Gas generant materials

Abstract

A gas generant composition includes a non-azide, organic, nitrogen-containing fuel; a substituted basic metal nitrate and at least one transition metal complex of diammonium bitetrazole. The substituted basic metal nitrate can be a reaction product of an acidic organic compound and a basic metal nitrate. The transition metal complex of diammonium bitetrazole is effective to enhance the burn rate presure sensitivity of the gas generant composition as compared to the same gas generant composition without inclusion of the at least one transition metal complex of diammonium bitetrazole.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No. 10/412,530, filed 11 Apr. 2003. The co-pending parent application is hereby incorporated by reference herein in its entirety and is made a part hereof, including but not limited to those portions which specifically appear hereinafter.

The subject matter of this application is also related to prior U.S. patent applications Ser. No. 09/998,122, filed 30 Nov. 2001, now U.S. Pat. No. 6,712,918, issued 30 Mar. 2004; U.S. Ser. No. 10/627,433, filed 25 Jul. 2003; U.S. Ser. No. 10/899,451, filed 26 Jul. 2004; and U.S. Ser. No. 10/899,452, filed 26 Jul. 2004. The disclosures of these related patent applications are also hereby incorporated by reference herein in their entirety and made a part hereof, including but not limited to those portions which specifically appear hereinafter.

BACKGROUND OF THE INVENTION

This invention relates generally to a material for use in gas generation such as for forming an inflation gas such as for inflating inflatable devices such as airbag cushions included in automobile inflatable restraint systems.

It is generally well known to protect a vehicle occupant using a cushion or bag, e.g., an “airbag cushion,” that is inflated or expanded with a gas when a vehicle experiences sudden deceleration, such as in the event of a collision. Such airbag restraint systems normally include: one or more airbag cushions, housed in an uninflated and folded condition to minimize space requirements; one or more crash sensors mounted on or to the frame or body of the vehicle to detect sudden deceleration of the vehicle; an activation system electronically actuated by the crash sensors; and inflator device that produces or supplies a gas to inflate the airbag cushion. In the event of a sudden deceleration of the vehicle, the crash sensors actuate the activation system which in turn actuates the inflator device which begins to inflate the airbag cushion in a matter of milliseconds.

Many types of inflator devices have been disclosed in the art for inflating one or more inflatable restraint system airbag cushions. Generally, such inflator devices may include one or more pyrotechnic compositions such as an igniter composition, the combustion of which may ignite a gas generating compound, or a gas generant composition, the combustion of which provides a gas such as may be used either alone or to supplement a stored and pressurized gas to inflate an associated airbag cushion.

Pyrotechnic gas generant compositions commonly utilized in the inflator devices of automobile inflatable restraint systems had previously most typically employed or been based on sodium azide. Such sodium azide-based compositions upon initiation normally produce or form nitrogen gas. While the use of sodium azide and certain other azide-base pyrotechnic materials meets current industry specifications, guidelines and standards, such use may involve or raise potential concerns such as involving safe and effective handling, supply and disposal of such azide-based pyrotechnic materials.

As a result, the development and use of other suitable gas generant compositions has been pursued. In particular, such efforts have been directed to the development of azide-free gas generant compositions for use in such inflator devices. Much research has gone into the identification and evaluation of non-azide or azide-free gas generant formulations or compositions that provide: a high gas output, typically greater than about 2 moles of gas per 100 grams of composition; a low combustion temperature such as a combustion flame temperature of less than 2000 K; a high burn rate, generally greater than about 0.85 inches per second at 3000 psi; low toxicity of effluent gases; and easily filterable particulate matter. Typically such azide-free formulations are less toxic and therefore easier to dispose of and more readily accepted by the general public.

Unfortunately, such formulations often have or exhibit burn rates that are generally lower than is desired or optimal to provide efficient and effective inflation of an associated airbag cushion. For some inflator device applications a low burn rate can be compensated for by using small particles of pyrotechnic composition having a relatively large surface area. However, in practice there are limits on the minimum size of pyrotechnic composition particles that can be manufactured in a desirably reproducible manner. Additionally, a higher burn rate than can be achieved with such pyrotechnic compositions may be desired for inflator programs requiring higher performance. Still further, it is generally desirable to increase or maximize the loading density of the gas generant or pyrotechnic and thus reduce or minimize the volume of the required associated chamber.

In general, the burn rate for a gas generant composition can be represented by the equation (1), below:
r_b=k(P)ⁿ   (1)
where,

• • r_b=burn rate (linear)
  • k=constant
  • P=pressure
  • n=pressure exponent, where the pressure exponent is the slope of a linear regression line drawn through a log-log plot of burn rate versus pressure.

