JP2002180144A - Refining method of cobalt material - Google Patents

Abstract

(57) [Problem] To efficiently refine a cobalt raw material containing a relatively large amount of impurities, such as cobalt scrap, so that it can be reused for applications requiring high purity. Close. SOLUTION: In melting and refining a cobalt material using a vacuum melting furnace, a cobalt raw material and an amount of carbon equivalent to a stoichiometric equivalent of the oxygen amount contained in the cobalt raw material are mixed in the furnace. Until the cobalt material is completely dissolved, the inside of the furnace is filled with 50-300 To
rr is maintained under reduced pressure, and then the furnace pressure is 0.1 to 3.0 ×
CO deoxidation is performed at a high vacuum of 10 ⁻³ Torr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of refining a cobalt material, and more particularly to a method of removing impurities from a low-purity cobalt raw material to obtain a high-purity cobalt material. In the present invention, the cobalt material includes not only metallic cobalt but also a cobalt alloy material containing an alloy element such as Ni.

[0002]

2. Description of the Related Art In producing a magnetic film for a large-capacity magnetic tape, a vacuum evaporation method is mainly used, and a cobalt material which is an excellent magnetic material is used as a target material. That is, the target material is changed to EB (Electr
After being melted and evaporated by, for example, on beam, ionization is performed, and cobalt ions are accelerated under the application of a potential difference and deposited on the surface of the magnetic tape to form a vapor-deposited layer (magnetic film).

In the above-described vacuum deposition method, it is required that a target material generate as little splash and spatter as possible during melting by EB or the like. I mean,
This is because when the scattered particles caused by such a splash or spatter fly into the deposition layer, the electromagnetic properties of the magnetic film are significantly deteriorated. Here, "splash" refers to a phenomenon in which relatively large metal particles are scattered due to the generation of gas from a molten metal. Is a phenomenon in which relatively small scattered particles are generated when the electron flow becomes unstable due to the formation of an insulating state.

[0004] The cause of the above-mentioned splash and spatter is mainly trace impurities contained in the target material. Therefore, high cleanliness is required for the target material. In other words, the upper limits of various trace impurity elements are severely restricted. For this reason, conventionally, various methods have been devised for the production of the target material through a melting and solidifying process.

In the above-described vacuum deposition method, the ratio of the target material actually deposited as a vapor deposition layer on a magnetic tape is only about 20 mass%, and the remainder adheres to the wall surface of the vapor deposition equipment and the like, excluding the loss. 60-70 mass% is recovered as scrap. However, such scraps
Pollution such as carbon and oxygen is remarkable, usually 0.005 to 0.02 mass
% Of carbon and 0.1 to 3.0 mass% of oxygen. In addition, inclusions such as MgO, SiO ₂ , CaO, etc.
About ss% is mixed.

[0006] If the cobalt material contains a large amount of impurities as described above, it is difficult to reuse it, and even if it can be reused, its application range is limited. At least, it cannot be reused for applications requiring high purity, such as a deposited layer for a magnetic tape. At present, since depletion of various rare metal resources has become a problem, scraps containing such a large amount of impurities have also been
If it is possible to improve its purity and reuse it,
Its technical value is extremely large.

[0007] In addition, the impurity level of the metallic cobalt raw material also varies greatly depending on the manufacturing method. Naturally, raw materials containing a large amount of impurities are inexpensive, and if high-quality products can be produced using these materials, products can be manufactured at lower cost. However, in general, the use of inferior materials lowers the melting yield and lengthens the refining time, which is not always advantageous in terms of total cost. for reference,
Table 1 shows examples of the components of the raw materials used.

[0008]

[Table 1]

[0009]

SUMMARY OF THE INVENTION The present invention has been developed in view of the above situation, and is effective in refining even a cobalt raw material containing a relatively large amount of impurities such as the above-mentioned scrap. It is an object of the present invention to propose a new refining method for a cobalt material, which can be reused for applications requiring high purity.

