Heterogeneous liquid-phase crystallization of diamond

 

(57) Abstract:

In the present invention set forth a principle of heterogeneous liquid-phase crystallization of diamond, which happens on a heterogeneous catalyst surface. This surface is characterized by the fact that in the process of high-temperature solid dehydrogenation of hydrocarbons bitumen-resins and asphaltenes catalyst hemosorbent hydrogen in atomic form. Hemosorbent the surface of the catalyst possesses the quality that is essential for the crystallization of the diamond, where the only possible growth of crystalline carbon-diamond. Described a method for the practical realization of this principle. As a result of implementation of this principle received over 3,000 carats of diamond crystals of different fractions from 100 to 1000 μm. Maximum value of the diamonds extracted in the experiments, achieved a size of 3.5 by 3.5 mm. While the problem of obtaining the maximum value of the diamond crystals was not raised. 4 Il.

THE TECHNICAL FIELD

The use of synthetic diamonds (SA) in the modern sphere of material production is very extensively. Virtually no sector of material production, which would not have applied synthetic diamond is the instrument;

diamond-abrasive metal grinding;

diamond honing;

diamond-abrasive machining of brittle non-metallic materials;

processing of wood materials, plastics and rubber;

the application of the tools of SA in drilling;

finishing of carbide and HSS tool on all tool factories.

Diamond in electronic engineering are widely spread. So, in the United States and Japan reported [2] on the development of diamond chips for computers (firm Sumitomo Electric), industrial output heatsinks (it) and acoustic membranes diamond films (Sony).

Currently created on the basis of diamond bipolar transistors, diodes-Schottky, point-contact transistors and field-effect transistors. Greatest practical interest microwave transistors with permeable base. High power microwave transistors, which is 20 W at a frequency of 30 GHz, and this higher power is the best modern devices of this type. Diamond, with its record-breaking heat conductivity can lead to a true revolution in the technology of substrates for large and ultralarge integrated circuits [2].

the e in the process of crystal growth, and natural diamonds are about 50 different impurities and defects in various combinations.

ART

Modern methods for the synthesis of diamond can be classified [1]:

1. Synthesis at high static pressures;

2. Synthesis at high loading;

3. Heterogeneous crystallization from the gas phase;

4. Laser synthesis;

5. Plasma synthesis of

The closest analogue of the present invention is a method of heterogeneous crystallization of diamond from the gas phase, described in [4].

In heterogeneous nucleation, we can distinguish two possible sources of atoms coming to the formation of critical embryo or joining a growing stage. Carbon atoms (molecule or radical) can join either directly from the gas phase (reaction a direct impact mechanism Ridilla), or from two-dimensional adsorbed gas due to surface migration (the Langmuir mechanism).

Consider a two-component system, such as methane and hydrogen. We introduce the following notation:

P1----P2- - partial pressure of methane and hydrogen;

1__2_ - degree of surface coverage of adsorbed methane (or is expressed as

~+J, (2.1)

where J is the flux of molecules of methane per unit surface area. Here the rst term corresponds to the nucleation of two-dimensional adsorbed layer, whereas the second term corresponds to the process of formation of the critical embryo by the mechanism of direct impact.

In the case of the applicability of the Langmuir isotherm for two-component systems

< / BR>
where b1and b2constants for adsorption of methane and hydrogen; K1and K2the rate constants for reactions, which depends primarily on temperature. When graphite is growing on some metals, the rate of its growth can be significantly more.

Metal carbides (for example, carbides, Nickel) can serve as a ready-critical nuclei. Another example of high-speed growth of graphite is the formation of whiskers. In them the basal plane oriented along the growth direction, which provides a high speed, and record the tensile strength.

Studies on the kinetics of growth of diamond in mainly in highly dispersed diamond powders. Each particle of the powder is an imperfect crystal with a high density of fractures, chips, i.e., the finished article is.

Analysis of experimental data suggests the following mechanism for the growth of diamond. Diamond diamond grows on the substrate in places free from chemisorbed methane and hydrogen, or through hemicorporectomy hydrogen, i.e.

V...(1-1-2)J1+2J1, (2.3)

here, the degree of surface coverage; J is the flow of hydrocarbon. When using the Langmuir adsorption

< / BR>
where K1and K2the rate constants of the reactions on a clean surface and on the surface, covered hammarbyhamnen hydrogen. It must be borne in mind that the adsorption constants in the formula (1.4) belong to the surface of the diamond. As can be seen from the formula, in certain conditions, the growth rate of diamond with increasing partial pressure of hydrogen in the gas phase will increase.

A joint analysis of the equations (1.2) and (1.4) shows that there can be such a process, when the growth rate of the diamond will be so much greater than the growth rate of graphite, which is the last acceptable to consider as an impurity, which can be sarashina diamond.

The proposed growth mechanism allows to make the assumption that graphite grows by methyl radicals, whereas the diamond, the l diamond in the region of thermodynamic stability of graphite more than Isobaric-isothermal potential of graphite. Therefore, the partial equilibrium pressure of carbon-containing gases over the diamond of more than graphite. Calculations show that the equilibrium pressure of methane over the diamond at temperatures above 1000oC 2 times higher than the corresponding to graphite. Therefore, at a given partial pressure of methane saturation above the diamond is always less than graphite. Depending on the temperature and total pressure relative difference solution over diamond and graphite will change. So will change the ratio of the rate of nucleation of diamond and graphite.

In the kinetic relation diamond behaves much more inert with respect to gases than graphite, which is connected with the peculiarities of their structure. As is known, the chemical bond in the lattice diamond character SP3- hybridization, whereas the graphite corresponds SP2- hybridization. The energy of a single SP3communication is 348 kJ/mol, while the energy SP2communication 607 kJ/mol, which is significantly less than the sum of the energies of single links. The replacement of two neighbors of carbon atoms in the diamond structure on hydrogen practically does not change the nature of electronic usaimage is it all carbon ring.

