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PYROTECHNIC GAS GENERANT COMPOSITION INCLUDING
~iIGH OXYGEN BALANCE FUEL
BACKGROUND OF THE INVENTION
s 1.FIELD OF THE INVENTION
The present invention relates to ingredients for use in pyrotechnic
gas generant compositions, and more specifically to fuels containing a high
oxygen balance. The gas generant compositions are useful as gas generant
propellants for air bag occupant restraint systems for automobiles, gun
io propellants, inflation and expulsion devices, flotation devices, ignition
materials, pyrotechnics, fire suppression devices and smokeless and smoke
producing rocket propellants.
2.BACKGROUND ART
There is high demand for pyrotechnic gas generant compositions
is which on combustion yield acceptable burning rates and provide, at
relatively low flame temperatures, a high volume of substantially non-toxic
gas and a low volume of solid particulate :matter that can produce smoke.
It is also important that resulting solid by-products from the combustion of
gas generant compositions be minimal, and the gaseous combustion
2o products be substantially non-toxic, and non-corrosive. Various
compositions of gas generants have been utilized in the past in an attempt
to reach the above desirable characteristics.
U.S. Patent No. 3,405,144 discloses a 1-azido-N,N,N'-
trifluoroformamidine that is useful in a propellant composition which
2s exhibits a high specific impulse. Specifically, the said material is
disclosed
to be useful in rocket fuel compositions.
Gas generant compositions have also been developed to include the
addition of modifiers to lower flame temperatures and increase gas
production. Further ingredients may be added such as binders, ignition
3o aids, slag formers, scavengers, and catalysts to improve various features
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of the underlying propellant. The modifiers and additional ingredients
often times, however, improve one aspect of the propellant composition
while also contributing to the production of undesirable by-products and
may increase the corrosiveness thereof. This is particularly
s disadvantageous in an automobile air bag environment.
One major gas generating composition having desirable
characteristics contains strontium nitrate and 5-aminotetrazole (SrNlSATZ)
as major constituents. This formulation is relatively non-toxic when
compared with sodium azide systems, has good ballistic properties and
~o retains the majority of solid combustion products as a slag or clinker
either
in the combustion or filtration areas of, for instance, an air bag system for
an automobile. These formulations also exhibit acceptable flame
temperatures of 2250°K to 2750°K depending upon the
stoichiometry of
the formulation and the oxygen to fuel ratio. Moreover, the strontium
is nitrate and 5-aminotetrazole formulations are relatively non-hygroscopic
and the ingredients do not exhibit crystalline phase changes aver the
operating temperature range of the air bag system.
Such a formulation, however, suffers with regard to gas output,
specifically, in the volume limited systems of a driver's side air bag. This
2o is because a high concentration of strontium nitrate is required to
maintain
a neutral oxygen to fuel (OIF) balance. Because inflator designs are
becoming smaller and smaller and, thus, more volume limited, propellants
are required to provide greater gas output and still retain the desirable
attributes of the s~ontium nitratel5-aminotetrazole systems.
2s Approaches have been taken to obl~ain the attractive features of the
above-noted propellants, while overcoming the low gas output thereof.
This has resulted in the development of propellants based on mixtures of
potassium perchlorate and oxygenated fuels such as guanidine nitrate and
aminoguanidine nitrate. These propellants are also relatively non-
3o hygroscopic, provide excellent gas output, high burning rates and only
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about two thirds of the solid combustion products of the above-noted
strontium nitrate and 5-amiaptetrazole based propellants. Unfortunately,
the solid combustion products do not form clinkers or slags which deposit
in the combustion or filtration area, but instead form very fme particulates
s in the gas stream which results in a smokey and dirty exhaust.
Smoke or dirty exhaust combustion products are not commercially
desirable, particularly, in automobile air bag systems since the production
of such product may cause undue anxiety on the part of drivers and
passengers involved in an automobile accident in which air bags are
to deployed. As a result, there is a need for a propellant material or gas
generant that exhibits high gas output upon combustion, but does not
produce unwanted by-products upon combustion.
SUMMARY OF THE INVENTION
The object of the present invention is to improve upon and to
~s overcome the deficiencies of the prior art and to provide a substantially
non-hygroscopic, substantially non-toxic gas producing pyrotechnic gas
generant composition that upon combustion produces a high gas output and
a high burn rate with limited non gaseous combustion products.
Another object of the present invention is to provide a pyrotechnic
2o gas generant composition including a high oxygen balance fuel, preferably,
azodiformamidine dinitrate, that produces the desirable high gas output at
a low combustion temperature and reduced non gaseous combustion
products.
Still another object of the present invention is to provide a
2s pyrotechnic gas generant composition including a high oxygen balance fuel,
preferably, azodiformamidine dinitrate, with the capability of self
deflagration similar to a solid monopropellant.
Yet another object of the present invention is to provide a
pyrotechnic gas generant composition including a high oxygen balance fuel
3o which will auto-ignite in an inflator at acceptable but low enough
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temperatures to ensure that the inflator only rupture but does not fragment
in a bonfire test.
Still another object of the present invention is to provide a gas
generating composition capable of producing a substantially high gas output
s upon combustion for use as an automobile air bag propellant. however,
the composition of the present invention may also be employed to inflate
such items as an inflatable raft or passenger escape chute of an airplane,
as well as for gun propellants, pyrotechnics, ignition mixtures, fire
suppression devices and rocket propellants. From a practical standpoint,
to the composition of the present invention also may include additives
heretofore used with other gas generant compositions, such as oxidizers,
gas conversion catalysts, ballistic modifiers, slag formers, ignition aids,
energetic plasticizers and binders, non-energetic binders, and compounding
aids .
~s The foregoing objects are generally achieved by a pyrotechnic gas
generant composition including a high oxygen compound or fuel,
preferably, azodiformamidine dinitrate, which is the resulting reaction
product of aminoguanidine nitrate and nitric acid prepared with or without
the use of potassium permanganate. Specifically, the reaction product is
2o a yellow precipitate that can be ignited and used alone, with no oxidizers
or other additives, for very rapid and substantially smokeless self
deflagration or combusted in combination with oxidizers and/or other
additives. In each instance; the gas generant composition provides both
high gas output and low production of solid decomposition products upon
2s combustion. Further, the precipitate is relatively non-hygroscopic and has
a high burn rate. As a result, cartridges used to contain the gas generating
composition are not required to withstand the extremely high pressures
associated with prior art gas generating compositions,, such as ammonium
nitrate based compositions, that exhibit the similar low solid combustion
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product production as the gas generating composition of the present
invention, but have low burn_rates and are generally hygroscopic.
Based upon the general physical characteristics of the above-noted
reaction product of the present invention, the product is believed to be
s 1,1'-azodiformamidine dinitrate. However, the pyrotechnic gas generant
composition of the_ present invention is directed separately to both the use
of the yellow reaction product of aminoguanidine nitrate and nitric acid and
to 1,1'-azodiformamidine dinitrate.
The azodiforrnamidine dinitrate may also be formed as the reaction
~o product of nitric acid and other aminoguanidine salts, such as
aminoguanidine bicarbonate, aminoguanidine sulfate, or any combination
thereof. Preferably, the aminoguanidine salt is aminoguanidine
bicarbonate. The use of such materials provide a cost effective means of
producing the azodiformamidine dinitrate of the present invention.
