US 3282752 A
Description (OCR text may contain errors)
United States Patent 3,282,752 SLURRY TYPE BLASTING AGENTS Robert B. Clay, Bountiful, and William N. Bryan, Salt Lake City, Utah, assiguors to lntermountain Research and Engineering Company, a corporation of Utah No Drawing. Filed Sept. 21, 1965, Ser. No. 489,052 17 Claims. (Cl. 149-22) This invention relates to an improved slurry type blasting agent comprising inorganic nitrates and a sensitizing agent. It relates more particularly to an aqueous gel or slurry in which certain ingredients are not dissolved and which is thickened in sucha manner as to hold the undissolved constituents in suspension.
In recent years the use of ammonium nitrate aqueous gels or slurries for hard rock blasting and analogous purposes has increased rapidly. Ammonium nitrate, particularly when wet or in an aqueous slurry or gel is practically impossible to detonate unless it is sensitized. Various materials have been proposed for such sensitization,
including granular TNT, finely divided metals, particu-- larly aluminum, and combinations of these and other in gredients. Examples are U.S. Patents 2,930,685 and Reissue 25,695. In general, reference to inorganic nitrates herein includes sodium nitrate, which in some respects at least, is an equivalent for ammonium nitrate and fre- Y I quently can be and is substituted in part therefor.
The sensitizing materials, mentioned above, especially the heat producing metals and metalloids, such as magnesium, ferro-silicon, ferro-phosphorus, some of the boron compounds, and particularly aluminum, in particulate form, when properly used, are effective for their purposes provided that they can be kept properly distributed throughout the blasting agent until it is set off. Because the undissolved particles, e.g. of aluminum and other metals, and also of explosive sensitizer materials and thickeners have been used, such as guar gum, and
flour, starch, etc. One object of the present invention is to make improvements in the thickening or gelling aspect of the explosive composition.
Another problem which has been encountered in the prior art is that of producing an explosive composition which is safe over the temperature ranges encountered in preparation, handling and use and which also has the necessary sensitivity at the time and conditions of detonation. Generally speaking, slurry or gel explosives, particularly those where water is present in any quantity, have a steep temperature-sensitivity gradient. At high temperatures they are undesirably sensitive, or, if made insensitive for high temperature safety, at low temperatures they are so insensitive that it is difficult to insure detonation, even with powerful boosters and detonators. Another object of this invention is to change this gradient so that the compositions are sensitive enough over a fairly wide range of temperature that they can be detonated with boosters and detonating devices of reasonable size and cost while at the same time being safe for handling over the entire temperature range, including an elevated temperature range at which they may be mixed originally.
Ammonium nitrate, alone or in an aqueous solution,
is normally quite insensitive and hence can be shipped and handled without danger, even at elevated temperatures. But ammonium nitrate is not sufliciently soluble at low or common ambient temperatures to be incorporated in some of the aqueous solutions that are otherwise desirable in sufficient proportions for good blasting compositions. For this reason, it is desirable to have in the finished explosive a concentrated solution of this material or its equivalent, e.g. of 2 to 3 or more parts by weight for each part of liquid. When the liquid is water, this requires a fairly high temperature. than Water, such as alcohols, lower amidies, ethylene glycol, and aqueous solutions thereof, for example, it is even less soluble. In practice therefore, a solution is often made up at a temperature of at least C., and it may be as high as 75 C. or more. Sensitizers and other undissolved or insoluble materials are not added to this hot solution until the latest convenient time but they must be added before the material is placed in the blasting hole or site. The insolubles, which include the sensitizers, such as particulate aluminum and/or TNT, a thickener, often a fuel, etc., are often in the form of a premix. A particularly desirable method of placing gel or slurry explosives in bore holes is to mix them at the site and pump them directly into the hole. As soon as the sensitizer material is added to the solution to form a slurry, the blasting agent is hazardousto a considerably greater degree. According to one aspect of the present invention, however, the hazard is minimized by so preparing the composition that it is only moderately more sensitive at the solution temperature than at the temperature of use, which is often considerably lower.
