US3652220A

US3652220A - Method of manufacturing synthetic diamonds

Info

Publication number: US3652220A
Application number: US37425A
Authority: US
Inventors: Cedric E Lindstrom
Original assignee: Scandimant AB
Current assignee: Scandimant AB
Priority date: 1966-02-11
Filing date: 1970-05-13
Publication date: 1972-03-28
Anticipated expiration: 1989-03-28
Also published as: BE693619A; DE1667362A1; GB1174940A

Abstract

Synthetic diamonds are produced by subjecting carbonaceous material to heat and pressure in the presence of a metallic solvent having projecting portions.

Description

United States Patent [151 3,652,220 Lindstrom [4 1 Mar. 28, 1972 [5 METHOD OF MANUFACTURING 5s rm 0! Search ..23/209.1

SYNTHETIC DIAMONDS 56 References Cited [72] inventor: Cedric E. Lindstrom, Robertsfors, Sweden I 1 73 Assignee: Scandimant Aktiebollg, Robertsfors, UNITED STATES PATENTS Sweden 2,947,609 8/1960 Strong ..23/209.1 22 Filed: M 13 1970 2,992,900 7/1961 Bovenkerk... ....23/209 1 3,031,269 4/1962 Bovenkerk ...23/209.1 1 PP 37,425 3,124,422 3/1964 Custers et al. ..23/209.i Rem Us. Application D." 3,407,445 10/1968 Strong ..23/209. l X [63] Continuation of Ser. No. 612,483, Jan. 30, 1967, Primary Examiner-Edward J. Meros abandoned. Attorney-Bailey, Stephens & Huettig [30] Foreign Application Priority Data [57] ABSTRACT Feb. 1 i, 1966 Sweden ..1754/66 Sy th ti diamonds are produced by subjecting carbonaceous June 23, 1966 Sweden "861 material to heat and pressure the presence ofa metallic solvent having projecting portions. [52] US. Cl..... /209.1 [5 l 1 Int. Cl. 01b 31/06 3 Claims, 9 Drawing Figures METHOD OF MANUFACTURING SYNTHETIC DIAMONDS RELATED APPLICATIONS This application is a continuation of application, Ser. No. 612,483, filed Jan. 30, 1967, now abandoned.

FIELD OF THE INVENTION The invention relates to the manufacture of synthetic diamonds.

THE PRIOR ART It is known that synthetic diamonds can be manufactured by subjecting a mixture of particles of a non-diamond carbonaceous material and particles of a solvent for carbon, for example iron or nickel or an alloy containing one of these metals, to temperatures and pressures in the diamond stable region, in which the temperature is sufficiently high for the solvent to occur in molten form in the presence of the carbonaceous material. It is also known instead of particles of solvent to use bodies of the solvent which have a substantial extension in relation to the reaction vessel, for example in the form of rods, cylinders, plates, etc.

SUMMARY or THE INVENTION According to the present invention it has been found possible to manufacture particularly large, well crystallized diamonds.

The present invention relates to a method of manufacturing synthetic diamonds by subjecting a reaction mixture comprising a non-diamond carbonaceous material and a solvent for carbon having the capacity to convert the carbonaceous material to diamond in a reaction vessel, to temperatures and pressures in the diamond stable region, whereby the reaction mixture is heated by an electric current led through the reaction mixture to a temperature sufficiently high to melt the solvent and the solvent is shaped as at least one body having a substantial extension in relation to the reaction vessel and arranged substantially perpendicular to the current direction, characterized in that the solvent body is shaped with several narrowing or projecting parts, for example in the form of peaks, points or ridges, facing the carbonaceous material and that a negative temperature gradient is effected in the direction from the carbonaceous material to the solvent body when heating the reaction mixture.

The diamond stable region is the region above the equilibrium line for graphite-diamond in the phase diagram for carbon published by Herman and Simon in Zeitschrift fiir Elektrochemie 59 (1955), page 333. ,m.

As is clear from the above, when carrying out the method according to the invention the temperature is at least so high that the solvent is melted in the presence of the carbonaceous material. Preferably a temperature of 50-250 C. above the eutectic melting point for a mixture of carbon and the solvent should not be exceeded. Temperatures above 2,200 C. should be avoided so that problems with the apparatus do not unnecessarily become more complicated.

