Title of Invention	CARBON NANOSTRUCTURES AND PROCESS FOR THE PRODUCTION OF CARBON-BASED NANOTUBES, NANOFIBRES AND NANOSTRUCTURES
Abstract	Continuous process for the production of carbon-based nanostructures, comprising the following steps: generating a plasma with electrical energy, introducing a carbon precursor and/or one or more catalysers and/or carrier plasma gas in a reaction zone of an airlight high temperature resistant vessel optionally having a thermal insulation lining, vaporizing the carbon precursor in the reaction zone at a very high temperature, preferably 4000°C and higher, guiding the carrier plasma gas, the carbon precursor vaporized and the catalyser through a nozzle, whose diameter is narrowing in the direction of the plasma gas flow, guiding the carrier plasma gas, the carbon precursor vaporized and the catalyser into a quenching zone for nucleation, growing and quenching operating with flow conditions generated by aerodynamic and electromagnetic forces, so that no significant recirculation of feedstocks or products from the quenching zone into the reaction zone occurs, controlling the gas temperature in the quenching zone between about 4000°C in the upper part of this zone and about 50°C in the lower part of this zone and controlling the quenching velocity between 103 K/s and 106 K/s, quenching and extracting carbon-based nanotubes, nanofibers and other nanostructures from the quenching zone, separating carbon-based nanotubes, nanofibers and nanostructures from other reaction products.

Title of Invention

CARBON NANOSTRUCTURES AND PROCESS FOR THE PRODUCTION OF CARBON-BASED NANOTUBES, NANOFIBRES AND NANOSTRUCTURES

Abstract

Continuous process for the production of carbon-based nanostructures, comprising the following steps: generating a plasma with electrical energy, introducing a carbon precursor and/or one or more catalysers and/or carrier plasma gas in a reaction zone of an airlight high temperature resistant vessel optionally having a thermal insulation lining, vaporizing the carbon precursor in the reaction zone at a very high temperature, preferably 4000°C and higher, guiding the carrier plasma gas, the carbon precursor vaporized and the catalyser through a nozzle, whose diameter is narrowing in the direction of the plasma gas flow, guiding the carrier plasma gas, the carbon precursor vaporized and the catalyser into a quenching zone for nucleation, growing and quenching operating with flow conditions generated by aerodynamic and electromagnetic forces, so that no significant recirculation of feedstocks or products from the quenching zone into the reaction zone occurs, controlling the gas temperature in the quenching zone between about 4000°C in the upper part of this zone and about 50°C in the lower part of this zone and controlling the quenching velocity between 103 K/s and 106 K/s, quenching and extracting carbon-based nanotubes, nanofibers and other nanostructures from the quenching zone, separating carbon-based nanotubes, nanofibers and nanostructures from other reaction products.

