Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
  • C23C16/442—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating using fluidised bed process
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/15—Nano-sized carbon materials
  • C01B32/158—Carbon nanotubes
  • C01B32/168—After-treatment
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
  • C23C16/26—Deposition of carbon only
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y40/00—Manufacture or treatment of nanostructures
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2202/00—Structure or properties of carbon nanotubes
  • C01B2202/06—Multi-walled nanotubes
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2202/00—Structure or properties of carbon nanotubes
  • C01B2202/20—Nanotubes characterized by their properties
  • C01B2202/34—Length
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2202/00—Structure or properties of carbon nanotubes
  • C01B2202/20—Nanotubes characterized by their properties
  • C01B2202/36—Diameter
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/11—Powder tap density

Definitions

• Such cylindrical carbon tubes can also be produced.
• Iijima (Nature 354, 1991, 56-8) reports the formation of carbon tubes in the arc process which consist of two or more graphene layers rolled up into a seamlessly closed cylinder and nested together. Depending on the rolling vector, chiral and achiral arrangements of the carbon atoms along the longitudinal axis of the carbon fiber are possible.
• the substrate is not spatially located above a support, but is moved through the reactor, for example along with a gas flow.
• a moving bed reactor graphitic carbon can be deposited on the carbon nanotube.
• a soot layer especially in the form of amorphous carbon, on the nanotubes was found.
• Oberlin, Endo and Koyama have been unable to observe any graphitic deposition of carbon even in the case of a flow reactor, ie a bedless reactor.
• the carbonaceous precursor may also contain or consist of an optionally substituted heterocyclic molecule.
• heterocyclic means a mono- or multicyclic ring system of from about 3 to about 10, preferably from about 5 to about 10, more preferably from about 5 to about 6 carbon atoms wherein one or more carbon atoms in the ring system are replaced by heteroatoms.
• Aromatic molecule or “aromatic compound” as used herein includes optionally substituted carbocyclic and heterocyclic compounds containing a conjugated double bond system. Heterocyclic aromatics are also referred to as “heteroaromatics.” Examples of aromatic molecules according to the invention are optionally substituted monocyclic aromatic rings having 0 to 3 heteroatoms independently selected from O, N and S, or 8 to 12 membered aromatic bicyclic ring systems 0 to 5 heteroatoms which are selected independently of one another from O, N and S.
• substituents may be purely aliphatic or one or more heteroatoms According to a preferred embodiment, the substituents are selected from the group consisting of C 1 -C 10 aliphatic, C 3 -C 10 cycloaliphatic, C 10 -C 10 aryl, 5-10-membered heteroaryl or 3-10-membered Heterocyclyl Ci- to Cö-haloalkyl, ci- bis
• carbonaceous precursors which have achieved good to very good results in practice are unsaturated hydrocarbons such as ethylene or acrylonitrile and aromatic molecules such as benzene or pyridine.
• a fluidized bed of a fluidized bed reactor is used as the moving bed.
• the substrate is deposited on a carrier, in particular a carrier plate.
• a gas stream is introduced into the substrate, so that the substrate and the gas stream form a so-called fluidized bed.
• the fluidized bed is characterized by a liquid-like behavior in which the individual particles of the substrate are mixed in the gas stream.
• a good heat and mass transfer is achieved in the fluidized bed, so that there are substantially homogeneous process conditions in the fluidized bed. This promotes uniform graphitic deposition of carbon on the carbon nanotubes.
• Stable fluidization means that the gas flow has a velocity that is greater than or equal to the minimum fluidization velocity.
• WO 2007/118668 A2 the content of which should be incorporated herein by reference.
• formula (1) on page 7 of WO 2007/118668 A2 for determining the minimum fluidization rate.
• a precursor entry into the reactor of 0.0001 to 1 g, preferably 0.001 to 0.2 g, in particular 0.005 to 0.1 g, per gram of substrate and set per minute. This precursor entry has proven to be advantageous for a high yield of the method. With a lower precursor entry, too little carbon is available for optimal graphitic deposition. With a higher precursor entry, a part of the precursor is not reacted or even deposited in non-graphitic form, so that the results of the method are impaired.
