DE2519116C2 - Process for treating diamond particles - Google Patents

Description

30th

The invention relates to a method of treatment of diamond particles, in the case of the ew container either only with discrete diamond crystals or only with loose ones crystalline embedding material is filled together with at least one diamond crystal and that Container and its contents in and under the diamond table Area is exposed to pressure and temperature conditions.

From DE-OS 19 53 800 and DE-OS 19 63 0S7 processes of the aforementioned type are already known in which diamond crystals form a uniform Bodies are sintered together. The sintered body formed from diamond particles bonded together has almost the hardness of diamond and can be used to equip cutting and squinting tools can be used.

In contrast, the object of the invention is to provide a method for solidifying discrete To create diamond plates.

This object is achieved by a method of the type mentioned, which is according to the invention characterized in that for producing discrete vetfestlgten Diamanttellchen the container with diamond crystals in Größenberelc ^h of about 5 microns to about 500 microns or Dlamantkrlstailen ranging in size from about 250 microns to 5 mm, which are embedded in diamond powder or powder consisting of cubic boron nitride, is filled, the container and its contents for a period of 1 to 30 minutes up to a maximum of 60 kb and ^{pressure and temperature conditions between 900 and 1500 0} C according to the in Flg . 1 is subjected to plastic deformation with limit curve, a diamond-diamond blinding is avoided.

In the method according to the invention, discrete diamond particles are plastically deformed and thereby solidified, so that the discrete diamond particles then have an improved wear resistance. The solidified Diamond plates can be used to manufacture diamond tools, for example diamond saws or diamond cutting tools can be used.

The invention will now be explained in more detail with reference to drawings in which show

1 shows the phase diagram of carbon in which the range of plastic deformation is indicated. Within which the method according to the invention can be carried out, and

2 shows a Nomarskl interference contra aerial micrograph, which shows solidified zones or lamellae protruding above a surface of a diamond, the surface being approximately a (135) plane.

The method according to the invention is preferably used in a device for generating high pressures and temperatures of those described in US Pat. No. 2,941,243 Kind of executed. Since this so-called "belt apparatus" from the aforementioned patent specification and It is well known in many other publications, so there is no need for a graphic representation.

The mortar apparatus essentially has two Wolframkarbldhartvaetall existing stamp on the arranged on opposite sides of a die belt made of the same material are. In the space enclosed by the punches and the belt die there is the reaction vessel and the reaction vessel surrounding it Seal isolation arrangements. High pressures are generated in the reaction vessel if they are equiaxed arranged punch within the die are moved relative to each other and thereby compressive forces exercise. Suitable devices are available for heating the reaction vessel during pressurization intended.

Various shapes of reaction vessels are in the patent literature, for example in US-PS 34 23 177. The reaction vessels or cells exist usually made up of several nested cylinders and end plugs, with the reaction system located in the innermost cylinder. In the case of indirectly heated reaction vessels, one of the cylinders is made of graphite, which is heated by passing electrical current through it and thereby in turn heats up the reaction mass.

Operating method for the simultaneous generation of high pressures and high temperatures in such apparatus are known to the person skilled in the art. There are of course various other devices with which the pressures and temperatures required in the process according to the invention can be generated.

Diamond is a brittle material and splits slightly under the action of shear stresses along (lll) planes. For the production of solidified Diamond must therefore be confined to every diamond crystal during the application of pressure so that Brittle fracture is prevented worldwide. The pressure transfer on the diamond crystal need not be hydrostatic itself, but the compressed one must Crystal sufficiently well or supported and the distribution acting on the crystal Forces must be uniform enough to allow the emergence of large forces acting in any direction To prevent shear forces that are not resisted.

The optimal size of intended for solidification Diamonds range from approximately 5 microns to

about 5 mm. A diamond crystal that is too large can crack if it is not properly enclosed when carrying out the method according to the invention and / or is exposed to the action of an uneven pressure distribution. If the diamond crystal is too small, it can break completely or adjust its position to the application of pressure without deformation. Using the method of the invention, both naturally occurring diamonds (type I and type II) and synthetic diamonds (type II) can be solidified.

