US3390028A - Aqueous slurry blasting explosive containing silicon and an aeration agent - Google Patents

Description

June 25, 1968 H. R. FEE ET AL 3,390,028

AQUEOUS SLURRY BLASTING EXPLOSIVE CONTAINING SILICON AND AN AERATION AGENT Filed Jan. 4, 1967 0 A9H3N3 NOOHS HARRY R. FEE ROBERT W. LAWRENCE ORIN W. MARKS INVENTORS AGENT United States Patent 3,390,028 AQUEOUS SLURRY BLASTING EXPLOSIVE CONTAINING SILICON AND AN AERA- TION AGENT Harry R. Fee, Hopatcong, N.J., and Robert W. Lawrence and Orin W. Marks, Wilmington, Del., assignors to Hercules Incorporated, Wilmington, Del., a corporation of Delaware Filed Jan. 4, 1967, Ser. No. 607,260 Claims. (Cl. 149-39) ABSTRACT OF THE DISCLOSURE An aqueous slurry blasting composition having an explosive sensitizer and containing silicon and an aeration agent. The aeration agent lowers the maximum specific gravity of the composition at the time of blasting.

This invention relates to aqueous slurry blasting explosives and more particularly to an improved aqueous slurry blasting explosive utilizing a metal fuel.

The use of metals as fuels to increase the energy of explosive compositions has for years been known throughout the art. Of the metals utilized, aluminum has been one of the metals most Widely used due to its ability to enter the explosive reaction. However, the use of aluminum in aqueous slurry blasting explosives has certain undesirable characteristics including that of high cost as compared to the present invention. This will be more readily appreciated from the following.

As previously pointed out, the prior art in the preparation of aqueous slurry blasting agents or explosives containing metals is well known. The use of fine, or mixtures of coarse and fine aluminum in combination with explosive ingredients has been demonstrated. The use of fine aluminum in connection with ammonium nitrate and water to the exclusion of explosive ingredients has also been demonstrated. In these cases the fineness of the aluminum was important to the operability of the compositions. In the presence of fine aluminum other metallic ingredients were also claimed to be useful. The use of fine aluminum introduced distinct disadvantages in that fine aluminum contributed to the hazard of dust explosions. In addition, the reaction between ammonium nitrate solutions and fine aluminum with evolution of hydrogen was encountered and special buffering and stabilizers were often necessary.

In other teachings in the addition of fine ingredients (200 microns or less), the absence of dissolved fuels was usually required. Inherent in the use of all fine ingredients is the cap sensitivity of such compositions, which in some instances is desirable depending on conditions of use while in other instances is undesirable, such as, where large quantities of slurry explosive are being bulk delivered to blasting sites. In addition, excluding dissolved fuels eliminates many of the most convenient fuels such as the glycols and the carbohydrates, some of which may be handled as liquids. The use of soluble fuels is also desirable in bulk delivered slurries because they do not add to the solids-to-liquid ratio. Additional advantages in using a soluble fuel will become evident in the examples to follow.

Furthermore, in order to avoid the problems inherent in using fine aluminum, other forms were tried. It was observed that flaked and balled aluminum would contribute a measure of sensitivity to the compositions (as contrasted 3,390,028 Patented June 25, 1968 with ordinary aluminum filings, for instance), and it has become common practice to use this form. Resorting to flaked aluminum has introduced a dilferent set of problems. The sensitizing etiect, i.e., the ability to change an insensitive composition to an explosive composition, of the flaked aluminum apparently results from the entrapment of air and the resulting inclusion of the air in the form of tiny bubbles in the slurry. It has been conjectured that the inclusion of such bubbles in an explosive serves to provide hot spots which help initiate the compositions (Moder, C. L., The Physics of Fluids, vol. 6, No. 3, page 375, 1963). One problem, therefore, is to maintain the air bubbles in the aqueous environment. Attempts have been made to solve this problem by coating the aluminum with hydrophobic material in a separate operation. The use of boron and magnesium has also been claimed to be effective after treatment which, of course, entails additional expense to the already expensive metal ingredient. A further disadvantage to flaked aluminum is the excessive thickening imparted when high energy compositions are required and the aluminum content is increased or the water content is lowered.

The primary object of the present invention is, therefore, to provide aqueous slurry blasting explosives which while being at least as energetic as convetnional metallized slurries, eliminate the short comings and disadvantages outlined above.

Other objects of the invention will appear hereinafter the novel features and combinations being set forth in the appended claims.

Generally described, the present invention contemplates an aqueous slurry blasting explosive comprising inorganic oxidizingsalt, explosive sensitizing agent, particulate silicon, thickener, and an aeration agent present in an amount to lower the maximum specific gravity of the aqueous slurry blasting explosive to between about 30 and of the maximum at the time of blasting.

