Patent Application
20140261929
The present disclosure relates to cool burning gas generant compositions having reduced combustion variability for inflatable restraint devices.
This section provides background information related to the present disclosure which is not necessarily prior art.
Passive inflatable restraint systems are used in a variety of applications, such as motor vehicles. Certain types of passive inflatable restraint systems minimize occupant injuries by using a pyrotechnic gas generant to inflate an airbag cushion (e.g., gas initiators and/or inflators) or to actuate a seatbelt tensioner (e.g., micro gas generators), for example. Automotive airbag inflator performance and safety requirements are continually increasing to enhance passenger safety, while concurrently striving to reduce manufacturing costs.
Thus, increasing functionality of a propellant or a gas generant used in airbag inflators, while improving performance and reducing costs of the entire airbag inflator system has been an ongoing objective in design of inflatable restraint systems. Gas generant selection involves addressing various factors, including meeting current industry performance specifications, guidelines and standards, generating safe gases or effluents, durational stability of the materials, and cost-effectiveness in manufacture, among other considerations. Improved gas generator performance may be achieved in a variety of ways, many of which ultimately depend on the gas generant formulation to provide the desired properties.
Suitable gas generants provide sufficient gas mass flow in a desired time interval to achieve a required work impulse for the inflating device. Further, gas generants having lower flame temperatures are advantageous. Also, it is generally desirable to develop gas generant materials which exhibit reduced or lessened combustion instability. For example, conventional gas generant materials that exhibit higher burn rate pressure sensitivity or temperature sensitivity can potentially lead to undesirable performance variability, such as when the corresponding material or formulation is reacted under different pressure or temperature conditions. Airbag inflators and modules are designed to function reliably and safely at operational temperature extremes, taking into account the increased performance of the gas generant at the upper temperature limit. If the change in performance of the gas generant can be minimized over the temperature extremes, less demand is placed on the inflator hardware design resulting in a lower cost, lighter weight product. For example, a gas generant having minimal change in performance over a range of temperatures (e.g., −40° C. to 80° C.—the maximum temperature extremes an automobile is likely to see in service) would be quite desirable.
Thus, it would be desirable to develop gas generant materials which exhibit reduced or lessened combustion instability and have lower flame temperatures, as gas generant materials exhibiting higher burn rate pressure and temperature sensitivity can potentially lead to undesirable performance variability, such as when the corresponding material or formulation is reacted under different temperature or pressure conditions.
This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
In various aspects, the present disclosure provides cool burning gas generant compositions. For example, in one aspect, the disclosure provides a cool burning gas generant composition that comprises a primary fuel, a secondary fuel distinct from the primary fuel, at least one oxidizer and a ballistic or burn rate modifier. The primary fuel comprises a salt of a dicarboxylic acid selected from a group consisting of: succinic acid, glutaric acid, adipic acid, and pimelic acid. Such a cool burning gas generant composition has a maximum flame temperature at combustion (Tc) of less than or equal to about 1700K.
In other variations, a cool burning gas generant composition comprises a primary fuel comprising a cupric salt of a dicarboxylic acid selected from a group consisting of: succinic acid, glutaric acid, adipic acid, and pimelic acid, a secondary fuel distinct from the primary fuel, at least one oxidizer, and a burn rate modifier comprising zinc oxide. Such a cool burning gas generant composition has a maximum flame temperature at combustion (Tc) of less than or equal to about 1700K and a linear burn rate pressure exponent of less than or equal to about 0.3.
In yet other variations, a cool burning gas generant composition comprises a primary fuel comprising a cupric salt of adipic acid, a secondary fuel comprising guanidine nitrate, an oxidizer comprising basic copper nitrate, and a burn rate modifier comprising zinc oxide. Such a cool burning gas generant composition has a maximum flame temperature at combustion (Tc) of less than or equal to about 1700K and a linear burn rate pressure exponent of less than or equal to about 0.3.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.
Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.
The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Although the terms first, second, third, etc. may be used herein to describe various components, elements, regions, layers and/or sections, these components, elements, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “primary,” “secondary,” “first,” “second,” or and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first or primary component, element, region, layer or section discussed below could be termed a secondary component, element, region, layer or section without departing from the teachings of the example embodiments.
Throughout this disclosure, the numerical values represent approximate measures or limits to ranges to encompass minor deviations from the given values and embodiments having about the value mentioned as well as those having exactly the value mentioned. Other than in the working examples provided at the end of the detailed description, all numerical values of parameters (e.g., of quantities or conditions) in this specification, including the appended claims, are to be understood as being modified in all instances by the term “about” whether or not “about” actually appears before the numerical value. “About” indicates that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein indicates at least variations that may arise from ordinary methods of measuring and using such parameters.
