WO1998024095A2

WO1998024095A2 - Bridgeless electrical initiatior and method of making the same

Info

Publication number: WO1998024095A2
Application number: PCT/US1997/019975
Authority: WO
Inventors: Lehi David Smith
Original assignee: Cordant Technologies, Inc.
Priority date: 1996-11-12
Filing date: 1997-11-12
Publication date: 1998-06-04
Also published as: AU6532198A; WO1998024095A3

Abstract

An energetic composition capable of being fired by heat generated when electrical energy is applied according to the present invention includes a firing material that fires in response to application of heat and contains less than 5 weight % of a resistive material, preferably graphitic nanotubes, that has strands having a width that are preferably smaller than 2 microns and a length that is substantially greater than the width. The strands of resistive material are dispersed in the energetic composition in a manner to create conductive paths which, upon application of sufficient electrical energy, will generate heat sufficient to fire the firing material. Initiators which use this energetic composition, as well as methods for making the energetic composition and initiators are also described.

Description

BRIDGELESS ELECTRICAL INITIATOR AND METHOD OF MAKING THE SAME

Field of the Invention

The present invention relates to a bridgeless initiator capable of being fired by heat generated when electrical energy is applied to an energetic composition and methods of making the energetic composition and an initiator using the same.

Background of the Invention

In order for a large explosion to occur, a chain of controlled explosions, each having a size that is greater than the preceding one, is typically created. An initiator is a known type of firing device that transforms an initiating energy to an initial firing to begin the chain of explosions.

While mechanical energy can be used to create pressure that will initiate the firing, electrical energy is often preferred as the initiating energy because it can be controlled with much greater precision. Initiators which are initiated with electrical energy, transform the electrical energy into heat through an element that is more resistive than the other conductors used in the circuit to initiate the firing. The amount of electrical energy required to generate the heat to initiate the initial firing varies. Typically it is defined in terms of an electrical energy or current that can be continuously supplied to the electrical initiator and not initiate a firing (known as a "all-fire energy or current") , and an energy or current that will always result in initiation of a firing (known as a "no- fire energy or current") .

While all electrical initiators transform electrical energy into heat, the firing material used in the initiator will determine the type of explosion that occurs. Certain initiators, called squibs, cause a fire to occur in a pyrotechnic material, which fire is then used to generate an explosion in another material. Other initiators, called detonators, cause a shock wave to be generated in a firing material, which shock wave is then used to generate a larger shock wave in another material .

Different types of materials have been proposed and/or have been used as the resistive element in electrical initiators. Bridgewire electrical initiators, which use a

"bridgewire" as the resistive element, are regarded as the most reliable and safe type of electrical initiators, and are the most commonly used electrical initiators. A conventional bridgewire initiator includes two spaced- apart conductive terminals. Between these terminals is a bridgewire, which typically is a thin wire having a resistance that is low, but is greater than the resistance of the other electrical elements in the circuit path. Surrounding the bridgewire is a firing material that will fire upon application of an electrical energy that generates sufficient heat as it passes through the bridgewire .

Bridgeless electrical initiators have also been proposed. U.S. Patent Nos. 2,918,871, 3,109,372, 3,713,385 and 3,726,217 all propose energetic compositions which contain a firing material and a resistive material mixed together. In these patents, conductive paths of the resistive material formed in the energetic composition will become sufficiently heated to fire the firing material when these energetic compositions are placed between two spaced apart terminals and electrical energy is applied. Resistive materials proposed for these bridgeless initiators variously include carbon black, carbon fibers, and metal powders. While these resistive materials may provide functioning bridgeless initiators, the bridgeless initiators described in these patents, like all conventional bridgeless initiators, are generally regarded as being inherently unsafe and unreliable products that do not have repeatable firing characteristics. Accordingly, conventional bridgeless initiators have never gained any substantial commercial acceptance. Furthermore, it is clear that certain of the bridgeless initiators described in these patents are nonfunctional combinations, use processes to make the energetic compositions that cannot be easily applied to mass production, require large amounts of energy to operate, exhibit less than optimum functional repeatability, and also require complex electrode shapes. As a result, bridgewire initiators presently remain the electrical initiator of choice, despite drawbacks such as high manufacturing cost.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a reliable, safe bridgeless electrical initiator that has repeatable firing characteristics.

It is another object of the invention to provide a reliable and safe bridgeless electrical initiator using graphitic nanotubes as the resistive material.

It is still another object of the invention to provide a bridgeless electrical initiator using a resistive material, preferably graphitic nanotubes, which has alterable all-fire/no-fire and resistive characteristics .

It is a further object of the present invention to provide an energetic composition that contains a firing material and a resistive material, preferably graphitic nanotubes, that is capable of being fired by heat generated when a short pulse of energy is applied.

