DELAY ELEMENTS, DETONATORS CONTAINING THE SAME AND METHODS OF

MAKING

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The present invention relates to composite reactive materials, for example, multilayer metal foils and metal coated wire meshes, and energetic delay elements incorporating the same, and methods of making such reactive materials and delay elements.

Related Art

[0002] It is known that reactive foils may be utilized in a muliilayered foil structure which, upon appropriate excitation, undergoes an exothermic chemical reaction to generate a significant amount of heat. Appropriate design of the multilayer foils provides precise control of the amount of heat generated and control of the geometric area which is heated. U.S. Patent 6,736,942, issued May 18, 2004 to T.E. Weihs et ah, discloses (column 1, lines 34-44) such multilayer foils and notes that they may be used primarily as sources of heat for welding, soldering or brazing, but could also be used in other applications requiring controlled local generation of heat, such as propulsion and ignition. As disclosed at column 2, line 26 et seq., upon reacting, reactive foils supply highly localized heat energy which allows rapid bonding to occur at room temperature in virtually any environment including air, vacuum, water, etc. At column 3, line 37 et seg., the materials used in fabrication of the reactive foil are stated to preferably be chemically distinct and preferably may include alternating layers of a transition metal such as titanium, nickel, etc., and a light element such as boron, aluminum, etc. The element pairs desirably react to form stable compounds with large negative heats of formation and high adiabatic reaction temperatures. Individual layers may have a thickness of from 1 to 1,000 nanometers and the total thickness of a layered foil may be from 10 μm to 1 centimeter (column 5, lines 15-19).

[0003] Such reactive multilayer foils are fabricated by depositing onto a substrate multiple alternating layers of dissimilar metals by processes such as rolling, chemical vapor deposi-

tion, vacuum deposition and/or sputter coating. These alternating layers may be composed of any materials which undergo mixing of neighboring atoms, for example, which undergo alloying of the metals, or changes in chemical bonding in response to a stimulus, e.g., a thermal stimulus. The alternating layers may be comprised of multiple individual layers, each of which may be as thin as approximately 1 nanometer (nm). Such combinations of materials may include elemental metals, suicides, aluminides (including Ni/ Al), borides, carbides, thermite reacting compounds, alloys, metallic glasses, and composites. Such foils may comprise hundreds of overlying layers of appropriate materials. Upon thermal excitation, chemical energy is released as a result of exchange of bonds between similar and dissimilar atoms, or alloying, thereby releasing heat. Examples of such reactive multilayer foils are described in U.S. Patent 6,863,992, issued March 8, , 2005 to Weihs et al., and the above-mentioned U.S. Patent 6,736,942. The two Weihs et al. patents mentioned in this paragraph are incorporated by reference herein.

[0004] Metallic multilayered foils comprising hundreds of alternating, extremely thin layers of dissimilar metals, e.g., nickel and aluminum, are commercially available from Reactive Nanotechnologies, Inc. of Hunt Valley, Maryland.

[0005] A commercial product called PYROFUZE ^® wire, manufactured by Sigmund Cohen, Inc., consists of two metallic elements in intimate contact with each other, including arrangements of one metal as a sheath, providing a laminated reactive multilayer wire. When these two elements are brought to the initiating temperature, they alloy rapidly, resulting in instant reaction without support of oxygen. The reaction is initiated by heat; all that is required is the exposure of the composite to a sufficiently high temperature. A fundamental difference between PYROFUZE wire and the multilayer foil devices such as those manufactured by Reactive Nanotechnologies, Inc. ("RNT") is that the RNT multilayer foil laminate is comprised of ultra thin layers, the thickness of individual layers being measured in nanometers and the thickness of the laminate being measured in microns. The laminate may comprise a large number of individual layers, usually hundreds or even a thousand or more. The different metals, e.g., nickel and aluminum, alternate in the layers, which are deposited by a vacuum sputtering process or the like. The thickness of individual layers and the total number of layers applied determine the characteristics of a given product.

[0006] U.S. Patent 3,503,814, issued March 31, 1970 to H.H. Helms et al., discloses pyrotechnic materials comprised of nickel and aluminum which may be made "by compressing the appropriate metal powders, by rolling, swaging, drawing or plating metal wires or strips." (column 1 , lines 23-29). Example 1 shows nickel at 40-80 weight percent and aluminum at 60-20 weight percent (column 1, lines 68-71). At column 2, line 26 et seq., it is disclosed that the "powder mixture of Example 1 is compacted into pellets and heated to approximately 660° C" resulting in a violent, exothermic reaction to produce molten NiAl and a temperature of over 1700 ⁰ C. The reaction is stated to be gasless and, once initiated, not to require the presence of oxygen. (See column 2, line 32 et seq.) At column 2, line 39 et seq., it is disclosed that the composition of Example 1 "may also exist in a composite strip formed by rolling sheet stock or powders or by plating either metal onto a base of the other metal. The composition further may be set forth in a wire by swaging and drawing the metals using either material as a core element and the other as a sheath around the core."

[0007] In blasting systems, it is known to mount detonators on the ends of signal lines such as electrical wires, detonating cord and signal transmission tubes ("shock tubes"). Shock tubes are well known in the art and comprise hollow plastic (synthetic polymer) tubes, the interior walls of which are coated with a reactive material, e.g., fine aluminum powder and an organic explosive such as HMX. In any case, the signal line carries an electric or non-electric energetic initiation signal to the detonator, which contains an explosive output charge that amplifies the signal from the signal line to initiate another device. Functioning of the detonator is often delayed after receipt of the signal from the signal line by interposing a delay element between the end of the signal line and the output charge of the detonator. As is well known in the blasting art, such delays, usually measured in thousandths of a second, must be precisely controlled in order to effectuate the desired timing of detonation of individual explosives in a given shot, which may contain hundreds of explosives in separate boreholes or the like.

[0008] A conventional pyrotechnic delay element comprises a slow-burning (relative to the signal velocity in the signal line) linear pyrotechnic delay composition, such as a mixture of silicon and red lead oxide (Pb ₃ O ₄ ). One end of the delay composition receives the incoming signal from the signal line and the other end of the delay composition is positioned in signal transfer

proximity to the output charge of the detonator. Upon being initiated by the signal from the signal line, the linear pyrotechnic delay burns at a controlled rate and, when it is at the end of the linear pyrotechnic delay, it initiates the output charge of the detonator. In this way, a selected delay period is imposed between receipt by the detonator of the signal from the signal line and the output of the detonator generated by functioning of its output charge. Conventional pyrotechnic delay units comprise a pulverulent pyrotechnic composition encased within a soft metal tube, such as a tube of lead, zinc, aluminum or pewter. Detonation of the output explosive charge is delayed by the time it takes the length of pyrotechnic material to burn from its input to its output end. See, for example, the detonator described in U.S. Patent 5,031,538. As is well known to those skilled in the art, it is necessary to very closely control the delay periods of individual detonators; typical delay periods range from 9 to 9,600 milliseconds or more, for example, 9, 25, 350, 500 and 1,000 milliseconds. Attainment of consistently accurate and precise delay times by burning of a column of pyrotechnic material is inherently limited, and the art is developing electronic delay units in order to increase delay time accuracy and precision, despite the increased cost of electronic delay units as compared to pyrotechnic delay units.

