Patent Application
20140238258
The present invention relates to a smoke-producing pyrotechnic composition that is useful primarily in pyrotechnics for the production of colored smokes. More particularly, the present invention is related to generally cool-burning, non-toxic, and non-corrosive smoke producing compositions, which incorporate at least one affordable nitrogen-rich compound in addition to an oxidizer-fuel system, smoke-forming substance, and binder. Affordable nitrogen-rich compounds that are suitable for use with the current invention can include guanidine nitrate, guanidine carbonate, or dicyandiamide; azodicarbonamide, melamine, and oxamide.
Effective and safe generation of colored smoke by the vaporization of an organic dye poses a challenging pyrotechnic problem. The military and the fireworks and entertainment industries rely on this technique for the generation of copious quantities of brilliantly colored smoke.
The requirements for an effective colored-smoke composition include:
In various contexts, it is desirable to have the capability to produce smoke suitable for a wide variety of applications. For example, the ability to produce smoke at a particular location may provide the basis for a remote signaling system. Such a system may have application in search and rescue operations and in military exercises. Smoke of a particular color and density may also be desirable for training purposes. For example, in order to train fire fighters, it would be advantageous to simulate specific types of smoke produced by various fire conditions. For individuals working in a fire-prone environment, such as on an aircraft or ship, it would also be desirable to have the capability of simulating smoke produced by a fire in order to provide a realistic fire drill.
Smoke can be used as a marker for various purposes. A smoke marker can be seen from substantial distances, both from the ground and from the air. Accordingly, a smoke marker would be useful in military operations, search and rescue, certain types of industrial projects, or in any other situation in which it is important to find and mark a particular location.
In a military context, the need for smoke-producing devices and compositions is well appreciated. Not only can smoke be used as a marker for search and rescue, but smoke may also be used to mark a particular target. It can also be used as a marker to determine the position of specific personnel and equipment.
Smoke can also be used to obscure vision. A smoke shield can be very helpful in conducting military operations in order to prevent adverse forces from obtaining a clear view of the operations. For example, it may be desirable to use a vision obscuring smoke in order to move troops and equipment under at least partial cover.
Various types of smoke-producing compositions and devices are presently known. It is known how to judiciously select the components of a smoke-producing composition that uses a sublimable organic coloring medium. By considering the kinetics of combustion and the desired yield of colored smoke, conventional smoke-producing compositions require a strongly exothermic composition, but struggle to limit the degradation of the coloring medium by combustion. A weakly exothermic composition is unsuitable because it permits only a minimal percentage of coloring medium and furnishes only a very mediocre smoke yield that is hardly visible, especially when there is a cloudy or dark sky. A weakly exothermic composition also is difficult to ignite to initiate smoke emission.
It is also known that it is advantageous to adjust the combustion speed, because a too rapid combustion provokes the destruction of the coloring medium or liberates the smoke too briefly or in a non-workable manner. In contrast, a two slow combustion produces a smoke yield of minimal consequence and tends toward self-extinction of the combustion process. It is known to consider the effects of the reaction thermodynamics by making an appropriate choice of the components of the composition and by the conditions of compression of the composition.
However, most existing smoke-producing compositions have severe limitations. One of the limitations is that of toxicity. Many smoke-producing compositions incorporate materials that are severely toxic or become irritants when subjected to the heat necessary to produce smoke.
A variety of dyes have been used in colored smoke mixtures. Many of these dyes are presently under investigation for carcinogenicity and other potential health hazards.
The materials that work best in colored smokes have several properties in common:
Prior art colored smoke formulations have employed the use of mixtures containing a fuel, an oxidizer, and a dye. The principle behind the use of such formulations lies in the reaction between the fuel and oxidizer, and the accompanying release of a large amount of energy during the reaction. The exothermic reaction releases the energy contained in the bonds of the highly structured fuel molecule as heat. This causes the dye component of the formulation to undergo a series of phase transitions from a solid to a liquid and ultimately to a gas. However, if the temperature of the fuel-oxidizer reaction is too high, the dye will degrade, and the quantity and color quality of smoke generated will be unsatisfactory.