It is another object of the invention to provide a reliable, safe, bridgeless electrical initiator composition that has repeatable firing characteristics in which numerous strands of a resistive material surround or envelope, in a web-like manner, at least a substantial plurality of the individual particles of the firing material within the energetic composition. By "surround" or "envelope" is meant that multiple strands will extend to at least some extent around one or more the particles in close proximity to the same, although not necessarily entirely covering, any individual particle. It is another object of the present invention to provide a method for making granules of an energetic composition. A solution that contains a colloid-like suspension of a firing material, a fibrous resistive material, a solvent and a binder is mixed, filtered and sieved to form granules that have a free- flowing characteristic and are processable on a commercial scale.

In order to attain the above recited objectives, among others, the present invention provides for an energetic composition capable of being fired by heat generated when electrical energy is applied. The energetic composition contains a firing material that fires in response to application of heat and a resistive material, preferably graphitic nanotubes, having individual strands with a width that is much smaller than a typical firing particle and a length that is substantially greater than its width. The strands of resistive material are randomly and substantially homogeneously dispersed in the energetic composition in a manner that they intersect each other and envelope individual particles in interconnected web-like structures so as to create conductive paths which, upon application of a sufficient electrical energy, will generate sufficient heat to fire the firing material . In a preferred embodiment, by adjusting the respective amounts of explosive, resistive material and binder in the energetic composition and the dimensions of electrical contacts and pressing force used to make the energetic composition, the all-fire/no-fire characteristics and resistance of the energetic composition can be set to predetermined desired levels, so that an initiator having the desired characteristics can be obtained. In another aspect of the present invention, a method of making granules of the energetic composition according to the present invention is described. In this method, less than 2 wt . % of the fibrous, resistive, material having relative dimensions as mentioned above, are mixed in a solvent containing a binder and a firing material to obtain a suitably mixed resistive composition suspension having the appearance of a colloidal suspension. In a preferred embodiment, a suspension of the solvent, binder and resistive material is first prepared with the firing material being subsequently mixed into the colloid-like suspension. Thereafter, the suspension containing the firing material is filtered to remove a substantial portion of the solvent containing the binder and obtain a wet cake, which wet cake is then sieved to obtain the desired granules.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages of the present invention can be appreciated from study of the following detailed description of the preferred embodiment together with the drawings in which:

FIGS. 1A-1C illustrate microscopic views of the energetic composition according to the present invention using graphitic nanotubes as the resistive material at various magnifications;

FIG. ID highlights graphitic nanotubes enveloping a firing particle in a web-like manner in the microscopic view of FIG. IC according to the present invention;

FIGS. IE and IF illustrate particle size distributions of zirconium and potassium perchlorate in the energetic composition illustrated in FIGS. 1A-1C;

FIG. 2 schematically illustrates a functional diagram of an electrical initiator utilizing the energetic composition according to the present invention;

FIG. 3 is a flowchart of the significant steps used in preparing the energetic composition according to the present invention; FIG. 4 illustrates one embodiment of electrical initiator utilizing the energetic composition according to the present invention;

FIG. 5A-5B illustrate a second embodiment of an electrical initiator utilizing the energetic composition according to the present invention;

FIGS. 6A-6G illustrate various modifications to the second embodiment of the electrical initiator utilizing the energetic composition according to the present invention; FIGS. 7A-7B illustrate a still further modification embodiment of the electrical initiator utilizing the energetic composition according to the present invention;

FIGS. 8A-8B illustrate a further modification to the second embodiment of the electrical initiator with the energetic composition according to the present invention;

FIG. 9 illustrates the function time vs. current for the second embodiment of electrical initiators containing the energetic composition according to the present invention; and

FIG. 10 illustrates the function time vs. current for another version of the second embodiment of electrical initiators containing the energetic composition according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1A-1C illustrate a portion of an energetic composition 10 according to the present invention at 2000x, 10,000x, and 20,000x times magnification, which includes particles 12 of a firing material and a resistive material which includes individual conductive paths 13, such as illustrated in FIG. IB. Each conductive path includes a plurality of strands 14 dispersed among the particles 12 of the firing material, as can be seen in FIGS IB and IC and highlighted in FIG. ID by lines 14-1 drawn to correspond to the individual strands 14 that can be seen in a portion of the FIG. IC microphotograph.

