WO2015034399A2

WO2015034399A2 - Method of obtaining a high-hardness carbon material and material obtained by said method

Info

Publication number: WO2015034399A2
Application number: PCT/RU2014/000654
Authority: WO
Inventors: Vladimir Davydovich Blank; Vladimir Zal'manovich MORDKOVICH; Sergej Alekseevich PERFILOV; Michail Yur`evich POPOV
Original assignee: Federal State Budgetary Institution "Technological Institute For Superhard And Novel Carbon Materials"
Priority date: 2013-09-03
Filing date: 2014-09-01
Publication date: 2015-03-12
Also published as: WO2015034399A3; RU2543891C1; RU2013140598A

Abstract

The claimed invention relates to a method of obtaining hard, superhard and ultrahard construction carbon materials used in aerospace and defense industries, as well as in processing hard and superhard materials. The proposed method of obtaining very hard carbon materials, comprising the exposure of a carbon-containing material to pressure and temperature, is characterized by the addition of a sulfur-containing compound, e.g. carbon disulfide, to the said carbon-containing material. The obtained high-hardness carbon material is characterized by its structure being formed by layers of fullerene molecules, 2-dimensionally polarized along the 2nd order rotation axis, said layers being bonded by covalent forces.

Description

Method of obtaining a high-hardness carbon material and material obtained by said method.

FIELD OF THE INVENTION

The invention relates to a method of obtaining hard, superhard and ultrahard carbon construction materials used in aerospace and defense industries and for treating hard and superhard materials.

STATE OF THE ART

By this time, an allotropic form of carbon called fullerene has been described, the same being used, inter alia, as an initial material to obtain diamonds ("The Fullerenes", edited by H.W. roto, J.E.Fischer, D.E.Cox, Pergamon Press, Oxford, New York, Seoul, Tokyo, 1993).

Fullerene is a molecule, in which atoms of carbon (60-240 in number) are interconnected in such a way as to form a hollow body of an almost spherical shape. Thus, for example, the fullerene C₆₀ molecule reminds of a football being formed with 20 hexagons and 12 pentagons. Interatomic distances in the fullerene C₆₀ molecule remain almost as short and strong as in a layer of graphite (i.e. graphene); the diameter of a molecule being about 0.7 nm.

A superhard carbon material and method of obtaining thereof are known, wherein an allotropic form of carbon namely fullerene C₆₀ is used as an initial carbon material (RF patent No 2127225, 1996).

Fullerene C ₀ is subjected to a pressure of 7.5-37 GPa and a temperature selected from the range of 20-1830°C in toroid type, Bridgeman anvil type and other high pressure apparatuses. Under the exposure of the initial fullerene to pressure and temperature, polymerization of fullerene molecules or fragments of molecules occurs. Compact samples of the material possess high mechanical and electrophysical properties.

Below are sources which describe methods of obtaining hard, superhard and ultrahard carbon construction materials (high-hardness carbon materials) from molecular fullerene C₆₀ and the materials themselves.

(RF patent # 2078033 1997; RF patent # 2096321 1997; patent # 2108288 1995; US 6245312 2001 ;V.D. Blank, V.N. Denisov, A.N. Ivlev, B.N. Mavrin, N.R.Serebryanaya. G.A. Dubitsky, S.A.Sulynov, M.Yu. Popov, N. Lvova, S.G. Buga and G.Kremkova. Carbon, V.36, P 1263-1267 (1998); Structures and physical properties of superhard and ultrahard 3D polymerized fullerites created from solid C₆₀ by high pressure high temperature treatment. V.D. Blank, S.G. Buga, N.R.Serebryanaya, G.A. Dubitsky, B. Mavrin, M.Yu. Popov, R.H.Bagramov, V.M.Prokhorov, S.A.Sulynov, B.A. Kulnitskiy and Ye.V.Tatyanin. Carbon, V.36, P 665-670 (1998)).

