Patent Application
20080202373
The present disclosure relates to energetic compositions containing a reactive thin-film for reactive fragment munitions. More specifically, the present disclosure relates to reactive fragments based, at least in part, on reactive thin-film energetic materials dispersed in a matrix.
In the discussion that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art.
A conventional munition includes a container housing, a high explosive, and optionally, fragments. Upon detonation of the high explosive, the container is torn apart forming fragments that are accelerated outwardly. In addition, to the extent that fragments are located within the container, these internal fragments are also propelled outwardly. The “kill mechanism” of the conventional fragmentation warhead is the penetration of the fragments (usually steel) into the device or target, which is kinetic energy dependent.
Reactive fragments are used to enhance the lethality of such munitions. A reactive fragment enhances the lethality of the device by transferring additional energy into the target. Upon impact with the target reactive fragments release additional chemical or thermal energy thereby enhancing damage, and potentially improving the lethality of the munition. The reactive fragment employs both kinetic energy transfer of the accelerated fragment into the target as well as the release chemical energy stored by the fragment. Moreover, the released chemical energy can be transferred to the surroundings thermally through radiant, conductive, and/or convective heat transfer. Thus, unlike purely kinetic fragments, the effects of such reactive fragments extend beyond the trajectory thereof.
Some reactive fragments employ composite materials based on a mixture of reactive metal powders and an oxidizer suspended in an organic matrix. However, certain engineering challenges are often encountered in the development of such reactive fragments. For example, a minimum requisite amount of activation energy must be transferred to the reactive fragments in order to trigger the release of chemical energy. There has been a general lack of confidence in the ignition of such reactive fragments upon impact at velocities less than about 4000 ft/s. The reactive fragments must possess a certain amount of structural integrity in order to survive shocks encountered upon launch of the munition, but must also begin to combust upon impact with a target. Thus, such conventionally constructed reactive fragments present an engineering challenge; they favor a low launch velocity to enhance survival of the fragment upon launch, yet also benefit from higher launch velocities which are desirable for energetic initiation.
Thus, it would be advantageous to provide an improved reactive fragment which may address one or more of the above-mentioned concerns.
Relevant publications include U.S. Pat. Publication Nos. 3,961,576; 4,996,922; 5,538,795; 5,700,974; 5,912,069; 5,936,184; 6,627,013; 6,679,960; 6,736,942; 6,863,992; 2001/0046597; 2002/0069944; 2003/0164289; and 2005/0142495, the entire disclosure of each of these publications is incorporated herein by reference.
According to the present invention, there is provided a munition including, but not limited to, a reactive fragment which possesses improved and tailorable energy reactive behavior that can, for example, reduce the impact velocity necessary to initiate an energetic reaction.
According to one aspect, the present invention includes, but is not limited to, a munition comprising a reactive fragment comprising a energetic material dispersed in a binder material, the energetic material comprises a thin layered structure, the thin layered structure comprises at least one layer comprising a reducing metal or metal hydride and at least one layer comprising a metal oxide.
According to another aspect, the present invention includes, but is not limited to, a method comprising forming a energetic material comprising a thin film or thin layered structure, the structure comprises at least one layer comprising a reducing metal and at least one layer comprising a metal oxide; combining the energetic material with a binder material to form a mixture; and shaping the mixture to form a reactive fragment.
The following detailed description of preferred embodiments can be read in connection with the accompanying drawings in which like numerals designate like elements and in which:
One embodiment of a reactive fragment 10 formed according to the principles of the present invention is illustrated in
As illustrated in
The binder material 20 can be formed from any suitable material. According to one embodiment, the binder material 20 comprises a polymeric material, including, but not limited to any epoxy or a polymer containing at least one azide group. According to a further optional embodiment, the binder may comprise a thermoplastic material such as polyethylene, polypropylene, polyetherimide, polyethylene teraphthalate, and acrylonitrile butadiene styrene
In addition, the binder material 20 may optionally include one or more reinforcing elements or additives. Thus, the binder material 20 may optionally include one or more of: an organic material, an inorganic material, a metastable intermolecular compound, and/or a hydride. For example, the binder may be reinforced using organic or inorganic forms of continuous fibers, chopped fibers, a woven fibrous material, filaments, whiskers, or dispersed particulate.