The burn rates of certain pyrotechnic compositions, particularly those including nitrogen-containing fuels, have been enhanced variously through the inclusion of one or more selected additives such as a selected high energy fuel ingredient or by the addition of co-oxidizers such as ammonium and potassium perchlorate. However, extensive reliance on the inclusion and use of such materials may add undesired expense to the manufacture of the pyrotechnic compositions such as via increased raw material costs and added process steps. Moreover, certain economic and design considerations such as industry competition has led to a desire for pyrotechnic compositions which are composed of less costly ingredients or materials and which are amenable to processing via more efficient or less costly techniques.

Still further, in view of an increased focus on passenger safety and injury prevention, many automotive vehicles typically include several inflatable restraint systems, each including one or more inflator devices. For example, a vehicle may include a driver airbag, a passenger airbag, one or more seat belt pretensioners, one or more knee bolsters, and/or one or more inflatable belts, each with an associated inflator device, to protect the driver and passengers from frontal crashes. The vehicle may also include one or more head/thorax cushions, thorax cushions, and/or curtains, each with at least one associated inflator device, to protect the driver and passengers from side impact crashes. Generally, the gaseous effluent or inflation gas produced by all of the inflator devices within a particular vehicle, when taken as whole, are required to satisfy strict content limitations in order to meet current industry safety guidelines. Thus, it is desired that gas generant compositions used in such inflator devices produce as little as possible of undesirable effluents such as hydrogen chloride, carbon monoxide, ammonia, nitrogen dioxide and nitric oxide.

While the manipulation of the equivalence ratio of gas generant materials is a technique commonly used to adjust the effluent levels of gas generant materials, such manipulation is prone to a performance limitation sometimes referred to as the equivalence ratio “teeter-totter”. That is, as the equivalence ratio is lowered, under-oxidized species, such as CO and NH₃, increase and over-oxidized species, such as NO and NO₂, decrease. The reverse is true when the equivalence ratio is increased.

Moreover, those skilled in the art and guided by the teachings herein provided will understand and appreciate that the combustion flame temperature of a gas generant material typically has a significant effect on the levels of carbon monoxide and nitrogen oxides in the gas effluent. More specifically at temperatures above 2000 K, the prevalence of reactions within and between gaseous species in the effluent such as to produce carbon monoxide and nitrogen oxides can dramatically increase. In contrast at combustion flame temperatures below 2000 K, these reactions occur to a significantly lesser extent such as may desirably result in cleaner, less toxic, effluent gases.

In view of the above, there is a need and a demand for a non-azide or azide-free gas generant material or composition that, while overcoming at least some of the potential problems or shortcomings of azide-based pyrotechnic compositions, may also provide relatively high gas yields as compared to typical azide-based pyrotechnic compositions. There is a further need and a demand for a material that when applied in such inflatable safety restraint applications provides or results in a sufficient and desirably high burn rate such as a burn rate of greater than about 0.85 inches per second at 3000 psi. There is also a need and a demand for gas generant materials or compositions that minimize or avoid the production or yield of incomplete products of combustion such as having the general form of CO_x and NOR_x, for example. There is a still further need or a demand for such gas generant compositions may be economically and efficiently manufactured. Yet still further, there is as need and a demand for such a gas generant composition that attains or permits desirably increased or maximized loading densities such as to reduce or minimize the required chamber volume associated therewith.

SUMMARY OF THE INVENTION

A general object of the invention is to provide an improved gas generant composition.

A more specific objective of the invention is to overcome one or more of the problems described above.

The general object of the invention can be attained, at least in part, through a gas generant composition that includes a non-azide, organic, nitrogen-containing fuel; a substituted basic metal nitrate comprising a reaction product of an acidic organic compound and a basic metal nitrate; and at least one transition metal complex of diammonium bitetrazole effective to decrease the burn rate pressure sensitivity of the gas generant composition as compared to the same gas generant composition without inclusion of the at least one transition metal complex of diammonium bitetrazole.

The prior art generally fails to provide gas generant compositions, particularly non-azide gas generant compositions that are capable of simultaneously providing or resulting in relatively high gas yields, as well as sufficient and desirably high burn rates while avoiding or minimizing production or yield of undesirable inflation gas constituents such as one or more of hydrogen chloride, carbon monoxide, ammonia, nitrogen dioxide and nitric oxide. Moreover, the prior art generally fails to provide such gas generant compositions that are conducive or easily adaptable to manufacture or production by alternative techniques such as via extrusion processing.

In accordance with another aspect of the invention, there is provided a gas generant composition that includes:

about 5 to about 60 composition weight percent of guanidine nitrate;

about 10 to about 60 composition weight percent of a combination of basic copper nitrate aminotetrazole adduct, copper diammonium bitetrazole and basic copper nitrate co-oxidizer; and

about 1 to about 20 composition weight percent of a polymeric binder effective to impart sufficient cohesive properties to the gas generant composition whereby the gas generant composition is extrudable. As described in greater detail below, such a gas generant composition can desirably be extrudably processed.

