DE1176623B - Process for the production of diamond crystals - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Boarding school Kl .: COIb

-31/06 .-

German KI .: 12 i- 31/06

Number: 1176 623

File number: G 31015 IVa / 12 i

Filing date: November 26, 1960

Opening day: August 27, 1964

The invention relates to a method for producing diamond crystals, in which non-diamond-shaped Carbon together with a metal or an alloy in the state diagram of Carbon pressures and temperatures above the graphite-diamond equilibrium line is subjected.

It is well known that in the manufacture of diamonds, carbonaceous material must be present of a metal, for example chromium, manganese, iron, cobalt, nickel, ruthenium, rhodium, palladium, Exposing osmium, iridium, platinum or tantalum to pressure and temperature conditions that are stable in the diamond Area of the state diagram of carbon. Metal alloys can also be used which have the advantage that slightly lower pressures are required for the extraction of diamonds are. Today we know that there is a state diagram for the metals and alloys that can be used of carbon gives a diamond formation area that is from the graphite-diamond equilibrium line and the melting point curve of the metal or alloy-carbon- Eutectic is limited. Within that fixed for each metal or alloy Diamond formation area, there is a so-called cubic area in which substantially predominantly cubic diamond crystals are formed. The cubic range is essentially the lowest Temperature range of for each metal or alloy in the state diagram of carbon specified diamond formation area. Usually, cubic diamond crystals are undesirable, because they do not have a particularly high strength.

The invention is now based on the object of creating a method in which the growth the diamond crystals are controlled in such a way that larger, flawless diamonds are produced.

It has been found that it is not sufficient to produce larger diamond crystals if one is within the diamond formation range specified for each metal and alloy Applies pressure and temperature conditions. Rather, one must also have a very precise temperature control make to diamonds not only of better quality but also of larger dimension to manufacture. It has been found that a change in the conditions in the reaction vessel, which in the Is small compared to the pressure and temperature range in which favorable results are achieved, has a much greater influence on the diamond reaction than was previously assumed.

Process for the production of diamond crystals.

Applicant:

Genera] Electric Company, Schnenectady, N.Y.

(V. St. A.)

Representative:

Dipl.-Ing. M. light,

Munich 2. Sendlinger Str. 55,

and Dr. R. Schmidt, Oppenau (Renchtal),

Patent attorneys

Named as inventor:

Harold Paul Bovenkerk, Royal Oak, Mich.

(V. St. A.)

Claimed priority:

V. St. v. America November 27, 1959

(855 787)

These changes in conditions relate not only to temperature, but also to the Pressure. Both change during the reaction as internal conditions change. After reaching the desired temperatures and during this some parts of the device expand while others melt with a corresponding decrease or increase in their volume. For example, the volume of pyrophillite becomes smaller due to a phase change, and so does the volume of a metal becomes larger as it melts. The pressure also causes the reaction vessel and the contents of the reaction vessel are compressed as the pores are filled and the used Parts have a certain compressibility. These changes in pressure, in turn, result in changes in the effects of the temperature used, since yes the reaction always depends on a correlation of the Depends on pressures and temperatures. Will continue the reaction mass by electrical resistance heating directly heated by electrical through the reaction mass in the reaction vessel If current is sent through, the following phenomena occur:

If the pressure and the temperature are increased and this is determined by a corresponding catalyst curve When the diamond formation region is reached, the conversion of non-diamond-shaped takes place

409 658/389

Carbon to diamond. However, this changes the specific electrical resistance of the filling very strong when more and more electrically conductive carbon in electrically non-conductive diamond transforms. The final temperature or resistance heating depends, among other things, on the carbon volume, on the shape and amount of diamonds formed, on the rate of growth and on the position of the crystals formed in the reaction vessel, on changes in resistance caused by the temperature and other variables.

As it turns out, accurate temperature control is just as important as pressure control, and the quality and size of diamonds can actually be influenced by controlling the temperature will.

In the method according to the invention for producing diamond crystals, in the non-diamond-shaped Carbon together with a metal or an alloy in the phase diagram of carbon subjected to pressures and temperatures above the graphite-diamond equilibrium line is to form diamonds from the non-diamond-shaped carbon, one proceeds so that the pressure to at least 3000 atmospheres above the minimum pressure required for diamond formation and the temperature is increased to a value which, starting from the equilibrium line, 50 ° C protruding into the diamond-stable area, but at least 30 ° C above the the minimum temperature required for diamond formation, the temperature at this value is longer Time is kept constant, then the temperature and pressure are reduced and the formed Diamond crystals are removed.