Fragment 10 may contain any suitable reactive energetic material 30, which is dispersed within the binder material 20. The volumetric proportion of binder with respect to reactive materials may be in the range of about 20 to about 80%, with the reminder of the fragment being comprised of reactive energetic materials. The energetic material 30 may have any suitable morphology (i.e., powder, flake, crystal, etc.) or composition.
The energetic material 30 may comprise a material, or combination of materials, which upon reaction, release enthalpic or work-producing energy. One example of such a reaction is called a “thermite” reaction. Such reactions can be generally characterized as a reaction between a metal oxide and a reducing metal which upon reaction produces a metal, a different oxide, and heat. There are numerous possible metal oxide and reducing metals which can be utilized to form such reaction products. Suitable combinations include but are not limited to, mixtures of aluminum and copper oxide, aluminum and tungsten oxide, magnesium hydride and copper oxide, magnesium hydride and tungsten oxide, tantalum and copper oxide, titanium hydride and copper oxide, and thin films of aluminum and copper oxide. A generalized formula for the stoichiometry of this reaction can be represented as follows:
M
x
O
y
+M
z
=M
x
+M
z
O
y+Energy
wherein MxOy is any of several possible metal oxides, Mz is any of several possible reducing metals, Mx is the metal liberated from the original metal oxide, and MzOy is a new metal oxide formed by the reaction. Thus, according to the principles of the present invention, the energetic material 30 may comprise any suitable combination of metal oxide and reducing metal which as described above produces a suitable quantity of energy spontaneously upon reaction. For purposes of illustration, suitable metal oxides include: La2O3, AgO, ThO2, SrO, ZrO2, UO2, BaO, CeO2, B2O3, SiO2, V2O5, Ta2O5, NiO, Ni2O3, Cr2O3, MoO3, P2O5, SnO2, WO2, WO3, Fe3O4, MoO3, NiO, CoO, Co3O4, Sb2O3, PbO, Fe2O3, Bi2O3, MnO2, Cu2O, and CuO. For purposes of illustration, suitable reducing metals include: Al, Zr, Th, Ca, Mg, U, B, Ce, Be, Ti, Ta, Hf, and La. The reducing metal may also be in the form of an alloy or intermetallic compound of the above. For purposes of illustration, the metal oxide is an oxide of a transition metal. According to another example, the metal oxide is a copper or tungsten oxide. According to another alternative example, the reducing metal comprises aluminum or an aluminum-containing compound. By way of non-limiting example, suitable metal oxide/reducing metal pairs include: Al/MoO3; Al/Bi2O3; AlCuO; and Al/Fe2O3.
As noted above, the energetic material components 30 may have any suitable morphology. Thus, the energetic material 30 may comprise a mixture of fine powders of one or more of the above-mentioned metal oxides and one or more of the reducing metals. This mixture of powders may be dispersed in the binder 20.
Alternatively, as schematically illustrated in
The reactive fragment 10 of the present invention can be formed according to any suitable method or technique.
Generally speaking, a suitable method for forming a reactive fragment includes forming an energetic material, combining the energetic material with a binder material to form a mixture, and shaping the combined energetic material and binder material mixture to form a reactive fragment.
The energetic material can be formed according to any suitable method or technique. For example, when the energetic material is in the form of a thin film, as mentioned above, the thin-film energetic material can be formed as follows. The alternating layers of oxide and reducing metal are deposited on a substrate using a suitable technique, such as vacuum vapor deposition or magnetron sputtering. Other techniques include mechanical rolling and ball milling to produce layered structures that are structurally similar to those produce in vacuum deposition. The deposition or fabrication processes are controlled to provide the desired layer thickness, typically on the order of about 10 to about 1000 nm. The thin-film comprising the above-mentioned alternating layers is then removed from the substrate. Removal can be accomplished by a number of suitable techniques such as photoresist coated substrate lift-off, preferential dissolution of coated substrates, and thermal shock of coating and substrate to cause film delamination. According to one embodiment, the inherent strain at the interface between the substrate and the deposited thin film is such that the thin-film will flake off the substrate with minimal or no intervention.
The removed layered material is then reduced in size; preferably, in a manner such that the pieces of thin-film having a reduced size are also substantially uniform. A number of suitable techniques can be utilized to accomplish this. For example, the pieces of thin-film removed from a substrate can be worked to pass them through a screen having a desired mesh size. By way of non-limiting example, the mesh size can be 25-60 mesh. This accomplishes both objectives of reducing the size of the pieces of thin-film removed from the substrate, and rendering the size of these pieces substantially uniform.
