US3166555A - Ammonium nitrate-hexamethylene-tetramine adduct - Google Patents

Description

Jan. 19, 1965 w. E. GORDON 3,166,555

AMMONIUM NITRATEl-I-IEXAMETI-IYLENETETRAMINE ADDUCT Filed June 6, 1962 2 Sheets-Sheet 1 o INITIAL CONCENTRATION OF HEXAHINE D INITIAL CONCENTRATION OF M- NITRATE son 1 SOLIIBILITY 3, (g/IOOg water) 6 mum: I: 20 no so so 100 TEMPERATURE (C) FIGURE 1 INVENTOR. WILLIAM E. GORDON ATTORNEY Jan. 19, 1965 w. E. GORDON AMMONIUM N ITRATE-HEXAMETHYLENETETRAMINE ADDUCT 2 Sheets-Sheet 2 Filed June 6, 1962 n22 6250mm 88 I INVENTOR. WILLIAM E. GORDON ATTORNEY 8 3 (maaaaa) HDNVUIWSNVHL United States Patent dice 3,166,555 AMWIONIUM. NI'I'RATE-HEXAMETHYLENE- TETRAMINE ADDUCT William E. Gordon, Bethesda, Md., assignor to Arthur 1).

Little, Inc, Cambridge, Mass, a corporation of Massachusetts Filed June 6, 1962, Ser. No. 200,439

3 Claims. (Cl. 260-2485) been useful only as blasting agents, as distinguished from stick dynarnites, i.e., cartridge explosives, unless ingredients of the molecular explosive type such as nitroglycerin are included in the formulations. Blasting agents require a large diameter charge and must be initiated with a 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 adiameter of about 1.25 inches.

The primary object of this invention is to provide im proved 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.

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

In accordance with my invention, I have discovered an adduct of hexamethylenetetramine and ammonium nitrate-which significantly increases the cap sensitivity of explosive formulations. This adduct has the empirical formula (CH N 2NH,N0

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.

Patented Jan. 19, 1965 Secondly, crystallization of the adduct is effected by removal of the water at a temperature below ahout 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 40 C. I

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 evapo-' rating 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 Biichner funnel and the crystals pressed with a rubber darn; rinsed twice with water-free acetone; and then again pressed to remove the acetone. The crystals were removed from the Biichner, 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 hexamethylenetetramine 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 oxidizerand 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.

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 C, crystals of the hexamethylenetetramine precipitated, but no adduct was detected by X-ray diffraction of the crystalline precipitate, and the melting point was that of the hexamethylenetetramine.

Reference to FIGURE 1 of the drawing suggests 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 exclusion of the other.

B. Crystallization fr'om melts The adduct may also be made without water by melting the two ingredients hexamethylenetetramine and ammonium nitrate in the proper molar ratio, i.e., one to two, and

then quickly 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 oxyg en-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 diiiicult. Acc ordingly, I prefer when making the adduct by the melting process to employ the proper molar ratio, but still to use the hot melting roll and the cooled crystallizing roll as described in the aforementioned 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 rpm. ;The molten material was then passed onto a counter-rotating cold metal roll which was maintained at about C. where the'molten material was congealed,

in the form of flakes. The latter consisted essentially of.

pure crystals of adduct.

II. ADDUCT: STRUCTURE A. X-ray diflraction pattern The fact that the crystals obtained as described above have a distinct crystalline structure different from either hexamethylenetetramine or ammonium nitrate was established by the use of X-ray diffraction techniques. The following table gives in approximate terms the relative intensities I/I of the adduct for different values of the interplanar spacings expressed in angstrom units, d(A.).

TAB LE I From this table it will be noted that the major peaks are at 4.07 A., 4.45 A., and 5.27 A.

B. Infrared analysis III. ADDUCT: PROPERTIES A. Empirical formula: (CH N -2NH NO B. Solubility in water: .Very soluble in hot or cold water. At'10 C. about 220 grams will dissolve in 100 grams of water. p C. Solubility in organic solvents: Sparingly soluble in acetone, ethyl alcohol and ether.

