Patent Application
20110011775
The present invention relates to improvements in the field of carbon filamentary structures production. More particularly, the invention relates to improved methods and apparatuses for purifying carbon filamentary structures such as carbon fibres, single-wall carbon nanotubes or multi-wall carbon nanotubes.
Carbon nanotubes are available either as multi-wall or single-wall nanotubes. Multi-wall carbon nanotubes have exceptional properties such as excellent electrical and thermal conductivities. They have applications in numerous fields such as storage of hydrogen (C. Liu, Y. Y. Fan, M. Liu, H. T. Cong, H. M. Cheng, M. S. Dresselhaus, Science 286 (1999), 1127; M. S. Dresselhaus, K. A Williams, P. C. Eklund, MRS Bull. (1999), 45) or other gases, adsorption heat pumps, materials reinforcement or nanoelectronics (M. Menon, D. Srivastava, Phy. Rev. Lett. 79 (1997), 4453). Single-wall carbon nanotubes, on the other hand, possess properties that are significantly superior to those of multi-wall nanotubes. For any industrial application such as storage or material reinforcement, the amount of single-wall carbon nanotubes produced must be at least a few kilograms per day. For most of the applications, they must be purified since they are often associated with impurities such as metallic particles, usually surrounded by graphitic shells, or amorphous carbon which can considerably diminish their properties.
Nowadays, the methods used for purifying single-wall carbon nanotubes use a chemical oxidizer. Also the methods frequently used comprise the step of heating to about 200° C. (Chiang et al., J. Phys. Chem. B, 105 (2001) 8297 and Zhou et al., Chem. Phys. Lett., 350 (2001) 6.). Such a treatment causes the magnetic metal particles to be oxidized. Thus, the magnetic metal particles in their oxide form are bigger which eventually causes breaking or cracking of graphite shells having magnetic metal particles trapped therein. Then, the oxidized magnetic metal particles are dissolved by means of concentrated acid as HCl, H2SO4 or HNO3. Finally, the nanotubes are heated to about 1150° C. so as to remove the amorphous carbon. Such a method of purifying nanotubes has a major drawback since the nanotubes can be functionalized or even be damaged. It is also a time consuming, polluting and costly method.
Thiên-Nga et al. (Nano Letters 2002, vol. 2, No. 12, 1349-1352) describe a method of mechanical purification of single-wall carbon nanotubes by removing therefrom ferromagnetic particles used for the catalytic growth of the nanotubes. In this method, the single-wall carbon nanotubes are dispersed in a solvent (such as toluene, N,N-dimethyl formamide or nitric acid) and inorganic particles (such as nanoparticles of zirconium oxide, diamond, ammonium chloride or calcium carbonate) are added to the suspension. The slurry thus obtained is then treated in an ultrasonic bath so as to cause ferromagnetic particles to be mechanically removed from their graphitic shell. Then, the magnetic particles are trapped with permanent magnetic poles, and a further chemical treatment is carried out on the nanotubes. The use of a liquid phase in the purification process can be time consuming since several steps such as filtration and drying are required.
Another major drawback in the synthesis of carbon nanotubes is that the methods that have been proposed so far are not continuous or in situ. In fact, to obtain a continuous method of producing carbon nanotubes, the synthesis and the depositing and/or purification must be ideally carried out in a continuous manner and/or integrated to the synthesis process. Moreover, in several proposed solutions, the produced carbon nanotubes are generated, isolated, manipulated and then purified. Therefore, several tasks and steps are required before obtaining a sufficient purity.
According to one aspect of the present invention, there is provided a method for treating a gaseous phase comprising carbon filamentary structures having metal particles attached or linked thereto, for separating at least a portion of the carbon filamentary structures from the metal particles. The method comprises submitting the gaseous phase to a disturbance, thereby reducing the amount of carbon filamentary structures having metal particles attached or linked thereto.
According to another aspect of the present invention, there is provided a method for treating carbon filamentary structures having metal particles attached or linked thereto, for separating the carbon filamentary structures from the magnetic metal particles. The method comprises the steps of:
a) providing a gaseous phase comprising the carbon filamentary structures and the magnetic metal particles; and
b) submitting the gaseous phase to a disturbance so as to cause the carbon filamentary structures to become substantially physically separated from the magnetic metal particles.
It was found that such methods are very useful for reducing the amount of carbon filamentary structures, which are linked or attached to metal particles. In fact, such methods permit to physically separate the carbon filamentary structure from the metal particle, for at least a portion of the totality of carbon filamentary structures contaminated with the metal particles. By submitting a gaseous phase to such a treatment, at least a portion of the carbon filamentary structures that are attached or linked to a metal will be separated from the metal. The metal particles treated with such a methods can be magnetic metal particles as well as non-magnetic metal particles.
According to another aspect of the invention, there is provided a method for purifying carbon filamentary structures contaminated with magnetic metal particles. The method comprises submitting a gaseous phase comprising the carbon filamentary structures contaminated with magnetic metal particles, to an inhomogeneous magnetic field for at least partially trapping the magnetic metal particles, thereby reducing the amount of the magnetic metal particles present in the gaseous phase.
