Gas generant compositions

Abstract

An auto ignition/gas generating composition is provided that contains DL-tartaric acid as a first fuel; a second fuel selected from carboxylic acids; amino acids; tetrazoles; triazoles; guanidines; azoamides; metal and nonmetal salts thereof; and mixtures thereof; and potassium chlorate as a first oxidizer. Potassium perchlorate is also preferably included as a second oxidizer. The composition is typically contained within a gas generating system such as an airbag inflator or seat belt assembly, or more broadly within a vehicle occupant protection system.

Claims

1 . A composition comprising: DL-tartaric acid as a first fuel provided at about 5-40 percent; a second fuel selected from carboxylic acids; amino acids; tetrazoles; triazoles; guanidines; azoamides; metal and nonmetal salts thereof; and mixtures thereof, said second fuel provided at about 0.1-30 percent; and potassium chlorate as a first oxidizer, provided at about 5-70 percent, wherein said percents are based on the weight of each constituent as compared to the weight of the total composition. 2 . The composition of claim 1 further comprising a secondary oxidizer provided at about 0.1-50 weight percent of the total composition, said second oxidizer selected from metal perchlorates, metal nitrates, metal nitrites, metal oxides, basic metal nitrates, and mixtures thereof. 3 . The composition of claim 1 further comprising a processing aid provided at about 0.1-15 weight percent of the total composition. 4 . The composition of claim 2 wherein said secondary oxidizer is selected from potassium perchlorate, strontium nitrate, potassium nitrate; potassium nitrite; basic copper nitrate; iron oxide, copper oxide; and mixtures thereof. 5 . The composition of claim 1 wherein said second fuel comprises a carboxylic acid selected from mucic acid, oxalic acid, salicylic acid, malic acid, fumaric acid, malonic acid, barbituric acid, glutamic acid, adipic acid, and mixtures thereof. 6 . The composition of claim 1 wherein said second fuel comprises an amino acid selected from glycine, histidine, arginine, and serine, and mixtures thereof. 7 . The composition of claim 1 wherein said second fuel comprises a tetrazole selected from 5-aminotetrazole; potassium 5-aminotetrazole; 5-aminotetrazole nitrate; 5-nitraminotetrazole; dipotassium 5-nitraminotetrazole; dipotassium 5-nitraminotetrazole; and mixtures thereof. 8 . The composition of claim 1 wherein said second fuel comprises a guanidine selected from nitroguanidine, dicyandiaide, guanidine nitrate, and mixtures thereof. 9 . The composition of claim 1 wherein said second fuel comprises an azoamide selected from azodicarbonamide, azodicarbonamide dinitrate, and mixtures thereof. 10 . A gas generating system containing the composition of claim 1 . 11 . A vehicle occupant protection system containing the composition 1 . 12 . A composition comprising: DL-tartaric acid as a first fuel; succinic acid as a second fuel; and potassium chlorate. 13 . The composition of claim 12 further comprising a second oxidizer selected from metal perchlorates, metal nitrates, metal nitrites, metal oxides, basic metal nitrates, and mixtures thereof. 14 . The composition of claim 2 wherein said second fuel is succinic acid and said second oxidizer is potassium perchlorate. 15 . The composition of claim 12 further comprising potassium perchlorate, wherein DL-tartaric acid is provided at about 22-24 weight percent, succinic acid is provided at about 14-16 weight percent, potassium chlorate is provided at about 20-22 weight percent, and potassium perchlorate is provided at about 44-46 weight percent. 16 . A composition comprising DL-tartaric acid provided at about 5-40 weight percent, succinic acid provided at about 0.1-30 weight percent, potassium chlorate provided at about 5-70 weight percent, and potassium perchlorate provided at about 0.1-50 weight percent.