When solidifying diamond, losses due to brittle fracture can be prevented and thus maximum Yield can be achieved if the following is observed:

a) The entire filling of the reaction vessel should be made of diamonds in the size range of approximately 5 microns to about 250 microns, each crystal for the required 2ö Before supporting neighboring crystals, and the use of graduated grain sizes ensures at the upper end of this range in a given filling advantageous, but not critical Is,

b) Diamond crystals should range in size from about 250 microns to about 5 mm Embedded in diamond powder or powder consisting of cubic boron nitride, whereby this mixture consisting of larger crystals and powder takes up the entire filling of the reaction volume matters, and

c) Diamonds can range in size from about 250 to about 500 microns solidified either according to a) or according to b).

When carrying out the method according to the invention Using a belt apparatus, a cylinder is made with the material intended for the filling Sleeve made of pyrophyllium, salt, hexagonal boron nitride or a similar material and filled with End plug (preferably made of the same material as the cylindrical sleeve) completed. The sleeve is then enclosed by the rest of the reaction vessel (for example by a graphite heating tube that is in turn enclosed by a cylinder made of pyrophyllium or salt).

Various pulverulent hard materials (boron carbide, silicon carbide, aluminum oxide, pyrophyllium, tungsten carbide, diamond and cubic boron nitride) were tried out as embedding materials. However, only diamond and cubic boron nitride are suitable as embedding materials for deforming diamond according to the method of the invention. The particle size of the embedding material should be in the range of 1/2, _c to V _{100 of} the longest linear dimension of the embedded diamond.

After the reaction vessel is assembled and placed in the high pressure apparatus inside the gasket isolation assemblies has been installed, pressure and temperature are raised simultaneously or separately a level in which In Flg. 1 specified area of plastic deformation increased (5-10 kb / mln; 50-200 ° C / mln) and for a period of at least one minute, for example for a range of about 1 to about 30 minutes, maintained. The heating current supply to the heating tube is switched off and the sample then cools quickly (in less than a minute) to below 50 ° C. The print is then at a speed of approximately lOkb / mln reduced to one atmosphere if a pressure of 10 kb or more was applied. If a pressure of less than 10 kb was applied, pressure is released to atmospheric pressure almost instantly.

As can be seen from FIG. 1, the area of plastic deformation extends both into the diamond-stable and graphite-stable area of the phase diagram of carbon (ie above and below the diamond-graphite equilibrium line). If pressure-temperature conditions are used that are below the diamond-stable area, but in the area of plastic deformation!, Some graphicalization of the solidified diamond occurs at the same time as the deformation. It has been found, however, that the graphitization can be reduced with a process duration of less than 5 minutes. During a process time of 15 minutes and when a sleeve made of pyrophyllite enclosing the reaction vessel filling was used, a thin surface layer of graphite was often observed, which is probably due to impurities which enter the diamond filling from the pyrophyllite.

It is not uncommon for a small amount of Dlarrant crystals to form during solidification Rupture, however, diamond-diamond blinding is to be avoided.

First, diamond crystals were made before the daeformatlon polished on at least one surface to determine the original microstructure. For comparison the diamond crystals were polished again on the same surface after performing the deformation. It was later found that the presence of new zones of deformation was clear by microscopic Observation can be determined without prior or subsequent polling. Originally clear Crisis all become cloudy and less with the deformation transparent. This change is usually seen at 20 to 50 times magnification.

So that the solidified diamonds can be extracted undamaged from the embedding material, should be the arrangement of the diamond in the working material With regard to the direction of action of the pressure forces must be taken into account. One arranges an octahedron in the reaction vessel in such a way that a group of (III) planes lie perpendicular to the direction of the compressive force comes, this is almost always split up in layers when it solidifies, because the octahedron crystal the embedding material is so firmly held that it splits along the (III) plane is torn apart when the ram move apart when releasing the print. On the other hand, if there is a [100] axis of the octahedron parallel to the When the axis of the stamp (direction of the compressive force) is arranged, most of the crystals are after the pressure is released undamaged, as the embedding powder surrounding a crystal pulls away from the crystal along the apex pyramids on either side of the octahedron's waistline. In a similar way should be cubic shaped crystals with the [lll] axis be arranged parallel to the axis of the pressure stamp, even if it has a (11 D gap area comes to lie perpendicular to the axis of the pressure stamp. If the [100] axis of the cubic shaped Crystal parallel to the axis of the DruckslemDel aineeord-

net, there is a higher probability that the crystal is split into layers. Considered one with the arrangement of a crystal in the reaction vessel these geometrical criteria, one obtains an optimal yield of completely intact solidified Diamond crystals from the embedding material.

