Method of making nitrocellulose-nitroglycerine water-bearing explosive compositions

3,668,027

Patented June 6, 1972

United States Patent Office

3,668,027

METHOD OF MAKING NITROCELLULOSENITROGLYCERINE WATER-BEARING EXPLOSIVE COMPOSITIONS Gordon M. Gay, Tacoma, Wash., assignor to Comercial Solvents Corporation, New York, N.Y. No Drawing. Filed Sept. 26,1969, Ser. No. 861,490

Int. Cl. C06b 5/04

U.S. Cl. 149—95 2 Claims

ABSTRACT OF THE DISCLOSURE

Water-bearing explosive compositions characterized by high detonation velocity comprising a mixture of an inorganic oxidizer salt, nitroglycerine and/or other nitrate esters, nitrocellulose, water and a water thickening agent. The water-bearing explosive compositions, gels and slurries, are prepared by first pregelling nitroglycerine and nitrocellulose followed by adding the remaining ingredients of the explosive composition.

This invention generally relates to explosive waterbearing compositions and in a particular aspect to a 25 water-bearing explosive composition characterized by high detonation velocity comprising a mixture of an inorganic oxidizer salt, nitroglycerine, nitrocellulose, at least 3% by weight of water, and a water thickening agent.

Explosive mixtures, such as gels and slurries, contain- 30 ing relatively large amounts of water are of considerable interest in the explosives art. They have greater versatility than dry mixtures, because they can be used under conditions where water cannot be excluded, and flowable slurries also may be brought more easily to certain types of 35 sites such as bore holes and rock crevices. The water content is more than that which is absorbed by the components of the mixture, and is sufficient to act as a suspending agent for the mixture. Such a water content in most cases ranges from about 3% to more than 25%, depending upon the materials present in the mixture and upon the consistency desired.

A slurry or a gel having a reasonably stiff consistency may be preferred for use in bulk in wet bore holes, where the composition may be diluted with water already present. Thickening or gelatinizing agents are employed when thick slurries or gels are required containing high proportions of water. A slurry which can be poured may be desired for use in bulk in dry bore holes, and such a slurry is easily obtained by using a rather large proportion of water, for example 15 to 25%, without a thickening or gelatinizing agent.

Water based gels and slurries as usually formulated contain an explosive sensitizer because of the relative insensitivity of ammonium nitrate, particularly in combination with large amounts of water. Sensitized aqueous explosives are described in U.S. Pat. No. 2,930,685 to Cook and Farnam. These compositions are based upon ammonium nitrate and sensitized with TNT, and may in addition contain powdered aluminum. Cook et al. point ⁶⁰out that the explosives art has always taken extensive precautions both in formulating and in storing explosives to exclude moisture, and that they formulate their slurries very carefully using coarse grained TNT particles in order to obtain an acceptable sensitivity. U.S. Pat. No. 3,083,127 ⁶⁵to Griffith and Wells, describes aqueous explosive slurries based upon an inorganic nitrate and sensitized with nitrostarch.

It is an object of the present invention to provide new water-bearing explosive compositions. 10

It is another object of the present invention to provide new aqueous gel explosive compositions.

It is still another object of the present invention to provide new aqueous slurry explosive compositions.

It is a further object of the present invention to provide new explosive compositions characterized by high detonation velocity comprising a mixture of an inorganic oxidizer salt, nitroglycerine and/or other nitrate esters, nitrocellulose, water, and a thickening agent.

It is an additional object of the present invention to provide a new process for producing water-bearing explosives, such as aqueous gels and aqueous slurries.

These and other objects and advantages of the invention will be understood from the description of the in15 vention.

The present invention provides an explosive water-bearing composition having high detonation velocity comprising a mixture of (a) an inorganic oxidizer salt, (b) nitroglycerine, (c) nitrocellulose, (d) water in an amount of at least about 3% by weight, and (e) a thickening agent for the water.

Although nitroglycerine is a well known and widely used explosive, heretofore it has not been commercially used in water-bearing explosives, especially as in the present explosive compositions, because water was considered to have an adverse effect on nitroglycerine and it was also considered by many to be dangerous to mix water with an explosive composition containing nitroglycerine because the nitroglycerine could migrate and collect in dangerous quantities.