To carry out the method according to the invention, an indirectly heated reaction vessel is required, this is particularly good for carrying out precise temperature control within the filling and is suitable during the reaction time. Such a reaction vessel with indirect heating is in the German patent specification 1136 312 described in more detail.

The invention is described in more detail with reference to drawings, in which shows

F i g. 1 is a family of curves, each of which shows the diamond formation region for a particular catalyst and indicates the equilibrium lines,

F i g. 2 shows the curve of the diamond-forming area and the preferred diamond-forming area as an example within this range for a nickel-chromium catalyst and

F i g. 3 shows a schematic representation of the same area and the same area for four further catalyst systems.

Each of the in Fig. 1 shows the pressure and temperature range required for diamond formation for a specific catalyst. Curves F, N, R, P, and T in FIG. 1 refer to iron, nickel, rhodium, palladium and platinum. Other catalysts and combinations give similar curves. It has been indicated earlier what type of catalysts are generally used in the diamond reaction. Equilibrium curves for other catalyst combinations are also given in German Auslegeschrift 1147 927. All of these ranges have not been determined with absolute or high accuracy, but rather have been found through numerous trials and hundreds of individual experiments which allow one to specify the range in which diamonds are either formed or not formed with a particular catalyst.

It should be noted that the right-hand branches of the curves are a theoretical dividing line of the Diamond phase and the non-diamond-shaped phases

ίο of carbon or a graphjt-diamond equilibrium line represent. The location of this line was determined with the help of the German Auslegeschrift 1 147926 described pressure and temperature measurement method determined. The temperature measurements were for example with commercially available platinum-platinum-rhodium (10 percent by weight of rhodium, based on the Total weight of platinum and rhodium), chromel-alumel, rhodium-platinum and other thermocouples carried out. The junction was generally placed in the center of the reaction vessel, and the lead wires were carefully inserted into the reaction vessel on opposite sides incorporated holes and then passed through holes in the seal to the measuring device.

It has been found that the high pressures acting on these and other thermocouples do not have a great influence on the measured values.

Today we know that in the formation of diamonds, the catalyst melts somewhat or is a solid one Solution must form before the conversion to diamond takes place. The lowest part of the curves is therefore generally determined by the melting point that the corresponding catalyst in Presence of carbon at the given pressure. The left part of the curves is general straight and does not deviate too much from a vertical line, because the points on it are determined by the melting temperature, which the catalyst in the presence of carbon at has the given pressures and which is roughly a linear function.

For example, diamond formation occurs at any point within any curve F i g. 1, which is generally near the bottom of the curve, being through a small Change the temperature and pressure in the reaction conditions from the diamond formation area the graphite area can pass over and thereby either no diamonds, depending on the change more are formed or already formed diamonds are partially converted to graphite.

In Fig. 2 shows, as an example, a diamond formation region known per se for a catalyst consisting of an alloy of 80 percent by weight nickel and 20 percent by weight chromium. If the temperature and the pressure are increased to a value which lies within the area formed by the curves A and O and C and D , and if the temperature is maintained within certain limits from a few seconds to an hour or more, so arise cubic diamond crystals which are generally of poor quality and are black. This area is referred to as the cubic area in the description. Both the upper bounds of the continuation of the line DEC and the line OA are unknown. There are therefore in FIG. 2 there are no closed curves, but the expression »surface within

a certain curve «understandable in this context.

If the temperature is increased further to a value lying within the curve FEC , then, as has been found in many experiments lasting from a few seconds to an hour or more, the diamond growth takes place very quickly, and the diamond yield is also very high, however, are the individual crystals are generally small and of poor quality, although the quality can be improved somewhat by moving further to the right in this area.

It has now been found, surprisingly, that there is a region along the line DB in which, with precise temperature and time control, extremely large crystals of excellent quality are formed, but in which diamond formation takes place considerably more slowly. This range, which is shown in FIG. 2 is represented by the grooved area, along the line DB just inside the diamond formation area. It is therefore endeavored to keep the pressure and temperature conditions above the cubic range in the vicinity of the line DB within the area lying by the curves DEEF and DB. The hatched area is approximately 50 ° C wide.

The area above the cubic area and just inside the curve DB is therefore well determined. However, in practice, it is extremely difficult to keep the temperature within this area, since in the conventional method and apparatus, the temperature changes in the manner described and the area is limited so that a small temperature change becomes conditions Can have consequence that lie completely outside of this area either to the right or left of the curve DB , without it being absolutely certain where the temperature is now.

