Method for making carbon nanotube metal composite

A method for making a carbon nanotube metal composite includes the following steps. A number of carbon nanotubes is dispersed in a solvent to obtain a suspension. Metal powder is added into the suspension, and then the suspension agitated. The suspension containing the metal powder is allowed to stand for a while. The solvent is reduced to obtain a mixture of the number of carbon nanotubes and the metal powder.

RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 from China Patent Application No. 201010102120.4, filed on Jan. 22, 2010, in the China Intellectual Property Office, incorporated herein by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to a method for making a carbon nanotube metal composite.

2. Description of Related Art

The discovery of carbon nanotubes has stimulated a great amount of research efforts around the world. Carbon nanotubes are characterized by the near perfect cylindrical structures of seamless graphite. Carbon nanotubes possess unusual mechanical, electrical, magnetic, catalytic, and capillary properties. A wide range of applications use carbon nanotubes as one-dimensional conductors in nanoelectronic devices, as reinforcing fibers in polymeric and carbon composite materials, as absorption materials for gases such as hydrogen, and as field emission sources.

In recent years, carbon nanotube metal composites have become a hot subject of research. However, there are still difficulties in the field of carbon nanotube metal composites. Because carbon nanotubes have great surface area and specific surface energy, it is difficult to evenly disperse the carbon nanotubes in a metal powder matrix. To solve this problem, carbon nanotubes undergo mechanical ball milling so they can be blended with metal particles to obtain a carbon nanotube metal composite. However, the structure of carbon nanotubes after mechanical ball milling may suffer serious damage.

What is needed, therefore, is to provide a method for making a carbon nanotube metal composite.

DETAILED DESCRIPTION

References will now be made to the drawings to describe, in detail, various embodiments of the present method for making a carbon nanotube metal composite.

Referring toFIG. 1, a method for making a carbon nanotube metal composite of one embodiment includes the following steps of:

(S10) dispersing a number of carbon nanotubes10in a solvent20to obtain a suspension containing the carbon nanotubes10;

(S20) adding metal powders12into the suspension containing the carbon nanotubes10, agitating the suspension containing the carbon nanotubes10to combine the carbon nanotubes10with the metal powders12, and letting the suspension stand;

(S30) reducing the solvent20to obtain a mixture30of the carbon nanotubes10and the metal powders12.

The carbon nanotubes10can be treated before step (S10) by the following substeps of:

(S101) providing and purifying the carbon nanotubes10; and

In step (S101), the carbon nanotubes10can be obtained by any method, such as chemical vapor deposition (CVD), arc discharging, or laser ablation. In one embodiment, the carbon nanotubes10are obtained by a CVD method including the following steps of:

providing a substrate;

forming a carbon nanotube array on the substrate by CVD; and

peeling the carbon nanotube array off the substrate by a mechanical method, thereby achieving a number of carbon nanotubes.

The carbon nanotubes10can be single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, or combinations of them. A diameter of each of the carbon nanotubes10can be less than about 50 nanometers. A length of each of the carbon nanotubes10can be less than about 2 micrometers. In one embodiment, the diameter of each of the carbon nanotubes10is less than about 50 nanometers, and the length of the carbon nanotubes10is in a range from about 50 nanometers to about 200 nanometers.

In step (102), the carbon nanotubes10can be chemically functionalized, which refers to the carbon nanotubes10being chemically treated to introduce functional groups on the surface. Chemical treatments include, but are not limited to, oxidation, radical initiation reactions, and Diels-Alder reactions. The functional groups can be any hydrophilic group, such as carboxyl (—COOH), aldehyde group (—CHO), amidogen group (—NH2), hydroxyl (—OH), or combinations of them. After being functionalized, the carbon nanotubes10are easily dispersed in the solvent20by the provision of the functional groups.

In step (S10), the carbon nanotubes10can be treated by the substeps of:

(S14) putting the carbon nanotubes10into the solvent20to obtain a mixture;

In step (S10), the above steps are repeated about 4 to 5 times to obtain the suspension of the carbon nanotubes10and the solvent20.

In step (S10), the solvent20can be alcohol, ethyl acetate, or N,N-Dimethylformamide (DMF). The carbon nanotubes10can be added into a container100containing the solvent20. The carbon nanotubes10can be dispersed in the solvent20by a method of ultrasonic dispersion. After ultrasonic dispersion, the carbon nanotubes can be evenly dispersed in the solvent20to form the suspension. Because the carbon nanotubes10are evenly dispersed in the suspension, the carbon nanotubes would not deposit even after long standing time of the suspension. Additionally, in the process of the ultrasonic dispersion, static charges formed on the carbon nanotubes10. In one embodiment, the solvent is DMF, and the time of ultrasonic dispersion is in a range from about 10 minutes to about 30 minutes.

