I’ve played with PSAN propellants and have been involved in some academic
research into them decades ago. Yes, the phase stabilization is a solved issue
albeit generally with Isp costing modifiers.
PSAN propellants are an avenue worth pursuing if you have (a) a cheap and
plentiful supply of Mg power which you are willing to include into the
propellant in serious proportions and (b) are satisfied in maintaining a low
chamber pressure and are satisfied with the specific impulse cost at low
altitude conditions.
There have been PSANCP gas generators formulated without metal inclusions
but not many practical propellants. You generally need that extra energy the
metal brings along with a AN oxidizer – not only the lowering of your fuel
average electronegativity, but to also utilise more of AN’s oxygen ie. AN will
offer about 20% active oxygen to non-metallic fuels, but all of its oxygen to
highly metalised (particularly Mg) propellants.
There have been practical PSAN composite propellants developed in the past
with a lowish portion combination of Mg and Al but generally also require
combustion catalysts such as a dichromate (Ammonium or Potassium) or a chromite
(say copper).
I have seen PSAN propellants successfully operate at high chamber pressures
before, but they’re a lot more susceptible to issues involving the burn-front
advancing beyond the propellant surface due to micro porosity or sub optimal
binder wetting.
I certainly wouldn’t recommend developing high pressure PSANCPs if you’re
phase stabilising the AN yourself. It needs to be done professionally with the
right modifiers.
Richard Nakka has done some interesting testing with AN propellants without
needing Mg – he utilised a neoprene binder with a decent percentage of Al – the
chlorine content in the neoprene helps breakdown Al’s tough oxide coating. The
downside is a more onerous preparation due to having to dry out the volatile
binder prior to incorporating with oxidizer.
Things I don’t like about AN compared to AP:
Needs to be phased stabilised.
Often needs to be run with a lower chamber pressure to achieve reliability.
Needs to be a good enough purity
PITA to process – very dry processing that often needs hydraulic pressing for
med-high chamber pressure operation.
Difficult to wet properly
Often needs lots of Mg or burn rate catalyst
Generally can’t use Al (an a metallic inclusion) alone as there’s not enough
energy or Cl- ions to assist with oxide layer penetration.
Hygroscopic
More limited binder options
Sensitive with some metals such as zinc with moisture.
Troy.
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Ray Rocket (Redacted sender "ar0cketman" for DMARC)
Sent: Saturday, 28 July 2018 6:08 AM
To: Arocket List <arocket@xxxxxxxxxxxxx>
Subject: [AR] Cheap Solids? Amonium Nitrate: catalysis vs sensitization
AN shows significant promise to significantly lower the cost of solid
propulsion. Phase stabilization is largely a solved problem, particularly if
long-term storage isn't an issue. Rather, burning rate seems to be the
unsolved problem.
AN's all-gaseous combustion products bodes well for theoretical performance.
However, AN formulations have traditionally relied on the addition of
combustible metals to increase decomposition rate. This is a relatively costly
method, so I have been reviewing the literature with respect to catalytically
improving AN decomposition/combustion rate. So far, I have seen little on the
mechanism or how sensitivity may be affected.
Can anybody here shed light on this matter?
Has anybody here worked with a no/low metals AN formulation they'd be willing
to discuss?
Can anybody here point to work addressing the sensitivity vs decomposition rate
problem?
Many thanks in advance,
Ray
