MXPA01001397A - Metal oxide containing gas generating composition - Google Patents

Abstract

A gas generating composition comprising ammonium nitrate and a non-toxic metal oxide which reduces the pressure exponent and enables the composition to sustain combustion at or near atmospheric pressure, thereby improving combustion efficiency. The composition is useful for various purposes, such as inflating a vehicle occupant restraint,i.e., an air bag for an automotive vehicle or aircraft, as well as aircraft escape chutes or the like.

Description

GAS GENERATING COMPOSITION CONTAINING METALLIC OXIDE TECHNICAL FIELD The present invention relates to gas generating compositions for generating a particulate free, non-toxic, odorless and colorless gas. The present invention is particularly useful in vehicle occupant restraint systems and aircraft ramps.

ANTECEDENTS OF THE TECHNIQUE The present invention relates generally to inflation compositions, and more particularly to solid inflating compositions useful as gas generators. The gas generating compositions must satisfy several criteria for optimum effectiveness. Gas generating compositions for use in fastening systems for vehicle occupants, for example air bags for automobiles or aircraft, must meet stringent criteria including toxicity requirements which are a concern in solid propellants for military or propulsion systems . The conventional gas generating compositions are plagued with problems, including a high pressure exponent, a low burning rate, poor combustion stability and inadequate stability of a prolonged use. The lower ballistic properties disadvantageously result in low gas yields and unburnt energy residues which remain at the end of the normal burn interval. It is not surprising that recently there has been a great demand for gas generating compositions which provide a high volume of gas and a low volume of solid particulates and which exhibit a low pressure exponent and have low pressure combustion stability. Attempts to improve the existing gas generating compositions for imparting these properties have not been successful for various reasons. For example, the addition of certain modifiers such as organometallic substances and certain oxides produce exhaust gases that are toxic in an environment where man prevails. Other additives previously used, although they do not produce toxic exhaust products, do not have an improved and successful low pressure combustion efficiency. In addition, other traditional techniques to solve these problems involve the use of relatively expensive deflagrating additives that interfere with the thermal or chemical stability of the total formulation during long-term thermal rinsing or conditioning to thermal cycles.

Those skilled in the art will have experienced difficulties in selecting from among the many potential additive candidates for gas generating compositions designed for air bag applications in order to obtain compositions wherein smoke and ash are considered unacceptable consequences. In addition, the propellant compositions are typically compacted in the form of grains in a suitable manner. Such propellant grains must be capable of sustaining thermal and voltage shock during operation of the ignition device and must show sufficient strength to remain intact during operation of the gas generator if the ballistic operation remains unaffected. Grains must retain such capacity after aging and cycling. There is a continuing need for gas generating compositions, particularly gas generating compositions for air bag installations, which exhibit a low pressure exponent, a high burn rate and good combustion efficiency at low pressures.

