# Why doesn't wood melt? Cecil? Wrong?! **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [May 30, 2008, 6:33pm UTC](https://boards.straightdope.com/t/why-doesnt-wood-melt-cecil-wrong/451178 "2008-05-30T18:33:24Z")\ **Posts on this page:** 17\ **Page:** 2
**Author:** ![Captain\_Awesome](https://avatars.discourse-cdn.com/v4/letter/c/a698b9/32.png) [@Captain\_Awesome](https://boards.straightdope.com/u/Captain_Awesome)\ **Post date:** [August 21, 2009, 9:49am UTC](https://boards.straightdope.com/t/why-doesnt-wood-melt-cecil-wrong/451178/21 "2009-08-21T09:49:19Z")
> [@Uncertain](#): > > It seems to me that in a “vacuum”, at equilibrium carbon would be a gas at any temperature (anything would). I put “vacuum” in quotes because the gas would necessarily make it not a vacuum. But it could be at as low a pressure as you like. However, the equilibrium would, at sufficiently low temperature, take a long time to reach. Nope. Where it is not thermodynamically favoured it will not become a gas, regardless of the time component. If you leave a solid lump of gold in a vacuum for infinity, and then come back and check on it, it will still be a solid lump of gold. ---
**Author:** ![Uncertain](https://avatars.discourse-cdn.com/v4/letter/u/6a8cbe/32.png) [@Uncertain](https://boards.straightdope.com/u/Uncertain)\ **Post date:** [August 21, 2009, 4:09pm UTC](https://boards.straightdope.com/t/why-doesnt-wood-melt-cecil-wrong/451178/22 "2009-08-21T16:09:14Z")
> [@Captain\_Awesome](#): > > Nope. Where it is not thermodynamically favoured it will not become a gas, regardless of the time component. But it _is_ thermodynamically favored at sufficiently low pressure, regardless of the temperature. Another way to look at it is that graphite has nonzero vapor pressure at any temperature. If the pressure remains below that vapor pressure, the gas is thermodynamically favored. This has to do with the fact that the vapor is dilute, which decreases its chemical potential; in the vacuum limit, it’s infinitely dilute. It’s no different from the fact that liquid water will boil at room temperature if the pressure is sufficiently low, and ice will sublimate. > [@](#): > > If you leave a solid lump of gold in a vacuum for infinity, and then come back and check on it, it will still be a solid lump of gold. Not so. Provided that the pressure is kept sufficiently low, it will be gold vapor (you do buy this for ice kept below the freezing point, right?). The pressure will have to be damn low–the vapor pressure of gold is miniscule–but we’re talking about vacuums. It might be that you’d need an evacuated box the size of Jupiter to pull this off, but that’s irrelevant to the thermodynamic question. ---
**Author:** ![DSYoungEsq](https://avatars.discourse-cdn.com/v4/letter/d/c6cbf5/32.png) [@DSYoungEsq](https://boards.straightdope.com/u/DSYoungEsq)\ **Post date:** [August 21, 2009, 4:31pm UTC](https://boards.straightdope.com/t/why-doesnt-wood-melt-cecil-wrong/451178/23 "2009-08-21T16:31:17Z")
> [@Uncertain](#): > > But it _is_ thermodynamically favored at sufficiently low pressure, regardless of the temperature. > > Another way to look at it is that graphite has nonzero vapor pressure at any temperature. If the pressure remains below that vapor pressure, the gas is thermodynamically favored. This has to do with the fact that the vapor is dilute, which decreases its chemical potential; in the vacuum limit, it’s infinitely dilute. It’s no different from the fact that liquid water will boil at room temperature if the pressure is sufficiently low, and ice will sublimate. > > Not so. Provided that the pressure is kept sufficiently low, it will be gold vapor (you do buy this for ice kept below the freezing point, right?). The pressure will have to be damn low–the vapor pressure of gold is miniscule–but we’re talking about vacuums. It might be that you’d need an evacuated box the size of Jupiter to pull this off, but that’s irrelevant to the thermodynamic question. Are you asserting that there can be no solids in equilibrium in vacuum? Substitute for “vacuum” the word “space” and I’m having trouble accepting this as being true… ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 21, 2009, 4:35pm UTC](https://boards.straightdope.com/t/why-doesnt-wood-melt-cecil-wrong/451178/24 "2009-08-21T16:35:21Z")
I think that gets back to the point about it taking a really long time to reach equilibrium. Looking at it on a micro-scale, if you have a lump of anything, at any temperature above absolute zero, occasionally you’ll get a particle of it way out in the tail of the thermal distribution that has enough energy to break free. But if you’re in a true vacuum, then once a particle breaks free, there’s no reason for it to ever come back. So yes, eventually anything will sublimate away. ---
