Method for preparing nanodiamonds with methane pyrolysis in electric field

FIELD: medicine.

SUBSTANCE: invention may be used in medicine in producing preparations for a postoperative supporting therapy. What is involved is the high-temperature decomposition of methane on silicone or nickel substrate under pressure of 10-30 tor and a temperature of 1050-1150°C. The heating is conducted by passing the electric current through a carbon foil, cloth, felt or a structural graphite plate whereon the substrates are arranged. An analogous plate whereon a displacement potential from an external source is sent is placed above the specified plate. Nanodiamonds of 4 nm to 10 nm in size are deposited on the substrates.

EFFECT: higher effectiveness of the method.

1 dwg, 6 ex

 

The invention relates to the field of fabricating films of crystalline carbon containing clusters of nanodiamonds, on substrates and can be used for the production of drugs used in therapy after surgical operations. Now for the synthesis of nanodiamonds in the industry uses the method of detonation, which involves the use of highly explosive substances (a mixture of TNT with RDX).

The known method (Z.Y.Chen, J.P.Zhao, T.Yano, T.Ooie, M.Yoneda, J.Sakakibara. Growth of nanocrystalline diamond by pulsed laser deposition in oxygen atmosphere. Journal of Crystal Growth 226 (2001) p.62-66) obtain nanocrystalline diamond on sapphire substrates in an oxygen atmosphere using a pulse laser. The method allows to obtain crystals of nanodiamond size of 30 nm, but is purely laboratory character. The cycle time of deposition of the film is 4 hours when using the small area of the substrate, which is unacceptable for industrial production.

The known method (May P. Diamond Thin Films: A 21stCentury Material. Phil. Trans. R. Soc. Lond. A 358 (2000) p.473-495) growing a thin diamond-like films during the pyrolysis of methane in a high-frequency microwave plasma. This method has been successfully developing, but its implementation requires very sophisticated and expensive equipment, and the process takes many hours.

The known method (Patent RF №2230702, IPC C1B 31/06, publ. 20.06.2004,) receipt of nanodiamonds, based on the use of detonation, which involves the use of explosives (a mixture of TNT with RDX). The explosive charge is placed inside the ice bookings in a sealed explosion chamber and produce a bombing, then the resulting suspension of nanodiamonds in the water is poured into the receiving tank, separate nanodiamonds and purified. The disadvantages of the known method are the use of explosives, low reproducibility and difficulty in purification of the synthesized nanodiamonds from the decay products of explosive mixture.

The closest to the technical nature of the claimed and adopted for the prototype is a method (Patent RF №2429315, IPC C30B 30/02,SW 31/04) pyrolytic growing nanocrystalline layers of graphite, including heating plates made of carbon material in a sealed water-cooled chamber direct transmission of electric current and thermal decomposition of methane in the gap between the plates with the deposition of nanocrystalline layers of carbon on substrates of silicon, is placed in the gap, and the temperature of the substrate maintained within the range of 1200-1350°C and pressure of methane from 10 to 30 Torr.

Prototype method has the following disadvantages:

1. In the narrow gap between two parallel carbon plates occurs different the th electric potentials at the level of 5-7 In due to the voltage drop on graphite gaskets and screws connecting plate. The field strength is about 70 V/cm, which corresponds to the pressure of the carbon ions C4-at 1 HPa, insufficient to obtain perfect nanodiamonds small size.

2. In the prototype circuit heating it follows that the electric field strength between the carbon plates has a maximum value at the boundary areas and due to the polarity (both at constant and alternating current) passes through zero at the center, which leads to heterogeneity of the conditions of the deposition of layers on substrate surfaces.

In the result, resulting in the implementation of the prototype method nanodiamonds have too large size (from 30 to 50 nm) for use in medicine, and their exit by weight of the grown layer is quite low.

The main distinguishing feature of the claimed method of producing nanodiamonds is passing electric current only through the bottom carbon plate and feed on the upper plate is electrically isolated from the lower, high voltage from an external source. During thermal decomposition of methane in the gap between the belts occurs a layer of ionized gas, and through which current flows between the upper and lower plates, the gap between which is placed the substrate. The electric field thus p is constant along the length of the plates.

The technical result obtained by the present method, is expressed in obtaining nanocrystals of diamond small size in a matrix of crystalline carbon and increase their output on the total weight of the layer of carbon.

Scheme of practical implementation of the proposed method is illustrated in Fig. 1.

In the gap between two parallel plates 1 and 2 of the carbon material are placed substrate 3 made of silicon or Nickel. The power current is passed through the tape 2 through the external electrodes 4 and 5. On the upper belt 1 through the external electrode 6 is supplied with alternating or constant high voltage. In the result, the difference voltage between the heating plate 2 and the upper plate 1 in a narrow gap between them creates a significant electric field, the intensity of which is up to 2000 In/see In insulated airtight chamber is methane at a pressure of 10-30 Torr, pirolizy according to the reaction CH4-4+4H+. When this electrically charged atoms of carbon have significant kinetic energy sufficient to create the perfect nanodiamonds. The temperature of the substrate maintained within the range of 1050-1150°C. On the surface of the substrate 3 grown layer of nanocrystalline carbon 7, in the matrix which contains the nanodiamonds.

