JP3463343B2 - Manufacturing method of aluminum - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing aluminum having a very low sodium content. More specifically, it relates to a method for producing aluminum having an extremely low sodium content by adding a specific amount of phosphorus and / or a phosphorus compound to molten aluminum and stirring the mixture.

[0002]

2. Description of the Related Art Usually, in an aluminum ingot obtained by a primary electrolysis without special treatment, non-metallic inclusions such as aluminum oxide and magnesium oxide, hydrogen gas, and other trace amounts such as sodium and potassium are contained. Contains metallic impurities. However, these non-metal inclusions, hydrogen gas, or trace metal impurities are contained in the ingot obtained by the aluminum ingot containing these impurities, or the product obtained by using this ingot as a material, depending on the purpose of use. However, it causes a serious defect.

For example, hydrogen gas causes pores in the ingot, which adversely affects the mechanical properties such as a decrease in tensile strength and yield strength of the ingot containing the pores and the processed product thereafter. Non-metallic inclusions such as aluminum oxide and magnesium oxide generate linear defects called stringers on the rolled surface of the wrought ingot, and in the subsequent surface treatment, color defects and streak defects after anodizing occur. Cause. It is also said that sodium promotes embrittlement due to intergranular cracking, that is, so-called high-temperature embrittlement, in a temperature range of 200 ° C to 400 ° C of a high-concentration Al-Mg-based alloy containing about 5% by weight or more of magnesium. .

In the ultra-high-purity aluminum (aluminum purity of 99.999% by weight or more) used as a wiring material for ICs and LSIs in the semiconductor industry which has been developing remarkably in recent years, alkali metals such as sodium and potassium are used. Is ppb due to the drawbacks such as causing a defective insulating film.
In some cases, products at a level (ppb is 10 ^-7 % by weight) are required.

Therefore, it is necessary to remove these undesirable impurities in advance before ingot casting. As a method for removing these impurities, for example, non-metallic inclusions such as hydrogen gas, aluminum oxide, and magnesium oxide are disclosed in Japanese Patent Publication No.
As disclosed in Japanese Patent Laid-Open No. 53934, under the atmosphere of dry air, molten aluminum is blown in an inert gas such as chlorine gas or argon gas in a molten state in a molten metal treatment tank, or a ceramic filter is combined. It is known that it can be effectively removed by the treatment method of 1) and has been industrially put to practical use.

As a method for removing sodium in aluminum of ordinary purity, the method of blowing chlorine gas into molten aluminum and the method of treating molten metal for removing non-metallic inclusions such as hydrogen gas and aluminum oxide are directly adopted. As a secondary effect, sodium is removed, but at most, it is several ppm as the concentration in molten aluminum.
The current situation is that the level has been achieved only (ppm is 10 ⁻⁴ wt%).

On the other hand, US Pat. No. 3,737,303 and US Pat. No. 3,737,304 propose a method for removing a trace amount of sodium, but a special molten metal treatment tank is required, and chlorine gas and an inert gas are used as a treatment gas. Need two kinds of. Further, unless the molten metal treatment is continuously performed, that is, while the casting is not performed, it is necessary to heat and keep the molten aluminum in the treatment tank so that it does not solidify. Not the way.

Further, in Japanese Patent Laid-Open No. 52-128815, molten aluminum having a temperature of 780 ° C. or higher is
A method of removing sodium in molten aluminum is disclosed which flows through a deposited layer of particulate matter at least partially of carbon. However, even in this method, it is necessary to keep the deposited layer of the granular material heated while the molten aluminum is not treated, and the deposited material is oxidatively consumed, which is not an economical method.

On the other hand, as a method for obtaining ultra-high-purity aluminum as a wiring material for ICs and LSIs, high-purity aluminum refined by a three-layer electrolysis method is used as a starting material, and is treated by a segregation method or a melting and refining method. A method for removing trace elements in aluminum has been put into practical use. However, with this method, potassium and calcium can be effectively removed, but sodium at most 10 to 30 ppb
It is up to the level of (0.01 to 0.03 ppm), and it is not possible to meet the requirement of the raw material aluminum whose sodium content is about several ppb level due to the tendency of the wiring width to become extremely fine with the recent increase in the degree of integration. .

