US3166452A - Explosive compositions containing ammonium nitrate-hexamethylenetetramine complexes - Google Patents

Description

19, 1965 w. E. GORDON 3,166,452

EXPLOSIVE COMPOSITIONS CONTAINING AMMONIUM NITRATE-HEXAMETHYLENETETRAMINE COMPLEXES Original Filed June 6, 1962 2 Sheets-Sheet 1 o INITIAL CONCENTRATION OF NEXANINE aoo D INITIAL couczmmon OF mm. mm:

600 SOLUBILITY 6 (9/l00g water) x00 zoo HEXNN NE TEMPERATURE (c) FIGURE 1 INVENTOR.

WILLIAM E. GORDON ATTOR N EY Jan. 19, 1965 w, go no 3,166,452

EXPLOSIVE COMPOSITIONS CONTAINING AMMONIUM NITRATE-HEXAMETHYLENETETRAMINE COMPLEXES Original Filed June 6,1962 2 Sheets-Sheet 2 INVENTOR. WILLIAM E.GORDON ATTORNEY (LNHDHHd) SDNVLLIWSNVHL United States Patent.

4 Claims. (Cl. 149-46) This invention relates to explosive compositions, and methods of making them, and, more particularly, to explosive compositions comprising hexamethylenetetramine andarru'nonium nitrate.

This application is a division of application Serial Number- 200,489,, filed June 6, 1962, for Explosive Compositions.

Explosive formulations comprising ammonium nitrate and hexamethylenetetramine are known. The ammonium nitrate serves as the oxidizer, and the hexamethylenetetramine as the fuel, or at least as a portion thereof, in such formulations. Such formulations, however, have been useful only as blasting agents, as distinguished from stick dynamites, i.e. cartridge explosives, unless ingredients of the molecular explosive type such as nitroglycerin are included 'in the formulations. Blasting agents require a largediameter charge and must be initiated witha high explosive primer. A cartridge explosive, on the other hand, is a stick-type charge that has a small diameter and is detonable by means of a No. 6 or a No. 8 blasting cap. In the trade, cartridge explosives are simply called dynamite. Throughout this specification the term cap sensitive cartridge explosive is intended to designate an explosive that may be detonated by a No. 6 or a No. 8 blasting cap in an eight-inch paper cartridge having a diameter of about 1.25 inches.

The primary object of this invention is to provide improved explosive formulations comprising ammonium nitrate and hexamethylenetetramine which not only may be used as blasting agents but also are eminently suitable as cap sensitive cartridge explosives. 1

Another object of this invention is to provide methods of making the afore-mentioned improved explosive formulations.

In accordance with my invention, I have discovered an adduct of hexamethylenetetrarnine and ammonium ni-' trate which significantly increases the cap sensitivity of explosive formulations. This adduct has the empirical formula (CH N 2NH NO Other objects and advantages of my invention will become apparent from the following description of this invention, and from the accompanying drawing in which FIGURE 1 is a plot of the solubilities of ammonium nitrate and hexamethylenetetramine in water at various temperatures.

FIGURE 2 is the infrared spectrogram of the adduct of ammonium nitrate and hexamethylenetetramine of this invention.

- I. ADDUCT--METHODS OF PREPARATION A- Crystallization from water solution: I prefer to prepare the adduct of this invention by crystallization from an aqueous solution of hexamethylenetetramine and ammonium nitrate. However, it is essential to the successful production of the adduct by this method to conduct the crystallization under the following two conditions.

Firstly, the hexamethylenetetramineand the ammonium nitrate are dissolved in the water in a molar ratio corre- Vi sponding substantially to one mole of the hexamethylenetetrarnine to two moles of the ammonium nitrate. Such EdhhASZ Patented Jan. 19, 1965 a molar ratio corresponds to 46.66 percent by weight of hexamethylenetetramine and 53.34 percent by weight of ammonium nitrate.

Secondly, crystallization of adduct is effected by removal of the water at a temperature below about 40 C., and preferably below 30 C. Such removal is preferably accomplished by air drying, that is, by evaporating the water in a stream of air passing over or through the aqueous solution. However, the water may be removed by other conventional means such as under vacuum, by spray drying, by azeotropic distillation with a solvent, etc., provided, always, that the temperature be maintained below 40C.

By way of example of the preferred method of preparation, 700 grams of hexamethylenetetramine and 800 grams of ammonium nitrate were dissolved in 700 grams of water at 20 C. The solution was placed in evaporating dishes and a stream of air was passed over the surface of the solution. After about 25 hours, virtually all the water was evaporated, leaving a heavy slush. The latter was filtered through a Buchner funnel and the crystals pressed with a rubber dam; rinsed twice with Water-free acetone; and then again pressed to remove the acetone. The crystals were removed from the Buchner, transferred to large filter papers and allowed to dry. The crystals were established to be pure adduct, as will be later set forth.

