NO147637B - PROCEDURE FOR MANUFACTURING A DIAMOND MATERIAL - Google Patents

Abstract

Method of making a diamond material.

Description

This invention relates to an improved method

in the production of diamonds from diamond seeds.

Synthesis of diamond crystals by methods where high pressure and high temperature are used is well known. Preferred methods for the production of diamonds are described in US patent documents 2,947,610 and 2,947,609. Apparatus for carrying out such methods is described in US patent document 2,941,248.

Diamond growth takes place in the above-mentioned methods by diffusion of carbon through a thin metallic film of a catalyst/solvent selected from a number of

different ones. Although such methods are very

well suited for the commercial production of industrial diamonds, the final crystal size of such diamond growth is limited by the fact that the carbon flow across the catalyst/solvent film is determined by the difference in solubility between graphite (the usual starting material) and the diamond that is formed. This difference in solubility has a general tendency to decrease significantly over a longer period of time, as a result of a reduction in the pressure in the system and/or poisoning effects from foreign atoms in the graphite being converted.

The expression "catalyst/solvent" used in the present description is intended to indicate that the metallic materials in question here have both a catalyst function and a solvent function.

Otherwise, in the technical literature, you will be able to come across both the term "catalyst" and the term "solvent" for these materials.

By the method for the production of diamond on

a diamond seed crystal1 which is described in US Patent 3,297,407, on the other hand, use is made of a difference

in temperature between the diamond seed and the carbon supply source to establish a carbon concentration gradient that leads to deposition on the seed. Catalyst/solvents described in the above-mentioned US patents 2,947,609 and 2,941,248 are also used in the temperature gradient method according to US patent

document 3 297 407. The growth of the diamond on the seed material is driven by the difference between the solubility of the carbon of diamond carbon in the molten catalyst/solvent metal at the carbon supply source and at the seed, between which places a temperature gradient applies. This general design of the reaction vessel provides a pressure-stable system, so that the pressure can easily be maintained in the diamond-stable area, which is very important.

By very careful adaptation of pressure and temperature and by using relatively small temperature gradients and a long growth time in relation to the growth times used in the thin film method, larger diamonds can be produced by the method according to US Patent 3,297,407 than by the thin film method.

To date, however, attempts to achieve reliable, very high quality diamond growth have involved a number of seemingly mutually exclusive but equally co-occurring problems. The main problems are (i) a strong tendency towards spontaneous seed formation, (ii) a tendency for the diamond seed material to dissolve prematurely and (iii) difficulties in producing and regulating colors and patterns of jewelery quality in the diamond products.

Spontaneous formation of diamond seed crystals near the diamond seed material (which takes place by increasing the temperature gradient beyond the "safety" value) is unfortunate for the reason that if the growth time is prolonged for the seed to lead to a diamond larger than 1/20 carat, the spontaneous nucleation and the subsequent growth of the formed nuclei will compete with the growth from the planted diamond seed, with subsequent collisions between several crystals, which leads to tension breakdown in them.

Partial or complete dissolution of the diamond seed material in the molten catalyst/solvent metal is unfortunate if it occurs at the wrong time, because dissolution of the seed leads to uncoordinated diamond growth proceeding from separate points, and such growing diamonds will, when they meet, lead to the formation of mixed, incomplete products.

The lack of opportunity to exercise control over the diamond growth process, so that reproducible results can be achieved, is unfortunate, because it will not be possible to use doping agents, getters ("getters"), compensators and the like, to produce diamond products with special color patterns, which are flawless and have optimal physical properties.

The production of large diamonds by step-by-step enlargement of a small diamond has been proposed in the art in the past. In such a method, a small diamond is placed in a mass of graphite and catalyst (the thin film method), and new diamond growth is deposited on it to the greatest extent possible. This enlarged crystal is fed back into the apparatus for further magnification, if desired. This step-by-step "onion skin" growth entails the disadvantage that embeddings or occlusions of pollutants always occur at the interface between old growth and the new layer. If layers of different colors are used during the emergence of the diamond, sharp dividing lines will form between successive layers.

It would be advantageous if one could avoid such embeddings and thereby be able to provide diffuse boundaries between the colours. In order to achieve such a diamond crystal, continuous growth is necessary, during which the desired colors are introduced under control. Such continuous diamond crystal growth has now been shown to be possible by using a special nucleation-suppressing barrier layer.

To this end, according to the invention, a method is provided for the production of a diamond material, in which a reaction vessel containing a diamond seed material and a carbon supply source separated by a mass consisting mainly of a catalyst/solvent is subjected to a pressure in the diamond-stable region of the phase diagram for carbon, at the same time as the reaction vessel up-

is heated in such a way that the diamond seed material is kept at a temperature close to the minimum temperature for the diamond stable region, while the carbon supply source is kept at a temperature close to the maximum temperature for this region, whereby a temperature gradient is produced between the diamond seed material

and the carbon supply source. The new procedure excels

in that at least one of the following layers is placed between the diamond seed material and the mass of catalyst/solvent: (a) a nucleation-suppressing barrier layer that is soluble in the catalyst/solvent under the operating conditions, and which is provided with at least one opening between the diamond seed material and the mass of catalyst /solvent, (b) a nucleation-suppressing barrier layer which is insoluble in the catalyst/solvent under the operating conditions, and which is provided with at least one opening between the diamond seed material and the bulk of the catalyst/solvent, and (c) an insulating layer, which, when there is contact with diamond, has a melting point that is higher than the melting point of the mass of catalyst/solvent when the mass is saturated with dissolved carbon.

Predetermined colors and patterns are formed in jewelry-quality products by the method by including dopants, dyes and compensators in the carbon supply source and/or catalyst/solvent.

The invention is further illustrated in the accompanying drawings, where: fig. 1 illustrates an embodiment of a high-pressure, high-temperature apparatus which is applicable for carrying out the method according to the invention,

fig. 2 illustrates in an enlarged cross-section a reaction construction which is applicable in a first embodiment of the method according to the invention, in which a nucleation-suppressing barrier with an opening is used,

fig. 3 is a further enlarged view of the area in the immediate vicinity of the diamond seed material shown in FIG. 2,

fig. 4 shows the relationship between the new diamond growth and the diamond seed in the embodiment shown in fig. 2,

fig. 5 shows an enlarged cross-section of a second reaction vessel construction, where an extension of the catalyst/solvent extends down to the diamond seed through a nucleation suppression barrier,

fig. 6 is a further enlarged section of the neighboring area of the diamond seed material as shown in fig. 5,

fig. 7 is an enlarged vertical cross-section of another reaction cell construction according to a third embodiment, where a nucleation suppression barrier is provided with limited growth paths for the diamond product,

fig. 8 is a further enlarged section of the neighboring area of the diamond growth paths according to the feature shown in Fig. 7,

fig. 9 is a section similar to fig. 8, which shows the diamond growth paths as openings without threads therein according to the embodiment shown in fig. 7,

fig. 10 is an enlarged vertical section of a reaction vessel structure assembled according to a fourth embodiment, where an isolation barrier is used to prevent premature melting of the diamond core,

fig. 11 is a further enlarged section through the neighborhood of the diamond seed material ">ph shown in Fig. 10,

fig. 12, 13, 14, 15 and 16 are enlarged sections

through the neighboring area of the diamond seed material, such that this area will appear in different variations of the construction shown in fig. 10,

fig. 17 shows the relationship between the new diamond growth, the diamond seed, and the catalyst/solvent bath in the embodiments described in fig. 10 - 16,

fig. 18 shows an enlarged vertical cross-section through a main reaction vessel intended to contain various

additives to provide coloring and/or pattern formation in a single growth step,

fig. 19 is an enlarged view of a vessel construction for use in the embodiment according to fig. 18, for manufacturing

ling of jewelry quality "star" diamonds, and

fig. 20, 21 and 22 are enlarged views of a series

of charge assemblies intended to be contained in a reaction vessel construction as shown in fig. 18, where colored zones and/or patterns are formed.

