Micro Detonator and Projectile Including a Micro Detonator

This application claims the benefit of U.S. provisional patent application Ser. No. 63/622,847, which was filed on Jan. 19, 2024, and entitled “Micro Detonator and Projectile Including a Micro Detonator.”

The present invention relates to micro detonators. More specifically, a micro detonator made from a layered thermite composite is provided. A projectile using the micro detonator is also provided.

Detonators for various explosives and munitions must be capable of providing both an elevated temperature and a mechanical shock in order to initiate detonation. This mechanical shock is necessary because detonation propagates supersonically through a material in the form of a shockwave. Providing only an elevated temperature without the mechanical shock results in ignition or deflagration, which propagates thermally at a subsonic speed, and achieves a very different result. Presently available detonators rely on primary explosives to achieve both the required temperature and the required mechanical shock. Presently available detonators have a minimum size which limits their application to smaller devices. For example, presently available detonators are insufficiently small for use within small projectiles such as bullets which are utilized within small arms.

Thermite can be used to create particularly small structures, particularly when using techniques which have been developed by the present inventors. However, previous thermite structures were only capable of ignition. The lack of susceptibility of thermite to mechanical impact has been found to be particularly desirable in multiple applications, providing an ignitable material which can be safely handled with relative ease. Despite the typical lack of sensitivity to mechanical initiation, the present inventors have developed thermite structures which can be initiated through mechanical ignition. Examples include U.S. Pat. No. 10,882,799, which was issued to K. R. Coffey et al. on Jan. 5, 2021, and U.S. Pat. No. 11,650,037, which was issued to D. Yates on May 16, 2023, both of which disclose primers for firearm cartridges which can be initiated through a mechanical impact from a firing pin. The entire disclosure of each of these references is expressly incorporated herein.

Mechanical ignition was achieved in part by manufacturing techniques which resist the formation of a continuous reducing metal oxide at the interface between metal oxide layers and reducing metal layers within the thermite structure.

Energy density is also affected by the amount of reducing metal oxide present. In any thermite structure, increasing the surface area of the metal oxide and reducing metal which is available for immediate reaction increases the reaction speed. However, with prior art thermite, increasing the surface area relative to the amount of each material present also increases the ratio of reducing metal oxide to reactants, reducing the energy density.

Accordingly, there is a need for a detonator having a significantly reduced size as compared to prior art detonators, and which is capable of providing both an elevated temperature and a mechanical shock. There is a further need to develop thermite structures which are capable of providing this mechanical shock in order to provide micro detonators having a size which is smaller than conventional detonators, and useable in applications wherein a conventional detonator would be too large.

The above needs are met by a micro detonator. The micro detonator comprises a substrate having a first side and a second side opposite the first side. The micro detonator also comprises alternating layers of metal oxide and reducing metal deposited upon the first side of the substrate. The alternating layers of metal oxide and reducing metal include a gradient interface layer disposed between each layer of reducing metal and each adjacent layer of metal oxide.

The above needs are also met by a projectile. The projectile defines a front end and a back end. The projectile comprises a burnable material forming at least a portion of the body of the projectile. The projectile also includes a penetrator disposed within the body of the projectile. A micro detonator is disposed forward of the penetrator, the micro detonator comprises a substrate having a first side and a second side opposite the first side. The micro detonator also comprises alternating layers of metal oxide and reducing metal deposited upon the first side of the substrate. The alternating layers of metal oxide and reducing metal include a gradient interface layer disposed between each layer of reducing metal and each adjacent layer of metal oxide.

These and other aspects of the invention will become more apparent through the following description and drawings.

Like reference characters denote like elements throughout the drawings.

Referring to, a layered thermite compositeis shown. The layered thermite composite is particularly useful as a portion of a detonator, as well as for other uses. The layered thermite compositeis deposited upon a substrate.

