DE1284405B - Process for the synthesis of diamond - Google Patents

Description

The invention relates to a method for the synthesis of diamond, in which graphite one over the Graphite-diamond equilibrium line in the diamond-stable area of the phase diagram of carbon is exposed to lying pressure.

The previous processes for the synthesis of diamond usually use carbonaceous material, for example graphite, in the presence of a metal 'catalyst in the diamond-stable area of the state diagram exposed to pressures and temperatures lying down by carbon. As a metal catalyst is a metal of group VIII of the periodic system, chromium, manganese or tantalum is used. An apparatus suitable for the synthesis of diamond is, for example, in the German patent 1 207 923. The apparatus has an annular die with one facing each side conically widening central opening is provided, in the two opposite conical stamps for Compression of a reaction chamber arranged in the central opening can be moved into it can. A ceramic or stone made of ceramic or stone is placed between the punches and the die for sealing Seal arranged, for example a seal made of pyrophyllite. For the synthesis of diamond the reaction chamber containing carbonaceous material and metal catalyst becomes above the graphite-diamond equilibrium line the phase diagram of carbon exposed to pressures and temperatures, with the metal catalyst is melted. The molten metal catalyst has a catalytic effect on the graphite Effect and a solution effect, and diamonds are created. After reducing the pressure and the temperature the diamonds are extracted. Those in the previous method of synthesis The high temperatures required by diamond are a critical factor. With the present Apparatuses could achieve significantly higher pressures at room temperature than at elevated temperatures. In addition, higher temperatures cause melting together, chemical reactions and / or decomposition of those surrounding the carbonaceous material and the metal catalyst Substances and thereby have a detrimental effect on the diamond formation reaction. Simultaneously arise at high temperatures due to fusion, decomposition and of Phase changes of the substances surrounding the carbonaceous material and the metal catalyst unwanted temperature and pressure fluctuations. Furthermore, with the previous method for the synthesis of diamond the metal catalyst takes up a considerable volume of the reaction chamber in Claim, whereby the diamond yield is reduced. The metal catalysts and the carbonaceous one The material and the substances surrounding the metal catalyst can take on undesirable chemical substances Reactions participate and the diamond formation reaction deleteriously influencing impurities contain. In addition, the properties of the extracted diamond depend on the metal catalyst used from, for example, the diamond can include inclusions made up of the metal catalyst exhibit.

The invention is therefore based on the object of a method for synthesizing diamond in this way to design that eliminates the difficulties encountered when using a metal catalyst will.

According to the invention, this object is now achieved in a method for synthesizing diamond, in which Graphite one above the graphite-diamond equilibrium line in the diamond-stable area of the state diagram is exposed to lying pressure by carbon, in that the graphite exposed to a pressure of about 120 kilobars and thermal energy to act is brought that by the interaction of pressure and temperature the graphite below the The melting line of carbon is converted into diamond, whereupon the supply of heat is cut off Pressure is reduced and diamond is extracted.

In the process according to the invention, no metal catalyst is required, rather the Graphite is instantly converted to diamond without the need to melt the graphite. The thermal energy is preferably generated by electrical resistance heating.

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

F i g. 1 is a view of an apparatus for implementing it the method according to the invention,

F i g. 2 is a sectional view of the with a sample charged reaction vessel according to Fig. 1,

F i g. 2a one from the reaction vessel according to FIG. 2 removed diamond mass,

F i g. 3 shows an oblique section of the reaction vessel according to FIG. 2 with graphite electrodes, loading and reaction vessel parts,

F i g. 4 shows, in section, a modified embodiment of the reaction vessel according to FIG. 2,

F i g. 4a one from the reaction vessel according to FIG. 4 removed diamond mass,

F i g. 5 shows a schematic representation of the in the apparatus according to FIG. 1 circuit used,

F i g. 6 shows a graph of the electrical power supplied, the thermal energy supplied and the resistance of a graphite sample as a function of time for a specific working example,

F i g. 7 shows a representation of the state diagram of carbon;

F i g. 8 is a graph of the melting point of carbon on a resistance curve; the supplied electrical power and thermal energy as a function of the time during melting of graphite and

F i g. 9 is a graphical representation of the processes shown in FIG. 6 shown resistance curve R 6 and in F i g. 8 shown resistance curve R 8 as a function of the supplied energy.

It has unexpectedly been found that one can do a more immediate transformation or transformation of carbon, for example graphite, in diamond can be achieved by using the graphite only subject to very high pressures and high temperatures. By using high temperatures in conjunction with a high pressure, the high pressure required for conversion is reduced. A material that is not in the form of a diamond is referred to as a carbonaceous material which Contains carbon and reacts under the reaction conditions before being converted into diamond, decomposes or otherwise results in non-diamond-shaped elemental carbon. Elemental coal

35

55

substance is that which is not in the form of a compound Form of carbon and includes amorphous carbon, lamp soot, coal, pitch, tar, etc. as a raw material is preferably high purity and high density graphite because of its well known and desired properties are used, for example because of its crystal structure, the relationship its crystal structure with that of diamond, its density, its content of impurities and because of its relatively easy convertibility into diamond.

The term "conversion" is used generically to denote the change or changes used in the carbon-diamond conversion, especially in the graphite-diamond conversion, where the crystal structure is changed directly from graphite to a diamond crystal structure without any facilitation of the Process a catalyst is required.

An excitation or movement of the carbon crystal lattice is achieved in a form that the graphite is exposed to very high temperatures for conversion into diamond. It has pointed out that no special material is required in such a method, which in the in the manner described in German patent specification 1,147,926 results in a catalytic effect or dissolving effect.

In one embodiment of the invention, an apparatus is used which is a modification of the in the apparatus described in German Patent 1 207 923. This modified apparatus is in the correct scale ratio in FIG. 1 shown. The apparatus 10 includes an annular one Die II with an opening 12, which extends from the Center widened to conically towards both ends. The die 11 is made of to increase the strength Enclosed hard steel rings (not shown). A material from which the die 11 is a hard metal consisting of tungsten carbide and cobalt. The modified one Embodiment of the die 11 has conical surfaces 13 that form an angle of approximately 52.2 with the horizontal, and a generally circular cylindrical chamber 14 with a diameter of 5.08 mm.

Two opposite conical punches 15 and 16 are arranged concentrically to the opening 12, the base part of which has an outer diameter of approximately 25 mm. The punches 15 and 16 together with the die 11 form a reaction chamber. The punches 15 and 16 are also enclosed by rings made of hard steel (not shown) to increase the strength. A material suitable for producing the punches 15 and 16 is a hard metal consisting of tungsten carbide and cobalt. The modified punches have conical side surfaces 17 which enclose an angle of 60, and end surfaces with a diameter of 3.81 mm. The conical parts of the punches have an axial length of approximately 14.2 mm. Because of the two different angles of 60 and 52.2 ", there is a wedge-shaped space between a punch and the die, provided for a seal. ⁽⁾ 5

Another modification concerns the sealants. Namely, it becomes for every space in between only a single seal 19 made of pyrophyllite is used. The seals 19 between the punches 15 and 16 and the die 11 are wedge-shaped so that they fit into the predetermined space, and have such a thickness that between the end faces 18 of the punch 15 and 16 a distance of 1.52 mm remains.

With the modified apparatus, pressures in the range from 100 to 180 kilobars and more can be achieved. The "essential features of the modified embodiment are the proportions of certain dimensions. These dimensions are: firstly the diameter of the punch end face 18, secondly the distance between the punch end faces 18 in the initial position shown in FIG. 1 before compression, and thirdly the inclined height of the seal 19 along the conical part 17. In the case of embodiments of the apparatus that are already in operation, the ratio of the distance G between the two end faces 18 to the diameter of an end face 18 is less than 2.0, preferably less than 1.75, and is 0.2 in the embodiment shown in Fig. 1. The length L of the seal 19, which is predetermined by the diameter of the punch face 18, is six times as large as the diameter, ie L / D = 6. 923, the ratio GjD has a value of 2.0 and the ratio L / D has a value of less than 1.0 In the last-mentioned conditions, the high pressures required in this invention cannot be achieved. The preferred ratios result in a greater lateral support of the punches 15 and 16 without the force component is significantly increased, which is necessary to compress the seal and therefore to achieve a pressure increase in the. Reaction vessel is required.