The present invention relates to a method for the production of jewelery quality diamonds. In order to give an understanding of the overall problem, a short introduction indicating the main problems will be presented before the detailed description of the various aspects of the invention. The main problem is to subject a reaction vessel containing a diamond synthesis mixture to pressure and temperature conditions in the diamond-stable region of the carbon phase diagram. The synthesis mixture includes a diamond seed material and a carbon supply source separated by a mass of catalyst/solvent. These elements are normally arranged in layers or stacked as discussed later, but other arrangements are also possible. The heating of the reactor vessel is regulated to provide

a temperature gradient within the mixture, so that the diamond seed material is at a temperature close to the minimum value of the diamond stable region, and the carbon supply source is at a temperature close to the maximum value. By inhibiting the action of the catalyst/solvent at the seed material and in its immediate vicinity until significant diamond growth has occurred, spontaneous nucleation and seed erosion, which counteracts the growth of jewelry-sized diamonds, can be reduced. This result is achieved by placing suppressive or insulating layers, or both, between the catalyst/solvent and the seed material.

In addition to inhibiting the catalyst/solvent reaction, controlled amounts of dopants, getters, compensators, mixtures thereof and the like are added to the mixture to produce reliably reproducible diamond crystal products with predetermined color, color patterns, zoned color and the like.

Preferably, the barrier layer or layers and the mass of catalyst/solvent will be of different materials in a given reaction vessel construction.

Preferably, a nucleation-suppressing layer

be of cobalt, iron, manganese, titanium, chromium, tungsten, vanadium, niobium, tantalum, zirconium, alloys of the aforementioned metals, naturally occurring mica, high density polycrystalline aluminum oxide, powdered aluminum oxide, quartz, silicon oxide glass, hexagonal boron nitride crystals, cubic boron nitride crystals, boron nitride crystals of wurtzic structure or silicon carbide protected with one of the metals in the platinum family.

Preferably, an isolation barrier will be constructed of a material different from the nucleation suppressing layer, if such is used, and be selected from platinum, molybdenum, titanium, tantalum, tungsten, iridium, osmium, rhodium, palladium, vanadium, ruthenium, chromium, hafnium, rhenium, niobium, zirconium and alloys thereof.

The carbon supply source and catalyst/solvent mixture will be any material suitably used for this purpose. Such materials are amply illustrated in said US patent 3,297,407. Preferred materials will be illustrated in what follows.

In the present description, the following designations have the following meanings.

a) dopant: an impurity which, if present at the place of diamond growth, will

form part of the growing diamond lattice and affect the physical, mechanical and/or electrical properties of the diamond growth, b) getter: a material whose atoms, if present at the diamond growth site,

will prevent or limit the entry of one or more doping materials into the developing diamond growth, and

<c>> compensators: a material whose atoms, if present at the diamond's growth site, will enter the growing diamond lattice and partially or completely offset the normal influence of one or more doping materials present in the lattice with respect to the diamond's physical, mechanical and/or electrical properties.

Such materials are well known in the art. Many of these will be illustrated in what follows. Bluish-white jewelery stones are produced e.g. if boron alone, or especially combined with aluminium, is added as a doping agent. Appropriately, the aluminum can be alloyed with the catalyst/solvent. Multiple layers of carbon supply material and catalyst/solvent can of course be used, each containing one or more dopants, getters, compensators and the like to produce the desired effects, as will be explained in the following. In one embodiment, e.g. aluminium, titanium, zirconium or an alloy thereof may be in one layer, while nitrogen, boron or sources for these may be in another layer. If the diffusion paths for the elements are of different lengths, color zones can be easily achieved in the finished diamond product.

Preferably, diamond seed materials will be a single crystal. It would be particularly preferred that a cube face of the crystal is oriented so that it is in contact with the carrier layer or the mass of metallic catalyst/solvent. In other preferred embodiments, the diamond seed material can also consist of single crystals arranged separately from each other.

A preferred form of a high-pressure and high-temperature apparatus in which the method according to the invention can be carried out is the subject of the previously indicated US patent document 2 941 248 and is schematically shown in fig. 1.

In fig. 1, the apparatus 10 includes a pair of cemented tungsten carbide stamps 11 and 11' and an intermediate belt or mold piece 12 of the same material. The die piece 12 delimits a centrally located gap and, in combination with the pistons 11, 11', delimits two annular volumes. Between piston 11 and mold 12 and between piston 11' and mold 12

are included packing tubes/insulation pieces 13, 13', each comprising a pair of thermal insulating and electrically non-conductive pieces of pyrophyllite 14 and 16 and an intermediate metal gasket 17. Each piston carries an end cap assembly which includes a pyrophyllite plug or disc 23 surrounded by an electrically conductive ring 24. The above assemblies 13, 13 together with the end assemblies 19, 19 ' and electrically conductive metal end discs 21, 21' serve to delimit the volume 22 occupied by the reaction vessel 30.

In a first preferred embodiment, the method according to the invention will make use of a nucleation-suppressing barrier layer with at least one opening therein. In fig. 2, the reaction vessel 30 is of the general type described in US patent 3 030 662 modified by the addition of steel holders 31 and 32.

Vessel 30 includes an outer hollow cylinder 33 which is preferably made of pure sodium chloride, but which may be made of other materials such as talc. General criteria for choosing the material for cylinder 33 are that the material a) does not transform under pressure into a harder and stiffer state, such as by phase transformation and/or compression and

b) is mainly free from volume changes caused by high temperature and high pressure, which e.g. takes place with pyrophyllite and porous aluminum oxide. Materials that meet these criteria are described in US Patent 3,030,552 (column 1, line 59 to column 2, line 2), and such are applicable for the production of cylinder 33. Arranged concentrically within and in the immediate vicinity of 33 is an electrical resistance heating tube 34 of graphite. When the reaction vessel 30

is placed in room 22, heater tube 34 forms electrical contact between the end skis 21, 21', so that heat can be supplied controllably during execution of the process. Within graphite heater-

pipe 34, a cylindrical salt-lining plug 36 is in turn arranged concentrically, on which a hollow salt cylinder 37 with contents is arranged.

Operative methods for the application of both high pressures

and high temperatures in this apparatus are well known in the art. The preceding description relates exclusively to a high-pressure

and high temperature equipment. Various other apparatus which are likewise capable of producing the necessary pressures and temperatures can also be used for carrying out the method according to the invention. Pressures, temperatures, metallic catalysts/solvents and calibration methods are described in the above-mentioned patents.

In fig. 2, the bottom of cylinder 37 has enclosed an embedment disc 38 with at least one diamond seed 39 embedded therein. The indication of the diamond seed is schematic. As shown, the seed 39 is located in a portion of the disk 38 and protrudes from surface 40 thereof a sufficient distance to present the exposed surface of the seed 39 through holes 41 in the seed suppressing layer 42, which is constituted by a layer of particulate material or a solid disk. Hole 41 is filled with the seed, which presents the exposed upper surface of the diamond seed material 39 (preferably a cube face) in contact with the lower surface of plug k3 of metallic catalyst/solvent.

(fig. 3) . The thickness of plug 43 is helpful in determining the temperature difference that takes effect in the cell. With a thicker plug, the temperature difference is greater.

Also located within salt cylinder 37, the carbon supply material 44 and salt cylinder 46 are arranged above this. The material 44 is the source for supplying carbon and can be composed of diamond or diamond plus graphite, or only graphite, if desired. When graphite is mixed with diamond, it occupies any void space. It is preferred that the carbon supply source contains predominantly diamond in order to reduce the volume loss that may occur during the execution of the process. When carrying out the process, any graphite present at the operating temperature and pressure will be converted to diamond before it dissolves in the catalyst/solvent metal. Thus, pressure loss due to volume change when graphite changes to diamond will be reduced to a minimum, so that the total pressure remains in the diamond-stable range at the operating temperature.

The vertical dimension of plug 4 3 also affects the temperature gradient.

Pressure transmitting parts 36, 37, 38 and 46 are produced

of material that meets the same criteria as the material for cylinder 33. All parts 33, 36, 37, 38 and 46 are dried in vacuum for at least 24 hours at 100 - 200°C, e.g. 124°C, before assembly. Other combinations of shapes for the pressure transmitting parts 36, 37, 38 and 46 can of course be used. However, it is the arrangement of these parts that is shown in fig. 2, found to be most convenient to manufacture and assemble. For example, it may be easier to produce cylinder 37 sufficiently long enough to enclose elements 38, 42, 43 and 44, in which case element 44 will be produced with a sufficiently large diameter to lie close to heater tube 34.