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of U.S. Provisional Application Ser. No. 60/795,077 filed on Apr. 25, 2006. TECHNICAL FIELD [0002] The present invention relates generally to gas generating systems, and to gas generant/auto ignition compositions employed in gas generator devices for automotive restraint systems, for example. BACKGROUND OF THE INVENTION [0003] The present invention relates to gas generant/auto ignition compositions that upon combustion produce a relatively smaller amount of solids and a relatively abundant amount of gas. It is an ongoing challenge to reduce the amount of solids and increase the amount of gas thereby decreasing the filtration requirements for an inflator. As a result, the filter may be either reduced in size or eliminated altogether thereby reducing the weight and/or size of the inflator. [0004] An equally important challenge is to manufacture gas generants that exhibit relatively low sensitivity with regard to impact, friction, or electrostatic discharge stimuli. [0005] It is also required that airbag inflators be subjected to environmental conditioning, such as high temperature heat aging, thermal aging, thermal cycling, thermal shock, humidity cycling, and so forth. These extreme tests can cause many problems, ranging from failure to inflate the airbag to over-pressurization of the inflator leading to rupture. It is therefore desirable to have a gas generant and inflator/gas generating system that performs the same regardless of conditioning. The present invention provides a solution to many of these possibilities. [0006] Related thereto, certain auto ignition compositions, that is those compositions employed to auto ignite at relatively low temperatures (below 200 C), are desirable because of their relatively low melting point and therefore their relatively low auto ignition temperature. Additionally, another emphasis is providing dual functionality with regard to gas generation and auto ignition. Nevertheless, certain chemistry that provides desirable auto ignition temperature unfortunately also contributes to more reactive and less stable compositions after USCAR heat aging testing. Typically, the inflator is subjected to about 400 hours at 107 C, as defined in SAE International Document SAE/USCAR-24 “USCAR INFLATOR TECHNICAL REQUIREMENTS AND VALIDATION”, herein incorporated by reference. [0007] It has been found, for example, that otherwise desirable compositions containing hydroxyl functionality exhibit poor thermal stability due to more reactive components included therein. More specifically, and by way of example only, compositions containing glucose and potassium chlorate function exceptionally well as auto ignition material. Nevertheless, when subjected to heat aging testing, the auto ignition temperature is elevated above 200 C and the thermal stability of this composition is compromised. It is believed that although hydroxyl functionality through electron localization increases the acidity of the terminal proton on each glucose molecule, it may have a propensity to produce water as a decomposition product over time when subjected to the extreme heat aging of the USCAR requirements. Glucose in particular has six hydroxyl groups that provide up to six mols of water per mol of glucose. [0008] Accordingly, it would be an improvement in the art to provide compositions that provide both auto ignition and gas generating functionality. Furthermore, these compositions must pass USCAR heat aging requirements while maintaining both thermal stability and auto ignition temperatures at or below 200 C. SUMMARY OF THE INVENTION [0009] The above-referenced concerns are resolved by gas generators or gas generating systems containing auto ignition/gas generating compositions including DL-tartaric acid as a primary fuel; a second fuel selected from carboxylic acids, amino acids, tetrazoles, triazoles, guanidines, and mixtures thereof; and potassium chlorate as an oxidizer. A secondary oxidizer selected from metal nitrates, metal nitrites, metal perchlorates, metal oxides, other known oxidizers, and mixtures thereof may also be employed. Non-hygroscopic oxidizers are preferred. [0010] In further accordance with the present invention, a gas generator or gas generating system, and a vehicle occupant protection system incorporating the auto ignition/gas generant composition are also included. BRIEF DESCRIPTION OF THE DRAWINGS [0011] FIG. 1 is a cross-sectional side view showing the general structure of an inflator in accordance with the present invention. [0012] FIG. 2 is a schematic representation of an exemplary vehicle occupant restraint