US3124495A

US3124495A - Explosive compositions

Info

Publication number: US3124495A
Authority: US
Publication date: 1964-03-10
Anticipated expiration: 1981-03-10

Description

March 10, 1964 J. R. HRADEL EXPLOSIVE COMPOSITIONS Filed Aug. 11. 1960 Me/a/ INVENTOR. Jose 0A R. Hraae/ HG'E United States Patent Ofiice Filed Aug. 11, 1960, Ser. No. 48,981 8 Claims. cl. 149-43 The present invention relates to explosive compositions and to methods of preparing the same. More specifically, the present invention contemplates novel explosive. compositions and a method wherein an oxidizing salt is present in the initial composition in admixture with a solid, light metal of relatively coarse particle size or configuration.

The present application is a continuationdn-part of my copending application, Serial No. 807,406, filed on April '20, 1959, now abandoned.

Heretofore, in the loading and shooting of bore holes, as in oil well and mining operations, conventional explosives such as nitroglycerine, TNT, composition C and other high explosive compositions have been employed. More recently, oxidizing salts, such as ammonium nitrate, have been utilized. These oxidizing salts have been used in granular form, in granular form admixed with oils, and, in aqueous slurry form as taught in my U.S. Patent 2,867,172..

It is also known that relatively. shock insensitive, unprimed granular oxidizing salts, such as ammonium ni: trate, can be rendered sensitive by admixture with finely divided metals of very small particle size. However, the admixtures resulting therefrom geenrally, because of their sensitivity, are somewhat hazardous to handle and use in the field.

Heretofore, the addition of metal to granular explosives, i.e., the metallization of explosives, has been carried out primarily on the theory that particles of extremely small size, e.1g., from one-half micron up to about one hundred mesh size, because of their large surface area per unit weight sensitize the relatively insensitive oxidizing salt. ln practice, as stated heretofore, these metallized loads have proven both to be unreliable and very dangerous to handle in many instances. Frequently the finely particulated metal is inadvertently prematurely reacted which causes the entire sensitized load to be exploded premateurely. Therefore, an important advance in the explosive art would be to develop explosive compositions using relatively insensitive oxidizing salts in conjunction with metal configurations wherein the initial loads have satisfactory safety margins with regards to handling and shock sensitivity.

Accordingly, an object of the present invention is to provide explosive compositions containing oxidizing salts and light metals in which the separate mix ingredients are substantially insensitive to shock.

Another object of the present invention is to provide explosive compositions in which the oxidizing salt, e.g., ammonium nitrate, may be present initially in solution form for example as in an aqueous ammoniacal solution.

Still another object of the present invention is to provide explosive compositions which, upon detonation, are substantially devoid of toxic gases, such as carbon monoxide, carbon dioxide and the noxious oxides of nitrogen, which toxic materials constitute serious health hazards.

Additional objects of the present invention include the provision of methods "for producing the relatively insensitive explosive composition together with novel detonation methods utilizing such compositions.

Still another object of the present invention is the provision of an explosive composition having high work powers.

3,124,495 Patented Mar. 10, 1964 These and other objects of the present invention will be apparent to those skilled in the art to which these inventions pertain from the detailed specification presented hereinafter when read in conjunction with the accompanying drawing.

FIGURE 1 is a graphical presentation of the explosive compositions encompassed by the present invention.

It has been found in the present invention that admixing ammonium nitrate with certain coarse, particulated light metals, contrary to the teachings of the prior art, provides relatively insensitive explosive compositions which exhibit high work powers. Preferably, these substantially insensitive compositions comprise generally a liquid solution of ammonium nitrate oxidizer, in which the solvent for the ammonium nitrate is a hydrogen-containing liquid containing either nitrogen and/or oxygen, and a light metal thermal carrier, preferably selected from the group consisting of magnesium, magnesium alloys, aluminum, aluminum alloys, magnesium-aluminum alloys, and mixtures thereof.

