Space Forum / Space Flight / April 2006

Messy posting replaced with:-)

http://www.webelements.com/webelements/elements/text/O/enth.html

The Diatomic enthalpy bond for O=O is 498 kJ/mol

The Diatomic enthalpy bond for O-H is 427 kJ/mol

http://www.webelements.com/webelements/elements/text/H/enth.html

The Diatomic enthalpy bond for H-H is 439 kJ/mol

So, to burn O2 and H2, the O=O bond must be broken and the H-H bond must
be broken before H-O-H can be formed. Breaking the bonds takes energy,
while recombining into H2O produces more energy that it took to break the
bonds.

O2 -> O + O - energy (breaking bond)
H2 -> H + H - energy (breaking bond)
H + H + O -> H2O + energy (bonding)

http://www.webelements.com/webelements/elements/text/Xe/enth.html

The Diatomic enthalpy bond for O=Xe is only 36 kJ/mol

Two compounds of Xe and O can be formed, XeO3 and XeO4. In the compound
XeO4, the higher energy O=O bond is replaced with a much, much lower
energy bond of O=Xe. Only 36 kJ/mol vs Oxygen's normal O=O bond of 498
kJ/Mol.

XeO4 -> Xe + O + O + O + O - energy (breaking bond)

O + O -> O2 + energy (bonding)

Or, the total reaction

XeO4 -> Xe + 2O2 + energy

So, the oxidizer XeO4 has more energy than O2 in that breaking the bond
takes much less energy. Essentially, an order of magnitude less energy to
break the bond.

On the negative side, the low bonding energy means that XeO4 becomes
unstable with elevated temperature. Elevated meaning "room" temperature,
the thermal energy is enough to break the Xe-O bond, the Oxygen combines
with itself and releases lots of energy. Also, it's a solid and explosive.

To be useful, something would have to be used to moderate the spontaneous
reaction that occurs at room temperature. I would think that mixing it
with liquid oxygen might work, maybe a gel of LOX-XeO4.

On the Fuel side of the equation and Argon.

http://www.webelements.com/webelements/elements/text/Ar/enth.html

The Diatomic Ar-Al has a low enthalpy bond of 5 kJ/mol

http://www.webelements.com/webelements/elements/text/Al/enth.html

Diatomic Al-Al has an enthalpy bond of 133 kJ/mol

Aluminum bonds with itself with an energy of 133 kJ/mol, with Argon it's
only 5 kJ/mol. Again, an order of magnitude less energy to break the
bond.

Aluminum by itself as a fuel has it's own problems. Pure aluminum when
exposed to Oxygen in the atmosphere spontaneously forms a coating of
Aluminum-Oxide on the outer surface. The Aluminum-Oxide coating protecting
the rest of the Aluminum from oxidizing. So, as aluminum is ground into a
fine powder, and exposed to oxygen, part of the Aluminum is already
reacted. The ratio of Aluminum to Aluminum-Oxide would go down as the
aluminum is ground finer and finer. But if the Aluminum is bound to Argon,
instead of itself or Oxygen, then...

If it were possible to make ArH4, it would be the "Cat Meow" of fuels.

I would think the ArAl (or H2) fuel and XeO4 oxidizer would by far have
more energy that any other fuel/oxidizer combinations discussed on this
group in the past.