Classifications

• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
  • C06B31/00—Compositions containing an inorganic nitrogen-oxygen salt
  • C06B31/28—Compositions containing an inorganic nitrogen-oxygen salt the salt being ammonium nitrate
  • C06B31/30—Compositions containing an inorganic nitrogen-oxygen salt the salt being ammonium nitrate with vegetable matter; with resin; with rubber
• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
  • C06B31/00—Compositions containing an inorganic nitrogen-oxygen salt
  • C06B31/28—Compositions containing an inorganic nitrogen-oxygen salt the salt being ammonium nitrate
• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
  • C06B23/00—Compositions characterised by non-explosive or non-thermic constituents
  • C06B23/006—Stabilisers (e.g. thermal stabilisers)
• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
  • C06B45/00—Compositions or products which are defined by structure or arrangement of component of product
  • C06B45/04—Compositions or products which are defined by structure or arrangement of component of product comprising solid particles dispersed in solid solution or matrix not used for explosives where the matrix consists essentially of nitrated carbohydrates or a low molecular organic explosive
  • C06B45/06—Compositions or products which are defined by structure or arrangement of component of product comprising solid particles dispersed in solid solution or matrix not used for explosives where the matrix consists essentially of nitrated carbohydrates or a low molecular organic explosive the solid solution or matrix containing an organic component
  • C06B45/10—Compositions or products which are defined by structure or arrangement of component of product comprising solid particles dispersed in solid solution or matrix not used for explosives where the matrix consists essentially of nitrated carbohydrates or a low molecular organic explosive the solid solution or matrix containing an organic component the organic component containing a resin
  • C06B45/105—The resin being a polymer bearing energetic groups or containing a soluble organic explosive
• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06D—MEANS FOR GENERATING SMOKE OR MIST; GAS-ATTACK COMPOSITIONS; GENERATION OF GAS FOR BLASTING OR PROPULSION (CHEMICAL PART)
  • C06D5/00—Generation of pressure gas, e.g. for blasting cartridges, starting cartridges, rockets
  • C06D5/06—Generation of pressure gas, e.g. for blasting cartridges, starting cartridges, rockets by reaction of two or more solids

Definitions

• 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.
• Propellant compositions are useful for a variety of applications.
• One such application is in vehicle air bag restraint devices.
• it is important to reduce the toxicity of gases produced upon combustion of the propellant.
• 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.
• propellant composition combustion products be smoke-free or nearly so.
• propellant compositions 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.
• rockets powered by propulsive propellant compositions be as undetectable as possible upon launch and during deployment.
• 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.
• HMX cyclotetramethylene tetranitramine
• RDX cyclotrimethylene trinitramine
• 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.
• 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) .
• 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.
• 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.
• 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.
• shelf-life of an ammonium nitrate propellant composition is considerably increased from about 1-2 years to about 5-20 years or more.
• 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.
• 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 substantially reduced and the shelf-life is substantially increased from about 1-2 years to about 5-20 years or more. Further, the term “safe” is used herein to refer to an ammonium nitrate propellant composition wherein the tendency to form grain fissures due to crystal phase changes is substantially reduced or altogether eliminated.
• non-strengthened/non-age- stabilized ammonium nitrate propellant compositions that have been stored (e.g., either in munitions or in vehicle air bag restraint devices) for more than about 1 to 2 years may have undergone several crystal phase changes to the extent that the physical integrity of the propellant has been compromised and the propellant will no longer perform in the desired manner. Consequently, the useful shelf-life of prior art ammonium nitrate propellant compositions is disadvantageously shortened. Thus, it is desirable to formulate a smoke-free (or substantially smoke free) yet safe ammonium nitrate propellant composition having an extended shelf-life.
• a propulsive or gas generating device containing a propellant composition requires a shelf-life from about 5 to about 20 years or more.
• the shelf-life of the device is largely dependent on the shelf-life of the propellant composition contained therein.