By analogy, the difference in the interaction of diamond and graphite with atomic hydrogen can be likened to the difference in the reactions of hydrogenation of ethane and acetylene or cyclohexane and benzene. This is based on the methods branch of diamond from graphite. So, when boiling perchloric acid (boiling point 203oC) released during the decomposition of the latter, atomic oxygen gasifies graphite, but does not interact with the diamond.

Approximately the rate of growth of diamond and graphite can be written in the form

V1= K1C1....,....V1= K1C1...., (2,5)

where C1the concentration of hydrocarbons; Ki1the rate constants for reactions.

If the environment has atomic hydrogen with a concentration considerably higher than the equilibrium at a given temperature, the speed of the reversible reactions of gasification can be written in the form

< / BR>
where C2the concentration of atomic hydrogen; Ki2the rate constants for reactions of gasification of atomic hydrogen. The absence of allocation of non-diamond carbon in the form will be

< / BR>
easy to find the critical concentration of atomic hydrogen

C2= (K1/K2)C1(2.8)

when danceyou and reverse reactions

< / BR>
Substituting the critical value of the concentration of atomic hydrogen, it is easy to obtain the growth rate of diamond without allocation of graphite

< / BR>
To the carbon could crystallize in the form of diamond, it is necessary to fulfill the condition

< / BR>
The above calculation was made without taking into account the effect of molecular hydrogen on the crystallization of diamond and graphite. In the latter case, the resulting formula is very bulky, but does not bring anything new. With kinetic peculiarities of growth of diamond and graphite are associated anomalous effects involving the fractionation of stable carbon isotopes12C and13C. it Was found that the growth of diamond latter absorbs a large proportion of the heavier isotope of carbon, whereas graphite "prefers" to lighter isotopes. The effect of various fractionation of carbon isotopes can be explained, if we assume that graphite is growing radicals H3while the growth of diamond formed complexes of N5. In this case, the partition coefficients are opposite in sign for graphite and diamond. As a result, the diamond turns out isotopically heavier than graphite. This structural effect fractionation of isotopo several orders of magnitude greater than thermodynamic fractionation effect.

Accreted from the gas phase diamond powders may have somewhat different properties than the original. So, their strength may be increased due to the healing of cracks and defects. In addition, it is possible grafting of various functional groups on the surface of the diamond.

Significant scientific and practical achievement is the development of methods for producing diamond-like films from atomic and ion beams.

With the growth of diamond-like films from atomic and ion beam carbon atoms (or complexes of several atoms) does not immediately lose their mobility. Only after some time they are "embedded" in the lattice, forming with other atoms in diamond and graphite types of links. Typically in these experiments, the substrate is cooled to liquid nitrogen temperature. Therefore, the authors divided into the near-surface layer, where the formation of nuclei of a new phase, particles which then pass directly into the "solid phase".

Outlined adsorption principle crystallization of diamond from the gas phase on substrates of various types (diamond, metal, dielectric) currently has no industrial application, as it allows to open the science, embodying this principle have not yet reached the necessary development to specify clearly the criteria of production technology for diamond synthesis from gas phase in a variety of ways:

thermal decomposition of hydrocarbons of different composition in the presence or in the atmosphere of various gases (hydrogen, argon, helium, and other gases thinners); plasma-chemical deposition methods hydrocarbon plasma on different substrates.

Of the many ways of implementing heterogeneous mechanism of SA synthesis from the gas phase, it is impossible to give preference to or to implement in production. Very rich experimental material, with no less rich theoretical justification of this principle, does not allow to unambiguously specify the path to production in the synthesis of SA. Experimentally obtained crystals are very small (about 50 μm), and diamond epitaxial films are obtained, usually polycrystalline with numerous defects, where there are graphite and various modifications of carbon. Moreover, when reaching a certain thickness (0.1 ám) for films grown on various substrates, epitaxial growth stops.

Currently produced metal catalysts (Fe, Co, Ni, Mn and others). The whole range of get SA this method is mainly used for machining various materials and diamond tools. In industries such as electronics and optics, get SA are not implemented due to poor properties or their absence altogether. The absence of the required characteristics is a consequence of the synthesis method.

The present invention fully solves all tasks which require industrial production from synthetic diamond. Moreover, the proposed method of diamond crystallization allows you to get diamonds with any predetermined properties, which are not able to offer industry none of the known methods of diamond crystallization.

Significant differences of the present invention from the prototype.

This object is achieved in that in the method of heterogeneous liquid-phase crystallization of diamond by the interaction of hydrocarbons with the catalyst according to the invention, in a hydrocarbon use dehydrogenated components of the bitumen and the adsorption process is carried out by the interaction of these components with hydride catalyst surface, Brazauskas the molecular components of the bitumen-resins and asphaltenes with subsequent adsorption transition in the crystalline state the diamond.

To date, despite the considerable efforts of many scientists who have studied various diamond deposits in Africa, Asia and Australia, has not been universally accepted theory of the formation of diamonds [1, C. 32].

From the analysis of natural sources of diamonds, kimberlites and their conditions of occurrence you may notice one characteristic that is inherent to all kimberlite pipes:

the host rock kimberlite pipes, as a rule, peschaniki, shale, quartzite, galleti and carbonate rocks [6, 7];

all of these types of breeds to some extent impregnated with bitumen [9, 16].

This is the main criteria of the diamond potential of kimberlites. But there are no rules without exceptions. Many exceptions to this rule exist. Thus, a significant number of kimberlite pipes, for example, Yakutia do not contain diamonds, and entirely gravitationaly (Belogorsky array [29]). The analysis of this kimberlite shows that it is strongly alkaline, kimberlite and in the presence of alkaline catalysts the catalytic dehydrogenation does not leak. It's a known fact [17, 30].

On the basis of this factual material and its analysis the authors concluded: the source of Vlada bituminous rocks, i.e. the host rock kimberlite magma. Kimberlite magma is the only source of heat for the occurrence of heterogeneous crystallization of the diamond.

