kilowatt
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High Temperature Specialty Thermite
Does anyone think it would be possible (hypothetically, if you could find a suitable container) to make a thermite using cerium, lanthanum, or
praseodymium to reduce tungsten(IV) oxide in order to release molten tungsten? Those rare earth metals seem to be the only highly reactive metals
with a suitably high boiling point.
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Bert
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I believe you will find Titanium sufficient, and easier to come by as well. Graphite might just barely serve as your container...
I also believe this belongs in the above sticky thread on exotic thermites, not in a new thread.
[Edited on by Bert]
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Sauron
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There's a document kicking around the forum on exotic thermites. I have posted it previously. Worth your while to look for it. UTFSE.
Sic gorgeamus a los subjectatus nunc.
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franklyn
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Problem with your choices is precisely their reactivity see _
http://www.webelements.com/webelements/elements/text/La/key....
http://www.webelements.com/webelements/elements/text/Ce/key....
http://www.webelements.com/webelements/elements/text/Pr/key....
You would need to work with the powders in an inert gas atmosphere
to prevent ignition from mere handling by their pyrophoricity. Titanium ,
and Praseodymium have practically the same boiling point , along with
Cerium all are less than the melting point of Tungsten. Lanthanum is
only 48º C higher. Depending on the temperature of reaction that won't
be enough of a margin.
http://www.webelements.com/webelements/elements/text/W/heat....
http://www.webelements.com/webelements/elements/text/La/heat...
http://www.webelements.com/webelements/elements/text/Ce/heat...
http://www.webelements.com/webelements/elements/text/Pr/heat...
http://www.webelements.com/webelements/elements/text/Ti/heat...
Although expensive Zirconium is not as much as the others which sell for
ten times more. It has a boiling point 987º C higher than what Tungsten
melts at and gives nearly the heat of Aluminum. Thorium is better still It's
boiling point is 1398º C higher than what Tungsten melts at and gives
just slightly more heat than magnesium. Can't be too stingy with Tungsten.
http://www.webelements.com/webelements/elements/text/Zr/heat...
http://www.webelements.com/webelements/elements/text/Th/key....
http://www.webelements.com/webelements/elements/text/Th/heat...
The surface of the melt will form Tungsten carbide in contact with graphite
so consider lining with a refractory powder of Thorium oxide.
Heats of formation derived from the CRC handbook.
Tungsten ( WO2 ) -590 _ KJ / mol
Tungsten ( WO3 ) -943 _ KJ / mol
Zirconium ( ZrO2 ) -1100 _ KJ / mol
Thorium ( ThO2 ) -1226 _ KJ / mol
WO2 + Zr -> W + ZrO2 __ -1100 - ( -590 ) = - 510 KJ per mol of W
WO2 + Th -> W + ThO2 __ -1226 - ( -590 ) = - 636 KJ per mol of W
Given the very high heat of fusion of Tungsten , WO3 gives higher results
2 WO3 + 3 Zr -> 2 W + 3 ZrO2 __ 3( -1100 ) - 2( -943 ) = - 707 KJ per mol of W
2 WO3 + 3 Th -> 2 W + 3 ThO2 __ 3( -1226 ) - 2( -943 ) = - 896 KJ per mol of W
WO3 and Thorium looks like a winner
________________________________
For comparison the thermite reaction of Iron oxide and Aluminum
Iron ( Fe2O3 ) -824 _ KJ / mol
Aluminum ( Al2O3 ) -1676 _ KJ / mol
Fe2O3 + 2 Al -> 2 Fe + Al2O3 __ -1676 - ( - 824 ) = - 426 KJ per mol of Fe
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kilowatt
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Wouldn't WO3 be too volatile?
Also is there a way this discussion may be moved to the exotic thermites thread?
[Edited on 28-11-2007 by kilowatt]
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franklyn
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| Quote: | Originally posted by kilowatt
Wouldn't WO3 be too volatile? |
An oddity of high melting temperature metals is that their oxides will boil at
much lower temperatures , it is a physical property and unavoidable. The
oxides of Tungsten are such. How the mixture is preheated and initiated will
determine the vigor of the reaction and mitigate gas formation. It may be
desirable to initiate from the bottom up instead of top down , this way
the heat is retained by the tungsten which sinks and the Thorium refractory
oxide as it forms protects the mixture above from excessive heating. Quite
the opposite from what occurs if started from the top. Another approach
might be to press the mixture at very high pressure into a solid which then
would be heated to initiation by high frequency magnetic induction.
theres a thread on induction heating here _ http://www.sciencemadness.org/talk/viewthread.php?tid=3626
another note here describing induction preheating of Calcium thermite _
http://img31.imagevenue.com/img.php?image=82480_P_u_31lo.jpg
also posted in the Thermite thread _
http://pyrobin.com/files/thermit(e)%20journal.pdf
This attachment is selections from _
Handbook of Preparative Inorganic Chemistry Vol 2 , George Brauer
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