DE102005029155B4 - Process for the production of particles - Google Patents

Abstract

Process for the production of fullerenes or carbon nanotubes, in which arc discharges are ignited in a pulsed manner between at least two electrodes (2a, 2b) arranged in a housing and / or operated with a modulated electrical current intensity and by means of a gas flow (5) which flows between the electrodes ( 2a, 2b) is passed through, formed particles are expelled and collected, and heating is carried out in which different temperatures are maintained in different zones (1a, 1b, 1c) in the flow direction of the gas stream (5); the internal temperature stabilized at 1200 ° C. in a first zone (1a), an internal temperature of 700 ° C. in a second adjoining zone (1b) and a temperature of 600 ° C. maintained in a subsequent zone (1c) will.

Description

The invention relates to an arrangement and a method for the production of particles, in particular fullerenes or carbon nanotubes.

Among other methods, it is known to produce particles plasma-chemically or by CVD or PVD technologies. In addition to the high manufacturing and equipment costs, the rate of particles that can be produced in this way is relatively low.

In addition, variations in the operation of the equipment used for this purpose, if at all carried out or considered only to a small extent.

That's how it is DE 101 35 434 A1 a method and apparatus for continuous cluster production with mass selection known. This creates clusters by plasma arc erosion at a cathode. The plasma is cooled in an inert atmosphere and then released adiabatically.

One way to form carbon nanotubes by a DC arc discharge on a carbon electrode is described by Y. Ando et al. in "Mass production of high quality single-wall carbon nanotubes by H ₂ -N ₂ arc discharge"; Diamond & Related Materials; Vol. 14, pp. 729-732; 2004 described.

H. Schulz et al. describe in "Ultra Hydrophobic Wetting Behavior of Amorphous Carbon Films"; Surface & Coatings Technology; 2005; Vol. 200, pp. 1123-1126 Avenues for the formation of amorphous carbon layers on substrates.

Toshiki Sugai et al. describe in "Production of fullerenes and single-wall carbon nanotubes by high-temperature pulsed arc discharge"; J. Chem. Phys. 112; pp. 6000-6005; (2000) how fullerenes or carbon nanotubes can be produced by means of pulsed arc discharge.

Out DE 103 12 494 A1 It is known to produce carbon nanostructures in a plasma at temperatures of about 4000 ° C and to cool the structures formed in the plasma at high quenching rate to about 50 ° C.

US 5 304 366 A describes a method and apparatus for providing and purifying fullerenes. In this case, unwanted constituents are to be retained with the aid of a plurality of filters, wherein desired constituents are to condense in a condensation tube.

It is therefore an object of the invention to propose possibilities for the cost-effective production of particles with increased yield.

According to the invention, this object is achieved by a method according to claim 1.

Advantageous embodiments and further developments of the invention can be achieved with the features described in the subordinate claims.

The arrangement is designed so that at least two electrodes are arranged in a housing at a distance from each other, which are connected as the cathode and anode and between which a pulsed arc discharge is operated. The arc discharge can also be operated with a modulated electric current alone or in addition to the pulsed operation, in which case the arc power can be varied by the changing electric current. Thus, an arc discharge can be operated at times with high power and then with low power until just before the extinction of the arc.

For expelling and possibly also for influencing the particle formation, a gas flow is conducted through the gas inlet between the electrodes and at least substantially orthogonally to the sheets burning between the electrodes and also along the respective surfaces of the electrodes. The particles thus formed can be collected behind the electrodes.

It is also possible to use more than two electrodes, in which case arc discharges between different electrodes can be ignited and operated, which can be achieved by corresponding electrical activation of the electrodes.

By electrical switching but also a change of the electrodes can be achieved so that one electrode can be cathode and after switching then anode, which is then to be done inversely for the respective other electrode.

Advantageously, the arc discharges can be ignited by means of a pulse laser also operated pulsed, which is directed for a respective ignition on a surface of one of the electrodes. By movement and / or pivoting of the laser beam, the place of impact can be varied and the respective base point of the ignited arc can be influenced.

The ignition of arc discharges can also with an increased ignition voltage, using additional ignition electrodes or the Generation of a temporary short circuit to two electrodes can be achieved. In this case, an ignition electrode can also be movable, so that ignition at different surface areas can be achieved.

In a preferred embodiment, one of the electrodes is designed as a hollow cylinder or also part of a cylinder, for example in the form of one or more cylinder segments.