The nature of the substratemay depend on the intended means of initiation. A micro detonator having a layered thermite compositemay be initiated either electrically or mechanically. Referring to, if electrical initiation is intended, then the substrateor a portion thereof may be electrically conductive. Some examples of the micro detonatorA may include a substrateA having a pair of conductive sectionsseparated by an electrically resistive section, so that a voltage applied to the opposing conductive sectionsresults in current flow through the thermite. Other examples may apply a voltage through a contact disposed on the substrateA and another contact disposed elsewhere on the micro detonatorA to induce current flow within the thermite. Other examples may include opposing electrical contact points within the thermitefor the application of an electrical voltage therethrough. If the electrical connection does not depend on the substrate, then any suitable material may be used for the substrate.

Referring to, if the thermite compositeis within a detonatorwhich is intended for mechanical initiation, then the substrateB in the illustrated example is a malleable disk, made from a material such as brass, copper, soft steel, and/or stainless steel, having a deposition surfaceupon which the layered thermite coatingis deposited, and a rear surface. The substrateis a sufficiently thin and malleable so that a firing pin strike to the rear surfacewill ignite the layered thermite coating, but is sufficiently thick for ease of manufacturing the detonator. A preferred substrate thickness is about 0.005 inch to about 0.1 inch, and is more preferably about 0.01 to about 0.025 inch.

The layered thermite coatingincludes alternating layers of metal oxideand reducing metal(with only a small number of layers illustrated for clarity). Examples of metal oxidesinclude LaO, AgO, ThO, SrO, ZrO, UO, BaO, CeO, BO, SiO, VO, TaO, NiO, NiO, CrO, MoO, PO, SnO, WO, WO, FeO, CoO, CoO, SbO, PbO, FeO, BiO, MnO, CuO, and CuO. Example reducing metalsinclude Al, Zr, Th, Ca, Mg, U, B, Ce, Be, Ti, Ta, Hf, and La.

The thickness of each metal oxide layerand reducing metal layerare determined to ensure that the proportions of metal oxideand reducing metalare such so that both will be substantially consumed by the exothermic reaction. As one example, in the case of a metal oxide layermade from CuO and reducing metal layermade from Al (), the chemical reaction is 3CuO+2Al→3Cu+AlO+heat. The reaction therefore requires 3 moles of CuO, weighing 79.5454 grams/mole, for every 2 moles of Al, weighing 26.98154 grams/mole. CuO has a density of 6.315 g/cm, and aluminum has a density of 2.70 g/cm. Therefore, the volume of CuO required for every 3 moles is 37.788 cm. Similarly, the volume of Al required for every 2 moles is 19.986 cm. Therefore, within the illustrated example of a composite layer, the metal oxideis about twice as thick as the reducing metal. In some examples, each composite layeris about 20 nm to about 100 nm thick.

As another example, in the case of a metal oxide layermade from CuO and reducing metal layermade from Mg, the chemical reaction is CuO+Mg→Cu+MgO+heat. The reaction therefore requires one mole of CuO, weighing 79.5454 grams/mole, for every one mole of Mg, weighing 24.305 grams/mole. CuO has a density of 6.315 g/cm, and magnesium has a density of 1.74 g/cm. Therefore, the volume of CuO required for every mole is 12.596 cm. Similarly, the volume of Mg required for every mole is 13.968 cm. Therefore, within this example, each layer of metal oxideis about the same thickness or slightly thinner than the corresponding layer of reducing metal. If other metal oxides and reducing metals are selected, then the relative thickness of the metal oxide and reducing metal can be similarly determined.

