US3177102A - Explosives - Google Patents

Description

United States Patent 3,177,102 EXPLOSIVES Joseph R. Hradel, Mount Pleasant, Mich, assignor to The Dow Chemical Company, Midland, Mich, a corporation of Delaware No Drawing. Filed Jan. 7, 1963, Ser. No. 249,587 2 Claims. (Cl. 149-43) The present invention relates to a method of preparing explosive compositions from insensitive components. More specifically, the present invention involves reacting a relatively insensitive oxidizer with a fuel for a period of time at ambient temperature during Which time the admixture undergoes auto-reaction thereby yielding a sensitive explosive composition.

This application is a continuation-in-part of my copending application Serial No. 48,820, filed August 11, 1960, now abandoned. This latter application in turn is a continuation-in-part of my copending applications Serial No. 807,406, filed on April 20, 1959, now abandoned, and Serial No. 763,908, filed on September 29, 1958, now abandoned.

It is the principal object of the present invention to provide a method of preparing explosive compositions containing an oxidizing salt and a fuel which are initially relatively insensitive. 7

It is a further object of the present invention to provide a process whereby initially insensitive explosive compositions after mixing, undergo auto-reaction, thereby yielding sensitive explosive compositions.

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

An additional object of the present invention is to provide a method of preparing a substantially insensitive initial explosive composition having an oxidizer .in solution form which oxidizer is capable of undergoing reaction with metals and other fuels, and thereby form a novel, sensitive explosive. composition possessing high explosive strength.

Still another object of the present invention is to provide sensitive explosive compositions that, 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.

These and other objects and advantages of the present invention will be apparentto those skilled in the art to which these inventions pertain.

In carrying out the process of the present invention, unexpectedly it has been found that upon admixing ammonium nitrate with a metal fuel, e.g., a particulate light metal component containing reactive amounts of magnesium, in the presence of a liquid which solubilizes or disassociates the oxidizer, said fuel being capable of undergoing corrosive action with the so-wetted or solubilized oxidizer, over a period of time provides a sensitive explosive composition.

In a preferred embodiment of the present invention, an admixture of ammonium nitrate with certain light metals is prepared. This initial mixture, contrary to the BJJKWZ Patented Apr. 6, 1965 teaching of the prior art, is an explosive composition that is substantially insensitive.

However, upon passage of time at ambient temperature, the insensitive explosive composition undergoes selfor auto-chemical reaction to form substantially solid, sensitive explosive compositions. These compositions have been demonstrated to possess unexpectedly high explosive strength not exhibited by prior art ammonium nitrate explosives. These novel sensitive explosive compositions, when detonated, produce much sharper movement of rock or material being treated, higher percussion or brisance and more intense shock waves than other ammonium nitrate explosive compositions.

The initial substantially insensitive compositions comprise generally a liquid solution of ammonium nitrate in which the solvent is selected from the group consisting of liquid ammonia, water and ammonium hydroxide, and a light metal thermal carrier, preferably selected from the group consisting of magnesium, magnesium alloys, magnesium-aluminum alloys and mixtures thereof which contain reactive amounts of magnesium.

Novel methods for the production at the situs of or in a bore hole itself of the sensitive explosive composition have been found. These comprise for example, the positioning of an ammoniacal solution of ammonium nitrate (about 50-75 percent NH NO, 5-15 percent water and 20-35 percent NH on a weight basis) in a bore hole in admixture with a light metal thermal carrier as defined heretofore, and interacting the resulting admixture at the ambient bore hole temperature until substantial exothermal activity resulting from said interaction has occurred. Such methods produce sensitive compositions, or reaction products, that are detonated preferably at the peak of the exothermal activity, or after this peak has been passed, to provide explosion with very high power factors.

In preparing the initial insensitive explosive compositions utilizing the ammoniacal ammonium nitrate solution, 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. The commercially available ammonium nitrate solutions are easy to transport, while maintaining a good safety margin above many conventional high explosive compounds. The metal is also conveniently transported to the site of use where the admixing of the oxidizer and fuel components is readily carried out. This mixing 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 the ammoniacal ammonium nitrate solution poured over it. The procedure can be reversed. The precise procedure to be followed will depend upon the nature of the explosive operation to be conducted.