Attempts to prepare the adduct in the manner set forth in the foregoing example failed when the molar ratio of the hexamethylenetetraminel and ammonium'nitrate was substantially different from'one to two. For example, when the molar ratio was one to ten (the ratio corresponding to an oxygen-balanced system of oxidizer and fuel), no adduct was precipitated. The ammonium nitrate crystallized separately leaving the hexamethylenetetramine in the mother liquor. However, if this oxygenbalanced system of hexamethylenetetramine and ammonium nitrate is prepared by taking the solution to complete dryness by evaporation at room temperature, then the adduct can be detected in small quantities by X-ray diffraction techniques. Similarly, if an intimate mixture of hexamethylenetetramine and ammonium nitrate is allowed to stand for several hours in the presence of a small amount of adsorbed moisture, adduct can be detected. I

Attempts to prepare the adduct by crystallization at a temperature above 40 C. failed, even though the molar ratio was one to two. For example, a solution of the two components in the proper ratio was prepared which was saturated with respect to the hexamethylenetetramine at 70 C. Upon removal of the water by vacuum drying at 70 0., crystals of the hexamethylenetetramine precipitated, but no adduct was detected by X-ray diffraction of the crystalline precip'i'ate, and the melting point was that of the hexamethylenetetrarnine.

Reference to FIGURE 1 of the drawing suggest a possible explanation of the above-described behavior. It will be noted that the solubility of ammonium nitrate in water accelerates rapidly with rising temperature, while that of the hexamethylenetetramine actually declines. The circle and the square represent the initial concentrations of the hexamethylenetetramine and the ammonium nitrate, respectively, used in adduct preparation. At these concentrations, the two components precipitate together, thus giving the adduct an opportunity to form. However, at higher temperatures, or with widely disparate concentrations, one component crystallizes preferentially to the ex- 'am-ine odor.

cooling the molten mixture. The adduct is successfully made provided that as soon as the mixture is molten, it is quickly cooled. Otherwise, the adduct decomposes as a result of exposure to the elevated temperatures. In my copending application Serial No. 146,944, I showed how the adduct is formed even when an oxygen-balanced mixture of hexamethylenetetramine and ammonium nitrate is melted and then rapidly cooled. It was in such a product that I first discovered the existence of the adduct. However, the separation of the adduct in pure form from that product is difficult. Accordingly, I prefer when making the adduct by the melting process to employ the proper molar ratio, but still to use the hot melting i roll and the cooled crystallizingroll as .described in the afore-mentioned application.

By way of example of the melting process, the required proportions of hexamethylenetetramine and ammonium nitrate (1:2) were thoroughly mixed, and then hammermilled. The resulting finely ground mixture was passed onto a hot metal roll which was maintained at a temperature of about 160 C. and which revolved at about one r.p.m. The molten material was then passed onto' a counter-rotating cold metal roll which was maintained at about 10 C. where the, molten material was congealed in the form of flakes. The latter consisted essentially of pure crystals of adduct.

II. ADDUCT-STRUCTURE tubes and boostered with a 25-gram tetryl pellet, adduct in a hammermilled form has a detonation velocity of 10,400f./s. at a density of 0.84 g./cc.

IV. ADDUCTEXPLOSIVE FORMULATIONS As pointed out above, the adduct itself is weak as an explosive, presumably because it is deficient in oxidizer. When mixedwith suflicient oxidizer to attain oxygen balance, explosive formulations are formed which are equal to or'better than the presently available commercial cartridge explosives, and which, furthermore, are considerably less expensive because of the relatively cheap ingredients, particularly when the added oxidizer is ammonium nitrate. The following is an example of an explosive formulation made from the adduct of this invention.

' Example I Adduct was blended with ammonium nitrate prills in the proportion of 1 to 4.02 parts by weight respectively. This proportion produces an oxygen-balanced formulation. Theresulting mixture was-tumbled to assure complete mixing and then passed through a hammermill.

Sieve analysis gave 74 percent of the material through 200 mesh. Samples 'of. the product were exploded in cartridges of ditferent sizes. The detonation velocity for each explosion was determined in conventional fashion.

I The data obtained are presented in the following Table II.

TABLE I d(A.) 4. 07 4. 5. 27 2. 95 5. 2. 79 I I/Ii 100 45 33 V 20 20 I 12 sult of a summation spectrum of these two compounds.