A reaction vessel 20 is arranged between the punch end faces 18. The reaction vessel 20 contains a cylindrical or coil-shaped sample holder 21 made of pyrophyllite with a central opening 22. In FIG. 2 the parts which are arranged in the opening 22 are shown in more detail in their correct mutual position. The reaction vessel 20 contains both the sample and a heating device in the form of a solid, straight circular cylinder, which consists of three concentrically juxtaposed / identical disks 23, 24 and 25. The disc 23 in turn consists of a larger _^(3/4) segment of pyrophyllite and a smaller (V ₄₎ segment 27 made of graphite, which serves to lead the electric current. The disk 25 consists of a larger _^(3/4) Segment 28 of pyrophyllite and a smaller ( '/ 4) segment 29 made of graphite, which serves to lead the electric current. The disk 24 consists of two spaced apart segments 30 and 31 (not shown) made of pyrophyllite, between which a rod-shaped or bar-shaped graphite sample 32 is arranged. The graphite sample is approximately 0.50 mm thick, 0.3 mm wide and 2.03 mm long. Each of the disks 23, 24 and 25 has a diameter of 2.03 mm and a thickness of 0.50 mm. In Fig. 3 is the reaction vessel according to FIG. 2 shown in an oblique section from above. It can be seen that there is an electrical current path, starting from the graphite segment electrode 27, via the sample 32 to the graphite segment electrode 29, which is used for electrical resistance heating of the sample 32.

In Fig. 4 is a modified embodiment

of the reaction vessel 20 is shown. The in Fig. The reaction vessel 33 shown in FIG. 4 contains two graphite disks 34 and 35 with a thickness of about 0.25 mm, which are used as graphite electrodes for the electrical Resistance heating of the sample are used. A pyrophyllite cylinder disposed between disks 34 and 35 36 has an equiaxed central opening 37 which is used to receive a sample 38. the Sample 38 is in the shape of a cylinder with a

be calibrated so that the approximate pressure in the reaction vessel can be specified.

The graphite sample 32 or 38 is exposed to high temperatures, required or optionally by electrical resistance heating, whereby a current discharge is passed through the sample can be. The stamps 15 and 16 are connected to a power source (not shown) connected, so that, for example, off

Diameter of 0.76 mm and a length of i ₀ going from the punch 15, over the graphite electrode 27, 1.02 mm. the sample 32 and the graphite electrode 29 a current

The apparatus 10 described provides a discharge to the punch 16 can take place, desired pressure in the area above the graphite slide-in to discharge current through the sample 32 or

The circuit 41 suitable for the mant equilibrium line E in the state diagram 38 is now illustrated by means of carbon, which is shown in FIG. 7 is shown. To the In- 15 F i g. 4 described. In the circuit shown operation, the apparatus 10 shown is a capacitor discharge circuit, the press tables are brought to a suitable press, with the aid of which current through the apparatus 10 can be used to load the punches 15 and 16 on one another, with the determination of being moved again so that the reaction vessel is pressed together with the sample that occurs during discharge and the sample is exposed to 32 or 38 high pressures 20 voltages and currents with the aid of an oscilloscope. To calibrate the apparatus to be measured on phen. The in F i g. 5 can be used that in German patent 41 contains a calibration electrolytic capacitor series with a capacitance of processes described as a capacitor 42 in documents 1 147 926 and 1 207 923. With this calibration procedure approx. 85,000 microfarads. The capacitor 42 ren are exposed to certain metals pressures, 25 can be charged up to approximately 120VoIt, at which a phase transition takes place which affects the electrical behavior of this. One pole of the capacitor 42 is due to a metal. Line 43 via a switch 44 and an inductive If, for example, iron is pressed together, then activity-free current resistance 45 of 0.00193 ohms occurs at a pressure of approximately 130 kilobars connected to the upper punch 15. A significant reversible change in the electrical 30 stand 45 is grounded via the line 46. The other resistance on. When calibrating the apparatus pole of the capacitor 42 is through the line 47, a change in contradiction in the iron via a choke coil 48 with an inductance means a pressure of 130 kilobars. of 25 microhenries and a resistance of

The following table lists the metals, 0.0058 ohms connected to the lower punch 16, for the calibration of the belt clamp 35 described. The capacitor 42 is of any suitable were used. . Power source 49 (not shown) charged. After this

The switch 44 can charge the capacitor 42

Table I will be closed and thereby the charged

Capacitor 42 can be discharged via sample 32 in reaction vessel 20. Based on cold graphite surrounded by substances such as pyrophyllite, magnesium oxide (MgO) and boron nitride (BN) and carried out on the basis of ordinary thermal conductivity and thermal capacity values thermodynamic calculations show that the temperature in the middle of a graphite sample is im Reaction vessel according to FIG. 2 in about 0.015 seconds drops by half. The electrical circuit described provides the required heating energy delivered in about 0.001 to 0.004 seconds.

The best way to observe the behavior of an electrically conductive sample is to measure the electrical contradiction of the sample. As is well known

metal

Bismuth I *).
Thallium ..
Cesium ...
Barium I *).
Bismuth III *)

iron

Barium II *)

lead

Rubidium ..

Transition pressure in kilobars

25th

37

42

59

89

130

141

161

193

*) Since some metals, with increasing pressure, several passages

^{Are the diC rotated}

designated.

with roman numerals _{55 graphite a} | _s electrical conductor and

considered electrical insulator. In the present case

the graphite sample 32 is a link in the circuit described, and the conversion of graphite into Diamond is therefore found in the following publications by an increasing number of occurrences: 60 Stand and or by an open one F. P. B u η d y. Calibration Techniques displayed in Ultra High Circuit Appropriate State. at

The implementation of the invention is therefore a 'Kelvin bridge resistor 50 between the upper Stamp 15 and the lower stamp 16 switched, of Scientific Instruments, Vol. 32, No. 3. S. 308 to 65 thus the resistance of the reaction vessel or the March 31, 1961. Sample 32 can be measured.

By using the electrical contradiction to graph the voltage and

Changes to the metals listed can be achieved by pressing the current flowing through the sample 32

A more detailed description of the process used to determine the above transition values

Pressures. Journal of Engineering for Industry, May 1961; S. Ba I a η and H. G. Drickamer, Transactions of the ASME, Series B and A, Review

the circuit 41 contains an oscilloscope 51 which is connected by a line 52 (for the voltage signal E) to the lower stamp 16 and by a line 53 (for the current signal E ₁ ) to the line 43 between the switch 44 and the resistor 45 . The oscilloscope 51 has a grounding line 40. The grounding 46 of the circuit 41 takes place between the sample 32 and the resistor 45, so that the E and the E, signals to the oscilloscope have a common ground. The oscilloscope has a recording interval corresponding to the discharge time, 0 to 5 and 0 to 10 milliseconds being used in the examples of the invention. The oscillogram was photographed by an instant camera placed in front of the screen.

Various arrangements can be used to generate a tilt signal for the oscilloscope 51 will. In the case of an appropriate sounding, a capacitor 54 with a capacitance of 1 microfarad into a line 55 leading from one side of the choke coil 48 to the oscilloscope 51 switched on. Another capacitor 54 'with a capacity of 1 microfarad is between ground 40 and the other side of choke coil 48 turned on. The deflection tilt signal therefore corresponds approximately the voltage drop across the inductor 48. For the intended purpose are of course also many arrangements still possible. For example, several oscilloscopes can be used or if no measurements are required, the oscilloscope and the associated part of the circuit can be omitted.

