His breakthrough was using a "belt" press, which was capable of producing pressures above and temperatures above . The press used a pyrophyllite container in which graphite was dissolved within molten nickel, cobalt or iron. Those metals acted as a "solvent-catalyst", which both dissolved carbon and accelerated its conversion into diamond. The largest diamond he produced was across; it was too small and visually imperfect for jewelry, but usable in industrial abrasives. Hall's co-workers were able to replicate his work, and the discovery was published in the major journal "Nature". He was the first person to grow a synthetic diamond with a reproducible, verifiable and well-documented process.
GE diamond project
Synthetic diamond
Synthetic diamond | GE diamond project
High pressure, high temperature. 1400 °C 1400 °C High pressure and high temperature
when was the first man made diamond made
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1954
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what are the materials required to make this?
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Pure carbon, the belt press, the cubic press and the split-sphere (BARS) press.
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what temperature-pressure conditions are required fopr this?
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In the HPHT method, there are three main press designs used to supply the pressure and temperature necessary to produce synthetic diamond: the belt press, the cubic press and the split-sphere (BARS) press. Diamond seeds are placed at the bottom of the press. The internal part of press is heated above 1400 °C and melts the solvent metal. The molten metal dissolves the high purity carbon source, which is then transported to the small diamond seeds and precipitates, forming a large synthetic diamond. The original GE invention by Tracy Hall uses the belt press wherein the upper and lower anvils supply the pressure load to a cylindrical inner cell.
Synthetic diamond | High pressure, high temperature
He left GE in 1955, and three years later developed a new apparatus for the synthesis of diamond—a tetrahedral press with four anvils—to avoid violating a U.S. Department of Commerce secrecy order on the GE patent applications.
Synthetic diamond | GE diamond project
The cubic press was created shortly thereafter to increase the volume to which pressure could be applied. A cubic press is typically smaller than a belt press and can more rapidly achieve the pressure and temperature necessary to create synthetic diamond. However, cubic presses cannot be easily scaled up to larger volumes: the pressurized volume can be increased by using larger anvils, but this also increases the amount of force needed on the anvils to achieve the same pressure. An alternative is to decrease the surface area to volume ratio of the pressurized volume, by using more anvils to converge upon a higher-order platonic solid, such as a dodecahedron.
Synthetic diamond | High pressure, high temperature
In 1941, an agreement was made between the General Electric (GE), Norton and Carborundum companies to further develop diamond synthesis. They were able to heat carbon to about under a pressure of for a few seconds. Soon thereafter, the Second World War interrupted the project. It was resumed in 1951 at the Schenectady Laboratories of GE, and a high-pressure diamond group was formed with Francis P. Bundy and H. M. Strong. Tracy Hall and others joined the project later. The Schenectady group improved on the anvils designed by Percy Bridgman, who received a Nobel Prize for his work in 1946.
Synthetic diamond | GE diamond project
His breakthrough was using a "belt" press, which was capable of producing pressures above and temperatures above . The press used a pyrophyllite container in which graphite was dissolved within molten nickel, cobalt or iron. Those metals acted as a "solvent-catalyst", which both dissolved carbon and accelerated its conversion into diamond. The largest diamond he produced was across; it was too small and visually imperfect for jewelry, but usable in industrial abrasives. Hall's co-workers were able to replicate his work, and the discovery was published in the major journal "Nature". He was the first person to grow a synthetic diamond with a reproducible, verifiable and well-documented process.
Synthetic diamond | GE diamond project
However, such a press would be complex and difficult to manufacture. The BARS apparatus is claimed to be the most compact, efficient, and economical of all the diamond-producing presses. In the center of a BARS device, there is a ceramic cylindrical "synthesis capsule" of about 2 cm in size. The cell is placed into a cube of pressure-transmitting material, such as pyrophyllite ceramics, which is pressed by inner anvils made from cemented carbide (e.g., tungsten carbide or VK10 hard alloy). The outer octahedral cavity is pressed by 8 steel outer anvils. After mounting, the whole assembly is locked in a disc-type barrel with a diameter about 1 meter.
Synthetic diamond | High pressure, high temperature
There are several methods used to produce synthetic diamonds. The original method uses high pressure and high temperature (HPHT) and is still widely used because of its relatively low cost. The process involves large presses that can weigh hundreds of tons to produce a pressure of 5 GPa at 1500 °C. The second method, using chemical vapor deposition (CVD), creates a carbon plasma over a substrate onto which the carbon atoms deposit to form diamond. Other methods include explosive formation (forming detonation nanodiamonds) and sonication of graphite solutions.
Synthetic diamond | Manufacturing technologies
The barrel is filled with oil, which pressurizes upon heating, and the oil pressure is transferred to the central cell. The synthesis capsule is heated up by a coaxial graphite heater and the temperature is measured with a thermocouple.
Synthetic diamond | High pressure, high temperature
Bundy and Strong made the first improvements, then more were made by Hall. The GE team used tungsten carbide anvils within a hydraulic press to squeeze the carbonaceous sample held in a catlinite container, the finished grit being squeezed out of the container into a gasket. The team recorded diamond synthesis on one occasion, but the experiment could not be reproduced because of uncertain synthesis conditions, and the diamond was later shown to have been a natural diamond used as a seed. Hall achieved the first commercially successful synthesis of diamond on December 16, 1954, and this was announced on February 15, 1955.
Synthetic diamond | GE diamond project
Diamond is an allotrope of carbon where the atoms are arranged in a modified version of face-centered cubic ("fcc") structure known as "diamond cubic". It is known for its hardness (see table above) and incompressibility and is targeted for some potential optical and electrical applications. The properties of individual natural diamonds or carbonado vary too widely for industrial purposes, and therefore synthetic diamond became a major research focus.
Superhard material | Diamond
This internal pressure is confined radially by a belt of pre-stressed steel bands. The anvils also serve as electrodes providing electric current to the compressed cell. A variation of the belt press uses hydraulic pressure, rather than steel belts, to confine the internal pressure. Belt presses are still used today, but they are built on a much larger scale than those of the original design. The second type of press design is the cubic press. A cubic press has six anvils which provide pressure simultaneously onto all faces of a cube-shaped volume. The first multi-anvil press design was a tetrahedral press, using four anvils to converge upon a tetrahedron-shaped volume.
