Home > Experiments > Not So Conductive Electro Conductive Silicone

Not So Conductive Electro Conductive Silicone

Sometimes there are things that aren’t working as intended. Inspired by some other works I tried to make electro conductive silicone myself. Highly motivated I mixed some 2 component silicone and  added graphite carbon powder used for lubricate doors. Scientist I am a series with different ratios of graphite and silicone was made. Since I lack a decent scale I went with volumetric ratios ranging from 10 parts silicon with 1 part graphite (10:1) to 1:2.

In the end it turned out to be not that easy. All silicone blocks were as insulating as one would expect for silicone. The graphite makes a appealing finish though. Deep black with a nice sparkling effect. For high ratios of graphite powder the silicone gets quite hard and the cut face will release graphite and you’re getting black fingers. But unfortunately no conductivity. Not even mega ohms.

Maybe one has to try even higher ratios of carbon graphite powder. An other direction for further experiments could be the grain size of the carbon powder. The commercially available electro conductive silicone shows no sparkling so the powder seems to be much finer.

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  1. Klinge
    February 8, 2010 at 11:19

    You should try even higher ratios for graphite.
    If you look at atomic packing fractions (describing the ratio of spherical atoms filling a cube) given the evenly distributed spheres touch one another – you end up with ratios from 52% up to 74%.
    This means if you use a ratio of “only” 50% the graphite powder (if you imagine it as spheres) could be evenly distributed in your silicone, without a single graphite particle having to touch another. This only holds if all your spheres are of the same size. If they are of random size, the filling ratio would be even higher. Since the graphite particles have to be in direct contact all together i recommend a ratio of 1:3 for silicone:graphite.

    • elims
      February 8, 2010 at 22:28

      Maybe I should try even higher ratios. Next time I will be messing around with silicone I’ll try.

  2. Secret Things
    February 8, 2010 at 20:37

    Is it only the cut face that gives you black hands? I’m thinking all sorts of uses for it, but some of them won’t work if the graphite will leave marks.

    • elims
      February 8, 2010 at 22:31

      Yes, it is only the cut face for the high graphite ratio of 2:1. The normal surface is smooth and doesn’t emit any graphite powder. The liquid silicone doesn’t vent properly though and you’re getting small bubbles of trapped air.

  3. threedg
    September 30, 2012 at 16:36

    You need to add thinner to help the graphite to distribute evenly in the silicone, and also add a thickener to help the silicon dry more evenly, google Oogoo II.

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