These compositions will comprise on a weight basis the area encompassed by ABCDE of the figure.

These compositions, as defined by ABCDE, will contain on a weight basis from about 10 to about 90 percent of ammonium nitrate, from about 0.5 to about 40 percent solvent for the ammonium nitrate and from about 10 to about percent of light metal.

Preferably the composition will range on a Weight basis from about 10 to about 83 percent ammonium nitrate, from about 2 to about 35 percent solvent for the ammonium nitrate and from about 15 to about 60 percent of light metal.

Desirably the compositions will contain from about 15 to about 45 percent of ammonium nitrate, from about 5 to about 35 percent of liquid carrier and from about 30 to about 50 percent of light metal.

Examples of liquid, hydrogen-containing solvents for the ammonium nitrate are water, liquid ammonia, ammonium hydroxide and hydrazine. To illustrate further, commercially available ammoniacal ammonium nitrate solutions in which both liquid ammonia and water are present as solvents may be employed in the explosive composition. These solutions, which have a specific gravity in excess of unity normally are marketed for use as liquid fertilizers. Specific examples of such useful ammonium nitrate solutions include the following:

Composition, 1fiereent by weig Solution Liquid NHANOa H2O Additionally, commercially available solutions of ammonium nitrate in liquid ammonia containing up to fifteen percent water also are useful in the instant compositions.

It has been observed that water in amounts up to about fifteen percent by weight of the ammonium nitrate in the ammoniacal solutions has little effect on the explosive. In fact, for some purposes it even has been desirable to use amounts of water substantially greater than fifteen percent. However, about five to seven percent water in admixture with liquid ammonia as shown in the table above provides an optimum aqueous solvent embodiment.

Likewise, admixtures of ammonium nitrate in ammo nium hydroxide, ammonia water, and other ammoniacal aqueous media wherein either partial or complete dis- 3 solution of the ammonium nitrate occurs have been prepared and used successfully.

In general, although substantially dry mixes have been shown to detonate satisfactorily, superior performance results from the use of ammonium nitrate dissolved in either a mixed liquid ammonia-water solvent system, as set forth in compositions A to D above, or in water alone.

Examples of operative light metals useful as thermal carriers or fuels in the instant compositions are magnesium, aluminum, magnesium alloys such as the ASTM designated ZKlO, ZK60, and AZ31, magnesium-aluminum binary alloys containing thirty-three percent of aluminum or more and aluminum-magnesium alloys containing thirty percent of magnesium or more. In general, the light metals operative in the compositions and methods of the present invention are metals of relatively low atomic weight, such as those found generally in the low atomic weight positions of groups I, II, and III of the periodic classification of the elements.

It has been found that the most effective thermal carriers are those in which an admixture of aluminum and magnesium, or alloys thereof, are employed. Mixed carriers containing about fifty percent by weight each of aluminum and magnesium produce excellent results.

It has also been observed that there is a general relationship between the amount of thermal carrier and the power factor exhibited by the explosive upon detonation. Higher percentages of metal tend to produce better power factors, the optimum being reached in the area of from about twenty-five to about 60 percent by weight of the explosive composition. In situations where maximum explosive power is not required, amounts of the thermal carrier of between four and about ten percent have been found to produce power factors in excess of those previously obtained with conventional ammonium nitrate explosives, e.g., with ammonium nitrate prills admixed with fuel oil.

Both the particle size and the configuration of the selected thermal carriers or fuels are important. Generally, light metal dusts and finely particulated powders, flakes, and atomized pellets are to be avoided since they do not yield the power factors obtained in the detonation methods employed in the persent invention and since these materials are in themselves sensitive and therefore hazardous. Magnesium dust, for example, is extremely explosive and its use in the compositions and methods of the present invention is considered dangerous. Further, a primary object of this invention is to provide an explosive composition that is substantially insensitive while loading or mixing.

