US3740278A - Halogenated polyethylene coated crystalline explosive mixed with second explosive - Google Patents

Abstract

SHAPED HIGH EXPLOSIVES PREPARED BY COATING A PARTICULATE CRYSTALLINE EXPLOSIVE HAVING A MELTING POINT OF AT LEAST 203*C. WITH A HALOGENATED POLYETHYLENE BY MIXING THE CRYSTALLINE EXPLOSIVE PARTICLES WITH AN AQUEOUS DISPRESION OF ISCRETE HALOGENATED POLYETHYLENE PARTICLES HAVING AN AVERAGE SIZE OF 0.1 TO 5 MICRONS TO DISTRIBUTE OVER THE CRYSTALLINE EXPLOSIVE PARTICLES ABOUT 2 TO 8 PERCENT BY WEIGHT OF HALOGENATED POLYETHYLENE PARTICLES, MIXING THE HALOGENATED POLYETHYLENE COATED CRYSTALLINE EXPLOSIVE PARTICLES WITH ABOUT 2 TO 8 PERCENT BY WEIGHT OF A SECOND EXPLOSIVE HAVING A MELTING POINT UP TO 105*C. AND HAVING A TRAUZL LEAD-BLOCK EXPRESION HIGHER THAN THAT OF TRINITROTOLUENE AND COMPRESSING THE MIXTURE AT A COMPRESSIVE LOAD OF AT LEAST 700 KP./CM.2 AND A TEMPERATURE ABOVE THE MELTING POINT OF THE SECOND EXPLOSIVE.

Description

United States Patent HALOGENATED POLYETHYLENE COATED CRYS- TALLINE EXPLOSIVE MIXED WITH SECOND EXPLOSIVE Robert Sakreis, Jettenbach, and Helmuth Nolte, Waldkraiburg, Germany, assignors to Wasagchemie G.m.b.H., Munich, Germany No Drawing. Filed Apr. 11, 1972, Ser. No. 243,080

Claims priority, application Germany, May 6, 1971, P 21 22 441.9 Int. Cl. C06b 19/02 US. Cl. 149-11 8 Claims ABSTRACT OF THE DISCLOSURE Shaped high explosives prepared by coating a particulate crystalline explosive having a melting point of at least 203 C. with a halogenated polyethylene by mixing the crystalline explosive particles with an aqueous dispersion of discrete halogenated polyethylene particles having an average size of 0.1 to microns to distribute over the crystalline explosive particles about 2 to 8 percent by weight of halogenated polyethylene particles, mixing the halogenated polyethylene coated crystalline explosive particles with about 2 to 8 percent by weight of a second explosive having a melting point up to 105 C. and having a Trauzl lead-block expansion higher than that of trinitrotoluene and compressing the mixture at a compressive load of at least 700 kp./cm. and a temperature above the melting point of the second explosive.

BACKGROUND OF THE INVENTION The field of the invention is explosive article shaping or treating by coating the base explosive with an organic compound.

The state of the art of explosives useful in the present invention and the testing and physical properties thereof may be ascertained by reference to the Kirk-Othmer Encyclopedia of Chemical Technology, 2nd ed., vol. 8 (1965), pages 581 to 658, particularly pages 622-624 which disclose cyclotrimethylenetrinitramine and cyclotetramethylenetetranitramine, pages 632-633 which disclose the sensitivity and explosive characteristics of high explosives, and pages 654-658 which disclose testing methods for explosives.

The disclosures of the following U.S. patents which show the state of the art of desensitizing high explosives by coating the crystalline particulate explosives with various materials are incorporated herein:

3,466,204, Gow, which issued Sept. 9, 1969; 3,544,360, Gardner, which issued Dec. 1, 1970; 3,000,720, Baer, which issued Sept. 19, 1961; 3,348,986, Sauer, which issued Oct. 24, 1967; 3,291,666, Thatcher, which issued Dec. 13, 1966; and 3,496,041, Riedl, which issued Feb. 17, 1970.

Gow discloses a method of desensitizing explosives wherein discrete particles of an explosive composition are coated with polytetrafluoroethylene by mixing the explosive composition particles with an aqueous dispersion of discrete polytetrafluoroethylene particles having an average size of 0.1 to 5 microns to distribute over the surfaces of the explosive composition particles 1-5 percent by weight of polytetrafluoroethylene particles and in which the coated particles are compressed to convert them to a coherent mass. Gow also discloses that a suitable 60 percent aqueous dispersion of polytetrafiuoroethylene is commercially available as Fluon, Grade GPI.