It has been discovered, according to the present invention, that the temperature-sensitivity gradient of a sensitized inorganic nitrate blasting slurry can be made considerably flatter thanit is normally, by incorporating substantial quantities of both sulfur andsodium nitrate but within narrower and lower ratio limits than was heretofore deemed desirable. By this means a composition which might otherwise be too sensitive for safety at an elevated mixing temperature, or if made less sensitive kind may be so sensitive at a mix-ing temperature of, say,
C., as to be hazardous and still be too insensitive for detonation when in place for blasting at a temperature of 10 or 15 C.
It has been suggested in the past that a combination of ammonium nitrate, sodium nitrate, water, and sulfur, to-
Patented Nov. 1, 1966- For liquids other 3 The theoretical optimum weight ratio of sodium nitrate to sulfur should be about 5.3, assuming that all the sulfur reacts to form Na SO Using ratios of around 1:1 of NaNO to sulfur, by
4 fiattest form at a SN /S ratio of around 1.2. Very satisfactory performance is shown at a ratio within the range of about 1 to 1.6 and a good useful range can be as low as 0.8 and up to about 3.0.
weight, it was found that sensitivity of the slurry in- 5 In a composition using more sodium nitrate and relacreased but that the tem-perature-sensitivity relationship tively less ammonium nitrate, the same trend was found. ch-anged drastically. With a slurry made up of about At low sulfur contents, these products were quite insensi- 80 to 90% of aqueous solution containing several times tive, even at 60 C. As sulfur was increased, other comas much ammonium nitrate as a sodium nitrate, and a ponents being held relatively constant, sensitivity insolids premix of aluminum powder, sulfur, powdered 10 creased up to the point where the sulfur almost equalled gilsonite (added as a fuel) and a finely ground guar gum the sodium nitrate, then declined. The same flattening (as a thickener), proportions of sulfur were varied rather of the temperature sensitivity gradient was observed. Rewidely. Results are shown in Table I. sults are given in Table 11:
TABLE II Mix No Parts Gil S SN SN/S 60 C., 40 0., Results, 60 0. Results, 40
Soln. g./cm. gJem. C.
82.8 6.5 20.2 1.34 1.38 3F, 4F, F1 6F. 79.8 4.5 5 19.7 3.9 1.34 1. 40 41 5, SE, 6F bottom- 76.8 2.5 19.2 1.9 1.34 1.38 21 1, 2 41) 4F5, 5D, 6D. 73.8 0.5 15 18.7 1.2 1.35 1.39 2D 4D, 5D. 69.3 0 18.1 0.9 1.35 1 39 21%, 2, D 4D, 51).
TABLE SULFUR CONTENT ON 25 In the mixes of Tables II, the solution had a composi- SENSITIVITY o tron of 52.8% AN (ammomum nitrate), 13.0% SN, Thefitandard formula employed a 70 solutlon Wlth 15.9% water and 0.1% of the phosphate inhibitor. Of lngredlems as follows: the dry ingredients, the guar gum thickener contributed Sol 7 Dry 1.5%, the coarser aluminum 1.9% and the fine aluminum 0.3% by weight. Sulfur and SN were added to AN SN Hi0 Gum MA MB Gil S make up the various mixes in proportions shown-Mix No. 11, with no sulfur, failed even in a 5-inch column 59A 13A 159 (L1 L5 L9 as L5 30 at 60 C. as did Mix No. 10 also, with 5% sulfur. The results changed dramatically when the sulfur began to This mix contains 88.8 solution and 11.2 parts drys. aPPfOaCh ProPomons the sQdlum For test variation the quantities of gum and aluminum Since sulfur and sodium nitrate are widely available were held fixed. The appropriate columns indicate the fl 10W f h may P Substantial q percentages sodium nitrate, sulfur, gilsonite, ratio of the tltles to obtain sensitive composltions which perform well total SN to S content and the number of parts of the 4" at moderately low temperatures and are still safe at higher identical solution that was used in the standard formula. temperatures.
Mix No. Parts Gil 8 SN SN/S 60 0., pC., Results, Results, 40
Soln. glam. gJ mfi C. C.
