On Thu, 16 Oct 2003, Randall Clague wrote:
> Especially with Al2O3 in the exhaust. Atomic weight of Al2O3 is 102,
> compared to 18 for H2O, 28 for CO, and 44 for CO2...
The molecular weight of Al2O3 is actually pretty irrelevant, since it will
condense to a liquid at quite high temperatures, taking it out of the
gas-expansion picture entirely. But its heat of formation is very large
(which is why people use powdered aluminum in solids).
> ...But if there's no real detonation
> hazard, which seems reasonable...
Not a safe assumption. John appears to be thinking that there shouldn't
be a significant detonation hazard because a powder suspended in a liquid
doesn't give you molecular-level mixing. However, that level of mixing is
not necessary. Many multi-component explosives are not mixed at the
molecular level. ANFO, as used in the Oklahoma City bombing, is powdered
oxidizer in liquid fuel -- miscibility zero, explosive hazard high.
LOX/charcoal combinations have been used as commercial blasting explosives.
> Yeah. Anyone know how to compute or look up the activation energy?
> That's going to determine whether a fire goes WHOOSH or KABOOM!
Given that light-metal hydrides generally aren't very stable, and that
AlH3 decomposition will release raw aluminum, which reacts explosively
with *water*, never mind peroxide, I'd bet heavily on KABOOM!
I bet it catalyzes peroxide, too.
> Still, if it can be done at all safely - wouldn't amateur SSTO be a
> kick?
Sure would... Alas, I don't think it's quite that easy. :-(
Henry Spencer
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