EP1831438A1 - Procede de croissance de nanofils de beta-sic ou de alpha-si3n4, eventuellement enrobes - Google Patents
Procede de croissance de nanofils de beta-sic ou de alpha-si3n4, eventuellement enrobesInfo
- Publication number
- EP1831438A1 EP1831438A1 EP05850533A EP05850533A EP1831438A1 EP 1831438 A1 EP1831438 A1 EP 1831438A1 EP 05850533 A EP05850533 A EP 05850533A EP 05850533 A EP05850533 A EP 05850533A EP 1831438 A1 EP1831438 A1 EP 1831438A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- growth
- sic
- carbon
- nanowires
- silicon
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/36—Carbides
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
- C30B25/005—Growth of whiskers or needles
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/38—Nitrides
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/60—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape characterised by shape
- C30B29/605—Products containing multiple oriented crystallites, e.g. columnar crystallites
Definitions
- the present invention relates to the technical field of processes for producing nanowires of material.
- the present invention relates to a method for producing cubic silicon carbide ( ⁇ -SiC) or trigonal silicon nitride ( ⁇ -Si 3 N 4 ) nanowires, optionally covered by one or more layers of another material.
- Nanowires or nanofibers are nanocomposed in the form of a solid cylinder with a diameter of a few tens of nanometers, typically 10 to 100 nm, and a length greater than 100 nm, or even several microns.
- nanowires For certain applications, it may be advantageous to have coated nanowires, over their entire length, of one or more layers of other materials, of a chemical and / or crystallographic nature different from the material constituting the nanowire corresponding to the core.
- These nanocomposites, most often coaxial, are named nanocables.
- nanocomposites have a wide range of properties related to both the chemical nature of the heart and the number and nature of successive layers. They can offer applications in the field of composite materials, and also in the field of optoelectronics.
- the outer layer can act as an interface between the matrix and the reinforcement.
- the prior art describes the use of nanowires and nanocables based on boron and / or silicon in particular.
- the first growth technique developed in 1994 for the synthesis of ⁇ -SiC nanofibers is called “template” and uses carbon nanotubes (CNTs) or silicon nanofibers (NFs Si).
- This technique consists in the use of a carbon nanotube, or more recently a silicon nanofiber, as a mold or “template”.
- the carbon nanotube (or Si nanofiber) is converted by a chemical treatment into a ⁇ -SiC nanofiber with conservation of the morphology of the starting structure.
- the mixture of Si and SiO 2 makes it possible to generate a volatile precursor containing silicon, silicon monoxide, SiO.
- silicon monoxide reacts on CNTs:
- the product obtained contains ⁇ -SiC NFs from 3 to 40 nm in diameter, covered with a thin layer of SiO 2 of variable thickness.
- Dai et al. (Nature, 375 (1995) 769) use a process similar in all respects to that described previously: they start from a mixture of silicon, Si, and iodine, I 2 , in order to generate, in situ during heating, a silicon halide as a volatile precursor containing silicon. The reaction of the latter with the CNTs takes place at 1200 ° C. and leads to ⁇ -SiC NFs of 2 to 20 nm in diameter. Many other authors (Applied Physics Letters 75 (13) (1999) 1875, WO
- Zhang et al. (Chemical physics Letters 330 (2000) 48) used silicon nanofibers as templates and methane as a volatile carbon precursor. The reaction at 1300 0 C leads to nanocables ⁇ -SiC coated with C.
- a second method is to use, either nanotubes or nanofibers as template to prepare nanowires of ⁇ -SiC by replication, but nanoparticles based on carbon (Journal of Crystal Growth 209 (2000) 801) and / or silicon to initiate nucleation of ⁇ -SiC nanowires.
- VLS Very-Liquid-Solid
- the nanoparticles are brought to a temperature higher than their melting temperature (liquid phase), elements brought by the gas phase are dissolved in the droplets of liquid metal.
- a supersaturation phenomenon of the liquid phase causes the growth of a solid phase, in this case a wire of diameter generally identical to that of the starting metal particle.
- the silicon and carbon reactants are transported in the gas phase to the molten metal nanoparticle.
- Several catalysts have been used: Ni, Fe, Co, ...
- One of the main characteristics of this technique is the presence of a residual metal nanoparticle incorporated at one of the two ends of each nanowire.
