US3432371A - Dry explosive composition containing particulate metal of specific mesh and gauge - Google Patents

Description

9 Claims ABSTRACT OF THE DISCLOSURE A novel dry explosive composition consisting essentially of: ammonium nitrate as oxidizer and a particulate light metal as fuel, said metal being within the range substantially of from about No. 4 to about No. 200 mesh and having a gauge of from about 0.25 mil to about 40 mils. Other inorganic oxidizers, fuels and explosive sensitizers can be incorporated into the composition.

CROSS-REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part of application Ser. No. 603,762, now abandoned filed Dec. 22, 1966, which in turn was a continuation-in-part of application Ser. No. 419,262, filed Oct. 16, 1964, now U.S. Patent No. 3,307,986, which in turn was a continuation-in-part of application Ser. No. 299,115, filed July 31, 1963, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to explosives and more particularly is concerned with a novel dry explosive composition exhibiting high energy which gives reliable, uniform energy releases from batch to batch. The terms dry mix, dry explosive, dry composition and dry explosive composition as used herein are to be taken in their generally accepted meaning in the explosive art and refer to explosives which are granular or thick, paste-like in nature and have substantially no free liquid phase thereby differentiating from the slurry type blasting compositions. These dry mixes are further characterized as being non-pumpable.

Dry, granular explosives based on ammonium nitrate, e.g. the common ANFO compositions containing generally about 94 weight percent prilled ammonium nitrate and about 6 weight percent fuel oil, have been used commercially for a number of years. These are satisfactory for many blasting operations but suffer from the disadvantages that they do not propagate in diameters smaller than about 1 inch and they have a relatively low bulk density of about 0.8 gram/cc.

The addition of other fuels and/ or sensitizers to such ammonium nitrate-fuel oil compositions has helped to upgrade the resulting product with respect to sensitivity, propagation and explosive work or power output. Commonly, light metals such as magnesium, aluminum, magnesium-aluminum binary alloys, magnesium silicide, aluminum silicide and other magnesium alloys and aluminum alloys have been used as fuels and/or sensitizers. Additionally, other carbon containing materials including conventional explosives, such as nitrostarch dinitrotoluene, trinitrotoluene and the like, as well as carbon black, sugars, molasses, etc. have been used to upgrade the ammonium nitrate-fuel oil compositions.

nited States Patent As indicated hereinbefore, such additions have upgraded the performance of such dry mixes, but there still remains the problem that such mixes may not always give high energies of predictable high levels and rapid detonation rates.

SUMMARY It is a principal object of the present invention to provide an improved dry explosive composition possessing high energy which composition provides reliable high energy release upon detonation.

This and other objects and advantages readily will become apparent from the detailed description presented hereinafter.

In general the improved explosive composition of the present invention comprises ammonium nitrate or ammonium nitrate in admixture with an inorganic alkali metal oxygen containing oxidizing salt or mixtures of such salts as oxidizer and a light metal fuel of predetermined mesh and gauge characteristics. Additionally, the composition can contain other non-detonable organic fuels, detonable explosive sensitizers, thickening agents and the like to assure the preparation of an explosive composition of predetermined characteristics.

These compositions are suitable for use in any of a wide variety of blasting operations including open pit and underground ore mining, hard rock mining and excavating operations, construction, demolition and the like operations.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Usually the present dry explosive composition comprises on a weight basis:

(a) Particulate ammonium nitrate from about 50 to about 97 percent,

(b) Particulate light metal from about 3 to about 50 percent, said light metal ranging substantially from about No. 4 to about No. 200 mesh US. Standard Sieve and having a gauge of from about 0.25 mil to about 40 mils.

(c) Particulate alkali metal nitrate, chlorate, perchlorate or mixtures thereof up to about 40 percent,

(d) Non-detonable organic fuel up to about 10 percent, and

(e) A gelling and/or thickening agent up to about 2.5 percent.

In a preferred embodiment, the present novel dry explosive composition comprises on a weight basis:

(a) Particulate ammonium nitrate from about to about 55 percent,

(b) Particulate aluminum, magnesium, magnesium alloys, aluminum alloys or mixtures thereof within the mesh and gauge ranges set forth hereinbefore from about 5 to about 40 percent,

(c) Sodium nitrate up to about 20 percent,

(d) Non-detonable liquid hydrocarbon up to about 6 percent, and

(e) Natural gum and/or synthetic polymeric thickening agent up to about 1 percent.

The dry explosive compositions may also contain up to about 16 percent of deton-able organic sensitizers.

The uniqueness, novelty and unexpected useful results realized with the present invention resides in the use of a particulate light metal having a predetermined mesh size and gauge (thickness). For operability the light metal to be employed in the present composition ranges substantially from about No. 4 to about No. 200 mesh (US.

