Classifications

• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B31/00—Diffusion or doping processes for single crystals or homogeneous polycrystalline material with defined structure; Apparatus therefor
  • C30B31/02—Diffusion or doping processes for single crystals or homogeneous polycrystalline material with defined structure; Apparatus therefor by contacting with diffusion materials in the solid state
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
  • C30B29/02—Elements
  • C30B29/04—Diamond
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B31/00—Diffusion or doping processes for single crystals or homogeneous polycrystalline material with defined structure; Apparatus therefor

Definitions

• This invention relates generally to impurity addition to crystalline structures and elements, and
• diamond is subject to the stress of grinding and potentially high temperatures. At high temperatures, diamond is subject to graphitization and/or chemical attack from oxygen. Impurities such as silicon and boron in a diamond crystal help the crystal to resist both the graphitization process and chemical attack from oxygen .
• Synthetic diamond which represents a large portion of the industrial diamond market, has inherent defects in the crystal structure due to the growth process. These defects have an adverse effect on the mechanical properties of the material. It has been shown that the mechanical properties of synthetic diamond can be improved by the addition of impurities into the crystal.
• Diamond and beryl are examples of crystalline elements wherein the optical properties thereof are important when they are used as gemstones .
• the optical properties of these crystalline elements can also be improved by the addition of impurities.
• the present invention is directed to overcoming one or more of the problems as set forth above .
• a low free energy method for more rapidly diffusing an impurity into a diamond or other crystalline element in powdered or granular form, without degradation of the crystalline structure includes the steps of providing a mixture of the diamond or other crystalline element and the impurity in a solid phase; treating the mixture to bring the impurity into substantially conforming contact with substantially all of the outer surface of the crystalline element; and heating the mixture to a temperature between about 200° C and about 2000° C.
• a feature of the present invention is the capability of diffusing the impurity into a crystalline element such as natural or synthetic diamond, beryl or goshanite in an individual crystal or powdered form having a grain size ranging from as small as a very small fraction of a micrometer to greater than a millimeter .
• the impurity can consist of a wide variety of substances, including, but not limited to, boron, lithium, nitrogen, oxygen, fluorine, sodium, aluminum, sulfur, chlorine and compatible mixtures thereof.
• the impurity can be diffused into the crystalline element in an amount ranging from as little as a fraction of one part of the impurity per 1 million parts of the crystalline element to as much as several thousand parts of the impurity per 1 million parts of the crystalline element or more .
• the heating of the mixture to diffuse the impurity into the crystalline element can be for a time period of as little as a fraction of a minute to several hundred hours .
• a diamond having an impurity diffused into the crystalline structure thereof at a ratio of from about 0.1 part of the impurity per 1 million parts of the diamond to about 600 parts of the impurity per 1 million parts of the diamond, is disclosed.
• Another feature of the invention is that the fundamental crystalline structure is virtually unchanged by the diffusion of the impurity therein, such that mechanical, chemical, optical and electrical properties of the diamond crystalline are unchanged and in some instances, are enhanced.
• the diamond becomes an N-type semi-conductor.
• Fig. la is a schematic representation showing mixing an impurity with crystalline element
• Fig. lb is a schematic representation showing the mixture of Fig. la being poured into a pressing fixture
• Fig. lc is a schematic representation of the mixture of Fig. la being compacted in the fixture of
• Fig. Id is a sectional representation showing conforming contact between the impurity and the outer surface of a crystalline element resulting from compaction;
• Fig. le is a schematic representation showing the compacted mixture of Figs, la-lc being heated in an oven;
• Fig. If is a schematic representation of the mixture of Fig. la being compacted in the fixture of lb by vibration;
• Fig. 2 is a graphical representation of weight change verses temperature for oxidation in air of diamonds having boron diffused therein according to the present invention and diamonds of a control sample without an impurity diffused therein;
• Fig. 3a is a scanning electron micrograph of diamonds from the control sample before oxidation thereof ;
• Fig. 3b is another scanning electron micrograph showing a diamond from the control sample before oxidation
• Fig. 3c is a scanning electron micrograph of diamonds from the control sample after oxidation
• Fig. 3d is another scanning electron micrograph of a diamond from the control sample after oxidation
• Fig. 3e is a scanning electron micrograph of diamonds having boron diffused therein according to the method of the present invention before oxidation thereof ;
• Fig. 3f is a scanning electron micrograph of a diamond having boron diffused therein according to the present invention before oxidation thereof;
• Fig. 3g is a scanning electron micrograph of diamonds having boron diffused therein according to the invention after oxidation thereof;
• Fig. 3h is a scanning electron micrograph of a diamond having boron diffused therein according to the present invention after oxidation thereof;
• Fig. 3i is a scanning electron micrograph of diamonds without boron diffused therein after annealing
• Fig. 3j is a scanning electron micrograph of a diamond without boron diffused therein after annealing
• Fig. 3k is a scanning electron micrograph of diamonds after annealing and oxidation thereof;
• Fig. 31 is a scanning electron micrograph of a diamond after annealing and oxidation; and Fig. 4 is a graphical representation of concentration of the boron in the diamond structure after diffusion according to the present invention.