- Different types of VLS process can be distinguished according to the heating technique used:
- the electric arc which implements a strong current (electric) applied between an anode and a cathode under an inert atmosphere (He), which causes heating, then the spraying of the anode.
- the decomposition products of the anode condense on a cooler wall.
- nanofibers or nanoparticles are formed between the anode and the cathode by passing a current of 25 to 30 A.
- Nanofibers can be crystallized by treatment at 1500 ° C. Individual nanofibers are only very rarely obtained and they are almost all coagulated. Nanofibers have diameters between 30 and 80 nm with fairly irregular surfaces.
- the nanofibers obtained at the end of the reaction are mixed with excess reagents and co-products and an additional purification step must be carried out.
- the use of specific equipment that is difficult and costly to implement is one of the most major drawbacks of the confined growth process which requires specific melt spinning equipment and high pressure growth process which requires an autoclave system for high pressure reactions.
- a dangerous parameter is added for carrying out such large-scale experiments and the implementation of purification techniques for separating the nanofibers from the co-products.
- a crippling drawback of this method is the systematic presence of a metal particle at one end of each nanofiber, which will alter its intrinsic properties. To this major disadvantage is added problems of lack of ease of implementation of experimental techniques, particularly for the electric arc and laser ablation.
- one of the objectives of the present invention is to propose a simple and reproducible process for the growth of nanofibers of cubic silicon carbide, ⁇ -SiC, or of trigonal silicon nitride OC-Si 3 N 4 , as well as nanocables.
- ⁇ -SiC or OC-Si 3 N 4 coated, for example, with one or more layers of SiO 2 , C, or BN.
- the process according to the invention must start from inexpensive starting materials, and in particular of any structure.
- Another objective that the invention proposes to achieve is to provide a method for directly obtaining, without additional purification step, the nanowires or nanocables mentioned above of high purity, and in particular not contaminated by the presence of catalysts.
- the subject of the invention is therefore a method of growth, at a given growth temperature T, of nanowires of cubic silicon carbide ( ⁇ -SiC), of trigonal silicon nitride (Ot-Si 3 N 4 ), or of a mixture of ⁇ -SiC and Ot-Si 3 N 4 , characterized in that the growth is carried out at the growth temperature T on a graphite support, by reaction, at the growth temperature T, of a derivative of carbon in the gaseous state and a derivative of silicon in the gaseous state, and optionally a nitrogen derivative in the gaseous state.
- the fg. 1 is a schematic representation of the experimental method.
- the fij. 2 represents a diagram of the experimental system
- Fig. 3 represents the Raman spectrum obtained on a sample of the crude product of Example 1.
- the fij. 4 is an SEM image of a sample of the crude product of Example 1.
- FIG. 5 and 6 are TEM images of a SiO 2 -coated ⁇ -SiC nanocable obtained in Example 1, FIG. 6 is a dark field shot of the snapshot shown in FIG. 5.
- Fig. 7 is a MET picture of a SiO 2 -coated ⁇ -SiC nanocable obtained in Example 2.
- Fig. 8 is a MET-plate of a C-coated ⁇ -SiC nanocable obtained in Example 3.
- FIG. 9 is an SEM image of a sample of the crude product of Example 4.
- FIG. 10 is a METHR image of a ⁇ -SiC nanocable coated with a first SiO 2 layer covered with a second BN layer, obtained in Example 4.
- Figs. 11 and 12 are respectively a light field and dark field image of a ⁇ -SiC nanocable surrounded by a first layer of SiO 2 covered with a second layer of BN, obtained in Example 4.
- Nanofibers and nanocables of the present invention are obtained using a method of synthesis which is similar to CVD (Chemical Vapor Deposition) and which consists in reacting on a graphite support, a gaseous derivative of silicon and a gaseous derivative of carbon.
- These gaseous derivatives preferably come from two different sources. These sources can be directly gaseous sources, or solid sources, which by heating will generate a desired gaseous derivative.
- the invention resides in the reaction at high temperature, in an oven, and in contact with a graphite condensation support of a gaseous silicon precursor, typically SiO (g), of a gaseous compound containing carbon and, if appropriate, a gaseous compound based on nitrogen.
- a gaseous silicon precursor typically SiO (g)
- this reaction leads to the formation of cubic silicon carbide ( ⁇ -SiC) or trigonal silicon nitride (0Si 3 N 4 ) nanowires, which may or may not be covered by an amorphous carbon layer, C, silica, SiO 2 , and / or another material, for example, boron nitride, BN if the necessary precursor is present.