7 Standard Sieve) and has a gauge of from about 0.25 mil to about 40 mils. The term mil is used in its usually accepted definition of being 0.001 of an inch.

Ordinarily, the light metal employed has a particle size distribution within the broad range specified wherein from about 25 to about 60 percent is larger than No. 50 mesh, the balance being substantially No. 50 to No. 100 mesh wherein from about 15 to about 100 percent of the particles have a gauge of from about 0.25 mil to about 4 mils and up to about 85 percent have a gauge of from about 4 to about 15 mils. Preferably, metal with a gauge of less than about 10 mils is employed. However, to obtain specific characteristics with a given explosive composition, various blends of metal within the mesh and gauge size ranges set forth herein can be employed in predetermined size ranges. By employing particulate metals within the above defined particle size and gauge ranges a more powerful explosive composition can be prepared. The metal particles as defined above will vary in shape from very thick (gauge) and coarse (mesh), to spherical (when mesh and gauge are approximately the same) to straw like (long with a small gauge). In general the particles are nonequiaxed in shape. It is thought that the particles having a smaller gauge perform similar to kindling in that they react very readily in the explosive reaction thus supplying the necessary heat to efficiently burn the larger metal particles which in turn supply the necessary power and sustained heat in the explosive reaction. It appears that the use of metal particles within the well defined size range allows for the production of a more powerful explosive over similar explosives wherein no gauge (thickness) limitations are placed on the metal particles. Also, the rate of the explosive reaction can be adjusted by varying the ratio of kindling size particles to coarser particles.

The term mesh or mesh size as applied herein to various materials means size determinations made by standard vibratory, controlled test procedures. Since US. Standard Sieve Series was employed in the size determinations of the present invention a certain No. mesh refers to the sieve designation. The size range of the metal particles in inches or millimeters can be readily determined for example, from a standard conversion table such as the table on page 931, Langes Handbook of Chemistry, Revised 10th Edition.

It is understood that in certain instances because of manufacturing conditions or other circumstances, the particulate metal may contain a small fraction up to 10 percent or more of metal passing a No. 200 mesh sieve. Such additions have not been found to detrimentally affect the operability of the present novel composition. This is particularly true in the case of some of the more brittle alloys; e.g., of the magnesium-silicon-aluminum type.

A typical aluminum metal employed in one of the embodiments of the present invention has a particle size and gauge distribution as set forth in Table I.

Table I Metal particle size, mesh Distribution, (U.S. Standard Sieve): percent NO. 30-50 60-70 No. 50-100 25-35 No. 100-150 about 5 Metal gauge, mils:

Up to 1 6-8 1 to 5 14-17 5-10 73-77 -15 3-7 15 .1

compositions limits set forth, a portion of the ammonium nitrate can be replaced with sodium-, lithium-, potassiumor other alkali metal nitrate, -chlorate or -perchlorate salts, if desired, to obtain compositions of varying densities, sensitivities or other predetermined properties. Conveniently, prilled ammonium nitrate as presently employed in blasting compositions has been found to be suitable in the practice of the present invention.

Small amounts of liquids such as petrolic liquids including natural mineral oils and fractionated products from oil refining as well as other liquid organics having a favorable carbon-oxygen ratio such that there is no detrimental competition of the carbon with the metal for available oxygen in the systems can be used to promote component packing and also act as additional fuel. Also, a small amount of natural occurring water may be present such as that naturally absorbed by the nitrates present in the compositions. The quantities of such materials at a maximum to be employed within the ranges disclosed herein are such that formation of separate liquid and solid phases is not realized and the product is a dry composition; i.e. granular or pasty.

Fuel oil, kerosene and other liquid hydrocarbons, monohydroxy alkanols containing from 1 to about 4 carbon atoms, ethylene glycol, propylene glycol, glycerol, formamide and mixtures thereof are particularly suitable organic liquids for use in the present composition.

Additionally, finely divided solid carbonaceous fuels can be incorporated into the composition. These include, for example, saw dust, nut meats and flours, sugars, bogasse, powdered coke coals and charcoals and the like.

If it is desired to impart water-resistivity to the composition, any of a variety of water-resistant natural gums and synthetic gelling and/or thickening agents can be employed. Particularly suitable gums for use in the present composition are the guar gums or mixtures of guar and karaya gums. These materials not only impart a water resistance, desired for many operations, to the product but also readily are cross-linked to any predetermined degree thereby providing a flow and non-rigid characteristic to the product when in thick paste-like form. Any of a variety of conventional crosslinking agents can be employed to achieve the crosslinking of the gum. The amount of crosslinking agent used is such that the resulting water resistant explosive is pliable and gelatinous. To illustrate, with a guar gum, about 2.5 weight percent (based on gum weight) of a 5 percent sodium dichromate solution has been found to be a satisfactory agent for preparing the present composition. Likewise, a saturated solution of ammonium nitrate in liquid ammonia (Divers liquid) can be used. Conveniently, to aid dispersion of this latter crosslinking material throughout the mix it can be diluted up to about percent or more by volume with water.

