Patent Application
20050255029
The present invention provides a method of combination of the graphite source used in the manufacture of synthetic diamonds and the catalyst used in the conversion of the graphite source to diamond. Additionally, the graphite and catalyst mixture, made by methods described herein or otherwise, can be processed into a form that may be used to improve manufacturing efficiencies in the diamond synthesis process.
The conventional understanding of the catalytic mechanism in the manufacture of synthetic diamond is based on a simple solution model, in which graphite dissolves into the molten metal form of the catalyst, and diamond precipitates out due to its lower solubility. However, this does not explain how the type of diamond formed is so significantly affected by the graphite microstructure. For example, non-graphitized forms of carbon can only form diamond, if at all, at a much higher pressure than graphitized forms, or must first be converted to graphite. The rates of diamond nucleation and growth are strongly dependent on the degree of graphitization of the carbon source: the higher the level of graphitization, the faster the diamond can nucleate and grow. The solution mechanism cannot explain why certain metals such as copper are unable to form diamond even though they may dissolve small amounts of carbon. A catalytic action is widely considered as the reason for the apparent dependency of diamond formation on graphite structure and metal chemistry.
The catalytic mechanism has been proposed to be based on the electronic interaction between the empty 3 d orbitals of transition metals and the unbonded (π bond) 2 p electron of carbon. Although such a model provides a basis for explaining certain empirical observations, it does not provide acceptable explanations for the impact of the graphite's stacking sequence nor the consequence of having catalytic metals such as titanium and vanadium with very high deficiencies of d-orbital electrons.
A more recent explanation for the sequence of events for diamond synthesis under high pressure has been provided: (1) the molten catalyst metal penetrates structurally weak regions of the graphite, forcing the graphite to disintegrate into microscopic flakes; (2) metal atoms penetrate the graphite flakes by intercalation and shuffle the graphite stacking sequence into the rhombohedral form; (3) the rhombohedral graphite flakes are puckered under the influence of molten catalyst sticking them together to form a diamond nucleus; (4) the diamond nucleus grows by continuously feeding on microscopic flakes, and, as the diamond grows in size, the molten catalyst is pulled in by the capillary effect, allowing the thin metal envelope to expand continuously around the growing diamond.
Presently, two methods are commonly used for combining the graphite with a catalyst material. The first is a layering method where alternate layers of graphite and catalyst are present in the reaction cell (the catalyst being typically in disk form). The second is a powder method where high purity graphite powder is mixed with alloy powder. The powder method has many benefits because of the inherent improvement in homogeneity. However, there are problems with the powder method because of the density differences between the catalyst metal and the graphite and consequent segregation. Much work has been done to develop manufacturing methods that will minimize this problem.
The scope of this invention is as set out in the appended claims in the light of the following description.
It is an object of this invention to provide methods for combining graphite with catalyst materials to facilitate intimate mixing, which in turn leads to improvement of the manufacturability of synthetic diamond. Significant yield improvements may also result from this mixing and processing.
Methods according to the present invention are based on utilization of standard catalyst materials and alloys used in diamond synthesis. However, certain embodiments of the invention offer an additional benefit in that the production of small batches of catalyst can be accomplished without the typical expense associated with the standard method of catalyst manufacture, that is, inert gas atomization of the catalyst alloy. Consequently, additional catalysts may be developed, and it is within the scope of this invention that all such catalysts developed according to methods of the invention be included in addition to those in current use from the transition metals and their alloys.
According to certain embodiments of the invention, catalyst materials are manufactured chemically using a wet chemical method instead of producing an alloy in melt form and passing the melt through an inert gas atomization system. Typically, the elements of the catalyst are provided in chemically bound form (e.g., as salts), dispersed to form a particulate material providing intimate contact of the elements of the catalyst, and then reduced to form the catalyst.
In certain exemplary embodiments, a mixed salt or mixture of salts of the catalyst elements is formed to provide intimate contact of the elements of the catalyst, the mixed salt or mixture of salts is then dispersed to provide a particulate form of the mixed salt or mixture of salts, and the particulate form of the mixed salt or mixture of salts is then reduced to the alloy.
According to one embodiment, the correct atomic ratios of insoluble metal carbonates are calculated and the metal carbonates are ball milled together in water to form a slurry. The slurry is spray-dried, generating a particulate metal carbonate mixture. The particulate material is calcined and the resulting oxide mixture reduced to metal powder. Reduction is accomplished using any of several methods that are described below.
544.216 g MnCO3 (˜46.25% Mn—Sigma Aldrich Cat No 37,744-9)
1549.39 g 2NiCO3.3Ni(OH)2.4H2O (˜45.05% Ni—Sigma Aldrich Cat No 33,977-6)
108.93 g CoCO3.xH2O (45.9% Co—Sigma Aldrich Cat No 20,219-3)
These ingredients are milled with 3.8 kg of alumina milling media in two liters of distilled water for approximately ten hours. The suspension is then dispersed in after three liters of distilled water and spray dried at ˜250° C. (˜500° F.). The particulate metal oxide mixture is calcined at 300° C./hour to 600° C. and held at 600° C. for four hours in an electric furnace, yielding approximately 1.15 kg of the catalyst material.