In FIG. 3 shows this corresponding area for other catalyst systems. This representation is only schematic, and therefore the individual pressure and temperature values are for the corresponding Catalysts are not so accurate. It serves to explain the present invention.

The line GH is the diamond-graphite equilibrium line which is intersected by the melting curves of the eutectic graphite-catalyst mixture. The drawing shows four catalyst systems for which the following minimum temperature and pressure values apply. It can be seen that the values are more accurate at lower temperatures.

catalyst temperature
⁰ C pressure
at Alloy from
30% Ni-70% Fe
Ni 1240 ± 10
1420 ± 10
1975 ± 30
1700 ± 30 62,000
71000
98,000
85,000 Pt Rh

The area enclosed by the melting point curve and the diamond-graphite equilibrium line forms the area in which diamonds can be formed. The zone immediately above the minimum temperature and pressure value established by the intersection of the catalyst melting point curve and the equilibrium line is the cubic area. The zone of poorest quality runs along the melting point curve and within 10 to 20 ^{° C of the minimum temperature.}

The zone according to the invention, in which large crystals of good quality are formed, extends over approximately 50 ° C. within the equilibrium line and, for the corresponding catalyst system, begins at a pressure of approximately 3000 atm. above the minimum pressure, and at a temperature approximately 30 ° C above the minimum temperature. This area is shown hatched. It should be noted, however, that only the lower part of this area is hatched. For each catalytic converter, this area extends laterally upwards between the line IK and the equilibrium line GH. For the sake of clarity, these areas have not been completely hatched, since the preferred area for a catalyst would overlap with the same areas of higher melting catalyst.

Methods are now given for achieving the pressure-temperature area according to the invention. From Fig. 2 it can be seen that the temperature of the device is initially at atmospheric pressure to a value in the hatched area and then the pressure can be increased so that the pressure-temperature point lies within the lower part of the hatched area. This method is not particularly beneficial, as the increase in temperature occurs before the increase in pressure affects the operation of the device. The pressure increase does not take place along a vertical line Line, but the pressure and also the temperature fluctuate greatly.

Depending on the size of the reaction vessel, the temperature setting time and total uptime will get better results with the following procedures

4 »scored. If a small reaction vessel is used, the time-temperature constant is very small, that is, when electrical energy is supplied, the temperature rises extremely quickly to a high value and then changes gradually in Fig. 2 specified value P 1 increased. Electrical energy is then supplied and the temperature is increased to a value T 1. An increase in pressure and temperature in this order of magnitude results in an increase in temperature which does not particularly affect the value of the pressure P1 . However, the temperature should be kept at the threshold T 1 for the following reasons. If one tries to reach the temperature T 2 immediately, even if the temperature rise time is extremely small, the probability is very high that the temperature will be increased beyond this point and finally reach the value Γ 3, which is outside the diamond formation range. A temperature profile that fluctuates back and forth between the diamond formation area and the area outside it has a considerable influence on the reaction. In addition, since the temperature only changes gradually after a very rapid rise in temperature, the time for a change in temperature from the value Π to the value Γ 2 can be so long that the temperature in the reaction vessel

Area between the temperature T 1 and the hatched area diamonds are formed, that is, the diamond formation begins in an area of poor quality, which affects the quality of the then applicable diamonds in the hatched area.

If, therefore, the temperature is initially only brought to the value T1 , then the temperature and the pressure in the reaction vessel before the diamond formation can settle in the area outside the diamond formation area. Then only a slight increase in temperature is then required in order to arrive at the value T1 lying within the hatched area. After the temperature T 1 has been reached and has recorded itself, the reaction vessel is supplied more energy, whereby the lying within the shaded area temperature TI is reached within a few seconds, so that possibly because of the rapid increase in temperature between the temperature Tl and the temperature Tl only a few diamond crystals can form before reaching the hatched area. The temperature can then be regulated within the hatched area for a period of time ranging from a few minutes to several hours in order to achieve larger diamond crystals.