As referred to herein, ranges are, unless specified otherwise, inclusive of endpoints and include disclosure of all distinct values and further divided ranges within the entire range. Thus, for example, a range of “from A to B” or “from about A to about B” is inclusive of A and of B. Disclosure of values and ranges of values for specific parameters (such as weight percentages, temperatures, molecular weights, etc.) are not exclusive of other values and ranges of values useful herein. It is envisioned that two or more specific exemplified values for a given parameter may define endpoints for a range of values that may be claimed for the parameter. For example, if Parameter X is exemplified herein to have value A and also exemplified to have value Z, it is envisioned that Parameter X may have a range of values from about A to about Z. Similarly, it is envisioned that disclosure of two or more ranges of values for a parameter (whether such ranges are nested, overlapping or distinct) subsume all possible combination of ranges for the value that might be claimed using endpoints of the disclosed ranges. For example, if Parameter X is exemplified herein to have values in the range of 1-10, or 2-9, or 3-8, it is also envisioned that Parameter X may have other ranges of values including 1-9, 1-8, 1-3, 1-2, 2-10, 2-8, 2-3, 3-10, and 3-9. Example embodiments will now be described more fully with reference to the accompanying drawings.
The present disclosure is drawn to gas generant compositions and methods for making such gas generant compositions. Gas generants, also known as propellants, gas-generating materials, and pyrotechnic materials are used in inflators of airbag modules, such as a simplified exemplary airbag module 30 comprising a passenger compartment inflator assembly 32 and a covered compartment 34 to store an airbag 36 of
The gas generant 50 can be in the form of a solid grain, a pellet, a tablet, or the like. “Slag” or “clinker” is another name for solid combustion products formed during combustion of the gas generant material. The composition of slag is mainly metals and metal oxides. Ideally, the slag will maintain the original shape of the gas generant (e.g., grain, pellet, or tablet) and be large and easily filtered. This is particularly important when the inflator design includes a reduced mass filtration system for the purpose of reducing the inflator size and weight such as can be used with cool burning gas generant formulations. As shown in
Various different gas generant compositions (e.g., 50) are used in vehicular occupant inflatable restraint systems. Gas generant material selection involves various factors, including meeting current industry performance specifications, guidelines and standards, generating safe gases or effluents, handling safety of the gas generant materials, durational stability of the materials, and cost-effectiveness in manufacture, among other considerations. It is preferred that the gas generant compositions are safe during handling, storage, and disposal, and preferably are azide-free.
In various aspects, the gas generant typically includes at least one fuel component and at least one oxidizer component, and may include other minor ingredients, that once ignited combust rapidly to form gaseous reaction products (e.g., CO2, H2O, and N2). One or more fuel compounds undergo rapid combustion to form heat and gaseous products; e.g., the gas generant burns to create heated inflation gas for an inflatable restraint device or to actuate a piston. The gas-generating composition also includes one or more oxidizing components, where the oxidizing component reacts with the fuel component in order to generate the gas product.
Improved gas generator performance in an inflatable restraint system may be achieved in a variety of ways, many of which ultimately depend on the gas generant formulation to provide the desired properties. Ideally, a gas generant provides sufficient gas mass flow in a desired time interval to achieve the required work impulse for an inflating device (e.g., airbag) within the inflatable restraint system. Although a temperature of gas generated by the gas generant influences the amount of work gases can do, high gas temperatures may be undesirable because burns and related thermal damage can result. In addition, high gas temperatures can also potentially lead to an excessive reliance or sensitivity of the gas to heat transfer and excessively rapid deflation profiles, which can likewise be undesirable. Thus, minimizing flame temperature is advantageous. In certain aspects of the present technology, a high flame temperature may be considered anything in excess of about 1700 K at combustion. In order to mitigate the effects of high flame temperatures, in conventional inflatable restraint system gas generators, a significant portion of mass of an inflator is often relegated to heat sink in combination with filtration. This impacts the efficiency of the system and, most significantly, the weight of the inflator.
Consequently, in certain aspects, it is desirable to provide a gas generant formulation for an inflatable restraint system that can achieve a high gas output at a high mass flow rate at relatively low flame temperatures. For example, a cool burning gas generant having combustion flame temperatures of less than approximately 1700 K has been shown to enable inflator devices with reduced filtration, which operate in a manner that provides adequate restraint and protection, without the risk of burns or injury to an automobile occupant in the event of a crash. Other important variables in inflator gas generant design include improving gas generant performance with respect to gas yield, relative quickness (as determined by observed burning rate), and cost.
As discussed above, gas generant materials exhibiting higher burn rate pressure and/or temperature sensitivity can potentially lead to undesirable performance variability, such as when the corresponding material or formulation is reacted under different pressure or temperature conditions. It is desirable to employ gas generant compositions that have relatively consistent performance during combustion, including burn rates that are relatively independent of temperature and/or pressure conditions. For example, a gas generant exhibiting a minimal change in performance over predetermined operating temperature ranges, including extreme service conditions, is advantageous. Gas generants that exhibit pressure and/or sensitivity during combustion may have variable or fluctuating burn rates during combustion depending on changing temperature and/or pressure conditions causing various potentially detrimental conditions, including variable and potentially unpredictable combustion performance and potentially excessive effluent species. Thus, a minimal change in performance over a temperature range of −40° C. to 80° C. is particularly desirable, which corresponds to typical maximum temperature extremes an automobile is likely to see in service.
As noted above, airbag inflators and modules are designed to function reliably and safely at the temperature extremes taking into account the increased performance of the gas generant at the upper temperature limit. The gas generants according to various aspects of the present technology are capable of desirably reducing or minimizing combustion variability, such as reduced or lessened burn rate pressure sensitivity and/or temperature sensitivity. Thus, for gas generants according to various aspects of the present disclosure, which exhibit minimal change in performance over the predetermined operating temperature extremes, inflator hardware can be designed as a lower cost, lighter weight product.
