US3886008A - Blasting composition for use under high temperature conditions - Google Patents

Abstract

A blasting composition suitable for use under exothermic ground conditions and in other high temperature operations is made up of a combination of a high melting temperature stable oxidizer, such as sodium nitrate, with a combination fuel which also is temperature stable; the fuel preferably comprises finely divided aluminum and finely divided solid carbonaceous fuel and a small amount of a high boiling organic liquid, such as formamide or a glycol or glycol ether. Some ammonium nitrate can be used, usually in smaller proportions than sodium nitrate.

Description

United States Patent [1 1 Cook May 27, 1975 [54] BLASTING COMPOSITION FOR USE 3,473,983 10/1969 Cook et al. 149/43 X UNDER HIGH TEMPERATURE 3,676,235 7/1972 Nuscher et al 149/43 X CONDITIONS 75 Inventor: Melvin A. Cook, Salt Lake City, Primary Examinersfephen Utah Attorney, Agent, or FzrmRobert A. Bmgham [73] Assignee: Ireco Chemicals, Salt Lake City,

Utah [57] ABSTRACT [22] Flled: 1974 A blasting composition suitable for use under exother- [21] Appl. No.: 434,765 mic ground conditions and in other high temperature operations is made up of a combination of a high melta I P qF a ing temperature stable oxidizer, such as sodium nil l Contlnuatlon of 876,568, 1969 trate, with a combination fuel which also is temperaabandoned' ture stable; the fuel preferably comprises finely divided aluminum and finely divided solid carbonaceous U-S. fuel and a Small amount of a Organic q uid, such as formamide or a glycol or glycol ether. [5 lift. s ammonium nitrate can be used usually in [58] Field of Search 149/41, 3, 1 smaller proportions than Sodium nitrate [56] References Cited 7 Claims N0 Drawings UNITED STATES PATENTS 3,390,029 6/1968 Preckel 149/43 X BLASTING COMPOSITION FOR USE UNDER HIGH TEMPERATURE CONDITIONS This is a continuation of application Ser. 43 876,568, filed Nov. l3, 1969, now abandoned.

BACKGROUND AND PRIOR ART In recent years, two relatively inexpensive general types of blasting compositions have come into wide use because of their good performance and relatively lower cost, as compared with the older types of high explosives such as dynamites, TNT, Composition B, etc. These new compositions are firstly a relatively dry type, especially a mixture of ammonium nitrate and fuel oil, commonly called ANFO, and, secondly, aqueous slurries containing oxidizer salts and fuel. Typically these slurries are based primarily on solutions of ammonium nitrate sensitized with water-insoluble fuel such as aluminum, with or without carbonaceous fuel. Sometimes the slurries include particulated selfexplosive materials such as TNT, smokeless powder, and the like. For many purposes the slurry explosives are superior to ammonium nitrate-fuel oil compositions, particularly under conditions where ground water is encountered and where maximum blasting power is desired. In some cases ANFO is more suitable than slurry, for special situations.

However, in some types of mining operations, for example where large quantities of pyrites and other sulfur-containing ores are present, unusually high temperature conditions may be encountered which make both the ammonium nitrate-fuel oil compositions and the slurry compositions quite unsuitable for blasting purposes. In some mines where these sulfur compounds are present, the borehole where explosive is to be placed reaches a very high temperature. The initial blasting operations apparently release large quantities of pyrites or other sulfides, or even sulfur itself, in finely divided or dust form. These particles, with their relatively very large surface areas, may react spontaneously with oxygen in the air to raise the temperature to levels which are hazardous for use of conventional explosives. Moreover, these high temperatures can destroy the blasting agent before it can be fired. Since it usually requires appreciable time to fill a series of boreholes and to get ready to detonate the explosive, the blasting agent may be exposed to high temperatures long enough to destroy its blasting efficiency. At very high temperatures, the water may be evaporated out of slurries, or the oil may be vaporized or fumed off the ammonium nitrate in ANFO explosives. Either effect is sufficient to destroy the effectiveness of the blasting agent. In some unusual cases where exothermic reactions of ore and atmospheric oxygen take place, the temperatures obtained in the mines may be so high as to cause premature burning and even detonation of the blasting explosive. Under some extreme conditions, temperatures as high as 800 C have been encountered and temperatures of the order of 80 to 200 C are quite common. It is desirable to have blasting agents that remain stable up to about 300 C in some cases. They should be reliable up to about 200 C. It is obvious that stability at still higher temperatures, though desirable, may be excessively difficult to achieve.

