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stygian
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an arc welder can melt an iron (1538C) electrode quite easily at a modest 100 amps or so. Using a carbon gouging rod and/or high current should
easily be able to attain the 2000C needed. But I'm talking primordial here!
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12AX7
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Yeah humm... no need for a crucible, it'll work fine just arcing inside a pile of the stuff, who cares. Graphite can be mined in a few places (I
don't remember what conditions it forms in), but you'll be looking hard to find good enough samples to cut electrodes from. Then you need
the <U>insulated</U> <U>copper</U> <U>wire</U>. Insulation as varnish, cotton (or other fiber) wrapping, etc.;
copper from ore is simple enough, but then you also need the iron (preferrably tool steel!) dies to draw it through, which needs the high technique of
making fine steel, plus drilling and reaming operations to form the die itself. Oh, and silicon steel for the dynamo- no idea where you'd get
that without ferrosilicon, so, you'll have to settle with a core about twice as large, made of mild steel, to handle the magnetic field. Which
then needs a rolling mill preferrably, which needs more tool steel and machining of course. (Read up on D. Gingery to get a feel for making machines
from minimum resources.)
Once you have a dynamo and source of rotational energy (waterfall preferred, but you'll probably already have a low-pressure steam engine from
your lathe's first project), you can connect them to your electrode clamps, graphite and blast away at a pile of charcoal and limestone (calcite
preferred, since limestone is often actually dolomite and magnesium doesn't do you any good).
Tim
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stygian
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I read that charcoal and coal tar are baked to form electrode for carbide furnaces.
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12AX7
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Yeah, but artificial graphite needs as much heat as calcium carbide to produce a reasonable product...so....yeah...
Tim
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IrC
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Is it all right with you people if I don't go totally caveman and just buy some items? I know it's cheating but I will keep it quiet if you
do.
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The_Davster
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Cheater!! Caveman arc welder is dinosaurs on big hamster wheel hooked up to a generator .
Are you seriously thinking of making carbide this way? I swear there was a thread on CaC2 somewhere herehere
Looks like Chemoleo has already tried it. Be sure to post results! I want to try this but have no arc welder, I read about how to make one from 8
microwave transformers, so I am looking for some of those now...
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stygian
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*I'm* not. Obviously. Maybe I was misunderstood. What I meant to say was:
"I know arc welders can do it."
Then separately
"Is there some 'primordial way'?"
And if you allow electrochemistry, I found it, it's in the carbide thread.
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Magpie
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Does the formationof CaC2 from CaO and C require DC current and/or a high voltage or just the very high temperature generated by the electric arc?
What I am getting at is if AC can be used why bother with the welder? Just buy a circuit breaker within the limitations of your house mains and some
large cables.
[Edited on 22-11-2005 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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stygian
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It's just the heat needed. You cant JUST use a circuit breaker because without some kind of ballast you will overload the breaker instantly.
Arcing through carbon should provide quite a bit of resistance though. Someone on roguesci a long time ago gave a real simple design. Ac plug, 2
wires, 2 electrodes, one wire having a nichrome coil in series for resistance (e.g. electric heater)
[Edited on 22-11-2005 by stygian]
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IrC
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That is incredibly power wasting though. I would look into cutting a section out of the core and making a way to slowly bring the core back together,
this way you are controlling the magnetic field. In the 80's I used to build tesla coils up to 20 or more feet tall, and used pole pigs to power
them. Taking an old variable core lincoln arc welder and wiring it as a variable reactor. You have a 240 volt primary, and here you put the primary in
series with the pole transformers. A very heavy buss bar dead shorts out the arc welding secondary. In this way you are using controlled magnetic
fields to energize the pole transformer from nada to as much amps as your mains supply can handle. Great use for the variable core arc welder and when
building something you just take it out of line and put it back to arc welding use so you are out nothing!
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Magpie
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Are you guys saying that for a very crude arc furnace one might install a carbon electrode in a mound of finely divided and mixed CaO/C,
locate the 2nd carbon electrode slightly above the mound (to provide an arc) and then as long as you had the appropriately sized inductor in series
(or parallel?) you could make CaC2 using 240VAC?
The single most important condition for a successful synthesis is good mixing - Nicodem
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stygian
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The nichrome element in series is a resistor, effectively turning your 240VAC to a lower voltage, much higher current. I think.
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mick
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Back to the origins. A good quality set of bellows with charcoal might get the temperature up to making calcium carbide.
mick
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stygian
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Speaking of, just found an old roguesci thread that I remember. Someone tells of using a paint stripping heat gun to fire a clay flower pot full of
charcoal. Supposedly does a quick job of liquifying cast iron. So, if you could heat air from a bellows somehow..
