The present invention relates to the formation of composite material, and more particularly, to composite material made from nanostructure composite sheets designed to promote shielding, absorption, and increased conductivity.
Carbon nanotubes are known to have extraordinary tensile strength, including high strain to failure and relatively high tensile modulus. Carbon nanotubes may also be highly resistant to fatigue, radiation damage, and heat. To this end, the addition of carbon nanotubes to composite materials can increase tensile strength and stiffness of the composite materials.
Within the last fifteen (15) years, as the properties of carbon nanotubes have been better understood, interests in carbon nanotubes have greatly increased within and outside of the research community. One key to making use of these properties is the synthesis of nanotubes in sufficient quantities for them to be broadly deployed. For example, large quantities of carbon nanotubes may be needed if they are to be used as high strength components of composites in macroscale structures (i.e., structures having dimensions greater than 1 cm.)
One common route to nanotube synthesis can be through the use of gas phase pyrolysis, such as that employed in connection with chemical vapor deposition. In this process, a nanotube may be formed from the surface of a catalytic nanoparticle. Specifically, the catalytic nanoparticle may be exposed to a gas mixture containing carbon compounds serving as feedstock for the generation of a nanotube from the surface of the nanoparticle.
Recently, one promising route to high-volume nanotube production has been to employ a chemical vapor deposition system that grows nanotubes from catalyst particles that “float” in the reaction gas. Such a system typically runs a mixture of reaction gases through a heated chamber within which the nanotubes may be generated from nanoparticles that have precipitated from the reaction gas. Numerous other variations may be possible, including ones where the catalyst particles may be pre-supplied.
In cases where large volumes of carbon nanotubes may be generated, however, the nanotubes may attach to the walls of a reaction chamber, resulting in the blockage of nanomaterials from exiting the chamber. Furthermore, these blockages may induce a pressure buildup in the reaction chamber, which can result in the modification of the overall reaction kinetics. A modification of the kinetics can lead to a reduction in the uniformity of the material produced.
An additional concern with nanomaterials may be that they need to be handled and processed without generating large quantities of airborne particulates, since the hazards associated with nanoscale materials are not yet well understood.
The processing of nanotubes or nanoscale materials for macroscale applications has steadily increased in recent years. The use of nanoscale materials in textile fibers and related materials has also been increasing. In the textile art, fibers that are of fixed length and that have been processed in a large mass may be referred to as staple fibers. Technology for handling staple fibers, such as flax, wool, and cotton has long been established. To make use of staple fibers in fabrics or other structural elements, the staple fibers may first be formed into bulk structures such as yarns, tows, or sheets, which then can be processed into the appropriate materials.
Accordingly, it would be desirable to provide a material that can take advantage of the characteristics and properties of carbon nanotubes, so that a sheet made of carbon nanotubes can be processed for end use applications, including (i) structural systems, such as fabrics, armor, composite reinforcements, antennas, electrical or thermal conductors, and electrodes, (ii) mechanical structural elements, such as plates and I-beams, and (iii) cabling or ropes.
The present invention provides, in accordance with one embodiment, a nanostructured sheet. The sheet includes a substantially planar body, a plurality of nanotubes defining a matrix within the body, and a protonation agent dispersed throughout the matrix of nanotubes for enhancing proximity of adjacent nanotubes to one another.
The present invention provides, in accordance with another embodiment, a method of forming a nanostructured sheet. The method includes generating a substantially planar body defined by a matrix of nanotubes, applying a protonation agent throughout the matrix of nanotubes, and allowing the presence of the protonation agent to bring adjacent nanotubes in closer proximity with one another.
The present invention provides, in an embodiment, a composite material made from nanostructured sheets designed to promote, for instance, electromagnetic interference shielding, absorption of signals or electromagnetic waves, and increased conductivity. In an embodiment, the sheet material may include a substantially planar body in the form of a composite sheet. A plurality of nanotubes may define a matrix within the planar body. As there may exist openings between adjacent nanotubes in the matrix, a protonation agent may be applied. A plurality of composite sheets may be then layered on one another.
