US3397095A - Gelled aqueous explosive composition having hydrogen cyanamide as antifreezing agent - Google Patents

Description

3,397,095 GELLED AQUEOUS EXPLOSIVE COMPOSITION HAVING HYDROGEN CYANAMIDE AS ANTI- FREEZING AGENT John Patrick Merryweather and John Aubrey McLean,

Niagara Falls, Ontario, and Trevor David Field, Chippawa, Ontario, Canada, assignors to American Cyanamid Company, Stamford, *Conn., a corporation of Maine No Drawing. Filed Dec. 14, 1966, Ser. No. 601,563 9 Claims. (Cl. 149-39) ABSTRACT OF THE DISCLOSURE Anti-freeze properties are provided in water-base, ammonium nitrate explosive gel compositions by the incorporation therein of a small amount of hydrogen cyanamide and especially by the incorporation of small amounts of both hydrogen cyanamide and urea.

This invention relates to new and improved aqueous gel explosive compositions. More particularly, it relates to gelled ammonium nitrate explosive compositions having outstanding anti-freeze properties.

Aqueous slurry-type explosive compositions comprising ammonium nitrate and an explosive sensitizer, such as trinitrotoluene, smokeless powder, dinitrotoluene, etc., have attained substantial commercial acceptance. It has been recognized, however, that these compositions, While highly useful, possess certain drawbacks. Thus, they tend to separate into layers, each containing different proportions of the various components. Because of this, these compositions are oftentimes not only difficult to handle, but their non-uniform consistency adversely affects their explosive characteristics and consequently their reliability in use.

Recently, it has been shown that the separation problem and difficulties attendant therewith can be counteracted to a substantial extent by the incorporation in the slurry compositions of various gel-forming materials which increase the viscosity of the compositions and thereby reduce the settling tendency of the solid components. Thus, the gelled compositions generally exhibit improved, uniform consistency and at the same time sufficient fluidity to permit easy handling and pouring.

It has been further recognized in the art with respect to explosive gel compositions that their stability is enhanced by the incorporation therein, along with the gelling agent, of a small amount of a cross-linking agent in the form of a polyvalent metal salt. Salts of aluminum, chromium, iron, tin, and the like have been used. The particular anion of the salt does not appear to be critical. Sulfates have been commonly used, particularly, aluminum sulfate. Nitrates and chlorides have also proved effective, particularly, chromium nitrate.

While the explosive gel compositions represent a substantial advance over the non-gelled, slurry-type compositions, they still possess a troublesome defect. Thus, the gels tend to harden considerably on standing, rather than remaining uniformly soft and pourable, particularly when exposed to temperatures in the order of F. or below. A prime characteristic and advantage of the explosive gels is, of course, their pourability, by virtue of which they are readily and elficiently loaded into bore-holes. In the hardened or semi-hardened state, this advantage is, of course, greatly reduced or lost entirely. Accordingly, it is evident that the hardening of the gels at the aforesaid temperatures, which are not uncommon in northern mining operations during the winter, constitutes 'a serious drawback to their use.

Although the gels in the hardened or semi-hardened nited States Patent 0 "ice state are sometimes referred to as being frozen, this is somewhat of a misnomer since the hardening of the gel is not the result of freezing in the conventional sense, but rather of the salting out of crystals from the saturated ammonium nitrate and/or sodium nitrate solution which is a component of the gel compositions. Thus, the solidifying effect can occur at temperatures well above freezing, although it becomes more pronounced as the temperature to which the compositions are exposed becomes lower. On this basis, a gel composition which exhibits pronounced hardening tendencies particularly when exposed to relatively low temperatures is said to have poor anti-freeze properties.

More recently, it has been shown in the prior art that the non-hardening or anti-freeze properties of the gelled explosive compositions can be substantially improved by the incorporation therein, in minor amounts, of certain compounds generally referred to as fiuidizing agents. A variety of such fiuidizing agents, including, inter alia, certain alcohols, organic acids, amines and amides, are shown for example in US. Patent No. 3,190,777. Also, the use of urea is shown in Canadian Patent No. 712,981.

