JPH0476733B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for synthesizing diamond powder.
More specifically, it relates to an improved method for synthesizing diamond powder under high temperature and high pressure using so-called shock waves, in which a flying plate accelerated by combustion gas from gunpowder collides with a raw material container at high speed to generate high temperature and high pressure to synthesize diamond.

Conventional technology The conventional method for synthesizing diamond powder using shock waves uses graphite or amorphous carbon as a starting material, and shock waves are applied to it to cause a solid-phase reaction due to a martensitic transformation transformation or to induce a solid phase reaction of carbon atoms. This method used a liquid phase to increase the diffusion rate.

That is, the conventional method was to synthesize diamond powder by a solid phase reaction or a reaction involving a liquid phase. Moreover, these methods
Requires a relatively strong shock wave of 300-1500kbar,
This required the equipment to be very strong, which led to the problem of high costs.

Purpose of the Invention The present invention uses carbonate as a starting material instead of the conventional method, and simultaneously performs a decomposition reaction and a reduction reaction during shock wave pressurization to generate free carbon, and converts the free carbon into diamond. The purpose of this invention is to provide a method for synthesizing diamond powder that also performs a phase reaction at the same time.

Composition of the Invention As a result of intensive research to achieve the above object, the present inventor used carbonate as a starting material, mixed powdered metal that reduces carbon dioxide gas with it, and pressure-molded this mixture to produce a shock wave. We obtained new knowledge that when given carbonate, the carbonate decomposes, and the carbon dioxide gas produced is reduced by a reducing metal to produce free carbon, which can be turned into diamond. The present invention was completed based on this new knowledge.

The gist of the present invention is a method for synthesizing diamond using high temperature and pressure instantaneously generated by shock waves, in which a carbonate with a particle size of 100 microns or less is used as a carbon source, and a reducing metal powder is added to the carbonate. The metal is mixed in a proportion of 67 mol% or more and press-molded, and the molded body is
A method for the synthesis of diamond powder, characterized by performing impact compression of ~500kbar.

Shock compression in the present invention is performed by accelerating a flying object with combustion gas from gunpowder and causing it to collide with a container containing a sample to generate a shock wave.
This gives the sample the high pressure and temperature necessary for diamond synthesis. The heat generated by shock wave pressure depends on the impact pressure, the material of the impacted body, and the porosity of the sample molded body.

The carbonate used in the present invention decomposes during shock wave pressurization to generate carbon dioxide gas, which is then treated with a reducing metal to generate free carbon. Therefore, the carbonate is preferably one that is easily decomposed at low temperature under normal pressure, and examples thereof include magnesium carbonate, iron carbonate, zinc carbonate, and the like. The particle size is preferably 100 microns or less, preferably 10 microns or less. This carbonate is mixed with a reducing metal powder that reduces carbon dioxide gas to generate free carbon, and then press-molded. Examples of reducing metals include iron, aluminum, magnesium, and the like. The particle size of this metal powder is preferably 100 microns or less, preferably 5 microns or less, in order to improve reactivity. The mixing ratio is 67% of the metal
It is mol% or more. This metal acts not only to reduce carbon dioxide gas but also as a cooling medium, and has a 67 mol%
If the amount is less than that, it is difficult to achieve the desired effect.

It is preferable that the mixture be pressure-molded to form a molded body with a porosity of 40% or less. This is to reduce the number of pores in the molded body and prevent an excessive rise in temperature.

The impact pressure applied to this molded body is 100 to 500 kbar.
It is preferable that If it is less than 100 kbar, it is difficult to generate diamonds, and if it exceeds 500 kbar, it will generate excessive heat, damaging the sample container and making it impossible to recover it.

Separate the diamond powder from the sample obtained by impact compression. Examples of this method include a method in which the sample is treated with a solution in which sodium chlorate is dissolved in concentrated nitric acid and heated to near the boiling point, or a treatment with hydrochloric acid. The means of impact compression can be carried out in the same manner as conventional methods.

Effects of the Invention The present invention pioneers and provides a completely new method of using carbonate, which is completely different from the starting material used in conventional methods, and generating free carbon through decomposition and reduction reactions during compression by shock waves, and converting this into diamond. That's what I got. This makes it possible to synthesize diamond powder at a lower impact pressure of 100 kbar than in conventional methods, resulting in diamond powder being obtained at a lower cost.

Example 30% by weight of magnesium carbonate with a particle size of 10 microns and 70% by weight of iron powder with a particle size of 5 microns were mixed, this mixed powder 4 was filled into a stainless steel sample container 3 shown in Fig. 1, and the sample container was pressurized. The powder inside was compressed to a porosity of 20%. Thereafter, threaded parts 5 and 6 were screwed. This sample container 3 was inserted into the insertion hole located at the center of the iron storage container 2, and the whole was placed inside the ring 1 to form a recovery assembly. A projectile accelerated by the single-stage powder gun method collided with this sample container to generate a shock wave, which was passed through the sample. The collision speed at this time was 1700m/
seconds, initial pressure is 200kbar, peak pressure is 400kbar
It was hot. After impact compression, the sample was taken out from the sample container 3, and the lattice constant was determined to be 4.293±0.002 using X-ray powder diffraction method.
Å magnesioustite was identified, and it was confirmed that the following reaction was occurring.

MgCO ₃ +2Fe=MgO·2FeO+C This sample was treated with hydrochloric acid to remove unreacted magnesite, iron, and magnesioustite, and the insoluble residue was collected to obtain powder crystals. This crystal was confirmed to be hexagonal diamond by electron diffraction.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of one embodiment of a retrieval assembly used to carry out the method of the present invention. 1...Ring, 2...Sample container storage container, 3
... Sample container, 4 ... Sample (press-molded body of mixed powder), 5, 6 ... Threaded portion.

Claims (1)

[Claims] 1 In a method of synthesizing diamond using high temperature and high pressure instantaneously generated by shock waves,
A carbonate with a particle size of 100 microns or less is used as a carbon source, a reducing metal powder is mixed with the carbonate at a ratio of 67 mol% or more of the metal, and the mixture is pressure-molded to form the compact.
A method of synthesizing diamond powder characterized by impact compression at 100-500 kbar.