90.0 5.3 1.0 13.7 13.7 1.29 1.36 2D 6F". 90.0 5.3 1.0 13.7 13.7 1.30 1.35 2F, 2%D 41%, 51 6F9. 88.8 4.5 3.0 13.4 4.5 1.30 1.35 2F 4D 6F. 87.5 3.8 5.0 13.2 2.6 1.30 1.35 D 86.2 3.1 7.0 13.0 1.9 1.31 1.39 D 84.9 2.4 9.0 12.9 1.4 1.34 1.37 83.7 1.6 11.0 13.6 1.1 1.34 1.40 81.3 0 15.0 12.3 0.8 1.35 1.39 87.3 0 9.0 13.2 1.5 1.37 1.40
l The length to diameter ratio for all charges was 6.
' No'ns.6Fnetc. signifies 6" dis. charge tailed leaving about 12 olslurry. 5D etc. signifies 5' dia. charge detonated leaving a crater.
It will be noted that the products in the first three mixes failed to detonate in 5 and 6-inch columns at 40 C. but detonated in 2, 2 /2 and 4-inch columns, respectively, at 60 C. This represents a large diiference in sensitivity. By contrast, the composition of Mix No. 5 failed at 60 C. in a 2 /2 inch column, fired in a 3-inch column, and also fired at 40 in a 5-inch column while failing in a 4-inch. The sensitivity-temperature gradient here is much flatter than in the first three mixes.
Also, it will be noted that Mix No. 8, having the lowest SN/S ratio of all, detonated readily at 60 C. in a 2-inch column. It failed in a 4-inch, but detonated in a 5-inch column at 40 C., showing a slightly steeper gradient than Mix No. 5. Mix No. 9, a relatively insensitive one failed at 60 C. in a 4-inch but fired in a 5-inch column. It failed at 40 C. in a 6-inch column. The reason for the insensitivity ofMix No. 9 is undoubtedly its large positive oxygen balance. From these data, it clearly appears that the temperature sensitivity gradient reaches its In lieu of the ammonium nitrate, chlorates and perchlorates may be used, at least in part, with similar results.
Another series of experiments were made, using constant proportions of sulfur and varying the sodium nitrate. Here it was found that sensitivity dropped as the SN content was lowered, especially sensitivity at lower temperature. This confirmed the observations above that optimum temperature-sensitivity performance is obtained when the SN-sulfur ratio is in the neighborhood of about 2.5:1 to 111. Too low a ratio is as bad or worse than a ratio that is too high.
In these experiments a standard procedure w-as followed, employing a 70 C. solution made up of 45.1% 'AN, 16.5% H 0, 20% SN (this ingredient was varied) and holding the coated aluminum at 2.0%, the fine at 0.2%, the gum at 1.2% and sulfur at 15%. Results are shown in Table III.
To check the blasting potential of mixes made according to this invention, a series of seismic tests were made.
Sensitivity and seismic strength do not necessarily coordinate. As a basis of comparison, some mixes of the following composition were made up and sulfur content 1 The PS refers to potato starch.
The sulfur content does not substantially affect seismic strength.
Starch thickeners have been used in the past in connecfact that the solution temperature for the potato starch was 70 C. while for guar gum it was 45 C. Other factors being equal, the lower the permissible miX temperature,-the more sensitive the slurry can be made at the borehole temperature, as a general rule. 7 v
The use of starches as thickeners is limited, however, by the fact that they will hydrate only at elevated tom'- peratures. Raw potato starch for example, will not thicken satisfactorily below about 58 C. This characteristic of starches may somewhat limit their application when the borehole temperatures are relatively low. Tapioca flour will hydrate at a temperature a few degrees lower than potato starch; hence it can be used in lieu thereof with advantage in some cases. However, the tapioca flour requires a little more fine aluminum as sensitizer for equivalent results. Table 5 shows a comparison of some sodium nitrate-sulfur containing slurries sensitized'with small proportions of fine aluminum, using various thickeners. In the first series a natural gum thickener (gmar gum) was employed, whereas in the second potato starch was used as thickener. The solutions were somewhat different because the first group were mixed at 41 C., with a 45 solution temperature, whereas the second was mixed at 56 C, with a 70 solution tion with slurry explosives of the same general type to temperature.
