Following a personal message from pnacze199204, here's an attempted estimation of carbon's vapour pressure at room temperature.
From Wiki's https://en.wikipedia.org/wiki/Vapor_pressures_of_the_elements_(data_page
) Press Temp Activation
Much can go horribly wrong:
- Data is for graphite. But diamond is only 1.9kJ/mol away, or 0.8×298K. Less than one magnitude error, my least concern here. It could even be computed away.
- Huge extrapolations use to fail the big way.
- Wiki doesn't tell if the vapour is C1, C2, C3 or C4. This open question changes completely the activation energy.
What encourages me to go on:
- The activation energy isn't constant in Wiki's data, which could be experimental hence.
- The activation energy (793kJ at 10Pa-100Pa) resembles the vaporisation enthalpy Hv (717kJ/mol for C1 at RT according to the CRC Hdbk of Chem&Phys)
So let's imagine that C1
evaporates at RT and that 95334K activation energy applies. For C1
it can't be very
different from Hv
anyway, but that difference makes magnitudes on the pressure. An improvement would take the experimental heat capacity of graphite or diamond, the theoretical heat capacity of C1
, and correct the heat of vaporisation over the temperature range - feel free to do it, I won't.
Then the extrapolated graphite vapour C1
pressure at 298K is, tadaa,10-124×10Pa
which is sub-nothing.
The rate of evaporation isn't measurable at 298K. Take 103
J/mol mean kinetic energy perpendicular to a diamond surface, then 10-2
kg C have mean 103
m/s and 10-23
kg×m/s momentum per vapour molecule, so 10-124
Pa suggest 10-101
. This model is knowingly wrong by 0 to 2 magnitudes.
Even if some means measures individual gaseous carbon atoms, it won't see any single gas atom in years
. But it would be a funny experiment at temperatures less cold, perhaps by ionisation and mass spectroscopy.
And if a diamond is 10-3
thick, evaporation in all directions takes
s = 10120yr
I'm confident that a decent cosmic ray
rips one carbon atom off. That's hugely faster than 10-101
evaporation. Ozone and nitrogen oxides are faster too, as we see at rubber.