- Nanomaterials are obtained pure on the surface of the condensation support, with a high chemical purity and a great homogeneity of their crystallographic structure: there is no mixture of different crystallographic phases. The yields in terms of quantity of nanomaterials produced are very important and no additional purification step is necessary.
- the reaction is therefore carried out on an initially virgin growth support, that is to say that before the initiation of the condensation of the nanowires or nanocables on the latter, it carries no solid element capable of contaminate the nanomaterials obtained. Growth is therefore conducted in the absence of catalyst. It is not, either, uses a mold or template.
- the growth support is also not carrying solid precursors of the gaseous derivatives that will react, thus avoiding the contamination of the nanowires or nanocables produced.
- the support is made of graphite.
- Graphite means the allotropic form of carbon, consisting of hexagonal sheets stacked parallel to each other, and those perpendicular to the crystallographic axis c.
- This support is preferably plane and of dimension chosen according to the size of the oven, and the amount of nanowires that it is desired to generate on its surface.
- Such a growth medium can not therefore correspond to the nanotubes or nanoparticles of carbon used in the techniques of the prior art, because, on the one hand, that this support is made of graphite, and on the other hand, that this support is in no way of nanometric size.
- SiH 4 (g) for example, or any other volatile compound based on Si such as CI 2 SiH 2 (g), etc. directly introduced at the growth support graphite, or a mixture of silicon, Si (s), and iodine, b (s), which at high temperature leads to the formation of SiI 4 (g).
- this carbon-based precursor can be either amorphous carbon, activated carbon, or a residue resulting from the decomposition at 600 ° C. of carbon compounds, such as sucrose, or polypropylene.
- carbon compounds such as sucrose, or polypropylene.
- nanofibers are not obtained because it is carbon-based gaseous species that will reduce the volatile precursor vapors based on Si to form nanofibers or nanocables.
- the graphite condensation support for example in the form of a plate, is, of course, distinct from the nacelles or receptacles carrying the solid precursors for generating the elements. gaseous that will react with each other.
- FIG. 1 A preferred embodiment of the invention is illustrated in FIG. 1. It consists of pyrolysis at high temperature, in an oven I, preferably a horizontal tubular furnace, amorphous carbon C, a mixture of silica powders and silicon Si + SiO 2 , in the presence of a support in graphite 1.
- a preferably stoichiometric mixture (in mole) of silicon, Si, powder and of silica, SiO 2 , arranged, for example, in a nacelle, will be used to generate in situ a silicon derivative volatile, gaseous SiO silicon monoxide.
- Different Si / SiO 2 ratios can be used, this simply affects the formation yield of SiO 2 gas.
- the chemical nature of the nacelle also has no influence: conventionally, we use nacelles alumina rectangular geometry (box type) and the same composition as the furnace tube.
- a solid silicon source is located near the graphite support and the gaseous carbon is brought to the level of the graphite support by a vector gas stream.
- the mixture of Si and SiO 2 powders is placed under the graphitic carbon support. It is, for example, possible to cover, in an unsealed manner, the nacelle containing the powder mixture with a graphite disc. In this case, the condensation disk must not cover the nacelle tightly to allow the diffusion of gaseous species based on carbon, on the one hand, and silicon, on the other hand, inside the nacelle .
- the introduction of the different reagents is advantageously carried out under an inert gas stream, in order to avoid an excessively high oxygen content at the beginning of the reaction, which would have the consequence of burning off the carbon precursor and the carbon condensation support, during the rise in temperature.
- the reaction is carried out under a stream of carrier gas G 5 promoting the diffusion of the different gaseous species and thus making it possible to bring the gaseous precursors towards the growth support.
- it may be provided to introduce a carbon-based precursor in the furnace upstream (in the scanning direction of the carrier gas) relative to the nacelle containing the silicon.
- precursor is meant a carbon species which will decompose during the rise in temperature and will generate gaseous species containing carbon. These gaseous species will be driven by the gas stream.
- the chemical composition of the carbonaceous gaseous derivative is not critical. This derivative can, for example, be methane. On the other hand, it is preferable that the gas does not contain water or oxygen so as not to damage the condensation disc and the carbon precursor.