According to another aspect of the present invention, there is provided a method for purifying carbon filamentary structures contaminated with magnetic metal particles. The method comprises the steps of:
a) providing a gaseous phase comprising the carbon filamentary structures and the magnetic metal particles, the carbon filamentary structures being substantially physically separated from the magnetic metal particles;
b) submitting the gaseous phase to an inhomogeneous magnetic field so as to substantially trap the magnetic metal particles, thereby reducing the amount of the magnetic metal particles in the gaseous phase.
It was found that the latter two methods are effective for purifying carbon filamentary structures. It was also found that such purification techniques carried in gaseous phase have several considerable advantages since the carbon filamentary structures can be purified in situ or directly after their synthesis, without requiring any step or task between the synthesis and the purification. In fact, the carbon filamentary structures that are preferably obtained from a gas phase synthesis such as a plasma torch are already in a gaseous phase and thus, the purification can be carried out directly without the necessity of recovering them and then treating them so as to remove the impurities. Such methods thus permit to carry out the synthesis and purification of carbon filamentary structures in a single sequence or in a “one-pot” manner. Such methods can also be applied to carbon filamentary structures that are produced by other methods than a gas phase synthesis. In fact, carbon filamentary structures in solid or powder form can be mixed with a gas in order to obtain a gaseous phase and then, such a gaseous phase can be treated with the methods previously mentioned.
According to another aspect of the present invention, there is provided a method for purifying carbon filamentary structures contaminated with magnetic metal particles. The method comprises treating a gaseous phase comprising the carbon filamentary structures contaminated with magnetic metal particles, with or without a disturbance for separating at least a portion of the carbon filamentary structures from the magnetic metal particles; and with an inhomogeneous magnetic field for at least partially trapping the magnetic metal particles, thereby reducing the amount of the magnetic metal particles present in the gaseous phase.
According to another aspect of the present invention, there is provided a method for purifying carbon filamentary structures contaminated with magnetic metal particles. The method comprises submitting a gaseous phase comprising the carbon filamentary structures contaminated with magnetic metal particles, optionally to a disturbance for separating at least a portion of the carbon filamentary structures from the magnetic metal particles; and to an inhomogeneous magnetic field for at least partially trapping the magnetic metal particles, thereby reducing the amount of the magnetic metal particles present in the gaseous phase.
According to another aspect of the present invention, there is provided a method for purifying carbon filamentary structures contaminated with magnetic metal particles. The method comprises the steps of:
a) providing a gaseous phase comprising the carbon filamentary structures having the magnetic metal particles attached or linked thereto;
b) submitting the gaseous phase to a disturbance so as to cause the carbon filamentary structures to become substantially physically separated from the magnetic metal particles; and
c) submitting the gaseous phase obtained in step (b) to an inhomogeneous magnetic field so as to substantially trap the magnetic metal particles, thereby reducing the amount of the magnetic metal particles in the gaseous phase.
It was found that by using the latter three methods purification of the carbon filamentary structures was carried out efficiently and rapidly. In fact, it was observed that when the carbon filamentary structures are first submitted to a disturbance and then to the inhomogeneous magnetic field, superior results were obtained i.e. a higher purity was observed. In fact, it is believed, without being bounded to such an explanation, that such better results are obtained since the treatment with the disturbance permits to obtain a higher content or proportion, in the gaseous phase, of metal particles that are not attached or linked to carbon filamentary structures. Thus, the disturbance permits to increase the efficiency of the purification carried out with the inhomogeneous magnetic field.
According to another aspect of the present invention, there is provided a method for purifying carbon filamentary structures contaminated with magnetic metal particles. The method comprises recovering the carbon filamentary structures from a gaseous phase including carbon filamentary structures contaminated with magnetic metal particles, wherein the gaseous phase was previously treated with or without a disturbance in order to reduce the amount of carbon filamentary structures having magnetic metal particles attached or linked thereto, present in the gaseous phase; and with an inhomogeneous magnetic field for at least partially trapping the magnetic metal particles, thereby reducing the amount of the magnetic metal particles present in the gaseous phase.
According to another aspect of the present invention, there is provided a method for purifying carbon filamentary structures contaminated with magnetic metal particles. The method comprises:
According to another aspect of the present invention, there is provided a method of purifying carbon filamentary structures contaminated with magnetic metal particles, the method comprising:
According to another aspect of the present invention, there is provided a method of purifying carbon filamentary structures contaminated with magnetic metal particles. The method comprises the steps of:
a) providing a gaseous phase comprising the carbon filamentary structures having the magnetic metal particles attached or linked thereto;
b) submitting the gaseous phase to a disturbance so as to cause the carbon filamentary structures to become substantially physically separated from the magnetic metal particles;
c) submitting the gaseous phase obtained in step (b) to an inhomogeneous magnetic field so as to substantially trap the magnetic metal particles, thereby reducing the amount of the magnetic metal particles in the gaseous phase; and
d) recovering the carbon filamentary structures from the gaseous phase.
It was found that the latter four methods are quite efficient for carrying out the purification of carbon filamentary structures. In fact, it was observed that such methods permit to rapidly purify and isolate the desired carbon filamentary structures.
