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Name: Cheryl B.
Status: Other
Age: 50s
Location: N/A
Country: N/A
Date: July 2002 


Question:
If you were to take a lump of coal and squeeze it for a long time at very high temperatures, would you end up with a diamond, or graphite?



Replies:
Cheryl,

I answered someone else's question about this previously. You can find an answer to this in the questions that have been answered on the web site.

However, briefly, if the pressure were high enough and last long enough, theoretically you could get a diamond, but it would be quite impure. Coal has a high level of impurities (it is not all carbon), so any resulting diamond would be of poor quality.

Squeezing a lump of coal would not produce graphite. Diamonds were formed from graphite, a pure form of carbon, under great pressure and heat.

David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory


It really depends on the temperatures and pressures. Coal that is metamorphosed may turn into graphite, but the pressures and temperatures required for graphite are not the same as those required for diamond formation. Diamond formation requires much higher temperatures and pressures. The relationships between pressure and temperature and what form of carbon exists can be plotted on a type of graph. There is a nice one at

http://invsee.asu.edu/Modules/carbon/condit.htm.

Interestingly, diamonds are not permanently stable at the temperatures and pressures we experience at the surface of the earth. Diamonds are very slowly changed into graphite.

Pat Rowe


Diamond is thermodynamically unstable with respect to graphite at ambient conditions, 300 K and 1atm. At 300 K it requires about 14,500 atm to transform graphite into diamond. That is how diamonds were formed (presumably) at great depths below the earth's surface.

You can find the phase diagram for carbon's various forms at the web site:

http://www.nau.edu/~chem/courses/chm440/lectures/lec9/lec9.html

You may have to enter this link somewhere upstream of the complete URL here.

Vince Calder



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