United States Patent 3658607

A dense explosive composition of extremely high energy and relatively high detonation velocity, with relatively long sustained application of high disruptive force, comprises a concentrated solution of ammonium nitrate, high proportions of finely divided aluminum, relatively small proportions of water, and a small amount of special combinations of cross-linking and thermally stable thickeners. The composition is prepared at elevated temperature, mixed very briefly, and delivered or packaged by pumping from mixer to receptacle where it sets up quickly. Density and sensitivity may be controlled by incorporating gas or porous inert filler material.

Cook, Melvin A. (Salt Lake City, UT)
Udy, Lex L. (Salt Lake City, UT)
Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
149/43, 149/44, 149/60
International Classes:
C06B47/14; (IPC1-7): C06B19/00
Field of Search:
View Patent Images:

Primary Examiner:
Quarforth, Carl D.
Assistant Examiner:
Lechert Jr., Stephen J.
What is claimed is

1. An explosive composition in the form of a highly viscous, near solid aqueous slurry stable for storage under wide temperature ranges, with a normal density of at least about 1.5 grams per cc and having high brisance and substantially greater total energy than an equal weight of trinitrotoluene, comprising the following ingredients in percentage by weight, based on the total composition:

2. Composition according to claim 1 wherein the thickener comprises 0.1 to 0.5 percent of guar gum combined with a small amount of xanthan gum.

3. Composition according to claim 1 wherein the thickener comprises a major proportion of a xanthan gum.

4. Composition according to claim 1 wherein there is added an inert filler material in proportions of 0.2 and 1.5 percent by weight, based on the total composition, to reduce composition density.

5. Composition according to claim 4 wherein the inert filler material comprises particles of foamed polystyrene plastic solid.

6. Composition according to claim 5 containing 0.5 to 1 percent of foamed polystyrene plastic solid beads.

7. The process of preparing an explosive slurry blasting composition which comprises, in combination, the steps of:


In U.S. Pat. No. 2,836,484 Streng and Kirshenbaum described an explosive composition made up of 38 to 49 percent by weight of particulate aluminum, 20 to 43 percent of a stable oxidizer such as ammonium nitrate or analogous oxidizer selected from the inorganic nitrates, perchlorates, etc., and enough water, about 28 percent, to bring the aluminum-water ratio into a range of 1.4 to 1.5. In their compositions there was enough water to fully dissolve the oxidizer. The aluminum content, particularly if it should consist of very finely ground aluminum, is so high as to make its dispersion into an aqueous liquid extremely difficult. Accordingly, the inventors in said patent suggested use of emulsifying agents to help disperse the finely divided metal. However, emulsifying agents are often objectionable in slurry explosives because they may cause extensive desensitization.

It is possible, when very large proportions of fine aluminum are used, that the particles may support each other mechanically. In such a case, there is no true slurry. By definition, a slurry is a suspension of solid particles in a liquid. Unless such a large quantity of solids is used that the particles support each other against gravity, they will not long remain suspended in an unthickened or non-viscous medium as a simple aqueous solution of ammonium nitrate. For this reason, the prior art has found it necessary to gel or otherwise thicken the liquid phase; otherwise, segregation of the solids by gravity occurs and the composition will fail to detonate. Gelling agents of the prior art, such as guar gum, starch, etc., with or without cross-linking agents, usually do not retain their high initial viscosity, particularly during extended storage under severe temperature conditions. For military use such compositions must be mechanically as well as chemically stable over temperatures ranging from well below freezing to tropical and desert sun temperatures of 130° F. and even up to 160° F. One aspect of this invention is to provide such storage stability.

High brisant explosives such as TNT are employed in military shells, bombs, etc., for use on hard targets such as concrete and steel structures, vehicles, etc., where an extremely high shattering effect at or very near the center of detonation is needed. The impact of the projectile and its detonation must be at or very close to such structures to be effective. TNT has a detonation velocity of about 7,000 meters per second and under favorable conditions it develops a detonation pressure as high as 2,250,000 psi, or more.

"Cyclotol", formed by slurrying granular "RDX" in molten TNT and casting the charge, produces even greater detonation pressures than TNT. Compositions of this type have also been combined with certain proportions of finely divided aluminum, to increase their energy and therby obtain very high brisance or shattering power.

