The physical properties of diamonds: no melting point?

In summary, the substance in this case is not a diamond, but rather it is charcoal. There is no melting point, and the transition from solid to gaseous state is called sublimation.
  • #1
h_hin
6
2
I had heard an opinion from my high school teacher, but I can't understand??

"An experimental record of a French scientist.
He heats the diamond and sublimates it. After cooling, it turns back to solid barbecue carbon.
In this case, although there is a physical transition, the substance seems to be a chemical change.
This is just my personal opinion: the physical properties of diamonds are not suitable for describing as melting point"

What?
No melting point how it transition??
 
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  • #2
Sublimation means it went directly from solid to gaseous state. There was no liquid state of the carbon in this case. Upon cooling of the gaseous carbon, it didn't make a diamond crystal, but rather simply charcoal. ## \\ ## I think there might exist a liquid form of carbon, but it would require enormous pressures to exist in the liquid state.
 
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  • #3
Charles Link said:
Sublimation means it went directly from solid to gaseous state. There was no liquid state of the carbon in this case.
get it,but is it good for describing diamond as no melting point?
 
  • #4
h_hin said:
get it,but is it good for describing diamond as no melting point?
See my added comment above about the liquid state. At 1.0 atmosphere, there is only a solid to vapor transition. The same is true for carbon dioxide. I believe ## CO_2 ## requires about 5 atmospheres in order to produce a liquid state. Let me see if I can get a phase diagram of ## CO_2 ##: https://chem.libretexts.org/Textbook_Maps/General_Chemistry/Map:_General_Chemistry_(Petrucci_et_al.)/12:_Intermolecular_Forces:_Liquids_And_Solids/12.4:_Phase_Diagrams ## \\ ## See also https://en.wikipedia.org/wiki/Carbon It lists the triple point of Carbon as 10.8 MPa which is about 100 atmospheres of pressure. For pressures below this, there is no liquid phase of carbon.
 
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  • #5
Charles Link said:
See my added comment above about the liquid state. At 1.0 atmosphere, there is only a solid to vapor transition. The same is true for carbon dioxide. I believe ## CO_2 ## requires about 5 atmospheres in order to produce a liquid state. Let me see if I can get a phase diagram of ## CO_2 ##: https://chem.libretexts.org/Textbook_Maps/General_Chemistry/Map:_General_Chemistry_(Petrucci_et_al.)/12:_Intermolecular_Forces:_Liquids_And_Solids/12.4:_Phase_Diagrams ## \\ ## See also https://en.wikipedia.org/wiki/Carbon It lists the triple point of Carbon as 10.8 MPa which is about 100 atmospheres of pressure. For pressures below this, there is no liquid phase of carbon.

okay get it all,thanks!
 
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FAQ: The physical properties of diamonds: no melting point?

What makes diamonds unique in terms of their physical properties?

Diamonds are unique because they are the hardest known naturally occurring substance on Earth. They also have a very high refractive index and are excellent conductors of heat and electricity.

Why do diamonds have no melting point?

Diamonds have no melting point because they are made up of a single element, carbon, which has a very high melting point of 3550°C. At atmospheric pressure, diamonds will instead undergo sublimation, meaning they will transition directly from a solid to a gas without passing through a liquid state.

Can diamonds be destroyed by heat?

No, diamonds cannot be destroyed by heat. They have a very high thermal conductivity, meaning they can dissipate heat quickly and efficiently. This makes them highly resistant to damage or destruction from heat.

How do diamonds behave under extreme temperatures?

Under extreme temperatures, diamonds will undergo graphitization, which is the conversion of diamond into graphite. This process occurs at temperatures above 2000°C and is irreversible.

Are there any other substances that share the same properties as diamonds?

No, there are no other substances that share the same combination of physical properties as diamonds. While some materials may have similar hardness or conductivity, diamonds are unique in their combination of hardness, refractive index, and thermal conductivity.

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