For the most part, methods of obtaining the above-mentioned materials consist in the following:

The initial molecular C₆₀ is subjected to pressure and temperature. Ultrahard (surpassing diamond in hardness) fullerite is obtained under shear conditions, a 18 GPa pressure and room temperature (in a shear diamond anvil cell (SDAC)) or under a 12.5-13 GPa pressure and a temperature in the range of 600 - 2000°C (in a toroid type hard-alloy cell); superhard (having hardness between cubic BN and diamond (on average 150 GPa for Ila diamond)) fullerites obtained under a pressure of 9 GPa when heated to 500-900°C, and hard (with hardness of between 10 GPa and cubic BN (50 GPa)) disordered phases are obtained under a pressure of 7-8 GPa when heated to 600-1600°C (in a toroid type hard-alloy cell). As a result, high-hardness materials (possessing hardness of above 10 GPa) are obtained.

The obtained materials have been investigated as follows.

Ultrahard fullerite has been examined by Raman scattering spectroscopy (RS). The Raman spectrum of ultrahard fullerite is characterized with broad lines. Besides a broad line in the 1,550 cm^'1 region (C₆o tangential modes), Raman spectra of ultrahard fullerite have a broad line in the 500 cm^"1 region, which fundamentally differentiates it from ta-C, a-C and graphite.

Indeed, the 1,550 cm^"1 band is located in the frequency region characteristic of the aforementioned carbon states, which differentiate themselves by the ratio of sp² and sp³ bonds. Graphite contains only sp bonds forming hexagons, and the respective Raman lines of graphite (1 ,355 cm^"1 1,580 cm^"1) are absent in the spectra of ultrahard fullerite. Diamond-like ta-C and a- C contain both types of bonds, with the presence of sp bonds being the reason for the displacement of the 1,580 cm^"1 band into the frequency region below 1 ,575 cm^"1.

Therefore, to make more definitive conclusions on the possible structure of ultrahard fullerite, examination of the entire spectrum region is essential.

The feature of Raman spectra of ultrahard fullerite distinguishing it from the spectra of other known carbon materials containing sp² and sp³ bonds consists in the presence of a broad 500 cm^"1 band that is not present in diverse carbon materials having, in the high-frequency part of the spectrum, a band of about 1,550 cm^"1. The 500 cm^"1 band was formed as a result of broadening and overlapping of C₆₀ frequencies at 268, 350, 443, 530, 600, 700 and 760 cm^"1.

The hardness of ultrahard fullerite exceeds that of diamond.

Superhard fullerite has also been characterized by Raman scattering spectroscopy. Raman lines of the initial C₆₀ are present in superhard fullerite spectra. However, those lines are broadened and displaced to the high-frequency region for symmetric vibrational modes of Ag (490→530 cm^"1) and for the Hg mode (431— >443 cm^"1), while for tangential modes, they are displaced to the low-frequency region ( 1468→1450 cm^"1 and 1574— >1560 cm^"1).

The broadening of the lines, their displacement and re-distribution of intensities is caused by polymerization of C₆o molecules under pressure. The spectrum of superhard fullerite is different from the spectra of the initial C₆₀ in that there are peculiarities near 350 and 600 cm^"1 and a shoulder at 1300 cm^'1, which testifies to the violation of rules of selecting the initial fullerite, because that frequency region has lines in the phonon density of C₆₀ states.

The hardness of superhard fullerite is in the range from that of cubic BN to that of diamond.

Disordered phases (obtained under a pressure of 7-8 GPa while heated to 600-1600 C) are characterized by X-ray diffraction. Diffractrograms show broad diffusion peaks, but the shape of the peaks is not Gaussian, which indicates a set of inter-layer distances. The most intense peak is located within 3.31-3.38 A.

The hardness of disordered phases is within the range of 10-40 GPa.

It is known that high mechanical properties of materials produced from fullerene are determined by the formation of chemical bonds between fullerene molecules in all directions (so called 3D polymerization). Chemical bonds located along C₆₀ chains (ID polymerization) and along planes (2D polymerization) are formed at lower pressures than 3D polymerization. Therefore, 3D polymerization of C₆o occurs, more often than not, as a process of chemical bond formation between layers of 2D-polymerized C₆₀.