In situations wherein loss of either oxidizer or fuel may occur upon mixing, for example in holes containing fissures or in water filled holes, the fuel and oxidizer may be introduced into a waterproof or leakproof container. It is to be understood that the container may first be inserted into the 'hole to be filled with explosive and the fuel and oxidizer then added thereto. Alternatively, the explosive mix components can be placed into the container and the so-filled holder then be inserted into the bore hole.

In addition to the exemplary compositions presented above, which have been cited to illustrate the method of the invention, I have found many other explosive compositions which are initially substantially insensitive, but which can be made to undergo autoreaction or interaction upon passage of time at ambient or bore hole temperature conditions to form, upon corrosion, sensitive reaction products. This method thereby provides an exceedingly safe explosive system.

Further, sensitive explosive compositions have been prepared wherein the oxidizing ammonium nitrate salt may be in substantially granular or powdered form, semifiuid mixture, and complete solution mixtures, as disclosed in this application. As long as there is suflicient water or other ionizing media present, even initially insensitive compositions that are substantially dry to the touch can be made to undergo reaction to form sensitive corrosion reaction products.

The actual time necessary to accomplish the desired interaction of the mix components will vary depending upon the type of oxidizer, fuel utilized and amount of dissociation solvent present in the composition. However, in any event, substantially complete sensitization reaction normally is obtained within a period of time ranging from about /2 hour to about 48 hours. For example, with a composition of about 60 parts aqueous ammoniacal ammonium nitrate (25 percent NH 6 percent H and 69 percent NH NO and 40 parts of a 50-50 mixture of substantially pure particulated magnesium and aluminum of greater than about 20 mesh U.S. standard sieve, essentially complete reaction is obtained within a period of from about 4 to about 8 hours. Similar reaction periods are found for such compositions of ammonium nitrate solution and these metals wherein the metal can vary from about 4-65 percent by weight and the solution from about 96 to about 35 percent by weight on the composition. On the other hand, if the aluminum content of the binary metal mixture in such compositions is increased, a corresponding increase in curing time is indicated. If more finely divided metals are utilized, or if more corrosion sensitive metals are used, the autogenetic reaction is found to take place in a shortened period of time, i.e., from about to about 2-3 hours.

Additionally with an ammonium nitrate explosive composition containing from about 2 to about 10 percent of granular 20-80 mesh magnesium or a magnesium alloy, such as ASTM designated ZKlO, ZK60, or A33 for example and from about 1 to about 6 percent water, the balance by weight being prilled fertilizer grade ammonium nitrate, the reaction is found to be completed in about 4-5 hours.

For compositions that remain substantially in granular form, but which are slightly wetted with such liquid solvents, reaction periods lasting from several hours to as much as several days in some instances have been found.

These findings have enabled me to work with and prepare many compositions that are initially safe to handle but which undergo interaction or auto-reaction under ambient conditions to form sensitized explosives. In many instances, exothermal auto-reactions that are nor-. mally quite slow have been speeded up by external application of heat or by application of additional liquid solvents.

Detonation of the resulting explosive mixes conveniently is carried out by means of a shaped charge, Tetryl, RDX, cast pentolite or other boosters of similar power factors.

The deton-ator ordinarily will be selected from those which are thennally stable against detonation to temperatures higher than that encountered in the interaction of the mix components.

In practice, the detonating booster, fitted with a nonarmed firing cord, or fuse type firing line ordinarily is placed in contact with the mix or within the mix proper. In the latter case, the booster will be placed in a bore hole along with the composition ingredients prior to the autogenetic reaction, while in the former case the booster may be inserted into the hole either prior to or after the desired mix reaction. The booster then can be armed by connection into a conventional firing device just prior to the time of detonation.

