US 3031269 A
Description (OCR text may contain errors)
April 24, 1962 H. P. BOVENKERK 3,031,269
METHOD OF DIAMOND GROWTH AND APPARATUS THEREFOR Filed Nov. 27, 1959 2 Sheets-Sheet l 1 IIIIIII IIIIIIIIIIIIIII 399 x In venfor y Hora/0 P. fiovenlrer/r His A flame y 2 Sheets-Sheet 2 H. P. BOVENKERK METHOD OF DIAMOND GROWTH AND APPARATUS THEREFOR Filed Nov. 2'7, 1959 April 24, 1962 United States Patent 3,tl31,269 METHGD 0F DIAMOND GRGWTH AND APPARATUS TEIEREFQR Harold P. Bovenkerk, Royal Gait, Mich, assignor to General Electric Company, a corporation of New York Filed Nov. 27, 1959, Ser. No. 855,787 15 Claims. Cl. 23-2091) This invention relates to an improved method and apparatus for growing good quality and larger diamond crystals, and more particularly to the feature of temperature control and its effect on diamond growth.
While'it has been stated that this invention relates to the growth of diamond crystals, the word growth is employed in its broader sense to include or to represent the transformation or change of a carbonaceous material, which is a non-diamond form of carbon, to diamond. One apparatus capable of obtaining and sustaining the high pressures and high temperatures necessary for diamond growth has been adequately disclosed and claimed in a copending application S.N. 707,432, H. Tracy Hall, filed January 6, 1958, now US. Patent 2,941,248, and assigned to the same assignee as the present invention, and a method of converting a non-diamond form of carbon to diamond has also been adequately described and claimed in copending application S.N. 707, 435, H. Tracy Hall et al., filed January 6, 1958, now U. S. Patent 2,947,610, and assigned to the same assignee as the pres ent invention. By reference, the disclosures of the aforementioned applications are incorporated herewith. In the elapsed time since the invention of the subject matter of the above-identified applications, considerable effort has been expended towards improving not only the particular method and apparatus as described in the aforementioned copending applications, but more particularly toward improving the quality of the diamond crystal it self. For example, investigations have been made towards producing a clearer or better quality crystal, a better formed crystal, a greater yield of crystal, and also a larger crystal. In some instances, improvements obtained have been combinations of those features mentioned; however, improvements in crystal size have been limited, and whether larger or smaller crystals are grown has been generally left to the reaction carried on within wide ranges of conditions without any explicit defining parameters for particular crystal growth. It is, of course, highly desirable that larger crystals be obtained for a variety of purposes not only for those industrial applications where single and larger crystals are widely employed as cutting and grinding elements, but also 'for gem use and other well known diamond applications too .numerous to mention at this time.
Accordingly, it is an object of this invention to provide a larger diamond crystal.
It is another object of this invention to provide an improved method for obtaining larger diamond crystals.
it is another object of this invention to define growth parameters for large diamond crystals.
It is yet another object of this invention to provide a temperature control method for growing larger diamond crystals.
It is again another object of this invention to increase reaction volume for good diamond crystal growth.
It is another object of this invention to provide a specific range of pressures and temperatures and a method of reaching these pressures and temperatures where good diamond crystals of large size are grown.
It is yet another object of this invention to provide specific reaction vessel configurations which together with specified heating means provides, when using the methods of this invention, larger diamond crystals.
Briefly described, this invention in one form comprises ice placing reaction material which is a catalyst and a nondiamond form of carbon in a reaction vessel in such a manner that the reaction material is indirectly heated and thereafter raising the pressure and temperature in a specified manner to a predetermined range where large diamond crystals may be grown.
This invention will be better understood when taken in connection with the following description and the drawings in which;
FIG. 1 is an illustration of the high temperature high pressure apparatus described as the belt;
FIG. 2 is an enlargement and assembled view of the center portion of FIG. 1 illustrating a reaction vessel and gasket assembly;
FIG. 3 illustrates a series of curves each defining a.
diamond growing region for a particular catalyst;
FIG. 4 is one form of a reaction vessel employing indirect heating;
ferred diamond growing area within a given region.
Various types of apparatus are available which. will.
maintain required high pressures and high temperatures necessary for diamond growth conditions. FIG. 1 is exemplary of one preferred form of apparatus together with appropriate proportion and scale.
Referring now to FIG. 1, there is illustrated what has been previously referred to as a belt apparatus 10. Apparatus 10 includes a pair of punch assemblies 11 and 11 together with a lateral pressure resisting or belt member assembly 12. Since the punch assemblies 11 and 11 are similar in nature a description of one sufiices for the other. Punch assembly 11 includes a central punch 13 of a hard material, such as tool steel, cemented tungsten. carbide etc. which is surrounded by a plurality of binding rings 14, 15 and 16. Punch 13 has a generally narrowing tapered portion 17, the taper of which is a smooth diametrical increase from the pressure area or surface 13 axially along the length of the punch to a given larger area 19. Tapered portion 17 includes an end portion 20 offrusto-conical configuration with, for example, an-
of punch 13 while subjecting each cross section to thesame total force as is imposed upon area 18.
Another principle employed to enable punch 13 to resist fracture is prestressing. In FIG. 1, punch 13 is prestressed by being mounted concentrically within a plurality of metal annular, backing or binding rings 14, 15 and 16. These binding rings may be assembled by well known methods of press fitting or shrink fitting. For example, punch assembly 11 consists of a punch 13, two hardened alloy steel press fitting backing rings 14 and 15, and an outer soft steel guard ring 16. Interference and proper stressing is supplied in one form by providing a taper and interference on each of the mating surfaces. When the above-mentioned binding rings are employed together with a Carboloy cemented carbide punch 13, fracture is maintained at a minimum. The principal'function of the binding rings is to provide sufiicient radially inward compressive force on punch 13 to oppose the radially outward force developed within the punch and to prevent the punch from fracturing at high pressures.
In considering the role of the binding rings 14, 15 andmaterial and fit of the rings and punch may be variedconsiderably from the dimensions given, due considera- 3 tion always being given to the forces and pressures to be withstood.
