Author Options:

candle's black smoke deposit seems not to be electrically conductive Answered

(This is the first topic of the "failed experiments" group.)

I was wondering if the black smoke of the candles could be electrically conductive (carbon) when deposited as a layer over a piece of glass.
After a quick and basic experimentation, it seems it is not.

Here is how I proceeded :
- I've put a piece of glass over the flame of a candle so a black smoke deposit appear on its surface.
- I did so that it becomes opaque (if you want to try, be careful that the piece of glass may break because of the heat)
- then, I used two crocodile clamps to make the contact (I've put a certain depth of aluminum foil between the claws of the clamp and the piece of glass)
- then, I tried to measure the resistance with a multimeter, but the multimeter displayed no value at all.


What about drying a graphite based lubricant on to the glass, it would be conductive and much less effort, also it would form unfirom structures that should be conductive mainly due to the way that graphite is assembled...

Hey, I did not know there was "graphite based lubricant" !

I've started to look on the net (french hardware stores) : the few lubricant containing graphite that I've found so far, all contains molybdenum disulfide (or something) ...

I will investigate this track a little more =o)
Thanks for the idea !

You could try making a paste of graphite powder in water or something that will evaporate- it might be more conductive than carbon black but would probably be an even more fragile coating so would need you to lacquer over the surface or something to hold it in place.

Lemme know how that goes, hmm if it works I have an idea, quarries use graphite lubricant but I might find some around the builders in our street, I still live in a building site.

Analysis of hydrocarbon soots shows it containing different carbon nanostructures. Investigations of carbon nanopowders revealed the presence of the amorphous carbon, carbon with small graphitic sheets or fullerene-like structures. The soot morphology depends on the hydrocarbon mixture and experimental parameters. In other words, depending on the composition of the wax of the candles (natural wax {bees}, paraffin, etc.) how it is combusted, and how much soot is gathered. It may have quite a high mixture of unburned hydrocarbons still in the soot, and would be either non-conductive or have a very VERY high resistance factor.

In other words - candle soot is too greasy, it's not just pure carbon...

Let's try to go back to the candle soot. Here's some things to try:

- Build up a very heavy layer of soot on the glass, then try to measure the resistance again. Aim for at least 3-4 times as much soot as you tried before.

- If and when that fails, heating the glass with the soot to a high enough temperature may allow the remaining candle grease to evaporate. Place your piece of glass over a bunsen burner and keep it there for a while. Make sure the glass doesn't start to melt though - that's a different instructable altogether...

- If that still doesn't give you a good conductivity - try compacting the soot layer using a second piece of glass that you lay on top of the first. Maybe the soot is just too powdery to give a good conductance.

I'd be surprised if you couldn't get at least some conductivity using a combination of these...

Thanks for your ideas =o)

Unfortunately, I don't have access to a Bunsen burner (neither a welding torch or equivalent), so I tried with a simple lighter ... But I did not heated it a too long time, because I was afraid the piece of glass was going to break again.

When try to compact the layer with an other piece of glass, some of the soot glue itself on this second piece of glass, thus, destroying the layer ...

Even with more soot, more compact, and "re-cooked", the multimeter still displayed nothing.

What about a wood fire's soot? Or a gas fire (Bunsen burner)?

One can try. Some wood, I would bet (no pun intended) have a higher concentration of non-conductive (and maybe non-oxidizing) materials in them (pine?). But a somewhat pure carbon (charcoal) is made by burning wood with most of the oxygen taken out of the picture, so it smolders very slowly. I thought I read either an instrucable or a MAKE project concerning making charcoal.

That's a great idea...there have been a few ibles on making charcoal. Chooseausername, try making some (or buying *gasp*) some charcoal, smashing it up, and compacting it onto your glass. But before you grind it, make sure the stick actually conducts. And do it outside, charcoal gets messy.

I failed to produce black smoke, and the few smoke did not "glued" itself on the surface of the piece of glass like do the more greasy candle soot ...
The charcoal's carbon seems to burn directly into CO2 ...

Never mind.



Well, as I knew that charcoal powder was not going to be thin enough (like candle's soot particles) I tried to generate charcoal soot instead ...
Then, I forgot it was not exactly what you proposed, and I posted my report as a reply to you =o]

My goal was actually to "create" a thin layer of carbon (particles of molecular scale) over the surface of the glass.
Charcoal powder would not fulfill this requirement ... =o/

Hmm, instead of using a hydrocarbon (like paraffin) have you tried any woods, papers, or other materials ?

I tried with some type of woods. The candle's black smoke seems to be generated by a bad/incomplete combustion of the vaporised wax. With the type of wood I tried, instead of a black smoke, I get a white smoke. The full combustion seems to continue into the ember. So, seems I can't collect particles with carbon thanks to the smoke. Never mind, it was just an experimentation.

No, it's ok, it gets us all to think about something....I am intrigued...and now that you mention it, I should have expected as much. Most of the carbon in smoldering wood would remain solid and become charcoal. I remember when I lived at home that we always knew when the furnace needed cleaning (it was fuel oil / forced air) by the "puffs" of carbon soot we'd see floating about. But I am not sure exactly what process caused that condition.

Not much soot will be produced by charcoal. It is to be used in place of the soot. :-)

It probably is: the "lead", i.e. graphite in a pencile (ones not having a really high clay content) are conductive. I have tested this with a no.2 pencil.....drawn a heavy line and test it for conductivity....it was conductive.

duh. haven't you heard of the amd L1 pencil trick? you draw across the li bridges with a graphite pencil to unlock the multiplier.

Ok, didn't know if you knew that "graphite" was a form of carbon or not. ;-)

Thanks Goodhart. I'm not sure, but I think these candles are made of paraffin.

. Since Carbon _does_ conduct, I'm guessing that the resistance of what you are trying to measure is pretty high (out of the range of your meter). I'll guess because the soot particles are not actually in intimate contact with each other. . Try depositing a very thick layer of soot and compressing it. Another piece of glass should work.

I tried to compact it a little, just to see, but I measured nothing.

Well, my goal was to try to deposit a thin layer of carbon over non conductive matter (like glass). Candle soot did not work as expected, so I'll try an other method =o)

. Does it have to be Carbon? You're going to have a hard time keeping deposited Carbon in place if there is any vibration or physical contact. Would some type of conductive paint work? Plus, I would think that you could achieve a much more consistent coating with spray paint.

Does it have to be Carbon?

Not necessarily ...
Actually, carbon was interesting for different reasons, and I tested candle soot because it was easy to produce.
It was just an easy and quick experiment to test out the possibilities.

You're going to have a hard time keeping deposited Carbon in place if there is any vibration or physical contact.

Yes, that's why candle soot seemed nice : it "glued" itself on the glass. =o)

Would some type of conductive paint work? Plus, I would think that you could achieve a much more consistent coating with spray paint.

Even with a spray paint, I'm not sure it would be thin enough for the potential applications I was imagining ...
I think I'd be more interested about vaporization of metals over a piece of glass (not even sure it's possible without breaking the glass).

Again, there no real project behind it : it's mainly for experimental purposes.

He might even collect it on a piece of aluminum foil, funnel it into some sort of cylinder, and than compress that?

try collecting more soot