Presently, there exist multiple processes and variations thereof for growing nanotubes, and forming yarns, sheets or cable structures made from these nanotubes. These include: (1) Chemical Vapor Deposition (CVD), a common process that can occur at near ambient or at high pressures, and at temperatures above about 400° C., (2) Arc Discharge, a high temperature process that can give rise to tubes having a high degree of perfection, and (3) Laser ablation.
The present invention, in one embodiment, employs a CVD process or similar gas phase pyrolysis procedures known in the industry to generate the appropriate nanostructures, including carbon nanotubes. Growth temperatures for a CVD process can be comparatively low ranging, for instance, from about 400° C. to about 1350° C. Carbon nanotubes, both single wall (SWNT) or multiwall (MWNT), may be grown, in an embodiment of the present invention, by exposing nanoscaled catalyst particles in the presence of reagent carbon-containing gases (i.e., gaseous carbon source). In particular, the nanoscaled catalyst particles may be introduced into the reagent carbon-containing gases, either by addition of existing particles or by in situ synthesis of the particles from a metal-organic precursor, or even non-metallic catalysts. Although both SWNT and MWNT may be grown, in certain instances, SWNT may be selected due to their relatively higher growth rate and tendency to form rope-like structures, which may offer advantages in handling, thermal conductivity, electronic properties, and strength.
The strength of the individual carbon nanotubes generated in connection with the present invention may be about 30 GPa or more. Strength, as should be noted, is sensitive to defects. However, the elastic modulus of the carbon nanotubes fabricated in the present invention may not be sensitive to defects and can vary from about 1 to about 1.2 TPa. Moreover, the strain to failure of these nanotubes, which generally can be a structure sensitive parameter, may range from a about 10% to a maximum of about 25% in the present invention.
Furthermore, the nanotubes of the present invention can be provided with relatively small diameter. In an embodiment of the present invention, the nanotubes fabricated in the present invention can be provided with a diameter in a range of from less than 1 nm to about 10 nm.
The nanotubes of the present invention can also be used as a conducting member to carry relatively high current similar to a Litz wire or cable. However, unlike a Litz wire or cable soldered to a connector portion, the nanotube conducting member of the present invention can exhibit relatively lower impedance in comparison. In particular, it has been observed in the present invention that the shorter the current pulses, the better the nanotube-based wire cable or ribbon would perform when compared with a copper ribbon or Litz wire. One reason for the observed better performance may be that the effective frequency content of the pulse, which can be calculated from the Fourier Transform of the waveform for current pulses that are square and short, e.g., about 100 ms to less than about 1 ms, can be very high. Specifically, individual carbon nanotubes of the present invention can serve as conducting pathways, and due to their small size, when bulk structures are made from these nanotubes, the bulk structures can contain extraordinarily large number of conducting elements, for instance, on the order of 1014/cm2 or greater.
Carbon nanotubes of the present invention can also demonstrate ballistic conduction as a fundamental means of conductivity. Thus, materials made from nanotubes of the present invention can represent a significant advance over copper and other metallic conducting members under AC current conditions. However, joining this type of conducting member to an external circuit requires that essentially each nanotube be electrically or thermally contacted to avoid contact resistance at the junction.
Carbon nanotubes of the present invention can exhibit certain characteristics which are shown in
It should be noted that although reference is made throughout the application to nanotubes synthesized from carbon, other compound(s), such as boron, MoS2, or a combination thereof may be used in the synthesis of nanotubes in connection with the present invention. For instance, it should be understood that boron nanotubes may also be grown, but with different chemical precursors. In addition, it should be noted that boron may also be used to reduce resistivity in individual carbon nanotubes. Furthermore, other methods, such as plasma CVD or the like can also be used to fabricate the nanotubes of the present invention.