~s The gas generant composition of the present invention is generally
prepared by the methods heretofore employed for prior art compositions
and generally, but not exclusively, involve the dry or wet blending and
compaction of the comminuted ingredients selected fox combination. In
view of the advantageous characteristics of the gas generant composition
20 of the present invention, namely, high gas output, low solid combustion
products production and high burn rate, the generant has applications in
automobile air bag systems, inflatable rafts or passenger escape chutes, gun
propellants, pyrotechnics, ignition mixtures, fire suppression devices and
rocket propellants.
2s For purposes of the present invention, the terms propellants) and
gas generant(s) are used interchangeably. Also, for the purposes of this
invention, the reactions shown are with anhydrous components. The use
of non-anhydrous components, however, is also contemplated.
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BRIEF DES~RIP'TION OF THE FIGURES
Figure 1 is a conventional passenger-side inflator that may be used
with the composition of the present invention.
Figure 2 is a conventional driver-side inflator that may be used with
s the composition of the present invention.
Figure 3 is an infrared absorption spectra of the reaction product of
embodiment 1 of the present invention.
Figure 4 is a differential scannning calorimetry of the reaction
product of embodiment 1 of the present invention.
io Figure S is a differential scanning calorimetry of the reaction
product of embodiment 2 of the present invention.
Figure 6 is a differential scanning calorimetry of the reaction
product of embodiment 3 of the present invention.
Figure 7 is an infrared absorption spectra of the reaction product of
is embodiment 1 of the present invention.
Figure 8 is an infrared absorption spectra of the reaction product of
embodiment 2 of the present invention:
Figure 9 is an infrared absorption spectra of the reaction product of
embodiment 3 of the present invention:
20 Figures 10(a)-(d) are infrared absorption spectra of the reaction
product of embodiments 4, 1, 2 and 3~, respectively, of the present
invention.
Figure 11 is a prior art infrared absorption spectra for
azodicarbamidine dinitrate.
2s Figure 12 is a graph showing a representative firing of the reaction
product of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIIVViENTS
The invention provides for a pyrotechnic gas generant, preferably
comprising azodiformamidine dinitrate, which when combusted provides
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high gas output and minimal solid combustion products and which is useful
for various purposes. It has been found that the reaction of the high
oxygen balance fuel of the present invention with an oxidizer produces a
high gas output volume with very little solid combustion products. In
s addition, the fuel, preferably azodiformamidine dinitrate, also exhibits a
high burn rate and is a self deflagrating monopropellant. As a result, the
gas generant composition of the present invention can be a single ingredient
auto-ignition pill (AIP); a solid monopropellant; a high oxygen balance fuel
in all pyro systems; a burning rate enhancing additive; and an ingredient
to in conventional and oxygenated hybrid inflation systems. As one can see,
the gas generant of the present invention is particularly useful as an
automobile air bag propellant, but also has applications as a gun propellant,
flotation device gas generant, propellant, pyrotechnic, gas generator,
ignition mixture, fire suppression device and rocket propellant.
is Additional objects and advantages. of the present invention will
become readily apparent to those skilled. in the art from the following
detailed description wherein the preferred embodiments of the invention are
shown and described simply by way of illustration of the best mode
contemplated for carrying out the invention. As will be realized, the
20 invention is capable of other and different embodiments and its several
details are capable of modifications of various obvious respects, all without
departing from the invention. Accordingly, the figures and description are
to be regarded as illustrative in nature and not as restrictive.
More specifically, the gas generant composition of the present
2s invention includes a high oxygen balance formamidine-type fuel prepared
from the reaction of nitric acid and aminoguanidine nitrate. The inventors
believe the fuel to be azodiformamidine dinitrate (also called
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azodicarbamidine dinitrate, azobicarbamidine dinitrate, and
azobisformamidine dinitrate) shown structurally as follows:
HN NH
~C -N ~N-~-~ C ~ ~ 2HN03
H2N/ \ NHZ
This invention is not limited, however, to only azodiformamidine dinitrate,
both crystallized and recrystallized, but instead is also directed to the
product from the reaction of nitric acid and aminoguanidine nitrate as
provided in detail below.
to The gas generant composition of the present invention may also be
formed from the reaction of nitric acid and other aminoguanidine salts,
such as aminoguanidine bicarbonate (AGB) or aminoguanidine sulfate
{AGS). Preferably, the aminoguanidine salt is AGB. The product from
the reaction of these salts with nitric acid similarly produces a solid,
bright
is yellow colored material believed to be azodiformamidine dinitrate as noted
above with respect to the reaction of nitric acid and aminoguanidine nitrate.
With regard to azodiformamidine dinitrate, reference is made to
J. Thiele, Ann 270, 39 { 1892) which describes this compound as
azodicarbonamidinnitrat. This previous synthesis was done in conjunction
2o with an investigation of materials for potential woolen dyes/pigments.
Moreover, the prior synthesis involved the addition of a solution of
a metallic oxidizing compound (potassium permanganate) to form a yellow
reaction product and did not add heat from an external source during the
process. The method of the present invention, as provided below, is
2s preferred because by adding heat, the reaction occurs rapidly without
requiring the addition of a metal oxidizing compound. By avoiding the use
of a metal oxidizing compound during the preparation of the yellow
reaction product, the high oxygen fuel gas generant of the present invention
can be prepared free of foreign solid minute particles or without the
so potential for formation of metallic oxide particles. Thus, gas generants
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using the high oxygen balance fuel of the present invention
can be prepared
without metal-containing contaminants.
In accordance with the present invention, the reaction to
form
azodiformamidine dinitrate will also occur without external
heat and with
s or without the use of potassium permanganate at ambient temperature
if
nitric acid and aminoguanidine nitrate are allowed to digest
over a longer
period of time. This also applies to the use of the above-identified
additional salts, namely, aminoguanidine bicarbonate (AGB)
and
aminoguanidine sulfate (AGS).
to Other high oxygen balance fuels hydrazodicarbonamidine,
diazoguanidine, formamidine, bisformamidine, and azobisformamidine
derivative fuels such as guanyl azide nitrate, diazoguanidine
nitrate,
azobisnitroformamidine, and 1,1'-azodiformamidine dipicrate
are also
useful gas generator ingredients in accordance with the present
invention.
is In addition, other derivatives and fuels containing a formamidine,
guanyl
azide, diazoguanidine, or hydrazodicarbonamidine group with
an oxidizing
group, e.g. (N02), (N03), (C104), (C103), or mixtures of
oxidizing groups,
or mixtures of different hydrazodicarbonamidine, guanyl azide,
diazoguanidine, formamidine, bisformamaidine, and azobisformamidine
2o compounds, with oxidizing groups with proper precautionary
measures, are
also useful in propellant compositions.
Prior art propellants, such as those containing ammonium
nitrate,
produce very little solid combustion products; but have a
number of other
properties that make them less desirable. Ammonium nitrate,
for instance,
2s is hygroscopic. Moreover, in gas generantlpropellant compositions,
its use
results in a low bum rate and a high pressure exponent at
operating
pressures of 1000-20~ psi. Consequently, a propellant composition
including ammonium nitrate as the principal oxidizer must
be burned at
very high pressures, e.g. 4000-6000 psi, and sealed to prevent
moisture
3o from contacting the composition. In addition, ammonium nitrate
typically
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requires the use of phase stabilizers, such as potassium compounds, which
generate solid combustion products.
The high oxygen balance fuel of the present invention overcomes a
number of the above-noted, less than desirable characteristics:
s Specifically, a gas generantlpropellant composition including the high
oxygen balance fuel of the present invention exhibits a high gas output with
no or little resulting solid combustion product or ash, while also being
relatively non-hygroscopic, having a high burn rate and providing a more
desirable pressure exponent. As a result, the composition of the present
to invention does not have to be held in such a high pressure and moisture
sealed container, since the operating pressures required for achieving
burning rates are much lower than for the above-noted ammonium nitrate
gas generant propellant compositions.
