US3108917A - Tnt-tetraborate gelled aqueous explosive slurry - Google Patents

Description

the laboratory to the commercial stage.

United States Patent 3,108,917 TNT-TETRABGRATE GELLED AQUEGEE EXPLQMVE SLURRY John Douglas Mclrvine, St. Hilaire, Quebec, tCanada, assignor to Canadian Industries Limited, Montreal,

Quebec, Canada, a corporation of Canada No Drawing. Filed Apr. 9, 1962, Ser. No. 185,835 Claims priority, applieationCanada July 3, 1961 4 Claims. (Cl. 149-105) This invention relates to the recently discovered slurr-ied blasting explosives which consist of an organic explosive and one or more inorganic oxidizing salt-s, slurr-ied in a saturated aqueous solution of said salts. Thus water, in an amount between about 8% and 26% by weight, is an essential ingredient of such explosives.

In Canadian Patent No. 617,006, there are disclosed sluiried blasting agents of the aforesaid type containing about 8% to 26% of water, 15% to 35% of particulate trinitrotoluene and from 0.1% to 1.0% of a gel-forming mannogalaotan, the remainder being substantially all oxidizing salt such as ammonium nitrate optionally mixed with up to 50% of sodium nitrate and minor amounts of other nitrates, chlorates and perchlorates. it is also disclosed in'the said patent that the inclusion in the slurries of mannogalactans, e.g. guar gum or carob seed gum, gives gelled slurries which are highly resistant to water. The gelled slurries may thus be poured gently into water and still remain coherent, and the resulting immersed masses are resistant to the ingress of water and to the leaching of the inorganic salts.

It is further disclosed in the above patent that a critical amount of borax may be added to the mannogalactancontaining slurries to give much more cohesive gels. It is believed that the bora-te ions in the borax cross-link the manno-galactan-thickened slurries to give greatly improved cohesiveness, md indeed a borax-eontaining slurry may be dropped from a considerable height into water and still retain its shape. These cross-linked slurries thus constitute extremely desirable explosives which are safe, powerful and much more water resistant than explosives such as ammonium nitrate/fuel oil mixtures, yet much more easily handled than waterproof packaged explosives. Furthermore, the problem of segregation of the particulate species is solved by the borax addition, even when the packaged explosives are subjected to varying ambient temperatures.

However, while ordinary borax (Na B O 10H O') gives a satisfactory cohesive gelled slurry on a laboratoryscale, it has been found that it is not possible on an industrial scale to produce the best and most desirable of the laboratory products using ordinary borax. The reasons for this are as follows. Firstly, if the borax and the mannogalacten are added to the slurry at the same time, they interact and the mannogalactan is rendered incapable of swelling, no gel at all being produced and still'less therequired cohesive gel. It is thus necessary to allow the mannogalactan to .pre-gel the salt solution for a lengthy period of time before adding the borax which is inconvenient and reduces production. Secondly, once the borax is added, the slurry gel becomes firmer and more cohesive so quickly that it 'soon cannot flow, and it is thus difficult to package it without'the inclusion of air pockets,

whereas the slurry without the borax can cheaply and easily be pumped or poured into packages.

It has now been discovered that certain fused'or glassy metallic tetraborates, in a substantially anhydrous state, can replace the borax in the slurry with the great advantage that the gelling thereof is delayed. This improvement enables a very desirable explosive to advance from The fused tetra- "ice borates can be used in such an amount that the ultimate gel strength is the optimum, but this strength may be dedeveloped up to 24 hours after mixing. Thus, immediately after mixing, the cohesiveness of the gel is quite low and the explosive slurry may be pumped, handled and packaged very readily. In order to achieve the best balance between low initial viscosity and final gelled strength, it isdesirable that the fused glassy metallic tetraborates be present in a concentration, calculated as B 0 of from 2% to 10% by weight of the mannogalactan.

It is thus an object of this invention to provide an improved readily manufa'otured cohesive gelled blasting explosive wherein water is an essential ingredient, which :is nevertheless highly water resistant in use. A further object is to provide a process for manufacturing such an explosive wherein the attainment of the cohesive gel is delayed for some time after all the ingredients are mixed, in order that the explosive can be handled and packaged in the fluid state. Additional objects will appear hereinafter.

In accordance with this invention, therefore, in an explosive blasting agent of the kind comprising an aqueous slurry of at least one oxidizing salt and a granular waterinsensitive organic explosive, said slurry being at least partially gelled with a mannogalactan, there is provided the improvement which comprises the presence in said slurry of a fused, glassy metallic tetrabora-te in a concentration, calculated as B 0 of from 2% to 10% by weight of the mannogalaotan.