Cyclonite particles coated with latex to be pressed or shaped are disclosed in the patent to Sauer. Baer discloses the coating of Cyclonite with dinitroethylbenzene to desensitize the explosive. Gardner discloses the coating of Cyclonite and Octogen with wax.

According to the patent of Thatcher, readily pressed explosive compositions of high thermal stability consisting essentially of crystalline organic compounds having a melting point of at least 325 F. selected from the group consisting of picryl sulfone, Cyclonite and Octogen are prepared by admixing with vinylidene fluoride or hexafluoropropylene in a concentration of 1-5 percent by weight.

The present invention is related particularly to a shaped high explosive of a high density, high strength, and high detonating velocity based upon high melting and high efiiciency components, such as cyclotetramethylenetetranitramine and cyclotrimethylenetrinitramine.

The chemistry of explosives encompasses, especially in the series of the aliphatic nitramines, substances having very high efiiciencies, which are relatively safe in handling and simultaneously exhibit a satisfactory chemical stability. It seems to be irrefutable that the optimum compound in this connection is cyclotetramethylenetetranitramine (Octogen, HMX), the fi-isomer of which has a maximum density of 1.92 as compared to 1.64 for trinitrotoluene (TNT). HMX detonates at a detonating velocity which is above 9,000 m./sec. for a density of 1.90. Similarly favorable efficiency values are demonstrated by the related compound cyclotrimethylenetrinitramine (Hexogen, Cyclonite, RDX), with a detonating velocity of 8,400 m./ sec. (at a density of 1.70) and a maximum density of 1.82. In contrast to the standard explosive for military purposes, namely trinitrotoluene, the above-mentioned substances cannot be directly cast into shape. The melting points are as high (Octogen 282 C., Cyclonite 203 C.) that the substances are decomposed during the melting step. The aforementioned compounds cannot be shaped, even by means of presses, without providing additives, since there is no binding power from crystal to crystal, and when very high compressive pressures are used, there is the danger of an explosion. In contrast thereto, TNT can be cast (M.P. C.) or pressed without additives.

The problem of shape-casting these high melting, high explosives has been solved for a long time in various ways. The substances were stabilized, i.e. provided with an addition of wax and shaped and compressed by means of presses in this form, as disclosed in US. Pat. 3,544,- 360. In this connection, the Wax serves to markedly re duce the impact sensitivity, as well as serving as a binder between the explosive crystals in the structure produced by the pressing step. In accordance with another method, the high melting explosive components are introduced into the melt of a lower melting explosive, preferably trinitrotoluene, and shaped by casting in this pasty form. Finally, shape casts have been successfully performed by introducing the high melting explosive into a liquid synthetic resin which has not as yet been cross-linked, and by-curing the synthetic resin binder with the use of curing agents and catalysts. According to German Pat. 1,172,590 natural rubber was used as the binder and the rubber was 'vulcanized after the explosive had been incorporated with TNT amenable to casting, much effort has been expended to raise the content of the high melting material to as high a level as possible by means of special casting methods (e.g. by the use of prolonged sedimentation, by pretreating the melt under vacuum and casting under pressure, by the use of positive forces, such as centrifugal action or pressing by means of screen surfaces), and thus to attain high densities and high detonation velocities.

The use of non-brisant binders does not always have a stabilizing effect. In certain Cyclonite and Octogen shape-castings bound with a plastic, a rather high impact sensitivity and firing sensitivity was surprisingly observed.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to propose a shaped high explosive and a process for the preparation thereof, wherein the aforementioned disadvantages are avoided. According to the present invention, the data relating to the explosive technology, particularly the density and the detonating velocity of the high efiiciency basic explosives, are retained in their full values or remain at almost the same level, but wherein, on the other hand, the sensitivity characteristics are markedly reduced and a shaped explosive is produced having a surprisingly high mechanical strength.

According to the present invention, the shaped high explosive is characterized in that the basic explosive, present in crystalline form, is coated with 2-8 percent by weight of a plastic selected from the group consisting of the halogenated polyethylenes, by treatment in an aqueous dispersion of the plastic; dried; mixed with another 8-2 percent of an explosive having a melting point up to 105 C. and having a Trauzl lead-block expansion higher than that of trinitrotoluene; and exposing the composition, at temperatures above the melting point of the added explosive, to a compressive load of at least 700 kp./cm.

TNT is used as the basis for the Trauzl lead-block test wherein TNT is rated as 100 percent and Cyclonite and HMX are rated as 170 percent and 153 percent respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Advantageously, the plastic from the group of halogenated polyethylene consists of polytetrafluoroethylene and polychlorotrifluoroethylene.