[0010]

In view of such circumstances, in view of the above circumstances,
The present inventors have conducted a simple and economical method for primary electrolysis without using a special treatment device such as a deposited layer of granular objects or a ceramic filter, or using a large amount of highly toxic chlorine gas. Purity obtained by the method 9
Aluminum of 9.0% by weight or more of normal purity (usually 10
The sodium concentration after the treatment is 1 ppm or less and the high-purity aluminum having a purity of 99.95% by weight or more is used as the raw material even when the raw material is (containing about 50 ppm of sodium). Is 10p
As a result of extensive studies to find a method for producing aluminum having a pb or less, the present invention has been completed.

[0011]

That is, according to the present invention, phosphorus and / or a phosphorus compound are converted into phosphorus atoms in terms of phosphorus atom to molten aluminum having a purity of 99.0% by weight or more which is dissolved and retained.
Another object of the present invention is to provide a method for producing aluminum having a sodium content of 1 ppm or less, which comprises adding 005% by weight to 0.05% by weight and stirring the mixture.

The method of the present invention will be described in more detail below.
In carrying out the method of the present invention, the raw material aluminum ingot used is an aluminum ingot obtained by a primary electrolysis method with a purity of 99.0% by weight or more, or these ingots are refined by a segregation method, or a three-layer electrolysis method. Purified by
High-purity aluminum of 9.95% by weight or more can be used.

The raw aluminum ingot is heated to about 700 ° C. to about 800 ° C., preferably about 720 ° C. in a melting furnace or a holding furnace.
To about 780 ° C., and holds phosphorus and / or a phosphorus compound in the molten aluminum in terms of phosphorus atoms in an amount of about 0.005 wt% to about 0.05 wt%, preferably about 0.007 wt% to about 0.04% by weight, more preferably about 0.01% to about 0.03% by weight, is added and stirred. The melting furnace referred to here may be any furnace as long as it has a means capable of melting the solid aluminum ingot as a raw material, and like the holding furnace, so as not to solidify the molten aluminum after melting, Any furnace may be used as long as it is provided with a means capable of maintaining the temperature of molten aluminum in its liquid phase state, and any of the furnaces is made of a refractory material,
The shape, size and dissolution means are not limited. Of course, a furnace having both functions of melting and holding furnace may be used.

In the present invention, when the amount of phosphorus added to the molten aluminum is less than about 0.005% by weight, the desired sodium removal effect cannot be obtained, while about 0.05
If the amount is more than 10% by weight, not only the effect corresponding to the added amount is not exhibited, but also a large amount of unreacted phosphorus remains in the molten aluminum after the treatment. The temperature of the molten aluminum to be subjected to the phosphorus treatment is not particularly limited as long as the aluminum is in the molten state, but it is about 7 from the viewpoint of the reactivity between the added phosphorus and the sodium present in the molten aluminum.
The temperature is not lower than 00 ° C, more preferably not lower than about 720 ° C. On the other hand, when the temperature of the molten aluminum becomes too high, the upper limit is not only that the added phosphorus burns violently, resulting in a large addition loss, but also the molten aluminum itself is in the furnace. Since it reacts with oxygen contained in the internal atmosphere to generate a large amount of oxides, a temperature of about 800 ° C. or lower is usually adopted.