TABLE v I Results Mix No. Coarse Fine S Gum AN Density, (g./cm.=)
Al Al 41 0. 25 0. 41 C. 25 c 1.0 0.2 6 1.2 6 1.30 1.37 Not cap sensitive- 6Fw 0.8 0.4 6 1.2 6 1 31 1.39 do 61% 0.2 0.4 a 1.2 7 127 1.35 do 6F1 0.6 0.6 6 1.2 7 1 29 1 36 Some reaction 6D 0.8 6 1.2 7 1.28 1 36, 3F2 with Cap 6D Results Mix N0. Coarse Fine Gil. S P.S Density, (gjcmfi) Al Al 25 0.
9 1.0 0.2 4 4.5 a 1. 32 1. 40 Some reaction 5 left bottom 15 1.0 0.2 4 5.0 2.5 1.25 1.34 do 6D which this invention relates. In connection with the In the first group the solution comprised 48.9% of particular ingredients which characterize the composition ammonium nitrate, 15.5% of sodium nitrate, 17.1% of of the present invention, however, they have some desirwater, and 0.1% of the aluminum-water reaction inhibiable properties that are unusual. For example, about 3% tor, the solution being made up at 45 C. The overall of starch is needed to be equivalent in thickening power mix, with dry ingredients added, had a temperature of to 1% of guar; however, the price of starch is so much 41 C. In the second case thesolution was made up at less that the economic difference frequently favors starch. 70 C. and consisted of 58.4% of ammonium nitrate, Moreover, starches thicken more rapidly than gums, a 13.3% sodium nitrate, 15.5% water, and 0.1% of the feature which makes them more desirable for pump truck inhibitor. The overall mix temperature was 56 C. A use where the thickening time is limited. More imsmall amount of coarsealuminum was used'along with portant even than this, is the fact that starch-thickened the fine aluminum and proportions of both were varied slu-rries, particularly of the type under consideration here, slightly as indicated. It will be noted that at the higher require less sensitizer for a given sensitization, i.e., less temperature indicated the products were not generally cap aluminum can be used than when guar gum is used as 4 sensitive, although some reaction was indicated in certain thlckener. A series of tests were made which showed instances. At the lower temperature, detonation was that so fas as sensitivity is concerned, 0.25% of fine slightly better with the potato starch composition, despite aluminum combined with a potato starch thickener was the fact that less of the fine aluminum was used than in as eifectlve as 0.6% of the same aluminum, using guar most of the other samples. Compare, for example, Mix
gum as thickener. This result is amplified further by the No. 1 with Mix No. 15, or Mix No. 7 with Mix No. 9.
The importance of particular aluminum qualities is emphasized in a copending application of Clay et al., Serial No. 460,857 filed June 2, 1965. The advantages of such compositions are considerably enhanced by the use of a combination of sulfur and sodium nitrate within particular ratio limits, according to the present invention.
There appears to be some uncertainty whether sodium sulfate is an important heat-producing reaction product. There is reason to believe that the exothermic reaction between sulfur and sodium nitrate may produce sodium sulfite and/or sodium sulfide. In any case, it appears to be clearly established .that the heat of the sodium nitratesulfur reaction is highly important. This is particularly true 'where very small quantities of aluminum are employed as the primary or conventional sensitizer. As noted above, by the use of starch in lieu of gum, or even in lieu of part of the gum, as a thickener, under favorable conditions the sensitizing quantities of aluminum required can be reduced even further.
In summary, the present invention is characterized in one respect by the use of very small quantities of finely divided metal, preferably aluminum, which aluminium is of a character suitable to establish many tiny voids as reaction centers. The more reaction centers :present, the more sensitive is the slurry. Because of the high heat of formation of aluminum oxide, these centers are highly 'efiicient as reaction initiators, and high temperatures are quickly established at the reaction centers. Moreover, the sodium nitrate-sulfur reaction, which possibly involves formations of sodium sulfate and/or sodium sulfite, and/or possibly some sulfide compounds, apparently helps provide the energy needed to drive the detonation wave thought the column of explosive.
In general, the compositions will include at leastv 45% of the oxygen-supplying salt and usually more than 50%, preferably 60% or more. Water may comprise from to 25%, or more in some cases. Sulfur may be from 1 to 15% and only enough sodium nitrate is used to keep the SN/S ratio below about 2 but above about 0.8. However, it is preferable to use at least 5.0% of sodium nitrate, and the appropriate amount of sulfur.