Synthetic diamond | High pressure, high temperature
Above the triple point, the melting point of diamond increases slowly with increasing pressure; but at pressures of hundreds of GPa, it decreases. At high pressures, silicon and germanium have a BC8 body-centered cubic crystal structure, and a similar structure is predicted for carbon at high pressures. At , the transition is predicted to occur at . Research results published in an article in the scientific journal "Nature" in 2010 suggest that at ultrahigh pressures and temperatures (about 10 million atmospheres or 1 TPa and 50,000 °C) diamond behaves as a metallic fluid. The extreme conditions required for this to occur are present in the gas giants of Neptune and Uranus.
Diamond | Thermodynamics
But diamonds (spC) are unstable against high temperature (above about ) under atmospheric pressure. The structure gradually changes into spC above this temperature. Thus, diamonds should be reduced under this temperature.
Diamond | Surface property
The equilibrium pressure and temperature conditions for a transition between graphite and diamond are well established theoretically and experimentally. The pressure changes linearly between at and at (the diamond/graphite/liquid triple point). However, the phases have a wide region about this line where they can coexist. At normal temperature and pressure, and , the stable phase of carbon is graphite, but diamond is metastable and its rate of conversion to graphite is negligible. However, at temperatures above about , diamond rapidly converts to graphite. Rapid conversion of graphite to diamond requires pressures well above the equilibrium line: at , a pressure of is needed.
Diamond | Thermodynamics
Ge-V can be created during the diamond growth, or by ion implantation and subsequent annealing at 800 °C. The former way results in lower lattice strain, as revealed by the spread in the position and width of the Ge-V ZPL.
Germanium-vacancy center in diamond | Formation
Diamane is a 2D form of diamond. It can be made via high pressures, but without that pressure, the material reverts to graphene. Another technique is to add hydrogen atoms but those bonds are weak. Using fluorine (xenon-difluoride) instead brings the layers closer together, strengthening the bonds. This is called f-diamane.
Allotropes of carbon | Diamane
Typically, diamond is formed by heating carbon at very high temperatures (>5,000 K) and pressures (>120,000 atmospheres). However, Narayan and his group used kinetics and time control of pulsed nanosecond laser melting to overcome thermodynamic limitations and create a supercooled state that enables conversion of carbon into Q-carbon and diamond at ambient temperatures and pressures. The process uses a high-powered laser pulse, similar to that used in eye surgery, lasting approximately 200 nanoseconds. This raises the temperature of the carbon to approximately 4,000 K (3,700 °C; 6,700 °F) at atmospheric pressure. The resulting liquid is then quenched (rapidly cooled); it is this stage that is the source of the "Q" in the material's name.
Amorphous carbon | Production
Carbon nitride is only stable at a pressure that is higher than that of the graphite-to-diamond transformation. The synthesis conditions would require extremely high pressures because carbon is four- and sixfold coordinated. In addition, CN would pose problems of carbide formation if they were to be used to machine ferrous metals. Although publications have reported preparation of CN at lower pressures than stated, synthetic CN was not proved superhard.
Superhard material | Carbon nitride
The company developed five generations of plasma reactor designs using software simulations of plasma physics to develop its technology for managing a high-density plasma for diamond growth at extremely high temperatures. As contrasted with diamond simulants (which are non-diamond material that appears similar to diamond) and natural mined diamonds, synthetic diamonds are actual diamonds that are produced by a manufacturing process. The company "grows" diamond using the chemical vapor deposition (CVD) method, by placing a small piece of natural diamond in a plasma reactor for a period of about two weeks. The resulting man-made diamond is essentially identical to natural diamond (atomically, molecularly, chemically, visually, in terms of hardness, optical brilliance, crystalline structure, etc.) but without the resource intensiveness, hazards, and environmental concerns that occur with diamond mining.
Diamond Foundry | Technology
Diamond transistors have been produced (for research purposes). FETs with SiN dielectric layers, and SC-FETs have been made. In April 2004, the journal Nature reported that below the superconducting transition temperature 4 K, boron-doped diamond synthesized at high temperature and high pressure is a bulk superconductor. Superconductivity was later observed in heavily boron-doped films grown by various chemical vapor deposition techniques, and the highest reported transition temperature (by 2009) is 11.4 K. (See also Covalent superconductor#Diamond)
Material properties of diamond | Electrical properties
Diamond nanocrystals (5 nm in diameter) can be formed by detonating certain carbon-containing explosives in a metal chamber. These nanocrystals are called "detonation nanodiamonds". During the explosion, the pressure and temperature in the chamber become high enough to convert the carbon of the explosives into diamond. Being immersed in water, the chamber cools rapidly after the explosion, suppressing conversion of newly produced diamond into more stable graphite. In a variation of this technique, a metal tube filled with graphite powder is placed in the detonation chamber. The explosion heats and compresses the graphite to an extent sufficient for its conversion into diamond.
Synthetic diamond | Detonation of explosives
The hardness of synthetic diamond (70–150 GPa) is very dependent on the relative purity of the crystal itself. The more perfect the crystal structure, the harder the diamond becomes. It has been reported that HPHT single crystals and nanocrystalline diamond aggregates (aggregated diamond nanorods) can be harder than natural diamond.
Superhard material | Synthetic diamond
It is reasonable to envisage the process as a "hail" of projectiles that produce localized, faster, nanoscale versions of the classic combinations of heat and pressure that produce natural and synthetic diamond. Because they occur independently at many places across the surface of a growing film or coating, they tend to produce an analog of a cobblestone street with the cobbles being nodules or clusters of sp bonded carbon. Depending upon the particular "recipe" being used, there are cycles of deposition of carbon and impact or continuous proportions of new carbon arriving and projectiles conveying the impacts needed to force the formation of the sp bonds.
Diamond-like carbon | Production
Synthetic diamonds are produced via high pressure, high temperature (HPHT) or chemical vapor deposition (CVD) technology. These diamonds have numerous industrial and commercial uses including cutting tools, thermal conductors and consumer diamond gemstones.
List of synthetic diamond manufacturers | Introduction
Nitrogen impurities hinder movement of lattice dislocations (defects within the crystal structure) and put the lattice under compressive stress, thereby increasing hardness and toughness.