The gas generant composition of the present invention can function
is alone as a self deflagrating monopropellallt, as noted above, or include an
oxidizer: Other materials may be added to the composition for processing,
aiding ignition, enhancing ballistics, improving thermal aging and stability,
improving hazardous properties, reducing particulates, binding, and
scavenging undesirable gaseous combustion products.
20 A single oxidizer or multiple oxidizers may be combined with the
high oxygen balance fuel of the present invention to supply additional
oxygen for achieving the desired oxygen to fuel balance (OIF) during
combustion. Since the high oxygen balance fuel of the present invention
includes a larger amount of oxygen than prior gas generating compositions,
2s a smaller amount of oxidizer for providing a desirable oxygen to fuel (O/F)
balance is necessary. Suitable metallic and non metallic oxidizers are
known in the art and generally compiise nitrites, nitrates, chlorites,
chlorates, perchlorates, oxides, hydroxides, peroxides, persulfates,
chromates and perchromates of non metals, alkali metals, alkaline earth
so metals, transition metals and transition metal complexes and mixtures
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thereof. Preferred oxidizers include ammonium perchlorate, potassium
perchlorate, strontium nitrate, potassium nitrate, sodium nitrate, barium
nitrate, potassium chlorate, and mixtures thereof.
Preferred oxidizers are non hygroscopic in order to preserve the
s advantageous characteristic of the high oxygen balance fuel of the present
invention. The preferred oxidizers are generally employed in a
concentration of about 0 % to 98 % by Weight of the total gas generant
composition and preferably in a concentratgon of 5 to 50 % by weight of the
total gas generant composition.
to Scavengers may be desirable to control the production of corrosive
combustion products. For example, if a non-metal oxidizer is used, such
as ammonium perchlorate, hydrogen chloride (HCl) can be produced as a
resulting reaction product, which is clearlly undesirable. To prevent the
production of HCI, a scavenger such as sodium nitrate can be used to form
is sodium chloride {NaCI) instead. Other corrosive/toxic gas scavengers may
also be employed.
The combustion of the high oxygen balance fuel of the present
invention may also be controlled by the addition of ballistic modifiers and
include burning rate catalysts which influence the temperature sensitivity,
2o pressure exponent and rate at which the propellant burns . Such ballistic
modifiers were primarily developed for solid rocket propellants, but have
also been found useful in gas generants far inflatable devices. Examples
of ballistic modifiers useful with the composition of the present invention
include oxides and halides of Group 4 to 12 of the Periodic Table of
2s Elements (as developed by IUPAC and published by the CRC Press, 1989);
sulfur and metal sulfides; transition metal salts containing copper,
chromium, cobalt, nickel and mixtures thereof; and alkali metal and
alkaline earth metal borohydrides. Guanidine borohydrides and
triaminoguanidine borohydrides have also been used as ballistic modifiers.
so Organometallic ballistic modifiers include, but are not limited to, metal
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chelates, oxalates, metallocenes, ferrocenes and metal acetyl acetonates.
Other ballistic modifiers include salts of dicyanamide, nitroguanidine,
guanidine chromate, guanidine dichromate, guanidine trichromate, and
guanidine perchromate. The ballistic modifiers are generally employed in
s concentrations varying from about 0. i to 2S % by weight of the total gas
generant composition. Because of the self deflagrating, high burning rate
characteristics of the high oxygen fuel of the present invention, Iow
concentrations of said fuel, namely, 0.1-25 % can be incorporated for use
as a ballistic modifier in other gas generant compositions.
to Filterable slag formation can be enhanced by the addition of a slag
former. Such a slag former may not, however, be necessary in the present
invention in view of the limited amount of solid combustion product
produced. Suitable slag formers, if deemed necessary, include lime,
borosilicates, vycor glasses, bentonite clay, silica, alumina, silicates,
1s aluminates, transition metal oxides, alkaline earth compounds, lanthanide
compounds, and mixtures thereof.
Another additive found to aid in the ease and temperature of ignition
and resulting combustion of gas generant compositions is an ignition aid.
Ignition aids include finely divided elemental sulfur, boron, boron-
2o potassium nitrate (BKN03), carbon, magnesium, aluminum; and Group 4
transition metals, transition metal oxides, hydrides and sulfides, the
hydrazine salt of 3-vitro-1,2,4-triazole-5-one and mixtures thereof. The
ignition aids are normally employed in concentrations of 0.1 to 15 % by
weight of the total gas generant composition.
2s It may be desirable to add compounding agents to facilitate
compounding and obtain homogeneous mixtures. Suitable binders and
processing or compounding aids include molybdenum disulfide, graphite,
boron nitride, alkali metal, alkaline earth and transition metal stearates,
various solvents, such as water, methanol, ethanol, ethyl ether, acetone,
3a isopropanol, methylene chloride, etc, polyethylene glycols, polyacetals,
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polyvinyl acetates, polyvinyl alcohols, polycarbonates such as Q-PAC,
cellulose acetate (CA), cellul9se acetate butyrate (CAB), cellulose nitrate
(CN), fluoropolymers commercially available under the tradename
TEFLON, and silicones. The compounding aids are typically, but not
s universally, employed in concentrations of about 0.1 to Z 5 % by weight of
the total gas generant composition.
In addition to the above-noted additives, the high balance fuel of the
present invention may also be combined with other fuels andlor energetic
vitro and/or nitrato plasticizers andlor energetic and non-energetic binders
to provide a gas generant/propellant composition. Suitable fuels for such
combination with the fuel of the present invention include but are not
limited to the families of azido, hydrazine, guanidine, tetrazole, triazole,
triazine, polyamine, nitramine (linear and cyclic), and derivatives of these
families of fuels, as well as mixtures thereof. Suitable energetic
~5 plasticizers include but are not limited to butanetriol trinitrate (BTTN),
nitroglycerine (NG), triethyleneglycol dinitrate (TEGDN),
trimethylolethane trinitrate (TMETN) and mixtures thereof. An example
of an energetic binder includes glycidyl azide polymer (GAP).
The manner and order in which the components of the gas generant
2o composition of the present invention are combined and compounded are not
critical so long as an intimate, unifonm mixture with. good structural
integrity is obtained and the compounding is carried out under conditions
which are not unduly hazardous, and, which do not cause decomposition
of the components employed. For example, the materials may be wet
2s blended in aqueous or nonaqueous liquids, or dry blended, with or without
binders or processing aids, in a ball mill or "RED DEVIL" type paint
shaker and then extruded, pelletized by compression molding, or foamed
into a castable or compression molded monolithic grain. The materials
may also be ground separately or together with or without binders andlor
other additives in a fluid energy mill, "SWECO" vibroenergy mill, or
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bantam micro-pulverizer and then blended or further blended
in a v-blender
prior to compaction.
The various components described hereinabove for use with
the
novel high oxygen balance fuel of the present invention have
been used
s heretofore in other gas generant compositions. References
involving gas
generant compositions describing various additives include
U. S ~ Patents
No. 5,035,7S7; 5,084,118; 5,139,588; 4,948,439; 4,909,549;
and
4,370,181. As taught in this art and as will be apparent
to those skilled in
the art, it is possible to combine the functions of two or
more additives into
to a single composition. Thus; alkaline earth metal salts of
tetrazoles,
bitetrazoles and triazoles not only function as gas generant
components but
can also be used as slag formers. It has also been found
that strontium
nitrate, for instance, acts not only as an oxidizer and a
slag former, but
also is effective as a ballistic modifier, ignition aid,
densifier and
is processing aid.
