METHOD FOR MANUFACTURING ALUMINUM BASE MATERIAL

Abstract

A manufacturing method can obtain Al-based particles. A particle-dispersed molten salt (an example of an Al base material), in which Al-based particles (liquid phase) are dispersed in molten salt, can be obtained by bringing Al-based foil into contact with molten salt. Through particle-dispersed molten salt, for example, Al-based powder (an example of Al base material) composed of Al-based particles (solid phase) can be efficiently or easily obtained. By classifying Al-based particle groups, Al-based powder with a desired particle size distribution can be obtained. The Al-based foil has a thickness of, for example, at most 0.5 mm, and even 0.1 mm. The Al-based foil is supplied to molten salt in the form of shredded foil pieces. This allows Al-based powder to be obtained with a particle size distribution including fine particles. It is preferred to use, for example, a mixed salt containing NaCl and KCl as molten salt.

Claims

1. A method for manufacturing an aluminum base material, comprising bringing an aluminum-based foil into contact with a molten salt to obtain aluminum-based particles.

2. A method for manufacturing an aluminum base material, comprising: a melting step of putting an aluminum-based foil in a molten salt layer to melt the foil; and a collecting step of collecting aluminum-based particles obtained after the melting step.

3. The method for manufacturing an aluminum base material according to claim 1, wherein the aluminum-based foil comprises shredded foil pieces.

4. The method for manufacturing an aluminum base material according to claim 1, wherein the aluminum-based foil has a thickness of less than 0.1 mm.

5. The method for manufacturing an aluminum base material according to claim 1, wherein the molten salt comprises a mixed salt.

6. The method for manufacturing an aluminum base material according to claim 5, wherein the mixed salt contains NaCl and KCl.

7. The method for manufacturing an aluminum base material according to claim 1, wherein the aluminum-based particles are liquid-phase particles, and the aluminum base material is a particle-dispersed molten salt in which the liquid-phase particles are dispersed in the molten salt.

8. The method for manufacturing an aluminum base material according to claim 1, wherein the aluminum-based particles are liquid-phase particles, and the aluminum base material is an aluminum-based molten metal obtained from the liquid-phase particles.

9. The method for manufacturing an aluminum base material according to claim 1, wherein the aluminum-based particles are solid-phase particles obtained by solidifying liquid-phase particles, and the aluminum base material is a particle-dispersed solidified salt in which the solid-phase particles are dispersed in a solidified salt obtained by solidifying the molten salt.

10. The method for manufacturing an aluminum base material according to claim 1, wherein the aluminum-based particles are solid-phase particles obtained by solidifying liquid-phase particles, and the aluminum base material is an aluminum-based powder comprising the solid-phase particles.

11. The method for manufacturing an aluminum base material according to claim 2, wherein the aluminum-based foil comprises shredded foil pieces.

12. The method for manufacturing an aluminum base material according to claim 2, wherein the aluminum-based foil has a thickness of less than 0.1 mm.

13. The method for manufacturing an aluminum base material according to claim 2, wherein the molten salt comprises a mixed salt.

14. The method for manufacturing an aluminum base material according to claim 13, wherein the mixed salt contains NaCl and KCl.

15. The method for manufacturing an aluminum base material according to claim 2, wherein the aluminum-based particles are liquid-phase particles, and the aluminum base material is a particle-dispersed molten salt in which the liquid-phase particles are dispersed in the molten salt.

16. The method for manufacturing an aluminum base material according to claim 2, wherein the aluminum-based particles are liquid-phase particles, and the aluminum base material is an aluminum-based molten metal obtained from the liquid-phase particles.

17. The method for manufacturing an aluminum base material according to claim 2, wherein the aluminum-based particles are solid-phase particles obtained by solidifying liquid-phase particles, and the aluminum base material is a particle-dispersed solidified salt in which the solid-phase particles are dispersed in a solidified salt obtained by solidifying the molten salt.

18. The method for manufacturing an aluminum base material according to claim 2, wherein the aluminum-based particles are solid-phase particles obtained by solidifying liquid-phase particles, and the aluminum base material is an aluminum-based powder comprising the solid-phase particles.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0030] FIG. 1A is a photograph of Al-based foil pieces (0.018 mm thick25 mm square).

[0031] FIG. 1B is a photograph of Al-based foil pieces (0.3 mm thick1 mm wide).