According to another aspect of the present invention, there is provided a continuous method for purifying carbon filamentary structures contaminated with magnetic metal particles, comprising the steps of:
a) treating a gaseous phase comprising the carbon filamentary structures contaminated with magnetic metal particles, with or without a disturbance in order to reduce the amount of carbon filamentary structures having magnetic metal particles attached or linked thereto, present in the gaseous phase;
b) submitting the gaseous phase to an inhomogeneous magnetic field for at least partially trapping the magnetic metal particles, thereby reducing the proportion of the magnetic metal particles present in the gaseous phase;
c) providing a device comprising:
d) passing the gaseous phase through the inlet of the device, the valve and a selected depositing unit; and applying a potential difference between the electrodes of the selected depositing unit to thereby deposit carbon filamentary structures on at least one electrode; and
e) selecting another depositing unit and repeating step (d).
According to another aspect of the present invention, there is provided a continuous method of purifying carbon filamentary structures contaminated with magnetic metal particles, comprising the steps of:
a) providing a gaseous phase comprising the carbon filamentary structures contaminated with magnetic metal particles;
b) optionally submitting the gaseous phase to a disturbance in order to reduce the amount of carbon filamentary structures having magnetic metal particles attached or linked thereto, present in the gaseous phase;
c) submitting the gaseous phase to an inhomogeneous magnetic field for at least partially trapping the magnetic metal particles, thereby reducing the proportion of the magnetic metal particles present in the gaseous phase;
d) providing a device comprising:
e) passing the gaseous phase through the inlet of the device, the valve and a selected depositing unit; and applying a potential difference between the electrodes of the selected depositing unit to thereby deposit carbon filamentary structures on at least one electrode; and
f) selecting another depositing unit and repeating step (e).
According to another aspect of the present invention, there is provided a continuous method of purifying carbon filamentary structures contaminated with magnetic metal particles. The continuous method comprises the steps of:
a) providing a gaseous phase comprising the carbon filamentary structures having the magnetic metal particles attached or linked thereto;
b) submitting the gaseous phase to a disturbance so as to cause the carbon filamentary structures to become substantially physically separated from the magnetic metal particles;
c) submitting the gaseous phase obtained in step (b) to an inhomogeneous magnetic field so as to substantially trap the magnetic metal particles, thereby reducing the amount of the magnetic metal particles in the gaseous phase;
d) providing a depositing device comprising:
e) passing the gaseous phase through the inlet of the device, the valve and a selected one of the depositing units; and applying a potential difference between the electrodes of the selected depositing unit to thereby deposit carbon filamentary structures on at least one electrode; and
f) selecting another one of the depositing units and repeating step (e).
According to another aspect of the invention, there is provided a continuous method of purifying carbon filamentary structures contaminated with magnetic metal particles, comprising the steps of:
a) providing an apparatus comprising:
b) providing the gaseous phase and passing it through the first inlet and introducing it in the chamber;
c) submitting the gaseous phase to the disturbance generated by the disturbance generator so as to cause the carbon filamentary structures to become substantially physically separated from the magnetic metal particles;
d) submitting the gaseous phase obtained in step (c) to the inhomogeneous magnetic field generated by the inhomogeneous magnetic field generated so as to substantially trap the magnetic metal particles, thereby reducing the amount of the magnetic metal particles in the gaseous phase; and
e) passing the gaseous phase obtained in step (d) through the inlet of the valve and a selected one of the depositing units; and applying a potential difference between the electrodes of the selected depositing unit to thereby deposit carbon filamentary structures on at least one electrode; and
f) selecting another of the depositing units and repeating step (e).
It was found that by using the latter four methods, it is possible to purify and recover carbon filamentary structures in a continuous manner. In fact, such methods can be particularly useful when a gas-phase synthesis of carbon filamentary structures is carried out. In such a case, the whole process of the production including, synthesis, purification, deposition and recovery can be carried out in a continuous manner and in situ. It thus constitutes a considerable advantage over previously known process in which the synthesis must be stopped for collecting the carbon filamentary structures and then, the carbon filamentary structures must be treated with various chemicals in order to purify them. The latter four methods thus permit to carry out the production of carbon filamentary structures rapidly, efficiently and by avoiding tedious tasks and use of various chemicals.
According to another aspect of the present invention, there is provided an apparatus for treating carbon filamentary structures contaminated with metal particles, in order to at least partially separate the carbon filamentary structures from the metal particles. The apparatus comprises:
a housing having a chamber dimensioned to receive a gaseous phase comprising the carbon filamentary structures contaminated with metal particles, an inlet and an outlet, the inlet and the outlet being in fluid flow communication with the chamber; and
a disturbance generator disposed inside or adjacent to the chamber, the disturbance generator being adapted to submit the gaseous phase to a disturbance in order to at least partially separate the carbon filamentary structures from the metal particles.
