TechMatch

Patent #4948438


Description
	BACKGROUND OF THE INVENTION This invention relates to explosives, particularly to explosive compositions based upon ammonium nitrate. Traditional general-purpose explosives comprise trinitrotoluene (TNT), which has several disadvantages. It is a Class-A explosive, requiring special mixing and handling procedures and storage facilities, all accordingly increasing the cost of use. The preparation of this explosive is through nitrate substitution of toluene by a mixed acid consisting of concentrated nitric acid and sulphuric acid. The cost of concentrated nitric acid is moderately expensive and any excess nitric acid in the product destabilizes the explosive and presents corrosion problems. Trinitrotoluene is not water soluble and bomb disposal cannot be done economically by steam or hot water. It is known to produce cast high explosive compositions by solidification of a molten mixture of ammonium nitrate (AN) and ethylenediamine dinitrate (EDDN). A binary mixture of ethylenediamine dinitrate and ammonium nitrate is water soluble, thereby having several advantages over trinitrotoluene such as safer storage as a non-explosive water solution and cheaper disposal. However, the binary mixture has a high melting point, has stability problems, and is expensive. It is known to add potassium nitrate (KN) to the AN/EDDN mixture to improve its stability. The problems associated with the binary mixture remain and the amount of chloride impurities is increased by the additional chloride impurities found in potassium nitrate (KN). If these impurities are not removed, the explosive has serious corrosion problems. If the impurities are removed the cost of the explosive increases greatly. The present method of making the ternary mixture is to mix solid ethylenediamine dinitrate, ammonium nitrate and potassium nitrate. Ethylenediamine dinitrate is not commercially availabe in large quantities and is expensive. Industrial grade ammonium nitrate and potassium nitrate are too impure to be used without the additional expense of purification. Dry mixing three explosives to form an explosive mixture requires special procedures and precautions, causing the cost of the process to increase significantly. Other explosives compositions based upon ammonium nitrate include AN/fuel oil, AN/TNT/RDX (cyclotrimethylenetrinitramine), AN/ammonium salt of a nitroazole/RDX, AN/EDDN/KN/NQ (nitroguanidine) and the like. It is known that ammonium nitrate is a hazardous material to manufacture on an industrial scale, to handle in large amounts, and to store in great masses, especially for relatively long periods of time. It is also known that the shock sensitivity of ammonium nitrate increases seriously after exposure to a few temperature cycles through the 32.3.degree. C. (90.degree. F.) transition point. (Up to 32.3.degree. C. the stable crystal form is orthorhombic bipyrimidal; from 32.3.degree. C. to 84.degree. C. the stable crystal form is orthorhombic). Military explosive formulations have consisted primarily of eutectic mixtures of fuel-rich components such as EDDN, quanidinium nitrate or NQ with oxidizer-rich components such as AN, sodium nitrate, KN or calcium nitrate. Commercial compositions have consisted primarily of gels, slurries or aqueous emulsions of AN with various fuels and additives. The high explosive eutectic formulations utilized for military applications have typically been plagued by problems relating to large critical diameters, performance variability as a response to particle size and fractional crystallization, and sensitivity to shock. The non-ideal behavior of composite explosive is believed to be a consequence of the relatively great distances, on the atomic and molecular scale, between the fuel-rich and oxidizer-rich components. These distances can exceed 10.sup.5 Angstroms between crystal centers. This is in contrast to mono-molecular (ideal) explosive in which reacting atoms are separated by less than 10.sup.1 Angstroms. It is well known that improvements in explosive properties, such as performance and critical diameter, can be achieved through greater fuel oxidizer intimacy. Traditional methods for attaining this increased intimacy have relied on reducing particle size through the use of exact eutectic formulations or emulsification. Accordingly, it is an object of this invention to provide a novel explosive composition based upon ammonium nitrate. Other objects and advantages of the present invention will be apparent to those skilled in the art from a reading of the following description of the invention. SUMMARY OF THE INVENTION In accordance with the present