[0032] FIG. 1C is a photograph of Al-based foil pieces (0.3 mm thick3 mm square).

[0033] FIG. 2 is a schematic diagram for exemplifying the manufacturing process for Al-based particles (powder).

[0034] FIG. 3 is a table showing the correspondence between the form (thickness/size) of Al-based foil pieces as raw materials and the form (photograph) of the obtained Al-based particles.

[0035] FIG. 4 is a set of SEM images of Al-based particles obtained from Al-based foil pieces (0.011 mm thick25 mm square).

[0036] FIG. 5 is a bar graph illustrating the relationship between the thickness of Al-based foil pieces as raw materials (25 mm square) and the particle size distribution of the obtained Al-based particles.

[0037] FIG. 6A is a bar graph illustrating the relationship between the size of Al-based foil pieces as raw materials (0.3 mm thick) and the particle size distribution of the obtained Al-based particles.

[0038] FIG. 6B is a bar graph illustrating the relationship between the size of Al-based foil pieces as raw materials (0.1 mm thick) and the particle size distribution of the obtained Al-based particles.

[0039] FIG. 6C is a bar graph illustrating the relationship between the size of Al-based foil pieces as raw materials (0.018 mm thick) and the particle size distribution of the obtained Al-based particles.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0040] One or more features freely selected from the present specification can be added to the above-described features of the present invention. In the contents described in the present specification, methodological features can also be features regarding a product (e.g., Al-based particles, Al base material).

Al-Based Foil

[0041] (1) For the Al-based foil as the raw material, an Al base material (such as plate material or ingot) processed (such as rolled) to a desired thickness may be used, or an Al base material already in a foil form may also be used without any modification. The Al base material may be waste material collected from the market, a factory, or the like or a recycled material (massive form, plate form, foil form, etc.) thereof. The collected or recycled Al-based foil may be used without any modification, or may be subjected to pretreatment such as ink removal or cleaning or thickness adjustment. Al-based foil laminated with resin, etc. may be added to the molten salt without any modification, or may also be added to the molten salt after the laminate layer is removed. The Al-based foil may or may not have wrinkles, folds, bends, etc.

[0042] (2) The Al-based foil may be pure aluminum (pure Al) or an aluminum alloy (Al alloy). A mixture of Al-based foils with different component compositions may be used. The component composition of the Al-based foil as the raw material is reflected in the component composition of the obtained Al-based particles. Accordingly, the components, compounding, etc. of the Al-based foil as the raw material may be adjusted to obtain Al-based particles of the desired composition.

[0043] (3) The thickness and size of the Al-based foil are appropriately selected. The thickness and size (size other than thickness) of the Al-based foil (foil pieces) added to the molten salt may be adjusted in accordance with the particle size distribution of the desired Al-based particle group (powder). In this case, Al-based foils (foil pieces) with different thicknesses and/or sizes may be mixed. Usually, the thinner and/or smaller the Al-based foil (foil pieces), the higher the proportion of fine (small-diameter) Al-based particles. Conversely, the thicker and/or larger the Al-based foil (foil pieces), the higher the proportion of coarse (large-diameter) Al-based particles.

[0044] The thickness of the Al-based foil is, for example, 0.5 mm, 0.3 mm, 0.2 mm, 0.1 mm, 0.07 mm, 0.03 mm, or 0.02 mm as the upper limit (threshold for being equal to or less than or otherwise being less than). Suffice it to say that the lower limit (threshold for being equal to or more than or otherwise being more than) is, for example, 0.001 mm, 0.005 mm, or even 0.008 mm. The thickness of the Al-based foil is measured with a micrometer or the like. The thickness of the Al-based foil may vary by about 10%. The arithmetic mean value of the thicknesses measured at any number of locations (e.g., 10 locations) may be appropriately used as the thickness of the Al-based foil. Unless otherwise stated, the foil as referred to in the present specification means a case in which the thickness is 0.5 mm or less (0.2 mm or less in an embodiment or less than 0.1 mm in another embodiment).

[0045] The size of the foil pieces is, for example, 200 mm, 150 mm, 100 mm, 50 mm, 30 mm, 20 mm, 10 mm, 5 mm, or 1 mm as the maximum length. The minimum length is, for example, 10 mm, 5 mm, 1 mm, or even 0.5 mm. The size of the foil pieces may be adjusted in accordance with the thickness of the foil pieces. For example, when the foil pieces are thin, larger foil pieces may be used, and when the foil pieces are thick, smaller foil pieces may be used. The foil pieces are obtained, for example, by shredding the Al-based foil (raw material) with a shredder or the like.

