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Author Topic: Why do metals melt, but not, for example, wood?  (Read 15496 times)

Offline Seany

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Why do metals melt, but not, for example, wood?
« on: 27/04/2007 20:52:58 »
Why do things like wood not melt? What is it, that stops it from melting? Metals, plastic, they melt! ;D
« Last Edit: 16/06/2007 11:47:37 by chris »


 

another_someone

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Re: Why do metals melt, but not, for example, wood?
« Reply #1 on: 27/04/2007 21:06:51 »
It is not that metals melt and wood does not, it is that as you heat wood it decomposes before if gets hot enough to melt, while all elements (including all elemental metals), and many other substances, will melt before they decompose.

Again, it is inappropriate to regard all plastics as doing anything - there are many plastics that will decompose before they melt, but many other plastics that will melt without decomposing.

Carbon dioxide is an interesting one, because at normal atmospheric pressure, it will vaporise before it melts, so goes straight from the solid phase to the gas phase.
 

Offline Batroost

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Re: Why do metals melt, but not, for example, wood?
« Reply #2 on: 27/04/2007 21:07:26 »
Metal and platic are (often) singel materials. Their behaviour as temperature rises is easy to see. Either tehy will melt, burn, decompose or evaporate (have I forgotten athything?) - but you'll be able to observe it because you're only looking at one thing.

Wood is not an homogenous material. Instead it is made up of a mixture of fluids and more robust materials such as cellulose and lignin. Some of the materials may well melt as the temperature rise but others will ignite or evaporate producing a lot of gas. It's difficult to sort out the mess when you are looking at it....
 

Offline Seany

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Re: Why do metals melt, but not, for example, wood?
« Reply #3 on: 27/04/2007 23:01:10 »
Thanks George and Batoost! The explanation was great ;)
 

jolly

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Re: Why do metals melt, but not, for example, wood?
« Reply #4 on: 30/04/2007 01:06:28 »
I think its all in how you look at it as plastic, metal and wood all create fire when heated and change through heating both metal and plastic lose parts of there structure from heating/melting as does wood- it becomes charcoal.
I think they all melt they just act in different ways as they melt because of there atomic make-up.
Plastic and metal after melting do not return to the same form the were before melting- as they lose somthing in the process.
Therefore I would say they all melt.
 

Offline lightarrow

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Re: Why do metals melt, but not, for example, wood?
« Reply #5 on: 30/04/2007 08:43:52 »
I think its all in how you look at it as plastic, metal and wood all create fire when heated and change through heating both metal and plastic lose parts of there structure from heating/melting as does wood- it becomes charcoal.
I think they all melt they just act in different ways as they melt because of there atomic make-up.
Plastic and metal after melting do not return to the same form the were before melting- as they lose somthing in the process.
Therefore I would say they all melt.
What I have coloured in red is wrong. You have never tried to melt a little piece of tin or lead or tin-lead soldering alloy?
Science is not based on subjective ideas; you should start to read some book one day or another.
« Last Edit: 30/04/2007 08:46:17 by lightarrow »
 

jolly

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Re: Why do metals melt, but not, for example, wood?
« Reply #6 on: 30/04/2007 09:16:08 »
hello I have worked in a steal mill- I worked there for two years and I am telling you now that any metal melted in liquid form once it has returned to solid does not have the same atomic structure-
It does in affect lose something in the heating process just because it still looks shiny and simlier does not mean it is the same as before it was heated.
In the mill we used to add all kinda of stuff to make it stronger or weaker depending on what type of steal your trying to form.
For example just melting it will naturally remove some carbon- so you add loads to help it maintain its strenght- they then run it down to the lab to check its structure. They had about 5 main types of steal they used where I worked; each suited to a different task- But there are thousands.   
« Last Edit: 30/04/2007 10:29:26 by jolly »
 

paul.fr

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Re: Why do metals melt, but not, for example, wood?
« Reply #7 on: 30/04/2007 10:43:02 »
what about memory metals, and plastics?
 

another_someone

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Re: Why do metals melt, but not, for example, wood?
« Reply #8 on: 30/04/2007 13:28:00 »
what about memory metals, and plastics?

Memory metals and plastics are not brought to melting point in order to return to their original shape.

As far as I can understand what Jolly has written, there seems to be a confusion between melting and any phase change undertaken by a material.  Clearly there are many different phase changes that a material can undergo, and one cannot simply label them all as melting.
« Last Edit: 30/04/2007 16:30:56 by another_someone »
 

paul.fr

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Re: Why do metals melt, but not, for example, wood?
« Reply #9 on: 30/04/2007 15:42:16 »


Memory metals and plastics are not brought to melting point in order to return to their original shape.

my error, George. i am having trouble understanding what is being gotten at here.

as you say, memory metals are not returned to their original state through melting, but through the application of heat.
 

Offline Bored chemist

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Re: Why do metals melt, but not, for example, wood?
« Reply #10 on: 30/04/2007 20:11:47 »
"hello I have worked in a steal mill- I worked there for two years and I am telling you now that any metal melted in liquid form once it has returned to solid does not have the same atomic structure- !
How long do you need to work in a steel mill to learn how to spell it?