[0009] International Application WO 2004/106268 A2 of Qinetiq Nanomaterials Limited for "Explosive Devices", published 9 December 2004, discloses explosive devices printed onto substrates from inks which may contain particles as small as 10 micrometers in diameter "or even...0.1 micrometer or less in diameter." (Page 4, lines 18-24.) Figures such as Figures 1 and 2 disclose serpentine or spiral patterns of printed explosive ink on a substrate. For example, there is described at page 15, lines 11-29, printing of the explosive ink in a single line which starts adjacent a heating element and terminates adjacent a secondary explosive material. The printed line of explosive ink initiates the secondary explosive. A zigzag pattern may be used and will increase the delay time provided by the device.

Summary of the Invention

[0010] In accordance with the present invention there is provided a delay element comprising a substrate, e.g., an aluminum substrate, upon which is disposed a reactive material selected from the group consisting of (a) a reactive multilayer laminate of at least two different ma-

terials, e.g., two different metals, and (b) a wire mesh of one of the at least two different materials, for example, nickel and aluminum, coated with a layer of the other of the two different materials to constitute a coated wire mesh. The two different materials, upon being thermally energized, react with each other in an exothermic and self-sustaining reaction. The reactive material has a starting point and a discharge point spaced from the starting point to define therebetween a travel path extending along the reactive material, so that when the reactive material is thermally energized at the starting point, the reaction propagates along the travel path at a propagation rate which is dependent upon the composition of the reactive material. In this way, a time period required for propagation of the reaction from the starting point to the discharge point may be selected by controlling the composition and configuration of the reactive material

[0011] Another aspect of the present invention provides a delay element comprising a substrate upon which is disposed a reactive material comprising a reactive multilayer laminate of at least two different metals (e.g., nickel and aluminum) which, upon being thermally energized, react with each other in an exothermic and self-sustaining reaction. The reactive material has a starting point and a discharge point spaced from the starting point to define therebetween a travel path extending along the reactive material, so that when the reactive material is thermally energized at the starting point, the reaction propagates along the travel path at a propagation rate which is dependent upon the composition of the reactive material. In this way, a time period required for propagation of the reaction from the starting point to the discharge point may be selected by controlling the composition and configuration of the reactive material.

[0012] Yet another aspect of the present invention provides a delay element comprising a reactive material comprising a wire mesh of one metal, e.g., aluminum, coated with a layer of another metal, e.g., nickel, which two different metals, upon being thermally energized, react with each other in an exothermic and self-sustaining reaction. The reactive material has a starting point and a discharge point spaced from the starting point to define therebetween a travel path extending along the reactive material, so that when the reactive material is thermally energized at the starting point, the reaction propagates along the travel path at a propagation rate which is dependent upon the composition of the reactive material. In this way, a time period re-

quired for propagation of the reaction from the starting point to the discharge point may be selected by controlling the composition and configuration of the reactive material.

[0013] One aspect of the present invention provides for the two different materials to comprise pairs selected from the group consisting of one or more of aluminum/titanium, aluminum/cobalt, aluminum/palladium, aluminum/platinum, aluminum/ruthenium, boran/titanium, zirconium/aluminum and nickel/aluminum.

[0014] Another aspect of the present invention provides that a colored ink is on the reactive multilayer laminate, which ink is acted upon by the exothermic reaction, e.g., it is vaporized and/or oxidized, to work a color change on the reactive multilayer laminate, thereby providing a visual indicator that the delay element has been functioned.

[0015] Other aspects of the present invention provide one or more of the following features, alone or in any suitable combination of two or more features. The substrate may have a first major surface and an opposite second major surface and the reactive material may be disposed upon both the first and second surfaces; the reactive material may define a continuous travel path from the first surface to the second surface; at least part of the travel path may be enclosed within a surround; the reactive material may define a serpentine travel path; the reactive material may be of flat, ribbon-like configuration; each individual one of the layers may have a thickness of from about 10 μm to about 100 μm; the delay element may comprise from about 20 to about 1 ,000 of the individual layers; each individual one of the layers may have a thickness of from about 30 μm to about 80 μm; at least part of the travel path of the reactive material is enclosed within a surround that overlies and is in contact with the reactive material along at least a part, e.g., the entirety of, of the travel path; the reactive material may be of wire-like configuration; the reactive material may be an open coil.

[0016] In one aspect of the invention, the reactive material may comprise a plurality of the wire-like configuration materials braided to form a cord of reactive material, which maybe over-extruded with a linear plastic jacket or surround.

[0017] Yet another aspect of the present invention provides a delay detonator comprising a cylindrical shell having a closed end and an opposite open end, an output explosive charge disposed at the closed end of the shell, a signal transmission line extending from within the shell to

the exterior thereof through the open end, the signal transmission line terminating within the shell in an output end thereof, and a bushing which seals the open end of the shell.

[0018] A delay element as described above has its starting point disposed in signal transfer communication with the output end of the signal transmission line, and the discharge point disposed in signal transfer communication with the output explosive charge.

[0019] A method aspect of the present invention provides for manufacturing a delay element by a method comprising the steps of: (a) applying to a substrate a plurality of overlying alternating layers of at least two different materials which materials, upon being thermally energized, react with each other in an exothermic and self-sustaining reaction; and (b) configuring the reactive material to define on the substrate a continuous travel path for propagation of the reaction, the travel path extending along the reactive material from a starting point to a discharge point spaced from the starting point.

[0020] Another method aspect of the present invention provides for making by the above-described method an individual substrate segment having a longitudinal axis and opposite first and second longitudinal edges, and step (b) of the above-described method further comprises cutting a first series of spaced-apart slits through the first longitudinal edge transversely of the longitudinal axis, each slit of the first series of slits stopping short of the opposite second longitudinal edge; and cutting a second series of spaced-apart slits through the second longitudinal edge transversely of the longitudinal axis, and longitudinally staggered with respect to the slits of the first series of slits, each slit being wide enough to stop propagation of the reaction whereby propagation of the reaction is constrained to travel along a serpentine travel path from the starting point to the discharge point.