Punch assemblies 11 and 11' are employed in conjunction with a lateral pressure resisting or die assembly 12, comprising a die 21 having a central opening or aperture 22 therein which is defined by a tapered or curved wall surface 23. Wall surface 23 generally describes a narrowing tapered or convergent die chamber or opening into which punches 13 and 13' may move or progress to compress a specimen or material, for example, a reaction vessel as illustrated in FIG. 2. This combination of tapered punches and tapered die chamber contributes to the strength of both punches 13 and 13 and die 21.
In order to minimize failures, die 21 is also made of a high strength material, such as Carboloy cemented carbide, for example, grade 44A, similar to that of punch 13. Prestressing of die 21 may be achieved in the same manner as prestressing of punch 13. Tapered wall 23 of chamber 22 is prestressed to its limitative hoop compression. Binding rings 24 and 25 are employed for purposes similar to rings 14 and 15 as described and are preferably of the materials, while ring 26 is preferably of low carbon steel similar to ring 16. Binding rings 24 and 25 and die 21 increase in height to provide approximately a 7 taper with the horizontal, a taper which provides an increase in cross section of material for imposed forces in the same manner as the taper of the frusto-conical portion of punch 13. In the embodiment illustrated in FIG. 1, tapered wall 23 includes a pair of frusto-conical sections 27 and 27 meeting at a horizontal center line of die 21 and having an angle of about 11 to the vertical. In order to provide motion or stroke for punches 13 and 13' to permit these punches or one of them to move into the chamber 22 to compress a reaction vessel or specimen therein, a gasket is employed between the opposed tapered surfaces of the die 23 and punch 13.
A gasket must have the property of gripping the surfaces of the punch and die and be capable of undergoing large plastic shear distortions without losing shear strength. The shear strength of the material should be great enough to prevent gasket blow-out during all parts of the operation cycle, yet not resist movement of the punch excessively. The force imposed upon the gasket structure is not uniform, but varies from a maximum adjacent the innermost edge of the frusto-conical portion'of the punch to a minimum at the outer extremity adjacent the 7 tapered portion 28.
A gasket serves several functions including; first, sealing in the contents of the chamber; second, allowing a rather large movement of the punch relative to the die; and third, providing electrical insulation between the die and the punches when resistance heating is employed.
Among materials having these general properties are certain ceramics or stones, for example, wonderstone (a homogeneous pyrophyllite stone). Minnesota pipestone (catlinite) also has satisfactory physical and chemical properties for this purpose.
There is also provided a metal gasket, for example mild steel, as the center element of a composite gasket sandwich structure to impart cohesiveness, tensile strength and ductility to the gasket structure as a whole. In addition, a metal which has the correct properties of drawing out uniformly without tearing, while work hardening in so doing, adds considerably to the confining strength of the gasket structure.
FIG. 1 provides an exploded view of the sandwich type frusto-conical gasket assembly 30 which surrounds tapered surface 17 of punch 13, and comprises a pair of thermally and electrically insulating, pressure resistant frusto-conical ceramic or stone gaskets 31 and 32 with a metallic frusto-conical gasket 33 between adjacent gaskets 31 and 32. Not only does gasket 31 serve to electrically in- Sulate the punch from the die, but also gaskets 32 on punches 13 and 13 meet in abutting relationship in chamber 22 to provide a liner or insulator therefor. Although specific configurations and compositions of gasket assembly 30 have been described above, it is obvious that any suitable gasket assembly meeting the requirements described may be employed.
One form of reaction vessel 34 is illustrated in FIG. 2. Referring now to FIG. 2, reaction vessel 34 is approximately 0.350 inch in diameter and 0.450 inch in length positioned in chamber 22 between punches 13 and 13 and includes a cylinder 35 of electrically insulating material such as prophyllite or catlinite, talc, etc, positioned between a pair of spaced electrically conductive discs 36 and 36'. A washer assembly 37 is positioned between each punch 13 and 13' and its associated disc 36 and comprises a heat insulating core '38 with a surrounding outer electrical conductive ning 39 in contact with punches 13 and 13, to complete the reaction vessel. Rings 39 and 39 are preferably of a hard steel and together with cores 38 provide a cap assembly for reaction vessel 34 which thermally insulates the centers of the punch faces and provides a current path to the material in reaction vessel 34. The punch and die assembly of FIGS. 1 and 2 is positioned between platens or pistons of any suitable press apparatus to provide motion of one or both punches.
Each punch assembly is provided with an electrical connection (FIG. 1) in the form of an annular conducting ring 40 or 40' with connectors 41 and 41, to supply electric current from a source of electrical power (not shown) through punch assemblies 11 and 11, to a high temperature high pressure reaction vessel 34.- Pressure is applied to the vessel 34 by movement of one or both punches 13 and 13' towards each other in a press apparatus. At the same time, electric current is supplied from one electrical connector, such as upper connector 41 to upper conducting ring 40 to the punch assembly 11. Referring then to FIG. 2, current flows from punch 13 to ring 39 and disc 36. From this point, current either flows through a suitable heater provided in the reaction specimen or through the specimen itself. The current path continues from lower disc 36', ring 39' to punch 13'. Referring again to FIG. 1, the current path continues through punch assembly 11, conductor ring 40' and connector 41' to the electrical source (not shown).
Pressures have been measured in this apparatus by a Well known method of utilizing the fact that certain metals undergo distinct changes in electrical resistance at particular pressures. For example, bismuth undergoes a phase change which results in a change of electrical resistance at 24,800 atmospheres, thallium undergoes such a phase change at 43,500 atmospheres, cesium at 53,500 atmospheres, and barium at 77,400 atmospheres. Thus, by determining the hydraulic press load necessary to cause a phase change in the metals mentioned, individual points on a pressure-press load curves are determined. By inserting germanium in reaction vessel 34, applying various press loads corresponding to those obtained by phase changes and heating the germanium to the temperature at which the germanium melts, as measured by a large decrease in electrical resistivity, a series of points on a pressure-melting point curve for germanium is determined.
Temperature in the reaction vessel is determined by fairly conventional means such as by placing a thermocouple junction in the reaction vessel and measuring the temperature of the junction in the usual manner. Electrical energy at a predetermined rate is then supplied the apparatus and the temperature produced by this power is measured by the thermocouple assembly. This same procedure is repeated a number of times with different power inputs to produce a calibration curve of power.