• a desirable shelf-life for a munition (propulsive) propellant composition or a vehicle air bag (gas producing) propellant composition is about 5 or more years, preferably, from about 7 to 20 years.
• efforts have been directed at solving the crystal phase stabilization problem (i.e., of ammonium nitrate) .
• phase stabilizing additives relate to the formation of large amounts of undesirable residue as combustion products.
• KF potassium nitrate
• it must be added to the molten phase (I) of ammonium nitrate. Thereafter, the KF modified ammonium nitrate is cooled.
• the requirement for melting ammonium nitrate before adding KF is cumbersome, expensive and time consuming.
• the effluent of a device using such a propellant is corrosive, smoky (with an enhanced radar cross section) and toxic.
• the use of the metal oxides also has several drawbacks.
• solid particulates are formed upon combustion when MgO, NiO, CuO and/or ZnO are used.
• Solid particulates contribute to the formation of primary smoke which is undesirable.
• NiO is carcinogenic.
• NiO and CuO present environmental hazards.
• both NiO and ZnO are only marginally effective. That is, once exposed to moisture, these oxides are no longer effective ammonium nitrate phase stabilizers. Further, NiO and ZnO increase the detonatability of the ammonium nitrate which is undesirable. Additionally, manufacturing propellant compositions including NiO and/or ZnO is more expensive.
• phase III in ammonium nitrate depends on the presence of water, e.g., down to as little as about 0.1% by weight of the ammonium nitrate. See Choi et al., J. Appl. Cryst., Vol. 13, p. 403 (1980).
• a high moisture content is said to favor III-IV phase transitions.
• U.S. Patent No. 4,486,396 to Kjohl et al. (at column 1, lines 30-32), these phase transitions render the ammonium nitrate less stable to thermal cycling.
• U.S. Patent No. 5,061,511 to Baczuk suggests the use of aluminum silicate molecular sieves (having a pore size of less than about 10 angstroms) as a stabilizer in propellant compositions such as single base or double base propellant.
• propellant compositions such as single base or double base propellant.
• propellant compositions include nitrocellulose and nitroglycerin, high energy fluorine containing propellants, single or double base nitrate ester propellants and composite propellants such as ammonium perchlorate/Al with rubber binders.
• ammonium nitrate is not a propellant of the class described by Baczuk (i.e., See '511) and it does not give off the N 2 , C0 2 , CO, N0 X or F 2 gases (i.e., see '511) during aging, there is no expectation that molecular sieves in general, much less those having a pore size of 10 angstroms or less would stabilize ammonium nitrate.
• ammonium nitrate is not a urethane cross- linked double base propellant (i.e., see '261)
• molecular sieves e.g., having a pore size of 10 angstroms or more, would stabilize ammonium nitrate against volumetric crystal phase changes.
• Kjohl et al. since water is associated with the undesirable crystal phase changes of ammonium nitrate, Kjohl et al., supra , used porous additives which could absorb water to stabilize ammonium nitrate. They further discovered that the presence of water absorbing porous particles resulted in no movement of water in the ammonium nitrate particles and that, during thermal cycling, swelling of ammonium nitrate was observed only to a small extent. Kjohl et al., however, state that the porous particles should be added to the ammonium nitrate after the ammonium nitrate is dried. Finally, they state that not any type of porous particle is suitable for stabilizing ammonium nitrate.
• silicates of the molecular sieve type can bind water, but it has been found difficult to give such particles the required particle size and binding to the ammonium nitrate particles.
• Kjohl et al. conclude that molecular sieves performed poorly in stabilizing ammonium nitrates (see column 3, lines 18-23).
