EP0938450A1

EP0938450A1 - Method for manufacturing synthetic diamond and device for implementing this method

Info

Publication number: EP0938450A1
Application number: EP97936554A
Authority: EP
Inventors: Marcel Gehrig
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-09-05
Filing date: 1997-09-02
Publication date: 1999-09-01
Also published as: WO1998009914A1

Abstract

The invention concerns a method for manufacturing synthetic diamond comprising the following steps: providing a mixture containing carbon and a metal catalyst, the carbon being in a solution and/or mounted in the metal catalyst which has a density higher than that of the carbon; providing a recipient, pre-heating the recipient, heating the mixture to reduce it to liquid; pouring the mixture into the pre-heated recipient, hermetically closing the recipient; hydro-extracting the liquid mixture in the recipient so as to separate the metal catalyst and the carbon, the metal catalysing the carbon is brought towards the centre to form a carbon lump there; cooling the recipient and the mixture until the mixture is solidified, in order to cause the recipient and the catalyst to shrink and to create sufficient pressure on said lump, so as to recrystallise the carbon in the form of diamond; extracting the recrystallised carbon from the metal catalyst.

Description

METHOD FOR MANUFACTURING SYNTHETIC DIAMOND AND DEVICE FOR CARRYING OUT SAID METHOD

The invention relates to a method of manufacturing synthetic diamond and a device for carrying out this method.

More particularly, the invention relates to a process for manufacturing synthetic diamond by recrystallization under pressure of carbon obtained by modification of its allotropic form.

Methods and devices are already known for manufacturing synthetic diamonds, of the type mentioned above, in which very high pressure presses and anvils are used in particular.

These diamond manufacturing techniques under high pressures (of the order of several tens of Kbars, typically 60 Kbars) call for the dissolution of carbon in a molten metal generally called a catalyst metal.

More precisely, these pressure recrystallization techniques require the use of multiple presses called cubic presses, comprising several anvils each associated with hydraulic multiplication devices which make it possible to obtain the necessary high pressures. These cubic presses are associated with heating means capable of ensuring the rise in temperature and the melting of the metal containing carbon, these heating means being, inter alia, constituted by two of the aforementioned anvils, through which one circulates a very high alternating current to produce powers of several thousand Watts. Other types of presses, frame or column can be used, presses in which a punch and a die work along an axis.

These devices have the disadvantage of being heavy and expensive and require for their implementation the use of significant amounts of energy, which makes the manufacture of synthetic diamond by recrystallization under pressure very expensive.

Thus, the main object of the invention is to remedy the drawbacks of the above-mentioned prior art by providing a method and a device of simple design, inexpensive and easy to implement.

To this end, the subject of the invention is a process for manufacturing synthetic diamond, characterized in that it comprises the following stages which consist in: providing a mixture comprising carbon and a metal known as a catalyst metal, the carbon being in solution and / or added to the catalyst metal which has a density greater than that of carbon; - provide a container having a wall capable of containing said mixture and of being hermetically closed, this wall having a melting temperature higher than that of the mixture; preheat the container, at a temperature Tl, to expand its wall; heating the mixture to a temperature T2> T1 to liquefy it; pour the mixture in the liquid state into the preheated container to cause further expansion of the wall of the container; close the container tightly; centrifuge the liquid mixture in the container in order to separate the catalyst metal and the carbon, the catalyst metal being brought by its higher density towards the wall of the container while the carbon is brought towards the center and forms at this location a carbon nut , * cooling the container and the mixture until the mixture solidifies, to cause withdrawal of the container and the catalyst and generate sufficient pressure on said nut, in order to recrystallize the carbon in the form of diamond; separating the solidified mixture from the container; and extract the recrystallized carbon from the catalyst metal.

It is thus understood that this process is in total rupture with the conventional processes described above, since it calls for less costly operations not requiring the implementation of a device requiring the supply of high mechanical and electrical powers, and thereby eliminating the use of large amounts of energy which were necessary for the implementation of conventional methods and devices.

According to yet another aspect, the invention relates to a device allowing the implementation of this method. Other characteristics and advantages of the invention will appear more clearly on reading the following detailed description of an embodiment of the invention given purely by way of non-limiting illustration, this description being made in conjunction with the drawings in which: FIGS. 1 to 16 very schematically represent the different stages of the method according to the invention; and FIG. 17 is a section also schematically showing a device for implementing the method according to the invention;

By first referring to FIGS. 1 to 16, an embodiment of the method according to the invention will be described below, which consists, according to a first step, of providing a mixture M (FIG. 1) comprising carbon and a metal called catalyst metal, this mixture being placed in a crucible 1.

