KR101509028B1 - Methods of manufacturing aluminium-carbon nanotube and aluminium-carbon nanotube composites manufactured by the methods - Google Patents

Abstract

A method for producing an aluminum-carbon nanotube composite material is disclosed. In the aluminum-carbon nanotube composite material, the carbon nanotubes are mechanically declustrated on the aluminum powder surface, and then the aluminum-carbon nanotube composite powder is produced through a ball mill process. The aluminum-carbon nanotube composite powder is sintered and extruded . When an aluminum-carbon nanotube composite material is produced by this method, a composite material having excellent ductility and strength can be produced.

Description

TECHNICAL FIELD The present invention relates to a method of manufacturing an aluminum-carbon nanotube composite material, and an aluminum-carbon nanotube composite material produced by the method. BACKGROUND OF THE INVENTION 1. Field of the Invention [0002]

The present invention relates to a method for producing an aluminum-carbon nanotube composite material and an aluminum-carbon nanotube composite material produced thereby, and a method for manufacturing an aluminum-carbon nanotube composite material capable of improving mechanical properties, And to an aluminum-carbon nanotube composite material produced thereby.

Aluminum is used for life in kitchens, foils, disposable tableware, windows, cars, aircraft and spaceships. The characteristics of aluminum are as small as one-third of the weight of iron and have excellent strength when alloyed with other metals. In addition, there is a chemically stable oxide film on the aluminum surface, and it is chemically stable since it prevents corrosion from progressing due to moisture or oxygen. For this reason, aluminum has been used in automobiles and aircraft. In particular, in the case of automobiles, aluminum parts are lighter than conventional steel parts, which can reduce their own weight, which leads to weight reduction of the vehicle body, which contributes to reducing fuel consumption.

However, since aluminum has a tensile strength of about 40% as compared with iron, when aluminum is used as a structural material, the thickness of the structural aluminum pipe or plate becomes very thick, which leads to an excessive amount of material, .

In order to solve these problems, researches for producing a composite material of a carbon material and aluminum have been actively conducted. Generally, however, when the strength of metal is increased, the ductility tends to be reduced, so that application of the carbon material and the aluminum composite material is limited.

It is an object of the present invention to provide a method for producing an aluminum-carbon nanotube composite material having improved mechanical strength and ductility.

Another object of the present invention is to provide an aluminum-carbon nanotube composite material produced by the above method.

A method of manufacturing an aluminum-carbon nanotube composite material according to an embodiment of the present invention includes: mechanically declustering a carbon nanotube on an aluminum powder surface; Performing a ball milling process on the aluminum powder and the carbon nanotubes declustrated on the aluminum surface to produce an aluminum-carbon nanotube composite powder; Sintering the aluminum-carbon nanotube composite powder to produce an aluminum-carbon nanotube composite; And extruding the aluminum-carbon nanotube composite to produce an aluminum-carbon nanotube composite material.

In one embodiment, the step of mechanically declustering the carbon nanotubes on the surface of the aluminum powder comprises mixing the carbon nanotubes having a diameter of 10 to 30 nm and a length of about 10 to 70 mu m with a diameter of 10 to 70 mu m And then mixing the carbon nanotubes and the aluminum powder by rotating the blade mixer at 10000 to 40000 rpm.

In one embodiment, the step of preparing the aluminum-carbon nanotube composite powder may be performed under the condition that oxygen and humidity are less than 1 ppm. Specifically, the ball mill process may be performed at 200 to 500 rpm for 20 to 60 minutes. The aluminum-carbon nanotube composite powder produced through the ball milling process may include carbon nanotubes encapsulated therein. In this case, the encapsulated carbon nanotubes may be embedded in the grain of aluminum constituting the composite powder Lt; / RTI >

In one embodiment, the step of preparing the aluminum-carbon nanotube composite comprises: filling the aluminum-carbon nanotube composite powder into a mold; And performing a spark plasma sintering process on the aluminum-carbon nanotube composite powders filled in the metal mold. In this case, the discharge plasma sintering process may be performed at a temperature of 200 to 600 ° C. for 10 to 30 minutes.

An aluminum-carbon nanotube composite material according to an embodiment of the present invention includes an aluminum matrix; And carbon nanotubes dispersed in the aluminum matrix. In this case, the carbon nanotubes may be dispersed in the grain of the aluminum matrix.

