Title:
LIQUID AND SLURRY EXPLOSIVES OF CONTROLLED HIGH SENSITIVITY
United States Patent 3765967
Abstract:
Dense liquid or slurry explosive compositions, which can be pumped or poured and detonated in very slender columns have a liquid menstruum made sufficiently sensitive per se for cap detonation in diameters as small as one-half inch. They comprise a complete solution of an alkali or alkaline earth metal perchlorate, e.g. sodium perchlorate, combined preferably with a small amount of ammonium or sodium nitrate, organic liquid fuel, preferably ethylene glycol, and solid particulate aluminum as fuel, TNT, PETN or RDX also can be added. Basic sensitivity is provided by molecularly adjacent fuel with all oxidizer in solution.
US Patent References:
Composition of low crystalization point and method of preparation
Clay et al. - May 1966 - 3249476
Inorganic oxidizer blasting slurry containing smokeless powder and aluminum
Cook et al. - July 1967 - 3331717
Inorganic oxidizer salt blasting slurry composition containing formamide
Cook - April 1968 - 3379587
Inorganic oxidizer salt explosive composition containing organic fuel solvent for said salt
Preckel - June 1968 - 3390029
Gelled aqueous slurry explosive composition containing as a gas generating agent a carbonate or bicarbonate with a nitrite
Albert - June 1968 - 3390032
Composition of low crystalization point and method of preparation
Clay et al. - May 1966 - 3249476
Inorganic oxidizer blasting slurry containing smokeless powder and aluminum
Cook et al. - July 1967 - 3331717
Inorganic oxidizer salt blasting slurry composition containing formamide
Cook - April 1968 - 3379587
Inorganic oxidizer salt explosive composition containing organic fuel solvent for said salt
Preckel - June 1968 - 3390029
Gelled aqueous slurry explosive composition containing as a gas generating agent a carbonate or bicarbonate with a nitrite
Albert - June 1968 - 3390032
Inventors:
Funk, Albert G. (Salt Lake City, UT)
Hansen, Boyd L. (Salt Lake City, UT)
Cook, Melvin A. (Salt Lake City, UT)
Hansen, Boyd L. (Salt Lake City, UT)
Cook, Melvin A. (Salt Lake City, UT)
Application Number:
05/237585
Publication Date:
10/16/1973
Filing Date:
03/23/1972
View Patent Images:
Export Citation:
Assignee:
Iresco, Chemicals (Salt Lake City, UT)
Primary Class:
Other Classes:
149/61, 149/42, 149/46, 149/43, 149/76, 149/60, 149/57, 149/83, 149/44, 149/2, 149/47, 149/69, 149/38, 149/85, 149/41, 149/39
International Classes:
C06B47/00; C06B47/14; C06B1/04
Field of Search:
149/2,61,21,70,44,76,60,83,42,85,41,38,43,39,46,47,57,69
US Patent References:
| 3395056 | Inorganic oxidizer salt-alcohol explosive slurry containing an alcohol thickening agent | July 1968 | Bronstein | |
| 3453158 | FUELED INORGANIC OXIDIZER SALT AQUEOUS EXPLOSIVE COMPOSITION CONTAINING INDEPENDENTLY DISPERSED GAS BUBBLES AND METHOD OF MAKING SAME | July 1969 | Clay | |
| 3465675 | PROCESS OF BLASTING WITH THICKENED SLURRIED INORGANIC OXIDIZER SALT-ALCOHOL WATER EXPLOSIVE MIXTURES | September 1969 | Bronstein | |
| 3485686 | AQUEOUS EXPLOSIVE SLURRY CONTAINING OXIDIZER-REDUCER CROSS-LINKING AGENT | December 1969 | Jessop et al. |
Primary Examiner:
Lechert Jr., Stephen J.
Parent Case Data:
This is a continuation, of application Ser. No. 876,576, filed Nov. 13, 1969.
Claims:
What is claimed is
1. A sensitive blasting composition comprising a substantially oxygen-balanced liquid mass which is detonable per se and which includes 0 to 25 percent by weight water and 5 to 30 percent by weight of a water-compatible organic liquid having fuel value of 7,000 British Thermal Units per pound or greater selected from the group consisting of diols; methyl, ethyl or propyl alcohols; aldehydes; ketones; amines; amides and alcohol-amines and mixtures of two or more of these and having completely dissolved therein an oxidizer salt, said salt comprising at least a major proportion of a perchlorate selected from the group which consists of ammonium, alkali metal, and alkaline earth metal perchlorates, in which liquid said perchlorate remains completely dissolved and hence in molecular contact with said water-compatible organic fuel at the temperature of preparation and also at the temperature of use, said liquid mass containing tiny entrapped gas bubbles, said composition having a bulk density of at least 1.0 grams per cubic centimeter.
2. Composition according to claim 1 which also contains a small amount of an inorganic nitrate oxidizing salt which is substantially dissolved both at manufacture and use in said liquid mass to lower its crystallization or fudge point.
3. Composition according to claim 1 which also comprises a finely divided solid fuel suspended in said liquid mass and a thickener for said liquid to substantially increase its viscosity and to stabilize said finely divided suspended fuel against segregation from said liquid mass.
4. Composition according to claim 3 in which the solid fuel comprises finely divided metallic aluminum up to 45 percent by weight of the total composition.
5. Composition according to claim 3 in which the solid fuel comprises a finely divided self-explosive.
6. Composition according to claim 5 in which the self-explosive is pentaerythritol tetranitrate.
7. Composition according to claim 1 which also comprises a finely divided solid fuel suspended in and insoluble in said liquid mass in proportions up to 65 percent by weight of the total.
8. Composition according to claim 1 which comprises 20 to 60 percent by weight of sodium perchlorate, an alcohol, a thickener sufficient to stabilize suspended particles against segregation from said liquid mass, and enough solid suspended particulate fuel to keep overall oxygen balance within limits of -50 to +10 percent.
9. Composition according to claim 8 which has its density lowered sufficiently by incorporation of additional quantities of air bubbles to increase its sensitivity.
10. Composition according to claim 8 wherein the solid fuel is a self-explosive in proportions up to 65 percent by weight of the total composition.
11. Composition according to claim 10 in which the self-explosive is pentaerythritol tetranitrate.
12. Composition according to claim 1 in which the liquid phase comprises 20 to 60 percent by weight of sodium perchlorate, up to 10 percent of sodium nitrate and a thickener.
13. Composition according to claim 12 in which the thickener is a cross-linked gum.
14. Composition according to claim 1 which has its density lowered by an amount of about 0.1 to 0.3 g/cc. by including a dispersed gas therein.
15. Composition according to claim 14 which includes a thickener for the liquid.
16. Composition according to claim 1 wherein said oxidizing salt comprises calcium perchlorate and the organic liquid comprises methanol.
17. Composition according to claim 1 which comprises formamide as an organic liquid.
18. Composition according to claim 1 which comprises a major proportion of a perchlorate and a minor proportion of a nitrate as the oxidizing salt, said composition containing sufficient widely dispersed gas entrapped therein to lower its density about 0.1 to 0.3 grams per cubic centimeter.
19. Composition according to claim 1 in which said oxidizing salt is calcium perchlorate.
20. Composition according to claim 1 where said organic liquid fuel is methanol.
21. A sensitive blasting composition comprising a substantially oxygen-balanced liquid mass which is detonable per se and which includes 0 to 25 percent water and 5 to 30 percent of a water-compatible organic liquid having fuel value of 7,000 British Thermal Units per pound or greater selected from the group consisting of diols; methyl, ethyl or propyl alcohols; aldehydes; ketones; amines; amides and alcohol-amines and mixtures of two or more of these and having dissolved therein an inorganic oxidizing salt, said salt comprising a nitrate selected from the group of alkali metal and alkaline earth metal nitrates, said water-compatible organic liquid having sufficient solvency such that said nitrate remains completely in solution and hence in molecular contact with said organIc liquid at the temperature of manufacture and also at the temperature of use, said liquid mass containing numerous tiny gas bubbles dispersed therein.