Accordingly, the preferred particle size range of the thermal carriers of this invention is such that the particles are retained on a US. standard twenty mesh sieve. Especially operative are those light metals having welldefined configuraitons, i.e., shapes and forms as in shavings, chips, chopped scraps, machine turnings, band saw shavings, millings, foils, strands, needles, bars, sponges, tubes, wools and the like. These forms may be one quarter inch or more in diameter and four to six inches or more in length. Scrap cast aluminum and magnesium materials, which are porous in nature, seem to give better results than scrap extrusion materials. Solids as well as perforated metal foils produce good results. Shavings and millings from aluminum and magnesium fabrication shops are useful.

It has been found that thermal carriers in the form of tubes, rolls, cylinders, curled chips and other predominantly circular or cylindrical forms yield peak performance in the explosive blast. In practice, it has been found desirable to place the generally circular contoured metal forms in random orientation in metal cylindrical canisters, preferably perforated. Such canisters, containing the thermal carrier particles, thus become a part of the completed thermal carrier that is then admixed with the liquid ammoniacal ammonium nitrate solution. Preferably, therefore, the canister also is made of a light metal, such as aluminum, magnesium and alloys thereof as set forth above. I

In preparing the explosive compositions, utilizing solutions of ammonium nitrate, it is of course most economical to admix the ammoniacal ammonium nitrate solutions with the light metal thermal carrier or fuel at the site of use. For example, the commercially available ammonium nitrate solutions are easy to transport, while maintaining a good safety margin well above that of many conventional high explosive compounds.. The metal is also conveniently transported to the site of use, where the admixing of the two components is readily carried out. This may be done above ground since the resulting admixture is initially insensitive, or it may be carried out at the bottom of the well or bore hole to be treated. In some instances, the metal carrier may be positioned at the bottom of the bore hole first and an ammoniacal ammonium nitrate solution poured over it. Alternatively the procedure can be reversed.

Where water intrudes the hole strata from above or below the situs of the proposed shot, a tubular polyethylene bag containing the metal for example, in perfo rated canisters, can be lowered into the bore hole and buttomed therein.

The ammonium nitrate solution is then poured into the bag at the top of the bore hole. This moves downward to mingle with the metal at the bottom of the bag. A detonator then is lowered into contact with the composition.

The loading of a dry and impermeable bore hole is vastly simplified inasmuch as the metal is dropped into the bore hole and then the ammonium nitrate composition is poured into the hole.

Useful detonators include for example, shaped charge, pentolite booster, dynamite, tetryl booster, RDX and the like. In practice, ordinarily the detonator is lowered into the hole in contact with the explosive mass. Initiation of the detonator thereby causes explosion of the explosive composition. The detonator is initiated by means of conventional shooting lines and tamping may or may not be inserted to overlay the charge.

The following examples illustrate the novel compositions and processes of the present invention but are not meant to limit it thereto.

Example 1 A fifteen pound total weight explosive load, as a control, containing ninety-four percent by weight of fertilizer grade ammonium nitrate prills and six percent by weight of fuel oil, was placed in a six inch diameter, six foot deep hole and tamped with four and one-half feet of sand. The frost penetration in the ground was about twelve inches and the snow covering was an additional eighteen inches. The charge was permitted to stand in the hole for one hour and then fired electrically using a shaped charge. The charge was fired successfully.

Results.-No cratering occurred. Some distortion was observed but there was no break through of the frost cap. The tamping material was blown out.

Following the precise loading and bore hole conditions as described above, a second fifteen pound total weight explosive charge, as a second control, containing eighty percent by weight or prilled fertilizer grade ammonium nitrate and twenty percent by weight of a liquid ammoniacal ammonium nitrate solution, which solution contained about 69.8 parts ammonium nitrate, 23.8 parts liquid ammonia, and 6.4 parts water, was fired successfully.