In one embodiment, the content of the carbon nanotubes is preferably 2 to 8 vol.% In order to improve ductility and strength of the aluminum-carbon nanotube composite material.

In the case of manufacturing an aluminum-carbon nanotube composite material according to an embodiment of the present invention, an aluminum-carbon nanotube composite material having excellent ductility and strength is manufactured by dispersing carbon nanotubes in a grain of aluminum, which is a matrix, can do.

1 is a flowchart illustrating a method of manufacturing an aluminum-carbon nanotube composite material according to an embodiment of the present invention.
FIGS. 2A and 2B are an optical micrograph and a confocal Raman microscope photograph of an aluminum-carbon nanotube composite material produced under conditions of oxygen and humidity of 1 ppm or more.
3 is stress-strain curves of an aluminum-carbon nanotube composite material prepared according to an embodiment of the present invention.
FIG. 4 is a graph for explaining changes in Young's modulus and Yield strength according to carbon nanotube content. FIG.
5 is a graph for explaining toughness change depending on the carbon nanotube content.
6A and 6B are electron backscattering diffraction (EBSD) images for explaining the microstructure after extrusion molding of a pure aluminum material and an aluminum-carbon nanotube composite material having a carbon nanotube content of 2 vol.%, 6B is a confocal Raman optical microscope image of the aluminum-carbon nanotube composite material, and FIG. 6D is an image showing the result of performing G band mapping from Raman spectra.
FIG. 7 is a graph showing the Raman spectra of the aluminum-carbon nanotube composite material of FIG. 6b.
8 is a graph for explaining grain size change according to the content of carbon nanotubes.
9 is a graph showing the results of an X-ray diffraction analysis of an aluminum-carbon nanotube composite material.
10 is a graph for explaining the dislocation density and the change of work hardening according to the carbon nanotube content.
11 shows TEM images of an aluminum-carbon nanotube composite material.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and similarities. It is to be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but on the contrary, is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the term "comprises" or "having" is intended to designate the presence of stated features, elements, etc., and not one or more other features, It does not mean that there is none.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

1 is a flowchart illustrating a method of manufacturing an aluminum-carbon nanotube composite material according to an embodiment of the present invention.

Referring to FIG. 1, a method of manufacturing an aluminum-carbon nanotube composite material according to an embodiment of the present invention includes declustering a carbon nanotube on a surface of an aluminum powder (S110) Carbon nanotube composite material by sintering the aluminum-carbon nanotube composite powder (S130); and extruding the aluminum-carbon nanotube composite material to form an aluminum-carbon nanotube composite material (S140). ≪ / RTI >

The step of declustering the carbon nanotubes on the surface of the aluminum powder (S110) may be performed using a blade mixer. For example, carbon nanotubes in the form of a cluster and aluminum powder may be put into a container, and then the blade mixer may be rotated at a high speed to de-cluster the carbon nanotubes on the surface of the aluminum powder. The carbon nanotubes may be single-walled carbon nanotubes, multi-walled carbon nanotubes, etc., and the carbon nanotubes before declustering may have a diameter of about 10 to 30 nm and a length of about 10 to 70 μm. And the aluminum powder may have a diameter of about 10 to 70 mu m.

Generally, carbon nanotubes exist in a cluster form because of their large specific surface area. If carbon nanotubes are present in a cluster form in the final composite material, the mechanical properties of the composite material deteriorate. In the present invention, carbon nanotubes are mechanically declustrated to facilitate encapsulation of carbon nanotubes as well as to solve such problems.

The de-clustering of the carbon nanotubes can be performed for about 10 to 30 minutes while rotating the blade mixer at about 10000 to 40000 rpm. When the carbon nanotubes are declustered while rotating the blade mixer at a high speed, the carbon nanotubes are cut so that the carbon nanotubes can be effectively encapsulated in the composite powder in the subsequent step of manufacturing the aluminum-carbon nanotube composite powder Its length can be reduced. For example, the carbon nanotubes having been subjected to the de-clustering may have a length of about 10 mu m or less.

Unlike the mechanical de-clustering process of the present invention, when carbon nanotubes are dispersed using ultrasound, the carbon nanotubes can be highly dispersed. However, since the ultrasonic process uses an oxygen-containing solvent, There is a problem that it is disturbed to be dispersed in the grain.