• the process time is adjusted so that the diameter distribution of the carbon nanotubes produced after the end of the process, a diameter ratio D90 / D10 of less than 4, preferably less than 3. More preferably, the process time is set so that the diameter ratio D90 / D10 of the produced carbon nanotubes is compared with the corresponding diameter ratio of the starting material, i. the carbon nanotube submitted as substrate is reduced by at least 20%, preferably by at least 30%, in particular by at least 40%.
• the graphitic deposition of the carbon is preferably on carbon nanotubes which have a below average diameter with respect to the substrate since they have a larger surface area to weight ratio and therefore in proportion a larger reaction area for the deposition of the carbon.
• the diameter value D90 or D10 means that 90% and 10%, respectively, of the carbon nanotubes are smaller than this diameter.
• the diameter ratio D90 / D10 corresponds to the quotient of D90 and D10.
• a first precursor may be introduced in a first step and a second precursor may be introduced into the moving bed in a second, temporally downstream step.
• a second precursor may be introduced into the moving bed in a second, temporally downstream step.
• successive different graphene-like layers in particular doped and undoped or differently doped layers, can be deposited on the carbon nanotube.
• the alternating introduction of different precursors can produce carbon nanotubes with layers that alternate with respect to their doping.
• a next preferred embodiment of the carbon nanotube is characterized in that the carbon nanotube has a third graphene-like layer, that the second layer is arranged in the cross section of the carbon nanotube within the third layer, and that the first and third layers are undoped.
• a carbon nanotube with alternating layers is provided in which a doped layer is surrounded by two undoped layers.
• Such a carbon nanotube can be produced, for example, by one of the methods described above, in which various precursors are introduced into the moving bed at a time interval.
• the object underlying the invention is further solved by a carbon nanotube powder containing the above-described carbon nanotubes.
• the carbon nanotubes of the carbon nanotube powder preferably have an average diameter of 3 to 100 nm, preferably 5 to 50 nm, in particular 10 to 25 nm. This diameter range corresponds to frequent technical specifications and can be easily achieved with the invention.
• the diameter distribution of the carbon nanotubes after carrying out the method has a diameter ratio D90 / D10 of less than 4, preferably less than 3. In a further embodiment, the diameter distribution of the carbon nanotubes after performing the method
• Diameter ratio which is at least 20%>, preferably at least 30%>, in particular at least 40% lower than the diameter ratio of the starting material introduced as a substrate.
• the carbon nanotube powder preferably has a purity of at least 90%, preferably of at least 95%, in particular of at least 97%.
• the purity in the present case is understood to mean the proportion in% by weight of carbon nanotubes in the powder compared with other constituents, in particular amorphous carbon and inorganic metal oxides. It has been found that carbon nanotube powders of high purity can be produced by the present invention.
• the area ratio D / G of the D band to the G band in the Raman spectrum can be used.
• the D band is about 1300 cm -1 and the G band (graphite band) is about 1588 cm -1 .
• the integrals of the Raman spectrum are calculated via the D band and the G band and then put into proportion.
• the carbon nanotube powder preferably has a D / G ratio of less than 1.5, preferably less than 1, in the Raman spectrum.
• a pulverulent substrate 18 made of carbon nanotubes as starting material is introduced into the reactor chamber 6 via an access 16 provided for this purpose (see arrow 20) and applied to the carrier plate 8 with a bulk density of, for example, 20 to 450 kg / m 3 .
• a process gas such as nitrogen is introduced via the gas inlet 12 into the reactor 2 (see arrow 22), which is guided through the nozzle openings 10 (see arrow 24) into the substrate 18.
• the process gas flowing through the nozzle openings 10 forms with the substrate 18 a fluidized bed 26, in which the mixture of the process gas and the substrate is in a fluidizing, ie a liquid-like, state. In the fluidized bed 26, there is a strong mixing of the substrate and a good heat balance.
• the substrate is in the reactor 2 in a moving bed 27 before.
