US3728173A - Dense explosive slurry compositions of high energy containing a gum mixture - Google Patents

Abstract

A DENSE EXPLOSIVE COMPOSITION OF HIGH ENERGY IS MADE UP IN HEAVY SLURRY FORM PRIMARILY OF CONCENTRATED AWUEOUS SOLUTION OF A PERCHLORATE, PERFERABLY SODIUM PERCHLORATE, FINELY DIVIDED METALLIC ALUMINUM, A SELV-EXPLOSIVE SUCH AS TNT OR RDX, AND A LONG TERM STABLE THICKNER COMPRISING A GUAR GUM OR STARCH IN COMBINATION WITH AA XANTHAN GUM. SODIUM NITRATE MAY BE ADDED TO REDUCE FUDGE POINT.

Description

3,728,173 Patented Apr. 17, 1973 3,728,173 DENSE EXPLOSIVE SLURRY COMPOSITIONS OF HIGH ENERGY CONTAINING A GUM MIXTURE Melvin A. Cook, Lex L. Udy, and Albert G. Funk, Salt Lake City, Utah, assignors to Intermountain Research & Engineering Co., Inc. No Drawing. Filed Oct. 17, 1969, Ser. No. 867,388

Int. Cl. C06b N US. Cl. 149-21 10 Claims ABSTRACT OF THE DISCLOSURE A dense explosive composition of high energy is made up in heavy slurry form primarily of concentrated aqueous solution of a perchlorate, preferably sodium perchlorate, finely divided metallic aluminum, a self-explosive such as TNT or RDX, and a long term stable thickener comprising a guar gum or starch in combination with a xanthan gum. Sodium nitrate may be added to reduce fudge point.

BACKGROUND AND PRIOR ART US. Pat. No. 2,836,484 suggested an explosive slurry could be made of high proportions of metallic aluminum in a concentrated aqueous solution of inorganic nitrates, perchlorates, etc., as oxidizers. More successful explosives were made up later, using lesser quantities of aluminum, adding thickeners, cross-linking agents for the thickeners, stabilizers, and the like. Others have taught the use of self-explosives such as TNT particles suspended in the slurry, as in Cook and Farnam US. Pat. No. 2,930,685.

It is well known that finely divided metallic aluminum can serve both as a fuel and as a sensitizer for blasting slurry compositions based on aqueous solutions of ammonium nitrate and/or other inorganic oxidizer salts. It is known also that, despite obvious theoretical advantages in use of high density slurry explosives, those of higher densities are extremely difficult and often impossible to detonate. For this reason, the industry has often found it expedient to accept less dense (and hence less powerful) explosives in slurry form in order to obtain detonability. Thus, various expedients have been proposed to reduce density by adding inert fillers, fibrous materials, and particularly to incorporate gas or gassing agents. Expedients such as aeration, carbonation, addition of gas generating substances such as nitrites, carbonates in combination with weak acids, have been suggested and some of these have been used commercially.

While it is well known that sensitivity of these explosive slurries usually increases with decreasing density, the higher seismic energy of the denser slurries is of great value when they can be detonated. Smaller boreholes, or more widely spaced boreholes, can be drilled, at substantially reduced drilling costs, when the explosives are to be used in mining or excavation. Concentration of energy in minimal volume obviously is desirable for military applications.

An object of the present invention is to make available unusually dense and powerful blasting agents that can be detonated by use of boosters of reasonable size and cost.

Another object is to provide dense blasting agents which are sufiiciently fluid when first produced that they can be poured or pumped into a receptacle, and still solidify or stiffen up sufi'iciently as to become essentially solid. In this way, any tendency of particulate components to separate from a liquid or gelled menstruum is prevented. Containers, such as large bombs, are dynamically stable because the contents do not remain liquid. This is important for safe transportation of large masses of such materials in vehicles where fluid motion would be objectionable, in aircraft or small water craft, for example.

SUMMARY Powerful dense explosives, of slurry form, which are relatively fluid when first mixed, but which essentially solidify and remain stable by reason of powerfully crosslin'ked gelling agents, are made up of relatively large proportions of metallic aluminum in combination with selfexplosive particles, in an aqueous solution of ammonium, alkali metal or alkaline earth metal perchlorate. Supplemental oxidizers, such as sodium nitrate, etc., may be added to the perchlorate. Thickening agents include conventional guar gum or starch combined with a small amount of a xanthan gum which imparts long-term stability and a viscosity of firm rubbery consistency.

DESCRIPTION OF PREFERRED EMBODIMENT This invention is based on the discovery that by a careful selection of ingredients and proportions, using a perchlorate as an important ingredient in the oxidizer, along with other known ingredients as the more important constituents, explosive agents of unusually high density and of very high seismic energy are obtained. These are useful in hard rock mining where high brisance, high shattering effects, are desired. They are useful also or other applications where their very high energies, considerably higher than TNT, are desired along with reasonably high brisance. Sodium perchlorate is specifically preferred as a major oxidizer ingredient but ammonium perchlorate and/ or calcium perchlorate are often just as satisfactory.

