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Specialty Chemistry Forums => Citizen Chemist => Topic started by: quentief on August 16, 2018, 07:16:11 PM

Title: Electrode for an electric arc furnace
Post by: quentief on August 16, 2018, 07:16:11 PM
Hello everyone :)

I create this post because I am working on a little project and I have to deal with a problem but I can't find any solution.

Indeed, I 'm trying to make a little electric arc furnace, to recycle some metal scraps. Unfortunately, I can't find any carbon electrodes. Obviously, I can buy some of them through the Internet but the delivery charges are too expansive for me. Moreover, I think to make my own carbon electrodes would be, well, cool  :)

So I tried different options to make a carbon electrode :
-zinc-battery : I cannot find any of these battery in shops
-charcoal : I was very surprised, it is an electric insulator
-carbonised cotton : It is a good electric conductor but it is also too fragile
-graphite from pencil : it just explodes on my face because of the current...  :'(

I think I will try to carbonize some plastic parts, maybe the result will be interessant. But if you have any advices, please please please, tell me :) I have been stucked on this problem for a long time, and I really want to success this project.

Thank you in advance. Oh and I'm sorry if my english is a little bit bad, actually I am French :)

Title: Re: Electrode for an electric arc furnace
Post by: Enthalpy on August 17, 2018, 07:56:40 AM
Bienvenue, quentief !

Zinc batteries are the banal saline 1.5V ones. That is, with negative casing, not the alkaline ones with positive casing. Broader cells have a thicker graphite electrode: LR03 < LR06 < LR14 < LR20. To my opinion, the easiest way.

Charcoal is a hydrocarbon plus other things. Little hydrogen in it, but it's not graphite.

Pencils contain graphite plus other things. Too thin for high current.

Carbonize plastics: not a very good idea.

First, please take care. Most plastics are badly toxic at heat. They may release cyanides, acrolein, chlorides and so on. Quite nasty.

It should be done without any air, which is difficult at home.

Graphite is obtained industrially by pyrolysis over days and weeks at very high temperature, and the items are replenished with carbon-rich paste (like tar) or gas regularly. If this isn't done, you get a very porous and brittle part like charcoal. Quite difficult at home.
Title: Re: Electrode for an electric arc furnace
Post by: skatebiker on November 28, 2018, 01:39:07 PM
These carbon rods are readily available on eBay or Aliexpress for decent prices.
I recently ordered 10 pieces of 200x8mm for $20 at Aliexpress.

Check my experiments:

Title: Re: Electrode for an electric arc furnace
Post by: quentief on February 02, 2019, 07:37:35 AM
Good morning everyone :)

I have found a way to make charcoal conductive. I don't know exactly how that works but apparently, if you roughly cool down a peace of burning charcoal in water,  its electric conductivity seems to be seriously improved. I assume that process is working like quenching for metal ; maybe this quick cooling down compress the charcoal to make it more conductive. I have measured with my multimeter a resistance of 30 ohms.

Currently, I don't have the time because of my studies but I will make more tests this summer.
Title: Re: Electrode for an electric arc furnace
Post by: Enthalpy on February 04, 2019, 01:56:27 PM
Or moisture? Or other compounds created by the combustion, especially ash which may contain potash?