RU2586140C1 - Chemical method of producing artificial diamonds - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to inorganic synthesis of artificial diamonds of size of up to 150 mcm, which can be used in production of abrasive and diamond lubricants, drilling equipment. Synthesis of diamonds is carried out in molten metal matrix with direct reaction of carbon-containing additive contained in concentrations of 2 to 10 wt% in molten chlorides and/or fluorides of alkali metals, with molten metal, such as aluminium, zinc, magnesium, tin, lead, as well as their alloys for 1-5 hours at temperature of 700-900 °C in an air atmosphere and further cooling and/or thermal treatment, carbon-containing additive is represented by carbides of metals or non-metals or solid organic substances relating to classes of hydrocarbons or carbohydrates, or carboxylic acids.

EFFECT: invention enables to obtain cubic nano- and micro-diamond at atmospheric pressure and low temperature without using complex processing equipment.

1 cl, 18 dwg, 1 tbl, 7 ex

Description

The invention relates to the inorganic synthesis of artificial diamonds up to 150 microns in size, which can find industrial application in the production of abrasives and diamond lubricants, drilling equipment.

Synthesis of artificial diamonds is an essential practical task. The synthesis of diamonds, carried out by a method called the NTNR method (“high temperature - high pressure”) from a graphite-metal mixture in high-pressure apparatuses (AED), was based on the fundamental article of the Soviet scientist O.I. Leipunsky from 1939 [1].

This method of artificial production of diamonds was first carried out in the laboratory of ASEA (Sweden) in 1953, then in 1954 in the laboratory of the American company General Electric and in 1960 at the Institute of High Pressure Physics of the Academy of Sciences of the USSR (IHP) by a group of researchers the leadership of Leonid Fedorovich Vereshchagin. This method is still used worldwide.

O.I. Leipunsky came to the important conclusion that it is more profitable to crystallize diamond from a solution in molten metals, rather than by directly converting graphite to diamond. And the main reason for this is the greater mobility of carbon atoms in solution than in the crystal lattice of graphite.

An outstanding Soviet scientist also mentioned other possibilities for synthesizing diamond: growing seed crystals in the gas phase, producing large polycrystalline diamonds by sintering fine diamond powders, and also formulated the necessary conditions for producing artificial diamond - a combination of medium, pressure and temperature. All these three areas are currently the most common diamond synthesis methods in the world.

The main industrial method for the synthesis of diamonds in our time is a solution - molten metal - carbon synthesis at high pressures (temperature 1400-1600 ° C, pressure 5000-6000 MPa) [2-4]. As the initial charge, graphite is usually used (although other carbon-containing substances are possible) and metals or alloys of iron, nickel, cobalt, platinum and palladium. Powerful hydraulic presses equipped with high-pressure chambers are used to create the necessary thermobaric parameters.

Currently, there are three main options for considering the mechanism of diamond formation - the simplest one, which describes the crystallization of diamond from a graphite melt in the RT region of diamond stability (> 100 kbar ~ 2000 ° C) and two discussion options - crystallization of diamond from a solution of graphite in a metal - "catalyst "and - phase transition of graphite to diamond in the solid phase in the presence of metals -" catalysts ". Both last processes proceed under milder conditions (40-60 kbar, 1400-1600 ° C) in comparison with the “direct” phase transition. Studies of the mechanism of diamond formation by discussion options have shown their equiprobability. The practical implementation of one mechanism or another will be determined by the nature of the carbon-containing raw material (for example, its tendency to graphitize) or the nature of the catalyst metal, for example, the ability to form carbides and the stability of carbide forms in the RT region of diamond synthesis, or some other reasons.