While these conventional military explosives are suitable for hard targets at close range, they are less suitable where a wider area blast effect of at least fairly high intensity is desired. In order to destroy softer targets over a much larger area, the blast duration must be prolonged considerably. The energy of conventional high brisance explosives is expended in a very brief period of time. Hence, although the peak pressure exerted may be very high, a pressure destructive to soft targets is not sustained for as long as is desirable to accomplish destruction or demolition of relatively softer targets farther from the detonation point.

One of the objects of the present invention is to make available an explosive composition which approaches the high brisance or detonation blast effect of TNT but which also begins to approach the area blasting effect, e.g., of an atomic bomb. An important aspect of the present invention is the discovery that viscous gel or slurry type explosives, based on powerful inorganic oxidizer salts, combined with large quantities of metallic aluminum, have the above described area blasting effects to a good degree.

In U.S. Pat. No. Re 25,695, Cook and Farnam have pointed out how high total energy can be obtained by reacting smaller quantities of water and aluminum with oxidizers such as ammonium nitrate (AN). The latter may be mixed with sodium nitrate (SN). With water and aluminum in proportions somewhat lower than suggested by Streng and Kirshenbaum, Cook and Farnam produced powerful explosives for hard rock blasting and they were compatible with borehole water. More recently, Cook, his associates, and others have produced a variety of effective and powerful blasting agents, based primarily on combinations of one or more of the powerful oxidizer salts named above, with fine particulate aluminum, using water to establish a substantially continuous liquid phase. Minor quantities of other ingredients such as stabilizers, thickeners, gassing agents, etc., are known. Guar gum and other gelling agents and/or starches which may or may not be cross-linked, have been used as thickeners along with borax, dichromates, etc., which accelerate or augment the desired thickening action.

Compositions of the types just described above have gone into wide use for blasting, particularly in hard rock mining, large scale rock excavation, etc. In some cases, self-explosive materials such as TNT in granular form have been combined with these slurries with good results. It is known that some of these agents have a higher total energy "Q" than comparable weights of TNT, etc.

In general, aluminized slurries based on ammonium nitrate, or on a combination of ammonium nitrate and sodium nitrate, and analogous oxidizers, have moderately high detonation velocities. Since they can be prepared in the field, by mixing the relatively safe ingredients together at or near the site of use, they have definite safety advantages. They normally are thickened somewhat but are liquid or semi-liquid in nature, at least when first prepared, so they can be poured or pumped directly into boreholes, packages or other receivers.

Streng and Kirshenbaum have suggested use of 38 to 49 percent aluminum. Cook and Farnam U.S. Pat. No. Re 25,695, mentioned above, showed lower proportions of water than suggested by Streng and Kirshenbaum and suggested that the slurry, with continuous liquid phase, should be so composed or formulated that it would remain stable in the presence of water. Thus, a thick mixture of aluminum, water, and inorganic oxidizer of the nitrate type (ammonium nitrate or mixtures thereof with sodium nitrate), can be introduced into a water-filled borehole and remain there undiluted for several days.

The use of thickeners is highly advantageous for stabilizing such materials in the presence of ground water in boreholes, for example.

The compositions thus described in the prior art have become the basis for current large-scale and successful use of blasting slurries. Most of them have had relatively low aluminum content, up to 15 to 20 percent by weight, but usually less.

Prior to the present invention it has not been the practice to use more than about 20 percent of aluminum, or 25 percent at most in slurries. There are several reasons for this. Aluminum is one of the most expensive ingredients in blasting compositions of the slurry type. If finely particulated, it is quite reactive with water. While some publications or patents mention use of more than 20 or 25 percent of aluminum, e.g., U.S. Pat. Nos. 3,307,986; 3,303,074; 3,377,909, and 3,214,307, the art simply has not found it desirable in practice, or economical, to use so much.

Aluminum, particularly in the finer grades, such as paint or pigment grades, is hard to disperse in aqueous systems in large proportions and for good sensitivity it is preferable that the aluminum be not completely wet by the aqueous phase. See Clay et al., U.S. Pat. No. 3,249,474.

For the above reasons, it is surprising to discover that a thickened slurry of very high aluminum content but low water content, and thickened in an unusually stable manner, has several particular advantages. The explosives of this invention have extremely higher total energy than TNT. They are relatively inexpensive. They can be made up in the field, using critical proportions of known major ingredients. Further improvements are obtained by the use of carefully chosen proportions of particularly effective thickeners having properties especially suitable for the needed physical properties of the slurry.

The explosives of the present invention are particularly suitable for area blasting, especially against relatively wide areas of targets softer than concrete or steel. These compositions are effective against such targets or target areas at greater distances from the explosion center than prior art explosives. It will be understood, however, that the compositions of this invention also are highly useful for industrial and other uses.