The following is one specific example of a transformation of carbonaceous material to diamond as carried on in apparatus similar to that of FIG. 1.
Example I The reaction vessel of FIG. 2 was assembled employing alternate small solid cylinders of commercially obtained graphite of spectroscopic purity and nickel, 99.6% nickel. The vessel was subjected to a pressure of about 90,000 atmospheres together with a temperature of about 1600 C. These conditions were maintained for about 3 minutes. After removal from the apparatus the reaction vessel was found to contain diamonds.
Literally, s of thousands of carats of diamonds (incontrolvertibly diamond) have been produced by this apparatus and similar examples. Diamonds so produced are presently commercially available.
The present invention to be applied to the foregoing description of one exemplary method and apparatus, is temperature control. This control should be as precise as possible under existing conditions. Pressure and temperature in the reaction vessel are constantly changing because of changing internal conditions. During and upon reaching the desired temperatures, some parts of the apparatus expand while others melt with a corresponding reduction or increase in volume. For example, stone loses volume due to a phase change and metal increases in volume when it melts, pressure causes contraction of the reaction vessel and contents because of such occurrences as filling of voids and general compressibility of the pants employed. It is, therefore, desirable that the changes relating to increase in Volume and the changes relating to decrease in volume balance each other and it is believed that this is somewhat true as indicated by pressure and temperature measurements over literally hundreds of operations. It has been discovered, however, that reasonably precise temperature and pressure control is necessary for the formation, not only of a better quality diamond but, even more necessary, in order that larger crystals of good quality may be grown. A change of conditions in a reaction vessel, even though small in comparison to a range of pressures and temperatures wherein desirable results are attained, affects the diamond reaction much more vigorously than had been previously realized. Accordingly, it has been discovered that control of temperature is as important as the control of pressure and that the whole reaction may be regulated by temperature control. It must be remembered, however, that the control of temperature does provide in effect, and indirectly, some control over pressure. It also must be understood that there are no means at present for accurately measuring the pressure in the reaction vessel with great precision while being heated in the 50 to 100,000 atmosphere pressure range and above. That there is a need of temperature control and also pressure control is more clearly understood when taken in connection with the following description of diamond growth conditions.
It has been discovered as described in the previously filed applications above-mentioned, that a catalyst should be employed in the reaction for good diamond growth conditions. These catalysts include generally those metals of the group VIII metals of the periodic table of elements and also manganese, tantalum and chromium. Catalysts may be employed in various forms, such as for example, elemental metal form, alloys of such metals, and numerous other arrangements and configurations. Alloys permit lower pressure operation and their description and operating parameters are best described in copending application S.-N. 655,885, H. M. Strong, filed April 29, 1957, now abandoned and continuation-in part thereof of SN. 707,433, now U.S. Patent 2,947,609, and assigned to the same assignee as the present invention. The subject matter of that application is incorporated herewith. However, not all catalysts will provide diamond growth in the same range of pressures and temperatures, since it has been further discovered that there exists a defined range for each catalyst metal and/ or also for each alloy and for each alloy composition.
In FIG. 3, there is illustrated a group of exemplary curves defining individual ranges of pressures and temperatures for diamond growth for given catalyst. In FIG. 3, curves F, N, R, P and T represent iron, nickel, rhodium, palladium and platinum respectively. Other catalysts and combinations provide similar curves. These indicated ranges have not been determined with absolute precision or defined with high exactness, but have been determined by numerous tests and experiments of hundreds of individual runs to define a region where diamonds are either formed or not formed with a particular catalyst. It should be noted that the right-hand portions of the curves generally define a theoretical line of separation of the diamond and non-diamond phases of carbon, or a graphite-to-diamond equilibrium line. Such a line is generally referred to as the diamond-to-graphite equilibrium line on the phase diagram of carbon. The position of this line has been determined by the pressure and temperature measuring methods set forth in this application in conjunction with hundreds of operations determining pressures and temperatures Where diamonds grow or do not grow. Temperature measurements, for example, were obtained with commercially available platinum-platinum rhodium (the rhodium being 10%, by Weight, of the total Weight of the platinum and rhodium), chromel-alumel, rhodium-platinum, etc. thermocouples. The thermocouple junctures were positioned generally centrally within the reaction chamber with lead wires extending laterally opposite through carefully drilled holes in the reaction vessel and then through holes in the gasket assembly to the measuring apparatus. High pressure effects on these and other thermocouples were not found to be seriously affecting the reading obtained.
Insofar as knowledge of diamond growth reaction has progressed, the particular catalyst metal must undergo some degree of melting or solid solution before transformation to diamond takes place. Therefore, the bottom or lowermost portion of the curves are defined generally by the melting temperature of the particular catalyst in the presence of carbon at the given pressure. The lefthand portion of the curves are generally straight and nearly vertical lines since the points therealong are determined by the melting temperature of the catalyst in the presence of carbon at the given pressures, an approximately linear function. In the course of concentrated experimentation not only to ascertain these exemplary curves but also simply to make diamonds, there were indications that the diamonds formed were not always of the same grade, size, quantity or quality for every curve point established, although certain areas within a given curve provided repetitious growths of similar quality. Diamond growth at the points establishing a curve is effected by the heretofore described changing temperature and pressure conditions, so for example, referring to any point within any curve of FIG. 3 generally adjacent the lower end on the curves, it is understood that a slight change in pressure and temperature may cause change of conditions out of the diamond growth region into the graphite region resulting in either no diamonds grown or, depending on the degree of change, graphitization of previously grown diamond. Such change may or may not take place, and the frequency or degree or rapidity there of, or the exact point at the completion of the test where pressure and temperature have remained constant may not be accurately ascertained. Because of these and other reasons and also that it is difficult to determine the precise reaction taking place, variations in diamond samples are found at points Within a given curve close to the line defining the curve. Temperature changes which permit movement in and out of the diamond range are more clearly understood when examined in light of the configuration of one prior reaction vessel, for example, that indicated in FIG. 2.