FIGURE 2 of the drawing is the infrared'spectrogram TABLE IL-EXPLOSIVE DATA 1 No. 6 electric blasting cap.

From'the above, it will be seenthat the blend of adduct and ammonium nitrate is a cap sensitive stick explosive. In general, it has a'reaction zone length, a of about 0.27 inch and a critical diameter, d =0.50 inch (approx). Its velocity in 1.25 inch diameter is about 7 13,300 f.p'.s. at 0.95 density'. Its gap sensitivity is about of the adduct. The characteristic absorption peaks occur at the following wave numbers: 2490, 2535, 2596, 2625, 2672, 2722, 2790, and- 2826 cmf as well as at 868, 1256 and 1291 GEL-'1.

V In. ADDUCT-PROPERTIE:SY A. Empirical formula: (CH2)6N4-2NH4NO3.

B. Solubility in water: Very soluble in hot or cold water. At 10 C. about'220 grams will dissolve in 100 grams of water.

C. Solubility in organic solvents: Sparingly soluble in acetone, ethyl alcohol and ether. g V 'D. Melting point: About 122 C. (completely liquid transparent as individual '3 inches.

Oxygen-balanced explosives containing the adduct of my invention may be prepared by the method described in the aforesaid application'Serial No. 146,944, that is, by melting a mixture of ammonium nitrate and hexamethylenetetramine in oxygen balanced proportions,

and thereafter rapidly chilling the molten mass. By

rapidly chilling the melt, crystals of ammonium nitrate are obtained that have a maximum dimension not ex such fashion'is about 0.95 in an unpacked state.-'Theyf are capable of being detonated in a cartridge having a 'F. Explosive properties: 'Theadduct per se 'is a weak I,

molecular explosive. 'It is heavily fuel-rich relative" to oxygen balance. It has little sensitivity but is detonable' with adequate boostering in proper confinement and diameter. In 2.0 inch diameter, 05inch thick steel walled ceeding microns. At'leasta potrion of these crystals is enveloped in a continuous crystalline matrix'of'the ,adduct and any hexamethylenetetramine which may not have formed adduct. X-ray diffraction tests performed on the resulting products showed a prominent X-ray' diffraction pattern peak at about 4.45 A. :This peak is not associated either with hexamethylenetetraniine or ammonium nitrate. The density of explosives prepared in diameter of about 1.25 inch by a-No. 6 Electric Blasting Cap with a detonation velocity of about 14,500 ft./sec. The gap sensitivity is about 4 inches. The following is an example of such an explosive formulation."

I Example 2 7 Into an electrically heated stainless steel kettle were placed 900 grams ammonium nitrate Y (uncoated prills tetramine. Without this preliminary mixing the abietic acid would tend to coagulate on the surface in the melt.

The mixture therefore consisted of 90 percent by weight ammonium nitrate, 9 percent by weight hexamethylenetetramine as the primary fuel and 1 percent by weight abietic acid as a crystallization modifier.

The mixture in the kettle was continuously stirred with moderate speed until a clear melt was formed at a temerature of about 145 C.

The resulting molten mass was then poured into a heated vessel having a multiplicity of si all perforations in the bottom. The melt was then allowed to drip onto a clean, smooth stone table top from a height of about two feet while the vessel was moved about in such a way as to distribute the resulting solidified splattered droplets uniformly over the surface. This material was then scraped together in a pile by means of a steel blade and briefly kneaded with gloved hands in order to break up or granulate the flakes. It was then sifted and rubbed through a 16 mesh screen and finally stored in a polyethylene bag. As an alternative to the kneading and sifting operation, the scraped-up flakes were placed directly in the polyethylene bag and the granulation accomplished by suitable kneading on the bag.

Due to the hydroscopic nature of ammonium nitrate, it is important to avoid high ambient humidity (greater than 50 to 60 percent relative humidity) and to keep the stored material in a moisture resistant container.

The resulting granulated material when packed into a 1.5 inch steel pipe, 12 inches long, at increasing densities gave the following measured detonation velocities.

Density, gm./cc.: Detonation velocity, ft./sec.

Explosive formulations may also be made using the adduct of this invention in which the fuel is not exclusively hexamethylenetetramine. However, in order to assure a formulation which is sensitive to a N0. 6 Electric Blasting Cap, the adduct should be present in an amount corresponding to at least ten percent by weight of the total amount of fuel and oxidizer in the formulation. The maximum amount of adduct is, of course, set bythat required for oxygen balance with the ammonium nitrate when no other fuel than the hexamethylenetetramine is used. In the latter case, the amount of adduct is about twenty percent by Weight of the total amount of fuel and oxidizer in the formulation. Accordingly, the range of eifective amount of adduct in a cap sensitive explosive formulation is to 20 percent by weight of the total amount of fuel and oxidizer in the formulation.

