US3072509A

US3072509A - Gelled ammonium nitrate blasting explosive and process

Info

Publication number: US3072509A
Application number: US23641A
Authority: US
Inventors: Robert E Barnhart; Frederick C Sawyer
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1960-04-21
Filing date: 1960-04-21
Publication date: 1963-01-08
Anticipated expiration: 1980-01-08

Description

United States Patent Ofifice 3,072,509 GELLED AMMONIUM NITRATE BLASTING EXPLOSIVE AND PROCESS Robert E. Barnhart, Hedgesville, W. Va., and Frederick C. Sawyer, Hagerstown, Md., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Apr. 21, 1960, Ser. No. 23,641 9 Claims. (Cl. 1492) The present invention relates to a novel blasting agent and to a method for its preparation. More particularly,

a the present invention relates to a gelled aqueous ammonican be effected by means of such compositions and loading techniques under certain circumstances have been the principal motivation for their extensive use. From a functional standpoint, however, such compositions leave much to be desired. They do not pack the punch required for many blasting operations and, since they are usually loaded in plastic bags or other similar containers, the bulk density of the blasting agent in the borehole is often undesirably low. Much work has been done in recent years in an attempt to raise the blasting efiiciency of ammonium nitrate compositions and also to raise the bulk density of such compositions, i.e., the amount of blasting agent which can be loaded into the borehole.

It has been proposed to prepare ammonium nitrate blasting agents in slurry form, especially in an aqueous slurry. One such composition recently suggested is an aqueous ammonium nitrate slurry containing a pelleted trinitrotoluene (TNT) high explosive sensitizer. A discussion of this composition can be found in Cook, M.A., The Science of High Explosives, ACS Monograph No. 139, published by the Rheinhold Publishing Corporation, New York, N.Y. (1958) page 316.

Aqueous ammonium nitrate-TNT slurries of the type described by Cook have met with some success in the field but their use has been limited to some extent with respect to boreholes containing large amounts of standing water and with seamy boreholes. In the latter case,

a large proportion of the aqueous slurries may be carried off out of the borehole before there is an opportunity to initiate the blast. In those instances where the boreholes contain a considerable amount of water, the concentration of the ammonium nitrate in the borehole is reduced considerably, thereby lowering the bulk density of the blasting agent, perhaps even to the point where the agent will not shoot.

To overcome these deficiencies in the aqueous ammonium nitrate-TNT slurries of the type described by Cook, it has been proposed to add a gelling agent to the composition to convert it from a loose fluid slurry to a gelatinous mass. The resulting gel may be generally water-compatible, i.e., not affected by exposure to water in a borehole, and may also tend to resist leakage from the borehole through small seams and cracks.

These gel compositions, however, are slow to form, usually requiring extensive mixing for about -45 minutes before a usable product is obtained. Shorter mixing periods usually result in non-uniform consistencies and the formation of large lumps of undissolved and undispersed ammonium nitrate. Up to the present time, it has not been convenient to prepare such gels which are consistently homogeneous in composition and uniform in consistency and storage qualities. In the latter regard, storage for a period of 3-4 days or longer often results in liquid segregation of the gel composition in the case of the currently known gels. These gels have also generally been lacking in body and toughness which are desirable for convenient loading and efiicient blasting.

It is an object of the present invention to prepare a new gelatinous blasting agent composition. It is a further object of the present invention to prepare a new high explosive-sensitized gelatinous blasting composition from an aqueous ammonium nitrate base. It is a Still further object of the present invention to prepare a new blasting agent of the aforementioned type which is economical and easy to manufacture and which is safe and convenient to use. Other and additional objects will become apparent from a consideration of the ensuing specification and claims.

Broadly stated, the present invention contemplates the preparation of a novel blasting agent by gelling a hot aqueous ammonium nitrate liquor containing no undissolved ammonium nitrate. The gelatinous composition of the invention also contains a high explosive sensitizer. such as pelleted TNT, which may be added to the hot ammonium nitrate liquor either before or after the liquor is gelled.