• the method according to the present invention can be utilized for impurity addition to a wide variety of crystalline elements and structures, including, but not limited to natural or mined diamond, high-pressure high temperature synthetic diamond crystals, diamond films, and goshanite .
• Impurities that have been diffused into the crystalline elements include lithium, boron, nitrogen, oxygen, fluorine, sodium, aluminum, sulfur, and chlorine. It is contemplated that compatible mixtures of the above impurities, as well as other impurities, can be successfully diffused into a crystalline element using the present method.
• the steps for diffusion of boron in a solid phase in powered form into diamond, also in powdered form is disclosed in reference to Figs, la-le.
• boron powder 1 is placed with diamond powder 2 in a mixing vessel 4 and the powders are mixed to generally uniformly disperse grains or particles of the diamond powder among the grains or particles of the boron powder, such as by hand mixing or shaking, to form a mixture 3 of the boron powder and diamond powder.
• mixture 3 is poured from mixing vessel 4 into a pressing fixture 5.
• the pressing fixture 5 is shown assembled by placing a plunger 8 in an upper opening thereof in communication with mixture 3.
• the pressing fixture 5 and plunger 8 are then placed on a lower pressure plate 9 of a conventional hydraulic press.
• An upper pressure plate 7 of the hydraulic press is brought into contact with the top of plunger 8.
• the hydraulic press is then operated to exert a compressive force on plunger 8 and pressing fixture 5 as denoted by arrows 6 and 10 to compact mixture 3.
• crystalline elements such as the individual grains or crystals of diamond powder 2 have multiple facetted outer surfaces.
• Suitable compaction of mixture 3 is achieved when the boron powder 1 is brought into substantially conforming contact with the outer surface of the grains or crystals of the diamond powder 2, as illustrated in Fig. Id. Compaction also serves to substantially reduce the number and size of interstices or spaces between the grains of the powders.
• the boron powder 1 has a grain or mesh size of from about 0.1 micrometer to about 10 micrometers diameter and the diamond powder 2 has a grain or mesh size of from about 50 micrometers to about 500 micrometers diameter, such that the diamond powder is the larger grain of the two.
• the boron powder 1 can be selected so as to have a grain size of from about 50 to about 500 micrometers and the diamond powder 2 can be selected so as to have a grain size of from about 0.004 micrometer to about 10 micrometers diameter.
• Mixture 3 can include a ratio of the boron powder to the diamond powder of from about 0.1:1 to about 50:1 by either weight or volume. A ratio of the boron powder 1 to the diamond powder 2 of about 5 : 1 by weight or volume is preferred.
• the compacted mixture 3 is then removed from pressing fixture 5 and placed on a screen 15 of stainless steel, tungsten, or other suitable material and a second screen 14 of the same material is placed on top of mixture 3.
• Mixture 3 with screens 14 and 15 thereover and thereunder are then placed as an assembly in a heating chamber 12 of a suitable oven, such as a conventional ceramic tube oven.
• An inlet gas line 11 and an outlet gas line 16 are attached in fluid communication to the heating chamber 12.
• a flow of gas is then introduced through inlet line 11 into heating chamber 12 wherein the gas flows through screen 14, around and or through mixture 3 so as to envelope mixture 3, and through screen 15 to outlet gas line 16, while mixture 3 is heated with heat as denoted by arrow 13 in a hot zone of the oven in the conventional manner.