The liquid is preferably water, but it maycomprise various water-compatible materials,- especially organic liquids having fuel value, such as formamide and other amides, alcohols and polyols. The aluminum or other metal particles should be of such a character as to form reactive sites by retaining very small or tiny pockets or bubbles of gas to cause the reaction. Where temperature of mixing, etc., permits, it is preferred to use starch as a thickener. These various features are contemplated individually as well as collectively, as aspects of the invention.
The discovery that highly effective and sensitive ex- Q plosives based mainly on ammonium nitrate in water can be prepared by the use of very small quantities of reactive aluminum having reaction site potentials, and that the power and sensitivity of such aluminum can be further enhanced by use of sodium nitrate and sulfur in optimum proportions is considered highly significant and technically and economically important. The further consideration that starch can be used to add further control over sensitivity under certain conditions is important, too. It is obvious that numerous variations can be made in the composition without departing from the spirit and purpose of the invention which comprehends all these factors individually and in combination. It is intended by the claims which follow to cover such as fully as the prior art properly permits.
What is claimed is: p
1. An explosive composition comprising at least 45% by weight of oxygen supplying salts, at least half of such salts being ammonium nitrate and at least 5% being'sodium nitrate, the remainder being selected from a group which consists of ammonium nitrate, alkali metal nitrate, alkaline arth metal nitrates, and the chlorates and perchlorates of ammonia and of the alkali metals, an amount of sulfur to make a weight ratio with the sodium nitrate between 0.8 and 3.0 SN/S, 0.1 to 8% of particulate metal selected from the group which consists of aluminum, magnesium, boron, and mixtures thereof, a sufficient quantity of Water to form a pourable slurry or gel, and 0.1 to 4% of a thickening agent to inhibit gravity separation of undissolved components of said slurry.
2. Composition according to claim 1 wherein the oxygen supplying salts consist of ammonium nitrate and sodium nitrate.
3. Composition according to claim 1 wherein the thickener is starch.
4. Composition according to claim 1 wherein the metal is finely divided particulate metal used in proportions not to exceed 2% by weight based on the total composition.
5. A slurry explosive comprising, in combination, a liquid solution of a powerful oxidizer selected from the group which consists of ammonium nitrate, sodium nitrate, and the chlorates and perchlorates of ammonia and the alkali metals, and mixtures of any two or more of these, at least 1% of sulfur by weight, based on the total composition, a finely divided particulate metal sensitizer in small proportions, and sodium nitrate (included in the oxidizer) in such proportions as to make a weight ratio with the sulfur between about 3 :1 and 9.8: 1. i
6. Composition according to claim 5 wherein the metal is aluminum.
7. Composition according to claim 5 wherein a major tion, of a powerful oxidizer a major part of which is ammonium nitrate, a metallic sensitizer, and at least 5% of sodium nitrate, and enough sulfur to produceia sodium nitrate/sulfur weight ratio between about 3.0 and 0.8.
13. Composition according to claim 12 wherein the metallic sensitizer is aluminum which has active thermal sites due to occlusion of tiny bubbles of gas.
14. Composition according to claim 12 wherein there is included a thickener to inhibit gravity separation of undissolved components.
15. An aqueous explosive slurry composition comprising a major proportion of solution of ammonium nitrate and sodium nitrate in water, 0.1 to 8% of suspended particles of a sensitizing metal having surface properties such as to hold small bubbles of gas while in the slurry, enough sulfur in suspension to make a weight ratio of sodium nitrate to sulfur between about 3.0 and 0.8, and 0.1 to about 4% of a thickener.
16. Composition according to claim 15 wherein the ratio is about 1.
17. Composition according to claim 15 wherein the metal is aluminum in proportions of 1 to 3%.
References Cited by the Examiner UNITED STATES PATENTS 3,092,528 6/ 1963 Loving 14973 X 3,113,059 12/1963 Ursenbach et al l49-41 3,249,477 5/1966 Clay et a1. 14941 L. DEWAYNE RUTLEDGE, Primary Examiner.
S. I. LECHERT, 111., Assistant Examiner.