Examples for operation of the invention are given as well as an example for preparing an aluminized aqueous slurry for comparison of the end products. In these exam ples parts are by weight unless otherwise indicated. Examples l and 2 contained no silicon, Example 3 contained silicon, Example 4 contained aluminum and Example 5 contained silicon Without an aeration agent. These examples are given in Table I and were prepared as follows:

EXAMPLE 1 1. Combine the pine oil, AN and SN with the water of solution (hot) and heat to F.

2. Mix the smokeless powder into the solution.

3. Adjust the pH to between 4.5 and 5.0 with acetic acid.

4. Disperse the guar gum in about 3 times its weight of ethylene glycol and mix into the solution.

5. Disperse the guar gum cross-linking agent in the remaining glycol and mix into the solution.

EXAMPLES 2, 3, 4 AND 5 Steps 1, 2, 3 and 4 are the same as for Example 1 except that pine oil is omitted in Step 1 and the silicon or alumi num are also added in Step 2.

Step 5.Disperse the sodium nitrite in about 3 /2 times its weight of water and add to the mix.

Step 6.--Disperse the guar gum cross-linking agent in the glycol remaining from Step 4 and mix into the solution.

TABLE Example No .1

Components:

Silicon type II Aluminum Granules (90% on 100 mesh) Water i'. Ammonium Nitrate, prills Sodium Nitrate, prills Ground Smokeless Powder. Ethylene Glycol Guar Gum Pine Sodium Nitrite- Oxygen Balance, percent. FEE], 24 Hour Specific, Gravity. p Detonation Rate, M/S..- Pipe Diameter, in

.ll. 0 1. ll.

ar-i- Slurry Temperature, F l0 l3 Underwater Measured Energy Weight Basis,

Relative to Confined 60% HP Gel:

Shock Energy l. 58 l. 78 l. 95 ll. 87 ll. 51 Thrust Energy ll. 71 l. 86 l. 94 ill. 92 l. 69

Maximum.

All of the gj Shawn in ,Table I tested, TABLE II.SILICON PARTICLE srzns AND PURITY x o r o eton'atlon rate W 1 e connne e pl slve ene gy an r gu Type 1 1 1 11 underwater. Detonation rates were measured over a length of cm. and were recorded on a counter chronograph. The underwater thrust i bubble) and shock energies were determined in the manner indicated by Cole (Cole, H.D., Underwater Explosions, Princeton University Press. Princeton, New Jersey {1948), pages 228 to 285) and as reported by Sadwin (Sadwin, L. D, Cooley, C. M., Porter, S. J., Stresau, R. H.; Underwater Evaluation of the Performance of Explosives, International Symposium on Mining Research, Missouri, February i961, vol. l) and his collaborators with some minor modifications.

The data are reported relative to confined 60% HP Gel. The charges, 20 lbs. to lbs. in weight, are confined in 5-inch diameter by 28-inch long black iron pipe. The pipes are suspended vertically, l2 feet below the surface of the water to the charge center, and 28 feet from the bottom of the pond. The charges were initiated from the bottom with XC-49 Pentolite boosters [/50 PETN/TNT), 3-inch diameter by l-inch high and 190 grams in weight. The pressures generated by the detonations were sensed by piezoelectric hydrophone transducers and were recorded on an oscilloscope. The bubble times were also sensed by the transducers and were recorded on the oscilloscope.

With reference to the examples and Table I, it will be seen as graphically presented in the attached drawing in linear form, that the shock energy and the thrust energy for the silicon compositions was higher than that for the aluminum. It was most surprising to discover, however, that the composition of Example 5 containing 14% silicon without aeration had shock and thrust energy values about equal to only that of Example 1 containing no metal or aeration. Thus, the improvement and importance in utilizing an aeration agent with silicon containing compositions may be fully appreciated. Although silicon is shown in the examples in an amount of 14% which represents a practical amount in aqueous slurry explosive compositions, the amount of silicon used depends primarily upon the explosive energy required but as a practical limit would start at about 3 and not ordinarily exceed 30% with from about 3 to about 20% being preferred. Typical particle size distribution and purity of preferred silicons are shown in Table II. The silicon designated Si II was used in the examples. In the operation of this invention, particle size and purity are not critical. This permits the use of economical technical grades of alloys and blends thereof. It will be further appreciated, however, that finely divided silicon can be used in accordance with this invention tree from the hazard of flammability as compared to that of finely divided aluminum, as shown in Table III.

82% smaller than 74 microns.

Do 325 Through 325 39% smaller than 44 microns.

i Sharples Micromerograph" particle size distribution analysis.