Specific examples of the commercially available halogenated polyethylenes include: Fluon, Grade GPI (60 percent aqueous dispersion of polytetrafluoroethylene having a particle size of 0.1 to microns): Hostaflon (polytrifiuoromonochloroethylene); Trithene (polytrifluo romonochloroethylene); Voltalef (polytrifiuoromonochloroethylene); Teflon (polytetrafluoroethylene); Hostaflon TF (polytetrafluoroethylene).

In a preferred embodiment of the invention, the brisant component which does not melt above 105 C. and has a Trazul lead-block test over 100 consists of aromatic nitramines or mixtures thereof, or nitrates high in nitrogen, such as hydrazine nitrate, trinitrophenylethylnitramine, trinitrophenylmethylnitramine, trinitrochlorobenzene and mixtures thereof.

The brisant component, in this connection, exhibits the property of an active binder.

The particulate crystalline high explosives of the present invention have a grain size of about 40 to 800 mi crons and include: cyclotetramethylenetetranitramine having a melting point of 282 C.; and cyclotrimethylenetrinitramine having a melting point of 203 C.

The process for the production of the high efficiency explosive consists of exposing the mixture of the basic explosive coated by treatment with an aqueous dispersion of a halogenated polyethylene and then dried, and of an explosive which does not melt above 105 C. and has a higher Trazul lead-block expansion than trinitrotoluene at temperatures above the melting point of the added explosive, to a shaping pressure of at least 700 kp./cm. The pressure is maintained during the subsequent cooling period until the added, lower melting explosive has passed over from the liquid phase into the solid phase. Thereby, a space filling of more than 99.5 percent is achieved and thus the highest possible density is attained which, in turn, is the prerequisite for a high detonating velocity. Furthermore, an advantage in this connection is to select, for this purpose, as the active binder a substance having a satisfactory inherent explosive capacity and, as the plastic binder, a substance having a high density, such as polytetrafluoroethylene or polychlorotrifluoroethylene. The pressure range is preferably 700 kp./cm. to 2000 kp./cm.

The firing sensitivity of the shaped explosive of this invention is surprisingly low (the explosive was subjected to a rifle bullet impact test with 6.2 x 54 mm. ammunition having a V (muzzle velocity of 1000 m./sec.). Smooth penetrations by the projectiles could be obtained without any noticeable reaction, although in accordance with experience gained otherwise with plastic-bound explosive compositions, positive firing sensitivities were to be expected. In the case of pure plastic binding procedures in the casting and cross-linking process, the percussion-sensitive grain of the high explosive Octogen is embedded in an unmeltable bond. However, according to the present invention, the grain is first encased with the plastic and then shaped in a pressing step together with a meltable active binder. Thus, the impact energy of the projectile is at least partially converted into heat for melting the active binder and, by the incipient melting of the active binder. Thereby a sliding yieldability of the impact-sensitive high explosive particles is attained.

The invention will be explained by the following examples.

EXAMPLE 1 900 g. of cyclotetramethylenetetranitramine (Octogen) having a grain size of 40-800 microns is introduced into 3 liters of a 1.5 percent strength aqueous dispersion of polychlorotrifluoroethylene and thoroughly agitated until the water of dispersion has become clear and the plastic material has been precipitated on the crystalline surfaces of the Octogen. The Octogen thus impregnated with 5 percent of synthetic resin is sucked-off, dried, and mixed with 45 g. of finely crystalline trinitrophenylethylnitramine (corresponding to 5 percent), and pressed at C. (somewhat above the melting point of trinitrophenylethylnitramine) with a pressure of 1,600 kp./cm. The pressure is maintained (by means of a press or of a die which is locked and provided with compression springs) until the trinitrophenylethylnitramine, which has entered into a state of melt flux, is again solidified. The densities attained in this connection exceed achieved with 99.5 percent possible space filling. After ejection, a shaped article is obtained, the density of which is 1.88 g./cm. having a detonating velocity of 8,850 m./sec., a Brinell hardness of 32-34, and a compressive strength of 46 kg./cm. In the determination of the firing sensitivity, no explosion is produced with several shots using 6.5 x 57 mm. ammunition, partial shell-S (pointed) without a blasting charge and with a V of 1,000 m./ sec.