The ammonium nitrate liquor employed is one which will produce a finished product containing about 12-20% by weight of water. This corresponds to an aqueous am monium nitrate liquor starting material containing about 60-80% by weight of ammonium nitrate.

The liquor is heated to a temperature in the range of about l20180 F. and the gelling agent, such as finelypowdered guar gum flour, is added. The latter is dispersed in the hot aqueous ammonium nitrate liquor by mixing for several minutes in any suitable mixing apparatus. Generally speaking, 10 minutes of agitation is more than adequate and in most cases 3-5 minutes fully suificient to disperse the gelling agent and form a high quality uniform gel at the elevated temperatures. The high explosive sensilizer, such as pelleted TNT, may be added to the mixture before or after gelling or simultaneously with the gelling agent, and dispersed with agitation. The gel is thickened with a small amount of borax (sodium tetraborate) as a cross-linking agent. A more complete understanding of the present invention will be gained from a consideration of the following examples.

Example 1 A gelatinous blasting agent composition is prepared from the following components:

Percent ,ammonium nitrate liquor 48.95 Finely powdered sodium nitrate 25.00

lelleted TNT (available as Pelletol No. 1, manufactured by E. I. du Pont de Nemours and Co.) 25.00 Finely ground guar gum flour 1.00 Borax 0.05

Patented Jan. 8, 1963 a composition was a fine, even, uniform gelatinous mass characterized by the appearance of fine needle-like crystals of ammonium nitrate dispersed evenly throughout the gel. The consistency of the mass was very uniform and there were no lumps of any type except for the TNT pellets which were thoroughly distributed in the gel matrix. The gel was tough, elastic, and had a firm body. The density of the mass was 1.45 grams per cc. The composition was sensitive to initiation by 100 grams of RDX and shot with a velocity of 4500 meters per second in a diameter column.

Example 2 Following the procedure described in Example 1, a blasting agent composition was prepared from the fol lowing component materials:

Percent 75% ammonium nitrate liquor 53.95 Finely powdered sodium nitrate 25.00 Flaked TNT 20.00 Finely ground guar gum flour 1.00 Borax 0.05

The physical properties of the gelatinous mass were similar to those of the product prepared in Example 1, including the uniformity of the composition. The product had a density of 1.43 grams per cc., was sensitive to initiation by 100 grams of RDX, and shot at a velocity of 3500 meters per second in a 5 /2" diameter column.

Example 3 A blasting agent composition was prepared from the following components:

To the ammonium nitrate liquor in a suitable container was added the dry soda and the RDX and TNT. The resultant composition was heated at a temperature of 185-190 F. The guar gum flour was thereafter added and mixed for a period of 3 minutes following which the borax was added under mixing for a further 2 minutes to thicken the gel. The resultant composition was a fine, uniform, gelatinous mass containing no lumps and characterized by the appearance of fine needle-like crystals of ammonium nitrate (visible only by microscopic examination) dispersed evenly throughout the gel. The TNT. and RDX were likewise dispersed uniformly throughout the gel matrix. There were no lumps of any kind in the gel and the gel was a tough elastic mass having a firm body. A 250 gram sample in the form of a small round sphere was stretched 6-8 feet before breaking. The composition was sensitive to initiation by 10 grams of RDX in a 1" diameter column.

Four hundred grams of this material was made in the laboratory by heating. The ammonium nitrate liquor and sodium nitrate were heated together to F. to dissolve most of the sodium nitrate. The guar gum flour was added and mixed for 2 minutes. Then the Composition A and the borax were added and mixed for 1 minute. The resultant composition at room temperature was a tough non-elastic gel resembling bread dough. The density was 1.47 g./cc. The material shot in 1" diameter with a l0-gm. RDX'booster.

