DE102004026976A1 - Producing a nanocrystalline diamond material with rod-shaped crystals, e.g. useful as a cutting, grinding or polishing material, comprises heat treating fullerene at high pressure - Google Patents

Abstract

Producing a nanocrystalline diamond material with rod-shaped crystals comprises heat treating fullerene at 1500-2300[deg]C and 15-25 GPa for at least 45 minutes. Independent claims are also included for: (1) diamond material produced as above in which the crystals are aggregated together; (2) metalworking tool with a working surface comprising rod-shaped nanocrystalline diamond crystals; (3) pressure stamp for a high-pressure cell comprising rod-shaped nanocrystalline diamond crystals.

Description

The The present invention relates to a process for the preparation of rod-shaped nanocrystalline Diamond as well as applications of this material.

In an article by Shenderova et al., NANO LET-TERS 2003, Vol. 3, No. 6, 805-809 theoretically calculated mechanical properties of diamond nanorods, i. of rod-shaped diamond crystals with diameters of a few 10 μm and lengths of a few 100 μm, compared with corresponding properties of carbon nanotubes. These calculations indicate that diamond nanorods in terms their tensile strength and breaking strength superior to nanotubes of the same diameter are. The authors therefore consider it a worthwhile task procedure for the synthesis of rod-shaped nanocrystalline To look for diamond. It is noted that since the 60s methods are known that allow to use diamond sticks Diameters of up to 10 μm and lengths of several 100 μm However, these techniques have obviously not been suitable so far. the diamond sticks in a for the actual experimental investigation of their mechanical properties sufficient Quantity and / or quality manufacture. To those specified in the above-mentioned article as known Process for producing rod-shaped nanocrystalline Diamond belongs the epitaxial growth from the gas phase under low pressure on diamond base crystals, by deposition from carbonaceous Gas under electron irradiation as well as under high pressure and at high temperature in a metal-carbon system. It is believed that too a synthesis utilizing the shockwave of a detonation possible could be. However, all these known processes apparently provide nanocrystalline Diamond not in one for practical applications appropriate amount.

at The vapor phase deposits are the carbon atoms before they settle on a growing diamond crystal, high movable, making a needle-shaped Growth of diamond crystals is explainable, if one assumes that the probability of an occurring carbon atom sticks, is higher at the crystal tip than at the sides. In the case of a synthesis by detonation, the propagation direction could the detonation wave represent a preferred direction, which for an anisotropic Crystal growth causal is.

It has long been known to synthetically produce diamonds by Graphite at high temperature under a high hydrostatic pressure is set. In such a system, neither are at the diamond crystal nuclei attaching carbon atoms as highly mobile as in deposition from the gas phase, nor does the reaction environment have an inherent preferential direction, the triggers for a anisotropic growth of the crystals could be. There is therefore no Reason to expect that rod-shaped diamond crystals with a high temperature high pressure process should be synthesized, and logically is about the production of diamond nanorods by high-pressure and high-temperature synthesis of graphite so far not reported.

Studies on the behavior of fullerene (C ₆₀ ) at high temperature and high pressure have been reported by a number of authors. TR Ravindran et al., Solid State Communications, 121, 391 (2002) report that microcrystalline diamonds were obtained by high pressure treatment at 25 to 30 GPa and a temperature of 300K. Brazhkin et al., Phys. Rev. B, 56, 11467-11471 obtained a diamond-graphite mixture by exposing fullerene to a pressure of 12.5 GPa for a few minutes at up to 900 ° C. H. Yusa, Diamond and Related Materials vol. 11, 87 (2002) received microcrystalline diamond at 2500 ° C and 17.5 GPa. VD Blank et al, Carbon, Vol. 36, 319 (1998) obtained polymerized C ₆₀ by treatment for up to 1800 ° C and up to 20 GPa for several minutes. The same result was obtained by RA Wood et al., J. Phys. Condensed Matter, Vol. 12, 10411-10421 (2000) by heating at 1000 ° C. for 10 to 20 minutes at 9 GPa and AV Talyzin et al., Phys. Rev. B, 2002, 6524 (24), 5413 by heating for several hours up to 1000 ° C at pressures of up to 25 GPa.

task On the one hand, it is the object of the present invention to provide a method which is the production of rod-shaped nanocrystalline Diamond in a simple way and in quantities required for technical applications allows and, on the other hand, an obtainable by such a method novel diamond material and applications of the method available Specify material.