According to another aspect of the invention, there is provided an apparatus for treating carbon filamentary structures having metal particles attached or linked thereto, to separate the carbon filamentary structures from the metal particles. The apparatus comprises:
a housing having a chamber dimensioned to receive a gaseous phase comprising the carbon filamentary structures and the metal particles, an inlet and an outlet, the inlet and the outlet being in fluid flow communication with the chamber; and
a disturbance generator disposed inside or adjacent to the chamber, the disturbance generator being adapted to submit the gaseous phase to a disturbance so as to cause the carbon filamentary structures to become substantially physically separated from the metal particles.
It was found that the latter two apparatuses are efficient and very useful for physically separating, at least a portion, of the carbon filamentary structures from the metal particles. In fact, such apparatuses permit to physically separate the carbon filamentary structure from the metal particle, for at least a portion of the totality of carbon filamentary structures contaminated with the metal particles. By treating a gaseous phase comprising carbon filamentary structures with such apparatuses, at least a portion of the carbon filamentary structures that are attached or linked to a metal will be separated from the metal, thereby reducing the amount of carbon filamentary structures having metal particles attached or linked thereto. The metal particles can be magnetic or non-magnetic metal particles.
According to another aspect of the present invention, there is provided an apparatus for purifying carbon filamentary structures contaminated with magnetic metal particles. The apparatus comprises:
a housing having a chamber dimensioned to receive a gaseous phase comprising the carbon filamentary structures contaminated with magnetic metal particles, an inlet and an outlet, the inlet and the outlet being in fluid flow communication with the chamber; and
an inhomogeneous magnetic field generator disposed inside or adjacent to the chamber, the magnetic field generator being adapted to at least partially trap the magnetic metal particles in order to reduce the proportion of magnetic metal particles present in the gaseous phase.
According to another aspect of the invention, there is provided an apparatus for purifying carbon filamentary structures contaminated with magnetic metal particles, comprising:
a housing having a chamber dimensioned to receive a gaseous phase comprising the carbon filamentary structures and the magnetic metal particles, the carbon filamentary structures being substantially physically separated from the magnetic metal particles, an inlet and an outlet, the inlet and the outlet being in fluid flow communication with the chamber; and
an inhomogeneous magnetic field generator disposed inside or adjacent to the chamber, the magnetic field generator being adapted to substantially trap the magnetic metal particles, thereby reducing the amount of the magnetic metal particles in the gaseous phase.
It was found that by using the latter two apparatuses, purification of carbon filamentary structures can be carried out rapidly and efficiently. It was also found that such apparatuses permitting to carry out the purification in gaseous phase have considerable advantages since the carbon filamentary structures can be purified directly after their synthesis, without requiring any step or task between the synthesis and the purification. In fact, the carbon filamentary structures that are preferably obtained from a gas phase synthesis such as a plasma torch are already in a gaseous phase and thus, the purification can be carried out directly without the necessity of recovering them and then treating them so as to remove the impurities. Such apparatuses thus permit to carry out the synthesis and purification of carbon filamentary structures in a single sequence or in a “one-pot” manner. Such apparatuses can also be used to purify carbon filamentary structures that are produced by other methods than a gas phase synthesis. In fact, carbon filamentary structures in solid or powder form can be mixed with a gas in order to obtain a gaseous phase and then, such a gaseous phase can be treated with one of the apparatuses. In fact, such apparatuses are in situ purification apparatuses, since the carbon filamentary structures are purified directly in the gaseous phase in which they have been generated.
According to another aspect of the present invention there is provided an apparatus for purifying carbon filamentary structures contaminated with magnetic metal particles. The apparatus comprises:
a housing having a chamber dimensioned to receive a gaseous phase comprising the carbon filamentary structures contaminated with magnetic metal particles, an inlet and an outlet, the inlet and the outlet being in fluid flow communication with the chamber;
a disturbance generator disposed inside or adjacent to the chamber, the disturbance generator being adapted to submit the gaseous phase to a disturbance in order to at least partially separate the carbon filamentary structures from the magnetic metal particles; and
an inhomogeneous magnetic field generator disposed inside or adjacent to the chamber, and preferably downstream of the disturbance generator, the magnetic field generator being adapted to at least partially trap the magnetic metal particles present in the gaseous phase in order to reduce the proportion of magnetic metal particles present in the gaseous phase.
According to another aspect of the invention, there is provided an apparatus for purifying carbon filamentary structures contaminated with magnetic metal particles, comprising:
a housing having a chamber dimensioned to receive a gaseous phase comprising the carbon filamentary structures having the magnetic metal particles attached or linked thereto, an inlet and an outlet, the inlet and the outlet being in fluid flow communication with the chamber;
a disturbance generator disposed inside or adjacent to the chamber, the disturbance generator being adapted to submit the gaseous phase to a disturbance so as to cause the carbon filamentary structures to become substantially physically separated from the magnetic metal particles; and
an inhomogeneous magnetic field generator disposed inside or adjacent to the chamber, the magnetic field generator being adapted to substantially trap the magnetic metal particles, thereby reducing the amount of the magnetic metal particles in the gaseous phase.