The nucleation suppressing barrier layer 42 is composed of a material different from the catalyst/solvent used and is selected from the group consisting of cobalt, iron, manganese, titanium, chromium, tungsten, vanadium, niobium, tantalum, zirconium, alloys of these metals, natural mica , high density polycrystalline alumina, powdered alumina, quartz, silica glass, hexagonal boron nitride crystals, cubic boron nitride crystals, wurtzite structure boron nitride crystals and silicon carbide protected with one of the platinum family metals. Silicon carbide particles are preferably mixed with an inert material, such as sodium chloride, and shaped as a solid disk with the upper surface thereof in contact with the underside of plug 4 3 covered with a thin layer of one of the platinum group metals. The thickness of the nucleation suppressing barrier layer 42 will vary from 2.5 µm to 254 µm. The natural glitter, e.g. muscovite, should first be heated to approx. 800°C for 12 - 15 hours. The preferred thickness of mica is 50.8 -

76.2 pm.

Sufficient of the surface of the underside of the catalyst/solvent plug 43 is covered with barrier layer 42 to provide an environment around the seed 39 that suppresses spontaneous diamond nucleation for a considerable distance around the diamond seed 39. Preferably, the entire underside of the plug 43 is covered. of the barrier layer 42, but if less than the entire surface is covered, the layer 42 should extend at least 50% greater distance in all directions from the seed than the lateral growth dimension desired for the diamond. If the barrier 42

is made from one of the above-mentioned metal materials,

there must be some space between the diamond core 39 and the wall of the hole 41

in which the material of disk 38 will extend. This relationship is shown more clearly in fig. 3. In the metal disc, the ratio between the diameter and the hole and the largest dimension of the seed is within the range 1.5:1 to 5:1 when hole 41 is calculated for

to surround the germ.

The exact mechanism (possibly mechanisms) by which the discs or layers of these diamond nucleation-suppressing

materials located in the described manner act to reduce or eliminate diamond nucleation in the immediate vicinity of the diamond nucleation 39, is not known with certainty. However, it has been found that in this way diamond nucleation can be held back at least until the nucleation becomes relatively large, well-formed and able to receive the full carbon flow supplied during operation by

temperature differences at which spurious diamond nucleation led to a clumped mass of diamond growth in identical systems without the nucleation-suppressing disk.

As shown in fig. 4, the growing new diamond protrudes

in bath 4 3 (Fig. 4 is the drawing of an arrangement in which the barrier layer 42 is dissolved by the catalyst/solvent metal) as it grows. After completion of the experiment and reduction of temperature and pressure to allow removal of the reaction vessel 30, the new diamond growth embedded in the now solidified metallic catalyst/solvent •• 43 is easily detached from the nucleation site. The diamonds produced in this way are easily removed by breaking up the mass 43. Any indentation or surface roughness can then be polished away.

Procedures carried out in such apparatus are illustrated

in examples 1 - 5.

In another preferred embodiment, the method of the invention will employ a nucleation suppression barrier having at least one opening therein, and there will be at least one small accumulation of catalyst/solvent extending through the opening to interconnect the mass of catalyst/solvent with a space which contains the diamond seed material. In fig. 5, the reaction vessel has many structural features in common with those described with reference to fig. 2. The operative methods are also the same. In the following description, elements corresponding to those previously described have the corresponding number indications.

In fig. 5 is a nucleation-suppressing barrier layer

42 placed in contact with the bottom of mass 43 of metallic catalyst/solvent and between mass 43 and disk 38.

A tag 43' of mass 43 projects through hole 41 in layer 42 into disk 38 to make contact with an exposed surface (preferably the cube face) of diamond seed 39. The seed 39 is embedded in disk 38 below the main surface of the disk with a surface exposed through hole 38' in main surface.

More than one such tag 43' can be used if desired, in which case a separate seed will be provided for each tag 43'. Preferably, the holes 38' and 41 are coaxial and of the same diameter. This arrangement of the parts can best be seen in fig. 6.

The temperature difference between the hot part of the cell (approximately halfway up the height of the cell) and the diamond pocket is preferably in a range of 20 - 30°C. This difference depends on the construction of the cell, e.g. the depth and location of the mass of metallic catalyst/solvent, the differential resistance in the heater tube, the thermal conductivity of the end discs, etc. Thus, the thickness and vertical placement of plug 43 help to determine the temperature difference that prevails in the reaction vessel. With a thicker mass of catalyst/solvent, the temperature difference is greater.

The reaction vessel construction shown in fig. 5 and 6 act simultaneously both to suppress spontaneous diamond seed formation and to reduce the amount of cracks in the main body of diamond produced from a diamond seed. The dimensional criteria for the layer or disk 42 are the same as previously described, with the exception that the tag 43' is not covered by layer 42. If the disk 42 in the construction shown in fig. 5 and 6, is made of one of the previously stated metal materials, there must be space between the diamond core 39 and the innermost part of the disk 42, and the material in the disk 38 protrudes into this space.

Experiments with various reaction vessel designs have established excellent nucleation-suppressing properties of cobalt and natural mica and useful nucleation-suppressing properties of tungsten. In the same vein, it has been found that synthetic mica, platinum and nickel (as well as molybdenum, see Example 6) are not useful as nucleation suppressing materials.

With regard to growth defects, it has been found that by placing the small protrusion or accumulation of catalyst/solvent metal 1 43' in contact with the diamond seed material, initial growth defects will accumulate in this small protrusion. By the time the diamond growth has advanced through the tag 43' and has reached the main accumulation of catalyst/solvent metal 1 43, the correct growth pattern is established, and faultless (or substantially faultless) growth takes place from this point as the continuously increasing growth becomes larger and protrudes into storage 43.

If the tag 43' is formed as a circular cylinder, the diameter thereof will be in the range of greater than 0.508 mm to 2.54 mm. For tags produced in other designs, the cross-sectional area across the axis of the reaction vessel 30 at a certain location along the tag should be equivalent to a circular cross-section with a diameter in the range from greater than 0.508 mm to 2.54 mm. When cylindrical tags with a diameter greater than 0.762 mm are used, a protrusion of diamond firmly attached to the new diamond growth will develop from the tag. This protrusion contains initial growth defects and will be ground away when the new diamond growth is transformed into the desired shape, e.g. a form of jewelry.

The height (from seed 39 to mass 43) of tag 43' should be in the range of 0.76 mm to 1.52 mm. As an example of a non-cylindrical tag, tag 43' may be conical with the apex thereof in contact with core 39. Tag 43' otherwise need not be integral with mass 43, but may originally be a separate mass part and provide direct contact with it, as long as it is made from, or contains a sufficient amount of catalyst/solvent. E.g. A piece of metallic catalyst/solvent connecting the mass 43 and the seed 39 may be in the form of a cube, sphere or other shape made of nickel or certain nickel-iron alloys, provided a large enough seed diamond is used to survive loss of carbon to the bite. The catalyst/solvent which such separate tag 43' constitutes (or which the sphere contains) in a given reaction vessel construction must have a melting point, when in contact with the diamond, which is higher than the melting point of the mass of catalyst/solvent metal1 43 when this' is con-

beat with the diamond.

Due to the ability of the tag 43' to collect initial growth defects, if a large enough seed diamond is used, some etching of the diamond by the tag metal can be tolerated in exchange for the time gain achieved with this design. Processes carried out in such an apparatus are illustrated in example 7.

In a third preferred embodiment, the reaction vessel and process will include an opening in the nucleation-suppressing barrier layer adapted to include a limited diamond growth path that runs through the barrier and connects the mass of catalyst/solvent with a space containing the diamond seed material. In fig. 7, the reaction vessel 30 is of the general type and construction described above. The operational methods for applying both high pressure and high temperature are described above.

In Figures 7 and 8, a salt plug 38 containing a pocket 39' with diamond crystals (or a single diamond if desired) is placed within the said sleeve 37 resting on the salt plug 36. Directly above is placed an inert barrier disc 42 with at least one fine wire running through this, with the lower end in contact with the pocket 39' of diamond crystals and the upper end in contact with the lower surface of the main catalyst/dissolution mass 43 to serve as the limited diamond growth path. The inert barrier disc 42 is made of a material which is insoluble in molten catalyst/solvent, preferably of sodium chloride. This slice vessel. however, be made of CaF2 (provided that adjacent reaction vessel components are made of materials compatible with this), poorly fusible oxides, such as Al2O3, MgO, ZrO2, CaO, SiO2, Th02 and BeO, e.g. natural mica, high-melting silicate glass (eg borosilicate) which is not reduced by hot carbon, porcelain or silicates (eg MgSiO-j or pyrophyllite heated at 750° C to drive off water). The thickness of the disc 4 2 should be in the range from 0.254 mm to 0.762 mm.