The rise in temperature in the sample is determined by calculation, since there are no instruments with which such high temperatures can be measured with sufficient accuracy within such a short time can. The temperature calculations are partly within a wide temperature range known values of the specific heat of graphite. These values were determined experimentally and compared with the values already known.

Record in degrees Kelvin. You can also add the table values above to the equation

τ Q = J Cp (T) dT

and get the same result. Q is the supplied heat in kilocalories per mole, T ₀ is the starting temperature, T is the end temperature and Cp is the specific heat. In the following table Ha, values of Q and T _{0 are given} as examples.

Table Ha

/ kcal \
^Q { mole J T (K) 0 300 5 1450 10 2250 15th 3050 20th 3800 25th 4600

Table II

7 ι κι / approx! \ 300 ^ Mole K ) 500 2.05 750 3.49 1000 4.48 1250 5.14 1500 5.35 2000 5.75 2500 6.0 3000 6.2 3500 6.35 4000 6.5 6.65

45

55

60

If the dependence of the specific heat on the temperature is represented graphically by plotting the specific heat as the ordinate and the temperature as the abscissa, then the area under the curve can be integrated and the amount of heat supplied per MoI graphite in kilocalories in a further curve depending on the temperature From the voltage curve and current curve supplied by the oscilloscope, the power supplied at any point in time can be calculated by multiplying the associated current and voltage values. In Fig. 6 shows the curve K the supplied power in kilowatts as a function of time.

The relationship between voltage and current is: R = U / 1. The U and / values can be taken from the oscillogram and in this way the values shown in FIG. 6 curve labeled J can be obtained.

When calculating the temperature reached in the sample, certain losses must be taken into account Take corrections into account. These corrections include: First, those in the end electrode areas generated heat, for example between the input of one of the electrodes 27 or 29 and the sample 32 (since the materials and cross-sectional changes are known, this heat loss can be calculated), second, the heat conduction losses to the walls of the reaction vessel (by carrying out experiments in reaction vessels with walls made of other substances, in which the cooling time is measured, the heat loss can be based on the known graphite melting temperature for a given reaction vessel arrangement) and thirdly, the electrical current loss due to the walls that are conductive at higher temperatures (which was determined by carrying out experiments in Reaction vessels with walls made of different materials and by comparing the results can be determined). Due to these more important correction factors, the temperature values can fluctuate by up to ± 10%. The purely numerical one However, the value is only of secondary importance, as there are different discharge energy values in the apparatus described Surrender to diamonds. The desired temperature in the sample is changed by changing it the electrical charge or capacitance of the circuit 41 is reached. The final temperature of the graphite

809 640/1659

sample 32 or 38 does not only depend on the supplied electrical energy, but also on the shape of the sample.

The pressures and temperatures occurring in the reaction according to the present invention will now be described in more detail with reference to FIG. 7, which shows a phase diagram of carbon, the pressure in kilobars being plotted on the ordinate and the temperature in degrees Kelvin being plotted on the abscissa. In the description, the absolute unit "bar", which is very pleasant at high pressures, is used to indicate the pressures. One kilobar is equal to 10 ⁹ dynes / cm ² and corresponds to 1020 kg / cm ² or 987 atmospheres.

The already known graphite-diamond equilibrium line between the graphite-stable area G and the diamond-stable area Dl is denoted by the letter E. Region G is a graphite stable region and a diamond metastable region since both graphite and diamond exist in this region, but diamond is thermodynamically unstable in this region. The region Dl is a diamond-stable region and a graphite-metastable region, since both carbon forms exist in this region, but graphite is thermodynamically unstable in this region. In this context, reference is made to the “Journal of Chemical Physics”, Vol. 35 (1961), No. 2, p. 390, fig. 15, shown diamond-graphite equilibrium line referenced. It should be clear that changes in the position of the equilibrium line E have no effect on the teaching according to the invention, since it is essentially necessary that the working conditions are independent of the course of the equilibrium line above this line and / or in the diamond-stable region of the carbon, which is with any Calibration method of a certain apparatus was established.

An important line in this diagram is the melting line S of graphite. As is known, the line S begins at a triple point Tl at approximately 4050 "K and 0.12 kilobars. This triple point is the triple point of carbon (graphite), which can be present at this point in solid, liquid and vapor state at the same time Through the point T1, together with the line VI, the region G in which carbon is present in solid form (graphite), the region L in which carbon is present in liquid form, and region V in which carbon is present in vapor form The line defining the liquid area is not shown and runs at normal pressure from 3860 "K to Tl. The vaporous area V is exaggerated so that it can be seen in FIG. 7 can be represented.

It has been found that the line S, which was previously regarded as the boundary line between solid and liquid carbon, does not run directly upwards from point Tl as a generally straight line and without any substantial inclination, but rather that it has the shape of the line shown Sl has. The line S1 runs from point T1 with a positive gradient upwards, then continues with a negative gradient and reaches the point Tl. The course of the curve S1 was determined in a series of experiments in which graphite melted at different pressures and the melting temperature was determined. The graphite melting process will now be explained in more detail.

The electrical resistance of graphite decreases with increasing temperature. When melting, however, the resistance of graphite decreases with a sharp kink in the resistance curve. If, for example, the apparatus according to FIG. 1 and the circuit according to FIG. 5, then current and voltage curves are obtained and the corresponding electrical resistance of the sample can be calculated. From the resistance curve it can be seen that when energy is supplied, the resistance decreases steadily for about 1.5 milliseconds, but then a sharp downward bend occurs. In Fig. 8, which shows a curve K, J and R for Example 3 below, a melting point Mj is shown as an example. The resistance curve has a kink at this melting point. This melting point Mj agrees well with the melting point in other examples. The melting temperature, which is extra polished to atmospheric conditions, agrees well with the melting point of graphite at 4050 ° K. The many melting tests carried out in graphite show that the melting temperature conditions correspond favorably with the known values given above by B asset and N o da. From studies performed on many graphite samples before and after a given experiment, it is very clear that the graphite was molten. Before melting, the cross-section of a graphite rod has a coarse, irregular grain structure. After melting and cooling, the cross-section of a similar graphite rod shows a dendritic structure of dendritic graphite needles, which are oriented radially from the colder edge part towards the center. Furthermore, X-ray diffraction patterns of ordinary graphite were compared with X-ray diffraction patterns obtained with a sample of recrystallized molten graphite at locations where the graphite was melted and not melted. The diffraction patterns of ordinary graphite were similar to the diffraction patterns taken on the unmelted part of the molten sample. However, the diffraction lines of the molten part were much sharper, as a result of which the size of the articulated crystallites of the solidified graphite is substantially larger than that of the crystallites of the unmodified or molten part. The appearance is quite similar to a cross-section of a quenched metal (chilled cast iron).

In the following Table III several examples are given which were carried out for melting down graphite. In each example, the graphite sample was examined as to whether it had melted in the manner described above. The term Em is used to describe the energy input per unit weight of the sample in kilocalories per mole that is required to bring the sample to its melting point. Spectroscopically pure graphite was used in the examples. Table III is given by way of example only as various other types of graphite listed below were also melted. To further confirm the results, the material from which the wall of the reaction vessel is made was also varied. For example, pyrophyllite (Py), katlinite, talc, magnesium oxide, aluminum oxide, thorium oxide and other similar materials can be used as wall and sealing materials

Stone and ceramic types can be used for all working conditions including diamond reaction. The disc segments 26, 28, 30 and 31 of FIG. 2 and the cylinder 36 from F i g. 4 manufactured. It has been found that within the calibration range of the apparatus, the various Wall materials do not noticeably influence the pressures used. The one through rapid heating The increase in temperature that can be traced back results in an increase in pressure in the reaction vessel. This pressure increase is estimated to be 10 to 20 kilobars, but it can also be greater.