The high oxygen balance fuel of th.e present invention can
utilize
conventional gas generator mechanisms of the prior art. These
are referred
to in U.S. Patent No. 4,369,079, incorporated herein by reference.
Generally, the methods of the prior art involve the use of
a hermetically
20 sealed metallic cartridge containing a gas generant composition.
Hydrazodicarbonamidine, diazoguanidine, formamidine, bisformamidine,
and azobisformamidine type fuels of the present invention
can be used in
such devices. Specifically, upon initiation of combustion
by the firing of
a squib, the sealing mechanism ruptures. This allows gas
to flow out of
2s the combustion chamber through several orifices. Of course,
other gas
generator mechanisms may equally be employed for use with
the gas
generant composition of the present invention.
With reference to an automobile air bag environment, Figure
1
depicts a conventional passenger-side hybrid inflator for
an automobile in
3o which the high oxygen balance fuel of the present invention
may be used.
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In practice, the initiator I ignites in response to a sensor (not shown) that
senses rapid deceleration indicative of a collision. The initiator gives off
hot gases that ignite the ignition charge 2 which causes the main generant
charge 8 to combust,thereby heating and fut~ther pressurizing the inflation
s gas mixture 3. When the pressure in the inflation gas mixture increases to
a certain point, the seal disk G ruptures, permitting the gas mixture to exit
the manifold 4 through the outlet portions ;5 and inflate an air bag. The
generant container 9 holds the main generant charge 8. All the charges in
the inflation gas mixture are enclosed in the pressure tank 7.
to Figure 2 illustrates an all pyrotechnic gas generator in which the
instant invention may be employed. Since no part of the inflator is
reserved .for storage capacity, the device is smaller than its counterpart
hybrid inflator. In this figure, there is an initiator 11 that will combust in
response to a signal from a sensor (not shown), that generates a signal as
is a result of a change in conditions, e.g., an excessive increase in
temperature or a sudden deceleration of a vehicle (indicative of a crash),
in which the inflator is installed. The initiator 11 gives off hat gases that
ignite the main generant charge lfi, which combusts, generating an inflation
gas mixture. The mixture exits the manifold 14 through the exit ports 15.
2o To insure that the gas generating propellant 16 will be ignited well below
its auto-ignition temperature (T;~) and well below that temperature where
the materials of construction of the hardware begin to weaken, an auto-
ignition propellant (AIP) 13 having a suitably low T;g may be needed to
ignite the ignition charge 12, which then ignites the propellant 16.
2s Because of the high burning rates exhibited by the high oxygen
balance fuel of the present invention at moderate to low operating
pressures, the invention may also be utilized in the physical form of a
monolithic grain.
Use of the high oxygen balance fuel of the present invention
3o desirably provides the capability of self deflagration similar to a solid
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monopropellant. In addition, the high oxygen balance fuel of the present
invention permits the use Qf much lower concentrations of oxidizer
components and results in a much lower concentration of solid combustion
products and greater gas output, which is particularly advantageous for
s volume limited systems. As a result, the high oxygen balance fuel of the
present invention has applications in botlx of the systems set forth above
and illustrated generally in Figures 1 and 2.
Although the yellow colored solid reaction product of
aminoguanidine nitrate and nitric acid, as well as the yellow colored solid
io reaction product of nitric acid and other aminoguanidine salts, such as
aminoguanidine bicarbonate andlor aminoguanidine sulfate, is assumed to
be azodiformamidine dinitrate (azobisformamidine dinitrate), this invention
is not limited only to this specific high oxygen balance fuel. The invention
is also directed specifically to azodiformamidine dinitrate
os (azobisformamidine dinitrate). However, for simplicity, use of the term
AZODN below refers both to the reaction product and azodiformamidine
dinitrate in anhydrous and hydrous versions, unless specifically indicated
otherwise. Similar results would also be obtained by utilizing the
azodiformamidine dinitrate formed from the reaction of nitric acid and
2o aminoguanidine bicarbonate andlor aminoguanidine sulfate.
A comparison of the high oxygen balance fuel of the present
invention, namely, AZODN, with other high oxygen balance fuels (HOB
and CAPS), shows that AZODN has a higher oxygen balance to carbon
dioxide and water than other high oxygen balance fuels, as provided in
2s Table 1.
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ABLE I.
Oxygen balance to CO,~ and H~O for HOB Fuels
Compound Oxy eg-n Balance to
CO~ and H~O
s Azobisformamidine dinitrate (AZODN), C2HgNg06 -13.3
Ethylenediamine dinitrate (EDDN), CZH~oN4O6 -25.8 %
Guanidine nitrate {GN), CH6N4O~ -26.2
The better oxygen balance of AZODN of the present invention over
that of other high oxygen balance fuels, such as guanidine nitrate, permits
to the use of a lower concentration of oxidizer to maintain a desired .9011 to
1.1/1 oxygen to fuel (O/F) balance in a resulting gas generant composition.
However, if a gas generant is desired that is totally or essentially free of
solid combustion product, an oxidizer, such as either phase stabilized or
non-phase stabilized ammonium nitrate, can be utilized with the high
Is oxygen balance fuel of the present invention. In such a case, the fuel of
the present invention should be present as 40-60 wt% of the total gas
generant composition. The use of AZODN of the present invention in
either the form of the reaction product of aminoguanidine nitrate and nitric
acid or, specifically, azobisformamidine dinitrate, produces higher gas
20 outputs and less solid combustion products.
As provided in Table 2 below, the prior art fuels, such as 5-
aminotetrazole (SATZ){discussed above in the Background of the
Invention), guanidine nitrate (GN), and ethylenediaminedinitrate (EDDN),
require a greater amount of strontium nitrate (SrN) in order to reach a
2s .9511 oxygen to fuel (OIF) balance. Moreover, gas generant compositions
including these fuels produce less gas output and more solid combustion
products than gas generant compositions including AZODN of the present
invention.
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TABLE 2
Comparison of High ~~gen Balance T~-IOBI Fuels With SrN'
Fuel SrN/Fuel Flame Temp~fK~, Gas Output Solid Products
AZODN 21.817$.2 2734 32.4 12.5
s EDDN 36.5/63.5 2546 32.4 17.9
GN 37.5/62.5 2236 30.6 2 i .6
5ATZ 37.9!62.1 2700 24.8 3I.2
O/F =0.9511
As demonstrated by the results set forth in Table 2, the compositions
io including EDDN, GN and SATZ required greater than 10% by weight
more SrN than the composition including the high oxygen balance fuel
(AZODN) of the present invention to provide the given 0.95/1 O/F ratio.
Although SATZ exhibited a similar flame temperature as the present
invention, the gas output was significantly lower and the content of solid
is combustion products was more than twice as high for the composition
including SATZ as compared with the composition including AZODN.
If tailoring of the ballistics is anticipated, partial substitution of
potassium perchlorate (KP) for strontium nitrate can be done. :Under these
conditions, the formation of solid combustion products decreases even
2o further, as provided in Table 3.
T. ABLE 3
Partial substitution of KP for ~ SrN with HOB Fuels
Fuel ~rN/KPIFuel Flame Temp~K~ Gas Output
Solid Products
2s AZODN 10.0110.2/79.8 2792 32.9 11.2
EDDN 17.1117.1 /65 . 8 2615 32.6 17 .6
GN 17.6!17.6/64.8 2304 32.7 18.1
Still, however, compositions including EDDN and GN as fuel,
required significantly more potassium perchlorate and strontium nitrate than
3a in the composition including AZODN. Although the gas output for all
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three of the above compositions were similar to one another, the solid
combustion products producti.9n for the composition utilizing AZODN was
much lower. Consequently, the gas generant of the present invention
including AZODN is preferred for pyrotechnic gas generator systems as
s illustrated in Figures Land 2.
