Melting point of graphite and diamond?

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SUMMARY

The discussion centers on the melting points of graphite and diamond, revealing significant discrepancies in reported values across various sources. Graphite's melting point is approximately 3,550°C (6,422°F), while tungsten's is about 3,422°C (6,192°F), leading to confusion among AI responses. Diamond's melting point is even more ambiguous, with estimates ranging from 3,000°C to over 4,000°C, depending on the source. The conversation highlights the challenges in defining melting points for these materials, particularly under normal pressure conditions, as they tend to sublimate rather than melt.

PREREQUISITES
  • Understanding of material science concepts, particularly phase transitions.
  • Familiarity with thermodynamic principles related to melting and sublimation.
  • Knowledge of the properties of carbon allotropes, including graphite and diamond.
  • Basic understanding of AI limitations and hallucinations in data interpretation.
NEXT STEPS
  • Research the thermodynamic properties of carbon allotropes, focusing on phase diagrams.
  • Explore the concept of sublimation in materials science, particularly for graphite and diamond.
  • Investigate the effects of pressure on the melting points of various materials, including diamond.
  • Study the reliability of AI-generated data and common pitfalls in AI responses regarding scientific facts.
USEFUL FOR

Material scientists, chemists, educators, and anyone interested in the properties of carbon allotropes and the challenges of AI in scientific data interpretation.

Warp
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TL;DR
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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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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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?
 
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?
 

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