• the process for forming a safe, age-stabilized ammonium nitrate propellant composition comprises the steps of providing a quantity of ammonium nitrate, adding a sufficient quantity of a silicate molecular sieve to absorb water from the ammonium nitrate, grinding the ammonium nitrate with the molecular sieve, maintaining contact between the ammonium nitrate and the sieve, then adding at least a binder (except any curing agent e.g., isocyanate curing agent), maintaining contact between the ground molecular sieve and the other ingredients and finally adding a curing agent, if any, to yield the safe, age-stabilized ammonium nitrate propellant composition having a long shelf-life.
• a binder except any curing agent e.g., isocyanate curing agent
• these and other objects are accomplished by the addition of a strengthening agent to a mixture of ammonium nitrate and at least a binder to yield a strengthened propellant composition.
• a molecular sieve may also be added to the strengthened ammonium nitrate propellant to yield an enhanced, strengthened and age- stabilized ammonium nitrate propellant composition.
• an age-stabilized ammonium nitrate composition may be formed by adding a molecular sieve to ammonium nitrate (e.g., at least about 1 gram of a molecular sieve per pound of ammonium nitrate) and then grinding the mixture. Thereafter, the mixture may be safely stored without deleterious changes for an extended period of time in a sealed container.
• a molecular sieve e.g., at least about 1 gram of a molecular sieve per pound of ammonium nitrate
• the first embodiment of the present invention relates to an age-stabilized ammonium nitrate propellant composition.
• the second embodiment relates to a strengthened ammonium nitrate propellant composition.
• the third embodiment relates to an age-stabilized and strengthened ammonium nitrate propellant composition.
• each embodiment may be used, with certain modifications, as a gas producing ammonium nitrate propellant composition or as a propulsive ammonium nitrate propellant composition.
• the gas producing ammonium nitrate propellant compositions are designed to be used in vehicle air bag restraint systems and the like wherein gas production is paramount.
• the propulsive ammonium nitrate propellant compositions are designed to be used in rockets and other munitions wherein energy output is paramount.
• the substantially smoke-free ammonium nitrate propellant composition comprises ammonium nitrate, a molecular sieve and a binder.
• the first embodiment may contain one or more of a variety of additives.
• additives include, but are not limited to, a nitroplasticizer (e.g., nitramines and/or nitrate esters which are in a liquid phase when added, typically, at room temperature such as at about 25°C) , an energetic additive (e.g., nitramines which are in a solid phase when added, typically, at room temperature) , a nitrate ester stabilizer, a curing agent, a cure accelerator, an opacifier and a polymer protector (i.e., an antioxidant) .
• the ammonium nitrate may be present as fines, prills, granules and the like.
• the size of the ammonium nitrate may vary between about 5 microns and about 5,000 microns (or any value therebetween) in thickness.
• a particle thickness is, preferably, from about 5 microns to about 400 microns and, most preferably, from about 30 to about 50 microns.
• the amount of ammonium nitrate included is dependent upon the application for which the propellant composition is designed.
• additives that increase the energy output (e.g., nitroplasticizers and/or energetic additives) of the first embodiment are preferably included therein.
• nitroplasticizers and/or energetic additives are often omitted from the first embodiment.
• nitroplasticizers and/or energetic additives may be optionally included therein.
• the amount of ammonium nitrate included in the first embodiment is varied depending upon the presence or absence of nitroplasticizers and/or energetic additives therein.
• the percent by weight values of the various propellant components denoted below refer to a percent of the total weight of the propellant composition.
• the ammonium nitrate when used for gas producing applications, is present in an amount of at least about 60%.
• the amount of ammonium nitrate present may range from about 65% to about 85%.
• the amount of ammonium nitrate added when combined with optional nitroplasticizers and/or energetic additives, the amount of ammonium nitrate added may range from about 40% to about 80% (or any value therebetween) . In the absence of such nitroplasticizers and energetic additives, the amount of ammonium nitrate added to the first embodiment designed for propulsive applications ranges from about 65% to about 85%.
• the first embodiment of the invention contains a molecular sieve.
• molecular sieve is an aluminosilicate type molecular sieve, commonly referred to as a zeolite molecular sieve.