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Magpie
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coke
I took a crack at making coke yesterday. It was a failure. 
I placed some "high volatile bituminous coal" (Utah) in 3 small crucibles each with the lid on. I then heated these crucibles for about 6 hours at
800-900C. Weight reduction was about 50% vs an expected 25-35%. There was a grey crust on the product which I took as inert cinder. Inside the
crust the product was blacker but I could not get it to burn even after heating it to red heat in a bunsen burner. I take this to mean that I
essentially had no carbon left.
My feeling is that it is a problem of scale in that I can't sufficiently keep my carbon from the oxygen in the atmosphere.
Does anyone have any ideas on what I could do to have success without building a huge oven?
The single most important condition for a successful synthesis is good mixing - Nicodem
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12AX7
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I've heard coke can be hard to burn, Idunno. Burns nice in a blast furnace at any rate, but being well above white heat, that isn't very suprising
Next time, you might try heating in a stronger reducing atmosphere -- some charcoal or sawdust on top could help.
Tim
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Magpie
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more coke tries
I made a couple more runs with my coal, this time not grinding it up as I had the first time. I got the temperature up to 1100C for a few hours.
Weight loss was about 50%. It looked like the other cinders so I didn't even try to get it started with the bunsen burner.
There is a blacksmith in my area who makes his own charcoal. I'm going to consult with him.
Maybe I need to cover the coal with dirt.
[Edited on 1-1-2006 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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IrC
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Your problem is oxygen. You cannot simply place a lid on and expect that no O2 will get in and burn the carbon. You need to build some type of furnace
or crucible to go in one which can completely eliminate the chance of air being sucked in.
After 20 or 30 hours of heat you then quench the coke with water to avoid it burning. The whole process will work much better if you make very large
amounts at a time.
http://www.lehigh.edu/~kaf3/cokedata/coking.html
[Edited on 1-1-2006 by IrC]
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Magpie
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Yes, I am now fully convinced that I'm not keeping out the oxygen sufficiently. This is a dramatic demonstration of the effect of scale on certain
chemical processes.
I'm doing this more out of curiosity and stubborness than anything. I won't likely go to the trouble of building a large set up just to make some
coke. I don't think I'll be blanketing my muffle furnace in argon either.
I am curious as to why it has to be heated for so long, however. The Lehigh write-up says something like 24-36 hours at what, 1100-1200C. Why would
it take that long other than some of the coal chunks being very large, say around 1 foot (0.3m) in diameter, and the coal piles also being very large?
[Edited on 1-1-2006 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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IrC
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I'm sure you're right, that the time is related to material quantity. I suppose only experimentation would give you some sort of scaling factor. I do
not believe it would be very hard to smooth the surfaces between the crucible and lid to make it air tight, especially if you had a weight with high
melting temperature (crucible material?) on top of the lid during the process.
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Magpie
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My procedure was to put a small lump of coal (if the lump of coal is too big it will push off the lid as it swells) in each of 3 crucibles, set them
in the hot furnace, and then put the lids on and close the furnace door. Within a minute great quantities of volatiles and smoke come out at the door
seal, some of it catching on fire (doing this in a hood or outside is advised).
With the above procedure it would be impossible to seal the lids as those volatiles have to get out. You might be able to just leave the lids off
until this rapid volatilization is finished and then place close fitting lids on for the rest of the heat, but I'm skeptical.
As a side note, coal is neat stuff. I'd never really played with it before. A very thin metal-like film forms on the inner surface of the crucible.
I'm assuming it's a condensation product. I'm curious as to what this is. If I wanted to know bad enough I could do a series of wet chemical
qualitative analyses. This sounds like too much work, however.
The single most important condition for a successful synthesis is good mixing - Nicodem
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12AX7
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Probably either glassy carbon or graphite deposited parallel to the surface (hence shiny). Brauer mentions synth with graphite oxide from solution,
or cracking alkanes at 800C+. You would have the latter 
Curiously, Brauer says a tinge of oxygen helps to make a shiny deposit, but on the other hand, you have a pretty graphite-like material to start with,
lots of aromatics and such being distilled, probably forms graphite much easier.
Tim
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IrC
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Put the coal in the crucible, then cast a lid with castable refractory around a ceramic exit tube and one way valve of some sort. After it is hardened
at lower temperatures crank up the heat.
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Magpie
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IrC: Along that line you could probably just build a small iron retort out of black iron pipe and lead the tube to a water seal. At T= 1100C I would
think that the iron would not suffer.
The single most important condition for a successful synthesis is good mixing - Nicodem
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IrC
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I started to mention iron earlier as a screw on lid would be great. I decided not to as I just was not sure about the temperatures involved. Then
again they do use these big metal furnaces in industry so why not for small scale also.
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