Full Text	March 22, 2004 Timcal SA E38182WO BUW/bra ARMINES Association pour la Recher- che et ie Developpement des Methodes et Processus Industriels Carbon nanostructures and process for the production of carbon-based nanotubes, nanofibres and nanostructures Field of the invention The invention relates to a process for the economical and continuous production of carbon-based nanotubes, nanofibres and nanostructures. The invention also relates to novel carbon nanostructures. Brief description of the Prior Art Carbon fibres have long been known and many methods for their production have been developed, see for example M. S. Dresselhaus, G. Dresselhaus, K. Suglhara; I. L. Spain, and H. A. Goldberg, Graphite Fibers and Filaments, Springer-Verlag, new York (1988). Short (micron) lengths of forms of fullerene fibres have recently been found on the end of graphite electrodes used to form a carbon arc, see T. W. Ebbesen and P. M. Ajayan, "Large Scale Synthesis of Carbon Nanotubes." Nature Vol. 358, pp. 220-222 (1992), and M. S. Dresselhaus, "Down the Straight and Narrow," Nature, Vol. 358, pp. 195-196, (16. Jul. 1992), and references therein. Carbon nanotubes (also referred to as carbon fibrils) are seamless tubes of graphite sheets with full fullerene caps which were first discovered as multi-layer concentric tubes or multi-wall carbon nanotubes and subsequently as single-wall carbon nanotubes in the presence of transition metal catalysts. Carbon nanotubes have shown promis- ing applications including nano-scale electronic devices, high strength materials, electronic field emission, tips for scanning probe microscopy, gas storage. Presently, there are four main approaches for synthesis of carbon nanotubes. These include the laser ablation of carbon (Thess, A. et al., Science 273, 483 (1996)), the electric arc discharge of graphite rod (Journet, C. et al., Nature 388, 756 (1997)), the chemical vapour deposition of hydrocarbons (Ivanov, V. et al., Chem. Phys. Lett. 223, 329 (1994); Li A. et al., Science 274, 1701 (1996)) and the solar method (Fields; Clark L et al., US patent 6,077,401). The production of multi-wall carbon nanotubes by catalytic hydrocarbon cracking is described in U.S. Pat. No. 5,578,543. The production of single-wall carbon nanotubes has been described by laser techniques (Rinzler, A. G. et al., Appl. Phys. A. 67, 29 (1998)), arc techniques (Haffner, J. H. et al., Chem. Phys. Lett. 296, 195(1998)). Unlike the laser, arc and solar techniques, carbon vapour deposition over transi- tion metal catalysts has been found to create multi-wall carbon nanotubes as a main product instead of single-wall carbon nanotubes. However, there has been some success reported in producing single-wall carbon nanotubes from the cata- lytic hydrocarbon cracking process. Dai et al. (Dai, H. et al., Chem. Phys. Lett 260, 471 (1996)) demonstrate web-like single-wall carbon nanotubes resulting from decomposition of carbon monoxide (CO). In PCT/EP94/00321 a process for the conversion of carbon in a plasma gas is de- scribed. Fullerenes can be produced by this process. The availability of these carbon nanotubes in quantities necessary for practical technology is problematic. Large scale processes for the production of high qual- ity carbon nanotubes are needed. Furthermore, carbon nanostructures with closely reproducible shapes and sizes constitute another object of this invention DETAILED DESCRIPTION OF THE INVENTION The invention and improvement we will describe now presents the improvements of the process necessary for the production of carbon-based nanotubes, nanofibres and novel nanostructures. According to the present invention, a method for pro- ducing carbon nanotubes is provided which avoids the defects and disadvantages of the prior art. The invention is defined in the independent claims. Preferred embodiments are shown in the dependent claims. In accordance with a first embodiment of the invention, there is provided a con- tinuous process for the production of carbon-based nanotubes, nanofibres and nanostructures. This process involves the following steps preferably in that se- quence. A plasma is generated with electrical energy. A carbon precursor and/or one or more catalysers or catalysts and/or a carrier plasma gas is introduced into a reaction zone. This reaction zone is in an airtight high temperature resistant vessel optionally, in some embodiments preferably hav- ing a thermal insulation lining. The carbon precursor is vaporized at very high temperatures in this vessel, pref- erably at a temperature of 4000°C and higher. The carrier plasma gas, the vaporized carbon precursor and the catalyser are guided through a nozzle, whose diameter is narrowing in the direction of the plasma gas flow. The carrier plasma gas, the carbon precursor vaporized and the catalyser are guided through the nozzle into a quenching zone for nucleation, growing and quenching. This quenching zone is operated with flow conditions generated by aerodynamic and electromagnetic forces, so that no significant recirculation of feedstocks or products from the quenching zone into the reaction zone occurs. The gas temperature in the quenching zone is controlled between about 4000°C in the upper part of this zone and about 50°C in the lower part of this zone. The carbon-based nanotubes, nanofibres and other nanostructures are extracted following the quenching. The quenching velocity is preferably controlled between 103 K/s and 106 K/s (K/s degrees Kelvin per second). Finally, the carbon-based nanotubes, nanofibres and nanostructures are separated from other reaction products. The plasma is generated in the preferred embodiment of this invention by direct- ing a plasma gas through an electric arc, preferably a compound arc created by at least two, preferably three electrodes. Further preferred features of the claimed process which can be used individually or in any combination encompass the following: • The plasma is generated by electrodes consisting of graphite. • The arc is generated by connecting an AC power source to electrodes, prefera- bly one where the current frequency lies between 50 Hz and 10 kHz. • The absolute pressure in the reactor lies between 0.1 bar and 30 bar. • The nozzle used consists of graphite at its inner surface. • The nozzle is formed as a continuous or stepped cone. • The nozzle used has a downstream end which abruptly expands from the noz- zle throat. • The carbon precursor used is a solid carbon material, comprising one or more of the following materials: Carbon black, acetylene black, thermal black, graphite, coke, plasma carbon nanostructures, pyrolitic carbon, carbon aerogel, activated carbon or any other solid carbon material. • The carbon precursor used is a hydrocarbon preferably consisting of one or more of the following: methane, ethane, ethylene, acetylene, propane, propyl- ene, heavy oil, waste oil, pyrolysis fuel oil or any other liquid carbon material. • Solid catalyst is used consisting of one or more of the following materials: Ni, Co, Y, La, Gd, B, Fe, Cu is introduced in the reaction zone. • A liquid catalyst is used consisting of one or more of the following materials: Ni, Co, Y, La, Gd, B, Fe, Cu in a liquid suspension or as a corresponding or- ganometallic compound which is preferably added to the carbon precursor and/or to the carrier gas. • A gas carrying a carbon precursor and/or carrying catalyst and/or to produce the plasma and/or to quench the products and/or to extract the products com- prises or consists of one or more of the following gases: Hydrogen, nitrogen, argon, carbon monoxide, helium or any other pure gas without carbon affinity and which is preferably oxygen free. • The gas temperature in the reaction zone is higher than 4000°C. • The gas temperature in the quenching zone is controlled between 4000°C in the upper part of this zone and 50°C in the lower part of this zone. • The carrier plasma gas flow rate is adjusted, depending on the nature of the carrier plasma gas and the electrical power, between 0.001 Nm3 /h to 0.3 Nm3/h per kW of electric power used in the plasma arc. • The quenching gas flow rate is adjusted, depending on the nature of the quenching gas, between 1 Nm3/h and 10 000 Nm3/h. • A portion of the off-gas from the reaction is recycled as at least a portion of the gas for generating the plasma. • A portion of the off-gas from the reaction is recycled as at least a portion of the gas for generating the quenching gas. • A carbon precursor is injected through at least one injector, preferably through two to five injectors. • A carbon precursor is injected into the reaction zone. • A carbon precursor is injected with a tangential and/or with a radial and/or with an axial flow component into the reaction zone. • A catalyst is injected into the reaction zone and/or the quenching zone. • The process is carried out in the total absence of oxygen or in the presence of a small quantity of oxygen, preferably at an atomic ratio oxygen/carbon of less than 1/1000. • If the plasma gas is carbon monoxide, the process is carried out in the pres- ence of oxygen with a maximum atomic ratio oxygen/carbon of less than 1001/1000 in the plasma gas. • One or more of the following products is recovered. i. Carbon black ii. Fullerenes iii. Single wall nanotubes iv. Multi-wall nanotubes v. Carbon fibres vi. Carbon nanostructures vii. Catalyst A yet further embodiment of this invention is a reactor to carry out the process of this invention. This reactor comprises in open flow communication A head section comprising i. at least two, preferably three electrodes ii. a carbon precursor supply and/or a catalyst supply and/or a gas supply. - At least one injector for carbon precursor and/or catalyst injection into the reaction zone, - a reaction zone designed in size, shape and choice of materials so that the gas temperature during operation is 4000°C or higher, preferably is well above 4000°C, - a quenching zone designed in size, shape and choice of materials so that the gas temperature is controllable between 4000°C in the upper part of this zone and 50°C in the lower part of this zone, - a nozzle shaped choke, narrowing the open flow communication direction between the reaction zone and the quenching zone. The electrodes are connected to means for creating an electric arc between the electrodes when a sufficient electric power is supplied. Thereby, an arc zone is generated into which the gas from the gas supply can be fed to generate a plasma gas and in which the carbon precursor can be heated at a vaporization temperature of 4000°C and higher, preferably well above 4000°C. The reactor in its preferred structure has substantially an interior cylindrical shape. Typically and preferably the reactor at the surfaces exposed to high temperatures is from graphite or respectively graphite containing high temperature resistant material. The reactor in the preferred embodiment comprises a chamber with a height between 0.5 and 5 m and a diameter between 5 and 150 cm. In a more specific embodiment the reactor of this invention comprises tempera- ture control means for the quench zone. These temperature control means are par- ticularly selected from thermal insulating lining, fluid flow, preferably water flow. indirect heat exchange means and flow and/or temperature controlled quench gas injection means. The nozzle mentioned is in the preferred embodiment a tapering choke followed by an abruptly expanding section. In accordance with a yet further embodiment of the invention, there are provided novel carbon nanostructures. These carbon nanostructures have the shape of a linear, i.e. essentially un-branched chain of connected and substantially identical sections of beads, namely spheres or bulb-like units or trumpet shaped units. These trumpet shaped units form carbon nanostructures the SEM or TEM of which resembles a necklace-like structure. These novel carbon nanostructures preferably have diameters of the spherical portions of the spheres or bulb-like units or respectively of the large end of the trumpet shaped units in the range of 100 to 200 nm. The shapes mentioned are those visible in TEM at very large magnification and in HRTEM. The carbon nanostructures of this embodiment of the invention are connected to fairly long chains and as a rule all of these chains have at least 5 beads connected to each other. The structures will preferably have 20 to 50 beads in one chain. In yet another variation of the carbon nanostructures of this invention, these are filled or at least substantially filled with catalyst metal, more specifically with nickel or nickel/cobalt. These metal filled nanostructures form an excellent source of catalyst for the process to produce such nanostructures. Separating these struc- tures from the product of the quenching zone and introducing the structures back into the reaction zone is a recirculation of the catalytic material in an encapsulated and finely divided form. In the reaction zone itself, the carbon and the metal are both evaporated. In one embodiment the bulb-like structures of the inventive carbon nanostructures are connected together at the neck portion. Preferred applications of these new nanostructures: The present carbon nanotubes are different in shape when compared to the con- vential multi-wall nanotubes which exhibit a perfect stacking of graphitic cylin- ders. In that sense, the described novel structures, in particular such bamboo- shaped structures