The preferred firing material is zirconium/potassium perchlorate ("ZPP") for pyrotechnic materials and lead azide for explosive materials. Other firing materials, including but not limited to zirconium subhydride/potassium perchlorate, titanium/potassium perchlorate, or titanium subhydride/potassium perchlorate as pyrotechnic materials and lead styphanate or mercury fulminate as explosive materials, can also be used. Typical particles sizes for zirconium are 2 microns and typical particle sizes for potassium perchlorate are 2.5 microns. FIGS. IE and IF illustrate the particle size distribution of zirconium and potassium perchlorate in the energetic composition illustrated in FIGS. 1A-1C. Particle sizes for lead azide are dependent upon recrystallization conditions, but lead azide particles that have sizes in the range of 10-20 microns are preferred, although sizes larger than 100 microns may be used. Generally, firing material particle sizes other than these specified in the above examples can be used according to the present invention, even though particle sizes that are generally less than 20 microns are preferred. Particle sizes less than 0.5 microns can be used, but they are presently difficult to obtain and more expensive . The strands 14 of resistive material generally have a length to width ratio of at least five, preferably at least 20, and typically at least 100-1000, with the width of the strands being less than 2 microns, preferably less than .05 microns, and typically being about .01 microns. At these dimensions and length to width ratios, the strands of the resistive material become intertwined in the interstitial spaces between and generally reside on the surface of the individual particles of the energetic material so as to at least partially surround the latter in a web-like configuration within the resulting overall composition. This is illustrated by the highlighted lines 14-1 as shown in FIG. ID and corresponding to the individual strands 14 that appear in the FIG. IC microphotograph . The resistive material presently preferred according to the present invention is graphitic nanotubes, also known as carbon nanotubes. The specifically preferred type of graphitic nanotube is a type CC graphite nanotube commercially available from by Hyperion Catalysis International, Inc. Characteristics of graphitic nanotubes are that they are small tubular shaped strands that are grown catalitically from carbon precursors and preferably being substantially free of pryrolytically deposited thermal carbon, which is a contaminant. Graphitic nanotubes are also much smaller than the particle size of firing materials used, as evidenced by a comparison of the sizes provided above and further illustrated by the presence of roughly 1-300 trillion graphitic nanotube strands in 1 gram of granules of the energetic composition according to the present invention. Such graphitic nanotubes are distinct from carbon fibers which are formed by carbonaceous deposits from a pyrolytic decomposition of a carbon-containing polymeric material. The graphitic nanotubes used in this invention are substantially free from pyrolytic carbon material. Type BN and DD graphite nanotubes made by Hyperion Catalysis International, Inc. can also be used as the resistive material according to the present invention. Other materials such as nanotubes, that have dimensions within the ranges specified in this application are also potentially usable as the resistive material .

Graphitic nanotubes generally are extremely small and have a length in the range of about lμ to about lOμ and a width in the range from about 3.5 nanometers to about 75 nanometers. Length to width aspect ratios of graphitic nanotubes are generally greater than 5 and typically at least about 100:1. Suitable graphitic nanotubes are described in further detail in U.S. Patent Nos. 5,171,560, 5,165,909, 5,098,771 and 4,663,230, which patents are incorporated herein by reference.

It should be noted that the term "width" is used interchangeably with the term "diameter, " with respect to the resistive material. Graphitic nanotubes, the presently preferred resistive material, have a cylindrical shape in which the width is the same as the diameter. Other resistive materials, which meet the conditions set forth in this application but have not been identified, may have different shapes. With respect to resistive materials in which the term "width" is not synonymous with diameter, "width" should be interpreted as the smallest cross sectional distance between opposite sides, and such resistive materials are intended to be within the scope of this invention.

FIG. 2 illustrates a functional diagram of an initiator 30, which includes two conductive terminals 32 and 34, between which is placed energetic composition 10 after it has been processed as described hereinafter. Conductive paths 36 that are generally throughout formed by the strands 14 of resistive material, the energetic composition 10 provide resistive paths which, when a sufficient electrical energy is applied, heat the firing material and cause it to fire. It should be noted that the terminals 32 and 34, as well as the wire conductors used to apply the electrical energy between them, will be much more conductive than the conductive paths 36 that are formed by the intertwined strands 14 of resistive material within the energetic composition 10.

During operation of the initiator 30 illustrated in FIG. 2, application of electrical energy in the form of a current for a predetermined duration to the firing material will cause heating of the resistive material when the electrical current passes therethrough. The electrical energy is transformed into thermal energy and cause firing of the firing material . As shown by the examples and tests described below, typical energies that can be used to fire the energetic composition according to the present invention are typically low, such as in the range of 1-10 millijoules, but can be lower or higher as needed for the specific application. These low energies, which are due to the resistance that is less than 300 ohms and is preferably less than 50 ohms of the energetic composition between the spaced apart terminals of the bridgeless initiator according to the present invention, allow for the use of relatively small sources of electrical power, such as a standard 12v car battery. Moreover, a very desirably very short firing time is provided. Thus, the initiatore 30 will fire when 10 amps is applied in less than 5 milliseconds, and typically less than 2 milliseconds,

A method of preparing the energetic composition according to the present invention will now be described with reference to the flowchart of FIG. 3.