Threads 47, 48 as shown in fig. 8 or holes 49, 50 as shown in fig. 9 may extend straight through the disc 42. They may have a zig-zag configuration or be arranged in a direction other than the perpendicular. In this embodiment shown in fig. 8, the threads 47, 48 preferably have a diameter varying from 0.0254 to 0.508 mm (or equivalent cross-section for non-circular threads) and, when possible, these are molded into the plug. The upper (hotter) end of the wires 47, 48 must be in contact with metallic catalyst/solvent 43, and the colder end of the wire must touch the diamond in pocket 39' (or the graphite in pocket 39' which is converted to diamond).

Pocket 39' will contain at least one diamond crystal and

can contain as much as 30% by weight graphite. It is preferred to have a small concentration of catalyst/solvent metal located in pocket 39' to slow down any erosion of the strands, such as strands 47, 48. This metal may be present as a disc placed between the contents of pocket 39' and the ends of the threads. The amount of catalyst/solvent metal used can vary from 10 - 50% by weight when this is used.

The diamond growth paths are made of (or, in the case of the holes 49, 50, are filled with) a catalyst/solvent metal having a melting point in contact with the diamond comparable to the melting point of the catalyst/solvent mass 43 in contact with the diamond. A single or multiple diamond growth paths may be provided depending on the size of the catalyst/solvent bath and the size of the desired diamond.

When operating pressure and temperature are reached, the metallic catalyst/solvent 43 in contact with diamond in the carbon supply source 44 melts first. Melting proceeds from the top downwards. Any graphite in mass 44 of nutrient medium is converted to diamond, and diamond dissolves in the catalyst/solvent. The wires 47, 48 melt and the carbon-rich molten catalyst/solvent is brought into flow communication with the diamond pocket 39' and the carbon begins to come out of solution as diamond using the diamond surface in contact with the colder end of the molten "wires" 47 , 4 8 as deposition surface. Diamond growth proceeds up through the molten

wires 47, 48 to catalyst/solvent metal bath 43,

with each thread at its upper end exhibiting a separate seed which initiates the large crystal growth which then extends into the bath 43. The size to which the large crystals (not shown) will develop depends on the available volume in the bath 43

for the magnification and the duration of the process. If more than one large crystal is produced, the experiment should be terminated before colli-

tion occurs between the growing crystals.

In the case of the embodiment shown in fig.

9, open channels 49, 50 with diameters in the same range as threads 47, 48 are used instead of the threads as shown in fig. 8. Operation is substantially the same in that at operating temperature and pressure the channels (if a strong material such as natural mica is used) will remain sufficiently open to provide passage of molten catalyst/solvent 43 to the diamond pocket 39: . This thus placed . catalyst/solvent creates molten "threads" in situ (which enable transport of carbon to the cold end, whereby diamond growth can be initiated and proceed up through channels 49, 50 to the upper side of disc 42' thereby providing a single kim for each hole or channel.

The diamond growth paths (threads 47, 48 or holes 49,

50) stays like la.ge thin threads of diamond, or diamond hair. After completion of the experiment and reduction of temperature and pressure to enable the removal of the reaction vessel 30, the new diamond growth embedded in the solidified metallic catalyst/dissolving part 43 can be easily removed by breaking up the mass 43. If desired, the diamond threads can be recovered by dissolving the salt disk 38.

During dccompression, the connection between the diamond wire in each growth path and the diamond formed from the seed is usually broken (apparently due to the concentration of stress at this point. Depending on the cross-sectional area of the growth path, a certain amount of the new growth will break without leaving some rough, incised flata. the smaller the cross-sectional area of the growth path, the shallower the depth of the worn portion will be. In the case of jewelry-grade diamonds, this damage must be ground smooth and minimal damage of this type will produce polished jewelry of large size. A maximum diameter of 0.508 mm (or equivalent cross-sectional area) of each growth path enables both the use of multiple seeds in the pocket 39' (while ensuring exposure of a single separated seed to the mass 43 via each growth path) and minimizes the above damage .

Unsuccessful diamond growth is in many cases due to poor cell assembly, whereby displacement of the threads occurs, so that no contact is made with the contents of the pocket 39'.

Formation of diamond materials according to this preferred feature of the invention is illustrated in Examples 8-16.

In a fourth preferred embodiment, the apparatus includes an isolation barrier having a melting point when in contact with diamond, which is higher than the melting point of the mass of catalyst/solvent when the mass is saturated with dissolved carbon. In fig. 10, the reaction vessel 30 is of the general type and construction described below. Operative methods for applying high pressure and high temperature in this apparatus are as previously described.

In fig. 10, the bottom end of cylinder 37 encloses the embedment disc 38 with at least one diamond seed 39 embedded therein. If multiple diamond seeds are used, they will be placed in separate locations with one seed at each location. Diamond seeds are preferably 1/4 to 1/2 cm in size and have a cube face, but diamond can crystallize from any face. Preferably, the entire underside of plug 43 is metallic catalyst/solvent covered with the device for suppressing diamond nucleation over a preselected area (e.g. disc or layer 42) except possibly for a hole therethrough, as shown in Fig. 12 - 16..

The isolation device 51 is initially placed between the diamond seed 39 and the catalyst/solvent to prevent premature contact between them, which could lead to dissolution (partial or complete) of the seed 39. The upper surface of the diamond seed material 39 should be oriented with a well-shaped surface, e.g. a cube surface in contact with the underside of disc 51.

Chemical insulating disc (barrier layer) 51 is preferably made of platinum, but may be made of a metal selected from any of the metals in the group consisting of platinum, molybdenum, titanium, tantalum, tungsten, iridium, osmium, rhodium, palladium, vanadium, ruthenium, chromium, hafnium, rhenium niobium and zirconium and alloys of these metals. By preventing damage to the exposed seed surface, the insulation or barrier metal prevents diamond growth from occurring from more than one location on the seed surface. When such protection is not provided, erosion of the diamond seed material takes place. Considering a given diamond seed, the erosion can either completely or partially destroy the seed. In the former case, diamond nucleation may take place at separate locations on the underside of the catalyst/solvent mass, and in the latter case, diamond growth will usually proceed from different locations on the eroded seed. In each case, the diamond growth suffers from a lack of coordination between the multiple growth formations, and many faults develop at the interfaces when these separate growth formations meet.

In any given reaction vessel construction, different metals are used for each of (a) the catalyst/solvent, (b) the barrier layer and (c) the nucleation suppressing layer. The nucleation-suppressing layer 42 is composed of the above-mentioned materials. When disc 42 is made of mica, high-density polycrystalline aluminum oxide, quartz, silica glass, or other material that provides a layer with which the molten catalyst/solvent system will not alloy and/or cannot penetrate, it is necessary to provide huM 41 ( shown in Figs. 12 - 14) through disc 42 to create contact between the molten catalyst/solvent bath and disc 51 for final contact with seed 39. Disc '42 can of course be equipped with a hole when it is manufactured

of metal, if desired.

In the case of the isolation device for the diamond seed material (disc 51), physical contact between the catalyst/solvent metal and the diamond seed is prevented until the catalyst/solvent metal 43 has melted and become saturated with carbon from the supply source. The time regulation is such that this carbon saturation takes place before barrier layer 51 is dissolved in molten catalyst/solvent. As soon as the barrier layer 51 is dissolved in molten catalyst/solvent, the exposed surface of diamond seed 39 produces growth patterns and development of new growth can take place.

Even those of the listed insulating disc materials that form carbides that are stable to diamond at the pressures and temperatures used perform well as the carbide forming process is slow relative to the rate at which the supply of catalyst/solvent metal1 becomes saturated with carbon. Any carbide formed eventually dissolves in the supply of catalyst/solvent metal. There was no evidence that platinum formed a carbide more stable than diamond.

In each of figures 12 and 13, a projecting part of the embedding disk 38 exhibits a barrier layer 51 in contact with the underside of the mass 43 of catalyst/solvent. The cast-in core 39 is placed directly under the disk 51 with a single surface thereof in direct contact with the disk 51. In fig. 12, the material of which disk 38 is composed shall separate the core 39

from the walls with holes 41. When thus in the arrangements shown in fig. 12 and 13 the nucleation suppressing disk 42

is non-metallic (and a cube surface of seed 39 is presented for the new diamond growth), the relationship between the diamond seed and the new growth 54 will be as shown in fig. 17. It is advantageous that the new growth does not enclose the germ, because much less of the new growth then needs to be polished away to remove defects.

