Properties Of Diamond

A diamond is a transparent crystal of tetrahedrally bonded carbon atoms (sp3) that crystallizes into the diamond lattice which is a variation of the face centered cubic structure. Diamonds have been adapted for many uses because of the material's exceptional physical characteristics. Most notable are its extreme hardness and thermal conductivity (900–2,320 W·m−1·K−1),as well as wide bandgap and high optical dispersion.Above 1,700 °C (1,973 K / 3,583 °F) in vacuum or oxygen-free atmosphere, diamond converts to graphite; in air, transformation starts at ~700 °C. Naturally occurring diamonds have a density ranging from 3.15–3.53 g/cm3, with very pure diamond typically extremely close to 3.52 g/cm3.

Hardness

Diamond is the hardest natural material known, where hardness is defined as resistance to scratching.Diamond has a hardness of 10 (hardest) on Mohs scale of mineral hardness. Diamond's hardness has been known since antiquity, and is the source of its name.

The hardest natural diamonds in the world are from the Copeton and Bingara fields located in the New England area in New South Wales, Australia. These diamonds are generally small, perfect to semiperfect octahedra, and are used to polish other diamonds. Their hardness is associated with the crystal growth form, which is single-stage crystal growth. Most other diamonds show more evidence of multiple growth stages, which produce inclusions, flaws, and defect planes in the crystal lattice, all of which affect their hardness.It is possible to treat regular diamonds under a combination of high pressure and high temperature to produce diamonds that are harder than the diamonds used in hardness gauges.

The hardness of diamonds contributes to its suitability as a gemstone. Because it can only be scratched by other diamonds, it maintains its polish extremely well. Unlike many other gems, it is well-suited to daily wear because of its resistance to scratching—perhaps contributing to its popularity as the preferred gem in engagement or wedding rings, which are often worn every day.

Industrial use of diamonds has historically been associated with their hardness; this property makes diamond the ideal material for cutting and grinding tools. As the hardest known naturally occurring material, diamond can be used to polish, cut, or wear away any material, including other diamonds. Common industrial adaptations of this ability include diamond-tipped drill bits and saws, and the use of diamond powder as an abrasive. Less expensive industrial-grade diamonds, known as bort, with more flaws and poorer color than gems, are used for such purposes.

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 when compared to alternatives.

These substances can scratch diamond:

* Some diamonds are harder than others.
* Nanocrystalline diamond aggregates produced by high-pressure high-temperature treatment of graphite or fullerite (C60).
* Cubic Boron nitride (Borazon)
* A hexagonal form of diamond called lonsdaleite, which is theoretically predicted to be 58% stronger than diamond.

Electrical conductivity

Other specialized applications also exist or are being developed, including use as semiconductors: some blue diamonds are natural semiconductors, in contrast to most other diamonds, which are excellent electrical insulators.The conductivity and blue color originate from the boron impurity. Boron substitutes for carbon atoms in the diamond lattice, donating a hole into the valence band.

Substantial conductivity is commonly observed in nominally undoped diamond grown by chemical vapor deposition. This conductivity is associated with hydrogen-related species adsorbed at the surface, and it can be removed by annealing or other surface treatments.

Toughness

Toughness relates to a material's ability to resist breakage from forceful impact. The toughness of natural diamond has been measured as 2.0 MPa·m1/2, and the critical stress intensity factor is 3.4 MN·m−3/2. Those values are good compared to other gemstones, but poor compared to most engineering materials. As with any material, the macroscopic geometry of a diamond contributes to its resistance to breakage. Diamond has a cleavage plane and is therefore more fragile in some orientations than others. Diamond cutters use this attribute to cleave some stones, prior to faceting.