The probability of diamond crystal nucleation is much less than the probability of the appearance of a graphite nucleus, but it still exists. If one way or another to prevent the formation of graphite, then diamond crystals can nucleate and grow. At the same time, employees of the Institute of High Pressure Physics of the Academy of Sciences of the USSR revealed [5] that, for different carbon materials, the transition to diamond occurs at different temperatures and pressures. So, if the calculations of O.I. Leypunsky give for the transition of graphite into diamond the value of 50,000 at at 1000 K, then for the transition of glassy carbon into diamond at the same temperature, only 15,000 at.

Not only the carbon atoms dissolved in the metal, but also various compounds with carbon, such as carbides, including metastable ones, are carriers of carbon to growing diamond. In any case, it is traditionally believed that the metal or alloy used in the synthesis of diamond should well wet diamond and graphite, dissolve carbon, and also have a sufficiently low melting point (otherwise the synthesis temperature, and therefore the applied pressure, will be very high).

The type of carbon material used and its dispersion have a significant effect on the synthesis rate and on the diamond yield in one press sintering. The ability to graphite carbon materials, i.e. to form a structure characteristic of graphite. If the starting material is graphitized, the synthesis ends faster and the diamond yield is greater than in the case of non-graphitized carbon material.

Attempts to synthesize diamonds in this way was one of the first historically carried out experiments. So, in 1893, professor of the St. Petersburg Military Medical Academy K.D. Khrushchov, upon rapid cooling of molten silver saturated with carbon, obtained crystals that scratched glass and corundum. His experience was successfully repeated in the same year by the French professor, Nobel laureate Henri Moissan [6], who replaced silver with iron. As a result, Moissant identified several grains, mostly black. These grains scratched corundum, burned almost completely in oxygen, had a density above 3 g / cm ³ . However, both contemporaries and descendants, despite the highest scientific authority of Moissan, considered these experiments on the synthesis of diamonds a hoax. For a long time, scientific thought was focused on the search for other directions in the synthesis of artificial diamonds, which were described in detail at the beginning of this introduction.

Numerous studies are currently being carried out on the synthesis of “carbonate-synthetic” diamond crystals in growth media with compositions similar to natural ones (highly compressed fluid-carbonatite syngenetic inclusions in natural kimberlite diamonds, carbonate-silicate diamondiferous rocks of the Kokchetav massif, Kazakhstan). The processes of intense spontaneous crystallization and diamond growth on substrates in multicomponent carbonate – carbon and carbonate – silicate – carbon melts are carried out at 5.5–8.5 GPa and 1200–2000 ° C.

Detonation synthesis should be considered as separate areas for the synthesis of artificial diamonds, which allows the mixture of amorphous carbon with nanodiamonds 1-3 nm in size and the CVC synthesis method to decompose methane under the influence of electric current using the method of explosion of fluorinated organic materials.

As the closest analogue to the proposed method, one can take the synthesis of diamonds, carried out in a molten metal matrix (metals of the iron group) at high pressures and temperatures, namely at a pressure of 60 kbar and a temperature of 1600 ° C, the so-called NRHT method. Almost 90% of artificial diamonds are currently produced industrially by the NRHT method [7–9]. However, for the production of synthetic diamonds by this method, it is necessary to use equipment capable of withstanding ultrahigh pressures, such as the Bell Belt or diamond anvil. Despite the fundamental possibility of synthesizing diamonds by this method directly from graphite powders, as a rule, the best results are achieved using diamond seeds. In addition, diamonds obtained by the NRHT method contain significant contaminants with a metal catalyst and nitrogen, they are painted in brown colors and are much more expensive than natural diamonds of a similar size and quality.

An object of the present invention is to synthesize artificial diamonds in a molten metal matrix at atmospheric pressure and temperatures below 1000 ° C.

To solve this problem, a chemical method for producing artificial diamonds is claimed, including the synthesis of diamonds in a molten metal matrix, which is carried out by direct interaction of a carbon-containing additive contained in concentrations from 2 to 10 wt.% In a melt of alkali metal chlorides and / or fluorides with molten metals such as aluminum, zinc, magnesium, tin, lead, as well as their alloys for 1-5 hours at a temperature of 700-900 ° C in an atmosphere of air and subsequent cooling and / or heat treatment, p and thus as a carbon-containing additive used carbides of metals or nonmetals or solid organic substances belonging to the class of hydrocarbons or carbohydrates, or carboxylic acids.

