White Yeti
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Boron rocket fuel.
I know this subject has been discussed before, but other posts don't contain the information I seek.
Elemental boron has an extremely high energy density, but it has limited applications in rocket boosters and aircraft engines because of the formation
of boron trioxide,a nasty, tough, glassy substance that clings to reactor blades, and rocket nozzles.
I looked up how rocket boosters were made. They are made from ammonium perchlorate and aluminium powder.
Here's the question: Why does NASA use aluminium in solid rocket boosters when they could be using boron instead?
Boron oxide melts at ~300C, so it should be expelled out through the nozzle as the fuel is consumed. Aluminium oxide melts at ~1000C.
Do you guys think boron would improve rocket booster energy content? If so, by how much? And is it worth it?
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Bot0nist
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On aluminum
"I suppose aluminum is in an ideal place on the periodic table. If it were to the left or lower down, the bonding would be more ionic and less
favorable (as aluminum can reduce sodium oxide, oxygen has a smaller atomic orbital and it is less favorable for it to hold a double negative charge).
If it were above or to the right, the element would not be as electropositive. So it could be said that aluminum is in a middle spot where it
experiences the best of both worlds, in terms of being able to reduce oxides of other elements." ~ Anders Hoveland http://www.sciencemadness.org/talk/viewthread.php?tid=10249&...
Is this relevant to your question about Al?
I assume you saw franklyn's post in the thermobaric thread. http://www.sciencemadness.org/talk/viewthread.php?tid=7769&a...
Would the formation of the aforementioned boron trioxide be the problem? Its melting points are 450 °C (trigonal) and
510 °C (tetrahedral), so I guess it would be melted and blown through with the exhaust.
I'm sorry I can't be of much help.
U.T.F.S.E. and learn the joys of autodidacticism!
Don't judge each day only by the harvest you reap, but also by the seeds you sow.
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The WiZard is In
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Quote: Originally posted by White Yeti  |
I looked up how rocket boosters were made. They are made from ammonium perchlorate and aluminium powder.
Here's the question: Why does NASA use aluminium in solid rocket boosters when they could be using boron instead? |
Easy Isp.
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The WiZard is In
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Logic would suggest they (NASA) uses aluminium vs
boron ... because it works better.
La European Space Agency agrees.
Mul, Korting and Schöuyer
A Search for New Sortable High-Permanence Propellants
ESA Journal 1990, Vol. 14 p. 264
[I had a free subscription.]
"The use of boron as an additive generally leads to
somewhat lower performance than when using Al.
Only for nitronium perchlorate is the reverse case."
"The best performance is obtained for the propellant
consisting of HNF as an oxidizer, Al as additive, and GAP
as binder. Isp 2943=m/s."
This is a bit confusing they ref table 12 which shows the Isp
as 3150 m/s. The reference propellant ammonium perchlorate,
Al, HTPb Isp is appx. 2943 m/s.
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White Yeti
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Ok, that makes sense. Thanks for the great info. I'll look into the HNF/Al rocket fuel a little further.
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The WiZard is In
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Table 12
HTPB =hydroxy-terminated polybutadiene
HNF = hydrazinium nitroformate (N2H5C (NO2)3
gAP = poly glycidyl azide ([C3H5N3O1]n
NP = nitronium perchlorate NO2ClO4
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