Example 5 A gelatinous blasting composition was prepared from the following components:

Percent RDX 14.9

TNT 10.0 Ammonium nitrate 55.2 Water 18.95 Finely ground guar gum 1.0 Borax (as a 10% aqueous solution) 0.05

Density1.30 g. cc.

The RDX, TNT, ammonium nitrate and water were heated to 190 F. together to melt the RDX and TNT and dissolve the ammonium nitrate. To this hot solution the guar gum flour was added and mixed two minutes. Then the borax solution was added and mixed one minute. In 1%" diameter, the composition shot with a 10-gm. RDX booster. At room temperature, the composition was a uniform gel, did not stick to a polyethylene bag but exhibited no elasticity.

Example 6 A gelatinous blasting composition was prepared from the following components:

The procedure followed was similar to that of Example 5. The sodium nitrate was combined with the RDX, TNT, ammonium nitrate and water for the initial heating. The resultant composition shot in 1%" diameter with a 10-gm. RDX booster. At room temperature, the composition was a uniform gel, did not stick to a polyethylene bag, and exhibited good elasticity. It had a density of 1.45 gms./cc.

Example 7 A gelatinous blasting composition was prepared from the following components:

Percent Flaked TNT 25.0 60% ammonium nitrate liquor 36.9 Finely ground sodium nitrate 25.0 Granular ammonium nitrate 12.0 Guar flour 1.0 Borax (as a 10% aqueous solution) 0.01

The hot 60% liquor is pregelled for 15-20 seconds by mixing with the guar flour. The pregelled liquor is added to a mixer, followed by the sodium nitrate, ammonium nitrate, TNT and borax and mixed for 1 minute. At room temperature, this composition is soft and sticky with moderate elasticity; but it is a good uniform gel which is firm at 40-50 F. and stiff at 0 F.

Example 8 A gelatinous blasting agent composition was prepared from the following components:

1 Percent 5 Water 15.27 Ammonium nitrate 43.9 Powdered sodium nitrate 19.9 Grained 60% RDX/40% TNT composition 19.9 Guar gum flour 1.0 10 Borax (as a 10% aqueous solution) 0.03

In this example, the RDX/TNT composition was grained by melting 85% of this composition with paraffin and stirring manually with a wooden paddle in a bucket until a fine material was formed. The ammonium nitrate was dissolved in the water and heated to 150 F. This liquor was added to the bowl, the sodium nitrate/ guar mixture added, and mixed 3 minutes. The grained RDX/TNT composition was then added, then the borax, and mixed 2 more minutes. The resultant mass shot in 1 /2 diameter with a 10-gm. RDX booster.

Half the ammonium nitrate was dissolved in water and heated to 150 F. This liquor was added to the mixer, followed by the sodium nitrate/guar mixture and mixed 3 minutes, then the Composition A, the ammonium nitrate remaining and borax solution were added and mixed 2 minutes. The resultant gel composition shot in 1 /2" diameter with a 10-gm. RDX booster.

Example 10 Gelatinous blasting compositions were prepared from the following components:

Comp. X, Comp. Y, Con p. Z, percent percent percent Water 18.77 15.07 15. 07 Granular ammonium nitrate. 35. 4 22. 1 34. 1 Sodium nitrate 19. 9 24. 9 24. 9 Fine-grainpd ammonium nitrate l2. 0

cited TNT 312% RDX/40% TNl composition" 'lum' gum flour liorax solution The mixing procedure for these formulations was pregel ling the granular ammonium nitrate and water with guar gum flour and heating the sol to l90l95 F. This sol was added to the mixer, which had been warmed with hot water, and immediately the melted TNT or molten RDX/TNT mixture was added and dispersed in the sol matrix by mixing for 1-2 minutes. The finegrained ammonium nitrate and sodium nitrate were then added, followed by the b rax solution. The purpose of the dry soda and ammonium nitrate is to cool the mix rapidly. Compositions Y and Z shot in 1%" diameter with a 10-grn. RDX booster and Composition X shot in 2 /2" diameter with the l0-gm. RDX booster.