Other sensitizers which can be incorporated into the composition, if desired, to impart certain characteristics to specific embodiments of the present novel explosive product include any of a wide variety of conventional detonable organic explosive compounds such as, for example, nitrostarch, nitroglycerine, nitrotoluenes such as trinitrotoluene and dinitrotoluene, nitronaphthalene, trimethylolethane trinitrate, pentaerythritol tetranitrate, pentolites, cyclodinitrotrimethylenetetramine and the like.

The present novel product safely can be stored, shipped and handled either in the bulk state or when placed in bags or other containers. Conveniently, for use in borehole blasting operations the product can be placed in polyethylene or other easily deformable bags so as to provide preweighed units of material.

In use, the bagged materials can be directly inserted into a borehole, or for enlarged, chambered holes, e.g., the bags can be slit or otherwise opened before placing in the hole. This latter action assures that the explosive 6 composition will fill the borehole volume and generally No. 325 mesh and about 1 mil, and an ANFO (-94 conform with the wall configuration of the hole. weight percent ammonium nitrate-6 weight percent fuel Detonation of the explosive generally is accomplished oil) composition, as controls.

TABLE I [Metal particulation, percent of total metal] Metal mesh size (U.S. sieve), metal gauge (mils) 25 to 35 15 to 25 to 1 to 10 l to 10 1 Control 100 Control (ANFO) by conventional 'boosters and primers, shaped charges TABLE TEST RESULTS and other high energy initiators.

The following examples will serve to further illustrate Run iggi gg E5132? 58%, the present lnventron, but are not meant to limit it thereto. (1 s./sq.m.) (KcaL/gmJ -la -la Example 1.A number of dry, granular explosive 21864 0 65 Q77 L 44 compositions were prepared using various size and gauge 2,783 0 68 0.81 1. 48

2, 504 0. 61 0. 7s 1. 37 fractions of a particulate 40 welght percent magnesium-6O 2,841 71 82 L 53 weight percent aluminum alloy blended with a mixture of gig g g; 8?? :3 particulate ammonium nitrate containing 94 weight per- 21854 0 74 cent NH NO and 6 weight percent fuel oil. Each com- 2,623 0 62 0. 78 1. 41 2,933 0.69 0.80 1. 49 position contained on a weight basis 80 percent of the 2386 M8 0'79 L27 ammonium nitrate-fuel 011 mixture and 20 weight per- 2,060 (H58 0.440 [L898 cent of the magnesium-aluminum alloy.

The mixes were made up in about 40 pound lots. About 20 pound samples were sealed in two-gallon Water resistant paint pails (total load about 20 pounds), along with a one-third pound composition B detonator attached to a strand of Primacord fuse line and the mixes tested in a :'standard underwater test. The detonator was placed inside the pail and the Primacord extended out through the lid. Water resistance was assured by a gasket sealing assembly where the Primacord came through the lid.

. the testing. Primacord was ccinnected to an The ammonium nitrate component consisted of about lmtiator and firlng line and the explosive charge was 54 parts by Weight primed ammonium nitrate (Us.

detonated in a body of water at about half the depth Standard Sieve; +8 meSh 2 7%, of a lake (mix placed at 42.5 feet beneath the surface of 5 2% +1 3g 7% 16/+2() h the water). The resulting pressure profile from the deto- 5.1%, 20/ +40 meshl.9%, -40 mesh0.2%) and nation was converted into electrical impulses by a piezobo t 46 parts by weight f crushed prilled ammonium electric gauge suspended in the water at the same level nitrate (sieve analysis 8/+ l2 mesh0.8%, 12/ +16 a known horizontal distance away from the charge. The mesh5.4%, 16/ +20 mesh-18.8%, 20/ +40 electrical impulses were recorded and converted to the mesh-431%, me$h corresponding pressures and from this the peak pressure, 325% shock energy, bubble energy and total energy of the The fixtures were P p by blending the Ff explosive readily were calculated by methods described Ponents and Placmg, the resultmg composltlons in Underwater Explosives, H. Cole Princeton in sealed canisters for duplicate shots by the standard University Press |(1948) underwater test following the technique and procedures described in Example 1. Tilble I presents the mesh. and gauge of the Table III lists the metal alloy composition, particle particulate alloys employed 1n the compositions and mesh size and gauge of the metal component used in Table II summarlzes the results of underwater test shots each of the compositions Table IV presents the explosive of H16 compositions of the Pmsent invention using Various test results obtained for the mixes set forth in Table III.

metal gauges as well as a composition containing 100 The run numbers in each of these tables identifies the percent of the metal all within minus No. 200 to plus same explosive composition.

