If you were to melt diamond, would it re-form into the diamond isotope, or would it become another form of carbon, like

Question: If you were to melt diamond, would it re-form into the diamond isotope, or would it become another form of carbon, like graphite? Or would it be a mixture of both?
- Keywords:
  carbon,
  diamond,
  graphite,
  isotope,
  melt,
  mixture
Asked by blackbird to Alan, Caspar, Diana, Murray, Sarah on 15 Mar 2011 in Categories: General.
- Sarah Thomas answered on 14 Mar 2011:
  
  Diamonds do not melt, they sublime! This means it goes straight from solid to gas! The gas that comes off is carbon dioxide (basically as the carbon gets really hot, it reacts with the oxygen in the air). If you were to heat the diamond in a vacuum, i.e. no air to react with, the diamond would slowly become graphite. You would get any diamond re-forming.
- Caspar Addyman answered on 14 Mar 2011:
  
  It depends upon how you cooled it down. Normally, it would solidify into a mixture of different types of carbon (graphite, buckyballs, carbon nanotubes, some small crystaline diamond-like structures). If you cooled it very slowly but keeping it under extreme pressure then I think you would be able to get back some diamond. But it might be cheaper not to melt it in the first place. And you would have to be very careful to keep oxygen out of the mixture or a lot of it would just burn. By the way, if you have access to some liquid oxygen it is possible to burn diamonds. But I wouldn’t recommend it.
  
  Diamond, graphite, etc are different material structures rather than different isotopes.
  
  Different isotopes have different radioactivity and depend upon how many neutrons there are in each atom.
- Alan Winfield answered on 15 Mar 2011:
  
  I’m really not sure. The first thing is that to melt diamond you would need an awesomely high temperature, about 2700 degrees C plus a very high pressure: 10 million atmospheres. I wouldn’t even like to make a guess about how diamond would then re-crystallise – but you may well be right – a mix of crystals, graphite and maybe other forms like Buckminsterfullerene.
- Diana Drennan answered on 15 Mar 2011:
  
  Oy. Why would you do that to a perfectly nice diamond ? If you were to melt diamond, (in an oxygen free environment so it doesn’t burn), it would almost certainly lose the crystalline arrangement of it’s atoms that makes it a diamond and just become amorphous (without structure) – i.e. graphite. Diamonds need high temperature and pressure (1500 degrees at 850,000 PSI) to gain the atom arrangement that makes them diamonds.