In step 50 shown on FIG. 3, a small weight percentage, less than about 2% and preferably only about 0.5% of resistive material having characteristics as described above, which is preferably graphitic nanotubes, is mixed into a solution containing about 2.5 wt . % binder in a suitable solvent. Although the concentration of the binder should be kept low, the exact concentration in the solution is not critical and may conveniently range from 1 wt . % to 10 wt . % , or more. The mixing is initiated using a centrifugal homogenizer for between 1 and 2 minutes in a container having a size corresponding to the size of the mixing head. Thereafter, this partially mixed suspension is further mixed in an ultrasonic homogenizer for about 30 seconds in a container having a size corresponding to the size of the mixing head such that all of the suspension is mixed. This produces a suitably mixed resistive material suspension having the appearance of a colloid, and preferably a colloidal gel.

In step 52, an amount of firing material is mixed into the resistive material solution so that a desired percentage of firing material is obtained, typically in the range of 95 wt . % to 99.9 wt . % firing material relative to the resistive material . The firing material 12 is mixed into the resistive material suspension using the ultrasonic homogenizer for about 30 seconds to obtain a firing suspension.

Although a multi-step mixing process as outlined above is preferred, it is anticipated that other mixing processes can be performed. For example, larger quantities of the energetic composition can be mixed in a single mixing step using a pump-type homogenizer, such as manufactured by APV located in Wilmington, MA and sold as model 15MK-8TA in which the constituents of the solution are mixed by being intaken to the pump in the pump-type homogenizer and then expelled therefrom under high pressure. Such a pump-type homogenizer can mix the energetic composition using a predispersion with or without a centrifugal homogenizer. In addition, processing aids such as emulsifiers or agents which help maintain a colloical suspension may be used. In any event, what is important is to use a resistive material having the very small dimensions, indicated above, and to ensure that individual strands of resistive material are dispersed throughout the colloidal suspension to efficiently dispense the resistive material throughout the firing material at a particle level. This will allow for an energetic composition that has highly repeatable characteristics that can also be produced in large scale with desirable free flowing characteristics. In contrast, the relatively larger resistive materials of the prior art, such as carbon fibers, form an undesirable fluffy mass that is difficult to dispense, and are, therefore, difficult to process. It should also be noted that the mixing that takes place in steps 50 and 52 cause undesired heating that results in less efficient mixing. As a result, although not always necessary, it has been found useful to chill the firing composition suspension during the mixing process .

In step 56, this firing suspension is filtered using a vacuum filter to remove about 80% of the solvent/binder solution and obtain a wet cake. Filtering off the solvent/binder solution ensures that the weight percent of binder in the resultant energetic composition 10 is less than about 5%, and preferably about 1-4%.

In step 58, the wet cake is sieved, preferably using a screen having a #24 mesh size, so that granules of the energetic composition are obtained.

In step 60, these granules are dried, preferably for 8-10 hours in an oven at a temperature of 100-124 to remove the remaining solvent .

The energetic composition according to the present invention, as described above, can be used with either pyrotechnic or explosive materials.

As also mentioned above, the presently preferred pyrotechnic firing material to obtain an energetic composition 10 according to the present invention is zirconium potassium perchlorate ("ZPP") . A typical mix of ZPP will contain about 50% by weight zirconium that has a particle size of about 2 microns and about 50% by weight potassium perchlorate that has a particle size of about 2.5 microns . A small percentage by weight of binder, such as VYLF- X is a necessary component to be retained in the formed energetic composition 10 to ensure that once mixing of the firing material and resistive materials is completed and a suitable dispersion is obtained, that this suitable dispersion is maintained during subsequent handling and processing. A binder, in an amount of about 4 wt . % compared to the zirconium and potassium perchlorate, such as a Union Carbide vinyl polymer known as VYLF-X can be used. Other binders, such as BF Goodrich Estane ^R5703P or Zeon Chemicals HyTemp™ 4454 can also be used. No matter which binder is used, however, if the percentage of binder becomes too large, this will inhibit the conductive paths formed by strands 14 of the resistive material and prevent safe, reliable and repeatable operation.

It should also be noted that for certain higher temperature and/or high current applications, the melting temperature of the binder can become an important factor, since resistive materials having properties as mentioned above, such as graphitic nanotubes, tend to be elastic and, as a result, may move from their dispersed positions without the presence of the higher temperature binder, especially after being subjected to a high temperature and/or current. Accordingly, for such higher temperature/current applications, binders having a higher melting point, such as DuPont Viton^R-A or 3M Kel-F™800, are preferably used.

