Patent Application
20100279097
1. Field of the Invention
The present invention is related to a vapor grown carbon fiber mat and a method for fabricating the same, especially, a vapor grown carbon fiber mat having a semi-continuous structure.
2. Description of the Related Art
With the progress of the times, traditional mechanical products have been substituted by 3C electronic products unconsciously in human daily life. Scientists are forced to dedicate to develop products with more powerful functions, higher efficiency and faster processing velocity for satisfying the demands of fast and convenience.
All electronic products with high efficiency have to face the issues of power conversion. The more powerful product is, the better electronic efficiency needed is, and accordingly, the bigger problem of waste heat produced is. Therefore, how to dissipate heat for maintaining working stability of a system is becoming an increasingly important issue.
Furthermore, lots of traditional heat-dissipating materials are gradually eliminated because of the critical customers' demands for small, light and portable products.
In other words, researches for novel heat-dissipating materials are urgent and have-to-face issues for scientists. The basic requirement of novel heat-dissipating materials is better in thermal conductivity and thinner in volume.
Accordingly, some composite materials with property of higher conductivity begin to be available. Among those composite materials, the heat-dissipating composite materials fabricated by using vapor grown carbon fibers as reinforcing materials is the most potential.
That is because the room temperature thermal conductivity of a graphitized vapor grown carbon fiber is up to 1950 W/m-K, which is approximately five times higher than that of copper, and the density of the vapor grown carbon fiber is ¼ or less than that of copper. Moreover, the room temperature resistance of the vapor grown carbon fiber is extreme low, i.e. about 0.6 μΩ·m, which is similar to that of titanium.
Among all carbon fibers, the vapor grown carbon fiber has the best thermal conductivity and resistance, and it also has good tensile stress and tension coefficient; therefore, the vapor grown carbon fiber is the best choice for developing composite materials with the property of high thermal conductivity.
The only drawback is that the length of traditional vapor grown carbon fiber is at most hundreds of microns, so that the composite materials fabricated by the traditional vapor grown carbon fiber have a lot of discontinuous scission points, which significantly restrict heat conduction and therefore reduce the thermal conductivity of the composite materials to be similar to or even lower than that of aluminum.
In view of the disadvantages of conventional technology, we provide a novel method for producing a vapor grown carbon fiber mat to fabricate carbon fiber mats having a semi-continuous structure for improving thermal conductivity of composite materials.
In view of foregoing, one object of the present invention is to provide a method for fabricating a carbon fiber mat. The method of present invention fabricates a vapor grown carbon fiber mat with a semi-continuous structure by vapor deposition method, wherein the semi-continuous length thereof can be longer than 10 centimeter. In contrast with the carbon fiber mats fabricated by traditional methods (length of the carbon fiber is tens to hundreds of microns), the carbon fiber mats fabricated by the method of present invention have better heat conduction and heat-dissipating efficiency, resulting from high thermal conductivity. The semi-continuous carbon fiber mats of the present invention successfully overcome the issues for the thermal resistance of scission point resulting from the discontinuities of carbon fibers of traditional vapor grown carbon fiber composite materials. Therefore, the thermal conductivity of the composite materials thereof is dramatically improved, and the composite materials also have the property of low density, which makes the composite materials easier to be fabricated.
Another object of the present invention is to provide a carbon fiber mat with a semi-continuous structure and the semi-continuous length thereof can be longer than 10 centimeter. The carbon fiber mat of the present invention has higher thermal conductivity because of the advantage in structure. The semi-continuous carbon fiber mats of the present invention successfully overcome the issues for the thermal resistance of scission point resulting from the discontinuities of carbon fibers of traditional vapor grown carbon fiber composite materials. Therefore, the thermal conductivity of the composite materials thereof is dramatically improved, and the composite materials also have the property of low density, which makes the composite materials easier to be fabricated.
Yet another object of the present invention is to provide a graphitized carbon fiber mat, which comprises carbon fibers with semi-continuous structure. Therefore, the issues for the thermal resistance of scission point resulting from the discontinuities of carbon fibers are overcome, and the thermal conductivity of the composite materials is significantly improved.
To achieve the above objects, the present invention provides a method for fabricating a carbon fiber mat, comprising the following steps: (a) providing a substrate with a catalyst on its surface; (b) placing said substrate in a furnace; (c) introducing hydrogen, ammonia, or combinations thereof into said furnace; (d) adjusting the temperature of said furnace to 400° C. to 900° C. to proceed a heat treatment for 15 to 90 minutes; (e) adding a carbon-containing compound into said furnace and adjusting the ratio of said carbon-containing compound and said hydrogen, ammonia, or combinations thereof; (f) adjusting the temperature of said furnace to 600° C. to 1200° C. to crack said carbon-containing compound and reacting for 1 to 3 hours, and thereby forming a carbon fiber mat.