As used herein, references to a specific composition, component or material as a “fuel” are to be understood to refer to a chemical which generally lacks sufficient oxygen to burn completely to CO₂, H₂O and N₂.

Correspondingly, references herein to a specific composition, component or material as an “oxidizer” are to be understood to refer to a chemical generally having more than sufficient oxygen to burn completely to CO₂, H₂O and N₂.

References to a “burn rate enhanced” material are to be understood to refer to materials or compositions which exhibit a burn rate of at least 0.85 inches per second at 3000 pounds per square inch (psi) or greater, preferably a burn rate of greater than about 1 inch per second at 3000 psi and, more preferably a burn rate of greater than about 1.2 inches per second at 3000 psi.

The term “equivalence ratio” is understood to refer to the ratio of the number of moles of oxygen in a gas generant composition or formulation to the number of moles needed to convert hydrogen to water, carbon to carbon dioxide, and any metal to the thermodynamically predicted metal oxide. Thus, a gas generant composition having an equivalence ratio greater than 1.0 is over-oxidized, a gas generant composition having an equivalence ratio less than 1.0 is under-oxidized, and a gas generant composition having an equivalence ratio equal to 1.0 is perfectly oxidized.

The expression “substantially free of”, as used herein in reference to possible gaseous effluent constituents such as hydrogen chloride, carbon monoxide, ammonia, nitrogen dioxide and nitric oxide similarly refer to a gaseous effluent or inflation gas that includes such constituent in an amount that is equal to or less than an amount of such constituent permitted by or allowed under current industry standards (USCAR specifications). For example, if a vehicle includes a single inflatable airbag cushion with a single inflator including a gas generant composition, the gaseous effluent or inflation gas produced by the combustion of the gas generant composition is substantially free of hydrogen chloride if it includes about 5 parts per million hydrogen chloride or less when the inflator is discharged into a 100 ft³ tank, is substantially free of carbon monoxide if it includes about 461 parts per million carbon monoxide or less when the inflator is discharged into a 100 ft³ tank; is substantially free of ammonia if it includes about 3 5 parts per million ammonia or less when the inflator is discharged into a 100 ft³ tank; is substantially free of nitrogen dioxide if it includes about 5 parts per million nitrogen dioxide or less when the inflator is discharged into a 100 ft³ tank; and is substantially free of nitric oxide if it includes about 75 parts per million nitric oxide or less when the inflator is discharged into a 100 ft³ tank.

Other objects and advantages will be apparent to those skilled in the art from the following detailed description taken in conjunction with the appended claims and drawing.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a simplified schematic, partially broken away, view illustrating the deployment of an airbag cushion from an airbag module assembly within a vehicle interior, in accordance with one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

There is provided an improved gas generant composition such as for use in the inflation of inflatable elements such as an airbag cushion of an automobile inflatable restraint system. In accordance with a preferred embodiment, such a gas generant composition includes a substituted basic metal nitrate including a reaction product of an acidic organic compound and a basic metal nitrate.

As described in greater detail below, non-azide or azide-free materials having an acidic hydrogen will react with a basic metal nitrate such as basic copper nitrate and partially replace the hydroxyl groups in the basic metal nitrate without liberating soluble metal nitrate. In other words, the structural integrity of the basic metal nitrate is not compromised by the substitution reaction.

In accordance with certain preferred embodiments, the material used desirably includes a substituted basic metal nitrate including a reaction product of an acidic organic compound and a basic metal nitrate. Suitably, the acidic organic compound is a nitrogen-containing heterocyclic compound including an acidic hydrogen.

Examples of suitable acidic organic compounds include, but are not limited to, tetrazoles, imidazoles, imidazolidinone, triazoles, urazole, uracil, barbituric acid, orotic acid, creatinine, uric acid, hydantoin, pyrazoles, derivatives thereof, and combinations thereof. Particularly suitable acidic organic compounds include tetrazoles, imidazoles, derivatives thereof, and combinations thereof. Examples of such acidic organic compounds include 5-amino tetrazole, bitetrazole dihydrate, and nitroimidazole. In certain preferred embodiments, the acidic organic compound includes 5-amino tetrazole.

Generally, basic metal nitrate compounds utilized in certain embodiments include basic metal nitrates, basic transition metal nitrate hydroxy double salts, basic transition metal nitrate layered double hydroxides, and combinations thereof. Examples of basic metal nitrates include, but are not limited to, basic copper nitrate, basic zinc nitrate, basic cobalt nitrate, basic iron nitrate, basic manganese nitrate and combinations thereof. In accordance with certain preferred embodiments, the basic metal nitrate includes basic copper nitrate.