22. Composition according to claim 21 in which said organic liquid is methanol.
23. Composition according to claim 21 in which said inorganic oxidizer salt is calcium nitrate.
24. Composition according to claim 21 wherein the organic liquid fuel is ethylene glycol.
1. A sensitive blasting composition comprising a substantially oxygen-balanced liquid mass which is detonable per se and which includes 0 to 25 percent by weight water and 5 to 30 percent by weight of a water-compatible organic liquid having fuel value of 7,000 British Thermal Units per pound or greater selected from the group consisting of diols; methyl, ethyl or propyl alcohols; aldehydes; ketones; amines; amides and alcohol-amines and mixtures of two or more of these and having completely dissolved therein an oxidizer salt, said salt comprising at least a major proportion of a perchlorate selected from the group which consists of ammonium, alkali metal, and alkaline earth metal perchlorates, in which liquid said perchlorate remains completely dissolved and hence in molecular contact with said water-compatible organic fuel at the temperature of preparation and also at the temperature of use, said liquid mass containing tiny entrapped gas bubbles, said composition having a bulk density of at least 1.0 grams per cubic centimeter.
2. Composition according to claim 1 which also contains a small amount of an inorganic nitrate oxidizing salt which is substantially dissolved both at manufacture and use in said liquid mass to lower its crystallization or fudge point.
3. Composition according to claim 1 which also comprises a finely divided solid fuel suspended in said liquid mass and a thickener for said liquid to substantially increase its viscosity and to stabilize said finely divided suspended fuel against segregation from said liquid mass.
4. Composition according to claim 3 in which the solid fuel comprises finely divided metallic aluminum up to 45 percent by weight of the total composition.
5. Composition according to claim 3 in which the solid fuel comprises a finely divided self-explosive.
6. Composition according to claim 5 in which the self-explosive is pentaerythritol tetranitrate.
7. Composition according to claim 1 which also comprises a finely divided solid fuel suspended in and insoluble in said liquid mass in proportions up to 65 percent by weight of the total.
8. Composition according to claim 1 which comprises 20 to 60 percent by weight of sodium perchlorate, an alcohol, a thickener sufficient to stabilize suspended particles against segregation from said liquid mass, and enough solid suspended particulate fuel to keep overall oxygen balance within limits of -50 to +10 percent.
9. Composition according to claim 8 which has its density lowered sufficiently by incorporation of additional quantities of air bubbles to increase its sensitivity.
10. Composition according to claim 8 wherein the solid fuel is a self-explosive in proportions up to 65 percent by weight of the total composition.
11. Composition according to claim 10 in which the self-explosive is pentaerythritol tetranitrate.
12. Composition according to claim 1 in which the liquid phase comprises 20 to 60 percent by weight of sodium perchlorate, up to 10 percent of sodium nitrate and a thickener.
13. Composition according to claim 12 in which the thickener is a cross-linked gum.
14. Composition according to claim 1 which has its density lowered by an amount of about 0.1 to 0.3 g/cc. by including a dispersed gas therein.
15. Composition according to claim 14 which includes a thickener for the liquid.
16. Composition according to claim 1 wherein said oxidizing salt comprises calcium perchlorate and the organic liquid comprises methanol.
17. Composition according to claim 1 which comprises formamide as an organic liquid.
18. Composition according to claim 1 which comprises a major proportion of a perchlorate and a minor proportion of a nitrate as the oxidizing salt, said composition containing sufficient widely dispersed gas entrapped therein to lower its density about 0.1 to 0.3 grams per cubic centimeter.
19. Composition according to claim 1 in which said oxidizing salt is calcium perchlorate.
20. Composition according to claim 1 where said organic liquid fuel is methanol.
21. A sensitive blasting composition comprising a substantially oxygen-balanced liquid mass which is detonable per se and which includes 0 to 25 percent water and 5 to 30 percent of a water-compatible organic liquid having fuel value of 7,000 British Thermal Units per pound or greater selected from the group consisting of diols; methyl, ethyl or propyl alcohols; aldehydes; ketones; amines; amides and alcohol-amines and mixtures of two or more of these and having dissolved therein an inorganic oxidizing salt, said salt comprising a nitrate selected from the group of alkali metal and alkaline earth metal nitrates, said water-compatible organic liquid having sufficient solvency such that said nitrate remains completely in solution and hence in molecular contact with said organIc liquid at the temperature of manufacture and also at the temperature of use, said liquid mass containing numerous tiny gas bubbles dispersed therein.
22. Composition according to claim 21 in which said organic liquid is methanol.
23. Composition according to claim 21 in which said inorganic oxidizer salt is calcium nitrate.
24. Composition according to claim 21 wherein the organic liquid fuel is ethylene glycol.
Description:
BACKGROUND AND PRIOR ART
In recent years a number of slurry explosives have been developed which are satisfactory for many purposes. Generally speaking, such a slurry comprises an aqueous continuous phase, usually a concentrated aqueous solution of ammonium nitrate, or of ammonium nitrate combined with sodium or other alkali or alkaline earth metal nitrate, or analogous inorganic salt of high oxidation potential, in which particulate fuels and/or sensitizers are suspended. Usually, a part of the oxidizer is suspended, too. Chlorates and perchlorates have been suggested as oxidizer components, as in U.S. Pat. No. 3,282,753, but these seldom have been used. Oxidizers have been suspended in water solutions (U.S. Reissue Pat. No. 25,695) and in solutions containing glycol and other organic solvents (U.S. Pat. No. 3,390,029, for example). thickeners such as guar gum or analogous polysaccharides, starches and the like, are commonly used as thickeners or gelling agents, in minor proportions, in the oxidizer solutions per se as well as in slurries, to increase viscosity of the liquid phase and/or to give the whole sufficient body to prevent gravitational segregation of suspended particles. These suspended particles comprise fuels, such as aluminum particles, for example. Another purpose of thickening is to give the slurry sufficient body to prevent intrusion of ground water into the blasting composition when placed in a hole where ground water is present.
While the slurry explosives and related materials mentioned above are highly satisfactory for many blasting purposes, particularly where columns or charges of large diameter are useful and where relatively high insensitivity is acceptable, they are often quite unsuitable for other uses. One reason is that they are too insensitive for detonation in slender columns, i.e. in boreholes of small diameter. They cannot be detonated, as a rule, with ordinary caps or with detonating cord. Frequently they are difficult and sometimes impossible to detonate at all, even with large and relatively expensive boosters. There is a real need for a mobile fluid or pumpable composition, i.e. a liquid or slurry-type explosive, which is sensitive enough to be detonated in small diameter mass or column, even at low temperatures, by means of an ordinary blasting cap or by means of conventional PETN cored fuse such as "Primacord" or analogous detonating fuse.
More specifically, a requirement has been expressed for an explosive which is cap-sensitive at temperatures as low as -40° C but which, at the same time, is not so sensitive as to be set off by a 30.06 U.S. Army calibre bullet when packaged in a plastic bag. Such specifications are extremely difficult to meet. Uses for such an explosive may include various formations in rock and other places where only small boreholes, fissures, or the like are available to receive the explosive charge. For demolition work, a safe but fluid or fluent explosive of good sensitivity may be needed. Wherever the slurry must flow by gravity into the place where it is to be used, or wherever it can be pumped into place in a relatively slender column, there may be need for a detonable composition having a critical cross-section that is very small, in any case no larger than the borehole diameter and preferably considerably smaller.
For a further example, a need exists for a flowable liquid or slurry explosive that can be dispensed, e.g. somewhat like conventional tooth paste, from a "squeeze" bottle or container containing a 1/4 to 1/2 inch hole. The blasting agent, in some cases, must be usable at a temperature of -40° C. It is desirable that it be sensitive enough so that it can be detonated at such a temperature by use of a cap. These requirements are very difficult to meet. Not all of the compositions of this invention will meet all these requirements, but some of them will and most of them will meet most of the essential requirements. Obviously, the high sensitivity required for detonation in such a slender column may be so inconsistent in some cases with the quality of being safe on impact of a rifle bullet that one requirement or the other must yield. Essentially, however, the required properties are quite well met by the present invention.
A number of attempts have been made in the past to make a "cap-sensitive" slurry, i.e. one which can be used in fairly small boreholes like sticks of dynamite, that is in columns about one to two inches in diameter. Single sticks of most nitroglycerine base or gelatin dynamites usually can be detonated by an ordinary blasting cap. In U.S. Pat. No. 3,153,606, a so-called slurry explosive which is said to be of this type is described. Such an explosive, however, usually has to be very low in content of water and other liquid. In fact, compositions of this type has been referred to as "stick" slurries. Some of these are not mobile slurries at all or, if they could be called slurries, they are so viscous that they do not flow readily. Fluid mobility is desired in many cases and usually is required for purposes of the present invention. In fact, compositions suitable for this invention should be capable of flowing by gravity and of being pumped mechanically through hoses, pipes, and other tubular conduits.