The second electrode can then be arranged completely or partially inside the first electrode. The second electrode may be plate, rod or cylindrical.

It can also be advantageous to subdivide at least one of the two electrodes into segments in the longitudinal direction, that is to say also in the flow direction of the gas stream, which are each individually electrically controllable, so that different parameters of the ignited and operated arc discharges can then be maintained at the segments. By suitable electrical circuit of the segments, an arc discharge can also be operated between the electrode and segments, which are not arranged directly opposite each other and so the arc is temporarily aligned at an obliquely inclined angle. With such an embodiment, a "pulling" of the foot of the arc on the surface of an electrode can be carried out so that a homogenization of the Abtrag to electrodes, similar to a locally changed ignition can be achieved with a laser beam.

In the case of the production of particles from or with carbon, at least one of the electrodes should be formed of pure carbon or predominantly carbon, in the latter case additional substances, for example Ni, Mo, Fe, Rh, Pt, Cr, Sc, Y, B, Tb, Er, Lu or mixtures of these may be included.

The gas flow can take place in controlled or regulated form through the gas inlet. The volume flow, the flow velocity and the internal pressure can be taken into account.

Preferred flow rates are in the range 0.01 to 100 m / s and the internal pressure should be maintained in the range 10 ³ to 10 ⁷ Pa.

In addition, the gas flow can be assisted and stabilized by an exhaust, which is arranged on the side opposite the gas inlet.

The gas stream can be formed from or with an inert gas, for example helium or argon, but also with nitrogen, oxygen, hydrogen or a gas of a metal or carbon compound.

In the flow direction behind the gas inlet, a second gas inlet may be arranged, via which a second gas stream can be fed. The second gas stream may preferably be formed from or with a reactive gas. With such a reactive gas can be influenced once on the particle formation. However, it is also possible to chemically convert compounds formed in the process so that, for example, toxic compounds can be converted into harmless compounds and released to the environment.

It should be provided a tempering, to be operated at elevated temperatures. For this purpose, the arrangement can be arranged with housing and electrodes in an oven, which should be particularly advantageous to a zone oven, with the different temperatures in the flow direction of the gas stream can be adjusted.

However, a temperature increase can also be achieved with at least one heating device which is present on the arrangement. Again, different temperatures should be adjustable in the direction of flow. It may also be favorable to heat the gas stream (s) before introduction.

The particle formation can already take place at room temperature. It can also be used in an average temperature range of about 500 ° C and in the range of high temperatures about 1000 ° C and beyond. Preference is given to temperatures in the range 600 to 1200 ° C.

The arc discharges can with electrical voltages between 10 and 50 V, electrical current between 50 A and 5 kA, with pulse durations of 10 ns to 10 ms, at a pulse frequency between 0.5 Hz and 10 kHz, preferably 100 Hz to 1.5 kHz operate. But for the ignition of the arc discharges significantly higher electrical voltages may be required.

The particles formed can then be fed to a collecting device and separated therefrom from the gas stream. In the simplest case, this can be an area on which the particle-carrying gas stream impinges or sweeps over it, so that the particles deposit on the surface and possibly grow there. In this case, it may be advantageous to reduce the flow velocity of the gas stream in the region of the collecting device.

However, a collecting device can also be formed electrostatically acting. However, it is also possible to provide magnets or electromagnets to a collector.

In the latter case, ferromagnetic particles can be separated and collected very effectively.

With the invention, fullerenes or carbon nanotubes can be obtained inexpensively and in comparison to the known solutions with increased formation rate.

With the invention, however, an agglomeration of particles formed, so-called "clusters", can be achieved.

With the invention, however, metallic particles, as pure metals, metal alloys or metal compounds (eg carbides) in particle form can also be produced. In this case, at least one electrode made of or with the respective metal and / or a suitable metal gas component can be used in the gas stream.

The invention will be explained in more detail by way of example in the following.

Showing:

1 in schematic form an example of an arrangement with which the method according to the invention can be carried out.

In the 1 arrangement shown is particularly suitable for producing single-walled carbon nanotubes and a felt from these (Bucky Paper) suitable.

The method can be described as follows:
Between the two concentrically arranged electrodes 2a / 2 B Burns a pulsed electric arc discharge from a generator 3 operated with about 1 kA pulse current and about 1 kHz pulse frequency and repetitive by a laser beam 4 is ignited.

