Breathable Carbon/Graphite ?

June 24, 2012 9:41 PM

I recently was playing with a cold solder gun, and I found the concept interesting. Is there an equivalent that can be filter air? I am looking for a type of graphite/carbon that can pass through air, and heats up when electricity is applied.
posted by digdan to science & nature (7 answers total)

Wait, are you looking at filtering and heating air by passing it thought hot graphite, or suspending graphite particles in the air and then heating them with current?

If you're talking about the second case, I think you're going to have the problem of catalytic form and would basically have a small scale grain elevator explosion the moment you brought it up to temperature. (Similarly, you can start a fire using iron as your fuel with medium to fine steel wool and a nine volt battery.)

If you're talking about something porous that would filter and heat the air, I think it would either clog very quickly (activated charcoal filters only last so long) or would ignite because of air flow and uneven heating.
posted by Kid Charlemagne at 9:55 PM on June 24, 2012

I'm having a hard time understanding the question you're asking.

In order for electricity to do anything, there has to be a circuit. That means that there has to be a continuous conductor (or resistor) all the way from the supply to ground. Air gaps don't conduct electricity, unless you convert the air into a plasma.

A suspension of graphite dust in air isn't a circuit, so no electricity can pass through it, and nothing is going to heat up.

Also, graphite powder suspended in air is subject to dust explosions. If it did somehow heat up, it would do so very rapidly (like milliseconds).
posted by Chocolate Pickle at 9:55 PM on June 24, 2012

I too am having difficulty understanding your question. Could you explain in more detail? I really am unsure what it is that you are proposing. What is "the concept" that you are referring to, and what do you mean by "can be filter air"? What do you mean by passing graphite/carbon through air? How do you plan to apply electricity to it?

I am finding your question extremely confusing and would appreciate more explanation.
posted by Scientist at 10:22 PM on June 24, 2012

Flow-through carbon fibre mesh, metal mesh (e.g. Tungsten), and porous ceramic block heaters exist for heating gases - but they're expensive & specialised parts. Think lab equipment, really specialised plastic moulding, etc..

They're really only useful where you want highly accurate & stable gas temperature (the low mass and high heat transfer means you can quickly control the amount of heat generated & transferred), and require filtered air/gas (else shit sticks to them, burns up, and clogs the element).

And you really don't want to breathe in the gases that are produced by burning dust…

FWIW, cold solder guns don't really work by heating up the carbon - they work by initially melting the solder due to the (relatively) high resistance joint at the contact points between the unmelted solder wire and the two sides of the jaw / tip. The bits of melted solder then make (again, relatively) low resistance contact with the two sides of the jaw, and the current passing through the solder between them melts the rest of it.

They're also crap soldering irons too…

The thing that makes them "cold" is that carbon is a crap conductor of heat - so the melted solder doesn't really heat the carbon tip up. This is how they differ from the old carbon-element Birko or Scope irons, which used the resistance of the carbon to produce heat.
posted by Pinback at 12:08 AM on June 25, 2012

If you blow air through hot porous carbon, you don't actually need electricity to keep it hot because it just burns.
posted by flabdablet at 5:53 AM on June 25, 2012

Graphite is a alomorphious crystalline structure, like a diamond. Technically, you can't really have a graphite dust. If it's ground up and the crystals are broken, you have amorphous, or partial, graphite. You would have a hard time stoking a diamond fire, or a graphite fire.

Graphite does not burn easily. It is one of the most nonreactive things that there are, that's why liquid steel is kept in graphite crucibles.

Lithium ion batteries are mostly graphite. I just shorted out a cell phone battery for a fraction of a second, and damn did that thing get hot. Stayed hot for a while. So you could use the battery as both the energy source and the heat radiator, I guess.
posted by StickyCarpet at 2:58 PM on June 25, 2012

Graphite is a alomorphious crystalline structure, like a diamond. Technically, you can't really have a graphite dust.

The term "alomorphious" made me curious, but I didn't find a single google hit for it. Was it meant to be something else? In any case, unless you grind it down to near the atomic scale, you can certainly have graphite dust, with the properties of graphite rather than amorphous carbon, diamond or any other structure.

Regarding the original question, this is essentially what hot-air guns do, although I believe the heating elements are usually made of a metal alloy rather than carbon. They can be used to solder plumbing, but not for electronics or other precision jobs.
posted by springload at 11:02 AM on June 26, 2012