Synthetic diamond | Impurities and inclusions
CVD can be used to produce a synthetic diamond by creating the circumstances necessary for carbon atoms in a gas to settle on a substrate in crystalline form. CVD of diamonds has received much attention in the materials sciences because it allows many new applications that had previously been considered too expensive. CVD diamond growth typically occurs under low pressure (1–27 kPa; 0.145–3.926 psi; 7.5–203 Torr) and involves feeding varying amounts of gases into a chamber, energizing them and providing conditions for diamond growth on the substrate. The gases always include a carbon source, and typically include hydrogen as well, though the amounts used vary greatly depending on the type of diamond being grown.
Chemical vapor deposition | Diamond
The similar atomic sizes of boron, carbon and nitrogen, as well as the similar structures of carbon and boron nitride polymorphs, suggest that it might be possible to synthesize diamond-like phase containing all three elements. It is also possible to make compounds containing B-C-O, B-O-N, or B-C-O-N under high pressure, but their synthesis would expect to require a complex chemistry and in addition, their elastic properties would be inferior to that of diamond. Beginning in 1990, a great interest has been put in studying the possibility to synthesize dense B-C-N phases. They are expected to be thermally and chemically more stable than diamond, and harder than c-BN, and would therefore be excellent materials for high speed cutting and polishing of ferrous alloys.
Superhard material | Boron carbon nitride
The inventors, respondents, filed a patent application for a "[process] for molding raw, uncured synthetic rubber into cured precision products." The process of curing synthetic rubber depends on a number of factors including time, temperature and thickness of the mold. Using the Arrhenius equation formula_1 which may be restated as "ln"("v") = "CZ" + "x" it is possible to calculate when to open the press and to remove the cured, molded rubber. The problem was that there was, at the time the invention was made, no disclosed way to obtain an accurate measure of the temperature without opening the press.
Diamond v. Diehr | The problem and its solution
There is a growing body of peer-reviewed theoretical work on synthesizing diamond by mechanically removing/adding hydrogen atoms and depositing carbon atoms (a process known as diamond mechanosynthesis or DMS). For example, the 2006 paper in this continuing research effort by Freitas, Merkle and their collaborators reports that the most-studied mechanosynthesis tooltip motif (DCB6Ge) successfully places a C carbon dimer on a C(110) diamond surface at both 300 K (room temperature) and 80 K (liquid nitrogen temperature), and that the silicon variant (DCB6Si) also works at 80 K but not at 300 K. These tooltips are intended to be used only in carefully controlled environments (e.g., vacuum).
Mechanosynthesis | Diamond mechanosynthesis
The equilibrium pressure and temperature conditions for a transition between graphite and diamond is well established theoretically and experimentally. The pressure changes linearly between at and at (the diamond/graphite/liquid triple point). However, the phases have a wide region about this line where they can coexist. At normal temperature and pressure, and , the stable phase of carbon is graphite, but diamond is metastable and its rate of conversion to graphite is negligible. However, at temperatures above about , diamond rapidly converts to graphite. Rapid conversion of graphite to diamond requires pressures well above the equilibrium line: at , a pressure of is needed.
Graphite | Thermodynamics
ADNRs (hyperdiamonds/nanodiamonds) are produced by compressing fullerite powder—a solid form of allotropic carbon fullerene—by either of two somewhat similar methods. One uses a diamond anvil cell and applied pressure ~37 GPa without heating the cell. In another method, fullerite is compressed to lower pressures (2–20 GPa) and then heated to a temperature in the range of . Extreme hardness of what now appears likely to have been nanodiamonds was reported by researchers in the 1990s. The material is a series of interconnected diamond nanorods, with diameters of between 5 and 20 nanometres and lengths of around 1 micrometre each. Nanodiamond aggregates ca.
Aggregated diamond nanorod | Synthesis
The high-pressure synthesis of diamond in 1953 in Sweden and in 1954 in the US, made possible by the development of new apparatus and techniques, became a milestone in synthesis of artificial superhard materials. The synthesis clearly showed the potential of high-pressure applications for industrial purposes and stimulated growing interest in the field. Four years after the first synthesis of artificial diamond, cubic boron nitride c-BN was obtained and found to be the second hardest solid. Synthetic diamond can exist as a single, continuous crystal or as small polycrystals interconnected through the grain boundaries. The inherent spatial separation of these subunits causes the formation of grains, which are visible by the unaided eye due to the light absorption and scattering properties of the material.
Superhard material | Synthetic diamond
Being a form of carbon, diamond oxidizes in air if heated over 700 °C. In absence of oxygen, e.g. in a flow of high-purity argon gas, diamond can be heated up to about 1700 °C. Its surface blackens, but can be recovered by re-polishing. At high pressure (~20 GPa) diamond can be heated up to 2500 °C, and a report published in 2009 suggests that diamond can withstand temperatures of 3000 °C and above. Diamonds are carbon crystals that form deep within the Earth under high temperatures and extreme pressures. At surface air pressure (one atmosphere), diamonds are not as stable as graphite, and so the decay of diamond is thermodynamically favorable (δ"H" = −2 kJ / mol).
Material properties of diamond | Thermal stability
Diamond is not suitable for machining ferrous alloys at high speeds, as carbon is soluble in iron at the high temperatures created by high-speed machining, leading to greatly increased wear on diamond tools compared to alternatives.
Diamond | Industrial-grade diamonds
In the traditional method the temperature of the mold press, which was apparently set at a fixed temperature and was controlled by thermostat, fluctuated due to the opening and closing of the press. The invention solved this problem by using embedded thermocouples to constantly check the temperature, and then feeding the measured values into a computer. The computer then used the Arrhenius equation to calculate when sufficient energy had been absorbed so that the molding machine should open the press.
Diamond v. Diehr | The problem and its solution
Diamond tools are suitable to process the following materials: As diamonds can react with Fe, Co, Ni, Cr, V under the high temperatures generated in the grinding processes, normally diamond tools are not suitable to process steels, including common steels and various tough alloy steels, while the other superhard tool, cubic boron nitride (CBN) tool, is suitable to process steels. The tools made with common abrasives (e.g. corundum and silicon carbide) can also do the task.
Diamond tool | Applicable materials
The majority of commercially available synthetic diamonds are yellow and are produced by so-called "high-pressure high-temperature" (HPHT) processes. The yellow color is caused by nitrogen impurities. Other colors may also be reproduced such as blue, green or pink, which are a result of the addition of boron or from irradiation after synthesis. Another popular method of growing synthetic diamond is chemical vapor deposition (CVD). The growth occurs under low pressure (below atmospheric pressure). It involves feeding a mixture of gases (typically to hydrogen) into a chamber and splitting them to chemically active radicals in a plasma ignited by microwaves, hot filament, arc discharge, welding torch or laser.