The carbon can be in solution in the catalyst metal, for example when a steel having a determined carbon content is used. This mixture is preferably in the form of a powder. This mixture can be prepared on the production site for the implementation of the process or be acquired from an external supplier.

According to an important characteristic of the invention, the catalyst metal has a density and a mass greater than that of carbon, for reasons which will be explained in more detail below. Advantageously, the catalyst metal is a fine carbon steel, typically comprising 2.5% carbon and designated under the reference ASP 60. Of course, the invention is not limited to this type of catalyst, but is also extends to other metals, such as nickel, having the desired density and mass characteristics.

The crucible 1 is of conventional design and can for example be made of sintered aluminum oxide, for example AL2O3.

The crucible 1 which is filled with said mixture is placed in an oven 2 (FIG. 2) which heats the assembly to bring said mixture M to the liquid state. By liquid state is meant here a state of the mixture sufficiently fluid so that it can be poured into a container.

The oven 2 is a conventional oven with front access comprising an enclosure 4 which can be closed by a door 6 and in which is housed a sliding bottom 8 of the drawer type, on which the crucible 1 can be placed. Other types of oven, for example a pot oven, can be used for the implementation of this heating step.

The heating of the mixture M in the enclosure 4 of the oven 2 takes place under a neutral atmosphere, for example in the presence of an inert gas, such as Argon, in order to avoid any physico-chemical modification or alteration of the mixture M .

In this step, the mixture is brought above its melting temperature, this heating temperature typically being 1800 ° C. (degrees Celsius) with a steel of the ASP 60 type. Furthermore, according to another step of this process, a container 10 (FIG. 3) is provided with a wall 12 capable of containing the mixture M in the liquid state. The wall 12 is made of a material having a melting temperature higher than that of the mixture M. In the example which is described here, the wall 12 of the container 10 is made of a cast iron having the above qualities.

The container 10 consists for example of a spherical body 14 delimited by the wall 12. The spherical body 14 has an internal diameter D. The container 10 has a filling opening 16 which is formed in the body 14 and which extends into an elongated cylindrical neck 18 made integrally with the wall 12 and extending from the body 14 along a first radial axis RI of said body.

The container 10 is advantageously provided with means for guiding in rotation 20a, 20b and with means for driving in rotation 20c which will be described in more detail below.

After having provided the container 10, it is placed in an oven 22 (FIG. 4) in which this container is preheated to a temperature T1 in order to obtain (FIG. 5) a first expansion of the wall 12. Au during this preheating step, the wall 12 expands and the inside diameter of the body increases to an inside diameter D2. The oven 22 shown in Figures 4 and 5 is of the same type as the oven 2 in Figure 2 and whose same elements have been designated for all these figures by the same reference numerals.

In this preheating step, the container 10 is held in position by a positioning support 24 resting on the sliding bottom 8 of the oven 22.

In the example which is described here, the container 10 is preheated to a temperature of the order of 850 ° C., also under a neutral atmosphere, in the presence of an inert gas, such as Argon. Although the two stages respectively of heating the mixture M and of preheating the container 10 have been described successively in the above order, it should be noted that they can be carried out in the reverse order and as far as possible not successively, but simultaneously.

In another step of the process, which may be optional, one or more non-ferrous additives (ANF) intended, on the one hand, are introduced (FIG. 6) into the container 10, prior to the preheating step previously described. to lower (in this example at least to 1300 ° C.) the solidification temperature of the liquid catalyst metal which will be poured into this same container 10 during a subsequent step and, on the other hand, to facilitate the separation of the carbon from the metal that contains it. These additives are chosen from all of the elements comprising copper and zinc.

Preferably, the amount of additive added is of the order of 2 to 3% by volume of the mixture M. We will now refer to FIGS. 7 and 8 which illustrate the step of filling the container 10 with the mixture M.

Once the preheating step has been completed, the door 6 of the oven 22 is opened and the sliding bottom 8 is pulled out to remove the preheated container 10 from the enclosure 4 of the oven.

By this operation, the container 10 is brought sufficiently outside the oven 22 to clear the opening 16 of this container (Figure 7). Then, the crucible 1 containing the mixture M in the liquid state is also taken out of the oven 2 and is transported to the container 10. As shown in FIG. 8, the container 10 is filled with the mixture M so as to leave no free space in the container 10, after the hermetic closing operation The closing operation is illustrated in FIG. 9. In this example, the container 10 is closed hermetically using a Morse cone 26 which can be driven into a through upper opening 28, formed in the neck 18 transversely thereto.