The procedure used in carrying out these examples is similar to that previously described Operation of the apparatus. A reaction vessel according to FIG. 2 or F i g. 4 assembled and this reaction vessel in the apparatus 10 according to F i g. 1 brought. With help a press, the punches 15 and 16 are moved towards one another in order to reduce the pressure in the reaction vessel to increase a given value. Subsequently, with the help of the circuit 41 through the sample

ίο discharge electrical energy in order to heat it up. The pressure specifications are comparable with one another and it is assumed that they are within the calibration range of the Apparatus are equivalent.

Table III

Reaction vessel Wall material pressure Electrical power farad Em example in kilobars 0.040 kcal Fig. 4 Py volt 0.040 Mole 1 Fig. 4 Py 117 30th 0.040 24 not melted 2 Fig. 4 Py 121 32 0.040 26 not melted 3 Fig. 4 Al ₂ O ₃ 118 40 0.085 28 melted 4th Fig. 2 BN 119 40 0.080 28 melted 5 - BN 115 25 ■ 0.080 29 melted 6th - BN 97 110 0.080 31.5 melted 7th - BN 77 110 0.080 33 melted 8th - BN 66 110 0.080 36 melted 9 - BN 60 110 35 melted 10 47 HO 33.5 melted

Examples 6-10 were run at lower pressures and became a belt apparatus and a reaction vessel of the type described in German Patent No. 1,207,923 is used. as The sample was a graphite rod with a diameter of 1.02 mm and a length of 7.1 mm used, which was enclosed by a boron nitride sleeve. In addition to the examples above many melting tests were carried out at low and high pressures to determine the position and shape determine the melting point line Sl of Fig..7. It was recognized in the course of the graphite melting tests that one enclosed by the curve S1 and the area adjacent to the line S is a graphite zone Gl. In some melting examples, small diamond nuclei embedded in the graphite sample, which turned out to be the diamond crystals had always been graphitized before reaching the melting point of graphite and that the graphitization threshold temperature is very sharp. Graphitization occurred at a temperature approximately 300 to 400 "K is lower than the melting line S1.

When attempting to melt graphite at higher pressures, it turned out unexpectedly found that graphite converted to diamond at lower temperatures than the temperature of point T 2 and before any Melting the graphite. The conversion took place without any previous requirement held catalyst was present. In an example of the invention, a device shown in FIG. 4 shown reaction vessel charged with a graphite sample 0.65 milligrams and into the belt apparatus shown in FIG brought. The apparatus was then a hydraulic one between the two press tables. Brought press with a capacity of 300 tons, and the reaction vessel 33 so compressed, that the pressure in the graphite sample 38 to about 130 kilobar in the area of the iron transition Calibration curve of the press increases. The pressure increase to the iron transition area can be slow or rapid be carried out gradually or evenly without changing the end result. In the present Example, the pressure increase was over after about 3 minutes:

After the pressure increase has ended and the circuit 41 has been charged, the switch 44 closed and thereby through the apparatus and the sample a capacitance of 0.085 Farad at approximately Discharge 17 volts. After discharge, the Kelvin bridge ohmmeter 50 indicated an increase in resistance, which indicates that the sample 38 from its electrically conductive state (graphite) to its elec-

■ trisch non-conductive state (diamond) is converted.

In this example and also in the table examples given below, a series of curves of the curve shown in FIG. 6. Got type shown. ItTF i g. 6 shows the curves K, J and R obtained in the example described above. The curve K shows the power supplied to the graphite sample in kilowatts. Curve J indicates the energy supplied to the sample in joules and curve R indicates the resistance of the sample in ohms. As above.

⁶ S was explained, the integration of the area under the power curve provides after the time the energy curve from which the temperature in the sample within the above limits calculated

13 14

can be. After the electrical 130 kilobars have been discharged and in the example of FIG. 8 an energy through the sample 38, the resistance drops until a pressure of 118 kilobars is applied. In the example of one at approximately 1.5 milliseconds on the FIG. 8 the graphite would have been converted into a diamond around the S-curve and then began to be converted when the pressure rose 130 kilobars. At this point the conversion would have been 5. From Fig. 9, in which the two mentions of graphite in diamond take place. Depending on the: contradicting curves of FIG. 6 and 8 can be compared with each other degree of conversion and the amount of conversion, it turns out that the conversion increases the curve R to infinity, which corresponds to an interrupted circuit according to the invention below the melting point, or takes place only on graphite.

a lower value, which corresponds to a partial um- io In F i g. 9 is the resistance curve R according to FIG. 6th

Conversion corresponds, ie only part of the graphite with R6 and the resistance curve according to FIG. 8th

is converted into diamond. denoted by R 8. These two curves are in

After the reaction vessel 33 had been removed from the dependence on the heating apparatus 10 supplied to the sample, the sample 38 was examined. It represented energy. It can be seen that the diamond was obtained, as can be seen from Fig. 4a, that when the sample 38a was formed on the curve R6 at about 7.5 joules, the removed sample 38a begins the cylindrical shape and then maintains the curve of the original sample 38 very sharply , but increases upwards. From this sample, diamond was obtained with a slight decrease in height. It can be seen from curve jR8 that was. Measurements show that the reduction in the melting of graphite begins at about 12 joules of the density difference between graphite and 20. Examining this sample in the above diamond corresponds. The removed cylindrical described manner revealed that the molten sample 38a was polycrystalline and contained a large one. The diamond formation point is about 4.5 joules away from the graphite number of very small diamond crystallites with a dark melting point. Color and having a greatest length of approximately 1 micron when performing the invention process. To prove that it really is. 25 is a given graphite sample a diamond handle, the sample was given in a hot given amount of electrical. Energy supplied Mixture of concentrated sulfuric acid and Ka and diamond extracted. Usually more lium nitrate is purified and applied to Kralz buoyancy and X-ray energy than is subject to radiation examinations, all of which are conclusive of the threshold temperature line, to determine that it is diamond to be exceeded. To achieve a more complete conversion with x-rays, and analyze a number of these samples to ensure that one got into the conversion area before and after cleaning, it was found to get into it. However, if pure graphite in diamond consisted of diamond in its entirety and essentially converts it, the discharge circuit is immediately borrowed and the entire graphite converted into diamond opens, since diamond is electrically non-conductive. This had been. The X-ray analysis showed none. 35 is a characteristic of the invention. Line of a material that was not already present in the starting When the energy supply was changed in parallel samples graphite or in the surrounding wall material, it was found that the circuit was interrupted. occurs at the same / time. So although the energy

The invention thus enables a direct circulation for melting graphite would be sufficient,

Conversion of graphite into diamond without the 4c being melted by the conversion process

previously required metals are necessary. This prevents the circuit from being interrupted

Transformation takes place in the "solid state" before becomes. Among the to carry out the invention

some normal melting occurs. Graphs used on the process are included

Conversion occurring before melting is, for example, also boron-containing graphites, which because of

now dealt with in more detail. 45 of the existing boron electrically conductive diamond