Referring to, the illustrated example of the thermite structurealso includes a gradient interface layerbetween each reducing metal layerand adjacent metal oxide layer. As used herein, a gradient interface layeris an interface between a reducing metal layerand a metal oxide layer, with the interface layercontaining metal oxide, reducing metal, and reducing metal oxide, all of which are at least partially intermixed to form a gradient structure within the interface layer. (Due to the intermixing of materials at the interface layer, reference charactersandrefer to metal oxide layers and reducing metal layers, respectively, while reference charactersandrefer to metal oxide and reducing metal, respectively, regardless of whether those materials are within a layeror.) Although the approximate thickness of the gradient interface layeris about 2 nm to about 5 nm, the gradient interface layerdoes not have precise boundaries. Instead, the amount of each material present in and around the gradient interface layerwill be a gradient with respect to proximity to either the reducing metal layeror metal oxide layer. As shown in the example of, moving from the bottom of the image to the top, the material transitions from aluminumwithin the reducing metal layer, to a combination of aluminum, aluminum oxide, and cupric oxideas the interface layerwithin the approximate center of the image is reached. Continuing upward in the image, the material again transitions from the mixture of aluminum, aluminum oxide, and cupric oxidein the interface layerto simply cupric oxide in the metal oxide layer.

A similar gradient pattern is shown in the examples of, withsimply showing the detail of box A in.focuses on the oxygenpresent within Box A. In, the aluminum layercontains no oxygen, but oxygen in relatively high concentration (appearing as pink) is present above the aluminumwithin the interface. Cupric oxideis present above the oxygenin relatively high concentration within the layeras well as the layer.focuses on aluminum(shown in green), showing the transition between pure aluminum within the layer, to a mixture of aluminumand other elements in the interface, and no aluminumin the layer. Similarly,focuses on the copper(shown in red), showing no copperin the layer, some copperin the interface, and a large percentage of copperin the layer. The atomic percent of each element within box A ofis also graphically illustrated in, with the left sideofcorresponding to the bottom of the images of, and the right sideofcorresponding to the top of the images-D. Lineshows aluminum, lineshows oxygen, and lineshows copper. As shown inthe atomic percent aluminum is maximized on the left side, decreasing towards zero at some position within the layer. The atomic percentage of oxygen (within aluminum oxide and cupric oxide) is very small in the layer, but becomes high in the layer, and decreases to a stable percentage within the layer. Copper (in the form of cupric oxide) is absent from the layer, but increases as the layeris entered, increasing throughout the layeruntil stabilizing in the layer. Although other examples of gradient interface layers will follow similar patterns, variation will occur in the location of the transitions, atomic percent of each element at various locations, and the overall thickness of the gradient interface layer.

The interface layerforms between completion of depositing one layer of reducing metalor metal oxideand the beginning of deposition of the next layer of reducing metalor metal oxide. Prior art interface layers would form as the surface of the reducing metal oxidized from exposure to atmospheric oxygen or water vapor, and were thus composed of reducing metal oxide. The gradient interface layer described herein is formed by a process which permits rapid transitions from depositing one type of layer to depositing the other type of layer, permitting a limited amount of reducing metal oxide to form along with reducing metal and metal oxide rather than as pure reducing metal oxide.

A layered thermite compositecan be made using a deposition system using a rotating drum. Such systems are described in the following patents or published applications, the entire disclosure of all of which are expressly incorporated herein by reference: US 2024/0361113, which was invented by D. Yates and published on Oct. 31, 2024, U.S. Pat. No. 8,758,580, which was issued to R. De Vito on Jun. 24, 2014; U.S. Pat. No. 5,897,519, which was issued to J. W. Seeser et al. on Mar. 9, 1999; and EP 0,328,257, which was invented by M. A. Scobey et al. and published on Aug. 16, 1989. The use of a rotating drum system permits the substrates to be rapidly transferred between different chambers for deposition of different layers made from different materials. In one example, some chamber(s) will be used to deposit the reducing metal, other chamber(s) will be used to deposit the metal oxide, and still other chamber(s) will be used to deposit the carbide-containing ceramic (described below). In a four chamber system, other chambers may be used to deposit the adhesion layers above and below the carbide-containing ceramic. One example may utilize between two and four chambers, with two targets per chamber. The atmospheric conditions within each chamber are maintained, and isolated from other portions of the system, by baffles which extend close to the drum while maintaining separation from the substrates. Substrates may thereby be moved between chambers by rotating the drum upon which the substrates are located while maintaining the correct pressure and atmospheric conditions of each chamber throughout the process of depositing multiple layers. Additionally, the pressure of an inert gas, for example, argon in the chamber utilized to deposit reducing metal may be greater than the pressure in the chamber utilized to deposit metal oxide, thus resisting the entry of oxygen into the reducing metal chamber. The need to pump down each chamber between layers of different material is thus avoided, speeding and simplifying the deposition process.

