DE2519116A1 - METHOD OF SOLIDIZING DIAMONDS - Google Patents

Description

2519116 Licht, Schmidt, Hansmann & Herrmann patent attorneys

Munich: Dipl.-Ing. Martin light

Dipl.-Wirtsch.-Ing. Axel Hansmann Dipl.-Phys. Sebastian Herrmann

'Patent attorneys light. Hansmann, Herrmann · 8 Munich 2 Theresienstr. 33 'Oppenau: Df. Reinhold Schmidt

8 Munich 2 ^ 9 April 19/5

Theresienstrasse 33

He / Lü

GENERAL ELECTRIC COMPANY River Road 1
Schenectady, New York, V. St. A.

Method of solidifying diamonds

Polished areas of framesite, a naturally occurring diamond of the border type, show certain surface stripes. About the The nature of these surface stripes is discussed in a treatise "Evidence for Plastic Deformation in the Natural Polycrystalline Diamond, Framesite "by R.C. DeVries (Mat.Res.Bull, Vol. 8, pages 733-742, 1973, reported. In this treatise, it is stated that the narrow areas represented by these strips become solidified and harder than any orientation in the diamond matrix as well as on that The presence of oriented deformation bands (sliding bands) appear to indicate within the grains. In this ab-

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Telephone (089) 281202 Telegram; Lipatli Munich Bayer. Vereinsbank Munich, account number 882495 Postscheck Munich number 163397-802

action concluded that the microstructure of framesit was due to it is that the diamond grains of the framesite have been elastically deformed under conditions that inhibit brittle fracture.

The production of diamond moldings is explained, for example, in US Pat. No. 3,141,746 and US Pat. No. 3,136,615. It will a binder together with pre-formed diamond crystals are exposed to high pressures and temperatures at the same time and thereby achieved a union of diamonds. The production of diamond moldings is now in contrast to that explained below Invention.

As evidenced by the extensive development of deformation bands in the crystal surfaces, diamond crystals can be made according to the invention solidify by simply filling a volume with diamond crystals (i.e. without using a binder) or only filled with diamond crystals embedded in a powder consisting of diamond or cubic boron nitride, and then the filled volume at the same time in a defined area of the state diagram of carbon lying high pressure and exposing to temperature conditions. The pressure and temperature conditions used in the process of the invention are sufficient does not stop the crystal-crystal bond of diamond (or any powdery cubic boron nitride that may be used) in to any significant extent. After reducing the temperature and the pressure, the solidified Diamonds are easily separated and in diamond tools, such as saws, or in tools with a single point can be used.

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The pressure and temperature conditions used in the process of the invention range, for example, from about 10 kb at about 1200 C to about 60 kb at about 900 C. When solidifying a larger diamond crystals, brittle fracture is prevented by converting the diamond crystal into powder, as already stated above embeds. As will be further explained, the area of plastic deformation comprises the solidification of diamonds can be carried out, within as well as outside the diamond-stable area lying pressure-temperature conditions. Preferred becomes the one below a pressure of 55 kb and below one

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Temperature of 1500 C lying part of the area of plastic deformation.

The sizes given below for the diamond crystals relate to the largest linear crystal dimension.

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

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

Figure 2 is a Nomarski interference contrast photomicrograph showing shows solidified zones or lamellae protruding over a surface of a diamond, being at the surface is approximately a (135) plane.

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The method according to the invention is preferably carried out in an apparatus designed for generating high pressures and temperatures of the type described in US Pat. No. 2,941,248. This one so-called "belt apparatus" is well known from the aforementioned patent specification and many other publications, is unnecessary a graphic representation.

The belt apparatus comprises essentially two of tungsten carbide hard metal existing punches on opposite sides of a die belt made of the same material are arranged. The reaction vessel and are located in the space not enclosed by the stamps and the belt die the seal-insulation arrangements surrounding the reaction vessel. High pressures are generated in the reaction vessel when the coaxially arranged punches are relatively within the die are moved towards each other and thereby exert pressure forces. For heating the reaction vessel during pressurization suitable facilities are provided.

Various shapes of reaction vessels are in the patent literature explained, for example in US Pat. No. 3,423,177. The reaction vessels or cells usually consist of several nested cylinders and end plugs, with the reaction system in the innermost cylinder. With indirectly heated One of the cylinders consists of a reaction vessel made of graphite, which is heated by passing an electric current through it and thereby in turn heats up the reaction mass.

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Operating methods for the simultaneous generation of high pressures and high temperatures in such apparatus are known to those skilled in the art known. There are, of course, various other apparatuses that can be used to perform those required in the process of the invention Pressures and temperatures can be generated.