The required minimum pressure is obtained in each case with a knowledge of the temperature used, from said phase diagram for carbon. To avoid unnecessarily complicating the method it is normally suitable to use a pressure not exceeding 120,000 atm.

Besides graphite, which is preferred, the carbonaceous material may consist of amorphous carbon, charcoal, anthracite or other naturally occurring carbon types, or of carbonaceous substances such as anthracene and naphthalene which disintegrate under the prevailing reaction conditions to liberate carbon. The solvent may consist of iron, nickel, cobalt, platinum metals and other metals having the capacity to dissolve carbon and convert carbonaceous material to diamond, or of alloys containing such metals, such as alloys consisting of nickel and iron, of nickel, chromium and iron, of

nickel and chromium, of nickel, cobalt, chromium and iron, for example stainless steel, and of nickel and copper. Compounds of said metals may also be used, such as carbides, for example iron carbide. All these metals, alloys and metal compounds having the capacity to dissolve carbon and convert carbonaceous material to diamond are known per se and form no part of the present invention.

The carbonaceous material and solvent are subjected to pressures and temperatures within the diamond stableregion for preferably 1 15 mins. However, it is also possible for them to be thus subjected for a longer time of the magnitude of l or several hours.

A possible explanation of the good result obtained according to the invention may be that the narrowing or projecting parts of the solvent body in contact with the hotter carbon melt before the other parts of the solvent body, a rather limited number of diamond crystals then being formed which then act as seeds for further crystal growth. This would then take place during continued melting of the solvent body and continued dissolving of thecarbon.

The narrowing or projecting parts can be produced mechanically, for example, by milling, stamping or drawing, the last mentioned if the solvent body consists of a thread-like body, for example a spiral. Instead of several projecting parts, one long projecting part may be used, for example a continuous spiral ridge.

The solvent body may, inter alia, be in the form of a disc having projecting parts in the form of, for example concentric ridges or in the form of a continuous, for example spiral, ridge. It may also be in the form of a layer of balls arranged close to each other or as a flat spiral, which may be wound with its adjacent turns close to each other.

According to a particularly advantageous embodiment of the invention the solvent body has several parts arranged with gaps between them which are filled with the non-diamond carbonaceous material and this is also arranged around the solvent body as such. The parts of the solvent body may then form a continuous unit and the narrowing or projecting parts a long narrowing or projecting part on the solvent body, facing the carbonaceous material. the gaps between the parts.

According to a second embodiment of the invention having gaps between the parts of the solvent body, these parts may have narrowing or projecting parts facing the carbonaceous material arranged around the solvent body as such and narrowing or projecting parts facing the carbonaceous material arranged in the gaps between the parts.

When the solvent body is arranged with gaps between the parts it is particularly advantageous to shape the solvent body as a loosely wound spiral, as several concentric rings or as a layer of balls arranged at a distance from each other.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further explained by describing a number of embodiments with reference to the accompanying drawing which shows schematically a reaction vessel in which the carbonaceous material and the solvent body are heated and subjected to the required pressure.

FIG. 1 shows the solvent body consists of a disc,

FIG. 2 shows a tightly wound spiral,

FIG. 3 shows a layer of balls arranged close to each other,

FIG. 4 shows a loosely wound spiral and FIG. 5 shows several concentric rings. FIG. 10, FIG. 2a, FIG. 4a and FIG. 5a show parts of the solvent body on a larger scale.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reaction chamber 10 shown in FIGS. 1 5 is cylindrical. It is limited sideways by an insulating tube 1 1 of, for example talcum and at the top by two

circular metal plates

12 and 13. The reaction chamber is heated electrically by leading an electrical current through it in vertical direction. The pressure can be generated, for example, with a vertically movable punch the insulating tube 11 being surrounded by a pressureabsorbing casing and a bearer being arranged at the end surface of the reaction chamber which is not influenced by the movable punch.

Examples of-diamond manufacture according to the invention which can be carried out in the above exemplified reaction vessels are as follows:

EXAMPLE 1 In accordance with FIG. 1 the solvent body consists of a plate 14 of a chromium-nickel alloy containing 20 percent by weight chromium and 80 percent by weight nickel. The plate is arranged between two pre-compressed graphite cylinders 15 and 16. The plate is provided on each side with projecting parts in the form of a continuous spiral ridge 17 (FIG. la) with a height h of about l min. and a width b at the base of about 1.5 mm., or in the form of several concentric ridges having, for example, the height and width mentioned. The projecting parts may also consist of several separate peaks arranged at a distance from each other. The reaction mixture is heated by an electric current as previously mentioned to a temperature of about l,480 C. and subjected to a pressure of about 65,000 atm. for 2 minutes.

