JP2000104128A - Method for refining aluminum and use of obtained aluminum - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for refining Al capable of efficiently reducing peritectic impurities such as Ti, V, Zr in Al and to provide Al foil for an electrolytic capacitor used with the obtd. Al as the raw material. SOLUTION: The method for refining Al is the one in which, where an elemental group M is composed of elements forming boride stabler than Al boride, an elemental group α is composed of the elements selected from Ti and Hf in the elemental group M, and an elemental group β is composed of the elements other than the elemental group α in the elemental group M, the molten metal of aluminum contg. one or more kinds of elements selected from the elemental group β and or moreover one or more kinds of elements selected from the elemental group α is mixed with the elemental group α in such a manner that X/Y (X denotes the total concn. of the atoms of the elemental group α to be added, and Y denotes the total concn. of the atoms of the elemental group β in the molten metal) is controlled to 0.2 to 100 and with B in such a manner that the quantity of the elemental group M in the molten metal is controlled to the one needed for forming hard-to-dissolve boride (MB2), and the formed hard-to- dissolved boride is separated away, and the quantity of the elemental group M is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for purifying aluminum and uses of the obtained aluminum. More specifically, a method for purifying aluminum capable of efficiently reducing elements (element group M) that form borides more stable than aluminum boride as impurities in aluminum, for example, Ti, V, Zr, and Hf. The present invention relates to an aluminum foil for an electrolytic capacitor using the obtained aluminum as a raw material.

[0002]

2. Description of the Related Art Among the group of elements M, as a method for reducing, for example, Ti and V, a so-called boron treatment for forming a hardly soluble boride by adding boron (B) and separating and removing the same is known. is there. For example, "Basic and Industrial Technology of Aluminum Materials" (Light Metal Association of Japan, 1991), page 343 states that "Ti, V is potassium borofluoride or A in molten aluminum.
In many cases, B is charged in the form of 1-B to form boride, and sedimentation and removal are often performed (boron treatment). "

However, among the group of elements M, there is an element having a low reduction efficiency because it is difficult to form a stable boride by boron treatment. For example, JP-A-59-104440 discloses that at least a main part of dissolved Ti and V impurities is insoluble (Ti, V) in the presence of a substance that acts as a flux for the (Ti, V) B ₂ complex. into contact with a sufficient amount of boron-containing materials to alter the V) B ₂ complex particles and stirring the molten aluminum, a method of removing dissolved Ti and V impurities from molten aluminum is shown, for example As described in the column, as much as 10 ppm by weight of V may remain after the boron treatment.
Needs to be reduced.

As an example of the concentration of an element group M such as V in aluminum, Japanese Patent Application Laid-Open No. 54-79462 discloses, for example, at least Ti and V as impurities in aluminum for an aluminum alloy foil for an anode of an electrolytic capacitor. 0.00001-0.001% of either element
(I.e., 0.1 to 10 ppm). JP-A-6-220561 describes that V is contained in an amount of 0.5 to 5 ppm as an impurity in aluminum for aluminum alloy foil for electrolytic capacitors having high bending strength after etching. further,
JP-A-7-169657 discloses that, as impurities in aluminum used for an aluminum alloy foil for an anode of an electrolytic capacitor, Ti: 0.1 to 1 ppm, V: 0.1 to
1 ppm and Zr: described as containing one or more of 0.1 to 1 ppm. That is,
For some applications, it is necessary to reduce the group of elements M in aluminum to below the upper limit concentration.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for purifying aluminum capable of efficiently reducing the element group M in aluminum and an aluminum foil for an electrolytic capacitor using the obtained aluminum as a raw material. Is to do. In the present invention, the element group M is composed of an element that forms a boride that is more stable than aluminum boride (for example, elements such as Ti, V, Zr, and Hf). Is defined as an element selected from Ti and Hf, and the element group β is composed of elements other than the element group α in the element group M.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, added a specific amount of Ti or Hf to a molten aluminum containing V or Zr in the element group M. It has been found that when boron treatment is performed, V or Zr in aluminum can be efficiently reduced. At this time, they have found that the element group α can be efficiently reduced at the same time, and have completed the present invention.