have advantages e.g. in gas storage (easier way to store hydro- gen between the graphitic cones), and also for field emission properties, which are known to depend on the topology at the nanotube tip apex, and more specifically to the conical angle (related to the number of pentagons present at the tip apex). On the other hand, the necklace-like nano-structures have never been reported before, and they allow in a preferred embodiment the combination in composite materials both when incorporated into the matrix in an oriented or in a non- oriented way. A preferred embodiment of the invention is thus a composite com- prising the necklace-like nano-structures in a matrix, preferably a polymer matrix. Such nano-objects increase the interaction between the nano-fiber and the host material, as compared to conventional tubes. They increase the mechanical prop- erties of composite materials. As the nano-spheres are intrinsically connected, and can contain metal catalyst, these nano-necklaces can also be used in nano- electronics. The invention will be further illustrated, preferred details and combination of de- tails of the invention shown in conjunction with examples and the accompanyingdrawing in which: Figure 1 shows a schematic view of a facility or an apparatus for carrying out the process of the invention. Figure 2 shows a variation of an apparatus of Figure 1. Figure 3 shows a yet further variation with some added specific features of an apparatus in accordance with the invention. Figure 4 shows a SEM picture of open multi-wall nanotubes. Figure 5 shows a SEM image of a spaghetti-like arrangement of multi-wall and necklace-shaped nanotubes. Figure 6 shows a TEM picture of necklace shaped carbon nanostructures in accor dance with the invention. Figure 7 shows a HRTEM picture of carbon necklace structures of bulb-like beads. Figure 8 shows a TEM picture of carbon nanotubes having a bamboo-like struc- ture. Figure 9 shows a HRTEM picture of single-wall nanotubes. The reactor 1 is designed in a way that it consists of two different but adjacent zones. Zone A, for the vaporization of the precursor (carbonaceous products and catalytic products), is maintained at a very high temperature due to the action of a thermal plasma and an appropriate thermal insulation. Zone B, for the nucleation and maturation of the carbon-based nanostructures, is kept between 4000°C in the upper part and less than 50°C in the lower part due to an adequate thermal insula- tion. In zone A, the geometry of the internal fittings has the shape of a venturi which is specifically designed to assure the complete vaporization of the precursors. Each of the three electrodes 3, of which only two are shown in Figure 1, is connected to one of the three phases of an electric three-phase generator and supplied with al- ternative current. After activation of the electric generator and the establishment of the plasma by the contact of the three electrodes, the electrodes are automati- cally drawn apart and a plasma flow is established in zone A of the reactor, which allows the complete vaporization of the precursor. Once the plasma is established, the control of the electrodes to compensate for their erosion is effectuated auto- matically. Together with a carrier plasma gas, the carbonaceous product and the catalytic product are continuously injected into zone A of the reactor, for example in 4. The electric power source is of the type "three-phase", whereby the frequency of the supply can vary between 50 Hz and 10 kHz. Each of the three phases of the electric source is connected to one of the three electrodes of the reactor. The in- ventors discovered that an increase of the frequency of the electric supply beyond 50 Hz, which can range from 50 Hz to 10 kHz, achieves particular advantages. This increase of the frequency allows on the one hand an increase in the stability of the plasma, and on the other hand a very advantageous increase in the homoge- neity of the mixture of the plasma gas with the carbonaceous product vaporized and the catalyst product due to important turbulence phenomena in the flow field of zone A. This turbulence is caused by the combined effects of arc rotation be- tween the three electrodes successively changing from anode and cathode with current frequency and the electromagnetic forces induced by the current in the electrodes and the arcs themselves. In zone B of the reactor, the zone of the nucleation and growing of the carbon- based nanostructures, the temperature of the flow in maintained between 4000°C in the upper part and less than 50°C in the lower part due to an adequate thermal insulation. The absolute pressure in zones A and B of the reactor can be between 100 mbar and 30 bar. Into this zone, a certain quantity of cold gas is injected in 5. allowing the quenching of the aerosols and their extraction from the reactor in 6 by means of an extraction system cooled by a liquid, a gas or any other means of refrigeration known within the state of the art. Afterwards, the aerosol is trans- ported to a heat exchanger in 7 where it is cooled down further to a stabilization temperature of the envisaged carbon-based nanostructures and finally passes through a separation system in 8 where the carbon-based nanostructures are sepa- rated from the gas phase. Eventually, the carbon-based nanostructures are taken out in 10 by means of an airtight valve represented in 9 and the gas is vented in 11. In accordance with a preferred embodiment of the invention, full control of the extraction conditions and the quenching rate is foreseen thereby controlling the quality of the nanostructures obtained. Both the temperature at which the aerosol is extracted and the quenching speed of the aerosol are preferably controlled to ensure high quality products. Preferred control approaches include the following. The temperature at which the extraction is effectuated and the residence time for product maturation is con- trolled by the variation of the axial position of the injection point of cold gas in 5 and the extraction point in 6 in zone B. The quenching velocity rate is controlled by a variation in the nature and the flow rate of cold gas injected in 5, by the ef- fectiveness of the extraction system cooled in 6 and by the effectiveness of the heat exchanger in 7. In a preferred embodiment shown in Figure 2, zone B of the reactor is modified by the installation of a recirculation system for the quenching gas flow as de- scribed hereafter. In zone B of the reactor where the temperature is maintained between 4000°C in the upper part and less than 50°C in the lower part, a device cooled by a liquid, a gas or any other means of refrigeration known within the state of the art is introduced in 5, which allows the extraction of the aerosols in 6 and the transport to a separation system in 7. The temperature of the zone of which the extraction is effectuated, is controlled by the variation of the axial posi- tion of the injection point of cold gas in 11 and the extraction point in 5. The quenching rate is controlled by a variation in the flow rate of cold gas injected into zone B in 11 by means of a blower 10, by the effectiveness of the extraction system cooled in 5 and by the effectiveness of the heat exchanger in 6. Therefore, the gas flow rate in the recirculation circuit is independent of the initial carrier gas flow entering in 4. The aerosol is transported to a heat exchanger in 6 where it is cooled down further to a stabilization temperature of the envisaged carbon-based nanostructures and finally passes through a separation system in 7 where the car- bon-based nanostructures are separated from the gas phase. Eventually, the car- bon-based nanostructures are taken out in 9 by means of a valve 8. The excess gas flow equivalent of the amount of gas entering in 4 is vented in 12. In a preferred embodiment shown in Figure 3, zone B of the reactor is modified by the installation of a recirculation system for the quenching gas flow and the carrier plasma gas supplying the plasma itself as described hereafter. In zone B of the reactor where the temperature is maintained between 4000°C in the upper part and less than 50°C in the lower part, a device cooled by a liquid, a gas or any other means of refrigeration is introduced in 5, which allows the extraction of the aerosols in 6 and the transport to a separation system 7. The temperature of the zone of which the extraction is effectuated, is controlled by the variation of the axial position of the injection point of cold gas in 12 and the extraction point 5. The quenching rate is controlled by a variation in the flow rate of cold gas in- jected into zone B in 12 by means of a blower 10, by the effectiveness of the ex- traction via extraction point5 and by the effectiveness of the heat exchanger 6. Therefore, the gas flow rate in the recirculation circuit is independent of the initial carrier gas flow entering in 18. The aerosol is transported to a heat exchanger 6 where it is cooled down further to a stabilization temperature of the envisaged carbon-based nanostructures and finally passes through a separation system 7 where the carbon-based nanostructures are separated from the gas phase. Eventu- ally, the carbon-based nanostructures are taken out in 9 by means of a valve 8. A part of the gas vented in 13 is used as carrier plasma gas in 14. A feeding system 15 with a gas feeding 18 and a valvel6 allows the continuous feeding of solid carbon material in 4. The excess gas flow equivalent of the amount of gas entering in 18 is vented in 17. The raw material used as a precursor consist of one or a combination of the fol- lowing elements: A carbonaceous product, a catalytic product and/or a gaseous product. The product used as carbonaceous product can be of solid, liquid or gaseous nature. In the case of solid carbonaceous materials, different types of products can be utilized, for example: Finely milled graphite, acetylene black, carbon black de- gassed, milled pyrolitic carbon, activated carbon, pyrolized carbon aerogels, plasma carbon nanostructures. The carbon content of the utilized carbonaceous material should be as high as possible, preferably higher than 99 weight %. The average particle size of the carbonaceous materials should be as small as possible, preferably smaller than 10 µm in diameter, to ensure its complete vaporization when passing through the plasma. In the case of liquid and gaseous carbon precursors any kind of hydrocarbon can be considered. The catalytic material associated with the carbonaceous material can consist of one or a mixture of elements well known for their catalytic characteristics in car- bon nanotubes synthesis, such as: Ni, Co, Y, La, Gd, B, Fe, Cu. The catalytic ma- terials are introduced in zone A (preferred) or zone B of the reactor, either in form of a powder mixed with the carbon material, or in form of a deposit on the carbon material, or in form of a solid whereby the morphology can vary corresponding to the hydrodynamic prevalent in the reactor, or in the form of a liquid. The mass ratio of catalyser to carbon can vary between 0.1% and 50%. In the case of liquid carbon precursors, the catalytic elements are preferably mixed with the liquid. In the case of gaseous carbon precursors, the catalytic elements are preferably introduced in form of a powder. In the case of solid carbon precursors, the catalytic elements are preferably intro- duced in form of a deposit on the carbon material. The plasma gas is preferably a pure gas: Helium, argon, nitrogen or a mixture of one of these gases with the following gases: Helium, argon, nitrogen, carbon monoxide, hydrogen. The quenching gas can be identical to the plasma gas or consist of any kind of gas mixture. In the following examples further preferred features, feature combinations and embodiments of this invention are illustrated. The examples were carried out in a reactor set-up substantially as shown in Fig- ures 1 and 2. Example 1: The reactor set-up, described in Figure 1, consists of a cylindrical reactor of a height of 2 meters in stainless steel with water-cooled walls and 400 mm internal diameter. The upper part of the reactor is fitted with thermal insulation cone- shaped in graphite of 500 mm height and an internal diameter between 150 and 80 mm. Three electrodes in graphite of 17 mm diameter are positioned through the head of the reactor by a sliding device system electrically insulated. A central in- jector of 4 mm internal diameter allows the introduction of the precursor by means of a carrier plasma gas in the upper part of the reactor. A plasma power supply, employing a three phase electricity source up to 666 Hz with a maximum power of 263 kVA, a RMS current range of up to 600 A and a RMS voltage range of up to 500 V, was used to supply electricity to the three graphite electrodes, their tips being arranged in the shape of an inversed pyramid. The carrier plasma gas is helium and the precursor is carbon black with a deposit of nickel - cobalt corresponding to a weight ratio in relation to the carbon of 2,5 weight % for the nickel and 3 weight % for the cobalt. The gas for the quenching is helium. The following table gives the main operating conditions. More than 98% of the injected precursor mass was removed from the filter. The recovered product is composed of: 40% of Single Walled Carbon Nanotubes, 5.6% of fullerenes whereby 76% of C60 and 24% of C70, 5% of Multi Walled Carbon Nanotubes, about 