Yeah, that’s the problem with nano sizing – the oxide layer goes from being a
welcome level of protection (in the micro scale) to something that can
noticeably affect performance if not controlled carefully.
Troy
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On ;
Behalf Of roxanna Mason
Sent: Wednesday, 4 May 2022 10:59 AM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: Regarding alitec propellants
A colleague of mine worked at a company called 'Technanogy'. They had a
patented process to make nanometer sized Al to alleviate the agglomeration
issue.
Don't know what became of them or their invention. Another problem with
aluminum powder is the oxide layer becomes a significant % of the total mass of
the particle unless it's kept under an argon or helium blanket. VallyMet makes
spherical Al powder by spraying moltyon Al in a helium atmosphere. If you keep
it in GHe the oxide can be avoided, IF you can keep it blanketed.
Ken
On Tue, May 3, 2022 at 3:31 PM Troy Prideaux <troy@xxxxxxxxxxxxxxxxxxxxx
<mailto:troy@xxxxxxxxxxxxxxxxxxxxx> > wrote:
Ben,
The problem isn’t HTPB – I’ve certainly measured APCPs with both HTPB and PPG
at 100% Isp efficiency – the problem is with the Al. Typically, a highly loaded
Al propellant will suffer some agglomeration issues. The more you load the AL,
the more likely this is to occur at some level ie. the turning of micro or
nanoscopic particles into much larger ones at the diffusion layer or
thereabouts.
With metals like Al, residence time is a big issue as you want all the metal
burned before it exits the nozzle and the size of the particles obviously
affect their times to complete combustion.
The apparent advantage with a coating of lithium is that the lithium, whilst
adding to chamber enthalpy, also *explodes* on a microscopic scale when heated
or combusted (I can’t remember the exact mechanism). This explosion apparently
dramatically reduces the tendency of the Al to agglomerate into much larger
particles on the surface of the propellant hence keeping the particles small
and residence time low and keeping c* closer to a more optimum efficiency.
Troy
From: arocket-bounce@xxxxxxxxxxxxx <mailto:arocket-bounce@xxxxxxxxxxxxx>
[mailto:arocket-bounce@xxxxxxxxxxxxx ;<mailto:arocket-bounce@xxxxxxxxxxxxx> ] On
Behalf Of Ben Brockert
Sent: Wednesday, 4 May 2022 3:12 AM
To: arocket@xxxxxxxxxxxxx <mailto:arocket@xxxxxxxxxxxxx>
Subject: [AR] Re: Regarding alitec propellants
Wouldn't that show up as variation of c* efficiency? The models assume the
chemicals are fully involved, if a significant amount of propellants are going
out the nozzle unreacted then there would be a performance shortfall between
the real motor and the model.
Does non-lithiated HTPB run at 85% c* typical?
Do lithiated rocket programs take into account that lithiated propulsion
engineers will be less worried about performance numbers?
On Tue, May 3, 2022 at 6:28 PM Barry Jolly <1bcjolly@xxxxxxxxxxxxx
<mailto:1bcjolly@xxxxxxxxxxxxx> > wrote:
Question: Do computer programs such as Micropep and NASA’s CET85 have the
ability to predict improvements in parameters, such as Isp, due to changes in
combustion phenomena? From my understanding of Alitec’s explanation, their
propellants increased performance is due to a difference in boiling temperature
of lithium as compared to aluminum in alloy form causing an explosion of the
alloy into nano-type particles which burn very close to the surface of the
propellant. Such explanation appears to me to be based on burning
characteristics of the propellant rather than differences between enthalpies of
propellant reactants and exhaust products.
Sent from my iPhone
