the present invention, in addition to this, the stored order to use the titanium sponge particles, titanium sponge particles of atmospheric exposure during processing to the compression molded product out the sponge titanium particles from the storage container By suppressing the time to 48 hours or less, the oxygen concentration of the high purity titanium ingot can be further suppressed.

It is explanatory drawing of the process until it manufactures a high purity titanium ingot from the sponge titanium lump manufactured by the crawl method.

  An embodiment of the present invention will be described below with reference to FIG. In the present embodiment, a high-purity titanium ingot that can be used for a semiconductor wiring material is manufactured from a sponge titanium block manufactured by the crawl method.

  In this embodiment, first, a titanium sponge lump is manufactured by a crawl method. Here, iron is used on the inner surface of a reduction reaction vessel made of stainless steel to prevent contamination by heavy metals such as Ni and Cr. After the vacuum separation, a substantially cylindrical sponge titanium lump is taken out from the reaction vessel. In order to collect a high-purity portion from the sponge titanium chunk, the central portion of the sponge titanium chunk is taken out. In other words, the outer peripheral portion that is in contact with the inner surface of the reaction vessel, and further the upper and lower portions, where there is a risk of Fe contamination, are excluded. Specifically, the outer peripheral part, upper part, and lower part of the substantially cylindrical sponge titanium lump taken out from the reaction vessel are cut out over 200 mm or more. In this way, a high-purity sponge titanium mass with few metal impurities is collected.

  The collected high-purity sponge titanium lump is further cut into small pieces and crushed to obtain high-purity sponge titanium particles. After the particle size adjustment, the high purity sponge titanium particles are filled in a storage container made of a drum can, and the opening is sealed with a lid, thereby enclosing the high purity sponge titanium particles in the storage container. After sealing, the storage container is evacuated to 40 Pa or less. The ultimate pressure was 500 Pa in the past, but in order to reduce this to 40 Pa or less, a mechanical booster was additionally installed in addition to the conventional rotary vacuum pump, and the suction piping distance from the pump to the storage container was also increased from the conventional 150 m to 30 m. And Moreover, in order to confirm the pressure in a storage container correctly, a vacuum gauge is installed in the place within 10 m from the container connection part of suction piping.

After the inside of the storage container is evacuated to 40 Pa or less in this way, low humidity gas is injected into the storage container until the atmospheric pressure is reached. The reduced pressure exhaust ultimate pressure is preferably as low as possible from the viewpoint of promoting the removal of crystal water. Specifically, it is preferably 20 Pa or less, and more preferably 10 Pa or less. The lower limit of the pressure reduction exhaust ultimate pressure is preferably 0.1 Pa or more as described above. With respect to the time for keeping the inside of the storage container at the reduced pressure exhaust ultimate pressure, it is desirable that the retention time is 1 minute or longer from the viewpoint of promoting the removal of crystal water, and it is further desirable to retain it for 5 minutes or longer. The upper limit of the holding time is preferably 48 hours or less, and more preferably 8 hours or less from the viewpoint of process processing speed. The low-humidity gas means a gas having an absolute humidity of 0.5 g / m ³ or less, and more preferably a gas having a humidity of 0.1 g / m ³ or less. As the gas species, a non-oxidizing gas such as a rare gas or nitrogen gas is desirable, and a rare gas such as Ar gas is particularly desirable.

What is important here is to reduce the vacuum exhaust ultimate pressure in the storage container after filling the titanium sponge particles into the storage container to 40 Pa or less, but in addition to this, from the start of crushing the high purity sponge titanium lump The time required until the start of decompression in the storage container, that is, the atmospheric exposure time before storage, is suppressed to 24 hours or less, desirably 7 hours or less, and more desirably 5 hours or less. The former measure removes moisture (crystal water) absorbed by MgCl ₂ on the grain surface before storage of high-purity titanium sponge grains, and suppresses diffusion of moisture (crystal water) inside the grains during storage. . In addition, the latter measure suppresses atmospheric moisture absorption into MgCl ₂ on the grain surface before storage of high-purity sponge titanium grains, and also suppresses diffusion of moisture (crystal water) inside the grains during storage. Contribute to. And all contribute to the oxygen concentration fall of the high purity titanium ingot finally manufactured.

  When the high-purity sponge titanium particles are sealed in the storage container in this way, the high-purity sponge titanium particles are stored in the storage container until the use time comes, and are transported together with the storage container to a necessary place. The storage period varies, and it is not uncommon to reach several months.

  When the high-purity sponge titanium particles in the storage container come to use, the high-purity titanium sponge particles are taken out of the storage container, and after a necessary procedure, a compact used as a consumable electrode for consumable electrode type vacuum arc melting (VAR) It is set as the compression molding body of the half disk called 1/4. The required number of compression-molded bodies are produced, and these are combined in a cylindrical shape and joined by welding in a reduced pressure atmosphere to form a consumable electrode.