Ammonium nitrate per se is a reactive material in the presence of fuel even at temperatures no higher than its melting point, about 170 C. Pure AN starts to decompose at about 300 C. When fuels, such as free sulfur particles, in finely divided form, or particles of unstable compounds containing sulfur are present and adjacent the AN, the latter may react very readily, even at temperatures below its melting point. Obviously, compositions based largely on ammonium nitrate can become dangerous in mining operations at temperatures well below 200 C.

The present invention is based on the discovery that by using substantial proportions of a more stable and higher melting oxidizer material, e.g., sodium nitrate, the blasting composition is safer, more reliable, and in many cases is considerably less expensive. Some AN can be used with SN. Because sodium nitrate is less active than ammonium nitrate, it may be desirable to use some of the latter. In some cases, the AN and SN may be used in about equal proportions. Usually the less active sodium nitrate should predominate. By reducing water content below that used in slurry, preferably replacing water by an organic liquid fuel of fairly high boiling point, the above disadvantages may be overcome. Reduction of water tends to offset the lower sensitivity of SN as compared with AN.

Another problem that may arise in aluminumsensitized aqueous slurries, at elevated temperatures particularly, is a premature aluminum-water reaction. By incorporating a stabilizing agent in the blasting composition, the tendency for premature decomposition of the slurry or for premature burning of any component of the explosive agent is greatly reduced; thereby, these compositions are made safe for use under conditions of temperature as high as 200 C.

Hence, a primary objeect of the present invention is to produce and make available blasting agents which will remain stable and are safe and reliable for use under high temperature conditions of the types specified above.

SUMMARY A safe blasting explosive, which is stable and effective at high temperature conditions, in underground mines, for example, to about 200 C is made up with a high sodium nitrate content, a fairly high aluminum content for fuel, with supplemental carbonaceous fuel and preferably at least a small amount of a supplemental oxidizer which is more sensitive than sodium nitrate, usually ammonium nitrate. The latter preferably is used in proportions not exceeding, and generally less than, the proportions of sodium nitrate, thus taking advantage of the relatively inert nature of sodium nitrate. The packing qualities of the blasting agent may be controlled by including a small amount of a liquid fuel in the form of an oxygenated aliphatic compound having a boiling point above about C. The latter may be either formamide or a diol or diol-ether. Preferably, the liquid fuel has a boiling point as high or nearly as high as the temperature of the borehole. For this reason formamide, or dimethyl formamide is particularly preferred as a liquid control agent for the packing qualities. Other high boiling liquids of analogous composition and some solvent action in the oxidizer salts may be used. They also should add some appreciable fuel value to the composition.

DESCRIPTION OF PREFERRED EMBODIMENT In some parts of the world large ore deposits are found which include substantial quantities of sulfides, such as pyrites, i.e., iron sulfides, and sulfides of various other metals. When these sulfur-containing ores are broken up into dusts or in any conditionwhere high surface areas are exposed, they tend to undergo combustion in the presence of the oxygen of the air. This applies particularly to pyrites because ores containing pyrites are readily oxidized by atmospheric oxygen. As a result, temperatures within enclosed mining passages, shafts, tunnels and especially in boreholes, can rise to dangerous levels in some circumstances. or at least high enough to present real difficulties in employment of blasting agents.

The inventor reasoned that by using a less sensitive oxidizer than ammonium nitrate, under conditions or with fuels, etc., that would offset the reduction in sensitivity, and by selecting all ingredients so that they would not evaporate, vaporize, or decompose to significant degrees during necessary storage or residence times in the high temperature environment, stability might be maintained without substantial sacrifice of performance.

A composition, Example 1, was made up experimen tally which consisted of 25 parts by weight of ammonium nitrate, 52 parts by weight of sodium nitrate, 15 parts of finely divided aluminum metal, 4 parts of formamide, and 4 parts of ground gilsonite, It was reasoned that a small amount of ammonium nitrate could be used, even if it should melt due to heat, because it could flow over and be absorbed largely by other ingredients. Ground coal can be used in place of the gilsonite with approximately equal results. This product had a somewhat damp consistency which it was felt might make it difficult in some circumstances to load into boreholes. Certain types of loading apparatus could be expected to encounter difficulties, for example those which function by blowing the composition into the borehole through a hose. In other respects this composition was proved to perform satisfactorily at temperatures up to 185 C.