• a zeolite molecular sieve is an aluminosilicate type molecular sieve, commonly referred to as a zeolite molecular sieve.
• a zeolite molecular sieve commonly referred to as a zeolite molecular sieve.
• An exemplary type A synthetic zeolite has the formula Na 12 ( (A10 2 ) 12 (Si0 2 ) 12 ) • 27H 2 0.
• a molecular sieve is obtained by heating a zeolite to about 350°C under a vacuum to remove the water of hydration.
• a typical molecular sieve such as Na 12 ( (Al 12 Si 12 0 48 ) • 27H 2 0
• a type A zeolite with anhydrous cubic microcrystals is formed.
• it must have two properties.
• the molecular sieve must retain the absorbed water molecules so that the water is not available to any other component of the ammonium nitrate propellant composition, especially the ammonium nitrate. Thus, the retention of the water in the molecular sieve/water adduct must be extremely robust.
• the water molecules must not be simply adsorbed onto the surface of the molecular sieve. It is believed that molecular sieves hold the water molecules within the pores present in the sieve. Further, without being bound by theory, it is believed that the water molecules may at first be adsorbed onto the surface of the molecular sieve. However, after a short period of time (e.g., up to about 48 hours) , the water molecules are transported to the interior of the molecular sieve via its pores.
• a short period of time e.g., up to about 48 hours
• the sieve has an adequate pore dimension (e.g., typically about 13 angstroms or less such as from about 3 to about 13 angstroms or any value therebetween) , then the water can be absorbed into the interior of the sieve.
• the other components of the ammonium nitrate propellant composition e.g., binders, nitroplasticizers, energetic additives, nitrate ester stabilizers, curing agents, cure catalysts, opacifiers and/or anti-oxidants
• the other components of the ammonium nitrate propellant composition e.g., binders, nitroplasticizers, energetic additives, nitrate ester stabilizers, curing agents, cure catalysts, opacifiers and/or anti-oxidants
• a pore size sufficient for this purpose is about 13 angstroms or less.
• the pore size is from about 3 to about 13 angstroms or any value therebetween. More preferably, the pore size is from about 3 to about 5 angstroms. The most preferred pore size is about 4 angstroms.
• molecular sieves compatible with the first embodiment of the invention include, but are not limited to, molecular sieves type 3A, 4A, 5A and 13X, respectively. These sieves are made by various companies, including Union Carbide (N.Y., N.Y.) which sells its molecular sieves under the trademark LINDE ® .
• Molecular Sieve 4A is a sodium form of the type A crystal structure. It is an alkali metal alumino-silicate. The type 4A sieve will absorb molecules with critical diameters up to about 4 angstroms.
• the molecular sieve is present in an amount from about 0.02% to about 6% (or any value therebetween). Preferably, the molecular sieve is present from about 0.2% to about 0.4% and, most preferably, from about 0.20% to about 0.22%.
• the preferred molecular sieve is the type 4A sieve.
• Binders compatible with the first embodiment of the present invention include, but are not limited to, thermoplastic elastomers (e.g., FinapreneTM, KratonTM or mixtures thereof) and a cure hardening material.
• cure hardening materials include, but are not limited to, a hydroxy terminated polybutadiene (HTPB) , hydroxy terminated polyether (HTPE) , polyglycol adipate (PGA) , glycidylazide polymer (GAP), poly bis-3 , 3 '-azido ethyl oxetane (BAMO) , poly-3-nitratomethyl-3-methyl oxetane (PNMMO) , polyethylene glycol (PEG) , polypropylene glycol (PPG) , cellulose acetate (CA) or mixtures thereof.
• An exemplary binder is a mixture of 7 parts by weight of BAMO and 3 parts by weight of PNMMO.
• the preferred binder is PGA. It is noted that other binders well-known in the art may be used.
• nitroplasticizers are incompatible with HTPB (i.e., they are insoluble in one another), preferably, they are not combined in any of the embodiments of the propellant composition.