By way of background, in general, a linear burn rate law (with temperature being taken into account) is as follows in Equation 1:
Rb=aebTPn (EQN. 1)
where Rb is burning rate as a function of temperature and pressure, a is a pressure coefficient, n is a pressure exponent, P is the functioning pressure, T is temperature of the environment, and b is sensitivity to temperature coefficient.
All of the parameters in the burning rate law can be graphically determined or calculated by performing burning rate experiments across a range of pressures and temperatures. For example, pressure coefficient (a) is the Y-intercept in a logarithmic-logarithmic plot of burning rate (Rb) versus pressure (P) at constant temperature (T). Likewise, the pressure exponent (n) is a slope of a linear regression line drawn through a logarithmic-logarithmic plot of linear burn rate (Rb) versus pressure (P) at constant temperature (T).
The coefficient of sensitivity to temperature (b), or as it is commonly also known (σp), can be calculated using the following Equation 2:
Another commonly used measure of performance or burning rate variability is designated (πk) or the variation in burning rate with temperature at a constant Klemmung or area ratio of an exit orifice of a device to a burning surface of the gas generant. πk is related to σp by the following Equation 3:
From Equation 3, it can be seen that minimization of burning rate variability (πk) can be accomplished by minimization of the coefficient of burning rate sensitivity to temperature (σp) and the linear burn rate pressure exponent (n). Both σp and n are functions of the ingredients selected for inclusion in a gas generant formulation. In typical conventional gas generant formulations, a linear burn rate pressure exponent (n) varies from 0.30 to 0.50, a coefficient of burning rate sensitivity to temperature (σp) varies from 0.10 to 0.20%/° C., and a resultant burning rate variability (πk) varies from 0.14 to 0.40%/° C.
In accordance with various aspects of the present disclosure, gas generants are provided that have desirable compositions that result in superior performance characteristics in an inflatable restraint device, while reducing overall cost of gas generant and inflator assembly production. Thus, in accordance with various aspects of the present teachings, an improved cool burning gas generant composition is provided that has a linear burn rate pressure exponent (n) of less than or equal to about 0.3 while also desirably having relatively low burning rate sensitivity to temperature (σp) and burning rate variability (πk) coefficients, along with a flame temperature of less than or equal to about 1700 K. In certain variations, a gas generant composition according to the present disclosure has a linear burn rate pressure exponent (n) of less than or equal to about 0.275, optionally less than or equal to about 0.25, optionally less than or equal to about 0.225, optionally less than or equal to about 0.2 and in certain aspects, less than or equal to about 0.175.
In various aspects, the present technology provides a cool burning gas generant composition that has a maximum combustion temperature (Tc) (also expressed as maximum combustion flame temperature) of less than or equal to about 1700K. In certain variations, the maximum combustion temperature is less than or equal to about 1600K, optionally less than or equal to about 1500K, and in certain variations, less than or equal to about 1400 K. In various embodiments, it is preferred that the flame temperature during combustion for a cool burning gas generant is greater than or equal to about 1300 K to less than or equal to about 1700 K.
Thus, in certain variations, the inventive technology provides a gas generant composition that has a linear burn rate pressure exponent (n) of less than or equal to about 0.3, while also desirably having a coefficient of burning rate sensitivity to temperature (σp) of less than or equal to about 0.1%/° C. and a burn rate variability (πk) of less than or equal to about 0.15%/° C., along with a flame temperature of less than or equal to about 1700 K. In certain other variations, the gas generant composition that has a linear burn rate pressure exponent (n) of less than or equal to about 0.2, while also desirably having a coefficient of burning rate sensitivity to temperature (σp) of less than or equal to about 0.1%/° C. and a burn rate variability (πk) of less than or equal to about 0.15%/° C., along with a flame temperature of less than or equal to about 1700 K.
Additionally, it is preferred that the cool burning gas generant has a high mass density in various embodiments. For example, in certain embodiments, the gas generant has a theoretical mass density of greater than or equal to about 2 g/cm3, optionally greater than or equal to about 2.25 g/cm3, optionally greater than or equal to about 2.5 g/cm3, and in certain variations, optionally greater than or equal to about 2.75 g/cm3.
Further, in accordance with the present disclosure, the gravimetric gas yield of the cool burning gas generant is relatively high. For example, in certain embodiments, the gas yield is greater than or equal to about 1.8 moles/100 grams of gas generant. In other embodiments, the gas yield is greater than or equal to about 1.9 moles/100 g of gas generant, optionally greater than or equal to about 2.0 moles/100 g of gas generant, optionally greater than or equal to about 2.1 moles/100 g of gas generant, optionally greater than or equal to about 2.2 moles/100 g of gas generant, optionally greater than or equal to about 2.3 moles/100 g of gas generant, optionally greater than or equal to about 2.4 moles/100 g of gas generant, optionally greater than or equal to about 2.5 moles/100 g of gas generant, and in certain variations, optionally greater than or equal to about 2.6 moles/100 g of gas generant. The product of gravimetric gas yield and density is a volumetric gas yield.
