KR20090048964A - Method for manufacturing metal hollow sphere - Google Patents

Abstract

The present invention relates to a method for producing a metal hollow sphere (hollow sphere) used in high-strength light material, and more specifically, to reducing the metal oxide using a sintering method for producing a foamed metal having high strength and light weight characteristics A method for producing a metal hollow sphere (hollow sphere). Metal hollow sphere manufacturing method according to the present invention by simplifying and improving the manufacturing process to improve the productivity and production cost is reduced, there is little restriction on the solvent selection used in the manufacturing, it is possible to manufacture the metal hollow sphere with improved surface roughness.

Hollow metal sphere, sintering method, foamed metal, lightweight material

Description

Method for manufacturing metal hollow sphere

The present invention relates to a method for producing metal hollow spheres for use in high strength light materials.

In recent years, interest in lightweight materials is increasing because weight reduction of structures or transportation devices has the advantage of increasing energy and work efficiency. In the case of a metal material, the workability is good, the electrical conductivity and the thermal conductivity are high, and the mechanical properties are excellent, but the specific gravity is higher than that of a polymer or a ceramic material.

The weight reduction of the metal material includes a method of using a material having a low specific gravity and a method of using a foam metal which artificially forms pores in the material. Light weight metals such as aluminum and magnesium have received a new spotlight because they have a lower specific gravity than iron or copper, but have a disadvantage in that electrical, thermal and mechanical properties are inferior to those of general metals.

Unlike existing organic-inorganic soundproof materials, foamed metal is not only excellent in durability and heat resistance, but also ultra-lightweight, and thus will be widely used in construction, acoustics, and electromagnetic shielding as next-generation soundproof materials. Therefore, it is expected to have a great ripple effect in the field of transportation equipment and all industries such as heat dissipation and heat sink materials.

Foam metal manufacturing technology uses powder metallurgy to mix and sinter the target metal powder and foaming agent, and gives proper viscosity and surface tension enhancement ability to molten metal, and then adds thickener and foaming agent to sponge of ingot type or continuous casting plate. The casting method for manufacturing porous metal solids is a key component.In the field of functional metal materials, new materials advanced technologies are used for vibration suppression by structure, sound insulation by the viscosity and elasticity of basic materials, sound insulation, sound insulation, vibration damping, heat resistance, and heat insulation. It has features such as high functionality and high added value, and is composed of porous production of laminated foam and provision of cutting function. In order to manufacture such foamed metals, research on manufacturing hollow spheres of metals is also actively conducted. The hollow sphere is a spherical structure having a hollow center, and can be used to manufacture foam metal having a free shape and size by using sintering or metal injection molding (MIM).

US Published Patent 2007 / 0108255A1 provides a method of making such metal hollow spheres. The method of reducing metal hollow spheres using carbon gas under vacuum atmosphere was used. However, this method requires a vacuum device, which may cause problems in productivity and production cost.

The present inventors previously studied a method of producing a copper hollow sphere of high purity by coating a slurry containing a mixture of copper oxide powder, water and polyacrylamide (PA) on a polymer ball and then sintering under a hydrogen atmosphere. -Myeong Koo and Seung-Boo Jung: Materials Science Forum, vol. 510-511 (2006), p. 730-733] Since copper has a higher specific gravity than aluminum or magnesium, it is difficult to manufacture foam metal through a general casting method, and precision casting method has a disadvantage in that production efficiency is low due to high unit cost. Therefore, research is being made to reduce the specific gravity while maintaining the excellent mechanical, thermal and electrical properties of copper. In addition, the copper foam material has the advantages of excellent heat resistance and high temperature corrosion resistance compared to aluminum and magnesium. However, it is pointed out that the polymer ball used in the above paper has a limitation in the selection of a solvent when preparing a slurry by dissolving in an organic solvent.

Accordingly, the present inventors completed the present invention by preparing metal hollow spheres, which are not limited to the use of an organic solvent, using paraffin balls or paraffin-coated polymer balls instead of the polymer balls.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a metal hollow sphere, which simplifies the manufacturing process and improves productivity and reduces production costs.

