Explosive and thermic compositions or charges – Structure or arrangement of component or product
Reexamination Certificate
1999-11-23
2002-09-24
Carone, Michael J. (Department: 3641)
Explosive and thermic compositions or charges
Structure or arrangement of component or product
C149S017000, C149S037000, C149S076000, C149S109600
Reexamination Certificate
active
06454886
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to compositions comprising metallic particles and solid oxidizer, and a method for preparing such compositions. The compositions comprise a homogeneous mixture of predetermined stoichiometry, suitable for use in a solid rocket propellant, of metallic particles and solid oxidizer wherein individual metallic particles are generally uniformly distributed throughout a solid oxidizer matrix.
BACKGROUND OF THE INVENTION
Solid rocket motor propellants are widely used in a variety of aerospace applications, such as launch vehicles for satellites and spacecraft. Solid propellants have many advantages over liquid propellants for these applications because of their good performance characteristics, ease of formulation, ease and safety of use, and the simplicity of design of the solid fueled rocket motor when compared to the liquid fueled rocket motor.
The conventional solid propellant typically consists of an organic or inorganic solid oxidizing agent, a solid metallic fuel, a liquid polymeric binder, and a curing agent for the binder. Additional components for improving the properties of the propellant, i.e., processability, curability, mechanical strength, stability, and burning characteristics, may also be present. These additives may include bonding agents, plasticizers, cure catalysts, burn rate catalysts, and other similar materials. The solid propellant is typically prepared by mechanical mixing of the oxidizer and metallic fuel particles, followed by addition of the binder and curing agent with additional mixing. The resulting mixture is then poured or vacuum cast into the motor casing and cured to a solid mass.
The solid propellant formulations most widely used today in such applications as the Space Shuttle solid rocket booster and Delta rockets contain as key ingredients aluminum (Al) particles as the metal fuel and ammonium perchlorate (AP) particles as the oxidizer. The Al and AP particles are held together by a binder, which is also a fuel, albeit one of substantially less energetic content than the metal. The most commonly used binder comprises hydroxy-terminated polybutadiene (HTPB). This particular type of propellant formulation is favored for its ease of manufacture and handling, good performance characteristics, reliability and cost-effectiveness.
A typical Al+AP solid rocket propellant formulation consists of 68 wt. % AP (trimodal particle size distribution, i.e., 24 wt. % 200 &mgr;m, 17 wt. % 20 &mgr;m, 27 wt. % 3 &mgr;m), 19 wt. % Al (30 &mgr;m average particle diameter), 12 wt. % binder (HTPB) and isophorone diisocyanate (IPDI) curing agent), and 1 wt. % burn rate catalyst (e.g., Fe2O3 powder).
The relative amounts of the components in this formulation are chemically stoichiometric. In other words, there should be just enough oxidizer molecules present in the formulation to completely react with all the fuel molecules that are present, with no excess of either oxidizer or fuel. This formulation contains one oxidizer (AP) and two distinct fuels, i.e., Al and binder. The weight ratio of AP to Al for a stoichiometric mixture, i.e., no excess oxidizer or fuel, is 42:19. The weight ratio of ammonium perchlorate to binder for a stoichiometric mixture is 26:12. These ratios are the same regardless of any other components that may be present in the mixture.
Because of their burn characteristics, conventional Al/AP propellants are most suitable for use in conjunction with a particular motor design. This design is the hollow core or center perforated (CP) core motor design in which the propellant grain is formed with its outer surface bonded to the inside of the rocket motor's casing with a hollow core extending through most or all of the length of the grain. The burning front progresses outwardly from the core to the case. This motor design is bar far the most common design for solid fuel motors. One example of a current application utilizing this design is the Space Shuttle, which uses solid motors which are 150 ft. long and 12 ft. in diameter with a 4 ft. hollow core.
The propellant grain in a CP design must have substantial structural integrity to keep the grain intact during operation. A binder is therefore used to “glue” the particulate components of the propellant together. During the initial mixing of the propellant, the percentage of the binder, initially in the form of a liquid resin, is high enough to maintain a relatively low viscosity, such that the propellant is in a slurry form, allowing the propellant mixture to be poured or injected into the motor casing. A mandrel is placed in the middle of the motor casing to create the hollow core (typically before the propellant is poured into the core) and is removed once the propellant has cured.
Propellants comprising a metal fuel in combination with a solid oxidizer may be used in other applications outside of aerospace, including gas generators. Solid propellants are also used in launch vehicles, e.g., NASA rockets, Space Shuttle, French Ariane rockets. Virtually all launch vehicles use a combination of liquid fuel motors with solid fuel boosters. Both the Delta III and the Space Shuttle are examples having combined liquid and solid motors. The Delta rocket has a main liquid motor with nine smaller strap-on solid boosters, while the shuttle has three onboard liquid motors with two strap-on solid boosters.
Although enormous innovations have occurred in guidance, electronics and virtually every part of spacecraft to date, the propulsion systems have remained essentially the same for decades. Boeing's Delta III, introduced in 1998, utilizes a liquid engine that was designed in the 1960's and is fueled by kerosene and oxidized by liquid oxygen. The solid boosters were designed in 1961 and are virtually unchanged since then, except for an epoxy motor casing. Additionally, over the past decade, almost every system on the Shuttle has been replaced or upgraded, except for its propellant. It is therefore desirable to provide a novel solid rocket propellant that affords superior performance to the conventional propellants in current use today.
SUMMARY OF THE INVENTION
In accordance with this invention, it has been found that a composition comprising a substantially homogeneous mixture of a metallic substance and a solid oxidizer can be prepared, wherein the metallic substance is generally uniformly distributed in the form of discrete particles throughout a matrix of solid oxidizer. Other embodiments include utilizing aluminum as the metallic substance, ammonium perchlorate as the solid oxidizer, and metallic particles less than about one micron in diameter. In a preferred embodiment the metallic substance and oxidizer are present in stoichiometric amounts.
In one embodiment of this invention, the mixture of metallic particles and solid oxidizer is prepared by a method that involves dissolving the oxidizer in a suitable solvent, mixing the metallic particles with the solution while agitating the solution to ensure a generally uniform dispersion, removing the solvent, and recovering a powder comprising individual metallic particles generally uniformly distributed throughout a solid oxidizer matrix. The solvent is removed so as to preserve the relative distribution of the metallic particles in the oxidizer matrix.
In one embodiment of this invention, freeze drying used to remove the solvent. The solution containing the metallic particles is rapidly frozen, then the solvent is removed by sublimation under vacuum conditions. Another embodiment utilizes spray drying to remove the solvent.
A further embodiment of this invention is to provide a composition wherein the solid oxidizer and the portion of the metallic substance capable of undergoing an oxidation reaction are present in substantially stoichiometric amounts.
A further embodiment of this invention is to provide a composition comprising a homogeneous mixture of metallic particles and solid oxidizer of a pre-selected stoichiometry, wherein the metallic particles comprise aluminum particles less than about one
Martin Joe A.
Welch Larry H.
Baker Aileen J.
Carone Michael J.
Knobbe Martens Olson & Bear LLP
Technanogy, LLC
LandOfFree
Composition and method for preparing oxidizer matrix... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Composition and method for preparing oxidizer matrix..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Composition and method for preparing oxidizer matrix... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2914118