US20250305803A1

US20250305803A1 - Micro detonator and projectile including a micro detonator

Info

Publication number: US20250305803A1
Application number: US19/033,429
Authority: US
Inventors: Timothy Mohler; Daniel Yates
Original assignee: Spectre Primer Technologies Inc
Current assignee: Spectre Primer Technologies Inc
Priority date: 2024-01-19
Filing date: 2025-01-21
Publication date: 2025-10-02

Abstract

A micro detonator is provided. The micro detonator is made from thermite consisting of layered metal oxide and reducing metal, separated by gradient interface layers. Oxidation of the reducing metal is resisted during and after deposition of the thermite layers until the exothermic reaction is initiated. Layer thickness can thus be reduced without significantly reducing energy density, resulting in rapid, mechanical propagation of the reaction. The micro detonator can be used as a standalone device or within a projectile containing a second charge.

Description

CROSS REFERENCE TO RELATED APPLICATION

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.”

TECHNICAL FIELD

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.

BACKGROUND INFORMATION

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.

SUMMARY

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.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a sectional side elevational view of an example of a layered thermite composite according to the present invention.

FIG. 2 is a cross-sectional side elevational view of an example of a detonator utilizing a layered thermite composite of FIG. 1 .

FIG. 3 is a cross-sectional side elevational view of another example of a detonator utilizing a layered thermite composite of FIG. 1 .

FIG. 4 is a sectional, side elevational view of a gradient interface layer between a metal oxide layer and a reducing metal layer of the thermite structure of FIG. 1 .

FIG. 5A is a sectional, side elevational view of the box A in FIG. 5 .

FIG. 5B is a sectional, side elevational view of the box A in FIG. 5 , showing the oxygen content within the box A of FIG. 5 .

FIG. 5C is a sectional, side elevational view of the box A in FIG. 5 , showing the aluminum content within the box A of FIG. 5 .

FIG. 5D is a sectional side elevational view of the box A in FIG. 5 , showing the copper content within the box A of FIG. 5 .

FIG. 6 is a graph showing the atomic percent of aluminum, oxygen, and copper with respect to position within the gradient interface of FIGS. 5-6D.

FIG. 7 is a cross-sectional side elevational view of a projectile utilizing a detonator of FIG. 5 .

FIG. 8 is a cross sectional side elevational view of a detonator made by stacking two or more detonators of FIG. 3 .

FIG. 9 is a cross sectional side elevational view of another example of a detonatr.

Like reference characters denote like elements throughout the drawings.