Prior art manufacturing methods typically required several minutes of deposition time for each of the reducing metal or metal oxide layers, with multiple minutes of additional time required to switch from depositing one material to depositing the other material. The above-described process permits each layer to be deposited in a time of, for example, about 15 seconds. Transitioning from one chamber to the next chamber can be accomplished in a time of, for example, about 2 seconds. The manufacturing process is thus significantly faster, as well as providing very little time for interface layers having undesirable characteristics to form. Without being bound by any particular theory, it is believed that the oxygen which reacts with the reducing metal during transitions between chambers is atmospheric oxygen and/or oxygen from the deposition of the metal oxide rather than oxygen from water vapor. Again without being bound by any particular theory, it is believed that interface layers formed by reactions with adsorbed water vapor are more likely to grow over time through additional reaction with the reducing metal. Interfaces formed by reactions with atmospheric oxygen and/or oxygen from the deposition of metal oxide are unlikely to grow once the interface is covered by the next layer of reactant. Because the gradient interface layerwill not grow over time, and because the gradient interface region includes not only reducing metal oxide but also metal oxide and reducing metal, the metal oxide and reducing metal remain in sufficiently close proximity to each other so that they can be ignited electrically or mechanically when desired.

Referring back to, a passivation layercovers the layered thermite coating, protecting the metal oxide and reducing metal within the layered thermite coating. One example of a passivation layeris silicon nitride. Alternative passivation layerscan be made from reactive metals that self-passivate, for example, aluminum or chromium. When oxide forms on the surface of such metals, the oxide is self-sealing, so that oxide formation stops once the exposed surface of the metal is completely covered with oxide.

illustrates a detonatormade by stacking a pair of detonators,together. Each of the detonators,is of the same design as the detonatorof. The number of stacked detonators can be greater than two, and in some examples may be four or more stacked detonators. In the example of a detonator, when the substrateB of the detonatoris struck to initiate detonation, this detonation strikes the substrateB of the detonator, initiating the detonator. The use of a stack of detonators has been found to increase the effectiveness of the detonator.

illustrates an example of a detonatorutilizing one or more carbide containing ceramic layerwithin the stacked layers of metal oxide and reducing metal. The carbide-containing ceramic layer(s)are disposed within the thermite layers. In the illustrated examples, one carbide-containing ceramic layeris disposed about ⅓ of the distance to the top of the thermite coating. In other examples, a carbide-containing ceramic layermay be located elsewhere in the thermite coating, such as a lower portion, a central portion, the top, the bottom, or elsewhere in the upper portion of the thermite coating. Some examples may include a plurality of layers carbide-containing ceramic layerswhich are located in different positions throughout the thermite coating. The thickness of the carbide-containing ceramic layer(s)is thicker than the metal oxide or reducing metal layers, and in the illustrated example is between about 100 nm and about 2 μm thick. Other examples of the carbide-containing ceramic layer(s)may be between about 500 nm and about 1 μm thick.

Carbide-containing ceramics are selected for their propensity to serve as gas producers when ignited by ignition of the adjacent reducing metal and metal oxide. Examples include ceramics such as zirconium carbide, titanium carbide, or silicon carbide, as well as aluminum carbide (which is a metal-ceramic composite but will be considered to be a carbide-containing ceramic herein), and combinations thereof. If more than one carbide-containing ceramic layer is present, then the different carbide-containing ceramic layers may be composed of the same carbide-containing ceramic, or different carbide-containing ceramics. Ignition of these carbides (or other suitable carbides) will result in the formation of carbon dioxide through the reaction with oxygen from the cupric oxide. This gas production will aid in increasing the mechanical forces generated by the detonator.