At this time, it is possible to obtain a very hard material with good mechanical properties only in high pressure apparatuses (7.5 - 15 GPa), wherein the strength of bonds between fullerene molecules is ensured during synthesis (determined by the formation of chemical bonds). The too high pressure of obtaining those materials is an obstacle to mass production thereof. The synthesis pressure could be reduced by means of using a catalyst, but no such catalyst is as yet known. To compare, the catalytic synthesis of diamond is performed under a pressure of about 5 GPa.

Besides, high pressure apparatuses known at this time (7.5-37 GPa) have small sizes; therefore they limit the size of a product that can be produced from the material obtained in such apparatuses.

The closest to the claimed method and material is the carbon material consisting of volumetrically polymerized molecules C₆₀ forming a tetrahedron, and a method of obtaining the same (US 6245312 2001; WO 98/16465; RU 2127225). That method of obtaining the material possesses though all the above-mentioned downsides.

BRIEF SUMMARY OF THE INVENTION

Thus, the purpose of this invention is the realization of the possibility to obtain high- hardness (hard, superhard and ultrahard) construction carbon materials on an industrial scale.

The objective of the invention is to create a method of obtaining high-hardness (hard, superhard and ultrahard) construction carbon materials by means of initiating the formation of 3D chemical bonds among the molecules of a carbon-containing material, and obtaining high- hardness carbon materials on the basis of that method.

DETAILED DISCLOSURE OF THE INVENTION

To solve that problem, a method of obtaining high-hardness carbon materials has been suggested that includes exposure of a carbon-containing material to pressure and temperature, characterized by the fact that a sulfur-containing compound is added to the carbon-containing material, and the treatment is performed under a pressure of from 0.2 to 12 GPa and a temperature of from 0 to 2,000 C.

According to research conducted by the present authors, it was found possible to pick out substances initiating chemical bonding between carbon-containing material molecules at sufficiently low pressures and temperatures (i.e. polymerization reaction catalysts). Besides the initiation of C₆₀ 3D polymerization (i.e. three-dimensional, where covalent forces bonding C₆o molecules are generated in all directions), such substance should be uniformly distributed over the volume of the initial material. If such initiator (catalyst) is uniformly distributed over the entire volume of fullerene, then the process of material formation (accompanied by the formation of chemical bonds) is expected to be steadier.

According to the authors' research, it may be a sulfur-containing compound selected from the group comprising carbon sulfide, or a compound out of the group of mercaptans, in particular, isoamyl mercaptan, or a product of interaction of a compound selected from the group of mercaptans with the elementary sulfur.

It was found that of that group, carbon disulfide CS₂ satisfied the above-said requirements in the most complete fashion. Indeed, under sintering the material decomposes with the evolution of elementary sulfur. (Tonkov EY, High Pressure Phase Transformations Handbook Vol. 1. Amsterdam: OPA; 1992). Thanks to high affinity to oxygen, sulfur atoms (after CS₂ decomposition) will form covalent C-S bonds with fullerene and transform the fullerene molecule into a chemical group, initiating, in turn, the formation of bonds with the surrounding molecules or other components of the material. Besides, CS₂ is a good solvent of molecular fullerene C₆₀ and, consequently, will easily penetrate into the molecular crystal of the initial C₆₀ Thus, the atoms of sulfur can be uniformly distributed over the space occupied by fullerene. Since such centers of initiation are uniformly distributed over the space occupied by fullerene, it means that ultimately an isotropic product may be obtained.

Given the above-said, molecular fullerene C₆₀ should be preferably used as a carbon- containing material. But the use of fullerene-containing fullerene soot as a carbon-containing material is also possible.

We also claim high-hardness carbon materials obtained by the claimed method, characterized by the fact that their structure is formed by layers of fullerene molecules, 2- dimensionally polarized along the 2^nd order rotation axis, said layers being bonded by covalent forces.

DESCRIPTION OF DRAWINGS.