It was found that the latter two apparatuses permit carry out efficiently and rapidly purification of carbon filamentary structures. In fact, it was observed that when the carbon filamentary structures are first submitted to a disturbance and then to the inhomogeneous magnetic field, superior results were obtained i.e. a higher purity was observed. In fact, it is believed, without being bounded to such an explanation, that such better results are obtained since the treatment with the disturbance permits to obtain a higher content or proportion, in the gaseous phase, of metal particles that are not attached or linked to carbon filamentary structures. Thus, the disturbance generator permits to increase the efficiency of the purification carried out with the inhomogeneous magnetic field as compared to an apparatus in which only an inhomogeneous magnetic field generator is used. In fact, such apparatuses are in situ purification apparatuses, since the carbon filamentary structures are purified directly in the gaseous phase in which they have been generated.
According to another aspect of the present invention, there is provided an apparatus for purifying carbon filamentary structures contaminated with magnetic metal particles. The apparatus comprises:
a housing having a chamber dimensioned to receive a gaseous phase comprising the carbon filamentary structures having the magnetic metal particles attached or linked thereto, an inlet and an outlet, the inlet and the outlet being in fluid flow communication with the chamber;
a disturbance generator disposed inside or adjacent to the chamber, the disturbance generator being adapted to submit the gaseous phase to a disturbance so as to cause the carbon filamentary structures to become substantially physically separated from the magnetic metal particles;
an inhomogeneous magnetic field generator disposed inside or adjacent to the chamber, and preferably downstream of the disturbance generator, the magnetic field generator being adapted to substantially trap the magnetic metal particles, thereby reducing the amount of the magnetic metal particles in the gaseous phase; and
at least two electrodes disposed downstream of the inhomogeneous magnetic field generator in the chamber, the electrodes defining therebetween a space dimensioned to receive the gaseous phase comprising carbon filamentary structures, the electrodes being adapted to generate an electric field for depositing the carbon filamentary structures on at least one of the electrodes.
According to another aspect of the invention, there is provided an apparatus for purifying carbon filamentary structures contaminated with magnetic metal particles, comprising:
a housing having a chamber dimensioned to receive a gaseous phase comprising the carbon filamentary structures having the magnetic metal particles attached or linked thereto, an inlet and an outlet, the inlet and the outlet being in fluid flow communication with the chamber;
a disturbance generator disposed inside or adjacent to the chamber, the disturbance generator being adapted to submit the gaseous phase to a disturbance so as to cause the carbon filamentary structures to become substantially physically separated from the magnetic metal particles;
an inhomogeneous magnetic field generator disposed inside or adjacent to the chamber, the magnetic field generator being adapted to substantially trap the magnetic metal particles, thereby reducing the amount of the magnetic metal particles in the gaseous phase; and
a first electrode and a second electrode disposed downstream of the inhomogeneous magnetic field generator in the chamber, and connected to the housing, the first and second electrodes defining therebetween a space dimensioned to receive the gaseous phase comprising carbon filamentary structures, the electrodes being adapted to generate an electric field for depositing the carbon filamentary structures on at least one of the electrodes.
It was found that the latter two apparatuses are efficient for carrying out the purification of carbon filamentary structures. In fact, it was observed that such apparatuses permit to rapidly purify and isolate the desired carbon filamentary structures.
An apparatus for purifying carbon filamentary structures contaminated with magnetic metal particles, comprising:
a housing having a chamber dimensioned to receive a gaseous phase comprising the carbon filamentary structures having the magnetic metal particles attached or linked thereto, an inlet and an outlet, the inlet and the outlet being in fluid flow communication with the chamber;
a disturbance generator disposed inside or adjacent to the chamber, the disturbance generator being adapted to submit the gaseous phase to a disturbance so as to cause the carbon filamentary structures to become substantially physically separated from the magnetic metal particles;
an inhomogeneous magnetic field generator disposed inside or adjacent to the chamber, and preferably downstream of the disturbance generator, the magnetic field generator being adapted to substantially trap the magnetic metal particles, thereby reducing the amount of the magnetic metal particles in the gaseous phase;
It was found that the latter apparatus is efficient for carrying out the purification of carbon filamentary structures. In fact, it was observed that such apparatuses permit to rapidly purify and isolate the desired carbon filamentary structures. Moreover, it was observed that such an apparatus permits to purify carbon filamentary structures in a continuous manner.
The expression “carbon filamentary structures contaminated with magnetic metal particles” as used herein refers to a mixture that can comprise carbon filamentary structures having magnetic metal particles attached thereto and/or linked thereto, magnetic metal particles that can be coated with or embedded in amorphous carbon and/or graphitic carbon, optionally carbon filamentary structures that are neither attached nor linked to metal particles, and optionally magnetic metal particles that are neither attached nor linked to carbon filamentary structures. The metal particles are preferably catalyst metal particles.
The expression “attached thereto” as used herein when referring to carbon filamentary structures and metal particles is intended to mean that there is a bonding between carbon filamentary structures and metal particles. This bonding preferably occurs at the surface or the extremities of the carbon filamentary structures. The bonding can be a chemical bonding such as a covalent, ionic or a metallic bonding that is strong. The metal particles are preferably magnetic metal particles.