The arrangement shown in fig. 11 and 14, enables the production of new diamond growth as shown in FIG. 17 when the nucleation suppressing layer 42 is metallic and thereby dissolved by the molten catalyst/solvent. As previously stated, the diamond configuration shown is developed when a cube face of seed 39 is in contact with the barrier layer 51. Projections 43' of the catalyst/solvent abut against the walls of hole 41 and project through hole 41 to contact the barrier layer.

team 51 over team 39.

The advantage of using both the barrier layer and the nucleation-suppressing layer can be assessed as follows: when only the barrier layer is used, approx. 70% of all attempts to produce simple, large, high-quality diamonds result in spontaneous diamond seed formation and the adverse impact of this on new diamond growth from the planted seed. Sometimes such an impact is not serious, but most often the growth from the germ will be seriously damaged. When a nucleation-suppressing layer is used, the improvement is so dramatic that only approx. 30% of attempts at

producing single, large, high-quality diamonds will be accompanied by spontaneous diamond nucleation. After the introduction of natural mica, spontaneous diamond nucleation has not actually occurred in a single case.

The arrangements shown in fig. 15 and 16, are applicable when solid, non-metallic nucleation-suppressing layer materials such as mica or machinable aluminum

oxide is used. In each case, a small hole 52 is drilled through disk 42. This hole is preferably in the range of 0.0254 to 0.508 mm in diameter. In the arrangement shown in fig. 15,

the catalyst/solvent ij 3 , when melted, will pass through hole 52 and after some time alloy with and melt insulating disc 51, so that it thereby reaches diamond seed 39 to initiate diamond growth up through hole 52 to provide nucleation for diamond growth over the barrier layer 42 In the arrangement shown in fig. 16, a thread 53 occupies hole 52. The thread can e.g. be of nickel or Fe-Al or Fe-Ni alloys and extend through disc 42 to then contact both plug 43 and insulation barrier 51. As catalyst/solvent 43 and then the material in wire 53 melts and carbon dissolves therein, the insulating barrier 51 is alloyed, and diamond growth starts to produce a seed at the upper side of the barrier layer 42.

The devices for maintaining a pressure difference between

the hot part of the cell (about halfway up the cell's height) and the diamond pocket have been described earlier. Illustrative processes relating to this preferred feature are described in Examples 17-24.

In a fifth preferred embodiment, the reaction vessel will include at least one barrier in combination with a further component selected from dopemi-Zier, getters, compensators, mixtures thereof and the like to provide colors, patterns, color zones and the like in the diamond product. In fig. 18, the reaction vessel 30 is of the general type and construction described earlier.

In fig. 18, cylinder 37 together with plug 36 and cylindrical plug 46 delimits a space 55 intended to contain a cylindrical batch device such as e.g. shown in each of Figs. 19 - 22. These batch devices allow (a) the introduction of quantities of boron and aluminum to enable the production of "Star" diamond and/or (b) the successive introduction into the growing diamond of varying color in the one large diamond crystal. Any of the elements and combinations described above can be used to form such a rate device.

By simultaneously making available to the growing diamond at least one part per million (ppm) boron and 2500 ppm aluminum, based on the weight of the catalyst/solvent used, and carefully orienting the diamond seed, a jewelry-grade diamond crystal can be produced symmetrically about a cube axis that exhibits a colorless or white pair of three-dimensional linear bands that cross each other when the crystal is viewed along the given axis of symmetry, the rest of the crystal having a blue colour. The overall appearance of the pattern appears to be symmetrical.

In addition, crystals can form where colored diamond growth is surrounded by colorless diamond growth. Similarly, the first colored diamond growth may be enclosed by a second colored diamond growth. A myriad of color combinations can be obtained depending on the choice of dopants, getters and/or compensating materials. For example, nitrogen will give color values varying from yellow to green diamonds, while boron will give deep blue colored diamonds and aluminium, titanium and zirconium both give colorless diamond growth.

Normally, sufficient nitrogen is present

in the metallic catalyst/solvent and all reaction vessel components to. to color the diamond strongly yellow whether it is produced by the thin film method or the temperature gradient method. Typical nitrogen content is 30 - 40 ppm. When carrying out the present invention, where diamonds produced by the thin film method are usually used in the carbon supply mass, will

thus the resulting diamond will be yellow in color (rich in nitrogen) in the absence of getter, compensator and/or dopant in the system.

Boron (and of course nitrogen) acts as a doping agent. Aluminum acts as a getter for nitrogen, and if sufficient amounts of aluminum are present, this will enter the lattice of the growing diamond and act as a compensator for such nitrogen as may enter the lattice. Titanium and zirconium both act as getters.

Contrary to the earlier teaching, it has been found that boron will not readily give the diamond a blue color on its own. Thus, if as little as 100 ppm aluminum is present in the molten catalyst/solvent, 20 micrograms of boron will cause the diamond to acquire a deep blue color. With no aluminum present, the diamond growth will be yellow-green, unless larger amounts (over 20 micrograms) are present in the catalyst/solvent bath. As commercial boron contains as much as 900 ppm aluminium, such boron will invariably produce a blue-coloured diamond if used, particularly as aluminum is usually present as an impurity in catalyst/solution forged Ime numbers.

In US patent 3 148 161 (column 5, lines 42 - 46 and column 9, lines 43, 46) it is stated that the use of boron in a concentration of from 0.1 to 20% by weight of the graphite (which is converted to diamond) will lead to a color shade varying from blue to deep purple, but the boron used contains traces of impurities including aluminium. Calculations of the total amount of boron additive stated in the above-mentioned US patent document (where it is assumed that commercial boron, which has a 900 ppm aluminum content) was used, states, however, that the maximum amount of aluminum that will be introduced into the system according to the above-mentioned US patent, is 200 ppm (based on the mass of catalyst/solvent), while the smallest amount of aluminum necessary for "star" formation (intersecting white bands in :. t blue field) appears to be approx. . 2500 ppm (based on mass of catalyst/solvent).

The formation of successive colors except for the growth is achieved by using combinations of dopants, getter substances and/or compensator materials arranged in the batch device structure, the initial growth medium will give a pre-selected colored diamond growth, after which the getter substance and/or compensator material after a predetermined time with diamond growth will enter the molten catalyst/solvent and cause colorless growth (or growth of another color, if desired) which envelops the original colored growth in an uninterrupted sequence.

Batch device 40 (shown in Fig. 19) has been used for the satisfactory production of dark blue star diamonds. When introducing a layer of non-metallic nucleation-suppressing material, e.g. mica (as described in connection with fig. 20 below), however, the arrangement shown in fig. 19, is made more reliable.

The core 39 is protected by the chemical insulating disc (barrier layer) 51, which is preferably made of platinum, but which may be made of any of the above-described metals for this purpose.

By using insulating disc 51, physical contact between the molten supply of catalyst/solvent metal and the diamond seed is prevented until the supply of catalyst/solvent metal 1 43 has been saturated with carbon from the carbon supply mass 44. The time regulation is such that this carbon saturation takes place before barrier layer 51 is dissolved by alloying with the molten catalyst/solvent. When such protection is not provided, erosion of the diamond seed material takes place as previously described.

Seed 39 is embedded in embedding layer 38 with a die face exposed and in contact with disk 51 to provide a secure "template" for the new diamond growth. Mass 43

of metallic catalyst/solvent is placed thereon with disk 51 in contact with the underside thereof and a layer 44 of carbon feed material (e.g. diamond plus a small amount of graphite over the catalyst/solvent) containing boron.

Boron-containing diamond for layer 44 can be easily produced as described in the previously cited US Patent 3,148,161 using commercial boron containing a sufficient amount of aluminum. The use of boron-added diamond is preferred, as such small concentrations of boron are necessary (in excess of 1 ppm on the basis of the weight of catalyst/solvent), but boron can, however, also be added in other ways. Thus, a small crystal of boron or boron carbide can be placed in layer 44.

The necessary aluminum content (at least 0.25% by weight of the catalyst/solvent) can best be provided by using an aluminum alloy of the catalyst metals, e.g. Fe + 3 wt% Al.