This improved blasting agent is prepared by mixing all the ingredients together, packaging the resultant slurry While .in the partially gelled state and allowing the packaged material to stand for at least 24 hours whereby a fully gelled cohesive slurried explosive is obtained.

In a preferred embodiment, the improved explosive of the invention consists essentially of a cohesive gelled aqueous slurry of at least one oxidizing salt and a granular Water-insensitive organic explosive, said slurry con- .taining from 8% to 26% by weight of water, from 15% to 40% by weight of the organic explosive, from 0.1% to 2.0% by weight of a gel-forming mannogalactan andfrom 0.002% to 0.2% by weight, calculated as B 0 of a fused, glassy metallic tetraborate, the remainder being substantially all oxidizing salt.

A very suitable oxidizing salt for inclusion in the improved explosives of this invention is ammonium nitrate. It is in some cases advantageous to replace some or all, suitably up to 50%, of the ammonium nitrate by sodium nitrate whereby a denser explosive results. Additionally, the chlorates and perchlorates of sodium and ammonium are excellent oxidizing salts, although less safe than the nitrates. The potassium salts are equally useful and are included within the scope of the invention, although they are at present more expensive than. the sodium salts. Mixtures of all these species may beused, together with minor amounts of other metallic nitrates, chlorates and perchlorates. The particle size of the oxidizing salts is not critical.

The organic explosives suitable for use in the irnproved blasting agents. of this invention are described herein as granular and water insensitive.

By granular, it is intended to exclude liquid explosive such as nitroglycerine and nitroglycerol, and to indicate that the explosives should be in powdered or particulate form. Three very suitableexplosives are trinitrotoluene (TNT), composition B (a mixture of a major part, viz. about 60% by weight, of RDX which is cyclotrimethylenetrinitramine and a minor part, viz. about 40% by weight, of TNT plus a little Wax) and smokeless powder. The latter is a solid material and consists of colloided nitrocellulose, with the addition, in the socalled double based powders, of up to 40% nitroglycerine. All these explosives are best used in the particulate form, i.e. in fairly large grains, such as grains coarser than a size 30 Tyler mesh. It is now known, however, that fine granular material can be used but there is a certain loss of sensitivity in small diameter charges. In addition, a large class of organic explosives which can be made in the granular form is suitable for use in this invention but, in many cases, these explosives prove more expensive than the preferred three above-mentioned. This class includes pentaerythritol tetranitrate (PETN), tetryl, RDX and pentolite (a mixture of about equal parts of TNT and PETN) By water insensitive, it is meant that the explosibility of the organic explosives and their granular form must not be affected by water in small amounts. Thus, for example, uncolloided nitrocellulose or nitrostarch are unsuitable since they readily absorb water to form a mat, and are then insensitive to detonation.

The fused, glassy metallic tetraborates suitable for use in the improved explosive and process of this invention are made by fusion of the more common powdered, generally hydrated forms. This fusion may be conducted by any heating means, and generally requires a temperature of 600 C. to 1000 C. The result is glassy granules which should be ground before use; a particle size between 8 and +30 Tyler mesh is suitable but not critical. However, not more than A; of the material should be fines, i.e. through 50 mesh. The following metallic tetraborates are suitable: lithium, sodium, potassium, magnesium, calcium and barium tetraborates and mixtures thereof. However, the cationic or metallic constitutent has little effect upon the efficiency of the fused tetraborates in this invention, and any metallic tetraborate capable of assuming the glassy form upon fusion, and having at least some solubility in water, is suitable. Furthermore, the tetraborate need not be pure. There are several suitable materials sold for fertilizer use, such as Rasorite and Fertilizer Borate 65 of the U5. Borax Chemical Corp., and Pyrobor of the American Potash and Chemical Corp. The former is described as a concentrated sodium tetraborate ore product containing 94-97% anhydrous sodium tetraborate and less than 1% (typically 0.4%) of water. Other fertilizing products are probably less pure. For this reason, and because of the different molecular weights of the various metallic tetraborates, the amounts of these materials to be included in the explosive of the present invention are defined herein on the basis of the contained amount of B That is, for example, a material containing one gram of calcium tetraborate contains only 0.72 gram calculated as B 0 The order of mixing the ingredients in the process of this invention is not critical, and excellent products can be made by comparatively crude procedures. Any type of stirred mixing vessel may be used, but a steam heated mixer wherein the action is a gentle folding, combined with a lifting of material from the bottom of the vessel to the top, is preferred. The ingredients may be added in any order, but due to the negative heat of solution of ammonium nitrate, it is preferred that hot water be used when this ingredient is present in a large proportion. In a preferred procedure, half the inorganic salt is added first, then the water, then the other half of the salt with the mannogalactan premixed therein. Finally, the granular organic explosive and the glassy metallic tetraborate are premixed and added to the thickened salt slurry. By this method, the mannogalactan is allowed to swell for a while before the granular explosive is added. This helps the explosive to become distributed throughout the slurry and to minimize settling, particularly when a minimum amount of mannogalactan is used. The addition of the glassy borate last gives the greatest possible time during which the slurry can be packaged before the extremely cohesive stage is reached.