Diamond | Synthetics
Iljin Diamond allegedly accomplished diamond synthesis in 1988 by misappropriating trade secrets from GE via a Korean former GE employee. Synthetic gem-quality diamond crystals were first produced in 1970 by GE, then reported in 1971. The first successes used a pyrophyllite tube seeded at each end with thin pieces of diamond. The graphite feed material was placed in the center and the metal solvent (nickel) between the graphite and the seeds. The container was heated and the pressure was raised to about 5.5 GPa. The crystals grow as they flow from the center to the ends of the tube, and extending the length of the process produces larger crystals.
Synthetic diamond | Later developments
So, contrary to De Beers' ad campaign extending from 1948 to at least 2013 under the slogan "A diamond is forever", diamonds are definitely not forever. However, owing to a very large kinetic energy barrier, diamonds are metastable; they will not decay into graphite under normal conditions.
Material properties of diamond | Thermal stability
The patent that issued after the decision was U.S. Patent 4,344,142, "Direct digital control of rubber molding presses." The patent includes 11 method claims, three of which are independent. All method claims relate to molding of physical articles. The only diagrams in the patent are flowcharts. There are no diagrams of machinery. As the dissenting opinion in "Diehr" noted, the patent specification "teaches nothing about the chemistry of the synthetic rubber-curing process, nothing about the raw materials to be used in curing synthetic rubber, nothing about the equipment to be used in the process, and nothing about the significance or effect of any process variable such as temperature, curing time, particular compositions of material, or mold configurations."
Diamond v. Diehr | The patent no 3591.978
Used in so-called diamond anvil experiments to create high-pressure environments, diamonds are able to withstand crushing pressures in excess of 600 gigapascals (6 million atmospheres).
Material properties of diamond | Pressure resistance
However, diamond has several limitations for mass industrial application, including its high cost and oxidation at temperatures above 800 °C. In addition, diamond dissolves in iron and forms iron carbides at high temperatures and therefore is inefficient in cutting ferrous materials including steel. Therefore, recent research of superhard materials has been focusing on compounds which would be thermally and chemically more stable than pure diamond. The search for new superhard materials has generally taken two paths. In the first approach, researchers emulate the short, directional covalent carbon bonds of diamond by combining light elements like boron, carbon, nitrogen, and oxygen.
Superhard material | Introduction
Natural diamond's conductivity is reduced by 1.1% by the naturally present, which acts as an inhomogeneity in the lattice. Diamond's thermal conductivity is made use of by jewelers and gemologists who may employ an electronic thermal probe to separate diamonds from their imitations. These probes consist of a pair of battery-powered thermistors mounted in a fine copper tip. One thermistor functions as a heating device while the other measures the temperature of the copper tip: if the stone being tested is a diamond, it will conduct the tip's thermal energy rapidly enough to produce a measurable temperature drop. This test takes about 2–3 seconds.
Synthetic diamond | Thermal conductivity
Diamond and Related Materials is a peer-reviewed scientific journal in materials science covering research on all forms of diamond and other related materials, including diamond-like carbons, carbon nanotubes, graphene, and boron and carbon nitrides. The journal is published by Elsevier and the editor-in-chief is Ken Haenen (University of Hasselt).
Diamond and Related Materials | Introduction
These characteristic properties are attributed to the diamond-like structure combined with the sp3 σ-bonds among carbon and the heteroatoms. BCN thin films were synthesized by chemical vapor deposition in 1972. However, data on the attempted synthesis of B-C-N dense phases reported by different authors have been contradictory. It is unclear whether the synthesis products are diamond-like solid solutions between carbon and boron nitride or just mechanical mixtures of highly dispersed diamond and c-BN. In 2001, a diamond-like-structured c-BCN was synthesized at pressures >18 GPa and temperatures >2,200 K by a direct solid-state phase transition of graphite-like (BN)C. The reported Vickers and Knoop hardnesses were intermediate between diamond and c-BN, making the new phase the second hardest known material.
Superhard material | Boron carbon nitride
After the 1797 discovery that diamond was pure carbon, many attempts were made to convert various cheap forms of carbon into diamond. The earliest successes were reported by James Ballantyne Hannay in 1879 and by Ferdinand Frédéric Henri Moissan in 1893. Their method involved heating charcoal at up to 3500 °C with iron inside a carbon crucible in a furnace. Whereas Hannay used a flame-heated tube, Moissan applied his newly developed electric arc furnace, in which an electric arc was struck between carbon rods inside blocks of lime. The molten iron was then rapidly cooled by immersion in water. The contraction generated by the cooling supposedly produced the high pressure required to transform graphite into diamond.
Synthetic diamond | History
Due to this, they propose that much of it can be effectively removed from the blocks. This can be done by heating them to the sublimation point of 3915 K (3642 °C, 6588 °F) which will release the carbon in gaseous form. After this blocks will be less radioactive and possibly easier to dispose of with most of the radioactive C having being extracted. Those researchers propose that this C gas could be collected and used to produce man-made diamonds by a process known as chemical vapor deposition using low pressure and elevated temperature, noting that this diamond would be a thin sheet and not of the stereotypical diamond cut.
Diamond battery | Proposed manufacturing
Diamond is hard, chemically inert, and has high thermal conductivity and a low coefficient of thermal expansion. These properties make diamond superior to any other existing window material used for transmitting infrared and microwave radiation. Therefore, synthetic diamond is starting to replace zinc selenide as the output window of high-power CO lasers and gyrotrons. Those synthetic polycrystalline diamond windows are shaped as disks of large diameters (about 10 cm for gyrotrons) and small thicknesses (to reduce absorption) and can only be produced with the CVD technique. Single crystal slabs of dimensions of length up to approximately 10 mm are becoming increasingly important in several areas of optics including heatspreaders inside laser cavities, diffractive optics and as the optical gain medium in Raman lasers.
Synthetic diamond | Optical material
Removing nitrogen also slowed the growth process and reduced the crystalline quality, so the process was normally run with nitrogen present. Although the GE stones and natural diamonds were chemically identical, their physical properties were not the same. The colorless stones produced strong fluorescence and phosphorescence under short-wavelength ultraviolet light, but were inert under long-wave UV. Among natural diamonds, only the rarer blue gems exhibit these properties. Unlike natural diamonds, all the GE stones showed strong yellow fluorescence under X-rays. The De Beers Diamond Research Laboratory has grown stones of up to for research purposes. Stable HPHT conditions were kept for six weeks to grow high-quality diamonds of this size.