The expression “linked thereto” as used herein when referring to carbon filamentary structures and metal particles is intended to mean that there is a bonding between carbon filamentary structure and metal particles. This bonding is a polarisation bonding like van der Waals interaction or hydrogen bonds between the carbon filamentary structure and the metal particles. This bonding preferably occurs at the surface or the extremities of the carbon filamentary structures. The carbon filamentary structure can also be indirectly bonded to the metal particles such as when metal particles are embedded in amorphous carbon, which is bonded to the carbon filamentary structures at their surface or extremities. The metal particles are preferably magnetic metal particles.
In the methods and apparatuses of the present invention, the carbon filamentary structures can be selected from the group consisting of single-wall carbon nanotubes, multi-wall carbon nanotubes, carbon fibres, and mixtures thereof. Preferably, the carbon filamentary structures are selected from the group consisting of single-wall carbon nanotubes, multi-wall carbon nanotubes, and a mixture thereof. More preferably, the carbon filamentary structures are single-wall carbon nanotubes.
In the methods and apparatuses of the present invention, the gaseous phase preferably comprises a carrier gas. The carrier gas can be selected from the group consisting of He, Ar, H2, H2O, H2S, CO2, CO, N2, Kr, Xe, Ne, and mixtures thereof. Preferably, the carrier gas is a mixture of argon and helium. The gaseous phase can contain a density of about 1×102 to about 1×1012 carbon filamentary structures per cm3 and preferably of about 1×107 to about 1×1010 carbon filamentary structures per cm3.
In the methods and apparatuses of the present invention, the metal of the magnetic metal particles can be selected from the group consisting of Co, Fe, Mo Ni, Pd, Rh, Ru, Y, La, Ce, and mixtures thereof. Preferably, the metal is selected from the group consisting of Co, Fe, Ni, and mixtures thereof. Alternatively, the magnetic metal particles can comprise at least one metal selected from the group consisting of Co, Fe, and Ni, together with a non-ferromagnetic metal. The magnetic metal particles may have a carbon coating.
In the methods and apparatuses of the present invention, wherein a disturbance is caused, the disturbance can be caused by an alternative current (AC) or pulsed electric field, an AC or pulsed magnetic field, ultrasounds, a turbulent gas stream, or combinations thereof. The electric field can be a macroscopic field having a value of about 1×103 V/m to about 1×107 V/m and preferably of about 1×105 V/m to about 1×106 V/m. When the disturbance is caused by an AC electric field, the AC electric field can have a frequency ranging from 1 KHz to 5 GHz and preferably from 20 KHz to 20 MHz. When the disturbance is caused by a pulsed electric field, the pulsed electric field can have a repetition rate ranging from 20 KHz to 20 MHz. The disturbance can also be caused by a mixture of an AC and a DC voltage. When the disturbance is caused by an AC magnetic field, the latter can have a frequency ranging from 20 KHz to 20 MHz. When the disturbance is caused by ultrasounds, the ultrasounds can have a power level ranging from 0.2 to 500 W/cm2, preferably from 1 to 150 W/cm2, the ultrasounds can also have a frequency ranging from 20 KHz to 500 MHz. The disturbance can be generated by a turbulent gas stream having a speed ranging from Mach 1 to 6. Such a gas can be selected from the group consisting of He, Ar, H2, H2O, CO2, CO, N2, Kr, Xe, Ne, and mixtures thereof. Preferably, the gas is selected from the group consisting of Ar, He, H2, and mixtures thereof.
In the methods and apparatuses of the present invention wherein an inhomogeneous magnetic field is generated, the latter can have an amplitude ranging from 0.001 to 15 Tesla and preferably from 0.1 to 5 Tesla. The inhomogeneous magnetic field can have a gradient having amplitude ranging from 0.01 to 10 Tesla/m and preferably from 0.1 to 100 Tesla/m. Such an inhomogeneous magnetic field can be generated by a permanent magnet, an electromagnet, a solenoid, a coil or a combination of coils. The gaseous phase can also be submitted to a centrifugal force while being submitted to an inhomogeneous magnetic field. The treatment with the inhomogeneous magnetic field can permit to reduce the proportion of the metal particles present in the gaseous phase. Such a treatment can also permit to reduce the proportion or content, in weight %, of the metal particles in the gaseous phase. The treatment with the inhomogeneous magnetic field can also permit to reduce the ratio magnetic metal particles:carbon filamentary structures, in the gaseous phase.
In the methods and apparatuses of the present invention the gaseous phase (and more particularly the carbon filamentary structures having magnetic metal particles attached thereto and/or linked thereto) can be substantially simultaneously submitted to the disturbance and the inhomogeneous magnetic field. In fact, the disturbance generator and the inhomogeneous magnetic field generator can be disposed in the apparatus in such a manner that at a least a portion of the carbon filamentary structures having magnetic metal particles attached thereto and/or linked thereto being treated, can be simultaneously submitted to the effect of both the disturbance and the magnetic field. The treating zone or effective zone of treatment of the disturbance and the magnetic field can thus overlap or be substantially the same. In a similar manner, the carbon filamentary structures can be substantially simultaneously submitted to the action of the inhomogeneous magnetic field and the electric field of the electrodes used for depositing the desired structures. They can also be substantially simultaneously submitted to the action of the disturbance, the magnetic field, and the electric field or submitted simultaneously to the disturbance and the electric field. The disturbance and magnetic field generators as well as the electrodes can thus be disposed accordingly so as to provide the desired overlapping zones of treatment.