However, it has now been discovered that effective explosive compositions having high detonation velocity may be prepared when both the nitroglycerine and the water are effectively immobilized in the explosive composition. This effective immobilization of nitroglycerine and water ⁴⁰ is one of the very important aspects of this invention and contirbutes to a “no-leak” product. The pregelling of the nitroglycerine and nitrocellulose develops a water-proof lacquer and sensitizer for intimate incorporation with the balance of the formula ingredients.

⁴⁵ Another significant facet of the present invention is the high detonation velocities possessed by the explosive compositions. Heretofore explosive compositions utilizing nitroglycerine and an inorganic oxidizer salt had relatively low detonation velocities and, further, when water was ⁵⁰ added to dry mixtures of nitroglycerine and inorganic oxidizer salt, the water tended to further lower the detonation velocity.

In accordance with the present invention, effective explosive compositions having high detonation velocity are prepared by first effectively immobilizing nitroglycerine by pregelling it with nitrocellulose followed by mixing of the nitroglycerine-nitrocellulose gel mixture with the inorganic oxidizer salt, water and a thickening agent for the water, the thickening agent for the water being used in sufficient quantity to effectively immobilize the water.

In a preferred embodiment of the present invention the explosive water-bearing composition contains on a weight basis:

(a) from about 40% to about 85% of inorganic oxidizer salt, (b) from about 5% to about 25% nitroglycerine, (c) from about .05% to about 5.0% nitrocellulose, (d) from about 3% to about 25% water, and (e) from about .2% to about 5% of a water thickening agent.

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Another embodiment of the present invention provides an explosive aqueous gel composition containing on a weight basis:

(a) from about 50% to about 85% of inorganic oxidizer salt, (b) from about 6% to about 16% nitroglycerine, (c) from about .1% to about 4% nitrocellulose, (d) from about 3% to about 15% water, and (e) from about .5% to about 5% of a water thickening agent.

A specific embodiment of the present invention provides an explosive aqueous gel composition containing on a weight basis:

(a) about 68.25% of inorganic oxidizer salt, (b) about 9.0% nitroglycerine, (c) about 0.2% nitrocellulose, (d) about 12% water, and (e) about 2.5% of a water thickening agent.

A further embodiment of the present invention provides an explosive aqueous slurry composition containing on a weight basis:

(a) from about 40% to about 65% of inorganic oxidizer salt, ²⁵ (b) from about 6% to about 22% nitroglycerine, (c) from about .2% to about 1% nitrocellulose, (d) from about 15% to about 25% water, and (e) from about .3% to about 3% of a water thickening agent. ³⁰

Another specific embodiment of the present invention provides an explosive slurry composition containing on a weight basis:

(a) about 52.5% of inorganic oxidizer salt, ³⁵ (b) about 21% nitroglycerine, (c) about .4% nitrocellulose, (d) about 17.5% water, and (e) about 1.0% of a water thickening agent. ₄θ

In accordance with the present invention, there are five necessary ingredients in the explosive composition, designated as (a), (b), (c), (d) and (e) herein, each of which are now more specifically described.

(a) The inorganic oxidizer salt 45

Amy suitable inorganic nitrate can be employed as the oxidizer. Ammonium nitrate, and nitrates of the alkali and alkaline earth metals, such as sodium nitrate, potassium nitrate, calcium nitrate, magnesium nitrate, stronti- ₅θ um nitrate and barium nitrate, are exemplary inorganic nitrates. Ammonium nitrate is preferred.

Excellent results are obtained with mixtures of ammonium nitrate and another inorganic nitrate, such as sodium nitrate; and mixtures of sodium nitrate with am- 55 monium nitrate are preferred. In such mixtures, the relative proportions of ammonium nitrate and other inorganic nitrate or nitrates in the mixture are important to the explosive effect. The ammonium nitrate should be in a proportion within the range from about 5% to about βθ 100%, and the other nitrate or nitrates in a proportion within the range from about 0 to about 95%. For optimum power, the proportions are from 75 to 90% ammonium nitrate and from 25 to 10% of the other nitrate or nitrates. A mixture of approximately 80 to 90% ammonium nitrate and 20 to 10% other nitrate, is in most cases the best. The particular proportions of oxidizers selected within these ranges will depend upon the sensitivity and explosive effect desired, and these in turn are dependent upon the particular nitrate or nitrates used. 70

The inorganic oxidizer salt, including mixtures thereof, is present in the range of from about 40 to about 85% of the explosive composition as a weight basis, preferably from about 55% to about 75%. For gel compositions the range is preferably from about 50% to

027 about 85%. For slurry compositions the range is preferably from 40% to 65%.