Of course, a person skilled in the art could provide other means for closing the container 10. As can be seen in FIG. 9, the liquid mixture M comes into contact with the closing means, here the Morse taper 26, so that the closed volume of the container 10 is completely filled.

The liquid mixture M having been poured into the container 10 at a temperature T2 higher than the preheating temperature T1 of said container, this higher temperature of the liquid M will temporarily increase the temperature of the container 10 and cause a second expansion of the wall 12 of the spherical body 14, increasing the internal diameter of the spherical body to a diameter D3.

This additional expansion will create a vacuum V (Figure 10) inside the container 10, which will have a very advantageous effect for a later stage of the process in which the carbon will be separated from the catalyst metal M by centrifugation.

As an indication, it will be specified that, in this example, the introduction of ASP 60 steel at 1800 ° C. into the container 10 preheated to 850 ° C. temporarily increases the temperature of this container to more than 900 ° C.

Next, the liquid mixture M is centrifuged rapidly (FIGS. 11 and 12), before it begins to solidify, by first placing the filled and hermetically closed container 10 on the centrifuge device 30. , according to the invention.

It will be noted in this regard that the device 30 shown in Figures 11 and 12 will be described in detail below in connection with Figure 17 and that for reasons of convenience the components of this device 30 are not all referenced in Figures 11 and 12. During this centrifugation step, the catalyst metal of the mixture M is displaced by centrifugation towards the wall 12, and the carbon is moved towards the center of the sphere 14 to form, at this location, a carbon nut N.

This separation phenomenon is obtained thanks to the fact that the catalyst metal has a density and a mass greater than that of carbon.

During this centrifugation step, the container 10 and its contents are allowed to cool, if necessary by assisting this cooling by spraying said device with the aid of a coolant until this assembly reaches the temperature. ambient. During cooling, the wall 12, previously expanded to its diameter D3, will retract to resume its initial diameter Dl and thus apply a high and uniform pressure on the catalyst metal in the solidification phase, to the center of the sphere, where there is in particular the carbon N nut which undergoes sufficient pressure for the carbon to recrystallize in the form of a synthetic diamond.

Tests have shown that, by choosing the appropriate proportions of the container and the quantity of mixture introduced into the container (volume), the phenomenon of post-expansion shrinkage makes it possible to obtain in the center of the container 10 a pressure high enough to recrystallize. the carbon present there in a synthetic diamond nut.

It will be noted in this regard that the vacuum created at the time of the second expansion facilitates the separation of carbon and of the catalyst metal.

After the container has reached room temperature, the container 10 is removed from the centrifuge device 30. Then, as seen in FIG. 13, the solidified mixture is separated from the container 10, by cutting or cutting the container 10, along a radial plane of the container, to release the solidified mixture in the form of a ball B which has in its center the synthetic diamond nut.

The N nut of synthetic diamond trapped in the solidified catalyst metal is then extracted. This extraction step can consist, for example, in heating the ball B to a temperature below its melting temperature to then subject it to a thermal shock (FIG. 15) intended at least to weaken it and / or disintegrate it. at least partially. This extraction step can be finalized, if necessary, by applying a mechanical shock to ball B, for example using a simple hammer (figure 16), to burst ball B and recover the nuts N.

The heating of the ball B (FIG. 14) can be carried out in an oven of the type of that of FIG. 2, heated in the example shown to a temperature of 800 ° C.

The thermal shock applied to the ball may consist in particular of quenching in a tank C with cold water EF, during which the catalyst metal splits and cuts partially or completely.

Referring to FIG. 17, a centrifugation device will be described below for implementing the above method.

The device 30 comprises a cage 32 which is intended to receive the container 10, this container being movable in rotation in this cage 32 between a bottom 34 and a cover 36 of the cage 32 intended to cooperate respectively with the guide means and '' rotation drive 20a, 20b and 20c. Thus, the cover 36, which is articulated in the upper part of the cage 32, has in its central part a recess ent 38 of circular shape provided for receiving, free to rotate, the end of the neck 18 of the container 10, forming said guide means 20a.

The cover 36 can be blocked on the cage 32. In the example shown, the cage 32 includes an extension 40 cooperating with an opening 42 formed in the cover 36, the extension 40 being able to be introduced into the opening 42 in the position closed cover. The blocking is achieved by means of a pin 44 driven into a clearance 46 provided for this purpose in the extension 40.

The container 10 comprises, in its part diametrically opposite the neck 18, the guide and drive means 20b and 20c respectively.

These means are formed by a cylindrical protuberance 48 preferably coming integrally with the spherical body 14 and extending externally from the spherical body 14 in the extension of the radial axis.

