Patent Grant
6955732
The invention disclosed herein relates to explosive formulations with improved combustion efficiency. More particularly, the explosive formulations of the invention are capable of maintaining a relatively high blast pressure in an oxygen poor environment, such as a tunnel or other confined spaces.
There is a long history of studying blast explosives, reactive metals and associated metal combustion technologies. The success of the development of Solid Fuel-Air-Explosive (SFAE) has been demonstrated providing 30–40% increased internal blast over a conventional explosive. SFAE is a singular event with combined mixing and initiation of the reaction. In confined spaces, transition to full detonation is not required for enhanced blast, if the solid fuel is ignited early in the dispersion process. A series of reflective shock waves generated by the detonation mixes the hot detonation gases with metal particles and compresses the metal particles at the same time. These actions provide the chemical kinetic support to maintain a hot environment, causing more metal to ignite and burn. This late time metal combustion process produces a significant pressure rise over a longer time duration (10–50 msec). This is a phase generally referred to as after burning or late-time impulse which can occur outside of where the detonation occurred, resulting in more widespread damage.
Aluminum has been used as the metal of choice, due to high heat of combustion, cost and availability. Billets of SFAE made with Al, provide savings in volume with increased fuel mass for blast performance. However, combustion efficiency has been an issue, especially in the event that the fuel content (35–60 wt %) is high with respect to the total weight of explosive composition. Poor combustion efficiency is often observed in many of the thermobaric warhead tests, which causes the severe ineffectiveness of the weapon. This is due to the high ignition temperature, 2200 K, typically required for proper combustion of AL. During the burning of Al, heat is produced and aluminum oxide is formed. However, the burning of all the metal to completion requires maintaining the hot environment. This environment can be best maintained if it is supported chemically by the combustion of other oxidizer species (i.e. AP or nitrate ester liquid, IPN (isopropyl nitrate)) that are much easier to ignite (AP has an ignition temperature of 250 C and IPN has a low flash point of 22 C). The combustion of these additives produce the hot gases to support the burning of metal, thus 100% combustion efficiency can be obtained. Metal composites, metal and oxidizer combined granules, produced from coating of particles with a binder, can be made easily with techniques well known in the art.
Another combined approach to further improve the metal combustion efficiency is to use a more reactive metal as part of or as the entire metal fuel component. New reactive metal materials such as nano-sized aluminum to increase the reactivity, titanium and boron alloy to increase the thermal output, and magnesium/aluminum alloy to lower the ignition temperature are among the most promising approaches to increase the metal combustion efficiency. More powerful explosives such as CL-20 that are capable of raising the detonation pressure and temperature are also extremely beneficial.
There exists a need in the art for new explosive formulations with new reactive metal and metal composites to have 50–100% higher blast energy than those by the baseline composition such as Tritonal or PBX N109. Further, the new formulations coupled with new warhead designs will have the potential to form one of the most powerful thermobaric warheads, when compared to the weapon systems that currently exist.
The present invention relates to a metal composite that combines a binder, a reactive metal and an oxidizer. In an embodiment of the present invention, a plasticizer and a catalyst are also included. In yet another embodiment of the present invention, the binder includes polymers capable of coating the reactive metal and oxidizer powder. Two embodiments include methods to produce the compositions of the present invention:
An embodiment of the present invention discloses a metal composite comprising about 60 to about 96 weight % of at least one reactive metal, about 4 to about 10 weight % of at least one binder and about 0 to about 36 weight % of an oxidizer. The reactive metal includes, but not limited to at least one of nano-sized metal particles, metastable mechanical alloy and any combination thereof. More specifically, the reactive metal includes, but not limited to at least one of nano-sized aluminum, nano-sized boron and nano-sized titanium, nano-sized magnesium, Al—Mg, Al—Mg—H, B—Mg, Al—B and Ti—B. The binder includes, but not limited to at least one of copolymer of vinylidine fluoride hexafluoropropylene, nitrocellulose, GAP and Zeon.
Embodiments of the present invention relating to castable compositions disclose an explosive having an annular construction. The explosive includes a cylindrical shell of solid fuel air explosive surrounding a cylindrically shaped high explosive. In other embodiments the solid fuel air explosive includes at least one of reactive metal and metal composite. The metal composite including about 60 to about 80 weight % of at least one reactive metal, about 4 to about 8 weight % of at least one binder and about 0 to about 36 weight % of an oxidizer. The reactive metal includes, but is not limited to at least one of nano-sized metal particles, metastable mechanical alloy and any combination thereof. More specifically, the reactive metal includes at least one of nano-sized aluminum, nano-sized boron and nano-sized titanium, nano-sized magnesium, Al—Mg, Al—Mg—H, B—Mg, Al—B and Ti—B, H-2 (2 μm spherical aluminum) and H-5 (5 μm spherical aluminum). The oxidizer includes, but is not limited to at least one of ammonium perchlorate, ammonium dinitramide and ammonium nitrate.
The present invention is to provide an explosive with enhanced combustion efficiently capable of sustaining a high pressure over a period of time in a confined environment with a limited oxygen supply.
The present invention is to provide an explosive capable of maintaining a relatively high pressure (30–60 psi) for up to 50 msec in an environment characterized with high rate of thermal quenching (cold air), this environment has a profound adverse effect for metal combustion, which is the main cause for combustion efficiency.
Additionally, embodiments the present invention is to provide an explosive with increased reactivity, increased thermal output and lower ignition temperatures.
Embodiments the present invention are also to provide thermobaric explosive formulations with reactive metals and metal composites which have a 100% higher blast energy than compositions such as Tritonal and PBX N109.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not to be viewed as being restrictive of the present invention, as claimed. These and other objects, features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments and the appended claims.
