Manifest
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Pyrolysis of sugar to make Carbon anodes
I'm doing electrolysis experiments for chlorates at the minute and my previous carbon anodes(obtained from batteries) have fallen apart.
So what i'm thinking is, why not get a mold of some sort, I could use a soup can to test and fill it with some sugar and simply heat the bottom of the
can.
Then if all goes well, I'll get a column of Carbon just like the popular H2SO4 + Sugar experiment.
The only relevant result I have found on Google is the following.
http://jes.ecsdl.org/content/143/10/3046.full.pdf
So what do you guys think? Feel free to pick at any problems you can see with this.
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blogfast25
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Relatively pure carbon (graphite) rods for use as electrodes aren't hard to find. Battery carbon anodes are like briquettes: a composite material held
together by a binder. That just does keep together for very long!
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Manifest
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Quote: Originally posted by blogfast25  | | Relatively pure carbon (graphite) rods for use as electrodes aren't hard to find. Battery carbon anodes are like briquettes: a composite material held
together by a binder. That just does keep together for very long! |
lantern batteries are hard to find and they're certainly expensive.
I searched ebay for carbon rods and they're £3.28 or $5 for two.
I don't want to pay that for carbon! Besides, I think this would be a fun project.
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Oopsy_daisy
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Graphite and carbon are not the same thing. The carbon atoms in graphite are set in layers with dislocated electrons that allow it to conduct
electricity. The carbon obtained from this method probably won't have the desired property.
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Pulverulescent
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| Quote: | | Then if all goes well, I'll get a column of Carbon just like the popular H2SO4 + Sugar experiment. |
The column will be porous and so cannot be used as anode . . .
Good quality gouging rods are graphite and make anodes that are much longer-lasting than amorphous carbon!
"I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones"
A Einstein
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Manifest
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| Quote: Originally posted by Oopsy_daisy | | Graphite and carbon are not the same thing. The carbon atoms in graphite are set in layers with dislocated electrons that allow it to conduct
electricity. The carbon obtained from this method probably won't have the desired property. |
Oh. That didn't even cross my mind. 
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Manifest
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I didn't think this out very well, maybe I was a bit quick in making a thread.
EDIT: What if I just cut a bit of coal?
Quote: Graphite may be considered the highest grade of coal
[Edited on 17-7-2013 by Manifest]
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Hexavalent
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Absolutely, the carbon made via dehydrating sugar is called "amorphous", because it has no definite crystal structure.
Has anyone had any success using replacement pencil leads (for mechanical pencils) as electrodes?
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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bfesser
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<strong>Manifest</strong>, there are many <a href="https://en.wikipedia.org/wiki/Coal#Types" target="_blank">types of coal</a>
<img src="../scipics/_wiki.png" />. I doubt you'd get any grade below graphite (<em>possibly</em> anthracite) to work for this.
Just order a few graphite rods or bars.
[edit] Anthracite won't work, unless your sample is <em>highly</em> graphitic.
Attachment: graphite_in_anthracite_conductivity.pdf (286kB)
This file has been downloaded 504 times
[Edited on 7/17/13 by bfesser]
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Manifest
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They're far too thin, they would corrode too fast.
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bbartlog
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The older implementations of the Hall-Heroult process generated their anodes in continuous fashion by adding pitch, which (at the high temperatures
involved) baked into a suitable carbon anode. Now, coal tar pitch has a much lower oxygen content than sugar, so the porosity that comes from gasses
being expelled will be a lot lower. And it may also be that the anodes are only good enough conductors at the high temperatures used in the process.
Anyway, your idea is not completely crazy: http://www.electrochemsci.org/papers/vol8/80202702.pdf
The less you bet, the more you lose when you win.
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phlogiston
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One way to make gouging rods last significantly longer is to impregnate them with linseed oil. The best way is to immerse them in linseed oil and
apply vacuum.
Beyond the anode lifetime, you will also have less suspended crap, which is often frustratingly difficult to remove well by filtration.
I once tried a few relatively thick pencil 'leads', about 1.5 cm diameter, but indeed they don't last very long.
-----
"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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Manifest
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| Quote: Originally posted by bbartlog | The older implementations of the Hall-Heroult process generated their anodes in continuous fashion by adding pitch, which (at the high temperatures
involved) baked into a suitable carbon anode. Now, coal tar pitch has a much lower oxygen content than sugar, so the porosity that comes from gasses
being expelled will be a lot lower. And it may also be that the anodes are only good enough conductors at the high temperatures used in the process.