system containing a gas generant composition in accordance with the present invention. DETAILED DESCRIPTION OF THE INVENTION [0013] The present invention provides a gas generant system that includes at least one of the following: auto ignition functionality for airbag inflators, enhanced thermal stability, reduced component reactivity, and/or improved sensitivity with respect to impact and friction. The present gas generating system employs a unique advantage to the ignition function of a chlorate-based auto ignition system. This advantage is achieved by reducing the most reactive components of a chlorate based auto ignition system to their minimal functional level while increasing gas yield. Preferred gas generant systems utilize an auto ignition/gas generating composition formed from a mixture of carboxylic acids as fuels, and uses one or more oxidizers selected from potassium chlorate, potassium perchlorate, strontium nitrate, potassium nitrate, and metal oxides. (See table 1) [0014] Although not thereby limited, it is believed that the following explains the theory of operation of the present invention. The primary fuel of choice is DL-tartaric acid. The preferred secondary fuel is succinic acid. The combination of these two carboxylic acids provides the mechanism for desired functionality to the system based on the acidity of the carboxylic acids as indicated by pKa value and by melting point. The degree of hydroxyl substitution on the carboxylic acid provides the necessary reactivity when coupled with the lower melting point of succinic acid. It is believed that this combined interaction with potassium chlorate is the mechanism responsible for auto ignition function. The D and L forms of tartaric acid function equally well within this system. However, it is the racemic mixture of tartaric acid and the effects of hydrogen bonding between the D and L forms that as presently informed provide optimum thermal stability. It must be appreciated that a relatively low auto ignition temperature is achieved by this relationship. The preferred content of tartaric acid is about 5-40 wt %, and more preferably at about 10-25 wt %. [0015] Succinic acid is a preferred co-fuel within this gas generant/auto ignition (AI) system based upon its melting point and lack of hydroxyl substitution. While hydroxyl substitution is typically required for auto ignition function, it is believed that too much hydroxyl substitution exacerbates decomposition, particularly when subjected to USCAR heat aging requirements. Succinic acid, as a co-fuel, provides a preferred compliment to this auto ignition/gas generant system. The preferred content of succinic acid is about 5-30 wt % and more preferably at about 5-20 wt %. [0016] This system will function with other suitable carboxylic acid co-fuels such as, but not limited to, mucic acid, oxalic acid, salicylic acid, malic acid, fumaric acid, malonic acid, barbituric acid, glutamic acid, and adipic acid. Alternate carboxylic acids are generally provided at about 0-20 wt %. [0017] Alternate co-fuels such as amino acids may be incorporated into the gas generant/AI system. Amino acids such as, but not limited to, Glycine, Histidine, Arginine, and Serine are generally provided at about 0-20 wt %. [0018] It has been further demonstrated that carboxylic acid interaction with other co-fuels such as tetrazoles, triazoles, and guanidines provides low auto ignition temperatures based upon depression of melting points between the fuel mixture. For example, DL-tartaric acid (mp 210 C) and 5AT (mp 206 C) interact to create a melting point of 151 C. This same phenomenon is observed between 5AT and succinic acid. This forced melting in the presence of potassium chlorate offers an alternate mechanism for low temperature auto ignition function. [0019] Secondary fuels include tetrazoles such as 5-aminotetrazole; metal salts of azoles such as potassium 5-aminotetrazole; nonmetal non-ammonium salts of azoles; nitrate salts of azoles such as 5-aminotetrazole; nitramine derivatives of azoles such as 5-aminotetrazole; metal salts of nitramine derivatives of azoles such as dipotassium 5-aminotetrazole; metal salts of nitramine derivatives of azoles such as dipotassium 5-aminotetrazole; nonmetal salts of nitramine derivatives of azoles such as 5-aminotetrazole and; guanidines such as dicyandiamide; salts of guanidines such as guanidine nitrate; nitro derivatives of guanidines such as nitroguanidine; azoamides such as azodicarbonamide; nitrate salts of azoamides such as azodicarbonamidine dinitrate; and mixtures thereof. The secondary fuel can be used within this system as co-fuels