It has also been suggested in the past that water, the usual liquid into which the oxidizer is dissolved, might be "extended" by use of a water compatible organic liquid having fuel valve. Thus, in U.S. Pat. Nos. 3,190,777, 3,235,423, 3,379,587, and others, compositions containing water plus ethylene glycol, formamide, dimethyl formamide, methyl alcohol, and other organic liquids are described. However, the purpose of the liquid organic fluids in these cases is primarily to extend the liquid phase, a purpose somewhat different from the purpose served by the organic liquids of the present invention. Here, the added liquids must be both of significant fuel value and have strong solvency for the oxidizers used in the present invention.
The prior art has described also the use of particulate self-explosives such as TNT and nitrocellulose (smokeless powder) as in U.S. Pat. No. 2,930,685, 3,235,425 and 3,331,717. In these cases, the explosive particles are generally fairly large, and some are entirely unsuitable for use in slender column explosive charges. The present invention contemplates the use of much more finely divided particles of a more sensitive self-explosive type, such as finely divided RDX or PETN, as an additional aspect.
A number of attempts have been made in the past also to produce slurry type blasting agents of higher sensitivity to detonation merely by using substantial quantities of heat producing metals, especially by using very finely divided aluminum metal. In particular, the fine flaked particle grades or so-called paint grade aluminums, having particle sizes such that most will pass through a 325 U.S. sieve, are known to have strong sensitizing properties. These fine flaked metal particles have high surface areas and are particularly beneficial, even in small proportions, for sensitizing aqueous slurries. Such metals can be used as an auxiliary fuel-sensitizer in the present invention.
However, even with paint grade aluminum, the sensitivity of typical prior art slurries, based usually on ammonium nitrate, or AN plus sodium nitrate, generally is not nearly sufficient for purposes of the present invention. Moreover, a mixture of water with such a finely divided aluminum sometimes tends to be unstable because of the aluminum-water reaction which can occur at ordinary temperatures. Such a reaction, of course, can be inhibited to some degree as described in U.S. Pat. No. 3,113,059, but there is a limitation on use of extremely active aluminum in mixtures which contain water.
It has now been found that the sensitivity of an explosive slurry is dependent, to some degree, not only on the temperature at which the slurry is detonated but also on the solubility at that particular temperature of the inorganic oxidizer salts in the liquid. The salt solution, of course, serves as the liquid body continuous phase of a typical slurry. The influence of temperature on sensitivity is illustrated by a typical explosive slurry composition which has a critical diameter at 25° C of 2 inches, but whose critical diameter increases to at least 2.5 inches when the temperature is dropped to 5° C. It appears likely, at least in theory, that if a true solution actually existed at the lower temperature, there should be little or no difference in sensitivity as measured by the critical diameter over this small temperature range. In many and probably in most slurries of the prior art, however, there usually is a very substantial change in critical diameter over a small temperature range. This appears to be due, at least in substantial part, to the fact that whereas a true solution of oxidizer, usually AN, is present in the higher temperature, at a moderately lower temperature some of the oxidizer salt has been precipitated or "fudged" out of solution. With AN particularly, this can occur with a relatively small temperature drop. The solubility of ammonium nitrate in water drops very rapidly with decreasing temperature. This is true, in varying degrees, with most powerful oxidizer salts. In those cases where there is actually a true solution of oxidizer and fuel, which can be maintained over a working temperature range, with oxidizer and fuel being intimately in contact, i.e. substantially in molecular contact with each other in the liquid regardless of the temperature changes, the adverse influence of temperature on the sensitivity and critical diameter of the composition can be either essentially eliminated or at least very significantly reduced.
Hence, one aspect of the present invention is the discovery of the importance of keeping the oxidizer salt in solution, and of ways of doing so, over the range of temperature that is most likely to be encountered in practical use. It appears, in fact, that the sensitivity of an oxidizer solution, other things being equal, can be substantially increased and maintained at an acceptable level over a reasonable temperature range according to the present invention by proper choice of solvent, even when relatively poor fuels or oxidizers are used. This can be accomplished by choice of either solvent or solutes (oxidizer salt) and by making as certain as can be that both a good quantity of an effective fuel and substantially all the oxidizer stay in solution together, and hence in molecular contact, over the expected temperature range.
It is therefore an object of the present invention to obtain in a fluid liquid or slurry type explosive, as nearly as possible, the general order and range of sensitivities of conventional solid or molecular type explosives such a TNT, RDX, and the like. Fluid compositions or slurries thus are prepared wherein at least substantial parts of essential fuel and oxidizer ingredients remain in solution together. Therefore, these compositions are not substantially affected by ordinary temperature changes.
By obtaining and keeping essentially true solutions of oxidizers and fuels in liquid, even in water, the necessary molecular relationships between fuel and oxidizer are maintained. Oxidizers, of course, must be appropriately selected, as well as fuels. By establishing eutectic points for two or more salt-type oxidizers chosen from a select group, it is possible according to this invention to obtain an even better solubility range of oxidizer ingredients in fuel-solvent solution, i.e. over a wider temperature range, than is possible with a single salt. At the same time, it is possible to obtain the advantages of maximum intermolecular contact within the composition by having most or substantially all of the oxidizer and at least a substantial part of the fuel in actual solution together. By this means a liquid body is obtained which is detonable per se.
A further aspect of the present invention is the discovery that the amount of water required can be reduced to or near a practical minimum. Enough solvent is needed to maintain a true solution at the temperature of use. Water may and often does enter into reaction with or in presence of finely divided aluminum or other metal such as magnesium, silicon, or boron, as a vigorous component. This happens provided requisite reaction temperature and other conditions can be reached and maintained. See Cook, "The Science of High Explosives", ACS Monograph No. 139 (1958), page 304.
Another aspect of the invention is its facilitating use of slurries at higher than normal density. Where liquid or slurry explosives can be used, and where they can be detonated at high densities the perchlorates, as oxidizers, have special advantages. For use in molecular-type sensitive slurries, as mentioned above, they have superior properties.
SUMMARY
A liquid or slurry explosive containing in fully dissolved state 20 to 60 percent by weight of alkali or alkaline earth metal perchlorate, or ammonium perchlorate, preferably a sodium or calcium perchlorate or a mixture of these two, 2 to 10 percent of sodium nitrate, 0 to 25 percent of water, and 5 to 25 percent of an organic fuel, which may be diol such as ethylene glycol, or a low molecular weight monoalcohol such as methyl or ethyl alcohol and, optionally, a suspended particulate fuel, such as finely divided self-explosive, or a fine paint grade aluminum in proportions up to 1 or 2 percent, has a sensitivity much greater than is expected in normal slurries. It has a density, even when aerated, of at least 1.0 g/cc. Such a slurry may be fortified by addition of conventional fuels in small or greater proportions when they do not desensitize the composition, such as aluminum, with or without insoluble carbonaceous particles; and/or soluble carbonaceous materials such as carbohydrates, e.g. sucrose or other sugars, and the like, or even with finely divided explosive sensitizers, such as particles of PETN (pentaerythritoltetranitrate). Particular advantages are obtained by using a small amount of thickener and a combination of two or more powerful oxidizer salts, which may include various combinations of sodium or other perchlorate, sodium nitrate, ammonium nitrate, and/or calcium nitrate to establish eutectic solubility properties in organic solvents and or water. Calcium perchlorate is especially useful with some particular fuels, such as methyl or ethyl alcohol. Use of lower alcohols and similar water compatible fuels in liquid form makes it possible to use relatively very little or no water. Particularly, organic liquid fuels and solvents of the group consisting of ethylene glycol, formamide or dimethyl formamide, methyl alcohol, ethyl alcohol, isopropyl alcohol, and mixtures of two or more of these, and/or sucrose, are useful. They preferably are used in solution in glycol or water. Aldehydes, ketones, amines, amides, and alcohol-amines may be used, as long as they are water-soluble or water-compatible and provided they stay in solution, at the temperature of use to a significant degree, when the inorganic oxidizer salt is wholly or at least largely in solution also.