A few representative substitution reactions, such as reactions (1) through (4) below, and substituted basic metal nitrate reaction products, particularly, 5-amino tetrazole substituted basic copper nitrate, bitetrazole dihydrate substituted basic copper nitrate, and nitroimidazole substituted basic copper nitrate, within the scope of the present invention are as follows:
3 Cu(OH)₂.Cu(NO₃)₂+2 CH₃N₅→2 Cu(OH)₂.Cu(CH₂N₅)₂.Cu(NO₃)₂+2 H₂O;   (1)
3 Cu(OH)₂.Cu(NO₃)₂+C₂H₂N₈.2 H₂O→2 Cu(OH)₂.Cu(C₂N₈).Cu(NO₃)₂+4 H₂O;   (2)
3 Cu(OH)₂.Cu(NO₃)₂+2 C₃H₃N₃O₂→2 Cu(OH)₂.Cu(C₃H₂O₂)₂.Cu(NO₃)₂+2 H₂O;   (3)
and
3 Cu(OH)₂.Cu(NO₃)₂+4 C₃H₃N₃O₂→Cu(OH)₂.2Cu(C₃H₂N₃O₂)₂.Cu(NO₃)₂+4 H₂O.   (4)

The described substituted basic metal nitrate materials may be utilized as a pyrotechnic composition such as may be included in an inflator device of an automobile inflatable restraint system. Alternatively, the described substituted basic metal nitrate materials may be used in a pyrotechnic composition such as an igniter composition or a gas generant composition including additional components such as a co-fuel. In accordance with certain preferred embodiments, the substituted basic metal nitrate can desirably serve to enhance the burn rate of an associated gas generant composition.

Generally, such pyrotechnic compositions include a substituted basic metal nitrate and a nitrogen containing co-fuel. In particular, such burn rate enhanced gas generant compositions include a reaction product of a basic metal nitrate such as basic copper, zinc, cobalt, iron and manganese nitrates, basic transition metal nitrate hydroxy double salts, basic transition metal nitrate layered double hydroxides, and combinations thereof and an acidic organic material such as tetrazoles, tetrazole derivatives, and combinations thereof.

In practice, such pyrotechnic compositions may desirably include about 5 to about 60 composition weight percent co-fuel, preferably a non-azide, organic, nitrogen-containing fuel such as suited for vehicular inflatable safety restraint applications. One particularly preferred pyrotechnic composition includes about 5 to about 60 composition weight percent guanidine nitrate co-fuel. The desirability of use of guanidine nitrate in the pyrotechnic compositions of the invention is generally based on a combination of factors such as relating to cost, stability (e.g., thermal stability), availability and compatibility (e.g., compatibility with other standard or useful pyrotechnic composition components, for example).

In addition, certain preferred gas generant compositions desirably involve the addition or inclusion of a quantity of at least one transition metal complex of diammonium bitetrazole to the gas generant formulation.

Suitable transition metals for use in the practice of the invention include copper, zinc, cobalt, iron, nickel and chromium. Preferred transition metals include zinc and copper. A copper complex of diammonium bitetrazole having an empirical formula of CuC₂H₆N₁₀ is a preferred transition metal complex of diammonium bitetrazole for use in certain preferred embodiments.

Those skilled in the art and guided by the teachings herein provided will appreciate that the invention can desirably be practice via the inclusion of a sufficient quantity of at least one transition metal complex of diammonium bitetrazole to the gas generant formulation such that the resulting formulation exhibits a desirable decrease in burn rate pressure sensitivity, as compared to the same formulation without the inclusion of such transition metal complex of diammonium bitetrazole. In general, however, it has been found preferable for a gas generant formulation in accordance with a preferred practice of the invention to include or incorporate the at least one transition metal complex of diammonium bitetrazole in a relative amount of at least 2 wt. %, preferably at least 5 wt. % and, more preferably, in a relative amount of at least 10 wt. % in order to provide gas generant formulations evidencing a sufficiently decreased burn rate pressure sensitivity, as may desired for at least certain such inflatable restraint system applications.

If desired, a pyrotechnic composition in accordance with the invention may advantageously include an additional oxidizer in an amount of up to about 50 composition weight percent. Such additional oxidizer materials are sometimes termed “a co-oxidizer.” Preferred such co-oxidizers materials include basic metal nitrates, such as basic copper nitrate, metal oxides, such as cupric oxide and ferric oxide, for example, as well as ammonium perchlorate, alkali metal perchlorate, strontium nitrate, basic copper carbonate and combinations of two or more of such preferred co-oxidizer materials of basic metal nitrates, metal oxides, ammonium perchlorate, alkali metal perchlorate, strontium nitrate and basic copper carbonate.

