Sciencemadness Discussion Board

Graphite making methods?

Funkerman23 - 24-4-2012 at 18:53

Pardon the dumb question but has anyone else figured out how graphite rods, sheets and blocks are properly made? I can't find a source with anything more than a simple over view of some of the processes. I am aware of the Acheson process but that only converts coal into more graphite. But to get a machinable solid mass is it something as simple as compression of powder or flake or are there other methods( sintering the powder with asphalt or another hydrocarbon maybe?)? I have bits and pieces of info but the few other forums I have run across don't seem to know...

Thanks and may your yields be high.

Pulverulescent - 25-4-2012 at 01:04

AFAIK, all graphite synthesis methods require either very high temperatures or pressures and frequently require both . . .
They'd be beyond the backshed experimenter, IMO!

fledarmus - 25-4-2012 at 10:35

You might be interested in this - Carbon and Graphite production

Apparently the rough forms are prepared by compressing crushed graphite and coal tar into the appropriate shape, then they are graphitized by heat to remove the impurities and enlarge the graphite structures through conversion of the coal tars. If you need precise shapes, the rough forms can be machined after the graphitization process.

bquirky - 25-4-2012 at 11:14

I have tried this on a small scale for messing around with battery chemistry.

I was interested in making carbon and copper powdered electrodes

I mixed the fine carbon powder together with some tar/solvent mix that came in a can from the hardware (presumably meant for sealing roofs against water) mixed as small amount as possible into a thick and extraordinarily messy dough

I then packed it into a test tube and baked it at a orange heat for about 4 - 5 hours using a home made gas kiln (an old bbq burner with half its jets welded up mounted on its side with the remaining gas jets facing vertically. boxed in with bricks)

I found it was important to heat it very very slowly at first because the volitile components seep out causing pops and cracks and flamey fun

After the firing had completed the test tube was naturally history but the carbon solid that remained was definitely graphite 'like'. it was hard, porous, had a low electrical resistance and seemed fairly strong. although it would breakup if i hit it with something hard. Im not sure if it could be machined but it could be molded into a specific shape.

It made a very good electrode

The copper powder was prepared in the same way however it lost its strength after a few electrochemical oxidization/reduction cycles

* ill allso note that the copper powder can be sintered without any tar binding at all however it requires compressing before firing i used a hydrolic car jack mounted in a steel frame for this . without pressing all you end up with is copper powder everywhere.

the sintered powder is more porous and has a lower electrical resistance but I found it quite brittle and difficult to make in larger sizes

[Edited on 25-4-2012 by bquirky]

barley81 - 25-4-2012 at 11:40

I need to try that. It sounds very interesting. A good graphite electrode would be useful for chlorate or bromate cells. What kind of carbon powder did you use? Activated charcoal or powdered graphite? Maybe if you used pure coal tar instead of solvent/tar mix, you would have less trouble with volatiles expanding?

bob800 - 25-4-2012 at 13:14

What's wrong with the electrodes from carbon-zinc cells? I've used them in electrolysis experiments with no complaints expect for some gradual erosion.

Now I've never tried chlorate production, but I can't imagine that a homemade electrode would work any better.

barley81 - 25-4-2012 at 17:35

Nothing's really wrong. It's just that an electrode that erodes less would be better. It's also fun to make things yourself...

What an anticlimactic 250th post. Nevertheless, BOOYAH!!!

[Edited on 26-4-2012 by barley81]

Funkerman23 - 25-4-2012 at 18:58

Well the reason I ask is in addition to Chemistry as a hobby I also restore Vacuum tube electronics. In a few cases the metals used to make the frames for the air condensers( or any number of other metal parts) cracks or fails and a replacement can't be found. when that happens the part sometimes has to be cast. That and I love to make things myself.

bquirky - 25-4-2012 at 21:09

I feel i should add that I did not use my electrodes for any kind of clorate production so i canont vouch for it working :)

watson.fawkes - 26-4-2012 at 00:31

Quote: Originally posted by Funkerman23  
I can't find a source with anything more than a simple over view of some of the processes. I am aware of the Acheson process but that only converts coal into more graphite
As the link fledarmus posted, graphitization happens at 3000 °C. That's really hot. Cone 10 porcelain, but comparison, is around a cozy 1250 - 1290 °C. There are really significant practical difficulties to dealing with this temperature. Cone 10 is notorious for prematurely burning out elements in electrical resistance furnaces, so already it's not trivial to go a lot higher than that. And cone temperatures don't go any higher than about 2000 °C, so you're totally out of the realm of ceramics.

The first difficulty is heating. The only two ways I know of to get to that temperature for sustained amounts of time are direct resistance heating and induction heating. For the former, you've got a bulk mass whose overall resistance is rather low, down in the few ohms, I'd guess, and you need to drive kW levels of power into it. That means you need a power supply that can supply kA of current at a few volts. That's not a trivial power supply; it's in the realm of welding equipment. And because the resistance changes during the firing process, which is days long, you either need shift work or some good control circuitry.

