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Thus diamonds do not exist forever. The conversion from diamond to graphite, however, has a very high activation energy and is therefore extremely slow. Despite the hardness of diamonds, the chemical bonds that hold the carbon atoms in diamonds together are actually weaker than those that hold together graphite.
Diamond is extremely strong owing to its crystal structure, known as diamond cubic, in which each carbon atom has four neighbors covalently bonded to it. Bulk cubic boron nitride (c-BN) is nearly as hard as diamond. Diamond reacts with some materials, such as steel, and c-BN wears less when cutting or abrading such material. [4]
Graphite consists of sheets of trigonal planar carbon. [20] [21] The individual layers are called graphene. In each layer, each carbon atom is bonded to three other atoms forming a continuous layer of sp 2 bonded carbon hexagons, like a honeycomb lattice with a bond length of 0.142 nm, and the distance between planes is 0.335 nm. [22]
Thus, graphite is much softer than diamond. However, the stronger bonds make graphite less flammable. [8] Diamonds have been adopted for many uses because of the material's exceptional physical characteristics. It has the highest thermal conductivity and the highest sound velocity.
According to the researchers, Q-carbon exhibits a random amorphous structure that is a mix of 3-way (sp 2) and 4-way (sp 3) bonding, rather than the uniform sp 3 bonding found in diamonds. [7] Carbon is melted using nanosecond laser pulses, then quenched rapidly to form Q-carbon, or a mixture of Q-carbon and diamond.
Diamond and graphite are two allotropes of carbon: pure forms of the same element that differ in crystalline structure.. Allotropy or allotropism (from Ancient Greek ἄλλος (allos) 'other' and τρόπος (tropos) 'manner, form') is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of the elements.
In diamond, all the carbon-to-carbon bonds, both within a layer of rings and between them, are in the staggered conformation, thus causing all four cubic-diagonal directions to be equivalent; whereas in lonsdaleite the bonds between layers are in the eclipsed conformation, which defines the axis of hexagonal symmetry.
Although a computational study employing density functional theory methods reached the conclusion that as T → 0 K and p → 0 Pa, diamond becomes more stable than graphite by approximately 1.1 kJ/mol, [47] more recent and definitive experimental and computational studies show that graphite is more stable than diamond for T < 400 K, without ...