The General theory of crystallization contained in [8, S. 57], says:

"Crystal growth proceeds in two stages. The first stage involves the formation of germs of microscopic size. The second stage consists in the subsequent growth of these nuclei to the formation of certain faces, which ultimately leads to a crystal with its habitus. The size and packing of the atoms in the crystal are determined by the nature of the crystal and the conditions of its cultivation.

Consider the conditions of formation of crystal nuclei (phase 2) of the homogeneous phase 1, for example steam, melt or solution.

The free energy of a supersaturated solution can be reduced by precipitation of the solid phase. However, such liquid is remarkably stable since the solid phase can be formed only if it decreases the total energy of the system. If the change in free energy at the transition between the solid and liquid phases have Gvthen the free energy of the system decreases by this amount for each unit of alhamadi unit area, formed in the surface of the solid-liquid.

In homogeneous nucleation the change in free energy is given by the expression

< / BR>
where V is the volume of the embryo, which has a face area of Aiand

< / BR>
here a is the number of ions formed from one molecule; R is the gas constant; T - temperature of the solution; C is the concentration at temperature T; C0the concentration at temperature T0.

The behavior of the newly formed structure with a lattice in a supersaturated environment depends on the size of this structure. It can grow or be dissolved again, and the result of the process should be lowering its free energy. The change in free energy, volumetric energy and free energy of nucleation G for spherical nuclei of radius r connected by the relation

< / BR>
and is illustrated in Fig. 1.

The minimum sustainable size of the critical nucleus size are obtained by differentiation of equation (3.3) for g, i.e.

< / BR>
and equating to zero, we find the critical radius of the embryo

< / BR>
The corresponding critical free energy is equal to

< / BR>
The dependence of G on r shows that the embryo is less than r*is the solution what Arsenium sl(i.e., supersaturation) and the increase of Gv(i.e., hypothermia).

The rate of nucleation J, i.e. the number of nuclei formed per unit volume, per unit time can be expressed by the Arrhenius equation:

< / BR>
where J0- prednisonecialis factor, K is Boltzmann's constant.

Using the ratio of the Gibbs-Thomson:

< / BR>
where M is the molecular volume, obtain

< / BR>
In equation (3.7) is the change in the difference between the chemical potential of the system. Thus, from equation (3.6) critical change in free energy is equal to

< / BR>
and from equation (3.7) the rate of nucleation is

< / BR>
Equation (3.11) shows that the temperature T, the degree of supersaturation C and the energy surfacesldetermine the rate of nucleation.

Reordering equation (3.11), with J equal to one embryo, so that LnJ equal to zero, we will have

< / BR>
Substituting the values of various parameters, we can estimate the critical supersaturation required for the spontaneous formation of nuclei. As a rule, in the process of growing use saturation is ~ 4.

The rate of nucleation depends to a significant extent ottsa natural finish areas, which initiate the process of nucleation. This process is also stimulated by the presence in the mould certain areas with locally high saturation (for example, near a cooling surface or on the surface of the liquid phase), the presence of cracks and crevices in the walls of the mold, as well as impurities in the solution, because the presence of a suitable foreign body, or a corresponding surface causes the nucleation in the solution smaller than that required for a spontaneous process. The total change in free energy associated with the formation of critical nuclei in terms of heterogeneous nucleation of Gget*must be less than for homogeneous nucleation (Ggom*), i.e.

G*gom= G*get, (3.13)

where the multiplier is less than one.

Consider now the process of nucleation of the crystalline phase from a liquid in the presence of the solid phase (Fig. 2). If the embryo of radius r forms a contact angle with the solid body and if we denote byclthe energy of the interface between the crystalline phase C and the liquid L throughslthe energy of the boundary between the surface of the solid body of the respective expression:

sl=cs+clcos.... (3.14)

or

< / BR>
Then we have

< / BR>
The multiplier can be expressed as

< / BR>
Then, ifis 180othe function cos is equal to minus unity, and equation (3.13) takes the form

G*get= G*gom. (3.17)

When lies between 0...180ohave less than 1, therefore,

< / BR>
At zero are equal to zero, then

G*get= 0.

Thus, when G*getzero energy for heterogeneous nucleation is the same as that required for homogeneous nucleation. In this case, there is no affinity between the surface of this crystalline solid body and solid body. In the case of a partial affinity, when greater than zero and less than 180othe birth easier. With full affinity ( zero) in the solution is not formed germ.

Because heterogeneous nucleation of Gget*less than or equal to G, it is easy to see [compare with equation (3.12)] that the nucleation takes place when the solution smaller than that required for spontaneous nucleation" [8].

For approximate quantitative characteristics can be calculated critical R is = 4,51022(the concentration of carbon atoms in the growing crystal and the melt bitumen when the carbon content in the bitumen 80%). Substituting these numerical values, find the critical radius of the diamond crystal r*= 22,510-8see If these settings are critical free energy Gibbs

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Substituting numerical values, find G = 1,0510-16J. This is the energy that is released during the formation of crystalline critical germ radius. Critical embryo with defined above radius contains in its volume 9000 carbon atoms. It is easy to determine that the average molecular weight of asphaltenes, turning into a diamond equals 750. The energy released during crystallization, one mole of the diamond, 7 kJ/mol. In reality, however, this energy decreases significantly with regard to heterogeneous factor f (), since the volume of the embryo critical size is not a sphere with radius r*and a spherical segment. From these elementary calculations obtained is acceptable, from the point of view of the implementation of this method, the quantitative characteristics of diamond crystallization. In these calculations is the value of the surface energy, which separates the molten bitumen from the growing crystal. However, in formasa energy, which has a construction material melt bitumen resins and asphaltenes. In fact the way it is, if you look at the end products of thermal degradation of the bitumen. The enthalpy of formation of these products [32, S. 62] H, kJ/mol is:

Graphite (monocrystalline) - 0

Pyrocarbon - 1,0

Diamond is 2.51

The glass carbon and 5.36

Cox - 8,08

Coke and graphite are products of homogeneous process, and pyrocarbon, diamond and glass carbon products of heterogeneous mechanism. All the difference in the heterogeneous mechanism of these products that they grow or completely devoid of hydrogen surface or on a surface partially covered with hydrogen. All of these products contain different amounts of hydrogen. The diamond in its composition contains hydrogen as an impurity, other products contain significant amounts to 8% by weight (Cox). This fact indicates that the external conditions of their education affected their inner content.