As noted above, whatever the binder is selected it should be sufficiently soluble in a solvent so that, after filtering and drying, enough binder remains to ensure that the firing material and the resistive material remain suitably dispersed. The solvent should provide adequate solubility to the binder at suitable concentration levels, e.g. up to 10 wt . % or more. Known solvents include methylethyl ketone "MEK" , acetone, and dimethyl formamide . Other binder/solvent combinations may also be used, such as Dupont Elvamide^R Nylon with methanol or aqueous mixtures containing guar gum, polyacrylamide or polyvinyl alcohol as the binders. Care should be used with aqueous solutions, however, since they will also dissolve many oxidizers that may be used, such as potassium perchlorate. The resistive material according to the present invention should be well wetted and dispersed in the solvent to create a resistive material suspension, which suspension has a consistency with the appearance of a colloid suspension, preferably a colloidal gel. As also mentioned above, one presently preferred explosive, or in other words detonable firing material, for incorporation into the energetic composition 10 is lead azide. A typical mix of a detonatable energetic composition will contain about 98 wt . % lead azide, which is a known decomposable explosive material that will fire when sufficient heat is applied to it and generate a shock wave. Binders and solvents that are used with ZPP, as mentioned above, can also be used in the same proportions with lead azide. Once granules of the energetic composition according to the present invention are obtained, they can be formed in different ways for use in a bridgeless initiator.

FIG. 4 illustrates an electrical initiator 70 containing a pellet 72, terminals 74 and 76 at opposite ends (or sites) thereof with a casing 78. The pellet 72 can be produced by placing about .4 grams of the granules of energetic composition 10 in a .5" diameter pellet and pressing the same for about 5 seconds at 20,000 lbs. force in a calibrated hydraulic press. This pellet 72 contains the desired firing and resistive properties such that application of a sufficient current to terminals 74 and 76 will cause the generation of heat and firing of the firing material in the pellet 72 made from energetic composition 10. Initiator 70 can then be placed into a casing 78 of a larger explosive device to initiate the explosive chain, as described previously.

FIGS. 5A and 5B illustrates an initiator 90 made from a conductive cup 92 having a casing which may have an inner diameter of about .25". After filling conductive cup with about .05 grams of the energetic composition 10, a insulative cap 96 having a diameter slightly larger than the inner diameter of conductive cup 92 is pressed into the conductive cup 92 at 130 lbs. force for about 2 seconds, to cause an interference fit between the conductive cup 92 and the cap 96. Insulative cap 96 also contains terminals 98 and 100 with accurate leads which are spaced apart a predetermined distance, typically in the range of 1-30 mils, indicated by space 102 in FIG. 5B and respectively connected to insulated lead wires 104 and 106. When cap 96 is pressed into the conductive cup 92, the energetic composition 10 within the conductive cup 92 is pressed against terminals 98 and 100 to establish conductive paths between them and the dispersed resistive material. Initiator 90 can then be used as part of a larger explosive device.

FIGS. 6A-6G illustrate other embodiments 96A-96G of insulative cap 96 wherein terminals 98A-G and 100A-G are respectively provided. These terminals 98A-G and 100A-G are arranged so that different numbers of conductive paths are formed with the resistive material in contact with the respective terminals 98A-G and 100A-G. These embodiments have contact pattern shapes that are easily made with photolithography. It should be noted that all of these contact pattern shapes performed equally well, and, accordingly, the specific contact pattern shape is not considered critical FIG. 7A-7B illustrates a further modified initiator 90J which, instead of using two insulated wires 104 and 106, uses an insulative cap 96J with only a single insulated wire 108 attached to a terminal 98J and uses the conductive cup 92 as a second terminal 100J, with a space 110 between the terminal 98J and the conductive cup 92 to establish conductive paths using the strands 14 of resistive material within energetic composition 10. The space 110 will be of the same dimensions as space 102 mentioned above.

FIG. 8A-8B illustrates a further modified initiator similar to that shown in FIGS. 5A-5B, except that in addition to the energetic composition 10, there is an additional energetic material 120. In this initiator, initiation of the energetic composition 10 in turn initiates energetic composition 120. Composition 120 may or may not contain strands 14 of resistive material, and may be either a pyrotechnic or explosive material as described previously. In addition to energetic composition 120, additional compositions or "stages" in the energetic process can be used in an initiator constructed according to the present invention.

The following examples are given to illustrate various embodiments which have been made or may be made in accordance with the present invention. These examples are given by way of example only, and it is understood that the following examples are not comprehensive or exhaustive of the many types of embodiments of the present invention which can be prepared in accordance with the present invention.

Example 1

47 wt . % zirconium, 47 wt . % potassium perchlorate, 2 wt . % type CC graphite nanotubes and about 4 wt . % VYLF-X plastic binder were dispersed in an MEK solvent and processed into granules as described above. FIGS. 1A-1D are microphotographs of such a granule at 2000x, 10,000x, 20,000x, and 20,000x times magnification, respectively. Highlighted as mentioned previously in FIG. ID are the individual strands 14 of graphitic nanotubes that surround or envelope in a web-like manner individual particles 12 of zirconium and potassium perchlorate. 0.22 g. of these granules were then pressed into a pellet measuring approximately 0.5" in diameter and 0.031" thick using a hydraulic press calibrated to provide 20,000 lbs . force for 5 seconds .

The pellet was placed in contact with an electrode at each large terminal surface. Resistance was about 15 ohms. Upon application of 1 amp for an extended number of seconds, no firing occurred. Upon application of 2.2 amps, firing occurred in less than 2 milliseconds. This test was repeated with identical results.