In FIG. 2, reaction vessel 34- is heated, in one form, by resistance heating. Accordingly, when pressure and temperature are raised to proceed into the diamond growing region defined by a particular catalyst curve, carbon transforms from the non-diamond form to diamond. However, in so doing, the resistivity of the sample changes drastically as more and more carbon transforms from the electrically conducting carbon form to electrically nonconducting diamond. It is, therefore, apparent that the final temperature or resistance heating may depend on such variables as the volume of carbon, the shape, the amount of diamond formed, formation rate, position of the crystals formed in the reaction vessel, changes of resistance with respect to temperature and other variables. In one respect, a further problem is encountered when employing larger reaction vessels. Larger vessels are employed for purposes including, to increase the yield of diamonds per run, and to increase the available volume for larger crystal growth. In the larger vessels, however, the time delay of temperature rise is of such length that it is extremely difficult to control by merely varying the power input, or by attempting to foresee conditions before their actual occurrence. A proposed and generally certain method of growing diamonds therefor has been an attempt to establish some sort of control at about the central portion of a given catalyst curve indicating a diamond growing region of a particular catalyst.
This invention, therefore, in one part, discloses an improved reaction vessel in which temperature can be more precisely controlled. One principle upon which this invention is based is temperature control. Temperature control is achieved, then, in the first instance through choice of materials and/or the arrangement of these materials in a preferred configuration. Although the reaction vessel illustrated in FIG. 2 has been described as being particularly susceptible to wide variations in temperature, proper choice of parts may minimize these variations. For example, the use of thicker or thinner end discs 36 as well as discs of greater or less electrical and thermal conductivity will provide different degrees of heating and will affect changes of the position of the hotter zone in the reaction vessel. The use of copper discs with high electrical and heat conductivity increases the heating at the central portion of the vessel, while lesser conductive metals increase the heating at the end portions of the vessel. Therefore, by choice of proper end discs and catalyst metals, a generally uniform degree of heating in the vessel may be established. Where the reaction vessel is quite small as described for FIG. 2, the time interval from the application of power to the proper temperature rise is quite small, for example, 1 to seconds. Therefore, changes in temperature may be quickly adjusted for in order to maintain constant temperature. The disadvantages of such a reaction vessel in practicing this invention in best form include, first, that with increasing size of vessel the time interval is proportionately longer, and control more difiicult, and larger vessels are physically necessary for larger crystal growth, second, that the vessel configuration under prolonged conditions of high temperature and high pressure develops leaks or the stone materials decompose with the products thereof affecting the reaction. So, for larger crystal formation in larger vessels, at substantially constant temperatures for prolonged periods, it has been discovered that indirect heating in the first instance, coupled with an advantageous vessel configuration provides excellent results and overcomes the prior discussed problems. Indirect heating in one form has been disclosed in copending application S.N. 488,027, Strong, now US. Patent 2,941,241, assigned to the same assignee as the present invention. In the Strong application, indirect heating is illustrated as a platinum wire surrounding a lava tube. While this type of indirect heating provides more of a temperature control than direct heating, it does not rise to the level of control necessary to practice this invention, because, in general, the platinum wire cannot carry the required current necessary to reach the higher temperatures, because the resistance of platinum wire changes greatly at the higher temperatures, because of reaction between the platinum and the stone, and more importantly, because the carbon undergoing transformation is next adjacent stone or pyrophyllite. It has been found, for the benefits to be obtained by this invention, that materials such as wonderstone, pyrophyllite or catlinite not be used adjacent the catalyst, or the carbon which undergoes transformation, simply because that for the longer runs, i.e., for about minutes and longer, and at the higher temperatures, it has been discovered that melting or decomposition of these stones occurs, and the melt or the products of decomposition adversely affects the diamond reaction so that fewer and poorer diamonds are recovered.
In order to grow diamond crystals of relatively large size and good crystal quality in any system, the conditions of the growth must be precisely controlled with respect to temperature and pressure. Also, such a system must permit temperature to be maintained constant with time. A reaction vessel which is particularly adaptable to this control is indicated in FIG. 4.
In FIG. 4, there is illustrated a reaction vessel which comprises in one example a pyrophyllite cylinder 51 of about inch wall thickness and %1 inch outside diameter. Placed concentrically Within the cylinder 51 is heating tube 52 of graphite, for indirect heating, which lies adjacent to and contiguous with cylinder 51. A further cylinder 53 of alumina is placed within the graphite heater tube 52 to the adjacent thereto. Graphite 54 from which diamonds are grown in is then placed in a diamond metal catalyst tube 55 and thereafter positioned centrally within the alumina cylinder 53. For other applications, 54 may be other reactants and tube 55 other catalysts. A plug of alumina 56 and 56 (not shown) fits with the upper and lower portions of graphite heater tube 52 to support and insulate the graphite and catalyst in the same manner as does the sides of vessel 56. Only one plug may be necessary for resistance heating since a single plug will prevent an electric circuit through the graphite. Suitable end discs 57 and 57 are provided to convey current to heater tube 52. Alumina cylinder 53 should be of the pre-fired variety so that it is relatively soft. Pre-firing is a firing temperature of about 1100 to l200 and generally not over this temperature because the alumina then becomes hard fired. Hard fired alumina is a deterrent to substantial hydrostatic pressure transmission at the higher pressures and temperatures. Other ceramic materials, such as zirconia, magnesia and boron nitride for example may also be employed for cylinder 53. Alumina cylinder 53, in one example, was of a commercial grade, 96 to 99+% aluminum oxide, with the remainder materials of a nature not affecting the diamond growing reaction, and about .0l0.050 inch in thickness. A general range of about .030-.100 inch thickness provides good results.
Graphite heater tube 52 is preferably spectroscopically pure, 99+ graphite with no impurities which will decompose or change electrical resistance at high pressures and temperatures.
