Diamond not just an allotrope of Carbon

Diamond is an allotrope of carbon. The most important properties of diamond are related to its structure. In diamond, each carbon atom is in sp3 hybridised state and is linked to four other neighbouring carbon atoms held at the corners of a regular tetrahedron by covalent bonds. This results in a very big three dimensional polymeric structure in which C – C distance is 1.54 Ao and bond angle is 109.5o. Owing to very strong covalent bonds by which the atoms are held together, diamond is the hardest substance known, possesses abnormally high melting point ( about 3600o C) and is extremely inert chemically. Thus diamonds burns in oxygen at 800o C and is attacked by sulphur vapours at about 1000o C. It is scarcely attacked by any other reagent except fused alkali.

Furthermore, since all the electrons are used in bond formation, there is no mobile electron in the system and hence the diamond crystals are non-conductor of electricity. Although diamond is the hardest substance, it has a series of cleavage planes parallel to its octahedral faces which help in shaping rough diamonds and in the formation of edges (by splitting the cleavage planes) which in turn are used for cutting glass. The density of diamond is 3.51 g/ml. Diamond has a very high refractive index (2.5), i.e. light rays are slowed down by the tightly bound electrons. As a result much of the light falling on a diamond is internally reflected off interior surface. Moreover, the refraction of different colours of light is not equal and, therefore, white passing light through it gives rise to brilliant play of colours which makes diamond as a valuable gem stone.

Diamond is used as precious stones for jewellery. Its hardness and high dispersion of light make it useful for industrial applications and jewellery. The hardness of diamond contributes to its stability as a gem stone. It maintains its polish very well. 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. However, diamond is a poor choice for machining ferrous alloys at high speeds. At the high temperatures created by high speed machining, carbon is soluble in iron, leading to greatly increased wear on diamond tools as compared to other alternatives. Common industrial adaptations of this ability include diamond tipped drill bits and saws, or use of diamond powder as an abrasive. Industrial-grade diamonds are either unsuitable for use as gems or synthetically produced, which lowers their value and make their use economically feasible. 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.

Toughness relates to a material’s ability to resist breakage from impact. The toughness of natural diamond has been measured as 3.4 MN m-3/2, which is good compared to other gem stones, but poor compared to most engineering materials. As with any material, the macroscopic geometry of a diamond contributes to its resistance to breakage. Diamond is therefore more fragile in some orientations than others.
Diamond color can occur in blue, green, black, translucent white, pink, violet, orange, purple and red, though yellow and brown are by far the most common colors. Colored diamonds contain impurities or structural defects that cause the coloration, while pure or nearly pure diamonds are transparent or colorless. Most diamond impurities replace a carbon atom in the crystal lattice, known as a carbon flaw. The most common impurity, nitrogen, causes a slight to intense yellow coloration depending upon the type and concentration of nitrogen present.

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