While all of the fiuidizing agents of the prior art improve tthe anti-freeze properties of the gelled explosive compositions, the extent of the improvement is generally limited. Thus, with few exceptions, the lowest temperature at which the compositions employing them will consistently retain the desired fluidity is about 0 C. A limiting factor with respect to the use of the known fiuidizing agents, especially for protection at sub-zero temperatures, is that the amounts thereof required are such as to adversely affect either the sensitivity or strength of the explosive compositions. The protection afforded by the prior art anti-freeze agents where the explosives are exposed to sub-zero temperatures has therefore, not been wholly satisfactory. The art has, therefore, sought fiuidizing agents capable of maintaining the gels in fluid or semifluid condition at sub-zero temperatures and which at the same time can be used in amounts sufficiently low as not to detract from the explosive properties of the explosive composition. It is an object of this invention to provide such a fiuidizing agent. Other and further objects will become apparent from the following description of the invention.

In accordance with the present invention it has been found that by employing hydrogen cyanamide as a fiuidizing agent in the gel compositions, the gels consistently retain the desired fluidity at temperatures down to 2() F. with no detraction from their sensitivity or strength. It has further been found that by replacing part of the hydrogen cyanamide with urea still further improved antifreeze properties are provided in the gels.

As is well known, hydrogen cyanamid-e, H NCN, is a normally unstable compound which tends to decompose rather rapidly into dicyanamide and urea. However, it is marketed by American Cyanamid Company in the form of a buffered 50% aqueous solution designated as either AC50 or Cyanamide SO. In this form the hydrogen cyanamide exhibits excellent stability for a period of at least three months, provided only that the solution is stored at low temperature, i.e., below about 50 F. and preferably below 30 F. It is this solution which is utilized to supply the hydrogen cyanamide fiuidizing agent in the compositions of the invention. It is referred to hereinafter as hydrogen cyanamide solution or AC-50 As is well known, water-based explosive gels ordinarily contain as essential components (a) ammonium nitrate either alone or in combination with a metal nitrate, such as sodium nitrate, (b) a sensitizer or sensitizing fuel, (c) water, and (d) a suitable gelling agent. The sensitizer (or sensitizing fuel) may be of the self-explosive type,

such as smokeless powder, TNT, pentaerythritol tetranitrate (PETN), cyclotrimethylenetrinitramine (RDX) and cyclotetramethylenetetranitramine (HMX) as well as mixtures thereof, such as pentolite (PETN/TNT), Composition B (RDX/TNT) and other known equivalents. The self-explosive sensitizer may be in any of the conventional forms, i.e., flake, pellets or crystals. Also, the sensitizer may be comprised of any of the known metallic fuels, such as aluminium, magnesium, iron or alloys thereof, or ferrosilicon or ferrophosphorus in finely divided form, which metallic fuels though not self-explosive provide sensitizing action when combined with an oxidizing salt, such as ammonium nitrate. Also, the sensitizer may be a carbonaceous material, such as charcoal, or a non-high explosive oil, such as dinitrotoluene or fuel oil.

The gelling agent may be any of the materials known to the art for this purpose, e.g., synthetic gelling agents, such as cross-linked acrylamide polymers of high molecular weight, various natural gelling agents, such as gum arabic, guar, starches, dextrins, cellulose derivatives, gelatin, etc. A particularly successful material however, is guar gum and it is preferred for the compositions of the present invention.

Various procedures used for the manufacture of aqueous explosive gels have been shown in the prior art. A common practice is so-called in bowl mixing whereby all of the ammonium nitrate, sodium nitrate, sensitizer and gelling agent are added as dry ingredients to a mixing bowl, followed by the addition of hot water with continued mixing in order to disperse and dissolve the gelling agent. If necessary, a cross-linking agent is then added with further mixing until the gelled product is obtained. Another well-known technique involves preparation of a saturated solution comprising a portion of the ammonium nitrate component and all of the sodium nitrate component. This stock solution is then combined with the remainder of the ammonium nitrate component, the sensitizer, the gelling agent and the cross-linking agent. However, this order of mixing is not always used. Thus, in preparing the compositions of the present invention using guar gum as the gelling agent, it has been found preferable not to include the sodium nitrate component in the ammonium nitrate stock solution, but to add it after the gelling agent has been added, since it tends to inhibit the initial gellation of the guar gum. For the same reason 4:

when the in bowl mixing procedure is used the sodium nitrate should be added after the guar gum.

Other variations in manufacturing technique will be apparent to those skilled in the art. It will be appreciated, therefore, that the present invention does not reside in, nor is it limited in any way by, the manufacturing procedure used to prepare the improved compositions thereof.