[0021] Still another method aspect of the invention provides for stacking a plurality of the substrates one above the other and disposing the reactive material on the substrates in a travel path which extends continuously from one substrate to the next stacked substrate.

[0022] Reference herein and in the claims to metals such as aluminum and nickel include, in addition to the metals, alloys of those metals, for example, aluminum alloys containing at least 50% by weight aluminum, and nickel alloys containing at least 50% by weight nickel.

Brief Description of the Drawings

[0023] Reference is now made to the figures, which illustrate exemplary embodiments:

[0024] Figure 1 is a schematic cross-section of a delay element according to one embodiment of the present invention;

[0025] Figure IA is a schematic perspective view of one embodiment of a delay element comprising a reactive multilayer wire in a coiled configuration;

[0026] Figure 2 is a schematic perspective view of one embodiment of a delay element in accordance with the present invention;

[0027] Figure 2A is a schematic perspective view of the body of a delay element in accordance with another embodiment of the present invention;

[0028] Figure 2B is a schematic side view of an embodiment of a delay element in accordance with the present invention which includes the body of Figure 2 A;

[0029] Figure 3 is a schematic cross-section of a delay element in accordance with yet another embodiment of the present invention;

[0030] Figure 4 is-a schematic cross-section of one embodiment of a detonator including the delay element of Figure 3;

[0031] Figure 5 is a cross-sectional view of an electric igniter containing a delay element, in accordance with another embodiment of the present invention;

[0032] Figure 6 is a side view of a delay element in accordance with yet another aspect of the present invention;

[0033] Figure 6A is an end view of the delay element of Figure 6 (both end views are identical to each other);

[0034] Figure 6B is a side view, with part broken away, of the delay element of Figure 6 connected to a fuse;

[0035] Figure 7 is a side view of an embodiment of the invention using a multilayer wire in a coiled configuration;

[0036] Figure 8 is a plan view of a fine wire mesh made of a first metal coated with a second metal, the two metals being reactive with each other to provide a reactive mesh in accordance with another aspect of the present invention;

[0037] Figure 8 A is a view of the coated wire mesh of Figure 8 folded upon itself to form, in the illustrated embodiment, a delay element comprising a three-layered mesh;

[0038] Figure 9 is a plan view of a delay element comprised of a serpentine substrate coated with a reactive multilayer laminate (part of which is broken away) in accordance with yet another embodiment of the present invention;

[0039] Figure 10 is a side view, reduced relative to Figure 8, of a delay fuse comprising an embodiment of the present invention and incorporating the coated substrate of Figure 8;

[0040] Figure 11 is a side view of stacked substrates coated with a reactive multilayer laminate to provide a delay element in accordance with yet another aspect of the present invention;

[0041] Figure 12A is a view of two reactive multilayer laminates on a substrate;

[0042] Figure 12B shows the reactive multilayer laminates of Figure 13 A connected to each other in overlapping relationship to comprise a delay element in accordance with yet another aspect of the present invention;

[0043] Figure 13 is a perspective view of a wire delay element in accordance with yet another embodiment of the present, invention; and

[0044] Figure 14 is a perspective view of a braided wire reactive material in accordance with an embodiment of the present invention.

Detailed Description of the Invention

[0045] The terms. "reactive multilayer laminate" or "reactive multilayer laminate foil", sometimes used herein and in the claims, whether in the singular or plural form, refers to multilayer foils, multilayer wires and the like. Sometimes the reactive multilayer laminate foil is referred to simply as a "foil". The reactive multilayer laminates of the present invention comprise at least two different materials, e.g., metals in a pre-alloyed state, and in which an exothermic self-sustaining alloying reaction can be initiated by being thermally energized, that is, by having an energetic input (an "energetic initiation signal") impinge on the reactive multilayer laminate. The energetic initiation signal may be a flame or spark or other source of heat such as an open flame, an electrical spark or the output signal (sometimes referred to as the "spit") of a shock tube or deflagration tube. The energetic initiation signal need contact the reactive multilayer laminate only at a starting point and raise the temperature at that point sufficiently to initiate the alloying reaction. Reactive multilayer laminates are usually disposed on a substrate such as a thin sheet of metal or a sheet of plastic (synthetic polymer) material such as a Mylar polyester film, on which the multiple layers of metal is disposed. In some cases it is desirable to anneal the reactive multilayer laminate. In such cases, metal substrates are preferred as they withstand the annealing heat without deforming better than do plastic substrates. Various metals such as tin, brass, copper and the like may be used for the metal substrates. Aluminum and aluminum alloys are, however, preferred because of low cost, good adherence of the multilayer laminates to the aluminum, and the ease with which the aluminum can be cut, stamped or otherwise shaped.

[0046] Reactive multilayer laminates can be fabricated into delay strands for use as, or as part of, delay elements. Generally, as used herein, a "delay element" refers to a reactive multilayer laminate disposed on a suitable substrate or a suitably supported reactive coated wire mesh, or a reactive multilayer wire or braid of wires. The term "delay fuse" generally refers to a delay element attached to fixtures which support and/or enable the connection of the delay element into an explosive or pyrotechnic or other initiating system. Delay elements are interposed between an input device such as an initiation signal line and an output charge or other device, such that the function of the output charge or other device in response to the initiation signal is delayed by the time interval required for a reaction to travel along a travel path defined by the reactive multi-

layer laminate from one end (the starting point) to the other end (the discharge point). A delay element may be used with, or may comprise, a transfer charge at one or both ends, to ensure signal transfer from the input signal line -to the delay element and/or signal transfer from the delay element to the output charge or other device. Optionally, the transfer charges may comprise nanosized energetic materials. In some embodiments, delay elements are employed in initiators (including detonators and non-explosive initiators) and are optionally configured to fit within a standard initiator shell such as a detonator shell, for example, a cylindrical shell having an interior diameter of about 0.26 inches, about 6.6 millimeters (mm). A reactive multilayer foil used as a delay element may be at least 5mm long measured linearly from end to end (but whose travel path, i.e., whose effective length, may be much longer) and may be 6 mm wide or less. Obviously, any suitable length and width dimensions may be employed. Reliable delay elements can be fabricated from very thin sections of the reactive multilayer laminate foil. In some embodiments, for example, the reactive laminate foil is about 10 micrometers (μm) to about 100 μm thick, e.g., from about 30 μm to about 80 μm thick. The reactive laminate foil may of course be made thicker than 100 μm by adding more individual layers and thereby obtaining a higher caloric output. Obviously, as the laminate foil is made thicker it becomes more costly and takes longer to produce. Reactive laminate foils thinner than about 10 μm would have a very limited caloric output. In various embodiments, the foil may comprise hundreds of layers of metals. For example, from about 20 to about 1 ,000, e.g., from about 200 or 300 to about 1,000, individual layers may comprise a reactive multilayer laminate foil. The thickness of each individual layer in the foil is measured in nanometers and such layers are sometimes referred to herein as "nano- layers". The thickness of each individual layer is desirably from about 10 to 200 nanometers ("nm"), for example, from about 10 to 100 ran.

