JPH11302751A - Method for refining aluminum and its application - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently refining aluminum by crystallizing the aluminum of a higher purity from molten aluminum contg. eutectic impurities, such as Si and Fe, and others by utilizing the principle of segregation. SOLUTION: This method for refining the aluminum consists in crystallizing and growing the refined aluminum on the outer peripheral surface of a cooling body provided with a gap between the outer peripheral surface of the cooling body internally having a cooling medium passage and the cooling medium passage in this cooling body by immersing the cooling body described above into the molten aluminum in such a manner that the top end of the gap exists above the surface of the molten aluminum and that the bottom end thereof exists at a place not affected with the temp. of the atmosphere above the molten aluminum surface and passing a cooling medium in the cooling medium passage within the cooling body while relatively displacing the outer peripheral surface of the cooling body and the molten aluminum, thereby cooling the cooling body in such a manner that the temp. of the outer peripheral surface of the cooling body below the surface of the molten aluminum is lower than the liquidus temp. of the molten aluminum. Aluminum foil for an electrolytic capacitor is formed by using the refined aluminum obtd. by this method as raw material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for purifying aluminum. Specifically, using the segregation principle, Si,
The present invention relates to a method for efficiently purifying aluminum by crystallizing higher-purity aluminum from molten aluminum containing eutectic impurities such as Fe and the like.

[0002]

2. Description of the Related Art Heretofore, as a method of purifying aluminum using the principle of segregation, a cooling body is immersed in molten aluminum, and the cooling body is rotated while supplying a cooling medium inside the cooling body. A method of crystallizing high-purity purified aluminum on the outer peripheral surface is known.

In a purification method using the segregation principle,
Refining efficiency is improved by removing the concentrated layer of impurities discharged into the molten aluminum near the solidification interface as much as possible, and by dispersing the impurities throughout the molten aluminum, the purification efficiency is improved. In order to achieve this, a method has been proposed in which the relative velocity between the crystallized aluminum and the molten aluminum is increased to enhance the effect of washing away the concentrated impurities into the molten aluminum containing less impurities. In Japanese Patent Publication No. 61-3385, the concentrated layer of impurities near the solidification interface is formed by rotating the cooling body so that the relative speed between the outer peripheral surface of the cooling body and the molten aluminum is 1600 mm / s to 8000 mm / s. It has been proposed to reduce the thickness and increase the purity of the purified aluminum. In this method, since the molten aluminum is radiated upward under the influence of the outside air, the temperature of the molten aluminum near the surface of the molten aluminum is lower than that of the other parts, and the temperature of the molten aluminum on the outer peripheral surface of the cooling body near the surface of the molten aluminum is reduced. Is easy to crystallize aluminum, and as a result, the crystallization speed of aluminum in this part becomes faster than the crystallization speed of aluminum in other parts of the outer peripheral surface of the cooling body. The purity is lower than the purity of aluminum crystallized on other portions of the outer peripheral surface of the cooling body.

[0004] In order to prevent such a decrease in refining efficiency, Japanese Patent Publication No. 59-45739 discloses a method for preventing the aluminum from crystallizing on the outer peripheral surface of a cooling body near the molten aluminum surface. A cylindrical cooling body in which the part in contact with and its vicinity is covered with a heat insulating material, the upper edge of the heat insulating material is located above the surface of the molten aluminum and the lower edge is not affected by the temperature of the outside air in the molten aluminum It has been proposed to immerse the cooling body in molten aluminum so that it is in position.

[0005]

In this method, however, the heat insulating material must be connected to the cooling body.
Generally, the heat insulating material is porous, the material itself is brittle, and the strength is not sufficient. In addition, relatively high-density ceramic materials such as alumina and silicon nitride have high strength, but the heat insulating effect is not always sufficient. An object of the present invention is to provide a more efficient method for purifying aluminum which has solved the above problems.

[0006]

Means for Solving the Problems The inventors of the present invention have made intensive studies in such a situation, and as a result, by providing a gap between the outer peripheral surface of the cooling body and the cooling medium flow passage inside the cooling body,
The present inventors have found a method for purifying aluminum with sufficiently improved cooling body strength and extremely high purification efficiency, and completed the present invention.