The present invention provides, in an embodiment, a composite material made from nanostructured composite sheets designed to increase conductivity of the carbon nanotubes within the sheet. As shown in
With reference now to
System 30, in one embodiment of the present invention, may also include a housing 32 designed to be substantially airtight, so as to minimize the release of potentially hazardous airborne particulates from within the synthesis chamber 31 into the environment. The housing 32 may also act to prevent oxygen from entering into the system 30 and reaching the synthesis chamber 31. In particular, the presence of oxygen within the synthesis chamber 31 can affect the integrity and compromise the production of the nanotubes 313.
System 30 may also include a moving belt 320, positioned within housing 32, designed for collecting synthesized nanotubes 313 made from a CVD process within synthesis chamber 31 of system 30. In particular, belt 320 may be used to permit nanotubes collected thereon to subsequently form a substantially continuous extensible structure 321, for instance, a non-woven or woven sheet. Such a sheet may be generated from compacted, substantially non-aligned, and intermingled nanotubes 313, bundles of nanotubes, or intertwined nanotubes (e.g., ropes of nanotubes), with sufficient structural integrity to be handled as a sheet.
To collect the fabricated nanotubes 313, belt 320 may be positioned adjacent the exit end 314 of the synthesis chamber 31 to permit the nanotubes to be deposited on to belt 320. In one embodiment, belt 320 may be positioned substantially parallel to the flow of gas from the exit end 314, as illustrated in
Looking at
To disengage the sheet 46 of intermingled nanomaterials from belt 44 for subsequent removal from housing 42, a scalpel or blade 47 may be provided downstream of the roller 45 with its edge against surface 445 of belt 44. In this manner, as sheet 46 moves downstream past roller 45, blade 47 may act to lift the sheet 46 from surface 445 of belt 44. In an alternate embodiment, a blade does not have to be in use to remove the sheet 46. Rather, removal of the sheet 46 may be manually by hand or by other known methods in the art.
Additionally, a spool or roller 48 may be provided downstream of blade 47, so that the disengaged sheet 46 may subsequently be directed thereonto and wound about roller 48 for harvesting. As the sheet 46 is wound about roller 48, a plurality of layers may be formed. Of course, other mechanisms may be used, so long as the sheet 46 can be collected for removal from the housing 42 thereafter. Roller 48, like belt 44, may be driven, in an embodiment, by a mechanical drive, such as an electric motor 481, so that its axis of rotation may be substantially transverse to the direction of movement of the sheet 46.
In order to minimize bonding of the sheet 46 to itself as it is being wound about roller 48, a separation material 49 (see
After the sheet 46 is generated, it may be left as a sheet 46 or it may be cut into smaller segments, such as strips. In an embodiment, a laser may be used to cut the sheet 46 into strips. The laser beam may, in an embodiment, be situated adjacent the housing such that the laser may be directed at the sheet 46 as it exits the housing. A computer or program may be employed to control the operation of the laser beam and also the cutting of the strip. In an alternative embodiment, any mechanical means or other means known in the art may be used to cut the sheet 46 into strips.
Once a sheet 46 is generated, the sheet 46 may undergo treatment to enhance conductivity and productivity of the nanotubes in the sheet. If strips are generated, the strips may also undergo a treatment processes to enhance conductivity and productivity of the nanotubes in the strip. Treatment of a sheet 46 after formation may, in an embodiment, include subjecting the sheet 46 to a protonation agent. One feature of the protonation agent may be to bring the carbon nanotubes in closer proximity with one another. By bringing the carbon nanotubes closer together, the protonation agent may act to reduce surface tension, reduce resistivity, and increase conductivity of the sheet. Examples of a protonation agent may include an acid such as hydronium ion, hydrochloric acid, hydrobromic acid, hydrofluoric acid, hydroiodic acid, carbonic acid, sulfuric acid, nitric acid, fluorosulfuric acid, chlorosulfonic acid, methane sulfonic acid, trifluoromethane sulfonic acid, oleum, an agent thereof, or a combination thereof, or other materials capable of being electrically and/or thermally conductive.
