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Textbooks and the online reference differ about this and there are more than two answers.

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  • $\begingroup$ Some additional information can be found here and the links within. $\endgroup$
    – Nicolau Saker Neto
    Feb 20, 2014 at 12:44
  • $\begingroup$ melting point of diamond is 3823K $\endgroup$
    – user10066
    Nov 29, 2014 at 7:26
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    $\begingroup$ I wish this question would include a question … $\endgroup$
    – Jan
    Oct 22, 2017 at 3:18
  • $\begingroup$ Liquid diamond certainly sounds cool. It even glows! $\endgroup$
    – Volker Siegel
    Mar 24, 2019 at 12:03

1 Answer 1

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Diamond (carbon) does not melt at 1 atm. It sublimes to vapor.

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).

phase diagram of carbon

Edit:

In fact, heating up diamonds at 1 atm turns them into graphite first. Only further heating would cause sublimation, as expected by observing the phase diagram. Here's a video:

http://www.youtube.com/watch?v=7L7BV3IBfFA

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  • $\begingroup$ It is 3783 K in reference books $\endgroup$
    – user3286264
    Feb 19, 2014 at 15:01
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    $\begingroup$ Note that if heating it in the atmosphere, it will burn to carbon dioxide much before it sublimates to vapour carbon. HEATING DIAMONDS IS A BAD IDEA! $\endgroup$
    – Gimelist
    Nov 29, 2014 at 8:11
  • $\begingroup$ While I understand that the phase diagram you're using is mainly focused on the high temperature and pressure region, I can't help but feel that the boundaries of the metastable region could use some fine-tuning. Taken literally, it seems to be claiming that diamond isn't (meta)stable at room temperature and pressure(!). (Apparently, the actual thermal stability limit of diamond at low pressure is about 2000 K.) $\endgroup$
    – Ilmari Karonen
    Feb 23, 2016 at 19:29
  • $\begingroup$ Definition (wikipedia): Sublimation - is the phase transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase. $\endgroup$
    – rtfminc
    May 23, 2017 at 4:30
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    $\begingroup$ Minor point: The quoted temperature conversion is mathematically correct, but in all probability no more than two digits are significant. Thus $5000 K=4700°C$. $\endgroup$
    – Oscar Lanzi
    Oct 22, 2017 at 10:01

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