RI.

This protuberance 48 is engaged freely in rotation in a cylindrical clearance 50 provided in the bottom 34 of the cage 32; it forms the rotating guide means 20b.

This clearance 50 communicates with a passage 52 opening towards the outside of the cage 32. The bottom of the cage 32 supports and guides, free in rotation, a drive shaft 54 provided at a first end with a square 56 intended to engage in a recess (not referenced) formed in the protuberance 48. The axis 54 has at its second end a pinion with bevel gear 58 meshing with a pinion of the same type 60 driven by another axis 62 mounted also free to rotate in an extension 64 provided in a lower part of the cage 32.

This second axis 62 extends perpendicularly to the first axis 54 and to the geometric axis of rotation Ri.

The second axis 62 comprises, on the side opposite to the bevel gear 60, a notched straight gear 66 in engagement with a toothed belt 68 also engaged with another toothed pinion 70.

The cage 32 is mounted to rotate freely in a frame 72 by means of two pivots 74 and 76 extending from two opposite lateral walls of the cage 32, along a second geometric axis R2 perpendicular to the axis Ri. These two pivots 74 and 76 are supported and guided in rotation inside the frame 72. The pivot 76 crosses the toothed pinion 70. A drive pulley 80 is driven on the pivot 76 and is driven in rotation by an electric motor 82, via another pulley 84 mounted on a motor shaft 86 of the electric motor 82, the two pulleys 80 and 84 being connected by a toothed belt 88.

It is understood that, thanks to this device, the electrical supply to the motor 82 causes the rotation ROT2 of the cage 32 around the axis R2 and the combined rotation ROTI of the container 10 around the axis Ri.

The combination of these two rotational movements around perpendicular axes Ri and R2 makes it possible to obtain the centrifugation effect necessary to separate the catalyst metal from the carbon to be recrystallized.

It is understood, of course, that the respective speeds of these two rotational movements can be modified by playing on the gear ratios of the elements involved in the drive kinematic chain of the device as described. Typically a rotation speed of the container 10 of 500 rpm can be used.

Claims

1. Method for manufacturing synthetic diamond, characterized in that it comprises the following stages which consist in: providing a mixture comprising carbon and a metal known as catalyst metal, this carbon being in solution and / or added to the catalyst metal which has a density greater than that of carbon; provide a container having a wall capable of containing said mixture and of being hermetically closed, this wall having a melting temperature higher than that of the mixture; preheat the container, at a temperature Tl, to expand its wall; heating the mixture to a temperature T2> τl to liquefy it; pour the mixture in the liquid state into the preheated container to cause further expansion of the wall of the container; - close the container tightly; centrifuge the liquid mixture in the container in order to separate the catalyst metal and the carbon, the catalyst metal being brought by its higher density towards the wall of the container while the carbon is brought towards the center to form a carbon nut there , - cooling the container and the mixture until the mixture solidifies, to cause a withdrawal of the container and the catalyst and generate sufficient pressure on said nut, in order to recrystallize the carbon in the form of diamond; separating the solidified mixture from the container; and extracting the recrystallized carbon from the catalyst metal.

2. Manufacturing method according to claim 1, characterized in that during the filling step of the container, the latter is filled with the mixture so as to leave no free space in said container, after its closure.

3. Method according to claim 1 or 2, characterized in that prior to the step of heating the container, there is introduced into this container at least one non-ferrous additive intended to reduce the solidification temperature of the catalyst metal.

4. Method according to claim 3, characterized in that the additives are chosen from all of the elements comprising copper and zinc.

5. Method according to one of the preceding claims, characterized in that the steps of preheating the container, respectively heating the mixture, are carried out under a neutral atmosphere, preferably under an atmosphere of Argon.

6. Method according to any one of the preceding claims, characterized in that the centrifugation step consists of a rotation of the container along two perpendicular axes.

7. Method according to any one of the preceding claims, characterized in that the step of separating the container and the solidified mixture is carried out by cutting out the container.

8. Method according to any one of the preceding claims, characterized in that the step of extracting the diamond nut consists in heating the solidified mixture to a temperature below its melting temperature, and in making it undergo a shock. thermal intended to disintegrate it at least partially.

9. Method according to any one of the preceding claims, characterized in that the step of extracting carbon in the form of diamond is finalized by the application of a mechanical shock to said solidified mixture.

10. Method according to any one of the preceding claims, characterized in that the container is made of cast iron.

11. Method according to any one of the preceding claims, characterized in that the catalyst metal is a carbon steel.

12. Device for implementing the method according to any one of claims 1 to 11.