Compositions including the high oxygen balance fuel of the present
invention (AZODN) and oxidizers are provided below in Tables 4-7 for
accomplishing the desired O/F balance of 0.90/ 1 to 1.1 / 1. Specifically,
compositions including AZODN and ammonium nitrate (AN) are provided
to in Table 4; AZODN, ammonium perchlorate (AP) and strontium nitrate
(SrN) are provided in Table 5; AZODN, ammonium perchlorate (AP) and
sodium nitrate (SN) are provided in Table 6; and AZODN, ammonium
perchlorate {AP) and potassium nitrate (KN) are provided in Table 7. It
should be noted that, although the compositions of Table 4 are
is hygroscopic, the production of solid combustion products is still very nil.
In addition, the use of phase stabilized ammonium nitrate is preferred.
TABLE 4
AZODN and Ammonium Nitrate Compositions
AZODNIwt%~ AN wt o O/F Balance
20 ~ ~75 25 :9I1
6?.35 32.65 .9511
60 40 1.0/1
52.94 47.06 1.0591
46.15 53.85 1.1/1
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TABLE 5
AZODN. Ammonium PerchIorate, and Strontium Nitrate
Compositions -
AZODNfwt%_l AP wt o ~rN ~ OIF Balance
s 82.3 9.3 8.4 .
9 /1
77.4 11.9 10.7 .9511
72.9 14.3 12.8 1.0/1
69.2 16.5 14.3 1.05/1
64.8 18.5 16.7 1.1/1
to TABLE 6
AZODN. Ammonium Perchlorate, and Sodium Nitrate Compositions
AZODNfwt%) AP wt% SN O/F Balance
83.7 9.S 6.8 .9/1
79.1 12.1 8.8 .9511
is 74.8 14.6 10.6 1.0/1
?0.8 16.9 12.3 1.0511
67.0 19.1 13.9 1.1/1
TABLE 7
AZODN. Ammonium Perchlorate, and Potassium Nitrate
2o Compositions
AZODNfwt%) AP wt KN O/F Balance
82.6 9.3 8.1 .911
77.8 11.9 10.3 .9511
77.3 14.3 12.4 1.0/1
2s 69.2 16.5 14.3 1.05/1
65.3 18.6 16.1 1.111
In order to better understand the functimn of the high balance fuel of
the present invention, examples of theoretical reactions of AZODN of the
present invention are provided below wherein the structural formula for the
3o AZODN is as follows:
HN ~ NH
~C N~N-C ~ 2HN03
H2N/ ~NHz
i~i
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and the molecular formula is:
CzHsNs06
(1) Neat AZODN as a mononronellant for use in hybrid or ignition
s s-y terns:
C2HaN8p6-_-> 4H20 + 2C0 + 4N2
240 72 56 112 = 240
100.0% 30.0% 23.33% 46.67%
1.667 M 0.833 M 1.667 M
Total Gas Output: 100.0 Wt.%
to Total Gas Output (Moles): 4.167 Moles/100 Gms.
Total Solid Combustion Products: Zero Wt:
(2) AZODIvI with ammonium nitrate (normal or phase stabilixedh
2C2HgNa06 + 3NH,N0,----> 14Hz0 + 3C02 + CO + 11N2
480 240 252 132 28 308 =720
66.67% 33.33% 35.00% 18.33% 3.89% 42.78%
1:944M 0.417M O.I39M 1.528M
Total Gas Output: 100.0 Wt.% (O/F=1.00) 100,0 Wt.%
(O/F=0.95)
Total Gas Output (Moles): 4.04 Moles/100 Gms.
Total Solid Combustion Products: Zero Wt.%
I!li
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(3) AZODN with lithium nitrate and ammonium nerchlorate~
SCZHgN$O6 + 2LiN0, + 2NH4C10; --> 2LiC1 + 24H20 + 1OCOZ + 22N2
1200 138 234 84 432 440 616 =1572
76.33% 8.78% 14.89% 5.34% 27.48% 27.99% 39.19%
0.127M 1.53M 0.636M 1.400M
Total Gas Output: 94.7 Wt% (O/F=1.00) 95.6 Wt% (O/F=0.95)
Total Gas Output (Moles): 3.~9 Moles/100 Gms.
Total Solid Combustion Products: 5.3 Wt.% (O/F=1.00) 4 . 4 W t
(OIF=0.95)
to (4) AZODN with sodium nitrate and ammonium perchlorate~
SCZH$N806 + 2NaN03 + 2NH,C1O4----> 2NaC1 + 24Hz0 + l OCOZ + 22Nz
1200 1?0 234 116 432 440 d16 =1604
74.81% 10.60% 14.59% 7.23% 26.93% 27.43% 38.41%
0.125M 1.SOM 0.623M 1.372M
is Total Gas Output: 92.8 Wt% (O/F=1.00) 93.8 Wt% (O/F~.95)
Total Gas Output (Moles): 3.50 Moles/l0U Gms
Total Solid Combustion Products: 7.2 Wt% (O/F=1.00) 6 . 2 W t
(O/F=0.95)
:i~~
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(S) AZODN with potassium nitrate and ammonium perchlorate
SCZH$NBO6 + 2KN03 + _ 2NH4C1O4---~> 2KC1 + 24HZ0 + IOCOz +22Nz
120(? 202 234 148 432 440 616 =1636
73.35% 12.35% 14.30% 9.05% 26.41% 26.89%
37.65%
0.122M 1.467M 0.611 M L~VI
Total Gas Output: 91.0 Wt% (O/F=1.00) 92.0 Wt% (OIF~.9S)
Total Gas Output {Moles): 3.42 Moles/100 Gms
Total Solid Combustion Products: 9.OWt% (O/F=1.00) 8 . 0 W t
to {O/F=0.95)
(6) AZODN with strontium nitrate and ammonium perchlorate~
SCZH,Ng06 + Sr(N03)x + 2NH4C1O4----> SrCl2 + 24H20 + lOCOZ + 22N2
1200 212 234 1S7 432 440 616 =1645
72.90% 12.89% 14.21% 9.54% 26.26% 26.75% 37.45%
1$ 0.061M 1.4S9M 0.608M 1.338M
Total Gas Output: 90.5 Wt% (O/F=1.00) 92.0 Wt% (OIF~.9S)
Total Gas Output (Moles): 3.405 Moles/100 Gms.
Total Solid Combustion Products: 9.S Wt% (O/F=1.00) 8 . 0 W t
{O/F=0.95)
20 (7) AZODN with lithium carbonate coolant and ammonium perchlorate,~
i ~,
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14CZH$N806+ 9NH4ClOa+ SLiZC03--> 9LiC1+ %zLi2p+ 74Hz0+ 27COz+ 6C0+ 60%zNz+
'/.02
3360 1053 3?0 ' 378 15 1332 1188 168 1694
8 =4783
70.25% 22.01% 7.74% 7.90°./0 0.31% 27.85% 24.84% 3.51% 35.42%
0.17%
.188M .OIOM 1.547M .565M .125M 1.265M
.005M.