to tartaric acid. U.S. Pat. Nos. 5,035,757 and 5,872,329, herein incorporated by reference, describes and exemplifies certain types of these fuels. [0020] Tartaric acid mixtures with potassium chlorate offer improvements over carbohydrate-chlorate (D-glucose) systems with respect to a more reliable auto ignition function after aging. Tartaric acids have less hydroxyl substitution than reducing sugars such as D-glucose thereby reducing the chemical generation of water as a decomposition product. The generation of water through the aging process compromises system stability and function. [0021] The primary oxidizer of this system is potassium chlorate. The content of potassium chlorate is critical to auto-ignition function but also must be attenuated to achieve the most desired safety factors. Utilization of potassium chlorate to the lowest functioning level allows for improved impact/friction and opportunity to increase gas yield by supplementing the oxygen requirement of the system. This may be achieved by utilization of secondary oxidizers with higher oxygen content and less solids. Potassium chlorate is generally provided at about 5-70 wt %. [0022] The most preferred secondary oxidizer is potassium perchlorate. Other preferred secondary oxidizers include metal nitrates such as strontium nitrate and potassium nitrate; metal nitrite salts such as potassium nitrite; basic metal nitrates such as copper nitrate; metal oxides such as iron oxide and copper oxide; and mixtures thereof. The secondary oxidizer is generally provided at about 0-50 wt %, and more preferably at about 10-40 wt %. [0023] Processing aids such as fumed silica, boron nitride, and graphite may also be employed. Accordingly, the gas generant may be safely compressed into tablets, or slugged and then granulated. The gas generant may also include binders such as cellulose derivatives, cellulose acetate, and cellulose acetate butyrate, and carboxymethylcellulose, salts of carboxymethylcellulose; silicone; polyalkene carbonates such as polypropylene carbonate and polyethylene carbonate. The processing aid and/or binder is generally provided at about 0-15 wt %, and more preferably at about 0-5 wt %. [0024] Slag formers may also be provided and are selected from silicon compounds such as elemental silicone; silicon dioxide; silicones such as polydimethylsiloxane; silicates such as potassium silicates; natural minerals such as talc and clay, and other known slag formers. The slag former is typically provided at about 0-10 wt %, and more preferably at about 0-5 wt %. [0000] TABLE 1 Preferred Preferred Preferred Ingredient % Range example % example % example % DL-tartaric 5–40 23 19 24 Acid Succinic Acid 5–30 15 13 15 Potassium 5–60 20 20 10.5 Chlorate Potassium 0–55 42 44 50 Perchlorate Potassium 0–55 0 0 0 Nitrate Strontium 0–55 0 0 0 Nitrate Metal Oxide 0–55 0 0 0.5 CAB 0–15 0 4 0 Hot Plate Temp 175 C. 172 C. 171 C. Gas yield 65.2% 64.2% 66.3% [0025] It is believed that the reactivity of potassium chlorate in an auto ignition system creates performance concerns with respect to impact sensitivity and the detrimental chlorous decomposition products, particularly when heat aged as per USCAR requirements. Carbohydrate-chlorate systems decompose significantly upon aging at 107 C for 400 hrs. The baseline auto ignition temperature on Hot Plate for carbohydrate-chlorate systems is 174 C, but after aging the auto ignition temperature increases to >220 C. It is generally recognized that for optimum inflator function, the auto ignition composition should exhibit an auto ignition temperature less than 200 C. See table 2. [0026] Certain known carboxylic acid-chlorate systems offer improvements for auto ignition systems with respect to thermal stability, but do not provide the dual functionality of gas generating compositions. The detrimental decomposition products of carboxylic-chlorate systems have the potential to interact with inflator components such as aluminum, steel, EDPM, and plastic. Because of this reactivity the amount of material is limited for use only as auto ignition system. Furthermore, certain known carboxylic acid-chlorate systems also rely upon a vapor scavenger, unlike the present invention. [0027] The proposed gas generant/AI system offers up to 75% gas generation per mol of gas generant/auto ignition composition, with a baseline hot plate value of 175 C which remains virtually unchanged (Table 1) after 600 hrs. aging at 107 C. Mass loss due to decomposition of the proposed system is limited to about 4-20% as compared to >20% for DL-tartaric/Potassium chlorate systems and carbohydrate-chlorate systems. (See table 3) [0000] TABLE 2 Auto ignition function after aging: AIM Baseline AI Aged Al Carbohydrate-chlorate (D- 174 C >220 C. glucose) system Aged 400 hrs sometimes does not ignite @ 107 C. Existing Carboxylic Acid- 177 C. 172 C.