That is, the gist of the present invention is as follows. 1. In melting and refining a cobalt material using a vacuum melting furnace, a cobalt raw material and an amount of carbon equivalent to a stoichiometric equivalent to the amount of oxygen contained in the cobalt raw material are mixed in the furnace. After charging, the inside of the furnace is filled with an inert gas until the cobalt material is completely dissolved.
Maintain a reduced pressure of 0 Torr, then raise the furnace pressure to 0.1 to 3.
A method for refining a cobalt material, comprising performing CO deoxidation at a high vacuum of 0 × 10 ⁻³ Torr.

2. After the above-mentioned CO deoxidation, 0.030 mass% of Si
2. The method for refining a cobalt material as described in 1 above, wherein Si deoxidation is performed so that [% O] is reduced to 0.0015 mass% or less.

3. After the above-mentioned CO deoxidation or Si deoxidation, a degassing process of lowering the temperature of the molten metal from (solidification temperature +60 to 100 ° C.) to a temperature close to the solidification temperature to remove gas components in the molten metal,
3. The method for refining a cobalt material according to 1 or 2, wherein the method is performed at least once.

4. 4. The method for refining a cobalt material according to the above 1, 2, or 3, wherein the cobalt raw material includes scrap generated by a vapor deposition process targeting Co or a Co alloy, or includes the scrap as a part of the raw material.

5. As refractory for furnace of vacuum melting furnace (CaO
(5) The method for refining a cobalt material according to any one of (1) to (4) above, wherein a basic refractory having a content of +90 mg% or more is used.

6. The method for refining a cobalt material according to any one of the above 1 to 5, wherein after the refining, the hot water is discharged through a refractory filter.

[0016]

The present invention will be specifically described below. In the present invention, first, cobalt is deoxidized by using the following CO reaction. In the Co system, since the activity coefficients of [% C] and [% O] are large, use of a CO reaction is considered as a crude deoxidation method in this system. Here, the deoxidation equilibrium constant at 1600 ° C. is represented by the following equation (1). [% C] × [% O] = 0.000136 Pco --- (1) Here, Pco is the CO partial pressure of the reaction system. By the way, Fe
This constant for the system is 0.0024 Pco, indicating the usefulness of CO deoxidation in the Co system.

In an actual operation, after a cobalt raw material and an amount of carbon equivalent to the stoichiometric equivalent of oxygen contained in the cobalt raw material are mixed and charged into a vacuum melting furnace, the furnace is charged. 50 to 300 Torr of inert gas such as argon gas
Enclose and dissolve the cobalt raw material while suppressing excessive CO reaction. After the cobalt raw material is completely dissolved, the furnace pressure is reduced.
0.1 to 3.0 × 10 in the molten metal as a high vacuum ^-3 Torr oxygen [%
O] is roughly deoxidized to about 0.0100 mass%. The stoichiometric equivalent refers to an amount of each constituent element that is not excessive or insufficient when a substance having a certain chemical composition is produced. In the present invention, the stoichiometric equivalent of O: 16 g and C: 12 g are used. Equivalent to equivalent.

In the above-mentioned CO deoxidation, the inert gas (argon gas) is sealed in the vacuum melting furnace in the range of 50 to 300 Torr until the cobalt raw material is completely dissolved. If the filling amount is less than 50 Torr, severe boiling occurs due to the CO reaction, while 300 T
This is because when the value exceeds orr, the above-described effect of suppressing boiling reaches saturation. The reason for setting the pressure to 300 Torr or less is also to maintain the pressure inside and outside the vacuum chamber at a pressure lower than the atmospheric pressure.

FIG. 1 shows that Pco = 0.13 atm.
(99 Torr) and Pco = 0.0 atm. (228 Torr) are substituted into the equation (1), and the calculated result is shown in comparison with the actual operation result. As is clear from the figure, if the amount of oxygen contained in the raw material (generally, 0.0100 mass% or more) is grasped in advance, crude deoxidation can be performed without the risk of deoxidizing elements remaining in the alloy. It can be performed.