In the methods of the present invention in which a recovering step is carried out, this step is carried out by depositing the purified carbon filamentary structures on at least one electrode and then collecting the purified and deposited carbon filamentary structures. The recovering step can be carried out by depositing and then collecting the purified carbon filamentary structures, the depositing step being carried out passing a gaseous phase comprising the carbon filamentary structures through a space defined between at least two electrodes generating an electrical field, for depositing the carbon filamentary structures on at least one of the electrodes. The carbon filamentary structures are preferably deposited by substantially preventing the deposited carbon filamentary structures from bridging the electrodes during the deposition. The carbon filamentary structures can be deposited by substantially removing, during the deposition of the carbon filamentary structures, any structures that are bridging the at least two electrodes from such a position by removing at least a portion of these structures from contacting one of the electrodes. The electrodes are preferably in rotation relation to one another in order to prevent being bridged by the deposited carbon filamentary structures.
In the method of the invention for purifying carbon filamentary structures contaminated with magnetic metal particles depositing of the carbon filamentary structures can be carried out as follows:
i) providing a set of electrodes comprising at least two electrodes, a first electrode and a second electrode defining a space therebetween;
ii) applying a potential difference between the electrodes in order to generate an electric field; and
iii) passing the gaseous phase through the space, thereby depositing the carbon filamentary structures on at least one of the electrodes.
Preferably, the deposit of carbon filamentary structures comprises a plurality of filaments of the carbon filamentary structures forming together a web-like structure. The deposit can have a foamy aspect. The first electrode can comprise a housing defining a chamber dimensioned to receive the second electrode. The second electrode can be longitudinally aligned with the first electrode. Preferably, the first and second electrodes are parallel. More preferably, the second electrode is disposed in a substantially coaxial alignment into the chamber. The second electrode can be disposed into the chamber in a substantially perpendicular manner to the housing. The second electrode can be rotated at a predetermined speed, thereby preventing the deposit from bridging the electrodes.
Preferably, the second electrode is rotated at a speed of about 10−2 to about 500 rpm and more preferably of about 0.1 to about 200 rpm and even more preferably of about 1 to about 30 rpm. The deposit is preferably rolled-up around the second electrode. The current density can have an intensity of about 0 to about 500 μA/cm2, preferably of about 0.1 to about 80 μA/cm2, which is collected to the electrodes. The electric field can be a macroscopic field having a value of about 1×103 V/m to about 1×107 V/m and preferably of about 1×105 V/m to about 1×106 V/m. The potential difference can be of about 0.1 to about 50000 V. Another gas can be injected through the space so as to slow down the carbon filamentary structures passing through the space. The other gas is preferably injected in a counter-current manner to the gaseous phase. The other gas is preferably helium. The potential difference applied between the electrodes is preferably a Direct Current voltage.
In the apparatuses of the invention, the disturbance generator can comprise an alternative current (AC) or pulsed electric field generator, an AC or pulsed magnetic field generator, an ultrasounds generator, a turbulent gas stream, or combinations thereof. The disturbance generator can comprise at least two electrodes defining therebetween a space dimensioned to receive the gaseous phase comprising carbon filamentary structures and magnetic metal particles, the electrodes being adapted to generate an electric field for causing a substantial separation of the carbon filamentary structures from magnetic metal particles. The disturbance generator can comprise a time variable magnetic field. The variable magnetic field can be generated by a solenoid, an electromagnet, a coil, or a combination of coils. The disturbance generator can comprise an ultrasounds generator. The disturbance generator can comprise a turbulent gas stream generator, preferably a supersonic gas generator. The generator can comprise at least two electrodes adapted to generate a time variable electric field. The inhomogeneous magnetic field generator can be a permanent magnet, an electromagnet, a solenoid, a coil, or a combination of coils. The disturbance generator can be disposed outside the chamber and connected to or in close proximity with the housing.
The first and second electrodes define therebetween a space dimensioned to receive the gaseous phase comprising carbon filamentary structures and magnetic metal particles. The electrodes are adapted to generate an electric field for causing substantial separation of the carbon filamentary structures from magnetic metal particles. A portion of the housing can constitute the first electrode. Alternatively, the disturbance generator can be an ultrasounds generator or a turbulent gas stream generator. Preferably, the second electrode is longitudinally aligned with the housing. The second electrode can be parallel to the first electrode. The second electrode can be disposed in a substantially coaxial alignment with the elongated member. The second electrode is preferably disposed into the chamber in a substantially perpendicular alignment to the housing. The second electrode can be rotatably mounted on the housing. The apparatus can also comprise a motor for rotating the second electrode. The first and second electrodes can be cylindrical electrodes.
In the apparatuses of the invention having an inhomogeneous magnetic field generator, the latter can be a permanent magnet, an electromagnet, a solenoid, a coil, or a combination of coils. The housing can have a curved portion and wherein the inhomogeneous magnetic field generator disposed inside or adjacent to the curved portion so as to submit the gaseous phase to a centrifugal force while being submitted to an inhomogeneous magnetic field. The inhomogeneous magnetic field generator is preferably disposed outside the chamber and connected to or in close proximity with the housing.