Due to the fact that the resistivity of graphite is considerably higher than that of the metallic material in the solvent body, the graphite will be heated to a higher temperature than the metallic solvent body by the electric current passing between the

metal plates

12 and 13. A negative temperature gradient is thus achieved in the direction from the carbonaceous material to the solvent body. Also in the following examples a negative temperature gradient is achieved in the same way.

EXAMPLE 2 A tightly wound spiral 18 of iron thread, in which adjacent turns, for example 19 and 20 (FIG. 2a) are in contact with each other, is arranged in accordance with FIG. 2 between two

pre-compressed cylinders

21 and 22 of graphite. The iron thread is flat along the contact surface between adjacent turns and has rounded edges 23 forming the narrowing or projecting parts. The reaction mixture is heated by an electric current as previously indicated to a temperature of about l,5l C. and subjected to a pressure of about 75,000 atm. for 4 minutes.

EXAMPLE 3 In accordance with FIG. 3 the solvent body consists of a layer of tightly packed balls 24 of iron. Adjacent balls are thus in contact with each other. The balls may have a diameter of about 0.5 mm. On either side of the layer of iron balls are arranged two pre-compressed graphite cylinders 25 and 26. Due to their geometrical form, the balls are provided with narrowing parts in a radial direction, perpendicular to a plane chosen arbitrarily through the center of the ball. The reaction mixture is heated by an electric current as mentioned previously to a temperature of about 1,450" C. and-subjected to a pressure of about 60,000 atm. for 9 minutes, whereby large diamonds with well defined crystals are formed.

EXAMPLE 4 Two loosely wound

flat spirals

28 and 29 having gaps 28a and 29a, respectively, (FIG. 4a) between adjacent turns 28b,

28c and 29b, 290, respectively, are arranged in accordance with FIG. 4 in graphite pre-compressed at approximately 3,000 kp./cm In this case the solvent bodies consist of the two

spirals

28 and 29 which are arranged perpendicular to the pressure direction and current direction. Each solvent body, for example 28, has parts consisting of its turns, two of which have been designated 28b and 28c, and between which parts there is thus a gap filled by graphite.

The spirals may be of nickel thread or cobalt thread with a diameter of about 1 mm. and the gaps'28a and 29a, respectively may be about 1 mm. wide. In the flat spiral according to FIG. 4 the metalthread, from an arbitrary axial plane in the thread, due to its own geometrical form, is provided with narrowing parts in a radial direction perpendicular to said plane. That part of the graphite surrounding the solvent bodies as such is designated 30 and that part of the graphite arranged in the gaps between the turns is designated 30a. The reaction mixture is heated in the manner previously indicated by an electric current to a temperature of about 1,550 C. and subjected to a pressure of about 65,000 atm. for 3 4 minutes, whereby large, well crystallized diamonds are formed.

EXAMPLE 5 In accordance with FIG. 5 the solvent body consists of several concentric rings 32, 33, 34 and 35 arranged with gaps 36. The solvent body thus has parts consisting of said rings 32, 33, 34 and 35. The rings may be, for example of a chromiumnickel alloy containing 20 percent by weight chromium and percent by weight nickel. Each ring has a square cross section with a side length of 1.5 mm. for the square. The distance between adjacent parts of two rings may be 2 mm. Due to its geometrical form each ring is provided with narrowing parts ending in axially directed

edges

37 and 38 and in radially directed

edges

39 and 40. The edges face the carbonaceous material the part of which surrounding the solvent body is designated 41 and that arranged in the gaps between the rings is designated 42. The reaction mixture is heated in the manner previously indicated by an electric current to a temperature of about l,480 C. and subjected to a pressure of about 65,000 atm. for 2 minutes. If rings having quadratic cross section are used, these may for example also be shaped so that they have inner and outer envelope surfaces parallel to the symmetry axis of the ring and end surfaces perpendicular to the symmetry axis. Of course rings having, for example, circular cross section may be used instead of rings having quadratic crosssection.

Instead of loosely wound spiral or concentric rings in accordance with FIGS. 4 and 5, the solvent body may among other things consist of a layer of balls in which adjacent balls are separated from each other by graphite.