–207 C. Chlorate systems aged 600 hrs Lower Al requires use of @ 107 C. vapor scavenger Improved Carboxylic- 174 C. 174 C. chlorate systems aged 600 hrs Does not depend upon a @ 107 C. vapor scavenger [0000] TABLE 3 Mass loss of 3 gram sample after aging 600 Hrs @ 107 C. in sealed 20 ml vial. AIM % Mass Loss Carbohydrate-chlorate system Aged 400 hrs 14.2% @ 107 C. Existing Carboxylic Acid-Chlorate systems   22% aged 600 hrs @ 107 C. Improved Carboxylic-chlorate systems  2.9% aged 600 hrs @ 107 C. [0028] It should be appreciated that Example 1 as given below defines the exemplary “improved carboxylic-chlorate system” referred to in Tables 2, 3, and 4. Example 2 as given below defines the “existing carboxylic acid-chlorate systems” referred to in Tables 2, 3, and 4. Example 9 as given below defines the “carbohydrate-chlorate system”. [0029] The combined functionality of the auto-ignition and gas generating composition will reduce cost with respect to inflator design. An appreciable caveat of this invention is auto ignition function coupled to good burn rate performance and high gas yields of about 60-75% as compared to about 50-55% yield of other chlorate systems. [0030] Safety margins for these formulations are significantly improved. Carbohydrate-chlorate systems and previous Carboxylic acid-chlorate systems have HD50 values of 2.06-2.64 inches. Friction safety is also a concern. These systems have demonstrated BAM friction values of 24N-128N. The proposed gas generate system offers HD50 Values of 4.5-7.3 inches for impact sensitivity and 216N−360N for friction sensitivity. ARC testing of these materials demonstrates additional advantages. Carbohydrate-Chlorate systems have a ARC value of 109.84 C and other carboxylic acid-chlorate systems have an ARC value ranging from 11 C-126 C. The compositions formed in accordance with the present invention demonstrated an ARC value of 131 C. [0031] Inflator component compatibility is also enhanced with the present gas generant/AI system in that reaction with aluminum, steel, EDPM, and plastics did not occur after extreme aging for 600 hrs at 107 C. (See table 4) [0000] TABLE 4 AIM Aging and Component Compatibility Formulation (1 gram samples) Improved Carboxylic Existing Carboxylic Acid/Chlorate System - Acid/Chlorate System Post Age Data Post Age Data % wt. Degree of % wt. Degree of Sample description loss HP © Corrosion loss HP © Corrosion auto ignition 3.34 174 n/a 22.0 206 n/a material alone auto ignition 2.02 172 n/a 4.5 170 n/a material + MS 13X auto ignition 4.14 174 None 24.1 198 significant material with steel alone (contact) auto ignition 4.66 175 None 23.3 202 significant material with Al alone (contact) auto ignition 3.56 177 None 19.0 205 significant material + shim adhesive (no- contact) auto ignition 3.34 179 None 22.0 205 significant material + SDI initiator (contact) auto ignition 3.25 178 None 13.6 195 significant material + EDPM cushion (contact) auto ignition 1.45 176 None 34.0 >260 significant material + initiator gasket (contact) auto ignition 2.32 175 None 6.8 186 significant material + SDI BBS O-ring (contact) [0032] The compositions of the present invention are formed from constituents as provided by known suppliers such as Aldrich or Fisher Chemical companies. The compositions may be provided in granulated form and dry-mixed and compacted in a known manner, or otherwise mixed as known in the art. The compositions may be employed in gas generators typically found in airbag devices or occupant protection systems, or in safety belt devices, or in gas generating systems such as a vehicle occupant protection system, all manufactured as known in the art, or as appreciated by one of ordinary skill. Application within other gas generating systems is also contemplated. [0033] The following examples further illustrate the benefits of the present invention. To form comparative compositions, dry mixes of formulations containing the various constituents described below were prepared in a known manner. EXAMPLE 1 [0034] In accordance with a preferred embodiment of the present invention, 23 wt. % of DL-tartaric acid (DL-TTA), 15 wt. % of succinic acid (SA), 20 wt. % potassium chlorate, and 42 wt. % of potassium perchlorate were provided in granulated form and homogeneously dry mixed, and then pelletized in a known manner. As evaluated by a differential scanning calorimeter (DSC), the auto ignition onset was 