While materials such as ammonium perchlorate and alkali metal perchlorate can be included in subject gas generant compositions in a homogeneous manner, in accordance with certain preferred embodiments, such perchlorate materials can desirably be heterogeneously included in particular subject gas generant compositions. To that end, it has been found that such perchlorate materials for inclusion in particular subject gas generant compositions be included or present in a relative amount of about 1 to about 10 composition weight percent and have a mean particle size in excess of 100 microns and, preferably, a mean particle size of at least about 200 microns can dramatically improve the effluent resulting from the combustion of a gas generant composition which includes such sized perchlorate particles, as compared to the effluent resulting from the combustion of the same gas generant composition but without the so sized perchlorate particles. In accordance with at least certain preferred embodiments of the invention, it has been found advantageous that such perchlorate particles included in gas generant compositions in accordance with the invention have a mean particle size in the range of about 350 to about 450 microns.

Gas generant composition in accordance with the invention and suited for extrusion processing desirably also include a binder component. Advantageously, the binder component is a polymeric binder material effective to impart sufficient cohesive properties to the gas generant composition whereby the gas generant composition is extrudable. Extrudable gas generant compositions in accordance with certain preferred embodiments will desirably include or contain about 1 to about 20 composition weight percent of such a polymeric binder component.

Examples of suitable binder materials can include cellulosics, natural gums, polyacrylates, polyacrylamides, polyurethanes, polybutadienes, polystyrenes, polyvinyl alcohols, polyvinyl acetates, silicones and combinations of two or more thereof. More particularly, suitable cellulosic binder materials may include ethyl cellulose, carboxymethyl cellulose, hydroxylpropyl cellulose and combinations of two or more thereof. Suitable natural gum binder materials may include guar, xanthan, arabic and combinations of two or more thereof. Those skilled in the art and guided by the teachings herein provided will further appreciate that the incorporation of binder materials, such as the above-described cellulosic binders, that result in or form compositions that burn at lower temperatures, sometimes referred to as “cooler burning” materials, can be advantageously preferred for various applications.

Those skilled in the art and guided by the teachings herein provided will appreciate that such gas generant compositions prepared via extrusion processing can desirably exhibit increased or maximized loading densities such as may desirably serve to reduce or minimize the required chamber volume associated therewith. Such extruded gas generant compositions may further desirably more easily burn at higher pressure conditions and can thus serve to reduce or minimize the production or yield of incomplete products of combustion such as having the general form of CO_x and NO_x, for example.

One or more of the materials or ingredients included in the subject compositions may serve multiple roles or functions in particular formulations. For example, binder materials can also typically act or function as a fuel components, as above defined. Thus, specific range limits for particular materials includable in the subject compositions are generally dependent, at least in part, on what other particular materials are included in a specific composition. Such specific range limits for particular materials includable in the subject compositions are readily identifiable by those skilled in the art and guided by the teachings herein provided

Additional additives such as slag forming agents, flow aids, plasticizers, viscosity modifiers, pressing aids, dispersing aids, or phlegmatizing agents may also be included in the pyrotechnic composition to facilitate processing or to provide enhanced properties. For example, pyrotechnic compositions in accordance with the invention may include a slag forming agent such as a metal oxide compound such as aluminum oxide. Generally, such additives may be included in the subject compositions in an amount of about 1 to no more than about 5 composition weight percent. Such additives typically are one or more metal oxide materials, with preferred such additives including metal oxides such as silicon dioxide, aluminum oxide, zinc oxide, and combinations thereof.

Thus, gas generating compositions such as herein above-described desirably provide or result in a burn rate of greater than about 0.85 inches per second at 3000 psi, preferably a burn rate of greater than about 1 inch per second at 3000 psi and, more preferably a burn rate of greater than about 1.2 inches per second at 3000 psi.

Moreover, gas generating compositions such as herein above-described desirably provide or result in a burn rate pressure sensitivity (as represented by the pressure exponent (n) in the burn rate equation (1) identified above) of less 0.5, preferably of less than about 0.48.

Still further, gas generating compositions such as herein above-described desirably provide or exhibit a combustion flame temeprature of less than 2000 K.

As will be appreciated, gas generating compositions in accordance with the invention can be incorporated, utilized or practiced in conjunction with a variety of different structures, assemblies and systems. As representative, the FIGURE illustrates a vehicle 10 having an interior 12 wherein an inflatable vehicle occupant safety restraint system, generally designated by the reference numeral 14, is positioned. As will be appreciated, certain standard elements not necessary for an understanding of the invention may have been omitted or removed from the FIGURE for purposes of facilitating illustration and comprehension.