Synthetic diamond | Later developments
The final, end use temperature of a coated component should be kept below the temperature at which a PVC DLC coating is applied.
Diamond-like carbon | Tribology
Naturally occurring diamond is almost always found in the crystalline form with a purely cubic orientation of sp bonded carbon atoms. Sometimes there are lattice defects or inclusions of atoms of other elements that give color to the stone, but the lattice arrangement of the carbons remains cubic and bonding is purely sp. The internal energy of the cubic polytype is slightly lower than that of the hexagonal form and growth rates from molten material in both natural and bulk synthetic diamond production methods are slow enough that the lattice structure has time to grow in the lowest energy (cubic) form that is possible for sp bonding of carbon atoms.
Diamond-like carbon | Distinction from natural and synthetic diamond
Diamond trees (tropostats) are a theoretical product of a future technology in molecular manufacturing that have been proposed as a method of long-term sequestration of atmospheric carbon into solid diamond products.
Diamond trees | Introduction
Synthesis of c-BN uses same methods as that of diamond: Cubic boron nitride is produced by treating hexagonal boron nitride at high pressure and temperature, much as synthetic diamond is produced from graphite. Direct conversion of hexagonal boron nitride to the cubic form has been observed at pressures between 5 and 18 GPa and temperatures between 1730 and 3230 °C, that is similar parameters as for direct graphite-diamond conversion. The addition of a small amount of boron oxide can lower the required pressure to 4–7 GPa and temperature to 1500 °C. As in diamond synthesis, to further reduce the conversion pressures and temperatures, a catalyst is added, such as lithium, potassium, or magnesium, their nitrides, their fluoronitrides, water with ammonium compounds, or hydrazine.
Boron nitride | Preparation of cubic BN
This early research of diamond synthesis in the U.S., Sweden and the Soviet Union yielded the discovery of the CVD diamond (chemical vapor deposition) and HPHT diamond (high-pressure high-temperature) processes. These two processes still dominate the production of synthetic diamond, but researchers have since discovered a third and fourth method of diamond synthesis. A third method, known as detonation synthesis, entered the diamond market in the late 1990s. In this process, the detonation of carbon-containing explosives creates nanometer-sized diamond grains. Scientists have also demonstrated a fourth method of diamond synthesis, treating graphite with high-power ultrasound, but this process currently has no commercial application.
Synthetic diamond | Introduction
Independent claim 1 of the allowed patent is representative. It provides: 1. A method of operating a rubber-molding press for precision molded compounds with the aid of a digital computer, comprising:
Diamond v. Diehr | The claims
Recent advances in the HPHT and CVD synthesis techniques have improved the purity and crystallographic structure perfection of single-crystalline diamond enough to replace silicon as a diffraction grating and window material in high-power radiation sources, such as synchrotrons. Both the CVD and HPHT processes are also used to create designer optically transparent diamond anvils as a tool for measuring electric and magnetic properties of materials at ultra high pressures using a diamond anvil cell.
Synthetic diamond | Optical material
In contrast, DLC is typically produced by processes in which high energy precursive carbons (e.g. in plasmas, in filtered cathodic arc deposition, in sputter deposition and in ion beam deposition) are rapidly cooled or quenched on relatively cold surfaces. In those cases cubic and hexagonal lattices can be randomly intermixed, layer by atomic layer, because there is no time available for one of the crystalline geometries to grow at the expense of the other before the atoms are "frozen" in place in the material. Amorphous DLC coatings can result in materials that have no long-range crystalline order. Without long range order there are no brittle fracture planes, so such coatings are flexible and conformal to the underlying shape being coated, while still being as hard as diamond.
Diamond-like carbon | Distinction from natural and synthetic diamond
Synthetic diamonds created by compressing graphite to several gigapascals and heating to temperatures above 1500 °C are usually rich in nitrogen. Nitrogen in those diamonds is dispersed through the lattice as single atoms and induces yellow color. Nickel is often added to graphite to accelerate its conversion into diamond. Incorporation of nickel and nitrogen into diamond induces brown color. Nickel is easily detectable by characteristic, sharp optical absorption and luminescence signals making such diamonds easily identifiable.
Brown diamonds | Brown synthetic diamonds
The product is always rich in graphite and other non-diamond carbon forms and requires prolonged boiling in hot nitric acid (about 1 day at 250 °C) to dissolve them. The recovered nanodiamond powder is used primarily in polishing applications. It is mainly produced in China, Russia and Belarus and started reaching the market in bulk quantities by the early 2000s.
Synthetic diamond | Detonation of explosives
Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. At room temperature and pressure, another solid form of carbon known as graphite is the chemically stable form of carbon, but diamond almost never converts to it. Diamond has the highest hardness and thermal conductivity of any natural material, properties that are utilized in major industrial applications such as cutting and polishing tools. They are also the reason that diamond anvil cells can subject materials to pressures found deep in the Earth. Because the arrangement of atoms in diamond is extremely rigid, few types of impurity can contaminate it (two exceptions being boron and nitrogen).
Diamond | Introduction
Heterodiamond is a superhard material containing boron, carbon, and nitrogen (BCN). It is formed at high temperatures and high pressures, e.g., by application of an explosive shock wave to a mixture of diamond and cubic boron nitride (c-BN). The heterodiamond is a polycrystalline material coagulated with nano-crystallites and the fine powder is tinged with deep bluish black. The heterodiamond has both the high hardness of diamond and the excellent heat resistance of cubic BN. These characteristic properties are due to the diamond structure combined with the sp σ-bonds among carbon and the hetero atoms. Cubic BCN can be synthesized from graphite-like BCN at pressures above 18 GPa and temperatures higher than 2200 K.
Heterodiamond | Introduction
Cubic boron nitride adopts a sphalerite crystal structure, which can be constructed by replacing every two carbon atoms in diamond with one boron atom and one nitrogen atom. The short B-N (1.57 Å) bond is close to the diamond C-C bond length (1.54 Å), that results in strong covalent bonding between atoms in the same fashion as in diamond. The slight decrease in covalency for B-N bonds compared to C-C bonds reduces the hardness from ~100 GPa for diamond down to 48 GPa in c-BN. As diamond is less stable than graphite, c-BN is less stable than h-BN, but the conversion rate between those forms is negligible at room temperature.