Thus, in certain aspects, the volumetric gas yield of a cool burning gas generant according to certain variations of the present disclosure is optionally greater than or equal to about 5.0 moles/100 cm3 of gas generant. In other embodiments, the gas yield is greater than or equal to about 5.1 moles/100 cm3 of gas generant, optionally greater than or equal to about 5.2 moles/100 cm3 of gas generant, optionally greater than or equal to about 5.3 moles/100 cm3 of gas generant, optionally greater than or equal to about 5.4 moles/100 cm3 of gas generant, optionally greater than or equal to about 5.5 moles/100 cm3 of gas generant, and in certain variations, optionally greater than or equal to about 5.6 moles/100 cm3 of gas generant.
The product of gravimetric gas yield and density is the volumetric gas yield given above. In various aspects, gas generants of the present disclosure comprise a pyrotechnic mixture comprising at least one fuel and at least one oxidizer. While all gas generants exhibit some pressure or temperature sensitivity, adverse or undesirable pressure sensitivity or temperature sensitivity potentially impacts combustion instability. As referred to herein, “pressure sensitivity” is meant to refer to undesirable pressure sensitivity of a gas generant resulting in combustion variability and instability. By way of example, an increase in pressure sensitivity at lower operating pressures (e.g., less than 1,000 psi) may lead to undesirable combustion instability. To minimize pressure sensitivity, it is desirable to have a gas generant material with a linear burn rate exhibiting a relatively constant slope (a slope of a linear regression line drawn through a logarithmic—logarithmic plot of burn rate (Rb) versus pressure (P)) over the range of typical operating pressure for a gas inflator, for example, about 1,000 psi (about 6.9 MPa) to about 5,000 psi (about 34.5 MPa). In various aspects, a gas generant composition is provided that has enhanced combustion stability performance, in particular, a reduced burn rate pressure sensitivity of the gas generant material as it is used in an inflator device. Similarly, “temperature sensitivity” is meant to refer to significant undesirable temperature sensitivity of a gas generant resulting in combustion variability and instability at different temperatures.
In certain aspects, a gas generant material having an acceptable combustion sensitivity has a linear burning rate slope (n) of less than or equal to about 0.3, optionally less than or equal to about 0.275, optionally less than or equal to about 0.25, optionally less than or equal to about 0.225, and in certain variations, optionally less than or equal to about 0.2. A material having a burn rate slope of less than or equal to about 0.3, optionally less than or equal to about 0.2 fulfills hot to cold performance variation requirements (at maximum and minimum service temperatures), and can reduce performance variability and pressure requirements of the inflator as well. In this regard the cool burning gas generants of the present disclosure have reduced combustion sensitivity, improved pressure sensitivity (i.e., reduced pressure sensitivity), improved temperature sensitivity (i.e., reduced temperature sensitivity), and enhanced combustion performance. Thus, the cool burning gas generants may have reduced linear burn rate pressure sensitivity (i.e., a relatively low pressure exponent (n) or slope of a linear regression line drawn through a log-log plot of burn rate (Rb) versus pressure (P)), a lower coefficient of burning rate sensitivity to temperature (σn), a lower burn rate variability (πk) value, higher gas yield, and/or combinations thereof as will be discussed in more detail below.
Thus, in certain aspects, the present technology provides a gas generant composition comprising a primary fuel, a secondary fuel distinct from the primary fuel (e.g., a co-fuel), at least one oxidizer, and a ballistic or burn rate modifier, which together provide a gas generant composition having a linear burn rate pressure exponent (n) of less than or equal to about 0.3. Materials are generally categorized as gas generant fuels due to their relatively low burn rates, and are often combined with one or more oxidizers in order to obtain desired burn rates and gas production. As appreciated by those of skill in the art, such a fuel component may be combined with additional components in the gas generant, such as co-fuels or oxidizers. More specifically, in various embodiments of the present disclosure, the gas generant comprises a primary fuel comprising a salt of a dicarboxylic acid. In certain preferred variations, the counter-ion of the salt comprises copper. The dicarboxylic acid may be selected from the group consisting of: succinic acid, glutaric acid, adipic acid, and pimelic acid.
In certain variations, the dicarboxylic acid is adipic acid (C6H10O4). In certain other preferred variations, the primary fuel comprises a cupric salt of adipic acid (CuC6H8O4) or copper adipate. By way of example, a suitable gas generant composition optionally includes greater than or equal to about 10% to less than or equal to about 25% by weight of the primary fuel, such as a cupric salt of adipic acid, in the gas generant composition. In certain aspects, the gas generant composition optionally includes greater than or equal to about 10% to less than or equal to about 20% by weight of the primary fuel in the gas generant composition.