Conventionally, the dye exists as a solid crystal at standard temperature and pressure. When heat generated by a fuel-oxidizer reaction is applied to the solid crystal, dislocations of the molecules occur within the crystalline lattice. As molecules of the dye become detached from the central lattice, a liquid is formed. As more heat energy is applied, the individual molecules of the dye begin to move faster and faster. The molecules, as a result, translate through space, rotating about the axes of the dye structure, and vibrate in many complex modes. This molecular activity is responsible for the transition of the dye molecules from the liquid phase to the gas phase.
Although heat is required for the dye to undergo the essential phase changes to produce colored smoke, individual molecules of the dye are subject to degradation at elevated temperatures. If the molecular structure of the dye is subject to forces and energies that are great enough to cleave the molecule's bonds, changes in smoke color or loss of color properties are likely to occur.
Another problem encountered in the search for a desirable smoke-generating composition is the production of a solid residue as conventional smoke-producing compositions burn. The solid residue reaction product contributes to the formation of waste products such as slag and solid clinkers. When such solid materials accumulate in the core of a pyrotechnic smoke-producing munition, they prevent the gas phase dye molecules from escaping into the environment. As a result, deflagration can occur, which can cause injury to bystanders, or result in only a limited release of colored smoke. Furthermore, the formation of slag increases the decomposition of the dye vapor, which may lead to color deterioration. Only a few dye materials have been found suitable for use in prior art smoke-producing compositions that rely upon the vaporization of an organic dye because most dye materials generate excessive slag or clinkers. The importance of obtaining uniform and porous slag reaction products is already known, as well as the possibilities of selecting components of the smoke-producing composition that enable obtaining such slag. It is also known that the extent of porosity of the slag regulates the smoke yield and favors heat exchange between the components of the smoke-generating composition.
Other known compositions have the drawback of burning at temperatures that are too high (600-800° C.) or leave too many carbonaceous residues, which are impermeable to the dye molecules in the gas phase. These conditions cause the destruction of the smoke-producing components and therefore demonstrate poor effectiveness in producing colored smokes. Another drawback may be the rapid ascent of the smoke because of the smoke's high temperature, which causes the smoke to dissipate too quickly for the desired effect to be achieved.
Another major drawback of using such mixtures is the hazard created by the creation of a flame front at the moment of ignition of the main filling composition. For example, a smoke grenade has been observed to emit a flame front with a height of approximately 4-10 inches through the grenade's emission ports. The flame from was observed to last from 1-5 seconds while the smoke charge began burning. This behavior can create safety hazards to personnel and equipment, as well as potentially causing brush and grass fires in dry environments with significantly elevated fire danger conditions.
In summary, there is a need for effective colored smoke-producing compositions. This need exists in both military and civilian operations. However, many smoke-producing compositions presently used are difficult to handle. Many such compositions are toxic and irritating, requiring special precautions during use. Many such compositions are also corrosive and damaging to both electronic and mechanical equipment. Finally, some compositions produce an excess of heat and flame, again limiting their usefulness and requiring that additional safety measures be taken. For these reasons, conventional smoke-producing compositions are found to be inadequate
Therefore, a need exists for a new and improved colored pyrotechnic smoke-producing composition that provides is generally non-toxic and non-corrosive, does not incorporate toxic or irritating materials such as zinc, phosphorous, and aromatic organic compounds, which is simple to manufacture and use, and is still in effective smoke producer. In this regard, the various embodiments of the present invention substantially fulfill at least some of these needs. In this respect, the flameless igniting slurry composition according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in doing so provides a composition primarily developed for the purpose of providing a cool-burning, non-toxic, and non-corrosive smoke producing composition.
The present invention provides an improved colored pyrotechnic smoke-producing composition, and overcomes the above-mentioned disadvantages and drawbacks of the prior art. As such, the general purpose of the present invention, which will be described subsequently in greater detail, is to provide an improved colored pyrotechnic smoke-producing composition that has all the advantages of the prior art mentioned above.