The figures attached represent the following:

Fig. 1 shows pressure distribution in a sample of C₆₀ with the addition of CS₂ put under stress in a diamond cell. The diameter of anvils is 600 μιη. In the central area of the sample (from 270-th to 380-th μηι counting from the anvil's edge), shown with arrows on the figure, a phase transition is seen according to the above-said pressure distribution anomaly.

Fig. 2 shows the Raman spectrum recorded from the central area of the sample at the pressure of 8 GPa, corresponding to the Raman spectrum of ultrahard fullerite.

Fig. 3 shows the Raman spectrum recorded from the peripheral area of the sample at a pressure of below 8 GPa, corresponding to the fullerite phase which is not ultrahard.

Fig. 4 shows pictures of the anvil with a deformed section. When the anvils rotate, the sample begins slipping on the culet of one of the anvils, leaving furrows on the surface of the diamond in the central part of the sample where the ultrahard fullerite is formed.

Fig. 5 shows a detailed picture of the furrows formed due to plastic deformation of the diamond (the image is obtained with the help of a scanning electronic microscope).

EXAMPLES

The examples provided illustrate the invention without restricting it as to scope.

Example 1

Liquid carbon disulfide CS₂ is added to molecular fullerene C₆₀ in the amount of 0.1 ml CS₂ per 1 g of C₆₀ (a necessary quantity of CS₂ is poured into C₆₀ powder at the ambient temperature in air). The obtained mixture is ground in an agate mortar until an even consistency is obtained, and stressed in a shear diamond anvil cell (SDAC). The sample is stressed in the SDAC without a pressure-transmitting medium until a pressure of 10-12 GPa is reached in the center of the anvil. Pressure is measured by the method of piezo-spectroscopy according to the shift in Raman frequency of the stressed diamond anvil. Controlled plastic deformation is applied to the stressed sample by means of rotation of one of the anvils around the load application axis. In the case of the first order phase transition, the pressure radial distribution curves of the sample (stressed in the SDAC) develop step-like anomalies due to a leap in elastic modules and volume caused by phase transition. Since those anomalies are associated with the boundaries between different phases, a possibility arises to determine the first order phase transition pressure according to the pressure radial distribution curves of the sample. Additionally, structural investigation is performed by the method of Raman scattering spectroscopy.

Fig. 1 shows pressure distribution in a sample of C₆o with the addition of CS₂ put under stress in a diamond cell. The diameter of anvils is 600 μηι. In the central area of the sample (from 270-th to 380-th μηι counting from the anvil's edge), shown with arrows on the figure, a phase transition is seen according to the above-said pressure distribution anomaly, with the pressure in the central part of the sample, where the phase transition took place, being in the range of from 8 to 10 GPa.

Beyond the above-said Raman spectra region (Fig. 3) another fullerite phase is observed, which is not ultrahard.

When the anvils rotate, the sample begins slipping on the culet of one of the anvils, leaving furrows on the surface of the diamond in the central part of the sample where the ultrahard fullerite is formed (Figs. 4 and 5). The furrows are formed due to plastic deformation of the diamond. Fig. 4 shows a picture of the anvil with a deformed area.

Fig. 5 shows a detailed picture of the furrows (the image is obtained with the help of a scanning electronic microscope).

The ploughing of the diamond by a specimen of ultrahard fullerite is possible only where the hardness of the ultrahard fullerite exceeds that of the diamond. This experiment is a direct proof of the hardness of the obtained ultrahard fullerite being greater than that of diamond.

Thus, the obtained material may be characterized by Raman spectra and hardness as ultrahard fullerite. Investigations performed with the help of a transmission electron microscope have shown that the structure of the obtained material is formed by layers of fullerene molecules. 2-dimensionally polarized along the 2^nd order rotation axis, said layers being bonded by covalent forces.