That is, the present invention provides the following [1] to
It relates to [3]. [1] The element group M is composed of elements that form a boride that is more stable than aluminum boride.
i, the element selected from Hf, the element group β is assumed to be composed of elements other than the element group α in the element group M, and one or more elements selected from the element group β, or from the element group α, X / Y (where X is the total atomic concentration of the element group α added, and Y is the total atomic concentration of the element group β in the molten aluminum containing one or more selected elements) ) Is from 0.2 to 100, and B is added so that the element group M in the molten metal is at least the amount necessary to produce boride (MB ₂ ). A method for purifying aluminum in which the element group M is reduced by separating and removing the boride. [2] A method for purifying aluminum obtained by repeating the method for purifying aluminum according to [1] one or more times with respect to aluminum obtained by performing the method for purifying aluminum according to [1]. [3] An aluminum foil for an electrolytic capacitor obtained by the method for purifying aluminum according to any one of the above [1] and [2], using aluminum having a concentration of the element group M of 10 ppm by weight or less as a raw material.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. In the present invention, an element (element group M) that forms a boride that is more stable than aluminum boride is defined as LB ₂ (L is in the temperature range of practical aluminum dissolution, that is, in the liquidus temperature range of aluminum to 850 ° C.). Gibbs free energy of formation of boride represented by
Represents an element smaller than that of AlB ₂ .

In the present invention, aluminum as a raw material to be purified, that is, the element group M is composed of an element that forms a boride that is more stable than aluminum boride, and the element group α is included in the element group M from Ti and Hf. The selected element, element group β is assumed to be composed of elements other than element group α in element group M, and one or more elements selected from element group β, or an element selected from element group α, In an aluminum melt containing at least one type, an element group α is added to X / Y (where X is an element group α
Indicates the total atomic concentration of the element group β, and Y indicates the total atomic concentration of the element group β in the molten metal. ) Is 0.2 to 100.
Note that the unit of the total atomic concentration here is atomic ppm. For elements less than 1.0 ppm by weight, 0 weight p
pm and the sum is calculated. If X / Y is less than 0.2, it is difficult to efficiently reduce the element group β. When X / Y exceeds 100, the reduction efficiency of the element group β does not increase any more, and the cost increases and there is no economic merit. X / Y is 1.0
When the element group α is added so as to be 100, the element group β
Can be more efficiently reduced.

The element group α is added so that X / Y becomes 1.0 to 100, and the element group α with respect to V in the element group β is added.
When Ti and / or Hf is selected as the element group, or when Hf is selected as the element group α with respect to Zr in the element group β, the reduction efficiency of the element group β is high, and specifically, the element group β Can easily be reduced to 2 ppm by weight or less.

In the present invention, the element group α is added to the molten aluminum. However, as shown in the embodiment of the present invention, the added element group α can be efficiently reduced at the same time. The present invention can also be applied to a molten aluminum that originally contains the element group α. For example, molten aluminum containing (V + Ti), (Zr + Ti), (V + Zr + Ti), (V + Hf), (Zr + Hf), (V + Zr + Hf), or (V + Zr + Ti + Hf) can be used. The total atomic concentration (X ′) of the element group α originally contained in the molten aluminum is not particularly limited. However, in the molten aluminum of X ′ ≦ Y, the purification efficiency of the element group β in the molten aluminum is even higher. It will be. The method of adding the element group α is not particularly limited. For example, a method of mixing with the aluminum containing the element group α in a relatively large amount, a metal simple substance of the element group α, a compound containing the element group α, or an Al-element group There is a method of adding an α alloy.

Further, in the present invention, the element group M in the molten aluminum containing the added element group α is in an amount (= theoretical B amount) required to produce a hardly soluble boride (MB ₂ ). B is added as described above. Here, the theoretical B amount means that the element group M in the molten metal is TiB ₂ and V
It represents the amount of B necessary to produce a diboride such as B ₂ .
If the B addition amount is less than the theoretical B amount, it is difficult to efficiently reduce the element group M. The upper limit of the amount of B added is not particularly limited. The higher the amount of B added, the higher the reduction efficiency of the element group M. However, the concentration of B remaining after the treatment increases at the same time. , So that the B concentration is below the allowable B concentration for aluminum
It is preferable to control the amount added. However, when B can be reduced by performing segregation purification of aluminum at the same time as or after the B treatment, B can be added in consideration of this effect. When B is contained in aluminum in advance, B can be added in consideration of the content. The method of adding B is not particularly limited. For example, a method of mixing with aluminum containing a relatively large amount of B, a method of adding metallic boron, a boron compound such as potassium borofluoride, or an Al-B alloy are used. No.

In the present invention, the conditions for adding the element groups α and B are not particularly limited as long as the added element groups α and B are dissolved in the molten aluminum. Taking the addition of Ti as an example, using aluminum containing 100 wt ppm to 10 wt% of Ti, 680
A method of dissolving in the molten metal at a temperature of from 680 ° C. to 850 ° C. using aluminum containing 100% by weight to 5% by weight of B.
A method of dissolving in 0 minutes to 5 hours can be adopted. Mechanically stirring the molten metal after the addition of the element groups α and B,
This has an effect of accelerating dissolution / diffusion of an additive element and boride formation, and is a preferred embodiment in the present invention.