As operating pressure and temperature are reached, the metallic catalyst/solvent 4 3 in contact with any graphite in the carbon supply source 44 will melt and convert this graphite to diamond. The catalyst/solvent in contact with the diamond in layer 4 4 melts at a slightly higher temperature

and dissolves the diamond. The molten catalyst/solvent penetrates layer 44, and melting proceeds from the top down into layer 43. When in this way the carbon-rich molten catalyst/solvent reaches and alloys with layer 51, it already contains boron and aluminum ready for entry in the new diamond growth that is initiated when the molten catalyst/solvent metal1 reaches the colder diamond nucleus 39 and deposits carbon from the solution. Some of the aluminum takes up some of the nitrogen in the system, while some of the aluminum enters the diamond lattice. Some of the aluminum that enters the lattice acts as a compensator for any nitrogen in the lattice and binds the nitrogen atom electrons, whereby these nitrogen atoms become optically inactive. The rest of the aluminum is uncompensated,

and for an unknown reason this collects in elongated thin vertically running planar zones in a crossed relationship to each other. These zones appear white in contrast to the dark blue color of the rest of the diamond growth. When the diamond is viewed in the direction of the cube axis of symmetry (ie from the top of the diamond, as it forms in layer 4 3), these zones appear as intersecting bands perpendicular to each other and running towards opposite corners of the crystal.

The batch assemblies in fig. 20 - 22 are arranged to produce successive colors during continuous growth of a single crystal. In each of these cell assemblies, the seed 39 is protected in insulating disc 51 and embedded in layer 38 with the desired orientation. The carbon supply source (excluding additions of dopant, getter and/or compensator) is the same as described for layer 44. Likewise, each of these batch assemblies uses diamond nucleation suppressing layer 42 (or 42').

Nucleation suppressing layer 42 is composed of a material different from both the catalyst/solvent used and the insulating disc used in any given batch assembly and is selected from the group of materials previously described. The advantage of using both the barrier layer and the nucleation-suppressing layer has been described previously.

In fig. 20 is the arrangement for the production of successive color zones the separate plugs 4 3, 56 of catalyst/solvent, double carbon supply layers 44, 57 and getters and/or compensator disc 58.

In order to produce a diamond crystal with this arrangement

stall with a yellow or green core covered with colorless growth,

shall the metallic catalyst/solvent layer plug 43

be substantially free of aluminum, titanium, zirconium and manganese, but may otherwise be of any of the applicable catalyst metals and alloys. For a yellow core, the carbon supply layer 44 must have diamond with uncorrected nitrogen content. Similarly, catalyst/solvent 43 will contain a normal nitrogen contaminant. In the absence of special efforts to remove the nitrogen normally present,

will this nitrogen content affect the immediate diamond growth that develops on seed 39 and give this original growth a deep yellow colour. Colorless growth can then be created using non-aluminum catalyst/solvent plug 56 in combination with a disc 58 of aluminum, titanium or zirconium. A high concentration of aluminum (from 1 to 10% by weight of the metallic catalyst/solvent) will ensure colorless growth as soon as the carbon supply source in layers

4 4 is used up.

If yellow color is to develop first, precautions must be taken to ensure a delayed diffusional entry of any significant amount of aluminium, titanium or zirconium into the melt before the yellow growth has been satisfactorily achieved. At the time when disc 58 has alloyed into catalyst/solvent 56 and worked its way through the diffusion path formed by carbon supply layer 44, a sufficient time delay will have been achieved for a yellow core to form.

To develop a green kernel, very large concentrations of nitrogen are necessary. This can be achieved by introducing nitrogen compounds, e.g. iron nitride, which will decompose and release additional nitrogen to the catalyst/solvent system (layer 43).

Various arrangements can be used to increase the time delay before the entry of the getter substance and/or the compensator into the diamond-forming medium. Thus, the getter substance and/or the compensator can be recessed into the pressure-transmitting plug 38 or plug 46 in the form of a wire, rod or ingot or be separated from the catalyst/solvent by a thin layer of a high-melting metal, e.g. platinum, iridium or tungsten.

To provide a blue diamond core covered with colorless growth, precautions must be taken that boron and aluminum are present simultaneously for the immediate growth and that all of the boron is used before catalyst/solvent plug 56

can be contaminated. The catalyst/solvent for both layers 43 and 56 must contain aluminum (e.g. iron +1-8% aluminum by weight). All of the table dopant must be located in the lower area of carbo supply layer 44. Non-metallic nucleation suppressing materials, e.g. mica, should be used for layer 42. Precautions for the colorless aftergrowth will be the same as described for the combination yellow/colorless growth.

The arrangement according to fig. 21 is designed in more or less the same way for producing a yellow or green core as the arrangement shown in fig. 20. A single catalyst layer 4 3 is used in combination with separate carbon supply layers 44, 57 with getters and/or compensator disc 58 placed between them. The composition of catalyst/solvent 43 and nutrient layer 44 will determine whether the core of the new diamond growth will be yellow or green as described in connection with fig. 20.

The arrangement according to fig. 22 is specific to the production of a blue core diamond for the use of a concentration of boron atoms located in disc 59 as an alloy or a

connection of boron.

Subsequent growth (after the boron atoms have been used up) can be colorless, light yellow or green if desired. Catalyst/solvent metal layer 43 preferably contains aluminum to allow blue staining of the drill. The nucleation suppressing layer 42 should be non-metallic. Carbon steel layer 44 in combination with the amount of aluminium. in layer 43 will determine whether the later growth will be colorless, light yellow or light green. If a sufficiently large concentration of aluminum is present in the catalyst/solvent layer 43, the initial growth may also be a "star".

Devices for achieving the temperature difference between the hot part of the cell (approximately half the cell's height) and the diamond pocket have previously been described.

Preferred catalyst/solvents for practice

of the color-giving features are Fe, FeNi, FeNiCo, FeAl, Ni-Al, Fe-Ni-Al and Fe-Ni-Co-Al. Preferred nucleation suppressants are natural mica and cobalt, and the preferred insulating barrier is platinum. When natural mica is used, it must first be burned as previously stated. When alloys with a higher iron content are used, the diamonds produced have a lighter yellow color. With larger amounts of Ni and/or Co, the resulting diamonds have a deeper yellow color.

For the reaction vessel construction described, pressure ranges from 55 to 57 kilobars are preferred, and preferred temperatures are in the range 1330 - 1430°C.

In each of the following examples 1 - 5, the reaction vessel configuration gave a temperature difference in the range 20 - 30°C, while the carbon feed material consisted of 1 part by weight SP-1 graphite and 3 parts by weight 325 mesh diamond produced by the thin film method. The seeds used were 1/4 to 1/2 mm, the catalyst/solvent was 70Ni30Fe, and the temperatures were measured using a Pt/Pt 10 Rh element.

Example 1 (Comparison example)

At least 10 yellow diamond crystals grew together into a clump. The 1/2 mm germ had dissolved somewhat and had grown back. The crystals were either octahedral or cubic-octahedral.

Example 2

Only one yellow diamond crystal growth was developed from the diamond seed. There was no spurious seeding on the diamond. The crystal was an octahedron with small cube faces at the corners.

Example 3

Simple sprouts were developed that were well-shaped, symmetrical and relatively flawless. The crystal was a yellow..octahedron with small cube faces at the corners. A small diamond crystal was developed where the underside of plug 43 was not covered with iron disk 42. This experiment demonstrated the nucleation suppressing abilities of Fe. However, there was partial dissolution of the germ before new growth started.

Example 4 (Comparison example)

The pressure, temperature of the weight of the carbon feed material were the same as in Example 1, and no nucleation suppressing layer was used. The time was 2 4.5 hours. As in Example 1, a clump of yellow crystals developed due to spontaneous nucleation.

The germ grew to approx. 2x2 mm with a diamond outgrowth attached to it. Also five other individual small crystals were developed due to nucleation.

Example 5

A single light yellow crystal was formed from the seed. There was no spontaneous nucleation on the diamond. The error content was minimal. The crystal had a very low nitrogen content.

Experiments with various reaction vessel designs have shown the excellent nucleation-suppressing ability of cobalt and natural mica and the useful nucleation-suppressing ability of tungsten. Similarly, it has been demonstrated that synthetic mica, platinum, nickel and molybdenum are unsuitable as nucleation suppressing materials.