- the flow of carrier gas may, for example, be between 0 and 5000 mL.min -1 , and preferably between 0 and 200 mL.min -1 .
- heating of all components is then performed under gas flow. The growth is carried out at a pressure less than or equal to 2 bars, for example, at a pressure corresponding substantially to atmospheric pressure.
- the nature of the gases present in the furnace and the value of the growth temperature are decisive because they will make it possible to control the nature of the nanomaterials formed: based on ⁇ -SiC or Ot-Si 3 N 4 .
- an inert gas typically argon, only ⁇ -SiC nanomaterials can be formed.
- a growth temperature of at least 1200 ° C is necessary for their formation.
- the nanofiber yield of ⁇ -SiC increases non-linearly with temperature and, preferably, the growth is carried out at a temperature of between 1400 ° C. and 1450 ° C.
- the diameter of the ⁇ -SiC nanowires also increases slightly with temperature. For example, for growth at 1200 ° C., a diameter of the order of 20 nm is obtained, and for growth at 1400 ° C., a diameter of about 50 nm is obtained.
- nanofibers or nanocables based on silicon nitride can also be obtained.
- a nitrogen derivative in the gaseous state such as nitrogen or ammonia
- a carrier gas such as nitrogen or ammonia
- nanofibers or nanocables based on silicon nitride can also be obtained.
- nitrogen flushing only ⁇ -SiC nanowires are obtained for a growth temperature of between 1200 and 1300 ° C.
- a mixture of ⁇ -SiC nanowires and OC-Si 3 N 4 is obtained between 1300 ° C. and 1400 ° C. and only nanowires of CX-Si 3 N 4 are obtained for a growth temperature above 1400 ° C.
- the presence of gaseous derivatives of carbon is necessary for the reduction of the volatile precursor based on Si.
- the yield of nanofibers also increases nonlinearly with temperature.
- the rise in temperature is generally linear.
- the temperature rise ramp is not a decisive parameter: a ramp of 400 ° C.sup.- 1 is used, for example, the growth temperature is maintained for a determined period of time, the time during which the growth temperature is maintained. is a parameter that significantly influences the reaction efficiency.
- the yield of nanofibers, ie the mass of nanofibers formed, increases non-linearly (quasi-parabolically) with the duration of the experiment.
- the heating is stopped and the whole is cooled to room temperature. If the gaseous derivatives of C and Si have been completely consumed, it is possible to recharge starting reagents and resume the reaction on the nanowires already formed. In this case, the yield is increased: the son obtained are longer, but their diameter is not significantly modified by the growth in recovery.
- the nanofibers or nanocables are then collected on the surface of the graphite growth support. In the case where the growth medium is positioned on a nacelle containing an Si / SiO 2 mixture, the growth is on the face of the graphite support "in contact" with the interior of the nacelle of alumina.
- the gaseous derivatives of Si and C come from two distinct sources, so that they react at the level of the growth support and not before reaching it. Indeed, it has been found that if amorphous carbon is introduced into a nacelle containing a silicon-silica mixture, the yield of the reaction is almost zero. Nanofibers are formed inside the nacelle, almost no growth occurs on the support of condensation. On the other hand, the distance between the carbon-based precursor and the nacelle containing the silicon is not a determining parameter.
- the process according to the invention also makes it possible to prepare nanowires coated with SiO 2 , C and / or another material. These nanomaterials consist of a wire coated with one or more layers are called nanocables.
- the gaseous carbon is in excess of gaseous silicon, nanowires, a layer of carbon, are formed on the surface.
- the gaseous silicon is in excess with respect to the gaseous carbon, nanowires, a layer of SiO 2 , are formed on the surface.
- the silicon compounds have a natural tendency to passivate over time, that is to say that the nanofibers of ⁇ -SiC and (X-Si 3 N 4 , obtained according to the process of the invention, will be likely to be covered with a silica layer by prolonged contact with the oxygen of the air. It is also possible to obtain another external coating, either directly on the nanowire of ⁇ -SiC or OC-Si 3 N 4 obtained, or on the layer of SiO 2 or C (nanocables) which covers it. In this case, a gaseous derivative of the material to be deposited, usually in the form of a solid precursor, is introduced into the furnace.
- an amorphous boron nitride powder is added to the mixture of Si and SiO 2 and allows the formation of a BN deposit on the nanowires or nanocables.
- a quantity of amorphous BN of at least 5% by weight relative to the total weight of silicon-based species will advantageously be used.
