KR20090014745A

KR20090014745A - Method for synthesizing carbonnanotube

Info

Publication number: KR20090014745A
Application number: KR1020070078929A
Authority: KR
Inventors: 황호수
Original assignee: 세메스 주식회사
Priority date: 2007-08-07
Filing date: 2007-08-07
Publication date: 2009-02-11

Abstract

A method for synthesizing carbon nanotubes is disclosed. According to the method for synthesizing carbon nanotubes, after forming a catalyst solution in which the molar ratio of magnesium oxide, iron and molybdenum is 1: 0.05 to 0.15: 0.005 to 0.015, it is subjected to sonication. Thereafter, the catalyst solution is burned at a temperature of 450 ° C. to 550 ° C. for 10 to 40 minutes to form a catalyst material, which is ground. Thereafter, a carbon source gas is supplied to the polished catalyst material to synthesize carbon nanotubes. The carbon nanotubes synthesized by the carbon nanotube synthesis method have a diameter of 15 nm or less.

Description

Synthesis method of carbon nanotubes {METHOD FOR SYNTHESIZING CARBONNANOTUBE}

The present invention relates to a method for synthesizing carbon nanotubes, and more particularly, to a method for synthesizing carbon nanotubes used in a conductive composite.

Carbon nanotubes have a hexagonal honeycomb structure formed by combining one carbon atom with three other carbon atoms in a round shape. That is, it has a structure like a cavity tube, and its diameter is about several tens of nanometers.

Such carbon nanotubes may optionally have electrical conductor characteristics such as metal or semiconductor characteristics, depending on the angle of the tube or the diameter of the tube. In addition, the carbon nanotubes are excellent in mechanical, electrical, and chemical properties, and can be applied to various fields such as field emission devices, hydrogen storage containers, and secondary battery electrodes, and are expected to be applied to tera-class semiconductor devices. It's becoming ...

In addition, depending on the number of bonds forming the wall can be classified into a single wall nanotube (SWNT), multi-walled nanotube (MWNT), a bundle nanotube (rope nanotube).

Since carbon nanotubes have excellent electrical conductivity, they can form a conductive composite when mixed with an insulating polymer material. Such a conductive composite may be applied to various fields such as a case of a semiconductor device and an electromagnetic shielding means. However, to be used as the conductive composite as described above, it must have a certain level or more of electrical conductivity. In order for a mixture of carbon nanotubes and a polymer material to have a certain level of electrical conductivity, various factors must be controlled, but in particular, the diameter of the carbon nanotubes must be controlled.

Accordingly, the technical problem of the present invention is to solve such a conventional problem, and an object of the present invention relates to a method for synthesizing carbon nanotubes capable of producing a conductive composite having excellent electrical conductivity.

Synthesis method of carbon nanotubes according to an embodiment of the present invention for achieving the above object comprises the steps of mixing the magnesium oxide, iron and molybdenum in a molar ratio of 1: 0.05 ~ 0.15: 0.005 ~ 0.015 to make a catalyst solution; Sonicating the catalyst solution; Burning the catalyst solution at a temperature between 450 ° C. and 550 ° C. for 10-40 minutes to form a catalyst material; Polishing the catalyst material; And synthesizing carbon nanotubes by supplying a carbon source gas to the polished catalyst material.

More preferably, the magnesium oxide, iron and molybdenum are mixed in a molar ratio of 1: 0.1: 0.01. In addition, the carbon source gas preferably includes methane gas.

The method of synthesizing carbon nanotubes according to an embodiment of the present invention may further include quenching the catalyst material at a rate of 150 ° C./min to 200 ° C./min before polishing the catalyst material.

The synthesizing of the carbon nanotubes may include supplying a reducing gas to the polished catalyst material to reduce the catalyst material; Loading the reduced catalytic material into a reaction chamber heated to 750 ° C. to 9500 ° C .; And supplying a carbon source gas to the catalyst material loaded in the reaction chamber.

According to such an inspection apparatus for an image element and an inspection method for an image element, the efficiency of light provided to the image element can be increased, light can be uniformly provided to the image element, and wiring can be formed on the second substrate. Sufficient space can be provided.

Specific details of other embodiments are included in the detailed description and drawings. Advantages and features of the present invention, and methods for achieving them will be apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms, and merely to make the embodiments of the present invention complete the present embodiment, and the general knowledge in the art to which the present invention belongs. It is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In this specification, the singular forms also include the plural unless specifically stated otherwise in the phrases. As used herein, “comprise” and / or “comprising” refers to one or more other components, steps, operations, and / or elements in the components, steps, operations, and / or elements mentioned. It does not exclude existence or addition. Also referred to herein as "up", "top", "top" or "bottom", "bottom" of a layer or film includes intervening another layer or film. In addition, as used herein, "overlapping" indicates a shape in which the lower structure and the upper structure have a common center and overlap each other, and includes a case where another structure is interposed between the lower structure and the upper structure, and the upper structure and the lower structure. Any one of the structures is meant to completely overlap the other structure. In addition, unless there is another definition for a term used herein, all terms used (including technical and scientific terms) may be used as meanings that can be commonly understood by those skilled in the art. There will be.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a flow chart showing a carbon nanotube synthesis method according to an embodiment of the present invention.