Molten graphite is not just an electri- cal product. These graphites include B344 and tric conductor, but also has a lower Shawinigan carbon black, which is electrically conductive, diaelectric resistance than solid graphite. Surrender to the mant. If such a graphite was used as the initial conversion of graphite into diamond according to the material, the resistance curve of the present invention increased, the contradiction curve bends 5 °, but not sharply upwards to infinity on an open R. This down-circuit corresponding value, so that essentially buckling occurs upwards. before any sharp borrowed more electrical energy than required the kink is present. Indeed, sample is being supplied. When performing the so ¹ in the conversion to diamond of the current invention, several samples of large energy cycles were opened. If, however, the temperature is supplied to such an extent that the temperature would rise so that diamond is also melted at a value lying in the liquid region L, then the resistance curve would have to be increased again. In these cases the graphite would fall off in downward direction. However, no melting occurs and the electrically conductive diamond is converted, since there is no drop in the resistance curve to be observed. Diamond is subsequently melted, which must be taken into account. This can also be seen by comparing the drop in resistance (for melted Koh resistance curve R according to FIG. 6 with the resistance drop) that was observed. In this way, the curve R according to FIG. 8. In Fig. 6 begins the diamond melt line S1 from FIG. 7. Conversion of graphite to diamond at 7.5 joules, 'In F i g. 7 is a general area in this way, while in FIG. 8 the melting only begins at 12 joules for the practice of this invention. This resistance curves were obtained the above-Nazi Graphil-Diamanl equilibrium line E samples from identical 65, wherein only the pressure im- state diagram of carbon is and and the electric power supply were different. which the temperatures are lower than that of the example according to FIG. 6 a pressure of the melting point of carbon (diamond fused

15 16

line S2). A special area of work that is driven by the melting point of carbon given the properties of the curve S1 and with many through- at the given pressure, i.e. by the

Examples given is related, now becomes diamond melt line 52. The line S 2 rises to one

with the parameters set out below, pressure on the order of 650 kilobars and

related to the transformation process. 5 a temperature of the order of 1200 ^° K

Since one has now determined the shape of the curve Sl. This pressure and this temperature has to define this curve via the triple point Tl a triple point T3. To create the · complete continue. The curve S1, which is lengthened over the trip point Tl, from carbon to curve S1 is referred to as curve M, FIG. 7 one can now refer to the state diagrams which are assumed to be a metastable 10 of other substances, for example the graphite melt line. Another basis of the state diagrams of InSb, Ge, etc. to confirm the continuation of the curve Sl or M is the many triple point T 3, which is given together with examples of the invention, including the area D3 in the lines S3 and S4 , within the examples given in Table II above, that another form of carbon exists. If the points shown as triangles 2 are undercut near 15, if a carbonaceous material of the curve M is thrown near the triple point T1, pressures above approximately 650 kilobars are found. As a result of the metastable graphite melt line M conversion into a metallic carbon form, a pressure and temperature area Dl is established, the density of which is 15 to 20% greater than that in which only diamonds exist. One takes known density of diamond. The line S4 indicates that the line M is an instantaneous melting point, not a pressure limit, but an upper pressure limit line for metastable graphite, on or above the line for the production of diamond, above which the graphite immediately has a molten state of carbon in metallic form is present,
similar intermediate country passes through to form diamond The transformation in area A will be best. There need not be a catalyst or solvent referred to as a solid state conversion medium to be present. The line M begins on 25 because there is obviously no dissolution or no diamond triple point T1 and intersects the ordinate or formation takes place from a solution. Any prior melting occurring in the Ge-O "-Kelvin line at approximately 400-450 kilobars near A is referred to as single-zone melting, or melting on a single molecular basis, generally encompassing the areas D1 and D1. Area D. This melting closes area D. If the described 30 can be based on an instantaneous melting within a very large area diagram, the conversion of diamond begins with the small areas with subsequent recrystallization carrying out the invention. The conversion takes place above graphite to carbon in area D1 and a diamantmctasUibilcn region will take, and terminated due to the line M, as between lines M to limited Schmclzcns is in wcscnt- and Sl only diamond exists. the conversion of 35 lent to a transformation in the solid state, may at room temperature at pressures The invention process is therefore based on temperatures approximately 400 to 450 kilobars or higher, which are lower than the temperatures set by the temperatures and lower pressures carried out by the Diamond Smelting Clinic S2, are limited until the triple point is reached. The one in the German Auslcgeschrifl 1 193 021

Experimental results show that the general procedure described will be the temperatures

Working area Dl and D2 contains a border area A , beyond the Diamantschmeizliiiic S2 into the

which is increased by the very near and below the line M liquid area. This will happen in one case

lying line Th is set. The border area A reached by using a graphite, the Frcmd-

is in Fig. 7 shaded and contains a broader substance, for example boron, so that the enl-

Part near the triple point Tl and tapered 45 standing diamond is electrically conductive. It therefore occurs

then and finally falls at room temperature - no interruption of the current path, - and it

conditions with the line M together. The width is supplied with so much energy that the temperature

of area A depends on the reaction time. rises to a value lying in the region L.

For example, when practicing the invention, melting occurs and from the melt

the reaction is relatively slow, in size 50 diamond is recrystallized in area D2.

Order of 3 to 5 milliseconds, so that the reac- When carrying out the invention in the described

tion several hundred degrees Celsius below the pressure and temperature range just above and below

Temperature on the line M can begin. However, where the line M in FIG. 7 graphite is converted into diamond

the response time changed by several orders of magnitude. According to the invention, a given

is less, in the range of microseconds, finds 55 graphite sample brought to a given pressure,

the reaction takes place closer to the line M , so that the and by the graphilprobc is preferably one

Area A becomes narrower with a shorter response time. given amount of electrical energy discharged to

The area A is an area in which graphite is transformed into diamond. It can

For the graphite-diamond conversion, there are also other raw materials that contain carbon

of single domain melting occurs but yields 60 or elemental carbon, d. H. so not

the reaction need not be complete and diamond-shaped carbonaceous substances are used

only partial conversion can occur. will. For example, in addition to graphite, more amorphous

In carrying out the invention, carbon begins to be used. But to others

Conversion of graphite to diamond in the area with carbonaceous substances in general

Dl. Especially in area A, and when reaching 65, related reactions are to be excluded,

the line M ended, and it existed between the was predominantly graphite as a starting material

Lines Λ / and S2 only diamond. used. For example, can be used as the starting graphite

The upper temperature limit of the invention - both amorphous carbon and spectral carbon

809 640/1659

pischer graphite, graphite Sp-I, graphite B344, pyrolytic Graphite, Ticonderoga graphite, etc. can be used.

Spectroscopic rod or electrode graphite is a multicrystalline pure graphite form that has a density of approximately 1.65 g / cm ³ and is used specifically for electrodes in spark spectral devices for chemical analysis. Since this graphite is used for the arc electrodes, with the help of which substances are vaporized in order to carry out a spectral analysis, it is particularly free of chemical elements that result in spectral lines in the part of the spectrum used in the analyzes, i.e. all metals, such as iron, Nickel, aluminum, etc., and semiconductor metals such as geranium, antimony, bismuth, etc., are absent.

Sp-1 graphite is a special high-purity graphite in flake form with very good crystal perfection. This graphite is manufactured by the National Carbon Company and designated Sp-I.

Graphite B344 is a high purity graphite that contains approximately 0.2 to 0.3 percent by weight boron carbide. The powdery starting materials are mixed, pressed and fired at about 1500 to 2000 "C. The density of this graphite is about 1.7 to 1.8 g / cm ³ .

A graphite is called pyrolytic graphite, which is produced by thermal decomposition of a carbon-containing gas, for example methane. It possesses high purity as well very well oriented crystal structure. This graphite gets at about 3000 "C for about 1 hour annealed, then it is called annealed pyrolytic graphite.

Ticonderoga graphite is a natural graphite mined in Ticondcroga, New York.

Shäwinigan soot is an amorphous lamp soot carbon, available from Shawinigan Chemicals Limited, Shawinigan, Quebec, Canada.

The examples given in Table IV below serve to illustrate a preferred implementation of the invention. In these examples, the procedure was similar to that in the diamond production example already described and in the graphite melt examples. All procedures used are similar to those given with respect to Table III. All wall materials are listed. L denotes a reaction vessel with a length of 2.015 mm, a height of 0.56 mm and a width of 0.635 mm and with S one with a length of 2.015 mm, a height of 0.457 mm and a width of 0.56 mm. In the case of the reaction vessels according to FIG. 4, the sample is 0.763 mm in diameter and 1.02 mm in length, unless otherwise specified. If no dimensions are given, it means that a sample of the dimensions described in connection with the reaction vessel was used. In Table IV, Tic is Ticonderoga graphite, Sp is spectroscopic graphite, Pg is pyrolytic graphite, Sb is Shawini black, Py is pyrophyllite, Alox is aluminum oxide and Mgox is magnesium oxide.