In each of the following examples 6 and 7, the reaction vessel configuration gave a temperature difference in the range of 20-30°C. The carbon feed material consisted of 1 part by weight SP-1 graphite (National Carbon Company) and 3 parts by weight 325 mesh diamond produced by the thin film method. The seed used was 1/4 to 1/2 mm, the catalyst/solvent was 70Ni30Fe, and the temperatures were measured using a Pt/Pt 10 RH thermocouple.

Example 6

Despite the molybdenum disc's inability as a nucleation suppressing material, a beautiful, yellow, clear growth developed from the nucleation. Four other diamond crystals grew spontaneously, collided and had a devastating effect on the optimal seed growth. The tag worked well to prevent failure in the growth that took place into bath 43. The seed growth was in the form of a truncated octahedron with modifying cube faces.

Example 7

A beautiful clear bright yellow crystal grew from the diamond seed.

No spontaneous diamond nucleation took place. The crystal was

in the form of a truncated octahedron with modifying cube faces. The tag 43' successfully prevented any significant defect formation in the initial growth of the crystal.

By thus utilizing the ability to suppress diamond nucleation and eliminate crack propagation from the main body of the new growth, a very significant improvement in the regulated growth of larger diamonds from the diamond seed material was achieved.

Each of the following examples is representative of

for jewelry quality growth. In each of examples 8-12, the operating pressure was 57 kilobars, while the operating temperature was 1500°C and

the carbon feed material layer 44 was a mixture of graphite and diamond in a ratio of 1:3 (except that smaller amounts of other materials were added in Examples 8, 10 and 11).

Example 8

A simple clear diamond (almost water clear) with few internal defects was produced from the wire-induced nucleation. The crystal was a truncated octahedron with modifying cube faces.

Example 9

The single diamond produced from the thread-induced nucleation was very bright yellow with only a few minor defects. This crystal phosphoresced and gave a blue glow under light of wavelength 2537 Å. This diamond was not semi-conducting, had a low nitrogen content and was a truncated octahedron with modifying cube faces.

Example 10

The single diamond crystal was obtained from nucleation provided by the nickel wire. Investigations showed that the nickel steel wire had not contacted the contents of the diamond pocket 39'. The crystal was deep blue, semi-conducting, phosphorescent weakly, and was a truncated octahedron with modifying cube faces.

in Example 11

The single crystal developed from the wire-induced nucleation was light blue in color, semi-conductive and phosphoresced clearly under 2537 Å ultraviolet light. This crystal was truncated octahedron • with modifying cube faces.

Example 12

Six colorless diamond crystals were formed (one

from each thread-induced nucleation). The six diamonds grew in parallel crystallographic orientation with an octahedral face up.

In each of the following examples 13 - 17, the operating pressure was 55 kilobars, while the operating temperature was in the range 1450 - 1500°C and the length of the experiment was 5 hours. The carbon supply layer 44 was a mixture of graphite and diamond in a ratio of 1:3, and the catalyst mass was of nickel-iron alloy (51 Ni 49 Fe). In all examples in which wire served as the growth path, nickel wire was used, and a disc of Fernico (FeNiCo) alloy (0.05 mm thick, 4.75 mm in diameter) was placed in contact with and between the growth paths and the diamond in seed pocket 39' . In some cases, the necessary contact was not achieved when the cell was filled and no growth took place. The seed pocket 39' consisted of 0.025 g of a mixture of diamond and graphite in a weight ratio of 3:1. In all examples, the crystals formed from the limited diamond growth paths ranged from 3/4 to 1 mm in size and had a clear yellow color.

Example 13

Example 14 Example 15

Example 16

The length of the limited diamond growth path from the seed pocket to the catalyst/solvent path is not so critical

as long as the distance of the diamond ion 39' from the hot region of the reaction vessel allows a temperature high enough to melt the catalyst/solvent web (eg wires 47, 48) where it contacts the diamond seed material. The preferred length is in the range of 0.5-1 mm.

In each of the following examples 17 - 24, the reaction vessel configuration gave a temperature difference in the range of 20 - 30°C. The carbon feed material consisted of 1 part by weight of Sp-1 (National Carbon Company) graphite and 3 parts by weight of 325 mesh diamond produced by the thin film method. The seeds used were 1/4

to 1/2 mm, and the temperatures were measured using a Pt/Pt 10 Rh thermocouple.

Example 17

Four yellow crystals were produced, one growing from each of the four nuclei. One germ formed a lump. The new diamond growth ranged in size from 10 - 20 mg (1/20 - 1/10 carat). The crystals had small inclusions near one face but were clear. In each case the crystal form was cubic-octahedral with modifying cube faces. Example 18

Five pale yellow crystals were obtained, one developed from each seed. The new growth had an average size of 1.52 mg and each measured approx. 1 mm along a cube face. The crystals were well-shaped, clear and relatively free of inclusions. In each case the crystal was cubisi-octahedral with modifying cube faces.

With multiple nucleation, the requirement for nucleation suppressants is reduced, and with safe operating conditions and a nucleation density of 1 nucleation per 8 - 10 mm 2 the nucleation-suppressing disk can be omitted.

Example 19

The diamond seed growth was yellow and of jewelry quality. Three other very small crystals grew out of the area occupied by the seed growth. The crystal form was a truncated octahedron with modifying cube faces.

Example 2 0

A simple beautiful jewelry grade yellow crystal was developed. The crystal form was cubic-octahedral.

Example 21

A simple beautiful gyldangu.l jewelry diamond was produced with a cubic-octahedral shape with modified octahedral edges.

Example 22

A simple beautiful, almost colorless crystal was developed. The crystal form was truncated cubic-octahedral with modifying cube faces, and which phosphoresced for 1 hour after being exposed to light of wavelength 2537 Å, which gave high, mainly flat transmission of ultraviolet light from 2250 Å - 3.30 pm and from 6 .00 µm to 50 µm, which were semi-conductive and thermo-luminescent. The thermal conductivity of the crystal at 80°K was at least 180 watts/cm°K.

Example 23

In addition to seed growth, a small (22 mg) diamond crystal grew up which to some extent inhibited seed growth, which was colorless and of jewelry quality. The cracks were polished out and gave a crystal of 19 4 mg. The crystal exhibited phosphorescent properties, ultraviolet transmission, electrical conductivity, thermal conductivity and thermoluminescence as in example 22. The abrasion resistance was very high. When very small amounts of diamond were removed when performing the grinding wheel test, the measurements were difficult to perform accurately when large amounts of corundum were removed. The test results gave grinding ratios varying from 120,000 to 168,000 in 3 g of diamond seed.

Example 2 4

A single almost flawless crystal was formed. The crystal had the shape of a truncated octahedron. In addition to the (111) faces, the crystal had cube faces (100), dodecahedron faces

(110) and (113) surfaces.

Tests have determined that synthetic mica, platinum, nickel and molybdenum are unsuitable as nucleation-suppressing materials.

After completion of each experiment and reduction of temperature and pressure to enable removal of reaction vessel 30,

the new diamond growth embedded in the solidified metallic catalyst/solvent 43 easily detaches from the seed surface. The diamonds produced in this way are easily removed by breaking up the mass 43. The indication of the diamond seed is schematic, and no attempt has been made to determine the preferred location.

The crystals obtained by carrying out the present invention are developed in symmetries which are determined by the face of the Rim crystal which is chosen as a pattern. Thus, a diamond crystal grown from a cube face (100) of the seed crystal will be symmetrical around the cube axis, and in the case of almost colorless diamonds, such a crystal will lead to a unique pattern of phosphorescence as previously described. Although crystals symmetrical about other axes can be formed using other faces of the seed crystal [eg. (110), (111),

(113)] to indicate the growth pattern, diamonds that are symmetric about the cube axis yield the most crystal and best quality for a given reaction cell volume during a given growth time. It is an important feature of the present invention that the seed crystal indicates the growth pattern for, but does not form any part of, the new diamond growth and thereby ensures symmetrical growth without the interior being darkened as a result of the presence of a seed.