EXAMPLE 2 900 g. of cyclotrimethylenetrinitramine (Cyclonite) having the same grain size as set forth in Example 1 is treated in the same manner with 3 liters of a 1.8 percent strength aqueous dispersion of polytetrafluoroethylene. The Cyclonite thus impregnated with 6 percent of plastic is sucked-off, dried, and mixed with 36 g. (corresponding to 4 percent), of a fine crystalline mixture of 30 percent trinitrophenylmethylnitramine (tetryl) and 70 percent of trinitrophenylethylnitramine (ethyl tetryl) and pressed at 103 C. (somewhat above the melting point of the mixture) at a pressure of 1,200 kp./cm. and the pressure is again maintained until the mixture has solidified. The pressed article obtained exhibits a density of 1.81, a detonating velocity of 8,600 m./sec. (literature value for pure Cyclonite=8,400 m./sec.), a Brinell hardness of 32-34, and a compressive strength of 45 kg./cm. In the determination of the firing sensitivity, no explosion occurs when several shots are fired into it with 6.5 x 57 mm. ammunition without explosive charge and at a V of 1,000 m./sec.

EXAMPLE 3 900 g. of Octogen of the same grain size as set forth in Example 1 is impregnated with a 4 percent polychlorotrifiuoroethylene, mixed with 56 g. (corresponding to 6 percent) of hydrazine nitrate and pressed at 73 C. (somewhat above the melting point of hydrazine nitrate) at a pressure of 900 kp./cm. until the mixture has cooled. The following data are determined: density 1.79; detonating velocity 8,900 m./sec.; Brinell hardness 26-28; compressive strength 38 kg./cm. In a firing test conducted in the same manner as described above, no explosion is obtained with 6.5 x 57 mm. ammunition in several shots.

EXAMPLE 4 900 g. of Cyclonite of the same grain size as described in Example 1 is prepared with 7 percent of polytetrafluoroethylene in the manner described in Example 1 and mixed with 27 g. (corresponding to 3 percent) of trinitrochlorobenzene (M.P. 82 C.) and then pressed at 84 C. at a pressure of 1,500 kp./cm. until the mixture has cooled. The data determined in this procedure are as follows: density 1.82; detonating velocity 8,600 m./sec.; Brinell hardness 28-30; compressive strength 48 kg./cm. When the firing sensitivity is determined in the aforementioned manner, there is no explosion or defiagration.

We claim:

1. A readily pressed explosive composition of high thermal stability comprising a particulate crystalline explosive having a melting point of at least 203 C. coated with about 2 to 8 percent by weight of halogenated polyethylene and admixed with a binder of about 2 to 8 percent by weight of a second explosive having a melting point up to 105 C., said particulate crystalline explosive selected from the group consisting of cyclotetramethylenetetranitramine, cyclotrimethylenetrinitramine, and triaminoguanidine nitrate and said second explosive selected from the group consisting of hydrazine nitrate, trinitrophenylmethylnitramine, trinitrophenylethylnitramine, trinitrochlorobenzene and mixtures thereof.

2. The composition of claim 1, wherein said halogenated polyethylene is selected from the group consisting of polytetrafluoroethylene and polychlorotrifluoroethylene.

3. The composition of claim 2, wherein said halogenated polyethylene particles have an average size of about 0.1 to 5 microns.

4. The composition of claim 1, wherein said particulate crystalline explosive has an average size of about 40 to 800 microns.

5. A readily pressed explosive composition of high thermal stability comprising a particulate crystalline explosive having a melting point of at least 203 C. coated with about 2 to 8 percent by weight of halogenated polyethylene and admixed with a binder of about 2 to 8 percent by weight of a second explosive having a melting point up to C., said particulate crystalline explosive comprising an aliphatic nitramine and said second explosive comprising an aromatic nitramine.

6. A shaped high efliciency explosive of high density, high strength and high detonating velocity comprising a particulate crystalline explosive having a melting point of at least 203 C. coated with about 2 to 8 percent by weight of halogenated polyethylene and bonded with a second explosive having a melting point up to 105 C., said particulate crystalline explosive selected from the group consisting of aliphatic nitramines and triaminoguanidine nitrate.

7. The shaped high efiiciency explosive of claim 6, wherein said particulate crystalline explosive is cyclotetramethylenetetranitramine and said second explosive is selected from the group consisting of hydrazine nitrate, trinitrophenylmethylnitramine, trinitrophenylethylnitramine, trinitrochlorobenzene and mixtures thereof.

8. The shaped high efficiency explosive of claim 6, wherein said particulate crystalline explosive is cyclotrimethylenetrinitramine and said second explosive is selected from the group consisting of hydrazine nitrate, trinitrophenylmethylnitramine, trinitrophenylethylnitramine, trinitrochlorobenzene and mixtures thereof.

References Cited UNITED STATES PATENTS 6/ 1967 Noddin 149--92 X 7/1969 Gow 149-11 X LELAND A. SEBASTIAN, Primary Examiner