Compositions of the present invention may be utilized for a wide variety of applications in oil well and mining operations, for example, oil well recovery processes, hard rock mining, quarrying, construction, waste disposal wells, and in porous rock blasting. The novel methods of the present invention have utility in the preparation of the explosive compositions at the general situs of a bore hole itself and in the direct area of intended use. However, if desired the reaction of the mix components can be carried out in a suitable container and the resulting solid explosive be stored and transported, using conventional explosive safety practices, to blast sites and utilized in much the same manner as other sensitive prepackaged explosives.

The following examples will serve to further illustrate the invention, but are not meant to limit it thereto.

EXAMPLE 1 Thermal profiles measuring exothermal activity of autos reaction iof explosive composition upon passage of time to form sensitive explosive reaction product In order to determine the amount of exothermal activity resulting from the autogenetic or self-reaction occurring in an initially insensitive explosive admixture upon passage of time, an extensive series of thermal profiles; was prepared. Illustrative thermal profiles are set forth below in Graph I.

In this series, the rise in temperature above ambient upon passage of time was measured by recording thermometer means. Also the role of water or other ionizing medium was ascertained.

Load number A was prepared from 72 percent by weight of an ammoniacal ammonium nitrate solution (formed from 69.8 parts of ammonium nitrate, 23.8 parts of liquid ammonia and 6.4 parts of water), and 28 percent by weight of mixed metal. Equal parts (14 percent each) of magnesium band saw chips and aluminum band saw chips were utilized. It is seen that the temperature of the test load was raised exothermally from ambient temperature of 20 F. to a maximum of about F., at which higher point the load solidified, indicating that the desired sensitive explosive reaction product had been formed. Thereafter, the temperature of the system gradually subsided.

Test load B contained 72 percent of the same liquid ammoniacal ammonium nitrate solution as used for load A together with 14 percent by weight each of coarse magnesium mill chips and aluminum bars approximately /8 inch by A inch by inch in configuration. Peak exotherm activity was observed at F. after about four and one-half hours passage of time. The role of the coarser metal particles in causing lengthening of the auto-reaction period was confirmed, these mixed metal particles of this load being substantially coarser than the mixed metals of test load A.

Test load C as initially prepared was identical to test load B. However, as the exothermal activity decreased noticeably after about six and one-half hours, a small amount of water was added. Within one and one-half hours later the exothermal reaction was again observed to liberate substantial quantities of heat with a new exotherm peak being reached at about 137 F., the reaction thereafter subsiding. From these data, it is suggested that the reaction is ionic and that the water present becomes chemically bound, perhaps in a manner discussed later in this specification.

5 pound explosive test load was formed by dissolving three pounds of fertilizer grade ammonium nitrate prillsin one pound of liquid anhydrous ammonia. The

,resulting ammoniacal ammonium nitrate solution was admixed with 1.5 pounds of mixed metal, formed from a fifty-fifty ratio of magnesium lathe s havings to aluminum shop scrap chips. .A six inch diameter by six foot deep bore hole was made in the ground in the test area. The

load was placed in the hole. Within forty minutes after the initial admixture wasplacedin the bore hole, exothermal activity was noted. Three hours later, the reaction was proceeding vigorously and the load solidified approximately four and one-half hours after being placed in the bore hole. A shaped charge then was placed on top of the load and the hole tamped with about five feet of sand. Forty-eight hours following solidification, the test load was fired electrically usingthe shaped charge.

The resulting blast produced a crater approximately 3-5 .feet in diameter.

Following the procedure of. Example 2 a similar ar'n monium nitrate solution wasprepared. Three percent water was added based on the weight of the total charge and this solution was then admixed with the mixed metal carrier as used in Example" 2. The solution solidified in three and one-half hours and was permitted to stand forty-eight hours before firing. The load was successfully fired, A crater about six feet in diameter was formed.

. EXAMPLE'4 Three and one-half pounds of a nearly saturated solution of ammonium nitrate in water, was admixed with 1.5 pounds of magnesium band saw chips and the resulting admixture placed in the bore hole. Peak exothermal activity occurred in a shorter period of time than was observed in Examples 24 inclusive. The load was fired successfully forty-eight hours later with a crater about six feetin diameter being produced.