After solidification, when the pressure and temperature have been reduced to ambient values the reaction vessel is removed from the apparatus and the solidified diamond from the filling removed (i.e. the diamond crystals are separated from each other or from the embedding powder). at When viewed under the microscope, signs of deformation appear in the form of straight lines that protrude slightly above the surface of the diamond in question and in the from Fla. 2 catfish visible in four different directions run. Each of these equations marks the surface of the diamond a deformation zone or deformation lamella. Usually the deformed area has a flat one Depth (about 100 microns), but it is common to find lamellas that almost cut through extend a crystal up to 1 mm in size. In Flg. 2 have the reference numerals 11, 12, 13 and 14 Lamellae solidified from the surface of a Dlamantkristails In four directions (corresponding to four different Krtstallrlchtungen) protrude.

With the aid of the method according to the invention In Deformailons lamellae introduced into diamond crystals seem identical in every respect with the earlier ones Deformation lamellae observed in Frameslt. When looking between crossed polarizers as well due to the fact that the lamellae In molten Etched with salt, it was found that the lamellae were associated with areas of high stress are.

It has been found that deformation lamellas or sliding lines have a higher wear resistance than even the (III) plane of the host diamond (with the (111) plane being the most wear-resistant surface of the Diamonds 1st.) For this reason, these zones protrude above the diamond surface after polishing.

Example 1 (Verglelchsbelsplel)

45

A type I natural diamond with a length of approximately 1 mm was placed in a reaction vessel In artificially made diamond powder with a particle size embedded from 90 to 106 meshes / cm. The reaction vessel had a final pressure of 60 kb and 5C exposed to a final temperature of 800 ° C (in the diamond-stable area). To this end, pressure was applied and temperature increased simultaneously at a rate of about 3 kb / mln and 50 ° C / mln. After this the reaction vessel was held at the peak temperature and pressure for 5 minutes was, the temperature and pressure were decreased to room temperature and atmospheric pressure, and the Crystal removed from the embedding powder. The diamond crystal showed no signs of plasticity Deformation.

Example 2

Example 1 was repeated with another diamond crystal approximately 1 mm in length, wherein however, a peak temperature of 1000 ° C was used in conjunction with the peak pressure of 60 kb.

These pressure-temperature conditions are in the diamond-stable range. After removing the Diamond crystals from the polycrystalline diamond powder matrix were signs of plastic deformation easy to recognize. The diamond crystal had spheres and was also no longer clear.

Example 3

A type I natural diamond with a size of approximately 1 mm was embedded in a reaction vessel in diamond powder with a particle size of 90 to 166 meshes / cm. The pressure was increased to 20 kb in about 7 minutes and at the same time the temperature was increased to HOO ⁰ C in the same tent. The reaction vessel was held at this brine pressure and peak temperature for 5 minutes. These pressure-temperature conditions are in the diamond-stable range. After switching off the power supply to the heating element in the reaction vessel, the pressure on the reaction vessel was released and the diamond was removed. In the distant diamond crystal girdles were observed.

Example 4

A type I natural diamond with a size of approximately 1 mm was placed in a reaction vessel In Diamond powder embedded with a grain size of 90 to 106 meshes / cm. In about 7 minutes it was at the same time the pressure increased to 20 kb and the temperature increased to 900 ° C. The reaction vessel was opened held this peak pressure and temperature for S minutes. On the diamond crystal no equilibria are observed, d. H. the diamond crystal was not deformed. During the short duration of the experiment, no graph could be observed, although the pressure and temperature conditions used were in the graphite-stable range.

Example 5

A Type II natural diamond with a size of approximately 1 mm was man-made Diamond powder embedded with a grain size of 90 to 106 meshes / cm. Pressure and temperature were simultaneously at 50 kb and 1200 ° C at rates of approximately 3 kb / mln and approx 100 ° C / min increased. These maximum pressure and temperature conditions were maintained for 8 minutes and then reduced to normal ambient conditions. The diamond crystal had similarities in strong concentrated scope and was therefore plastically deformed.