In various embodiments, the gas generant composition also comprises a secondary fuel as a co-fuel. Preferably, the secondary fuel component is a nitrogen-containing compound, but is an azide-free compound. In certain aspects, preferred fuels include guanidine nitrate, nitro guanidine, amino guanidine nitrate and the like. By way of example, a suitable gas generant composition optionally includes greater than or equal to about 5% to less than or equal to about 20% by weight of the secondary fuel, such as guanidine nitrate, in the total gas generant composition. In certain embodiments, the gas generant comprises at least guanidine nitrate as a secondary fuel component along with a cupric salt of adipic acid as a primary fuel. By way of example, a suitable gas generant composition optionally includes about 5 to about 20% by weight (wt. %) of guanidine nitrate secondary fuel and about 10 to about 25% by weight of cupric salt of adipic acid as a primary fuel. In certain alternative variations, the gas generant compositions of the present technology may optionally comprise other suitable fuels, as well. Thus any other suitable fuels known or to be developed in the art that can provide gas generants having the desired burn rates, and gas yields, are contemplated for use in various embodiments of the present disclosure.
In certain variations of the present disclosure, the gas generant composition further comprises an oxidizer. In certain aspects, such an oxidizer may comprise a basic metal nitrate. Certain particularly suitable oxidizers for the gas generant compositions of the present disclosure include, by way of non-limiting example, basic copper nitrates. Basic copper nitrate has a high oxygen-to-metal ratio and good slag forming capabilities upon burn. Therefore, in certain preferred variations, the oxidizer comprises basic copper nitrate. By way of example, a suitable gas generant composition optionally includes greater than or equal to about 50% to less than or equal to about 70% by weight of the oxidizer, such as basic copper nitrate, in the total gas generant composition.
In accordance with the present technology, the gas generant composition further comprises a ballistic performance modifier, such as a burn rate modifying component. A ballistic performance modifier may increase burn rate, cool flame temperature or otherwise modify one or more ballistic properties of the gas generant. In certain variations, the ballistic performance modifier is a burn rate modifier. In certain preferred variations, the burn rate modifier enhances burn rate and comprises zinc oxide (ZnO). The gas generant composition optionally comprises greater than or equal to about 1 to less than or equal to about 10% by weight of the burn rate modifier component, such as zinc oxide; optionally greater than or equal to about 1 to less than or equal to about 6% by weight of the burn rate modifier component; and optionally greater than or equal to about 2 to less than or equal to about 5% by weight of the burn rate modifier component.
The gas generant compositions according to certain aspects of the present disclosure optionally comprise a cupric salt of adipic acid (CuC6H8O4) as a fuel and a burn rate modifier comprising zinc oxide (ZnO). By way of example, a suitable gas generant composition optionally includes greater than or equal to about 10% to less than or equal to about 25% by weight of the cupric salt of adipic acid and greater than or equal to about 1% and less than about 10% by wt. of zinc oxide in the total gas generant composition. In yet other aspects, the gas generant comprises greater than or equal to about 10% to less than or equal to about 20% by weight of the cupric salt of adipic acid and greater than or equal to about 1% and less than about 10% by wt. of zinc oxide in the total gas generant composition.
Other suitable conventional additives for gas generants may likewise be introduced into the gas generant composition, including slag forming agents, flow aids, viscosity modifiers, pressing aids, dispersing aids, phlegmatizing agents, and the like. Such additional additives may be cumulatively present in the gas generant composition at greater than or equal to 0 to less than or equal to about 10% by weight of the total gas generant composition.
For example, press aids for use during compression processing, include lubricants and/or release agents, such as graphite, calcium stearate, magnesium stearate, molybdenum disulfide, tungsten disulfide, graphitic boron nitride, may be optionally included in the gas generant compositions, by way of non-limiting example. The press aids may be added to the gas generant composition prior to tableting or pressing and can be present in the gas generant at 0 to about 2%, for example. While in certain aspects it is preferred that the gas generant compositions are substantially free of polymeric binders, in certain alternate aspects, the gas generant compositions optionally comprise low levels of certain acceptable binders or excipients to improve crush strength, while not significantly harming effluent and burning characteristics. Such excipients include microcrystalline cellulose, starch, and carboxyalkyl cellulose (e.g., carboxymethyl cellulose (CMC)), by way of example. When present, such excipients can be included in gas generant compositions at less than or equal to about 10 wt. %, optionally less than or equal to about 5 wt. %, and optionally less than or equal to about 2.5 wt. %.
Thus, in certain embodiments, a gas generant comprises a primary fuel component mixed with a secondary fuel component and at least one oxidizer to form a gas generant composition. In certain variations, a gas generant composition comprises at least a primary fuel component comprising a cupric salt of adipic acid and a secondary co-fuel comprising guanidine nitrate, mixed with an oxidizer, such as basic copper nitrate, to form a gas generant composition. Such a gas generant further comprises a burn rate modifying component, such as zinc oxide. The gas generant may further include one or more conventional gas generant additives well known to those of skill in the art, as discussed above.
In certain aspects, a suitable gas generant composition comprises a primary fuel component present at about 10 to about 25% by weight of the total gas generant composition; a secondary fuel component present at about 5 to about 20% by weight of the total gas generant composition; at least one oxidizer component present at about 50 to about 70% by weight of the total gas generant composition; a burn rate modifier component present at about 1 to about 10% by weight of the total gas generant composition; and one or more conventional gas generant additives, where if present are cumulatively present at less than 10% by weight of the total gas generant composition.