System (melt bitumen-catalyst) tends to equilibrium, destroying adsorption by such a large surface energy in 5-10 j/m, but the adsorbed asphaltenes and resins, the surface energy of 0.025-0,031 j/m, lowering your energy to Maintain energy in 5-10 j/m, but with a critical germ diamond. The process of diamond growth phase may continue if the saturation near the border growth is maintained in the required interval. In this way the growth of diamond crystals from the liquid phase (bitumen), which according to current data is microheterogeneous dispersion liquid [9, 10, 11].

The complex composition of the bitumen, which consists mainly of components such as asphaltenes, resins and high molecular weight hydrocarbons (oil). Most of these components are determined by the intrinsic properties of the bitumen. Asphaltenes in bitumen is the most high-molecular hydrocarbons, in which are concentrated all contained in the oils of the metals V, Ni, Fe, Co, Mn, and others, most of the nitrogen, oxygen and sulfur [11, p. 8]. The asphaltene molecule consists mainly of carbon atoms (80-85 %), and the ratio of carbon atoms to hydrogen atoms of C: H ranges from 0.8 to 0.87. The content of heteroatoms (metals, oxygen, nitrogen, sulfur) is from 5 to 11-14% [9, 16]. Asphaltenes are products of condensation resins. It is established that these two components (resins and asphaltenes), under certain conditions, can transform into each other. For bitumen, resins, plasticizers are asphaltenes and have Blarney weight (500 - 1200), while the asphaltenes have an average molecular weight (900 - 6000) [9 C. 32]. Asphaltenes unlike resins when heated do not melt, but decomposes in the temperature range 175 - 240oC and the maximum amount of asphaltenes in the bitumen can be up to 40% [9] . Among all components of the bitumen of the most highly polar asphaltenes are, therefore, such a polydisperse solution as bitumen, is considered as the surfactant solution in hydrocarbons. It should be noted a very important factor, as the ratio12C/13C, equal 90,9 for bitumen [13, S. 106], and for natural diamonds this ratio is in the range from 89,55 to 91,55 (diamonds black diamond, X, variant) [12, S. 34]. All of these elements during crystallization go into the diamond as impurity elements. During crystallization of diamond increased pressure in the system will accelerate the growth of diamond phase as the reaction proceeds with a decrease in volume.

The well-known relation of chemical thermodynamics, where the equilibrium constant K of a chemical reaction depends not only on temperature but also on pressure, and constant temperature, the partial derivative of Gibbs energy on pressure expressed as [15, 19]

< / BR>
where V is the change of Gibbs energy in the reactions of decay and Opatov; K is a constant of the reaction equilibrium of the considered reactions; V - volume of solution in thermal decomposition of the heavy oil feedstock.

As follows from theory of absolute reaction rates, the rate of densification and crystallization, and these reactions we consider, which contain the decay reaction as a continuous mechanism, we can write:

< / BR>
In this ratio the value of V*there is a change of the activation volume of the reaction path, which represents the movement of the energy surface. The change in activation volume, which is approaching the reaction system, is expressed as the ratio

< / BR>
where is the activation volume of the reaction solution of heavy hydrocarbons, and V0- initial volume of the solution. In the activation volume Vxas a result of condensation increases as the number of asphaltenes, and the molecular weight of asphaltenes [9, 11, S. 38-40], in accordance with this movement increases the density of the solution due to negative changes V*.

In accordance with the provisions of the modern theory of these changes are taken into account

V*= V*m+V*r0. (3.22 is complex and fragmented. This situation can be considered as a transition resins asphaltenes, and the change in molecular weight asphaltenes. The second component of equation (3.22) V*r0- less than zero - change in the volume of solvent accompanying the transition to the activated complex [15, S. 243] . Both values V*mand V*r0less than zero and, respectively, V*less than zero, then the condensation reaction and crystallization of the diamond will be much faster if the pressure in the system. Carrying out the reaction to a final point, we get the reaction product - coke - under homogeneous conditions in the heterogeneous mechanism will receive a crystalline carbon-diamond.

In natural conditions betonomeshalki rocks are mostly dolomite, limestone and peschaniki [9, 16]. These rocks serve as catalysts for crystallization of the diamond.

Adsorption of components of the bitumen on the surface of these rocks, which undergo a series of significant transformations [9; 11, C. 56]. The pores of these minerals penetrate components of bitumen with a relatively low molecular weight. On the contrary, the hydrocarbons with a relatively high molecular weight, as resins and asphaltenes, adsorbed on the external surface is a mask, reaching 50% by weight of the weight of the breed. Thus, the film of bitumen covering the external surface of the considered mineral mainly composed of resins and asphaltenes, which are the most polar components of the bitumen.