The presence of carbon disulfide CS₂ in molecular fullerene C₆o in the amount of 0.1 ml CS₂ per 1 g of C₆₀ makes it possible to obtain ultrahard fullerite at a room temperature and under a pressure of 8-10 GPa. In that case, carbon disulfide CS₂ is a catalyst for the formation of covalent bonds between molecules of C ₀, and the hardness of the obtained sample exceeds that of diamond, similarly to ultrahard fullerite produced without the addition of carbon disulfide.

Example 2.

Carbon disulfide CS₂ is added to molecular fullerene C₆₀ in the amount of 0.1 ml CS₂ per 1 g of C₆o- The obtained mixture is ground in an agate mortar until an even consistency is obtained, and used for the fabrication of a series of specimens. For that purpose, the said mixture is loaded into a toroid type high pressure cell, stressed until the pressure of 3 GPa is achieved, and heated to a fixed temperature selected from the range of 600-1600 C with a fixed exposure time selected from the range of 0.1 - 180 sec at that temperature. Specimens were obtained at temperatures of 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500 and 1600 C with exposure times of 0.1, 1, 10, 30, 60, 120 and 180 sec. After destress, the obtained series of specimens is examined by X-ray diffraction, Raman spectroscopy and transmission electron microscope, and their hardness determined.

Structural examination has shown that the structure of the obtained material is formed by layers of fullerene molecules, 2-dimensionally polarized along the 2^nd order rotation axis, said layers being bonded by covalent forces.

The hardness of the obtained material is in the 10-70 GPa range.

Example 3.

Carbon disulfide CS₂ is added to molecular fullerene C₆₀ in the amount of 0.1 ml CS₂ per 1 g of C₆₀. The obtained mixture is ground in an. agate mortar until an even consistency is obtained, and used for the fabrication of a series of specimens. For that purpose, the said mixture is loaded into a cylinder-piston type high pressure cell, stressed until a fixed pressure of 0.2 or 0.5 GPa is achieved, and heated to the temperature of 1000 C with an exposure time of 30 sec. After destress, the obtained specimen is examined by X-ray diffraction, Raman spectroscopy and transmission electron microscope, and its hardness determined.

Structural examination has shown that the structure of the obtained material is formed by layers of fullerene molecules, 2-dimensionally polarized along the 2^nd order rotation axis, said layers being bonded by covalent forces. The hardness of the obtained (under the 0.5 GPa pressure) material is 10 GPa. The specimen obtained at the pressure of 0.2 GPa fell apart into fragments.

Example 4.

Carbon disulfide CS₂ is added to molecular fullerene C₆o in the amount of 0.1 ml CS₂ per 1 g of C₆₀. The obtained mixture is ground in an agate mortar until an even consistency is obtained, and used for the fabrication of a series of specimens. For that purpose, the said mixture is loaded into a toroid type high pressure cell, stressed until a pressure in the range of 2 to 4 GPa is achieved, and heated to a fixed temperature selected from the range of 800 - 1000 C with a fixed exposure time selected from the range of 10 - 180 sec at that temperature. After destress, the obtained series of specimens is examined with the help of a transmission electron microscope and X-ray photoelectron spectroscopy (XPS).

Without using CS₂, treatment of C₆₀ under such conditions results in the formation of tetragonal 2D structures. Polymerization takes place along the <1 10> fullerene cubic crystal, wherein C₆₀ molecules are oriented in respect of each other along the 2^nd order axis. At the same time, covalent sp³ bonds are formed with the length of ~0.15-0.16 nm. However, there remains van der Waals bonding between such layers, and no additional increase of pressure and temperature results in the formation of 3D polymerized structures, since C₆₀ destruction begins. In the event of the introduction in the process of catalyst CS₂ containing linear molecules S=C=S, these molecules decompose under thermobaric treatment at T = 450-500°C, which results in the formation of covalent bonds between 2D C₆o layers.

Since the length of the (C-S) bond almost coincides with the length of the covalent bond C-C, constituting 1=0.15 nm, it results in the formation of a 3D polymerized structure with a simple "cubic" lattice. It is confirmed by electronic microscopy data, where diffraction pictures are characteristic of the "cubic" symmetry with typical cell sizes of a=0.80 ± 0.03 nm, or a=1.6±0.1 nm. Such lattice constant corresponds to the length of 3D polymerized C₆o bond of 0.667 nm (C₆o molecule diameter) + 0.153 nm (interatomic bond length) = 0.82 nm.