The vehicle occupant safety restraint system 14 includes an open-mouthed reaction canister 16 which forms a housing for an inflatable vehicle occupant restraint 20, e.g., an inflatable airbag cushion, and an apparatus, generally designated by the reference numeral 22, for generating or supplying inflation gas for the inflation of an associated occupant restraint. As identified above, such a gas generating device is commonly referred to as an “inflator.”

The inflator 22 contains a quantity of a gas generant composition in accordance with the invention and such as described above. The inflator 22 also includes an ignitor, such as known in the art, for initiating combustion of the gas generating composition in ignition communication with the gas generant composition. As will be appreciated, the specific construction of the inflator device does not form a limitation on the broader practice of the invention and such inflator devices can be variously constructed such as is also known in the art.

In practice, the airbag cushion 20 upon deployment desirably provides for the protection of a vehicle occupant 24 by restraining movement of the occupant in a direction toward the front of the vehicle, i.e., in the direction toward the right as viewed in the FIGURE.

The present invention is described in further detail in connection with the following examples which illustrate or simulate various aspects involved in the practice of the invention. It is to be understood that all changes that come within the spirit of the invention are desired to be protected and thus the invention is not to be construed as limited by these examples.

EXAMPLES

Example 1 and Comparative Examples 1-3

In these tests, 500 pound batches of each of the gas generant formulations having the compositions (values are in weight percent) identified in TABLE 1 below were prepared in the following manner:

Comparative Example 1 (CE1)

Guanidine nitrate (GN) was dissolved in approximately 30% water (i.e., 30% as a percentage of the total solids in mix on a wet basis, i.e., 214 lbs water) at 190° F. Basic carbon nitrate (bCN), alumina and silica were added thereto to make a slurry. The slurry was pumped through a lance and sprayed into a drying tower where it dried to a powder as it fell from the top to the bottom of the drying tower.

Comparative Example 2 (CE2)

The same procedure as in Comparative Example 1 was followed except that 5-aminotetrazole and bCN were reacted in water at 190° F. for 1 hour in order to make the 5-AT/bCN complex prior to the addition of the other ingredients.

Comparative Example 3 (CE3)

The same procedure as in Comparative Example 1 was followed except that cupric oxide and diammonium bitetrazole were reacted in water at 190° F. for 1 hour in order to make the copper diammonium bitetrazole prior to the addition of the other ingredients.

Example 1

The same procedure as in Comparative Example 1 except that, 1) 5-aminotetrazole and bCN were reacted in water at 190° F. for 1 hour in order to make the 5-AT/bCN complex and 2) cupric oxide and diammonium bitetrazole were reacted in water at 190° F. for 1 hour in order to make the copper diammonium bitetrazole prior to the addition of the other ingredients.

	TABLE 1
	CE 1	CE 2	CE 3	Example 1
	GN	50.38	27.49	24.66	28.58
	bCN	46.62	14.35	51.72	21.36
	CuDABT	—	—	20.62	4.00
	bCuATN	—	55.16	—	43.36
	Al2O3	2.70	1.50	1.50	1.50
	SiO2	0.30	1.50	1.50	1.20

where,

GN=guanidine nitrate

bCN=basic copper nitrate

CuDABT=copper diammonium bitetrazole and

bCuATN=5-amino tetrazole substituted basic copper nitrate

The gas generant formulation of each of Comparative Examples 1-3 and Example 1 was then tested. The burn rate and combustion flame temperature (T_c) values identified in TABLE 2 below were obtained. In particular, the burn rate data was obtained by first pressing samples of the respective gas generant formulations into the shape or form of a 0.5 inch diameter cylinder using a hydraulic press (12,000 lbs force). Typically enough powder was used to result in a cylinder length of 0.5 inch. The cylinders were then each coated on all surfaces except the top one with a krylon ignition inhibitor to help ensure a linear burn in the test fixture. In each case, the so coated cylinder was placed in a 1-liter closed vessel capable of being pressurized to several thousand psi with nitrogen and equipped with a pressure transducer for accurate measurement of vessel pressure. A small sample of igniter powder was placed on top of the cylinder and a nichrome wire was passed through the igniter powder and connected to electrodes mounted in the vessel lid. The closed vessel was then pressurized to the desired pressure and the sample ignited by passing a current through the nichrome wire. Pressure vs. time data was collected as each of the respective samples were burned. Since combustion of each of the samples generated gas, an increase in vessel pressure signaled the start of combustion and a “leveling off” of pressure signaled the end of combustion. The time required for combustion was equal to t₂-t₁ where t₂ is the time at the end of combustion and t₁ is the time at the start of combustion. The sample length was divided by combustion time to give a burning rate in inches per second. Burning rates were typically measured at four pressures (900, 1350, 2000, and 3000 psi). The log of burn rate vs the log of average pressure was then plotted. From this line the burn rate at any pressure can be calculated using the gas generant composition burn rate equation (1), identified above.