On a pressure-time graph the new compositions exhibit slightly lower pressure peaks than TNT at points very close to the center of detonation. However, while the pressure curve for TNT drops rapidly to zero from its peak, compositions of the present invention show a pressure vs time curve, which is somewhat lower initially than that for TNT, but which maintains a relatively high level for a much longer period of time. The result is that the area under the curve, which is a measure of delivered total energy, is very substantially greater for the new slurry explosive than that for TNT. This is true, in general, not only for TNT but for other explosives of the prior art including those discussed above.


A high "Q" explosive of reasonably high detonation velocity and outstanding area blasting properties, effective especially against "soft" targets, is made up of ammonium nitrate, enough water to make a stiff slurry, and 32 to 43 percent by weight of finely divided metallic aluminum. A special thickener composed of xanthan gum and cross-linked guar gum (or starch) gives good storage stability under extreme temperature conditions.


The single FIGURE of drawing shows graphically a pressure vs. time graph comparing cast TNT with the composition of this invention.


The invention will now be described with reference to specific examples.


A composition was made up of the following ingredients in percentage by weight:

Ammonium nitrate 50.0 Particulate aluminum, finely divided 35.0 Water 14.0 Thickener-stabilizer X (described below) 1.0 Total: 100.0

From its inclusion of such a high percentage of aluminum, and the fact that its oxygen balance was about -22 percent, one would expect that this particular composition should not have the extremely high blasting power needed for wide area blasting of the type described above. This composition proved to be extremely powerful in tests, as will be shown below. The process of preparation was as follows:

The pre-mixed aluminum and the thickener (which in this case was a combination of a specially treated self cross-linking gum with a small amount of ammonium phosphate, to inhibit water-aluminum reaction) were metered into a mixing funnel. In the funnel these were blended with a saturated water solution of ammonium nitrate in proportions to form a thin slurry with the aluminum. This slurry was thickened, thereafter, by adding dry prills of ammonium nitrate to bring total ammonium nitrate up to 50 percent. The slurry as thus compounded was mixed for a few seconds to make it smooth and homogeneous. Then it was pumped immediately, before the thickener became fully effective, and forced continuously through a length of rubber hose to the point of use. At the time of delivery, about 30 seconds after combining the ingredients, the slurry was still reasonably fluid and was still pumpable, with a viscosity in the neighborhood of about 3,000 centipoises. After this pump-delivered slurry had set for 15 minutes, the cross-linking reaction of the thickener had developed sufficiently that the entire slurry mass was gelled to a stiff rubber-like consistency. After further setting it hardened or toughened somewhat further so that it approached the consistency of an ordinary gum rubber eraser.

Because of its initial fluidity, this material can conveniently be poured or pumped into bombs, for example. Choice of an effective, stable thickener is very important. Also, when the slurry thickens up to a stiff rubbery consistency and retains such consistency, it can be transported in aircraft without concern for shifting of center of gravity. Such a shift can cause a serious problem in transportation by air of less viscous or liquid slurries, particularly in bombs of large size. The military uses intended for this explosive composition may involve large bombs and analogous containers. For practical purposes, after the composition of Example 1 has set for a short time, it is substantially as stable as a solid explosive, e.g., cast TNT, so far as handling or shipment are concerned.

This composition was found not to be impact sensitive to standard 30-calibre rifle bullets. Also, at 20° C., it was not sensitive to a No. 6 electric blasting cap. The composition and all its ingredients are non-toxic; hence, it can be handled without special clothing requirements. If spilled, there is no dangerous contamination or hazard to personnel and the spills can readily be cleaned up with water.


Another quite similar but more viscous composition was made up of the following ingredients in percentage by weight:

Ammonium nitrate 49.55 Water 14.00 Aluminum 35.00 Thickening gums and stabilizer 1.45 Total: 100.00

This product, after standing briefly, was a stiff slurry with a density of about 1.50 grams per cc, a critical diameter for detonation of 2.5 inches, a detonation velocity of about 5,275 meters per second, and a total energy "Q" of about 1,900 calories per gram. Its seismic strength, compared to TNT, on a weight basis, was 1.45. The material of Example 2 does not detonate in a 2-inch capped steel pipe fired with a 30.06-calibre bullet from 25 yards distance.