DETAILED DESCRIPTION OF THE INVENTION E n t i t i o n t i o n t i o n t i n t i t i t i t i t i t i t i t t i t t i t t i t t i t t i t t i t t i t t t t t t t t t t t t t t t t t t t t t t t t t t a component, guanidine nitrate (GN) due to its low cost, availability and safety. For example, a commercially available gas generating composition such as ARCAIR 102A, which is described in patent number 5,726,382 and includes guanidine nitrate, ammonium nitrate, potassium nitrate and polyvinyl alcohol. Another commercially available gas generating composition is ARCAIR 102B which is described in the application serial number 08 / 663,012 filed on June 7, 1996 and which includes guanidine nitrate, ammonium nitrate, potassium perchlorate and polyvinyl alcohol. A conventional air bag gas generating composition is described in U.S. Patent No. 5,538,567 to Olin. The gas generating composition of '567 includes guanidine nitrate, an oxidant, a flow improver and a binder. However, conventional air bag gas generating compositions such as those described in the patent may show one or more disadvantages such as a high pressure exponent, a low burn rate, and poor combustion efficiency. The present invention solves and solves such problems by incorporating a strategically selected additive such as a metal oxide, for example iron oxide in AN / GN compositions which surprisingly and unexpectedly improves the ballistic properties of the oxidized propellants of AN, in particular those that contain GN or guanidine derivatives as highly oxygenated fuel sources. The composition, when in the form of a pressed granule, provides a generator to produce a particulate-free, nontoxic, odorless and colorless gas to inflate an air pocket, without the tendency of the pellet to fracture and with a reduced phase change of AN due to temperature cycles. In addition, the pressure exponent is decreased, and the combustion efficiency at low pressure is improved. In addition, the addition of iron oxide does not adversely affect the thermal stability of the base mixture. Accordingly, an object of the present invention is to provide a gas generating composition which exhibits an exponent of lower pressure and sustains combustion "at pressures between ambient pressure and 1.4 MPa (200 psi)." Another objective of the present invention is provide a method for generating a non-toxic, odorless and colorless particulate free gas In accordance with the present invention, the above and other objects are obtained in part by a gas generating composition comprising ammonium nitrate and a metal oxide Non-toxic Another object of the present invention is a method for generating a gas, comprising the steps of a) providing an enclosed pressure chamber having an outlet orifice, b) placing within the chamber a gas generating composition that comprises ammonium nitrate and a non-toxic metal oxide, and c) provides a means to initiate combustion upon detection of the pressure chamber ue is subjected to a sudden deceleration, so that the gas is generated instantaneously and is conducted through the outlet orifice of the pressure chamber. The additional objects and advantages of the present invention will be readily apparent to those skilled in the art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration in the best manner contemplated. to carry out the invention. As will be appreciated, the invention is capable of other different embodiments, and various details are capable of modifications in the various obvious aspects, all without departing from the invention. Accordingly, the drawings and description should be considered illustrative and not restrictive in nature.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a sectional side elevation view of a conventional passenger side inflator; and Figure 2 is a sectional elevation view of a conventional pyrotechnic generator.

THE DRAWINGS Figure 1 shows a conventional hybrid apparatus for use in the generation of gas for inflating a motor vehicle airbag. As easily seen from the drawing, the exit holes are provided at the de facto end of the device. In Figure 1, the initiator (1) turns on in response to a detector (not shown) that detects rapid deceleration, indicative of a collision. The initiator generates hot gas that ignites the ignition charge (2) which causes the main generator charge (8) to ignite, mix with an inert gas in the pressure tank (7) and generate a mixture (3) of inflation gas. When the pressure in the gas mixture increases to a certain extent, a seal disc (6) is broken which allows the gas mixture to exit the manifold (4) through the outlet holes (5) and inflate the bag of air (not shown). The generator vessel (9) maintains the main generator charge (8). All the loads and the mixture of inflation gas are enclosed in the pressure tank (7).

Figure 2 is a drawing of the pyrotechnic generator of the present invention. Since there is no part of the inflation device reserved for storage capacity, the device is smaller than its hybrid inflator counterpart. A cartridge (21) maintains a generator (22) which can be a composition according to the present invention. At one end of the cartridge (21) is an initiator (23) that will turn on in response to a signal from a detector (not shown) which generates the signal as a result of a change in conditions, for example an excessive increase in the temperature or a sudden deceleration of a vehicle (indicative of a crash), in which the inflator is installed. The initiator (23) is held in place by an initiator (24). A ring (25) in O serves as a gasket to return the inflator essentially gas-tight at the end where the initiator (23) is located. The end of the inflator opposed to that containing the initiator (23) maintains a mesh (27) on which any particulate of gas produced is retained, a spring (29) to maintain the dimensional stability of the generating combination, and a disc ( 28) which breaks when the gas pressure exceeds a predetermined value, which allows the gas to escape from the cartridge (21) through the outlet holes (not shown) located like those in Figure 1. To ensure that the expelled gas is not released in an unduly strong stream, a diffuser (30) is attached to the discharge end of the inflator.