The above-mentioned reduced-size pieces of layered film are then combined with matrix material to form a mixture. The binder material can be selected from many of the above-mentioned binder materials. This combination can be accomplished by any suitable technique, such as mixing or blending. Optionally, the pieces of thin-film and/or the binder material can be treated in a manner that functionalizes the surface(s) thereof, thereby promoting wetting of the pieces of thin-film in the matrix of binder. Such treatments are per se known in the art. For example, the particles can be coated with a material that imparts a favorable surface energy thereto. Additives or additional components can be added to the mixture. As noted above, such additives or additional components may comprise one or more of: an organic material, an inorganic material, a metastable intermolecular compound, a hydride, and/or a reinforcing agent. Suitable reinforcing agents include fibers, filaments, and dispersed particulates.
This mixture can then be shaped thereby forming a reactive fragment having a desired geometrical configuration. The fragment can be shaped by any suitable technique, such as casting, pressing, forging, cold isostatic pressing, hot isostatic pressing, etc. The pressure necessary to form the fragment being less than a pressure necessary to ignite the energetic material 30. As noted above, the reactive fragment can be provided with any suitable geometry, such as cylindrical, spherical, polygonal, or variations thereof.
There are number of potential applications for a reactive fragment formed according to principles of the present invention. As depicted in
Although in the illustrated example, the reactive fragments 10 in the explosive charge 70 are randomly combined within the warhead 50, it should be recognized at the reactive fragments 10 and the explosive charge 70 can be arranged in different ways. For example, reactive fragments and an explosive charge may be separated or segregated, and may have spacers or buffers placed between them. Such an arrangement may be advantageous when it is desired to lessen the sensitivity of the reactive fragments. That is, upon impact of the warhead 50 with an appropriate target, the energy imparted to the reactive fragments is delayed via the above noted physical separation and/or spacers or buffers. Thus, the chemical energy released upon activation of the reactive fragments can also be delayed, which may be desirable to maximize the destructive effects of the warhead upon a particular target or groups of targets.
One advantage of a reactive fragment formed according to principles of the present invention is that both the composition and/or morphology of the reactive material 30 can be used to tailor the sensitivity of the reactive fragment to impact forces. While the total chemical energy content of the reactive material is primarily a function of the quantity of the reducing metal and metal oxide constituents, the rate at which that energy is released is a function of the arrangement of the reducing metal and metal oxide relative to one another. For instance, the greater the degree of mixing between the reducing metal and metal oxide components of the energetic material, the quicker the reaction that releases thermal energy will proceed. Consider the embodiment of the thin-film 32′ depicted in
Similarly, the timing of the release of chemical energy from a thin-film formed according to the principles of the present invention can also be controlled, at least to some degree, by the selection of materials, and their location, within a thin-film. For example, in the thin-film 32′ depicted in
The ability to tailor the rate of release of thermal energy from a reactive fragment can be advantageous in the design of certain munitions. For example, in the case of a penetrating warhead containing reactive fragments, it can be desirable to maximize the release of energy from the warhead after the target has been penetrated, thereby maximizing the destructive effects of the warhead. This behavior is schematically illustrated in
One alternative munition in which the reactive fragments (10) of the present invention may be utilized (not shown) comprises a warhead designed to detonate prior to impacting the target, the reactive fragments (10) are propelled into the target and can then release the chemical energy stored therein.
Another advantage provided by the present invention is the ability to design reactive fragments which can react at lower impact velocities, for example, at impact velocities on the order of 2,000 ft/sec. or less. This is an improvement over the existing technology because: (1) it permits reduced launch velocity thereby improving the survivability of the fragment; (2) extends the reactive envelope of the fragment by allowing the fragment to travel further before it lacks the kinetic energy to ignite; and (3) opens the system design space by potentially reducing the size of the warhead.
All numbers expressing quantities of ingredients, constituents, reaction conditions, and so forth used in the specification are to be understood as being modified in all instances by the term “about”. Notwithstanding that the numerical ranges and parameters setting forth, the broad scope of the subject matter presented herein are approximations, the numerical values set forth are indicated as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective measurement techniques.
Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without departing from the spirit and scope of the invention as defined in the appended claims.