In the larger reaction vessels that are now generally used, the rise in temperature over time takes place much more slowly (for example within a time of up to 15 minutes) because of the larger volume. Holding the temperature at a value of Tl and then increasing it according to the present invention is therefore more difficult. The following procedure is therefore used for larger reaction vessels. The pressure is increased to the value Pl. Subsequently, sufficient electrical energy is supplied that the temperature rises as quickly as possible, the temperatures Tl and Γ 2 being passed through as quickly as possible and finally the temperature T 3, for example, is reached. This results in graphite diamonds in the area between Tl and Tl , which, however, regardless of their size and quality, are converted back into graphite by increasing the temperature to the value T 3, so that at point T 3 neither diamonds are formed nor diamonds in the reaction vessel available. The temperature is then lowered to the value Tl and kept as close as possible to the line OB , since larger diamond crystals are only formed here.

According to the method according to the invention, the results can be improved considerably. With The known processes can produce diamond crystals with a size of less than 0.5 mm. With the method according to the invention, diamond crystals can be produced by the factor 4 are larger. The invention will now be explained in more detail by means of examples.

example 1

An indirectly heated reaction vessel, which is described in more detail in German Patent 1136 312 and was approximately 19 mm in diameter and approximately 25 mm in length, was used with a catalyst made of 80 percent by weight nickel and 20 percent by weight chromium and with spectroscopy pure graphite filled. The threshold temperature was 1250 ° C, the maximum pressure 72 000 atmospheres and the maximum temperature 1320 ° C. To achieve a temperature of 1250 up to 1320 ° C a time of 1 to 3 seconds was required. The total response time was approximately 2 hours. The reaction vessel removed from the press contained three diamond crystals with one average diameter of 0.5 to 2 mm.

Example 2

The reaction vessel shown in Example 1 was also used here, and it also became the same Procedure carried out. A nickel-iron catalyst of 35 percent by weight was used as the catalyst Nickel and 65 weight percent iron used. The maximum pressure was 66,000 atmospheres, the Threshold temperature around 1150 ° C, the maximum temperature about 1250 ° C and the reaction time 3 hours. After removing the reaction vessel From the press it turned out that there were several diamond crystals with an average size of a little less than 2 mm.

₂ "Example 3

The procedure, reaction vessel and catalyst of Example 2 were used. The temperature was increased very quickly so that the diamond formation area was passed through very quickly. They left the Temperature come to rest at around 1400 ° C. Subsequently, the temperature was raised to approximately Decreased 1250 ° C and maintained IV2 hours. The reaction vessel was removed and contained several diamond crystals with a size of about 1.5 mm in the longer direction.

The X-ray diffraction patterns of the diamonds made according to the invention agreed with those of correct diamonds match. The diamonds produced scratched sapphire and withstood acid cleaning attempts and burned in oxygen, leaving only negligible remains. In In the present invention, graphite has been cited only as an example of a carbonaceous material. Any carbonaceous material which char when heated can of course be used and forms graphite before the diamond formation reaction takes place. From a raw material like Carbon, wood, pitch, diamond luster, etc., diamonds were made.

Claims (3)

Patent claims: 1. Process for the production of diamond crystals, in which non-diamond-shaped carbon substance together with a metal or an alloy in the phase diagram of carbon subjected to pressures and temperatures above the graphite-diamond equilibrium line is to form diamonds from the non-diamond-shaped carbon, thereby characterized in that the pressure is increased to at least 3000 atmospheres above the for Diamond formation required minimum pressure and the temperature is increased to a value that in a 50 ° C projecting from the equilibrium line into the diamond-stable area Range, but at least 30 ° C above the minimum required for diamond formation temperature, the temperature is kept constant at this value for a longer period of time, then the temperature and pressure are reduced and the diamond crystals formed are removed. 2. The method according to claim 1, characterized in that the carbon and the metal or the alloy for one not in the diamond formation range of the given metal or metal given alloy lying temperatures are subjected to a pressure which is the im Diamond formation area corresponds to the required pressure, and then maintained of this pressure the temperature is raised to a value which is close to but outside the diamond formation area of the given metal or alloy, maintain this threshold temperature for stabilization and finally the temperature is increased to the selected value. 10 3. The method according to claim 1, characterized in that the carbon and the metal or the alloy is first subjected to a pressure equal to that in the diamond formation area corresponds to the pressure required for the given metal or alloy, then the temperature on the temperature curve from the non-diamond-forming area above the diamond-forming area is increased to a value lying in the graphite area, the Maintain pressure and temperature conditions for stabilization in this graphite area and finally the temperature is reduced until the selected value is reached will. Considered publications:
Nature No. 4471 of July 9, 1955, pp. 51 to 55; No. 4693 of 10.10.1959, pp. 1094 to 1098. 1 sheet of drawings