20% of fullerene soots, about 30% of undefined carbon nanostructures with catalyst particles. Quantitative and qualitative measurements of carbon nanostructures are achieved using Scanning Electronic Microscopy and Transmission Electronic Microscopy. Quantitative and qualitative measurements of the fullerenes (C60 and C70) are achieved using UV - visible spectroscopy at the wavelengths 330 nm and 470 nm after Soxhlet-extraction with toluene. Example 2 One operates in similar conditions to example 1 but according to the configuration corresponding to Figure 2. Carrier plasma gas is nitrogen at a flow-rate of 2 Nm3/h. The quenching gas is nitrogen at a flow-rate of 50 Nm3/h. Electrical con- ditions are 350 A and 200 V. In these conditions necklace shaped carbon nanos- tructures are produced in very high concentration. Example 3 One operates in similar conditions to example 1 but according to the configuration corresponding to Figure 2. Carrier plasma gas is helium at a flow rate of 3 Nm3/h. The quenching gas is a mixture of nitrogen/helium at a flow rate of 50 Nm3/h. Electrical conditions are those of example 1. The precursor is ethylene (C2H4) mixed with nickel-cobalt powders corresponding to a weight ratio in relation to the carbon of 3 weight % for the nickel and 2 weight % for the cobalt. The recov- ered product is composed of: 55 weight % of single walled carbon nanotubes, 13 weight % of carbon nanofibres and multi walled carbon nanotubes, the rest of undefined carbon nanostructures with catalyst particles. The carbon nanostructures of Fig. 4-9 illustrate embodiments of the invention. The preferred carbon nanostructures of this invention have the structure of a linear chain of connected, substantially identical sections of beads, namely spheres or bulb-like units or trumpet shaped units, preferably having a diameter of the spheres of the spherical section of the bulb-like units or respectively the large di- ameter of the trumpet shaped section in the range of 100 to 200 nanometres. All spheres or bulb-units exhibit nearly the same diameter. These periodic graphitic nano-fibers are characterized by a repetition of multi-wall carbon spheres ('neck- lace'-like structure), connected along one direction, and containing frequently a metal particle encapsulated in their structure. The periodicity of these nanostruc- tures relates them to the bamboo nanotubes, but they clearly differ by their peri- odic necklace-like structure and the presence of these metal inclusions. We Claim: 1. Continuous process for the production of carbon-based nanostructures, comprising the following steps: • generating a plasma with electrical energy, • introducing a carbon precursor and/or one or more catalysers and/or carrier plasma gas in a reaction zone of an airlight high temperature resistant vessel optionally having a thermal insulation lining, • vaporizing the carbon precursor in the reaction zone at a very high temperature, preferably 4000°C and higher, • guiding the carrier plasma gas, the carbon precursor vaporized and the catalyser through a nozzle, whose diameter is narrowing in the direction of the plasma gas flow, • guiding the carrier plasma gas, the carbon precursor vaporized and the catalyser into a quenching zone for nucleation, growing and quenching operating with flow conditions generated by aerodynamic and electromagnetic forces, so that no significant recirculation of feedstocks or products from the quenching zone into the reaction zone occurs, • controlling the gas temperature in the quenching zone between 4000°C in the upper part of this zone and 50°C in the lower part of this zone and controlling the quenching velocity between 103 K/s and l06 K/s • quenching and extracting carbon-based nanotubes, nanofibers and other nanostructures from the quenching zone, • separating carbon-based nanotubes, nanofibers and nanostructures from other reaction products. 2. Process as claimed in claim 1, wherein plasma is generated by directing plasma gas through an electric arc, preferably a compound arc, created by at least two electrodes. 3. Process as claimed in claim 1 or 2, wherein by one or more of the following features: a. The plasma is generated by electrodes consisting of graphite; b. The arc is created by connecting an AC power source to electrodes, preferably one where the current frequency lies between 50 Hz and 10 kHz; c. The absolute pressure in the reactor lies between 0.1 bar and 30 bar; d. The nozzle used consists of graphite at its inner surface; e. The nozzle is formed as a continuous or stepped cone; f. The nozzle used has a downstream end which abruptly expands from the nozzle throat; g. The carbon precursor used is a solid carbon material, comprising one or more of the following materials: Carbon black, acetylene black, thermal black, graphite, coke, plasma carbon nanostructures, pyrolitic carbon, carbon aerogel, activated carbon, or any other solid carbon material; h. The carbon precursor used is a hydrocarbon preferably consisting of one or more of the following: methane, ethane, ethylene, acetylene, propane, propylene, heavy oil, waste oil, pyrolysis fuel oil, preferably a liquid carbon material; i. Solid catalyst is used consisting of one or more of the following materials: Ni, Co, Y, La, Gd, B, Fe, Cu, is introduced in the reaction zone; j. A liquid catalyst is used consisting of one or more of the following materials Ni, Co, Y, La, Gd, B, Fe, Cu in a liquid suspension or as organometallic compound, which is preferably added to the carbon precursor and/or to the carrier gas, k. A gas carrying a carbon precursor and/or carrying catalyst and/or to produce the plasma and/or to quench the products and/or to extract the products comprises or consists of one or more of the following gases: Hydrogen, nitrogen, argon, carbon monoxide, helium or any other pure gas without carbon affinity and which is preferably oxygen free; 1. The gas temperature in the reaction zone is higher than 4000°C; m. The gas temperature in the quenching zone is controlled between 4000°C in the upper part of this zone and 50°C in the lower part of this zone; n. The carrier plasma gas flow rate is adjusted, depending on the nature of the carrier plasma gas and the electrical power, between 0.001 Nm /h to 0.3 Nm/h per kW of electric power used in the plasma arc; o. The quenching gas flow rate is adjusted, depending on the nature of the quenching gas, between 1 Nm3/h and 10 000 Nm3/h; p. A portion of the off-gas from the reaction is recycled as at least a portion of the gas for generating the plasma, q. A portion of the off-gas from the reaction is recycled as at least a portion of the gas for generating the quenching gas, r. A carbon precursor is injected through at least on injector, preferably through two to five injectors, s. A carbon precursor is injected into the reaction zone, t. A carbon precursor is injected with a tangential and/or with a radial and/or with an axial flow component into the reaction zone, u. The process is carried out in the total absence of oxygen or in the presence of a small quantity of oxygen, preferably at an atomic ratio oxygen/carbon of less than 1/1000, v. If the plasma gas is carbon monoxide, the process is carried out in the presence of oxygen with a maximum atomic ratio oxygen/carbon of less than 1001/1000 in the plasma gas, w. One or more of the following products is recovered: i. Carbon black ii. Fullerence iii. Single wall nanotubes iv. Multi-wall nanotubes v. Carbon fibres vi. Carbon nanostructures vii. Catalyst 4. Reactor to carry out the process as claimed in one of the claims directed to processes comprising in open flow communication a. A head section comprising: i. At least two, preferably three electrodes ii. A carbon precursor supply and/or a catalyst supply and/or a gas supply for creating an electric arc between the electrodes when a sufficient electric power is supplied, and creating an arc zone, into which the gas from the gas supply can be fed to generate a plasma gas and for heating the carbon precursor at a vaporization temperature higher than 4000°C b. At least one injector for carbon precursor and/or catalyst injection into the reaction zone c. A reaction zone where the gas temperature during operation is 4000°C or higher d. A quenching zone where the gas temperature is controllable between 4000°C in the upper part of this zone and 50°C in the lower part of this zone e. A nozzle shaped choke, narrowing the open flow communication between the reaction zone and the quenching zone. 5. Reactor as claimed in claim 4, having substantially interior cylindrical shape. 6. Reactor as claimed in claim 4 or 5, whereby the high temperature exposed surfaces are of graphite containing high temperature resistant material. 7. Reactor as claimed in claim 4, 5 or 6 comprising a chamber with a height between 0.5 and 5 m and a diameter between 5 and 150 cm. 8. Reactor as claimed in one of the claims directed to reactors comprising temperature control means for the quenching zone selected from thermal insulating lining, fluid flow, preferably water flow, indirect heat exchange means and flow and/or temperature controlled quench gas injection means. 9. Reactor as claimed in one of the claims directed to reactors wherein the nozzle shaped choke is a tapering choke followed by an abruptly expanding section. 10. Reactor as claimed in one of the claims directed to reactors, characterized by one or more apparatus features of one or more of the process claims. 11. Carbon nanostructures having the structure of a linear chain of connected, substantially identical sections of beads, namely spheres or bulb-like units or trumpet shaped units, preferably having a diameter of the spheres of the spherical section of the bulb-like units or respectively the large diameter of the trumpet shaped section in the range of 100 to 200 nanometres, more preferably having all spheres or bulb-units exhibiting nearly the same diameter, and in particular comprising periodic graphitic nano-fibers being characterized by a repetition of multi-wall carbon spheres ('necklace'-like structure), connected along one direction, and several of the spheres containing a metal particle encapsulated in their structure. 12. Carbon nanostructures as claimed in claim 11, wherein at least 5 beads are connected to one chain, preferably 20 to 50 beads are in one chain. 13. Carbon nanostructrues as claimed in one of claims directed to carbon nanostructures, wherein one or more of the beads is filled with catalyst, in particular with ferromagnetic metal catalyst, more specifically with nickel or nickel/cobalt. 14. Carbon nanostructures as claimed in one of claims directed to carbon nanostructures wherein the bulb-like or bell-like are connected to each other by external graphitic cylindrical layers. 15. Carbon nanotube exhibiting a multi-wall structure, wherein several nanoconical structures (bamboo shaped structures) are stacked, said nanotubular structures preferably possessing a closed end conical tip apex the other end being either open or filled with a metal nanoparticle. 16. Carbon nanotube as claimed in claim 15 having an external diameter of 100 to 120 nm and comprising a set of discontinuous concical cavities. 17. Carbon nanostructures and carbon nanotubes as claimed in one of claims directed to such products being arranged in a random form, the SEM of which resembles cooked spaghetti. 18. Carbon nanostructures being single walled and having preferably one or more of the following properties - one, preferably both ends are open - one layer having a diameter between about 0.8and about 2nm. - length of the tubes is a few microns. 19. Carbon nanostructure having substantially a shape defined by its SEM or TEM view as shown in one of the Figures showing nanostructures. 20. A composite of carbon nanostructures as claimed in one of the claims directed to such carbon nanostructures and a polymer matrix. 21. A composite as claimed in claim 20 comprising, preferably consisting of, polyethylene, polypropylene, polyamide, polycarbonate, polyphenylenesulfide, polyester. Continuous process for the production of carbon-based nanostructures, comprising the following steps: generating a plasma with electrical energy, introducing a carbon precursor and/or one or more catalysers and/or carrier plasma gas in a reaction zone of an airlight high temperature resistant vessel optionally having a thermal insulation lining, vaporizing the carbon precursor in the reaction zone at a very high temperature, preferably 4000°C and higher, guiding the carrier plasma gas, the carbon precursor vaporized and the catalyser through a nozzle, whose diameter is narrowing in the direction of the plasma gas flow, guiding the carrier plasma gas, the carbon precursor vaporized and the catalyser into a quenching zone for nucleation, growing and quenching operating with flow conditions generated by aerodynamic and electromagnetic forces, so that no significant recirculation of feedstocks or products from the quenching zone into the reaction zone occurs, controlling the gas temperature in the quenching zone between about 4000°C in the upper part of this zone and about 50°C in the lower part of this zone and controlling the quenching velocity between 103 K/s and 106 K/s, quenching and extracting carbon-based nanotubes, nanofibers and other nanostructures from the quenching zone, separating carbon-based nanotubes, nanofibers and nanostructures from other reaction products.