**Author:** ![Captain\_Awesome](https://avatars.discourse-cdn.com/v4/letter/c/a698b9/32.png) [@Captain\_Awesome](https://boards.straightdope.com/u/Captain_Awesome)\ **Post date:** [August 21, 2009, 4:54pm UTC](https://boards.straightdope.com/t/why-doesnt-wood-melt-cecil-wrong/451178/25 "2009-08-21T16:54:29Z")
> [@Uncertain](#): > > But it _is_ thermodynamically favored at sufficiently low pressure, regardless of the temperature. Not at 0K. Wait till the end of time and the lump of graphite, or gold, will still be there. ---
**Author:** ![John\_W.Kennedy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_w.kennedy/32/1031_2.png) [@John\_W.Kennedy](https://boards.straightdope.com/u/John_W.Kennedy)\ **Post date:** [August 21, 2009, 5:36pm UTC](https://boards.straightdope.com/t/why-doesnt-wood-melt-cecil-wrong/451178/26 "2009-08-21T17:36:25Z")
> [@Captain\_Awesome](#): > > Not at 0K. Wait till the end of time and the lump of graphite, or gold, will still be there. That depends on whether any of the various baryon-decay hypotheses are true. By the way, my CRC handbook (I also have my mother’s from the 30s) is the last edition that was printed in actual handbook size. It’s almost cubical, which is why they switched the next year to octavo. ---
**Author:** ![Uncertain](https://avatars.discourse-cdn.com/v4/letter/u/6a8cbe/32.png) [@Uncertain](https://boards.straightdope.com/u/Uncertain)\ **Post date:** [August 21, 2009, 9:52pm UTC](https://boards.straightdope.com/t/why-doesnt-wood-melt-cecil-wrong/451178/27 "2009-08-21T21:52:20Z")
> [@Captain\_Awesome](#): > > Not at 0K. Wait till the end of time and the lump of graphite, or gold, will still be there. I’ll forgo a discussion of what happens at that unattainable temperature and just say this: so what? Perhaps I should have said “at any nonzero temperature”, but my point stands (and your “nope” response puts no constraints on temperature either). ---
**Author:** ![Uncertain](https://avatars.discourse-cdn.com/v4/letter/u/6a8cbe/32.png) [@Uncertain](https://boards.straightdope.com/u/Uncertain)\ **Post date:** [August 21, 2009, 10:09pm UTC](https://boards.straightdope.com/t/why-doesnt-wood-melt-cecil-wrong/451178/28 "2009-08-21T22:09:27Z")
> [@DSYoungEsq](#): > > Are you asserting that there can be no solids in equilibrium in vacuum? Substitute for “vacuum” the word “space” and I’m having trouble accepting this as being true… Well, you can accept it as true for ice, right? And solid CO2. The solids we’ve been discussing have much lower vapor pressures, which makes this less of a practical issue, but the same principle applies. We need to make sure that the pressure stays sufficiently low despite the sublimation of the solid. In a textbook piston and cylinder experiment with a lump of gold, at sufficiently low pressure all you’ll have is gold vapor (well, there’s the issue, usually idealized away, that the cylinder itself is made of something with its own vapor pressure). You’ll need a really big cylinder though. This is according to classical phase diagram thinking. I don’t pretend to know about low-temperature effects that depend on whether the atoms are bosons or fermions, or whether the gold will eventually transmutate to other elements or decay to neutrons. ---
**Author:** ![Captain\_Awesome](https://avatars.discourse-cdn.com/v4/letter/c/a698b9/32.png) [@Captain\_Awesome](https://boards.straightdope.com/u/Captain_Awesome)\ **Post date:** [August 21, 2009, 10:47pm UTC](https://boards.straightdope.com/t/why-doesnt-wood-melt-cecil-wrong/451178/29 "2009-08-21T22:47:17Z")
> [@Uncertain](#): > > I’ll forgo a discussion of what happens at that unattainable temperature and just say this: so what? Perhaps I should have said “at any nonzero temperature”, but my point stands (and your “nope” response puts no constraints on temperature either). Well I wasn’t initially considering the question in terms of infinity. I was dealing in a human reference frame. Yes it stands where the vapour pressure is non-zero, \>0K, you’d end up with a gas at infinity, neglecting other crazy phenomena. Regardless, graphite it still floating about in the vacuum of space and makes sense on phase diagrams drawn for non-infinite time-scales. ---