DESCRIPTION OF THE PREFERRED MODALITIES According to the present invention, an additive comprising a metal oxide, for example Fe203, is strategically incorporated into the AN / GN gas generating compositions resulting in a concomitant decrease in the pressure exponent and a significant increase in the combustion efficiency. As metal oxides, particularly Fe203 result in the generation of smoke and ash, such metal oxides can not be considered as suitable additives for incorporation into gas generating compositions in an air pocket. However, by extensive experimentation and research, it has been found that the addition of from about 0.25 to about 2% by weight of iron oxide, preferably Fe203 results in an unexpectedly significant improvement in ballistic properties. It is also evident that at higher amounts of iron oxide, for example 10% or greater, the ballistic properties in certain propellant compositions are also improved. The metal oxide component in the present compositions should produce non-toxic exhaust products, i.e., base metals or metal oxides.

Examples of suitable metal oxides are Ti, Fe, Tn, strontium, bismuth, aluminum, magnesium, copper, silicon, boron and rare metal oxides. The inclusion of a metal oxide reduces the pressure exponent of the propellant composition and advantageously allows the composition to sustain combustion at low pressure, for example at atmospheric pressure. It has been found that the efficiency of the burn rate is increased by increasing the specific surface area of the metal oxide. It has also been found that a specific surface area of from 10 m / g to approximately 1000 2/9 for example from approximately 50 m2 / g to approximately 750 m / g, for example, from approximately 100 m2 / g to approximately 500 m2 / g obtains particularly desirable results. Preferred metal oxides are iron oxides, particularly ferric oxide, that is, Fe203. Various grades of iron oxide can be used. A particularly suitable iron oxide is the superfine iron oxide NANOCAT which is commercially available from MACH I, Inc., of King of Prussia, PA. The metal oxide may be present in the range from about 0.25% to about 10%. More preferably in the range of from about 0.5% to about 5.0%, and more preferably in the range of from about 0.5% to about 2.0%. All percentages (%) through the specification mean percent by weight, unless otherwise indicated. Iron oxide is evaluated in both ARCAIR 102A and ARCAIR 102B propellants at concentrations up to 2%. The effects on burning speed are less. The pressure exponent is reduced in some cases to approximately 0.8 between 6.9 MPa and 27.6 MPa (1,000-4,000 psi). The exponent drop is due to a drop in velocity at higher pressure. This effect is different from the action of iron oxide in an AP oxidized propellant where the velocity usually increases at low pressure. The effects of iron oxide are more pronounced in the propellant ARCAIR 102A versus ARCAIR 102B. Open-air burning tests were carried out on pressed ARCAIR 102B propellants with or without iron oxide. Nanocat provides a more vigorous flame than the Harcros iron oxide from Harcros Chemicals Inc. of Kansas City, Kansas. Both mixtures with iron oxide produce a weak flame, although stable at ambient pressure, while pure ARCAIR 102B does not sustain combustion. Iron oxide does not adversely affect the hazard properties, aging or stability of the propellant cycles. The compressive strength of the pressed pellets is slightly reduced. The effect of iron oxide on temperature sensitivity and combustion efficiency at low temperatures (eg -40 ° C) are evaluated motor tests (table 4.1-2). A series of engine tests is performed at -40 ° C using extruded ARCAIR 102B containing 0, 0.5, 1.0 and 2.0 percent Nanocat superfine iron oxide. These tests are performed at an almost constant Kn of approximately 780. At -40 ° C, the mixtures without iron oxide show a high degree of dispersion in the present bottle and an integral total pressure in relation to the mixtures containing Nanocat, and the Average combustion efficiency is low. The performance of Nanocat is similar for contents that vary between 0.5 and 2.0 percent. The iron oxide Nanocat is superior to that of Harcros, which has a larger particle size and a smaller surface area. These data show that the low levels of Nanocat are effective in improving the combustion efficiency of the ARCAIR 102B propellant. At ambient temperatures of approximately 21 ° C, the pressure in the chamber and the operation of the flat ARCAIR 102B propellant is similar to that of mixtures containing iron oxide. Therefore, the sensitivity of pressure to temperature (pj between -40 ° and 21 ° C dramatically improves in the presence of iron oxide.