Example 2

An energetic composition using the same components as described above was prepared and pressed into a pellet, except 46 wt . % zirconium, 46 wt . % potassium perchlorate, 4 wt . % type CC graphite nanotubes and about 4 wt . % VYLF-X plastic binder by weight were used.

The pellet was placed in contact with an electrode at each large terminal surface. Resistance was about 9 ohms. Upon application of 2 amps for an extended number of seconds, no firing occurred. Upon application of 4.4 amps, firing occurred in less than 2 milliseconds. This test was repeated with identical results. Example 3

Granules were obtained in the same way as those in Example 1 above, and 0.05 grams of same were placed in a conductive cup together with an insulative cap as illustrated in FIGS. 5A-5B and pressed using a pneumatic press calibrated to provide 130 lbs. force. The space 102 between the conductive surfaces on the insulative cap was about 0.020 inches. Forty-two such units were constructed. Resistance between the terminals for the units while at 130 lbs. pressing force averaged 3.1 ohms with a standard deviation of 0.5 ohms. Resistance between the terminals for the units when subsequently released to 0 lbs. force averaged 6.1 ohms with a standard deviation of 1.2 ohms. The units were then each individually subjected to a firing current level. The range of firing current levels was varied from 0.25 amps to 9 amps.

FIG. 9 is a plot of function time versus firing current for these forty-two initiators. For each of the units, a specific current was applied for up to 20 seconds to determine whether the initiator fired. If the initiator fired, the time from application of current until the unit fired was recorded. Firing was evidenced by light output from the initiator. Units that fired are represented by diamonds while units that did not fire are indicated by squares. In cases where there were a number of units that did not fire at a given current level, a minus sign above the square indicates the number of units that did not fire at that current level. The solid vertical line was drawn at the lowest current level for which there was an initiator which fired. The dotted vertical line was drawn at the highest current level for which there was an initiator which did not fire.

Five additional units were constructed in similar fashion, and each of those five units was twice subjected to a firing current of 0.8 amps for 5 minutes. None of the units fired.

Example 4

Granules were obtained in the same way as Example 2 above, and 0.05 grams of same were placed in a conductive cup together with an insulative cap and pressed as in Example 3. Thirty-three such units were constructed. Resistance between the terminals for the units while at

130 lbs. pressing force averaged 1.6 ohms with a standard deviation of 0.3 ohms. Resistance between the terminals for the units when subsequently released to 0 lbs. force averaged 3.1 ohms with a standard deviation of 0.5 ohms. The units were then tested as in Example 3 over a firing range of 0.5 to 8 amps .

FIG. 10 plots the test of these 33 initiators in the same manner as described for the FIG. 9 plot.

From the foregoing examples above it can be seen that numerous important properties of an initiator can be altered in a variety of meaningful ways by numerous methods which utilize the present invention.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is understood that the invention is not limited to the disclosed embodiment, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

I claim:

1. An energetic composition capable of being fired when a predetermined electrical energy is applied therethrough comprising: a firing material that fires in response to application of heat; a plurality of strands of graphitic nanotubes, each strand of said plurality having a length that is at least five times greater than a width, said strands dispersed in said energetic composition in a manner to create conductive paths which, upon application of said predetermined electrical energy, will generate heat sufficient to fire said firing material; and a binder material dispersed in said energetic composition in a manner that assists in maintaining relative positioning of said plurality of strands of said graphitic nanotubes dispersed in said firing material.

2. An energetic composition according to claim 1 wherein said length of said graphitic nanotubes is in the range of about lμ to about lOμ and said width of said graphitic nanotubes is in the range from about 0.05 nanometers to about 75 nanometers.

3. An energetic composition according to claim 2 wherein said energetic composition contains graphitic nanotubes in the range of 0.01 to 5 weight percent.

4. An energetic composition according to claim 3 wherein said predetermined energy is a current that is less than 10 amps applied for less than 5 milliseconds.

5. An energetic composition according to claim 3 wherein said firing material has an average particle size of less than 5 microns .

6. An energetic composition according to claim 5 wherein said firing material is a pyrotechnic firing material .

7. An energetic composition according to claim 6 wherein said pyrotechnic firing material is zirconium potassium perchlorate.

8. An energetic composition according to claim 5 wherein said energetic composition includes less than 10 weight % of said binder.

9. An energetic composition according to claim 1 wherein said energetic composition contains graphitic nanotubes in the range of 0.01 to 5 weight percent.

10. An energetic composition according to claim 9 wherein said graphitic nanotubes strands have a length that is at least 20 times greater than a width.

11. An energetic composition according to claim 1 wherein said graphitic nanotubes strands have a length that is at least 20 times greater than a width.

12. An energetic composition according to claim 11 wherein said firing material has an average particle size of less than 5 microns.