Diamond is a brittle material and easily splits under the Action of shear stresses along (111) planes. For the production of solidified diamond, every diamond crystal must therefore be enclosed during the application of pressure in such a way that Brittle fracture is largely prevented. The pressure transfer to the diamond crystal does not need to be hydrostatic itself, however, the compressed crystal must be sufficiently well or supported and the distribution must act on the crystal Forces must be uniform enough to create large shear forces that act in any direction and that have no resistance is opposed to prevent.

The optimal size of diamonds intended for solidification ranges from about 5 micrometers to about 5 mm. A diamond crystal that is too large can crack if it is executed of the method according to the invention is not properly included and / or the action of an uneven Is exposed to pressure distribution. If the diamond crystal is too small it can break completely or adjust its position to the action of pressure without deformation. According to the method of the invention Both naturally occurring diamonds (Type I and Type II) and synthetic diamonds (Type II) can be solidified will.

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When solidifying diamond, there can be losses due to brittle fracture prevented and thus maximum yield can be achieved if one observes the following:

a) The entire filling of the reaction vessel should be made of diamonds ranging in size from about 5 microns to about 250 microns, with each crystal provides the necessary support for neighboring crystals and the use of graded grain sizes at the upper end of this range is advantageous but not critical in a given filling,

b) Diamond crystals in the size range from about 250 microns to about 5 mm should be in diamond powder or powder consisting of cubic boron nitride can be embedded, this being made up of larger crystals and powder existing mixture makes up the entire filling of the reaction volume, and

c) Diamonds in a size range (from approx. 250 to approx. 500 micrometers) can be produced either according to a) or solidified according to b).

In carrying out the method of the invention using Using a belt apparatus, the material provided for the filling is used to create a cylindrical sleeve made of pyrophyllite, salt, hexagonal Boron nitride or a similar material filled with end plugs (preferably made of the same material as the cylindrical sleeve) closed. The sleeve is then removed from the rest of the reaction vessel

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enclosed (for example by a graphite heating tube, which in turn is enclosed by a cylinder made of pyrophyllite or salt).

Various powdery hard materials were used as the embedding material (Boron carbide, silicon carbide, aluminum oxide, pyrophyllite, Tungsten carbide, diamond and cubic boron nitride). However, only diamond and cubic boron nitride are used as embedding materials suitable for deformation of diamond according to the method of the invention. The particle size of the embed- materials should be in the range from 1/10 to 1/100 of the longest linear Dimension of the embedded diamond lying.

After the reaction vessel is assembled and in the high pressure apparatus Has been installed inside the seal-isolation arrangement, pressure and temperature are simultaneous or separately increased to a level in the range of plastic deformation specified in Fig. 1 (5-10 kb / minj 50-200 ° C / min) and for a period of at least one minute, for example for a period ranging from about 1 to about 30 minutes Time span, maintained. The heating current supply to the heating tube is switched off and the sample then cools quickly (in less than one

Minute) to below 50 C. The pressure is then at a speed decreased from about 10 kb / min to one atmosphere if a pressure of 10 kb or more was applied. If a Pressure below 10 kb is applied, pressure is released to atmospheric pressure almost instantaneously.

As can be seen from Fig. 1, the area extends plastic deformation both in the diamond-stable and graphite-stable area of the phase diagram of carbon

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(i.e. above and below the diamond-graphite equilibrium line). If pressure-temperature conditions are used which are below the diamond-stable range, but in the range of the plastic Deformation occurs, some graphitization of the solidified diamond occurs simultaneously with the deformation. It has, however found that the graphitization is negligible with a process duration of 5 minutes. With a duration of proceedings of 15 minutes and when using one the reaction vessel filling surrounding the pyrophyllite sleeve, a thin surface layer of graphite was often observed, which is likely to appear Is due to impurities that enter the diamond filling from the pyrophyllite.

It is not uncommon when solidifying in low levels A large number of diamond crystals break, however diamond-diamond bonds should be avoided.

First, diamond crystals were at least before deformation polished to determine the original microstructure. For comparison, the diamond crystals were used after performing the deformation is polished again on the same surface. Later it was found that the presence of new deformation zones can be clearly ascertained by microscopic observation without prior or subsequent polishing. Originally clear crystals become cloudy and less transparent as they deform. This change is usually 20-50 times Determine enlargement.

So that the solidified diamonds can be recovered undamaged from the embedding material, the arrangement of the diamond

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manten inn embedding material with regard to the effective direction of the pressure forces. If you order an octahedron in the Reaction vessel in such a way that a group of (111) planes comes to lie perpendicular to the direction of the compressive force this almost always split up in layers when solidifying, because the octahedron crystal is so strong due to the embedding material it is stated that it is by cleavage along the (111) plane is torn apart when the rams move apart when the pressure is released · If on the other hand a jJOOj-axis of the octahedron is arranged parallel to the axis of the punch (direction of the compressive force), most crystals are after the release of pressure undamaged, since the embedding powder surrounding a crystal moves away from the crystal the top pyramids on either side of the octahedron's waistline. Similarly, should be cubic shaped Crystals with the "~ 111, axis parallel to the axis of the pressure stamp even if a (111) cleavage surface is perpendicular comes to rest on the axis of the pressure stamp. If the I 100 axis of the cubic shaped crystal is parallel to the axis When the plunger is placed, there is a higher likelihood that the crystal will split into layers. If one considers these geometric criteria when arranging a crystal in the reaction vessel, one obtains an optimal one Yield of completely undamaged solidified diamond crystals from the embedding material.