Anyway, your idea is not completely crazy: http://www.electrochemsci.org/papers/vol8/80202702.pdf
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Thank you, I was starting to think I was going mad after a user reminded me that graphite is an allotrope of Carbon.
So, basically my idea is plausible but not very practical.
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halogen
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You could look into carbonization of carboniferous materials. Lightbulb filaments have been made from carbonized celoluse. For example, but the main
memory this thread is something about phenol formaldehyde. Why is porosity bad? In any case the quickest found http://link.springer.com/article/10.1007%2FBF00540472 and obviously many things. Apparently's a American Carbon Society! You might find something
interesting there. Ya know what else is an allotroph of carbon? Yo' mama. Hah hah.
[Edited on 17-7-2013 by halogen]
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LanthanumK
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Try to find a cheap source of "heavy duty" or "super heavy duty" C or D cells at your local bargain store. You can often get up to 4 for a dollar,
which is much cheaper than paying 6 dollars for a lantern battery, which is essentially 4 D cells. Pyrolyzing sugar, as previously mentioned, will not
result in a conductive form of carbon, and even if it did, it would disintegrate extremely rapidly.
When I created a small amount of bromates from bromides using a similar electrolysis process, I used a lower voltage to limit the corrosion of the
carbon anodes, which IIRC were from AA batteries.
hibernating...
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tubelectric
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I have tried pencil leads, both those "refill" leads and from wooden pencils and they weren't very good. Too thin and too much additives. Maybe
"drawing"/"art" type pencils would be better (thicker core + probably more graphite and less additives).
Some arc gouging rods have copper coating but otherwise they should be good. However, I would just try to find pure graphite rods from ebay or
somewhere.
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bfesser
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The softest grade pencil leads (9B) are highest in graphite and lowest in clay. These will also have the highest conductivity and should have the
best chemical resistance. At any art shop worth a damn, you can purchase blocks and rods of pure graphite.
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halogen
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"Pyrolyzing sugar, as previously mentioned, will not result in a conductive form of carbon, and even if it did, it would disintegrate extremely
rapidly."
I think that's wrong. Will char up some sugar to be sure, actually honestly I probably won't one of you guys can do it, well I might, but don't count
on it  But if the big deal is that it's already s'thin that it falls apart after
moderate eatching, so be it. There...
But check this out - glassy carbon is indeed conductive, and even used as electrodes! http://en.wikipedia.org/wiki/Glassy_carbon
Apparently it can make a doped semiconductor. So my phenol guess was right, some kind phenol resin in an inert atmosphere. Even probably to make your
own crucibles and other(?) stuff for a home experimenter.
[Edited on 20-7-2013 by halogen]
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Endimion17
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This would work only if you need heavy duty carbon electrodes for things where you need:
- extremely high currents
- low voltage
- extremely high temperatures
Hall-Héroult process i.e. production of aluminium. I think it's pretty obvious that such applications are out of reach for nearly everyone except
heavy industry.
In such situations, those electrodes can be more than enough. Hall–Héroult process uses coke, which is a pretty pathetic electrical conductor
compared to graphite. I'm pretty sure decently treated sugar, without large pores, could be used as well.
For aqueous electrolysis they're piece of crap, obviously. Only high quality graphite can be used if you want some serious yields. For demonstration
purposes, crappy clay-ridden pencil leads and porous battery rods are enough.
I'll say this again - start differentiating demonstration experiments and production procedures. They are never the same thing.
Industry is not just chemistry theory. It's chemical engineering, as well. There are massive calculations people and computers do, just to make
something possible and to increase yields. It goes from simple things like applied voltages to very complex like liquid shear forces depending on
reactor geometry, etc.
You can see those coke anodes here.
http://www.youtube.com/watch?feature=player_detailpage&v...
[Edited on 20-7-2013 by Endimion17]
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macckone
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MG Chemicals 832HT epoxy might be a good product to use for making glassy carbon. A fully thermosetting phenol epoxy would probably be better but
those aren't commonly available in the US for consumers.
It looks like any epoxy that doesn't off-gas a lot would work.
This process of course requires extreme heat (3000C) which is going
to be difficult for the home experimenter to achieve.
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