US2978864A - Ammonium nitrate explosives - Google Patents

Description

United States PatentfO AMMONIUM NITRATE EXPLOSIVES.

Leonard A. Stengel, Terre Haute, Ind., assignor' to Commercial Solvents Corporation, Terre Haute, Ind., a corporation of Maryland 7 No Drawing. Filed May 19, 1958, Ser.N0. 735,987

7 Claims. 01. 603'5.4)

My invention relates to new ammonium nitrate compositions, and more particularly to compositions prepared from ammonium nitrate and monomethylamine which are suitable for use as explosives and propellants and to processes for using same.

Ammonium nitrate has long been known'to' be flammable and explosive and these properties have been made use of extensively. -For example, ammonium nitrate is now widely used as an explosive although it. possesses certain inherent disadvantages, such as low density, and relative insensitivity. It is a Well known fact that ammonium nitrate explosives, as used in normal mining operations, are usually incapable of propagating a sul ficient detonation'wave. through the ammonium nitrate explosive to detonate completely a column of explosive. It is also well known that the ammonium nitrate explosives customarily used are insensitive to such a degree as torequire'the use of a primer charge to initiate the explosion, as ,well'ias to reinforce the detonation propagation wave as the ex-' amine is increased beyond a preferred amount the sensitivity decreases, and with this reduced sensitivity the practical utility of the composition as a propellant in-- creases. Such compositions of higher monomethylamine content are not only highly effective propellants but also possess the important added advantage of being decidedly more economical than some propellants presently available for use in ballistic projectiles, rockets, and the like. It is extremely dangerous to prepare ammonium nitrate explosives containing trinitrotoluene or other similar explosives outside ofa permanent industrial explosives factory meeting all known safety requirements and run by personnel experienced in the manufacture :of explosives. Furthermore, the ammonium nitrate and carbonaceous materials ordinarily used therewith must be thor-' oughly mixed and combined in equipment which is only found in an industrialplant for the manufacture of ex plosives. =As large amounts of ammonium nitrate and sensitizers are always present in factory operations, there is the ever present danger of disastrous explosions which may demolish the area surrounding-the industrial plant for the production of explosives. 1

My new compositions containing ammonium nitrate as the essential explosive ingredient are not subject to the hazards in production and handling present in the use of previously known explosives containing ammonium nitrate by reason of the fact that they can be easily and simply prepared at the site at which they'are to be used. In many instances, the explosives can be prepared directly in the bore hole by simply placing the ammonium nitrate charge in the bore hole and passing a suitable amount of gaseous monomethylamine through the ammonum nitrate therein. a

My new explosive compositions can also be prepared in the bore hole by dis'solving the monomethylamine and a liquid in which it is soluble, such as ethanol, and pouring the resulting amine solution over the ammonium nitrate charge. The charge can, of course, include carbon black, fuel oil, or other ingredients ordinarily incorporated into ammonium nitrate explosive compositions. The ammonium nitrate-monomethylamine compositions of my invention require primer charges to initiate and propagate detonation waves through the charge. If the bore hole in which the exjplosive is to be detonated is wet, horizontal, or slanting, the ammonium nitrate may be placed in a container such as a polyethylene bag or metal cartridge and the monoethylamine or monomethyl amine solution introduced into the container or cartridge just prior to its insertion in the bore hole.. .In thi sfmanner all of the hazards of mixing and transporting the fin- -Z ished explosive compositions are avoided. It should be noted that the incorporation of the monomethylamine into the ammoniumnitrate mixture at the site of-usage reduces the necessity of preparinglarge amounts of the sensitive explosive at any one place, and thereby Inaterially reduces the hazard to life and'health of the'per sonnel-working in the'area. p

My ammonium nitrate compositions consist essentially;-

vof ammonium nitrate and monomethylamine. To these compositions I can add from 1 to 20% inert additives Such additives must be inert to the extent that they do not react with ammonium nitrate, monomethylamine, or other additives present in the compositions in such a manner as to materially reduce the desired explosive or propellant properties of the mixture. The inert addi tives may be introduced into my mixtures to sensitize or desensitize them, to add oxidizing or reducing potentials to the compositions, to catalyze the burning rate of; the compositions, to make the mixtures hypergollic with strong oxidants, to depress the freezing points of the mixtures,'to lower the average molecular weight of the' exhaust gases or to reduce the burning temperatures of. the mixtures. Any materials known to'perform or ca ble of performing these functions in ammonium nitrate explosives can be used in my compositions. Fuels which I have found to be useful in my explosives include ammonia; metals, such as aluminum or magnesium; petroleum fractions, such as fuel oil; wood flour; carbon black; alcohols, such as methanol or ethanol; etc. -I prefer to use fuel oil as the fuel in myexplosive compositions due to the fact that it is an inexpensive and easily handled liquid. Where fuel oil is 'added to the explosive, the monomethylamine must be introduced into the ammonium nitrate prior to the addition of the added fuel. Inertfuels which I have found to be useful in my propellant compositions include metals, such as mag nesium and aluminum; ammonia; unsymmetrical dimethylhydrazine; hydrazine, etc. I have found that salts, such as ammonium perchlorate, lithium perchlorate, etc.,

can be used to increase oxidizing potentials in my propellant mixtures, while water can be used to lower the combustion temperature of my mixtures.