Preferably, nucleation points are obtained after processing said catalyst through said step (a) to said step (d), wherein the density of said nucleation points distributes between 1˜50 sites/μm2, and the size of said nucleation points distributes between 10˜2000 nm.
Preferably, said catalyst is a transition metal, an alloy comprising one or more transition metals, or a compound comprising one or more transition metals. Said catalyst is powder, solution, or film. More preferably, said transition metal is iron.
Preferably, said substrate in said step (a) comprises any materials with properties of retractable and plane-surface structure (for instance, said substrate includes but not limited to a quartz substrate, a graphite substrate, a silicon substrate, a ceramic substrate, a carbon/carbon composite substrate and a bamboo carbon plate).
Preferably, said furnace is a horizontal high temperature furnace or a vertical high temperature furnace.
Preferably, the temperature of said heat treatment in said step (d) is 500° C. to 850° C.; the time of said heat treatment is 25 to 60 minutes.
Preferably, said carbon-containing compound in said step (e) comprises a hydrocarbon (for instance, includes but not limited to methane, ethane, propane, butane, pentane, hexane, ethene, ethyne, and benzene) or other carbon-containing organic compound (for instance, includes but not limited to methanol, ethanol, propanol, formic acid, acetic acid, propionic acid, native gas and petroleum). The ratio of said carbon-containing compound and said hydrogen, ammonia, or combinations thereof in said step (e) is a mole ratio of 1:100 to 200:100; more preferably, is 5:100 to 150:100.
Preferably, the cracking temperature in said step (f) is 700° C. to 1100° C. In this step (f), said carbon-containing compound is cracked to carbon elements. Said carbon elements are diffused into said catalyst and then formed a carbon fiber at 600° C. to 1200° C. Because of the appropriate density and size of said nucleation points, said carbon fiber crosses and interacts with other carbon fibers in the neighborhood and is influenced by gravity and flow of specific gas to bend and grow onto said substrate to form a carbon fiber mat along the direction of the gas flow in said furnace.
Preferably, said hydrogen, ammonia, or combinations thereof is introduced into said furnace at a flow velocity of 0.5˜10% of volume of said furnace per minute.
To achieve the above objects, the present invention provides a carbon fiber mat, which is fabricated by the method of the present invention. The carbon fiber mat provided by the present invention has a carbon fiber structure with semi-continuous length of 1˜50 centimeter.
To achieve the above objects, the present invention provides a graphitized carbon fiber mat, which is obtained by heating the carbon fiber mat of the present invention in inert gases at 2400° C. to 2800° C., wherein the graphitized degree is 99˜100%.
To sum up, the method provided by the present invention can fabricate a carbon fiber mat with a semi-continuous structure. The graphitized semi-continuous vapor grown carbon fiber mat of the present invention can be used to produce a composite material. Because of the semi-continuous structure thereof, the produced composite material successfully overcomes the issues for the thermal resistance of scission point resulting from the discontinuities of carbon fibers in traditional vapor grown carbon fiber composite materials.
The thermal conductivity of the polymer matrix composite material fabricated by the aforementioned graphitized carbon fiber mat used as a reinforced material is 400 W/m-K to 600 W/m-K.
As mentioned above, the present invention provides a method for fabricating a carbon fiber mat, comprising the following steps: (a) providing a substrate with a catalyst on its surface; (b) placing said substrate in a furnace; (c) introducing hydrogen, ammonia, or combinations thereof into said furnace; (d) adjusting the temperature of said furnace to 400° C. ˜ 900° C. to proceed a heat treatment for 15 to 90 minutes; (e) adding a carbon-containing compound into said furnace and adjusting the ratio of said carbon-containing compound and said hydrogen, ammonia, or combinations thereof; (f) adjusting the temperature of said furnace to 600° C. to 1200° C. to crack said carbon-containing compound and reacting for 1 to 3 hours, and thereby forming a carbon fiber mat.
Please refer to
Then, the temperature of said furnace and the volume ratio of said hydrocarbon and said hydrogen or said ammonia can be adjusted optionally to make the carbon fiber mat, which is gradually formed, grow successively until the top (80) of said carbon fiber mat is out of the reaction area. The adjusting ranges of the temperature and the volume ratio of said hydrocarbon and said hydrogen or said ammonia are with the same as the aforementioned cracking step. No matter the structure of or the length and diameter of carbon fibers of said semi-continuous vapor grown carbon fiber mat cannot be achieved by traditional method for fabricating vapor grown carbon fibers.