This type of reaction vessel provides the important features of a vessel in that it will not leak under high pressure and high temperature conditions, maintains a practically constant (temperature over all of the graphite undergoing transformation both in the vertical and horizontal directions, maintains its particular geometry under the high pressures and high temperatures, and provides a heater tube, i.e., graphite, whose resistance does not change appreciably under high pressures and temperatures and, therefore, constant heating is obtained. The desired geometric stability and the prevention of extensive catalyst intermixing are achieved by insulating the reactants from the heater tube with such materials as alumina, zirconia, magnesia, etc'. The molten catalyst wets alumina cylinder 53 and causes it to remain intact, sealed, protected, etc., since the alumina becomes entirely covered with the catalyst. This also permits heating the reactants to any reasonable temperature up to at least the melting point of the insulation with no change in geometry with respect to time. The use of a metal catalyst in tube form permits sbstantial compression of the reaction vessel together with marked decrease in axial dimension without cracking or leaking of either the cylinder 53 or the tube, which would result in the decomposition products or melt of the cylinder 51 affecting the diamond reaction. Tube 55 being also of good thermal conductivity aids in avoiding a large axial temperature gradient. A further advantage of this system is that when diamond starts to grow inwardly from the catalyst tube, the growth is in the direction of extremely low temperature gradient. This also provides better control of the diamond growing conditions and reduces the rate of growth. The result of using these stable growing conditions is the production of a larger diamond crystal. For example, using nickel as a catalyst, it has been possible to grow diamond crystals from 500 microns to over 1 millimeter in length (considerably larger than by any other system) with pressures in the region of 76 to 78 kiloatmospheres, a temperature of 1500 centigrade, and a growth rate period of about 30 minutes.
Together, with larger vessels, at modification of an indirect heating reaction vessel may be employed. In FIG. 5, there is illustrated a multiple concentric cylinder vessel 60. Vessel 60, in one example, includes an outer cylinder 61 similar to cylinder 51 of FIG. 4. A graphite heater tube 62 is positioned concentrically within cylinder 61 to provide resistance heating. Thereafter, a cylinder of alumina 63 is positioned within graphite tube 62 to act as insulation and a catalyst stabilizer. The core of the reaction vessel includes a central rod 64 of alumina about which is a tube of catalyst metal 65. Catalyst metal tube 65 is surrounded by a cylinder of graphite 66 for diamond growth, and another cylinder 67 of catalyst metal. It is thus understood that diamond growth occurs in an annular space represented by graphite cylinder 66. While the space available is limited, barring an increase in size of the vessel, there is provided an increase in stabilized catalyst surface area for better diamond growth in addition to increased temeprature control with diamonds growing in an area of low temperature gradient and removed from the center of the vessel.
Insofar as this description has proceeded, there has been disclosed an operative example of a high pressure high temperature apparatus in which the invention is to be practiced, together with preferred and modified forms of reaction vessels in which the diamonds are to be grown with respect to a temperature control principle. In conjunction with the apparatus and the reaction vessel, there has been described the diamond forming regions of pressure and temperature necessary to grow diamond crystals. The remaining principle to be described in this invention is a method and a preferred range to be employed, utilizing the press apparatus and reaction vessels as heretofore described and disclosed.
Referring now to FIG. 6, there is illustrated, for the purposes of explanation, the diamond forming region as previously determined for an alloy of 80% nickel and 20% chrome (by weight) as a catalyst. It is a relatively simple manipulation to increase the pressure and temperature of the reaction vessel in accordance with this invention to the range enclosed by the curve OA and OB. Now that the reaction vessel is of such a nature that the temperature may be more precisely controlled FIGS. 4 and 5 particularly), the following results have been found. When raising the pressure and temperature to the general area indicated by O, A, C, D, and maintaining that temperature within controlled limits from a few seconds to an hour or longer, it has been found that the diamond crystals grow in the form of cubes, which are generally of a very poor grade, and black in color. For the purposes of description, this region is hereinafter referred to as the cube region. The upper limit of extension of line DEC is unknown as is the upper extension of line OA. When increasing temperature to reside in the further area generally included within curve FEC, as a result of many tests, some ranging from a few seconds to an hour or longer, it has been found that diamond crystals grow extremely fast and in very high yield, but that individual crystals themselves are generally of a poor quality and small. It has been found that when pressures and temperatures are adjusted to lie within curve PEG and in the right-hand portion thereof, diamond crystals grow very quickly and, while generally small, are of a good quality and grade. In the many operations previously referred to, to define curve OB between the diamond forming and graphite regions no large crystals were grown because of many reasons including, the short pe riod of time used for growing diamonds, lack of temperature control for extended periods together with lack of a proper constant temperature reaction vessel and also of knowledge of the effect of temperature control in specific areas. It has been discovered that a range exists along the line DB wherein by precise control of time and temperature extremely large excellent quality crystals may be grown. The total region for the catalysts mentioned may be defined as commencing at about 1200 C. and 60,000 atmospheres ranging upwardly to points unknown and lying just inside the diamond growing region along the line DB as indicated by the shaded area in FIG. 6. It is more desirable to maintain temperature and pressure conditions at the lower extremity of this range just above the cube region and adjacent the line DB or the area within the curve DEF and DE. The width of the shaded area is about 50 C. Therefore, the area being just above the cube region and just inside of the righthand portion of the curve DB is well defined. Here diamend growth rate is considerably slowed. In actual practice, to maintain a temperature within this abovedescribed area is extremely difficult, because in prior ap para-tus, temperature varies as described, and the defined area is so limited that a small temperature change may result in conditions being completely out of the area to the left of the curve DB and out of the area to the right of the curve DB with no absolute certainty where the temperature is. However, the described shaded area is the desired one and the only area thus far found wherein the largest good crystals so far produced have been grown.
No other large reaction vessel has been satisfactory so far in attempting to stay within the described area to grow larger diamonds. Therefore, the method portion of this invention is to raise the temperature and pressure to a particular diamond forming area within a particular region defined by a given catalyst; where the area is closely adjacent a curve of the diamond forming region defined by an equilibrium line between graphite and dia mond, and to maintain the temperature constant with respect to time in that area to provide the desired crystal formaion.
