Melting point of graphite and diamond?

  • #1
Warp
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TL;DR Summary
It's strangely difficult to find these temperatures online. Different sources give wildly different values. What are the actual temperatures?
I was conversing with ChatGPT when I asked which material has the highest melting point, and it answered "tungsten" (giving its melting temperature). It so happened that in the previous question the melting point of graphite had come up, and it was listed as higher than that. When I asked which one of the two has the higher melting point, it insisted that it's tungsten, even though in that very response it listed a higher temperature for graphite. ("Graphite has a melting point of approximately 3,550°C (6,422°F), while tungsten has a melting point of approximately 3,422°C (6,192°F). Tungsten has the higher melting point between the two materials.")

In fact, other similar AIs also give wildly different answers (and most of them incorrect by the numbers).

This seemed to be an AI hallucination, so I googled what the melting point of graphite is, and to my surprise I found wildly different answers from different sources, varying by, like, a thousand degrees.

(Yes, I know that graphite, and diamond, do not melt per se, they sublimate. However, by "melting point" I mean "the temperature at which it stops being a solid.)

Turns out that also the melting point of diamond seems equally vague. Googling for it gives wildly different results:

"Diamond has a very high melting point (almost 4000°C)"
"Thus, we infer that diamond melts at about 9,000 K and between 0.60 and 1.05 TPa along the Hugoniot."
"In case of Diamond, the melting point is 3550 degrees Celsius"
"However, the melting point of diamond is estimated to be around 3,000-3,500°C (5,432-6,332°F)."
"Using carbon's theoretical phase diagram below (from Wikimedia), "liquid diamond" could be achieved at about 10 GPa (99 thousand atmospheres) and 5000 K (4700 °C)."
"Diamond has the highest melting point (3820 degrees Kelvin)"
"The ultimate melting point of the diamond is around 4,027° Celsius (7,280° Fahrenheit)"

No wonder the AIs are confused about it. So am I.

In comparison, the melting point of tungsten seems to be quite universally agreed upon (and likewise all AIs give a very consistent value for it).

What is the melting (well, sublimation) point of graphite and diamond? (I suppose I should add, under normal pressure conditions.)
 
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  • #2
Warp said:
Turns out that also the melting point of diamond seems equally vague.
A diamond will burn in the air at about 400°C. That makes melting diamond difficult, as it will often react chemically before it melts.
 
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Likes Vanadium 50
  • #3
Graphite, grapheme. diamond and liquid carbon are all phases. At atmospheric pressure, there may not be a direct phase transition from one phase to another. What is the freezing point of steam?
 
  • #4
Vanadium 50 said:
Graphite, grapheme. diamond and liquid carbon are all phases. At atmospheric pressure, there may not be a direct phase transition from one phase to another. Where is the freezing point of steam?
It doesn't freeze here, but it does in Oymyakon. So is it somewhere near Omsk?
 

Related to Melting point of graphite and diamond?

What is the melting point of graphite?

The melting point of graphite is approximately 3,600 to 3,700 degrees Celsius (6,512 to 6,692 degrees Fahrenheit) under normal atmospheric pressure.

What is the melting point of diamond?

The melting point of diamond is around 4,027 degrees Celsius (7,280 degrees Fahrenheit) under normal atmospheric pressure.

Why does diamond have a higher melting point than graphite?

Diamond has a higher melting point than graphite because of its strong covalent bonds in a three-dimensional tetrahedral lattice structure, which requires more energy to break compared to the layers of hexagonally arranged carbon atoms in graphite.

Can graphite and diamond melt under normal atmospheric conditions?

Under normal atmospheric conditions, both graphite and diamond do not melt but rather sublimate, turning directly from solid to gas. Melting them requires extremely high pressures.

What happens to diamond and graphite at extremely high temperatures?

At extremely high temperatures and pressures, graphite can transform into diamond, and diamond can convert into graphite. Under controlled conditions, both can theoretically melt, but this requires pressures of over 100,000 atmospheres.

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