Total Gas Output: 9I .79 Wt% (OIF=i .00) 9 2 . 0 0 W t
(OIF=0.95)
to Total Gas Output (Moles): 3.S 1 Mol.es/100 Gms. 3 . 7 3
Moles/100 Gms
Total Solid Combustion Products: 8.20 Wt.% (O/F=1.00) 8.00 Wt.%
(O/F~.9S)
(8) AZODN with scandium nitrate and ammonium perchlorate:
2C2H$Na06 + ~I3SC(NO,), + 3IsNH,CIO4 ---> y/3ScClZ + 9~/aH20 + 4C02 + 9N1 +
11602
480 77 78 38 167.4 176 251 2.6
=635
75.59% 12.13% 12.28% 5.98% 26.36% 27.72% 39.53%
0.41%
O.OSM. 1.46M. 0.63M. 1.41M.
O.O1M
Total Gas Output: 94.0 Wt.% (O/F=1.00) 3.51 Moles/lU0 Gms
(O/F=1.00)
Total Solid Combustion Products: 6.0 Wt.% (O/F=1.00)
I II
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(9) AZODN with sodium nitrate:
SCZH8N806 + 4NaN0, ----> 2Na20 + 20Hz0 + 1OC02 + 22N2
1200 340 124 360 440 616 = 1540
77.92% 22.08% 8.OS% 23.38% 28.s7% 40.00%
0.130M L299M 0.649M 1.429M
Total Gas Output: 92.0 Wt.% (O/F=1.00) 93.0 Wt.% (OIF=0.95)
Total Gas Output (Moles): 3.38 Moles/100 Gms.
Total Solid Combustion Products: 8.0 Wt.% (O/F=1.00) 7.00 Wt.%
(OlF=0.95)
to (10) AZODN with strontium nitrate:
SCZHgNBOb + 2Sr(NO,)~ ----> 2Sr0 + 20Hi0 + IOC02 + 22N2
1200 424 208 360 440 616 = 1624
73.89% 26.1 I% 12.81% 22.17% 27.09% - 37.93%
0.123M 1.232M 0.616M 1.35sM
is Total Gas Output: 87.2 Wt.% (OlF=1.00) 8 9 . 3 W t .
(O/F~.95)
Total Gas Output (Moles): 3.20 Moles/100 Gms.
Total Solid Combustion Products: 12.8 Wt.% (OlF=1.00) 10.7 Wt.%
{O/F=0.95)
20 (11) AZODN with potassium perchlorate:
2C2H$N806 + KC10, --> KCl + 8Hz0 + 4C0z + 8N2
480 i38 74 144 176 224 = 618
77.67% 22.33% 11.97% 23.30% 28.48% 36.2s%
till
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0.162M 1.294M 0.64?M 1:295 M
Total Gas Output: 88.03 Wt.% (ol~=l.oo) 89.90 Wt.%
(O/F=0.95)
Total Gas Output (Moles): 3.24 Malesl100 Gms: 3 . 5 6
s Molesl100 Gms
Total Solid Combustion Products: 11.97 Wt.% (O/F=1.00) 10.10 Wt.%
(ol~=a.9s)
(I2) AZODN with aminoauanidine hexanitratocerate:
CeCzHI2N,4O,g + 3CxH$N806 ____> Ce02 + 18H20 + 8C02 + 19N2
660 720 172 324 352 532 = 1380
47.82% 52.18% 12.46% 23.48% 25.51% 38.55%
= 100%
Total Gas Output: 87.54%
Total Solid Combustion Products: 12.46%
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(13) AZODN with amino~zanidine hexanitratoscandate~
SCCZH,ZN14018 + 3CxHgNa06 _ _-__> ScOz + 18HZ0 + 8C0z + 19N2
565 720 77 324 352 s32 = 1285
43.97% 56.03% 5.99% 25.21% 27.39% 41.40%=100%
s Total Gas Output: 94.01
Total Solid Combustion Products: 5.99%
As provided by the above theoretical reactions of AZODN, a
substantial gas output is possible by utilizing the fuel of the present
invention. In most cases, the gas output is over 90 wt%. Even at the
to greater level of solid combustion products formed, the gas generant of the
present invention utilizing AZODN produces less solid combustion products
than prior art gas generant compositions.
The specific process of obtaining the resulting reaction product of the
present invention from the reaction of aminoguanidine nitrate and nitric
is acid is provided below. Further, use of this resulting reaction product
with
various additives are also provided to demonstrate the advantageous features
thereof. Consequently, the term AZODl~1 as used in Examples i-I2
provided below refers to the actual yellow precipitate of Example 1. As
noted above, the reaction product of nitric acid and other aminoguanidine
20 salts, such as aminoguanidine bicarbonate or aminoguanidine sulfate, would
provide substantially the same results as the AZODN utilized in the
following examples. This is substantiated by the additional tests conducted
to demonstrate that the product resulting from the reaction of nitric acid and
these additional salts has the same characteristics as the AZODN of
2s Example 1.
Example I
The high oxygen balance fuel of the present invention was prepared
by the following method. First, I O grams of aminoguanidine nitrate (AGN)
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was weighed into a 400 ml glass beaker. Then, water, preferably distilled,
up to about 20-25 ml volume was added whereupon a slurry of AGNlwater
resulted. A dispersion was formed by slowly pouring 150 ml of reagent
grade nitric acid (70%), while stirring, into the AGN/water slurry, which
s brought the total volume up to about 170-175 ml. A 10 degree temperature
rise occurred as the acid was first added. As the acid was continually
added, the temperature came back down. The dispersion was then heated
to 55-65°C with moderate stirring on a hot plate. This caused any
remaining AGN to go into solution.
Heating was continued at 55-b5°C during which time the solution
went through a color transition from a water-white color to a straw color
to an intensely bright yellow color (resembling the color of a solution of
potassium dichromate). [Use of a hood and a ready ice bath are strongly
suggested. Moreover, the reaction should be limited to a temperature
15 ceiling of below 65°C. It should be noted that the solution will
turn a
deeper yellow color just before exotherming.
The beaker was then placed in an ice bath to cool down the contents
and allow the effervescence to subside. A yellow precipitate appeared as
the temperature dropped below 12°C after the reaction mixture was held
in
20 the ice bath at about 0-5°C. The yellow precipitate was vacuum
filtered
and washed with several rinses of distilled water. The precipitate was then
washed several times with ethanol and then dried at 62°C.
Example 2
The infrared absorption spectra for the reaction product formed from
25 the procedure set forth in Example 1 was determined and is provided in
Figure 3. The absorption spectra was compared with the infrared
absorption spectra of azodicarbamidine dinitrate found in the literature,
Anal. Chem. 23, 1594 (I951). A comparison of Figure 3 with the reference
spectra (Figure 11 ) showed that the synthesized azobisformamidine-type
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reaction product of the present invention is considered to be 1,1'-
azodiformamidine dinitrate (ayzodicarbamidine dinitrate).
Example 3
Differential scanning calorimetry (DSC) was used to compare the
s thermal stability of the washed reaction product of Example 1 and a
thermally aged reaction product (17 days at 107°C). The DSC plots for
the
washed reaction product and the thermally aged reaction product showed
that aging only slightly changed the material's exotherm peak and the
material's exotherm onset. Specifically, the exotherm onset changed from
160.82°C to 170.21°C and the exotherm peak changed from
183.32°C to
185.47°C. Consequently; the AZODN fuel of the present invention
exhibits
good aging characteristics.