Results.-No cratering occurred but there was more distortion of the hole than was observed with the ammonium nitrate-fuel oil load. Evidence of distortion was shown by the existence of cracks over fifteen feet in diameter. The frost cap was not broken out. The tamp was blown out.

EXAMPLES 2-4, INCLUSIVE Following the precise experimental procedure and utilizing the liquid ammoniacal solution and metal particles the same as described in Example 1, the following test loads were prepared and fired.

Example 2 Seventy percent liquid ammoniacal ammonium nitrate solution, 15 percent magnesium chips-15 percent aluminum chips.

Results,-Excellent blast occurred with a crater fifteen feet across being formed. The crater was somewhat deeper than the crater of Example 1.

Example 3 Fifty-five percent liquid ammoniacal ammonium nitrate solution22.5 percent magnesium chips22.5 percent aluminum chips.

Resalts.Excellent blast occurred, a crater fifteen feet three inches across being formed. Excellent breakage of the earth occurred and the crater was very deep. Considerably more earth was moved in this test shot than in either Example 1 or 2.

Example 4 Forty percent liquid ammoniacal ammonium nitrate solution-30 percent magnesium chips-30 percent aluminum chips.

Results-Excellent blast of high percussion occurred. A considerable amount of fire was visible at the instant of detonation. This test blast did not actually move as much earth as in Example 3, although the fourteen foot crater was just about as deep.

Example 5 Following the general procedure of Example 1, a 5.5 pound test load was placed in a six inch bore hole about six feet deep and tamped with five feet of sand. The test load contained 70 percent by weight of ammonium nitrate fertilizer grade prills and 30 percent by weight of the liquid ammoniacal ammonium nitrate solution as described in Example 1. The load was fired electrically using the Munroe jet.

Results.-The load was fired successfully, but no distortion or rupture of the surface occurred.

COMPARISON Following the procedure as described above, a composition containing (a) 85 percent by weight of ammonium nitrate fertilizer grade prills, (b) 2.5 percent by weight magnesium chips and 2.5 percent by weight aluminum chips placed in an aluminum canister, and (c) percent by weight of the liquid ammoniacal ammonium nitrate solution of Example 1 was prepared, most of the prills remaining in prill form.

Results.The shot was conducted successfully, but no crater was formed, although slight distortion of the ground was observed.

Following the test procedure of Example 5, the following compositions were prepared and tested as shown in Examples 6-11 utilizing 5.5 pound test loads tamped with five feet of sand.

'6 Example 6 A composition containing 90 percent by weight of the ammoniacal ammonium nitrate solution of Example 1 and 10 percent by weight of mixed magnesium and aluminum metal chips about .010 inch thick by /4 inch wide by 1 inch long (5 parts each) in an aluminum cylindrical canister container was prepared.

Results-The shot was successfully fired, a small crater (5 /2 feet across) being formed, with distortion around the crater being observed.

Example 7 A composition containing 85 percent by weight of the ammoniacal ammonium nitrate solution of Example 1 and 15 percent mixed metal (7 /2 parts each of magnesium and aluminum chips) in an aluminum container was prepared.

Kendra-The shot was successfully fired, a small crater (5 /2 feet across) being formed with distortion around the crater being observed.

Example 8 A composition containing percent by weight of the ammom'acal ammonium nitrate solution of Example 1, and 20 percent mixed metal (10 parts each of magnesium and aluminum chips) in an aluminum container was prepared.

Resalts.The shot was fired successfully, a crater 8 feet being formed with distoration around the crater being observed.

Example 9 A composition containing 72 percent by weight of the ammoniacal ammonium nitrate solution of Example 1 and 28 percent mixed metal (14 parts each of magnesium and aluminum chips) in aluminum container was prepared.

Resulz's.-The shot was successfully fired, a crater 11 feet across being formed with distortion around the crater being observed.

Example 10 A composition containing 72 percent by weight of the ammoniacal ammonium nitrate solution of Example 1, and 28 percent magnesium band saw chips in an aluminum container was prepared.