These compositions are made up of about 32 to 45% by weight of an oxidizer consisting mainly of an inorganic perchlorate dissolved or at least dissolved to a substantial degree in aqueous liquid to provide an essentially continuous liquid phase. This liquid may be thickened or gelled; hence, the expression continuous liquid phase will be understood to include a continuous, or substantially continuous gel phase. The aqueous liquid, which may include minor proportions of water compatible organic liquid such as ethyl or methyl alcohol, ethylene or diethylene glycol, formamide, dimethyl formamide, or analogous aldehydes, ketones, ethers, etc., comprises 10 to 17% by weight of the total, preferably 11 to 15%.

Suspended in the liquid or gel phase to form a slurry are particles of metallic aluminum or magnesium, or both, and particles of a powerful self-explosive. The latter may be TNT, RDX or similar materials. The total weight proportions of metallic and self-explosive particles is substantially higher than proportions of self-explosive normally used in explosive of the general type mentioned in Cook and Farnam US. Pat. No. 2,930,685, mentioned above. Preferably, the total weight of these particulate ingredients is between 45 and 55% of the total composition, although in some cases the total may be as little as 40% or as much as 60%.

Of particular importance for purposes of this invention is the choice of thickener. For convenient handling, the composition when freshly prepared, should be pourable and pumpable by means of a conventional slurry pump, such as one of rotary or piston type. However, because the slurry contains suspended particles of density which may differ considerably from that of the liquid or gel phase, these may segregate and/or separate from the continuous phase unless the viscosity of the latter soon becomes suflicient to prevent such separation. Hence, the viscosity imparting or gelling agent must be one which is not so immediately effective as to make the slurry too thick to pump, pour, etc., but it must thicken up substantially and very soon after pumping or pouring so that the suspended particles remain in reasonably homogeneous dispersion throughout.

In addition, particularly if the composition is to be used or carried in large metal containers, it is preferred that the gel become highly viscous soon, i.e. substantially solid. This is desirable because if large liquid filled containers are carried on certain vehicles, e.g. in aircraft, and such containers usually contain at least a small void, motion of the vehicle may cause or permit liquid contents to move and slosh around. This movement can contribute to instability in aircraft, even in small water craft and it may be desirable to avoid such where reasonably possible.

Generally, the thickening or gelling agent should have at least the following properties: It should be highly effective in small proportions because, as a rule, it has little value as a contributor to the energy of explosion. It should show at least a short delay in its thickening effect, for handling, pumping, etc., for reasons already mentioned. It should set up fairly soon to produce a high viscosity. For certain applications, e.g. at a distance from the place where the slurry is prepared, it should be highly stable over long periods of time and over fairly wide temperature ranges. This is less important for many minmg applications but is still desirable. It should be effective and stable, quite independently of the acidity or pH of the liquid phase. Some of the prior art thickening agents, such as some of the cross-linked guar gums are quite dependent, both in their thickening effect and in their storage stability, on such pH. Of course, pH may be ad usted, as by adding acid, but this is not desirable in most cases. The thickeners used in the compositions of this invention are not limited to gels and slurries of low pH in their usefulness.

The preferred thickeners or gelling agents for the compositions of this invention are made up in part of known materials, or a combination, of conventional thickeners. These are carbohydrates, especially polysaccharides such as a guar gum or starch, or a combination, preferably combined with a cross-linking agent or component. However, a thickener of thermal stability superior to guar gum, such as a xanthan gum, is added, too. The latter 18 found to be needed for imparting storage stability. Such gums becomes essential, particularly for extended storage of the slurry where high ambient temperatures are likely to be encountered. Under the latter conditions, ordinary guar gum or starch type thickeners are inadequate.

A preferred thickener combination, therefore, is made up of a composite of about 3 to 5 parts by weight of a thermally stable xanthan gum, plus about two parts of a known type of guar gum. A small amount, preferably 0.3 to 0.6 part of a cross-linking agent is added to activate the guar gum. Boric acid is useful for the latter purpose. Alkali metal dichromates also can be used. This composite thickener can be used in proportions broadly of 0.1 to 2% usually at least 0.25% based on the total weight of the composition. Preferred proportions usually are about 0.5 to 1.5% of total slurry weight.

The liquid component is aqueous, i.e. consists of or comprises water, which may contain organic solvents such as alcohols, glycols, amides, etc., as pointed out more fully below. All liquid components preferably are solvents for the oxidizer salts or for a major part thereof. Specific examples are given below to illustrate the invention further.

Example No I Critical diameter In the above examples all of the compositions were sufficiently insensitive that they would not detonate with a No. 6 electric blasting cap at 25 C. Neither would they detonate in a 2-inch steel pipe capped, when fired at with a 30.06-calibre rifle at 25 yards range.