That is, the present invention provides (1) a cooling body having a gap between an outer peripheral surface of a cooling body having a cooling medium flow passage therein and a cooling medium flow passage inside the cooling body. It is immersed in the molten aluminum so that the upper end is located above the surface of the molten aluminum and the lower end is located at a position above the surface of the molten aluminum that is not affected by the temperature of the atmosphere. By flowing the cooling medium through the cooling medium flow passage inside the cooling body while relatively displacing the aluminum, the temperature of the outer peripheral surface of the cooling body below the surface of the molten aluminum becomes lower than the temperature of the molten aluminum. A method of purifying aluminum by cooling to a temperature lower than the phase line temperature to crystallize and grow purified aluminum on the outer peripheral surface of the cooling body; and (2) the method of (1) above. The purified aluminum, which is relate aluminum foil, electrolytic capacitor used as the raw material. Hereinafter, the present invention will be described in detail.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the method of the present invention, a cooling body is immersed in molten aluminum, and while the outer peripheral surface of the cooling body and the molten aluminum are relatively displaced, the cooling body is located below the surface of the molten aluminum. Cooling is performed so that the temperature of the outer peripheral surface of the cooling body is lower than the liquidus temperature of the molten aluminum, and purified aluminum is crystallized and grown on the outer peripheral surface of the cooling body, thereby producing higher-purity aluminum. obtain. The cooling body is provided with a gap between a portion of the outer peripheral surface in contact with the surface of the molten aluminum and the vicinity thereof, and a cooling medium flow passage inside the cooling body. The presence of the voids suppresses the heat conduction in the horizontal direction (toward the center of the cooling body) in the cooling body, and as a result, the cooling medium is not affected by the temperature of the atmosphere on the surface of the molten aluminum. The cooling of the part in contact with the surface of the molten aluminum on the outer peripheral surface of the cooling body and its vicinity is suppressed, so that the aluminum in the part in contact with the surface of the molten aluminum and its vicinity hardly crystallizes, and even if it crystallizes, The crystallization speed is lower than that of aluminum crystallized in other parts in aluminum. The aluminum crystallized in this portion does not have a lower purity than the aluminum crystallized in other portions in the molten aluminum.

In the present invention, the presence of the voids suppresses the horizontal heat conduction in the cooling body at and near the portion in contact with the surface of the molten aluminum.
There is no need to connect porous insulation to the cooling body. For this reason, it is possible to solve the problem that the heat insulating material is peeled off by the movement of the cooling body or the flow of the molten aluminum, or the heat insulating material itself is cracked.

In the present invention, the cooling body may be any material as long as it has a relatively high thermal conductivity.
Steel, silicon carbide, silicon nitride, aluminum nitride, graphite and the like can be used. Graphite is preferred because it does not contaminate the molten aluminum.

In the present invention, the space may be filled with a gas or a vacuum. The gas filling the void is not particularly limited as long as the gas has a smaller thermal conductivity than the constituent material of the cooling body, and air, argon gas,
Gases such as nitrogen gas and carbon dioxide gas are preferable because they have extremely low thermal conductivity than the material of the cooling body and thus have an excellent heat insulating effect. If the gap is in a vacuum state, higher effects can be expected.

A cooling medium flow passage is provided inside the cooling body, through which air, argon gas, nitrogen gas, water, steam, etc., and a mixture thereof are passed to cool the outer peripheral surface of the cooling body. I do.

In the present invention, as a method of relatively displacing the outer peripheral surface of the cooling body and the molten aluminum, any method other than the method of rotating the cooling body as described above is possible. For example, a method in which the cooling body is stationary and the molten aluminum is swirled around the cooling body, a method in which the cooling body is rotated and the molten aluminum is swirled in the opposite direction or in the same direction at a different speed, and the cooling body is horizontally moved in the molten aluminum. A method of vibrating in the vertical or vertical direction is possible. Next, the details of the present invention will be described with reference to the drawings.

The first device is shown in FIG. The cooling body has a cylindrical shape, and a gap is provided between an outer peripheral surface of the cooling body and a cooling medium flow passage inside the cooling body. When the cooling body is immersed in the molten aluminum, the outer diameter of the cooling body corresponding to the portion in contact with the surface of the molten aluminum and the vicinity thereof is smaller than the outer diameter of the portion where aluminum is crystallized, and the outside thereof is cylindrical. The void is provided by covering with a sleeve. A cooling medium introduction pipe having a cooling medium outlet at the end is inserted into the cooling medium flow passage inside the cooling body. The cooling body is immersed in the molten aluminum such that the upper end of the void is located above the surface of the molten aluminum and the lower end is located below the surface of the molten aluminum. While rotating the cooling body, a cooling medium is supplied into the cooling body from the cooling medium blowing port at the tip through the cooling medium introduction pipe, and the temperature of the surface of the cooling body is lower than the liquidus temperature of the molten aluminum. And refined aluminum is crystallized and grown on the surface of the cooling body. After cooling for a predetermined time, high-purity aluminum crystallized on the cooling body is recovered.