• energetic additives e.g., solid phase nitramines such as RDX, HMX
• other plasticizers such as dioctyl adipate (e.g., in an amount of about 3 to about 10% or any value therebetween) may be used.
• Other plasticizers compatible with HTPB are well known to those skilled in the art and may be used therewith.
• thermoplastic elastomeric binders compatible with the first, i.e., age-stabilized, embodiment of the present invention are those that have melting points or plasticized melting points above the expected use and storage temperatures of the propellant compositions. Typically, the use and storage temperatures range from about -65°F to about 200°F. Further, the thermoplastic elastomers must melt in their plasticized state below the decomposition temperature of ammonium nitrate and/or any nitroplasticizer present therein. In the first embodiment, the binder is present from about 3% to about 40% (or any value therebetween) , preferably, from about 5% to about 30%.
• the first embodiment may additionally contain an energetic additive (i.e., a solid phase component that increases energy output, e.g., some nitramines) and/or a nitroplasticizer (i.e., a liquid phase component that increases energy output, e.g., some nitrate esters and some nitramines) .
• an energetic additive i.e., a solid phase component that increases energy output, e.g., some nitramines
• a nitroplasticizer i.e., a liquid phase component that increases energy output, e.g., some nitrate esters and some nitramines
• Typical nitroplasticizers compatible with the age-stabilized ammonium nitrate propellant composition (i.e., the first embodiment) of the present invention include, but are not limited to, tri ethylol ethane trinitrate (TMETN) , triethylene glycol dinitrate (TEGDN) , triethylene glycol trinitrate (TEGTN) , butanetriol trinitrate (BTTN) , diethyleneglycol dinitrate (DEGDN) , ethyleneglycol dinitrate (EGDN) , nitroglycerine (NG) , diethylene glycerin trinitrate (DEGTN) , dinitroglycerine (DNG) , nitrobenzene (NB) , N-butyl-2- nitratoethylnitramine (BNEN) , methy1-2-nitratoethylnitramine
• the preferred nitroplasticizer is a 50-50 by weight mixture of TMETN and TEGDN.
• the nitroplasticizer is optionally present up to about 40% by weight.
• energetic additives compatible with the first embodiment include, but are not limited to, dinitroxydiethylnitramine (DNDEN) , cyclotrimethylene trinitramine (RDX) , cyclotetramethylene tetranitramine (HMX) or mixtures thereof.
• the preferred energetic additives are RDX, HMX or mixtures thereof. In the first embodiment, they are preferably present up to about 40%. As other similar nitroplasticizers and energetic additives become commercially available, they can be included in this list as one of ordinary skill in the art would recognize.
• nitroplasticizers and energetic additives tend to increase the energy output, flame temperature and explosive nature of an ammonium nitrate propellant composition, these materials are not always included within the first embodiment of the invention when used for gas producing applications, rather they may be optionally included therein.
• the nitroplasticizer and/or energetic additive may be present (i.e., as an optional additive) in an amount of up to about 35%.
• the nitroplasticizer and/or energetic additive is typically present in an amount from about 5% to about 40% or any value therebetween.
• the amounts of the binder plus any nitroplasticizer and energetic additive must total at least about 20% to form a physically acceptable first embodiment and, preferably, from about 20% to about 35%.
• physically acceptable means a composition that can be formed into various desirable shapes, (e.g., grains, etc.) and which can be maintained in those shapes.
• a nitroplasticizer which is a nitrate ester is included in the first embodiment, it is preferred that a nitrate ester stabilizer be added as well.
• the nitrate ester stabilizer may be omitted from the propellant composition.
• the nitrate ester stabilizer may be present in an amount of up to about 3%, more preferably, from about 0.1% to about 2% and, most preferably, from about 0.35% to about 0.5%.
• Nitrate ester stabilizers compatible with the first embodiment of the present invention include, but are not limited to, N-methyl- 4-nitroaniline (MNA) , 2-nitrodiphenylamine (NDA) , ethyl centralite (EC) or mixtures thereof.