invention there is provided a melt/cast explosive composition comprising about 20 to 100 wt. % of a binary complex of ammonium nitrate (AN) and methynitroguanidine (MeNQ) in a molar ratio of about 0.55:1 to 1.35:1. This binary complex may be used alone or it may be formulated with up to about 80 wt. % compatible fuels and/or oxidizers to tailor the formulation for specific military or commercial applications . DESCRIPTION OF THE DRAWING In the drawing FIG. 1 is a temperature-composition phase diagram for the two component system, ammonium nitrate (AN) and methylnitroguanidine (MeNQ). Referring to FIG. 1, it can be seen that as the mole fraction of AN (MFa) is varied from 0.0 to 1.0, eutectic points are defined at MFa''s of 0.3719 (116.9.degree. C.) and 0.5678 (117.5.degree. C.). The region between these eutectic points, labeled "COMPOUND", defines a binary complex between AN and MeNQ. It can also be seen that a 1:1 mixture of AN and MeNQ has a mdelting point of 118.4.degree. C. DETAILED DESCRIPTION OF THE INVENTION Although the AN/MeNQ system may be used alone, to be compatible with existing melt/cast loading facilities it is necessary that the melt/cast explosive formulations have a melting point below 110.degree. C., preferably below 100.degree. C. The mdelting point can be reduced by the addition of a melting point depressant, such as, for example, nitroguanidine, guanidine nitrate, aminoquanidine nitrate, urea, potassium nitrate, sodium nitrate, lithium nitrate, calcium nitrate, ammonium perchlorate, and the like. The amount of such depressant can range from about 0.1 to about 25 wt. %. The explosive composition may contain up to about 80 wt. % of at least one other fuel-rich or oxidizer-rich component such as, for example, nitroguanidine (NQ), RDX, HMX, PETN, ammonium perchlorate, aluminum powder, and the like. Certain of these compounds are also listed in the list of melting point depressants, above. Accordingly, the combined quantity of depressant and fuel-rich or oxidizer-rich component should not exceed about 80 wt. % of the melt/cast composition. The explosive compositions of this invention can be prepared by heating a mixture of the components, with stirring. When a high explosive, such as NQ, RDX, HMX, or PETN it to be incorporated, it is preferable to prepare a melt comprising AN, MeNQ and, optionally, one or more melting point depressants, and add the high explosive to the melt. The explosive composition can be flaked, using a chiller belt, or cast into molds. The following example illustrates the invention: EXAMPLE Composition I was prepared by melting and mixing 39.2 parts AN, 45 parts MeNQ (Aldrich Chemical Co., Milwaukee, Wis.), 11.3 parts NQ and 4.5 parts sodium nitrate at 105.degree.-110.degree. C. After melting, 20 inches Hg vacuum was applied for 15 minutes to remove water and trapped air. The mixture was cast at 95.degree.-100.degree. C. and cooled slowly. Composition II was similarly prepared using 40 parts Composition I and 60 parts high bulk density nitroguandidine. Composition III was similarly prepared using 30 parts of Composition I, 20 parts 5-10 micron aluminum powder and 50 parts high bulk density nitroguanidine. The properties of these compositions are given in the Table below in comparison to the properties of Tritonal (80% TNT/20% Al), EAK (46% EDDN/46% AN/8% KN) and PBX 9502 (95% triaminotrinitrobenzene/5% Kel-F binder): TABLE ______________________________________ 50% Impact Detonation Initiation Sensitivity Velocity Pressure Formulation 5 Kg wt Density (km/sec) (kbar) ______________________________________ Tritonal 70 1.72 6.6 10 EAK 20 1.63 7.6 14 PBX 9502 >200 1.89 7.5 70 I 88 1.52 7.4 35 II 112 1.63 7.6 50 III 143 1.72 7.4 85 ______________________________________ A series of compositions were prepared to illustrate the effects of various melting point depressants. The recipes are given below: ______________________________________ Composition IV (melt point 104.degree. C.): ______________________________________ MeNQ 42.4 AN 36.9 NQ 10.5 KN 5.9 NaNO.sub.3 4.3 ______________________________________ ______________________________________ Composition V (melt point 101.degree. C.): ______________________________________ MeNQ 31.3 AN 45.0 Guanidinium nitrate 23.7 ______________________________________ ______________________________________ Composition VI (melt point 100.degree. C.): ______________________________________ MeNQ 43.5 AN 36.0 NQ 10.5 NH.sub.4 ClO.sub.4 10.0 ______________________________________ Various modifications may be made to the invention as described without departing from the spirit of the invention or the scope of the appended claims.