Referring to FIG. 1, the carbon nanotube synthesis method according to the present invention includes a step of preparing a catalyst and a step of synthesizing carbon nanotubes using the prepared catalyst.

Catalysts for synthesizing carbon nanotubes include a catalyst support material, a catalytic metal material and a catalytically active material supported on the catalyst support material. The catalyst support material allows the catalyst to maintain a constant size even at high temperatures at which carbon nanotubes are synthesized. As the catalyst support material, a magnesium-based material or an alumina-based material is used. The catalytic metal material reacts with the source gas for carbon nanotube synthesis to form carbon nanotubes. As the catalyst raw material, a transition metal material is used. For example, the transition metal material includes iron (Fe), cobalt (Co), nickel (Ni) and the like. The catalytically active material activates the reaction of the catalytic metal material with the carbon source gas for the synthesis of carbon nanotubes. Molybdenum (Mo) is used as the catalytically active mole.

In order to prepare a catalyst, first, iron (Fe), molybdenum (Mo) and magnesium oxide (MgO) are mixed to form a catalyst solution (S100).

Specifically, the catalyst solution is formed by dissolving a source material of iron, a source material of molybdenum and a source material of magnesium oxide in a small amount of water. As a source material of iron, an iron compound which can be burned with iron oxide is preferable. For example, the iron source material is iron (III) nitrate, iron sulfite, iron sulfate, iron carbonate, iron acetate, iron citrate, iron gluconate, iron hexacyanoferat, iron oxalate, and the like. Used. Preferably, hydrated iron (III) nitrate is used as the source of iron. As a source material of molybdenum, a molybdenum compound which can be burned with molybdenum oxide is preferable. For example, ammonium heptamolybdate tetrahydrate or the like is used as a source material of molybdenum. As a source material of magnesium oxide, a magnesium compound which can be burned with magnesium oxide is preferable. For example, magnesium nitrate is used as the magnesium oxide source material.

In the case of forming a conductive composite by mixing carbon nanotubes and an insulating polymer material, in order to apply it to a product, the surface resistance thereof should generally be 10 ⁹ [Ω / cm ² ] or less. In order to form the conductive composite, the amount of carbon nanotubes mixed in the insulating polymer material is about 2% to 3% of the total. In the case of adding a larger amount of carbon nanotubes, other additional problems occur in addition to the increase in production cost.

When carbon nanotubes having a diameter of 15 nm or more are added to the insulating polymer material by about 2% to 3% to form a conductive composite, the conductive composite has a surface resistance of 10 ¹² [Ω / cm ² ] or more. However, when carbon nanotubes having a diameter of 15 nm or less are added to the insulating polymer material by about 2% to 3% to form a conductive composite, the conductive composite has a surface resistance of 10 ⁹ [Ω / cm ² ] or less. Therefore, in order to form a conductive composite that can be applied to a product, carbon nanotubes having a diameter of 15 nm or less must be added to the insulating polymer material.

The diameter of the carbon nanotubes synthesized is influenced by the composition ratio of the catalyst solution. In particular, the composition ratio of iron plays an important role in the diameter of the carbon nanotubes synthesized. Specifically, as the composition ratio of iron increases, the diameter of the carbon nanotubes synthesized tends to increase. In order to form carbon nanotubes having a diameter of 15 nm or less, the molar ratio of magnesium oxide, iron, and molybdenum is set to 1: 0.05 to 0.15: 0.005 to 0.015. Preferably, in order to synthesize carbon nanotubes having a diameter of 15 nm or less, the molar ratio of magnesium oxide, iron, and molybdenum is preferably 1: 0.1: 0.01.

The catalyst solution in which the source material of iron, the source material of molybdenum, and the source material of magnesium oxide are dissolved are mixed while sonicating (S200). The size of the catalyst material can be controlled according to the conditions of the intensity of the ultrasonic wave, the time of the ultrasonic treatment, and the like, and as a result, the diameter of the carbon nanotubes synthesized can be controlled.

Citric acid and urea are added to the catalyst solution. Citric acid and urea serve to increase the surface area of the catalyst.

The catalyst solution to which citric acid and urea are added is heated to a predetermined temperature or more and burned (S300). The temperature and the combustion time for burning the catalyst solution affect the diameter of the carbon nanotubes synthesized. In order to form carbon nanotubes having a diameter of 15 nm or less, the catalyst solution is preferably burned by heating for 10 minutes to 40 minutes in a temperature range of 450 ° C to 550 ° C. The combustion temperature and combustion time have a great influence on the diameter of the carbon nanotubes synthesized.

The heated catalyst solution evaporates the solvent rapidly bubbling with the added citric acid and urea and forms a solid having a low density and high surface area. The solid has a composition of iron oxide and molybdenum oxide supported on magnesium oxide.