The claimed method is based on the following. The main criterion for choosing a solvent metal for the synthesis of artificial diamonds is the low solubility of carbon in it, and as a result, low carbide-forming ability, as well as a melting point below 800 ° C.

In the interaction of carbon, which is part of an inorganic or organic compound, in air with molten low-melting metal such as aluminum, as well as all of the above metals and their alloys, spontaneous nucleation of a diamond nucleus in a molten metal matrix can occur in the medium of molten salts.

The solubility of carbon in the above metals is extremely small: in aluminum 0.03 at.%, In lead 0.0004 at.%. In addition, neither aluminum nor lead, as well as all of the above metals and their alloys, moisten graphite and diamond, because up to 1100 ° C have contact angles greater than 130 °. Carbides of aluminum, magnesium and zinc are chemically unstable, dissociate completely in water with the formation of the corresponding hydroxides and gaseous hydrocarbons. The existence of lead carbide and tin carbide is a debatable issue. In any case, if they existed, they would also be chemically unstable. The melting point of all of the above metals is 232 ° C for tin, 327 ° C for lead, 419 ° C for zinc, 665 ° C for magnesium and 666 ° C for aluminum. Therefore, the salt electrolyte was selected so that the melting temperature of the salt mixtures was below 700 ° C, and also that the electrolyte included either non-hygroscopic salts or salts that could be easily dried by fusion with ammonium chloride, for example. Therefore, the composition of the salt electrolyte included chlorides and fluorides of alkali metals, as well as aluminum and ammonium.

The carbon-containing additive in the claimed method is a source of atomic carbon, which, when it is supersaturated in the metal and further cooling, forms diamonds in the metal matrix. As a carbon-containing additive, carbides of metals or non-metals or solid organic substances belonging to the classes of hydrocarbons or carbohydrates or carboxylic acids are used. These can be saturated hydrocarbons: paraffins or ceresins with the general formula C ₁₀ and higher; dibasic carboxylic acids: oxalic acid, succinic acid; hydroxyacids: tartaric acid, lactic acid, malic acid, citric acid, quinic acid; products of partial oxidation of sugars; carbohydrates: glucose, fructose, sucrose, maltose, as well as polysaccharides such as starch and a number of others in the form of powders with a particle size of from 0.5 to 200 microns. There were no significant differences in the synthesis of diamonds when using various precursors belonging to the same class of organic or inorganic substances.

Possible reactions for the release of free carbon during the interaction of liquid metals with carbides of metals and non-metals in air are presented in the table.

It is known that the interaction of aluminum, as well as the above metals and alloys, and carbon at the macro level does not occur up to a temperature of 1100 ° C. Therefore, the introduction of carbon into these metals and alloys in amounts exceeding solubility is possible only at the atomic level. Carbon is released as atoms on a metal surface and diffuses inside a liquid metal droplet.

The carbon inclusions formed inside the above metals are well retained in the metal matrix and do not crumble when cutting the metal matrix and polishing it, which also indicates the formation of diamond nanocrystals from carbon atoms due to local carbon supersaturations.

Since the mobility of atomic carbon in molten metals (Al, Mg, Zn, Pb, Sn) is of the same order of magnitude as in molten alkali metal halides, it is obvious that the interaction of molten metals with a carbon-containing halide melt actually achieves a carbon content in them , which is tens and hundreds of times higher than the solubility known from the literature, because, probably, these data were obtained by direct dissolution of bulk carbon in the molten metals listed above, which and void is very limited.