The Task is solved by a method according to claim 1, by a material according to claim 7, a tool according to claim 8, a plunger according to claim 10 and uses according to claim 11 or 12.

Even though in the high-pressure and high-temperature treatment of fullerene neither easy and with big free path lengths moving automobile carbon still has an inherent anisotropy present, which is a growth of diamond crystals in a preferred direction could stimulate turns out surprisingly found out that among those studied by the above cited authors Parameter ranges of pressure and temperature during diamond synthesis from Fulleren an area exists, in which, a suitable period of time the treatment provided, rod-shaped diamond crystals arise.

The Duration of treatment should be at least 45 minutes and preferably at the most 120 minutes, preferably from 60 to 80 minutes. The treatment pressure is between 15 and 25 GPa, preferably between 18 and 21 GPa.

The Heating temperature should be between 1500 and 2300 ° C. Preferred is a Temperature between 1900 and 2100 ° C, but can not be ruled out that with sufficient duration of treatment also lower temperatures between 1500 and 1900 ° C lead to success. In particular, close that of Blank et al. at investigations up to 1800 ° C, this is not the case out, because the one chosen there Treatment time of a few minutes in the light of the present Invention for the production of rod-shaped nanocrystalline Diamond should have been too short in any case.

Around to eliminate as far as possible foreign atoms bound in the fullerene, the could lead to lattice defects in the diamond to be produced, should be before the heat treatment a step of outgassing the fullerene be performed. To outgass can the fullerene in particular for several hours in a high vacuum several 100 ° C, preferably about 300 ° C, to be heated.

Of the obtainable by the method Nanocrystalline diamond is particularly suitable to make a working surface of a Tool for material processing, in particular for metalworking, train. While by conventional Process of diamond production by high-temperature and high-pressure treatment often obtained microcrystalline diamond in powder form, can with the method according to the invention an aggregated shaped body be manufactured with dimensions of several millimeters, the as a whole or piecewise can be used to make it the working surface of the tool.

For such Tools are outstanding To expect properties, since, surprisingly, how later to be more specific, the hardness of the rod-shaped nanocrystalline diamond even the hardest crystal face conventional macroscopic diamond exceeds.

A Another notable feature of inventively produced rod-shaped nanocrystalline Diamants is its high stability against graphitization, which allows the material to be processed of iron alloys, which is not possible with conventional diamonds.

Further Features and advantages of the invention will become apparent from the following Description of exemplary embodiments. Show it:

1 a pT diagram showing the results of diamond-making experiments by high-temperature and high-pressure treatment of fullerene;

2 an electron micrograph of the material obtained by the method according to the invention;

3 an electron diffraction image of the 2 shown material sample;

4 a sample of material at higher magnification and a LEED diffraction pattern of the same;

5 a scanning tunneling micrograph of the surface of a sample of material according to the invention;

6 a surface of a natural diamond carved by the material of the invention;

7 EELS spectra of fullerene and of various synthetic diamond samples;

8th Raman spectra of natural and inventively obtained synthetic diamond;

9 an enlarged view of a machined with a tool according to the invention stainless steel cylinder;

10 a picture of a natural diamond after processing stainless steel; and

11 an illustration of a sample of the material according to the invention after processing of stainless steel.

manufacturing of the diamond material

The diamond material according to the invention with rod-shaped crystals was obtained as follows: the starting material used was commercially available fullerene (C ₆₀ ) with a purity of 99.95%. This was first heated under high vacuum at pressures of the order of 10 ^-6 bar and a temperature of 300 ° C for 24 hours. The material was then loaded into a platinum foil lined MgO octahedron with heating. Octahedra with edge lengths of 10 or 18 mm were used. The octahedron was compressed between tungsten carbide tungsten carbide tungsten carbide cubes 32 mm and 54 mm long and pyrophyllite gaskets 1200 and 5000 t respectively. The temperature was controlled by a thermocouple placed in parallel to the heater near the capsule. The sample was compressed to the desired pressure at the beginning of the experiment, then the temperature was raised to the desired experimental temperature. After maintaining the desired test temperature for the desired test duration, the sample was quenched by switching off the heater, then slowly decompressed. At the end of the experiment, the capsule was carefully removed. The samples treated in the 5000-tonne press had a compact cylindrical shape of 3 mm in length and 1.8 mm in diameter. The samples obtained with the 1200-ton press were smaller in size, otherwise the properties were similar.

