JPH0263542A - Synthesis of diamond powder - Google Patents

Abstract

PURPOSE:To prepare diamond powder inexpensively by press-molding a mixture of a carbonate with reducing metal powder, and exerting impact compression to the press-molded body. CONSTITUTION:A carbonate (e.g., CaCO3) having <=100mum grain size as carbon source, is mixed with reducing metal powder (e.g., Fe) in a proportion of >=67mol.% the metal basing on the amt. of the mixture. The powder mixture 4 is filled in a stainless steel sample vessel 3, and the powder in the vessel 3 is compressed to 20% void by pressing with a press. Threads 5, 6 of the vessel 3 are then fastened. The vessel 3 is inserted into an insertion hole located at a center of a housing vessel 2 made of iron, and the whole body is laid in a ring 1 constructing thus a recovery assembly. A shock wave is generated by colliding a flying body accelerated by a single stage powder gun, and the shock wave is made to penetrate through the sample. Diamond powder is prepd. inexpensively by exerting 100-500Kbar impact compression to the molded body by this method.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a method for synthesizing diamond powder.

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

Prior art The conventional method for synthesizing diamond powder using shock waves uses graphite or amorphous carbon as a starting material, and applies shock waves to it to cause a solid-phase reaction due to a martensitic transformation transition, 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, with these methods, 300 to 1500 kba
A relatively strong shock wave of r is required, and the device must be strong accordingly, which poses a problem of high cost.

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.

Structure 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 create 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 of synthesizing diamond using high temperature and high 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 reducible metal powder is added to the carbonate. A method for synthesizing diamond powder, characterized in that the mixture is mixed in a proportion of 67 mol% or more, pressure molded, and the molded body is subjected to impact compression at 100 to 500 kbar.
It is in.

Shock compression in the present invention is performed by accelerating a flying object with combustion gas of 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 10 to improve reactivity.
0 microns or less, preferably 5 microns or less. The mixing ratio of the metal is 67 mol % or more.

This metal acts not only to reduce carbon dioxide gas but also as a cooling medium, and if it is less than 67 mol %, it is difficult to achieve this effect sufficiently.

The mixture is preferably pressure-molded into a molded body with a porosity of 40% or less, in order 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 kba.
Preferably it is r. If it is less than 100 kbar, it is difficult to generate diamonds, and if it exceeds 500 kbar, excessive heat is generated, damaging the sample container and making it impossible to collect 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 results in a lower impact pressure of 100 k than in the conventional method.
It is possible to synthesize diamond powder even in a bar, and diamond powder can be obtained at low 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, and this mixed powder 4
was filled into the stainless steel sample container 3 shown in Fig. 1, and the powder in the sample container was compressed by pressurization to a porosity of 20%.
And so. Thereafter, the screws 5 and 6 were tightened. 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 1700 m/s, the initial pressure was 200 kbar, and the peak pressure was 400 kb.
It was ar. After impact compression, the sample was taken out from the sample container 3 and determined by X-ray powder diffraction to have a lattice constant of 4.293±0.00.
Two magnesioustites were identified, and the following reactions were confirmed to occur.

MgC0++2Fe-MgOH2FeO+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 macrogonal diamond by electron beam 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: Storage container for sample container, 3:
Sample container, 4: Sample (press-molded body of mixed powder), 5.6: Threaded part.

Claims (1)

[Claims] A method of synthesizing diamond using high temperature and high 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 in such a way that the metal is 67 mol% or more. 1. A method for synthesizing diamond powder, which comprises mixing the diamond powders in the same proportions, press-molding the powder, and subjecting the compact to impact compression at 100 to 500 kbar.