In certain aspects, a suitable gas generant composition consists essentially of a primary fuel component present at about 10 to about 25% by weight of the total gas generant composition; a secondary fuel component present at about 5 to about 20% by weight of the total gas generant composition; at least one oxidizer component present at about 50 to about 70% by weight of the total gas generant composition; a burn rate modifier component present at about 1 to about 10% by weight of the total gas generant composition; and one or more conventional gas generant additives, where if present are cumulatively present at less than 10% by weight of the total gas generant composition.
In certain aspects, a suitable gas generant composition consists of a primary fuel component present at about 10 to about 25% by weight of the total gas generant composition; a secondary fuel component present at about 5 to about 20% by weight of the total gas generant composition; at least one oxidizer component present at about 50 to about 70% by weight of the total gas generant composition; a burn rate modifier component present at about 1 to about 10% by weight of the total gas generant composition; and one or more conventional gas generant additives, where if present are cumulatively present at less than 10% by weight of the total gas generant composition.
In other aspects, a suitable gas generant composition comprises a primary fuel component comprising a cupric salt of adipic acid present at about 10 to about 25% by weight of the total gas generant composition; a secondary fuel component comprising guanidine nitrate at about 5 to about 20% by weight of the total gas generant composition; at least one oxidizer component comprising basic copper nitrate at about 50 to about 70% by weight of the total gas generant composition; a burn rate modifier component comprising zinc oxide present at about 1 to about 10% by weight of the total gas generant composition; and one or more conventional gas generant additives, where if present are cumulatively present at less than 10% by weight of the total gas generant composition.
In other aspects, a suitable gas generant composition consists essentially of a primary fuel component comprising a cupric salt of adipic acid present at about 10 to about 25% by weight of the total gas generant composition; a secondary fuel component comprising guanidine nitrate at about 5 to about 20% by weight of the total gas generant composition; at least one oxidizer component comprising basic copper nitrate at about 50 to about 70% by weight of the total gas generant composition; a burn rate modifier component comprising zinc oxide present at about 1 to about 10% by weight of the total gas generant composition; and one or more conventional gas generant additives, where if present are cumulatively present at less than 10% by weight of the total gas generant composition.
In other aspects, a suitable gas generant composition consists of a primary fuel component comprising a cupric salt of adipic acid present at about 10 to about 25% by weight of the total gas generant composition; a secondary fuel component comprising guanidine nitrate at about 5 to about 20% by weight of the total gas generant composition; at least one oxidizer component comprising basic copper nitrate at about 50 to about 70% by weight of the total gas generant composition; a burn rate modifier component comprising zinc oxide present at about 1 to about 10% by weight of the total gas generant composition; and one or more conventional gas generant additives, where if present are cumulatively present at less than 10% by weight of the total gas generant composition.
In accordance with various aspects of the present disclosure, a gas generant composition has a stable combustion profile, reduced burn rate temperature sensitivity and optionally reduced burn rate pressure sensitivity. In certain aspects, the gas generant includes a primary fuel material comprising a cupric salt of adipic acid (CuC6H8O4) and at least one oxidizer, along with a burn rate modifier comprising zinc oxide (ZnO). In certain variations, the gas generant composition further includes at least one nitrogen-containing non-azide secondary fuel, such as guanidine nitrate, and at least one oxidizer, such as basic copper nitrate.
In certain aspects, the gas generants can be formed in unique shapes that optimize the ballistic burning profiles of the materials contained therein, such as monolithic grains that are substantially free of binders, as disclosed in U.S. Pat. No. 7,758,709 to Hussey et al. entitled “Monolithic Gas Generant Grains,” the relevant portions of which are incorporated herein by reference.
In certain aspects, the gas generant is formed from a gas generant powder created by a spray drying process. In certain aspects, an aqueous mixture including a mixture of a primary fuel, a secondary fuel, at least one oxidizer, a burn rate modifier, is spray dried to form a powder material. In certain aspects, the aqueous mixture includes various other optional conventional gas generant additives ingredients, as well. The powder is then pressed to produce grains of the gas generant.
The gas-generating composition may be formed from an aqueous dispersion of one or more fuel components that are added to an aqueous vehicle to be substantially dissolved or suspended. The oxidizer components may be dispersed and stabilized in the fuel solution either dissolved in the solution or optionally present as a stable dispersion of solid particles. The solution or dispersion may also be in the form of a slurry. The aqueous dispersion or slurry is spray-dried by passing the mixture through a spray nozzle in order to form a stream of droplets. The droplets contact hot air to effectively remove water and any other solvents from the droplets and subsequently produce solid particles of the gas generant composition, as will be described in greater detail below.
The mixture of components forming the aqueous dispersion may also take the form of a slurry, where the slurry is a flowable or pumpable mixture of fine (relatively small particle size) and substantially insoluble particle solids suspended in a liquid vehicle or carrier. Thus, the slurry may contain flowable and/or pumpable suspended solids and other materials in a carrier. Suitable carriers include aqueous solutions that may be mostly water; however, the carrier may also contain one or more organic solvents or alcohols. In some embodiments, the carrier may include an azeotrope, which refers to a mixture of two or more liquids, such as water and certain alcohols that desirably evaporate in constant stoichiometric proportion at specific temperatures and pressures. The carrier should be selected for compatibility with the fuel and oxidizer components to avoid adverse reactions and further to maximize solubility of the several components forming the slurry. Non-limiting examples of suitable carriers include water, isopropyl alcohol, n-propyl alcohol, and combinations thereof.
