The difference in the properties of diamond and graphite can be easily explained in terms their structures.
1. Diamond is vary hard whereas graphite is soft:
In diamond there is a three dimensional network of strong covalent bonds. This makes diamond extremely hard. Because of hardness, diamond is used in making cutting and grinding tools.
On the other hand, in graphite there are flat layers of carbon atoms. These layers are held by weak van der Waal’s forces and hence can easily slip one over the other. This makes graphite extremely soft and slippery. Because if this soft and slippery nature graphite is used as a lubricant.
2. Density of diamond is more than that of graphite:
In graphite, there are large spaces between adjacent layers due to weak forces between them.
On the other hand, in diamond, atoms are held by strong covalent bonds and relatively more closely packed. Hence, diamond has higher density than graphite. Density of diamond is 3510 kg/m3 whereas that of graphite is 2250 kg/m3.
3. Diamond is bad conductor of electricity whereas graphite is a good conductor
In diamond, each carbon atom is directly linked to four other carbon atoms through covalent bonds. Thus, in diamond all the four valence electrons carbon are involved in covalent bonds and are not free to conduct electricity. This makes diamond a bad conductor of electricity.
On the other hand, in graphite each carbon atom is directly bonded to only three other carbon atoms. Thus, each carbon atoms utilizes only three valence electrons for forming covalent bonds with other carbon atoms, the fourth valence electron is relatively free, can move from one carbon atom to the other in a layer, and hence is responsible for conducting electricity. Hence, graphite is a good conductor of electricity.
4. Melting points of graphite and diamond are very high:
In diamond as well as in graphite carbon atoms are held by strong net work of covalent bonds. Therefore, both have very high melting points. The melting point of graphite is slightly higher than the melting point of diamond because in graphite C___C bonds have partial double bond character and hence are stronger and difficult to break. In factor, carbon as graphite has the highest melting point among all the elements.
5. Formation of Diamonds in Nature:
Diamonds are formed from the carbon present in the upper mantle at depths of over 150 kilometres under the effect of high pressure and high temperature prevailing there. The temperature in this region being about 1500`C and pressure about 70000 atmospheres. Diamonds formed in this way are brought to the surface of the earth by the igneous rock, kimberlite, which is also formed at the same depth as the diamonds. However, for the diamonds to reach intact at the surface the kimberlite rock must shoot up fast enough (at a speed of about 15 kilometres per hour) from the upper mantle towards the surface. This is due to the fact that though diamonds are quite stable at upper mantle depths and at the earth’s surface, they are readily changed to graphite at intermediate depths. Under the effect of weathering of rocks, the diamonds present in them are loosened. These diamonds are then recovered from the soil in which they are present.
6. Artificial Diamonds:
Graphite can be converted into diamonds by the action of high temperature (~ 20000 C ) and high pressure (100000 atmosphere) in the presence of transition metals (such as platinum).The artificial diamonds, however, are small in size and generally grey in colour and hence cannot be used as gems. These are used for making cutting and grinding tools.
Uses of Diamond
Main uses of diamond are:
1. Diamond is the hardest naturally occurring substance. Due to this extreme hardness, it I used for making tools for cutting grinding other hard material and also in oil-well drills for drilling holes through the earth’s rocky layers.
2. It is used in dies for the manufacture of tungsten filaments for electric light bulbs.
3. Diamond is transparent and has very high refractive index. It posses extra-ordinary brilliance. Because of these properties it is used for making jewellery.
4. Sharp-edged diamonds are used by eye surgeons t remove cataract from eyes high precision.
5. Because of its extra-ordinary sensitivity to heat rays, it is used in high precision thermometers.
6. It is used in protective windows for space probes as it can keep out harmful radiations.
Uses of Graphite
Main uses of graphite are:
1. Graphite is used as lubricant either as a powder or as a dispersion in oil (oil-dag) or as a dispersion in water (aqua-dag).
2. Mixed with clay it is used in ‘lead pencils’.
3. Since it is good conductor of electricity and is inert, it is used for making carbon electrodes in electrolytic cells and in dry cells.
4. Because of its high melting point, it is used for making graphite crucibles. Crucibles made of graphite are not attacked by dilute acids or fused alkalies.
5. It is a component of printers’ ink.
6. Graphite is used as moderator in nuclear reactors.
7. Graphite under the effect of high temperature and high pressure can be converted into diamonds.