A somewhat drier mix was made as Example 2, which was roughly similar to the first example but which consisted of 36 parts by weight of ammonium nitrate, 43 parts of sodium nitrate, 15 parts of aluminum, 2 parts of formamide, and 4 parts of gilsonite. Reduction of the formamide content reduced the tendency of the composition to pack within a borehole loading hose. This material had an oxygen balance of 0.l3 and proved on test to be more suitable for loading through a hose than the first composition.

The first example, as described above, was repeated except that it was dried up somewhat by reducing the formamide to 2 percent and increasing the gilsonite to 5 percent; however, this material was in some respects too dry. The gilsonite tended to separate from the other components in stirring and handling. This third example had an oxygen balance of about 0.73.* It showed no tendency to decompose and in other respects ap peared to be satisfactory for the purpose.

For testing their sensitivity, portions of the compositions of the above three examples were each placed in a piece of steel pipe 1 /2 inches in diameter and inches long. the Oxygen balance is given here as per centage excess oxygen or percentage deficiency blasting material was compacted in the pipe by tamping and was fired with a No. 6 cap. In some other tests, a pipe 2 inches in diameter and 13 inches long was used, with or without tamping. The untamped material required a somewhat larger detonator and a Cordtex knot was used, this being a blasting primer fuse material. These compositions were mixed at an ambient temperature of 1 10 F.

Another mixture was prepared and tested in an attempt to eliminate altogether the ammonium nitrate, which is known to be more sensitive under high temperature conditions than sodium nitrate. This Example 4 contained 73 percent sodium nitrate, 13 percent formamide, 10 percent aluminum and 4 percent gilsonite. It had a density of 1.09 g/cc. and an oxygen balance of+l .4. At lower temperatures it fired weakly but shot strongly at C and withstood a temperature of 450 F before any sign of decomposition was observed.

Another composition, Example 5, contained 72 percent by weight of sodium nitrate, 15 percent of aluminum, 8 percent of formamide, and 5 percent of gilsonite. It had an oxygen balance of -2.12. This mixture failed to detonate in the 2 X 13-inch steel pipe when tamped and fired with a Cordtex knot.

Underground tests were also conducted on composition Example 5 in a mine in typical overhead ring firings. The sublevel caving method was used in a section of the mine. Boreholes were 2% inches in diameter, ranging in depth from 41 to 78 feet. The mixes tested were loaded by blowing into four holes for a total charged footage of 222 linear feet. The remaining footage of 220 linear feet was charged with ammonium nitrate-fuel oil of standard composition, that is, about 6 percent fuel oil on ammonium nitrate prills. In this particular mine ground temperature loading time was 174 C. The ANFO reacted, reached a temperature of 404 C in a test case, and fired weakly. Example 5 showed no reaction. However, the ring shot of Example 5 was noted to be somewhat stronger than usualv This was evidenced from ground vibration and later from visual observation of the blasting results.

Compositions like Example 5 containing formamide were somewhat more difficult to load into deep slender boreholes than ANFO. Some of them were quite difficult to pack into the holes. It was found necessary to manipulate the discharge valve on the loading machine and to tap the loader with a steel rod to keep the mix feeding through the loading tube. Addition of a small amount of water, for example, 2 cups per 100 pounds of ammonium nitrate-fuel oil, was found to facilitate packing it into boreholes. Half this quantity was added to the above mix, Example 5, for one chamber load. It helped pack the mix in the hole, but it added to difficulty of feeding at the loading machine. The formamide dampened composition also had a tendency to plug a slender loading hose, which in this case was a plastic tube 90 feet long and 1 inch in internal diameter.

To determine the effect of temperature on stability, samples loaded in pipes, as above, were nearly immersed in a bath of formamide which was gradually heated to various temperatures, up to its boiling point (about at the test site altitude, about 4,500 feet above sea level). For higher temperatures, the tubes were fitted into notches in a length of 8 X 24 inches stove pipe with a gas burner at the bottom. With the latter, temperatures were attainable up to 500 C or more.

