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The Sparkling Diamond And The Humble Charcoal
Carbon is one of the most widely distributed elements in nature. Although it makes up less than 0.13% of the earth’s crust and atmosphere, compounds of carbon are found in all living things (plants and animals) as proteins and carbon-hydrates. Carbon has the distinction of being the element which forms the largest number of compounds.
The element carbon has been known from early times in the form of soot, charcoal, graphite and diamonds. But the ancient didn’t know the sparkling diamond and the humble charcoal were actually different forms of same element.
Carbon exists in two crystalline forms - diamond and graphite - and several amorphous forms, such as coal and charcoal. All these forms are made of carbon atoms, yet they differ widely in their properties. You are familiar with the brilliance of diamonds; they are hard, crystalline and transparent.
Carbon is found in nature in the free or natural state and in combination with other elements.
In the free state it exists in
- the crystalline form as diamond and graphite and
- the amorphous form as coal
In the combined state, it exists as carbonates in the earth’s crust. these carbonates are:
- Limestone, marble and chalk, all three chemically known as calcium carbonate (CaCO3)
- dolomite (MgCO3 .CaCO3)
- hydraocarbons in the form of petroleum and natural gas.
Soot was one of the most widely used form of carbon. Soot or lamp black is obtained by burning oils rich in carbon such as kerosene, vegetable oil or turpentine. The oil is burnt in a limited supply of air and the smoke is passed into large chambers where coarse blankets are hung. Ancient Chinese made ink from burning pine in an ink furnace and catching the soot in a jar. Then soot was mixed with glue from animal horns such as young deer to make ink. Ink was then sold as a solid stick, which was ground upon an ink stone and mixed with water to make liquid ink for the calligrapher to work with.
Graphite is a soft, dark grey solid with a metallic lustre, smooth and slippery to touch. It is a good conductor of heat and electricity. Graphite is not easily affected by ordinary chemical reagents. When strongly heated in air, it burns with the formation of carbon dioxide.
Because of its smoothness, it is powdered, mixed with oil, and used as lubricant for machines. Graphite marks paper, and is used in “lead” pencils. The word lead is a misnomer, as it is not lead but graphite which forms the core of the pencil. Graphite is mixed with clay to give it greater hardness in pencils.
Charcoal is black, amorphous solid. It is hard to believe that the sparkling diamond and the humble charcoal are different forms of the same element, carbon.
Diamond and graphite, although made of the same carbon atom, differ widely in their properties. these differences in their properties arise from differences in the way which the carbon atoms are bonded. In graphite, each carbon atom is bonded to three other carbon atoms in the same plane to form a hexagonal layer. these hexagonal layers are arranged one on top of the other and held together by loose bonds. These planes can slide over one another. and it is this property which makes graphite slippery to touch and a good lubricating agent.
In diamond, the arrangement of carbon atoms is quite different. Each carbon atom is attached to four other carbon atoms giving rise to a rigid, three-dimensional structure. It is this structure with makes diamond one of the hardest substances known.
Diamonds are mined in South Africa, USA, Brazil, the Siberian portion of the Russian Federation, and in India. In India, diamonds are found in the Panna mines in Madhya Pradesh and in Andhra Pradesh. Two world famous diamonds, the Khinoor and the Pitt, were mined in India. The Cullinan diamond, the largest ever found, was mined in South Africa. The unit of weight for diamonds in the carat (1 carat = 20 mg).
Pure diamonds are colourless, and transparent. Some diamonds are coloured and may be tinged with yellow, blue, pink, brown, or even black. The colour is due to some impurity present in the diamond.
Properties of Diamond
- Diamond is the purest allotrope of carbon. Pure diamond is a colourless, lustrous, crystalline solid.
- It is the hardest substance known. Only a diamond can cut another diamond.
- It has a very high refractive index of 2.4. A beam of light falling on it is dispersed into a rainbow and the diamond sparkles with a play of beautiful colours.
- It has a specific gravity of 3.5.
- Natural diamond is transparent to X-rays whereas artificial diamonds are opaque to X-rays. This property is used to distinguish natural from artificial diamonds.
- It is not affected by ordinary chemical reagents and is insoluble in most solvents.
- It is a poor conductor of electricity.
- At the very high temperature of 900oC, it burns in air to give carbon dioxide.
Uses of Diamond
- Diamonds are found in very few places on earth. They are greatly valued as jewels because of the lustre and brilliance produced when they are cut to shape.
- Being one of the hardest substances known, diamonds, particularly the black variety, are used for cutting, grinding and drilling. They are hard enough to be used for drilling through rocks.
- They are used as phonograph needles.
Manufacture of Artificial Diamond
Artificial diamonds were first prepared by Moissan in 1886. Graphite can be converted to diamond by subjecting it to very high pressures at very high temperatures in the presence of catalysts.
Graphite is mined in India, Sri Lanka, Italy, Siberia, and the USA.