After solidification, when the pressure and temperature are reduced to ambient values, the reaction vessel becomes removed from the apparatus and the solidified diamond off

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removed from the filling (i.e. the diamond crystals are separated from each other or separated from the embedding powder). When viewed under a microscope, signs of deformation appear in shape straight lines which protrude slightly above the surface of the diamond in question and in the manner shown in FIG. 2 in four different directions run. Each of these sliding lines marks a deformation zone or deformation lamella on the surface of the diamond. Usually the deformed one has The area is shallow (about 100 microns), but it is common to find lamellas that cut almost through one Crystal can extend from a size up to 1 mm. In Fig. 2 show the reference numerals 11, 12, 13 and 14 indicate slats, which are of the Surface of a solidified diamond crystal protrude in four directions (corresponding to four different crystal directions).

With the help of the method according to the invention into diamond crystals The deformation lamellae introduced seem identical in every respect to the deformation lamellae previously observed at Framesit. When looking between crossed polarizers as well due to the fact that the lamellae are etched in molten salt, it was found that the lamellae areas are assigned to high stress.

It has been found that deformation lamellae or sliding lines have a higher wear resistance than even the (111) plane of the host diamond (where the (111) plane is the wear-resistant Area of the diamond.) For this reason, these zones protrude beyond the diamond surface after polishing.

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example 1

A type I natural diamond with a length of approximately 1 mm was placed in a reaction vessel in man-made diamond powder embedded with a particle size of 90-106 mesh / cm. The reaction vessel was a final pressure of 60 kb and a final temperature of 800 C (in the diamond-stable area). For this purpose pressure and temperature were used increased simultaneously at a rate of about 3 kb / min and 50 C / min. After the reaction vessel 5 minutes was maintained at the peak temperature and pressure for a long time, the temperature and pressure became room temperature and atmospheric pressure and the crystal is removed from the embedding powder. The diamond crystal showed no signs plastic deformation.

Example 2

Example 1 was repeated with another diamond crystal approximately 1 mm in length, but in conjunction with FIG with the peak pressure of 60 kb a peak temperature of

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1000 C was applied. These pressure-temperature conditions are in the diamond-stable range. After removing the diamond crystal from the polycrystalline diamond powder matrix, signs of plastic deformation were easily seen. The diamond crystal showed slip lines and was also no longer clear.

Example 3

A type I natural diamond with a size of approximately 1 mm was in a reaction vessel in diamond powder with a partial

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size of 90-106 meshes / cm embedded. The pressure was increased to 20 kb in about 7 minutes and at the same time in at the same time the temperature increased to 1100 C. The reaction vessel was held at this peak pressure and temperature for 5 minutes. These pressure-temperature conditions are in the diamond-stable area. After switching off the power supply to the heating element in the reaction vessel, the The pressure on the reaction vessel is released and the diamond is removed. Slip lines were observed in the removed diamond crystal.

Example 4

A type I natural diamond with a size of approximately 1 mm was in a reaction vessel in diamond powder with a grain size of 90-106 meshes / cm embedded. In about 7 minutes the pressure went up to 20 kb and so did the temperature increased to 900 C. The reaction vessel was held at this peak pressure and temperature for 5 minutes. At the Diamond crystal could not be observed slip lines, i.e. the diamond crystal was not deformed. With the short duration of the experiment no graphitization 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 embedded in artificially produced diamond powder with a grain size of 90-106 meshes / cm. Pressure and temperature were simultaneously on 50 kb and 1200 C at one speed

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increased by about 3 kb / min and about 100 C / min, respectively. This maximum Pressure and temperature conditions were for 8 minutes maintained and then reduced to normal ambient conditions. The diamond crystal showed slip lines in a strongly concentrated extent and was therefore plastically deformed.

In the examples given in Table 1 below, a total of approximately 7.9 g of clean, unidirectional synthetic diamond crystals with a grain size of 9.8-11.8 mesh / cm were used, the specified pressure and temperature conditions in the area of plastic deformation at the same time have been applied for the specified period of time. These diamond crystals, which have approximately the same size, were processed in 16 tests, with each test using a reaction vessel containing approximately 0.5 g of diamond crystals for a belt apparatus. In each experiment, after removing the reaction vessel from the apparatus, solidified diamonds in the form of discrete crystals could be obtained for further use without difficulty. No graphitization was observed. A total of 73 % (5.8 g) of the solidified diamonds remained on a screen with 15.7 mesh / cm, while the remaining 27% had a finer grain size due to the fractures that occurred during the deformation.