Table IV

example Reaction vessel Reaction
wall material Sample material pressure
in kilobars Electrical power farad Result volt 0.040 1 Fig. 4 Py Annealed Pg 110 16 0.040 diamond 2 Fig. 4
Prnhp Py Annealed Pg 130 27 diamond IT LKJ UC
rectangular 0.84-9.4 mm 0.040 3 Fig. 4
Prnhp Py Annealed Pg 125 36 diamond riuuc
rectangular 0.84-9.4 mm 0.040 4th Fig. 4 Py Pg annealed; 139 25th 0.085 diamond 5 Fig. 2 Py Annealed Pg 130 18th 0.085 • diamond 6th Fig. 2 Py Annealed Pg 130 22nd 0.085 diamond 7th Fig. 2 Py Sp 130 16 0.085 diamond 8th Fig. 2 Mgox Sp 130 18th 0.085 diamond 9 Fig. 2 Mgox Sp 130 18th 0.040 diamond 10 Fig. 2 Py Sp 138 33 0.085 diamond U Fig. 2 S, Py Sp 130 16 0.085 diamond 12th Fig. 2 L ₁ Py Sp 140 20th 0.040 diamond 13th Fig. 4 Py Sp 130 32 0.040 diamond 14th Fig. 4 Alox Sp 140 30th 0.040 Diamond ■ 15th Fig. 4 Mgox Sp 140 30th 0.040 diamond 16 Fig. 2 Py Sp 140 25th 0.085 diamond 17th Fig. 4 Py B 344 180 22nd diamond

continuation

example Reaction vessel Reaction
wall material Sample material pressure
in kilobars Electric 3 energy Result volt farad 18th Fig. 4 Py Dixon HB 140 31 0.040 diamond Pencil- graphite 19th Fig. 2 Py B 344 130 20th 0.085 diamond 20th Fig. 2 Py B 344 130 22nd 0.085 diamond 21 Fig. 2 Py B 344 130 18th 0.085 diamond 22nd Fig. 4 Py Sp-I 139 34 0.040 diamond 23 Fig. 4 Py Sp-I 120 30th 0.040 diamond 24 Fig. 4 Py Sb 140 26th 0.040 diamond 25th Fig. 4 Py Sb 140 20th 0.040 diamond 26th Fig. 2 Py Tic 130 14th 0.085 diamond

The in F i g. The examples given in 4 serve to illustrate a number of experiments. To determine the minimum conditions were several examples with stepwise higher pressures and Temperatures are carried out to determine when the conversion takes place. For example When using spectroscopic graphite, the conversion takes place at a minimum pressure between approximately 120 and 130 kilowatts. The minimum energy input required per unit weight of the sample results in about 16 to 17 kilocalories per mole of graphite. Through this supply of energy defines the point at which the resistance curve rises upwards. To complete the conversion therefore requires more energy. Be practical with the specified Samples fed an average of about 25 kilocalories per mole.

The above examples serve to illustrate the implementation of the invention with a preferred one Apparatus and a preferred circuit. There are also other devices known and available, which provide the given conditions, in particular equipment which is at least in The area of iron transition in the general range of 120 to 135 kilobars deliver pressures. The in F i g. 1 shown belt apparatus can be enlarged and / or the shape of the reaction vessel can be appropriately changed to allow a larger reaction volume to carry out the Invention is available. The circuit can also be changed. However, the circuit must deliver the required energy in a period of time that is shorter than that required for melting Time span or the elapsing time before harmful chemical reactions occur in the wall materials Period of time. With the discharge circuit used, the sample material reaches the required level Temperature and begins to cool again before the materials surrounding the sample have absorbed too much heat. It can also do that in the German Auslegeschrift 1 147 926 The heating method described can be used in which the sample is normally slowly passed through Resistance heating is heated. The temperature rise can occur in the practice of the invention can be changed considerably with the circuit described. This is done by using different Capacities and tensions reached. The from Fig. 4 apparent voltage range from 30 to 16 volts corresponds to a delay in the temperature

increase of about 2Y ₂ milliseconds.

A known variable resistance heating circuit described in German Auslegeschrift 1 147 926 was also used to carry out the invention. For example, when using a reaction vessel made from thorium oxide according to FIG. 2 increased the electrical resistance heating over a period of several seconds and reached a maximum temperature of approximately 2500 to 2800 ^° K, which was maintained at a pressure of approximately 160 kilobar for 2 to 3 seconds, with diamonds being formed. The reaction occurring in the process of the invention differs from the reactions described in German Auslegeschrift 1 147 926 in that no molten metals are present in the present invention, since no metals are used and the transformation temperatures prevent the graphite from melting, although to a limited extent some scattered individual areas can melt. In higher temperature ranges the reaction proceeds so quickly that the transformation temperature in the graphite is reached, and cooling begins before high temperatures are reached in the surrounding substances. So the reaction or transformation that occurs first can best be described as a solid state transformation. A process for the production of diamonds by recrystallization of molten carbon, in which the carbon is essentially melted, is the subject of German Auslegeschrift 1 193 021.

To the examples illustrating the teaching of the invention, parallel experiments were made to the Determine the effect of the metals required up to now on this transformation process. For example the reaction vessel according to FIG. 2 used in one of the experiments listed in Table IV, whereby diamonds were formed. In parallel to this experiment, a second experiment was carried out, in which a mixture of graphite and nickel powder was used. Because nickel is one of the metals previously required. After performing the parallel experiment, the content was or

⁶ S the central part of the reaction vessel was examined, and no different reaction or no different reaction product was found. The same diamond was formed in both cases. Another-

on the other hand, the nickel powder was relatively unchanged, since the reaction line was so short that none Solution took place. Repeating the above procedure * with other metals also showed no noticeable change and the reactions were not affected by the added metal. From countless tests carried out in the manner described above, it was found that various Metals, graphite, the impurities of the graphite and other substances cause the conversion reaction affect only insofar that the temperature at which the conversion takes place, is slightly Dimensions is changed.

During the conversion process, reaction vessel retains 20 and sample 32 in general the geometric texture. This is especially true for sample 38 according to FIG. 4. The entire sample 38 is converted into a single cylindrical diamond mass converted, as denoted by -38a in Fig. 4a. You can therefore get different diamond shapes by simply choosing the graphite sample accordingly. The design and shape the sample -according to fig. 2 and that of circuit 41 added charge can be sized so that essentially all of the graphite sample is in diamond is converted. The from the reaction vessel shape according to Fig. 2 obtained sample is shown in Fig. 2a and has the shape of a square block, the length of which corresponds to approximately one third of the length of the sample 32. The long edges of the sample 32 " are sharp, while the end parts are slightly rounded. As with the sample 38 «also corresponds to the Sample 32 ″ the reduction in the amount of change in density from graphite to diamond. Is the original one Oriented graphite sample, d. H. annealed pyrolytic graphite, then covered the diamond mass formed also consists of diamond crystals with a similar orientation.

The movement or excitation of the Kohlensloffgitlers for the purposes of the invention is by direct Supply of energy to the graphite sample achievable. This direct energy supply results in a more direct transition from graphite to diamond without the need for any intermediate mills, for example that in the known Diamanthcrstelluhgsverfahren required molten metal. The excitation or movement of the carbon lattice will by thermal energy, electrical energy or by this. that a crystal different Forces such as "pressure, tensile or shear forces" through the use of high-frequency sound waves and radiation exposed to radioactive particles. Preferably so much energy is supplied that graphite is converted into diamond. The excitation of the carbon crystal must take place or be effective when the graphite is below one of the diamond-stable areas of carbon lying pressure steal. so the resulting Effect on chemical and electrical bonds consists in that some carbon atoms are precipitated in the form of diamonds. Carbon atom excitation includes in itself. that all atoms in a given crystal lattice are so excited, that the crystal structure is changed. d. H. excitement both between lattices and between atoms.