The following Examples illustrate the products and process of the present invention but the scope of the in vention is not to be restricted to the details described. The gelled slurried explosives may, for example, additionally contain other materials normally used in explosives, including metallic powders, ammonium picrate, cellulosic pulps and other similar species.

EXAMPLE 1 The following mixing procedure was used to manufacture a large batch of the blasting explosive of this invention, a heated ribbon mixer being used.

300 lbs. of ammonium nitrate and 200 lbs. of sodium nitrate were Weighed into the empty mixer and the steam heat was then turned on and 192 lbs. of hot water added and mixed in. Meanwhile, a further 300 lbs. of ammonium nitrate and 200 lbs. of sodium nitrate were weighed out, and 8 lbs. of guar gum roughly mixed into the solids, which were then added to the mixer. Then 217 grams of Rasorite, a proprietary fused, glassy sodium tetraborate, were added to 400 lbs. of pelleted TNT, and the whole added to the now thickened slurry. As soon as the composition was homogeneous, it was dumped to a hold tank, and thence dropped by gravity into polythene bags. After 24 hours the explosive had become cohesive; it would no longer flow as a fluid, but rather on inversion of a bag, the whole body would fall out as a plastic mass, necking down and separating cleanly from the polythene bag. If dropped into water, the mass did not separate or diffuse, but sank as a cohesive body. It can thus be seen that a material of remarkable properties, particularly suitable for field use as a blasting agent, is produced by the method of this invention.

Furthermore, the blasting explosive detonated unconfined in a 2 inch diameter tube, using a gram pentolite booster. It was extremely powerful, having a density of 1.55 g./cc. and a borehole pressure of 66,700 atm., but was quite insensitive to shock, friction, or even a blasting cap.

EXAMPLE 2 Since the viscosity of the slurried blasting agents is ditficult to measure, due to their inhomogeneity, a laboratory experiment was performed to show the delayed gelling of the fused tetraborates. A Brookfield rotational viscometer was used to measure the increase of viscosity of 60% ammonium nitrate solution containing three sets of additives, namely 1.0% guar gum,

1.0% guar gum plus 0.03% Rasorite, and 1.0% guar gum plus 0.03% borax added after 15 minutes.

The contents of both borates were calculated as B 0 The results are given in Table I.

Table l 60% NH4NO3, 60% NH4NO:, 60% NHANOS, 1.0% guar, 1.0% guar, Time 1.0% guar, cp. 0.03 0.03% borax Rasorite, op. added at 15 minutes, cp.

The borax was added 15 minutes late to prevent segregation and this is the only possible way to use it on a plant scale. However, it immediately gelled the slurry, and it can be seen that in the critical period, 1 to 2 hours after mixing, when the slurry must be packaged, the Rasorite slurry is only slightly more viscous than that thickened by guar alone, whereas the borax has given a much higher viscosity. In addition the improvement in final (24 hrs.) gel strength by the use of a boratc is shown.

EXAMPLE 3 :Slurriecl explosives were made from the following ingredients:

Sodium chlorate--- percent by weight" 62. 4. 44. 2 Flaked TNT -do 25.0 34. 8 Guar gnm do 0. 6 0. 63 Water do 12.0 19. 8 Fertilizer borate (impure fused glassy sodium tetraborate) pereent by weight" 0.02 0.02

The resulting slurries slowly gelled over 24 hours with no segregation, to give strong cohesive gells that would separate cleanly from their polythene bags. The explosive power of the gelled slurry was measured by the ballistic pendulum, to give a so-called Triton value ('I NT=10.0). The Triton value of A was 8.5 that of B was 9.5.