- an amount of amorphous BN powder of between 5 to 80%, and preferably 20 to 50% will be placed in the oven.
- This technique can be extended to all compounds of type III-V, that is to say to all compounds of XY type with X: Boron, Aluminum, Gallium or Indium and Y: Nitrogen, Phosphorus or Arsenic, as well as 'to any more complex combination of these elements (such as the InGaN ternary, etc.).
- This technique can also be extended to metals or any type of material which has a non-zero vapor pressure at the growth temperature: for example, aluminum, magnesium, copper, silver, and gold. for example.
- the nanowires formed have, in general, a mean diameter of between 10 and 100 nm and a length of several tens of microns.
- the various coating layers have, most often, a thickness of 2 to 30 nm.
- Furnace I and the experimental system used in the examples are shown in detail in FIG. 2.
- the furnace comprises a non-porous alumina tube 2 equipped with sealing flanges 3 and 4.
- This system makes it possible to work under vacuum or under gas (nitrogen, argon) flushing.
- the heating elements are composed of silicon carbide, which makes it possible to work up to 1500 ° C.
- the size of the tubes limits the size of the samples to 4 cm in height or diameter.
- the oven is degassed beforehand under vacuum (connection with a vacuum pump 5 and a pressure gauge 6) at room temperature.
- the reactants are introduced into the furnace under a stream of inert gas (gas cylinder 7).
- the temperature rise ramp, the duration of the bearing as well as the cooling rate are controlled by means of an electronic regulator.
- Flow meters 8 allow the control of gas flows at the entrance of the oven.
- the samples were analyzed by infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM).
- the product obtained is in the form of a cottony foam, because of the interlacing of the nanostructures with each other.
- the nanostructures have uniform diameters, which vary according to the working temperature (typically from 20 nm to 1200 ° C. up to 50 nm at 145 ° C.), and lengths that may reach several hundred microns.
- the graphite condensation disk is a rectangle 5 mm thick, at least equal in width to that of the nacelle and shorter in length than the open portion of the nacelle of alumina, with 5 mm of opening on each side.
- the cliché of the fîg. 5 makes it possible to determine that the central ⁇ -SiC nanofiber has a diameter of approximately 30 to 40 nm and that it is covered by a homogeneous deposit with a thickness of approximately 30 to 40 nm, to form a nanocable of a diameter of about 100 nm.
- Example 2 Synthesis of ⁇ -SiC nanowires coated with a SiO 2 layer with modification of the nature of the carbon precursor with respect to Example 1
- a mass of 3 g of polypropylene is decomposed in the oven at 800 ° C for 2 hours.
- a nacelle containing an equimolar mixture of silicon (1.10 g, Aldrich powder of Si 95 mesh) and of silicon dioxide (2.35 g, Silica Gel, Aldrich) is introduced into the oven and heated to room temperature. at 1400 ° C. (heating rate 400 ° C.s -1 ) under argon sweep (10 ml.min -1 ).
- the SEM analysis of the harvested foam shows no significant difference from the samples prepared from amorphous carbon according to Example 1). It consists solely of entangled SiO 2 -coated ⁇ -SiC nanocables. Transmission electron microscopy (high resolution) analysis. METfHEQ:
- nanostructures Chemical analysis of the nanostructures was performed by dispersive energy X-ray spectroscopy (DSS) during the METHR observations. As before, it is very clear that the nanostructures are nanocables of SiO 2 -coated ⁇ -SiC, ie they consist of cubic ⁇ -SiC nanofibers surrounded by amorphous silica. MET images of the SiO 2 -coated ⁇ -SiC nanocables obtained are presented on FIG. 7.
- the MET picture presented on the fîg. 7 is representative of SiO 2 -coated ⁇ -SiC nanocables obtained from amorphous carbon generated in the furnace tube by decomposition of polypropylene, or any other carbon compound such as sucrose.
- the nanocables obtained have diameters smaller than those obtained from activated carbon (Fluka, Charcoal animal).
- the diameter of the central nanofiber is identical to that measured on the samples of Example 1, that is to say approximately 30 to 40 nm.
- the thickness of the amorphous silica layer around the central nanofiber is much smaller and of the order of magnitude of about 5 nm.
- a more complete analysis METHR confirms the small thickness of the silica layer obtained in this example.