DESCRIPTION OF PREFERRED EMBODIMENT
Example 1
A basic explosive solution was prepared by combining 52 percent by weight of sodium perchlorate, 18.5% water, 5.5% sodium nitrate, and 24% ethylene glycol. This composition had a rather high density of 1.58 g/cc. This is advantageous when it is desired to place as much weight as possible of the explosive and hence maximum energy in a given volume. Of course, the density can be readily reduced and the composition made more sensitive by aerating it with air, or other gas in fine, widely distributed bubbles. This particular composition, which was a liquid free of suspended solids, was not cap-sensitive at this density but it was fully detonable per se. It had a critical diameter at 25° C of 2 inches, which critical value increased to 2 1/2 inches at 5° C. It was possible to initiate a detonation of the same liquid by slurrying into it substantial proportions of a particulate self-explosive. Sixty parts by weight of the above solution, for example, were combined with forty parts by weight of particulate pentaerythritoltetranitrate (PETN), using a small amount of a guar gum, 0.2% by weight, based on the total, to thicken the solution so that the suspended solid particles of PETN would not settle out by gravity. This slurry mixture had a density of 1.78 g/cc. It was cap-sensitive in relatively small masses and in an unconfined column diameter of 0.5 inches (paper tube). It was initiated with a No. 6 blasting cap at various temperatures ranging from 30° C down to as low as -30° C.
EXAMPLE 2
Another example of a slurry made according to the foregoing principles, comprised 90 parts by weight of the solution described above in Example 1, that is, of sodium perchlorate, water, sodium nitrate, and ethylene glycol. To this were added 8 percent by weight of a finely divided aluminum designated "LSA 132" and 2 parts of a still finer aluminum designated "VM 804". The resulting slurry had a viscous consistency, achieved by adding a thickening guar gum in quantities of 0.2 percent, using 0.1 percent of a cross-linking agent, H 3 BO 3 . The composition had a density of 1.43 g/cc. The density indicates there was probably a significant amount of air entrained in the form of fine bubbles. The composition was cap-sensitive in a 3/8-inch diameter. It was initiated with a No. 6 blasting cap, down to a temperature of 0° C. In a diameter of 1/2-inch it was initiated with a similar cap at -15° C. It detonated at -30° C in a 1-inch diameter with a 40 gram, 50/50 pentolite booster.
Comparison of detonation velocities is interesting. The liquid mixture, by itself, had a detonation velocity of 2,300 m/sec., whereas the same mixture with aluminum added had a detonation velocity of 5,300 m/sec.
A slurry made up of the liquid of Exampes 1 and 2 in proportions of 60 percent, with 40% PETN suspended therein and unconfined, was not detonated by 30.06 rifle bullet impact. However, the aluminum mixture of Example 2 did detonate when fired by such a bullet. The solution itself, without PETN or aluminum, was found on different thermal analysis to be stable up to 300° C. It showed an exotherm when PETN was added at 170° C and exploded spontaneously at 178° C. The aluminum mixture was stable up to 265° C.
Example 3
Another composition was prepared consisting of 31.2 percent by weight of sodium perchlorate, 11.1% water, 3.3% sodium nitrate, and 14.4% ethylene glycol, as the liquid menstruum, and 0.1% guar gum thickener, plus 40 percent of particulate PETN obtained from a source in Sweden. The solution without the PETN was explosive per se. This slurry, including PETN, had a calculated energy, Q, of 1,085 cal/g and a density of 1.78 g/cc. PETN as used here was made to a particle size of approximately 90 percent between -35 and +100 mesh. Attempts to make the same formulation but with a finer PETN, of which 40 percent would pass a 325 mesh sieve failed, apparently because the mix became too viscous and became a semi-gel at -40° C. The solution per se required an initiator more powerful than a No. 6 blasting cap to detonate it in a 3 inches diameter column at 30° C.
Under some conditions, it appears that other explosives than PETN can be used, such as RDX or TNT. It was found in experiments, however, that finely divided RDX was less satisfactory than PETN at very low temperatures. It is expected that TNT, which is less sensitive would be even less satisfactory.
EXAMPLE 4
Another composition was made up of 22 percent by weight of sodium perchlorate, 17% water, 3% sodium nitrate, 8% ethylene glycol, all in solution, to which were added 0.2% of guar gum thickener, and 50 percent by weight of finely divided PETN obtained from U.S. manufacturer. This slurry failed to shoot at 20° C in 1/2-inch columns with both No. 6 and No. 8 caps. In a 1-inch column it failed with a No. 6 cap but fired satisfactorily with a No. 8 cap. The explosion made a substantial dent in a 1/2-inch steel plate. This slurry had a density of 1.77 g/cc and was very viscous at 20° C.
EXAMPLE 5
Using 60 percent of the same liquid composition as that of Example 1, which had an oxygen balance per se of -1.3, with 40 percent by weight of finely ground PETN (about 40 percent of which passed through a 325 mesh Tyler screen), the resulting composition was mobile enough to flow slowly, i.e. could be pushed out of a squeeze bottle, but it was almost too dry to call a slurry, at 20° C. At -40° C it set up solid. It detonated with a No. 6 cap in a 3/8-inch column. Using 50 percent of the same liquid and 50 percent by weight of the same PETN, the composition was much too dry to be considered a slurry. A mixture of 65 percent of the solution and 35 percent fine PETN was somewhat more fluid than the 60-40 mix but still quite putty-like in consistency. It had a density of 1.81 g/cc. This PETN contained 40 percent fine enough to pass a 325 mesh Tyler screen. The 65-35 mix detonated in 1/2-inch diameter at -25° C. When 5 percent of paint grade aluminum was added, the mixture was too dry to flow and would not detonate with a cap. This illustrates the point that the compositions with both the oxidizer and the fuel largely or entirely in solution can be more sensitive than drier mixes. Ordinarily, the drier slurries are easier to detonate than wet ones.
EXAMPLE 6
A composition was made up of the following ingredients, percentage by weight:
Sodium perchlorate 19% Water 15.0 Sodium nitrate 2.6 Ethylene glycol 3.4 Boric acid 0.05 Guar gum 0.2 Fine aluminum 10.0 PETN - fine ground 50.0
This was too dry at 20° C to be called a slurry. It had a density of 1.82 g/cc at 20° C and detonated in a 1/2-inch column, with a No. 6 blasting cap, making a dent in a 1/2-inch thick steel plate. It detonated also at 20° C in a 1/4-inch column, with a similar No. 6 blasting cap. The PETN used here wa a medium fine ground product from Trojan Powder Co. of which 40 percent passed a 325 mesh sieve.
EXAMPLE 7
Another composition was preared consisting of 33.3 percent by weight of sodium perchlorate, 3.5 percent sodium nitrate, 11.8% water, 15.4% ethylene glycol, 1% guar gum thickener, and 33 and 2 percent respectively of the fine and ultrafine aluminums described in Example 2. This mix, with an oxygen balance of -33.4 percent, had a density of 1.65 g/cc and a detonation velocity of 5,390 m/sec.
EXAMPLE 8
Another composition was prepared with a solution containing 47 parts by weight of sodium perchlorate, 5 parts of sodium nitrate, b 24 parts water and 21 parts ethylene glycol. To this solution was added 1 part of a guar gum thickener and small quantities of gas producing agents to aerate the slurry and reduce its density. The properites of the initial solution and the solution after being thickened and gassed are compared below:
Solution with Thickener Solution Alone and Gassing Agents Density (g/cc) 1.54 1.25 Critical Diameter (inches) 3 (minimum) 0.75 Detonation Velocity (m/sec) less than 2500 4800 Minimum Booster 30 grams No. 6 Blasting Cap Pentolite
While the foregoing examples deal largely with sodium perchlorate and sodium nitrate based explosives, i.e. where sodium perchlorate is the major oxidizer used in he solution, other perchlorates and nitrates can be substituted in part or even in full.