For those listed in Table 1 below Examples were using a total of approximately 7.9 grams of clean, unidirectional synthetic diamond crystals a grain size of 9.8 to 11.8 mesh / cm is used, with the specified pressure and temperature conditions Applied simultaneously for the specified period in the area of plastic deformation became. These diamond crystals, which are roughly the same size, were processed in 16 experiments, with a reaction vessel for a belt apparatus containing approximately 0.5 g of diamond crystals for each experiment was used. In each experiment, after removing the reaction vessel from the apparatus Solidified diamonds in without difficulty

Discrete crystals can be obtained for later use. No graph clearing was observed. A total of 73% (5.8 g) of the solidified diamonds remained on a 15.7 sieve Meshes / cm back, while the remaining 27% is due to that which occurred during the deformation BrucH had a finer grain size.

Table 1

10

Attempt no.

P (kb)

T ( ⁰ C)

Time (min)

73-138

73-141 73-142

73-145 73-146

73-149 73-150

73-153

40

51

57.5

1200

nnn

1400

1400

30th

30th

30th

20th

25th

Between the physical appearance of a solidified ^ n diamond and its appearance before the There are notable differences in the introduction of deformation bands. These differences in appearance are independent of whether the size of the originally clear crystal has been diminished or not due to breakage. To determine the differences in the case of smaller crystals, an observation with a relatively small magnification required be. Naturally occurring diamond crystals that may be colored, but are usually transparent, received upon treatment according to the process of the invention a cloudy or matt appearance and thereby lost transparency. The matte appearance results from diffuse light scattering on those formed when the crystal is deformed many new surfaces (i.e., those shown in FIG Slip lines). Man-made diamonds usually have a (yellow, green, green-yellow, blue, blue-green stc.) Color due to the touch with the solvent catalyst in manufacture etched surfaces and generally contain impurities in varying amounts. the areas of man-made diamonds that are not etched or occupied by impurities usually transparent. After solidification, however, the artificially produced diamonds also show a lower transparency and a frosty appearance, which can be attributed to the diffuse light scattering that occurs for the reasons given above.

When diamond crystals of approximately the same size are subjected to the deformation, they remain usually some faces of each solidified crystal wholly or partly unchanged, depending on the extent, In which the crystals have been pressed together. For the production of tools in which substantial proportions of the hardened crystalline surface are used machining of a workpiece are used, but it is not necessary that every surface has been plastically deformed

After the solidified diamonds are removed from the reaction vessel in the form of discrete crystals They can be sized and graded and Industrial In the same catfish as previous diamonds are used for machining workpieces (e.g. In Squares, saws, files, tool tips, etc.).

One works preferentially when executing the | Method according to the invention In the part of In Flg. 1 defined range of plastic deformation, which is limited by line 10, line 11 (at 55 kb) and line 12 (at 1500 ⁰ C). If an embedding material is used, it is preferable to use relatively coarse diamond powder (106 to 157 meshes / cm) as the embedding medium.

Optimal pressure and temperature conditions are in the diamond-stable range of the preferred part of the Area of plastic deformation, d. H. In the sub-area enclosed by line 10, line 11 and the Dlamant-Graphlt-GJelchgewlchtsllnle.

For the method according to the invention, it is best to use clean, rectified (i.e. block-type) Suitable for diamond crystals. Impurities present in the crystals and / or on the surfaces of the Etchings present in crystals do not seem to have any influence on the plastic deformation.

A simultaneous increase in pressure and temperature to the operating value (peak value) is closed preferred, but not essential. The shortest possible effective deformation times are also required prefer.

When using diamond crystals with a grain size in the range of 100 to 200 mesh / cm for The filling of the reaction vessel (not as an embedding material) should correspond to the packing density of these crystals can be optimized by using crystals of graded grain size.

For this purpose 2 sheets of drawings

Claims (1)

Claim: Process for treating diamond particles, in which a container is filled either only with discrete diamond crystals or only with loose crystalline embedding material together with at least one diamond crystal and the container and its contents are exposed to pressure and temperature conditions in and below the diamond-stable area, wherein mm for manufacturing of discrete solidified diamond the container with diamond crystals ranging in size from about 5 microns to about 500 microns or with diamond crystals ranging in size from about 250 microns to S, dia embedded in Dlamentpulver or cubic boron nitride öesiehendem powder filled the container and its contents for a period of 1 to 30 minutes up to a maximum of 60 kb and between 900 and 1500 ° C under pressure and temperature conditions according to the following Flg. 1 is subjected to the area of plastic deformation shown mli limit curve (10), a diamond-diamond bond being avoided.