The electrodes 2 are in an oven 1 that is made up of three zones 1a - 1c and the internal temperature in the first zone ( 1a ) is stabilized at 1200 ° C.

The material of the outer electrode 2a is graphite, the inner electrode 2 B consists of graphite with a share of about 1% nickel and about 1% cobalt. Nickel and cobalt are distributed homogeneously in the material.

The arc discharge is in a gas flow 5 operated, the gas is used to transport the species released in the arc discharge. The gas used is pure nitrogen. During and shortly after the arc discharge, the released species form single-walled carbon nanotubes, which are transported in the gas stream and into the next zone 1b enter the oven. There is at an internal temperature of 700 ° C through the second gas inlet 6 Methane introduced that is dissociated by the elevated temperature, wherein the released carbon attaches to the existing carbon nanotubes and leads to a length increase of these.

The now grown carbon nanotubes get in the gas stream in the next zone 1c of the oven 1 , There is at a temperature of about 600 ° C through the third gas inlet 7 Oxygen in the oven 1 calmly. As a result, the impurities remaining in the gas stream oxidize and exit from the furnace in gaseous form 1 out. In the gas flow 5 then remain only single-walled carbon nanotubes and metal particles bound thereto. These carbon nanotubes with the metal particles bound to them are deposited on the cooled roll 9 as part of the collection facility 8th from. The deposit is supported by the fact that the roller 9 is magnetic or magnetized. The resulting felt of single-walled carbon nanotubes becomes as the roll rotates 9 lifted off this and on a second roller 10 wound. On this the final product accumulates (felt from single-walled carbon nanotubes) and can be removed.

Claims (15)

Process for the production of fullerenes or carbon nanotubes, in which between at least two electrodes arranged in a housing ( 2a . 2 B ) Arc discharges are pulsed ignited and / or operated with modulated electrical current and by means of a gas flow ( 5 ) between the electrodes ( 2a . 2 B ), expelled and collected particles formed and a heating, in which different temperatures in different zones ( 1a . 1b . 1c ) in the flow direction of the gas stream ( 5 ) is carried out; where in a first zone ( 1a ) the internal temperature is stabilized at 1200 ° C, in a second adjoining zone ( 1b ) an internal temperature of 700 ° C and in a subsequently arranged zone ( 1c ) a temperature of 600 ° C are maintained. A method according to claim 1, characterized in that as the gas nitrogen, helium, argon, oxygen, hydrogen, a gas of a Carbon compound, a gas of a metal compound or a gas mixture is used. The method of claim 1 or 2, characterized in that the gas stream is a carbon and / or metal compound is added in aerosol form. Method according to one of claims 1 to 3, characterized in that arc discharges by means of a on one of the electrodes ( 2a . 2 B ) directed laser beam are ignited. A method according to claim 4, characterized in that the base point of the ignited arc discharges by movement and / or pivoting of the laser beam ( 4 ) is changed. Method according to one of claims 1 to 5, characterized in that in the gas flow ( 5 ) a flow rate between 0.01 and 100 m / s is maintained. Method according to one of claims 1 to 6, characterized in that working at a pressure in the range 10 ³ to 10 ⁷ Pa. Method according to one of claims 1 to 7, characterized in that the arc discharges at electrical voltages in the range 10 to 50 V, electric current in the range 50 A to 5 kA, with a pulse duration between 1 ns and 10 ms and a frequency between 0, 5 Hz and 10 kHz are operated. Method according to one of claims 1 to 8, characterized in that at least a second gas stream is fed into the first gas stream. A method according to claim 9, characterized in that the second gas stream is fed in the flow direction of the first gas stream behind the arc discharges. A method according to claim 9 or 10, characterized in that the second gas stream is formed from a reactive gas or contains a reactive gas. Method according to one of claims 1 to 11, characterized in that at least outside the region in which the electrodes ( 2a . 2 B ) are arranged, an inert atmosphere is formed. Method according to one of claims 1 to 12, characterized in that the electrodes ( 2a . 2 B ) are alternately switched as the anode and cathode. Method according to one of claims 1 to 13, characterized in that on segments of electrodes ( 2a . 2 B ) Arc discharges are ignited and operated, each with different electrical parameters. Method according to one of claims 11 to 14, characterized in that the arc discharges with increased ignition voltage, a starting electrode and / or by a short circuit between two electrodes ( 2a . 2 B ) are ignited.

Images