The protonation agent may be applied, in an embodiment, through the use of an apparatus 60, such as that shown in
Treating the sheet 68 with a protonation agent may involve positioning a bobbin or roll of sheet 68 on the third roller 66. The sheet 68 may then move downstream, passing from the third roller 66, through the first roller 64, into the tub 61 containing the protonation agent, and onto the second roller 65 and across the fourth roller 67.
In certain circumstances after treatment, the resulting sheet 68 may be acidic or basic. To bring the pH of the resulting sheet 68 to approximately neutral, a rinsing solution may be applied to the sheet 68. The rinsing solution may, in an embodiment, be applied continuously with the protonation agent or it may be applied independently of the protonation agent.
In another embodiment, treatment of the sheet 68 may further include spraying the sheet 68 with a second solution as it exits the furnace and is collected on the belt 320. The solution may contain a mixture of compounds that cover the outer surface of the nanotubes in such a manner as to enhance alignment of the carbon nanotubes and allow the carbon nanotubes to come into closer proximity with one another.
In an embodiment, the mixture of the second solution may include a solvent, a polymer, a metal, or a combination thereof. The solvent used in connection with the solution of the present invention can be used to lubricate the sheet in order to gain better alignment and enhancement in the properties of the carbon nanotubes. Examples of a solvent that can be used in connection with the solution include toluene, kerosene, benzene, hexanes, any alcohol including but not limited to ethanol, methanol, butanol, isopropanol, as well as tetrahydrofuran, 1-methyl-2-pyrrolidinone, dimethyl formamide, methylene chloride, acetone or any other solvent as the present invention is not intended to be limited in this manner. In an embodiment, the solvent may be used as a carrier for a polymer, monomer, inorganic salt, or metal oxide to.
Examples of a polymer that can be used in connection with the solution include a small molecule or polymer matrix (thermoset or thermoplastic) including, but not limited to, polyurethane, polyethylene, poly(styrene butadiene), polychloroprene, poly(vinyl alcohol), poly(vinyl pyrrolidone), poly(acrylonitrile-co-butadiene-co-styrene), epoxy, polyureasilazane, bismaleimide, polyamide, polyimide, polycarbonate, or any monomer including styrene, divinyl benzene, methyl acrylate, and tert-butyl acrylate. In an embodiment, the polymer may include polymer particles, that are difficult to obtain in liquid form.
Examples of a metal that can be used in connection with the solution include a salt (any transition metal, alkali metal, or alkali earth metal salt or mixture thereof including, but not limited to, nickel hydroxide, cadmium hydroxide, nickel chloride, copper chloride, calcium zincate (CaZn2(OH)6)), or metal oxide (any transition metal, alkali metal, or alkali earth metal oxide or mixture thereof, including but not limited to: zinc oxide, iron oxide, silver oxide, copper oxide, manganese oxide, LiCoO2, LiNiO2, LiNixCo1-xO2, LiMn2O4). In an embodiment, the metal may include polymers or volatile solvents to create a carbon nanotube metal matrix composite. Examples of such polymers or volatile solvents include powdered forms of aluminum or its alloys, nickel, superalloys, copper, silver, tin, cobalt, iron, iron alloys, or any element that can be produced in a powdered form including complex binary and ternary alloys or even superconductors.
To disperse the solution, a spraying apparatus may be used. The spraying apparatus may be any apparatus that is commercially available. In an embodiment, at one end of the spraying apparatus, there may be a spray head, through which the solution may be sprayed onto the sheet 46. In an embodiment, the spray head may be flat, round, or any other shape so long as it can permit solution to exit therethrough. To the extent desired, the spray head may emit a solution in a continuous manner or in a preprogrammed manner.