[0047] In some embodiments, delay elements include modifying layers or substrates that may or may not participate in the alloying reaction of the multilayer laminate. A modifying layer or substrate may be selected principally to facilitate the manufacture of devices that employ the delay element, e.g., by serving to provide adequate rigidity and resilience to the laminate to facilitate its manufacture into an energetic device. Materials for modifying layers suitable for

this purpose include metals such as zinc, stainless steel, aluminum, etc.', thermoplastics, paper laminates, reactive fluoropolymers and other materials.

[0048] Alternatively, a modifying layer or a substrate may be selected principally for its effect on the rate of the reaction in the laminate. For example, a substrate may act as a heat sink to draw heat from the alloying reaction of the multilayer composite, and thus slow the reaction. A modifying layer may retard the kinetics of the alloying process, possibly by reducing the exo- thermicity of the reaction, thereby slowing the reaction. Materials for modifying layers suitable for this purpose include materials with high thermal conductivities such as titanium, aluminum, copper, silver, gold, etc., or those having thermal conductivities of around 1.0 (cal/sec)/(cm ² C/cm) or greater. When an otherwise reactive material such as aluminum is used for a modifying layer or (as discussed elsewhere herein) a substrate, the aluminum modifying layer or substrate does not fully enter the reaction because it is many orders of magnitude thicker than the thickness, measured in nanometers, of a reactive layer of aluminum or other metal. For example, a layer of nickel whose thickness is measured in nanometers would be consumed reacting with a commensurate nanometers-deep depth of aluminum. The reaction would then be stopped because there is a thickness of aluminum remaining and no nickel left to react with it.

[0049] In some embodiments, a substrate for the multilayer foil in a delay element comprises a non-metallic material such as a polymeric material. Suitable non-metallic substrates include Mylar ^® polyester sheet, high-density polyethylene (such as TYVEK ^® sheet), ceramic material, silicon, fiberglass reinforced plastic, etc. The multilayer foil delay strand may be deposited directly on the substrate in a conventional manner, i.e., by chemical vapor deposition, sputtering, etc.

[0050] Optionally, the substrate may be masked to permit the application onto the substrate of a multilayer foil of a predetermined configuration, for example, a serpentine, wavy or other dilatory configuration as described elsewhere herein.

[0051] Alternatively, the deposited foil may be masked and subsequently etched in order to produce the desired pattern.

[0052] In yet another approach, the surface of a substrate may be coated with the reactive multilayer laminate and the substrate is then shaped, by cutting or otherwise, to provide a reactive multilayer laminate of a desired configuration.

[0053] Generally, a number of different multilayer reactive foils were prepared on different substrates by depositing hundreds of alternating layers of nickel and aluminum onto the respective substrates. A spark will initiate a highly exothermic reaction in which nickel aluminide is formed by reaction of the aluminum and nickel layers. The reaction is self-sustaining; that is, oxygen is not required to support the reaction and therefore the multilayer foil may be used in oxygen-free environments, e.g., encased within a suitable extruded or molded plastic, epoxy or other potting material. The nickel aluminide product of reaction is neither toxic nor hazardous and thus may be disposed of without taking special precautions.

[0054] Metal substrates have proved to be more successful than plastic substrates such as polyester (Mylar ^® ) substrates. Generally, any suitable substrate may be used, e.g., any suitable metal substrate with aluminum being preferred because of its low cost, good adherence of the metal layers to the aluminum and ease of cutting the aluminum substrate to the desired shape. Metals such as tin, steel and brass may also be used for the substrate. It has been found that the nickel and aluminum nano-layers adhere better to aluminum than to brass, to which the nickel and aluminum layers show poor adhesion. Attempts to use a thick polyester material as the substrate resulted in cracks in the metal layers when a delay unit was cut from the metal-coated polyester sheet. While polyester substrates are nonetheless usable, in cases where it is elected to anneal the delay elements, the annealing temperature often warps the polyester substrate. Aluminum provides a good base for adhering of the multi layers, is easy to cut, is relatively inexpensive and, at an appropriate thickness, is not warped by annealing. Annealing may be carried out to partially alloy adjacent layers in order to reduce the rate of the alloying reaction and thereby the propagation rate of the "burn" along the delay element. This is because the burn rate is so high it is often desired to slow it down to attain the requisite delay period.

[0055] In another approach, a metal wire may be coated with one or more layers of a metal with which it is reactive to provide, upon being heated to a sufficiently high temperature, the desired exothermic, self-sustaining reaction. For example, an aluminum wire may be coated

with a layer of nickel. When aluminum-nickel combinations are used, it is often desirable to have an intermediate zinc strike coat plated between them. A single layer may be plated onto the wire or multiple alternating layers may be plated onto the core wire. For example, an aluminum wire may be coated with alternating layers of nickel and aluminum. Two or more metal wires may be twisted together to form a "cord" or "rope" in order to provide a heavier per unit length reactive material having a higher caloric output. Regardless of how formed, the resulting multilayer laminate wire then may be used as the delay element, for example, it may be formed into an open coil, e.g., a helical or spiral coil to provide a desired effective length or travel path along the wire. In all cases, the wire or braid may be enclosed in an over-extruded plastic jacket or surround.

[0056] Since reactive multilayer laminates often lack sufficient physical resilience to withstand various manufacturing processes, it is sometimes useful to dispose a reactive multilayer laminate (which typically comprises a metal or plastic substrate such as a thin aluminum sheet or Mylar ^® polyester film) onto a second substrate that provides the desired resilience. The second substrate may comprise metal, a printed circuit board, a ceramic material, or the like. In one embodiment, a delay element comprising a reactive multilayer laminate may be prepared by creating a laminate of the reactive multilayer laminate and a second substrate using transfer printing techniques commonly used to create embossed metallized characters or designs. One such process is hot foil printing.