- a powder consisting of an equimolar mixture of silicon (2.20 g, Aldrich 95 mesh Si powder) and silicon dioxide (4.70 g, Silica Gel, Aldrich) is heated to 1400 0 C (ramp 400 0 Ch “1 ), under argon flushing (flow rate of 10 mL.mn " 1 ), in the presence of a nacelle containing 8 g of polypropylene, located upstream of the nacelle of silicon with respect to the path of the carrier gas . After ten hours
- the nanostructures formed are carbon-coated ⁇ -SiC nanocables, ie they consist of cubic ⁇ -SiC nanofibers surrounded by a heterogeneous carbon deposition.
- the latter is sometimes quite irregular in terms of thickness, and can be broadly described as amorphous.
- the carbon deposition of the C-coated nanocable ⁇ -SiC is not evenly distributed around the nanofiber; in this case, the nanocomposite axis differs from that of the ⁇ -SiC nanofiber.
- the diameter of the ⁇ -SiC nanofiber was approximately half that of the corresponding nanocable.
- the diameter of the C-coated ⁇ -SiC nanocables varies between about 20 and 100 mu.
- the table below shows the link between the operating conditions used and the nature of the nanostructures obtained. There are 3 mentioned parameters which are: quantity of carbon passing in the gaseous phase (in gram) divided by the quantity of the equimolar mixture of Si and SiO 2 (in gram), nature of the carrier gas and type of nanostructures obtained. This table was constructed from the results obtained with the experimental system of fig. 2 (alumina tube 40 mm in diameter and 400 mm effective heating length).
- the silica thickness at the surface of the nanofiber evolves linearly with the ratio of the masses of carbon and the Si / SiO 2 mixture.
- a homogeneous mixture consisting of 3.45 g of an amorphous boron nitride powder BN, 1.10 g of a silicon powder, Si, and 2.35 g of a silica powder is prepared beforehand. , SiO 2 .
- the SEM analysis is performed to determine the presence of nanostructures within the sample.
- the SEM image (Fig 9) shows the presence of interwoven nanofibers. Their diameters are between about 20 and 100 nm and their lengths can reach several hundred micrometers.
- the chemical analysis of the nanostructures was performed by SED during the high resolution TEM (METHR) observations of the sample and revealed that the nanostructures are ⁇ -SiC nanocables surrounded by SiO 2 and BN, namely that they consist of cubic ⁇ -SiC nanofibers surrounded by a first layer of amorphous silica, itself covered by a layer of boron nitride.
- the latter is globally turbostratic, that is to say that it has an imperfect organization of hexagons, parallel to the axis of the nanofiber of the heart.
- a METHR image of a nanocable obtained is presented in FIG. 10.
Abstract
Description
Claims
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FR0413630A FR2879627B1 (fr) | 2004-12-21 | 2004-12-21 | Procede de croissance de nanofils de beta-sic ou de alpha-si3n4, eventuellement enrobes |
PCT/FR2005/003145 WO2006067308A1 (fr) | 2004-12-21 | 2005-12-15 | Procede de croissance de nanofils de beta-sic ou de alpha-si3n4, eventuellement enrobes |
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EP1831438A1 true EP1831438A1 (fr) | 2007-09-12 |
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KR100802182B1 (ko) * | 2006-09-27 | 2008-02-12 | 한국전자통신연구원 | 나노선 필터, 그 제조방법 및 흡착물 제거방법, 이를구비한 필터링 장치 |
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US5404836A (en) * | 1989-02-03 | 1995-04-11 | Milewski; John V. | Method and apparatus for continuous controlled production of single crystal whiskers |
CA2043679A1 (fr) * | 1990-07-24 | 1992-01-25 | Lanxide Technology Company, Lp | Preparation de fibres whiskers a base de carbure de silicium |
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2004
- 2004-12-21 FR FR0413630A patent/FR2879627B1/fr not_active Expired - Fee Related
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2005
- 2005-12-15 EP EP05850533A patent/EP1831438A1/fr not_active Withdrawn
- 2005-12-15 WO PCT/FR2005/003145 patent/WO2006067308A1/fr active Application Filing
Non-Patent Citations (1)
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Also Published As
Publication number | Publication date |
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FR2879627B1 (fr) | 2007-09-21 |
WO2006067308A1 (fr) | 2006-06-29 |
FR2879627A1 (fr) | 2006-06-23 |
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