EXAMPLE 4 Two blasting agents were made up wherein the organic explosive consisted of a mixture of TNT and a rifle type smokeless powder. (This powder consisted of 89.5% nitrocellulose gelled by 9.7% clinitrotoluene, and 0.4% dibutylphthalate.) The formulae and properties of the blasting agents were:

Ammonium nitrate percent by weight 53. 61. 5 Sodium nitrate... o 9.0 1.0 Smokeless powder cdo. 12. 5 18. 75 TNT (flake) 10 12.5 6.25 Guar gum." do- 0.5 O. 5 Water do 12.0 12.0 Fused sodium tetraborat'x d0 0. 02 0. 02

(as B203) (as 13203) V.O.D. 4 diam it./sec 4, 390 4, 520 Triton Value 10.8 10. 0

The samples on which the velocities of detonation (V.O.D.) were measured were primed with a pentolite primer of 160 g. weight. Other effective blasting agents were prepared using no TNT and 28% to 38% smokeless powder. The latter agent had the formula:

Ammonium nitrate 29.0% by weight. Sodium nitrate 19.4% by weight. Smokeless powder 38.0% by weight. Guar gum 0.6% by weight. Water 13.0% by weight. Fertilizer borate 0.02% by weight (as B 0 V.O.D. at 1 /2" diam 5380 ft./sec.

EXAMPLE 5 Apart from the tetraborate, the composition was that of Example 1.

Table II Viscosity (in arbitrary units) alter- Fused, glassy tetrnborate hr. 1 hr. 2 hrs. 3V hrs. 24 hrs.

184 293 453 508 520 255 349 622 151 269 394 458 628 224 394 583 l, 178 878 573 1,080 NazBtO1 209 328 442 421 1, 330 Fertilizer grade sodium tetraborate 168 266 382 1, 090

What I claim is:

1. An improved explosive blasting agent consisting essentially of a cohesive gelled aqueous slurry of at least one inorganic salt, granular trinitrotoluene, a gel-forming mannogala'ctan and a substantially anhydrous fused glossy metallic tetraborate in a concentration calculated as B 0 of from 2% to 10% by weight of said mannogalactan, the particle size of at least /8 of said tetraborate being larger than a 50 Tyler mesh.

2. An improved explosive blasting agent consisting essentially of a cohesive gelled aqueous slurry containing from 8% to 26% by weight of water, from 15% to 40% by weight of granular trinitrotoluene, from 0 .1% to 2% by weight of a gel-forming mannogalactan and from 0.002% to 0.2% by weight, calculated at B 0 of a substantially anhydrous fused, glossy metallic tetraborate, the remainder being substantially all inorganic oxidizing salt, the particle size of at least of said tetraborate being larger than a 50 Tyler mesh.

3. An improved process for making a cohesive gelled slurried blasting agent which comprises mixing together water, at least one inorganic oxidizing salt, granular trinitrotoluene, a gel-forming mannogalactan and a substantially anhydrous fused, glossy metallic tet'raborate in an amount, calculated as B 0 of from 2% to 10% by weight of said mannogalactan, the particle size of at least /8 of said tetraborate being larger than a 50 Tyler mesh.

4. An improved process for making a cohesive gelled slurried blasting agent which comprises mixing together from 8 to 26 parts by weight of water, from 15 to 40 parts by weight of granular trinitrotoluene, from 0.1 to 2.0 parts by weight of a gel-forming mannogalactan, from 0.002 to 0.2 part by weight, calculated as B 0 of a sub stantially anhydrous fused glossy metallic tetraborate, the particle size of at least of said tetraborate being larger than a 50 Tyler mesh, and sufficient inorganic oxidizing salt to make a total of 100 parts by weight.

References Cited in the file of this patent UNITED STATES PATENTS 868,636 Braunstein Oct. 22, 1907 2,063,572 Woodburry Dec. 8, 1936 2,358,384 Davis Sept. 19, 1944 2,733,139 Winning Jan. 31, 1956 2,768,073 Davidson Oct. 23, 1956 2,839,374 Taylor et al June 17, 1958 2,847,291 Sakurai Aug. 12, 1958 2,860,041 Griflith Nov. 11, 1958 2,867,172 Hradel Ian. 6, 1959 3,037,417 Andrew et a1 June 5, 1962 3,049,043 Milani Aug. 14, 1962 3,072,509 Barnhart Jan. 8, 1963

Claims (1)

1. AN IMPROVED EXPLOSIVE BLASTING AGENT CONSISTING ESSENTIALLY OF A COHESIVE GELLED AQUEOUS SLURRY OF AT LEAST ONE INORGANIC SALT, GRANULAR TRINITROTOLUENE, A GEL-FORMING MANNOGALACTAN AND A SUBSTANTIALLY ANHYDROUS FUSED GLOSSY METALLIC TETRABORATE IN A CONCENTRATION CALCULATED AS B2O3, OF FROM 2% TO 10% BY WEIGHT OF SAID MANNOGALACTAN, THE PARTICLE SIZE OF AT LEAST 7/8 OF SAID TETRABORATE BEING LARGER THAN A 50 TYLER MESH.