Full Text

March 22, 2004
Timcal SA E38182WO BUW/bra
ARMINES Association pour la Recher-
che et ie Developpement des Methodes
et Processus Industriels
Carbon nanostructures and process for the production of carbon-based
nanotubes, nanofibres and nanostructures
Field of the invention
The invention relates to a process for the economical and continuous production
of carbon-based nanotubes, nanofibres and nanostructures. The invention also
relates to novel carbon nanostructures.
Brief description of the Prior Art
Carbon fibres have long been known and many methods for their production have
been developed, see for example M. S. Dresselhaus, G. Dresselhaus, K. Suglhara;
I. L. Spain, and H. A. Goldberg, Graphite Fibers and Filaments, Springer-Verlag,
new York (1988).
Short (micron) lengths of forms of fullerene fibres have recently been found on
the end of graphite electrodes used to form a carbon arc, see T. W. Ebbesen and P.
M. Ajayan, "Large Scale Synthesis of Carbon Nanotubes." Nature Vol. 358, pp.
220-222 (1992), and M. S. Dresselhaus, "Down the Straight and Narrow," Nature,
Vol. 358, pp. 195-196, (16. Jul. 1992), and references therein. Carbon nanotubes
(also referred to as carbon fibrils) are seamless tubes of graphite sheets with full
fullerene caps which were first discovered as multi-layer concentric tubes or
multi-wall carbon nanotubes and subsequently as single-wall carbon nanotubes in
the presence of transition metal catalysts. Carbon nanotubes have shown promis-
ing applications including nano-scale electronic devices, high strength materials,
electronic field emission, tips for scanning probe microscopy, gas storage.
Presently, there are four main approaches for synthesis of carbon nanotubes.
These include the laser ablation of carbon (Thess, A. et al., Science 273, 483
(1996)), the electric arc discharge of graphite rod (Journet, C. et al., Nature 388,
756 (1997)), the chemical vapour deposition of hydrocarbons (Ivanov, V. et al.,
Chem. Phys. Lett. 223, 329 (1994); Li A. et al., Science 274, 1701 (1996)) and the
solar method (Fields; Clark L et al., US patent 6,077,401).
The production of multi-wall carbon nanotubes by catalytic hydrocarbon cracking
is described in U.S. Pat. No. 5,578,543. The production of single-wall carbon
nanotubes has been described by laser techniques (Rinzler, A. G. et al., Appl.
Phys. A. 67, 29 (1998)), arc techniques (Haffner, J. H. et al., Chem. Phys. Lett.
296, 195(1998)).
Unlike the laser, arc and solar techniques, carbon vapour deposition over transi-
tion metal catalysts has been found to create multi-wall carbon nanotubes as a
main product instead of single-wall carbon nanotubes. However, there has been
some success reported in producing single-wall carbon nanotubes from the cata-
lytic hydrocarbon cracking process. Dai et al. (Dai, H. et al., Chem. Phys. Lett
260, 471 (1996)) demonstrate web-like single-wall carbon nanotubes resulting
from decomposition of carbon monoxide (CO).
In PCT/EP94/00321 a process for the conversion of carbon in a plasma gas is de-
scribed. Fullerenes can be produced by this process.
The availability of these carbon nanotubes in quantities necessary for practical
technology is problematic. Large scale processes for the production of high qual-
ity carbon nanotubes are needed. Furthermore, carbon nanostructures with closely
reproducible shapes and sizes constitute another object of this invention
DETAILED DESCRIPTION OF THE INVENTION
The invention and improvement we will describe now presents the improvements
of the process necessary for the production of carbon-based nanotubes, nanofibres
and novel nanostructures. According to the present invention, a method for pro-
ducing carbon nanotubes is provided which avoids the defects and disadvantages
of the prior art.
The invention is defined in the independent claims. Preferred embodiments are
shown in the dependent claims.
In accordance with a first embodiment of the invention, there is provided a con-
tinuous process for the production of carbon-based nanotubes, nanofibres and
nanostructures. This process involves the following steps preferably in that se-
quence.
A plasma is generated with electrical energy.
A carbon precursor and/or one or more catalysers or catalysts and/or a carrier
plasma gas is introduced into a reaction zone. This reaction zone is in an airtight
high temperature resistant vessel optionally, in some embodiments preferably hav-
ing a thermal insulation lining.
The carbon precursor is vaporized at very high temperatures in this vessel, pref-
erably at a temperature of 4000°C and higher.
The carrier plasma gas, the vaporized carbon precursor and the catalyser are
guided through a nozzle, whose diameter is narrowing in the direction of the
plasma gas flow.
The carrier plasma gas, the carbon precursor vaporized and the catalyser are
guided through the nozzle into a quenching zone for nucleation, growing and
quenching. This quenching zone is operated with flow conditions generated by
aerodynamic and electromagnetic forces, so that no significant recirculation of
feedstocks or products from the quenching zone into the reaction zone occurs.
The gas temperature in the quenching zone is controlled between about 4000°C in
the upper part of this zone and about 50°C in the lower part of this zone.
The carbon-based nanotubes, nanofibres and other nanostructures are extracted
following the quenching. The quenching velocity is preferably controlled between
103 K/s and 106 K/s (K/s degrees Kelvin per second).
Finally, the carbon-based nanotubes, nanofibres and nanostructures are separated
from other reaction products.
The plasma is generated in the preferred embodiment of this invention by direct-
ing a plasma gas through an electric arc, preferably a compound arc created by at
least two, preferably three electrodes.
Further preferred features of the claimed process which can be used individually
or in any combination encompass the following:
• The plasma is generated by electrodes consisting of graphite.
• The arc is generated by connecting an AC power source to electrodes, prefera-
bly one where the current frequency lies between 50 Hz and 10 kHz.
• The absolute pressure in the reactor lies between 0.1 bar and 30 bar.
• The nozzle used consists of graphite at its inner surface.
• The nozzle is formed as a continuous or stepped cone.
• The nozzle used has a downstream end which abruptly expands from the noz-
zle throat.
• The carbon precursor used is a solid carbon material, comprising one or more
of the following materials: Carbon black, acetylene black, thermal black,
graphite, coke, plasma carbon nanostructures, pyrolitic carbon, carbon aerogel,
activated carbon or any other solid carbon material.
• The carbon precursor used is a hydrocarbon preferably consisting of one or
more of the following: methane, ethane, ethylene, acetylene, propane, propyl-
ene, heavy oil, waste oil, pyrolysis fuel oil or any other liquid carbon material.
• Solid catalyst is used consisting of one or more of the following materials: Ni,
Co, Y, La, Gd, B, Fe, Cu is introduced in the reaction zone.
• A liquid catalyst is used consisting of one or more of the following materials:
Ni, Co, Y, La, Gd, B, Fe, Cu in a liquid suspension or as a corresponding or-
ganometallic compound which is preferably added to the carbon precursor
and/or to the carrier gas.
• A gas carrying a carbon precursor and/or carrying catalyst and/or to produce
the plasma and/or to quench the products and/or to extract the products com-
prises or consists of one or more of the following gases: Hydrogen, nitrogen,
argon, carbon monoxide, helium or any other pure gas without carbon affinity
and which is preferably oxygen free.
• The gas temperature in the reaction zone is higher than 4000°C.
• The gas temperature in the quenching zone is controlled between 4000°C in
the upper part of this zone and 50°C in the lower part of this zone.
• The carrier plasma gas flow rate is adjusted, depending on the nature of the
carrier plasma gas and the electrical power, between 0.001 Nm3 /h to 0.3
Nm3/h per kW of electric power used in the plasma arc.
• The quenching gas flow rate is adjusted, depending on the nature of the
quenching gas, between 1 Nm3/h and 10 000 Nm3/h.
• A portion of the off-gas from the reaction is recycled as at least a portion of
the gas for generating the plasma.
• A portion of the off-gas from the reaction is recycled as at least a portion of
the gas for generating the quenching gas.
• A carbon precursor is injected through at least one injector, preferably through
two to five injectors.
• A carbon precursor is injected into the reaction zone.
• A carbon precursor is injected with a tangential and/or with a radial and/or
with an axial flow component into the reaction zone.
• A catalyst is injected into the reaction zone and/or the quenching zone.
• The process is carried out in the total absence of oxygen or in the presence of
a small quantity of oxygen, preferably at an atomic ratio oxygen/carbon of less
than 1/1000.
• If the plasma gas is carbon monoxide, the process is carried out in the pres-
ence of oxygen with a maximum atomic ratio oxygen/carbon of less than
1001/1000 in the plasma gas.
• One or more of the following products is recovered.
i. Carbon black
ii. Fullerenes
iii. Single wall nanotubes
iv. Multi-wall nanotubes
v. Carbon fibres
vi. Carbon nanostructures
vii. Catalyst
A yet further embodiment of this invention is a reactor to carry out the process of
this invention. This reactor comprises in open flow communication
A head section comprising
i. at least two, preferably three electrodes
ii. a carbon precursor supply and/or a catalyst supply and/or a gas supply.
- At least one injector for carbon precursor and/or catalyst injection into the
reaction zone,
- a reaction zone designed in size, shape and choice of materials so that the gas
temperature during operation is 4000°C or higher, preferably is well above
4000°C,
- a quenching zone designed in size, shape and choice of materials so that the
gas temperature is controllable between 4000°C in the upper part of this zone
and 50°C in the lower part of this zone,
- a nozzle shaped choke, narrowing the open flow communication direction
between the reaction zone and the quenching zone.
The electrodes are connected to means for creating an electric arc between the
electrodes when a sufficient electric power is supplied. Thereby, an arc zone is
generated into which the gas from the gas supply can be fed to generate a plasma
gas and in which the carbon precursor can be heated at a vaporization temperature
of 4000°C and higher, preferably well above 4000°C.
The reactor in its preferred structure has substantially an interior cylindrical shape.
Typically and preferably the reactor at the surfaces exposed to high temperatures
is from graphite or respectively graphite containing high temperature resistant
material. The reactor in the preferred embodiment comprises a chamber with a
height between 0.5 and 5 m and a diameter between 5 and 150 cm.
In a more specific embodiment the reactor of this invention comprises tempera-
ture control means for the quench zone. These temperature control means are par-
ticularly selected from thermal insulating lining, fluid flow, preferably water flow.
indirect heat exchange means and flow and/or temperature controlled quench gas
injection means.
The nozzle mentioned is in the preferred embodiment a tapering choke followed
by an abruptly expanding section.
In accordance with a yet further embodiment of the invention, there are provided
novel carbon nanostructures. These carbon nanostructures have the shape of a
linear, i.e. essentially un-branched chain of connected and substantially identical
sections of beads, namely spheres or bulb-like units or trumpet shaped units.
These trumpet shaped units form carbon nanostructures the SEM or TEM of
which resembles a necklace-like structure. These novel carbon nanostructures
preferably have diameters of the spherical portions of the spheres or bulb-like
units or respectively of the large end of the trumpet shaped units in the range of
100 to 200 nm. The shapes mentioned are those visible in TEM at very large
magnification and in HRTEM.
The carbon nanostructures of this embodiment of the invention are connected to
fairly long chains and as a rule all of these chains have at least 5 beads connected
to each other. The structures will preferably have 20 to 50 beads in one chain.
In yet another variation of the carbon nanostructures of this invention, these are
filled or at least substantially filled with catalyst metal, more specifically with
nickel or nickel/cobalt. These metal filled nanostructures form an excellent source
of catalyst for the process to produce such nanostructures. Separating these struc-
tures from the product of the quenching zone and introducing the structures back
into the reaction zone is a recirculation of the catalytic material in an encapsulated
and finely divided form. In the reaction zone itself, the carbon and the metal are