Another object of the present invention is to provide a method of improving the polymer ball to prevent melting in a solvent and at the same time improving the roughness of the hollow sphere surface.

In order to achieve the above object, the present invention provides a method for producing a metal hollow sphere using the sintering method under the normal pressure of the hydrogen atmosphere.

The present invention also provides a method for coating a slurry of a metal oxide powder, a binder and a solvent on a paraffin ball or a paraffin-coated polymer ball.

In one embodiment, the present invention comprises the steps of (a) preparing a slurry consisting of a metal oxide, a binder and a solvent; (b) coating the prepared slurry on a spherical paraffin ball or paraffin coated polymer ball surface; (c) drying to evaporate the solvent; And (d) provides a method for producing a metal hollow sphere comprising the step of sintering the coated slurry.

Metal oxides in the present invention include, but are not limited to, for example, metal oxides such as silver oxide, nickel oxide, iron oxide, alumina and chromium oxide. In the present invention, the metal oxide may be broken and used to facilitate sintering. In addition, the metal oxide may be used to produce pure metal hollow spheres using one single metal oxide, or to produce alloy hollow spheres using two or more kinds of mixtures.

The solvent may be water, alcohol or acetone. When using acetone, there is an advantage that the drying time is shortened.

Coating of the slurry on the surface of the polymer ball may be carried out using, but not limited to, spraying and dipping.

The evaporation of the solvent is preferably dried at a temperature of 10-200 ° C. and a humidity of 70% RH or less.

According to the present invention, it is possible to control the shape, size, pore size, density and surface roughness of the metal hollow sphere, the diameter of the hollow sphere from 0.1 mm to 10 cm, the thickness of the metal skin produced from 0.01 mm to 1 cm Is possible. In theory, the thickness and size of the hollow spheres are not limited.

The metal hollow sphere according to the present invention can be used as a material for producing a foamed metal using secondary sintering or MIM (metal injection molding), and can also be used as a separate cell.

The roughness of the surface of the hollow sphere and the pores after sintering vary greatly depending on the viscosity, and the smaller the viscosity, the more beautiful and uniform the thickness of the hollow sphere can be produced. It is possible to produce a hollow sphere having. The viscosity of 1,000-10,000 cP is preferable.

The metal hollow sphere manufacturing method of the present invention uses a principle that the sintering is carried out under atmospheric pressure, the density increases by diffusion of atoms during heating, the structure of the manufacturing apparatus is simple and inexpensive, the production speed is high, productivity improvement and production Cost-effective metal hollow spheres can be produced. In addition, through the oxidation and reduction reactions of the sintering process, impurities can be removed to produce high purity metal hollow spheres.

In addition, by using a polymer ball rather than a precision casting mold, it is excellent in price competitiveness, and by replacing the previously used polymer ball from polystyrene with paraffin, there is little restriction on solvent selection and manufacturing a metal hollow sphere with improved surface roughness. It is possible.

Hereinafter, the present invention will be described in detail. Those skilled in the art will appreciate that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention as set forth in the claims below.

Production Example

Sample Preparation

Scrap or bulk metal is crushed to facilitate sintering. Bulk, scrap, dust (powder) waste metals can be produced by collecting and recycling, and even a large amount of impurities are reduced during sintering to produce high quality foamed metal.

Heated and oxidized to remove oxides and contaminants from metal scrap and to make oxides. If necessary, the prepared metal oxide powder or ribbon is crushed again to produce a metal oxide of an appropriate size, and the final metal oxide powder or ribbon has a particle size of 1/50 or less of the size of the hollow sphere to be manufactured.

Polyvinyl alcohol (PVA: Poly Methyl Meth Acrylate) or polyacrylamide (PA: Poly Acrilamide) is prepared as a binder, and water, alcohol or acetone is prepared as a solvent. . At this time, when manufacturing a thin thickness PMMA and acetone, when coating a thick thickness PA and water is preferred.