The step (S120) of producing the aluminum-carbon nanotube composite powder may be performed through a ball mill process. For example, aluminum powder and decarclined carbon nanotubes may be put into a ball mill container rotatably coupled to a disk together with a ball mill ball, followed by a ball mill process. The ball mill process can be performed under conditions of oxygen and humidity less than 1 ppm. Generally, aluminum is known to have high oxidizing power. Therefore, it has been reported that oxidation has occurred even at 10 ^-6 torr so far reported. The thickness of the oxide film is about 10 nm, which is similar to the diameter of carbon nanotubes. Such an oxide film is known to exhibit a great limitation in dispersing carbon nanotubes into aluminum particles or grain. Therefore, in the present invention, the ball mill process was performed under the condition that oxygen and humidity were less than 1 ppm. The declustered carbon nanotubes can be encapsulated by aluminum and dispersed even inside the grain of aluminum, thereby greatly improving the dispersibility of the carbon nanotubes. On the other hand, when the ball milling process is performed under the condition of oxygen or humidity of 1 ppm or more, there arises a problem that the carbon nanotubes can not penetrate into the grain of the aluminum due to the oxidation of aluminum, .

The ball mill process may be performed at low energy, for example, at about 200 to 500 rpm for about 20 to 60 minutes. When a high-speed ball milling process at a high rotation speed, that is, a speed exceeding 500 rpm is performed, the structure of the carbon nanotubes may be destroyed during the ball milling process, resulting in deterioration of the mechanical properties of the composite material.

When the ball milling process is carried out, the aluminum powder is ground and then welded between the pulverized aluminum powders. In this process, the carbon nanotubes penetrate into the aluminum powder and are encapsulated by the aluminum powder. When the ball milling process is performed under conditions of oxygen and humidity of less than 1 ppm, the carbon nanotubes encapsulated in the aluminum powder can be dispersed into the grain of the aluminum. On the other hand, when the ball milling process is performed under the condition of oxygen and humidity of 1 ppm or more, the carbon nanotubes encapsulated in the aluminum powder can not penetrate into the grain of the aluminum, and are mainly dispersed at the grain boundary.

In contrast to the present invention, when a ball milling process is performed without a mechanical de-clustering process of carbon nanotubes, a high-energy ball milling process must be performed in order to improve the degree of dispersion of carbon nanotubes. There is a problem that the mechanical properties of the composite material are deteriorated because the structure of the carbon nanotubes is destroyed as described above.

The step of manufacturing the aluminum-carbon nanotube composite (S130) may be performed by sintering the aluminum-carbon nanotube composite powder produced through the ball milling process. For example, aluminum-carbon nanotube composite powders can be sintered through a spark plasma sintering process. Specifically, the spark plasma sintering process can be performed at a temperature of about 200 to 600 DEG C for about 10 to 30 minutes. For example, aluminum-carbon nanotube composite powders are filled in a mold, sintered at a temperature of about 200 to 600 ° C. for about 1 minute to 1 hour under a pressure of about 50 MPa to 700 MPa, Aluminum-carbon nanotube composite powders can be sintered.

The step of extruding the aluminum-carbon nanotube composite (S140) may be carried out using an extrusion die. For example, the aluminum-carbon nanotube composite is heated at a temperature of about 200 to 600 ° C. for about 1 minute to 1 hour, and extruded under an applied pressure of about 50 MPa to 700 MPa using an extrusion die to form aluminum- The nanotube composite can be extruded.

FIGS. 2A and 2B are optical microscope photographs and confocal Raman microscope photographs of the aluminum-carbon nanotube composite material produced under the conditions of oxygen and humidity of 1 ppm or more (hereinafter referred to as "oxidation atmosphere").

Referring to FIGS. 2A and 2B, when the aluminum-carbon nanotube composite material is produced by performing the ball milling process in an oxidizing atmosphere, the encapsulated carbon nanotubes are limitedly distributed on the grain boundary of aluminum. That is, when the aluminum-carbon nanotube composite material is produced by a ball milling process in an oxidizing atmosphere, oxidation of aluminum occurs. Oxidation of the aluminum interferes with the dispersion of the carbon nanotubes in the aluminum grain, As a result, the carbon nanotubes are dispersed only in a limited region called aluminum grain boundary. As described above, carbon nanotubes intensively dispersed at the grain boundaries of aluminum interfere with dislocation movement to enhance the strength of the composite material but can not interact with the dislocation in the grain, I can not contribute.