Calcium nitrate, though less sensitive in most cases than the perchlorates, is a particularly desirable ingredient in liquid explosives which contain methyl alcohol. Calcium nitrate has good solubility in water, in methyl alcohol, ethyl alcohol, and in ethylene glycol, even at low temperatures. Alone, or in combination with sodium perchlorate, it has a low eutectic solubility point. In proportions as high as 70 to 75 percent of the total solution, commercial grades of calcium nitrate, which contain 14 to 16 percent water of crystallization and normally contain a few percent of ammonium nitrate, have better (i.e. lower) fudge points than more dilute solutions of ammonium nitrate combined with sodium nitrate. See U.S. Pat. No. 3,249,476. Data are given in Table 1. ##SPC1##
Obviously, calcium nitrate has desirable properties where it is desired to keep the oxidizer in solution (low fudge point) as required by the present invention.
Calcium perchlorate as oxidizer or as a part of it, and methyl or ethyl alcohol, as the liquid fuel, or part of it, appear to have merit because they both are highly soluble in water and have good reactivity.
From the foregoing, a preferred explosive composition will be seen to include both fuel and oxidizer in the solution, and preferably all or substantially all of the oxidizer is in the dissolved state. This component comprises from as little as 20 to about as much as 60 percent by weight of oxidizer, and preferably includes at least one perchlorate selected from the group which consists of ammonium perchlorate, alkali metal perchlorates, and alkaline earth metal perchlorates. The perchlorate is the major oxidizer component but it is combined together with a small amount of at least one other powerful oxidizer salt, preferably a nitrate selected from the group which consists of ammonium, alkali metal and alkaline earth metal nitrates. The salts should be selected to give a low eutectic solubility or "fudge" point temperature-wise so that they will not salt out of the composition to any large degree at the temperature of use.
The liquid may comprise 0 to 25 percent of water and 5 to 30 percent of fuel; usually ethylene glycol is preferred but it can sometimes be replaced or supplemented by one of the simple alcohols. A combination of about 0 to 20 percent of water and a little more glycol or other organic solvent, say 15 to 25 percent is particularly desirable to make the explosive solution per se. The organic liquid chosen should have at least reasonably good combustion value, 7,000 btu. per pound or greater. Diethylene glycol has a value of about 7,600, methyl alcohol about 9,500, and ethyl alchol about 13,600 btu., but the former is usually preferred for this invention.
To maintain its integrity, in presence or absence of water, even when no insolubles are added, this liquid preferably y is thickened at least moderately by incorporation of a small amount of a thickener. Guar gum in proportions of 0.10 to 1.0 percent by weight is particularly suitable. Starches may be used in larger quantities. Cellulosic gums and their derivatives are required in some cases. Examples of such gums are methyl cellulose and hydroxyethylcellulose. The gum or starch preferably is cross-linked by use of a cross-linking agent such as borax or an alkali metal dichromate. This not only guards against undue water intrusion from extraneous sources; it helps to hold suspended fuel or self-explosive particles against segregation. It also enables the liquid phase to trap and hold tiny bubbles of air or other gas which are needed for increasing sensitivity. Such air or other gas may be introduced by mixing or beating the thickened liquid per se or by stirring particulate solids into the liquid menstruum. Particles of fuels and/or self-explosives, such as aluminum and/or particulate PETN, RDX, TNT, and the like, may be added. The liquid mass per se is a potent explosive, and is substantially oxygen-balanced, without these particulate fuels or self-explosives. In this respect it is quite distinct from the prior art slurries.
When particulate non-explosive fuels are used, those preferred comprise aluminum, sulfur, and carbonaceous solids such as ground coal or gilsonite. Preferred self-explosives are PETN, RDX, Composition B, EDNA (ethylenediaminedinitrate), or TNT. These should be chosen and used in proportions suitable to impart the desired sensitivity and to hold the oxygen balance within reasonable limits, in any case between -50 and +10 percent. For finely divided aluminum, proportions up to 45 percent of the total composition, by weight, may be used. Proportions of 20 to 40 percent are preferred when maximum power is needed. Part of this aluminum may be paint grade fine flaked aluminum; proportions of 1 to 2 contribute to sensitivity. Sensitive self-explosives such as PETN may be used in proportions up to 65 percent by weight of the total slurry. Obviously mixtures of PETN, RDX, Composition B, TNT, and aluminum, or any two or more of these may be used. Since the liquid phase per se is fairly well oxygen-balanced, the particulate materials should bring at least part of their own oxygen (as with self-explosives) or should be reactive with water (as is aluminum under favorable conditions when water is present), or solid oxidizer should be present in the particulate or suspended phase. This may be the principal oxidizer (perchlorate) partly precipitated from the liquid or added separately, or it may be a separate oxidizer salt such as AN, SN, calcium nitrate, etc., added separately. As already noted, use of a small amount of one or more of these salts is often preferred because it lowers the "fudge" point.
The compositions of this invention are particularly versatile. They can be "tailor-made" both to the desired sensitivity and the desired power by appropriate selection of components by type and proportions. This has not been true of the prior art slurries which, in general, are much less sensitive and less subject to sensitivity control. The liquid components that are high in dissolved sodium perchlorate or other perchlorate, and high also in ethylene glycol or other organic fuel molecularly adjacent to each other, are quite sensitive per se. By adding substantial proportions of finely ground self-explosives of the more sensitive type, which are reasonably in oxygen balance per se, such as PETN, still more highly sensitive products are obtained. These can propagate a detonation wave in a very slender column, e.g. a column as small as 1/2-inch or less in diameter or mean cross-section.
Where such high sensitive explosives are not needed, the content of self-explosive, such as PETN, may be reduced, or eliminated. Alternatively, this particular self-explosive may be replaced fully or in part by one or more of the other self-explosives named above and/or by aluminum powder.
In many cases, addition of a small amount of very finely divided aluminum, especially the flaked paint grade, is desirable because of its high fuel or energy value. It contributes very substantially to high sensitivity, even in well balanced liquid compositions. It is desirable, also, for the mechanical handling properties it imparts to the composition. It helps to lubricate the flow of the composition through conduits and orifices as when it is dispensed through valves, pumps, hoses and other flow devices.
Two further examples were made. The first contained 73.5% calcium perchlorate and 26.5% methyl alcohol. This solution per se had a density of 1.54 g/cc and was detonated in a 0.75-inch diameter column with a 9-gram Pentolite booster. The second contained 60% lithium perchlorate and 40% formamide. This solution per se had the density of 1.57 g/cc and was detonated in a 1-inch diameter column with a 9-gram Pentolite booster.
It will be obvious that the above and other modifications, which will suggest themselves to those skilled in the art, can be made within the spirit and purpose of the invention.
In recent years a number of slurry explosives have been developed which are satisfactory for many purposes. Generally speaking, such a slurry comprises an aqueous continuous phase, usually a concentrated aqueous solution of ammonium nitrate, or of ammonium nitrate combined with sodium or other alkali or alkaline earth metal nitrate, or analogous inorganic salt of high oxidation potential, in which particulate fuels and/or sensitizers are suspended. Usually, a part of the oxidizer is suspended, too. Chlorates and perchlorates have been suggested as oxidizer components, as in U.S. Pat. No. 3,282,753, but these seldom have been used. Oxidizers have been suspended in water solutions (U.S. Reissue Pat. No. 25,695) and in solutions containing glycol and other organic solvents (U.S. Pat. No. 3,390,029, for example). thickeners such as guar gum or analogous polysaccharides, starches and the like, are commonly used as thickeners or gelling agents, in minor proportions, in the oxidizer solutions per se as well as in slurries, to increase viscosity of the liquid phase and/or to give the whole sufficient body to prevent gravitational segregation of suspended particles. These suspended particles comprise fuels, such as aluminum particles, for example. Another purpose of thickening is to give the slurry sufficient body to prevent intrusion of ground water into the blasting composition when placed in a hole where ground water is present.
While the slurry explosives and related materials mentioned above are highly satisfactory for many blasting purposes, particularly where columns or charges of large diameter are useful and where relatively high insensitivity is acceptable, they are often quite unsuitable for other uses. One reason is that they are too insensitive for detonation in slender columns, i.e. in boreholes of small diameter. They cannot be detonated, as a rule, with ordinary caps or with detonating cord. Frequently they are difficult and sometimes impossible to detonate at all, even with large and relatively expensive boosters. There is a real need for a mobile fluid or pumpable composition, i.e. a liquid or slurry-type explosive, which is sensitive enough to be detonated in small diameter mass or column, even at low temperatures, by means of an ordinary blasting cap or by means of conventional PETN cored fuse such as "Primacord" or analogous detonating fuse.