My mixtures are hypergollic with red and white tum ing nitric acid when more than about 15 to 20% by weight of unsymmetrical dimethylhydrazine is added to my monomethylamine-ammonium nitrate mixtures; Thus, small amounts of red fuming nitric acid can be 3 utilized as an igniter for gas generators or monopropellant systems and excellent bipropellant systems can be obtained from various mixtures of my invention and red and white fuming nitric acid.

The ammonium nitrate compositions of my invention containing amounts of monomethylamine ranging from 2 to 12% by weight, serve as highly effective explosives. I have found, however, that compositions containing amounts of monomethylamine as low as 2% are satisfactory in ammonium nitrate compositions containing carbonaceous materials or other inert additives customarily used in ammonium nitrate explosives. My explosives may be solids or fluids and are much more powerful than previously known ammonium nitrate explosives. I prefer to use about 6.5 to 9.0% monomethylamine in my ammonium nitrate explosives. I have found that an explosive mixture containing 7.95% by weight of mono methylamin'e has the following properties when compared with a number of commercial explosives, using nitroglycerine as the standard:

Ratio Ratio Ratio Ratio Loading Rate of Deto- Deto- Work of Composition Density, Detonation nation AdlagmsJcc. nation Temp. Pressure batic Expansron Nitroglycerin 1. 6O 1. 1. 000 1. 000 1. 000 60% Ammonia dynam c 1. 50 0. 83 0. 770 0. 706 0. 859 Ammonium Nitrate-monomethylamine 1. 45 0. 74 0. 566 0. 548 0. 678 10% Ammonia dynamite 0. 98 0. 521 0. 555 0. 228 0. 641 Akremite I 0. 80 0. 445 0. 525 0. 147 0. 585

I An explosive containing approximately 92% ammonium nitrate and 8% carbon black.

From the above data, it can be seen that the explosives of my invention are comparable in effectiveness with 50% ammonia dynamite. My explosives, however, are decidedly more inexpensive and are much more safely handled than the latter due to the fact that the explosives of my invention can be prepared at the detonation site as required and in the amounts needed.

Molded solid explosives can also be prepared in desired shapes for blasting purposes by first forming a liquid composition containing about 15% monomethylamine, stirring an inert fuel additive, such as aluminum powder or carbon black into the liquid mixture and thereafter evaporating about 80% of the monomethylamine. from the solution to obtain a homogeneous explosive. In this way sticks of explosives similar to dynamite can be prepared which can be utilized in blasting operations as easily as 50% ammonia dynamite.

My compositions are easily adapted to a variety of uses in the propellant field. Compositions containing from about 2 to about 6% by weight monomethylamine and desired amounts of solid inert fuel additives, such as aluminum, carbon black, etc., are solids and can be used as solid propellants for ballistic projectiles and rockets; compositions containing from about 6 to about 15% monomethylamine are crystalline slurries and can be utilized as fluid monopropellants; compositions containing from about 15 to about 40% monomethylamine are liquids and are useful as gas generator fuels, as fuels for air-breathing engines, and as fuels for bipropellant reaction motor systems.

The solid compositions and slurries of my invention compare favorably with the double base solid propellant Ballistite in respect to specific impulse, density, exhaust velocity, etc.

While the explosive compositions of my invention containing as little as 2% monomethylamine are sensitized to some extent, about 10% monomethylamine is required to produce maximum sensitivity. While my compositions are not cap sensitive, they have high sen sitivity for a mixture of such high density, i.e., a 92.1%-

by weight ammonium nitrate-7.9% monomethylamine mixture was found to require only a 70 g. pressed tetryl booster to completely detonate a column of explosive having a length of 28" and a minimum diameter of 7". The liquid compositions of my invention containing from about 15-40% monomethylamine are relatively insensitive and have far greater stability than other known propellants such as n-propyl nitrate, 78% and 100% hydrogen peroxide, etc. In fact, I have determined that the liquid compositions of my invention have about the same order of sensitivity as pure ammonium nitrate at sea level pressure.