Example 6 was next prepared to test use of diphenylamine as a fuel, using only a small amount of paint grade fine aluminum to assist in sensitizing. This was made up of 62.2 percent by weight of sodium nitrate, 20 percent of ammonium nitrate, 1 1.5 percent diphenylamine and 2 percent of the aluminum. It had a density of 1.14 g/cc. and detonated with a No. 6 blasting cap. It was stable up to 240 C, when it caught fire. It remained quite solid up to 200 C.

Example 7 consisted of 76 percent of sodium nitrate, 11.8 percent ammonium nitrate, 8.2 percent diphenylmethane, 2 percent of fine granulated aluminum and 2 percent of fine flaked paint grade aluminum. 1t detonated with a knotted detonating fuse but not with a No. 6 blasting cap. Density was 1.19 g/cc. at 5 C. The mix was stable up to about 200 C. At 240 C it became exothermic.

Several experiments were conducted to test hexamethylenetetramine as a sensitizer. A composition, Example 8, consisting of 66.4 percent sodium nitrate, 12.9 percent ammonium nitrate'and 20.7 percent HMT failed to detonate after being heated to 380 F (193 C). A 4 foot helix of grain (per foot) detonating cord was used in the attempt to detonate the mixture. This failure indicated there was too much fuel. By reducing the HMT, increasing the AN moderately, and adding a little paint grade aluminum, or adding a small plus the gilsonite, the formamide, and the relatively large proportion of ammonium nitrate.

Example 16 contained too much AN. 1t melted at 173 F (78 C) and caught fire at 147.5 C. Example 18, which contained 2 percent grade aluminum along with 13.9 percent formamide was too sensitive, indicating that either the paint grade aluminum should be omitted, or the formamide reduced, or both.

The test data suggested that 11 percent or more of formamide is too much for compositions of this type. They were not wet enough to be slurries but were too damp to be loaded like dry explosives (e.g., ANFO with 6 percent fuel oil) and were more sensitive than they needed to be. Formamide is a desirable ingredient, nevertheless. It has a high boiling point, is easy to handle, and is widely available. It is superior to the diols, alcohols and amines in most respects, for hot borehole" explosives.

Three more compositions were made up and tested. The following data indicate that AN contributes substantially to the explosive strength:

Ex. No. SN AN Formamide Al Gil SS AN/Ox(%) amount of fine granular aluminum and of formamide, detonation was achieved.

Specifically, an Example 9 consisted of 65.4 percent by weight of sodium nitrate, 17.5 percent AN, 15 percent HMT and 3 percent paint grade aluminum. This had an oxygen balance of +1.54. It failed to detonate in a 3 inch diameter steel pipe at 10 C with a 3C booster, but at 150 C it detonated with a 36 inch helical initiator of 26 grain detonating cord.

Example 10, consisting of 65.4 percent of SN, 15.6 percent AN, 15 percent HMT, 2 percent formamide, and 2 percent fine aluminum powder failed to detonate in a 1% inch pipe at 95 C but detonated strongly at 127 C. The formamide was added to cut down dust and to hold the HMT and aluminum from sifting out of the mixture.

Additional tests are tabulated:

No. l l was very fluid, then set up solid. It detonated in a 1% inch pipe at 5 C with a No. 6 cap and also in a bucket at 260 F (127 C). No. 12 was too damp to be loaded by blowing. 1t detonated at 22 C and at 240 C. No. 13 showed some caking. Neither No. 13 nor 14 was detonated and the latter was considered particularly unsatisfactory. No. 15 and 17 were cap sensitive at ordinary temperatures, probably too sensitive for use at even moderately elevated temperatures. This was probably oversensitized by a content of 2 percent paint grade aluminum along with 12 percent other aluminum The last column above shows the ratio of ammonium nitrate to total oxidizer. Obviously, ammonium nitrate contributes the strength as measured, for example, by the seismic method. It also contributes to instability at elevated temperatures and these good and bad effects must be balanced. Where temperatures in the borehole are likely to be very high, the AN should be almost or entirely eliminated, other factors being equal. Where the temperatures are only moderately high, say 150 C, or less, ammonium nitrate may constitute as much as half the total oxidizer. For the hot borehole" working range of 100 to 200 C, AN content should be reduced from about half at the lower temperature down to not more than 25 percent or less of the total oxidizer at higher temperature. The composition of Example 1 (SN 52, AN 25 Al 15, Formamide 4, Gil 4) is a good one if it can be loadedotherwise formamide should be reduced to l to 3 percent of the total to leave the mix quite dry. A preferred working range in mines which approach a 200 C borehole temperature is as follows:

Sodium nitrate Ammonium nitrate Aluminum Carbonaceous fuel (Gilsonite or coal) Formamide 40 to 65% by weight 10 to 30% 10 to 20% 1 to 8%, preferably 2 to 6% 2 to 7% S 30 to AN 10 to 40 1 8 to 20 Oil or coal 1 t 10 -Continued Formamidc l to Stabilizing agent (ammonium hydrogen phosphate or equivalent) 0.00l to 0.5%

Glycol or glycol ether or equivalent liquid boiling at about 140 C or higher may be substituted for part or all the formamide.

It is to be emphasized that none of these hot borehole explosives is a slurry (a slurry is a true suspension of undissolved particles in a continuous liquid medium). by hot borehole, it is intended to refer to holes where the temperatures can be expected to be above 100 C and up to 200 C. By carbonaceous fuel it is intended to refer to gilsonite or coal and also to any of the organic fuels named herein.

It will be understood by those skilled in the art that the proportions of the various ingredients may be varied within the limits stated above, which are approximate, and that substitutions may be made for some of the ingredients, without departing from the spirit of the invention.

What is claimed is:

1. An explosive blasting composition free of water and stable at temperatures as high as from about 100 to about 200C consisting essentially of in parts by weight:

3070 percent of sodium nitrate 0-40 percent of ammonium nitrate 220 percent of aluminum 1-10 percent of solid carbonaceous fuel l-l0 percent of an oxygen-containing liquid fuel selected from the group which consists of formamide, dimethylformamide, glycols, and glycol ethers and combinations thereof having a boiling point of at least 140C.

2. Composition according to claim I in which the liquid fuel comprises formamide.

3. Composition according to claim 1 which contains 10 to 40 percent by weight of ammonium nitrate and 8 to 20 percent of aluminum.

4. A blasting composition according to claim 1 which consists essentially of 10 to percent by weight of ammonium nitrate, 40 to 65 percent of sodium nitrate, 10 to 20 percent finely divided aluminum, 1 to 8 percent finely divided solid carbonaceous fuel, and 2 to 7 percent of the liquid fuel.

5. Composition according to claim 4 which contains 2 to 6 percent solid carbonaceous fuel.

6. Composition according to claim 4 which the liquid fuel is formamide.

7. Composition according to claim 1 which contains 0.02 to 1 percent of a phospate inhibitor selected from the group which consists of ammonium, alkali metal, and alkaline earth metal phosphates and the corresponding hydrogen phosphates

Claims (7)

1. AN EXPOLOSIVE BLASTING COMPOSITION FREE OF WATER AND STABLE AT TEMPERATURE AS HIGH AS FROM ABOUT 100* TO ABOUT 200*C CONSISTING ESSENTIALY OF IN PARTS BY WEIGHT: 30-70 PERCENT OF SODIUM NITRATE 0-40 PERCENT OF AMMONIUM NITRATE 220 PERCENT OF ALUMINM 1-10 PERCENT OF SOLID CARBONACEOUS FUEL 1-10 PERCENT OF AN OXYGEN-CONTAINING LIQUID FUEL SELECTED FROM THE GROUP WHICH CONSISTS OF FORMAMIDE, DIMETHYLFORMAMIDE, GLYCOLS, AND GLYCOL ETHERS AND COMBINATIONS THEREOF HAVING A BOILING POINT OF AT LEAST 140*C.

2. Composition according to claim 1 in which the liquid fuel comprises formamide.

3. Composition according to claim 1 which contains 10 to 40 percent by weight of ammonium nitrate and 8 to 20 percent of aluminum.

4. A blasting composition according to claim 1 which consists essentially of 10 to 30 percent by weight of ammonium nitrate, 40 to 65 percent of sodium nitrate, 10 to 20 percent finely divided aluminum, 1 to 8 percent finely divided solid carbonaceous fuel, and 2 to 7 percent of the liquid fuel.

5. Composition according to claim 4 which contains 2 to 6 percent solid carbonaceous fuel.

6. Composition according to claim 4 which the liquid fuel is formamide.

7. Composition according to claim 1 which contains 0.02 to 1 percent of a phospate inhibitor selected from the group which consists of ammonium, alkali metal, and alkaline earth metal phosphates and the corresponding hydrogen phosphates.