More specifically, a requirement has been expressed for an explosive which is cap-sensitive at temperatures as low as -40° C but which, at the same time, is not so sensitive as to be set off by a 30.06 U.S. Army calibre bullet when packaged in a plastic bag. Such specifications are extremely difficult to meet. Uses for such an explosive may include various formations in rock and other places where only small boreholes, fissures, or the like are available to receive the explosive charge. For demolition work, a safe but fluid or fluent explosive of good sensitivity may be needed. Wherever the slurry must flow by gravity into the place where it is to be used, or wherever it can be pumped into place in a relatively slender column, there may be need for a detonable composition having a critical cross-section that is very small, in any case no larger than the borehole diameter and preferably considerably smaller.
For a further example, a need exists for a flowable liquid or slurry explosive that can be dispensed, e.g. somewhat like conventional tooth paste, from a "squeeze" bottle or container containing a 1/4 to 1/2 inch hole. The blasting agent, in some cases, must be usable at a temperature of -40° C. It is desirable that it be sensitive enough so that it can be detonated at such a temperature by use of a cap. These requirements are very difficult to meet. Not all of the compositions of this invention will meet all these requirements, but some of them will and most of them will meet most of the essential requirements. Obviously, the high sensitivity required for detonation in such a slender column may be so inconsistent in some cases with the quality of being safe on impact of a rifle bullet that one requirement or the other must yield. Essentially, however, the required properties are quite well met by the present invention.
A number of attempts have been made in the past to make a "cap-sensitive" slurry, i.e. one which can be used in fairly small boreholes like sticks of dynamite, that is in columns about one to two inches in diameter. Single sticks of most nitroglycerine base or gelatin dynamites usually can be detonated by an ordinary blasting cap. In U.S. Pat. No. 3,153,606, a so-called slurry explosive which is said to be of this type is described. Such an explosive, however, usually has to be very low in content of water and other liquid. In fact, compositions of this type has been referred to as "stick" slurries. Some of these are not mobile slurries at all or, if they could be called slurries, they are so viscous that they do not flow readily. Fluid mobility is desired in many cases and usually is required for purposes of the present invention. In fact, compositions suitable for this invention should be capable of flowing by gravity and of being pumped mechanically through hoses, pipes, and other tubular conduits.
It has also been suggested in the past that water, the usual liquid into which the oxidizer is dissolved, might be "extended" by use of a water compatible organic liquid having fuel valve. Thus, in U.S. Pat. Nos. 3,190,777, 3,235,423, 3,379,587, and others, compositions containing water plus ethylene glycol, formamide, dimethyl formamide, methyl alcohol, and other organic liquids are described. However, the purpose of the liquid organic fluids in these cases is primarily to extend the liquid phase, a purpose somewhat different from the purpose served by the organic liquids of the present invention. Here, the added liquids must be both of significant fuel value and have strong solvency for the oxidizers used in the present invention.
The prior art has described also the use of particulate self-explosives such as TNT and nitrocellulose (smokeless powder) as in U.S. Pat. No. 2,930,685, 3,235,425 and 3,331,717. In these cases, the explosive particles are generally fairly large, and some are entirely unsuitable for use in slender column explosive charges. The present invention contemplates the use of much more finely divided particles of a more sensitive self-explosive type, such as finely divided RDX or PETN, as an additional aspect.
A number of attempts have been made in the past also to produce slurry type blasting agents of higher sensitivity to detonation merely by using substantial quantities of heat producing metals, especially by using very finely divided aluminum metal. In particular, the fine flaked particle grades or so-called paint grade aluminums, having particle sizes such that most will pass through a 325 U.S. sieve, are known to have strong sensitizing properties. These fine flaked metal particles have high surface areas and are particularly beneficial, even in small proportions, for sensitizing aqueous slurries. Such metals can be used as an auxiliary fuel-sensitizer in the present invention.
However, even with paint grade aluminum, the sensitivity of typical prior art slurries, based usually on ammonium nitrate, or AN plus sodium nitrate, generally is not nearly sufficient for purposes of the present invention. Moreover, a mixture of water with such a finely divided aluminum sometimes tends to be unstable because of the aluminum-water reaction which can occur at ordinary temperatures. Such a reaction, of course, can be inhibited to some degree as described in U.S. Pat. No. 3,113,059, but there is a limitation on use of extremely active aluminum in mixtures which contain water.
It has now been found that the sensitivity of an explosive slurry is dependent, to some degree, not only on the temperature at which the slurry is detonated but also on the solubility at that particular temperature of the inorganic oxidizer salts in the liquid. The salt solution, of course, serves as the liquid body continuous phase of a typical slurry. The influence of temperature on sensitivity is illustrated by a typical explosive slurry composition which has a critical diameter at 25° C of 2 inches, but whose critical diameter increases to at least 2.5 inches when the temperature is dropped to 5° C. It appears likely, at least in theory, that if a true solution actually existed at the lower temperature, there should be little or no difference in sensitivity as measured by the critical diameter over this small temperature range. In many and probably in most slurries of the prior art, however, there usually is a very substantial change in critical diameter over a small temperature range. This appears to be due, at least in substantial part, to the fact that whereas a true solution of oxidizer, usually AN, is present in the higher temperature, at a moderately lower temperature some of the oxidizer salt has been precipitated or "fudged" out of solution. With AN particularly, this can occur with a relatively small temperature drop. The solubility of ammonium nitrate in water drops very rapidly with decreasing temperature. This is true, in varying degrees, with most powerful oxidizer salts. In those cases where there is actually a true solution of oxidizer and fuel, which can be maintained over a working temperature range, with oxidizer and fuel being intimately in contact, i.e. substantially in molecular contact with each other in the liquid regardless of the temperature changes, the adverse influence of temperature on the sensitivity and critical diameter of the composition can be either essentially eliminated or at least very significantly reduced.
Hence, one aspect of the present invention is the discovery of the importance of keeping the oxidizer salt in solution, and of ways of doing so, over the range of temperature that is most likely to be encountered in practical use. It appears, in fact, that the sensitivity of an oxidizer solution, other things being equal, can be substantially increased and maintained at an acceptable level over a reasonable temperature range according to the present invention by proper choice of solvent, even when relatively poor fuels or oxidizers are used. This can be accomplished by choice of either solvent or solutes (oxidizer salt) and by making as certain as can be that both a good quantity of an effective fuel and substantially all the oxidizer stay in solution together, and hence in molecular contact, over the expected temperature range.
It is therefore an object of the present invention to obtain in a fluid liquid or slurry type explosive, as nearly as possible, the general order and range of sensitivities of conventional solid or molecular type explosives such a TNT, RDX, and the like. Fluid compositions or slurries thus are prepared wherein at least substantial parts of essential fuel and oxidizer ingredients remain in solution together. Therefore, these compositions are not substantially affected by ordinary temperature changes.
By obtaining and keeping essentially true solutions of oxidizers and fuels in liquid, even in water, the necessary molecular relationships between fuel and oxidizer are maintained. Oxidizers, of course, must be appropriately selected, as well as fuels. By establishing eutectic points for two or more salt-type oxidizers chosen from a select group, it is possible according to this invention to obtain an even better solubility range of oxidizer ingredients in fuel-solvent solution, i.e. over a wider temperature range, than is possible with a single salt. At the same time, it is possible to obtain the advantages of maximum intermolecular contact within the composition by having most or substantially all of the oxidizer and at least a substantial part of the fuel in actual solution together. By this means a liquid body is obtained which is detonable per se.
A further aspect of the present invention is the discovery that the amount of water required can be reduced to or near a practical minimum. Enough solvent is needed to maintain a true solution at the temperature of use. Water may and often does enter into reaction with or in presence of finely divided aluminum or other metal such as magnesium, silicon, or boron, as a vigorous component. This happens provided requisite reaction temperature and other conditions can be reached and maintained. See Cook, "The Science of High Explosives", ACS Monograph No. 139 (1958), page 304.
Another aspect of the invention is its facilitating use of slurries at higher than normal density. Where liquid or slurry explosives can be used, and where they can be detonated at high densities the perchlorates, as oxidizers, have special advantages. For use in molecular-type sensitive slurries, as mentioned above, they have superior properties.