There are several methods generally available for reaching this area. One of these methods is somewhat less than satisfactory with the particular apparatus described. From examination of FIG. 6 and bearing in mind the operation of the press apparatus, it may be seen that at one atmospheric pressure the temperature of the apparatus may be raised to approach the vicinity of the temperature in the shaded area and thereafter the pressure raised so that the combined pressure temperature point lies within the lower portion of the shaded area. This operation is rather unsatisfactory since raising of temperature previous to raising of pressure affects the operation of the apparatus. Pressure rise will not follow along a vertical line but will fluctuate widely. Temperature will also fluctuate. With further improvements and/or other apparatus such a procedure as just described may be employed to reach the area desired or various incremental steps of increasing temperature and/ or pressure may be employed to reach the area. For the pur poses of this invention, with the apparatus as described for FIG. 2, the following procedures are more satisfactory depending on the size of reaction vessel employed, in temperature response time, and total time of operation. For example, when using a small reaction vessel of the size described with relation to the prior art apparatus description of FIG. 2, the time temperature constant of such a reaction vessel is very small, that is, with the application of electrical power the temperature rises extremely rapidly to a high point and tapers off gradually; therefore, with a small reaction vessel, pressure is applied to raise the pressure to, for example, a point P1, FIG. 6. Thereafter, electrical power is applied to raise the temperature to a point T1. Raising of the pressure and temperature in this order results in a temperature rise which does not affect the pressure point P1 to any appreciable degree. However, the temperature should be held at point T1, a threshold temperature, for the following reasons. If an attempt were made to reach temperature T2 immediately even though the temperature time rise is extremely small, chances are excellent for overshooting the mark and ending about T3 which is in the non-diamond or graphite stable region, and variances of temperature back and forth between the diamond growing region and the non-diamond or graphite stable region affects the reaction to a considerable degree. Secondly, since the time temperature rise levels out gradually after a very rapid rise, the period of time necessary to change the temperature from T1 to T2 may be so extensive that diamonds are formed in the reaction vessel in that pediod of time and in that range between temperature T1 and the shaded area so that diamonds start to form in the region of poor growth affecting the quality of the diamond then grown in the shaded area. Therefore, the method of raising the temperature to point T1 permits the reaction vessel temperature and pressure to become stabilized in the non-diamond growing region before diamond growth and thereafter only a small temperature rise is necessary to proceed immediately to T2 in the shaded area. After temperature T1 is reached and stabilized, more power is added to the reaction vessel to raise the temperature in a matter of a few seconds to T2 in the shaded area and because of the rapidity of temperature rise from T1-T2 very few, if any, diamond crystals are grown prior to reaching the shaded area. The temperature may thereafter be controlled in the shaded area for varying periods from a few minutes to several hours to grow larger diamond crystals.
In proceeding to larger size reaction vessels and generally to those vessels presently employed, the time temperature rise is again much slower (up to 15 minutes, for example) because of the larger volume. It is, therefore, difficult to stop at a temperature T1 and then proceed with the foregoing described satisfactory method. The method employed with larger reaction vessels is as follows. Pressure is raised to a point P2 corresponding to T2. Thereafter, electrical power is increased to raise the temperature as rapidly as possible so that the temperature curve proceeds immediately through T1 and also through T2 to stop at a point, for example, T3. It so happens in this method that in proceeding from T1 to T2, diamonds may be grown from graphite, but regardless of the size or quality the increase in temperature to the point T3 results in regraphitization of the diamonds so that conditions exist at point T3 where no diamonds are formed nor are in existence in the reaction vessel. Thereafter, the temperature is descreased, a decrease which is possible by the improvements in the reaction vessel described to the point T2 and thereafter maintained as close to the line DB as possible. Here, only the larger size diamond crystals are formed.
The results of the practice of the teachings of this invention are markedly distinctive. Where prior practices result in a diamond size ranging Well under /2 mm., this invention produces diamond crystals greater by a factor of 4. Specific examples of the teachings of this invention are as follows:
Example I A reaction vessel (34 of FIG. 2 approximately inch diameter and inch in length) was assembled with a substantially pure nickel slug in the hollow core and a spectroscopically pure graphite slug at each end of the nickel slugs to fill the core. Pressure on the reaction vessel was raised to about 78,000 atmospheres. Temperature was stabilized to about 1350" C. and thereafter increased to about 1450 C. in from l-3 seconds. This temperature was maintained for about 10 minutes. Upon removal from the press, the reaction vessel was found to contain several diamond crystals from .2 to .4 mm. in the longer dimension.
Example 2 The procedure of Example 1 was followed but with a nickel chromium catalyst of nickel and 20% chromium (by weight) and the reaction vessel of FIG. 4 (about inch diameter and 1 inch in length). Threshold temperature was 1250 C., maximum pressure was 72,000 atmospheres, maximum temperature was 1320 C. Elapsed time was about 2 hours. Upon removal of the reaction vessel from the press, it was found to contain 3 diamond crystals from /2 to 2 mm. average diameter.
Example 3 The procedure and reaction vessel of Example 2 was again followed but with a nickel iron catalyst, 35% nickel, 65% iron (by weight). Maximum pressure was 66,000 atmospheres, threshold temperature was about 1150 C., maximum temperature about 1250" C., and elapsed time 3 hours. Upon removal of the reaction vessel from the press, it was found to contain several diamond crystals somewhat smaller than 2 mm. average.
Example 4 The procedure, reaction vessel, and catalyst of Example 3 was followed wherein temperature was quickly increased to pass through the diamond growing region to stabilize, out of said region, about 1400 C. The temperature was thereafter reduced to about 1250 C. and maintained for about 1 /2 hours. Upon removal of the reaction vessel, it was found to contain several diamond crystals of about 1.5 mm. in the longer dimension.
Since diamond forming regions of pressures and temperatures have been previously ascertained and diamonds obtained incontrovertibly proven as diamonds, exhaustive tests of the diamond produced by this invention were not necessary. X-ray diffraction patterns were, however, made for other purposes and did show true diamond pattern. These diamonds scratched sapphire, withstood acid cleaning tests, and burned in oxygen leaving inconsequential amounts of residue. It is understood, from this description, that this invention discloses means and methods for the growing of larger diamond crystals of no limitation with respect to method and contemplates a combination of a predetermined area of pressures and temperatures together with constant temperatures and preferred reaction vessel configurations to be employed with constant temperatures. It is understood that the method and apparatus may be employed for any carbonaceous material, the graphite being merely exemplary for this application. Broadly speaking, any carbon-containing material may be employed which when heated will carbonize and form graphite before the diamond reaction takes place. Diamonds have been produced when the initial material has been carbon, wood, pitch, adamantane, etc.