	TABLE 2
	CE 1	CE 2	CE 3	EXAMPLE 1
rb (1000)	0.47	1.17	0.84	0.97
rb (3000)	0.82	2.11	1.24	1.58
n	0.50	0.54	0.35	0.44
k	0.015	0.028	0.107	0.047
Tc	1845	2025	1851	1959

where,

• • r_b (1000)=burn rate at 1000 psi in inch per second (ips);
  • r_b (3000)=burn rate at 3000 psi in inch per second (ips);
  • n=pressure exponent in the burn rate equation (1) identified above, where the pressure exponent is the slope of the plot of the log of pressure along the x-axis versus the log of the burn rate along the y-axis;
  • k=the constant in the burn rate equation (1) identified above; and
  • T_c=combustion flame temperature (T_c)
    Discussion of Results

As shown in TABLE 2 wherein the gas generant formulation of CE 1 serves as a baseline formulation, the inclusion of CuDABT in CE 2 while resulting in a formulation with an increased burn rate also significantly increased the pressure sensitivity of the burning rate (as represented by the pressure exponent (n)). The inclusion of copper diammonium bitetrazole in CE 3, as compared to the performance of the formulation of CE 1, resulted in a formulation reduced burn rate pressure sensitivity. Example 1, however, shows that gas generant inclusion of both bCuATN and copper diammonium bitetrazole, albeit in the relatively low relative level of 4%, provided a desirably increased or elevated burn rate while also exhibiting a desirably reduced or decreased burn rate pressure sensitivity.

TABLE 2 also shows that the gas generant material of Example 1 exhibited a combustion flame temperature of below 2000 K. As discussed above, with gas generant materials having a combustion flame temperature of below 2000 K undesirable effluent reactions resulting in increased levels of undesirable species such as carbon monoxide and nitrogen oxides can be avoided or minimized.

Thus, non-azide or azide-free gas generant materials or compositions are provided that, while overcoming at least some of the potential problems or shortcomings of azide-based pyrotechnic compositions, may also provide relatively high gas yields as compared to typical azide-based pyrotechnic compositions. These gas generant compositions also desirably provide or result in a sufficient and desirably high burn rate, e.g., a burn rate of greater than about 0.85 inches per second at 3000 psi, preferably a burn rate of greater than about 1 inch per second at 3000 psi and, more preferably a burn rate of greater than about 1.2 inches per second at 3000 psi. Moreover, at least particular embodiments of the subject gas generant compositions are particularly adapted and well-suited for extrudable production and can thus provide new or facilitate alternative economic and efficient gas generant production techniques. Furthermore, such gas generant compositions can attain or permit desirably increased or maximized loading densities such as to reduce or minimize the required chamber volume associated therewith.

The invention illustratively disclosed herein suitably may be practiced in the absence of any element, part, step, component, or ingredient which is not specifically disclosed herein.

While in the foregoing detailed description this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purposes of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.

Claims

1. A gas generant composition comprising:

a non-azide, organic, nitrogen-containing fuel;

a substituted basic metal nitrate comprising a reaction product of an acidic organic compound and a basic metal nitrate; and

at least one transition metal complex of diammonium bitetrazole effective to decrease the burn rate pressure sensitivity of the gas generant formulation as compared to the same gas generant composition without inclusion of the at least one transition metal complex of diammonium bitetrazole.

2. The gas generant composition of claim 1 wherein the non-azide, organic, nitrogen-containing fuel is guanidine nitrate.

3. The gas generant composition of claim 1 wherein the acidic organic compound is a nitrogen-containing heterocyclic compound including an acidic hydrogen.

4. The gas generant composition of claim 1 wherein the acidic organic compound is selected from the group consisting of tetrazoles, imidazoles, imidiazolidinone, triazoles, urazole, uracil, barbituric acid, orotic acid, creatinine, uric acid, hydantoin, pyrazoles, derivatives thereof, and combinations thereof.

5. The gas generant composition of claim 1 wherein the acidic organic compound is selected from the group consisting of tetrazoles, imidazoles, derivatives thereof, and combinations thereof.

6. The gas generant composition of claim 1 wherein the acidic organic compound comprises 5-amino tetrazole.

7. The gas generant composition of claim 1 wherein the acidic organic compound comprises bitetrazole dihydrate.

8. The gas generant composition of claim 1 wherein the acidic organic compound comprises nitroimidazole.

9. The gas generant composition of claim 1 wherein the basic metal nitrate is selected from the group consisting of basic copper, zinc, cobalt, iron, and manganese nitrates, basic transition metal nitrate hydroxy double salts, basic transition metal nitrate layered double hydroxides, and combinations thereof.