In step (S20), the metal powders12are added in the suspension containing the carbon nanotubes10. The carbon nanotubes10in the solvent20adhere to the metal powders12by electrostatic force between the carbon nanotubes10and the metal powders12in the process of agitating. The carbon nanotubes10combine with the metal powders12and deposit on the bottom of the container100. After standing, the carbon nanotubes10deposit on the bottom of the container100with the metal powders12. Two layers are formed in the container100. There is a boundary40between the two layers, the layers being an upper layer and a bottom layer. The upper layer in the container100comprises mostly the solvent20. The bottom layer in the container100comprises mostly of the carbon nanotubes10and the metal powders12. The carbon nanotubes10are evenly dispersed in a matrix made of the metal powders12at the bottom layer in the container100.

The metal powders12can be made of metal or alloy. A volume ratio of the metal powders12to the carbon nanotubes10can be in a range from about 1:1 to about 50:1. The metal powders12can be made of magnesium (Mg), zinc (Zn), manganese (Mn), aluminum (Al), thorium (Th), lithium (Li), silver (Ag), lead (Pb), or calcium (Ca). The metal powders12can be made of an alloy which includes magnesium and any combination of elements, such as Zn, Mn, Al, Th, Li, Ag, and Ca. A mass ratio of the magnesium metal to the other elements in the alloy can be more than 4:1. In one embodiment, the metal powder12is Pb powder. The volume ratio of the Pb powder to the carbon nanotubes is 20:1.

The step (S30) can include the following substeps of:

(S301) filtering out the solvent20to obtain the mixture30of the carbon nanotubes10and the metal powder12;

(S302) drying the mixture30of the carbon nanotubes10and the metal powder12.

In step (S301), the solvent20in the upper layer of the container100can be poured out of the container100. The carbon nanotubes10and the metal powder12can be filtered by filter paper.

In step (S302), the mixture30of the carbon nanotubes10and the metal powder12can be put into a vacuum oven to evaporate remains of the solvent20. A temperature of the vacuum oven can range from about 40° C. to about 50° C. for a period of time (e.g. about 10 minutes to about 60 minutes).

FIG. 2is an SEM image of a mixture of the carbon nanotubes and the Pb powder of one embodiment. As can be seen inFIG. 2, the carbon nanotubes are evenly dispersed in a mixture of the Pb powder. The carbon nanotubes are attracted to the surface of each of the Pb powder particles.

A method for making a carbon nanotube metal composite of one embodiment includes the following steps:

(S10) dispersing a number of carbon nanotubes10in a solvent20to obtain a suspension containing the carbon nanotubes10;

(S20) adding metal powder12into the suspension containing the carbon nanotubes10, agitating the suspension containing the carbon nanotubes10to make the carbon nanotubes10combine with the metal powders12, and letting the suspension stand;

(S30) reducing the solvent20to obtain a mixture30of the carbon nanotubes10and the metal powder12.

(S40) treating the mixture30of the carbon nanotubes10and the metal powder12with a molding process.

In step (S40), in one embodiment, the mixture30of the carbon nanotubes10and the metal powder12is treated by the following substeps of:

heating the mixture30in a protective gas to achieve a semi-solid-state paste;

stirring the semi-solid-state paste using an electromagnetic stirring force to disperse the carbon nanotubes into the paste;

injecting the semi-solid-state paste into a die; and

cooling the semi-solid-state paste to achieve a carbon nanotube metal composite.

Referring toFIG. 3, a hot-pressing machine200includes a container230, and two boards210positioned in the container230. The boards210can be heated to a predetermined temperature. A vacuum pump (not shown) can be connected to the container230to evacuate the air in the container230. A protective gas can be pumped into the container230through a pipe (not shown inFIG. 3) connected thereto. The protective gas can be nitrogen (N2) and/or a noble gas.

In step (S40), mixture30of the carbon nanotubes10and the metal powder12can be treated by a hot-pressing molding method including the following substeps of:

(S401) locating the mixture30between the two boards210;

(S402) evacuating the air in the container230and filling a protective gas into the container230;

(S403) applying a pressure on the mixture30through the two boards210at an elevated temperature for a period of time (e.g. about 5 hours to about 15 hours); and

(S404) relieving the pressure on the mixture30and cooling the mixture30to room temperature to achieve the carbon nanotube metal composite material.

By hot pressing, the mixture30of the carbon nanotubes10and the metal powders12is formed into a composite material. The pressure can be in the approximate range from about 50 Mega Pascal (MPa) to about 100 MPa. The temperature can be in the approximate range from about 300° C. to about 400° C.

Depending on the embodiment, certain of the steps of methods described may be removed, others may be added, and the sequence of steps may be altered. It is also to be understood that the description and the claims drawn to a method may include some indication in reference to certain steps. However, the indication used is only to be viewed for identification purposes and not as a suggestion as to an order for the steps. Finally, it is to be understood that the above-described embodiments are intended to illustrate rather than limit the disclosure. Variations may be made to the embodiments without departing from the spirit of the disclosure as claimed. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure.