Can Diamonds Burn?


Diamonds can be found in rocks like kimberlite, which form as magma cools. These highly-prized gemstones may originate deep underground in extreme temperatures, but under what conditions can diamonds burn? “Diamond in Kimberlite 3” by James St. John is licensed under CC By 2.0
Diamonds can be found in rocks like kimberlite, which form as magma cools. Although these highly-prized gemstones originate deep underground in extreme temperatures, under what conditions can diamonds burn? “Diamond in Kimberlite 3” by James St. John is licensed under CC By 2.0

Question

I came across this statement and was wondering if anyone can verify it:

“A diamond is the hardest natural substance on earth, but if it is placed in an oven and the temperature is raised to about 763º Celsius (1405º Fahrenheit), it will simply vanish, without even ash remaining. Only a little carbon dioxide will have been released.”

Is this true? Can diamonds burn up and simply vanish?

J.

Diamonds Burn Like Anything Carbon

Diamond is pure crystalline carbon, exactly the same chemically as graphite and charcoal. If any of these are strongly heated in the presence of oxygen (air), the carbon will react with the oxygen (burn) to form carbon dioxide (CO2) gas. Other compounds containing carbon, such as plant material or flesh, will decompose quickly when heated strongly. At normal temperatures and in the presence of moisture and bacteria, they will decompose very slowly into various gases, including methane (CH4) and CO2.

We all finish up as carbon dioxide and dust eventually. Recycling, anyone?

Cheers.

John Burgess, Mapua Nelson, NZ

Impure Diamonds Burn And Leave Ashes

Yes, diamonds burn. There are many substantiated insurance claims of diamonds being destroyed in fires. As far as I know, the bit about no ash remaining is theoretical. Being pure carbon, the combustion of diamond does produce CO2. But just how many absolutely pure diamonds are there? Any color in diamonds is produced by non-carbon impurities. In addition to the oxygen which takes up residence on the surface of a diamond (attaching itself almost automatically to the free molecular bonding sites), most diamonds are at least partially nitrogenated.

So, technically, if you have a non-nitrogenated, flawless, pure-white diamond, you can turn it into CO2 with the application of heat. But who would want to?

Boy, isn’t a CRC Handbook of Chemistry and Physics a handy thing to have around?

D.R.

How To Make Diamonds Vanish

Diamonds burn, but the temperature at which they burn depends on whether or not the diamonds are in contact with air. The temperature of diamond ignition in pure oxygen is 690º C to 840º C.  In a stream of oxygen gas, diamonds burn at a low red heat initially. They will gradually rise in temperature and reach a white heat. Then, the diamonds will burn uninterruptedly with a pale blue flame, even after the oxygen heat source is removed. The diamond crystals will gradually decrease in size and finally disappear. The flame at the last moment will flicker brightly and then disappear, leaving not a trace of ash or residue.

For this to take place in an air mixture, the heat must be kept directly applied on the diamonds at all times. If removed, the diamonds will not continue to burn, due to oxygen being diluted with nitrogen that does not support combustion.

Ron Campbell, Central Coast Gem Lab

“Measuring A Diamond” by Mauro Cateb is licensed under CC By 2.0
“Measuring A Diamond” by Mauro Cateb is licensed under CC By 2.0