What is important here is the atmospheric exposure time of high-purity sponge titanium particles before use after storage until the high-purity sponge titanium particles are taken out from the storage container and processed into a compression molded body, and this atmospheric exposure time is 48 hours or less. It is preferably suppressed to 14 hours or less, more preferably 10 hours or less. Thereby, after storage of the high-purity sponge titanium grains, moisture absorption in the atmosphere into MgCl ₂ on the grain surface before use is suppressed, and diffusion of moisture (crystal water) into the grains thereafter is suppressed. Although the effect is small compared to the suppression of the atmospheric exposure time before storage, this also contributes to the reduction of the oxygen concentration of the high purity titanium ingot that is finally produced.

  Finally, the completed consumable electrode is subjected to consumable electrode type vacuum arc melting (VAR) to produce a high purity titanium ingot. In the consumable electrode type vacuum arc melting (VAR), a consumable electrode is set in a melting furnace, and the inside of the furnace is depressurized and replaced with an inert atmosphere. Then, an arc is generated between the molten metal in the water-cooled copper mold and the consumable electrode suspended thereon, and the consumable electrode is sequentially melted from the bottom by the arc heat to be cast into the mold. Repeat this lysis operation 2 or 3 times as necessary. In the second and subsequent melting operations, a titanium ingot is used as the consumable electrode material.

  Thus, a high purity titanium ingot with a low oxygen content is produced.

  In the above embodiment, a high-purity titanium ingot is manufactured by using high-purity sponge titanium particles having the same specifications manufactured under the same conditions, and variously changing the atmospheric exposure time before storage and the pressure reduction pressure P during storage. This confirmed the effectiveness of the present invention.

As a common condition, the storage container is a drum having a capacity of 200 liters. The average particle size of the high purity sponge titanium particles is D50 of 100 mm. The average amount of high purity sponge titanium particles filled in the storage container is 150 kg. The holding time T of the reduced pressure exhaust pressure P in the storage container is 30 minutes. The low-humidity gas injected into the storage container is Ar gas having an absolute humidity of 0.1 g / m ³ or less. The storage period of high-purity titanium sponge particles in a storage container is 3 months, except for some parts. After storage, the atmospheric exposure time before use is 48 hours. The weight of the manufactured high-purity titanium ingot is 5 tons.

  The exposure time to the atmosphere before storage of the high-purity sponge titanium particles and the reduced pressure exhaust pressure P during the storage are such that the oxygen concentration of the high-purity sponge titanium particles, particularly the high-purity sponge titanium particles in the stage immediately before processing into a compression molded product. Table 1 shows the results of investigation on the influence on oxygen concentration. The oxygen concentration of the sponge titanium particles at the stage immediately after crushing is 185 ppm in common in each example, and the target value of the oxygen concentration of the high purity sponge titanium particles at the stage immediately before processing into the compression molded body is 200 ppm.

  As can be seen from Table 1, the oxygen concentration of the high-purity sponge titanium particles in the stage immediately before processing into a compression molded article is obtained by setting the reduced pressure P in the container when storing the high-purity sponge titanium particles in the storage container to 40 Pa. Clears the target value. Even if the storage period is extended from 3 months to 5 months, this oxygen concentration does not increase. By reducing the pressure reduction Pa, the oxygen concentration further decreases. Shortening the exposure time to the atmosphere before storing high purity sponge titanium particles is also effective in reducing the oxygen concentration.

  In addition, although not investigated in the experiment of Table 1, by another experiment, by increasing the holding time T of the reduced pressure exhaust ultimate pressure P, the high purity sponge titanium particles in the stage immediately before processing into the compression molded body Even if the oxygen concentration decreases, and even after the high-purity titanium sponge particles have been stored and the atmospheric exposure time before use is shortened, this oxygen concentration will decrease, but the extent of this will depend on the atmospheric exposure time before storage. Confirmed that the oxygen concentration of the high-purity titanium ingot decreases as the oxygen concentration of the high-purity sponge titanium particles decreases in the stage immediately before processing into the compression molded body. doing.

Claims (5)

The center part of the sponge titanium mass produced by the crawl method was taken out, and when the sponge titanium particles obtained by crushing were sealed in the storage container, the inside of the storage container filled with the sponge titanium particles was decompressed to 40 Pa or less. A method for storing high-purity sponge titanium particles in which a low-humidity gas is injected into the storage container later and the time required from the start of crushing of the sponge titanium mass to the start of decompression in the storage container is suppressed to 24 hours or less . The method for storing high-purity sponge titanium particles according to claim 1 , wherein the time required from the start of crushing of the sponge titanium mass to the start of decompression in the storage container is suppressed to 7 hours or less. When the high-purity sponge titanium particles stored by the storage method for high-purity sponge titanium particles according to claim 1 are taken out of the storage container and processed into a compression-molded body , A method for producing a high-purity titanium ingot that suppresses the exposure time of sponge titanium particles to the atmosphere for 48 hours or less when the sponge titanium particles are taken out from a storage container and processed into a compression molded body. The high purity titanium ingot manufacturing method according to claim 3 , wherein the time required from the start of crushing of the sponge titanium lump to the start of decompression in the storage container in the storage method is suppressed to 7 hours or less. Te high-purity titanium ingot production method smell of claim 3 or 4, suppresses high-purity air exposure time of the sponge titanium particles when processed into compacts and take out the sponge titanium particles from the storage container below 14 hours Titanium ingot manufacturing method.

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