All of the compositions shown in the foregoing table are high energy and high explosive slurries which can be made at relatively low costs. They detonate well under pressure. Some of these compositions have been stored for a period of twelve months or more with no apparent degradation. Because water is a substantial ingredient, it is necessary, of course, that the containers for these compositions be kept air tight to prevent loss of the water by evaporation over long periods of time.

While water is used as the solvent in the examples above, it is sometimes advantageous to add or substitute a small quantity of an organic water miscible liquid, e.g. alcohol, preferably a glycol, such as ethylene or diethylene glycol. These normally will be used in small proportions, e.g. 0.2 to 3 or 4 percent of the total. Proper use of such organic liquid may involve blending the gumtype thickener into it to facilitate the dispersion of the thickener into the slurry. The thickener advantageously can be first dispersed in such liquid, e.g. alcohol or glycol, and then stirred into the mixture to get a homogeneous distribution of the gum throughout the whole mass before the thickener begins to set up. The xanthan gum is important because it has higher temperature stability than guar gum.

While aluminum is the preferred metal, it can be replaced in part, or under some circumstances completely, with magnesium. Generally speaking, a small part of the aluminum preferably is of a very finely divided or fine flaked paint grade. In such condition it is an extremely powerful sensitizer.

The total proportions of aluminum and high explosive, preferably range between about 45 and of the whole composition. Of this, the aluminum should comprise from about 20 to 45% and the remainder is made up of the self-explosive, i.e. TNT or equivalent. In lieu of TNT, other granular high explosives, such as RDX, Composition B or PETN may be used, or a combination of TNT with one or more of such substituted high. explosives can be used without departing from the invention. Water is used as needed to give required fluidity and viscosity over the temperature range of use. Usually it will make up not less than 10% nor more than 20% by weight of the total, preferably 11 to 15% Other ingredients may be used within the limits described above and various conventional components may be added in small proportions, such as finely divided carbonaceous fuel, and the like. It is often desirable to include a small amount of a water-aluminum stabilizer, particularly if the slurry is likely to remain in liquid condition for any extended period of time. A small proportion, such as 0.05 to 0.2% of ammonium phosphate or equivalent is useful for this purpose, as is already known in the art.

What is claimed is:

1. A dense high energy explosive composition comprising about 32 to 45% by weight, based on the total composition, of an oxidizer which consist essentially of an inorganic perchlorate selected from the group which consists of ammonium, alkali and alkaline earth metal perchlorates, said oxidizer being dissolved in 10 to 20% by weight, based on said total composition, of aqueous liquid, said composition containing as fuel and sensitizer a combination totaling between 45 and 65% by Weight of a combination of finely divided metallic powder, selected from the group which consists of aluminum, magnesium, and mixtures thereof, with a high brisance selfexplosive compound, said composition being viscous and gel-like in form and including 0.1 to 2% of a gelling agent, said gelling agent comprising a mixture of a waterswelling gum and a cross-linking agent combined with another gum of higher temperature stability than guar gum.

2. Composition according to claim 1 wherein the oxidizer is primarily sodium perchlorate.

3. Composition according to claim 1 wherein the oxidizer is made up primarily of sodium perchlorate with a minor proportion of sodium nitrate.

4. Composition according to claim 1 wherein the fuel comprises 15 to 40% by weight, based on the total composition, of metallic particles, the remainder of said fuel being a high explosive compound in particulate form and of high briSance.

5. Composition according to claim 4 wherein the metallic particles are of finely divided particulate aluminum.

6. Composition according to claim 1 wherein the oxidizer is primarily sodium perchlorate in proportions of 33 to 45% by weight, based on the total composition.

7. Compositiona ccording to claim 6 wherein the fuel is a mixture of 16 to 35 parts of particulate aluminum and 20 to 30 parts of pelletized trinitrotoluene.

8. Composition according to claim 1 which contains 33 to 41% by weight of sodium perchlorate, which contains aluminum and a highly brisant high explosive compound, both said aluminum and said high explosive being in particulate form, and sufficient thermally stable gum in the thickener to produce a consistency approximately 6 similar to that of gum rubber, said composition having a density of at least about 1.8.

9. Composition according to,claim 8 wherein the total fuel and high explosive constitute 45 to by weight of the total composition, the proportions of aluminum to said high explosive compound being approximately Within the limits of 35 to 15 and 15 to 35, said composition having a seismic strength ratio of at least 1.2/1 compared to cast trinitrotoluene.

10. A composition according to claim 1 in which the gelling agent is made up of a combination of about two parts by weight of guar gum and 3 to 5 parts of a thermally stable xanthan gum stabilizer, and wherein the guar gum is cross-linked.

References Cited UNITED STATES PATENTS 3,153,606 10/1964 Breza et a1. 149-42 X 3,318,740 5/1967 Fee et a1 149-38 3,331,717 7/1967 Cook et a1 14942 X STEPHEN J. LECHERT, J R., Primary Examiner US. Cl. X.R.

149 3s, 39, 41, 42, 44, 76, so,