13. An energetic composition according to claim 12 wherein said energetic composition contains graphitic nanotubes in the range of 0.01 to 5 weight percent.

14. An energetic composition according to claim 1 wherein said firing material is a pyrotechnic firing material .

15. An energetic composition according to claim 14 wherein said pyrotechnic firing material has an average particle size less than 5 microns.

16. An energetic composition according to claim 15 wherein said pyrotechnic firing material is zirconium potassium perchlorate.

17. An energetic composition according to claim 1 wherein said energetic composition includes less than 10 weight % of said binder.

18. An energetic composition according to claim 17 wherein said binder has a working temperature range from 65°F to 500°F.

19. An energetic composition according to claim 1 wherein said predetermined energy is a current that is less than 10 amps applied for less than 5 milliseconds.

20. An energetic composition according to claim 1 wherein said predetermined energy is a predetermined current applied for a predetermined period of time and a second predetermined energy having an associated second predetermined current that is less than said predetermined current such that application of said second predetermined current will not result in firing of said firing material.

21. An energetic composition according to claim 20 wherein a difference between said first and second predetermined currents is less than 2 amps.

22. An energetic composition according to claim 20 wherein the difference between said first and second predetermined currents is less than 0.5 amps.

23. An energetic composition capable of being fired when a predetermined electrical energy is applied therethrough comprising: a plurality of firing material particles that will fire in response to application of heat; a plurality of web-like conductive paths, each conductive path formed of a plurality of strands of a resistive material having a width that is less than 2 microns and a length at least 5 times greater than said width, said web-like conductive paths intersecting with each other and enveloping discrete ones of said firing material particles so that application of said predetermined electrical energy will cause generation of heat sufficient to fire said firing material; and a binder material which assists in maintaining relative positioning of said plurality of strands of said resistive material and said discrete ones of said firing material particles.

24. An energetic composition according to claim 23 wherein said length of said resistive material is in the range of about lμ to about lOμ and said width of said resistive material is in the range from about 0.05 nanometers to about 75 nanometers.

25. An energetic composition according to claim 24 wherein said energetic composition contains resistive material in the range of 0.01 to 5 weight percent.

26. An energetic composition according to claim 25 wherein said predetermined energy is a current that is less than 10 amps applied for less than 5 milliseconds.

27. An energetic composition according to claim 25 wherein said firing material has an average particle size of less than 5 microns.

28. An energetic composition according to claim 27 wherein said firing material is a pyrotechnic firing material .

29. An energetic composition according to claim 28 wherein said pyrotechnic firing material is zirconium potassium perchlorate.

30. An energetic composition according to claim 27 wherein said energetic composition includes less than 10 weight % of said binder.

31. An energetic composition according to claim 23 wherein said energetic composition contains resistive material in the range of 0.01 to 5 weight percent.

32. An energetic composition according to claim 31 wherein said resistive material strands have a length that is at least 20 times greater than a width.

33. An energetic composition according to claim 23 wherein said resistive material strands have a length that is at least 20 times greater than a width.

34. An energetic composition according to claim 33 wherein said firing material has an average particle size of less than 5 microns .

35. An energetic composition according to claim 34 wherein said energetic composition contains resistive material in the range of 0.01 to 5 weight percent.

36. An energetic composition according to claim 23 wherein said firing material is a pyrotechnic firing material .

37. An energetic composition according to claim 36 wherein said pyrotechnic firing material has an average particle size less than 5 microns.

38. An energetic composition according to claim 37 wherein said pyrotechnic firing material is zirconium potassium perchlorate.

39. An energetic composition according to claim 23 wherein said energetic composition includes less than 10 weight % of said binder.

40. An energetic composition according to claim 39 wherein said binder has a working temperature range from

65°F to 500°F.

41. An energetic composition according to claim 23 wherein said predetermined energy is a current that is less than 10 amps applied for less than 5 milliseconds.

42. An energetic composition according to claim 23 wherein said predetermined energy is a predetermined current applied for a predetermined period of time and a second predetermined energy having an associated second predetermined current that is less than said predetermined current such that application of said second predetermined current will not result in firing of said firing material.

43. An energetic composition according to claim 42 wherein a difference between said first and second predetermined currents is less than 2 amps.

44. An energetic composition according to claim 42 wherein the difference between said first and second predetermined currents is less than 0.5 amps.

45. An initiator responsive to electrical energy comprising: a pair of conductive terminals spaced apart from each other; and an energetic composition disposed under pressure between said pair of conductive terminals that is capable of being fired by heat generated when electrical energy is applied, said energetic composition including: a firing material that fires in response to application of heat; a plurality of strands of a resistive material, each strand of said plurality having a width that is smaller than 2 microns and having a length that is at least five times greater than said width, said strands dispersed in said energetic composition in a manner to create conductive paths which, upon application of said predetermined electrical energy, will generate heat sufficient to fire said firing material; and a binder material dispersed in said energetic composition in a manner that assists in maintaining relative positioning of said plurality of strands of said resistive material dispersed in said firing material .

