Explosive and thermic compositions or charges – Structure or arrangement of component or product – Solid particles dispersed in solid solution or matrix
Reexamination Certificate
1996-11-26
2002-04-02
Miller, Edward A. (Department: 3641)
Explosive and thermic compositions or charges
Structure or arrangement of component or product
Solid particles dispersed in solid solution or matrix
C149S019100, C149S019500, C149S019600, C149S019900, C149S046000
Reexamination Certificate
active
06364975
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to ammonium nitrate propellant compositions. More particularly, it is directed to age-stabilized and/or strengthened ammonium nitrate propellant compositions and methods for making the same.
BACKGROUND OF THE INVENTION
Propellant compositions are useful for a variety of applications. One such application is in vehicle air bag restraint devices. In such restraint devices, it is important to reduce the toxicity of gases produced upon combustion of the propellant. It is also desirable that the propellant composition burn in a smokeless or nearly smokeless fashion because the presence of smoke can cause various problems. For example, after an accident in which an air bag has been deployed, smoke not only hinders visibility, it also interferes with any ongoing rescue efforts. Thus, it is desirable that propellant composition combustion products be smoke-free or nearly so.
Another application of propellant compositions is their use in rockets and in other munitions as propulsive propellant compositions. Combustion of propulsive propellant compositions in rockets and the like provides the energy required to transport them over long distances towards a given target. During battle, it is critical to maintain the advantage of surprise and stealth. Therefore, it is desirable that rockets powered by propulsive propellant compositions be as undetectable as possible upon launch and during deployment.
To maintain the advantages of stealth and surprise, it is important that the propellant composition be smoke-free or nearly so during combustion. In an effort to meet the requirement of a smoke-free combustible propellant composition, several compositions have been developed by the U.S. military. Among the compositions developed are the “double base” propellant compositions. As is known in the art, “double base” refers to a propellant composition containing both nitroglycerine (NG) and nitrocellulose (NC). Double base propellants are prone to premature explosion or premature deflagration in response to various unplanned stimuli (e.g., fire, heat, shrapnel, bullets, other fragments etc.) that may be encountered in battle. In addition, for propulsive applications, the energy output upon combustion of double base propellants is sometimes insufficient. Thus, the addition of energetic additives such as cyclotetramethylene tetranitramine (HMX) and/or cyclotrimethylene trinitramine (RDX) is often required to provide the energy output sought during combustion. However, the addition of such energetic additives exacerbates the already hazardous tendency of double base propellants to premature explosion or premature deflagration.
Nevertheless, to fulfill the smoke free and high energy requirements of propulsive propellants, as defined herein, propellant compositions including double base propellants were pursued at the expense of safety, especially in regards to naval operations. Consequently, the U.S. Navy has taken the lead in formulating a series of standards concerning insensitive ammunition requirements, formalized as MIL-STD-2105B, incorporated herein by reference in its entirety. Equivalent insensitive ammunition standards have been adopted by most major military powers (e.g., England, France, Germany, etc.). These standards require that propellant compositions meet or exceed insensitive ammunition safety standards for the weapons platforms for which they were designed.
Further, with regards to military propulsive applications, various smoke characteristics required of propellant compositions have been strictly defined. Based on the empirical work performed by the U.S. Missile Command at Redstone Arsenal and some of their counterparts in other countries, industry accepted definitions of “minimum smoke” and “reduced smoke” have been promulgated in STANAG 6016 (NATO Standardized Agreement Solid Propellant Smoke Classification). STANAG 6016 is incorporated herein by reference in its entirety. The smoke effluent is calculated by a number of thermo-chemical codes that are well known in the industry. For example, STANAG 6016 classifications “AA” and “AC” correspond to the definitions of minimum smoke and reduced smoke, respectively. The “smoke-free”, “nearly smoke free” and/or “substantially smoke free” terms as used herein are synonymous with the definition of minimum smoke (i.e., code AA).
To meet these requirements (i.e., smoke free—minimum smoke in accordance with STANAG 6016; high energy output and safety—in accordance with Insensitive Ammunitions Requirements formalized as MIL-STD-2105B) attempts have been made to develop non-double base propellant compositions that are smoke free, yet safe for handling. For example, ammonium nitrate, metal nitrate, alkali earth metal nitrate, ammonium perchlorate and metal perchlorate propellant compositions and the like have been used. However, these propellant compositions present several problems. Metal nitrates, typically, produce solid particles upon combustion. These solid particles form a visible smoke referred to as “primary smoke” which is undesirable. Ammonium or metal perchlorates produce hydrogen chloride during combustion. Hydrogen chloride reacts with moisture in the ambient air to yield a liquid/gas aerosol. The aerosol forms another visible smoke referred to as “secondary smoke”. Either “primary smoke” or “secondary smoke” formed as an effluent from the combustion of a propulsive propellant composition negates the advantage of surprise. The smoke trail aids opposing forces in destroying or otherwise countering the incoming missile. In addition, such effluent smoke points to the launch position. During battle, such smoke places launch personnel in greater danger of potentially successful retaliation, e.g., by counter battery fire.
Ammonium nitrate as a propellant ingredient may produce a propellant that does not produce primary or secondary smoke upon combustion. However, ammonium nitrate presents other drawbacks as a propellant component. Principally, it is recognized that ammonium nitrate undergoes several crystal phase changes at various well-recognized temperatures. Pure ammonium nitrate undergoes a series of structural and volumetric crystal phase transformations over typical operating temperature ranges. In pure ammonium nitrate, structural crystal phase transitions are observed at about −18° C., 32.3° C., 84.2° C. and 125.2° C., respectively. The phase transition at about 32.3° C. is particularly troublesome. A large volumetric change (about 3.7%) in the crystal phase of ammonium nitrate is observed when the temperature cycles above and below about 32.3° C. (i.e., transition between phase IV (below 32.3° C.) and phase III (above 32.3° C.)). As the ammonium nitrate cycles between phase IV and phase III, it expands and contracts. Repeated cycling through the phase IV to phase III transition temperature (i.e., about 32.3° C.) is associated with ammonium nitrate grain growth and destruction of grain integrity. The result is that there is porosity and loss in mechanical strength of ammonium nitrate based propellant compositions.
As used herein, the term “age-stabilized” refers to a state of ammonium nitrate wherein the crystal phase III-IV and volumetric changes associated with thermal cycling are substantially reduced. Thus, the shelf-life of an ammonium nitrate propellant composition is considerably increased from about 1-2 years to about 5-20 years or more.
Further, the term “strengthened”, as used herein, refers to a state of ammonium nitrate propellant wherein the tensile strength of the propellant is increased without unduly sacrificing elongation or, alternatively, is accompanied by an increase in elongation. The strengthened ammonium nitrate propellant composition is substantially resistant to physical destruction of the propellant.
As also used herein, the term “safe” refers to an ammonium nitrate propellant composition that meets or exceeds the insensitive ammunition requirements promulgated in MIL-STD-2105B wherein the tendency to violent deflagration or explosion is substa
Fleming Wayne C.
McSpadden Hugh J.
Olander Donald E.
Holden Jerry J.
Miller Edward A.
Universal Propulsion Co., Inc.
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