The inorganic nitrate (s) may be fine, coarse or a blend of fine and coarse materials. Mill and prill inorganic nitrates are quite satisfactory. For best results, sodium nitrate should pass a 20 mesh (U.S. Standard) sieve, and at least 50% of the ammonium nitrate should be fine-grained. In mixtures of these nitrates, the more sodium nitrate that is present, the higher the proportion 10 of fine grain ammonium nitrate that is desirable for optimum explosive power.

(b) Nitroglycerine

As used herein, nitroglycerine itself as well as the vari15 ous other liquid explosive nitric esters and nitroglycerine mixtures commonly employed in the explosives industry, are embraced by the term “nitroglycerine.” The term “explosive nitric esters” is commonly used to refer to such explosive materials. Nitrated mixtures of 35% gly20 cerol and 65% ethylene glycol by weight are typical.

The nitroglycerine component is present in the explosive composition in an amount of from about 5% to about 25%, preferably from about 7.5% to about 15%, by weight. For explosive gels the range is preferably from about 6% to about 15%. For explosive slurries the range is preferably from about 6% to about 25%.

(c) Nitrocellulose

The nitrocellulose is used in amount of from about 0.05% to 5.0% of the explosive composition. For explosive gels the range is preferably from 0.1% to 4%. For explosive slurries the preferred range is from about 0.2% to about 1%. The nitrocellulose is used in an amount sufficient to gel the nitroglycerine. It is well known to gel nitroglycerine with nitrocotton or other nitrocellulose material. In general the pregelling requires from about 1 to about 10 minutes; however longer times may be used.

Pregelling of the nitroglycerine, or other liquid explosive nitric ester, effectively immobilizes the nitroglycerine; that is, the pregelling with the nitrocellulose prevents the liquid nitroglycerine from migrating in the aqueous explosive composition and collecting in dangerous amounts.

(d) Water ,

The water is used in amount of at least 3% by weight of the final mixture. The water content is more than that which is absorbed by the components of the mixture, and is sufficient to act as a suspending agent for the mixture. Such a water content in most cases ranges from about 3% to about 25%, and preferably from about 7.5% to about 20%, depending upon the specific materials present in the mixture and upon the consistency desired. In general, when a gel type of consistency is desired the water will preferably be from about 3% to 15%. When a slurry type of consistency is desired the water will preferably be from 15% to 25%.

A slurry having a relatively thick consistency containing as little as 15% water may be preferred for use in bulk in wet bore holes, where the composition may be diluted with water already present. A slurry which can be poured may be desirable for use in bulk in dry bore holes and such a slurry is easily obtained by using a rather large proportion of water, for example 20% or more.

(e) Water thickening agent

This is an important item of the present invention and is used in a sufficient amount to thicken the composition and to effectively immobilize the nitroglycerine. In general, from about 0.2 to 5% of a water thickening agent is used. The amount used will, of course, depend upon the desired consistency of the final explosive product. For gel type explosives the range will preferably be from about .5% to about 5%. For slurry type explosive lesser 75 amounts will be used, preferably from about .3% to about

3,668,027

3%. The specific amount of water thickening agent will, of course, depend upon the desired consistency as well as the amount of water in the final exposive product Water thickening agents are well known in the slurry and gel explosives art and any suitable one may be used. Examples 5 of operable thickening agents are the galactomannans, particularly guar gum. Guar compositions sufficiently crosslinked for good water resistance yield relatively immobile gelled masses. The combination of polyacrylamide and cross-linked galactomannan is a typical example of a suit- 10 able thickening agent. Other examples are sodium carboxymethylcellulose, water swellable starches and the like. Sodium cellulose glycollate or methylcellulose and similar starch derivatives may be used. Recently developed wettable water thickening agents are water soluble copolymers 15 or methyl vinyl ether and maleic anhydride and water soluble copolymers of styrene and maleic anhydride.

