Molecular sieve abstract
A dual stabilization system for urethane - crosslinked double base
propelt. The stabilization system includes N-Methyl-p-Nitroaniline
and Aluminum Silicate molecular sieve. The two stabilizers function
in a complementary fashion wherein the N-Methyl-p-Nitroaniline reacts
with and makes harmless the nitrogen (III) oxide during the propellant
aging process. The Aluminum Silicate molecular sieve is selected
to have a pore size of more than about 10 angstroms and reacts with
and makes harmless the nitrogen (V) oxides, primarily nitric acid,
during the propellant aging process.
Molecular sieve claims
What is claimed is:
1. A solid urethane - crosslinked double base propellant comprising
nitrocellulose, nitroglycerin, HMX, amonium perchlorate, aluminum,
N-Methyl-p-Nitroaniline and aluminum silicate molecular sieve.
2. The propellant composition of claim 1 wherein said aluminum
silicate molecular sieve has a pore size selected to be greater
than about 10 angstroms.
3. The propellant composition of claim 2 wherein said N-Methyl-p-Nitroaniline
comprises about 2.0 percent by weight of said propellant and said
aluminum silicate molecular sieve comprises about 0.2 percent by
weight of said propellant.
Molecular sieve description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a urethane-crosslinked double
base propellant and more particularly to a stabilization system
for urethane - crosslinked double base propellants.
2. Description of the Prior Art
One of the problems encountered in nitrate ester systems such as
propellant casting powder and explosives and urethane - cross-linked
nitrate ester propellants is that their aging process during storage
and the like may result in the generation of certain undesirable
products that partially interfere with or destroy the desirable
characteristics of the propellant. The principal products generated
in the aging process of nitrate esters include N.sub.2 O.sub.4
NO.sup.+, NO.sub.3.sup.-, NO.sub.2.sup.+, NO.sub.2.sup.-, HNO.sub.3
N.sub.2 CO.sub.2 and NO. Other products are also produced.
The present invention is a complementary dual stabilizer system
that converts the most harmful of the above described products into
relatively harmless products.
SUMMARY OF THE INVENTION
Briefly, the present invention comprises a dual stabilization system
for urethane - crosslinked double base propellant. The stabilization
system includes N-Methyl-p-Nitroaniline and Aluminum Silicate molecular
sieve. The stabilizers function in a complementary fashion wherein
the N-Methyl-p-Nitroaniline reacts with and makes harmless the nitrogen
(III) oxide during the Propellant aging process. The Aluminum Silicate
molecular sieve is selected to have a pore size of more than about
10 angstroms and reacts with and makes harmless the nitrogen (V)
oxides, primarily nitric acid, during the propellant aging process.
STATEMENT OF THE OBJECTS OF THE INVENTION
An object of the present invention is to provide a propellant that
retains its desired characteristics during aging.
Another object of the present invention is to provide a propellant
that includes an effective dual stabilizer system that minimizes
the retention of harmful chemicals during the aging process.
Still another object of the present invention is to provide a stabilization
system that is particularly effective for urethane - crosslinked
double based propellants.
Other objects, advantages and novel features of the invention will
become apparent from the following detailed description of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A urethane - crosslinked double base propellant with which the
stabilization system of the present invention has been found to
be effective includes a binder, a binder-oxydizer, one or more principal
oxydizers, fuel and a burning rate modifier. These constituents
may be chemically characterized as follows:
Binder ##STR1## where R is a polymer chain radical
R.sup.1 is a polymer chain radical that may or may not be the same
as R.
Binder-oxydizer [Nitrocellulose (NC)] ##STR2## where n = the number
of repeating units which is the function of the type of nitrocellulose.
Principal Oxydizer [Nitroglycerin (NG)] ##STR3##
Principal Oxydizer (HMX) ##STR4##
Burning Rate Modifier (Ammonium Perchlorate)
fuel -- Aluminum
The stabilizers comprising the dual complementary stabilizer system
of the present invention include:
N-Methyl-p-Nitroaniline (hereafter referred to as MNA) and ##STR5##
Aluminum Silicate (Al,Si,O) (molecular sieve powder) ##STR6##
It is important that the pore size of the Aluminum Silicate molecular
sieve is selected to be greater than about 10 angstroms.
Mechanism
Nitrogen dioxide (NO.sub.2), the principal product generated in
the aging process of nitrate esters, disproportionates in the following
manner: ##STR7## where NO.sub.2 is nitrogen dioxide
N.sub.2 o.sub.4 is nitrogen tetroxide
No.sup.+ is nitrogen (III) oxide (nitrosonium ion)
No.sub.2.sup.+ is a nitrogen (V) oxide (nitronium ion)
No.sub.3.sup.- is a nitrogen (V) oxide which eventually leads to
nitric acid (HNO.sub.3)
Reaction (1) causes an auto catalytic decomposition of the nitrocellulose
(NC) and the nitroglycerin (NG) in the propellant to breakdown to
yield more NO if not stabilized. This produces undesirable heat
and can cause propellant burning.
The products of both equations (1) and (2) are present when the
stabilizer MNA is not present is the propellant and only the nitrogen
V oxides are present when the stabilizer MNA is present. MNA is
desirable as the stabilizer for nitrocellulose (NC) and nitroglycerin
(NG).
The disproportionation to nitrosonium nitrate, equation (1), is
the perdominant equilibrium in propellants, containing a RNH functionality,
forming nitroso derivatives which readily decompose to gases: ##STR8##
The nitric acid also generated is undesirable as it can acid saponify
ester and urethane functional groups to degrade the binder and also
can degrade nitrate esters as well.
The stabilizer system of the present invention eliminates this
nitrosation of the binder and completely removes all nitrogen oxides
produced in the aging of nitrate ester explosives. First, MNA nitrosates
much faster than the urea of urethane functionalities, forming a
stable N-nitroso derivative which can rearrange to a stable C-nitroso
derivative (N-methyl-o-nitroso-p-nitroaniline): ##STR9##
Referring to equation (4) the first product, ##STR10## is non-reactive
and harmless in the propellant; the third product, ##STR11## does
not occur as a product during the normal stored life of a propellant
for rocket motors. However, the second product HNO.sub.3 (nitric
acid) is harmful and undesirable.
The function of the second stabilizer (aluminum silicate - molecular
sieve) is to eliminate or minimize the effect of HNO.sub.3 as follows:
##STR12##
Nitric acid scavenging by the porous aluminosilicates is primarily
an acid-base interaction. The primary benefit achieved in this process
comes from this buffering action as the nitrate ion is inocuous
as a neutral ion but an oxidizing ion in an acid environment. The
products of the neutralization are then the protonated aluminosilicate
and nitrate ion which is absorbed into the matrix of the aluminosilicate
also.
Experiments have shown that the use of the second stabilizer (Aluminum
Silicate molecular sieve having a pore size that is selected to
be greater than about 10 angstroms) has reduced the acidity from
a pH of 1.4 (without second stabilizer to a pH of 7.2 (with second
stabilizer). |