When hardening from 700-900 ° C to room temperature, the volume of a drop of aluminum, for example, decreases by 12-13%. Such a change in volume does not allow us to suggest a strong increase in pressure inside the drop during solidification, which could be sufficient for the transition of graphite into diamond. The proposed mechanism is the formation of a solution in the molten metal supersaturated with atoms or clusters of carbon atoms. Therefore, even a small pressure arising from the solidification of an aluminum, magnesium, zinc, lead or tin drop under highly nonequilibrium conditions is sufficient for the formation of high-quality micro diamonds. This mechanism allows you to get diamonds in any part of the solidified metal - in the center of the aluminum bead and at a depth of not more than 5 mm from its surface.

After cooling, a metal drop was dissolved in a 20% HCl solution, after which the formed nano and micro diamonds remained in the solution, from where they were deposited on various metal substrates, in particular, on a titanium foil.

In all likelihood, this method of producing diamonds inside a molten aluminum matrix in an environment of molten alkali metal halides is the most simple and cheap hardware, because can be carried out without the use of high-pressure apparatuses, high vacuum, as well as without the use of expensive consumables. The method is environmentally friendly and can be attributed to green chemistry. The transition to a similar technology for the production of artificial diamonds could significantly change the availability and cost of artificial diamonds used in various fields of production. At present, no reasons have been identified that could interfere with the direct synthesis of diamonds in an aluminum matrix by the proposed method.

For the first time, the synthesis of diamonds in molten aluminum was carried out by its interaction with a carbon-containing halide melt at 700-750 ° C at normal atmospheric pressure. It is shown that the formed diamond crystals have a cubic syngony, are well faceted, their sizes vary from 20 nm to 20 μm.

A new technical result achieved by the claimed invention consists in the synthesis of cubic nanodiamonds and microdiamonds at atmospheric pressure and lowering the temperature of the process without the use of sophisticated technological equipment, as well as in reducing labor intensity and ensuring environmental safety of the process.

The claimed invention is illustrated by the following. In FIG. 1 shows a SEM image of a cross section of an aluminum-diamond composite material obtained by chemical interaction of an aluminum melt with tungsten carbide at 900 ° C, containing 2 wt.% Carbon in the form of a cubic diamond; in FIG. 2 - Raman spectrum of diamond inclusion; in FIG. 3 - Kikuchi lines of cubic diamond, shot in EBDS mode; in FIG. 4 is a SEM image of a cross section of a lead-diamond composite obtained by reacting pure lead with powdered boron carbide at 700 ° C. containing 0.58 wt.% Carbon; in FIG. 5 - Raman spectrum of diamond inclusion in the form of nano needles; in FIG. 6 - Kikuchi lines of cubic diamond, shot in EBDS mode; in FIG. 7 is a SEM image of a cross section of a magnesium-diamond composite obtained by reacting a magnesium melt with tartaric acid at 800 ° C. containing 0.8 wt.% Carbon; in FIG. 8 - Raman spectrum of diamond inclusion; in FIG. 9 - Kikuchi lines of cubic diamond, shot in EBDS mode; in FIG. 10 is a SEM image of a cross section of a zinc-diamond composite obtained by reacting a zinc melt with silicon carbide at 800 ° C. containing 1.2 wt.% Carbon; in FIG. 11 - Raman spectrum of diamond inclusion; in FIG. 12 is a SEM image of a cross section of a magnesium-diamond composite obtained by reacting a magnesium melt with glucose at 800 ° C. containing 1.8 wt.% Carbon; in FIG. 13 - Raman spectrum of diamond inclusion; in FIG. 14 is an SEM image of a cubic diamond crystal after dissolution of the aluminum matrix in a solution of hydrochloric acid deposited on a titanium substrate. In FIG. 15 is an optical image of a transverse section of an aluminum-diamond composite material obtained by chemical interaction of an aluminum melt with paraffin at 700 ° C, containing 2.7 wt.% Carbon in the form of cubic diamond (magnification × 800); in FIG. 16 - Raman spectrum of diamond inclusion; in FIG. 17 is an optical image of a transverse section of an aluminum-diamond composite material obtained by chemical interaction of a silumin melt with sucrose at 750 ° C, containing 0.8 wt.% Carbon in the form of a cubic diamond; in FIG. 18 - Raman spectrum of diamond inclusion.