Additional thickening and immobilization is achieved by inclusion of a cross-linking agent, such as the widely used potassium dichromate, which functions with the par- 20 ticular gelling agent which is used. In many cases, these are metal salts, preferably chlorides or nitrates, but also acetates, hydroxides, chromates and sulfates of such metals as tin, chromium, lead, zirconium, iron, copper, zinc, nickel, potassium, manganese, cobalt, titanium and alu- 25 minum may be used. Other gelling agents are disclosed in U.S. Pats. Nos. 2,655,476 and 2,711,393. These are well known materials, and any of these known to the art can be used. The amount of such thickening agent will depend on the consistency desired, and usually will be with- 30 in the range from 0.5 up to about 5 %. Enough thickener can be added to gel the water, and water-proofing agents such as are disclosed in U.S. Pats. Nos. 2,554,222, 2,655,476 and 2,711,393 can be incorporated as well to impart water resistance to the gel or slurry. Cross-linked water 35 thickening agents are preferred because they form a substantially permanently colloided product that holds all the other components of the product in substantially secure captivity at any viscosity level desired.

In addition to these materials, which are the essential ^4tJingredients, the explosive compositions may include a solid carbonaceous fuel such as powdered coal, coal dust, charcoal, bagasse, dextrin, starch, wood meal, flour, bran, pecan meal or similar nut shell meals. Liquid fuels such as petroleum oil, fuel oils (Example #5 oil) and paraffin 45 oil can be used, with enough nitrate or solid fuel to act as a carrier therefor. The carbonaceous fuel is employed in an amount of at least 75% of that required to oxygen-balance the inorganic nitrate, and will usually comprise from about 1 to about 25% by weight of the ex- 50 plosive water-bearing mixture. In addition to the carbonaceous fuel, a particulate metal can also be used, such as aluminum powder, flake aluminum, magnesium and ferrosilicon. A metal fuel, when present, will usually comprise from about 1 to about 15% by weight of the ex- 55 plosive mixture.

An antacid or stabilizer such as zinc oxide, calcium carbonate, aluminum oxide and sodium carbonate, may also be added, if desired, and sulfur can also be added. Amounts up to 5% of each of these are satisfactory for 60 most purposes.

The ranges in the 5 essential ingredients enables one skilled in the explosives art to achieve desirable velocity of detonation rate and sensitivity demands for commercially marketable products. 65

The explosive mixture is readily prepared by simple mixing of the ingredients. However, as hereinbefore set forth, the nitrocellulose and nitroglycerine are pregelled before mixing with the remaining ingredients. The solid materials, including the inorganic nitrate and sensitizer, 70 and addtional fuel and antacid, if any, would usually be mixed first to form a homogeneous blend, and then sufficient water, and lastly the water thickener, would be added to bring the mixture to the desired consistency, which can range from a machinable gel or thick, barely pourable 75 mixture to a quick-flowing liquid slurry. The water thickening agent is preferably first dispersed in a non-aqueous medium, such as, for example, a light oil, glycerine ethylene glycol, etc., prior to adding it to the water so as to avoid the tendencyof the thickener to lump.

In a preferred method of manufacture of the aqueous explosive compositions of this invention, the pregelled nitroglycerine-nitrocellulose is mixed with only a portion of the remaining dry ingredients (but not the thickening agent), for a time to achieve an intimate admixture. In general from 1 to 10 minutes of mixing are sufficient.

This premixing of the gel with a portion of the dry ingredients, generally from 10 to 50% of the dry ingredients, and preferably from 25 to 40% of the dry ingredients introduces a buffer zone between the nitrocellulose-nitroglycerine gel and the succeeding introduction of water. Also, an increment of sensitization of the explosive composition appears to occur by this step.

All of the water desired in the final composition is then added, preferably water at from 100° to 150° F. and more preferably at from 130 to 140° F. The use of warm water insures a high level of inorganic nitrate, especially ammonium nitrate, solution which is reflected in the high velocity rate in the finished product.

The water, pregel and the added portion of the dry ingredients are mixed to achieve a uniform blend, generally from 1 to 10 minutes being sufficient.

The remainder of the dry ingredients and the water thickening agent are then added and mixed to achieve the desired uniformity of blend. The thickening agent is preferably first dispersed in a non-aqueous medium before contacting the thickening agent with water. This predispersion assists in achieving a final uniform blend. In general 1 to 10 minutes of mixing are sufficient.

