At what temerature and pressure is the stable form of carbon a diamond crystal?

Hello Bill,

Thank you for your very interesting question.

At Wikipedia's article for "diamond", we find that:

"At surface air pressure (one atmosphere), diamonds are not as stable
as graphite (...) However, owing to a very large kinetic energy
barrier, diamonds are metastable; under normal conditions [1], it
would take an extremely long time (possibly more than the age of the
Universe) for diamond to decay into graphite."
(http://en.wikipedia.org/wiki/Diamond )

[1](Researcher's note) "Normal conditions" links to the article for
"Standard temperature and pressure": "In chemistry, the term standard
temperature and pressure (abbreviated STP) denotes an exact reference
temperature of 0 °C (273.15 K) and pressure of 100 kPa (1 bar)."
(http://en.wikipedia.org/wiki/Standard_temperature_and_pressure )

The School od Chemistry at UK's University of Bristol publishes on the
internet at least since 1996 the Molecule of the Month page. In the
one related to diamonds, written by Dr Paul May, it reads:

"Diamond is created deep underground under conditions of extreme
pressure and temperature. Under these conditions diamond is actually
the more stable of the two forms of carbon [2], and so over a period
of millions of years carbonaceous deposits slowly crystallise into
single crystal diamond gemstones."
(http://www.chm.bris.ac.uk/motm/diamond/diamond.htm )
[2] Graphite and diamond(Researcher's note).

Those "conditions of extreme pressure and temperature" in which
diamonds get formed, are described in detail at Wikipedia's article
for "diamond":

"Under continental crust, diamonds form starting at depths of about
150 kilometers (90 miles), where pressure is roughly 5 gigapascals and
the temperature is around 1200 degrees Celsius (2200 degrees
Fahrenheit). Diamond formation under oceanic crust takes place at
greater depths because of higher temperatures, which require higher
pressure for diamond formation. Long periods of exposure to these high
pressures and temperatures allow diamond crystals to grow larger."
(http://en.wikipedia.org/wiki/Diamond )

Therefore, according with these two sources, a diamond crystal is more
stable than graphite - thus, the stable form of carbon - at
temperatures of 1200 degrees Celsius (2200 degrees Fahrenheit) or
higher, and pressures of 5 gigapascals or higher.

I believe that this answers your question. If any clarification is
needed, please do not hesitate to ask.

Search strategy:
"stable diamond" (://www.google.com/search?sourceid=navclient&ie=UTF-8&rls=GGLG,GGLG:2005-38,GGLG:en&q=%22stable+diamond%22
)

Regards,

Guillermo

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Request for Answer Clarification by bill22-ga on 25 Jan 2006 16:55 PST

This must change with various pressures is there a pressure temperature graph?

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Clarification of Answer by guillermo-ga on 25 Jan 2006 20:03 PST

Yes, you're right. Maybe you didn't notice the comments below -- the
"phase diagram for carbon"
(http://www.chm.bris.ac.uk/motm/diamond/cphased.gif ) included in the
"Molecule of the Month" text quoted and linked to in my answer, and
the one provided by my colleague Hedgie-ga in his comment, both relate
pressure and temperature.

Guillermo

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Clarification of Answer by guillermo-ga on 26 Jan 2006 04:59 PST

Thank you, Bill, for the rating and tip!

Guillermo

The information given in the answer is shown here as a phase diagram:
http://phycomp.technion.ac.il/~anastasy/teza/teza/node5.html

And, BTW, you never posted a followup to your clever question
http://answers.google.com/answers/threadview?id=434301

"It turns out that this question is the same as asking: is the universe closed"
http://phycomp.technion.ac.il/~anastasy/teza/teza/node5.html

The singularity would be in the 'mother universe', not in ours.

Thanks Hedgie-ga, for the complementary information. Also, in the
"molecule of the month" page quoted in the answer, there is within the
text a link to a similar diagram labeled "phase diagram for carbon",
for which the URL is
http://www.chm.bris.ac.uk/motm/diamond/cphased.gif

Guillermo

By the way, Bill, my colleague Hedgie-ga brought to my antention your
now closed question about black-holes, and I thought that you might
find some interest in these two answers -- specially the links --
that, while not addressing the subject of blackholes, I think that
somehow hang around your focus:

Accelerating galaxies: http://answers.google.com/answers/threadview?id=591921

and

Cosmology: http://answers.google.com/answers/threadview?id=514046

Guillermo

Yes, you're right. Maybe you didn't notice the comments below -- the
"phase diagram for carbon"
(http://www.chm.bris.ac.uk/motm/diamond/cphased.gif ) included in the
"Molecule of the Month" text quoted and linked to in my answer, and
the one provided by my colleague Hedgie-ga in his comment, both relate
pressure and temperature.

Guillermo

ok got the phase diagram new question posted on this thread please go check it out.