• the gas flow through heating chamber 12 can include hydrogen gas mixed with an inert component, for instance, a rare gas such as helium, neon, zeon, krypton, argon, and mixtures thereof, for safety.
• the gas flow can be provided with a flow rate from about 0.1 cc per minute to about 100 liters per minute, with a ratio of from about 100 parts to about 0.01 part rare gas or inert component to 1 part hydrogen component by weight.
• the hydrogen component of the gas flow functions to combine with oxygen atoms in and around mixture 3 to reduce or inhibit oxidation of the diamond.
• the gas flow can include inert gases alone.
• mixture 3 can be heated in a partial or full vacuum environment .
• Mixture 3 can be heated for different time periods and at different temperatures to achieve a desired diffusion of the boron into the diamond. Time periods of from about 1 minute to about 500 hours have been found to be satisfactory. Suitable temperatures within the heating chamber 12 are between about 200° C and about 2000° C. Temperatures closer to 200° C will generally require a longer heating time, and will achieve a lower degree of diffusion, whereas heating at a higher temperature will achieve a greater degree of diffusion. However, it should be noted that detectable graphitization of the diamond begins to occur at about 1400° C, such that exposure of the diamond to temperatures above that temperature should be limited.
• different temperatures and heating times will be required. For instance, goshanite has been found to develop heat caused surface fractures when heated to about 400° C or above. Therefore, when diffusion an impurity into goshanite, a lower temperature should be selected.
• the boron powder 1 can alternatively be brought into conforming contact with the outer surfaces of the individual grains or crystalline elements of diamond powder 2 by application of vibration.
• mixture 3 is shown in pressing fixture 5 being vibrated so as to be compacted to achieve the desired contact between the boron and surfaces of the diamond elements.
• a quantity of diamond powder having a maximum grain size of about 1 millimeter diameter was proportioned into about five cubic centimeter samples, including a control sample to receive no boron diffusion, samples 1, 2 and 3 to be subject to the above described method according to the present invention, and a sample 4 which was also not subjected to the present method, but which was annealed.
• the diamond powder was a conventionally commercially available diamond powder obtained from General Electric Company.
• Each of samples 1, 2, and 3 was placed in a mixing vessel with boron in a solid phase powder having a maximum grain size of about 10 micrometers in a ratio of about 1 part by volume of the diamond powder to about 5 parts by volume of the boron powder.
• the boron powder used is conventional laboratory grade boron available from a wide variety of commercial chemical suppliers. The samples were mixed in the mixing vessels in the above described manner to achieve a uniform dispersion of the diamond powder and the boron powder.
• Each sample 1, 2 and 3 was then compacted by pressing in a conventional hydraulic press sufficiently such that the individual grains of the powders were observed to stick together such that the samples were capable of being removed from the fixture and handled as solid or unitary plugs.
• sample 3 was placed in the heat chamber of a conventional ceramic tube oven heated to 1453 K and left there for 8 hours. During that time, a hydrogen gas flow was maintained through the oven sufficient to provide a pressure condition in the heating chamber slightly greater than atmospheric pressure so as to exclude oxygen from the heating chamber.
• Sample 2 was placed in the oven heated to 1273 K for 8 hours under the same gas flow.
• Sample 1 was placed in the oven at 1173 K for 1 hour under the same gas flow condition.
• Sample 4 consisting of 5 cc of the diamond powder was placed between two fine mesh stainless steel screens in a ceramic tube and positioned in the tube furnace and was heated at 1453 K for 8 hours under the same gas flow as samples 1, 2 and 3.
• Prompt gamma neutron activation analysis is a standard procedure in nuclear science for measuring levels of impurities in samples. It is achieved by irradiating the sample in the high neutron flux region of a nuclear reactor core. The sample is sent into the core by a pneumatic tube, irradiated for a specific period and then is pneumatically transported to a gamma detector. The detector measures the gamma energy and intensity as a function of time. The energy, intensity and time dependence of the gamma spectrum provides data about the impurity content of the sample.
• the TGA was programmed for a heating rate of 20° C per minute to a final temperature of 1370 K. Air with a flow rate of 9.0 cc per minute at atmospheric pressure was used as a carrier gas.