To attain this, the preferred embodiment of the present invention essentially comprises a composition of an oxidizer, a fuel, a flame retardant, a dye, a coolant, and a binder. The oxidizer may be potassium chlorate. The fuel may be starch, dextrose, lactose, and/or sucrose. The coolant may be sodium bicarbonate or magnesium carbonate. The binder may be nitrocellulose or a halogen-free thermoplastic. The flame retardant may be one or more nitrogen-rich compounds. The composition may be in pelletized form or in the form of a solid charge. The composition may consist of on a mass basis oxidizer 20-35%, fuel 15-25%, flame retardant 5-15%, dye 27-40%, coolant 8-18%, and binder 1-2%. The invention may be a device consisting of a body filled with the composition and a first fire starter composition, and an attached squib igniter. The body may be a grenade. A process for producing the composition is also disclosed. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject matter of the claims attached.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood and in order that the present contribution to the art may be better appreciated.
The same reference numerals refer to the same parts throughout the FIGURE.
An embodiment of the process for manufacturing a colored pyrotechnic smoke-producing composition of the present invention is shown and generally designated by the reference numeral 10.
The invention relates to a smoke-producing pyrotechnic composition and more particularly, is related to generally cool-burning, non-toxic and non-corrosive smoke producing compositions, which incorporate:
It is clear from a vast array of studies that traditional pyrotechnics are a severe source of pollution. Environmentally friendly or “green” formulations are therefore based on nitrogen-rich compounds to avoid the use of heavy metals and perchlorates. High-nitrogen compounds gain their energetic character not by oxidation of carbon, but from their high heats of formation. They offer not only environmentally compatible combustion products, but in many cases even better color quality and intensity than older formulations.
Nitrogen-rich materials combine several advantages:
Compounds for use in pyrotechnics should be cheap, easy to produce, and non-hygroscopic. High nitrogen content is desirable for reduction of smoke and particulate matter resulting from combustion. The reaction rate must therefore be adjusted for that purpose. High-energy reactions are generally classified as “burning” (approximate reaction velocity in the range of mm or cm s−1), “deflagration” (m s−1), or “detonation” (km s−1).
An ideal dye material for this application transforms “sublimes” directly from the solid phase to the gas phase with little or no intermediate liquid phase. The direct transformation to a gas enhances the likelihood of the dye molecules escaping from the solid matrix made of fuel, oxidizer, and dye to the external environment without the dye molecules reaching an undesirably high temperature. Thus, dyes are sought for the composition that have the property of sublimation at increased temperatures and normal pressures.
In general, flame suppressant/flame retardant compounds act in one of two ways: either by preventing ignition of a product or by preventing the spread of a fire once a product is ignited. First, the ignition susceptibility of a product is lowered when the flame retardant increases the net heat capacity of the product. Second, once a fire has already begun, flame retardants can reduce the tendency of the fire to spread by reacting with the product and forming a less flammable char or noncombustible gaseous layer along the boundary of the fire. Within these two general flame-retardant mechanisms, Kirk-Othmer's Encyclopedia of Chemical Technology (Kirk-Othmer, 2001) provides a more detailed summary of five specific mechanisms by which flame retardancy may occur: physical dilution, chemical interaction, inert gas dilution, thermal quenching, and protective coatings.
The use of nitrogen-rich compounds as both nitrogen producing agents and flame retardants overcomes many of the severe problems encountered in the existing art. In particular, the present invention provides compositions that are generally non-toxic, non-corrosive, and that can be formulated to burn at lower temperatures and with a lower energy output while still producing effective smoke output.
If potassium chlorate is used without the addition of a nitrogen-rich material to the smoke-producing composition, the combustion temperature is at least 400° C. (750° F.). At this temperature, the dye is nearly completely destroyed, making the composition ineffective at producing smoke. However, because the present invention adds a nitrogen-rich material to the smoke-producing composition, the combustion temperature of the smoke-generating composition of the present invention is reduced to a range from 100° to 250° C. (200 to 480° F.). At the lower end of this range, thermal degradation of the dye is largely prevented, resulting in the effective production of colored smoke. As an example, by using guanidine nitrate in combination with the potassium chlorate, the combustion temperature drops to a range between 190° and 300° C. (375 to 575° F.). The temperature reduction is achieved by the guanidine nitrate catalyzing the decomposition of the chlorate, which makes it possible for the decomposition reaction to occur at a lower temperature than would be conventionally required.
