CN1036061C

CN1036061C - Preparation of diamond from graphite or carbonaceous solid matter

Info

Publication number: CN1036061C
Application number: CN93112537A
Authority: CN
Inventors: 王季陶; 郑培菊
Original assignee: Fudan University
Current assignee: Fudan University
Priority date: 1993-08-23
Filing date: 1993-08-23
Publication date: 1997-10-08
Anticipated expiration: 2013-08-23
Also published as: CN1084489A

Abstract

The present invention relates to a method for preparing diamond from graphite or carbon containing solids. The existing methods for preparing artificial diamonds use high temperature and high pressure and have the disadvantage of complicated technological equipment, or the low production efficiency by using gas as raw materials. Particles of the graphite or the carbon containing solids are continuously turned over or floated in a reactor filled with hydrogen gas or mixed hydrogen gas, the excitation energy of the gas in the reactor can be introduced in the form of heating bodies or plasma, and reactions are carried out for 0.5 to 50 hours under the conditions of the gas pressure of 50 to 10<6> Pa and a temperature of 700 to 1273K. Raman spectrum detection proves that reaction products are diamond crystals by being diffracted by X rays.

Description

Method for preparing diamond from graphite or carbon-containing solid

The present invention is a method for preparing diamond from graphite or a carbon-containing solid.

Diamond has a distinct advantage over all other materials, not only is it hard, but its thermalconductivity, optical properties, and other properties are superordinate. Natural diamond sources are limited and therefore continuous improvements in synthetic diamond manufacturing processes have been the goal of people for many years. As early as 1955, the american general electric company produced synthetic diamonds by a high temperature and high pressure process. Eversole obtained synthetic diamond by vapor growth under low pressure in 1958 and 1959 and applied for us and canadian patents (U.S. patent nos. 3030187 and 3030188, Can Patent No. 628567). The soviet union b.v. deryagin also obtained the certificate of soviet union at almost the same time. The work of Deryagin et al was repeated in 1982 by Setaka et al, Japan institute for inorganic materials, and synthetic diamond was also obtained by the low-pressure vapor phase growth method. To date, these existing high pressure processes are complex and expensive in equipment; the low pressure gas phase method is mainly used for growing films and has low efficiency.

The invention aims to overcome the problem of low efficiency of the prior method for preparing artificial diamond by using gas as raw material for preparing artificial diamond under low pressure, and provides a method for preparing artificial diamond powder particles from graphite or carbon-containing solid.

The method comprises the steps of preparing diamond from graphite or a carbon-containing solid under the conditions of low pressure and high temperature, placing particles of the graphite or the carbon-containing solid into a reactor, filling hydrogen or mixed gas of the hydrogen and oxygen-containing component gas or hydrogen and hydrocarbon into the reactor, wherein the gas pressure is 50-10%⁶And when the reaction temperature is 700-1273K, the solid powder particles are in a continuous turning state in the reactor, gas excitation energy in the reactor isintroduced in the form of a heating body or plasma, and the diamond fine powder or particles can be obtained after reaction for 0.5-50 hours.

The reaction condition of the invention is that the gas pressure is 50-10⁶The reaction temperature is 700-1273K, the reaction pressure is low, the temperature requirement is not very high, and the method is easy to implement in a common reaction system. The gas in the reactor may be hydrogen alone, or a small amount of oxygen-containing component gas or a small amount of hydrocarbon may be added to mix with hydrogen in order to improve the reaction efficiency or lower the temperature. The raw materials and the resultant solid particles in the reaction system are in a continuous turning or floating state. This is because the fine powder or particles of the raw material and the product are continuously turned over in a high concentration region of the gas-phase excited particles because the gas-phase excited particles are unstable and they easily lose their activity by collisionThe gas excited particles move or float, so that the gas excited particles have sufficient contact with the surfaces of the solid raw materials and the product powder particles in a continuous turning or floating state, and the reaction efficiency is improved.

The introduction of excitation energy into the reactor can be achieved by a heating element or by forming a plasma. The most commonly used heating element is a tungsten wire which is heated by current through an electrode connecting wire, and the introduction mode of the heating element is simple; the plasma is generated by radio frequency, microwave, electron spin resonance or AC/DC voltage to discharge gas. The way of providing excitation energy to the reactor is substantially the same as that of the existing gas phase method for preparing diamond.

In order to make the particles of the raw materials andthe products turn over continuously and contact with the excited particles, the reactor can rotate at the speed of 4-100 revolutions per minute, and the two ends of the center of the reactor are arranged in a rotating shaft wheel.

The gas in the reactor can be single hydrogen, or can be a hydrogen mixed gas containing 0.1-10% of oxygen-containing component gas or 0.2-2% of hydrocarbon by volume. The gas containing oxygen is, for example, oxygen, water or carbon monoxide. When oxygen and hydrogen are directly used as the mixed gas, the oxygen content must be lower than the explosive limit. When the hot filament is used as the excitation energy source, the oxygen-containing gas cannot be used in the reaction system, and the oxygen component may exist when other external excitation energy sources are used.