FIG. 2 shows a second apparatus. The apparatus shown in FIG. 2 is the same as the apparatus shown in FIG. 1 except that the method of setting a gap between the outer peripheral surface of the cooling body and the cooling medium flow passage inside the cooling body is different. In this apparatus, when the cooling body is immersed in molten aluminum, a number of vertical holes are formed between a portion of the outer peripheral surface of the reject body in contact with the surface of the molten aluminum and the vicinity thereof and the cooling medium flow passage inside the cooling body. The void is provided by emptying.

The gap of the cooling body in FIG. 1 is intentionally provided by a sleeve, and the gap of the cooling body in FIG. 2 is a gap formed without providing a sleeve. The case is also included in the present invention. The cooling body used in the present invention may be of any shape,
For example, the cylindrical shape shown in FIGS. 1 and 2 can be used. FIG. 3 shows another example of the shape of the cooling body that can be used in the present invention. Cylindrical shape a with upwardly tapered cylinder a, cylindrical shape b with downward spread, cylindrical shape c with upper portion spread downward and taper with upper portion spread upward, cylindrical shape with upper portion expanded and tapered lower portion Although d and polygonal columnar shapes e can be used, they are not necessarily limited to these. Also, even if the properties of the outer peripheral surface of the cooling body are smooth,
There may be uneven portions. The irregularities here are vertical grooves,
The term refers to an annular groove, a spiral groove, a large number of dents, irregularities due to oxidation consumption, a rough surface formed by a roughening treatment, a combination thereof, and the like formed on the entire circumference.

In the apparatus used in the present invention, the method of setting the gap and the shape of the gap are not necessarily limited to the above examples, and the heat conduction in the horizontal direction in the cooling body is suppressed, and If it is difficult to crystallize aluminum in and around the portion of the outer peripheral surface that is in contact with the surface of the molten aluminum, and even if it is crystallized, if the crystallization speed is lower than that of aluminum crystallized in other parts of the molten aluminum, any installation is possible. It may be a method.

In the present invention, the thickness of the void portion is a thickness that suppresses heat conduction in the horizontal direction in the cooling body, and varies depending on the material used for the cooling body.
Preferably it is 0.5 mm or more. When the gap is formed by a sleeve, the material used for the sleeve does not contaminate the molten aluminum and any material having high strength can be used. For example, graphite, silicon carbide, silicon nitride, aluminum nitride , Alumina and the like. Further, the sleeve may be made of the same material as the cooling body.

Further, if the thermal conductivity of the sleeve is smaller than the material of the cooling body, a higher effect of suppressing the heat conduction in the horizontal direction can be expected. Conversely, if the thermal conductivity of the sleeve is larger than the material of the cooling body, the effect of suppressing the horizontal heat conduction is reduced, so that it is necessary to increase the thickness of the gap.

In the cooling body of the present invention, the depth of the gap from the surface of the molten aluminum is reduced by the presence of the gap, so that the heat conduction in the horizontal direction (toward the center of the cooling body) in the cooling body is suppressed. It is sufficient that the temperature is not affected by the temperature of the atmosphere on the surface of the molten aluminum, and it depends on the size and material of the apparatus.
/ 2.

The refined aluminum obtained by the method of the present invention is described, for example, in "Basics and Industrial Technology of Aluminum Materials".
As described on pages 347 to 350 of the Japan Light Metal Association, the aluminum foil is processed into aluminum foil for electrolytic capacitors through processes such as slab casting, hot rolling, cold rolling, and foil rolling.

[0022]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples.

Example 1 This example was performed using the apparatus shown in FIG. The cooling body and the sleeve were made of graphite, and air was used as a cooling medium. The cooling body is provided with a gap of 1 mm in thickness and 11 cm in length, and is made of stainless steel so as to be in contact with the wall surface of the cooling medium flow passage inside the cooling body in order to prevent the inside of the cooling body from being consumed by the cooling medium. An inner tube was provided. 240m inside diameter
0.022w Si as an impurity in a graphite crucible
The molten aluminum containing 0.1% by weight of Fe and 0.034% by weight of Fe was charged and heated and maintained at 665 ° C. by a heater. Then, a cooling body having an outer diameter of 100 mm is immersed in the gap at a depth of 6.
It is immersed in molten aluminum so as to have a diameter of 5 cm, and a cooling medium is supplied to the inside of the cooling body through a cooling medium introduction pipe through a blowing outlet at a tip, and the cooling body is rotated at a rotation speed of 450 r.
Rotated at pm. The sleeve did not come off or break during rotation of the cooling body. After cooling for 20 minutes, the cooling body was pulled out of the molten aluminum. The aluminum crystallized on the cooling body had the shape shown in FIG. Did not crystallize. When the concentration of the impurity element in the aluminum crystallized on the outer peripheral surface of the cooling body was measured, it was found that Fe was present in the portion in contact with the surface of the molten aluminum and in the vicinity thereof, and in any other portion of the molten aluminum except for the above.
0.0013 wt% and 0.0033 wt% of Si.