In each of the following examples 25 - 29 gave reaction

o the vessel configuration a temperature difference in the range 20 - 30 C, while the carbon supply material consisted of 1 part by weight SP-1 graphite and 3 parts by weight 325 mesh diamond produced by the thin film method. The seeds used were 1/4 to 1/3 mm, and the temperatures were measured using a Pt/Pt 10 Rh thermocouple:

Example 2 5

The diamond nucleation was dark blue with the characteristic contrasting intersecting bands, or zones, previously described. This high-quality crystal1 had few internal defects, phosphoresced to some extent after exposure to 2537 Å light, and was strongly semi-conducting. Another small crystal grew out of the growth field of the large seed crystal. The large diamond was a truncated octahedron with modifying cube faces and was symmetrical about the cube axis which was parallel to the vertical axis of vessel 30.

Example 2 6

A single crystal was obtained<,> which was found to be relatively flawless under 30x magnification. The color was •dark blue with a white cross even more distinct than in the diamond produced in Example 25. This crystal also phosphoresced to some extent, except from the band, which was dark, and the stone was strongly semi-conducting. The diamond was a truncated octahedron with modifying cube faces.

When similar experiments were carried out using a substantially aluminum-free system, the seed crystal growth was yellow-green.

Example 2 7

A yellow-green diamond crystal grew from the diamond seed

and consisted of an octahedron with small cube faces at the corners. The boron content was found to be high and non-uniform, and the crystal was strongly semi-conducting. The crystal showed no absorption in the infrared region at a wavelength of 2800 cm, indicating that no un-ionized (uncompensated) aluminum was present.

Example 28

A yellow-green diamond crystal was produced which had dark blue-green striations. The boron content (of the order of 500 ppm) was high but not uniform. The crystal form, electrical conductivity and IR absorption were as for the product in Example 27.

Yellow-green diamonds found in nature are not semi-conducting. Such crystals have the unique combination of size, semi-conductivity, strength and lack of absorption in the radiation range 3.30 pm - 3.75 pm. As such, these crystals can be used as embedded windows in high pressure reaction vessels and used to monitor absorption bands for materials under pressure and regulated stress.

Example 2 9

Application of too low a temperature led to clumped growth. Some crystals were colourless, some yellow and one single crystal had a colorless part close to a yellow part. The initial growth was the yellow colour. All diamonds were small, approx.

1 mm in size.

Diamonds of jewelry quality have been produced by carrying out the present invention as practically colorless diamonds and as diamonds with clear light yellow and clear dark yellow color. "Colorless" is used interchangeably with "white" and "water-clear". The almost colorless crystals are typically truncated octahedral with modifying cube faces, while the yellow stones are well-developed octahedra with smaller truncations and with a reduced corner. The latter shape is excellent for achieving a high weight when the diamond is cut as a round brilliant.

The almost colorless stones were graded from H to J on the GIA grading scale, which has values varying from D (colorless) to N (yellow). Random embeddings of catalyst/solvent occurred in the crystals when they were removed from the apparatus, but many of these can be cut away when making a shaped diamond.

Under 45% magnification, these crystals may show tiny white inclusions that are not symmetrical under a standard 10x magnification used in grading diamonds. These tiny inclusions do not affect the crystal's brilliance and are not considered defects.

The almost colorless diamond growth from a cube face phosphoresces after irradiation with ultraviolet light (2537 Å) with a characteristic pattern in which a pair of non-phosphorescent linear bands crossing each other contrasts with the rest of the crystal, which phosphoresces. In contrast to the natural diamonds that phosphoresce, these almost colorless diamonds phosphoresce for a very long time, e.g. in a time period of the order of 1 hour. The phosphorescent diamonds all have a low nitrogen content.

Although all natural stones graded G or lower (versus N) in the GIA color grading system have a large ultraviolet absorption band at 4155 Å, none of the nearly colorless H-J diamonds produced according to the invention exhibit any such ultraviolet absorption band, i.e. these crystals give an essentially flat response from 2250 Å to more than 4500 Å. This phenomenon makes such stones particularly suitable as spectrometer crystals for monitoring radiation in the visible to ultraviolet range.

Furthermore, the colorless diamonds in the H-J range (GIA scale) produced according to the invention are good semiconductors when traces of boron are present. More boron (about 1/4 ppm or more) begins to color the crystal blue. The combination of the crystal size (larger than 1/20 carat, especially those larger than 1/5 carat), the semi-conductivity and the almost colorless clarity that these diamonds provide, which is not observed in natural diamonds, represent excellent opportunities for construction of high-pressure cells for monitoring absorption bands of materials that are simultaneously subjected to high pressure and electrical voltage. Thus, such large, almost colorless single-crystal diamonds can be used as embedded windows in high-pressure cells to be able to make observations during high-pressure processes.

Obviously, due to (a) the difference in nitrogen content and (b) the manner in which the nitrogen is present, the almost colorless diamonds produced according to the invention exhibit a much better thermal conductivity at temperatures in the range of 10 - 100°K and an abrasion resistance better than what exists for natural single crystal diamonds that are subjected to the cut test. Nitrogen content of less than 10<16>

atoms of nitrogen per cm 3 (less than 20 ppm N) in the diamonds produced according to the invention are particularly effective in increasing both the thermal conductivity and wear resistance.

Thus, the thermal conductivity of natural diamond will not exceed 120 watts/cm°K (at 80°K), while almost colorless diamonds produced according to the invention have a value of 180 watts/cm°K at the same temperature.

In the grinding wheel test, the grinding strength (grinding ratio) is calculated as the volume of corundum (removed from a 60 grain corundum wheel) in cubic centimeters removed per grams of diamond consumed. During the test, the diamond is oriented with the most resistant grinding direction [(110) direction of the cube face]

against the wheel. During the test, the insertion was against corundum-

the wheel 0.0254 mm for each pass. An almost colorless diamond produced according to the invention (less than 20 ppm N content) showed grinding conditions varying from ever 52.4 • lo <4> to 4 3

32 7 . 10 cm /g diamond, while colorless natural diamonds gave

4 4 3 grinding conditions varying from 19.7.10 to 104.9.10 cm /g diamond.

The almost colorless diamonds produced according to the invention do not fluoresce under long-wave ultraviolet light (3660 A). Under short-wave ultraviolet light (2537 Å), however, these diamonds fluoresce strongly in tones of yellow and green.

It can therefore be concluded that they are almost colourless

(H to J on the GIA grading scale) diamonds with a low nitrogen content produced according to the invention are better than natural diamonds for use as heat absorbers at cryogenic temperatures and will provide more wear-resistant (and thus more durable) jewelry teeth.

Claims (6)

1. Method for the production of a diamond material, in which a reaction vessel containing a diamond seed material and a carbon supply source separated by a mass consisting mainly of a catalyst/solvent is subjected to a pressure in the diamond-stable region of the phase diagram for carbon, at the same time that the reaction vessel is heated at such way that the diamond seed material is kept at a temperature close to the minimum temperature for the diamond stable area, while the carbon supply source is kept at a temperature close to the maximum temperature for this area, whereby a temperature gradient is produced between the diamond seed material and the carbon supply slide, characterized in that at least one of the following layers is placed between the diamond seed material and the mass of catalyst/solvent: (a) a nucleation-suppressing barrier layer which is soluble in the catalyst/solvent under the operating conditions, and which is provided with at least one opening between the diamond seed material and the mass of catalyst /solvent, (b) a nucleation-suppressing barrier layer which is insoluble in the catalyst/solvent under the operating conditions, and which is provided with at least one opening between the diamond seed material and the bulk of the catalyst/solvent, and (c) an insulating layer which, when in contact with diamond, has a melting point that is higher than the melting point of the mass of catalyst/solvent when the mass is saturated with dissolved carbon. 2. Method according to claim 1, alternative (a), characterized in that the catalyst/solvent is arranged so that it extends through the opening or openings in the nucleation-suppressing barrier layer and down into a depression under each opening to thereby connect the mass of catalyst/ solvent and the diamond seed material. 3. Method according to claim 1, alternative (b), characterized in that at least one is used opening through the barrier layer, which opening forms a limited diamond growth path extending through the barrier layer and connecting the mass of catalyst/solvent and a pocket containing the diamond seed material. 4. Method according to claim 3, characterized in that a solid thread of a catalyst/solvent for the diamond formation reaction is placed in the opening or in each opening. 5. Method according to claim 1, characterized in that both a layer (a) and a layer (c) are used, and that these are placed so that the nucleation-suppressing barrier layer separates the insulation layer from the mass of catalyst/solvent. 6. Method according to claim 1, characterized in that both a layer (b) and a layer (c) are used, and that these are placed so that the nucleation-suppressing barrier layer separates the insulation layer from the mass of catalyst/solvent.