The aqueous ammonium nitrate liquor used in the preparation of the new blasting agent contains a percentage of water which will produce a gelatinous product containing about 1220% water. As noted above, this corresponds to a 80% aqueous ammonium nitrate liquor starting material. The liquor is heated to a temperature in the range of -180 F. and preferably in the vicinity of l60 F. at which temperatures the ammonium nitrate is completely dissolved in the concentrations used. The elevated temperatures employed are a critical feature of the invention. If a uniform, high quality product is to be obtained, it is important that substantially none of the ammonium nitrate remain in an undissolved state. The gelling agent is then added to the liquor, either alone or in admixture with finely powdered sodium nitrate. The latter represents an excellent vehicle for addition of the gelling agent and serves also to depress the freezing point of the gelatinous endproduct and to elevate the density of the composition. Sodium nitrate also contribute to the elasticity of the product where this is desired. It is not a critical ingredient of the new compositions, however, and may be omitted especially where freezing temperatures are not expected to be encountered in the field.

Guar gum flour, a gelactomannan substance, has been found to be an excellent gelling agent for the ammonium nitrate liquor inasmuch as its gelling ability is substantially unaffected by the presence of large amounts of dissolved nitrate salts. As the gelling agent, guar gum flour, therefore, represents the much preferred embodiment of the invention since it yields vastly superior results compared with any other known gelling agents. Other gelling agents are operable, however, including locust bean flour, and may be used in lieu of guar gum flour provided that their ability to form a gel is not materially inhibited by the nitrates in solution. In order to achieve the full benefits of the invention, the gelling agent, i.e., the guar gum flour, must be extremely fine. Coarse grades of guar gum flour tend to require an undesirably long amount of time for gel formation. Preferably, 50% of the guar gum flour should pass through a 325-mesh screen (U.S. Sieve Series).

Any high explosive composition may be used as a sensitizer, including TNT, RDX, PETN, pentolite, Cyclotol, HBX, Torpex, tetryl, Tetratol, and the like. Compositions formulated with RDX have greater sensitivity to initiation in small diameter. However, TNT is especially preferred as the sensitizer for economic reasons and in view of its favorable safety characteristics. The TNT may be used in any suitable particulate form which is susceptible of dispersion in the gelatinous matrix, including for example, pelleted TNT, flaked TNT, grained TNT, and the like. Other high explosive sensitizers in these forms may also be used or the sensitizer may be added to the composition in molten form where convement.

Borax is used as the cross-linking agent for the gelling agent. Any common commercial grade of borax may be used, including the product available for household pur poses. For best and fastest dispersion, the borax is best added to the system in aqueous solution, for example, as a 10% aqueous solution. Adding the borax in aqueous solution also tends to enhance the evenness and uniformity of the cross-linking of the gelling agent. About ODS-0.1% by weight of borax is used. based on the weight of the fully formulated composition. Proportions greater than this should be avoided si ce they may result in degradation of the gel due to ingredient segregation.

The essential components of the novel blasting compositions of the present invention are ammonium nitrate, water. high explosive sensitizer, gelling agents, and a cross-linking agent. Generally speaking, these components may be present in the composition within the following proportions expressed as percentages by weight:

Cross-linking agent 0.05-- 0.1

In addition, up to one-half of the ammonium nitrate in the composition may be replaced by sodium nitrate.

The novel gelatinous blasting agent compositions of the present invention are characterized by a very fine and uniform consistency. In the product, much of the ammonium nitrate remains in solution in the wet gel; the remainder crystallizing out in the form of fine, uniform, evenly-dispersed, needle-like crystals of microscopic size. The composition is free from lumps of any kind except for the high explosive sensitizer itself when the latter is in a solid particulate form. The new compositions are, in general, tough,-elastic compositions of firm body, as more particularly described below, which tend to hold their shape but which will undergo moderate plastic flow in the borehole to completely fill the borehole. The extent of plastic fiow which these compositions exhibit, however, is not generally so severe as to permit the compositions to run quickly out of the borehole into seams, cracks, or crevices which may be present.