3 is stress-strain curves of an aluminum-carbon nanotube composite material prepared according to an embodiment of the present invention.

Referring to FIG. 3, the maximum value of the engineering stress was increased as the content of the carbon nanotubes was increased. However, the engineering strain before the fracture did not decrease even when the content of the carbon nanotubes was increased. That is, when the aluminum-carbon nanotube composite material is manufactured according to the embodiment of the present invention, the carbon nanotubes are dispersed in the grain of the aluminum, and the carbon nanotubes up to the inside of the grain interfere with the movement of the potential, It is possible to minimize the work hardening of the carbon nanotube composite material and further reduce the elongation of the aluminum-carbon nanotube composite material.

FIG. 4 is a graph for explaining changes in Young's modulus and Yield strength according to carbon nanotube content. FIG.

Referring to FIG. 4, when the content of carbon nanotubes is less than 2 vol.%, The elastic modulus increases with increasing carbon nanotube content. When the content of carbon nanotubes is 2 to 8 vol.%, , The elastic modulus does not change much, and when the carbon nanotube content is more than 8 vol.%, The elastic modulus decreases as the carbon nanotube content increases. This is because the carbon nanotubes are degraded when the carbon nanotube content is 8 vol.% Or more.

The yield strength is similar to the elastic modulus of carbon nanotubes up to 8 vol.%, But the yield strength is maintained at a constant level even when the carbon nanotube content is more than 8 vol.%.

5 is a graph for explaining toughness change depending on the carbon nanotube content.

Referring to FIG. 5, toughness is increased up to 2 vol.% Of carbon nanotubes, but toughness is decreased at higher carbon nanotube concentration.

6A and 6B are electron backscattering diffraction (EBSD) images for explaining the microstructure after extrusion molding of a pure aluminum material and an aluminum-carbon nanotube composite material having a carbon nanotube content of 2 vol.%, 6B is a confocal Raman optical microscope image of the aluminum-carbon nanotube composite material, and FIG. 6D is an image showing the result of performing G band mapping from Raman spectra. FIG. 7 is a graph showing the Raman spectra of the aluminum-carbon nanotube composite material of FIG. 6b.

Referring to FIG. 6A, it can be seen that the grain structure of aluminum has an elongated shape with a narrow diameter. Since the extrusion molding process causes plastic deformation in the extrusion direction, the grain shape of aluminum has a shape extending in the extrusion direction.

Referring to FIGS. 6B to 6D and 7, when the carbon nanotubes are added in the amount of 2 vol.%, Grain reinforcement phenomenon occurs in which the grain size decreases. Also, as shown in FIG. 6D and FIG. 7, it can be seen that the carbon nanotube distribution is not related to the grain structure. From these observations, it can be seen that the carbon nanotubes encapsulated are located not only in the grain boundary but also in the interior.

8 is a graph for explaining grain size change according to the content of carbon nanotubes.

Referring to FIG. 8, it can be seen that as the carbon nanotube content increases, the grain size, especially the length and average diameter, decreases. When the content of carbon nanotubes is less than 2 vol.%, The grain size decreases sharply as the content of carbon nanotubes increases. When the content of carbon nanotubes is more than 2 vol.%, The content of carbon nanotubes increases It can be seen that the grain size does not change greatly. This reduction in grain size demonstrates grain enhancement during the carbon nanotube encapsulation process.

9 is a graph showing the results of an X-ray diffraction analysis of an aluminum-carbon nanotube composite material.

Referring to FIG. 9, as the content of carbon nanotubes increases, a phenomenon that a peak is widened is observed. This indicates that the lattice defects increase as the content of carbon nanotubes increases.

10 is a graph for explaining the dislocation density and the change of work hardening according to the carbon nanotube content.

10, when the content of carbon nanotubes is less than 4 vol.%, The dislocation density increases as the content of carbon nanotubes increases. When the content of carbon nanotubes is more than 4 vol.%, It can be seen that the dislocation density is kept constant. As the carbon nanotube content increases, dislocation density increases due to thermal mismatch due to different thermal expansion coefficients of carbon nanotubes and aluminum.

Work hardening was also similar to dislocation density. Work hardening delays the necking of the tensile specimen, thus greatly affecting the ductility of the material. Thus, as the work hardening improves, the specimen can be elongated longer.

11 shows TEM images of an aluminum-carbon nanotube composite material.