A full understanding of the invention will be had by reference to the following specific examples and tests.

EXAMPLES 1-24 Parts Weight percent Ammonium Nitrate 30 62. 5O Urea. 3 6. 25 Water 15 31. 25

The other ingredients of the compositions, including any additional solid ammonium nitrate to satisfy formulation requirements, were then added to the stock solution in a ribbon blender at 110-l20 F. Sodium nitrate was omitted from the stock solution and added to the blender last because it was found to inhibit the initial gelling of the guar gum gelling agent.

A typical procedure was that of Example 19, as follows. To 5 pounds of ammonium nitrate and 20 pounds of flake TNT in the blender, 48 pounds of stock solution were added and the whole mixed for one minute. Two pounds of hydrogen cyanamide solution were then added and mixed in for /2 minute after which a premix of 14 pounds of aluminium powder and 1 pound of guar gum were added. The mixing was then continued until hydration had advanced to a thick enough consistency to suspend the solids, i.e., about 4 minutes. Finally, 10 pounds of sodium nitrate were added and mixing continued until the mix was homogeneous, about one minute.

In the case of those compositions which did not contain hydrogen cyanamide solution and/or aluminium the procedure was similar, except that the addition of these ingredients was omitted.

The compositions of Examples l-4 and 9-16 which did not contain urea were prepared by an in bowl mixing procedure. The preparation of Example 16 which is typical was as follows. To 30 pounds of ammonium nitrate and 25 pounds of TNT prills in the blender there was added 16 pounds of hot (-180" F.) water and the whole mixed to dissolve most of the ammonium nitrate (about 2-3 minutes). Four pounds of hydrogen cyanamide solution were then added and the whole again mixed for half a minute. A premix of 14 pounds of aluminium powder and 1 pound of guar gum were then added and the mixing continued until hydration had advanced to a thick enough consistency to suspend the solids (about 4 minutes). Finally, 10 pounds of sodium nitrate was added and the mixing continued until the whole composition was homogeneous (about 1 minute).

Here again, in the case of those compositions which did not contain hydrogen cyanamide solution and/or aluminium, the procedure was similar to that of Example 16, except that the addition of these ingredients was omitted.

Upon completion of preparation each of the 24 compositions was magazine-stored for 24 hours to permit cooling and complete hydration of the guar gum before being subjected to cold storage tests. The average temperature of the gels at the end of this period was 60 F.

Anti-freeze tests Samples of each of the 24 compositions were extruded into plastic bags of uniform size and placed in low temperature storage at controlled temperatures of 20 F., 0 F., -10 F., -15 F., and 20 F. for seven days, after which they were examined and rated for their anti-freeze properties as follows.

Poor: Gels which were hard and did not yield under hand pressure or which yielded with fracture.

Fair: Gels which were firm but which deformed under hand pressure.

Good: Gels which were soft and pliable.

Very good: Gels which were very soft and very pliable.

The pertinent data with respect to the 24 compositions and the test results are summarized in Table I, in which the proportions of components are given in weight percents.

As will be seen from the table, control Examples 1-4 which contained no fluidizing agent (i.e., either AC-50 or urea) rated poor (P) at 20 F.

Also, of Examples 5-8, which contained 3% urea, three, i.e., Examples 5-7, rated poor (P) at 0 F. while Example 8 rated fair (F) at 0 C. and poor at l0 F.

Further, it is seen that Examples 9-12 which contained 2% AC-50 showed either good (G) or very gOOd (VG) anti-freeze properties at -10 F. with these properties declining at -15 F. and being lost entirely at 20 F. in the case of Examples 9 and 10.

TABLE I Ammonium Sodium TNT Type Guar Anti-Freeze Rating F. Ex. No. Nitrate Nitrate Urea AC-50" Aluminum Gum Water Flake Prill 20 15 10 +20 49 25 1 44 10 30 1 40 10 1 35 10 1 46 10 25 1 41 10 w 1 37 10 20 1 32 10 25 1 46 10 2 o 25 1 P 43 10 2 28 1 P 37 10 2 20 1 F 32 10 2 25 1 F 44 10 4 25 1 F 41 10 4 28 1 F 10 4 20 1 G 30 10 4 14 25 1 G 44 10 3 2 25 1 F 39 10 3 2 30 1 V G 35 10 3 2 14 20 1 G 30 7 3 2 14 28 1 G 42 10 3 4 25 1 VG 37 10 3 4 30 1 V G 33 10 3 4 14 20 1 VG 30 5 3 4 14 28 1 VG Still further, it is seen that Examples 13-16 which contained 4% of AC-50 had improved ratings over Examples 9-12, with Examples 13 and 14 being fair (F) and Examples 15 and 16 being good (G) at -20 F.

