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Can Diamonds Be Melted or Dissolved?

Komal B. Patil Feb 17, 2019
Diamonds may be a girl's best friend, but they are certainly not forever. This post explains how, under the right conditions, it is quite possible to burn, melt, and even dissolve these beautiful gems.

Diamond Speaker Domes

The hardness of diamonds allows them to vibrate for a long time without being warped. This promotes the production of extremely clear and crisp audio.
The strongest allotrope of carbon, the diamond, is an optically isotropic crystal that has its comprising carbon atoms bound to each other in a cubic lattice pattern. This pattern involves the bonding of each carbon atom to four neighboring carbon atoms via strong covalent bonds.
The strong bonds between each atom of the crystal renders it extremely hard and strong. It is the hardest known substance to man, presently. But the property of hardness does not imply that it is indestructible. Just because a substance is harder than another, does not imply that it cannot be destroyed.
For example, glass (natural or toughened) is considerable harder than steel, yet, a bar of steel can easily break the glass. On heating, glass melts faster than steel, and can be eroded (by chemicals) faster as well.
A diamond is not indestructible. The fact that diamonds are cut and shaped to be used as jewelry indicates that, it is possible to shatter or break the crystal under the right conditions.
Under normal conditions of atmospheric temperature and pressure, a diamond retains all its physical and chemicals properties, since the covalent bonds between the carbon atoms require an immensely high amount of energy to be broken.
If a high-enough temperature and pressure environment is provided, along with suitable catalysts it is possible to change the physical or chemical nature of a diamond.

Burning a Diamond

Diamonds are crystals made up purely of carbon atoms, and carbon is known to react with oxygen to form carbon dioxide. If one heats a diamond crystal normally, it doesn't have any observable effect.
However, as the French chemist Antoine L. Lavoisier demonstrated, if a diamond is heated up to 600 to 800°C in a pool of liquid oxygen, it is possible to break the carbon-carbon bonds, allowing the atoms to react with oxygen and form carbon dioxide gas.
Since no solid residue is left behind, a diamond in the presence of oxygen can be described as a sublimating substance. This does not take place in the normal atmosphere, since the oxygen concentration in the air is not enough (only 20%) to oxidize the crystal. Instead, the crystal may transform into graphite, which is a more stable form of pure carbon.

Melting a Diamond

A diamond has an average melting temperature of 3,550°C in a vacuum. If a diamond is heated to that temperature, it may either become charred, will burn off, or show no effect.
In a vacuum, it is possible to melt small quantities of diamonds. When the crystals are subjected to super-strong magnetic fields, and a pressure a million time the normal value, small amounts of the diamond are observed to melt and liquefy.
The strength of the magnetic field and the intense pressure induce the necessary thermal energy required for the process. Some researchers have also achieved similar results by utilizing a focused high-intensity laser beam and high pressure conditions.
When the pressure is reduced, the molten diamond re-solidifies into a solid crystal. This behavior has prompted scientists to ponder over the possible existence of seas of liquid nitrogen on planets like Neptune and Uranus, as a consequence of intense pressure and abundance of carbon.

Dissolving a Diamond

This compact crystal of pure carbon does not dissolve in any liquid at room temperature. Concentrated acids, at a very high temperature and pressure, may be able to decompose minute quantities of a diamond.
A better job of dissolution is done when a solution of molten sodium hydroxide and sodium nitrate is heated and used. Researchers at the National University of Singapore have discovered a novel way to degrade, etch, or basically dissolve a diamond.
It involves coating the crystal with a layer of graphene, which is a one-atom thick substance composed of pure carbon. When the coated crystal is heated to high temperatures in order to bond the two substances, a restructuring and bonding between the two elements can be observed.
Since both substances are impermeable, the water trapped between them transforms into a supercritical phase, that can corrode the surface of the diamond. However, the purpose of the experiment is not only focused on etching the diamond, but also to study the effect of high temperature and pressure on the characteristics and behavior of different liquids.
Hence, contrary to popular belief, diamonds are not really indestructible. But it must also be noted that, these pure carbon crystals can only be destroyed in the presence of extremely high temperature and pressure.