Molten Salt

[0046] The molten salt may be obtained, for example, from a stable metal halide (in particular, a chloride and/or bromide) as the raw material. The metal element constituting the halide is, for example, one or more of Ca, Na, Li, Sr, K, Mg, Cs, Ba, etc. In particular, Na and/or K halides are inexpensive and stable, and are suitable for the molten salt.

[0047] The temperature of the molten salt may be adjusted by compounding the raw materials (adjusting the components). The temperature of the molten salt may be preferably at least equal to or higher than (or exceeding) the melting temperature of the Al-based foil. The molten salt is not limited to a single layer, but may be a multi-layer. The molten salt may be preferably a molten salt reservoir (bath) with a depth or amount sufficient to immerse at least the Al-based foil. Normally, the Al-based particles (liquid phase) will remain or settle below the molten salt due to the density difference.

Al-Based Particles

[0048] (1) The particle size of the Al-based particles (referred to as a particle diameter regardless of the particle shape) may be constant or distributed. The thinner and smaller the Al-based foil pieces are melted, the more likely it is that a particle size distribution with a large number of fine Al-based particles will occur.

[0049] The Al-based particles may be liquid or solid particles as obtained from the Al-based foil (pieces), or may also be liquid or solid particles configured such that the particles are connected (bonded) to each other to be integrated (larger in diameter) or alloyed. The Al particles may be used without any modification, or may also be used after particle size adjustment (classification). According to the manufacturing method of the present invention, it is possible to obtain an Al powder composed of Al-based particles with a particle size of more than 1.7 mm, and it is also possible to obtain an Al powder composed of Al-based particles with a particle size of less than 0.1 mm.

[0050] As referred to in the present specification, unless otherwise stated, the particle size (or particle diameter) of powder is specified by sieving and expressed by the nominal sieve opening (mesh size) of the sieve (in accordance with JIS Z 8801). The particle size to (<) means that the powder is composed of particles (groups) that do not pass through a sieve with a nominal sieve opening of m, but pass through a sieve with a nominal sieve opening of m. Particle size <-0 means that the powder is composed of particles (groups) that do not pass through a sieve with a nominal sieve opening of m. Particle size < means that the powder is composed of particles (groups) that pass through a sieve with a nominal sieve opening of m. The particle diameter of the liquid-phase particles is considered to be approximately equal to the particle diameter of the solid-phase particles, excluding the thermal shrinkage.

[0051] (2) Al-based particles and Al base materials have various uses. For example, Al-based powder (solid-phase particles), which is one form of Al-based particles, can be used as a filler (such as thermally conductive filler or electrically conductive filler) that is dispersed in a host material (such as resin, dissimilar metal, or ceramics) to constitute a composite material, raw powder of a sintered material (such as main element powder or alloy element powder), raw material (such as reducing agent) that causes a chemical reaction (such as thermit reaction), pigment added to paint, etc.

EXAMPLES

[0052] Al-based foil was added to molten salt to produce Al-based particles (liquid-phase particles), which were then solidified. The present invention will be described in more detail based on such specific examples.

Preparation of Samples

(1) Raw Materials

[0053] Various foil pieces with different dimensions (size (planar size) and thickness) were prepared as raw materials. All foil pieces used were composed of pure Al (JIS 1000 series/purity of 99% or more) with a size of 100 mm100 mm or more (Al-based foil). The foil thickness was 0.011 mm, 0.018 mm, 0.025 mm, 0.05 mm, 0.1 mm, 0.3 mm, or 0.8 mm.

[0054] The sizes of the foil pieces were 25 mm square (almost square), 3 mm square, 5 mm wide (25 mm long), and 1 mm wide (25 mm long). For both the 5 mm wide and 1 mm wide pieces, the size was adjusted by further shredding the 25 mm square foil pieces to a predetermined width.

[0055] The foil or foil pieces were cut (shredded) in the atmospheric air using scissors for metals. Thus, various foil pieces were obtained. The appearances of some of them are shown in FIGS. 1A to 1C.