When heated, such betonomeshalka rocks to temperatures of 400-600oC will be exposed to the processes of dehydrogenation, disproportionation and polycondensation; [11, 14), which has a light steam and gas hydrocarbons and hydrogen. The evolving hydrogen in atomic form, and molecular will absorb betonomeshalki rocks. The absorption of hydrogen occurs in the form of chemisorption, i.e., in atomic form. Indeed, experimental evidence to confirm this statement of chemisorption of hydrogen on the surface of the minerals. It is found that hydrogen has significant permeability in quartz, for example at 500 K the permeability coefficient of hydrogen

h= 0,010810-15molm/Spa, (3.23)

and the diffusion coefficient of hydrogen

DH= 1,310-12... m/c, (3.24)

at a temperature of 750 To these values increase accordingly

H= 0,17610-15molm/MSPA (3.25)

DH= 310-11... m2/c. (3.27)

How kind is vodorodopronitsaemosti occurs with increasing temperature. At the same time, the permeability of hydrocarbon gases emitted in the process of dehydrogenation, for example, methane in the same quartz at 750 K, the diffusion coefficient has a value of

= 610-22, (3.27)

which is eleven orders of magnitude lower than hydrogen [17, S. 119-120]. Data on the chemisorption of hydrogen on the oxides under the conditions of dehydrogenation show that the adsorption of hydrocarbons (paraffins, olefins) is less than the adsorption of hydrogen. So, when 500-700oC hydrogen chemisorbents catalyst and retained in the reactor [17] . Thus, the dehydrogenation reaction is accompanied by the chemisorption of hydrogen on the surface bitumoemulsion minerals under consideration, leads to the formation of a heterogeneous surface, on which the possible emergence of centers of crystallization of the diamond.

Emitting paragators hydrocarbon condensation occurs bitumen and lowering of free energy. From the data of thermal analysis method TDA (differential thermal analysis) [18, S. 351] various grades of bitumen, it follows that in the heating process there are several endothermic effects and one exothermic effect. Endothermic effects are characterized by softening, melting, gas is C melt and secondary smelting, which is also accompanied by gas evolution. For ecoeffect it is characteristic that in this temperature region solidification takes place and the cessation of gas evolution. This is a very important moment in thermal destruction of solid hydrocarbons. In this moment there is a seal bitumen, accompanied by an increase as the molecular weight of asphaltenes and themselves asphaltenes [9; 11, C. 39]. Increase the percentage of asphaltenes is due to the resinous components of the bitumen. Described ecoeffect refers to the asphalt and asphaltites, which is in the same temperature range 300-400oC. the Resulting surface layer on the particles of the considered minerals can be expressed schematically in accordance with [19, S. 234]

V<---R--->S--->C.

In this scheme reflects the process of formation of coke, which is formed as a step-wise process for homogeneous reactions. When the reaction proceeds in a heterogeneous mechanism, the reaction is crystalline carbon (diamond). Heterogeneous reaction path before us, is characterized monoclonal coating the surface of minerals hammarbyhamnen hydrogen. Such surfaces have qualitatively different characteristics than the surface R is Yes changes the surface charge on the ZnO crystals.

It should be noted that the density of surface States increases to 1013cm2due to the hydrogen donor. Due to this increase of the surface density of electrons decreases the work function [20, S. 83]. These newly acquired properties of a surface by chemisorption of hydrogen creates a qualitatively different surface. On such a surface it is possible adsorption with the formation of purely covalent bonds.

As follows from the text of the description, the main characteristic of the claimed method of diamond crystallization is that in the process of thermal decomposition of the components of the bitumen in the presence of catalysts on the surface of the latter, chemisorbents released hydrogen, forming hemosorption the surface on which the crystal growth of carbon-diamond.

To address this question was experimental setup Fig. 4, which schematically shows:

1 - heated container with molten bitumen;

2 - Nickel membrane sensor hydrogen;

3 - copper membrane sensor hydrogen;

4 - thermocouple HC;

5 - glass vacuum valves;

6 - glass thermostatic bulb;

7 - gauge availability of hydrogen from explosimeter With the intelligent crane;

10 - vacuum pump NVR-DM.

The container 1, which melts the bitumen to a predetermined temperature 340-420oC, was made of steel 18CR10NITI volume of 2 liters, a height of 200 mm and a diameter of 110 millimeters. The outer cylindrical surface of the container has a heater (Fig. 1 is not shown).

Membrane sensors for hydrogen 2 (Nickel) and 3 (copper) were performed in the form of cylinders with a diameter of 16 mm, a wall thickness of 0.15 mm and a length of 230 mm. To one of the ends of the sensors were welded copper tube with an inner diameter of 4 mm, and the second end sensors brew relevant internal inserts. In position 5 illustrates a typical vacuum glass valves. The next element of the vacuum fasting is temperature-controlled vacuum vessel 6 with a volume of 700 cubic centimeters, which were mounted to the recording of the hydrogen sensor 7 explosimeter CTX-17-8 and the sensor 8 residual pressure (PMT-M-1) from vacuumer WT-003. thermostatic bulb 6 connected vacuum rubber hose through the three-way vacuum glass valve 9 to a vacuum pump 10 of the type NVR-DM.

All vacuum system was pumped up to full Degas,33 PA, then cut off the vacuum pump three-way valve 9 and made the calibration of the hydrogen explosimeter, whose sensitivity was reached 400 ppm.

During the experiment vodorodopronitsaemosti sensors 2 (Nickel) and 3 (copper) vacuum system was pumped to a residual pressure of 13.3 PA, then cut off the sensors vodorodopronitsaemosti 2 and 3 from the vacuum system. Then continued pumping system to a residual pressure of 1.33 PA, after which they cut off the vacuum line through the three-way valve 9 from the bulb 6. The next step in the experiment was carried out by immersion sensors vodorodopronitsaemosti 2 and 3 in the melt bitumen, in the container 1 at a temperature of 340oC. the temperature of the melt bitumen has chosen not at random, but from the experimental data. When the temperature of the melt bitumen 380-420oC is the rapid growth of diamond film on the side surface of the Nickel membrane sensor 2. If the shutter speed is within one hour of sensors 2 and 3 in the melt bitumen, and then the sequential opening of the shut-off valves 5 and registered readings of hydrogen explosimeter 7, the readings of which has not been changed. At this point of time the displacement of the Nickel sensor 2 from the diamond film by polishing with diamond paste followed by elektrodinamicheskoi and the experiment was repeated. A similar operation was performed with a copper sensor 3, which was only the growth of graphite-like film that is easily removed with petroleum ether. In a further experiment the bitumen temperature of the melt was lowered to 340oC to the process of growth of diamond film on the side surface of the Nickel sensor to extend in time. A series of experiments was registered penetration of hydrogen from the melt bitumen through the membrane of the Nickel sensor 2 at the level of 700 ppm on the testimony of hydrogen explosimeter 7. A similar experiment was performed with a copper sensor 8, the results of which were negative. After 2 hours of immersion of the membrane sensors 2 and 3 in the melt bitumen, the latter was removed and washed in gasoline B-70. The Nickel sensor were recorded diamond film thickness of 25-30 μm, while at the copper sensor all the film is easily removed by this solvent, and the sensor has got its original form. After washing sensors 2 and 3 from the remnants of bitumen system was flushed with atmospheric air to remove hydrogen from the system and re prepared to experiment.

