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Author: Subject: Pyrophoric Lead - Nanopowder?
W1PHD
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[*] posted on 8-12-2002 at 12:42
Pyrophoric Lead - Nanopowder?


I'm doing an article on Nanotechnology and want to argue that nano-powders have been around for a long time. I think that old-time magicians used pyrophoric lead dust to create the flash and smoke when they waved their hand? May have been made by decomposing lead tartrate in a loosely stoppered vial. Does anyone know if the resulting ultra-fine lead powder is nanoscale?
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Polverone
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[*] posted on 8-12-2002 at 14:33


Nanoscale as in less than 1x10^-8 meters in diameter? I don't think so. Some colloids are on that order of size, though I don't know if one could actually isolate them as bulk powders.
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[*] posted on 9-12-2002 at 05:43
Nanopwders


I appreciate the reply that pyrophoric lead may not get down to nanometric dimensions. Let's expand the topic.

Can anyone suggest traditional processes that may possibly produce nanopowder (as opposed to colloidal suspensions, etc.)?

PS. This topic is now in the wrong category. Where should it be, general chem?
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[*] posted on 9-12-2002 at 10:39


Milling in isolation from oxygen (in sealed vessel or under hydrocarbons) is one method. Another, mentioned by W1PHD, is cautious thermal decomposition of carboxylic acid salts (tartrates, oxalates, etc.) in isolation from oxygen. I know that pyrophoric lead and iron can be prepared by this method, perhaps cobalt and manganese too.

Oxide removal won't generally lead to pyrophoricity, since particles have to be extremely fine size to self-oxidize to ignition. Some metals are of course more pyrophoric than others. The cerium-iron alloy used in lighter flints is quite pyrophoric. I imagine that you could prepare a pyrophoric powder from it by grinding/crushing under a hydrocarbon layer.

Pyrophoric powders prepared by chemical means (at least for chemistry demos) are formed in sealed glass ampoules and released into the air by breaking the glass and pouring out the powder. I suppose that they could be made in larger quantities and stored if you could keep a reaction vessel flooded with an inert gas during the thermal decomposition, then store the powder under inert solvent.

W1PHD, I don't know exactly what you would count as a traditional process, but carbon-60 (Buckminsterfullerene, "buckyball"), though discovered and isolated only in the 1980s, is naturally produced in many combustion processes (such as the smoldering of a cigarette). But I'm not sure that counts if you don't want colloids... Basically, I think that you will have a very hard time finding (older) processes that yield nanoscale powders without colloids, because Brownian motion is going to keep all particles of that size (except, perhaps, for very dense metals) suspended in whatever surrounding medium they appeared in.
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[*] posted on 9-12-2002 at 11:41
Nanotech


Turns out that digging into Nanotechnology is akin to opening up a can of "nano-worms". My orginal hypothesis was that some of the nanotech claims can be achieved using classical methods. (Forbes magazine tells us to beware of the Nano Pretenders).
But I'm no longer sure of the definition of nanotechnology. Some descriptions fit chemistry. Others sound like a hybrid of chemistry/mechnanical engineering as practiced by non-chemists using "atomic tweeezers". I'll grant that if one uses an atomic force manipulator to make a compound, its not traditional chemistry - at least the process. But what if we make the same product in a test tube? Is it still a nano-material?
So maybe we should define traditional methods as those used before the invention of nanotechnology. What date? Some say that nanotechnology was invented by IBM when the wrote "IBM" with atoms. IBM modestly claims that they only invented nanoscale science. I think the date was the mid-1980's - at least the Nobel Prize was granted in 1986.
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