**Author:** ![DSYoungEsq](https://avatars.discourse-cdn.com/v4/letter/d/c6cbf5/32.png) [@DSYoungEsq](https://boards.straightdope.com/u/DSYoungEsq)\ **Post date:** [August 22, 2009, 1:12am UTC](https://boards.straightdope.com/t/why-doesnt-wood-melt-cecil-wrong/451178/30 "2009-08-22T01:12:03Z")
> [@Uncertain](#): > > Well, you can accept it as true for ice, right? And solid CO2. Given that they are talking about finding ice on the moon, no, I’m having some trouble with this, though I could suppose that the lack of a breeze will keep the water vapor from moving away, thus affecting the situation. > [@](#): > > The solids we’ve been discussing have much lower vapor pressures, which makes this less of a practical issue, but the same principle applies. > > We need to make sure that the pressure stays sufficiently low despite the sublimation of the solid. In a textbook piston and cylinder experiment with a lump of gold, at sufficiently low pressure all you’ll have is gold vapor (well, there’s the issue, usually idealized away, that the cylinder itself is made of something with its own vapor pressure). You’ll need a really big cylinder though. > > This is according to classical phase diagram thinking. I don’t pretend to know about low-temperature effects that depend on whether the atoms are bosons or fermions, or whether the gold will eventually transmutate to other elements or decay to neutrons. If you are telling me that, given something substantially more than the few billion years since the formation of the solar system, the rocks floating around in it would eventually sublimate into rock vapor and stop being solid, then I will simply say that such a discussion is meaningless. If you can assert that this would happen in a much shorter period of time, say, over the course of half the time the solar system has existed, then let’s discuss this as being “true.” ---
**Author:** ![Uncertain](https://avatars.discourse-cdn.com/v4/letter/u/6a8cbe/32.png) [@Uncertain](https://boards.straightdope.com/u/Uncertain)\ **Post date:** [August 22, 2009, 3:23am UTC](https://boards.straightdope.com/t/why-doesnt-wood-melt-cecil-wrong/451178/31 "2009-08-22T03:23:38Z")
> [@DSYoungEsq](#): > > Given that they are talking about finding ice on the moon, no, I’m having some trouble with this, though I could suppose that the lack of a breeze will keep the water vapor from moving away, thus affecting the situation. I was expecting this one to be uncontroversial. That’s how freeze drying works: you freeze stuff, and pull a vacuum, and the ice turns to vapor. Snow sublimating is a similar phenomenon (the total pressure is not so low, but the partial pressure of water in the atmosphere is below the frost point). This is a very real thing that doesn’t involve waiting for millenia. > [@](#): > > If you are telling me that, given something substantially more than the few billion years since the formation of the solar system, the rocks floating around in it would eventually sublimate into rock vapor and stop being solid, then I will simply say that such a discussion is meaningless. If you can assert that this would happen in a much shorter period of time, say, over the course of half the time the solar system has existed, then let’s discuss this as being “true.” I think that sublimation of planets is indeed a ludicrously slow process, although it’s complicated by deposition of new material. But let’s get back to the wood question. I don’t know how long it would take for graphite to sublimate at several thousand Kelvins. I did say it might take a long time, and others said it wouldn’t happen (with gold) even given infinite time. ---
**Author:** ![Civil\_Guy](https://avatars.discourse-cdn.com/v4/letter/c/d78d45/32.png) [@Civil\_Guy](https://boards.straightdope.com/u/Civil_Guy)\ **Post date:** [August 22, 2009, 3:27am UTC](https://boards.straightdope.com/t/why-doesnt-wood-melt-cecil-wrong/451178/32 "2009-08-22T03:27:32Z")
Erm. I really shouldn’t get into this - I’m no expert in planetary dynamics at all. (I got good chemistry grades in college, but it was a state college, and so what? I’ve forgotten it all, mostly.) But it seems to me that there’s one word that no one’s mentioned yet: gravity. Sublimation aside, however many molecules per fortnight, those sublimated molecules will still be attracted to the original mass they were released from, and thus will be that much more likely to re-acrete as to walk off anywhere - would that explain any of the dilema here? ---