The invention is also applicable to the growth of various crystals where an equilibrium line of pressure and temperature exists, where temperature control is desirable and where it is not desirableto pass current through the reactant material. For example, this invention is applicable to crystal growth of silicon, germanium, etc., as Well as to the cubic form of boron nitride disclosed and claimed in copending application S.N. 707,434, Wentorf, filed January 6, 1958, now US. Patent 2,947,617, and assigned to the same assignee as the present invention.
While other modifications of this invention and variations of apparatus and methods which may be employed within the scope of the invention have not been described, the invention intended to include all such as may be embraced Within the following claims.
What I claim as new and desire to secure by Letters Patent of the United States is:
1. In a method of producing diamond crystals from a combination of a non-diamond carbon together with a catalyst which includes subjecting the said non-diamond form of carbon and the catalyst to high pressures and high temperatures above the graphite-to-diamond equilibrium line on the phase diagram of carbon to provide diamond growth from said non-diamond carbon, the improvement of growing larger diamonds comprising, raising the said pressure and temperature to that range of pressures and temperatures in the diamond growing region for the given catalyst, above the said graphite-todiamond equilibrium line on the phase diagram of carbon, at a point closely adjacent the said graphite to diamond equilibrium line and above the cube region wherein diamonds crystallize predominantly in cube form, maintaining the temperature constant over an extended period of time at said point, reducing the temperature and pressure, and recovering diamond so grown.
2. In a method of producing diamond crystals from the combination of non-diamond carbon together with a catalyst which includes subjecting the said, combination to combined pressures and temperatures above the graph.- ite to diamond equilibrium line on the phase diagram of carbon to provide diamond growth from said non-diamond carbon, the improvement of producing larger crystals comprising, raising the pressure to above the said graphite to diamond equilibrium line and within the diamond forming region of the given catalyst at a temperature less than existing in said region, increasing the temperature to a point corresponding to said pressure and adjacent to but outside of the diamond forming region of the said given catalyst, maintaining this threshold temperature for stabilization purposes, thereafter increasing the temperature on said combination of catalyst and non-diamond carbon to a point closely adjacent and above the graphite to diamond line and above the cube region wherein diamond crystallizes predominantly in cube form, maintaining temperature constant over an extended period of time at said point, reducingsaid temperature and pressure, and recovering diamond so grown.
3. In a method of producing diamond crystals from a combination of a non-diamond. carbon together with a catalyst which includes subjecting said combination to pressures and temperatures above the graphite to diamond equilibrium line on the phase diagram of carbon to provide diamond growth from said non-diamond carbon, the improvement of producing large crystals comprising, raising the pressure to about opposite a point in the diamond forming region of the given catalyst and outside of said diamond forming region, increasing the temperature on said combination for the temperature curve to pass from outside the said diamond forming region through the said diamond forming region for the given catalyst and thereafter into the non-diamond form of graphite region, maintaining the pressure and temperature conditions for stabilization in the non-diamond form of graphite region, thereafter reducingthe temperature until a point is reached in the diamond forming region for the given catalyst at a point closely adjacent and above the graphite to diamond line and slightly above the cube region, maintaining the temperature constant at this point over an extended period of time, reducing said temperature and pressure, and recovering diamond so grown.
4. The invention as claimed in claim 3 wherein said temperature point above and closely adjacent the graphite to diamond line is within about 50 C. thereof.
5. A method of producing large diamond crystals from the combination of a non-diamond carbon together with a catalyst taken from the metals consisting of those metals of group Vill of the periodic table of elements, chromium, manganese and tantalum, and alloys of these metals which comprises subjecting said non-diamond carbon and catalyst to a pressure generally corresponding to a temperature in the diamond forming region of said catalyst, employing an indirectly heated reaction vessel to ,eat said catalyst and non-diamond carbon to a temperature generally corresponding to said pressure and lying within the diamond forming region of the given catalyst above the cube region where diamond crystallizes predominantly in cube form and closely adjacent the graphite to diamond dividing line, maintaining the temperature constant for an extended period of time at said point, reducing said temperature and pressure, and recovering diamond so grown.
6. The invention of claim 5 wherein said indirectly heated reaction vessel comprises in combination, a thermally insulating and electrically nonconductive vessel having an opening therein, a relatively thin electrically conductive heater tube positioned Within said opening and contiguous with said vessel, a hollow electrically conductive and thermally insulating cylinder positioned concentrically within and contiguous with said heater tube, a diamond catalyst metal cylinder whose length is less than that of said tube positioned concentrically within said tube and contiguous therewith, a non-diamond form of carbon within said catalyst cylinder, an electrically nonconductive and thermal insulating stone plug positioned within said heater tube adjacent one end of said heater tube and non-diamond form of carbon to provide a substantially solid reaction vessel, an electrically conductive disc on each end of said heater tube and vessel and in contact therewith, so that an electrical current applied to said end discs flows through said heater tube to indirectly heat the combination of the catalyst and a non-diamond form of carbon.
7. The invention as claimed in claim 5 wherein said indirectly heated reaction vessel comprises in combination, a first hollow stone electrically nonconductive and thermally insulating cylinder, an electrically conductive graphite heater tube positioned concentrically within and contiguous with said hollow cylinder, a hollow electrically nonconducting and thermally insulating second stone cylinder positioned concentrically within said heater tube and contiguous therewith, a catalyst metal tube of less axial dimension than said first cylinder positioned within and concentrically with said second cylinder and contiguous therewith, a non-diamond form of carbon within said catalyst tube, a stone plug positioned Within said reaction vessel on each end thereof to provide a solid cylindrical configuration, an electrically conductive metal disc positioned on each end of said reaction vessel so that current applied to said end discs flows through said graphite heater tube to indirectly heat the combination of carbon and catalyst metal in said reaction vessel.