Viscosity of the slurry is such that it can be injected or pumped during the spray drying process. In some embodiments, the viscosity is kept relatively high to minimize water and/or solvent content, for example, so less energy is required for carrier removal during spray drying. However, the viscosity may be lowered to facilitate increased pumping rates for higher pressure spray drying. Such adjustments may be made when selecting and tailoring atomization and the desired spray drying droplet and particle size.
In certain aspects, the gas generant may include about 15 to about 45 parts by weight, more preferably about 15 to about 40 parts by weight of fuels, including both the primary fuel (e.g., a cupric salt of adipic acid) and the secondary fuel (e.g., guanidine nitrate), about 50 to about 70 parts by weight of oxidizers (e.g., basic copper nitrate), and about 1 to about 10 parts by weight of a burn rate modifier (e.g., zinc oxide). In certain variations, one or more conventional gas generant additives may be included at about 1 to about 10 parts by weight. By way of example, a suitable gas generant composition optionally includes greater than or equal to about 10% to less than or equal to about 45% by weight of the primary and secondary fuels (e.g., cupric salt of adipic acid and guanidine nitrate), greater than or equal to about 50 to less than or equal to about 70% by weight of at least one oxidizer (e.g., basic copper nitrate), greater than or equal to about 1% by weight to about 10% by weight of burn rate modifier (e.g., zinc oxide) and optionally 0% to less than or equal to about 10% of other conventional gas generant additives, such as slag forming agents, press aids, lubricants, or the like. Significant improvements in gas generant performance, including higher combustion stability are achieved in accordance with the present teachings when a combination of the primary fuel and burn rate modifiers are employed in the gas generant compositions.
In certain aspects when forming the aqueous dispersion, the composition is mixed with sufficient aqueous solution to dissolve substantially the entire fuel component at the spray temperature; however, in certain aspects, it is desirable to restrict the amount of water to a convenient minimum in order to minimize the amount of water that is to be evaporated in the spray-drying process. For example, the dispersion may have less than or equal to about 100 parts by weight of water for about 30 to about 45 parts by weight of fuel component.
Samples 1-12 are gas generants formed by mixing the constituents indicated in Table 1 below at the indicated mass percentages. The gas generants are formed by blending the appropriate amount of each ingredient in approximately 30% by weight hot water to form a slurry of approximately 20 grams of material based on dry weight. The slurry is then dried at approximately 80° C. with stirring to produce a granular powder. The dried granular powder is then pressed into several pellets each 0.5 inches in diameter and approximately 0.5 inches in length. The pellets are then ignited in a pressurized, closed vessel and the time of burning from one end measured. This process is repeated at multiple pressures to produce data of burning rate versus pressure.
The generant mixtures for each of Samples 1-12 are similar to one another, respectively containing a primary fuel of copper adipate (CuAdip), a secondary fuel of guanidine nitrate (GuNO3), an oxidizer of basic copper nitrate (bCN), and a burn rate modifier of zinc oxide (ZnO) at differing mass amounts indicated in Table 1.
Samples 1, 5, and 8 contain a minimum amount of only 5% by weight of primary fuel copper adipate, while Samples 4, 7, and 20 contain a maximum amount tested of 20 wt. %. Samples 1-4 contain 1% by weight of burn rate modifier ZnO, while Samples 5-7 contain 3% by weight of ZnO, and Mixtures 8-12 contain 5% by weight of ZnO.
Samples 1-12 are tested for density and to characterize combustion data of each respective gas generant, including burn rates at 1,000 pounds per square inch (about 6.9 MPa) and 3,000 psi (about 20.7 MPa). Combustion performance is measured in a 60-liter inflator tank. Gas volume and mass of gas produced during combustion, along with maximum combustion flame temperature (Tc) are calculated with a standard thermochemical computer program. The burn rate profile is also characterized to find the pressure exponent (n−slope of a log-log plot of burn rate (Rb) versus pressure (P)), the coefficient of sensitivity to temperature (σn), and performance or burning rate variability is designated (πk) variables (see discussion in context of Equations 1-3 above).
As can be seen from Table 1, while moles of gas generated and gas volume are highest, the flame temperature at combustion (Tc) undesirably exceeds 1700K for Samples 1, 5, and 8 where copper adipate is present at only 5 wt. %. Further, for Samples 1, 5, and 8, the pressure exponent n is equal to or greater than 0.3. For Samples 2-4, 6-7, and 9-12, the copper adipate is present at greater than 5% by weight (ranging from 10-20 wt. %) and the flame temperature (Tc) is desirably less than 1700K, while producing adequate moles and volume of combustion gas. Moreover, for Samples 2-4, 6-7, and 9-12, pressure exponent n is desirably less than 0.3 in all cases. Samples 4, 7, and 11, and 12 have a pressure exponent n of less than 0.2. Further, the coefficient of sensitivity to temperature (σn) is less than 0.10 for Samples 4, 7, and 12, while burning rate variability (πk) is less than 0.14 for Samples 4, 7, 11, and 12.