Example 1

An alundum crucible was placed in a vertical heating furnace, 40 g of a dry mixture of ammonium chlorides and fluorides containing 2 g of tungsten carbide powder with a particle size of up to 200 μm were placed on its bottom. On top of the carbide-containing salt mixture, an aluminum disk of A999 purity or its alloys is placed on which 10 g of finely divided salt mixture is poured. After that, the furnace was heated to a temperature of 900 ° C and kept in an atmosphere of air for 5 h, after which it was quickly cooled with intensive ventilation. In this case, tungsten carbide passed into the aluminum melt with the formation of an aluminum-diamond composite. A cross sectional view of an aluminum-diamond composite material is shown in FIG. 1. Raman spectroscopy data presented in FIG. 2 indicate the formation of cubic diamond, the Kikuchi lines shown in FIG. 3 also indicate the formation of cubic diamond.

Example 2

An alundum crucible was placed in a vertical heating furnace; 40 g of a dry mixture of lithium chloride containing 2 g of boron carbide powder containing 4 g of boron carbide powder with a particle size of up to 100 μm was placed at its bottom. On top of the carbide-containing salt mixture, a C1 grade lead alloy disk is placed on which 10 g of finely divided the same salt mixture with boron carbide powder are poured. After that, the furnace was heated to a temperature of 700 ° C and kept in an atmosphere of air for 2 h, after which it was quickly cooled by pouring a melt containing salt and metal into an alundum crucible placed in snow. In this case, boron carbide passed into the melt with the formation of a lead-diamond composite. A cross sectional image of a lead-diamond composite is shown in FIG. 4. The Raman spectroscopy data of the nano-needles shown in FIG. 5 indicate the formation of cubic diamond, the Kikuchi lines shown in FIG. 6 also indicate the formation of cubic diamond.

Example 3

An alundum crucible was placed in a vertical heating furnace; 40 g of a dry mixture of sodium chloride and fluoride containing 1 g of tartaric acid powder was placed on its bottom. Magnesium was placed on top of the carbon-containing salt mixture, onto which 10 g of the same mixture was poured. After that, the furnace was heated to a temperature of 800 ° C and kept in an atmosphere of air for 1 h, after which the molten mixture was cooled in a furnace. Then, the magnesium – diamond composite was washed from salts, dried, and subjected to additional thermal annealing at a temperature of 360 ° C for 6 h. At the same time, atomic carbon transferred to the magnesium melt to form a magnesium – diamond composite. A cross-sectional image of a magnesium-diamond composite material is shown in FIG. 7. Raman spectroscopy data presented in FIG. 8 indicate the formation of cubic diamond, the Kikuchi lines shown in FIG. 9 also indicate the formation of cubic diamond.

Example 4

An alundum crucible was placed in a vertical heating furnace; 40 g of a dry mixture of potassium chlorides and fluorides containing 4 g of silicon carbide powder was placed on its bottom. Granulated zinc was placed on top of the carbide-containing salt mixture, onto which 10 g of the same mixture was poured. After that, the furnace was heated to a temperature of 800 ° C and kept in an atmosphere of air for 1 h, after which the molten mixture was cooled in a furnace. Then, the zinc-diamond composite was washed from salts, dried, and subjected to additional thermal annealing at a temperature of 300 ° C for 2 h. At the same time, atomic carbon transferred to the zinc melt with the formation of the zinc-diamond composite. A cross-sectional image of a zinc-diamond composite material is shown in FIG. 10. The Raman spectroscopy data presented in FIG. 11 indicate the formation of cubic diamond.