After mixing, the ingredients may be directly packed into suitable explosives containers as are known in the explosives art.

The explosive will ordinarily be cap-insensitive, that is not reliably detonated by a No. 6 blasting cap and will be fired with the aid of a booster charge and under high confinement, and combinations of the water-bearing explosive and a booster in the same container or separately packaged as a composite in one container can be prepared and marketed as a combined blasting agent. Any conventional booster charge available in the art can be employed, of which pentaerythritol tetranitrate and pentolite are exemplary. Blasting caps can be used as the booster when the water-bearing explosive product is sufficiently sensitive.

The following examples, in the opinion of the inventor, represent the best embodiments of the invention.

EXAMPLE 1

An explosive aqueous gel composition is prepared as follows:

Nitrocotton(3.6288 grams) and nitroglycerine (163.2960 grams) are mixed for 5 minutes to form a relatively thick gel. The nitroglycerine used is a nitrated mixture of 65% ethylene glycol and 35% glycerine. The nitrocotton represented 0.20% and the nitroglycerine 9.0% by weight of the final product.

A dope mix is prepared by intimately admixing the following ingredients:

Ingredient

Grains

Wt. of final product

Starch__________ 45.3600

Fine sulfur........... 27.2160

Coal (-20 mesh)__________________________ 36.2880

Fine grain ammonium nitrate.............. 1,081.3824

Fine ground sodium nitrate................ 156.9456

Carbon black....___________________________ 0.9072

Chalk................. 18.1440 $668,027

A dope mix is prepared by intimately admixing the following ingreidents.

One-third of the dope mix is added to the 166.9248 grams of the nitrocotton-nitroglycerine gel and is mixed for 1 minute.

After 1 minute of mixing, 217.7280 grams (12.0% of final product) of water at 135° F. is added and mixed for 2 minutes. The remainder of the dope mix and a previously prepared mixture of 18.1440 grams (1.0% of final product) of No. 5 light oil with 45.3600 grams (2.5% of final product) cross-linked guar gum are then added and mixed for an additional 5 minutes.

The resultant nitroglycerine aqueous gel was tested in IVt x 8 cartridges 19 hours later and was not detonatable by a No. 6 blasting cap. The gel explosive was, however, reliably detonated by a commercial 1 lb. booster. The detonation velocity was 14,929 feet/second. The gel had good packing characteristics. A test was conducted on the 1W x 8 cartridges 22 hours later and all failed to detonate with a No. 8 blasting cap.

For comparative purposes, a dry explosive mixture was prepared by the same process as set forth above, except without the added water.

Ingredient: Weight percent

Nitroglycerine (65% ethylene glycol=35% glycerine)14.5

No. 1 nitrocotton 0.1

Ammonium nitrate76.5

Sodium nitrate 3.8

Bagasse 2.1

No. 1 meal 1.0

T-14 pulp 0.5

Guar gum 1.0

Chalk 0.5

The resulting explosive slurry was mildly cohesive. The explosive mixture was not cap-sensitive but was detonated by a 1 lb. commercial booster. The detonation velocity averaged 10,218 feet/second.

EXAMPLE 2

An explosive aqueous slurry composition is prepared as follows:

Nitrocotton (0.4 lb.) and nitroglycerine (21.0 lbs.) are mixed for 5 minutes to form a relatively thick gel. The nitroglycerine used is a nitrated mixture of 65% ethylene glycol and 35% glycerine.

Ingredient:Lbs.

Starch 2.5

Fine sulfur 1.5

Coal (—20 mesh) 2.0

Fine grain ammonium nitrate32.50

Fine ground sodium nitrate20.00 mesh coal 7.18

One-third of the dope mix is added to the 21.4 lbs. of the nitrocotton-nitroglycerine gel and is mixed for 1 minute.

After 1 minute of mixing, 17.5 lbs. of water at 135° F. is added and mixed for 2 minutes. The remainder of the dope mix and a previously prepared mixture of 0.25 lb. of No. 5 light oil with 1.04 lbs. cross-linked guar gum are then added and mixed for an additional 5 minutes.

The resultant nitroglycerine aqueous slurry was tested in UA x 8 cartridges 19 hours later and was not detonatable by a No. 6 blasting cap. The detonation velocity was 17,000 feet/second. The gel had good packing characteristics.