D. Melting point: About 122 C. (completely liquid by 132 C.). Prolonged heating above this temperature vturns the melt yellowish. After eighteen hours 1 at 125 C., the melt becomes a viscous tar-like liquid with a strong amine odor. Before reaching this state, fumes of ammonia are given off.

E. Color: Colorless and transparent as individual crystal.

F. Explosive properties: The adduct per se is a weak molecular explosive. It is heavily fuel-rich relative to oxygen balance. It has little sensitivity but is detonable with adequate boostering in proper confinement I and diameter. In 2.0 inchdiameter, 0.5 inch thick steel 'walled tubes and boostered with a 25-gram tetryl-pel' let, adduct in a hammermilled form has a detonation velocity of 10,400 f./s. at a density of 0.84 g./cc.

IV. ADDUCT: EXPLOSIVE FORMULATIONS 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. The resulting mixture was tumbled to assure com plete 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 differentsizes. The detonation velocity for each explosion was determined in conventional fashion. The data obtained are presented in the following Table II.

TABLE II.EXPLOSIVE DATA Cartridge Size (in) Densit Primer Velocity gJcc. (f./s.)

1.25 x 8 0 No. GEBO 1 18, 300

1.0x8 0. 95 No.6 EBC 11,900

0.75 x10 0. 95 No. 6 EBO 10,400

1 N0. 6 Electric Blasting Cap.

From the above, it will be seen that 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 (appr Its velocity in 1.25 inch diameter is about 13,300 f-P at 0.95 density. Its gap sensitivity is about 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 exceeding microns. At least a portion of these crystals is enveloped in a continuous crystalline matrixoftheadduct and any I 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 hexamethylenetetramine or ammonium nitrate. The density of explosives prepared in such fashion is about 0.95 in an unpacked state. They are capable of being detonated in a cartridge having a 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 a been first briefly ground together in amortar in order to disperse the abietic acid throughout thehexamethylene 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 temperature of about 145 C.

The resulting molten mass was then poured into a heated vessel having a multiplicity of small 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 glovedhands 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. 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 hygroscopic 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 No. 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 by that 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 effective 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 hexamethylenetetramine 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 had 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 -weight of adduct, and 2.7 percent by weight of finely divided anthracite coal. This second formulation was also in rod ced to :1 1254 1. a 5- nc cartridge s d y As an alternative to the kneading and 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 good 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 suitabel 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 appended claims, the invention may be practiced otherwise than as specifically illustrated and described. In particular, it should be understood that other ingredientsconventionally used in explosive formulations for special purposes may be included in my explosive formulations.

I claim:

1. The adduct of ammonium nitrate and hexamethylenetetramine in the molar ratio of 2 to 1.

2. The crystalline adduct of ammonium nitrate and hexamethylenetetramine which has a melting point of about 122 C. and which has an infrared spectrogram showing characteristic absorption peaks at the following wave numbers: 868, 1256, 1291, 2490, 2535, 2596, 2625, 2672, 2722, 2790 and 2826 cm.- and an X-ray dilfraction pattern with major peaks at 4.07 A., 4.45 A., and 5.27 A.

3. The method of making an adduct of ammonium nitrate and hexamethylenetetramine which comprises dissolving said ammonium nitrate and hexamethylenetetramine in water in the molar ratio of about 2 to 1, and removing the water at a temperature below about 40 C. until the adduct is formed.

References Cited in the file of this patent UNITED STATES PATENTS 1,720,459 Wyler July 9, 1929 2,345,582 Carey Apr. 4, 1944 2,548,428 Fiedorek Apr. 10, 1951 2,579,494 Hermann Dec. 25, 1951

Claims (2)

1. THE ADDUCT OF AMMONIUM NITRATE AND HEXAMETHYLENETETRAMINE IN THE MOLAR RATIO OF 2 TO1.

3. THE METHOD OF MAKING AN ADDUCT OF MAMMONIUM NITRATE AND HEXAMETHYLENETETRAMINE WHICH COMPRISES DISSOLVING SAID AMMONIUM NITRATE AND HEXAMETHYLENETETRAMINE IN WATER IN THE MOLAR RATIO OF ABOUT 2 TO 1, AND

Images