The physical nature and consistency of the new gelatinous blasting agents will vary somewhat from case to case depending upon the precise formulation in each instance. Generally speaking, this is advantageous since it permits tailoring the composition to the job to be done, i.e., the physical properties of the composition may be adjusted to some extent in accordance with anticipated field conditions where the composition is expected to be used. Since temperature has a profound effect on the consistency of the products, compositions to be used in warm or hot climates will desirably be tough and tafiylike to hard at ordinary room temperature, i.e. temperatures in the vicinity of 70 F. Such compositions will be quite hard at 4050 F., but will be plastic and workable at 90 -l00 F. The products prepared in Examples 4 and 5 are illustrative of such compositions. Compositions intended to be used in cold climates, on the other hand, where temperatures are likely to be near or below freezing will desirably be much less viscous at room temperature, i.e., toothpaste-like in consistency. At 0 R, such compositions will generally appear much like a firm, friable rubber. A composition of this type is illustrated by the product of Example 7. In general, the substitution in the formulation of sodium nitrate for ammonium nitrate, within the prescribed limits, tends to increase viscosity and increase elasticity of the composition at room temperature.

By using the hot aqueous ammonium nitrate liquor containing no undissolved ammonium nitrate as the starting material, it is possible to prepare a fine, uniform gel upon addition of the gelling agent in a matter of a few minutes, usually no more than 3-5 minutes, and this represents a distinct advantage from the manufacturing standpoint. Prior art techniques for preparing gel compositions of this general type at room temperature have invariably required much more extensive mixing, along the order of 30-45 minutes at a minimum. By means of the manufacturing technique of the present invention, substantial operating economies are effected in the cost of manufacturing the new blasting agent.

In the foregoing description of the preparation of the new gelatinous blasting compositions, the preferred orders of the addition of the component materials has been indicated inasmuch as these methods of manufacture generally lead to the highest quality, most uniform gel products. It is possible, however, to prepare blasting gels within the scope of the present invention by mixing the ingredients specified in other ways and in difierent orders than those described, and the invention is not limited to any specific order of addition. The use of a hot ammonium nitrate liquor containing no undissolved ammonium nitrate and heated to the temperatures specified, on the other hand, does represent a critical feature of the invention inasmuch as the superior gelatinous blasting agents of the present invention cannot be obtained in any other way.

. water.

The gelatinous blasting agents of the present invention may be loaded directly into the borehole along with suitable primers and conventional initiating means. One convenient arrangement is to package the blasting agent in plastic bags, such as polyethylene, which are slit at the blasting site and dropped into the borehole. Since the density of the gel compositions is significantly greater than that of water, the bagged product will sink to the bottom of the borehole even in holes containing standing Nor will the latter have any material efiect on the gelatinous compositions. Due to its gelatinous plastic nature, the composition will ooze from the bag containers through the slits. The weight of the blasting column overhead will cause the gel to leave the bags through the slits at a suitably fast rate'so that the gelatinous composition will substantially fill the borehole regardless of its internal configuration. Even irregular holes will be substantially completely filled thus insuring the maximum possible loading density of blasting agent in the borehole. On the other hand, the rate of plastic flow of the new compositions is not so great that any substantial amount of composition will be dissipated in the boreholes due to escape via scams or cracks in the walls of the borehole prior to initiation of the blasting agent.

The new blasting agents of the present invention and their method of manufacture have been disclosed in the foregoing specification. It will be readily apparent to those skilled in the art that many variations may be made in the compositions and procedures described without varying from the spirit of the present invention. It is, therefore, intended to be limited only by the following claims.