The phosphorus added to the molten aluminum here is in the form of a simple phosphorus such as yellow phosphorus or red phosphorus, a phosphorus compound such as phosphorus pentachloride, or a master alloy such as phosphorus-iron or phosphorus-copper. Alternatively, a mixture of phosphorus or a phosphorus compound and so-called fluxes used for the purpose of degassing and removing inclusions, for example, Nuclear 10 (red phosphorus 10% and hexachloroethane Such as a mixture with potassium chloride). Of these,
It is recommended to use phosphorus or a mixture of phosphorus compounds and fluxes because it is easy to handle and does not mix extra elements such as iron and copper into the molten metal and can be expected to remove degassing and inclusions at the same time. It

As a method for adding phosphorus to molten aluminum, various methods are adopted depending on the form of phosphorus described above and are not particularly limited. For example, when a mixture of red phosphorus and a flux is added, the mixture is powdered in order to increase the contact efficiency with the molten aluminum to be treated and to suppress the loss due to combustion oxidation of red phosphorus in the treatment furnace. It is also possible to use a lance pipe to blow chlorine gas or an inert gas at the same time, or to wrap the mixture in an aluminum foil and then add it by immersing it in molten aluminum using a phosphorizer. Further, the stirring method of the molten aluminum after adding phosphorus or a phosphorus compound may be a method that can uniformly stir phosphorus in the molten aluminum, even mechanical stirring by a stirrer or bubbling operation by gas blowing, or these May be used in combination. The molten aluminum after the treatment is kept for about 30 minutes or more, usually for about 1 to 3 hours, and then suspended matters such as metal oxides on the molten aluminum are removed and cast into a desired shape.

The sodium concentration of the molten aluminum after the treatment obtained by the above method is about 1 ppm or less and the purity of 99.95% by weight or more when the aluminum metal obtained by the primary electrolysis is usually used as the raw material. Normally 10p when high-purity aluminum produced by the three-layer electrolysis method is used.
It is pb or less.

In the present invention, molten aluminum after phosphorus or a phosphorus compound is added and stirred is not unique depending on the amount of phosphorus added during the treatment and the treatment method, but about 10 to 100 ppm remains. Therefore, the phosphorus or phosphorus compound remaining in the molten aluminum may be removed depending on the required quality of the cast ingot. As a method for removing phosphorus from the aluminum, an effective method for removing solute elements that form a eutectic phase diagram with aluminum such as Fe, Si, and Cu that are mainly contained in normal-purity aluminum (normal purity) As the aluminum refining method), the segregation method which has been industrially put to practical use can be most effectively applied.

Specific examples of such a segregation method include a fractional crystallization method and a unidirectional solidification method. In any case, for example, JP-A-56-55530 and JP-B-63-16452. Further, as described in JP-A-4-32526, a segregation method having means for effectively stirring the molten aluminum to be treated is more effective.

When the phosphorus content remaining in the molten aluminum after phosphorus treatment is about 10 to 100 ppm, when the molten aluminum is treated by a segregation method without stirring, 1
/ 30, that is, the concentration of phosphorus remaining in the molten aluminum after the segregation method is about 0.3 to 3.3 ppm, while it is 1/10 when the segregation method with stirring is used.
It is possible to reduce it to 0 or less, that is, 1 ppm or less.

[0021]

As described in detail above, according to the method of the present invention, phosphorus and / or a phosphorus compound is added to molten and held aluminum and the mixture is stirred, which is an extremely simple operation and is an economical method. However, when an aluminum ingot having a normal purity of 99.0% by weight or more obtained by the primary electrolysis method is used as a raw material, the sodium concentration is 1 p
In the case of using a high-purity aluminum ingot of 99.95% by weight or more obtained by a segregation treatment method and / or a three-layer electrolysis method as a raw material, the sodium concentration is reduced to 10 ppb or less. It is possible to obtain, and by additionally segregating the aluminum after the treatment, phosphorus remaining in the aluminum is also 5 ppm or less,
Normally, it can be reduced to 3 ppm or less, and the obtained aluminum ingot can be used in various fields as an Al-Mg alloy material or as a wiring material used for highly integrated circuits. The value is enormous.

[0022]

EXAMPLES The method of the present invention will now be described in more detail with reference to examples, but the method of the present invention is not limited to these examples. In this example, the analysis of sodium and phosphorus was carried out by a glow discharge ion mass spectrometer (GDMS).