Anyway, some metals have a number of crystal forms and melting and recasting may change the crystal structure and, therefore, the properties. The annealing, quenching and tempering of steel make a good example. For many if not most metals you don't get this complexity; what you get is the crystalline solid first time you melt it or any subsequent time.  These changes are nothing to do with the atomic structure- that stays the same every time, blast furnaces are not nuclear reactors. What changes is the arrangement of the atoms in the crystal.
In principle, there's nothing lost when you melt metals, in practice some oxidation may take place for some metals but this can be avoided by using an inert atmosphere.  If you melt something and let it cool slowly then repeat this process you will always get the same result. 
« Last Edit: 30/04/2007 20:18:06 by Bored chemist »
 

Offline dentstudent

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Re: Why do metals melt, but not, for example, wood?
« Reply #11 on: 13/06/2007 14:50:46 »
I think its all in how you look at it as plastic, metal and wood all create fire when heated and change through heating both metal and plastic lose parts of there structure from heating/melting as does wood- it becomes charcoal.
I think they all melt they just act in different ways as they melt because of there atomic make-up.
Plastic and metal after melting do not return to the same form the were before melting- as they lose somthing in the process.
Therefore I would say they all melt.

I've only just seen this thread, and this bit needs sorting. Charcoal is formed in the absence of oxygen (hence char) - it loses many of its gasses and materials in the process, leaving about 80 - 90% carbon. So, yes you do lose material through burning, but you don't get charcoal. If you burn wood in the presence of oxygen, what you get is ash, and an annoyed charcoal burner.
 

Offline Madidus_Scientia

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Why do metals melt, but not, for example, wood?
« Reply #12 on: 21/01/2009 08:54:14 »
So charcoal is made mostly of carbon, and on wikipedia it says the melting point of carbon is 3652 C. So would wood start melting at this temperature? (or what remained of your original wood)
 

Offline Chemistry4me

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Why do metals melt, but not, for example, wood?
« Reply #13 on: 21/01/2009 08:59:40 »
If you can get it to that temperature without it burning, I would say so...
 

lyner

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Why do metals melt, but not, for example, wood?
« Reply #14 on: 21/01/2009 09:08:00 »
Wouldn't it have stopped 'being wood' long before it got to that temperature?
 

Offline Chemistry4me

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Why do metals melt, but not, for example, wood?
« Reply #15 on: 21/01/2009 09:12:22 »
Don't think anybody has ever tried it... What would be the point?
 

Offline Madidus_Scientia

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Why do metals melt, but not, for example, wood?
« Reply #16 on: 21/01/2009 09:19:11 »
The point of all science, to see what happens? And I didn't say we should try it, just wondering if I was right or not in my speculation when a mate at work asked me today.

If there was no air would it be liquid? Otherwise it would combine with oxygen to form carbon dioxide wouldn't it?
« Last Edit: 21/01/2009 09:27:48 by Madidus_Scientia »
 

Offline Chemistry4me

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Why do metals melt, but not, for example, wood?
« Reply #17 on: 21/01/2009 09:27:56 »
If there was no air would it be liquid?
Say that one again ??????
 

Offline Madidus_Scientia

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Why do metals melt, but not, for example, wood?
« Reply #18 on: 21/01/2009 09:29:48 »
If there was no air in its presence as you were heating it, would it become liquid
 

Offline Chemistry4me

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Why do metals melt, but not, for example, wood?
« Reply #19 on: 21/01/2009 09:30:23 »
Otherwise it would combine with oxygen to form carbon dioxide wouldn't it?

If it does not burn (which is just a reaction with oxygen). Carbon is quite inert anyway.
 

Offline Madidus_Scientia

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Why do metals melt, but not, for example, wood?
« Reply #20 on: 21/01/2009 09:36:58 »
What? It would burn as long as it doesn't burn?
 

Offline Chemistry4me

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Why do metals melt, but not, for example, wood?
« Reply #21 on: 21/01/2009 09:53:49 »
It melts without burning (i.e, catch on fire)
 

Offline dentstudent

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Why do metals melt, but not, for example, wood?
« Reply #22 on: 21/01/2009 10:10:40 »
Perhaps you need to go back and find a definition of "melting"?

I am absolutely no chemist, so take this with a pinch of salt. If you heat ice, the energy it receives mobilises the water molecules and allows them to become free from the crystal structure. But they are still linked/attracted, but in a much looser framework, and so become liquid. Could it be the case that carbon molecules do not have the same level of attraction, and therefore go straight into the gaseous state? OR - perhaps it DOES become a liquid, it's just that the state has such a narrow window that it evaporates without our own perceiving it?

I am quite open to all the above being total dogs' danglers.....
 

Offline Chemistry4me

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Why do metals melt, but not, for example, wood?
« Reply #23 on: 21/01/2009 10:18:11 »
on wikipedia it says the melting point of carbon is 3652 C.
Hmmm... I've just noticed that on my periodic table, it states that the boiling point of carbon is 3827 degrees but it doesn't have the melting point so going by that data I assume that carbon sublimes. But what should we believe? Wikipedia or a good old periodic table of the elements?
 

Offline dentstudent

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Why do metals melt, but not, for example, wood?
« Reply #24 on: 21/01/2009 10:25:35 »
Wiki (again)

At atmospheric pressure it (Carbon) has no actual melting point as its triple point is at 10 MPa (100 bar) so it sublimates above 4000 K.[13]
 

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Why do metals melt, but not, for example, wood?
« Reply #24 on: 21/01/2009 10:25:35 »

 

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