An analysis of chemical bond states with the help of XPS spectroscopy of such specimens has shown that the ratio of sp² and sp³ bonds is ~10%±2%, which also corresponds to 3D polymerization along the 2^nd order axis. The presence of sp³-states has also been confirmed with the help of EELS. In the case of an ideally polymerized cubic structure, the amount of sp³ is 13.3%, which quite satisfactorily coincides with the experiment.

Thus, the structure of the obtained material is formed by layers of fullerene molecules, 2- dimensionally polarized along the 2^nd order rotation axis, said layers being bonded by covalent forces. Example 5.

Isoamyl mercaptan C₅HnSH is added to molecular fullerene C₆₀ in the amount of 0.1 ml of C₅Hi )SH per 1 g of C₆₀. The obtained mixture is ground in an agate mortar until an even consistency is obtained, and used for the fabrication of a series of specimens. For that purpose, the said mixture is loaded into a toroid type high pressure cell, stressed until the pressure of 3 GPa is achieved, and heated to a fixed temperature selected from the range of 600-1600 C with a fixed exposure time selected from the range of 0.1 - 180 sec at that temperature. Specimens were obtained at temperatures of 600, 700, 800, 900, 1000, 1 100, 1200, 1300, 1400, 1500 and 1600 C with the exposure times of 0.1 , 1, 10, 30, 60, 120 and 180 sec. After destress, the obtained series of specimens was examined by X-ray diffraction, Raman spectroscopy and transmission electron microscope, and their hardness determined.

The hardness of the obtained material is equal to 10-70 GPa.

Example 6.

Carbon disulfide CS₂ is added to fullerene soot in the amount of 0.1 ml CS₂ per 1 g of fullerene soot. The obtained mixture is ground in an agate mortar until an even consistency is obtained, and used for the fabrication of a series of specimens. For that purpose, the said mixture is loaded into a toroid type high pressure cell, stressed until the pressure of 3 GPa is achieved, and heated to a fixed temperature selected from the range of 600-1600 C with a fixed exposure time selected from the range of 0.1 - 180 sec at that temperature. Specimens were obtained at temperatures of 600, 700, 800, 900, 1000, 1 100, 1200, 1300, 1400, 1500 and 1600 C with exposure times of 0.1, 1, 10, 30, 60, 120 and 180 sec. After destress, the obtained series of specimens was examined by X-ray diffraction, Raman spectroscopy and the transmission electron microscope, and their hardness determined.

Structural examination has shown that the obtained material is partially amorphous, but still contains clusters formed by layers of fullerene molecules, 2-dimensionally polarized along the 2^nd order rotation axis, said layers being bonded by covalent forces.

The hardness of the obtained material is equal to 10-20 GPa.

Claims

WHAT IS CLAIMED IS:

1. A method of obtaining a high-hardness carbon material comprising the exposure of a carbon-containing material to pressure and temperature, wherein a sulfur-containing compound is added to the said carbon-containing material, and the said exposure is conducted at the pressure ranging from 0.2 to 12 GPa and a temperature of from 0 to 2000 C.

2. The method according to claim 1, wherein the sulfur-containing compound is carbon disulfide.

3. The method according to claim 1, wherein the sulfur-containing compound is a compound selected from the group of mercaptans, or a product of interaction of a compound selected from the group of mercaptans with elementary sulfur.

4. The method according to claim 1, wherein the carbon-containing compound is molecular fullerene C₆₀.

5. The method according to claim 1, wherein the carbon-containing compound is fullerene soot.

6. A high-hardness carbon material obtained by the method according to 1, characterized by the fact that its structure is formed by layers of fullerene molecules, 2-dimensionally polarized along the 2^nd order rotation axis, said layers being bonded by covalent forces.