To achieve kazanovichyakov result in a known way, including heating plates made of carbon material in a sealed water-cooled chamber direct transmission of electric current and thermal decomposition of methane in the gap between the plates at a pressure of 10-30 Torr with a deposition of nanocrystalline layers of carbon on substrates placed in the gap, the current is passed only through the bottom plate and the top serves bias potential from the external voltage source, thermal decomposition of methane is carried out at a temperature of 1050-1150°C on a substrate of silicon or Nickel, as the material of the plates can be used carbon foil, structural graphite, carbon-graphite fabric or felt.

During thermal decomposition of methane occurred in the electric field carbon ions gain kinetic energy, allowing them to create contact with a growing layer of pressure up to 30 GPA, which is comparable, and according to other sources exceeds the pressure attained when the detonation of TNT. The temperature of the substrate maintained within the range of 1050-1150°C and pressure of methane from 10 to 30 Torr.

If the partial pressure of methane below 10 Torr, then its concentration in the atmosphere chamber is not sufficient to produce a dense layer of crystalline carbon.

If you raise the partial pressure of methane above 30 Torr, the surface of the substrate planted soot, which makes the growing content of asego nanodiamonds crystalline carbon layer is not possible.

If the temperature of the heated carbon plates is below 1050°C, the specified range of pressures of methane noticeable sediment carbon will not occur.

With increasing temperature above 1150°C substrate enter into chemical interaction with heated above this temperature the lower the carbon plate is plastic deformation and partial melting.

When using as a substrate of polished silicon wafers, which are synthesized film after cooling, can be easily separated from the substrate due to the large difference in CTE, but the reuse of expensive silicon substrates impossible due to impaired quality polishing their surfaces after ion bombardment by carbon.

When using cheaper substrates of Nickel adhesion of the synthesized films are great and their departments need to dissolve the Nickel substrate in a heated aqueous solution of sulfuric acid.

Example 1

Between the two plate - lower 1 (made of 3 layers of flexible carbon foil and connected to the output bus of the power transformer) and 2 - top (made of solid carbon felt isolated from the plate 1 and is connected to an adjustable source of alternating voltage, a width of 120 mm and a length of 230 mm each - set of two substrates 3 of monokristally the definition of silicon with a diameter of 100 mm each. After sealing and evacuation of the reaction chamber it has filled with methane qualification microwave until a pressure of 20 Torr and turned on the heat by passing current through the plate 2. The temperature of the silicon substrate has reached a temperature of 1070±20°C. Then filed a voltage 05 In the external electrode 6 of the upper plate 2 and recorded by the ammeter in the circuit: top plate - phase pole of the external voltage source current of 1-2,5 A. in the gap between the plates 1 and 2 was observed blue glow. Operating cycle duration was 8 minutes. After removing the substrate 3 on their polished surfaces the detected film 7 with a metallic sheen thickness of 3-5 μm. After mechanical separation of the obtained films from substrates in their composition nanodiamonds found in sizes from 4 to 10 nm in an amount up to 80 wt.%.

Example 2

Same as in example 1, but the pressure of methane in the reaction chamber was maintained at a level of 7 Torr, and the length of the operating cycle is 17 minutes. After removing the silicon substrates detected amorphous yellow tape, easy to remove organic solvents.

Example 3

Same as in example 2, but the pressure of methane in the reaction chamber was maintained at a level of 45 Torr. The surface of a silicon substrate covered with a thick layer of soot. After removal of soot traces crystal layer is not about naruhina.

Example 4

Same as in example 2, but the temperature of the silicon substrates was 950°C. On the surface of the substrate precipitation of crystalline carbon is not detected.

Example 5

Same as in example 2, but the temperature of the silicon substrates was 1200°C. the Plates are strongly deformed, cracked and partially melted. Layer pyrographite on their surface is observed, but their further use is not possible.

Example 6

Same as in example 2, but as substrates used plates of Nickel foil with a thickness of 30 μm, and the length of the operating cycle was 5 minutes. After removal of the substrate detected film with a metallic luster thickness of 2-3 μm. After etching in 30% sulfuric acid solution with the addition of 5% chromic anhydride at 60°C for 2 hours, the Nickel was removed and the composition of the residual carbon films nanodiamonds found in sizes from 4 to 8 nm in an amount up to 80 wt.%.

The method of producing nanodiamonds in the pyrolysis of methane in an electric field, comprising heating plates made of carbon material in a sealed water-cooled chamber direct transmission of electric current and thermal decomposition of methane in the gap between the plates at a pressure of 10-30 Torr with a deposition of nanocrystalline layers of carbon on substrates placed in the gap is, characterized in that the current is passed only through the bottom plate and the top serves bias potential from the external voltage source, thermal decomposition of methane is carried out at a temperature of 1050-1150°C on a substrate of silicon or Nickel, as the material of the plates can be used carbon foil, structural graphite, carbon-graphite fabric or felt.



 

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