Diamond is the most popular gemstone on earth, it is the hardest natural material known to man. Diamonds originate from deep underground and are formed under extreme conditions of temperature and pressure. Diamond is an allotrope (a form) of carbon that exists in a pure crystalline form. In chemistry, we study that substances are made up of atoms that are joined to each other by chemical bonds. Does carbon burn?
Each carbon atoms in a diamond is bonded to four other carbon atoms by a strong covalent bond (covalent bond is the strongest kind of chemical bond) – this is what accounts for the strength of diamond. Diamond, apart from its unique strength, is the least compressible substance on earth and is turgid i.e. it has the ability to resist breakage from drops or crashes. Other properties of diamond include high refractive index, high dispersion, high luster and high thermal conductivity.
Apart its use in making jewelries, diamond due to its strength, ability to withstand heat and other unique properties, is used industrially for making cutting, drilling, grinding and polishing tools. It is also used as an abrasive because of its hardness. How much heat does it take for a diamond to burn?
Diamonds do not last forever, they melt and burn.
As opposed to the old saying: “diamonds lasts forever”, diamond do not actually last forever. Under certain conditions they degrade to form graphite. It is also possible to take diamond to a state of non-existence through burning. Also, the state of diamond can be changed into liquid through melting. So much for being hard! You might be wondering how possible it is for the hardest substance known to man to burn and or even melt- it is possible.
Burning of Diamond
Diamond is an allotrope of carbon and carbon burns in the presence of oxygen. As a matter of fact, burning of carbon is one of the most common forms of burning in our day-to-day life (from when you burn wood, to when you burn coal and even when you cook with your cooking gas, you are burning carbon). As a general rule, carbon (whether in form of coal, graphite or diamond) burns partially in the presence of oxygen to produce carbon monoxide or completely to give off carbon dioxide.
The carbon- carbon bond in diamond is very strong (this is what makes it a very hard substance), it is in a tight three-dimensional array and thus very large amount of heat energy is required to break the carbon-carbon bond to produce free carbon that would combine with oxygen for burning to proceed.
How much heat does it take for diamond to burn?
It takes heat at about 900oC and 1bar to burn diamond.
Burning diamond is tantamount to making it vanish. Given the right condition of temperature, pressure and oxygen, diamond will burn to give off an odorless and colorless carbon dioxide. This gas is the only product from burning diamond hence no ash or other substance would be produced when carbon is burnt, it will simply vanish into thin air. Air contains oxygen but will not be able to burn diamond because it also contains nitrogen which will not support combustion. Pure oxygen rather, is used to burn diamond. Pure diamond begins to burns in pure oxygen at around 690oC. By the time the temperature gets to 900OC the diamond must have vanished into thin air as CO (carbon monoxide) with no traces of ash or its previous existence. Impure diamonds (e.g. colored diamonds) may give off ash when burnt due to the presence of non-carbon impurities like nitrogen and boron.
Burning of diamonds is an oxidation process (essentially, the addition of oxygen).Upon introduction of oxygen gas, pure diamonds burns with low red heat, the oxygen would gradually rise in temperature and reach then the flames would become white and later pale blue even after removal of heat source (indicating complete combustion). The flames becoming pale blue is an indication of the temperature approaching 900oC, at this stage the diamond gradually decreases in size and soon disappears.
When burning diamonds the heat source must be in contact with the diamond at all times, this is because when the heat source is removed the oxygen would be diluted with nitrogen from the air and oxygen diluted with nitrogen won’t support burning of diamond.
Diamond may burn at lower temperature
The major factor required to burn carbon (diamond inclusive) is the presence of oxygen. Diamond may burn at a lower temperature in liquid oxygen. To burn diamond in liquid oxygen, simply burn the diamond to red hot (this is a much lower temperature than when the flames becomes white or pale blue) and then drop in liquid oxygen. The process releases heat until the diamond has completely reacted with the oxygen and vanished. This process is particularly dangerous because of the liquid oxygen used; liquid oxygen is a very powerful oxidizing agent and may cause explosion if there is any slight source of ignition.
Diamonds can also be melted
Diamond melts at a temperature of about 4500oC and pressure of about 100,000atm, but the liquid diamond obtained would be converted to graphite upon cooling. Melting of diamond using normal pressure is an impossible scientific process because, before it attains melting state, in the presence of oxygen, would have burnt away and in the absence of air, would become graphite before melting temperature is reached.
In recent times scientists have been able to melt diamonds using very strong magnetic fields and subjecting the diamonds to 10 million times normal atmospheric pressure.
Diamonds can also become something else- they can become that substance inside your pencil!
Diamonds do not have very stable structures. A more stable allotrope of carbon is graphite. Graphite is a substance used in making pencils- it is the part of pencils used in writing. Diamonds can be converted to graphite in the absence of oxygen through heating. This process cannot be referred to as burning despite the heat. A process can only be referred to as burning when oxygen is involved.