Example 4
Neat AZODN powder, produced by the method of Example 1,
15 containing no oxidizers or other additives, self deflagrated very rapidly
when ignited at ambient temperature and pressure. Specifically, a small
quantity ( 1l2 gram) of the high oxygen balance fuel of Example 1 was
placed in a heap in the center of a watch glass and the flame of a burning
splint was impinged on the sample. The sample immediately ignited and
20 combusted very rapidly and cleanly similar to smokeless rifle powder:
Such rapid self deflagration makes the AZODN fuel of the present
invention very beneficial for use in heterogeneous and/or hybrid inflators
or auto-ignition pills (AIP's) and all-pyro gas generating systems.
Example 5
25 A 0.269 gram quantity of AZODN of the present invention was
placed in a pre-weighed aluminum pan and. ignited with a burning splint.
The pan was reweighed after igniting. Of the initial AZODN reaction
product 0.005 grams of a tan residue remained, leaving a bum residual of
1.84% by weight.
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Additional tests were performed on small propellant batches
containing the AZODN reac,~ion product of the present invention for
determining sensitivity, thermal aging, weight Moss, and ballistics
properties.
The density of the product and propellants made from the product was
s determined from the weight and pellet dimension measurements to be 1.66
g/cc or greater.
Example 6
When 1/4 inch x 5/8 inch pressed pellets of neat AZODN of the
present invention were burned in a strand bomb, without any oxidizer or
other additives, they exhibited burning rates of 0.122, 0.342, and 0:428
inches per second (ips) at 100,. 500, and 750 psi, respectively. These rates
yielded a burning rate exponent of 0.63.
Example 7
A propellant (Batch # 1 I 899) containing 10.60% sodium nitrate (SN)
is as an oxidizer and scavenger, 14.59% ammonium perchlorate (AP), and
74.8 I % AZODN of the present invention was formulated at an OlF ratio
of 1.0 to provide, when combusted, 7% solid combustion products and 3:7
moles of substantially non-toxic gas per 100 grams of composition product.
This formulation gave burning rates of 0.32 and 0.46 ips, respectively, at
20 500 and 750 psi. These rates yielded a pressure exponent of 0.90.
Example 8
Another propellant (Batch # 11900) containing 22.05% sodium nitrate
(SN) oxidizer and 77.92% AZODN of the present invention was formulated
to provide, when combusted, an 8% solid combustion products level and 3.4
25 moles of substantially non-toxic gas per 100 grams of composition. When
1/4 x 5/8 inch pellets were tested for ballistic properties, burning rates at
250, 500, 750, 1000 and 1250 psi were respectively 0.17, 0.32, 0.47, 0.59,
and 0.73 ips. These values yielded a pressure exponent of 0.90.
Example_9
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Another propellant {Batch # 11901 ) containing 7.74% lithium
carbonate (LC) scavenger and coolant, 22.01 % AP oxidizer, and 70.25%
AZODN of the present invention provided a burning rate of 0.34 ips at 500
psi but suffered severe weight loss of 5.9% after 24 hours at 107°C.
The
s DSC for this formulation provided an onset temperature of 146°C and
an
exotherm peak at 179°C.
Example 10
A propellant {Batch #11903) containing weight percents of 12.35%
potassium nitrate (KN) acting as a scavenger/oxidizer, 14.3% ammonium
to perchlorate (AP), and 73.35% AZODN of the present invention was
formulated at an O/F ratio of 1.0 to provide on combustion, a theoretical
solid combustion products level of 9% and 3.6 moles of substantially non-
toxic gas per 100 grams of composition. V~hen pressed into 1/4 x 518 inch
pellets and tested for ballistic properties, the formulation gave a burning
is rate of 0.40 and 0.52 ips at 500 and 750 psi, respectively, with a pressure
exponent of 0.56.
Example 11
Another propellant (Batch # 11905) containing 12.89% strontium
nitrate (SrN), 14.21 % AP, and 72.90% A~ODN of the present invention
2o was formulated (with SrN acting as a clinkerlscavengerloxidizing agent) at
an OlF ratio of 1.0 to provide, when connbusted, a solid decomposition
product level of 9.5% resulting in 3.5 moles of substantially non-toxic gas
per 100 grams of composition. This mixture gave a burning rate of 0.34
and 0.61 ips at 500 and 1000 psi with a pressure exponent of 0.85.
2s Onset temperatures and exotherm peaks for the various propellant
mixtures provided above are given in Table 8. These temperatures were
obtained from DSC plots conducted for each of the above-noted batches.
i ii
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TABLE 8
Exotherm Peak and peratures Observed
Exotherm Onset Tem via
DSC
Batch Component Compositio~wt%)Onset G P a
a
k
s
Neat AZODN 100 16I 183
B I 1899 AZODN 74.8 I S 8 182
SN 10.6
AP 14.6
is BI1900 AZODN 77.9 158 181
SN 22.1
B I 190 I AZODN 70.3 146 179
LC 7.7
AP 22.0
1s B11903 .AZODN 73.35 157 183
KN 12.35
AP 14.3
Batch Com op nent Composition~wt%)Onset C P a
a
k
2o B 11905 AZODN 72.9 160 184.5
SrN 12.9
AP 14.2
The pressurized burn rates for the above Examples of AZODN
propellants are provided below in Table 9.
2s TABLE 9
Pressurized Burn Rates for AZODN Propellants
Burning Rate
Pressure Inches per second at Pressure (Psia)
Batch Exponent 100 250 500 750 1000 1250
3o Neat AZODN 0.63 0.12 ---- 0.34 0.43 ---- ----
B11899 0.90 ---- ---- 0.32 0.46 ---- -_--
I III
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B 11900 0.90 ---- 0.17 0.32 0.47 0.59 0.73
B 11903 0.56 ---- ---- 0.40 0.52 - - ----
B 11905 0.85 ---- ---- 0.34 - 0.61 ----
Weight loss during aging is presented in Table 10 for the various
s AZODN formulations
provided above.
TABLE 10
Pellet Weight Lass
Vs. Days at Temperature
Cumulative
i o Weight
Loss
at
Temperature
Days at 90C 107C
Batch Temperature
Neat AZODN 1 ~ 0.16 0.60
3 0.41 1.09
is 7 0.58 1.48
13 0.64 1.65
25 0.87 1.79
B 11899 1 0.27 0.54
2 0.57 0.83
20 3 0.62 0.98
7 0.88 1.30
i 6 1.08 1.66
B 11903 1 0.27 0.44
2 0.39 0.62
2s 3 0.44 0.66
7 0.61 0.96
16 0.74 . 1.16
B 11905 1 0.23 0.43
2 0.36 0.61
30 3 0.42 0.78
7 0.60 1.11
16 0.78 1.43
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Each of the above examples used filtered, washed and dried but
unrecrystallized AZODN. Table 10 shows that very little weight is lost
during accelerated aging at 107 and 90°C. The pellets ('/Z inch in
diameter
x 'h inch in height) were dried at b2°C {without a vacuum) prior to
placing
in either aging oven. Some weight loss ~ occurs during the first day (24
hours) and is likely due to aqueous or non-aqueous volatile content.
Exam Ip a 12
Reformulation of the above propellant batches at an O/F ratio of 0.90
and 0.95 resulted in solid combustion products levels in the range of 6 to
71h%. Substitution of SN for a KN scavenger and oxidizer in APIAZODN
systems (where the scavenger inhibits andlor eliminates formation of
hydrogen chloride) resulted in solid combustion products levels of 6 and
4'/2% at O/F ratios of 0.95 and 0.90, respectively.
