B Why is Carbon considered volatile?

[Qshadow]

TL;DR Summary

Why Carbon is considered volatile in spite of its very high sublimation point?

Carbon is considered volatile by planetary science, eg Moon lacks volatiles and thus lacks carbon. However volatiles are defined as "elements or substances with low boiling point", but Carbon boiling point is very high! Its sublimation point is 3900K, so it should be refractory and not volatile.
I am confused why it is volatile with such high sublimation point.
Regards, Alex

 

[hutchphd]

Lacking a specific reference one can only surmise that "planetary science" is talking about hydrocarbons.

 

[Qshadow]

Lacking a specific reference one can only surmise that "planetary science" is talking about hydrocarbons.

I do not think they refer only to hydrocarbons, here are some links:
https://www.sciencedirect.com/science/article/abs/pii/0079194677900064
https://ui.adsabs.harvard.edu/abs/2017AGUFM.V22A..01M/abstract
https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/96GL03931

all these papers talk about Carbon as element and not it's particular compounds (be it hydrocarbons, or CO, CO2).
It is like Carbon behaves al volatile always even in elemental form.

 

[hutchphd]

I believe much is in the form of carbonaceous Chondrites. After you read the article you will know as much as I do...carbon is very gregarious!

 

[Bandersnatch]

I've only done some cursory reading. From what I see, it would appear that carbon in planetary sciences is treated as a volatile because it readily forms compounds that then outgas from magma (or crust in general).
Similar to how 'carbon' in climate science refers to all carbon-containing greenhouse gasses, even though none of them is elemental carbon.
The third source linked above (the only one not behind a paywall) talks about the uncertainty of what form does the carbon took (in 'the early surface volatiles' section).
The one below appears to be discussing speciation of magmatic volatiles, i.e. what forms does e.g. carbon take under different chemical conditions:
https://www.sciencedirect.com/science/article/abs/pii/S0016703720302763
This paper (section V) talks about carbon as a volatile that is 'stored' in magma as e.g. diamond and then outgassed as CO2.
http://www.geo.mtu.edu/EHaz/ConvergentPlatesClass/wallace/Wallace & Anderson (1999).pdf

 

[stefan r]

If you mix graphite with magma you will get carbon monoxide and carbon dioxide gas. Steel is made by taking iron oxide ore and mixing it with coke. Graphite will also react with water to form hydrogen and carbon monoxide, carbon dioxide, hydrocarbons and/or carbohydrates depending on temperature and pressure.

A chunk of graphite sitting on the moon's surface will be bombarded by solar wind particles. The graphite is not subliming. It would be adsorbing and reacting with hydrogen or oxygen and then gassing off.