Furthermore, as can been seen in the data in Table 1, increasing the amount of burn rate modifier ZnO can serve to desirably reduce pressure exponent n, when copper adipate is present at 20 wt. %. For example, comparison of Samples 4, 7, and 12 have copper adipate at 20 wt. %, but have 1 wt. %, 3 wt. %, and 5% by weight of ZnO respectively and thus exhibit pressure exponent n of 0.192, 0.190, and 0.152, respectively. Thus, a formulation composed of bCN as the oxidizer, a minimum of 10% of the cupric salt of adipic acid (CuAdip-CuC6H8O4) as the primary fuel, guanidine nitrate as a secondary fuel, and a minimum of 1% zinc oxide as a burning rate modifier can achieve a n value less than 0.30, low σp value and πk values and a flame temperature less than 1700 K. Furthermore, if the level of the cupric salt of adipic acid is 20% or greater, n values of less than 0.20, σp values of less than 0.10, πk values of less than 0.14%, and a flame temperature of less than 1450 K are obtained.
Samples 2-4, 6-7, and 9-12 all demonstrate minimal or reduced combustion variability and cool burn temperatures (Tc of less than 1700K) by exhibiting reduced pressure sensitivity via pressure exponent “n,” reduced coefficient of sensitivity to temperature (σn) and low burning rate variability (πk) parameters.
In accordance with certain aspects of the present disclosure, it is believed that the combination of a primary fuel comprising a salt of a dicarboxylic acid selected from a group consisting of: succinic acid, glutaric acid, adipic acid, and pimelic acid, e.g., a cupric salt of adipic acid, and a burn rate modifier, such as zinc oxide, when combined with certain secondary fuels and oxidizers lessen pressure sensitivity and temperature sensitivity of combustion.
In various aspects, the present technology thus provides a cool burning gas generating compositions having minimal performance variation at temperature and pressure extremes. Thus, the present disclosure provides a cool burning gas generant composition, which comprises a primary fuel comprising a salt of a dicarboxylic acid selected from a group consisting of: succinic acid, glutaric acid, adipic acid, and pimelic acid; a secondary fuel distinct from the primary fuel; at least one oxidizer, and a burn rate modifier. In certain variations, the primary fuel comprises a cupric salt of adipic acid and the secondary fuel optionally comprises guanidine nitrate. In certain other variations, the oxidizer comprises basic copper nitrate. The burn rate modifier optionally comprises zinc oxide. The present disclosure thus provides in certain aspects, a family of gas generant formulations containing copper adipate and guanidine nitrate as fuels, basic copper nitrate as an oxidizer, and zinc oxide as a burning rate modifier that achieves desired improvements for flame temperature, σp and πk values. In certain aspects, a gas generant composition in accordance with the present technology has a maximum flame temperature at combustion (Tc) of less than or equal to about 1700K and a linear burn rate pressure exponent of less than or equal to about 0.3. Such a gas generant has superior combustion stability, while still exhibiting desirably high gas output. Moreover, such a cool burning gas generant enables an improved, lighter and more efficient inflator assembly with fewer inflator components necessary to serve as a heat sink or as filters.
In certain aspects, a particularly suitable gas generant composition comprises a primary fuel comprising copper adipate at greater than or equal to about 10% by weight to less than or equal to about 20% by weight of the total gas generant composition, guanidine nitrate as a secondary fuel at greater than or equal to about 5% by weight to less than or equal to about 20% by weight of the total gas generant composition, basic copper nitrate as an oxidizer at greater than or equal to about 50% by weight to less than or equal to about 70% by weight of the total gas generant composition, zinc oxide as a ballistic modifier at greater than or equal to about 1% by weight to less than or equal to about 10% by weight of the total gas generant composition. Other processing and slagging agents known in the art may be included in this formulation up to a maximum level of 10% by weight of the total gas generant composition.
In certain aspects, the present teachings provide gas generant compositions having a pressure exponent value n of less than 0.30, along with relatively low coefficient of sensitivity to temperature (σn) and low burning rate variability (πk) values and a maximum flame temperature (Tc) of less than or equal to about 1700 K. In certain variations, such a gas generant may have a σp value less than or equal to about 0.10% and a πk value of less than or equal to about 0.15%. Furthermore, in certain variations, gas generant compositions according to the present technology may have a pressure exponent value n of less than 0.20, along with relatively low coefficient of sensitivity to temperature (σn) and low burning rate variability (πk) values and a maximum flame temperature (Tc) of less than or equal to about 1700 K. In certain variations, such a gas generant may have a σp value less than or equal to about 0.10% and a πk value of less than or equal to about 0.15%.
In certain aspects, another method further comprises spray drying an aqueous mixture comprising a primary fuel, a secondary fuel, at least one oxidizer, a burn rate modifier, and optionally one or more conventional gas generant additives, as described previously above, to produce a spray dried powder. For example, in certain embodiments, a primary fuel comprising a salt of a dicarboxylic acid selected from a group consisting of: succinic acid, glutaric acid, adipic acid, and pimelic acid; a secondary fuel distinct from the primary fuel; at least one oxidizer, and a burn rate modifier, are mixed together with an aqueous vehicle to form the aqueous mixture. After spray drying, the powder is then pressed to produce a gas generant grain.
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.