SUMMARY
A liquid or slurry explosive containing in fully dissolved state 20 to 60 percent by weight of alkali or alkaline earth metal perchlorate, or ammonium perchlorate, preferably a sodium or calcium perchlorate or a mixture of these two, 2 to 10 percent of sodium nitrate, 0 to 25 percent of water, and 5 to 25 percent of an organic fuel, which may be diol such as ethylene glycol, or a low molecular weight monoalcohol such as methyl or ethyl alcohol and, optionally, a suspended particulate fuel, such as finely divided self-explosive, or a fine paint grade aluminum in proportions up to 1 or 2 percent, has a sensitivity much greater than is expected in normal slurries. It has a density, even when aerated, of at least 1.0 g/cc. Such a slurry may be fortified by addition of conventional fuels in small or greater proportions when they do not desensitize the composition, such as aluminum, with or without insoluble carbonaceous particles; and/or soluble carbonaceous materials such as carbohydrates, e.g. sucrose or other sugars, and the like, or even with finely divided explosive sensitizers, such as particles of PETN (pentaerythritoltetranitrate). Particular advantages are obtained by using a small amount of thickener and a combination of two or more powerful oxidizer salts, which may include various combinations of sodium or other perchlorate, sodium nitrate, ammonium nitrate, and/or calcium nitrate to establish eutectic solubility properties in organic solvents and or water. Calcium perchlorate is especially useful with some particular fuels, such as methyl or ethyl alcohol. Use of lower alcohols and similar water compatible fuels in liquid form makes it possible to use relatively very little or no water. Particularly, organic liquid fuels and solvents of the group consisting of ethylene glycol, formamide or dimethyl formamide, methyl alcohol, ethyl alcohol, isopropyl alcohol, and mixtures of two or more of these, and/or sucrose, are useful. They preferably are used in solution in glycol or water. Aldehydes, ketones, amines, amides, and alcohol-amines may be used, as long as they are water-soluble or water-compatible and provided they stay in solution, at the temperature of use to a significant degree, when the inorganic oxidizer salt is wholly or at least largely in solution also.
DESCRIPTION OF PREFERRED EMBODIMENT
Example 1
A basic explosive solution was prepared by combining 52 percent by weight of sodium perchlorate, 18.5% water, 5.5% sodium nitrate, and 24% ethylene glycol. This composition had a rather high density of 1.58 g/cc. This is advantageous when it is desired to place as much weight as possible of the explosive and hence maximum energy in a given volume. Of course, the density can be readily reduced and the composition made more sensitive by aerating it with air, or other gas in fine, widely distributed bubbles. This particular composition, which was a liquid free of suspended solids, was not cap-sensitive at this density but it was fully detonable per se. It had a critical diameter at 25° C of 2 inches, which critical value increased to 2 1/2 inches at 5° C. It was possible to initiate a detonation of the same liquid by slurrying into it substantial proportions of a particulate self-explosive. Sixty parts by weight of the above solution, for example, were combined with forty parts by weight of particulate pentaerythritoltetranitrate (PETN), using a small amount of a guar gum, 0.2% by weight, based on the total, to thicken the solution so that the suspended solid particles of PETN would not settle out by gravity. This slurry mixture had a density of 1.78 g/cc. It was cap-sensitive in relatively small masses and in an unconfined column diameter of 0.5 inches (paper tube). It was initiated with a No. 6 blasting cap at various temperatures ranging from 30° C down to as low as -30° C.
EXAMPLE 2
Another example of a slurry made according to the foregoing principles, comprised 90 parts by weight of the solution described above in Example 1, that is, of sodium perchlorate, water, sodium nitrate, and ethylene glycol. To this were added 8 percent by weight of a finely divided aluminum designated "LSA 132" and 2 parts of a still finer aluminum designated "VM 804". The resulting slurry had a viscous consistency, achieved by adding a thickening guar gum in quantities of 0.2 percent, using 0.1 percent of a cross-linking agent, H 3 BO 3 . The composition had a density of 1.43 g/cc. The density indicates there was probably a significant amount of air entrained in the form of fine bubbles. The composition was cap-sensitive in a 3/8-inch diameter. It was initiated with a No. 6 blasting cap, down to a temperature of 0° C. In a diameter of 1/2-inch it was initiated with a similar cap at -15° C. It detonated at -30° C in a 1-inch diameter with a 40 gram, 50/50 pentolite booster.
Comparison of detonation velocities is interesting. The liquid mixture, by itself, had a detonation velocity of 2,300 m/sec., whereas the same mixture with aluminum added had a detonation velocity of 5,300 m/sec.
A slurry made up of the liquid of Exampes 1 and 2 in proportions of 60 percent, with 40% PETN suspended therein and unconfined, was not detonated by 30.06 rifle bullet impact. However, the aluminum mixture of Example 2 did detonate when fired by such a bullet. The solution itself, without PETN or aluminum, was found on different thermal analysis to be stable up to 300° C. It showed an exotherm when PETN was added at 170° C and exploded spontaneously at 178° C. The aluminum mixture was stable up to 265° C.
Example 3
Another composition was prepared consisting of 31.2 percent by weight of sodium perchlorate, 11.1% water, 3.3% sodium nitrate, and 14.4% ethylene glycol, as the liquid menstruum, and 0.1% guar gum thickener, plus 40 percent of particulate PETN obtained from a source in Sweden. The solution without the PETN was explosive per se. This slurry, including PETN, had a calculated energy, Q, of 1,085 cal/g and a density of 1.78 g/cc. PETN as used here was made to a particle size of approximately 90 percent between -35 and +100 mesh. Attempts to make the same formulation but with a finer PETN, of which 40 percent would pass a 325 mesh sieve failed, apparently because the mix became too viscous and became a semi-gel at -40° C. The solution per se required an initiator more powerful than a No. 6 blasting cap to detonate it in a 3 inches diameter column at 30° C.
Under some conditions, it appears that other explosives than PETN can be used, such as RDX or TNT. It was found in experiments, however, that finely divided RDX was less satisfactory than PETN at very low temperatures. It is expected that TNT, which is less sensitive would be even less satisfactory.
EXAMPLE 4
Another composition was made up of 22 percent by weight of sodium perchlorate, 17% water, 3% sodium nitrate, 8% ethylene glycol, all in solution, to which were added 0.2% of guar gum thickener, and 50 percent by weight of finely divided PETN obtained from U.S. manufacturer. This slurry failed to shoot at 20° C in 1/2-inch columns with both No. 6 and No. 8 caps. In a 1-inch column it failed with a No. 6 cap but fired satisfactorily with a No. 8 cap. The explosion made a substantial dent in a 1/2-inch steel plate. This slurry had a density of 1.77 g/cc and was very viscous at 20° C.
EXAMPLE 5
Using 60 percent of the same liquid composition as that of Example 1, which had an oxygen balance per se of -1.3, with 40 percent by weight of finely ground PETN (about 40 percent of which passed through a 325 mesh Tyler screen), the resulting composition was mobile enough to flow slowly, i.e. could be pushed out of a squeeze bottle, but it was almost too dry to call a slurry, at 20° C. At -40° C it set up solid. It detonated with a No. 6 cap in a 3/8-inch column. Using 50 percent of the same liquid and 50 percent by weight of the same PETN, the composition was much too dry to be considered a slurry. A mixture of 65 percent of the solution and 35 percent fine PETN was somewhat more fluid than the 60-40 mix but still quite putty-like in consistency. It had a density of 1.81 g/cc. This PETN contained 40 percent fine enough to pass a 325 mesh Tyler screen. The 65-35 mix detonated in 1/2-inch diameter at -25° C. When 5 percent of paint grade aluminum was added, the mixture was too dry to flow and would not detonate with a cap. This illustrates the point that the compositions with both the oxidizer and the fuel largely or entirely in solution can be more sensitive than drier mixes. Ordinarily, the drier slurries are easier to detonate than wet ones.
EXAMPLE 6
A composition was made up of the following ingredients, percentage by weight:
Sodium perchlorate 19% Water 15.0 Sodium nitrate 2.6 Ethylene glycol 3.4 Boric acid 0.05 Guar gum 0.2 Fine aluminum 10.0 PETN - fine ground 50.0
This was too dry at 20° C to be called a slurry. It had a density of 1.82 g/cc at 20° C and detonated in a 1/2-inch column, with a No. 6 blasting cap, making a dent in a 1/2-inch thick steel plate. It detonated also at 20° C in a 1/4-inch column, with a similar No. 6 blasting cap. The PETN used here wa a medium fine ground product from Trojan Powder Co. of which 40 percent passed a 325 mesh sieve.