It is evident that all the compositions had a high peak pressure and total energy than either of the controls.

Example 2.A number of dry granular explosive compositions were prepared from particulate ammonium nitrate, fuel oil and magnesiumsilicon-aluminum alloys. In each of these preparations the mix concentration was about 86.4 Weight percent ammonium nitrate, about 3.6 weight percent No. 2 fuel oil and about 10 weight percent of the alloy.

TABLE IIL-METAL COMPOSITION AND PARTICULAIION Alloy composition (wt. Particle Mesh Size (US. Standard Sieve) Particle gauge (mils) 113.1111). percent) (Percent of metal component) Mg Si Al 20/+40 40/+100 1 200 1 1/5 5/20 10/15 15/20 20 1 1 Substantially all between 20 and 40 mils.

TABLE IV.-EXPLOSIVE TEST RESULTS Run Peak Pressure Shock Energy Bubble Energy Total Energy N0. (lbs/sq. in.) (Kcal./gm.) (KcaL/gm.) (KcaL/gm.)

3, 487 O. 72 0. 68 1. 40 3, 675 0. 73 0. 68 1. 41 3, 785 0. 84 0. 67 1. 51 3, 483 0. 72 0. 68 1. 4O 3, 599 0. 73 0. 69 1. 42 3, 519 0. 77 0. 69 1. 46 3, 442 0. 67 0. 66 1. 33 3, 475 0. 67 0. 67 1. 33 3, 505 0. 75 0. 69 1. 44 3, 552 0. 80 0. 67 l. 47 3, 429 0. 68 0. 68 1. 36 3, 813 0. 77 0. 68 1. 45

Various modifications can be made in the present invention without departing from the spirit or scope thereof for it is understood that I limit myself only as defined in the appended claims.

I claim:

1. A dry explosive composition consisting essentially of, on a weight basis:

(a) particulate ammonium nitrate from about 50 to about 97 percent;

(b) particulate light metal from about 3 to about 50 percent, said light metal ranging substantially from about No. 4 to No. 200 mesh US. Standard Sieve and having a gauge of from about 0.25 mil to about 40 mils;

() up to about 40 percent of an inorganic oxidizing salt selected from the group consisting of particulate alkali metal nitrate, chlorate, perchlorate and mixtures thereof;

(d) up to about percent of non-detonable organic fuel; and

(e) up to about 2.5 percent of a member selected from the group consisting of gelling or thickening agents.

2. The dry explosive composition as defined in claim 1 wherein the particulate metal has a particle size distribution of from about 25 to about 60 percent larger than about No. 50 mesh, the balance being substantially No. 50 to about No. 100 mesh and from about to 100 percent of the particles have a gauge of from about 0.25 mil to about 4 mils and up to about 85 percent have a gauge of from about 4 to about 15 mils.

3. The dry explosive composition as defined in claim 1 wherein the particulate metal has a gauge of less than about 10 mils.

4. The dry explosive composition as defined in claim 1 which includes in addition up to about 16 percent of a detonable organic sensitizer.

5. The dry explosive composition as defined in claim 1 wherein the particulate ammonium nitrate ranges from about to 95 percent; the particulate light metal is a member selected from the group consisting of particulate aluminum, magnesium, magnesium alloys, aluminum alloys and mixtures thereof; the inorganic oxidizing salt consists of up to about 25 percent of sodium nitrate; the non-detonable organic fuels consist of up to about 6 percent of non-detonable liquid hydrocarbons; and said gelling or thickening agent consists of natural gums, synthetic polymeric thickening agents or mixtures up to about 1 percent.

6. The dry explosive composition as defined in claim 5 wherein said non-detonable liquid hydrocarbon consists of fuel oil.

7. The dry explosive composition as defined in claim 5 wherein the particulate metal has a particle size distribution of from about 25 to about percent larger than about No. 50 mesh, the balance being substantially N0. 5 0 to about No. 100 mesh and from about 15 to 100 percent of the particles having a gauge of from about 0.25 mil to about 4 mils and up to about percent have a gauge of from about 4 to about 15 mils.

8. The dry explosive composition as defined in claim 5 wherein the particulate metal has a gauge of less than about 10 mils.

9. The dry explosive composition as defined in claim 5 which includes in addition up to about 16 percent of a detonable organic sensitizer.

References Cited UNITED STATES PATENTS 3,255,058 6/1966 Wyman et al 1491 14 X 3,307,986 3/1967 Grant 14944 X 3,331,717 7/1967 Cook et a1. 14943 X CARL D. QUARFORTH, Primary Examiner.

S. J. LECHERT, Assistant Examiner.

U.S. c1. X.R.