Next, in the present invention, after the above-mentioned CO deoxidation,
Preferably, finish deoxidation by Si is performed. The Co-based alloy is characterized in that the activity coefficient of Si is larger than that of the Fe-based alloy and conversely, the activity coefficient of Al is smaller. In other words, it suggests that effective deoxidation is possible by adding a small amount of Si. Here, assuming that the activity of SiO ₂ is 1, Co-based Si at 1600 ° C.
The deoxidation constant is represented by the following equation (2). [% Si] × [% O] = 1.038 × 10 ⁻⁸ (2) Incidentally, this constant in the Fe system is 3.18 × 10 ⁻⁵ .

FIG. 2 shows a comparison between the theoretical value of Si deoxidation and the actual operation value. As shown, [% Si] is 0.010ma
If it is about ss%, [% O] can be reduced to 0.0010 mass% or less.

For reference, FIG. 3 shows theoretical values of Al deoxidation equilibrium similar to the above. In order to reduce [% O] to 0.0010 mass% or less, [% Al] needs to be 0.010 mass% or more. As described above, Al not only has a low deoxidizing efficiency but also forms inclusions containing a large amount of alumina (Al ₂ O ₃ ) after final solidification. Since this alumina has a high melting point and a low electrical conductivity, it disturbs the flow of dissolved electrons and causes sputtering. In contrast, in the case of Si deoxidation, silicate-based inclusions are formed after solidification, which generally have a low melting point and a relatively high electrical conductivity, so that they rarely cause spatter.

Further, according to the present invention, after the above-mentioned CO deoxidation or Si deoxidation, the temperature of the molten metal is lowered from (solidification temperature +60 to 100 ° C.) to a temperature close to the solidification temperature to remove gas components in the molten metal. (Coagulation degassing treatment) is preferably performed. When the molten metal is exposed to a high vacuum, it should be degassed in an equilibrium theory. However, in the region where the mass is already close to the equilibrium value and the amount of mass transfer is small, the C
Gas components such as O, N ₂ and H ₂ can be effectively removed from the molten metal, which is effective in obtaining a lower gas level and in shortening the processing time.

In the present invention, it is preferable to use a basic refractory having (CaO + MgO) of 90 mass% or more as a furnace refractory for a vacuum melting furnace. As suggested from FIG. 3 described above, if the deoxidation by Si is strengthened, alumina generally contained in the crucible refractory is decomposed according to the following formula (3), and into the molten Co [ % Al] and [% O]. Al ₂ O ₃ = 2 [% Al] +3 [% O] (3) Accordingly, it is advantageous to use a furnace refractory having as low an alumina content as possible. Therefore, in the present invention, a (CaO + MgO) -based basic refractory having an alumina content of less than 10 mass% is used as a preferable material as a refractory for a furnace.

As shown in Table 2, Ca having an impurity amount of 5 mass% or less
The examination result of [% O] level when the O crucible and A1 ₂ 0 ₃ was dissolved using MgO crucible containing 30 mass%, in comparison to FIG. In both cases, [% S
i] was adjusted to be 0.008 to 0.010 mass%.

[0026]

[Table 2]

As shown in FIG. 4, when the MgO crucible was used, [% Al] and [% O] were high even though Al was not added to the molten metal, and the refractory material was high. This suggests decomposition of the alumina in it.

Further, in the present invention, it is advantageous to use a refractory filter when tapping water after refining. As described above, an extremely clean molten alloy can be obtained by taking various measures during refining, but it is still difficult to completely eliminate the risk of inclusion of foreign inclusions at the time of tapping. However, after refining, the above risk can be remarkably reduced by tapping into the mold through a refractory filter.

FIG. 5 shows a conceptual diagram of a mounting place of the refractory filter. FIG. 6 shows a comparison of the results of a study on the frequency of occurrence of splash and spatter during EB dissolution when the refractory filter is used and when it is not used. As shown in the figure, even in the case where there is no refractory filter, the result is acceptable in most cases, but abnormalities such as splash and spatter sometimes occur. This suggests that some kind of disturbance has introduced foreign inclusions.