157-160 C. The baseline hot plate auto ignition temperature was 170-172 C. The hot plate auto ignition temperature of the same composition, after extreme aging for 600 hours at 107 C within a passenger inflator and a driver side inflator of known design, was about 174 C. Decomposition of the composition after aging was relatively minimal. Reactivity of decomposition products with inflator components was relatively minimal. This example illustrates how the compositions formed in accordance with the present invention provide relatively low and similar auto ignition temperature before and after aging, with limited reactivity. Furthermore, compositions formed in accordance with the present invention therefore exhibit excellent thermal stability after aging. EXAMPLE 2 [0035] For comparative purposes, 35.0 wt. % of DL-tartaric acid (DL-TTA) and 65.0 wt. % potassium chlorate were provided in granulated form and homogeneously dry mixed, and then pelletized in a known manner. As evaluated by a differential scanning calorimeter (DSC), the auto ignition onset was 166 C. The baseline hot plate auto ignition temperature was 177 C. The hot plate auto ignition temperature of the same composition, after extreme aging for 600 hours at 107 C within the same inflators of Example 1, was 193 C. Decomposition of the composition after aging was relatively high. Reactivity of decomposition products with inflator components was relatively high. This example illustrates how decomposition and inflator component reactivity is increased by the absence of a secondary fuel such as succinic acid, and by the increase in the chlorine-containing oxidizer. EXAMPLE 3 [0036] For comparative purposes, 44.0 wt. % of DL-tartaric acid (DL-TTA), 10.0 wt. % potassium chlorate, and 46.0 wt. % potassium perchlorate were provided in granulated form and homogeneously dry mixed, and then pelletized in a known manner. As evaluated by a differential scanning calorimeter (DSC), the auto ignition onset was 170 C. The baseline hot plate auto ignition temperature was nonexistent as no flame occurred. The hot plate auto ignition temperature of the same composition, after aging for 600 hours at 107 C within a 20 ml. vial, was also nonexistent as no flame occurred. Decomposition of the composition after aging was relatively minimal. Reactivity of decomposition products with inflator components was relatively minimal. This example illustrates how auto ignition functionality is adversely affected with the increase of chlorine-containing oxidizers, and the absence of a secondary fuel such as succinic acid. EXAMPLE 4 [0037] For comparative purposes, 42.5 wt. % of DL-tartaric acid (DL-TTA), 20 wt. % potassium chlorate, and 36 wt. % of potassium perchlorate were provided in granulated form and homogeneously dry mixed, and then pelletized in a known manner. As evaluated by a differential scanning calorimeter (DSC), the auto ignition onset was 171 C. The baseline hot plate auto ignition temperature was 176 C. The hot plate auto ignition temperature of the same composition, after aging for 600 hours at 107 C within a 20 ml. vial, was 175 C. Decomposition of the composition after aging was relatively minimal. Reactivity of decomposition products with inflator components was relatively moderate. This example illustrates how the absence of succinic acid or a secondary fuel results in decomposition products that increase the reactivity with inflator components. EXAMPLE 5 [0038] For comparative purposes, 12.0 wt. % of DL-tartaric acid (DL-TTA), 23.5 wt. % of succinic acid (SA), 13.0 wt. % potassium chlorate, and 51.5 wt. % of potassium perchlorate were provided in granulated form and homogeneously dry mixed, and then pelletized in a known manner. As evaluated by a differential scanning calorimeter (DSC), the auto ignition onset was 159 C. The baseline hot plate auto ignition temperature, although a weak auto ignition, was 176 C. The hot plate auto ignition temperature of the same composition, after aging for 600 hours at 107 C within a 20 ml. vial, was nonexistent as no flame occurred. Decomposition of the composition after aging was relatively minimal. Reactivity of decomposition products with inflator components was relatively minimal. This example illustrates how auto ignition functionality after aging is affected by variation of the amount of the constituents. EXAMPLE 6 [0039] For comparative purposes, 31 wt. % of succinic acid (SA), 20 wt. % potassium chlorate, and 49 wt. % of potassium perchlorate were provided in granulated form and homogeneously dry mixed, and then pelletized in a known manner. As evaluated by a differential scanning calorimeter (DSC), the melting point onset was 184 C. The baseline hot plate melting point temperature was 207 C. The hot plate melting point temperature of the same composition, after aging for 600 hours at 107 C within a 20 ml. vial, was 210 C. Decomposition of the composition after aging was relatively minimal. Reactivity of decomposition products with inflator components was relatively minimal. This example illustrates the auto ignition functionality of DL-tartaric acid, and the absence of auto ignition functionality without DL-tartaric acid. EXAMPLE 7 [0040] DSC evaluations of succinic acid, DL-tartaric acid, and D-tartaric acid resulted in respective melting points of 189.05 C, 212.27 C, and 167.66 C. This supports the belief that hydrogen bonding increases the melting point of DL-tartaric acid. EXAMPLE 8 [0041] A composition formed in accordance with EXAMPLE 1 was found to have a baseline auto ignition temperature ranging from 154-159 C. After aging at 107 C for 400 hours, the composition still exhibited an auto ignition temperature ranging from 154-159 C. This composition exhibited 65.2 wt % gaseous products with a combustion temperature of 1989 C and a heat of reaction (cal/g) of 90°. The combustion temperature and heat of reaction are relatively lower than known auto ignition materials, as shown in EXAMPLE 9, thereby mitigating the cooling requirements of the gaseous effluent. EXAMPLE 9 [0042] A composition containing 27 wt. % of d-glucose and 73 wt. % of potassium chlorate was mixed and pelletized as given in EXAMPLE 1. This composition was found to have a baseline auto ignition temperature ranging from 150-175 C. After aging at 107 C for 400 hours, the carbohydrate-chlorate system exhibited an auto ignition temperature in excess of 220 C. This composition exhibited 55.5 wt % gaseous products with a combustion temperature of 2290 C and a heat of reaction (cal/g) of 1126. The combustion temperature and heat of reaction of this know composition are relatively higher than compositions of the present invention, as shown in EXAMPLE 8, thereby increasing the cooling requirements of the gaseous effluent. EXAMPLE 10 [0043] As measured by DSC, a composition containing 25 wt. % succinic acid and 75 wt. % DL-tartaric acid exhibited a melting point of 174.67 C. As measured by DSC, a composition containing 10 wt. % succinic acid and 90 wt. % DL-tartaric acid exhibited a melting point of 180.84 C. As measured by DSC, a composition containing 75 wt. % succinic acid and 25 wt. % DL-tartaric acid exhibited a melting point of 176.82 C. As measured by DSC, a composition containing 50 wt. % succinic acid and 50 wt. % DL-tartaric acid exhibited a melting point of 176.57 C. This example illustrates the ability to modulate the auto ignition temperature while retaining other benefits of the present invention. EXAMPLE 11 [0044] As measured by DSC, a composition containing 43 wt. % D-tartaric acid and 57 wt. % potassium chlorate, exhibited a melting point of 167.66 C and an auto ignition temperature of 144 C. As measured by DSC, a composition containing 35 wt. % DL-tartaric acid and 65 wt. % potassium chlorate, exhibited a melting point of 212.27 C and an auto ignition temperature of 164 C. As measured by DSC, a composition containing 29 wt. % succinic acid and 71 wt. % potassium chlorate, exhibited a melting point of 189.05 C and an auto ignition temperature of 185 C. As measured by DSC, a composition containing succinic acid, DL-tartaric acid, and potassium chlorate exhibited a melting point of 176.57 C and an auto ignition temperature of 157 C. This example illustrates the ability to modulate the auto ignition temperature while retaining other benefits of the present invention. EXAMPLE 12 [0045] A composition formed in accordance with EXAMPLE 1 exhibited burn rates of: about 0.3 inches per second (ips) at 100 psig; about 0.45 ips at 500 psig; about 0.59 ips at 1000 psig; about 0.73 ips at 1500 psig; about 0.75 ips at 2000 psig; about 0.88 ips at 2500 psig; about 0.98 ips at 3000 psig; about 1.05 ips at 3500 psig; and about 1.07 ips at 4000 psig. Burn rate testing was conducted in a steel bomb wherein each sample was placed. The bomb may be pressurized from 0-5500 psi. Propellant samples 0.5 inches in length are encased along the length in epoxy along with a thermocouple. The naked end of the propellant is then ignited with an electric match. The samples were ignited at various pressures while the testing temperature was maintained at about 20-24 C. Burns rate were then measured for each trial. This example illustrates how the present compositions provide acceptable burn rates for both auto ignition