The invention disclosed herein relates to an explosive capable of enhanced combustion efficiently capable of sustaining a high pressure over a period of time in a confined environment, such as an air tight room or a cave, where oxygen may be in limited supply.
The reactive metal used in an embodiment of the present invention includes nano-sized metal particles, metastable mechanical alloys and any combination thereof. The metal fuel in these explosive formulations of the present invention incorporates nano-sized aluminum, including, for example, Alex®, boron, manganese and titanium, those having a size of about 20–500 nm. The metastable mechanical alloys include Al—Mg, Al—Mg—H, B—Mg, Al—B, Ti—B, H-2 and H-5 made from high energy milling. The metastable mechanical alloys include nano-crystalline metastable phases with particle sizes of about 1–50 μm. The reactive metal used also includes Ti, B or Mg. In another embodiment of the present invention, the reactive metal includes about 60–80 weight % of the total metal composite, or at about 74 weight %.
The thermobaric explosive formulations of the present invention incorporates high energy explosive material including, but not limited to hexa-nitro-hexa-aza-isowurtzitane (CL-20), cyclotrimethylenetrinitramine (RDX) and cyclotetramethylene tetranitramine (HMX). The powerful oxidizers, including ammonium perchlorate (AP), ammonium dinitramide (ADN), ammonium nitrate (AN) and barium nitrate are selected to be used in the metal composite or castable PBX's. Another embodiment of the present invention uses ammonium perchlorate (AP) particles, or about 11–100 μm in size. The oxidizer includes about 12–36 weight % of the total metal composites, or at about 20 weight %.
The binder includes polymers capable of coating the reactive metal and high explosive powder. The binder includes, but is not limited to at least one of copolymer of vinylidine fluoride hexafluoropropylene, including Viton®, nitrocellulose, glycidyl azide polymer (GAP) or an acrylic acid ester polymer, including Zeon®. In another embodiment of the present invention, the binder includes about 4–6 weight % of the total metal composites, or at about 4 weight % for the total metal composite. The binders used for castable PBX's include, for example, hydroxy-terminated polybutadienes (HTPB), hydroxy-terminated polycaprolactone (PCP), hydroxy-terminated polyesters, hydroxy-terminated polyethers (HTPE), Glycidyl azide polymer (GAP), trifluoroethyl-terminated poly (1-cyano-1-difluoramino)-polyethylene glycol (PCDE) and any combination thereof. Typically, 5 to 7 weight % is used for castable PBX embodiment.
In other embodiments, a plasticizer and a burn rate catalyst are added. The plasticizer includes bis-(2,2-ro-2-fluoroethyl) formal (FEFO). However, other plasticizers utilized, include energetic plasticizers selected from those compounds, which are liquids and contain energetic moieties or groups in their chemical structures. These moieties include, but not limited to nitro or nitrate ester groups, azido groups, or nitramino groups. Suitable plasticizers include TEGDN (triethyleneglycol dinitrate), or Butyl NENA (n-butyl-2-nitratoethyl-nitramine). Other suitable plasticizers include DEGDN (diethyleneglycol dinitrate), TMETN (trimethylolethane trinitrate), and BTTN (butanetriol trinitrate). These plasticizers are used independently or in combination. Other fluoramino groups including bis-(2,2-ro-2-fluoroethyl) formal (FEFO) and bis-[2,2-bis(difluoramino)-5,5-dinitro-5-fluoropentoxy]methane (SYFO) could also incorporated into the formulations. In other embodiments of the present invention, the plasticizer include about 4 weight % of the formulations.
Iron oxide (Fe2O3), nano-sized is a suitable burn rate catalyst and is optional to exotic burn rate catalysts including superfine iron oxide, chromic oxide, catocene, or carboranes. In other embodiments aluminum oxide is also used. In embodiments of the present invention, the burn rate catalyst comprises about 1 weight % of the total metal composites. Tables I and II disclose a number of the formulations of the present invention.
The novel thermobaric explosives of the present invention are spherical particles of composite material containing high explosive, oxidizer, reactive metal and binder. Plasticizer and burn rate catalyst are added to manipulate performance. A method of making the novel thermobaric explosives described herein is disclosed in U.S. Pat. No. 5,750,921 issued to Chan et al. on May 12, 1998, hereby incorporated herein by reference.
In an embodiment of the present invention, a solid fuel-air explosive annular construction is used as shown in
Embodiments of the compositions of the present invention are formed into a unicharge. The unicharge construct uses spherical aluminum as the reactive metal. Table II discloses ranges of ingredients for the formulations of the unicharge embodiment. As noted previously, a plasticizer and/or a burn rate catalyst are added to the formulations to tailor the formulations to particular needs. Although specific binders are listed, any of the binders previously noted are also used in the formulations. Similarly, any of the oxidizers previously noted are also substituted for AP and any of the high explosives previously noted are substituted for HMX.
It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and the scope of the appended claims.
This is a divisional application, claiming the benefit of, parent application Ser. No. 10/326,958 filed on Dec. 23, 2002, whereby the entire disclosure of which is incorporated hereby reference.
The invention described herein may be manufactured and used by or for the government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
| Number | Name | Date | Kind |
|---|---|---|---|
| 3804683 | Baldwin et al. | Apr 1974 | A |
| 5750921 | Chan et al. | May 1998 | A |
| 5996501 | Spencer et al. | Dec 1999 | A |
| 6503350 | Martin et al. | Jan 2003 | B2 |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10326958 | Dec 2002 | US |
| Child | 10779545 | US |