It is noted that the semi-continuous vapor grown carbon fiber mats can be graphitized and have a room temperature thermal conductivity of up to 1950 W/m-k by simply process of heat treatment in inert gases at 2600° C. The graphitized semi-continuous vapor grown carbon fiber mats (as shown in
The following examples are used to demonstrate the technical features and advantages of the present invention clearly. It shall be understood that the technical features of the present invention have already described in the above summary of the invention, those skilled in the art can easily accomplish the present invention in accordance with the above summary of the invention. The following examples are only used as examples but not used to limit the technical features of the present invention.
Iron catalyst was sprayed evenly onto a ceramic substrate (8 cm×6 cm), and then the substrate was placed into a horizontal high temperature furnace tube. 800 sccm of argon was introduced into the high temperature furnace, and the temperature of the furnace was adjusted to 600° C. After that, 100 sccm of hydrogen was introduced immediately to substitute the argon and the catalyst was processed for heat treatment. Then, the temperature of the furnace was raised to 1100° C., and 50 sccm of methane was introduced therein; in the mean time, the mole ratio of said methane and said hydrogen is 50:100. After maintaining the temperature (1100° C.) for 2 hours, a 8 cm×6 cm semi-continuous vapor grown carbon fiber mat was obtained and average diameter of carbon fiber thereof was about 5 μm.
The preparation procedures were the same as example 1 except that the substrate was replaced with a 8 cm×6 cm carbon/carbon composite substrate. Eventually, a 8 cm×6 cm semi-continuous vapor grown carbon fiber mat was obtained and average diameter of the carbon fibers thereof was about 5 μm.
Iron catalyst was sprayed evenly onto a ceramic substrate (35 cm×10 cm), and then the substrate was placed into a horizontal high temperature furnace tube. 1000 sccm of argon was introduced into the high temperature furnace, and the temperature of furnace was adjusted to 600° C. After that, 600 sccm of hydrogen was introduced immediately to substitute the argon and the catalyst was processed for heat treatment. Then, the temperature of the furnace was raised to 1100° C., and 300 sccm of methane was introduced therein; in the mean time, the mole ratio of said methane and said hydrogen is 50:100. After maintaining the temperature (1100° C.) for 2 hours, a 35 cm×10 cm semi-continuous vapor grown carbon fiber mat was obtained and average diameter of the carbon fibers thereof was about 6 μm.
Iron catalyst was sprayed evenly onto a carbon/carbon composite substrate (50 cm×12 cm), and then the substrate was placed into a horizontal high temperature furnace. 800 sccm of argon was introduced into the high temperature furnace, and the temperature of furnace was adjusted to 600° C. After that, 600 sccm of hydrogen was introduced immediately to substitute the argon and the catalyst was processed for heat treatment. Then, the temperature of the furnace was raised to 1100° C., and 700 sccm of methane was introduced therein; in the mean time, the mole ratio of said methane and said hydrogen is 116.67:100. After maintaining the temperature (1100° C.) for 2 hours, a 50 cm×12 cm semi-continuous vapor grown carbon fiber mat was obtained and average diameter of the carbon fibers thereof was about 8 μm. A polymer matrix composite material was fabricated by graphitizing the obtained carbon fiber mat at 2600° C., wherein the thermal conductivity of the polymer matrix composite material was 530 W/m-K.
To sum up, the semi-continuous vapor grown carbon fiber mat with high thermal conductivity of the present invention is a high thermal conductivity semi-continuous vapor grown carbon fiber mat fabricated by chemical vapor deposition method. The size of said mat depends on the substrate used; that is, the size of said mat can be varied easily. The semi-continuous vapor grown carbon fiber mats not only have the advantages of the traditional vapor grown carbon fiber mats, such as high thermal conductivity, but also overcome the disadvantages of the composite materials fabricated by traditional non-continuous vapor carbon fibers, such as the heat-dispensing issue due to the large thermal resistance resulting from too many discontinuities. Therefore, the thermal conductivity is significantly improved to much higher than that of composite materials fabricated by traditional vapor grown carbon fibers. Moreover, the structure of the mats of the present invention is also beneficial for the fabrication of composite materials. The embodiments and the technical principles used are described above. All variations and modifications of the present invention and the uses thereof are included in the scope of the present invention if they do not depart from the spirit of the disclosure of this specification and drawings.
All characteristics disclosed herein can be combined in any combination. And the characteristics disclosed herein can be replaced by any characteristics to be used for the same, equal, or similar purpose. Thus, unless otherwise specified, the characteristics disclosed herein are examples of a series of equal or similar characteristics.
In addition, based on the disclosure herein, appropriate changes and modifications may be made by those skilled in the art according to different uses and situations without departing from the spirit and scope of the invention. Therefore, other embodiments are included in the claims of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 98114687 | May 2009 | TW | national |