Experiments were carried out with different treatment pressures, temperatures and durations; the results are summarized in the following table: TABLE 1

The cooling at slow cooling was 10 ° C / min.

Comparative tests were performed with other starting materials as summarized in Table 2.

Table 2

Of the Comparison of Experiments 2, 6 and 7 shows that the rod-shaped diamond crystals according to the invention can be obtained only when using fullerene as the starting material. Graphite or ground diamond as starting materials with otherwise identical experimental conditions different results.

Of the Comparison of Experiments 1 and 2 teaches that the type of cooling for the test result is not crucial, and that also some deviations in treatment pressure can be admitted. The Duration of treatment, however, is of importance for success, as the comparison with experiment 5 shows.

The experimental results as well as the results of other investigations on fullerenes under high temperature and high pressure cited in the introduction are in 1 summarized. Reference numerals 1 to 3 respectively correspond to Experiments 1 to 3 made by the inventors, and Reference Numerals 4 to 9 respectively correspond to the results of the above-cited researches of Ravindran, Badding, Yusa, Blank, Wood and Talyzin in this order. Experiments 3 and 6 show that at temperatures of 1000 ° and below or 2500 ° and above, the formation of the rod-shaped crystals observed by the inventors is no longer to be expected. Although it was also by Blank et al. (4) observed only the formation of polymeric C ₆₀ in the temperature range below 1800 ° C, but here was the duration of the heating phase with a few minutes apparently too short to observe the formation of the rod-shaped diamond crystals can.

characterization of the material

2 Figure 4 shows a bright field TEM photograph of a polycrystalline diamond aggregate obtained under the conditions of Experiment 1 or 2. Needle-shaped crystals (nanorods), whose length can exceed 1000 nm, are shown, while the thickness of the needle is at most 20 nm.

3 shows an electron diffraction pattern (SAED) at the in 2 was obtained. The diffraction pattern was recorded with a large fine area diaphragm so that complete diffraction rings can be recognized. The lattice plane distances are fully compatible with the diamond structure.

4 shows the elongated diamond crystals on a larger scale than 2 , The long sides of the crystals are parallel to the (111) plane; the needle axes are approximately parallel to [211] *.

5 is a high-resolution transmission electron micrograph (HRTEM) of the surface of a diamond nanocrystallite, which proves that this is an ideal structure without stacking failure or has other defects.

Results the hardness test

hardness provisions on super hard matter like diamond or diamond-like carbon layers (DLC) prove to be problematic because such measurements are plastic Assume deformation of the material to be tested. This must be the Hardness of Penetration tool over that of the material to be tested. The hardness of the (111) face of a Diamonds of the type IIa could not be determined so far, since this surface with the previously available Tools resist any scoring attempts. It did not succeed with a IIa natural diamond tip of a scoring tool of the type Vickers at a load of 500g scratches or notches on the surface of diamond crystallites produced in Experiment 1 or 2. Also by means of Scanning electron microscopy could not show any marks through the Tool be identified, which justifies the presumption that the diamond material according to the invention harder as IIa natural diamond is.

To test this assumption, two natural (type IIa) diamonds with polished (111) faces were placed in a Mao-Bell diamond stamp cell. Small diamond chips synthesized from different starting materials were inserted between the diamond punches of the cell. Under the 3N load, the two diamond punches were rotated around an axis. Diamonds obtained in the high temperature / high pressure amorphous carbon, graphite and natural diamond process as shown in Table 2 did not leave scratches on the surfaces of the diamond punches. The material obtained in experiments 1 and 2, on the other hand, left behind the diamond punches in 6 shown scratches. Thus, the new material is capable of scoring the (111) faces of Type IIa diamonds, allowing for the surprising statement that the hardness of the new material is greater.

Graphitisierungsverhalten

Tests on graphitization behavior were carried out on natural Ib diamond and the rod-shaped diamond nanocrystals obtained according to experiments 1 and 2. For this purpose, the samples were exposed to temperatures between 1000 and 1900 K (in 100 K increments) in an inert atmosphere (Ar + 2% H ₂ ). The samples were held at each temperature level for two hours and then gradually cooled. To control graphitization, EELS spectra ( 7 ) and Raman spectra ( 8th ), since both methods are very sensitive to the detection of graphitization-indicating sp ² -bonded carbon in the material.