[0057] In another embodiment, a reactive multilayer laminate may comprise a metallic modifying layer to slow the alloying reaction. For example, a metallic modifying layer may comprise a layer of copper in the multilayer laminate. A modifying layer might also be a layer that slows the propagation rate (the speed of travel) of the alloying reaction by virtue of its increased thickness relative to other layers in the laminate.

[0058] The velocity of the reaction in a particular multilayer laminate may be about 1 to about 10 meters per second (m/s) in the absence of modifying layers; in some embodiments, with suitable modifying layers, the reaction velocity may be reduced to as low as about 0.2 m/s. Optionally, the rate of the linear alloying reaction of the laminate maybe modified by varying the

thickness of one or more layers, and/or by providing one or more additional modifying layers in the reactive multilayer laminate.

[0059] Another aspect of the invention is that annealing the reactive multilayer laminate can retard, i.e., slow, the reaction rate, as described by Gavens et al., in "Effect of Intermixing on self-propagating exothermic reactions in Al/Ni nanolaminate foils," 87 J. of Applied Phys., No. 3, Feb 1, 2000. Thus, annealing the multilayer foil slows the propagation rate of the alloying reaction, i.e., slows the rate of travel of the "burn". This is usually desirable as the multilayer foil laminate is intended as a delay element. The annealing is believed to cause a modest nickel- aluminum reaction at the interfaces of the layers, thereby initially reducing the driving force for the alloying reaction.

[0060] In one embodiment, a multilayer laminate comprises alternate layers of aluminum and nickel having thickness ratios of 3:2 respectively, and each layer having a thickness of about 10. nanometers ("nm") to about 200 nm. There may be from 300 to 700 or more, e.g., up to 1,000, alternating layers of nickel and aluminum on the substrate; the total thickness of the layers in the reactive multilayer laminate may be from about 30 to 80 μm. At 30 μm thickness there might be, for example, 700 alternating nickel and aluminum layers. At a 50 μm thickness of the laminate foil, there might be a thousand such layers. Generally, thicker metal nano-layers slow down the reaction propagation rate (the speed of travel of the reaction) while thinner metal nano- layers increase the reaction propagation rate.

[0061] Some embodiments of the invention utilize a nickel-coated aluminum wire mesh instead of nano-layers of metal. Tape, epoxy or other inert substance placed atop a single layer of the mesh stops the reaction of a single layer of reactive coated mesh. This is in contrast to the reactive multilayer laminate which reacts even when a cover material is in contact with it, for example, when the delay element is potted or encapsulated per one aspect of the invention. However, it has been found that if the mesh is doubled on itself, i.e., provided in at least two layers, the reaction will then continue even if the doubled or multilayered mesh is covered by a cover material, tape, an inert body or the like.

[0062] In use, an initiation signal at a first end (the "input end") of the delay element is provided, and a reaction is initiated at the first end and proceeds along the fuse strand until the

reaction front reaches the opposite second end of the strand (the "output end"). At the output end, a target device or reactive or energetic material is disposed in signal transfer relation to the fuse strand so that the heat released by the reaction at the output end of the fuse strand initiates the target device or material. In an alternative embodiment, the delay element comprises a substrate that extends beyond the multilayer foil thereon, and a transfer charge can be deposited on the substrate in signal transfer relation to the multilayer foil, i.e., where it is positioned to initiate, or be initiated by, the multilayer foil. For example, an ink comprising a transfer charge composition may be printed on the substrate. Optionally, the flash charge comprises a nanosized pyro- technical material.

[0063] In various embodiments, a delay element may be configured to increase the end- to-end reaction time relative to what would occur in a delay element that extends linearly between its two ends, i.e., a delay element may be formed in a coiled, serpentine or other non- straight line configuration to increase its effective length (and, therefore, the delay interval it provides), relative to being configured as a direct linear path between the input end (starting point) and the output end (discharge point). The "effective length" of a delay element is the continuous length along the reactive multilayer laminate therein between its starting point and discharge point, sometimes herein referred to as the "travel path" of the "burn". For example, the reactive multilayer laminate may be configured in a convoluted path between its input end and the output end by providing the fuse in a zigzag pattern on the substrate. Another option is to wrap a length of the delay element around a core (such as a wire), e.g., to form a helical configuration between the two ends. When in a coiled, zigzag or other such configuration the travel path must not cross itself in order to avoid a "short circuit" unless the delay element has a thermal insulating jacket around it which prevents short-circuiting of the signal. One or both ends of the delay element may be unwound to facilitate signal transfer with an initiation line or with a transfer charge. In still another embodiment, a dilatory configuration is achieved by folding the laminate back on itself, for example, in a fan-fold configuration.

[0064] There is shown in Figure 1 a delay element 10 which comprises a layer of multilayer foil 12 disposed on an optional Mylar ^® polyester substrate 14. Any other suitable substrate material may be used, for example, a metal substrate such as aluminum maybe substituted for

the polyester substrate 14. The multilayer foil 12 comprises alternating layers of aluminum and nickel (not shown) and has a total thickness of about 35 μm comprised of about 10 μm total thickness of aluminum layers and 25 μm total thickness of nickel layers, the individual layers of nickel and aluminum being applied to the substrate in successive alternating layers by vapor deposition or other suitable techniques. When substrate 14 comprises Mylar ^® polyester film, it may be about .006 to .020 inch in thickness. Delay element 10 may have in plan view a ribbon- like configuration as shown in Figure 2, discussed below. Tn any case, delay element 10 may be employed, as shown, as a delay element in various energetic devices.

[0065] Figure IA shows another embodiment of a delay element 10' comprising a reactive multilayer wire 12' disposed in an open helical coil configuration by being wound around an optional core 14'. The ends of wire 12' are separated from the core 14' to facilitate disposing them in signal transfer relation to transfer charges. By winding wire 12' around the core 14' and leaving air gaps g between windings or lacquering the wire 12' to prevent lateral winding-to- winding signal transfer, the effective length of wire 12' between its ends is increased relative to extending the wire in an uncoiled, linear configuration between the transfer charges. Core 14' may be made of any suitable material, plastic, etc. It may be grooved to hold the wire 12' in place, e.g., core 14' may be the shaft of a threaded bolt or screw.

[0066] There is shown in Figure 2 a delay fuse 16 which comprises a ribbon-shaped delay element 18 and a surround plug 20. Plug 20 comprises a transfer biphenol, glass-loaded molding compound, for example, a halogen-free epoxy compound containing an antimony flame retardant available from Hitachi under the designation CEL 9700 ZHFlO, that has been molded around delay element 18 with the opposite ends 18a, 18b of delay element 18 exposed at the ends of plug 20. Plug 20 may be configured to fit within a standard size detonator shell. In use, delay fuse 16 is positioned between an input device such as a signal transmission tube and an output device such as a detonator output charge, and interposes a delay interval between the receipt of an initiation signal from the input device and the initiation of the output device.