both evaporated.
In one embodiment the bulb-like structures of the inventive carbon nanostructures
are connected together at the neck portion.
Preferred applications of these new nanostructures:
The present carbon nanotubes are different in shape when compared to the con-
vential multi-wall nanotubes which exhibit a perfect stacking of graphitic cylin-
ders. In that sense, the described novel structures, in particular such bamboo-
shaped structures have advantages e.g. in gas storage (easier way to store hydro-
gen between the graphitic cones), and also for field emission properties, which are
known to depend on the topology at the nanotube tip apex, and more specifically
to the conical angle (related to the number of pentagons present at the tip apex).
On the other hand, the necklace-like nano-structures have never been reported
before, and they allow in a preferred embodiment the combination in composite
materials both when incorporated into the matrix in an oriented or in a non-
oriented way. A preferred embodiment of the invention is thus a composite com-
prising the necklace-like nano-structures in a matrix, preferably a polymer matrix.
Such nano-objects increase the interaction between the nano-fiber and the host
material, as compared to conventional tubes. They increase the mechanical prop-
erties of composite materials. As the nano-spheres are intrinsically connected, and
can contain metal catalyst, these nano-necklaces can also be used in nano-
electronics.
The invention will be further illustrated, preferred details and combination of de-
tails of the invention shown in conjunction with examples and the accompanyingdrawing in
which:
Figure 1 shows a schematic view of a facility or an apparatus for carrying out the
process of the invention.
Figure 2 shows a variation of an apparatus of Figure 1.
Figure 3 shows a yet further variation with some added specific features of an
apparatus in accordance with the invention.
Figure 4 shows a SEM picture of open multi-wall nanotubes.
Figure 5 shows a SEM image of a spaghetti-like arrangement of multi-wall and
necklace-shaped nanotubes.
Figure 6 shows a TEM picture of necklace shaped carbon nanostructures in accor
dance with the invention.
Figure 7 shows a HRTEM picture of carbon necklace structures of bulb-like
beads.
Figure 8 shows a TEM picture of carbon nanotubes having a bamboo-like struc-
ture.
Figure 9 shows a HRTEM picture of single-wall nanotubes.
The reactor 1 is designed in a way that it consists of two different but adjacent
zones. Zone A, for the vaporization of the precursor (carbonaceous products and
catalytic products), is maintained at a very high temperature due to the action of a
thermal plasma and an appropriate thermal insulation. Zone B, for the nucleation
and maturation of the carbon-based nanostructures, is kept between 4000°C in the
upper part and less than 50°C in the lower part due to an adequate thermal insula-
tion.
In zone A, the geometry of the internal fittings has the shape of a venturi which is
specifically designed to assure the complete vaporization of the precursors. Each
of the three electrodes 3, of which only two are shown in Figure 1, is connected to
one of the three phases of an electric three-phase generator and supplied with al-
ternative current. After activation of the electric generator and the establishment
of the plasma by the contact of the three electrodes, the electrodes are automati-
cally drawn apart and a plasma flow is established in zone A of the reactor, which
allows the complete vaporization of the precursor. Once the plasma is established,
the control of the electrodes to compensate for their erosion is effectuated auto-
matically. Together with a carrier plasma gas, the carbonaceous product and the
catalytic product are continuously injected into zone A of the reactor, for example
in 4.
The electric power source is of the type "three-phase", whereby the frequency of
the supply can vary between 50 Hz and 10 kHz. Each of the three phases of the
electric source is connected to one of the three electrodes of the reactor. The in-
ventors discovered that an increase of the frequency of the electric supply beyond
50 Hz, which can range from 50 Hz to 10 kHz, achieves particular advantages.
This increase of the frequency allows on the one hand an increase in the stability
of the plasma, and on the other hand a very advantageous increase in the homoge-
neity of the mixture of the plasma gas with the carbonaceous product vaporized
and the catalyst product due to important turbulence phenomena in the flow field
of zone A. This turbulence is caused by the combined effects of arc rotation be-
tween the three electrodes successively changing from anode and cathode with
current frequency and the electromagnetic forces induced by the current in the
electrodes and the arcs themselves.
In zone B of the reactor, the zone of the nucleation and growing of the carbon-
based nanostructures, the temperature of the flow in maintained between 4000°C
in the upper part and less than 50°C in the lower part due to an adequate thermal
insulation. The absolute pressure in zones A and B of the reactor can be between
100 mbar and 30 bar. Into this zone, a certain quantity of cold gas is injected in 5.
allowing the quenching of the aerosols and their extraction from the reactor in 6
by means of an extraction system cooled by a liquid, a gas or any other means of
refrigeration known within the state of the art. Afterwards, the aerosol is trans-
ported to a heat exchanger in 7 where it is cooled down further to a stabilization
temperature of the envisaged carbon-based nanostructures and finally passes
through a separation system in 8 where the carbon-based nanostructures are sepa-
rated from the gas phase. Eventually, the carbon-based nanostructures are taken
out in 10 by means of an airtight valve represented in 9 and the gas is vented in
11.
In accordance with a preferred embodiment of the invention, full control of the
extraction conditions and the quenching rate is foreseen thereby controlling the
quality of the nanostructures obtained. Both the temperature at which the aerosol
is extracted and the quenching speed of the aerosol are preferably controlled to
ensure high quality products.
Preferred control approaches include the following. The temperature at which the
extraction is effectuated and the residence time for product maturation is con-
trolled by the variation of the axial position of the injection point of cold gas in 5
and the extraction point in 6 in zone B. The quenching velocity rate is controlled
by a variation in the nature and the flow rate of cold gas injected in 5, by the ef-
fectiveness of the extraction system cooled in 6 and by the effectiveness of the
heat exchanger in 7.
In a preferred embodiment shown in Figure 2, zone B of the reactor is modified
by the installation of a recirculation system for the quenching gas flow as de-
scribed hereafter. In zone B of the reactor where the temperature is maintained
between 4000°C in the upper part and less than 50°C in the lower part, a device
cooled by a liquid, a gas or any other means of refrigeration known within the
state of the art is introduced in 5, which allows the extraction of the aerosols in 6
and the transport to a separation system in 7. The temperature of the zone of
which the extraction is effectuated, is controlled by the variation of the axial posi-
tion of the injection point of cold gas in 11 and the extraction point in 5. The
quenching rate is controlled by a variation in the flow rate of cold gas injected
into zone B in 11 by means of a blower 10, by the effectiveness of the extraction
system cooled in 5 and by the effectiveness of the heat exchanger in 6. Therefore,
the gas flow rate in the recirculation circuit is independent of the initial carrier gas
flow entering in 4. The aerosol is transported to a heat exchanger in 6 where it is
cooled down further to a stabilization temperature of the envisaged carbon-based
nanostructures and finally passes through a separation system in 7 where the car-
bon-based nanostructures are separated from the gas phase. Eventually, the car-
bon-based nanostructures are taken out in 9 by means of a valve 8. The excess gas
flow equivalent of the amount of gas entering in 4 is vented in 12.
In a preferred embodiment shown in Figure 3, zone B of the reactor is modified
by the installation of a recirculation system for the quenching gas flow and the
carrier plasma gas supplying the plasma itself as described hereafter. In zone B of
the reactor where the temperature is maintained between 4000°C in the upper part
and less than 50°C in the lower part, a device cooled by a liquid, a gas or any
other means of refrigeration is introduced in 5, which allows the extraction of the
aerosols in 6 and the transport to a separation system 7. The temperature of the
zone of which the extraction is effectuated, is controlled by the variation of the
axial position of the injection point of cold gas in 12 and the extraction point 5.
The quenching rate is controlled by a variation in the flow rate of cold gas in-
jected into zone B in 12 by means of a blower 10, by the effectiveness of the ex-
traction via extraction point5 and by the effectiveness of the heat exchanger 6.
Therefore, the gas flow rate in the recirculation circuit is independent of the initial
carrier gas flow entering in 18. The aerosol is transported to a heat exchanger 6
where it is cooled down further to a stabilization temperature of the envisaged
carbon-based nanostructures and finally passes through a separation system 7
where the carbon-based nanostructures are separated from the gas phase. Eventu-
ally, the carbon-based nanostructures are taken out in 9 by means of a valve 8. A
part of the gas vented in 13 is used as carrier plasma gas in 14. A feeding system
15 with a gas feeding 18 and a valvel6 allows the continuous feeding of solid
carbon material in 4. The excess gas flow equivalent of the amount of gas entering
in 18 is vented in 17.
The raw material used as a precursor consist of one or a combination of the fol-
lowing elements: A carbonaceous product, a catalytic product and/or a gaseous
product. The product used as carbonaceous product can be of solid, liquid or
gaseous nature.
In the case of solid carbonaceous materials, different types of products can be
utilized, for example: Finely milled graphite, acetylene black, carbon black de-
gassed, milled pyrolitic carbon, activated carbon, pyrolized carbon aerogels,
plasma carbon nanostructures. The carbon content of the utilized carbonaceous
material should be as high as possible, preferably higher than 99 weight %. The
average particle size of the carbonaceous materials should be as small as possible,
preferably smaller than 10 µm in diameter, to ensure its complete vaporization
when passing through the plasma.
In the case of liquid and gaseous carbon precursors any kind of hydrocarbon can
be considered.
The catalytic material associated with the carbonaceous material can consist of
one or a mixture of elements well known for their catalytic characteristics in car-
bon nanotubes synthesis, such as: Ni, Co, Y, La, Gd, B, Fe, Cu. The catalytic ma-
terials are introduced in zone A (preferred) or zone B of the reactor, either in form
of a powder mixed with the carbon material, or in form of a deposit on the carbon
material, or in form of a solid whereby the morphology can vary corresponding to
the hydrodynamic prevalent in the reactor, or in the form of a liquid. The mass
ratio of catalyser to carbon can vary between 0.1% and 50%.
In the case of liquid carbon precursors, the catalytic elements are preferably mixed
with the liquid.
In the case of gaseous carbon precursors, the catalytic elements are preferably
introduced in form of a powder.
In the case of solid carbon precursors, the catalytic elements are preferably intro-
duced in form of a deposit on the carbon material.
The plasma gas is preferably a pure gas: Helium, argon, nitrogen or a mixture of
one of these gases with the following gases: Helium, argon, nitrogen, carbon
monoxide, hydrogen.
The quenching gas can be identical to the plasma gas or consist of any kind of gas
mixture.
In the following examples further preferred features, feature combinations and
embodiments of this invention are illustrated.
The examples were carried out in a reactor set-up substantially as shown in Fig-
ures 1 and 2.
Example 1:
The reactor set-up, described in Figure 1, consists of a cylindrical reactor of a
height of 2 meters in stainless steel with water-cooled walls and 400 mm internal
diameter. The upper part of the reactor is fitted with thermal insulation cone-
shaped in graphite of 500 mm height and an internal diameter between 150 and 80
mm. Three electrodes in graphite of 17 mm diameter are positioned through the
head of the reactor by a sliding device system electrically insulated. A central in-
jector of 4 mm internal diameter allows the introduction of the precursor by