Heretofore, the 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 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 more 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 volume-temperature relationships. This results in greater power since the rock breakage, for example, as observed in the blasting of taconite ore with these novel, reacted compositions is in the order of thirty-five tons per pound of initial insensitive explosive load as against twenty tons per pound of load wherein non-reacted, metal-containing dry and semi-fluid ammonium nitrate loads have been detonated by me.

While the above examples illustrate the unexpected power factor exhibited by the reacted or aged explosive compositions of the present invention, other observations have been made that are helpful in determining the nature' of the complex reactions occurring in these systems.

The initially substantially insensitive explosive compo sition undergoes auto-reaction chemically, as evidenced by the strong exotherms recorded in the experiments conducted under Example 1 above. There is some indication that'when magnesium is present that the following reaction occurs in the presence of water:

At the same time, there is evidence that the magnesium for example, may be undergoing reaction with the am monium nitrate to form magnesium nitrate, the water present being taken up perhaps as the hexahydrate of the resulting salt, or the dihydrate, forexample, in accord with the following reaction:

This is supported by the above data which indicate that when the exothermal reaction tapers off, it can be initiated again by adding a small quantity of water to the charge. Further, when the auto-reaction has been completed, usually within twenty-four hours, the completed reaction product has been observed to be substantially in solid form. Usually after about five hours with the above described mixes, sufiicient exothermal activity has occurred so that the resulting reaction products can be detonated successfully. Close examination reveals that while much of the elemental metal thermal carriers or fuels are still present as such, a very substantial portion has been converted to a metal salt or a group of salts. Such reaction product has been removed from the bore hole, permitted to remain at ambient temperature for several days, returned to the bore hole and detonated by shaped charges'as a completely dry, granular explosive.

After the mixture is placed in a bore hole, there is frequently a lag in time of up to as much as one or more hours before any appreciable exothermal activity is observed when using coarse metal particles. The speed of V the reaction and, hence, the quantity of exotherm produced, can be controlled appropriately by regulating the particle size and configuration of the metal carrier and by controlling the amount of water or other oxidizer dissociation solvent present in the initial insensitive explosive composition. increasing the amount of water, tends to speed up the reaction. It has been found that the auto-reaction can be made sufliciently violent so as to actually throw the material out of the bore hole. Experimentation has produced the operable limits, as set out above in this specification, for controlling these factors.

Generally, the auto-reaction is completed within twentyfour hours although it is generally preferred to detonate Decreasing the particle size and- 7 the reaction product while the exothermal activity of the system is at or near its peak.

Experimental evidence points towards the possibility that with higher metal loads, vaporization of magnesium uses substantially all of the oxygen present and liberated. This is accomplished by a tremendous rise in heat, the magnesium being vaporized primarily as magnesium oxide. The light colored magnesium oxide vapor has been carefully observed in small test shots. No residual magnesium is observed, even when the theoretical maximum amount of thermal carrier based on magnesiumoxygen mix stoichiometry is present. Thus, the magnesium, not already involved in the auto-reaction product, serves as the fuel, producing intense heat that raises the temperature of aluminum, if present for example in admixture with or alloyed with the reactive magnesium, which has a higher ignition point than magnesium, to its boiling or vaporizing point, causing it to probably undergo the following reaction:

2Al+N =2AlN+262.8 K-calories per mole This reaction occurs at temperatures in the area of about 32503500 degrees Fahrenheit, with the resulting tremendous amount of heat being liberated. The lcalorie value more than overcomes any loss of gaseous nitrogen. This excessive heat, together with its effect on the volume of gas liberated in the detonation, may be largely responsible for the unusually high power factor obtained with the explosives of the present invention. Evidence points toward the reaction forming an aluminum nitride rather than the formation of an aluminum oxide, and as such precludes the formation of noxious oxides of nitrogen which heretofore constituted a safety hazard in the muck or rubble remaining upon detonation of conventional ammonium nitrate explosives.

Frequently, conventional ammonium nitrate explosions result in substantial residual amounts of ammonia, readily evidenced by the ammonia smell. With the explosive compositions of the present invention, no residual ammonia odor is present upon detonation, the ammonia being completely converted to nitrogen and hydrogen at the high temperatures involved in the reaction system.