TYPICAL ASSAY OF SILICON Types I and 111 Type 11 Percent Silicon 85 Silicon type II is a preferred material due to its ability to enter the explosive reaction and its economy. Type II is a silicon alloy blend averaging about 85% silicon, with a nominal silicon range of 82 to 88%. The range analysis of major residual elements bound in the alloy is as follows:

Silicon types I and III are silicon alloys containing to 97% silicon and having a range analysis of major residual elements bound in the alloy as follows:

Aluminum 0.20-0.65 Calcium 0.02-0.05 Carbon 0.04-0.09 IChromium 0.01-0.03 Copper 0.01-0.03 Nickel 0.035-0.06 Titanium 0.03-0.07 Phosphorous 0002-0006 Sulfur 0.060.10 Vanadium 0.06-0.10 Manganese 0.01-0.03 llron 0.5-1.5

TABLE III.DUST FLAMMABILITY TESTS Paint grade aluminum (97% 74 microns) Tests were conducted by dropping approximately 100 grams of sample, about 16 inches down an 8-inch diameter tubejiventilated at the bottom and open at the top and simultaneously initiating an electric squib.

The inorganic oxidizing salts are shown in the examples pertaining to silicon as being present in amount of 40.6% of the compositions. If requirements so dictate, these salts could comprise between about 25 and 75% of the compositions. The physical form of the salts is not critical, coarse or fine, or mixtures of coarse and fine prilled and/ or granular to powdery material all being suitable. In fact, in some preferred applications of this invention, the oxidizing salts are introduced into the compositions as an aqueous solution. Ammonium nitrate (A.N.), because of its availability, is the preferred oxidizing salt but sodium nitrate (S.N.) in practice almost always makes up a portion of the oxidizing salts, preferably to the extent of about to 25% of the composition but 0% to about 30% may be used. Although the examples given are all formulated with inorganic nitrates, the use of other inorganic oxidizing salts are within the scope of this invention. For instance, various of the alkali or alkaline earth nitrates may be used for all or a portion of the A.N., but in practice, not more than about 80 of the A.N. would be so substituted. A preferred range for the presence of A.N. is from about 20 to about 50%. In addition, salts selected from the percholorates, such as, ammonium, sodium and potassium percholorate may be used.

The explosive sensitizing agent, smokeless powder, appears in the examples as being present in amount of 25% of the compositions. Where a reduction in the critical diameter is desired or where the availability of the sensitizing agent is particularly convenient up to about 50% may be utilized as a practical maximum. Generally, however, about 10 to 40% will be present. Other suitable sensitizing agents include TNT, RDX, HMX, PETN, Pentolite, Cyclotol, HBX and the like. These materials may be pelleted, flaked or grained.

The non-explosive carbonaceous fuel, ethylene glycol, appears in the examples as being present in amount of 2.5% of the compositions. Depending upon the conditions, 0 to about of the compositions may be made up of one or more carbonaceous fuels, but a maximum of about 7% is more commonly used. Where insoluble carbonaceous fuel or immiscible carbonaceous liquids are used, they must, of course, be suspended in or dispersed throughout the aqueous phase.

Water is shown as 17% by weight of the compositions in the examples. Between about 10 and 30% of the compositions may be composed of water but in conventional practice about 14 to 24% is more commonly employed.

It will be appreciated that the compositions of this invention are composed of a blend of liquid and solid components. It is essential that the solid phase (or non-homogeneous liquid phase, when such is utilized) be evenly dispersed throughout the liquid phase. This is accomplished by employing thickening agents which retard or arrest the settling of the solid material. Suitable thickeners include carboxymethylcellulose, methyl cellulose, water soluble starches, cereal flour and the like. Preferred practice is to employ guar gum and to cross-link (gel) the gum with a suitable cross-linking agent. The cross-linking agent may be combined with the gum and is commercially available in such form or may be added as a separate ingredient in very small amounts, usually less than 0.1% of the total composition. The gum may be used in as low amount as 0.4% or thereabouts and up to about 4%, but more generally about 0.7% to 1.8% is used.

Furthermore, it will be appreciated that the specific gravity of the compositions of this invention at the time of blasting is important. A specific gravity of between about 30 and 95% of the maximum specific gravity of the aqueous slurry blasting explosives and preferably between about 50 and at the time of blasting has been found to enhance the explosive energy of the compositions of this invention. The adjustment and maintenance of the compositions to the specific gravities given above are accomplished by incorporation of an aeration agent into the composition. The term an aeration agent as used herein means an agent which causes the composition to be combined with or charged with gas. The term maximum specific gravity as used herein means the specific gravity of the aqueous slurry blasting explosive exclusive of gas.