means of a carrier plasma gas in the upper part of the reactor. A plasma power
supply, employing a three phase electricity source up to 666 Hz with a maximum
power of 263 kVA, a RMS current range of up to 600 A and a RMS voltage range
of up to 500 V, was used to supply electricity to the three graphite electrodes,
their tips being arranged in the shape of an inversed pyramid.
The carrier plasma gas is helium and the precursor is carbon black with a deposit
of nickel - cobalt corresponding to a weight ratio in relation to the carbon of 2,5
weight % for the nickel and 3 weight % for the cobalt. The gas for the quenching
is helium.
The following table gives the main operating conditions.
More than 98% of the injected precursor mass was removed from the filter. The
recovered product is composed of: 40% of Single Walled Carbon Nanotubes,
5.6% of fullerenes whereby 76% of C60 and 24% of C70, 5% of Multi Walled
Carbon Nanotubes, about 20% of fullerene soots, about 30% of undefined carbon
nanostructures with catalyst particles. Quantitative and qualitative measurements
of carbon nanostructures are achieved using Scanning Electronic Microscopy and
Transmission Electronic Microscopy. Quantitative and qualitative measurements
of the fullerenes (C60 and C70) are achieved using UV - visible spectroscopy at
the wavelengths 330 nm and 470 nm after Soxhlet-extraction with toluene.
Example 2
One operates in similar conditions to example 1 but according to the configuration
corresponding to Figure 2. Carrier plasma gas is nitrogen at a flow-rate of 2
Nm3/h. The quenching gas is nitrogen at a flow-rate of 50 Nm3/h. Electrical con-
ditions are 350 A and 200 V. In these conditions necklace shaped carbon nanos-
tructures are produced in very high concentration.
Example 3
One operates in similar conditions to example 1 but according to the configuration
corresponding to Figure 2. Carrier plasma gas is helium at a flow rate of 3 Nm3/h.
The quenching gas is a mixture of nitrogen/helium at a flow rate of 50 Nm3/h.
Electrical conditions are those of example 1. The precursor is ethylene (C2H4)
mixed with nickel-cobalt powders corresponding to a weight ratio in relation to
the carbon of 3 weight % for the nickel and 2 weight % for the cobalt. The recov-
ered product is composed of: 55 weight % of single walled carbon nanotubes, 13
weight % of carbon nanofibres and multi walled carbon nanotubes, the rest of
undefined carbon nanostructures with catalyst particles.
The carbon nanostructures of Fig. 4-9 illustrate embodiments of the invention.
The preferred carbon nanostructures of this invention have the structure of a linear
chain of connected, substantially identical sections of beads, namely spheres or
bulb-like units or trumpet shaped units, preferably having a diameter of the
spheres of the spherical section of the bulb-like units or respectively the large di-
ameter of the trumpet shaped section in the range of 100 to 200 nanometres. All
spheres or bulb-units exhibit nearly the same diameter. These periodic graphitic
nano-fibers are characterized by a repetition of multi-wall carbon spheres ('neck-
lace'-like structure), connected along one direction, and containing frequently a
metal particle encapsulated in their structure. The periodicity of these nanostruc-
tures relates them to the bamboo nanotubes, but they clearly differ by their peri-
odic necklace-like structure and the presence of these metal inclusions.
We Claim:
1. Continuous process for the production of carbon-based
nanostructures, comprising the following steps:
• generating a plasma with electrical energy,
• introducing a carbon precursor and/or one or more catalysers and/or
carrier plasma gas in a reaction zone of an airlight high temperature
resistant vessel optionally having a thermal insulation lining,
• vaporizing the carbon precursor in the reaction zone at a very high
temperature, preferably 4000°C and higher,
• guiding the carrier plasma gas, the carbon precursor vaporized and the
catalyser through a nozzle, whose diameter is narrowing in the
direction of the plasma gas flow,
• guiding the carrier plasma gas, the carbon precursor vaporized and the
catalyser into a quenching zone for nucleation, growing and
quenching operating with flow conditions generated by aerodynamic
and electromagnetic forces, so that no significant recirculation of
feedstocks or products from the quenching zone into the reaction zone
occurs,
• controlling the gas temperature in the quenching zone between
4000°C in the upper part of this zone and 50°C in the lower part
of this zone and controlling the quenching velocity between 103 K/s
and l06 K/s
• quenching and extracting carbon-based nanotubes, nanofibers and
other nanostructures from the quenching zone,
• separating carbon-based nanotubes, nanofibers and nanostructures
from other reaction products.
2. Process as claimed in claim 1, wherein plasma is generated by
directing plasma gas through an electric arc, preferably a
compound arc, created by at least two electrodes.
3. Process as claimed in claim 1 or 2, wherein by one or more of the
following features:
a. The plasma is generated by electrodes consisting of graphite;
b. The arc is created by connecting an AC power source to
electrodes, preferably one where the current frequency lies
between 50 Hz and 10 kHz;
c. The absolute pressure in the reactor lies between 0.1 bar and 30
bar;
d. The nozzle used consists of graphite at its inner surface;
e. The nozzle is formed as a continuous or stepped cone;
f. The nozzle used has a downstream end which abruptly expands
from the nozzle throat;
g. The carbon precursor used is a solid carbon material,
comprising one or more of the following materials: Carbon
black, acetylene black, thermal black, graphite, coke, plasma
carbon nanostructures, pyrolitic carbon, carbon aerogel,
activated carbon, or any other solid carbon material;
h. The carbon precursor used is a hydrocarbon preferably
consisting of one or more of the following: methane, ethane,
ethylene, acetylene, propane, propylene, heavy oil, waste oil,
pyrolysis fuel oil, preferably a liquid carbon material;
i. Solid catalyst is used consisting of one or more of the following
materials:
Ni, Co, Y, La, Gd, B, Fe, Cu, is introduced in the reaction zone;
j. A liquid catalyst is used consisting of one or more of the
following materials Ni, Co, Y, La, Gd, B, Fe, Cu in a liquid
suspension or as organometallic compound, which is preferably
added to the carbon precursor and/or to the carrier gas,
k. A gas carrying a carbon precursor and/or carrying catalyst
and/or to produce the plasma and/or to quench the products
and/or to extract the products comprises or consists of one or
more of the following gases: Hydrogen, nitrogen, argon, carbon
monoxide, helium or any other pure gas without carbon affinity
and which is preferably oxygen free;
1. The gas temperature in the reaction zone is higher than 4000°C;
m. The gas temperature in the quenching zone is controlled
between 4000°C in the upper part of this zone and 50°C in the
lower part of this zone;
n. The carrier plasma gas flow rate is adjusted, depending on the
nature of the carrier plasma gas and the electrical power,
between 0.001 Nm /h to 0.3 Nm/h per kW of electric power
used in the plasma arc;
o. The quenching gas flow rate is adjusted, depending on the
nature of the quenching gas, between 1 Nm3/h and 10 000
Nm3/h;
p. A portion of the off-gas from the reaction is recycled as at least
a portion of the gas for generating the plasma,
q. A portion of the off-gas from the reaction is recycled as at least
a portion of the gas for generating the quenching gas,
r. A carbon precursor is injected through at least on injector,
preferably through two to five injectors,
s. A carbon precursor is injected into the reaction zone,
t. A carbon precursor is injected with a tangential and/or with a
radial and/or with an axial flow component into the reaction
zone,
u. The process is carried out in the total absence of oxygen or in
the presence of a small quantity of oxygen, preferably at an
atomic ratio oxygen/carbon of less than 1/1000,
v. If the plasma gas is carbon monoxide, the process is carried out
in the presence of oxygen with a maximum atomic ratio
oxygen/carbon of less than 1001/1000 in the plasma gas,
w. One or more of the following products is recovered:
i. Carbon black
ii. Fullerence
iii. Single wall nanotubes
iv. Multi-wall nanotubes
v. Carbon fibres
vi. Carbon nanostructures
vii. Catalyst
4. Reactor to carry out the process as claimed in one of the claims
directed to processes comprising in open flow communication
a. A head section comprising:
i. At least two, preferably three electrodes
ii. A carbon precursor supply and/or a catalyst supply and/or a gas
supply
for creating an electric arc between the electrodes when a sufficient
electric power is supplied, and creating an arc zone, into which the
gas from the gas supply can be fed to generate a plasma gas and for
heating the carbon precursor at a vaporization temperature higher
than 4000°C
b. At least one injector for carbon precursor and/or catalyst
injection into the reaction zone
c. A reaction zone where the gas temperature during operation is
4000°C or higher
d. A quenching zone where the gas temperature is controllable
between 4000°C in the upper part of this zone and 50°C in the
lower part of this zone
e. A nozzle shaped choke, narrowing the open flow
communication between the reaction zone and the quenching
zone.
5. Reactor as claimed in claim 4, having substantially interior
cylindrical shape.
6. Reactor as claimed in claim 4 or 5, whereby the high temperature
exposed surfaces are of graphite containing high temperature
resistant material.
7. Reactor as claimed in claim 4, 5 or 6 comprising a chamber with a
height between 0.5 and 5 m and a diameter between 5 and 150 cm.
8. Reactor as claimed in one of the claims directed to reactors
comprising temperature control means for the quenching zone
selected from thermal insulating lining, fluid flow, preferably
water flow, indirect heat exchange means and flow and/or
temperature controlled quench gas injection means.
9. Reactor as claimed in one of the claims directed to reactors
wherein the nozzle shaped choke is a tapering choke followed by
an abruptly expanding section.
10. Reactor as claimed in one of the claims directed to reactors,
characterized by one or more apparatus features of one or more of
the process claims.
11. Carbon nanostructures having the structure of a linear chain of
connected, substantially identical sections of beads, namely
spheres or bulb-like units or trumpet shaped units, preferably
having a diameter of the spheres of the spherical section of the
bulb-like units or respectively the large diameter of the trumpet
shaped section in the range of 100 to 200 nanometres, more
preferably having all spheres or bulb-units exhibiting nearly the
same diameter, and in particular comprising periodic graphitic
nano-fibers being characterized by a repetition of multi-wall
carbon spheres ('necklace'-like structure), connected along one
direction, and several of the spheres containing a metal particle
encapsulated in their structure.
12. Carbon nanostructures as claimed in claim 11, wherein at least 5
beads are connected to one chain, preferably 20 to 50 beads are in
one chain.
13. Carbon nanostructrues as claimed in one of claims directed to
carbon nanostructures, wherein one or more of the beads is filled
with catalyst, in particular with ferromagnetic metal catalyst, more
specifically with nickel or nickel/cobalt.
14. Carbon nanostructures as claimed in one of claims directed to
carbon nanostructures wherein the bulb-like or bell-like are
connected to each other by external graphitic cylindrical layers.
15. Carbon nanotube exhibiting a multi-wall structure, wherein several
nanoconical structures (bamboo shaped structures) are stacked,
said nanotubular structures preferably possessing a closed end
conical tip apex the other end being either open or filled with a
metal nanoparticle.
16. Carbon nanotube as claimed in claim 15 having an external
diameter of 100 to 120 nm and comprising a set of discontinuous
concical cavities.
17. Carbon nanostructures and carbon nanotubes as claimed in one of
claims directed to such products being arranged in a random form,
the SEM of which resembles cooked spaghetti.
18. Carbon nanostructures being single walled and having preferably
one or more of the following properties
- one, preferably both ends are open
- one layer having a diameter between about 0.8and about 2nm.
- length of the tubes is a few microns.
19. Carbon nanostructure having substantially a shape defined by its
SEM or TEM view as shown in one of the Figures showing
nanostructures.
20. A composite of carbon nanostructures as claimed in one of the
claims directed to such carbon nanostructures and a polymer
matrix.
21. A composite as claimed in claim 20 comprising, preferably
consisting of, polyethylene, polypropylene, polyamide,
polycarbonate, polyphenylenesulfide, polyester.