• MNA N-methyl- 4-nitroaniline
• NDA 2-nitrodiphenylamine
• EC ethyl centralite
• the preferred nitrate ester stabilizer is a mixture of MNA and NDA, preferably, in a weight ratio of about 1:1.
• Curing agents compatible with the first embodiment of the present invention include, but are not limited to, hexamethylene diisocyanate (HMDI) , isophorone diisocyanate (IPDI) , toluene diisocyanate (TDI) , trimethylxylene diisocyanate (TMDI) , dimeryl diisocyanate (DDI) , diphenylmethane diisocyanate (MDI) , naphthalene diisocyanate (NDI) , dianisidine diisocyanate (DADI) , phenylene diisocyanate (PDI) , xylylene diisocyanate (MXDI) , other diisocyanates, triisocyanates, higher isocyanates than the triisocyanates, polyfunctional isocyanates (e.g., Desmodur N 100) , other polyfunctional isocyanates or mixtures thereof.
• HMDI hexamethylene diiso
• the isocyanate have at least two reactive isocyanate groups. If there are no binder ingredients with a functionality that is greater than 2, then the curative functionality (e.g., number of reactive isocyanate groups per molecule of isocyanate curing agent) must be greater than 2.0.
• the amount of the curing agent is determined by the desired stoichiometry (i.e., stoichiometry between curable binder and curing agent) .
• the curing agent is present in an amount of up to about 5%. However, if a curable binder (e.g., binder having reactive hydroxy1 groups such as HTPB) is used, the curing agent is present from about 0.5% to about 5%.
• a cure catalyst is preferably added to the propellant composition.
• the cure catalyst is used to accelerate the curing reaction between the curable binder and the curing agent.
• Cure catalysts compatible with the first embodiment of the present invention include, but are not limited to, a tin dilaurate (e.g., an alkyl tin dilaurate, butyl tin dilaurate, isopropyl tin dilaurate etc.), metal acetylacetonate, triphenyl bismuth, maleic anhydride, magnesium oxide or mixtures thereof.
• a preferred cure catalyst is an equal % by weight mixture (i.e., 33 1/3%) of each of triphenyl bismuth, maleic anhydride and magnesium oxide.
• the cure catalyst is present up to about 0.3% by weight.
• one opacifier which is compatible with the first embodiment is carbon black.
• the opacifier is present up to about 2%. Those skilled in the art are aware of other opacifiers that may be used.
• Antioxidants may also be added to the first embodiment of the present invention.
• Antioxidants compatible with the first embodiment of the present invention include, but are not limited to, 2, 2 '-bis (4-methyl-6-tert- butylphenol) , 4,4 '-bis (4-methyl-6-tert-butylphenol) or mixtures thereof.
• Other antioxidants well known in the art are within the scope of the present invention. The antioxidant is present in an amount of up to about 1%.
• the propellant composition comprises ammonium nitrate, a strengthening agent and a binder.
• the ammonium nitrate component included in this embodiment is the same as that previously described with respect to the first embodiment.
• Preferred strengthening agents compatible with the second embodiment of the present invention include, but are not limited to, azodicarbonamide, dicyandiamide, oxamide or mixtures thereof.
• the most preferred strengthening agent is azidocarbonamide.
• the strengthening agent is present in an amount from about 2% to about 20%.
• the strengthening agent is present from about 3% to about 12% and, most preferably, from about 8% to about 12%.
• Optional additives compatible with the second embodiment include, but are not limited to, a curing agent, a cure accelerator, a nitroplasticizer, an energetic additive, a nitrate ester stabilizer, an opacifier, and/or an antioxidant.