As is discussed in the reference previously given, the presence of small evenly dispersed air or gas bubbles throughout an explosive can be beneficial to initiation and propagation. The operation of this embodiment is in accord with the aforementioned hot spot theory and encompasses the inclusion of small amounts of tiny gas bubbles throughout the liquid phase. Examples of this type of composition are given in Table I where sodium nitrite is used as the aeration agent in amount of 0.065%. Also, gas bubbles may be generated as disclosed by Ferguson et al. (US. 3,288,658) and Swisstack (US. 3,288,661). However, a particularly eflicacious aeration agent for use in lowering and maintaining specific gravities in accordance with this invention is sodium nitrite in an amount of from about 0.01 to about 0.2% by weight of the blasting composition. As demonstrated in the examples and the drawing, this aeration agent present in the small amount of 0.065% gave final 24 hour specific gravities of about 1.25-1.35 at a pH of 4.5-4.9 and gave extremely improved and surprising performance of the aerated silicon containing composition in respect to detonation rate, shock energy, and thrust energy.

It is evident that the inclusion of various minor ingredients is within the scope of this invention. Adjustments are routinely made with appropriate acids and bases to obtain desired pH ranges. Other variations and modifications are apparent to those versed in the art and the examples given are not intended to nor do they represent limits on the scope of this invention.

The advantages of the invention are multifold. Unlike some conventional compositions the use of fine easily flammable and overly reactive metallic sensitizers is not required. Where it is convenient or desirable to use the energetic metal fuel com ponent partially in the fine particulate form, the compositions of the invention represent a great improvement through a decreased susceptibility to dust explosions. No special bufiering is required for the compositions of this invention other than the normal pH adjustments. The form of the metallic energizer whether chemically pure or technical grade is not critical in these compositions and no special treatment of the energizer component is necessary, thus providing improved economy. Through the availability of these compositions it will be possible to obtain the explosive energy of conventional compositions while avoiding their shortcomings and disadvantages.

It will be seen, therefore, that this invention may be carried out by the use of various modification and changes without departing from its spirit and scope with only such limitations placed thereon as are imposed by the appended claims.

What we claim and desire to protect by Letters Patent are:

1. An aqueous slurry blasting explosive comprising inorganic oxidizing salt, self-explosive sensitizing agent, particulate silicon, water, thickener, and an aeration agent present in an amount to provide sufl'lcient air or gas bubbles to lower the maximum specific gravity of the wzrasopzs ii aqueous slurry blasting explosive to between about 30 and 95% of the maximum.

2. The aqueous slurry blasting explosive of claim 1 wherein the silicon is present in an amount of from about 3 to about 30% by weight.

3. The aqueous slurry blasting explosive of claim 2 wherein the silicon is present as a silicon alloy containing from about 80 to about 97% silicon by weight of said alloy.

4. The aqueous blasting explosive of claim 2 wherein the silicon is present as a mixture of silicon alloys containing from about 80 to about 97% silicon by weight of said mixture.

5. An aqueous slurry blasting explosive comprising from about 20 to about 50% ammonium nitrate, from about 5 to about 25% of sodium nitrate, from about 10 to 50% of self-explosive sensitizing agent, from about 3 to about 20% of particulate silicon, from to about 15% of carbonaceous fuel, from about 0.4 to about 4% of thickening agent, from about 10 to about 30% of water, all percentages by weight, and an aeration agent present in an amount to provide sufiicient air or gas bubbles to lower the maximum specific gravity of the aqueous slurry blasting explosive to between about 50 and 90% of the maximum.

6. The aqueous slurry blasting explosive of claim 5 wherein the silicon is present as a silicon alloy containing from about 80 to about 97% silicon by weight of said alloy.

7. The aqueous slurry blasting explosive of claim 5 wherein the silicon is present as a mixture or silicon alloys containing from about 80 to about 97% silicon by Weight of said mixture.

18. An aqueous slurry blasting explosive comprising by weight from about 20 to about 50% ammonium nitrate, from about 5 to about of sodium nitrate, from'about l0 to of self-explosive sensitizing agent, from about .3 to 20% of particulate silicon alloy mixture containing about to 97% silicon by weight, from 0 to about 15% of carbonaceous fuel, from about 0.4 to about 4% of thickening agent, from about 10 to about 30% of water, and from about 0.01 to about 0.2 of sodium nitrite as an aeration agent to provide sufficient gas bubbles to lower and maintain the maximum specific gravity of the aqueous slurry blasting explosive to between about 50 and of the maximum.

F9. The aqueous slurry blasting explosive of claim 8 wherein the sensitizing agent is smokeless powder.

10. The aqueous slurry blasting agent of claim 8 wherein the sensitizing agent is trinitrotoluene.

References Cited UNITED STATES PATENTS 3,164,503 11/1965 Gehrig 149-60 X 13,249,474 15/1966 Clay et al. 14944 X 3,288,661 ll/1966 Swisstack 14960 13,294,601 l2/1966 Gordon 14960 BENJAMIN R. PADGETT, Primary Examiner.

CARL D. QUARFORTH, Examiner.

5. J. LECHERT, JR., Assistant Examiner.

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