[0067] Figures 2A and 2B show a delay element 22 (Figure 2B) comprising an extruded or molded body 24 (Figure 2A) having a slot 26 of generally rectangular cross section formed therein and extending longitudinally therethrough. Slot 26 is open at both opposite ends of body

24. A substrate-supported reactive multilayer laminate 28 is retained within slot 26. The substrate-supported reactive multilayer laminate 138 as shown in Figure 2B, protrudes at either end from body 134. The length of such protrusion may typically be about 3/32 of an inch. This insures an adequate protruding length so that the substrate-supported laminate 28 may reliably receive an incoming ignition as from a shock tube or the like, and reliably generate an outgoing signal by insertion of the protruding end into the reactive material which is to be initiated by delay element 22. Body 24 may be made of an electrically conductive plastic such as a conductive high-density polyethylene or conductive polypropylene. Body 24 is made of a conductive material in order to dissipate static electricity charges. Substrate-supported laminate 28 may be force- fit into slot 26, or body 24 may be heated to expand it for insertion of substrate-supported laminate 28 therein, or the latter may be staked through body 24 to retain it in place.

[0068] A tube encapsulated delay element comprising a reactive multilayer laminate is shown in Figure 3. Delay fuse 40 is suitable for use with shock tube, and comprises a delay element 42 mounted in a sleeve 44. Delay element 42 protrudes from each end of sleeve 44 into optional transfer charges 44a and 44b comprising first fire mixes that are secured to sleeve 44 by caps 46a and 46b. Transfer charges 44a, 44b may be omitted in some embodiments. First fire mixes are known in the art; in one embodiment, first fire mix is sensitive to the output of a shock tube and is sufficiently brisant to initiate the delay element 42. Known first fire mixes include mixtures of molybdenum and potassium perchlorate (MO/KCIO ₄ ), silicon and red lead oxide (PbSO ₄ ); zirconium and potassium perchlorate; titanium and potassium perchlorate; boron and red lead oxide; zirconium and iron (III) oxide (Fe ₂ Os); zirconium and potassium chlorate (K.CIO3); zirconium and lead chromate (PbCrO ₄ ); titanium and lead chromate; magnesium and barium chromate (BaCrO ₄ ); boron and potassium nitrate (KNO ₃ ); and combinations thereof. Caps 46a and 46b are provided with apertures 47a and 47b, respectively, to facilitate the transfer of an initiation signal from the signal line to the transfer charge 44a and from transfer charge 44b to the target device.

[0069] A detonator comprising tube encapsulated delay fuse 40 is shown in Figure 4. Detonator 110 is shown with a signal transmission tube 1 11, such as a shock tube (transmission tube), received in an open end 112 of a detonator housing 115. The detonator housing 115 is

generally cylindrical shaped with a hollow interior and a closed end 116 opposing the open end 1 12. The housing 115 should possess sufficient strength to resist internal detonating and deflagrating reaction forces during combustion of signal transition compositions, and external forces which may be applied in field use. The preferred housing material is aluminum.

[0070] An end of the transmission tube 111 is secured firmly in the housing by crimping the housing near the open end 118. This crimping action secures the housing against the transmission tube exterior to hold the tube in place without crushing or otherwise interfering with signal propagation within the transmission tube. An elastomeric material may be employed as a bushing 119 between the housing and the transmission tube in the crimped region.

[0071 ] The interior of the housing 115 forms a chamber 120 in which delay element 40 is disposed. Delay element 40 and the chamber 120 are both preferably cylindrical in shape and are correspondingly configured to fit tightly together. The tight fit prevents direct signal communication between opposing ends of delay element 40.

[0072] A polymeric alignment and isolation cup 140 may be employed at the output end of transmission tube 111 to direct the transmission tube signal between the transmission tube and the transition element.

[0073] An output charge 152 is located adjacent to and abutting the delay element 40. Output charge 152 provides a detonation signal, in response to the initiation of transfer charge 44b sufficient to initiate detonation and explosion of a borehole explosive charge or other explosive device. The output charge 152 comprises an initiating explosive such as lead azide pressed onto a high-velocity explosive, such as pentaerythritol tetranitrate (PETN).

[0074] In normal operation, an incoming initiation signal will be transmitted from the transmission tube 111, through the alignment cup 140, to delay element 40. The signal is in the form of a pulsed shock wave and/or flame front, and is focused at aperture 47a in cap 46a by the alignment cup such that the signal impinges on a pyrotechnic initiating transfer charge 44a contained therein. Delay element 40 functions to control the rate of signal transfer from one side of delay element 40 to the other, i.e., from transfer charge 44a to transfer charge 44b, and thus from transmission tube 111 to output charge 152.

[0075] After the delay interval imposed by delay element 40, transfer charge 44b initiates output charge 152, via aperture 47b at the output end of the fuse. Output charge 152 rapidly detonates to generate an explosive detonator output signal.

. [0076] In an alternative embodiment, delay element 40 is employed in a non-explosive initiator having a pyrotecnnical output charge rather than an explosive output charge. The term "delay initiator" refers to explosive and non-explosive initiators that comprise delay elements; "delay detonator" refers to a detonator (an initiator that emits an explosive output signal) comprising a delay element.

[0077] Although delay element 40 is illustrated as being used in a detonator, it would work equally as well as an in-line signal transmission tube delay unit, such as the delay unit disclosed in U.S. Patent 4,742,773, the disclosure of which is hereby incorporated by reference.

[0078] Delay elements as described herein can function reliably at very low temperatures, for example at temperatures as low as -346°F. For example, some delay elements fabricated from the reactive laminates will function when immersed in liquid nitrogen. The rate at which a delay element reacts varies much less with temperature, especially at temperatures below room temperature, than the rate at which conventional delay elements react. Since low temperature reliability and timing accuracy are perennial problems experienced with conventional pyrotechnic delay elements and electronic delay circuits, this aspect of the invention offers the possibility of more reliable and more accurate timing of devices incorporating such fuses, thus providing an important improvement over the prior art. Furthermore, because multilayer foils are typically quite uniform, sample delay element strips cut from foil sheets can be used to characterize the entire sheet quite accurately, thereby providing a means to produce fuses that time with improved accuracy and precision as compared to conventional pyrotechnical delay elements.

