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I tried to burn a bunch of 8B pencil lead in a gas flame the other day. None of it actually caught fire, but being made of carbon (in the form of graphite) should cause it to burn, as graphite is essentially purified coal. What temperature is required to set it burning, and is extra oxygen required?

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    $\begingroup$ Well, it depends. I was easily able to ignite graphite by using point 5 - point 9 lead, using a simple concoction of alligator clips (Copper) holding up the lead, and connecting it to a mere 18 volts of energy! $\endgroup$ – user40353 Jan 24 '17 at 20:33
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    $\begingroup$ 8B (the softest lead) contains about 15 % clay. $\endgroup$ – Loong Jan 24 '17 at 21:09
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    $\begingroup$ @user40353 if it didn't continue glowing after removing the electricity then it wasn't really "burning", just oxidizing endothermically. $\endgroup$ – sadljkfhalskdjfh Jan 25 '17 at 0:10
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    $\begingroup$ Nothing endothermic about graphite oxidation. $\endgroup$ – Curt F. Sep 21 '17 at 12:43
  • $\begingroup$ Curt F. I should have said "dissipating more energy than it liberates" $\endgroup$ – sadljkfhalskdjfh Oct 8 '17 at 12:39
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You have two problems.
1.) pencil lead graphite is actually a graphite-clay composite.
2.) carbon does not sustain burning easily unless it is held at very high temperatures.

Pencil lead will not burn effectively for the first reason as clay is non-combustible and smothers any fire load. If you did have pure graphite to burn, a simple flame wouldn't be hot enough to combust it. You need to sustain temperatures of around $1000\mathrm{-}2000~^\circ\mathrm{C}$ in order for pure carbon to burn.

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    $\begingroup$ Probably worth noting that the situation would change if you could enrich the air with oxygen. $\endgroup$ – Curt F. Jan 24 '17 at 21:22
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    $\begingroup$ @CurtF. Eh, not really. Graphite is heavily used in glassblowing/lampworking. Those flames are oxygen/propane flames and you can put chunks of solid graphite directly into the flame without any obvious combustion occurring. You might get a bit from carbon dust, but the block doesn't degrade at all. $\endgroup$ – Necoras Sep 20 '17 at 20:55
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    $\begingroup$ Is a flame really an oxygen-enriched environment? Also, my.rsc.org/video/318 $\endgroup$ – Curt F. Sep 21 '17 at 12:53
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It’s all in the bonds. It doesn’t matter what you have, if it is in a tight covalent bond structure it is going to take a lot of input energy to trigger oxidation. What many people don’t understand is that anything can burn unless it has already been fully burned. Other than that, you can burn it, no questions ask. Eventually, with a high input energy, graphite carbon will tear off its tight covanent structure and pick up some oxygen, but that might take a lot more energy than the reaction will release, meaning that you probably won’t get a self sustained combustion flame going. No cool fire, but definitely some toxic CO and CO2 and some very hot carbon!

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protected by Loong Apr 26 '18 at 15:44

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