It is seen further that Examples 17-20, which contained a combination of 3% urea and 2% AC-50 exhibited anti-freeze properties at least equal to Examples 13-16, with an improvement in Example 18 to a rating of very good (VG) at -20 F.

Finally, it will be seen that Examples 21 to 24, which contained 3% urea and 4% AC-50, all rated very good (VG) at 20 F.

It is evident, therefore, that hydrogen cyanamide is an effective anti-freeze agent for gelled water-based explosive compositions and that the combination of hydrogen cyanamide and urea provides outstanding anti-freeze properties in these compositions.

The compositions of the invention were also subjected to initiation propagation and detonation tests at temperature ranging from 70 F. down to 20 F. without indication of any adverse effect.

As previously indicated, the anti-freeze improvements of this invention can be applied to water-based explosive gel compositions in general, the examples given herein being merely illustrative of such compositions. Thus, such compositions generally may contain from about 15-50% by weight of ammonium nitrate, about 5-25% by weight of sodium nitrate, about 5-40% by weight of sensitizer (or fuel), from about 0.5-2% by weight of gelling agent and from about 5-25% by weight water. Also, while it has been shown by the examples herein that certain specified amounts of hydrogen cyanamide, or of hydrogen cyanamide and urea together, provide outstanding antifreeze properties in the gel compositions, it will be appreciated that the amounts of these materials used may be varied over a wider range than encompassed by the examples with significant anti-freeze benefits still being attained. Thus, expressed on a dry basis (as distinguished from the hydrogen cyanamide solution used to supply it) at least about 1% and preferably about 2% of hydrogen cyanamide is required for sub-Zero anti-freeze protection. However, as little as 0.5% will provide significant improvement and even full protection at temperatures upwards of about 0 F. Also, higher amounts than designated in the examples may be used without substantial detraction from the benefits of the invention. In general, therefore, the amount of hydrogen cyanamide to be used in the gel compositions can range from about 0.5 to about 10% with the preferred amounts being from about 1% to about 2%. For the sake of clarity, it is pointed out the percentages of hydrogen cyanamide recited in the following claims are also expressed on a dry basis.

With respect to urea, the amount which may be used in conjunction with the hydrogen cyanamide can range from about 1% to about 10% with the preferred amount being from about 1% to about 3 Having now fully described the invention, what is claimed as new and patentable is:

1. An explosive gel composition of improved antifreeze properties comprising on a weight basis (a) from about 15-50% of ammonium nitrate, (b) from about 5-25% of sodium nitrate, (c) from about 5-40% of a sensitizer, (d) from about 0.5-2% of a gelling agent, (e) from about 5-25% of water, (f) from about 05-10% of hydrogen cyanamide and (g) from 0-10% urea.

2. An explosive gel composition according to claim 1 wherein the sensitizer is trinitrotoluene.

3. An explosive composition according to wherein the sensitizer is fuel oil.

4. An explosive composition according to wherein the sensitizer is aluminum.

5. An explosive composition according to wherein the gelling agent is guar gum.

6. An explosive composition according to claim 1 wherein the gelling agent is a high molecular weight polyacrylamide.

7. An explosive gel composition according to claim claim 1 claim 1 claim 1 1 wherein the urea is present in an amount of from about 1% to about 3%.

8. An explosive gel composition of claim 6 wherein the hydrogen cyanamide is present in an amount of from about 1% to about 2% and urea is present in an amount of from about 1 to about 3%.

9. An explosive composition according to claim 1 wherein the sensitizer is comprised of trinitrotoluene and aluminum.

References Cited UNITED STATES PATENTS 3,004,842 10/ 1961 Rowlinson 149-43 X 3,052,578 9/1962 Davis et a1 149-600 3,190,777 6/1965 Breza et al 149--46 X 3,238,074 3/1966 Griflith et al. l49-44 X 3,249,476 5/1966 Clay et al. 149-39 X 3,296,042 1/ 1967 Quadfiieg et a1 149-60 X CARL D. QUARFORTH, Primary Examiner.

S. J. LECHERT, JR., Assistant Examiner.