Explosive and thermic compositions or charges – Structure or arrangement of component or product – Solid particles dispersed in solid solution or matrix
Reexamination Certificate
2000-12-21
2003-11-18
Hardee, John (Department: 1751)
Explosive and thermic compositions or charges
Structure or arrangement of component or product
Solid particles dispersed in solid solution or matrix
Reexamination Certificate
active
06648998
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to melt-cast explosives, and in particular to melt-cast explosives suitable for use in mortars, grenades, artillery shells, warheads, and antipersonnel mines.
2. Description of the Related Art
Melt-cast explosives based on a 2,4,6-trinitrotoluene (TNT) melt-cast binder have been used in a wide array of military applications. Among the TNT-based compositions known for making melt-cast explosives, COMP B (also commonly referred to in the art as Composition B) is one of the more widely known and practiced. Generally, COMP B comprises a mixture of TNT, RDX (1,3,5-trinitro-1,3,5-triaza-cyclohexane), and beeswax. Although the precise concentrations of these ingredients may vary somewhat in industry practice, generally COMP B includes about 39.5 wt % TNT, about 59.5 wt % RDX class 1 (100 &mgr;m) and about 1 wt % wax.
COMP B is typically prepared by initially melting the TNT melt-cast binder, which has a relatively low melting temperature of about 81° C. RDX particles and wax (optionally pre-coated on the RDX particles) are then stirred into the melted TNT until a slurry or homogeneous dispersion is obtained. The molten slurry can be poured into shells or casings for mortars, grenades, artillery, warheads, mines, and the like by a casting process, then allowed to cool and solidify. The melt pourability of COMP B is characteristic of melt-cast explosives.
As widely acknowledged in the art, however, melt-cast explosives compositions such as COMP B have several drawbacks. One of the most acknowledged of these drawbacks is the tendency of melt-cast explosives to shrink and crack upon cooling. Separation of the melt-cast explosive from its shell or casing and the formation of cracks within the explosive significantly increases the shock (or impact) sensitivity of the melt-cast explosive. Due to this increase in shock/impact sensitivity, melt-cast explosives made of COMP B and the like have been determined to lack sufficient predictability for some military applications. In particular, such melt-cast explosives are particularly prone to premature detonation when used adjacent to an ordnance motor. Moreover, due to the high thermal sensitivity and toxicity of TNT as a melt-cast binder, safety precautions are often required in practicing melt-cast techniques, thereby adding to manufacturing costs, slowing production rates, and raising worker safety issues. TNT is no longer produced domestically. The primary reason is because the manufacture of TNT produces toxic by-products known as pink water. During the TNT purification process, the meta isomers produced during the nitration of toluene react with the sodium sulfite to produce water soluble, sulfated nitro toluene that is red and highly toxic. The waste stream clean up is labor intensive, thereby increasing cost significantly.
SUMMARY OF THE INVENTION
It is, therefore, an object of this invention to address a significant need in the art by providing a melt-cast explosive that shares comparable explosive properties to those of COMP B explosives and is melt-pourable and castable under conditions comparable to those of COMP B explosives, but experiences less impact, shock, and thermal sensitivity and avoids the issues of toxicity associated with COMP B.
In accordance with the principles of this invention, the above and other objects are attained by replacing a fundamental and well-accepted component of COMP B, i.e., the trinitrotoluene (TNT) melt-cast binder, with one or more mononitro-substituted arenes or dinitro-substituted arenes, such as dinitroanisole. It has been discovered that mononitro-substituted and dinitro-substituted arenes such as dinitroanisole can be melt cast without presenting the toxicity drawbacks experienced with the use of TNT. Additionally, many mononitro-substituted and dinitro-substituted arenes are lower in costs and more widely available than TNT. Mononitro- and dinitro-arenes are less detonable than tri-nitrated arenes. Therefore, the mononitro- and dinitro-arenes do not require the explosive transportation, storage, and packaging infrastructure that tri-nitrated compounds, such as TNT, mandate.
Generally, the use of mononitro-substituted and dinitro-substituted arenes in place of TNT for melt-cast compositions has been disfavored (if not overlooked) in the melt-casting art due to the lower energetic oxygen content of the mononitro-substituted and dinitro-substituted arenes compared to TNT. This drawback has been recognized and overcome by the inventors by the addition of coarse oxidizer particles to the melt-cast composition. As referred to herein, coarse means particles having a granular appearance. The coarse oxidizer particles compensate for the energy loss experienced by the replacement of TNT with the less-energetic mononitro-substituted and/or dinitro-substituted arene melt-cast binder. Further, relatively large coarse oxidizer particles reduce the shock, impact, and thermal sensitivities. Inorganic oxidizers are preferred.
Additionally, the different melting points of mononitro-substituted and dinitro-substituted arenes from that of TNT have also disfavored the melt-cast binder substitution proposed by the inventors. Melt casting requires heating of the melt-cast binder to a temperature higher than its melting point, so that the binder can be mixed with the energetic filler and cast by melt pouring. A typical and useful melting point range for the melt or pour process is 80° C. to 110° C. However, melt-cast compositions should not be heated close to or above their autoignition temperatures, since the compositions will ignite automatically and generate an exothermic burn or explosion if heated to their autoignition temperatures. Preferably, a relatively wide “safety margin” is present between the melt temperature of the melt-cast binder and the autoignition temperature of the melt-cast composition. TNT has a melting point of about 80.9° C., and COMP B has an autoignition temperature of 167° C., giving a reasonably wide safety margin between the binder melting temperature and the autoignition temperature. On the other hand, many mononitro-substituted and dinitro-substituted arenes have melting points exceeding that of TNT, thereby narrowing the safety margin for melt casting. For example, dinitroanisole has a melting point of 94° C.
The inventors have also discovered a way of overcoming this drawback by combining with the melt cast binder a processing aid selected from the group consisting of alkylnitroanilines and arylnitroanilines. The processing aid combines with the melt-cast binder to lower the overall melting temperature of the melt-cast composition, preferably into a range of from 80° C. to 90° C., while raising the autoignition temperature, preferably to about 149° C. (300° F.), of the composition to widen the safety margin.
Additionally, in accordance with the present melt-cast composition the high impact and shock sensitivity commonly associated with melt-cast explosives such as COMP B is mitigated by providing at least a portion of the energetic filler (e.g., RDX) in a fine powder form. It has been discovered by the inventors that the provision of the energetic filler in fine powder form lowers the shock and impact sensitivities of the melt-cast composition. Fine powders have high surface area relative to coarse material. Fine powders stay suspended in the melt phase significantly better than coarse material and will not settle out of the binder as rapidly. This mitigates the formation of a surface rich melt phase and the formation of voids and cracks.
This invention is also directed to ordinances and munitions in which the melt-cast composition of this invention can be used, including, by way of example, mortars, grenades, artillery shells, warheads, and antipersonnel mines.
These and other objects, aspects and advantages of the invention will be apparent to those skilled in the art upon reading the specification and appended claims which, explain the principles of this invention.
DETAILED DESCRIPTION OF THE INVENTION
The
Doll Daniel W.
Hanks Jami M.
Highsmith Thomas K.
Lund Gary K.
Niles John B.
Alliant Techsystems Inc.
Hardee John
TraskBritt
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