Superhard material | Structure and properties
Nanodiamond or hyperdiamond was convincingly demonstrated to be produced by compression of graphite in 2003 and in the same work found to be much harder than bulk diamond. Later it was also produced by compression of fullerene and confirmed to be the hardest and least compressible known material, with an isothermal bulk modulus of 491 gigapascals (GPa), while a conventional diamond has a modulus of 442–446 GPa; these results were inferred from X-ray diffraction data, which also indicated that ADNRs are 0.3% denser than regular diamond. The same group later described ADNRs as "having a hardness and Young's modulus comparable to that of natural diamond, but with 'superior wear resistance'".
Aggregated diamond nanorod | Discovery
Diamond is the allotrope of carbon in which the carbon atoms are arranged in the specific type of cubic lattice called diamond cubic. Diamond is crystal that is transparent to opaque and which is generally isotropic (no or very weak birefringence). Diamond is the hardest naturally occurring material known. Yet, due to important structural weaknesses, diamond's toughness is only fair to good. The precise tensile strength of bulk diamond is unknown;however, compressive strength up to 60 GPa has been observed, and it could be as high as 90–100 GPa in the form of nanometer-sized wires or needles (~100-300 nanometers in diameter),with a corresponding local maximum tensile elastic strain in excess of 9%.
Material properties of diamond | Introduction
The thermal conductivity of CVD diamond ranges from tens of W/m-K to more than 2000 W/m-K, depending on the defects, grain boundary structures. As the growth of diamond in CVD, the grains grow with the film thickness, leading to a gradient thermal conductivity along the film thickness direction. Unlike most electrical insulators, pure diamond is an excellent conductor of heat because of the strong covalent bonding within the crystal. The thermal conductivity of pure diamond is the highest of any known solid. Single crystals of synthetic diamond enriched in (99.9%), isotopically pure diamond, have the highest thermal conductivity of any material, 30 W/cm·K at room temperature, 7.5 times higher than that of copper.
Synthetic diamond | Thermal conductivity
The isotopes of carbon can be separated in the form of carbon dioxide gas by cascaded chemical exchange reactions with amine carbamate. Such CO can be converted to methane and from there to isotopically pure synthetic diamonds. Isotopically enriched diamonds have been synthesized by application of chemical vapor deposition followed by high pressure.
Isotopically pure diamond | Manufacture
Diamond turning is specifically useful when cutting materials that are viable as infrared optical components and certain non-linear optical components such as potassium dihydrogen phosphate (KDP). KDP is a perfect material in application for diamond turning, because the material is very desirable for its optical modulating properties, yet it is impossible to make optics from this material using conventional methods. KDP is water-soluble, so conventional grinding and polishing techniques are not effective in producing optics. Diamond turning works well to produce optics from KDP. Generally, diamond turning is restricted to certain materials. Materials that are readily machinable include: The most often requested materials that are not readily machinable are:
Diamond turning | Materials
An independent diamond synthesis was achieved on February 16, 1953 in Stockholm by ASEA (Allmänna Svenska Elektriska Aktiebolaget), one of Sweden's major electrical manufacturing companies. Starting in 1949, ASEA employed a team of five scientists and engineers as part of a top-secret diamond-making project code-named QUINTUS. The team used a bulky split-sphere apparatus designed by Baltzar von Platen and Anders Kämpe. Pressure was maintained within the device at an estimated 8.4 GPa for an hour. A few small diamonds were produced, but not of gem quality or size. The work was not reported until the 1980s. During the 1980s, a new competitor emerged in Korea, a company named Iljin Diamond; it was followed by hundreds of Chinese enterprises.
Synthetic diamond | Later developments
In fact this property has been exploited to study atom-by-atom wear at the nanoscale in DLC.
Diamond-like carbon | Distinction from natural and synthetic diamond
The CVD growth involves substrate preparation, feeding varying amounts of gases into a chamber and energizing them. The substrate preparation includes choosing an appropriate material and its crystallographic orientation; cleaning it, often with a diamond powder to abrade a non-diamond substrate; and optimizing the substrate temperature (about ) during the growth through a series of test runs. The gases always include a carbon source, typically methane, and hydrogen with a typical ratio of 1:99. Hydrogen is essential because it selectively etches off non-diamond carbon. The gases are ionized into chemically active radicals in the growth chamber using microwave power, a hot filament, an arc discharge, a welding torch, a laser, an electron beam, or other means.
Synthetic diamond | Chemical vapor deposition
Diamond is a solid form of pure carbon with its atoms arranged in a crystal. Solid carbon comes in different forms known as allotropes depending on the type of chemical bond. The two most common allotropes of pure carbon are diamond and graphite. In graphite the bonds are sp orbital hybrids and the atoms form in planes with each bound to three nearest neighbors 120 degrees apart. In diamond they are sp and the atoms form tetrahedra with each bound to four nearest neighbors. Tetrahedra are rigid, the bonds are strong, and of all known substances diamond has the greatest number of atoms per unit volume, which is why it is both the hardest and the least compressible.
Diamond | Material properties
Here, each atom is bonded tetrahedrally to four others, forming a 3-dimensional network of puckered six-membered rings of atoms. Diamond has the same cubic structure as silicon and germanium, and because of the strength of the carbon-carbon bonds, it is the hardest naturally occurring substance measured by resistance to scratching. Contrary to the popular belief that ""diamonds are forever"", they are thermodynamically unstable (Δ"G"°(diamond, 298 K) = 2.9 kJ/mol) under normal conditions (298 K, 10 Pa) and transform into graphite. Due to a high activation energy barrier, the transition into graphite is so slow at normal temperature that it is unnoticeable.
Carbon | Allotropes
In synthetic diamond grown by the high-pressure high-temperature synthesis or chemical vapor deposition, defects with symmetry lower than tetrahedral align to the direction of the growth. Such alignment has also been observed in gallium arsenide and thus is not unique to diamond.
Crystallographic defects in diamond | Defect symmetry
Such nitrogen-vacancy centers are preferentially aligned to the growth direction. Diamond is notorious for having a relatively large lattice strain. Strain splits and shifts optical transitions from individual centers resulting in broad lines in the ensembles of centers. Special care is taken to produce extremely sharp N-V lines (line width ~10 MHz) required for most experiments: high-quality, pure natural or better synthetic diamonds (type IIa) are selected. Many of them already have sufficient concentrations of grown-in N-V centers and are suitable for applications. If not, they are irradiated by high-energy particles and annealed. Selection of a certain irradiation dose allows tuning the concentration of produced N-V centers such that individual N-V centers are separated by micrometre-large distances.
