Material properties of diamond

Diamond is transparent to opaque, optically-isotropic, 3D-graphite has that distinction.

Hardness and crystal structure

See also: Crystallographic defects in diamond

Known to the ancient Greeks as adamas ("tame'sles" or "bridleless") and sometimes called adamant, diamond is the hardest known naturally occurring material, scoring 10 on the old GPa (±6) when scratched with an ultrahard fullerite tip, while a ultrahard fullerite sample has a value of 310 GPa when tested with a fullerite tip. However, the test only works properly with a tip made of harder material than the sample being tested. This means that the true value for ultrahard fullerite is likely somewhat lower than 310 GPa.

Cubic diamonds have a perfect and easy octahedral Cleavage also plays a helpful role, especially in large stones where the cutter wishes to remove flawed material or to produce more than one stone from the same piece of rough.

Diamonds typically crystallize in the Cullinan Diamond, have been shapeless or massive. These diamonds are Type II and therefore contain little if any nitrogen (see Composition and color).

The faces of diamond octahedrons are highly Bort diamonds, found in Brazil, Venezuela, and Guyana, are the most common type of industrial-grade diamond, also cryptocrystalline or otherwise poorly crystallized, but possessing cleavage, translucency, and lighter colors.

Due to its great hardness and strong molecular bonding, a cut diamond's diamond simulant.

Diamond is so strong because of the shape the carbon atoms make. It's a very strong 3D shape, each carbon atom having four joined to it with covalent bonds.

Toughness

Unlike hardness, which only denotes resistance to scratching, diamond's toughness or tenacity is only fair to good. Toughness relates to the ability to resist breakage from falls or impacts: due to diamond's perfect and easy cleavage, it is vulnerable to breakage. A diamond will shatter if hit with an ordinary hammer.

Ballas and carbonado diamond are exceptional, as they are polycrystalline and therefore much tougher than single-crystal diamond; they are used for deep-drilling bits and other demanding industrial applications. Particular cuts of diamonds are more prone to breakage—such as marquis or other cuts featuring tapered points—and thus may be uninsurable by reputable insurance companies. The culet is a facet (parallel to the table) given to the pavilion of cut diamonds designed specifically to reduce the likelihood of breakage or splintering. Extremely thin, or very thin girdles are also prone to much higher breakage.

Solid foreign crystals are commonly present in diamond—these and other inclusions, such as internal fractures or "feathers"—can compromise the structural integrity of a diamond. Cut diamonds that have been ultrasonic cleaning or the rigors of the jeweler's torch. Fracture-filled diamonds may shatter if treated improperly.

Optical properties

The diamond cut and its associated proportions (particularly crown height), although the body color of fancy diamonds may hide their fire to some degree.

Some diamonds exhibit X-rays is generally bluish-white, yellowish or greenish. Some diamonds, particularly Canadian diamonds, show no fluorescence.

Cape series diamonds have a visible spectroscope) consisting of a fine line in the violet at 415.5 nm—however, this line is often invisible until the diamond has been cooled to very low temperatures. Associated with this are weaker lines at 478 nm (often only this line is visible), 465 nm, 452 nm, 435 nm, and 423 nm. Other stones show additional bands: brown, green, or yellow diamonds show a band in the green at 504 nm, sometimes accompanied by two additional weak bands at 537 nm and 495 nm. Type IIb diamonds may absorb in the far red, but otherwise show no observable visible absorption spectrum.

liquid nitrogen to detect tell-tale absorption lines that are not normally discernible.

Electrical properties

Except for most natural blue diamonds—which are LED) producing 235 nm UV light.

In April of 2004 Nature reported that below the superconducting transition temperature 4 K, boron-doped diamond synthesized at high temperature and high pressure is a bulk, type-II superconductor[4]. In October of 2004 superconductivity was found to occur in heavily boron-doped microwave plasma-assisted chemical vapor deposition (MPCVD) diamond below the superconducting transition temperature of 7.4 K[5].

Thermal properties

Unlike most electrical insulators, diamond is a good conductor of heat because of the strong covalent bonding within the crystal. Most natural blue diamonds contain microstates, to reach 41,000 W·m/m²·K at 104 K. The same diamond at .99999-¹²C is predicted to 200,000 W·m/m²·K (20 kW·mm/cm²·K).^[4]

Diamond's thermal conductivity is made use of by jewellers and gemologists who may employ an electronic thermal probe to separate diamonds from their imitations. These probes consist of a pair of battery-powered moissanite, an imitation of diamond introduced in 1998 which has a similar thermal conductivity.