Example 5

An alundum crucible was placed in a vertical heating furnace; 40 g of a dry mixture of cesium chloride and fluoride containing 5 g of glucose was placed at its bottom. A tin alloy was placed on top of the carbon-containing salt mixture onto which 10 g of the same mixture was poured. After that, the furnace was heated to a temperature of 800 ° C and kept in an atmosphere of air for 1 h, after which the molten mixture was cooled in an oven at a rate of 1 deg per min. At the same time, atomic carbon transferred to the tin melt with the formation of a tin-diamond composite. A cross-sectional image of a tin-diamond composite material is shown in FIG. 12. The Raman spectroscopy data presented in FIG. 13 indicate the formation of cubic diamond.

In the chemical interaction of a salt melt containing carbides of metals or nonmetals or solid organic substances with molten aluminum, magnesium, lead, tin, and zinc, composites can be obtained with a volume content of up to 2 wt.% Nano- and microdiamonds, depending on temperature, concentration and the type of carbon-containing additive, the time of high-temperature interaction, as well as the subsequent cooling and / or heat treatment under unsteady conditions. Upon dissolution of metal-aluminum composites in a 20% hydrochloric acid solution, individual crystals of cubic syngony diamonds with sizes from 1 to 10 μm were isolated, which are shown in FIG. fourteen.

Example 6

An alundum crucible was placed in a vertical heating furnace, 40 g of a dry mixture of chlorides and fluorides of lithium, sodium, potassium, cesium containing 10 g of paraffin were placed on its bottom. Technical aluminum was placed on top of the carbon-containing salt mixture onto which 10 g of the same mixture was poured. After that, the furnace was heated to a temperature of 700 ° C and kept in an atmosphere of air for 1 h, after which the molten mixture was rapidly cooled in air with forced ventilation. At the same time, atomic carbon transferred to the aluminum melt with the formation of an aluminum-diamond composite. A cross sectional view of an aluminum-diamond composite material is shown in FIG. 15. Raman spectroscopy data presented in FIG. 16 indicate the formation of cubic diamond.

Example 7

An alundum crucible was placed in a vertical heating furnace, 40 g of a dry mixture of lithium, sodium, potassium, cesium chloride and fluoride containing 10 g of sucrose were placed on its bottom. On top of the carbon-containing salt mixture, a disk of silumin (an aluminum alloy containing 9 wt.% Silicon) was placed on which 10 g of the same mixture was poured. After that, the furnace was heated to a temperature of 750 ° C and kept at this temperature in an atmosphere of air for 1 h, after which the furnace temperature was lowered to 350 ° C and kept at this temperature for 3 h, then the crucible was cooled to room temperature under natural ventilation. At the same time, atomic carbon transferred to the silumin melt with the formation of an aluminum-diamond composite. A cross sectional view of an aluminum-diamond composite material is shown in FIG. 17. The Raman spectroscopy data presented in FIG. 18 indicate the formation of cubic diamond.

Thus, the claimed chemical method for producing diamonds of cubic syngony in the direct interaction of the carbon-containing components of the halide melt with molten metal (aluminum, magnesium, zinc, tin, lead) or a matrix from their alloys can become the basis for creating a new technology of nano synthesis, which has no analogues - and micro diamonds.

Literature:

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Claims (1)

A chemical method for producing artificial diamonds, including the synthesis of diamonds in a molten metal matrix, characterized in that the synthesis of diamonds is carried out by direct interaction of a carbon-containing additive contained in concentrations from 2 to 10 wt.% In a melt of alkali metal chlorides and / or fluorides with molten metals such as aluminum, zinc, magnesium, tin, lead, as well as their alloys for 1-5 hours at a temperature of 700-900 ° C in an atmosphere of air and subsequent cooling and / or heat treatment, while As a carbon-containing additive, carbides of metals or nonmetals or solid organic substances belonging to the classes of hydrocarbons or carbohydrates or carboxylic acids are used.

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