One The first sign of partial graphitization became apparent a natural one Diamond at 1100 K detect, at 1500 K took the graphitization quickly closed, the sample lost its transparency.

7 shows EELS spectra of the fullerene used as the starting material of the experiments (curve a) of synthetic graphite obtained from graphite (curve b), for rod-shaped nanocrystalline diamond obtained from the fullerene before (curve c) or after (curve d) one Graphitisierungsversuch at 1800 K. The local maximum at about 285 meV of the curve a indicates a share of sp ² -bonded carbon in the fullerene; in the synthesized diamond, this maximum is completely absent, in the rod-shaped nanocrystalline material according to the invention even after the graphitization experiment.

8th shows Raman spectra of natural diamond before a graphitization treatment (curve a), after a graphitization treatment at 1500 K (curve b) and rod-shaped nanocrystalline diamond after a graphi tisierungsbehandlung at 1100 K (curve c), 1800 K (curve d) resp 1900 K (curve e). The natural diamond shows a single, very sharp maximum at 1300 cm ^-1 . By heating to 1500 K (curve b), this maximum widened very strongly, and a second broad maximum appears at 1600 cm ^-1 , which indicates the formation of graphite bonds. The Raman spectra of the rod-shaped diamond nanocrystals according to the invention show none of these maxima. The lack of the maximum for the diamond structure at 1320 cm ^-1 may be due to the fact that due to the small size of the crystallite surface effects move the diamond lattice vibration at 1320 cm ^-1 or broaden beyond recognition. Nevertheless, in the case of graphitization of the rod-shaped nanocrystals at high temperatures, it would be expected that the graphite oscillation would be visible at 1600 cm ^-1 since graphitization is known to occur at the crystal surfaces. The fact that even the curve e shows no evidence of graphitization suggests a very high temperature resistance of the material.

applications

diamond makes an ideal cutting, grinding or polishing material for numerous Applications, but unfortunately could not be processed iron-containing alloys are used, since at high temperature conditions while the machining process is likely either a metal carbide or because iron acts as a catalyst to reverse the conversion of diamond into Promotes graphite. There is therefore a considerable need for processing Iron and its alloys suitable cutting, grinding or Polishing materials with a hardness similar or higher than Diamond. In view of the observed high temperature behavior the rod-shaped diamond nanocrystals was tentatively a cylinder made of stainless steel (type SS301) in a conventional industrial lathe with tools edited with a natural Ib diamond or an aggregate body made of rod-shaped diamond nanocrystals stocked were.

In 9 the stainless steel cylinder can be seen after processing with the equipped with the diamond material according to the invention tool in the lathe at a rotational speed of 141 m / min; through the processing, the furrows were created on the circumference.

10 shows a photograph of the used for processing the steel cylinder natural Ib brilliant cut diamond, and 11 shows the also used for processing the stainless steel cylinder synthetic diamond body with rod-shaped nanocrystals according to the invention. The natural diamond is etched clearly visible at its upper edge; the synthetic material is free of traces of wear.

Claims (12)

Process for producing nanocrystalline diamond material with rod-shaped crystals by a step of heat treating of fullerene at a temperature between 1500 and 2300 ° C below a Pressure of 15 to 25 GPa over a period of at least 45 minutes. Method according to claim 1, characterized in that that the heating time is at most 120 minutes, preferably from 60 to 80 minutes. Method according to claim 1 or 2, characterized that the pressure is between 18 and 21 GPa. Method according to one of the preceding claims, characterized characterized in that the heating temperature is between 1900 and 2100 ° C is. Method according to one of the preceding claims, characterized characterized in that before the step of heat treating, a step of Outgassing of fullerene executed becomes. Method according to claim 5, characterized in that that for outgassing the fullerene for several hours in a high vacuum to several 100 ° C is heated. Diamond material with rod-shaped crystals, available with a method according to any one of the preceding claims, characterized characterized in that the crystals are aggregated with each other. Tool for material processing, characterized that a work surface of the tool rod-shaped nanocrystalline Diamond crystals has. Tool according to claim 8, characterized that the diamond crystals are aggregated with each other. Pressure stamp for a high-pressure cell, characterized in that it is rod-shaped nanocrystalline Diamond crystals has. Use of rod-shaped nanocrystalline diamond as a cutting, grinding or polishing material, in particular for processing of ferrous metals. Use of rod-shaped nanocrystalline diamond as a reference material for hardness analysis tions.