CA2333942A1 - Pyrotechnic gas generant composition including high oxygen balance fuel - Google Patents

Abstract

A pyrotechnic gas generant composition includes a high oxygen balance compound or fuel, preferably, azodiformamidine dinitrate, which is the resulting reaction product of an aminoguanidine salt and nitric acid. Specifically, the high oxygen balance compound or fuel of the present invention is the resulting reaction product of aminoguanidine salts, such as aminoguanidine nitrate, aminoguanidine bicarbonate, or aminoguanidine sulfate with nitric acid.
Preferably, the aminoguanidine salt is aminoguanidine bicarbonate. The resulting reaction product is a yellow precipitate that can be used alone, with or without oxidizers or other additives, for very rapid self-deflagration or in combination with oxidizers and additives. In each instance, the gas generant composition provides both high gas output and low production of solid combustion products. Further, the precipitant is relatively non-hygroscopic and has a high burn rate. The gas generating composition is useful as a gas generator for an air bag of an occupant restraint system for an automobile, gun propellants, inflation and expulsion devices, flotation devices, pyrotechnics, fire suppression devices and smokeless, reduced smoke and smokey rocket propellants.

Description

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 w0 00/00365 PCT/US99/07049 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

-3-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

-4-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 wo ao~oo~ss PCTIUS99/07049 -s-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.

5 PCTlUS99107049

-6-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 _7_ 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 .g_ 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 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 WO OOIOO365 PCTIUS99/07049 .
- ld -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 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 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, w0 00100365 PCT/US99l07049 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 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 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.

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 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.

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.

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 w0 OOI00365 PCT/US99/07049 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.

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 AZODN. Ammonium PerchIorate, and Strontium Nitrate Compositions -AZODNfwt%_l AP wt o ~rN ~ OIF Balance s 82.3 9.3 8.4 .

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 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 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 (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~~

WO 00!00365 PCT/US99/0'7049 (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 ~, WO 00100365 PG"TIUS99107049 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 +

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

(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 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%

_27_ (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) _~8_ 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 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.

WO 00/00365 PCTNS99/o7049 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 WO 00/00365 PCTIUS99l07049 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 -3z_ 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

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.

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 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 WO 00/00365 PCTIUS9910'7049 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 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 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.

w0 00/00365 PCTIUS99/07049 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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w ~ w 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.

Claims (25)

What is claimed is:

1. A pyrotechnic gas generant composition comprising:
a high oxygen balance fuel, wherein said high oxygen balance fuel is a resulting solid yellow reaction product of nitric acid and an aminoguanidine salt.

2. A pyrotechnic gas generant composition of claim 1, wherein said aminoguanidine salt is selected from the group consisting of aminoguanidine bicarbonate; aminoguanidine sulfate and mixtures thereof.

3. A pyrotechnic gas generant composition of claim 2, said high oxygen balance fuel comprising 2-100% by weight of said pyrotechnic gas generant composition.

4. A pyrotechnic gas generant composition of claim 3, said high oxygen balance fuel comprising 40-100% by weight of said pyrotechnic gas generant composition.

5. A pyrotechnic gas generant composition of claim 2, wherein said resulting yellow reaction product of said aminoguanidine salt and nitric acid is prepared by a process comprising:
(a) providing said aminoguanidine salt;
(b) combining said aminoguanidine salt with nitric acid to form a dispersion, wherein said dispersion proceeds through a color transition from water white to straw to bright yellow color, said color being comparable to a potassium dichromate solution.

6. A pyrotechnic gas generant composition of claim 5, wherein 70% reagent grade nitric acid is combined with said aminoguanidine salt.

7. A pyrotechnic gas generant composition of claim 2, wherein said resulting yellow reaction product of said aminoguanidine salt and nitric acid is prepared by a process comprising:
(a) combining said aminoguanidine salt and water to form a slurry;
(b) stirring 70% nitric acid into said slurry to form a dispersion;

(c) heating said dispersion during which time said dispersion dissolves and proceeds with effervescence through a color transition from water white to straw to a bright yellow color to form a solution, said bright yellow color being comparable to a potassium dichromate solution;
(d) cooling said solution to precipitate said solid yellow reaction product.