(2) Molten Salt

[0056] A mixed salt of potassium chloride and sodium chloride (KCl-44 mass % NaCl): 100 g was placed in an alumina crucible (available from NIKKATO CORPORATION, B3) and heated in a furnace to 700 C. Thus, a molten salt (layer, reservoir) composed of the mixed salt was obtained.

(3) Melting Step

[0057] As illustrated in FIG. 2, a step of putting foil pieces (2.5 g) into the molten salt (100 g) and melting them was performed for respective foil pieces. No stirring was performed during this step, and the foil pieces were statically placed (for about 10 minutes) until they were dispersed and melted in the molten salt.

(4) Collecting Step

[0058] After the melting step, the crucible was left to cool outside the furnace (cooling step), and the molten salt (particle-dispersed molten salt) was solidified (solidification step). The solidified material (particle-dispersed solidified salt) taken out from the crucible was washed with water (water washing step/salt removal step). The particles remaining after salt removal were filtered and dried (filtration step, drying step). The particle groups corresponding to respective foil pieces thus obtained are collectively shown in FIG. 3.

(5) Classification Step

[0059] Respective particle groups were classified using sieves. Five types of sieves with opening dimensions (mesh sizes) of 1.7 mm, 0.85 mm, 0.425 mm, 0.212 mm, and 0.106 mm were used. The particle size distributions (mass ratios) of respective particle groups are illustrated in FIG. 5 and FIGS. 6A to 6C (collectively referred to as FIG. 6). FIG. 5 illustrates the relationship between the thickness of the foil pieces (25 mm square) used as the raw material and the particle size distribution of the obtained particle group. FIG. 6 illustrates the relationship between the size of the foil pieces and the particle size distribution.

(6) Comparative Sample

[0060] An Al ingot (50 g) was put into a crucible containing the above-described molten salt (100 g) to melt the Al ingot. The molten Al (bulk) formed in the molten salt was stirred with an alumina rod to disperse the molten Al in granular form in the molten salt. In the same manner as described above, the crucible was left to cool, and the solidified material obtained was washed with water, after which the obtained particles were filtered, dried, and classified.

Observation

[0061] An SEM image when observing with a scanning electron microscope (SEM) particles (particle size: <0.212 mm) obtained using foil pieces of 0.011 mm thick25 mm square is shown in FIG. 4, along with its enlarged image.

Evaluation

(1) Particle Shape

[0062] As apparent from FIG. 4, it has been found that the Al-based particles obtained by bringing the Al-based foil pieces into contact with the molten salt are almost spherical even without stirring during the melting step. The shape of the Al-based particles of the comparative sample was slightly flattened and spherical.

(2) Particle Size Distribution

[0063] As apparent from FIG. 5, the thinner the Al-based foil used, the larger amount of fine particles was included in the particle size distribution obtained. Conversely, the thicker the Al-based foil used, the larger amount of large-diameter particles was included in the particle size distribution.

[0064] As apparent from FIG. 6A, when Al-based foil with a thickness of 0.3 mm or more (over 0.3 mm) was used, large-diameter particles were stably obtained regardless of the size. This appears to be because the thick Al-based foil (pieces) gradually melted from each end surface, increasing the opportunities for bonding with other Al-based particles (liquid phase) before spheroidization. Most of the Al-based particles of the comparative sample had a particle size of over 1.7 mm.

[0065] As apparent from FIGS. 6B and 6C, it has been found that the particle size distribution can be adjusted by the thickness of the Al-based foil and the size of the foil pieces. For example, when thin and small foil pieces were used, a powder with a particle size distribution containing a large amount of relatively fine particles was obtained. This appears to be because the thin and small foil pieces melted and became spherical within a short time, making them easier to disperse. Such a tendency was prominent when the thickness of the Al-based foil was 0.1 mm or less (or even less) or the width of the Al-based foil pieces was 1 mm or less (or even less).

[0066] Incidentally, Al-based particles (liquid phase) with a particle diameter (diameter) of approximately 2 mm or less were difficult to integrate and were easy to maintain a dispersed state in the molten salt.

[0067] Thus, according to the present invention, by using Al-based foil, a particle-dispersed molten salt in which Al-based particles are dispersed in the molten salt can be obtained. Furthermore, a desired Al base material (such as powder) can be obtained efficiently or easily from the particle-dispersed molten salt.