Once the sheet 68 has been treated, the treated sheet 68 may be subject to a heat source for processing of the sheet. For example, the sheet may be subject to sintering, hot isostatic pressing, hot pressing, cold isostatic pressing so as to yield a composite sheet or the desired form of the final product.
Treatment of the composite sheet may, in another embodiment, further include infusing the composite sheet with a glassy carbon material so as to increase the structural integrity of the sheet and provide substantially low resistance coupling. Glassy carbon, in general, may be a form of carbon related to carbon nanotubes and can contain a significant amount of graphene like ribbons comprising a matrix of amorphous carbon. These ribbons include sp2 bonded ribbons that can be substantially similar to the sp2 bonded nanotubes. As a result, they can have relatively good thermal and electrical conductivity. Examples of precursor materials from which glassy carbon can be made include furfuryl alcohol, RESOL resin (i.e., catalyzed alkyl-phenyl formaldehyde), PVA, or liquid resin or any material known to form glassy carbon when heat treated. Of course, other commercially available glassy carbon materials or precursor materials can be used.
The systems and methods of the present invention can provide bulk nanomaterials of high strength, lower or similar weight, in a composite sheet. By providing the nanomaterials in a composite sheet, the bulk nanomaterials can be easily handled and subsequently processed for end use applications, including (i) structural systems, such as fabrics, armor, composite reinforcements, antennas, electrical or thermal conductors, heaters, and electrodes, (ii) mechanical structural elements, such as plates and I-beams, and (iii) cabling or ropes. Other applications can include hydrogen storage, batteries, or capacitor components.
Moreover, the composite sheet may be incorporated into composite structures for additional end use applications, such as sporting goods products, helmets, antenna, morphing applications, aerospace, lightning protection flame proofing, etc. Composite sheets may further be nickel free, meaning they may be less toxic than standard products. Additionally, composite sheets may be repairable to eliminate the need to replace the composite sheets entirely or in part. In one embodiment, a composite material may be formed by impregnating the composite sheet with a matrix precursor, such as Krayton, vinyl ester, PEEK, bispolyamide, BMI (bismaleimide), epoxies, or polyamides, and subsequently allowing the matrix to polymerize or thermally cure.
Composite sheets of carbon nanotubes made from the present invention can have a wide variety of applications. Examples of specific applications include electromagnetic interference shielding (EMI shielding) which may either absorb, reflect, or transmit electromagnetic waves. Shielding may be beneficial to prevent interference from surrounding equipment and may be found in stereo systems, telephones, mobile phones, televisions, medical devices, computers, and many other appliances. For these and similar applications, it may be important that the glassy carbon precursor be provided in a substantially thin layer, so that infiltration into the carbon nanotube sheet can be minimized to prevent degradation to the properties of the sheet.
EMI shielding may further be useful in minimizing insertion loss from sheets of carbon nanotubes. Insertion loss represents the difference in power reception prior to and after the use of a composite sheet. As illustrated in
Composite sheets of carbon nanotubes can have additional applications, such as utilizing the resulting assembly in the absorption of radar signal (EMI shielding) or to provide other desirable properties, such as lighting protection, heat sinks, or actuators. For such applications, it may not be critical if the bonding agent penetrates the carbon nanotube sheet. Accordingly, the glassy carbon material can be coated with less care than for that carried out in capacitor, battery or fuel cell applications. In one embodiment, the substrate for applications in this example can be a graphite epoxy, e-glass epoxy, or combinations with other types of matrices.
While the present invention has been described with reference to certain embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt to a particular situation, indication, material and composition of matter, process step or steps, without departing from the spirit and scope of the present invention. All such modifications are intended to be within the scope of the claims appended hereto.
This application claims priority to U.S. Provisional Patent Application Ser. No. 61/051,249, filed May 7, 2008, which is hereby incorporated herein by reference in its entirety.
Number | Date | Country | |
---|---|---|---|
61051249 | May 2008 | US |