Examples of explosive formulations in which other fuels were used in addition to hexamethyleuetetramine are as follows. A formulation was made which consisted of a mixture of 83 percent by weight of ammonium nitrate, 12.5 percent by weight of the adduct, and 4.5 percent by weight of wood flour. This formulation was introduced into a 1.25-inch x 8-inch cartridge. Its density was 0.95. It was detonable by a No. 6 Electric Blasting Cap and has a detonation velocity of 12,300 f./s. Similarly, a formulation was made which consisted of 85.7 percent by weight of ammonium nitrate, 11.7 percent by weight of adduct, and 2.7 percent by weight of finely divided anthracite coal. This second formulation was also introduced into a 1.25-inch x 8-inch cartridge. Its density was 0.95. It, too, was detonable by a No. 6 Electric Blasting Cap and had a detonation velocity of 11,900 f./s.

Not only may the fuel of the explosive formulations of this invention be in part other than hexamethylenetetramine, but also the oxidizer may in part be other than ammonium nitrate. Many oxidizers are known in the art. However, even as described above with respect to the partial use of other fuels, the adduct should be present in an amount between 10 and 20 percent by weight of the combined weight of fuel and oxidizer if the maximum cap sensitivity is to be reliably attained.

A natural question is why not simply mix ammonium nitrate and hexamethylenetetramine, instead of resorting to such methods of making adduct, as presented above. A goo-d blasting explosive formulation can be obtained by using the simple mixture with an adequate primer. However, when packed in cartridge form, 1.25 inches in diameter, the mixture is not detonated by a No. 6 Electric Blasting Cap and furthermore its gap sensitivity, even when initiated with a tetryl pellet primer, is only one inch. For these reasons the simple mixture is not suitable for use as stick dynamite, although quite useful, as mentioned, in normal blasting operations.

In view of the improved performance resulting from the presence of the above-described adduct in explosive formulations, I have concluded that the improvement results from the pseudo-molecular mixture formed by the fuel and the oxidizer. In other words, the adduct of fuel and oxidizer acts as a molecular explosive, and thereby improves the performance of any explosive formulation in which it is present.

According to the provisions of the patent statutes, I have explained the principle, preferred construction and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described. In particular, it should be understood that other ingredients conventionally used in explosive formulations for special purposes may be included in my explosive formulations.

I claim:

1. An explosive composition comprising an adduct of ammonium nitrate and hexamethylenctetramine in the molar ratio of 2 to 1 and sufficient oxidizer to render the composition in substantial oxygen balance.

2. A cap sensitive cartridge explosive consisting essentially of an adduct of ammonium nitrate and hexamethylenetetrarnine in the molar ratio of 2 to 1 and sufficient additional ammonium nitrate to render the explosive in substantial oxygen balance.

3. An explosive composition comprising fuel and oxidizer in substantial oxygen balance, at least a portion of said fuel and of said oxidizer being in the form of an adduct of ammonium nitrate and hexamethylenetetramine in the molar ratio of 2 to 1, said adduct constituting between 10 to 20 percent by weight of the combined weight of fuel and oxidizer.

4. The method of making a cap sensitive cartridge explosive which comprises first making the adduct of ammonium nitrate and hexamethylenetetramine in the molar ratio of 2 to 1, and thereafter blending said adduct with ammonium nitrate in the proportion of about 1 to 4 parts by weight respectively.

References Cited by the Examiner UNITED STATES PATENTS 1,720,459 7/29 Wyler 1492 2,345,582 4/44 Carey 149-46 3,066,139 11/ 62 Zhivadinovich 149-46 X CARL D. QUARFORTH, Primary Examiner,

Claims (2)

1. AN EXPLOSIVE COMPOSITION COMPRISING OF ADDUCT OF AMMONIUM NITRATE AND HEXAMETHYLENETETRAMINE IN THE MOLAR RATIO OF 2 TO 1 AND SUFFICIENT OXIDIZER TO RENDER THE COMPOSITION IN SUBSTANTIAL OXYGEN BALANCE.

2. A CAP SENSITIVE CARTRIDGE EXPLOSIVE CONSISTING ESSENTIALLY OF AN ADDUCT OF AMMONIUM NITRATE AND HEXAMETHYLENETERTRAMINE IN THE MOLAR RATIO OF 2 TO 1 AND SUFFICIENT ADDITIONAL AMMONIUM NITRATE TO RENDER THE EXPLOSIVE IN SUBSTANTIAL OXYGEN BALANCE.

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