The Nickel sensor 2 diamond ocherednoi experiment showed a negative result on vodorodopronitsaemosti sensors 2 and 3. On the basis of this factual material, we believe that experimental confirmation of the occurrence khemosorbirovannykh the surface of the catalyst Ni (membrane probe) we believe proven.

The permeability of hydrogen is only possible in the form of chemisorption, and it indicates that on the inlet side of the membrane of the sensor surface is hemicorporectomy nature of hydrogen. It should be noted that any character of the input surface of the membrane, if the membrane surface is covered with oxide (NiO), this surface is easily reduced with hydrogen, which is present in abundance in the surface layer. The restored surface Ni will chemosensitivity hydrogen, where the growth of diamond. If the surface is not completely covered hammarbyhamnen hydrogen, her growth is possible, but not diamond, and glass carbon or pyrocarbon. Therefore, the catalysts do not require high purity surface and can be used repeatedly. Consider qualitatively the physical processes that occur during crystallization of diamond from solid hydrocarbon-type bitumen. As the most important aspect of diamond crystallization is released hydrogen is die [21, 22].

"The process of penetration of molecules of hydrogen through metals includes several activated stages: dissociative chemisorption, the transition from the adsorbed state in absorption (dissolution), diffusion in the volume of metal.

The hydrogen atoms in the gas phase have increased in comparison with molecular hydrogen potential energy of ~ 2 eV due to the rupture of a chemical bond in the hydrogen molecule ~ 4 eV. This increased potential energy is released at the moment of contact of the atom with the metal surface (the heat of chemisorption in the system N---Fe Q is equal to 133 kJ/mol, in the H---Ni, Q is equal to 125 kJ/mol [22, 23]), and proceeds mainly in the vibrational energy of the surface metal atoms. For atomic hydrogen, the process of dissolution will always ectothermic."

Chemisorption of hydrogen can have a significant impact on the work function of metals. In some cases, when the saturation of the surface with hydrogen, changing the work function is almost 1 eV, but in most cases the change is not greater than 0.4 eV, while the sign of the change can be both positive and negative [22, 25]. This is an important energy characteristics of the surface, as between RA khemosorbirovannykh metal surface,

N is the Avogadro's number, a is the lattice parameter of the metal.

When considering the emerging border khemosorbirovannykh metal surface consisting of polycondensation film of bitumen, gradually turning into a crystalline form of carbon is diamond.

The evolving hydrogen from a solution of bitumen covering the grains of the catalyst, and difundir through a film of bitumen to the surface of the catalyst will be hemoderivates on the surface of metal catalysts. At the same time if the surface is adsorbed carbon, it is removed from the surface by hydrogen, as the latter has strong reducing properties.

In the surface layer of the metal grains of the catalyst flow as chemisorption processes, and the processes of absorption of hydrogen atoms. As a result of these processes forms a transition zone in the field of liquid bitumen, where the concentration of hydrogen, CHtends to zero, and from the metal surface of the catalyst CHtends to unity, i.e. when the surface is completely covered hammarbyhamnen hydrogen. Thus arises the driving force of the crystallization process.

Formed in the diffusion layer thickness is Anna hydrogen surface of the metal-catalyst. Since the free energy of the solution of bitumen can only be reduced in the process of thermal degradation, adsorption of carbon is exothermic process. Released heat during chemisorption of hydrogen QHand released heat during adsorption of carbon QCwill be

Qr= QH+QC, (3.30)

where through Qridentified total reaction heat of crystallization, which is also the driving force of the crystallization process.

Now, when uncovered physical mechanism of crystallization of the diamond, you can go to the kinetic description of the crystallization process, described in the paper, we will highlight significant moments [8, S. 92].

"When growth is severely limited by bulk diffusion, mass flow Jmsolution volume of solution with a concentration of CCcarbon due to bulk diffusion and drift diffusion flux and is given by the expression.

< / BR>
where x is the distance from the face of the crystal, andsthe density of the solution.

The growth rate is equal to

< / BR>
wherecthe density of diamond, C, and C0the concentration of carbon in the solution (x ) and on the crystal surface (x 0), respectively, a is the thickness of the diffusion layer. (3.32) the graph of V from

< / BR>
gives a straight line with slope

< / BR>
Therefore, ifcknown, we can determine (mass transfer coefficient):

< / BR>
The mass transfer coefficient Kdcan be obtained from the relation

< / BR>
where Nsh- the Sherwood number equal to

< / BR>
and NRe- Reynolds number

< / BR>
and Nscthe number of Schmidt

< / BR>
when this constant is assumed to be In 2 areas of the octahedra. In the equation for Reynolds number, Schmidt and Sherwood x - size of the crystal, is the kinematic viscosity, and W is the relative velocity between the crystal and the volume.

At low relative speeds, or in the case of stationary solutions, where the first term in the right-hand side of equation (3.36), have

< / BR>
At high relative speeds, when the significant second member when the mold is mixing), have

< / BR>
or when x is equal to the unit

< / BR>
In addition to mass transfer on the rate of growth may be affected by the release or absorption of heat at the surface, caused by the growth (equation (3.30)).