The nitrogen-rich compounds suitable for use in this invention have been found to be excellent additives for use in a smoke-producing composition containing a degradable dye. The cited additives have been found to be a very efficient coolant because they are nitrogen producing agents that act as flame retardants. Because the additives' decomposition process generates the liberation of gases (carbon dioxide and nitrogen), they assist sublimation of the organic dye and provide thermal protection from the fuel-oxidizer reaction. The additives also inhibit slag build-up and facilitate the production of uniformly porous slag. These slag characteristics enhance the production of color in the smoke generated. In contrast, conventional pyrotechnic compositions pass the vaporized dye through significant amounts of hot slag of limited porosity before the dye escapes into the environment, which has a deleterious effect on the color of the vaporized dye.
Nitrogen-rich compounds are not only remarkable energy-rich and oxygen-nitrogen-containing compounds that act exothermically to supply heat to the smoke-generating reaction. The nitrogen-rich compounds also simultaneously yield decomposition products that neutralize the acids generated by the smoke-producing composition of the present invention.
The dyes, which may be used in this invention corresponding to the color standard FED-STD-595C color chip, are listed by the Society of Dyers and Colorists in dye classification materials according to chemical structure, and include the following:
The compositions of the present invention also incorporate at least one binder to provide the desired consistency. A binding agent from the group of the halogen-free thermoplastics can be used for the physical stabilization of the mixture of the pyrotechnic smoke-producing composition. The binding agent can preferably be polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl ester, or polyvinyl ether. In the present invention, nitrocellulose is specifically desirable in that it results in a decreased solid residue within the burned grain. Nitrocellulose is used in solution (6 to 12% nitrocellulose dissolved in acetone).
Binders of these types, in addition to providing desirable binding characteristics, produce only a small energy output upon combustion. This is important in avoiding very high-energy outputs, high temperatures, and flames, which render smoke producing compositions dangerous and difficult to handle.
The composition of the present invention also includes one or more oxidizer compounds. It is found that potassium chlorate (KClO3) is an efficient oxidizer and produces good results when coupled with the fuel and previously mentioned nitrogen-rich compounds.
The present invention includes a fuel. The fuel is preferably a relatively low energy fuel similar to the binder. It is also preferred that the fuel produce gaseous reaction products capable of carrying the smoke producing agent into the environment. Some suitable fuels include starch, dextrose, and polyhydroxylic compounds such as lactose and sucrose.
Certain other materials may also be added to produce specific desirable results. One suitable material is magnesium carbonate. Magnesium carbonate acts as a buffer, which prevents autocatalytic decomposition of the KClO3. Magnesium carbonate also functions as a coolant when the smoke-producing composition combusts. Alternatively, sodium bicarbonate can be used. Another useful additive in the present invention is aluminum. In some cases, atomized aluminum can provide additional thermal conductivity within the composition. This results in more uniform heat transfer and ignition of the fuel.
In general, the ingredients of the composition may be within the ranges indicated in Table 2:
The following examples illustrate various embodiments of the invention, but it will be obvious that various changes and modifications may be made therein without departing from the scope of the invention.
More specifically, excellent results are obtained with the formulation set forth in the following examples:
Referring now to
The composition's ingredients can also be blended together as dry powders using standard pyrotechnic techniques. However, the wet mixing technique using acetone is preferable because it is safer and produces a more homogeneous mixture.
The smaller spherical chunks are poured (40) from the mixing bowl into drying trays. The mix is spread on the drying trays so the mix is flat at a uniform level in the trays. The trays are placed in an oven (42) maintained at 60±5° C. (140±10° F.), for 24 to 36 hours to evaporate any residual acetone. After drying, the material is ground (44) to achieve small grains of pyrotechnic mixture, which can be further loaded or preferably pelletized (46).