Referring to FIG. 11A, it is confirmed that the carbon nanotube is located in the grain. The carbon nanotubes located in the grain can interact with the electric potential to improve the strength and ductility of the composite material.

Referring to Figs. 11B and 11C, a linear potential can be generated by twisting the specimen during the TEM measurement. In this case, as shown in Fig. 11B, some linear potentials are accumulated in the vicinity of the carbon nanotubes. This phenomenon is more apparent when viewed at a higher resolution as shown in FIG. 11C. 11C is a cross-sectional image of a carbon nanotube having an interlayer distance of 0.385 to 0.5 nm.

Carbon nanotubes located in the grain interfere with the movement of dislocations, and as a result, carbon nanotubes can cause dispersion enhancement, which affects work hardening. That is, the carbon nanotubes dispersed in the grain affect the work hardening, and as a result, the elongation of the specimen can be improved. When the content of the carbon nanotubes increases, the carbon nanotubes become clusters as shown in FIG. 11 (d), which decreases the degree of dispersion of the carbon nanotubes and results in a decrease in the reinforcing efficiency. 11D is a TEM image of an aluminum-carbon nanotube composite material having a carbon nanotube content of 8 vol.%.

In summary, in the aluminum-carbon nanotube composite, the higher the dispersion strength of carbon nanotubes is, the higher the strength enhancement efficiency is, and the decrease in elongation can be minimized even though the strength is increased.

The carbon nanotubes dispersed in the grain can improve the strength and ductility of the aluminum-carbon nanotube composite material by the load transfer mechanism as well as the dispersion strengthening mechanism described above. The carbon nanotubes dispersed in the grain can not only absorb a part of the external force but also inhibit the potential movement. As a result, the carbon nanotubes dispersed in the grain can improve not only the Young 's modulus of the aluminum - carbon nanotube composite material but also the yield strength before plastic deformation.

That is, the potential movement during the plastic deformation is suppressed by the carbon nanotube located in the grain, and as a result, the strength and ductility of the aluminum composite material can be improved. Through the strong interface formed by the sintering process, the outer rod can be transferred to the carbon nanotube, and the carbon nanotube can generate an inverse force against the outer rod, which may interfere with the deformation of the composite material.

According to the present invention, since the carbon nanotubes are dispersed in the grain of aluminum, an aluminum-carbon nanotube composite material having excellent ductility and mechanical strength can be produced.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention as defined by the following claims. It can be understood that it is possible.

Claims (8)

Cutting the clustered carbon nanotubes to a first length or less and dispersing the carbon nanotubes on the surface of the aluminum powder;
Performing a ball milling process on the aluminum powder in which the carbon nanotubes are dispersed on the surface to produce an aluminum-carbon nanotube composite powder;
Sintering the aluminum-carbon nanotube composite powder to produce an aluminum-carbon nanotube composite; And
And then extruding the aluminum-carbon nanotube composite to produce an aluminum-carbon nanotube composite material. The method according to claim 1,
The step of cutting the cluster-type carbon nanotubes to a length less than the first length and dispersing the carbon nanotubes on the surface of the aluminum powder,
The carbon nanotubes having a diameter of 10 to 30 nm and a length of 10 to 70 μm and the aluminum powder having a diameter of 10 to 70 μm are put into a container and the blade mixer is rotated at 10000 to 40000 rpm, And mixing the aluminum powder with the aluminum powder to form an aluminum-carbon nanotube composite material. The method for producing an aluminum-carbon nanotube composite material according to claim 1, wherein the step of preparing the aluminum-carbon nanotube composite powder is performed under the condition that oxygen and humidity are less than 1 ppm. 4. The method of claim 3, wherein the ball milling is performed at 200 to 500 rpm for 20 to 60 minutes. The method of claim 3, wherein the aluminum-carbon nanotube composite powder includes carbon nanotubes encapsulated therein,
Wherein the encapsulated carbon nanotubes are dispersed in a grain of aluminum constituting the composite powder. The method as claimed in claim 1, wherein the step of sintering the aluminum-carbon nanotube composite powder to produce the aluminum-carbon nanotube composite comprises:
Filling the aluminum-carbon nanotube composite powders into a mold; And
And performing a spark plasma sintering process on the aluminum-carbon nanotube composite powders filled in the mold,
Wherein the discharge plasma sintering process is performed at a temperature of 200 to 600 ° C for 10 to 30 minutes. delete delete

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