I have found that the liquid compositions of my invention can be readily utilized in reaction motors adapted for use with monopropellants. My compositions containing from about 6 to about 15 monomethylamine have specific impulses up to about 200 seconds at 250 p.s.i.a. and density impulses of about 300 seconds. To utilize the compositions of my invention I merely flow them, at a desired rate, into a combustion chamber containing a suitable heating element, such as a white hot platinum grid, to initiate combustion. Once combustion has begun the heating element can be removed or may remain within the reaction motor to catalyze the burning rate of the propellant.

As previously stated, compositions containing from about 15 to about monomethylamine are useful as fuels for gas generators and air-breathing engines, and as fuels for bipropellant systems. These compositions burn at relatively low temperatures with the formation of large amounts of gases in gas generators. They have an added advantage in that no free carbon forms during combustion which would coke up gas turbine blades. The use of such mixtures as fuels for bipropellant systems means that less oxidant is required as the high specific gravity fuel carries considerable amounts of oxygen.

Oxidants which may be utilized with my fuel mixtures in bipropellant systems are any of the commonly used oxidants such as liquid oxygen, red and white fuming nitric acid, dinitrogen tetroxide, etc.

When my compositions are used in air breathing engines, such as turbojet engines, ramjet engines, diesel engines, etc., principles of operation which apply are similar to those applicable to present day engines employing ordinary hydrocarbon fuels. In all of these engines the oxygen in the air is mixed with the fuel so that the fuel-air ratio is approximately stoichiometric. In this way complete burning and efficient operation is assured. For example, when a 39% ammonium nitrate- 61% by weight monomethylamine mixture is used as a turbojet engine fuel, a Weight ratio of air to fuel of at least about 7:1 is desired. After combustion of my preferably anhydrous.

fuels in the combustion chambers of a turbojet engine, additional air is bled into the exhaust gases prior to passing them through the gas turbine blades in order that the turbine blades may be maintained at a temperature of about l500-1600 F.

' My ammonium nitrate-monomethylamine compositions are of especial interest as they require little special equipment to maintain them in usable form and are essentially non-hazardous to the personnel working with them. The compositions of my invention present no storage problems as they are essentially non-corrosive to cold rolled steel and aluminum containers and they have very low vapor pressures, of the order of one pound at 75 F.

The ammonium nitrate utilized in my invention for explosives is preferably essentially anhydrous pure ammonium nitrate or fertilizer grade ammonium nitrate which is coated with various coating agents such as resin, dicalite, etc. Pure anhydrous ammonium nitrate is preferred when my mixtures are to be used as propellants. The monomethylamine used in my invention is When ammonium nitrate and sufficient quantities of the amine are brought into conra e;

tact a solution quickly forms. My solutions are preferably formed-by passing the amine, the liquid state;

into ammonium nitrate.

The bulk density of granular ammonium nitrate of the grade ordinarily usedforexplosive purposes is approximately.0.9 0. By adding 7,0 80% monomethylamine to the same grade ammonium nitrate the bulk density of the ammonium nitrate is increased to approximately 1.5. This increase in'bulk density materially increases Explosive compositions The following table sets out some of the physical properties of my solutions.

Physical properties of ammonium nitrate-monomethylaminc solutions Percent wt. monomethylamine 18.1 27.1 n 5 1. 4462 1.4344 Density, C

7.8 11.47 6.9 10. 06 6. 2 8. 86 6. 5 30 o 7.96 5.0 Va or ressure,

40. 3 --mm. abs-- 567 1, 126 n1n1 abs 375 763 mm abs 691 --mm. abs- 243 447 -.mm. abs 176 (+09) 333 a 2 Freezing oint Ignition tgmperature C 400-450 400-450 The following examples more fully illustrate my invention but it is not intended that my invention be limited to the motors, fuels or processes described. It is intended that all equivalents obvious to those skilled in the art be included within the scope of my invention as claimed.

EXAMPLE I To test my propellant in gas generators 0.241 lb./sec. of a propellant mixture of 28.5% monomethylamine, 66.5% ammonium nitrate, and 5% of anhydrous hydrazine, which serves to lower the freezing point, was introduced into a gas generator decomposition chamber somewhat similar to the decomposition chamber of the German Walter 109-509 rocket unit. The unit used in my process consists of a stainless steel tube, flanged and drilled on both ends so that the chamber can be sealed by bolting covers on each end. The upper cover is equipped with a fuel inlet containing six diverging injector nozzles. The lower cover is equipped with a gas outlet attachment and a perforated plate which serves to es ormroeotorotc aH MNOOI-DN support a steel, catalyst, basket containing platinum precipitated on alumina. The propellant was ignited by means of a glow plug inserted into the chamber and produced 23 c.f.s. of gas at a temperature of about 1520 F. and atmospheric pressure. J