• the precursor reacts in the fluidized bed 26 and, under suitably adjusted process conditions, leads to the deposition of graphitic carbon onto the carbon nanotube.
• the process product i. the modified by the deposition of graphitic carbon Kohlenstoffiianorschreibchen the substrate 18 are removed through the access 16 again from the fluidized bed reactor 2 (arrow 28).
• the carbon nanotubes in the substrate 18 have, on average, an increased diameter and an increased bulk density at the end of the process, since graphite-like layers have formed around the individual carbon nanotubes due to the graphitic deposition.
• the access 16 may have a lock through which the starting material or at the end of the process, the product can be performed at the beginning of the process. In this case, a gas exchange of the fluidized bed reactor take place.
• a lock is provided in particular for discontinuous operation. However, a continuous or quasi-continuous procedure is also possible.
• Fig. 3d shows another carbon nanotube 90 in cross-section, which has a first inner layer 92 in the form of a wound structure and an outer layer 94 with a tubular structure.
• the inner layer 92 is undoped while the outer layer 94 is doped with nitrogen.
• This carbon nanotube can be prepared by the described method by applying the tubular, nitrogen-doped graphene-like second layer 94 to a carbon nanotube having a wound structure from the substrate by introducing a carbon- and nitrogen-containing precursor into the moving bed.
• Fig. 4 shows a schematic representation of a graphene-like layer.
• the carbon atoms 122 are in a characteristic hexagonal crystal structure arranged diatomic base, which gives a honeycomb-shaped arrangement of the carbon atoms 122.
• a proportion of foreign atoms 124 is deliberately introduced into the graphene layer 120.
• the foreign atoms can sit at carbon lattice sites (124a), replacing one carbon atom at a time.
• Process gas flow N2 Nitrogen gas flow through the fluidized bed in 1 / min.
• Process gas flow F hydrogen gas flow through the fluidized bed in 1 / min.
• Yield Weight increase of the substrate in percent, calculated from: 100% * (weighted weight) / initial weight.
• TEM D90 / D10 ratio of diameter values D90 and D10.
• the experiments C to F are a series of experiments with pyridine as a precursor, in which the process temperature was changed at otherwise substantially constant experimental conditions. At 1000 ° C in experiment C, a good yield of 41% is achieved. The ratio of the Raman signals at 0.78 indicates a predominant graphitic deposition of the carbon. With decreasing process temperature, a decrease in the yield was observed until at a process temperature of 850 ° C only a yield of 9% was reached. Since the precursor pyridine is a carbon- and nitrogen-containing precursor, the deposited graphene-like layers are nitrogen-doped in the experiments C to F. Exposure values of 1.5 at.% To 2.8 at.% Were detected by XPS studies.
• experiment G acid-purified carbon nanotubes from another manufacturer, namely the type Nanocyl (TM) NC 7000, were used as the substrate. Even with these carbon nanotubes, a very good yield of 70% could be achieved.
• carbon nanotubes of the type Baytubes (R) C 150 P were used as a substrate, which, however, were not acid washed, so that the substrate contained a certain proportion of catalyst residues. Nevertheless, a yield of 53% could be achieved at a temperature of 1000 ° C.
• experiment H shows that targeted thickness growth of carbon nanotubes can be achieved even in the presence of catalyst residues, for example, if the process parameters are chosen so that in particular the kinetic constant for the thickness growth is greater than the kinetic constant for the growth of carbon nanotubes caused by catalyst components ,
• Tables 1 and 2 show the D90 / DIO ratio of the TEM-determined diameter distribution of the carbon nanotubes. These values provide information about the diameter distribution of the carbon nanotubes. Since the graphitic deposition is preferentially on the smaller diameter carbon nanotubes, the diameter distribution becomes narrower in the course of the process. In the experiments carried out, the process duration in the range of 6 and 20 minutes was still relatively short. In all deposition experiments, this resulted in a D90 / D10 diameter ratio of significantly less than 4, while the starting material had a ratio significantly greater than 4. By increasing the process time to at least 20 or at least 30 minutes can be achieved that the diameter distribution becomes even narrower and the D90 / D10 ratio is correspondingly smaller.

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