46. An initiator according to claim 45 wherein said conductive terminals are spaced apart in the range of 1 to 100 mils.

47. An initiator according to claim 46 wherein each of said conductive terminals have a predetermined area that contacts said energetic composition.

48. An initiator according to claim 45 wherein a resistance of said initiator between said pair of conducive terminals is less than 50 ohms.

49. An initiator according to claim 45 wherein a resistance of said initiator between said pair of conductive terminals is variable in production by changing one of a shape of said conductive terminals, an area of contact between said conductive terminals and said energetic composition, percentage of said resistive material in said energetic composition, and said pressure of said energetic composition.

50. An initiator according to claim 49 wherein said variable resistance is variable in a range between 0.01 ohm and 300 ohms .

51. An initiator according to claim 45 wherein said predetermined energy is variable in production by changing one of a shape of said conductive terminals, an area of contact between said conductive terminals and said energetic composition, percentage of said resistive material in said energetic composition, and said pressure of said energetic composition.

52. An initiator according to claim 51 wherein said variable predetermined energy is variable in a range between 0.05 and 10 amps.

53. An initiator according to claim 45 wherein said predetermined energy is a current that is less than 10 amps applied for less than 5 milliseconds.

54. An initiator according to claim 45 wherein said predetermined energy is a predetermined current applied for a predetermined period of time and a second predetermined energy having an associated second predetermined current that is less than said predetermined current such that application of said second predetermined current will not result in firing of said firing material.

55. An initiator according to claim 54 wherein a difference between said first and second predetermined currents is less than 2 amps.

56. An initiator according to claim 54 wherein the difference between said first and second predetermined currents is less than 0.5 amps.

57. A method of making firing granules capable of being fired by heat generated when an electric current is applied, said method including the steps of: mixing less than 5% by weight strands of a resistive material and a firing material into a solution containing a solvent and a binder to obtain a colloidal suspension, said strands having a width that is smaller than 2 microns and a length that is at least five times greater than said width; filtering said colloidal suspension to remove a substantial portion of said solvent containing said binder and obtain a wet cake; and sieving said wet cake to obtain said firing granules.

58. A method according to claim 57 wherein less than 2% by weight of said resistive material is mixed into said solution.

59. A method according to claim 58 wherein said step of mixing mixes graphitic nanotubes as said resistive material .

60. A method according to claim 58 wherein less than 10% by weight of said binder is mixed into said solution.

61. A method according to claim 60 wherein said step of mixing mixes graphitic nanotubes as said resistive material .

62. A method according to claim 57 wherein less than 10% by weight of said binder is mixed into said solution.

63. A method according to claim 57 wherein said step of filtering uses a vacuum filter.

64. A method according to claim 57 wherein said step of mixing mixes graphitic nanotubes as said resistive material .

65. A method according to claim 57 wherein said step of mixing includes the steps of: mixing said resistive material in said solution containing said solvent and said binder to obtain a uniformly mixed resistive material colloidal suspension; mixing said firing material into said uniformly mixed resistive material colloidal suspension to obtain said colloidal suspension;

66. A method according to claim 65 wherein said step of mixing said resistive material in said solution mixes graphitic nanotubes as said resistive material .

67. A method according to claim 65 wherein said step of mixing said resistive material mixes less than 2% by weight of said strands of said resistive material.

68. A method according to claim 67 wherein said step of mixing said resistive material in said solution mixes graphitic nanotubes as said resistive material .

69. A method according to claim 57 wherein said step of mixing uses a pump type homogenizer.

70. A method according to claim 69 wherein said step of mixing said resistive material in said solution mixes graphitic nanotubes as said resistive material.

71. A method of making an initiator that is responsive to a electrical energy comprising the steps of: preparing first and second conductive terminals; and placing an energetic composition that fires in response to application of heat between said first and second conductive terminals, said energetic composition including a firing material mixed with a plurality of strands of a resistive material, each strand of said plurality having a width that is smaller than 2 microns and a length that is at least five times greater than said width.

72. A method according to claim 71 wherein said resistive material is graphitic nanotubes.

73. A method according to claim 71 wherein said step of placing said energetic composition between said two conductive terminals includes the steps of: pressing together a plurality of granules of said energetic composition to obtain a pellet of said energetic composition; and placing said pellet between said first and second conductive terminals.

74. A method according to claim 71 wherein said step of placing said energetic composition between said first and second conductive terminals includes the steps of: filling a cup shaped vessel with granules of said energetic composition; and pressing an end cap containing said conductive terminals into said cup shaped vessel so that said granules become compacted together and disposed between said first and second conductive terminals.

75. A method according to claim 74 wherein said step of filling said cup shaped vessel with granules of said energetic composition is preceded by filling said cup shaped vessel with another energetic material.