The dimensionless parameter, defined as

< / BR>
considers simultaneous mass transfer and heat. Here is the change partialviewname (bulk) diffusion becomes equal to the reaction rate without regard to the conditions of this process. "Indeed, since the crystallization process occurs within the moving boundary surface thickness , all processes belong to this boundary surface. From the surface into the volume of the solution can diffuse hydrocarbon radicals, combined-cycle components of thermal degradation of bitumen and hydrogen in atomic and molecular form.

In the heterogeneous mechanism of diamond crystallization can distinguish several stages. In the first stage of the process is education khemosorbirovannykh surface hydrogen on grain mold (Fe, Ni). On the metal chemisorption of hydrogen can be described theoretically [21, 22, 23].

"If the molecule H2adsorbed dissociatively at two positions, then the process proceeds

< / BR>
the rate of adsorption

< / BR>
The rate of desorption is always proportional to the amount of adsorbed substanceHso for them a fair expression

V-2= k-2H. (3.46)

From the formula (3.42) and (3.43) when the equilibrium rate of adsorption and desorption will get

< / BR>
Denote by a ratio equal , then the relation (3.44) we write

< / BR>
WhenHseeking to unity, all poverhnosti germ diamond. In the third stage of the diffusion growth of diamond crystals.

Set out the mechanism of diamond crystallization in comparison with the described analog, where quantitatively describes the adsorption mechanism without dissociation of hydrogen in the practical implementation does not lead to a positive result, as noted by the authors of theory [4].

Currently, the production of synthetic diamonds is carried out by the method of hydrostatic extrusion [3, 5] in the presence of metal catalysts (Fe, Ni, Mn, Co and other metals). The whole range of get SA this method is mainly used for machining various materials and diamond tools. In industries such as electronics and optics, get SA will not apply because of the unsatisfactory characteristics for these areas of industrial production.

The present invention fully solves all tasks that require industry from synthetic diamond. Moreover, the proposed method of diamond crystallization allows you to get a diamond with any predetermined properties, which are not able to offer industry none of the known methods crystallization during crystallization of diamond from the size of the critical embryo.

2. In Fig. 2 shows a vector diagram of the surface forces in the process of diamond crystallization. Thus vectors of the surface forces, denoted bycl,cs,slcorrespond to the notation adopted in the text of the description, respectively, by cl,cs,sl.

3. In Fig. 3 shows the dependence of molecular weight of bitumen components in the heating process. In this case the curve 1 corresponds to the oils, curve 2 corresponds to silicagel resins, curve 3 corresponds asphaltenes.

4. Photo 1 (Fig. 4) shows the crystals obtained by the crystallization of the oxides corresponding to the natural environment.

5. Photo 2 (Fig. 5) shows the spherical crystals obtained on the oxides corresponding to the natural environment.

6. Photo 3 (Fig. 6) shows the crystals obtained with the use of metal catalysts of Fe and Ni (powders).

7. Photos 4 and 5 (Fig. 7 and 8) shows filamentary crystals obtained by the use of metal catalysts of Fe and Ni (powders).

INFORMATION CONFIRMING THE POSSIBILITY OF CARRYING OUT THE INVENTION

Explain the principle of diamond crystallization was n is a natural limestone and the mixture of these minerals in varying proportions. Moreover, an experiment was conducted with road asphalt surface, which after prolonged use (approximately 10 years) were taken apart. This is the road surface before the experiment were ground and laid in the container 70, on Top of this reaction bituminous rocks was filled powdered zeolite for sealing the vaporous and gaseous hydrocarbons formed during thermal degradation of bitumen.

The results of experiments obtained with round diamonds both transparent and milky white in color (photo 1, 2). Thus was proven set forth the principle of diamond crystallization, which is implemented in the natural environment in kimberlite pipes.

In the heterogeneous crystallization of diamond from high-temperature solution of bitumen in the catalysts from natural minerals discussed above, there is a very low yield of diamond crystals, no more than 1% of the parent solution or 0.2% by weight of the bituminous rocks. This is the maximum yield of crystals, registered in experiments with this type of catalysts and bitumen, which did not undergo heat treatment.

Technical Rea the liquids called for improved catalysts. Conducted a search for the most effective catalysts, which does not cover all the diversity of existing catalysts allowed us to find more effective. These catalysts were fine powders of iron and electrolytic Nickel. Experiments using iron powders and electrolytic Nickel in varying proportions helped to increase the yield of diamond crystals up to 60% on raw materials (bitumen).

In experiments with these catalysts we used:

iron powder Agrocomplex - 0.1 mm;

Nickel powder POE 1-0,05 mm

A mechanical mixture of powders were prepared both in volume and in weight ratio. The volumetric ratio corresponded to the following proportions:

60% by volume took metal powder, Fe;

40% by volume took a metal powder of Ni.

Taken in this ratio, the powders were thoroughly mixed. Similarly were prepared metal powders in weight ratio.

Significant differences in the course of the experiments, between volumetric and gravimetric methods from a technical point of view we are not found. The prepared catalyst method vol for two hours.

As a solid hydrocarbon was taken bitumen grade BND. Pre-bitumen were subjected to 2-hour heating at a temperature of 410 degrees Celsius. The temperature of thermal processing of bitumen was chosen not by chance, but from the experimental data by coking a heavy oil feedstock [11, 14] . As mentioned in section 3, when this temperature is the decomposition of bitumen components, greatly increases the amount of asphaltenes and reaches its maximum (Fig. 3). Quality control the amount of asphaltenes was carried out by fluorescent method on the microscope MIN-8. On a glass slide was applied film of bitumen, the last heat treatment of the chloroform extract. According to the intensity of fluorescent light, which has a white-blue color of varying intensity depending on the party of bitumen and quality of heat treatment. Thus, the prepared raw materials and selected based on the maximum luminescence intensity were taken for experiments. Usually, after 2 hours of heat treatment of bitumen his weight was no more than 50-55 percent of the original.