• the binders, nitroplasticizers, energetic additives, nitrate ester stabilizers, curing agents, cure catalysts, opacifiers and/or anti-oxidants compatible with the first embodiment are equally compatible with the second embodiment. Further, the amounts of ammonium nitrate, nitroplasticizer, energetic additive, nitrate ester stabilizer, curing agent, cure catalyst, opacifier and/or anti-oxidant described with respect to the first embodiment are equally applicable to the second embodiment.
• the binder included in the second embodiment is present in an amount from about 3% to about 40% or any value therebetween.
• the binder is preferably present in the subject embodiment in an amount from about 3% to about 20%.
• the binder plus any nitroplasticizer and energetic additive must total at least about 20% to form a physically acceptable second embodiment and, preferably, from about 20% to about 35%. It should be noted that the second embodiment does not contain a molecular sieve.
• a strengthening agent to a propellant composition reduces its impulse.
• nitroplasticizers and/or energetic additives are added.
• ammonium nitrate propellant compositions lose their detonatable characteristic when the impulse is less than or equal to about 229 lb. force - seconds/lb. mas ⁇ .
• a sufficient amount of one or more nitroplasticizers and/or energetic additives is added to an ammonium nitrate propellant composition containing a strengthening agent, then the advantages of the strengthening agent are obtained without loss of impulse.
• this embodiment comprises ammonium nitrate, a molecular sieve, a strengthening agent and a binder.
• ammonium nitrates, molecular sieves, strengthening agents, binders, nitroplasticizers, energetic additives, nitrate ester stabilizers, curing agents, cure catalysts, opacifiers and/or anti-oxidants compatible with the first and/or second embodiments are equally compatible with the third embodiment.
• the amounts of ammonium nitrate, nitroplasticizer, energetic additive, nitrate ester stabilizer, curing agent, cure catalyst, opacifier and/or anti-oxidant described with respect to the first and/or second embodiments are equally applicable to the third embodiment.
• the third embodiment contains both a molecular sieve and a strengthening agent in accordance with the first and second embodiments, respectively.
• the amounts of strengthening agent added to the second embodiment are equally applicable to this third embodiment.
• the amounts of the molecular sieve added to the first embodiment are equally applicable to the third embodiment.
• the binder is present in an amount from about 5% to about 30%.
• the binder plus any nitroplasticizer and energetic additive must total at least about 20% to form a physically acceptable third embodiment and, preferably, from about 20% to about 35%.
• the molecular sieve to be ultimately added is mixed with the ammonium nitrate.
• the molecular sieve is added to the extent of at least about 1 gram per pound of ammonium nitrate.
• the mixture of the ammonium nitrate and the molecular sieve may be allowed to stand for a first aging period.
• the first aging period is up to about 48 hours or longer, preferably, from about 0.25 hour to about 16 hours and, most preferably, as close to zero as possible.
• the mixture of the molecular sieve and the ammonium nitrate is exposed to the ambient air (i.e., including the moisture therein) , it is preferably ground immediately after mixing (i.e., the first aging period is zero minutes or nearly so) . If, however, the mixture is held in a sealed container (i.e., with limited exposure to ambient air and the moisture therein) , then the mixture may be maintained indefinitely without grinding.
• the first aging period may be up to about 48 hours (or more) such as from about 4 to about 16 hours. However, it is preferred to grind the mixture immediately (or, for example, as soon as it is practical to do so on a production or assembly line) after mixing to yield a first mixture.
• grinding allows the molecular sieve to be in closer physical proximity to the ammonium nitrate and the water associated with it. Thereby, it is further believed that grinding allows the molecular sieve to more effectively and efficiently absorb (and retain) water away from the ground ammonium nitrate.
• the particle characteristics e.g., particle thickness, particle size, particulate for —grains, prills, crystals size etc.
• the size of the ammonium nitrate should be, as previously noted, from about 5 microns to about 400 microns, preferably, from about 30 microns to about 50 microns in thickness.
• first aging period zero hours
• second mixture the remaining components of the propellant composition (except for any curing agent) are added to the first mixture to yield a second mixture. Thereafter, the second mixture is allowed to stand for a second aging period.