All of the propellant batches utilizing the high oxygen balance fuel
1s of the present invention, as well as neat AZODN, when tested, responded
with acceptable hazards properties with respect to impact, friction, and
electrostatic sensitivity performed on powders. All initial propellant impact
tests showed 10 negatives at 2.0 kg at 50 cm (100 kg-cm). Later tests with
drier ingredients indicated acceptable hazards properties. However, the
2o impact test values from these later tests indicated somewhat greater
sensitivity, e.g. 50 kg-cm. All electrostatic discharge tests showed 10
negatives at six joules and SkV. All friction tests (type ABL) showed 10
negatives at 300 psi-90° with LC, SN and IAN propellants (see examples
below) showing 10 negatives at 1800 psi-90°.
2s Thermal stability studies, which included differential scanning
calorimetry (DSC) and accelerated aging at elevated temperatures, were
conducted on several batches containing the high oxygen balance product
believed to be AZODN prepared according to Example I. A DSC plot of
a propellant respectively containing 12.9, 14.2, and 72.9 weight percentages
30 of strontium nitrate (SrN}, ammonium perchlorate (AP), and
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unrecrystallized AZODN showed an exothermic onset occurring at I6I°C
with major decomposition at X84.5°C.
Differential scanning calorimetry {DSC) indicated the onset of
exothermic decomposition to be about 160°C for all of the above
propellants. This suggests that an auto-ignition pill {AIP) may not be
necessary with propellants containing the high oxygen balance fuel of the
present invention or AZODN. Because neat AZODN and propellants
containing AZODN possess low, but acceptable auto-ignition temperatures
and acceptable pressure exponents combined with high burning rates at low
operating pressures, this invention will be very effective for use volume
limited, reduced weight inflator hardware. Tn addition, if manufactured
from aluminum, high performance plastics, or lower gauge steel
components, operation of an inflator using the propellants of the present
invention will more likely pass bonfire tests that require an inflator to
burst
1s without fragmenting.
ale 13
The high oxygen balance fuel of the present invention was prepared
by the method of Example 1, but instead of aminoguanidine nitrate,
aminoguanidine bicarbonate was combined with nitric acid to provide an
2o embodiment 2 of the high oxygen balance fuel of the present invention.
Example 14
The high oxygen balance fuel of the present invention was prepared
by the method of Example 1, but instead of aminoguanidine nitrate,
aminoguanidine sulfate was combined with nitric acid to provide an
25 embodiment 3 of the high oxygen balance fuel of the present invention.
Example 15
The high oxygen balance fuel of the present invention was prepared
by the method of Example 1, but instead of aminoguanidine nitrate;
aminoguanidine sulfate was combined with nitric acid: Further, the acid
3o utilized in the method of Example 1 was used as the nitric acid component
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WO 00100365 PCTIUS99107049
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to provide an embodiment 4 of the present invention. Consequently, the
nitric acid can be recycled after the fuel of the present invention is
recovered to improve the yield of the final product. The nitric acid used
in one reaction can be used in a subsequent reaction no matter which
s aminoguanidine salt is used ' in the initial reaction or the subsequent
reaction.
Figure 4 provides an additional DSC plot of the AZODN of Example
1. As can be seen from this Figure, the exothermic onset occurred at
approximately 160°C with major decomposition at 185.1°C. Figure
5
to shows a DSC plot of the fuel produced by Example 13 (Embodiment 2)
with an exothermic onset occurring at 157.69°C and major decomposition
at 184.98°C. Consequently, the fuel of Example 13 utilizing
aminoguanidine bicarbonate is the substantially the same as the fuel of
Example 1 and, thus, is azodiformamidine dinitrate. Use of aminoguanidine
~s bicarbonate at the aminoguanidine salt is preferred in the present
invention:
Figure 6 shows a DSC plot of the fuel produced by Example 14
{Embodiment 3) with an exothermic onset occurring at 150.39°C and major
decomposition at 182.44°C. Consequently, the fuel of Example 14
utilizing
aminoguanidine sulfate is also the substantially the same as the fuel of
2o Example 1 and, thus, is azodiformamidine dinitrate.
Figures 7, 8 and 9 are IR. spectral of the fuel of Examples l, I3 and
14, respectively. Figures 10(a)-(d) are also IR spectra of the fuel of
Examples 15, l, 13 and 14, respectively. By comparing these spectras with
the IR spectra of Figure 11 taken from Analytical Chemistry. Vol. 23, p.
2s 1594 {1951), it can be seen that the high oxygen balance fuel of the
present invention utilizing aminoguanidine salt, including aminoguanidine
nitrate, aminoguanidine bicarbonate, and aminoguanidine sulfate, produces
azodiformamidine dinitrate. The same is true with respect to the recycled
acid of Example 15.
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Tables 11-14 are provided to show the use of representative AZODN
made from aminoguanidine_ nitrate, arninoguanidine bicarbonate, or
aminoguanidine sulfate, or combinations thereof. As can be seen from the
results of Table 11, the total ash is production is low, flame temperatures
s are acceptable and the hazard tests are designated as "green" meaning
acceptable. Specifically, Table 11 shows t~~e AZODN propellant properties
exhibited by five (5) different formulations without the use of a binder
Table 12 is an evaluation of the use of binders in AZODN propellant
compositions and particularly comparing the use of QPAC-40 binder
io (golycarbonate) made by PAC Polymers, Inc. and CAB (cellulose-acetate
butyrate) made by Eastman Chemical, Inc. This table generally shows that
an increase in binder content increases the initial crash strength of the
AZODN propellant composition.
Tables 13 and 14 demonstrate the effect of annealing time and fine
is particle size on the crush strength and b~uning rate of various AZODN
propellant compositions with and without a QPAC-40 binder.
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CA 02333942 2000-11-30
WO 00/00365 PC1'/US99/07049
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CA 02333942 2000-11-30
WO 00/00365 PCT/US99/07049
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CA 02333942 2000-11-30
WO 00/00365 PCT/US99107049
-42-
TABLE 15
SAMPLE ID FIRE TEMP F INSOLUBLE WT. SOLUBLE WT. pH
BI2020 70 0.835938 3.46708/-I3lmg 7.0
AA-106 A 70 1.231378 1.56758/+9mg 7.5
I
AA-106 A ?0 1.301 198 1.593Ig/-55mg 6.0
AA-106 A 70 0.6I248g 0.75238/-27mg 5.5
12020112019 70 0.5678tig 2.73538/-65mg 6.1
AA-I06 A -40 0.490028 1.55588/-33mg 6.0
AA-106 A -40 0.490588 9.0
(inside)
AA-106 A -40 0.447108 0.95768 6.0
AA-106 B -40 0.543278 1.32178 5.5
Table 15 shows the amount of insoluble and soluble decomposition product
produced
during an unfiltered inflator test of the gas generator propellant composition
of the present
invention made from the reaction of nitric acid .and aminoguanidine salt, such
as
aminoguanidine nitrate, aminoguanidine sulfate, or the preferred salt,
aminoguanidine
bicarbonate. Specifically, the test involved a PD-67 full size heavy weight
test hardware
inflator firing unit without any filter collection system. The sample
propellant was feed in
a 60 liter tank and then rinsed to measure the amount of solid decomposition
product in the
tank. The pH of the resulting solid decomposition product was also obtained.
As can be seen
from the results set forth above in Table 15, the pH of the decomposition
product is relatively
neutral which is important to prevent harm to passengers of an automobile in
which the
propellant of the present invention is utilized during a collision in an air
bag unit. Further,
the amount of unfiltered insoluble and soluble decomposition product is
relatively low.
As can be seen from the above Examples and corresponding testing, the high
oxygen
balance fuel of the present invention, preferably, azodiformamidine dinitrate,
exhibits
attractive propellant attributes and should be useful in a large number of-
pyrotechnic gas
generant environments.
