30-May-2008: Why doesn’t wood melt? Does it still cost less than one cent to mint a penny?
No it wouldn’t. There exists no liquid phase of carbon below its triple point pressure of about 10 megapascals, least of all in a vacuum.
You had to look it up, Mr. Adams, didn’t you? Well I don’t blame you, there’s still a lot of ignorance to fight. Even reputable and relatively recent textbooks get this wrong half of the time and stubbornly list a normal melting point.
Never mind textbooks, my old Handbook gives a melting point for carbon. If you can’t trust C.R.C., whom can you trust?
(Come to think of it, shouldn’t the allotrope make a difference? Of course, in this case, it would be graphite.)
Never mind melt, why wouldn’t wood in a vacuum sublime at room temperature?
Because if the answer was “It doesn’t melt, it sublimates, like CO[sub]2[/sub].” that wouldn’t make for much of a column, would it?
I haven’t had a chemistry class since Community College, but I’d guess there’s a technical distinction between sublimation and decomposition. Certainly, “sublimation” is closer to what’s going on than “melting”.
That’s a good question. I guess wood is made of polymers, and those have a hard time just picking up into the air.
We use the term “melting” for a reversible phase change without chemical transformation. Wood is a mixture of many different substances. As you heat up wood, cellulose and lignin, the main polymers that give wood its mechanical strength, will undergo chemical transformations long before they would melt. When you heat up wood in the absence of oxygen, you can obtain a black viscous liquid, wood tar. However, I would not call this “melted wood”, as it contains many components that are the products of pyrolytic destruction of the original substances in the wood.
In other words, “frozen melted wood” != wood.
Do buckyballs (C60) have a liquid phase in the absence of oxygen?
I suspect C60 would turn to graphite before it melted.
What would you define as melted wood? I’ve been making violins for 30 years and i know that if you get wood hot enough, preferably a wet steamy heat,it becomes remarkably plastic, and when it cools it retains its new shape for 100’s of years. Using steaming and laminating with modern adhesives large load bearing structures can be formed. People have been melting wood for a long time.
The phase diagram for carbon can be seen here (Bernasconi et al. 1989), demonstrating that in a vacuum, suggested by Cecil, it would instead sublimate at c. 4200K (3927 degrees centigrade).
Wood decomposes before it melts.
martin andrews, while the process you describe is fascinating and does make wood more flexible, it is not melting.
Just because lead can be deformed at room temperature does not mean it has melted. Same with deforming wood.
I’d still like to know why my CRC Handbook gives Carbon a melting point.
John,
Do you believe the rubber bible is the inerrant word of god?
Well carbon does have a melting point, albeit pressure dependent and not one that exists at less than c. 100 bar. Presumably there’s no usage note given in your handbook? Sounds like reasonable grounds for writing a letter of complaint to the London Times.
It’s damned well supposed to be. Hmmph!
I still treasure my rubber bible*, even though Google has made it almost obsolete.
If he points out any errors you’ll just stretch it until it fits. Criticism of the rubber bible just bounces right off.
Not as obsolete as you might think-- Our department is currently suffering from a CRC shortage. Every year, come time for the Comprehensive Exam, the department puts out a call for CRCs to borrow, for use by the poor schlubs taking the test. This year, there weren’t enough to go around.
Unfortunately, I can’t help on this one: My CRC is the massive Chemistry and Physics tome, and it’s the Mathematics one they want for the comps.
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.