There is also evidence that substantial amounts of hydrogen are made available during the explosion reaction and that these also play an important role in the superior performance observed. For example, in test shots in the field, following detonation, a characteristic bluish flame has been observed in cracks and fissures in the rock opened up by the blast in which oxygen is apparently reacting with the residual hydrogen, as secondary explosives.

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.

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

I claim:

1. A method for preparing a sensitive solidified explosive composition from insensitive components which comprises; admixing from about 96 to about 35 parts by weight of a solution of ammonium nitrate with about 4 to about parts by weight of a light metal fuel selected from the group consisting of magnesium, magnesium alloys, admixtures of magnesium and aluminum and mixtures thereof, said light metal fuel further being characterized in having at least about 50 Weight percent magnesium content, said solution containing at least about 50 weight percent ammonium nitrate, and the solvent for said ammonium nitrate being a member selected from the group consisting of water, ammonia and ammonium hydroxide, said light metal fuel being capable of undergoing chemical reaction With said ammonium nitrate solution, and, reacting said solution and said metal fuel at ambient temperature for a period of time of from about /2 to about 24 hours thereby to provide a sensitive solidified explosive composition.

2. A method of preparing a sensitive solidified explosive composition from insensitive components which comprises;

(a) admixing from about 96 to about 35 parts of an ammoniacal solution of ammonium nitrate with from about 4 to about 65 parts of a light metal thermal carrier, said ammoniacal solution of ammonium nitrate containing from about 5 to about 15 percent Water and from about 20 to about 35 percent ammonia, said light metal thermal carrier being selected from the group consisting of magnesium, magnesium alloys, admixtures of magnesium and aluminum and mixtures thereof, said light metal thermal carrier being further characterized in having at least about 50 weight percent magnesium content, and, interacting the resulting admixture at ambient temperature until peak exothermal activity'resulting from the interaction has occurred and the admixture has solidified.

References Cited by the Examiner UNITED STATES PATENTS 2,836,481 5/58 Strenge et al. 149-42 2,903,969 9/59 Kolbe 149-46 2,978,864 4/61 Stengel 149-1 X 2,992,086 7/61 Porter 149-43 3,034,874 5/62 Emmons 149-41 X 3,094,443 6/63 Hr-adel et al. 149-1 CARL D. QUARFORTH, Primary Examiner.

L. D. ROSDOL, Examiner.

Claims (1)

1. A METHOD FOR PREPARING A SENSITIVE SOLIDIFIED EXPLOSIVE COMPOSITION FROM INSENSITIVE COMPONENTS WHICH COMPRISES; ADMIXING FROM ABOUT 96 TO ABOUT 35 PARTS BY WEIGHT OF A SOLUTION OF AMMONIUM NITRATE WITH ABOUT 4 TO ABOUT 65 PARTS BY WEIGHT OF A LIGHT METAL FUEL SELECTED FROM THE GROUP CONSISTING OF MAGNESIUM, MAGNESIUM ALLOYS, ADMIXTURES OF MAGNESIUM AND ALUMINUM AND MIXTURES THEREOF, SAID LIGHT METAL FUEL FURTHER BEING CHARACTERIZED IN HAVING AT LEAST ABOUT 50 WEIGHT PERCENT MAGNESIUM CONTENT, SAID SOLUTION CONTAINING AT LEAST ABOUT 50 WEIGHT PERCENT AMMONIUM NITRATE, AND THE SOLVENT FOR SAID AMMONIUM NITRATE BEING A MEMBER SELECTED FROM THE GROUP CONSISTING OF WATER, AMMONIA AND AMMONIUM HYDROXIDE, SAID LIGHT METAL FUEL BEING CAPABLE OF UNDERGOING CHEMICAL REACTION WITH SAID AMMONIUM NITRATE SOLUTION, AND, REACTING SAID SOLUTION AND SAID METAL FUEL AT AMBIENT TEMPERATURE FOR A PERIOD OF TIME OF FROM ABOUT 1/2 TO ABOUT 24 HOURS THEREBY TO PROVIDE A SENSITIVE SOLIDIFIED EXPLOSIVE COMPOSITION.