Being a form of carbon, they can burn in the presence of oxygen if heated over 800°C. Nevertheless, in absence of oxygen they can stand higher temperatures.

Composition and color

See also: Crystallographic defects in diamond

Diamonds occur in a restricted variety of colors—black, brown, yellow, grey, white, blue, orange, purple to pink, red, and chartreuse. Colored diamonds contain crystallographic defects, including substitutional impurities and structural defects, that cause the coloration. Theoretically, pure diamonds would be transparent and colorless. Diamonds are scientifically classed into two main types and several subtypes, according to the nature of defects present and how they affect light absorption:

Type I diamond has ultraviolet region, from 320 nm. They also have a characteristic fluorescence and visible absorption spectrum (see Optical properties).

Type II diamonds have very few if any nitrogen impurities. Type IIa diamond can be colored pink, red, or brown due to structural anomalies arising through plastic deformation during crystal growth—these diamonds are rare (1.8 percent of gem diamonds), but constitute a large percentage of Australian production. Type IIb diamonds, which account for 0.1 percent of gem diamonds, are usually a steely blue or grey due to scattered boron within the crystal matrix; these diamonds are also hydrogen can also impart a blue color; these are not necessarily Type IIb. Type II diamonds absorb in a different region of the infrared, and transmit in the ultraviolet below 225 nm, unlike Type I diamonds. They also have differing fluorescence characteristics, but no discernible visible absorption spectrum.

Certain radioactive to some degree.

It should be noted that some irradiated diamonds are completely natural—one famous example is the Dresden Green Diamond. In these natural stones the color is imparted by "radiation burns" in the form of small patches, usually only skin deep. Additionally, Type IIa diamonds can have their structural deformations "repaired" via a high-temperature, high-pressure (HTHP) process, removing much or all of the diamond's color.

In the late 18th century, diamonds were demonstrated to be made of carbon by the rather expensive experiment of igniting a diamond (by means of a burning-glass) in an 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 (δH = −2 kJ / mol). Diamonds had previously been shown to burn during Roman times.

So, despite De Beers' 1948 ad campaign, diamonds are definitely not forever. However, owing to a very large kinetic energy barrier, diamonds are normal conditions.

References

• O'Donoghue, Michael, and Joyner, Louise. (2003). Identification of gemstones, pp. 8–11. Butterworth-Heinemann, Great Britain. ISBN 0-7506-5512-7
• Pagel-Theisen, Verena. (2001). Diamond grading ABC: The manual (9th ed.), pp. 84–85. Rubin & Son n.v.; Antwerp, Belgium. ISBN 3-9800434-6-0
• Read, Peter G. (1999). Gemmology (2nd ed.). p. 52, 53, 275, 276. Butterworth-Heinemann, Great Britain. ISBN 0-7506-4411-7
• Webster, Robert, and Jobbins, E. Allan (Ed.). (1998). Gemmologist's compendium, p. 21, 25, 31. St Edmundsbury Press Ltd, Bury St Edwards. ISBN 0-7198-0291-1
• Webster, Robert, and Read, Peter G. (Ed.) (2000). Gems: Their sources, descriptions and identification (5th ed.), pp. 17–72. Butterworth-Heinemann, Great Britain. ISBN 0-7506-1674-1[6]
• Properties of diamond (Dr. Stephen Sque from the University of Exeter)

1. ^ Telling, R. H.; C. J. Pickard, M. C. Payne, and J. E. Field (May 2000). "Theoretical Strength and Cleavage of Diamond". Physical Review Letters 84 (22): 5160 - 5163. The American Physical Society.
2. ^ "Diamond Semiconductors Operate at Highest Frequenncy Ever". Nippon Telegraph and Telephone Corporation. August 20, 2003.
3. ^ "NTT verifies diamond semiconductor operation at 81 GHz". EE Times. 08/22/2003.
4. ^ ^{a b} http://aip.org/pnu/1993/split/pnu131-2.htm
5. ^ http://hone.mech.columbia.edu/pdf/hone_thermal_ency_nano.pdf "Carbon Nanotubes: Thermal Properties"