Flameless Fire

Here's something weird I discovered while playing with my torch. I had a little chunk of flint about 1" long, and 3/16" wide, and wondered what would happen if I heated it up with my torch. Would it make thousands of small sparks, or one big spark? So I tried it out. I heated up the tip of the flint with the torch until it glowed red. I removed the flame thinking the stick of flint would cool off, when to my surprise, it glowed brighter and brighter, and the heat spread. Pretty soon the flint was melting, and about to drip onto the floor, so I tried to blow it out. When that didn't work, I took a spray bottle full of water, and threw water on it to extinguish it. after it dried off, I could see the silvery flint turned a rusty color.

Unlike those "flameless" lighters, that you can still see a faint flame, I could see no flame at all in this experiment, only a spreading glowing red. I'm not really sure if this is technically a fire, but it did spread and continue to "burn".

From Reinhard Walter Buchner (rw.buchner@verbund.net): 

	Actually this is very easy to explain. The flints are composed
	of cerium and iron oxide. Using your torch, you achieve the
	ignition temperature of this "thermite" composition and it continues
	to burn w/o the need for additional energy (heat). It is a very
	exothermic (i.e.: creates heat) process and will continue until
	there is no more iron oxide or cerium left over. All that is left
	over is a white ash product.

	Another thermite composition is aluminum and iron oxide. This
	requires a pretty high ignition temperature of a few thousand
	degrees Celsius. However, using Mg ribbon or powder, this is
	easily achieved. Once this reaction is started, there is almost
	no way to extinguish it (with the exception of maybe gobs of
	sand). Water will NOT extinguish the fire! The resulting heat will
	melt through almost anything made of metal. Try it (using small
	amounts) and place this mixture across two 3/16" strips of iron.
	After the thermite reaction is over, examine the iron. You will find
	that they are welded together! If you use a large enough amount,
	you can burn through a huge chunk of iron (like a V-8 block) with
	ease. If you try it, PLEASE do be careful, tho. In WW2, Germans
	used Thermite to weld railroad tracks together.

	The reaction that takes place is a so-called Red-Ox reaction.
	This holds true because the reaction, that takes place, is dual
	action. A reduction and an oxidation takes place (which is also
	where the name "red-ox" comes from) at the same time.

		2AL+Fe˛Oł->AL˛Oł+2Fe (for the true thermite reaction)
		
	Following the electronegativity rules, this works out to:

		Reduction: 2Fe3(+) + 6e(-)  -> 2Fe
		Oxidation: 2Al -> 2Al3(+) + 6e(-)

	For the flints, the chemical equations would be:
	
		2Ce+Fe˛Oł->Ce˛Oł+2Fe

		Reduction: 2Fe3(+) + 6e(-)  -> 2Fe
		Oxidation: 2Ce -> 2Ce3(+) + 6e(-)

	I forgot to mention (in case you want to try the true Thermite)
	the weight (!) ratio is 1:3 for aluminum  vs. iron oxide. This is
	a very hefty reaction. The reason why the flints simply "glow"
	and do not throw a shower of sparks, like the true Thermite,
	is (more than likely) because the mixture is not chemically
	"proper". In other words, the mixture ratio of cerium to iron
	oxide is not 1:3, but rather some other ratio. For their normal
	use (to make sparks), this isn´t necessary and as cerium is a
	rare element, it makes for cheaper production, not using too
	much of this in the flints.

Note that it was found, thanks to another e-mail, that the flint is actually an alloy of cerium and iron, not iron oxide. But the above information is still interesting to think about.

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