At a ; Embodiment of the invention is an electric discharge through the graphite, which is under the required pressure Carbon atom excitation used. When the current is discharged through the graphite, the temperature rises of graphite, so that current discharge and temperature can be related to each other. This temperature is called the "threshold temperature" designated. Such a threshold temperature can, however, also be achieved by other heating means and heating methods can be achieved, for example by a thermite reaction or by an external heating device.

In conversion processes and in many chemical processes In reactions, temperature plays an important role. In particular, the reaction speed depends on temperature, and higher temperatures result in faster reaction rates. In the invention, temperature also affects the rate of conversion, and so are higher temperatures desirable. The threshold temperature is a temperature at which the Conversion rate is so great that a sufficient amount of diamond in a relative is generated for a short time, d. H. a measurable and finite amount of diamond is obtained in this cell. It is assumed that the conversion process according to the invention is started by excitation of carbon atoms and the rate of conversion is determined by the temperature. It can therefore more effective and better stimulating agents at lower temperatures or lead to other slower temperature increases. A slower temperature rise or The lower temperature immediately results in a more favorable control of the process and enables it the use of various other reaction vessels and materials for the walls of the reaction vessel, which are more sensitive to help, but at lower temperatures are more desirable.

Studies carried out on various types of graphite show that the threshold temperature at which conversion begins or takes place at a given pressure is a function of the type of graphite. The types of graphite converted to diamond in accordance with the present invention include specroscopic graphite, Sp-I graphite, Ticondcroga graphite, pyrolytic graphite, annealed pyrolytic graphite, types of graphite with different densities, with different levels of impurities and mixtures of different graphites. It has been found that each type of graphite or graphile mixture used has a different threshold temperature at which the conversion reaction takes place. Furthermore, the conversion reaction takes place at different minimum pressures. The threshold temperature decreases with increasing pressure. There is therefore a threshold temperature for every printing condition. The threshold temperature is the temperature required for conversion at a given pressure and a given sample material. One can therefore establish a threshold temperature curve for a given graphite sample by performing a series of experiments. In Fig. 7, the curve Τ / τ represents the threshold temperature curve of spectroscopic graphite. The method used to determine the curve Th is essentially the same as the method used in the examples according to Table IV for determining the minimum pressures. For a given pressure there will be different amounts

23 24

Electrical discharge energy supplied in order to ensure that the control of the pressure is not noticeably influenced, from which amount of energy a conversion is made. Pressure and temperature are therefore of one another ^; takes place. One then knows this threshold value independently. As shown in FIG. 7 can be seen, the amount of energy, then one also knows the threshold value - after a conversion into diamond, the pressure temperature. For every starting material there are 5 in the diamond-stable area above the graphite-diamond - a threshold temperature curve, so that one takes for equilibrium line E , so that no graphilial starting materials get a whole family of curves. ization of the diamond occurs. This important control in connection with the threshold temperatures is now possible with reference to FIG. 7 results in more detail from the resistance curve of some graphite - explained. When implementing the erfindungsgearten that "the conversion without using 10 MAESSEN method, the pressure can be increased via the graphite energy, for example thermal energy or electrical diamond equilibrium line £, and the Schalscher discharge energy can be discharged at very low pressures device 41. The For example, both annealed must be limited so that the graphite fused pyrolytic graphite as well as Ticonderoga graphite point is not reached at lower pressures, with a high degree of crystal orientation in diamond 15 so that the diamond formed does not turn into molten one with the help of relatively low pressures. This graphite is so phits in the liquid state that the pressure drops into the graphite-stable area, which is parallel to the end faces of the punches 15 and 16 Graphite g is won. Are the pressure beds. It is observed that during compression there are 20 temperature conditions in the diamond-stable compound of, for example, annealed pyrolytic graphite, then the pressure at the desired room temperature, the resistance must be kept at about the temperature in this area, since 110 kilobars begins to rise, which leads to a change. when the pressure drops below the line E, the conversion into electrically non-conductive diamond - already formed diamond because of the high temperature. After reducing the pressure, the 25 door is graphitized again. Squeeze and tempera resistance again. It is assumed that doors must therefore form small diamond cores in correct interrelationship, what. stand by the rise, so that given conditions are established and the resistance is displayed, these diamond cores can be maintained. However, when the pressure is reduced, the pressure can continue to be increased and tized by any desired amount. A stabilization of the formed 30 can be lowered. The independent control is a diamond core can for example by an important feature of the invention., Ringcre electrical energy charge and fast. The invention is described on the basis of static pressure heating of the sample at the end of the resistance apparatus, in which the conversion increased can be achieved, whereupon the diamond from graphite to diamond then takes place. In such an apparatus under atmospheric conditions, the pressure can, if appropriate, first be obtained. In one example, the initial resistance of a sample of annealed pyrolytic span, generated within a variable and prolonged period of time, was 0.112 ohms and before the temperature increased graphite. had after application or the circuit 41 is discharged. It gets a value of 0.247 ohms from pressure alone. After a slow increase in pressure, preference was given to achieving an even and complete increase in resistance in the various fabrics. Discharge energy (0.085 farads at about 16 volts) The term "slow" is to be understood to mean that the was supplied, after which diamonds were then extracted. Although the pressure increase is preferably in minutes, he-Dicsc conversion indicates a considerable follow-up, but also one lasting only a few seconds below the curve Th in FIG. 7 lying 77i. Curve pressure increase is included. Stability of the pressures. An additional explanation of this conversion 45 within a reasonable time limit results in a low pressure assumption that, on the one hand, the more favorable mode of operation and a more complete curve M, an instantaneous metastable graphite conversion. Although both pressure and melt line are controlled while area A is a reaction temperature, the pressure or transformation time element of the size is more subject to control, since it is. from the initial value to a few milliseconds. One could thus -50 to the final value is controlled The controlled pressure expect that reactions below the area A- is therefore from one generated by shock waves. (however above, curve E) occur where the time-pressure differ, as it is to be sustained element for the reaction is considerably longer. In the case of can and.not only temporarily present , pressures that are far from area A can be controlled and the rate of pressure change can be controlled, the required reaction line is unusually long. At high temperature is the length of time to choose. ; rend that the pressure can be maintained, One of the salient features of the invention only through the work-finding used in the apparatus concerns the control. Both the temperature substances are specified. As the pressure in stages in as well as the pressure can be individually controlled in one or more stages, so can the temperature. For example, the temperature can be increased in steps when carrying out the process of the invention if, in the process of the invention, a desired pressure is generated using an ordinary resistance heater for a given material and this pressure circuit applies delayed thermite reactions or is changed for various purposes. Thereafter, the temperature can be discharged to a given voltage value below the threshold temperature and capacitance values by the circuit 41 by various means. The increased to <»5 and then a capacitor discharge to complete the slight rise in temperature, which is due to the rapid heating, is estimated to be less than 5 to 10 kilobars