Results.-The shot was fired successfully, a crater in excess of 11 feet being formed with distortion around the crater occurring.

Example 11 A composition containing 60 percent by weight of the ammoniacal ammonium nitrate solution of Example 1,

25 percent magnesium chips and 15 percent aluminum chips in an aluminum container was prepared.

Results.The shot was fired successfully, a crater approximately 11% feet being formed. Distortion around the crater was observed.

Example 12 Three and one-half pounds of a nearly saturated solution of ammonium nitrate in water formed by dissolving ammonium nitrate in water, was admixed with 1.5 pounds of magnesium band saw chips and the resulting admixture placed in the bore hole. The load was fired successfully forty-eight hours later with a crater about six feet in diameter being produced.

In a manner similar to the foregoing, useful explosive compositions can result from the combination on a Weight basis of (1) about 10 percent of loose rolled magnesium Grignard chips (.010" x .130" x .500), 88 percent prilled fertilizer grade ammonium nitrate, and 2 percent ammonium hydroxide, (2) about 70 percent AZ31 alloy chips, 20 percent water and about 10 percent ammonium nitrate, (3) about 40 percent ammonium nitrate, 40 percent metal (+20 mesh particles of a 70 Mg-3O Al binary 7 alloy) and about 20 percent liquid ammonia, and (4) about 80 percent ammonium nitrate, 15 percent alumimum and about percent aqueous ammonia.

Heretofore, ammonium nitrate explosions have been regarded generally as slower detonating reactions, based primarily upon the volume of gases liberated. In distinct contrast, the test loads of the compositions of the present invention, as illustrated in the above examples, provide a quick, sharp reaction accompanied by high percussion and brisance and by intense shock waves.

The enhanced power factor resulting from the detonation of the compositions of the present invention seems to be derived primarily from the intense heat generated and only secondarily from the initial liberation of gases. The effect of the extremely high heats that are generated is, of course, to increase tremendously the volume of gas made available, in accord with the normal gas volumetemperature relationships. This results in greater power.

The tremendous power factor achieved by the explosive compositions of the present invention has made it possible to accomplish many blasting operations with a very small amount of explosive as compared with conventional ammonium nitrate explosives.

In hard rock blasting, it has been possible to load and shoot one bore hole moving an amount of rock that heretofore required three or four borings and loadings with conventional ammonium nitrate explosives.

For example, in the Columbia Mine in Minnesota the economics of the use of ammonium nitrate solutions with metal sensitization, as set forth, where compared with prior prilled ammonium nitrate using oil sensitization (a common practice). In the latter method, 3228 cubic yards of Taconite ore were broken requiring seven drill holes and 1291 pounds of ammonium nitrate and oil which, along with primers and Primacoard cost .0286 dollar per cubic yard of broken ground at a drilling expense of .1433 dollar per cubic yard of ground broken. Using the explosive materials set out in the instant application and breaking 3228 cubic yards of Taconite, only three holes were required and 335 pounds of explosive compound, the latter at a cost, including sensitizing metal, shaped charge blasting caps and blasting wire, of .0151 dollar per cubic yard of break. The drilling cost based on 2.50 dollars per foot as in the comparative loading, was only .0596 dollar per cubic yard of break. This comparative work indicates 56.5 percent saving and an upgrading of power factor from .40 pound of explosive per cubic yard of break to .110 pound of explosive compound using the explosive compounds herein expressed.

Various modifications can be made in the composition and processes of the present invention without departing from the spirit or scope thereof and it is to be understood that the invention is limited only as defined in the appended claims.

I claim:

1. An explosive composition which comprises in the proportions by weight defined by the area ABCDE of the drawing, (1) ammonium nitrate, (2) a light metal selected from the group consisting of magnesium, magnesium alloys, aluminum, aluminum alloys, and mixtures thereof, said light metal having a particle size greater than that which passes a number 20 U.S. standard sieve, and (3) a liquid, hydrogen-containing solvent for ammonium nitrate, said solvent also containing at least one 8 atom selected from the group consisting of nitrogen and oxygen.

