Melting Wood

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jewish_scientist
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Melting Wood

Postby jewish_scientist » Mon Dec 25, 2017 11:45 am UTC

A friend asked me if wood could melt. He had heard that everything has a melting point. My answer was that it would break into its components before it could get hot enough to melt. I was wondering though if you did weird stuff with the atmosphere's chemical make up and pressure, could you get wood to melt? What are other compounds that cannot melt under normal conditions and can any of them melt under abnormal conditions?
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Re: Melting Wood

Postby Xanthir » Mon Dec 25, 2017 3:54 pm UTC

Yeah, you've basically got it right - all solids do have a melting point, but many of them will do *other* things before they hit that temperature, which removes the possibility. Wood is, like most living things, mostly just a mixture of C, H, O, and N, and many of the molecules built out of that will just combust or otherwise break down before reaching the material's theoretical melting point.
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Re: Melting Wood

Postby Eebster the Great » Mon Dec 25, 2017 9:59 pm UTC

Every chemical substance has a melting point, but wood is not a pure substance. Even if you could somehow prevent all reactions within the wood, different components would still melt and boil at different points, with many volatile compounds boiling long before many salts even melt.

Also consider that wood isn't exactly a "solid" per se. It is a complex mixture of multiple phases with the majority of the mass actually a liquid, at least unless it is very dry (and even then, it contains many liquids).

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Re: Melting Wood

Postby morriswalters » Tue Dec 26, 2017 12:09 am UTC

Nor on topic, but as an amusing experiment, heat wood at low temperatures for long enough and you can light a 2 by 4 with a kitchen match.

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Re: Melting Wood

Postby Eebster the Great » Wed Dec 27, 2017 3:01 am UTC

morriswalters wrote:Nor on topic, but as an amusing experiment, heat wood at low temperatures for long enough and you can light a 2 by 4 with a kitchen match.

That's just drying out the wood.

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Re: Melting Wood

Postby MostlyHarmless » Wed Dec 27, 2017 9:36 am UTC

jewish_scientist wrote:What are other compounds that cannot melt under normal conditions and can any of them melt under abnormal conditions?


This might be a little (a lot?) more pedantic than you were looking for, but many substances cannot melt under standard conditions (i.e., room temperature, atmospheric pressure, etc.) because they are not solid. For those substances, they can only melt if you first drop the temperature below their melting point. I wouldn't mention it (not even I'm that annoying) except that the melting point of Helium is actually 0K at standard pressure, which means that at 1 atmosphere pure helium can actually never melt. If you want to melt helium, you need to get a pressure of about 25 atmospheres first (and even then, the melting point is only a couple of Kelvin).

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Re: Melting Wood

Postby morriswalters » Wed Dec 27, 2017 10:42 am UTC

Eebster the Great wrote:
morriswalters wrote:Nort on topic, but as an amusing experiment, heat wood at low temperatures for long enough and you can light a 2 by 4 with a kitchen match.

That's just drying out the wood.
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Re: Melting Wood

Postby Eebster the Great » Wed Dec 27, 2017 5:31 pm UTC

MostlyHarmless wrote:
jewish_scientist wrote:What are other compounds that cannot melt under normal conditions and can any of them melt under abnormal conditions?


This might be a little (a lot?) more pedantic than you were looking for, but many substances cannot melt under standard conditions (i.e., room temperature, atmospheric pressure, etc.) because they are not solid. For those substances, they can only melt if you first drop the temperature below their melting point. I wouldn't mention it (not even I'm that annoying) except that the melting point of Helium is actually 0K at standard pressure, which means that at 1 atmosphere pure helium can actually never melt. If you want to melt helium, you need to get a pressure of about 25 atmospheres first (and even then, the melting point is only a couple of Kelvin).

Sure, but perhaps a better point is that many substances have a triple point at a much higher pressure than 1 atm, so they won't melt in our atmosphere either, only sublimate. You can't melt dry ice, for instance.

