Can Diamonds Burn?

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?

Answer: Although diamonds originate deep underground and form under extreme temperatures, diamonds can indeed burn under certain conditions.

Diamonds Burn Like Anything Carbon

As pure crystalline carbon (C), diamonds have the exact same chemistry as graphite (though they have different molecular structures). If strongly heated in the presence of oxygen (air), carbon will react with the oxygen (burn) to form carbon dioxide gas (CO₂). 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 carbon dioxide.

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 exist? 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 initially at a low red heat. 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 removal of the oxygen heat source. 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 remain applied directly on the diamonds at all times. If removed, the diamonds won't continue to burn, because oxygen diluted with nitrogen won't support combustion.

Ron Campbell, Central Coast Gem Lab