Allotropes of Carbon Presented by: Harshit Gupta and Akshit Jindal
There are eight Allotropes of Carbon <ul><li>Diamond </li></ul><ul><li>Graphite </li></ul><ul><li>Lonsdaleite </li></ul><ul><li>C 60 , Buckminsterfullerene or Buckyball </li></ul><ul><li>C 540 </li></ul><ul><li>C 70 </li></ul><ul><li>Amorphous Carbon </li></ul><ul><li>Single-walled Carbon nanotube or Buckytube </li></ul>
Diamond The hardness and high dispersion of light of diamond make it useful for both industrial applications and jewelry. Diamond is the hardest known natural mineral. This makes it an excellent abrasive and makes it hold polish and luster extremely well. No known naturally occurring substance can even scratch a diamond, except another diamond. The market for industrial-grade diamonds operates much differently from its gem-grade counterpart. Industrial diamonds are valued mostly for their hardness and heat conductivity, making many of the gemological characteristics of diamond, including clarity and color, mostly irrelevant. This helps explain why 80% of mined diamonds are unsuitable for use as gemstones and known as bort , are destined for industrial use.
Diamond The dominant industrial use of diamond is in cutting, drilling, grinding, and polishing. Diamonds are embedded in drill tips or saw blades, or ground into a powder for use in grinding and polishing applications. Garnering much excitement is the possible use of diamond as a semiconductor suitable to build microchips from, or the use of diamond as a heat sink in electronics. In 1772, Antoine Lavoisier used a lens to concentrate the rays of the sun on a diamond in an atmosphere of O 2 , and showed that the only product of the combustion was CO 2 , proving that diamond is composed of carbon.
Diamond Experts in gemology use methods of grading diamonds based on the characteristics most important to their value as a gem. Four characteristics, known as the four Cs , are commonly used as the basic descriptors of diamonds: these are carat , cut , color , and clarity . It is an excellent insulator of electricity except for blue diamond. Synthetic diamonds are diamonds manufactured in a laboratory. The gemological and industrial uses of diamond have created a large demand for rough stones. This demand has been satisfied in large part by synthetic diamonds. Diamond identification relies on its thermal conductivity. Electronic thermal probes are used in the gemological centers to separate diamonds from their imitations.
Graphite Graphite was named by Abraham Gottlob Werner in 1789 for its use to draw and write. Graphite is an electrical conductor and the most stable form of carbon under standard conditions. Graphite is used as a dry lubricant. During a fire the graphite intumesces (expands and chars) to resist fire penetration and prevent the spread of fumes. A typical start expansion temperature (SET) is between 150 and 300 °C. It’s specific gravity is 2.3, which makes it lighter than diamond. At high temperatures and pressures, it can be transformed into diamond. At about 700 °C it burns in O 2 forming CO 2 .
Graphite It is slightly more reactive than diamond because the reactants are able to penetrate between the hexagonal layers of carbon atoms in graphite. It is unaffected by ordinary solvents, dilute acids, or fused alkalis. However, chromic acid (H 2 CrO 4 ) oxidizes it to carbon dioxide. Historically, graphite was called blacklead and plumbago. Natural graphite is mostly consumed for refractories, steelmaking, expanded graphite, brake linings, foundry facings and lubricants.
Lonsdaleite Lonsdaleite (named in honor of Kathleen Lonsdale), also called hexagonal diamond in reference to the crystal structure, is an allotrope of carbon with a hexagonal lattice. Lonsdaleite was first identified in 1967 from the Canyon Diablo meteorite, where it occurs as microscopic crystals associated with diamond. In nature, it forms when meteorites containing graphite strike the Earth. The great heat and stress of the impact transforms the graphite into diamond, but retains graphite's hexagonal crystal lattice.
Lonsdaleite It is translucent, and has an index of refraction of 2.40 to 2.41 and a specific gravity of 3.2 to 3.3. A simulated pure sample has been found to be 58% harder than diamond. 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 110 °C.
C 60 Buckminsterfullerene is a spherical fullerene molecule with the formula C 60. It was first intentionally prepared in 1985 by Harold Kroto, James Heath, Sean O'Brien, Robert Curl and Richard Smalley at Rice University. Kroto, Curl, and Smalley were awarded the 1996 Nobel Prize in Chemistry for their roles in the discovery of buckminsterfullerene and the related class of molecules, the fullerenes.
C 60 The structure of a buckminsterfullerene is a truncated icosahedron (whose faces are two or more types of regular polygons) made of 20 hexagons and 12 pentagons, with a carbon atom at the vertices of each polygon and a bond along each polygon edge. The name is a homage to Richard Buckminster Fuller, whose geodesic domes it resembles. Buckminsterfullerene was the first fullerene molecule discovered and it is also the most common in terms of natural occurrence, as it can be found in small quantities in soot.
Amorphous Carbon Amorphous carbon or free, reactive carbon, is an allotrope of carbon that does not have any crystalline structure. Coal and soot or carbon black are informally called amorphous carbon. While entirely amorphous carbon can be produced, most amorphous carbon actually contains microscopic crystals of graphite-like, or even diamond-like carbon.
Amorphous Carbon The coal industry divides coal up into various grades depending on the amount of carbon present in the sample compared to the amount of impurities. The highest grade, anthracite, is about 90% carbon and 10% other elements. Bituminous coal is about 75–90% carbon, and lignite is the name for coal that is around 55% carbon.
Buckytube Carbon nanotubes ( CNTs ) are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material. These cylindrical carbon molecules have unusual properties, which are valuable for nanotechnology, electronics, optics and other fields of materials science and technology.
Buckytube In particular, owing to their extraordinary thermal conductivity and mechanical and electrical properties, carbon nanotubes find applications as additives to various structural materials. For instance, in (primarily carbon fiber) "baseball bats, car parts" and even "golf clubs", where nanotubes form only a tiny portion of the material (s). Nanotubes are members of the fullerene structural family, which also includes the spherical buckyballs, and the ends of a nanotube may be capped with a hemisphere of the buckyball structure. Their name is derived from their long, hollow structure with the walls formed by one-atom-thick sheets of carbon, called graphene.