• Fig. 2 shows results for the oxidation rates of the diamond with 600 parts per million of boron from sample 3 as curve 17, the oxidation rates of the diamond with 100 parts per million of boron from sample 2 as curve 18, the oxidation rates of the diamond with 10 parts per million of boron from sample 1 as curve 19, and the oxidation rate for the diamond of the control sample without boron, as curve 20.
• the normalized remaining weight values shown can be multiplied by 100 to obtain a percent remaining weight.
• FIGs. 3a-31 scanning electron micrographs of diamonds from the samples are shown.
• Fig. 3a is a scanning electron micrograph of diamonds from the control sample before oxidation thereof;
• Fig. 3b is another scanning electron micrograph showing a diamond from the control sample before oxidation;
• Fig. 3c is a scanning electron micrograph of diamonds from the control sample after oxidation;
• Fig. 3d is another scanning electron micrograph of a diamond from the control sample after oxidation. Comparing Figs. 3c and Figs. 3d to Figs. 3a and 3b, break down of the corners and edges between the facets of the individual diamonds due to the oxidation is evident.
• Fig. 3e is a scanning electron micrograph of diamonds having boron diffused therein according to the method of the present invention before oxidation thereof;
• Fig. 3f is a scanning electron micrograph of a diamond having boron diffused therein according to the present invention before oxidation thereof;
• Fig. 3g is a scanning electron micrograph of diamonds having boron diffused therein according to the invention after oxidation thereof;
• Fig. 3h is a scanning electron micrograph of a diamond having boron diffused therein according to the present invention after oxidation thereof.
• the diamonds of Fig. 3e through 3h were taken from sample 3 and have a boron concentration of about 600 parts per million. Comparing the diamond crystals shown in Fig. 3g and 3h to those of Fig. 3e and 3f, little degradation of the crystals after oxidation is present, particularly with regard to the edges and corners .
• Fig. 3i is a scanning electron micrograph of diamonds without boron diffused therein after annealing
• Fig. 3j is a scanning electron micrograph of a diamond without boron diffused therein after annealing
• Fig. 3k is a scanning electron micrograph of diamonds after annealing and oxidation thereof
• Fig. 31 is a scanning electron micrograph of a diamond after annealing and oxidation.
• the diamonds of Figs. 3i through 31 were taken from sample 4. Contrasting the diamonds before and after oxidation, it can been seen that oxidation of annealed diamond results in substantial degradation of crystalline structure.
• Figs. 3e through 3h having boron diffused therein, with both non-annealed diamonds as shown in Figs. 3a through 3d, and annealed diamonds as shown in Figs. 3i through 31, it can been seen that diffusion of boron into the diamond crystals provides substantial resistance to oxidation resultant degradation.
• Fig. 4 boron concentration into the surface of a specimen diamond from sample 3 is illustrated, showing substantial boron concentration in the diamond lattice structure to a depth of at least 0.8 micrometer into the surface of the diamond. This concentration is consistent throughout the entire surface area of the diamond crystal .
• the boron depth profile was performed using boron-neutron depth profiling. This is a technique used in nuclear science which measures the energy of alpha particles given of in a boron- neutron capture reaction. From the alpha particle energy spectra, the depth of the boron diffusion is determined and expressed as the concentration of born atoms per cubic centimeter of the diamond.
• the present method for contact diffusion of impurities into diamond and other crystalline structures has utility for a wide variety of different applications, including for providing diamonds and other crystalline elements with enhanced mechanical, chemical and electrical properties.
• the diamonds having boron diffused therein according to the above described method are anticipated to have utility for use in abrasive applications in a wide variety of constructions, including in slurries and in composites.
• the diamonds having boron diffused therein according to the invention are anticipated to have wide utility for abrading ferrous materials which currently cause serious oxidation of diamond.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Crystallography & Structural Chemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)
• Carbon And Carbon Compounds (AREA)

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• 1999
  • 1999-06-16 AU AU46871/99A patent/AU4687199A/en not_active Abandoned
  • 1999-06-16 EP EP99930308A patent/EP1102876A4/de not_active Withdrawn
  • 1999-06-16 WO PCT/US1999/013566 patent/WO1999066109A1/en not_active Ceased

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