I wish to know thw specifice energy available from using fluorine as
an oxidant in rocket engines rather than Lox (liquid Oxygeen)

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Request for Question Clarification by mathtalk-ga on 02 Aug 2003 20:19 PDT

Hi, haroldrabbit-ga:

Do you still wish to know the difference in potential energy available
from the reaction H2 + F2 => 2 HF versus 2 H2 + O2 => 2 H2O  ?

[Hydrogen Fluoride]
http://www.inchem.org/documents/pims/chemical/hydfluor.htm

regards, mathtalk-ga

The molecular weight of florine is about 15% higher than oxygen so
this will reduce the performance as a rocket engine oxidizer, but
florine may still have an edge The big disadvantage is even trace
amounts of water make hydrofloric acid which would destroy the florine
tank unless it was made of wax or lead. I suppose some light weight
metal resists hydrofloric acid, but it is likely very expensive, bucky
tubes perhaps?    Neil

To echo the general thrust of neilzero's comments, although the
electronegativity of Fluorine is somewhat higher than that of Oxygen
(3.98 vs. 3.44 on the Pauling scale), its atomic weight is
proportionately even higher (roughly 19 for Fluorine vs. almost
exactly 16 for Oxygen).  Thus the increased reactive potential of
Fluorine fails to keep pace with its greater mass.

Also the only compounds that are "stable" in the presence of Fluorine
are those which are already chemically saturated by Fluorine,
excepting the "noble gases" which would not be useful as containers. 
(In fact one of the otherwise "inert" noble gases, xenon, was found in
1961 to form a stable fluoride, XeF4.)

This makes the safe preparation and storage of Fluorine, a highly
noxious gas, in large quantities problematic (and prohibitively
expensive).

regards, mathtalk-ga

Teflon (polytetrafluoroethylene) would be a good material to store
fluorine in.  Don't know about its thermal and mechanical properties
for a combustion vessel though.

Nickel-plating will work well in the container, since HF will react
with Ni to form a coating of NiF2, which is quite resistant to further
attack.

Dick