and gas generating functionality. [0046] In view of the examples, a preferred composition as exemplified in example 1 will include: 22.0-24.0 wt. % DL-tartaric acid, 14.0-16.0 wt. % succinic acid, 19.0-21.0 wt. % potassium chlorate, and 41.0-43.0 wt. % potassium perchlorate. Stated another way, an optimum ratio of fuels, as exemplified here, results in the relatively low auto ignition temperatures and excellent thermal stability after aging. Furthermore, the optimum ratio of oxidizers, as exemplified here, results in reliable auto ignition functionality, and limited reactivity after aging. [0047] It will appreciated that known auto ignition materials such as carbohydrate-chlorate systems, containing d-glucose and potassium chlorate for example, are more sensitive and therefore pose handling concerns. Accordingly, special accommodations must be made for the transfer of these materials. On the other hand, the auto ignition/gas generating compositions of the present invention are non-hygroscopic, more easily transported, and less sensitive than known auto ignition materials. [0048] As shown in FIG. 1 , an exemplary inflator or gas generating system 10 incorporates a dual chamber design to tailor containing a primary gas generating/auto ignition composition 12 formed as described herein, may be manufactured as known in the art. U.S. Pat. Nos. 6,422,601, 6,805,377, 6,659,500, 6,749,219, and 6,752,421 exemplify typical airbag inflator designs and are each incorporated herein by reference in their entirety. [0049] Referring now to FIG. 2 , the exemplary inflator or gas generating system 10 described above may also be incorporated into an airbag system 200 . Airbag system 200 includes at least one airbag 202 and an inflator 10 containing a gas generant composition 12 in accordance with the present invention, coupled to airbag 202 so as to enable fluid communication with an interior of the airbag. Airbag system 200 may also include (or be in communication with) a crash event sensor 210 . Crash event sensor 210 includes a known crash sensor algorithm that signals actuation of airbag system 200 via, for example, activation of airbag inflator 10 in the event of a collision. [0050] Referring again to FIG. 2 , airbag system 200 may also be incorporated into a broader, more comprehensive vehicle occupant restraint system 180 including additional elements such as a safety belt assembly 150 . FIG. 2 shows a schematic diagram of one exemplary embodiment of such a restraint system. Safety belt assembly 150 includes a safety belt housing 152 and a safety belt 100 extending from housing 152 . A safety belt retractor mechanism 154 (for example, a spring-loaded mechanism) may be coupled to an end portion of the belt. In addition, a safety belt pretensioner 156 containing gas generating/auto ignition composition 12 may be coupled to belt retractor mechanism 154 to actuate the retractor mechanism in the event of a collision. Typical seat belt retractor mechanisms which may be used in conjunction with the safety belt embodiments of the present invention are described in U.S. Pat. Nos. 5,743,480, 5,553,803, 5,667,161, 5,451,008, 4,558,832 and 4,597,546, incorporated herein by reference. Illustrative examples of typical pretensioners with which the safety belt embodiments of the present invention may be combined are described in U.S. Pat. Nos. 6,505,790 and 6,419,177, incorporated herein by reference. [0051] Safety belt assembly 150 may also include (or be in communication with) a crash event sensor 158 (for example, an inertia sensor or an accelerometer) including a known crash sensor algorithm that signals actuation of belt pretensioner 156 via, for example, activation of a pyrotechnic igniter (not shown) incorporated into the pretensioner. U.S. Pat. Nos. 6,505,790 and 6,419,177, previously incorporated herein by reference, provide illustrative examples of pretensioners actuated in such a manner. [0052] It should be appreciated that safety belt assembly 150 , airbag system 200 , and more broadly, vehicle occupant protection system 180 exemplify but do not limit gas generating systems contemplated in accordance with the present invention. [0053] It should further be understood that the preceding is merely a detailed description of various embodiments of this invention and that numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the scope of the invention. The preceding description, therefore, is not meant to limit the scope of the invention. Rather, the scope of the invention is to be determined only by the appended claims and their equivalents.

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