In the present invention, the temperature of the molten metal at the time of separating and removing the hardly soluble boride formed from the molten aluminum is not particularly limited as long as it is within a practical aluminum melting temperature range. In order to efficiently reduce the temperature, it is preferable that the temperature of the molten metal be higher than the liquidus temperature of the molten metal and 800 ° C. or less. When the temperature of the molten metal is lower than the liquidus temperature, a solidified phase is formed in the molten metal, and a boride is taken into the solidified phase. In some cases, the formed hardly soluble boride cannot be separated and removed. In addition, the molten metal temperature is 800
If the temperature is higher than ℃, it may be difficult to efficiently reduce the element group M. The temperature of the molten metal at the time of separating and removing the formed hardly soluble boride from the molten metal is more preferably higher than the liquidus temperature of the molten metal, and 750 ° C. or lower, more preferably lower than the liquidus temperature of the molten metal. High and 700 ° C
It is as follows.

In the present invention, the element group β is the element group M
Among them, elements other than the element group α are included. Among them, an element selected from the group IVa, Va, or VIa of the periodic table, particularly an element selected from V and Zr, has a large reduction efficiency according to the present invention. The present invention can be applied to an aluminum melt containing at least one element group β alone in an amount of 2 ppm by weight or more. The upper limit of the concentration of the element group β is not particularly limited. However, when at least one kind of the element group β is independently contained in an amount of 30 ppm by weight or more, the method according to the present invention may be repeated twice or more to obtain a trace amount of the element. The group β can be reduced. That is, by repeating the method for purifying aluminum according to [1] one or more times with respect to aluminum obtained by performing the method for purifying aluminum according to [1], the element group can be reduced to a trace amount. β can be reduced. At this time, in the second and subsequent purifications, it is preferable to set the temperature of the molten metal at the time of separating and removing the hardly soluble boride lower than the temperature of the molten metal performed in the previous purification.

Next, the method of separating and removing the hardly soluble boride generated from the molten aluminum is not particularly limited. However, since the hardly soluble boride generated has a higher specific gravity than the molten aluminum, it is most easily used. Spontaneous settling and separation of the boride by allowing the molten metal to stand can be employed. For example, after adding and dissolving the element groups α and B, the molten aluminum is adjusted to 1 to 1
For example, a method of collecting the supernatant of the molten metal after settling for 00 hours, or a method of solidifying the molten aluminum once for 1 to 100 hours and then solidifying the molten metal and removing a portion containing boride by cutting or the like. No. Other methods for separating and removing the boride include centrifugal separation using centrifugal force, flotation separation by blowing gas into molten aluminum, filtration separation using a fire-resistant filter, or a combination of two or more of these. A method can be adopted.

Further, even if the method for purifying aluminum of the present invention is carried out in combination with a method for purifying aluminum by segregating and purifying the aluminum by generating a relative velocity between the solidified aluminum and the molten aluminum, it is difficult to remove the aluminum from the purified aluminum. Can be separated and removed.

The aluminum obtained by the method of the present invention, in which the element group M is reduced, can be used as a usual electrolytic capacitor foil, sputtering target, hard disk substrate,
It can be used as a raw material for superconducting stabilizers, bonding wires, etc. Among them, it can be suitably used for foil for electrolytic capacitors.

The aluminum obtained by the method of the present invention, in which the element group M is reduced, is used, for example, in the case of foil for an electrolytic capacitor, when the element group M is 10 wt ppm.
The following are preferred, and the element group M is more preferably 5 ppm by weight or less, and most preferably the element group α, V, and Zr are 2 ppm by weight or less and the concentration of the other element group M is less than 5 ppm. Each is 5 ppm by weight or less, and can be easily achieved by the purification method of the present invention.

The method for processing the foil for electrolytic capacitors may be in accordance with a usual method. For example, "Basic and industrial technology of aluminum material" (Light Metal Association of Japan, 1991)
As described in pages 347-350 of the year, a method of processing into a foil for an electrolytic capacitor through steps such as slab casting, hot rolling, cold rolling, and foil rolling can be adopted.

[0021]

EXAMPLES Next, the purification method of the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. In the present invention, the analysis of impurities in aluminum used as the T raw material was performed by GDMS (VG Microt).
race (United Kingdom) VG9000). The analysis of impurities in aluminum after the treatment
The i, V, Zr, and B concentrations were measured using an emission spectrometer (CQM-75 manufactured by Shimadzu Corporation), and the Hf concentration was measured using an IC.
P-AES [manufactured by Seiko Denshi Kogyo KK, SPS120
0VR].