EXAMPLE 11 .To test the use of my propellants as monopropellants 0.27 lb./sec. of a propellant mixtureof 14.5% monomethylamine, 65.5% ammonium nitrate, and 20% of unsymmetrical dimethylhydrazine, which lowers the freezing point to about 22 C. and makes the fuel hypergollic with red fuming nitric acid, was injected into a thrust chamber containing a platinum plated grid flame holder. Ignition was started by injecting approximately 15 grns. of RFNA into the chamber. This propellant burns well, has a specific impulse of 161 sec. and produces 25.4 c.f.s. of gas at a temperature of about 1475 F; and atmospheric pressure.

EXAMPLE III To test my propellant in a bipropellant system a small rocket thrust chamber made up from available 1'' LD. stainless steel pipe and stainless steel pipe fittings was prepared. The fuel injection nozzle was made from a pipe'plug. An orifice of 0.040" diameter was drilled in the pipe plug and a needle valve assembly was seated into the orifice and welded on the plug. For ease of repair a 1" union was used to attach the plug to a .4" pipe which comprised the burning chamber. A reducing coupling was utilized as the motor nozzle. An oxygen inlet tube and a Bourbon-type pressure gauge with a range of 0-600 p.s.i. were attached to the burning chamber through the plug. A propellant mixture consisting of 27.9% monomethylamine and 72.1% ammonium nitrate was introduced into the thrust chamber through the injector nozzle. A stoichiometrically equal amount of gaseous oxygen was also introduced into the thrust chamber. Ignition was initiated by preheating the chamber to 625 C. One hundred eighty-one (181) pound seconds per second thrust was created by this small reaction motor at 300 lbs. pressure.

This application is a continuation-in-part of my US. Patent application Serial No. 681,437 filed September 3, 1957, now abandoned.

Now having described my invention what I claim is:

1. Ammonium nitrate compositions useful as explosives and propellants consisting essentially of ammonium nitrate with 2-10% by weight of monomethylamine, based on the weight of the ammonium nitrate, and from 120% of an inert additive material, based on the weight of the ammonium nitrate selected from the group consisting of hydrazine, lower alkylhydrazines, and lower alkanols.

2. A process for creating thrust in monopropellant burning reaction motors which comprises burning within said reaction motors mixtures of ammonium nitrate, from about 6 to 15 weight percent of monomethylamine, and from about 1 to 20% selected from the group consisting of hydrazine, lower alkylhydrazines, and lower alkanols and exhausting the resultant gases.

3. The process of claim 2. wherein the inert additive material is anhydrous unsymmetrical dimethylhydrazine.

4. The process of, claim 2 wherein the inert additive material is anhydrous hydrazine.

5. A process for creating thrust in bipropellant burning-reaction motors which comprises burning within said motors stoichiometrically equivalent amounts of a fuel mixture of ammonium nitrate, from about 15 to 40 weight percent of monomethylamine, from about 5 to 20 Weight percent of an additive selected from the group consisting of hydrazine, dimethylhydrazine and lower alkanols, and an oxidant selected from the group consisting of red fuming nitric acid and white fuming nitric acid.

of an inert additive material the Weight 'of; the ammonium nitrate, and 1 -20 percent of hydrazine; ba'sed on'the weightof the ammonium nitrate. 3 7. Ammonium nitratecompositions us eful as. propei- I lants consisting essentially of ammonium nitrate with '21-'10 percent byweight of monomethylamin, based on the weight of the ammonium nitrate, and from 1-20 percent of unsymmetrical dimethylhydrazine, based on the weight'ofihe'ammoniumnitrate;.

LAstronautiquef 1930,, pages 146447; copy in Wertheim:

i Von Loenen p'mER REFERENCES Textbook 6f organi Chem? Q2116: 1. I I I I I Blakiston 00., Philadelphia, pp. 302-303, 1945.

Claims (1)

1. 2. A PROCESS FOR CREATING THRUST IN MONOPROPELANT BURNING REACTION MOTORS WHICH COMPRISES BURNING WITHIN SAID REACTION MOTORS MIXTURES OF AMMONIUM NITRATE, FROM ABOUT 6 TO 15 WEIGHT PERCENT OF MONOMETHYLAMINE, AND FROM ABOUT 1 TO 20% OF AN INERT ADDITIVE MATERIAL SELECTED FROM THE GROUP CONSISTING FO HYDRAZINE, LOWER ALKYLHYDRAZINES, AND LOWER ALKANOLS AND EXHAUSTING THE RESULTANT GASES.