EXAMPLE 7
Another composition was preared consisting of 33.3 percent by weight of sodium perchlorate, 3.5 percent sodium nitrate, 11.8% water, 15.4% ethylene glycol, 1% guar gum thickener, and 33 and 2 percent respectively of the fine and ultrafine aluminums described in Example 2. This mix, with an oxygen balance of -33.4 percent, had a density of 1.65 g/cc and a detonation velocity of 5,390 m/sec.
EXAMPLE 8
Another composition was prepared with a solution containing 47 parts by weight of sodium perchlorate, 5 parts of sodium nitrate, b 24 parts water and 21 parts ethylene glycol. To this solution was added 1 part of a guar gum thickener and small quantities of gas producing agents to aerate the slurry and reduce its density. The properites of the initial solution and the solution after being thickened and gassed are compared below:
Solution with Thickener Solution Alone and Gassing Agents Density (g/cc) 1.54 1.25 Critical Diameter (inches) 3 (minimum) 0.75 Detonation Velocity (m/sec) less than 2500 4800 Minimum Booster 30 grams No. 6 Blasting Cap Pentolite
While the foregoing examples deal largely with sodium perchlorate and sodium nitrate based explosives, i.e. where sodium perchlorate is the major oxidizer used in he solution, other perchlorates and nitrates can be substituted in part or even in full.
Calcium nitrate, though less sensitive in most cases than the perchlorates, is a particularly desirable ingredient in liquid explosives which contain methyl alcohol. Calcium nitrate has good solubility in water, in methyl alcohol, ethyl alcohol, and in ethylene glycol, even at low temperatures. Alone, or in combination with sodium perchlorate, it has a low eutectic solubility point. In proportions as high as 70 to 75 percent of the total solution, commercial grades of calcium nitrate, which contain 14 to 16 percent water of crystallization and normally contain a few percent of ammonium nitrate, have better (i.e. lower) fudge points than more dilute solutions of ammonium nitrate combined with sodium nitrate. See U.S. Pat. No. 3,249,476. Data are given in Table 1. ##SPC1##
Obviously, calcium nitrate has desirable properties where it is desired to keep the oxidizer in solution (low fudge point) as required by the present invention.
Calcium perchlorate as oxidizer or as a part of it, and methyl or ethyl alcohol, as the liquid fuel, or part of it, appear to have merit because they both are highly soluble in water and have good reactivity.
From the foregoing, a preferred explosive composition will be seen to include both fuel and oxidizer in the solution, and preferably all or substantially all of the oxidizer is in the dissolved state. This component comprises from as little as 20 to about as much as 60 percent by weight of oxidizer, and preferably includes at least one perchlorate selected from the group which consists of ammonium perchlorate, alkali metal perchlorates, and alkaline earth metal perchlorates. The perchlorate is the major oxidizer component but it is combined together with a small amount of at least one other powerful oxidizer salt, preferably a nitrate selected from the group which consists of ammonium, alkali metal and alkaline earth metal nitrates. The salts should be selected to give a low eutectic solubility or "fudge" point temperature-wise so that they will not salt out of the composition to any large degree at the temperature of use.
The liquid may comprise 0 to 25 percent of water and 5 to 30 percent of fuel; usually ethylene glycol is preferred but it can sometimes be replaced or supplemented by one of the simple alcohols. A combination of about 0 to 20 percent of water and a little more glycol or other organic solvent, say 15 to 25 percent is particularly desirable to make the explosive solution per se. The organic liquid chosen should have at least reasonably good combustion value, 7,000 btu. per pound or greater. Diethylene glycol has a value of about 7,600, methyl alcohol about 9,500, and ethyl alchol about 13,600 btu., but the former is usually preferred for this invention.
To maintain its integrity, in presence or absence of water, even when no insolubles are added, this liquid preferably y is thickened at least moderately by incorporation of a small amount of a thickener. Guar gum in proportions of 0.10 to 1.0 percent by weight is particularly suitable. Starches may be used in larger quantities. Cellulosic gums and their derivatives are required in some cases. Examples of such gums are methyl cellulose and hydroxyethylcellulose. The gum or starch preferably is cross-linked by use of a cross-linking agent such as borax or an alkali metal dichromate. This not only guards against undue water intrusion from extraneous sources; it helps to hold suspended fuel or self-explosive particles against segregation. It also enables the liquid phase to trap and hold tiny bubbles of air or other gas which are needed for increasing sensitivity. Such air or other gas may be introduced by mixing or beating the thickened liquid per se or by stirring particulate solids into the liquid menstruum. Particles of fuels and/or self-explosives, such as aluminum and/or particulate PETN, RDX, TNT, and the like, may be added. The liquid mass per se is a potent explosive, and is substantially oxygen-balanced, without these particulate fuels or self-explosives. In this respect it is quite distinct from the prior art slurries.
When particulate non-explosive fuels are used, those preferred comprise aluminum, sulfur, and carbonaceous solids such as ground coal or gilsonite. Preferred self-explosives are PETN, RDX, Composition B, EDNA (ethylenediaminedinitrate), or TNT. These should be chosen and used in proportions suitable to impart the desired sensitivity and to hold the oxygen balance within reasonable limits, in any case between -50 and +10 percent. For finely divided aluminum, proportions up to 45 percent of the total composition, by weight, may be used. Proportions of 20 to 40 percent are preferred when maximum power is needed. Part of this aluminum may be paint grade fine flaked aluminum; proportions of 1 to 2 contribute to sensitivity. Sensitive self-explosives such as PETN may be used in proportions up to 65 percent by weight of the total slurry. Obviously mixtures of PETN, RDX, Composition B, TNT, and aluminum, or any two or more of these may be used. Since the liquid phase per se is fairly well oxygen-balanced, the particulate materials should bring at least part of their own oxygen (as with self-explosives) or should be reactive with water (as is aluminum under favorable conditions when water is present), or solid oxidizer should be present in the particulate or suspended phase. This may be the principal oxidizer (perchlorate) partly precipitated from the liquid or added separately, or it may be a separate oxidizer salt such as AN, SN, calcium nitrate, etc., added separately. As already noted, use of a small amount of one or more of these salts is often preferred because it lowers the "fudge" point.
The compositions of this invention are particularly versatile. They can be "tailor-made" both to the desired sensitivity and the desired power by appropriate selection of components by type and proportions. This has not been true of the prior art slurries which, in general, are much less sensitive and less subject to sensitivity control. The liquid components that are high in dissolved sodium perchlorate or other perchlorate, and high also in ethylene glycol or other organic fuel molecularly adjacent to each other, are quite sensitive per se. By adding substantial proportions of finely ground self-explosives of the more sensitive type, which are reasonably in oxygen balance per se, such as PETN, still more highly sensitive products are obtained. These can propagate a detonation wave in a very slender column, e.g. a column as small as 1/2-inch or less in diameter or mean cross-section.
Where such high sensitive explosives are not needed, the content of self-explosive, such as PETN, may be reduced, or eliminated. Alternatively, this particular self-explosive may be replaced fully or in part by one or more of the other self-explosives named above and/or by aluminum powder.
In many cases, addition of a small amount of very finely divided aluminum, especially the flaked paint grade, is desirable because of its high fuel or energy value. It contributes very substantially to high sensitivity, even in well balanced liquid compositions. It is desirable, also, for the mechanical handling properties it imparts to the composition. It helps to lubricate the flow of the composition through conduits and orifices as when it is dispensed through valves, pumps, hoses and other flow devices.
Two further examples were made. The first contained 73.5% calcium perchlorate and 26.5% methyl alcohol. This solution per se had a density of 1.54 g/cc and was detonated in a 0.75-inch diameter column with a 9-gram Pentolite booster. The second contained 60% lithium perchlorate and 40% formamide. This solution per se had the density of 1.57 g/cc and was detonated in a 1-inch diameter column with a 9-gram Pentolite booster.
It will be obvious that the above and other modifications, which will suggest themselves to those skilled in the art, can be made within the spirit and purpose of the invention.