Continuous process for the production of carbon-based nanostructures,
comprising the following steps: generating a plasma with electrical energy,
introducing a carbon precursor and/or one or more catalysers and/or carrier
plasma gas in a reaction zone of an airlight high temperature resistant vessel
optionally having a thermal insulation lining, vaporizing the carbon
precursor in the reaction zone at a very high temperature, preferably 4000°C
and higher, guiding the carrier plasma gas, the carbon precursor vaporized
and the catalyser through a nozzle, whose diameter is narrowing in the
direction of the plasma gas flow, guiding the carrier plasma gas, the carbon
precursor vaporized and the catalyser into a quenching zone for nucleation,
growing and quenching operating with flow conditions generated by
aerodynamic and electromagnetic forces, so that no significant recirculation
of feedstocks or products from the quenching zone into the reaction zone
occurs, controlling the gas temperature in the quenching zone between about
4000°C in the upper part of this zone and about 50°C in the lower part of this
zone and controlling the quenching velocity between 103 K/s and 106 K/s,
quenching and extracting carbon-based nanotubes, nanofibers and other
nanostructures from the quenching zone, separating carbon-based nanotubes,
nanofibers and nanostructures from other reaction products.

Documents:

2066-kolnp-2005-granted-abstract.pdf

2066-kolnp-2005-granted-claims.pdf

2066-kolnp-2005-granted-correspondence.pdf

2066-kolnp-2005-granted-description (complete).pdf

2066-kolnp-2005-granted-drawings.pdf

2066-kolnp-2005-granted-examination report.pdf

2066-kolnp-2005-granted-form 1.pdf

2066-kolnp-2005-granted-form 18.pdf

2066-kolnp-2005-granted-form 2.pdf

2066-kolnp-2005-granted-form 26.pdf

2066-kolnp-2005-granted-form 3.pdf

2066-kolnp-2005-granted-form 5.pdf

2066-kolnp-2005-granted-reply to examination report.pdf

2066-kolnp-2005-granted-specification.pdf

2066-kolnp-2005-granted-translated copy of priority document.pdf

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Patent Number

233855

Indian Patent Application Number

2066/KOLNP/2005

PG Journal Number

16/2009

Publication Date

17-Apr-2009

Grant Date

16-Apr-2009

Date of Filing

20-Oct-2005

Name of Patentee

ARMINES ASSOCIATION POUR LA RECHERCHE ET LE DEVELOPPMENT DES METHODES ET PROCESSUS INDUSTRIELS

Applicant Address

60 BD SAINT MICHEL, 75272 PARIS

Inventors:

#	Inventor's Name	Inventor's Address
1	FRÉDÉRIC FABRY	N° 2, LE CLOS FLEURI 271, AVENUE DU GÉNÉRAL DE GAULLE 06110 LE CANNET
2	JOSE GONZALEZ	1, AVENUE DE L 'ESTEREL 06160-JUAN LES PINS
3	EUSEBIU GRIVEI	AV. CROIX DE LORRAINE, 6 B-1310 KA HULPE
4	THOMAS M. GRUENBERGER	191, CHEMIN DE L 'AUBE 06220 LE GOLFE JUAN/VALLAURIS
5	JEAN-CHRISTOPHE CHARLIER	CHEMIN DE SOULME, 38 5600 SURICE (PHILLIPEVILLE)
6	GILLES FLAMANT	MAS PATIRAS, 66800 LLO
7	LAURENT FULCHERI	56, TRAVERSE DU ROUGON 06 370 MOUANS-SARTOUX
8	HANAKO OKUNO	RUE DE BONNE ESPÉRANCE 12 BT 2 B-1348 LOUVAIN-LA-NEUVE
9	NICOLAS PROBST	77, AV DES FRÉRES BECQUÉ B-1082 BRUXELLES

PCT International Classification Number

C01B 31/02

PCT International Application Number

PCT/EP2004/003000

PCT International Filing date

2004-03-22

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10312494.2	2003-03-20	Germany