Examples 1 to 5 2 kg of raw aluminum containing impurities described in Table 1 was
It was melted in a graphite crucible (inner diameter 100 mmΦ) using an electric furnace. Argon gas was flowed into the atmosphere at 4 l / min.
An aluminum mother alloy (made on the basis of 5N Al) containing about 1000 ppm by weight of Ti or Hf was added so that the element group α had the concentration shown in Appendix 1 at a melt temperature of 750 ° C. The calculated X / Y (where X represents the total atomic concentration of the element group α and Y represents the total atomic concentration of the element group β in the molten metal) was 0.3 to 13 (element). In group M, <
1.0 ppm by weight is calculated assuming 0 ppm by weight). At a molten metal temperature of 820 ° C., B was changed to Al-4 so that the element group M in the molten metal became an amount necessary for generating MB ₂ or more.
% B master alloy was added, and the melt was stirred several times using a graphite bar every 30 minutes, and melted at the melt temperature for 2 hours. Thereafter, the temperature of the molten metal was lowered to the settling temperature shown in Table 1 and then settled for 15 hours, and the formed boride particles were settled and separated. The calcined melt was taken out of the furnace together with the graphite crucible to solidify the melt. The molten metal was taken out of the furnace and it took about 5 minutes for the molten metal to solidify completely. After settling, the solidified sample was cut horizontally 1 cm above the bottom from the bottom, and the cut surface was subjected to elemental analysis. The amount of impurities after the boron treatment is shown in Table 1. As shown in Table 1, the content of the element group M was efficiently reduced, and the residual amount was 10 ppm by weight or less.

Comparative Examples 1 and 2 2 kg of raw aluminum containing the impurities described in Table 1 was
It was melted in a graphite crucible (inner diameter 100 mmΦ) using an electric furnace. Boron treatment was performed by the method described in the example, except that the element group α was not added. After settling, the solidified sample was cut horizontally 1 cm above the bottom from the bottom, and the cut surface was subjected to elemental analysis. The amount of impurities after boron treatment is shown in Table 1. The element group M was not reduced, or remained at 10 ppm by weight or more even if it was reduced.

Table 1 shows the conditions of the above Examples and Comparative Examples and the obtained results. Note that the concentrations of the element groups M not described in the table are all less than 1.0 ppm by weight.

[0025]

[Table 1]

Heretofore, among the impurity elements in aluminum, there are elements that are difficult to reduce efficiently in the element group M, and as shown in Comparative Examples 1 and 2, The element group M was not reduced by the ordinary boron treatment, or a relatively large amount of the element group M remained after the boron treatment. On the other hand, according to the purification method of the present invention shown in Examples 1 to 5, it can be seen that the element group M can be efficiently reduced.

[0027]

According to the present invention, T in aluminum
elements that form borides more stable than aluminum boride, such as i, V, and Zr, can be efficiently reduced;
The aluminum obtained by purification according to the present invention can be used as a raw material for foil for electrolytic capacitors, sputtering targets, hard disk substrates, superconducting stabilizers, bonding wires, and the like. Among them, it can be suitably used for foil for electrolytic capacitors.

Claims (9)

[Claims] An element group M is composed of an element that forms a boride more stable than aluminum boride. An element group α is an element selected from Ti and Hf in the element group M, and an element group β is an element group of the element group M. In the molten aluminum containing at least one element selected from the element group β, or at least one element selected from the element group α, the element group α , X / Y (where X represents the total atomic concentration of the element group α and Y represents the total atomic concentration of the element group β in the molten metal), and 0.2 to 100, and B is added so that the amount of the element group M in the molten metal is equal to or more than that necessary for generating a boride, and the generated boride is separated and removed to reduce the element group M. Purification method. 2. The method for purifying aluminum according to claim 1, wherein X / Y is 1.0 to 100. 3. The method for purifying aluminum according to claim 1, wherein the temperature of the molten metal at the time of separating and removing the formed boride is higher than the liquidus temperature of the molten metal and 800 ° C. or less. 4. The method for purifying aluminum according to claim 1, wherein the element group α is an element of Ti alone. 5. The method for purifying aluminum according to claim 1, wherein the element group α is an element of Hf alone. 6. The method for purifying aluminum according to claim 1, wherein the element group β is an element selected from the group IVa, Va and VIa. 7. The method for purifying aluminum according to claim 1, wherein the element group β is an element selected from V and Zr. 8. The method for purifying aluminum obtained by performing the method for purifying aluminum according to claim 1 to 7, wherein the method for purifying aluminum is further repeated one or more times. Characteristic method of refining aluminum. 9. An aluminum for an electrolytic capacitor, characterized by using, as a raw material, aluminum having a concentration of the element group M of not more than 10 ppm by weight, obtained by the method for purifying aluminum according to claim 1. Foil.