809 640/1659

move the temperature conditions, that is to say from or to the transition areas, with greater accuracy and control. If, for example, pressure and temperature conditions are to be moved or shifted into area A or into area Dl of the state diagram of carbon, one can use a. Take a path that does not pass through areas in which no conversion takes place, such as the liquid carbon area and the graphite area (apart from the initial traversal). In particular, the return route from a conversion area can also be precisely defined and adhered to. For example, at a given pressure, graphite can be converted into diamond during the temperature rise, but at the end of the temperature rise the temperatures can be so high that the diamond formed melts in the carbon melt area, which at the same time reduces the pressure so that only graphite is obtained. Furthermore, after the conversion of graphite into diamond, if the pressures are not kept at a high value, the temperature curve can extend into the graphite area and the diamond can be converted into graphite. However, the control enables the pressure and the temperature to be increased uniformly or in steps, so that the conversion area A or D2 can be entered from a starting point to the left of the line S starting from different directions. The starting point can either be the normal state or a state in which higher pressures and temperatures are already present. For example, one can increase the pressure in the diamond region D starting from normal conditions, ie atmospheric conditions. Then you can increase the temperature so that you get directly into the area A or Dl . The pressure and / or temperature increase can take place alternately in stages. At an intermediate point at which there is already a high pressure, a temperature rise can also result in the area 4 or D 1 being reached directly. At a point in the graphite region G at which the temperature is high, the pressure and the temperature can be increased so that the region A or D 2 can be reached. In other words, different combinations of vertical and horizontal movements of the state conditions are possible in order to get into the area D1 . Furthermore, the pressure and temperature conditions can be selected so that they lie at or within the triple point T1 , since the triple point T1 can encompass a small area. Subsequently, when the temperature is reduced, by increasing the pressure, the conversion target A or D 2 can be achieved. With these and other indirect ways to the transformation area: there are also further pressure-temperature change problems, since a temperature change affects the pressure and solid substances,: are converted into liquid substances and vice versa. In this respect it should be noted that the position of the point. T2 or is not precisely determined by the point Tl upward sloping line Sl. The point T1 and the line S 2 are, however, within a reasonable range. for example, within a range of approximately ± 10 kilobars and ± 300 ° K, so that the present invention can be carried out without difficulty because of the measurement accuracy.

Of the various graphite shafts used in the present invention, hexagonal graphite, graphite containing rhombohedral graphite, and various other types of graphite have been converted to diamond by applying the pressure either perpendicular to or: parallel to the C-axis. In the present invention, graphite samples were placed in the reaction vessels, the crystal planes running both perpendicular and parallel to the punch surfaces 19.
In the 'extraction of the diamonds would be from the reaction vessels, in particular from the reaction vessels according to Fi g. 4, a single piece of diamond mass removed, that is, essentially all of the graphite had been converted to diamond. Such a single piece is very durable and can be used as an abrasive element. The individual diamond crystals in such a mass are very small, that is, they are on the order of a micron in size, and their color ranges from black to translucent gray. Your overall configuration is not visible. Such compacts can also be made of other materials in addition to graphite. It has also already been found that jiexagonal boron nitride converts into cubic boron nitride

Application of high pressures and high temperatures can be transferred. Cubic boron nitride is a diamond-like substance that can also be used as an abrasive. You can therefore also choose one from Make diamond and cubic boron nitride crystals existing compact; by making a mixture from, for example, granular or powdery !! Converts graphite and hexagonal boron nitride. Furthermore, a diamond-graphite mixture can be used as the starting material, for example in fine-grained or powdery form, use so that the Compact can be viewed as a diamond sintered compact. One made of cubic boron nitride and hexagonal Mixture of boron nitride can also be converted into a cubic compact of boron nitride: In the following Table V are some examples. listed for the production of such compacts. Py means pyrophyllite.

example Rcaklion
feet Wall-
materiu ί Fig. 2 Py

Table V

Probcnmulurial '

Powdered (140 mesh / cm ² ) diamond and spectroscopic graphite were mixed in a weight ratio of 50:50 and compacted into a sample weighing 65 mg.

130

Electrical power

Fully

120

farad

0.00225

continuation

example Reaction
Gefäß Wall
material Sample material! Drupk in
Kilobars Electric
volt e energy
Fated 2 Fig. 2 Py Powdery (140 mesh / cm ² )
hexagonal boron nitride and spectro
scopic graphite were in weight
50:50 ratio mixed and one
Sample weighing 65 mg
condensed. 75 0.0045

In each of these examples, the central third of the sample was placed in a compact of the type shown in Figure 2a Type converted. A diamond sintered compact was used in the first example and a diamond compact was used in the second example a compact made of diamond and cubic boron nitride. These compacts are suitable as Abrasive elements and can either be used individually, with others or mixed.

X-ray diffraction patterns of the present invention Diamonds made in the invention contain only diamond lines or lines from others substances already present in the graphite. This means that the manufactured according to the invention Diamonds have predetermined properties depending on the original graphite. This is underlined by the fact that the diamond crystals are oriented in the compact in the same way as that Graphite crystals in the starting graphite.

The inclusions or added substances in the graphite are retained - when the transformation takes place in diamond. The purity of the diamond therefore depends on the purity of the starting graphite away. For example, a starting graphite with an impurity ratio of 1 to 10 parts was used used per million and the diamond produced from it subjected to an analysis from which found the diamond to be of similar purity. Natural diamonds with one such The degree of purity has not yet become known. B344 graphite is used as the starting material, then a semiconducting diamond is created because of the boron content. The semiconductor properties depend on the amount of boron present in the starting graphite. In Examples 10, 11 and 12 of Table IV increased the resistance curve is not at infinity, d. That is, the circuit was not interrupted because the Diamond is electrically conductive due to its boron content. The final resistance after the Conversion for Examples was 2, 94, 0.913 and 2.396, respectively, while the initial resistance (Graphite resistance) was 0.107, 0.120 and 0.104, respectively. In Examples 2 and 3, the initial resistance was (Graphite resistance) 0.0954 and 0.0856 ohms, while the terminal resistance was not measured could be because the circuit was broken, d. i.e. the diamond does not conduct. the general properties of a diamond can therefore be specified. This includes the shape or configuration of the sample, the degree of purity, the electrical conductivity, the crystal orientation a compact, etc.

Both graphite and amorphous carbon have been converted to graphite by the present process using high pressures and temperatures within such a short period of time that any intermediate reaction between the starting material and the diamond is unknown, for example, amorphous carbon could be an intermediate before conversion to diamond result in graphitic carbon. Only general limits are given for the pressure, the temperature corresponding to the electrical energy input and the carbon melting point. More specific limits based on calculations are, for example, at least about 3000 "K at 120 kilobars at the upper end of the temperature and at least about 400 to 450 kilobars at room temperature. The term" at least about "is intended to include, within reasonable limits, both areas above and below a given value In the process of the invention, a graphitic material lying above the graphite-diamond line E and finally lying in the conversion area A (D 2) is subjected to pressure and temperature conditions. One can also pass through the triple point Tl Carbon is present in metallic form.

In summary, it can be said that when carrying out the invention for the production of diamonds within an area D1 including an area A , pressures of approximately 125 to 400 to 450 kilobars are used. The temperature can be maintained at room conditions since any temperature rise caused by increasing the pressure is diverted during the control of the pressure rise. ^{The temperature can be increased to approximately 4000 °} K by separate or external heating means (as opposed to the rise in temperature due to compression or impact). A preferred temperature range is approximately between 2500 and 4000 ^° K.

Diamond made according to the present invention can be made in the same manner as natural diamond used for many industrial purposes such as grinding or cutting material. In particular, the diamonds produced according to the invention can also be used for bearing journals, bearings, Semiconductors, gemstones, etc. find use.

Claims (2)

Patent claims: 1. Process for the synthesis of diamond in which graphite is above the graphite-diamond equilibrium line is exposed to pressure lying in the diamond-stable area of the phase diagram of carbon, thereby characterized in that the graphite is exposed to a pressure above approximately 120 kilobars. Γ 284 405 and thermal energy is brought into action in such a way that the interaction of pressure and temperature converts the graphite below the melting line from carbon to diamond, whereupon the heat supply is reduced ^: broken, the pressure relieved and diamond recovered. 2. The method according to claim 1, characterized in that the thermal energy through electrical resistance heating is generated. For this purpose 2 sheets of drawings