8. The invention as claimed in claim 5 wherein said indirectly heated reaction vessel comprises in combination, a hollow electrically nonconducting and thermally insulating stone vessel, a thin graphite heater tube positioned within and contiguous with said vessel, a hollow cylindrical electrically nonconductive and thermally insulating stone cylinder positioned with said heater tube and contiguous therewith, a metal catalyst cylinder positioned within said second stone cylinder and contiguous therewith, said catalyst cylinder being axially shorter than the said first cylinder, an annulus of a non-diamond form of carbon positioned Within said catalyst metal tube and contiguous therewith, a second cylinder of catalyst metal positioned within said non-diamond carbon annulus and contiguous therewith, a central core of stone material positioned within said latter catalyst cylinder, a plug of stone material positioned within said heater tube in one end of said reaction vessel to provide a substantially solid vessel, a pair of electrically conductive metal discs positioned on each end of said vessel and in contact with said heater tube so that current applied to said end discs flows through said heater tube to indirectly heat said carbon and catalyst.
9. An indirectly heated reaction vessel comprising in combination, a hollow electrically nonconductive and thermally insulating vessel, a thin electrically conductive heater tube positioned within and contiguous with said vessel, a hollow electrically nonconductive and thermally insulating cylinder positioned concentrically within and contiguous with said heater tube, a metallic cylinder whose length is less than that of said tube positioned concentrically within said tube and contiguous therewith and adapted to contain a reactant material, an electrically nonconductive and thermal insulating plug positioned within one end of said reaction vessel to provide a substantially solid reaction vessel, an electrically conductive disc on each end of said heater tube and in contact therewith so that an electrical current applied to said end discs flows through said heater tube to indirectly heat the combination of the catalyst and reactant.
10. An indirectly heated reaction vessel comprising in combination, a hollow electrically nonconductive and thermally insulating cylinder, a thin electrically conductive heater tube positioned concentrically within and contiguous with said cylinder, a hollow electrically nonconductive and thermally insulating cylinder positioned concentrically within and contiguous with said heater tube, a' diamond catalyst metal cylinder whose length is less than that of said tube positioned concentrically within said tube and contiguous therewith, a non-diamond form of carbon within said catalyst cylinder, an electrically nonconductive and thermal insulating plug positioned within one end of said reaction vessel to provide a substantially solid cylindrical vessel, an electrically conductive disc on each end of said cylinder and in contact therewith so that an electrical current applied to said end discs flows through said heater tube to indirectly heat the combination of the catalyst and a non-diamond form of carbon.
11. An indirectly heated reaction vessel comprising in combination, a first hollow electrically nonconductive and thermally insulating stone cylinder, a graphite heater tube positioned concentrically within and contiguous with said hollow cylinder, a second hollow electrically nonconducting and thermally insulating stone cylinder positioned concentrically within said heater tube and contiguous therewith, a catalyst metal tube of less axial dimension than first cylinder positioned within and concentrically with said second cylinder and contiguous therewith, a non-diamond form of carbon within said catalyst tube, a stone plug positioned within said reaction vessel on one end thereof to provide a solid cylindrical configuration, an electrically conductive metal disc positioned on each end of said reaction vessel such that current applied to said end discs flows through said graphite heater tube to indirectly heat the combination of carbon and catalyst metal in said reaction vessel.
12. An indirectly heated reaction vessel comprising in combination, a first hollow electrically and thermally nonconducting stone cylinder, a thin graphite heater tube positioned concentrically within and contiguous with said cylinder, a second hollow cylindrical electrically nonconductive and thermally insulating stone cylinder positioned within said heater and contiguous therewith, a metal catalyst cylinder positioned within said second stone cylinder and contiguous therewith, said catalyst cylinder being axially shorter than the said first cylinder, an annulus of a non-diamond form of carbon positioned within said catalyst metal tube and contiguous therewith, a second cylinder of catalyst metal positioned within said nondiarnond carbon annulus and contiguous therewith, a central core of stone material positioned within said latter catalyst cylinder, a plug of stone material positioned within said heater tube at one end of said reaction vessel to provide a substantially solid cylinder, a pair of electrically conductive metal discs positioned on each end of said cylinder and in contact with said heater tube so that current applied to said end discs flows through said heater tube to indirectly heat said carbon and catalyst.
13. A method of growing large diamond crystals comprising in combination, subjecting graphite and an alloy metal catalyst taken from the group consisting of those metals of group VIII of the periodic table of elements, manganese, tantalum and chromium, to a temperature and pressure lying above the graphite to diamond dividing line on the phase diagram of carbon in the diamond forming region for the particular catalyst employed and above the cube region where diamond crystallizes predominantly in cube form, and closely adjacent the said dividing line, maintaining the temperature constant and within 50 C. of said line for a period of time in the range of at least about 2 minutes to several hours and thereafter reducing the temperature and pressure and recovering diamond formed.
14. A method of growing large diamond crystals comprising in combination, subjecting graphite and a metal catalyst which includes nickel to a temperature and pressure lying above the graphite-to-diamond dividing line on the phase diagram of carbon and out of the diamond forming region for said catalyst, reducing the temperature to a point lying within the diamond forming region for said catalyst above the graphite to diamond equilibrium line and within about 50 C. of said line, maintaining the temperature constant for a period of time from about 2 minutes to several hours and thereafter reducing the temperature and pressure and recovering diamond grown.
15. In a method of producing diamond crystals from the combination of a non-diamond carbon together with a catalyst which includes subjecting the said combination to combined pressures and temperatures above the graphite to diamond equilibrium line on the phase diagram of carbon to provide diamond growth from said non-diamond carbon, the improvement of producing larger diamond crystals comprising, raising the pressure-temperature conditions to a point where said conditions are outside. of those conditions existing within the diamond forming region of the given catalyst and at a point closely adjacent to and below said graphite to diamond equilibrium line, maintaining the said conditions at said point for stabilization purposes for a period of time, thereafter changing these conditions from said point to a further point closely adjacent to and above the graphite-to-diamond line and above the cube region where diamond crystallizes predominantly in the cube form, maintaining said pressure-temperature conditions at this point constant over an extended period of time, reducing said pressuretemperature conditions, and recovering diamonds so grown.