CN1673075A - Process of preparing diamond film with coal - Google Patents

Abstract

The present invention is process of preparing diamond film with coal, and relates to coal cracking and hot plasma chemical vapor deposition of cracked gas. Hydrogen-containing gas is excited in plasma generator to generate plasma jet, and coal powder is provided into the jet for fast temperature raising, cracking and chemical reaction to generate acetylene. Excessive hydrogen-containing gas may be used in preparing diamond film through combustion process without need of separation and is made to combust directly through contact with oxygen. On the water cooled substrate in the flame reduction area, diamond film is deposited. The diamond film may be used in cutter, ornament, heat sink, and infrared window.

Description

Method for preparing diamond film by using coal

The technical field is as follows:

the invention relates to a method for preparing a diamond film by a chemical vapor deposition method after coal plasma cracking, in particular to improvement of raw materials and steps thereof.

Background art:

at present, diamond films are produced by combustion with acetylene under open atmosphere conditions or at low pressures of several thousand Pa. C₂H₂And O₂Reaction: $\mathrm{\Δ}{H}_R^0=-448\mathrm{KJ}/\mathrm{mol}$ flame temperatures up to 3000K, at which temperature H₂Decomposition to produce diamond growthThe high number of atoms H, which is generally referred to as atoms H, is a prerequisite for plasma chemical vapor deposition of diamond films because there are enough groups that can etch the graphite and prevent the generation of gaseous graphite precursors. The flame of oxyacetylene flame is divided into inner flame, outer flame and reducing flame in the middle position, the substrate for growing diamond is placed in the reducing flame area, and is cooled by water.

Currently, acetylene can be prepared by coal or carbon cracking; the method comprises the steps of enabling hydrogen to pass through a plasma generator, providing hydrogen plasma jet flow with the temperature of 3700K above, supplying carbon powder or coal powder to the jet flow through an entrained flow bed, enabling C-containing powder to be heated quickly, enabling bridge bonds of the C-containing powder to be broken, enabling chemical group components to generate free radicals at high temperature and to generate free radical reaction, enabling part of the C-containing powder to become high-temperature acetylene gas, and enabling the acetylene gas to generate secondary dehydrogenation reaction at high temperature to generate carbon black and hydrogen, so that rapid cooling measures are taken for reaction mixed gas flow after cracking. Cooling, separating gas from solid by cyclone separator, and refining. The preparation of acetylene by plasma cracking of coal is a new technology with wide industrial prospects, and is currently under research and experiments.

The invention content is as follows:

the invention aims to provide a method for preparing a diamond film by using coal, which combines the two processes and improves the raw materials and the steps, therebyhaving low cost, wide gas source and simple process steps.

The invention is realized by the following technical scheme: natural gaseous hydrocarbon or hydrogen is excited by a plasma generator to form a thermal plasma jet, the same kind of gas is used for conveying coal powder or carbon powder into the jet, and the carbon-containing powder is cracked in a reactor and undergoes a chemical reaction to generate high-temperature acetylene and other gases; then using water or other medium to make quick cooling, then making gas-solid phase separation, finally making the reaction gas be directly contacted with oxygen gas for combustion, and depositing diamond film in the reduction zone of flame.

When the coal or the carbon enters the reactor and the oxygen is conveyed, the ratio of the oxygen to the carbon is 0.7-1.2.

The ratio of carbon to hydrogen entering the plasma generator and entering the jet flow is 1: 1-1: 3.

The invention uses cheap natural gaseous hydrocarbon to replace hydrogen to crack coal, the cheapest gas source is natural gas, coal bed gas and marsh gas, the main component is methane (CH)₄) The raw material gas cost can be reduced by using the coal cracking catalyst to crack coal; and after the same volume of gas is cracked, they can increase the number of H and CH functions by half more than hydrogen. The reaction gas after coal cracking and gas-solid separation is directly used for preparing the diamond film by a combustion method without extracting acetylene, so that the steps of gas separation and refining can be omitted, excessive hydrogen exists, the deposition of the diamond film is not influenced, and the etching of a non-diamond carbon phase of the diamond film in the deposition process is facilitated.

Description of the drawings:

FIG. 1 is a process flow diagram of the present invention;

the specific implementation mode is as follows:

as shown in figure 1, hydrogen or natural gaseous hydrocarbon is excited into thermal plasma jet by electric arc in plasma generator 1, carbon powder is conveyed into the jet by the same kind of gas, and the carbon powder is heated and cracked into C in reactor 2₂H₂And functional group C₂H. H, and the reaction mixed gas flow is rapidly cooled through the cooling chamber 3, then is subjected to gas-solid phase separation through the cyclone separator 4, and then is combusted after being contacted with oxygen in the combustion zone 6 through the pipeline 5 to form thermal plasma with the temperature of more than 3000K. A substrate 7 for depositing a diamond film was placed on the reduction flame zone of the combustion chamber and cooled with water.

And controlling the input amount of the carbon powder or the coal powder entering the reactor and the conveying pressure of the oxygen to ensure that the ratio of the oxygen to the carbon is between 0.7 and 1.2. The carbon is reactive carbon, and cannot be completely reacted in practice, and the coal powder is improved by more than one time because the coal powder is not reacted generally from five to six times due to the different particle sizes of the coal powder or the carbon powder and the difference of the reactors. Meanwhile, the ratio of carbon to hydrogen entering the plasma generator and entering the fluid jet is controlled, so that the ratio of C to H is controlled to be between 1: 1 and 1: 3 (the carbon also refers to the carbon for reaction), and if the prepared diamond film is used for cutters, ornaments and heat sinks after being cut by laser, the ratio of carbon to hydrogen can be larger, so that the deposition speed is accelerated; if optical grade is to be made, the carbon to hydrogen ratio of the diamond film used in the infrared window material can be smaller because H is more favorable for improving the quality of the diamond film. Any gaseous hydrocarbon can be excited by the plasma generator and then the coal powder is cracked to prepare acetylene. Such as gaseous saturated hydrocarbons:

the equation for the macro chemical reaction is: (n＝1，2，3，4)

gaseous olefins: ethylene: propylene: 。

Claims (3)

1. a method for preparing diamond film with coal, its step is to prepare acetylene by coal or charcoal cracking first, and then prepare the diamond film from acetylene by combustion method, characterized by that it uses the natural gaseous hydrocarbon or hydrogen to become the thermal plasma jet after the plasma generator is excited first, supply the coal dust or powdered carbon in the jet, crack and take place the chemical reaction in the reactor and produce acetylene and other reaction mixed gas flows; then the reaction mixed gas flow is cooled rapidly, then gas-solid phase separation is carried out, finally the reaction gas contacts with oxygen for combustion, and a diamond film is deposited in a reduction area of the flame.

2. A method of making a diamond film using coal as in claim 1 wherein the ratio of oxygen to carbon is between 0.7 and 1.2 when the coal or char is fed into the reactor and oxygen is delivered.

3. A method of making a diamond film from coal as recited in claim 1 in which the ratio of carbon to hydrogen entering the plasma generator and entering the jet stream is between 1: 1 and 1: 3.