Nitrogen-vacancy center | Production
During the growth, the chamber materials are etched off by the plasma and can incorporate into the growing diamond. In particular, CVD diamond is often contaminated by silicon originating from the silica windows of the growth chamber or from the silicon substrate. Therefore, silica windows are either avoided or moved away from the substrate. Boron-containing species in the chamber, even at very low trace levels, also make it unsuitable for the growth of pure diamond.
Synthetic diamond | Chemical vapor deposition
The sphere is rotated for a short period of time (less than 20 seconds for a 0.1 to 5 micrometre thickness) but due to the abrasive nature of the diamond paste this is sufficient time to wear a crater through thin coatings.
Calo tester | Introduction
As this assembly is compressed, it extrudes out between the cubes, forming a gasket. A cylinder is drilled out between two opposite faces to accommodate the experiment. Experiments that require heating are surrounded by a cylindrical graphite or LaCrO3 cylinder furnace, which can produce considerable heat by electrical resistance. However, the graphite furnace can be troublesome at higher pressures due to its tendency to transform into diamond. The DIA multi-anvil is the main alternative to the Kawai cell: it uses six anvils to compress a cubic sample.
Anvil press | Basic design
As this assembly is compressed, it extrudes out between the cubes, forming a gasket. A cylinder is drilled out between two opposite faces to accommodate the experiment. Experiments that require heating are surrounded by a cylindrical graphite or LaCrO3 cylinder furnace, which can produce considerable heat by electrical resistance (figure 4). However, the graphite furnace can be troublesome at higher pressures due to its tendency to transform into diamond. The DIA multi-anvil is the main alternative to the Kawai cell: it uses six anvils to compress a cubic sample.
Multi-anvil press | Basic design
Diamond nanocrystals can also be synthesized from a suspension of graphite in organic liquid at atmospheric pressure and room temperature using ultrasonic cavitation. The yield is approximately 10%. The cost of nanodiamonds produced by this method are estimated to be competitive with the HPHT process. An alternative synthesis technique is irradiation of graphite by high-energy laser pulses. The structure and particle size of the obtained diamond is rather similar to that obtained in explosion. In particular, many particles exhibit multiple twinning. A research group from Case Western Reserve University produced nanodiamonds 2–5 nm in size at near-ambient conditions by a microplasma process.
Detonation nanodiamond | Alternative synthesis methods
Robert H. Wentorf Jr. (May 28, 1926 in West Bend, Wis. – April 3, 1997 in Easton, N.Y.) was a staff scientist at General Electric Corporate Research and Development Laboratory in Schenectady, N.Y. and a professor of chemical engineering at Rensselaer Polytechnic Institute in Troy, N.Y. Wentorf was a chemical engineer and physical chemist who specialized in the synthesis of diamond and other superhard materials under conditions of high temperature and pressure. He is best known as the inventor of cubic boron nitride (trade name, "Borazon"), the second-hardest material known. Borazon is used industrially as a substitute for diamond where chemical reactivity or high temperature is a problem in grinding or cutting.
Robert H. Wentorf Jr. | Introduction
Well defined equations of state are needed when adjusting temperature and pressure, two parameters that affect the lattice parameters of materials.
Diamond anvil cell | Measuring pressure
Lonsdaleite is a hexagonal allotrope of the carbon allotrope diamond, believed to form from graphite present in meteorites upon their impact to Earth. The great heat and stress of the impact transforms the graphite into diamond, but retains graphite's hexagonal crystal lattice. Hexagonal diamond has also been synthesized in the laboratory, by compressing and heating graphite either in a static press or using explosives. It can also be produced by the thermal decomposition of a polymer, poly(hydridocarbyne), at atmospheric pressure, under inert gas atmosphere (e.g. argon, nitrogen), starting at temperature .
Allotropes of carbon | Lonsdaleite (hexagonal diamond)
It was known since experiments of Antoine Lavoisier that diamond was a form of carbon. Wells's story appeared a few years after the claims of James Ballantyne Hannay in 1879 and Ferdinand Frédéric Henri Moissan in 1893, that they had made artificial diamonds. Moissan heated charcoal (a form of carbon) and iron in a furnace until the iron melted; then rapidly cooled, the iron would generate high pressure and transform the charcoal into diamonds. Others tried to repeat this experiment in later years, and very small diamonds were created; commercially successful production of synthetic diamonds was not achieved until the 1950s.
The Diamond Maker | Historical background
Diamonds are naturally lipophilic and hydrophobic, which means the diamonds' surface cannot be wet by water, but can be easily wet and stuck by oil. This property can be utilized to extract diamonds using oil when making synthetic diamonds. However, when diamond surfaces are chemically modified with certain ions, they are expected to become so hydrophilic that they can stabilize multiple layers of water ice at human body temperature. The surface of diamonds is partially oxidized. The oxidized surface can be reduced by heat treatment under hydrogen flow. That is to say, this heat treatment partially removes oxygen-containing functional groups.
Diamond | Surface property
Synthetic diamond is the hardest known material, where hardness is defined as resistance to indentation. The hardness of synthetic diamond depends on its purity, crystalline perfection and orientation: hardness is higher for flawless, pure crystals oriented to the [111] direction (along the longest diagonal of the cubic diamond lattice). Nanocrystalline diamond produced through CVD diamond growth can have a hardness ranging from 30% to 75% of that of single crystal diamond, and the hardness can be controlled for specific applications. Some synthetic single-crystal diamonds and HPHT nanocrystalline diamonds (see hyperdiamond) are harder than any known natural diamond.
Synthetic diamond | Hardness
It has low adhesion and friction, and its coefficient of thermal expansion is extremely low. Its optical transparency extends from the far infrared to the deep ultraviolet and it has high optical dispersion. It also has high electrical resistance. It is chemically inert, not reacting with most corrosive substances, and has excellent biological compatibility.