DETAILED DESCRIPTION

Referring to FIGS. 1-3 , a layered thermite composite 10 is shown. The layered thermite composite is particularly useful as a portion of a detonator, as well as for other uses. The layered thermite composite 10 is deposited upon a substrate 12.
The nature of the substrate 12 may depend on the intended means of initiation. A micro detonator having a layered thermite composite 10 may be initiated either electrically or mechanically. Referring to FIG. 2 , if electrical initiation is intended, then the substrate 12 or a portion thereof may be electrically conductive. Some examples of the micro detonator 11A may include a substrate 12A having a pair of conductive sections 13 separated by an electrically resistive section 15, so that a voltage applied to the opposing conductive sections 13 results in current flow through the thermite 10. Other examples may apply a voltage through a contact disposed on the substrate 12A and another contact disposed elsewhere on the micro detonator 11A to induce current flow within the thermite. Other examples may include opposing electrical contact points within the thermite 10 for the application of an electrical voltage therethrough. If the electrical connection does not depend on the substrate 12, then any suitable material may be used for the substrate 12.
Referring to FIG. 3 , if the thermite composite 10 is within a detonator 42 which is intended for mechanical initiation, then the substrate 12B 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 surface 19 upon which the layered thermite coating 10 is deposited, and a rear surface 21. The substrate 12 is a sufficiently thin and malleable so that a firing pin strike to the rear surface 21 will ignite the layered thermite coating 10, but is sufficiently thick for ease of manufacturing the detonator 14. 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 coating 10 includes alternating layers of metal oxide 14 and reducing metal 16 (with only a small number of layers illustrated for clarity). Examples of metal oxides 12 include La₂O₃, AgO, ThO₂, SrO, ZrO₂, UO₂, BaO, CeO₂, B₂O₃, SiO₂, V₂O₅, Ta₂O₅, NiO, Ni₂O₃, Cr₂O₃, MoO₃, P₂O₅, SnO₂, WO₂, WO₃, Fe₃O₄, CoO, Co₃O₄, Sb₂O₃, PbO, Fe₂O₃, Bi₂O₃, MnO₂, Cu₂O, and CuO. Example reducing metals 14 include Al, Zr, Th, Ca, Mg, U, B, Ce, Be, Ti, Ta, Hf, and La.
The thickness of each metal oxide layer 14 and reducing metal layer 16 are determined to ensure that the proportions of metal oxide 14 and reducing metal 16 are such so that both will be substantially consumed by the exothermic reaction. As one example, in the case of a metal oxide layer 12 made from CuO and reducing metal layer 14 made from Al (FIG. 1 ), the chemical reaction is 3CuO+2Al→3Cu+Al₂O₃+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/cm³, and aluminum has a density of 2.70 g/cm³. Therefore, the volume of CuO required for every 3 moles is 37.788 cm³. Similarly, the volume of Al required for every 2 moles is 19.986 cm³. Therefore, within the illustrated example of a composite layer 17, the metal oxide 14 is about twice as thick as the reducing metal 16. In some examples, each composite layer 17 is about 20 nm to about 100 nm thick.
As another example, in the case of a metal oxide layer 14 made from CuO and reducing metal layer 16 made 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/cm³, and magnesium has a density of 1.74 g/cm³. Therefore, the volume of CuO required for every mole is 12.596 cm³. Similarly, the volume of Mg required for every mole is 13.968 cm³. Therefore, within this example, each layer of metal oxide 14 is about the same thickness or slightly thinner than the corresponding layer of reducing metal 16. 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 FIGS. 4-6D, the illustrated example of the thermite structure 10 also includes a gradient interface layer 24 between each reducing metal layer 16 and adjacent metal oxide layer 14. As used herein, a gradient interface layer 24 is an interface between a reducing metal layer 16 and a metal oxide layer 14, with the interface layer 24 containing metal oxide 20, reducing metal 22, and reducing metal oxide, all of which are at least partially intermixed to form a gradient structure within the interface layer 24. (Due to the intermixing of materials at the interface layer 24, reference characters 14 and 16 refer to metal oxide layers and reducing metal layers, respectively, while reference characters 20 and 22 refer to metal oxide and reducing metal, respectively, regardless of whether those materials are within a layer 14 or 16.) Although the approximate thickness of the gradient interface layer 24 is about 2 nm to about 5 nm, the gradient interface layer 24 does not have precise boundaries. Instead, the amount of each material present in and around the gradient interface layer 24 will be a gradient with respect to proximity to either the reducing metal layer 16 or metal oxide layer 14. As shown in the example of FIG. 4 , moving from the bottom of the image to the top, the material transitions from aluminum 22 within the reducing metal layer 16, to a combination of aluminum 22, aluminum oxide, and cupric oxide 20 as the interface layer 24 within the approximate center of the image is reached. Continuing upward in the image, the material again transitions from the mixture of aluminum 22, aluminum oxide, and cupric oxide 20 in the interface layer 24 to simply cupric oxide in the metal oxide layer 14.
A similar gradient pattern is shown in the examples of FIGS. 5A-5D, with FIG. 5A simply showing the detail of box A in FIG. 5 . FIG. 5B focuses on the oxygen 26 present within Box A. In FIG. 5B, the aluminum layer 16 contains no oxygen 26, but oxygen in relatively high concentration (appearing as pink) is present above the aluminum 28 within the interface 24. Cupric oxide 20 is present above the oxygen 26 in relatively high concentration within the layer 24 as well as the layer 16. FIG. 5C focuses on aluminum 28 (shown in green), showing the transition between pure aluminum within the layer 16, to a mixture of aluminum 28 and other elements in the interface 24, and no aluminum 28 in the layer 14. Similarly, FIG. 5D focuses on the copper 30 (shown in red), showing no copper 30 in the layer 16, some copper 30 in the interface 24, and a large percentage of copper 30 in the layer 14. The atomic percent of each element within box A of FIG. 4 is also graphically illustrated in FIG. 6 , with the left side 32 of FIG. 6 corresponding to the bottom of the images of FIGS. 4-5D, and the right side 34 of FIG. 6 corresponding to the top of the images 4-5D. Line 36 shows aluminum, line 38 shows oxygen, and line 40 shows copper. As shown in FIG. 6 the atomic percent aluminum is maximized on the left side 32, decreasing towards zero at some position within the layer 24. The atomic percentage of oxygen (within aluminum oxide and cupric oxide) is very small in the layer 16, but becomes high in the layer 24, and decreases to a stable percentage within the layer 14. Copper (in the form of cupric oxide) is absent from the layer 16, but increases as the layer 24 is entered, increasing throughout the layer 24 until stabilizing in the layer 14. 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 layer 24 forms between completion of depositing one layer of reducing metal 16 or metal oxide 14 and the beginning of deposition of the next layer of reducing metal 16 or metal oxide 14. 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 composite 10 can 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 layer 24 will 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 FIGS. 2-3 , a passivation layer 18 covers the layered thermite coating 14, protecting the metal oxide and reducing metal within the layered thermite coating 14. One example of a passivation layer 18 is silicon nitride. Alternative passivation layers 18 can 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.