The thickener used in Examples 1 and 2 was a combination of a small amount of conventional guar gum dispersed in the aqueous solution to thicken it enough to hold finely dispersed gas bubbles, a small amount of a self-complexing guar gum which is a very effective slurry thickener, giving a rubbery structure, but of poor storage stability, and a small amount of a "xanthan" gum, obtained from General Mills Corporation, and understood to be derived by bacterial action from polysaccharide materials, probably guar gum. The latter has a highly effective stabilizing effect so that the thickened gel retains its tough, rubbery structure over extended periods of storage time, even at high temperatures. A small amount of boric acid, also used, tends to assist in cross-linking and also contributes to chemical stability in repressing reaction between the fine aluminum and water.

The compositions of Examples 1 and 2 were tested for minimum booster requirements. Boosters were made up of molten 50/50 pentolite composition (50% PETN and 50% TNT) poured, i.e., cast, in a 1.95 -inch diameter steel tube with a wall one-fourth inch thick which served as a container for the booster. An 80-gram booster failed to detonate the composition of Example 2 at 20° C. A 90-gram booster detonated the same at 20° C. and a 100 -gram booster detonated it at 5° C.

Several other formulations and test results are indicated in the table. ##SPC1##

One general mixing procedure is given above. A preferred specific mixing procedure is as follows:

1. Place the oxidizer solution and accompanying crystals in an aluminum or stainless steel pot of adequate size and heat until the crystals are all dissolved. It should not be necessary to exceed a temperature of about 50° C. for this purpose. Allow the solution to cool to between about 35° and 40° C.

2. add further dry oxidizer, preferably predominantly ammonium nitrate (but it may comprise sodium nitrate), to the solution and stir until the prills are evenly distributed. These remain in suspension in the saturated solution. Depending on the temperature at which the solution is made and/or slurry is prepared, more or less, or in some cases no dry oxidizer will be added, as will be obvious, since solubility varies widely with temperature.

3. Add the entire quantity of dry fuel to the above mix at one time and stir vigorously until all of the dry pre-mix is blended and the thickener renders the mix thicker. Total mixing time usually does not exceed one minute.

4. Fill the testing containers with the mix as soon as possible after mixing, otherwise; cross-linking will set on to such an extent that the slurry will not flow (approximately 2 minutes after thickening to the stage described in (3) above).

This procedure applies to the slurries which are not modified or lightened in density by inclusion of filler material, such as particles of foamed cellular polymer, specifically, foamed polystyrene in bead form, well known commercially as "Styrofoam" beads or equivalent inert matter which does not detract from the explosive properties but reduces specific gravity. When these are added, proportions are between 0.2 and 1.5 percent, preferably 0.5 to 1 percent. The preferred procedure for mixing in the latter, as in Example 6 in the table, is as follows:

Heat oxidizer solution until all of the crystals are dissolved and add dry oxidizer as above in (1) and (2). Then add "Styrofoam" beads and stir until they are uniformly distributed throughout the mix. Add the entire quantity of dry fuel to the mix at one time and stir as in (4) above. Then fill the testing containers as described in (5) above.

In the composition of Example 6 the amount of dry oxidizer is reduced slightly to permit the use of "Styrofoam" beads to obtain low density. The product is a highly aluminized low density slurry. All components and the slurry itself are stable and non-toxic. Example 6 was repeated in another 20-pound batch with similar procedure and results. This lower density slurry has the following properties:

Density 1.25 g per cc Critical diameter 2.0 inches Minimum booster required 20.0 g of 50/50 pentolite as compared with 90 or 100 g shown above

It detonates when fired with a 30.06-calibre bullet at 25 yards in a 2-inch capped steel pipe. In this respect it is, of course, not quite as safe as the denser product.

One problem encountered in filling receptacles such as bombs with slurry compositions which have been aerated to any substantial extent has been that of cavities. Such develop frequently in bombs and other containers after filling. Probably because the slurries are necessarily aerated somewhat on mixing, shrinkage occurs which leaves the receptacle partly unfilled especially after it stands for a while. This can be avoided by using a procedure which involves filling under pressure. The details of such procedure form no part of the present invention.

An effective composition is made up of the following ingredients, it being understood that variations in quantity of paint grade aluminum will influence sensitivity to detonation.