2. An explosive composition which comprises by weight (1) about 10 to about 83 percent of ammonium nitrate, (2) about 15 to about 60 percent of a light metal selected from the group consisting of magnesium, magnesium alloys, aluminum, aluminum alloys, and mixtures thereof, said light metal having a particle size greater than that which passes a number 20 U.S. standard sieve, and (3) about 2 to about 35 percent of a liquid hydrogencontaining solvent for ammonium nitrate, said solvent also containing at least one atom selected from the group consisting of nitrogen and oxygen.

3. An explosive composition which comprises by weight (1) about 15 to about 45 percent ammonium nitrate, (2) about 30 to about 50 percent of a light metal selected from the group consisting of magnesium, magnesium alloys, aluminum, aluminum alloys, and mixtures thereof, said light metal having a particle size greater than that which passes a number 20 U.S. standard sieve, and (3) about 5 to 35 percent of a liquid, hydrogen-containing solvent for ammonium nitrate, said solvent also containing at least one atom selected from the group consist ing of nitrogen and oxygen.

4. An explosive composition which comprises by weight (1) about 15 to about 65 percent of particulated magnesium and aluminum, said metal having a particle size greater than that which passes a number 20 U.S. standard sieve, and (2) about 85 to about 35 percent of an aqueous ammoniacal solution of ammonium nitrate, said solution of ammonium nitrate containing from about 5 to about 15 percent water and from about 20 to about 35 percent ammonia.

S. An explosive composition which comprises, in the proportions by weight defined in the area A, B, C, D, and E of the drawing, (1) ammonium nitrate, (2) about 15 to about 65% of a mixture of particulated magnesium and particulated aluminum, said metal having a particle size greater than that which passes a No. 20 U.S. sieve, and (3) a liquid, hydrogen-containing solvent for ammonium nitrate, said solvent also containing at least one atom selected from the group consisting of nitrogen and oxygen.

6. An explosive composition which comprises in the proportions by weight defined in the area ABCDE of the drawing, (1) ammonium nitrate, (2) about 15 to 65 of equal amounts of particulated magnesium and particulated aluminum, said metal having a particle size greater than that which passes a No. 20 U.S. standard sieve, and (3) a liquid, hydrogen-containing solvent for ammonium nitrate, said solvent also containing at least one atom selected from the group consisting of nitrogen and oxygen.

7. The explosive composition of claim 5 wherein the particulated magnesium is magnesium alloy.

8. The explosive composition of claim 5 wherein the particulated aluminum is aluminum alloy.

References Cited in the file of this patent UNITED STATES PATENTS 2,393,594 Davis July 8, 1941 2,816,012 Walton Dec. I10, 1957 2,836,484 Streng et al May 27, 1958 2,903,969 Kolbe Sept. 15, 1959 3,044,911 Fritzlen July 17, 1962

Claims

1. AN EXPLOSIVE COMPOSITION WHICH COMPRISES IN THE PROPORTIONS BY WEIGHT DEFINED BY THE AREA ABCDE OF THE DRAWING, (1) AMMONIUM NITRATE, (2) A LIGHT METAL SELECTED FROM THE GROUP CONSISTING OF MAGNESIUM, MAGNESIUM ALLOYS, ALUMINUM, ALUMINUM ALLOYS, AND MIXTURES THEREOF, SAID LIGHT METAL HAVING A PARTICLE SIZE GREATER THAN THAT WHICH PASSES A NUMBER 20 U.S. STANDARD SIEVE, AND (3) A LIQUID, HYDROGEN-CONTAINING SOLVENT FOR AMMONIUM NITRATE, SAID SOLVENT ALSO CONTAINING AT LEAT ONE ATOM SELECTED FROM THE GROUP CONSISTING OF NITROGEN AND OXYGEN.