COMPARATIVE EXAMPLE This comparative example was performed under the same conditions as in the above embodiment except that a cooling member having no gap between the outer peripheral surface of the cooling member and the cooling medium flow passage inside the cooling member was used. . The shape of the obtained aluminum was as shown in FIG. 5, and aluminum was crystallized in a portion of the outer peripheral surface of the cooling body that was in contact with the surface of the molten aluminum and in the vicinity thereof. When the concentration of the impurity element in the aluminum crystallized on the outer peripheral surface of the cooling body was measured, in the portion in contact with the surface of the molten aluminum and in the vicinity thereof, Fe 0.0033 wt%, Si 0.0045
wt%, in other parts of the molten aluminum, Fe 0.0023 wt%, Si 0.00
It was 38 wt%.

As is evident from the results shown above,
According to the present invention, an outer peripheral surface of a cooling body having a cooling medium flow passage therein, and a cooling body provided with a gap between the cooling medium flow passage inside the cooling body, the upper end of the gap is formed of molten aluminum. Immersed in the molten aluminum such that it is located above the surface and the lower end is located below the surface of the molten aluminum, while relatively displacing the outer peripheral surface of the cooling body and the molten aluminum, The cooling medium is cooled so that the temperature of the outer peripheral surface of the cooling body below the surface of the molten aluminum is lower than the liquidus temperature of the molten aluminum by flowing a cooling medium inside. By purifying aluminum by crystallizing and growing purified aluminum, extremely high-purity aluminum can be obtained. On the other hand, as in the comparative example, a cooling body having no gap between the portion in contact with the surface of the molten aluminum on the outer peripheral surface of the cooling body and the vicinity thereof and the cooling medium flow passage inside the cooling body was used. in case of,
The purity of the resulting aluminum is low. In addition, compared with a cooling body (JP-B-59-45739) in which a portion of the outer peripheral surface in contact with the surface of the molten aluminum and the vicinity thereof are covered with a heat insulating material, the structure of the surface of the cooling body is simpler in structure. In addition, it is excellent in strength, for example, a material having sufficient strength can be used.

[0026]

According to the present invention, while operating stably from molten aluminum containing eutectic impurities such as Si and Fe,
Aluminum can be purified by efficiently crystallizing high-purity aluminum. The obtained high-purity aluminum is suitably used for foil for electrolytic capacitors, sputtering targets, substrates for hard disks, superconducting stabilizers, bonding wires, and the like.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an apparatus according to an embodiment of the present invention, and a horizontal sectional view of a portion where a gap exists.

FIG. 2 is a longitudinal sectional view of one embodiment of a cooling body according to the present invention,
FIG. 4 is a horizontal sectional view of a portion where a gap exists.

FIG. 3 is an example of a shape of a cooling body that can be used in the present invention.

FIG. 4 is a view illustrating the shape of aluminum crystallized on a cooling body in an example of the present invention.

FIG. 5 is a diagram illustrating the shape of aluminum crystallized on a cooling body in a comparative example of the present invention.

Claims (2)

[Claims] 1. A cooling body having a gap between an outer peripheral surface of a cooling body having a cooling medium flow passage therein and a cooling medium flow passage inside the cooling body, wherein the upper end of the gap is higher than the surface of the molten aluminum. Immersed in the molten aluminum so as to be located above and at a position where the lower end is below the surface of the molten aluminum and is not affected by the temperature of the atmosphere above the surface of the molten aluminum; The cooling medium flows through the cooling medium flow passage inside the cooling body while relatively displacing the molten aluminum and the molten aluminum, so that the temperature of the outer peripheral surface of the cooling body below the surface of the molten aluminum becomes lower than the molten aluminum. Cooling to a temperature lower than the liquidus temperature of the above, and crystallizing and growing the purified aluminum on the outer peripheral surface of the cooling body. 2. An aluminum foil for an electrolytic capacitor using purified aluminum obtained by the method according to claim 1 as a raw material.