We claim:

1. A blasting agent composition consisting essentially of a uniform dispersion of fine needle-like crystals of ammonium nitrate and a dispersed high explosive sensitizer in a tough, elastic, gelatinous mass formed by thoroughly mixing a gelling agent selected from the group consisting of guar gum flour and locust bean flour, the sensitizer, and sodium tetraborate as a cross-linking agent for the gelling agent into a hot aqueous solution of ammonium nitrate containing no undissolved salt at a temperature in the range of about 180 F., said composition containing by weight 30-60% ammonium nitrate, 12-20% water, 15-30% high explosive sensitizer, 0.5l.5% gelling agent, and 0.050.1% sodium tetraborate.

2. A blasting agent composition as in claim 1 in which a portion of the ammonium nitrate is replaced by sodium nitrate.

3. A process for the manufacture of a gelatinous blasting agent of the type defined in claim 1 comprising heating an aqueous ammonium nitrate liquor to a temperature in the range of l20-180 F., thoroughly mixing the hot aqueous ammonium nitrate liquor with a high explosive sensitizer, a gelling agent and borax as a crosslinking agent for the gelling agent to form a fine, uniform gel in which the ammonium nitrate is evenly and uniformly dispersed, the ratio of ammonium nitrate to water in the aqueous ammonium nitrate liquor starting material being such that at the temperatures specified no substantial amount of the ammonium nitrate remains in the undissolved state.

4. A process as in claim 3 wherein the aqueous ammonium nitrate is heated to a temperature in the range of l60 F.

S. In the process of manufacturing a gelatinous blasting agent of the type defined in claim 1, the novel steps of heating an aqueous ammonium nitrate liquor to a temperature in the range of 120l80 F. and adding to said hot aqueous ammonium nitrate liquor, a gelling agent selected from the group consisting of guar gum flour and locust bean flour and sodium tetraborate as a cross-linking agent therefor.

6. A process as in claim 5 wherein the aqueous am- 10 monium nitrate is heated to a temperature in the ran after slitting the bag-like containers in order to facilitate of 140-160 F. egress of the contents of the bag in the borehole, and

7. A process as in claim 6 wherein the hot aqueous amthereafter detonating the charge. monium nitrate liquor is dynamically mixed with the gelling agent for a period of not more than 10 minutes. 5 References Cited in the file Of this Patent 8. A blasting agent as in claim 1 packaged in bag- UNITED STATES PATENTS like containers.

A blasting process which comprises drilling a boreg z Z 11010 In the m e la to be blasted, loading therein a 2:768:073 Davidson c 23: 19

charge of blasting agent of the type defined by claim 8 10

Claims

1. A BLASTING AGENT COMPOSITION CONSISTING ESSENTIALLY OF A UNIFORM DISPERSION OF FINE NEEDLE-LIKE CRYSTALS OF AMMONIUM NITRATE AND A DISPERSED HGIH EXPLOSIVE SENSITIZER IN A TOUGH, ELASTIC, GELATINOUS MASS FORMED BY THOROUGHLY MIXING A GELLING AGENT SELECTED FROM THE GROUP CONSISTING OF GUAR GUM FLOUR AND LOCUST BEAN FLOUR, THE SENSITIZER, AND SODIUM TETRABORATE AS A CROSS-LINKING AGENT FOR THE GELLING AGENT INTO A HOT AQUEOUS SOLUTION OF AMMONIUM NITRATE CONTAINING NO UNDISSOLVED SALT AT A TEMPERATURE IN THE RANGE OF ABOUT 120*-180*F., SAID COMPOSITION CONTAINING BY WEIGHT 30-60% AMMONIUM NITRATE, 12-20% WATER, 15-30% HHIGH EXPLOSIVE SENSITIZER, 0.5-1.5% GELLING AGENT, AND 0.05-0.1% SODIUM TETRABORATE.