Slurry manufacturing

The slurry consists of a metal oxide powder, a solvent and a binder. After stirring sufficiently for slurry preparation, the weight ratio of metal, oxide powder and solvent is between 1: 1 and 10: 1, and the binder is added by mixing less than 10% of the total weight of the slurry. If necessary, a metal ball or a ceramic ball is added to facilitate stirring. The roughness of the surface of the hollow sphere and the pores after sintering vary greatly depending on the viscosity. As the viscosity becomes smaller, it is possible to manufacture hollow spheres having a beautiful and uniform thickness, and as the viscosity becomes larger, it is possible to manufacture hollow spheres having large, large and large pores. Viscosity change according to powder, binder, and solvent is shown in Table 1 below.

TABLE 1

Viscosity is preferably in the range of 1,000 to 10,000 cP.

Slurry coating and drying

Paraffin has the advantage of leaving no residue at all by sublimation at elevated temperature, so when a slurry of acetone and PMMA is added to the paraffin ball or paraffin-coated polymer ball surface, the surface is beautiful and the production of high purity hollow sphere is easy. Therefore, the prepared slurry is coated on the surface of the polymer ball or paraffin ball by spraying or dipping.

Acetone may be used as a solvent, and paraffin balls or polymer balls coated with paraffins are useful because they do not dissolve in acetone and are completely sublimed during heating to leave no residue. In addition, the advantage of rapid drying is that the slurry coating and drying can be repeated for the desired thickness coating. The surface of the polymer ball may be coated to a desired thickness and then dried naturally. In order to shorten the drying time, the solvent may be evaporated by drying at a temperature of 20 ° C. or higher and a humidity of less than 70% RH (relative humidity) as necessary.

Sintered

An intermediate dock is installed before the sintering step to remove oxygen through a nitrogen supply, and the sintering step is carried out in a hydrogen atmosphere for 1 to 500 minutes under a temperature of 500 ° C. to a temperature below the melting point of the metal used.

When heated under a hydrogen atmosphere, the metal oxide is reduced to a metal through the following chemical reaction, and the polymer balls and paraffin inside disappear.

MOx + xH _2- > M + xH ₂ O (Scheme)

Hydrogen 90% or more of purity was continuously supplied into the sintering furnace to maintain the partial pressure of hydrogen, and the sintering temperature was maintained at 500 ° C. or higher. Sintering time was 1 minute or more. During sintering, the hollow sphere shrinks, reducing the diameter and increasing the thickness. Figure 2 is a graph showing the shrinkage of the hollow sphere with the sintering temperature. When calculating the diameter of the polymer ball with reference to Figure 2, it is possible to produce a hollow sphere of a precise size. In addition, in order to prevent the inflow of oxygen when entering the initial sintering furnace, an intermediate furnace was installed to sufficiently inject nitrogen and entered the main sintering furnace to prevent explosion. In order to prevent explosion and to improve the characteristics of the hollow sphere, the temperature increase rate may be adjusted to 10 to 100 ° C./min as needed, and the cooling rate may be adjusted to −1 to −100 ° C./min as needed during cooling. After the sintering step, the metal hollow spheres produced by slow cooling under nitrogen atmosphere to remove thermal shock before exposure to the atmosphere are prevented from being destroyed.

inspection

Sort and inspect for sintering to the desired shape, size and purity. If necessary, in order to improve the strength, ductility, impact absorbency, etc. of the manufactured hollow sphere, the hollow sphere may be maintained at a temperature range of 50 to 900 ° C. for at least 1 minute to relieve stress generated therein and to reduce pores to increase density.

Example

Example 1: Preparation of Copper Hollow Spheres

Oil scraps and contaminants on the copper scrap were removed and heated and oxidized to form oxides. As a binder and a solvent, PMMA and acetone were prepared, and copper oxide powder, PMMA and acetone were sufficiently stirred to prepare a slurry. At this time, the weight ratio of the solvent and the copper oxide powder was 3: 7, PMMA was added at 3 wt.% Based on the total weight of the slurry. After coating on the paraffin ball by quenching the prepared slurry, the solvent was evaporated by drying in 25 ℃, 50% RH atmosphere. The copper oxide was reduced by heating at 900 DEG C for 1 hour in a hydrogen atmosphere. At this time, the temperature increase rate was 15 ° C / s, the cooling rate was -15 ° C / s. Therefore, the paraffin ball inside was extinguished, completing the copper hollow sphere according to the present invention. Figure 3 is a photograph of a copper hollow sphere prepared according to Example 1 of the present invention, Figure 4 is a strength-strain graph showing the compression test results of the copper hollow prepared. 5 is a cross-sectional photograph of a foamed metal prepared by heating at 700 ° C. for 1 hour under a hydrogen atmosphere with the above components. By lowering the sintering temperature to suppress the diffusion of atoms to maximize the density of the pores to produce a high hollow copper spheres.