Table 4.1-2 Comparison of the average ballistic data showing the effects of iron oxide at -40 ° C. ! l > Kn = the ratio of surface area burned to the hole area in cross section! 2) PC = chamber peak pressure (3) P / T = pressure integral time i) Efficiency = the ratio of P / T supplied to a theoretical P / T based on theoretical C. Ammonium nitrate (AN) is an oxidizer commonly used because it provides a high energy in horsepower of gas per unit of weight and provides a non-toxic and non-corrosive exhaust gas at low flame temperatures. In addition, it contributes to burn speeds lower than that of other oxidants, is cheap, is easily available and is safe to handle. The AN may be partly AN or it may be an AN containing phase stabilization additives and additives that prevent the formation of cake. AN may be present in the range of from about 40% to about 80%, more preferably in the range of 50% to about 70%, and most preferably in the range of from about 55% to about 65%. Guanidine derivatives suitable for use in the present invention include, for example, aminoguanidine nitrate (AGN), guanidine nitrate (GN), triaminoguanidine nitrate (TAGN), diaminoguanidine nitrate (DAGN) and ethylenebis- (aminoguanidinium dinitrate) ). The guanidine derivative may be present in the range of from about 10% to about 50%, more preferably in the range of from about 20% to about 40%, and most preferably in the range of from about 25% to about 35%. %. The compositions of the present invention may further comprise one or more alkali metal salts such as nitrates or perchlorates. The preferred salts of an alkali metal are nitrate salts and potassium and cesium perchlorate salts. The nitrate salt of an alkali metal may be present in the range of from about 1% to about 20%, for example from about 3% to about 7%, for example from about 4% to about 6%. The perchlorate of the alkali metal may be present in the range of from about 1% to about 20%, for example from about 3% to about 15%, for example from about 9% to about 12%. An equivalent formulation can be prepared from an aqueous mixture of ammonium perchlorate and potassium nitrate which provides the same concentration of K + and C104"ions, together with N03" in solution and NH4 + ions. The compositions of the present invention are preferably processed to form a eutectic mixture or solid solution, and may also comprise a minor amount of a water-soluble organic binder. A wide range of molecular weights and grades can be used. The water-soluble organic binder may comprise cellulosic materials, such as cellulose acetate butyrate, polyvinyl alcohol (PVA), hydroxy-terminated polybutadiene (HTPB), polyesters or epoxy resins. The water-soluble organic binder may be present in the range of from about 1% to about 10%, more preferably in the range of from about 3% to about 7% and much more preferably in the range from about 3% to about approximately 6%. Additives conventionally used in gas generating compositions may also be incorporated, provided they are not inconsistent with the objects of the present invention. Dry products can be granulated to various particle sizes depending on the final shape and its use, which can take the form of granules, powders, pressed tablets or extruded forms. Frequently, the end use requires a particle size distribution that varies from -18 mesh to -40 (standard US sieve). Separate fractions can be recorded through the process. The characterization and batch qualification can be carried out by a series of tests, the most important of which include (1) thermal stability under accelerated aging conditions that include dimensional, resistance and weight stability; (2) stability to cycles over a wide range of ambient temperatures that include dimensional and compressive strength; (3) ballistic properties; and (4) hazard properties that include sensitivity to impact, friction, static and thermal sensitivity.

The samples for the thermal and stability tests are nominally aged for 17 days at 107 ° C and exposed for more than 3000 hours without loss of the pellets. Similarly, the samples are subjected to cycles between extreme temperatures of -40 and + 107 ° C for 200 cycles, although intervals of up to 800 cycles have been evaluated with good results. At the conclusion of a series of tests, the exposed samples have been tested and compared with respect to baseline properties. The ballistic properties are measured using a standard nitrogen pump apparatus to which a pressure purge tank is placed to maintain a constant pressure and through the use of a heavy wall motor tool that simulates the "final article configuration" or by using the batch acceptance test (LAT) tool in the "final article configuration". The ballistic tests are carried out nominally over a range of pressures that span the operational pressure range of the unit supplied, (ie ENVIRONMENT up to 69 MPa (10,000 psi).) Hazard properties are measured using the ABL friction apparatus. industry standard a BM impact tester, static sensitivity at 5000 volts and thermal sensitivity using a Dupont 2000 or equivalent differential scanning calorimeter (DSC).