10. The gas generant composition of claim 1 wherein the basic metal nitrate comprises basic copper nitrate.

11. The gas generant composition of claim 1 wherein the substituted basic metal nitrate comprises 2 Cu(OH)2.Cu(CH2N5)2.Cu(NO3)2.

12. The gas generant composition of claim 1 wherein the substituted basic metal nitrate comprises 2 Cu(OH)2.Cu(C2N8).Cu(NO3)2.

13. The gas generant composition of claim 1 wherein the substituted basic metal nitrate comprises 2 Cu(OH)2.Cu(C3H2N3O2)2.Cu(NO3)2.

14. The gas generant composition of claim 1 wherein the at least one transition metal complex of diammonium bitetrazole comprises a transition metal selected from the group consisting of copper, zinc, cobalt, iron, nickel and chromium.

15. The gas generant composition of claim 14 wherein the at least one transition metal complex of diammonium bitetrazole comprises the transition metal copper.

16. The gas generant composition of claim 1 additionally comprising a polymeric binder material effective to render the gas generant composition extrudable.

17. The gas generant composition of claim 16 wherein the polymeric binder material is selected from the group of cellulosics, natural gums, polyacrylates, polyacrylamides, polyurethanes, polybutadienes, polystyrenes, polyvinyl alcohols, polyvinyl acetates, silicones and combinations of two or more thereof.

18. The gas generant composition of claim 17 wherein the polymeric binder material is a cellulosic material selected from the group consisting of ethyl cellulose, carboxymethyl cellulose, hydroxylpropyl cellulose and combinations of two or more thereof.

19. The gas generant composition of claim 17 wherein the polymeric binder material is a natural gum selected from the group consisting of guar, xanthan, arabic and combinations of two or more thereof.

20. The gas generant composition of claim 16 wherein the composition comprises:

about 5 to about 60 composition weight percent of the non-azide, organic, nitrogen-containing fuel;

about 10 to about 60 composition weight percent of a combination of the substituted basic metal nitrate, the at least one transition metal complex of diammonium bitetrazole and, if present, any co-oxidizer; and

about 1 to about 20 composition weight percent of the polymeric binder.

21. The gas generant composition of claim 1 additionally comprising a quantity of at least one co-oxidizer.

22. The gas generant composition of claim 21 wherein said co-oxidizer is selected from the group consisting of basic copper nitrate, strontium nitrate, basic carbon carbonate, metal oxides and combinations thereof.

23. The gas generant composition of claim 21 wherein said co-oxidizer comprises basic copper nitrate.

24. The gas generant composition of claim 1 additionally comprising a quantity of perchlorate additive selected from the group consisting of ammonium perchlorate, alkali metal perchlorate or a combination thereof present in an amount effective to result in a gaseous effluent that is substantially free of hydrogen chloride when the gas generant composition is combusted.

25. The gas generant composition of claim 24 wherein the composition comprises a quantity of at least one alkali metal perchlorate with a mean particle size in excess of 100 microns, the at least one alkali metal perchlorate being present in a relative amount of about 1 to about 10 composition weight percent and effective to result in a gaseous effluent that is additionally substantially free of carbon monoxide, ammonia, nitrogen dioxide and nitric oxide, when the gas generant composition is combusted.

26. The gas generant composition of claim 24 wherein the composition comprises a quantity of ammonium perchlorate and said ammonium perchlorate is present in a relative amount of about 1 to about 10 composition weight percent and with a mean particle size in excess of 100 microns.

27. A gas generant composition comprising:

about 5 to about 60 composition weight percent of guanidine nitrate;

about 10 to about 60 composition weight percent of a combination of basic copper nitrate aminotetrazole adduct, copper diammonium bitetrazole and basic copper nitrate co-oxidizer; and

about 1 to about 20 composition weight percent of a polymeric binder effective to impart sufficient cohesive properties to the gas generant composition whereby the gas generant composition is extrudable.

28. The gas generant composition of claim 27 additionally comprising a quantity of perchlorate additive selected from the group consisting of ammonium perchlorate, alkali metal perchlorate or a combination thereof present in an amount effective to result in a gaseous effluent that is substantially free of hydrogen chloride when the gas generant composition is combusted.

29. The gas generant composition of claim 27 wherein inclusion of the basic copper nitrate aminotetrazole adduct and the copper diammonium bitetrazole is effective to increase the burn rate and decrease the burn rate pressure sensistivity of the composition as compared to the same gas generant composition without inclusion of the basic copper nitrate aminotetrazole adduct and the copper diammonium bitetrazole.