The catalyst material is then reduced to an alloy powder in a hydrogen reduction furnace. Graphite powder is then combined with the finely divided catalyst alloy. The mixture of graphite and alloy powder is used as a precursor material in the manufacture of synthetic diamonds in any number of standard ways, as is understood by those skilled in the art.
Other examples of standard alloys which may be manufactured by this method and which are commonly used in the manufacture of synthetic diamonds are as follows:
(A) An alloy of Fe 65%, Ni 35% may be manufactured. A small quantity of catalyst material may be produced from the following starting materials:
776.9 g 2NiCO3.3Ni(OH)2.4H2O (˜45.05% Ni—Sigma Aldrich Cat No 33,977-6)
921.1 g precipitated Fe2O3 (˜69.96% Fe—Fisher Scientific Cat No I/1150/53)
A carbonate of iron is not commonly available, and thus precipitated iron (III) oxide is used in this example. These ingredients are milled with 3.8 kg of alumina milling media in two liters of distilled water for approximately ten hours. The suspension is then dispersed in a further three liters of distilled water and spray dried at ˜250° C. (˜500° F.). The particulate metal oxide mixture is calcined at 300° C./hour to 600° C. and held at 600° C. for four hours in an electric furnace, yielding approximately 1.22 kg of the catalyst material which may then be reduced to an alloy.
(B) An alloy of Ni 70%, Mn 30% may be manufactured. A small quantity of catalyst material may be produced from the following starting materials:
1553.8 g 2NiCO3.3Ni(OH)2.4H2O (˜45.05% Ni—Sigma Aldrich Cat No 33,977-6)
648.6 g MnCO3 (˜46.25% Mn—Sigma Aldrich Cat No 37,744-9)
These ingredients are milled with 3.8 kg of alumina milling media in two liters of distilled water for approximately ten hours. The suspension is then dispersed in a further three liters of distilled water and spray dried at ˜250° C. (˜500° F.). The particulate metal oxide mixture is calcined at 300° C./hour to 600° C. and held at 600° C. for four hours in an electric furnace, yielding approximately 1.3 kg of the catalyst material which may then be reduced to an alloy.
(C) An alloy of Ni 40%, Fe 30%, and Mn 30% may be manufactured. A small quantity of catalyst material may be produced from the following starting materials:
887.9 g 2NiCO3.3Ni(OH)2.4H2O (˜45.05% Ni—Sigma Aldrich Cat No 33,977-6)
428.8 g precipitated Fe2O3 (˜69.96% Fe—Fisher Scientific Cat No I/1150/53)
648.6 g MuCO3 (˜46.25% Mn—Sigma Aldrich Cat No 37,744-9)
A carbonate of iron is not commonly available, and thus precipitated iron (III) oxide is used in this example. These ingredients are milled with 3.8 kg of alumina milling media in two liters of distilled water for approximately ten hours. The suspension is then dispersed in a further three liters of distilled water and spray dried at ˜250° C. (˜500° F.). The particulate metal oxide mixture is calcined at 300° C./hour to 600° C. and held at 600° C. for four hours in an electric furnace, yielding approximately 1.25 kg of the catalyst material which may then be reduced to an alloy.
In all of the above examples hydrogen reduction will yield approximately 1 kg of alloy metal. Reduction at a temperature below the alloy melting point, coupled with natural decrepitation of the metal in the hydrogen atmosphere will ensure that the reduced catalyst is finely powdered.
The salt or salts (e.g. carbonates) used in this invention may be produced by a displacement reaction in which soluble salts are used to produced an insoluble product. In certain exemplary embodiments of this invention, a mixture of soluble chloride salts may be precipitated in situ with ammonium carbonate to form the insoluble carbonates.
In an example of this embodiment, a standard catalyst mixture is ball milled as above. The suspension is then dispersed in a further ten liters of distilled water and mixed with approximately 2.5 kg of suitable graphite powder, such as, for example, Morgan-National PCP23, together with a dispersing/wetting agent such as aryl sulphonate. The mixture is spray dried at ˜250° C. (˜500° F.) and then calcined within a sealed saggar at 300° C./hour to 600° C. and held at 600° C. for four hours in an electric furnace. This procedure yields approximately 3.25 kg of intimately mixed graphite and catalyst according to the invention.
In all the above embodiments, yield benefits can be obtained because the catalyst and graphite powders are in intimate contact because of the fineness of the catalyst materials and because of the methods by which catalyst materials are combined with graphite powders. This intimacy is not obtained in current standard manufacturing routes without complex process steps involving blending and/or partial compaction.
The foregoing description of the exemplary embodiments of the invention has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to explain the principles of the invention and their practical application so as to enable others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope.
| Number | Date | Country | Kind |
|---|---|---|---|
| 60375608 | Apr 2002 | US | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB03/01787 | 4/25/2003 | WO | 10/21/2004 |