Some examples of the thermite compositionmay include an adhesion layerabove and below each carbide-containing ceramic layer. In the illustrated example, the adhesion layersare made from titanium or chromium. Nickel may also be used as an adhesion layer in some examples. The illustrated examples of the adhesion layersare about 5 nm to about 10 nm thick.

The thermite structurecan be used within a micro detonator having a size which is significantly smaller than conventional detonators. Referring to, an example of a detonatorA,(below) can have a width W as small as about 2 mm.

Some examples of the detonatorA,may be used as standalone devices. Other examples of the detonatorA,may be used within projectiles to initiate an ignitable or detonatable material within the projectile. Referring to, the illustrated example of a projectileis a bullet which is intended to be discharged from a firearm. As used herein, bullet shall be defined as including any projectile that is fired from a firearm, including rifle bullets, handgun bullets, shotgun slugs, bullets fired by machine guns, and bullets that are propelled by means other than smokeless powder. As used herein, a firearm is defined as “A personal weapon that uses a pressure-producing propellant to propel a projectile,” which is a modified version of a definition from the American Heritage Dictionary. Although the example described and illustrated below is a bullet, a detonatormay be used with other projectiles.

Referring to, each bulletincludes a copper jacketcovering the baseand extending from the basealong the sidesto a pointthat is relatively close to (but does not necessarily correspond exactly with) the beginning of the ogivein a manner that will be familiar to those skilled in the art of bullet construction. A firing pinis located within the baseof the jacket. The firing pinis made from a hard, dense material, for example, tungsten carbide or tantalum. Each firing pinincludes a basewhich in the illustrated examples is flat, and a pointwhich in the illustrated examples is located along the longitudinal axis A of the bullet. Each firing pinis itself centered along each longitudinal axis A, being held in place by a firing pin retainerwhich in some examples is made from a dense, soft material such as lead. In the illustrated example, the sidesare tapered so that the firing pinis narrowed towards the base. A detonatoris disposed in front of the pointof each firing pin.

A second charge, which in the illustrated example is made from high explosive, occupies a portion of the space within the bullet above the detonator. The illustrated example of an explosive chargeincludes a top endhaving a concave configuration, which in the illustrated example has the configuration of an inverted cone. This shape directs the blast from the chargeforward in a manner which is well known to those skilled in the art of shape charges, enhancing the penetration of the detonation into the target.

Each of the bulletsincludes a shape charge linercovering the inverted cone-shaped front endof the charge. In the illustrated examples, the charge lineris made from tantalum. Some examples of the bulletalso include a sleeveextending along the side outer surfaceof each chargeas well as over the back endof the charge. Some examples of the sleeveare made from a hardened steel or tantalum. Each bulletalso includes an ogive/body pieceforming the ogiveof each bullet, as well as extending between the sleeveand jacketalong substantially the entire charge. Some examples of the ogive/body pieceare made from tungsten carbide or hardened steel. This construction leaves a hollow spacebetween the charge linerand ogive.

The present invention therefore provides a micro detonator which is useful in applications wherein a conventional detonator is too large. The micro detonator is made from thermite which has been deposited in a manner which creates a gradient interface layer between the alternating layers of metal oxide and reducing metal. The thickness of the gradient interface layer and any tendency of the gradient interface layer to grow through additional oxidation of the reducing metal are resisted, thereby maximizing energy density even as the thickness of individual metal oxide and reducing metal layers are reduced. When the thermite reaction is initiated, this reaction can therefore propagate mechanically as well as thermally. The increased reaction speed combined with the increased energy density generates sufficient mechanical impact to detonate rather than ignite a conventional high explosive. The micro detonator can be utilized within projectiles as small as conventional bullets for firearms to initiate a second charge within the projectile.

A variety of modifications to the above-described embodiments will be apparent to those skilled in the art from this disclosure. Thus, the invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention. The appended claims, rather than to the foregoing specification, should be referenced to indicate the scope of the invention.