**Author:** ![Captain\_Awesome](https://avatars.discourse-cdn.com/v4/letter/c/a698b9/32.png) [@Captain\_Awesome](https://boards.straightdope.com/u/Captain_Awesome)\ **Post date:** [August 22, 2009, 9:12am UTC](https://boards.straightdope.com/t/why-doesnt-wood-melt-cecil-wrong/451178/33 "2009-08-22T09:12:28Z")
To put it into some sort of perspective, if you take the average carbon content of a piece of 2x4 (weighing approx. 10.24 lbs, or 4.64 kg, of which _c_. 52% is carbon for a pine) my calculations based on an ideal, theoretical model suggests it’ll take _c_. 63.5 million years to completely sublime at 1850K, and stupidly longer at lower T. The force of gravity between the atomised carbon and the 2x4 is trivial compared to the vacuum, though re-condensation will occur in any experimental set-up on Earth, so the actual rate will be slightly slower than the theoretical predicted here. ---
**Author:** ![Normal\_Phase](https://avatars.discourse-cdn.com/v4/letter/n/5f9b8f/32.png) [@Normal\_Phase](https://boards.straightdope.com/u/Normal_Phase)\ **Post date:** [August 22, 2009, 1:56pm UTC](https://boards.straightdope.com/t/why-doesnt-wood-melt-cecil-wrong/451178/34 "2009-08-22T13:56:05Z")
> [@John\_W.Kennedy](#): > > I’d still like to know why my CRC _Handbook_ gives Carbon a melting point. Me, too. CRC wrong? My life has lost its purpose. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 22, 2009, 3:54pm UTC](https://boards.straightdope.com/t/why-doesnt-wood-melt-cecil-wrong/451178/35 "2009-08-22T15:54:34Z")
> [@](#): > > Sublimation aside, however many molecules per fortnight, those sublimated molecules will still be attracted to the original mass they were released from, and thus will be that much more likely to re-acrete as to walk off anywhere - would that explain any of the dilema here? It’ll slow down the process, certainly, but it won’t stop it. Just as you’ll occasionally get a particle far enough out in the tail of the distribution that it’ll overcome the intermolecular bonds, you’ll also occasionally get one that’s above the gravitational escape speed. ---
**Author:** ![DSYoungEsq](https://avatars.discourse-cdn.com/v4/letter/d/c6cbf5/32.png) [@DSYoungEsq](https://boards.straightdope.com/u/DSYoungEsq)\ **Post date:** [August 22, 2009, 9:34pm UTC](https://boards.straightdope.com/t/why-doesnt-wood-melt-cecil-wrong/451178/36 "2009-08-22T21:34:33Z")
> [@Uncertain](#): > > I was expecting this one to be uncontroversial. That’s how freeze drying works: you freeze stuff, and pull a vacuum, and the ice turns to vapor. Snow sublimating is a similar phenomenon (the total pressure is not so low, but the partial pressure of water in the atmosphere is below the frost point). This is a very real thing that doesn’t involve waiting for millenia. Not meaning to be snarky here, truly not. How, then, can there be ice on the moon? 😕 > [@](#): > > I think that sublimation of planets is indeed a ludicrously slow process, although it’s complicated by deposition of new material. Let’s not talk planets, then. Let’s talk a small hunk of rock asteroid, say, oh, 50m in radius. > [@](#): > > I did say it might take a long time, and others said it wouldn’t happen (with gold) even given infinite time. Fair enough; perhaps they aren’t thinking about what infinite truly means. 😃 ---
**Author:** ![dracoi](https://avatars.discourse-cdn.com/v4/letter/d/90db22/32.png) [@dracoi](https://boards.straightdope.com/u/dracoi)\ **Post date:** [August 22, 2009, 10:28pm UTC](https://boards.straightdope.com/t/why-doesnt-wood-melt-cecil-wrong/451178/37 "2009-08-22T22:28:10Z")
> [@DSYoungEsq](#): > > Not meaning to be snarky here, truly not. How, then, can there be ice on the moon? 😕 Here’s an article talking about [water ice sublimation in comets](http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V6T-3Y21V17-F&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=987820490&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=86d9173b9892f6a10540c7de686a410d). Alas, no details are available without paying for them, but it shows that sublimation does happen and that it is not a trivial thing to calculate. In reference to the moon, I’m sure a certain amount of ice is replenished both from cosmic impacts and from the Earth. Volcanoes can throw rocks out of orbit and I’m sure they’ve done so with a few chunks of ice too. But I do think it’s noteworthy that the Moon isn’t covered evenly with ice. The ice that’s there is surviving for a reason. And, to revisit black holes: they sublimate too (if Hawking radiation can be considered sublimation). So if even black holes are losing minuscule amounts mass into vacuum, I think it’s safe to assume that everything else is too. [Previous page](https://boards.straightdope.com/t/why-doesnt-wood-melt-cecil-wrong/451178.md?page=1)