FIG. 8 illustrates a detonator 82 made by stacking a pair of detonators 84, 86 together. Each of the detonators 84, 86 is of the same design as the detonator 42 of FIG. 3 . 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 82, when the substrate 12B of the detonator 82 is struck to initiate detonation, this detonation strikes the substrate 12B of the detonator 86, initiating the detonator 86. The use of a stack of detonators has been found to increase the effectiveness of the detonator 82.
FIG. 9 illustrates an example of a detonator 88 utilizing one or more carbide containing ceramic layer 90 within the stacked layers of metal oxide and reducing metal. The carbide-containing ceramic layer(s) 90 are disposed within the thermite layers 92. In the illustrated examples, one carbide-containing ceramic layer 90 is disposed about ⅓ of the distance to the top of the thermite coating 92. In other examples, a carbide-containing ceramic layer 90 may be located elsewhere in the thermite coating 10, such as a lower portion, a central portion, the top, the bottom, or elsewhere in the upper portion of the thermite coating 92. Some examples may include a plurality of layers carbide-containing ceramic layers 90 which are located in different positions throughout the thermite coating 92. The thickness of the carbide-containing ceramic layer(s) 90 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) 16 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 composition 92 may include an adhesion layer 94 above and below each carbide-containing ceramic layer 90. In the illustrated example, the adhesion layers 94 are made from titanium or chromium. Nickel may also be used as an adhesion layer in some examples. The illustrated examples of the adhesion layers 94 are about 5 nm to about 10 nm thick.
The thermite structure 10 can be used within a micro detonator having a size which is significantly smaller than conventional detonators. Referring to FIGS. 2-3 , an example of a detonator 11A, 42 (below) can have a width W as small as about 2 mm.
Some examples of the detonator 11A, 42 may be used as standalone devices. Other examples of the detonator 11A, 42 may be used within projectiles to initiate an ignitable or detonatable material within the projectile. Referring to FIG. 7 , the illustrated example of a projectile 44 is 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 detonator 42 may be used with other projectiles.
Referring to FIG. 7 , each bullet 44 includes a copper jacket 46 covering the base 48 and extending from the base 48 along the sides 50 to a point 52 that is relatively close to (but does not necessarily correspond exactly with) the beginning of the ogive 54 in a manner that will be familiar to those skilled in the art of bullet construction. A firing pin 56 is located within the base 48 of the jacket 46. The firing pin 56 is made from a hard, dense material, for example, tungsten carbide or tantalum. Each firing pin 56 includes a base 58 which in the illustrated examples is flat, and a point 60 which in the illustrated examples is located along the longitudinal axis A of the bullet 44. Each firing pin 56 is itself centered along each longitudinal axis A, being held in place by a firing pin retainer 62 which in some examples is made from a dense, soft material such as lead. In the illustrated example, the sides 64 are tapered so that the firing pin 56 is narrowed towards the base 58. A detonator 42 is disposed in front of the point 60 of each firing pin 56.
A second charge 66, which in the illustrated example is made from high explosive, occupies a portion of the space within the bullet above the detonator 42. The illustrated example of an explosive charge 66 includes a top end 68 having a concave configuration, which in the illustrated example has the configuration of an inverted cone. This shape directs the blast from the charge 66 forward 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 bullets 44 includes a shape charge liner 70 covering the inverted cone-shaped front end 68 of the charge 66. In the illustrated examples, the charge liner 70 is made from tantalum. Some examples of the bullet 44 also include a sleeve 72 extending along the side outer surface 74 of each charge 66 as well as over the back end 75 of the charge 66. Some examples of the sleeve 72 are made from a hardened steel or tantalum. Each bullet 44 also includes an ogive/body piece 76 forming the ogive 54 of each bullet 44, as well as extending between the sleeve 72 and jacket 46 along substantially the entire charge 66. Some examples of the ogive/body piece 76 are made from tungsten carbide or hardened steel. This construction leaves a hollow space 78 between the charge liner 70 and ogive 54.
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.

Claims

What is claimed is:

1. A micro detonator, comprising:

a substrate having a first side and a second side;

alternating layers of metal oxide and reducing metal deposited upon the first side of the substrate; and

a gradient interface layer disposed between each layer of reducing metal and each adjacent layer of metal oxide.

2. The micro detonator according to claim 1, wherein the substrate is made from a malleable material.

3. The micro detonator according to claim 1, wherein the substrate further comprises a pair of electrically conductive portions separated by an electrically insulative portion.

4. A projectile, the projectile defining a front end portion and a back end portion, the projectile comprising:

an explosive material forming at least a portion of the body of the projectile;

a penetrator disposed within the body of the projectile;

a micro detonator disposed forward of the penetrator, the micro detonator comprising:

a substrate having a first side and a second side;

5. The projectile according to claim 4, wherein the substrate is made from a malleable material.

6. The projectile according to claim 4, wherein the projectile is a bullet.

7. The projectile according to claim 4, wherein the explosive material defines an inverted cone within the forward portion of the projectile.

8. The projectile according to claim 4, wherein the penetrator and micro detonator are disposed in the back end portion of the projectile, and the explosive material is disposed forward of the micro detonator.