Example 2: Preparation of Nickel Hollow Spheres

Oil residues and contaminants on nickel scraps were removed and heated and oxidized to form oxides. The binder and the solvent were prepared with PA and water, and the nickel oxide powder, PA and water were sufficiently stirred to prepare a slurry. At this time, the weight ratio of the solvent and the copper oxide powder was 3: 7, and PA was added at 5 wt.% Based on the total weight of the slurry. After coating on the paraffin ball by quenching the prepared slurry, the solvent was evaporated by drying in 25 ℃, 50% RH atmosphere. Nickel oxide was reduced by heating at 800 DEG C for 1 hour in a hydrogen atmosphere. At this time, the temperature increase rate was 15 ° C / s, the cooling rate was -15 ° C / s. Therefore, the paraffin ball inside was extinguished, completing the nickel hollow sphere according to the present invention. 6 is a cross-sectional photograph of a nickel hollow sphere prepared by sintering at 930 ° C. for 1 hour according to Example 1 of the present invention. As a result of analysis by an energy dispersive X-ray analyzer, nickel oxide is completely reduced to form a nickel hollow sphere. Became.

Metal hollow sphere manufacturing method according to the present invention by simplifying and improving the manufacturing process, productivity and production cost is reduced, there is little restriction on the solvent selection used in the manufacturing, it is possible to manufacture the metal hollow sphere with improved surface roughness . Through this, it is possible to manufacture economical foam metal using a metal material having excellent mechanical and thermal properties but high density, which was difficult to manufacture by a general casting method. Unlike the existing organic / inorganic soundproof materials, the foamed metal thus manufactured is not only excellent in durability / heat resistance but also ultra-lightweight, and thus will be used in the construction and sound fields as the next-generation soundproof material. It is useful for all industries such as transportation equipment and electromagnetic shielding.

1 is a flow chart of the manufacturing process of the metal hollow sphere according to the present invention.

Figure 2 is a graph showing the shrinkage of the hollow sphere according to the sintering temperature of the present invention.

3 is a photograph of a copper hollow sphere prepared according to the present invention.

Figure 4 is a strength-strain graph showing the compression test results of the copper hollow spheres prepared according to the present invention.

Figure 5 is a photograph showing a cross-sectional picture of a copper hollow sphere prepared by sintering at 700 ℃ in accordance with the present invention.

6 is a cross-sectional photograph of a nickel hollow sphere prepared by sintering nickel oxide at 800 ° C. according to the present invention.

Figure 7 is a schematic diagram of the construction on the ondol among the applications of the copper hollow sphere prepared according to the present invention.

Claims (8)

As a method of manufacturing a metal hollow sphere, (a) preparing a slurry consisting of a metal oxide, a binder and a solvent; (b) coating the slurry of step (a) on a paraffin ball or paraffin coated polymer ball surface; (c) drying to evaporate the solvent; (d) heating under a hydrogen atmosphere to reduce the metal oxide. The method of claim 1, wherein the diameter of the metal oxide is 1/50 or less of the diameter of the metal hollow sphere. The method of claim 1, wherein the solvent is water, alcohol or acetone. The method of claim 1, wherein the binder is polyvinyl alcohol (PVA), polymethyl methacrylate (PMMA) or polyacrylamide (PA). 2. The method of claim 1, wherein the weight ratio of metal oxide to solvent is from 1: 1 to 10: 1. The method of claim 1, wherein the binder is less than 10% by weight of the total weight of the slurry. The method of claim 1, wherein the metal oxide is an alloy metal oxide, which is one pure metal oxide or a mixture of two or more thereof. A metal hollow sphere made according to the method of claim 1.

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