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TABEL

Experiment no. P (kb) T ( ⁰ C) time (min)

40 1200

45 1300

51 1400

57.5 1400

There are notable differences between the physical appearance of a solidified diamond and its appearance prior to the introduction of deformation bands. These differences in appearance are independent of whether the size of the originally clear crystal has been reduced by breakage or not. In order to determine the differences in the case of smaller crystals, it may be necessary to observe with a relatively small magnification. Naturally occurring diamond crystals, which may have a color but are usually transparent, took on a cloudy or matt appearance when treated according to the process of the invention and thus lost their transparency. The matt appearance results from diffuse light scattering on the many new surfaces formed during the deformation of the crystal (ie the slip lines shown in FIG. 2). Man-made diamonds usually have a (yellow, green, green-yellow, blue,

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blue-green etc.) due to contact with the Solvent catalyst in the production etched surfaces and generally contain various impurities Amounts. The unetched or contaminated areas of man-made diamonds are common transparent. After solidification, however, the artificially produced diamonds are also less transparent and frosty Appearance, which is due to the diffuse light scattering occurring for the reasons given above.

When diamond crystals of approximately the same size of deformation are subjected, usually some faces of each solidified crystal remain wholly or partially unchanged, depending according to the extent to which the crystals have been pressed against one another. For the production of tools where essential Portions of the solidified crystalline surface are used for machining a workpiece, however, it is not required that every surface has been plastically deformed.

After the solidified diamonds have been removed from the reaction vessel in the form of discrete crystals, they can be moved to Large sized and classified and industrially in the same way as previous diamonds for machining used by workpieces (e.g. in grinding tools, saws, files, tool tips, etc.).

When carrying out the method according to the invention, one preferably works in the part of the range defined in FIG plastic deformation caused by line 10, line 11 (at

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55 kb) and line 12 (at 1500 C) is limited. If an embedding material is used, it is preferably used proportionally Coarse diamond powder (106-157 meshes / cm) as an embedding medium.

Optimal pressure and temperature conditions are in the diamond-stable Area of the preferred part of the plastic deformation area, i.e. in that by the line 10, the line 11 and the Diamond-graphite equilibrium line enclosed sub-area.

Clean, unidirectional (i.e., block-like) diamond crystals are most suitable for the method of the invention. In Impurities present on the crystals and / or etchings present on the surfaces of the crystals do not appear to have any influence to have the plastic deformation.

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

When using diamond crystals with a grain size in the range of 100-200 mesh / cm to fill the reaction vessel (not as embedding material), the packing density of these crystals should be achieved by using crystals of graded grain size be optimized.

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Claims (9)

PATENT CLAIM E. 1 . Method of making solidified diamond which is then applied according to its intended use thereby marked that a) an enclosed space either only with discrete diamond crystals or only together with at least one diamond crystal is filled with loose crystalline embedding material for the diamond crystal, b) the enclosed space and the filling for a period of more than approximately one minute of simultaneous exposure to Is exposed to pressure and temperature conditions in the range of plastic deformation, which is generally in the Fig. 1 the state diagram of carbon shown is set, c) the temperature is reduced to below 50 C, d) the pressure is reduced to atmospheric pressure, e) obtained from the filling deformation lamellas containing diamond in the form of discrete, solidified, crystalline material and f) the discrete, solidified, crystalline material for machining a workpiece is attached to a base. 2. The method according to claim 1, characterized in that the filling only consists of diamond crystals in the size range of approximately 5 microns to about 500 microns. - 18 - 509851/07 15 3. The method according to claim 1 or 2, characterized in that the embedding material is diamond or cubic boron nitride is used. 4. The method according to claim 3, characterized in that the filling consists only of at least one diamond crystal embedded in coarse diamond powder. 5. The method according to claims 1-4, characterized in that the pressure and temperature conditions applied simultaneously lie in the diamond-stable area of the phase diagram of carbon. 6. The method according to claims 1-4, characterized in that the pressure and temperature conditions applied simultaneously lie in the graphite-stable area of the phase diagram of carbon. 7. The method according to claims 1-4, characterized in that that a pressure of a maximum of 55 kilobar and a temperature of ο
a maximum of 1500 C is used. 8. The method according to claim 7, characterized in that the simultaneously acting pressure and temperature conditions in the diamond-stable area of the phase diagram of carbon lie. 9. The method according to claims 1-8, characterized in that the diamond used as the starting material is noticeable Has transparency and is essentially non-transparent after solidification. 50985 1/07 15 Blank page