Diamond | Material properties
The wide band gap of diamond (5.5 eV) gives it excellent dielectric properties. Combined with the high mechanical stability of diamond, those properties are being used in prototype high-power switches for power stations. Synthetic diamond transistors have been produced in the laboratory. They remain functional at much higher temperatures than silicon devices, and are resistant to chemical and radiation damage. While no diamond transistors have yet been successfully integrated into commercial electronics, they are promising for use in exceptionally high-power situations and hostile non-oxidizing environments. Synthetic diamond is already used as radiation detection device. It is radiation hard and has a wide bandgap of 5.5 eV (at room temperature).
Synthetic diamond | Electronics
Micron-sized diamond crystals can be synthesized from a suspension of graphite in organic liquid at atmospheric pressure and room temperature using ultrasonic cavitation. The diamond yield is about 10% of the initial graphite weight. The estimated cost of diamond produced by this method is comparable to that of the HPHT method; the crystalline perfection of the product is significantly worse for the ultrasonic synthesis. This technique requires relatively simple equipment and procedures, but it has only been reported by two research groups, and has no industrial use. Numerous process parameters, such as preparation of the initial graphite powder, the choice of ultrasonic power, synthesis time and the solvent, are not yet optimized, leaving a window for potential improvement of the efficiency and reduction of the cost of the ultrasonic synthesis.
Synthetic diamond | Ultrasound cavitation
The rapid cooling of the system increases nanodiamond yields as diamond remains the most stable phase under such conditions. Detonation synthesis utilizes gas-based and liquid-based coolants such as argon and water, water-based foams, and ice. Because detonation synthesis results in a mix of nanodiamond particles and other graphitic carbon forms, extensive cleaning methods must be employed to rid the mixture of impurities. In general, gaseous ozone treatment or solution-phase nitric acid oxidation is utilized to remove sp2 carbons and metal impurities.
Nanodiamond | Production methods
At 15 GPa graphite changes to a hard transparent form, that is not diamond. Diamond is very resistant to pressure, but at about 1 TPa (1000 GPa) transforms to a BC-8 form.
Geochemistry of carbon | Carbon
The C center corresponds to electrically neutral single substitutional nitrogen atoms in the diamond lattice. These are easily seen in electron paramagnetic resonance spectra (in which they are confusingly called P1 centers). C centers impart a deep yellow to brown color; these diamonds are classed as "type Ib" and are commonly known as "canary diamonds", which are rare in gem form. Most synthetic diamonds produced by high-pressure high-temperature (HPHT) technique contain a high level of nitrogen in the C form; nitrogen impurity originates from the atmosphere or from the graphite source. One nitrogen atom per 100,000 carbon atoms will produce yellow color.
Crystallographic defects in diamond | C-nitrogen center
Most materials with high thermal conductivity are also electrically conductive, such as metals. In contrast, pure synthetic diamond has high thermal conductivity, but negligible electrical conductivity. This combination is invaluable for electronics where diamond is used as a heat sink for high-power laser diodes, laser arrays and high-power transistors. Efficient heat dissipation prolongs the lifetime of those electronic devices, and the devices' high replacement costs justify the use of efficient, though relatively expensive, diamond heat sinks. In semiconductor technology, synthetic diamond heat spreaders prevent silicon and other semiconducting devices from overheating.
Synthetic diamond | Thermal conductor
For economic reasons, the growth of most synthetic diamonds is terminated when they reach a mass of to .
Synthetic diamond | Later developments
The concept that brown color might be related to lattice imperfections has led to a technique to convert brown diamonds into more valued light-yellow or even colorless ones: the diamond is subjected to high pressures of 6–10 GPa and temperatures above 1600 °C that heals (anneals) those defects. The technique has been demonstrated in several research laboratories in Russia and the United States. In March 1999, Pegasus Overseas Ltd (POL) from Antwerp, Belgium, a subsidiary of Lazare Kaplan International, started marketing such diamonds that were processed by General Electric (GE). Those diamonds therefore received the name GE POL (or GEPOL) and were marketed in the US as "Bellataire" diamonds.
Brown diamonds | Heat-treated brown diamonds
The diamond yield after detonation crucially depends on the synthesis condition and especially on the heat capacity of the cooling medium in the detonation chamber (water, air, CO, etc.). The higher the cooling capacity, the larger the diamond yield, which can reach 90%. After the synthesis, diamond is extracted from the soot using high-temperature high-pressure (autoclave) boiling in acid for a long period (ca. 1–2 days). The boiling removes most of the metal contamination, originating from the chamber materials, and non-diamond carbon. Various measurements, including X-ray diffraction and high-resolution transmission electron microscopy revealed that the size of the diamond grains in the soot is distributed around 5 nm.
Detonation nanodiamond | Properties
Chemical vapor deposition is a method by which diamond can be grown from a hydrocarbon gas mixture. Since the early 1980s, this method has been the subject of intensive worldwide research. Whereas the mass-production of high-quality diamond crystals make the HPHT process the more suitable choice for industrial applications, the flexibility and simplicity of CVD setups explain the popularity of CVD growth in laboratory research. The advantages of CVD diamond growth include the ability to grow diamond over large areas and on various substrates, and the fine control over the chemical impurities and thus properties of the diamond produced. Unlike HPHT, CVD process does not require high pressures, as the growth typically occurs at pressures under 27 kPa.
Synthetic diamond | Chemical vapor deposition
Detonation——Purification——Shaping——Grading——Finished Product
Poly diamond powder | Production method
As De Beers Industrial Diamond, the company was set up initially to concentrate on the industrial applications of natural diamond. Following the development of diamond synthesis in the early 1950s, the company acquired the technology and by 1958 was able to manufacture material based on a high pressure, high temperature process. By the 1960s, the company was offering a range of diamond grit products that was followed by nickel and coated diamond materials plus grinding products based on cubic boron nitride. In 1992, breakthroughs in chemical vapour deposition technology opened the opportunity to synthesize diamond films and a new raft of application areas became possible.
Element Six | History
They only show that the hard parts of an optimal "ta-C" material will break natural diamond rather than the inverse. Nevertheless, from a practical viewpoint it does not matter how the resistance of a DLC material is developed, it can be harder than natural diamond in usage. One method of testing the coating hardness is by means of the Persoz pendulum.
Diamond-like carbon | Hardness
These new materials would have structures based on carbon tetrahedra, and represent the densest of such structures. On the opposite end of the density spectrum is a recently theorized tetrahedral structure called T-carbon. This is obtained by replacing carbon atoms in diamond with carbon tetrahedra. In contrast to superdense allotropes, T-carbon would have very low density and hardness.
Superdense carbon allotropes | Carbon tetrahedra