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Author Topic: Why does aluminum react exothermically with palladium?  (Read 6301 times)

Offline lightarrow

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http://en.wikipedia.org/wiki/Pyrotechnic_initiator
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Palladium-aluminium

Palladium-clad aluminium wires can be used as a fuse wire, known as Pyrofuze. [9] The reaction is initiated by heat, typically supplied by electric current pulse. The reaction begins at 600 C, the melting point of aluminium, and proceeds violently to temperature of 2200-2800 C. The reaction does not need presence of oxygen, and the wire is
consumed. [10]



 

Offline RD

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Why does aluminum react exothermically with palladium?
« Reply #1 on: 01/03/2009 19:14:17 »
The reaction does not need presence of oxygen

The Aluminium wire would include oxygen in the form of aluminium oxide ...
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a thin surface layer of aluminium oxide that forms when the metal is exposed to air
http://en.wikipedia.org/wiki/Aluminum
 

Offline Bored chemist

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Why does aluminum react exothermically with palladium?
« Reply #2 on: 01/03/2009 19:29:08 »
The reaction is a weird one. The product is just an alloy of the 2 metals and I don't know why it's so enthusiastic about forming. I believe that platinum does the same sort of thing
I can vouch for the fact that if you wrap bits of Pd wire with foil then heat them till the Al melts they light up like burning magnesium.

Incidentally while it's true that Al forms an oxide layer it's not relevant in this case.
There's at least one case history of someone "discovering" this reaction by measuring the temperature of molten Al with a Pt vs Pt/Ir thermocouple. The thermocouple was under the liquid when the reaction started so there would have been no oxygen present.
 

Offline lightarrow

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Why does aluminum react exothermically with palladium?
« Reply #3 on: 01/03/2009 19:50:53 »
Next to the video it's written: "Palladium and aluminium ignite in an intense intermetallic reaction."
What is an "intermetallic reaction" and why can it be so exothermic? Somewhere someone says it could be due to electronic transfer from the electropositive metal to the noble one.

Yes platinum works too; in the same link you read:

"Pyrofuze comes as a solid wire of different diameters (from 0.002" to 0.02"), braided wire, ribbon, foil, and granules. Palladium, platinum, or palladium alloyed with 5% ruthenium can be used together with aluminium. [11][12] Pyrofuze bridgewires can be used in squibs and electric matches. Pyrofuze foils can be used for e.g. sealing of various dispensers or fire extinguishing systems. [13]"
« Last Edit: 01/03/2009 19:57:51 by lightarrow »
 

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Why does aluminum react exothermically with palladium?
« Reply #3 on: 01/03/2009 19:50:53 »

 

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