I claim:

1. Method of manufacturing synthetic diamonds by subjecting a reaction mixture comprising a non-diamond carbonaceous material and a metallic solvent for carbon having the capacity to convert the carbonaceous material to diamond, in a reaction vessel, to temperatures and pressures in the diamond stable region, in which the reaction mixture is heated by an electric current led through the reaction mixture to a temperature sufficiently high to melt the solvent is shaped to extend over the greater part of the cross section of the reaction vessel transverse to the direction of the current and arranged substantiallyperpendicular to the current direction and embedded on all sides in the carbonaceous material, in which the solvent is constituted by a plurality of spaced apart substantially coplanar sections the spaces between which extend in the direction of the current completely through the solvent body and are filled by the carbonaceous material, said sections having portions tapering in the direction of the current embedded in the carbonaceous material and the sections being connected together in a unit, so that a negative temperature gradient is effected in the direction from the carbonaceous material to the solvent body.

2. Method of manufacturing synthetic diamonds by subjecting a reaction mixture comprising a non-diamond carbonaceous material and a metallic solvent for carbon having the capacity to convert the carbonaceous material to diamond, in a reaction vessel, to temperatures and pressures in the diamond stable region, in which the reaction mixture is heated by an electric current led through the reaction mixture to a temperature sufficiently high to melt the solvent, and the solvent is shaped to extend over the greater part of the cross section of the reaction vessel transverse to the direction of the current and arranged substantially perpendicular to the current direction and embedded on all sides in the carbonaceous material, in which the solvent is constituted by a spirally wound solid member, the coils of which are substantially coplanar and have portions tapering in the direction of the current embedded in the carbonaceous material, so that a negative temperature gradient is effected in the direction from the carbonaceous material to the solvent body.

3. Method of manufacturing synthetic diamonds by subjecting a reaction mixture comprising a non-diamond carbonaceous material and a metallic solvent for carbon having the capacity to convert the carbonaceous material to diamond, in a reaction vessel, to temperatures and pressures in the diamond stable region, in which the reaction mixture is heated by an electric current led through the reaction mixture to a temperature sufficiently high to melt the solvent, and the solvent is shaped as a spirally wound solid member, the coils of which are substantially coplanar and spaced apart, and extending over the greater part of the cross section of the reaction vessel transverse to the direction of the current and arranged substantially perpendicular to the current direction and embedded on all sides in the carbonaceous material, the spaces between the coils being filled by the carbonaceous material, the coils beingshaped so as to have portions tapering in the direction of the current embedded in the carbonaceous material, so that a negative temperature gradient is effected in the direction from the carbonaceous material to the solvent body.

Claims

2. Method of manufacturing synthetic diamonds by subjecting a reaction mixture comPrising a non-diamond carbonaceous material and a metallic solvent for carbon having the capacity to convert the carbonaceous material to diamond, in a reaction vessel, to temperatures and pressures in the diamond stable region, in which the reaction mixture is heated by an electric current led through the reaction mixture to a temperature sufficiently high to melt the solvent, and the solvent is shaped to extend over the greater part of the cross-section of the reaction vessel transverse to the direction of the current and arranged substantially perpendicular to the current direction and embedded on all sides in the carbonaceous material, in which the solvent is constituted by a spirally wound solid member, the coils of which are substantially coplanar and have portions tapering in the direction of the current embedded in the carbonaceous material, so that a negative temperature gradient is effected in the direction from the carbonaceous material to the solvent body.
3. Method of manufacturing synthetic diamonds by subjecting a reaction mixture comprising a non-diamond carbonaceous material and a metallic solvent for carbon having the capacity to convert the carbonaceous material to diamond, in a reaction vessel, to temperatures and pressures in the diamond stable region, in which the reaction mixture is heated by an electric current led through the reaction mixture to a temperature sufficiently high to melt the solvent, and the solvent is shaped as a spirally wound solid member, the coils of which are substantially coplanar and spaced apart, and extending over the greater part of the cross-section of the reaction vessel transverse to the direction of the current and arranged substantially perpendicular to the current direction and embedded on all sides in the carbonaceous material, the spaces between the coils being filled by the carbonaceous material, the coils being shaped so as to have portions tapering in the direction of the current embedded in the carbonaceous material, so that a negative temperature gradient is effected in the direction from the carbonaceous material to the solvent body.