[0030]

Example 1 A production example in the case of the following component standard values will be described. C ≦ 0.0050 mass%, Si ≦ 0.015 mass%, Mn ≦ 0.020 mass
%, P ≦ 0.010 mass%, S ≦ 0.0050mass%, Cu ≦ 0.050
mass%, Ni ≦ 0.050 mass%, Cr ≦ 0.010 mass%, Fe ≦ 0.
030 mass%, Al ≦ 0.010 mass%, O ≦ 0.0050mass%, N
≦ 0.0050mass%, Mg ≦ 0.0050mass%, Bal: Co. FIG. 7 shows the operation progress of melting and refining in chronological order. The furnace used was a nominal 1 ton vacuum melting furnace. As a cobalt raw material, metal cobalt shown in Table 1a: about 50 mass
%, The same evaporation c as in Example c: about 50 mass% of the mixed material was used. The components of the furnace refractories used are as follows. Ca
O: 89.0mass%, MgO: 10.2mass %, SiO 2: 0.2 mass%
Below, other: 0.5 mass% or less. Table 3 shows the components and characteristics of the refractory filter used.

[0031]

[Table 3]

As shown in FIG. 7, the initial mounting amount is about 8
37 kg. After evacuation in the furnace, energization was started. At this time, in order to adjust intense boiling, argon was introduced together with the energization, and the inside of the furnace was maintained at about 100 Torr until complete melting.
In this example, the oxygen content in the raw material cobalt was about
It is known in advance that it is about 0.0350 mass%, and its absolute amount is 837 (kg) x 0.0350 / 100 = 0.29 kg.
Therefore, a stoichiometric equivalent of 0.22 kg of carbon was added and mixed into the raw material cobalt at the initial charging.
After complete melting, the first sampling (No. 1) was performed. As a result, the melt temperature was 1590 ° C., [% O] was 0.0080 mass%,
[% C] was 0.002 mass%. In addition, [% C]
When it exceeds 0.004 mass%, it is preferable to add a new Co raw material as an oxygen source and decarburize while adjusting the degree of vacuum in the furnace until [% C] becomes 0.0030% or less.

After sampling No. 1 and exhausting, 3 × 10 ^-3 To
rr for about 20 minutes to stabilize CO equilibrium and [% H],
[% N] was removed. In this paragraph, [% C] is approximately 0.
0020 mass% or less, [% O] is approximately 0.0020 mass% or less.

Then, Si was added to the molten metal so as to be 0.015 mass% or less, and Si deoxidation was performed. This operation has the purpose of fixing oxygen at the time of solidification after casting and has the purpose of facilitating the inevitable deoxidation product to adhere to the filter as a soft silicate. After the above-mentioned Si deoxidation, the second sampling (No. 2) was performed. As a result, [% O] was 0.0011 ma.
ss%, [% C] is 0.0012 mass%, [% Si] is 0.008 mass
%Met. After confirming the sampling result of No. 2, a small amount of [% C] adjustment and an appropriate amount of [% Si] adjustment may be performed.

Next, a so-called coagulation degassing process was carried out twice, in which the temperature of the molten metal was switched between a solidification temperature (about 1490 ° C.) and 1550 ° C. by an on / off operation of input electric power. Then, after the temperature of the molten metal was raised to the tapping temperature, Ar was introduced into the container to about 200 Torr, and after the third sampling (No. 3, ladle analysis), tapping was performed. At the time of tapping from the vacuum melting furnace to the mold, a refractory filter was used on the way to prevent mixing of internal and foreign inclusions. No.3 sampling result, [% O] is 0.00
10 mass%, [% C] is 0.0010 mass%, [% Si] is 0.007
mass%.

The ingot obtained as described above is
Table 4 shows the component results (actual values A and B) obtained by analyzing the sample obtained by rolling the sample into a round bar.

[0037]

[Table 4]

As shown in the table, by refining according to the present invention, impurities in the cobalt material could be remarkably reduced.