[0079] Referring now to Figufe 5, there is shown electric header 48 comprising a tubular body 50 having an electrically insulating base 52 within which a pair of electrical connectors 54a, 54b are mounted. A reactive mixture 56, which may be an explosive or a pyrotechnic material, is contained within the end of tubular body 50 opposite from the end which contains the base 52. A delay element 58 in accordance with the invention connects electrical connectors

54a, 54b and reactive mixture 58. Delay element 58 may be coated on both its major surfaces 58a, 58b with a reactive multilayer laminate which may be applied in a linear pattern to provide the shortest distance between connectors 54a, 54b and reactive mixture 56, or it may be applied in a wavy, open coil, zigzag or other non-linear pattern to increase its effective travel length and thereby increase the delay period. When electrical energy is applied across connectors 54a, 54b, a spark is generated which ignites the reactive multilayer laminate coating which, after the selected delay period, reaches reactive mixture 56 to ignite it.

[0080] In various embodiments, the delay element may be packaged in an encapsulation to facilitate its use as a delay element. For example, a delay element may be packaged in a plug sized appropriately to fit inside a standard detonator, with at least the ends of the strand exposed at both ends of the plug. The strand may be packaged thus using an insert molding technique to form the plug a moldable polymeric resin. Similarly, in an alternative embodiment, the delay element may be incorporated into a tubular package, e.g., by disposing the delay element in a glass capsule having cupped end caps that contain transfer charges to enhance the pickup and/or output characteristics of the delay element, for example, to resemble a Buss-type fuse. Parting the reactive multilayer foil from its substrate or uncoiling the ends of a delay element having a dilatory configuration facilitates transferring the energy into and out of the strand for initiation of the alloying reaction and the subsequent initiation of an output transfer charge.

[0081] In some applications, where there is a susceptibility to "blow-by" that is, a susceptibility of the incoming signal, such as the spit from a shock tube, to by-pass all or some of the nano-layer coated surfaces of the delay element. Thus, "blow-by" is by-passing of the delay element or a portion of it by the input signal, thereby failing to attain the correct delay timing.

[0082] One solution to the blow-by problem is to provide a structure which blocks the input signal from by-passing the delay element. For example, a plurality of ribs may be provided about the delay element so that when pushed into a tube, or the tube-like drawn "cup" of a detonator shell, the ribs seal the delay elements within the tube or shell, thereby preventing blow-by.

[0083] Some of the above-described forms of construction are illustrated in Figures 6-7 as follows.

[0084] Figure 6 shows a delay fuse 50 comprising two solid plastic pieces 62a, 62b, each of which is semicircular in cross section and between which is sandwiched a delay element 64 having a reactive multilayer laminate 66a, 66b formed on each of its opposite major surfaces. The laminates 66a, 66b do not contact each other; they provide redundancy in case of failure of one of them. The edges of delay element 64 not covered by solid pieces 62a, 62b (which may be made of plastic or other material inert to the reaction of the reactive multilayer laminate 66a, 66b) may be sealed by any appropriate material or structure. Rubber ribs 68a, 68b encircle delay fuse 60 in case it is to be inserted into a tubular shaped structure such as the shell of a standard detonator. Rubber ribs 68a, 68b will be deformed by being inserted in a force-fit into a tubular shape and will serve not only to secure delay fuse 60 in place to prevent "blow-by". That is, it will prevent the incoming signal from by-passing delay fuse 60 thereby eliminating all or most of the delay provided by delay element 64.

[0085] Figure 6B shows partial viewed delay element 60 inserted into a fuse 70 which may be any suitable fuse including detonating cord. Mechanical means to secure fuse 70 to delay fuse 60 are omitted from Figure 6B for clarity of illustration. An input energetic impulse I (Figure 6) will start the reaction of reactive multilayer laminate 66a, 66b which will result in an output signal O to initiate a suitable device such as fuse 70.

[0086] Figure 7 is a side view of a delay fuse 72 comprising a coiled laminate wire 74 contained with a tubular body 76 (which is rendered in Figure 7 as though it were transparent, for clarity of illustration) which is closed at either end by plugs 78a, 78b. An input end 76a of coiled laminate wire 74 protrudes from one end of tubular body 76 and an output end 76b protrudes from the other end. Input end 76a is ignited by a suitable energetic input and the alloy reaction or burn travels along the coiled laminate wire 74 until it reaches the output end 76b thereof to provide an outgoing signal. The manufacturer of a multilayer laminate wire such as wire 74 is described below.

[0087] Figure 8 shows a fine wire coated mesh 80 which mesh may be made of an aluminum wire mesh coated with nickel. As is known in the art, an intermediate strike of zinc may be applied to the aluminum wire mesh prior to applying the nickel coating. Mesh 80, if ignited by a flame, will undergo an exothermic, self-sustaining reaction. In order to enable that reaction

to be self-sustaining (i.e., to take place in the absence of oxygen or when the mesh is in contact with or covered entirely by an inert material, such as by being potted in a suitable potting compound) wire mesh 80 is folded upon itself at least once to provide a double layer and may be folded upon itself more than two times to provide a triple, quadruple, etc., layer. Delay element 82 (FigureδA) shows wire mesh 80 folded upon itself to provide a three-layered delay element.

[0088] The nickel-aluminum reaction will not jump even the smallest crack or discontinuity in the coatings. Therefore, if it is desired to produce a serpentine delay element, the multilayer coated substrate may be cut to a tooth-like pattern thereby compelling the reaction to travel along a serpentine path as it will not jump the slits or cut-outs in the substrate. Alternatively, a multilayer wire may be coiled to provide an extended travel path, e.g., a serpentine path. The serpentine pattern can be applied by photolith or other suitable method.

[0089] Figure 9 shows a delay element 84 comprising a substrate 86 which may be made of aluminum and having disposed over the entire major surface seen in Figure 9 the reactive multilayer laminate 68, a portion of which at the left-hand side of Figure 9 is broken away to show the aluminum substrate 86. An energetic input I applied to reactive multilayer laminate 88 to initiate an alloying reaction or burn which will travel along the serpentine path to generate an output signal O. The serpentine path is defined by slits 90 which are disposed transversely, perpendicularly in the illustrated embodiment, to the longitudinal axis of delay element 84. Although in the illustrated embodiment the slits 90 are shown to have a significant width, they could be much narrower and many more than illustrated could be utilized for a given length of delay element 84. Thus, slits 90 should have a width no greater than the blade or die used to cut them because it has been found that the alloying reaction will not jump over even a very narrow width.