EXAMPLES Tables 1 and 2 show that iron oxide concentrations of 2% are effective in reducing the pressure exponent in the pressure range of 6.9 to 27.6 MPa (1000 to 4000 psi) from about 1.0 decreasing to 0.8 to 0.85. The data further demonstrate that the addition of iron oxide allows sustained combustion at atmospheric pressure. In contrast, the comparative composition which is free of iron oxide does not sustain combustion below 1.4 MPa (200 psi).

TABLE 1 TABLE 2 Variation of ARCAIR 102B Approximate surface area Minimum pressure for Fe203 m2 / g ignite psi Only the preferred embodiments of the invention and examples of its versatility are those shown and described in the present description. It is understood that the invention is capable of use in various combinations and additional environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein. t *

Claims (18)

1. A gas generating composition, characterized in that it comprises: ammonium nitrate and a non-toxic metal oxide.

2. The composition according to claim 1, characterized in that the metal oxide is an iron oxide.

3. The composition according to claim 2, characterized in that the surface area of the iron oxide varies between about 5 m2 / g and about 1000 m2 / g.

4. The composition according to claim 1, characterized in that it also comprises guanidine nitrate or aminoguanidine nitrate or both.

5. The composition according to claim 4, characterized in that it comprises from about 0.25 to about 2% iron oxide by weight.

6. The composition according to claim 4, characterized in that it is a eutectic mixture or a solid solution.

7. A composition for generating a particulate free, nontoxic, odorless and colorless gas, which composition is characterized in that it comprises: ammonium nitrate, an iron oxide, a guanidine derivative, an alkali metal salt, and an organic binder soluble in water.

8. A method for generating a particulate-free, non-toxic, odorless and colorless gas, which method is characterized in that it comprises: a) providing a closed pressure chamber having an outlet orifice, b) placing a generating composition within the chamber of gas, composition which comprises ammonium nitrate and a non-toxic metal oxide, and c) providing a means for igniting the composition upon detection of a pressure chamber that is subjected to a sudden deceleration, whereby the gas is generated Instantly and transported through the outlet orifice of the pressure chamber.

9. The method according to claim 8, characterized in that it is carried out in a motor vehicle equipped with at least one air bag, where the generated gas passes through the outlet hole and enters the air bag to inflate it

10. A method for reducing the pressure exponent of a gas generating composition, which method is characterized in that it comprises: formulating the gas generating composition with a non-toxic metal oxide.

11. The method according to claim 10, characterized in that the metal oxide is iron oxide.

12. The method of confinement with claim 10, characterized in that the metal oxide has a surface area between about 5 m / g and about 1000 m2 / g.

13. The composition according to claim 7, characterized in that the guanidine derivative is guanidine nitrate or aminoguanidine nitrate, or both, the salt is potassium nitrate and the binder is polyvinyl alcohol.

14. The composition according to claim 7, characterized in that the guanidine derivative is guanidine nitrate or aminoguanidine nitrate, or both, the salt is potassium perchlorate and the binder is polyvinyl alcohol.

15. The composition according to claim 13, characterized in that it is a eutectic mixture or a solid solution.

16. The composition according to claim 14, characterized in that it is a eutectic mixture or a solid solution.

17. The composition according to claim 7, characterized in that the guanidine derivative is guanidine nitrate or aminoguanidine nitrate or both, and the alkali metal salt is cesium nitrate or cesium perchlorate.

18. The composition according to claim 13, characterized in that it also comprises ammonium perchlorate.