[AR] Re: Stopping/restarting solids
- From: "Anthony Cesaroni" <anthony@xxxxxxxxxxx>
- To: <arocket@xxxxxxxxxxxxx>
- Date: Fri, 27 Mar 2020 20:59:54 -0400
Hi Terry,
As you know, NH4ClO4 is a mono-propellant but is usually treated as an
oxidizer. Squeeze it into the right conditions and it runs quite nicely on its
own. I've always been impressed with ammonium dinitramide (H4N4O4). IIRC, one
of its typical decomposition steps is NH4NO3 and N2O. It's been a while but
everything goes downhill from there and with a lot of exothem.. We tested it's
compatibility with H2O2 as that would be a very attractive proposition. Poof.
It's not.
How are you BTW?
Best.
Anthony J. Cesaroni
President/CEO
Cesaroni Technology/Cesaroni Aerospace
http://www.cesaronitech.com/
(941) 360-3100 x101 Sarasota
(905) 887-2370 x222 Toronto
-----Original Message-----
From: arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> On Behalf Of
Terry McCreary
Sent: Friday, March 27, 2020 8:39 PM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: Stopping/restarting solids
On 3/27/2020 5:43 PM, Henry Spencer wrote:
On Fri, 27 Mar 2020, ken mason wrote:
Not the same mechanism, Keeping F&Ox apart is different than solid
propellant which already has F&Ox intimately mixed.
But combustion still takes place largely in the gas phase, so things
introduced into the gas could still have an effect. Halon does *not*
separate fuel from oxidizer, it chemically clogs up the combustion
reactions themselves.
Pardon my remarks below, most of you probably know this stuff already, but I
can't help it, taught college chem in one place or another from 1976-2018.
(Elder daughter once commented rather ruefully, "Dad's a teacher... *anywhere*
is the classroom." :-))
Virtually every chemical reaction occurs as a series of what are called
elementary steps, each step involving collision or decomposition of one or two
(rarely three) species---molecules, atoms, ions, free radicals. The products of
one step are involved in a subsequent step unless they're final products of the
reaction. The sum of the elementary steps is the overall reaction. (Rocket
significance: possibly the most common example of an un-catalyzed vs. catalyzed
mechanism used in chem textbooks is hydrogen peroxide decomposition, alone and
in the presence of iodide ion.)
Often one or a few of the steps is significantly slower than the others.
That step(s) is the rate-determining step. Speed it up or provide an alternate,
faster step with a catalyst and the reaction goes faster.
Throw in a 'poison' (like Halon) that slows the step and the reaction slows or
stops completely.
One of the more important (rate-determining) steps in AP combustion is the
dissociation of solid NH4ClO4 into gaseous ammonia and perchloric acid (HClO4)
vapor--you'll see references to "A/PA vapor" in the literature. It's an
*endothermic* process, part of the reason the stuff can be so hard to ignite.
Those two species migrate away from the surface, then undergo all sorts of
other collisions.
Even simple fuels burn by complicated multi-step reaction chains, not
in a single step, and partially-burned products of one fuel molecule's
combustion catalyze combustion of the next one. The details are quite
complicated, and not too hard to interrupt if something grabs hold of
an intermediate product and won't let go.
Quite complicated indeed; a proposed mechanism for one combustion reaction--I
don't recall which one, octane maybe?--involved over 200 elementary steps.
What probably *would* be a problem with Terry's idea: while
combustion takes place largely in the gas phase, the key part of it
takes place not far above the surface, and the wind is blowing
*outward* from the surface as the solid decomposes. So even though
you don't need much Halon to interrupt combustion, getting even a low
concentration of it into the right place might be difficult.
True. It depends in part on whether there are other rate-determining steps that
occur farther away from the surface, and might be subject to poisoning.
Quiz on Monday. ;-)
Best -- Terry
--
Dr. Terry McCreary
Professor Emeritus
Murray State University
Murray KY 42071
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