[0090] Figure 10 shows a delay tube 92 comprising a tubular body 94 which, for clarity of illustration, is rendered in Figure 10 as though it were transparent. The opposite end of tubular body 94 are closed by plugs 96a, 96b and delay element 84 is received therein and has its opposite extreme ends 84a, 84b protruding from tubular body 94. Tubular body 94 could be hollow or it could be filled with a potting compound. (The same applied to tubular body 16 of Figure 7.)

[0091] Figure 11 shows a delay element 98 comprised of three substrates 100a, 100b and 100c stacked one above the other. Openings 102a and 102b are formed at opposite ends of, respectively, substrates 100a and 100b. The substrates are coated with a reactive multilayer laminate in a suitable pattern on the respective top surfaces thereof so that initiation by an energetic input I of the reactive multilayer laminate on substrate 100a will initiate a reaction whose travel path TP is indicated by the arrow so marked. The travel path will travel along substrate 100a down through opening 102a thence along substrate 100b and downward through opening 102b thence along the surface of substrate 100c to generate the output signal O. Suitable vertical spaces or other means may be utilized to maintain the substrates 100a, 100b, 100c in alignment and a downward connector may be provided to carry the reactive multilayer laminate downward through opening 102a and downward through opening 102b to the next adjacent substrate.

[0092] Figure 12A shows a delay element 126 having a length a and a delay element 128 having a length b. Delay element 126 has coated on its substrate a reactive multilayer laminate which has a burn rate which is higher than the burn rate of delay element 128.

[0093] Figure 12B shows delay element 126 fastened by any suitable means to delay element 128 with delay element 128 overlapping one-quarter of the length (0.25a) of delay element 126. The result is a finished or combined delay element 130 having a total length of 0.75a plus b and exhibiting a faster burn rate along the exposed portion of delay element 126 than that which occurs along the exposed entirety of delay element 128. In this way, an increased bum time and therefore increased delay between the time of the energetic input I and the output signal O is attained.

[0094] In Figures 12A and 12B the pattern of the reactive laminate layer is not indicated and the entire surface of the delay elements visible in Figures 12A could be coated with the reactive laminate layer. Alternatively, the reactive laminate layer could be applied to those surfaces in a serpentine, zigzag or other suitable pattern.

[0095] The reactive multilayers can be initiated directly by the spit from a shock tube. Note that conventional shock tube provides a signal pulse of about 1,200 to about 1,800 pounds per square inch and the signal travels at about 2,000 meters per second through the tube. Alternatively to direct shock tube initiation, a fire material may be utilized to receive the shock tube

signal and initiate the reaction of the multilayer foil, especially if the input "spit" impinges on the edge of the substrate. It should be noted in this regard that an input signal such as the spit from a shock tube must be directed onto the multilayer surface(s) inasmuch as directing the spit of the shock tube onto the uncoated edge of the multilayered dual-coated element will not initiate the multi layers.

[0096] The reactive multilayer material does not generate a "spit" of its own so in order to transmit an output signal from it, it is usually necessary to use a fire material or directly contact the multilayer in the pyrotechnic delay train or primary explosive to be initiated by the delay element. (Or looked at another way, in such cases, the pyrotechnic train or primary output explosive provides the fire material.)

[0097] For use in conventional detonators, a strip of the multilayered dual-coated substrate will have a width equal to or very slightly less than the inside diameter of a conventional detonator shell, i.e., 255 one-thousandths of an inch. Generally, the width of the delay element of the invention will be from about 50 to 255 one-thousandths of an inch.

[0098] A typical delay element in accordance with one of the embodiments of the invention is connected to a shock tube which provides the input signal. The input signal is then transmitted by the dual-coated substrate to a target initiator or other device. #4

[0099] Optionally, a calibration multilayer foil wire may be used with the delay element, for testing purposes. The calibration multilayer foil wire is configured similarly to the delay element. By initiating the calibration multilayer foil wire and ascertaining its reaction rate, the expected delay interval to be provided by the delay element can be calculated on the basis that the delay element strip has the same reaction rate as the calibration multilayer foil wire. Using the delay interval information obtained from the calibration strip, the delay element can be prepared for improved accuracy and precision. For example the effective length of the delay element in a delay element can be selected in response to the delay interval information. In one embodiment, the distance between transfer charges at opposite ends of a strip of reactive multilayer laminate in a delay element can be adjusted. Alternatively, if the rate data obtained from a calibration strip indicates that a planned first strip of a first reactive multilayer laminate in a delay element will impose a longer delay than was planned, part of the strip of reactive multilayer

laminate in the delay element can be circumvented by applying a section of a faster-reacting second strip between an intermediate portion of the first strip and the transfer charge with which it communicates. The present invention thus provides for adjusting the expected delay interval of the delay element in a manner analogous to the interrogation of electronic delay units to ascertain that they are properly programmed to provide the desired delay period. The capability greatly enhances the delay period accuracy and precision of the delay element.

[00100] In another embodiment, a delay element of increased delay time is attained by stacking the dual-coated multilayer substrate in, say, three layers, one above each other, with provision for sending the signal from one layer to the next adjacent layer to generate a delay. A signal can travel through the substrate by means of suitably positioned holes and/or multilayer wires to help conduct the reaction signal from one stacked substrate to the next adjacent one.

[00101] Bidirectional delay elements, e.g., delay elements in which either end may be the input or the output end, can readily be manufactured from the multilayer foils and meshes of the invention.

[00102] The timing of the delay may be adjusted by overlapping two co-axially aligned substrates as shown in Figure 13B. Thus, a faster burning substrate may be paired with a slower burning substrate, or equal burning rate substrates may be employed. The amount of overlap of the substrates relative to each other provides infinite adjustment of the overall speed of the delay element.

[00103] Figure 13 shows a wire laminate 104 which is comprised of a core wire

106 over which one or more layers of a reactive metal or metals have been plated as an overlayer 108. Overlayer 108 may comprise a single layer of a metal which is reactive with the metal of core wire 106 or it may comprise alternating layers of reactive metal. For example, core wire _v 106 may be aluminum and overlayer 108 may be a single layer of nickel. Alternatively, over- layer 108 may comprise alternating layers of nickel and aluminum. As disclosed elsewhere herein, a number of layers of another metal may be interspersed between alternating layers of nickel and aluminum in order to help control the rate of propagation of the reaction along wire laminate 104.

[00104] Figure 14 shows a plurality of wire laminates 104 of Figure 13 braided together to form a reactive material cord 107.

[00105] While the invention has been described in detail with respect to specific embodiments thereof, it will be appreciated that the invention has other applications and may be embodied in numerous variations of the illustrated embodiments.