Material Percentage by weight Ammonium nitrate (AN), industrial grade prills 49.25 Water 14.0 Aluminum 35.0 (a. atomized type -- 33-35) (b. flaked paint grade 0-2) Ethylene glycol 0.3 Conventional guar gum 0.15 Cross-linking guar gum 0.3 Xanthan gum 0.9 Boric acid 0.1 Total: 100.00

At various temperatures and pressures, the density of a slurry of the general types described in examples above varied as follows:

Temp °C. P. (psig) Vol. ml. Density 12° 0 114.0 1.49 " 11 107.8 1.57 " 23 106.0 1.61 " 49 104.0 1.64 45° 21 114.0 1.49 " 30 112.0 1.51 " 40 111.0 1.53 " 60 110.0 1.54 " 80 109.5 1.55

Area blasting results from slurry compositions of various types, including those of this invention, showing peak pressures obtained by probes positioned at various distances from the center of the explosion as compared with TNT, are tabulated below. The densities of the composition (like Example 5) were varied, either by incorporating gas or by adding inert filler, "Styrofoam" beads, as in Examples 6 and 7. ##SPC2##

Compositions designated Example 1, H-1 and I-2, respectively, were of the same general density range, i.e., 1.19 to 1.25 g/cc. Composition I-3 was more dense, about 1.45 g/cc. The precise constituents of compositions H-1 and H-2 are not known. They were tested merely as representative examples of known explosive slurries.

The composition of Example 1 gave lower pressure than TNT at 10 feet, equal or slightly superior at 16 feet, greatly superior at 22 feet, and moderately superior at 28 feet. Slurries I-2 and I-3 were aluminized, water-ammonium nitrate compositions containing respectively 25 and 10 percent of aluminum.

It will be obvious to those skilled in the art that many variations may be made in formulation without departing from the spirit of the invention. For example, particles of self-explosive materials, e.g., TNT, RDX, nitrocellulose, etc., may be added. An important aspect of the invention is the discovery that a distinct optimum power, particularly superior for area blasting purposes, is obtained by combining about 45 to 55 percent by weight of powerful oxidizer, preferably comprising mostly or at least two-thirds ammonium nitrate, with 32 to 43 percent of finely particulated aluminum, part of which preferably is flaked paint grade, using about 11 to 18 percent, preferably 13 to 16 percent, of liquid of which the major proportion is water. A substantial part of this liquid, however, may be a glycol, alcohol, ketone, aldehyde or amide. Such, if used, should be water soluble or at least water compatible. A thickener must be used which is highly effective in low proportions (preferably 0.5 to 1 percent, but proportions as high as 5 percent may be used, especially where superior gel stiffness and stability are required for prolonged storage at high temperatures) to make the slurry stiff, rubbery, and stable. Pre-gelled starch, when used, may go as high as 2 percent. Gum-type thickeners are preferred and should be strongly cross-linked. Proportions of 0.35 to 1.3 percent by weight are recommended.

For the stable highly viscous or rubbery consistency preferred for storage and transportation, at least 0.5 percent of highly cross-linked thickener preferably including a xanthan gum, should be included. Preferably, at least part of the thickener is added to the solution before the insolubles are added. This aids in trapping large numbers of fine gas bubbles in the solution, which materially aid in promoting sensitivity to detonation, even with very minor reduction in density. The thickener preferably is a polysaccharide, i.e., a starch or gum of delayed action type, so that the slurry can be pumped or poured for at least a few seconds after mixing, but it also includes a component which produces high and lasting viscosity in the liquid phase. For this reason, two components, i.e., cross-linking guar gum plus the xanthan gum are preferred. This combination thickening system is particularly important when the gel is to be stored for extended periods. It is stable at temperatures which may range from well below freezing to as much as 160° F. and for periods of a year or more.

In a typical case the composition may contain about 10 to 15 percent of the oxidizer in solid state. It is insoluble, not by nature but by reason of the pre-saturation of the solution. For this particular composition ammonium nitrate is preferred as the oxidizer but up to 25 percent of such oxidizer may be sodium nitrate.

As shown in the drawing which is based on the data of Example 1 and other compositions given in the above table, the composition of this invention was outstanding in its performance at distances of 16 to 28 feet from the center of the explosion. The area bounded by the rectangle ABCD was regarded by the testing party as one of prime importance. TNT started high but dropped to a low pressure of 8.6 psi at 22 feet, as compared with 14.6 psi for a typical composition of this invention. Composition I-2 was a standard rock-blasting slurry of good quality for mining purposes. Composition I-3 was a relatively inexpensive slurry of low aluminum content. With TNT, there was small increase of pressure at a distance of 28 feet over that at 22 feet, probably due to ground reflection of pressure waves.

It will be obvious that reasonable variations in the composition, in its components, and in proportions of various ingredients may be made by those skilled in the art without departing from the concept and spirit of the invention.