Example 2 Refining was carried out in the same manner as in Example 1 using the cobalt raw materials having the compounding ratios shown in Table 5, and thereafter, an ingot was obtained.
Table 6 shows the component results obtained by analyzing a sample collected from the obtained ingot.

[0040]

[Table 5]

[0041]

[Table 6]

As shown in the table, even when a low-grade material containing a relatively large amount of impurities is used as a cobalt raw material, refining according to the present invention significantly reduces impurities in the cobalt material. I was able to.

In the above, the case of refining metallic cobalt using cobalt new material and cobalt scrap as main raw materials has been mainly described. However, the cobalt material in the present invention is not limited to metallic cobalt alone. It also includes a (Co + Ni) alloy containing Ni. That is, Ni is an excellent magnetic material like Co, and is similar in physical properties. Therefore, a (Co + Ni) alloy can be suitably refined by applying the present invention.

[0044]

Thus, according to the present invention, even a cobalt raw material containing a relatively large amount of impurities such as cobalt scrap can be effectively refined to obtain a high-purity cobalt material. Further, the refining technique of the present invention is a technique which is advantageously adapted to manufacture not only a high-purity cobalt material for a target material but also a magnetic material or an electronic material containing nickel and cobalt as main components.

[Brief description of the drawings]

FIG. 1 is an equilibrium diagram of [% C] [% O].

FIG. 2 is an equilibrium diagram of Si deoxidation.

FIG. 3 is an equilibrium diagram of Al deoxidation.

Fig. 4 CaO crucible containing 5 mass% or less of impurities and A1 ₂
0 ₃ is a diagram comparatively showing [% O] level when dissolved with MgO crucible containing 30 mass%.

FIG. 5 is a schematic diagram showing a mounting location of a refractory filter.

FIG. 6 is a graph showing a comparison of the frequency of occurrence of splash and spatter during EB melting when a refractory filter is used and when it is not used.

FIG. 7 is a diagram showing the time course of the melting / smelting operation according to the present invention.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C22B 9/04 C22B 9/04 F27D 1/00 F27D 1/00 N (72) Inventor Yasuhide Ouchi Taihaku, Sendai City, Miyagi Prefecture 7-20-1, Ward Nagamachi, Tohoku Special Steel Co., Ltd. F-term (reference) in Matsushita Electric Industrial Co., Ltd. 4K001 AA07 BA22 DA05 EA02 EA03 EA06 GA14 GB11 HA01 HA02 4K051 AA05 BE03

Claims (6)

[Claims] When a cobalt material is melted and refined using a vacuum melting furnace, a cobalt raw material and an amount of carbon equivalent to a stoichiometric equivalent to the amount of oxygen contained in the cobalt raw material are introduced into the furnace. After the mixture is charged, the inside of the furnace is kept under a reduced pressure of 50 to 300 Torr filled with an inert gas until the cobalt raw material is completely dissolved, and then the furnace pressure is set to 0.1 to 3.0 × 10 ^A method for refining a cobalt material, comprising performing CO deoxidation at a high vacuum of ^-3 Torr. 2. The method according to claim 1, wherein after the CO deoxidation, Si is added within a range not exceeding 0.030 mass%, and the Si deoxidation is performed to reduce [% O] to 0.0015 mass% or less. The method for refining a cobalt material as described above. 3. A degassing treatment for lowering the temperature of the molten metal from (solidification temperature +60 to 100 ° C.) to a temperature close to the solidification temperature after the CO deoxidation or Si deoxidation to remove gas components in the molten metal is at least one step. 3. The method for refining a cobalt material according to claim 1, wherein the refining is performed once. 4. The method for refining a cobalt material according to claim 1, wherein the cobalt raw material is scrap produced by a vapor deposition process targeting Co or a Co alloy or includes the scrap as a part of the raw material. 5. As a refractory for a furnace of a vacuum melting furnace, (CaO +
The method for refining a cobalt material according to any one of claims 1 to 4, wherein a basic refractory (MgO) of 90 mass% or more is used. 6. The method for refining a cobalt material according to claim 1, wherein after the refining, tapping is performed through a refractory filter.