Examples 1 to 50 50 kg of high-purity aluminum (containing 0.2 ppm of sodium) obtained by the three-layer electrolysis method with a purity of 99.99% by weight was placed in a graphite crucible and melted in an electric furnace, and then Table 1 The molten aluminum was held at the temperature shown in Table 1, and the amount of phosphorus flux in the molten aluminum in terms of the phosphorus conversion value was as shown in Table 1 (Nucleclear 10 manufactured by Foseco Japan Ltd .;
%) Was wrapped in an aluminum foil having a purity of 99.99% by weight , added using a phosphorizer, stirred with a graphite stirring jig, and after 30 minutes, suspended matters on the molten aluminum were removed. The content of sodium and phosphorus in the molten aluminum after the treatment thus obtained was analyzed. The results are shown in Table 1. For comparison, sodium and phosphorus in molten aluminum before addition of phosphorus (referred to as “before treatment”) were analyzed, and the results are shown in Table 1.

Comparative Example 1 In the method of Example 1, 760 was used instead of phosphorus treatment.
Chlorine gas was added to the aluminum melt-held at 0.
The sodium removal treatment was performed by blowing in 1 kg. Table 1 shows the analysis results of sodium and phosphorus in the molten aluminum after the treatment.
Shown in.

[0025]

[Table 1] * 1: Quantitative limit of GDMS analysis

Example 4 Approximately 50 kg of molten aluminum that had been treated with phosphorus in Example 3
, A segregation device with a stirrer (the upper part has a heating device that can control the ambient temperature in the molten aluminum container,
A turntable capable of rotating the molten aluminum container at the bottom and a device having a function of cooling the bottom of the container with air), and then the rotation speed of the turntable is periodically reversed at 20 rpm to stir the molten aluminum in the container. While the flow was being supplied, the bottom of the container was cooled with air and subjected to segregation treatment for 8 hours. After the molten aluminum was discharged from the container after the treatment, the solid-phase solidified aluminum (50% by weight of the raw material molten aluminum) in the container was taken out, transferred to another container, and then remelted in an electric furnace, The contents of sodium and phosphorus in aluminum were analyzed. The results are shown in Table 2.

Example 5 The same process as in Example 4 was performed except that a turntable was not used in the segregation process, that is, stirring was not performed.
The contents of sodium and phosphorus in the solidified aluminum were analyzed. The results are shown in Table 2.

[0028]

[Table 2]

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-48-20709 (JP, A) JP-A-52-128815 (JP, A) JP-A-56-55530 (JP, A) JP-A-57- 9846 (JP, A) JP 57-108227 (JP, A) JP 57-198226 (JP, A) JP 4-32526 (JP, A) JP 63-16452 (JP, B1) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22B 1/00-61/00

Claims (6)

(57) [Claims] 1. A method of adding phosphorus and / or a phosphorus compound in an amount of 0.005% by weight to 0.05% by weight in terms of phosphorus atom to the molten aluminum having a purity of 99.0% by weight or more, which has been dissolved and retained, and stirring the mixture. Characteristic sodium content is 1p
A method for producing aluminum of pm or less. 2. The method according to claim 1, wherein the molten aluminum after phosphorus and / or a phosphorus compound is added and stirred is subjected to a segregation treatment, which has a phosphorus content of 5 ppm or less and a sodium content of 1 ppm or less. Aluminum manufacturing method. 3. The segregation treatment is either a fractional crystallization method or a unidirectional solidification method.
The method for producing aluminum described above. 4. The molten aluminum has a purity of 99.0% by weight .
As described above, it is aluminum obtained by primary electrolysis with a sodium concentration of 3 ppm or more.
3. The method for producing aluminum according to any one of 3 above. 5. Molten aluminum is aluminum obtained by a segregation treatment method and / or a three-layer electrolytic refining method having a purity of 99.95% by weight or more, and the sodium content in the treated molten aluminum is 10 ppb or less. The method for producing aluminum according to claim 1, wherein: 6. The molten aluminum after adding phosphorus and / or a phosphorus compound and stirring the mixture is subjected to a segregation treatment, wherein the phosphorus content is 5 ppm or less and the sodium content is 10 ppb or less. Aluminum manufacturing method.