A portion of the heat-treated bitumen in the amount of 100 grams was placed in a container which predstavljeno 10 millimeters. On the outer surface of this cylinder was placed three electric heater with a capacity of 750 Watts.

Bitumen is placed in the container was heated until complete melting. Into the molten mass of bitumen was filled metal catalyst of the metal powders of Ni and Fe in the above volume ratios. The number of sleeps catalyst was 200-240 grams. Sleeps catalyst was mixed mechanically with molten bitumen to a state of homogeneity. On top of this reaction mass was filled additional catalyst of the same composition in the amount of 400 grams to create excess pressure in the reaction zone of the container, and 10 mm from the bottom of the container was set thermocouple HC for recording potentiometer temperature in the crystallization zone. This was the end of the preparation process for conducting the reaction of diamond crystallization.

Prepared container mould was connected to a voltage regulator, which regulate the heat of crystallization mass. Maximum temperature does not exceed 550 degrees Celsius. When such a predetermined temperature occurred crystallization of diamond. The time for reaction limited 4 is elementally by, which was equal to 6 hours. Additional exposure at a given temperature did not lead to significant changes in the final result.

In the performed series of experiments, the output of the diamond crystals was 40-50 percent by weight of the reaction of bitumen. In absolute terms, this amount corresponded to 40 to 50 grams of diamond crystals in the raw form. This value of the output of the diamond crystals was robust and is average in experiments.

Removing the diamond crystals after the experiment was carried out by the method of magnetic separation, which was preceded by the operation of mechanical crushing the sintered crystallization mass. At the end of the process of magnetic separation of metal catalyst again sifted in a sieve and subjected to annealing at a given temperature is 550 degrees Celsius in a muffle furnace. The time of annealing does not exceed 1.5 hours, after which the container was cooled with a muffle oven. Refrigerated container was removed and its contents were again subjected to mechanical crushing and magnetic separation. The result of this operation is again removed the diamond crystals in the amount of 10-15 grams. When such a t is conducted series of experiments was received over 3,000 carats of diamonds of various fractions from 100 μm to 1000 μm. It should be noted that the fraction of diamonds less than 100 μm is extracted. The maximum size of the diamonds extracted in the process of conducting experiments did not exceed 3.5 mm. The task of extracting the maximum size of the diamond crystals during the experiments were not set.

To conduct the research was obtained crystals of diamonds processed in a mixture of sulfuric acid and nitric standard industrial method. When processed in this way was observed loss in weight of the extracted crystals. Changing the weight of the crystals reached 15 percent of the original. This fact is natural, since the extracted diamond crystals were covered with a layer of graphite, which is present as ultra-fine powder.

The density of diamond crystals was in the range of at 3.35 grams per cubic centimeter (milky-white variety, foam) to 3,54 grams per cubic centimeter (clear crystals). The refractive index, measured according to the method of C. N. Lodochnikova, was equal to 2.4. To measure more exactly the argument the authors was not possible.

When conducting comparative studies of the obtained diamond crystals with the natural, and the obtained crystals in the groundmass lumines cent of white-blue color upon excitation by light of a mercury lamp DRSH-250, passed through an ultraviolet filter UFS-Z. In addition, we also detected spontaneous polarized luminescence, which is typical only for natural crystals. In the study of whiskers (photo 4, 5) luminescence is observed in all threads (white-blue glow). Especially intensively lumines cent of an individual fiber light blue glow. Whiskers diamonds obtained in the experiments do not have spontaneous polarized luminescence, at least we could not find. The thread length, extracted from the chaotic weave, has reached more than one meter. The diameter of the filaments 35 μm as average.

In the study of crystals in polarized light (crossed Nicoli) found crystals with inclusions of type diamond diamond. While the extinction of the parent crystal is accompanied by the enlightenment of crystal inclusions. As in the study of photoluminescence method, and polarization method different from natural diamonds were found. This actual experimental material oala, i.e., the mother liquor of carbon.

The described technology of diamond crystallization allows no significant economic costs to organize the production, which will fully satisfy the needs of all sectors of material production in this unique material. In the technological aspect of the implementation of the stated principle of diamond crystallization is possible by various methods, for example by the method of direct static compaction with the use of catalysts, intensely absorbing hydrogen in the form of chemisorption. By this method it is possible to get the diamond crystals with predetermined properties, shape and size, which is essential for various industries that use diamonds. In the existing production of synthesis of diamond with his cameras high pressure and high temperatures as technological stages of production become excessive in light of the above. The exclusion of these elements of production and replacement of conventional molds only greatly reduce the cost of production of diamonds natural groups according to the classification.

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How heterogeneous liquid-phase crystallization of diamond by the interaction of hydrocarbons with a catalyst, characterized in that a hydrocarbon is used dehydrogenated components of the bitumen and the adsorption process is carried out by the interaction of these components with the hydride surface catalyzers macromolecular components of the bitumen-resins and asphaltenes with subsequent adsorption transition in the crystalline state the diamond.

 

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FIELD: carbon materials.

SUBSTANCE: invention concerns manufacture of diamond films that can find use in biology, medicine, and electronics. Initial powder containing superdispersed diamonds with level of incombustible residue 3.4 wt %, e.g. diamond blend, is placed into quartz reactor and subjected to heat treatment at 600-900оС in inert of reductive gas medium for 30 min. When carbon-containing reductive gas medium is used, heat treatment is conducted until mass of powder rises not higher than by 30%. After heat treatment, acid treatment and elevated temperatures is applied. Heat treatment and acid treatment can be repeated several times in alternate mode. Treated powder is washed and dried. Level of incombustible impurities is thus reduced to 0.55-0.81 wt %.

EFFECT: reduced level of incombustible impurities.

4 cl, 3 ex

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