Further features and advantages of the invention will become more readily apparent from the following description of preferred embodiments as illustrated by way of examples in the appended drawings wherein:
Referring first to
In
In
The apparatus 28 for treating carbon filamentary structures and preferably carbon nanotubes having metal particles attached or linked thereto, as shown in
The apparatus 29 for treating carbon filamentary structures and preferably carbon nanotubes having metal particles attached or linked thereto, as shown in
In system 9 (
The apparatus 30 for purifying carbon filamentary structures (preferably carbon nanotubes) and shown in
When a gaseous phase comprising carbon nanotubes and magnetic metal particles is introduced in the apparatus 30, preferably single-wall carbon nanotubes, in which at least a portion of them are substantially physically separated from the magnetic metal particles or at least weakly linked thereto, the gaseous phase is submitted to the inhomogeneous magnetic field generated by the permanent magnets 54. The majority of the magnetic metal particles free of carbon filamentary structures and/or coated with carbon is thus attracted and trapped by magnets while an important portion (preferably at least the major portion) of carbon nanotubes (free of metal or not) pass through the chamber 49 and are exited via the outlet 44 because of their higher inertia. Thus, the amount of magnetic metal particles in the gaseous phase is reduced. Moreover, the ratio magnetic metal particles:carbon filamentary structures is also reduced in view of the reasons previously mentioned. The portion of magnetic metal particles attracted by the magnets will depend on the intensity of the inhomogeneous magnetic field, the residence time of the particles in the purification apparatus, the metal concentration, the degree of separation between nanotubes and magnetic metal particles, etc. The apparatus 30 can be disposed downstream of an apparatus selected from the group consisting of apparatuses 24, 26, 28, 29, and mixtures thereof. The apparatus 30 can also be disposed directly downstream of an apparatus for producing carbon filamentary structures.
The apparatus 32 for purifying carbon filamentary structures and preferably carbon nanotubes, as shown in
When a gaseous phase comprising carbon filamentary structures (preferably carbon nanotubes) and magnetic metal particles is introduced in the apparatus 32 (
In
When a gaseous phase comprising carbon nanotubes and magnetic metal particles is introduced in the apparatus 34 (
The carbon nanotubes, when entering in the unit 84 of
In
When a gaseous phase comprising carbon nanotubes and magnetic metal particles is introduced in the apparatus 36 (
Since the deposited carbon nanotubes have tendency to bridge electrodes 104 and 110 in
The apparatus 38 shown in
However, with the apparatus 38 of
It should be noted that the apparatuses shown in
The following examples represent only preferred embodiments of the present invention.
An experiment was carried out by using an apparatus for purifying carbon nanotubes according to a preferred embodiment of the invention. For this experiment, an apparatus similar to the one schematically represented in
The purification apparatus was provided with eight rare earth (NdFeB) permanent magnets of 0.4 Tesla disposed symmetrically in a protective coating (not shown), with a length and diameter of respectively 12 and 10 cm, in order to generate a strong inhomogeneous magnetic field with a radial gradient, i.e. perpendicular to the flow of gas (see
The thermogravimetric analysis (TGA) graph shown in
Surprisingly, such a simple in situ purification technique using only an inhomogeneous field permitted to remove about 12% to about 14% by weight of impurities in the gaseous phase. In fact, an amount about 12% to about 14% by weight (based on the total weight of the unpurified gaseous phase) of undesired or side products such as amorphous or graphitic carbon and magnetic metal particles was removed. In other words, an amount of about 5% to about 7% by weight, based on the total weight of the unpurified gaseous phase, of magnetic metal particles was removed from the gaseous phase. It thus permitted to remove considerable amounts of carbon (such as graphitic carbon or amorphous carbon) that was not under the nanotube form, as well as magnetic metal particles. Some tests demonstrate that with a disturbance before the inhomogeneous field the carbon filamentary structures can have a higher degree of purity when such a disturbance is used.
In the experiment previously mentioned, an amount of about 400 mg of single-wall nanotubes was obtained in one hour and the purity was about 50% to about 60% by weight. When a similar experiment or synthesis is carried without the use of an apparatus for purifying carbon filamentary structures according to the present invention, the purity obtained is only of about 40% to about 50% by weight.
Transmission electron microscope (TEM) analyses were carried out on the deposit recovered on the permanent magnets and compared with the deposit of carbon filamentary structures recovered from the depositing apparatus in order to support these conclusions. In
While the invention has been described with particular reference to the illustrated embodiment, it will be understood that numerous modifications thereto will appear to those skilled in the art. Accordingly, the above description and accompanying drawings should be taken as illustrative of the invention and not in a limiting sense.
The present application is a continuation of U.S. Non-provisional application Ser. No. 11/387,804 filed on Mar. 24, 2006 and which claims priority on U.S. provisional application No. 60/664,952 filed on Mar. 25, 2005. These two documents are incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60664952 | Mar 2005 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11387804 | Mar 2006 | US |
| Child | 12893758 | US |