• the second aging period allows the molecular sieve to absorb (and retain) a sufficient amount of the water present to age-stabilize the second mixture.
• the second aging period is up to about 48 hours or longer, preferably, from about 0.25 hour to about 24 hours and, most preferably, from about 16 to about 24 hours.
• the curing agent if any, (e.g., isocyanate curing agent) is optionally added to the second mixture to complete and form the final age- stabilized ammonium nitrate propellant composition or the final age-stabilized/strengthened propellant composition.
• the propellant composition of Example 8, infra was prepared wherein the first aging period was set to zero hours and the second aging period was set to zero, 2 hours and 48 hours, respectively.
• the effect of varying the second aging period on hardness (Shore A) , ultimate tensile strength (psi) and elongation at break (%) for the propellant composition of Example 8, infra is given in Table III below.
• Elongation is an indication of elasticity. It indicates the length through which the propellant composition can be stretched before it breaks.
• An increase in tensile strength with a concurrent increase in elongation indicates an increase in "toughness” .
• the increase in "toughness” indicates that less damage will occur in bullet or fragment impact scenarios. Less damage means less surface area to burn and therefore the reaction to unplanned stimuli (e.g., bullet or fragment impact) will be less violent.
• the aging periods significantly increase the shelf-life (e.g., to 20 years or more) of the ammonium nitrate propellant composition.
• the ammonium nitrate is ground by ball milling, fluid energy milling or micropulverizing. Other grinding methods well known in the art may also be used. Thereafter, the ground ammonium nitrate is mixed with the remainder of the other components of the propellant composition, including the strengthening agent.
• a strengthening agent e.g., the second embodiment
• the ground ammonium nitrate is mixed with the remainder of the other components of the propellant composition, including the strengthening agent.
• an increase in the elasticity and the maximum stress of a propellant composition indicates that the propellant composition is less prone to cracking, etc. , and less prone to violent deflagration or premature explosion.
• propellant compositions were prepared using the components in the quantities indicated below. However, where indicated the examples are prophetic. It should be noted that in all the prophetic examples, a nitrate ester plasticizer and a cure catalyst are included where appropriate as previously explained. Further, all components in each formulation add up to a total of 100% by weight.
• Prophetic examples 9, 10, 11 and 12 indicate age-stabilized and mildly strengthened propellant compositions with a slight loss in propellant composition impulse.
• Prophetic examples 13, 14, 15 and 16 indicate age-stabilized and moderately strengthened propellant compositions with a moderate loss in propellant composition impulse.
• Prophetic examples 17, 18, 19 and 20 indicate age-stabilized and strongly strengthened propellant compositions with a significant loss in propellant composition impulse.
• Example 1 (Age-Stabilized) Chemical Component Relative Percentage by Weight
• Cellulose acetate (4.0 grams) was dissolved in 25 ml of acetone.
• AN was ground according to Example 21 without molecular sieve being added.
• Ground AN 60 grams
• RDX 36 grams
• Acetone was added as necessary to form a thick paste.
• the paste was then formed into sheets or extruded into strands or made into granules by screening while still damp.
• 7019-A was formed into sheets about 0.030 inches thick, then dried in a vacuum oven at 140°F. The sheets were then broken into smaller pieces and then screened through a 5 mesh screen.
• composition 7019-A with age-stabilization The procedure followed was the same as Example 22 except that the AN was ground with molecular sieve according to Example 21.
• Example 24 (Strengthened Propellant Composition) The same procedure as in Example 7 was followed except that the molecular sieve was omitted from the composition. The amount of binder was increased by 0.22% by weight. Otherwise the procedure followed was identical to Example 7.
• Example 7 The same procedure as in Example 7 was followed except that the strengthening agent was omitted from the composition. The amount of binder was increased by 4.0% by weight. Otherwise the procedure followed was identical to Example 7.

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