8. A pyrotechnic gas generant composition of claim 7, wherein said dispersion is heated to 55-65°C and said solution is cooled to below 12°C.

9. A pyrotechnic gas generant composition of claim 2, further comprising at least one oxidizer, said oxidizer comprising from 0-98% by weight of said pyrotechnic gas generant composition.

10. A pyrotechnic gas generant composition of claim 9, wherein said at least one oxidizer comprises from 0-60% by weight of said pyrotechnic gas generant composition.

11. A pyrotechnic gas generant composition of claim 9, wherein said at least one oxidizer is substantially non-hygroscopic.

12. A pyrotechnic gas generant composition of claim 9, further including at least one additive selected from the group consisting of a scavenger, ignition aid, ignition initiator, gas conversion catalyst, ballistic modifier, slag formers, binders, energetic; binders, plasticizers, energetic plasticizers, fuels, stabilizers, curing agents, cure catalysts, cross linkers, inorganic coolants, organic coolants and compounding aids and mixtures thereof.

13. A pyrotechnic gas generant composition of claim 9, wherein said at least one oxidizer is selected from the group consisting of non-metallic, alkali metal, alkaline earth metal, transition metal and transition metal complex nitrates, nitrites, chlorates, chlorites, perchlorates, chromates, or mixtures thereof.

14. A pyrotechnic gas generant composition of claim 13, wherein said oxidizer comprises sodium nitrate.

I5. A pyrotechnic gas generant composition of claim 14, wherein said oxidizer further comprises ammonium perchlorate.

i6. A pyrotechnic gas generant composition of claim 9, wherein said oxidizer comprises phase stabilized ammonium nitrate.

17. A pyrotechnic gas generant composition of claim 9, wherein said oxidizer comprises ammonium perchlorate, said composition further comprising an additive selected from at least one of the group consisting of ammonium perchlorate, ammonium nitrate, potassium perchlorate, strontium nitrate, potassium nitrate, lithium. nitrate, lithium carbonate and mixtures thereof.

18. A pyrotechnic gas generant composition of claim 2, wherein said reaction product is crystallized or recrystallized.

19. A pyrotechnic gas generant composition of claim 1, further comprising at least one other high oxygen balance fuel.

20. A pyrotechnic gas generant composition of claim 19, wherein said other high oxygen balance fuel is selected from the group consisting ofhydrazodicarbonamidine, diazoguanidine, formamidine, bisformamidine, azobisformamidine derivative fuels and mixtures thereof.

21. A pyrotechnic gas generant composition of claim 20, wherein said azobisformamidine derivative is selected from the group consisting of guanyl azide nitrate, diazoguanidine nitrate, azobisnitroformamidine, 1,1'-azodiformamidine dipicrate, and mixtures thereof.

22. A chemical delivery system for fire suppression comprising a vessel including:
a high oxygen balance fuel, wherein said high oxygen balance fuel is a resulting reaction product of an aminoguanidine salt and nitric acid;
and a fire suppression chemical.

23. A chemical delivery system for fire suppression of claim 22, wherein said aminoguanidine salt is selected from the group consisting of aminoguanidine bicarbonate, aminoguanidine sulfate, and mixtures thereof.

24. A method for inflating an article capable of retaining gas, comprising the steps of:
igniting a gas generant composition comprising a high oxygen balance fuel, wherein said high oxygen balance fuel is a yellow reaction product of an aminoguanidine salt and nitric acid;
generating gas and solid material as reaction products of said reaction of said high oxygen balance fuel;
passing said gas and solid material into a filter, retaining at least a portion of solid material on the filter, and allowing the gas to exit;
passing the filtered gas into an article, thereby filling or inflating the article.

25. A method of claim 24, wherein said aminoguanidine salt is selected from the group consisting of aminoguanidine bicarbonate, aminoguanidine sulfate and mixtures thereof.