It has been found useful to pelletize the pyrotechnic composition of this invention, rather than to use the composition in powder form, to achieve predictable combustion performance of the composition. Pelletizing can be achieved by harshly mixing the powdered ingredients and then using a pill press to produce pellets. Alternatively, the powdered mixture can be granulated and then formed into noodles by extruding the mixture through a screen. Pelletizing has been found advantageous because the mixed powder has some undesirable characteristics. First, the powder tends to separate, with the oxidizer at the bottom and the fuel at the top. As a result, when the powder burns, it burns with different characteristics depending upon the degree to which the powder mixture is homogeneous. Second, the powder may be loosely packed or tightly packed, which also affects its combustion characteristics. These variations in homogeneity and packing can lead to inconsistent combustion results when using the composition in powder form. When using the composition in pellet form, the combustion results are more consistent.
After drying, the pellets are hydraulically loaded (48) into grenade bodies 50 or pelletized to adjust the combustion characteristics of the composition so the devices have the required burning time. The load applied to the surface of the mix in the grenade body is about 5000 to 7000 pounds per square inch (psi). A MIL SPEC No. 508 first fire starter mixture or a flameless first fire starter mixture 52 is applied to the grenades, and tops 54 are sealed onto the bodies (56). A No. 565 squib igniter 58 can be used to ignite the grenade. The loaded and sealed grenades are the end result (60) of the process.
The colored smokes produced by the pyrotechnic compositions of the present invention were compared to smoke produced by conventional formulations based on 1,4-benzendicarboxylic acid or aliphatic dicarboxylic acids. Each smoke color produced by the pyrotechnic compositions of the present invention was also compared to the corresponding color standard FED-STD-595C color chip. This was accomplished by making the various pyrotechnic mixtures and forming them into grenades in the manner previously described. The grenades were then burned adjacent to one another to enable side-by-side visual comparison. The subjective evaluation of the color quality the smoke produced provided a reliable indication of the improved effectiveness and efficiency of the pyrotechnic composition of the present invention.
Another indication of the greater efficiency of smoke munitions that include the pyrotechnic compositions of the present invention was the length of flaming time recorded during the burn. It was found that flaming of the compositions of the present invention was reduced in comparison to the more frequent flaming of the standard mixtures based on 1,4-benzendicarboxylic acid or aliphatic dicarboxylic acids. The improved effectiveness and efficiency of the composition of the present invention was shown throughout the comparison.
Various smoke-producing pyrotechnic compositions of the present invention, previously detailed above as Examples 1 to 5, were placed in standard military-style metal cans used for signal colored smoke grenade. The compositions were compacted as pressed pellets as a first experimental design, and as solid charges in a second experimental design (see the second column of Table 3 below). In both experimental designs, the weight of pyrotechnic filling was about 210 to 235 grams (7.5 to 8.2 oz.). The pressed or pelletized grains were ignited, and their burning characteristics, including ignition time and flame, burning time, burning temperature, can temperature and pressure were recorded. The results of these tests are summarized in Table 3.
The use of a flame retardant and a coolant within the colored pyrotechnic smoke-producing composition of the current invention is counterintuitive for two reasons. First, the goal of a colored pyrotechnic smoke-producing composition is to burn with sufficient intensity to vaporize the dye component of the composition, so the use of ingredients that impede burning is contraindicated. Second, guanidine salts, such as guanidine nitrate, are conventionally employed in the an of ignition as an exothermic reactant in a smoke grenade (U.S. Pat. No. 4,238,254), or as an additional fuel for a flare igniter (U.S. Pat. No. 6,170,399). This makes their usage in the current invention for their flame retardant properties nonobvious.
While current embodiments of a colored pyrotechnic smoke-producing composition and methods of preparation have been described in detail, it should be apparent that modifications and variations thereto are possible, all of which fall within the true spirit and scope of the invention.
With respect to the above description then, it is to be realized that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention.
Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.