After combustion, the heated solid is rapidly cooled with cooling water. It is preferable to make cooling rate into 150 degreeC / min-200 degreeC / min.

Grinding the cooled solid to prepare a catalyst in the form of particulates (S400).

In the case of preparing the catalyst as described above, the diameter of the carbon nanotubes synthesized can be controlled by controlling the composition of the catalyst, the sonication conditions, the combustion conditions, and the like.

Hereinafter, a step of forming carbon nanotubes using the prepared catalyst will be described.

FIG. 2 is a flowchart illustrating a step of synthesizing carbon nanotubes using the catalyst material shown in FIG. 1.

Referring to FIG. 2, a catalyst which is polished and has a particulate form is loaded on a substrate. Thereafter, the substrate is exposed to a cleaning gas. This is to remove foreign substances remaining on the substrate. When foreign matter is present in the substrate, the productivity of the carbon nanotubes is reduced, and the properties of the carbon nanotubes synthesized are reduced. An inert gas is used as the cleaning gas. For example, argon gas may be used as the cleaning gas.

Thereafter, the substrate loaded with the catalyst is loaded into the reaction chamber (S510). The interior of the reaction chamber into which the substrate is loaded is heated and maintained at a constant temperature for carbon nanotube synthesis. The internal temperature of the reaction chamber affects the diameter of the carbon nanotubes synthesized. In order to synthesize carbon nanotubes having a diameter of 15 nm or less, it is preferable to maintain the temperature inside the reaction chamber at 650 ° C to 9500 ° C. The higher the temperature inside the reaction chamber, the smaller the diameter of the synthesized carbon nanotubes, and more preferably, the temperature inside the reaction chamber is maintained at 750 ° C to 9500 ° C.

The particulate catalyst is present in the form of a metal oxide supported on magnesium oxide. Therefore, in order to react the catalyst with the carbon source gas, the catalyst is activated and used (S520). The step of activating the catalyst is carried out by exposing the catalyst in particulate form to the reducing agent. Hydrogen may be used as the reducing agent.

Thereafter, the carbon source gas is supplied to the reduced catalyst (S530). As the carbon source gas, methane gas, acetylene gas, propane gas, ethylene gas, carbon monoxide and / or mixed gas thereof, and the like may be used. The type of carbon source gas also affects the diameter of the carbon nanotubes synthesized. For example, when methane gas is used as the carbon source gas, the diameter of the carbon nanotubes synthesized is smaller than when acetylene gas or ethylene gas is used as the carbon source gas. In order to synthesize carbon nanotubes having a diameter of 15 nm or less, it is preferable to use methane gas as the carbon source gas.

In the above description, it was described that the carbon source gas is supplied after the catalyst is activated, but the activation step of the catalyst and the supply step of the carbon source gas may be simultaneously performed. That is, it is also possible to supply hydrogen gas which is a reducing agent with a carbon source gas.

Due to the high temperature environment in the reaction chamber, carbon is separated from the carbon source gas, and the separated carbon is adsorbed and grown on the catalytic metal.

When the production of the carbon nanotubes is completed, the substrate is unloaded from the reaction chamber to recover the synthesized carbon nanotubes.

As described in detail above, according to the present invention, carbon nanotubes having a diameter of 15 nm or less may be formed by controlling conditions that may affect the diameter of the carbon nanotubes in the catalyst preparation step and the carbon nanotube synthesis step. . When carbon nanotubes with a diameter of 15 nm or less are mixed with an insulating polymer to form a conductive composite, they have excellent electrical properties.

In the detailed description of the present invention described above with reference to the preferred embodiments of the present invention, those skilled in the art or those skilled in the art having ordinary skill in the art will be described in the claims to be described later It will be understood that various modifications and variations can be made in the present invention without departing from the scope of the present invention.

Claims

Forming a catalyst solution having a molar ratio of magnesium oxide, iron, and molybdenum in a range of 1: 0.05 to 0.15: 0.005 to 0.015;

Sonicating the catalyst solution;

Burning the catalyst solution at a temperature between 450 ° C. and 550 ° C. for 10-40 minutes to form a catalyst material;

Polishing the catalyst material to form catalyst powder; And

Supplying a carbon source gas to the catalyst powder to synthesize carbon nanotubes.

The method of claim 1, wherein the molar ratio of magnesium oxide, iron, and molybdenum is 1: 0.1: 0.01.

The method of claim 1, wherein the carbon source gas comprises methane gas.

The method of claim 3, further comprising quenching the catalyst material at a rate of 150 ° C./min to 200 ° C./min before forming the catalyst powder.

The method of claim 1, wherein synthesizing the carbon nanotubes

Loading the catalyst material into a reaction chamber heated to 750 ° C. to 9500 ° C .;

Supplying a reducing gas to the catalyst material to reduce the catalyst material; And

The carbon nanotube synthesis method comprising the step of supplying a carbon source gas to the reduced catalyst material.