The second difficulty is insulation. Remember that radiative heat loss goes up as the fourth power of the temperature. That's around 30 times the losses from a cone 10 furnace. So to work at this temperature you need to get familiar with insulating refractories. This is an area where scale matters. The square-cube relation means that the larger the furnace, the lower the surface-area to volume ratio is, and thus the lower the specific heat loss per unit of product. Conversely, to do this at garage scale means lots and lots of insulation and a relatively small reaction chamber.

The third difficulty is construction materials. Did I say "really hot" enough yet? The working temperature is above the boiling point of alumina, at 2977 °C , and also above the melting point of zirconia, at 2715 °C. The reason you see carbon, carbon, and more carbon in these furnaces is that there's little else that can possibly be used. High-alumina refractories are only available up to 1500 - 1800 °C or so, so the first half of your temperature loss curve needs to be carbon or something more exotic than high-alumina, which means carbon.

If you want to pursue this, I wish you well. I'd recommend some shakedown projects at lower temperatures first, though.

hissingnoise - 26-4-2012 at 01:14

Graphite synthesis @ room temperature . . .

MrHomeScientist - 26-4-2012 at 06:09

@bquirky: How did your homemade electrodes hold up? Did they erode less than the graphite sticks from carbon-zinc batteries? That's really neat that you were able to make something like that yourself, instead of scavenging from old batteries.

bquirky - 26-4-2012 at 07:33

well i was deliberately trying to avoid producing gas so my electrodes where never subjected to a vigorous electrolysis, and I never took them over 2 volts. the carbon electrodes changed colour during charge (zinc reduction) but didn't seem to suffer any permanent effects.

I wanted to experiment with oddball batteries so i needed a highly porous and conductive substrate.
the idea that i had was copy the concept of the Lithium ion cell where the li ions shift from one electrode to the other and hang out in the interstitial spaces in the electrode

except instead of using lithium which requires a fancy non aqueous electrolyte i used zinc in an aqueous electrolyte. It did work but not particularly well i could get a few amps peek current out of a pair of small test-tube sized carbon electrodes but it was low capacity and didn't seem to scale with size.

I ended up having much more success with a copper oxide/ zinc metal chemistry using a copper foil substrate folded in a concertenia shape with copper powder between the folds this required no heat no sintering and no messy carbon powder and was quicker to prepare. a few charge/discharge cycles seemed to bond the copper powder together ( copper foil peices where plated with zinc to form the other electrode).

I got the cycle life past 100 cycles but it required alot of work figuring out how to make decent microporus separators. Surprisingly the cycle life limit i hit was not from the zinc but from the copper becoming soluble in alkaline conditions. several hundred years ago this may have been a profitable way to dye fabrics blue.

I could reduce the problem by running a more dilute electrolyte or by adding other salts in excess but that reduced the peak current output

I came to the conclusion that Evan if i succeeded in engineering a decent home made secondary battery it wouldn't be of much benefit anyway. so i moved on to other projects

White Yeti - 29-4-2012 at 07:47

Quote: Originally posted by hissingnoise  
Graphite synthesis @ room temperature . . .

Perhaps room temperature, but not STP :P

@Funkerman23 You may be interested in the process by which carbon-carbon composites are made.

It really depends on what you're planning on doing with this "graphite". If you're planning on electrolyzing stuff, making graphite is just not worth it. If you're planning on making a nose cone for a missile, then I'd suggest carbon carbon composites:D–carbon#Prod...

Also, diamonds will spontaneously turn back into graphite over the course of millions of years @STP.

AJKOER - 5-5-2012 at 00:08

If you are good at building things consider an Atomic Hydrogen torch (AHT). To quote from Wikipedia:

"Atomic hydrogen welding (AHW) is an arc welding process that uses an arc between two metal tungsten electrodes in a shielding atmosphere of hydrogen. The process was invented by Irving Langmuir in the course of his studies of atomic hydrogen. The electric arc efficiently breaks up the hydrogen molecules, which later recombine with tremendous release of heat, reaching temperatures from 3400 to 4000 °C. Without the arc, an oxyhydrogen torch can only reach 2800 °C.[1] This is the third hottest flame after cyanogen at 4525 °C and dicyanoacetylene at 4987 °C. An acetylene torch merely reaches 3300 °C. This device may be called an atomic hydrogen torch, nascent hydrogen torch or Langmuir torch. The process was also known as arc-atom welding.

The heat produced by this torch is sufficient to melt and weld tungsten (3422 °C), the most refractory metal. The presence of hydrogen also acts as a gas shield and protects metals from contamination by carbon, nitrogen, or oxygen, which can severely damage the properties of many metals. It eliminates the need of flux for this purpose."

Note, once you get the AHT to operate, you may even be able to prepare C4N2. To quote Wiki: "Dicyanoacetylene can be prepared by passing nitrogen gas over a sample of graphite heated to temperatures between 2673 to 3000 K." And then using a Dicyanoacetylene torch as this tale goes, you can achieve a flame temperatures approaching 5,000 C or 9,032 F! Note, Dicyanoacetylene is a highly endothermic (and explosive) compound that can achieve these temperatures and best employed by professional's only.

So even in the back shed, heating something to over 3,000 C may be achievable, but make sure that you protect yourself appropriately (including inhalation of metal vapors) as you are about to be able to vaporize anything in the house.

[Edited on 5-5-2012 by AJKOER]