The hydrogen or hydrogen mixed gas is excited into particles by an external energy source, such as hydrogen atoms, oxygen atoms, hydroxyl groups or hydrogen ions, and participates in the reaction of carbon to generate gaseous intermediate products, such as methane and acetylene, and the gaseous intermediate products are decomposed to generate the diamond. The hydrogen atoms play a role of energy carrying, and the hydrogen atoms release chemical energy when being associated into hydrogen molecules, and are similar to a pump to stably graphite carbon atoms with low energyThe delivery of the sub-species to the higher energy metastable state-forming diamond may be referred to as a chemical pumping process. The reaction equation is as follows: . In order to generate a sufficient concentration of excited particles, excitation energy must be continuously supplied to the system. The region where the diamond fines or grains are generated and grown is a high concentration region of gas phase excited particles. Therefore, the purpose isPreviously, gaseous compounds have been used to produce synthetic diamonds, but only part of the conversion process for producing synthetic diamonds from graphite or fine carbonaceous solids. Under the present experimental conditions, graphite or carbon-containing solid particles can be converted into diamond at low pressure in the presence of hydrogen atoms, and gaseous compounds such as methane, acetylene and the like are only intermediate products of the conversion process.

In order to facilitate the nucleation and growth of diamond, solid fine powder or particles which are beneficial to induce the nucleation and growth of diamond, such as silicon powder, silicon carbide powder and the like, are doped into the reaction raw materials to be used as substrate materials for inducing and generating a large amount of new diamond nuclei, and the yield of the diamond fine powder or particles is accelerated by the large substrate surface. It is also effective to incorporate diamond fine powder directly into the raw material. The nucleation process is basically consistent with the existing gas phase method for preparing diamond.

The graphite or carbonaceous solid used as the feedstock may be fine powders or granules of pure or impure carbon allotropes such as graphite, amorphous carbon, coal, and the like. The fine particles of the raw material are preferably fine, and the particles of 10-500 microns are preferred in the invention, so that the fine particles are beneficial to reaction, the fine particles of the raw material fully react with the excited particles to generate the fine diamond powder, and the finer the particles, the shorter the reaction time, and vice versa.

The invention can react to generate diamond under the condition of lower than normal pressure, and even if the reaction is carried out under the normal pressure or slightly higher than the normal pressure, the invention can be realized on process equipment without difficulty. Compared withthe high-pressure method in the prior art, the method has the advantages of simple equipment, convenient operation and cost reduction; the solid carbon allotrope is used as raw material, the density of the solid carbon allotrope is far higher than that of the gas raw material, the production efficiency is greatly improved, the density of the solid carbon source is higher than that of the gas carbon source, and byproducts such as hydrogen generated by a gas source are reduced. The continuous turning or floating state of the solid material and the product powder provides effective opportunity for the gas excited particles to contact the surface of the solid material and the product powder, so the method for manufacturing the artificial diamond fine powder or particles has simple process equipment and high efficiency.

The first embodiment is as follows:

amorphous carbon fine powder and a small amount of diamond fine powder with the diameter of 1 micron are put into a quartz tubular container filled with 50-250 Pa hydrogen (containing 0.05-1% of water vapor by volume ratio), the reaction temperature of the whole quartz container is kept at 800-1223K, and the hydrogen in the quartz container is discharged to form plasma by a high-frequency induction method through a 13.56MHz high-frequency generator. Rotating or turning over the quartz tubular container for 20-60 revolutions per minute (times), so that the solid fine powder in the container is in a continuous turning or floating state, and after 0.5-5 hours, the raw material amorphous carbon fine powder is converted into the product diamond fine powder. X-ray diffraction and electron microscope observation prove that the diamond fine powder with good quality is obtained, the diamond fine powder comprises single crystal particles and polycrystalline particles, and the particle diameter of the generated diamond fine powder is 5-50 micrometers. Example two:

putting graphite fine powder with the diameter of less than 500 microns and 1 weight percent of silicon powder into a quartz sealed container filled with an electrified tungsten wire to promote nucleation of diamond fine powder, filling hydrogen into the container, wherein the temperature of the tungsten wire is 2000-2200K, and the pressure in the container is 5 multiplied by 10³～5×10⁴And keeping the quartz container at 1073-1273K, continuously rotating the quartz container at 50-100 rpm to continuously turn the solid fine powder, obtaining diamond powder particles after 2-20 hours, and obtaining diamond crystals by X-ray diffraction detection of reaction products. Detecting with Raman spectrum at 1333cm^-1There was a very sharp peak indicating that good quality diamond was indeed obtained.

Claims

1. A method for preparing diamond from graphite or carbon-containing solid under the conditions of low pressure and high temperature is characterized in that particles of graphite or carbon-containing solid are placed in a reactor, hydrogen or mixed gas of hydrogen and oxygen-containing component gas or hydrogen and hydrocarbon is filled in the reactor, and the gas pressure is 50-10%⁶And when the reaction temperature is 700-1273K, the solid powder particles are continuously turned or floated in the reactor, the gas excitation in the reactor can be introduced in the form of a heating body or plasma, and the reaction time is 0.5-50 hours.

2. A method of producing diamond from graphite or a carbonaceous solid according to claim 1, wherein the reactor is rotated at a speed of 4 to 100 revolutions per minute.

3. The method ofclaim 1, wherein the gas in the reactor is hydrogen alone, or a mixture of hydrogen and oxygen containing component gas in an amount of 0.1 to 10 atomic% or hydrocarbon containing component gas in an amount of 0.2 to 2 vol%.

4. A method of producing diamond from graphite or a carbonaceous solid as claimed in claim 1, wherein the particle size of the graphite or carbonaceous solid is in the range of 10 to 500 μm.