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Re: Melting Wood

Postby Pfhorrest » Wed Dec 27, 2017 5:43 pm UTC

What is the melting point of a human?
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Re: Melting Wood

Postby Zohar » Wed Dec 27, 2017 5:54 pm UTC

I don't know but I'm getting Raiders of the Lost Ark flashbacks.
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Re: Melting Wood

Postby MostlyHarmless » Wed Dec 27, 2017 10:23 pm UTC

Eebster the Great wrote:
MostlyHarmless wrote:
jewish_scientist wrote:What are other compounds that cannot melt under normal conditions and can any of them melt under abnormal conditions?


This might be a little (a lot?) more pedantic than you were looking for, but many substances cannot melt under standard conditions (i.e., room temperature, atmospheric pressure, etc.) because they are not solid. For those substances, they can only melt if you first drop the temperature below their melting point. I wouldn't mention it (not even I'm that annoying) except that the melting point of Helium is actually 0K at standard pressure, which means that at 1 atmosphere pure helium can actually never melt. If you want to melt helium, you need to get a pressure of about 25 atmospheres first (and even then, the melting point is only a couple of Kelvin).

Sure, but perhaps a better point is that many substances have a triple point at a much higher pressure than 1 atm, so they won't melt in our atmosphere either, only sublimate. You can't melt dry ice, for instance.


Good point. And dry ice is exactly the sort of thing you would think you could melt.

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Re: Melting Wood

Postby p1t1o » Thu Jan 04, 2018 9:20 am UTC

Pfhorrest wrote:What is the melting point of a human?


Somewhere close to zero degrees Celsius - at room temperature/pressure we are already mostly in liquid phase :)

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Re: Melting Wood

Postby LaserGuy » Thu Jan 04, 2018 9:40 pm UTC

jewish_scientist wrote:A friend asked me if wood could melt. He had heard that everything has a melting point. My answer was that it would break into its components before it could get hot enough to melt. I was wondering though if you did weird stuff with the atmosphere's chemical make up and pressure, could you get wood to melt? What are other compounds that cannot melt under normal conditions and can any of them melt under abnormal conditions?


Well, the bulk of the structure of wood is cellulose, which decomposes above 350C, and doesn't really melt in the classic sense of the term. Most of the compounds that it decomposes into are gases at that temperature... the remaining carbon will only melt above 10 atm and 3500C; otherwise it will sublimate.

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Re: Melting Wood

Postby SDK » Thu Jan 04, 2018 11:22 pm UTC

You asked for other compounds, and a common one around the house would be thermoplastics (ie: most of the hard plastics you're familiar with). They'll break down chemically before melting.
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Eebster the Great
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Re: Melting Wood

Postby Eebster the Great » Fri Jan 05, 2018 1:27 am UTC

Isn't lignin also a major component? I don't know too much about plant chemistry. Of course, the result is similar. As you heat it, it will decompose into a wide variety of organic compounds, most of them simple. Some will be volatile and boil almost immediately, others more slowly, and still others will remain as liquids or solids until the temperature is increased further. I don't think you will actually end up with any elemental carbon (or at least not much), but maybe in a vacuum that could happen.

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Re: Melting Wood

Postby Pfhorrest » Fri Jan 05, 2018 1:32 am UTC

Isn't coal basically melted and refrozen wood? (Only made possible because of extreme pressure).
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Re: Melting Wood

Postby morriswalters » Fri Jan 05, 2018 2:20 am UTC

I always thought of melting as a phase change, where you end with the same thing you began with in a different state. Say for instance some waxy substances whose name plumb eludes me. Wait, paraffin. Carry on.

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Re: Melting Wood

Postby p1t1o » Fri Jan 05, 2018 11:56 am UTC


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Re: Melting Wood

Postby jewish_scientist » Sun Jan 07, 2018 12:29 am UTC

I am confused. In that article's abstract, it never says that they actually melted cellulose. It just says that they made cellulose into really thin disks and then analyzed them.
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